1 00:00:01,627 --> 00:00:03,242 Lying just beneath everyday reality 2 00:00:03,337 --> 00:00:06,124 is a breathtaking world, 3 00:00:06,256 --> 00:00:10,249 where much of what we perceive about the universe is wrong. 4 00:00:10,344 --> 00:00:14,212 physicist and best-selling author Brian Greene takes you 5 00:00:14,306 --> 00:00:17,514 on a journey that bends the rules of human experience. 6 00:00:17,601 --> 00:00:20,559 BRIAN GBEENE:Why don't we ever see events unfold in reverse order? 7 00:00:20,646 --> 00:00:24,355 According to the laws of physics, this can happen. 8 00:00:26,109 --> 00:00:28,441 It's a world that comes to light 9 00:00:28,570 --> 00:00:31,983 as we probe the most extreme realms of fhe cosmos, 10 00:00:32,115 --> 00:00:35,073 from black holes to the Big Bang 11 00:00:35,160 --> 00:00:37,025 to the very heart of matter itself. 12 00:00:37,120 --> 00:00:38,906 I'm going to have what he's having. 13 00:00:38,997 --> 00:00:42,831 Here, empty space teems with ferocious activity. 14 00:00:42,960 --> 00:00:46,544 The three-dimensional world may be just an illusion, 15 00:00:46,630 --> 00:00:47,790 and there's no distinction 16 00:00:47,923 --> 00:00:51,290 between past, present and future. 17 00:00:53,303 --> 00:00:55,294 GREENE: But how could this be? 18 00:00:55,389 --> 00:00:59,098 How could we be so wrong about something so familiar? 19 00:00:59,184 --> 00:01:00,173 Does it bother us? 20 00:01:00,310 --> 00:01:00,924 Absolutely. 21 00:01:01,019 --> 00:01:02,350 There's no principle 22 00:01:02,479 --> 00:01:04,470 built into the laws of nature 23 00:01:04,565 --> 00:01:08,558 that say that theoretical physicists have to be happy. 24 00:01:08,652 --> 00:01:10,984 It's a game-changing perspective 25 00:01:11,113 --> 00:01:14,105 that opens up a new world of possibilities. 26 00:01:14,199 --> 00:01:15,530 Coming up... 27 00:01:15,659 --> 00:01:18,867 What if new universes were born all the time... 28 00:01:18,996 --> 00:01:22,614 MAN: In this picture, the Big Bang is not a unique event. 29 00:01:22,708 --> 00:01:26,542 ...and ours was one of numerous parallel realities? 30 00:01:26,670 --> 00:01:30,003 GREENE: Somewhere there's a duplicate of you and me 31 00:01:30,132 --> 00:01:31,372 and everyone else. 32 00:01:31,508 --> 00:01:36,628 Are we in a universe or a multiverse? 33 00:01:39,016 --> 00:01:40,381 Right now on NOVA. 34 00:01:56,033 --> 00:01:59,150 Major funding for NOVA is provided by the following: 35 00:02:05,626 --> 00:02:07,287 And... 36 00:02:18,013 --> 00:02:22,097 And by the Corporation for Public Broadcasting 37 00:02:22,225 --> 00:02:25,183 and by contributions to your PBS station from: 38 00:02:32,319 --> 00:02:34,935 Major funding for "The Fabric of the Cosmos" 39 00:02:35,072 --> 00:02:37,859 is provided by the National Science Foundation. 40 00:02:45,499 --> 00:02:47,660 And... 41 00:02:50,420 --> 00:02:53,082 Supporting original research and public understanding 42 00:02:53,173 --> 00:02:59,260 at science, technology,engineering and mathematics. 43 00:02:59,388 --> 00:03:01,379 Additional fundingis provided by... 44 00:03:12,984 --> 00:03:15,100 And the George D.Smith Fund. 45 00:03:38,635 --> 00:03:40,296 BRIAN GBEENE: New York City. 46 00:03:40,429 --> 00:03:43,637 They say there's nowhere else like it-- 47 00:03:43,724 --> 00:03:49,264 home to eight million people, countless structures, monuments 48 00:03:49,354 --> 00:03:53,597 and landmarks, every one of them unique. 49 00:03:53,692 --> 00:03:55,273 Or so we think. 50 00:03:58,989 --> 00:04:01,651 Uniqueness is an idea so familiar, 51 00:04:01,783 --> 00:04:04,320 we never even question it. 52 00:04:04,453 --> 00:04:10,699 Experience tells us people and objects are one of a kind. 53 00:04:10,834 --> 00:04:17,672 Why else would we visit museums and collect great masterpieces? 54 00:04:17,799 --> 00:04:19,585 Yet a new picture at the cosmos 55 00:04:19,676 --> 00:04:24,045 is coming to light in which nothing is unique. 56 00:04:24,181 --> 00:04:28,049 Not that the world's great masterpieces are fakes. 57 00:04:28,185 --> 00:04:31,723 Instead, I'm talking about something far more profound: 58 00:04:31,855 --> 00:04:33,686 a new picture of the cosmos 59 00:04:33,815 --> 00:04:36,932 that challenges the very notion at uniqueness, 60 00:04:37,027 --> 00:04:40,360 one in which duplicates are inevitable. 61 00:04:40,489 --> 00:04:42,605 And that's just the beginning. 62 00:04:42,699 --> 00:04:45,611 There might be duplicates not just of objects, 63 00:04:45,702 --> 00:04:50,742 but of you and me and everyone else. 64 00:04:50,874 --> 00:04:54,037 But if this new picture is right, 65 00:04:54,127 --> 00:04:55,992 where are these duplicates 66 00:04:56,087 --> 00:04:58,373 and why haven't we ever seen them? 67 00:05:01,384 --> 00:05:05,753 The answer may lie outside our universe. 68 00:05:05,889 --> 00:05:08,426 There was a time when the word "universe" 69 00:05:08,558 --> 00:05:11,846 meant "all there is," everything. 70 00:05:11,937 --> 00:05:14,178 The notion of more than one universe, 71 00:05:14,272 --> 00:05:18,436 more than one "everything," seemed impossible. 72 00:05:18,568 --> 00:05:23,904 But perhaps if we could go beyond our solar system, 73 00:05:23,990 --> 00:05:29,405 beyond the Milky Way, even beyond other distant galaxies, 74 00:05:29,538 --> 00:05:32,905 past the end of the observable universe, 75 00:05:32,999 --> 00:05:39,586 we'll find that there's more, a lot more, 76 00:05:39,714 --> 00:05:43,172 that our universe is not alone. 77 00:05:43,260 --> 00:05:45,967 There may be other universes. 78 00:05:46,096 --> 00:05:50,260 In fact, there might be new ones being born all the time. 79 00:05:53,270 --> 00:05:54,760 We may actually live 80 00:05:54,896 --> 00:05:59,640 in an expanding sea of multiplying universes: 81 00:05:59,776 --> 00:06:01,107 a"multiverse." 82 00:06:02,612 --> 00:06:07,106 If we could visit these other universes, 83 00:06:07,200 --> 00:06:10,613 we'd find that some might have basic properties of nature 84 00:06:10,704 --> 00:06:14,492 so foreign that matter as we know it couldn't exist. 85 00:06:19,963 --> 00:06:24,423 Others might have galaxies, stars, even a planet 86 00:06:24,509 --> 00:06:29,048 that looks familiar, but with some surprising differences. 87 00:06:33,435 --> 00:06:35,471 And if there are an infinite number at universes 88 00:06:35,562 --> 00:06:38,178 in the multiverse, somewhere there's a place 89 00:06:38,315 --> 00:06:41,603 where almost everything is identical to ours 90 00:06:41,693 --> 00:06:45,857 except for the slightest details. 91 00:06:45,989 --> 00:06:48,571 Like maybe there's another Brian Greene 92 00:06:48,658 --> 00:06:51,149 who ends up in a different line of work. 93 00:06:56,499 --> 00:07:00,037 STEVEN WEINBERG: If the multiverse is indeed infinite, 94 00:07:00,170 --> 00:07:03,412 "then one is going to have to confront a lot of possibilities 95 00:07:03,506 --> 00:07:05,212 that are very hard to imagine. 96 00:07:05,342 --> 00:07:07,583 There will be other places where there will be Alan Guths 97 00:07:07,677 --> 00:07:10,168 who will look and think and act exactly like me, 98 00:07:10,305 --> 00:07:13,012 as well as many where the Alan Guths look and think 99 00:07:13,141 --> 00:07:16,178 almost exactly like me, but with some small differences. 100 00:07:16,269 --> 00:07:19,102 LEONARD SUSSKIND: Is it science? 101 00:07:19,189 --> 00:07:20,895 Is it a part of metaphysics? 102 00:07:21,024 --> 00:07:22,889 Is it just philosophy? 103 00:07:23,026 --> 00:07:24,687 Is it religion? 104 00:07:24,819 --> 00:07:27,276 Physicists tend not to ask those questions. 105 00:07:27,364 --> 00:07:30,856 They just say, "Let's follow the logic." 106 00:07:30,992 --> 00:07:33,074 And the logic seems to lead there. 107 00:07:35,664 --> 00:07:40,249 GREENE: However unfamiliar and strange the multiverse might seem, 108 00:07:40,377 --> 00:07:43,790 a growing number of scientists think it may be the final step 109 00:07:43,880 --> 00:07:45,916 in a long line of radical revisions 110 00:07:46,049 --> 00:07:48,131 to our picture of the cosmos. 111 00:07:48,218 --> 00:07:54,054 That is, there was a time when we thought that the Earth 112 00:07:54,140 --> 00:07:57,223 was at the center of the cosmos 113 00:07:57,352 --> 00:08:04,975 and that everything else revolved around us. 114 00:08:05,068 --> 00:08:08,401 Then, along came scientists like Galileo and Copernicus, 115 00:08:08,488 --> 00:08:09,477 and they showed us 116 00:08:09,572 --> 00:08:12,689 that it's the sun,not the Earth, 117 00:08:12,784 --> 00:08:16,402 that's at the center of our solar system. 118 00:08:16,538 --> 00:08:18,028 And our solar system? 119 00:08:18,123 --> 00:08:19,863 It's just a little neighborhood 120 00:08:19,958 --> 00:08:23,826 in the outskirts of a gigantic galaxy. 