
20221214: How Can Matter Be BOTH Liquid AND Gas?
 14:55: And while this stuff is rare on this mostly wet and gassy rock, supercritical fluids are surprisingly abundant in other parts of space time.
 16:53: Dark matter suffuses the nearvacuum of space, where we mostly just have the elementary quantum fields.


20221208: How Are Quasiparticles Different From Particles?
 14:27: But a field is just some property that can vary over space.
 15:11: All part of the magnificent complexity emergent from simple fields spanning space time.
 15:21: ... genres as varied as science, history, true crime, nature and, of course, space. ...
 15:32: ... adds more than 20 hours of new content weekly, and in the Space category you can watch documentaries that explore cosmic ideas – titles ...


20221123: How To See Black Holes By Catching Neutrinos
 00:30: There’s the James Webb Space Telescope and its infrared supervision and of course LIGO with its ability to see gravitational waves.
 02:35: And space does generate a lot of neutrinos.
 07:05: Which is why it’s taken a decade of collecting neutrinos to confidently detect the amazing space object that we’re finally ready to talk about.
 07:26: There’s only about 50 neutrinos more than you would expected from cosmic rays in the atmosphere, but it’s pretty clearly something out there in space.
 11:00: The only other sure neutrino detections from space are the Sun and the remnant of supernova 1987A in the large magellanic cloud.
 12:30: The future of neutrino astronomy is bright, and it’s hard to even guess what we’ll learn as we slowly build our neutrino map of space time.
 13:33: ... If you’d like to check it out, there’s a special Black Friday deal for Space Time fans at piavpn.com/SpaceTime and a link in the ...


20221116: Are there Undiscovered Elements Beyond The Periodic Table?
 15:46: ... gain new ground in humanity's journey to further and future horizons of space ...


20221109: What If Humanity Is Among The First Spacefaring Civilizations?
 11:11: No new life has the chance to evolve, because every planet is already occupied by spacefairing advanced life.
 11:17: ... civilisation: a civilisation that expands in every direction through space at close to the speed of light, making visible changes wherever they go, ...
 11:54: ... even if it takes us a million years to work out how to expand into space and another million to cross the galaxy at 10% light speed, this delay ...
 13:50: The simulation tells us all sorts of weird and surprising things about how space is populated.
 14:09: It predicts that only around one in a thousand intelligent civilisations eventually become spacefaring and spread through the cosmos.
 15:02: ... filled with aliens rushing in to grab this rare remaining patch of empty space ...
 16:41: ... it’s daunting to think about producing PBS Space Time for that long, your help makes it more possible that we’ll ...


20221026: Why Did Quantum Entanglement Win the Nobel Prize in Physics?
 13:32: This is a rare episode of Space Time in which both Einstein and Feynman were wrong.
 14:14: All because a few scientists were willing to challenge the status quo, and seek the hidden secrets of space time.
 14:31: The space time audience has always been amazing at filling out the survey and we’d love to continue the trend!
 15:24: He was such a deep lover of the mysteries of physics and space he named his hamster Sputnik and his fish was named Quark.
 15:33: So Alek, from all of us here at Space Time, we thank you for the light that you so clearly brought to science and to your community.
 16:04: Antoine Micard brought up an important point: how do the spacecraft send their messages back home?
 18:49: ... they’re analogous to the spurious spaces that appear when you choose a coordinate system whose dimensions ...


20221019: The Equation That Explains (Nearly) Everything!
 03:36: ... can think of it as the distance an object or system travels through the space of all possible quantum states. For classical physics it simplifies to ...
 06:57: ... In other words, this is like the energy of the photons as they change in space and time, and this is true for all the derivatives we are going to see ...
 07:51: ... written has to be repeated several times depending on the dimensions of spacetime, the number of charges, the number of different particles, or things like ...
 12:52: ... D, now applied to the Higgs field. It tells us how that field changes in space and time and how it interacts with the massive bosons of the weak ...
 14:43: ... on a coffee mug, and to a deeper description of the mechanisms ruling space ...
 15:13: ... we get to comments, for all the space time fans who are also history buffs, we’d like to let you know about a ...
 15:40: ... galaxies. Maelstroms of power and mystery shining out to us from across space and time, just like you Vivaan. We wish you a most luminous ...


20221012: The REAL Possibility of Mapping Alien Planets!
 00:03: ... has a good chance of actually happening. A train of spacecraft sailing the sun’s light to a magical point out there in ...
 00:33: ... it’d be nice to know a bit more than that. The James Webb Space Telescope is helping  it can detect different molecules in ...
 01:25: ... it’s detailed surface features. And that’s by sending a spaceship. Not TO the planet  that would take way too long. In fact, ...
 04:12: ... tells us that gravity is due to curvature in the fabric of spacetime due to massive objects. But that curvature also bends the ...
 07:45: ... this isn’t even some scifi farfuture tech. In 2010 the Japanese space agency sent the IKAROS probe to Venus using a 20 meter solar ...
 09:31: ... spacecraft starts out by launching backwards compared to Earth’s orbital ...
 10:07: ... day light travel time back to Earth. As you might have noticed, our spacecraft have no way of actually stopping. But that’s OK. ...
 12:52: ... time, the image that the train of spacecraft sends back to Earth will get clearer and clearer. It should be ...
 14:06: ... worlds, brought into focus by our own Sun and its lens of curved spacetime. ...
 15:25: ... the show and let everyone in your immediate patch of Space Time know that it’s never aliens until it is at any rate. ...
 15:45: ... last two episodes; the one on how to use the James Webb space telescope, and the one were we talked about the ...
 18:29: ... effectively raises the temperature of that tiny patch of space, and that can change the way the quantum fields behave  ...


20220928: Why Is 1/137 One of the Greatest Unsolved Problems In Physics?
 02:55: ... of the electron, divided by four times pi, the permittivity of free space, Planck's constant and the speed of ...
 11:20: ... speed of light is the translation factor between the dimensions of space and time in relativity; it’s also the relationship between mass ...
 14:13: And perhaps that number was 1/137, the fine structure constant  whose value sets the rules of this particular space time.


20220921: Science of the James Webb Telescope Explained!
 00:03: You’ve probably heard about the James Webb Space Telescope and seen some cool pictures.
 00:19: ... James Webb Space Telescope has now been in full operational science mode for several ...
 01:18: It was built by NASA with significant contributions from the Canadian and European Space Agencies, but it was built for everyone.
 01:39: The James Webb Space Telescope, JWST, or “the Webb” has been in the works for decades.
 01:47: Really, from right after the launch of the Hubble Space Telescope in 1990.
 01:52: ... properties started to crystalize for what was then the “Next Generation Space Telescope” ...
 02:27: ... get an 8m mirror into space under the incredible stresses of space launch, it was realized ...
 03:06: ... NGST became the James Webb Space Telescope after NASA’s administrator for most the 60's  a controversial ...
 08:07: ... data is accessed through the Mikulski Archive for Space Telescopes, or MAST, which also includes the data from Hubble, Gaia, ...
 11:26: ... in from Earth’s Lagrange 2 point over the next years as the James Webb Space Telescope shows us things never before seen, and some never imagined, ...
 11:58: ... machine shop that’s built parts the Mars Rover and the International Space Station, that expertise allows them to prevent the blade from flexing, ...


20220914: Could the Higgs Boson Lead Us to Dark Matter?
 02:17: ... a way to represent the interactions of particles, plotting time versus space so we have two particles coming together, undergoing some interaction ...
 03:51: ... this case the time and space axes are flipped, so now we’re looking at the annihilation of a particle ...
 04:06: ... example, two dark matter particles somewhere in space could annihilate to produce gamma ray photons, which could be picked up ...
 13:20: But certainly a portal beyond the familiar physics of our luminous space time.


20220824: What Makes The Strong Force Strong?
 07:55: ... the very early universe or at impact point in a large particle collider, space gets sort of saturated so that new quarks can’t be ...
 15:09: As you can imagine, there’s a lot more to it  and so in future episodes we’ll dive deeper into the strongest force in all of space time.
 15:45: Links are in the description and tell them, politely, that Space Time sent you!


20220817: What If Dark Energy is a New Quantum Field?
 00:36: ... mainstream physical explanation for dark energy is that the vacuum of space has a constant energy density. Empty space buzzes with random activity ...
 01:25: ... to Einstein’s equations of general relativity to represent the fabric of space having a constant, nonzero energy ...
 01:41: ... the fabric of space has energy  dark energy  then the expansion of the universe creates ...
 03:33: ... of the smallness of this, if you could take all the dark energy in a space the size of the earth and convert it to mass by E=mc^2, you’d only get ...
 08:36: ... spheres beyond the earth. It’s an apt because it's field fills all of space and also it can be thought of as another force on top of the commonly ...
 09:13: ... take on a simple numerical value  a field strength  everywhere in space. The equation of state depends on this field strength and the kinetic ...
 12:31: ... if omega is less than 1  that’s the big rip, in which all points in space eventually become infinitely far apart. Fortunately, that seems ...
 13:27: ... is its main competitor. The now fully operational James Webb Space Telescope will help by pushing our measurements of the expansion rate ...
 14:41: ... dark energy, or scalar quantum fields shift in a quintessencesaturated space ...
 15:05: ... us exponentially expand our awesomeness or at the very least preventing Space Time collapsing in on itself. So, thank ...


20220803: What Happens Inside a Proton?
 09:50: ... path integral, but instead of trajectories through physical space we add up trajectories through the space of field ...
 10:43: ... randomly choose a selection of field configurations of a pixelated space that get us from the start to the end of our ...
 11:28: ... yet. We’re going to pretend that time is just another dimension of space. This operation is called the Wick rotation and it eliminates the ...
 12:52: ... not all the way there yet. After all, spacetime isn’t really a discrete lattice of points. But it ...
 14:32: ... we’re going to learn so much just simulating such tiny patches of spacetime. ...


20220727: How Many States Of Matter Are There?
 12:50: Just think of our universe as nested layers of states of matter, from the smallest to the largest scales of space time.


20220720: What If We Live in a Superdeterministic Universe?
 07:40: ... a local realist theory, every point in space and time  every event  can only be influenced by a spacetime event in ...
 08:18: Let’s play out the Bell test on something called a spacetime diagram  with one dimension of space only on the x axis and time on the y.
 08:28: Alice and Bob start out together, acquire their entangled electrons, and then move sideways in space and up in time.
 14:30: ... that you can choose whether or not to believe in a superdeterministic space ...


20220630: Could We Decode Alien Physics?
 11:52: ... when we warp into the galactic civilization with our spaceship on backwards, but the important thing is we get ...
 13:42: ... It points to the existence of an underlying symmetry of space ...
 14:09: ... incomplete laws of physics. We actually ran out of space to include a lot of technology. We had to ditch the space shuttle ...


20220622: Is Interstellar Travel Impossible?
 00:00: Space is pretty deadly.
 02:05: ... would take the fastest spacecraft we’ve ever built  that’s the 163 km/s of the Parker solar probe  over ...
 02:57: But there are proposed advanced forms of propulsion that could in principle accelerate a proper spacecraft to a fair fraction of the speed of light.
 03:18: ... … if it weren’t for the second problem  which is that that interstellar space wants to murder ...
 03:36: The space between the stars in our galaxy is far from empty.
 04:54: How far do we get before we’re obliterated by tiny space junk?
 08:02: Interstellar space is quite a bit less dense than the upper atmosphere  by a factor of around 10^16.
 09:56: ... missions, but rather on missions like Breakthrough Starshot where the “spaceship” is a waferthin chip for which a millimeter ablation is ...
 12:11: At any relativistic speed, spacewalks outside the ship are out of the question.
 12:22: Interstellar space is flooded with high energy particles, from simple protons to massive iron nuclei.
 14:02: ... us from stretching our species’ reach to distant tracts of interstellar space ...
 14:15: Making Space time would not be possible without the generous support of everyone who’s joined us on Patreon.


20220615: Can Wormholes Solve The Black Hole Information Paradox?
 00:26: ... relativity, from which followed our modern description of gravity, space and time in general relativity. Now, there’s an ...
 03:20: ... emitting virtual particles. We can think about the vacuum of space as being filled with a boiling flux of particle/antiparticle pairs ...
 04:21: ... and the black hole loses its internal storage space. Meanwhile the black hole’s entropy decreases. Actually, the ...
 08:14: ... gravitational path integral you analyze some patch of spacetime changing from one geometry to another. And you do this by ...
 09:17: ... geometries should be included which include spacetime folding into itself in a way required to build wormholes. ...
 09:36: ... go into a little bit more detail. What do these crazy topological spacetimes look like? It’s very difficult to properly picture ...
 10:42: ... Renyi entropy is found using the gravitational path integral. For a spacetime geometry where none of the black holes interact with each ...
 11:13: ... you take this spacetime topology into account, and then you set n equal to 1 single black ...
 13:07: ... our universe, past an infinity of strange topologies and imaginary spacetime. ...


20220601: What If Physics IS NOT Describing Reality?
 12:09: ... that our only direct experience is with an entirely informational space ...
 15:25: ... when galaxies merge. Given that most of the galaxy is empty space, what’s the probability of stars colliding? Well for any given ...
 16:52: ... in particular the strength of the various forces. Yet to expand space you just need to change space, and general relativity ...


20220525: The Evolution of the Modern Milky Way Galaxy
 06:57: ... has been dubbed ‘GaiaEnceladus’  named for the Gaia Space Telescope which was used to discover the event by identifying star ...
 13:54: ... foolish enough to stray into the Milky Way’s little patch of space ...
 14:08: ... This incredible tool allows you to search the entire Space Time catalog for any word or phrase and get links to ...
 14:38: ... for the fermi paradox, and the one where we showed why space is not expanding inside gravitationally bound systems like the ...
 17:21: ... asks “If space doesn't expand inside a gravitational field, then what ...
 18:41: ... Marsh asks if space inside gravitationally bound systems actually ...


20220518: What If the Galactic Habitable Zone LIMITS Intelligent Life?
 13:03: ... and yet mundane star in the apparently uninhabited reaches of space ...


20220504: Space DOES NOT Expand Everywhere
 00:00: ... Space is big, and it’s getting bigger. But where does all that new space ...
 00:52: ... on the most enormous scales, but what about the here and the now? If space is expanding everywhere, is it expanding inside the solar system, ...
 01:24: ... in space tend to move around due to nearby gravitational influences  planets ...
 01:59: ... Hubble flow could be interpreted as everything moving THROUGH space, but there’s a cleaner picture. Soon after Einstein finished general ...
 02:24: ... of the Earth, a metric in GR is the coordinate system of a chunk of spacetime with 3 spatial and 1 temporal ...
 02:38: ... could be the 3D analog of our surface of a sphere, which would be a space that loops back on itself in all directions. Or it could be an infinite ...
 03:48: ... at the math. This is the FLRW metric  it’s basically Pythagorus for 4D spacetime  the squared proper distance between two points is the sum of the ...
 05:19: ... fact the shape of spacetime around massive objects is NOT the FLRW metric because the matter isn’t ...
 06:04: ... answer is no. Space within any gravitationally bound system is unaffected by the surrounding ...
 06:51: ... other way the balloon analogy fails is that the fabric of spacetime doesn’t get stretched in the way the rubber gets stretched  it doesn’t ...
 07:12: ... try something else. Lose another dimension of space so the universe becomes an expanding ring instead of a ,sphere, with ...
 07:45: ... expansion of space is seen in the divergence of our FLRW coordinate gridlines. Now the ...
 08:34: ... certain regions expansion won, and threw apart objects and the spacetime grids they trace. But in sufficiently dense regions gravity won and ...
 08:51: ... told you that space doesn’t get stretched out like rubber. In a sense new space gets created ...
 09:16: ... general relativity, space can be infinitely divided. That means we can start with a universe ...
 09:38: ... Similarly, we can take the universe of the present and define a grid of space  or a grid of points on our 1D ring universe. Then we rewind the ...
 10:06: ... of geodesic completeness, which we’ve talked about before. All spacetime paths can be traced to the infinite future or past until they hit a ...
 10:33: ... all works if space is infinitely divisible. But we know that at the smallest scales, ...
 10:52: ... out of the old Planck lengths. That implies an infinitely divisible space emerging from within each Planck ...
 11:22: ... go there today. But long story short  even with a quantized fabric of space, it’s still possible to expand it or condense it infinitely without ...
 11:59: ... that’s even true if empty space contains something. Like dark energy. Empty space has a very weak energy ...
 12:56: ... there’s your answer. The infinite scalability of space means the universe can and probably will expand forever with no effect ...
 13:16: ... we never would have even known that we live in an infinitely expanding spacetime. ...
 16:38: ... Maybe the universal wavefunction is the just that wavefunction in the space of infinite possible wavefunctions that constructively ...


20220427: How the Higgs Mechanism Give Things Mass
 01:48: ... point in space can wiggle, twist, oscillate in different ways. A ...
 02:31: ... The exact phase of the quantum wavefunction from one point in space to the next  local phase  doesn’t affect measurable ...
 08:09: ... just means there’s a numerical strength of the field everywhere in space. The potential energy part is the “shape” of the field, and is made ...
 09:34: ... to still make sense if there are rotations from one point in space to the next. That means adding a new gauge field in the ...
 16:02: ... will lead us to new clues about yet deeper unifying symmetries of space ...
 17:09: ... bit about you and what you'd like to see happen in the Space Time universe. There’s a link in the ...


20220420: Does the Universe Create Itself?
 04:57: ... In his words, “Every it — every particle, every field of force, even the spacetime continuum itself — derives its function, its meaning, its very existence ...
 08:42: ... maybe according to some secret pattern. Every answer narrows the space of possible correct answer, even if Alice still doesn’t know what the ...
 12:27: ... we just need to keep asking the right questions of a participatory space ...
 14:02: ... that could be complete nonsense. But I can say with certainty that PBS Space Time is generated by participation of its observers  that’s you guys  ...
 14:50: ... fair as long as you explain what you mean by that  or point them to PBS Space Time episode for the ...


20220330: Could The Universe Be Inside A Black Hole?
 01:07: We can think of the event horizon as the surface where the flow of space itself is like a river moving at the speed of light.
 01:15: ... black hole looks like an orb of blackness at a particular location in space, due to the fact that nothing that not even light can travel back out ...
 01:30: ... when all matter was compressed to infinite density and all points in space ...
 01:43: From the Big Bang space expanded, and it’s still expanding.
 01:49: ... space is expanding evenly everywhere, then there are distant regions of the ...
 02:46: ... black hole singularity seems to us to be a point of infinite density in space, while the big bang singularity is a time of infinite density that ...
 03:01: ... the big bang and black hole singularities do occupy all of space  the difference is that the big bang singularity exists in the past for ...
 03:44: These are the straightest paths that can be taken through a curved spacetime.
 03:48: In a sense geodesics form the grid that defines the fabric of spacetime.
 03:54: ... possible to define a geodesic at some point in space and time  say, the arc of a ball thrown through the air  and then you ...
 04:53: We call the Big Bang a past, spacelike singularity because it occupies all of space  in the past.
 05:01: A black hole contains a future, spacelike singularity.
 05:05: Which means that all geodesics within a black hole spacetime end at the singularity in the future.
 05:19: ... black hole singularity is the allencompassing future for the spacetime that lives beneath the event horizon in the same way that the big bang ...
 06:13: ... past, spacelike singularity of the white hole is surrounded by an event horizon that is ...
 06:24: Space flows at the speed of light across the event horizon from within.
 06:28: That’s starting to look like our universe  a past, spacelike singularity and an event horizon that can’t be crossed from the outside.
 06:35: But there’s still an “outside” in which the white hole appears as a bright, localized point in space.
 07:15: Same trick gave us wormholes and mirror universes, by the way, and we mapped these weird spaces in a previous episode.
 07:27: For one thing its made of pure spacetime  no matter included , and it;s highly inhomogeneous.
 07:48: And the spacetime curvature is nearly flat, so no crazy tidal forces like in a white or black hole.
 07:54: ... spacetime of our universe is well described by the ...
 08:36: ... but within the collapsing cloud the matter remains homogeneous and the spacetime is flat until it becomes a ...
 09:20: In fact you can describe the spacetime of a collapsing star by patching an FLRW metlric inside a Schwarzschild metric.
 09:35: So you can have what looks like a black hole from the inside, but looks like comfortably flat space inside the stillcollapsing star.
 09:47: Just flip the timel axis and you have a white hole containing a bubble of expanding space that looks much like our universe.
 10:27: ... don’t form singularities, but rather bounce back outward to create a new spacetimes from the resulting white hole  which itself creates new black holes, ...
 12:16: ... on ad infinitum in a series of black holes, forming an infinitely nested space ...


20220323: Where Is The Center of The Universe?
 01:53: It looks like the Milky Way is at the center of an colossal explosion, or as Calvin more poetically named it  a horrendous space kablooie.
 02:01: But the Big Bang isn’t an explosion emanating from one point in space.
 02:05: The recession of the galaxies is just as well explained if all of space is expanding evenly everywhere.
 02:12: Galaxies appear to be receding due the space between them stretching.
 02:20: In this picture the Big Bang isn’t something that happened at a single point in space, instead it happened everywhere at the same time.
 02:27: All space was created at that instant.
 02:57: His general theory of relativity explains gravity as the warping of space and time due to the presence of mass and energy.
 03:03: Explains gravity as the warping of space and time due to the presence of mass and energy.
 03:04: General relativity can be used to calculate the spacetime curvature produced by the Earth or the Sun to determine their gravitational effects.
 03:11: It can also give us the gravitational field of the entire universe, which tells us the shape of all of spacetime.
 03:22: ... into the universe into a fine paste and spreading it evenly through space. ...
 04:03: The FLRW metric also predicts that there are only three possible global shapes to 4D spacetime, determined entirely by one number the curvature.
 04:47: Positively curved 3D space is the easiest.
 05:37: So could it be that there’s a higher dimensional space in which our 4D hypersphere lives?
 05:43: Could there be an equivalent of “down” in that space that we are just too dimensionallychallenged to point to?
 05:52: Space can have curvature without there being anything for it to curve into.
 07:55: And if the universe really is closed, you’re also pointing at the point where all space occupied the geometrical center of the hypersphere.
 08:41: They’re the grid that defines the fabric of space time in general relativity, and correspond to the paths followed by light.
 08:58: In the language of GR, we call this ending of spacetime paths “geodesic incompleteness”.
 09:19: ... say that the Big Bang is a past, spacelike singularity  which means it occupies all space at t=0 and is in the ...
 12:09: ... symmetric cloud, but beyond that cloud the density could change, or space could be ...
 13:11: ... that our universe is just one bubble of relatively slowly expanding space embedded within an unthinkably colossal region of exponentially ...
 13:51: ... even you personally, are not at the very center of a very nonCopernican spacetime. ...
 18:31: ... that were not clearly associated with stars and had radio frequency spacing similar to Earthly ...


20220316: What If Charge is NOT Fundamental?
 13:24: We’ll find out soon as we continue to unravel the tangled symmetries of spacetime.
 13:57: You can check it out over on PBS Voices, link in our description, and let them know (politely) that Space Time sent you.


20220308: Is the Proxima System Our Best Hope For Another Earth?
 15:04: ... there, on a planet around Sol, AlphaCentauri’s nearest neighbor across spacetime. ...
 15:31: ... telescope to ever leave Earth, turned in its first photo of outer space. ...
 16:08: ... we managed to find a loophole in the international space treaty and have claimed ownership of Proxima B. As a sign of our ...
 17:27: ... being “hit” by the nonlinearities across the wavefunction introduce by spacetime ...
 17:38: And on the subject of gravity, Jan Wester asks why the curvature of spacetime can’t be in a superposition.
 17:58: ... which all the quantum weirdness can play  those are the dimensions of space and ...
 18:09: Even including relativity and the shifting nature of space into time and vice versa, you still have a consistent if mutable underlying grid.
 19:37: ... we can see the difference in the phase angle between two points in space. ...


20220223: Are Cosmic Strings Cracks in the Universe?
 00:58: ... thickness but prodigious mass and they lash through space at a close to the speed of light. They could be the most ...
 05:59: ... That means we can ascribe an angle to every point in space defining the relative value of the two components of the ...
 07:33: ... cyclones to swirls of hair on your head. But in a 3D space, like, you know, actual space, this sort of defect manifests ...
 10:09: ...  which is the warping of background light sources due to the spacetime warping effect of gravity. When a massive object sits ...
 12:19: ... workings of the universe than to find a crack in the fabric of spacetime. ...


20220216: Is The Wave Function The Building Block of Reality?
 05:00: The behavior of the wave function is described by the Schrodinger equation, which tracks its evolution through space and over time.
 09:25: ... General relativity says that the mass from that object will warp the spacetime around it. But quantum mechanics says that this object can be in a ...
 12:55: ... of shifting realities give rise to our solid, familiar, and singular space ...
 13:19: ... you for collapsing our wave function in the direction of making more space ...
 14:52: ... exactly right. Gravitational waves have to move along the same fabric of spacetime as everything else. After all, they are wiggles in that very fabric. So ...
 18:37: ... And I'll refer you to that episode for more answers. dannymac63 likens Space Time to a black hole, in which it’s captivating and radiates information ...


20220210: The Nature of Space and Time AMA
 00:03: ... dennis of space time i hope you could hear me okay this is the second or third in our ...


20220127: How Does Gravity Escape A Black Hole?
 00:35: ... traditional force, but rather in terms of the curvature of the fabric of space and ...
 00:54: These are objects of such extreme density that the fabric of space is dragged inwards at greater than the speed of light.
 02:02: For example we have gravitational waves  ripples in spacetime caused by certain types of motion.
 02:36: It would take 8 minutes for us to notice the sudden darkness, and the Earth would continue to orbit the nowempty patch of space for the same time.
 02:46: It would take 8 minutes for the Sun’s deep indentation in the fabric of space to smooth itself  in the wake of some pretty crazy gravitational waves.
 03:34: In GR, the gravitational field  the curvature of spacetime  has an independent existence to the mass that causes it.
 03:54: ... space around a black hole doesn’t need to know about the mass of the central ...
 04:02: There’s this old analogy of space as a sheet of rubber stretched by a heavy mass.
 04:24: ... way to think about the action of gravity: instead of a stretching spacetime, we can think about space as flowing towards the massive ...
 04:32: The “speed of space” is just the speed of a freefalling, or inertial observer.
 04:38: Falling from very far away, an observer and the patch of space that they occupy reach light speed at the event horizon of the black hole.
 04:51: The water is the fabric of space, and it accelerates towards the drop.
 05:27: One patch of space doesn’t need to see the ultimate source of the field  it only needs to see the next patch along.
 06:08: Now in quantum mechanics  or more specifically quantum field theory  forces are mediated by particles, not by the geometry of spacetime.
 10:06: ... gravity is communicated by the curvature of spacetime or by virtual gravitons, we maintain a causal connection to the mass ...
 11:18: You interact with the local curvature of spacetime, which is produced by the past mass, which from your point of view is on the event horizon.
 12:00: ... continue to exert its gravitational influence on exterior regions of space ...
 12:41: In one of those simulations you live 3000 years and become emperor of space, and in another you star in Interstellar instead of Matthew McConaughey.
 16:04: Distant galaxies appear to be moving away because space on the largest scales is expanding evenly everywhere.


20220119: How To Build The Universe in a Computer
 12:01: ... it inside our computers, and then peering into that simulated space ...


20220112: How To Simulate The Universe With DFT
 01:48: ... of a quantum particle  that’s this psi thing  changes over space, assuming the particle is in some environment described by a sum of ...
 02:46: Our Schrodinger equation just dealt with one dimension of space, x.
 04:25: That’s a 1dimensional space of possibilities.
 04:32: Our total outcome space includes 6 possible outcomes of the second die for each of the 6 possible outcomes of the first  so 36 outcomes.
 04:42: We can represent this by first drawing a line to represent the 1D outcome space of the first die.
 04:48: The second die expands this space to 2D.
 06:29: Well, these systems do sort of exist in a manydimensional space called configuration space.
 06:37: ... for the classical case we can throw away most of configuration space and consider just the few points in that space where the particles ...
 06:48: In quantum mechanics, we’re dealing with the wavefunction, and the wavefunction fills all of configuration space.
 08:02: But if we want to keep the quantum behaviour of quantum mechanics we can’t throw away most of configuration space like we do in Newtonian mechanics.
 10:21: It’s a 3D entity  just a map of how much “electronness” exists through space.
 13:51: Our computationally tractable reality, due to its very few dimensions of spacetime.
 15:07: The assumption in this calculation is that the black hole came from interstellar space and fell into the solar system.
 20:19: ... Dyson Spheres to power a hash cashing matryoshka brain. Our awesome spacefaring, megastructurebuilding future suddenly sounds a lot more ...


20211229: How to Find ALIEN Dyson Spheres
 00:56: Not by covering the entire Earth, but by building solar collectors in space.
 04:47: But our infrared telescopes advanced quickly, and crucially they found their way into space.
 13:55: ... noticed by younger species when they emerge in distant, future parts of space ...


20211220: What Happens If A Black Hole Hits Earth?
 01:12: The early universe was a wild place. All space everywhere was a boiling particle soup.
 04:26: ... fast when it hit the earth  it must have fallen in from interstellar space, and so should be traveling from several 10s to 100s of km per ...
 13:02: ... the crazy blackholespawning chaos that defined the birth of this space ...
 13:13: ... Above the Noise that dives into the research and debates the merits of Space Tourism and Billionaires in Space. I know from previous episodes that ...
 13:52: ... when they’re first released, you actually help spread the show to other Space Time subscribers and to new viewers. So if you’re already part of the ...
 16:33: ... gravitational field is fundamentally the same as inertial motion in free space. That means that an observer falling through a black hole event horizon ...
 17:30: ... that vibrations in a quantum field on the surface of a 4D hyperbolic space are equivalent to objects inside that space. And if this sounds ...


20211210: 2021 End of Year AMA!
 00:02: ... hi welcome to the end of year space time ama i'm meadow dowd as you may know um and i'm very excited to be ...


20211117: Are Black Holes Actually Fuzzballs?
 05:52: ... strands that themselves are embedded within complex, manydimensional spaces. ...
 11:28: It’s not that the interior is empty, but rather that space and time literally end at the surface.
 11:35: ... into stringy mess, is pushed up to the surface and the interior grid of spacetime is deleted from the ...
 12:38: For a fuzzball, spacetime closes on itself at the event horizon.
 13:43: Perhaps that’ll come when we find evidence of fuzziness surrounding those distant holes in the fabric of space time.
 14:35: The Space Time audience has always had a great showing on the annual survey and we’d love for that to continue this year.


20211110: What If Our Understanding of Gravity Is Wrong?
 02:52: ... of relativity, which explains gravity as the curvature in the fabric of space and time rather than just as a classical ...
 08:35: ... field  a multicomponent object that describes the curvature of spacetime. ...
 08:44: These guys added a new scalar field  a field that’s just a single numerical value everywhere in space.
 14:01: ... particles, or beyond general relativity by hidden gravitational modes of space ...
 14:31: For instance, CuriosityStream has Black Holes: Messages from The Edge of Space, which examines not only black holes, but neutrino astronomy.
 14:54: For more information, go to curiositystream.com/PBSSPACETIME and use the code SPACETIME for a trial.
 15:32: Check out Vitals in the link in the description, and tell them that Space Time sent you!
 15:45: ... Smith asks, if the configuration space Lagrangian seems to bridge quantum mechanics and relativity, ...
 16:46: Isn’t it spacetime that bends, not light?
 16:52: Light does travel a straight line if you look at an infinitesimally small patch of space.
 16:58: Imagine light traveling through curved space as like an and walking across a disco ball.
 17:10: Well, in space the disco ball mirrors are infinitesimally small, but over those regions the path is straight.


20211102: Is ACTION The Most Fundamental Property in Physics?
 05:52: ... describes the force of gravity in terms of the bending of the fabric of space and time. One of Einstein’s motivations in developing general relativity ...
 07:09: ... an observer in their own frame of reference. All objects moving through space time move through paths that minimize the time measured on that ...
 11:59: ... paths that take the shortest path, but not the shortest path through space, the shortest path through something called configuration ...
 12:16: ... this “configuration space” is what ties all of this together. Configuration space is the space of ...
 13:23: ... us to track the evolution of all quantum fields through configuration space, and so predict the behavior of all known ...
 13:46: ... and Dirac and Feynman, each seeking a path through the configuration space of ideas, guided by mysterious principles, not least of which is the ...
 17:24: ... Andy points out that constructor theory seeks to narrow down the space of all possible functions that might represent physical laws into the ...
 17:54: ... operates under certain assumptions (infinite/finite, discrete/continuous spacetime, invariance, quantum etc.) then constructor theory gives us insights as ...


20211020: Will Constructor Theory REWRITE Physics?
 05:31: ... task: as a freefalling body the apple must follow a geodesic through spacetime, which results in it falling towards the ...
 06:55: ...  by applying counterfactual statements  we can rule out a much larger space of impossible processes than in the mechanistic ...
 11:04: ...  of what is possible and what is impossible within this physical space ...
 11:25: ... Check it out, link in our description, and let them know that Space Time sent ...
 11:52: ... Ari Paul. Ari, without your support, the task of Space Time would be impossible, which in the language of ...
 12:30: ... nothing. As in could it quantum teleport even through empty space in Fact do particles even travel at all or do their ...
 14:00: ... side of the barrier without crossing the intervening space. This is a tough one. It’s not clear that the particle itself is ...
 14:48: ... If every particles wavefunction is really spread over all of space can anything really move at all except in relation to something, ...
 15:34: ... be a simulation. TBatlas says that the universe saves CPU space by not fully rendering particles that aren't being viewed ...


20211013: New Results in Quantum Tunneling vs. The Speed of Light
 07:01: Launch a particle through empty space with a well defined starting position, and it’s position wavefunction will spread out before the finish line.
 07:28: ... by a barrier faster than you can transmit the same message through empty space? ...
 08:17: Should you send the message through empty space, or through a barrier?
 12:37: The universe insists that we take the long way around, and as fast as we can find them it seals up any new shortcuts through spacetime.


20211005: Why Magnetic Monopoles SHOULD Exist
 10:05: ... arrow that points in a particular direction  not pointing in physical space, but in the space of those 3 degrees of ...
 10:24: There should be no noticeable effect even if the direction of the Higgs field changes smoothly across space.
 10:47: These are topological discontinuities  points that can’t be removed by a smooth defomation of space.
 13:24: ... also look for magnetic monopoles coming from space  typically using cosmic ray observatories  or contributing to the ...
 13:48: And so many of us remain obsessed with this elusive beast, and convinced of its inevitability according to the symmetries of space time.
 16:51: When degeneracy pressure is broken it’s because new space in quantum states opens up.


20210921: How Electron Spin Makes Matter Possible
 05:59: ... the position of a particle can look like a sine wave moving through space. If you have two such wavefunctions overlapping  like two photons in a ...
 06:49: ... spinor wavefunction of the electron can “wave” through space, but it includes another wavy part. It has its rotational degree of ...
 14:26: ... mysteries. But that is a risk we’ll always take for you here on space ...
 18:44: ... finally, Steve Bogucki tells us that Space Time made him realize that he’s more interested in quantum physics than ...


20210915: Neutron Stars: The Most Extreme Objects in the Universe
 01:02: ... For this journey we’re going to need an unthinkably advanced spacecraft. In fact, there is no imaginable technology that could ...
 02:00: ... magnetosphere is very different from the magnetized space around the earth or sun. It’s filled with electrons ...
 03:07: ... are mostly hydrogen and helium, captured from the nearlyempty space surrounding the ...
 03:27: ... 100 km thick, depending on how you define the edge of space, the neutron star’s atmosphere is barely a meter thick, with most of ...
 07:06: ...  neutrons leak from nuclei into the evernarrowing space between them. Now we don’t know exactly how deep this phenomenon ...
 07:43: ... the neutron drip intensifies, the space between the nuclei fills with a neutron gas. Meanwhile the ...
 13:06: ... and leave behind the strangest and most extreme parts in all of space ...


20210907: First Detection of Light from Behind a Black Hole
 00:56: ... thought it would be worth doing a space time journal club on the Nature paper by Wilkins, Gallo, Costantini, ...
 11:54: ... just love it when we can map the space around black holes by watching flickering points in the sky, and in that ...
 14:54: The difference is that in the preinflation universe, space was expanding exponentially quickly due to the high value of that field.


20210818: How Vacuum Decay Would Destroy The Universe
 00:21: ... by the properties of the quantum fields that pervade all space. The quantum fields give rise to the particles that make up all ...
 01:31: ... that let’s try an analogy. Think of all space as being sort of springy at every point. As a simplistic ...
 05:43: ... then no big deal. Even if the field at one location of space tunneled or was excited into the false minimum, it ...
 06:08: ... filled with the Higgs field in a false vacuum. At a single point in space, a quantum tunneling event drops the field into the true vacuum. ...
 10:10: ... there’s a tiny but real probability that a patch of space will tunnel between the false and true vacuums. Wait long enough ...
 10:54: ... energy minima. If enough energy can be pumped into a patch of space, the Higgs field can hop between minima without tunneling. ...
 12:07: ... of years  before vacuum decay swallows this fragile and metastable space ...


