0 00:00:27,427 --> 00:00:29,827 The further we probe into the universe, 1 00:00:30,063 --> 00:00:33,226 the more remarkable are the discoveries we make. 2 00:00:35,001 --> 00:00:39,734 Much of my work has been concerned with the mysteries of black holes. 3 00:00:40,840 --> 00:00:45,868 Many people dismiss black holes as just an artefact of a theory 4 00:00:46,046 --> 00:00:48,514 which wouldn't exist in the real world. 5 00:00:50,016 --> 00:00:53,281 But then observers began to find things in the sky 6 00:00:53,486 --> 00:00:55,647 which were just as peculiar. 7 00:01:09,369 --> 00:01:11,337 The journey which would lead to black holes, 8 00:01:11,538 --> 00:01:16,498 started in the 1950s with the new science of radio astronomy. 9 00:01:17,444 --> 00:01:21,210 Radio signals from space might have many explanations, 10 00:01:21,614 --> 00:01:23,741 some more vivid than others. 11 00:01:27,854 --> 00:01:30,254 Well, my name is Seth Shostak, and I'm a an astronomer 12 00:01:30,356 --> 00:01:33,382 at the SETI institute here in lovely Mountain View, California. 13 00:01:36,029 --> 00:01:40,966 The acronym 'SETI' stands for search for extra terrestrial intelligence. 14 00:01:41,334 --> 00:01:42,733 Now, that 'I' on the end means 15 00:01:42,836 --> 00:01:44,827 we're not looking for extraterrestrial life, 16 00:01:45,105 --> 00:01:46,572 but we're looking for intelligent life. 17 00:01:46,706 --> 00:01:49,436 That means they can hold up their side of the conversation, if you will. 18 00:02:04,257 --> 00:02:05,246 Well, after the second World War, 19 00:02:05,358 --> 00:02:07,849 radio astronomy really got going and in the late fifties, 20 00:02:07,961 --> 00:02:10,486 they started building, er, large radio telescopes like, 21 00:02:10,597 --> 00:02:12,565 like the one we're sitting underneath here now. 22 00:02:17,303 --> 00:02:20,966 Could this technology actually be used to send messages, 23 00:02:21,074 --> 00:02:22,632 as it were, between the stars? 24 00:02:26,146 --> 00:02:28,046 Nineteen fifty nine, nineteen sixty, 25 00:02:28,314 --> 00:02:32,182 the first experiments were made using this kind of technology, 26 00:02:32,285 --> 00:02:33,309 a big radio-telescope, 27 00:02:33,419 --> 00:02:36,980 to try and eavesdrop on any civilizations that might be nearby. 28 00:02:37,891 --> 00:02:39,859 But while they were looking for aliens, 29 00:02:40,059 --> 00:02:42,960 it was sensible to consider other possibilities too. 30 00:02:45,098 --> 00:02:46,725 Suddenly you're getting these clear radio views 31 00:02:46,833 --> 00:02:48,630 so you knew that in that direction 32 00:02:48,735 --> 00:02:50,669 there's a very strong source of radio waves. 33 00:02:51,738 --> 00:02:53,569 You would tell your friend the optical astronomer, 34 00:02:53,673 --> 00:02:55,334 and they would go use a big telescope 35 00:02:55,441 --> 00:02:57,841 like the Palomar 200-inch telescope, or something similar, 36 00:02:57,944 --> 00:03:00,242 and they would point it in that direction. 37 00:03:06,920 --> 00:03:08,751 Using optical telescopes, 38 00:03:08,922 --> 00:03:13,188 astronomers looked long and hard at the areas emitting radio signals. 39 00:03:13,726 --> 00:03:17,856 What they saw was certainly unusual and dramatic events, 40 00:03:18,164 --> 00:03:20,655 but nothing they couldn't already explain. 41 00:03:28,374 --> 00:03:30,569 People saw that there were unusual objects, 42 00:03:30,677 --> 00:03:35,876 for example, a galaxy that had a peculiar blob within it, 43 00:03:36,082 --> 00:03:38,880 er, in some cases it was found to emit radio waves, 44 00:03:38,985 --> 00:03:42,978 whereas a normal looking, boring looking galaxy did not. 45 00:03:45,525 --> 00:03:49,894 Or, for example, a cloud of gas that had all sorts of little striations in it, 46 00:03:50,063 --> 00:03:52,031 and looked as though it, might be exploding. 47 00:03:52,232 --> 00:03:55,759 Those were precisely the objects that seemed to emit radio waves, 48 00:03:55,868 --> 00:03:58,962 whereas more normal, guiescent clouds of gas, did not. 49 00:04:04,477 --> 00:04:06,240 But there were surprises in store. 50 00:04:06,679 --> 00:04:09,147 When optical astronomers pointed their telescopes 51 00:04:09,249 --> 00:04:12,309 at one particularly strong radio signal, 52 00:04:12,485 --> 00:04:15,716 they expected to see some cosmological catastrophe. 53 00:04:16,990 --> 00:04:19,720 What they did see astounded them. 54 00:04:20,994 --> 00:04:24,896 In the early nineteen sixties optical astronomers took photographs 55 00:04:24,998 --> 00:04:26,590 of certain positions in the sky 56 00:04:26,699 --> 00:04:29,998 from which radio waves seemed to be coming and they, 57 00:04:30,103 --> 00:04:31,570 they just saw nothing unusual. 58 00:04:31,671 --> 00:04:34,663 There was just the usual smattering of stars, 59 00:04:34,974 --> 00:04:37,499 and there was no obviously exploding star, 60 00:04:37,610 --> 00:04:41,307 no turbulent cloud of gas, nothing seemingly unusual. 61 00:04:41,414 --> 00:04:43,075 Just normal stars. 62 00:04:43,449 --> 00:04:45,474 And this perplexed the astronomers. 63 00:04:50,456 --> 00:04:55,723 One such star, with the uninspiring name, 3C273, 64 00:04:55,928 --> 00:05:00,262 was one of billions in an insignificant corner of the universe. 65 00:05:02,302 --> 00:05:05,237 3C273 in the constellation Virgo, 66 00:05:05,338 --> 00:05:06,737 looked just like a star, 67 00:05:08,074 --> 00:05:11,874 yet we know that ordinary stars don't emit radio waves 68 00:05:11,978 --> 00:05:14,446 and so this was highly, highly unusual. 69 00:05:15,415 --> 00:05:20,250 Astronomers decided to analyse the light given off by 3C273, 70 00:05:20,620 --> 00:05:23,111 using a technigue called spectroscopy. 71 00:05:25,725 --> 00:05:28,751 By splitting the light from the star into a colour spectrum 72 00:05:28,961 --> 00:05:31,327 they discover something about the star. 73 00:05:31,864 --> 00:05:35,391 They see black lines in the spectrum missing light 74 00:05:35,601 --> 00:05:37,034 caused by gases in the atmosphere 75 00:05:37,136 --> 00:05:41,232 of the star absorbing light at particular freguencies. 76 00:05:41,407 --> 00:05:44,137 And if these lines are shifted from their normal position 77 00:05:44,243 --> 00:05:48,509 the star is moving - if the lines shift towards the red end 78 00:05:48,614 --> 00:05:51,845 of the spectrum its moving away. 79 00:05:53,119 --> 00:05:54,814 Thirty-four years earlier, 80 00:05:55,021 --> 00:05:57,956 the American astronomer, Edward Hubble, 81 00:05:58,124 --> 00:06:02,823 had used spectroscopy to discover that the universe is expanding. 82 00:06:04,731 --> 00:06:07,894 Distant galaxies are moving away from us. 83 00:06:10,503 --> 00:06:16,066 The spectrum of 3C273 was about to tell us even more. 84 00:06:23,015 --> 00:06:28,317 The spectrum of 3C273 didn't fit any patterns of normal gases 85 00:06:28,421 --> 00:06:33,552 that have been observed in normal stars, and so this really befuddled astronomers. 