0:00:28 > 0:00:30Good evening. For this programme,
0:00:30 > 0:00:35we are going to talk about the material that makes up the universe.
0:00:35 > 0:00:39But before that, can you remember our Moore Winter Marathon?
0:00:39 > 0:00:43We asked you to look at and describe the most interesting object
0:00:43 > 0:00:45you can see in the night sky? Now, to find out
0:00:45 > 0:00:50what we can see this month, Pete and Paul.
0:00:51 > 0:00:54Peter and I have come to Wirksworth in Derbyshire
0:00:54 > 0:00:57in the Peak District, to see this lovely work of art
0:00:57 > 0:00:59called a star disc.
0:00:59 > 0:01:02It has all the constellations which make up the sky
0:01:02 > 0:01:06and its creator is Aidan Shingler.
0:01:06 > 0:01:08So, Aidan, what inspired the star disc?
0:01:08 > 0:01:10I've always been enchanted by the mystery and magic
0:01:10 > 0:01:13of the stars, and my interest in the stars
0:01:13 > 0:01:17lies in our emotional response to them,
0:01:17 > 0:01:20in particular, the power they possess to ignite
0:01:20 > 0:01:23our imagination and sense of wonder.
0:01:23 > 0:01:26Yeah, it is true. If you look at all the constellations,
0:01:26 > 0:01:30they are all the dreams of the human civilisation are put up there.
0:01:30 > 0:01:34It's a perfect location to talk about our Moore Winter Marathon.
0:01:34 > 0:01:37Fifty objects for you to see in the winter night sky
0:01:37 > 0:01:41and many of you have already started.
0:01:41 > 0:01:43Here are some images which you've posted on our Flickr site.
0:01:46 > 0:01:51Mick Hyde's Kemble's Cascade is at Number 17. It's lovely.
0:01:51 > 0:01:54So too is Number 8, the star cluster in Auriga,
0:01:54 > 0:01:56taken by Paul Hutchinson.
0:01:57 > 0:02:00This wide shot has lots of objects,
0:02:00 > 0:02:03Number 7, 8, 9 and 10 on our list.
0:02:03 > 0:02:07You just need your Mark One Eyeball for many of the objects.
0:02:07 > 0:02:11To help you find them, try using a planisphere.
0:02:11 > 0:02:14So, this month we're going to look at some
0:02:14 > 0:02:17of the naked eye objects you can see with the Moore Winter Marathon
0:02:17 > 0:02:20and I've brought a fantastically simple tool with me
0:02:20 > 0:02:22to help me locate these objects.
0:02:22 > 0:02:24A planisphere, I've got one of these. These are good
0:02:24 > 0:02:27if you're learning your way around the sky.
0:02:27 > 0:02:31It's basically the star disc, with a piece of plastic on top
0:02:31 > 0:02:33showing the night sky that's available.
0:02:33 > 0:02:36That's right, all the stars... shouldn't pull it apart like this...
0:02:36 > 0:02:38all the stars you can see underneath represent
0:02:38 > 0:02:41all the stars you can see in the sky
0:02:41 > 0:02:43- throughout the entire year.- Yeah.
0:02:43 > 0:02:46Of course you can't see that in one go, so what happens
0:02:46 > 0:02:49is that there is an overlay printed on the top with a window in it.
0:02:49 > 0:02:53That window represents just the stars you can see at a specific date
0:02:53 > 0:02:56and time of the year. So what we have to do is put that window
0:02:56 > 0:03:00- in the correct position for your current date and time.- Right.
0:03:00 > 0:03:03So, for example, if we wanted to observe the sky
0:03:03 > 0:03:06at 10pm in the middle of November,
0:03:06 > 0:03:09let's rotate that round so that the time,
0:03:09 > 0:03:11- which is 10pm, which is there...- OK.
0:03:11 > 0:03:13...lines up with the middle of November.
0:03:13 > 0:03:16Now those stars in that window that we can see represent the stars
0:03:16 > 0:03:19we can see in the sky at 10pm.
0:03:19 > 0:03:21We also have some other interesting things,
0:03:21 > 0:03:24we have the western horizon, the eastern horizon, north and south.
0:03:24 > 0:03:27- Those are useful for orientating the thing.- Absolutely.
0:03:27 > 0:03:30Let's start with the south, we've got the southern horizon here,
0:03:30 > 0:03:34if you hold it up so that the southern bit is at the bottom,
0:03:34 > 0:03:36then that part of the sky
0:03:36 > 0:03:38you can see would be what you'd see to the south.
0:03:38 > 0:03:42But they are incredibly simple and they don't cost very much...
0:03:42 > 0:03:45- No, they don't.- ... a few pounds and it's a great way of finding out
0:03:45 > 0:03:49- what's in your particular night sky at any time of the year.- I agree.
0:03:49 > 0:03:51So, let's go on to the Moore Winter Marathon.
0:03:51 > 0:03:54Yes, we are going to start over here, aren't we?
0:03:54 > 0:03:56Actually, I'm very near to where we're going to start.
