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	2022-12-14: How Can Matter Be BOTH Liquid AND Gas? 07:12: ... a proportional amount, but this temperature is also causing thermal expansion in the liquid, which reduces the volume of the gas, which further ...
	2022-11-09: What If Humanity Is Among The First Spacefaring Civilizations? 12:43: But for that we also need to estimate the speed of grabby expansion. 12:58: Counterintuitively, this fact implies that grabby expansion is incredibly fast, around a third of the speed of light. 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.
	2022-08-24: What Makes The Strong Force Strong? 19:07: Yes, they very much would. So changing quintessence means changing strength of dark energy, which means changing rate of accelerating expansion!
	2022-08-17: What If Dark Energy is a New Quantum Field? 00:00: ... - there’s some kind of anti-gravitational effect that’s causing the expansion to accelerate. We don’t know what it is - just that it competes against ... 00:36: ... virtual particles popping into and out of existence, driving accelerated expansion. But there are enough problems with this that we need to explore other ... 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 ... 06:25: ... Hubble tension.When we measure the Hubble constant - the current rate of expansion of the universe, based on supernova explosions over the past several ... 07:31: ... there’s a final reason to look for a mechanism for accelerating expansion due being some other than quantum fluctuations. It’s because we know ... 11:51: ... equation of state. Any value of omega less than -⅓ means accelerating expansion, and omega -1 is a constant energy density. Quintessence is often used to ... 12:31: ... pressure still dominates over the inward pull of regular gravity, so expansion still accelerates - but that expansion is restricted to regions outside ... 13:27: ... even a scenario 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 ... 06:25: ... over the past several billion years, we get one number for that expansion rate. But if we calculate the current expansion rate based on observations of ... 13:27: ... James Webb Space Telescope will help by pushing our measurements of the expansion rate back billions of years from the current supernova measurements. There ... 06:25: ... get one number for that expansion rate. But if we calculate the current expansion rate based on observations of the very early universe we get a different number. ... 01:41: ... acceleration. Exactly why the creation of dark energy accelerates expansion requires a dive into the hairy math of general relativity - and we tried that in ...
	2022-06-01: What If Physics IS NOT Describing Reality? 16:52: ... misinterpreted a couple of comments that said that   the expansion of the universe could be thought  of as matter shrinking rather ...
	2022-05-25: The Evolution of the Modern Milky Way Galaxy 17:21: ... no. First, assuming no cosmological  constant and dark energy, the expansion of   the universe does not continue to tug on  the space ...
	2022-05-04: Space DOES NOT Expand Everywhere 00:52: ... know the effect of cosmic expansion on the most enormous scales, but what about the here and the now? If ... 01:24: ... Hubble flow, after Edwin Hubble, the guy who first measured the rate of expansion. ... 06:04: ... within any gravitationally bound system is unaffected by the surrounding expansion. In the balloon analogy it’s tempting to think of the galaxy as being ... 07:12: ... trace lines. This is nice because you can show the changing rate of expansion - perhaps a period of rapid accelerating growth during inflation, then ... 07:45: ... expansion of space is seen in the divergence of our FLRW coordinate gridlines. Now ... 08:34: ... certain regions expansion won, and threw apart objects and the spacetime grids they trace. But in ... 07:12: ... trace lines. This is nice because you can show the changing rate of expansion - perhaps a period of rapid accelerating growth during inflation, then the ...
	2022-04-20: Does the Universe Create Itself? 15:24: ... collapse, and an open one expand forever, and a flat one tend to zero expansion. The answer is absolutely yes in the good old days when we didn’t have ...
	2022-03-30: Could The Universe Be Inside A Black Hole? 01:46: That expansion gives us our event horizon. 02:22: ... the accelerating expansion of the universe means the cosmological event horizon is closer to us ...
	2022-02-10: The Nature of Space and Time AMA 00:03: ... universe asks whether there's a difference between the notions of expansion or stretching or space being created uh or things just moving apart ...
	2022-01-27: How Does Gravity Escape A Black Hole? 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.
	2021-10-05: Why Magnetic Monopoles SHOULD Exist 12:09: Many physicists think that a period of prodigious exponential growth kicked off the expansion of our universe.
	2021-08-18: How Vacuum Decay Would Destroy The Universe 00:21: ... is how it is. Its just the right size,   has just the right expansion rate, and has just the right particle properties to allow stars ... 07:01: ... bubble surface,   so more surface tension to resist that  expansion. But the interior of the bubble   increases with the cube of ... 11:34: ... starts beyond several billion   light years, the accelerating expansion of the universe will throw us away from it faster than ... 00:21: ... is how it is. Its just the right size,   has just the right expansion rate, and has just the right particle properties to allow stars ...
	2021-07-07: Electrons DO NOT Spin 16:45: ... mutual connection to the outside. In the early universe, the extreme expansion of cosmic inflation may have permanently separated entangled  ...
	2021-04-21: The NEW Warp Drive Possibilities 07:22: ... a new insight - in 2002, Jose Natario demonstrated that the whole expansion and contraction of space was only a side-effect of Alcubierre’s choice ... 10:27: This would resulting in expansion and contraction of space in similar regions.
	2021-03-23: Zeno's Paradox & The Quantum Zeno Effect 13:22: ... gave you an update on the crisis in cosmology - the tension between the expansion rate of the universe measured at the beginning of the universe with the ... 13:40: ... the CMB number isn't actually a "measurement" of the current rate of expansion - which of course it can't be because that light comes from the ... 13:55: Instead, it provides us with an enormous amount of information about the composition and expansion of the universe back then. 14:04: We then use our cosmological models to predict what the expansion rate should be today. 14:09: For example, based on the amount of matter and dark energy, we can figure out now much the expansion should have slowed or sped up. 13:40: ... the CMB number isn't actually a "measurement" of the current rate of expansion - which of course it can't be because that light comes from the beginning ... 13:22: ... gave you an update on the crisis in cosmology - the tension between the expansion rate of the universe measured at the beginning of the universe with the ... 14:04: We then use our cosmological models to predict what the expansion rate should be today.
