
20221109: What If Humanity Is Among The First Spacefaring Civilizations?
 11:54: ... galaxy at 10% light speed, this delay will have basically no effect on cosmological ...


20220817: What If Dark Energy is a New Quantum Field?
 01:25: ... model for dark energy is that it can be described with a socalled cosmological constant. This is just a static number that you can add to Einstein’s ...
 03:22: Standard “cosmological constant” dark energy has omega 1. This is just what you get when you say that the vacuum has a constant energy density.
 05:50: ... such a large number down to nearly zero but not quite zero. This is the cosmological constant problem, and we’ve discussed it ...
 07:31: ... is yes, one could  and if that’s true then a lot of problems with cosmological constant dark energy could be solved. There are a few options for dark ...
 09:51: ... solve some of the uncomfortable coincidences that seem necessary with a cosmological constant dark energy. Currently around 70% of the energy in the universe ...
 10:55: ... able to form. This same “tracker” behavior could also help solve the cosmological constant problem. If quintessence shifts to match the matter fields, it ...
 13:27: ... would be strong support for quintessence, because that would refute the cosmological constant model, and quintessence is its main competitor. The now fully ...
 14:41: ... will teach us about its fabric, its origin, and its fate. Either the cosmological constant problem is coincidental with a quintessentially consistent dark ...


20220601: What If Physics IS NOT Describing Reality?
 16:52: ... predicts that this should happen. Also, we wouldn’t expect cosmological redshift if matter is shrinking because there’s no stretching of ...


20220525: The Evolution of the Modern Milky Way Galaxy
 17:21: ... a kind of tugofwar between the two?” Yes and no. First, assuming no cosmological constant and dark energy, the expansion of the universe does ...
 18:10: ... the Schwarzschild metric isn’t really valid in a universe with a cosmological constant. There would indeed be an additional effect ...
 18:41: ... towards a black hole. In the same way, an inertial frame at the cosmological event horizon is flowing away from us at the speed of light. ...


20220420: Does the Universe Create Itself?
 17:39: ... other black holes, etc  then it’s event horizon is the same size as our cosmological even horizon. Sounds too much of a coincidence, right? Well actually, this is ...


20220330: Could The Universe Be Inside A Black Hole?
 02:09: This is the cosmological event horizon.
 02:22: ... the accelerating expansion of the universe means the cosmological event horizon is closer to us than the spot where recession equals the ...
 10:21: That’s the Cosmological Natural Selection idea by Lee Smolin, and yeah, we did an episode.
 11:45: Cosmological natural selection might be a path to that, but we also need some evidence for that in order to proceed.


20220323: Where Is The Center of The Universe?
 01:04: This is called the Cosmological principle.
 01:06: ... neither the Copernican principle nor the Cosmological principle are actual laws of physics  they’re philosophical positions  ...
 11:28: He assumed a homogeneous universe and assumed the cosmological principle.
 12:47: ... should point out that this doesn’t necessarily break the Cosmological principle because it could still be that our bubble is small on the most ...


20220210: The Nature of Space and Time AMA
 00:03: ... the same change in distance over time and uh as an example uh we have cosmological redshift okay so a photon of light traveling from one galaxy to the ...


20220119: How To Build The Universe in a Computer
 05:26: ... example, in a cosmological simulation we’re trying to watch the detailed formation of individual ...
 10:14: And then we have cosmological simulations which create entire virtual universes, from the moment the first atoms formed to the modern day.
 10:39: ... the current largest cosmological simulations is AbacusSummit, which just last year simulated 70 ...


20211110: What If Our Understanding of Gravity Is Wrong?
 10:17: But the main problem with TeVeS is cosmological in nature.


20210323: Zeno's Paradox & The Quantum Zeno Effect
 14:04: We then use our cosmological models to predict what the expansion rate should be today.


20210316: The NEW Crisis in Cosmology
 06:22: ... errors that are affecting one or both. For example, the cosmological distance ladder could have a broken rung. The ...


20200728: What is a Theory of Everything: Livestream
 00:00: ... does that number come from why are there three generations what's the cosmological constant telling us should those not be used as the as the occam's ...


20200615: What Happens After the Universe Ends?
 10:41: ... by this sort of conformal rescaling, the universe needs a positive cosmological ...