20210810: How to Communicate Across the Quantum Multiverse
 03:30: ... equation describes how the wavefunction of a quantum system changes over space and time  and so it should completely determine the measurements we can ...
 04:30: ... in a particular way  whether that medium is water, air, the fabric of spacetime itself. Waves can happen in any elastic medium  anything that tends to ...
 12:47: ... me. There are, after all, many worlds in the greater Everettian space ...
 13:40: ... experiments. If you check it out, remember to tell them, politely, that Space Time sent ...
 16:27: ... goes supernova. And then guesses the correct answer  it dissipates into space with the matter, potentially leading to electromagnetic radiation. And ...


20210803: How An Extreme New Star Could Change All Cosmology
 05:24: ... the European Space Agency’s GAIA satellite changed that by measuring parallaxes for a ...
 07:24: ... First let’s think about what happens when you add mass to less weird spacestuff, say a planet or a star. The matter inside is crushed closer together ...
 13:41: ... a powerful clue towards a better understanding of this generally weird space ...
 14:14: ... show. Without your support and enthusiasm, we’d probably have sunk to spacethemed reaction videos and quantum mechanics based pranks. As always, thanks ...
 17:08: ... or to explain dark energy? Or could magnetic fields be used to power spacecraft? So the answer is no, although magnetic fields do have important effects ...


20210721: How Magnetism Shapes The Universe
 00:39: It would mean seeing the literal threads of the fabric of spacetime.
 00:50: But there’s really only one gravitational field in the universe  manifest as the fabric of spacetime itself.
 05:20: ... that far  or rather magnetometers  on board the Voyager 1 and 2 spacecraft which crossed the boundary into interstellar space a few years ...
 06:00: The interstellar medium  the space between the stars  is scattered with tiny specks of dust produced in past supernova explosions.
 10:44: Their material tends to spill into the space around the galaxy before slowly raining back in, where it can be used for new star formation.
 12:59: ... magnetic fields, to better understand the mysteries of this magnetic space ...


20210713: Where Are The Worlds In Many Worlds?
 04:38: To calculate this we use the Schrodinger equation, which tells us how the amplitude of the wavefunction changes over time and space.
 12:26: But that’s for another time  and I’ll do my best to bring it to every future branch of our splitting quantum space time.


20210707: Electrons DO NOT Spin
 08:50: ... That’s also true of vectors  which are just arrows pointing in some space. But for a spinor you need to rotate it twice  or 720 degrees  to ...
 13:30: ... things we call spinors  strange little knots in the subatomic fabric of spacetime. ...


20210623: How Quantum Entanglement Creates Entropy
 13:09: ... long  only until our next episode on this informationtheoretic space ...
 13:44: ... the one on the Kessler syndrome  the exponential buildup of space junk around the earth. And then the one about the Plank ...
 15:02: ... there’s a threshold in the exponential increase of space debris where we can no longer operate safely in space, which ...
 16:20: ... Johnson asks a good one. If space is like a 3D grid of Plancklength scale, and movement ...
 16:39: ... beyond your adjacent grid points. But really we can’t think of space as a simple rectilinear grid. For example, Michal ...
 18:41: ... the Kessler syndrome is like zombies  getting hit by other space debris turns you into space debris. Which could mean there’s ...
 18:54: ...  formally the worst zombie type. Fortunately there’s no sound in space so you can’t here all the gurgling and screaming that ...


20210616: Can Space Be Infinitely Divided?
 00:40: ... you can half a number, but the same might not be true of space. The planck length is thought to represent the minimum ...
 02:38: ... of constants so important? Well, it represents the scale at which space itself is thought to “become quantum”. I say “thought” ...
 05:08: ... For example, we should be able to measure location in space down to any conceivable precision, perhaps even infinite ...
 05:45: ... and second, that mass and energy warp the fabric of spacetime. So back to Heisenberg’s ...
 06:39: ... one last dip into the math to see how big this uncertainty is. Space is stretched by a factor equal to the effective mass ...
 07:10: ... increases your measurement uncertainty due to the warping of space. So this is one way of thinking about it  the Planck ...
 07:48: ... and so represents the fundamental limit of the measurability of space. ...
 09:58: ... that mean that smaller sizes/lengths/chunks of space don’t exist? Does that mean space is not continuous on the tiniest ...
 10:55: ... we don’t really know how well this picture represents space on this scale. The nature of space is defined by Einstein’s ...
 11:26: ... meaningful length, at least for any intuitive conception of space. Quantum uncertainty thwarts our attempt to understand the ...


20210609: Are We Running Out of Space Above Earth?
 00:23: Boosters, dead satellites, and sometimes even old space stations get dropped out of the sky fairly often.
 00:37: Just last month a hole was found in a robotic arm on the international space station  punctured clean through by a fastmoving piece of shrapnel.
 00:46: ... accumulation of space junk poses a huge risk to all human operations in space especially if we ...
 01:06: ... launch of Sputnik in 1957 kicked off a space race, and the number of satellites in space has grown ever since, and in ...
 02:04: ... now there are probably over 3 million kilograms of space junk, vastly outweighing our operational satellites and nearby natural ...
 02:14:  forming a giant spacetornado of death above our heads.
 02:18: The main thing protecting satellites from space junk is space itself.
 02:23: Space is, as the name implies, spacious, and so collisions are relatively rare, or at least for the moment they're rare.
 02:37: And collisions produce more space junk that produces more collisions.
 03:23: The more space junk we have, the more space junk we make.
 03:44: And that needs to happen faster and better than the rate that space junk is made.
 03:52: Large pieces of space junk can be tracked using ground based radar and more precise optical and lidar methods.
 04:10: The international space station has to dodge tracked space junk roughly once a year.
 04:31: ... it also means we can lose track of space junk because the amount of drag can change  in particular, during times ...
 04:47: The smaller the space junk the more susceptible it is to atmospheric drag.
 05:12: And there are something like half a million of these hypervelocity space bullets flitting around up there.
 06:36: OK, let’s look a bit harder at the sources of space junk to see if these mitigating processes have any hope of saving us.
 06:43: Over 40% of the catalogued space junk is debris from the upper stages of a handful of US rockets that exploded after releasing their payloads.
 06:53: These plus few other catastrophic events are responsible for most of the fragmentary space junk.
 07:26: Relatively few events have produced as much of our most dangerous space junk.
 08:33: So bringing this all together we can paint a picture of our trashed orbital space.
 08:54: ... example, even though the International Space Station orbits several hundred kilometers below where the IridiumKosmos ...
 10:06: We’re currently in the slow part of the exponential rise, so we have years or decades of useful space ahead of us.
 10:22: SpaceX plans to launch constellation of over 40,000 satellites as a global internet network.
 10:34: Now SpaceX insists that they have collision mitigation systems planned, even if they haven’t told us exactly what those are.
 11:12: Presumably, at some point, some of them without the same care that SpaceX claims to be taking.
 11:29: Some scifi writers like to present Kessler syndrome as an impassable maelstrom, a giant space blender, effectively imprisoning us on the Earth.
 12:17: At the late stages of the Kessler Syndrome, the space below a couple of thousand km may be largely unusable  at least for a while.
 13:14: ... our cosmic front yard, and continue our safe use of Earth’s orbital space ...
 13:28: This show would be much, much harder to do without the help of the Space Time community on Patreon.
 13:49: Tiffany, we’ve used your contributions to fund a research program to solve the space junk problem.
 14:31: Well first of all, Planck relics would be so impossibly tiny that all matter would be like empty space to them.


20210525: What If (Tiny) Black Holes Are Everywhere?
 04:19: One big assumption is that the space near the event horizon isn’t TOO strongly curved compared to the smallest quantum scale.
 06:48: ... conflict, and is sometimes thought of as the smallest possible chunk of space. ...
 09:52: It also breaks another rule about how much information a given region of space can contain  the Bekenstein bound.
 09:58: A way around this has been proposed  what if space inside black holes actually expands to a region larger than the event horizon?
 11:00: Because that’s how empty most of space is.
 11:07: ... black hole, a tiny hole punctured in your neighborhood’s fabric of spacetime. ...
 15:45: Thanks  by these are just standard tricks used in film … by us space aliens.


20210519: Breaking The Heisenberg Uncertainty Principle
 05:01: ... Gravitational Wave Observatory measures ripples in the fabric of space caused by cataclysmic events up to billions of light years ...
 08:03: ... phase space, this amounts to a shrinking of the uncertainty in one dimension, and a ...
 10:17: ... possible to force ever more certain measurements of this uncertain space ...


20210511: How To Know If It's Aliens
 00:00: ... follow one rule on Space Time: It’s never aliens. But every rule has an exception and this rule ...
 00:19: 45 years ago, a pair of small Earth spacecraft inserted themselves into orbit around Mars.
 06:27: ... solar system just fast enough that it most likely fell from interstellar space. Its pulsing was interpreted as being due to an elongated object ...
 08:28: ... of an extrasolar ice world similar to Pluto, ejected into interstellar space by an impact. Pluto also has a red tinge due to radiation processing its ...
 09:21: ... the star’s light i n a way consistent with clouds of particulates  space dust, rather than an opaque object. So we’re probably looking at a ...
 13:10: ... may finally prove that we’re not the only living denizens in all of space ...
 15:39: ... direction. This would have so much energy on release that even just the space dust from a short interstellar trip would become a beam of energy ...


20210421: The NEW Warp Drive Possibilities
 00:15: He showed us that space and time can be warped  and so the warp drive was conceived.
 00:31: In 1915, Albert Einstein’s general theory of relativity revealed that the fabric of space and time is mutable and dynamic.
 00:39: You can’t travel through space at faster than the speed of light  but there’s no speed limit for the fabric of space itself.
 01:06: In Islands of Space, its authorJohn Cambell talks about increasing the cosmic speed limit by curving the fabric of space.
 01:16: ... historical dictionary of science fiction, the first mention of a “spacewarp” as a propulsion mechanism was in J. Williamson’s 1936 story The ...
 01:27: Spacewarp drives, timewarp drives, and eventually just warp drives became an increasingly popular way of breaking Einstein’s rules.
 02:46: ... certain circumstances we can think of space itself as moving  and there’s no limit to the relative motion of two ...
 03:01: For example inside black holes where we can think of space as flowing downwards faster than light.
 03:13: The warp drive takes advantage of this loophole by accelerating a patch of space relative to its surroundings.
 03:37: It includes a comfortable, flat region of space surrounded by a region of extreme spatial curvature.
 03:43: The space behind this bubble is expanded, while the space in front is contracted.
 03:49: The resulting pushpull propels the bubble and any spaceship that it contains.
 04:01: ... distribution of mass, energy, on the right side and it spits out the spacetime geometry on the ...
 07:22: ... Jose Natario demonstrated that the whole expansion and contraction of space was only a sideeffect of Alcubierre’s choice of warp field, and he ...
 07:38: Natario, and now Bobrick and Martire, define warp fields as bubbles that slide through space  potentially at superluminal speeds.
 08:06: This seems in conflict with Alcubierre himself, who wrote that the warp bubble “pushes” the spaceship  accelerates it from rest.
 08:44: ... negative energy and an enormous amount of it for any decent sized spaceship. ...
 09:33: We can think of the warp field as a special type of isolated wave moving through space  what we call a soliton.
 09:45: ... example in the Alcubierre field the warp is in front and behind the spaceship, while the exotic matter is in a ring around the direction of ...
 10:27: This would resulting in expansion and contraction of space in similar regions.
 10:31: The entire patch of spacetime would travel at superluminal speeds, carrying a spaceship with it.
 12:47: And possibly also building a starship, to propel humanity into the galaxy on waves of warped space time.
 12:55: Space Time gets an enormous amount of help from our Patreon supporters.
 17:47: So maybe Odin learned his quantum mechanics watching space time like the rest of us.


20210413: What If Dark Matter Is Just Black Holes?
 01:06: These hyperdense holes in the fabric of spacetime seem to be great dark matter candidates  being so black and holey and all.
 07:44: ... like a black hole passes in front of a distant light source, the warped spacetime around the black hole acts like a lens, magnifying the source in an ...
 11:39: Whatever the case, dark matter is freaky stuff, fitting as the main material ingredient of our generally freaky space time.


20210407: Why the Muon g2 Results Are So Exciting!
 11:56: And that dance, may just have revealed to us the next step on our path to a more complete understanding of our quantum space time.


20210323: Zeno's Paradox & The Quantum Zeno Effect
 02:13: In order to travel from start to end, it has to flick between these states without occupying intervening space.
 03:18: ... travel its path smoothly and gradually, but still without occupying the space in ...
 12:27: So there you have why a watched quantum pot never boils. And it's because you did watch space time.


20210316: The NEW Crisis in Cosmology
 01:16: ... is. So you may have heard that the universe is expanding. Space on the largest scales is stretching, throwing galaxies apart ...
 06:22: ... as direct a method as you can get, short of building a giant space ruler. Ultimately, refining the supernova distance measurements ...
 08:03: ... Things started to get better when we put telescopes in space  above the blurring effect of Earth’s atmosphere ...
 10:40: ... light around massive objects due to their warping of spacetime. One manifestation of this is when a distant quasar  a giant, ...
 12:25: ... case, of the strange forces driving our everexpanding spacetime. ...
 12:52: ... constant is. But your support grants some much needed stability to spacetime  the youtube show, not the expanding fabric of ...
 13:38: ... relativity. In relativity, there's this thing called the spacetime interval which describes the separation between two events ...
 14:47: ... would also need to justify why the c in the spacetime interval has to be the speed of light. It's worth a full episode to ...


20210309: How Does Gravity Affect Light?
 05:13: Let’s start with the goodold equivalence principle again, and a spaceship attacked by giant alien spiders.
 06:31: To get technical: any massive object has a component of its 4dimensional spacetime velocity  its 4velocity in the time direction.
 09:55: But notice that I said LOCAL speed of light  that means everyone measures the same speed of light passing through their own local patch of space.
 10:12: A photon passes by, and the amount of time it takes to cross that space is larger than if Earth wasn’t there.
 10:19: ... your clock is ticking faster than clocks in the gravitational field, and space within the gravitational field is ...
 11:02: But for you, tracking this from a distance, the effective speed of light decreases downwards, because time slows and space stretches.
 12:08: ... way, you can show that gravity is due to a freefalling waterfall of space, rather than a gradient in ...
 12:32: Light is a wave and a particle; time slows or space flows in gravitational fields.
 12:38: ... of some more fundamental reality underlying this generally relative spacetime. ...


20210224: Does Time Cause Gravity?
 00:04: If even a tiny bit of your breakneck temporal velocity leaks into one of the dimensions of space.
 01:50: I lA nice china teapot hanging in space, minding its own business.
 02:02: At least, it stays motionless with respect to the three dimensions of space.
 02:09: We can show this with our old friend the spacetime diagram.
 02:13: Let’s have just two dimensions of space and so we have space … for time.
 02:21: You could say that it has a positive velocity through time, and zero velocity through space.
 02:33: We know that the presence of mass and energy warp spacetime  and the most intense part of that warping is in time  our gravitational time dilation.
 03:49: In Einstein’s relativity you have to remember that time and space are not independent of each other.
 03:54: Objects don’t just have a velocity through space or through time  they have a velocity through spacetime.
 04:47: All individual 4velocities start out being purely in time, but the sum is rotated partially into space.
 05:22: ... travels at the speed of light through space  obviously enough  and we know that nothing with mass can reach that ...
 05:31: But if we interpret time as a dimension like space, then a stationary mass really is moving at the fastest possible speed in the temporal direction.
 05:50: On the other hand, light itself travels at the speed of light through space only, and not at all through time  a photon’s clock is frozen.
 05:57: ... it’s 4velocity is entirely rotated out of the time direction into space  although technically photons and other massless particles don’t have a ...
 06:13: In this picture, a falling object trades some of its enormous velocity through time to pay for a small velocity through space.
 06:21: To us currency exchange looks favorable for space  a teapot gains a rapid plummet to its doom for an imperceptible slowing of its clock.
 07:11: ... nothing truly occupies only a single, perfectly defined position in space  quantum uncertainty means that everything is always at multiple places ...
 08:29: ... it settle, and we’re going to need some time to make that new episode of space ...


20210217: Gravitational Wave Background Discovered?
 00:00: ... wave detector that may have detected a foundational element of space itself the gravitational wave background when the laser interferometer ...


20210210: How Does Gravity Warp the Flow of Time?
 00:25: ... within a gravitational field from a frame of reference floating off in space in the absence of ...
 01:30: General relativity, or “GR” explains the force of gravity as being due to curvature in space and time.
 01:45: John Archibald Wheeler put this notion the most pithily: Spacetime tells matter how to move; matter tells spacetime how to curve.
 02:12: ... one thing, it implies that curvature in the fabric of space is the cause of gravitation  but that’s only half  actually less than ...
 02:22: Matter tells space AND time how to curve, and it’s the curvature of time that’s mostly responsible for telling matter how to move.
 06:05: But first, let’s try this  build our lab into a giant, ringshaped space station.
 06:18: Let’s also suit up a physicist and have them float in space at one spot as the space station turns.
 07:36: We can see that when we use a spacetime diagram to show how the traveler tracks the passage of time back on Earth.
 07:52: Here’s the spacetime diagram for our rotating lab.
 07:56: Now 2 dimensions of space instead of one.
 07:58: The spacetime path or worldline of the lab is a helix, and the lab’s perception of “now” is this shifting plane.
 08:07: It’s easier to see if we just take a slice out of this  one dimension of space again.
 09:53: ... to be in a gravitational well with a constant acceleration equal to her spaceship’s ...
 10:17: ... motion in a gravitational field is very different from our rotating space station then both gravitational time dilation and kinematic time ...
 11:51: The curvature of space by matter isn’t nearly enough to give gravity at the strength we feel it.
 12:04: And I’ll show you exactly why that’s true real soon, when we explore the tangled connections between time and gravity in a curved spacetime.


20210126: Is Dark Matter Made of Particles?
 12:35: ... to this completely invisible and vastly more massive sector of dark spacetime. ...
 12:47: ... go, we just wanted to let you know that while we love talking about Space, if you have more Earthly concerns, you should check out PBS Terra on ...
 13:39: Would a spaceship traveling near the speed of light cause a closed universe to contract so much that it would smash into its own ass?


20210119: Can We Break the Universe?
 00:26: But from that can the inevitable conclusion that space and time themselves were relative  depended on the velocity of the observer.
 01:04: Say we have a spaceship traveling from Earth to a nearby star at a good fraction of the speed of light.
 01:09: ... relativity tells us that the clocks on the spaceship will appear to tick more slowly from the point of view of a stationary ...
 01:18: And the spaceship would also appear squished in the direction of its motion in what we call length contraction.
 01:28: The spaceship can think of itself as stationary  it perceives the Earth as racing away from it and its destination star racing towards it.
 01:42: ... contradictions only become paradoxes if the different observers  on the spaceship and on Earth  can compare the results of an experiment and get ...
 02:23: Imagine our spaceship can travel very, very close to the speed of light.
 02:26: So close that the distance across the entire universe contracts to a size smaller than the spaceship itself.
 02:41: ... the frame of a spaceship moving at near lightspeed, the universe could contract to the point ...
 03:24: ... of a pair of twin hops in a spaceship and travels at a good fraction of the speed of light to a nearby star ...
 04:07: The best way to see this is on a spacetime diagram.
 04:12: We have time on the yaxis and just one dimension of space on the x.
 04:15: Let’s say we’re in Earth’s reference frame so the Earth doesn’t move in space  just straight up, which means forward in time.
 04:22: The spaceship moves in both space and time  first away from the earth and then back towards it.
 04:33: ... the spacetime diagram, the set of simultaneous events for a motionless observer lie on ...
 05:12: ... the spacetime diagram, that’s whenever one of these lines of constant time extending ...
 05:46: Our ultimate question is about a spaceship crashing into itself in a closed universe  and trust me we’re getting there.
 06:20: But to see why we need a much weirder version of the spacetime diagram.
 06:24: We’re still just doing one dimension of space, but now that dimension loops back on itself.
 06:29: We end up with a spacetime cylinder.
 09:46: Again, the best way to see this is on a spacetime diagram.
 09:53: The doors of the barn are a certain separation apart in space  solid lines in the diagram.
 10:48: Does a nearlightspeed spaceship smash into it’s own rearend in a closed universe?
 11:01: ... happens to a ladder in a pacman barn, or a spaceship in a closed universe, when the barn or universe are length contracted to ...
 11:12: The answer is in our looped spacetime diagram.
 11:18: So that’s also the line on which we lay down points along the length of our spaceship.
 11:23: That’s the “current” spaceship as it sees itself.
 11:26: And look  the spaceship DOES cross this point in space  our seam  and sort of exists there simultaneously.
 11:34: But there’s no collision, because the nose of the spaceship exists in the future, and the tail in the past.
 11:40: They exist at the same point in space at different points in time.
 11:44: ... no matter how fast the spaceship travels, it will only elongate along this helix  safe from collision ...
 11:54: Long story short nearlightspeed spaceships in closed universes or ladders in pacman barns are safe from colliding with their own asses.
 12:05: ... deeply strange, but unfailingly selfconsistent theory of Einstein’s spacetime. ...


20210112: What Happens During a Quantum Jump?
 00:36: ... orbit or energy level to another, without ever occupying the intervening space. ...
 09:57: Well, the spacing between events did appear to be random, as Bohr thought.
 12:06: ... random processes, or is driven by rigidly deterministic mechanic of space ...


20201222: Navigating with Quantum Entanglement
 11:40: ... physics to flock together to navigate the hidden lines of a geomagnetic space ...
 12:07: ...  you once asked me a question about space contraction in special relativity and whether or not a spaceship could ...


20201215: The Supernova At The End of Time
 00:35: ... holes evaporate  and even those will be relatively weaksauce as far as space explosions ...
 07:35: ... all white dwarfs must cool to the temperature of the ambient space  now a frigid 3 Kelvin, but in the future even colder than that as the ...
 11:45: ... look forward to  Iron stars exploding in unimaginably distant future of space ...
 12:54: ... from the increase in correlations between your brain  or any patch of space  and both the surrounding universe and the ...


20201208: Why Do You Remember The Past But Not The Future?
 04:36: Time increases upwards, while the horizontal axis is separation in space.
 11:34: ... and memory away from the inexplicably low entropy beginning of space ...


20201118: The Arrow of Time and How to Reverse It
 01:58: ... use our goodold block universe picture, where we have 2dimensions of space and one dimension of time, with time flowing ...
 02:08: ...  let’s say, electrons. They move up in time and towards each other in space. When they get close they deflect due to the repulsive electrostatic ...
 02:53: ... don’t even require time to “flow”  it’s just another dimension like space. ...
 05:10: ... can also do it by clustering the particles in one spot in the available space. Let’s give those particles random velocities and see what happens in the ...
 09:39: ... entanglement, so we need another episode. Or more than one. Because on Space Time we’ve always given plenty of time to space, but it’s timely to ...


20201111: Can Free Will be Saved in a Deterministic Universe?
 00:19: So of course, "Space Time" needs to weigh in on the subject of physics and free will.
 00:36: In it, the past and future have a sort of eternal timeless existence from the point of view of some godlike observer outside both space and time.
 03:05: Two dimensions of space and one of time, the slices of the block universe represent the causal ordering of the universe.
 05:30: You are freewilled if you or fundamentally unpredictable information can emerge from your brain's patch of space time.
 06:21: Think about a new thread of quantum information starting from nothing, let's say emerging from a packet of space time where no information enters.
 13:20: I'm now gonna exercise my free will to not end this episode with me saying, "Space Time." (mysterious music continues) (intense music)


20201104: Electroweak Theory and the Origin of the Fundamental Forces
 05:01: Quantum mechanical equations of motion like the Schrodinger equation describe how the wavefunction evolves through space and time.
 05:18: ... it should be possible to change it however you like at any point in space and still get the same physical ...
 06:05: ... said that at each point in space, the physics shouldn’t change when we shift both the real and complex ...
 13:19: ... they enable, inevitable consequences of the broken symmetries of spacetime. ...
 13:45: ... next host of space time asks if physicists tend to be dubious about infinities, why are we ...
 14:51: ... parallel from any trapped surface must converge in any positively curved spacetime. ...


20201027: How The Penrose Singularity Theorem Predicts The End of Space Time
 05:01: ... did it in a clever way  by showing that the grid of spacetime literally comes to an end inside a black hole. In general ...
 06:38: ... it’s meaningless to continue to track the progression of space and time beyond one of these focal points. In other ...
 07:05: ... incompleteness. Because they are the grid we use to map space and time, geodesic incompleteness means space and/or time end at ...
 08:11: ... don’t reach the end of north, you reach the end of time or space. They are deadends to ...
 08:49: ... traced indefinitely into the past and future. All of spacetime should be a smooth, if curved structure  a manifold  ...
 11:10: ... and merge. And even, hopefully, what geodesics  and space and time  really are. Penrose’s singularity theorem is ...
 12:11: ... how light rays travel and terminate at the singular dead ends of spacetime. ...
 12:51: ... infinitely into the future AND the past. With your help Space Time might do the same. Well, not into the past  hard to ...


20201020: Is The Future Predetermined By Quantum Mechanics?
 00:00:  Einstein's Special Theory of Relativity combines space and time into one dynamic unified entity, spacetime.
 00:07: But if time is connected to space, can the universe be anything but deterministic?
 00:16: ... Space Time" theme song) In the last episode, we saw that we could think of the ...
 01:27: The idea that all space and time exist from a sort of God's eye view from outside of both space and time.
 01:47: ... big question, given that relativity is definitely a good description of space and time, what would it take for our future to remain ...
 02:14: And the only aspect of the present that exists is a vanishingly small patch of spacetime around your own brain.
 06:38: In fact, any part of spacetime, not in your future light cone is potentially the past for another observer in your present.
 12:15: Or how time even arises in the first place, but we'll have plenty more time for time another time, on "Space Time".
 16:09: Think of it as a corequisite study course to "PBS Space Time".


20201013: Do the Past and Future Exist?
 02:08: Newton assumed that all particles, all observers, all points in space were ruled by a single, constantly ticking clock.
 02:27: Here’s a nice way to represent Newton’s picture of space and time.
 02:31: Let’s cut out one dimension of space  space then becomes a 2D slice at a given instant in time.
 03:01: But we can also imagine a perspective from outside both space AND time in which this entire structure just exists.
 03:17: Time is just a dimension like space, and we only observe a flow of time if we play the slices in sequence like a flipbook.
 03:26: We sometimes use the term “block universe” or “block time” to refer to this view of all space and time just existing in this 4dimensional chunk.
 04:24: Another way I like to think about it is that 4D spacetime is a vinyl record, and our subjective experience is the music coded in the grooves.
 07:16: That means as time passes you move straight up  fixed in space, only moving through time.
 08:02: At the same time, their entire perception of the spacetime grid is warped due to their motion.
 08:29: ... that’s the effect of Einstein’s special relativity  space and time tilt into each other, so that different observers will slice up ...
 09:33: At a given location in space, you can lay down all possible timeslices representing possible presents.
 10:14: They have future light cones, simil to our, offset in space from ours.
 10:19: ... space beneath their future light cones defines all possible defines all ...
 12:35: ... time, determinism, and what it would mean to live in a block multiverse space ...
 14:03: ... to kickstart life from scratch on two planets independently, or have a spacefaring bugs propogate after ...
 14:36: ... terms of a great filter  something reliably stops planets from spawning spacefaring ...


20201005: Venus May Have Life!
 09:44: ... how these spores can survive crazy conditions  including the vacuum of space and the extreme temperatures and pressures of meteor impact or ...
 12:29: ...  granting us a grander perspective on humanity’s place in a lifefilled space ...
 13:11: So head over to Terra, and make sure to (politely) tell them Space Time sent you!


20200928: Solving Quantum Cryptography
 12:32: Imagine that you’re forming giant parallelepipeds to cover the whole space.
 14:11: ... attempt to decrypt your embarrassing emails across the parallel quantum space ...


20200921: Could Life Evolve Inside Stars?
 01:13: ... by physicists Luis Anchordoqui and Eugene Chudnovsky, and today on Space Time Journal Club we’re going to see how legit this idea actually ...
 02:23: And that’s the common feature of a topological defect  a sudden change in the “grain” of some space that can’t easily be disentangled.
 09:27: Or perhaps the nuclear reactions in the core proceed faster, hastening the dissipation of the star’s energy through space.
 10:23: And who knows what other bizarre life forms may be waiting to be discovered, in distant, stranger parts of space time.
 10:32: ... to comments It's that time of year again where PBS DIgital Studios and Space Time want to hear from you Every year we do an audience survey that ...
 10:47: ... Space Time audience has always done a great job making their voices heard on ...
 10:56: ... regardless going to keep making Space Time and keep making it better  and a big part of what makes that ...
 11:06: ...  added bonus is that we have this hoppin Patreon discord channel where space and physics geeks from around the world ponder the nature of ...


20200908: The Truth About Beauty in Physics
 02:50: And general relativity is also more explanatory than Newton  it tells us that gravity results from the warping of space and time.
 04:17: ... law is unchanged by some transformation  whether shifts in time, space, angle, or something more abstract like the phase of the ...
 10:13: Just add an additional degree of freedom  actually a symmetry  at each point in space and electromagnetism appears, almost miraculously.
 11:30: His idea of introducing a new symmetry to space was translated to adding a new symmetry to the wavefunction in quantum mechanics.
 13:02: ... truths, leading to the most beautifully fundamental explanations of space ...
 14:47: ... the other hand, if you have a cloud of gas hanging out in space like a nebula  it will be illuminated by stars but you're not looking ...


20200901: How Do We Know What Stars Are Made Of?
 04:28: By the time a photon reaches the photosphere it has a 5050 chance of traveling the final 100km to space without bumping into anything.
 10:46: ... out for us  the giant balls of burning hydrogen scattered across space ...


20200824: Can Future Colliders Break the Standard Model?
 10:04: The FCC will eventually graduate to protonproton collisions which will open up the discovery space further.
 13:17: Of coordinating thousands of scientists over many decades to build these crazy machines that can crack open the inner workings of spacetime.
 13:26: ... so as you know  filming a youtube show in space takes a lot of resources, and I just want to thank all our Patreon ...
 13:35: Without you we’d probably have to film in, like, lowearth orbit rather than deep space.
 14:28: ... a single, warped event horizon, shouldn’t there be a thin sliver of space in between that is not flowing towards either ...
 14:44: The key point is that space doesn’t have to flow directly towards the singularity.
 14:59: In the case of the merging black holes, you can think of space as more flowing towards the center of mass  although it’s not quite that simple.
 15:28: ... flow of space anywhere on the event horizon has to be exactly perpendicular to the ...
 15:47: But everywhere else  including above and below that point the space is still flowing inwards.
 16:54: ... Leandro asks how we manage to get such good sound quality out here in space. ...
 17:04: Well space isn’t really empty  there’s an average density of one atom per cubic meter, so technically sound is possible.
 17:20: ... green screen technology  I mean, replicator technology out here in SPACE, why should we deprive ...


20200817: How Stars Destroy Each Other
 00:02: Forget TMZ  Here on Space Time we have all the latest details on the dysfunctional, explosive relationships between the stars.
 01:22: ... ripped around the planetsized white dwarf, spraying its atmosphere into space and for a couple of weeks shining 10s of thousands of times ...
 10:10: ... little petulant. Like the final slamming of doors from distant parts of spacetime. ...
 10:25: As you know, at the start of the pandemic we all had to quarantine on Earth to avoid contaminating space with the virus.
 11:32: Well, below that event horizon, we can think of space flowing downwards faster than the speed of light.
 13:56: ... horizon  the surface below which there’s a fasterthanlight flow of space. ...
 14:07: Here’s a simulation from the SXS  simulating extreme spacetimes group at ... that shows how the event horizons merge.
 14:16: ... reason episodes get easier is that you’re getting smarter with all that Space Time you’re ...
 14:46: So if you’re comprehending Space Time does that make you Einstein?


20200810: Theory of Everything Controversies: Livestream
 00:00: ... so this is the second in our very unusual twopart series here on space time our great quest to understand the universe to find the mechanics ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... everyone so this is a very special and rather unusual event space time has always been about digging towards the deepest layers of ...


20200720: The Boundary Between Black Holes & Neutron Stars
 00:29: ... deal that we regularly read the infinitesimal ripples in the fabric of spacetime due to a cataclysmic collision of black holes billions of light years ...
 01:41: ... on Space Time Journal Club we’re going to try to figure it out  and we’ll do ...
 11:16: Billionyearold secrets carried to us on ripples in spacetime As always guys, I want to give our deep thanks to all of your support.


20200708: Does Antimatter Explain Why There's Something Rather Than Nothing?
 11:51: ... so. Apparently we have another one of these Space Time episodes where scientists busted ass to break physics and … didn’t. ...
 12:37: ... meantime have a wonderful next orbital revolution  from me and all the space time ...


20200630: Dissolving an Event Horizon
 00:30: Space and time switch roles, pathways open up to other universes, and in some cases time travel becomes possible.
 00:44: ... the surface around the central singularity where the inward flow of space reaches the speed of light, and time freezes from the perspective of the ...
 00:57: In the most real possible sense, the interior of the black hole is its own separate spacetime, excised from our universe.
 02:45: With nothing to counter the inward flow of space, an event horizon is inevitable.
 03:09: The same rotation that f orms the ring also drags the fabric of space into a vortex which counters the inward pull due to the singularity’s mass.
 03:18: The result is that we get this region around the singularity where the fasterthanlight inward flow of space is halted.
 03:34: As the spin of a Kerr black hole increases, the spacetime waterfall is beaten back, and so the inner horizon grows.
 03:46: There’s no longer a region where the inward flow of space exceeds light speed.
 03:51: Instead, there’s a smooth run of normal  albeit rapidly spinning space all the way down to the singularity ring.
 04:20: ReisnerNordstrom black holes also have an inner horizon, interior to which space and time seem normalish.
 07:55: ... because space gets dragged around the rotating black hole, giving the gas a sort of ...
 10:59: ... upcoming deeper dive to witness the horrors of the cosmicly uncensored spacetime. ...
 11:46: ... in those representations take a 3dimensional space and take a two dimensional slice out of it, so the black hole or ...
 12:08: ... singularity, and the narrowing of the funnel represents extremely curved spacetime. ...
 12:25: ... arong the wall of the tube would feel like traveling through a 3D space, but travel around the tube and you’d get back to where you ...
 13:11: ... confirmation of this interpretation of conformal cyclic cosmology: the space between atoms in one aeon would be infinite from the point of view of ...
 14:40: ... full of photons  I THINK the idea is that when you rescale both space and time by the same factor, you also rescale the interaction ...


20200622: Building Black Holes in a Lab
 00:16: ... in the center of our galaxy, superheated disks of gas pouring into tiny spaces in quasars or Xray binary systems. Gravitational waves that perfectly ...
 03:05: ... replace sound with light and the water with spacetime itself and you have a black hole. The surface around the central, ...
 03:26: ... in a form that is a close analogy to the equations governing the flow of spacetime  the equations of general relativity. And a vortex expressed in those ...
 08:04: ... That’s the region around the event horizon where the circular flow of space becomes irresistible. It turns out that water vortices also have the ...
 12:34: ... Hawking radiation, and the nature of the underlying, you guessed it, spacetime. ...


20200615: What Happens After the Universe Ends?
 00:45: ... particle has decayed into faint radiation .... that infinite stretch of space and time is identically the SAME THING as the infinitesimal and ...
 01:39: A conformal transformation is just some mathematical function that you apply to a geometric space which preserves all of the angles in that space.
 02:27: A conformal scaling of spacetime means scaling both space and time.
 04:06: To really compare the sizes of two chunks of spacetime we need to grid them up with rulers and clocks.
 04:15: ... things by gridding up an imaginary universe with only one dimension of space on the xaxis and one dimension of time on the y, and we choose our axes ...
 04:41: This is a spacetime diagram.
 04:42: Let’s take two instantaneous events in this universe, separated in both space and time.
 04:48: The separation between them can be determined by the number of gridlines of space and time you pass on your journey.
 05:23: ... best way to define the separation between two events in spacetime is by the travel time of something taking the most direct path between ...
 05:36: ... is the socalled spacetime interval, and it’s equal to the amount of time that passes on the clock ...
 06:17: Both space and time lose meaning for a photon.
 06:20: As Roger Penrose puts it: in order for time, and hence space to be meaningful, a universe must be able to build a clock.
 06:26: A clock must see the spacetime grid  and to do that it must travel at sublight speed.
 08:08: Filled with only timeless radiation, it would possess no spacetime grid, so perhaps could be considered sizeless.
 09:34: ... diagrams  these are ways of mathematically transforming our grid of spacetime to fit infinite distance and time into the one map, while at the same ...
 09:48: The edges of this map represent “conformal infinity”  where infinite space and time are compressed onto an edge.
 09:56: That’s for one dimension of space and one dimension of time.
 10:00: ... the full 4D spacetime the edge becomes a 3D “hypersurface” in which infinite distance and ...
 10:12: Similarly, the infinitesimal or “zerosized” point of the Big Bang can be rescaled into a finite space.
 14:24: ... and try to have fun in this infinite chain of conformally rescaled spacetime. ...
 15:23: ... for them to survive, and definitely the current virus didn’t come from space ... but it’s not totally ruled out that maybe it once ...
 15:40: Drakenkorin27, who is a bona fide virologist, gave us even more reason to doubt that any viruses from space have ever infected earth life.
 17:11: The outer space treaty demands all space samples be quarantined in a biosafe level 3 facility.
 18:01: Well sorry Aurora, but if 2020 watches spacetime then in we’re trouble.