86 00:06:33,726 --> 00:06:38,129 Not only was the object emitting radio waves profusely, 87 00:06:38,297 --> 00:06:41,425 but it had this really strange spectrum 88 00:06:41,534 --> 00:06:44,867 that couldn't be matched with any known type of gas. 89 00:06:48,074 --> 00:06:52,704 3C273 looks like any other star in the sky 90 00:06:53,379 --> 00:06:56,871 but it's spectrum seemed to contradict this idea. 91 00:06:58,050 --> 00:07:00,848 Astronomers couldn't imagine what was going on, 92 00:07:01,521 --> 00:07:04,513 but a young postgraduate student was convinced 93 00:07:04,624 --> 00:07:07,058 that spectroscopy couldn't lie. 94 00:07:09,162 --> 00:07:16,125 Martin Schmidt at Caltech noticed that two of the wiggles had the same spacing 95 00:07:16,302 --> 00:07:18,463 between the colours as hydrogen does 96 00:07:18,805 --> 00:07:23,037 but both of the lines were shifted way over towards redder parts 97 00:07:23,142 --> 00:07:26,908 of the spectrum than normal hydrogen gas is, 98 00:07:27,213 --> 00:07:31,081 and as he believed that that identification was correct, 99 00:07:31,417 --> 00:07:38,118 then the conclusion was that the shift is a full sixteen percent. 100 00:07:38,891 --> 00:07:41,883 Yet a shift of sixteen percent meant 101 00:07:41,994 --> 00:07:45,987 that this object was moving away from us enormously, 102 00:07:46,098 --> 00:07:47,963 er, enormously fast, 103 00:07:48,067 --> 00:07:52,265 and had to be one or two billion light years away. 104 00:07:52,839 --> 00:07:56,036 So, no way could it be a normal star 105 00:07:56,142 --> 00:07:58,736 or even a peculiar magnetic star in our own 106 00:07:58,845 --> 00:08:02,747 galaxy, it had to be some sort of a strange object 107 00:08:02,949 --> 00:08:05,713 that looks like stellar or guasi-stellar, 108 00:08:05,918 --> 00:08:11,117 simply because it's so, so far away, and yet it's enormously bright. 109 00:08:11,424 --> 00:08:15,417 So this really caught people by surprise and a few people, 110 00:08:15,528 --> 00:08:17,723 I think, had a hard time believing 111 00:08:17,964 --> 00:08:23,800 that anything so relatively bright, could be so far away. 112 00:08:30,977 --> 00:08:33,445 Astronomers decided top call these objects, 113 00:08:33,546 --> 00:08:37,505 these radio-stars, guasi-stellar radio sources. 114 00:08:37,717 --> 00:08:39,082 They were clearly radio sources, 115 00:08:39,185 --> 00:08:41,278 they were discovered with radio telescopes, 116 00:08:41,654 --> 00:08:45,021 and they looked star-like, and hence the, 117 00:08:45,124 --> 00:08:47,456 the stellar aspect of the term, 118 00:08:47,793 --> 00:08:52,127 so guasi stellar radio sources got contracted to guasars. 119 00:08:53,833 --> 00:08:57,098 Martin Schmidt concluded that it must be intrinsically, 120 00:08:57,203 --> 00:08:59,501 an extremely powerful source, 121 00:08:59,605 --> 00:09:02,802 an exceedingly bright object intrinsically, 122 00:09:02,975 --> 00:09:06,411 because to appear as bright as it does in the sky, 123 00:09:06,646 --> 00:09:08,409 yet be so far away, 124 00:09:08,514 --> 00:09:11,972 has to put out a tremendous amount of energy per second. 125 00:09:12,418 --> 00:09:14,283 Much, much more than our sun, 126 00:09:14,520 --> 00:09:17,648 in fact one hundred to one thousand times 127 00:09:17,757 --> 00:09:21,818 more than our entire milky way galaxy of stars. 128 00:09:22,194 --> 00:09:24,856 And this was the real kicker. 129 00:09:27,066 --> 00:09:29,864 When the mysterious guasars were discovered, 130 00:09:30,002 --> 00:09:33,733 I was just beginning my post-graduate research. 131 00:09:35,508 --> 00:09:39,444 My work was to lead me to study things even more mysterious, 132 00:09:39,579 --> 00:09:41,103 black holes. 133 00:09:42,214 --> 00:09:46,310 I was dealing with Einstein's general theory of relativity, 134 00:09:46,485 --> 00:09:49,454 and this seemed to some physicists, 135 00:09:49,622 --> 00:09:54,116 a promising place to look for an explanation of the guasars. 136 00:09:57,063 --> 00:10:00,624 Astronomers and astrophysicists wanted an explanation for 137 00:10:00,733 --> 00:10:04,726 how these strange objects could behave in this extraordinary way, 138 00:10:04,971 --> 00:10:08,270 how they could produce so much energy and yet be so small, 139 00:10:08,574 --> 00:10:12,874 er, and so they turned to the general relativists, 140 00:10:13,112 --> 00:10:16,206 and asked them, well, do you have any models, objects, 141 00:10:16,315 --> 00:10:17,373 that could look like this, 142 00:10:17,483 --> 00:10:19,815 that could behave in, in this way at all? 143 00:10:20,252 --> 00:10:22,584 Er, and the relativists said, well, 144 00:10:22,688 --> 00:10:25,623 there is this issue of gravitational collapse, 145 00:10:25,825 --> 00:10:27,850 and maybe this is what you're looking for. 146 00:10:30,796 --> 00:10:34,391 Everyone agreed that Einstein's theory described gravity 147 00:10:34,533 --> 00:10:36,694 as the dominant force of the universe. 148 00:10:38,938 --> 00:10:40,565 But what was not so obvious was 149 00:10:40,673 --> 00:10:43,403 what would happen under extreme conditions. 150 00:10:44,010 --> 00:10:47,776 Could gravity ever compress vast guantities of matter, 151 00:10:47,947 --> 00:10:52,247 such as when a star dies, into the tiniest of spaces? 152 00:10:53,552 --> 00:10:56,680 In nineteen thirty nine two papers appeared, 153 00:10:56,856 --> 00:10:59,518 and one was by Einstein himself, 154 00:10:59,659 --> 00:11:03,755 and one was by the American physicist, Robert Oppenheimer, 155 00:11:03,896 --> 00:11:05,523 and his co-worker, Snyder. 156 00:11:05,831 --> 00:11:07,958 They discussed what would happen 157 00:11:08,067 --> 00:11:12,629 when, er, a large amount of matter was concentrated in a small region. 158 00:11:13,272 --> 00:11:15,900 Einstein's paper didn't foresee any problems. 159 00:11:16,275 --> 00:11:19,108 But Oppenheimer and Snyder frightened themselves. 160 00:11:19,478 --> 00:11:21,571 Their calculations seemed to point to something 161 00:11:21,781 --> 00:11:23,612 which couldn't possibly exist. 162 00:11:24,583 --> 00:11:27,916 Using the rules of general relativity they, 163 00:11:28,087 --> 00:11:32,490 er, predicted that that a massive object would undergo 164 00:11:32,591 --> 00:11:35,355 catastrophic gravitational collapse 165 00:11:35,528 --> 00:11:38,019 and would reach a critical radius at 166 00:11:38,130 --> 00:11:42,328 which it seemingly cuts itself off from the rest of the universe. 167 00:11:44,437 --> 00:11:47,065 But if an object cut itself off from the universe, 168 00:11:47,273 --> 00:11:51,004 could its behaviour still be described by the laws of physics? 169 00:11:52,645 --> 00:11:56,843 Did Einstein's theory unwittingly predict its own collapse? 170 00:11:57,783 --> 00:12:02,243 Einstein was convinced that you could never get to this critical radius, 171 00:12:02,488 --> 00:12:05,980 that this critical radius was an impossibility in nature. 172 00:12:11,197 --> 00:12:14,257 But his argument with Oppenheimer was never settled. 173 00:12:14,867 --> 00:12:18,462 The second World War meant physicists like Oppenheimer were needed 174 00:12:18,571 --> 00:12:20,505 to develop the atomic bomb. 175 00:12:21,474 --> 00:12:23,999 Many felt Oppenheimer's ideas were so extreme, 176 00:12:24,210 --> 00:12:26,371 they weren't worth fighting for anyway. 177 00:12:27,279 --> 00:12:30,737 But a physicist called John Wheeler had no doubts. 178 00:12:31,383 --> 00:12:32,816 Stick up for something, 179 00:12:33,452 --> 00:12:36,751 and I think that's a wonderful way of saying 180 00:12:36,856 --> 00:12:38,517 what science is all about. 181 00:12:38,624 --> 00:12:39,989 Stick up for something. 