What is the universe made of? If you answered stars, planets, gas and dust, you'd be dead wrong. Thirty years ago, scientists first realized that some unknown dark substance was affecting the way galaxies moved. Today, they think there must be five times as much dark matter as regular matter out there. But they have no idea what it is — only that it's not made of atoms, or any other matter we are familiar with. And Dark Matter is not the only strange substance in the Universe — a newly discovered force, called Dark Energy, seems to be pushing the very fabric of the cosmos apart.
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LearningTranscript
00:00All around the universe, stars are exploding.
00:07They are cosmic catastrophes.
00:11But to these scientists, they are beacons in the depths of space.
00:16They illuminate an epic battle between two mysterious and invisible forces.
00:22To one we owe our very existence.
00:26The other is trying to tear us apart.
00:29Now we're in a struggle of our own.
00:32To understand these colossal forces.
00:35To learn to see beyond the darkness.
00:44Space.
00:45Time.
00:47Life itself.
00:51The secrets of the cosmos lie through the wormhole.
01:00You.
01:01Me.
01:02The sun.
01:04Stars.
01:06Everything we see has one thing in common.
01:09We're all made of atoms.
01:11Atoms make up almost all the matter in the known universe.
01:15But there is a whole lot more to the cosmos.
01:20A side we're only just beginning to see.
01:23Our bodies.
01:25Our homes.
01:27Our world.
01:29Even the vast void of space is teeming with a mysterious substance.
01:35A form of matter so strange that many scientists once doubted its very existence.
01:42But in 2009, an incredibly sensitive particle detector caught the first glimpse of it.
01:50It's an earth-shaking discovery.
01:52It's an earth-shaking discovery.
01:55And it's forcing us to radically reassess our place in the universe.
01:59And even our eventual fate.
02:04As a boy, I used to lie in my room at night, gripped by fear that something was out there in the darkness.
02:12Was that a demon?
02:14Or my clothes slung over the back of a chair?
02:17I'd shine my flashlight at the furthest corner of the closet.
02:21Hoping to catch the phantom presence I sensed lurking there.
02:26Well, I never did find anything in the shadows.
02:29But just because you can't see something doesn't mean there's nothing there.
02:40In the 1960s, a young astronomer called Vera Rubin decided to explore an area of space that was little studied.
02:48I had two children, one almost two and one almost four.
02:52And I didn't like the idea of competing with astronomers for real hot topics.
03:01Vera Rubin knew if she studied something sexy like black holes, other astronomers would end up beating her to publication.
03:08So instead, she began surfing the galactic backwaters.
03:13I'm not sure I really know why I was studying galaxies, except they seemed very mysterious to me.
03:19And there was not a lot known, especially about their motions, almost nothing.
03:25Vera first trained her telescope on the Milky Way's closest galactic neighbor, Andromeda.
03:32Like most galaxies, it had a dense central bulge of stars.
03:37She expected the billions of stars circling around this central bulge to orbit just like the planets in our solar system,
03:44obeying Isaac Newton's laws of gravity.
03:47The further away they are from the center, the slower they orbit.
03:58This is a model of the solar system that my father built for me about 40 years ago when he retired.
04:05It shows exactly what Newton knew from his theories.
04:09The four that you're seeing here, Mercury, Venus, Earth and Mars.
04:14Mars is going the slowest, the Earth the next slowest.
04:18Mercury is the most rapidly moving.
04:22Because the force of gravity is considerably less for Mars than it is for Mercury, the orbit is correspondingly slower.
04:33This is exactly the pattern Vera expected to see when she studied stars as they orbited in their galaxies.
04:40The further from the center, the slower they should be moving.
04:44But that's not what Vera found.
04:49It took us about two years to get velocities of 90 stars in the Andromeda galaxy.
04:56And the results were rather startling.
05:00We found that all of the stars were moving at the same velocity, the same number, 250 kilometers per second.
05:09For the next few years, every galaxy Vera looked at gave her the same seemingly crazy results.
05:17All the stars, all the way to the edge of the galaxies, were moving at the same speed.
05:24Completely different from the way the solar system works.
05:28The only explanation was that the force of gravity did not get weaker the further a star was from the center of a galaxy.
05:36But that could only happen if the galaxies had more mass than astronomers could see.
05:44The explanation was that there must be very significant amounts of matter that are invisible.