20200608: Can Viruses Travel Between Planets?
 01:13: The new coronavirus  SarsCoV2, the virus that causes COVID19 did absolutely not fall to earth from space.
 06:25: Both Europa and Enceladus spray geysers of ocean water into space that can be captured by probes.
 06:39: OK, all this talk of viruses hitching rides into space brings us to our last, and most scifihorrormovie relevant point.
 07:21: From there they can travel across the globe, but also perhaps be lifted into space.
 07:26: ... magnetic field and then swept into interplanetary or even interstellar space by the radiation from the ...
 07:51: In fact it would be surprising if there were not quite a lot of viral and other microbial material riding the solar wind into interstellar space.
 08:06: Viruses can also be launched into space embedded in rocks that are ejected in asteroid or comet impacts.
 08:45: And it's the ability of viruses to survive long spaceflight that becomes the real question.
 08:53: ... space is deadly  it’s a freezing cold vacuum bathed in intense ...
 09:33: Polioviruses and bacteriophages have stayed infectious after spacelike environments of highaltitude balloon and rocket rides.
 09:43: ... also shown resistance to UV exposure in experiments on the international space station, however their viability after that exposure hasn’t been ...
 10:24: All of that said, radiation from stars is probably our best hope for obliterating space viruses.
 13:13: ... our currently notsofavourite, but still fascinating fellow denizen of space ...


20200527: Does Gravity Require Extra Dimensions?
 00:16: That steampunk contraption may even reveal the existence of extra dimensions of space.
 01:28: ... the behavior of gravity in terms of the warping of the fabric of space and ...
 02:43: So gravity sort of gets diluted in strength because it’s increasingly spread out over a 2D spherical surface within our 3D space.
 03:46: ... other forces actually propose that there are MORE than 3 dimensions of space, and that these additional dimensions may explain the hierarchy problem  ...
 04:20: Now we perceive the 3rd dimension, but perhaps our 3 spatial dimensions are similarly embedded in a higher dimensional space that we can’t perceive.
 11:23: And while that may seem anticlimactic, it’s actually extremely useful, ruling out some theories and constraining the space of possibility from others.
 12:18: what were they again? space, space space, ... time.
 13:15: Christina, with your great generosity and excellent taste in youtube shows, I hereby appoint you mayor of spacetime city.
 13:23: Because no one said spacetime city was a democracy, and I think you’d do an amazing job.
 14:16: Now the multiverse through the black hole arises from tracing the paths of spacetime through the black hole mathematically.
 15:33: ... the assumption that the impossibly unstable inner structure of the Kerr spacetime doesn't collapse ...
 16:09: Instead of "You're in for a weird time.” I should have said "I'm in for a weird space!" because space and time switched places inside the blackhole.


20200518: Mapping the Multiverse
 00:02: Or in physicsese, it’s the maximally extended Penrose diagram of a Kerr spacetime.
 01:01: ... black hole results when enough mass is concentrated in a small enough space that the gravitational field becomes too strong for even light to ...
 01:47: It describes the way spacetime warps and flows in the vicinity of a spinning mass.
 02:29: ... the event horizon is the ergosphere  a place where the fabric of space itself is whipped into a vortex so fast that not even light can resist ...
 03:11: Time flows up  for the most part  and one dimension of space is left or right.
 03:53: Down becomes the future, because falling space drags us there faster than the speed of light.
 03:59: Space and time switch places.
 04:39: On the other side, space and time switch back to their proper order.
 05:00: It’s surrounded by a second ergosphere, where again the rotational flow of space exceeds light speed.
 05:33: ... order to create these maps of spacetime, physicists use the equations of general relativity to trace what we call ...
 06:02: ... example, if you drop a trillion balls from space they’ll trace the downward cascade of space  and that flow would be ...
 07:17: ... ring is like a portal to a new, very different region of spacetime  and that’s because the geodesics passing through one side do not map ...
 08:13: There are trajectories in this torus that lead you back to your starting location  in both space AND time.
 08:24: This is the Carter time machine, after the aussie physicist Brandon Carter who did much of the early exploration of the Kerr spacetime.
 09:14: So what’s with this conveyor belt of space taking you out of the black hole?
 09:24: Well you sort of cross the same space, but not through the same time.
 11:21: The complete Penrose diagram for the Kerr spacetime has not one, but two inner event horizons leading to two parallel wormholes.
 13:57: Never travel the multiverse without a CarterPenrose diagram of the maximally extended Kerr spacetime.
 15:31: So to do better you'd need a device traveling faster than that  essentially impossible even for a spacecraft, at least currently.
 16:07: ... As you rewind the universe towards zero age, distant points in space end up closer and closer  and there is no point that is so distant that ...


20200511: How Luminiferous Aether Led to Relativity
 01:34: ... while aether is the immutable and indestructible element that filled space and in crystalline state formed celestial bodies. That’s right, aether ...
 02:33: ... Rene Descartes asserted that there could be no such thing as empty space, and Aristotle’s aether therefore both filled and gave reality to the ...
 04:06: ... luminiferous aether was bunk. He reasoned that if any medium filled the space between the planets, surely it would cause a sort of drag that would ...
 12:25: ... of the gravitational field, and which we now think of the fabric of spacetime. Paul Dirac suggested that a “particulate aether” could explain the near ...
 13:18: ... theory that revealed a much weirder, but still totally luminiferous space ...
 16:14: ... far to go, it's just that they were swimming against the expansion of space that whole ...


20200504: How We Know The Universe is Ancient
 12:59: ... years since the fiery beginning of timeasweknow it, the birthday of spacetime. ...
 13:45: ... us at the big bang level. Radu as an official representative of both space and time, I want to thank you on behalf of the universe for ensuring ...
 15:09: ... one. Is the tube connecting the ends of the wormhole meant to be in 4D spacetime, or somewhere else? The answer is ... somewhere else. The tube Lucid ...


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... today but for now here's to you that is Jewish so this is the first space time livestream I don't know why we thought this was a good idea ...


20200422: Will Wormholes Allow Fast Interstellar Travel?
 00:42: ... episode, the Schwarzschild solution describes two symmetric regions of spacetime, and the funnel itself is the wormhole connecting ...
 02:34: ... and Wheeler realized that such a “multiply connected” spacetime could allow nearinstantaneous travel across the universe because the ...
 03:33: ... represents the fabric of only 2 dimensions of space at a single instant in time. The technical name is an embedding diagram ...
 04:50: ... the space and time coordinates are blended and mutated so that time doesn’t freeze ...
 05:43: ... diagram we saw was a particular timeslice of the Schwarzschild spacetime. If we instead take a slice a little further in the future we see the ...
 07:52: ... general relativity permit any smoothlyvarying shape for the fabric of spacetime, and any topology. The only limitation is the nature of the matter and ...
 10:15: ... of cubic wormhole  wires of exotic matter define sharp edges, while space is relatively flat and safe for travel on the sides. It turns out there ...
 12:17: ... of exotic matter. To create a shortcut between two regions of space, the topology of that space needs to be altered. Which is probably ...
 12:51: ... possible scales, the geometry and even the topology of the fabric of spacetime may fluctuate wildly, its form shifting due to Heisenberg’s uncertainty ...
 13:26: ... with entanglement and may provides a passage not to distant parts of spacetime, but to deeper understanding of its nature. Which we will of course ...
 14:15: ... be releasing a regular episode. Instead we’re going to do the very first Space Time Livestream. It’ll be an AMA ask me anything style, at least you can ...
 15:35: ... Belhaj asks about the interstellar medium  isn't the space between the stars and galaxies an empty void? Actually no. Particularly ...
 16:15: ... good reason. I said that, here in my apartment I'm not floating off in space somewhere. But morpheox points out that I really am. We all ...
 16:25: Along with the entire planet. Way to make me feel better about being locked in my apartment, which I now see as a cool spaceship.


20200414: Was the Milky Way a Quasar?
 00:21: You may be wondering why I'm not floating somewhere off in space.
 02:19: ... Centre for Astrophysics were using the Fermi Gammaray Space Telescope to look for evidence of dark matter in the innermost regions ...
 06:02: ... the gas within the bubbles measured at nearly 9000 km/s by the Hubble Space Telescope  the bubbles must have been growing for a few million ...
 12:56: ... large influence on the Milky Way  a notsoinactive galactic denizen of space ...


20200407: How We Know The Earth Is Ancient
 04:32: ... time and deep space. We’d known since Copernicus and Galileo that earth was just one planet ...
 12:35: ... cares  it’s revolved around the sun 4.5 billion times through deep space and out of deep time, and it’ll do the same again. Into what I guess you ...


20200331: What’s On The Other Side Of A Black Hole?
 00:00: ... the ultimate point of no return as you approach a black hole  time and space themselves change their ...
 01:38: ... map the universe we need 3 dimensions of space instead of two, plus the dimension of time. And maps of the universe in ...
 01:53: ... first map of the spacetime of a black hole was the Schwarzschild metric  a relatively simple bit ...
 04:31: ... are even more popular for intergalactic travelers. On Penrose diagrams, space and time also bunch up at infinite distance so tha t the entire universe ...
 05:00: ... relativity uses null geodesics  the paths taken by light rays  to grid spacetime, and we also assume that those lines don’t just end. There’s no abrupt ...
 06:15: ... version of our universe, at least in terms of the coordinates of space and ...
 07:57: ... a black hole to try to get to the other side. Within the black hole, space and time have switched roles. These lines represent steps towards the ...
 08:22: ... escape and will ultimately fail, dragged down by the cascading fabric of space. ...
 08:44: ...  that is manifest as an inevitable crushing future, in which the space around you becomes infinitely ...
 09:55: ... the Mercator projection, traveling off the edge of the Schwarzschild spacetime brings you back somewhere else in the same spacetime. Exactly where ...
 10:58: ... a sublightspeed path through a Kerr black holes into parallel regions of spacetime. ...
 11:37: ... Everyone. Welcome to the new Space Time studio aka my apartment because New York is in lockdown, but as you ...


20200324: How Black Holes Spin Space Time
 00:21: ... situation. Schwarzschild’s eponymous metric describes the warping of space and time around a spherically symmetric mass. And if that mass is ...
 03:27: ... we’re going to look at what the Kerr solution can tell us about the spacetime outside a rotating black hole. We’ll save the even weirder details of ...
 04:11: ... field and its rotation can be thought of as properties of the spacetime ...
 04:26: ... holes are selfsustaining holes in the fabric of spacetime. Space at the event horizon cascades downwards, dragging more space ...
 05:14: ... flow of space around a rotating black hole is known as framedragging. We see it ...
 07:33: ... bizarre region called the ergosphere. There, frame dragging carries space around the black hole at faster than the speed of light. That means ...
 07:50: ... here is actually similar to the state below the event horizon where space moves downwards faster than light. In the math, that fasterthanlight ...
 09:37: ... hole’s spin. To get a little more technical  it works because the weird spacetime flip in the Kerr metric of the ergosphere allows one half of the object ...
 10:51: ... flow of material around the black hole in an accretion disk. The flow of space in the ergosphere spins up the magnetic field into a gigantic particle ...
 12:11: ... we drop below the event horizon into the deeper weirdness of the Kerr spacetime. ...


20200316: How Do Quantum States Manifest In The Classical World?
 00:04: ... episode of space time is brought to you from the information flowing through an ...
 13:47: ... maintain their correlations, no matter how far separated in boring old space ...


20200303: Does Quantum Immortality Save Schrödinger's Cat?
 10:34: Anyway, if your name appears you’re one of the winners of the challenge question and you get your pick from the space time merch store.
 11:06: So let’s stick it to all those alternate realities, and make this the best of infinitely many diverging histories of space time.
 11:44: Check out the episode in the description below, and tell them, politely, that SPACE TIME sent you.
 13:20: eddybox on the spacetime discord asked about the quantum eraser, as did several people in the comments.
 15:41: AKA, a space time nerd.


20200224: How Decoherence Splits The Quantum Multiverse
 14:38: ... that itself contains so much more than our little, decohered slice of space ...


20200218: Does Consciousness Influence Quantum Mechanics?
 12:49: ... deeper dive into the quantumclassical divide, on an upcoming episode of Space ...
 13:12: This subject was actually suggested on the Space Time discord channel  so a big thanks to you lot for the great idea.
 13:20: ... check it out if you haven't  247 discussions of all things physics and space  questions are answered, episode suggestions are heard, and there's ...
 13:31: You get access with the lowest $2 per month tier on Patreon, which has the added bonus of helping us keep the space time lights on.
 15:01: ... and new particles if other fundamental constants turned out to vary over space, in the same way that a variable theta constant is hypothesized to give ...
 15:14: Well a field is, by definition, anything that takes on a numerical value everywhere in space.


20200211: Are Axions Dark Matter?
 05:16: ... what if theta isn’t a constant, but can change in value, both over space and over time. In other words, make theta a new type of field  a ...
 09:45: ... are other spacey tests for axions. Magnetars  highly magnetic pulsars  and quasars may ...
 10:36: ... and upgrades of existing experiments will whittle away the parameter space of possible axion properties  and eventually we’ll either spot it or ...
 11:08: ... for one of the tiniest and most elusive potential particles in all of spacetime. ...


20200203: Are there Infinite Versions of You?
 01:41: ... capital "A" is as likely as small "a." Then the second character  a space  1 in 100 again and so on. “A tempestuous noise of thunder and ...
 09:14: ... Hawking showed that the maximum amount of entropy in any region of space is proportional to the number of tiny Planck areas covering its ...
 12:10: And at risk of over quoting whatshisname: I could be bounded in a nutshell, and count my self a King of infinite spacetime.
 12:56: That's because objects in orbit are all moving, so the curvature of the background spacetime is constantly changing.
 14:20: RobTheImpure would like to know what is meant when we talk about "spaceless timeless particle scattering" in the context of the smatrix.
 14:48: But in smatrix theory and quantum field theory, time and space in the interaction region are fuzzy.
 15:24: Another example is the schannel  tchannel duality, in which you get identical scattering results when space and time switch places.


20200127: Hacking the Nature of Reality
 01:08: ... equation and Paul Dirac’s notation representing evolution in a space of quantum ...
 03:50: ... binding these subnuclear particles together must be so strong that space and time should break down at those scales, and our even best field ...
 12:56: ... mechanics of quantum field theory, it removes the very concepts of space and ...
 13:10: These only emerge later as a consequence of spaceless, timeless particle scattering.
 13:17: ... bootstraps towards a better understanding of the quantum weirdness of space ...
 13:34: ... fastest way to get smart people answering your questions is to join the Space Time discord ...
 13:43: It's hopping with lively conversations about everything space, physics, or things that spacey physicsy people are into.


20200120: Solving the Three Body Problem
 03:18: ... and the moon was critical for nautical navigation. Now it’s essential to space ...
 06:43: ... call these the Lagrange points, and they’re useful places to park our spacecraft. ...
 07:56: ... discover new specialized threebody solutions, we had to search the vast space of possible orbits using computers. The key was to find threebody ...
 10:30: ... angular momentum of the system. The system explores what we call a phase space  a space of possible arrangements of position and velocity. Well, for a ...
 11:21: ... Stone and Leigh found that they could identify the regions of phase space where these ejections were likely  and by doing so they could map the ...
 12:55: ... orbit, trying to astronavigate around two other gravitating denizens of space ...
 15:41: ... a huge fan of PBS Space Time and, if you like them, you’ll like ours as well. In fact, I’d like ...


20200113: How To Capture Black Holes
 00:00: ... getting closer to reality, at least according to the papers in today’s Space Time Journal ...
 00:59: ... last forever. As they circle each other, black holes whip the fabric of space into expanding ripples  gravitational waves  which saps orbital energy ...
 02:16: ... of searing gas that surround some of these monsters? Well today on Space Time Journal Club we’ll be looking at a pair of 2019 papers that talk ...
 08:50: ... by McKernan and collaborators comes in. If black holes merge in empty space then the event should invisible  it should emit no electromagnetic ...
 11:50: Awesome, sure, but what else would you expect from this supremely badass and frankly, totally metal Space Time.
 12:17: ... and that is inflation, in which the rapid exponential expansion of space can create a ridiculously large universe that multiplies the density of ...
 12:49: ... required by that initial creationary event  it only needs to produce a spacetime capable of exponential growth  after that the fundamental constants ...
 13:26: ... If it grows by some inflationlike expansion into an entirely new spacetime then it may not care about the later evolution of its parent black hole ...


20200106: How To Detect a Neutrino
 00:35: ... (𝘧𝘢𝘥𝘦 𝘰𝘶𝘵) ♪ ♪ (𝘴𝘱𝘢𝘤𝘦𝘺 𝘱𝘪𝘯𝘨 𝘳𝘦𝘷𝘦𝘳𝘣𝘦𝘳𝘢𝘵𝘦𝘴) ♪ ♪ (𝘧𝘢𝘥𝘦 𝘰𝘶𝘵) ♪ (title) "SPACE TIME" (title) "SPACE TIME" ♪ (𝘫𝘰𝘺𝘧𝘶𝘭 / 𝘢𝘯𝘵𝘪𝘤𝘪𝘱𝘢𝘵𝘰𝘳𝘺 𝘴𝘺𝘯𝘵𝘩 𝘨𝘶𝘪𝘵𝘢𝘳 ...
 09:19: ♪ ♪ DR. DON: You know, you're welcome to come anytime, ♪ ♪ we love Space Time.
 09:36: ♪ ♪ It's honestly one of my goto resources when I'm researching ♪ ♪ a new episode of a Space Time.
 09:42: ... 𝘣𝘦𝘭𝘭𝘴 𝘴𝘭𝘰𝘸𝘭𝘺 𝘧𝘢𝘥𝘦 𝘰𝘶𝘵) ♪ ♪ (𝘦𝘵𝘩𝘦𝘳𝘦𝘢𝘭 𝘣𝘦𝘭𝘭𝘴 𝘴𝘭𝘰𝘸𝘭𝘺 𝘧𝘢𝘥𝘦 𝘰𝘶𝘵) ♪ (title) "SPACE TIME" (text): "Matt is currently lost in the Fermilab tunnels, so ...


20191217: Do Black Holes Create New Universes?
 03:38: ... to exit the event horizon of the black hole, it forms a new region of spacetime, effectively creating a new ...
 07:38: ... the most black holes would be produced by the biggest universes  more space means more chances for these quantum ...
 12:08: ... one of them is likely to be true, but they help us explore the vast space of all possible realities  where somewhere is hidden the true nature of ...
 12:19: Or, you know, our universe's momma might be a black hole, and we live in an endlessly evolving, proliferating space time.


20191209: The Doomsday Argument
 12:12: Best answers get a pick from the Space Time merch store.
 12:29: Which means you’ll be around for next week’s episode of space time.
 12:34: ... a huge difference  ensuring we'll be able to keep making and expanding Space Time until doomsday  whether it's soon or ...
 13:11: ... any level  even $2  also gets you access to our new Space Time discord channel, where at this very moment brilliant and curious ...
 13:39: ... Habunelahack asks if it's ever be possible to measure the curvature of space to get an estimate on the size of the entire ...
 15:57: These are basically flat mappings of a donut. And there are weirder, multiply connected finite space times that are also flat.
 16:05: ... while these are valid geometries for spacetimes that can be constructed within Einstein's general relativity, it's not ...


20191202: Is The Universe Finite?
 00:04: Space is big.
 00:50: And within this light, a group of scientists have just found evidence of the limits of space.
 01:02: ... on Space Time Journal Club we’ll delve into the Nature Astronomy paper that just ...
 03:08: ... 2D analogy for this is the surface of a sphere, so a our 3D space would be like the surface of a 4dimensional sphere  also known as a ...
 03:44: All paths through space diverge from each other.
 03:46: Such a universe is open  space goes on forever.
 03:56: Parallel lines stay parallel, your high school geometry still works, and again, space in such a universe goes on forever.
 12:01: ... energy, and perhaps verifying the positively curved, finite geometry of space ...
 12:12: If you want to dive deeply into understanding the building blocks of space time then you need to study quantum theory.
 12:56: But before we get to that, I want to invite you to check out the Space Time discord, which you can access with the lowest $2 patreon tier.
 13:17: ... do all PhD physicists casually talk about complex stuff like on Space Time videos, or do most employed physicists just shut up and ...
 14:10: ... that if there are to be trillions or quadrillions of humans in future spacefaring civilizations, isn't it weird that we happen to be in the first 100 ...
 16:02: ... a typical universe is mostly empty Singapore Breaking News likes to play space time loudly so mom thinks they're getting more brainy but in the ...


20191118: Can You Observe a Typical Universe?
 13:03: ... given your privileged status as a typical conscious observer of space ...
 14:03: So from your students and everyone here at Space Time we wish you well.
 15:09: Much of the parameter space that the constants of nature could have taken eliminate one or more of these factors.
 15:16: ... while there may be many small parts of that parameter space where observers can arise, most of it  hence most universes  should be ...


20191111: Does Life Need a Multiverse to Exist?
 08:59: Physicists knew that empty space itself could have its own energy.
 09:04: ... quantum fields, which fill all of space and whose oscillations produce the familiar particles of matter or ...
 11:47: And there are other proposals for how the fundamental constants might vary over space or between universes.
 12:04: ... popular  bubble universes forming in a larger exponentially expanding spacetime, and in each bubble the constants of nature  and especially the vacuum ...
 12:58: And we will test it  next time, and so perhaps make a little more sense of our extremely finetuned patch of space time.


20191104: Why We Might Be Alone in the Universe
 05:59: ... generates a powerful magnetic field that protects Earth from dangerous space radiation and solar ...
 12:11: We find ourselves in the only place we could be: gazing out from our rare earth into the untamed, unpopulated reaches of spacetime.
 12:39: The strings of string theory have a somewhat physical interpretation  the fact that they can hold energy and vibrate and exist in space.
 12:59: Well, crudely, they're a mathematical way to describe the geometry of space  which means they aren't in space, they sort of ARE space.
 13:09: Or at least familar 3D space emerges in an abstract way when we think about a network of these loops.
 13:17: But that doesn't mean the loops are physical, they're just a way to parameterize the quantumscale geometry of space.
 14:00: ... if space is quantized on tiny scales, then we expect the very shortest ...
 14:22: ... can travel around to end up back where you started  in both time and space. ...


20191021: Is Time Travel Impossible?
 00:58: ... uses only special relativity, which describes how intervals of time and space are stretched or contracted depending on relative ...
 01:08: A fastmoving spaceship appears to experience a slower rate of time compared to someone waiting back on Earth.
 01:45: The spaceship’s clock slows down as it speeds up, and it stops completely at the speed of light.
 01:56: So if you could travel faster than light you could navigate a path to a point in spacetime before you departed.
 03:16: ... explains the force of gravity as a result of curvature in the fabric of spacetime due to the presence of mass and ...
 03:29: But GR describes a warping of space AND time.
 03:46: ... if space can be warped, then perhaps it can be stretched in such a way as to ...
 04:00: This has the obvious benefit of allowing you to teleport between distant points in space, but also between distant points in time.
 04:41: ... to miniscule wormholes appearing and vanishing on the tiniest scales of space and ...
 07:22: It will drag spacetime in its vicinity into a sort of vortex.
 07:26: This generates sublightspeed paths through spacetime that form closed loops, ending up back where they started in both space and time.
 07:40: A spaceship traveling along one of these curves could return to a point in its own past.
 07:55: Stephen Hawking showed that unless the cylinder is infinitely long this doesn’t work – unless you also modify the spacetime with negative energy.
 08:38: Dragging the fabric of space in a circle can give us our timeloops in very special, and frankly useless cases.
 08:51: The maelstrom of spinning spacetime may generate closed timelike curves deep down below the event horizon.


20191015: Loop Quantum Gravity Explained
 01:58: Like actors on a stage, where the actors are particles and wavefunctions and fields and the stage is the coordinates of space and time.
 02:31: They describe how the presence of mass and energy warp the fabric of spacetime.
 02:41: ... metric  the object encapsulating the geometry and causal structure of spacetime  evolves in the equations of GR. So those equations need to work ...
 02:54: In string theory, a type of background independence emerges in an abstract space of moving strings and with that comes a gravitational field.
 04:00: Absent measurement, they exist in a fuzzy space of possibilities called a wavefunction.
 05:45: ... that describes the quantum evolution of the properties of an object in spacetime, maybe there’s an equation that describes the quantum evolution of the ...
 06:07: ADM starts by defining this abstract space of spaces  3D spatial metrics, 3D space slices cut out of 4D spacetime.
 06:25: You can imagine a funky coordinate system describing where you are in this abstract space of metrics.
 06:32: As you move through this coordinate system, the geometry of space changes.
 06:37: You can also imagine analogies of the position and momentum in this space of metrics.
 06:48: The result is a quantum equation for the fabric of space.
 07:16: ... gravity does  it takes us down the abstraction rabbit hole  past our space of metrics into a space of something called ...
 07:33: Connections are mathematical functions that tell you how something, like a vector, changes as it moves between two points in a space.
 07:46: As you move the base of a vector along a path in curved space, the vector rotates.
 07:58: ... connections contain all the information about spacetime, them maybe we can represent spacetime with these connections instead of ...
 08:47: In this formalism, the “space of metrics” looks just like a space of fields in quantum field theory.
 09:29: ... realized it was possible to define any geometry of 3D space out of a sort of weave of these closed loops, with each loop like an ...
 09:42: ... now you have a space of loops with which to construct the fabric of space  and that space of ...
 10:10: Not with chunks of spacetime but with quantum circuits of gravitational field.
 10:15: 3D space can be sort of woven from these loops into something called a spinnetwork  which is a concept too abstract for even this episode.
 10:26: But the resulting 3D space looks normal on large scales  it looks like space.
 10:38: At the nexuses of this weave you have quantized volume elements – irreducible grains of space  connected by quantized area faces like facets.
 10:50: But even that description is too spacelike  probably the underlying weave of the fabric of space doesn't resemble anything intuitive at all.
 11:37: ... it’s not actually clear that this independence extends to 4D spacetime. ...
 12:41: ... the way they propagate through the graininess of a loop quantum gravity spacetime. ...
 13:40: One way or another, we live in a seriously loopy space time.
 14:38: ... gravitationally lensed so as to arrive via two separate paths through space. ...
 16:16: ... few of you asked a really onpoint question: if the fabric of space and time can be stretched and if can have waves, that means it must have ...
 16:26: So just how resilient is the fabric of spacetime?
 16:29: ... of general relativity That equation says that the amount stretching of spacetime is proportional to the mass and and energy contained by that ...
 16:40: The constant of proportionality can be thought of as the tensile strength of space  the resistance to stretching.
 16:47: The smaller the number, the more energy is needed to stretch spacetime.
 16:58: Spacetime is a very, very stiff fabric.


20191007: Black Hole Harmonics
 00:04: ... crash two together and you end up with this roiling blob of inescapable space that vibrates like a beaten ...
 00:14: And the rich harmonics of those vibrations, seen through gravitational waves, could hold the secrets to the nature of the fabric of spacetime itself.
 00:22: Today on space time journal club we’ll explore two papers that claim to have detected black hole harmonics.
 01:52: ... then it’s an oscillating spheroid – like a ball of water wriggling in space. ...
 02:06: The event horizon seems to define the surface of the black hole, but really it’s the fabric of spacetime itself that’s vibrating.
 02:14: ... two inspiralling black holes make powerful spacetime ripples – gravitational waves – which intensify as the black holes ...
 02:27: ... then the merged black hole continues to radiate these spacetime ripples as it oscillates, but these quickly die away as the black hole ...
 05:53: ... a simulated merger by the SXS – Simulating Extreme Spacetimes  project basically the result of teaching a supercomputer general ...
 12:59: ... and through them better understand the fundamental nature of extreme spacetime. ...


20190930: How Many Universes Are There?
 00:00: Space is big, but it’s peanuts compared to the eternally inflating multiverse.
 00:42: Bubbles that are continuously appearing and growing within a vastly larger spacetime that itself expands at an exponentially accelerating rate.
 00:52: A greater inflationary spacetime whose expansion never ends.
 01:14: ... – or multiverse  is to expand exponentially due to the vacuum of space itself having a large and constant energy ...
 01:31: ... that inflating space, tiny patches stop inflating – the inflaton field in that patch loses its ...
 01:48: ... bubble has an edge, and the edge spreads into the surrounding inflating spacetime at the speed of light, causing inflation to stop within the growing ...
 03:05: We assumed that there’s a fixed but unknown probability that a bubble universe will form in any given volume of inflating space.
 05:05: As soon as the inflating spacetime is big enough to make one universe, in the next second it should make 10^10^34 universes, and so on.
 05:43: ... ideas, they probably have the same number of dimensions as ours – 3 space, 1 time – but their contents and physics could be very ...
 07:46: The vast space of possible configurations of these compact dimensions is referred to as the string landscape.
 12:09: If they form too far apart then the intervening inflating spacetime will throw them apart at faster than light speed before they can merge.
 13:28: But here’s something that’s not hard to get – Space Time swag.
 13:56: It’s the best humorous science apparel in all of spacetime.
 14:00: Did you get enough spacetime today?
 14:14: We just launched a spacetime discord for 247 conversations on all of the above.
 14:43: Alexander has been traveling the bubble universes for many years, supporting local youtube space shows where he finds them.
 15:19: ... section echoed these thoughts  but special props to Regolith on the spacetime discord, who's a bona fide planetary ...


20190923: Is Pluto a Planet?
 00:56: Astronomers are all about space taxonomy.
 13:48: And anyway, the word “world” still applies to Pluto  and it's a rather more poetic label for one of the greatest dwarf planets in known spacetime.
 14:01: First up, we're launching a Space Time discord  It'll be the perfect place to ponder and discuss the fundamental nature of the universe, 24/7.
 14:20: ... answered by the smartest people on the internet  that is to say, other spacetime viewers  and sometimes by ...
 15:31: Kazeshi wants to do O'Neill cylinders or rotating habitats in space.
 15:45: ... a rotating habitat or cylinder in space can produce the effect of gravity for its inhabitants, but without an ...
 17:24: A couple of meters of Martian rock above your head is plenty to protect against space radiation and micrometeorites.


20190916: Could We Terraform Mars?
 00:07: As we master space travel, we’ll hop from one cold dead world to the next. Terraforming as we go.
 00:53: ... or their descendants, will need to be able open the airlocks, shed their spacesuits, and step out onto a survivable ...
 01:47: Light from the Sun, which is already fainter due to Mars’ distance – is radiated directly back out into space.
 03:20: There’s a real risk that Mars actually lost its atmosphere to space, rather than absorbed it into the surface.
 04:06: The ablation of what is left of the Martian atmosphere has now been directly observed by NASA’s MAVEN spacecraft, as we’ve also discussed before.
 04:23: ... on observations of NASA’s Mars Reconnaissance Orbiter and Mars Odyssey spacecraft. ...
 12:17: ... this  a vast fleet of robotic spacecraft swarming the Kuiper belt, nudging its plentiful iceballs in just the ...
 13:19: The easiest would be to do that in space – an orbiting field generator placed between Mars and the Sun, like a giant space umbrella.
 14:48: Now, without a real atmosphere, space radiation is gonna be a problem for our worldhouse, as is the constant bombardment of micrometeors.
 15:23: However we do it, Mars will surely be our first step, our proof of concept if we choose that destiny  if we choose to terraform space time.
 15:48: ... sets inspired by real aerospace technology, LEGO City Space aims to inspire future space explorers to imagine what role they can ...
 16:31: This is the simplest type of quantum field, consisting of only a single scalar value at all points in space.


20190903: Is Earth's Magnetic Field Reversing?
 00:00: Earth’s magnetic field protects us from deadly space radiation.
 00:20: Spaceship Earth has a literal deflector shield.
 01:15: Would life be extincted by crazy space radiation?
 12:34: For now at least we remain protected from the worst ravages of solar storms, and of our dangerously irradiated space time.
 13:15: But, until then, Space Time and PBS Digital Studios want to hear from all of YOU.
 13:28: Space Time fans have always been amazing at taking the time and making their voices heard on the survey and we’d love for that to continue.


20190826: How To Become an Astrophysicist + Challenge Question!
 00:00: ... rejections and got some offers Ultimately deciding to head to NASA's Space Telescope Science Institute in Baltimore, which is a great town By the ...
 10:46: ... there's a set chance of the new universe forming in any given volume of space So every second many bubble universes are forming across the great sir ...
 11:51: ... can Submit answers within two weeks of release of this episode to PBS space time at gmail.com with the subject line Eternal inflation challenge and ...


20190819: What Happened Before the Big Bang?
 00:50: The idea is that the energy trapped in the socalled "Inflaton field" caused exponential expansion of space.
 02:17: This is actually the simplest type of quantum field because it's described by a single number, a scalar everywhere in space.
 08:49: So, and up your fluctuation in a tiny patch of space would very quickly outgrow its surroundings; producing a new inflating region.
 09:06: ... stops, but rather forms a fractal structure of infinitely expanding space in dispersed with bubble universes of all different ...
 09:27: A millionth of a gram in a space 10^(35) meters across should do the trick.
 10:14: Good material for the eternally expanding future library of PBS Space Time.
 12:39: ... inflation doesn't explain where the very first speck of spacetime and energy came from but it does give a potential explanation for the ...


20190812: Exploring Arecibo in VR 180
 00:13: ... learn mastery over matter and the forces of nature and built cities and spaceships? and this thing, it's the tip of an enormous machine built to map the ...
 01:02: ... of one of the transmitting antennas. Yeah Transmitting Arecibo is also a space radar that can bounce rate of pulses off planets and asteroids as far as ...
 03:24: ... facility in the 1950s the height of the Cold War the arms race and the space race made it Strategically important to really understand the ionosphere ...


20190806: What Caused the Big Bang?
 02:54: Anything that causes the fabric of space itself to have energy  anything that has a constant energy density pushes rather than pulls.
 03:23: ... the upshot is that if the vacuum of space has a constant energy density, then Einstein's equations end up having a ...
 03:48: ... so dark energy only works because it adds up over an enormous amount of space. On the other hand, in order to solve the smoothness, flatness, and ...
 05:02: Now, a field is just some property that takes on a numerical value at every point in space.
 05:22: ... the field. If a quantum field has energy in the form of particles and if space is expanding  as is the case for our universe  then that energy gets ...
 09:07: ... of space adjacent to that point would also be dragged out of the local minimum ...
 09:53: ... the bubble, space would still be expanding out whatever speed it had at the end of ...
 10:14: ... like the entire floor of the field is shifted down at every point in space; what was once pure inflaton field is converted to a stack of inflaton ...
 13:08: Space Time.


20190725: Deciphering The Vast Scale of the Universe
 02:54: ... when you look through a telescope it flattens 3D space into a twodimensional image a dome above our heads that the ancients ...
 05:52: ... here at the Hayden have turned that dome into a spaceship. It can fly us through a virtual universe built from the most complete 3D ...
 06:04: And unlike regular spaceships, this dome can fly at many times the speed of light.
 08:55: If we continue exploring – if we keep looking deeper and further – who knows what we’ll find in the expanding horizons of space time?
 09:55: ... is bringing you the universe with the SUMMER OF SPACE, which includes six incredible new science and history shows airing on ...


20190718: Did Time Start at the Big Bang?
 00:25: ...  purely according to Einstein's equations, it seems inevitable that all space and mass and energy should once have been compacted into an ...
 01:02: And before the Big Bang singularity, well, they say that there was no 'before' because time and space simply didn't exist.
 01:56: ... can see pretty much directly that all space and matter in the universe was once crunched at least a thousand times ...
 03:27: ... terms of the scale factor That's the distance between any two points in space at some moment in time Relative to their distance at some other ...
 05:15: ... infinitesimal all points become the same point and threedimensional space becomes zero dimensional That's the singularity We say that it didn't ...
 06:02: ... to see what time does at the Big Bang We have to trace a path through space and time back to the singularity We trace a path called a geodesic which ...
 08:52: ... description and so he probably shouldn't believe its prediction that all space was compacted into a single point and that this is where Time started. ...
 09:52: ... expanding bubble in an unimaginably larger continuously inflating spacetime in that case before the Big Bang was a period of exponential expansion ...
 11:36: ... things we'll discuss in the future as we travel beyond the beginning of SpaceTime. ...


