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Something Is Hiding Beneath What We Call Reality — Transcript

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0:00What do you think of when I mention
0:03extra dimensions? [music]
0:04Do you think of portals in the fabric of
0:06space-time? Parallel universes? Do you
0:10think of your favorite sci-fi movie?
0:12Well, if you're anything like me, you
0:13struggle to think of anything concrete.
0:16After all, I live in three dimensions,
0:18four if you count time. So, I don't know
0:21what I'm supposed to be thinking of when
0:23I think of extra dimensions. But
0:25physicists, they're a bit different. The
0:28extra dimensions they have in mind are
0:30much stranger, more subtle, and in many
0:33ways more plausible. And they're using
0:35them to solve three of the biggest
0:37mysteries in modern physics: dark
0:40matter, dark energy, and even gravity
0:42itself. Increasingly, some researchers
0:45think that they might not need three
0:47separate [music] explanations for these
0:49mysteries at all.
0:50Instead, they all point towards one
0:53unsettling possibility: that reality
0:55contains hidden dimensions beyond the
0:58ones we can see.
0:59>> [music]
0:59>> At New Scientist, we've been following
1:01this idea pretty close to its birth
1:04[music] in the 1920s.
1:06As it's evolved from speculative
1:07mathematics into something that
1:09physicists are beginning to test. In
1:11fact, a recent discovery from the DESI
1:14telescope suggests that one of our best
1:16explanations for the expansion of the
1:18universe may be wrong. And some
1:21researchers think that hidden dimensions
1:23might be to blame.
1:25>> [music]
1:25>> In this video, we're going to be
1:26exploring what physicists actually mean
1:29by extra dimensions, why they keep
1:31appearing in attempts to explain the
1:32universe, how they could solve the three
1:35biggest unsolved problems in physics,
1:37and why scientists are now searching for
1:39the first real evidence that they exist.
1:42Because if they're right, extra
1:44dimensions wouldn't just be another
1:46strange, slightly arcane feature of
1:49physics, but they'd fundamentally change
1:51how we grapple with reality.
1:55Chapter 1: The discovery that revived an
1:58impossible idea.
2:01For decades, hidden extra dimensions
2:03seemed like one of physics' strangest
2:06ideas. But it basically keeps cropping
2:09up every single time physicists search
2:11for a theory of everything. When they
2:13try to merge or unify seemingly
2:16disparate forces of nature together. So,
2:19let's back up a bit. We know that there
2:21are about four fundamental forces in the
2:23standard model. There's gravity, which
2:25causes masses to attract.
2:27Electromagnetism responsible for light.
2:30The strong nuclear force that binds the
2:32building blocks of matter known as
2:34quarks into protons and neutrons. The
2:36weak nuclear force, which is a slightly
2:39strange one that's behind the decay of
2:41certain radioactive particles. And as
2:43scientists show how different
2:44fundamental forces could emerge from one
2:46bigger parent force, they need to write
2:49in the existence of extra dimensions
2:50[music]
2:51to serve as a connective webbing between
2:53these fundamental forces. But since the
2:551920s, [music] other have begun taking
2:58the idea of hidden dimensions one step
3:01further. Starting with a crack in our
3:04[music] best model of the universe. In
3:07the late 1990s, observations of distant
3:10exploding stars shocked astronomers by
3:13revealing that the universe is expanding
3:16at an accelerating rate.
3:17>> [music]
3:18>> These stars are called type 1A
3:20supernova, and they're known as
3:21something called standard candles in
3:23astronomy.
3:25We see that they all have the same
3:26intrinsic brightness to them.
3:28>> [music]
3:28>> And because light gets dimmer the
3:29farther away things are in a predictable
3:31way, we can measure huge distances in
3:34space with them. But scientists actually
3:37think that space is expanding, [music]
3:39causing the wavelength of light from
3:40these supernovae to stretch and become
3:43redder.
3:44>> [music]
3:44>> By measuring that stretch, we can infer
3:46how fast the space must be expanding.
3:49>> [music]
3:49>> In the '90s, measurements of this
3:51redshifted light told us that space was
3:53expanding really fast.
3:55>> [music]
3:56>> Too fast in fact, if you consider that
3:58all the matter in the universe should be
4:00actually gravitationally pulled
4:02together.
4:03To explain this rapid expansion,
4:06scientists theorized the existence of a
4:08mysterious repulsive substance capable
4:11of counteracting gravity.
4:12>> [music]
4:13>> They called it dark energy.
