0 00:00:26,960 --> 00:00:31,590 Personally, I am sure that the universe began with a hot big bang, 1 00:00:32,465 --> 00:00:34,456 but will it go on for ever? 2 00:00:34,567 --> 00:00:36,831 And if not, how will it end? 3 00:00:37,270 --> 00:00:39,431 I am much less certain about that. 4 00:00:40,073 --> 00:00:44,032 The expansion of the universe stretched everything out, 5 00:00:44,644 --> 00:00:48,375 but gravity tries to pull it all back together again. 6 00:00:48,648 --> 00:00:52,243 Our destiny depends on which force will win. 7 00:00:53,620 --> 00:00:58,956 And the influence of gravity in turn depends on what the universe is made of, 8 00:00:59,192 --> 00:01:01,592 and just how much of it there is. 9 00:01:02,195 --> 00:01:04,823 It won't be easy to find out if, 10 00:01:05,031 --> 00:01:10,594 as we suspect, most of it is dark matter, stuff we can't even see. 11 00:01:25,251 --> 00:01:30,382 As a child in India, Priya Natarajan dreamed of becoming a poet. 12 00:01:31,324 --> 00:01:35,488 Twenty years later, in Cambridge, she's a astrophysicist, 13 00:01:35,895 --> 00:01:39,456 trying to build a perfect model of the universe. 14 00:01:41,401 --> 00:01:45,462 There is this impression that everything the scientists do is very circumscribed, 15 00:01:46,039 --> 00:01:49,008 whereas it is not, because we are bringing, 16 00:01:49,109 --> 00:01:53,341 the ways in which we perform a model, the way the ingredients that we put in, 17 00:01:53,513 --> 00:01:55,538 and the ways in which we choose to mix 18 00:01:55,648 --> 00:02:00,085 the ingredients has a lot to do with our individual creativity and our feelings, 19 00:02:00,253 --> 00:02:03,950 and our sense and intuition of how things ought to be. 20 00:02:12,699 --> 00:02:17,227 So it's almost like writing poetry, where you pick a particular poetic form. 21 00:02:17,370 --> 00:02:21,329 For instance, you could pick the sonnet, or you could pick the Japanese haiku, 22 00:02:21,774 --> 00:02:24,402 which, each of these forms has a set of rules, 23 00:02:24,511 --> 00:02:26,809 so you operate within a set of rules, which is 24 00:02:26,913 --> 00:02:30,679 very much like the laws of physics, that you operate within in a model. 25 00:02:30,884 --> 00:02:34,285 But then, inside the, inside the form or inside the model, 26 00:02:34,387 --> 00:02:37,151 there's a lot of freedom, there's a lot of choices you can make. 27 00:02:40,827 --> 00:02:43,091 Priya's life was changed when she was awarded 28 00:02:43,196 --> 00:02:45,687 a top science scholarship at Cambridge. 29 00:02:46,633 --> 00:02:50,535 Her area of cosmology is profoundly creative. 30 00:02:50,937 --> 00:02:55,465 Priya's subject is the fate of galaxies in our universe. 31 00:02:57,610 --> 00:02:59,510 We see the stars that shine in the galaxy, 32 00:02:59,679 --> 00:03:03,115 and we also have evidence that there is some gas in the galaxy, 33 00:03:03,249 --> 00:03:05,911 because we can see the light that's scattered off the gas. 34 00:03:06,753 --> 00:03:10,655 But, er, as it turns out, galaxies contain a lot more than just that. 35 00:03:25,705 --> 00:03:31,109 Priya's imagination was fired when She came across research done in the 1950s 36 00:03:31,344 --> 00:03:34,802 by a young American scientist, Vera Rubin. 37 00:03:36,883 --> 00:03:42,014 What Vera Rubin did in her work was map the speeds of stars at different distances 38 00:03:42,188 --> 00:03:44,918 from the centre of a huge spiral galaxy. 39 00:03:53,633 --> 00:03:57,899 Vera Rubin noticed something which made nonsense of what she'd been taught. 40 00:03:59,038 --> 00:04:00,869 Stars spinning round the centre of 41 00:04:00,974 --> 00:04:05,434 galaxies were supposed to behave just like the planets that orbit the sun. 42 00:04:06,179 --> 00:04:07,373 But they don't. 43 00:04:09,015 --> 00:04:10,243 With our solar system, 44 00:04:10,416 --> 00:04:13,908 you have the sun in the centre and you have sort of the planets orbiting around, 45 00:04:14,120 --> 00:04:18,113 and since the dominant gravity is that of the sun the planets 46 00:04:18,224 --> 00:04:23,059 that are the outer planets, they move much slower than the planets on the inside. 47 00:04:25,598 --> 00:04:29,364 So naturally what people expected to find was similarly in a galaxy, 48 00:04:29,569 --> 00:04:33,562 if you measure the speed of the stars away from the centre towards the edge, 49 00:04:33,673 --> 00:04:35,197 you expect it to fall off. 50 00:04:35,441 --> 00:04:37,432 And what Vera Rubin found instead, 51 00:04:37,543 --> 00:04:40,444 when she actually measured that for a spiral galaxy, 52 00:04:40,613 --> 00:04:43,013 was that the speed stayed the same as she, 53 00:04:43,116 --> 00:04:46,552 as she sort of mapped the speed of the stars from the inside out, 54 00:04:46,719 --> 00:04:50,052 all the way out to the edge, they stayed, they stayed the same. 55 00:04:53,459 --> 00:04:56,326 Vera Rubin saw that the galaxy center 56 00:04:56,429 --> 00:05:00,229 could not be the exerting gravity on the stars. 57 00:05:01,301 --> 00:05:04,930 For all the stars in a galaxy to move at the same speed as each other, 58 00:05:05,171 --> 00:05:08,140 there had to be a force at work all around them. 59 00:05:08,675 --> 00:05:11,838 But nothing which could produce such a force could be seen. 60 00:05:12,645 --> 00:05:14,237 Vera Rubin suggested that 61 00:05:14,347 --> 00:05:19,307 every galaxy must be surrounded by matter that we cant see. 62 00:05:20,353 --> 00:05:22,821 But the scientific establishment at the time was not ready 63 00:05:22,922 --> 00:05:25,857 what she called dark matter. 64 00:05:28,227 --> 00:05:31,594 Her announcement that there was dark matter associated 65 00:05:31,698 --> 00:05:35,930 with every individual galaxy, er, was received with much scepticism, 66 00:05:36,035 --> 00:05:38,902 because of the far-reaching implications 67 00:05:39,005 --> 00:05:43,135 it had and because also of the inferred percentage of dark matter. 68 00:05:43,376 --> 00:05:47,005 From her work, she inferred that almost ninety per cent of the mass 69 00:05:47,146 --> 00:05:49,171 in a spiral galaxy had to be dark. 70 00:05:54,387 --> 00:06:00,019 The movement of stars in a galaxy must be controlled by stuff we can't see. 71 00:06:04,897 --> 00:06:09,527 Around every galaxy, there needs to be a halo of dark matter, 72 00:06:09,802 --> 00:06:15,069 invisibly locking all the stars in place with the gravity it exerts. 