
20221019: The Equation That Explains (Nearly) Everything!
 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 ...


20221012: The REAL Possibility of Mapping Alien Planets!
 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 ...
 14:06: ... worlds, brought into focus by our own Sun and its lens of curved spacetime. ...


20220803: What Happens Inside a Proton?
 09:50: ... that is much harder to do, for three reasons. First, any patch of spacetime technically contains an infinite number of points and ...
 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. ...


20220720: What If We Live in a Superdeterministic Universe?
 07:40: ... point in space and time  every event  can only be influenced by a spacetime event in its causal past  so, near enough to have sent a ...
 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.


20220615: Can Wormholes Solve The Black Hole Information Paradox?
 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. ...


20220504: Space DOES NOT Expand Everywhere
 01:59: ... metric. You can think of a metric as the coordinate system of a patch of spacetime. ...
 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: ... of 3D spaces. But those 3D spaces are also just slices out of 4D spacetimes  representing single instants in time. If you use general relativity to ...
 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: ... gravitational field isn’t somethin,g that lies on top of the fabric of spacetime. The gravitational field IS the fabric of spacetime. If the gravitational ...
 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 ...
 08:34: ... certain regions expansion won, and threw apart objects and the spacetime grids they trace. But in sufficiently dense regions gravity won and ...
 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 ...
 13:16: ... we never would have even known that we live in an infinitely expanding spacetime. ...


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 ...


20220330: Could The Universe Be Inside A Black Hole?
 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.
 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 ...
 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.
 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, ...


20220323: Where Is The Center of The Universe?
 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.
 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.
 08:58: In the language of GR, we call this ending of spacetime paths “geodesic incompleteness”.
 09:19: ... it occupies all space at t=0 and is in the past of all paths through spacetime. ...
 13:51: ... even you personally, are not at the very center of a very nonCopernican spacetime. ...


20220316: What If Charge is NOT Fundamental?
 13:24: We’ll find out soon as we continue to unravel the tangled symmetries of spacetime.


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. ...
 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.


20220223: Are Cosmic Strings Cracks in the Universe?
 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?
 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 ...
 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 ...


20220210: The Nature of Space and Time AMA
 00:03: ... general as possible in fact that covers the entire scope of this show spacetime and so the topic for the day is the nature of space and the nature of ...


20220127: How Does Gravity Escape A Black Hole?
 02:02: For example we have gravitational waves  ripples in spacetime caused by certain types of motion.
 03:34: In GR, the gravitational field  the curvature of spacetime  has an independent existence to the mass that causes it.
 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 ...
 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.


20220112: How To Simulate The Universe With DFT
 13:51: Our computationally tractable reality, due to its very few dimensions of spacetime.


20211210: 2021 End of Year AMA!
 00:02: ... object whose light traveling through einstein's universe of curved spacetime follow curvy paths and sometimes those curvy paths are deflected ...


20211117: Are Black Holes Actually Fuzzballs?
 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.


20211110: What If Our Understanding of Gravity Is Wrong?
 08:35: ... field  a multicomponent object that describes the curvature of spacetime. ...
 14:54: For more information, go to curiositystream.com/PBSSPACETIME and use the code SPACETIME for a trial.
 16:46: Isn’t it spacetime that bends, not light?


20211102: Is ACTION The Most Fundamental Property in Physics?
 12:16: ... this to relativity we see the configuration space becomes configuration spacetime, where the shortest path minimizes proper time. In quantum mechanics ...
 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 ...


20211013: New Results in Quantum Tunneling vs. The Speed of Light
 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.


20210810: How to Communicate Across the Quantum Multiverse
 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 ...


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.


20210707: Electrons DO NOT Spin
 13:30: ... things we call spinors  strange little knots in the subatomic fabric of spacetime. ...


20210616: Can Space Be Infinitely Divided?
 05:45: ... and second, that mass and energy warp the fabric of spacetime. So back to Heisenberg’s ...
 09:58: ... subatomic scales, on the Planck scale you get virtual spacetime fluctuations, and even virtual black holes and wormholes  ...
 10:55: ... we can’t sensibly define distances. We think that space AND time  spacetime  “go quantum” at that scale  but we just don’t know in ...
 11:26: ... what might lie beneath the smallest possible scale of measurable spacetime. ...


20210525: What If (Tiny) Black Holes Are Everywhere?
 11:07: ... black hole, a tiny hole punctured in your neighborhood’s fabric of spacetime. ...