05:52In fact, perhaps 90 or 95 percent of the material in the galaxy is invisible.
06:02This was a truly revolutionary idea.
06:06Galaxies might be filled with an unseeable substance.
06:10Something scientists could only think to call dark matter.
06:15But such a radical theory demanded ironclad evidence.
06:20Soon, dozens of astronomers were checking Vera's observations,
06:24either struggling to disprove her or scrambling to discover what or where this mysterious dark matter might be.
06:32I did find it amazing and amusing that I had picked this field because I was interested in doing something that no one would care about.
06:42And suddenly I was involved with lots and lots of astronomers who had ideas and observations and it was a hot topic.
06:56Across the Atlantic and England, leading cosmologist Carlos Frank began to investigate the idea of dark matter,
07:03using not telescopes, but equations.
07:07Take Newton's laws of gravity and feed them into a highly sophisticated computer simulation.
07:13Then go for lunch.
07:17This is a cosmology machine, a very large supercomputer whose only purpose is to simulate the universe.
07:24It's made up of 1,300 computers all working together.
07:29Even then, it takes months to complete a simulation of a small part of our universe.
07:36This is awesome computing power, almost beyond imagination, but that's what it takes if you want to emulate the universe.
07:46Carlos started out his simulation with what scientists think the early universe was made of,
07:51a giant cloud of gas floating in empty space.
07:57Then he sat back and waited to see if his cosmology machine could build a galaxy like the ones we see.
08:04What happens if you try to make a galaxy in a computer using simply the material that we can see?
08:10What happens is you end up with a failed galaxy.
08:14Stars form, they evolve, the biggest ones explore a supernovae and they inject so much energy,
08:21but there just isn't enough gravity to keep these gases together,
08:25so the galaxy essentially blows itself apart.
08:29The gas dissipates, leaving very little behind.
08:32This is not how a universe is made.
08:38So Carlos started to add dark matter to his equations,
08:42first a little, then more, and eventually five times as much of it as visible matter.
08:49After several weeks, something strange came out of the cosmology machine.
08:55Strange because it was so familiar.
08:58This is a computer simulation of the formation of a galaxy,
09:02now with invisible dark matter and gas shown here in green.
09:06About a billion years after the Big Bang, clumps of dark matter formed,
09:10gas fell into these clumps, turned into stars,
09:14but attracted by the force of invisible dark matter gravity,
09:18these clumps came together, fused to build ever larger structures,
09:24so that 10 billion years later, a beautiful spiral galaxy like our own Milky Way was formed.
09:31Carlos has shown that galaxies should form when filled with dark matter,
09:36but is there any way to prove that this is what actually happened?
09:45In Edinburgh, Scotland, Richard Massey is still trying to answer that question
09:51and is pioneering a new way of detecting dark matter,
09:55gravitational lensing.
09:58It's all thanks to the genius of this man.
10:02Albert Einstein saw space in a new way,
10:06as a bendable, malleable material that is influenced by gravity.
10:11Anything that has mass, a star, or a galaxy,
10:16can bend the fabric of space and act like a lens.
10:21As it bends space, so the light traveling past it is also bent.
10:29Dark matter doesn't reflect light, it doesn't absorb light, it doesn't emit light.
10:33Light just passes straight through it, unaffected.
10:36So we have to look for something else.
10:38The way it affects gravitationally, things around it that we can see.
10:42This idea of light being deflected and bent by warped space-time sounds crazy,
10:46but actually it's very familiar.
10:48We see light being bent all the time,
10:50every time you look through the bottom of a wine glass.
10:53Let me show you what I mean.
10:55Although the bottom of the wine glass is transparent
10:57and light passes straight through it,
10:59you know it's there because of these distorted images in the background.
11:02Dark matter is exactly the same.
11:04It bends light through a different physical effect,
11:06but the net result is the same.
11:08That these images of very distant galaxies appear distorted
11:11whenever there's some dark matter in front of them.
11:15For two years, Richard has been leading a team of international astronomers
11:19and directing a fleet of telescopes to scour one section of the night sky
11:24for every single visible gravitational lens arc.
11:30So what we're seeing here is gravitational lensing in action.
11:33All of the yellow blobs that we see are galaxies in a group
11:36which are fairly near to us.
11:38These strange shapes, these arcs, are actually very distant galaxies,
11:41and the light from those distant galaxies
11:43has to pass near the yellow blobs, which are foreground galaxies.