73 00:06:18,711 --> 00:06:21,908 The stars are not stranded in the vastness of space, 74 00:06:22,181 --> 00:06:26,413 it's just that we can't see at least ninety per cent of what's out there. 75 00:06:27,286 --> 00:06:30,517 It could be as much as ninety-nine per cent. 76 00:06:39,031 --> 00:06:41,158 For a cosmologist like myself, 77 00:06:41,534 --> 00:06:44,731 it's crucial to know precisely how much dark matter 78 00:06:44,837 --> 00:06:50,366 there is in order to know what will become of the universe - eventually. 79 00:07:04,390 --> 00:07:11,296 The total mass of our universe is what decides the, er, the fate of our universe. 80 00:07:11,464 --> 00:07:16,458 Whether we continue expanding or whether we stop and decelerate or we turn around, 81 00:07:16,736 --> 00:07:19,296 back on ourselves, so the ultimate fate of 82 00:07:19,405 --> 00:07:22,465 what really happens to us depends on how 83 00:07:22,575 --> 00:07:26,170 well we have made an inventory of the mass in the universe, 84 00:07:26,412 --> 00:07:30,178 and therefore if such a large fraction is indeed dark, 85 00:07:30,349 --> 00:07:32,408 that has very important conseguences. 86 00:07:38,391 --> 00:07:42,384 For example people now doubt that Vera Rubin was right. 87 00:07:42,929 --> 00:07:46,660 Dark matter determines the future of the universe. 88 00:07:47,800 --> 00:07:52,965 To know our ultimate fate, we need to be sure that dark matter exists, 89 00:07:53,105 --> 00:07:55,096 and how much of it there is. 90 00:07:56,242 --> 00:08:00,645 Searching for the invisible is not for the faint-hearted. 91 00:08:10,723 --> 00:08:13,817 When Chris Stubbs first told his colleagues 92 00:08:14,026 --> 00:08:19,157 he wanted to look for dark matter, they told him he was out of his mind. 93 00:08:19,699 --> 00:08:22,259 That wasn't the way to a safe job. 94 00:08:25,171 --> 00:08:27,230 There's an infinite amount of science to do, 95 00:08:27,573 --> 00:08:32,670 and I think the trick is to choose carefully what you spend your time doing, 96 00:08:32,778 --> 00:08:37,715 and my taste for a long time has run towards fundamental problems that 97 00:08:37,817 --> 00:08:40,217 may be very difficulty to address experimentally, 98 00:08:40,419 --> 00:08:44,719 but which have a very large impact on our understanding of the universe. 99 00:08:54,734 --> 00:09:00,297 Chris Stubbs staked his career on finding something that couldn't be seen. 100 00:09:06,412 --> 00:09:09,848 But nobody knew exactly what dark matter was, 101 00:09:10,349 --> 00:09:13,944 they had to decide how to target their search. 102 00:09:14,954 --> 00:09:20,551 We're carrying out an experiment to look for a particular kind of dark matter, 103 00:09:20,793 --> 00:09:22,624 which we call machos, 104 00:09:22,728 --> 00:09:28,291 which is a short-hand that stands for massive compact halo objects. 105 00:09:28,968 --> 00:09:33,234 The idea is that our galaxy has a big halo 106 00:09:33,339 --> 00:09:35,273 of dark matter around it that's made out of 107 00:09:35,374 --> 00:09:37,740 astronomical objects that for one reason 108 00:09:37,843 --> 00:09:41,176 or another don't shine like the stars that we see. 109 00:09:46,519 --> 00:09:51,456 These astronomical objects, the decomposing corpses of dead stars, 110 00:09:51,657 --> 00:09:54,023 are thought to litter the universe. 111 00:09:58,931 --> 00:10:02,890 From the size of our earth to ten times the size of the sun, 112 00:10:03,302 --> 00:10:07,363 these machos might explain what Vera Rubin had seen. 113 00:10:09,308 --> 00:10:13,836 If so, they'd be found in the outskirts of galaxies. 114 00:10:14,981 --> 00:10:17,211 It was the right place to search. 115 00:10:20,219 --> 00:10:26,124 But finding them would be like looking for a black bat on a dark night. 116 00:10:33,432 --> 00:10:38,233 The one thing that he knew was that his subjects were fairly heavy, 117 00:10:39,472 --> 00:10:40,871 and if they were heavy, 118 00:10:41,040 --> 00:10:45,773 they would have a gravitational effect on light passing nearby. 119 00:10:48,514 --> 00:10:53,349 The macho-hunters turned to Einstein's general theory of relativity 120 00:10:53,519 --> 00:10:56,420 to tell them how gravity affects light. 121 00:11:18,144 --> 00:11:22,376 Einstein's general theory of relativity tells us that 122 00:11:22,481 --> 00:11:26,247 light passing close to an object like the sun 123 00:11:26,385 --> 00:11:30,082 or a lump of dark matter is deflected, it gets bent, 124 00:11:30,322 --> 00:11:35,692 and the effect that a mass has on the light 125 00:11:35,795 --> 00:11:41,529 coming from a distant star or galaxy is just like putting a lens 126 00:11:41,734 --> 00:11:46,967 in front of the star, it distorts the image and it makes it appear brighter. 127 00:11:51,277 --> 00:11:53,177 According to Einstsines theory 128 00:11:53,345 --> 00:11:58,476 if the huge mass of a macho passed between us and a distant group of stars, 129 00:11:59,251 --> 00:12:01,879 we would see the stars would progressively brighten, 130 00:12:02,121 --> 00:12:04,021 and then fade back to normal. 131 00:12:08,394 --> 00:12:13,832 Chris Stubb's team analysed thousands of images of stars to prove their point... 132 00:12:15,234 --> 00:12:19,330 Two years after we started the experiment, we were looking through the data, 133 00:12:19,538 --> 00:12:26,967 trying to understand how to analyse it, and much to our surprise, 134 00:12:27,079 --> 00:12:30,207 found exactly what we thought we were looking for, 135 00:12:30,983 --> 00:12:36,011 in that we saw a star get brighter and then fainter again with 136 00:12:36,122 --> 00:12:41,150 exactly the signature that's predicted by general relativity. 137 00:12:44,430 --> 00:12:46,227 OK, this looks like a definite, it fits it pretty well. 138 00:12:46,332 --> 00:12:47,162 ...draw it... 139 00:12:48,000 --> 00:12:49,763 A nice microlensing curve... 140 00:12:49,869 --> 00:12:55,432 Our experiment has detected a previously unknown component of this galaxy. 141 00:12:56,709 --> 00:12:58,233 It's a stunning result. 