121 00:08:23,920 --> 00:08:25,626 And our galaxy? 122 00:08:25,755 --> 00:08:28,542 It's one of hundreds of billions of galaxies 123 00:08:28,633 --> 00:08:30,419 that make up our universe. 124 00:08:30,552 --> 00:08:34,545 Now, all of these ideas sounded outrageous 125 00:08:34,639 --> 00:08:35,799 when they were first proposed, 126 00:08:35,932 --> 00:08:38,765 but today, we don't even question them. 127 00:08:38,893 --> 00:08:42,101 The idea of a multiverse may be similar. 128 00:08:42,188 --> 00:08:45,021 It simply may require a drastic change 129 00:08:45,108 --> 00:08:47,144 in our cosmic perspective. 130 00:08:47,277 --> 00:08:48,517 On the other hand, 131 00:08:48,611 --> 00:08:50,772 some scientists think that the multiverse 132 00:08:50,864 --> 00:08:52,980 is nothing but a dead end for physics. 133 00:08:56,661 --> 00:08:59,619 ANDREAS ALBRECHT: I'm very uncomfortable with the multiverse. 134 00:08:59,748 --> 00:09:03,366 To become solid science, it's got a lot of growing up to do. 135 00:09:03,460 --> 00:09:06,827 You know, it exists in the same way that, 136 00:09:06,963 --> 00:09:09,454 you know, angels might exist. 137 00:09:09,549 --> 00:09:11,540 We have to make our bets, 138 00:09:11,634 --> 00:09:14,376 and I think right now the multiverse is a pretty good bet. 139 00:09:14,471 --> 00:09:17,304 I think there's a good chance that the multiverse is real 140 00:09:17,390 --> 00:09:18,800 and that a hundred years from now, 141 00:09:18,892 --> 00:09:20,302 people might be convinced that it's real 142 00:09:22,145 --> 00:09:25,637 GREENE: So, where did this idea come from, 143 00:09:25,774 --> 00:09:28,732 and what's the evidence for it? 144 00:09:28,818 --> 00:09:31,355 Well, several surprising discoveries suggest 145 00:09:31,488 --> 00:09:35,902 that we really may be part of a multiverse. 146 00:09:35,992 --> 00:09:37,277 The first of these discoveries 147 00:09:37,368 --> 00:09:39,825 has to do with the generally accepted theory 148 00:09:39,954 --> 00:09:43,287 of the origin of our universe: the Big Bang. 149 00:09:46,336 --> 00:09:47,746 According to this theory, 150 00:09:47,837 --> 00:09:51,000 our universe began some 14 billion years ago 151 00:09:51,132 --> 00:09:56,172 in an intensely violent explosion. 152 00:09:56,304 --> 00:10:00,468 Over billions of years, the universe cooled and coalesced, 153 00:10:00,558 --> 00:10:05,143 allowing the formation of stars, planets and galaxies. 154 00:10:08,191 --> 00:10:10,022 As a result of that explosion, 155 00:10:10,151 --> 00:10:14,110 the universe is still expanding today. 156 00:10:14,197 --> 00:10:18,156 But if you coud run the history of our universe in reverse, 157 00:10:18,243 --> 00:10:20,575 all the way back to the beginning, 158 00:10:20,703 --> 00:10:23,866 you'd find that the Big Bang theory tells us nothing 159 00:10:23,957 --> 00:10:26,289 about what sent everything hurtling outward 160 00:10:26,376 --> 00:10:29,618 in the first place. 161 00:10:29,712 --> 00:10:31,953 GUTH: It's called the Big Bang theory, 162 00:10:32,048 --> 00:10:34,414 but the one thing that it really says nothing about at all 163 00:10:34,551 --> 00:10:36,382 is the bang itself. 164 00:10:36,511 --> 00:10:37,842 It says nothing about what banged, 165 00:10:37,929 --> 00:10:39,715 why it banged, or what happened before it banged. 166 00:10:42,559 --> 00:10:47,223 GREENE: So, what fueled that violent explosion? 167 00:10:47,313 --> 00:10:51,431 What force could have driven everything apart? 168 00:10:51,568 --> 00:10:54,401 The quest to figure that out would bring scientists 169 00:10:54,487 --> 00:10:56,978 face to face with the multiverse. 170 00:10:59,742 --> 00:11:02,154 One physicist whose work 171 00:11:02,245 --> 00:11:04,156 unexpectedly helped lay the foundation 172 00:11:04,247 --> 00:11:07,614 for the multiverse idea is Alan Guth. 173 00:11:07,750 --> 00:11:11,709 Today he's a professor at MIT. 174 00:11:11,796 --> 00:11:16,756 But back in 1979, Guth and a colleague, Henry Tye, 175 00:11:16,885 --> 00:11:21,254 were pursuing a new idea about how particles might have formed 176 00:11:21,389 --> 00:11:23,345 in the early universe. 177 00:11:23,433 --> 00:11:25,719 GUTH: Henry suggested to me that we should maybe look 178 00:11:25,810 --> 00:11:28,176 at whether or not this new process that we were thinking of 179 00:11:28,271 --> 00:11:30,557 would influence the expansion rate of the universe. 180 00:11:34,110 --> 00:11:36,396 GREENE: Guth and Tye hadn't set out to investigate 181 00:11:36,487 --> 00:11:38,773 the expansion rate of the universe 182 00:11:38,865 --> 00:11:41,902 in the first moments after the Big Bang. 183 00:11:41,993 --> 00:11:44,029 But Henry Tye's question 184 00:11:44,120 --> 00:11:48,659 caused Guth to review their calculations one more time. 185 00:11:48,791 --> 00:11:50,952 GUTH: I stayed up quite late that night 186 00:11:51,044 --> 00:11:53,285 and went over the calculations very cerefully 187 00:11:53,379 --> 00:11:56,416 trying to make sure everything was correct. 188 00:11:56,507 --> 00:11:58,463 GREENE: As the night wore on, 189 00:11:58,551 --> 00:12:01,964 Guth discovered something extraordinary in the equations 190 00:12:02,096 --> 00:12:03,836 describing how new particles might have formed 191 00:12:03,973 --> 00:12:07,136 in the early universe. 192 00:12:07,268 --> 00:12:09,259 GUTH: I came to the shocking conclusion 193 00:12:09,354 --> 00:12:11,094 that these new-fangled particle theories 194 00:12:11,189 --> 00:12:12,304 would have a tremendous effect 195 00:12:12,440 --> 00:12:13,805 on the expansion rate of the universe. 196 00:12:17,820 --> 00:12:20,562 The kind of process henry and I were talking about 197 00:12:20,657 --> 00:12:21,988 would drive the universe 198 00:12:22,075 --> 00:12:24,817 into a period at incredibly rapid exponential expansion. 199 00:12:26,537 --> 00:12:28,698 GREENE: What Guth found in the math 200 00:12:28,831 --> 00:12:31,413 was evidence that in the extreme environment 201 00:12:31,501 --> 00:12:35,335 at the very early universe, gravity can act in reverse. 202 00:12:37,757 --> 00:12:40,373 Instead of pulling things together, 203 00:12:40,510 --> 00:12:44,173 this "repulsive gravity" would repel everything around it, 204 00:12:44,305 --> 00:12:46,842 causing a huge expansion. 205 00:12:46,975 --> 00:12:49,057 "GUTH: I immediately became very excited about it 206 00:12:49,185 --> 00:12:51,016 and scribbled out the calculation in my notebook, 207 00:12:51,145 --> 00:12:53,727 and then at the end I wrote "spectacular realization" 208 00:12:53,856 --> 00:12:56,313 with a double box around it, 209 00:12:56,401 --> 00:12:58,813 because I realized that if it was right, 210 00:12:58,903 --> 00:13:00,359 it could be very important. 211 00:13:00,488 --> 00:13:03,855 GREENE: By discovering this"repulsive gravity," 212 00:13:03,950 --> 00:13:06,942 Alan Guth had unintentionally shed light 213 00:13:07,036 --> 00:13:10,995 on the very beginning of the Big Bang. 214 00:13:11,082 --> 00:13:15,371 Described mathematically, this force was so powerful, 215 00:13:15,503 --> 00:13:19,166 it could take a bit of space as tiny as a molecule 216 00:13:19,257 --> 00:13:21,873 and blow it up to the size of the Wilky Way galaxy 217 00:13:22,010 --> 00:13:26,049 in less than a billionth of a billionth of a billionth 218 00:13:26,139 --> 00:13:27,379 at a blink of an eye. 219 00:13:31,352 --> 00:13:34,890 After this incredibly short outward burst, 220 00:13:35,023 --> 00:13:39,232 space would continue to expand more slowly and cool, 221 00:13:39,360 --> 00:13:42,227 allowing stars and galaxies to form, 222 00:13:42,363 --> 00:13:44,649 just as they do in the Big Bang theory. 223 00:13:47,243 --> 00:13:51,282 Guth called this short burst of expansion "inflation," 224 00:13:51,414 --> 00:13:53,245 and he believed it explained 225 00:13:53,374 --> 00:13:57,617 what set the universe expanding in the first place. 226 00:13:57,754 --> 00:14:00,791 The powerful, repulsive gravity of inflation 227 00:14:00,923 --> 00:14:03,460 was the "bang" in the the Big Bang. 228 00:14:05,011 --> 00:14:07,753 But despite having made a momentous breakthrough, 229 00:14:07,889 --> 00:14:11,427 Alan Guth had an even more pressing concern. 230 00:14:11,517 --> 00:14:14,179 I had no idea what my employment might be. 231 00:14:14,270 --> 00:14:17,353 I was really looking for a more permanent job. 232 00:14:17,440 --> 00:14:20,477 The inflationary universe scenario looks very exciting. 233 00:14:20,610 --> 00:14:23,272 GUTH: So I went on actually a pretty long trip, 234 00:14:23,404 --> 00:14:26,396 giving talks about this. 235 00:14:26,491 --> 00:14:29,574 WEINBERG: Suddenly this idea caught on. 236 00:14:29,660 --> 00:14:32,367 ALBRECHT: Talks about inflation were packed with people 237 00:14:32,455 --> 00:14:33,865 from all areas of physics. 