1 00:00:09,060 --> 00:00:10,740 There's an idea, once thought 2 00:00:10,740 --> 00:00:15,586 so radical that just mentioning it was considered pure insanity. 3 00:00:20,390 --> 00:00:24,463 But now, these scientists are daring to believe it's actually true. 4 00:00:25,900 --> 00:00:30,620 They think that our universe is not alone. 5 00:00:30,620 --> 00:00:35,216 It's just one of an infinite number of weird and wonderful worlds. 6 00:00:36,770 --> 00:00:39,740 Some, where life is familiar. 7 00:00:39,740 --> 00:00:42,971 Others, where things turned out a little differently. 8 00:00:44,410 --> 00:00:47,660 The dinosaur-killing asteroid, that was our lucky break, 9 00:00:47,660 --> 00:00:52,740 missed Earth, so there are no humans, just dinosaurs in Winchester today. 10 00:00:52,740 --> 00:00:56,410 Some of these worlds are so strange that the laws of nature no 11 00:00:56,410 --> 00:00:57,854 Ionger apply. 12 00:01:00,250 --> 00:01:02,740 So these students might, for example, be going to 13 00:01:02,740 --> 00:01:05,851 class in five dimensions, rather than four dimensions. 14 00:01:05,851 --> 00:01:08,900 Or they might be talking about a whole different force, 15 00:01:08,900 --> 00:01:11,300 the blue force, that we don't have in our universe. 16 00:01:13,340 --> 00:01:17,410 In others, infinite copies of you are playing out every 17 00:01:17,410 --> 00:01:20,290 possible storyline of your life. 18 00:01:20,290 --> 00:01:24,101 So, I every time I flip a coin, say heads or tails, that is 19 00:01:24,101 --> 00:01:26,650 just some little quantum accident. 20 00:01:26,650 --> 00:01:30,340 The universe is splitting into two worlds. 21 00:01:30,340 --> 00:01:33,380 It sounds like a plot stolen straight from Hollywood, 22 00:01:33,380 --> 00:01:37,130 but some scientists think they've actually found the evidence 23 00:01:37,130 --> 00:01:39,981 to prove the theory is true. 24 00:01:39,981 --> 00:01:45,250 I was so elated and happy and couldn't believe my eyes that 25 00:01:45,250 --> 00:01:48,651 I allowed myself for a few minutes to jump up and down. 26 00:01:57,971 --> 00:02:01,450 And if these scientists are right, the question isn't 27 00:02:01,450 --> 00:02:06,308 whether multiple universes exist, it's which one are we in? 28 00:02:21,460 --> 00:02:25,368 Ever since we've been studying the night sky, we've been able to 29 00:02:25,368 --> 00:02:29,658 rely on one simple idea to describe everything around us, 30 00:02:29,658 --> 00:02:35,298 everything on Earth and beyond, all the planets, all the stars 31 00:02:35,298 --> 00:02:36,651 and all the galaxies. 32 00:02:40,768 --> 00:02:43,657 This idea is what we call "our universe". 33 00:02:48,658 --> 00:02:53,138 The universe as one beautiful unique thing, the sum total of all 34 00:02:53,138 --> 00:02:56,301 the stuff we can see and everything we know about. 35 00:02:57,498 --> 00:03:03,018 And for a long, long time, we've been pretty happy with this idea. 36 00:03:03,018 --> 00:03:04,747 It makes total sense. 37 00:03:11,538 --> 00:03:14,538 But recently, a few inconvenient 38 00:03:14,538 --> 00:03:16,368 scientists are finding flaws 39 00:03:16,368 --> 00:03:18,711 with this long-cherished idea. 40 00:03:21,098 --> 00:03:24,298 In fact, they think it's time to throw the whole notion out 41 00:03:24,298 --> 00:03:25,583 the window. 42 00:03:35,778 --> 00:03:39,618 For cosmologists, the universe extends to the furthest point from 43 00:03:39,618 --> 00:03:43,968 which light has had time to reach us, since the beginning of time. 44 00:03:43,968 --> 00:03:47,788 It's what we call the Observable Universe, 45 00:03:47,788 --> 00:03:49,983 beautifully captured in this one image. 