20210421: The NEW Warp Drive Possibilities
 04:01: ... distribution of mass, energy, on the right side and it spits out the spacetime geometry on the ...
 10:31: The entire patch of spacetime would travel at superluminal speeds, carrying a spaceship with it.


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 ...


20210316: The NEW Crisis in Cosmology
 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?
 06:31: To get technical: any massive object has a component of its 4dimensional spacetime velocity  its 4velocity in the time direction.
 12:38: ... of some more fundamental reality underlying this generally relative spacetime. ...


20210224: Does Time Cause Gravity?
 02:09: We can show this with our old friend the spacetime diagram.
 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.
 03:54: Objects don’t just have a velocity through space or through time  they have a velocity through spacetime.


20210217: Gravitational Wave Background Discovered?
 00:00: ... exactly what it was built to detect vast ripples in the fabric of spacetime produced by colliding black holes a billion light years away since then ...


20210210: How Does Gravity Warp the Flow of Time?
 01:45: John Archibald Wheeler put this notion the most pithily: Spacetime tells matter how to move; matter tells spacetime how to curve.
 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.
 07:58: The spacetime path or worldline of the lab is a helix, and the lab’s perception of “now” is this shifting plane.
 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. ...


20210119: Can We Break the Universe?
 04:07: The best way to see this is on a spacetime diagram.
 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 ...
 06:20: But to see why we need a much weirder version of the spacetime diagram.
 06:29: We end up with a spacetime cylinder.
 09:46: Again, the best way to see this is on a spacetime diagram.
 11:12: The answer is in our looped spacetime diagram.
 12:05: ... deeply strange, but unfailingly selfconsistent theory of Einstein’s spacetime. ...


20201104: Electroweak Theory and the Origin of the Fundamental Forces
 13:19: ... they enable, inevitable consequences of the broken symmetries of spacetime. ...
 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 ...
 08:49: ... traced indefinitely into the past and future. All of spacetime should be a smooth, if curved structure  a manifold  ...
 12:11: ... how light rays travel and terminate at the singular dead ends of spacetime. ...


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.
 00:16: ... song) In the last episode, we saw that we could think of the unified spacetime in terms of the block universe, an a temporal entity that sort of just ...
 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.


20201013: Do the Past and Future Exist?
 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.
 08:02: At the same time, their entire perception of the spacetime grid is warped due to their motion.


20200824: Can Future Colliders Break the Standard Model?
 13:17: Of coordinating thousands of scientists over many decades to build these crazy machines that can crack open the inner workings of spacetime.


20200817: How Stars Destroy Each Other
 10:10: ... little petulant. Like the final slamming of doors from distant parts of spacetime. ...
 14:07: Here’s a simulation from the SXS  simulating extreme spacetimes group at ... that shows how the event horizons merge.


20200810: Theory of Everything Controversies: Livestream
 00:00: ... many many tiny constituents which are sometimes called the atoms of spacetime but um you know you shouldn't take this too seriously in any case the ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... of sort of the quantum qubit structure informational structure of spacetime right i mean even as an experimentalist you know with six years 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 ...
 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.


20200630: Dissolving an Event Horizon
 00:57: In the most real possible sense, the interior of the black hole is its own separate spacetime, excised from our universe.
 03:34: As the spin of a Kerr black hole increases, the spacetime waterfall is beaten back, and so the inner horizon grows.
 10:59: ... upcoming deeper dive to witness the horrors of the cosmicly uncensored spacetime. ...
 12:08: ... singularity, and the narrowing of the funnel represents extremely curved spacetime. ...


20200622: Building Black Holes in a Lab
 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 ...
 12:34: ... Hawking radiation, and the nature of the underlying, you guessed it, spacetime. ...


20200615: What Happens After the Universe Ends?
 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.
 04:41: This is a spacetime diagram.
 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 ...
 06:26: 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 ...
 10:00: ... the full 4D spacetime the edge becomes a 3D “hypersurface” in which infinite distance and ...
 14:24: ... and try to have fun in this infinite chain of conformally rescaled spacetime. ...
 18:01: Well sorry Aurora, but if 2020 watches spacetime then in we’re trouble.


20200527: Does Gravity Require Extra Dimensions?
 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 ...