238 00:14:33,956 --> 00:14:36,948 WEINBERG: Lots of astrophysical theorists, 239 00:14:37,085 --> 00:14:40,452 including me, got very enthusiastic. 240 00:14:40,588 --> 00:14:45,002 ALBRECHT: It was a very, very exciting time. 241 00:14:45,134 --> 00:14:47,716 WEINBERG: If you have a really good idea 242 00:14:47,804 --> 00:14:51,012 that allows other people to move the field forward, 243 00:14:51,140 --> 00:14:52,880 peope are going to pay attention. 244 00:14:52,975 --> 00:14:55,557 GUTH: An amazing feeling 245 00:14:55,645 --> 00:14:57,510 that suddenly I had crossed that gap 246 00:14:57,647 --> 00:14:59,183 from being an unknown post-doc 247 00:14:59,315 --> 00:15:01,556 to being one of the major players, 248 00:15:01,651 --> 00:15:08,739 and it was very hard to absorb, but it certainly felt good. 249 00:15:10,159 --> 00:15:12,616 GREENE: One reason inflation was so exciting 250 00:15:12,703 --> 00:15:14,318 was that it made predictions 251 00:15:14,455 --> 00:15:17,868 that could be tested through observation. 252 00:15:18,000 --> 00:15:21,834 Scientists realized that if the theory were correct, 253 00:15:21,963 --> 00:15:26,502 evidence for it should be found in the night sky. 254 00:15:26,592 --> 00:15:29,049 Imagine that we could shut off the sun 255 00:15:29,178 --> 00:15:32,511 and take away all the stars. 256 00:15:32,640 --> 00:15:33,846 If our eyes could detect 257 00:15:33,933 --> 00:15:36,345 the rest of the energy that's still there, 258 00:15:36,436 --> 00:15:41,556 we'd see a warm glow everywhere in the cosmos. 259 00:15:41,691 --> 00:15:46,025 This sea of radiation is called the cosmic microwave background. 260 00:15:46,154 --> 00:15:51,399 It's the last remnants at heat from the Big Bang itself. 261 00:15:51,534 --> 00:15:54,697 Theory predicted that the violent expansion of space 262 00:15:54,787 --> 00:15:59,531 during inflation would leave an imprint on this radiation. 263 00:15:59,667 --> 00:16:03,159 These telltale "fingerprints" would form a precise pattern 264 00:16:03,254 --> 00:16:05,119 of temperature variations-- 265 00:16:05,214 --> 00:16:09,799 slightly hotter spots and slightly colder spots-- 266 00:16:09,886 --> 00:16:12,878 that would look something like this. 267 00:16:12,972 --> 00:16:15,088 But it woud be about ten years 268 00:16:15,224 --> 00:16:17,681 before the technology was sensitive enough 269 00:16:17,768 --> 00:16:20,635 to test this prediction. 270 00:16:20,730 --> 00:16:22,311 Then in 1989, 271 00:16:22,398 --> 00:16:26,562 NASA launched the Cosmic Background Explorer satellite, 272 00:16:26,652 --> 00:16:30,941 followed by a second satellite, WMAP, in 200l 273 00:16:31,073 --> 00:16:34,691 that would put inflation to the test. 274 00:16:34,785 --> 00:16:36,491 The missions measured the radiation 275 00:16:36,579 --> 00:16:42,165 with tremendous precision, and the results were stunning. 276 00:16:42,251 --> 00:16:45,163 The temperature variations found in the cosmos 277 00:16:45,254 --> 00:16:46,960 were am almost identical match 278 00:16:47,089 --> 00:16:51,503 with the predictions of the theory of inflation. 279 00:16:51,594 --> 00:16:54,631 It's just a theory, mathematics on the page, 280 00:16:54,764 --> 00:17:00,384 until it makes predictions that are confirmed. 281 00:17:00,478 --> 00:17:03,345 WMAP found what the math of inflation predicted. 282 00:17:03,439 --> 00:17:05,395 That is enormously convincing. 283 00:17:05,483 --> 00:17:09,442 So inflation has had a number of chances now to fail. 284 00:17:09,529 --> 00:17:11,941 It made predictions, data came in, 285 00:17:12,031 --> 00:17:15,649 and inflation has come through with flying colors. 286 00:17:15,785 --> 00:17:19,073 GREENE: Guth's work on inflation, along with that of other physicists, 287 00:17:19,163 --> 00:17:20,949 was hailed as a milestone 288 00:17:21,082 --> 00:17:24,449 toward understanding the origin at the universe. 289 00:17:24,544 --> 00:17:27,126 In the process, its expanse... 290 00:17:27,255 --> 00:17:29,917 GREENE: But soon, two Russian physicists would discover 291 00:17:30,007 --> 00:17:36,503 that the equations of inflation held a shocking secret: 292 00:17:36,639 --> 00:17:40,223 our universe may not be alone. 293 00:17:43,479 --> 00:17:46,141 One of these physicists was Andrei Linde, 294 00:17:46,232 --> 00:17:48,814 who had already made pivotal contributions 295 00:17:48,901 --> 00:17:51,313 to inflationary theory. 296 00:17:51,404 --> 00:17:53,861 The other was Alex Vilenkin, 297 00:17:53,990 --> 00:17:57,733 who happened to attend one at the talks Alan Guth gave 298 00:17:57,827 --> 00:17:59,488 during his road trip. 299 00:17:59,620 --> 00:18:02,362 ALEX VILENKIN: He gave a wonderful talk. 300 00:18:02,498 --> 00:18:04,204 I hadn't met him before, 301 00:18:04,333 --> 00:18:09,453 but what I heard was rather unexpected. 302 00:18:09,547 --> 00:18:12,129 In one shot, inflation explained very well 303 00:18:12,216 --> 00:18:15,128 many features of the Big Bang 304 00:18:15,219 --> 00:18:17,130 and was quite remarkable. 305 00:18:17,221 --> 00:18:21,339 ...why the universe is the way it is. 306 00:18:21,475 --> 00:18:23,431 VILENKIN: So I went home greatly impressed. 307 00:18:28,107 --> 00:18:31,019 GREENE: Alex Vilenkin was so impressed that for months afterward, 308 00:18:31,110 --> 00:18:35,444 he couldn't stop thinking about inflation. 309 00:18:35,531 --> 00:18:39,570 VILENKIN: Usually I have my thought of the day in the shower, 310 00:18:39,702 --> 00:18:41,488 which I tend to take long. 311 00:18:43,789 --> 00:18:48,783 GREENE: The more Vilenkin considered the process of inflation, 312 00:18:48,878 --> 00:18:51,711 the more he wondered about what would make it stop. 313 00:18:51,797 --> 00:18:57,042 How would a region of space transition out of inflation? 314 00:18:57,178 --> 00:19:02,514 What exactly would Happen at the moment inflation ends? 315 00:19:02,600 --> 00:19:07,845 VILENKIN: As I thought about it, it turns out that the end of inflation 316 00:19:07,938 --> 00:19:12,056 doesn't happen everywhere at once. 317 00:19:12,151 --> 00:19:13,857 GREENE: Vilenkin suddenly realized 318 00:19:13,944 --> 00:19:17,277 that if inflation doesn't end everywhere at once, 319 00:19:17,406 --> 00:19:19,522 then there's always some part of space 320 00:19:19,617 --> 00:19:21,482 where it's still happening. 321 00:19:21,577 --> 00:19:23,067 VILENKIN: So in this picture, 322 00:19:23,162 --> 00:19:27,906 the Big Bang is not a unique event that happened. 323 00:19:28,042 --> 00:19:31,500 There were multiple bangs that happened before ours, 324 00:19:31,587 --> 00:19:34,078 and there will be countless other bangs 325 00:19:34,173 --> 00:19:36,004 that will happen in the future. 326 00:19:38,094 --> 00:19:40,836 GREEPE: It was a striking and unexpected new picture 327 00:19:40,930 --> 00:19:43,888 in which inflation would stop in some regions, 328 00:19:43,974 --> 00:19:46,636 but always continue somewhere else. 329 00:19:46,769 --> 00:19:49,226 New big bangs are always occurring 330 00:19:49,313 --> 00:19:51,895 and new universes are always being born, 331 00:19:51,982 --> 00:19:56,066 yielding an eternally expanding multiversa. 332 00:19:56,153 --> 00:19:58,018 Linde and Vilenkin in particular 333 00:19:58,114 --> 00:20:01,732 pushed the idea that inflation might never end, 334 00:20:01,826 --> 00:20:03,691 that this ballooning process 335 00:20:03,786 --> 00:20:05,447 could happen over and over again, 336 00:20:05,538 --> 00:20:07,779 giving one universe after another ofter another. 337 00:20:09,959 --> 00:20:12,996 So was this a revolution in science 338 00:20:13,129 --> 00:20:16,713 or a theory that's full of holes? 339 00:20:16,799 --> 00:20:20,007 The idea became known as "eternal inflation," 340 00:20:20,136 --> 00:20:22,548 and you can picture it something like this. 341 00:20:22,638 --> 00:20:26,972 Imagine that this block at cheese is all of space 342 00:20:27,059 --> 00:20:29,345 before the formation of stars and galaxies. 343 00:20:29,478 --> 00:20:31,139 Now, according to inflation, 344 00:20:31,272 --> 00:20:36,483 space is uniformly filled with a huge amount of energy, 345 00:20:36,610 --> 00:20:41,855 and that energy causes space to expend at an enormous speed. 346 00:20:41,991 --> 00:20:45,449 As it does, here and there the energy discharges, 347 00:20:45,536 --> 00:20:49,495 sort of like a spark of static electricity. 348 00:20:49,623 --> 00:20:54,208 But this is like static electricity on a cosmic scale, 349 00:20:54,336 --> 00:20:56,793 and when it discharges... 350 00:20:59,175 --> 00:21:03,794 ...all that energy is rapidly transformed into matter 351 00:21:03,888 --> 00:21:07,005 in the form of tiny particles. 