0:03:56 > 0:03:59- The Hyades and the Pleiades. - Those are the first two items
0:03:59 > 0:04:03on the Moore Winter Marathon. We've also, at the moment got
0:04:03 > 0:04:06- a wandering object down there... - Oh, we have!- ..which is Jupiter.
0:04:06 > 0:04:09- It's not on the star disc, because it moves about...- That's right.
0:04:09 > 0:04:12- ..over time.- That's right, it's a wandering star.- A wandering star.
0:04:12 > 0:04:16I feel really guilty because I'm standing on Orion at the moment
0:04:16 > 0:04:19and I shouldn't do that to the mighty hunter! If you can locate Orion,
0:04:19 > 0:04:21and most people know what Orion looks like,
0:04:21 > 0:04:23the belt stars, these three stars in the centre here,
0:04:23 > 0:04:26act as a signpost, because if you follow them up
0:04:26 > 0:04:29and to the right, they point to Aldebaran.
0:04:29 > 0:04:32That's an indicator of how to get to the V-shaped Hyades cluster.
0:04:32 > 0:04:35Which is here, this is the Hyades cluster, isn't it?
0:04:35 > 0:04:37That's right. But we can also use the Hyades
0:04:37 > 0:04:40to locate another object in the Moore Winter Marathon,
0:04:40 > 0:04:42- because they're like an arrow head. - Oh, yes!
0:04:42 > 0:04:44If you use the arrow head and point it this way,
0:04:44 > 0:04:48you come to a variable star, which is known as Lambda Tauri.
0:04:48 > 0:04:51Sticking with the naked-eye stuff, we should move over to the constellation
0:04:51 > 0:04:55of Perseus and Cassiopeia.
0:04:55 > 0:04:58- Cassiopeia, a very distinctive constellation.- A W in the night sky.
0:04:58 > 0:05:02- And around about here... - You go from the centre star of the W
0:05:02 > 0:05:05to the next one to its left and then follow the line down
0:05:05 > 0:05:08- for the same distance again. - And here's the double cluster.
0:05:08 > 0:05:10Yeah, which we can see has a sort of misty patch
0:05:10 > 0:05:13with your eyes, but really the best view
0:05:13 > 0:05:15- is with a pair of binoculars.- It is. - It's quite stunning.
0:05:15 > 0:05:18It's that wonderful tornado of stars spilling out into space,
0:05:18 > 0:05:21- it's quite wonderful. - Nice description.- You like that?
0:05:21 > 0:05:22It's mine!
0:05:22 > 0:05:26Let's go back now to an object, well it's not an object at all,
0:05:26 > 0:05:29- it's a pattern.- It's your made-up pattern, your asterism.
0:05:29 > 0:05:32- It's an unofficial pattern. - OK, I'll show it out,
0:05:32 > 0:05:34I'll walk it out on the star disc.
0:05:34 > 0:05:37This is the celestial G and this is what's known as an asterism,
0:05:37 > 0:05:40an unofficial pattern of stars in the night sky.
0:05:40 > 0:05:42To start out you're going to have to go to Aldebaran.
0:05:42 > 0:05:46- Right, OK.- You've got a bit of a walk ahead of you.- OK, off we go.
0:05:46 > 0:05:50- So head up to Capella, which is in Auriga.- OK, here we go.
0:05:50 > 0:05:52- The yellow star. - OK, now down to Castor and Pollux,
0:05:52 > 0:05:56- the two bright stars in Gemini, the twins.- There we go.
0:05:56 > 0:05:59OK, now down to Procyon the brightest star in Canis Minor, the little dog
0:05:59 > 0:06:02down to Sirius, the brightest star in the night sky,
0:06:02 > 0:06:05and then Rigel, up to Bellatrix,
0:06:05 > 0:06:07and then across to Betelgeuse.
0:06:07 > 0:06:10- It's most of the sky. - It IS most of the sky,
0:06:10 > 0:06:13but it's a really fun pattern in the sky,
0:06:13 > 0:06:14especially for kids to point out
0:06:14 > 0:06:17- some of the brightest stars that you can see.- It is.
0:06:17 > 0:06:20Let's hope we get some cold, clear nights in November
0:06:20 > 0:06:23for you to take part in our Moore Winter Marathon.
0:06:23 > 0:06:27You can find the lists, guides and information on our website.
0:06:33 > 0:06:34Next month we will talk about
0:06:34 > 0:06:37some of the things you can see with a pair of binoculars,
0:06:37 > 0:06:42a whole world of clusters and even a galaxy.
0:06:42 > 0:06:44Now, over to Chris Lintott, on Selsey beach,
0:06:44 > 0:06:46on the trail of dark matter.
0:06:46 > 0:06:50It's the story of stuff and what makes up our universe.
0:06:52 > 0:06:55Everything's the same here on Earth
0:06:55 > 0:06:57whether it's the sea, the air, the rocks,
0:06:57 > 0:07:00they're all made of atoms, whether it's hydrogen,
0:07:00 > 0:07:03oxygen, nitrogen or any of the rest, it's all the same.
0:07:03 > 0:07:06But that's not true of the universe.
0:07:09 > 0:07:13Wherever we look in the universe, rather frustratingly,
0:07:13 > 0:07:15something just doesn't quite add up.