46 00:04:00,428 --> 00:04:03,658 This is what we affectionately call "our universe", 47 00:04:03,658 --> 00:04:07,008 this spherical region of space from which light has the time to 48 00:04:07,008 --> 00:04:11,650 reach us so far, during the 13.8 billion years since our Big Bang. 49 00:04:15,148 --> 00:04:18,949 You can ask - is that really everything that is or is this 50 00:04:18,949 --> 00:04:21,178 just everything we can see? 51 00:04:21,178 --> 00:04:24,178 And we've come a long way in cosmology to a point where we 52 00:04:24,178 --> 00:04:27,378 have pretty strong evidence that the actual universe, 53 00:04:27,378 --> 00:04:30,258 the whole universe, is much, much bigger than this. 54 00:04:30,258 --> 00:04:33,949 It's hard to imagine how we cannot ask the question - what is 55 00:04:33,949 --> 00:04:38,227 beyond the walls of this object and what was there before the Big Bang? 56 00:04:41,939 --> 00:04:45,418 So, although I think this is everything that we can observe, 57 00:04:45,418 --> 00:04:49,088 I don't think this is everything that exists. 58 00:04:49,088 --> 00:04:52,578 So, this may really only be just 59 00:04:52,578 --> 00:04:55,258 a small part of something that, 60 00:04:55,258 --> 00:04:58,182 you know, is really much, much bigger. 61 00:05:00,939 --> 00:05:04,788 So this universe, stretching out 13.8 billion light 62 00:05:04,788 --> 00:05:10,018 years into space, is a beautiful thing, but it's not the only thing. 63 00:05:10,018 --> 00:05:11,898 So I'm afraid, universe, 64 00:05:11,898 --> 00:05:15,578 it's time for you to retire as the only thing out there. 65 00:05:15,578 --> 00:05:18,458 You've had a good run, given us a lot of good times, 66 00:05:18,458 --> 00:05:20,328 but it's time to go. 67 00:05:20,328 --> 00:05:23,738 Why don't you just go down to Florida and buy a condo? 68 00:05:23,738 --> 00:05:25,182 A very large condo. 69 00:05:36,819 --> 00:05:41,051 Sending the universe into retirement might seem like a bad joke, 70 00:05:43,538 --> 00:05:45,618 but for these scientists, 71 00:05:45,618 --> 00:05:51,158 the idea of just one universe simply doesn't make sense. 72 00:05:59,618 --> 00:06:02,949 They are convinced that for different reasons, 73 00:06:02,949 --> 00:06:06,533 our universe is just one of an infinite number of others. 74 00:06:11,658 --> 00:06:16,118 One universe in a vast, vast multiverse. 75 00:06:22,408 --> 00:06:24,819 # If I was a flower growing wild and free 76 00:06:24,819 --> 00:06:27,498 # All I'd want is you to be my sweet honey bee 77 00:06:27,498 --> 00:06:30,218 # And if I was a tree growing tall and green 78 00:06:30,218 --> 00:06:31,378 # All I'd want is... # 79 00:06:31,378 --> 00:06:35,338 The maths is devilishly complicated, but they stem from questions 80 00:06:35,338 --> 00:06:37,888 so simple, a child could ask them. 81 00:06:37,888 --> 00:06:40,664 So, where does the universe really end? 82 00:06:48,819 --> 00:06:51,689 Max Tegmark is a professor of cosmology. 83 00:06:51,689 --> 00:06:55,058 When he isn't playing Lego, he spends his time contemplating 84 00:06:55,058 --> 00:06:59,028 some of the big questions about life, the universe and everything. 85 00:07:01,028 --> 00:07:04,100 # All I'd want is you to shade me and be my leaves... # 86 00:07:06,258 --> 00:07:10,388 And there's one particular question that's been bothering him. 87 00:07:10,388 --> 00:07:15,748 Is there an end to space? Or does it go on for ever? 88 00:07:15,748 --> 00:07:17,878 When I was a little kid, 89 00:07:17,878 --> 00:07:21,978 I used to wonder whether space went on for ever and I used to think 90 00:07:21,978 --> 00:07:26,898 - it has to be infinite, because it would be silly for it to have an end. 91 00:07:26,898 --> 00:07:31,628 Would there be a sign there, saying 'Warning, space ends here. 92 00:07:31,628 --> 00:07:35,519 'Mind the gap'? And if so, what's on the other side? 93 00:07:37,748 --> 00:07:41,378 So we don't have a shred of evidence suggesting that space actually 94 00:07:41,378 --> 00:07:43,949 ends here, exactly at the edge of what we can see 95 00:07:43,949 --> 00:07:47,809 and I don't have a single colleague in physics either who believes that. 96 00:07:47,809 --> 00:07:50,898 It would be a little bit like believing if you're 97 00:07:50,898 --> 00:07:54,338 in the boat in the ocean, that the ocean ends exactly at your horizon. 