352 00:21:07,099 --> 00:21:11,012 That process is the birth of a new universe, 353 00:21:11,103 --> 00:21:16,689 what we have traditionally called "the Big Bang." 354 00:21:16,776 --> 00:21:18,767 Inside these new universes, 355 00:21:18,861 --> 00:21:21,523 which are like holes in the cheese, 356 00:21:21,655 --> 00:21:26,069 space continues to expand, but much more slowly. 357 00:21:26,202 --> 00:21:30,195 And sometimes, galaxies, stars and planets form, 358 00:21:30,289 --> 00:21:35,124 much as we see in our universe today. 359 00:21:35,211 --> 00:21:38,795 Meanwhile, outside of these new universes, 360 00:21:38,881 --> 00:21:42,715 the rest of space is still full of undischarged energy 361 00:21:42,802 --> 00:21:46,761 and is still expanding at enormous speed. 362 00:21:46,889 --> 00:21:48,379 And more expanding space 363 00:21:48,516 --> 00:21:51,178 means more places where the energy can discharge 364 00:21:51,268 --> 00:21:57,013 into more big bangs and create more new universes. 365 00:21:57,107 --> 00:22:01,726 And that means this process could go on forever. 366 00:22:01,862 --> 00:22:04,194 In other words, when it comes to eternal inflation, 367 00:22:04,281 --> 00:22:07,773 that cheese is more like Swiss cheese, 368 00:22:07,910 --> 00:22:15,328 in which new universes endlessly form, creating e multiverse. 369 00:22:19,421 --> 00:22:23,289 The multiverse-- a profound implication 370 00:22:23,425 --> 00:22:26,963 of eternal inflation. 371 00:22:27,096 --> 00:22:29,553 But, as Alex Vilenkin would soon learn, 372 00:22:29,640 --> 00:22:33,224 one that would not be easily accepted. 373 00:22:33,310 --> 00:22:35,426 VLENKIN: I thought I realized something important 374 00:22:35,521 --> 00:22:37,136 about the universe, 375 00:22:37,273 --> 00:22:42,563 and I wanted to share this with my fellow physicists, 376 00:22:42,653 --> 00:22:46,771 and one at the first, of course, had to be Alan Guth. 377 00:22:46,866 --> 00:22:51,610 Now, we know that quantum fluctuations in the scalar field 378 00:22:51,704 --> 00:22:54,116 are different in different regions in space. 379 00:22:54,248 --> 00:22:56,660 VILENKIN: I thought he would be excited about it. 380 00:22:56,792 --> 00:23:00,250 As a result, in some regions... 381 00:23:00,337 --> 00:23:02,703 But this encounter didn't go as planned. 382 00:23:02,798 --> 00:23:08,919 ...inflation will last longer than in others. 383 00:23:09,013 --> 00:23:10,719 The delay of inflatien... 384 00:23:10,806 --> 00:23:16,142 VILENKIN: As I was describing to him my new picture at the universe, 385 00:23:16,228 --> 00:23:17,718 inflating regions and so forth... 386 00:23:18,981 --> 00:23:20,812 ...expansion. 387 00:23:20,941 --> 00:23:24,399 VILENKIN: I noticed that Alan is begining 388 00:23:24,486 --> 00:23:26,397 to doze off a little bit. 389 00:23:28,616 --> 00:23:33,952 VILENKIN: Actually I was of course very unhappy about that, 390 00:23:34,038 --> 00:23:36,996 so I thought that I probably should go. 391 00:23:43,839 --> 00:23:46,455 GREENE: One problem with the concept at a multiverse 392 00:23:46,550 --> 00:23:51,544 was that there seemed to be no way to detect it. 393 00:23:51,680 --> 00:23:54,342 Not only is each universe expanding, 394 00:23:54,433 --> 00:23:58,267 but so is the space in between them. 395 00:23:58,354 --> 00:24:00,936 That means that nothing, not even light, 396 00:24:01,023 --> 00:24:05,733 can travel from any of the other universes to reach us. 397 00:24:05,861 --> 00:24:08,568 VILENKIN: Physicists did not really respond very well 398 00:24:08,697 --> 00:24:12,610 to this idea of eternal inflation. 399 00:24:12,701 --> 00:24:15,864 Once I said that I'm going to tell them 400 00:24:15,996 --> 00:24:18,453 something about things beyond our horizon 401 00:24:18,540 --> 00:24:21,577 that cannot in principle be observed, 402 00:24:21,710 --> 00:24:24,873 most ot them just lost interest right there. 403 00:24:25,005 --> 00:24:28,998 GREENE: Alex Vilenkin thought he was on to something big, 404 00:24:29,093 --> 00:24:30,879 but others were skeptical. 405 00:24:31,011 --> 00:24:32,717 So Vilenkin reluctantly tried 406 00:24:32,805 --> 00:24:37,174 to put his work on eternal inflation out of his mind. 407 00:24:37,267 --> 00:24:39,053 ALBRECHT: Who wants to talk about a universe 408 00:24:39,186 --> 00:24:41,552 you're never going to see? 409 00:24:41,689 --> 00:24:45,056 The multiverse can't make predictions, it can't be tested. 410 00:24:45,192 --> 00:24:48,605 You could make the case that it's not really science. 411 00:24:48,737 --> 00:24:51,103 how can you ever be confident of it 412 00:24:51,240 --> 00:24:54,073 when you can't see the other parts of the multiverse? 413 00:24:54,201 --> 00:24:55,987 We can only see our little patch, 414 00:24:56,078 --> 00:24:59,115 our little expanding cloud of galaxies. 415 00:24:59,248 --> 00:25:00,579 How are we ever going to know? 416 00:25:00,666 --> 00:25:03,123 You can't prove the multiverse exists. 417 00:25:03,252 --> 00:25:04,583 It's not wrong. 418 00:25:04,712 --> 00:25:06,327 You can't prove that it doesn't exist. 419 00:25:06,422 --> 00:25:08,128 So why should we believe it? 420 00:25:11,135 --> 00:25:15,094 GREENE: Alex Vilenkin tried to stop thinking about the multiverse. 421 00:25:17,099 --> 00:25:20,011 With no hard evidence to support it, 422 00:25:20,102 --> 00:25:22,058 the idea seemed to have hit a deed end. 423 00:25:23,981 --> 00:25:25,937 VILENKIN: Many people thought that it's just not science 424 00:25:26,066 --> 00:25:28,773 to talk about things that you cannot observe. 425 00:25:28,861 --> 00:25:35,152 So I did not return to the subject for almost ten years. 426 00:25:35,284 --> 00:25:38,868 GREENE: Meanwhile, Vilenkin's Russian colleague Andrei Linde 427 00:25:38,954 --> 00:25:41,411 kept the flame alive. 428 00:25:41,498 --> 00:25:42,988 He had independently come up 429 00:25:43,125 --> 00:25:45,286 with his own version of eternal inflation, 430 00:25:45,419 --> 00:25:48,752 but unlike Vilenkin, he would not be deterred. 431 00:25:48,839 --> 00:25:51,171 ANDREI LINDE: Maybe I am a little bit more arrogant. 432 00:25:51,300 --> 00:25:54,918 When I got the idea for this multiverse, 433 00:25:55,012 --> 00:25:57,469 I understood that this may be the most important thing 434 00:25:57,598 --> 00:25:59,338 which I ever do in my life. 435 00:25:59,475 --> 00:26:01,807 And if somebody doesn't want to hear it, 436 00:26:01,894 --> 00:26:02,724 that's their problem. 437 00:26:04,521 --> 00:26:07,354 GREENE: Linde published more than a dozen papers, 438 00:26:07,483 --> 00:26:10,316 but his work would meet an equally chilly reception. 439 00:26:10,444 --> 00:26:15,655 It seemed no one wanted to hear about the idea of a multiverse. 440 00:26:22,539 --> 00:26:24,996 If the equations of eternal inflation 441 00:26:25,125 --> 00:26:27,741 were the only clues pointing to the multiverse, 442 00:26:27,836 --> 00:26:31,795 that's where the story might have ended. 443 00:26:31,882 --> 00:26:35,374 But the multiverse idea would gain some unexpected support 444 00:26:35,511 --> 00:26:39,550 from two completely unrelated areas at science. 445 00:26:39,681 --> 00:26:43,640 One was an idea called string theory, 446 00:26:43,727 --> 00:26:46,184 designed to explain how the universe works 447 00:26:46,271 --> 00:26:49,138 at the tiniest scales. 448 00:26:49,233 --> 00:26:51,724 The other was an astounding discovery 449 00:26:51,860 --> 00:26:53,851 made by astronomers exploring the universe 450 00:26:53,987 --> 00:26:56,194 on the largest scale, 451 00:26:56,281 --> 00:26:58,146 a discovery thats utterly mysterious 452 00:26:58,242 --> 00:27:00,278 if there's only one universe. 453 00:27:00,369 --> 00:27:03,202 But if we're part of a multiverse, 454 00:27:03,288 --> 00:27:04,698 it's a whole new ballgame. 455 00:27:07,709 --> 00:27:10,166 It has to do with the expansion of the universe, 456 00:27:10,254 --> 00:27:13,041 and its easy to explain using a baseball. 457 00:27:13,173 --> 00:27:15,664 Now, if I toss this ball up in the air, 458 00:27:15,759 --> 00:27:18,045 we all know what will happen. 459 00:27:18,137 --> 00:27:21,925 As it rises, it slows down because of gravity. 460 00:27:23,976 --> 00:27:27,343 Now, astronomers knew that the universe was expanding, 461 00:27:27,437 --> 00:27:30,053 and they assumed that the expansion would slow down 462 00:27:30,190 --> 00:27:33,557 because of the gravitational pull of stars and galaxies, 463 00:27:33,652 --> 00:27:35,734 just as the ball slows down 464 00:27:35,863 --> 00:27:39,105 because of the gravitational pull of the Earth. 465 00:27:39,241 --> 00:27:41,732 But when they actually did the measurements, 466 00:27:41,869 --> 00:27:44,906 they found something astonishing, 467 00:27:44,997 --> 00:27:47,329 something that rocked the foundations of physics. 