
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 equations of ...
 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 energy as ...
 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 is dark ...
 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 could ...
 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 energy, ...


20220525: The Evolution of the Modern Milky Way Galaxy
 18:10: ... the Schwarzschild metric isn’t really valid in a universe with a cosmological constant. There would indeed be an additional effect due to the tiny vacuum ...


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 razor you ...


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


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 the ...
 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 value ...
 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 that our ...
 03:31: ... refined his estimate of the cosmological constant to be the value that most astronomers across the multiverse would ...
 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 class was an ...
 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 doomsday ...


20191202: Is The Universe Finite?
 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 ...


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 constant ...


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 what if ...
 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 we can ...
 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 factor of ...


20190320: Is Dark Energy Getting Stronger?
 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 largest ...
 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
 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 the ...
 08:50: ... Farnes acknowledges that his proposal gives a negative cosmological constant that ultimately decelerates, but there’s some contradiction because he ...
 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 turnaround ...


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 equations of ...
 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, many times, ...
 05:44: ... Laureates also claimed a significance of 3sigma or lower for a positive cosmological constant based on that early supernova data ...


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 constant. ...


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 doesn't ...


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.
 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 suggested this ...
 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 little ...
 07:00: ... the cosmological constant is positive, this works on the side of the density term to help bring ...
 07:31: The expression "cosmological constant" is a clue.
 07:43: The weird stuff described by the cosmological constant doesn't do that.
 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.