20190715: The Quantum Internet
 11:21: ... enables us to take advantage of the incredible properties of our quantum space ...
 15:03: Battlemechs, submarines, spaceships, DeLorean time machines  nuclear is probably the easiest option for the badass vehicles of the future.


20190701: Thorium and the Future of Nuclear Energy
 02:49: ... fuel thorium That's the thorium reactor Thorium is another actinide two spaces lighter on the periodic table compared to uranium It's not naturally ...
 15:29: ... stage and send us to greater distances and further futures in spacetime In a recent episode we talked about how black holes influence the ...
 16:59: ... is yes, but not very far Frame dragging is the dragging of the fabric of space around a rotating massive object in the case of a black hole it's most ...
 18:26: Probably the same evil conspiracy That got Firefly cancelled after one season Why do the powers that be fear space cowboys so much?


20190620: The Quasar from The Beginning of Time
 04:20: ... to twinkle off sodium atoms at 90km height, right off the edge of space. ...
 07:10: ... bring us closer to understanding this mysterious, this magnificent space ...
 07:38: We can now see ripples in the fabric of space time itself.
 08:16: ... is bringing you the universe with the SUMMER OF SPACE, which includes six incredible new science and history shows airing on ...


20190617: How Black Holes Kill Galaxies
 10:49: ... to leave raging starbursts and fiery quasars to an earlier epoch of SpaceTime. ...


20190606: The Alchemy of Neutron Star Collisions
 02:47: ... when the LIGO and Virgo gravitational wave Observatories spotted the spacetime ripples from the merger of a pair of neutron stars many of the world's ...


20190516: The Cosmic Dark Ages
 00:24: ... side of the universe. But there’s an up side. If the light from some space object took billions of years to get to us then we see that object as it ...
 04:29: ... this while space was expanding. At the beginning of the dark ages the universe was around ...
 12:16: ... era; Probably the only habitable epoch in the past and future history of space ...


20190509: Why Quantum Computing Requires Quantum Cryptography
 13:50: Your browsing history may one day depend on it, and I assume that history isn’t just old episodes of Space Time.
 14:09: ... of Britain and the device that measures the temperature of the sea from space. ...
 14:30: Visit audible.com/spacetime OR text spacetime to 500500 to learn more.
 14:40: To learn more, visit audible.com/spacetime OR text spacetime to 500500.


20190501: The Real Science of the EHT Black Hole
 01:20: By comparison, the Hubble Space Telescope would struggle to see a large watermelon over that distance.
 03:08: ... the size of the object you’re looking at to the actual distance through space to that ...
 05:18: We see them by their influence on surrounding space.
 08:55: ... flow and magnetic fields, in this case with the addition of the warped spacetime of a black hole using Einstein’s theory of general ...
 10:54: ... hole, Einstein’s wildest prediction and the strangest object in all of space ...


20190424: No Dark Matter = Proof of Dark Matter?
 00:03: ... of two galaxies that appear to have no dark matter at all today on spacetime journal Club we'll look at the papers that reveal this discovery the ...


20190410: The Holographic Universe Explained
 00:00: We live in a universe with 3 dimensions of space and one of time.
 00:24: ... our 3+1 dimensional universe may better described as resulting from a spacetime one dimension lower – like a hologram projected from a surface ...
 00:51: ... the past several months on Space Time, we’ve seen those close clues, and we’ve built a the foundations ...
 01:34: This Bekenstein bound represents maximum possible entropyslashinformation of any volume of space.
 01:42: Oddly, that maximum in is proportional to the surface area of that space, not its volume.
 01:48: ... was surprising – surely the information in a volume of space depends on the volume – like, 1 bit per infinitesimal voxel – not one ...
 03:19: This is the first glimpse of a holographic spacetime: a 2D surface that encodes the properties of the 3D interior.
 04:32: Let’s say we start with a plane – a flat, 2D spacetime.
 09:57: These are like multidimensional strings that can serve as start and end points for strings, but also as spaces embedded within higherdimensions.
 10:23: ... found that the resulting braney structure looked just like a Minkowski spacetime of 3+1 dimensions on which their lived a field theory that arose from ...
 10:57: This quality fcame from the energyscaleinvariance of the strings embedded in the construction of this space.
 11:12: The 3D space became a 4D space.
 11:15: While the original space was flat, the new space had negative curvature – it was a hyperbolic, antide Sitter or AdS space.
 11:24: The conformal field theory in the original space included no gravity, but in the higherdimensional space it became a full quantum theory of gravity.
 11:46: ... higherdimensional gravitational structures in the higher dimensional space would be weak and ...
 11:58: ... strong gravitational fields in the higher dimensional space – like in black holes – look like a solvable configuration of particles ...
 12:09: ... in a black hole persists perfectly comfortably in the lowerdimensional space. ...
 12:37: The lower dimensional CFT space is the surface of the AdS space because the field theory exists where the new dimension becomes infinite.
 12:49: That’s tough to imagine – so let’s go back to our depiction of an infinite hyperbolic space from the last episode.
 12:58: Represent a 2D hyperbolic space as a compactified map and it has an edge – at least a mathematical one.
 13:06: Anyone inside the hyperbolic space still has to travel infinitely far to get to that edge.
 13:15: The resulting column has a geometrically flat and finite surface that is a spacetime all on its own.
 13:41: ... because our universe doesn’t appear to be negatively curved AdS space, nor does it have 4 spatial dimensions as in Maldecena’s ...
 14:27: An abstract mathematical surface infinitely far from our location and from our intuition, projecting inwards our familiar holographic spacetime.
 14:55: Last week was the warmup to today's episode, in which we looked out how an infinite spacetime can have a finite boundary.
 15:10: A few of you asked whether our percieved universe is just the surface of a higher dimensional space.
 16:00: ... we say there would be no gravity on the surface of the (2+1)Minkowski spacetime. ...
 16:12: So first  the "surface" in current AdS/CFT spacetime is 3+1. 3 spatial, one temporal dimensions.


20190403: The Edge of an Infinite Universe
 01:17: We visited these cosmic horizons in one of the early Space Time episodes.
 01:34: But these correspond to actual spherical boundaries in space, whose distances can be calculated.
 03:00: In general relativity we call a universe with this geometry de Sitter space, after Dutch astronomer Willem de Sitter.
 03:17: In GR this is Minkowski space, after Hermann Minkowski, teacher and colleague of Albert Einstein’s.
 03:40: In GR this is antide Sitter space because it’s the “opposite” of the positive curvature de Sitter space.
 03:48: Terrible name, so we abbreviate it AdS space.
 04:07: You’re probably one of the former, so let’s ignore puny de Sitter space and for today assume we’re in one of the infinite ones.
 04:20: ... in the early 60s when physicists tried to find ways to map infinite spacetime –to the edge of an infinite universe or across the event horizon of a ...
 04:32: Regular coordinates of space and time are useless there – they blow up to infinities.
 04:38: Physicists found mathematical ways to fuse space and time into new coordinates that suppressed the infinities.
 05:40: As a quick review: start with a graph of space versus time – a spacetime diagram – then compactify.
 05:49: ... across the universe, while the verticalish lines are set locations in space in only one spatial ...
 06:03: The contours bunch up towards the boundaries so that every step on the map covers more and more space and time.
 06:56: Any sublightspeed paths, which means anything with mass, will be swept along with the contours of space.
 07:05: ... matter must originate at this point representing all of space in the infinite past, and must also converge to this point which ...
 07:44: ... inside, but at its boundaries the simple rules of noncurved, Minkowski spacetime ...
 08:01: That’s handy because flat space is the only space where quantum mechanics is fully solvable.
 08:15: ...  where he could define the state of the quantum vacuum in solvable flat space. ...
 09:38: But this time we’re not mapping space versus time – we’ll just map two dimensions of hyperbolic space.
 09:45: In fact, let’s use the most famous conformal compactification of hyperbolic space.
 09:51: That’s right, there is a most famous conformal compactification of hyperbolic space, and you’ve probably seen it.
 11:20: This is an example of tessellation – tiling a space with regular repeated shapes.
 11:27: ... space is fascinating because there are literally infinite ways it can be ...
 11:49: Each tile represent the same size region of space.
 12:07: But the real power of AdS space isn’t the cool art you can do with it.
 12:16: ... a mouthful: the boundary of a conformallycompactified antide Sitter space is itself a conformallycompactified Minkowski space with one fewer ...
 12:43: They give you a cylinder and representing an AdS spacetime with 2 spatial and one temporal dimensions – let’s call that 2+1 dimension.
 12:53: On the other hand the surface of the disk has only one dimension of space – the circumference – and the same oneD of time – 1+1.
 13:03: ... of the interior volume  is mathematically exactly a flat, Minkowski space. ...
 13:32: ... the crazy thing is that you can treat that surface space and the interior space – also called the “bulk”  as separate spacetimes ...
 13:56: In 1997 Argentinian physicist Juan Maldacena found an incredible correspondence between these spaces.
 14:04: ... define a conformal quantum field theory in a 3+1dimensional Minkowski space, that corresponded to an interesting mathematical structure in the ...
 14:31: Quantum mechanics in the form of a conformal field theory in one space is a theory of quantum gravity in a space with one higher dimension.
 14:40: The hologram part is because the lower dimensional space can be thought of as the infinitely distant boundary of the higher dimensional space.
 15:01: The deeply abstract relationship between these two spaces needs an entire episode.
 15:06: Stay tuned for the final installment of the holographic principle in notsoinfinitelydistant future of spacetime.
 15:16: ... end of the universe when we talked about the Big Rip  in which space tears itself to shreds on subatomic scales due to runaway increase in ...
 15:45: ... all, if space is expanding faster than light at the event horizon, that should counter ...
 16:01: ... produce a global state where everything just looks like an inflationary spacetime. ...
 16:25: ... that are time symmetric  systems where the global properties of the spacetime don't evolve over ...


20190328: Could the Universe End by Tearing Apart Every Atom?
 00:05: ... then tragically separated by the infinitely accelerating expansion of space on subatomic ...
 00:25: ... density of dark energy the same amount of this stuff in every block of space which means if you increase the volume you increase the overall amount ...
 06:20: ... with no gravitational bodies left to resist the expansion, all points in space will eventually be racing apart from each other faster than the speed of ...
 06:51: ... faster than light recession of space is already happening but right now four patches of space very far apart ...
 07:02: ... two patches of space are moving away from each other, faster than light, then they can never ...
 10:03: ... isolated elementary particles separated by infinitely expanding space. That's a hell of a ...
 12:53: ... ripped to shreds by the infinitely accelerating subatomic structure of spacetime. ...
 13:18: ... week we did a spacetime journal Club on that paper that actually presented evidence that dark ...
 15:23: ... originally chicken sized. The tiny bird bones grew with the expansion of space. ...


20190320: Is Dark Energy Getting Stronger?
 00:41: Today we’re doing a Space Time Journal Club to reveal another clue.
 01:59: ... us that we can this accelerating expansion is what you expect if empty space has a constant energy density – so that more space means more dark ...
 02:32: We see its effect in the rotation and movement of galaxies and in the bending of light due its spacewarping gravity.
 04:33: If we have lots of supernovae at different distances when we have a set of rulers spanning both time and space.
 07:31: ... spray into the galaxy, giant jets that can punch out into intergalactic space, and also, hovering above the accretion disk we have a hot atmosphere ...
 12:00: At the moment, dark energy is only strong enough to accelerate the expansion of space on the largest scales.
 12:06: It’s not strong enough to have any effect on the space inside a galaxy, so the Milky Way, and certainly the solar system are safe.
 12:34: It’s a potential end of the universe in which spacetime rips itself to shreds at subatomic scales due to the increasing strength of dark energy.
 14:27: One way or another I guess it’d be nice to know whether dark energy will one day rip to shreds the subatomic fabric of space time.
 15:02: ... then you'll want to check out the course: Black Holes, Tides, and Curved Spacetime: Understanding ...
 15:30: ... a conversation with Richard Branson about his recent successful tests of SpaceShipTwo, which recently carried the first private passenger into space on a ...
 15:47: Richard also shared his dreams for the future of human space travel.
 15:54: A few of you dispute the use of the term spaceship for a craft that doesn't reach orbit.
 16:00: Indeed, Virgin Galactic's Spaceship1 and Spaceship2 crossed the boundary into space  past the higher Karman line in the case of spaceshipone.
 16:12: They followed suborbital trajectories, which left them in space for only minutes.
 16:17: Now in my book if it shipped you into space it's a spaceship, but these terms aren't well defined yet, so you can insist on your definition too.
 16:37: IT's called launcherone, and it'll launch from WhiteKnightTwo  the same plane that carries spaceshiptwo.
 16:45: Paul C mentioned a couple of other promising spacecraft that aren't getting as much attention as they should.
 16:55: ... mentions Stratolaunch  an airlaunch plane  MUCH bigger than the SpaceShipTwo launcher and designed for orbital rocket launches as well as space ...
 17:42: I mean, when the spaceplane is in the shop.


20190313: Will You Travel to Space?
 00:00: The private space race has been on for a while now.
 00:02: The attention has been on SpaceX and Blue Origin with their reusable rockets.
 00:07: But there's one private space program that's been doing things a little differently.
 00:11: Richard Branson's Virgin Galactic isn't building rockets at all – it's building spaceships.
 00:23: ... other displays, Virgin Galactic achieved something that no other private space company ever ...
 00:38: ... 2014 it became the first to put an actual person in space on board its SpaceShipOne, turning its pilot into an astronaut. And then ...
 00:59: The attention of space nerds everywhere, long distracted by the selflanding rocket club, suddenly turned back to Virgin Galactic.
 01:08: Questions abound! Is there a future in these strange airlaunch spaceships?
 01:13: Why is Richard Branson building spaceships at all?
 01:57: VSS Unity, SpaceShipTwo, successfully kissed space December 13th.
 02:17: ... was just fantastic that two wonderful nowastronauts managed to get into space. And we've got another test flight just coming ...
 02:31: ... move the whole operation to New Mexico where we've got this beautiful spaceport I'm hoping to go up in July. And then have many others who've signed up ...
 02:56: [RICHARD] The reason we built a spaceship and a spaceship company was because I wanted to go up.
 03:02: [MATT] OK, wanting to go to space is a pretty good reason to build a spaceship.
 03:12: [RICHARD] Everybody I know who's been into space who said it was earth changing, to be able to be in space looking back on it.
 03:21: ... Overview Effect which is infused with all these people who've been into space. And also, space I think can do a lot to protect the ...
 03:44: There's an awful lot of good that has already come out of space and will come out in the years to come.
 04:01: ... you'll know that its business model is to sell tickets for rides into space. ...
 04:14: Your first strategy though has been space tourism.
 04:26: [RICHARD] There's only been since the Space Shuttle began about 500 people who are astronauts who've had the chance to go to space.
 04:42: And I think that can, if we if we're right about that, we can build more and more spaceships.
 04:57: ... overriding all of this, both space and pointtopoint travel and satellites in space, is a desire to bring ...
 05:35: I love these images of SpaceShipOne and SpaceShipTwo dropping off and flying up.
 05:42: [RICHARD] I think somehow if you're going to go into space you should be on a spaceship.
 05:46: [MATT] Let's take a look at what humanity's first private spacecraft looks like, and why it might be the solution to affordable space access.
 05:54: This is the VSS Unity on its second trip to space on February 22nd.
 06:08: ... first two space flights took it to around 83 and 90 kilometers respectively. For ...
 06:20: This is still below the 100 kilometer Karman Line, an alternate definition to the space boundary.
 06:32: ... a few minutes in space the craft reenters and lands. It never reaches orbital velocity so it's ...
 06:45: Unity is actually the second of the SpaceShipTwo class space planes.
 06:55: ... previous generation, SpaceShipOne, was actually the first private piloted craft to cross the Karman Line in ...
 07:16: It's worth a quick word on. Obviously the space plane itself needs less fuel than a craft launched from the ground.
 08:09: ... And this is what Richard means when he says pointtopoint travel. These spacekissing trajectories could one day allow us to travel halfway across the globe ...
 08:30: Perhaps in the future everyone who travels overseas will also become an astronaut. But I'm less patient than that When do WE get to go to space?
 08:42: You already have a couple of hundred more than that signed up to fly to space with Virgin Galactic.
 09:17: ... if we're right in believing that a spaceship company is going to be successful and we can attract people who are ...
 10:03: Okay, so we have suborbital joyrides and saving the world by improving our access to space.
 10:35: And then we can have little spaceships that can whisk them around the moon and back in the evenings for dinner.
 10:52: ... or Elon or Jeff Bezos, we will be looking at a deeper and deeper space exploration. But in order to afford that we need thousands of people to ...
 11:47: ... quest to send himself, and before too long many of the rest of us into space, is reaching its fruition, with lofty goals ...
 12:08: ... Elon Musk is hot on Richard Branson's heels. On March 2nd SpaceX's Dragon 2 spacecraft made its first successful trip to space, and not on ...
 12:20: It actually docked with the International Space Station.
 12:23: ... is the first private spacecraft designed to carry humans to make it into true orbit. Now Dragon 2 didn't ...
 12:37: It's a hell of a time to be alive, watching humanity's first tentative steps off the Earth, and into the fringes of space time.


20190306: The Impossibility of Perpetual Motion Machines
 11:29: You do get your pick from the Space Time store.
 12:21: Had only da Vinci known that his own perpetual motion machines could’ve score him such cool swag from Space Time.
 12:56: ... can learn more at curiositystream dot com slash spacetime Hey guys, quick announcement  if you’re in New York this week I’m going ...


20190220: Secrets of the Cosmic Microwave Background
 12:34: ... that in that noise can be found the secrets of the earliest epochs of Spacetime Thank you to Curiosity Stream for supporting PBS Digital Studios ...


20190207: Sound Waves from the Beginning of Time
 00:29: [PBS Space Time intro] The field of cosmology and the study of the universe on its larger scales was once the least precise in all of astrophysics.
 01:37: For the first few hundred thousand years in the life of our universe, All of the space was filled with hydrogen and helium in plasma form.
 12:39: I mean think about it. There are rings in the sky inscribed in galaxies, frozen echoes of the very first sound waves to reverberate across spacetime.
 16:18: That's kind of like having parallel spacetimes, one with positive and one with negative masses, which can still interact gravitationally.
 16:26: ... that occurs if you put both positive and negative masses in the same spacetime. ...
 17:28: [PBS Space Time outro]


20190130: Perpetual Motion From Negative Mass?
 00:41: ... to faster than light travel because it’s the only stuff that can curve space in the right way to hold open wormholes and construct warp ...
 06:04: ... that can distinguish between the feeling of acceleration in empty space and the feeling of weight in a gravitational ...
 06:31: General relativity describes gravity as the warping of the fabric of spacetime.
 06:36: ... and of energy, momentum, pressure, and more, change the geometry of spacetime and that new geometry defines the paths objects can ...
 07:20: Let’s take the goodold 2dimensional rubber sheet analogy to depict the warping of 3D space.
 07:26: Positive mass causes spacetime to curve inwards – what we call positive curvature.
 10:18: In this case, the basic nature of the positive versus negative gravitational fields – the way the fabric of spacetime gets stretched has to be right.
 10:58: ... of general relativity – the paths carved into the geometry of Einstein’s spacetime – are the GR analogs of Newton’s second law and give the equations of ...
 14:07: 6 randomly selected correctslashcreative answers will receive their choice of any piece space time swag from our brand new merchandise store.
 14:21: Winning perpetual motion machines will be revealed in an upcoming episode of space time.


20190124: The Crisis in Cosmology
 01:07: The galaxies appear to be racing away from us, because the intervening space is expanding.
 05:32: ...uses the Hubble Space Telescope to match old supernovae observations...
 13:12: ...and for what it'll tell us of the origin and fate of our expanding spacetime.
 17:07: ...and presumably reassemble itself into the stars, spaceships, monkeys,... that originally fell in.


20190116: Our Antimatter, Mirrored, TimeReversed Universe
 10:54: ... our perfect mirror universe it's a reflection of all three: charge, space, ...
 13:52: ... I really want to address a few points made by FieldStrength on the PBS Space Time subreddit: they covered all the most important points, now first I ...
 16:06: ... other point is that the large undefined parameter space of string theory  the so called 'String landscape' is no more of a ...


20190109: Are Dark Matter And Dark Energy The Same?
 00:55: Today on Space Time Journal Club, let’s pick apart J.S.
 01:57: That acceleration matches the effect you would get if empty space itself had a tiny bit of energy.
 02:03: As more space comes into existence because of that expansion thing the more“dark energy” you get, which causes more acceleration.
 02:18: The standard picture of dark energy is that it’s an actual greaterthanzero energy of the vacuum of space.
 02:53: But here’s the punchline: if empty space has a constant, positive energy density then it also has a negative pressure.
 12:05: What we call antideSitter space.
 12:59: ... a negative mass, antigravitational, positive pressure, antideSitter space ...


20181220: Why String Theory is Wrong
 02:35: He was playing around with the newfangled general relativity in five dimensions, 4 space and 1 time, because why not.
 02:43: ... found that in the right sort of 5D spacetime, you can separate the resulting Einstein equations into a 4D component ...
 03:08: It appeared that gravity acting in this fifth dimension looks like electromagnetism to being trapped in our 4D spacetime.
 03:58: At every point in space, there's another direction to move: up, down, left, right, forward, back, and around.
 06:28: All required six compactified extra dimensions of space.
 06:32: What differs is the detailed geometries and symmetries of those spaces, and the way strings vibrate within them.
 09:19: ... described a type of duality, in this case tduality, short for target space ...
 15:00: ... seek an even more beautiful and ultimately more right understanding of spacetime. ...
 15:37: ... and differential equations you can learn more at brilliant org slash spacetime Now before I get to comments don't forget to check out our all new ...


20181212: Quantum Physics in a Mirror Universe
 00:02: ... where this holds in the universe is symmetric to coordinate shifts in spacetime and even the rather abstract phase of the wave function in quantum ...


20181206: Did Life on Earth Come from Space?
 00:37: ... now we know that debris from planetary surfaces can be ejected into space during asteroid or comet impacts hundreds of meteorites have been found ...


20181121: 'Oumuamua Is Not Aliens
 00:07: To repeat the "Space Time" maxim, it's never aliens, until it is.
 00:50: Rather it appeared to have fallen in from interstellar space and was on its way back out again.
 01:03: It's the first chunk of interstellar space debris we've ever spotted passing through our solar system.
 01:34: Today on "Space Time Journal Club," I want to do two things.
 01:47: Its changing brightness suggests it's a highly elongated object tumbling through space.
 02:00: It's a space baguette perhaps after going through a space sandwich press.
 02:26: ... certainly expect there to be a bunch of space junk floating between the stars, probably ejected in the violent early ...
 04:58: ... thin and light, thinner and lighter than any conceivable natural space object, ergo ...
 05:37: It may also explain why we saw something at all given that natural space debris the size of Oumuamua should be much rarer between the stars.
 06:06: And there shouldn't be enough interstellar space junk for something like Oumuamua to have been spotted by chance.
 08:26: And finally, what about the sheer unlikelihood of a random encounter with an interstellar space rock?
 08:31: ... order for our spotting of a more moon to have been likely, interstellar space needs to contain something like 10 to 100 times the number of ...
 08:44: And by that I mean the expected density of space rocks that are ejected during the planetary formation process.
 08:53: First, there could be more space debris than we expected.
 09:16: Maybe interstellar space junk is rare, but we caught a 0.1% or 1% or 10% chance.
 10:06: Interstellar space would need to be filled with broken lightsails, something like 10 to the power of 15 probes per star in the Milky Way.
 12:59: Whether or not it's aliens, it's likely our first encounter with the natural or unnatural denizens from interstellar space time.
 14:23: As a neutrino travels through empty space, they oscillate between the three types, electron neutrino, muon neutrino, and tau neutrino.


20181114: Supersymmetric Particle Found?
 04:50: When ultra high energy cosmic rays travel through space, they bump into the photons of the cosmic microwave background.
 12:00: Perhaps we will verify the existence of the stau and with it confirm the supersymmetric nature of space time.
 14:32: ... invariance only works for the 2D world sheet, which has one dimension of space and one of time, this is the shape traced out by a string moving through ...
 15:11: ... special dimension that has the same scale as the familiar three, so a 4d space in which we live on an embedded 3D manifold called a ...


20181107: Why String Theory is Right
 02:06: ... space of possible versions of string theory is so vast that nothing can be ...
 03:29: When a point particle is moving through space and time it traces a line.
 03:34: On a spacetime diagram, time versus one dimension of space, this is called its world line.
 04:32: When strings move on a spacetime diagram, they trace out sheets or columns.
 07:52: It's when you can redefine some variable in different ways everywhere in space and still get the same physics.
 08:19: ... of the peaks and valleys in different ways at different points in space without screwing up the ...
 09:36: It says that changing the scale of space itself shouldn't affect the physics of strings.
 10:09: Turns out that in 4D spacetime it does matter whether you change the scale of space and the separation of its tracks.
 10:30: ... the 2D sheet traced out in spacetime by a vibrating 1D string has this symmetry that lets us redefine the ...
 13:30: Philosophical points to consider as we continue to follow the mathematical beauty hopefully towards an increasingly true representation of spacetime.


20181031: Are Virtual Particles A New Layer of Reality?
 02:05: In it, particles are excitations in fundamental fields that exist everywhere in space.
 05:09: They sure make it look like virtual particles are doing regular particle stuff like traveling through space but that's just not the case.
 07:46: And that uncertain momentum gives them real locations, real trajectories through space.
 12:59: That will be the family of lattice field theories in which spacetime itself is defined on discrete grid.
 13:25: At best, they can be interpreted as a small component of possibility space for a quantum field doing something real.
 13:32: That said, for something that doesn't exist, they're surprisingly useful for describing the weird underlying machinery in our quantum spacetime.
 14:38: ... to play their hands, tentacle, pseudo pods, whatever to a big space ...


20181025: Will We Ever Find Alien Life?
 02:48: We can't see this effect on earthlike planets yet, but the James Webb Space Telescope to launch in a year or so will get close to doing so.
 04:26: ... dependence of the dips is consistent with dust, so likely natural space junk, not any type of artificial ...
 04:38: As we like to say on Space Time, it's never aliens until it is.
 05:25: But actually the best instrument for finding Dyson swarms is the European Space agency's GAIA mission.
 09:00: ... that in order for us not to see any aliens, the chance of going from space rock to high tech society must be less than half a ...
 12:40: The alternative may be eternal quiet across the lifeless reaches of space time.
 13:15: And use the code spacetime during the sign up process.


20181018: What are the Strings in String Theory?
 08:05: The strings are real physical strands, and the waves are wiggles in actual space.
 10:01: ... they need to vibrate in more than just the three dimensions of space. ...
 10:34: It's a theory that works in a universe that is clearly not our own with its measly three dimensions of space.
 11:30: Three large dimensions of space and six tiny PacMan dimensions that only strings experience.
 11:44: Our universe of 3D space and 1D time is like flatland on this 5D object called a 5brane.
 13:17: And you can decide for yourself whether you accept the fundamental stringy nature of space time.
 13:24: Thanks to 23andMe for supporting PBS Digital Studios and "Space Time".


20181010: Computing a Universe Simulation
 00:44: ... binary notion of existence or nonexistence like if the tiniest chunks of space time or chunks of quantum field or elements in the abstract space of ...
 02:59: ... which tells us the maximum information that can be stored in a volume of space is proportional to the surface area of that ...
 11:03: If you see your name, you are a lucky winner of a spacetime tshirt.
 11:57: And these insights may also lead to real paradigm shifts, perhaps ultimately revealing the fundamentally informational nature of space time.
 12:49: ... light a little bit, effectively increasing the index of refraction of space, in the same way that light is slowed in air or ...
 13:04: Light traveling through space is slowed down from the full light speed of the perfect vacuum.
 13:15: But that's radio, which can interact strongly with the rare charged electrons and protons in intergalactic space.
 13:57: Science works by forcification, and null results rule out huge chunks of theory space, greatly advancing our certainty.
 14:48: Seriously, Hollywood screenwriters really need to hire Space Timers as consultants to get their terminology right and pay us lots of money.


20181003: How to Detect Extra Dimensions
 00:43: ... on "Space Time Journal Club," I want to tell you about one in particular described ...
 01:11: These superdense remnants of dead stars churned the fabric of space and time in their death spiral.
 01:59: This allowed us to make some really important conclusions about how gravity travels through space.
 02:05: In the case of today's paper, it allows us to measure how many dimensions that space actually has.
 02:15: We think of space as threedimensional.
 02:17: Add one dimension of time to give us 4D spacetime, which we'll also refer to as 3plus1dimensional spacetime.
 02:38: But before we get all hyperdimensional, let's think a bit more about 3 plus 1D spacetime and how gravity, light, and matter behave there.
 03:25: But what if we, instead, lived in 2D space?
 03:56: So in 4plus1dimensional spacetime, brightness should drop off more quickly than in 3D space.
 04:27: In general, general relativity in 3 plus 1 spacetime does a great job at describing gravity in the largescale universe.
 06:35: ... can imagine a threedimensional brane, a 3brane, embedded in a spacetime with four spatial dimensions, where the extra dimension of space is ...
 08:41: ... waves should lose energy to that extra dimension as they travel through space. ...
 09:02: In regular 3D space, gravitational waves drop in intensity proportional to just distance, not distance squared.
 09:11: If space has four or more dimensions, then gravitational waves should drop off in intensity faster than you'd expect in three dimensions.
 10:42: The gravitational wave lost the right amount of intensity for a 3plus1dimensional spacetime.
 11:43: And apparently, that truth doesn't include a 3brane embedded in an extended 4plus1dimensional spacetime.
 12:20: And use the code SPACETIME during the signup process.
 13:08: But they still end up with a spacetime fabric that is fragmented on its smaller scales.
 13:17: One thing that it's hard to do is to keep spacetime continuous on the smaller scales.
 13:22: If spacetime is indefinitely divisible, then you get hopeless conflicts with quantum theory.
 15:40: Brilliance, wit, and/or whining that's what it takes to make it on "Space Time."


20180920: Quantum Gravity and the Hardest Problem in Physics
 00:34: First, Einstein's relativity utterly changed the way we think about space, time, motion, and gravity.
 01:12: ... today, on "Space Time," I'm going to begin our discussion of the great quest for this ...
 01:45: In it, the presence of mass and energy warp the fabric of space and time.
 01:56: General relativity incorporates the earlier special relativity, which describes how our perceptions of space and time also depend on motion.
 02:06: ... the earlier ideas of Isaac Newton, in which space and time are treated as separate and universal, special and general ...
 02:41: That math started with the Schrodinger equation, which tracks these probability waves through space and time.
 02:49: But the Schrodinger equation treats space and time as fundamentally separate in the oldfashioned Newtonian way.
 03:06: Nowadays, modern quantum field theories fully incorporate the melding of space and time predicted by special relativity.
 03:13: And yet they still don't directly incorporate the warping of space and time predicted by general relativity.
 04:30: In fact, it's very possible to shoehorn the curved geometry of general relativity into the way quantum field theory deals with space and time.
 04:38: ... when you have strong gravitational effects on the smaller scales of space and time, like the central singularity of the black hole or at the ...
 04:54: But even thinking about the structure of curved space on the smaller scales leads to craziness and catastrophic conflicts.
 05:08: ... what it means to talk about very, very tiny chunks in the fabric of space. ...
 05:21: In order to measure a location in space say, the location of a particle you need to interact with it.
 05:57: ... a meter, the amount of energy you would need to put into that region of space would make a tiny black hole with an event horizon one Planck length in ...
 07:54: Standard quantum theories treat the fabric of spacetime as the underlying arena on which all the weird quantum stuff happens.
 08:19: But in the resulting math, the new quantum fields still lie on top of a smooth, continuous grid of space and time.
 08:28: The gravitational field doesn't lie on top of spacetime.
 08:32: It is spacetime.
 08:34: To quantize gravity, you have to quantize spacetime itself.
 08:59: Any energy must cause spacetime curvature.
 09:08: In quantum gravity, gravity itself becomes an excitation in our quantized spacetime.
 09:14: The energy of those excitations should themselves precipitate more spacetime curvature, represented as further excitations.
 11:03: We say that a quantized spacetime of general relativity is nonrenormalizable.
 11:18: Space and time simply cannot behave in the familiar way below the Planck scale.
 11:23: And so the simplest approach to quantizing gravity and spacetime must be wrong.
 11:54: ... gravity, or you just assume that GR and, indeed, the mutable fabric of spacetime itself are emergent phenomena from a quantum theory deeper than our ...
 12:11: ... greatest problem in modern physics, the quest for a theory of quantum spacetime. ...
 14:09: The rotating black hole drags space around with it.
 15:36: youteub akount asks whether the universe has ever been in a state of too much information in too little space, particularly during the Big Bang.


20180912: How Much Information is in the Universe?
 00:25: ... and radiation in between the stars and galaxies, not to mention space itself, with its fluctuating quantum fields, dark energy, blah blah, ...
 01:44: ... is that the maximum amount of information that can fit in a volume of space is not proportional to that ...
 01:54: It's proportional to the surface area of that region of space.
 02:05: ... equally a limit on how much information you can fit into any region of space. ...
 02:32: But instead of storage capacity, let's think about the information needed to perfectly describe a patch of space.
 03:01: It's the smallest possible chunk of space, so let's it can contain the smallest amount of information.
 04:21: ... will be better to use the number of grid points in a quantum phase space, which includes position, but also other degrees of freedom, like ...
 05:24: So how do you encode a whole universe in a space far smaller than the universe itself?
 05:51: Most of space is indeed empty.
 05:53: Let's say instead, you only need a single bit of information for every element in phase space that's occupied.
 08:55: ... if we started to fill up those empty Plancksized cubes of space throughout the universe until it contained more information than the ...
 09:14: It would be the end of space time.
 10:41: ... using it among other things to give you a bit of a behind the scenes on "Space Time" stuff, especially graphics, as well as the extra details on ...
 11:19: ... switches off the simulation, I'll see you next week for a new episode of "Space Time." So we're a bit behind on comment responses due to my ...
 13:50: ... it's really useful to be able to ignore insignificant amounts of space, or time, or energy in the presence of much larger ...


20180905: The Black Hole Entropy Enigma
 00:53: Also, we've seen them in their gravitational effects on their surrounding space and in the gravitational waves caused when they merge.
 05:07: ... region of space in which the black hole formed appears to have gone from high entropy to ...
 10:25: Bekenstein's formula was derived for black holes, but it also gives the maximum amount of information that can be fit into any volume of space.
 10:34: In this respect, it's called the Bekenstein bound, and it's proportional to the surface area of that space.
 10:44: ... the maximum amount of information you can fit into some patch of space depends on the volume of that space as in one bit per tiny volume ...
 10:55: But in fact the rule is one bit per tiny area element on the surface of that space.
 11:00: That also means that the information needed to describe any volume of space, no matter its contents, is proportional to the area bounding that space.
 11:34: It might also be true, and obviously we'll be back before too long to talk about string theory and the holographic nature of spacetime.
 11:58: You can get the first 60 days free if you sign up at curiositystream.com/spacetime and use the code spacetime during the signup process.


20180830: Is There Life on Mars?
 07:08: ... of Mars, probably ejected from Mars's gravitational field after another space rock smashed into the ...
 11:42: ... the end of July, the European Space Agency announced that this lake was discovered using radar reflections ...
 13:07: ... we want to understand our own place in what so far seems an eerily empty spacetime. ...


20180823: How Will the Universe End?
 06:53: That means all of the planets, black dwarfs, space dust, everything.
 09:09: ... become more and more diffuse and dim as the accelerating expansion of space continues and the infinitely long progression to absolute heat death is ...
 12:19: Dark energy may tear space to shreds in the Big Rip.
 12:34: We'll explore these extreme futures of spacetime time in the near future of "Space Time." Before we get to comments, two things.
 12:48: ... websites, regardless if you want to show off your collection of highres space images or build a complex online business that will eventually compete ...
 15:50: Now, we can think of a quantum wave function as having a size because it can be spread out over space.


20180815: Quantum Theory's Most Incredible Prediction
 12:31: We have to conclude that we are getting closer and closer to the truth in our search for theories to explain the underlying mechanics of space time.