468 00:27:47,416 --> 00:27:52,251 They found that the expansion is not slowing down. 469 00:27:52,337 --> 00:27:53,952 It's speeding up. 470 00:27:56,425 --> 00:27:59,508 It's as if I took this baseball and when I throw it... 471 00:28:02,097 --> 00:28:08,468 ...instead of slowing down as it rush away,it speeds up. 472 00:28:08,604 --> 00:28:11,562 Now, if you saw a ball do that, 473 00:28:11,648 --> 00:28:13,434 you'd assume there's some invisible force 474 00:28:13,567 --> 00:28:16,775 that's counteracting gravity, pushing on the ball, 475 00:28:16,862 --> 00:28:19,399 forcing it to speed away ever more quickly. 476 00:28:19,489 --> 00:28:23,778 Astronomers came to the same conclusion about the universe: 477 00:28:23,911 --> 00:28:26,368 that some kind of energy in space 478 00:28:26,455 --> 00:28:29,288 must be pushing all the galaxies apart, 479 00:28:29,416 --> 00:28:33,125 causing the expansion to speed up. 480 00:28:33,212 --> 00:28:34,793 Because we don't see the energy, 481 00:28:34,922 --> 00:28:39,632 the astronomers called it "dark energy." 482 00:28:39,760 --> 00:28:43,628 It's among the most important experimental discoveries ever 483 00:28:43,722 --> 00:28:45,053 in the history of soience. 484 00:28:45,140 --> 00:28:48,348 It took most of us completely by surprise. 485 00:28:48,477 --> 00:28:51,139 And so, we're still trying to come to grips with that. 486 00:28:52,856 --> 00:28:54,596 GREENE: Discovering that dark energy 487 00:28:54,691 --> 00:28:56,522 is pushing every galaxy in our universe 488 00:28:56,652 --> 00:28:59,860 away from every other at an accelerating rate 489 00:28:59,988 --> 00:29:02,320 was shocking enough. 490 00:29:02,407 --> 00:29:06,650 But even more surprising was the strength of that dark energy. 491 00:29:06,787 --> 00:29:10,496 For over a decade, scientists have been unable to explain 492 00:29:10,624 --> 00:29:15,539 why such a peculiar amount of it exists in empty space. 493 00:29:15,671 --> 00:29:19,380 But that mystery seems easier to resolve 494 00:29:19,508 --> 00:29:22,671 if we're part of a much larger mutiverse. 495 00:29:25,514 --> 00:29:26,754 Now, the idea that space 496 00:29:26,848 --> 00:29:29,510 contains any energy at all sounds strange. 497 00:29:29,601 --> 00:29:34,686 But our theory at small things like molecules and atoms, 498 00:29:34,773 --> 00:29:37,059 the theory called quantum mechanics, 499 00:29:37,192 --> 00:29:39,433 tells us that theres a lot of activity 500 00:29:39,528 --> 00:29:41,359 in the microscopic realm, 501 00:29:41,488 --> 00:29:44,946 activity that can contribute an energy to space. 502 00:29:45,033 --> 00:29:47,240 And according to the math, 503 00:29:47,369 --> 00:29:51,203 the amount of energy generated by that microscopic activity 504 00:29:51,331 --> 00:29:52,867 is enormous. 505 00:29:52,958 --> 00:29:56,542 The problem is, when astronomers measured the amount at energy 506 00:29:56,628 --> 00:29:57,959 thats actually out there, 507 00:29:58,046 --> 00:30:02,085 the amount of energy required to force the galaxies apart 508 00:30:02,217 --> 00:30:04,833 at the accelerating rate that's observed, 509 00:30:04,928 --> 00:30:07,670 they get a numder like this: 510 00:30:07,764 --> 00:30:13,100 a decimal point followed by 122 zeroes, and then a one. 511 00:30:13,228 --> 00:30:16,846 An incredibly tiny amount, very close to zero, 512 00:30:16,940 --> 00:30:19,727 and nothing at all like what the theory predicted. 513 00:30:19,860 --> 00:30:22,647 In fact, it's trillions and trillions 514 00:30:22,738 --> 00:30:25,730 and trillions and trillions of times smaller, 515 00:30:25,824 --> 00:30:27,985 a colossal mismatch. 516 00:30:28,076 --> 00:30:30,738 We have tried everything 517 00:30:30,829 --> 00:30:35,414 to explain why the dark energy is as small as it is. 518 00:30:35,542 --> 00:30:39,160 We have tried everything, and everything fails. 519 00:30:39,254 --> 00:30:40,494 Hopeless! 520 00:30:40,589 --> 00:30:43,080 I once called this the worst failure 521 00:30:43,216 --> 00:30:44,797 of an order of magnitude estimate 522 00:30:44,926 --> 00:30:46,257 in the history of science. 523 00:30:46,386 --> 00:30:47,466 Does it bother us? 524 00:30:47,596 --> 00:30:48,711 Absolutely. 525 00:30:48,805 --> 00:30:51,763 Finding that the amount of energy in space 526 00:30:51,850 --> 00:30:55,217 is so much less than our theory predicts 527 00:30:55,312 --> 00:30:57,849 is not just on academic problem. 528 00:30:57,939 --> 00:31:01,773 The precise strength of that repulsive gravity, well, 529 00:31:01,902 --> 00:31:04,735 that has profound implications for all of us. 530 00:31:04,821 --> 00:31:06,106 For example, 531 00:31:06,198 --> 00:31:08,610 it I were to increase the strength of the darh energy 532 00:31:08,742 --> 00:31:14,829 just a little bit by erasing four or five of these zeroes, 533 00:31:14,956 --> 00:31:17,618 I still have a tiny number, 534 00:31:17,751 --> 00:31:19,992 but the universe would be radically different. 535 00:31:20,128 --> 00:31:23,791 That's because a slightly stronger dark energy 536 00:31:23,924 --> 00:31:28,884 would push everything apart so fast 537 00:31:28,970 --> 00:31:30,585 that stars, planets and galaxies 538 00:31:30,680 --> 00:31:33,012 would never have formed. 539 00:31:33,141 --> 00:31:37,384 And that means we simply would not exist. 540 00:31:37,479 --> 00:31:39,640 And yet here we are. 541 00:31:41,817 --> 00:31:44,229 So, why is the amount of dark energy 542 00:31:44,319 --> 00:31:46,776 so much less than our theory predicts 543 00:31:46,863 --> 00:31:49,650 and also just right to allow the formation 544 00:31:49,783 --> 00:31:52,900 of galaxies, stars, planets and life? 545 00:31:52,994 --> 00:31:55,736 We just don't know. 546 00:31:55,831 --> 00:31:58,163 The mismatch between the theoretical predictions 547 00:31:58,291 --> 00:32:01,203 of dark energy and what astronomers have observed 548 00:32:01,336 --> 00:32:05,500 is one of the great mysteries that science faces today. 549 00:32:06,925 --> 00:32:08,665 But consider this: 550 00:32:08,802 --> 00:32:12,465 If we do live in a multiverse, then the mystery of dark energy 551 00:32:12,556 --> 00:32:17,721 might not be so mysterious after all. 552 00:32:17,853 --> 00:32:20,310 In fact, if we're part at a multiverse, 553 00:32:20,397 --> 00:32:22,479 the value at dark energy we've measured 554 00:32:22,566 --> 00:32:24,978 might actually make total sense. 555 00:32:29,448 --> 00:32:30,403 Hi. 556 00:32:30,532 --> 00:32:31,897 reservation for Greene. 557 00:32:33,618 --> 00:32:37,202 To see how the multiverse might solve the dark energy puzzle, 558 00:32:37,330 --> 00:32:39,241 imagine you're checking into a hotel 559 00:32:39,374 --> 00:32:43,208 and you get a room number like this: 560 00:32:43,295 --> 00:32:45,752 ten million and one. 561 00:32:45,881 --> 00:32:46,745 Hmm 562 00:32:46,882 --> 00:32:48,088 Thanks. 563 00:32:48,216 --> 00:32:49,205 Enjoy your stay. 564 00:32:52,137 --> 00:32:53,468 Ten million and one 565 00:32:53,555 --> 00:32:56,171 would seem like a pretty strange room number, 566 00:32:56,266 --> 00:33:00,054 and getting a room number like this would be surprising, 567 00:33:00,145 --> 00:33:03,137 much as the value of dark energy in our univese 568 00:33:03,231 --> 00:33:05,722 is a number that scientists have found surprising. 569 00:33:05,817 --> 00:33:07,182 But here's the thing: 570 00:33:07,277 --> 00:33:11,065 if this hotel had a huge number of rooms... 571 00:33:16,161 --> 00:33:18,573 say, billions and billions, 572 00:33:18,663 --> 00:33:20,745 then getting room number ten million and one 573 00:33:20,832 --> 00:33:21,992 wouldn't be so surprising. 574 00:33:23,585 --> 00:33:28,420 In a hotel this big, you expect to find a room with that number. 575 00:33:33,637 --> 00:33:36,094 Similarly, if we're part of a multiverse 576 00:33:36,223 --> 00:33:38,259 with a huge number of universes, 577 00:33:38,391 --> 00:33:41,383 each with a different value of the dark energy, 578 00:33:41,478 --> 00:33:43,093 then you'd expect to find one 579 00:33:43,188 --> 00:33:46,180 with the value as small as what we've measured. 580 00:33:46,274 --> 00:33:50,768 If you think of each of these rooms as a universe, 581 00:33:50,862 --> 00:33:53,103 and each universe has a different value 582 00:33:53,198 --> 00:33:54,938 for the dark energy, 583 00:33:55,033 --> 00:33:57,740 then most of these universes won't be hospitable 584 00:33:57,827 --> 00:34:00,068 to life as we know it. 585 00:34:00,163 --> 00:34:03,121 The reason is that the value of the dark energy wouldn't allow 586 00:34:03,250 --> 00:34:06,959 the formation of galaxies, stars and planets. 587 00:34:07,087 --> 00:34:10,830 Universes with much less dark energy than ours 588 00:34:10,966 --> 00:34:13,207 would collapse in on themselves. 