11:46And because they bend space,
11:48they bend the light rays from the distant galaxies,
11:50distorting their images into these circular, arc-like patterns.
11:55But when Richard runs calculations
11:57on the amount the light from the distant galaxies is bent
12:01and compares it to the visible mass of the foreground galaxies,
12:05he finds it's warped much more than it should be.
12:08His conclusion?
12:10An invisible shroud of dark matter must engulf all the galaxies.
12:15From the amount of gravitational lensing they produce,
12:18we find that there's about five times as much of this dark matter
12:21as there is the ordinary material.
12:23So what we can see is but the tip of an iceberg in the universe.
12:26Most of it is dark matter.
12:31Everywhere astronomers look,
12:33they are starting to sense the heavy presence of dark matter.
12:38But Richard Massey is about to go a huge step further
12:42and take the first picture of this cosmic giant.
12:45And when he does,
12:47we discover that dark matter is more important to us
12:50than we ever imagined.
12:57This is a real picture of the sky.
12:59The Hubble Space Telescope sees an incredible number of galaxies
13:03with minute precision,
13:05so we're able to measure their shapes very accurately.
13:08And it's the distortion in those shapes
13:10from when the light from those galaxies is bent on its way to us,
13:13past dark matter,
13:15that lets us map out the invisible part of the universe.
13:20As it bends its way towards Earth,
13:23past galaxy after galaxy,
13:25that light traces the contours of a cosmic map of dark matter.
13:33For one section of the universe,
13:35he's rendered the invisible visible.
13:39For the first time, this is the map in 3-D
13:41of what the universe actually looks like,
13:43what the main constituents of the universe are.
13:45And if some alien were to come to our universe and start to look around,
13:48and if he could see all of the constituents of our universe,
13:51this is what he would say it would look like.
13:53The cosmic soup of dark matter.
13:56Wherever the soup is thickest, that's where galaxies form.
14:01Here we see the same map of dark matter, just seen end on.
14:05On the left, what we see is actually the positions of all the galaxies
14:08and all the gas in the universe, all the ordinary material.
14:11So wherever there's a giant cluster of galaxies,
14:13there's a large concentration of dark matter.
14:15Here we have a large cluster of galaxies,
14:17and here is the corresponding halo around it of dark matter.
14:20What we find when we overlay them
14:22is that they're in the same place that the ordinary matter
14:25lives inside this dark matter scaffolding.
14:29And what Richard has done for one corner of the sky,
14:32Carlos Frank has now done with a simulation of the whole universe.
14:37We can see here the intricate patterns that the dark matter forms,
14:42this network of filaments and lumps
14:45that we refer to as the cosmic web.
14:48It is in these clumps of dark matter
14:50that galaxies like the Milky Way would have formed
14:53as these gases cooled and condensed inside them,
14:56eventually producing stars.
14:58The dark matter is the skeleton of the universe.
15:02It is the scaffolding that allows galaxies to form.
15:08The implication is extraordinary.
15:11Dark matter has allowed everything we know to form.
15:17Without dark matter, there would be no galaxies.
15:19Without galaxies, there would be no stars.
15:21Without stars, there would be no planets.
15:23Without planets, there would be no life.
15:29Dark matter, an idea that came out of left field 40 years ago,
15:33is now much more than an idea.
15:36It turns out to be crucial to our very existence.
15:40And slowly, we're closing in on how it works.
15:44We know it doesn't interact with light.
15:46We know it feels the force of gravity.
15:50Then, in 2004, a telescope caught this image,
15:54and we learned something new about dark matter.
16:00Four billion light-years away,
16:02that's one-third of the way across the known universe,
16:06two clusters of galaxies are colliding.
16:09It's a strike of incredible power.
16:13Trillions of stars hurtle past one another
16:16at 3,000 miles per second.
16:19One galaxy cluster is distorted by the shock wave
16:22into a bullet shape and gives the event its name.
16:26The bullet cluster collision.
16:28It's the kind of cosmic spectacle that delights astronomers.
16:32But even more exciting,
16:34it reveals dark matter to be stranger
16:37than anyone could possibly have imagined.
16:40This cluster is actually two separate clusters of galaxies,
16:43both of which contain dark matter, shown in blue,
16:46and ordinary material, here shown in pink.
16:48And when they smashed into each other,
16:50it was like a giant cosmic car crash,
16:52that the ordinary material slowed down.
