1 00:00:24,433 --> 00:00:26,599 "Stephen Hawking's Universe" is made possible 2 00:00:26,600 --> 00:00:29,365 by Alfred P. Sloan foundation to enhance public understanding 3 00:00:29,366 --> 00:00:31,532 of the role of science and technology, 4 00:00:31,533 --> 00:00:35,533 the Arthur Vining Davis foundations, 5 00:00:36,133 --> 00:00:39,332 the corporation for public broadcasting, 6 00:00:39,333 --> 00:00:41,532 and viewers like you. 7 00:00:41,533 --> 00:00:44,199 Corporate funding is provided by Amgen, 8 00:00:44,200 --> 00:00:46,232 unlocking the secrets of life through biotechnology. 9 00:00:46,233 --> 00:00:48,132 at Amgen, we produce medicines 10 00:00:48,133 --> 00:00:50,332 that improve people's lives today 11 00:00:50,333 --> 00:00:54,333 and bring hope for tomorrow. 12 00:00:57,566 --> 00:01:00,265 Hawking: The farther we probe into the universe, 13 00:01:00,266 --> 00:01:03,665 the more remarkable are the discoveries we make. 14 00:01:03,666 --> 00:01:07,666 Much of my work has been concerned 15 00:01:07,800 --> 00:01:10,465 with the mysteries of black holes. 16 00:01:10,466 --> 00:01:13,665 Many people dismiss black holes 17 00:01:13,666 --> 00:01:16,665 as just an artifact of the theory, 18 00:01:16,666 --> 00:01:19,065 which wouldn't exist in the real world. 19 00:01:19,066 --> 00:01:23,066 But then observers began to find things in the sky 20 00:01:23,733 --> 00:01:27,733 which were just as peculiar. 21 00:01:33,666 --> 00:01:36,398 Narrator: In the end, scientists would find 22 00:01:36,399 --> 00:01:38,865 some very peculiar things -- 23 00:01:38,866 --> 00:01:42,332 impossibly bright objects blazing from the distant past, 24 00:01:42,333 --> 00:01:46,333 and forces of impenetrable darkness. 25 00:01:46,399 --> 00:01:50,399 The first thing they found was signals, 26 00:01:50,399 --> 00:01:52,532 radio waves from space. 27 00:01:52,533 --> 00:01:56,533 Astronomers tuned in in search of aliens. 28 00:01:58,600 --> 00:02:00,799 man: well, my name is Seth Shostak, 29 00:02:00,800 --> 00:02:02,799 and i'm a an astronomer at the SETI institute 30 00:02:02,800 --> 00:02:06,800 here in lovely Mountain View, California. 31 00:02:06,866 --> 00:02:09,365 The acronym "SETI" stands for 32 00:02:09,366 --> 00:02:11,865 Search for Extra-Terrestrial Intelligence. 33 00:02:11,866 --> 00:02:13,465 Now, that "I" on the end 34 00:02:13,466 --> 00:02:15,865 means we're not looking for extraterrestrial life, 35 00:02:15,866 --> 00:02:17,832 but we're looking for intelligent life. 36 00:02:17,833 --> 00:02:20,265 That means they can hold up their side of the conversation, 37 00:02:20,266 --> 00:02:24,266 if you will. 38 00:02:35,266 --> 00:02:36,798 After the second world war, 39 00:02:36,799 --> 00:02:38,265 radio astronomy really got going. 40 00:02:38,266 --> 00:02:39,732 And in the late '50s, 41 00:02:39,733 --> 00:02:41,732 they started building large radio telescopes, 42 00:02:41,733 --> 00:02:45,733 like the one we're sitting underneath. 43 00:02:48,066 --> 00:02:49,565 Could this technology 44 00:02:49,566 --> 00:02:52,599 actually be used to send messages, as it were, 45 00:02:52,600 --> 00:02:56,265 between the stars? 46 00:02:56,266 --> 00:03:00,266 In 1959, 1960, the first experiments were made 47 00:03:01,066 --> 00:03:04,465 using this kind of technology -- a big radio telescope -- 48 00:03:04,466 --> 00:03:06,865 to try and eavesdrop on any civilizations 49 00:03:06,866 --> 00:03:08,532 that might be nearby. 50 00:03:08,533 --> 00:03:12,065 Narrator: No aliens found, granted, 51 00:03:12,066 --> 00:03:14,065 but there was no mistaking the signals. 52 00:03:14,066 --> 00:03:16,798 Shostak: suddenly, you were getting 53 00:03:16,799 --> 00:03:18,599 these clear radio views, so you knew that 54 00:03:18,600 --> 00:03:20,099 in that direction 55 00:03:20,100 --> 00:03:21,999 there's a very strong source of radio waves. 56 00:03:22,000 --> 00:03:23,932 You would tell your friend the optical astronomer, 57 00:03:23,933 --> 00:03:26,265 and they would go use a big telescope, 58 00:03:26,266 --> 00:03:27,932 like the Palomar 200-inch telescope, 59 00:03:27,933 --> 00:03:29,599 or something similar, 60 00:03:29,600 --> 00:03:33,600 and they would point it in that direction. 61 00:03:37,000 --> 00:03:39,798 Narrator: Where the universe emitted a radio signal, 62 00:03:39,799 --> 00:03:43,799 optical astronomers now trained their gaze. 63 00:03:43,866 --> 00:03:47,265 What they saw defied explanation. 64 00:03:47,266 --> 00:03:51,266 But at first, its significance eluded them. 65 00:03:52,199 --> 00:03:56,065 Man: People saw that they were unusual objects. 66 00:03:56,066 --> 00:03:59,932 For example, a galaxy that had a peculiar blob within it 67 00:03:59,933 --> 00:04:02,732 in some cases was found to emit radio waves. 68 00:04:02,733 --> 00:04:06,733 Whereas a normal-looking, boring-looking galaxy did not. 69 00:04:09,299 --> 00:04:10,632 Or, for example, 70 00:04:10,633 --> 00:04:12,198 a cloud of gas that had 71 00:04:12,199 --> 00:04:13,665 all sorts of little striations in it, 72 00:04:13,666 --> 00:04:16,865 and looked as though it might be exploding -- 73 00:04:16,866 --> 00:04:18,265 those were precisely the objects 74 00:04:18,266 --> 00:04:20,265 that seemed to emit radio waves. 75 00:04:20,266 --> 00:04:24,266 Whereas more normal, quiescent clouds of gas did not. 76 00:04:26,999 --> 00:04:30,065 Narrator: Gradually, the strange evidence mounted. 77 00:04:30,066 --> 00:04:32,465 When observers turned their telescopes 78 00:04:32,466 --> 00:04:35,998 on the source of particularly strong radio signals, 79 00:04:35,999 --> 00:04:39,999 they expected to see cosmological catastrophes. 80 00:04:40,966 --> 00:04:43,265 Instead, they were left with cosmic questions. 81 00:04:43,266 --> 00:04:47,132 Filippenko: in the early 1960s, 82 00:04:47,133 --> 00:04:49,632 optical astronomers took photographs 83 00:04:49,633 --> 00:04:51,132 of certain positions in the sky 84 00:04:51,133 --> 00:04:53,399 from which radio waves seemed to be coming, 85 00:04:53,400 --> 00:04:55,798 and they just saw nothing unusual. 86 00:04:55,799 --> 00:04:58,965 There was just the usual smattering of stars, 87 00:04:58,966 --> 00:05:01,865 and there was no obviously exploding star, 88 00:05:01,866 --> 00:05:05,532 no turbulent cloud of gas, nothing seemingly unusual -- 89 00:05:05,533 --> 00:05:07,532 just normal stars. 90 00:05:07,533 --> 00:05:09,498 And this perplexed the astronomers. 91 00:05:09,499 --> 00:05:13,499 Narrator: Take the case of 3c273, 92 00:05:15,200 --> 00:05:17,832 a star of no particular distinction. 93 00:05:17,833 --> 00:05:19,998 It hardly seemed worth notice, 94 00:05:19,999 --> 00:05:23,999 that is, until observers began to look a little closer. 95 00:05:24,533 --> 00:05:28,533 Filippenko: 3c273 in the constellation Virgo 96 00:05:29,066 --> 00:05:30,798 looked just like a star, 97 00:05:30,799 --> 00:05:34,799 yet we know that ordinary stars don't emit radio waves, 98 00:05:35,200 --> 00:05:37,798 and so this was highly, highly unusual. 99 00:05:37,799 --> 00:05:41,632 Narrator: using a technique called spectroscopy, 100 00:05:41,633 --> 00:05:43,965 astronomers studied the light 101 00:05:43,966 --> 00:05:47,798 emitted by 3c273. 102 00:05:47,799 --> 00:05:50,532 When you take a spectrum of an ordinary star, 103 00:05:50,533 --> 00:05:52,865 that is when you pass the light through a prism 104 00:05:52,866 --> 00:05:54,332 and break it up into a rainbow, 105 00:05:54,333 --> 00:05:58,333 you can see small dips, small wiggles in the spectrum. 106 00:05:58,733 --> 00:06:02,599 And those are the wiggles that are produced by atoms, 107 00:06:02,600 --> 00:06:05,932 by gases in the atmosphere of those stars 108 00:06:05,933 --> 00:06:08,632 that are absorbing some of the light. 109 00:06:08,633 --> 00:06:12,633 And by identifying the pattern of these lines, 110 00:06:13,666 --> 00:06:16,832 these little wiggles that appear in a star, 111 00:06:16,833 --> 00:06:19,065 you can deduce whether the atmosphere of the star 112 00:06:19,066 --> 00:06:21,865 has hydrogen or helium and oxygen -- 113 00:06:21,866 --> 00:06:23,465 things like that. 114 00:06:23,466 --> 00:06:27,466 But if that pattern is shifted toward redder colors, 115 00:06:27,933 --> 00:06:31,199 then you deduce not only that the star has hydrogen 116 00:06:31,200 --> 00:06:33,932 or other common elements, 117 00:06:33,933 --> 00:06:37,933 but also that the star is moving away from you. 118 00:06:39,866 --> 00:06:42,332 Hawking: 34 years earlier, 119 00:06:42,333 --> 00:06:45,399 the american astronomer, Edwin Hubble, 120 00:06:45,400 --> 00:06:48,332 had used spectroscopy to discover that 121 00:06:48,333 --> 00:06:50,932 the universe is expanding. 122 00:06:50,933 --> 00:06:54,933 Distant galaxies are moving away from us. 123 00:06:57,933 --> 00:07:01,933 The spectrum of 3c273 was about to tell us even more. 124 00:07:08,999 --> 00:07:11,765 Filippenko: The spectrum of 3c273 125 00:07:11,766 --> 00:07:14,798 didn't fit any patterns of normal gases 126 00:07:14,799 --> 00:07:16,998 that have been observed in normal stars. 