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	2022-12-14: How Can Matter Be BOTH Liquid AND Gas? 10:53: Here's another one. The lowest density solids in the universe, Aerogels are made the same way. A gel is a molecular scaffold full of water.
	2022-11-23: How To See Black Holes By Catching Neutrinos 00:23: There’s been a lot of hype about our shiny new observatories and the new windows to the universe that they open. 08:59: The most powerful AGNs are called quasars, and shine out from across the universe.
	2022-11-16: Are there Undiscovered Elements Beyond The Periodic Table? 16:37: ... cut off at some point, or else humanity is too surprisingly early to the universe. ... 16:47: And the cut off is when the universe is fully colonized by … yep, grabby aliens. 16:52: eliyah zayin has a thoughtful criticism of the use of the Copernican principle to argue that we can’t especially early in the universe. 18:25: ... why can’t I define my reference class as “those who observes an empty universe?” After all, I am my mental experience, and the mental experience of ... 19:26: So if this dynamic happened on earth it makes sense it could happen across the universe. 19:39: They may not be eaten - but they can’t emerge naturally in a fully colonized universe. 19:53: For example medic likes that we might one day be referred to as "the old ones”, with our ancient tec and ruins scattered across the universe.
	2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations? 00:02: Half of the universe is filled with expansionist alien civilizations, and it’s only a matter of time before they’ll reach us. 00:31: But even the current age of the universe is itself a blink of an eye compared to the amount of time yet to come. 00:38: ... burning for another hundred trillion years, and the heat death of the universe is a googol years in the future, that’s 1 with a hundred ... 00:48: From this point of view, we’re living pretty much at the beginning of the universe. 01:02: Which may mean that humanity is super early in the history of life in the universe. 01:14: ... expect to find ourselves in a particularly special place in the universe. ... 01:23: Named for Nikolaus Copernicus, who showed that the Earth is NOT the center of the universe, as previously thought. 01:46: ... which states that we can only find ourselves in a location in the universe capable of forming and supporting ... 02:14: Maybe the future history of the universe isn’t as hospitable to life after all. 02:22: I mean, how can we know what the future history of the universe will be? 02:43: ... and how we can use them to calculate other surprising things about our universe, including our expiry date, check out our video on the Doomsday ... 03:07: They try to answer it building a simple model of the emergence and spread of intelligent life in our universe. 04:23: In the first couple billion years, the universe didn’t contain enough heavy elements for rocky planets to form. 05:44: The number of hard steps is a big deciding factor in how fast the universe can spawn intelligent life. 13:34: ... time, in which some civilizations become grabby and spread through the universe, ending with a universe totally full of ... 13:58: It tells us that the colonization of the universe has already begun: in fact, around half of the volume of the universe is currently colonised. 14:33: Don’t expect to meet any aliens any time soon, even if they do fill half the universe. 15:02: ... if - then it may be that our empty sky is one piece of evidence for a universe filled with aliens rushing in to grab this rare remaining patch of empty ... 16:29: ... the paper we just discussed is correct, then humanity is early and this universe has countless trillions of years of life and civilization ahead of ... 19:21: ... a super deterministic universe, the not-actually-random RNG could be correlated with the event that ...
	2022-10-26: Why Did Quantum Entanglement Win the Nobel Prize in Physics? 00:00: ... who make sense of nature; those whose discoveries render the  universe more ... 00:08: But the 2022 Nobel has been awarded to three physicists who revealed that the universe is even stranger than we thought. 11:16: ... choosing the measurement direction,   so ultimately the universe has no  choice but to always hide the existence of hidden ... 12:27: One way or another, our Nobel laureates have revealed a universe stranger than many are comfortable with. 18:57: ... are black hole coordinate systems that seem to imply alternate universes beyond the singularity - but more likely that’s just an artifact of ... 19:52: ... of reality, slipping backwards into this infinite regress of imaginary universes. ...
	2022-10-19: The Equation That Explains (Nearly) Everything! 01:48: ... electromagnetism can be explained as being due to the fact that the universe has this particular rather simple symmetry - which we call a U(1) ... 06:36: ... behave and how they’ll interact with each other. Alone, this describes a universe with no matter whatsoever. The Fs are actually shorthand for the ... 09:24: ... make the universe more interesting by introducing some matter. That’s what the second term ... 13:49: ... correct masses, you can calculate behavior of any known particle in the universe. ... 15:40: ... those you who don’t know, quasars are the most brilliant objects in the universe. They are the hearts of galaxies. Maelstroms of power and mystery shining ...
	2022-10-12: The REAL Possibility of Mapping Alien Planets! 15:45: ... current value, and quickly approached 1/137 as   the universe cooled. By the time fhe first stars were formed ti was essentially ... 18:29: ... constant isn’t even relevant. There aren’t many natural places in the universe   where this happens today. Not in the centers of stars or accretion ... 20:21: ... was set when the 4D experimentalists   coding our universe meant to type "1337" for the seed phrase and made a typo. ...
	2022-09-28: Why Is 1/137 One of the Greatest Unsolved Problems In Physics? 04:50: ... clear the number is trying to tell us something important about the universe, and now more than 100 years after Sommerfeld  discovered the ... 08:33: ... don’t know why our universe  ended up with this particular   value for the fine structure ... 08:41: Many physicists believe that these constants  were set more or less randomly at the beginning of the universe. 08:49: ... allow for the formation of life - unless of course there are many, many universes with different values for the ... 10:14: It’s equal to 1/137-ish for everyone in the universe. 12:43: ... represents the relationship between many real, physical aspects of the universe, seems to be telling us ... 13:51: ... and we don't know how He pushed the pencil.” In other words, to build a universe it may be that only one number needs to be decided in the beginning and ...
	2022-09-21: Science of the James Webb Telescope Explained! 04:00: A big one is to study the early universe. 04:03: The very first galaxies shone with intense ultraviolet light as the dense, young gas of the early universe collapsed into the first stars. 04:11: ... now been traveling to us for most of cosmic history, and the expanding universe has stretched the light by more than a factor of ... 05:09: ... which is an important step towards finding other life out there in the universe. ... 06:13: ... and why these observations are going to advance our understanding of the universe in really important ways and why YOU are definitely going to be able to ... 08:49: ... spot on the sky, but which reveals 10,000 galaxies back into the early universe. ... 09:42: Some of these things are shining at us from out of the very early universe - maybe when it was 7% its current age. 10:07: ... by other telescopes, which might seem redundant, but JWST sees the universe very differently, so studying the same objects in this new light really ... 17:09: ... themselves that they’re hunting for the fundamental substrate of the universe, so far chasing their tails in the ... 17:21: ... the big bang, dark matter and dark energy, and figure out how the universe is going to ...
	2022-09-14: Could the Higgs Boson Lead Us to Dark Matter? 00:49: The matter that we perceive out there in the universe is a small fraction of the matter that exists. 01:01: These particles dominate our experience of the universe because they are strongly interacting. 01:33: We know that there’s some source of gravity out there in the universe NOT caused by the particles of the standard model. 01:40: We see its effect in the way galaxies move and in how the universe on the largest scales evolves. 07:46: Physicists playfully called it a portal since the Higgs could be the doorway that connects our standard sector of particles to the dark universe.
	2022-08-24: What Makes The Strong Force Strong? 00:53: The protons on the other hand are packed together in the nucleus as tightly as any matter in the universe. 07:55: ... enough energy, like in the very early universe or at impact point in a large particle collider, space gets sort of ... 12:23: That would probably be very bad - or at least very different from the universe that we know. 18:57: ... Quintessence evolves over time, would our estimates for the age of the universe be ... 19:24: If dark energy has gotten stronger then the universe would be older, because it would have been expanding slower in the past than expected. 19:32: On the other hand if dark energy has weakened then the universe might be older than expected.
	2022-08-17: What If Dark Energy is a New Quantum Field? 00:00: ... know that something is up with the way the universe is expanding - there’s some kind of anti-gravitational effect that’s ... 00:36: ... a constant density expected of a vacuum energy. That would cause the universe to eventually tear itself apart on a subatomic scale in the so-called ... 01:41: ... the fabric of space has energy - dark energy - then the expansion of the universe creates the stuff. And it’s this process that actually accelerates the ... 02:31: ... almost everything about what your dark energy candidate will do to the universe. For dark energy, omega is negative due to the negative pressure on the ... 03:33: ... adds up and ultimately this becomes the dominant form of energy in our universe. So its antigravitational effect not only overcomes its own positive ... 06:25: ... we measure the Hubble constant - the current rate of expansion of the universe, based on supernova explosions over the past several billion years, we ... 07:31: ... and Paul Steinhardt in 1998, the same year as the acceleration of the universe was ... 09:05: Alternatively, it can be thought of as a fifth energetic component of the universe on top of baryons, dark matter, neutrinos, and photons. 09:13: ... For example, if the strength of dark energy has changed since the early universe then the Hubble tension could be ... 09:51: ... constant dark energy. Currently around 70% of the energy in the universe is dark energy with the remaining 30% mostly matter, including dark ... 10:08: ... doesn’t sound very close, but it actually is. As the universe expands, matter dilutes away while most versions of dark energy stay ... 10:55: ... and matter, and its behavior could be connected to the density of the universe. For example, in so-called k-essence models, the equation of state is ... 12:31: ... outside galaxies. The Milky Way survives a quintessence-dominated universe. That’s not true if omega is less than -1 - that’s the big rip, in which ... 13:04: ... big rip is possible, so are time machines, and we escape the end of the universe every time it comes ... 13:27: ... in which the field evolves in such a way to halt the expansion of the universe and cause it to collapse back on itself. But this flexibility makes it ... 14:41: ... story short - measuring the equation of state of the universe with increasing precision will teach us about its fabric, its origin, ...
	2022-08-03: What Happens Inside a Proton? 00:00: ... we ever want to simulate a universe, we should probably start by learning to simulate even a   ... 00:22: ... at  finding the underlying rules by which the   universe operates. It helps that a lot  of those rules seem to be ... 00:45: ... episode, it takes as many bits as there   are particles in the universe to store all the information in the wavefunction of a single ... 08:30: ... could do that even given the entire life of  the universe. For QED, Feynman diagrams let   us reduce the number of field ... 14:32: ... of a single atom. We will never simulate  a whole universe this way - nor any way in   all likelihood. But we’re going to ... 19:17: ... we  do, because what else can we do?   Whether or not the universe is deterministic, there's still only one question that ...
	2022-07-27: How Many States Of Matter Are There? 06:10: However in the very early universe everything was a quark-gluon plasma, and that may also be true in the cores of massive neutron stars. 12:50: Just think of our universe as nested layers of states of matter, from the smallest to the largest scales of space time.
	2022-07-20: What If We Live in a Superdeterministic Universe? 00:19: On its most elementary scale the universe exists in a state of fundamental indeterminacy. 00:57: Others - perhaps most - prefer to think of the universe as having a concrete existence independent of the observer. 10:47: ... is, well, it's just determinism - the statement that the universe and any system therein evolves in a way that’s uniquely predictable by ... 11:54: And that’s … impossible because if you trace the past lightcone of any two points in the observable universe back far enough they will overlap. 13:20: That pushed back any possible local-realist influence more than half the age of the universe. 13:43: ... locality or realism are wrong OR there are multiple realities OR the universe evolves in unalterable lock-step determinism in a way that preserves ... 15:26: Adam, I don't know whether the universe is superdeterministic on its deepest level, but it sure seems pretty uncertain up here. 17:45: ... avoid revealing their physics conventions - any basic description of the universe they live in beyond the actual laws of physics would reveal ...
	2022-06-30: Could We Decode Alien Physics? 00:00: ... It’s gotta map to our own physics - I mean, we live in the same universe after all.   We start by noticing that the alien ... 05:33: ... be identical except for   having exactly opposite charges. The universe is mostly symmetric under charge conjugation - switch   ... 07:38: ... To understand why, imagine that all right hands in the universe were transformed into left hands and   vice versa. In other ... 10:41: ... chirality for particles with quantum spin,   and in our universe P-symmetry is broken in  much more obvious ways than charge ...
	2022-06-22: Is Interstellar Travel Impossible? 14:02: ... universe may be trying to kill us, but it’s not trying quite hard enough. Not ...
	2022-06-15: Can Wormholes Solve The Black Hole Information Paradox? 00:00: ... multiple imaginary black holes via wormholes. And you thought  the universe couldn’t get any ... 00:26: ... of the most profound leaps in  our understanding of the universe   have come when we noticed inconsequential seeming inconsistencies ... 01:40: ... that went into making the black hole   is erased from the universe.  This conflicts with the law of   conservation of quantum ... 06:01: ... of string theory that reveals that a   particular type of universe with three spatial  dimensions is encoded on its own 2-D ... 13:07: ... true path - a path that leads to deeper   understanding of our universe, past an infinity of strange topologies and imaginary ...
	2022-06-01: What If Physics IS NOT Describing Reality? 00:25: ... trying to do? Is it to find  the mathematical laws that govern the universe?   Not quite - no one has to solve the Schrodinger  equation in order ... 01:41: ... Quantum mechanics tells us that asking questions  of the universe radically changes how it behaves.   Wheeler followed that ... 11:24: ... that governs it   describe our information about the  universe, not the universe ... 13:13: ... the universe almost certainly is not a simulation. But you can’t be too careful. ... 16:52: ... a couple of comments that said that   the expansion of the universe could be thought  of as matter shrinking rather than the ...
	2022-05-25: The Evolution of the Modern Milky Way Galaxy 02:19: ... know about galaxy evolution  based on all the other galaxies in the universe. ... 03:22: ... regions in the hot hydrogen and helium   gas that filled the universe after the Big Bang.  It’s hard to see the galaxies in the first ... 16:41: ... to miscalculations of the bombardment rate. OK, on to the expanding universe ... 17:21: ... constant and dark energy, the expansion of   the universe does not continue to tug on  the space within gravitationally ... 18:10: ... that the Schwarzschild metric isn’t really valid in a universe with a cosmological constant.   There would indeed be an ... 18:41: ... contracts, rather than simply not  expanding with the rest of the universe.   The answer is kind of, yes. You can interpret the  math that way. ...
	2022-05-18: What If the Galactic Habitable Zone LIMITS Intelligent Life? 00:00: ... solar system is a tiny bubble of habitability  suspended in a vast universe that mostly wants to   kill us. In fact, a good fraction of ... 01:07: ... enough to explain one of  the most perplexing mysteries of the universe? In   a galaxy of 200+ billion stars, why don’t we see  ... 06:56: ... the near perfectly smooth cloud of particles   that filled the universe after the Big Bang. As  it cooled, our local lump started to pull ... 07:36: ... gas in colossal supernova explosions.   The metallicity of the universe began to ...
	2022-05-04: Space DOES NOT Expand Everywhere 00:19: ... of observations and theoretical ideas came together to reveal the universe is expanding on the largest scales. The distant galaxies are all racing ... 01:59: ... four scientists independently solved its equation for the entire universe, giving us the Friedman-Lemaitre-Robertson-Walker or FLRW metric. You can ... 02:38: ... surface of the Earth, the FLRW metric gives the geometry or shape of the universe. The spatial part of that geometry could be the 3-D analog of our surface ... 03:27: ... FLRW metric makes some pretty big assumptions - that the matter in the universe is perfectly evenly spread out - homogeneous, and it looks the same in ... 03:48: ... this thing is the scale factor, which represents the overall size of the universe, and this is the thing that has to change. In our universe it’s getting ... 04:26: ... a classic classroom representation of the expanding universe that’s actually pretty useful here. Glue galaxies to a balloon and ... 06:04: ... In fact, the spacetime inside the Milky Way doesn’t even know that the universe is ... 07:12: ... try something else. Lose another dimension of space so the universe becomes an expanding ring instead of a ,sphere, with grid points instead ... 08:21: ... there is no constant tug of war between the expanding universe and the gravitationally bound systems it contains. That tug of war did ... 09:16: ... space can be infinitely divided. That means we can start with a universe that’s small and grid it up and watch it expand. The grid lines diverge, ... 09:38: ... never run out of subdivisions. Similarly, we can take the universe of the present and define a grid of space - or a grid of points on our ... 10:06: ... until they hit a singula,rity - the big bang or a black hole. As the universe expands, we don’t have new patches of space appearing between the old ... 10:52: ... that they change -then the Planck length remains the same. But as the universe expands it adds more and more of these “Planck lengths” which must ... 11:59: ... out. The result of this is that the total dark energy content of the universe depends on the amount of space in the universe, which means dark energy ... 12:56: ... there’s your answer. The infinite scalability of space means the universe can and probably will expand forever with no effect on this little ... 13:35: ... episodes - there was the one on John Archibald Wheeler’s Participatory Universe, and the episode on the Higgs mechanism and the mass of the W boson. ... 14:34: ... collapses the wavefunction,  or in this case manifests the universe. Rather than for example saying that “interaction” is doing the work. ... 15:31: ... Wheeler’s wacky-sounding ideas. The other famous one is the one-electron universe, in which all electrons are actually the same electron bouncing back and ... 16:05: ... Z asks us to address the elephant in the room. If the participatory universe interpretation is true, then what are entities that initiated the first ...
	2022-04-27: How the Higgs Mechanism Give Things Mass 02:50: ... field to   the Schrodinger equation that lets the  universe counteract these phase shifts.   That gauge field turns out to ... 03:36: ... of totally abstract degrees of   freedom and demand that the universe be  invariant to transformations of these.   We call this ... 04:37: ... isospin and weak hypercharge,   but no electric charge. In our universe  these three quantities are sort of   locked together, only ... 05:24: ... all free to be whatever they  want, unlike the real universe where   isospin and hypercharge are tightly coupled,  and ... 05:38: ... that violates the symmetries of their  ruling equations, maybe the universe can ... 07:01: ... let’s just see if we can break  the symmetries of the universe   in a similar way. The equivalent of the  simple valley exists. A ... 10:50: ... same global U(1) symmetry as the original.   But if the universe suddenly transitions from the  old potential to this one then we ... 12:26: ... vacuum state - there’s a rin g of valid states.   The universe will just have  chosen one state randomly.   But the ... 12:59: ... valley you are. It matters if two adjacent   patches of the universe are in different parts of  the valley - the relative difference in ... 17:09: ... you and what you'd like to see   happen in the Space Time universe.  There’s a link in the ...
	2022-04-20: Does the Universe Create Itself? 00:00: ... before the game is done. Well it could be that’s what the entire universe is doing as it creates our reality. I hope it thinks of something ... 00:30: ... are fairly attached to the idea that the universe is real. We’re fond of the realist viewpoint: that there’s an objective ... 00:59: ... of measurement. Others were desperate to maintain a physical and realist universe, including Albert Einstein himself. We’ve talked about this debate ... 01:59: ... better sense of why we need to go to these crazy lengths to explain the universe, let’s review some quantum weirdness. We’ll start with the good ol’ ... 04:57: ... binary choices, bits.” In other words, he came to believe that the universe is fundamentally ... 07:08: ... variations of it, have now been performed. They seem to verify that the universe really does exist in a superposition of all possible states until the ... 08:05: ... it seems that when you interrogate the universe, the answers that you get depend on the questions you ask. Wheeler became ... 09:48: ... came to the view that the universe was one giant game of negative 20 questions, in which the reality we ... 10:30: ... called this the “participatory universe.” He symbolized his idea with a sketch of a giant “U”. On one side of the ... 12:27: ... John Archibald Wheeler’s version of an informational universe, he felt that the information - the bits - resided in the answers ... 13:57: It may be that we live in a participatory universe that’s self-generated by its observers. 14:02: ... Evans, who’s supporting us at the big bang level. Mark, in creating a universe or a show about the universe, every little bit counts, but there’s ... 14:37: ... two most recent episodes in which we asked: Where is the center of the universe? (if it even has one) and could a universe actually be inside a black ... 14:50: ... reference to the question “What is the universe expanding into?”, John Retherford asks whether a fair answer would be ... 15:24: ... of Perístanom asks if the geometry of the universe - close, open, flat - dictates the “temporal shape”. As in does a closed ... 16:10: ... the possibility of detecting Hawking radiation in the case that the universe is a black hole. Actually, we should expect a type of Hawking radiation ... 16:56: ... argues that the universe can't be a black hole because the difference between the masses of our ... 17:08: ... would mean for the universe, for the universe to be a black hole would require very different ... 17:39: ... you calculate the size of a black hole with the mass of our observable universe - adding together all the stars, dark matter, other black holes, ...
	2022-03-30: Could The Universe Be Inside A Black Hole? 00:03: Gateways to other universes? 01:26: The universe also has a singularity and an event horizon. 01:30: ... Big Bang, which we think of as a point in time at the beginning of the universe when all matter was compressed to infinite density and all points in ... 01:49: ... is expanding evenly everywhere, then there are distant regions of the universe that are being propelled away from us faster than the speed of ... 02:22: ... the accelerating expansion of the universe means the cosmological event horizon is closer to us than the spot where ... 02:41: Complications aside, there are striking similarities between the black hole and the universe. 03:22: ... in a couple of episodes - in our recent one on the center of the universe, and also when we asked what happened before the big ... 04:49: All geodesics in the universe come together and terminate at the big bang. 05:19: ... way that the big bang is the encompassing past for the for the outside universe. So the black hole and the big bang singularities are starting to look ... 05:50: We’ll need to make the black hole interior mathematically indistinguishable from a universe for somebody inside that black hole. 06:28: That’s starting to look like our universe - a past, space-like singularity and an event horizon that can’t be crossed from the outside. 06:54: So could they be fooled into thinking they are in a regular universe? 06:59: At first glance, despite the similarities the interior of the white hole looks nothing like our universe. 07:15: Same trick gave us wormholes and mirror universes, by the way, and we mapped these weird spaces in a previous episode. 07:22: The interior of this type of white hole looks nothing like our universe. 07:37: ... our universe appears to be highly homogeneous - matter and energy are very evenly ... 07:54: ... spacetime of our universe is well described by the Friedmann-Lemaitre-Robertson-Walker metric, ... 09:06: ... Friedmann made when he first solved the Einstein equations for the whole universe, and it’s the assumption behind the FLRW ... 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. 09:55: If such a white hole was big enough, it could look exactly like our universe. 10:14: There’s also the idea that universes are born as white holes produced after the collapse of a black hole. 11:08: ... a very specific construction for white holes to make them look like our universe from within, and Hawking’s argument that equates white holes with black ... 11:25: So is the universe a black hole? 11:32: There’s no good reason to believe that this is the case, so we shouldn’t believe the universe is a black hole. 12:16: ... a universe inhabited by people asking exactly the same question, with the same ...
	2022-03-23: Where Is The Center of The Universe? 00:02: We can all be a little self-absorbed sometimes, acting like we’re the center of the universe or something. 00:08: Well first let me tell you where the center of the universe actually is before you decide that’s where you are. 00:37: Ever since then, astronomers have embraced the Copernican principle, which states that we are NOT in a special place in the universe. 00:51: And the Copernican principle inspired another important idea - not only are we not the center of the universe, but the universe doesn’t have a center. 01:00: Once you zoom out far enough, the universe looks basically the same everywhere. 01:29: The question is this: If the universe has a center, where is it? 01:34: You might imagine that the center of the universe is the place where the Big Bang happened. 02:30: Google “where is the center of the universe”, or “where did the big bang happen” and you’ll get this basic story for the first 50 pages. 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: ... - doing the mathematical equivalent of grinding up everything into the universe into a fine paste and spreading it evenly through ... 03:35: That gave him equations of motion that described how the universe must evolve. 03:52: ... one thing it predicted that the universe could not be static - it had to be contracting or expanding, and that as ... 04:14: ... is determined by the relative amounts of matter and dark energy in the universe. ... 05:01: The surface is finite, but there’s no edge and there’s no center - or at least, no center that’s part of the 2-D universe. 05:09: A closed 3-D universe is like the 3-D surface of a 4-dimensional hypersphere. 05:20: If I were to ask a denizen of the surface of the sphere to point to the center of the universe, they couldn’t do it. 05:56: And that’s the most straightforward interpretation of the FLRW metric for a closed universe. 06:19: Our universe is expanding. 06:21: In the case of the closed universe, that means it started out as a very, very tiny hypersphere surface and got bigger. 07:39: ... line loops around the closed universe as the sphere shrinks, until eventually all points in the universe, ... 07:49: It’s the same with our universe - point in any direction and you’re pointing at the Big Bang. 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. 08:04: A lot of this stuff is also true for a flat or open universe. 08:09: ... 2-D analog of the flat universe is an infinite flat plane, while the open universe corresponds to a sort ... 08:48: No matter the geometry of our FLRW universe, all geodesics converge to a single point in the past, and end there. 09:09: ... the Big Bang if traced backwards, and that’s true anywhere in the universe. ... 09:31: OK, so maybe the location of the Big Bang isn’t at one point in this universe. 09:40: ... - if all geodesics emerged from that point - does that mean the universe started out ... 09:52: In the case of the closed universe that’s easier to imagine - rewind the growing sphere and it approaches a single point at t=0. 10:01: But what about an infinite universe? 10:16: So did the universe start out pointlike at t=0 and then suddenly become infinite in size? 10:23: Well the size of the universe at t=0 is zero times infinity … which is neither zero nor infinity - it’s the point where the math breaks. 10:34: And that’s the nature of singularities - they are discontinuities in the math we use to describe the universe. 11:08: OK, so we have the state of the current wisdom on the shape of the universe, and the non-existence of its center. 11:18: ... that Alexander Friedman came up with his solution for the shape of the universe by assuming that matter and energy are evenly spread out ... 11:28: He assumed a homogeneous universe and assumed the cosmological principle. 11:35: ... observation of the receding galaxies that doesn’t require an infinite universe, nor a hyperspherically looping ... 11:57: Lemaitre asked what the universe might look like if it was NOT homogeneous. 12:02: He sought solutions to the Einstein equation for a universe that is lumpy on the largest scales. 12:19: ... was expanding or contracting would observe an expanding or contracting universe that looks exactly like a FLRW ... 12:32: ... the same discovery, and so we have the Lemaitre-Tolman metric. Such a universe would have a center - the center of the cloud, assuming the cloud is ... 12:47: ... if you zoom out to many, many, many times larger than the observable universe, everything evens out ... 13:04: So you can find a Lemaître-Tolman universe inside a greater FLRW universe. 13:11: ... might be the case: that’s eternal inflation, which proposes that our universe is just one bubble of relatively slowly expanding space embedded within ... 13:33: ... story short: the universe probably doesn’t have a center, and if it does we may never know - the ... 17:02: In fact the universe seemed to be made of only six particles, three quarks and three leptons. 17:09: When the universe cooled down and the electroweak symmetry was broken, particles were locked in whatever isospin state they happened to be in.
	2022-03-16: What If Charge is NOT Fundamental? 01:20: But actually, in the case of electric charge we have at least one or two more “but why’s” with which we can annoy the universe. 01:30: ... the birth of Particle Physics, and, in fact, through the birth of the universe ... 12:31: ... happened to that force in the very early universe to force these charges to only take on a specific combination of values ... 12:50: So we now know that electric charge is a sort of shadow of the ancient fields from the birth of the universe.
	2022-03-08: Is the Proxima System Our Best Hope For Another Earth? 16:48: And the one on cosmic strings - topological defects that may span the length of the universe. 19:51: ... filaments and voids in the large scale distribution of galaxies in the universe, and whether they could explain the cosmic microwave background and dark ... 20:12: ... leave an imprint on the CMB- on the density fluctuations from the early universe. ...
	2022-02-23: Are Cosmic Strings Cracks in the Universe? 00:00: ... quantum fields come into all of this? Well, it turns out the   universe is a gigantic ice cube, and the imperfect freezing of its quantum ... 00:58: ... has cracks in it. Universe-spanning  filaments of ancient Big Bang energy,   formed from ... 04:51: ... quite suddenly the Higgs  field everywhere in the universe   found itself sitting at a higher energy than it  needed. It was ... 05:59: ... textures of slowly shifting phase angles across   the universe. But if multiple bubbles join with  different phase angles then ... 07:33: ... quantum fields amidst the first bawlings of the baby universe and woven some cosmic strings.   What do they look like and ... 08:50: ... and the completion of vacuum decay and then the  expanding universe stretched them up to the size   of the observable universe. We ... 12:19: ... For one thing, they’re ridiculously   tiny instead of universe-sized. However the  universe may have found a way to confuse the two. ...
	2022-02-16: Is The Wave Function The Building Block of Reality? 03:59: ... of reality, unlike pilot wave theory. And one which avoids multiple universes by insisting that collapse does really happen. But it also avoids ...
	2022-02-10: The Nature of Space and Time AMA 00:03: ... they're the dimensions that form the stage on which the play of the universe takes place in the case of space it's the coordinate system it's the ...
	2022-01-27: How Does Gravity Escape A Black Hole? 00:20: So how does a black hole manage to communicate its gravitational force to the outside universe? 02:56: ... event horizon, how does its gravity get out to influence the surrounding universe? ... 03:07: Shouldn’t a black hole’s event horizon protect the universe from its own malicious influence? 09:46: ... signals of that collapsing star continue to make their way out into the universe over infinite ... 10:55: ... event horizon, but is happily exerting its influence on the surrounding universe. ... 12:29: ... asked our friends at Center for Computational Astrophysics to run a few Universe simulations and track the evolution of the entity known as Alex ... 13:02: Our two recent episodes were all about simulating the universe. 13:06: ... simulations of everything from the sizes of planets to the size of the universe. ... 13:33: do the ACTUAL interactions also require that much effort from the universe? 15:39: ... Robert Herd asks the following: how can it be that in an expanding universe, where all the galaxies are rushing away from us, that we could be on ... 15:54: Well the answer is sort of what you say in your own question: the real universe is more chaotic than implied by simple expansion. 16:57: ... years. Now Roli follows with another question: if we simulate a perfect universe containing beings that themselves are able to simulate a perfect ... 17:23: ... the way up to the top layer - you have to have beings who simulated a universe containing beings who could simulate a universe, but they themselves ...
	2022-01-19: How To Build The Universe in a Computer 01:04: We routinely simulate the universe on all of its scales, from planets to large fractions of the cosmos. 01:11: Today we’re going to see how it’s possible to build a universe in a computer - and to see whether there’s a limit to what we can simulate. 01:26: ... Holmberg  conducted what was probably the first simulation of the universe, right when the first  programmable computers were being ... 07:52: The universe started as an ocean of gas a few hundred thousand years after the Big Bang. 10:02: ... settling into spiral structures - just like we see in the real universe. ... 10:14: And then we have cosmological simulations  which create entire virtual universes, from the moment the first  atoms formed to the modern day. 10:56: Can we ever simulate a real universe, in which creatures evolve that can themselves simulate universes? 11:08: None of these simulations contain the full information of an actual universe - or even a tiny part of it. 11:23: No conceivable technology could  fully simulate a quantum universe,   except perhaps a cosmically-sized quantum computer. 11:32: Which is kind of what the universe is anyway. 12:01: ... there’s no limit to what we can learn about the outside universe by rebuilding it inside our computers, and then  peering into that ...
	2022-01-12: How To Simulate The Universe With DFT 00:00: ... you used every particle in the observable universe to solve the schrodinger equation and do full quantum simulation of some ... 00:30: Let’s learn how to cheat the universe. 03:05: Of course the real universe has 3 spatial dimensions, so for most real applications we’d want Psi(x,y,z). 09:14: So how does DFT do a calculation that should need to manipulate vastly more bits of information than there are particles in the entire universe? 12:33: Without taking, like, the entire age of the universe and a solar-system sized computer. 13:12: But what does DFT actually tell us about the universe? 13:28: For one thing, it’s good news if we ever want to simulate another universe. 13:31: We won’t need a computer bigger than the universe.
	2021-12-29: How to Find ALIEN Dyson Spheres 12:08: There are hundreds of billions of galaxies in the observable universe. 13:40: The discovery of a single alien megastructure of any sort would massively change the way we think about our place in the universe.
	2021-12-20: 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. 01:18: A glob of that material in the modern universe would immediately collapse into a black hole. 01:23: ... back then the universe had the same insane density everywhere - matter was smoothly spread out ... 01:49: ... it was the smoothness of the early universe that saved all of matter from collapsing into black holes. But that ... 02:10: ... in such stupendous numbers that they account for 86% of the mass of the universe, and are therefore an explanation for dark ... 03:25: ... insane number of them out there to account for most of the mass in the universe. Which means we can wait for them to come to ...
	2021-12-10: 2021 End of Year AMA! 00:02: ... the people and so just like them i wanted to tell people about the universe let's move on um before i wanted to tell people about the universe i ...
	2021-11-17: Are Black Holes Actually Fuzzballs? 00:50: And we see these black holes - or at least their incontrovertible evidence - in many places out there in the universe. 08:32: That’s different to pretty much everything else in the universe, which are crunched down to smaller size if you increase the power of gravity. 11:35: ... up to the surface and the interior grid of spacetime is deleted from the universe. ...
	2021-11-10: What If Our Understanding of Gravity Is Wrong? 00:57: It sure looks like 80% of the mass in the universe is completely invisible to us. 10:21: One of the most important pieces of evidence  for dark matter as a particle is seen in the light that comes from the very early universe. 10:58: ... after the universe had expanded and cooled  enough for regular matter to be released ... 11:45: ... managed to tweak their equations so that  in the early universe, that field behaved a bit like a type of matter, which Złosnik calls ... 16:02: In simple terms, the universe at its very core seems to be a set of symmetries which are manifest in the Lagrangian. 16:10: ... means that if we knew all the symmetries  the universe follows we could describe it perfectly, but we don't know all the ...