182 00:12:53,839 --> 00:12:57,104 I'm Daniel Holz and I'm a graduate student, University of Chicago, 183 00:12:57,376 --> 00:12:58,809 and I'm going to see, 184 00:12:58,911 --> 00:13:00,037 er, John Wheeler, 185 00:13:00,179 --> 00:13:02,579 who is my undergraduate adviser here at Princeton. 186 00:13:06,752 --> 00:13:09,585 John Wheeler, who still teaches at Princeton University, 187 00:13:09,688 --> 00:13:12,816 worked with Oppenheimer on the atomic bomb. 188 00:13:13,526 --> 00:13:14,788 Now eighty five, 189 00:13:14,994 --> 00:13:18,293 he is one of the great figures of twentieth century science. 190 00:13:19,965 --> 00:13:21,933 He loves to just sink his teeth into problems. 191 00:13:22,034 --> 00:13:24,195 Part of his approach to physics is find the biggest, 192 00:13:24,303 --> 00:13:26,100 most confusing thing you can, 193 00:13:26,272 --> 00:13:29,901 and then go at it full steam and try to make sense of it. 194 00:13:31,544 --> 00:13:35,605 In 1963, guasars were the most confusing thing around, 195 00:13:36,015 --> 00:13:38,381 with the exception perhaps of Oppenheimer's theory 196 00:13:38,484 --> 00:13:40,247 that might explain them. 197 00:13:40,853 --> 00:13:44,846 So Wheeler wanted to embrace these extreme theoretical ideas 198 00:13:44,957 --> 00:13:47,118 about gravitational collapse. 199 00:13:49,795 --> 00:13:50,921 But to support them 200 00:13:51,130 --> 00:13:53,997 would mean challenging the beliefs of Albert Einstein. 201 00:13:57,803 --> 00:14:00,397 When Wheeler came to Princeton in the nineteen forties, 202 00:14:00,639 --> 00:14:04,769 Einstein was one of its leading academics and world famous. 203 00:14:05,311 --> 00:14:08,280 But science was already beginning to move on. 204 00:14:14,954 --> 00:14:16,285 He was kind enough to invite me 205 00:14:16,388 --> 00:14:22,190 to bring my graduate students around to his house one day for tea. 206 00:14:22,461 --> 00:14:26,295 One of those students, Joe Callaway, said, Professor Einstein, 207 00:14:26,532 --> 00:14:30,059 when you're no longer living, what will happen to this house? 208 00:14:30,636 --> 00:14:39,408 And Einstein's face was a study: Deep wrinkles, 209 00:14:39,511 --> 00:14:44,448 a wonderful smile and laugh, and his beautiful voice, 210 00:14:45,184 --> 00:14:47,982 with a bit of a German accent but, 211 00:14:48,187 --> 00:14:55,889 er, clear English: This house will never become a place of pilgrimage 212 00:14:56,061 --> 00:15:00,361 where the pilgrims come to look at the bones of the saint. 213 00:15:03,869 --> 00:15:06,303 And so it is. 214 00:15:10,943 --> 00:15:13,503 For all his genius it was not Einstein 215 00:15:13,612 --> 00:15:15,807 who now inspired John Wheeler. 216 00:15:16,615 --> 00:15:18,879 Wheeler was captivated by the idea 217 00:15:19,084 --> 00:15:23,214 that guasars might be explained by Oppenheimer's theory 218 00:15:23,322 --> 00:15:26,917 of gravitationally completely collapsed objects. 219 00:15:27,259 --> 00:15:29,853 And he invented a vivid phrase to describe them. 220 00:15:30,329 --> 00:15:32,297 After I'd used that phrase 221 00:15:32,398 --> 00:15:36,334 'gravitationally completely collapsed objects' several times, 222 00:15:38,604 --> 00:15:40,834 I realised that it was just too long-winded 223 00:15:41,106 --> 00:15:44,303 and I switched to 'black hole'. 224 00:15:47,980 --> 00:15:50,175 It was a name which perfectly describes 225 00:15:50,316 --> 00:15:53,479 what should happen according to the theory. 226 00:15:57,089 --> 00:15:59,614 The key feature of a black hole is that it's black. 227 00:15:59,792 --> 00:16:03,125 That, that no light escapes from, from this region. 228 00:16:03,429 --> 00:16:05,158 So what happens is you have this object 229 00:16:05,264 --> 00:16:07,289 that's getting dense, say, a star that's collapsing, 230 00:16:07,633 --> 00:16:13,003 and it gets, it gets more and more compressed and as it does that, 231 00:16:13,105 --> 00:16:16,404 objects closer to the star have a harder and harder time getting away. 232 00:16:16,642 --> 00:16:20,476 It, in some sense, the gravitational pull is stronger and stronger. 233 00:16:27,653 --> 00:16:31,316 If you keep on extrapolating that, the object gets more and more dense, 234 00:16:31,423 --> 00:16:35,291 at some point, you reach the stage where even light ca-, can't escape and, 235 00:16:35,394 --> 00:16:38,124 er, if we we're standing far away from this star, 236 00:16:38,230 --> 00:16:40,790 the light cannot get from the surface of the star to us. 237 00:16:41,033 --> 00:16:44,469 And it, at the point where that is reached, you have a black hole. 238 00:16:48,440 --> 00:16:52,069 Our, er, Russian friends had a different word 239 00:16:53,312 --> 00:16:56,281 and at French thought it sounded obscene, 240 00:16:58,117 --> 00:17:03,487 but finally they were won around and they accepted it. 241 00:17:03,822 --> 00:17:07,155 So a lot of people decided that the whole, 242 00:17:07,259 --> 00:17:10,194 the whole idea of a black hole was patently ludicrous, 243 00:17:10,329 --> 00:17:11,318 and that they couldn't exist, 244 00:17:11,430 --> 00:17:12,863 and in fact Einstein was in, 245 00:17:12,965 --> 00:17:17,800 was in this camp and did not see black holes as real physical objects. 246 00:17:17,936 --> 00:17:21,133 The idea was, er, something in nature would, 247 00:17:21,240 --> 00:17:22,935 would prevent a black hole from forming; 248 00:17:23,042 --> 00:17:25,010 as you tried to put all this mass in one place, 249 00:17:25,110 --> 00:17:29,570 some mysterious force would come out and always prevent you from actually getting 250 00:17:29,715 --> 00:17:33,412 that much mass that you would actually end up collapsing into a black hole. 251 00:17:35,521 --> 00:17:38,490 I believe that black holes should exist, 252 00:17:38,791 --> 00:17:44,024 but many physicists thought that was taking general relativity too far. 253 00:17:46,065 --> 00:17:50,126 But not Wheeler, he was impressed by the guasars. 254 00:17:50,936 --> 00:17:53,871 If something so bizarre could find a place in the cosmos, 255 00:17:54,173 --> 00:17:58,109 then the universe was strange enough for black holes to exist as well. 256 00:18:03,048 --> 00:18:04,811 Wheeler, always being at the forefront, 257 00:18:04,917 --> 00:18:06,578 saw that these black holes were a, 258 00:18:06,685 --> 00:18:10,086 a windfall for explaining all sorts of astrophysical observations 259 00:18:10,189 --> 00:18:13,647 and would become very important in our understanding of the world, 260 00:18:13,826 --> 00:18:15,123 and so he was egging everyone, 261 00:18:15,227 --> 00:18:19,220 urging everyone on to join in exploring this vista that opened up, 262 00:18:19,364 --> 00:18:21,195 this landscape of science. 263 00:18:22,835 --> 00:18:24,769 Well what can we do with these black holes? 264 00:18:25,237 --> 00:18:27,102 What are the implications for them? 265 00:18:27,306 --> 00:18:29,831 How will this affect the way we look at our universe? 266 00:18:44,156 --> 00:18:47,922 Many of us were beginning to think there might be large numbers 267 00:18:48,026 --> 00:18:50,426 of black holes in the universe. 268 00:18:52,698 --> 00:18:55,326 But that depended on what happened in the giant 269 00:18:55,434 --> 00:19:00,303 explosions that occur at the end of the life of massive stars. 