98 00:07:54,338 --> 00:07:56,101 Why should it? 99 00:07:57,668 --> 00:08:01,528 The idea that space goes on for ever seems simple enough. 100 00:08:01,528 --> 00:08:06,261 But this relatively straightforward concept has profound implications. 101 00:08:08,338 --> 00:08:11,338 Just as this house is made out of fundamental building 102 00:08:11,338 --> 00:08:14,819 blocks that we call Legos, everything in our world is 103 00:08:14,819 --> 00:08:18,588 made of fundamental building blocks we call elementary particles. 104 00:08:18,588 --> 00:08:21,418 And if you have some random process, 105 00:08:21,418 --> 00:08:25,338 arranging elementary building blocks in a finite volume, there 106 00:08:25,338 --> 00:08:29,178 are of course very many different ways in which it could do this. 107 00:08:29,178 --> 00:08:32,128 And that means that if this process repeats, 108 00:08:32,128 --> 00:08:35,178 and an infinite number of other volumes of the same size, 109 00:08:35,178 --> 00:08:37,388 then we're guaranteed that eventually, 110 00:08:37,388 --> 00:08:39,982 it's going to create every possible arrangement. 111 00:08:44,618 --> 00:08:48,908 According to Max, and the hard and fast laws of probability, 112 00:08:48,908 --> 00:08:52,898 our universe is one of an infinite number of others, 113 00:08:52,898 --> 00:08:55,898 each one about 90 billion light years across 114 00:08:55,898 --> 00:08:59,778 and each containing a finite number of particles. 115 00:08:59,778 --> 00:09:04,898 And just like Max, if you assembly these Lego bricks enough times, 116 00:09:04,898 --> 00:09:08,418 you'll create every possible variation of them, 117 00:09:08,418 --> 00:09:12,778 eventually ending up with two model houses exactly the same. 118 00:09:12,778 --> 00:09:16,898 Likewise, rearrange the particles in the universe often enough 119 00:09:16,898 --> 00:09:22,488 and you end up with an identical universe and an identical Earth. 120 00:09:22,488 --> 00:09:28,898 And even a Max over there who is identical to me, not just 121 00:09:28,898 --> 00:09:34,258 in his physical appearance, but in that he actually feels that he is me. 122 00:09:34,258 --> 00:09:39,768 So, the answer to Max's question of what's at the edge of space 123 00:09:39,768 --> 00:09:43,618 Ieads unavoidably to a world where other universes are not only 124 00:09:43,618 --> 00:09:46,781 Iikely, but are a mathematical certainty. 125 00:09:49,488 --> 00:09:52,548 But there's another idea that questions our unique 126 00:09:52,548 --> 00:09:54,061 place in the cosmos. 127 00:09:56,468 --> 00:10:00,178 This time, it's based not on a question of where space ends, 128 00:10:00,178 --> 00:10:02,988 but rather, how did it all begin? 129 00:10:17,699 --> 00:10:21,308 Professor Anthony Aguirre has been grappling with the sticky 130 00:10:21,308 --> 00:10:24,277 matter of the origins of our universe. 131 00:10:28,188 --> 00:10:31,498 And his attempts to find answers lead to a completely 132 00:10:31,498 --> 00:10:33,557 different sort of multiverse. 133 00:10:40,188 --> 00:10:43,418 This picture is actually something pretty amazing. 134 00:10:43,418 --> 00:10:45,978 It's a picture of our observable universe, 135 00:10:45,978 --> 00:10:48,699 just a couple of hundred thousand years after what 136 00:10:48,699 --> 00:10:51,858 we call the Big Bang and it's a picture that's been 137 00:10:51,858 --> 00:10:56,138 taken in what's called the cosmic microwave background radiation. 