	2021-11-02: Is ACTION The Most Fundamental Property in Physics? 01:22: ... and miraculous power to explain the motion of all particles in the universe. To do this, all you needed to do was know the exact vector forces on ... 05:24: ... that it really seems like it must be telling us something deep about the universe. But what? It’s hard to interpret what this Action property really ... 07:09: ... notion of change in energy, but working with a more precise model of the universe we see Action is much easier to understand. Action is now just how much ... 17:24: ... find there are still infinite functions that can perfectly describe the universe. ... 17:54: ... Habel also puts it well: If we assume the universe operates under certain assumptions (infinite/finite, discrete/continuous ...
	2021-10-20: Will Constructor Theory REWRITE Physics? 00:32: describe some aspect of the universe with numbers - like the temperature, pressure, etc of a gas or the position, velocity, etc. of a particle Step 2. 11:52: ... that, as one of the deciders of  what is and isn’t possible in this universe,   you’ve decided that the laws of physics  should permit the ... 15:34: ... example we could be a simulation. TBatlas says   that the universe saves CPU space by not fully  rendering particles that aren't being ...
	2021-10-13: New Results in Quantum Tunneling vs. The Speed of Light 12:28: All signals in our universe, whether via quantum tunneling or quantum entanglement, seem to be bound by the same limits imposed by relativity. 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. 15:20: Try to make a flawless crystal the size of the universe.
	2021-10-05: Why Magnetic Monopoles SHOULD Exist 08:13: ... to be discrete if there’s even a single magnetic monopole in the entire universe. ... 09:37: ... is a scalar field - it takes on a numerical value everywhere in the universe, but with no direction - it’s not a ... 11:12: ... in extremely high-energy environments like in the very early universe. ... 11:36: GUTs predict that monopoles should be produced in enormous numbers in the very early universe - as abundantly as protons and electrons. 11:47: They should also be very massive - quadrillions of times the mass of the proton - and so should have quickly recollapsed the universe. 12:09: Many physicists think that a period of prodigious exponential growth kicked off the expansion of our universe. 12:16: ... far apart that there may be very few remaining in our entire observable universe. ... 14:18: Kyle, we are taught by Paul Dirac that if there's even a single magnetic monopole in the entire universe then electric charge must be quantized. 14:55: ... week we talked about how quantum spin leads to the universe as we know it - for example all the structure of solids, via the Pauli ...
	2021-09-21: How Electron Spin Makes Matter Possible 00:26: ... some particles have this property is the entire reason that stuff in our universe has structure, and that matter doesn’t immediately collapse. It’s the ... 03:19: ... that “quantum” - it’s a natural function of how it’s connected to the universe. So allow me to introduce you to the belt trick, first conceived by Paul ... 03:46: ... - say an electron - and the belt is its connection to whatever - the universe, or to maybe another electron. Now rotate the electron a full 720 degrees ... 14:26: ... structural integrity of my pants situation. Revealing mysteries of the universe sometimes comes at the risk of revealing mysteries. But that is a risk ...
	2021-09-15: Neutron Stars: The Most Extreme Objects in the Universe 00:00: ... journey that has got to be   the weirdest place in the modern universe  - a place where matter exists in states   that I bet you’ve ... 00:25: ... stars are arguably the strangest objects in the universe - if we don’t count black holes   as actual objects. And ... 01:02: ... find states of matter that exist nowhere else in   the universe. For this journey we’re going  to need an unthinkably advanced ... 01:42: ... is its magnetosphere. This is the strongest magnetic field in the universe. Even   the weakest neutron star fields are a billion  ... 08:15: ... is perhaps the least known and most freaky state of matter in the universe.   When nuclei start to touch they rearrange, forming exotic shapes. ... 09:34: ... pasta   might even be the strongest material in the  universe, a quintillion times stronger than ... 11:29: ... the most extreme conditions in the   entire modern universe. Here, pairs  of spin-½ neutrons become connected   in a ...
	2021-09-07: First Detection of Light from Behind a Black Hole 00:46: ... what happens in the vicinity of the largest black holes in the universe. ... 00:56: ... Brandt & Blandford so I get to talk about my favorite subject in the universe. ... 03:13: ... the way, is the actual technical term for the largest black holes in the universe - anything more than a million or so times the mass of the ... 12:46: And then the episode on how vacuum decay could destroy the universe .. or universes, if the ideas in the first episode are right. 14:54: The difference is that in the pre-inflation universe, space was expanding exponentially quickly due to the high value of that field. 15:03: ... means a new vacuum decay event now wouldn’t yield universe whose interior is expanding quickly - in the sense of particles racing ... 16:18: ... not to do video intros in which I say I’m going to send messages between universes … in a Scottish ... 16:44: But to that I answer - you people have no idea what Scottish accents sound like in parallel universes.
	2021-08-18: How Vacuum Decay Would Destroy The Universe 00:00: ... universe is going to end. But of all the  possible ends of the universe ... 00:21: ... seems pretty lucky that the universe  is how it is. Its just the right size,   has just the right ... 01:00: ... one mechanism that could rewrite  the laws of physics across the universe.   That mechanism is vacuum decay, and  some physicists think it’s ... 03:11: ... has a real, positive value. This means that   the entire universe is filled with this soup of  Higgsiness. Most elementary particles ... 05:03: ... worryingly, we don’t know which of these minima our universe’s Higgs field is in right ... 05:43: ... for reasons I’ll get to. But what if the   entire universe is in the false vacuum? Then a tunneling event would be a little ... 06:08: ... a universe filled with the Higgs field in a false vacuum. At a single point in ... 07:01: ... is unstoppable, and will drag  the Higgs field through the entire universe   down into the true vacuum. This is vacuum decay. It’s a phase ... 10:10: ... a single timescale - they vary from roughly the current age of the universe to 10^hundreds times   the age of the universe for a single ... 11:34: ... lifetime. Of course, in an   infinitely or sufficiently large universe then vacuum decay has definitely started somewhere.   But ...
	2021-08-10: How to Communicate Across the Quantum Multiverse 08:08: ... need to send regular, sub-light-speed information. It’s almost like the universe conspires to prevent any superluminal ...
	2021-08-03: How An Extreme New Star Could Change All Cosmology 00:00: ... light on the sky whose weirdness could change the way we think about the universe on the largest ... 09:18: ... that could have done this - one that we know must happen in the universe, but that we’ve never seen conclusive evidence for it. Zee could be the ... 11:36: ... that's true then it may actually affect our understanding of the universe on the largest scales. That’s because observations of type 1a supernovae ... 13:41: ... on the edge of explosion, and may force us to rethink how we measure our universe on the largest scales. It’s a glimmer of weirdness that tells us that ... 14:14: ... the help of your support we’ve deciphered their song, come to us from a universe ... 15:05: ... last time we took a magnetic tour of the universe, exploring how magnetism shapes our cosmos from the scale of planets up ... 17:08: ... of you ask questions about the potential role of magnetic fields in the universe that all have the answer I just gave - can magnetic fields be used to ...
	2021-07-21: How Magnetism Shapes The Universe 00:50: But there’s really only one gravitational field in the universe - manifest as the fabric of spacetime itself. 00:56: And it governs the formation of every major structure in the universe, from the smallest moon to the largest cluster of galaxies. 01:51: That means magnetic fields can add up - and magnetism adds up to having enormous influence on the development of structure in our universe. 11:47: Those fields grab particles of matter and accelerate them to incredible energies, flinging cosmic rays out into the universe. 15:47: If you mean every possible configuration of particle properties in the universe - then the answer is there are infinite worlds.
	2021-07-13: Where Are The Worlds In Many Worlds? 00:00: ... mechanics proposes that every time a quantum event gets decided, the universe splits so that every possible outcome really does ... 00:35: ... the popular conception of Many Worlds: that of a many-branching tree, a universe that divides into unthinkably many alternate ... 03:42: It tells us that everything in the universe can be described by a wavefunction. 06:11: ... that includes every electron and every other particle in the universe. ... 12:07: Splitting happens when phase relations are scrambled due to interactions - and that’s - the entire universe doesn’t split with every atomic wiggle.
	2021-07-07: Electrons DO NOT Spin 09:59: ... think of electrons as being connected to  all other points in the universe by invisible strands. One rotation causes a twist, two brings it back to ... 15:09: ... so low at the Big Bang - and that’s one of the central mysteries of the universe. But, I’ll give it a shot ... 15:31: ... is that at some very,  very small amount of time after t=0, the universe was extremely compact - which meant hot and  dense, and it was also ... 16:45: ... properties due to their mutual connection to the outside. In the early universe, the extreme expansion of cosmic inflation may have permanently separated ... 17:20: In other words, the universe - or our patch of it - may have started out unentangled and at low entropy, even if it was at thermal equilibrium.
	2021-06-23: How Quantum Entanglement Creates Entropy 16:39: ... directions in   space. But we know for sure that this universe has a continuous rotational symmetry - there   is no preferred ...
	2021-06-16: Can Space Be Infinitely Divided? 05:08: ... constant represents the limit to which we can measure the universe. We recently talked about   how with a bit of clever physicsing ... 09:58: ... the universe seems to be conspiring to stop us measuring distances or sizes ... 11:26: ... of space. Quantum uncertainty thwarts our attempt to understand the universe   by simply splitting it into smaller parts. You’ll have to stay ...
	2021-05-25: What If (Tiny) Black Holes Are Everywhere? 00:00: It’s fair to say that black holes are the scariest objects in the universe. 07:16: But assuming that they a[re allowed in the theory, are they also allowed in the real universe? 07:22: The only way to make black holes in the modern universe is in the deaths of massive stars. 07:37: That’s much longer than the current age of the universe, none of these black holes will have become Planck relics. 08:35: And you’d need a lot to say the least because dark matter makes up 80% of the mass of the universe. 08:48: This is the hypothetical time just when the universe was expanding exponentially quickly, and can be thought of as the bang in the big bang. 09:28: So you completely evaporate a black hole and then all the quantum information that went into it is deleted from the universe. 10:22: This conjures images of insane numbers of minuscule black holes swarming through the universe, and in each one a new inflation - a new universe? 10:30: OK, we’re getting a bit too far out there - which is saying something given that we’re talking about the most out-there objects in the universe. 10:52: Just one Planck relic per 30km cube, and that’s enough to make up most of the mass in the universe.
	2021-05-19: Breaking The Heisenberg Uncertainty Principle 00:00: Quantum mechanics forbids us from measuringthe universe beyond a certain level of precision. 00:20: Engineers have gifted physicists with some pretty incredible machines for measuring the universe. 01:13: ... to nature - an absolute limit to how precisely we can measure the universe. ... 03:13: He thought the uncertainty principle was hinting at a far more fundamental law of the universe. 03:54: The universe only reveals to us the answers to the questions that we ask it, and there are certain questions that we can’t ask simultaneously.
	2021-05-11: How To Know If It's Aliens 06:27: ... that it must be aliens cause it couldn't be anything else. The universe is weirder that we can ever imagine, and it’s arrogant to assume you’ve ... 12:35: ... fact is, no matter now long we study the universe, it will always come up with natural phenomena that we’ve never seen ... 14:48: ... true. Stephen hawking’s chronology protection conjecture states that the universe will always find a way to make time travel impossible - and it’s been ...
	2021-04-21: The NEW Warp Drive Possibilities 03:07: Or beyond the cosmic horizon, the expanding universe is carrying galaxies away from us faster than light. 05:11: ... required more energy than is contained in all the matter in the visible universe to move a moderate-sized ... 12:18: Einstein and the universe appear to be trolling us - alternately inspiring and crushing our hopes for a star-hopping future. 12:37: They’ll continue to try to “make it so” by exploring Einstein’s theory - hoping to build starship, but in the process learning how our universe works.
	2021-04-13: What If Dark Matter Is Just Black Holes? 00:00: ... may be that for every star in the universe there are billions of microscopic black holes streaming through the ... 00:18: 80% of the mass of our universe is completely invisible to us - its existence only revealed through its immense gravitational influence. 00:25: This is dark matter, and it is one of the universe’s most perplexing mysteries. 01:39: ... dark matter makes up roughly 80% of the mass of the universe, but it’s much more spread out than regular matter - for example, in our ... 02:02: In other words, most of the physical universe needs to be vast swarms of black holes that outweigh all the atoms in the universe by a factor of four. 03:31: When we look into the distance we’re actually looking back in time, so we can literally see star formation happening in the early universe. 04:23: Fortunately for our hypothesis, there is a reason to think that colossal numbers of black holes may have formed in the very early universe. 04:53: ... know there were regions of the early universe that had a bit more matter than other regions - we see that in the ... 05:13: ... mass - but that mass depends on the details of the state of the early universe, and could be anything from a grain of salt to tens of thousands of ... 05:43: The most massive black holes in the universe weigh in at millions to billions of times the mass of our Sun. 06:30: I’m talking somewhere between a billion to a billion billion times more of them than there are stars in the universes..
	2021-03-23: Zeno's Paradox & The Quantum Zeno Effect 13:22: ... the crisis in cosmology - the tension between the expansion rate of the universe measured at the beginning of the universe with the cosmic microwave ... 13:40: ... of course it can't be because that light comes from the beginning of the universe. ... 13:55: Instead, it provides us with an enormous amount of information about the composition and expansion of the universe back then. 14:17: And the value we get is different to what we observe in the modern universe.
	2021-03-16: The NEW Crisis in Cosmology 00:22: ... careful, increasingly precise measurements of how fast the universe   is expanding which should agree with each other, and yet they ... 01:16: ... what the issue actually   is. So you may have heard that the universe is expanding. Space on the largest scales   is stretching, ... 03:13: ... supernovae to get distances   to galaxies halfway across the universe, they found something totally unexpected - not only is   ... 04:42: ... the expansion rate is to study the oldest light in the   universe - the cosmic microwave background. This  light was released only a ... 05:52: ... has had a   constant density for the  entire age of the universe. ... 07:28: ... and our quest to measure it has been central to understanding our universe   for hundreds of years. Prior to the invention  of the telescope, ... 10:08: ... patterns in the   way galaxies are scattered across the universe and use those rings as a sort of standard ruler.   These “baryon ... 10:40: ... time offset due to the fact that  these different paths through the universe   have slightly different lengths. By measuring the time delay in ... 11:57: ... the Hubble constant. These waves get stretched by the expanding universe, just like   light does. But unlike light, they also ... 12:25: ... clear that there’s a hole in   our understanding of the universe - whether it’s a crack in the rung of the cosmic distance ladder ...
	2021-03-09: How Does Gravity Affect Light? 12:22: Relativity is relative - because so is our universe. 12:38: ... our guiding star is that the universe is deeply self-consistent, our explanatory stories are all “true” in ...
	2021-02-24: Does Time Cause Gravity? 08:39: Last time we talked about the gravitational wave background - the ambient buzz of gravitational waves from the distant and ancient universe. 09:44: ... it ceased in isolated bubbles - corresponding to the formation of a new universe. ... 09:57: It makes more sense to talk about the end of inflation as the beginning of such a universe, rather than the beginning of global inflation.
	2021-02-17: Gravitational Wave Background Discovered? 00:00: ... 50 similar signals from merging black holes and neutron stars across the universe these sweep past the earth every few days causing space itself to ...
	2021-02-10: How Does Gravity Warp the Flow of Time? 00:53: But otherwise, as far as the universe is concerned, the sense of floating you feel in both circumstances is exactly the same.
	2021-01-26: Is Dark Matter Made of Particles? 00:07: The particle or particles of the dark sector make up the vast majority of the mass in the universe - so to them, you are the ghostly one. 00:33: It’s become disturbingly clear that we can’t see around 80% of the matter in the universe. 00:45: ... family of particles that exists in parallel to those we can see - a dark universe that overlaps our own, but so far is hidden from even our most ingenious ... 01:44: ... visible universe is made of these particles, interacting with each other through the ... 02:34: ... fields fill the universe, overlapping each other - and if a particle field is connected to - ... 03:05: ... we’d be able to detect it when it blocked light from the more distant universe - in the same way we “see” the black lanes of dust that block the light ... 04:51: More accurately, it tells us how far dark matter particles were able to travel in the early universe. 05:06: In the early universe, that distance influenced the size of the seed structures which galaxies would later form from. 05:35: For a long time people thought the neutrino might be dark matter - being neutral and the most abundant known particle in the universe. 06:17: ... type searches for new evidence out there in the universe or in our particle experiments here on Earth for evidence of particles ... 08:35: ... they may have been produced in the insanely energetic early universe, and the leftovers from that time could still be throwing their weight ... 10:07: ... obvious enough - it helps if you want to make up 80% of the mass in the universe, and also slows the particle down - helps make it ... 10:22: ... important - it may have governed how every interesting thing in our universe first ... 10:53: As the universe cooled and energy dropped, that process ceased. 10:57: We were left with a universe full of particle-antiparticle pairs that would then just annihilate over time. 11:02: But its possible some particles may not have been able to find an antiparticle counterpart before the expanding universe pulled them too far apart. 11:20: The universe didn’t expand fast enough to throw these particles apart, and so almost all annihilated. 12:03: ... ecosystem of particles are going about their dark business across the universe - interacting by dark forces, all of them oscillations in their own dark ... 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? 15:42: It turns out that there’s no distinction between all the types of time dilation as far as the universe is concerned.
	2021-01-19: Can We Break the Universe? 00:09: ... just getting started - he was already rocking our understanding of the universe with his special theory of ... 00:43: ... paradoxes of special relativity and see why, against our intuition, the universe really does work in this seemingly nonsensical ... 00:53: But the point of this episode is to go much further - we’re going to try to break the universe by pushing these paradoxes beyond the limit. 02:26: So close that the distance across the entire universe contracts to a size smaller than the spaceship itself. 02:33: ... also imagine that we live in a closed universe - one that loops back on itself, so by traveling far enough you can get ... 02:41: ... the frame of a spaceship moving at near light-speed, the universe could contract to the point that the spaceship wraps all the way around ... 05:46: Our ultimate question is about a spaceship crashing into itself in a closed universe - and trust me we’re getting there. 05:53: Let’s first look at the twin paradox in a closed universe. 06:03: She could keep traveling in a straight line all the way around the universe. 07:07: So by traveling around the universe, she’s actually traveling towards one of those future versions. 07:25: It seems that in this closed universe there IS a fundamental difference between frames of reference. 07:50: But the universe as a whole can have a special frame. 07:54: In the case of the closed universe, that closed topology DOES pick out a special frame - it’s the one with these closed constant time loops. 08:02: Our own universe also has a special frame - whether it’s closed or infinite. 08:17: Let’s zoom in from the whole universe to just a simple barn and a simple ladder. 10:48: Does a near-light-speed spaceship smash into it’s own rear-end 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 be smaller than the ... 11:44: ... along this helix - safe from collision even if it wraps around the universe multiple ... 11:54: Long story short -near-light-speed spaceships in closed universes or ladders in pacman barns are safe from colliding with their own asses. 12:41: ... them to near the speed of light, causing them to wrap around the universe several times and ... 14:58: This could be one of the weirdest things about the universe.
	2020-12-22: Navigating with Quantum Entanglement 13:08: ... star supernova, which may be the very last explosions at the end of our universe. ... 14:57: ... last option is described in the book five ages of the universe by Fred Adams and Gregory Laughlin Broken silence asks whether all this ...
	2020-12-15: The Supernova At The End of Time 00:00: Good news everyone: it looks like the universe is going to end with a series of catastrophic explosions. 00:10: ... await the Earth, then solar system, then galaxy, and ultimately the universe. ... 00:21: ... very very long story short is that the universe ends in heat death, as it approaches maximum entropy, and its eternal ... 00:54: ... - a new type of supernova that can only happen at the end of the universe. ... 01:14: ... your popcorn because your favorite TV show - AKA the far future of the universe - just got renewed for another ... 07:35: ... - now a frigid 3 Kelvin, but in the future even colder than that as the universe expands and the cosmic background radiation ... 08:02: ... neatly in its assigned column and row for many times the age of the universe. ... 09:13: But assuming protons are stable, we’ll reach a point where the universe consists of only iron stars and radiation. 10:25: The result is iron-56 - the most stable element in the universe. 12:14: ... all 10^3600 years of black dwarf supernovae across the entire end of the universe as a barely-adequate fireworks celebration of your generous ... 12:54: ... between your brain - or any patch of space - and both the surrounding universe and the ... 13:21: When you look at the whole universe at once, it can be said to remember its future. 13:31: The problem arises when we zoom in on only a portion of the universe. 13:53: ... so you no longer need to look at them both." So there you have it - the universe remembers both past and future perfectly, but individual chunks of the ... 14:35: John Ring correctly summarizes that observers in a reverse-time universe wouldn't know the difference. 15:01: ... that's it - if we think of time as just a stack of slices of the block universe, a prefered direction of time only emerges in our instantaneous awareness ...
	2020-12-08: Why Do You Remember The Past But Not The Future? 00:29: INTRO In our last episode we gave one explanation for why the universe as a whole sees an arrow of time. 04:02: ... violence, then fast forward many, many times the current age of the universe and the asteroid will decay into a mist of subatomic ... 04:23: ... let’s go as simple as possible - in the crazy energy of the early universe, a positron and a neutral pion particle combine to form a ... 05:01: ... a perfectly deterministic universe, knowing the exact state of all parts of a system lets you perfectly ... 07:14: Let’s look at the asteroid after its very last interaction with the outside universe. 07:56: Just rewind the clock to the moment before the asteroid’s very last interaction with the outside universe. 09:54: ... universe started in a state of extremely low entropy - spatially separated ... 10:17: ... is increasing universe-wide, but the smallest chunks of the universe - asteroids, brains for example ... 10:53: ... form memories in one direction and not the other is because the early universe started out with this incredibly rich resource of correlation-lite ... 11:14: ... also connected to the spreading of quantum entanglement. If you have a universe of only pure quantum states they’ll become more and more entangled in ... 11:52: ... our recent episode we explored how our universe gains its directionality to time from entropy and the 2nd law of ... 12:10: ... the universe were reversed - time ran backwards to the big bang, wouldn’t entropy ... 12:23: ... the big bang theory The distribution of matter and energy in the early universe does appear to have been random - which we normally associate with high ... 12:38: The answer is that the low entropy came from how compact the universe was compared to how spread out it could be. 12:58: ... Penrose puts it this way - in the early universe the low entropy was not in the degrees of freedom of the matter - that ...
	2020-11-18: The Arrow of Time and How to Reverse It 00:24: ... laws of physics describe how the universe at one instant evolves into the universe at the next. But those laws ... 00:54: ... when you drop it, but will never spontaneously reassemble. Our whole universe decays in the inexorable rise in entropy as time ticks forward. The ... 01:38: ... of time? Basically, if you reversed the motion of all particles in the universe - sent them back exactly in the direction they came, and used the laws ... 01:58: ... look at a simple example. We’re going to use our good-old block universe picture, where we have 2-dimensions of space and one dimension of time, ... 02:08: ... block universe just sort of exists a-temporally. The experience of time is had by ... 02:53: ... They just describe the relationship between time slices of our block universe. Time has a symmetry in the sense that the past and future aren’t ... 04:50: ... direction ends up being chosen, we need to return to the block universe. ... 05:43: ... this case, we defined the “up” time direction in the block universe as “towards the future”. But what does this look like going backwards in ... 06:19: ... minimum dictates the arrow of time - on either side of that minimum, the universe is overwhelmingly likely to evolve in a very particular ... 07:17: ... what does all of this mean for our universe and the universal arrow of time? Well it’s no accident I chose ... 08:11: ... If we think of time as just a series of instances - slices of the block universe connected by the laws of physics, then we can break the symmetry in the ... 09:25: ... reverse back then? Would that reverse Big Bang lead to a time-reversed universe? ... 10:58: ... the universe went thorugh another phase transition - a vacuum decay - then the weak ... 11:16: ... information doesn’t need to arise in the decision-making patch of the universe - AKA our brain - in order for us to consider that region the origin of ...
	2020-11-11: Can Free Will be Saved in a Deterministic Universe? 00:25: ... we explored the notion of determinism in the context of the block universe idea that we get from Einstein's ... 00:57: ... vast intellect that had perfect knowledge of the current state of the universe, like the positions and velocities of all particles, and perfect ... 03:00: Let's paint a cartoon representation of quantum information in a block universe. 03:05: Two dimensions of space and one of time, the slices of the block universe represent the causal ordering of the universe. 04:07: ... can parcel that decision-making machine off from the rest of the universe, and we can ask, what has to happen inside this patch for us to ... 07:01: ... could say that the cause arises outside the universe in a supernatural sense, but then all we need to do is expand our ... 07:39: Even in a deterministic universe, Laplace's demon is a fiction.
	2020-11-04: Electroweak Theory and the Origin of the Fundamental Forces 00:00: Our universe seems pretty complicated. 00:30: ... best way to understand how the universe went from a simpler, more symmetric state to its current complicated ... 12:08: The entire universe was that hot when it was less than a trillionth of a second old. 13:45: ... about infinities, why are we then typically ok that the size of the universe is ... 14:19: ... infinite universe doesn’t have the same problem, and I guess it’s often accepted because ... 14:29: You can as well ask why does the universe stop where it does, as you can ask why does it go on forever.
	2020-10-27: How The Penrose Singularity Theorem Predicts The End of Space Time 00:00: ... us to the limits Einstein’s  great theory and to the origin of the universe. ... 01:17: ... himself doubted that  the black holes could form in the real universe,   and even if they could, they certainly  shouldn’t harbor ... 09:31: ... behavior of geodesics traced   backwards through our entire universe towards the Big Bang. Now at this point we’d known for ... 10:15: ... infinitely dense knot. This might be the case if the universe underwent cyclic big ... 10:36: ... arguments  about black holes also applied to the   universe - that geodesics traced backwards in an expanding universe had to ... 12:11: ... the existence of black holes, which means their are places in the universe where   general relativity must break down or ... 12:51: ... our discussion of  determinism in relativity and the block universe,   but this time weaving in what quantum  mechanics had to say about ... 13:38: ... relevant for addressing the  reality of other parts of the block universe.   Alan Foxman struggles with the concept that there’s no ...
	2020-10-20: Is The Future Predetermined By Quantum Mechanics? 00:07: But if time is connected to space, can the universe be anything but deterministic? 00:16: ... saw that we could think of the unified spacetime in terms of the block universe, an a temporal entity that sort of just ... 00:31: In a block universe of Einstein's relativity, there's no way to cleanly define the present and so no way to cleanly separate the future from the past. 00:43: To us it looks like a particular slice through the block universe. 01:07: But how does this give us a deterministic universe? 01:34: ... it suggests a deterministic universe where every slice through the block universe is completely determined by ... 02:00: ... the entire block universe is defined, past, present, and future, or everything outside our past ... 02:31: Where relativity is the key to understanding the universe of the large and the very fast, we also need to understand the universe of the very tiny. 02:38: We need to see what quantum mechanics says about determinism and how it plays with relativity and the block universe. 02:46: According to quantum mechanics, physical systems, parts of the universe evolve as wave functions. 02:53: ... of probability that describe all possible states that, that chunk of the universe could be in, if it were to be ... 03:10: ... precise and frequently replicated experiments, tell us that the universe really does exist in this indeterminate state in certain ... 03:41: Now exploring those interpretations again, may help us understand the state of the universe beyond our immediate selves and the immediate moment. 04:19: The Copenhagen interpretation gives us a non-deterministic universe. 05:07: The Many-Worlds Interpretation gives us a deterministic universe or rather a deterministic multiverse. 06:09: But now let's say we believe that other observers in the universe can also collapse the same universal wave function with their observations. 06:17: Well, no problem so far, you can imagine this fleet of observers collapsing the universe all the way up to what you perceive as the present. 07:24: That's the hardest to gel with a non-deterministic universe, unless you are the only observer in the universe. 08:24: In the block universe picture, it's tempting to depict this as the entire block multiplying with every quantum event. 08:32: A division in the block universe can only propagate as quickly as the result of that quantum event can become known. 08:46: Really what's happening here is that parts of the universe become entangled with each other, correlated at a quantum level. 08:55: Each such web defines a set of properties of the universe correlated with some prior quantum decision. 11:27: ... universe of pilot wave theory is really a block universe but unfortunately, no ... 11:39: So it's a very simple block universe and it's not a good representation of ours. 12:23: ... we introduced the idea of the relativity of simultaneity and the block universe and what this might tell us about the reality of the past and ... 12:49: So does that mean that the idea of a now slice through the block universe is meaningless? 12:54: ... but two observers can certainly construct a map of events across the universe that they would define as happening simultaneously at a given instant in ... 13:11: ... and currently existing to the exclusion of other slices in the block universe. ... 13:27: ... you can ascribe actual existence to one slice of the block universe, to one observer's definition of the present, then you should ascribe ... 13:41: And that fills the block universe past and future. 15:21: That means that at least a short chunk of the block universe has a real current existence, much larger than the plank time. 15:32: Guilherme Marquesani takes issue with my characterization of Einstein as the smartest man in the block universe. 15:38: Dude, I said, block universe not universes.
	2020-10-13: Do the Past and Future Exist? 01:21: Newton was the first to come up with a set of laws that allow us to predict the motion of all objects in the universe. 01:27: ... revelations led to the notion of the deterministic universe - the idea that, by knowing the current position and velocity of every ... 01:54: Newton’s picture of the universe included one other assumption that we know for sure is wrong. 02:44: Every slice is the same universe at a particular instant, and it evolves from one slice to the next according to the laws of physics. 02:52: We only experience a single slice at a time, and we usually think of the universe in that slice as the one that currently exists. 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 4-dimensional chunk. 03:36: ... flip-book of the block universe has to be played in the right direction to see emergent phenomena like ... 03:56: Our awareness of the universe rides this forward-moving wave of the present. 04:01: To us, none of the rest of the block universe exists, because our existence emerges from the forward evolution of a razor-thin slice. 04:41: Nothing “plays” the block universe - it just is, and temporal phenomena like us are just embedded in it, when you look at it in the right way. 05:11: ... - that’s the idea that this shock-front of the present creates the block universe as it proceeds forward, weaving the past out of ... 05:24: Believe it or not, we can actually science these very philosophical ideas, with just a little help from the smartest guy in the block universe. 05:33: The representation of the block universe that I showed you is very Newtonian. 05:47: Newton says there’s only one way to slice the universe. 06:08: How do we even say what “now” means for other parts of the universe? 06:22: ... represent the region of the block universe that we can possibly perceived with a light-cone - signals from things ... 06:38: Whatever events live on that cone represents the universe that we see around us, carried to us by light. 09:04: ... the effect is tiny, but the “present” at the edge of the observable universe veers back and forth by a couple of centuries every time you switch ... 09:23: Imagine that the future is created as the wave of the present sweeping out the block universe. 10:19: ... present time slice with observers and their remains no part of the block universe that couldn't be considered the past according to someone who lives in ... 10:40: ... that only the present exists, that only the current “slice” of the block universe has a meaningful reality - because it’s impossible to define what that ... 10:54: ... exists and the future doesn’t - at least in the sense of a growing block universe, again, because the “present” of someone else on your slice of present ... 11:09: ... we’re left with two options: 1) the entire block universe has a meaningful existence; or 2) if you don’t want the future to exist ... 11:28: Nothing outside that section of the block universe can be ascribed a definite reality until you interact with it. 11:45: ... palatable the materialist - to those who like to believe in an actual universe independent of the ... 13:07: ... we're officially designating you the coolest dude in the block universe - that means past, future, and present - never mind that all of those ...
	2020-10-05: Venus May Have Life! 12:15: The discovery of alien life in our nearest planetary neighbor would totally change our calculations about the frequency of life in the universe.
	2020-09-28: Solving Quantum Cryptography 11:38: Computing in parallel universes just isn’t helpful here. 17:05: ... "we’re creatures made of light and energy and are at the center of the universe, and we're orbited by specks of dust infested with some sort of mud-based ...
	2020-09-21: Could Life Evolve Inside Stars? 00:39: Which is understandable - carbon-based chemistry enables the most complex structures that we know of in this universe. 01:03: ... proposes that fundamental kinks and defects in the fabric of the universe - cosmic strings beaded with magnetic monopoles - may evolve into ... 03:04: These may have been formed soon after the Big Bang when massive phase transitions swept across the universe. 04:02: ... are called domain walls - they’re the boundaries between regions of the universe with different properties - for example, different vacuum ... 06:02: ... example, there’s this scenario in this early universe symmetry-breaking stuff where, after the monopoles form, they split in ... 08:56: Little low-entropy blips like life ultimately accelerate the increase in entropy of the universe. 13:16: Because beauty is not a fundamental property of the universe - it is, by definition, a subjective sense.
	2020-09-08: The Truth About Beauty in Physics 04:29: The universe does obey deep, underlying symmetries that are reflected on all scales of complexity. 08:20: Dirac knew he was on the right track based on an abstract sense that the underlying laws of the universe SHOULD be elegant. 10:22: But Weyl’s theory made some predictions that simply did not reflect the real universe - ultimately it was just plain wrong.
	2020-09-01: How Do We Know What Stars Are Made Of? 00:39: A hundred years ago, we were starting to plumb the deepest mysteries of the universe with Einstein’s relativity and with quantum theory. 07:49: In astrophysics, these sort of messy, competing effects rule the universe. 10:33: Stars went from being utterly mysterious to one of the best-understood denizens of the universe.
	2020-08-17: How Stars Destroy Each Other 10:05: Those supernovae are visible not just across the galaxy, but in galaxies across the universe. 10:32: ... in my apartment we finally managed to develop protocols to protect the universe from Earthly lurgies and so here I am, floating in the void once ... 12:12: ... black holes may have formed from the extremely dense matter of the early universe, and these would have different mass restrictions than stellar black ... 12:44: ... primordial black holes exist in some abundance at these masses, then the universe should be very faintly humming with a gravitational wave background from ...
	2020-08-10: Theory of Everything Controversies: Livestream 00:00: ... two-part series here on space time our great quest to understand the universe to find the mechanics of base reality and to understand why our ...