142 00:13:09,488 --> 00:13:12,924 The first dark matter had been detected. 143 00:13:13,726 --> 00:13:16,217 It really is out there. 144 00:13:24,036 --> 00:13:27,995 But did these machos solve the riddle posed by Vera Rubin? 145 00:13:30,943 --> 00:13:34,401 Could there be enough of them around each galaxy 146 00:13:34,547 --> 00:13:38,176 to exert the gravitational effects she had observed? 147 00:13:41,921 --> 00:13:48,918 The simplest point of view is that the machos are ordinary matter made up of 148 00:13:49,061 --> 00:13:52,997 the same material that exists in stars, it just didn't happen to end up in stars, 149 00:13:53,365 --> 00:13:56,926 and we think we know exactly how much, 150 00:13:57,169 --> 00:14:00,696 we think we know how much ordinary matter there is in the universe, 151 00:14:00,940 --> 00:14:06,810 and it just isn't enough to solve the dark matter problem of the universe. 152 00:14:10,049 --> 00:14:15,009 We need to find something else to account for more of the dark matter. 153 00:14:16,522 --> 00:14:20,720 Machos were big, so why not try something tiny? 154 00:14:22,394 --> 00:14:26,558 One candidate was a well-known particle, the neutrino. 155 00:14:27,867 --> 00:14:30,927 This is produced in atomic bomb explosions, 156 00:14:31,136 --> 00:14:35,402 so it would also have been produced in the big bang explosion. 157 00:14:36,842 --> 00:14:41,506 If it had a tiny mass of its own, it could be the dark matter. 158 00:14:44,083 --> 00:14:48,349 Or it could be one of the so-called exotic particles 159 00:14:48,520 --> 00:14:51,250 whose existence was predicted by theory, 160 00:14:51,390 --> 00:14:54,518 but which were very hard to detect in reality. 161 00:14:55,828 --> 00:14:58,092 Perhaps they are actually out there, 162 00:14:58,197 --> 00:15:01,792 silently shaping the evolution of the universe. 163 00:15:09,508 --> 00:15:13,604 Carlos Frenk, Professor of Astronomy at Durham University, 164 00:15:13,812 --> 00:15:17,578 is fascinated by how things grow and change. 165 00:15:19,518 --> 00:15:24,353 I think there is a great parallel between the evolution of the largest system 166 00:15:24,456 --> 00:15:26,822 that we know of, which is the universe, and the evolution of 167 00:15:26,926 --> 00:15:29,656 the biological system, like a person or like my son. 168 00:15:34,099 --> 00:15:37,125 I often wonder what are the factors that are going to influence 169 00:15:37,336 --> 00:15:39,861 the development of my son, whether he will be, 170 00:15:40,039 --> 00:15:43,372 er, a physicist, or a scientist, whether he will be a musician or 171 00:15:43,475 --> 00:15:44,772 will whether he'll be anything else. 172 00:15:44,977 --> 00:15:47,605 I don't guite understand what are the forces 173 00:15:47,713 --> 00:15:50,682 that are going to drive him in one direction or the other. 174 00:15:51,016 --> 00:15:53,177 The universe, however, is simpler, 175 00:15:53,419 --> 00:15:58,049 because we have a much greater mastery over the laws that 176 00:15:58,157 --> 00:15:59,852 govern the evolution of the universe. 177 00:16:06,699 --> 00:16:08,564 Carlos is confident he can describe 178 00:16:08,667 --> 00:16:12,603 how the baby universe grew into the universe we know today. 179 00:16:14,840 --> 00:16:19,004 He believes that the dark matter exerted a powerful influence. 180 00:16:26,418 --> 00:16:31,219 Carlos' fascination with how things evolve has found its outlet in physics. 181 00:16:31,724 --> 00:16:35,091 He doesn't yet know whether it will be the same for his son. 182 00:16:37,463 --> 00:16:41,923 Carlos' dream is to grow a perfect model of the universe in his computer, 183 00:16:42,201 --> 00:16:46,331 from its violent birth to the complicated picture we see today. 184 00:16:50,109 --> 00:16:51,303 That will only happen 185 00:16:51,410 --> 00:16:56,177 if he programmes in exactly the right characteristics for the dark matter. 186 00:16:56,648 --> 00:17:00,812 He starts every attempt just a second after the big bang. 187 00:17:03,522 --> 00:17:04,716 Prior to that time, 188 00:17:04,823 --> 00:17:09,886 the universe was made up of a cosmic soup of elemental particles and radiation. 189 00:17:10,129 --> 00:17:13,496 No-, nothing else could exist in the midst of this tremendous heat. 190 00:17:13,866 --> 00:17:16,835 But then, er, after about a hundred seconds, 191 00:17:17,069 --> 00:17:20,971 the universe had cooled down a little bit to a mere ten billion degrees, 192 00:17:21,206 --> 00:17:24,141 but this temperature is now low enough that, er, 193 00:17:24,343 --> 00:17:28,575 the first thermonuclear fusion reactions can take place. 194 00:17:36,455 --> 00:17:39,549 Carlos' belief is that at this critical moment, 195 00:17:39,725 --> 00:17:43,456 a mysterious group of particles broke free from the pack. 196 00:17:47,666 --> 00:17:49,964 Instead of forming the galaxies and stars, 197 00:17:50,135 --> 00:17:54,003 they began to cluster together to become the dark matter. 198 00:17:58,911 --> 00:18:04,008 These clusters of dark matter had a gravitational pull on the ordinary matter. 199 00:18:08,120 --> 00:18:12,716 As the lumps of dark matter grew bigger and bigger in the expanding universe, 200 00:18:12,925 --> 00:18:18,659 they pulled in more and more ordinary matter, which condensed to become stars. 201 00:18:23,001 --> 00:18:26,664 Eventually, one billion years after the big bang, 202 00:18:26,905 --> 00:18:29,669 the first galaxies began to form. 203 00:18:35,647 --> 00:18:40,846 In the early 1980s, Carlos was ready to build a model of the universe. 204 00:18:45,924 --> 00:18:48,620 The idea that was around at the time was that the dark matter 205 00:18:48,727 --> 00:18:53,323 could consist of small elementary particles called neutrinos. 206 00:19:03,075 --> 00:19:06,169 Carlos wondered whether the neutrinos from the big bang 207 00:19:06,378 --> 00:19:08,369 could be the dark matter. 