16:54It started glowing in X-rays, and it slowed down,
16:57it stopped basically close to the point of impact.
17:00But the dark matter, shown in blue,
17:02kept going after the impact and ended up further away
17:05from the point of collision than the ordinary material.
17:08So what's going to happen?
17:10We need a crash course in galactic collisions.
17:13So in this experiment, we're going to represent
17:15the ordinary material with the cars,
17:17but we're going to add an extra ingredient,
17:19these particles representing dark matter.
17:22We're going to see how they behave differently
17:24during a collision.
17:39CRASH!
17:53The ordinary matter behaves just like you'd expect it to.
17:56It stops. Dark matter is fundamentally different.
17:59The dark matter doesn't interact in any way,
18:01so it just passed straight through the collision.
18:03It kept on going, and we now see it
18:05further from the point of impact than the ordinary material,
18:07which stopped.
18:09The bullet cluster is the best proof that we have
18:11that all this missing material that astronomers have seen
18:14for decades has very different properties
18:16to the ordinary matter.
18:18It's something completely new, and science knows
18:20very little about it.
18:22It doesn't feel ordinary matter. It doesn't even feel itself.
18:24And when the two lumps of dark matter smashed into each other,
18:27they didn't even notice. They just passed straight through.
18:30Cosmic disasters halfway across the universe
18:33have proved that dark matter is out there,
18:36and unlike anything we know,
18:38invisible, intangible, almost like a ghost.
18:44Could we ever devise a way to see
18:46a piece of this elusive substance?
18:49Some scientists believe it may be possible,
18:52but to find it, they're not looking up in the heavens.
18:55They're headed down into the deep, dark bowels of the Earth.
19:01We live in a universe of matter and light.
19:05Matter that makes us, and light that sustains us.
19:09But now we know that's only a small fraction of reality.
19:13Our universe is also teeming with a mysterious substance
19:17we call dark matter.
19:20We can't see it. We can't touch it.
19:24But it's everywhere.
19:26Billions of dark matter particles
19:28pass through our bodies every second.
19:31Now, if science can somehow
19:34track one of these particles and study it,
19:38then we might finally understand
19:41what most of the universe is made of
19:44and what this really means for us.
19:48In the past century,
19:50physicists have worked out that all matter
19:53is built from about 20 basic subatomic particles.
19:57They go by names like bosons, electrons, quarks, and neutrinos.
20:03But they also suspect other, more exotic particles exist.
20:08There are plenty of theories out there
20:10for what dark matter might be.
20:12We're gradually working through the list
20:14and trying to rule them out one by one.
20:16That's the scientific method.
20:18The most, or the favorite theory for what dark matter is
20:21is a supersymmetric particle.
20:23That is to say that all the ordinary particles that we know about
20:26have this sort of a mirror image
20:28that there's this extra set of particles
20:30that is in the dark sector
20:32that don't interact in any way with the ordinary material
20:34except through the force of gravity, which is very weak.
20:41Scientists have another name for these dark matter particles.
20:46Weakly Interacting Massive Particles.
20:50WIMPs, for short.
20:52WIMPs hardly ever interact with atoms of normal matter,
20:56so capturing and studying them is really hard.
21:01And since the world is full of particles of regular matter,
21:05it's all too easy to end up snagging them by mistake
21:09and letting the WIMPs get away.
21:15Dan Bauer has found the perfect place to hunt for WIMPs.
21:19Down an abandoned Minnesota iron mine half a mile underground.
21:29We're now heading down underground into the Sudan Underground Laboratory.
21:33It'll be about a three-minute trip down.
21:36This is the same way the miners used to go down before 1960
21:41to do the iron mining.
21:43It's about 23, 41 feet underground, or about half a mile.
21:48It's not the first place you'd think of to do physics,
21:51but on the other hand, we're down here for a reason.
21:54We're down here to avoid the particles coming from space,
21:57the so-called cosmic ray particles.
22:00We've arrived at level 27.
22:05You'd think half a mile of bedrock would be enough of a shield
22:08from background noise to make WIMP hunting a cinch.
22:11But it's not.
22:14The WIMP detectors are buried inside several more feet of solid metal
22:19and heavy plastic shielding.
22:22Throughout the rock of the cavern, the materials around us,
22:25even in us, there are small amounts of radioactivity.