	2020-07-28: What is a Theory of Everything: Livestream 00:00: ... brian and his amazing work trying to understand the origins of the universe that's where to look so brian thanks for joining us yeah thanks matt ...
	2020-07-20: The Boundary Between Black Holes & Neutron Stars 00:00: When we detected the very first gravitational wave, a new window was opened to the mysteries of the universe. 08:26: We also see the results of these mergers in gamma ray bursts - frequent flashes of energetic light from the distant universe. 10:52: But if it IS a neutron star then we’ve learned a ton about the most extreme states of matter in the universe. 13:53: A couple of you asked why we think there had to be an actual imbalance in the number of antimatter versus matter particles in the early universe. 14:01: Couldn’t the two just have become separated in the early universe and now occupy different parts of the universe? 14:33: ... if there WAS an antimatter section of the universe, you’d have a great wall thorugh the universe where hydrogen and ...
	2020-07-08: Does Antimatter Explain Why There's Something Rather Than Nothing? 00:00: The most precious substance in our universe is not gold, nor oil. It’s not even printer ink. 00:06: ... it may hold the answer to the question of why anything exists in our universe at ... 00:22: ... particle in our universe has its exact counterpart: an anti-particle identical in every way, but ... 01:25: ... most likely answer seems to be that the universe started out with a little more matter compared to anti-matter. If there ... 02:04: ... seems there must be something inherently different in the way the universe interacts with particles versus anti-particles. The universe must not ... 02:12: ... physicists think the answer lies in the fundamental symmetries of the universe, or, rather, in the breaking of these symmetries. We’ve discussed this ... 02:51: ... - then it becomes its own antiparticle. Because we expect the universe to be CPT symmetric, we expect it to treat antimatter in exactly the ... 03:13: ... Wu’s famous cobalt-60 experiment proving that a mirror image of our universe would be distinguishable from our own. Then, charge and parity combined, ... 03:38: ... have contributed to the asymmetry of matter and anti-matter in the early universe, in a process called “electroweak baryogenesis.” But, at least at the ... 04:05: ... CPT symmetry really IS violated however it may explain why we live in a universe of matter, and would undo a lot of what we think we know about quantum ... 04:48: ... must hold. But, we already know that our current understanding of the universe is incomplete. It doesn’t explain dark energy, dark matter, or this ... 10:56: ... cause all sorts of terrible consequences to our current model of the universe, so scientists aren’t holding their breath. They’re pretty sure ... 11:51: ... matter-antimatter imbalance and to the fact that we have matter in the universe at all. Maybe it’ll come from CPT violations measurable only in future ...
	2020-06-30: Dissolving an Event Horizon 00:00: Black hole singularities break physics - fortunately, the universe seems to conspire to protect itself from their causality-destroying madness. 00:30: Space and time switch roles, pathways open up to other universes, and in some cases time travel becomes possible. 00:44: ... the speed of light, and time freezes from the perspective of the outside universe. ... 00:57: In the most real possible sense, the interior of the black hole is its own separate spacetime, excised from our universe. 01:12: Without it, the infinitely dense singularity and its surrounding madness is exposed to the outside universe. 01:59: ... a naked singularity might be formed in the first place, and how the universe seems to work very hard to protect itself from ... 06:31: ... situation - in the far distant future, even if all particles in the universe decay, we may be left with only radiation and these naked, charged ... 10:32: Once again, the universe appears to have a mechanism to avoid the naked singularity. 12:54: ... hypothesized to be the rescaled infinite late-time forever of a previous universe, leading to a potentially endless chain of universes, or ... 13:27: ... corresponds not to just the very, very large late time of the previous universe, but actually to the “conformal infinity” of the previous - so all the ... 13:46: Inyobill asks if we’re assuming that the lightest particles are without dimension, so they have an undefined size relative to the universe. 14:04: It has the same relative size compared to the universe whether that universe is trillions of light years across or a millimeter across. 14:13: But that’s not enough to make the universe scale invariant. 14:40: ... the case of a universe full of photons - I THINK the idea is that when you rescale both space ... 15:14: ... cosmology, photons and gravitational waves can pass the boundary from universe end to new big bang, and so there may be a way to send messages between ...
	2020-06-22: Building Black Holes in a Lab 00:16: ... holes are about the worst subjects for direct study in the universe. First there’s the whole thing about never being able to see inside one ... 07:41: ... recently. Very deeply in fact - we’ve traveled through them to other universes. Their physics is extremely speculative, but some of that physics is now ...
	2020-06-15: What Happens After the Universe Ends? 00:00: Our universe began in a state of ultimate heat and compression in what we call the big bang. 00:20: What, if anything, happens after our universe? 00:36: Conformal Cyclic Cosmology is a story of the origin and the end of our universe from great mathematical physicist Sir Roger Penrose. 00:45: ... goes like this: the infinitely far future, when the universe has expanded exponentially to to an unthinkably large size, and every ... 01:31: Here, conformal is for the “conformal scaling” needed to turn your gigantic end of the universe into a tiny new big bang. 02:08: We would say that our universe has conformal invariance under scale changes - so the angles don’t change if you change the size smoothly. 02:17: It makes a big difference whether every atom in the universe is right next to each other or a billion light years apart. 02:31: For example, consider a universe that’s one light-second across, and it exists for the span of a single second. 02:42: Scale it up by around 30 quintillion times to describe a second universe that’s a billion light years across and lasts a billion years. 02:54: Let’s say these universes contain no matter - only photons - light. 02:59: ... although obviously they’re packed much closely together in the smaller universe. ... 03:08: ... the life of both universes, those rays trace out the same pattern - all the angles between them stay ... 03:28: Remember, the universes contain only light - no observers and no clocks. 03:39: For those photons, the beginning of their journey is the same as their end, and these universes are equivalent. 03:44: So there’s a crude notion of how a tiny early universe could be equivalent to a gigantic late universe. 04:11: Surely, then, the big universe will have more length and time ticks. 04:15: ... simplify things by gridding up an imaginary universe with only one dimension of space on the x-axis and one dimension of time ... 04:42: Let’s take two instantaneous events in this universe, separated in both space and time. 04:54: Now in Einstein’s universe it’s not quite that simple. 05:48: So it turns out that we grid up the universe by the rate of ticking of the clocks of its travelers. 05:55: But what if the universe has no clocks? 05:59: That would be the case of a universe that contained only light. 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. 06:36: ... if you have even a single electron in the universe you can build a clock and can tell the difference between the one ... 06:47: But with only light or other light-speed radiation there’s nothing internal to those universes that can tell them apart. 06:58: So how does this apply to our universe? 07:00: Well, it may be that in the extreme far future our universe will contain only radiation. 07:16: ... that’s speculative, but it may be the case that we’re left with only a universe of photons, electrons and positrons, and neutrinos, as well as gravitons ... 07:31: But the others do have mass, so presumably there’s still a way for the universe to tell that it’s gigantic. 08:06: So that’s the late universe. 08:15: But what about the early universe? 08:57: ... a lower energy - could eliminate elementary particle masses in the late universe ... 09:05: In the first tiny fraction of a second we can think of the universe as being full of effectively or actually massless particles. 09:13: Hence the concept of time is as meaningless as in the late universe. 10:29: So you stitch these rescaled “conformal hypersurfaces” together and you get this endless chain of universes. 10:37: Penrose calls each universe in the chain an “aeon”. 10:41: ... of time to be stitched together by this sort of conformal rescaling, the universe needs a positive cosmological ... 10:57: Which our universe has, so no problem, but it’s interesting that it worked out so neatly. 11:18: ... radiation can pass between universes, conformal cyclic cosmology gives a natural explanation for the extreme ... 11:28: This was actually Penrose’s motivation in the first place: to explain the apparent smoothness of the early universe. 11:45: ... is a standard explanation for the smoothness of the early universe - its cosmic inflation - a period of extreme exponential expansion that ... 12:13: That then inspired this daisy-chaining of universes, which eliminated the need for inflation. 12:28: ... period is equivalent to the rescaled late-time forever of the previous universe, where exponential expansion was fueled by dark ... 13:16: ... radiation can travel between universes, and if the end of the previous universe was not completely smooth that ... 13:28: Penroses proposes that the collisions of super massive black holes in the previous universe may leave rings on the sky in the next. 13:56: They wonder if civilizations might be able to communicate between universes. 14:09: ... of gigantic black holes, they could potentially send information between universes. ... 15:01: ... inscribing your name on the Cosmic Microwave Background of the next Universe to continue your glory and to seriously confuse the astronomers of the ... 18:05: ... while being blasted by a supernova, and frozen by the heat death of the universe all at the same ...
	2020-05-27: Does Gravity Require Extra Dimensions? 02:53: ... our universe were 2-dimensional - say, a flat plain - then gravity would be spread ... 03:09: ... if our universe had more dimensions, say 4, then gravity would spread out over the ... 04:05: ... perceive a 3-D universe, but most of our movements from day to day are only in 2 of them - ... 05:45: And that’s the sense in which there may be more than 3 spatial dimensions in this universe. 05:57: ... spatial dimensions, coiled-up tight at every point in the extended 3-D universe. ... 09:47: ... high-precision measurements to learn about the fundamental nature of the universe. ... 12:11: For now, we'll have to content ourselves with our merely 4-dimensional universe - four... 13:29: ... regions like the Carter time machine and the infinite string of parallel universes. ... 14:04: ... accept Hugh Everett's many worlds interpretation, which implies that the universe splits at every quantum ... 14:48: Well, the universe on the other side of the black hole is probably a figment in the math - which I suppose you can call broken math if you like. 15:03: After all, the universe may be incredibly well described and modeled by the math, but that doesn't mean the universe is the math. 15:16: And in the case of the black holes, several unreasonable assumptions allow us to trace geodesics into alternate universes. 15:24: ... example, the parallel universe through the non-rotating Schwarzschild black hole requires the ... 15:33: ... the string of universes through the rotating Kerr black hole requires the assumption that the ... 15:44: ... in reality, impossible-seeming things like an infinite string of universes or a time machine indicate that the math may have led our physical ...
	2020-05-18: Mapping the Multiverse 00:09: ... equations of general relativity for a rotating black hole, the universe does not come to an abrupt halt at the bottom of the gravitational pit ... 07:41: Also, there are no horizons above you - there’s a straight path to the outside universe - but it is certainly not our universe. 10:11: But not only is the black hole in your past - the entire universe that you came from is in your past. 10:18: You caught a glimpse of the entire history of that universe the moment you crossed into the white hole. 10:33: Well this has to be a new universe, because it’s definitely not the one you came from. 10:37: ... not the bizarro negative time traveling universe either - here, the laws of physics are the same as where you started - ... 10:58: If you enter that you’ll be able to take the entire fair ground ride once again, skipping ahead to yet another universe, and so on ad infinitum. 12:42: ... shutting off any potential magical portals to time machines or new universes - probably before they ever ... 13:30: You have the same inner horizon and chain of wormhole-connected universes. 16:07: ... lazy - what I wanted to get across was the following: As you rewind the universe towards zero age, distant points in space end up closer and closer - and ... 16:27: So in an infinite universe, every definable galaxy or definable location ends up right here on top of us at some point in the rewind. 16:36: The universe approaches infinite density in the limit as time approaches zero.
	2020-05-11: How Luminiferous Aether Led to Relativity 13:52: ... how it is that astronomers could possibly calculate the age of the universe, given that we don't even have light from its very beginning. There were ... 14:06: ... Lord asks how we reconcile the idea that "the universe is infinite in size" and "the universe has a finite age" if the universe ... 14:23: ... let's pretend that the expansion rate is constant. And for an infinite universe the "size" is just the average distance between galaxies. Half that age ... 14:42: ... divided by any positive number is still infinity. So even when the universe was a tiny fraction of a second old, it was still infinite, even though ... 15:13: ... all that aside - we don't actually know A) if the universe truly is infinite, or B) what happened before 10^-43 seconds - the ... 15:32: ... Jeffryes has another mind-bender. As we look farther out into the universe, we are looking at the inner surfaces of spheres which are progressively ... 16:07: Well that’s easy - the universe has expanded by a factor of 1100 since the CMB was released. 17:25: Robert Smith quips the universe was smaller and hotter when it was young, weren't we all?
	2020-05-04: How We Know The Universe is Ancient 00:00: ... universe is precisely 13.8 billion year old - or so our best scientific methods ... 00:17: ... of thousands of years old. We could be forgiven for assuming that the universe above is fixed and unchanging. But the Earth was also thought to be ... 00:55: ... there are no rocks from the beginning of the universe. There aren’t even any photons from the time right after the Big Bang. So ... 01:35: ... of stars - other “Milky Ways”, or as Immanuel Kant called them, island universes. We now call them galaxies. It all changed in the 1920s. First Vesto ... 02:57: ... Until then, science had provided no reason to imagine that the universe was anything but static – that it had always been there, and that it had ... 03:09: ... new picture was far more dynamic. We live in an evolving, expanding universe. The recession of the galaxies makes perfect sense in the context of ... 03:24: ... Friedmann solved Einstein’s equations and found the possibility of a universe that could change in size - a result that Einstein himself dismissed at ... 04:40: ... idea that the universe has a beginning brings to mind the creation stories of various mythic or ... 06:22: ... - and a big part of the motivation is that it tells us the age of the universe. In fact if you take the fraction one over the Hubble constant - in the ... 07:07: ... did this calculation in the early 1930s, they figured that the universe is a bit less than two billion years old. Even then that figure didn’t ... 07:40: ... he got distances wrong about a factor of two too small. Overnight the universe doubled in ... 08:17: ... measures which I’ll come back to, Baade calculated a new age for the universe. At a conference in 1952, he announced that it must be 3.6 billion years ... 08:58: ... to galaxies, and so calculate the Hubble constant and the age of the universe. It’s similar to the Cepheid method because it’s based on comparing the ... 09:39: ... the problem with HII Regions he came up with a new age estimate for the universe - 5.5 billion years. That was in the 50s. As the decade went on, Sandage ... 11:07: ... out how much of all that stuff there actually is. The mass of the universe - which is mostly in dark matter - can be found by adding up the ... 12:09: ... the slowing effect of gravity to ultimately give us an age of the universe very close to the roughly 13.8 billion years that we ... 12:25: ... days, the gold standard for measuring the age of the universe is to get the matter content, and the dark energy content, and the ... 12:59: ... for plugging into the Friedman equations, which define the way the universe would expand in the many billions of years following the release of that ... 13:45: ... of both space and time, I want to thank you on behalf of the universe for ensuring that we keep paying attention to it despite ... 14:36: ... its most open, entering the event horizon ejects you into the parallel universe. You can construct a wormhole in general relativity that does not have an ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... interest hardcore physics and astrophysics but it turns out that the universe is big end and deep and I cannot think of an end to topics that I want ...
	2020-04-22: Will Wormholes Allow Fast Interstellar Travel? 00:00: ... have long been one of our favorite method for traveling across fictional universes. But they've also been a very serious field of study for some of the ... 01:09: ... two regions described by the Schwarzschild solution not as parallel universes, but rather as overlapping layers of the same universe. It’s easier to ... 02:08: ... layers of reality - it could instead connect distant regions of our universe. ... 02:34: ... connected” spacetime could allow near-instantaneous travel across the universe because the wormhole throat would remain the same, very short length no ... 04:08: ... back to a representation of the black hole that we saw in our parallel universe episode. This is the Kruskal-Szekeres diagram. Now I don’t want to go ... 04:50: ... and Rosen discovered is represented as a mirror reflection to our universe. The black hole also has a mirror reflection that we call the white ... 05:17: ... is a so-called “eternal” black hole - no matter where you are in the universe, if you travel to the left at any possible speed you’ll find the event ... 11:03: ... can’t exist, if for no other reason than our very strong sense that the universe has to make sense at a fundamental level. Stephen Hawking expressed this ... 13:26: ... of our star-faring future we’ll have to take the long way around the universe. But even if we can’t use them as intergalactic shortcuts, wormholes are ...
	2020-04-14: Was the Milky Way a Quasar? 00:00: The Milky Way galaxy is relatively calm by the destructive standards of the rest of the Universe, and compared to its own very violent past. 00:38: Whatever is happening here on Earth, the universe remains awesome. 01:03: Yet as extreme as it may sound, the present-day Milky Way is actually relatively calm by the standards of many other galaxies in the Universe. 01:19: But across the Universe, there are loads of “active” galaxies - ones that harbour active galactic nuclei, or AGNs, at their centers. 15:12: ... Current theories on the creation of the Universe state that, if it was created at all and didn't just start, as it were, ...
	2020-04-07: How We Know The Earth Is Ancient 00:00: ... recent - as recent as our discovery of the true spatial vastness of our universe. And it came as scientists tried to measure the age of the Earth. What ... 03:43: ... speculated about the existence of galaxies beyond the Milky way - Island Universes, as he called ... 04:32: ... the Copernican principle - Earth is not in a privileged position in the universe, and so the laws of physics work the same everywhere. Hutton’s ... 10:35: ... around the same time that astronomers proved that Immanuel Kant’s Island Universes were indeed other galaxies, many millions of light years away. The world ...
	2020-03-31: What’s On The Other Side Of A Black Hole? 00:10: ... continue beyond. In these maps, black holes become wormholes, and new universes lie on the other ... 01:38: ... map the universe we need 3 dimensions of space instead of two, plus the dimension of ... 04:14: ... can travel faster than light, this makes very clear what parts of the universe are accessible. Close to the event horizon, even a light-speed path has ... 04:31: ... space and time also bunch up at infinite distance so tha t the entire universe fits on the one diagram. Well, the whole universe? Not ... 06:15: ... we trace our light ray backwards from our universe we encounter a region that looks just like the black hole - but with ... 06:51: ... abound: is this parallel universe real? Can we get there? Well before I go on, I should say - the map I ... 07:16: For now, let’s see if we can travel to the parallel universe of the eternal black hole. 07:21: ... only way to pass between these universes is to travel faster than light. You can see that by the fact that the ... 07:32: ... which would dip beneath the event horizons and emerge in the mirror universe. You’ve just traversed an Einstein-Rosen bridge - a wormhole. We’ll come ... 08:22: ... inside the black hole what do you see? Light can reach you from the universe behind - those are photons that overtake you heading towards the central ... 09:00: ... - instead you’re ejected through the parallel horizon into the parallel universe. Within the black hole, you see an event horizon both behind AND ahead of ... 09:39: ... you could reach the parallel universe, what would you see? This is where opinion is divided. Some think that ... 10:35: ... parallel universe and white hole are needed in the map of the eternal Schwarzschild black ... 10:58: ... though the parallel universe of the Schwazschild black hole isn’t likely to be real, there are ...
	2020-03-24: How Black Holes Spin Space Time 00:03: ... futuristic power generators, galactic-scale bombs, and portals to other universes. ... 00:21: ... and where the flow of time halts from the perspective of the outside universe. It predicts the inescapable region of space that we now call the black ... 01:01: ... observations of the universe have since told us that black holes are very real. We’ve seen the ... 03:27: ... your past within a Kerr black hole. For the bit about visiting other universes you’ll just have to ... 10:51: ... last process we’ll talk about is actually important in the real universe. It’s the Blandford-Znajek process. In this case you have a magnetic ... 12:11: ... black holes are very real and powerful players in the energetics of our universe - but they’re also very worrying to physicists, because they threaten ...
	2020-03-16: How Do Quantum States Manifest In The Classical World? 16:29: ... is it inevitable that there are exceptionally rare timelines where the universe gets to a state of low entropy to produce another Big Bang? In other ... 18:58: ... Keith Richards, I hope you enjoy watching the heat death of the universe. ...
	2020-03-03: Does Quantum Immortality Save Schrödinger's Cat? 04:21: ... we need to do it for nearly a million times the entire age of the universe in order for the physicist to be likely to survive ... 16:24: ... confronted with clues to greatest mysteries of the universe, are you gonna be like "hmm, how can I obscure these cosmic insights in ...
	2020-02-24: How Decoherence Splits The Quantum Multiverse 12:16: ... and complexify as it mixes with the wavefunction of the rest of the universe. ...
	2020-02-18: Does Consciousness Influence Quantum Mechanics? 09:33: Then there’s the idea that external reality doesn’t have an objective existence - our minds invent the universe. 10:59: He denied what he called the solipsistic view: that the mind is foremost, that consciousness generates the universe. 11:37: ... and, well, the rest of reality and there are no other observers in the universe to give conflicting ... 14:15: The result would have been a cold soup of axions filling the universe.
	2020-02-11: Are Axions Dark Matter? 01:05: ... of physics to be symmetric with respect to certain properties of the universe. If the equations describing a given physical process do not change when ... 05:16: ... to zero - because that reduces the overall energy of the vacuum, and the universe always seeks the lowest energy ... 11:08: ... to explain the invisible source of gravity that seems to dominate the universe - what we call dark matter. If axions do turn out to be real they may ... 12:33: ... week we tried to figure out whether a universe that is infinite in size should contain infinite repetitions of ... 12:47: ... that claimed that even if inflation proceded for the entire age of the universe, the universe would still not be large enough to get duplicate regions. I ... 14:14: ... any rate, it would therefore take way longer than the age of the universe for inflation to make a volume 10^10^90 or 123 times our obserable ... 14:39: ... eternal inflation. Of course all of this is assuming that the universe is spatially finite. The simplest interpetation of the cosmological ... 15:20: ... Gaither asks how far away are these duplicate universes. Very, very far away. Roughly speaking you'd need to travel all the way ...
	2020-02-03: Are there Infinite Versions of You? 00:00: If the universe goes on forever, does that mean there are infinite versions of you? 00:14: ... cosmological equations that so beautifully describe our universe make an uncomfortable prediction: interpreting them in the most ... 00:26: ... not; it could turn out that the universe contains enough matter and energy to close in on itself and be finite, ... 00:37: But according to our best theoretical understanding, an infinite universe seems at least possible - and some would say likely. 00:50: An infinite universe may literally contain every possible thing allowable by the laws of physics - each in infinite multitude. 01:41: ... in which there are as many raffle tickets as there are particles in the universe. ... 03:13: Perhaps you can start to see how this applies to there being infinite yous in an infinite universe. 03:19: ... a perfectly deterministic universe, the starting conditions in any given region - like positions, ... 03:38: The properties of each region are effectively random - set in the beginning of the universe by quantum processes. 03:45: ... the future history of that region will be identical to our part of the universe, leading to the formation of the Milky Way, the Earth, William ... 04:06: ... it’s not a zero probability, and so with infinite regions of the universe - infinite trials, the infinite monkey theorem tells us it’s got to ... 04:36: ... up, in such an infinite universe we wouldn’t find everything - only everything that COULD happen from the ... 05:14: OK, so refining our question: in an infinite universe, does every POSSIBLE thing happen infinite times? 05:24: If there are infinite possible starting configurations for any one region of the universe, then there can be infinite regions without any doubling up. 05:41: ... we could imagine that OUR part of the universe is unique and it’s just other regions that are duplicated, but we have ... 06:02: So what does it mean for two regions of the universe to have the same starting conditions? 07:24: ... expect these values to repeat themselves infinite times in an infinite universe - eventually leading to an exact-enough repetition of both the laws of ... 07:48: If one or more properties of the universe can take on values over an infinite range then no repetitions would be necessary. 08:17: But universes with large vacuum energies will exponentially expand, until that vacuum energy decays to lower values in smaller regions within. 08:27: In fact that’s essentially the eternal inflation picture - one of the most popular ways to produce infinite universes. 09:00: In fact, quantum randomness could allow different starting conditions to evolve into a universe that looks like this one. 09:07: There’s actually a much simpler proof that there’s a finite number of different possible configurations of any region of the universe. 09:40: For our 46-billion light year observable universe there are definitely no more than 2^10^123 possible unique configurations. 09:52: As long as the greater universe has more than than that many observable universe-sized regions, one of them should be identical to this one. 10:10: ... hiding in the laws of physics that we don’t understand, an infinite universe probably does duplicates its parts infinite ... 10:28: That the universe is actually infinite at all. 10:31: ... this may never be testable - we can measure the observable part of the universe to greater and greater precision and see if it has an open or closed ... 10:47: ... the eternal inflation picture then it’s very hard to avoid an infinite universe, or at least one that’s infinite-enough to duplicate ... 10:59: ... allowing infinities into any models describing the physical universe - and their intuition shouldn’t be entirely ... 11:12: But let’s get back to the real question: in an infinite universe, is it inevitable that somewhere a monkey will type out Shakespeare? 11:39: ... who knows - perhaps there’s a near duplicate region of the universe where Shakespeare’s plays are just long strings of S’s underscored with ... 12:04: Now I think it’s hard to avoid that conclusion ... assuming an infinite universe.
	2020-01-27: Hacking the Nature of Reality 02:07: They remained reductionists, and the quest continued for a detailed, mechanical description of the hidden inner workings of atoms and of the universe. 02:16: ... particles are described by vibrations in elementary fields that fill the universe, and all interactions are calculated by adding up the exchanges of ... 10:41: Quantum field theories like QCD surely gives us insights into the nature of the fundamental workings of the universe. 12:13: ... think that the largest structures in the universe today - galaxies and galaxy clusters - as collapsed from quantum ...
	2020-01-20: Solving the Three Body Problem 00:20: ... bodies orbit each other sans any other gravitational influence in the universe. ... 11:21: ... useful for understanding the evolution of dense regions of the universe, where three-body systems of stars or black holes may form and then ...
	2020-01-13: How To Capture Black Holes 00:24: ... but the real promise lay ahead. Every time we learn to observe the universe in a new way we discover new things. When we figured out how to see in ... 04:08: ... disks glow bright enough to be visible from the other side of the universe. More generally, these feeding supermassive black holes are called active ... 11:59: ... on cosmological natural selection - Lee Smolin's idea that maybe new universes are born inside black ... 12:17: ... number of you made a similar observation/question: Shouldn't a universe that's born inside a black hole be limited in mass by the amount of ... 12:49: ... couple of you point out that the idea of black holes birthing universes still doesn't explain where the first something-from-nothing actually ... 13:26: ... what happens when a black hole is absorbed by another black hole? Do the universes collide? Do the constants average out? The answer to this is ... no one ... 14:02: ... On that note New Message feels a bit better learning that even whole universes can be a disappointment to their ... 14:13: ... also commented that they'd thought of the whole black holes creating new universes thing independently to Lee Smolin. I'm making a list, guys. If it turns ...
	2020-01-06: How To Detect a Neutrino 00:13: ... geniuses of Fermilab are tackling ♪ ♪ the most feeble particle in the universe: ♪ (𝘩𝘪𝘨𝘩 𝘥𝘪𝘨𝘪𝘵𝘢𝘭 𝘴𝘺𝘯𝘵𝘩 𝘦𝘯𝘵𝘦𝘳𝘴 𝘳𝘩𝘺𝘵𝘩𝘮𝘪𝘤𝘢𝘭𝘭𝘺) ♪ the ... 07:26: ... and antimatter ♪ ♪ Which, also hopefully, will tell us why we live in a universe made of matter in the first ... 07:38: ... 𝘴𝘺𝘯𝘵𝘩 𝘧𝘢𝘥𝘦𝘴) ♪ should have been created in equal quantities in the early universe, ♪ (𝘩𝘪𝘨𝘩 𝘦𝘯𝘥 𝘰𝘧 𝘴𝘺𝘯𝘵𝘩 𝘥𝘳𝘰𝘯𝘦 𝘸𝘪𝘵𝘩 𝘴𝘰𝘧𝘵, 𝘵𝘢𝘱𝘱𝘪𝘯𝘨 𝘳𝘩𝘺𝘵𝘩𝘮) ♪ and so, should ... 07:51: ... ♪ The fact that we see a universe full of matter ♪ (𝘷𝘰𝘭𝘶𝘮𝘦 𝘣𝘶𝘪𝘭𝘥𝘴, 𝘴𝘺𝘯𝘵𝘩 𝘴𝘵𝘳𝘪𝘯𝘨 𝘱𝘭𝘶𝘤𝘬 𝘧𝘢𝘥𝘦𝘴 𝘰𝘷𝘦𝘳) ♪ means ... 08:31: ... to leptogenesis, ♪ ♪ DR. DON (voiceover): neutrinos in the early universe may have decayed into other matter particles, ♪ ♪ with matter neutrinos ... 09:25: ♪ ♪ ♪ ♪ And that is how you study the most elusive particle in the universe.
	2019-12-17: Do Black Holes Create New Universes? 00:03: What if every single black hole that formed in our universe sparked the big bang of a new universe? 00:24: Physicists have been struggling for some time to figure out why our universe is so comfy. 00:37: Tweak them too much and life, stars, galaxies, the universe as we know it wouldn’t exist. 00:50: ... there are countless universes with different fundamental constants, then it’s not surprising that a ... 01:10: You only need to accept two things: that our universe formed inside a black hole, and that universes can evolve. 01:18: Our universe appears, in some sense, designed. 01:54: It goes like this: the formation of a black hole triggers the formation of a new universe “on the other side” in a new big bang. 02:02: Those daughter universes go on to expand and make their own black holes and hence their own daughter universes. 02:10: ... in their formation the fundamental constants of the daughter universes are shifted slightly and randomly from their parent - mutations are ... 02:20: Some of those shifts improve the daughter universe’s ability to form new black holes. 02:25: ... universes have an advantage in propagating their cosmic genetics, and so gradually ... 02:52: The universe that is better at making stars is better at making planetary systems is better at making us. 03:12: First up, for any of this to make sense black holes need to create universes. 03:38: ... hole, it forms a new region of spacetime, effectively creating a new universe. ... 04:02: ... hole idea by suggesting that the fundamental constants of these new universes could be different to their ... 04:34: ... by this idea, Smolin added one thing: what if, when universes reproduces, the constants aren’t randomly reconfigured but rather change ... 04:58: We have no good reason to believe any of this procreating universe stuff - and Lee Smolin has readily admitted that. 05:14: ... nature of the proposed process means that the ensemble of all universes should very quickly be dominated by ones that are extremely good and ... 05:24: ... given universe may not be totally optimal because its constants varied randomly from ... 05:36: ... that define black hole production should be close to optimal in a given universe, at least for a given mechanism for making black ... 05:49: In our modern universe, black holes are made when the most massive stars explode as supernovae. 05:59: So we should expect our universe to be optimized for producing as many of the most massive stars as possible. 07:16: ... physicist and cosmologist Alexander Vilenkin proposed that if a universe lasts forever then in the distant future, quantum fluctuations of that ... 07:38: ... this is true then the most black holes would be produced by the biggest universes - more space means more chances for these quantum ... 07:52: And that is definitely not our universe. 09:54: ... then, if universes evolve to maximize the number of black holes, then the strange quark ... 10:14: So, if this universe is optimized for black hole production then there should be no neutron stars more massive than 2 solar masses. 12:19: Or, you know, our universe's momma might be a black hole, and we live in an endlessly evolving, proliferating space time. 13:24: ... at the large hadron collider - they’re going to make you a black hole universe. ...
	2019-12-09: The Doomsday Argument 00:25: ... seen how it can be used to explain the fact that both our planet and our universe seem very finely tuned to allow the development of ... 00:37: ... planet and/or universe can be rare and unlikely as long as there are enough other planets ... 00:52: ... how this controversial idea can be used to predict the physics of our universe, and also to predict the imminent demise of the human ... 01:07: ... else being equal, we should expect to be in a pretty typical part of the universe. ... 01:48: ... amount of dark energy, which is the stuff causing the expansion of the universe to ... 01:57: ... the cosmological constant could take on different values in different universes, and its value could be extremely high compared to this universe - up to ... 02:24: But it’s a good thing ours IS low because otherwise our universe would have blown itself up too quickly for stars and life to ever form. 02:33: ... for the anthropic principle - perhaps we’re just in one of the lucky universes with a low cosmological constant because where else could we ... 02:43: But if that’s true, then we should be in the most common type of lucky universe. 02:49: ... were less likely than higher ones, Steven Weinberg reasoned that our universe should have the maximum cosmological constant that would allow galaxies ... 03:18: He had assumed that we should be in the most common type of universe that allows our existence. 03:31: ... observe, with a few assumptions like that the number of astronomers in a universe is proportional to the amount of mass that ends up forming galaxies in ... 04:15: ... future) in their reference class." If a type of environment or type of universe produces more observers, then they are more likely to find themselves in ... 10:42: ... your current self exists besides evolving on a rare planet in a rare universe. ... 13:31: OK, so our last episode was a journal club looking at a study that claimed to have evidence that the universe is not infinite after all. 13:39: ... the curvature of space to get an estimate on the size of the entire universe. ... 13:51: ... the answer is maybe: if the universe is closed and has positive curvature then measuring that curvature ... 14:02: If it turns out to the universe is negatively curved then well it's infinite. 14:22: Daniel M. and Sam Harper ask whether a universe can transition between different geometries. 14:29: ... a universe like ours where matter and energy is evenly distributed on the largest ... 14:39: ... flat or hyperbolic universe remains flat or hyperbolic respectively and so remains infinite, while a ... 14:50: That said, patchs of the universe CAN change in curvature depending on the behavior of matter in those patches. 14:57: ... and galaxies can be positively curved patches in a flat or hyperbolic universe. ... 15:07: That means it's also possible to produce a closed, positively curved bubble universe within an infinite inflating multiverse. 15:16: One commenter, O.N., pointed out that an infinite universe is technically possible within a bubble that otherwise looks finite from the outside. 16:05: ... within Einstein's general relativity, it's not clear how such a universe would form, and certainly forming a 3-torus as a bubble out of eternal ... 16:21: ... wisdom from Ethan Seigel, whose excellent Forbes article on this closed universe paper emphasized a point that we mentioned only in passing that is worth ...