	2021-03-16: The NEW Crisis in Cosmology 01:16: ... the redshifts and distances of many, many galaxies and you have the expansion rate of the universe,   typically expressed as Hubble’s ... 03:13: ... unexpected - not only is   the universe expanding, but that expansion is accelerating. And so dark energy was discovered   - a ... 03:55: ... VERY important to perfect our measurements of the   expansion rate - both to confirm dark energy’s existence and to learn of its ... 04:42: ... map of the CMB using the   Planck satellite can give us the expansion rate. The Planck team calculated a Hubble constant of   ... 10:40: ... measurement of cosmic distances, and with that a measurement of the expansion rate that’s   independent of the cosmic distance ladder. So ... 03:13: ... unexpected - not only is   the universe expanding, but that expansion is accelerating. And so dark energy was discovered   - a mysterious and ... 01:16: ... the redshifts and distances of many, many galaxies and you have the expansion rate of the universe,   typically expressed as Hubble’s constant ... 03:55: ... VERY important to perfect our measurements of the   expansion rate - both to confirm dark energy’s existence and to learn of its ... 04:42: ... about half a percent, making it the most precise measurement of the expansion rate ever ... 10:40: ... measurement of cosmic distances, and with that a measurement of the expansion rate that’s   independent of the cosmic distance ladder. So ... 03:55: ... VERY important to perfect our measurements of the   expansion rate - both to confirm dark energy’s existence and to learn of its nature. ... 10:40: ... measurement of cosmic distances, and with that a measurement of the expansion rate that’s   independent of the cosmic distance ladder. So far we’ve only done ... 03:55: ... The other is to find a totally independent measurement of the expansion rate.   A good reason to do that is that the  supernova method is a pretty ... 04:42: ... map of the CMB using the   Planck satellite can give us the expansion rate. The Planck team calculated a Hubble constant of   67.6 km/s/Mpc - ... 11:57: ... distance they’ve traveled,   and so can be used to measure the expansion rate without the cosmic distance ladder.   We’re calling these ...
	2021-02-24: Does Time Cause Gravity? 09:33: ... have the big bang, then you have an instant of inflation, then regular expansion. ...
	2021-02-17: Gravitational Wave Background Discovered? 00:00: ... the big bang cosmic inflation was driving exponentially accelerating expansion and huge gravitational waves would have been produced in the phase ...
	2020-12-15: The Supernova At The End of Time 00:21: ... death, as it approaches maximum entropy, and its eternal exponential expansion drives it to effective utter emptiness and absolute ...
	2020-11-18: The Arrow of Time and How to Reverse It 07:17: ... other, which means they were once more closely clustered. This is the expansion of the universe, and it’s the manifestation of the 2nd law on the ...
	2020-06-15: What Happens After the Universe Ends? 11:45: ... early universe - its cosmic inflation - a period of extreme exponential expansion that smoothed things out in the first fraction of a ... 12:28: ... rescaled late-time forever of the previous universe, where exponential expansion was fueled by dark ...
	2020-05-11: How Luminiferous Aether Led to Relativity 14:23: ... let's pretend that the expansion rate is constant. And for an infinite universe the "size" is just the ... 16:14: ... that they had far to go, it's just that they were swimming against the expansion of space that whole ... 14:23: ... let's pretend that the expansion rate is constant. And for an infinite universe the "size" is just the average ...
	2020-05-04: How We Know The Universe is Ancient 03:24: ... Vesto Slipher’s observed redshifts could be a sign of the universe’s expansion. Lemaitre put forward the idea that the world began in a state that he ... 04:40: ... the fact that galaxies aren’t only moving away from us due to the expansion of the universe - they also have random motion as they’re tugged by the ... 06:06: ... there’s the fact that the expansion rate has changed over time. You can’t just assume that the galaxies were ... 09:39: ... continued to revise those estimates. He eventually concluded that the expansion rate of the universe – the Hubble constant – was about 75 kilometers per ... 11:07: ... years, you need to take into account the effect of matter slowing down expansion through its gravity and also the effect of dark energy speeding it up. ... 12:21: from assuming the expansion rate hasn't changed at all. 12:25: ... is to get the matter content, and the dark energy content, and the expansion rate, and more all from the one source - the cosmic microwave background ... 11:07: ... effect in galaxies and in galaxy clusters, and also by tracking the past expansion history of the universe to observe the slowing effect of all of those galaxies ... 03:24: ... Vesto Slipher’s observed redshifts could be a sign of the universe’s expansion. Lemaitre put forward the idea that the world began in a state that he referred to ... 06:06: ... there’s the fact that the expansion rate has changed over time. You can’t just assume that the galaxies were ... 09:39: ... continued to revise those estimates. He eventually concluded that the expansion rate of the universe – the Hubble constant – was about 75 kilometers per ... 12:21: from assuming the expansion rate hasn't changed at all. 12:25: ... is to get the matter content, and the dark energy content, and the expansion rate, and more all from the one source - the cosmic microwave background ...
	2020-04-28: Space Time Livestream: Ask Matt Anything 00:00: ... now in an expanding universe time is not symmetric if you reverse the expansion then the universe is getting smaller rather than larger okay so the ...
	2020-01-13: How To Capture Black Holes 12:17: ... very little matter and that is inflation, in which the rapid exponential expansion of space can create a ridiculously large universe that multiplies the ... 13:26: ... of the black hole singularity. If it grows by some inflation-like expansion into an entirely new spacetime then it may not care about the later ...
	2019-12-17: Do Black Holes Create New Universes? 07:47: That favours lots of dark energy generating rapid expansion.
