0:00:12 > 0:00:17In 1929, Edwin Hubble made an alarming discovery.
0:00:19 > 0:00:22He found that wherever he pointed his telescope,
0:00:22 > 0:00:25it revealed that everything was getting further away.
0:00:27 > 0:00:31The universe seemed to be expanding, and if it was expanding -
0:00:31 > 0:00:35they checked and it was - and you think about it for any
0:00:35 > 0:00:37length of time, which they did,
0:00:37 > 0:00:40you have to conclude that it must be
0:00:40 > 0:00:43expanding from some kind of starting point.
0:00:45 > 0:00:49Hubble had stumbled across what was then a revolutionary idea,
0:00:49 > 0:00:53but something that is now scientific orthodoxy.
0:01:00 > 0:01:06Our universe started 13.8 billion years ago in an instant.
0:01:06 > 0:01:10ALL: This was the first period of the birth of the universe.
0:01:10 > 0:01:12It is known as the Big Bang.
0:01:14 > 0:01:17Nowadays, our understanding of the birth of the universe is
0:01:17 > 0:01:18extremely detailed.
0:01:20 > 0:01:23Then it underwent a dramatic expansion.
0:01:23 > 0:01:26ALL: This was the second period in the birth of the universe.
0:01:26 > 0:01:29It is called inflation.
0:01:29 > 0:01:33Thanks to science, we think we know exactly how we got to now.
0:01:34 > 0:01:37- BOTH:- Atomic matter condensed to form the stars
0:01:37 > 0:01:39and planets that make our universe.
0:01:39 > 0:01:42ALL: This is the standard model of cosmology.
0:01:43 > 0:01:46And not content with painting the biggest picture of all,
0:01:46 > 0:01:48science has also created a comprehensive list
0:01:48 > 0:01:52of what the atoms we're made from, are made from.
0:01:52 > 0:01:54There are six quarks.
0:01:54 > 0:01:56ALL: Four types of gauge bosons.
0:01:56 > 0:01:58ALL: Six leptons.
0:01:58 > 0:02:00And the Higgs boson.
0:02:00 > 0:02:03ALL: This is the standard model of particle physics.
0:02:07 > 0:02:11Together, these two paradigms should explain everything.
0:02:17 > 0:02:21And yet, just at the point where things seem to be coming together,
0:02:21 > 0:02:24some researchers are worried that there's an increasingly
0:02:24 > 0:02:27strong possibility that we might have got the science wrong.
0:02:29 > 0:02:32That our current theories are looking shaky.
0:02:34 > 0:02:36That we don't understand our universe
0:02:36 > 0:02:40or what we're made of, or anything, really.
0:02:43 > 0:02:46How does any theorist sleep at night knowing that the standard
0:02:46 > 0:02:51model of particle physics is off by so many orders of magnitude?
0:02:51 > 0:02:53We have no idea what 95% of the universe is.
0:02:53 > 0:02:55It hardly seems that we understand everything.
0:02:55 > 0:02:58This is about what the universe is made of.
0:02:58 > 0:02:59This is about our existence.
0:02:59 > 0:03:03What is it that they say? They say that cosmologists are always wrong but never in doubt.
0:03:03 > 0:03:06There are more theories than there are theoreticians.
0:03:06 > 0:03:10OK, I'm going to be honest here, but we're in the strange situation
0:03:10 > 0:03:14that it seems like every other year there's a new unexplained signal.
0:03:14 > 0:03:16Maybe we're just going to have to scratch our heads
0:03:16 > 0:03:18and start all over again.
0:03:45 > 0:03:49Nestling beneath the huge Andes Mountains that dominate
0:03:49 > 0:03:52the whole of Chile lies its capital.
0:03:52 > 0:03:57It was founded by the Conquistadors in 1541, who gave it its name,
0:03:57 > 0:04:01Santiago, St James, after the patron saint of the motherland.
0:04:03 > 0:04:08But in Spanish, Iago also means Jacob, and it was Jacob who,
0:04:08 > 0:04:11according to the Bible, dreamt about climbing a ladder to heaven.
0:04:13 > 0:04:16While the mountains may hint at a metaphorical stairway
0:04:16 > 0:04:20to paradise, they also provide a practical route to enlightenment.
0:04:24 > 0:04:27That's why British astrophysicist Bob Nichol is here.
0:04:27 > 0:04:31He's en route to some of the biggest telescopes on the planet,
0:04:31 > 0:04:35perched aloft on the roof of the world, where he's continuing
0:04:35 > 0:04:38the work of trying to understand how the universe works.
0:04:41 > 0:04:45So the amazing thing about cosmology is that it only really started
0:04:45 > 0:04:49in the 1920s, so when people started looking through their telescopes,
0:04:49 > 0:04:53they didn't know whether these fuzzy things out there in the universe
0:04:53 > 0:04:57were actually within our own galaxy or actually separate galaxies from
0:04:57 > 0:05:00our own. And then it was the great astronomers like Hubble that came
0:05:00 > 0:05:04along and measured the distances to these faint nebulae that you
0:05:04 > 0:05:07could see in your telescopes, and suddenly discovered that they were
0:05:07 > 0:05:12much further away than we expected and therefore had to be outside
0:05:12 > 0:05:16our galaxy and therefore discovered a universe of other galaxies.
0:05:18 > 0:05:21The discovery of a universe that was far more complicated
0:05:21 > 0:05:23than anyone could have imagined...
0:05:27 > 0:05:29..and the idea that it all started in an instant...
0:05:33 > 0:05:36..suddenly provided a credible creation story
0:05:36 > 0:05:38that didn't rely on myths and magic.
0:05:39 > 0:05:43The idea of the Big Bang and the expanding universe was
0:05:43 > 0:05:46a triumph for modern astronomy.
0:05:46 > 0:05:48And everyone was happy with it,
0:05:48 > 0:05:53until 1974, when astronomers discovered a big problem.
0:06:03 > 0:06:05So in the solar system,
0:06:05 > 0:06:09we have a sun in the middle, which provides all the gravity.
0:06:09 > 0:06:13And then coming further out from that, we have all the planets.
0:06:13 > 0:06:17They're lined up and rotate around the sun,
0:06:17 > 0:06:21and the speed by which they go round the sun decreases
0:06:21 > 0:06:25as a function of the distance away from the sun.
0:06:25 > 0:06:28So by the time you get to the outer planets,
0:06:28 > 0:06:31they are moving a lot slower than the ones in the centre.
0:06:31 > 0:06:37So, for example, Neptune takes 165 Earth years to go round the sun.
0:06:37 > 0:06:41So if I was to draw a graph of that, it would look a bit like this.
0:06:41 > 0:06:43So...
0:06:44 > 0:06:47..you would expect the speed of the planets in the centre to be
0:06:47 > 0:06:51high, and as the gravity got weaker,
0:06:51 > 0:06:52the speed would get smaller
0:06:52 > 0:06:55and smaller and smaller until you got out here.
0:06:55 > 0:06:59Now, we have the same set-up in our galaxy.
0:06:59 > 0:07:02We have a large supermassive black hole in the centre
0:07:02 > 0:07:06and we have stars orbiting around the centre of the galaxy.
0:07:06 > 0:07:09So you'd expect that the stars further away from the centre
0:07:09 > 0:07:13of the galaxy would be moving slower than the ones on the inside.
0:07:13 > 0:07:15But that's not what we see.
0:07:15 > 0:07:20What we see is the speed of the stars is constant with distance,
0:07:20 > 0:07:24so the stars out here are travelling at the same
0:07:24 > 0:07:26speed as the stars in the centre.
0:07:35 > 0:07:39Wherever the speed of stars in spiral galaxies were measured,
0:07:39 > 0:07:44they produced the logic-defying flat rotation curves.
0:07:44 > 0:07:48The only way they made sense was if there was more matter than
0:07:48 > 0:07:51we thought, producing more gravity.
0:07:51 > 0:07:54And since the extra stuff couldn't be seen, it was given
0:07:54 > 0:07:58the slightly sinister title "dark matter".
0:08:14 > 0:08:17Dark matter is a really interesting problem.
0:08:17 > 0:08:20It sounds exotic, but it doesn't have to be.