589 00:34:15,136 --> 00:34:18,003 And universes with much more dark energy than ours 590 00:34:18,139 --> 00:34:22,257 would expand so fast that matter would never have the chance 591 00:34:22,352 --> 00:34:27,267 to coalesce into clumps and form stars and planets. 592 00:34:27,357 --> 00:34:30,895 So, of course we find ourselves in a universe 593 00:34:30,986 --> 00:34:34,649 where the value of the dark energy is hospitable to life. 594 00:34:34,739 --> 00:34:38,072 Otherwise we woudn't be here to talk about it. 595 00:34:44,165 --> 00:34:46,907 If we're part of a multiverse, 596 00:34:47,002 --> 00:34:50,494 the mystery of dark energy becomes not so mysterious. 597 00:34:52,591 --> 00:34:55,458 But there's a piece of the puzzle missing 598 00:34:55,552 --> 00:34:58,840 How do we know if there's enough diversity within the multiverse 599 00:34:58,972 --> 00:35:01,088 so that every value for dark energy, 600 00:35:01,182 --> 00:35:05,346 including the strange value we observe in our universe, 601 00:35:05,478 --> 00:35:07,343 can be found somewhere? 602 00:35:07,439 --> 00:35:08,724 The answer would emerge 603 00:35:08,857 --> 00:35:13,226 from an entirely different area of physics. 604 00:35:13,361 --> 00:35:15,852 I'm talking about a ground-breaking theory 605 00:35:15,989 --> 00:35:18,696 that comes from investigating the universe 606 00:35:18,825 --> 00:35:20,781 on the tiniest scale. 607 00:35:22,662 --> 00:35:26,325 We know that inside atoms are even tinier bits of matter, 608 00:35:26,416 --> 00:35:27,747 protons and neutrons, 609 00:35:27,876 --> 00:35:32,415 which are made of still smaller particles called quarks. 610 00:35:32,547 --> 00:35:34,959 But physicists realized 611 00:35:35,050 --> 00:35:38,463 that this might not be the end of the line. 612 00:35:38,553 --> 00:35:40,043 These subatomic bits 613 00:35:40,180 --> 00:35:43,593 might actually be made of someting even smaller- 614 00:35:43,725 --> 00:35:50,096 tiny vibrating strands or loops of energy called strings. 615 00:35:50,231 --> 00:35:53,268 This set of ideas, called string theory, 616 00:35:53,401 --> 00:35:56,518 says everythng that exists 617 00:35:56,613 --> 00:35:58,945 is made of this one kind of ingredient. 618 00:36:03,912 --> 00:36:06,403 And just as a single string on a cello 619 00:36:06,539 --> 00:36:09,576 can produce many different notes depending on how it vibrates, 620 00:36:09,668 --> 00:36:12,410 strings can take on different properties 621 00:36:12,545 --> 00:36:14,456 depending on how they vibrate, 622 00:36:14,589 --> 00:36:18,457 creating may kinds of particles. 623 00:36:18,593 --> 00:36:23,553 From this theory came the promise of elegant simplicity: 624 00:36:23,640 --> 00:36:26,882 a single master equation that would explain what we see 625 00:36:26,976 --> 00:36:30,184 in the would around us. 626 00:36:30,271 --> 00:36:33,434 SUSSKND: String theory would be beautiful, it would be elegant, 627 00:36:33,566 --> 00:36:35,852 and calculation from that very simple theory 628 00:36:35,944 --> 00:36:37,900 would produce the world as we know it. 629 00:36:39,781 --> 00:36:44,024 GREENE: But for this beautiful theory to work, there was a catch. 630 00:36:44,119 --> 00:36:45,700 The math of string theory 631 00:36:45,787 --> 00:36:49,405 required something that defies common sense, 632 00:36:49,499 --> 00:36:53,617 a feature that would open the door to the multiverse: 633 00:36:53,753 --> 00:36:56,039 extra dimensions of space. 634 00:36:59,426 --> 00:37:03,089 We're all familiar with three dimensions of space: 635 00:37:03,179 --> 00:37:05,921 height, width and depth. 636 00:37:08,268 --> 00:37:10,304 But the math of string theory 637 00:37:10,395 --> 00:37:13,478 says these aren't the only dimensions. 638 00:37:13,606 --> 00:37:18,817 JOSEPH POLCHINSKI: The mathematics works only if the strings move and vibrate, 639 00:37:18,945 --> 00:37:20,936 not just in the three directions that we see, 640 00:37:21,030 --> 00:37:23,817 but in those and, say, six more- 641 00:37:23,908 --> 00:37:26,024 nine space dimensions in all. 642 00:37:26,161 --> 00:37:29,494 so if string theory is right, 643 00:37:29,622 --> 00:37:32,204 where are these extra dimensions, 644 00:37:32,333 --> 00:37:34,824 and why can't we see them? 645 00:37:34,919 --> 00:37:37,831 Think about the cable supporting a traffic light. 646 00:37:37,964 --> 00:37:41,832 From a distance, it looks like a line, one-dimensional. 647 00:37:41,926 --> 00:37:46,761 But if you could shrink down to, 648 00:37:46,848 --> 00:37:49,180 you'd find another dimension, 649 00:37:49,309 --> 00:37:53,427 a circular dimension that curls around the cable. 650 00:37:53,521 --> 00:37:56,558 And string theory says that if we could shrink down 651 00:37:56,691 --> 00:37:59,774 billions of times smaller than that ant, 652 00:37:59,861 --> 00:38:02,853 we'd find tiny extra dimensions like this 653 00:38:02,989 --> 00:38:06,106 are curled up everywhere in space. 654 00:38:06,201 --> 00:38:08,738 SUSSKIND: At every point of space, 655 00:38:08,870 --> 00:38:11,452 there's extra dimensions of space 656 00:38:11,539 --> 00:38:13,700 that are curled up into little tiny knots 657 00:38:13,792 --> 00:38:16,158 that you can't see because they're too small. 658 00:38:16,252 --> 00:38:19,119 GREENE: And the shape of these extra dimensions 659 00:38:19,214 --> 00:38:23,048 determines the fundamental features of our universe. 660 00:38:23,134 --> 00:38:24,965 Just the way the air streams 661 00:38:25,053 --> 00:38:27,715 that are going through an instrument like a French horn 662 00:38:27,847 --> 00:38:29,337 have vibrational patterns 663 00:38:29,432 --> 00:38:32,720 that are determined by the shape of the instrument, 664 00:38:32,852 --> 00:38:34,058 the shape at the extra dimensions 665 00:38:34,187 --> 00:38:36,223 determins how the little strings vibrate. 666 00:38:36,314 --> 00:38:40,557 Those vibrational patterns determine particle properties, 667 00:38:40,652 --> 00:38:44,144 so all of the fundamental features of our universe 668 00:38:44,239 --> 00:38:48,858 may be determiend by the shape of the extra dimensions. 669 00:38:48,952 --> 00:38:53,571 SUSSKIND: The way those extra dimensions of space are put together 670 00:38:53,665 --> 00:38:59,706 is in many respects like the DNA of the universe. 671 00:38:59,796 --> 00:39:03,505 They determine the way the universe is going to behave, 672 00:39:03,591 --> 00:39:05,377 just exactly the same way 673 00:39:05,468 --> 00:39:08,756 as DNA determines the way an animal is going to look. 674 00:39:08,847 --> 00:39:12,431 GREENE: The problem was, the more string thearists looked, 675 00:39:12,559 --> 00:39:14,925 the more ways they found that extra dimensions 676 00:39:15,019 --> 00:39:16,725 could be curled up. 677 00:39:16,813 --> 00:39:18,599 And the math provided no clues 678 00:39:18,731 --> 00:39:21,063 as to which shape was the right one 679 00:39:21,150 --> 00:39:23,562 corresponding to our universe. 680 00:39:23,653 --> 00:39:25,689 SHAMIT KACHRU: I think the consensus right now 681 00:39:25,780 --> 00:39:28,271 is that that number seems to be astronomical. 682 00:39:28,408 --> 00:39:29,693 There are published papers 683 00:39:29,784 --> 00:39:32,366 suggesting upwards of 10 the 500- 684 00:39:32,453 --> 00:39:36,037 that's 10 followed by 500 zeroes- 685 00:39:36,124 --> 00:39:37,284 different possible shapes. 686 00:39:39,627 --> 00:39:42,289 GREENE: Ten to the 500 different possible shapes 687 00:39:42,422 --> 00:39:48,167 for the extra dimensions, each appearing equally valid. 688 00:39:48,303 --> 00:39:51,966 It seemed preposterous. 689 00:39:52,056 --> 00:39:53,466 Especelly for a theory 690 00:39:53,558 --> 00:39:56,550 that was looking for one, single master equation 691 00:39:56,644 --> 00:39:58,350 to describe our universe. 692 00:40:06,571 --> 00:40:08,903 But then it occurred to some string theorists 693 00:40:08,990 --> 00:40:11,231 that perhaps there was a different way 694 00:40:11,326 --> 00:40:14,489 to look at the problem, and this different perspective 695 00:40:14,621 --> 00:40:19,411 would breathe new life into the idea of a multiverse. 696 00:40:19,500 --> 00:40:22,333 Ten to the 500 different string theories. 697 00:40:22,420 --> 00:40:26,754 This sounded like a complete disaster. 698 00:40:26,841 --> 00:40:28,923 What good is it to have a theory 699 00:40:29,010 --> 00:40:31,877 that has ten to the 500 solutions? 700 00:40:32,013 --> 00:40:34,504 You can't find anything in there. 701 00:40:34,641 --> 00:40:36,848 well, that left string theorists 702 00:40:36,935 --> 00:40:40,519 somewhat unhappy, somewhat depressed. 703 00:40:40,605 --> 00:40:43,017 My own reaction to it at the time is, "This is great. 