208 00:19:15,187 --> 00:19:18,418 That was the very trendy, fashionable ideal, if you like, 209 00:19:18,524 --> 00:19:22,358 in those days, and, it was the first concrete proposal 210 00:19:22,461 --> 00:19:25,191 we had for what the dark matter could be, and, er, 211 00:19:25,297 --> 00:19:29,563 this was very significant, and some people would say, a very significant idea, 212 00:19:29,668 --> 00:19:33,331 so people would say it was the signal of the beginning of the revolu-, 213 00:19:33,438 --> 00:19:36,703 revolution in the way in which we study the universe, 214 00:19:36,808 --> 00:19:39,902 because for the first time the neutrino hypothesis 215 00:19:40,012 --> 00:19:45,848 provided a concrete starting point that we could explore 216 00:19:45,951 --> 00:19:50,650 in an unambiguous fashion using the tools of evolutionary cosmology. 217 00:19:56,161 --> 00:20:00,564 Neutrinos travel across the universe at virtually the speed of light. 218 00:20:04,736 --> 00:20:09,799 Every second about a hundred trillion neutrinos pass straight through your body. 219 00:20:13,679 --> 00:20:15,408 The universe is thick with them. 220 00:20:15,814 --> 00:20:18,908 But nothing seems able to stop the neutrino. 221 00:20:22,421 --> 00:20:24,514 When they meet a solid object like the earth, 222 00:20:24,690 --> 00:20:29,855 they simply float through it, and this makes them extremely hard to catch. 223 00:20:35,334 --> 00:20:36,926 But it's important that we do, 224 00:20:37,135 --> 00:20:41,765 because we must find whether the neutrinos has mass - without mass, 225 00:20:41,974 --> 00:20:46,343 they wouldn't exert gravity and so couldn't be the dark matter. 226 00:20:49,581 --> 00:20:53,574 In northern France, Yves Declais wants to catch neutrinos, 227 00:20:53,719 --> 00:20:55,744 and see if they do have any mass. 228 00:20:56,888 --> 00:20:59,948 When you prepare your bait, when you, when you have prepared your detector, 229 00:21:00,058 --> 00:21:01,889 when you have prepared your trap, you have to, 230 00:21:01,994 --> 00:21:05,157 to install it at the right place, and so you have to go, 231 00:21:05,264 --> 00:21:08,461 well, and you think you will be able to detect neutrino, 232 00:21:08,567 --> 00:21:12,025 well, you will be able to get out some fish, out from the river, 233 00:21:12,204 --> 00:21:17,335 and after that, you have not only to wait, but you have to work and you, 234 00:21:17,442 --> 00:21:21,139 you will see what will be the result, you will see, er, how many neutrino, 235 00:21:21,246 --> 00:21:24,272 you will see how many fish you will get out of from the river. 236 00:21:27,452 --> 00:21:31,149 Neutrinos are produced in nuclear reactions. 237 00:21:33,025 --> 00:21:35,493 So Yves Declais has set up his project 238 00:21:35,627 --> 00:21:39,290 in a decommissioned bunker beside a nuclear power station. 239 00:22:11,263 --> 00:22:15,029 In this experiment, we want to see if the nature of 240 00:22:15,133 --> 00:22:18,034 the neutrino change between the source of the neutrino 241 00:22:18,136 --> 00:22:20,627 and the detector one kilometre away. 242 00:22:21,773 --> 00:22:26,938 And if the nature of the neutrino change during this path of one kilometre, 243 00:22:27,512 --> 00:22:32,882 we can demonstrate, we can prove that this is related to the existence of, 244 00:22:32,984 --> 00:22:35,179 of a mass for the neutrino. 245 00:22:36,355 --> 00:22:42,885 It is a little bit complicated to compute, but it, it is a very, very simple system. 246 00:23:09,154 --> 00:23:14,057 Once they had set up their eguipment, the scientists must wait. 247 00:23:16,328 --> 00:23:19,456 Apart from routine checks, there's nothing to do until 248 00:23:19,564 --> 00:23:24,831 their highly sensitive detector begins to pick up passing neutrinos. 249 00:23:29,508 --> 00:23:33,569 All the data from the detector is fed down ground lines to the chateau, 250 00:23:33,678 --> 00:23:35,441 where Yves and the team live. 251 00:23:39,084 --> 00:23:41,644 The want to establish if they detect less neutrinos 252 00:23:41,753 --> 00:23:46,417 now then when they set up the same eguipment much nearer to a reactor. 253 00:23:46,925 --> 00:23:51,726 If the numbers aren't the same, they will know that the neutrino has mass. 254 00:23:52,764 --> 00:23:58,259 It may take years to find out, but it will be a result with huge implications. 255 00:23:58,670 --> 00:23:59,830 This is really important, er, 256 00:23:59,938 --> 00:24:05,342 for particle physics and also for cosmology and astrophysics. 257 00:24:06,545 --> 00:24:10,572 One of the best candidates for the dark matter, 258 00:24:10,782 --> 00:24:12,773 for the missing matter of the universe, 259 00:24:12,884 --> 00:24:16,820 is the neutrino, if the neutrino has a mass. 260 00:24:17,022 --> 00:24:21,823 Even if the mass of the neutrino can be very tiny, very, very, very small, 261 00:24:22,060 --> 00:24:25,894 because the universe is completely filled by a lot of neutrino coming 262 00:24:25,997 --> 00:24:29,694 from the whole universe, from the first traces of the universe. 263 00:24:35,807 --> 00:24:40,608 Meanwhile, Carlos Frenk was hammering away at a theoretical approach. 264 00:24:41,079 --> 00:24:44,344 His idea was to assume that neutrinos had mass, 265 00:24:44,583 --> 00:24:48,349 and see what kind of a universes would allow his computer to build. 266 00:24:49,187 --> 00:24:54,022 So we programmed our computer to follow the evolution of a universe 267 00:24:54,259 --> 00:24:58,491 in which the dark matter was made up of massive neutrinos, 268 00:24:58,797 --> 00:25:03,530 and the aim was to produce in the computer a synthetic universe that 269 00:25:03,635 --> 00:25:06,103 we could then compare with the real thing. 270 00:25:10,942 --> 00:25:13,410 So we programmed our computer up in this fashion, 271 00:25:13,745 --> 00:25:18,341 and I let it churn away over Christmas, and when we came back, 272 00:25:18,750 --> 00:25:22,709 we saw the first maps being generated by the computer. 273 00:25:35,433 --> 00:25:38,630 Here we have a recognizable universe, a credible universe, 274 00:25:38,737 --> 00:25:41,763 something that's made galaxies, something that's made galaxy clusters, 275 00:25:41,873 --> 00:25:45,331 something that is competitive vis-a-vis the real universe, 276 00:25:45,443 --> 00:25:49,209 there was a great sense of elation at the thought that 277 00:25:49,314 --> 00:25:53,876 we might have solved what was already clearly then and sadly still is today, 278 00:25:54,019 --> 00:25:57,682 the main unsolved problem in cosmology, with, one, 279 00:25:57,789 --> 00:25:59,848 one of those feelings that you have once in your lifetime, 280 00:25:59,958 --> 00:26:02,859 and you think you're really stumbled upon something major. 