20200428: Space Time Livestream: Ask Matt Anything
 00:00: ... of just put this one up here because it was lying around the anthropic cosmological principle now this isn't we talked a lot about the cosmological ...


20200211: Are Axions Dark Matter?
 14:39: ... that the universe is spatially finite. The simplest interpetation of the cosmological equations derived from general relativity tell us that it it may be ...


20200203: Are there Infinite Versions of You?
 00:14: ... cosmological equations that so beautifully describe our universe make an ...
 00:26: ... on itself and be finite, or perhaps the simplest interpretation of the cosmological equations is too ...
 10:31: ... even then we still have to hope that it’s reasonable to extrapolate our cosmological equations ...


20200127: Hacking the Nature of Reality
 12:27: ... Nima ArkaniHamed and collaborators have performed what they call a cosmological bootstrap to understand the nature of those early subatomic scale ...


20200113: How To Capture Black Holes
 11:59: ... couple of episodes, but today we're doing comments from our episode on cosmological natural selection  Lee Smolin's idea that maybe new universes are born ...
 12:49: ... of the fundamental constants, not the origin of everything. Ideas like cosmological natural selection and eternal inflation are helpful because they reduce ...
 13:26: ... average out? The answer to this is ... no one has any idea. The cosmological natural selection hypothesis doesn't really define the ongoing ...
 14:13: ... to Lee Smolin. I'm making a list, guys. If it turns out the whole cosmological natural selection thing is true, I'll send that list to the Swedish ...


20191217: Do Black Holes Create New Universes?
 00:10: Cosmological natural selection proposes exactly this  but even better, it claims to be able to test the hypothesis.
 01:46: Inspired by biological evolution, theoretical physicist Lee Smolin came up with Cosmological Natural Selection.
 08:51: ... cosmological natural selection is true, then the fundamental parameters favouring ...
 10:44: ... like to add my own objection: cosmological natural selection is meant to explain the fine tuning in the fundamental ...
 11:38: ... cosmological natural selection is an appealing idea because it seeks a natural ...


20191209: The Doomsday Argument
 01:38: In 1987, physicist Steven Weinberg used this form of anthropic reasoning to estimate the value of the cosmological constant.
 01:48: ... a quick refresher: the cosmological constant defines the amount of dark energy, which is the stuff causing ...
 01:57: ... in physics from string theory to eternal inflation predict that the cosmological constant could take on different values in different universes, and its ...
 02:18: Getting a low cosmological constant is extremely unlikely according to these pictures.
 02:33: ... principle  perhaps we’re just in one of the lucky universes with a low cosmological constant because where else could we ...
 02:49: ... the assumption that lower cosmological constants were less likely than higher ones, Steven Weinberg reasoned ...
 03:31: ... refined his estimate of the cosmological constant to be the value that most astronomers across the multiverse ...
 04:49: This sort of reasoning seems useful  it enabled a decent guess at the cosmological constant.
 08:39: ... Steven Weinberg’s case the question was “what sort of cosmological constant is the typical astronomer likely to observe  so reference ...
 11:20: ... reasoning can lead to powerful predictions, like the value of the cosmological constant, it can lead to dubious but worrying predictions like the ...


20191202: Is The Universe Finite?
 11:51: The tension between the Planck results and other cosmological measurements seems to be growing.
 13:58: ... to tell you about a very clear one: Stephen Weinberg's prediction of the cosmological constant years before dark energy was ever ...
 15:52: ... probably some massively exponentially accelerating universe because the cosmological constant in most universes seems likely to be a lot higher than ...


20191118: Can You Observe a Typical Universe?
 04:37: ... the 1986 book the Anthropic Cosmological Principle, John Barrow and Frank Tipler misinterpret the strong ...


20191111: Does Life Need a Multiverse to Exist?
 08:37: But an even more finelytuned parameter appears to be the cosmological constant.


20190930: How Many Universes Are There?
 05:53: For example the cosmological constant – the strength of dark energy – could be different.
 06:51: ... are so many bubble universes that at least some will have a low enough cosmological constant for life to ...
 07:54: Each different configuration results in a different family of particles and also a different cosmological constant.
 08:32: As well as a decent cosmological constant.


