1 00:00:56,350 --> 00:00:58,216 stephen Hawking: Personally, i am sure 2 00:00:58,217 --> 00:00:59,815 that the universe began 3 00:00:59,816 --> 00:01:03,816 with a hot big bang, but will it go on forever? 4 00:01:03,883 --> 00:01:05,382 And if not, 5 00:01:05,383 --> 00:01:06,915 how will it end? 6 00:01:06,916 --> 00:01:09,616 I am much less certain about that. 7 00:01:09,617 --> 00:01:13,617 The expansion of the universe spreads everything out, 8 00:01:13,750 --> 00:01:17,750 but gravity tries to pull it all back together again. 9 00:01:18,350 --> 00:01:21,815 Our destiny depends on which force will win. 10 00:01:21,816 --> 00:01:25,816 And the influence of gravity in turn depends 11 00:01:26,217 --> 00:01:28,549 on what the universe is made of, 12 00:01:28,550 --> 00:01:31,349 and just how much of it there is. 13 00:01:31,350 --> 00:01:35,350 It won't be easy to find out if, as we suspect, 14 00:01:35,683 --> 00:01:39,683 most of it is dark matter, stuff we can't even see. 15 00:01:44,883 --> 00:01:46,716 Narrator: In our age-old attempts 16 00:01:46,717 --> 00:01:48,549 to give the universe definition, 17 00:01:48,550 --> 00:01:51,549 we've often grappled with phenomena we could not see. 18 00:01:51,550 --> 00:01:54,650 Priya Natarajan is an astrophysicist 19 00:01:55,550 --> 00:01:59,550 studying something that may be beyond our imagination. 20 00:02:00,383 --> 00:02:04,315 But working with the unseen may be easier for her than many, 21 00:02:04,316 --> 00:02:08,316 for she once aspired to be a poet. 22 00:02:10,083 --> 00:02:13,015 Natarajan: There is this impression that everything 23 00:02:13,016 --> 00:02:14,815 the scientists do is very circumscribed, 24 00:02:14,816 --> 00:02:17,716 whereas it is not, because we are bringing 25 00:02:17,717 --> 00:02:19,216 the ways in which 26 00:02:19,217 --> 00:02:20,982 we perform a model, 27 00:02:20,983 --> 00:02:22,949 the ways ... the ingredients that we put in. 28 00:02:22,950 --> 00:02:24,582 And the ways in which we choose 29 00:02:24,583 --> 00:02:26,116 to mix the ingredients 30 00:02:26,117 --> 00:02:28,282 has a lot to do with our individual creativity 31 00:02:28,283 --> 00:02:30,549 and our feelings and our sense and intuition 32 00:02:30,550 --> 00:02:34,550 of how things ought to be. 33 00:02:41,816 --> 00:02:44,015 So it's almost like writing poetry, 34 00:02:44,016 --> 00:02:46,515 where you pick a particular poetic form. 35 00:02:46,516 --> 00:02:48,849 For instance, you could pick the sonnet 36 00:02:48,850 --> 00:02:51,082 or you could pick the japanese haiku, 37 00:02:51,083 --> 00:02:53,749 which, each of these forms has a set of rules, 38 00:02:53,750 --> 00:02:55,949 so you operate within a set of rules, 39 00:02:55,950 --> 00:02:58,349 which is very much like the laws of physics 40 00:02:58,350 --> 00:03:00,482 that you operate within in a model. 41 00:03:00,483 --> 00:03:03,815 But, then, inside the form or inside the model, 42 00:03:03,816 --> 00:03:05,216 there's a lot of freedom, 43 00:03:05,217 --> 00:03:06,982 there's a lot of choices you can make. 44 00:03:06,983 --> 00:03:10,983 Narrator: Natarajan grew up in India. 45 00:03:11,083 --> 00:03:14,182 Her life changed when she was awarded a scholarship 46 00:03:14,183 --> 00:03:16,482 to Cambridge university in Britain. 47 00:03:16,483 --> 00:03:18,082 Here she's taken on a quest, 48 00:03:18,083 --> 00:03:20,482 as spiritual as it is scientific. 49 00:03:20,483 --> 00:03:24,349 She ponders the ultimate destiny of the universe. 50 00:03:24,350 --> 00:03:28,350 Natarajan: We see the stars that shine in the galaxy, 51 00:03:28,816 --> 00:03:32,349 and we also have evidence that there is some gas in the galaxy, 52 00:03:32,350 --> 00:03:35,616 because we can see the light that's scattered off the gas. 53 00:03:35,617 --> 00:03:37,882 But as it turns out, 54 00:03:37,883 --> 00:03:41,883 galaxies contain a lot more than just that. 55 00:03:53,950 --> 00:03:56,482 Narrator: Natarajan owes her inspiration 56 00:03:56,483 --> 00:03:59,949 to a maverick astronomer named Vera Rubin, 57 00:03:59,950 --> 00:04:02,182 who, in the late 1960s, 58 00:04:02,183 --> 00:04:03,982 dared question a basic premise of astronomy. 59 00:04:03,983 --> 00:04:07,082 Natarajan: What Vera Rubin did in her work 60 00:04:07,083 --> 00:04:11,083 was map the speeds of stars at different distances 61 00:04:11,816 --> 00:04:15,816 from the center of a huge spiral galaxy. 62 00:04:23,383 --> 00:04:25,549 Narrator: Vera Rubin noticed something 63 00:04:25,550 --> 00:04:27,582 which defied accepted wisdom. 64 00:04:27,583 --> 00:04:31,583 Stars spinning around the center of galaxies 65 00:04:31,750 --> 00:04:34,082 were supposed to behave like the planets 66 00:04:34,083 --> 00:04:35,749 that orbit the sun. 67 00:04:35,750 --> 00:04:37,249 They don't. 68 00:04:37,250 --> 00:04:38,949 Natarajan: With our solar system, 69 00:04:38,950 --> 00:04:41,149 you have the sun in the center 70 00:04:41,150 --> 00:04:43,616 and you have sort of the planets orbiting around. 71 00:04:43,617 --> 00:04:46,616 And since the dominant gravity is that of the sun, 72 00:04:46,617 --> 00:04:48,882 the planets that are the outer planets, 73 00:04:48,883 --> 00:04:52,883 they move much slower than the planets on the inside. 74 00:04:53,316 --> 00:04:57,316 So naturally what people expected to find 75 00:04:57,516 --> 00:04:59,216 was similarly in a galaxy, 76 00:04:59,217 --> 00:05:01,082 if you measure the speed of the stars 77 00:05:01,083 --> 00:05:02,949 away from the center towards the edge, 78 00:05:02,950 --> 00:05:04,415 you expect it to fall off. 79 00:05:04,416 --> 00:05:06,682 And what Vera Rubin found, instead, 80 00:05:06,683 --> 00:05:09,682 when she actually measured that for a spiral galaxy, 81 00:05:09,683 --> 00:05:12,282 was that the speed stayed the same. 82 00:05:12,283 --> 00:05:15,082 As she sort of mapped the speed of the stars 83 00:05:15,083 --> 00:05:17,482 from the inside out, all the way out to the edge, 84 00:05:17,483 --> 00:05:19,082 they stayed the same. 85 00:05:19,083 --> 00:05:23,083 Narrator: Rubin was the first to pose a question 86 00:05:24,750 --> 00:05:27,349 that has baffled scientists ever since. 87 00:05:27,350 --> 00:05:31,350 If all the stars in a galaxy move at the same speed, 88 00:05:32,616 --> 00:05:34,682 regardless of their distance from the center, 89 00:05:34,683 --> 00:05:36,549 then the center couldn't be 90 00:05:36,550 --> 00:05:38,816 the only source of gravity affecting them. 91 00:05:38,817 --> 00:05:42,749 Something else would have to be exerting a powerful force, 92 00:05:42,750 --> 00:05:46,750 something we simply can't see. 93 00:05:48,083 --> 00:05:49,749 What she found was 94 00:05:49,750 --> 00:05:52,882 that in order to explain the speeds that she observed, 95 00:05:52,883 --> 00:05:55,816 she needed to have a lot more stuff 96 00:05:55,817 --> 00:05:58,549 in the galaxy than we see, 97 00:05:58,550 --> 00:06:00,882 and since the stuff is not visible 98 00:06:00,883 --> 00:06:02,282 and it's not emitting any light, 99 00:06:02,283 --> 00:06:03,949 she coined the term "dark matter" 100 00:06:03,950 --> 00:06:06,249 to refer to that. 101 00:06:06,250 --> 00:06:10,250 Narrator: Rubin had every reason to believe 102 00:06:10,317 --> 00:06:12,615 her discovery would be met with great excitement. 103 00:06:12,616 --> 00:06:16,616 It was, though not the kind she might have expected. 104 00:06:16,850 --> 00:06:19,549 Natarajan: Her announcement that there was dark matter 105 00:06:19,550 --> 00:06:22,816 associated with every individual galaxy 106 00:06:22,817 --> 00:06:25,549 was received with much skepticism, 107 00:06:25,550 --> 00:06:28,849 because of the far-reaching implications it had, 108 00:06:28,850 --> 00:06:30,415 and because, also, 109 00:06:30,416 --> 00:06:32,749 of the inferred percentage of dark matter. 110 00:06:32,750 --> 00:06:36,082 From her work, she inferred that almost 90% of the mass 111 00:06:36,083 --> 00:06:40,083 in a spiral galaxy had to be dark. 112 00:06:45,283 --> 00:06:47,482 Narrator: Rubin's findings suggested 113 00:06:47,483 --> 00:06:49,216 that the destiny of galaxies 114 00:06:49,217 --> 00:06:52,415 is governed by a vast and inscrutable network. 