20180801: How Close To The Sun Can Humanity Get?
 00:08: The source of all life and sustenance for our little blue space rock.
 03:12: We already monitor it constantly with groundbased telescopes and spacecraft orbiting the earth or orbiting the sun at a safe distance.
 05:47: While we've used heat shields before on a spacecraft or rovers for entering atmospheres, this one is different.
 06:12: ... one of the biggest challenges with this mission is getting the spacecraft that close to the sun, even ignoring its ability to survive ...
 06:28: Why not just let the spacecraft fall towards it?
 06:51: Parker will use the same trick as many of our outbound spacecraft, like Voyager or Pioneer gravitational assists.
 08:41: This time if our luck holds, we'll come close to touching our home star to unlock the mysteries of our closest stellar neighbor in space time.
 09:09: And Space Time fans have always been a huge help.


20180725: Reversing Entropy with Maxwell's Demon
 03:20: The particles would quickly flow to fill the available space, and you could extract energy from that flow.
 11:30: ... get tangled up in all of that in an upcoming episode of "Space Time." Last time, we delved into the true nature of entropy and the ...


20180718: The Misunderstood Nature of Entropy
 06:47: We call this space of properties a phase space.
 06:49: And instead of particles being distributed through position space, a microstate is really defined by how energy is distributed through phase space.
 06:58: The average distribution of individual particles in phase space defines the thermodynamic properties of the system.
 08:14: For example, if we try to draw pictures or write words in phase space, this is where we get to a point of common confusion.
 10:45: ... that brilliant macrostate that is you, until I see you next week on "Space Time." The field of statistical mechanics has given us some of the most ...
 11:43: Brilliant, Math and Science Done Right, is proud to support "Space Time." To learn more about Brilliant, go to brilliant.org/spacetime.


20180711: Quantum Invariance & The Origin of The Standard Model
 03:40: The function is an oscillation in quantum possibility, moving through space and time.
 07:34: ... is for us to introduce a new fundamental field that pervades all of space. ...
 11:02: We should be amazed that we can learn that language and through it, comprehend the underlying nature of space time.
 11:10: Last time on Space Time Journal Club, we looked at a new result potentially detecting a particle beyond the standard model, the sterile neutrino.


20180704: Will A New Neutrino Change The Standard Model?
 00:18: ... on "Space Time" Journal Club, we'll look at a paper that reports a compelling hint ...
 10:33: Either way, we'll have peered just a little deeper into the fundamental building blocks of space time.
 10:53: You can get the first 60 days free if you sign up at curiositystream.com/spacetime and use the code spacetime during the signup process.
 13:06: For one thing, our moon is protected from exploitation by the Outer Space Treaty, which prohibits nations from claiming any sovereignty there.


20180627: How Asteroid Mining Will Save Earth
 02:40: They have high abundance of water, an extremely valuable resource in space.
 03:29: During its formation when it's still a giant bowl of molten space rock, heavier iron and nickel will sink to the asteroid's center.
 06:04: ... bring back to Earth, but they can go towards building infrastructure in space, including more asteroidmining ...
 06:44: It also needs to be large enough to be worth the effort and accessible by an economical spacecraft.
 07:46: Planetary Resources is developing its Arkyd spacecraft with that initial goal.
 07:52: And its main competitor, Deep Space Industries, is working on a range of lowcost prospector craft.
 09:31: This can then be collected and processed by the spacecraft.
 10:26: ... can begin of expanding humanity's reach into more distant regions of space ...
 10:42: Today's episode of "Space Time" was sponsored by Audible.
 11:18: Go to audible.com/spacetime, or if you're in the US, text spacetime to 500500.
 11:25: Once again, that's audible.com/spacetime, or text spacetime to 500500.


20180620: The Black Hole Information Paradox
 11:22: ... field of string theory, and hinted at the possible holographic nature of spacetime. ...
 11:44: Einstein's general theory of relativity reveals them to be regions of frozen time and cascading space.
 12:36: Brilliant, math and science done right, is proud to support "Space Time".
 13:20: ... hole produces a negative pressure that actually halts the cascade of space within the black hole and propels it back ...
 15:10: ... when you're trying to throw together a quick graphic and forget that "Space Time" viewers notice ...


20180613: What Survives Inside A Black Hole?
 00:34: At that horizon, time is frozen and the fabric of space itself cascades inwards at the speed of light.
 03:24: In Einstein's general theory of relativity, we think of the gravitational field as curvature in the fabric of spacetime.
 04:12: The spacetime at the location of Earth's orbit would remain curved until the elastic fabric straightened itself out at the speed of light.
 04:20: ... but that mass is remembered in the gravitational field, the curvature of spacetime above the event ...
 04:32: In fact, the space at the event horizon is already falling inwards.
 04:46: There's an extremely important law in physics that describes how the universe remembers the contents of a region of space.
 05:56: The universe remembers the total charge that exists in the region of space enclosed by the surface.
 07:34: ... so Gauss's law demands that the mass and charge content of any region of space are remembered in the gravitational and electric fields on the surface ...
 07:50: ... conserved quantities, the only way to change the contents of a region of space is for more mass or charge to cross its ...
 08:52: In Einstein's general relativity, a spinning mass drags the fabric of space time around with it in a phenomenon known as frame dragging.
 09:19: ... or a whirlpool of gas, it will either add or subtract from this flow of space above the event ...
 09:36: I hope I've given you a sense of why mass, charge, and angular momentum are remembered by the space outside a black hole.
 11:03: We will delve into all of that in an upcoming episode of "Space Time".


20180523: Why Quantum Information is Never Destroyed
 09:27: That measurement itself is just a thing that happens in one part of the possibility space.
 10:02: In an upcoming episode, we'll see whether quantum information really can be deleted from the otherwise perfect memory of space time.
 10:24: You can get the first 60 days free if you sign up at curiositystream.com/spacetime and use the code spacetime during the signup process.
 10:42: "Space Time" is going to go quiet for the next couple of weeks to get our house in order.
 11:42: Space is not globally expanding or contracting on those scales and so energy is absolutely conserved.


20180516: Noether's Theorem and The Symmetries of Reality
 01:18: As the universe expands, light traveling through that expanding space is stretched out.
 04:35: See, Einstein's description of gravity reveals the dimensions of space and time to be dynamic and changeable.
 04:43: If the very nature of space can change over time, then continuous time symmetry is broken.
 05:00: The law of conservation of energy is fundamental in Newtonian mechanics, in which space and time are unvarying and eternal.
 05:14: It only applies for parts of the universe where we can approximate space as unchanging over time.
 07:22: ... means we can apply it to not just the symmetries in the dimensions of space and time, but also to more abstract ...
 09:27: ... workings of the universe through the continuous symmetries of "Space Time." Thank you to Brilliant for supporting PBS Digital ...
 10:07: Fabrice, your continuously timesymmetric contributions are fundamental to the conservation of "Space Time." So thank you.
 10:49: LSST won't do as well in that regard, in part because it's on the ground, in the Atacaman Andes, in Chile, rather than in space.
 12:47: ... people, on "Space Time," we only ask that you start with a passing familiarity with ...


20180509: How Gaia Changed Astronomy Forever
 00:22: [MUSIC PLAYING] The Gaia satellite was launched in late 2013, entirely built and operated by the European Space Agency.
 01:10: That's 1,000 to 2,000 times smaller than the resolution of the Hubble Space Telescope.
 01:37: The spacecraft orbits the sun at Lagrange point two, tracking the Earth's orbit, but 1.5 million kilometers further from the sun.
 08:40: This is our Milky Way, and we just became much more familiar with our galactic home in space time.


20180502: The Star at the End of Time
 08:38: ... huddle in the warmth of the last stars to burn in the darkening end of space ...
 10:15: They get way too close to allow anything but a single black hole to exist in that tiny space.


20180425: Black Hole Swarms
 01:07: ... this episode of Space Time Journal Club, we're going to delve into the recent nature paper, ...
 08:24: ... in what has to be the craziest and most terrifying environment in nearby spacetime. ...
 09:06: ... if you sign up at curiositystream.com/spacetime and use the promo code, space time, during the signup ...
 10:38: Two gravitational waves crossing paths will add together at any one point in space and time.
 10:44: This is either constructively producing a stronger stretching or contraction of space or destructively, meaning their effect cancels out.


20180418: Using Stars to See Gravitational Waves
 04:08: That's LISA, the Laser Interferometer Space Antenna.
 04:12: This spacecraft by the European Space Agency is scheduled for a 2034 launch.
 04:57: The universe is flooded with spacetime ripples.
 06:17: ... shifts could indicate tiny fluctuations in the fabric of space within the pulsar array volume due to the passage of impossibly vast ...
 07:05: ... passes by, the beads are free to follow the expansion and contraction of space while the rod resists due to the atomic forces between its ...
 08:27: ... incredible wealth of information carried to us in the rippling fabric of spacetime. ...
 08:56: ... gravity is also your next step toward understanding Einstein's view of spacetime. ...
 09:32: To support spacetime and learn more about Brilliant, go to brilliant.org/spacetime and sign up for free.
 10:03: And you always ask the best questions on the spacetime hangout YouTube stream.


20180411: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!)
 10:28: ... dullness, an agent in the inexorable trend to maximize the entropy of spacetime. ...
 12:52: Before they get to us, they'll find themselves in a patch of space that is moving away from us faster than the speed of light.


20180404: The Unruh Effect
 01:19: To understand this, we don't need general relativity with its spacetime curvature and conflicts with quantum mechanics.
 01:26: We just need a little special relativity and a spacetime diagram.
 01:34: A spacetime diagram has two axes, time and, well, space, with time on the vertical axis.
 01:40: We can show an object's path through space and time using world lines on the diagram.
 02:04: On the spacetime diagram, this is a line with a 45degree angle from the vertical axis.
 02:11: It's just determined by the unit of space and time that we choose.
 02:26: ... our observer defines what we call the past light cone, the region of spacetime that can have a causal influence on the ...
 03:42: Just before they reach my spacetime location, that constant acceleration brings them to a halt, and they start moving back in the opposite direction.
 06:08: ... derivation requires a switch between inertial or Minkowski and Rindler space via the beloved Bogoliubov transformations, which are also used in the ...
 06:53: This is because that distant point of spacetime is smoothly connected to the spacetime near the horizon.
 06:58: I mean, it's all one big spacetime.
 07:06: ... same location as an inertial observer, the former will see that patch of space filled with radiation, but the latter will see an empty vacuum in the ...
 08:24: But what does this look like for someone not accelerating but in the same patch of space?
 09:58: According to Einstein's equivalence principle, remaining stationary in a gravitational field is equivalent to acceleration in free space.
 10:42: Right now I have to jet but not too fast, lest I combust in a FullingDaviesUnruh thermal bath as I accelerate to that future point in spacetime.


20180328: The AndromedaMilky Way Collision
 04:01: ... a fraction of a percent of the angular width of one of the Hubble Space Telescope's tiny ...
 04:19: Well, we use the Hubble Space Telescope over several years, of course, with a heavy dose of being extremely clever.
 04:26: A team of researchers, led by Roeland van der Marel of the Space Telescope Science Institute, did just this.
 07:56: And that could slingshot our solar system into intergalactic space.
 09:06: Will those astronomers ever figure out that there are countless other island universes stretching across a much vaster space time?
 11:28: Instead of Tshirts, we're sending some stacks of Space Time stickers.


20180321: Scientists Have Detected the First Stars
 00:13: [MUSIC PLAYING] Sometimes, space news sneaks by without getting much attention.
 00:23: Not everything wows, like gravitational waves or spacefaring sports cars.
 00:57: Today, we're doing a Space Time Journal Club to explain this discovery.
 08:27: So we chose six correct answers to receive "Space Time" tshirts.
 08:58: Nice way to show your appreciation for PBS "Space Time."


20180315: Hawking Radiation
 00:30: This is "Space Time." And it's time for Hawking radiation.
 00:50: ... places of extreme density like the dead core of a massive star, space and time could be dragged inwards to create a hole in the universe, a ...
 01:51: Empty space seethes with activity.
 02:40: ... ready, let's take a deep dive into the quantum field theory of curved space time to glimpse the true nature of Hawking ...
 02:52: Space is filled with quantum fields.
 04:09: This is all fine in flat space.
 04:25: Stephen Hawking knew that black holes with their insane spacetime curvature would wreak havoc on quantum fields in their vicinity.
 04:58: He imagined a single spacetime path, a lightspeed trajectory called a null geodesic.
 05:37: By the time this trajectory has found its way back out into flat space again, those fluctuations look like real particles.
 05:54: ... allowed him to compare the state of the vacuum in two regions of flat space far from the black hole, regions where the nature of vacuums, quantum ...
 06:23: These can be used to approximate the effect of curved spacetime on quantum fields by smoothly connecting regions of flat space.
 06:30: They describe a sort of mixing of the positive and negative frequency vibrational modes that are caused by that curved space.
 09:17: To them, space is locally flat.
 11:49: ... the brilliant mind of Stephen Hawking and a mysterious quirk of quantum spacetime. ...


20180307: Should Space be Privatized?
 00:11: This time people watched with anticipation as SpaceX launched its new Falcon Heavy rocket.
 00:26: The subsequent view of a cherry red Tesla Roadster drifting through space was like something out of a Douglas Adams novel.
 00:33: The landmark launch of the Falcon Heavy rocket is a milestone in a new space race, not one between nations, but instead between private companies.
 00:43: Is this the best thing for the future of human space travel?
 00:47: [MUSIC PLAYING] The private funding of space is not something new.
 01:38: Just as with air flight, the US government has taken steps over the years to pave the way for commercial space flight.
 01:44: Ronald Reagan signed the Commercial Space Launch Act of 1984, which for the first time made commercial launches legal.
 01:52: Under each of the following presidents, NASA's monopoly on space flight was further diminished.
 01:57: ... agency's directive became increasingly focused on science and deep space travel, while private industry was encouraged to take over the day to ...
 02:16: COTS awarded government contracts for resupplying the International Space Station.
 02:21: And this is where SpaceX made its grand entrance.
 02:24: Funded by COTS, its Dragon Module was the first private spacecraft to dock with the ISS in 2012.
 02:37: The Sierra Nevada Corporation is expected to join the ISS Private Club when it docks its Dream Chaser spacecraft in late 2020.
 02:55: But what about manned space flight?
 03:06: To date, only one privately developed craft has carried a person to space.
 03:12: This was SpaceShipOne.
 03:24: And only just kissing space.
 03:29: SpaceShipOne's adventure won its maker, Scaled Composites, the cool $10 million of the Ansari XPRIZE.
 03:36: ... Galactic teamed up with Scaled Composites to form the spaceship company, with the plan to turn its SpaceShipTwo into a regular space ...
 03:48: So why hasn't private manned spaceflight become a thing yet?
 03:58: And besides the distant dream of space tourism, there isn't much money in sending people to space, at least compared to launching satellites.
 04:18: In 2015, Barack Obama signed the US Commercial Space Launch Competitiveness Act, which will allow US companies to own materials extracted from space.
 04:41: So here we get to the main argument for public versus private space programs.
 05:01: ... Hubble Space Telescope and other spacebased observatories have revealed the deepest ...
 05:22: National space agencies have done incredible things.
 05:42: He seeded SpaceX with cash from his first project, PayPal.
 05:46: Now that SpaceX has a working heavy launch vehicle with reusable boosters, Musk is eyeing colonies on Mars and beyond.
 06:00: In 2015, his New Shepard rocket performed the first successful vertical landing after a spaceflight.
 06:07: ... SpaceShipOne was solely funded by Microsoft cofounder, Paul Allen, while its ...
 07:25: ... example, SpaceshipX recently put out a video of how not to land a booster and estimated that ...
 07:37: Virgin Galactic SpaceShipTwo is still forging ahead, even after the fatalities of a test flight crash and an earlier tank explosion.
 08:13: Despite its struggles with shifting politics, NASA has been at the forefront of science and space exploration for 60 years.
 08:25: Will this be true of the space programs built by today's billionaires after control slips to boards of directors?
 09:00: Private spaceflight is here to stay.
 09:06: ... we may ensure the benefit of all in our next steps in exploring outer space ...
 09:34: The future of human space travel is starting to look promising.
 09:40: We have the history of human space travel to thank.
 09:42: As it happens, Curiosity Stream has an excellent documentary on the dangerous early days of putting people in space.
 09:53: ... if you sign up at CuriosityStream.com/SpaceTime and use the premier code spacetime during the sign up ...
 10:03: Speaking of private space funding, I want to give a huge thanks to all of our Patreon supporters.


20180228: The Trebuchet Challenge
 08:12: We'll choose six correct entries to receive "Space Time" Tshirts.
 08:16: That way, next time you besiege a fortress, you can do it under the banner of "Space Time."


20180221: The Death of the Sun
 08:47: ... and to look to the greater galaxy for a new home across far reaches of space ...
 09:18: ... gigantic rocket and landing most of it again, and sending your car into space to give us all hope that maybe one day we, too, will ride on rockets and ...


20180214: What is Energy?
 04:19: That's true even if the gravitational acceleration changes from one point in space to the next.
 10:53: ... general theory of relativity due to the potential time evolution of space. ...
 11:17: It's a clue to the deeper truly fundamental properties of spacetime.
 12:19: In our recent Space Time journal club, we talked about the discovery of the amazing Chronos, the planet eating star.


20180131: Kronos: Devourer Of Worlds
 00:24: It's also what we'll be discussing on today's "Space Time" Journal Club.
 00:28: [FUTURISTIC MUSIC] Our story begins where every story begins, in the heart of a vast cloud of gas and dust drifting through interstellar space.
 02:38: ... primary tool is Gaia, an orbiting telescope launched by the European Space Agency in 2013 on a fiveyear mission to measure the precise positions ...
 07:36: ... be sure to keep you updated on future episodes of "Space Time." We recently discussed the gradual brightening of the sun and the ...


20180124: The End of the Habitable Zone
 06:44: ... into hydrogen and oxygen and the light hydrogen atoms will be lost to space. ...
 09:11: It'll be lost to space just like its initial atmosphere was.
 09:47: ... red giant expanding to consume the only home we've ever known in all of space ...
 10:00: Listening to me yap on about space and physics may be fun and all, but that's not enough if you really want to learn this stuff.
 10:35: To support spacetime and learn more about brilliant, go to brilliant.org/spacetime and sign up for free.
 10:49: Last week we talked about how slicing a piece out of space time caused different observers to disagree on the nature of the vacuum.
 11:09: Actually, all quantum fields are affected by the presence of a space time horizon.
 11:48: Empty space would look hot.
 13:22: I think it's up to "Space Time" standards and you guys will enjoy it.
 13:34: But come on, "Space Time." I know you went back on "Space Time," Gabe?


20180117: Horizon Radiation
 01:17: Generally speaking, a horizon is a boundary in space time from beyond which no influence can pass.
 01:29: As weird as the space times with horizons may be, the statement from before holds.
 02:03: ... but inaccurate explanations of Hawking radiation around, and here at Space Time, we want to be as simple as we can, but no ...
 02:33: In QFT, we think about each particle type as having its own quantum field that exists at all locations in space.
 02:45: That oscillation can be distributed over some region of space, representing the possible positions of the particle.
 03:14: ... observers, be they floating in empty space or accelerating or orbiting a black hole, should agree on the basic ...
 04:35: A particle perfectly localized in space a single spring or a single point on the drum skin.
 05:03: This coupling allows the oscillation the particle to evolve through space.
 05:08: But it also makes it devilishly difficult to solve those equations because the individual oscillations in space can't be solved independently.
 05:44: So instead of writing the field as having a value at every possible position in space, we can write it as having a value for every possible momentum.
 05:56: So let's take our spatial quantum field our drum skin, with its single, localized particle, and transform to momentum space.
 06:13: ... in momentum space, that single, perfectly localized position oscillation can also be ...
 07:37: But why exchange a single spatial equation for infinite equations in momentum space?
 08:22: OK, so a single particle can be described as many oscillations in momentum space.
 09:29: In momentum space, we can think of it as a superposition of infinitely many momentum modes.
 11:31: In some cases, changing the boundaries of space time actually reduces the number of particles, for example, in the Casimir effect.
 11:53: So this year, keep your eye on the horizon the event horizon and the strange things it does to the quantum contents of space time.


20180110: What Do Stars Sound Like?
 07:32: To see that faint flickering, we have to go to space.
 09:09: Because the science of asteroseismology can now translate the messages of stars twinkling at us from across space time.
 09:23: Now, listening to me yap on about space and physics may be fun and all, but that's not enough if you really want to learn this stuff.
 10:00: To support SpaceTime and learn more about Brilliant, go to brilliant.org/spacetime and sign up for free.
 10:43: Because SpaceTime the podcast just wouldn't be as cool.


20171222: Space Time VR
 00:36: It's quite pretty to look at, so if you can get your hands on a Gear VR, download Space Time VR at the Oculus store, and let me know what you think.


20171220: Extinction by GammaRay Burst
 02:46: ... particles so cosmic rays into the surrounding interstellar space. ...
 09:41: Maybe we can hold out a little longer against the series of calamities flung at us, one after the other, from outer spacetime.
 12:10: And there's some smaller chance that it will miss that jump, coming up short, and end up in intergalactic space.


20171213: The Origin of 'Oumuamua, Our First Interstellar Visitor
 00:12: This is the first time we've ever seen an asteroid like object that came to us from interstellar space.
 00:19: Today, on Space Time Journal Club, we'll see what mysteries it can unlock.
 01:31: For this Space Time Journal Club, we'll be discussing what we've learned about Oumuamua since its discovery.
 01:59: ... highly elongated, like a cigar or the monolith from "2001: A Space Odyssey." Hundreds of meters long, it's size and shape can't be ...
 04:24: That means Oumuamua has enough speed to climb out of the sun's gravitational well and escape back to interstellar space.
 06:16: It may come from a vast population of random debris floating around in interstellar space.
 06:38: Given how many stars there are, there should be a ton of asteroidal objects floating around in interstellar space.
 07:11: ... of interstellar debris that we've found so far, and on the volume of space scanned by Pan Starrs, PZ 17 extrapolate to estimate the density of the ...
 09:00: In the meantime, it joins its countless interstellar cousins, orphaned planetary debris, stretching across the reaches of space time.
 09:46: And use the promo code Space Time during the login process.
 11:14: [INAUDIBLE] 777 asks, if you try to do a Fourier transform of PBS Space Time, do you get PBS infinite series?
 11:23: Actually, I think you need an infinite series of PBS Space Time to get a Space Time localization of PBS infinite series.


20171206: Understanding the Uncertainty Principle with Quantum Fourier Series
 06:15: Like the sound wave, it oscillates through space at a particular frequency.
 06:25: It only changes with position in space.
 07:21: So any particle, any wave function, can be represented as a combination of many locations in space, with accompanying intensities.
 07:29: ... intensities, in which case the particle would be smeared in momentum space. ...
 08:38: So if we measure a particle's position, then from our point of view, it's wave function is highly localized in space.
 10:26: ... particle, a quantum field vibration, perfectly localized at one spot in space, can so be described as infinite oscillations in momentum space, spanning ...
 10:39: But each of these oscillations in momentum space are equivalent to particles with highly specific momenta.
 11:01: ... only by manipulating quantum fields in this strange momentum space, by adding and removing these spatially infinite particles, that we can ...


20171129: Citizen Science + ZeroPoint Challenge Answer
 02:59: If you're more the artistic type and you want to use a sciencegrade instrument on a spaceship, then probably JunoCam is for you.
 09:45: Plus, of course, the original Space Time Tshirts.
 09:58: See you all next week for a fresh new episode of Space Time.


20171122: Suicide Space Robots
 00:27: Human space travel is tough.
 06:34: Where some spacecraft are destroyed to protect future science, in other cases their destruction is the scientific experiment.
 07:13: A large fraction of the spacecraft's mass was a 317 kilogram impactor really a robotic probe all on its own.
 07:33: Tens of millions of kilograms of comet were ejected in a debris cloud to be analyzed by the surviving spacecraft component of Deep Impact.
 08:33: Pioneer 10 and 11, Voyager 1 and 2, and New Horizons are all on trajectories that will fling them into interstellar space.
 08:58: ... unlike the long silent Pioneer spacecraft, Voyager 1 still sends faint radio signals, bringing us our first and ...
 09:54: ... gave their little silicon lives to blaze the very first paths into outer space ...
 11:20: I guess we shouldn't be surprised at the insane depth and specialization of the knowledge of Space Time viewers.
 13:10: We actually did a Space Time journal club on that paper.
 14:57: Those false powers sometimes sound pretty cool because they imply things like infinite free energy or fast space travel.


20171108: ZeroPoint Energy Demystified
 00:19: [MUSIC PLAYING] It seems pretty crazy that space itself might contain a higher density of energy than the nucleus of the atom.
 01:35: ... warp fields or pushing against the vacuum energy in propulsionalist space ship ...
 04:08: In fact, we need to reduce the vacuum energy in one region of space.
 07:09: And regardless of its strength, it's not accessible to us as an energy source or as a miracle resource for far space travel.
 09:35: We'll choose six correct answers to win one of our Tshirts so you can show off your mastery of the mysteries of spacetime.


20171102: The Vacuum Catastrophe
 00:51: ... a quantum fuzziness in the amount of energy contained at every point in space a nonzero zero point energy in the quantum fields that can briefly ...
 01:06: This suggests that space itself contains energy, but how much energy?
 01:30: From the perspective of quantum field theory, every point in space is represented by a quantum oscillator, one for each elementary particle type.
 02:09: ... a perfect vacuum, every single possible frequency mode at every point in space must have that amount of ...
 03:49: ... made by John Wheeler and Richard Feynman, who noted that one teacup of space with this energy density would contain enough energy to boil all of the ...
 05:18: An energy of space itself should cause exponential expansion, at least in the case of an already expanding universe.
 09:04: In the meantime, the conundrum continues to perplex physicists and will do so until we reach a deeper understanding of the true nature of spacetime.


20171025: The Missing Mass Mystery
 07:40: At the same time, this stuff is expected to be extremely lowdensity, only around 10 times that of intergalactic space.
 10:22: ... matter in our universe is spread out in the vastness of intergalactic space, still flowing with rivers of dark matter into the galaxy ...
 10:51: The stuff of countless future solar systems is still riding the cosmic web, falling in from the darkest reaches of space time.
 11:10: Michael asks whether the space containing an intrinsic energy also means that it has intrinsic mass?


20171019: The Nature of Nothing
 00:07: This episode of "Space Time" is about nothing, because it turns out that nothing is one of the most interesting somethings in all of physics.
 00:45: The jar contain only empty space.
 00:49: But it turns out that empty space is far from nothing.
 01:42: But hypothetically, what would perfectly empty space look like, far from the nearest particle of matter or radiation?
 01:50: The answer will bring us closer to understanding the nature of space itself.
 01:55: Our modern understanding of the quantum nature of space is described by quantum field theory.
 02:08: In short, space itself is comprised of fundamental quantum fields, one for each elementary particle.
 07:50: Virtual particleantiparticle pairs in the space between the orbitals and the nucleus align themselves with the electric field.
 08:30: Completely empty space should have some real energy.
 11:18: ... of nothing and what it might tell us about the underlying workings of spacetime. ...


20171011: Absolute Cold
 06:56: We'll need another episode to explore the quantum nature of nothing as we peer deeper into the coldest, darkest, and emptiest patches of Space Time.
 07:20: It's also a great place to study up on some of the concepts we cover in Space Time.
 07:34: ... if you sign up at curiositystream.com/spacetime and use the promo code spacetime during the signup ...
 07:53: We never would've guessed we'd reach this point when we started making Space Time early in 2015.
 08:09: Of course, we have to give a Space Time tshirt out 1 millionth subscriber.
 08:20: And for everyone else, how about we keep making Space Time for as long as humanly possible?
 08:26: ... week in Space Time Journal Club, we talked about the new observation of a potential ...


20171004: When Quasars Collide STJC
 00:38: ... MUSIC] Today on Space Time Journal Club, we're going to dig into a paper that reports the ...
 03:43: In order to measure such a small separation at such a large distance, we need resolution around 100 times better than the Hubble Space Telescope.
 10:08: ... understanding the incredible growth of the largest black holes in all of spacetime. ...


20170928: Are the Fundamental Constants Changing?
 00:30: [MUSIC PLAYING] The laws of physics are the relationships we observe between space and time, and the fields and particles that occupy it.
 01:33: They predict that the fundamental constants may not be constant at all, and instead, may vary over time and space.
 02:54: ... speed of light defines the relationship between space and time, so is it even meaningful to talk about it changing ...
 11:04: We may one day find that our sacred laws of physics and their underlying constants aren't so constant after all beyond our little patch of space time.
 12:23: ... may vary, but you guys really help with the stability of "Space Time." And today, I want to give a big shout out to Richard Sinegor, ...
 12:42: Last week, we talked about some possibilities for future advanced space telescopes.
 12:55: Well, it's funny you should mention that, because this is the future Space telescope that got cut from the last script due to length.
 13:10: It would send a spacecraft to at least 550 times the Earth's orbital radius, out beyond the edge of the solar system.


20170920: The Future of Space Telescopes
 00:27: ... new observatories currently being built. One of those, the James Webb Space Telescope, will succeed the Hubble Space Telescope with more than a ...
 00:42: Getting such a large telescope into space is a major challenge.
 00:52: Those things are really hard to get into space in one piece.
 02:43: It's actually a spacecraft outfitted with thrusters to align itself between a space telescope and a star.
 03:33: ... compact bud for launch, and then open up like an actual flower once in space, a bit like the James Webb Space ...
 05:41: And that's a problem when you're trying to launch your telescope into space.
 06:25: ... source that's 100 or 1,000 times better in resolution than the Hubble Space ...
 08:15: So it would be an independent spacecraft, just like the starshade.
 09:57: It may be possible to launch multiple such telescopes that have several times the light collecting power of the Hubble Space Telescope.
 10:05: NASA has some brilliant plans to overcome the limitations of traditional spacebased telescopes.
 10:22: As we launch our new observatories, our vision will be keener, allowing us to peer more sharply and to ever greater depths into space time.
 11:40: They have to travel along the same spacetime fabric as light waves, after all.


20170913: Neutron Stars Collide in New LIGO Signal?
 02:39: ... that result in jets of near light speed particles that sweep through space like a ...
 03:09: This binary pair stirs up spacetime in its vicinity, creating ripples that travel outwards as gravitational waves.
 07:25: A Hubble Space Telescope observation was triggered a few days later to look at the location of this gamma ray burst.
 11:17: ... rays and by sensing the faint ripples it made in the very fabric of spacetime. ...
 11:58: ... if you sign up at cruiositystream.com/spacetime and use the promo code "spacetime" during the signup ...
 14:34: After all, that's how we found them, using the Kepler Space Telescope.
 15:00: What I mean by that is that the Big Bang happened everywhere at once, not at an infinitesimal point in space.
 15:07: The origin of all space is the Big Bang, and so all space came into being in that event.


20170830: White Holes
 00:37: ... to take this mathematical description of an inescapable region of spacetime. ...
 01:31: ... black hole is defined as a region of inward flowing space time with a one way boundary called the event horizon, from inside of ...
 01:41: That makes a white hole a region of outward flowing space time.
 02:31: ... a very particular case a single point of mass in an otherwise empty space ...
 03:03: We've talked quite a bit about the bizarre behavior of space and especially time at and below the event horizon of a black hole.
 03:34: Once you fall into the black hole, the Schwarzschild metric tells us that space and time switch their roles.
 04:42: To refresh your memory, in a Penrose diagram, the x and yaxes are redefined from space and time to merge space and time into new coordinates.
 04:53: They compactify space time so that time bunches up towards the edges, and the borders correspond to infinite past and future.
 05:50: There the dimensions of space and time switch roles.
 05:54: The once vertical contours of space are now timelike and flow inexorably towards the future singularity.
 06:32: ... Space within is timelike, but instead of flowing towards the singularity, it ...
 10:32: It's an expanding outpouring of space time containing a vast amount of energy, and the bang itself can never be entered.
 11:38: In fact, what we did was to maximally extend space time.
 11:42: We required that all paths be traceable through infinite past and future space, provided they don't hit the singularity.
 11:57: The mathematics of the Schwarzschild metric describes an entirely independent region of space time parallel to our own.
 12:19: In the not too distant future, we'll investigate the reality of this mysterious parallel patch of space time.
 12:55: LegalZoom is offering "Space Time" viewers 15% off their next purchase from LegalZoom.


20170824: First Detection of Life
 00:05: In 1990, an experiment conceived by Carl Sagan was performed using the Galileo spacecraft.
 00:12: To detect life on a planet based on measurements by a space probe.
 00:33: [THEME MUSIC] In December of 1990, during its first gravity assist flyby, the Jupiterbound Galileo spacecraft turned its eye towards the earth.
 00:58: ... probe could positively detect life on a world using only data taken from space, and with as few prior assumptions as ...
 01:29: But first, let's talk about what life on Earth looks like to an observer in space.
 08:06: The parent star was observed using the Hubble and Spitzer Space Telescopes during a transit.
 08:57: But that will all change next year in 2018, the James Webb Space Telescope will launch.
 09:03: ... infrared spectrograph, coupled with the clarity granted by being in space, will enable us for the first time to perform Sagan's 1990 experiment on ...
 10:31: Perhaps that answer is already traveling to us in the light of a distant planet's atmosphere calling to us from across spacetime.
 11:06: LegalZoom is offering Space Time viewers 15% off their next purchase from LegalZoom.


20170816: Extraterrestrial Superstorms
 01:09: We may be close to finding some answers following the Juno spacecraft's recent flyby of Jupiter's Great Red Spot.
 10:48: ... on Juno's discoveries on its interactive website and by staying tuned to "Space Time." Thanks to LegalZoom for sponsoring this ...
 11:23: LegalZoom is offering "Space Time" viewers 15% of their next purchase from LegalZoom.
 12:41: To prove this to yourself, try drawing a spacetime diagram, time on the yaxis and space on the xaxis.


20170810: The OneElectron Universe
 01:46: ... of antimatter into his path integral formulation and the following spacetime interpretation of quantum mechanics, which won him the 1965 Nobel Prize ...
 02:34: It exists as a line traced by its passage through space and time, rather than as a pointlike particle at one instant in time.
 02:41: The pointlike electron is just a segment of that worldline if we take a slice through space time at one instant in time.
 09:00: That makes each of us a tangled knot in the one single thread weaving back and forth across the reaches of spacetime.
 10:19: If you see your name below, you're a lucky winner, and we have a space time tshirt for you.
 11:34: That force would have been exerted by a high density patch of space in the preinflationary period at the beginning of the universe.


20170802: Dark Flow
 00:17: [THEME MUSIC] Space is not static.
 00:37: Distant galaxies are thrust apart from each other as the space between them grows.
 09:40: ... region of the greater universe, beyond the horizon of observable spacetime. ...
 11:57: ... through the infinite possible interactions within the virtual space of the Feynman ...


20170726: The Secrets of Feynman Diagrams
 01:56: There are "Spacetime" tshirts at stake.
 02:40: Throw these on a plot of space versus time, and we have a Feynman diagram a useless one.
 06:06: Each possible diagram that results in the same ingoing and outgoing particles is a valid part of the possibility space for that interaction.
 11:34: We'll randomly choose five correct answers to win a "Spacetime" tshirt, and that includes a choice from brand new tshirt designs.
 11:53: ... coming, a fun reminder in tshirt form of the eventual cold dark end of spacetime. ...
 12:26: ... also, one last call for anyone wanting one of our special "Spacetime" eclipse glasses if you sign up on Patreon at the $5 level or above or ...
 12:53: Last week, we talked about the history and danger of space militarisation.
 13:38: As space junk builds up, a runaway effect is possible in which more and more satellites are destroyed, exponentially increasing the amount of debris.
 13:51: Currently, there are a couple of thousand operational satellites, but several hundred thousand pieces of space junk.
 13:58: And currently, around one satellite is destroyed every year by space junk.
 14:07: ... out what was perhaps the greatest tragedy in the entire sorry history of space militarisation the really inexcusable failure to nickname the ...


20170719: The Real Star Wars
 00:06: ... space, used and shared peacefully, offers incredible benefits to humanity in ...
 00:43: It seemed to many that we were on a trajectory to a spacefaring technological utopia.
 00:54: But the possibility of a much darker space age also loomed.
 01:00: One in which the space around the Earth became highly militarized and, in fact, massively weaponized.
 01:21: The Space Race had begun, and it inspired some incredible advances in science and exploration, culminating in the moon landing in '69.
 01:48: Those ICBMs were the first space weaponry.
 02:01: Despite definitely being in space, these are called suborbital trajectories because they don't actually reach orbital velocity.
 02:46: As the arms race proceeded, both superpowers also turned to space to defend against this rising existential threat.
 03:27: These were the Almaz space stations.
 04:41: This was the Excalibur program, and it very nearly saw the launch of what could only be described as a spacebased superweapon.
 05:31: But in the vacuum of space, these lasers can have ranges of many hundreds, even thousands of kilometers.
 07:01: Another slight issue with the Excalibur program was that it would pretty thoroughly violate the Outer Space Treaty.
 07:19: The treaty is now ratified by 107 nations and seriously limits the potential for nuclear space war.
 07:35: The Outer Space Treaty does have its loopholes.
 07:38: Socalled "conventional weapons" are allowed in space.
 08:08: Besides not violating the Outer Space Treaty, this plan beat Excalibur because you didn't need to destroy the weapons platform to use it.
 09:00: Very sudden precision strikes with no surface launch signature to serve as warning, and they wouldn't violate the Outer Space Treaty.
 10:02: The program was even upgraded in the late '70s to be effective against the upcoming US Space Shuttle.
 10:24: ... there was the Polyus spacecraft, a fullfledged orbiting the battle station that would have had a ...
 11:00: One, the resulting debris massively increased the amount of space junk in lowEarth orbit.
 12:31: For the most part, and for the moment, saner heads have prevailed, and humanity remains committed to the peaceful use of outer spacetime.
 13:52: Spacetime remains a passion project for all of us.
 14:17: ... speaking of weaponized space, for anyone who doesn't want to get their eyes burned out by accidentally ...