4:15>> Dark energy is one of the components of
4:18our universe. Um and we believe it is
4:20the the biggest component of our
4:22universe that makes up about 70% of the
4:25energy of the universe.
4:27>> [music]
4:27>> It's different from dark matter.
4:30Um and these two components are both
4:31called dark because basically we don't
4:34know what they are. So, that's a
4:35placeholder for our ignorance. And what
4:37dark energy does is it causes things to
4:41it's more of a repulsive force. So, it's
4:43causing the expansion rate of the
4:45universe to speed up. It's driving the
4:48universe apart.
4:49>> As for what this dark energy actually
4:51is, yeah, that's [music] when things get
4:53a bit tricky.
4:55In the decades since its discovery, it's
4:56been widely assumed that dark energy
4:58must emanate from something called the
5:00vacuum.
5:01>> [music]
5:01>> See, quantum mechanics states that empty
5:04space isn't actually empty. There are
5:07fields and particles constantly blipping
5:10in and out of existence faster than we
5:12could ever measure. But together, they
5:14result in an energy known as the vacuum
5:17energy. It's also been assumed that this
5:19vacuum energy is fixed and unchanging,
5:22which is why it's called a cosmological
5:24constant. A kind of fudge factor that we
5:26write into our models of cosmology to
5:29explain why the universe is actually
5:31expanding at an accelerating rate. And
5:34so far, it's explained the origins and
5:37evolution of our universe and matched
5:39perfectly with all manner of
5:41observations so far.
5:43Then,
5:43>> [music]
5:43>> in 2025, a powerful new telescope in
5:47called the Dark Energy Spectroscopic
5:50Instrument, or [music] DESI, changed
5:52everything.
5:53>> So, they're looking at, you know,
5:55galaxies and other, you know, bright
5:57objects in the sky, quasars and so on.
5:59The aim is to try to measure
6:02the expansion rate of the universe as a
6:04function of time. And
6:07once you know the expansion rate of the
6:08universe, then you can ask a lot of
6:09interesting questions. For example, what
6:11is driving this expansion? Is it Is it
6:13the cosmological constant?
6:15>> Mapping millions of distant galaxies
6:17[music] to trace a deep expansion of the
6:19universe with unprecedented precision,
6:22DESI's observations revealed something
6:24[music]
6:25completely unexpected. An expansion
6:28history that [music] suggested that dark
6:30energy can't be a cosmological constant
6:33after all. To be specific, researchers
6:36combined DESI data with the latest
6:38measurements for the type 1a supernovae
6:40that we talked about with a far older
6:42source of radiation
6:44>> [music]
6:44>> known as the cosmic microwave
6:45background. This background was formed
6:48when the universe was just 380,000
6:51years old. So, these measurements should
6:53tell us how it's expanding in these very
6:56early moments. What they found is two
6:59drastically different rates of
7:00inflation, which implied that the
7:03cosmological constant was changing.
7:06>> Once you include DESI to with other,
7:08you know, cosmological observations like
7:11the CMB, like supernovae, and so on,
7:13then
7:14you can no longer somehow model dark
7:17energy as a constant, as a cosmological
7:18constant. It seems like a better fit is
7:21provided by by a dynamical dark energy
7:24component. So, by a dark energy
7:25component that is changing with time.
7:27>> This has caused a crisis in cosmology,
7:30and the dust is barely settling. But at
7:33the moment, as more and more data
7:34trickles in, it really does look like
7:36this result is going to hold up. And if
7:38it does, it'd be with
7:40twist. The standard model of cosmology
7:43is wrong. Dark energy can't be a
7:46cosmological constant, and it seems to
7:49be depleting over time.
7:50>> [music]
7:51>> The DES results were genuinely shocking
7:53for cosmologists, even if they were
7:56exactly what many had been waiting for.
7:58Because the truth is that dark energy
8:00was always kind of a placeholder. Like,
8:02we don't really know what it is.
8:04And now, for the first time in 25 years,
8:06they have a clear steer on what its
8:08physical properties might actually be.
8:11>> So, this this substance is changing over
8:15the the history [music] of the universe.
8:17And that's really important for us,
8:19because if that's true,
8:21>> [music]
8:21>> it would be the first kind of handle we
8:23get into studying what this thing
8:25actually is, right? We can we can then
8:27delve deeper into building models that
8:29kind of fit that evolving behavior.
8:31>> With every great crisis comes great
8:33creativity.