115 00:06:52,416 --> 00:06:56,416 Every galaxy is enveloped in dark matter, 116 00:06:58,350 --> 00:07:01,682 invisibly locking all the stars in its embrace 117 00:07:01,683 --> 00:07:04,382 with the gravity it exerts. 118 00:07:04,383 --> 00:07:07,149 The black emptiness of space, 119 00:07:07,150 --> 00:07:09,549 it seems, isn't that empty after all. 120 00:07:09,550 --> 00:07:13,550 99% of the universe could well be made up 121 00:07:13,650 --> 00:07:15,149 of dark matter, 122 00:07:15,150 --> 00:07:19,150 a sprawling, cosmic web. 123 00:07:22,650 --> 00:07:25,415 For cosmologists like myself, 124 00:07:25,416 --> 00:07:28,849 it's crucial to know precisely how much dark matter there is 125 00:07:28,850 --> 00:07:31,016 in order to know 126 00:07:31,017 --> 00:07:35,017 what will become of the universe eventually. 127 00:07:46,883 --> 00:07:50,883 Natarajan: The total mass of our universe is what decides 128 00:07:50,916 --> 00:07:54,916 the fate of our universe, whether we continue expanding, 129 00:07:55,750 --> 00:07:58,649 Or whether we stop and decelerate, 130 00:07:58,650 --> 00:08:01,882 or we turn around back on ourselves. 131 00:08:01,883 --> 00:08:05,082 So the ultimate fate of what really happens to us 132 00:08:05,083 --> 00:08:07,516 depends on how well we have made an inventory 133 00:08:07,517 --> 00:08:10,049 of the mass in the universe. 134 00:08:10,050 --> 00:08:13,282 And therefore, if such a large fraction is indeed dark, 135 00:08:13,283 --> 00:08:17,283 that has very important consequences. 136 00:08:21,600 --> 00:08:25,600 Hawking: Few people now doubt that Vera Rubin was right. 137 00:08:25,900 --> 00:08:29,900 Dark matter determines the future of the universe. 138 00:08:30,733 --> 00:08:33,265 To know our ultimate fate, 139 00:08:33,266 --> 00:08:36,199 we need to be sure that dark matter exists, 140 00:08:36,200 --> 00:08:39,332 and how much of it there is. 141 00:08:39,333 --> 00:08:43,333 Searching for the invisible is not for the faint-hearted. 142 00:08:53,833 --> 00:08:57,833 When Chris Stubbs first told his colleagues 143 00:08:57,867 --> 00:09:00,965 he wanted to look for dark matter, 144 00:09:00,966 --> 00:09:03,965 they told him he was out of his mind. 145 00:09:03,966 --> 00:09:07,966 That wasn't the way to a safe job. 146 00:09:09,133 --> 00:09:12,632 There's an infinite amount of science to do, 147 00:09:12,633 --> 00:09:15,532 and i think the trick is to choose carefully 148 00:09:15,533 --> 00:09:17,299 what you spend your time doing. 149 00:09:17,300 --> 00:09:19,166 And my taste, for a long time, 150 00:09:19,167 --> 00:09:21,632 has run towards fundamental problems 151 00:09:21,633 --> 00:09:24,332 that may be very difficult to address experimentally, 152 00:09:24,333 --> 00:09:27,032 but which have a very large impact 153 00:09:27,033 --> 00:09:31,033 on our understanding of the universe. 154 00:09:31,367 --> 00:09:33,366 Narrator: Chris Stubbs has made a career 155 00:09:33,367 --> 00:09:35,999 of shooting in the dark. 156 00:09:36,000 --> 00:09:38,932 He's part of an international team 157 00:09:38,933 --> 00:09:41,932 of 18 scientists and 3 institutions, 158 00:09:41,933 --> 00:09:44,866 all with one improbable goal. 159 00:09:44,867 --> 00:09:47,166 Stubbs: We're carrying out 160 00:09:47,167 --> 00:09:50,699 an experiment to look 161 00:09:50,700 --> 00:09:52,699 for a particular kind of dark matter, 162 00:09:52,700 --> 00:09:56,465 which we call "machos" which is a shorthand 163 00:09:56,466 --> 00:09:59,866 that stands for "massive compact halo objects". 164 00:09:59,867 --> 00:10:02,532 The idea is that our galaxy 165 00:10:02,533 --> 00:10:05,199 has a big halo of dark matter around it 166 00:10:05,200 --> 00:10:07,699 that's made out of astronomical objects 167 00:10:07,700 --> 00:10:09,866 that, for one reason or another, 168 00:10:09,867 --> 00:10:12,532 don't shine like the stars that we see. 169 00:10:12,533 --> 00:10:16,533 Narrator: Stubbs believes these strange vestiges of stars, 170 00:10:17,266 --> 00:10:19,599 their compressed corpses, 171 00:10:19,600 --> 00:10:22,132 litter the universe. 172 00:10:22,133 --> 00:10:26,099 Machos range from the size of the earth 173 00:10:26,100 --> 00:10:28,066 to 10 times that of the sun. 174 00:10:28,067 --> 00:10:31,865 If they are the secret phantoms that govern the motion of stars, 175 00:10:31,866 --> 00:10:35,866 they would be most numerous on the fringes of galaxies. 176 00:10:38,633 --> 00:10:42,633 Hawking: It was the right place to search, 177 00:10:42,967 --> 00:10:46,799 but finding them would be like 178 00:10:46,800 --> 00:10:50,800 looking for a black bat on a dark night. 179 00:10:56,467 --> 00:11:00,467 The one thing that he knew was that his subjects 180 00:11:01,133 --> 00:11:03,166 were fairly heavy. 181 00:11:03,167 --> 00:11:05,099 And if they were heavy, 182 00:11:05,100 --> 00:11:07,032 they would have a gravitational effect 183 00:11:07,033 --> 00:11:11,033 on light passing nearby. 184 00:11:12,733 --> 00:11:14,966 The macho-hunter turned 185 00:11:14,967 --> 00:11:17,932 to Einstein's general theory of relativity 186 00:11:17,933 --> 00:11:21,933 to tell him how gravity affects light. 187 00:11:23,600 --> 00:11:27,032 Narrator: Stubbs set out to find stealth stars 188 00:11:27,033 --> 00:11:29,066 in the dark reaches of space. 189 00:11:29,067 --> 00:11:31,899 By shedding a little einsteinian light on them. 190 00:11:31,900 --> 00:11:34,466 According to relativity, 191 00:11:34,467 --> 00:11:36,899 space and time can be thought of as one. 192 00:11:36,900 --> 00:11:40,900 An object marks its place in the fabric of space-time 193 00:11:41,700 --> 00:11:45,499 with a dent, a pocket into which other objects 194 00:11:45,500 --> 00:11:49,265 that pass within its sphere must fall. 195 00:11:49,266 --> 00:11:51,499 This is how gravity works, 196 00:11:51,500 --> 00:11:52,699 and nothing is immune to its power, 197 00:11:52,700 --> 00:11:56,700 not even light. 198 00:11:57,866 --> 00:12:01,866 We're used to the idea that light travels in straight lines, 199 00:12:03,800 --> 00:12:05,699 and when space-time itself 200 00:12:05,700 --> 00:12:07,499 is curved, light still tries 201 00:12:07,500 --> 00:12:09,399 to travel in a straight line, 202 00:12:09,400 --> 00:12:10,832 but it can't, 203 00:12:10,833 --> 00:12:12,699 because space-time itself 204 00:12:12,700 --> 00:12:15,265 actually has shape and dents and warps in it. 205 00:12:15,266 --> 00:12:18,166 So just like matter, 206 00:12:18,167 --> 00:12:21,265 light which is traveling in a space-time 207 00:12:21,266 --> 00:12:23,265 where there's some large massive object 208 00:12:23,266 --> 00:12:25,732 will actually be attracted to the object, 209 00:12:25,733 --> 00:12:29,733 and its path will be bent towards it. 210 00:12:43,633 --> 00:12:46,966 This effect of the bending of light 211 00:12:46,967 --> 00:12:50,432 is what is used by astronomers 212 00:12:50,433 --> 00:12:54,433 in their search for machos in the halo of our galaxy. 213 00:13:03,833 --> 00:13:07,833 Stubbs: Einstein's general theory of relativity tells us 214 00:13:08,600 --> 00:13:11,565 that light passing close to an object, 215 00:13:11,566 --> 00:13:14,499 like the sun or a lump of dark matter, 216 00:13:14,500 --> 00:13:17,232 is deflected ... it gets bent. 217 00:13:17,233 --> 00:13:21,233 And the effect that a mass has 218 00:13:22,023 --> 00:13:25,551 on the light coming from a distant star or galaxy 219 00:13:25,552 --> 00:13:29,552 is just like putting a lens in front of the star. 220 00:13:30,623 --> 00:13:34,623 It distorts the image, and it makes it appear brighter. 221 00:13:35,164 --> 00:13:37,282 Narrator: If a macho passes between us 222 00:13:37,283 --> 00:13:39,419 and a distant group of stars, 223 00:13:39,420 --> 00:13:42,704 they would brighten, then fade back to normal, 224 00:13:42,705 --> 00:13:45,790 a telltale sign of the macho's presence. 225 00:13:45,791 --> 00:13:49,791 Stubbs used the stars as a million cosmic spotlights, 226 00:13:50,116 --> 00:13:52,461 hoping one might flare, 227 00:13:52,462 --> 00:13:55,966 magnified by the chance sweep of a stray macho. 