20200518: Mapping the Multiverse
 00:02: Or in physicsese, it’s the maximally extended Penrose diagram of a Kerr spacetime.
 01:47: It describes the way spacetime warps and flows in the vicinity of a spinning mass.
 05:33: ... order to create these maps of spacetime, physicists use the equations of general relativity to trace what we call ...
 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 ...
 08:24: This is the Carter time machine, after the aussie physicist Brandon Carter who did much of the early exploration of the Kerr spacetime.
 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.


20200511: How Luminiferous Aether Led to Relativity
 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 ...


20200504: How We Know The Universe is Ancient
 12:59: ... years since the fiery beginning of timeasweknow it, the birthday of spacetime. ...
 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: ... of space and the dimensions of time in a sense just all exist spacetime exists from the beginning of the universe to the end and we as ...


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: ... name is an embedding diagram  a 2D spatial sheet sliced out of 4D spacetime. ...
 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 ...
 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 ...


20200407: How We Know The Earth Is Ancient
 12:35: ... time, and it’ll do the same again. Into what I guess you could call deep spacetime. ...


20200331: What’s On The Other Side Of A Black Hole?
 01:38: ... the dimension of time. And maps of the universe in this 4dimensional spacetime also have coordinate singularities  for example around the black ...
 01:53: ... first map of the spacetime of a black hole was the Schwarzschild metric  a relatively simple bit ...
 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 ...
 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. ...


20200324: How Black Holes Spin Space Time
 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: ... case. But in the case of a Kerr black hole, this circular dragging of spacetime changes ...
 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 ...
 12:11: ... we drop below the event horizon into the deeper weirdness of the Kerr spacetime. ...


20200303: Does Quantum Immortality Save Schrödinger's Cat?
 13:20: eddybox on the spacetime discord asked about the quantum eraser, as did several people in the comments.


20200211: Are Axions Dark Matter?
 11:08: ... for one of the tiniest and most elusive potential particles in all of spacetime. ...


20200203: Are there Infinite Versions of You?
 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.


20200113: How To Capture Black Holes
 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 ...


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 ...


20191209: The Doomsday Argument
 16:05: ... while these are valid geometries for spacetimes that can be constructed within Einstein's general relativity, it's not ...


20191111: Does Life Need a Multiverse to Exist?
 12:04: ... popular  bubble universes forming in a larger exponentially expanding spacetime, and in each bubble the constants of nature  and especially the vacuum ...


20191104: Why We Might Be Alone in the Universe
 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.


20191021: Is Time Travel Impossible?
 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 ...
 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.
 07:55: Stephen Hawking showed that unless the cylinder is infinitely long this doesn’t work – unless you also modify the spacetime with negative energy.
 08:51: The maelstrom of spinning spacetime may generate closed timelike curves deep down below the event horizon.


20191015: Loop Quantum Gravity Explained
 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 ...
 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.
 07:58: ... connections contain all the information about spacetime, them maybe we can represent spacetime with these connections instead of ...
 10:10: Not with chunks of spacetime but with quantum circuits of gravitational field.
 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. ...
 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 ...
 16:47: 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
 00:14: And the rich harmonics of those vibrations, seen through gravitational waves, could hold the secrets to the nature of the fabric of spacetime itself.
 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?
 00:42: 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.
 01:48: ... 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 ...
 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.
 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.
 13:56: 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.
 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?
 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.
 14:20: ... answered by the smartest people on the internet  that is to say, other spacetime viewers  and sometimes by ...


20190826: How To Become an Astrophysicist + Challenge Question!
 10:46: ... bubble universes are forming across the great sir Eternally, inflating spacetime and every second more universes form than in the previous second because ...
 11:51: ... by subject line We'll select six correct answers to win your pick of spacetime merch From the merch store as well as the conference of the degree of ...


20190819: What Happened Before the Big Bang?
 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
 03:24: ... the world to learn whether or not we are the only living rock in all of spacetime ...


20190718: Did Time Start at the Big Bang?
 06:02: ... a geodesic which in general relativity is the shortest path between two spacetime coordinates These are the grids we use to map spacetime Remember that ...
 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. ...


20190701: Thorium and the Future of Nuclear Energy
 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 ...


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 ...


20190509: Why Quantum Computing Requires Quantum Cryptography
 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
 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 ...