0:08:25 > 0:08:28Professor Katie Freese is a theoretical physicist.
0:08:30 > 0:08:34That is to say, the physics she deals with is theoretical.
0:08:34 > 0:08:35Katie herself is real.
0:08:37 > 0:08:41There's a lot of dark things out there in the universe.
0:08:41 > 0:08:45Until I shine my light at these bottles, I can't see them
0:08:45 > 0:08:49and as soon as I take away the light, they're dark.
0:08:49 > 0:08:52That's what people thought. They thought it might be gas,
0:08:52 > 0:08:53it might be dust.
0:08:53 > 0:08:57The dark matter could just be ordinary stuff that you can't see.
0:09:03 > 0:09:09These ordinary, but dark, dark matter creatures are called MACHOs -
0:09:09 > 0:09:11massive compact halo objects.
0:09:13 > 0:09:15But the trouble was that even the most generous
0:09:15 > 0:09:20estimates for how much the MACHOs might weigh fell pathetically
0:09:20 > 0:09:22short of what would be needed to explain the strange
0:09:22 > 0:09:25goings-on in spiral galaxies like ours.
0:09:26 > 0:09:29Another explanation was required.
0:09:32 > 0:09:35Well, there's an alternative idea for what the dark matter could be.
0:09:35 > 0:09:38What we think it is, is that it's some new kind of fundamental
0:09:38 > 0:09:44particle. Not neutrons, not protons, not ordinary atomic stuff
0:09:44 > 0:09:47but something entirely new.
0:09:47 > 0:09:50And these particles are everywhere in the universe.
0:09:50 > 0:09:53They're flying around in our galaxy, they're in this room.
0:09:53 > 0:09:57Actually, there would be billions going through you every second.
0:09:57 > 0:10:00You don't notice, but they're there.
0:10:05 > 0:10:09These theoretical dark matter candidates are called WIMPs -
0:10:09 > 0:10:12weakly interacting massive particles.
0:10:14 > 0:10:17But because they interact weakly with ordinary matter,
0:10:17 > 0:10:21the stuff from which we and scientific instruments are made,
0:10:21 > 0:10:23catching them is about as straightforward
0:10:23 > 0:10:25as trapping water in a sieve.
0:10:26 > 0:10:29In fact, in the early days of dark matter, these particles were
0:10:29 > 0:10:34so theoretical that no-one had any idea at all about how
0:10:34 > 0:10:37they might get hold of one, even in theory.
0:10:38 > 0:10:42Then, in 1983, freshly minted theoretical physicist
0:10:42 > 0:10:45Katie Freese had an epiphany.
0:10:45 > 0:10:48I was at a winter school in Jerusalem
0:10:48 > 0:10:51and that's where I got into the dark matter business.
0:10:51 > 0:10:54I met a man named Andre Drukier.
0:10:54 > 0:10:57He's a brilliant, eccentric person.
0:10:57 > 0:10:59He's Polish,
0:10:59 > 0:11:02he speaks English, French, German, Polish,
0:11:02 > 0:11:04all at the same time.
0:11:04 > 0:11:07And he knew where to go for the New Year's party.
0:11:07 > 0:11:10And he started, believe it or not, in that evening,
0:11:10 > 0:11:12over the cocktails -
0:11:12 > 0:11:15cocktails have always been good for science -
0:11:15 > 0:11:19started telling me about work that he'd been doing.
0:11:19 > 0:11:24Drukier had hit upon a way of detecting neutrinos, real particles
0:11:24 > 0:11:27that share some characteristics with the proposed WIMPs.
0:11:28 > 0:11:32So what we realised is you could use exactly that same
0:11:32 > 0:11:34technique for WIMPs.
0:11:34 > 0:11:36WIMPs have the same kind of interactions,
0:11:36 > 0:11:41they have the weak interactions, the same ones that the neutrinos do.
0:11:41 > 0:11:46I, at the time, was a post-doc at Harvard and I convinced
0:11:46 > 0:11:49Andre to come to Harvard for a few months. And there, we also
0:11:49 > 0:11:54worked with David Spergel, and the three of us wrote down some of the
0:11:54 > 0:11:58basic ideas for what you might do if you wanted to detect the WIMPs.
0:12:01 > 0:12:05WIMPs, the particles that could be dark matter, are like ghosts.
0:12:05 > 0:12:07They travel through ordinary matter.
0:12:07 > 0:12:09But they are particles,
0:12:09 > 0:12:11so every once in a while, one of them
0:12:11 > 0:12:15should collide with the nucleus of an atom, in theory.
0:12:15 > 0:12:18What's more, the theoretical collision should release
0:12:18 > 0:12:23a photon, a tiny flash of light - dark matter detected.
0:12:23 > 0:12:25Simple, in theory.
0:12:26 > 0:12:30If you were to try to build one of these experiments on a table top
0:12:30 > 0:12:33or in a laboratory on the surface of the Earth,
0:12:33 > 0:12:37then your signal would be completely swamped by cosmic rays.
0:12:37 > 0:12:41These would just ruin your attempt to do the experiment,
0:12:41 > 0:12:44because the count rate from the cosmic rays would be so high
0:12:44 > 0:12:46that you'd never be able to see the WIMPs.
0:12:46 > 0:12:48So what you have to do is go underground.
0:12:51 > 0:12:55It is because of the ideas that Katie had in the 1980s that
0:12:55 > 0:12:58thousands of scientists have been scurrying underground
0:12:58 > 0:13:00in search of the dark ever since.
0:13:04 > 0:13:05Juan Collar is one of them.
0:13:06 > 0:13:11His search for dark matter has taken him to Sudbury, a small
0:13:11 > 0:13:15town in Canada, perched just above the North American Great Lakes.
0:13:22 > 0:13:23To look at it now,
0:13:23 > 0:13:26you wouldn't think that this place owes its existence to
0:13:26 > 0:13:30one of the most catastrophic events the world has ever witnessed.
0:13:38 > 0:13:42Millions of years ago, a gigantic comet crashed into what is
0:13:42 > 0:13:46now Sudbury, creating, to date, the second largest crater on Earth.
0:13:48 > 0:13:51The comet brought with it lots of useful metals that ended up
0:13:51 > 0:13:54under what became known as the Sudbury Basin.
0:13:56 > 0:13:58When humans became clever enough,
0:13:58 > 0:14:02they sunk holes into the crater so they could get the metals out.
0:14:02 > 0:14:06The area's nickel mines are responsible for, amongst other
0:14:06 > 0:14:10things, the town of Sudbury's main tourist attraction, the Big Nickel.
0:14:16 > 0:14:18What they're less well known for is the part
0:14:18 > 0:14:21they play in the search for dark matter.
0:14:24 > 0:14:27Juan and his colleagues regularly make the two-kilometre
0:14:27 > 0:14:31descent into the darkness in pursuit of the universe's missing mass.
0:14:38 > 0:14:41He's been making the journey for some time.
0:14:42 > 0:14:45How long have you been doing experiments underground?
0:14:45 > 0:14:49In my case, since 1986.
0:14:50 > 0:14:52It's been a while.
0:14:52 > 0:14:55- So you haven't found anything yet? - No.
0:14:56 > 0:14:58Do you ever feel like giving up?
0:14:59 > 0:15:02Well, after walking a mile underground like this...
0:15:02 > 0:15:06This is not the right time to ask me that question, don't you think?
0:15:06 > 0:15:10There's ups and downs, of course, but, yeah.
0:15:10 > 0:15:14Every so often you have to wonder about the fact that we may be
0:15:14 > 0:15:17looking in the wrong place, right?
0:15:17 > 0:15:18But someone has to do that job.
0:15:18 > 0:15:22I mean, in physics a negative result is also important.
0:15:22 > 0:15:24You close a door,
0:15:24 > 0:15:27and then we can get to work looking for other possibilities.
0:15:28 > 0:15:30The scientists are heading for an underground
0:15:30 > 0:15:34laboratory in which it is hoped that the super-shy dark matter
0:15:34 > 0:15:37particle may one day show its face.