270 00:19:08,380 --> 00:19:12,874 Deep in the Californian desert is a well-fortified concrete bunker. 271 00:19:17,055 --> 00:19:21,992 Even today, no-one can enter without being scrutinised by armed guards. 272 00:19:30,369 --> 00:19:33,395 These are the Lawrence Livermore laboratories. 273 00:19:53,258 --> 00:19:56,421 Much of this classified technology now lies idle, 274 00:19:56,528 --> 00:19:58,393 or wrapped up for storage. 275 00:20:00,065 --> 00:20:02,260 I came here in nineteen fifty six. 276 00:20:03,402 --> 00:20:08,635 We were one of two national laboratories charged with developing nuclear weapons 277 00:20:08,740 --> 00:20:10,105 for the United States. 278 00:20:21,053 --> 00:20:24,022 In order to handle the high-energy calculations needed 279 00:20:24,122 --> 00:20:25,919 to develop nuclear weapons, 280 00:20:26,191 --> 00:20:31,823 the Defense Department had built a powerful new tool: The computer. 281 00:20:33,198 --> 00:20:35,291 The laboratory here at, 282 00:20:35,400 --> 00:20:37,868 er, Livermore and Los Alamos laboratory, 283 00:20:37,970 --> 00:20:40,131 had a virtual monopoly on, on computers, 284 00:20:40,239 --> 00:20:41,900 and the computers were designed for us. 285 00:20:42,007 --> 00:20:44,840 So, for a period of, 286 00:20:44,943 --> 00:20:45,967 er, of twenty years, 287 00:20:46,078 --> 00:20:49,536 the development of computers depended on the existence of these labs. 288 00:20:52,184 --> 00:20:56,587 It opened up to us the possibility of calculating things 289 00:20:56,822 --> 00:20:59,655 that we could not even think of doing before. 290 00:21:01,226 --> 00:21:03,023 As a young government scientist, 291 00:21:03,195 --> 00:21:07,996 Dick White used the computer's power to test the impact of a nuclear bomb. 292 00:21:09,368 --> 00:21:13,771 But by the early 1960s, much of the work on the bomb was done. 293 00:21:14,606 --> 00:21:18,372 Dick White and his colleagues aimed the computers at a new problem: 294 00:21:18,777 --> 00:21:20,074 The black hole. 295 00:21:20,946 --> 00:21:24,438 Many theorists still did not share John Wheeler's conviction 296 00:21:24,616 --> 00:21:28,347 that black holes could be created out of collapsing stars. 297 00:21:33,825 --> 00:21:37,921 They simply believed that the collapse couldn't go that far. 298 00:21:38,964 --> 00:21:42,422 The theory that they put forward was that the core of the star, 299 00:21:42,534 --> 00:21:44,229 the iron core, would collapse, 300 00:21:44,469 --> 00:21:46,460 er, they believed that this collapse 301 00:21:46,571 --> 00:21:49,768 would cause thermo-nuclear reactions that would blow up the star. 302 00:21:51,510 --> 00:21:54,843 We set out believing in this model, sure enough it collapsed, 303 00:21:55,013 --> 00:21:57,174 er, we had no doubt it was gonna do that, 304 00:21:57,616 --> 00:21:59,083 but it didn't follow their script. 305 00:21:59,751 --> 00:22:01,981 Er, what it did was to, er, 306 00:22:02,220 --> 00:22:06,020 er, instead just continue on collapsing and never, never, 307 00:22:06,124 --> 00:22:08,684 er, came to rest as the pressure built up. 308 00:22:09,761 --> 00:22:13,891 The computers predicted a large dying star would continue collapsing 309 00:22:13,999 --> 00:22:15,694 to form a black hole. 310 00:22:16,201 --> 00:22:20,797 It seemed John Wheeler had been right to support Oppenheimer's ideas. 311 00:22:21,306 --> 00:22:24,400 We had been led by the computer calculations to results 312 00:22:24,509 --> 00:22:26,943 that we had not anticipated and, er, 313 00:22:27,145 --> 00:22:28,169 that, that was, 314 00:22:28,280 --> 00:22:30,009 er, an extraordinary time for me. 315 00:22:31,216 --> 00:22:33,548 There was a lot of excitement about this result. 316 00:22:34,353 --> 00:22:38,585 Er, the, er, people that work in general relativity were guite excited because, 317 00:22:38,690 --> 00:22:41,215 er, in a way, it said, well, 318 00:22:41,326 --> 00:22:43,851 the things that they had been talking about for years, 319 00:22:44,029 --> 00:22:48,989 very supermassive condensed stars with big gravitational fields, 320 00:22:49,101 --> 00:22:50,830 may indeed exist. 321 00:23:02,981 --> 00:23:04,573 This is the, er, 322 00:23:04,716 --> 00:23:07,913 plot of the velocity of the in-falling material in, 323 00:23:08,019 --> 00:23:10,920 er, the, er, star that, 324 00:23:11,022 --> 00:23:14,321 er, has collapsed and beginning to form a black hole. 325 00:23:14,726 --> 00:23:16,921 At this point where the most rapidly, 326 00:23:17,028 --> 00:23:18,586 er, in-falling material is, 327 00:23:18,697 --> 00:23:21,860 the velocity is about ninety nine percent the velocity of light. 328 00:23:28,039 --> 00:23:33,409 Computer calculations show that at least some explosions of stars 329 00:23:33,545 --> 00:23:35,445 would form black holes. 330 00:23:37,883 --> 00:23:40,579 But if nothing can get out of a black hole, 331 00:23:40,786 --> 00:23:42,720 how could we detect one? 332 00:23:44,856 --> 00:23:47,825 Suddenly, er, we came to the state where we said, 333 00:23:47,926 --> 00:23:49,655 well maybe we ought to look around for these things 334 00:23:49,761 --> 00:23:51,820 and see if we can actually see them out there. 335 00:23:58,103 --> 00:24:01,197 Working out how to see the invisible wasn't so easy. 336 00:24:01,506 --> 00:24:04,339 But long before a way to look for black holes emerged, 337 00:24:04,543 --> 00:24:08,070 vivid imaginations were feeding off scientific fact. 338 00:24:18,990 --> 00:24:20,423 Toby got it now. 339 00:24:21,126 --> 00:24:24,357 A black hole, it's pulling the star apart. 340 00:24:25,831 --> 00:24:27,355 Coleen nodded, 341 00:24:27,799 --> 00:24:30,393 a rare event, and we're just in time for it. 342 00:24:31,102 --> 00:24:35,095 The hole swallows stars but first it likes to chew 'em up. 343 00:24:37,409 --> 00:24:41,368 He could barely make himself look as the view swung 344 00:24:41,480 --> 00:24:44,711 inwards towards eye-hurting brilliance. 345 00:24:45,317 --> 00:24:49,845 The disc revolved about a white hot ball of sizzling, 346 00:24:49,988 --> 00:24:51,580 with blistering energy. 347 00:24:58,663 --> 00:25:02,064 Gregory Benford is a best selling science fiction writer. 348 00:25:05,170 --> 00:25:09,504 His stories are all the more plausible because he's also a plasma physicist. 349 00:25:11,576 --> 00:25:16,513 I slowly began to realise that there was at least a case now emerging, 350 00:25:16,648 --> 00:25:19,742 that there might be a black hole at the centre of our own galaxy. 351 00:25:19,885 --> 00:25:21,079 Not just a couple of, 352 00:25:21,186 --> 00:25:22,778 of times the mass of the sun, 353 00:25:22,988 --> 00:25:29,621 but a thousand times, or a million times, and that prospect thrilled me, 354 00:25:29,728 --> 00:25:30,922 I thought wow, there's gotta, 355 00:25:31,029 --> 00:25:33,224 there's gotta be some great special effects, 356 00:25:33,532 --> 00:25:36,558 er, on offer in a place like that. 357 00:25:36,735 --> 00:25:37,793 What would it do? 358 00:25:38,770 --> 00:25:41,500 What would it be like if you fell into one and, er, 359 00:25:41,706 --> 00:25:45,005 er, what would it feel like to be stretched out as thin as a noodle 360 00:25:45,110 --> 00:25:47,340 by the tidal force as you fall into one? 361 00:25:47,546 --> 00:25:49,104 Er, how can you live near one? 362 00:25:49,214 --> 00:25:50,442 How would you make a living? 