	2019-12-09: The Doomsday Argument 01:48: ... defines the amount of dark energy, which is the stuff causing the expansion of the universe to ...
	2019-12-02: Is The Universe Finite? 02:06: ... about this so-called crisis in cosmology - the Planck team calculate an expansion rate for the universe that does not match the expansion rate observed ... 04:23: And 2) the rate of expansion. 04:26: Rapid expansion tends to give negative curvature and open the universe - make it infinite. 07:14: ... created a model that included all of the relevant parameters - the expansion rate, details of inflation, the amount and behavior of all different ... 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. 09:48: ... may have led to the unexpected results for both the geometry and the expansion history of the ... 10:46: In the case of the discrepancy in the expansion rate, hidden physics is the great hope of many physicists. 10:59: ... example, if the expansion rate of the universe really has evolved it may mean that the behavior of ... 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. 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. 09:48: ... may have led to the unexpected results for both the geometry and the expansion history of the ... 02:06: ... about this so-called crisis in cosmology - the Planck team calculate an expansion rate for the universe that does not match the expansion rate observed today - ... 07:14: ... created a model that included all of the relevant parameters - the expansion rate, details of inflation, the amount and behavior of all different types of ... 10:46: In the case of the discrepancy in the expansion rate, hidden physics is the great hope of many physicists. 10:59: ... example, if the expansion rate of the universe really has evolved it may mean that the behavior of dark ... 07:14: ... created a model that included all of the relevant parameters - the expansion rate, details of inflation, the amount and behavior of all different types of mass and ... 02:06: ... not match the expansion rate observed today - particularly the modern expansion rate determined from supernova ... 10:46: In the case of the discrepancy in the expansion rate, hidden physics is the great hope of many physicists. 02:06: ... calculate an expansion rate for the universe that does not match the expansion rate observed today - particularly the modern expansion rate determined from supernova ... 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.
	2019-11-11: Does Life Need a Multiverse to Exist? 08:45: ... energy was discovered in the 90s as astronomers tried to measure the expansion rate of the universe, only to find that expansion was ... 09:16: ... buzz of energy everywhere in the universe that would accelerate its expansion. ... 08:45: ... energy was discovered in the 90s as astronomers tried to measure the expansion rate of the universe, only to find that expansion was ...
	2019-10-21: Is Time Travel Impossible? 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.
	2019-09-30: How Many Universes Are There? 00:52: A greater inflationary spacetime whose expansion never ends. 01:31: ... – the inflaton field in that patch loses its energy and so accelerating expansion stops ... 02:46: But we can figure some stuff out just based on the exponential nature of the expansion. 05:01: The exponential nature of the expansion guarantees that. 06:31: ... much stronger then our universe would have restarted its accelerating expansion too quickly for galaxies and stars and life to ever ... 05:01: The exponential nature of the expansion guarantees that. 01:31: ... – the inflaton field in that patch loses its energy and so accelerating expansion stops ...
	2019-09-16: Could We Terraform Mars? 16:37: Give such a field a constant energy density and you get exponential expansion. 17:20: ... it's possible that it could now be powering the current accelerating expansion that we call dark ...
	2019-08-19: What Happened Before the Big Bang? 00:50: The idea is that the energy trapped in the so-called "Inflaton field" caused exponential expansion of space. 01:50: Now, in a recent episode we talked about how such a field could drive exponential expansion. 08:06: ... slow roll inflation, exponential expansion should grind to a halt over large regions as the inflaton field decays ... 08:35: Such fluctuations would be extremely rare and so you wouldn't think they'd count for much, but remember, Inflation causes exponential expansion. 08:45: To further up the slope, the inflaton field gets pushed the faster that expansion. 10:33: ... A couple of people mentioned George Lemaitre, who predicted the expansion of the universe before Edwin Hubble's ... 12:15: ... the standard Big Bang Theory doesn't explain the initial expansion at all, it includes an expansion rate in its initial conditions and then ... 12:29: ... a physical reason for the universe to have started with a rapid outward expansion rate in terms of pretty well understood ... 13:17: ... of Big Bang, many scientists now mean the period of regular Hubble like expansion that followed the initial kick and we think that kick was caused by ... 12:15: ... Bang Theory doesn't explain the initial expansion at all, it includes an expansion rate in its initial conditions and then tries to explain everything that ... 12:29: ... a physical reason for the universe to have started with a rapid outward expansion rate in terms of pretty well understood ...
	2019-08-06: What Caused the Big Bang? 00:00: Every astronomy textbook tells us that soon after the Big Bang there was this period of exponentially accelerating expansion called Cosmic Inflation. 00:09: ... a tiny fraction of a second, inflationary expansion multiplied the size of the universe by a larger factor than in the ... 01:31: ... the exponential expansion ended the universe would have continued to coast outwards just like a ... 01:44: ... for one: the problems of smoothness, flatness, missing monopoles, and expansion are all solved if we assume a single ... 02:37: They describe how its expansion or contraction depend on the matter and energy it contains. 02:43: Mostly, the stuff in the universe pulls the universe back together; resists the expansion with a positive gravitational effect. 03:04: Now, we know that something like this exists because we've observed it in the accelerating expansion produced by dark energy. 03:39: That means exponential expansion. 03:42: The speed of that exponential expansion depends on the strength of the vacuum energy density. 04:13: ... needed to stop inflating at some point giving way to the regular Hubble expansion that we see ... 09:53: ... be expanding out whatever speed it had at the end of inflation, but that expansion would no longer be exponentially ... 00:00: Every astronomy textbook tells us that soon after the Big Bang there was this period of exponentially accelerating expansion called Cosmic Inflation. 03:42: The speed of that exponential expansion depends on the strength of the vacuum energy density. 01:31: ... the exponential expansion ended the universe would have continued to coast outwards just like a thrown ... 00:09: ... a tiny fraction of a second, inflationary expansion multiplied the size of the universe by a larger factor than in the following 13 and ... 03:04: Now, we know that something like this exists because we've observed it in the accelerating expansion produced by dark energy.