	2019-12-02: Is The Universe Finite? 00:27: This is the cosmic microwave background radiation - the left-over heat-glow from the very early universe. 00:56: A clue that our universe may be actually be finite in size. 01:02: ... Astronomy paper that just reported this: Planck evidence for a closed Universe and a possible crisis for cosmology by Eleonora Di Valentino, Alessandro ... 01:25: ... thousand years after the big bang, only to be frozen in place as the universe ... 01:38: ... satellites, and the initial analysis from the Planck map, pointed to a universe that is infinitely large and geometrically flat, and is dominated by the ... 01:56: For the most part this has agreed with our observations of the modern universe. 02:06: ... in cosmology - the Planck team calculate an expansion rate for the universe that does not match the expansion rate observed today - particularly the ... 02:24: ... this tension, the teams agree on lots of things, including fact that the universe is, as close as we can tell, geometrically flat and ... 02:41: ... claim to have found clear evidence in the Planck data that the universe is NOT flat, but rather curved inward on ... 02:50: If they’re right, the universe is not infinite in extent. 02:59: Albert Einstein’s general theory of relativity allows for three simple geometries for our universe. 03:04: We have 1) a universe with positive curvature. 03:19: Just like with the 2-D spherical analog, lines that start parallel in such a universe eventually come together. 03:26: Such a universe has a finite volume, just as a sphere has a finite surface area. 03:36: Then there’s 2) the negatively curved universe, analogous to a hyperbolic plane - an infinite saddle shape. 03:46: Such a universe is open - space goes on forever. 03:50: And finally 3) the universe with zero curvature - a geometrically flat universe. 03:56: Parallel lines stay parallel, your high school geometry still works, and again, space in such a universe goes on forever. 04:04: The geometry of the universe is determined by two things: 1) the mass and energy it contains. 04:10: ... stuff in the universe - a higher energy density - means more gravity, which tends to pull a ... 04:26: Rapid expansion tends to give negative curvature and open the universe - make it infinite. 04:34: Like I said, previous studies were pointing to a flat universe. 06:02: ... passes through a universe full of galaxies and galaxy clusters - all of which have enormous ... 06:15: The result is like looking at the universe through a lumpy pane of glass. 06:31: ... CMB map - and they found way more than would be expected for an open universe. ... 06:45: More lensing suggests the universe has a higher energy density than previously thought. 06:56: ... enough extra matter revealed by that lensing to actually close the universe into a finite hypersphere surface rather than an infinite flat ... 07:33: That curvature was slight - meaning the universe is still unthinkably vast, but if this is right then it’s not infinitely large. 07:50: So, is the universe really closed and finite? 08:04: Well even if the universe is finite, it’s still expanding and that expansion is accelerating. 08:15: Also, beyond a certain distance from us that expansion exceeds the speed of light, so there’s no lapping the universe regardless of its geometry. 08:25: ... also a reason to be cautious before we conclude that the universe is closed at all The researchers looked at a different indicator of the ... 08:50: The four-point correlation function found an amount of lensing consistent with the old result of less energy density and a flat universe. 09:19: ... assumptions are correct then there’s less than 1% chance that a flat universe would look like a positively curved universe just due to random ... 09:30: So, there are three possibilities really: one is that the universe really is positively curved and finite. 09:48: ... results for both the geometry and the expansion history of the universe. ... 10:34: That would be surprising because most data points to a flat universe. 10:53: That “missing physics” could turn out to be the subtle clue needed to push our understanding of the universe to the next level. 10:59: ... example, if the expansion rate of the universe really has evolved it may mean that the behavior of dark energy is ... 11:09: In fact, if the universe really is curved and closed, the discrepancy between the early universe and modern expansion rates becomes even stronger. 11:20: That’s because the previous calculations of that discrepancy assumed a flat universe. 11:40: ... new possibility, and also hones in on the real physics of our universe - even if that means honing in on any errors we’ve made in our ... 14:57: Penny Lane notes that anyone believing in a Goldilocks universe clearly never experienced English weather. 15:04: ... gets to an important point: anthropic seletion only demands that our universe be able to produce observers who think about the nature of the ... 15:15: There's no reason they need to be in any way happy about the universe they observe. 15:29: Regis Bodnar has a great point: while it may be technically possible to observe a typical universe, it's perhaps impossible to define one. 15:40: ... do we define a typical universe? Well it would be one whose particular configuration of fundamental ... 15:52: ... that's probably some massively exponentially accelerating universe because the cosmological constant in most universes seems likely to be a ... 16:02: ... a typical universe is mostly empty Singapore Breaking News likes to play space time loudly ...
	2019-11-18: Can You Observe a Typical Universe? 00:07: The anthropic principle guarantees that you are NOT seeing the universe in its most typical state. 00:34: ... system which demoted the Earth from its position at the center of the universe into just one of several planets orbiting the ... 00:45: ... an ordinary galaxy among 100s of billions of galaxies in the observable universe. ... 01:00: ... notion that we occupy neither a central nor privileged position in the universe is called the Copernican principle after the guy who started it ... 01:11: It’s extremely important - it allows us to study the distant universe confident that its laws of physics are the same as we experience on Earth. 01:52: Nor, perhaps, is our entire universe. 01:55: ... planet and our universe must have at least one non-typical quality - they must have been able to ... 02:13: ... certain observations of the uniqueness both of our planet and of the universe, and how these feed into two versions of the anthropic ... 02:35: ... anthropic principle states that we must live in a place and time in the universe capable of supporting observers - in our case, a habitable biosphere, ... 03:01: That means the fundamental constants and initial conditions of the universe must be just right to allow nice habitable planets to form. 03:10: ... capable of producing observers; be that environment a planet within a universe or a universe within a ... 03:31: ... things get interesting when you add the fact that our universe seems to have fundamental constants and initial conditions that seem ... 03:44: ... for this fine-tuning besides blind luck or design: if there are enough universes or enough regions within this universe, and their properties can vary, ... 04:04: And we shouldn’t be surprised that we find ourselves in one, even though Earth and a life supporting universe might be quite atypical. 04:21: ... constants take on the values that they do - or why they may vary between universes. Or even why their should be multiple ... 04:37: ... somehow had some causal influence on the initial formation of the universe. ... 05:33: The universe’s most finely-tuned parameter is its unthinkably low initial entropy. 05:45: All particles in the observable universe were packed together in a subatomic-sized dot. 06:01: ... universe will spend the vast majority of its perhaps-infinite life in a state of ... 06:16: ... high entropy states must be the norm - in the full timeline of our universe, but probably also across the multiverse, if it ... 06:32: We certainly don’t observe the universe in a typical, observer-hostile state, and and so it’s tempting to use the anthropic principle here. 07:54: And by cosmos I mean the sum total of reality, be it universe or multiverse. 08:33: For example a fluctuation the size of a galaxy is insanely more likely than one the size of our observable universe. 09:08: ... the assumption that our universe resulted from a simple random fluctuation in an otherwise high-entropy ... 09:32: ... expand for the right amount of time, so that life may always be in big universes. ... 09:46: If we then assume that the starting conditions for our universe were typical, that can tell us something about the physics of how universes are born. 11:41: The anthropic principle in its proper form is without question an important thing to take into account whenever we observe the universe. 11:49: It’s one possible explanation for why our planet and our universe appear to fit us so well, even if they weren’t intentionally made for us. 13:03: ... reasoning real soon, and talk about what you can know about your universe, given your privileged status as a typical conscious observer of space ... 14:08: ... about how the constants of nature seem to be fine tuned for life in our universe - and how this may imply that there are countless universes beyond our ... 14:21: ... people had the following objection: they say that the universe isn't really fine-tuned for life or for observers because there could be ... 14:43: ... can probably assume that for an intelligent observer to emerge in any universe, that universe must be capable of forming complex structures - whether or ... 14:56: ... the universe needs to last a reasonable amount of time, have stable regions and ... 15:16: ... that parameter space where observers can arise, most of it - hence most universes - should be devoid of ... 15:44: ... but the point is that UNLESS that principle is somehow connected to the universe's later developing life and structure, why should it have landed on one of ... 15:59: ... just as easy to imagine a physical principle that gives you only one universe with an unavoidable combination of fundamental constants that was ... 16:11: So I still count this option as either "getting lucky" or that the later emergence of life was somehow retrocausal of the universe's knob-setting. 16:26: ... makes a great point: surely if this were the Goldilocks universe there would be life on almost every planetary body, even in this solar ... 16:36: That would certainly be true if such fertile universes where anywhere near as common as our relatively barren one. 16:43: ... observer - so maybe the most typical observers are in relatively barren universes, and there are just way more of those ... 17:18: ... tuning that may be just as bad as the fine tuning needed for life in our universe. ... 18:01: If anyone does this they get a free universe. 18:06: Although if you can do this you can probably also build your own portal gun and visit all the universes you want.
	2019-11-11: Does Life Need a Multiverse to Exist? 00:03: Life exists in our universe. 00:07: Therefore our universe is capable of producing and supporting life. 00:16: Therefore there are countless universes. 00:26: Our universe seems to operate according to a set of fundamental rules that we try to understand and model with the equations of our laws of physics. 00:43: We can’t determine the values of these constants from pure theory - we have to measure them in the real universe. 01:11: 20 free parameters, like movable dials that seem to be tuned to very specific numbers in this universe. 01:21: Perhaps in other universes they could be set to other values entirely. 01:34: ... there are few or many free parameters defining the physics of this universe, one thing is becoming increasingly clear: it’s good that they have the ... 01:44: ... the constants defining our universe were different - a tiny bit different in some cases - then our universe ... 01:58: ... seem to live in a fine-tuned universe - a goldilocks universe - and this seems to imply one of the following ... 02:37: ... the anthropic principle as it related to where we find ourselves in this universe - necessarily within what may be an extremely rare habitable ... 02:50: We must find ourselves at a place and time in the universe capable of producing observers. 03:05: Well, Carter also has a strong version. The universe must be such as to admit the creation of observers within it at some stage. 03:13: ... version of the anthropic principle explain why life-friendly planets or universes exist; they just say that if such places do exist at all, that’s where ... 03:27: ... bias that may help us understand why we live in such a finely-tuned universe. ... 03:36: ... that explanation to work, we need to propose that many NON-finely tuned universes exist as well - in the same way that many uninhabitable planets ... 03:54: Today I want to set the stage by showing you just how finely-tuned this universe seems to be. 04:02: In our universe, quarks tend to stick together to form protons and neutrons, which stick together and attract electrons to form atoms. 04:30: There’s no other mechanism in the universe capable of similar natural complexity - at least as far as we can tell - which is, frankly, pretty far. 04:40: But it wasn’t at all inevitable that our universe had to be capable of life-enabling chemistry, or of complex chemistry at all. 04:48: One of the first clues to the fine-tuned nature of this universe was noticed by astrophysicist Fred Hoyle in the early 80s. 04:56: He realized that with a tiny tweak of certain properties of the carbon nucleus, the universe would have hardly any carbon. 05:05: The vast majority of carbon in the universe is produced in the cores of massive stars. 06:01: ... a diproton - a neutron-free version of helium which is unstable in our universe. ... 06:12: ... this stuff would be like superfuel for stars - meaning all stars in the universe would have burned out before life ever got a ... 06:36: Now, this all assumes that the universe has the same strength of gravity as our real one. 07:05: The stability of atoms and the rate of fusion in stars and in the early universe depends on the balance between electromagnetism and the strong force. 07:14: Mess with these much in either direction and the universe remains a mist of subatomic particles. 07:19: ... that there are about the same number of protons as neutrons in the early universe. ... 08:25: ... is just right for things like stars and complex matter to form in our universe. ... 08:45: ... in the 90s as astronomers tried to measure the expansion rate of the universe, only to find that expansion was ... 09:16: ... around, resulting in a quantum buzz of energy everywhere in the universe that would accelerate its ... 09:45: Such a universe would expand so quickly that no structure would ever form. 10:25: ... vacuum energy to take on different values in different regions of the universe - or in different universes - and I’ll come back to ... 10:35: But even so, odds are stacked enormously against a universe that doesn’t blow itself up before life has a chance. 10:43: We don’t know why the dials of our universe are set the way they are. 10:55: ... there are many universes, and the physics of these universes can vary, then maybe we’re just in ... 11:39: Countless such configurations are possible, with any given universe - or perhaps every section of the same universe - having different properties. 11:47: And there are other proposals for how the fundamental constants might vary over space or between universes. 11:54: But how to get enough universes to make sure that our extremely improbable configuration of dials becomes a sure thing? 12:04: ... Linde’s eternal inflation is perhaps the most popular - bubble universes forming in a larger exponentially expanding spacetime, and in each ... 12:21: ... Lee Smolin’s idea that universes are born when black holes form, with each new universe having slightly ... 12:34: ... principle seems to make sense of the incredible fine tuning of our own universe. ... 15:08: ... also true of properties of our universe - yeah you might be able to get different types of complexity and even ... 15:24: ... tuning of the universe is hard to deny - the fine tuning of our planet is less clear, but the ...
	2019-11-04: Why We Might Be Alone in the Universe 00:00: ... so crazy that I just happen to be in one of the rare places in our universe where I don’t instantly asphyxiate or freeze or vaporize or ... 00:12: Actually, it turns out that our very privileged perspective on the universe from Earth’s comfortable biosphere may tell us a lot about our reality. 00:30: It shouldn’t be surprising that we live on a planet that can support our existence, in a universe that can produce such planets. 00:57: ... strong anthropic principle tells us that an observed universe must be able to produce observers - and we’ll get to the implications of ... 01:17: It says that we must find ourselves in a part of the universe capable of supporting us. 01:29: ... for this observer selection bias is important to understanding why the universe looks the way it does from our ... 01:44: When combined with the apparent absence of alien civilizations, it may tell us that intelligent life is incredibly rare in our universe. 02:33: For example, if there’s only one life-bearing planet in the galaxy, or in the universe, you’re going to be on it.
	2019-10-21: Is Time Travel Impossible? 04:41: ... are a number of ways they might – from connections between universes in the interiors of black holes to miniscule wormholes appearing and ... 08:20: His involved an entire universe, rotating about a central axis and with matter and dark energy perfectly balancing it against collapse or expansion. 08:29: So to build this time machine we just need construct an entire universe – which allows us to travel back in time only within that universe. 10:12: In other words, the universe has to make sense, time-travel or no. 10:54: ... many-worlds interpretation of quantum mechanics, in which every possible universe exists, splitting off in an infinite ...
	2019-10-15: Loop Quantum Gravity Explained 00:16: ... with that of the vast scales of planets, galaxies, and the entire universe. ... 13:22: Both currently live deep in their respective theoretical rabbit-holes, not yet able to make experimental contact with the real universe. 13:31: But the mathematics have yielded intriguing clues to the nature of the fabric of the universe – and that nature is very weird. 15:49: ... then the event horizon evaporates, exposing the singularity to the universe - or in the case of a rotating black hole, an infinite density ...
	2019-10-07: Black Hole Harmonics 01:30: Imagine it: two event horizons – two roughly spherical black surfaces that are literal boundaries to our universe.
	2019-09-30: How Many Universes Are There? 00:06: But just how many bubble universes does the eternally inflating multiverse contain? 00:24: ... it: the observable part of our universe is 93 billion light years across, and that’s just a small fraction of ... 00:34: But in the eternal inflation picture, ours is just one among uncountable bubble universes. 01:14: ... the scenario: the default state of the greater universe – or multiverse - is to expand exponentially due to the vacuum of space ... 01:42: Within each bubble we get a new Big Bang that kicks off a more slowly expanding universe. 01:58: If lots of these bubbles form, they could collide with each other to produce a connected network of non-inflating universe. 02:18: Some questions spring to mind: - I mean, besides “What?!?” For example, how many bubble universes can be made this way? 02:28: Are those universes similar to each other, or wildly different? 02:52: ... question I asked you to calculate the RELATIVE number of new bubble universes that formed in one second compared to the previous ... 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. 03:13: That means the number of bubbles forming at each point in time should be proportional to the volume of the inflating universe at that time. 03:21: So the rate at which that volume is increasing is the same as the rate at which bubble universes multiply. 03:28: We assumed the minimum inflation rate that we think was needed to kick off our own universe. 03:34: The scale factor – or radius of the universe – increased by a factor of at least 10^26 in less than 10^-32 seconds. 03:59: Every 10^-32 seconds one cubic meter of volume becomes 10^78 cubic meters, which is approximately the volume of our entire universe. 04:11: And then in the next 10^-32 seconds each of those 10^78 new 1-meter cubes spawns just as many new entire universe-sized volumes. 04:44: And our number of new bubble universes should multiply by the same insane factor each second. 04:51: This gives us a ridiculously large number of universes even if the probability of making one per unit of volume is insanely low. 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. 05:33: Here’s another one: do all of these bubble universes the same laws of physics, or could they be wildly different from each other? 06:31: ... awfully lucky – if dark energy were much stronger then our universe would have restarted its accelerating expansion too quickly for galaxies ... 06:43: Here’s a possible explanation: what different bubble universes can end up with different vacuum energies? 06:51: ... energies like ours might be extremely rare, but there are so many bubble universes that at least some will have a low enough cosmological constant for life ... 07:02: Naturally, we would be in such a universe. 07:06: ... is an example of using the Anthropic Principle - we must exist in a universe capable of producing us, so if there are many universes it is natural ... 08:01: We don’t know why our universe has the particular string vacuum state that it does. 08:14: Enter the anthropic principle once again: eternal inflation gives us enough universes to easily populate the entire string landscape. 08:24: All different vacuum states exist, and our universe necessarily has one that leads to life-friendly particles. 08:58: ... argument goes like this: if the number of new universes increases by a factor of some impossibly large number every second, then ... 09:16: There are vastly more universes born one second after ours than were born at the same time as ours. 09:24: Now, imagine that there’s a set amount of time for the first intelligent life to form in any one of these universes. 09:34: Pretend that it’s the same in all universes down to the second. 09:44: So, the first intelligence appears in our universe after exactly 10 billion years – we’ll call that moment “second one”. 09:54: The same happens in the exact same second for universes that formed at the same time as ours. 10:01: One second later – “second two” – you might get some more intelligent lifeforms forming in those same universes. 10:12: But consider the wave of universes that formed one second after our own. 10:26: And of course there are vastly more of those slightly younger universes – more than all the atoms in all the universes that are one second older. 10:37: So first civilizations in those younger universes will always outnumber all the civilizations in all older universes. 10:45: ... beings in the eternally inflating multiverse are in the youngest universes that have had time to form intelligent ... 10:58: ... type across the multiverse, which means we’re the first to appear in our universe. ... 11:29: He proposes that there may be something off in the logic of weighing up probabilities over bubble universes. 11:40: OK, the last thing I want to talk about is colliding universes. 12:35: The implication is that universes don’t collide very often unless their rate of production is extremely high. 12:51: But it still should NOT be surprising that we don’t see evidence of bubble collisions in our observable universe. 13:24: Just that the universe – or multiverse is playing hard to get. 14:04: Need more of a fix of that existenial awe at the wonder and weirdness of the universe? 14:43: Alexander has been traveling the bubble universes for many years, supporting local youtube space shows where he finds them.
	2019-09-23: Is Pluto a Planet? 01:56: This definition of “planet” was the most sensible classification for thousands of years based on our observations and understanding of the universe. 02:07: ... Spheres” which cast the Sun, not the Earth, as the center of the universe and the Earth in its proper place among the ... 11:46: As we’ve peered deeper into our universe, we’ve realized that it’s full of weird, beautiful, and important worlds, some we now call planets, some not. 13:41: The language we use to describe the universe becomes more precise as we learn more about its nature. 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.
	2019-09-16: Could We Terraform Mars? 14:56: People who live in glass houses shouldn’t throw stones, nor live under a stone-throwing universe.
	2019-08-26: How To Become an Astrophysicist + Challenge Question! 00:00: ... a Challenge question for our recent episodes on the eternally inflating universe Let me start by telling you about my own path. It was typical enough I ... 08:51: Are you want to gaze upon the wonders of the universe and bring this incredible perspective to enrich humanity? 08:59: ... frustration and boring stuff as it does on locking the mysteries of the universe You've got to love the latter enough to get through the former Don't do ... 10:46: ... estimate Let's assume that every second there's a set chance of the new universe forming in any given volume of space So every second many bubble ...
	2019-08-19: What Happened Before the Big Bang? 00:04: That is as long as you define 'The Big Bang' as the universe's early hot dense expanding state that's well described by Einstein's equations. 00:35: The universe almost certainly did not explode from a singular point. 01:27: And in fact, our universe is but one bubble among countless others in an eternally inflating greater universe. 02:03: ... we make any real predictions about the behavior of an inflating universe, we probably should know more about the field that drives it. To start ... 03:54: When that state decays, potential energy is released as real particles, ending inflation, and re-heating the universe in an expanding bubble. 04:02: The random nature of this version of inflaton decay means that many such bubbles should form, ie. multiple universes exist. 04:16: Old inflation predicts empty firewall bubbles that look nothing like the early phase of our universe. 05:13: ... the entire region of the inflating universe would approach this minimum at the same time Inflation would shut down ... 05:26: This gives us the expanding hot dense universe that we know and love in our Big Bang model. 05:33: But if slow roll inflation stops everywhere at once, how does it last forever and how does it give us multiple universes? 06:09: These theories predict phase transitions in the behavior of fields as the temperature of the universe changes. 06:17: As the universe cools, different vacuum states can appear possibly trapping the inflaton field. 07:01: ... means some regions of the universe would finish inflation a little ahead of others And that will lead to ... 07:53: But seeding all of the structure in our universe is probably the least impressive thing those quantum fluctuations did. 08:01: They also give eternal inflation and multiple universes. 08:58: That region would then continue to decay spawning new universes, but also spawning new inflating regions. 09:06: ... fractal structure of infinitely expanding space in dispersed with bubble universes of all different ... 09:40: The exponential nature of the process will take over and the speck becomes infinite universes. 10:33: ... of people mentioned George Lemaitre, who predicted the expansion of the universe before Edwin Hubble's ... 10:51: ... observations of receding galaxies could be explained by an expanding universe and solved Einstein's equations to show ... 11:07: ... to Slifer's galaxies and so we couldn't properly test this expanding universe ... 11:19: Pup314 asks if the reheating of the universe after inflation is what gave us the cosmic background radiation. 11:28: The CMB was released about 400,000 years after the end of inflation when the reheated universe first became transparent. 11:38: The reheating i'm talking about happened right at the end of inflation, which is basically corresponding to the beginning of our universe. 11:56: Enough to give the universe a temperature of 10 to the power of 27 or 28 Kelvin. 12:29: ... actually gives a physical reason for the universe to have started with a rapid outward expansion rate in terms of pretty ... 13:05: What's the meaning of life, the universe and everything? 13:08: 42 for the right definition of life, the universe, and everything.
	2019-08-12: Exploring Arecibo in VR 180 00:06: It's the only known world in the universe with life. Come closer. You can see this. 00:13: ... and this thing, it's the tip of an enormous machine built to map the universe beyond and to search for other technological organisms out there and to ... 03:24: ... as a technological civilization It's our most sensitive ear to the universe and the most powerful voice If we choose to user it may one day answer ...
	2019-08-06: What Caused the Big Bang? 00:09: ... fraction of a second, inflationary expansion multiplied the size of the universe by a larger factor than in the following 13 and a half billion years of ... 00:43: ... is matter and energy so smoothly spread out across the entire observable universe? ... 00:55: - and why is the geometry of the universe so flat? 00:58: Neither should be expected unless the universe expanded much more rapidly early on. 01:09: And these are strange particles predicted to have been produced in the early universe. 01:22: In addition, inflation gives us an explanation for why the universe is expanding in the first place. 01:31: ... the exponential expansion ended the universe would have continued to coast outwards just like a thrown ball continues ... 02:31: Our modern theory of gravity can be used to predict the behavior of the universe as a whole. 02:43: Mostly, the stuff in the universe pulls the universe back together; resists the expansion with a positive gravitational effect. 03:23: ... cosmological constant means a constant doubling rate for the size of the universe. ... 03:48: ... flatness, and monopole problems inflation needs to expand the universe by a factor of 10 to the power of 25 in less than 10 to the power of ... 04:13: ... than dark energy. Also, for inflation to make sense presumably the universe also needed to stop inflating at some point giving way to the regular ... 04:55: There's some more homework for you. For now, a review: the universe is filled with quantum fields. 05:22: ... the form of particles and if space is expanding - as is the case for our universe - then that energy gets more and more spread out over ... 07:26: ... proposed by Alan Guth in 1979 goes something like this: In the early universe this mysterious in flattened field has a high field strength due to the ... 07:50: The universe keeps cooling, but the inflaton field can't lose more strength. 07:59: ... the exponential nature of inflation quickly blows up the volume of the universe, rendering it, basically, empty and cools it to a low temperature. In ... 08:43: Somewhere in the inflating universe, the inflaton field is going to fluctuate to the other side of this local minimum barrier. 10:44: We say the universe was 'rethermalized' or reheated by this process. 10:50: In fact, this process would reheat the universe to the extreme energies that we expect existed right after the Big Bang. 10:59: ... this point, the universe should evolve as the rest of the Big Bang story predicts: An extremely ... 11:26: ... fire walls - that are otherwise empty - which isn't exactly what our universe looks ... 12:12: ... flattened field so that allows a smooth exit from inflation across the universe rather than in a series of ... 12:49: eternally - Only stopping in patches where a bubble universe forms. And once started, inflation should produce infinite such universes.
	2019-07-25: Deciphering The Vast Scale of the Universe 00:05: For much of human history, people believed that the planet Earth was the center of the universe. 00:13: We now know that it's a speck compared to the Universe. 00:30: In fact there are surely more entire worlds in the observable universe than there are grains of sand on this one. 00:43: Less than a century ago we didn’t know that a universe existed beyond our own Milky Way Galaxy. 01:01: But before we could map the universe, first we had to discover the universe. 01:05: ... Hubble made a paradigm-shifting discovery: in 1924 he proved that the universe exists beyond the Milky ... 01:57: The philosopher Immanual Kant guessed that theses nebulae might be entire “island universes”, of their own. 02:24: But to prove that these spiral nebulae were really island universes, we needed to find their distances. 04:36: ... measurements it became clear that all spiral nebulae were island universes of their ... 04:50: ... away from the Milky Way – paving the way for the discovery that the universe is expanding, meaning it must once have started with the Big ... 05:07: With this telescope, Edwin Hubble not only discovered the universe beyond the Milky Way, but he opened the door to discovering its very origin. 05:16: And to our exploration of the true vastness of the universe that followed. 05:20: ... of exploration has led us, we'll need a little help from the Digital Universe built by the Hayden Planetarium at the American Museum of Natural ... 05:52: ... have turned that dome into a spaceship. It can fly us through a virtual universe built from the most complete 3D atlas of our Universe ever ... 06:09: It’s the perfect place to explore the scale of the vast universe that Edwin Hubble unlocked for us. 06:17: We’re now flying through the American Museum of Natural History’s Digital Universe, rendered by the OpenSpace Software. 06:34: ... the shape and motion of our home galaxy – once imagined to be the entire universe and now our very familiar island ... 07:32: ... times the speed of light we see the extent of our modern mapping of the universe – galaxies assembled into many vast filaments, flowing together on ... 08:07: That distant light comes to us from a much younger universe. 08:37: Yet it was Edwin Hubble’s observations that opened the door to our current appreciation of the immensity of our universe. 09:33: ... and stories about the people who hacked the moon If the size of the Universe is enormous, why haven’t we seen other signs of ... 09:55: ... is bringing you the universe with the SUMMER OF SPACE, which includes six incredible new science and ...
	2019-07-18: Did Time Start at the Big Bang? 00:00: Thank you to LastPass for sponsoring PBS Digital Studios Our universe started with the Big Bang. 00:05: But only for the right definition of our universe and "started" for that matter. In fact, the Big Bang is probably nothing like what you were taught. 00:21: A hundred years ago, we discovered the beginning of the Universe. 00:25: ... - then - brand-new general theory of relativity, revealed that our universe is expanding and if we reverse that expansion far enough - ... 01:22: ... just a theory" Let me be very clear, the evidence for a hot dense early universe is practically ... 01:46: ... Cosmic Microwave Background is a direct line of sight to the universe as it was Only a few hundred thousand years after the hypothetical ... 01:56: ... can see pretty much directly that all space and matter in the universe was once crunched at least a thousand times closer together There's also ... 03:27: ... idea is especially weird if the universe is infinite Now the universe may or may not be infinite but if we can ... 04:38: ... it enough times and the universe could end up as hot and dense as you like But it'll still be infinite, ... 05:15: ... the infinite universe becomes infinitesimal all points become the same point and ... 06:02: ... get that you can't think about the universe as having one big clock that Rewinds and then winks out of existence of ... 07:22: ... picture There is no before the Big Bang because no time line in this universe can be traced there. This is called geodesic in completeness and it also ... 08:14: ... That's what's happening here We used general relativity to rewind the universe, but we already know that despite its incredible successes GR Is an ... 08:52: ... resolutions before But the upshot is that we just don't know how the universe behaves in those conditions But we do know that pure general relativity ... 09:52: ... inflation suggests that our universe appeared as a regularly expanding bubble in an unimaginably larger ... 11:12: ... are some less abstract ways to get a new universe out of an old one for example an extreme quantum fluctuation could ... 11:36: ... from the new Big Bang singularity people love cyclic and regenerating universes They appeal to our sense of narrative which might be a reason to be wary ...
	2019-07-15: The Quantum Internet 04:18: ... about before - it comes from the fact that every quantum state in the universe must be perfectly traceable - single quantum state to single quantum ...
	2019-06-20: The Quasar from The Beginning of Time 00:04: ... has provided another window: it allows us to observe a time when the universe was still cooling from the fire of its own ... 00:53: To Hawaiians it is a sacred site. And to astronomers, it's where the Earth meets the universe. 02:06: ... quasars are the most luminous objects in the universe. What was strange about this one was its distance. Its light was SO red ... 02:56: This is our window to the universe. 03:34: That's why we create telescopes – the universe looks very, very different at different wavelengths. 03:45: ... to visible light, so a ground-based telescope can see a visible universe, as can we. Gemini is built to be sensitive to the ... 05:12: ... traveling through the expanding universe sapped energy and stretched the wavelength of that light so that it was ... 05:43: ... after the Big Bang, when things had cooled down a bit, the universe was filled with hydrogen gas. It was murky, especially for ultraviolet ... 05:58: Those stars eventually melted away the remaining hydrogen in a process called reionization, leaving a crystal-clear universe. 06:15: Much of the quasars once ultraviolet light was sucked up before it escaped the early universe. 06:43: ... it could grow to that insane size in a tiny fraction of the age of the universe. We are expanding our understanding of physics to figure this one ... 06:56: ... and a mystery. It literally shines a light on the earliest epochs of our universe, teaching us about our most fundamental ... 07:10: ... our great telescopes – our portals to the universe past and present – will tackle those questions too and ultimately bring ... 07:27: ... advances in technology, there are other ways humanity can see the universe beyond the electromagnetic spectrum that we observe with traditional ... 08:16: ... is bringing you the universe with the SUMMER OF SPACE, which includes six incredible new science and ...
	2019-06-17: How Black Holes Kill Galaxies 00:08: ... that they may be responsible for ending Star formation across the entire Universe When we first realized that Black Holes could have masses of Millions or ... 02:54: ... directly from the gas Now, Based on our understanding of Physics of the Universe especially the nature of Dark Matter and Dark Energy we expect 'Bottom ... 03:59: then why is it so surprising that they appear so closely correlated in the Modern Universe. 04:05: ... Black Hole Mass Relationships' seem to evolve through the history of the Universe many Supermassive Black Holes were in place early leaving the ... 05:24: ... star formation activity in particular, the largest galaxies in the Universe are the Giant Elliptical's and we say they are 'Red and Dead' not ... 07:21: ... formation died or is dying not just in largest galaxies but across the universe after the first stars formed around 150 million years after the big bang ... 10:49: ... the modern universe Giant Dead galaxies harbor fossil quasars supermassive Black Holes whose ...
	2019-06-06: The Alchemy of Neutron Star Collisions 00:00: ... nuclear furnaces and explosive deaths of stars that lived in the ancient universe in recent years it's become clear that the truth is even more ... 02:47: ... dark ages that mysterious time before the first stars formed in our universe let's see what you had to say BloodyAlbatross reasonably asks, "why is ... 12:15: ... Jan Pieter Cornet asks something that I hoped one of you would: "if the universe was transparent before recombination when electrons were free of their ... 13:02: ... at that time although even by then most of the light was infrared the universe then expanded by a factor of a hundred over the next couple hundred ...
	2019-05-16: The Cosmic Dark Ages 00:04: ... Somewhere between 10 and 1000 billion trillion stars fill the observable universe with light. But there was a time before the first star ... 00:24: ... almost impossibly faint when you view them from the other side of the universe. But there’s an up side. If the light from some space object took ... 01:34: ... about before, but it never gets dull, right? Prior to recombination, the universe was filled with hydrogen and helium atoms stripped of their electrons - ... 02:19: ... and the fog of atomic and molecular hydrogen and helium that filled the universe. ... 02:31: ... those stars would also burn away the remnants of that gas, ionizing the universe and beginning the epoch of reionization. This is how we think it ... 03:52: ... the ultraviolet aura. By now the dark ages were well over and the universe was in the epoch of reionization. It would take a billion years for ... 04:29: ... this while space was expanding. At the beginning of the dark ages the universe was around 1/1000 of its current size. It expanded by a factor of 100 ... 04:46: ... including one from right near the beginning of reionization when the universe was only 400 million years old. But our best evidence isn’t from the ... 05:13: ... thick neutral hydrogen of the early universe was mostly transparent, but it did block some very particular types of ... 05:45: ... wavelength has now been stretched – redshifted – by the expanding universe. The amount of that redshift tells us the when the very first stars ... 08:36: ... By the time the quasar’s light reaches the edge of that bubble, the universe has expanded slightly. Photons that were once at the Lyman-alpha ... 09:21: ... rest of the quasar’s light continues on its way towards us, but the universe keeps expanding. Wavelength by wavelength, photons get absorbed as they ... 10:10: ... trough, seen only in quasars that are embedded in the early neutral universe.. ... 11:17: ... and ended. The width of the Gunn-Peterson trough tells us when the universe finally became fully ionized. And the scant Lyman-alpha light that made ...