0:15:47 > 0:15:50Because anything brought in from the outside world could
0:15:50 > 0:15:54give off radiation that might look a bit like dark matter,
0:15:54 > 0:15:57every trace must be removed before entering the lab.
0:15:57 > 0:16:00No-one is allowed near the ultra-sensitive detectors
0:16:00 > 0:16:02without being thoroughly cleaned
0:16:02 > 0:16:05and given a special non-radiating outfit to wear.
0:16:11 > 0:16:15Here in this near-clinically clean environment is a bewildering
0:16:15 > 0:16:19collection of experiments, some of them several storeys tall,
0:16:19 > 0:16:23all designed to catch dark matter in the act of existence.
0:16:26 > 0:16:29Most of the experiments intend to record the hoped-for
0:16:29 > 0:16:32flash of light, produced when WIMPs collide with atoms.
0:16:34 > 0:16:38But Juan's experiment works in a totally different way.
0:16:38 > 0:16:42Juan has decided to listen, rather than look, for dark matter.
0:16:46 > 0:16:50So, Peter, this is the inner vessel of Pico-2-L,
0:16:50 > 0:16:51what we call this project.
0:16:51 > 0:16:56And it goes inside that big recompression chamber.
0:16:56 > 0:16:59We have cameras that look inside
0:16:59 > 0:17:01and the principle of operation of this detector is the following -
0:17:01 > 0:17:03we put a liquid in there that is
0:17:03 > 0:17:06a rather special liquid. It's what we call a super-heated liquid.
0:17:06 > 0:17:11It makes it sensitive to radiation, so when particles like the liquid
0:17:11 > 0:17:15that goes in there normally - it's now empty - they produce bubbles.
0:17:15 > 0:17:18The number of bubbles tells us about the nature of the particle
0:17:18 > 0:17:19that interacted.
0:17:19 > 0:17:22You can see these copper things here. These are electric sensors.
0:17:22 > 0:17:25They are very sophisticated microphones and through sound
0:17:25 > 0:17:27we are actually able to distinguish...
0:17:27 > 0:17:29differentiate between different types of particles as well.
0:17:29 > 0:17:32What sound would dark matter make?
0:17:32 > 0:17:35It's actually very soft. It's not the loudest.
0:17:35 > 0:17:38So if you find a WIMP it'll have a wimpy noise?
0:17:38 > 0:17:40Very wimpy indeed, yes.
0:17:45 > 0:17:48Juan has scaled up this idea in his latest detector.
0:17:50 > 0:17:54Because a bigger detector means a greater hit rate.
0:17:54 > 0:17:58Assuming, of course, that there's anything doing the hitting.
0:17:59 > 0:18:01So this is 260.
0:18:01 > 0:18:03It's a much larger bubble chamber,
0:18:03 > 0:18:06about 30 times larger in active volume than
0:18:06 > 0:18:08the one we were looking at before.
0:18:08 > 0:18:09We explore the same principle.
0:18:09 > 0:18:12We listen to the sound of particles, etc.
0:18:12 > 0:18:14It's just a much bigger version.
0:18:14 > 0:18:17In some of the models they have developed for these dark matter
0:18:17 > 0:18:21particles, the rate of interaction is as small as one interaction,
0:18:21 > 0:18:27one bubble in our case, per tonne of material per year, or less.
0:18:27 > 0:18:28Confident?
0:18:28 > 0:18:30Confident? Not really.
0:18:30 > 0:18:33You do your job the best you can
0:18:33 > 0:18:35and then you hope for the best, but...
0:18:36 > 0:18:40..nobody knows if there's WIMPs out there or not. We're trying.
0:18:40 > 0:18:41But confidence is not something that
0:18:41 > 0:18:44you typically find among experimentalists.
0:18:53 > 0:18:56The fact is, though, that though the hunt for dark matter has
0:18:56 > 0:19:00so far proved to be the world's least productive experiment,
0:19:00 > 0:19:04the world's large telescopes are providing increasing evidence that
0:19:04 > 0:19:08the elusive WIMPs, whatever they are, really are the dark matter.
0:19:18 > 0:19:22This array forms one of the world's largest telescopes.
0:19:22 > 0:19:25In fact, its name is the VLT -
0:19:25 > 0:19:27the Very Large Telescope.
0:19:30 > 0:19:33We're in the Atacama Desert in Chile,
0:19:33 > 0:19:37at the top of a big mountain at the European Southern Observatory,
0:19:37 > 0:19:40so there are four massive telescopes
0:19:40 > 0:19:42that we use to stare into deep space
0:19:42 > 0:19:45and they give us even more information
0:19:45 > 0:19:48on the dark matter that fills our universe.
0:19:53 > 0:19:57The Very Large Telescope has produced some staggering images,
0:19:57 > 0:20:01but perhaps one of the most compelling is this one.
0:20:05 > 0:20:09This image shows a large cluster of galaxies.
0:20:09 > 0:20:13Such large objects can bend light
0:20:13 > 0:20:16of the galaxies that are behind it.
0:20:16 > 0:20:19We call this technique gravitational lensing.
0:20:19 > 0:20:23These arcs are distant galaxies behind the cluster
0:20:23 > 0:20:26that have been brightened and stretched
0:20:26 > 0:20:30as the light passes through the cluster and gets bent.
0:20:30 > 0:20:32And what's very interesting is this technique
0:20:32 > 0:20:35allows us to measure the mass of the lens,
0:20:35 > 0:20:38and when we do that using these arcs,
0:20:38 > 0:20:42we find the mass of the lens is about 100 times more
0:20:42 > 0:20:45than the light we see in this image.
0:20:45 > 0:20:47But second of all, and more importantly,
0:20:47 > 0:20:50it tells us that the dark matter that we can't see
0:20:50 > 0:20:55is more distributed and acts as a dark matter cloud of particles.
0:20:55 > 0:20:59So this is conclusive evidence of dark matter,
0:20:59 > 0:21:03but it also is conclusive evidence that that dark matter
0:21:03 > 0:21:06must be more spread out than the galaxies we see here,
0:21:06 > 0:21:10and in fact it tells us it has to be a cloud of dark matter particles,
0:21:10 > 0:21:14not just individual objects in the cluster.
0:21:15 > 0:21:19So here's the thing. Dark matter has to have mass.
0:21:19 > 0:21:22Remember, that's the reason it has to be there in the first place -
0:21:22 > 0:21:25all those speeding stars. And it seems that
0:21:25 > 0:21:29it's not just matter we can't see because it's not shining.
0:21:29 > 0:21:31So it has to be some kind of other stuff
0:21:31 > 0:21:34that we can't see by definition.
0:21:34 > 0:21:37And more than that, it has to be some kind of material
0:21:37 > 0:21:41that's capable of clumping together in something like a gas.
0:21:41 > 0:21:44And all this adds up to one thing -
0:21:44 > 0:21:47we're looking for a new particle.
0:21:54 > 0:21:56And when it comes to new particles,
0:21:56 > 0:22:00there's really only one place to come - Switzerland...
0:22:00 > 0:22:02and France.
0:22:04 > 0:22:06This place might look like a third-rate
0:22:06 > 0:22:08provincial technical college,
0:22:08 > 0:22:11but if the hunt for dark matter has taught us nothing else,
0:22:11 > 0:22:14it has shown that a book should never be judged by its cover.
0:22:16 > 0:22:18And so it is with this place,
0:22:18 > 0:22:20because beneath the dismal architecture
0:22:20 > 0:22:25lies the most exciting piece of scientific apparatus ever created.
0:22:32 > 0:22:36This is CERN, the world's biggest physics lab,
0:22:36 > 0:22:39home to the Large Hadron Collider,
0:22:39 > 0:22:42the largest particle accelerator on the planet.
0:22:42 > 0:22:46It's here where scientists investigate what stuff is made of...
0:22:46 > 0:22:49by smashing it apart.
0:22:49 > 0:22:54Protons are fired around its 27-kilometre-long circular tube
0:22:54 > 0:22:57in opposite directions at nearly the speed of light,
0:22:57 > 0:22:59before being smashed together.
0:22:59 > 0:23:01EXPLOSION
0:23:05 > 0:23:08Waiting to trawl through the debris resulting from those collisions
0:23:08 > 0:23:12are two-thirds of the world's particle physicists.