704 00:40:43,107 --> 00:40:44,392 "This is fantastic. 705 00:40:44,525 --> 00:40:47,642 "This is exactly what the cosmologists are looking for: 706 00:40:47,737 --> 00:40:50,524 "enormous diversity of possibilities. 707 00:40:50,615 --> 00:40:52,651 "Don't be unhappy about this. 708 00:40:52,742 --> 00:40:54,403 "That says that string theory 709 00:40:54,535 --> 00:40:57,402 "fits extremely well with cosmology 710 00:40:57,538 --> 00:41:00,200 and with all the interesting ideas about multiverses." 711 00:41:01,834 --> 00:41:05,418 GREENE: Turning what seemed like a vice into a virtue, 712 00:41:05,546 --> 00:41:08,003 some string theorists became convinced 713 00:41:08,091 --> 00:41:10,548 that the multiple solutions of string theory 714 00:41:10,677 --> 00:41:15,671 might each represent a real and very different universe. 715 00:41:15,765 --> 00:41:20,384 In other words, string theory was describing a multiverse- 716 00:41:20,478 --> 00:41:24,141 and an extremely diverse one at that. 717 00:41:24,232 --> 00:41:27,065 JOHNSON: To everyone's surprise, 718 00:41:27,193 --> 00:41:29,775 string theory was actually quite readily describing 719 00:41:29,904 --> 00:41:33,192 huge numbers of different kinds of solutions, 720 00:41:33,282 --> 00:41:37,400 each of which corresponds to a possible universe. 721 00:41:37,495 --> 00:41:40,362 So we just got this multiverse for free. 722 00:41:40,456 --> 00:41:44,119 DELIA SCHWAETZ-PEELOV: Both from string theory and from inflation, 723 00:41:44,252 --> 00:41:47,415 you have these universes that are produced. 724 00:41:47,547 --> 00:41:50,505 These different univeses would all naturally have 725 00:41:50,591 --> 00:41:53,253 different amounts of dark energy. 726 00:41:53,386 --> 00:41:58,471 GREENE: In fact, according to the math, the amount of dark energy 727 00:41:58,599 --> 00:42:02,763 would span such a wide range of values from universe to universe 728 00:42:02,854 --> 00:42:07,939 that the strange amount we've measured would surely turn up. 729 00:42:08,067 --> 00:42:12,106 String theory, without even trying, solved that problem. 730 00:42:12,238 --> 00:42:16,277 GREENE: So, over a decade after Linde and Vilenkin 731 00:42:16,367 --> 00:42:19,404 had come up with their ideas about eternal inflation, 732 00:42:19,495 --> 00:42:20,951 the multiverse was revived. 733 00:42:24,125 --> 00:42:27,208 Three lines of reasoning were now all pointing 734 00:42:27,295 --> 00:42:30,253 to the same conclusion: 735 00:42:30,339 --> 00:42:36,926 enternal inflation, dark energy and string theory. 736 00:42:37,013 --> 00:42:40,426 Just the way it takes three legs to support a stool, 737 00:42:40,516 --> 00:42:44,304 these three ideas taken together support the argument 738 00:42:44,395 --> 00:42:47,637 that we may live in a multiverse. 739 00:42:47,732 --> 00:42:52,943 When different lines of research all converge on one idea, 740 00:42:53,029 --> 00:42:54,394 that doesn't mean it's right, 741 00:42:54,489 --> 00:42:58,983 but when all the spokes of the wheel are pointing at one idea, 742 00:42:59,118 --> 00:43:01,154 that idea becomes pretty convincing. 743 00:43:02,747 --> 00:43:07,582 Today the multiverse is hotly debated. 744 00:43:07,668 --> 00:43:10,330 Many critics remain. 745 00:43:10,421 --> 00:43:13,879 David Grace is going to tell us, "No, no, no." 746 00:43:14,008 --> 00:43:15,999 GREENE: But mutiverse advocates 747 00:43:16,135 --> 00:43:22,176 like Alex Vilenkin, Alan Guth and Andrei Linde 748 00:43:22,266 --> 00:43:24,382 are no longer alone. 749 00:43:24,519 --> 00:43:26,555 VILENKIN: The tide appears to be turning. 750 00:43:26,687 --> 00:43:30,145 Now these ideas are accepted to a much larger degree. 751 00:43:30,233 --> 00:43:32,349 The genie is out of the bottle. 752 00:43:32,443 --> 00:43:34,604 You cannot put it back. 753 00:43:37,698 --> 00:43:39,939 GREENE: So, what would it be like? 754 00:43:40,034 --> 00:43:42,650 if we could travel to some of these other universes, 755 00:43:42,745 --> 00:43:44,701 what would we see? 756 00:43:47,708 --> 00:43:52,202 Some might be vastly different from our own, 757 00:43:52,338 --> 00:43:54,829 with properties unlike anything we've ever seen. 758 00:43:58,803 --> 00:44:02,887 In fact, some universes in the multiverse 759 00:44:02,974 --> 00:44:07,809 might not have light or matter or anything recognizable at all. 760 00:44:13,234 --> 00:44:16,067 And there might be other universes with features 761 00:44:16,154 --> 00:44:19,362 not unlike the familiar ones we know, 762 00:44:19,448 --> 00:44:22,155 but where life takes a completely different form, 763 00:44:22,243 --> 00:44:25,906 Perhaps communicating in ways we'd find utterly bizarre. 764 00:44:28,749 --> 00:44:30,080 And the math shows 765 00:44:30,209 --> 00:44:33,872 that if we were able to visit enough of these universes, 766 00:44:33,963 --> 00:44:36,454 we might eventually find ones like ours, 767 00:44:36,591 --> 00:44:42,086 with a Miky Way galaxy, a solar system and an Earth. 768 00:44:42,180 --> 00:44:45,013 Except with some slight differences. 769 00:44:45,099 --> 00:44:47,260 In one, maybe the asteroid 770 00:44:47,393 --> 00:44:54,890 that killed off the dinosaurs 65 million years ago missed, 771 00:44:54,984 --> 00:44:57,316 and evolution charted a new course. 772 00:45:04,660 --> 00:45:07,322 In another, there might be an Earth 773 00:45:07,455 --> 00:45:09,320 with people similar to us... 774 00:45:09,457 --> 00:45:11,118 (phone ringing) 775 00:45:11,209 --> 00:45:15,373 ...but better at multitasking. 776 00:45:15,463 --> 00:45:19,547 But there's someting even stranger. 777 00:45:19,634 --> 00:45:21,124 Somewhere out there, 778 00:45:21,260 --> 00:45:23,376 we should find exact copies of our universe 779 00:45:23,471 --> 00:45:27,840 with duplicates of everything and everyone. 780 00:45:31,729 --> 00:45:33,640 How could this be? 781 00:45:33,731 --> 00:45:36,689 How could there be exact duplicates of ourselves 782 00:45:36,817 --> 00:45:39,650 out there in the multiverse? 783 00:45:39,737 --> 00:45:43,821 To see how, take this deck of cards. 784 00:45:43,908 --> 00:45:46,945 It's made up of 52 different cards, 785 00:45:47,036 --> 00:45:51,530 and if I deal them, everyone will get a different hand. 786 00:45:51,666 --> 00:45:56,581 But, over the course of many, many rounds, 787 00:45:56,671 --> 00:45:59,333 eventually some of the combinations 788 00:45:59,423 --> 00:46:03,541 will start to repeat. 789 00:46:03,678 --> 00:46:05,339 That's because with 52 cards, 790 00:46:05,471 --> 00:46:08,178 there's a limited number of different hands you can deal. 791 00:46:08,266 --> 00:46:11,474 So if you deal the cards an infinite number of times, 792 00:46:11,560 --> 00:46:14,552 then repeating hands are inevitable. 793 00:46:14,689 --> 00:46:18,477 And in the multiverse, a similar principle applies. 794 00:46:20,319 --> 00:46:23,356 That's because, according to the laws of nature, 795 00:46:23,489 --> 00:46:26,572 the fundamental ingredients of matter, or particles, 796 00:46:26,701 --> 00:46:29,192 are kind of like a deck of cards: 797 00:46:29,287 --> 00:46:32,620 in any region of space, they can only be arranged 798 00:46:32,707 --> 00:46:35,164 in a finite number of different ways. 799 00:46:35,251 --> 00:46:38,038 So if space is infinite, 800 00:46:38,129 --> 00:46:40,791 if there are an infinite number of universes, 801 00:46:40,881 --> 00:46:43,543 then those arrangements are bound to repeat. 802 00:46:43,676 --> 00:46:46,042 And since each one of us 803 00:46:46,137 --> 00:46:49,721 is just a particular arrangement of particles, 804 00:46:49,807 --> 00:46:53,516 somewhere there's a duplicate of you and me 805 00:46:53,602 --> 00:46:56,685 and everyone else. 806 00:46:56,772 --> 00:46:59,354 This can be shocking. 807 00:46:59,442 --> 00:47:00,852 It could be that in another universe 808 00:47:00,943 --> 00:47:03,229 I was a rock star and my life much better. 809 00:47:03,321 --> 00:47:05,733 Or much worse, depending on your opinion of rock stars. 810 00:47:05,865 --> 00:47:08,982 It means all those things that I've never found time to do 811 00:47:09,076 --> 00:47:12,489 are maybe being done by some copy of me somewhere else. 812 00:47:12,580 --> 00:47:15,413 I was rather depressed, actually. 813 00:47:15,499 --> 00:47:17,911 This picture robs us of our uniqueness. 814 00:47:18,044 --> 00:47:19,625 It is a consequence of the ideas, 815 00:47:19,754 --> 00:47:22,291 and the ideas seem very well motivated. 816 00:47:24,759 --> 00:47:26,420 GREENE: Yet critics argue 817 00:47:26,552 --> 00:47:29,419 the multiverse is just too convenient an explanation 818 00:47:29,555 --> 00:47:31,921 for thing we don't understand, 819 00:47:32,058 --> 00:47:34,595 like the tiny value of dark energy in our univese 820 00:47:34,727 --> 00:47:36,843 and the huge number of possible shapes 821 00:47:36,937 --> 00:47:39,929 for the extra dimensions in string theory. 