	2019-05-09: Why Quantum Computing Requires Quantum Cryptography 00:27: But in fact much of our technological world depends on our understanding of the quantum properties of the subatomic universe.
	2019-04-24: No Dark Matter = Proof of Dark Matter? 00:03: ... its existence one of these is true either most of the matter in the universe is invisible and formed by something not explained by modern particle ...
	2019-04-10: The Holographic Universe Explained 00:00: We live in a universe with 3 dimensions of space and one of time. 00:24: ... of the most startling possibilities is that our 3+1 dimensional universe may better described as resulting from a spacetime one dimension lower – ... 00:44: The holographic principle emerged from many subtle clues – clues discovered over decades of theoretical exploration of the universe. 07:36: Crudely, this is how an extra dimension can be coded in a holographic universe. 09:02: We now have a several versions string theory that try to explain how vibrating strings can lead to the familiar particles of this universe. 09:45: Strange because it provided the first concrete description of a holographic universe. 12:29: But the more startling implication of AdS/CFT is that it’s the first concrete realization of a holographic universe. 13:35: AdS/CFT is a hint that we may live in a holographic universe. 13:41: ... doesn’t represent THIS universe, because our universe doesn’t appear to be negatively curved AdS space, ... 13:53: But there are efforts to generalize this to a universe more like our own. 13:58: ... wrestle with is this: a series of mathematical clues indicate that our universe may be holographic – or at least have a dual representation in a lower ... 14:16: Maybe, but perhaps our familiar 3+1 universe has an alternative – perhaps a more true representation out there. 14:44: Including the return of our Game of Thrones inspired shirt the heat death of the universe is coming. 15:08: The universe is just that weird. 15:10: A few of you asked whether our percieved universe is just the surface of a higher dimensional space. 15:16: ... behind the holographic principle, which suggests that our percieved universe is the volume, but it can be encoded on its lower dimensional ... 15:50: So that obviously doesn't directly correspond to our universe. 16:40: KI9 asks whether the things we learn from AdS/CFT are applicable to the universe we live in given that our universe doesn't have negative curvature. 17:02: Measurements of the geometry of the universe indicate flatness, but we may never know whether it's truly flat, or just flat as far as we can see.
	2019-04-03: The Edge of an Infinite Universe 00:00: Have you ever asked “what is beyond the edge of the universe?” And have you ever been told that an infinite universe that has no edge? 00:11: We can define a boundary to an infinite universe, at least mathematically. 00:16: And it turns out that boundary may be as real or even more real than the universe it contains. 00:29: Our universe may be infinite. 00:37: For example we have the “observable universe” – that patch that we can see, and beyond which light has not yet had time to reach us. 00:57: Our observable universe is like a tiny patch of land in a vast plain. 01:42: There’s another way to define the boundary of the universe that isn’t so shy in the face of an infinite cosmos. 01:50: In fact, if we twist our human intuition and our mathematics to its limit we can build our picket fence around an infinite universe. 02:00: ... for doing calculations in physics, but may be as real as the physical universe it ... 02:11: It may encode that universe as a hologram on its surface. 02:26: Let’s start with a quick review of types of universe. 02:35: ... only type of non-infinite universe – or closed universe – is the one that curves back on itself – like a ... 02:52: Geometry is a bit broken in such a universe – for example, two parallel lines will eventually converge and cross each other. 03:00: In general relativity we call a universe with this geometry de Sitter space, after Dutch astronomer Willem de Sitter. 03:08: Then there’s the flat universe – classic, straightforward geometry – parallel lines stay parallel – and it goes on forever. 03:25: Finally there’s the universe with negative curvature, and the 2-D analog of that is the hyperbolic surface, like an infinite saddle or pringle. 03:51: OK, so 2 out of 3 possible universes are infinite. 03:57: ... these types exist, there should be infinitely more people in infinite universes compared to people in non-infinite ... 04:20: ... tried to find ways to map infinite spacetime –to the edge of an infinite universe or across the event horizon of a black ... 05:03: ... was Roger Penrose who defeated the true infinity of an infinitely large universe. ... 05:31: We’ve used these before to understand black hole event horizons, but these were originally conceived to understand the boundaries of the universe. 05:49: ... contours are our old time ticks - moments of constant time across the universe, while the vertical-ish lines are set locations in space in only one ... 07:44: ... diagrams represent a universe that is “asymptotically flat” – it may have some local curvature due to ... 09:09: Penrose diagrams define the infinite boundary of a flat universe as a useful tool in calculation. 09:16: For the holographic principle we need the infinite boundary of a negatively-curved universe – an anti-de Sitter, AdS universe. 11:40: So this disk can represent an infinite anti-de Sitter universe with 2 spatial dimensions at a single instant in time. 12:01: If we wanted to represent a 3-D AdS universe we could use a Poincaré ball instead. 15:16: ... week we enjoyed another potential end of the universe when we talked about the Big Rip - in which space tears itself to shreds ... 16:45: However our universe on its largest scales is not time symmetric - it's expanding, so the past looks very different to the future.
	2019-03-28: Could the Universe End by Tearing Apart Every Atom? 00:00: Of all the unlikely ends to the universe the big rip has to be the most spectacular. 00:25: ... universe is expanding and that expansion is accelerating and we don't know what's ... 03:05: ... it's basically the equivalent of Newton's law of gravity for the whole universe describing the acceleration or deceleration of the expansion rate which ... 05:32: ... It would mean the stuff is diluted away a little less quickly than the universe ... 06:20: ... that's the case where the density doesn't just stay constant as the universe expands, but it actually increases. The result would be that the ... 08:37: ... release and I guess we still thought it was a sign of the end of the universe. ... 10:03: ... and then presumably anything smaller. In its final state a big rip universe will be nothing but hopelessly isolated elementary particles separated ... 12:53: ... probably - the universe will still end in a long cold heat death in which the stars of our ... 14:21: We should do a statistical analysis of cosmology papers that predict saving the universe versus it dying horribly. 14:28: I'm guessing the save the universe theories are more numerous than their plausibility warrants. 14:34: ... and decreases to zero - in fact even if it became zero tomorrow, the universe is now expanding too fast to ever ...
	2019-03-20: Is Dark Energy Getting Stronger? 00:04: ... currently accepted cosmological description of our universe is called the Lambda CDM Model and is built on the idea about the ... 00:15: It’s accepted because it does a great job of explaining our observations of the universe. 01:03: ... this is true, then our prediction for the future of our universe looks VERY different, and may involve the entire universe tearing itself ... 01:38: They were measuring the distances to supernovae to track the changing size of the expanding universe. 02:51: ... alongside the cosmological constant as our best description of how the universe behaves on the largest ... 03:19: ... of the cosmic microwave background reveal the starting conditions of the universe – the balance of dark energy, dark matter, and everything else at the ... 03:36: ... the Concordance model to these starting conditions to calculate how the universe should have evolved from those early times, and how fast it should be ... 03:54: The expansion history of the universe is typically measured using the same type of supernova observations that first discovered dark energy. 04:40: The most distant supernova we’ve seen is so far away that its light has been traveling to us for around 75% of the age of the universe. 05:12: In particular, the universe appears to be expanding faster than expected given what we see in the cosmic microwave background. 05:21: It may be an issue with how we determine the starting conditions of the universe, or it may be our measurements of supernovae. 05:44: ... surprisingly, our measurement of the state of the early universe via the CMB may be more reliable than our measurement of its subsequent ... 06:23: In order to properly measure the full expansion history of the universe - we want a new, brighter standard candle. 06:52: If it’s a supermassive black hole doing the feeding, its accretion disk shines so bright that it can be seen to the ends of the universe. 10:11: The final sample spans nearly the entire history of the universe. 10:15: The most distant existed when the universe was less than 10% of its current age. 10:25: ... how much the quasar’s light got stretched as it traveled the expanding universe. ... 10:52: And that dashed line – that reflects the expansion history expected in a universe with constant dark energy – a Lambda-CDM, concordance universe. 11:22: ... that black line is a model of the expansion history of the universe in which dark energy is NOT constant, but instead is getting stronger as ... 11:35: ... roughly speaking – if the expansion of the universe is accelerating even more than we thought, that could explain the extra ... 12:15: ... if dark energy is getting stronger, then eventually it could cause the universe to expand inside galaxies, inside planetary systems, and eventually even ... 12:34: It’s a potential end of the universe in which space-time rips itself to shreds at subatomic scales due to the increasing strength of dark energy. 13:57: What we have here is a tantalizing clue that our accepted understanding the factors that drive the expansion of the universe may be off.
	2019-03-13: Will You Travel to Space? 13:27: ... are hydrogen atoms that have been ticking for the entire age of the universe. ... 15:56: But remember, the house is the entire universe.
	2019-03-06: The Impossibility of Perpetual Motion Machines 11:13: ... goes to Epsilon Centauri, whose machine requires an entire bubble universe with closed, pac-man borders, trapping the ever-accelerating ... 13:27: In which we deciphered the cryptic patterns embedded in the oldest light in the universe. 14:43: Recombination happened when the universe became cool enough nuclei capture electrons to form the first atoms. 14:54: And in general the entire universe didn't make this transition instantaneously. 14:59: It took several tens of thousand years - which is a lot considering the universe was less than 400,000 years old. 15:07: ... the CMB and in galaxy rings were blurred out quite a bit because the universe took a moment to become fully ...
	2019-02-20: Secrets of the Cosmic Microwave Background 00:08: ... The remnants of the heat glow released when the hot dense early Universe became transparent for the first time It sounds like random static But ... 01:34: ... waves reverberated through the first few hundred thousand years of the Universe's ... 02:05: ... at the formation of the first atoms the moment of Recombination As the universe evolved those frozen shells collapsed into galaxies We still see them ... 07:42: ... of time that they had to collapse Factoring in the expansion of the universe over that time that size should be about half a million light years at ... 11:14: ... peak relative to the first peak to measure the baryon content of the Universe And those measurements tell use that that baryons constitute only about ... 12:34: ... relative contents of all three components extrapolate that to the modern Universe and we get the baryons constitute only about 5% of the mass and energy ... 14:23: ... you should actually have overlapping bubbles of galaxies throughout the Universe But we only see a 2D projection of that Universe When we look through ...
	2019-02-07: Sound Waves from the Beginning of Time 00:04: Invisible to the naked eye, Our night sky is scattered with the hundreds of billions of galaxies that fill the known universe. 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. 00:54: ... the properties that govern the very birth, evolution, and the end of our universe. ... 01:22: They are the fossils of the first sound waves in the universe, imprinted on the distribution of galaxies on the sky. 01:30: And in these patterns, we could read the expansion history of the universe. 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. 02:36: There are three profound differences between the behaviour of matter in this state Compared to the gentle gas nebula of the modern universe. 03:21: ... means it was, by far, the dominant gravitational influence in the early universe as it still ... 03:38: Okay, so, the universe is filled with this hot ocean of baryons, photons, and dark matter. 03:51: ... probably were the remnants of random quantum fluctuations From when the universe was subatomic in ... 04:49: But as it expanded, so did the universe. 04:52: ... energies, themselves were stretched, redshifted to ower energies, the universe ... 05:43: The universe went from opaque to transparent over a period of several thousand years. 05:49: As the wave of plasma and photons decoupled, light began to stream freely through the universe as the cosmic background radiation. 06:12: The radius of that shell became fixed to the rate of expansion of the universe. 06:20: Well, the exact distance that sound could travel over the age of the universe at that time. 06:46: ... stars and galaxies work of collapsing into stars and galaxies as the universe continued to ... 07:03: And now over thirteen and a half billion years later, the universe is expanded by a factor of 1,100. 07:16: So how does this primordial history lesson help us understand the subsequent expansion of the universe? 08:27: Those rings were further smeared out over the thousands of years it took for the universe to fully transition from plasma to gas. 08:35: Collapse that web into galaxies over the age of the universe, and at first glance, it looks like a random smattering of galaxies on the sky. 08:54: Redshift is just the amount by which a galaxy's light has been stretched as it travelled through the expanding universe. 09:08: ... the sky, a redshift survey can produce a three-dimensional atlas of the universe. ... 09:54: In your atlas of the universe, take slices of the universe, each slice a certain distance from us. 11:00: Dark energy was first discovered by using distant supernovae as distance measurements- to track the rate of expansion of the universe. 11:47: ... and we can see how big they are at different points in the modern universe from our redshift ... 12:02: They allow us to track the expansion rate of the universe. 12:06: The baryon acoustic oscillations agree with and confirm what we measure using supernovae distances- The expansion of the universe is accelerating. 13:26: ... Chess Guy has a fun one. To paraphrase: As the universe expands towards the infinite future, does that expansion outpace the ... 13:43: Well, the answer is- it depends on what size you consider. For the entire observable universe?
	2019-01-30: Perpetual Motion From Negative Mass? 09:37: They are a set of conditions against negative energies that seem necessary in order for general relativity to describe a sensible universe.
	2019-01-24: The Crisis in Cosmology 00:05: ...the rate of expansion of our universe,... 00:21: ...some of the most basic assumptions about the universe. 00:29: In 1929, Edwin Hubble... discovered the universe. 00:59: An impossibly vast universe had been discovered beyond the Milky Way,... 01:03: ...and at the same time that universe was revealed to be expanding. 01:12: We encapsulate the expansion of the universe with a single number, called the Hubble constant. 01:18: ... apart But, more fundamentally, H0 tells us the rate of expansion of the universe... ... 01:42: ...the rate of expansion of the universe, combined with the gravitational effect... 01:54: And it's fundamental for interpreting our observations of the distant universe,... 03:09: ...which was stretched as it travels to us through an expanding universe. 05:05: ...that the expansion of the universe is actually accelerating,... 06:19: What if we could measure the expansion rate of the universe at the very beginning? 06:41: ...or with our understanding of how the universe evolved. 06:47: ... another reason to try to calculate H0 from observation of the early universe It's that that observation I'm referring to is far more reliable than ... 07:07: The Cosmic Microwave Background is the remnant heat glow of the universe's initial hot dense state. 07:15: ...when the universe had finally cooled down enough to become transparent to light. 07:26: ...through an expanding universe. 07:50: ...would go on to collapse into the vast clusters of galaxies of the modern universe. 08:16: ...really vast sound waves that rippled across the universe. 09:05: ...as well as the expansion rate of the universe in that early epoch. 09:29: ...you figure out how the universe described by these parameters... 11:38: Insufficient numbers could skew the energy balance of the early universe, and mess up the calculation. 12:18: ...that could explain why we observe a higher H0 in the modern universe... 12:22: ...than is predicted by extrapolating from the early universe. 12:50: The near centennial quest to measure the expansion rate of the universe will be concluded. 15:36: If the universe has this sort of T symmetry,... 15:41: ...the universe will evolve exactly backwards, to its initial state. 15:54: But the universe IS symmetric under full CPT inversion. 15:59: Now, a CPT inverted universe is not the same as this universe,...
	2019-01-16: Our Antimatter, Mirrored, Time-Reversed Universe 00:03: ... on its symmetries for example it should be impossible to distinguish our universe from one that is a perfect mirror opposite in charge handedness and the ... 00:29: ... on physics Richard Feynman talks about what it means to expect the universe to be identical in the mirror for it to be parity symmetric he invites ... 00:42: ... opposite direction to their nucleus speed axis but in a mirror reflected universe the same decay should be in the opposite direction so with that spin ... 03:02: ... original direction down and the clock ticks as normal so even though the universe isn't parity symmetric maybe it is under a charge parity a CP ... 08:43: ... time reversal operation needs to bring us from a broken CP reflected universe into a fixed CP T universe but that means a T transformation from our ... 10:26: ... maybe that's why he was so into building antimatter clocks. So, yeah the universe is not symmetric under this simple version of T reversal. It's the ... 10:54: ... understood like I said this simple interpretation of T as rewinding the universe is not what we usually mean by the T in CPT - that T is more accurately ... 17:15: ... may be currently untestable due to the energy scales involved but the universe has no obligation to make itself currently testable to any particular ...
	2019-01-09: Are Dark Matter And Dark Energy The Same? 01:31: So we conclude that galaxies, and for that matter the universe, has 5-10 times as much matter as we can actually see. 01:52: Observations of distant supernovae tell us that the expansion of the universe is accelerating. 02:47: That’s the solution to the Einstein equations that tells you the rate of acceleration of the expansion of the universe. 03:20: In the case of dark energy the latter wins, and so the expansion of the universe accelerates. 03:27: An important part of this is that the energy density of dark energy is constant, so it doesn’t dilute as the universe expands. 06:22: ... he programs a virtual universe into his computer with both positive and negative mass particles, along ... 07:07: The problem is that our negative masses will dilute away as the universe expands. 07:12: To fix this, Farnes proposes that these negative masses are constantly created as the universe expands. 07:26: The result is a very diffuse negative mass fluid that fills the universe and constantly replenishes itself. 07:32: ... who proposed similar things in their severely debunked steady state universe ... 08:42: But that effect is overwhelmed by the effect of the pressure, which in this case is attractive – it works to recollapse the universe. 09:06: And yet a negative cosmological constant gives you an extremely different universe. 09:15: ... Friedmann equation – that’s this thing - to correctly conclude that a universe with a negative cosmological constant should have a sinusoidal scale ... 09:25: He interprets that to mean the universe should oscillate endlessly in size. 09:31: ... sinusoidal solution is only valid for the bit of the sine wave where the universe is expanding from zero time – the big bang - slowing down towards the ... 09:51: The end of this universe is here, where it gets back to zero size. 10:16: Does a universe with a constant negative energy density fit the observations? 10:31: Those supernova results suggest a universe that started expanding rapidly and then slowed down due to the gravity of matter – mostly dark matter. 11:00: ... calculates an age for his universe of 13.8 billion years assuming a very low negative energy density, but ... 11:39: Just quickly, the density fluctuations seen in the afterglow of the Big Bang reveal a universe that is spatially flat. 11:47: ... both regular and dark matter, are needed to explain this spatially flat universe. ... 11:57: If you replace both dark energy and dark matter with negative-energy stuff, then the universe becomes negatively curved.
	2018-12-20: Why String Theory is Wrong 02:43: ... component that looks exactly like the familiar general relativity in our universe, plus an extra bit of math from the extra special ... 09:30: In a duality two apparently contradictory way of describing the mechanics of the universe can lead to exactly the same results. 13:36: It seems an impossible task to find which one corresponds to our universe, if any do. 15:37: ... description now last week we peered into the looking-glass and saw how a universe that's spatially reflected in a mirror has fundamentally different laws ... 16:28: ... when you reverse parity charges and time do you get a universe that behaves like, ours one full of mirror reflected antimatter ...
	2018-12-12: Quantum Physics in a Mirror Universe 00:02: ... think you see a perfect reflection but you're actually looking at a universe whose laws are fundamentally different when we think about symmetry the ...
	2018-12-06: Did Life on Earth Come from Space? 00:37: ... most outlandish interpretations do we eventually get bored by the real universe give kids too much candy and they won't eat their vegetables in this ...
	2018-11-21: 'Oumuamua Is Not Aliens 11:44: And a few days after that, "Centauri Dreams" and "Universe Today" wrote about it.
	2018-11-14: Supersymmetric Particle Found? 03:48: The universe itself is a pretty good particle accelerator. 03:52: ... to blast high energy particles like electrons and atomic nuclei into the universe. ... 04:57: That's the leftover heat glow of the very early universe. 13:11: ... the universe has no obligation to operate in a way that is currently testable by any ...
	2018-11-07: Why String Theory is Right 12:23: Our universe has three spatial dimensions. 16:10: ... believe it or not, it's a serious question as to whether the universe has counter-factual definiteness, whether or not we can make a ...
	2018-10-31: Are Virtual Particles A New Layer of Reality? 00:08: Out there in the emptiest places of the universe, phantom particles appear and vanish again out of nowhere. 00:14: They borrow the energy for their existence so briefly that they cheat the watch fly of the universe.
	2018-10-25: Will We Ever Find Alien Life? 14:04: ... that string theorists need to search through to find the geometry of our universe's extra ...
	2018-10-18: What are the Strings in String Theory? 00:10: There are these tiny vibrating strings, and that's where all the force's particles, including gravity, in the entire universe come from. 05:24: So wiggly strings could explain the whole universe. 10:34: It's a theory that works in a universe that is clearly not our own with its measly three dimensions of space. 10:44: There's a way to add extra special dimensions that is still consistent with our perceived 3D universe. 10:51: To get our heads around this, imagine we lived in 2D, flatland universe. 11:44: Our universe of 3D space and 1-D time is like flatland on this 5D object called a 5-brane. 12:25: Find the right location in this string landscape, and you perfectly describe the universe. 12:53: Tuning that string landscape to match our universe is daunting and perhaps impossible. 13:50: ... week we talked about the fundamental computational limits of our universe, and incidentally, what it would take to compute a universe simulation on ... 14:22: ... in Hawking radiation, which would take until long after the last star in universe has died to even give you a small fraction of that ... 14:59: But most of the information in the universe is in black holes, or more accurately, most entropy or hidden information is in black holes. 15:17: ... old video that quotes me saying to Neil deGrasse Tyson, "To simulate the universe, you need a computer the size of the universe", in direct contradiction ... 15:38: You can build a universe simulator smaller than the universe. 15:42: The universe simulator that you'd build inside this universe has limits. 15:47: It couldn't simulate a universe so perfectly that the simulated universe could also contain an equally good universe simulator.
	2018-10-10: Computing a Universe Simulation 00:00: [MUSIC PLAYING] Physics seems to be telling us that it's possible to simulate the entire universe on a computer smaller than the universe. 00:19: [MUSIC PLAYING] Look, I'm not saying the universe is a simulation. 00:32: ... if this is the prime, the original, physical universe, rather than somewhere deep in the simulation nest, we can still think of ... 00:44: ... a universe in which the most elementary components are stripped of all properties ... 01:04: ... of the emergent laws of physics, physical structure, and ultimately the universe. ... 01:22: In this picture, the universe is a multi-dimensional version of Conway's game of life. 01:27: ... a universe could be reasonably thought of as a computation, cells stripped of all ... 02:07: ... come back to the question is the universe a computer, and we'll look at cellular automata and pan computationalism ... 02:22: If the universe is a computer, how good a computer is it? 02:26: And an even more fun question-- could you build a computer inside this universe to simulate this universe? 02:54: The first one, the memory capacity of the universe, is a topic we've looked at. 03:27: If you fill a region of the universe with information equal to its Bekenstein bound, it'll immediately become a black hole. 03:34: ... saw in our episode on the information content of the universe that the maximum information content, the Bekenstein bound, of the ... 03:59: ... suggests that we could hold all of the information in the observable universe within a storage device smaller than the observable universe, which ... 04:21: How large would that black hole need to be to store all of the information about all of the particles in the universe? 04:33: So there is something like 10 to the power of 80 hydrogen atoms in the universe. 05:13: ... informationally speaking, you could store the entire observable universe of non-radiation particles on the surface area of a black hole the size ... 05:40: ... a picturesque European nation with the mass of the heaviest stars in the universe and with the storage capacity to register every atom in the universe, ... 06:20: But remember, we're storing all of the information in the universe on just one of these black holes. 06:27: Storing all of the information in the universe is one thing, but a real computer must compute. 07:54: Using this theorem, we can also figure out the computational capacity of the entire universe. 08:04: ... the energy of the system, we use the mass of the observable universe, around 10 to the power of 52 kilograms, and then apply good old e equals ... 08:14: ... get that, if every single particle in the universe were used to make a computation, it should process 5 by 10 to the power ... 08:28: That's why the universe can dial up its graphic settings so high. 08:32: The universe has been around for 13.8 billion years or 4 by 10 to the power of 17 seconds. 08:45: And that's actually independent of the number of particles or degrees of freedom the universe is using to do that computation. 09:03: Instead of using the mass of the universe to figure out the computation speed, we only have 30 solar masses. 09:09: ... 10 to the power of 20 slower than the computational speed of the whole universe. ... 09:20: ... the universe is computing its own evolution at maximum speed, our black hole computer ... 09:53: ... can instead estimate the computational history of the universe by assuming that all entropy generated over the history of the universe ... 10:39: But hey, you could simulate 10 to the power of 70 universes in that time. 11:25: It's first that our universe can be simulated within the universe. 11:41: ... and quantum mechanics, to figure out the computational properties of our universe. ... 14:06: ... exciting because they let us put narrower constraints on the way the universe can behave." It's such a good ... 14:29: Squirrel Bacon is bothered when people use the term dimension to refer to parallel universe. 14:39: An extra dimension would add infinite layers to the current universe, while a parallel universe would just add a single separate 3D universe.
	2018-10-03: How to Detect Extra Dimensions 00:18: ... era of gravitational wave astronomy is going to open new windows to the universe and unlock many ... 04:07: In our universe, gravity appears to diminish according to the inverse square law, as reflected in Newton's law of universal gravitation. 04:27: In general, general relativity in 3 plus 1 space-time does a great job at describing gravity in the large-scale universe. 05:26: It needs to be intrinsically strong, but then become weakened in the low-energy, large-scale regime of the familiar universe. 05:48: But you restrict all the other stuff in the universe-- matter, radiation, astronomers-- to only three spatial dimensions. 06:47: Most of the stuff in such a universe, including all of the fundamental forces besides gravity, would be restricted to the 3-brane. 07:35: But in short, the expansion of the universe seems to be accelerating. 07:48: In our hypothetical universe with four spatial dimensions, gravity is already weak on the scale of the solar system and the galaxy. 08:14: ... which defines the three-dimensional structure on which our observable universe exists, can actually expand into the extra fourth spatial ... 08:27: To us, that would look like an accelerating expansion of the universe. 09:29: Does that match what you expect in a universe with three spatial dimensions? 11:35: Ruling them out narrows the vast scope of possible theoretical models for our universe, bringing us closer and closer to the truth. 14:57: ... between deleting quantum information and just removing it from the universe, e.g., by dropping it into a black hole, is an interesting philosophical ...
	2018-09-20: Quantum Gravity and the Hardest Problem in Physics 02:17: Where general relativity describes the universe of the large and the massive, quantum mechanics talks about the subatomic world. 02:32: Our experience of the universe appears to be plucked from this landscape of possibilities in strange, but mathematically predictable, ways. 03:33: ... swallow information in a way that can remove it completely from the universe, especially when those black holes evaporate via Hawking ... 03:54: ... information swallowed by black holes can be radiated back out into the universe via their Hawking ... 13:17: How much information does the universe contain? 14:35: dabeste points out that it's important to emphasize that you're talking about the observable universe, not the entire universe. 14:43: ... storage device needed to store all of the information in the observable universe. ... 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.
	2018-09-12: How Much Information is in the Universe? 00:00: [MUSIC PLAYING] Can you fit all of the information in the universe into a region smaller than the universe? 00:10: [MUSIC PLAYING] There's quite a bit of stuff in the universe, to put it mildly. 00:38: But is the universe actually made of stuff? 00:41: ... increasing number of physicists view the universe, view reality, as informational at its most fundamental level, and its ... 00:59: How big a memory bank would you even need to compute a universe? 01:07: How much information does it take to describe the entire observable universe? 01:17: I casually mentioned in the last episode that our 3D universe may just be a projection of information imprinted on its two-dimensional boundary. 02:39: You'd think that to fully describe, say, the universe, you'd need to know what's going on in every tiniest possible 3D chunk. 03:10: ... kind of like saying we can describe the universe completely if we go through all of its quantum voxels, and answer the ... 03:20: This probably way underistimates how much info you really need to describe the universe, but let's start with this anyway. 03:28: So how many Planck volumes are there in the universe? 03:31: Well, the radius of the universe is something like 47 billion light years, which is a few times 10 to the power of 61 Planck lengths. 03:39: 4 on 3 pi r cubed, so the universe contains 10 to the power of 183 Planck volumes. 03:47: ... see estimates that the radius of the universe is a mere 10 to the 60 Planck lengths, rather than 10 to the 61, and ... 04:12: You might argue that more than one bit can fit at each grid point in the universe. 04:30: In other words, we should count all possible quantum states in the universe. 04:38: But as we we'll see, we're already way, way higher than the actual information limit of the universe. 05:04: ... observable universe has a surface area of 10 to the power of 120 to 10 to the power of 124 ... 05:16: So the storage capacity of the universe is around 10 to 60 lower than the number of volume elements it contains. 05:24: So how do you encode a whole universe in a space far smaller than the universe itself? 05:40: See, you don't really need one bit per volume element of the universe. 06:02: The observable universe contains something like 10 to the power of 80 protons. 06:27: The cosmic microwave background has around 10 to the power of 89 photons across the observable universe. 06:42: The situation with dark matter is unclear, so let's just round up to 10 to the power of 90 bits of information in particles in our universe. 07:02: As I mentioned last time, black holes contain most of the entropy in the universe. 08:04: So the Milky Way's black hole has as much entropy and hidden information as all of the matter and radiation in the entire rest of the universe. 08:14: And there are some hundreds of billions of galaxies in the universe, each with its own supermassive black hole. 08:26: Black holes contain, by far, most of the entropy in the universe, and require most information to fully describe. 08:33: But again, we're still below the Bekenstein bound for the whole universe. 08:40: We are nowhere near the universe's memory limit. 08:43: The universe can keep having particles, and you can leave your horribly bloated email inbox alone. 08:49: But what would actually happen if the universe contained too much information? 08:55: ... to fill up those empty Planck-sized cubes of space throughout the universe until it contained more information than the Bekenstein bound ... 09:05: ... the moment the universe reaches information limit, it would immediately become a black hole with ... 09:17: The Bekenstein bound does apply equally to engineered information storage as it does to black holes and universes. 09:47: How large a black hole computer would you need in mass and radius to contain enough data to simulate the entire observable universe? 10:13: Go and read the paper "Computational Capacity of the Universe" by Seth Lloyd. 10:21: How long would that black hole computer take to simulate the entire universe? 10:51: ... email them to pbsspacetime@gmail.com, and use the subject line simulated universe ... 11:30: ... going to catch up on responses to the life on Mars and the end of the universe episodes today, and next week, we'll get to responses to black hole ... 11:51: Yeah, for a show that's about a 13.8-billion-year-old universe, we do try to keep it on human time scales, at least most of the time. 13:21: And now onto our episode on the end of the universe. 13:31: Yeah, that's the weird thing about time scales of the end of the universe. 14:51: So if these decays happen at all, then after 10 to the power of 40 years, every proton in the universe will have had a 50% chance of decaying. 15:24: ... eliminate all of the 10 to the power of 80 protons in the observable universe, you need around 265 half-lives, or 10 to the power 42 to 43 ...
	2018-09-05: The Black Hole Entropy Enigma 00:07: Black holes seem like they should have no entropy, but in fact they hold most of the entropy in the universe. 00:25: Well, it turns out they contain most of the entropy in the universe. 00:28: Let's see why because this fact may force us to conclude that the universe is a hologram. 01:30: ... insight launched an entire new way of thinking about the universe in terms of information theory and ultimately led to the holographic ... 01:42: But first, you are going to need to know more about why black holes contain most of the universe's entropy. 02:08: From the point of view of the outside universe, black holes can only have three properties-- mass, spin, and electric charge. 02:16: ... about anything that falls into a black hole is lost to the outside universe. ... 02:55: From there it could be imprinted on the outgoing Hawking radiation, allowing the information to escape back into the universe. 04:41: We have almost no information about the individual particles, but that information still exists in the universe. 05:30: And then why not radiate the entropy back into the universe as Hawking radiation? 10:06: In fact, they have enormous entropies, the maximum possible, so much that black holes are now believed to contain most of the entropy in the universe. 10:21: It changed our thinking about the informational content of the universe. 11:10: ... to the holographic principle, the idea that the entire 3D volume of the universe is just a projection of information encoded on a 2D surface surrounding ...
	2018-08-30: Is There Life on Mars? 13:07: ... another planet would tell us worlds about the likelihood of life in the universe-- kind of a big deal if we want to understand our own place in what so far ...