0:23:14 > 0:23:16One of them is Dave from Birmingham.
0:23:23 > 0:23:25He is in charge of one of the huge detectors
0:23:25 > 0:23:28which record each and every collision.
0:23:32 > 0:23:35I have to admit, I come down here a few times a week
0:23:35 > 0:23:37and pretty much every time I come in,
0:23:37 > 0:23:40my jaw still drops when I see ATLAS in front of me.
0:23:40 > 0:23:43I mean, it's incredible that we built this detector
0:23:43 > 0:23:45and that we're able to operate it.
0:23:47 > 0:23:52So the whole detector itself is about eight or nine storeys tall,
0:23:52 > 0:23:54and so we're about halfway up at the moment,
0:23:54 > 0:23:57so four or five storeys above the base of the detector.
0:23:57 > 0:24:00The total weight of the detector is about 7,000 tonnes,
0:24:00 > 0:24:04which is about the same as the weight of the Eiffel Tower.
0:24:04 > 0:24:07While it might weigh the same, the ATLAS detector
0:24:07 > 0:24:12shares few other characteristics with Paris's most famous flagpole.
0:24:12 > 0:24:15Fitted with 100 million detectors,
0:24:15 > 0:24:18it produces the equivalent of a digital photograph
0:24:18 > 0:24:2340 million times a second, providing Dave and his team
0:24:23 > 0:24:26with a permanent record of the precise nature
0:24:26 > 0:24:29of each particle's demise.
0:24:29 > 0:24:30When the protons collide,
0:24:30 > 0:24:32most of the time the particles they produce... Nearly always
0:24:32 > 0:24:35some new particles are created, but they tend to be
0:24:35 > 0:24:38low-mass particles so they tend to be the familiar quarks,
0:24:38 > 0:24:41the familiar hadrons, the protons, the neutrons, pions,
0:24:41 > 0:24:43which are also light hadrons.
0:24:43 > 0:24:45But sometimes, very rarely,
0:24:45 > 0:24:47you produce these much more massive particles,
0:24:47 > 0:24:50and that's where we're looking for. So if we are producing
0:24:50 > 0:24:52Higgs particles or we're producing even more massive particles -
0:24:52 > 0:24:54which would be ones we don't know about,
0:24:54 > 0:24:56they would be ones beyond the standard model -
0:24:56 > 0:25:00these are the guys that we're really looking for.
0:25:00 > 0:25:05The LHC has been switched off for two years while it's been upgraded.
0:25:05 > 0:25:07Now it's been switched on again
0:25:07 > 0:25:10and will run at twice the energy it did before.
0:25:10 > 0:25:15It might be that more new particles might emerge.
0:25:15 > 0:25:18If they do, they could well be the elusive WIMPs,
0:25:18 > 0:25:21one of which could well be the dark matter.
0:25:23 > 0:25:28The idea is that we're looking for imbalances of momentum in the event
0:25:28 > 0:25:30that signify that there are unobserved particles
0:25:30 > 0:25:34going off with high energy carried out of the detector.
0:25:34 > 0:25:38So what you're actually seeing is an absence of something?
0:25:38 > 0:25:39What we're seeing is an absence of something,
0:25:39 > 0:25:43an imbalance of something, yes. It's some particles that we can't observe
0:25:43 > 0:25:46and we can infer that they're there by looking at the rest of the event.
0:25:46 > 0:25:50So that's beautiful, isn't it? That you can find dark matter which you can't by definition see
0:25:50 > 0:25:53- and you discover it by not seeing it?- Exactly, yes.
0:25:55 > 0:25:58On the face of it, this is an extraordinary,
0:25:58 > 0:26:01not to say logically contradictory idea,
0:26:01 > 0:26:04that ordinary matter smashes into itself
0:26:04 > 0:26:08to produce invisible matter that can't readily be detected
0:26:08 > 0:26:10because it only interacts weakly
0:26:10 > 0:26:13with the stuff that produced it in the first place.
0:26:13 > 0:26:16And yet this is precisely what is being predicted
0:26:16 > 0:26:18in another part of CERN
0:26:18 > 0:26:21by theoretical physicists like John Ellis.
0:26:21 > 0:26:24My job as a theoretical physicist is to try to understand
0:26:24 > 0:26:27the structure of matter, what makes up everything in the universe,
0:26:27 > 0:26:30the stuff that we can see, the stuff that we can't see.
0:26:32 > 0:26:34It's the stuff we can't see
0:26:34 > 0:26:37that is currently occupying most of John's time.
0:26:37 > 0:26:41So the astronomers tell us that there are these dark matter particles
0:26:41 > 0:26:43flying around us all the time,
0:26:43 > 0:26:45between us as we speak.
0:26:46 > 0:26:49But they've never detected these things.
0:26:51 > 0:26:54Now, we were going to try to produce them at the LHC.
0:26:58 > 0:27:00It sounds like a bold statement
0:27:00 > 0:27:03but it's based on a very conventional idea -
0:27:03 > 0:27:07namely, that everything we can see and can't see
0:27:07 > 0:27:10has its origins at the point of the Big Bang
0:27:10 > 0:27:13when things were as hot as it's possible to be.
0:27:13 > 0:27:18And it's only in the LHC that, at least in theory, energy levels
0:27:18 > 0:27:21approaching those not seen since the moment of creation
0:27:21 > 0:27:22can be reproduced.
0:27:24 > 0:27:26EXPLOSION
0:27:26 > 0:27:27Now, at those very early epochs,
0:27:27 > 0:27:30we think that there were other particles
0:27:30 > 0:27:34besides the ones that are described by the standard model,
0:27:34 > 0:27:36particles that we can't see.
0:27:36 > 0:27:40Now, we believe that this dark matter must exist,
0:27:40 > 0:27:42because if we look at galaxies,
0:27:42 > 0:27:44if we look at the universe around us today,
0:27:44 > 0:27:48there has to be some sort of unseen dark stuff,
0:27:48 > 0:27:53and we think that stuff must have been liberated from the particles
0:27:53 > 0:27:56that we can see very early in the history of the universe.
0:27:58 > 0:28:02If John and Dave can make a suitable WIMP at CERN,
0:28:02 > 0:28:04the picture will become much clearer
0:28:04 > 0:28:06for Juan and the deep mine fraternity.
0:28:06 > 0:28:09Suddenly there'll be something to shoot at.
0:28:09 > 0:28:13If the astronomers find a dark matter particle, you know,
0:28:13 > 0:28:15hitting something in the laboratory,
0:28:15 > 0:28:18they don't know what type of particle it is.
0:28:18 > 0:28:22But if we put our two experiments together,
0:28:22 > 0:28:24like pieces of a jigsaw puzzle,
0:28:24 > 0:28:27we may be able to figure out what this dark matter actually is.
0:28:32 > 0:28:34Linking a manufactured particle from CERN
0:28:34 > 0:28:36to underground WIMP detections
0:28:36 > 0:28:39would indeed connect two pieces of the jigsaw.
0:28:42 > 0:28:44But there's a third piece -
0:28:44 > 0:28:48one that provides evidence of dark matter in its native habitat.
0:28:51 > 0:28:53This is Chicago, Illinois.
0:28:54 > 0:28:58# You only love me for my record collection
0:29:03 > 0:29:07# You say you never felt a deeper connection... #
0:29:10 > 0:29:14Chicago is the home of the deep-dish pizza, Barack Obama,
0:29:14 > 0:29:19and Reggies blues club at 2105 South State Street.
0:29:21 > 0:29:24# Let the record spin cos you like it like that
0:29:29 > 0:29:34# We're hanging on by the way it spins round
0:29:34 > 0:29:38# You love me for my records and you wanna get down... #
0:29:41 > 0:29:44Guitarist Charlie Wayne and his band The Congregation
0:29:44 > 0:29:48are entertaining the crowd with one of their newest songs.
0:30:03 > 0:30:05MUSIC CONTINUES
0:30:05 > 0:30:09Charlie has been in many bands over the years, and has often been
0:30:09 > 0:30:12in two minds as to whether he should become a professional musician.