	2019-07-18: Did Time Start at the Big Bang? 00:25: ... revealed that our universe is expanding and if we reverse that expansion far enough - mathematically - purely according to Einstein's equations, ... 01:56: ... to the power of negative 32 seconds Included a period of extremely rapid expansion called cosmic inflation We've talked about the reasons we need inflation ... 04:20: So when I talk about rewinding the expansion, I mean running the clock backwards to track a shrinking scale factor. 09:52: ... space-time in that case before the Big Bang was a period of exponential expansion that could have lasted indefinitely We'll get to the nitty-gritty of ... 01:56: ... to the power of negative 32 seconds Included a period of extremely rapid expansion called cosmic inflation We've talked about the reasons we need inflation in ...
	2019-05-16: The Cosmic Dark Ages 01:34: ... - in the searing heat left by the Big Bang. After 400,000 years of expansion things had cooled down enough for nuclei to recapture their electrons ...
	2019-04-03: The Edge of an Infinite Universe 17:49: ... I guess the painful part would be when expansion is fast enough that it starts to disrupt the way chemistry works, ...
	2019-03-28: Could the Universe End by Tearing Apart Every Atom? 00:05: ... together and then tragically separated by the infinitely accelerating expansion of space on subatomic ... 00:25: ... universe is expanding and that expansion is accelerating and we don't know what's causing that acceleration but ... 01:55: ... gravity but as long as dark energy doesn't increase there'll be no expansion inside those lonely galaxies they'll be safe to fade to heat death as we ... 03:05: ... the whole universe describing the acceleration or deceleration of the expansion rate which depends on how much stuff there is in the universe because ... 04:32: ... after all, in the future dark energy will completely dominate the expansion so we have the energy density of the vacuum and the pressure that it ... 05:32: ... positive which means dark energy is pushing outwards to increase the expansion rate. In fact, any equation of state parameter less than -1/3 would ... 05:51: ... parameter is below -1/3 but larger than -1, that's still accelerating expansion but in that case the dark energy is decreasing over ... 06:20: ... regular old dark energy except that it is much crazier. As the rate of expansion increases and with no gravitational bodies left to resist the expansion, ... 07:02: ... region of space is called the 'cosmic event horizon'. Now, if the expansion is accelerating, then, over time the distance between patches of ... 15:23: ... actually originally chicken sized. The tiny bird bones grew with the expansion of ... 06:20: ... regular old dark energy except that it is much crazier. As the rate of expansion increases and with no gravitational bodies left to resist the expansion, all ... 01:55: ... gravity but as long as dark energy doesn't increase there'll be no expansion inside those lonely galaxies they'll be safe to fade to heat death as we ... 00:25: ... you increase the overall amount of dark energy hence the accelerating expansion mathematically we describe a constant energy density with the cosmological constant in ... 03:05: ... the whole universe describing the acceleration or deceleration of the expansion rate which depends on how much stuff there is in the universe because this is ... 05:32: ... positive which means dark energy is pushing outwards to increase the expansion rate. In fact, any equation of state parameter less than -1/3 would cause that ...
	2019-03-20: Is Dark Energy Getting Stronger? 01:45: Instead of slowing down, as was expected, that expansion turned out to be accelerating. 01:59: ... textbooks tell us that we can this accelerating expansion is what you expect if empty space has a constant energy density – so ... 03:54: The expansion history of the universe is typically measured using the same type of supernova observations that first discovered dark energy. 04:50: Our rulers span much of cosmic time, and together they give an expansion history. 05:44: ... via the CMB may be more reliable than our measurement of its subsequent expansion history via ... 06:16: This motivated Risaliti and Lusso to seek a completely new way to measure that expansion history. 06:23: In order to properly measure the full expansion history of the universe - we want a new, brighter standard candle. 10:38: Putting these two together measures the expansion history. 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 ... 11:35: ... roughly speaking – if the expansion of the universe is accelerating even more than we thought, that could ... 12:00: At the moment, dark energy is only strong enough to accelerate the expansion of space on the largest scales. 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. 03:54: The expansion history of the universe is typically measured using the same type of supernova observations that first discovered dark energy. 04:50: Our rulers span much of cosmic time, and together they give an expansion history. 05:44: ... via the CMB may be more reliable than our measurement of its subsequent expansion history via ... 06:16: This motivated Risaliti and Lusso to seek a completely new way to measure that expansion history. 06:23: In order to properly measure the full expansion history of the universe - we want a new, brighter standard candle. 10:38: Putting these two together measures the expansion history. 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 ... 10:52: And that dashed line – that reflects the expansion history expected in a universe with constant dark energy – a Lambda-CDM, concordance universe. 01:45: Instead of slowing down, as was expected, that expansion turned out to be accelerating.
	2019-03-06: The Impossibility of Perpetual Motion Machines 05:01: ... Carnot described the most efficient possible engine – It’s a sequence of expansion and contraction of gas in a piston chamber that will provide the maximum ... 15:22: Julio Toboso García points out that the method used to model the CMB fluctuations - multipole expansion - sounds a like Fourier Analysis.
	2019-02-20: Secrets of the Cosmic Microwave Background 02:05: ... the right size to get a single collapse or one collapse and then an expansion or two complete collapses et cetera The oscillations happened at the ... 07:42: ... times the amount 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 ... 12:34: ... and clusters and the dark energy based on measuring the accelerating expansion rate of the Universe So that's how you lay bare the secrets of the ... 14:23: ... ring would have if it existed in the modern Universe given the rate of expansion of the Universe The surveys that measure these rings look so far in ... 12:34: ... and clusters and the dark energy based on measuring the accelerating expansion rate of the Universe So that's how you lay bare the secrets of the cosmic ... 14:23: ... would have in the modern Universe But to do that you have to assume an expansion rate for the Universe the Hubble constant The power spectrum I showed is from ...