228 00:13:55,967 --> 00:13:58,970 It was a painstaking hunt for a faint glimmer 229 00:13:58,971 --> 00:14:02,971 from something that may not even exist. 230 00:14:04,256 --> 00:14:07,176 This is just before peak brightness. 231 00:14:07,177 --> 00:14:09,593 It still stands out from the rest of the stars. 232 00:14:09,594 --> 00:14:13,594 Stubbs: Our experiment has made more measurements 233 00:14:13,779 --> 00:14:16,449 of the brightness of individual stars 234 00:14:16,450 --> 00:14:20,427 than the entire cumulative history of astronomy combined, 235 00:14:20,428 --> 00:14:24,428 and we then sift through all of these records 236 00:14:24,769 --> 00:14:28,028 in order to find the one time in a million 237 00:14:28,029 --> 00:14:30,532 when a star gets brighter 238 00:14:30,533 --> 00:14:32,500 as a result of a macho 239 00:14:32,501 --> 00:14:34,539 traveling close to the line of sight 240 00:14:34,540 --> 00:14:38,540 between us and the star. 241 00:14:38,543 --> 00:14:40,729 Narrator: Hours of patient observation, 242 00:14:40,730 --> 00:14:43,439 months of marshaling data ... 243 00:14:43,440 --> 00:14:47,440 a lot was riding on little more than a good guess. 244 00:14:50,314 --> 00:14:52,752 Stubbs: two years after we started the experiment, 245 00:14:52,753 --> 00:14:54,574 we were looking through the data, 246 00:14:54,575 --> 00:14:58,440 trying to understand how to analyze it, 247 00:14:58,441 --> 00:15:02,022 and much to our surprise 248 00:15:02,023 --> 00:15:05,981 found exactly what we thought we were looking for, 249 00:15:05,982 --> 00:15:09,525 in that we saw a star get brighter 250 00:15:09,526 --> 00:15:13,526 and then fainter again with exactly the signature 251 00:15:13,893 --> 00:15:17,893 that's predicted by general relativity. 252 00:15:19,364 --> 00:15:20,771 Okay, this looks like it definitely 253 00:15:20,772 --> 00:15:21,861 fits pretty well. 254 00:15:21,862 --> 00:15:24,901 It's easy to draw a nice curve. 255 00:15:24,902 --> 00:15:27,299 Stubbs: Our experiment has detected 256 00:15:27,300 --> 00:15:31,300 a previously unknown component of this galaxy. 257 00:15:31,661 --> 00:15:35,661 It's a stunning result. 258 00:15:48,812 --> 00:15:50,665 Narrator: Chris Stubbs clinched it. 259 00:15:50,666 --> 00:15:52,975 Dark matter is no fantasy. 260 00:15:52,976 --> 00:15:55,648 It's actually out there. 261 00:15:55,649 --> 00:15:57,818 But a mystery lingers. 262 00:15:57,819 --> 00:16:00,075 To power the fast rotation of stars 263 00:16:00,076 --> 00:16:04,076 vera rubin had detected would take a lot of dark matter. 264 00:16:04,215 --> 00:16:06,876 It seems there are just not enough machos 265 00:16:06,877 --> 00:16:10,877 to account for that kind of colossal gravitational pull. 266 00:16:16,853 --> 00:16:19,379 Stubbs: The simplest point of view 267 00:16:19,380 --> 00:16:22,907 is that the machos are ordinary matter 268 00:16:22,908 --> 00:16:26,079 made up of the same material that exists in stars. 269 00:16:26,080 --> 00:16:28,109 It just didn't happen to end up in stars. 270 00:16:28,110 --> 00:16:31,484 And we think we know exactly how much ... 271 00:16:31,485 --> 00:16:34,055 we think we know how much ordinary matter 272 00:16:34,056 --> 00:16:38,056 there is in the universe, and it just isn't enough 273 00:16:38,132 --> 00:16:42,132 to solve the dark matter problem of the universe. 274 00:16:44,579 --> 00:16:46,750 We need to find something else 275 00:16:46,751 --> 00:16:50,751 to account for more of the dark matter. 276 00:16:51,662 --> 00:16:55,662 Machos were big, so why not try something tiny? 277 00:16:57,750 --> 00:17:01,345 One candidate was a well-known particle, 278 00:17:01,346 --> 00:17:03,348 the neutrino. 279 00:17:03,349 --> 00:17:06,572 This is produced in atomic bomb explosions, 280 00:17:06,573 --> 00:17:08,781 so it would also have been produced 281 00:17:08,782 --> 00:17:12,278 in the big bang explosion. 282 00:17:12,279 --> 00:17:14,846 If it had a tiny mass of its own, 283 00:17:14,847 --> 00:17:18,847 it could be the dark matter, 284 00:17:19,492 --> 00:17:23,492 or it could be one of the so-called exotic particles 285 00:17:23,836 --> 00:17:26,836 whose existence was predicted by theory, 286 00:17:26,837 --> 00:17:30,837 but which were very hard to detect in reality. 287 00:17:31,350 --> 00:17:33,748 Perhaps they are actually out there, 288 00:17:33,749 --> 00:17:37,749 silently shaping the evolution of the universe. 289 00:17:43,133 --> 00:17:44,501 Narrator: Professor Carlos Frenk 290 00:17:44,502 --> 00:17:47,948 believes small things can have a powerful influence, 291 00:17:47,949 --> 00:17:51,949 in the case of neutrinos and in the case of his son David. 292 00:17:54,543 --> 00:17:56,063 Frenk: I think there is a great parallel 293 00:17:56,064 --> 00:17:57,743 between the evolution 294 00:17:57,744 --> 00:17:59,939 of the largest system that we know of, 295 00:17:59,940 --> 00:18:01,045 which is the universe, 296 00:18:01,046 --> 00:18:02,937 and the evolution of the biological system, 297 00:18:02,938 --> 00:18:06,938 like a person or like my son. 298 00:18:09,049 --> 00:18:10,808 I often wonder what are the factors 299 00:18:10,809 --> 00:18:13,841 that are going to influence the development of my son, 300 00:18:13,842 --> 00:18:17,208 whether he will be a physicist or a scientist, 301 00:18:17,209 --> 00:18:18,880 whether he will be a musician, 302 00:18:18,881 --> 00:18:20,278 or whether he will be anything else. 303 00:18:20,279 --> 00:18:22,698 I don't quite understand what are the forces 304 00:18:22,699 --> 00:18:26,087 that are going to drive him in one direction or the other. 305 00:18:26,088 --> 00:18:28,490 The universe, however, is simpler, 306 00:18:28,491 --> 00:18:31,709 because we have a much greater mastery 307 00:18:31,710 --> 00:18:35,710 over the laws that govern the evolution of the universe. 308 00:18:43,897 --> 00:18:46,096 Narrator: Frenk is determined to reconstruct the way 309 00:18:46,097 --> 00:18:50,097 the young universe evolved into the universe we know today. 310 00:18:50,159 --> 00:18:51,725 The most crucial piece of the puzzle 311 00:18:51,726 --> 00:18:53,421 is the most elusive ... 312 00:18:53,422 --> 00:18:57,422 the role played by dark matter. 313 00:18:59,271 --> 00:19:02,067 David's science class relies on models. 314 00:19:02,068 --> 00:19:04,360 It is the lot of the probing mind 315 00:19:04,361 --> 00:19:05,916 to require the concrete 316 00:19:05,917 --> 00:19:09,917 to envision concepts beyond our grasp. 317 00:19:10,223 --> 00:19:13,663 So it is, for David's father. 318 00:19:13,664 --> 00:19:16,597 Frenk experiments with computerized representations 319 00:19:16,598 --> 00:19:20,192 of a universe largely unseen, 320 00:19:20,193 --> 00:19:21,602 from its elemental birth 321 00:19:21,603 --> 00:19:25,603 to the rich complexity we know today. 322 00:19:25,964 --> 00:19:28,827 But his model will only work if he programs in 323 00:19:28,828 --> 00:19:32,817 the precise characteristics for dark matter. 324 00:19:32,818 --> 00:19:36,818 He starts each recreation just a second after the big bang. 325 00:19:38,592 --> 00:19:39,788 Frenk: Prior to that time, 326 00:19:39,789 --> 00:19:42,390 the universe was made up of a cosmic soup 327 00:19:42,391 --> 00:19:45,141 of elementary particles and radiation. 328 00:19:45,142 --> 00:19:46,575 Nothing else could exist 329 00:19:46,576 --> 00:19:49,304 in the midst of this tremendous heat. 330 00:19:49,305 --> 00:19:52,243 But then, after about 100 seconds, 331 00:19:52,244 --> 00:19:54,283 the universe had cooled down a little bit 332 00:19:54,284 --> 00:19:56,356 to a mere 10 billion degrees, 333 00:19:56,357 --> 00:19:58,869 but this temperature is now low enough 334 00:19:58,870 --> 00:20:02,870 that the first thermonuclear fusion reactions can take place. 335 00:20:12,944 --> 00:20:14,624 Narrator: At that critical instant, 336 00:20:14,625 --> 00:20:16,730 according to Frenk's scenario, 337 00:20:16,731 --> 00:20:20,731 a mysterious group of particles broke free from the pack. 338 00:20:22,504 --> 00:20:25,812 Long before the appearance of stars and galaxies, 339 00:20:25,813 --> 00:20:29,813 they swarmed into great clusters of dark matter. 340 00:20:32,567 --> 00:20:36,567 These vast aggregates exerted a powerful gravitational pull 341 00:20:37,366 --> 00:20:41,366 on the remaining ordinary matter. 