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
 00:24: ... our 3+1 dimensional universe may better described as resulting from a spacetime one dimension lower – like a hologram projected from a surface ...
 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.
 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 ...
 13:15: The resulting column has a geometrically flat and finite surface that is a spacetime all on its own.
 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.
 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
 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 ...
 05:40: As a quick review: start with a graph of space versus time – a spacetime diagram – then compactify.
 07:44: ... inside, but at its boundaries the simple rules of noncurved, Minkowski spacetime ...
 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.
 13:32: ... space and the interior space – also called the “bulk”  as separate spacetimes with their own ...
 15:06: Stay tuned for the final installment of the holographic principle in notsoinfinitelydistant future of spacetime.
 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?
 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 ...


20190320: Is Dark Energy Getting Stronger?
 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.
 15:02: ... then you'll want to check out the course: Black Holes, Tides, and Curved Spacetime: Understanding ...


20190306: The Impossibility of Perpetual Motion Machines
 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
 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. ...


20190130: Perpetual Motion From Negative Mass?
 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 ...
 07:26: 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 ...


20190124: The Crisis in Cosmology
 13:12: ...and for what it'll tell us of the origin and fate of our expanding spacetime.


20181220: Why String Theory is Wrong
 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.
 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: ... pleased to announce today's episode is brought to you by our brand new spacetime merch store we have all new nerd tastic tshirts mugs hats posters and ...


20181107: Why String Theory is Right
 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.
 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?
 12:59: That will be the family of lattice field theories in which spacetime itself is defined on discrete grid.
 13:32: That said, for something that doesn't exist, they're surprisingly useful for describing the weird underlying machinery in our quantum spacetime.


20181025: Will We Ever Find Alien Life?
 13:15: And use the code spacetime during the sign up process.


20181010: Computing a Universe Simulation
 11:03: If you see your name, you are a lucky winner of a spacetime tshirt.


20181003: How to Detect Extra Dimensions
 00:43: ... one in particular described in a new paper, "Limits on the Number of Spacetime Dimensions from GW170817," by Pardoa, Fishbachb, Holzb, and ...
 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.
 03:56: 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 ...
 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.


20180920: Quantum Gravity and the Hardest Problem in Physics
 02:06: ... and general relativity blend them together into a combined and mutable spacetime. ...
 07:54: Standard quantum theories treat the fabric of spacetime as the underlying arena on which all the weird quantum stuff happens.
 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.
 11:23: 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. ...


20180905: The Black Hole Entropy Enigma
 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?
 13:07: ... we want to understand our own place in what so far seems an eerily empty spacetime. ...


20180823: How Will the Universe End?
 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.


20180704: Will A New Neutrino Change The Standard Model?
 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.


20180627: How Asteroid Mining Will Save Earth
 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. ...


20180613: What Survives Inside A Black Hole?
 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 ...


20180523: Why Quantum Information is Never Destroyed
 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.


20180425: Black Hole Swarms
 08:24: ... in what has to be the craziest and most terrifying environment in nearby spacetime. ...


20180418: Using Stars to See Gravitational Waves
 04:57: The universe is flooded with spacetime ripples.
 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. ...


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.
 02:04: On the spacetime diagram, this is a line with a 45degree angle from the vertical axis.
 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.
 06:53: 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.
 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.


20180315: Hawking Radiation
 00:50: ... could be dragged inwards to create a hole in the universe, a boundary in spacetime called an event horizon that could be entered, but from beyond which ...
 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.
 06:23: These can be used to approximate the effect of curved spacetime on quantum fields by smoothly connecting regions of flat space.
 11:49: ... the brilliant mind of Stephen Hawking and a mysterious quirk of quantum spacetime. ...


20180307: Should Space be Privatized?
 09:53: ... if you sign up at CuriosityStream.com/SpaceTime and use the premier code spacetime during the sign up ...


20180214: What is Energy?
 11:17: It's a clue to the deeper truly fundamental properties of spacetime.


20180124: The End of the Habitable Zone
 10:35: To support spacetime and learn more about brilliant, go to brilliant.org/spacetime and sign up for free.


20180110: What Do Stars Sound Like?
 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.


20171220: Extinction by GammaRay Burst
 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.


20171108: ZeroPoint Energy Demystified
 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
 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.


20171019: The Nature of Nothing
 11:18: ... of nothing and what it might tell us about the underlying workings of spacetime. ...


20171011: Absolute Cold
 07:34: ... if you sign up at curiositystream.com/spacetime and use the promo code spacetime during the signup ...