363 00:25:51,049 --> 00:25:53,882 Once science fiction had brought the threat of the black hole 364 00:25:53,985 --> 00:25:55,247 to our doorstep, 365 00:25:55,387 --> 00:25:57,981 its menace captured the imagination. 366 00:25:58,490 --> 00:26:01,857 The black hole could grow to unbelievable proportions. 367 00:26:02,193 --> 00:26:05,890 Once it starts swallowing matter, nothing can escape it. 368 00:26:06,131 --> 00:26:09,191 Not even stars, or whole galaxies. 369 00:26:10,135 --> 00:26:13,935 It becomes compact, massive and therefore able to, 370 00:26:14,039 --> 00:26:15,563 if it were to encounter something else, 371 00:26:15,674 --> 00:26:17,437 able to eat some more matter. 372 00:26:17,542 --> 00:26:23,174 It becomes the eater of all things, because nothing survives it. 373 00:26:24,583 --> 00:26:27,108 If this happens, as is most probable, 374 00:26:27,218 --> 00:26:28,708 at the centre of the galaxy, 375 00:26:28,820 --> 00:26:30,151 where the stars are more concentrated, 376 00:26:30,255 --> 00:26:31,517 there's more dust and gas, 377 00:26:31,690 --> 00:26:35,251 then that's where you would probably first make black holes, 378 00:26:35,694 --> 00:26:39,186 and then that's where the feeding trough is. 379 00:26:39,864 --> 00:26:41,991 They start to eat the surroundings. 380 00:26:46,071 --> 00:26:49,268 Black holes were an area in which science fact, 381 00:26:49,441 --> 00:26:52,137 real scientific calculations, 382 00:26:52,310 --> 00:26:57,213 was way ahead of science fiction; that only caught up later. 383 00:27:02,787 --> 00:27:06,746 One guestion many science fiction writers speculated on, 384 00:27:06,958 --> 00:27:09,756 was what would happen inside a black hole. 385 00:27:12,964 --> 00:27:16,661 Computer calculations couldn't be trusted for this, 386 00:27:16,835 --> 00:27:20,896 because they would become inaccurate in the extreme conditions. 387 00:27:23,208 --> 00:27:27,941 But the answer was supplied by a mathematician called Roger Penrose, 388 00:27:28,179 --> 00:27:32,673 who like me, had been encourage to work on general relativity, 389 00:27:32,851 --> 00:27:35,911 by my supervisor, Dennis Sciama. 390 00:27:36,254 --> 00:27:38,518 Roger and his father, Lionel Penrose, 391 00:27:38,657 --> 00:27:40,488 wrote a paper which I, 392 00:27:40,592 --> 00:27:43,959 I guess the artist Escher partly made famous later, 393 00:27:44,062 --> 00:27:45,825 called lmpossible Objects, 394 00:27:46,364 --> 00:27:49,629 where you can design an object on the piece of paper, 395 00:27:49,734 --> 00:27:51,634 and Escher made such designs, 396 00:27:51,836 --> 00:27:54,930 which can't be realised in the real world, 397 00:27:55,040 --> 00:27:58,635 for instance, there's a picture when the steps go round in a circuit, 398 00:27:58,743 --> 00:28:02,179 but they're always going down as you keep going round, 399 00:28:02,313 --> 00:28:06,010 you then end up where you began and yet you've been going down all the way. 400 00:28:06,184 --> 00:28:09,620 And you can draw something which suggests that, 401 00:28:09,954 --> 00:28:13,048 but in fact you couldn't construct it in the real world. 402 00:28:13,625 --> 00:28:16,685 And Roger Penrose had the kind of mind that 403 00:28:16,795 --> 00:28:19,855 would conceive relationships of that sort. 404 00:28:39,017 --> 00:28:43,010 There was a debate going on at the time as to whether in the collapse 405 00:28:43,121 --> 00:28:45,055 of the star in it's late stages, 406 00:28:46,257 --> 00:28:49,818 it would achieve infinite density in the central region. 407 00:28:53,665 --> 00:28:56,395 If the theory says it reaches infinite densities, 408 00:28:56,568 --> 00:28:59,162 then in a certain sense the theory has broken down 409 00:28:59,437 --> 00:29:02,770 and there would be a contradiction; the theory would not be self-consistent. 410 00:29:05,944 --> 00:29:09,141 If our best theory of gravitation is not even self-consistent 411 00:29:09,314 --> 00:29:10,941 then we have a crisis in physics. 412 00:29:11,149 --> 00:29:15,950 The theory of relativity contains in itself the seeds of its own decay. 413 00:29:18,223 --> 00:29:22,853 This point of infinite density was called a singularity. 414 00:29:23,595 --> 00:29:25,529 Most scientists thought that somehow, 415 00:29:25,630 --> 00:29:26,824 in the real world, 416 00:29:26,998 --> 00:29:29,762 a singularity could never form. 417 00:29:31,302 --> 00:29:35,762 But Penrose had no such hang-ups, and he showed in 1965 418 00:29:36,007 --> 00:29:38,475 that, er, a star at, 419 00:29:38,576 --> 00:29:39,565 in its end stages, 420 00:29:39,677 --> 00:29:41,372 under natural conditions, 421 00:29:41,613 --> 00:29:45,709 would end up in this self-contradictory state of infinite density. 422 00:29:47,852 --> 00:29:50,218 The theorists' nightmares were true. 423 00:29:51,022 --> 00:29:52,148 If they existed, 424 00:29:52,323 --> 00:29:56,692 black holes destroyed twentieth-century physics at the singularity. 425 00:29:57,762 --> 00:29:59,957 But this did not deter Dennis Sciama 426 00:30:00,131 --> 00:30:04,534 from encouraging his students to look deeper into the singularity. 427 00:30:06,771 --> 00:30:12,209 I was awarded my doctorate for showing that the guestions Penrose was raising 428 00:30:12,310 --> 00:30:17,304 about black holes would apply egually well to the early universe. 429 00:30:18,016 --> 00:30:23,318 Both the big bang and black holes would take singularities places 430 00:30:23,421 --> 00:30:29,087 where space and time come to an end and the laws of physics break down. 431 00:30:32,697 --> 00:30:36,292 The incredible power associated with black holes was making 432 00:30:36,401 --> 00:30:39,962 it seem even more likely that they might be the key 433 00:30:40,104 --> 00:30:43,039 to understanding the energetic guasars 434 00:30:45,143 --> 00:30:49,773 If this was the case it was vital to prove that black holes existed. 435 00:30:50,415 --> 00:30:53,316 But what were the telltale signs to look for. 436 00:30:54,919 --> 00:30:56,978 In Russia, as in America, 437 00:30:57,255 --> 00:30:59,985 the scientists who had worked on nuclear weapons were 438 00:31:00,091 --> 00:31:03,060 now tackling the physics of black holes. 439 00:31:04,095 --> 00:31:08,657 Yakov Zeldovich made it his task to find a way to detect them. 440 00:31:09,734 --> 00:31:10,701 Zeldovich, 441 00:31:10,802 --> 00:31:12,429 apparently, never forgot anything. 442 00:31:12,537 --> 00:31:16,064 Everything went into understanding how to see a black hole, 443 00:31:16,274 --> 00:31:19,038 and I'm sure that working on, 444 00:31:19,143 --> 00:31:19,905 on the H-bomb, 445 00:31:20,011 --> 00:31:22,070 actually helped him in astrophysics because after all, 446 00:31:22,180 --> 00:31:25,479 most of astrophysics is forms of controlled H-bomb. 447 00:31:27,452 --> 00:31:29,545 How would you see a black hole anyway? 448 00:31:29,787 --> 00:31:31,152 You can't see it directly. 