138 00:10:56,138 --> 00:10:59,709 This is radiation that's come to us to telescopes like this one 139 00:10:59,709 --> 00:11:04,978 and many others since and it gives us an actual image 140 00:11:04,978 --> 00:11:08,835 of what the state of the universe was like at incredibly early times. 141 00:11:11,898 --> 00:11:15,699 The image, which depicts both the edge of the universe as well as the 142 00:11:15,699 --> 00:11:20,848 earliest light we can see, revealed that all the matter in the universe, 143 00:11:20,848 --> 00:11:25,046 all the stars and all the galaxies, were very evenly distributed. 144 00:11:25,978 --> 00:11:29,687 It suggested something happened to make it that way. 145 00:11:31,709 --> 00:11:36,188 And that something is a process called inflation. 146 00:11:36,188 --> 00:11:38,498 The theory of inflation is that early on, 147 00:11:38,498 --> 00:11:42,488 the universe didn't just expand, but it expanded exponentially, 148 00:11:42,488 --> 00:11:45,949 meaning it doubled in size over and over again in a very small 149 00:11:45,949 --> 00:11:47,618 fraction of a second. 150 00:11:47,618 --> 00:11:53,218 Now, what this did was it took a pattern of variations 151 00:11:53,218 --> 00:11:57,468 in the density of the universe, the same pattern we see now, and it took 152 00:11:57,468 --> 00:12:01,108 it from a tiny size and stretched it over the entire observable universe. 153 00:12:05,188 --> 00:12:08,748 According to inflation, while our universe was just a hot 154 00:12:08,748 --> 00:12:12,978 pool of fire, the very fabric of space inflated. 155 00:12:12,978 --> 00:12:15,768 It was so rapid that that the uniformity of the baby 156 00:12:15,768 --> 00:12:17,178 universe was preserved. 157 00:12:19,468 --> 00:12:24,058 But for Anthony, inflation was more than just a method of expansion. 158 00:12:24,058 --> 00:12:28,699 It was a driving force that created our universe in the first place and 159 00:12:28,699 --> 00:12:33,128 if it could happen once, there was nothing to stop it happening again. 160 00:12:33,128 --> 00:12:34,498 And again. 161 00:12:34,498 --> 00:12:35,783 And again. 162 00:12:38,218 --> 00:12:41,348 This is eternal inflation. 163 00:12:41,348 --> 00:12:46,478 So inflation was a little bit like a genie that you let out of a bottle. 164 00:12:46,478 --> 00:12:50,188 You open the bottle and you ask the genie, "Make me a universe," 165 00:12:50,188 --> 00:12:52,428 and the genie does a spectacular job of it, 166 00:12:52,428 --> 00:12:55,548 but then the genie says, "Well, I'm going to make another universe." 167 00:12:55,548 --> 00:12:57,068 "Wait a minute, I just wanted one." 168 00:12:57,068 --> 00:13:00,138 "Nah, I'm going to make ten more universes." "No, I just wanted one." 169 00:13:00,138 --> 00:13:02,338 "I'm going to make an infinite number of universes." 170 00:13:02,338 --> 00:13:04,858 That's what we're talking about with eternal inflation. 171 00:13:04,858 --> 00:13:08,066 Once the genie gets out of the bottle, it just never stops. 172 00:13:11,138 --> 00:13:15,778 So, asking two simple questions have, for different reasons, 173 00:13:15,778 --> 00:13:18,569 Ied to the same conclusion. 174 00:13:18,569 --> 00:13:23,268 What we see when we look up at the night sky is just a tiny 175 00:13:23,268 --> 00:13:26,499 fraction of the story of our existence. 176 00:13:30,468 --> 00:13:32,829 However, things get even stranger 177 00:13:32,829 --> 00:13:35,434 when you consider the hardest question of all. 178 00:13:41,198 --> 00:13:43,405 How does the universe actually work? 179 00:13:51,988 --> 00:13:55,678 Professor Seth Lloyd resides in the totally weird world of quantum 180 00:13:55,678 --> 00:13:59,637 physics, where nothing is quite as it seems. 181 00:14:03,068 --> 00:14:07,118 And where things can be in two places at the same time. 182 00:14:07,118 --> 00:14:11,218 HE CHUCKLES 183 00:14:11,218 --> 00:14:14,868 The important thing to remember about quantum mechanics is it's weird. 