20171004: When Quasars Collide STJC
 10:08: ... understanding the incredible growth of the largest black holes in all of spacetime. ...


20170920: The Future of Space Telescopes
 11:40: They have to travel along the same spacetime fabric as light waves, after all.


20170913: Neutron Stars Collide in New LIGO Signal?
 03:09: This binary pair stirs up spacetime in its vicinity, creating ripples that travel outwards as gravitational waves.
 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 ...


20170830: White Holes
 00:37: ... to take this mathematical description of an inescapable region of spacetime. ...


20170824: First Detection of Life
 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.


20170816: Extraterrestrial Superstorms
 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 ...
 09:00: That makes each of us a tangled knot in the one single thread weaving back and forth across the reaches of spacetime.


20170802: Dark Flow
 09:40: ... region of the greater universe, beyond the horizon of observable spacetime. ...


20170726: The Secrets of Feynman Diagrams
 01:56: There are "Spacetime" tshirts at stake.
 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 ...


20170719: The Real Star Wars
 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: ... looking at the August 21st total solar eclipse, we made some SpaceTime eclipse ...


20170712: Solving the Impossible in Quantum Field Theory
 12:16: ... if you sign up at curiositystream.com/spacetime and use the promo code spacetime during the signup ...


20170707: Feynman's Infinite Quantum Paths
 08:10: This action quantity is a function of the particle's path through spacetime.
 15:07: Quantum field theory describes particles as a field vibration in 4D spacetime.


20170621: AntiMatter and Quantum Relativity
 05:45: The resulting Dirac equation describes the spacetime evolution of this weird fourcomponent particlewave function, represented by the symbol psi.
 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 ...
 14:02: ... where the vacuum energy can come to a rest in an eternally inflating spacetime, halting inflation in that ...


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 ...


20170419: The Oh My God Particle
 10:01: ... if you sign up at CuriosityStream.com/spacetime and use the promo code spacetime during the signup ...


20170329: How Time Becomes Space Inside a Black Hole
 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.
 02:23: Reversing causality means flipping the sign of the spacetime interval.
 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.
 03:29: ... than rs, that stuff in the two brackets describes extreme warping of spacetime. ...
 03:48: A negative spacetime interval still means causal movement.
 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 ...
 08:14: It's trying to swim upstream and failing against the faster than light cascade of spacetime.
 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: ... space blend together in what is perhaps the strangest place in all of spacetime. ...


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.
 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.
 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 ...
 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 ...


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.


20170215: Telescopes of Tomorrow
 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.
 00:54: 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.
 03:25: 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.
 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: ... in both space and time can be separated from that origin by the same spacetime interval as an event that is very distant in both space and ...
 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 ...
 10:23: ... 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 ...
 12:07: ... string theory, which proposes that particles that we see in regular 4D spacetime result from oscillations within many more coiled dimensions, socalled ...


20170125: Why Quasars are so Awesome
 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.


20170104: How to See Black Holes + Kugelblitz Challenge Answer
 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: ... below that shell remains comfortably flat, but above the shell, spacetime is cascading behind the shell towards the soon to be formed ...
 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?
 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.
 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.


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: ... time, allowing us to fit onto the one diagram the infinitely stretched spacetime in the vicinity of a black hole's event ...
 02:21: Below that horizon, but above the stillshrinking surface of the star, spacetime takes on the mad properties of the black hole interior.
 02:47: 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.


20161208: What Happens at the Event Horizon?
 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.
 02:30: 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.
 03:16: ... crawl out of the vicinity of the event horizon before escaping to flat spacetime, no longer following 45 degree ...
 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.
 04:42: 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.
 05:38: Let's drop a black hole into this spacetime.
 06:03: The compactified grid lines there now represent the stretched spacetime near the event horizon.
 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.


20161130: Pilot Wave Theory and Quantum Realism
 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?


20161109: Did Dark Energy Just Disappear?
 12:07: ... look at the evidence for dark energy, and its effect on the expansion of spacetime. ...


20161026: The Many Worlds of the Quantum Multiverse
 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.


20161019: The First Humans on Mars
 08:30: Be sure to help us out by using the promo code spacetime.


20161012: Black Holes from the Dawn of Time
 09:58: I mean, how long can the universe expect to hide vast numbers of holes punched in the fabric of spacetime?


20160914: SelfReplicating Robots and Galactic Domination
 09:45: Perhaps that's us, preparing to explore the young and still untamed reaches of this spacetime.