0:07:16 > 0:07:18In the cosmic sweet jar,
0:07:18 > 0:07:22the coloured jellybeans represent the stuff that makes up you and me,
0:07:22 > 0:07:25which makes up the planets, the stars and even the galaxies.
0:07:25 > 0:07:30The rest, amounting to six times as much, is made of something
0:07:30 > 0:07:35we don't see, a mysterious substance known as dark matter.
0:07:35 > 0:07:38In our cosmic sweet jar, the result is more black jellybeans
0:07:38 > 0:07:40than anyone could possibly devour,
0:07:40 > 0:07:44but in space, the consequences are rather more serious.
0:07:44 > 0:07:49Dark matter is responsible for shaping everything that we see.
0:07:49 > 0:07:52What's so shocking is that there's so much dark matter
0:07:52 > 0:07:54and yet it eludes direct detection.
0:07:54 > 0:07:59We can see its effects, we just can't hold it up for inspection.
0:08:01 > 0:08:04So, Carlos, I think we've got some jellybeans
0:08:04 > 0:08:06to help us illustrate dark matter.
0:08:06 > 0:08:09Both Carlos Frenk and Chris North are joining me
0:08:09 > 0:08:10in the search for dark matter.
0:08:10 > 0:08:12We must make sure, though, that people realise
0:08:12 > 0:08:15that the dark matter is NOT made of jellybeans.
0:08:15 > 0:08:18Well, even with jellybeans,
0:08:18 > 0:08:19it seems like a strange idea
0:08:19 > 0:08:22that we don't know what most of the universe is made of.
0:08:22 > 0:08:25- But it's not a new idea, is it? - It's not a new idea
0:08:25 > 0:08:27but it's certainly the case that dark matter
0:08:27 > 0:08:31is one of the most profound mysteries in science today.
0:08:31 > 0:08:34The story goes back to the 1930s,
0:08:34 > 0:08:37when astronomers realised that galaxies
0:08:37 > 0:08:39are not just uniformly distributed around the cosmos,
0:08:39 > 0:08:46but they like to collect in entities that are well defined.
0:08:46 > 0:08:49The most visible of those are galaxy clusters.
0:08:49 > 0:08:51Big cities of galaxies, hundreds of galaxies.
0:08:51 > 0:08:53Hundreds or thousands of bright galaxies,
0:08:53 > 0:08:57all making a galaxy cluster.
0:08:57 > 0:08:59So, what does a cluster tell you about dark matter?
0:08:59 > 0:09:04It was recognised that galaxies in the clusters are swarming around
0:09:04 > 0:09:08and astronomers asked a very simple question -
0:09:08 > 0:09:10what keeps a galaxy cluster together?
0:09:10 > 0:09:13What is confining the galaxies in the cluster?
0:09:13 > 0:09:15It must be the force of gravity, what else?
0:09:15 > 0:09:21Then came the real shock, because when astronomers worked out
0:09:21 > 0:09:26how much gravity the galaxies that we could see produced,
0:09:26 > 0:09:29they realised there was a gravity deficit.
0:09:29 > 0:09:34They realised that there had to be 10 times more mass in the cluster
0:09:34 > 0:09:38than the mass they could see in the form of stars.
0:09:38 > 0:09:42Essentially, we can weigh the stuff we can see, we can weigh the stars
0:09:42 > 0:09:44and the gas and the dust in these galaxies.
0:09:44 > 0:09:46by essentially counting stars.
0:09:46 > 0:09:48We understand stars, stars are nice and simple...
0:09:48 > 0:09:51But they're not enough. They were not enough.
0:09:51 > 0:09:56It was recognised that something else that's not stars, it's not gas,
0:09:56 > 0:09:59it is something else - hopefully not jellybeans!
0:09:59 > 0:10:04Something else was responsible for keeping galaxy clusters together.
0:10:04 > 0:10:07And this news came as a shock. It was a real stunner.
0:10:07 > 0:10:11The universe is full of stuff we cannot see.
0:10:11 > 0:10:15So, that was the 1930s and this endured as a mystery
0:10:15 > 0:10:18and then I guess the next shock came when people looked,
0:10:18 > 0:10:21not at clusters of galaxies, but at galaxies themselves,
0:10:21 > 0:10:23individual galaxies like our own Milky Way.
0:10:23 > 0:10:27Exactly. And the story was exactly the same.
0:10:27 > 0:10:29In a galaxy, a beautiful galaxy,
0:10:29 > 0:10:31these amazing things that nature has made,
0:10:31 > 0:10:34these galaxies with stars, going round and round
0:10:34 > 0:10:36the centre in circular motion.
0:10:36 > 0:10:40- Just like the sun goes round the centre of the Milky Way.- Exactly.
0:10:40 > 0:10:45- Why does the Milky Way not just fly apart?- The answer is gravity again.
0:10:45 > 0:10:48Not the gravity we can see because that's only a very small fraction
0:10:48 > 0:10:51of the gravity that's needed,
0:10:51 > 0:10:54so we now know that galaxies like our own Milky Way
0:10:54 > 0:10:57are sitting in a clump
0:10:57 > 0:11:00of something we cannot see, a clump of dark matter
0:11:00 > 0:11:04and it is that dark matter that keeps our galaxy in place.