22:28Those particles, if they got to our detectors,
22:31would be a huge background such that we would never be able to see WIMPs.
22:35And this shield prevents those particles from reaching the detectors
22:39because we're trying to find WIMPs, not background particles.
22:45Inside the shield is a stack of 18 hockey-puck-sized crystals
22:50of solid germanium.
22:52They're designed to pick up the faintest of vibrations
22:56if and when a WIMP bumps into one of the germanium atoms.
23:00To have a chance of doing that,
23:03they have to be ultra-pure and ultra-cold.
23:06This is our model of a germanium crystal.
23:09These tennis balls represent the germanium atoms in the crystal,
23:13and at room temperature, what's happening is that
23:16all of these atoms are moving relative to one another.
23:19This is what we know as heat.
23:21What would happen if you tossed a WIMP into this crystal?
23:25You wouldn't even notice the difference
23:27because the crystal is vibrating so much.
23:29However, if I cool this crystal down to very near absolute zero
23:35so that the motion of the atoms stops,
23:38then if I toss our WIMP into the crystal,
23:42I see the vibration of the crystal,
23:44and that's the signal we're looking for.
23:47Looking for particles that hardly ever interact with normal matter
23:52is not a job for the impatient.
23:54There are millions of WIMPs passing through us every second,
23:58and because they're weakly interacting, they do exactly that.
24:01They pass right through us and just go on their way.
24:04They pass through the entire Earth and go on their way.
24:07We maybe expect one or two of these
24:09to interact in our detectors per year.
24:11It's an incredibly low rate.
24:15To help prevent false positives,
24:18the data is blindly collected in a sealed box
24:21on the hard drive of a computer.
24:24No one on the team is allowed to search it for WIMP signals
24:28for an entire year.
24:30And then they look and hope.
24:35In 2007, when we last opened the box and found nothing,
24:39it was certainly a bit disappointing
24:42because we had been running the experiment for a year,
24:45but it had taken us almost seven years to build the experiment,
24:49and so it would have been nice to find something at that point.
24:53But after seven years and tens of millions of dollars,
24:57Dan and his team of WIMP catchers were not about to give up.
25:02And in late 2009,
25:05they opened the box on another entire year's worth of data.
25:11What you see in this region
25:13is where the background radiation would be.
25:16These are events we're not interested in.
25:18We know that they're not WIMPs.
25:20In this area, bordered by the magenta and above this green line,
25:24is where we should see WIMPs.
25:27If any of these are WIMP candidates,
25:29then they will turn red when we open the box.
25:34So let's just click through.
25:36This detector doesn't have any red dots in that area,
25:39so there are no WIMP candidates.
25:41Same with this one and this one.
25:44Ah, but look here.
25:46We do have one that appears right here in the region
25:49that we would expect a WIMP to appear.
25:53Nothing here, nothing here.
25:56Oh, but look right down here.
25:58We have one that just made it
26:00into the region that we think is the WIMP region.
26:04Two events.
26:06Two possible WIMP impacts
26:08in one year of 24-hour-a-day detecting.
26:13For the first time,
26:15we may have actually trapped pieces of this elusive dark matter.
26:21This could be a giant leap toward understanding
26:24what dark matter really is.
26:28But Dan's not 100% sure that what he has are even WIMPs at all.
26:33So the search must go on.
26:38It's exciting, but you have to temper that excitement as a scientist
26:42and realize that you haven't proven it yet.
26:44If we see half a dozen WIMPs, say, in this next run,
26:48what we will be able to say is,
26:50definitively, there is dark matter getting down to this level at Sudan,
26:55which means that Earth is surrounded by dark matter
26:58and the Milky Way has dark matter.
27:00If a WIMP is found, it opens up a whole new range of physics.
27:03If there is this extra supersymmetric class of particles out of there,
27:06they're doing their own interactions, they're doing their own thing,
27:09and that's really, since it's the main stuff in the universe,
27:11that's what's going on in the universe.
27:13We're just, you know, the little bit on the side.
27:16But just as scientists begin to feel they're getting a handle on dark matter,
27:20they discover something very strange.
27:23Dark matter may be the stuff that's allowed our galaxy to form,
27:27but it's not the end of the story.
27:30At the dawn of the 21st century,
27:32a space probe found something else hiding in the darkness.
27:36While dark matter strives to hold us all together,
27:39this force might be preparing us for a new era.