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.


20160803: Can We Survive the Destruction of the Earth? ft. Neal Stephenson
 01:58: Finding the answer is a big responsibility, possibly even too big for spacetime alone to handle.


20160720: The Future of Gravitational Waves
 04:14: We now have more confidence in our understanding of the spacetime around black holes.


20160615: The Strange Universe of Gravitational Lensing
 00:00: [MUSIC PLAYING] The curvature of spacetime plays tricks on our eyes.
 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.
 05:07: You can see the nearby spiral galaxy, whose gravitational field bends spacetime to create these paths.
 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.


20160525: Is an Ice Age Coming?
 13:58: ... as we learned when we studied Newtonian mechanics, is a feature of flat spacetime. ...
 14:10: Curved spacetime changes things.


20160518: Antigravity and the True Nature of Dark Energy
 11:48: Energy can be forever lost or gained from nothing within an expanding curved spacetime.


20160420: Why the Universe Needs Dark Energy
 02:46: Spacetime will be curved, no matter what.
 08:46: ... the insight we need to understand dark energy's effect on the future of spacetime. ...
 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. ...


20160413: Will the Universe Expand Forever?
 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." ...
 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.


20160406: We Are Star Stuff
 10:13: We are "starstuff." But more, we our universe stuff, the most complex component that has risen from a beautiful and chaotic spacetime.
 11:10: So constant time spatial curvature, which is different to the curvature of spacetime.


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.
 07:30: The cosmological constant represents something that can happen to our spacetime.


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 ...
 01:35: 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 ...
 04:26: Spacetime is stretched and squeezed as the wave passes by.


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 ...
 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.


20151125: 100 Years of Relativity + Challenge Winners!
 00:10: [THEME MUSIC] November 25, 2015 is the hundredth birthday of spacetime.


20151111: Challenge: Can you save Earth from a Killer Asteroid?
 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]


20151028: Is The Alcubierre Warp Drive Possible?
 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 ...
 02:24: ... 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.


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: ... ripples an outflowing fluctuation of expanding and contracting spacetime. ...
 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.


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.
 04:17: This transformation thing, it's like a mathy magic wand that you wave at your description of spacetime or your physical laws.
 05:31: As an example, there's a link to the derivation via the spacetime interval in the description.
 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 ...


20150930: What Happens At The Edge Of The Universe?
 00:54: This is "SpaceTime." OK.
 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.
 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.
 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.
 07:36: ... 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 ...


20150827: Watch THIS! (New Host + Challenge Winners)
 00:00: Hey, Spacetimers, two weeks ago we issued a challenge question.
 05:20: These are the Spacetimers.
 05:21: Spacetimers, this is Matt O'Dowd.


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 ...
 04:39: 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?


20150812: Challenge: Which Particle Wins This Race?
 00:30: No spacetime, no relativity.


20150805: What Physics Teachers Get Wrong About Tides!
 02:07: But curved spacetime will only add complexity without actually making things clearer.
 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.
 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.
 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.
 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 ...
 01:39: ... 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 ...
 03:22: 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.
 03:39: 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.
 05:09: But then again, so does Newton's flat spacetime picture that has gravity injected as a kicker.
 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.
 07:02: And around Earth, spacetime curvature manifests itself in clocks much more than in rulers.
 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. ...


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.
 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.
 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.
 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
 06:29: I wanted to make sure this was on better footing before we moved on to flat spacetime geometry in the next episode.


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 ...
 01:42: 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.
 04:56: ... B. In fact, in some spaces that have weird distance formulas, like flat spacetime, geodesics are sometimes the longest curves between two ...
 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.
 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 ...


20150603: Is Gravity An Illusion?
 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.


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 ...


20150513: 9 NASA Technologies Shaping YOUR Future
 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 ...


20150422: Are Space and Time An Illusion?
 00:25: What is spacetime, exactly?
 00:46: Spacetime refers to whichever external reality underlies our collective experiences of the space between things and the time between events.
 00:57: Why add spacetime as an extra concept?
 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 ...
 04:42: That 4D mathematical space is spacetime.
 05:01: They correspond to spacetime intervals, which are geometric relations, a nonEuclidean version of the distances between points.
 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.
 05:57: 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.


20150401: Is the Moon in Majora’s Mask a Black Hole?
 06:54: If I did, I'm sure you SpaceTimers will let me know.