0:30:15 > 0:30:16CHEERING
0:30:21 > 0:30:24But for the time being, he has a day job.
0:30:27 > 0:30:29And a day name, too.
0:30:32 > 0:30:36During the day, guitarist Charlie Wayne becomes
0:30:36 > 0:30:40Associate Professor Dan Hooper, physicist.
0:30:41 > 0:30:43So, I'm a professor of astronomy and astrophysics
0:30:43 > 0:30:45at the University of Chicago, but I also do
0:30:45 > 0:30:49research here at Fermilab, as part of the theoretical astrophysics group.
0:30:49 > 0:30:51In addition to being the centre of particle physics
0:30:51 > 0:30:52in the United States,
0:30:52 > 0:30:57they have a strong programme in cosmology and particle astrophysics.
0:30:57 > 0:31:00They study questions like, how did the universe begin?
0:31:00 > 0:31:03How did it evolve? What's dark matter and dark energy?
0:31:03 > 0:31:05Some of my favourite questions.
0:31:10 > 0:31:13And while Charlie dreams of commercial success
0:31:13 > 0:31:17and induction into the Rock and Roll Hall of Fame, Dan has his eyes
0:31:17 > 0:31:21on the glittering prizes that can be won through academic study.
0:31:25 > 0:31:28So, this is my office, this is where I do my work.
0:31:28 > 0:31:30So what does work mean, Dan?
0:31:30 > 0:31:34So, I'm a theoretical astrophysicist. Which means my research is
0:31:34 > 0:31:38done on chalk boards, and pads and paper, and my computer.
0:31:38 > 0:31:41I don't run any experiments. I don't build anything.
0:31:44 > 0:31:48Fermilab is named for Italian-American
0:31:48 > 0:31:51Nobel Prize-winning physicist, Enrico Fermi,
0:31:51 > 0:31:56whose name is also given to a class of subatomic particles, fermions.
0:31:58 > 0:32:01It's appropriate, then, that Dan works here,
0:32:01 > 0:32:04because it's possible that he, too, has identified
0:32:04 > 0:32:09a type of particle - something that could be a dark matter WIMP,
0:32:09 > 0:32:13something that Dan's colleagues are already calling the Hooperon.
0:32:19 > 0:32:23OK, so in many theories of dark matter,
0:32:23 > 0:32:26these particles of dark matter are themselves stable.
0:32:26 > 0:32:29They'll sit around and basically do nothing, throughout
0:32:29 > 0:32:32the history of the universe, but in those rare instances where
0:32:32 > 0:32:36they collide with each other, they can get entirely destroyed or
0:32:36 > 0:32:40annihilated and leave behind in their wake these energetic
0:32:40 > 0:32:43jets of ordinary material. So these jets might include
0:32:43 > 0:32:48things like an electron that might fly around here and just move
0:32:48 > 0:32:51through the magnetic fields of the universe, or they might
0:32:51 > 0:32:57include particles called neutrinos, which are really hard to detect.
0:32:57 > 0:33:01And then they could also include, and usually do, some particles
0:33:01 > 0:33:05that we call gamma rays which are just really high-energy photons.
0:33:05 > 0:33:09So if the Fermi telescope, which is my cartoon picture
0:33:09 > 0:33:12of the Fermi telescope here, happens to be looking
0:33:12 > 0:33:16in the direction that the gamma ray came from, you could record them
0:33:16 > 0:33:19and maybe see evidence of this sort of process going on,
0:33:19 > 0:33:21especially in the centre of the Milky Way,
0:33:21 > 0:33:23where there's so much dark matter.
0:33:23 > 0:33:27Liftoff of the Delta rocket carrying the gamma ray telescope,
0:33:27 > 0:33:30searching for unseen physics in the stars of the galaxies.
0:33:32 > 0:33:36The gamma ray-detecting Fermi telescope is also
0:33:36 > 0:33:39named for Enrico Fermi, but confusingly,
0:33:39 > 0:33:43it has nothing to do with Fermilab. But because the data it records
0:33:43 > 0:33:48is made public, anyone, including Dan, can take a view on what it's seeing.
0:33:49 > 0:33:52In 2009, I was sitting at my laptop just like this.
0:33:52 > 0:33:56And I had a mathematical routine written to, you know,
0:33:56 > 0:34:01plot the spectrum in the galactic centre regions. So how the different
0:34:01 > 0:34:04photons came with different energy, how many of them were different energies,
0:34:04 > 0:34:08and most of the backgrounds predict something pretty flat,
0:34:08 > 0:34:12not exactly flat, but pretty flat, and dark matter predicts a bump.
0:34:12 > 0:34:15So I plotted up, and for the first time I hit enter
0:34:15 > 0:34:19and, you know, run the plotting routine and this plot comes up,
0:34:19 > 0:34:22and there's this big old bump. You just couldn't miss it.
0:34:22 > 0:34:24It was a giant bump in the inner galaxy.
0:34:25 > 0:34:28The bump of gamma ray activity that Dan has seen
0:34:28 > 0:34:30could be due to many things.
0:34:30 > 0:34:36Pulsars emit gamma rays, for a start, and there are plenty of them in the Milky Way.
0:34:36 > 0:34:39But the energy levels that make up Dan's bump
0:34:39 > 0:34:43theoretically matches the annihilation profile of particles that could,
0:34:43 > 0:34:49theoretically, be dark matter - Dan's particle, the Hooperon.
0:34:49 > 0:34:52It really was the thing I did the analysis looking for.
0:34:52 > 0:34:53And it just stared back at me
0:34:53 > 0:34:56and said, "This is the thing you might have been looking for."
0:34:56 > 0:34:58It was exciting.
0:35:00 > 0:35:02Exciting it may be, but, as yet,
0:35:02 > 0:35:07the data that feeds Dan's bump is currently just raw data.
0:35:07 > 0:35:11The Fermi telescope collaboration has not yet confirmed it.
0:35:11 > 0:35:15Until they do, the excess gamma rays could be anything,
0:35:15 > 0:35:17even a problem with the gamma ray detector.
0:35:25 > 0:35:28But if it is real, if this third part of the jigsaw
0:35:28 > 0:35:32falls into place, it will not only be good for Dan's career, it will
0:35:32 > 0:35:37also confirm what this man has been saying for more than 30 years.
0:35:42 > 0:35:47He is Professor Carlos Frenk, FRS, creator of universes.
0:35:50 > 0:35:52So, Carlos, what is this place?
0:35:52 > 0:35:53Well, this is my institute,
0:35:53 > 0:35:56the Institute for Computational Cosmology of Durham University.
0:35:56 > 0:35:58This is where I work.
0:35:58 > 0:36:00That's my office up there,
0:36:00 > 0:36:04and it's here that we build replicas of the universe.
0:36:06 > 0:36:10Back in the day, when WIMPs and MACHOs were still debated,
0:36:10 > 0:36:14and Carlos was just starting out in his scientific career, he and his
0:36:14 > 0:36:19friends made a compelling case for one particular type of dark matter.
0:36:19 > 0:36:23"Dark matter," they announced - with all the certainty of youth -
0:36:23 > 0:36:29"is not only of the WIMP variety, but, furthermore, it is also cold."
0:36:30 > 0:36:34It was 1984 and the University of California in Santa Barbara
0:36:34 > 0:36:38had organised a six-month workshop on the structure of the universe.
0:36:38 > 0:36:42I was there with my three very close colleagues, and they were
0:36:42 > 0:36:46George Efstathiou from England, Simon White and Marc Davis.
0:36:46 > 0:36:49We were very young, at the time, we were only in our 20s,
0:36:49 > 0:36:53and my first job was to try and figure out,
0:36:53 > 0:36:56together with my colleagues, how galaxies formed. And to
0:36:56 > 0:37:00our amazement we realised that a particular kind of dark matter
0:37:00 > 0:37:05known as cold dark matter, was just... Would do the job just beautifully.
0:37:05 > 0:37:08Now that idea, at the time, was really not accepted.
0:37:08 > 0:37:12It was very unconventional. Because the idea that dark matter existed
0:37:12 > 0:37:15was not generally accepted and that it should be an elementary particle,
0:37:15 > 0:37:19and cold dark matter was just outrageous, but that's how we were.