	2018-08-23: How Will the Universe End? 00:22: So how will the universe and its far-future denizens spend eternity? 00:27: ... MUSIC] In 100 trillion years, the last star in the universe will expand, the final atoms of hydrogen fuel and settle quietly into a ... 00:50: That 100 trillion years is 10,000 times the current age of the universe. 00:58: But even when they are done, the universe will be young in comparison to the long, dark ages to follow. 01:05: In fact, our universe will spend almost all of its infinite time in darkness, slowly crawling towards maximum entropy and ultimate heat death. 01:19: ... are many fascinating ways in which the universe can still decay to increasingly less interesting states-- or, ... 01:44: Life and structure can only exist as long as the universe is not in perfect equilibrium, what we call heat death. 01:51: ... we're going to figure out how long before the universe reaches its final maximum entropy, minimum interesting state, and answer ... 02:05: And what will happen to the universe as it approaches that moment? 03:09: But they'll have lost all connection with the greater universe before it ends. 03:13: ... before the last red dwarf fades out, the accelerating expansion of the universe will have dragged all galaxies beyond the Virgo Supercluster outside of ... 03:25: That's the boundary of our patch of the universe beyond which no new light can reach us. 03:31: The greater universe will fade from view, and even the cosmic microwave background will also dim to undetectability within the era of red dwarfs. 03:40: There'll be no evidence of a universe beyond the local galaxy and no evidence that there was ever a Big Bang. 03:48: So at this point in the universe's future history, the Age of Stars has passed and no starlight will ever shine again. 03:55: The universe contains nothing but cold, dark nuggets of superdense matter. 05:33: ... into the void in something like 10 to the power of 18 years when the universe is a million times older than the age of the last stars' ... 06:45: So in something like 10 to the power of 39 or 10 to the power 40 years, all protons in the observable universe will be gone. 06:58: The universe will contain only photons, electrons, and black holes. 07:06: If protons decay, black holes would be the only mass of bodies left in the universe after 10 to the power 40 years. 09:09: ... last stuff in the universe will become more and more diffuse and dim as the accelerating expansion ... 09:29: In that case, there will be structure in the universe for a very, very long time. 09:54: ... the remaining matter in the universe, quantum tunneling allows the elements lighter than iron to fuse ... 10:03: In the end of this scenario, every atom in the universe must fuse or decay into iron, the most stable element on the periodic table. 11:36: ... and 10 to the power of 10 to the power of something ridiculous, the universe will be nothing but an increasingly diffuse void of elementary particles ... 11:49: At this point, there's really no hope for extracting useful energy from the universe. 11:54: ... don't have technology so advanced that they arrest the expansion of the universe itself or develop a portal gun-- not ... 12:11: The end of the universe will probably be this eternally expanding, cooling nothingness. 12:23: Vacuum decay may drop the universe to an even lower energy state, wiping out the laws of physics as we know them. 12:29: Or quantum fluctuations may spawn new universes from the void. 13:28: Next, if anyone is interested in hearing two serious experts go into more detail about the far future of the universe, well, you're in luck.
	2018-08-15: Quantum Theory's Most Incredible Prediction 00:50: Quantum field theory describes a universe filled with different quantum fields in which particles are excitations, quantized vibrations.
	2018-07-25: Reversing Entropy with Maxwell's Demon 00:31: As we saw in our episode on the physics of life, structure can develop in one region even as the entropy of the universe rises. 06:20: But all of this appears to have been done without exchanging energy or entropy with the outside universe. 06:26: ... remain constant or increase, unless energy is exchanged with the outside universe. ... 08:07: The demon has to radiate heat, which means transferring entropy back into the box or to the universe. 09:26: ... entropy of the universe must increase, and yet knowing the microstate of a system, no matter how ... 12:55: On the other hand, if the universe lasts for infinite time, then principal entropy drops of all sizes should eventually happen. 13:20: ... the Go board made him think of the game of Life and wonder whether the universe is a giant quantum cellular automata, which led him to a Wikipedia page ... 13:40: ... Wiki browsing choices became Turing complete long ago, and several new universes have been simulated in David Durant's yes-no click ... 13:51: Could we be one of those universes?
	2018-07-18: The Misunderstood Nature of Entropy 00:07: ... defying the arrow of time, predicting the ultimate heat death of the universe, and providing the driving force for the development of structure as well ... 00:23: But what is entropy really, and how fundamental is it to our universe? 00:38: The entropy of the universe must always increase, so says the second law of thermodynamics. 01:24: ... role in black hole thermodynamics and how it will lead to the end of our universe. ... 09:34: Heat must flow between your system and the outside universe in a way that increases the entropy of the universe as a whole. 10:11: This is where the second law appears to add something new to the universe not seen in the more fundamental laws. 11:39: When done right, it gives you a whole new way to look at the universe itself.
	2018-07-11: Quantum Invariance & The Origin of The Standard Model 00:03: ... with stunning accuracy the fundamental quantum building blocks of our universe. ... 00:28: As far as we can tell, mathematics is the language in which the universe is written. 01:57: But it turns out that these gauge symmetries are an important feature of most of our physical theories describing the universe. 10:58: Mathematics truly seems to be the language in which the universe is written.
	2018-07-04: Will A New Neutrino Change The Standard Model? 01:09: ... existence would have had a huge influence on the expansion of the early universe. ... 09:49: ... by the Planck satellite shows that the early rates of expansion of the universe is consistent with only three neutrino ... 09:59: Add more neutrino types like the sterile neutrino and the early universe would have expanded faster. 11:15: With perfect knowledge of the current universe, it should be possible to perfectly trace the universe backwards and forwards in time. 11:33: The statement about the retraceability of the universe doesn't actually care about event horizons, whether cosmic or black hole. 11:41: The idea is that if the information is still existent somewhere, then the universe could be put in rewind and it would end up back where it started. 11:53: ... would get stuck at the point of information destruction because the universe wouldn't know which of multiple possible histories that led to that ... 12:05: But you're absolutely right in thinking that we can't have perfect knowledge of the universe. 12:09: We also can't rewind the universe, so this is just a thought experiment.
	2018-06-27: How Asteroid Mining Will Save Earth 10:51: ... trips, beach days, and those long starry night when you contemplate the universe. ... 11:00: And to help you understand the universe, I recommend "Our Mathematical Universe" by Max Tegmark.
	2018-06-20: The Black Hole Information Paradox 00:22: [MUSIC PLAYING] Black holes are engines of destruction that remove from our universe anything that crosses their event horizon. 01:13: And the quest for its solution may have completely overturned our understanding of the fundamental nature of the universe. 01:20: It may have revealed that the universe is a hologram. 01:27: In recent episodes, we've explored some critical facts about the universe and about black holes. 01:43: With perfect knowledge of the current universe, it should be possible to perfectly trace the universe backwards and forwards in time. 02:01: The inescapable event horizon shields the outside universe from any other influence within the black hole. 02:27: ... that requires information to remain within our accessible part of the universe, just that it continue to exist ... 05:27: ... that the formation of a rotating black hole gives birth to an entire new universe accessible by a ... 05:40: So what if all of the information lost into the black hole ends up in the new universe? 06:03: So it stays in this universe. 06:05: No new universe is required. 06:14: For the outside universe, everything that ever fell into the black hole remains frozen in time and smeared flat over that horizon. 06:31: On one side, John Preskill bet that information somehow leaked back out into the universe. 06:36: On the other side, Stephen Hawking and Kip Thorne bet that it was forever lost from our universe. 07:33: That means their information would radiate back out into the universe and be absorbed into the black hole. 07:57: ... the black hole doesn't even exist on the same timeline as the external universe, it's arguable that those copies don't even exist at the same ... 09:29: This led him to realize that the union of quantum mechanics and gravity may require that the entire 3D universe be a projection on a 2D structure. 09:47: ... be stored on the surface of a black hole, it may imply that the entire universe is a ... 10:09: ... with the holographic horizon and carry information back out into the universe. ... 12:32: But when done right, it can give you a whole new way to look at the universe itself. 13:29: In the mathematics, it looks as though anything falling into a charged black hole is ejected into a separate universe. 13:37: That's a universe of weirdness that we'll do an episode on at some point.
	2018-06-13: What Survives Inside A Black Hole? 01:00: ... fact, every black hole in the universe, no matter how it formed or what happened to it afterwards, can be ... 02:15: The interior of a black hole is cut off from the external universe. 02:20: Nothing beneath the event horizon can influence the exterior universe because no signal can escape the event horizon to carry that influence. 04:20: ... the case of the event horizon, the outside universe can't see the mass inside the black hole, but that mass is remembered in ... 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. 08:08: By the way, it's worth mentioning that real black holes out there in the universe are never going to have a net electric charge. 09:59: If matter with these properties falls into a black hole, information about those properties is lost to the outside universe. 10:24: So what if the universe forgets what type of particles a black hole is made of? 10:37: It's fundamental to quantum mechanics that the universe keeps track of its quantum states, which also means the types of particles it contains. 12:54: Peter K. asks how the universe can be deterministic given the fundamental probabilistic random nature of the quantum world.
	2018-05-23: Why Quantum Information is Never Destroyed 00:07: If you have perfect knowledge of every single particle in the universe, can you use the laws of physics to rewind all the way back to the Big Bang? 00:16: Is the entire history of the universe perfectly knowable? 00:44: These laws can be used to predict how the universe will evolve into the future. 02:38: ... entire universe would be time-reversal symmetric if knowing the exact state of every ... 02:50: That would mean that the exact configuration of the universe at any point in time defines the exact configuration at any other point. 05:36: ... atom's electric field, or it could mean the wave function of the entire universe in its own impossibly complex and changing ... 11:36: The key is that on the scale of these systems, the universe is time translation symmetric. 12:11: Dark energy now comprises 70% of the energy density of the universe and is getting larger. 13:13: The universe was basically just a special case. 13:26: Guys, you really think the universe uses assembly language, or Haskell, or hell, even Java?
	2018-05-16: Noether's Theorem and The Symmetries of Reality 01:18: As the universe expands, light traveling through that expanding space is stretched out. 01:30: In 1915, the expansion of the universe hadn't yet been discovered. 02:08: For every continuous symmetry of the universe, there exists a conserved quantity. 04:49: That's the case with the expanding universe. 05:08: But in Einstein's universe, energy conservation is only valid as a special case. 05:14: It only applies for parts of the universe where we can approximate space as unchanging over time. 05:33: ... saves energy conservation by incorporating the entire universe's gravitational potential energy to offset the seeming gains or losses to ... 06:02: ... falls like magic out of another deep lore of the universe-- the principle of least action, which states that the universe will ... 08:30: ... they lead to the family of particles and interactions that make up our universe. ... 09:27: ... us a big step closer to understanding the fundamental workings of the universe through the continuous symmetries of "Space Time." Thank you to ... 09:57: As always, thanks to all of our Patreon supporters that helped keep us explaining the universe.
	2018-05-09: How Gaia Changed Astronomy Forever 08:22: These maps help us to better understand our place in the universe. 08:48: Last week, we talked about the last stars that will shine in our universe-- the humble, red dwarf. 09:37: Many of you point out that there will be useful sources of energy in the universe long after the last red dwarf fades away. 09:52: Super advanced civilizations clustered around black holes, in an utterly dark universe.
	2018-05-02: The Star at the End of Time 01:20: And the deepest wells of accessible energy in the universe are stars. 01:29: To know the future of life, we must understand the life cycles of the longest-lived stars in the universe. 07:11: That dark future is inevitable, but for several trillion years, red dwarfs will be the last warm places in the universe. 07:19: ... an awfully long time at many times the current age of the universe, Red dwarfs will surely be the places our own starfaring descendants will ... 08:33: It's very possible that most of the life in the universe is yet to evolve.
	2018-04-25: Black Hole Swarms 03:55: Some nearly as old as the universe itself.
	2018-04-18: Using Stars to See Gravitational Waves 04:57: The universe is flooded with space-time ripples. 05:00: ... a faint gravitational wave background buzz from an earlier epoch of the universe in which binary supermassive black holes were common, or from cosmic ... 10:57: Bose-Einstein asks, is life causing the universe to reach high entropy faster than if life didn't exist? 11:33: Plant a tree, and you accelerate the heat death of the universe. 12:30: Michael always wanted to be a supervillain, and now takes comfort that his mere existence is helping to unravel the universe.
	2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!) 00:00: [MUSIC PLAYING] Our universe is prone to increasing disorder and chaos. 00:52: The universe tends toward disorder, decay, and equilibrium. 00:56: A hot cup of coffee will tend towards the same temperature as the room, and the hot, dense of our universe must expand. 01:24: ... concentrated in your cup of coffee or all the matter in the observable universe being crunched into an infinitely dense point are low ... 01:54: The universe will only get more boring. 10:20: These blips in order are actually serving the second law helping the universe disperse its early extreme low entropy state. 12:26: Moma the Belly Dancer asks whether this means that the expansion of the universe also causes an event horizon? 12:44: But the accelerating expansion of the universe will prevent any photons emitted today from galaxies at that distance or beyond from ever reaching us. 13:09: On the other hand, during the inflationary epoch in the extremely early universe, the cosmic event horizon was very close to every point. 13:17: The inflating universe should have been bathed in intense Hawking radiation.
	2018-04-04: The Unruh Effect 00:51: They found that the simple act of acceleration cuts off your causal access to a region of the universe. 02:47: ... than light, their past light cone should eventually contain the entire universe. ... 02:56: Well, that's if you ignore the expansion of the universe, and this makes sense. 02:59: If you wait long enough, photons from anywhere in the universe can catch up to you. 04:33: So after draining all of the energy in the universe, they'd finally have to stop accelerating, and my message would overtake them. 05:36: All parts of the universe beyond that horizon are out of causal connection with the Rindler observer as long as they continue to accelerate. 10:12: ... there's one place in the universe where the gravitational acceleration can get that high, and that's right ...
	2018-03-28: The Andromeda-Milky Way Collision 01:25: The Andromeda Galaxy was our first clue that there existed a universe outside the Milky Way. 02:01: In the mid 1700s, he hypothesized that Andromeda was an island universe, a vast sea of stars distant to our own. 02:55: It was finally clear that Andromeda was, after all, an island universe far outside the Milky Way. 03:01: Hubble went on to combine distance measurements to many galaxies with measurements of their velocities to discover the expansion of the universe. 08:37: ... a time when we have such a clear view of our dynamical evolving universe, when we have a neighbor whose visible stars revealed its great distance, ... 09:06: Will those astronomers ever figure out that there are countless other island universes stretching across a much vaster space time? 10:06: ... name we give to the effect, whereby the gravitational response of the universe doesn't match the visible matter given our understanding of that matter ... 10:43: ... hypothesis that dark matter was responsible for the cooling of the early universe relies on it being some sort of stuff that can interact with either ...
	2018-03-21: Scientists Have Detected the First Stars 00:00: [MUSIC PLAYING] What do the first stars in the universe, dark matter, and superior siege engines have in common? 00:28: That's the case with the recent discovery of the earliest stars in the universe. 00:34: In a nature paper published just a few weeks ago, Judd Bowman and collaborators, report a signal from the very first stars to form in our universe. 01:05: [MUSIC PLAYING] So the very early universe was full of hydrogen gas and light. 01:47: ... the early universe, the rate of hydrogen spin flip was in equilibrium with the CMB, meaning ... 02:51: [MUSIC PLAYING] The TLDR is that there should have been this brief period of time when the universe was eating up 21 centimeter photons from the CMB. 03:04: Now, remember also, that the universe was expanding back then, just like it is now. 03:14: In fact, there should be this broad dip at a range of wavelengths, representing the epoch of the universe in which this absorption was occurring. 04:10: Measuring this range in itself, is a stunning discovery that will really help us understand the early universe. 05:10: Or expand the universe, but that's already been taken into account. 08:42: That includes new heat death of the universe is coming shirt.
	2018-03-15: Hawking Radiation 00:06: Stephen Hawking peered behind the curtain of reality and glimpsed the true workings of the universe. 00:50: ... star, space and time could be dragged inwards to create a hole in the universe, a boundary in spacetime called an event horizon that could be entered, ... 01:07: Once formed, there was nothing in theory or imagination that could bring material consumed back to the outside universe.
	2018-03-07: Should Space be Privatized? 11:56: Of course, we've never seen the results of this, because no red dwarf has ever died in this universe yet. 12:13: The first red dwarf will end its life when the universe is something like 100 billion years old.
	2018-02-28: The Trebuchet Challenge 00:00: [JINGLE PLAYING] Energy is a powerful tool for predicting the behavior of our universe, from quantum to cosmological scales.
	2018-02-14: What is Energy? 06:47: Tracking the shift between different forms of energy allows us to predict the behavior of the universe in ways that would otherwise be impossible. 07:06: The universe is complicated. 07:14: But try to describe the behavior of the countless particles in, say, a stream of water or a universe, and it's pretty hopeless. 09:34: ... a powerful accounting tool for describing the behavior of the physical universe, it's also a hint, a hint of something more ... 10:00: In fact, for every symmetry in our universe, there exists a conserved quantity. 10:29: What if the universe as a whole is not time symmetric, for example, in the case of an expanding universe? 10:36: Our universe looks fundamentally different from one moment to the next, at least on cosmic scales, where it's expansion becomes significant. 10:48: This leads to effects like dark energy and the accelerating expansion of the universe. 11:59: A good example is the course Physics and Our Universe by Richard Wolfson.
	2018-01-24: The End of the Habitable Zone 10:09: To really gain intuition about our often very unintuitive universe, you need to start solving problems in physics, math, and astronomy.
	2018-01-17: Horizon Radiation 01:01: ... can travel or the cosmological horizon that limits the observable universe. ... 01:24: It limits an observer's causal connection to a part of the universe. 06:24: Now, each one of these momentum modes exists at all spatial points in the universe. 06:40: The superposition of infinite universe size momentum oscillators-- momentum particles can represent a single spatial oscillator. 06:51: One particle at one point in the universe. 10:15: Well, the same is true of the universe. 10:26: ... and annihilate the same particles as we had in an infinite, horizonless universe. ... 12:07: It's hard to be sure of anything in this relative universe, whether it's the existence of a particle or funds for a YouTube show.
	2018-01-10: What Do Stars Sound Like? 09:32: To really gain intuition about our often very unintuitive universe, you need to start solving problems in physics, math, and astronomy.
	2017-12-22: Space Time VR 00:27: Three experiences are out now, and three more covering general relativity, black holes, and the shape of the universe, are on the way for early 2018.
	2017-12-20: Extinction by Gamma-Ray Burst 01:11: The ends of the world, end of the universe, will come.
	2017-12-06: Understanding the Uncertainty Principle with Quantum Fourier Series 00:40: It expresses the fundamental limit on the knowability of our universe. 00:58: ... universe we experience seems to be constructed of singular particles with ... 10:51: So a perfectly specially localized particle is equally an infinite number of momentum particles that themselves occupy all locations in the universe.
	2017-11-29: Citizen Science + Zero-Point Challenge Answer 00:43: ... it seems like the scientific exploration of our universe is now in the hands of full-time career astroprofessionals, a ton of ... 09:29: There's the heat death of the universe is coming, which is also available for anyone to purchase.
	2017-11-22: Suicide Space Robots 00:07: To unlock the mysteries of the universe, some sacrifices will have to be made. 14:35: There's a certain way that the universe is-- an actual objective reality that is a true nature that science is trying to find out. 14:44: There's one way that the universe is and infinite ways that it isn't. 14:50: In our quest to find the true nature of reality, we must explore a lot of the ways that the universe isn't in order to rule them out.
	2017-11-08: Zero-Point Energy Demystified 00:32: ... from the non-zero zero-point energies of the quantum field that fill our universe. ... 00:53: ... the other hand, our observations of the accelerating expansion of the universe suggest a vacuum energy density of only 10 to the power of minus 8 ergs ... 02:27: The universe tends towards disorder, and so a highly unusual arrangement will decay over time. 04:12: The universe would then try to fill that energy hole, and we could harness that to extract energy. 06:59: Vacuum energy is real, and it's part of the fundamental clockwork of the universe.
	2017-11-02: The Vacuum Catastrophe 05:18: An energy of space itself should cause exponential expansion, at least in the case of an already expanding universe. 05:26: It should also massively increase the spatial curvature of the universe. 05:37: ... value predicted by theory, then our gently expanding geometrically flat universe would not ... 07:09: ... the late '90s, astronomers discovered that the expansion of the universe is, in fact, accelerating in exactly the way we'd expect from a non-zero ... 08:38: ... exist in an extremely rare universe whose fundamental fields canceled out their zero point energies, at ... 08:50: That would imply countless other universes with different, less comfortable vacuum energies.
	2017-10-25: The Missing Mass Mystery 00:00: [MUSIC PLAYING] For years, astronomers have been unable to find up to half of the matter in the universe. 00:18: ... PLAYING] Our astronomical surveys have revealed an observable universe full of hundreds of billions of galaxies, each of them with as many ... 00:41: When we extrapolate observations to the entire observable universe, we find a billion trillion suns worth of mass. 00:49: However, we've known for some time that around 95% of the energy content of the universe is in dark matter and dark energy. 01:06: The remaining 5%, the light sector, represents all of the regular matter in the universe. 01:52: It comprises 80% of the mass of the universe or around 25% of its total energy content. 01:59: Its gravity holds galaxies together and governed to the growth of large-scale structure in our universe throughout cosmic time. 02:13: It's anti-gravitational and causes the expansion of the universe to accelerate. 02:19: This energy of the vacuum comprises 70% of the universe's energy content. 05:43: Now surveys of galaxies confirm that this is what the large-scale structure of the universe looks like. 08:01: And so those solitary baryons could add up to more mass than all of the galaxies in the universe. 10:22: ... it seems that most of the regular matter in our universe is spread out in the vastness of intergalactic space, still flowing with ... 10:44: In fact, this verifies that the epoch of star formation in our universe is far from over. 11:29: Yet, it would still push the universe towards positive spatial curvature. 11:34: So enough vacuum energy could result in a closed, rather than infinite, universe. 11:39: And rather differently to regular matter, vacuum energy doesn't dilute in an expanding universe. 11:51: And this is, of course, what our universe is doing. 11:59: ... of virtual matter anti-matter particles would introduce energy into the universe and therefore violate the law of conservation of ...
	2017-10-19: The Nature of Nothing 02:15: ... neutrinos, photons, gluons, et cetera, that comprise the stuff of our universe. ... 04:20: ... to be the machinery under the hood of all particle interactions in the universe, at least as described by quantum field ... 07:06: But they do nonetheless leave their ghostly mark on the universe. 10:14: The observation is the accelerating expansion of the universe. 15:36: HK Norman would like us to do a mention of the recent discovery of half of the missing matter in the universe.
	2017-10-11: Absolute Cold 06:21: For example, the quantum fields that fill our universe also fluctuate due to the Uncertainty Principle resulting in what we know as vacuum energy. 06:46: To understand the universe, we need to understand how it behaves absent heat, absent light, and absent matter.
	2017-10-04: When Quasars Collide STJC 11:50: ... answer, I would ask you to imagine that the entirety of our universe-- or even the multiverse-- has the same laws of physics, including the ... 12:00: ... then that the universe wasn't set up specifically to be able to produce life, then is it not ... 12:12: The alternative is that many universes or patches of universe exist that encompassed an extremely wide range of physical states.
	2017-09-28: Are the Fundamental Constants Changing? 00:06: The laws of physics are the same everywhere in the universe-- at least, we astrophysicists hope so. 00:12: After all, it's hard to unravel the complexities of different parts of the universe if we don't know the basic rules. 00:20: There is a hint of evidence that the fundamental constants that govern our universe may evolve over time, and even from one location to another. 00:50: ... the existence and behavior of the particle building blocks of our universe. ... 02:13: It's been suggested that a changing speed of light might be an alternative to inflation theory, or even to the apparent expansion of the universe. 04:13: But if you change it by much, our universe would look very different. 06:37: Remember quasars, insanely luminous maelstrom drums of superheated matter surrounding the most massive black holes in the universe? 06:58: By looking at many quasars, we can find absorbing clouds that existed in different past epochs of the universe. 08:26: ... redshifted-- their wavelengths stretched out due to the expansion of the universe. ... 10:16: It might seem lucky that Alpha is fine tuned for a universe with the warmth of stars, and a rich and complex chemistry-- both essential for life. 10:25: ... place, then it's not surprising that we find ourselves in a part of the universe conducive to stars, and to planets, and to ...
	2017-09-20: The Future of Space Telescopes 00:03: The mysteries of the universe seemed limitless. 10:12: What once seemed like fundamental limits to our ability to observe the universe are now being overcome by some incredible human ingenuity. 10:47: ... rainbow is launched and that sparkling glitter cloud is thrown into the universe, we will consider it to be a celebration of your great ... 11:33: Nicholas Martino asks whether gravitational waves are redshifted by the expansion of the universe.
	2017-09-13: Neutron Stars Collide in New LIGO Signal? 00:37: ... waves from a pair of merging black holes, an entirely new realm of the universe opened up to ... 00:49: We now have an observatory that can explore the most extreme gravitational phenomena in the universe. 03:56: Well, because the universe makes far more neutron stars than black holes. 05:10: We can see black hole merges across 1,000 times more universe compared to neutron star mergers.
	2017-08-30: White Holes 00:19: Some even think that these could be the origin of our universe. 02:12: ... a fascinating one, and the idea may help us understand the origin of the universe. ... 03:16: The time that happens inside a black hole is not part of the past or future history of the outside universe. 04:20: From the point of view of the outside universe, the eternal black hole singularity exists both in the infinite future and in the infinite past. 06:04: ... two regions, our universe and the black hole interior, are just the Schwarzschild metric mapped ... 07:42: That suggests they must exit into the outside universe. 08:27: The universe hasn't existed for eternity, and it didn't even begin with black holes in place. 09:12: ... hole in general relativity, there are other laws of physics that the universe needs to obey-- for example, the second law of ... 11:08: ... to suggest that the resulting white hole is the Big Bang of a new baby universe and that, in fact, our universe formed that ... 11:25: But speaking of other universes, it turns out that we haven't finished building our Penrose diagram yet. 12:05: ... looks like an identical alternate universe on the other side of the black hole, accessible through what we call an ...
	2017-08-24: First Detection of Life 05:08: ... water is basically everywhere we look in the universe, liquid water is a little harder to come by, yet it's incredibly ... 05:16: Even if we ignore the fact that all Earth life requires it, water is by far the best substance in the universe for brewing up and supporting life. 10:24: This would answer one of the oldest questions in science and philosophy-- are we alone in the universe?
	2017-08-16: Extraterrestrial Superstorms 11:50: Last week, we talked about John Archibald Wheeler's one electron universe idea as well as gave the solution to the Feynman diagram challenge. 12:00: Andreas64 asks why we don't also talk about the one proton or one neutron universe. 12:25: Keith Gaughan wonders if the imbalance between matter and anti-matter is due to the time in the history of the universe that we're observing.
	2017-08-10: The One-Electron Universe 00:01: ... profound advances-- for example, the idea that every electron in the universe is really the one same electron traveling forwards and backwards in ... 00:51: Wheeler went on to describe his one-electron universe idea-- that there exists only one electron. 01:01: ... in time, eventually traversing the entire past and future history of the universe in both directions and interacting with itself countless times on each ... 01:12: In this way, it fills the universe with the appearance of countless electrons. 01:46: ... Wheeler's one-electron universe idea inspired Feynman to build this representation of anti-matter into ... 02:04: ... one-electron universe was motivated by an odd fact about electrons that had troubled Wheeler-- ... 03:25: That one electron zigzagging back and forth 10 to the power of 80 times looks like all of the electrons in the universe. 07:18: ... we draw a Feynman diagram for the whole universe, we can have only one electron undergo countless scattering events, some ... 07:39: Now, there are some big problems with the one-electron universe idea. 08:15: It's certainly not widely accepted that there's only one electron in this universe, nor whether that's even a meaningful statement. 10:36: That includes our brand new shirt-- the heat death of the universe is coming. 10:59: ... about the controversial evidence that many galaxies in the observable universe are drifting very slightly towards a point beyond the cosmic ... 11:23: ... caused by a gravitational influence beyond the edge of the observable universe, then yeah, it no longer exerts a force on ... 11:34: That force would have been exerted by a high density patch of space in the pre-inflationary period at the beginning of the universe.
	2017-08-02: Dark Flow 00:03: There's controversial evidence that, on the largest scales, the universe is flowing. 00:08: It may be that much of the matter in the cosmos is drifting due to the ancient gravitational pull of something outside the observable universe. 00:34: And of course, the universe is expanding. 00:44: Motion due to the expansion of the universe-- what we call the Hubble flow-- is equal in all directions. 00:58: On the largest scales of the universe, there should be no preference for up or down or left or right. 01:44: The CMB is the leftover heat glow from the hot dense early universe. 02:43: In that reference frame, if you added together the peculiar velocities of all galaxies in the universe, you'd expect them to cancel out. 03:39: ... the most massive galaxy clusters in our universe are vast conglomerations of thousands of galaxies and are bathed in a ... 05:07: But what if you could measure the effect from hundreds of clusters across the observable universe? 05:38: It's like a lot of the matter in the universe is flowing toward some point beyond the edge of our universe. 05:52: The universe should be homogeneous and isotropic on the largest scales. 06:10: Isotropic means that the universe shouldn't have a preferred direction. 06:22: So the idea of a universe-wide dark flow surprised a lot of people, and made others very skeptical. 07:26: Since 1973, we've noticed that galaxies in the local part of the universe seem to be drawn in that direction due to an unseen gravitational influence. 07:50: ... flow, because that flow seems to affect galaxies across the observable universe, or to two and a half billion light years at least, far beyond the ... 08:08: ... attraction towards something beyond the edge of the observable universe. ... 08:17: Now, that part of the greater universe can no longer influence us. 08:32: In the earliest instance of the Big Bang, the observable universe was compressed into a subatomic scale. 08:58: ... exists a region of much more stuff, a different bubble of observable universe with more galaxies, more clusters, more dark ... 09:10: ... a region may have given our entire universe such a gravitational tug that even 13.7 billion years later, we still ... 09:40: ... for the first time the influence of a neighboring region of the greater universe, beyond the horizon of observable ...
	2017-07-26: The Secrets of Feynman Diagrams 11:53: ... to everyone, including challenge winners-- the heat death of the universe is coming, a fun reminder in t-shirt form of the eventual cold dark end ...
	2017-07-07: Feynman's Infinite Quantum Paths 00:25: [MUSIC PLAYING] There's a fundamental limit to the knowability of our universe. 04:08: For example, there are paths that loop in circles or take detours to the edge of the universe. 05:06: For the large-scale classical universe, minimizing proper time lets you derive all equations of motion. 05:17: Basically, the universe is lazy. 05:20: However, in the quantum universe, there is no single path. 09:31: ... able to deal with all of this weirdness because it's able to describe a universe of oscillating fields just as well as it can describe a universe of ... 11:50: The universe may obey the principle of least action, but Mr. Levine is more of a maximum action guy. 14:06: ... in pairs, shouldn't there be just as much antimatter as matter in the universe? ... 14:16: Up to around a millionth of a second after the Big Bang, the universe was hot enough for photons to be continuously forming matter-antimatter pairs. 14:38: It indicates a break in what we once thought to be a fundamental symmetry of the universe. 14:44: This so-called charge parity or CP violation has been seen in experiments, implying that the universe does treat antimatter differently to matter.
	2017-06-28: The First Quantum Field Theory 00:06: ... "the jewel of physics." Of all of our mathematical descriptions of the universe, this one has produced the most stunningly precise ... 01:18: ... fields that exist at all points in space and time through the universe. ... 04:26: Everywhere in the universe, that value is usually zero, but just like the string or the air density field, it could oscillate.
	2017-06-21: Anti-Matter and Quantum Relativity 00:24: And the emerging field of quantum mechanics had radically altered our understanding of the fundamental building blocks of the universe. 07:00: Imagine an infinitely deep ocean of electrons that exists everywhere in the universe. 08:14: Of course, there is something in our universe that acts exactly like holes in the Dirac sea. 10:53: ... quantum mechanics and relativity reveal an entire flip side of our universe, with its prediction of ... 12:17: ... microwave background was due to supervoids or a collision with another universe. ... 13:12: ... username asks whether colliding universes in the bubble universe scenario means that we redefine "universe" to be ... 13:31: I mean the definition of universe is semantic. 13:34: But this bubble universe idea does suggest a greater universe beyond our bubble. 13:39: ... scenario means it makes sense to talk about those bubbles as separate universes and as the whole ensemble, including the inflating part, as a ... 13:50: Galdo145 asks whether bubble universes with different vacuum energies would convert to the lower energy state after colliding? 14:38: ... vacuum energy state would propagate at the speed of light to fill that universe, fundamentally changing the way its elementary particles ...
	2017-06-07: Supervoids vs Colliding Universes! 00:17: Is this feature a statistical fluke, the signature of vast supervoids, or even the imprint of another universe? 00:30: Is that giant cold spot in the cosmic microwave background really evidence of a collision with another universe? 01:01: ... radiation as that radiation passed through a giant empty regions of the universe, so-called ... 01:52: When it formed in the early hot universe, it was mostly infrared light with a temperature of 3,000 Kelvin. 02:28: These were then amplified by a period of exponential expansion in the very early universe that we call inflation. 03:18: Simulations show that you should get a spot that size in the CMB in around 1 in 50 universes. 03:25: So we might be in one of those slightly rarer universes with a big CMB splotch. 03:31: Really, in any given universe, there should be a few weird 1 in 50 things, but the odds are low enough that it's worth investigating. 04:13: But by the time the photon is on its way out, the expansion of the universe has actually stretched out the cluster, weakening its gravitational pull. 04:39: It loses energy going in, because it's being pulled backwards by the higher density universe behind it. 04:53: The ISW effect would be tiny, in fact negligible, in a universe without dark energy. 05:07: ... around 4 billion years ago, dark energy caused the expansion of our universe to begin accelerating, whereas previously it had been slowing down due ... 05:18: In an accelerating universe, the difference in the ingoing and outgoing boosts can be large enough to be detected. 05:46: ... shift in the wavelengths of those spectra due to the expansion of the universe, i.e., they measured ... 06:03: ... all the way out to the point where dark energy started to dominate the universe. ... 08:22: They're ideas like the amplification of topological defects in the universe or an inhomogeneous reheating at the end of a nonstandard inflation. 08:32: But the one that gets most people most excited is, of course, that the cold spot is the mark left due to a collision with another universe. 09:03: But in an eternal inflation scenario, a normal universe begins when a small patch of the inflating universe stabilizes. 09:22: This can happen spontaneously anywhere in the greater inflating space time, resulting in bubble universes. 09:37: But regardless, in an infinitely inflating space time, collisions between bubble universes are eventually expected. 09:45: So what happens when two bubble universes collide? 09:53: Chang, Claiborne, and Levi, 2009, figured out that this should result in a temperature gradient across each universe. 10:21: If real, this would be the first piece of evidence that a universe beyond our own exists. 12:22: A few of you asked about looking back into the old universe to find population three stars, and that is indeed where we focus our search. 12:36: You can see galaxies forming in the very early universe, but they're incredibly faint. 13:17: [INAUDIBLE] et al., 2015, found a galaxy in the old universe whose light is very hard to explain without a lot of pop three stars.