8:34>> [music]
8:35>> Theorists have been exploring all kinds
8:36of exotic possibilities that could
8:38explain a changing value for dark
8:40energy.
8:41>> [music]
8:41>> For instance, dark energy could be a
8:43field similar to that that describes
8:45light or the nuclear forces holding
8:47atoms together. Or maybe dark energy
8:49could somehow interact with gravity or
8:51dark matter. But, one of the strangest
8:53and most intriguing ideas has been one
8:55that's been kicking around for a good
8:56while.
8:57>> [music]
8:57>> The idea that the universe might contain
9:00hidden extra dimensions. [music] Now,
9:03how could an invisible dimension
9:05possibly affect the expansion of [music]
9:07the entire universe?
9:09It's not immediately obvious, to be
9:11fair. And by now, you're probably
9:13thinking, "What do I actually mean when
9:16I talk about extra dimensions?" You're
9:19fascinated by expanding your [music] own
9:21personal horizons, and perhaps into new
9:23dimensions, then you're our kind of
9:25person. It's exactly the quest for a
9:27better understanding of the universe
9:29that New Scientist has been exploring
9:31[music] since 1956.
9:33We've worked across disciplines to
9:35explore [music] not just what we know,
9:37but what we don't know yet and why that
9:39matters. From human origins and ancient
9:42[music] cultures to breakthroughs in
9:44physics, space, and technology, we focus
9:47on ideas that reshape how we understand
9:49the [music] universe and our place
9:51within it. If you want to go deeper than
9:53a single story, a New Scientist digital
9:55subscription gives you access to all of
9:57this award-winning science and
9:59technology journalism. That includes
10:01daily reporting on new discoveries as
10:04they happen and in-depth features,
10:06sometimes commissioned by me, that
10:08unpack complex debates like this one
10:11long [music] after the headlines fade.
10:13To get a special discounted New
10:15Scientist digital subscription,
10:17>> [music]
10:17>> head to newscientist.com/youtube.
10:19And if you're drawn to the kind of
10:21scientific discoveries that [music] set
10:23your mind spinning to the farthest
10:25corners of space and time, then you're
10:27going to love this next part.
10:30Chapter two, [music] the dimensions we
10:32can't see.
10:34It's not too difficult to define a
10:36spatial dimension. Our universe has
10:38three, one that goes forwards and back,
10:41left and right, up and down. [music]
10:44Any other direction that we might choose
10:46to move can be described as a
10:48combination of these three directions.
10:51[music]
10:51There's also time, of course, and that's
10:54a funny one. We don't really have a
10:56great definition of what time is, but
10:59that's maybe a video for a future time.
11:02You just got to know that time is
11:04something that we move through and can
11:05help us define [music] the order that
11:07events occur in.
11:08Good so far? Not for long. We run into
11:11trouble when we try to imagine extra
11:13spatial dimensions. To explain this, I
11:16think I'll invoke an analogy that
11:18appears in a bizarre 19th-century
11:21novella called Flatland, [music]
11:23A Romance of Many Dimensions by Edwin
11:26Abbott. The story's protagonist is quite
11:28literally [music] a square that lives in
11:30a strictly two-dimensional world. One
11:33day the [music] square is visited by a
11:35sphere, which is of course a
11:37three-dimensional object. The square is
11:39unable to observe [music] the sphere's
11:41true form, seeing it only in
11:44cross-sections,
11:45>> [music]
11:45>> a dot that grows into a big circle
11:47before diminishing back to a dot again
11:49and disappearing. Gradually, the square
11:52makes [music] the horrifying realization
11:55that his 2D world might not be the full
11:57extent of reality. Those of you that
11:59like philosophy might think that this is
12:01quite similar to Plato's fear, that we
12:04only ever observe a single aspect of
12:06reality, which he compared to just
12:08seeing the shadows projected on a cave
12:10wall, never seeing the complex
12:12three-dimensional objects that cast
12:15them.
12:15>> [music]
12:15>> Scientists can empathize with this
12:18anxiety. What if we're in the same
12:20position as the square? [music]
12:22What if reality does contain dimensions
12:24that we can't access? Well, plenty of
12:27physicists argue that it could. Probably
12:30the most famous suggestion comes from
12:32string theory. Remember the beginning
12:34when I told you that physicists [music]
12:36want to unify the forces of nature to
12:38create one grand force to rule them all?
12:41Well, that requires that we reunite the
12:43currently clashing theories of quantum
12:45mechanics and general relativity, our
12:48two best theories of the universe.