0:11:04 > 0:11:08Thank God for dark matter, otherwise our galaxy would not exist!
0:11:08 > 0:11:10And it's distributed differently,
0:11:10 > 0:11:13so if you think of our galaxy, as Patrick would say
0:11:13 > 0:11:15as two fried eggs back-to-back, a disc,
0:11:15 > 0:11:17and a bulge at the centre, where's the dark matter?
0:11:17 > 0:11:20The dark matter is very much not in the disc,
0:11:20 > 0:11:24it's in a much larger volume, it's in what we call a halo.
0:11:24 > 0:11:27It's a spherical region, roughly, around the galaxy,
0:11:27 > 0:11:31so if we look at other galaxies, we see the discs of stars
0:11:31 > 0:11:34and gas and dust and all the normal matter, the ordinary matter.
0:11:34 > 0:11:36And if we then say where the dark matter is,
0:11:36 > 0:11:40it's in this roughly spherical blob, this halo
0:11:40 > 0:11:43around them and quite a lot larger than stars are as well,
0:11:43 > 0:11:47it's normally a few times bigger and you get this halo...
0:11:47 > 0:11:50It's the gravity from the halo that keeps the discs stable
0:11:50 > 0:11:53- and enables it to be able to turn. - Most of the exciting stuff, really,
0:11:53 > 0:11:57- is the dark matter.- You're a fan of the black jelly beans in other words.
0:11:57 > 0:12:01I like the black jelly beans. The coloured ones, I never know which colour to choose.
0:12:01 > 0:12:06I don't really know what's inside them.
0:12:06 > 0:12:10Dark matter is almost certainly some elementary particle,
0:12:10 > 0:12:15some mysterious and yet to be discovered elementary particle
0:12:15 > 0:12:18Some physicists believe that they narrow down the possibilities
0:12:18 > 0:12:23and that, in fact, we are zooming into the identity
0:12:23 > 0:12:25of the dark matter. Whatever it is,
0:12:25 > 0:12:28we know it's everywhere, it's not just in galaxies, it's everywhere.
0:12:28 > 0:12:31- It permeates...- It's passing through this room right now?
0:12:31 > 0:12:34It's passing through the room and as we speak,
0:12:34 > 0:12:38there are billions of particles of dark matter going through
0:12:38 > 0:12:41your body, you just don't feel them
0:12:41 > 0:12:44because they produce gravity but gravity's a very weak force.
0:12:44 > 0:12:49They don't interact with the rest of me or my normal matter, they just pass through?
0:12:49 > 0:12:51They pass straight through, they leave no sign,
0:12:51 > 0:12:54they're not radioactive, they do not collide with any of your atoms
0:12:54 > 0:12:58- and that's good for health and safety reasons.- Yes, good.
0:12:58 > 0:13:00It's bad if you're an experimental physicist
0:13:00 > 0:13:02and you want to detect them.
0:13:02 > 0:13:06- You want to catch them as they go past.- You can't - they go through your instrument.
0:13:06 > 0:13:10The only way we measure dark matter is through its gravitational pull,
0:13:10 > 0:13:13- for its effect on other particles. - For the most part.
0:13:13 > 0:13:18The problem is that gravity... the mass is really hard to measure,
0:13:18 > 0:13:20that's why it's so hard to pin down.
0:13:20 > 0:13:23We can work out it's roughly in these spherical blobs,
0:13:23 > 0:13:25these halos around galaxies,
0:13:25 > 0:13:27but working out exactly what shape they are
0:13:27 > 0:13:30is actually really very tricky.
0:13:30 > 0:13:33- Surely you're really fishing in the dark?- Yeah.
0:13:33 > 0:13:36We need more evidence to support such a strange theory,
0:13:36 > 0:13:37so what else have you got?
0:13:37 > 0:13:40Well, I agree. Extraordinary claims
0:13:40 > 0:13:42require extraordinary evidence
0:13:42 > 0:13:47and the other source of evidence for the existence of dark matter
0:13:47 > 0:13:50comes from the phenomenon of gravitational lensing.
0:13:50 > 0:13:54- So, this is Einstein's old idea? - Einstein's old idea.
0:13:54 > 0:13:56Let me explain to you how gravitational lensing works.
0:13:56 > 0:14:01In everyday life, light travels in a straight line.
0:14:01 > 0:14:06Not so when light wanders near a concentration of mass.
0:14:06 > 0:14:08A large concentration of mass.
0:14:08 > 0:14:13A very large concentration of mass, light can be bent by mass.
0:14:13 > 0:14:17Now, imagine Chris is a background galaxy.
0:14:17 > 0:14:19OK. You're doing a very good job.
0:14:19 > 0:14:21He looks like one. He looks galactic.
0:14:21 > 0:14:24Here is a galaxy cluster...
0:14:24 > 0:14:27With some dark matter and some ordinary matter.