127 00:07:16,999 --> 00:07:19,132 and so this really befuddled astronomers. 128 00:07:19,133 --> 00:07:23,133 Not only was the object emitting radio waves profusely, 129 00:07:24,400 --> 00:07:27,798 but it had this really strange spectrum 130 00:07:27,799 --> 00:07:31,799 that couldn't be matched with any known type of gas. 131 00:07:32,066 --> 00:07:36,066 Narrator: A star's spectrum is its signature, 132 00:07:36,333 --> 00:07:38,998 and this one was an aberration. 133 00:07:38,999 --> 00:07:42,999 It was enough to leave many astronomers confounded. 134 00:07:43,466 --> 00:07:47,466 But for one, 3c273 was a revelation. 135 00:07:48,966 --> 00:07:52,966 He was convinced spectroscopy couldn't lie. 136 00:07:55,333 --> 00:07:57,132 Filippenko: Martin Schmidt at Caltech 137 00:07:57,133 --> 00:07:59,798 noticed that two of the wiggles 138 00:07:59,799 --> 00:08:03,465 had the same spacing between the colors 139 00:08:03,466 --> 00:08:06,532 as hydrogen does, but both of the lines 140 00:08:06,533 --> 00:08:10,533 were shifted way over toward redder parts of the spectrum 141 00:08:10,900 --> 00:08:13,465 than normal hydrogen gas is. 142 00:08:13,466 --> 00:08:17,466 And if he believed that that identification was correct, 143 00:08:17,600 --> 00:08:21,600 then the conclusion was that the shift is a full 16%. 144 00:08:24,866 --> 00:08:28,866 Yet a shift of 16% meant that this object 145 00:08:29,533 --> 00:08:33,533 was moving away from us enormously fast, and had to be 146 00:08:35,266 --> 00:08:39,266 one or two billion light years away. 147 00:08:39,266 --> 00:08:42,465 So, no way could it be a normal star 148 00:08:42,466 --> 00:08:45,199 or even a peculiar magnetic star in our own galaxy. 149 00:08:45,200 --> 00:08:48,599 It had to be some sort of a strange object 150 00:08:48,600 --> 00:08:52,398 that looks stellar or quasi-stellar 151 00:08:52,399 --> 00:08:55,332 simply because it's so, so far away, 152 00:08:55,333 --> 00:08:58,232 and yet it's enormously bright. 153 00:08:58,233 --> 00:09:00,732 So this really caught people by surprise, 154 00:09:00,733 --> 00:09:04,332 and a few people, i think, had a hard time believing 155 00:09:04,333 --> 00:09:08,199 that anything so relatively bright 156 00:09:08,200 --> 00:09:12,200 could be so far away. 157 00:09:16,800 --> 00:09:19,398 Astronomers decided to call these objects, 158 00:09:19,399 --> 00:09:21,265 these radio-stars, 159 00:09:21,266 --> 00:09:23,665 quasi-stellar radio sources. 160 00:09:23,666 --> 00:09:25,532 they were clearly radio sources -- 161 00:09:25,533 --> 00:09:27,465 they were discovered with radio telescopes -- 162 00:09:27,466 --> 00:09:30,332 and they looked star-like, 163 00:09:30,333 --> 00:09:34,065 and hence the stellar aspect of the term. 164 00:09:34,066 --> 00:09:38,066 So "quasi-stellar radio sources" got contracted to "quasars." 165 00:09:38,600 --> 00:09:42,600 Martin Schmidt concluded that it must be, intrinsically, 166 00:09:43,533 --> 00:09:45,998 an extremely powerful source -- 167 00:09:45,999 --> 00:09:49,065 an exceedingly bright object intrinsically -- 168 00:09:49,066 --> 00:09:52,532 because to appear as bright as it does in the sky, 169 00:09:52,533 --> 00:09:54,665 yet be so far away, 170 00:09:54,666 --> 00:09:58,332 it has to put out a tremendous amount of energy per second -- 171 00:09:58,333 --> 00:10:00,732 much, much more than our sun -- 172 00:10:00,733 --> 00:10:04,398 in fact, 100 to 1,000 times more 173 00:10:04,399 --> 00:10:08,265 than our entire milky way galaxy of stars. 174 00:10:08,266 --> 00:10:12,266 And this was the real kicker. 175 00:10:13,566 --> 00:10:16,998 Hawking: When the mysterious quasars were discovered, 176 00:10:16,999 --> 00:10:20,299 i was just beginning my post-graduate research. 177 00:10:20,300 --> 00:10:24,300 My work was to lead me to study things 178 00:10:25,066 --> 00:10:27,065 even more mysterious -- 179 00:10:27,066 --> 00:10:30,132 black holes. 180 00:10:30,133 --> 00:10:32,632 I was dealing with Einstein's general theory of relativity, 181 00:10:32,633 --> 00:10:36,532 and this seemed, to some physicists, 182 00:10:36,533 --> 00:10:38,865 a promising place to look 183 00:10:38,866 --> 00:10:42,866 for an explanation of the quasars. 184 00:10:43,266 --> 00:10:46,265 Astronomers and astrophysicists wanted an explanation 185 00:10:46,266 --> 00:10:48,332 for how these strange objects 186 00:10:48,333 --> 00:10:51,132 could behave in this extraordinary way -- 187 00:10:51,133 --> 00:10:53,065 how they could produce so much energy, 188 00:10:53,066 --> 00:10:55,599 and yet be so small. 189 00:10:55,600 --> 00:10:59,132 And so they turned to the general relativists, 190 00:10:59,133 --> 00:11:00,632 and asked them, 191 00:11:00,633 --> 00:11:02,332 "well, do you have any models for objects 192 00:11:02,333 --> 00:11:03,799 "that could look like this, 193 00:11:03,800 --> 00:11:05,699 that could behave in this way at all?" 194 00:11:05,700 --> 00:11:08,732 And the relativists said, 195 00:11:08,733 --> 00:11:11,998 "well, there is this issue of gravitational collapse, 196 00:11:11,999 --> 00:11:14,665 and maybe this is what you're looking for." 197 00:11:14,666 --> 00:11:17,265 Narrator: Gravity is the dominant force 198 00:11:17,266 --> 00:11:18,865 in the universe. 199 00:11:18,866 --> 00:11:22,732 This tenet of Einstein's was irrefutable. 200 00:11:22,733 --> 00:11:25,998 But there was no such consensus about what would happen 201 00:11:25,999 --> 00:11:29,932 under violent conditions, like the death of a large star. 202 00:11:29,933 --> 00:11:33,933 Einstein wondered, could its gravitational collapse 203 00:11:34,133 --> 00:11:36,998 crush its vast quantities of matter 204 00:11:36,999 --> 00:11:39,265 into the tiniest of points? 205 00:11:39,266 --> 00:11:41,865 Dowker: In 1939, two papers appeared. 206 00:11:41,866 --> 00:11:45,532 one was by Einstein himself, 207 00:11:45,533 --> 00:11:48,365 and one was by the american physicist, 208 00:11:48,366 --> 00:11:51,998 Robert Oppenheimer, and his co-worker, Snyder. 209 00:11:51,999 --> 00:11:54,132 They discussed what would happen 210 00:11:54,133 --> 00:11:56,265 when a large amount of matter 211 00:11:56,266 --> 00:11:58,465 was concentrated in a small region. 212 00:11:58,466 --> 00:12:01,132 Narrator: Einstein rejected 213 00:12:01,133 --> 00:12:03,265 the prospect of infinite collapse. 214 00:12:03,266 --> 00:12:06,465 But Oppenheimer and Snyder's calculations 215 00:12:06,466 --> 00:12:09,732 made the conceptual leap. 216 00:12:09,733 --> 00:12:13,733 Dowker: Using the rules of general relativity, 217 00:12:13,833 --> 00:12:17,833 they predicted that that massive object 218 00:12:18,133 --> 00:12:21,398 would undergo catastrophic gravitational collapse 219 00:12:21,399 --> 00:12:23,799 and would reach a critical radius 220 00:12:23,800 --> 00:12:26,732 at which it seemingly cuts itself off 221 00:12:26,733 --> 00:12:28,132 from the rest of the universe. 222 00:12:28,133 --> 00:12:32,133 Narrator: For many, the idea of a star 223 00:12:33,266 --> 00:12:36,398 descending into such an abyss was unthinkable -- 224 00:12:36,399 --> 00:12:39,665 all the more so when the view was shared 225 00:12:39,666 --> 00:12:42,932 by the greatest living scientist. 226 00:12:42,933 --> 00:12:45,132 Dowker: Einstein was convinced 227 00:12:45,133 --> 00:12:48,332 that you could never get to this critical radius, 228 00:12:48,333 --> 00:12:52,333 that this critical radius was an impossibility in nature. 229 00:12:52,666 --> 00:12:56,666 Narrator: The controversy was short-lived for now. 230 00:12:57,866 --> 00:12:59,865 with the second world war, 231 00:12:59,866 --> 00:13:02,665 Oppenheimer's talents were needed elsewhere, 232 00:13:02,666 --> 00:13:05,265 developing the atomic bomb. 233 00:13:05,266 --> 00:13:08,398 his earlier work languished, dismissed by peers 234 00:13:08,399 --> 00:13:11,065 as a radical departure from Einstein. 235 00:13:11,066 --> 00:13:15,066 But Oppenheimer had convinced one colleague, 236 00:13:15,066 --> 00:13:17,199 John Wheeler. 237 00:13:17,200 --> 00:13:19,265 stick up for something. 238 00:13:19,266 --> 00:13:22,465 and I think that's a wonderful way of saying 239 00:13:22,466 --> 00:13:24,665 what science is all about. 240 00:13:24,666 --> 00:13:28,666 Stick up for something. 241 00:13:39,466 --> 00:13:41,865 Man: i'm Daniel Holz, i'm a graduate student 242 00:13:41,866 --> 00:13:43,665 at the university of Chicago, 243 00:13:43,666 --> 00:13:45,932 and i'm going to see John Wheeler, 244 00:13:45,933 --> 00:13:49,933 who was my undergraduate adviser here at Princeton. 245 00:13:52,633 --> 00:13:54,265 Narrator: For Holz, 246 00:13:54,266 --> 00:13:57,332 these periodic visits with his mentor are a privilege. 247 00:13:57,333 --> 00:14:01,199 At age 85, John Wheeler is still a luminary 248 00:14:01,200 --> 00:14:05,200 of 20th century science. 249 00:14:05,333 --> 00:14:09,065 Holz: He's certainly one of the greatest physicists alive, 250 00:14:09,066 --> 00:14:11,599 and he's contributed in important ways 251 00:14:11,600 --> 00:14:14,099 in many different aspects of physics. 