12:50String theory for a long time was our
12:53best shot at getting that to play
12:54[music] nice. It basically says that
12:57fundamental particles like electrons and
12:59quarks are made of vanishingly small
13:02strings that vibrate. They're invisible
13:04because are curled up or compactified in
13:07multiple extra dimensions. [music]
13:09In this view, extra dimensions are
13:12everywhere. They just happen to be
13:14ludicrously small and tightly scrunched
13:16up that we can't detect them directly.
13:18>> Instead of thinking about point
13:20particles,
13:21we think about strings as the
13:22fundamental constituents
13:24of our universe. And uh strings have
13:27they can, you know, they can vibrate in
13:29many different ways. Each one of the
13:31vibrations of the string appears as a
13:33different particle to us humans who are
13:35much much larger than the size of the
13:36string. Everything comes from the
13:38vibrations of one string.
13:39>> And then there's another theory that
13:41says that our four-dimensional universe
13:43is [music] actually a cosmic membrane or
13:46brane floating in a higher-dimensional
13:48space [music] sometimes called
13:50hyperspace. In one version of this idea,
13:53the membrane constraining our universe
13:55is the edge between hyperspace
13:57>> [music]
13:57>> and nothing. That would put us right on
14:00the border of a cosmic void. Here, the
14:03fundamental particles that we're
14:04familiar with would be [music] the very
14:07ends of five-dimensional strings that
14:09live in hyperspace. But we'd never be
14:12able to see the entire [music] string,
14:14just like the square in Flatland would
14:16never be able to see any shape more
14:18complicated than a line. At this point,
14:21you're probably wondering why are
14:22physicists seemingly inventing these
14:24convoluted concepts and extra
14:26dimensions? Like, what are we trying to
14:29achieve here? It's questions like that,
14:31which is why string theory has received
14:33quite a bit of popular backlash. It
14:36sounds a bit unscientific to some
14:38people, a little bit like science
14:39fiction,
14:40>> [music]
14:40>> but that's not quite right. In fact, we
14:43see that they emerge quite naturally
14:45from our most ambitious and
14:47mathematically justified theories.
14:49>> [music]
14:49>> Indeed, the reason why physicists have
14:51been thinking about extra dimensions for
14:53decades is because they could solve a
14:56mystery that has [music] confounded us
14:58for more than a century.
15:01Chapter 3. Where is gravity going?
15:06Gravity.
15:07It might seem familiar and even mundane,
15:10but it's a bit of an oddball.
15:12>> Gravity is very different from the other
15:13fundamental forces. For one thing, it it
15:15is much weaker than the other
15:17fundamental forces. You know, any of the
15:18other forces, you can choose what
15:20particles talk to to strong force, what
15:22particles talk to the weak force, what
15:23particles talk to electromagnetism.
15:26Uh gravity is universal, so you cannot
15:27choose uh what talks to gravity.
15:30>> Consider for instance the fact that a
15:32small fridge magnet is able to
15:35counteract the gravitational pull of the
15:37entire planet [music]
15:38to stop itself from falling off. That's
15:41because gravity is 10 to the power of 40
15:43times weaker than the electromagnetic
15:45force.
15:46Nobody really knows why.
15:49That's not to say that physicists don't
15:50have ideas. They always do. One of the
15:53most intriguing is that gravity is so
15:55bizarrely weak because unlike the other
15:57three forces, [music]
15:59it leaks out into extra dimensions.
16:01First proposed in the late 1990s by
16:04theorists Lisa Randall and Raman
16:06Sundrum, the idea is that our
16:08four-dimensional universe is actually a
16:10brain world floating in a much
16:13higher-dimensional hyperspace.
16:15They argue that while matter and light
16:18would be trapped on the brain, gravity
16:20could escape into a higher dimension
16:22beyond.
16:23>> The idea is that our universe is
16:25confined to that sheet of paper. So
16:27everything you know is on that sheet,
16:29which here is representing [music]
16:31four dimensions. Obviously, your sheet
16:33in your mind only has like two
16:34dimensions.
16:35But that somehow gravity is able to
16:37propagate into the box.
16:39>> In which case, we would only experience
16:41a diluted version of gravity and a
16:44fraction of the force's true strength.
16:46All of which goes to show that higher
16:48dimensions aren't just wild figments of
16:51the imagination. They're taken seriously
16:53by many theorists [music]
16:55because they could plausibly solve one
16:57of the deepest problems in physics.