	2019-02-07: Sound Waves from the Beginning of Time 01:30: And in these patterns, we could read the expansion history of the universe. 06:12: The radius of that shell became fixed to the rate of expansion of the universe. 07:16: So how does this primordial history lesson help us understand the subsequent expansion of the universe? 11:00: Dark energy was first discovered by using distant supernovae as distance measurements- to track the rate of expansion of the universe. 11:08: Those observations revealed that the expansion rate is accelerating due to an unknown influence what we call dark energy. 11:19: It requires an independent test of the expansion history. Enter the baryon acoustic oscillations. 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: ... As the universe expands towards the infinite future, does that expansion outpace the probability of collapsing into a big crunch due to ... 01:30: And in these patterns, we could read the expansion history of the universe. 11:19: It requires an independent test of the expansion history. Enter the baryon acoustic oscillations. 13:26: ... As the universe expands towards the infinite future, does that expansion outpace the probability of collapsing into a big crunch due to everything ... 11:08: Those observations revealed that the expansion rate is accelerating due to an unknown influence what we call dark energy. 12:02: They allow us to track the expansion rate of the universe.
	2019-01-24: The Crisis in Cosmology 00:05: ...the rate of expansion of our universe,... 01:12: We encapsulate the expansion of the universe with a single number, called the Hubble constant. 01:18: ... their distance apart But, more fundamentally, H0 tells us the rate of expansion of the ... 01:42: ...the rate of expansion of the universe, combined with the gravitational effect... 01:47: ...can be used to determine its entire expansion history,... 05:05: ...that the expansion of the universe is actually accelerating,... 06:12: So it's a more or less direct measurement of the CURRENT expansion rate. 06:19: What if we could measure the expansion rate of the universe at the very beginning? 06:23: Then, we could figure out what its current expansion rate should be, given our best understanding... 06:28: ...of all the gravitational influences that affected that expansion since the Big Bang. 09:05: ...as well as the expansion rate of the universe in that early epoch. 09:09: So, how do you get the Hubble constant, i.e., the current expansion rate, from all of this? 09:26: ...as well as the initial expansion rate. 12:50: The near centennial quest to measure the expansion rate of the universe will be concluded. 01:47: ...can be used to determine its entire expansion history,... 06:12: So it's a more or less direct measurement of the CURRENT expansion rate. 06:19: What if we could measure the expansion rate of the universe at the very beginning? 06:23: Then, we could figure out what its current expansion rate should be, given our best understanding... 09:05: ...as well as the expansion rate of the universe in that early epoch. 09:09: So, how do you get the Hubble constant, i.e., the current expansion rate, from all of this? 09:26: ...as well as the initial expansion rate. 12:50: The near centennial quest to measure the expansion rate of the universe will be concluded.
	2019-01-09: Are Dark Matter And Dark Energy The Same? 01:52: Observations of distant supernovae tell us that the expansion of the universe is accelerating. 02:03: As more space comes into existence because of that expansion thing the more“dark energy” you get, which causes more acceleration. 02:11: Actually, we gotta think a bit harder about why dark energy causes accelerated expansion, it’s important for the new paper. 02:33: So why does it result in an outward-pushing, accelerating expansion? 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. 03:42: And a positive Lambda means accelerating expansion. 10:23: First, does it predict an expansion history that fits the supernova observations that originally discovered dark energy? 10:40: But then that deceleration turned around as dark energy kicked in, resulting in the current accelerating expansion. 10:48: ... a negative cosmological constant and this sinusoidal expansion, any slowdown happens near the turnaround point presumably tens of ... 11:00: ... straight part in the rise in the sine curve, which is almost a constant expansion ... 11:19: We already know that a constant expansion rate happens to give a similar age to the standard dark energy age. 11:25: But a constant or near-constant expansion rate definitely does not fit the supernova data. 10:23: First, does it predict an expansion history that fits the supernova observations that originally discovered dark energy? 11:00: ... straight part in the rise in the sine curve, which is almost a constant expansion rate. ... 11:19: We already know that a constant expansion rate happens to give a similar age to the standard dark energy age. 11:25: But a constant or near-constant expansion rate definitely does not fit the supernova data. 02:03: As more space comes into existence because of that expansion thing the more“dark energy” you get, which causes more acceleration.
	2018-10-25: Will We Ever Find Alien Life? 06:39: ... all, it would only take one of these worlds to spawn an expansion of species, or even a single individual among that species to launch a ...
	2018-10-03: How to Detect Extra Dimensions 07:35: But in short, the expansion of the universe seems to be accelerating. 08:27: To us, that would look like an accelerating expansion of the universe.
	2018-08-23: How Will the Universe End? 03:13: ... before the last red dwarf fades out, the accelerating expansion of the universe will have dragged all galaxies beyond the Virgo ... 09:09: ... universe will become more and more diffuse and dim as the accelerating expansion of space continues and the infinitely long progression to absolute heat ... 11:54: ... to, assuming they don't have technology so advanced that they arrest the expansion of the universe itself or develop a portal gun-- not ...
	2018-07-04: Will A New Neutrino Change The Standard Model? 01:09: ... being the first expansion of the standard model family since the Higgs boson, sterile neutrinos ... 09:49: ... radiation by the Planck satellite shows that the early rates of expansion of the universe is consistent with only three neutrino ...
	2018-05-16: Noether's Theorem and The Symmetries of Reality 01:30: In 1915, the expansion of the universe hadn't yet been discovered.