20170712: Solving the Impossible in Quantum Field Theory
 02:06: We think of the electromagnetic field as existing everywhere in space, whether or not there's an electron present.
 03:23: The other axis represents space, although the actual distances aren't relevant.
 11:46: In future episodes, we'll talk more about what is now the most complete description we have for the smaller scales of space time.
 12:16: ... if you sign up at curiositystream.com/spacetime and use the promo code spacetime during the signup ...
 12:44: ... another reminder to current or wouldbe Patreon patrons we made some "Space Time" eclipse glasses super handy for not going blind watching the ...
 14:37: ... taken separately, but rather, they're pointing in the complex vector space, rotates so that each path adds differently to the total ...


20170707: Feynman's Infinite Quantum Paths
 01:27: ... both slits, not as a particle but as a wave that fills the intervening space interacts with itself and defines the probability of that particle ...
 03:27: But when something travels through empty space, it's like it's traveling through infinitely packed barriers, each with infinite slits.
 03:51: ... step allow the particle to take any conceivable straightline step in space. ...
 06:15: We can think of each path's probability amplitude as a vector or an arrow of a certain length and direction in an imaginary 2D space.
 08:10: This action quantity is a function of the particle's path through spacetime.
 08:16: That means it treats space and time symmetrically and so works very naturally with Einstein's theory of special relativity.
 11:35: Find out how on the next episode of "Space Time." Thanks a ton to all of our supporters on Patreon.
 12:14: But astrophysicists agree that the most stylish way to view this event is with the official "Space Time" eclipse glasses.
 15:07: Quantum field theory describes particles as a field vibration in 4D spacetime.
 15:24: These, in turn, may exist in a space of 11 or even 26 dimensions, most of which are compactified.


20170628: The First Quantum Field Theory
 01:18: ... as vibrational modes in fundamental fields that exist at all points in space and time through the ...
 02:59: Every point in space has some displacement in some imaginary extra direction analogous to but not the same as a fourth dimension.
 03:29: We describe air density as a field because it has some value everywhere in the space of the room.
 03:36: And that's all a field is some property that has some value throughout a space.
 07:22: He imagined each point in space as being an oscillator.
 07:43: So Dirac described a space of quantum states, including position and momentum/frequency, like an infinite array of springs.
 12:15: And we're going to need another episode of Space Time.
 14:46: ... doesn't work for the infinities you get when you think about curved space on the quantum ...


20170621: AntiMatter and Quantum Relativity
 00:16: Einstein's theory of special and general relativity had changed forever the way we think about motion, space, and time.
 01:47: In relativity, the dimensions of space and time are intrinsically connected and they float into each other as frames of reference change.
 05:45: The resulting Dirac equation describes the spacetime evolution of this weird fourcomponent particlewave function, represented by the symbol psi.
 08:38: We now know that every elementary particle has an associated field, that fills all of space.
 11:17: And that's a quantum rabbit hole that we'll jump into very soon, right here on "SpaceTime." I'd like to thank Skillshare for sponsoring this episode.
 12:06: ... link in the description or go to skillshare.com and use the promo code SPACETIME at ...
 12:17: ... the last episode, we did a "SpaceTime" journal club on a new paper investigating whether the cold spot in the ...
 13:05: Also, those wide spots near the center of the map are the result of Doppler shift due to Earth's motion through space.
 14:02: ... where the vacuum energy can come to a rest in an eternally inflating spacetime, halting inflation in that ...
 14:54: Pradhyumn asks if I can make a video recommending some good books on space and time?


20170607: Supervoids vs Colliding Universes!
 00:38: That's what all the media hype is saying, which means, it's time for another Space Time Journal Club to sort it out.
 09:22: This can happen spontaneously anywhere in the greater inflating space time, resulting in bubble universes.
 09:30: And it could happen frequently or rarely, depending on the completely unknown details of the string theory parameter space.
 09:37: But regardless, in an infinitely inflating space time, collisions between bubble universes are eventually expected.
 10:38: But if not, perhaps once upon a time, we really did collide with an entirely separate bubble of space time.


20170531: The Fate of the First Stars
 03:59: Massive stars live fast, die young, and leave beautiful spacetime warping corpses.
 10:45: But their influence is still felt across the reaches of spacetime.
 10:50: ... today's episode, and also for making it possible for me to research spacetime while riding crowded New York ...


20170517: Martian Evolution
 00:14: But there may be nothing at all familiar about these distant future space farers.
 03:36: We know that the zeroG experienced in orbital or interplanetary space leads to decreased bone density and muscle mass in astronauts.
 05:46: We'll always need some degree of technology both for a survivable air pressure and oxygen level and to protect us from space radiation.
 10:31: ... their way planet to planet, then star to star across the reaches of space ...
 12:35: The first batch of Homo martiansis will be shipped to Mars as soon as that Musk guy finishes the spaceship.


20170510: The Great American Eclipse
 03:01: In fact, the spaces between the leaves act like pinhole cameras, projecting the sun's image to the ground.
 08:54: Without it, I may never have ended up doing a show like "Space Time." Thanks to legalzoom for sponsoring this episode.
 09:25: legalzoom is offering Space Time viewers 15% off their next purchase from legalzoom.


20170503: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson
 12:11: Just for now, I strongly recommend that we proceed as though we are real life observers, part of the original space time.
 12:46: You make "Space Time" possible.


20170426: Are You a Boltzmann Brain?
 10:12: ... fluctuations in the infinite chaos of a max maximally entropic space ...


20170419: The Oh My God Particle
 02:40: It turns out they were coming from space.
 06:58: Empty space isn't really empty, it's full of lowenergy microwave photons leftover from the heat glow of the very earliest of times.
 09:30: Studying cosmic rays may crack open the mysteries of both the largest and the smallest scales of space time.
 09:53: It delves into some of the biggest mysteries and challenges facing astronomy and space exploration.
 10:01: ... if you sign up at CuriosityStream.com/spacetime and use the promo code spacetime during the signup ...
 10:57: ... Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies, or, the Outer Space ...
 11:12: It restricts the use of space for peaceful purposes, but otherwise grants free access to nation states.
 11:25: David Connolly emailed to remind us that the Constellation Program and its Ares rockets was discontinued in 2009 in favor of the Space Launch System.


20170410: Here's Why I Love PBS
 00:00: ... guys, this is Matt from "Space Time." As a lot of you know, there is a proposal to massively cut the ...


20170405: Telescopes on the Moon
 02:06: OK, so it's not quite the Hubble Space Telescope.
 02:20: ... scope to collect more light, increasing sensitivity, but when you're in space or on the moon, aperture size defines image ...
 02:52: Normally, there's a pretty strict limit on how big a mirror you can get into space.
 02:58: Even clever solutions like the upcoming James Webb Space Telescope's folding mirrors still have a limit.
 05:54: ... Ching, at NASA's Goddard Space Flight Center, proposes shipping a relatively small amount of epoxy and ...
 09:03: ... Earth's lookout tower, granting the clearest views of all the rest of space ...
 10:30: Last week on "Space Time," we talked about time space, the way time and space, which rolls, beneath the event horizon of a black hole.
 10:41: Feinstein 100 asks whether energy could be extracted from the flowing space time inside a black hole.
 10:48: Well, not really from the flow of space time actually inside the black hole.
 11:03: Hydroelectric power plants on earth do it with the flow of space time that we experience as Earth's gravitational field.
 12:26: ... extra angular components in the line element, AntiTwister over at the Space Time subreddit had some interesting ...
 12:39: The sideways components, angular or orbital components in spherical coordinates, stay spacelike.


20170329: How Time Becomes Space Inside a Black Hole
 00:06: ... on Space Time, we're going to talk about timespace, or the strange switching in ...
 00:20: [MUSIC PLAYING] What does this bizarre statement, space and time switching roles, even mean?
 00:30: Is this spacetime dyslexia purely a mathematical quirk?
 00:49: First we'll think about what the flow of time looks like without black holes or even spacetime curvature.
 00:55: ... the geometry of causality, we saw that this quantity that we call the spacetime interval governs the flow of cause and effect, the only reliable ...
 01:16: The spacetime interval is defined like this, for boring old flat or Minkowski space.
 01:30: However all observers record the same spacetime interval.
 01:34: If one event causes a second event, the spacetime interval must be 0 or negative.
 01:47: You could say that an object at a given spacetime instant is caused by way of a version of itself existed an instant earlier.
 01:55: So world lines of objects have decreasing spacetime intervals.
 02:00: In fact forward temporal evolution requires a negative spacetime interval.
 02:05: In flat space time, that negative sign in front of the delta t drives that forward evolution.
 02:11: This makes t, the timelike coordinate, while x is the spacelike coordinates.
 02:23: Reversing causality means flipping the sign of the spacetime interval.
 02:29: In our episode on superluminal time travel, we saw that in flat space, this means traveling faster than light, which is, of course, impossible.
 02:37: But if we introduce a black hole, we now have a second way to flip the side of the spacetime interval.
 02:50: Add a nonrotating, uncharged black hole, and the spacetime interval becomes this.
 03:26: And time and space nicely separated.
 03:29: ... than rs, that stuff in the two brackets describes extreme warping of spacetime. ...
 03:48: A negative spacetime interval still means causal movement.
 04:26: Space itself is falling inwards faster than the speed of light towards the central singularity.
 04:50: Meanwhile the coordinate previously known as time, t, lost its negative sign and become spacelike.
 05:19: On our ever popular spacetime diagram, we see a sharp division between the two.
 05:25: ... past light cone encompasses all of spacetime that could have influenced us, while that future light cone shows us the ...
 05:40: Ahead along our time axis and at right angles to all of our space axes.
 05:56: Close to a massive object, your future is no longer at right angles to space.
 06:33: It deals with the extreme stretching of space and time by compact defined lines of constant space or time close to its boundaries.
 06:44: But an important thing to remember is that the lines of constant space and time are curved so that light cones remain upright.
 08:05: As we fall with the faster than light flow of space time, we overtake light that is outward pointing.
 08:14: It's trying to swim upstream and failing against the faster than light cascade of spacetime.
 09:11: You can traverse in either direction making it spacelike.
 09:53: However the old radial dimension isn't spacelike, it's timelike.
 10:28: In fact the Schwarzschild metric really gives two separate spacetime maps in a single equation, one for above and one for below the event horizon.
 10:47: ... dimensional flip does give us some fascinating insight into how time and space blend together in what is perhaps the strangest place in all of ...
 11:13: I think Space Time viewers would really enjoy Cowboy Bebop, a Scifi noir that follows the adventures of a gang of space bounty hunters.
 11:23: Crunchyroll is offering Space Time viewers a 30 day free trial if you go to Crunchyroll.com/spacetime.
 11:34: ... guys, in our recent Space Time journal club, we talked about a paper describing a recipe for ...
 14:35: It's worth commenting here that our goal on Space Time is a little bit different to most science media.
 14:50: That's especially true of Space Time Journal Club.


20170322: Superluminal Time Travel + Time Warp Challenge Answer
 01:23: We'll do this in flat space, so we need a flat or Minkowski spacetime diagram.
 01:29: We're going to add spacetime interval contours.
 02:08: In the olden days, the same time axis of a space time diagram would apply to everyone, but no longer.
 02:19: Instead, every space time traveler carries their own clock.
 02:34: Everyone draws their space time diagram time axis parallel to their direction of motion, because that's their experience of stillness.
 02:50: And everyone also has a different space axis, representing chains of simultaneous events according to their perspective.
 03:13: These are contours of constant spacetime interval.
 03:26: ... spacetime interval is special because every traveler will agree on which contours ...
 03:37: ... we write the spacetime interval for flat space with a negative sign in front of the time part, ...
 04:43: Let's see what that looks like on the spacetime diagram.
 05:56: To see what the Annihilator sees, let's transform the space time diagram to their perspective.
 06:05: Their time axis is their own world line, and their space axis is symmetrically reflected around the path of light.
 06:12: Now, add hyperbolic spacetime into our contours.
 06:15: These are the spacetime intervals as calculated from the zero point in space and time, the beginning of the race.
 06:23: ... the spacetime interval is invariant to Lorentz transformations, when we shift to the ...
 06:45: ... can figure out the paradox world line because we know which spacetime interval contours it's on when it departs from Earth and arrives at its ...
 08:03: Let's look at the perspective of a different space time traveler, one traveling at very near the speed of light.
 08:22: Well, no, not if we can find a way to bring the Paradox back to a point in space before it was built.
 08:30: To do that, we first need to outrace photons that were admitted at the space time point that we want to perceive.
 08:48: Let's fill in the space time diagram with all four quadrants.
 09:39: ... that would be fine, because spacetime events marking the different stages of a sublightspeed journey ...
 10:29: Even our fantasies of time travel are just another pattern emerging from our oneway trajectory through the temporal part of spacetime.
 10:43: If you see your name below, we randomly selected your correct answer to win a spacetime tshirt.
 11:05: ... it tell you which Disney princess you are, but it will really help both Spacetime and PBS figure out what you guys are into and what you want for the ...


20170315: Time Crystals!
 00:15: In today's edition of "Space Time Journal Club," we find out.
 00:18: [MUSIC PLAYING] In "Space Time Journal Club," we review new scientific papers that are making waves.
 01:21: The analogy is that regular crystals have a periodic cycle through space.
 07:15: A time crystal within a space crystal.
 09:21: And unlike in relativity, quantum mechanics treats space and time very differently to each other.
 09:29: ... in regular crystals, perhaps it's a first step in a quantum union of space ...
 11:31: The Kepler Space Telescope has so far discovered 2,330 confirmed exoplanets in 578 planetary systems.


20170308: The Race to a Habitable Exoplanet  Time Warp Challenge
 00:13: Any FTL journey will appear to someone, somewhere in spacetime, as time travel.
 00:51: In that episode, we talked about the spacetime diagram and how it transforms between observers traveling at different speeds.
 01:11: It lets us figure out what spacetime looks like for every observer, no matter what his or her velocity is.
 01:17: If two events happen in spacetime, observers with different velocities will report different separations between them, in both space and time.
 01:27: We can combine those space and time intervals into the spacetime interval.
 01:35: ... we represent lines of constant spacetime interval with respect to x and to equal zero as contours, then we can ...
 01:50: To increase your spacetime interval, to cross these contours backwards uphill, you must travel faster than light.
 03:29: To answer this, you'll need to draw a spacetime diagram showing the world lines of the two ships.
 03:49: It will be helpful to draw the hyperbolic spacetime interval contours on your diagram.
 04:12: Note that the endpoints of the world lines stay on the same contours, because their spacetime intervals don't change.
 04:21: ... a spacetime trajectory that allows you to fly the Paradox all the way back to the ...
 04:43: Submit your answers with full explanations and spacetime diagrams within two weeks of the release of this video to be in the running.
 04:51: A selection of correct submissions will receive a Space Time Tshirt and a habitable exoplanet.
 05:08: See you next week for a new episode of Space Time.


20170301: The Treasures of Trappist1
 00:43: Follow up with the Spitzer Space Telescope has now revealed an additional four planets.
 06:50: ... Hubble Space Telescope has confirmed that the a, b, and h planets don't have hydrogen ...
 07:01: ... spectroscopy from the James Webb Space Telescope will hopefully provide us with atmospheric composition data ...
 08:38: ... a giant boost in the number of possible homes for life out there in space ...
 09:14: LegalZoom is offering Space Time viewers 15% off their next purchase from LegalZoom.


20170222: The Eye of Sauron Reveals a Forming Solar System!
 00:24: The incredible Hubble Space Telescope picture of the star Fomalhaut does excite the imagination, doesn't it?
 01:38: Here are some infrared pics from the Herschel Space Telescope and from Elma.
 05:11: The closer an object orbits to a given star, the faster it moves through space.
 09:39: But one does not simply cease questioning on space time.
 10:08: ... if you sign up at curiositystream.com/spacetime, and use the promo code Space Time during the signup ...


20170215: Telescopes of Tomorrow
 00:22: ... PLAYING] The Hubble Space Telescope is the most important observatory ever built. Its stunning ...
 00:50: First up, is the Hubble Space Telescope's much publicized successor, the James Webb Space Telescope.
 04:03: Space is good for that, because the heat glow of the atmosphere is so bright.
 04:24: This fragile structure has the added benefit of blocking small space debris.
 04:37: The true successors to Hubble will not be in space at all.
 06:05: For telescopes, it blurs the crisp diffractionlimited images seen in space.
 06:17: If we build GMT's giant mirror in space, it would produce images 10 times sharper than Hubble's.
 08:15: In a way, LSST focuses more on the dimension of time rather than space.
 09:41: ... didn't even expect to find unknown unknowns in the deepest reaches of space ...
 11:10: So last time, I showed you how you can visualize the effects of special relativity on spacetime using geometry.
 11:39: ... wondered about the relationship between the geometry I depicted on the spacetime diagram and the geometry that comes from mass and energycurving ...
 11:49: The spacetime diagram I showed is for flat or Minkowski space.
 11:57: The hyperbolic geometry is just what you did when you map the spacetime interval to a third dimension.
 12:02: So you have time, space, and spacetime interval.
 12:14: ... the way, a lot of people express the spacetime interval with a minus sign in front of the delta X and a plus for the ...


20170202: The Geometry of Causality
 00:15: ... of cause and effect emerges when we discover the causal geography of spacetime. ...
 00:32: Recently, we've been talking about the weirdness of spacetime in the vicinity of a black hole's event horizon.
 00:43: ... space and time switch roles, but to truly understand that bizarre statement, ...
 00:54: Today, we're going to look at the amazing geometric structure that time, or more accurately causality, imprints on the fabric of spacetime.
 02:00: ... counting those clock ticks isn't the best way for everyone to agree on spacetime ...
 02:13: ... this thing called the spacetime interval that relates observer dependent perspectives on the length and ...
 02:35: But we want that intuition because, more than proper time, the spacetime interval defines the flow of causality.
 02:42: In relativity, 3D space and 1D time become a 4D entity called spacetime.
 02:49: To preserve our sanity, we represent this on a spacetime diagram plotting time and only one dimension of space.
 03:03: There is no standing still on a spacetime diagram.
 03:06: If I don't move through space, I still travel forward in time at a speed of exactly one second per second according to my proper time clock.
 03:25: Now, let's say we have a group of spacetime travelers.
 03:43: The path they cut through spacetime is called their world line.
 04:11: Accounting for this, we find that our spacetime travelers are arranged on a curve that looks like this.
 04:29: ... the gradient of causality down which time flows, and etched into spacetime by the equations of special ...
 04:40: To understand why, we need to see how these proper time contours appear to other spacetime travelers.
 04:51: First, we need to draw the spacetime diagram from the perspective of one of the other travelers.
 04:58: To transform the diagram, we need to figure out what they see as their space and time axes.
 05:15: ... from my stationary point of view, I define my xaxis as a long string of spacetime events at different distances, but that all occur simultaneously at time ...
 06:27: That comes from insisting that we all see the same speed of light, 45 degrees on the spacetime diagram.
 07:21: Those intersections represent locations of spacetime events relative to the origin.
 07:33: ... time count, but more generally, each represents a single value for the spacetime ...
 07:45: ... on who is watching, but the hyperbolic contour that they landed on, the spacetime interval, will ...
 07:59: ... is because the spacetime interval itself comes directly from the Lorentz transformation, as the ...
 08:20: ... seem counterintuitive that an event very close to the origin in both space and time can be separated from that origin by the same spacetime ...
 08:59: The spacetime interval tracks this causal proximity.
 09:08: ... way I define the spacetime interval, it becomes increasingly negative in the forward time ...
 09:40: In fact, the nearest downhill contour defines the forward light cone for anyone anywhere on the spacetime diagram.
 09:59: To reverse the direction of your changing spacetime interval is to reverse the direction of causality, to travel backwards in time.
 10:08: ... spacetime diagram we looked at today was for a flat or Minkowski space, in which ...
 10:18: But in the crazy curved space within a black hole, it gets flipped for you.
 10:23: ... predictions when we try to calculate the sub event horizon interval of spacetime. ...
 10:37: ... today's episode, and also for making it possible for me to research spacetime while riding crowded New York ...
 10:58: ... Caleb Scharf's "Gravity's Engines" gets into my favorite space things of all quasars, and especially how important they are in the ...
 11:18: "Space Time" is possible only through your support.
 12:07: ... string theory, which proposes that particles that we see in regular 4D spacetime result from oscillations within many more coiled dimensions, socalled ...
 15:43: No, watching "Space Time" doesn't count as extra credit, but it can't hurt.


20170125: Why Quasars are so Awesome
 00:22: [MUSIC PLAYING] Space stuff is awesome.
 01:26: Yep, quasars are clearly the most metal of all the space things.
 03:24: ... many galaxies worth of light from a seemingly impossibly small region of space. ...
 05:34: ... we see them blasting through the galaxy and even filling intergalactic space with beautiful radio ...
 06:55: ... region less than 100,000 times smaller than a single pixel on the Hubble Space ...
 09:45: ... and a new quasar will shine forth, illuminating this little patch of spacetime. ...
 11:18: Tambe, your own personal spacetime quasar is in the mail.


20170119: The Phantom Singularity
 00:29: In fact, we still use it to fly spacecraft around the solar system today.
 02:39: An example of a frame dependent singularity that might be familiar to space time viewers is the event horizon of the black hole.
 05:07: Hey, this is "Space Time." We can deal.
 05:17: The Schwarzschild metric allows us to compare two points or events in space time around a massive object from the perspective of different observers.
 05:26: For example, a short space time path of some object, so it's world line, might move an object a distance delta r over a short timestep delta t.
 05:44: That delta s squared thing is the space time interval, and it's a strange and interesting quantity.
 05:50: Every inertial, so nonaccelerating observer, will agree on the same space time interval for every pair of events and for every world line.
 06:07: ... doesn't require faster than light motion, then the square root of the space time interval is equal to the amount of time that the object itself ...
 08:12: The entire space time interval for a nonmoving point at the event horizon is 0.
 08:18: But remember, for sublight speed world lines, the space time interval tells us the rate of flow of proper time.
 08:51: No temporal thing, nothing that normally experiences the passage of time, can have a space time interval of 0.
 08:59: At the event horizon the only way to get a nonzero space time interval is to have a nonzero delta r.
 09:30: There is one thing that can have a space time interval of 0, light.
 09:36: Actually, anything capable of traveling at light speed can only have a space time interval of 0.
 10:36: There are ways to construct our space time axes so this singularity just evaporates.
 10:41: For example, EddingtonFinkelstein Tortoise Coordinates that compactify with the stretching of space time to cancel out the infinities.
 11:45: There, the causal roles of space and time switch places, and the central singularity becomes not so much a location in space but an inevitable future.
 12:03: Standby to explore what happens when you switch the causal rolls of time versus space to space time.
 12:24: And as always, a big thank you to our Patreon supporters for really making space time a lot easier to do.
 12:53: ... week, we inaugurated the "Space Time" Journal Club by looking at Harold White et al's paper on an ...
 13:28: A scientist who decided to look into this has to divert grant money, lab space, personnel, and most critically a lot of their own time and energy.
 14:39: That would be true even if it's not ultimately useful for spaceflight, which I'm not saying it wouldn't be.
 16:37: Stephen Bachman asks why we don't just put one of these devices in space to see if it works.
 16:50: The state owned China Academy of Space Technology announced in December that it's testing the device in orbit.
 17:22: ... Scatterty reminds us, the first rule of "Space Time" Journal Club is we talk over our thoughts and remain open to all ...


20170111: The EM Drive: Fact or Fantasy?
 00:00: [MUSIC PLAYING] One of Space Time's most requested topics is the controversial EmDrive.
 00:21: Today, we inaugurate the Space Time Journal Club by taking a very careful look at this result.
 01:23: ... for edition one of the Space Time Journal Club, we're jumping into Harold "Sonny" White, et al., 2016 ...
 05:16: But eliminating the need for propellants may mean that measly thrust to power ratio is useful for very longrange spaceflight.
 09:14: This is Space Time Journal Club, which means it's now open for discussion.
 09:22: Back to our regularly scheduled, slightly less speculative science next week on Space Time.
 13:59: ... fiction books, I'll be stealing every single one of my ideas from old Space Time ...


20170104: How to See Black Holes + Kugelblitz Challenge Answer
 02:20: They show crazy slingshot orbits around an empty patch of space.
 02:49: The Event Horizon Telescope is right now in the process of mapping space around the Milky Way's Sag A star black hole.
 04:28: ... waves observations, over the next few years, we'll have mapped the space around black holes in ways that were once thought ...
 06:13: You can think of the verticalish lines as representing points in space that are a constant distance from our center point.
 06:59: ... triangle above the collapsing star's surface actually has the crazy spacetime behavior of the interior of a black ...
 07:25: ... smaller than its own Swarzschild radius, an event horizon forms as spacetime flows faster than the speed of light towards that superdense region of ...
 07:53: Even after the true event horizon forms, there remains this shrinking patch of normal flat spacetime.
 08:28: ... Space below that shell remains comfortably flat, but above the shell, ...
 08:38: ... it is indeed perfectly reflected, straight back into a region of spacetime that will carry even that light inexorably downwards to form the ...
 09:39: Just above the sphere, which is only a bit larger than that event horizon that was going to form, the spacetime curvature is pretty insane.
 10:36: In Einsteinian terms, spacetime is flat within the sphere.
 10:53: Maybe we can just build a mini sun inside after we blast the aliens and save spacetime.


20161221: Have They Seen Us?
 01:41: ... on Kepler Space Telescope observations, that also means thousands of potentially ...
 12:51: ... doubt carry only the best wishes for their noisiest neighbors in nearby spacetime. ...
 13:48: It's trying to walk upwards on a downward escalator of spacetime.
 15:35: The probably impossible technology of the warp drive allows you to cause a patch of space to move at really any speed you have the energy to reach.
 15:44: So you could resist the fasterthanlight flow of space within the black hole.
 16:59: The correct way to get this number is by using general relativity to find the point where the flow of spacetime reaches the speed of light.
 17:18: Cornerrecord asks about that thing when you're in a black hole and time becomes space and space becomes time?


20161214: Escape The Kugelblitz Challenge
 00:00: ... we looked at an extremely powerful tool for understanding the strange spacetime both in and around black ...
 00:14: ... compactifies our representation of the dimensions of space and time, allowing us to fit onto the one diagram the infinitely ...
 02:21: Below that horizon, but above the stillshrinking surface of the star, spacetime takes on the mad properties of the black hole interior.
 02:30: Space and time switch places, and the singularity soon forms, with all space within the black hole flowing towards it faster than the speed of light.
 02:47: The shape of spacetime outside the horizon warps to make this diagonal line, a line of constant radius, the radius of the new black hole.
 02:59: ... are regions in this otherwise normal space where everything is doomed to fall into the singularity, even though the ...
 03:27: On the Penrose diagram, we should extend our effective event horizon backwards to include that space.
 04:31: Their spaceships form a sphere around the solar system and blast a pulse of light inwards.
 05:33: Space inside the collapsing kugelblitz would remain comfortably flat until the collapsing shell overtakes it, even after the event horizon forms.
 07:03: They've heard that you watched PBS Space Time, and so they want your opinion on the plans.
 07:29: ... within two weeks of release of this episode for a chance to win a Space Time tshirt and, obviously, to save the ...
 07:44: So assuming there's no kugelblitz apocalypse, I'll see you next week for a new episode of Space Time.


20161208: What Happens at the Event Horizon?
 00:06: At the event horizon of the black hole, space and time are fundamentally changed.
 02:08: It's a special type of spacetime diagram designed to clarify the nature of horizons.
 02:15: But first, a quick refresher on basic spacetime diagrams.
 02:19: ... graphing time versus just one dimension in space, we can look at the limits of our access to the universe due to its ...
 02:30: With the right choice of space and time units, the speed of light becomes a diagonal line on the spacetime diagram.
 02:37: ... by the socalled lightlike paths defines all future events or spacetime locations that we could potentially travel to or influence constrained ...
 03:01: Let's drop a black hole onto our spacetime diagram.
 03:04: It lives at x=0 on the space axis, but exists through all the times on the graph.
 03:16: ... mass of the black hole stretches space and time so that light rays appear to crawl out of the vicinity of the ...
 03:48: The problem with the regular spacetime diagram is that the path of light and the shape of the light cone changes as spacetime becomes warped.
 04:10: It transforms the regular spacetime diagram to give it two powerful features.
 04:15: It crunches together, or compactifies, the grid lines to fit infinite spacetime on one graph very useful for black holes.
 04:25: It also curves the lines of constant time and constant space in what we call a conformal transformation so that light always follows a 45 degree path.
 04:42: This is the Penrose diagram for flat spacetime with no black holes.
 04:48: ... as with a regular spacetime diagram, blue verticalish lines represent fixed locations in one ...
 05:01: Now, those lines get closer and closer together towards the edge of the plot to encompass more and more spacetime.
 05:24: ... hugs the edge of the diagram and crosses an enormous number of time and space steps, only reaching us in our very distant ...
 05:38: Let's drop a black hole into this spacetime.
 05:44: And because we only have one dimension of space, and any motion to the left brings us closer to the black hole.
 06:03: The compactified grid lines there now represent the stretched spacetime near the event horizon.
 06:21: Space flows at greater than the speed of light inwards, towards the central singularity.
 07:08: Our spacefaring simian begins its journey and emits a regular light signal that we observe from a safe distance.
 07:14: ... rays have further and further to travel through increasingly curved spacetime and so the interval between receiving signals also ...
 07:35: It's trying to travel at the speed of light against light speed cascade of spacetime.
 08:07: It will, nonetheless, have experienced far less time than us when it emerges into flat spacetime in our far future.
 08:32: ... these diagonal lines because it has to contend with the same stretched spacetime as the ...
 10:00: All spacetime within the black hole is flowing toward the singularity faster than the speed of light.
 11:19: Then our Penrose diagram blooms outwards to include potentially infinite parallel regions of spacetime.
 17:42: ... wave is a physical reality, even the [INAUDIBLE] wave in configuration space. ...


20161130: Pilot Wave Theory and Quantum Realism
 04:13: That's the equation at the heart of all quantum mechanics that tells the wave function how to change across space and time.
 12:10: Maybe something like pilotwaves really do drive the microscopic mechanics of spacetime.


20161116: Strange Stars
 09:43: And who knows which are actually out there, waiting to be discovered in the expanse of spacetime?
 09:52: ... about it long and hard and we decided that we want to keep making Space Time forever and ever and ever and ever, and to keep making it better ...
 10:18: It'll really help us keep pushing Space Time forward.
 10:43: Now, pixel girl asks whether in a curved 3D space, shouldn't the triangles appear flat to us?
 11:10: A flat 3D space means that the rules of geometry in that space work just like on an actually flat 2D surface.
 11:45: ... a giant triangle in geometrically curved space will definitely have weird angles, less than 180 degrees for a ...
 12:25: That's because light would also have to follow the curve of that space.


20161109: Did Dark Energy Just Disappear?
 09:27: In a relatively empty, expanding universe as is represented by this part of the graph, space would not be flat.
 11:03: ... the gravitational effect of matter and flattening the geometry of space. ...
 12:07: ... look at the evidence for dark energy, and its effect on the expansion of spacetime. ...


20161102: Quantum Vortices and Superconductivity + Drake Equation Challenge Answers
 06:06: ... in brain capacity, and then you need it to survive long enough to become spacefaring. ...
 08:43: For everyone else, thanks for playing, and you can always pick up your own Space Time tshirt: link in the description.
 08:50: See you guys next week on Space Time!


20161026: The Many Worlds of the Quantum Multiverse
 02:04: ... mechanics, the act of measurement was thought to collapse possibility space into a single reality, at least with respect to the measured ...
 11:00: Think of it as a choose your own adventure, and steer this version of you towards one of the more awesome many world branches of spacetime.
 11:12: This is Dianna from Physics Girl right here on Space Time.
 11:17: It's cool to be in space here.
 12:30: So keep watching PBS Space Time to make sure that Matt follows up with that challenge.


20161019: The First Humans on Mars
 00:36: SpaceX plans a spacecraft capable of transporting 100 people at a time to Mars, not to visit, but to settle.
 01:05: First step a spaceship is launched into orbit by a rocket booster.
 01:14: It relaunches and delivers to the orbiting spaceship enough fuel for the fourmonth journey to Mars.
 01:25: That means many return trips to Mars, but it also allows the booster to carry the spaceship and the fuel in separate launches.
 01:33: ... a result, the spaceship itself can have a much bigger payload, translating to 100 passengers, ...
 02:46: That 450ton cargo capacity of the spaceship will help there.
 02:52: ... Activity Module, BEAM, that's already in use on the International Space ...
 06:12: This has been proposed for artificial gravity on longterm space missions, but it's also possible on a planetary surface.
 07:32: In fact, the proposed spacecraft is meant to be a general purpose solar system explorer.
 07:39: Mars will be fun, but we're really holding out for those Venusian cloud cities here at Space Time.
 07:46: We want to thank Curiosity Stream for supporting this episode of Space Time.
 08:30: Be sure to help us out by using the promo code spacetime.


20161012: Black Holes from the Dawn of Time
 00:35: As long as a volume of space contains a high enough density of mass or energy, general relativity tells us that a black hole will form.
 02:06: It reveals tiny differences in the density of matter from one point in space to the next.
 05:07: For one thing, if these little knots of warped space time are everywhere, then they should produce obvious gravitational lensing.
 05:16: We'd expect them to frequently pass in front of other space stuff.
 09:58: I mean, how long can the universe expect to hide vast numbers of holes punched in the fabric of spacetime?


20161005: Are We Alone? Galactic Civilization Challenge
 05:53: Submit your answers with full work to pbsspacetime@gmail.com within two weeks of release of this video for a chance to win a Space Time tshirt.
 06:09: See you next week for a new episode of Space Time.


20160929: Life on Europa?
 00:19: ... PLAYING] This new evidence of water plumes was found by the Hubble Space Telescope, which took ultraviolet images as Europa passed in front of ...
 02:29: And the Cassini spacecraft found that ring to contain salt.
 07:46: The original plan was a lightweight spacecraft carrying several instruments.
 09:31: ... we'll see you next week on "Space Time." Last week we talked about the weirdness of quantum entanglement ...


20160921: Quantum Entanglement and the Great BohrEinstein Debate
 11:11: ... get back to these in an upcoming episode of "Space Time." Last minute announcement tomorrow night, Thursday, the 22nd, is ...
 11:29: OK, last week we talked about selfreplicating spacecraft and why it may be surprising that none have found their way to earth.
 13:31: But if these artificial panspermianic seeds are common, then we should expect to find them in space and on other planetary surfaces.


20160914: SelfReplicating Robots and Galactic Domination
 00:06: Space is big, maybe even too big to be easily colonized by real, living aliens.
 00:16: I mean spacecraft capable of replicating themselves and exponentially spreading across the galaxy.
 00:41: Space stuff gravitates around in slow, stately arcs that would make Newton proud.
 02:06: ... robotic spacecraft that's right, completely unmanned or unkerbled vessels capable of ...
 02:48: Because these may be the future of space development.
 03:50: ... is a tiny spacecraft that will be powered by a solar sailfed ion drive that could harvest ...
 04:40: ... construction, and terraforming really any largescale automatable space operation might be best handled with selfreplicating ...
 04:55: This outline is inspired by Robert Freitas' vision for a selfreplicating version of the Daedalus spacecraft.
 05:06: So a spacecraft is launched from the home Solar System with an engine capable of taking it to 10% or 20% lightspeed.
 07:33: The Kepler Space Telescope showed us this.
 08:38: ... of individuals, and not one of them builds a single selfreplicating spacecraft? ...
 09:45: Perhaps that's us, preparing to explore the young and still untamed reaches of this spacetime.
 10:16: ... actually learned a lot about the future of robotics, including space robots and evolving selfassembling machines, from Professor John Long's ...


20160907: Is There a Fifth Fundamental Force? + Quantum Eraser Answer
 06:51: For the rest of you, you can still grab a "SpaceTime" tshirt of your very own via the link in the description.
 08:04: Nonetheless, there is a clue somewhere in all this weirdness to the fundamental workings of spacetime.