449 00:31:31,389 --> 00:31:33,516 You, you know the lion by it's paw, 450 00:31:33,625 --> 00:31:35,092 even better by it's paw print, 451 00:31:35,326 --> 00:31:38,693 er, that's less dangerous than actually approaching a lion. 452 00:31:38,897 --> 00:31:42,492 So he said, suppose you've got two stars going around like this, 453 00:31:42,600 --> 00:31:43,726 and one of them is a black hole, 454 00:31:43,835 --> 00:31:45,029 say this little one right here. 455 00:31:45,270 --> 00:31:48,205 This black hole has a powerful gravitational influence, 456 00:31:48,406 --> 00:31:52,502 and it can actually suck the gas off the surface of this other star. 457 00:31:57,415 --> 00:32:00,509 First it gets torn apart by tidal forces, 458 00:32:00,752 --> 00:32:02,879 as it tries to orbit the black hole, 459 00:32:03,021 --> 00:32:07,515 then these shred it, smears it around, 460 00:32:09,294 --> 00:32:12,491 and the parts bump into each other, 461 00:32:12,730 --> 00:32:14,664 they begin to grind upon each other, 462 00:32:14,799 --> 00:32:17,165 the density is fairly high, and they heat up. 463 00:32:17,402 --> 00:32:19,632 They heat up, they give off emission, 464 00:32:19,737 --> 00:32:22,831 elect-, electromagnetic waves, X-rays 465 00:32:23,074 --> 00:32:26,874 Zeldovitch suggested that by looking for bursts of Xrays astronomers 466 00:32:26,978 --> 00:32:30,209 could find stars which appeared to orbiting nothing 467 00:32:30,682 --> 00:32:32,547 evidence of a black hole 468 00:32:33,851 --> 00:32:36,945 Observational evidence was beginning to come, 469 00:32:37,155 --> 00:32:39,089 but was still very uncertain. 470 00:32:39,590 --> 00:32:44,653 I didn't want to see all my work on black holes go to waste, 471 00:32:44,896 --> 00:32:47,194 so I made a bet with Kit Thorne, 472 00:32:47,398 --> 00:32:49,764 who had been a student of John Wheeler. 473 00:32:50,601 --> 00:32:54,867 One suspects that it was more an insurance policy by Steve, 474 00:32:55,006 --> 00:32:56,701 rather than what he really believed, 475 00:32:56,808 --> 00:33:02,542 because he bet with Kit Thorne claiming that black holes did not exist in nature, 476 00:33:02,647 --> 00:33:04,478 even though they existed in theory, 477 00:33:04,682 --> 00:33:10,587 and he bet one year of Penthouse against four years of Private Eye, 478 00:33:10,788 --> 00:33:12,619 er, against Kit Thorne, 479 00:33:12,857 --> 00:33:16,190 on the grounds that if black holes do exist, 480 00:33:16,427 --> 00:33:19,396 he has to pay Kit Thorne a relatively modest amount, 481 00:33:19,530 --> 00:33:23,022 but if they don't exist and all his work on black holes is wasted, 482 00:33:23,134 --> 00:33:24,328 at least he gets, 483 00:33:24,435 --> 00:33:25,959 er, copies of a nice magazine. 484 00:33:37,248 --> 00:33:39,182 A new generation of astronomers, 485 00:33:39,350 --> 00:33:42,410 including Alex Filippenko were inspired to 486 00:33:42,520 --> 00:33:47,981 look for stars which appeared to be trapped in orbit around a black hole. 487 00:33:51,295 --> 00:33:53,729 You choose the ones that are the most likely candidates, 488 00:33:53,831 --> 00:33:56,766 and those, by the hypothesis of Zeldovich and others, 489 00:33:56,934 --> 00:33:58,959 were the X-ray-emitting stars. 490 00:33:59,504 --> 00:34:06,103 So we found an object which had burst out into the X-ray world in 1988, 491 00:34:06,577 --> 00:34:12,174 and we wanted to wait until it guieted down at X-ray energies because, 492 00:34:12,283 --> 00:34:14,012 along with the X-ray outburst, 493 00:34:14,118 --> 00:34:17,315 you get an outburst of optical light, radio light, 494 00:34:17,422 --> 00:34:19,151 everything, and so what happens is for, 495 00:34:19,257 --> 00:34:22,556 for guite a while the matter 496 00:34:22,660 --> 00:34:28,189 which is being dumped into the black hole glows so much at all wavelengths 497 00:34:28,399 --> 00:34:34,463 that it completely dominates the light from the star which we might find 498 00:34:34,572 --> 00:34:36,506 to be oscillating back and forth. 499 00:34:36,607 --> 00:34:40,441 So you have to wait for a while until this thing fades, 500 00:34:40,812 --> 00:34:43,542 er, until the black hole stops stealing material 501 00:34:43,648 --> 00:34:45,081 from the companion star. 502 00:34:45,283 --> 00:34:46,443 So we waited. 503 00:34:55,359 --> 00:34:57,850 Seven years after they first observed it, 504 00:34:58,129 --> 00:35:02,862 the heat and light from the disk matter surrounding the object started to fade. 505 00:35:03,568 --> 00:35:06,537 Filippenko and his colleagues got themselves ready. 506 00:35:09,207 --> 00:35:12,802 We want to find as direct evidence as we can, 507 00:35:12,944 --> 00:35:16,243 that a mass of compact objects, a dark star, 508 00:35:16,481 --> 00:35:18,847 is pulling on a companion star. 509 00:35:19,217 --> 00:35:24,154 So the way to do that is to measure the motion of the companion star 510 00:35:24,255 --> 00:35:27,247 and so you can never directly take a photograph of a black hole, 511 00:35:27,425 --> 00:35:28,323 it just appears black, 512 00:35:28,426 --> 00:35:33,295 the best you can really do is measure it's influence on material around it. 513 00:35:34,799 --> 00:35:39,099 We can then look for minute shifts in the colour 514 00:35:39,337 --> 00:35:41,567 of the light coming from this star, 515 00:35:42,106 --> 00:35:44,540 and if these shifts are found, 516 00:35:44,876 --> 00:35:47,538 and they go back and forth periodically, 517 00:35:48,012 --> 00:35:52,210 then that's an indication that something is tugging on the star. 518 00:36:03,995 --> 00:36:06,429 With a telescope finally locked on the star, 519 00:36:06,764 --> 00:36:10,131 Filippenko begins to analyse the light it emits. 520 00:36:10,835 --> 00:36:13,497 There's the star we think is orbiting a black hole. 521 00:36:14,705 --> 00:36:16,297 Let's get a spectrum of it. 522 00:36:21,445 --> 00:36:24,437 As the star moves round some unseen object, 523 00:36:24,882 --> 00:36:28,181 the light from the star shifts from the red end of the spectrum, 524 00:36:28,386 --> 00:36:31,253 towards the blue end and back again. 525 00:36:31,989 --> 00:36:36,983 From the speed of this shift Filippenko can calculate the size of the object. 526 00:36:38,462 --> 00:36:39,827 Wow, what a beauty. 527 00:36:46,904 --> 00:36:47,962 It's a black hole, 528 00:36:50,408 --> 00:36:52,569 Here we are trying to prove that, 529 00:36:53,311 --> 00:36:57,338 er, an extreme form of nature exists, a, 530 00:36:57,448 --> 00:36:59,780 a form of nature predicted by Einstein's general theor-, 531 00:36:59,884 --> 00:37:01,283 theory of relativity, 532 00:37:01,485 --> 00:37:06,286 but which is not necessarily something that nature chooses to adopt, OK. 533 00:37:06,490 --> 00:37:08,253 I mean, black holes, you know, 534 00:37:08,359 --> 00:37:10,657 they're in science fiction and everything else so, 535 00:37:10,861 --> 00:37:13,352 it's a, it's a wonderful topic, it's a wonderful concept. 536 00:37:20,271 --> 00:37:22,034 The more evidence that builds up, 537 00:37:22,273 --> 00:37:26,505 the more scientists are convinced that black holes do exist. 538 00:37:29,614 --> 00:37:35,553 Clever theorists can come up with many explanations for individual objects. 539 00:37:35,786 --> 00:37:38,050 But when you find a whole collection of objects, 540 00:37:38,522 --> 00:37:41,719 all of which collectively show the same phenomenon 541 00:37:41,826 --> 00:37:46,024 that can be explained guite naturally under the black hole hypothesis, 542 00:37:46,163 --> 00:37:49,724 and guite unnaturally using other hypotheses, 543 00:37:49,900 --> 00:37:50,889 that leaves you with a, 544 00:37:51,002 --> 00:37:52,128 sort of a, 545 00:37:52,236 --> 00:37:54,204 er, an unfulfilled feeling. 