	2018-04-18: Using Stars to See Gravitational Waves 07:05: ... a gravitational wave passes by, the beads are free to follow the expansion and contraction of space while the rod resists due to the atomic forces ...
	2018-04-11: The Physics of Life (ft. It's Okay to be Smart & PBS Eons!) 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.
	2018-04-04: The Unruh Effect 02:56: Well, that's if you ignore the expansion of the universe, and this makes sense.
	2018-03-28: The Andromeda-Milky Way Collision 03:01: Hubble went on to combine distance measurements to many galaxies with measurements of their velocities to discover the expansion of the universe. 03:23: ... attraction between it and the Milky Way overcomes the outward expansion, allowing them to fall ...
	2018-02-14: What is Energy? 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.
	2017-11-08: Zero-Point Energy Demystified 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 ...
	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. 07:09: ... the late '90s, astronomers discovered that the expansion of the universe is, in fact, accelerating in exactly the way we'd expect ... 07:20: ... the Lamb shift or the Casimir effect, the observation of accelerating expansion allows us to measure the absolute density of vacuum ...
	2017-10-25: The Missing Mass Mystery 02:13: It's anti-gravitational and causes the expansion of the universe to accelerate. 11:45: This leads to the unintuitive result that it acts repulsively, accelerating expansion.
	2017-10-19: The Nature of Nothing 10:14: The observation is the accelerating expansion of the universe.
	2017-09-28: Are the Fundamental Constants Changing? 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. 08:26: ... are massively redshifted-- their wavelengths stretched out due to the expansion of the ...
	2017-09-20: The Future of Space Telescopes 11:33: Nicholas Martino asks whether gravitational waves are redshifted by the expansion of the universe.
	2017-08-02: Dark Flow 00:44: Motion due to the expansion of the universe-- what we call the Hubble flow-- is equal in all directions. 08:45: Then, the event known as cosmic inflation caused an exponential expansion that threw these once neighbors far, far apart.
	2017-06-07: Supervoids vs Colliding Universes! 01:59: ... and 1/2 billion years of cosmic expansion later, and it stretched to microwave wavelengths, and to a temperature ... 02:28: These were then amplified by a period of exponential expansion in the very early universe that we call inflation. 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. 05:07: ... around 4 billion years ago, dark energy caused the expansion of our universe to begin accelerating, whereas previously it had been ... 05:46: ... and determined the shift in the wavelengths of those spectra due to the expansion of the universe, i.e., they measured ... 08:50: The idea is that the initial period of exponential expansion that we call inflation actually lasts forever.
	2017-05-03: Are We Living in an Ancestor Simulation? ft. Neil deGrasse Tyson 15:17: That perfect time reversal would include the reverse of every particle interaction that happened in the original expansion. 16:08: An example of that would be the perfect time reversal of an expansion.
	2017-02-15: Telescopes of Tomorrow 02:43: That light has been stretched out by that expansion deep into the infrared.
	2017-01-11: The EM Drive: Fact or Fantasy? 06:05: The big one seems to be that thermal effects could still be a factor, in particular, deformation of the device or the scale due to thermal expansion.
	2016-11-09: Did Dark Energy Just Disappear? 00:21: ... 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. 01:46: They claim the data are consistent with there being no dark energy; no accelerating expansion. 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. 03:38: ... it finds that the data is also consistent with a wider range of possible expansion histories, and that range now includes a history in which there never ... 03:51: An accelerating expansion is still preferred, it's just that a non-accelerating history is not excluded with quite the same confidence. 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. 06:27: But that means we have to consider all off the things affecting that expansion when we decide whether dark energy is part of that equation. 06:35: ... the way our universe expands: there are things that tend to accelerate expansion, which we call dark energy, and there are things that slow expansion, ... 11:03: ... up: everything we know about the way gravity works, combined with the expansion history that we measure tells us that there has to be something out ... 11:18: It's not even like accelerating expansion is that weird anymore. 12:07: ... and careful look at the evidence for dark energy, and its effect on the expansion of ... 03:38: ... it finds that the data is also consistent with a wider range of possible expansion histories, and that range now includes a history in which there never was any ... 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. 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. 11:03: ... up: everything we know about the way gravity works, combined with the expansion history that we measure tells us that there has to be something out there ... 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.
	2016-10-12: Black Holes from the Dawn of Time 01:36: Also, the gravitational pull needs to be strong enough to overcome the expansion of the universe. 03:00: ... models that some of these fluctuations were, at some point in the early expansion, intense enough to resist the local expansion of the universe and form a ...
	2016-09-14: Self-Replicating Robots and Galactic Domination 01:08: ... for long enough that any previous civilizations with any inclination to expansion or exploration should have been able to cross, even colonize the entire ...
	2016-06-15: The Strange Universe of Gravitational Lensing 05:57: ... allowed us to measure the Hubble Constant, which tells us the rate of expansion of the universe, independently confirming the results from other ...
	2016-06-08: New Fundamental Particle Discovered?? + Challenge Winners! 09:12: And how many times it would double in size in the future before matter no longer has any significant influence on expansion.
	2016-05-18: Anti-gravity and the True Nature of Dark Energy 01:07: And three, the expansion of the universe is accelerating. 01:12: We know this, because we've mapped its past expansion history using distant supernovae. 01:30: It both flattens the universe and leads to exponential expansion. 02:18: OK, the big, weird fact about a constant vacuum energy density is that leads to exponential expansion. 02:59: To see why dark energy pushes outwards and accelerates the expansion, we need to go deeper. 03:11: The first Friedmann equation is all about the rate of expansion of the universe. 03:18: It's about the acceleration or deceleration of that expansion. 03:22: It describes the forces pushing or pulling on the expansion. 03:37: And a double dot is the rate at which the expansion is changing. 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. 04:36: ... an outward push in pressure, then is this how dark energy is causing expansion to accelerate, by causing positive ... 07:50: So dark energy's density isn't causing expansion to accelerate by itself. 07:58: But we just discussed how positive pressure can't cause expansion to accelerate outwards. 08:54: Weirdly, the inward pulling pressure of dark energy ultimately drives expansion outwards. 10:22: Negative pressure means energy is gained on expansion. 11:01: But both agree that a constant energy density and the resulting negative pressure leads to accelerating expansion. 01:12: We know this, because we've mapped its past expansion history using distant supernovae. 08:54: Weirdly, the inward pulling pressure of dark energy ultimately drives expansion outwards.