	2017-05-31: The Fate of the First Stars 00:05: Soon after the Big Bang, the first generation of monstrously large stars ignited, lit up the universe, and then died. 00:13: The resulting swarms of supernova explosions enriched the universe with the first heavy elements and lots of black holes. 00:30: [MUSIC PLAYING] The sun is a late-comer to our universe. 02:12: They were born long ago, when galaxies like the Milky Way were still forming in the early universe. 02:32: ... galaxies, born of the pristine hydrogen and helium gas that filled the universe soon after the Big ... 03:03: OK, so these things formed at the beginning of the universe. 03:17: Even stars a little smaller than our sun-- the orangish K-type stars-- live for longer than the current age of the universe. 03:31: But stars of the sun's mass and higher that formed over 13 billion years ago, near the beginning of the universe, would now be long gone. 05:33: With masses that high, all population three stars would have gone supernova while the universe was still in its infancy. 08:03: ... in the gas-rich environment of the old universe, we expect that there were violent waves of star formation followed by ... 08:16: Those first stars changed the face of the universe. 08:27: They pumped out ultraviolet radiation, which began the work of energizing, of ionizing, the atomic and molecular hydrogen that filled the universe. 08:36: ... began epoch of re-ionization, which saw the universe shift from being a hazy, nearly opaque fog of hydrogen gas to the ... 09:26: Such black holes power quasars, which themselves, had a huge influence on the later evolution of our universe. 10:12: When we look out into the universe, as far as our telescopes can see, we do see primitive looking galaxies shining out from the earliest of times. 10:36: The hunt continues for the first stars in the universe.
	2017-05-03: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson 01:22: And so they program in enough detail to completely simulate every molecule in this universe. 02:03: So the idea that if you need to produce one universe capable of producing universe simulations. 02:09: ... if that universe produces billions of universe simulations, then any universe that you ... 02:52: It can't simulate the whole universe, because to simulate a universe perfectly, you need a computer the size of a universe. 03:23: That under certain assumptions, virtual minds should vastly outnumber real minds in our universe. 03:43: Let's avoid the idea that the entire universe is simulated, right down to every atom, electron, or vibrating quantum field. 03:59: Instead, today I want to talk about the idea that it's our experience of the universe that is simulated. 04:05: That we are simulated minds in a virtual universe that has just enough detail to convince us of its reality. 08:27: It tells us that we aren't in a special place in the universe. 08:37: Our place in the universe must have been able to produce and sustain us, so we're somewhere habitable. 08:47: We must observe a universe or a part thereof that can have observers. 10:34: These simulations can only cover a tiny fraction of the universe. 10:40: ... discovery of these inconsistencies than it is to simulate enough of the universe so that inconsistencies don't ... 11:12: ... a philosopher telling a cosmologist that we must surely live in a universe capable of producing the most brains, because that universe would give ... 11:34: The universe that has the most minds must be the one we're in. 12:00: With a little imagination, yet more mind factory universes can be conceived and simulated "usses" multiply exponentially. 12:27: There we talk about how confident we can really be in our understanding of the galaxy and the universe and of scientific knowledge in general. 14:09: ... even in a perfectly deterministic universe, there's a pseudo randomness that arises due to massive complexity, say, ...
	2017-04-26: Are You a Boltzmann Brain? 01:49: Any part of the universe, left to its own devices, always tends to flow back to equilibrium. 02:07: But why does the universe have to return to equilibrium? 04:01: ... would take vastly longer than the age of the universe for it to happen, so in practice we never observe the second law of ... 04:17: Imagine an infinitely large room-- a universe that's in perfect thermal equilibrium for infinite time. 04:50: All the particles in a region much larger than our universe could randomly end up in almost the exact same location. 05:00: It's not known whether the big bang originated as a low-entropy dip in an otherwise high-entropy universe. 05:27: In the far future, the universe will reach maximum entropy. 05:37: The universe will spend almost all of its time in that high-entropy state. 05:41: Nonetheless, it shouldn't really be so surprising that we observe a low-entropy blip in an otherwise mostly high-entropy universe. 05:50: After all, our existence is a byproduct of the universe's progression towards that high-entropy state. 06:06: ... not surprising that we view the universe from the comfy biosphere of a terrestrial planet, even though the volume ... 06:18: Similarly, we must have appeared at a time and in a universe capable of producing biospheres. 06:58: We observe the universe from as typical a vantage point as is consistent with our experience. 07:12: For example, why collapse a whole universe worth of particles? 07:45: ... a universe where structure results from entropy fluctuations, the vast majority of ...
	2017-04-19: The Oh My God Particle 00:51: ... by the University of Utah to spot the highest energy cosmic rays in the universe. ... 06:05: It turns out that the universe is full of natural particle accelerators. 06:53: See, the universe is basically opaque to particles with such high energies. 09:07: ... is becoming an increasingly powerful tool for investigating our amazing universe. ...
	2017-04-05: Telescopes on the Moon 01:07: The lunar-based ultraviolet telescope, LUT, isn't large at only around 15 centimeters diameter, yet it has one of the clearest views in the universe. 07:56: Such a telescope could gaze on the universe from when it was just 500 million years old.
	2017-03-29: How Time Becomes Space Inside a Black Hole 00:55: ... of cause and effect, the only reliable ordering of events in a relative universe. ... 05:13: Back out here in the regular universe, it's pretty obvious where the past and the future are. 05:25: ... influenced us, while that future light cone shows us the part of the universe that we might never hope to encounter or ... 07:02: Watch what happens to our view of the universe as we approach it. 07:38: The outside universe exits our future light cone, which now just contains the singularity. 08:39: Also in our past light cone are light rays that are pointed inwards, some of them coming from the outside universe. 10:12: In the same way that all world lines move towards the future in the outside universe, time is laid radially. 15:01: But please persist, because understanding our universe is well worth all of the work.
	2017-03-22: Superluminal Time Travel + Time Warp Challenge Answer 00:20: The reality of the vast scale of our universe, even with our galaxy, is inconvenient for tales of star-hopping adventure or warring galactic empires. 01:54: ... was assumed that the entire universe exists simultaneously in a state of now, and that all points move ... 10:15: Our experience of the universe is a thing that emerges from the forward causal evolution of the matter that we're composed of.
	2017-03-15: Time Crystals! 02:49: Cups of coffee cool down, planets orbit the sun, the universe expands. 02:54: But cups of coffee in the universe are not in equilibrium, and the planets are macroscopic moving objects.
	2017-02-15: Telescopes of Tomorrow 00:14: But the telescopes of tomorrow will continue this advance and allow us to crack open some of the greatest mysteries of the universe. 00:22: ... Its stunning images and spectra have opened up incredible windows on our universe. ... 02:23: This will provide another set of baby pictures, the formation of the very first stars and galaxies in our universe. 02:36: Light from these earliest of galaxies has been traveling through our expanding universe since near the beginning of time. 07:36: It's hoped that GMT will even find traces of the very first population of stars that formed in our universe. 08:21: It will see how things in our universe move and change over days, months, and years. 09:06: ... counterparts to gamma ray bursts, the most energetic explosions in the universe or record the twinkling of objects in the distant universe as their ... 09:24: This will allow us to map the universe using gravity itself as a lens. 09:34: They are designed to tackle some of the biggest questions about our universe-- known unknowns. 10:19: Alex Filippenko's course, "Understanding the Universe," is a pretty incredible survey of pretty much the entire field of astronomy.
	2017-02-02: The Geometry of Causality 10:50: Janna Levin's "Black Hole Blues" is a wonderful take on the new window that gravitational waves are opening on our universe. 10:58: ... quasars, and especially how important they are in the evolution of the universe. ... 15:13: "When my dad was in college, he needed one of those easy classes for credit, so he took a class on quasars and black holes in the universe.
	2017-01-25: Why Quasars are so Awesome 00:16: Let's talk about what happens when the largest black holes in the universe start to feed. 01:19: Sometimes they even have jets of near light speed particles filling the surrounding universe with giant radio plumes. 01:36: Quasars helped shape our universe. 03:05: For one thing, its spectrum was redshifted, the wavelength of its light stretched out as those photons traveled through the expanding universe. 04:33: The heat glow of the accretion disk is so bright that we can see quasars to the ends of the universe. 06:07: ... when a supermassive black hole feeds and blasts energy into the universe, what we see depends on its orientation, whether or not it has a jet, the ... 06:49: But when viewed from halfway across the observable universe, that is impossibly tiny. 07:16: Anything as energetic as a quasar must have had an influence on the universe. 07:21: The first quasars turned on in a very young universe that was still thick with the raw hydrogen gas produced in the Big Bang. 07:29: As the first galaxies coalesced from this gas, the universe entered a long period of violent star formation. 08:20: ... black holes that had been growing since the beginning of the universe. ... 08:52: A few billion years after the Big Bang, when the universe was around a quarter of its current age, both starbursts and quasars started to dwindle. 09:13: Active galactic nuclei still do fire up in the modern universe, although usually they are at full quasar power.
	2017-01-19: The Phantom Singularity 04:45: ... the simple case of a spherically symmetric mass in an otherwise empty universe. ...
	2017-01-11: The EM Drive: Fact or Fantasy? 12:01: At some level, we start to have a pretty thorough grasp of what is possible in this universe.
	2017-01-04: How to See Black Holes + Kugelblitz Challenge Answer 01:09: That accretion disk shines so brightly that we see them to the ends of the universe. 06:46: This is because there are regions of the universe that are doomed to end up in the singularity even before the true event horizon forms.
	2016-12-21: Have They Seen Us? 02:58: There, the natural universe is especially quiet. 07:33: One of its primary purposes will be to catch the radio emission from hydrogen gas in the extremely early universe. 07:49: But if such radio waves travel to us from the earliest of times, then they become stretched out as they travel through an expanding universe. 11:48: That redshifted 21-centimeter hydrogen emission really is one of the most important keys to understanding the very early universe.
	2016-12-14: Escape The Kugelblitz Challenge 00:27: The Penrose diagram allows us to easily understand the limits of our access to this universe. 00:44: ... the real, astrophysical black holes that actually dwell out there in the universe. ... 01:45: Let's start with a nice, empty universe. 02:40: Outside the black hole, the event horizon becomes the new edge of the universe on our Penrose diagram. 03:41: Any observers within this extended event horizon are cut off from any future causal connection with the rest of the universe.
	2016-12-08: What Happens at the Event Horizon? 00:38: ... that falls below the event horizon can never escape and is lost to the universe forever while we see falling objects freeze as time stands still at the ... 01:38: For example, are objects falling through the event horizon really physically frozen there from the point of view of the outside universe? 01:48: Would you see the entire future history of the universe playing fast forward at the instant that you crossed the event horizon? 02:19: ... one dimension in space, we can look at the limits of our access to the universe due to its absolute speed limit, the speed of ... 02:54: Our past light cone defines the region of the past universe that could potentially have influenced us. 03:57: That makes it difficult to figure out what parts of the past and future universe the monkey can witness or escape to. 06:28: It becomes uni-directional, flowing inexorably downwards, just as time flowed inexorably forward in the outside universe. 06:52: The only way to escape back to the outside universe would be to widen your light cone by traveling faster than light. 07:55: Its future light cone still includes a tiny sliver of the outside universe. 08:15: ... through the event horizon, watching the entire future history of the universe play out above it at that last ... 08:32: ... monkey's last view of the outside universe is defined by its past light cone that encompasses all of the light that ... 08:50: There's no future universe spoiler promo. 08:54: ... it could instead hover above the event horizon, then it would see the universe in fast forward, although that view would be compressed into a small ... 10:47: ... black hole has two additional regions, one corresponding to a parallel universe on the other side of untraversable wormhole, the Einstein-Rosen ... 11:54: For an excellent overview of basically all physics, I really liked Richard Wolfson's "Physics and the Universe" course. 16:05: ... this uncertainty just arises from our imperfect knowledge and that the universe itself knows exactly where all these particles ... 19:17: I like the idea of a deterministic theory, but the universe has often demonstrated that it couldn't care less about our pet theories.
	2016-11-30: Pilot Wave Theory and Quantum Realism 00:55: ... defines reality, cats are both alive and dead, or even that the universe is constantly splitting into infinite alternate ... 02:36: ... Heisenberg insisted that in the absence of measurement, the unobserved universe is only a suite of possibilities of the various states it could take ... 05:10: But this hypothetical predictability means that a pilot-wave universe is completely deterministic. 10:27: ... it certainly demonstrates that this sort of thing does happen in this universe, at least on some ... 12:59: Burak asks why quark/strange matter isn't found naturally in the universe given that it's supposed to be so stable. 13:07: OK, so the hypothesis is that strange matter is the most stable matter in the universe. 13:39: But during the quark era, the universe was full of this quark-gluon plasma. 13:45: And the problem is that the universe at this time wasn't dense enough and was expanding too quickly for strange matter to form in any great abundance.
	2016-11-16: Strange Stars 00:14: [MUSIC PLAYING] The mathematics of modern physics that emerged through the 20th century explained so much about our universe. 01:18: But just shy of that final transition, and on the fringe of our understanding of the quantum universe, a star may become very strange indeed. 02:07: The rest of the in-falling star collides with the new neutron star and ricochets outwards in the most powerful explosion in the universe, a supernova. 02:49: ... of almost pure neutrons, neutronium, the densest known substance in the universe. ... 04:05: ... gas-like quark matter, a so-called quark-gluon plasma, filled the entire universe until around a millionth of a second after the Big Bang, the Quark ... 05:58: ... means that strange matter may be the most stable form of matter in the universe, more stable even than iron, which is the most stable atomic ... 11:01: So when I say that the universe is flat, of course I don't mean that it's flat like a pancake. 12:04: Your comparison was for people living in a 2D flatland universe that has the geometry of the surface of a 3D sphere. 12:12: ... flatlander analyzing a triangle in that universe would measure its angles to be greater than 180 degrees, but would also ... 12:30: Same with triangles in a curved 3D universe. 12:46: But it isn't actually part of this universe.
	2016-11-09: Did Dark Energy Just Disappear? 00:21: ... of astronomers made an extremely controversial announcement: that the universe is not only expanding, but that expansion is ... 00:44: With a set of reliable distances extending back several billion years, the teams were able to map the expansion history of the universe. 00:52: They expected to see that this expansion rate was slowing down due to the gravitational effect of all of the matter in the universe. 01:00: Instead, they found the expansion rate has been accelerating for half of the age of the universe. 01:54: They suggest the universe may be just expanding at a constant rate: never speeding up, but also not slowing down. 02:43: As with the initial discovery of dark energy, these scientists used Type 1-A supernovae to track the expansion history of the universe. 03:31: It finds that an accelerating universe containing dark energy still fits the data best. 04:32: ... the time the uncertainties, so the messiness in the data, would cause a universe with no dark energy to just happen to look like one with dark ... 06:09: If we include other stuff about the universe, our confidence in the existence of dark energy rockets well above 5-sigma for all of these studies. 06:19: We can't yet observe dark energy directly; we can only infer its existence based on how it affects the expansion of the universe. 06:35: ... fact, there are only two factors that can change the way our universe expands: there are things that tend to accelerate expansion, which we ... 07:11: ... Lambda and Omega m, represent the fraction of the total energy in the universe that these two types would comprise, assuming that the universe is flat, ... 08:19: Except that bottom-left corner of the graph also represents a universe that has almost no matter in it either. 08:32: But our universe definitely has matter in it. We even have a pretty good idea how much. 09:04: Another really powerful piece of evidence is that the balance of Omega-Lambda and Omega-m define the geometry of the universe. 09:12: ... these add together to equal one, then the universe is flat, and by that I mean that parallel lines stay parallel, and the ... 09:27: In a relatively empty, expanding universe as is represented by this part of the graph, space would not be flat. 09:38: ... going to have to refer you to another vid for details on universe geometries, but the main point is that we can also figure out where we ... 09:51: ... the patterns in the cosmic microwave background to measure the angles of universe-sized ... 10:03: Their geometry appears to be very flat, so our universe should lie on this line here. 10:11: In fact, I oversimplified slightly, but the CMB results place our universe somewhere in these orange regions. 11:23: ... call "cosmic inflation." So this is a thing that seems to happen in our universe. Dark energy, whatever it is, is still a ...
	2016-11-02: Quantum Vortices and Superconductivity + Drake Equation Challenge Answers 03:24: ... the number of civilizations that will develop in any given region of the universe -- that's this "A" number -- is equal to the number of habitable planets ...
	2016-10-26: The Many Worlds of the Quantum Multiverse 00:02: The weird rules of the subatomic world are very, very different to those of the familiar large-scale universe. 00:18: One answer to this question suggests that the entire universe is so much weirder than we imagined, or should I say the multiverse. 00:39: We can't describe the most fundamental building blocks of our universe with defined singular properties. 03:29: And what about the entire rest of the universe that's not currently being observed by physicists or cats? 04:19: By the Copenhagen interpretation, we might say that the universe chooses the final outcome of all those histories. 04:38: If a larger number of possible histories lead to a given result, then it's more likely that the universe will select that outcome. 04:51: The universe plays dice, even if the dice are weighted towards certain results. 05:23: ... decay, beyond the cat, and includes the observer and, indeed, the entire universe, ... 07:07: ... for example, at every particle interaction everywhere in the universe. ... 07:21: ... timelines or worlds that contain all possible realizations of this universe since the Big ... 07:31: It seems extravagant to propose uncountable eternally-branching universes just to get out of collapsing a wave function. 08:04: ... slices of a universal wave function that diverge from each other as the universe evolves, but none ever ... 08:29: ... mechanics, even if it isn't particularly economical in the number of universes it ... 10:43: In a purely deterministic universe, what happens to free will?
	2016-10-19: The First Humans on Mars 10:42: Those seeds may have been from the very first generation of supernovae, near the beginning of the universe. 10:54: ... we see some pretty gigantic supermassive black holes in the early universe, and it's quite tricky to explain how they got that big if they grew from ...
	2016-10-12: Black Holes from the Dawn of Time 00:44: In the modern universe, there is only one natural way to get such insane densities. 00:58: But that's the modern universe. 01:00: Once upon a time, the entire universe had the density of a stellar corpse. 01:05: In fact, soon after the Big Bang, the density of the universe was vastly higher. 01:11: So why didn't all the matter in the universe become black holes then? 01:36: Also, the gravitational pull needs to be strong enough to overcome the expansion of the universe. 01:43: Now, matter in the early universe was pretty smoothly spread out, and the universe was expanding fast. 02:11: The universe was very slightly lumpy at the moment the CMB was created, about 400,000 years after the Big Bang. 02:35: It's thought that these fluctuations originally formed when the entire observable universe was smaller than a single atom. 03:00: ... the early expansion, intense enough to resist the local expansion of the universe and form a black ... 03:21: For example, the collapse of cosmic string moves and the collision of bubble universes? 03:57: Discovering PBHs and learning their masses would tell us a huge amount about the earliest moments of our universe. 04:05: We need to hunt for these black holes or their influence in the modern universe. 04:48: This is a slightly terrifying possibility that 80% of the mass in the universe is in the form of countless, swarming black holes. 04:59: That's a lot of primordial black holes, and so we expect them to leave their mark on the universe in different ways. 09:58: I mean, how long can the universe expect to hide vast numbers of holes punched in the fabric of spacetime?
	2016-10-05: Are We Alone? Galactic Civilization Challenge 00:03: Are we alone in the universe? 03:03: ... that humanity is the only technological civilization in the entire known universe, what would that say about the biological and sociological factors in the ... 03:25: ... advanced civilization to have ever arisen in the history of the known universe, the chance for each habitable planet to produce such a civilization ...
	2016-09-29: Life on Europa? 12:13: ... spooky action at a distance, but it involves absolute determinism in the universe-- the complete absence of free ... 12:47: ... a what measurement has been carried out on particle B because the universe, including particle A, already knows what that measurement and its ...
	2016-09-21: Quantum Entanglement and the Great Bohr-Einstein Debate 01:04: ... yet the idea that the universe keeps existing when we're not looking at it is a pretty fundamental ... 01:13: Indeed, most of science takes it for granted that the universe is real, whether or not we're looking at it. 01:19: This notion that the universe exists independent of the mind of the observer is called realism in physics. 01:39: On the one hand, Niels Bohr insisted that it was meaningless to assign reality to the universe in the absence of observation. 02:08: And our experience of a well-defined material universe only has meaning at the moment of measurement. 02:15: This peekaboo universe is the heart of Bohr's Copenhagen interpretation. 03:00: Locality is the idea that each bit of the universe only acts on its immediate surroundings. 04:17: ... thought that every special point in the universe must be real and physical and defined by knowable quantities, local ... 09:02: Do we live in a peekaboo universe that vanishes into quantum abstraction when we aren't looking at it? 10:15: The universe seems to conspire to avoid the paradox of information traveling faster than light, or backwards in time. 10:28: Niels Bohr's peekaboo universe may be the universe we live in.
	2016-09-14: Self-Replicating Robots and Galactic Domination 09:35: In any universe that produces intelligence, someone, somewhere, at some point has to ask, why are we alone?
	2016-09-07: Is There a Fifth Fundamental Force? + Quantum Eraser Answer 03:51: But the researchers suggest it could mediate interactions between the so-called dark sector and the visible universe.
	2016-08-24: Should We Build a Dyson Sphere? 08:37: However, there's enough mass in the solar system to run a type 3 civilization's Kugelblitz swarm for many times the current age of the universe.
	2016-08-10: How the Quantum Eraser Rewrites the Past 01:42: Does observation of the particle's location force the universe into settling down and deciding which particular reality we happen to be in? 02:42: Turns out the universe is on to us. 03:01: ... just like the wave function is collapsing retroactively, as if the universe is saying, OK, ... 04:17: Physicists hate being outsmarted by the universe.
	2016-07-27: The Quantum Experiment that Broke Reality 08:44: ... almost like the universe is allowing all possibilities to exist simultaneously but holds off ... 09:25: ... Copenhagen interpretation, that final choice of the experiment of the universe is fundamentally random within the constraints of the final wave ...
	2016-07-20: The Future of Gravitational Waves 04:20: We also now know that our estimates of the number of binary black holes in the universe and their masses are at least in the right ballpark. 05:01: ... for one to happen because we're sensitive to a smaller volume of the universe. ...
	2016-07-06: Juno to Reveal Jupiter's Violent Past 00:14: ... Jupiter is the second most important planet in the universe, at least from our point of view, and it holds the secrets to the ...
	2016-06-22: Planck's Constant and The Origin of Quantum Mechanics 00:15: You might not expect the quantum behavior of the microscopic to be observable on all scales of the universe, but it is. 02:56: In fact, the mystery of why hot things glow the color that they do led us to discover the quantum universe in the first place. 03:03: Science fact-- everything in the universe glows with the light of its own internal heat. 05:58: It paints the crazy picture of a universe full of infinite extreme energy gamma radiation.
	2016-06-15: The Strange Universe of Gravitational Lensing 00:06: Much of the deep universe is shifted and magnified by the warping effect of gravitational lensing. 01:04: Well, it turns out that the whole universe is a giant funhouse mirror, a rippling pond, and many things are not where or what they seem. 01:14: In the real universe, both space and time can be curved. 01:27: ... general theory of relativity describes the real universe as a flexible, dynamic dimensional grid that only resembles our mind's ... 03:15: When we look out there at the universe, we see gravitational lensing everywhere. 03:21: It's become a very powerful tool for studying the universe. 03:52: When brains don't suffice, we instead build model universes in our computers. 04:02: Within these simplified virtual universes, we can hunt through vast possibility space. 04:31: And we've confirmed that the vast majority of mass in this universe is in the form of dark matter. 05:00: In fact, each of these spots is that one quasar viewed via four different paths through the universe. 05:57: ... measure the Hubble Constant, which tells us the rate of expansion of the universe, independently confirming the results from other ... 06:50: Weak gravitational lensing slightly warps the shapes of essentially all galaxies in the universe. 07:44: It's allowed us to decode the universe in ways that would've been impossible in boring Euclidean space. 08:16: But just outside the event horizon, we find the most extreme gravitational lensing in the universe.
	2016-06-08: New Fundamental Particle Discovered?? + Challenge Winners! 01:21: So a tiny spot for a tiny instant resembles the state of the universe at a trillionth of a second after the Big Bang. 09:03: For the main question, I asked you to figure out how many times the universe doubled in size after dark energy first started to show its influence. 09:20: More precisely, for how many past and future doublings of the scale factor are they both at least 10% of the energy content of the universe? 09:30: Let's think about a giant box of space that is expanding with the rest of the universe. 09:50: Right now, 70% of the energy in any volume in the universe is in the form of dark energy. 10:36: And we can just use the scale factor of the universe as the side length of our box. 11:05: ... 70 units of dark energy and 30 units of matter, and we get that the universe was 36% of its current size when dark energy had a 10% ... 11:36: It will happen when the universe is larger by a factor of 1.57, or about 0.7 of a single doubling. 13:08: Is there something about the tipping point between the dominance of matter versus dark energy that makes the universe more hospitable for life?
	2016-06-01: Is Quantum Tunneling Faster than Light? 02:48: You're everywhere in the universe, but not very much. 10:00: One book that I read recently is "How the Universe Got its Spots" by Janna Levin. 10:06: It lays out some amazing ideas connecting our universe's topology in extent to the spots in the cosmic background radiation.
	2016-05-25: Is an Ice Age Coming? 12:12: 4798Alexander4798 asks, is the universe behaving its way because math, or is math behaving its way because universe? 12:28: My guess-- the universe doesn't know any math. 12:37: Mathematics is a model that we use to describe the behavior of the universe. 12:55: So to summarize, as the universe expands, the energy in matter in any one co-moving volume or expanding volume is conserved. 13:28: ... make up only a tiny energetic contribution to the modern universe-- far less, even, than baryonic matter, which itself is far less than dark ... 13:50: Eugene Khutoransky points out that the idea that energy is not conserved in an expanding universe is still pretty speculative. 14:23: Described in general relativity, you can still come up with conserved quantities-- energy analogies that are invariant in, say, an expanding universe. 14:39: This gets us back to the idea of whether the universe knows math. 14:43: The universe is mechanistic and its behavior results in emergent mathematical laws that allow us to model and predict its behavior. 14:57: We draw energy life bars in our animation sometimes, but the universe doesn't have any hidden energy counter.
	2016-05-18: Anti-gravity and the True Nature of Dark Energy 00:19: ... theory of relativity and its description of the vaster of scales of our universe. ... 00:37: One, the universe is expanding. 00:46: Two, such an underdense universe should be geometrically weird, a negatively curved hyperbolic hyperplane. 01:07: And three, the expansion of the universe is accelerating. 01:30: It both flattens the universe and leads to exponential expansion. 02:45: It only tells us that dark energy produces an exponential change in the size of the universe, not necessarily an exponential growth. 03:11: The first Friedmann equation is all about the rate of expansion of the universe. 03:32: a is the scale factor, sort of like the size of the universe. 03:48: The more matter and energy in the universe, the harder gravity pulls inwards, trying to stop the expansion or speed up the collapse. 05:09: But on the larger scales, the universe is pretty smooth. 05:39: ... ultimate effect is that the massive of a region of the universe is higher if its particles are moving quickly compared to a region where ... 06:01: So it looks like as long as there's anything in the universe whatsoever, that whole right side is negative. 06:18: Described this way, the universe is never static. 06:32: He wanted a static universe. 07:17: ... our far future universe, regular matter will have diluted away and will only have the density and ... 07:33: It has to be, because dark energy helps regular matter flatten the geometry of the universe. 07:39: That means its density term also works on the side of matter to try to slow down the universe in the regular attractive gravity way. 09:05: The direct effect of dark energy's negative pressure doesn't do anything, because that negative pressure is the same everywhere in the universe. 09:53: Let's say I'm holding a volume of the universe that has a constant energy density. 10:29: As the universe expands, more dark energy is created because its energy density has to stay constant. 11:09: OK, so it takes work to expand the volume of the universe. 11:29: See, the law of conservation of energy no longer applies in an expanding universe. 11:35: This law is a property of a Newtonian universe, in which space and time are fixed static dimensions. 11:43: In a universe governed by general relativity, this is no longer true.
	2016-05-11: The Cosmic Conspiracy of Dark Energy Challenge Question 00:03: ... tools we need to really understand dark energy and its influence on the universe. ... 00:36: The balance between dark energy and matter in the modern universe is on the side of dark energy. 00:42: ... expansion of the universe has been accelerating for some billions of years now, ever since it ... 02:06: But if our universe were chocolate-- which it isn't, sadly-- then it's only been deliciously dark for a relatively short period. 02:30: Its density stays constant and so the amount of dark energy increases at the same rate as the volume of the universe. 02:38: When the universe has doubled in size, there'll be twice as much dark energy, joule for joule. 02:55: That means the density of matter decreases as the universe expands. 03:05: Very roughly, it was when the universe was half its current volume because that would mean half the current amount of dark energy. 03:14: A given giant box in the universe currently has around 30 parts matter and around 70 parts dark energy. 03:38: We can think of that linear size as the scale factor of the universe. 03:43: ... the scale factor, the size of the universe, only needed to be around 20% smaller than it is currently for the volume ... 04:06: Dark energy has dominated the universe only during the tenure of life on Earth, although its effect has been felt for a bit longer than that. 04:16: ... the end of the inflationary epoch, when the universe was about 10 to the power of minus 32 seconds old and around the size of ...
	2016-05-04: Will Starshot's Insterstellar Journey Succeed? 01:00: ... to look at the details of the plan, what it will teach us about the universe, and whether we can actually do this ... 08:35: ... how dark energy causes this exponentially accelerating expansion of the universe and you guys had a lot to say in the ... 09:06: But if dark energy diluted away, like regular matter does, that effect would diminish as the universe expanded. 09:19: That means the larger the universe is, the more dark energy there is and so the more of this anti-gravity. 09:40: Does the universe expand to such a ridiculous size that it's filled ultimately with only stellar remnants and darkness? 10:06: The universe expands exponentially forever and eventually the stars die out, the black holes evaporate, and the universe undergoes heat death. 10:49: The density of matter inside galaxies is much, much higher than in between galaxies and even much, much higher than the average for the universe. 11:57: Adrian Abdel reminds us that the universe is dark and full of terrors. 12:02: And the heat death of the universe is coming.
	2016-04-27: What Does Dark Energy Really Do? 00:03: The idea that the fate of our universe is governed by forces that we can see was abandoned with the discovery of dark matter. 00:09: However, we now know that the evolution of our universe is driven by something even more mysterious-- dark energy. 00:16: ... PLAYING] In the last two episodes, we talked about how the fate of the universe can be described using Einstein's general theory of relativity via the ... 00:33: Observations show that out universe is infinitely expanding. 00:52: ... which itself came from an independent attempt to determine whether the universe would ... 01:01: See, measuring the density of the universe is one way to determine its fate because the future expansion rate does depend on density. 01:23: That history is coded in every photon of light that reaches our telescopes from the distant universe. 01:43: ... also know how long a given photon was traveling through that expanding universe, then its redshift tells us the total amount of expansion that happened ... 02:07: To measure the expansion history of the universe, we need to measure the redshift-distance relationship. 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. 02:35: And the two are connected by the universe's expansion history. 02:53: ... things to get in astronomy, especially for things so far away that the universe will have expanded significantly in the time it took their light to ... 04:28: ... distance turns out to be on the large side, then that would mean the universe expanded a lot during the corresponding light travel ... 04:40: Now, that actually points to a more dense universe. 04:46: ... if the redshifts are large, then the universe was expanding much faster in the past, which means something would have ... 05:04: So measuring a rapidly-expanding universe in the past points to it having had its gravity brakes on between then and now. 05:13: ... distance turned out to be on the small side, that would mean that the universe expanded less while that photon was ... 05:23: And so a lower density of matter would be needed to explain how the universe slowed down to the current rate of expansion. 05:32: ... smallest redshifts you'd expect would be if the universe has always been expanding at the rate we see now, so almost no matter ... 05:42: Such a universe would certainly expand forever. 05:46: ... expect supernovae to be bright or closer in a high-density, recollapsing universe and faint or more distant in a low-density, infinitely-expanding ... 06:03: ... of light years away to measure the past expansion history of the universe. ... 06:15: They thought this would tell them whether the universe would expand forever or recollapse. 06:22: In 1998, both teams announced that the universe was expanding even slower in the past than it is now. 06:32: Or conversely, the supernovae were fainter than you'd expect, even for a universe that has no matter in it at all. 06:41: That means the expansion rate of the universe has actually sped up, accelerated, while that supernova light was traveling to us. 06:50: ... discovery of the accelerating expansion of the universe earned both teams the Nobel Prize in 2011, and it's considered to be the ... 07:01: See, this observation actually came before the discovery of the inexplicable geometric flatness of the universe that we talked about last time. 07:28: But we also see that the constant nature of this term means that the larger the universe, the more of this stuff there is. 07:43: And it must eventually dominate the evolution of the universe. 07:48: But why should a constant vacuum energy cause the universe to accelerate? 07:53: Let's take a mathematical ride into the far future, when the galaxies will be so far away that the density of the universe will be basically zero. 08:03: We know that the universe is flat, so the curvature is also zero. 08:09: For that far-future universe, we can write the first Friedmann equation like this. 08:34: We also call this the Hubble Parameter, and it could be thought of as the rate at which the universe doubles in size. 08:50: But with a positive cosmological constant, the universe will eventually have a constant Hubble Parameter. 09:04: Currently, there's still enough matter in the universe to influence the expansion rate, but we're already at the point where dark energy dominates. 09:13: In fact, the universe has been accelerating in its expansion for six billion years or so. 09:38: ... about how a general relativistic description of the expansion of the universe requires dark ... 09:52: Pravar Parekh points out that we can't really know that the universe is flat because we can only see a small part of it. 10:11: The universe could be positively or negatively curved below that level. 10:16: If positively curved, that would mean a finite but very, very large greater universe with a volume at least 250 times that of our observable universe. 10:32: ... the balance between expansion and density is much, much greater than our universe ... 10:42: Even if the greater universe is curved, we still need dark energy. 10:47: Yeshwanth Vejendla would like to know how we can possibly measure the density of such a huge universe. 10:53: ... the handy thing about a universe that's smooth on its larger scales is you don't have to measure the ... 11:12: And even then, they don't cover the entire observable universe. 11:16: However, they do sample a large enough fraction of it to tell us that matter in the universe is pretty smoothly distributed.