184 00:14:14,868 --> 00:14:16,548 So, stop, stop, stop, stop! 185 00:14:16,548 --> 00:14:18,348 I don't understand that, 186 00:14:18,348 --> 00:14:21,988 but I console myself with the fact that nobody understands that. 187 00:14:24,298 --> 00:14:27,569 It was from an attempt to make sense of this strange quantum 188 00:14:27,569 --> 00:14:30,504 world that the idea of many universes was born. 189 00:14:33,208 --> 00:14:35,338 It all began in the 1950s, 190 00:14:35,338 --> 00:14:39,348 when maverick genius Hugh Everett tried to explain weird 191 00:14:39,348 --> 00:14:43,671 phenomena at the heart of the now infamous Double Slit experiment, 192 00:14:46,558 --> 00:14:49,948 where electrons can be waves and particles at the same time. 193 00:14:51,658 --> 00:14:55,118 The famous Double Slit experiment in quantum mechanics where 194 00:14:55,118 --> 00:14:59,218 a beam of electrons go through space and then they go through two slits. 195 00:14:59,218 --> 00:15:02,658 Now, the wave goes through both slits at once and on the far side, 196 00:15:02,658 --> 00:15:05,988 the wave interferes with itself and then hits a screen 197 00:15:05,988 --> 00:15:09,648 and makes an interference pattern. You might say - come on! 198 00:15:09,648 --> 00:15:11,498 There's lots of electrons. 199 00:15:11,498 --> 00:15:13,858 Like some of the electrons have waves, big deal. 200 00:15:13,858 --> 00:15:16,658 But in fact, if you attenuate this beam of electrons, 201 00:15:16,658 --> 00:15:19,589 so there's only one electron going through at a time, 202 00:15:19,589 --> 00:15:22,478 you still see this interference pattern, even though 203 00:15:22,478 --> 00:15:23,988 there's only one electron, 204 00:15:23,988 --> 00:15:26,868 so the wave for one electron goes through both slits at once. 205 00:15:26,868 --> 00:15:30,278 Ends up on the screen, interferes and makes this pattern. 206 00:15:30,278 --> 00:15:31,589 In the experiment, 207 00:15:31,589 --> 00:15:34,658 when single electrons are fired through two slits, 208 00:15:34,658 --> 00:15:38,579 you'd expect them to create two vertical stripes on the screen 209 00:15:38,579 --> 00:15:43,548 behind, but in fact, they mysteriously create three. 210 00:15:43,548 --> 00:15:46,348 The pattern is only possible 211 00:15:46,348 --> 00:15:49,508 if the individual electrons behave as waves, 212 00:15:49,508 --> 00:15:53,988 passing through both slits at the same time. 213 00:15:53,988 --> 00:15:56,548 It's completely counterintuitive 214 00:15:56,548 --> 00:15:58,829 and simply doesn't make sense. 215 00:15:58,829 --> 00:16:03,218 The trouble is it seems to be true. 216 00:16:03,218 --> 00:16:08,068 It's a problem that even the finest minds in physics have battled with. 217 00:16:08,068 --> 00:16:11,988 Actually, there's a lot of resistance to quantum mechanics. 218 00:16:11,988 --> 00:16:16,058 The most famous resistor of quantum mechanics was Einstein, 219 00:16:16,058 --> 00:16:20,988 who famously got his Nobel prize for work he did on quantum mechanics, 220 00:16:20,988 --> 00:16:26,428 but he nonetheless didn't like it, "God doesn't play dice," he said. 221 00:16:26,428 --> 00:16:28,840 But he was wrong. Suck it up, Albert! 222 00:16:32,709 --> 00:16:36,748 And like Einstein, Hugh Everett was also unhappy with the existing 223 00:16:36,748 --> 00:16:38,864 interpretation of the experiment. 224 00:16:40,218 --> 00:16:43,392 And so, he came up with a radical new theory. 225 00:16:44,589 --> 00:16:48,308 In the mid 20th century, Hugh Everett came up with what 226 00:16:48,308 --> 00:16:52,378 he originally called the Many Worlds theory of quantum mechanics. 227 00:16:52,378 --> 00:16:54,228 So, the idea here is that 228 00:16:54,228 --> 00:16:57,228 when you make a measurement of a particle that's here 229 00:16:57,228 --> 00:17:00,868 and there at the same time, and you find the particle over here, 230 00:17:00,868 --> 00:17:05,348 then there's a you which finds the particle over here in this world, 231 00:17:05,348 --> 00:17:09,298 but at the same time, there's another world over there where another 232 00:17:09,298 --> 00:17:12,148 you has found the particle over there. 