	2016-05-11: The Cosmic Conspiracy of Dark Energy Challenge Question 00:42: ... expansion of the universe has been accelerating for some billions of years now, ... 03:55: Assuming a constant expansion rate, a constant increase in the scale factor, that means it was only two to three billion years ago.
	2016-05-04: Will Starshot's Insterstellar Journey Succeed? 08:35: ... we talked about how dark energy causes this exponentially accelerating expansion of the universe and you guys had a lot to say in the ... 08:56: Does dark energy cause expansion? 08:58: Does expansion cause dark energy? 09:01: Dark energy does drive the expansion rate, causing a sort of anti-gravity effect. 09:26: So expansion results in more dark energy and more dark energy results in faster expansion. 09:33: It's a positive feedback cycle that leads to exponential expansion. 09:01: Dark energy does drive the expansion rate, causing a sort of anti-gravity effect.
	2016-04-27: What Does Dark Energy Really Do? 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. 01:11: However, so does is its past expansion history. 01:14: In fact, measuring the past expansion history should tell us the future expansion without ever having to count any galaxies. 01:33: During that expansion, it increases the wavelength of these electromagnetic waves, resulting in what we see as redshift, cosmological redshift. 01:43: ... that expanding universe, then its redshift tells us the total amount of expansion that happened during that ... 02:07: To measure the expansion history of the universe, we need to measure the redshift-distance relationship. 02:35: And the two are connected by the universe's expansion history. 02:39: Measuring many different redshifts and distances independently of each other tells us that expansion history. 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. 06:03: ... exploding in galaxies billions of light years away to measure the past expansion history of the ... 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 ... 07:10: However, this accelerating expansion can be explained with the same bit of math, the cosmological constant, pointing to the same physics, dark energy. 08:16: Expansion will only depend on the cosmological constant. 08:21: So does that mean the expansion will become constant? 08:25: See, it's not the expansion rate-- the A-dot-- that's constant in this equation. 08:59: That's exponential growth, and it looks like an accelerating expansion. 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: ... episode, we talked about how a general relativistic description of the expansion of the universe requires dark ... 10:32: ... by the first Friedmann equation to agree with the balance between expansion and density is much, much greater than our universe ... 01:11: However, so does is its past expansion history. 01:14: In fact, measuring the past expansion history should tell us the future expansion without ever having to count any galaxies. 02:07: To measure the expansion history of the universe, we need to measure the redshift-distance relationship. 02:35: And the two are connected by the universe's expansion history. 02:39: Measuring many different redshifts and distances independently of each other tells us that expansion history. 06:03: ... exploding in galaxies billions of light years away to measure the past expansion history of the ... 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. 06:41: That means the expansion rate of the universe has actually sped up, accelerated, while that supernova light was traveling to us. 08:25: See, it's not the expansion rate-- the A-dot-- that's constant in this equation. 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.
	2016-04-20: Why the Universe Needs Dark Energy 00:52: ... Friedmann equations, can describe the cosmic balance between the outward expansion of the universe and the resistance to this expansion due to the ... 01:16: So it turns out that this cosmic conflict will be won by expansion. 01:56: We know for sure that, the left side of this equation, the sum of the expansion and density terms don't cancel out to zero. 02:04: In fact, they come out positive, which means that the expansion term wins over the inward-pulling density term. 02:50: Which is what gives us the expansion described here. 07:13: ... even though the density is still too low to reverse the expansion, with this new player in the game, geometry is no longer tied to the fate ... 08:14: At that point, dark energy will govern expansion. 09:51: And expansion is not occurring. 10:05: Only outside that influence does expansion become significant. 02:04: In fact, they come out positive, which means that the expansion term wins over the inward-pulling density term.
	2016-04-13: Will the Universe Expand Forever? 00:46: ... observations have revealed something even stranger-- the future expansion of the universe will be dominated by a mysterious influence that ... 03:53: ... on the amount of stuff in the universe, there's some current expansion speed that would allow the future expansion rate of the universe to ... 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. 06:09: ... the kinetic energy of expansion and the potential energy of collapse are perfectly balanced, then the ... 06:22: Essentially, that's if the expansion is exactly equal to the escape velocity. 06:39: There will be some expansion energy remaining after gravity is diluted to nothing, and the universe will expand forever, never stopping. 06:48: And if the left-hand side is negative, in that case there was never a high-enough expansion rate to reach that extreme size. 07:11: Well, we know the expansion speed. 07:18: The expansion rate now is what we call the "Hubble constant." It's around 70 kilometers per second per megaparsec. 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. 07:53: The density term, the recollapsing term, falls short of the expansion term. 08:40: ... Friedmann equation, the fate of the universe-- as determined by its expansion and density-- should be intrinsically tied to its ... 09:20: Dark energy won't save us from infinite expansion. 09:26: Dark energy accelerates the expansion. 06:39: There will be some expansion energy remaining after gravity is diluted to nothing, and the universe will expand forever, never stopping. 03:53: ... there's some current expansion speed that would allow the future expansion rate of the universe to slowly grind to a halt over infinite ... 06:48: And if the left-hand side is negative, in that case there was never a high-enough expansion rate to reach that extreme size. 07:18: The expansion rate now is what we call the "Hubble constant." It's around 70 kilometers per second per megaparsec. 03:53: ... on the amount of stuff in the universe, there's some current expansion speed that would allow the future expansion rate of the universe to slowly ... 07:11: Well, we know the expansion speed. 07:53: The density term, the recollapsing term, falls short of the expansion term.