20190806: What Caused the Big Bang?
 03:23: ... density, then Einstein's equations end up having a term that we call the cosmological constant  A positive value for the cosmological constant means a ...


20190403: The Edge of an Infinite Universe
 16:01: ... on physics stackexchange, in which he suggests that the shrinking cosmological horizon could merge with the event horizon to produce a global state ...


20190328: Could the Universe End by Tearing Apart Every Atom?
 00:25: ... expansion mathematically we describe a constant energy density with the cosmological constant in the equations of Einstein's general theory of relativity but ...
 04:25: ... let's add dark energy in the form of a cosmological constant it usually hangs out outside the brackets because it's emo, but ...
 04:32: ... volume increases density does not go down, the basic definition of the cosmological constant. So now the pressure term is A, negative and B because of this ...


20190320: Is Dark Energy Getting Stronger?
 00:04: ... currently accepted cosmological description of our universe is called the Lambda CDM Model and is built ...
 00:45: ... looking at a new paper in Nature Astronomy, “Cosmological constraints from the Hubble diagram of quasars at high redshifts” by ...
 00:55: It hints that the cosmological constant may not be so constant after all.
 02:13: Mathematically we represent a constant vacuum energy with Einstein’s cosmological constant – or Lambda.
 02:51: ... the textbooks, this type of cold dark matter sits alongside the cosmological constant as our best description of how the universe behaves on the ...
 05:32: Perhaps the cosmological constant is not so constant, or dark matter is not so cold after all.
 11:47: Are concordance and the cosmological constant dead?


20190207: Sound Waves from the Beginning of Time
 12:20: They also confirm the dark energy behaves just as is predicted by Einsteins cosmological constant.


20190124: The Crisis in Cosmology
 09:15: Well, first you figure out what starting cosmological parameters...
 12:08: The current calculations assume that dark energy is described by the cosmological constant,...


20190109: Are Dark Matter And Dark Energy The Same?
 03:34: In Einstein’s equations and the Friedmann equations, that constant energy density is represented by the cosmological constant, or Lambda.
 07:49: So, you remember I said that a constant POSITIVE energy density can be expressed as a cosmological constant?
 08:02: Well a constant NEGATIVE energy density – like the one proposed by Farnes, gives a negative cosmological constant.
 08:18: ... gravity for the whole cosmos, this negative mass fluid – as a negative cosmological constant – has the same competing effects as regular dark energy, but in ...
 08:50: ... Farnes acknowledges that his proposal gives a negative cosmological constant that ultimately decelerates, but there’s some contradiction ...
 09:06: And yet a negative cosmological constant gives you an extremely different universe.
 09:15: ... this thing  to correctly conclude that a universe with a negative cosmological constant should have a sinusoidal scale ...
 09:43: The negative cosmological constant is the source of that slowdown and for the subsequent accelerating collapse.
 10:48: ... a negative cosmological constant and this sinusoidal expansion, any slowdown happens near the ...


20180523: Why Quantum Information is Never Destroyed
 11:11: Merissan has plans to use the loss of energy in cosmological redshift as a refutation of conservation of energy arguments.
 11:59: Could the energy lost to cosmological redshift actually become dark energy?
 12:23: But it's dropped off since then due to cosmological redshift.


20180516: Noether's Theorem and The Symmetries of Reality
 01:14: The simplest example of this is the case of cosmological redshift.
 04:52: Energy can be lost in the case of cosmological redshift, and it can be created from nowhere in the case of dark energy.
 06:32: ... any object moving on any path or indeed any system quantummechanical to cosmological evolving between two ...


20180321: Scientists Have Detected the First Stars
 04:20: The absorption dip was predicted by our cosmological models, and it was right where we thought it would be.
 04:50: Our cosmological models can't explain how this early hydrogen gas could possibly be this cold.


20180228: The Trebuchet Challenge
 00:00: [JINGLE PLAYING] Energy is a powerful tool for predicting the behavior of our universe, from quantum to cosmological scales.


20180117: Horizon Radiation
 01:01: ... horizon of a black hole, out of which no information can travel or the cosmological horizon that limits the observable ...


20170928: Are the Fundamental Constants Changing?
 10:50: ... surveys with future generations of telescopes, more refined cosmological models, and better atomic clocks will also help scientists shave down ...