27:44This force might be preparing to destroy the entire universe.
27:55We now know that the visible universe is nothing more than a layer of foam
28:01floating on a vast sea of dark matter.
28:05Astronomers find themselves adrift on this unfamiliar ocean.
28:09Saul Perlmutter has been navigating these waters for the past two decades,
28:14trying to determine what dark matter might mean for our eventual fate.
28:20As a young student in physics,
28:22I very much wanted to measure something that seemed fundamental,
28:26which is, what's the fate of the universe?
28:28Will the universe last forever, or someday will it come to a halt and collapse?
28:32Saul chose to walk in the footsteps of the 20th century's most illustrious astronomer,
28:37Edwin Hubble.
28:39Back in the 1920s, Hubble began a meticulous survey of dozens of galaxies in the night sky.
28:47But he noticed something strange.
28:50Almost all of the galaxies were tinged red.
28:54Just as sound coming from objects moving away from us gets lower,
29:01light gets redder.
29:04Hubble deduced that every galaxy in the universe is actually hurtling away from us.
29:11There was only one conclusion.
29:13The universe must be expanding.
29:16But he couldn't tell how fast.
29:19Why?
29:20Because galaxies that are close and relatively dim
29:23look very similar to those that are far away but very bright.
29:26So he couldn't judge their distance.
29:30Of course, the tricky thing is that you need to know how bright the actual galaxies are
29:35if you're going to tell how far away they are.
29:37If you're a sailor out at sea and you're looking at a distant lighthouse through the fog,
29:41you don't know whether it's a very bright lighthouse and you're very far away
29:45or whether it's a very faint lighthouse and you're very nearby.
29:48This is a fundamental problem, then, that astronomers have had to struggle with
29:51through the last centuries.
29:54But there is a solution to this problem.
29:58Astrophysicists have known since the 1980s about a particular type of star explosion
30:04called a Type Ia supernova.
30:08When a star slightly bigger than our sun runs out of fuel to burn,
30:13it shrinks down into a dimmer, denser state known as a white dwarf.
30:19There it hangs in a netherworld between life and death.
30:23But the dwarf still has the potential to spring back into life if it can find fresh fuel.
30:30When a white dwarf is part of a two-star system, the neighboring star can provide that fuel.
30:37Once the gravity of the white dwarf has snagged enough mass from its companion,
30:42there's no turning back.
30:44It explodes.
30:48The temperature rises to more than a billion degrees,
30:52and most of its gas is blown off into space.
30:57These Type Ia supernovae are just perfect for our purpose
31:01because it's always the same amount of mass just when it explodes,
31:05and so it makes the same brightness when it reaches its peak.
31:08It brightens in a few weeks, it fades away in a few months,
31:11and if you can catch it and watch just that little bit of an event,
31:15a few years later when the light arrives at us,
31:17you have a standard star, a standard candle to recognize distances with.
31:23Brilliant explosions born from identical mass,
31:26all giving off exactly the same amount of light.
31:29How much reached us should tell us how far away each was.
31:33In principle, the idea should have worked.
31:36But in practice, there was a problem.
31:40Now, it sounds great, but they're a real pain in the neck to work with.
31:44You can find a couple of them per millennium in any given galaxy that you look at,
31:48and you never know when one's going to go off,
31:50so it's not very easy to schedule the largest telescopes in the world
31:53which have to be booked months in advance.
31:56It doesn't make a very good proposal to say,
31:58I would like the night of March the 3rd,
32:01because sometime in the next 500 years a supernova is going to explode.
32:05Then, Saul and his team had a flash of inspiration.
32:10They took identical wide-angle pictures of the sky several weeks apart
32:14and used an automated program to search them for the flashes of supernovas.
32:19The idea being that if we could develop a sophisticated enough computer software,
32:24it could compare those thousands and thousands of galaxies that we have in those images that we collected
32:29and find the ones that had a new speck of light that wasn't there three weeks earlier.
32:33And those specks would be the supernova discoveries.
32:38In just over five years, Saul and his team spot 38 different stars in 38 different galaxies called supernova.
32:46Their ability to spot these exploding fireballs becomes legendary.
32:51And when they finally have enough data to measure what is happening to the universe,
32:56they produce the biggest shock in astronomy since the great Hubble himself.