342 00:20:44,101 --> 00:20:45,852 As the dark empire grew 343 00:20:45,853 --> 00:20:48,531 in tandem with the expanding universe, 344 00:20:48,532 --> 00:20:51,811 it reined in more and more ordinary matter, 345 00:20:51,812 --> 00:20:55,812 ultimately giving rise to the stars. 346 00:20:56,867 --> 00:21:00,867 Eventually, one billion years after the big bang, 347 00:21:01,360 --> 00:21:04,304 congregations of stars drew together 348 00:21:04,305 --> 00:21:08,305 to from the earliest galaxies. 349 00:21:09,227 --> 00:21:11,558 Frenk's tale was an epic one. 350 00:21:11,559 --> 00:21:14,585 He had its framework by the early 1980s, 351 00:21:14,586 --> 00:21:17,953 but it was missing one crucial ingredient. 352 00:21:17,954 --> 00:21:20,977 What was the dark matter? 353 00:21:20,978 --> 00:21:22,729 The idea that was around at the time 354 00:21:22,730 --> 00:21:24,735 was that the dark matter could consist 355 00:21:24,736 --> 00:21:28,736 of small elementary particles called neutrinos. 356 00:21:31,013 --> 00:21:33,991 Narrator: Could this minute shrapnel from the big bang 357 00:21:33,992 --> 00:21:37,992 work as the dark matter in his model? 358 00:21:40,681 --> 00:21:42,344 Frenk: That was a very trendy, 359 00:21:42,345 --> 00:21:45,616 fashionable idea, if you like, in those days, 360 00:21:45,617 --> 00:21:48,811 and it was the first concrete proposal we had 361 00:21:48,812 --> 00:21:50,622 for what the dark matter could be, 362 00:21:50,623 --> 00:21:52,691 and this was very significant. 363 00:21:52,692 --> 00:21:55,177 And some people would say ... a very significant idea, 364 00:21:55,178 --> 00:21:57,620 and so people would say it signalled 365 00:21:57,621 --> 00:22:00,090 the beginning of a revolution in the way 366 00:22:00,091 --> 00:22:02,384 in which we study the universe, 367 00:22:02,385 --> 00:22:05,636 because for the first time, the neutrino hypothesis 368 00:22:05,637 --> 00:22:09,637 provided a concrete starting point 369 00:22:10,056 --> 00:22:13,033 that we could explore in an unambiguous fashion 370 00:22:13,034 --> 00:22:17,034 using the tools of evolutionary cosmology. 371 00:22:22,048 --> 00:22:24,534 Narrator: Neutrinos stream through the universe 372 00:22:24,535 --> 00:22:28,535 at virtually the speed of light. 373 00:22:30,456 --> 00:22:33,457 Every second, about 100 trillion 374 00:22:33,458 --> 00:22:37,458 shoot straight through your body. 375 00:22:38,738 --> 00:22:42,714 These tiny particles suffuse the universe, 376 00:22:42,715 --> 00:22:44,944 they are everywhere, 377 00:22:44,945 --> 00:22:46,949 yet they will slip through any barrier, 378 00:22:46,950 --> 00:22:50,523 so they're almost impossible to nab. 379 00:22:50,524 --> 00:22:54,524 For particle physicists, no catch is more challenging. 380 00:22:55,835 --> 00:22:59,835 Their goal is to find out if neutrinos have mass. 381 00:23:02,365 --> 00:23:05,680 Without mass, they wouldn't have a gravitational effect, 382 00:23:05,681 --> 00:23:09,681 and they wouldn't be a candidate for dark matter. 383 00:23:12,973 --> 00:23:14,657 In northern France, 384 00:23:14,658 --> 00:23:17,433 Yves Declais is leading an ambitious effort 385 00:23:17,434 --> 00:23:21,434 to reel in neutrinos. 386 00:23:22,403 --> 00:23:23,693 Declais: when you prepare your bait, 387 00:23:23,694 --> 00:23:25,507 when you have prepared your detector, 388 00:23:25,508 --> 00:23:27,037 when you have prepared your trap, 389 00:23:27,038 --> 00:23:29,858 you have to install it at the right place, 390 00:23:29,859 --> 00:23:31,052 and so you have to go 391 00:23:31,053 --> 00:23:34,137 where you think you will be able to detect neutrino, 392 00:23:34,138 --> 00:23:36,401 where you will be right to get out some fish 393 00:23:36,402 --> 00:23:38,049 out from the river. 394 00:23:38,050 --> 00:23:39,351 And after that, 395 00:23:39,352 --> 00:23:42,621 you have not only to wait, but you have to work, 396 00:23:42,622 --> 00:23:44,493 and you will see what will be the result. 397 00:23:44,494 --> 00:23:48,222 You will see how many neutrino, how many fish 398 00:23:48,223 --> 00:23:52,223 you will get out from the river. 399 00:23:52,618 --> 00:23:56,101 Narrator: The best place to cast a line is already known. 400 00:23:56,102 --> 00:23:59,710 Neutrinos are produced where there's radioactive decay. 401 00:23:59,711 --> 00:24:03,711 Both are governed by the physics of nuclear reactions. 402 00:24:05,624 --> 00:24:08,432 Fred Reines worked on the atomic bomb, 403 00:24:08,433 --> 00:24:12,433 then became the first neutrino hunter. 404 00:24:12,643 --> 00:24:14,585 Declais: He thought it was possible to see 405 00:24:14,586 --> 00:24:16,969 the flash of light produced 406 00:24:16,970 --> 00:24:18,367 by the introduction of a neutrino 407 00:24:18,368 --> 00:24:20,269 into some water detector, 408 00:24:20,270 --> 00:24:22,621 when you have the explosion of the bomb, 409 00:24:22,622 --> 00:24:25,327 And in order to detect this flash 410 00:24:25,328 --> 00:24:29,268 with respect to the natural background around. 411 00:24:29,269 --> 00:24:32,789 But it was quite difficult to install such an experiment 412 00:24:32,790 --> 00:24:36,790 near an atomic bomb. 413 00:24:39,727 --> 00:24:42,453 Narrator: Eventually, reines shifted his experiments 414 00:24:42,454 --> 00:24:46,454 to a safer source of neutrinos, a nuclear power plant. 415 00:24:49,866 --> 00:24:53,866 In 1956, he became the first to trap a neutrino. 416 00:24:54,650 --> 00:24:58,650 The achievement won him the nobel prize. 417 00:24:58,822 --> 00:25:02,732 But reines wasn't able to learn if the neutrino had any mass. 418 00:25:02,733 --> 00:25:06,733 That challenge now falls to yves Declais. 419 00:25:08,697 --> 00:25:11,731 Like Reines, he will stalk his tiny quarry 420 00:25:11,732 --> 00:25:15,732 in the bowels of a colossal furnace. 421 00:25:15,798 --> 00:25:19,515 Beside a nuclear power station is an underground bunker, 422 00:25:19,516 --> 00:25:23,516 shielded by the earth from the interference of cosmic rays. 423 00:25:25,035 --> 00:25:26,573 Declais: You have to be in the right place, 424 00:25:26,574 --> 00:25:29,676 very strong neutrino source in order to be able 425 00:25:29,677 --> 00:25:33,140 to see some interaction of these neutrino. 426 00:25:33,141 --> 00:25:34,352 And you have, also, 427 00:25:34,353 --> 00:25:37,607 to protect your detector against the background. 428 00:25:37,608 --> 00:25:40,597 And when you detect low-energy neutrinos, 429 00:25:40,598 --> 00:25:43,605 the main background comes from the sky, 430 00:25:43,606 --> 00:25:45,418 comes from cosmic rays, 431 00:25:45,419 --> 00:25:47,463 so you have to install your detector 432 00:25:47,464 --> 00:25:51,464 as deep as possible underground. 433 00:26:07,469 --> 00:26:09,813 In this experiment we want to see 434 00:26:09,814 --> 00:26:12,029 if the nature of the neutrino 435 00:26:12,030 --> 00:26:14,509 change between the source of the neutrino 436 00:26:14,510 --> 00:26:18,032 and the detector one kilometer away. 437 00:26:18,033 --> 00:26:21,275 And if the nature of the neutrino change 438 00:26:21,276 --> 00:26:23,800 during this path of one kilometer, 439 00:26:23,801 --> 00:26:25,432 we can demonstrate, 440 00:26:25,433 --> 00:26:27,832 we can prove that this is related 441 00:26:27,833 --> 00:26:31,833 to the existence of a mass for the neutrino. 442 00:26:32,667 --> 00:26:34,648 It is a little bit complicated to compute, 443 00:26:34,649 --> 00:26:38,649 but it is a very, very simple system. 444 00:27:06,095 --> 00:27:07,844 Narrator: Neutrinos, by definition, 445 00:27:07,845 --> 00:27:10,113 must have mass if they undergo 446 00:27:10,114 --> 00:27:14,114 a subtle distinguishable transformation. 447 00:27:15,204 --> 00:27:17,549 Declais and his team have already conducted 448 00:27:17,550 --> 00:27:20,898 a neutrino census nearby the reactor. 449 00:27:20,899 --> 00:27:24,063 Now they want to take a comparative tally here, 450 00:27:24,064 --> 00:27:28,064 two-thirds of a mile away. 451 00:27:28,772 --> 00:27:31,682 you can see yours ... no, passed too quickly. 452 00:27:31,683 --> 00:27:33,190 Two events very far apart. 