252 00:14:14,100 --> 00:14:16,199 He's had fresh ideas 253 00:14:16,200 --> 00:14:20,200 that have pushed the very edges of our knowledge. 254 00:14:24,466 --> 00:14:27,132 He loves to just sink his teeth into problems. 255 00:14:27,133 --> 00:14:28,832 Part of his approach in physics is, 256 00:14:28,833 --> 00:14:31,398 find the biggest, most confusing thing he can, 257 00:14:31,399 --> 00:14:34,998 and then go at it full steam and try to make sense of it. 258 00:14:34,999 --> 00:14:38,999 Narrator: Wheeler was witness to a remarkable chapter 259 00:14:39,899 --> 00:14:41,565 in the annals of physics. 260 00:14:41,566 --> 00:14:45,566 He worked with Oppenheimer on the atomic bomb. 261 00:14:45,633 --> 00:14:48,132 But before that, 262 00:14:48,133 --> 00:14:49,798 when Wheeler arrived at Princeton 263 00:14:49,799 --> 00:14:51,532 in the 1940s, 264 00:14:51,533 --> 00:14:54,665 Einstein was the most eminent member of the faculty. 265 00:14:54,666 --> 00:14:58,666 In 1963, the controversy about collapsing stars 266 00:15:00,166 --> 00:15:03,732 was rekindled by the discovery of quasars. 267 00:15:03,733 --> 00:15:07,665 Wheeler had a difficult choice between two convictions 268 00:15:07,666 --> 00:15:10,398 and two cherished colleagues. 269 00:15:10,399 --> 00:15:13,199 Though he differed with Einstein, 270 00:15:13,200 --> 00:15:17,200 he recalls him fondly. 271 00:15:19,533 --> 00:15:21,732 Wheeler: He was kind enough to invite me 272 00:15:21,733 --> 00:15:25,532 to bring my graduate students around to his house 273 00:15:25,533 --> 00:15:28,132 one day for tea. 274 00:15:28,133 --> 00:15:30,065 One of those students, Joe Callaway, said, 275 00:15:30,066 --> 00:15:31,732 "professor Einstein, 276 00:15:31,733 --> 00:15:35,532 when you're no longer living, what will happen to this house?" 277 00:15:35,533 --> 00:15:39,533 and Einstein's face was a study -- 278 00:15:39,866 --> 00:15:43,866 deep wrinkles, a wonderful smile and laugh, 279 00:15:46,399 --> 00:15:50,399 and his beautiful voice 280 00:15:50,399 --> 00:15:54,265 with a bit of a german accent, but in clear english -- 281 00:15:54,266 --> 00:15:58,266 "this house will never become a place of pilgrimage 282 00:16:00,533 --> 00:16:04,533 where the pilgrims come to look at the bones of the saint." 283 00:16:05,799 --> 00:16:08,665 [ laughter ] 284 00:16:08,666 --> 00:16:11,432 And so it is. 285 00:16:11,433 --> 00:16:15,433 Narrator: Wheeler was never one to shy away from controversy. 286 00:16:16,266 --> 00:16:19,398 To him, the notion of extreme gravitational collapse 287 00:16:19,399 --> 00:16:21,865 was the stuff of inspiration. 288 00:16:21,866 --> 00:16:25,866 And at Oppenheimer's bidding, he took up the cause. 289 00:16:26,266 --> 00:16:29,465 In fact, the idea was predicted 290 00:16:29,466 --> 00:16:32,332 by the laws of general relativity. 291 00:16:32,333 --> 00:16:34,798 But to Einstein, in this case, 292 00:16:34,799 --> 00:16:37,599 there was just so far his own theory could go 293 00:16:37,600 --> 00:16:40,398 before it defied reality. 294 00:16:40,399 --> 00:16:44,399 Wheeler: He seemed to have a psychological block 295 00:16:45,533 --> 00:16:47,932 against considering collapse. 296 00:16:47,933 --> 00:16:49,832 I don't know why. 297 00:16:49,833 --> 00:16:53,265 Narrator: The truth is, even earlier theorists 298 00:16:53,266 --> 00:16:55,599 had no such misgivings. 299 00:16:55,600 --> 00:16:57,465 As early as the 18th century, 300 00:16:57,466 --> 00:17:01,466 the mathematician pierre laplace pondered the possibility. 301 00:17:02,233 --> 00:17:05,932 Oppenheimer went on to calculate the mathematics, 302 00:17:05,933 --> 00:17:08,332 but Wheeler coined the name. 303 00:17:08,333 --> 00:17:11,065 Wheeler: After i'd used that phrase, 304 00:17:11,066 --> 00:17:14,198 "gravitationally completely collapsed object," 305 00:17:14,199 --> 00:17:17,065 several times, 306 00:17:17,066 --> 00:17:19,732 i realized that it was just too long-winded, 307 00:17:19,733 --> 00:17:23,599 and i switched to "black hole." 308 00:17:23,600 --> 00:17:26,465 Narrator: The name stuck. 309 00:17:26,466 --> 00:17:28,398 A black hole, by definition, 310 00:17:28,399 --> 00:17:31,465 is a place where gravity is so great, 311 00:17:31,466 --> 00:17:34,732 it engulfs everything around it. 312 00:17:34,733 --> 00:17:37,198 Holz: The key feature of a black hole 313 00:17:37,199 --> 00:17:39,065 is that it's black, 314 00:17:39,066 --> 00:17:42,299 that no light escapes from this region. 315 00:17:42,300 --> 00:17:43,932 So what happens is you have this object 316 00:17:43,933 --> 00:17:46,132 that's getting dense, say, a star that's collapsing, 317 00:17:46,133 --> 00:17:49,865 and it gets more and more compressed. 318 00:17:49,866 --> 00:17:53,065 As it does that, objects close to the star 319 00:17:53,066 --> 00:17:55,198 have a harder and harder time getting away. 320 00:17:55,199 --> 00:17:56,898 In some sense, 321 00:17:56,899 --> 00:18:00,899 the gravitational pull is stronger and stronger. 322 00:18:06,066 --> 00:18:08,365 If you keep on extrapolating that, 323 00:18:08,366 --> 00:18:10,132 the object gets more and more dense. 324 00:18:10,133 --> 00:18:11,799 At some point, you reach the stage 325 00:18:11,800 --> 00:18:13,932 where even light can't escape, 326 00:18:13,933 --> 00:18:16,932 and if we we're standing far away from this star, 327 00:18:16,933 --> 00:18:19,932 the light cannot get from the surface of the star to us. 328 00:18:19,933 --> 00:18:22,065 At the point where that is reached, 329 00:18:22,066 --> 00:18:26,066 you have a black hole. 330 00:18:26,066 --> 00:18:30,066 Wheeler: Our russian friends had a different word, 331 00:18:31,333 --> 00:18:34,765 and the french thought it sounded obscene, 332 00:18:34,766 --> 00:18:38,766 but finally they were won around and they accepted it. 333 00:18:42,399 --> 00:18:46,399 So a lot of people decided that the whole idea 334 00:18:46,399 --> 00:18:48,999 of a black hole was patently ludicrous, 335 00:18:49,000 --> 00:18:50,499 and that they couldn't exist. 336 00:18:50,500 --> 00:18:52,665 In fact, Einstein was in this camp 337 00:18:52,666 --> 00:18:56,398 and did not see black holes as real physical objects. 338 00:18:56,399 --> 00:18:59,865 The idea was something in nature 339 00:18:59,866 --> 00:19:01,865 would prevent a black hole from forming -- 340 00:19:01,866 --> 00:19:03,865 as you tried to put all this mass in one place, 341 00:19:03,866 --> 00:19:06,065 some mysterious force would come out 342 00:19:06,066 --> 00:19:07,265 and always prevent you 343 00:19:07,266 --> 00:19:09,065 from actually getting that much mass 344 00:19:09,066 --> 00:19:13,066 that you would actually end up collapsing to a black hole. 345 00:19:15,000 --> 00:19:18,332 Hawking: I believed that black holes should exist, 346 00:19:18,333 --> 00:19:20,332 but many physicists thought 347 00:19:20,333 --> 00:19:24,333 that was taking general relativity too far. 348 00:19:26,333 --> 00:19:28,499 Narrator: Wheeler had another agenda 349 00:19:28,500 --> 00:19:31,599 in embracing the unlikely premise of black holes. 350 00:19:31,600 --> 00:19:34,332 Quasars had become a nagging mystery. 351 00:19:34,333 --> 00:19:37,932 Could it be, he wondered, that one phenomenon 352 00:19:37,933 --> 00:19:41,099 could somehow explain the other? 353 00:19:41,100 --> 00:19:43,065 Holz: Wheeler, always being at the forefront, 354 00:19:43,066 --> 00:19:45,665 saw that these black holes were a windfall 355 00:19:45,666 --> 00:19:48,398 for explaining all sorts of astrophysical observations, 356 00:19:48,399 --> 00:19:50,532 and would become very important 357 00:19:50,533 --> 00:19:52,398 in our understanding of the world. 358 00:19:52,399 --> 00:19:55,165 and so he was egging everyone, urging everyone on 359 00:19:55,166 --> 00:19:57,932 to join in exploring this vista that opened up 360 00:19:57,933 --> 00:20:00,065 this landscape of science. 361 00:20:00,066 --> 00:20:03,465 What can we do with these black holes? 362 00:20:03,466 --> 00:20:05,732 What are the implications for them? 363 00:20:05,733 --> 00:20:09,733 How will this affect the way we look at our universe? 364 00:20:22,433 --> 00:20:24,665 Hawking: Many of us were beginning to think 365 00:20:24,666 --> 00:20:28,666 there might be large numbers of black holes in the universe. 366 00:20:30,966 --> 00:20:32,732 But that depended on what happened 367 00:20:32,733 --> 00:20:34,232 in the giant explosions 368 00:20:34,233 --> 00:20:38,233 that occur at the end of the life of massive stars. 369 00:20:49,059 --> 00:20:51,358 Narrator: In the scrublands of central California 370 00:20:51,359 --> 00:20:54,759 is a facility where scientists produced 371 00:20:54,760 --> 00:20:58,760 some of the most important weapons of our time. 372 00:21:00,046 --> 00:21:04,046 Even today, it is a compound shrouded in secrecy. 373 00:21:07,893 --> 00:21:10,625 The Lawrence Livermore national laboratory 374 00:21:10,626 --> 00:21:14,626 still buzzes with important scientific work. 375 00:21:29,860 --> 00:21:33,860 But some of its technology, outdated now after the cold war, 376 00:21:34,293 --> 00:21:36,425 lies idle, awaiting the day 377 00:21:36,426 --> 00:21:40,426 it will be scrapped or carted away. 378 00:21:42,093 --> 00:21:45,425 Among its guarded prizes is a powerful tool 379 00:21:45,426 --> 00:21:48,025 the defense department helped create, 380 00:21:48,026 --> 00:21:50,058 the first supercomputer. 