16:59[music]
17:00And not just one as it happens, because
17:02in recent years, physicists have come to
17:04realize that extra dimensions could also
17:06solve something even more mysterious.
17:09Dark matter.
17:12Chapter 4: The Hidden Universe.
17:16Pretty much all our cosmological
17:18observations seem to suggest that the
17:20normal matter we can see, you, me, the
17:23planets, the stars, the galaxies, is far
17:26outweighed by the existence of invisible
17:29matter. [music]
17:30When we measure the rotation of
17:32galaxies, we find that the material on
17:34the outer rim rotates very quickly.
17:37It doesn't make sense if we consider
17:39that the matter we see is clustered
17:41[music] in the middle of galaxies. So,
17:44there must be some sort of invisible
17:46matter distributed in the outer
17:48perimeter of galaxies that causes those
17:51regions to spin much faster than we
17:53expect.
17:54We also have observed light bending
17:56around dark regions of space, seemingly
17:59around nothing. Another hint of what
18:01scientists call
18:02>> [music]
18:02>> dark matter.
18:04>> So, the dark matter is is one of the I
18:06don't know, it's one of the biggest
18:07mysteries, you know, that we have. It's
18:09one of the biggest unanswered questions
18:10that we have
18:11uh in in cosmology and physics. But,
18:13it's dark, so we have really no way of
18:15of probing it by means of the
18:17experiments that we usually do.
18:18>> We call this dark matter because it
18:20neither absorbs nor emits light. But, we
18:23think that it makes up 80% of all matter
18:26in the universe.
18:27Without it, we know that galaxies just
18:29don't have enough gravity to hold
18:31themselves together.
18:32And yet, just as with dark energy, we
18:34don't really know what dark matter is.
18:37Despite the decades [music] of effort
18:39trying to figure that out, to find the
18:41exotic particle or particles that it's
18:43made of, we remain stumped as to its
18:46true nature. But, a new possibility has
18:48recently emerged in the form of, you
18:50guessed it, an extra dimension. In 2022,
18:54Cumrun Vafa, a theorist at Harvard
18:56University, and his colleagues proposed
18:58a model in which spacetime has a large
19:01hidden dimension.
19:02>> So, I and others uh
19:04so, Prateek Agrawal and Cumrun Vafa, we
19:06were studying a model
19:08uh
19:08which which is uh motivated by uh by
19:11string theory, by our current
19:13understanding of string theory. Because
19:14the dark energy density that we observe
19:16is so small, then we think, yeah, and
19:18other people have also argued in
19:19different papers that there should be
19:21uh, you know, a large extra dimension.
19:23>> This one would be curled up like those
19:25minuscule ones from string theory, only
19:27way bigger. As large as a micrometer, a
19:30thousandth of a millimeter. Baffa and
19:32his colleagues suggest that hypothetical
19:34particles of gravity, known as
19:36gravitons, produced soon after the Big
19:39Bang, could have escaped into [music]
19:41this dark dimension.
19:42>> A graviton is a hypothetical particle
19:45that mediates the force of gravity. One
19:47way to think of a graviton is that it's
19:48just a ripple in in in space-time.
19:50[music]
19:51>> And although we would never be able to
19:53detect them directly, their
19:55gravitational influence would be felt in
19:57other dimensions, like our universe,
20:00>> [music]
20:00>> where it helps to shape galaxies and
20:02galaxy clusters.
20:03>> And so, if you have a graviton that has
20:06uh, that that propagates along this
20:08extra dimension, then uh, it would look
20:10like a massive particle to us.
20:12>> The proposal then is that dark matter
20:15may not be a new particle after all, but
20:17rather the gravitational effect of dark
20:20gravitons concealed in the dark
20:22dimension. What's really striking about
20:25all of this is that when you think about
20:27it, the same idea keeps cropping up
20:29again and again. [music]
20:31Dark matter, dark energy, and the
20:33weakness of gravity. But what's
20:36different now is that there are genuine
20:38promising pathways to proving that extra
20:41dimensions might actually exist.
20:45Chapter 5, the hunt for hidden
20:47dimensions.
20:49For all that extra dimensions could
20:51plausibly resolve several big questions
20:53about the deepest workings of reality,
20:55there's never been a realistic prospect
20:57of actually testing these theories
20:59because there's been no realistic way to
21:01detect hidden dimensions. That's
21:03actually one of the biggest criticisms
21:05people have of string theory. But over
21:07the past few years, researchers have
21:09developed several techniques that could
21:11finally snare some proof. In [music]
21:14fact, physicists are now actively
21:16searching for signs of them in our
21:17four-dimensional universe.