453 00:27:33,191 --> 00:27:35,212 Narrator: They want to see if there are fewer 454 00:27:35,213 --> 00:27:37,082 of the kind of neutrinos they clocked 455 00:27:37,083 --> 00:27:39,439 closer to the reactor. 456 00:27:39,440 --> 00:27:42,122 The rest, then, would have undergone 457 00:27:42,123 --> 00:27:43,370 the telltale transformation 458 00:27:43,371 --> 00:27:45,683 by the time they traveled this distance, 459 00:27:45,684 --> 00:27:49,684 proving the particles have mass. 460 00:27:50,074 --> 00:27:54,074 It may take years, but yves is persistent. 461 00:27:54,813 --> 00:27:57,152 Declais: This is really important 462 00:27:57,153 --> 00:27:58,603 for particle physics 463 00:27:58,604 --> 00:28:02,604 and also for cosmology and astrophysics. 464 00:28:02,803 --> 00:28:06,803 One of the best candidates for the dark matter, 465 00:28:07,052 --> 00:28:09,234 for the missing matter in the universe, 466 00:28:09,235 --> 00:28:13,235 is the neutrino, if the neutrino has a mass. 467 00:28:13,585 --> 00:28:16,710 Even if the mass of the neutrino can be very tiny ... 468 00:28:16,711 --> 00:28:18,416 very, very, very small ... 469 00:28:18,417 --> 00:28:20,507 because the universe is completely filled 470 00:28:20,508 --> 00:28:23,819 by a lot of neutrino coming from the early universe, 471 00:28:23,820 --> 00:28:27,820 from the first three seconds of the universe. 472 00:28:30,844 --> 00:28:32,299 Narrator: Meanwhile, Carlos Frenk 473 00:28:32,300 --> 00:28:34,455 wasn't waiting for word. 474 00:28:34,456 --> 00:28:38,250 He kept hammering away at his digital reenactment of creation. 475 00:28:38,251 --> 00:28:41,868 His approach was to assume neutrinos have mass, 476 00:28:41,869 --> 00:28:45,869 and see what kind of universe would result. 477 00:28:45,974 --> 00:28:47,810 Frenk: So we programmed our computer 478 00:28:47,811 --> 00:28:50,282 to follow the evolution of the universe 479 00:28:50,283 --> 00:28:54,283 in which the dark matter was made up of massive neutrinos, 480 00:28:54,928 --> 00:28:58,202 and that the aim was to produce in the computer 481 00:28:58,203 --> 00:28:59,665 a synthetic universe 482 00:28:59,666 --> 00:29:03,666 that we could then compare with the real thing. 483 00:29:07,227 --> 00:29:10,425 So we programmed our computer up in this fashion, 484 00:29:10,426 --> 00:29:12,961 and let it churn away over christmas, 485 00:29:12,962 --> 00:29:16,962 and when we came back, we saw the first maps 486 00:29:17,338 --> 00:29:21,338 being generated by the computer. 487 00:29:31,541 --> 00:29:33,882 Here we have a recognizable universe, 488 00:29:33,883 --> 00:29:36,672 a credible universe, something that's made galaxies, 489 00:29:36,673 --> 00:29:38,043 something that's made galaxy clusters, 490 00:29:38,044 --> 00:29:41,543 something that is competitive vis-a-vis the real universe. 491 00:29:41,544 --> 00:29:44,747 There was a great sense of elation, 492 00:29:44,748 --> 00:29:46,635 and the thought that we might have solved 493 00:29:46,636 --> 00:29:50,368 what was already, clearly then, and sadly still is today, 494 00:29:50,369 --> 00:29:52,691 the main unsolved problem in cosmology. 495 00:29:52,692 --> 00:29:56,071 It was one of those feelings you have once in a lifetime, 496 00:29:56,072 --> 00:29:59,792 when you think you've really stumbled upon something major. 497 00:29:59,793 --> 00:30:03,793 Now, that was our first impression. 498 00:30:04,896 --> 00:30:08,896 Narrator: The impression was fleeting. 499 00:30:09,732 --> 00:30:11,185 Frenk was so elated 500 00:30:11,186 --> 00:30:13,806 to have concocted his own digital universe, 501 00:30:13,807 --> 00:30:17,807 at first he didn't notice a fatal flaw. 502 00:30:18,880 --> 00:30:21,986 On closer inspection, his model for creation 503 00:30:21,987 --> 00:30:25,987 didn't quite look like the real thing. 504 00:30:26,700 --> 00:30:28,599 And that was very depressing. 505 00:30:28,600 --> 00:30:31,534 We thought for a while, for a few weeks, perhaps, 506 00:30:31,535 --> 00:30:33,878 that we really had found the key to the universe, 507 00:30:33,879 --> 00:30:36,735 and that key evaporated, 508 00:30:36,736 --> 00:30:40,736 and it was a terribly disappointing period. 509 00:30:43,878 --> 00:30:46,083 Narrator: In failure, there can be lessons. 510 00:30:46,084 --> 00:30:49,282 In perseverance there can be results. 511 00:30:49,283 --> 00:30:53,283 Frenk wasn't about to give up. 512 00:30:53,415 --> 00:30:55,634 Frenk: It is paradoxical that we can understand the universe 513 00:30:55,635 --> 00:30:57,721 better than we can understand a tiny little part. 514 00:30:57,722 --> 00:30:59,954 My son is an insignificant little speck 515 00:30:59,955 --> 00:31:01,278 in this gigantic universe, 516 00:31:01,279 --> 00:31:03,292 and yet I can understand the universe better 517 00:31:03,293 --> 00:31:05,636 than I can understand my son. 518 00:31:05,637 --> 00:31:07,803 And so often I regard myself as being very lucky 519 00:31:07,804 --> 00:31:08,991 that I am a physicist, 520 00:31:08,992 --> 00:31:10,948 rather than a biologist or a psychologist. 521 00:31:10,949 --> 00:31:13,330 They have a much tougher time than we do, 522 00:31:13,331 --> 00:31:17,150 because we deal with systems that are intrinsically simple. 523 00:31:17,151 --> 00:31:19,033 Biologists and psychologists 524 00:31:19,034 --> 00:31:22,234 deal with this much more complex, 525 00:31:22,235 --> 00:31:24,561 and in some ways magical world of humans, 526 00:31:24,562 --> 00:31:28,562 who are essentially unpredictable. 527 00:31:29,431 --> 00:31:33,055 Narrator: Particle physicists urged a startling alternative, 528 00:31:33,056 --> 00:31:34,647 to replace the neutrino 529 00:31:34,648 --> 00:31:38,648 with an entirely hypothetical component. 530 00:31:39,041 --> 00:31:43,041 Frenk dubbed it "cold dark matter" 531 00:31:43,931 --> 00:31:46,829 His long struggle with neutrinos hadn't worked, 532 00:31:46,830 --> 00:31:50,745 but he had learned much in the process. 533 00:31:50,746 --> 00:31:54,746 Now, maybe, practice would make his model perfect. 534 00:31:57,939 --> 00:31:59,619 Frenk: Our next step, then, 535 00:31:59,620 --> 00:32:02,220 was to change our starting assumption, 536 00:32:02,221 --> 00:32:05,375 and now take the dark matter to be composed 537 00:32:05,376 --> 00:32:08,331 of cold dark matter. 538 00:32:08,332 --> 00:32:12,332 [ plays Schumann's "melody" ] 539 00:32:12,442 --> 00:32:16,185 [ plays wrong notes ] 540 00:32:16,186 --> 00:32:17,950 Frenk: I must say, we were very skeptical 541 00:32:17,951 --> 00:32:18,962 when we started this new project. 542 00:32:18,963 --> 00:32:20,530 By then we had got slightly fed up 543 00:32:20,531 --> 00:32:22,807 with particle physicists trying to tell us astronomers 544 00:32:22,808 --> 00:32:24,113 what our universe was made of. 545 00:32:24,114 --> 00:32:26,564 Particle physicists are supposed to be working on something else, 546 00:32:26,565 --> 00:32:29,269 and they have no right to come and tell us astronomers 547 00:32:29,270 --> 00:32:32,110 what our universe is made of. 548 00:32:32,111 --> 00:32:36,111 So our approach at first was really, frankly, cynical ... 549 00:32:36,275 --> 00:32:38,343 we started off saying, right, let's go and put 550 00:32:38,344 --> 00:32:39,418 these particle physicists right. 551 00:32:39,419 --> 00:32:41,978 We ruled out neutrinos. 552 00:32:41,979 --> 00:32:44,144 Now let's go rule out cold dark matter as well, 553 00:32:44,145 --> 00:32:45,954 and get those guys off our backs so they can 554 00:32:45,955 --> 00:32:47,617 go and do their own thing with accelerators 555 00:32:47,618 --> 00:32:51,304 and we can keep on trying to understand how galaxies form. 556 00:32:51,305 --> 00:32:55,305 [ playing Schumann's "Melody" ] 557 00:32:55,720 --> 00:32:57,457 Frenk: What happened was that, 558 00:32:57,458 --> 00:33:00,306 these cold dark matter universes turned out to be 559 00:33:00,307 --> 00:33:03,003 far richer and far more interesting 560 00:33:03,004 --> 00:33:07,004 than we ever had any right to expect. 561 00:33:08,103 --> 00:33:10,834 Narrator: Frenk's new model works at last, 562 00:33:10,835 --> 00:33:12,283 but there's a catch. 