381 00:21:50,059 --> 00:21:51,392 Its purpose -- 382 00:21:51,393 --> 00:21:53,692 to help make the elaborate calculations 383 00:21:53,693 --> 00:21:56,025 needed for nuclear weapons. 384 00:21:56,026 --> 00:21:58,492 Dick White was one of the first scientists to use it. 385 00:21:58,493 --> 00:22:02,225 White: I came here in 1956. 386 00:22:02,226 --> 00:22:04,525 we were one of two national laboratories 387 00:22:04,526 --> 00:22:08,159 charged with developing nuclear weapons 388 00:22:08,160 --> 00:22:11,959 for the United States. 389 00:22:11,960 --> 00:22:14,959 The laboratory here at Livermore, 390 00:22:14,960 --> 00:22:16,892 and Los Alamos laboratory, 391 00:22:16,893 --> 00:22:19,358 had a virtual monopoly on computers. 392 00:22:19,359 --> 00:22:21,492 The computers were designed for us. 393 00:22:21,493 --> 00:22:24,692 So for a period of 20 years, 394 00:22:24,693 --> 00:22:26,225 the development of computers 395 00:22:26,226 --> 00:22:30,226 depended on the existence of these labs. 396 00:22:30,460 --> 00:22:32,825 It opened up to us 397 00:22:32,826 --> 00:22:35,558 the possibility of calculating things 398 00:22:35,559 --> 00:22:38,492 that we could not even think of doing before. 399 00:22:38,493 --> 00:22:40,358 Narrator: At first, 400 00:22:40,359 --> 00:22:42,225 white needed the computer's power 401 00:22:42,226 --> 00:22:44,892 to test each new generation of the bomb. 402 00:22:44,893 --> 00:22:48,893 But by the early '60s, the work was largely done, 403 00:22:51,159 --> 00:22:52,892 so white and his colleagues 404 00:22:52,893 --> 00:22:55,159 aimed their computer at a new problem, 405 00:22:55,160 --> 00:22:58,958 black holes. 406 00:22:58,959 --> 00:23:02,425 Many theorists still didn't believe in them. 407 00:23:02,426 --> 00:23:04,425 They envisioned a very different outcome 408 00:23:04,426 --> 00:23:08,426 for a large star. 409 00:23:11,626 --> 00:23:13,858 A massive supernova 410 00:23:13,859 --> 00:23:16,759 would blast it into oblivion. 411 00:23:16,760 --> 00:23:18,892 White: The theory that they put forward 412 00:23:18,893 --> 00:23:21,559 was that the core of the star, 413 00:23:21,560 --> 00:23:23,592 the iron core, would collapse. 414 00:23:23,593 --> 00:23:25,059 They believed that this collapse 415 00:23:25,060 --> 00:23:26,559 would cause thermonuclear reactions 416 00:23:26,560 --> 00:23:28,059 that would blow up the star. 417 00:23:28,060 --> 00:23:32,060 We set out believing in this model. 418 00:23:32,226 --> 00:23:34,092 Sure enough it collapsed. 419 00:23:34,093 --> 00:23:36,625 We had no doubt it was going to do that, 420 00:23:36,626 --> 00:23:39,092 but it didn't follow their script. 421 00:23:39,093 --> 00:23:40,659 What it did was to 422 00:23:40,660 --> 00:23:44,025 instead, just continue on collapsing, 423 00:23:44,026 --> 00:23:45,825 and never came to rest 424 00:23:45,826 --> 00:23:48,525 as the pressure built up. 425 00:23:48,526 --> 00:23:50,492 Narrator: White confirmed 426 00:23:50,493 --> 00:23:53,492 that a large dying star would continue collapsing 427 00:23:53,493 --> 00:23:56,025 and end up as a black hole. 428 00:23:56,026 --> 00:23:58,825 It seems Wheeler and oppenheimer had been right. 429 00:23:58,826 --> 00:24:02,792 White: we had been led by the computer calculations 430 00:24:02,793 --> 00:24:04,759 to results that we had not anticipated, 431 00:24:04,760 --> 00:24:08,760 and that was an extraordinary time for me. 432 00:24:09,959 --> 00:24:12,225 There was a lot of excitement about this result. 433 00:24:12,226 --> 00:24:15,159 The people that worked in general relativity 434 00:24:15,160 --> 00:24:19,160 were quite excited, because in a way, it said, 435 00:24:19,760 --> 00:24:21,358 well, the things that they had been 436 00:24:21,359 --> 00:24:23,225 talking about for years -- 437 00:24:23,226 --> 00:24:26,292 very supermassive condensed stars 438 00:24:26,293 --> 00:24:30,293 with big gravitational fields -- may indeed exist. 439 00:24:41,293 --> 00:24:45,293 This is a plot of the velocity 440 00:24:45,426 --> 00:24:49,426 of the in-falling material in a star that has collapsed 441 00:24:50,559 --> 00:24:53,025 and beginning to form a black hole. 442 00:24:53,026 --> 00:24:57,026 at this point, where the most rapidly in-falling material is, 443 00:24:57,226 --> 00:25:01,226 the velocity is about 99% the velocity of light. 444 00:25:06,226 --> 00:25:09,158 Hawking: Computer calculations 445 00:25:09,159 --> 00:25:12,292 showed that at least some explosions of stars 446 00:25:12,293 --> 00:25:14,525 would form black holes. 447 00:25:14,526 --> 00:25:18,526 But if nothing can get out of a black hole, 448 00:25:19,360 --> 00:25:23,360 how could we detect one? 449 00:25:23,959 --> 00:25:27,725 Narrator: Sighting the unseeable wasn't going to be easy. 450 00:25:27,726 --> 00:25:31,726 Except, that is, for a select breed of thinker, 451 00:25:32,626 --> 00:25:35,625 science fiction writers. 452 00:25:35,626 --> 00:25:39,626 Black holes were just too hot an idea to pass up. 453 00:25:44,693 --> 00:25:47,492 Man: Toby got it now. 454 00:25:47,493 --> 00:25:51,493 "The black hole? it's pulling the star apart?" 455 00:25:52,393 --> 00:25:54,825 Colleen nodded. 456 00:25:54,826 --> 00:25:58,492 "A rare event, and we're just in time for it. 457 00:25:58,493 --> 00:26:00,325 "the hole swallows stars, 458 00:26:00,326 --> 00:26:03,025 but first it likes to chew them up." 459 00:26:03,026 --> 00:26:07,026 He could barely make himself look as the view swung inwards 460 00:26:09,626 --> 00:26:12,625 towards eye-hurting brilliance. 461 00:26:12,626 --> 00:26:16,626 The disc revolved about a white-hot ball, 462 00:26:16,926 --> 00:26:20,926 sizzling with blistering energy. 463 00:26:26,260 --> 00:26:29,492 Narrator: Gregory Benford is a best-selling author. 464 00:26:29,493 --> 00:26:33,359 His science fiction is remarkably convincing, 465 00:26:33,360 --> 00:26:36,492 because he also happens to be a physicist. 466 00:26:36,493 --> 00:26:40,493 Benford: I slowly began to realize 467 00:26:41,026 --> 00:26:43,892 that there was, at least, a case now emerging 468 00:26:43,893 --> 00:26:45,792 that there might be a black hole 469 00:26:45,793 --> 00:26:47,325 at the center of our own galaxy -- 470 00:26:47,326 --> 00:26:50,158 not just a couple of times the mass of the sun, 471 00:26:50,159 --> 00:26:53,425 but a thousand times, or a million times, 472 00:26:53,426 --> 00:26:56,225 and that prospect thrilled me. 473 00:26:56,226 --> 00:26:59,359 I thought, wow, there's got to be 474 00:26:59,360 --> 00:27:03,360 some great special effects on offer in a place like that. 475 00:27:03,593 --> 00:27:05,092 What would it do? 476 00:27:05,093 --> 00:27:08,158 What would it be like if you fell into one, 477 00:27:08,159 --> 00:27:11,692 and what would it feel like to be stretched out 478 00:27:11,693 --> 00:27:13,892 as thin as a noodle by the tidal force 479 00:27:13,893 --> 00:27:15,692 as you fall into one? 480 00:27:15,693 --> 00:27:16,958 How can you live near one? 481 00:27:16,959 --> 00:27:18,425 How would you make a living? 482 00:27:18,426 --> 00:27:21,158 Narrator: In science fiction, 483 00:27:21,159 --> 00:27:24,492 black holes became the ultimate cosmic monster. 484 00:27:24,493 --> 00:27:27,692 They could weigh as much as a billion suns. 485 00:27:27,693 --> 00:27:31,693 They could swallow matter whole, even stars, 486 00:27:31,693 --> 00:27:34,958 and once one starts moving in for the kill, 487 00:27:34,959 --> 00:27:37,225 there's no stopping it. 488 00:27:37,226 --> 00:27:41,226 Benford: It becomes compact, massive, and therefore able to, 489 00:27:41,560 --> 00:27:43,425 if it were to encounter something else, 490 00:27:43,426 --> 00:27:45,292 able to eat some more matter. 491 00:27:45,293 --> 00:27:47,692 It becomes the eater of all things, 492 00:27:47,693 --> 00:27:51,693 because nothing survives it. 493 00:27:52,193 --> 00:27:54,892 If this happens, as is most probable, 494 00:27:54,893 --> 00:27:56,559 at the center of the galaxy 495 00:27:56,560 --> 00:27:58,158 where the stars are more concentrated, 496 00:27:58,159 --> 00:27:59,759 there's more dust and gas, 497 00:27:59,760 --> 00:28:02,358 then that's where you would probably first make black holes, 498 00:28:02,359 --> 00:28:06,359 and then that's where the feeding trough is. 499 00:28:06,493 --> 00:28:10,493 They start to eat the surroundings. 500 00:28:13,459 --> 00:28:15,292 Hawking: Black holes were an area 501 00:28:15,293 --> 00:28:19,293 in which science fact, real scientific calculations, 502 00:28:19,359 --> 00:28:22,158 was way ahead of science fiction. 503 00:28:22,159 --> 00:28:26,159 That only caught up later. 504 00:28:30,060 --> 00:28:32,825 One question many science fiction writers 505 00:28:32,826 --> 00:28:36,158 speculated on was, 506 00:28:36,159 --> 00:28:40,159 what would happen inside a black hole? 507 00:28:40,260 --> 00:28:44,260 computer calculations couldn't be trusted for this, 508 00:28:45,026 --> 00:28:47,792 because they would become inaccurate 509 00:28:47,793 --> 00:28:51,158 in the extreme conditions. 