20160824: Should We Build a Dyson Sphere?
 00:11: ... the power output of entire stars, the as yet inexplicable Kepler Space Telescope observation of swarms of somethings partially eclipsing a ...
 04:21: ... is that its gravity is low enough that launching mined raw material into space for construction is pretty ...
 04:33: We start with limited mining, space launch, and orbital construction facilities, all of it autonomous.
 05:41: Engineers are in the serious planning phases for all sorts of spacebased assembly projects, including 3D printing of giant telescope mirrors.
 07:40: The show "Space" also did a great episode on the Kugelblitz.
 09:43: Admittedly, the fading that the Kepler Space Telescope observed in Tabby's star is sort of consistent with a partial swarm.
 10:05: And we don't go in for that hokey stuff here on "Space Time." Thanks to "The Great Courses plus" for sponsoring this episode.


20160817: Quantum Eraser Lottery Challenge
 04:02: ... to the screen, which could theoretically be very distant in both space and ...
 05:27: We'll choose five correct answers to receive "Space Time" tshirts.
 05:40: See next week for a fresh new episode of "Space Time." [MUSIC PLAYING]


20160810: How the Quantum Eraser Rewrites the Past
 01:03: There's a fuzzy space in which we don't know the particle's location or path.
 01:08: The Copenhagen interpretation would tell us that in this space, a particle is only its wave function, a distribution of possible properties.
 09:50: Perhaps the evolving tapestry of entanglement in all its impossible complexity is what really defines reality in this space time.
 10:00: This episode of "Space Time" is supported by Audible.com.
 10:03: Right now, Audible is offering "Space Time" viewers a 30day trial period.
 13:04: In the event of End of World, you guys should show up at your local spaceport.


20160803: Can We Survive the Destruction of the Earth? ft. Neal Stephenson
 01:25: Some of these events were probably caused by giant space rocks.
 01:58: Finding the answer is a big responsibility, possibly even too big for spacetime alone to handle.
 03:42: ... one of the coolest concepts in "Seveneves" is that of the space ark, a vessel designed to support potentially many generations of people ...
 04:18: And it's not quite enough to really do a terrific job of it, but it's enough to put a survivable ark into space.
 05:40: Space is trying to kill us, the Earth is trying to kill us, and at the moment we are trying to kill us.
 05:57: Big space rock.
 05:59: This is the biggest threat from space itself.
 07:56: Colonies on Mars, Venus, the moon, and in artificial habitations space arks are excellent insurance against global annihilation.
 08:14: But there is one threat that no settlement on any planetary surface or space hotel in the solar system can protect us from that's an exploding star.
 09:44: No planetary surface or space ark in the solar system would be safe from a supernova or a gamma ray burst.
 10:46: See you next time on "Space Time." Last week we talked about the spectacular weirdness of the single particle doubleslit experiments.
 11:35: ... conceal what we call hidden variables, that may change over time and space according to the wave function, but that at any one instant are ...


20160727: The Quantum Experiment that Broke Reality
 07:26: Within that mysterious span between the creation and the detection, is the particle anything more than a space of possibility?
 08:27: ... Copenhagen interpretation calls this transition from a possibility space to a defined set of properties "the collapse of the wave function." It ...
 10:12: ... we get to the many worlds interpretation, which we will right here on "Space Time." Thanks to The Great Courses Plus for sponsoring this ...


20160720: The Future of Gravitational Waves
 00:31: ... arms as the gravitational wave stretched and compressed the fabric of space as it passed ...
 04:14: We now have more confidence in our understanding of the spacetime around black holes.
 08:06: And I'll see you next time for a brand new episode of "Space Time." [THEME MUSIC]


20160706: Juno to Reveal Jupiter's Violent Past
 00:02: Two days ago on the 4th of July, 2016, the Juno spacecraft entered orbit around the planet, Jupiter after a fiveyear journey from Earth.
 09:52: The key to finding Jupiter's birth orbit is in its internal composition, and that is one of the things the Juno spacecraft was sent to discover.
 10:03: We'll keep you up to date right here on Space Time.
 11:41: ... I said that the assumption of infinite divisibility of space was a problem with the scenario in this paradox, that the real ...


20160629: Nuclear Physics Challenge
 03:43: Submit your answers with full work to PBSSpacetime@gmail.com within two weeks, so by July 13, for a chance to win a "Space Time" tshirt.
 04:06: And I'll see you next week for a new episode of "Space Time."


20160622: Planck's Constant and The Origin of Quantum Mechanics
 01:05: There are a few problems with this paradox, but one is that it assumes that space is infinitely divisible.
 10:47: And combined with a small handful of other fundamental constants, it governs the behavior of everything in this space time.
 11:30: Help support "Space Time" and start your onemonth trial by going to thegreatcoursesp lus.com/spacetime.
 14:52: Gravitational waves are ripples in the fabric of space time, so they have to go where the space time goes.
 14:58: Dylan T tells us that he met his wife by suggesting that they Space Time and Chill.


20160615: The Strange Universe of Gravitational Lensing
 00:00: [MUSIC PLAYING] The curvature of spacetime plays tricks on our eyes.
 00:22: We have hardware to build internal models of our environment in which space is a simple 3D grid, static with time.
 01:14: In the real universe, both space and time can be curved.
 01:21: Here's our playlist on curved spacetime, time, if you want to go deep into this idea.
 03:46: The illusion results from our mind's eye projecting straight lines onto a curved spacetime.
 03:58: Their spacetimes can curve any way we choose.
 04:02: Within these simplified virtual universes, we can hunt through vast possibility space.
 04:09: ... in that parameter space is a configuration of lens and light source that will collapse those ...
 04:45: Sometimes we see the same object through multiple paths through space.
 05:07: You can see the nearby spiral galaxy, whose gravitational field bends spacetime to create these paths.
 07:44: It's allowed us to decode the universe in ways that would've been impossible in boring Euclidean space.
 08:00: The lightspeed flow of spacetime at the event horizon results in old light paths pointing inwards.
 09:23: But look through a telescope at very distant galaxies, and all are brightened, shifted and warped by the weird lens of a curved spacetime.


20160608: New Fundamental Particle Discovered?? + Challenge Winners!
 05:02: We're going to talk about everything space time.
 05:05: So space and time, really anything physics or astrophysics.
 09:30: Let's think about a giant box of space that is expanding with the rest of the universe.
 12:40: If your name appears on screen below me, you got this right, and were randomly selected to receive a space time Tshirt.
 13:29: We're come back to both of these ideas in future episodes of "Space Time." [MUSIC PLAYING]


20160601: Is Quantum Tunneling Faster than Light?
 01:04: The reduction of a fuzzy possibility space into a specific measurable property is sometimes referred to as the collapse of the wave function.
 03:55: But that possibility space does not end suddenly at the force barrier.
 04:19: ... resolve its position in that unlikely outside bit of its possibility space that looks like the particle teleporting out of the ...
 08:49: When you add the barrier, all you're really doing is reshaping the wave packet, selecting only the possibility space of early arrival.
 09:39: Stay tuned for the implications of this on both quantum and cosmic scales of space time.
 09:46: This episode of Space Time is supported by Audible.com.
 09:49: Right now, Audible is offering Space Time viewers a 30 day trial period.


20160525: Is an Ice Age Coming?
 11:57: See you next week for more cold, hard facts on Space Time.
 13:58: ... as we learned when we studied Newtonian mechanics, is a feature of flat spacetime. ...
 14:10: Curved spacetime changes things.
 14:51: Conservation of energy is one such law that work in flat space time.


20160518: Antigravity and the True Nature of Dark Energy
 01:00: This is only possible if we missed some unknown type of energy pervading all of space.
 02:03: A constant cosmological constant represents a nonzero energy of empty space, a vacuum energy.
 02:12: The more space you have, the more dark energy you have.
 04:18: In general relativity, energy slash mass and pressure both curve space time.
 05:17: Instead, the overall effect of pressure on the curvature of space time is a purely relativistic effect.
 11:35: This law is a property of a Newtonian universe, in which space and time are fixed static dimensions.
 11:48: Energy can be forever lost or gained from nothing within an expanding curved spacetime.


20160511: The Cosmic Conspiracy of Dark Energy Challenge Question
 01:05: If you add up the energy in any large volume of space, about 70% of it is dark energy and the remaining 30% is in the form of regular matter.
 03:43: ... around 20% smaller than it is currently for the volume of any patch of space to be smaller by ...
 06:07: I'll choose three correct answers at random for both the main and the extra credit questions to receive Space Time tshirts.
 06:48: See you next week for a fresh new episode of Space Time.


20160504: Will Starshot's Insterstellar Journey Succeed?
 00:02: Breakthrough Starshot plans to send spacecraft to the nearest star within your lifetime.
 00:11: [MUSIC PLAYING] Do you remember when the future had spaceships?
 00:20: I grew up in the afterglow of the Apollo program, in the era of the space shuttle.
 00:32: We've been waiting so long now that this surety of a spacefaring future has started to slip into the realm of science fiction.
 01:31: A spacecraft is propelled as the light from the sun or from a giant laser accelerates a sail of reflective material.
 02:19: This solar sail has buzzed past Venus and now explores the interplanetary space in an orbit between Earth and Venus.
 03:06: ... which would be focused by a 1,000 kilometer diameter microwave lens in space. ...
 08:35: ... with the first up close alien snapshots in around 50 years right here on "Space Time." In the last episode, we talked about how dark energy causes this ...
 09:47: Or does space itself rip itself apart?
 09:54: ... constant and so has an unchanging density with time, then no, space time doesn't get ripped ...
 10:20: The one where space time rips itself apart at a fundamental level, the socalled Big Rip, happens when the density of dark energy increases.
 10:33: Sandeep Siwach would like to know why dark energy only effects the space between galaxies and not within galaxies.


20160427: What Does Dark Energy Really Do?
 01:29: See, as space expands, it stretches out the light that is traveling through it.
 01:59: So we need to figure out how far it traveled, the actual physical amount of space the photon had to traverse to get to us.
 02:26: Redshift is the amount the universe expanded during a photon's journey, and distance is the amount of physical space it travelled through.
 02:47: Just measure redshifts and distances for a bunch of things out there in space.
 07:36: This lets us interpret the cosmological constant as representing a sort of vacuum energy, a property of space itself.
 09:33: That all depends on what this energy of empty space really is.
 09:38: ... that, we'll need another episode of "Space Time." In the last episode, we talked about how a general relativistic ...


20160420: Why the Universe Needs Dark Energy
 00:08: ... the behavior of the cosmos on the largest scales of a volume of space vastly beyond our capacity to physically explore and at a time billions ...
 02:30: It describes the curvature of space.
 02:46: Spacetime will be curved, no matter what.
 03:59: And surfaces hold less volume than in flat space.
 07:54: We call it "dark energy," and we interpret it as an energy possessed by empty space itself by the vacuum.
 08:46: ... the insight we need to understand dark energy's effect on the future of spacetime. ...
 09:25: A number of you were curious to know, on what scales of space is the universe really expanding?
 09:43: Within these regions, the shape of spacetime is dominated by the gravitational field of the densely packed matter.
 09:53: ... field of the Milky Way and Andromeda to not dominate the shape of local spacetime. ...
 10:10: Now there are certain models of dark energy that could have space on smaller scales expand, resulting in the socalled Big Rip.


20160413: Will the Universe Expand Forever?
 00:38: Combined with observations of the redshifts of galaxies, this showed us that the fabric of space itself is expanding.
 01:50: And it defines the shape, the curvature, of spacetime.
 01:57: And it describes all of the energy, the pressure, the momentum, and more all of the stuff within that spacetime.
 02:16: ... Archibald Wheeler put it more simply "Spacetime tells matter how to move, while matter tells spacetime how to curve." ...
 04:13: ... of the galaxies and galaxy clusters are very evenly dusted across all of space. ...
 08:50: After all, matter tells spacetime how to curve.
 09:36: It'll shatter our intuitions about energy conservation and gravity on the largest scales of spacetime.
 11:23: ... the core to be carried to the surface by convection and then blown into space as the outer layers are blown away into a planetary ...


20160406: We Are Star Stuff
 00:31: Space, time, energy, mass.
 01:30: So the tapestry of our universe is woven across the dimensions of space and time and complexity.
 07:38: In this explosion, all those elements are spread into interstellar space, providing fuel for later stars to form.
 10:13: We are "starstuff." But more, we our universe stuff, the most complex component that has risen from a beautiful and chaotic spacetime.
 10:51: Let me clarify a few things about space geometry first, and I'll get to what flat means in a minute.
 10:58: ... flat positive or negatively curved, I should say that the curvature of space at a single, constant moment in time has to be one of these ...
 11:10: So constant time spatial curvature, which is different to the curvature of spacetime.
 11:17: The time part is certainly curved, which leads to the expansion of space, even if the space part itself can be flat.
 11:28: So what does flat space mean?
 11:34: Space is still three dimensional, and perhaps infinite in all three dimensions.
 11:39: ... spatial curvature refers to the fact of the geometry of space on the largest scales in the universe works just like the geometry on a ...
 11:57: That stuff isn't necessarily true on a curved 2D surface like a ball, nor in curved 3D space, like within a gravitational field.
 12:14: Well, the speed of light is an absolute speed limit for a thing in the universe traveling through space.
 12:21: The limit doesn't apply to space itself.
 12:25: General relativity allows that two patches of space can move apart faster than the speed of light.
 13:21: Guess what we're talking about next week on "Space Time?" The end of the universe.


20160330: Pulsar Starquakes Make Fast Radio Bursts? + Challenge Winners!
 08:29: If you see your name scrolling below, we've chosen your correct answer to receive the "PBS Space Time" Tshirt.
 08:57: See you all next week for brand new episode of "Space Time." [MUSIC PLAYING]


20160323: How Cosmic Inflation Flattened the Universe
 01:29: We can use the apparent size of the very subtle fluctuations in the CMB to measure the flatness of the fabric of the universe, of spacetime.
 02:07: Triangles in 3D space obey exactly the same rules as on 2D surfaces, and their geometry measures the curvature of space.
 06:08: For this to work, that inflationary expansion had to throw neighboring regions of space apart at many times faster than the speed of light.
 06:57: ... he added this as a way to allow his theory to describe a static space time, a universe that's neither expanding nor ...
 07:30: The cosmological constant represents something that can happen to our spacetime.
 07:38: The cosmological constant adds some energetic stuff to empty space.
 07:43: It doesn't tell us what this stuff is, just that it's a property of space itself and that it acts to drive expansion.
 07:52: The more space, the more of this stuff.
 07:54: And so the more space, the more expansion.
 08:15: ... now, let's just go with the fact that empty space can propel its own expansion and will do so if the vacuum contains a ...
 10:02: ... so we'll rewind to before the beginning of the universe very soon on "Space Time." In a recent episode, we told you why space things are the shape ...


20160316: Why is the Earth Round and the Milky Way Flat?
 00:02: Why are space things the shape they are?
 02:06: In the case of all the really big space stuff, one of the important forces is always gravity.
 02:15: Here it's fine to think about gravity Newtonianly as a force rather than as an Einsteinian warping of space time.
 02:34: ... has spherical symmetry in the sense that, if you're some distance from a space thing of any shape and there's nothing else around, a surface of ...
 10:34: Symmetries really do shape the universe on all the scales of space time.
 12:26: This patch of space, the Milky Way, the Earth, has been bombarded with cosmic background radiation for all of cosmic time.


20160309: Cosmic Microwave Background Challenge
 01:41: In fact, all of those blobs of plasma were a mere 43 million light years away from the patch of space that would later contain the Milky Way.
 01:50: Back then, this patch of space just contained a slight overdensity of plasma that looked pretty much the same as the rest of those blobs.
 01:58: ... a lot further than those 43 million light years to reach this patch of space because it was traveling through an expanding ...
 03:46: Email your answers to pbsspacetime@gmail.com within two weeks for a chance to win a PBS Space Time tshirt.
 04:38: And as long as we still have space, you'll receive full details.
 04:47: Happy physicing, and see you next week for a full new episode of Space Time.


20160302: What’s Wrong With the Big Bang Theory?
 03:46: We do think that we can describe gravity and the shape of space time at these densities and temperatures.
 04:05: And pack all of the galaxies in the entire observable universe into a space 10 to the power of minus 20th of the width of a proton.
 05:13: The universe is space sized.
 09:44: We'll get back to that on future episodes of Space Time.
 10:25: ... from the FriedmannLemaîtreRobertsonWalker metric, which describes a space time in which all matter is perfectly smoothly ...
 10:38: That works on the largest scales in which galaxies and galaxy clusters are a speckled foam on top of a much vaster space time.
 11:00: In that metric, space is most certainly not expanding.
 11:04: So you can have regions of nonexpanding space embedded in a globally expanding universe.
 11:11: ... neutron, and electron in the universe, you could fit them all into a space the size of a grain of ...


20160224: Why the Big Bang Definitely Happened
 01:50: ... relativity, the only sensible interpretation for this fact is that space itself is expanding and light traveling through expanding space is ...
 03:05: So we know that at some point in our rewind, pure general relativity will give us the wrong predictions for the behavior of space time.
 08:40: ... rewind to the very beginning of space time on the next episode of "Space Time." A couple of weeks ago, the ...
 11:58: ... observations grant us stunning insights into the fundamental nature of space ...


20160217: Planet X Discovered?? + Challenge Winners!
 04:11: The best way to illustrate this is with a spacetime diagram.
 04:21: So a photon clock that stationary on the spacetime diagram moves straight up.
 07:30: We chose three random entries from those to get brand new "SpaceTime" tshirts.
 08:16: So don't be shy about supporting the show by clicking on the link below for your very own "SpaceTime" tshirt.
 08:23: And I hope you'll join us next week for a brand new episode of "SpaceTime."


20160211: LIGO's First Detection of Gravitational Waves!
 00:10: The Advanced LIGO Observatory has seen the spacetime ripples caused by black holes at the moment of merger.
 00:49: ... detect the passage of gravitational waves, of ripples in the fabric of spacetime caused by extreme gravitational events in the distant ...
 01:13: And when here at "Space Time" we realized this was probably the real deal, we were too.
 01:35: Since then, ripples from mergers of black hole pairs in distant galaxies have changed the shape of spacetime here on Earth.
 03:22: ... holes or neutron stars produce such strong ripples in the fabric of spacetime that LIGO can see them out through vast ...
 03:56: Advanced LIGO can feel the ripples produced by merging black holes through a volume of space equal to about 0.1% of the observable universe.
 04:26: Spacetime is stretched and squeezed as the wave passes by.
 05:49: The signals are expected to carry information about the strange warping of space in the region of the event horizon.
 06:35: ... upcoming Evolved Laser Interferometer Space Antenna eLISA will see an entirely different part of this spectrum, ...
 07:18: ... keep you up to date in future episodes of "Space Time." In a recent episode, we heated up the debate on the question of ...
 07:47: Astronauts on the International Space Station lose bone mass at 1% to 1.5% per month, and lose muscle mass also.


20160203: Will Mars or Venus Kill You First?
 03:49: In 1966, a NASA vacuum chamber space suit test went horribly wrong, leaving Jim LeBlanc exposed to a vacuum.
 04:29: See, space is flooded with extremely energetic solar radiation and cosmic rays.
 05:08: ... as far as risks for space travel go, this might be considered acceptable for a single trip, but ...
 05:43: This is a serious issue for all space travel, but it's also a concern for Martian colonies.
 05:57: Now, this isn't feasible for an entire spacecraft or Mars base.
 07:55: You have a think atmosphere above to protect you from bad space radiation.
 08:31: So we'll be around for many more episodes of "Space Time." In the last episode, we finished our series on the origin of matter and time.


20160127: The Origin of Matter and Time
 00:42: And of course, things occupy a location in space.
 01:13: A while ago, we introduced the space time diagram.
 01:17: It's just a graph of position in space just one special dimension for simplicity versus position in time.
 01:24: In this picture, a thing ends up tracing a path through time and space.
 01:31: In fact, thinking in four dimensional space time, a thing is its world line.
 01:47: If it's not moving in space, it'll just sit in the same spot on the xaxis.
 01:52: But it will move up at a nice steady space in time.
 02:01: Now, it moves both in space and time, because position is changing.
 02:46: For example, we could make the time divisions 1 second, and the space divisions 300,000 kilometers, because that's how far light travels each second.
 03:10: They're separated more by time than space.
 03:20: They're called space lag.
 03:23: There's not enough time for anything to travel that much space.
 03:56: But It is unmoving in space.
 05:01: The whole space time diagram can be transformed to give the second clock's world line a constant location in space.
 05:17: Our space and time axes shift.
 05:41: So what this means is that there's no single preferred vertical time axis, or indeed, horizontal space axis.
 05:48: We can draw that time axis along any constant velocity timelike path, and just Lorentz transform to get a valid perception of space time.
 07:04: And on our space time diagram, our object becomes an impossibly complex ensemble of light speed world lines confined in equally complex ways.
 07:28: We're extrapolating the validity of space time diagrams, and these tiny lifelike segments into the quantum realm.
 08:18: One of them a point on the space time diagram can influence another if a signal can travel between the two.
 09:09: Great questions for future episodes of "Space Time." For our recent episode on when time breaks down, you guys had some amazing questions.
 11:16: And special relativity only describes the relative effects on time and space due to a constant relative motion.


20160120: The Photon Clock Challenge
 01:44: ... random entries from the correct submissions to receive brandnew PBS Space Time Tshirts, which are also available for anyone to preorder at a link ...
 02:03: We'll see you next week for a fresh new episode of Space Time.


20160113: When Time Breaks Down
 04:57: ... clock in an accelerating reference frame say on a rocket ship in empty space will also tick slower compared to a non accelerating ...
 07:51: We'll have time for all of this on a future episode of Space Time.


20160106: The True Nature of Matter and Mass
 06:23: ... we accept Einstein's description of spacetime as described by general relativity, it's not so surprising that the ...
 06:33: ... principle tells us that the feeling of being accelerated out in space is fundamentally the same thing as the feeling of weight in a ...
 06:44: Holding up our photon box against Earth's surface gravity has to be just as hard as trying to accelerate it at 1 g in empty space.
 07:16: Mass curves the fabric of space.
 07:19: Actually, it turns out that it's not just mass that bends space.
 07:23: The presence in the flow of energy and momentum as well as pressure all have their quite different effects on the curvature of spacetime.
 07:31: Individual photons affect spacetime.
 08:18: ... delve deeper into the mystery of matter and time in the next episode of "Space Time." In the last episode of "Space Time," we talked about how the ...
 08:34: Caleb Limb asks, does this mean the Higgs field makes a little friction in space?
 09:44: ... by PowerPoint wonders whether there could be a point in space somewhere where the Higgs field takes on the value of zero, and what the ...


20151216: The Higgs Mechanism Explained
 01:25: In empty space, that level hovers around zero.
 03:52: There's something in the substrate of space everywhere that impedes the electron.
 05:06: While most quantum fields hover around zero in empty space, the Higgs field has a positive strength at all points in the universe.
 07:33: ... deeper to the mysteries of matter and time in the next episode of "Space Time." In the last episode, we told you how to build a real ...


20151209: How to Build a Black Hole
 00:21: ... talked about them as general relativistic entities, as space time regions whose boundary curvature effectively removes the interior ...
 00:56: Yet, to actually form a black hole, Einstein's descriptions of mass energy and space time are not enough.
 02:51: ... understand how space works for a quantum object like this, we need to think not in regular 3D ...
 03:04: For a neutron star, this is the space of both 3D position and 3D momentum.
 03:15: ... exact way that the matter of a neutron star fills this 6D quantum phase space depends on two important principles of quantum theory, the Pauli ...
 03:48: Now, by place, I mean location in quantum phase space.
 04:09: In the case of a neutron star, position momentum phase space is completely full of neutrons.
 04:26: This weird state of matter where phase space is completely full we call it degenerate matter.
 06:40: Very, very large neutron velocities become part of the possibility space.
 06:44: To put it another way, the neutrons are packed so close together in position space that their momentum space becomes gigantic.
 06:53: Phase space expands.
 06:55: And here's the thing the denser the neutron star becomes, the more momentum space you get.
 07:19: But it doesn't expand in position space.
 07:22: The star expands in momentum space.
 07:25: In position space, it actually gets smaller.
 07:41: The space time curvature at the neutron star's surface is pretty extreme.
 08:45: Space time is radically altered inside the star with all geodesics, space time paths, turning inward, towards the center.
 09:13: All position space collapses towards the singularity.
 09:17: Well, momentum space expands accordingly, with the corresponding enormous velocities all inward pointing.
 10:43: ... this means, for black holes and for the universe, in another episode of "Space Time." In a previous episode, we talked about the Alcubierre ...
 11:07: Now, "The Good Stuff" guys talk some smack about the lack of beards here on "Space Time." And sure, they have some pretty luxuriant flavor savers.
 11:27: ... whether, instead of the gravitational tractor, you could just land a spacecraft on the asteroid and push it with its ...
 13:05: NASA, this is "Space Time." Tell Mr. Willis to stand down.


20151125: 100 Years of Relativity + Challenge Winners!
 00:10: [THEME MUSIC] November 25, 2015 is the hundredth birthday of spacetime.
 00:36: ... beautiful theory is an essential part of what inspires us here at "Space Time." General relativity's profound description of space and time, of ...
 01:08: It inspires us at "Space Time" to try to share those mysteries with you.
 01:57: ... pulsed fusion drive spacecraft is to intercept the asteroid in the 2029 pass and pull Apophis 25,000 ...
 02:57: ... gravitational force between the spacecraft and Apophis is providing all of the acceleration and hence velocity ...
 03:10: Well, we know that the spacecraft's mass is changing because it needs to burn fuel to accelerate.
 03:16: But we can just calculate the average acceleration based on the average mass of the spacecraft plus fuel over the seven years.
 03:34: So the mass that we're going to calculate is the average mass of the spacecraft in fuel over the seven years.
 04:06: Our spacecraft is hovering 325 meters from the center of mass of Apophis.
 04:18: It also gives us the acceleration experienced by Apophis due to the mass of the spacecraft and the fuel.
 04:51: This is around 80% of the mass of the space shuttle so we can definitely do this.
 05:01: ... velocity of the fuel and the ratio of fueled to unfueled or wet to dry spacecraft ...
 05:16: We're trying to pull the entire asteroid, so we have to include its mass as part of the spacecraft mass.
 05:23: But the mass of Apophis is enormous compared to the spacecraft 30 billion kilograms compared to the 1.6 million kilograms we got earlier.
 06:41: So the fuel mass we need is around 16 metric tons, which is great because that's only 1% of the spacecraft mass.
 07:11: ... pulsed future drive and so we need almost as much initial fuel mass as spacecraft ...
 07:47: And be sure to join us in two weeks because we're going to learn how to build a black hole on the next episode of "Space Time." [THEME MUSIC]


20151118: 5 Ways to Stop a Killer Asteroid
 00:11: ... PLAYING] Space is swarming with lots of really fast moving rocks, like the planet ...
 00:33: (RUSSIAN ACCENT) In postSoviet Russia, space explore you.
 00:39: The Tunguska event of 1908 was even bigger, when a 100meter space rock exploded to flatten 2,000 square kilometers of forest in Siberia.
 02:58: ... around the world have worked together as part of the Spaceguard Program to find and track most of the biggest, one kilometer plus, ...
 03:39: These things are very faint specks in the deep dark of space.
 05:04: Just slam a heavy spaceship into the NEO to knock it off course.
 05:47: Seriously, arm a spacecraft with a cosmicsized can of spray paint, and color one side of the asteroid white.
 06:11: Fly a 20 ton spacecraft alongside the object for 10 years, and their mutual gravity will pull the impactor off course.
 08:31: ... giant asteroids hit in the meantime, I'll see you on the next episode of "Space Time." In a recent episode we talked about the origin of life and the ...


20151111: Challenge: Can you save Earth from a Killer Asteroid?
 00:58: Launch a spacecraft to intercept Apophis during its 2029 pass.
 01:03: ... spacecraft will hover just in front of the asteroid and act as a gravitational ...
 01:23: ... kilometers per second ready by the launch data, can we feasibly build a spacecraft that would give the necessary bump to ...
 01:38: How massive would the spacecraft, including the fuel, need to be?
 02:05: ... constant propellant use over the seven years and calculate an average spacecraft ...
 02:15: ... release some clues over the "SpaceTime" Twitter if you need help, but submit your answers to "PBS SpaceTime" at ...
 02:49: Next week, we'll be back with a killer episode of "SpaceTime." [MUSIC PLAYING]


20151105: Why Haven't We Found Alien Life?
 00:17: We've asked this question before here on "Space Time," and if you haven't seen that episode you should check it out.
 00:26: ... Kepler Space Observatory has told us there are a couple of hundred billion nice, ...
 06:00: ... like that, and two, it didn't happen on Earth life was seeded from space, an idea called ...
 06:10: Look, there's no question that lots of rock gets ejected into space after meteor impacts and can move between planets.
 06:42: ... the solar wind pushes infested material into interstellar space so that tens of thousands, even millions, of years later a single bug ...
 07:18: These cosmic cooties should be findable in space, too.
 08:42: plants, animals, a species capable of making the Kerbal Space Program.
 08:46: And speaking of space programs, technological life took a little while longer, but not really so long on the overall scale once we had complex life.
 09:43: It's part of the first 8%, according to recent Hubble Space Telescope based calculations.
 10:20: Well, there's something to work towards on the next episode of "Space Time." Last week we talked about Miguel Alcubierre's warp drive.
 10:37: We cram a lot of details into each episode of "Space Time" and sometimes things like this do slip through, so thank you for catching it.


20151028: Is The Alcubierre Warp Drive Possible?
 01:27: That limit, the speed of light, refers to things mass, energy, information traveling through space.
 01:34: However, according to general relativity, there's no limit on the relative speeds of two separate patches of spacetime.
 01:51: ... below the event horizon of a black hole, spacetime cascades towards the central singularity faster than light, carrying ...
 02:03: ... the spacetime around and within a black hole is predicted by solving Einstein's field ...
 02:12: Basically, mass and energy tell us how space should warp.
 02:24: ... developed a spacetime description, a metric tensor, that describes a volume of nice, flat ...
 02:42: As a result, the bubble is pushed and pulled by spacetime itself, moving at speeds only limited by the intensity of the warp.
 02:55: It's sort of like building a conveyor belt out of spacetime.
 03:05: ... you just make up a spacetime description and then essentially solve the Einstein equations backwards ...
 03:34: That means our ship looks something like this in order to produce a spacetime curvature like this.
 04:21: One possible quantum disaster is that the extreme spacetime curvature of the warp bubble walls would roast the interior with crazy Hawking radiation.
 05:33: ... oscillate the warp field, and you hypothetically soften the fabric of space via higher dimensional effects literally, a hyper space warp ...
 07:09: ... make it so on the next episode of "Space Time." Last week, we talked about gravitational waves, and whether the ...
 07:25: LISA is amazing, although now it's ELISA, the Evolved Laser Interferometer Space Antenna.
 07:42: The program is being developed by the European Space Agency.
 08:49: ... wants our thoughts on that amazing new Kepler Space Telescope result that the media is hyping that there's an alien ...
 08:57: Now, this is a stunning result. But as we say on "Space Time," it's never aliens.
 09:24: Although I imagine it could possibly be insanely vast ragtag colony of space structures surrounding a parent planet== except it's never aliens.


20151022: Have Gravitational Waves Been Discovered?!?
 00:29: Instead, mass warps the fabric of 4D spacetime, leading to what we see as gravitational motion.
 00:48: There's the dragging of spacetime by spinning masses.
 01:09: The idea of gravity not as a force, but as warped spacetime is often depicted in analogy as a flexible rubber sheet being depressed by a heavy ball.
 01:39: ... a mass through space in the right way, and you produce gravitational ripples an outflowing ...
 02:08: ... and indeed, gravity itself propagate according to the stiffness of spacetime in other words, at the speed of ...
 02:34: It's worth pointing out that this speed limit is really the speed of causality the speed at which spacetime talks to itself.
 02:58: They propagate as a fluctuation of squeezed and stretched space in a sort of crosslike pattern.
 03:16: ... giant black holes these make gwaves that lengthen or contract our space here on Earth by a factor of 10 to the power of minus 21 or ...
 09:24: ... we hear any more, we'll definitely tell you on a future episode of "Space Time." Last week, we talked about real spaceship options for getting to ...
 09:35: Eshan Das asks, how do we avoid hitting meteors and other space stuff at such high speed?
 09:40: Large bodies like asteroids are rare enough in interstellar space that hitting one is very unlikely.
 09:48: A 10 milligram grain would strike with the kinetic energy of around 100 kilograms of TNT if your spaceship was moving at 10% the speed of light.
 11:05: ... born too early to explore the galaxy, born just in time to watch PBS "Space ...


20151015: 5 REAL Possibilities for Interstellar Travel
 00:31: Recently, there's been some pretty wild talk of some crazy ideas for space travel technologies.
 01:07: Hell, this thing is so big we're going to have to assemble it in space.
 02:07: Propellant is the big limiting challenge with space travel.
 02:18: The rocket equation tells us that maximum speed is based on exhaust velocity, fuel mass, and spacecraft mass.
 03:51: This means we'd need three generations of humans on board that ship and pray that space babies turn out OK.
 04:05: Although the 1963 test ban treaty says no space nukes, maybe we can make an exception for the future of humanity.
 06:13: ... a kilometer wide sapphire coated sail, riding the beam of a gigantic space laser blasting the power equivalent of 100 nuclear ...
 06:39: This is an update to Robert Forward's Star Wisp spacecraft, but it should be scalable.
 07:56: ... of laser light focused in a small enough region would bend the fabric of space time enough to produce a singularity, the Kugelblitz, German for ball ...
 10:49: We hit warp seven next time on Space Time.


20151007: The Speed of Light is NOT About Light
 00:36: In fact, spacetime couldn't care less about light.
 00:46: In a previous episode, we talked about causality by way of the spacetime interval.
 02:46: It would imply that space and time and matter don't exist.
 03:56: This tells us that the electromagnetic force holds clues to the fundamental interplay between space, time, and velocity.
 04:06: ... seamlessly between reference frames the transformation that represents space and time in our ...
 04:17: This transformation thing, it's like a mathy magic wand that you wave at your description of spacetime or your physical laws.
 04:28: An example is the Galilean transformation, which basically says that velocities add together and space and time don't depend on velocity.
 05:17: ... was Einstein who realized that the Lorentz transformation tells us how space and time are connected and that it also predicts the speed of ...
 05:31: As an example, there's a link to the derivation via the spacetime interval in the description.
 05:39: This transformation is so profound that it is inevitable based on a few simple statements about the nature of space and time.
 09:12: In fact, the very existence of mass and space and time tells us that the universal speed limit is finite.
 09:36: ... are unavoidable conclusions once we have the basic relationship between space and time as described by the Lorentz transformation and we accept ...
 10:02: There is no time and space, no cause or effect, because all locations and times communicate with each other instantly.
 10:29: ... we want a universe so I can see you back here on the next episode of "SpaceTime." Last time on "SpaceTime," we talked about the edge of the universe and ...
 10:52: Imagine an infinitely long ruler with markings spaced at every inch.
 10:56: If we stretched the ruler so that the markings are spaced at every two inches, the ruler is still infinitely long.
 11:02: But every section of the ruler has twice as much space.


20150930: What Happens At The Edge Of The Universe?
 00:20: The universe defines all of space and time that exists.
 00:54: This is "SpaceTime." OK.
 02:00: ... universe froze in its expansion and you were traveling through static space. ...
 02:19: That's not how spacetime works.
 02:21: The shortest path in spacetime is defined by the geodesic, the path of light between two points.
 02:29: So we have to factor in the time interval, especially when space is changing.
 02:33: To travel to the particle horizon, we need to move through expanding space.
 02:38: And the closer we get to our destination, the more space will have expanded over the remaining distance.
 02:44: Bad news, you'd have to travel infinitely far, even if you were in a spaceship that could travel at the speed of light.
 03:21: The same thing applies to our light speed spaceship.
 03:23: We can ever get to anything beyond the cosmic event horizon because that space will be moving away from us faster than light before we reach it.
 04:09: There's no doubt that Einstein was right in setting that limit for objects moving through space.
 04:13: But two regions of space can have superluminal relative speeds.
 05:07: On the largest scales, the geometry of spacetime is very flat.
 05:26: If spacetime really is perfectly flat, then, with the most simplistic application of Einstein's equations, we get that the universe is infinite.
 06:05: But get some perspective by taking a ride on the International Space Station and it's clearly curved.
 07:36: ... cross that edge into the multiverse in another episode of "SpaceTime." Squishina and others ask whether it's contradictory or circular to use ...
 09:11: No monkeys were harmed in the making of "SpaceTime" and any events that can be consistently assigned to our clocks at PBS.