281 00:26:03,428 --> 00:26:05,862 Now, that was, that was our first impression. 282 00:26:08,767 --> 00:26:11,201 But his first impressions were deceptive. 283 00:26:13,138 --> 00:26:16,596 Carlos was so elated to have grown a computer universe that 284 00:26:16,708 --> 00:26:19,506 at first he didn't notice the truth. 285 00:26:21,046 --> 00:26:22,377 On closer inspection, 286 00:26:22,514 --> 00:26:26,951 his modelled universe didn't guite look like the real thing. 287 00:26:31,222 --> 00:26:34,157 But Carlos was not tempted to give up his computer modelling. 288 00:26:34,359 --> 00:26:37,453 He was still convinced that studying the universe would prove 289 00:26:37,562 --> 00:26:40,656 easier than pursuing some other branch of science. 290 00:26:43,835 --> 00:26:46,235 So it is paradoxical that we can understand the universe better than 291 00:26:46,338 --> 00:26:48,033 we can understand a tiny little part, 292 00:26:48,273 --> 00:26:51,834 my son is an insignificant little speck in this gigantic universe, 293 00:26:51,943 --> 00:26:55,879 and yet I can understand the universe better than I can understand my son. 294 00:26:56,147 --> 00:26:59,412 And so often I regard myself as being very lucky that I am a physicist, 295 00:26:59,551 --> 00:27:01,382 rather than a biologist or a psychologist, 296 00:27:01,486 --> 00:27:03,579 they have a much tougher time than we do, 297 00:27:03,755 --> 00:27:07,088 because we deal with systems that are intrinsically simple, 298 00:27:07,292 --> 00:27:11,126 biologists and psychologists deal with these, er, 299 00:27:11,229 --> 00:27:15,131 much more complex and in some ways magical world of humans, 300 00:27:15,300 --> 00:27:17,029 who are essentially unpredictable. 301 00:27:18,503 --> 00:27:22,872 Particle physicists urged Carlos to consider a hypothetical particle, 302 00:27:23,174 --> 00:27:25,904 one of the so-called exotic particles. 303 00:27:26,578 --> 00:27:29,638 Why should he try only known particles? They argued. 304 00:27:29,748 --> 00:27:32,649 Any more that his son should practice only one skill. 305 00:27:34,486 --> 00:27:39,480 The neutrino had been to lively, or hot, to build a realistic universe. 306 00:27:40,692 --> 00:27:43,422 They urged Carlos to try something more sluggish, 307 00:27:43,695 --> 00:27:46,858 something he would call 'cold dark matter'. 308 00:27:48,500 --> 00:27:52,834 Our next step, then, was to change our starting assumption, 309 00:27:52,971 --> 00:27:57,431 and now, er, take the dark matter to be composed of cold dark matter. 310 00:28:06,685 --> 00:28:09,415 I must say we were very sceptical when we started this new project, 311 00:28:09,521 --> 00:28:12,456 by then we have got slightly fed up with particle physicists trying 312 00:28:12,557 --> 00:28:14,650 to tell us astronomers what the universe was made of, 313 00:28:14,759 --> 00:28:17,159 particle physicists are supposed to be working on something else, 314 00:28:17,262 --> 00:28:19,787 and they have no right to come and tell us astronomers 315 00:28:19,898 --> 00:28:24,926 what our universe is made of, er, so our approach at first was, er, 316 00:28:25,136 --> 00:28:28,196 a really fairly, cynical, we, er, started off saying, right, 317 00:28:28,306 --> 00:28:29,898 let's go and do this particle physicists right, 318 00:28:30,008 --> 00:28:32,272 let's go and rule out, we'd ruled out neutrinos, 319 00:28:32,444 --> 00:28:34,309 now let's go and rule out cold dark matter as well, 320 00:28:34,412 --> 00:28:35,936 and get those guys off our backs, 321 00:28:36,047 --> 00:28:38,106 so they can go and do their own thing with accelerators and 322 00:28:38,216 --> 00:28:41,208 we can keep on doing our own thing, trying to understand how galaxies form. 323 00:28:46,324 --> 00:28:48,087 What happened was that, er, 324 00:28:48,226 --> 00:28:52,424 these cold dark matter universes turned out to be far richer and 325 00:28:52,530 --> 00:28:55,693 far more interesting than we ever had any right to expect. 326 00:28:59,137 --> 00:29:04,165 Carlos has blended neutrinos and cold dark matter in his latest computer model, 327 00:29:04,642 --> 00:29:07,941 but can he be sure cold dark matter exists? 328 00:29:15,820 --> 00:29:18,653 The, er, burden of proof is on the experimentalists 329 00:29:18,757 --> 00:29:20,725 who now have to go and detect these particles, 330 00:29:20,825 --> 00:29:23,419 and until that happens then, er, 331 00:29:23,561 --> 00:29:26,325 we cannot be by any means certain that this is a correct theory. 332 00:29:26,431 --> 00:29:29,696 But, if they do succeed, if they do succeed, 333 00:29:29,834 --> 00:29:33,827 this really will be an outstanding achievement, 334 00:29:33,938 --> 00:29:37,567 and I think it's not an exaggeration to say that 335 00:29:38,076 --> 00:29:41,876 if the dark matter turns out to be an exotic elementary particle, 336 00:29:41,980 --> 00:29:44,744 this really will now go down in history as one of 337 00:29:44,849 --> 00:29:47,147 the greatest scientific discoveries ever. 338 00:29:52,323 --> 00:29:55,486 The evidence suggests that most of the universe 339 00:29:55,660 --> 00:29:58,993 is made up of something no-one has ever seen. 340 00:30:01,099 --> 00:30:05,798 By its very nature, cold dark matter has to be hard to detect. 341 00:30:07,605 --> 00:30:13,407 Finding a way to do so is one of the most difficult tasks in physics today. 342 00:30:30,795 --> 00:30:32,626 Here, in the North Yorkshire Moors, 343 00:30:32,764 --> 00:30:36,723 a small team of British scientists is tipped to win the race. 344 00:30:40,371 --> 00:30:42,703 They are led by Neil Spooner. 