20170607: Supervoids vs Colliding Universes!
 03:58: It's a cosmological tugofwar.


20161109: Did Dark Energy Just Disappear?
 04:06: The new study claims a 3sigma confidence that there is a positive cosmological constant.
 04:14: ... quick aside: the cosmological constant, written as lambda, is the thing you add to Einstein's ...
 04:26: If the cosmological constant exists, and is larger than zero, then dark energy is a real thing.
 04:32: ... so 3sigma confidence in a positive cosmological constant basically means this: if you repeated this experiment many, ...
 05:44: ... Laureates also claimed a significance of 3sigma or lower for a positive cosmological constant based on that early supernova data ...


20160622: Planck's Constant and The Origin of Quantum Mechanics
 14:21: This can change the power spectrum, so the distribution of the sizes of its blobs, which is really important for measuring cosmological parameters.


20160525: Is an Ice Age Coming?
 12:46: ... Lidster and a few others have wondered whether the energy lost in the cosmological redshift of photons could account for the energy gained by dark ...


20160518: Antigravity and the True Nature of Dark Energy
 01:24: This dark energy is described by the cosmological constant in the equations of general relativity.
 01:48: Today, we're going to talk about the simplest interpretation of dark energy, one where the cosmological constant really is constant.
 02:03: A constant cosmological constant represents a nonzero energy of empty space, a vacuum energy.
 06:26: This was actually Einstein's motivation for adding the cosmological constant in the first place.
 06:47: The cosmological constant was designed to work in the opposite direction to regular matter and energy.
 07:08: The effect of the cosmological constant is the combined effect of dark energy's own density and pressure.


20160511: The Cosmic Conspiracy of Dark Energy Challenge Question
 02:16: ... that are derived from those, dark energy is described by a positive cosmological ...
 06:20: Feel free to propose any solutions you come up with for this apparent cosmological coincidence.


20160504: Will Starshot's Insterstellar Journey Succeed?
 09:54: ... it's really fully described by a constant cosmological constant and so has an unchanging density with time, then no, space time ...


20160427: What Does Dark Energy Really Do?
 00:40: And this is only allowed if we introduce a new type of energy represented by the cosmological constant.
 01:33: During that expansion, it increases the wavelength of these electromagnetic waves, resulting in what we see as redshift, cosmological redshift.
 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.
 07:22: Add the cosmological constant to the first Friedmann equation, and we reconcile the left and the right side.
 07:36: This lets us interpret the cosmological constant as representing a sort of vacuum energy, a property of space itself.
 08:16: Expansion will only depend on the cosmological constant.
 08:50: But with a positive cosmological constant, the universe will eventually have a constant Hubble Parameter.
 09:23: If the cosmological constant stays constant, we can expect an exponential growth to continue.
 11:45: ... is so thoroughly verified in so many other ways, and the addition of the cosmological constant works so well to describe the discrepancy, it's strongly ...
 12:03: As we saw today, the cosmological constant solves two measure discrepancies.


20160420: Why the Universe Needs Dark Energy
 06:34: We missed the cosmological constants.
 06:50: ... we derive the first Friedmann equation with the cosmological constant included that's the lambda symbol, here we end up with this ...
 07:00: ... the cosmological constant is positive, this works on the side of the density term to help ...
 07:27: But what does this cosmologicalconstant thing actually do?
 07:31: The expression "cosmological constant" is a clue.
 07:43: The weird stuff described by the cosmological constant doesn't do that.
 08:04: ... some point, drop below that of this vacuum energy, as described by the cosmologicalconstant ...
 08:39: Soon, we'll get to the second and most compelling piece of evidence for dark energy and for the cosmological constant.


20160323: How Cosmic Inflation Flattened the Universe
 06:48: Actually, Einstein came up with the exact mathematical description that we need an antigravity term called the cosmological constant.
 07:30: The cosmological constant represents something that can happen to our spacetime.
 07:38: The cosmological constant adds some energetic stuff to empty space.


20150930: What Happens At The Edge Of The Universe?
 03:37: Given our best measurements of cosmological parameters, we think that the cosmic event horizon is around 16 billion light years away.


20150325: Cosmic Microwave Background Explained
 04:28: ... the wavelength of free streaming light through a process called cosmological ...


20150225: How Do You Measure the Size 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.