21:19>> [music]
21:20>> One possibility is that we can spot an
21:22extra dimension by watching gravity in
21:25the form of gravitons leaking into it.
21:28We have a chance to do that thanks to
21:30super sensitive instruments
21:31>> [music]
21:31>> capable of detecting gravitational waves
21:34or ripples in space-time
21:36>> [music]
21:36>> caused by the epic collision between
21:38black holes in the distant cosmos. If
21:42you could observe these waves diminish
21:43in power as they swish towards us, that
21:46would be a sign that gravity is leaking
21:48into an extra dimension.
21:50What we need are more collisions between
21:52two neutron stars because they allow
21:55astronomers to see both gravitational
21:57waves as well as the visible light
21:59produced.
22:00>> [music]
22:00>> This allows us to calibrate how far the
22:03collisions were.
22:04If gravity is leaking into extra
22:06dimensions, the gravitational wave
22:08signal would arrive appearing weaker
22:11than expected as if the source was
22:13further away than it really was.
22:15Another option is to look harder at the
22:17large-scale structure of the universe.
22:20The arrangement of galaxies is
22:21especially sensitive to the laws of
22:23gravity. So, if gravity escapes into
22:26higher dimensions, we would see
22:28signatures of that in the way that
22:30galaxies cluster. Cosmologists like
22:32Tessa Baker at the University of
22:34Portsmouth are already running
22:36simulations on how extra dimensions
22:38could affect galaxy clustering.
22:41>> [music]
22:41>> The plan is to then compare it with ever
22:43more precise observations to spot any
22:45tiny differences that would give them
22:47[music] away.
22:48Extra dimensions may even reveal their
22:50presence in high-energy particle
22:52collisions such as those at the Large
22:54Hadron Collider near Geneva in
22:56Switzerland.
22:57>> [music]
22:57>> If the hypothetical graviton or even
23:00familiar force carriers like the W and Z
23:03bosons that carry the weak nuclear force
23:05can move through hidden dimensions, they
23:08wouldn't just have momentum in three
23:10dimensions we can see, but also the
23:12extra ones that we can't. For us, that
23:15would show up as extra energy in the
23:17particles we observe.
23:19And because energy and mass are
23:20equivalent as per the famous equation E
23:23= mc squared, that would make the
23:25particles behave as if they were heavier
23:28than we would expect. In practice, we
23:31would expect to see look-alikes of these
23:33familiar force carrying particles with
23:35the exact same properties as the ones
23:37that we know and love, but with two or
23:39three times more mass than usual,
23:41[music] depending on the number of extra
23:43dimensions out there. Intriguingly, it
23:46may be that we've already seen the first
23:48signs of an extra dimension.
23:52Chapter 6, the first signs of a dark
23:55dimension.
23:56Those DESI results we mentioned earlier
23:58are showing that dark energy, the
24:00mysterious stuff thought to be driving
24:02the accelerating expansion of the
24:04universe, might [music] be weakening.
24:06Well, that's just what Vafa and his
24:08colleagues predicted back in 2022 when
24:11they proposed that the universe contains
24:13a large extra dimension. [music]
24:15The researchers argued that the size of
24:18this dimension gradually changes over
24:20cosmic time, [music]
24:22and that as it does, the amount of
24:24energy in the universe changes, too.
24:26They said at the time that this would
24:28show up as a dark [music] energy that
24:30slowly weakens. Then several years
24:32later, those DESI results came in.
24:34They're not concrete evidence for the
24:36existence of an extra dimension, but
24:39they're a good start. The next step
24:41would be for theorists to build a
24:43sharper model that makes more precise
24:45predictions distinct from explanations
24:47for weakening dark energy
24:49>> [music]
24:49>> that don't involve extra dimensions, and
24:52to find observational evidence in
24:54support of them. If weakening dark
24:56energy really is our first [music] clue
24:59that extra dimensions exist, then
25:01understanding dark energy has suddenly
25:03become one of the most important
25:05problems in physics.
25:07>> [music]
25:07>> In our next video, you can see more of
25:09our chat with cosmologist Tessa Baker,
25:11who unpacks the latest DESI discoveries,
25:14where they may have broken our best
25:16model of the universe,
25:17>> [music]
25:17>> and what dark energy could actually be.

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