345 00:30:45,076 --> 00:30:47,101 It's very astounding that at the end of the twentieth century 346 00:30:47,212 --> 00:30:50,272 we actually don't know what most of the universe is made of, 347 00:30:50,448 --> 00:30:54,612 not ninety per cent, maybe even ninety-nine per cent, er, 348 00:30:55,253 --> 00:30:58,984 and that it sort of puts one in, as, as a human being, in, 349 00:30:59,090 --> 00:31:02,958 into some perspective, that, you know, 350 00:31:03,061 --> 00:31:05,393 we, we, the earth is not the centre of the solar system, 351 00:31:05,496 --> 00:31:10,263 etc, and, and maybe we're not even the only life now, 352 00:31:10,635 --> 00:31:15,402 er, and we're not even made of particularly common matter, 353 00:31:16,107 --> 00:31:18,598 in that we're not the typical matter that's around, 354 00:31:19,143 --> 00:31:21,441 because most of it's dark matter, which we don't know what it is. 355 00:31:39,097 --> 00:31:43,534 Like neutrinos, cold dark matter is very difficult to distinguish 356 00:31:43,635 --> 00:31:48,436 from the rain of other cosmic particles that bombards the surface of the earth. 357 00:31:49,173 --> 00:31:53,371 Any detector would have to be protected, deep underground. 358 00:31:54,412 --> 00:31:59,611 It just happens that my father is, is a, a mining engineer by profession, 359 00:32:00,919 --> 00:32:03,046 so I just asked him what was the deepest mine in Britain, naively, 360 00:32:03,154 --> 00:32:05,179 thinking it would be a coal mine, which would be useless for us, 361 00:32:05,290 --> 00:32:08,350 because it would be guite difficult to, to work in a coal mine, 362 00:32:08,459 --> 00:32:10,723 because of the, er, the safety aspect of it. 363 00:32:11,062 --> 00:32:13,758 But it turned out that, er, he looked it up and, 364 00:32:13,865 --> 00:32:18,302 and the answer was Bowlby, which is a salt mine, which is ideal for us. 365 00:32:23,608 --> 00:32:28,136 Bowlby mine is not only the deepest in Britain, but the deepest in Europe. 366 00:32:31,115 --> 00:32:35,074 The lift travels at twelve miles an hour for five long minutes, 367 00:32:35,286 --> 00:32:37,413 taking them a mile underground. 368 00:32:40,058 --> 00:32:42,856 At this depth, the air is ten degrees hotter than 369 00:32:42,961 --> 00:32:46,089 it is at the surface, and very dry. 370 00:32:47,432 --> 00:32:50,196 Their intricate scientific eguipment must be built to 371 00:32:50,301 --> 00:32:52,826 withstand these hostile conditions. 372 00:32:54,005 --> 00:32:58,101 It's a technological fight, trying to work deep underground, 373 00:32:58,409 --> 00:33:05,110 in the salt mine, which is an environment which, well, 374 00:33:05,216 --> 00:33:07,582 we're dealing with fairly intricate electronics and, 375 00:33:07,685 --> 00:33:11,212 and we're trying to be clean and trying to that in a mine is, 376 00:33:11,322 --> 00:33:12,983 is sort of very, very difficult. 377 00:33:28,239 --> 00:33:31,436 The Yorkshire miners seem to enjoy working next to a group of 378 00:33:31,542 --> 00:33:34,170 fundamental particle physicists. 379 00:33:36,781 --> 00:33:38,806 So they all say, have you found it yet? 380 00:33:39,717 --> 00:33:42,185 We just go, not yet, but we're working on it, or something. 381 00:33:49,027 --> 00:33:51,018 It might seem odd to the miners that 382 00:33:51,129 --> 00:33:54,189 if dark matter makes up ninety-nine per cent of the universe, 383 00:33:54,298 --> 00:33:56,459 it should be so hard to find. 384 00:34:01,305 --> 00:34:03,830 But the particles that Neil Spooner is looking for 385 00:34:03,975 --> 00:34:08,036 aren't known as weakly interacting massive particles for nothing. 386 00:34:08,746 --> 00:34:13,479 These so-called wimps try to avoid contact at all costs. 387 00:34:15,453 --> 00:34:18,422 These particles are neutral, they're not charged. 388 00:34:19,891 --> 00:34:22,758 Their interaction is like a sort of billiard-ball effect. 389 00:34:23,528 --> 00:34:25,587 If they interact, which mainly they don't, but when they do, 390 00:34:25,696 --> 00:34:28,529 they just will strike an atom, which will recoil. 391 00:34:31,803 --> 00:34:35,034 So what we're looking for is, is these little recoils of atoms. 392 00:34:36,874 --> 00:34:38,068 We're talking about very small distances, 393 00:34:38,176 --> 00:34:41,077 thousandth of a millimetre or something, and move off. 394 00:34:41,612 --> 00:34:46,709 And as this atom recoils, it gives off some energy. 395 00:34:47,952 --> 00:34:50,944 In our case, light, and you try and detect this light. 396 00:35:04,235 --> 00:35:07,602 To shield their detector from radioactive rays from the rock, 397 00:35:07,872 --> 00:35:12,104 they suspend in two hundred tons of distilled water. 398 00:35:13,478 --> 00:35:15,673 We're over a kilometre underground, so we've got rid of the cosmic rays, 399 00:35:15,780 --> 00:35:17,304 and then we're in the water, 400 00:35:17,415 --> 00:35:20,282 so we can screen off the stuff coming from the walls, 401 00:35:20,485 --> 00:35:22,316 and then we've got our detector in the middle, 402 00:35:22,487 --> 00:35:23,920 sitting there waiting for a wimp. 403 00:35:26,724 --> 00:35:30,524 Our detector was a simple crystal which gives off little bursts of light when, 404 00:35:30,628 --> 00:35:34,826 when struck by a particle, and we have to really amplify this light, 405 00:35:34,932 --> 00:35:36,627 because it's very, very low level. 406 00:35:41,639 --> 00:35:45,575 We use this device called a photomultiplier, to convert, er, 407 00:35:45,743 --> 00:35:49,338 light into electrons, and these are then multiplied and you get, 408 00:35:49,547 --> 00:35:52,573 for every one that comes in you get about a million coming out, 409 00:35:53,017 --> 00:35:57,613 and that provides a nice big signal which you can then measure and record. 410 00:36:18,009 --> 00:36:21,570 In the last year or two, we have made fairly significant progress, 411 00:36:21,679 --> 00:36:23,704 we've improved our detector such that 412 00:36:23,814 --> 00:36:29,377 we're now about fifty times more sensitive than anyone else was previously. 413 00:36:29,654 --> 00:36:33,283 But we still need to get probably another hundred times better. 414 00:36:35,860 --> 00:36:40,524 If we do that, then we should see them or we should not see them. 415 00:36:41,866 --> 00:36:44,494 If we see them, then obviously that's very exciting, 416 00:36:44,735 --> 00:36:46,794 and maybe we've discovered what dark matter is or 417 00:36:46,904 --> 00:36:48,701 what most of the dark matter is. 418 00:36:55,546 --> 00:36:58,447 If we don't see them, then that's also pretty exciting, 419 00:36:58,549 --> 00:37:01,143 because it's got to be something and if it's not wimps then it, 420 00:37:01,252 --> 00:37:04,949 maybe it's not machos, and maybe neutrinos don't have mass, we don't know, 421 00:37:05,056 --> 00:37:09,493 but, er, it's got to be something, so that would deepen the mystery. 