546 00:37:54,305 --> 00:37:56,830 You're, you're thinking up a new theory for every object, 547 00:37:57,041 --> 00:37:58,770 and it just doesn't sit well, you know, 548 00:37:58,876 --> 00:38:00,002 it doesn't seem right, 549 00:38:00,111 --> 00:38:01,339 it doesn't feel right. 550 00:38:01,612 --> 00:38:05,139 Yet when you have a whole class of objects which are behaving the same way 551 00:38:05,383 --> 00:38:08,511 and are well explained with one simple theory, 552 00:38:08,753 --> 00:38:13,713 that gives you some confidence that what we're really seeing is a black hole. 553 00:38:19,563 --> 00:38:22,794 The evidence for black holes was now so good 554 00:38:23,000 --> 00:38:26,231 that I no longer felt the need for insurance. 555 00:38:27,071 --> 00:38:28,663 I have conceded my bet, 556 00:38:28,873 --> 00:38:32,331 and Kit Thorne started to receive Penthouse magazine, 557 00:38:32,510 --> 00:38:35,741 greatly to the disgust of his liberated wife. 558 00:38:39,216 --> 00:38:41,650 Once it was clear that black holes had to exist, 559 00:38:41,919 --> 00:38:45,047 astronomers began to work out what exactly their connection 560 00:38:45,156 --> 00:38:49,058 might be with guasars, and the way the universe evolved. 561 00:38:50,361 --> 00:38:54,388 Quasars appear to be denizens of the early universe, 562 00:38:54,498 --> 00:38:56,227 they just don't exist nowadays, 563 00:38:56,467 --> 00:39:00,961 yet if they are powered by material falling into a black hole, 564 00:39:01,305 --> 00:39:03,899 long ago, back when the universe was young, 565 00:39:04,408 --> 00:39:07,070 then it seems reasonable 566 00:39:07,211 --> 00:39:13,707 that their remains exist here today in the centres of normal-looking galaxies. 567 00:39:14,018 --> 00:39:19,718 So that with the passage of time the guasars centre gradually used up 568 00:39:19,924 --> 00:39:22,791 all the gas and other material in its vicinity, 569 00:39:22,960 --> 00:39:28,159 it stopped eating this material, and hence it faded with time, 570 00:39:28,265 --> 00:39:32,258 because the guasar glows only while it's swallowing material, 571 00:39:35,306 --> 00:39:41,370 Astronomers have found evidence of stars moving around very rapidly, 572 00:39:42,380 --> 00:39:45,349 in the central region of what appears to be a completely boring 573 00:39:45,483 --> 00:39:47,280 and inactive galaxy, 574 00:39:49,019 --> 00:39:51,954 where material seems to be going around so guickly, 575 00:39:52,390 --> 00:39:55,416 in such a small space that no theorist have, 576 00:39:55,526 --> 00:40:00,463 has dreamed up anything else other than a black hole that could be hidden inside 577 00:40:00,698 --> 00:40:02,962 the central region of this galaxy. 578 00:40:09,373 --> 00:40:15,437 The disc revolved about a white hot ball sizzling with blistering energy. 579 00:40:18,482 --> 00:40:19,710 Why is everything so hot? 580 00:40:20,451 --> 00:40:21,577 Friction. 581 00:40:21,852 --> 00:40:25,083 All that stuff orbiting tighter and tighter around the hole, 582 00:40:26,390 --> 00:40:28,483 it rubs up against other stuff, 583 00:40:28,626 --> 00:40:31,356 gas, dust and what not. 584 00:40:31,729 --> 00:40:32,821 Heats up. 585 00:40:39,770 --> 00:40:40,998 There's so much of it, 586 00:40:41,105 --> 00:40:45,098 whole stars are being ground down into, 587 00:40:45,309 --> 00:40:47,277 er, gas and dust, 588 00:40:47,745 --> 00:40:49,610 and they churn against each other, 589 00:40:49,747 --> 00:40:53,012 they heat up, the entire disc becomes lit up. 590 00:40:53,250 --> 00:40:56,742 It's brightest at the centre where the velocities are highest because you, 591 00:40:56,854 --> 00:40:58,014 the velocity gets higher and higher 592 00:40:58,122 --> 00:41:00,283 and higher the closer you get to the black hole. 593 00:41:00,491 --> 00:41:03,927 This big shining disc, 594 00:41:04,061 --> 00:41:06,825 not a compact disc a, a cosmic disc, 595 00:41:08,065 --> 00:41:13,628 is visible at immense distances because it shines particularly out, 596 00:41:13,838 --> 00:41:16,932 in the directions perpendicular to the disc of the galaxy, 597 00:41:17,107 --> 00:41:18,699 across the whole universe. 598 00:41:18,876 --> 00:41:21,504 That's what we believe guasars are. 599 00:41:22,780 --> 00:41:24,907 The discs and their surrounding environment, 600 00:41:25,015 --> 00:41:26,983 which also gets heated up by all this radiation, 601 00:41:27,117 --> 00:41:31,076 shining out toward us from the far past, 602 00:41:31,222 --> 00:41:35,056 because the guasars we see are all dead now. 603 00:41:35,259 --> 00:41:36,817 They don't last a long time, 604 00:41:36,927 --> 00:41:38,690 they're burning up their energy so guickly. 605 00:41:38,829 --> 00:41:42,595 So we're looking millions and billions of years into the past, 606 00:41:42,700 --> 00:41:48,002 and seeing galaxies burning their inheritance prolificantely, 607 00:41:48,205 --> 00:41:51,641 er, so that they may send us this momentary signal, 608 00:41:51,775 --> 00:41:52,742 and then they go, 609 00:41:52,843 --> 00:41:55,437 they turn into cinders eventually, they go out. 610 00:41:55,646 --> 00:41:58,376 Er, our, our centre of our galaxy was never in that league, 611 00:41:58,582 --> 00:42:01,107 er, it, it was never a billion stellar masses, 612 00:42:01,285 --> 00:42:02,047 it was maybe a million, 613 00:42:02,152 --> 00:42:06,486 but, er, once it shone more brightly than it does now. 614 00:42:07,024 --> 00:42:09,788 Er, it would have been dangerous to live right next to it then 615 00:42:15,533 --> 00:42:20,061 We may now understand how black holes and guasars are related, 616 00:42:20,204 --> 00:42:22,832 but there is plenty of mystery left. 617 00:42:25,476 --> 00:42:27,444 Strange as it may sound, 618 00:42:27,611 --> 00:42:31,308 I have found that things can get out of black holes. 619 00:42:34,418 --> 00:42:36,579 On a microscopic scale, 620 00:42:36,720 --> 00:42:40,918 there is always a bit of uncertainty in the speed of a particle. 621 00:42:41,592 --> 00:42:45,426 This means that particles can travel faster than light, 622 00:42:45,596 --> 00:42:48,156 and can escape from a black hole. 623 00:42:49,900 --> 00:42:53,768 Other people call this black hole Hawking radiation, 624 00:42:53,871 --> 00:42:56,237 but I don't feel I can use the term. 625 00:42:57,241 --> 00:43:02,076 Many physicists believe that this radiation will be completely determined 626 00:43:02,179 --> 00:43:04,613 by what fell into the black hole, 627 00:43:05,215 --> 00:43:10,414 but I think the radiation will be random and will not carry any information 628 00:43:10,521 --> 00:43:12,216 about what fell in. 629 00:43:14,325 --> 00:43:17,590 I therefore have another bet with Kip Thorne on it, 630 00:43:17,795 --> 00:43:21,026 but this time he and I are on the same side. 631 00:43:22,466 --> 00:43:26,197 We bet against another physicist, John Briscil, 632 00:43:26,403 --> 00:43:29,668 that information is lost in black holes. 633 00:43:30,874 --> 00:43:35,368 The loser will by the winner an encyclopaedia from which information 634 00:43:35,479 --> 00:43:37,447 can easily be retrieved. 635 00:43:40,951 --> 00:43:43,920 Scientists have learnt from the discovery of black holes 636 00:43:44,154 --> 00:43:47,920 that it is unwise to resist unlikely ideas. 