0:14:27 > 0:14:31And some ordinary matter. And Chris is a source of light,
0:14:31 > 0:14:35the light ray from Chris coming towards me -
0:14:35 > 0:14:40I'm the observer - will be bent by the concentration of mass.
0:14:41 > 0:14:45Bending of the light will cause Chris to become blurred
0:14:45 > 0:14:47and distorted.
0:14:47 > 0:14:49In a characteristic way, right?
0:14:49 > 0:14:52- In a characteristic way. - What he means...- We will see you
0:14:52 > 0:14:55as an arc and if you look at galaxy clusters,
0:14:55 > 0:14:58you see these arcs, don't you, around the outside of the cluster?
0:14:58 > 0:15:01And if you get it exactly lined up, you get a full ring,
0:15:01 > 0:15:02it's called an Einstein ring.
0:15:02 > 0:15:05Now, how does this tell us about dark matter?
0:15:05 > 0:15:08- Well, I was about to ask.- Well, you can look at a galaxy cluster
0:15:08 > 0:15:11and the way it bends light and you soon conclude,
0:15:11 > 0:15:14if you can do your sums correctly,
0:15:14 > 0:15:18that the amount of mass in the divisible part of the galaxy
0:15:18 > 0:15:20- is nowhere near enough.- We are using this as a way of weighing
0:15:20 > 0:15:24this cluster that's in the way, essentially.
0:15:24 > 0:15:28The answer is it weighs about ten times more than the mass
0:15:28 > 0:15:32that you can see directly in the form of stars. Ten times more.
0:15:32 > 0:15:35The number we got from looking at the movement of the galaxies.
0:15:35 > 0:15:39Two very different ways of weighing the cluster and they tie together.
0:15:39 > 0:15:41And they give us the same answer.
0:15:41 > 0:15:45How can we get a better understanding of how much dark matter there is?
0:15:45 > 0:15:48Astronomically, the evidence gives us an approximate number,
0:15:48 > 0:15:52but indeed the universe has a way to tell us
0:15:52 > 0:15:55exactly what it is made of.
0:15:55 > 0:15:59That takes us back to the very beginning
0:15:59 > 0:16:02of our universe. Almost to the Big Bang itself.
0:16:04 > 0:16:10We now know that when the universe was a mere 350,000 years old,
0:16:10 > 0:16:13the fog of the Big Bang lifted
0:16:13 > 0:16:16and the glow of the Big Bang explosion
0:16:16 > 0:16:21was able to propagate freely until we detect it.
0:16:21 > 0:16:25And we see this as the cosmic microwave background. You studied this.
0:16:25 > 0:16:27As we look further out into space,
0:16:27 > 0:16:30because light travels at a particular speed, we see things
0:16:30 > 0:16:32as they were further ago. We see the sun
0:16:32 > 0:16:35as it was eight minutes ago and so on and so forth.
0:16:35 > 0:16:38If we look really far away, we look billions of years back in time
0:16:38 > 0:16:41and so we see the universe as it was when it was very young
0:16:41 > 0:16:44and we see it in microwaves, it's actually all very similar -
0:16:44 > 0:16:47the early universe was very uniform -
0:16:47 > 0:16:50but there are bits that are more dense and bits that are less dense
0:16:50 > 0:16:53and we can map out the temperature of the early universe
0:16:53 > 0:16:55and the density of the early universe.
0:16:55 > 0:16:58The first map of these hot and cold spots
0:16:58 > 0:17:01really changed our perception of the universe,
0:17:01 > 0:17:04because here we were, looking at the baby universe
0:17:04 > 0:17:09and this baby universe reveals the secrets of the cosmos
0:17:09 > 0:17:12and in particular, the pattern of hot and cold spots
0:17:12 > 0:17:17allows us to infer, using the laws of physics,
0:17:17 > 0:17:20the exact composition of the universe,
0:17:20 > 0:17:25the exact mixture of ordinary material and dark matter.
0:17:25 > 0:17:28And that, through measurements of these, that is what tells us
0:17:28 > 0:17:33with great precision that 84.5%
0:17:33 > 0:17:35of the matter in the universe is dark
0:17:35 > 0:17:41and the remaining 14.5% is, in fact, ordinary matter.
0:17:41 > 0:17:46Approximately, one part of visible for six parts of dark.
0:17:46 > 0:17:49And it is this precision with which we can measure this
0:17:49 > 0:17:54that allows us now to go on to the next important question -
0:17:54 > 0:17:57what is the dark matter?
0:17:57 > 0:18:01One way to solve that mystery is to try and make some dark matter.
0:18:03 > 0:18:05We can see the effects of dark matter in space,
0:18:05 > 0:18:08but for the last quarter of a century,
0:18:08 > 0:18:11astronomers have been trying to find it here on Earth.
0:18:11 > 0:18:14They bury their detectors deep underground and just a few years ago,
0:18:14 > 0:18:17The Sky At Night descended into Boulby salt mine
0:18:17 > 0:18:22in Yorkshire to see what a dark matter detector would look like.
0:18:22 > 0:18:26Here I am, in a lift going three-quarters of a mile underground
0:18:26 > 0:18:30in Boulby mine towards this strange observer thing.