0:37:19 > 0:37:22We were outrageous, too. We were young, reckless.
0:37:22 > 0:37:25I remember George Efstathiou used to wear a leather jacket
0:37:25 > 0:37:29and drive a bike, very, very fast motorbike.
0:37:29 > 0:37:32Simon and Marc were completely reckless skiers.
0:37:32 > 0:37:35I was the only reasonable individual of the gang of four,
0:37:35 > 0:37:38and then in the summer of 1984, we had
0:37:38 > 0:37:42a conference in Santa Barbara - by the beach, sun shining,
0:37:42 > 0:37:44beautiful day... I will never forget.
0:37:44 > 0:37:47I gave my first ever talk on cold dark matter,
0:37:47 > 0:37:50and at the end of it, I thought it had gone rather well,
0:37:50 > 0:37:53but at the end of it, a very, very eminent astronomer came up
0:37:53 > 0:37:56to me, whom I had met before when I was a student in Cambridge,
0:37:56 > 0:38:00and he says to me, "Carlos, I've got something important to tell you."
0:38:00 > 0:38:05He says, "I regard you as a very promising young scientist but
0:38:05 > 0:38:10"let me tell you something, if you want to have a career in astronomy,
0:38:10 > 0:38:16"the sooner you give up this cold dark matter crap, the better."
0:38:16 > 0:38:21And I remember how my world crumbled. And I went up to Simon,
0:38:21 > 0:38:24and I said, "Simon, this is what I've just been told."
0:38:24 > 0:38:27And Simon just looked at me for what seemed a very long time,
0:38:27 > 0:38:31and he said, "Just ignore him, he's an old man."
0:38:31 > 0:38:33He was 42.
0:38:33 > 0:38:35HE CHUCKLES
0:38:36 > 0:38:40Since he was told to drop it, Carlos has shown again
0:38:40 > 0:38:44and again that his ideas about cold dark matter really do seem to
0:38:44 > 0:38:47hold water, at least mathematically.
0:38:50 > 0:38:53And with the advent of computer visualisations,
0:38:53 > 0:38:57bare numbers have been transformed into the intensely beautiful
0:38:57 > 0:38:59infrastructure of our universe.
0:39:13 > 0:39:16This is not a picture of the real universe,
0:39:16 > 0:39:20this is the output of our latest simulation. So what
0:39:20 > 0:39:24we do to simulate the universe is that we create our own Big Bang
0:39:24 > 0:39:29in a computer, and then, crucially, we make an assumption about the
0:39:29 > 0:39:33nature of the dark matter, and in this particular case we have assumed
0:39:33 > 0:39:37that the dark matter is cold dark matter, and this is what comes out.
0:39:39 > 0:39:43An artificial virtual universe, but it is essentially
0:39:43 > 0:39:48indistinguishable from the real one. And it is this that validates
0:39:48 > 0:39:52our key assumption that the universe is made of cold dark matter.
0:39:53 > 0:39:56Of course, the obvious drawback with dark matter is that you can't
0:39:56 > 0:39:58see it...
0:39:58 > 0:40:02But in his universe, Carlos can simply colour it in,
0:40:02 > 0:40:04mainly purple in this case.
0:40:08 > 0:40:11So this is the backbone of the universe, this is
0:40:11 > 0:40:16the large-scale structure of the dark matter coming to us vividly.
0:40:16 > 0:40:21You can almost touch it from this realistic computer simulation.
0:40:21 > 0:40:23This is cold dark matter.
0:40:24 > 0:40:27When I look at these amazing structures that come
0:40:27 > 0:40:30out of the computers, and the fact that
0:40:30 > 0:40:33I have largely contributed to cold dark matter becoming
0:40:33 > 0:40:38the standard model of cosmology, I'm just so glad I didn't listen
0:40:38 > 0:40:43to my eminent colleague in the 1980s, who told me that the quicker I gave
0:40:43 > 0:40:47this up, the likelier it was that I would have a successful career.
0:40:47 > 0:40:49I'm just so glad I didn't listen to him.
0:40:55 > 0:40:57So cold dark matter it is, then.
0:40:57 > 0:41:00Carlos and his young guns were right.
0:41:00 > 0:41:03Their ideas are now enshrined in the standard model of cosmology.
0:41:08 > 0:41:11And the standard model of cosmology is a theory that's
0:41:11 > 0:41:14accounted for everything very well.
0:41:15 > 0:41:18It explains how Hubble's expanding universe originated.
0:41:20 > 0:41:22Our universe started...
0:41:22 > 0:41:2413.8 billion years ago...
0:41:24 > 0:41:26In an instant.
0:41:27 > 0:41:30It tells us how the universe got to be the size it is.
0:41:30 > 0:41:34ALL: This was a second period in the birth of the universe.
0:41:34 > 0:41:36It is called inflation.
0:41:36 > 0:41:41It predicts precisely how much dark matter there is in our universe.
0:41:41 > 0:41:43ALL: 26% dark matter.
0:41:43 > 0:41:47But it's a description of a problem, rather than of a thing,
0:41:47 > 0:41:50and this is where it gets frustrating, because there
0:41:50 > 0:41:53should be an answer from the standard model of particle physics.
0:41:53 > 0:41:55There are six quarks...
0:41:55 > 0:41:57ALL: Four types of gauge bosons.
0:41:57 > 0:41:59Six leptons.
0:41:59 > 0:42:01And the Higgs boson.
0:42:01 > 0:42:05But there isn't, because, so far, there isn't a particle
0:42:05 > 0:42:09in the standard model of particle physics that provides us with
0:42:09 > 0:42:13dark matter for the standard model of cosmology, cold or otherwise.
0:42:15 > 0:42:18At CERN, they're hoping to put that right.
0:42:18 > 0:42:21John Ellis thinks they might have found some likely dark matter
0:42:21 > 0:42:26particle candidates down the back of a mathematical sofa, twice as
0:42:26 > 0:42:30many particles as the standard model currently provides, to be precise.
0:42:30 > 0:42:33This idea goes under the name of...
0:42:33 > 0:42:34Supersymmetry.
0:42:34 > 0:42:36Supersymmetry.
0:42:36 > 0:42:37Supersymmetry.
0:42:39 > 0:42:42So the particles of the standard model include the electron,
0:42:42 > 0:42:45and then there's a couple of other heavier particles
0:42:45 > 0:42:49very much like it - called mu and tau.
0:42:49 > 0:42:55Other particles include neutrinos and quarks, up, down, charm,
0:42:55 > 0:42:59strange, top and bottom quarks.
0:42:59 > 0:43:05Photons, gluons and W and Z are force-carrying particles.
0:43:05 > 0:43:08Now, as I've written it, these particles wouldn't have any mass,
0:43:08 > 0:43:12but there is the missing link, the infamous Higgs boson,
0:43:12 > 0:43:17which gives masses to these particles and completes the standard model.
0:43:17 > 0:43:21Now, what supersymmetry says is that in addition to these particles,
0:43:21 > 0:43:24everyone has a partner or mirror particle, if you like,
0:43:24 > 0:43:26which we denote by twiddle,
0:43:26 > 0:43:29so there's a selectron, there's a smuon,
0:43:29 > 0:43:33there's a stau, there's a photino, there's a gluino, sneutrinos...
0:43:39 > 0:43:43Supersymmetry, or SUSY if you're in the know,
0:43:43 > 0:43:46is, according to its devotees, a rather beautiful notion that
0:43:46 > 0:43:50not only explains an awful lot of problems in physics
0:43:50 > 0:43:54and cosmology, but also provides us with a dark matter particle,
0:43:54 > 0:43:59perhaps, if it's real, as opposed to just a nice idea.
0:43:59 > 0:44:03And so far, it's been as elusive as, well, as dark matter itself.
0:44:06 > 0:44:10We were kind of hopeful that with the first run of the LHC,
0:44:10 > 0:44:14we might see some supersymmetric particles, but we didn't.