	2016-04-06: We Are Star Stuff 11:17: The time part is certainly curved, which leads to the expansion of space, even if the space part itself can be flat. 13:14: mukul gupta asks whether the expansion of the universe will stop at some point.
	2016-03-23: How Cosmic Inflation Flattened the Universe 00:00: [MUSIC PLAYING] Cosmic inflation describes a period of insane exponential expansion right after the instant of the Big Bang. 04:21: Both seem strange if we assume that regular gravity was always the only force affecting the rate of expansion after the initial kick of the Big Bang. 05:00: ... causally disconnected, at which point inflation stops and regular expansion takes ... 06:08: For this to work, that inflationary expansion had to throw neighboring regions of space apart at many times faster than the speed of light. 07:17: But this bit of math gives us exactly the type of expansion that we need for inflation. 07:43: It doesn't tell us what this stuff is, just that it's a property of space itself and that it acts to drive expansion. 07:54: And so the more space, the more expansion. 08:15: ... now, let's just go with the fact that empty space can propel its own expansion and will do so if the vacuum contains a ubiquitous constant energy ... 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: ... there isn't necessarily a good reason to think that there was a normal expansion period before, if there was even was a "before inflation." In fact, the ... 05:00: ... causally disconnected, at which point inflation stops and regular expansion takes ...
	2016-03-02: What’s Wrong With the Big Bang Theory? 06:11: ... based on the simplistic expansion you predict from general relativity, when the CMB was released, there ... 07:52: ... and then enter the state of insane, exponentially accelerating expansion in which it increased in size by a factor of at least 10 to the power of ... 08:09: So 100 trillion trillion to something like our grain of sand size at which point it slowed down to its regular expansion rate. 08:56: ... origin of the universe, but instead as a theory describing the period of expansion from a subatomic to a cosmic ... 09:55: ElectroMechaCat asks why if the universe is expanding, doesn't matter also get stretched with that expansion. 10:06: ... surprising the matter would not be stretched by expansion because the bonds between and within atoms are vastly stronger than any ... 10:19: That's if it were even valid to extrapolate that expansion to the scale of objects or even to galaxies. 10:25: ... we call the Hubble expansion of the universe arises from the FriedmannLemaîtreRobertsonWalker metric, ... 08:09: So 100 trillion trillion to something like our grain of sand size at which point it slowed down to its regular expansion rate.
	2016-02-24: Why the Big Bang Definitely Happened 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 ...
	2016-02-17: Planet X Discovered?? + Challenge Winners! 07:12: ... the same time, 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 ...
	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 ...
	2015-10-07: The Speed of Light is NOT About Light 11:39: ... you travelled that distance-- again, assuming the universe froze in its expansion, which it won't-- then you'd get back to your starting point a long, ...
	2015-09-30: What Happens At The Edge Of The Universe? 02:00: ... distance that you would have to travel only if the universe froze in its expansion and you were traveling through static ... 06:46: ... to the particle horizon to get back to where you started, assuming expansion froze for the whole ...
	2015-05-27: Habitable Exoplanets Debunked! 09:34: You can loosely think of that energy as going into the expansion, but even that's not quite correct.
	2015-04-01: Is the Moon in Majora’s Mask a Black Hole? 08:56: However, that's only if you're moving along with the overall cosmic expansion of space.
	2015-03-25: Cosmic Microwave Background Explained 04:52: ... you throw in another 13 plus billion years of space expansion, all that light has redshifted into the microwave band to become what we ...
	2015-03-11: What Will Destroy Planet Earth? 05:04: ... the universe is expanding and currently that expansion is speeding up due to an unidentified material permeating the cosmos ... 05:14: ... useful to think of that process-- the expansion-- not as galaxies flying apart through space, but instead as the space ... 05:29: ... of this mysterious dark energy that can be used to do some space expansion ...
	2015-03-04: Should We Colonize Venus Instead of Mars? 06:23: First, the speed of light speed limit is for things moving through space, not about expansion of space itself. 06:54: We're talking about expansion of space in general. 06:56: Inflation refers to a very specific expansion of space that occurred in just the first few instances after The Big Bang. 07:11: What the Hubble Bubble offers is a potential alternative to the currently observed, accelerated expansion of space.
	2015-02-25: How Do You Measure the Size of the Universe? 02:18: ... two facts, the expansion of space and the fact that it can expand at a variable rate, complicate ... 02:49: So how can we possibly know the expansion history of the universe? 02:53: Using something called cosmological redshift, which is like a fingerprint that the expansion of space leaves on beams of light. 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. 04:17: Once you have the expansion history, how do you actually determine the size of the universe? 04:27: ... the movie of the rising dough backwards, at the rate given to us by the expansion history, eventually nearby raisins will sit on top of each ... 04:38: Our best current estimate, using that expansion history, is 13.8 billion years, give or take. 04:54: ... we run the movie forward, at the rate given to us by the expansion history, those imaginary beams would travel through the expanding space ... 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. 04:17: Once you have the expansion history, how do you actually determine the size of the universe? 04:27: ... the movie of the rising dough backwards, at the rate given to us by the expansion history, eventually nearby raisins will sit on top of each ... 04:38: Our best current estimate, using that expansion history, is 13.8 billion years, give or take. 04:54: ... we run the movie forward, at the rate given to us by the expansion history, those imaginary beams would travel through the expanding space and reach ... 04:27: ... the movie of the rising dough backwards, at the rate given to us by the expansion history, eventually nearby raisins will sit on top of each ...

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