	2016-04-20: Why the Universe Needs Dark Energy 00:02: Can we try to predict the fate of the universe? 00:35: ... theory with real astronomical observations tell us that the fate of the universe is governed by something we call "dark energy." To truly understand dark ... 00:52: ... can describe the cosmic balance between the outward expansion of the universe and the resistance to this expansion due to the gravitational effect of ... 01:26: ... weighing up all of the matter in the universe, astronomers have figured out that there just isn't enough of anything to ... 01:38: And the universe will expand forever. 01:41: There are two powerful and completely independent measurements that can test this prediction of the fate of the universe. 01:48: Today, let's look at one of these measurements-- the geometry of the universe, which points to a discrepancy in the first Friedmann equation. 02:11: The universe is too low-density to recollapse. 02:35: k is, in a sense, the shape of the universe-- its spatial curvature, as well as its spatial extent, finite or infinite. 02:53: But the spatial geometry of the universe at a fixed instant in time can be flat or curved. 03:05: "k equals plus 1" means the universe has a positive-curvature spatial geometry. 03:23: In a universe like that, geometry is weird. 03:39: But the total spatial volume of such a universe is finite. 03:43: And we call that a "closed geometry." If k is minus 1, the universe is the 3D version of a negatively curved hyperbolic plane. 04:04: Such a universe is infinitely large, or "open." But "k equals 0" means the universe is flat. 04:16: Geometry works just as you learned in school, and a flat universe is still infinite-- open-- in all three spatial dimensions. 04:26: ... on the left side of the first Friedmann equation, when we measured the universe's ... 04:39: So, assuming we got the equation correct, then the shape of the universe should be intrinsically tied to its fate. 04:47: An overdense, recollapsing universe should have a spherical geometry. 04:51: An underdense, infinitely expanding universe should be hyperbolic. 04:56: ... only a universe with exactly the right density, that's expanding at exactly its escape ... 05:17: See, we can measure the shape of the universe and, so, measure k, just by checking how geometry works on cosmic scales. 05:31: Because that gives us a positive right-hand side to match the positive left-hand side we got from weighing our universe. 05:46: ... background features allow us to verify that the longest triangles in the universe have angles that add up to exactly 180 ... 05:58: That's the straight-up geometry of a flat, Euclidean universe-- flat to within 0.4%. 06:13: This is totally inconsistent with the level of positive curvature we'd expect from an infinitely expanding universe. 06:26: But when we tried to describe the universe by reducing the Einstein field equations into the Friedmann equations, we missed something. 07:00: ... density term to help bring the left side down to zero, to flatten the universe. ... 07:13: ... new player in the game, geometry is no longer tied to the fate of the universe. ... 07:23: A flat, k-equals-zero universe can expand forever. 07:38: As the universe expands, regular matter and energy get diluted away. 07:51: So the bigger the universe, the more of this energy. 08:04: ... the universe gets large enough, the density of regular matter will, at some point, ... 08:25: In fact, the universe reached that tipping point pretty recently, on cosmic time scales. 08:31: We now live in a universe dominated by dark energy. 09:19: Now, last week we talked about the fate of the universe. 09:25: A number of you were curious to know, on what scales of space is the universe really expanding? 09:31: So the universe is only expanding on the largest scales, not at all inside atoms, inside humans, the Earth-- even inside the Milky Way. 10:28: ... density that we calculate when we figured out the fate of the universe does include dark matter, which we can measure by its gravitational ... 10:38: Even with dark matter, the universe is just not dense enough to recollapse.
	2016-04-13: Will the Universe Expand Forever? 00:02: How will this universe end? 00:19: ... Russian named Alexander Friedmann-- applied the new theory to the whole universe. ... 00:46: ... have revealed something even stranger-- the future expansion of the universe will be dominated by a mysterious influence that physicists have come to ... 01:17: For today's episode, we're going to start by describing the universe without dark energy. 01:26: And the answer we get for the fate of our own universe will still be right in one very important aspect. 02:05: ... field equations to describe the response of the fabric of the universe to everything it ... 03:40: ... this Newtonian analogy-- and, remember, ignoring dark energy-- the universe also has an escape velocity that lets distant galaxies escape each ... 03:53: ... on the amount of stuff in the universe, there's some current expansion speed that would allow the future ... 04:05: How do we calculate the escape velocity for the whole universe? 04:09: By solving the Einstein field equations for the whole universe, of course. 04:26: ... bumps and wiggles caused by individual galaxies, the resulting smooth universe lets us reduce those 10 Einstein equations to only two relationships, ... 04:48: That letter a is called the "scale factor," and it represents the size of the universe. 05:04: That's what that a with a dot on top represents-- the speed of the expansion of the universe. 05:29: That first piece, the a-dot over a squared, is analogous to the kinetic energy of expansion-- how much outflowing oomph the universe has. 05:40: But that oomph is resisted by the gravitational effect of all the master and energy in the universe. 05:47: That's this rho thing-- the density-- how packed with stuff the universe is. 05:53: So this second piece represents the capacity of the universe to slow itself down and is analogous to the gravitational potential energy. 06:01: The balance between these two energy like terms tells us the fate of the universe. 06:09: ... and the potential energy of collapse are perfectly balanced, then the universe will expand to a ginormous size and grind to a near ... 06:39: There will be some expansion energy remaining after gravity is diluted to nothing, and the universe will expand forever, never stopping. 06:56: ... universe will eventually fall back inwards, and we'll see many of those distant ... 07:07: Will the universe expand forever, or collapse? 07:26: ... until the late '90s-- it was believed that the answer to whether the universe would recollapse lay in measuring rho-- the density of the ... 07:36: Astronomers worked for decades to weigh up the galaxies across vast swaths of the universe, including their dark matter. 07:45: But the density of the universe turns out to be too low-- only about a quarter of what is needed to reverse the expansion. 08:03: There's no way around it-- the universe will expand forever. 08:35: It describes the shape of the universe-- its spatial curvature. 08:40: ... to the first Friedmann equation, the fate of the universe-- as determined by its expansion and density-- should be intrinsically ... 09:08: ... why the Friedmann equations tell us that dark energy must exist in this universe, and what these equations can tell us about its true ... 10:49: ... the 10 most abundant elements in the universe, only two have an odd number of protons-- hydrogen and nitrogen. However, ...
	2016-04-06: We Are Star Stuff 00:20: [MUSIC PLAYING] We live in a complex universe. 00:39: ... the building blocks of matter, the elementary fields that fill our universe, and the particles that they manifest through their vibrations, these all ... 01:18: ... course, this capacity for complexity is what makes it possible for a universe to have things like planets, life, and minds to try to comprehend it all ... 01:30: So the tapestry of our universe is woven across the dimensions of space and time and complexity. 01:38: What makes it possible for this universe to have such a depth of complexity? 02:25: ... was at one point forged in one of the most cataclysmic events in the universe. ... 03:06: In fact, those protons will outlast almost every other nonelementary particle in the universe. 03:28: ... about 20 minutes after the Big Bang, the entire universe was hot and dense enough for nuclear fusion, for protons to slam ... 04:48: While the early universe had around 20 minutes to forge its nuclei, stars have millions to billions of years. 05:16: But that won't help the universe. 07:24: ... born neutron star and ricochet back in the largest explosion in the universe, a ... 09:16: ... may be that many heavy elements, including a lot of the gold in the universe, were formed not in a supernova, but in the collision of two neutron ... 10:04: Our universe is an element factory, producing building blocks capable of becoming you in all your stunning complexity. 10:13: We are "starstuff." But more, we our universe stuff, the most complex component that has risen from a beautiful and chaotic spacetime. 10:42: A lot of you asked about what I meant by a flat universe. 10:58: ... I talk about the geometry of the universe and describe it as flat positive or negatively curved, I should say that ... 11:31: It does not refer to a universe that's pancake-like. 11:39: ... refers to the fact of the geometry of space on the largest scales in the universe works just like the geometry on a nice, flat 2D sheet of ... 12:07: A few of you asked about my statement that the universe expanded faster than the speed of light. 12:14: Well, the speed of light is an absolute speed limit for a thing in the universe traveling through space. 12:35: It's happening right now in regions of the universe beyond what we call the Hubble Horizon, which is 13.7 billion light years away. 12:52: How much faster than the speed of light did the universe blow up during inflation? 12:56: Well, we can sort of answer that for two particles at opposite sides of the currently observable part of the universe. 13:14: mukul gupta asks whether the expansion of the universe will stop at some point. 13:21: Guess what we're talking about next week on "Space Time?" The end of the universe.
	2016-03-30: Pulsar Starquakes Make Fast Radio Bursts? + Challenge Winners! 00:00: [MUSIC PLAYING] It's mind-blowing how much we've been able to figure out about how our universe. 00:16: Until recently, we had no idea what the sudden flashes of radio emission coming from mysterious events out there in the universe really were. 02:49: And it did that for 13.7 billion years, the age of the universe. 03:08: ... asked you what average distance a photon could travel through the universe before the moment of recombination, the moment when the cosmic microwave ... 03:18: At this time, the universe was full of plasma, atomic nuclei, and free electrons. 04:21: ... and helium nuclei, the other common charged particles hanging around the universe at this time, have much smaller scattering cross-sections than electrons ... 04:44: But let's use a number that's easy to find online, the baryonic mass of the universe, which is estimated at 10 to the power of 53 kilograms. 04:55: That's the mass of all the protons and neutrons in the observable universe. 05:11: ... and we get that there are 6 by 10 to the 79 protons in the observable universe, and just as many ... 05:52: So that's also how much smaller the universe was back then. 08:08: But 7,500 light years is still very small compared to the size of the universe, even back then. 08:16: And so we still consider the pre-recombination universe as being opaque.
	2016-03-23: How Cosmic Inflation Flattened the Universe 00:09: It calls into question our very understanding of what the beginning of the universe even means. 00:15: [MUSIC PLAYING] The Big Bang theory describes the earliest epochs of our universe amazingly well. 00:49: The observable universe is impossibly huge. 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. 02:43: It should be 1 degree, assuming the universe is flat. 02:48: It should be larger if the universe is positively curved, smaller if negatively curved. 03:08: The universe is flat. 03:12: An expanding universe doesn't tend to stay flat, even if it starts that way. 03:33: Same with the universe. 03:35: If the center of the alley represents a flat universe, then the gutters represent extreme curvature in the positive or negative directions. 03:44: If the universe starts out even a little bit not flat, then that not-flatness will amplify quickly. 03:51: ... if our universe is flat to within 0.4 of a percent now, then in the first instant, the ... 04:15: Nice bowling, universe. 04:49: It goes like this-- start with a universe so crunched down that the entire currently observable part of it was all causally connected. 05:14: This works because even a very blotchy, curvy universe is going to be much smoother and flatter on its smallest scales. 05:23: Inflation takes a very tiny, smooth, flat speck of that blotchy, curvy greater universe and blows it up to a macroscopic volume really, really fast. 05:36: That inflated speck subsequently grows into the universe that we know, but retains its once subatomic smoothness and flatness. 05:46: According to inflation, the universe that we see is a tiny part of a vastly larger universe that itself may well be curved. 06:17: ... needed to increase the size of the universe by a factor of at least 10 to the power of 26 in less than 10 to the ... 06:34: In the subsequent 13.7 billion years since, the universe has expanded by about the same amount that it did during inflation. 06:57: ... this as a way to allow his theory to describe a static space time, a universe that's neither expanding nor ... 07:10: When it was later discovered that the universe is indeed expanding, Einstein retracted his constant. 08:32: The universe slowed down from exponential to the regular old expansion that we see today, what we call Hubble expansion. 08:56: But it's also possible that inflationary expansion is the default state of the greater universe-- I should say multiverse at this point. 09:25: ... that inflation ended can perhaps be thought of as the moment that our universe as we know it came into ... 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 ...
	2016-03-16: Why is the Earth Round and the Milky Way Flat? 00:10: The reason will get into some of the fundamental realities of our universe. 00:20: Our universe really seems to be into two shapes in particular. 10:14: Now, these fundamental symmetries don't just define the shapes of some of the largest things in our universe. 10:34: Symmetries really do shape the universe on all the scales of space time. 11:12: Felix Ironfist asks, "why didn't the universe collapse into a black hole, if it was so dense and massive?" This is a classic question. 11:33: Instead, the early universe is described as a very high density over an extremely large, and possibly infinite, volume. 11:42: Our observable universe was a tiny speck in that volume. 11:46: ... was no net gravitational attraction towards our patch of the greater universe. ... 11:56: Therefore, no universe-sized black hole. 12:16: And at the moment of recombination, when the CMB was emitted, it was emitted by all of the observable universe and beyond at the same time. 12:38: But as the universe got older, radiations from further and further away had time to get to us.
	2016-03-09: Cosmic Microwave Background Challenge 00:15: It tells us that the universe was once most certainly much smaller, hotter, and denser than it is today. 00:23: ... photons of the cosmic background radiation were released when the universe was around 380,000 years old, and had just cooled down enough for the ... 00:43: In the process, the distance that the average photon could travel went from not very far to greater than the length of the entire observable universe. 00:53: When we look at the CMB today, we really are looking at the universe from 13.7 billion years ago. 01:37: The universe was much smaller when the CMB light was emitted. 01:58: ... reach this patch of space because it was traveling through an expanding universe. ... 02:10: ... the time it reaches us, right now, the universe has expanded so that the galaxies and clusters that those blobs evolve ... 02:28: So first question-- what physical distance did that light from the CMB travel through an expanding universe to reach us today? 02:42: ... and the math-y question-- just before the CMB was created, the universe was filled with this plasma that consisted mostly of protons, electrons, ... 03:01: ... universe became transparent when it cooled enough for those electrons to be ... 03:24: ... need an estimate of the baryonic mass and volume of the observable universe, you'll need the redshift of the CMB, and the Thomson Scattering ...
	2016-03-02: What’s Wrong With the Big Bang Theory? 00:07: We see that the universe is expanding. 00:10: The Big Bang Theory suggests that once the entire universe was compacted into an infinitely small speck at the beginning of time. 00:41: Direct and convincing evidence tells us that the universe was once much smaller, hotter, and denser than it is now. 01:00: And at that point, the entire observable universe was around the size of a grain of sand. 01:25: Now, remember, when the universe was younger than 400,000 years, it was too hot for atoms to exist. 02:30: We pretty much know this happened because we can actually make bits of the universe do this. 03:52: But we can't confidently describe this stuff that the universe contained, the weird state of matter that far back. 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. 04:40: We're leaving it alone today because we don't actually know whether the universe was really ever this small. 04:46: Remember, we've been rewinding the universe using basic general relativity. 05:13: The universe is space sized. 05:15: But it's still 1,000 times smaller than the modern universe. 05:40: ... smoothness tells us that all of the material in the universe when the CMB was released was almost exactly the same temperature, ... 06:08: Well, the universe works in the same way. 06:23: ... in order for the most distant patch of the universe we can see in that direction to have the same temperature and density as ... 06:45: Let's take this grain-of-sand-sized universe at 10 to the minus 32 seconds. 06:59: See, although light is fast, those opposite edges of the universe were traveling apart even faster. 07:05: Another way to say this is that those edges of the universe have always been beyond each other's particle horizons. 07:16: So those edges shouldn't be in each other's observable universes, not then, not now. 07:30: ... only way around this problem is to somehow have the universe, once upon a time, be small enough so it could easily get all nicely ... 07:52: ... idea is the universe started subatomic, small enough that it was able to even out its ... 08:56: ... to think of the Big Bang Theory not as a theory of the origin of the universe, but instead as a theory describing the period of expansion from a ... 09:28: Perhaps the theory will eventually encompass a true origin for this universe. 09:55: ElectroMechaCat asks why if the universe is expanding, doesn't matter also get stretched with that expansion. 10:06: ... than any degree of expansion on the scale of any material object in the universe. ... 10:25: ... we call the Hubble expansion of the universe arises from the FriedmannLemaîtreRobertsonWalker metric, which describes ... 11:04: So you can have regions of non-expanding space embedded in a globally expanding universe. 11:11: ... this mean if you were to take every proton, neutron, and electron in the universe, you could fit them all into a space the size of a grain of ... 11:22: ... would be correct if you add the word "observable" before the word "universe." Everything that we can see to our cosmic horizon, so the observable ... 11:45: If our universe is infinite, then you can compact it as much as you like and it will still be infinite. 11:54: We don't know how large the greater universe is. 12:21: The Big Bang describes a series of events that happened to the universe following its existence in an extremely hot, dense state. 12:31: We have a ton of evidence that the universe was once in such a state. 12:36: Perhaps our understanding of this state will eventually lead to a theory of the origin of the universe.
	2016-02-24: Why the Big Bang Definitely Happened 00:00: Our universe started with the Big Bang, or did it? 00:27: ... Bang theory gives an accurate description of the earliest epochs of this universe. ... 01:04: ... Big Bang theory is a set of descriptions detailing the expansion of the universe from a tiny, super dense, super hot speck to the enormous cosmos that we ... 01:39: The universe is expanding. 02:06: The universe is definitely expanding now. 02:15: ... can look at the current state of the universe, or even just a tiny part of the universe, and run the laws of physics ... 02:28: If we rewind the universe using the mathematics of general relativity, then the further back you go, the smaller the universe is. 02:36: ... fact, with raw general relativity, we get that the entire observable universe was once compacted into an infinitesimal point, a singularity at time t ... 03:23: ... enough to make some pretty bold and testable predictions about what the universe must have looked like at various ... 03:34: One such prediction is that the entire universe was once as hot and dense and opaque as the inside of a star. 03:47: As the universe expanded, this plasma cooled. 03:51: ... at a very particular moment when the universe was around 400,000 years old and about 1,000 times smaller than it is ... 04:27: Having been stretched into microwaves as it traveled through an expanding universe, it's the cosmic microwave background. 04:38: ... that this ubiquitous radiation is almost impossible to explain without a universe that was once much smaller, hotter, and ... 06:03: We see galaxies back when the universe was 5% its current age. 06:11: The universe is clearly evolving. 06:54: At an age of a few seconds, we predict that all of the universe was much hotter than the very center of a star and remained so for around 20 minutes. 07:37: ... we don't have direct evidence for what the universe looks like in its very first second, our understanding of physics is ... 08:01: Because we've recreated the conditions of the universe at this time.
	2016-02-17: Planet X Discovered?? + Challenge Winners! 06:56: By the way, this is an effect that we see out there in the universe all the time. 07:12: ... supernovae that are moving away from us due to the expansion of the universe appear to die away far more slowly due to the combined effect of time ...
	2016-02-11: LIGO's First Detection of Gravitational Waves! 00:27: It opens a whole new window through which we can now observe our amazing universe. 00:49: ... of spacetime caused by extreme gravitational events in the distant universe. ... 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. 06:28: However, now that we know that these things are detectable, it opens up an entirely new spectrum for observing the universe. 07:11: It's a new window on the universe that will reveal phenomena and physics that we never expected.
	2016-02-03: Will Mars or Venus Kill You First? 00:22: It's the only patch of the universe that we know of that won't kill you almost instantly. 08:43: Jona Storm asks, if there's no such thing as universal time, how can we say the universe is 13.8 billion years old? 09:28: The universe is 13.8 billion years old here, and that measurement of age is really just a measurement of how much change has happened in our frame. 09:46: ... the Big Bang model back far enough, then any two world lines in the universe will eventually become arbitrarily close to each ... 10:00: We just don't understand the physics well enough to confidently project the size of the universe to infinitesimal smallness, to a singularity.
	2016-01-27: The Origin of Matter and Time 08:30: Two infinitesimally nearby bits of the universe can affect each other at exactly the speed of light.
	2016-01-06: The True Nature of Matter and Mass 00:27: It's the maximum speed at which two neighboring bits of the universe can talk to each other. 05:36: ... particles that are prevented from streaming freely through the universe, as well as the fields that confine those ... 10:17: Only when the universe cooled down did the Higgs field gain a nonzero value in a phenomenon called spontaneous symmetry breaking.
	2015-12-16: The Higgs Mechanism Explained 01:08: Now, QFT describes the fundamental particles as excitations in fields, fields that fill our entire universe. 01:20: Imagine that every point in the universe has a certain level of electron-ness. 01:54: Now, this is a very simplistic explanation of a theory that has produced an astoundingly accurate description of the subatomic universe. 03:40: ... simplest is to say that while the photon can cross the entire observable universe without bumping into a single thing, the electron is never not bumping ... 04:03: Here, I need to tell you about a really odd fact about the universe. 04:43: It's an open question why the universe cares which direction you're spinning. 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.
	2015-12-09: How to Build a Black Hole 00:00: [MUSIC PLAYING] Black holes are one of the strangest objects in our universe. 00:21: ... boundary curvature effectively removes the interior from our observable universe. ... 06:23: So a neutron star is comprised of the densest matter in the universe. 07:52: However, despite this, the star is still very much a thing in this universe. 08:42: Everything inside is lost from this universe. 09:58: The material of the star and all of events that happened to it are no longer part of the timeline of the external universe. 10:28: And these continue to influence the outside universe, sometimes in very important ways. 10:43: ... get to what this means, for black holes and for the universe, in another episode of "Space Time." In a previous episode, we talked ...
	2015-11-25: 100 Years of Relativity + Challenge Winners! 00:21: Not the show, the fabric of the universe. 00:36: ... description that flowers from those statements describes our universe with stunning ... 01:01: The elegance of this theory has inspired so many students of physics to follow in Einstein's path exploring the mysteries of the universe.
	2015-11-18: 5 Ways to Stop a Killer Asteroid 09:45: ... everything we've seen in this universe, the arrangement of atoms into molecules and molecular structures, via ...
	2015-11-05: Why Haven't We Found Alien Life? 00:04: Recent amazing discoveries have given us more hope than ever that our universe is full of life. 02:01: ... anthropic principle, which states that an observer will always observe a universe that can make observers or a planet that ... 09:33: ... ever form over the full past and future history of star formation in our universe, Earth is ... 09:48: ... have emerged in the epoch of life in a universe abundant in the rich resources of past supernova explosions, but after ...
	2015-10-28: Is The Alcubierre Warp Drive Possible? 01:40: ... example, as we talk about in this episode, the expansion of the universe means that very distant galaxies are moving apart from each other faster ... 05:08: In fact, it would take significantly more negative energy than there is positive mass/energy in the entire observable universe.
	2015-10-22: Have Gravitational Waves Been Discovered?!? 03:16: ... most insane gravitational phenomena in the universe-- neutron stars or black holes in-spiraling just before merger, or ... 04:42: ... be able to study black holes, neutron stars, even the extremely early universe in ways never before ... 07:24: ... sensitive, which actually means it sees 1,000 times more volume of the universe-- much more chance of spotting crazy gravitational ...
	2015-10-15: 5 REAL Possibilities for Interstellar Travel 02:30: And to do that with any liquid rocket fuel, you'd need a fuel tank larger than the observable universe. 11:05: And what would happen to the universe if it were different? 11:33: ... fundamental forces, et cetera, are important for the properties of this universe. ... 11:43: And you change them too much and the universe as we know it doesn't exist.
	2015-10-07: The Speed of Light is NOT About Light 00:14: ... does the universe seem to conspire to, one, keep photons from traveling at any speed but ... 00:32: The universe doesn't arrange itself to keep the speed of light constant. 01:07: ... book supporting Copernicus and the whole, Earth is not the center of the universe, ... 06:23: Finally, assume that the universe make sense. 07:05: It's the only one that satisfies all of these pretty fundamental statements about the relativity, symmetry, and consistency of our universe. 08:43: It's the maximum speed at which any two parts of the universe can talk to each other. 08:48: In fact, it's the maximum speed at which any observers can see two parts of the universe talk to each other. 10:11: The universe is an infinitesimal here-and-now This is all pretty paradoxical. 10:23: The finite speed of causality is fundamental to us having a universe in the first place. 10:29: ... we want a universe so I can see you back here on the next episode of "SpaceTime." Last time ... 10:41: Denny Hiu asks how a universe that is already infinite expand? 11:06: Now replace the markers with galaxies, and that's basically what's happening with our universe. 11:26: ... that number, 18 times the particle horizon, only applies if the universe has positive curvature, making it a hyposphere and the curvature is the ... 11:39: ... if you travelled that distance-- again, assuming the universe froze in its expansion, which it won't-- then you'd get back to your ... 11:48: If you travelled at the speed of light, it would take around 750 billion years, or 55 times the current age of the universe. 12:04: Epsilon Lazerface says that if you go outside the universe, you become a Super Saiyan. 12:09: Well, there really would be no way to know that unless you traveled outside (ECHOING) the universe.
	2015-09-30: What Happens At The Edge Of The Universe? 00:00: [MUSIC PLAYING] What's at the edge of the universe and what happens if we try to get there? 00:11: You might be thinking, wait, how is there an edge to the universe if it's infinite? 00:20: The universe defines all of space and time that exists. 00:23: So that's one definition of universe. 00:26: But is it even part of our universe if we can never interact with it? 00:29: And what if our universe is very, very different beyond the edge? 00:32: The universe is infinite because general relativity tells us that the universe is demonstrably flat and therefore the galaxies go on forever. 00:41: Are you sure you measured the universe's curvature with infinite precision? 00:57: Before we get carried away, let's talk about the edge or edges of the universe and what it might take to get there. 01:04: In a previous episode, we talked about the size of what we call the observable universe. 01:24: We defined that as the current radius of the known universe. 01:37: ... clusters that blob evolved into, racing away from us with the expanding universe, as it ... 01:47: We call this the particle horizon of the universe. 01:49: It's the current instantaneous distance to the most distant part of the universe that could possibly have a causal connection to us. 01:56: Anything inside the particle horizon is referred to as the known universe. 02:00: ... I mean it's the distance that you would have to travel only if the universe froze in its expansion and you were traveling through static ... 02:51: Just as black holes have event horizons, so too do universes. 03:02: It's a boundary to the observable universe. 03:05: There's a region of this universe from which we can never receive any new signal. 03:33: The event horizon of the universe is actually closer to us than the particle horizon. 03:50: We're sort of seeing ghost images from outside the part of the universe that we could ever interact with. 03:56: As our universe expands, more and more of it will cross the event horizon and eventually almost all of that will be lost to it forever. 04:31: Almost certainly, just more universe. 04:40: Move to my left, and my observable universe moves with me. 05:04: Well, that all depends on the geometry of the universe. 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. 05:41: The universe just goes on, and on, and on, and on, and on, and on, and on, and on, and on, and on. 05:49: And there are many types of infinity, including some that involve infinitely repeating versions of this bit of the universe. 05:56: But is our universe really perfectly flat? 06:12: What if the curvature of the universe is so small that we're just not seeing far enough or measuring precisely enough to detect it? 06:21: It's very possible that the universe has curvature just inside the uncertainty range of the best measurements to date. 06:28: If that curvature is positive, then it may be that the universe is really the surface of a hypersphere, the 3D surface of a 4D sphere. 06:46: ... on a recent estimate of the minimum radius of the curvature of the universe, you'd need to travel an absolute minimum of 18 times the distance to the ... 07:12: ... ideas for the origin of cosmic inflation suggest that our universe may just be a slowly expanding bubble in an exponentially ... 07:22: Now, bubble universes may be finite in size regardless of internal geometry.
	2015-09-23: Does Dark Matter BREAK Physics? 00:34: Either we're missing and frankly don't understand at least 80% of all the matter in the universe or our current understanding of gravity is wrong. 01:09: And galaxy clusters do this all the time, turning the background universe into a funhouse mirror of stretched out and duplicated galaxies. 02:08: It underpins everything we know about the subatomic universe. 03:10: Either particle physics is wrong, or at least horribly incomplete, in that we're missing 80% to 90% of the mass in the universe, or Einstein is wrong. 05:53: Remember the hot, smooth plasma way back in the early universe that produced the CMB? 05:59: ... that highly smooth ocean of orange plasma to today's highly structured universe of clusters and galaxies, something had to act with enough gravity to ... 07:48: ... a black hole's event horizon should see the entire future history of the universe happen in the instant before it crosses ... 08:30: ... anyway, the photons from the future universe will never catch up to the monkey because that light has to contend with ... 08:39: ... signals from the monkey to the outside universe can be received at arbitrarily distance times in the future, only ... 08:48: The monkey may see some time dilation effects from the local part of its universe. 09:54: ... falling through the event horizon, the monkey's clock, its universe, now contains events that happen at the horizon, including the horizon's ... 10:21: It never even happens in the distant observer's universe, either before or after the black hole's evaporation.
	2015-08-19: Do Events Inside Black Holes Happen? 03:58: ... every external observer's self-consistent record of the history of the universe. ... 10:05: ... Einstein equations also allow for an empty universe that has an eternal black hole that didn't form from anything, a ...
	2015-07-02: Can a Circle Be a Straight Line? 04:08: ... entire universe is that spherical surface, and it requires criteria for parallel, ...
	2015-05-27: Habitable Exoplanets Debunked! 09:24: Gareth Dean asked, if all the photons in the universe have been red shifting as the universe expands, that means they're losing energy. 09:38: The bottom line answer is that in general relativity, there actually is no such thing as energy conservation for the universe as a whole.
	2015-04-22: Are Space and Time An Illusion? 02:21: So is everyone's experience of the universe entirely subjective?
	2015-04-15: Could NASA Start the Zombie Apocalypse? 00:27: Most fictional zombie universes share two basic features.
	2015-04-08: Could You Fart Your Way to the Moon? 07:35: But it would still take ten thousand trillion trillion times the current age of the universe to do so.
	2015-04-01: Is the Moon in Majora’s Mask a Black Hole? 07:43: ... Joe Hanson explained that the average color of all visible stars in the universe comes out to an off-white called Cosmic ... 08:22: Gareth Dean pointed out that the early universe contains not just hydrogen but also helium, and asks whether CMB analysis takes this into account. 08:39: SD Marlow asked how the CMB can look the same from all directions if we're not sitting at the center of the universe. 08:44: Well, there is no center to the universe. 08:45: The CMB was emitted from all points of the universe simultaneously.
	2015-03-25: Cosmic Microwave Background Explained 00:00: Outer space looks black, but the entire universe used to be this color. 01:03: ... background, or CNB, was the process that formed the first atoms in the universe almost 13 and 1/2 billion years ... 01:20: That's right, the universe used to be orange. 03:58: With no more free electrons to redirect the light, the universe became, for the very first time, transparent. 04:04: ... of an infinite number of orange bulbs going off at every point in the universe more or less ... 04:16: And now, that light could free stream through the universe forever.
	2015-03-18: Can A Starfox Barrel Roll Work In Space? 05:42: ... which is apparently the official unit of measurement in the "Star Fox" universe. ...
	2015-03-11: What Will Destroy Planet Earth? 04:53: ... anyway just because of the sheer awesomeness factor-- death by expanding universe. ... 05:04: ... the universe is expanding and currently that expansion is speeding up due to an ... 05:54: ... systems, inside planets themselves until literally, everything in a universe is ripped apart by stretching space-- atoms, nuclei, individual protons, ...
	2015-03-04: Should We Colonize Venus Instead of Mars? 06:12: Last week, we asked how you measure the size of the universe?
	2015-02-25: How Do You Measure the Size of the Universe? 00:00: [MUSIC PLAYING] The universe is huge. 00:05: But how huge and how can we possibly measure the size of the universe? 00:45: Now, let's talk about the whole universe. 00:52: So we're going to focus on the observable universe. 01:18: In a nutshell, you start with the age of the universe. 01:31: And that's the radius of the observable universe. 02:18: ... at a variable rate, complicate how we measure the size of the observable universe. ... 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: ... know exactly how far though, and calculate the size of the universe, you need to know how quickly space has been expanding at every moment in ... 02:49: So how can we possibly know the expansion history of the universe? 03:50: If we knew the answer in numerical detail, we could figure out the expansion history and in turn the size of the universe. 04:12: And from that, how fast the universe was expanding at every moment ever. 04:17: Once you have the expansion history, how do you actually determine the size of the universe? 04:21: Remember, as I said a long, long time ago, we first need to get the universe's age. 04:35: And how long it takes to get back to this point is the current age of the universe. 05:13: So that's how we know that the observable universe is about 90 billion light years in diameter. 05:19: But what about the unobservable universe?
	2015-02-18: Is It Irrational to Believe in Aliens? 00:00: [MUSIC PLAYING] A lot of people, including many scientists, seem pretty confident that aliens have to exist somewhere in the universe. 03:07: ... whole model of the universe, dating back to Copernicus, is rooted in the democratic notion that our ...
	2015-02-11: What Planet Is Super Mario World? 05:23: Well, a planet with a solid surface where Mario could jump exactly the way he does in the game is unlikely to exist, at least in our universe.

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