637 00:43:48,726 --> 00:43:52,924 Seth Shostak of SETI sees implications of his own work. 638 00:43:54,431 --> 00:43:56,797 In many ways the black hole story is somewhat analogous 639 00:43:56,900 --> 00:43:58,561 to what we're doing because black holes, 640 00:43:58,669 --> 00:44:00,227 in fact, were found on, 641 00:44:00,437 --> 00:44:03,463 on blackboards actually before they were found in the sky. 642 00:44:03,607 --> 00:44:05,666 That's not the normal way things work in astronomy. 643 00:44:05,776 --> 00:44:07,073 Normally in astronomy, 644 00:44:07,177 --> 00:44:09,509 you, you go to the telescope and you find something you hadn't expected 645 00:44:09,613 --> 00:44:11,080 and then you try and explain it. 646 00:44:12,182 --> 00:44:12,944 But black holes, 647 00:44:13,050 --> 00:44:17,487 they were found by theoreticians years before anybody had any hope 648 00:44:17,588 --> 00:44:18,885 of finding them with a telescope. 649 00:44:19,089 --> 00:44:20,784 Well, here we have the same thing in SETI, 650 00:44:20,891 --> 00:44:26,659 er, We expect that the galaxy is rife with civilisations, 651 00:44:26,764 --> 00:44:28,231 with technological civilisations, 652 00:44:28,332 --> 00:44:29,492 that's what we expect, 653 00:44:29,600 --> 00:44:31,431 that's our belief, and it's based on, 654 00:44:31,535 --> 00:44:33,662 no, I think, reasonable assumption. 655 00:44:33,871 --> 00:44:35,361 Now we're using the, the telescope, 656 00:44:35,472 --> 00:44:36,734 the radio telescope in this case, 657 00:44:36,840 --> 00:44:39,104 to go out and see well, is it actually there? 658 00:44:39,309 --> 00:44:40,901 Can we actually here ET? 659 00:44:42,913 --> 00:44:46,178 There is a crucial difference between the search for black holes 660 00:44:46,383 --> 00:44:48,408 and the search for ET. 661 00:44:49,186 --> 00:44:50,676 So far, in thirty six years of listening, 662 00:44:50,788 --> 00:44:54,622 we have not heard a single confirmed peep from the cosmos. 663 00:44:54,725 --> 00:44:55,384 I mean, that's a fact, 664 00:44:55,492 --> 00:44:56,686 that's the bottom line. 665 00:44:58,495 --> 00:45:01,931 But the bizarre predictions of black hole physics do throw up 666 00:45:02,032 --> 00:45:04,023 new possibilities for SETI. 667 00:45:06,170 --> 00:45:07,398 We don't broadcast in SETI. 668 00:45:07,504 --> 00:45:08,471 We don't send signals out. 669 00:45:08,572 --> 00:45:11,939 The reason we don't do that is because the distances are, are guite large, 670 00:45:12,076 --> 00:45:15,170 er, if, if say the nearest civilization is a hundred light years away, 671 00:45:15,279 --> 00:45:16,610 you send a, an inguiry, 672 00:45:16,714 --> 00:45:17,840 it takes a hundred years to get there. 673 00:45:17,948 --> 00:45:20,178 If they deign to reply it takes another hundred years for their, 674 00:45:20,284 --> 00:45:21,376 their answer to come back, 675 00:45:21,485 --> 00:45:23,112 and that's two hundred years by that point. 676 00:45:23,253 --> 00:45:25,551 You've lost interest and your funding's probably gone away too. 677 00:45:26,457 --> 00:45:28,857 But their may not even be a problem with time. 678 00:45:29,493 --> 00:45:31,324 When the laws of physics break down, 679 00:45:31,462 --> 00:45:33,054 deep inside a black hole, 680 00:45:33,330 --> 00:45:36,458 even more extraordinary possibilities exist. 681 00:45:37,301 --> 00:45:41,169 Theorists talk seriously of time travel, and worm holes. 682 00:45:41,505 --> 00:45:43,996 Kinds of tunnels in space and time through 683 00:45:44,108 --> 00:45:47,635 Which we might escape our universe and arrive in another. 684 00:45:48,645 --> 00:45:51,239 Mathematically, it's all possible. 685 00:45:52,483 --> 00:45:56,180 Black hole physics gets down to the real nitty gritty in the edges of 686 00:45:56,286 --> 00:45:57,844 what we know about physics, 687 00:45:57,955 --> 00:46:01,015 and of course, that's why attracts the, the top theoreticians, 688 00:46:01,125 --> 00:46:03,025 because it's a chance to make that breakthrough, 689 00:46:03,127 --> 00:46:05,027 you're going to unknown territory. 690 00:46:05,729 --> 00:46:08,323 There are suggestions that this speed limit 691 00:46:08,432 --> 00:46:10,195 on communication and transport, 692 00:46:10,334 --> 00:46:11,198 the speed of light, 693 00:46:11,301 --> 00:46:13,098 you can't go faster than the speed of light, 694 00:46:13,237 --> 00:46:16,604 and you can't send information faster than the speed of light. 695 00:46:17,007 --> 00:46:19,134 But the physics of black holes suggest, 696 00:46:19,309 --> 00:46:20,867 although it's still uncertain, 697 00:46:20,978 --> 00:46:24,778 that there may be other ways to send information, 698 00:46:24,882 --> 00:46:27,578 using the physics of black holes, or black holes themselves. 699 00:46:27,818 --> 00:46:31,185 That might imply there's some practical way to take advantage of that. 700 00:46:34,725 --> 00:46:37,250 And if you have truly advanced civilisations in the galaxy, 701 00:46:37,461 --> 00:46:38,723 and you might, remember, 702 00:46:38,862 --> 00:46:40,454 we're the new kids on the block, 703 00:46:40,631 --> 00:46:42,929 right, the earth has been here four or five billion years, 704 00:46:43,100 --> 00:46:45,625 but the galaxy has been here at least twice that long, 705 00:46:45,736 --> 00:46:47,636 so there may be some civilizations that are very, 706 00:46:47,738 --> 00:46:49,535 very much more advanced than we are, 707 00:46:49,706 --> 00:46:53,005 they may be taking advantage of that and it may be that we're sitting around 708 00:46:53,110 --> 00:46:55,408 with our radio receivers hoping to get signals, 709 00:46:55,512 --> 00:46:59,039 and all the really interesting traffic is being communicated in a way 710 00:46:59,149 --> 00:47:00,616 that we're not yet aware of. 711 00:47:02,452 --> 00:47:03,111 So of course, 712 00:47:03,220 --> 00:47:05,415 everybody will pay lip service to the fact that yes, 713 00:47:05,656 --> 00:47:08,181 these bizarre predictions coming out of black hole research, 714 00:47:08,392 --> 00:47:11,293 yes, well I'm not sure I believe in time travel, 715 00:47:11,395 --> 00:47:13,863 or being able to drop into a black hole and go to another universe, 716 00:47:13,964 --> 00:47:15,397 that doesn't sound right to me but, 717 00:47:15,499 --> 00:47:18,866 er, they do it with great caution because they've learned the lesson 718 00:47:19,036 --> 00:47:23,735 that what is today's unthinkable is tomorrow's convention. 719 00:47:27,978 --> 00:47:31,846 Black holes are a remarkable prediction of Einstein's theory 720 00:47:32,015 --> 00:47:35,382 that seems to be born out by our observations. 721 00:47:37,888 --> 00:47:42,188 But the theory may allow even more extraordinary possibilities 722 00:47:42,359 --> 00:47:46,659 like rapid intergalactic transit or time travel. 723 00:47:48,765 --> 00:47:49,993 If it does, 724 00:47:50,100 --> 00:47:55,299 why haven't we been visited by aliens or tourists from the future? 725 00:47:56,974 --> 00:48:00,910 Of course, some people will claim we have been visited 726 00:48:01,078 --> 00:48:03,512 and that's what UFO's are. 727 00:48:04,381 --> 00:48:08,249 But I think any such contacts would be much more obvious 728 00:48:08,352 --> 00:48:11,412 and probably very nasty.