563 00:33:12,284 --> 00:33:15,060 It relies on an invented particle, 564 00:33:15,061 --> 00:33:18,669 a symbol tapped out on a keyboard. 565 00:33:18,670 --> 00:33:22,670 Does cold dark matter exist? 566 00:33:25,106 --> 00:33:28,324 The burden of proof is on the experimentalists 567 00:33:28,325 --> 00:33:30,310 who now have to go and detect these particles. 568 00:33:30,311 --> 00:33:32,246 And until that happens, 569 00:33:32,247 --> 00:33:34,354 then we cannot be by any means certain 570 00:33:34,355 --> 00:33:35,978 that this is a correct theory. 571 00:33:35,979 --> 00:33:39,321 But if they do succeed, 572 00:33:39,322 --> 00:33:43,322 this really will be an outstanding achievement, 573 00:33:43,454 --> 00:33:46,381 and i think it's not an exaggeration 574 00:33:46,382 --> 00:33:48,219 to say that if the dark matter 575 00:33:48,220 --> 00:33:51,452 turns out to be an exotic elementary particle, 576 00:33:51,453 --> 00:33:53,705 this really will go down in history 577 00:33:53,706 --> 00:33:57,706 as one of the greatest scientific discoveries ever. 578 00:34:01,666 --> 00:34:05,021 Hawking: The evidence suggests that most of the universe 579 00:34:05,022 --> 00:34:09,022 is made up of something no one has ever seen. 580 00:34:10,530 --> 00:34:12,494 By its very nature, 581 00:34:12,495 --> 00:34:16,495 cold dark matter has to be hard to detect. 582 00:34:16,935 --> 00:34:18,964 Finding a way to do so 583 00:34:18,965 --> 00:34:22,965 is one of the most difficult tasks in physics today. 584 00:34:34,163 --> 00:34:36,456 Narrator: Now, in search of a particle 585 00:34:36,457 --> 00:34:38,325 that can't be seen, 586 00:34:38,326 --> 00:34:40,352 one that has only pure conjecture 587 00:34:40,353 --> 00:34:42,502 to vouch for its existence, 588 00:34:42,503 --> 00:34:44,250 a team of scientists has come 589 00:34:44,251 --> 00:34:48,251 to the mining country of northern England. 590 00:34:49,839 --> 00:34:53,839 Leading them is Neil Spooner. 591 00:34:54,438 --> 00:34:55,501 Spooner: It's fairly astounding 592 00:34:55,502 --> 00:34:56,531 that at the end of the 20th century, 593 00:34:56,532 --> 00:34:57,402 we actually don't know 594 00:34:57,403 --> 00:34:59,592 what most of the universe is made of ... 595 00:34:59,593 --> 00:35:03,283 not 90%, maybe even 99% ... 596 00:35:03,284 --> 00:35:06,467 and that it sort of 597 00:35:06,468 --> 00:35:08,163 puts one in, as a human being ... 598 00:35:08,164 --> 00:35:12,164 into some perspective that we ... 599 00:35:13,549 --> 00:35:14,875 the Earth is not the center 600 00:35:14,876 --> 00:35:16,038 of the solar system, et cetera, 601 00:35:16,039 --> 00:35:18,156 and maybe we're not even 602 00:35:18,157 --> 00:35:21,437 the only life now. 603 00:35:21,438 --> 00:35:23,832 And we're not even made 604 00:35:23,833 --> 00:35:25,451 of particularly common matter, 605 00:35:25,452 --> 00:35:27,291 in that we're not the typical 606 00:35:27,292 --> 00:35:28,962 matter that's around, because 607 00:35:28,963 --> 00:35:29,844 most of it's dark matter, 608 00:35:29,845 --> 00:35:33,845 which we don't know what it is. 609 00:35:42,476 --> 00:35:43,845 Narrator: Spooner's first challenge 610 00:35:43,846 --> 00:35:47,625 was finding a way to glimpse the particles he was after. 611 00:35:47,626 --> 00:35:49,034 as with neutrinos, 612 00:35:49,035 --> 00:35:52,849 the search for cold dark matter must be conducted underground, 613 00:35:52,850 --> 00:35:56,850 Beyond the reach of cosmic rays. 614 00:35:57,245 --> 00:36:00,706 His team is going to great lengths to find dark matter, 615 00:36:00,707 --> 00:36:03,830 and great depths. 616 00:36:03,831 --> 00:36:04,982 Spooner: It just happens 617 00:36:04,983 --> 00:36:08,983 that my father is a mining engineer by profession. 618 00:36:10,244 --> 00:36:12,060 So I just asked him what was the deepest mine in britain, 619 00:36:12,061 --> 00:36:14,374 naively thinking it would be a coal mine, which would be 620 00:36:14,375 --> 00:36:16,588 useless for us because it would be quite difficult 621 00:36:16,589 --> 00:36:17,902 to work in the coal mine, 622 00:36:17,903 --> 00:36:20,607 because of the safety aspect of it. 623 00:36:20,608 --> 00:36:23,399 But it turned out that he looked it up, 624 00:36:23,400 --> 00:36:25,796 and it was boulby, which is a salt mine, 625 00:36:25,797 --> 00:36:29,797 which is ideal for us. 626 00:36:32,835 --> 00:36:35,501 Narrator: Boulby mine is not only the deepest in Britain, 627 00:36:35,502 --> 00:36:39,502 but in all Europe. 628 00:36:39,648 --> 00:36:41,555 the elevator bores into the ground 629 00:36:41,556 --> 00:36:43,271 for five long minutes, 630 00:36:43,272 --> 00:36:47,272 plummeting a mile below the surface. 631 00:36:48,445 --> 00:36:51,946 At this depth, the air is 18 degrees hotter 632 00:36:51,947 --> 00:36:55,105 than at the surface, and choked with dust. 633 00:36:55,106 --> 00:36:56,821 Building delicate instruments 634 00:36:56,822 --> 00:36:59,378 that can stand up to these corrosive conditions 635 00:36:59,379 --> 00:37:03,379 was a daunting prospect. 636 00:37:03,452 --> 00:37:05,582 Spooner: It's a technological fight, 637 00:37:05,583 --> 00:37:07,808 trying to work deep underground 638 00:37:07,809 --> 00:37:11,809 in the salt mine, which is an environment which, 639 00:37:14,422 --> 00:37:17,117 well, we're dealing with fairly intricate electronics, 640 00:37:17,118 --> 00:37:19,084 and we're trying to be clean. 641 00:37:19,085 --> 00:37:23,085 And trying to do that in a mine is sort of very, very difficult. 642 00:37:36,049 --> 00:37:38,899 Narrator: Deep in the earth, it's hard to tell the locals, 643 00:37:38,900 --> 00:37:40,665 working their picks and shovels, 644 00:37:40,666 --> 00:37:44,666 from the particle physicists mining for matter. 645 00:37:46,148 --> 00:37:49,185 Spooner: They all say, "Have you found it yet?" 646 00:37:49,186 --> 00:37:53,186 We usually say, "Not yet, but we're working on it." 647 00:37:59,893 --> 00:38:02,000 Narrator: Even though dark matter may occupy 648 00:38:02,001 --> 00:38:04,501 99% of the universe, 649 00:38:04,502 --> 00:38:08,502 the particles Spooner and his team are after are elusive. 650 00:38:11,656 --> 00:38:15,656 They aren't known as "weakly interacting massive particles," 651 00:38:16,247 --> 00:38:18,765 or "wimps," for nothing. 652 00:38:18,766 --> 00:38:22,766 They meekly shun contact with anything else. 653 00:38:24,727 --> 00:38:26,836 Spooner: These particles are neutral. 654 00:38:26,837 --> 00:38:29,334 They're not charged. 655 00:38:29,335 --> 00:38:32,864 Their interaction is like a sort of a billiard-ball effect 656 00:38:32,865 --> 00:38:34,367 if they interact, which mainly they don't. 657 00:38:34,368 --> 00:38:36,764 But when they do, they just will strike an atom 658 00:38:36,765 --> 00:38:40,765 which will recoil. 659 00:38:41,207 --> 00:38:45,207 So what we're looking for is these little recoils of atoms. 660 00:38:46,255 --> 00:38:47,828 I'm talking about very small distances ... 661 00:38:47,829 --> 00:38:51,098 thousandths of a millimeter or so. 662 00:38:51,099 --> 00:38:55,099 And as this atom recoils, it gives off some energy, 663 00:38:57,249 --> 00:38:58,706 in our case, light. 664 00:38:58,707 --> 00:39:02,707 And you try and detect this light. 665 00:39:08,873 --> 00:39:11,770 Narrator: That glint would be so faint and evanescent 666 00:39:11,771 --> 00:39:15,771 that even slight radiation from surrounding rocks might mask it. 667 00:39:16,648 --> 00:39:18,908 So the detector is further insulated 668 00:39:18,909 --> 00:39:22,843 within 200 tons of distilled water. 669 00:39:22,844 --> 00:39:24,617 Spooner: We're over a kilometer underground, 670 00:39:24,618 --> 00:39:25,973 so we've got rid of the cosmic rays, 671 00:39:25,974 --> 00:39:26,993 and then we're in the water, 672 00:39:26,994 --> 00:39:29,808 so we can screen off the stuff coming from the walls, 673 00:39:29,809 --> 00:39:31,694 and then we've got our detector in the middle, 674 00:39:31,695 --> 00:39:35,695 sitting there waiting for a wimp. 675 00:39:36,036 --> 00:39:37,828 Our detector was a simple crystal, 676 00:39:37,829 --> 00:39:39,914 which gives off little bursts of light 677 00:39:39,915 --> 00:39:42,307 when struck by the particle. 