510 00:28:51,159 --> 00:28:53,158 But the answer was supplied by a mathematician 511 00:28:53,159 --> 00:28:54,658 called Roger Penrose, 512 00:28:54,659 --> 00:28:58,125 who, like me, had been encouraged to work 513 00:28:58,126 --> 00:29:00,292 on general relativity 514 00:29:00,293 --> 00:29:03,458 by my supervisor, Dennis Sciama. 515 00:29:03,459 --> 00:29:06,225 Roger and his father, Lionel Penrose, 516 00:29:06,226 --> 00:29:08,625 wrote a paper, which i guess 517 00:29:08,626 --> 00:29:11,358 the artist Esher partly made famous later, 518 00:29:11,359 --> 00:29:14,125 called "impossible objects," 519 00:29:14,126 --> 00:29:17,358 where you can design an object on a piece of paper -- 520 00:29:17,359 --> 00:29:19,125 and Esher made such designs -- 521 00:29:19,126 --> 00:29:21,592 which can't be realized in the real world. 522 00:29:21,593 --> 00:29:24,225 For instance, there's a picture 523 00:29:24,226 --> 00:29:25,959 where the steps go round in a circuit, 524 00:29:25,960 --> 00:29:29,625 but they're always going down as you keep going round. 525 00:29:29,626 --> 00:29:31,325 You then end up where you began, 526 00:29:31,326 --> 00:29:33,759 and yet you've been going down all the way. 527 00:29:33,760 --> 00:29:36,959 And you can draw something which suggests that. 528 00:29:36,960 --> 00:29:38,292 But in fact, 529 00:29:38,293 --> 00:29:41,092 you couldn't construct it in the real world. 530 00:29:41,093 --> 00:29:43,892 Roger Penrose had the kind of mind 531 00:29:43,893 --> 00:29:47,425 that would conceive relationships of that sort. 532 00:29:47,426 --> 00:29:50,492 Narrator: Penrose grasped concepts 533 00:29:50,493 --> 00:29:52,492 no computer ever could. 534 00:29:52,493 --> 00:29:55,425 But his imagination also took him to a conclusion 535 00:29:55,426 --> 00:29:59,158 other scientists were desperately trying to avoid. 536 00:29:59,159 --> 00:30:01,959 Oppenheimer's idea of gravitational collapse 537 00:30:01,960 --> 00:30:03,825 was strange enough. 538 00:30:03,826 --> 00:30:05,692 Now Penrose was claiming 539 00:30:05,693 --> 00:30:08,425 the awesome power unleashed in that collapse 540 00:30:08,426 --> 00:30:11,359 would break the known laws of physics. 541 00:30:11,360 --> 00:30:15,360 Sciama: there was a debate going on at the time 542 00:30:15,360 --> 00:30:19,360 as to whether, in the collapse of a star in it's late stages, 543 00:30:19,426 --> 00:30:22,925 it would achieve infinite density 544 00:30:22,926 --> 00:30:24,558 in the central region. 545 00:30:24,559 --> 00:30:27,492 If the theory says it reaches infinite densities, 546 00:30:27,493 --> 00:30:30,092 then in a certain sense the theory has broken down 547 00:30:30,093 --> 00:30:32,359 and there would be a contradiction. 548 00:30:32,360 --> 00:30:34,425 The theory would not be self-consistent. 549 00:30:34,426 --> 00:30:36,625 If our best theory of gravitation 550 00:30:36,626 --> 00:30:38,125 is not even self-consistent, 551 00:30:38,126 --> 00:30:40,225 then we have a crisis in physics. 552 00:30:40,226 --> 00:30:42,492 The theory of relativity contains in itself 553 00:30:42,493 --> 00:30:46,092 the seeds of its own decay. 554 00:30:46,093 --> 00:30:50,093 Narrator: It's called a singularity... 555 00:30:50,960 --> 00:30:53,692 a point of infinite density. 556 00:30:53,693 --> 00:30:57,693 Most scientists thought it utterly impossible. 557 00:30:57,826 --> 00:31:00,625 Sciama: But Penrose had no such hangups, 558 00:31:00,626 --> 00:31:03,025 and he showed in 1965 559 00:31:03,026 --> 00:31:07,026 that a star in its end stages 560 00:31:07,093 --> 00:31:09,625 under natural conditions would end up 561 00:31:09,626 --> 00:31:12,692 in this self-contradictory state of infinite density. 562 00:31:12,693 --> 00:31:16,693 So the whole space-time has gone pathological. 563 00:31:18,093 --> 00:31:22,093 Narrator: It was a physicist's nightmare. 564 00:31:22,159 --> 00:31:23,625 In a black hole, 565 00:31:23,626 --> 00:31:26,759 matter could actually exit the known universe. 566 00:31:26,760 --> 00:31:29,225 Time and space drew to a close, 567 00:31:29,226 --> 00:31:32,759 and physics as we know it became meaningless. 568 00:31:32,760 --> 00:31:36,760 Still, Dennis Sciama encouraged his students to delve deeper. 569 00:31:37,226 --> 00:31:41,226 Sciama: Stephen said to me, in a certain sense, 570 00:31:41,226 --> 00:31:43,359 the universe is like a big star -- 571 00:31:43,360 --> 00:31:45,092 of course, the universe is expanding -- 572 00:31:45,093 --> 00:31:47,692 if in your mind you reverse the sense of time, 573 00:31:47,693 --> 00:31:49,959 then the universe is collapsing. 574 00:31:49,960 --> 00:31:51,825 It's a bit like a collapsing star, 575 00:31:51,826 --> 00:31:53,492 a very large star. 576 00:31:53,493 --> 00:31:57,493 Should i work on that? 577 00:31:58,726 --> 00:32:01,092 Hawking: I was awarded my doctorate 578 00:32:01,093 --> 00:32:03,292 for showing that the questions 579 00:32:03,293 --> 00:32:06,359 Penrose was raising about black holes 580 00:32:06,360 --> 00:32:09,892 would apply equally well to the early universe. 581 00:32:09,893 --> 00:32:13,893 Both the big bang and black holes would 582 00:32:14,293 --> 00:32:16,625 contain singularities, 583 00:32:16,626 --> 00:32:19,092 places where space and time come to an end, 584 00:32:19,093 --> 00:32:23,093 and the laws of physics break down. 585 00:32:25,760 --> 00:32:27,692 Narrator: Singularities, it seems, 586 00:32:27,693 --> 00:32:30,492 are cauldrons of staggering energy. 587 00:32:30,493 --> 00:32:32,158 In black holes, 588 00:32:32,159 --> 00:32:34,425 they can consume everything in their path. 589 00:32:34,426 --> 00:32:36,292 With the big bang, 590 00:32:36,293 --> 00:32:40,025 a singularity willed the whole universe into being. 591 00:32:40,026 --> 00:32:42,158 And what else, scientists wondered, 592 00:32:42,159 --> 00:32:46,159 could be behind the force unleashed in quasars? 593 00:32:48,893 --> 00:32:51,892 Sciama: They were actually applying Einstein's theory, 594 00:32:51,893 --> 00:32:53,558 not just to mathematical 595 00:32:53,559 --> 00:32:57,559 or mathematically dominated situations on paper, 596 00:33:00,226 --> 00:33:03,359 but to actual objects in the sky that were exploding. 597 00:33:03,360 --> 00:33:07,292 In fact, a quasar is the most violent explosion we know of 598 00:33:07,293 --> 00:33:11,293 other than the big bang itself. 599 00:33:13,659 --> 00:33:14,959 Narrator: In Russia, 600 00:33:14,960 --> 00:33:16,825 as in America, 601 00:33:16,826 --> 00:33:19,492 scientists who had worked on nuclear weapons 602 00:33:19,493 --> 00:33:23,025 were now tackling the unlikely physics of singularities. 603 00:33:23,026 --> 00:33:27,026 But first they had to prove these black holes, 604 00:33:27,159 --> 00:33:30,225 immense yet hidden, really existed. 605 00:33:30,226 --> 00:33:33,158 One set out to find the invisible, 606 00:33:33,159 --> 00:33:36,292 Yakov Zeldovich. 607 00:33:36,293 --> 00:33:39,892 Benford: Zeldovich, apparently, never forgot anything. 608 00:33:39,893 --> 00:33:42,492 Everything went into understanding 609 00:33:42,493 --> 00:33:44,292 how to see a black hole. 610 00:33:44,293 --> 00:33:47,492 I'm sure that working on the h-bomb 611 00:33:47,493 --> 00:33:49,292 actually helped him in astrophysics, 612 00:33:49,293 --> 00:33:51,025 because after all, most of astrophysics 613 00:33:51,026 --> 00:33:55,026 is forms of controlled h-bombs. 614 00:33:55,193 --> 00:33:57,158 How would you see a black hole anyway? 615 00:33:57,159 --> 00:33:58,959 You can't see it directly. 616 00:33:58,960 --> 00:34:00,959 You know the lion by its paw, 617 00:34:00,960 --> 00:34:02,892 or even better by its paw print. 618 00:34:02,893 --> 00:34:06,825 That's less dangerous than actually approaching a lion. 619 00:34:06,826 --> 00:34:08,692 So he said, suppose you've got 620 00:34:08,693 --> 00:34:10,259 two stars going around like this, 621 00:34:10,260 --> 00:34:11,759 and one of them is a black hole, 622 00:34:11,760 --> 00:34:13,259 say this little one right here. 623 00:34:13,260 --> 00:34:15,759 This black hole has a powerful gravitational influence, 624 00:34:15,760 --> 00:34:18,425 and it can actually suck the gas 625 00:34:18,426 --> 00:34:22,426 off the surface of this other star. 626 00:34:24,826 --> 00:34:28,292 First it gets torn apart by tidal forces 627 00:34:28,293 --> 00:34:30,325 as it tries to orbit the black hole. 628 00:34:30,326 --> 00:34:33,558 then these shred it, 629 00:34:33,559 --> 00:34:37,559 smears it around, 630 00:34:37,559 --> 00:34:39,892 and the parts bump into each other -- 631 00:34:39,893 --> 00:34:42,225 they begin to grind upon each other. 632 00:34:42,226 --> 00:34:44,625 The density is fairly high, and they heat up. 633 00:34:44,626 --> 00:34:46,892 They heat up, they give off emission -- 634 00:34:46,893 --> 00:34:48,759 electromagnetic waves, 635 00:34:48,760 --> 00:34:51,625 x-rays, visible, infrared -- 636 00:34:51,626 --> 00:34:55,626 and from that we can see this disc of hot material. 