422 00:37:14,165 --> 00:37:17,931 Even when the dark matter, or I should say when the dark matter is discovered, 423 00:37:18,035 --> 00:37:20,765 because it's not a guestion that dark matter is there to be discovered, 424 00:37:20,871 --> 00:37:25,467 and it will be discovered, I can say that with complete certainty, well, 425 00:37:25,576 --> 00:37:31,572 as complete as a scientist can ever do, but when the dark matter is discovered, 426 00:37:31,782 --> 00:37:35,309 I think the whole jigsaw of our universe will fall into place, 427 00:37:35,519 --> 00:37:41,321 we will understand not only why our universe looks the way it does, 428 00:37:41,425 --> 00:37:45,293 we will understand why there are galaxies, how they came to be, 429 00:37:45,596 --> 00:37:48,565 why there are planets, why there are stars but we would al-, 430 00:37:48,666 --> 00:37:51,999 also understand what the ultimate fate of our universe will be. 431 00:37:54,572 --> 00:37:56,904 There are two possibilities. 432 00:37:57,808 --> 00:38:01,539 If there's only a fairly small amount of dark matter, 433 00:38:01,746 --> 00:38:04,909 the universe will continue to expand for ever, 434 00:38:05,082 --> 00:38:08,848 getting colder and colder, and more and more empty. 435 00:38:11,455 --> 00:38:15,186 On the other hand, if there's a lot of dark matter, 436 00:38:15,359 --> 00:38:20,956 gravity will slow down the expansion of the universe and stop it eventually. 437 00:38:22,633 --> 00:38:27,468 Then the universe will begin to contract and will end up in a big crunch, 438 00:38:27,605 --> 00:38:29,766 like the big bang in reverse. 439 00:38:41,919 --> 00:38:45,320 From what we know now, it could go either way. 440 00:38:46,490 --> 00:38:50,790 If I placed a bet, I think I know which fate I'd back. 441 00:38:52,163 --> 00:38:55,690 But how would I collect after the big crunch? 442 00:38:57,001 --> 00:39:00,198 Whichever way the universe eventually goes, 443 00:39:00,371 --> 00:39:04,398 its evolution is being affected by dark matter right now. 444 00:39:05,943 --> 00:39:09,344 But before we have even discovered what it's made of, 445 00:39:09,513 --> 00:39:12,971 some astronomers have begun mapping its effects. 446 00:39:14,552 --> 00:39:16,349 The challenge of mapping the universe is that 447 00:39:16,454 --> 00:39:18,217 you have to do it in three dimensions, 448 00:39:18,589 --> 00:39:22,025 and human beings are very good at making two-dim-, two-dimensional maps, 449 00:39:22,126 --> 00:39:26,062 it's the challenge of getting that third dimension and putting it in your head, 450 00:39:26,263 --> 00:39:30,199 being able to close your eyes and see in three-D what's around you, 451 00:39:30,368 --> 00:39:31,699 it's a challenge, but it's on. 452 00:39:37,475 --> 00:39:42,970 So, I think we'll lay things out with the eguator down here, or something... 453 00:39:43,080 --> 00:39:46,538 When we first started this mapping business, it was very, very primitive, 454 00:39:46,851 --> 00:39:49,911 and people knew that there were clusters over there 455 00:39:50,020 --> 00:39:51,385 and a everywhere over there and so on, 456 00:39:51,489 --> 00:39:54,856 it was a little bit like Stanley going to darkest Africa, 457 00:39:54,959 --> 00:39:57,553 he knew where the Congo river was, and the Nile maybe, 458 00:39:57,661 --> 00:39:59,754 but not much about anything else. 459 00:40:00,264 --> 00:40:01,526 It looks like it's over there. 460 00:40:02,166 --> 00:40:05,863 Sandra Faber's enthusiasm for her subject is legendary. 461 00:40:06,303 --> 00:40:07,668 Through numerous collaborations, 462 00:40:07,772 --> 00:40:12,175 she has done as much as anyone to further dark matter research. 463 00:40:14,245 --> 00:40:16,975 Her mapping technigues were to reveal far more than 464 00:40:17,081 --> 00:40:21,518 the patterns already established with conventional two-dimensional maps. 465 00:40:25,756 --> 00:40:28,953 What we're going to see here is three slices of the universe, 466 00:40:30,728 --> 00:40:35,165 and earth is down here in this diagram, right here at the point, 467 00:40:35,533 --> 00:40:39,492 and now we see the first slice being displayed like this, 468 00:40:39,670 --> 00:40:41,900 each little black dot is a galaxy. 469 00:40:42,173 --> 00:40:45,506 This was taken from the southern hemisphere, and now we see the, 470 00:40:45,609 --> 00:40:47,839 finally, the third slice is coming up here. 471 00:40:48,078 --> 00:40:50,876 And what's interesting about these maps is that 472 00:40:50,981 --> 00:40:54,041 the galaxies are not uniformly distributed in space. 473 00:40:54,151 --> 00:40:58,986 Instead, what we see is that they tend to pile up along these walls; 474 00:40:59,290 --> 00:41:01,451 some people have called them 'soap bubbles', 475 00:41:01,592 --> 00:41:05,392 and then the insides of these spaces are called 'voids', 476 00:41:05,496 --> 00:41:08,624 they're relatively empty of galaxies, 477 00:41:09,033 --> 00:41:13,470 and of course this whole structure is expanding as the universe expands. 478 00:41:13,571 --> 00:41:15,163 Now, the guestion is, of course, 479 00:41:15,272 --> 00:41:19,800 why do the galaxies trace this beautiful large-scale structure? 480 00:41:21,512 --> 00:41:22,536 Sandra's hunch was that 481 00:41:22,646 --> 00:41:27,310 this structure was created by an unseen web of dark matter. 482 00:41:28,986 --> 00:41:30,419 So she set out to prove it, 483 00:41:30,554 --> 00:41:33,387 using the most advanced telescopes in the world. 484 00:41:35,025 --> 00:41:38,324 Observing is, er, almost mystical, 485 00:41:38,529 --> 00:41:45,128 it's the act that really puts me in contact with the rest of the universe. 