20150923: Does Dark Matter BREAK Physics?
 00:09: My name is Matt and this is "SpaceTime." Physics has a problem.
 07:22: We also watch the heavens for the equally elusive gamma radiation produced when dark matter particles annihilate each other out in space.
 07:36: ... any previously undiscovered dark matter particles on the next episode of "SpaceTime." Last time on "SpaceTime," we talked about black ...
 08:30: ... the monkey because that light has to contend with the same crazycurved spacetime that the monkey ...
 09:14: ... this is that the freefalling monkey doesn't see anything weird about space at the moment it crosses the event ...
 09:22: The space itself is in free fall with the monkey.


20150827: Watch THIS! (New Host + Challenge Winners)
 00:00: Hey, Spacetimers, two weeks ago we issued a challenge question.
 03:01: Oh, so you're the new host of Space Time?
 05:20: These are the Spacetimers.
 05:21: Spacetimers, this is Matt O'Dowd.
 05:37: So I'll see you guys in a couple weeks for a fresh episode of Space Time.


20150819: Do Events Inside Black Holes Happen?
 00:37: ... help a lot if I can rely on technical terms like "geodesic" or "flat spacetime" and if I can draw a spacetime diagram or ...
 04:34: The horizon is not just a spherical surface in space.
 04:39: It's a surface in spacetime.
 04:56: ... determines the spacetime geometry in its neighborhood, the resulting geodesics of which ...
 05:19: So as far as Earth is concerned, that black hole generates the same spacetime geometry out here that the Sun does.
 05:36: ... this special radius, called the Schwarzschild radius, will leave the spacetime that's originally external to that object ...
 06:26: See, spacetime geometry in this region is very foreign.
 10:05: ... that has an eternal black hole that didn't form from anything, a spacetime that has an event horizon even though there's no stuff anywhere, ...
 10:46: It's like a hole that's been punched out of spacetime.
 10:53: Is it associated with the curvature of spacetime, with all of spacetime?
 11:46: ... to the challenge questions, this is officially my final episode of "Space Time." Our last full episode dealt with misconceptions about what causes ...


20150812: Challenge: Which Particle Wins This Race?
 00:02: Hey Space Timers.
 00:22: ... means clocks run at the same rate everywhere, space and time are two separate things, and gravity is an actual force that ...
 00:30: No spacetime, no relativity.
 05:47: But I will see you guys next week for my final episode of Space Time.


20150805: What Physics Teachers Get Wrong About Tides!
 00:00: [MUSIC PLAYING] As we've seen before on "Space Time," gravity affects the motion of all objects identically.
 02:07: But curved spacetime will only add complexity without actually making things clearer.
 02:49: ... relative to a frame out in the ambient space, Block A accelerates toward the Moon more than Earth's center and Earth's ...
 07:33: Now, when Earth, the Moon, and the Sun all line up in space, the effects are additive and you get extralarge spring tides.
 07:39: When, instead, they make a 90 degree angle in space, there's partial cancellation and you get extra small neap tides.
 08:59: ... be more important than the stretching, even in the craziest regions of spacetime. ...
 09:10: Last week, we finished our series on general relativity and curved spacetime.
 09:24: ... prior to the airing of that episode, at the 2015 NASA Space Apps Challenge, a colleague of mine Professor Emily Rice from the ...
 09:49: ... link to her talk about alien atmospheres it's very good at the NASA Space Apps Challenge, along with a link to other information from her ...
 10:18: So if gravity is not a force and it's considered spacetime curvature, then why do people talk about gravitons?
 10:28: Thinking about things in terms of gravitons and thinking about spacetime curvature are not necessarily mutually exclusive.
 12:13: There's really only spacetime curvature.
 12:14: You can't really break it up into separate space and time curvatures.
 13:35: In the fourdimensional curved spacetime sense, you need to give something some kind of inherent, absolute 4D geometric meaning.
 14:27: In other words, Einstein says the standard of nonacceleration can only be defined locally in small spacetime patches.


20150729: General Relativity & Curved Spacetime Explained!
 00:08: If you haven't seen them then pause me now, go watch them in order, and meet me back here after the music to hear about curved spacetime.
 00:36: But Einstein says, nuhuh, it's the apple's frame that behaves like a frame in deep space.
 01:01: Remember that inertial frame in deep space?
 01:11: Today we're finally going to show how curved spacetime makes Einstein's model of the world just as self consistent as Newton's.
 01:18: ... one is to express both Newton's and Einstein's viewpoints in geometric spacetime terms, since that's the only way to compare them in a reliably objective ...
 01:26: Remember, humans experience the world and talk about the world dynamically, as things moving through space over time.
 01:39: ... into tenseless statements about static geometric objects in 4D spacetime. ...
 01:52: He says that spacetime is flat.
 01:54: ... think about it, on the flat spacetime diagrams of inertia observers, the world lines of other inertial ...
 03:14: Flat space definitions of straightness apply over small areas, but big ones.
 03:22: Inertial frames, that means axes plus clocks, are the spacetime equivalent of the ant's xy grid.
 03:27: If spacetime is curved, then those frames are only valid over tiny spacetime patches.
 03:32: ... when an observer in deep space says that the falling apple is accelerating, he's pushing his frames ...
 03:39: In other words, global inertial frames don't exist in spacetime.
 03:47: ... frames, provided that we think of them as being reset in each successive spacetime ...
 04:09: Remember, no one can really see or draw spacetime.
 04:32: ... because the apples are on initially parallel geodesics that, since spacetime is curved, can and do cross just like on the ...
 04:52: In order to compare distant parts of the Earth, you'd need a single frame that extends across spacetime patches.
 05:04: OK, so Einstein's gravityfree curved space time sounds like it's self consistent.
 05:09: But then again, so does Newton's flat spacetime picture that has gravity injected as a kicker.
 05:21: ... yet, but there's one experimental fact that I can use to show you that space time must be curved, just based on what we've seen in this series of ...
 05:44: On a flat spacetime diagram the world lines of those photons should be parallel and congruent.
 05:59: Now if spacetime is flat, then clocks on the ground and on the roof should run at the same rate.
 06:24: And that's geometrically impossible if spacetime is flat.
 06:27: Thus, the very existence of gravitational time dilation, regardless of its degree, requires that spacetime be curved.
 06:36: ... fact, to the extent that we can speak about space and time separately at all, most of the everyday effects on earth that ...
 06:45: The 3D space around Earth is almost exactly Euclidean.
 07:02: And around Earth, spacetime curvature manifests itself in clocks much more than in rulers.
 07:07: ... looks spatially circular in frames of reference that cover too big a space time ...
 07:18: So why is spacetime curved in the first place?
 07:27: Consider a region of spacetime.
 07:46: What comes out is a map of the geodesics in the sun's spacetime neighborhood.
 08:17: As far as I know, most of us have no special ability to visualize or directly experience 4D spacetime.
 08:32: ... easier to say the word gravity than say curvature of four dimensional spacetime. ...


20150722: SPECIAL ANNOUNCEMENT + Flat Spacetime Geometry Comments
 00:03: Last week, part 2 of our general relativity series went a little deeper into some aspects of flat space time geometry.
 00:24: ... sad to say that I'm stepping down as the writer and host of "PBS Space Time." This fall, I'll be starting fulltime work at the US National ...
 00:31: And while I'd love to keep doing "Space Time," I just won't have the time to do it right.
 00:36: "Space Time" will continue.
 01:14: Without question, "Space Time" has one of the most curious, most cerebral, bestbehaved audiences on YouTube.
 01:38: Let's do some space time questions.
 02:36: ... ordinarily see moving with a constant threedimensional velocity through space. ...
 03:05: ... a space time picture the flat space time picture tells you is that in a ...
 03:27: And they are distinguishable from noninertial observers in a geometric way in space time.
 03:33: ... corrected my French, and also corrected an error that we had made in the space time diagrams that we showed at Minute 504 in the ...
 03:42: Some of the dots and we had placed in the two red guy and blue guy space time diagrams were placed inconsistently.
 04:32: ... notice that all the space time diagrams that I drew in the last episode were from the point of ...
 05:41: ... have another week, now, before we dive into Part 3 curved space time, and, finally, an explanation of Einstein's selfconsistent view of ...
 05:51: See you next week on "Space Time."


20150715: Can You Trust Your Eyes in Spacetime?
 00:00: We've talked before about flat spacetime here.
 00:02: But before we can graduate to the curves version and general relativity, we need a stronger foundation in spacetime geometry.
 00:08: So today, on "Space Time," it's spacetime.
 00:45: Eventually, we want to do the same thing in curved spacetime.
 00:47: However, tiny patches of curved spacetime don't look Euclidean.
 00:51: They look like flat spacetime, which although not curved, still has a geometry that doesn't always agree with our visual intuitions.
 00:57: So we won't know what to do in each tiny patch unless we first understand what straight line, tangent vector, and parallel mean in flat spacetime.
 01:07: Now, we're not going to do a complete treatment of special relativity or all aspects of flat spacetime geometry.
 01:22: Our principle tool for exploring flat spacetime geometry will be something called a spacetime diagram for representing physical events.
 01:38: This gravityfree world is what flat spacetime describes.
 02:21: Now recall from our earlier flat spacetime episode that points on this blackboard are not locations in a twodimensional physical space.
 02:28: Rather, they are events, each of which occurs somewhere along my axis in a onedimensional physical space and at some moment according to my clock.
 04:34: ... spacetime diagrams are great for visualizing cool phenomena like time dilation, or ...
 04:45: Instead, I just want to use these diagrams to establish how parallel transport works in flat spacetime.
 04:51: Because here's the thing, the answer is not clear a priori since you can't trust your eyes in spacetime diagrams.
 05:04: And thus, these are the same line segments in spacetime.
 05:19: ... spacetime diagrams preserve the spacetime interval between points with its weird ...
 05:30: So while these diagrams help quasivisualize things, spacetime doesn't really look like this.
 06:07: For starters, this spacetime really is flat.
 06:44: But in spacetime, we can also distinguish those classes of observers geometrically.
 06:53: And that's kind of the whole point of talking about spacetime in the first place.
 06:57: ... world as geometric objects and relations in a tenseless mathematical space, we can discover facts about physics just by exploring geometry in that ...
 07:25: But that interpretation doesn't work on a spacetime diagram.
 07:34: So ordinary velocity would not be a frame invariant geometric vector in spacetime.
 07:39: Also, things don't move through spacetime.
 07:42: It's not this kind of space.
 07:44: Instead, we want to represent some aspect of dynamical motion over time through space as a static geometric object.
 08:17: It's called the monkey's 4velocity, even though that's a bit of a misnomer since there's no motion through spacetime.
 08:23: And more interestingly, the length of that vector, at least in the sense of spacetime interval length, is minus the speed of light squared.
 08:37: ... if we call the spacetime length of a 4velocity vector a spacetime speed, then the world line of ...
 08:54: Chew on all that because it's our departure point for talking about curved spacetime in the next episode.
 09:03: I know it's a lot to take in, but you've got a week to mull it over before we plunge headfirst into curved spacetime.


20150708: Curvature Demonstrated + Comments
 00:03: You guys had a lot of questions and comments regarding last week's episode about straight lines and curved spaces.
 04:19: ... Shi and SamBskate were both asking how the dimensionality of the ambient space in which the surface of the sphere is embedded namely, the 3D ambient ...
 04:31: The ambient space is just there as a visual aid for you, but everything we've been discussing is intrinsic to the sphere itself.
 05:00: Therefore, you can determine just by living on Earth's surface that Earth's surface is a curved space.
 05:06: There is one point where I did mention the ambient 3D space, but only intrinsically, to talk about parallel transport in a 3D space.
 05:27: ... you wanted to know if the three dimensional space around Earth is curved, you would follow the procedure of using ...
 05:39: If you do, then the 3D space around Earth is flat.
 05:42: But if you don't, then the 3D space around Earth is curved.
 05:46: Finally, aamod joshi asked, how can two geodesics actually converge or diverge in a curved space?
 05:58: If they do, you know your space is curved.
 06:24: I hope this explains away some of the confusion you guys were having regarding geodesics and curved spaces.
 06:29: I wanted to make sure this was on better footing before we moved on to flat spacetime geometry in the next episode.
 06:34: ... after that, we'll be putting the notions of curvature and flat space time together to discuss what curved space time is, what the curves and ...
 06:46: All of that will be coming up in the forthcoming episodes of Space Time.


20150702: Can a Circle Be a Straight Line?
 00:05: Instead, he said, it's a manifestation of spacetime curvature.
 00:16: ... they're simply following straight line constant speed paths in a curved spacetime. ...
 01:02: ... way around those objections is to realize that if the world is a curved spacetime, then the familiar meanings of terms like a constant velocity straight ...
 01:33: ... we really mean by straight line and by flat verses curved mathematical spaces. ...
 01:42: In part two we'll acquaint ourselves with the specific geometry of 4D flat spacetime, which is already weird, even without curvature present.
 01:50: ... finally, in part three we'll put curvature and spacetime together to tie up all the loose ends that we raised at the end of our ...
 01:57: We'll end up seeing that all the supposedly gravitational effects on motion can be accounted for just by the geometry of spacetime.
 02:17: Today is part one, that's straight lines and curved spaces with no physics, just geometry.
 02:33: ... if we want to do geometry on arbitrary spaces like on the surface of a sphere or a saddle or on some funky hillside, ...
 04:08: ... and straight that it can apply solely within that two dimensional space. ...
 04:47: By the same process you can find geodesics on a saddle or a hillside or in three dimensional spaces.
 04:56: ... though it's not the shortest curve joining A and B. In fact, in some spaces that have weird distance formulas, like flat spacetime, geodesics are ...
 05:15: And in other curved spaces, multiple straight lines can join the same two points.
 05:19: As a result, the notion of distance between two points is ambiguous in a curved space.
 05:29: All right, now that we know what it means for a line in a given space to be straight, let's figure out what it means for an entire space to be curved.
 05:48: If the result you get is the same, same vector at point B, then your space is flat, otherwise it's curved.
 06:00: If you end up with the same vector you started with, your space is flat.
 06:11: If they always remain parallel, your space is flat.
 06:14: But if those geodesics start converging or diverging at any point, then the space is curved.
 06:46: The difference between the cylinder and the plane in topology, i.e. in the connectedness of different regions of the space.
 06:57: Now in a three dimensional space you can test curvature the same way we've been describing.
 07:03: If you end up with the same vector you started with space is flat, if not, it's curved.
 07:17: So is the three dimensional space around Earth curved?
 07:24: And 3D curved space isn't what explains away gravity, it's four dimensional curved spacetime.
 07:29: Why is the spacetime part so critical?
 07:31: To understand that, we need to get a better grip on how geometry works in flat spacetime.
 07:40: In flat spacetime that line has a length of zero, and these two lines are perpendicular.
 07:49: Flat spacetime geometry is part two, which is next week.
 07:51: To prepare for that, you should watch our episode "Are Space and Time an Illusion?" Watch it like 10 times.
 08:07: In the meantime, you can put your questions about geodesics and curved mathematical spaces down in the comments below.
 08:12: ... do my best to address them during the week and on the next episode of "Spacetime." Last week we asked whether Australia would ever get a White Christmas in ...


20150624: The Calendar, Australia & White Christmas
 02:22: But it doesn't track Earth's 360degree orbit in space the way you might think.
 02:33: So the location in space of January 1 is constantly moving.
 05:27: If we're a spacefaring species by then, then locking time exclusively to Earth's seasons might be weird.
 05:50: That's our episode, Space Timers.
 05:58: Also, if you'd like to see an episode on what Earth's orbit and rotation really look like in space and why, let us know that, too.
 06:04: ... usual, I'll report and respond on the next episode of "Space Time." Last week we talked about different possible ways to signal ...
 06:27: And the operating assumption of SETI for several decades is that maybe aliens are broadcasting such a beacon into space.


20150617: How to Signal Aliens
 00:50: ... to pick up the radio and TV transmissions that we've been leaking into space since around World War ...
 00:58: ... growing consensus is that, even if nearby aliens have spacebased radio receivers with the total area equivalent to a large city pointed ...
 02:53: So you could target the pulse to individual star systems and avoid wasteful transmission into empty space.
 04:49: ... if that could be automated or if space maintenance missions inside the solar system become easier for us in the ...
 06:07: As always, I'll report back on the conversation on the next episode of Space Time.
 08:42: ... only ones that are relatively close to the origin of your frame in both space and ...
 09:30: The frame of the falling van should be equivalent to a frame that's an intergalactic space away from gravity.
 09:35: Now, if you put a helium balloon, even in a van filled with air in intergalactic space, how would it know which way to go?
 10:12: ... by letting it free fall or alternately going out to intergalactic space, the air below doesn't have to hold the air above ...


20150610: What Happens to a Helium Balloon in Freefall?
 00:00: [SOUND EFFECTS PLAYING] [MUSIC PLAYING] Hey, Space Timers.
 01:31: And I'll see you next week with the answer to the challenge and a fresh episode of Space Time.


20150603: Is Gravity An Illusion?
 01:02: That's just some XYZ axes to label points in space and a clock to track time.
 06:19: The falling frame of the box behaves just like a stationary inertial frame that's way out in intergalactic space where there's no gravity.
 07:02: Stationary frames in intergalactic space pass that test.
 07:11: More to the point, Newton, if you're inside the box, there's no way for you to know that you're not in intergalactic space.
 08:27: Second, by your criterion, Einstein, orbiting frames of reference like on the space station should also be considered inertial.
 09:00: ... instead the world is a nonEuclidean and curved spacetime, then straight line at constant speed doesn't mean what you think it ...
 09:26: And one of the central precepts of general relativity is that we inhabit the curved spacetime.
 09:30: And in that curved spacetime, the orbit of the ISS is a constantspeed straight line.
 10:03: We'll reconvene next time our accelerated paths cross in curved spacetime.
 10:16: Many of you asked about the upcoming James Webb Space Telescope or JWST.
 11:35: ... suggested that maybe interest in space without sensationalist headlines won't happen until space travel becomes ...


20150527: Habitable Exoplanets Debunked!
 05:34: ... was a proposal for a terrestrial planet finder, or TPF, a space telescope that could have analyzed the atmospheres of Earthsized ...
 06:41: ... comments, and we'll see what you guys have to say on the next episode of "Space Time." Last week, we talked about e equals mc squared and issued a ...
 07:10: ... true, if aliens came along with some spaceships and lowered down some cranes and lifted the hammers for you and put them ...
 08:15: This is PBS "Space Time," and we have standards.


20150520: The Real Meaning of E=mc²
 02:59: ... that rest mass is a property all observers agree about, much like the spacetime interval that we discussed in a previous ...
 09:11: ... must also have correct explanations to count, on the next episode of "Space Time." Last week we talked about NASA ...
 09:25: ... NASA spinoffs microwave ovens, Tang, Velcro, cordless power tools, the space pen, MRI machines none of those are NASA ...
 09:39: Ryan Brown brought up space blankets, David Shi brought up oxygen permeable contact lenses, and UndamagedLama2 brought up robotic endoscopic surgery.


20150513: 9 NASA Technologies Shaping YOUR Future
 00:21: Problem say you're an astronaut working outside the ISS using a wrench for hours at a time while wearing a bulky spacesuit.
 00:48: ... and repetitive motion stress for astronauts working on equipment during space ...
 00:56: Next problem the space station orbits Earth so fast that each new sunrise happens every 90 minutes.
 01:50: ... you'd want to make the spacecraft a selfcontained, closed ecosystem that can produce its own oxygen, ...
 03:34: Next problem, a space shuttle take off.
 04:45: Inside a space suit, a rise in core body temperature from overexertion could be incredibly dangerous since there's no easy way to get that heat out.
 04:54: So how do you monitor a person's core temperature when that person is inside a space suit, floating in space?
 05:51: ... problem, say you want to grow plants in space for food and oxygen. Now, plants need water, which is a precious ...
 05:59: So, how do you know when to water plants in space?
 06:41: We might shout you out on the next episode of "Spacetime." Last week we asked whether the first Mars mission should be all women.
 06:50: ... below and let us know the kind of material that you'd like to see on "Spacetime." Second, in next week's episode I'll be explaining some more relativity ...
 07:03: Not directly time and space things, something else, but there will be a challenge question posed at the end of next week's episode, so please tune in.
 08:27: ... we should send men and women in order to collect more data on long term space travel for both sexes, and 99sins said that this whole thing seems to ...
 08:56: ... up osteoporosis as a bigger negative for women, and the reason is that spaceflight basically gives everyone the equivalent of osteoporosis, and so far men ...


20150506: Should the First Mars Mission Be All Women?
 00:18: Look, it's no secret that we here at "Space Time" love the idea of cloud cities on Venus.
 01:21: ... accompanied by anatomical changes to the eye, both during and after space ...
 01:58: Women are more prone to space motion sickness when they first hit zero G, but that goes away.
 02:24: It's why NASA allows women only half as much lifetime space flight as it allows men.
 02:54: Well, the same NASA study reports no sexbased difference in psychology or behavior during spaceflight.
 03:03: However, other sources and space programs tend to give women the edge in this category.
 03:07: ... example, the British newspaper "The Guardian" reported Chinese space officials as saying that their female astronaut candidates exhibit ...
 03:45: There's still another argument for preferring women to men on longer space missions namely that it costs less to send them to other planets.
 04:55: For whatever reason, the calorie requirements in space and on Earth are basically the same.
 05:55: ... need to add fuel to move that fuel and so on and so on this is why space flight costs so much ...
 06:33: ... even if SpaceX manages to get those launch costs to 1/10 of what I've quoted, we're ...
 07:23: ... report on the evolving discussion on the next episode of "Space Time." Last week we asked what the most realistic artificial gravity in ...
 09:43: The reason is that if he's driving along the axis of the space station, there would be no Coriolis effects.
 10:25: The more people we get watching, the better we can make "Space Time."


20150429: What's the Most Realistic Artificial Gravity in SciFi?
 00:24: ... rationale for inventing some kind of mechanism for artificial gravity on spaceships. ...
 00:58: There's simply no known way to produce the equivalent of 1 Earth g on stacked, flat surfaces, like decks of a ship, in any localized region of space.
 01:20: ... way we know of to get artificial gravity, namely rotating your spaceship. ...
 02:10: ... there's a radially outward directed "gravity." Now, if you were out in space, Earth's real gravity, which also pulls you down, wouldn't be in the ...
 03:05: Let's start with the iconic scene of Frank Poole jogging around the rotating command module in "2001: A Space Odyssey." Poole's height is 1.8 meters.
 07:12: ... the closest thing I could think of was the space station on "Babylon 5." The key is that "Babylon 5" abandons the ring ...
 08:30: So I'll report any blanks that you all fill in for us on the next episode of "Space Time." Last week, we asked whether space and time are an illusion.
 09:20: Why exactly am I concluding that space and time are illusions?
 09:53: ... been present at both events, which corresponds to a zero or negative space time interval between those ...
 10:08: ... when we disagree about sequence, we're really agreeing that the space time interval between them is positive and that neither event could have ...


20150422: Are Space and Time An Illusion?
 00:00: [INTRO MUSIC] Today's episode is about space, time, and the nature of reality.
 00:09: ... name is Gabe, and this time, it really is "Space Time." [THEME MUSIC] If you pay attention, this episode is going to ...
 00:25: What is spacetime, exactly?
 00:31: Give up your intuitions about how time and space work.
 00:46: Spacetime refers to whichever external reality underlies our collective experiences of the space between things and the time between events.
 00:55: Why can't space and time just be a reality?
 00:57: Why add spacetime as an extra concept?
 01:14: Fact they don't fully agree on how much space there is between things at any given moment.
 02:25: Or phrased another way, if time and space as we usually conceive of them aren't part of objective reality, then what is?
 02:46: It's called the spacetime interval, or spacetime separation between two events.
 02:52: ... elapsed times between the same two events, they always agree about the spacetime interval between those ...
 03:05: Now if everyone agrees about spacetime intervals, they must signify something.
 03:12: We'll notice that since it involves subtraction, a spacetime interval can be positive, zero, or negative.
 03:34: ... it appears that the spacetime interval between events A and B tells you whether A can influence B. In ...
 04:07: So what does causality have to do with spacetime?
 04:13: ... math professor of Einstein's named Hermann Minkowski noticed that the spacetime interval resembles a weird version of a distance formula in what's ...
 04:25: So he proposed the following radical idea maybe reality is not a three dimensional space that evolves in time.
 04:33: Instead, it's a four dimensional nonEuclidean mathematical space that's just there.
 04:42: That 4D mathematical space is spacetime.
 04:50: And in this view, only things that correspond to geometric relations in that 4D space are objectively real, like for instance, causal relations.
 05:01: They correspond to spacetime intervals, which are geometric relations, a nonEuclidean version of the distances between points.
 05:08: In contrast, our experiences and measurements of time and space don't correspond to anything, per se.
 05:31: ... the events of which you were present, then you are a geometric object in spacetime, a line segment joining the points representing the events of your birth ...
 05:47: There's no motion through spacetime.
 05:49: It's not this kind of space.
 05:57: There's some zen in trying to express what spacetime is without misleading you, but I think the following gets the flavor right.
 06:39: So have I told you all there is to know about spacetime?
 06:43: All of this has just been a loose introduction to what's called a flat spacetime.
 06:47: ... relativity entered the mix, we'll find that there are many possible spacetimes with different geometries, making it hard to ascertain which one this ...
 07:05: I'll do my best to answer them at the next causallyconnected point of spacetime.
 07:15: Daniel Jenkins commented that a spacebased zombie outbreak assumes that a more virulent organism would actually spread better.
 07:22: It's enough for the bug to just be more harmful and harder fight off with your spacedepressed immune system.
 07:27: ... second, as Nicholas Garrison pointed out, germs do spread more easily space capsules for a variety of reasons, including the fact that the gunk in ...
 07:38: Joe G.P. and Dikasad2 both asked what it is about space exactly that enhances virulence?


20150415: Could NASA Start the Zombie Apocalypse?
 00:13: Could a zombie apocalypse start with a routine trip to space?
 01:08: But maybe they should because one scenario that's more plausible than you might think is that a zombie apocalypse could start in space.
 01:16: But spaceflight introduces some unique wrinkles into how infectious diseases might originate and spread.
 01:22: In 2006, researchers sent some salmonella on the space shuttle, brought it back down to Earth, and then infected mice with it.
 01:46: Bottom line, a few days of spaceflight can make certain bacteria significantly deadlier.
 02:18: ... blood samples taken from astronauts during various stages of spaceflight show reactivation of dormant viruses that they already carry like ...
 02:32: Now this could be happening due to changes in the viruses themselves or because space flight generally weakens the human immune system or both.
 02:47: Now zombies aside, NASA and other space agencies research infectious disease extensively.
 02:52: But that research is tricky because you need to put people in space for long periods to collect data.
 03:24: Plus, the future of space travel won't just be government space agencies.
 03:28: ... you fast forward a few decades, you're going to have an era of space tourism or space hotels where ordinary people are taking vacations to ...
 03:35: ... most space passengers aren' t professional astronauts anymore, you are going to ...
 03:52: So to recap, space flight can strengthen and change the operation of pathogens.
 04:06: Since our understanding of the nuances of disease in space is still in its infancy, it's not like anyone was in a position to say its impossible.
 04:16: Will the zombie apocalypse start in space.
 04:18: Should fear of "The Walking Dead" feature space flight in its upcoming origin story for the "Walking Dead" zombie virus.
 04:23: Let us know in the comments along with any cool scenarios you might have in mind for a good, spacebased zombie apocalypse backstory.
 04:29: I will report the best ones on the next episode of "Space Time." Last week's episode was about farting your way to the moon.
 05:37: ... asks, "Could you not swim through space?" There were a lot of responses indicating no because there's nothing to ...
 05:45: ... directing me to a paper by an MIT physicist indicating that in a curved space time, you may actually be able to do this actually have reactionless ...


20150408: Could You Fart Your Way to the Moon?
 00:07: Could you fart your way through space?
 00:09: [THEME MUSIC PLAYING] If space suits didn't put a firm barrier between you and the outside environment, space would kill you.
 00:20: ... with a special valve that would allow you to pass gas into the vacuum of space. ...
 02:23: The same is true inside the space station.
 02:33: But in the near total vacuum of space, expelling gas would have to make you move.
 03:47: Cutting the cheese just won't cut it for long distance space travel.
 03:53: But maybe your space travel goals are more modest.
 05:32: If you stick to moving sideways, can technically fart your way through space, but you're much better off peeing.
 05:58: ... always, I'll report any findings on the next episode of "Space Time." Last week I considered whether the moon in Majora's Mask might ...
 06:10: This weekend, April 11 and 12, I'll be hosting NASA's Space Apps Challenge at the Main Stage in New York City.
 06:19: Check out spaceappschallenge.org.


20150401: Is the Moon in Majora’s Mask a Black Hole?
 06:05: Leave some empty space around it for good measure, and this might work.
 06:54: If I did, I'm sure you SpaceTimers will let me know.
 07:00: ... you come up with or conclusions you find on the next episode of "Space Time." Last week we talked about why the cosmic microwave background ...
 07:13: ... April 11 and 12, I will be hosting part of NASA's International Space Apps Challenge, a global, multicity twoday hackathon where people, ...
 07:29: For more information and to register to participate, go to spaceappschallenges.org.
 07:37: Now, back to why space used to be orange.
 07:39: KnowledgePlaylists asks, isn't the color space Cosmic Latte?
 07:53: Kieron George and Sergio Garza were discussing whether water could have existed when space went dark.
 08:56: However, that's only if you're moving along with the overall cosmic expansion of space.
 09:27: But once I do, if they check out, I'll report the answers here on "Space Time." [MUSIC PLAYING]


20150325: Cosmic Microwave Background Explained
 00:00: Outer space looks black, but the entire universe used to be this color.
 00:12: Stars and galaxies notwithstanding, space is pitch black.
 00:29: ... microwave band static that's just always there in the darkness of space, emitting the same pattern over and ...
 01:13: And what if I also told you that the source of the CNB also caused all of space to look orange for millions of years?
 02:38: Problem is, space is pretty much empty.
 02:51: To answer that and to see why space used to be orange, we need to turn the clock back to about 400,000 years after the Big Bang, give or take.
 03:00: During that era, a supercharged particle with a temperature of several thousand degrees permeated all of space.
 03:43: So at this moment, it was as if flash bulbs were constantly going off everywhere in space, but the light was being snuffed out by a fog.
 04:21: Before, during and after this event, space was expanding.
 04:28: ... we talked about in a prior episode that you can revisit here, expanding space stretches the wavelength of free streaming light through a process ...
 04:52: ... you throw in another 13 plus billion years of space expansion, all that light has redshifted into the microwave band to ...
 05:10: ... is pretty compelling evidence that when it comes to the color of space, black is the new ...
 05:24: I'll tackle as many as I can on the next episode of "Space Time." Last week, I challenged you to stabilize a gyrodriven Star Fox barrel roll.


20150318: Can A Starfox Barrel Roll Work In Space?
 00:00: Few things exhibit as much as disdain for basic physics as the space levels in Nintendo's "Star Fox," except the barrel roll.
 00:10: [MUSIC PLAYING] Space battles in games and movies are laughably unrealistic.
 00:25: Joe Hanson, over at "It's Okay to be Smart" has a great episode on how pop culture gets space battles all wrong.
 00:38: In general, "Star Fox" flushes physics down the toilet during the space levels.
 00:49: Now, let me be clear, we're only talking about the space levels.
 01:40: Back to space.
 01:41: Ailerons don't do anything for you in space, because there's no air pushing on the wings.
 01:54: There's basically no friction in space.
 02:36: But in space, there's no air to push on the wings.
 04:51: So that, more or less, is a barrel roll in space.
 04:56: Space telescopes, like Hubble and Kepler, also use angular momentum conservation to turn without thrusters.
 05:42: ... there are still lots of unanswered questions, including what a space meter is, which is apparently the official unit of measurement in the ...
 07:00: ... shout out people who submit correct answers on the next episode of "Space Time." Last week, we talked about what might destroy planet Earth, and ...
 08:28: ... so much empty space between star systems and galaxies that the probability of any two of ...


20150311: What Will Destroy Planet Earth?
 04:21: See, the growing sun will also develop a stronger solar wind that sprays a lot of the sun's material out into space.
 05:14: ... of that process the expansion not as galaxies flying apart through space, but instead as the space between distant galaxies stretching, like ...
 05:22: Note that the Earth and you and I stay in one piece because the space inside galaxies is not stretching at least not yet.
 05:29: ... properties of this mysterious dark energy that can be used to do some space expansion ...
 05:43: ... data, sometime between 100 billion and a few trillion years from now, space could start to stretch not just at faster rates, but on smaller and ...
 05:54: ... until literally, everything in a universe is ripped apart by stretching space atoms, nuclei, individual protons, ...
 06:15: ... up to further experiments, I mean, having your atoms disassembled by space itself would be a pretty epic way to ...
 06:42: We'll see what you all came up with on the next episode of "Space Time".
 07:13: Maybe we should be building floating colonies in space.
 07:26: ... that exercise alone can recover the bone density astronauts lose in space it can recover the density, but the structural integrity seems to be ...


20150304: Should We Colonize Venus Instead of Mars?
 00:42: And that hurts our sister planet, not just in culture and media but in space policy.
 01:29: ... colonize another world, because bear in mind, there's no Craigslist in space. ...
 01:53: That means better protection from space radiation and meteorites for our enterprising colonizers and their future cities.
 04:33: That means humans would need heatresistant clothing and oxygen masks, but not spacesuits to walk around in that environment.
 06:07: If we start a grassroots movement, I'll let you know on the next episode of "Space Time".
 06:16: awtizme asked, how can space be expanding faster than light if the speed of light is the ultimate speed limit?
 06:23: First, the speed of light speed limit is for things moving through space, not about expansion of space itself.
 06:29: I shouldn't be talking about space expanding at a given speed.
 06:54: We're talking about expansion of space in general.
 06:56: Inflation refers to a very specific expansion of space that occurred in just the first few instances after The Big Bang.
 07:02: The Mattman1313 says that the Hubble Bubble is a possible alternative to the idea that space is expanding at all.
 07:10: Space is expanding period.
 07:11: What the Hubble Bubble offers is a potential alternative to the currently observed, accelerated expansion of space.
 07:19: And to Brandon Spears, sure, we could always use help here at "Space Time".
 07:22: Like the Hubble Space Telescope, we've got schmutz on our lens too, so give it a wipe and help us out.


20150225: How Do You Measure the Size of the Universe?
 01:38: To understand why, it's critical to realize that space itself is expanding.
 01:47: Each raisin represents a cluster of galaxies in the dough space.
 02:05: It's just the relatively empty space between those large clusters of galaxies.
 02:18: ... two facts, the expansion of space and the fact that it can expand at a variable rate, complicate how we ...
 02:26: In fact, space itself can expand at any rate it wants to, even faster than the speed of light.
 02:32: So over the lifetime of the universe, the birthplace of a beam of light can be carried ridiculously far away by the expanding space dough.
 02:40: ... and calculate the size of the universe, you need to know how quickly space has been expanding at every moment in history, ...
 02:53: Using something called cosmological redshift, which is like a fingerprint that the expansion of space leaves on beams of light.
 03:07: ... space were not expanding, then light from a distant galaxy would be the same ...
 03:14: But because space is expanding, the wavelength of light gets stretched as it travels to us, making the blue light red; hence, the term redshift.
 03:39: So it spends more time in the expanding space, in the rising dough.
 04:54: ... history, those imaginary beams would travel through the expanding space and reach us at different ...
 05:32: ... on any interesting threads from that conversation on the next episode of "Space Time." Last week, we asked whether it's irrational to believe in ...
 05:42: PantsuMann and others point out that it would really low odds to accidentally bump into a "Millennium Falcon" in space.
 06:04: ... that a really advanced civilization might not try to expand outward into space, but inward into, let's say, advanced computer circuitry, pretty good ...


20150218: Is It Irrational to Believe in Aliens?
 04:17: ... species that's jetted around the cosmos, something like radio signals, space station probes, a broken down Millenium Falcon, I don't know, an alien ...
 04:37: ... if our ability to send stuff into space isn't special, and alien intelligence really is inevitable on the ...
 05:07: Maybe aliens hate exploring space, OK.
 06:40: Anyway, now you know how legit scientists and scholars handle the question of space aliens.
 06:53: I'll report any interesting findings on the next episode of "Space Time." Last week we asked, what planet is Super Mario World?
 07:11: The Gentleman Physicist points out that Super Mario World could be a platform accelerating through space with rockets at 70 meters per second squared.


20150211: What Planet Is Super Mario World?
 00:10: My name is Gabe, and this is "Space Time." [MUSIC PLAYING] So how can we understand Mario's crazy jumping ability?
 01:14: Low gravity, for instance, is why astronauts in heavy spacesuits could jump so high on the moon.
 05:55: I'll report any interesting discoveries on the next episode of "Space Time." And hey, if you like space stuff, please subscribe.