637 00:34:57,593 --> 00:35:00,158 That's one way to see a black hole indirectly. 638 00:35:00,159 --> 00:35:03,292 The most gaudy way is if you've got a black hole 639 00:35:03,293 --> 00:35:07,293 that is really spending its energy account. 640 00:35:09,826 --> 00:35:12,292 Meanwhile, magnetic fields 641 00:35:12,293 --> 00:35:16,293 have been dragged into this giant salvage dump, 642 00:35:16,559 --> 00:35:19,492 perhaps, at the center of a galaxy. 643 00:35:19,493 --> 00:35:21,692 These magnetic fields tend to get ordered, 644 00:35:21,693 --> 00:35:23,825 and they go like this. 645 00:35:23,826 --> 00:35:25,825 They come out of the accretion disc 646 00:35:25,826 --> 00:35:27,359 and peel away outside. 647 00:35:27,360 --> 00:35:29,625 This set of straight field lines, 648 00:35:29,626 --> 00:35:32,625 perpendicular to the disc, means that material, 649 00:35:32,626 --> 00:35:33,825 if it gets really hot, 650 00:35:33,826 --> 00:35:36,092 can take off along these field lines, 651 00:35:36,093 --> 00:35:38,558 and head on out all the way -- 652 00:35:38,559 --> 00:35:42,559 perhaps with enough energy to blow off the field lines, 653 00:35:42,693 --> 00:35:44,892 and to take off and leave the galaxy, 654 00:35:44,893 --> 00:35:46,759 in which case you have a bright stream 655 00:35:46,760 --> 00:35:49,958 of well-ordered material, like water out of a fire hose, 656 00:35:49,959 --> 00:35:52,158 spewing out into intergalactic space, 657 00:35:52,159 --> 00:35:54,225 and radiating, because it's still hot. 658 00:35:54,226 --> 00:35:55,958 It's got lots of energy. 659 00:35:55,959 --> 00:35:57,958 That we call a galactic jet. 660 00:35:57,959 --> 00:36:01,692 and if you see two of them, then it's clear evidence 661 00:36:01,693 --> 00:36:03,759 that there is a kind of an interesting symmetry 662 00:36:03,760 --> 00:36:05,558 at the center of a galaxy. 663 00:36:05,559 --> 00:36:07,558 You get two discs -- sorry, you get one disc, 664 00:36:07,559 --> 00:36:09,058 and you get two jets. 665 00:36:09,059 --> 00:36:10,558 And those -- a double pair of jets is, of course, 666 00:36:10,559 --> 00:36:12,359 the most beautiful thing to find. 667 00:36:12,360 --> 00:36:16,360 Hawking: Observational evidence was beginning to come, 668 00:36:16,793 --> 00:36:19,425 but was still very uncertain. 669 00:36:19,426 --> 00:36:21,325 I didn't want to see 670 00:36:21,326 --> 00:36:25,158 all my work on black holes go to waste. 671 00:36:25,159 --> 00:36:27,359 So i made a bet with kip thorne, 672 00:36:27,360 --> 00:36:30,558 who had been a student of John Wheeler. 673 00:36:30,559 --> 00:36:31,825 One suspects that it was 674 00:36:31,826 --> 00:36:34,825 more an insurance policy by Steve, 675 00:36:34,826 --> 00:36:36,825 rather than what he really believed. 676 00:36:36,826 --> 00:36:38,825 Because he bet with Kip Thorne -- 677 00:36:38,826 --> 00:36:42,225 claiming that black holes did not exist in nature, 678 00:36:42,226 --> 00:36:44,558 even though they existed in theory, 679 00:36:44,559 --> 00:36:47,958 and he bet one year of Penthouse 680 00:36:47,959 --> 00:36:50,158 against four years of Private Eye 681 00:36:50,159 --> 00:36:52,492 against Kip Thorne 682 00:36:52,493 --> 00:36:55,958 on the grounds that if black holes do exist, 683 00:36:55,959 --> 00:36:59,425 he has to pay Kip Thorne a relatively modest amount, 684 00:36:59,426 --> 00:37:01,092 but if they don't exist, 685 00:37:01,093 --> 00:37:03,225 and all his work on black holes is wasted, 686 00:37:03,226 --> 00:37:07,226 at least he gets copies of a nice magazine. 687 00:37:08,959 --> 00:37:11,025 Narrator: While Hawking was hedging his bets, 688 00:37:11,026 --> 00:37:14,225 the evidence for black holes was starting to mount. 689 00:37:14,226 --> 00:37:16,492 Galactic jets had been sighted. 690 00:37:16,493 --> 00:37:18,892 But this still wasn't proof. 691 00:37:18,893 --> 00:37:20,625 There was no guarantee 692 00:37:20,626 --> 00:37:23,092 the emissions came from black holes. 693 00:37:23,093 --> 00:37:25,692 So a new generation of astronomers 694 00:37:25,693 --> 00:37:27,625 tried a different tact. 695 00:37:27,626 --> 00:37:30,892 They began to look for stars that might be trapped in orbit 696 00:37:30,893 --> 00:37:33,692 around a black hole. 697 00:37:33,693 --> 00:37:36,392 For Alex Filippenko, the search was on. 698 00:37:36,393 --> 00:37:38,292 Filippenko: You choose the ones 699 00:37:38,293 --> 00:37:39,759 that are the most likely candidates. 700 00:37:39,760 --> 00:37:42,625 And those, by the hypothesis of zeldovich and others, 701 00:37:42,626 --> 00:37:46,359 were the x-ray-emitting stars. 702 00:37:46,360 --> 00:37:49,225 So we find an object which had burst out 703 00:37:49,226 --> 00:37:52,192 into the x-ray world in 1988. 704 00:37:52,193 --> 00:37:54,858 We wanted to wait 705 00:37:54,859 --> 00:37:57,892 until it quieted down at x-ray energies, because, 706 00:37:57,893 --> 00:38:00,025 along with the x-ray outburst, 707 00:38:00,026 --> 00:38:02,025 you get an outburst of optical light, 708 00:38:02,026 --> 00:38:04,092 radio light, everything. 709 00:38:04,093 --> 00:38:06,358 And so what happens is, for quite a while, 710 00:38:06,359 --> 00:38:10,359 the matter which is being dumped into the black hole 711 00:38:10,626 --> 00:38:13,825 glows so much at all wavelengths 712 00:38:13,826 --> 00:38:16,959 that it completely dominates the light from the star, 713 00:38:16,960 --> 00:38:20,960 which you might find to be oscillating back and forth. 714 00:38:22,093 --> 00:38:25,959 So you have to wait for a while until this thing fades, 715 00:38:25,960 --> 00:38:29,325 until the black hole stops stealing material 716 00:38:29,326 --> 00:38:30,759 from the companion star. 717 00:38:30,760 --> 00:38:32,092 So we waited. 718 00:38:32,093 --> 00:38:36,093 [ alarms buzz and ring ] 719 00:38:38,493 --> 00:38:40,159 Narrator: They waited a long time. 720 00:38:40,160 --> 00:38:41,825 After seven years, 721 00:38:41,826 --> 00:38:44,358 the object they believed to be a black hole 722 00:38:44,359 --> 00:38:47,292 began to quiet down, leaving the companion star 723 00:38:47,293 --> 00:38:50,125 circling it in stark relief. 724 00:38:50,126 --> 00:38:54,126 Filippenko and his team were ready. 725 00:38:54,426 --> 00:38:58,225 Filippenko: We want to find as direct evidence as we can 726 00:38:58,226 --> 00:39:02,226 that a massive compact object, a dark star, 727 00:39:02,760 --> 00:39:04,892 is pulling on a companion star. 728 00:39:04,893 --> 00:39:06,358 So the way to do that 729 00:39:06,359 --> 00:39:10,025 is to measure the motion of the companion star. 730 00:39:10,026 --> 00:39:12,092 Since you can never directly take a photograph 731 00:39:12,093 --> 00:39:13,592 of a black hole, it just appears black, 732 00:39:13,593 --> 00:39:15,492 the best you can really do 733 00:39:15,493 --> 00:39:18,959 is measure its influence on material around it. 734 00:39:18,960 --> 00:39:22,892 We can then look for minute shifts 735 00:39:22,893 --> 00:39:26,525 in the color of the light coming from this star, 736 00:39:26,526 --> 00:39:30,259 and if these shifts are found, 737 00:39:30,260 --> 00:39:33,159 and they go back and forth periodically, 738 00:39:33,160 --> 00:39:35,292 then that's an indication 739 00:39:35,293 --> 00:39:38,092 that something is tugging on the star, 740 00:39:38,093 --> 00:39:41,225 because stars on their own don't just go around, 741 00:39:41,226 --> 00:39:43,225 going back and forth, 742 00:39:43,226 --> 00:39:45,192 or going around in circles in the sky. 743 00:39:45,193 --> 00:39:47,759 By Newton's laws, there has to be something 744 00:39:47,760 --> 00:39:51,760 tugging on them in order to induce that motion. 745 00:40:06,126 --> 00:40:07,825 Narrator: With his telescope finally witness 746 00:40:07,826 --> 00:40:09,459 to the companion star, 747 00:40:09,460 --> 00:40:12,625 Filippenko can analyze its light. 748 00:40:12,626 --> 00:40:14,292 Okay, there's the star 749 00:40:14,293 --> 00:40:17,858 we think is orbiting a black hole. 750 00:40:17,859 --> 00:40:21,859 Let's get a spectrum of it. 751 00:40:22,592 --> 00:40:25,624 Narrator: As it orbits, its spectrum shifts. 752 00:40:25,625 --> 00:40:29,625 By the amount of that shift, Filippenko can measure 753 00:40:29,959 --> 00:40:33,158 the speed of the star, and the gravitational effect 754 00:40:33,159 --> 00:40:35,624 the object it's circling is exerting. 755 00:40:35,625 --> 00:40:39,625 The bigger the pull, the bigger the object. 756 00:40:41,092 --> 00:40:45,092 Wow, what a beauty. 757 00:40:49,492 --> 00:40:53,458 It's a black hole, at least five times the mass of the sun. 758 00:40:53,459 --> 00:40:55,891 Here we are, trying to prove 759 00:40:55,892 --> 00:40:59,892 that an extreme form of nature exists, 760 00:41:00,026 --> 00:41:01,891 a form of nature predicted 761 00:41:01,892 --> 00:41:04,691 by Einstein's general theory of relativity, 762 00:41:04,692 --> 00:41:07,291 but which is not necessarily 763 00:41:07,292 --> 00:41:09,424 something that nature chooses to adopt. 