678 00:39:42,308 --> 00:39:44,129 We have to really amplify this light, 679 00:39:44,130 --> 00:39:48,130 because it's very low level. 680 00:39:50,166 --> 00:39:51,302 Seems to be okay. 681 00:39:51,303 --> 00:39:53,621 Spooner: We use this device called a photomultiplier 682 00:39:53,622 --> 00:39:56,932 to convert light into electrons. 683 00:39:56,933 --> 00:39:58,141 These are then multiplied, 684 00:39:58,142 --> 00:40:00,503 and you get ... for every one that comes in, 685 00:40:00,504 --> 00:40:02,318 you get about a million coming out. 686 00:40:02,319 --> 00:40:03,997 And that provides a nice, big signal, 687 00:40:03,998 --> 00:40:07,998 which you can then measure and record. 688 00:40:27,248 --> 00:40:29,356 In the last year or two, 689 00:40:29,357 --> 00:40:31,091 we have made fairly significant progress. 690 00:40:31,092 --> 00:40:32,589 We've improved our detectors 691 00:40:32,590 --> 00:40:36,388 such that we're now about 50 times more sensitive 692 00:40:36,389 --> 00:40:39,065 than anyone else was previously. 693 00:40:39,066 --> 00:40:40,830 But we still need to get 694 00:40:40,831 --> 00:40:44,831 probably another 100 times better. 695 00:40:45,010 --> 00:40:46,680 If we do that, 696 00:40:46,681 --> 00:40:48,785 then we should see them 697 00:40:48,786 --> 00:40:51,270 or we should not see them. 698 00:40:51,271 --> 00:40:53,129 If we see them, then obviously 699 00:40:53,130 --> 00:40:54,273 that's very exciting, 700 00:40:54,274 --> 00:40:55,506 And maybe we've discovered 701 00:40:55,507 --> 00:40:56,809 what dark matter is, or what 702 00:40:56,810 --> 00:41:00,810 most of the dark matter is. 703 00:41:04,952 --> 00:41:08,054 If we don't see them, that's also pretty exciting, 704 00:41:08,055 --> 00:41:09,378 Because it's got to be something, 705 00:41:09,379 --> 00:41:12,567 And if it's not wimps, maybe it's not machos, 706 00:41:12,568 --> 00:41:14,070 and maybe neutrinos don't have mass. 707 00:41:14,071 --> 00:41:16,716 We don't know, but it's got to be something. 708 00:41:16,717 --> 00:41:20,717 So that would deepen the mystery. 709 00:41:23,774 --> 00:41:25,348 Frenk: If and when the dark matter ... 710 00:41:25,349 --> 00:41:27,444 or i should say, when the dark matter is discovered, 711 00:41:27,445 --> 00:41:28,577 because it's not a question 712 00:41:28,578 --> 00:41:29,582 that dark matter is there to be discovered 713 00:41:29,583 --> 00:41:31,082 and it will be discovered. 714 00:41:31,083 --> 00:41:34,870 I can say that with complete certainty ... 715 00:41:34,871 --> 00:41:38,497 well, as complete as a scientist can ever do. 716 00:41:38,498 --> 00:41:41,236 But when the dark matter is discovered, 717 00:41:41,237 --> 00:41:43,530 i think the whole jigsaw of our universe 718 00:41:43,531 --> 00:41:45,160 will fall into place. 719 00:41:45,161 --> 00:41:48,466 We will understand not only 720 00:41:48,467 --> 00:41:50,761 why our universe looks the way it does, 721 00:41:50,762 --> 00:41:53,408 we will understand why there are galaxies, 722 00:41:53,409 --> 00:41:56,097 how they came to be, why there are planets, 723 00:41:56,098 --> 00:41:58,879 why there are stars, but we would also understand 724 00:41:58,880 --> 00:42:02,880 what the ultimate fate of our universe will be. 725 00:42:04,026 --> 00:42:07,377 There are two possibilities. 726 00:42:07,378 --> 00:42:11,094 If there's only a fairly small amount of dark matter, 727 00:42:11,095 --> 00:42:14,376 the universe will continue to expand forever, 728 00:42:14,377 --> 00:42:18,377 getting colder and colder, and more and more empty. 729 00:42:20,802 --> 00:42:24,679 On the other hand, if there's a lot of dark matter, 730 00:42:24,680 --> 00:42:28,345 gravity will slow down the expansion of the universe 731 00:42:28,346 --> 00:42:32,002 and stop it eventually. 732 00:42:32,003 --> 00:42:34,865 Then the universe will begin to contract, 733 00:42:34,866 --> 00:42:38,866 and will end up in a big crunch, like the big bang in reverse. 734 00:42:51,141 --> 00:42:55,141 From what we know now, it could go either way. 735 00:42:55,841 --> 00:42:57,570 If I placed a bet, 736 00:42:57,571 --> 00:43:01,571 I think I know which fate I'd back. 737 00:43:01,639 --> 00:43:05,639 But how would i collect after the big crunch? 738 00:43:06,603 --> 00:43:09,600 Whichever way the universe eventually goes, 739 00:43:09,601 --> 00:43:13,601 its evolution is being affected by dark matter right now. 740 00:43:15,569 --> 00:43:18,856 Before we have even discovered what it's made of, 741 00:43:18,857 --> 00:43:22,857 some astronomers have begun mapping its effects. 742 00:43:24,150 --> 00:43:25,933 Woman: The challenge of mapping the universe 743 00:43:25,934 --> 00:43:28,043 is that you have to do it in three dimensions. 744 00:43:28,044 --> 00:43:31,493 and human beings are very good at making two-dimensional maps. 745 00:43:31,494 --> 00:43:34,047 It's the challenge of getting that third dimension 746 00:43:34,048 --> 00:43:37,037 and putting it in your head, being able to close your eyes 747 00:43:37,038 --> 00:43:39,700 and see in 3D what's around you. 748 00:43:39,701 --> 00:43:43,701 It's a challenge, but it's fun. 749 00:43:46,723 --> 00:43:50,194 So I think we'll lay things out 750 00:43:50,195 --> 00:43:52,381 with the equator down here. 751 00:43:52,382 --> 00:43:54,263 Faber: When we first started this mapping business, 752 00:43:54,264 --> 00:43:56,425 it was very, very primitive, 753 00:43:56,426 --> 00:43:59,398 and people knew that there were clusters over there 754 00:43:59,399 --> 00:44:00,685 and a few over there and so on. 755 00:44:00,686 --> 00:44:02,600 It was a little bit like Stanley 756 00:44:02,601 --> 00:44:04,305 going to darkest Africa. 757 00:44:04,306 --> 00:44:07,003 He knew where the Congo river was, and the Nile maybe, 758 00:44:07,004 --> 00:44:09,299 but not much about anything else. 759 00:44:09,300 --> 00:44:11,970 Looks like it's over there. 760 00:44:11,971 --> 00:44:14,528 Narrator: Exploring a dark continent of her own, 761 00:44:14,529 --> 00:44:18,529 sandra Faber has spent years charting unknown terrain. 762 00:44:21,709 --> 00:44:24,219 Her mapping techniques have revolutionized 763 00:44:24,220 --> 00:44:28,220 the way we look at the universe and contemplate its future. 764 00:44:35,043 --> 00:44:36,079 Faber: What we're going to see here 765 00:44:36,080 --> 00:44:40,080 is three slices of the universe. 766 00:44:40,212 --> 00:44:43,450 And Earth is down here in this diagram, 767 00:44:43,451 --> 00:44:44,936 right here at the point. 768 00:44:44,937 --> 00:44:47,451 And now we see the first slice 769 00:44:47,452 --> 00:44:48,991 being displayed like this. 770 00:44:48,992 --> 00:44:51,960 Each little black dot is a galaxy. 771 00:44:51,961 --> 00:44:54,139 This was taken from the southern hemisphere, 772 00:44:54,140 --> 00:44:57,539 and now we see finally the third slice is coming up here. 773 00:44:57,540 --> 00:44:59,761 What's interesting about these maps 774 00:44:59,762 --> 00:45:03,435 is that the galaxies are not uniformly distributed in space. 775 00:45:03,436 --> 00:45:06,864 Instead, what we see is that they tend to pile up 776 00:45:06,865 --> 00:45:09,218 along these walls. 777 00:45:09,219 --> 00:45:11,030 Some people have called them soap bubbles. 778 00:45:11,031 --> 00:45:14,839 And then the insides of these spaces are called voids. 779 00:45:14,840 --> 00:45:18,316 They're relatively empty of galaxies. 780 00:45:18,317 --> 00:45:20,004 And, of course, this whole structure 781 00:45:20,005 --> 00:45:22,709 is expanding as the universe expands. 782 00:45:22,710 --> 00:45:24,771 Now, the question is, of course, 783 00:45:24,772 --> 00:45:27,263 why do the galaxies trace 784 00:45:27,264 --> 00:45:30,455 this beautiful large-scale structure? 785 00:45:30,456 --> 00:45:32,917 Narrator: Sandra's hunch was that this structure 786 00:45:32,918 --> 00:45:36,195 was created by the unseen influence of dark matter. 787 00:45:36,196 --> 00:45:37,428 She set out to prove it 788 00:45:37,429 --> 00:45:41,429 with the most advanced telescopes in the world. 789 00:45:44,359 --> 00:45:48,359 Observing is almost mystical. 790 00:45:48,714 --> 00:45:52,368 It's the act that really puts me in contact 791 00:45:52,369 --> 00:45:54,578 with the rest of the universe. 