33:01The picture that we all had at the time was that the universe is expanding,
33:05that all of the stuff in the universe gravitationally attracts all the other stuff in the universe,
33:10so it should be slowing the expansion.
33:12The question has always been, how far will that go, how long will it last, will it slow to a halt someday?
33:17What we found when we put the points on the plot was none of the above.
33:21It wasn't slowing at all. Apparently, the universe is, in fact, speeding up in its expansion.
33:27Saul's team had discovered a totally unexpected and unexplained repulsion between galaxies
33:33that is gradually blowing the universe apart.
33:38They called it dark energy.
33:42It was startling to think that the universe is apparently not mostly the stuff that we're used to seeing that gravitationally attracts,
33:49but maybe dominated by something that we've never studied before.
33:52We call it now dark energy, where the dark refers to our ignorance, not to the color of the stuff.
33:59We know very little about it except that it does want the universe, makes the universe expand faster and faster.
34:05Ignition. Liftoff. We have liftoff.
34:10In the summer of 2001, a Delta II rocket hurls a small scientific probe into space.
34:18Little does anyone know at the time, but this probe will tell us something truly astonishing about dark energy.
34:26It is called WMAP, and its task is to peer further out across space and further back in time than ever before
34:36to study the faint echoes of the Big Bang.
34:40David Spergel is a WMAP scientist.
34:44We're really getting a snapshot of what the universe looked like, you know, very close to the Big Bang,
34:50back in a time when it was very simple, and we can use that information about the early universe to learn a great deal.
34:56We like to think about this as kind of taking the universe's baby picture.
35:00For six months, WMAP probes slowly builds up a mosaic of the baby universe,
35:06reading the tiny fluctuations in the temperature of the embers of the Big Bang.
35:13You can think about the early universe a lot like this lake.
35:17Nearly perfectly uniform and smooth.
35:21In the early universe, there were tiny variations in density from place to place.
35:26These variations set off sound waves, a lot like these ripples you see in the lake here.
35:32The way these ripples behave depends upon the depth of the lake, the properties of the water,
35:37and these ripples would look a lot different if I was throwing this in a lake filled with mercury.
35:44So by measuring the rate at which the ripples move, how they spread with time,
35:51I can learn about the properties of the lake.
35:54Works the same way with the early universe.
35:57By studying the size and shape of the ripples in the microwave background,
36:02we can infer the composition of the lake or the early universe.
36:07Untangling all those ripples in the echo of the Big Bang
36:12is a monumental task of data analysis.
36:16David and his team crunch piles of numbers
36:19and wrestle with complex equations tirelessly for an entire year and a half.
36:25But eventually, they unravel with incredible precision just what the universe is made of.
36:31So today, atoms make up about 5%, 4.6 to be precise.
36:36Dark matter makes up about 23%.
36:39And what's very strange is 72% is made up of this dark energy.
36:45Put another way, dark matter dwarfs us.
36:49But dark energy, a mysterious repulsive force that scientists do not understand at all, dwarfs dark matter.
36:59It makes up very nearly three quarters of the universe.
37:04In the last century, we've come on from thinking that the entire universe was within our own Milky Way
37:08to knowing that there are actually billions of other galaxies out there like the Milky Way, but separate from us.
37:14We now even know that the universe is expanding. They're all moving away from us.
37:17And what's more, that expansion is actually accelerating.
37:20The universe has gone from being this very familiar sort of homely place
37:24to being this huge, vast, vast expanse of emptiness.
37:28Dark energy rules the universe.
37:31And it appears to be growing stronger day by day.
37:35How long will it be before this mysterious force rips apart every atom in the cosmos?
37:43Peering into the darkness is revolutionizing the way we see the cosmos and ourselves.
37:50Only 5% of the universe is made of atoms, the stuff we're made of.
37:56Almost a quarter of the universe is dark matter, a substance that allowed galaxies to form.
38:03And three quarters is dark energy.
38:06An inexplicable force that's trying to push everything apart.
38:11How will this struggle end?
38:14Could it eventually tear our universe to pieces?
38:22Brenner Flower plans on solving this puzzle by measuring just how powerful dark energy is.
38:29And this is the secret.
38:32And this is the device she's going to use.
38:35It's the digital eye of a new telescope called the Dark Energy Camera.
38:40We want to understand dark energy as best we can.
38:43We need to gather as much information as possible.
38:46This sensor has an incredible 520 megapixels.