764 00:41:09,425 --> 00:41:13,425 Black holes -- 765 00:41:12,385 --> 00:41:14,917 they're in science fiction and everything else, 766 00:41:14,918 --> 00:41:18,918 so it's a wonderful topic, it's a wonderful concept. 767 00:41:21,918 --> 00:41:24,184 Narrator: As the evidence builds, 768 00:41:24,185 --> 00:41:26,717 scientists have become convinced 769 00:41:26,718 --> 00:41:28,450 black holes do exist. 770 00:41:28,451 --> 00:41:31,050 Filippenko: Clever theorists can come up with 771 00:41:31,051 --> 00:41:33,350 many explanations 772 00:41:33,351 --> 00:41:35,717 for individual objects. 773 00:41:35,718 --> 00:41:37,717 But when you find a whole collection of objects, 774 00:41:37,718 --> 00:41:41,583 all of which collectively show the same phenomenon, 775 00:41:41,584 --> 00:41:43,984 that can be explained quite naturally 776 00:41:43,985 --> 00:41:45,784 under the black hole hypothesis 777 00:41:45,785 --> 00:41:49,717 and quite unnaturally using other hypotheses 778 00:41:49,718 --> 00:41:51,850 where you conjure up special conditions 779 00:41:51,851 --> 00:41:54,250 for each of these different objects, 780 00:41:54,251 --> 00:41:57,917 that leaves you with an unfulfilled feeling. 781 00:41:57,918 --> 00:42:00,617 You're thinking up a new theory for every object, 782 00:42:00,618 --> 00:42:04,618 and it just doesn't sit well, you know, it doesn't seem right, 783 00:42:04,718 --> 00:42:06,250 it doesn't feel right. 784 00:42:06,251 --> 00:42:08,317 Yet, when you have a whole class of objects 785 00:42:08,318 --> 00:42:10,250 which are behaving the same way, 786 00:42:10,251 --> 00:42:13,117 and are well explained with one simple theory, 787 00:42:13,118 --> 00:42:15,184 that gives you some confidence 788 00:42:15,185 --> 00:42:19,185 that what we're really seeing is a black hole. 789 00:42:24,318 --> 00:42:26,517 Hawking: The evidence for black holes 790 00:42:26,518 --> 00:42:29,517 was now so good that i no longer felt 791 00:42:29,518 --> 00:42:31,217 the need for insurance. 792 00:42:31,218 --> 00:42:32,884 I conceded my bet, 793 00:42:32,885 --> 00:42:36,885 and Kip Thorne started to receive Penthouse magazine, 794 00:42:37,251 --> 00:42:41,251 greatly to the disgust of his liberated wife. 795 00:42:41,651 --> 00:42:45,651 Narrator: In the passing of one mystery 796 00:42:46,185 --> 00:42:48,517 comes the answer to another. 797 00:42:48,518 --> 00:42:52,518 Could black holes power the brightest beacons in space? 798 00:42:53,385 --> 00:42:56,517 Filippenko: Quasars appear 799 00:42:56,518 --> 00:42:59,184 to be denizens of the early universe, 800 00:42:59,185 --> 00:43:01,050 they just don't exist nowadays. 801 00:43:01,051 --> 00:43:03,850 Yet, if they are powered by material 802 00:43:03,851 --> 00:43:06,983 falling into a black hole long ago, 803 00:43:06,984 --> 00:43:08,717 back when the universe was young, 804 00:43:08,718 --> 00:43:12,517 then it seems reasonable that their remains 805 00:43:12,518 --> 00:43:15,583 exist here today in the centers 806 00:43:15,584 --> 00:43:19,417 of normal-looking galaxies. 807 00:43:19,418 --> 00:43:20,984 So that with the passage of time, 808 00:43:20,985 --> 00:43:24,517 the quasar's center gradually used up 809 00:43:24,518 --> 00:43:27,783 all the gas and other material in its vicinity. 810 00:43:27,784 --> 00:43:31,784 It stopped eating this material, and hence it faded with time, 811 00:43:32,651 --> 00:43:34,450 because the quasar glows 812 00:43:34,451 --> 00:43:36,783 only while it's swallowing material. 813 00:43:36,784 --> 00:43:39,317 So a natural conclusion was 814 00:43:39,318 --> 00:43:41,984 that nearby normal-looking galaxies 815 00:43:41,985 --> 00:43:44,717 might have very massive centers, 816 00:43:44,718 --> 00:43:47,317 which do not appear active anymore 817 00:43:47,318 --> 00:43:50,317 simply because there's no material for them to swallow. 818 00:43:50,318 --> 00:43:54,318 Astronomers have found 819 00:43:54,651 --> 00:43:58,651 evidence of stars moving around very rapidly 820 00:43:59,185 --> 00:44:02,184 in the central region of what appears to be 821 00:44:02,185 --> 00:44:06,185 a completely boring and inactive galaxy -- 822 00:44:07,251 --> 00:44:09,717 where material seems to be going around so quickly 823 00:44:09,718 --> 00:44:13,650 in such a small space that no theorist 824 00:44:13,651 --> 00:44:16,650 has dreamed up anything else other than a black hole 825 00:44:16,651 --> 00:44:18,584 that could be hidden inside 826 00:44:18,585 --> 00:44:21,184 the central region of this galaxy. 827 00:44:21,185 --> 00:44:25,185 So black holes appear to form in the centers of galaxies. 828 00:44:25,918 --> 00:44:28,383 and in particular, large galaxies 829 00:44:28,384 --> 00:44:32,384 appear to preferentially harbor black holes at their centers. 830 00:44:41,585 --> 00:44:45,585 Benford: The disc revolved about a white-hot ball, 831 00:44:46,218 --> 00:44:48,584 sizzling with blistering energy. 832 00:44:48,585 --> 00:44:51,250 "Why is everything so hot?" 833 00:44:51,251 --> 00:44:53,750 "Friction -- all that stuff 834 00:44:53,751 --> 00:44:56,383 "orbiting tighter and tighter around the hole -- 835 00:44:56,384 --> 00:45:00,150 "it rubs up against other stuff, 836 00:45:00,151 --> 00:45:02,117 "gas, dust, and whatnot -- 837 00:45:02,118 --> 00:45:06,118 heats up." 838 00:45:08,918 --> 00:45:10,550 There's so much of it. 839 00:45:10,551 --> 00:45:13,817 Whole stars are being ground down 840 00:45:13,818 --> 00:45:16,717 into gas and dust, 841 00:45:16,718 --> 00:45:19,250 and they churn against each other, 842 00:45:19,251 --> 00:45:22,717 they heat up, the entire disc becomes lit up. 843 00:45:22,718 --> 00:45:24,250 It's brightest at the center 844 00:45:24,251 --> 00:45:26,184 where the velocities are highest, 845 00:45:26,185 --> 00:45:27,817 because the velocity gets higher and higher and higher 846 00:45:27,818 --> 00:45:29,317 the closer you get to the black hole. 847 00:45:29,318 --> 00:45:33,318 This big shining disc, not a compact disc, 848 00:45:34,518 --> 00:45:36,383 a cosmic disc, 849 00:45:36,384 --> 00:45:40,384 is visible at immense distances, 850 00:45:40,918 --> 00:45:43,250 because it shines particularly out 851 00:45:43,251 --> 00:45:44,984 in the directions perpendicular 852 00:45:44,985 --> 00:45:47,984 to the disc of the galaxy across the whole universe. 853 00:45:47,985 --> 00:45:51,450 That's what we believe quasars are. 854 00:45:51,451 --> 00:45:54,583 The discs and their surrounding environment, 855 00:45:54,584 --> 00:45:56,784 which also gets heated up by all this radiation 856 00:45:56,785 --> 00:46:00,450 shining out toward us from the far past, 857 00:46:00,451 --> 00:46:04,451 because the quasars we see are all dead now. 858 00:46:04,451 --> 00:46:06,484 They don't last a long time. 859 00:46:06,485 --> 00:46:08,317 They're burning up their energy so quickly. 860 00:46:08,318 --> 00:46:11,450 So we're looking millions and billions of years 861 00:46:11,451 --> 00:46:13,517 into the past, and seeing galaxies 862 00:46:13,518 --> 00:46:17,518 burning their inheritance prolificately, 863 00:46:18,518 --> 00:46:21,117 so that they may send us this momentary signal. 864 00:46:21,118 --> 00:46:23,784 And then they turn into cinders eventually, 865 00:46:23,785 --> 00:46:25,450 they go out. 866 00:46:25,451 --> 00:46:27,850 Our center of our galaxy was never in that league. 867 00:46:27,851 --> 00:46:30,417 It was never a billion stellar masses, 868 00:46:30,418 --> 00:46:32,984 it was maybe a million, 869 00:46:32,985 --> 00:46:35,583 but once it shone more brightly than it does now. 870 00:46:35,584 --> 00:46:39,584 It would have been dangerous to live right next to, then. 871 00:46:44,651 --> 00:46:46,650 Hawking: We may now understand 872 00:46:46,651 --> 00:46:49,450 how black holes and quasars are related, 873 00:46:49,451 --> 00:46:52,317 but there is plenty of mystery left. 874 00:46:52,318 --> 00:46:56,318 Strange as it may sound, 875 00:46:56,651 --> 00:47:00,583 i have found that things can get out of black holes. 876 00:47:00,584 --> 00:47:04,584 On a microscopic scale, 877 00:47:05,651 --> 00:47:08,650 there is always a bit of uncertainty 878 00:47:08,651 --> 00:47:10,850 in the speed of a particle. 879 00:47:10,851 --> 00:47:14,851 This means that particles can travel faster than light 880 00:47:14,851 --> 00:47:17,717 and can escape from a black hole. 881 00:47:17,718 --> 00:47:21,718 Other people call this Hawking radiation, 882 00:47:22,851 --> 00:47:26,117 but i don't feel i can use the term. 883 00:47:26,118 --> 00:47:29,383 Many physicists believe that this radiation 884 00:47:29,384 --> 00:47:31,717 will be completely determined 885 00:47:31,718 --> 00:47:33,984 by what fell into the black hole, 886 00:47:33,985 --> 00:47:37,184 but i think the radiation will be random 887 00:47:37,185 --> 00:47:40,050 and will not carry any information 888 00:47:40,051 --> 00:47:42,417 about what fell in. 889 00:47:42,418 --> 00:47:46,418 I therefore have another bet with kip thorne on it, 890 00:47:46,918 --> 00:47:50,918 but this time he and i are on the same side. 891 00:47:51,718 --> 00:47:55,617 We bet against another physicist, John Friscil, 892 00:47:55,618 --> 00:47:58,850 that information is lost in black holes. 