233 00:17:12,148 --> 00:17:15,197 And both of these worlds are equally real. 234 00:17:17,709 --> 00:17:21,778 Hugh Everett's big idea was that at the point when the particle can go 235 00:17:21,778 --> 00:17:26,659 through one slit or the other, the universe literally splits in two. 236 00:17:27,858 --> 00:17:31,308 The particle goes through both slits at once, 237 00:17:31,308 --> 00:17:34,311 but it does so in two separate universes. 238 00:17:36,438 --> 00:17:39,078 It was both ingenious and terrifying, 239 00:17:39,078 --> 00:17:43,799 and at the time, it seemed totally bonkers. 240 00:17:45,998 --> 00:17:49,108 Despite the fact that now it really is a widely accepted 241 00:17:49,108 --> 00:17:52,508 theory of quantum mechanics, at the time, it got a very frosty reception. 242 00:17:52,508 --> 00:17:55,159 And he couldn't get a position in physics. 243 00:17:56,709 --> 00:17:59,378 Everett's extreme idea set him at loggerheads 244 00:17:59,378 --> 00:18:02,138 with the establishment, and sadly, he died 245 00:18:02,138 --> 00:18:05,298 before ever receiving the recognition he deserved. 246 00:18:05,298 --> 00:18:10,388 But in recent years, there's been a remarkable turn-around. 247 00:18:10,388 --> 00:18:13,428 Everett's idea of many universes, 248 00:18:13,428 --> 00:18:16,868 bizarre and counter-intuitive as it seems, 249 00:18:16,868 --> 00:18:20,918 is now considered by many to be the only way to explain 250 00:18:20,918 --> 00:18:22,886 how the world really works. 251 00:18:24,918 --> 00:18:27,358 Everybody's intuition about quantum mechanics is wrong 252 00:18:27,358 --> 00:18:30,198 and so if you're going to demand that your intuition be right, 253 00:18:30,198 --> 00:18:32,628 you're just going to be unhappy. On the other hand, 254 00:18:32,628 --> 00:18:36,388 if you can just accept that your intuition is wrong, you know, 255 00:18:36,388 --> 00:18:39,428 grab your quantum surfboard and surf that quantum wave, 256 00:18:39,428 --> 00:18:40,486 then life can be good. 257 00:18:43,918 --> 00:18:48,918 In spite of the weight of evidence now pointing towards a multiverse, 258 00:18:48,918 --> 00:18:53,946 until very recently, anyone dabbling in this field risked career suicide. 259 00:18:55,428 --> 00:18:57,138 I couldn't get a job to save my life. 260 00:18:57,138 --> 00:18:58,638 When I was a grad student, 261 00:18:58,638 --> 00:19:02,908 I used to secretly print out my multiverse related papers 262 00:19:02,908 --> 00:19:06,018 when my adviser was far from the laser printer 263 00:19:06,018 --> 00:19:08,418 and I didn't even show these papers to him 264 00:19:08,418 --> 00:19:10,628 until after he'd signed my dissertation 265 00:19:10,628 --> 00:19:12,668 because it was considered mostly science fiction 266 00:19:12,668 --> 00:19:13,868 and speculation back then. 267 00:19:13,868 --> 00:19:19,278 This job at MIT was the only job I was ever interviewed for. 268 00:19:19,278 --> 00:19:23,208 I was on the verge of having to drive a taxi cab. 269 00:19:23,208 --> 00:19:24,675 HE CHUCKLES 270 00:19:26,388 --> 00:19:31,558 Three entirely different questions have all led to the same conclusion, 271 00:19:31,558 --> 00:19:35,392 the multiverse is now impossible to ignore. 272 00:19:39,878 --> 00:19:43,228 Beyond the realm of our most powerful telescopes, 273 00:19:43,228 --> 00:19:47,722 Max believes infinite universes to be a mathematical certainty. 274 00:19:49,028 --> 00:19:52,361 He thinks the universe simply cannot end... 275 00:19:54,228 --> 00:19:57,589 ..while for Anthony, the quest to understand our origins 276 00:19:57,589 --> 00:20:01,228 provides a tantalising glimpse of a time before, 277 00:20:01,228 --> 00:20:05,585 when inflation brought countless other universes into existence. 