0:18:30 > 0:18:34Despite all this effort, dark matter is still elusive, and so, instead
0:18:34 > 0:18:37of waiting for a direct hit down in a mine,
0:18:37 > 0:18:41some scientists have grown impatient and they're trying to produce
0:18:41 > 0:18:46their own dark matter at the world's was famous laboratory, CERN.
0:18:48 > 0:18:52We think of objects like this rock as being pretty solid,
0:18:52 > 0:18:55but it is not, it's full of billions of separate atoms,
0:18:55 > 0:18:58each one has a nucleus, with protons and neutrons,
0:18:58 > 0:19:01surrounded by a cloud of electrons.
0:19:03 > 0:19:07Inside each proton is a whole world of even smaller particles,
0:19:07 > 0:19:11whose effects become apparent when protons are smashed together.
0:19:11 > 0:19:14In Geneva is the world's largest machine,
0:19:14 > 0:19:16the Large Hadron Collider, or LHC.
0:19:16 > 0:19:20It's probably the most sophisticated experiment ever carried out
0:19:20 > 0:19:25and it's certainly impressive. Here, protons are accelerated
0:19:25 > 0:19:26to close to the speed of light
0:19:26 > 0:19:31and then smashed together so that physicists can pick over the debris.
0:19:31 > 0:19:34It's weird that the very small stuff that we look at
0:19:34 > 0:19:37actually influences the very big-scale stuff in the universe.
0:19:37 > 0:19:40Astronomy and particle physics together.
0:19:40 > 0:19:43John Butterworth was part of the team that used the LHC
0:19:43 > 0:19:46to find the infamous Higgs-boson particle,
0:19:46 > 0:19:49the one that gives everything mass.
0:19:49 > 0:19:52In looking for the Higgs, they had to recreate the conditions
0:19:52 > 0:19:56that existed in the early universe, just after the Big Bang.
0:19:56 > 0:20:00- How's the early universe different from today?- It's about symmetries
0:20:00 > 0:20:02and the best way to explain it is with a wine bottle.
0:20:02 > 0:20:05Good. I like wine bottles, so that's excellent.
0:20:05 > 0:20:08I look down the bottom, it's symmetric, all round the middle.
0:20:08 > 0:20:11So any direction's the same at the end of the bottle.
0:20:11 > 0:20:12That's right. Put something in it.
0:20:12 > 0:20:14I've got one of Carlos's jellybeans, luckily,
0:20:14 > 0:20:16- so let's drop that in.- That'll do.
0:20:16 > 0:20:19- If you look down, it's not symmetric.- The bean's at the bottom.
0:20:19 > 0:20:22- The bean has broken the symmetry. Yeah?- Yeah, that makes sense.
0:20:22 > 0:20:25- That's no longer symmetric.- The early universe was very symmetric.
0:20:25 > 0:20:27The reason was a lot of energy, so the bean was jigging round.
0:20:27 > 0:20:30There's an equal chance it'll be anywhere around the sides of the bottle
0:20:30 > 0:20:34- It might be on the left... - It's symmetric round the middle.
0:20:34 > 0:20:37- We're back to a symmetric universe. - That's right.
0:20:37 > 0:20:39But as you cool down past where the energies of the LHC are...
0:20:39 > 0:20:42The universe expands, as everything cools down,
0:20:42 > 0:20:44if you don't have a collider, the bean drops to the bottom.
0:20:44 > 0:20:48This is everyday life, the bean is off on one side, the symmetry's broken.
0:20:48 > 0:20:51It's only by having the symmetry, the symmetry's still in the bottle,
0:20:51 > 0:20:54- we haven't changed...- We haven't changed the universe or physics.
0:20:54 > 0:20:57It's the cold bit when the bean's no longer got loads of energy,
0:20:57 > 0:21:00then the symmetry's broken. And that symmetry breaking there
0:21:00 > 0:21:02is actually how mass occurs in the universe,
0:21:02 > 0:21:06the only way we can have the symmetry we need in the theory
0:21:06 > 0:21:10at high energies or have mass in everyday life, which is clearly there...
0:21:10 > 0:21:13- Yes.- ..is to have, basically, a bean in a wine bottle.
0:21:13 > 0:21:16The symmetry that's broken, that's broken by the thing slowing down,
0:21:16 > 0:21:18but is there again if you give it lots of energy.
0:21:18 > 0:21:21And that idea of symmetry is so fundamental to physics.
0:21:21 > 0:21:25- And there we are with a wine bottle and a bean. Fabulous.- That's right.
0:21:27 > 0:21:29Whenever the particles collide,
0:21:29 > 0:21:33all the debris should fly off in a roughly symmetrical fashion.
0:21:35 > 0:21:37If that doesn't happen,
0:21:37 > 0:21:40then that might be the signature of dark matter.
0:21:40 > 0:21:43The sign we're looking for might be there already,
0:21:43 > 0:21:46buried in the data that the LHC has already provided.
0:21:48 > 0:21:51Now, you found your Higgs so particle physicists are happy,
0:21:51 > 0:21:53though you've other stuff to look for. For us, as astronomers,
0:21:53 > 0:21:55what we need you to do is to find dark matter.