822 00:47:40,066 --> 00:47:41,772 STEINHAEDT: The problem with that kind of reasoning 823 00:47:41,901 --> 00:47:43,266 is that it doesn't explain 824 00:47:43,402 --> 00:47:45,438 why the dark energy is the way it is. 825 00:47:45,571 --> 00:47:47,937 It just says it's random chance. 826 00:47:48,032 --> 00:47:50,114 I don't find that satisfactory. 827 00:47:50,242 --> 00:47:53,234 You can apply this kind of reasoning 828 00:47:53,329 --> 00:47:55,695 any time you don't have a better explanation. 829 00:47:57,541 --> 00:47:59,953 GREENE: On the other hand, supportesrs of the multiverse 830 00:48:00,086 --> 00:48:03,419 point out that sometimes a better or depper explanation 831 00:48:03,506 --> 00:48:08,091 for the way things are simply does not exist. 832 00:48:08,177 --> 00:48:12,011 Take, for example, the Earth's orbit around the Sun. 833 00:48:12,139 --> 00:48:15,802 We find ourselves at a distance of 93 million miles, 834 00:48:15,893 --> 00:48:18,100 perfect for life. 835 00:48:18,187 --> 00:48:20,803 If we were much closer to the Sun, 836 00:48:20,898 --> 00:48:25,767 our planet would be too hot for life as we know it to exist. 837 00:48:28,030 --> 00:48:30,316 And if we were much farther from the Sun, 838 00:48:30,449 --> 00:48:34,943 it would be too cold for life. 839 00:48:35,037 --> 00:48:37,995 So, why are we in this sweet spot? 840 00:48:40,000 --> 00:48:41,831 Well, starting in the late 1500s, 841 00:48:41,919 --> 00:48:47,334 the famous astronomer Jonannes Kepler asked that very question, 842 00:48:47,425 --> 00:48:50,883 and he spent years trying to find a physical reason, 843 00:48:51,011 --> 00:48:53,127 some law of nature 844 00:48:53,222 --> 00:48:58,933 that requires the Earth to be 93 million miles from the Sun. 845 00:48:59,019 --> 00:49:03,513 But Kepler never found it, because it doesn't exist. 846 00:49:03,649 --> 00:49:07,517 There isn't any physical law requiring the Earth to be 847 00:49:07,653 --> 00:49:10,019 93 million miles from the Sun. 848 00:49:10,114 --> 00:49:14,153 It's simply one possibility of the many you'd expect to find 849 00:49:14,243 --> 00:49:18,987 in a universe we know is full of solar systems. 850 00:49:19,081 --> 00:49:21,948 SUSSKIND: You might think it was an extraordinary accident. 851 00:49:22,042 --> 00:49:23,327 It's not. 852 00:49:23,419 --> 00:49:25,751 It's just that there are a lot of planets out there. 853 00:49:25,880 --> 00:49:30,499 GREENE: Similarly, some suggest that the true explanation 854 00:49:30,593 --> 00:49:34,006 for many of the fundamental features of our world 855 00:49:34,096 --> 00:49:38,135 will elude us if we don't consider the possibility 856 00:49:38,225 --> 00:49:41,934 that we live in a multiverse. 857 00:49:42,062 --> 00:49:44,223 GUTH: Clearly if we had a good physical reason, 858 00:49:44,315 --> 00:49:46,351 that would be great and we would understand it. 859 00:49:46,442 --> 00:49:47,397 We'd be much happier. 860 00:49:47,485 --> 00:49:49,066 We may have to live with that. 861 00:49:49,195 --> 00:49:53,234 There's no principle built into the laws of nature 862 00:49:53,324 --> 00:49:57,909 that say that theoretical physicists have to be happy. 863 00:49:58,037 --> 00:50:00,028 It's a hypothesis. 864 00:50:00,122 --> 00:50:01,908 It's the leading hypothesis 865 00:50:01,999 --> 00:50:04,741 because nobody has another hypothesis 866 00:50:04,877 --> 00:50:06,162 which makes as much sense. 867 00:50:09,507 --> 00:50:14,092 GREENE: The multiverse, a tantalizing possibility. 868 00:50:14,178 --> 00:50:18,467 But with no experimental evidence, should you belivee it? 869 00:50:18,599 --> 00:50:20,590 We can't believe in anything 870 00:50:20,726 --> 00:50:23,968 until there's observational or experimental support. 871 00:50:24,104 --> 00:50:27,312 But what we have found over the last few centuries 872 00:50:27,441 --> 00:50:31,104 is that mathematics provides a sure-footed guide 873 00:50:31,237 --> 00:50:32,943 to the nature of things 874 00:50:33,030 --> 00:50:36,648 that we haven't yet been able to see, observe or experiment with. 875 00:50:36,784 --> 00:50:40,743 Math predicted things like black holes 876 00:50:40,829 --> 00:50:42,865 and certain subatomic particles 877 00:50:42,957 --> 00:50:46,165 long before we ever observed them. 878 00:50:46,293 --> 00:50:48,204 And math is suggesting 879 00:50:48,295 --> 00:50:50,877 that there may be these other universes. 880 00:50:50,965 --> 00:50:54,799 That doesn't mean it's right, but often it's leading you 881 00:50:54,927 --> 00:50:57,919 to a deeper understanding of reality. 882 00:50:58,013 --> 00:51:00,800 If you choose not to believe it, that's perfectly fine, 883 00:51:00,933 --> 00:51:03,800 because we have not given you any evidence yet, 884 00:51:03,936 --> 00:51:06,678 and one of the wonderful things about science 885 00:51:06,814 --> 00:51:09,430 is it's about evidence; it's not about belief. 886 00:51:09,525 --> 00:51:13,985 GREENE: And some scientists now think we might just be able 887 00:51:14,071 --> 00:51:16,312 to find that evidence. 888 00:51:16,407 --> 00:51:18,864 They propose that if our universe and another 889 00:51:18,993 --> 00:51:20,858 were born close together, 890 00:51:20,995 --> 00:51:23,452 the two might have collided. 891 00:51:26,417 --> 00:51:29,909 That collision could have left its own telltale sign 892 00:51:30,004 --> 00:51:32,746 in the form of a pattern of temperature differences 893 00:51:32,840 --> 00:51:36,833 that we might detect in the cosmic background radiation, 894 00:51:36,927 --> 00:51:41,170 the heat left over from the Big Bang. 895 00:51:41,265 --> 00:51:42,880 My guess is yes, that in 100 years 896 00:51:43,017 --> 00:51:45,929 we will know one way or another whether these ideas are right. 897 00:51:46,020 --> 00:51:47,510 A hundred years from now 898 00:51:47,605 --> 00:51:50,187 it may be an amusing historical episode. 899 00:51:50,274 --> 00:51:51,639 We don't know. 900 00:51:53,068 --> 00:51:54,683 But if you only work on the things 901 00:51:54,820 --> 00:51:56,435 that are already well established, 902 00:51:56,530 --> 00:51:59,738 you're not going to be part of the next big excitement. 903 00:52:01,493 --> 00:52:05,361 GREENE: If we do verify the multiverse, it would change our perspective 904 00:52:05,456 --> 00:52:09,870 much as Copernicus did 500 years ago when he showed 905 00:52:10,002 --> 00:52:13,460 that the Earth is not the center of the cosmos. 906 00:52:13,547 --> 00:52:17,881 And some might say that if our universe is just one of many 907 00:52:18,010 --> 00:52:22,344 our descent from the center would be complete. 908 00:52:22,431 --> 00:52:24,387 SCHWARTZ-PERLOV: Regardless, I think it's more important 909 00:52:24,475 --> 00:52:28,684 just that we're so lucky that we can understand the universe. 910 00:52:28,771 --> 00:52:30,727 I think it's a great ride, 911 00:52:30,814 --> 00:52:32,520 and I think it's really good for physics 912 00:52:32,608 --> 00:52:34,018 that we have this tension. 913 00:52:34,109 --> 00:52:36,065 I don't know where we're going to end up. 914 00:52:39,573 --> 00:52:43,031 GREENE: So, what does this all mean? 915 00:52:43,118 --> 00:52:45,109 Are there infinite duplicates 916 00:52:45,245 --> 00:52:49,705 of you and me and everything existing right now 917 00:52:49,792 --> 00:52:52,579 in an infinite number of other universes? 918 00:52:55,422 --> 00:52:59,085 Is the multiverse the next Copernican revolution? 919 00:52:59,218 --> 00:53:02,631 We don't know at least not yet. 920 00:53:02,763 --> 00:53:06,347 But if the idea that we live in a multiverse proves true, 921 00:53:06,433 --> 00:53:08,674 we'd be witnessing one of the most exciting 922 00:53:08,769 --> 00:53:10,475 and dramatic upheavals 923 00:53:10,604 --> 00:53:14,267 to our understanding of the fabric of the cosmos. 924 00:53:26,370 --> 00:53:28,861 Major funding for NOVA is provided by: 925 00:53:31,291 --> 00:53:32,656 And... 926 00:53:43,470 --> 00:53:46,837 And by the Corporation for Public Broadcasting 927 00:53:46,974 --> 00:53:51,138 and by contributions to you PBS station from: 928 00:53:57,776 --> 00:54:00,358 Major funding for "The Fabric of the Cosmos" 929 00:54:00,487 --> 00:54:03,149 is provided by the National Science Foundation. 930 00:54:10,914 --> 00:54:12,450 And... 931 00:54:15,502 --> 00:54:18,335 Supporting original research and public understanding 932 00:54:18,422 --> 00:54:24,292 of science, technology, engineering and mathematics. 933 00:54:24,386 --> 00:54:26,297 Additional funding is provided by... 934 00:54:38,192 --> 00:54:40,183 And the George D. 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