792 00:45:54,579 --> 00:45:57,904 Sitting there and accepting these photons, 793 00:45:57,905 --> 00:46:01,905 i imagine projecting myself back along that same path, 794 00:46:02,317 --> 00:46:05,347 and in some way, i know this sounds ridiculous, 795 00:46:05,348 --> 00:46:07,982 being in communication and communion 796 00:46:07,983 --> 00:46:09,401 with where they came from. 797 00:46:09,402 --> 00:46:12,629 I often think if somebody's looking back at me, 798 00:46:12,630 --> 00:46:16,630 I wonder if their telescope is bigger than mine. 799 00:46:26,518 --> 00:46:29,023 Narrator: Even through the most powerful instruments, 800 00:46:29,024 --> 00:46:33,024 galaxies millions and billions of light-years away 801 00:46:33,138 --> 00:46:37,138 appear as tiny specks. 802 00:46:39,308 --> 00:46:42,796 Yet Faber's work demands the most exacting measurements, 803 00:46:42,797 --> 00:46:46,797 even of these far-flung galaxies. 804 00:46:50,398 --> 00:46:53,407 So sensitive are the telescope's detectors 805 00:46:53,408 --> 00:46:56,049 that before each run they must be cooled 806 00:46:56,050 --> 00:46:57,763 with liquid nitrogen. 807 00:46:57,764 --> 00:47:00,491 At over 300 degrees below zero, 808 00:47:00,492 --> 00:47:04,492 their very atoms are stilled. 809 00:47:17,148 --> 00:47:18,806 Faber: having checked everything out, 810 00:47:18,807 --> 00:47:21,746 we then walk into the control room off the dome. 811 00:47:21,747 --> 00:47:23,660 Gone are the days of standing in the cold. 812 00:47:23,661 --> 00:47:27,661 We don't do that anymore. 813 00:47:30,964 --> 00:47:33,268 We aim the telescope 814 00:47:33,269 --> 00:47:37,269 and we sit there and we wait, we expose. 815 00:47:58,541 --> 00:48:00,802 Ah! so this is our next observation. 816 00:48:00,803 --> 00:48:02,776 What was this galaxy? 817 00:48:02,777 --> 00:48:05,965 This was ngc-5813. 818 00:48:05,966 --> 00:48:07,200 5813, okay. 819 00:48:07,201 --> 00:48:08,611 Narrator: sandra and her colleagues 820 00:48:08,612 --> 00:48:10,344 developed their mapping technique 821 00:48:10,345 --> 00:48:12,750 to fathom the role dark matter plays 822 00:48:12,751 --> 00:48:15,042 in the architecture of the universe. 823 00:48:15,043 --> 00:48:19,043 This looks different from our previous spectrum. 824 00:48:19,748 --> 00:48:21,037 Narrator: That dark matter governs 825 00:48:21,038 --> 00:48:25,038 the motion of individual stars, there's no question. 826 00:48:27,467 --> 00:48:31,467 At stake is how it guides the paths of entire galaxies 827 00:48:31,903 --> 00:48:35,903 as they drift through space. 828 00:48:36,492 --> 00:48:38,111 Bit by bit, the data 829 00:48:38,112 --> 00:48:39,689 is falling together 830 00:48:39,690 --> 00:48:43,690 into an awesome portent of our galaxy's fate. 831 00:48:52,249 --> 00:48:54,188 Faber: Suddenly it came to us 832 00:48:54,189 --> 00:48:58,189 that if we plotted all of these motions of galaxies, 833 00:48:58,660 --> 00:49:02,298 that an enormous region of space, including us, 834 00:49:02,299 --> 00:49:06,299 was moving roughly in parallel, like a big river of galaxies, 835 00:49:06,561 --> 00:49:08,032 at the break-neck speed 836 00:49:08,033 --> 00:49:10,611 of 600 kilometers per second, 837 00:49:10,612 --> 00:49:14,479 and that was a definitely new thought for us. 838 00:49:14,480 --> 00:49:17,485 That really struck us very strongly. 839 00:49:17,486 --> 00:49:19,079 We said, what have we discovered? 840 00:49:19,080 --> 00:49:21,055 This is truly remarkable. 841 00:49:21,056 --> 00:49:22,843 Then we began to look at our survey 842 00:49:22,844 --> 00:49:24,477 in more detail, and we saw 843 00:49:24,478 --> 00:49:28,084 that, in fact, off in the distance there, 844 00:49:28,085 --> 00:49:30,755 towards which this great river was flowing, 845 00:49:30,756 --> 00:49:34,318 was a very large structure, which one of us later named 846 00:49:34,319 --> 00:49:35,768 "the great attractor" 847 00:49:35,769 --> 00:49:38,559 and it turned out to be a very, very big supercluster, 848 00:49:38,560 --> 00:49:41,303 a super-supercluster of galaxies, 849 00:49:41,304 --> 00:49:45,089 and our motion towards that is due to its gravity. 850 00:49:45,090 --> 00:49:46,706 It's pulling all of us in. 851 00:49:46,707 --> 00:49:50,346 and at something like 50 to 100 billion years from now, 852 00:49:50,347 --> 00:49:54,347 our galaxy will be one of several thousand on an orbit 853 00:49:54,988 --> 00:49:58,988 in the great supercluster called the great attractor. 854 00:50:09,514 --> 00:50:11,471 Narrator: A staggering force, 855 00:50:11,472 --> 00:50:14,247 emanating from a huge concentration of matter, 856 00:50:14,248 --> 00:50:16,159 known and unknown, 857 00:50:16,160 --> 00:50:20,160 is relentlessly reeling us in across intergalactic space. 858 00:50:21,183 --> 00:50:22,882 The fate of the universe 859 00:50:22,883 --> 00:50:26,241 is shaped by a vast sprawl of dark matter, 860 00:50:26,242 --> 00:50:29,735 by a cosmic specter drawing the galaxies together 861 00:50:29,736 --> 00:50:32,129 into clusters and superclusters, 862 00:50:32,130 --> 00:50:36,130 turning great patches of sky into empty voids. 863 00:50:37,531 --> 00:50:40,278 Faber: The way the dark matter clusters 864 00:50:40,279 --> 00:50:43,154 will affect exactly how galaxies form 865 00:50:43,155 --> 00:50:47,155 and how superclusters, voids, walls, and so on form. 866 00:50:47,668 --> 00:50:49,258 Dark matter is key. 867 00:50:49,259 --> 00:50:53,259 It is controlling the motion of everything else. 868 00:50:53,533 --> 00:50:55,185 It's making the galaxies form. 869 00:50:55,186 --> 00:50:57,089 It's making the large-scale structure form. 870 00:50:57,090 --> 00:51:01,090 It's in charge. 871 00:51:01,100 --> 00:51:02,452 Narrator: We can still only guess 872 00:51:02,453 --> 00:51:05,287 what dark matter holds in store for us. 873 00:51:05,288 --> 00:51:09,288 And it seems not all great minds guess alike. 874 00:51:10,675 --> 00:51:13,782 Faber: Well, currently, it looks as though 875 00:51:13,783 --> 00:51:16,692 there's not enough matter in the universe, quite, 876 00:51:16,693 --> 00:51:19,025 to retard the expansion. 877 00:51:19,026 --> 00:51:22,220 If we had to bet right now, we'd probably bet 878 00:51:22,221 --> 00:51:26,221 that the universe will expand forever. 879 00:51:31,859 --> 00:51:33,472 It's a fascinating idea. 880 00:51:33,473 --> 00:51:35,366 If the universe expands forever, 881 00:51:35,367 --> 00:51:39,367 what will happen to it as it cools off? 882 00:51:40,045 --> 00:51:44,045 Stars are gradually consuming all the gas in galaxies. 883 00:51:44,159 --> 00:51:46,366 Over time, it will all be used up. 884 00:51:46,367 --> 00:51:50,367 Those stars will burn and use up their fuel and die, 885 00:51:50,969 --> 00:51:54,446 become cold, dead remnants, white dwarves, 886 00:51:54,447 --> 00:51:57,070 maybe some black holes in there. 887 00:51:57,071 --> 00:52:01,071 Galaxies are ever merging to make yet larger structures, 888 00:52:01,174 --> 00:52:05,174 but will become ever dimmer as the stars in them die out. 889 00:52:05,584 --> 00:52:07,142 And ultimately, 890 00:52:07,143 --> 00:52:09,256 even the very stuff of which stars are made ... 891 00:52:09,257 --> 00:52:13,070 the protons, neutrons, and so on ... will decay. 892 00:52:13,071 --> 00:52:16,535 And it may be that the ultimate state of the universe 893 00:52:16,536 --> 00:52:20,536 is to have no matter at all ... a sea of elementary particles, 894 00:52:23,821 --> 00:52:27,821 dead photons, and nothing else. 895 00:52:33,794 --> 00:52:36,238 Hawking: And the alternative of a big crunch 896 00:52:36,239 --> 00:52:38,747 is not much better. 897 00:52:38,748 --> 00:52:42,393 A few years ago, when i was giving a lecture, 898 00:52:42,394 --> 00:52:46,364 i was asked not to mention the end of the universe, 899 00:52:46,365 --> 00:52:50,174 in case it depressed the stock market. 900 00:52:50,175 --> 00:52:53,496 But I can reassure worried investors, 901 00:52:53,497 --> 00:52:55,735 either way, the universe is good 902 00:52:55,736 --> 00:52:59,141 for many billions of years more. 903 00:52:59,142 --> 00:53:03,142 The end may be coming, but not just yet.