0:21:55 > 0:21:58Is there any hope of the LHC helping us out?
0:21:58 > 0:22:01There is indeed hope. You may be surprised to hear that, actually,
0:22:01 > 0:22:05because dark matter is, of course, dark and hard to see.
0:22:05 > 0:22:08But there is a chance that the LHC is actually a dark matter factory,
0:22:08 > 0:22:12- that were actually making dark matter in there.- Right now?- Yes.
0:22:12 > 0:22:16It will be hard to see, in fact, the particles themselves, we will not see,
0:22:16 > 0:22:19but we surround the beam with these huge detectors
0:22:19 > 0:22:22which are essentially concentric layers of different technologies
0:22:22 > 0:22:26to interrogate these collisions. So, if we see something
0:22:26 > 0:22:29flying off in one direction and nothing in the other direction,
0:22:29 > 0:22:32then we know something's missing, we know the event's imbalanced,
0:22:32 > 0:22:35- and something must have been there. - The rules of physics say,
0:22:35 > 0:22:38- roughly, things have to go in equal directions.- The momentum is conserved.
0:22:38 > 0:22:41That would look like in your detector if you've got your collision here,
0:22:41 > 0:22:44you'd have stuff going in this direction, and if you see nothing,
0:22:44 > 0:22:46- you know you were missing something.- Exactly.
0:22:46 > 0:22:48- Any sign of dark matter yet?- No.
0:22:48 > 0:22:51And that's expected, right? It's going to take a while.
0:22:51 > 0:22:54There are a lot of theorists who thought we might have found it by now
0:22:54 > 0:22:58and would have told us experimentalists we would have done, but we haven't yet.
0:22:58 > 0:23:02The thing is... the whole business of the galaxy
0:23:02 > 0:23:05is that we're looking at this completely new regime of physics,
0:23:05 > 0:23:07where these forces unify, where the Higgs lives...
0:23:07 > 0:23:10- As you said, that's the point. - That's right.
0:23:10 > 0:23:12There's a very good chance that if dark matter
0:23:12 > 0:23:15is a new fundamental particle, this is the region where it lives.
0:23:15 > 0:23:18There's still plenty of space to look. We started looking
0:23:18 > 0:23:21and we've kind of landed on a shore of a new country of physics,
0:23:21 > 0:23:24OK, the dark matter wasn't hanging around on the beach,
0:23:24 > 0:23:27but it might be further inland, we're exploring that now
0:23:27 > 0:23:28and we've got a lot of exploring to do.
0:23:28 > 0:23:31To understand dark matter,
0:23:31 > 0:23:34we have to go almost all the way back to the Big Bang.
0:23:34 > 0:23:38In that maelstrom of rapidly moving and colliding particles,
0:23:38 > 0:23:42the very building blocks of matter itself were being formed.
0:23:44 > 0:23:46In the early universe, we don't just have ordinary matter,
0:23:46 > 0:23:49we have antimatter, particles of the same mass
0:23:49 > 0:23:52but with a different charge. Look, this sand castle
0:23:52 > 0:23:54has about a billion sand grains in it,
0:23:54 > 0:23:56but in the early universe we'd also have
0:23:56 > 0:23:58a billion particles of antimatter.
0:23:58 > 0:24:02Now, when matter and antimatter collide, they annihilate,
0:24:02 > 0:24:05producing light, so if we mix these two together,
0:24:05 > 0:24:09we lose everything, we get a universe just filled with radiation.
0:24:09 > 0:24:12The only thing that saves us is that as it turns out,
0:24:12 > 0:24:15for every billion antimatter particles,
0:24:15 > 0:24:181,000,000,001 matter particles existed
0:24:18 > 0:24:21and it's from these leftover particles that you, me, the Earth,
0:24:21 > 0:24:24the sun, even the dark matter forms.
0:24:26 > 0:24:29Why this should be, we have absolutely no idea.
0:24:29 > 0:24:33But one day, the LHC just might be able to answer
0:24:33 > 0:24:36this fundamental mystery, too.
0:24:36 > 0:24:40We're still only in the very early stages of its voyage of exploration,
0:24:40 > 0:24:44but nature doesn't give up its dark secrets easily or quickly.
0:24:45 > 0:24:49In the meantime, astronomers can still see the evidence
0:24:49 > 0:24:53for dark matter. The most powerful telescopes in the world
0:24:53 > 0:24:55stared at this collection of galaxies
0:24:55 > 0:24:59and by watching how light is bent as it passes,
0:24:59 > 0:25:02we can build this computer simulation of the dark matter,
0:25:02 > 0:25:07showing the galaxies embedded in a wider cosmic web.
0:25:07 > 0:25:12We don't have computer simulations, but we do still have our jellybeans.
0:25:13 > 0:25:18Dark matter's great fun, this great mystery, this unknown of the universe,
0:25:18 > 0:25:22but why does it matter, why do we care about dark matter, Carlos?
0:25:22 > 0:25:25Why does dark matter matter? Well, it matters a lot.
0:25:25 > 0:25:29In a sentence, without dark matter,
0:25:29 > 0:25:31we would not be here.