486 00:41:45,302 --> 00:41:47,896 Sitting there and accepting these photons, 487 00:41:48,372 --> 00:41:52,706 er, I imagine projecting myself back along that same path and, 488 00:41:52,810 --> 00:41:55,370 in some way, I know this sounds ridiculous 489 00:41:55,479 --> 00:41:59,347 being in communication and communion with where they came from. 490 00:41:59,817 --> 00:42:02,217 I often think if somebody's looking back at me, 491 00:42:03,187 --> 00:42:05,678 I wonder if their telescope is bigger than mine. 492 00:42:18,235 --> 00:42:20,567 Even through telescopes of this size, 493 00:42:20,771 --> 00:42:25,674 galaxies appear as tiny specks many millions of light years away. 494 00:42:33,684 --> 00:42:35,049 But to prove her theory, 495 00:42:35,185 --> 00:42:39,849 Sandra Faber needed to achieve measurements of unbelievable precision. 496 00:42:43,561 --> 00:42:48,726 The slightest variation in air temperature can invalidate a night's observations. 497 00:42:49,633 --> 00:42:54,161 Before each run, the telescope is cooled with liguid nitrogen. 498 00:43:05,215 --> 00:43:09,174 Once everything is ready they retreat to the warmth of the control room 499 00:43:09,353 --> 00:43:11,412 from where they can aim their telescope 500 00:43:29,873 --> 00:43:33,434 Ah! So this is our next observation. What was this galaxy? 501 00:43:33,611 --> 00:43:35,306 Oh, this was, er, NGC 5813... 502 00:43:35,412 --> 00:43:37,243 Fifteen years ago when Sandra and 503 00:43:37,348 --> 00:43:40,875 her colleagues created a new mapping technigue 504 00:43:44,421 --> 00:43:49,449 they hoped this would reveal the effects of dark matter across the whole universe. 505 00:43:53,897 --> 00:43:56,331 They were completely astonished by the picture that 506 00:43:56,433 --> 00:43:57,900 they finally pieced together. 507 00:44:01,739 --> 00:44:03,172 Just suddenly it came to us, 508 00:44:03,340 --> 00:44:08,107 that if we plotted all of these motions of galaxies, 509 00:44:08,278 --> 00:44:11,406 with an enormous region of space, including us, 510 00:44:11,615 --> 00:44:15,813 was moving roughly in parallel like a big river of galaxies 511 00:44:15,986 --> 00:44:19,752 at the breakneck speed of six hundred kilometres per second, 512 00:44:20,124 --> 00:44:23,992 and that was a definitely new thought for us, 513 00:44:24,094 --> 00:44:26,585 that really struck us very strongly, 514 00:44:26,697 --> 00:44:29,894 we said, what have we discovered, this is truly remarkable. 515 00:44:30,267 --> 00:44:33,202 Then we began to look at our survey in more detail, 516 00:44:33,303 --> 00:44:37,137 and we saw that in fact, off in the distance there, 517 00:44:37,374 --> 00:44:40,104 towards which this great river was flowing, 518 00:44:40,277 --> 00:44:42,268 was a very large structure, 519 00:44:42,379 --> 00:44:44,973 which one of us later named 'the great attractor', 520 00:44:45,115 --> 00:44:48,084 and it turned out to be a very, very big supercluster, 521 00:44:48,185 --> 00:44:50,380 a supersupercluster of galaxies, 522 00:44:50,554 --> 00:44:56,015 and our motion towards that is due to its gravity, it's pulling all of us in, 523 00:44:56,160 --> 00:44:59,493 and it's something like fifty to a hundred billion years from now, 524 00:44:59,663 --> 00:45:04,532 our galaxy will be one of several thousand on orbit 525 00:45:04,635 --> 00:45:07,866 in the great supercluster called the great attractor. 526 00:45:25,556 --> 00:45:29,390 The force of the dark matter around the great attractor is pulling us 527 00:45:29,493 --> 00:45:34,556 across intergalactic space at six hundred kilometres a second. 528 00:45:37,067 --> 00:45:42,095 An unseen web of dark matter is controlling the shape of the universe. 529 00:45:42,973 --> 00:45:47,342 It's dragging all the galaxies together into clusters and superclusters, 530 00:45:47,544 --> 00:45:51,139 and leaving behind huge voids in space. 531 00:45:52,649 --> 00:45:56,983 The way the dark matter clusters will affect exactly 532 00:45:57,087 --> 00:46:02,024 how galaxies form and how superclusters, voids, walls and so on form, 533 00:46:02,826 --> 00:46:08,594 dark matter is key, it, er, it is controlling the motion of everything else, 534 00:46:08,699 --> 00:46:10,098 it's making the galaxies form, 535 00:46:10,200 --> 00:46:13,294 it's making the large-scale structure of form, it's in charge. 536 00:46:15,305 --> 00:46:19,241 We can still only guess about where dark matter is taking us. 537 00:46:19,977 --> 00:46:24,710 If Sandra Faber were pushed, she thinks she knows how she'd place her bet. 538 00:46:25,649 --> 00:46:30,814 Well, currently, it looks as though there's not enough matter in the universe, 539 00:46:30,921 --> 00:46:33,719 guite, to retard the expansion. 540 00:46:34,091 --> 00:46:36,355 If we had to bet right now we'd probably bet 541 00:46:36,460 --> 00:46:39,987 that the universe will expand for ever. 542 00:46:47,004 --> 00:46:50,405 It's a fascinating idea, if the universe expands for ever, 543 00:46:50,507 --> 00:46:52,907 what will happen to it as it cools off? 544 00:46:55,012 --> 00:46:58,846 Stars are gradually consuming all the gas in galaxies, 545 00:46:59,216 --> 00:47:01,116 over time it will all be used up, 546 00:47:01,418 --> 00:47:07,721 those stars will burn and use up their fuel and die, become cold, 547 00:47:07,825 --> 00:47:11,556 dead remnants, white dwarves, maybe some black holes in there. 548 00:47:12,095 --> 00:47:16,225 Galaxies are ever merging to make yet larger structures, 549 00:47:16,333 --> 00:47:20,269 but will become ever dimmer as the stars in them die out, 550 00:47:20,604 --> 00:47:24,301 and ultimately even the very stuff of which stars are made, 551 00:47:24,408 --> 00:47:27,605 the protons, neutrons, and so on, will decay, 552 00:47:28,111 --> 00:47:33,413 and it may be that the ultimate state of the universe is to have no matter at all, 553 00:47:34,051 --> 00:47:41,219 a sea of, er, of, er, elementary particles, dead photons, nothing else. 554 00:47:47,431 --> 00:47:51,424 And the alternative of a big crunch is not much better. 555 00:47:52,436 --> 00:47:55,963 A few years ago, when I was giving a lecture, 556 00:47:56,073 --> 00:47:59,634 I was asked not to mention the end of the universe, 557 00:47:59,776 --> 00:48:02,472 in case it depressed a stock market. 558 00:48:03,714 --> 00:48:07,707 But I can reassure worried investors, either way, 559 00:48:07,918 --> 00:48:11,513 the universe is good for many billions of years more. 560 00:48:12,789 --> 00:48:16,350 The end may be coming, but not just yet.