38:51Each one, chilled by liquid helium, is capable of picking up particles of light
38:56that have traveled across the universe for billions of years.
39:00We're going deeper than other cameras have in the past.
39:04So we're measuring stuff further and further back in time.
39:07And also doing it quickly with this big camera.
39:11The Dark Energy Camera will be able to cover huge swaths of the sky in a single night.
39:18And will keep on doing so for five years, slowly building up more detail in its images.
39:25Searching for clues about how dark energy has evolved as our universe has evolved.
39:31Right now, the information that we have about dark energy is that it's getting stronger and stronger.
39:36And the universe is expanding faster and faster.
39:39And we don't know why.
39:41And since we don't know why, we don't know what comes next.
39:44We want to go, we want to take these deeper surveys to try to understand that.
39:48The hope is that these surveys will reveal our universe's future
39:52by looking back at its 14 billion years of development in unprecedented detail.
39:59As best as scientists understand it now,
40:02dark matter was the dominant force in determining the form of the universe
40:06in its first 7 billion years.
40:09It was dark matter, after all, that led to dark energy.
40:13In its second 7 billion years, Dark Energy Group overtook dark matter
40:19and now seems to be winning the cosmic contest,
40:22driving galaxies further and further away from one another.
40:26The way that we're going to understand better what is this dark energy
40:30that's accelerating through the universe today is to go back in time
40:33and look at how dark matter has evolved.
40:36The way that we're going to understand better what is this dark energy
40:40that's accelerating through the universe today is to go back in time
40:43and look at when did dark energy first start to become important?
40:46When did we switch from a universe that was slowing down
40:49to a universe that's speeding up?
40:51And how did that happen?
40:53What was the actual history of the switch from slowing to speeding?
40:57If you can get a very detailed history of the expansion of the universe,
41:00that will differentiate between these different theories of dark energy.
41:04That's one of the jobs that we're tackling right now.
41:08Where will this mighty battle end?
41:11A truce or a crushing victory for one side?
41:15It all depends on what dark energy actually is.
41:19And there are several competing theories.
41:22One of the more ominous calls it phantom energy.
41:26Of all these many theories of dark energy,
41:28one of them is that it's this phantom energy it's called.
41:31And that has this interesting consequence
41:33that it's accelerating the expansion of the universe,
41:35making it bigger and bigger.
41:37This acceleration gets faster and faster and faster.
41:39If dark energy is this phantom energy,
41:41it's accelerating the expansion of the universe
41:43so much that the universe gets bigger and bigger,
41:45more rarefied and diluted,
41:47and eventually galaxies will start to get torn apart.
41:49Even after that, solar systems will get pulled apart,
41:51and then stars, and eventually even the constituent atoms and particles
41:54that the universe is made of will get ripped apart
41:57in what's known as the Big Rip.
41:59But there's one bright spot in this dark and threatening picture,
42:02one thing that we know little about.
42:05Dark matter may end up being the best tool to study dark energy.
42:10Dark energy is a force that's trying to push the universe apart.
42:14Dark matter is trying to clump things together.
42:17And it's the interplay of these two things
42:19that has led to the formation of the structures
42:22that we see in the universe today.
42:24And so by understanding how fast the galaxy clusters form
42:28and clump together, that tells us about dark matter,
42:31but also about how much dark energy is pushing it apart at the same time.
42:35Scientists using something they barely understand
42:38to try to get a handle on something they don't understand at all.
42:43These are truly strange days in cosmology.
42:47We have come a long way in our quest to understand the universe.
42:51I remember 30 years ago when the mere concept of dark matter
42:56was deemed to be revolutionary.
42:58It was speculative.
43:00Somewhat heretical.
43:02I would have never dreamt then that 30 years later,
43:05truly alien concepts like dark matter and dark energy
43:09are actually taken for granted.
43:13Turns out I was right.
43:15There really is something in the shadows.
43:18But I never knew just how important it was.
43:22From the corner of my own bedroom to the farthest reaches of space,
43:27darkness dominates the universe and controls our fate.
43:33So far, the struggle between dark matter and dark energy has been good to us.
43:37After all, without it, there would be no galaxies, no planets,
43:41no you, no me.
43:45But our days may be numbered.
43:49One day, darkness could extinguish the light.
43:54Forever.
43:56Until we fully understand these colossal forces,
44:01what ultimately lies in store,
44:04heaven only knows.
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