0:25:31 > 0:25:34Nothing of what we know in the universe would exist
0:25:34 > 0:25:36without dark matter.
0:25:36 > 0:25:39Dark matter is the architect of the universe,
0:25:39 > 0:25:43it's the agent that has enabled the universe
0:25:43 > 0:25:47to create all these amazing galaxies and stars that we see around us.
0:25:47 > 0:25:50Without dark matter, the universe would be completely boring,
0:25:50 > 0:25:54it would be totally uniform and there would be nothing.
0:25:54 > 0:25:56- Let me show you this.- Yeah, sure.
0:25:56 > 0:25:58We start off with a very smooth universe.
0:25:58 > 0:26:00The universe was very smooth. It was very tiny.
0:26:00 > 0:26:03There were more irregularities.
0:26:03 > 0:26:05- Here's how you smooth the universe. - OK, full of dark matter.
0:26:05 > 0:26:08- Nothing, full of dark matter. In the proportion of 1 to 6.- OK.
0:26:08 > 0:26:13All mixed up and all without any structure, without any shape,
0:26:13 > 0:26:15without anything interesting.
0:26:15 > 0:26:20Then, inexorably, gravity begins to work
0:26:20 > 0:26:22and the way it does it,
0:26:22 > 0:26:25it exploits small irregularities in this initial...
0:26:25 > 0:26:29So, the places that just happened to have more stuff...
0:26:29 > 0:26:31- ..accumulate more.- They pull more in, the rich get richer,
0:26:31 > 0:26:34the poor get poorer. A fundamental rule of the universe.
0:26:34 > 0:26:36Low-density regions become void,
0:26:36 > 0:26:40the high-density regions become clusters
0:26:40 > 0:26:42and the voids and the clusters
0:26:42 > 0:26:45produce intricate patterns
0:26:45 > 0:26:48that we refer to as the cosmic web.
0:26:48 > 0:26:51So, one of those blobs in the microwave background
0:26:51 > 0:26:53is representing a pattern of the universe
0:26:53 > 0:26:55that was slightly denser than the ones around it.
0:26:55 > 0:26:58- They had more stuff. - Slightly more stuff in it,
0:26:58 > 0:27:01and because it had more stuff, more gravitational attraction,
0:27:01 > 0:27:03it pulled more stuff in, it got denser still
0:27:03 > 0:27:05and that gradually accumulated stuff and gravity did its work
0:27:05 > 0:27:08to give us the universe we see today.
0:27:08 > 0:27:10Yes, the dark matter particles accumulate
0:27:10 > 0:27:13and the ordinary matter just follows.
0:27:13 > 0:27:17We've talked almost entirely about looking up at the skies
0:27:17 > 0:27:19to see dark matter, we've talked about...
0:27:19 > 0:27:23trying to make our own dark matter, but we can also try and detect
0:27:23 > 0:27:26the billions of dark matter particles that are passing through us.
0:27:26 > 0:27:30There's a group in Italy who tell you they've seen the effect of dark matter.
0:27:30 > 0:27:34Yes, I think this is like the 100m race in the Olympics,
0:27:34 > 0:27:38that you get, as the tension builds up, you get false starts.
0:27:38 > 0:27:40We've had a few false starts.
0:27:40 > 0:27:44I don't think these claims are yet conclusive,
0:27:44 > 0:27:48they are disputed by many other groups
0:27:48 > 0:27:50who've failed to find the signals,
0:27:50 > 0:27:53but it tells us, this turmoil in the community
0:27:53 > 0:27:57and that to me smells like something very close.
0:27:57 > 0:28:00So, I personally, I have a feeling
0:28:00 > 0:28:02that we're really homing in and if we don't find it,
0:28:02 > 0:28:06then I think things will get very interesting.
0:28:06 > 0:28:09Because if we don't find it, then we can't explain this universe.
0:28:09 > 0:28:12Exactly. Or it tells us dark matter is not what we think it is.
0:28:12 > 0:28:15So, if we don't find it within a reasonable amount of time -
0:28:15 > 0:28:17I won't tell you exactly how many years -
0:28:17 > 0:28:22then we will have to conclude that these...
0:28:22 > 0:28:25we're going up the wrong path.
0:28:25 > 0:28:27And we have to turn, make a turn,
0:28:27 > 0:28:30- and look for a different kind of particle.- We'll see what happens,
0:28:30 > 0:28:32but I think it's amazing that we've come so far
0:28:32 > 0:28:36and yet there's so much of the universe that we don't understand.
0:28:36 > 0:28:40I think we should consume this universe. What flavour do you want?
0:28:40 > 0:28:42- I'll go for some red matter. - I'm eating the dark matter.
0:28:42 > 0:28:46Yeah, me too, I think it's really what's most important.
0:28:46 > 0:28:47It's made of strawberries.
0:28:49 > 0:28:51Now, on our next programme,
0:28:51 > 0:28:55we're going to talk about Mercury and the moon.
0:28:55 > 0:28:57So, until then, good night.
0:28:59 > 0:29:01Subtitles by Red Bee Media Ltd