0:44:14 > 0:44:19And the fact of the matter is that we can't calculate from first principles
0:44:19 > 0:44:21how heavy these supersymmetric particles
0:44:21 > 0:44:27might be, and so what the LHC has told us so far is that they have
0:44:27 > 0:44:31to be somewhat heavier than maybe we'd hoped. But when we increase
0:44:31 > 0:44:35the energy of the LHC, we'll be able to look further, produce heavier
0:44:35 > 0:44:38supersymmetric particles, if they exist, so let's see what happens.
0:44:41 > 0:44:43Also waiting to see what happens
0:44:43 > 0:44:46and interpret the 40 million pictures per second that the
0:44:46 > 0:44:50ATLAS detector will produce, will be Dave Charlton and his team,
0:44:50 > 0:44:55but not all of them are convinced they'll see supersymmetry at all.
0:44:55 > 0:44:58I have to say, I'm not the hugest fan of supersymmetry.
0:44:58 > 0:45:03It seems slightly messy, the way you just add in, sort of, one extra
0:45:03 > 0:45:06particle for every other particle that we know about.
0:45:06 > 0:45:09I would prefer something a bit more elegant.
0:45:09 > 0:45:12People have been looking for SUSY for decades, right,
0:45:12 > 0:45:14and we've been building bigger and bigger machines
0:45:14 > 0:45:17and it's always, it's always been just out of reach, like it
0:45:17 > 0:45:19always just moves a little bit further away.
0:45:19 > 0:45:21It's always receding over the horizon.
0:45:21 > 0:45:24And it's getting to the point where, now with the LHC, it's going up in
0:45:24 > 0:45:29energy and that's such a huge reach now that if we still don't find it,
0:45:29 > 0:45:31then...you know,
0:45:31 > 0:45:33it starts to look like it's probably not the right idea.
0:45:33 > 0:45:36As an experimentalist, it's really my job to have an open mind
0:45:36 > 0:45:39and really to look at all of the possibilities and try
0:45:39 > 0:45:41and explore everything we might discover.
0:45:41 > 0:45:43The theorists might have their own favourite theories
0:45:43 > 0:45:46and say, you know, you should discover supersymmetry,
0:45:46 > 0:45:48or you should discover something else.
0:45:48 > 0:45:50I don't know. Nature will tell us what's there.
0:45:58 > 0:46:02If you're beginning to think supersymmetric particles that
0:46:02 > 0:46:06may or may not be there, and that in any case we might not be able
0:46:06 > 0:46:11ever to detect, are looking less and less likely, then you're not alone.
0:46:17 > 0:46:19In Seattle, at the University of Washington,
0:46:19 > 0:46:23Professor Leslie Rosenberg is on his own search.
0:46:32 > 0:46:34And he's not looking for SUSY.
0:46:38 > 0:46:41So, Leslie, what's wrong with supersymmetry?
0:46:41 > 0:46:44Well, I don't know that anything is wrong with it.
0:46:45 > 0:46:49As an experimenter, I suppose I'm not spun up about it.
0:46:49 > 0:46:53It's not something that I could squeeze and break like a balloon.
0:46:53 > 0:46:58If I try and squeeze it, the balloon expands and evades me.
0:46:58 > 0:47:00It's... Things are loosy-goosy
0:47:00 > 0:47:03unless you've got something definite to look at.
0:47:03 > 0:47:05So imagine that you're looking for Martians
0:47:05 > 0:47:10and you have no idea what a Martian looks like and you do an
0:47:10 > 0:47:13experiment where you're looking for someone that's purple, and they're
0:47:13 > 0:47:18half-a-metre tall, with three antennae. And you publish a paper saying
0:47:18 > 0:47:22you've excluded this particular Martian. Well, Martians could be
0:47:22 > 0:47:2612 metres tall and they could have no antennas and they could be
0:47:26 > 0:47:30a nice shade of puce, and you really haven't excluded Martians.
0:47:35 > 0:47:39Professor Rosenberg has dug his own hole in the ground, in which
0:47:39 > 0:47:42his dark matter search is about to begin.
0:47:42 > 0:47:45He's looking for yet another theoretical particle that
0:47:45 > 0:47:48nobody has ever seen, except in the form of mathematics.
0:47:49 > 0:47:54But it's not supersymmetrical, and it has a name.
0:47:54 > 0:47:57It's a type of WIMP called an axion.
0:47:59 > 0:48:03This is the axion dark matter experiment, ADMX.
0:48:03 > 0:48:07This piece of it is one of the major components.
0:48:07 > 0:48:12It's a large, super-conducting magnet, 8-Tesla...
0:48:12 > 0:48:14much, much bigger than the Earth's field.
0:48:16 > 0:48:20And this is the actual insert being assembled for the next run here.
0:48:20 > 0:48:23So the idea of the experiment is so straightforward.
0:48:23 > 0:48:28When we insert this insert into the large magnetic field here,
0:48:28 > 0:48:32nearby axions scatter off the magnetic field -
0:48:32 > 0:48:34and, oh, my goodness, there are a lot of axions.
0:48:34 > 0:48:37But the number of scatters is very small.
0:48:37 > 0:48:40That's why it's a hard experiment.
0:48:40 > 0:48:45And those few microwave photons, as a result of that scatter,
0:48:45 > 0:48:49get amplified, get pushed out of the experiment
0:48:49 > 0:48:51and detected by the
0:48:51 > 0:48:53low-noise room-temperature electronics,
0:48:53 > 0:48:57and if the axion is the dark matter, we should be able to answer
0:48:57 > 0:49:01the question - does it or does it not exist as dark matter?
0:49:03 > 0:49:07As ever, it's a simple enough question to ask, but unlike
0:49:07 > 0:49:11certain other set-ups, Leslie is hopeful that his experiment is
0:49:11 > 0:49:16straightforward enough to stand some chance of providing a simple answer.
0:49:16 > 0:49:20I can really see it as being a particle in nature,
0:49:20 > 0:49:25and I'm really driven, as we all are driven here, to try and find it.
0:49:27 > 0:49:28And if you don't?
0:49:28 > 0:49:31We will dust ourselves off and move on.
0:49:31 > 0:49:33I mean...
0:49:33 > 0:49:38God can be tough, and if God decides axions are not
0:49:38 > 0:49:40part of nature, then that's the answer.
0:49:40 > 0:49:43There's not much I can do about it.
0:49:43 > 0:49:45We will have an answer, though.
0:49:45 > 0:49:50I-I will be still living when we have an answer.
0:49:50 > 0:49:53There are many other theories where people will be long-dead
0:49:53 > 0:49:56by the time the theory is fully, fully vetted.
0:50:01 > 0:50:03But it's not just axions.
0:50:03 > 0:50:06There are other cold dark matter candidates
0:50:06 > 0:50:08competing for God's attention.
0:50:09 > 0:50:13One that glories in the name of the sterile neutrino
0:50:13 > 0:50:16isn't even cold, it's warm.
0:50:16 > 0:50:20Carlos and the gang of four may have been wrong all along.
0:50:21 > 0:50:23In recent years,
0:50:23 > 0:50:27Carlos has been flirting with the idea of warm dark matter and has
0:50:27 > 0:50:31even created a computer simulation of it in our own Milky Way.
0:50:32 > 0:50:35Cold on the left, warm on the right.
0:50:37 > 0:50:38This is still tentative.
0:50:38 > 0:50:40It's still controversial.
0:50:40 > 0:50:44But here's a prediction for what the halo of the Milky Way should
0:50:44 > 0:50:48look like if the universe is made of warm dark matter.
0:50:48 > 0:50:52It should be much smoother with far fewer small clumps.
0:50:52 > 0:50:56And the beauty of this is here we have a prediction,
0:50:56 > 0:51:00cold dark matter versus warm dark matter, that's eminently testable.
0:51:00 > 0:51:03It's now incumbent upon observational astronomers to
0:51:03 > 0:51:08tell us, with their telescopes, whether the Milky Way is
0:51:08 > 0:51:13in a halo like that or whether the Milky Way is in a halo like this.
0:51:13 > 0:51:17If it turns out to be that the universe is not made of cold dark matter,
0:51:17 > 0:51:20I will be rather depressed, given that I've
0:51:20 > 0:51:23worked all my life on cold dark matter.