893 00:47:58,851 --> 00:48:02,851 The loser will buy the winner an encyclopedia 894 00:48:03,384 --> 00:48:07,384 from which information can easily be retrieved. 895 00:48:08,651 --> 00:48:11,050 Narrator: The confirmation of black holes 896 00:48:11,051 --> 00:48:13,717 has taught scientists it's unwise 897 00:48:13,718 --> 00:48:16,383 to resist unlikely ideas. 898 00:48:16,384 --> 00:48:19,484 Seth Shostak of SETI 899 00:48:19,485 --> 00:48:23,485 sees implications for his own work. 900 00:48:23,584 --> 00:48:25,350 Shostak: In many ways, the black hole story 901 00:48:25,351 --> 00:48:27,750 is somewhat analogous to what we're doing, 902 00:48:27,751 --> 00:48:30,617 because black holes, in fact, were found on blackboards, 903 00:48:30,618 --> 00:48:32,650 actually, before they were found in the sky. 904 00:48:32,651 --> 00:48:35,184 That's not the normal way things work in astronomy. 905 00:48:35,185 --> 00:48:37,117 Normally, in astronomy, you go to the telescope, 906 00:48:37,118 --> 00:48:38,783 you find something you hadn't expected, 907 00:48:38,784 --> 00:48:40,283 and then you try and explain it. 908 00:48:40,284 --> 00:48:44,117 But black holes, they were found by theoreticians 909 00:48:44,118 --> 00:48:46,717 years before anybody had any hope 910 00:48:46,718 --> 00:48:48,617 of finding them with a telescope. 911 00:48:48,618 --> 00:48:50,050 Well, here we have the same thing in SETI. 912 00:48:50,051 --> 00:48:51,950 We expect 913 00:48:51,951 --> 00:48:55,951 that the galaxy is rife with civilizations, 914 00:48:56,051 --> 00:48:57,917 with technological civilizations. 915 00:48:57,918 --> 00:48:59,717 That's what we expect, that's our belief, 916 00:48:59,718 --> 00:49:03,684 and it's based on, i think, reasonable assumption. 917 00:49:03,685 --> 00:49:04,984 Now we're using the telescope, 918 00:49:04,985 --> 00:49:07,417 the radio telescope in this case, 919 00:49:07,418 --> 00:49:09,117 to go out and see, well, is it actually there? 920 00:49:09,118 --> 00:49:11,184 can we actually hear E.T.? 921 00:49:11,185 --> 00:49:12,850 Narrator: But there's one crucial difference 922 00:49:12,851 --> 00:49:14,850 between the discovery of black holes 923 00:49:14,851 --> 00:49:16,417 and the search for E.T. 924 00:49:16,418 --> 00:49:20,083 Shostak: So far, in 36 years of listening, 925 00:49:20,084 --> 00:49:24,084 we have not heard a single, confirmed peep from the cosmos. 926 00:49:24,185 --> 00:49:26,417 I mean, that's a fact, that's the bottom line. 927 00:49:26,418 --> 00:49:30,418 Narrator: Still, SETI enthusiasts are patient. 928 00:49:30,451 --> 00:49:31,883 The question is, 929 00:49:31,884 --> 00:49:34,383 will their cosmic counterparts be, as well? 930 00:49:34,384 --> 00:49:36,684 Shostak: We don't broadcast in SETI. 931 00:49:36,685 --> 00:49:38,184 We don't send signals out. 932 00:49:38,185 --> 00:49:39,684 The reason we don't do that 933 00:49:39,685 --> 00:49:41,717 is because the distances are quite large. 934 00:49:41,718 --> 00:49:44,717 If the nearest civilization is 100 light years away, 935 00:49:44,718 --> 00:49:47,384 you send an inquiry, it takes 100 years to get there. 936 00:49:47,385 --> 00:49:49,184 If they deign to reply, it takes another 100 years 937 00:49:49,185 --> 00:49:50,983 for their answer to come back, 938 00:49:50,984 --> 00:49:52,583 that's 200 years by that point. 939 00:49:52,584 --> 00:49:54,083 You've lost interest, 940 00:49:54,084 --> 00:49:55,983 and your funding has probably gone away, too. 941 00:49:55,984 --> 00:49:59,184 Narrator: While we await some faint murmur from far away, 942 00:49:59,185 --> 00:50:01,784 our imaginations are carrying us 943 00:50:01,785 --> 00:50:03,917 to the very brink of the universe. 944 00:50:03,918 --> 00:50:07,450 Today, theorists talk seriously of time travel 945 00:50:07,451 --> 00:50:09,784 and what they call "worm holes," 946 00:50:09,785 --> 00:50:12,317 elusive tunnels in space and time, 947 00:50:12,318 --> 00:50:14,983 through which we could escape our universe 948 00:50:14,984 --> 00:50:16,784 and slip into another. 949 00:50:16,785 --> 00:50:20,250 Mathematically, it's all possible. 950 00:50:20,251 --> 00:50:22,917 Shostak: Black hole physics 951 00:50:22,918 --> 00:50:24,850 gets down to the real nitty gritty, 952 00:50:24,851 --> 00:50:27,517 the edges of what we know about physics. 953 00:50:27,518 --> 00:50:29,117 And of course, that's why it attracts 954 00:50:29,118 --> 00:50:30,617 the top theoreticians, 955 00:50:30,618 --> 00:50:32,384 because it's a chance to make that breakthrough. 956 00:50:32,385 --> 00:50:34,250 You're going to unknown territory. 957 00:50:34,251 --> 00:50:37,650 There are suggestions that this speed limit 958 00:50:37,651 --> 00:50:40,317 on communication and transport, the speed of light, 959 00:50:40,318 --> 00:50:43,284 you can't go faster than the speed of light, 960 00:50:43,285 --> 00:50:45,717 and you can't send information faster than the speed of light. 961 00:50:45,718 --> 00:50:48,317 But the physics of black holes suggest, 962 00:50:48,318 --> 00:50:50,517 although it's still uncertain, 963 00:50:50,518 --> 00:50:53,850 that there may be other ways to send information 964 00:50:53,851 --> 00:50:55,583 using the physics of black holes, 965 00:50:55,584 --> 00:50:57,250 or using black holes themselves. 966 00:50:57,251 --> 00:50:59,184 That might imply there's some practical way 967 00:50:59,185 --> 00:51:01,884 to take advantage of that. 968 00:51:01,885 --> 00:51:05,885 And if you have truly advanced civilizations in the galaxy, 969 00:51:06,584 --> 00:51:07,950 and you might, remember, 970 00:51:07,951 --> 00:51:09,917 we're the new kids on the block, 971 00:51:09,918 --> 00:51:12,317 the earth has been here four or five billion years, 972 00:51:12,318 --> 00:51:14,717 but the galaxy has been here at least twice that long, 973 00:51:14,718 --> 00:51:16,384 so there may be some civilizations 974 00:51:16,385 --> 00:51:18,717 that are very, very much more advanced than we are. 975 00:51:18,718 --> 00:51:20,450 They may be taking advantage of that, 976 00:51:20,451 --> 00:51:22,917 and it may be that we're sitting around 977 00:51:22,918 --> 00:51:24,784 with our radio receivers hoping to get signals, 978 00:51:24,785 --> 00:51:26,650 and all the really interesting traffic 979 00:51:26,651 --> 00:51:30,651 is being communicated in a way that we're not yet aware of. 980 00:51:33,518 --> 00:51:35,250 But it also has led 981 00:51:35,251 --> 00:51:37,583 to predictions that are so strange 982 00:51:37,584 --> 00:51:41,584 as to be held in -- well, they're obviously suspect. 983 00:51:41,584 --> 00:51:43,083 I mean, the idea of time travel, 984 00:51:43,084 --> 00:51:46,250 the idea that you can somehow drop into a worm hole 985 00:51:46,251 --> 00:51:48,583 and come out in possibly even another universe -- 986 00:51:48,584 --> 00:51:52,517 that is such a bizarre idea, and yet it's this, 987 00:51:52,518 --> 00:51:54,384 these probings on the frontier 988 00:51:54,385 --> 00:51:56,717 that sometimes present you with a completely new way 989 00:51:56,718 --> 00:51:59,784 of looking at things that make the biggest progress. 990 00:51:59,785 --> 00:52:02,850 So, of course, everybody will pay lip service to the fact that 991 00:52:02,851 --> 00:52:04,650 yes, these bizarre predictions 992 00:52:04,651 --> 00:52:06,250 coming out of black hole research -- 993 00:52:06,251 --> 00:52:08,784 yes, well i'm not sure i believe in time travel, 994 00:52:08,785 --> 00:52:10,784 or being able to drop into a black hole 995 00:52:10,785 --> 00:52:12,184 and go to another universe -- 996 00:52:12,185 --> 00:52:13,650 that doesn't sound right to me. 997 00:52:13,651 --> 00:52:15,317 But they do it with great caution, 998 00:52:15,318 --> 00:52:16,917 because they've learned the lesson 999 00:52:16,918 --> 00:52:20,918 that what is today's unthinkable is tomorrow's convention. 1000 00:52:25,651 --> 00:52:29,250 Hawking: Black holes are a remarkable prediction 1001 00:52:29,251 --> 00:52:32,050 of Einstein's theory that seems to be 1002 00:52:32,051 --> 00:52:36,051 borne out by our observations. 1003 00:52:36,518 --> 00:52:38,117 But the theory may allow 1004 00:52:38,118 --> 00:52:40,784 even more extraordinary possibilities, 1005 00:52:40,785 --> 00:52:44,785 like rapid intergalactic transit or time travel. 1006 00:52:46,951 --> 00:52:50,517 If it does, why haven't we been visited 1007 00:52:50,518 --> 00:52:54,384 by aliens or tourists from the future? 1008 00:52:54,385 --> 00:52:58,184 Of course, some people would claim 1009 00:52:58,185 --> 00:53:02,185 we have been visited, and that's what UFOs are. 1010 00:53:02,484 --> 00:53:06,484 But i think any such contacts would be much more obvious 1011 00:53:07,451 --> 00:53:11,451 and probably very nasty. 1012 00:53:20,318 --> 00:53:23,250 To learn more about "Stephen Hawking's Universe," 1013 00:53:23,251 --> 00:53:26,250 visit pbs online at the internet address 1014 00:53:26,251 --> 00:53:30,251 on your screen.