0:51:23 > 0:51:26I will be disappointed, but not for very long,
0:51:26 > 0:51:28because that's the way science is.
0:51:28 > 0:51:32You have to accept the evidence and if it turns out that I've
0:51:32 > 0:51:36wasted my life working on the wrong hypothesis, so be it.
0:51:36 > 0:51:39What I really want to know is - what is the universe made of?
0:51:39 > 0:51:40Let it be cold, let it be warm.
0:51:40 > 0:51:42I just want to know what it is.
0:51:45 > 0:51:49At Fermilab, that answer might be inching slightly closer.
0:51:51 > 0:51:54CHATTER
0:51:54 > 0:51:58A representative of the Fermi telescope collaboration is
0:51:58 > 0:52:00preparing to make an announcement.
0:52:00 > 0:52:04This is the moment Dan Hooper has been waiting for,
0:52:04 > 0:52:08ever since he first identified the excess gamma rays in the centre
0:52:08 > 0:52:12of the Milky Way and saw the bump they produced in his graph.
0:52:12 > 0:52:16Professor Simona Murgia will shortly reveal
0:52:16 > 0:52:20whether the raw data that hints at the presence of a Hooperon
0:52:20 > 0:52:24is real or simply the product of a loose wire on the satellite.
0:52:31 > 0:52:37OK, so here is some more information about the Fermi mission.
0:52:37 > 0:52:40Professor Murgia's analysis of the Fermi telescope data
0:52:40 > 0:52:43is rigorous and extensive.
0:52:43 > 0:52:47So this spectrum in gamma rays of the globular class gives you
0:52:47 > 0:52:50a good indication of the spectrum of population in the second pulsars,
0:52:50 > 0:52:52so these...
0:52:52 > 0:52:55But there's only one thing Dan wants to hear.
0:52:55 > 0:52:58The signal was consistent with dark matter annihilating again.
0:52:58 > 0:53:02I will have, hopefully, new interesting results to come. Thanks.
0:53:09 > 0:53:12So what we find when we look at the data with our analysis,
0:53:12 > 0:53:17is that there seems to be an excess which is consistent with
0:53:17 > 0:53:19a dark matter interpretation, meaning that it has
0:53:19 > 0:53:24a distribution that is very similar, very consistent with what we
0:53:24 > 0:53:28think the dark matter distribution in our galaxy should look like.
0:53:28 > 0:53:31As I see it, they see, essentially, the sort of excess we've been
0:53:31 > 0:53:33talking about for years.
0:53:33 > 0:53:35That's a great step.
0:53:35 > 0:53:37They haven't been saying that until very recently.
0:53:37 > 0:53:39So I think it's very exciting because this could be
0:53:39 > 0:53:42the first time that we are seeing dark matter shining.
0:53:42 > 0:53:45However, there is a lot more work that we need to do to
0:53:45 > 0:53:48actually confirm that what we're seeing is dark matter.
0:53:48 > 0:53:51- So, we're heading in the right direction?- Right direction.
0:53:51 > 0:53:53Maybe not there yet, but definitely in the right direction.
0:53:53 > 0:53:55So you're happy that the last few years' work
0:53:55 > 0:53:57hasn't been a complete waste of time?
0:53:57 > 0:54:00It doesn't seem to have been a complete waste of time.
0:54:00 > 0:54:02OK, good.
0:54:20 > 0:54:24It might be that, finally, science is making inroads
0:54:24 > 0:54:29into the mysterious non-visible world of dark matter, perhaps.
0:54:31 > 0:54:33If the Hooperon checks out,
0:54:33 > 0:54:36and if all the fingers being crossed in Switzerland
0:54:36 > 0:54:41and France pay off, then, at least in theory, the deep-mine scientists
0:54:41 > 0:54:45will simply have the formality of looking in the right place.
0:54:45 > 0:54:49Dark matter identified, standard models intact,
0:54:49 > 0:54:51Nobel prizes handed out.
0:54:58 > 0:55:02You would think that would be that, the end of the story.
0:55:02 > 0:55:07But you'd be wrong, because there's another problem, another
0:55:07 > 0:55:12dark thing that is a description of something we don't understand.
0:55:12 > 0:55:15It's called dark energy.
0:55:15 > 0:55:20So, 15 years ago some astronomers observing distant supernovae
0:55:20 > 0:55:23saw that the distance to those supernovae was larger
0:55:23 > 0:55:26than they expected, and so the only way that they could
0:55:26 > 0:55:30understand that was to have a universe that started accelerating
0:55:30 > 0:55:34three billion years ago, and whether that carries on accelerating
0:55:34 > 0:55:38or not, we don't know, but what we do know is that there has to be
0:55:38 > 0:55:42another component to the universe which we call this dark energy.
0:55:43 > 0:55:46- But you don't know what it is? - No idea. Not at all.
0:55:46 > 0:55:47No-one knows what it is?
0:55:47 > 0:55:49No-one. No-one.
0:55:50 > 0:55:52There are more theories than there are theoreticians.
0:55:55 > 0:55:58And that's a problem, because according to the standard
0:55:58 > 0:56:02model of cosmology, it makes up most of the universe.
0:56:02 > 0:56:06Our universe consists of 4% baryonic matter.
0:56:06 > 0:56:0826% dark matter.
0:56:08 > 0:56:10And 70% dark energy.
0:56:12 > 0:56:15And because dark energy seems to make sense,
0:56:15 > 0:56:17at least at a theoretical level,
0:56:17 > 0:56:20it's the role of experimentalists like Bob
0:56:20 > 0:56:23to think of ways to explain it.
0:56:23 > 0:56:26That's why he's come here to the Dark Energy Survey
0:56:26 > 0:56:32at Cerro Tololo, where one of the world's largest digital cameras
0:56:32 > 0:56:36scans the night sky in search of more supernovae
0:56:36 > 0:56:40and an ever more accurate picture of the universe's expansion history.
0:56:42 > 0:56:45You can probably see some of the stars, and in here will be
0:56:45 > 0:56:49some of the supernovae that we're hunting to measure dark energy.
0:56:49 > 0:56:51So are you hopeful?
0:56:51 > 0:56:52I am hopeful.
0:56:52 > 0:56:56I think we will be able to make at least a factor-of-ten improvement
0:56:56 > 0:57:00with using this instrument, than we have today.
0:57:00 > 0:57:03And then if we don't get that, we'll have to wait for LSST.
0:57:07 > 0:57:11The LSST, the Large Synoptic Survey Telescope,
0:57:11 > 0:57:16is being built on another Chilean mountain and is due to come
0:57:16 > 0:57:21on stream in 2021, representing a significant jump in resolution.
0:57:24 > 0:57:28With this instrument, we can observe about 3,000 supernovae.
0:57:28 > 0:57:31With the LSST we'll be able to observe about a million supernovae,
0:57:31 > 0:57:33and that should really nail it.
0:57:34 > 0:57:38OK. It won't though, will it? Actually?
0:57:38 > 0:57:41THEY LAUGH
0:57:41 > 0:57:42See...
0:57:42 > 0:57:45It'll nail it, it will nail it.
0:57:45 > 0:57:47What, what will it nail?
0:57:47 > 0:57:50Well, it'll nail the expansion history of the universe
0:57:50 > 0:57:53and then, hopefully, some bright theorist will come up with...
0:57:53 > 0:57:55So it's not going to nail dark energy.
0:57:55 > 0:57:57It'll just show you how it's expanding?
0:57:57 > 0:57:59It'll show us how the universe is expanding
0:57:59 > 0:58:03and then, hopefully, that will give us some direction
0:58:03 > 0:58:06in which to understand the true nature of dark energy.
0:58:07 > 0:58:11It could be that cosmology stands on the cusp of revealing
0:58:11 > 0:58:13the true nature of our universe.
0:58:15 > 0:58:18Then again, it may stand on the cusp of nothing at all.
0:58:19 > 0:58:24It might be that the only way to progress is not to look harder,
0:58:24 > 0:58:27but to embrace a new physics that's currently,
0:58:27 > 0:58:30like the dark universe, just out of reach.
0:58:41 > 0:58:42HE EXHALES
0:59:00 > 0:59:03HE LAUGHS