278 00:20:08,709 --> 00:20:13,868 And, as if that wasn't enough, Seth's strange quantum world 279 00:20:13,868 --> 00:20:18,020 suggests the universe splitting into multiple others all around us. 280 00:20:20,098 --> 00:20:23,308 The notion of one universe is clearly resting 281 00:20:23,308 --> 00:20:26,348 on perilously shaky foundations. 282 00:20:26,348 --> 00:20:29,948 It's a dramatic turn of events that could fundamentally change 283 00:20:29,948 --> 00:20:32,633 the way we view ourselves for ever. 284 00:20:39,068 --> 00:20:43,148 But while these scientists might agree that the universe needs 285 00:20:43,148 --> 00:20:48,788 to be retired, deciding what the multiverse actually looks like 286 00:20:48,788 --> 00:20:51,393 is an entirely different matter. 287 00:21:08,348 --> 00:21:11,719 The first and perhaps most straightforward model is 288 00:21:11,719 --> 00:21:14,233 the infinite patchwork multiverse. 289 00:21:15,918 --> 00:21:19,348 Arguably, it's the least controversial idea, 290 00:21:19,348 --> 00:21:23,114 but nonetheless, it has some pretty astounding consequences. 291 00:21:28,998 --> 00:21:32,719 Even if the multiverse, all of space, is infinite, 292 00:21:32,719 --> 00:21:35,158 the part of space that we can observe, 293 00:21:35,158 --> 00:21:38,518 our universe, is finite, with a finite amount of stuff. 294 00:21:38,518 --> 00:21:40,878 Only about 10 to the power of 80 atoms, 295 00:21:40,878 --> 00:21:44,228 which can only be arranged in a finite number of ways. 296 00:21:44,228 --> 00:21:48,078 So if you start considering all the other regions of space, 297 00:21:48,078 --> 00:21:50,648 if you roll the dice infinitely many times, 298 00:21:50,648 --> 00:21:53,878 eventually, we are guaranteed to find an identical copy 299 00:21:53,878 --> 00:21:57,928 of our whole universe, as well as countless variations 300 00:21:57,928 --> 00:22:01,034 where things are similar to here but still different. 301 00:22:04,548 --> 00:22:08,918 The infinite multiverse is a bit like an endless patchwork quilt. 302 00:22:08,918 --> 00:22:13,459 Each patch is another universe, the same size as our own, 303 00:22:13,459 --> 00:22:16,508 each one containing a finite number of particles, 304 00:22:16,508 --> 00:22:20,194 each with its own configuration that forms a universe. 305 00:22:23,798 --> 00:22:26,719 So what might these other universes be like? 306 00:22:26,719 --> 00:22:32,268 We know exactly what our universe looks like, the familiar everyday. 307 00:22:32,268 --> 00:22:34,428 And yet another one, 308 00:22:34,428 --> 00:22:38,508 the dinosaur-killing asteroid that was our lucky break 309 00:22:38,508 --> 00:22:41,078 missed Earth, so there are no humans, 310 00:22:41,078 --> 00:22:43,399 just dinosaurs in Winchester today. 311 00:22:44,668 --> 00:22:47,678 There is another one where the powers that be decided 312 00:22:47,678 --> 00:22:50,998 to film this interview not here in Winchester 313 00:22:50,998 --> 00:22:52,948 but at Niagara Falls, 314 00:22:52,948 --> 00:22:55,798 and yet another one, I didn't make it as a physicist, 315 00:22:55,798 --> 00:22:58,798 but I'm actually enjoying life working as a bartender. 316 00:22:58,798 --> 00:23:01,898 Then there's a whole bunch which are very similar 317 00:23:01,898 --> 00:23:04,988 where I just chose to dress a little bit differently. 318 00:23:04,988 --> 00:23:10,469 In this multiverse, every single possibility is played out somewhere. 319 00:23:10,469 --> 00:23:14,008 There are infinite copies of Earth, some familiar, 320 00:23:14,008 --> 00:23:18,479 others where history took an entirely different course. 321 00:23:18,479 --> 00:23:22,078 One where, actually, Germans won World War I I 322 00:23:22,078 --> 00:23:24,228 and wir reden alle Deutsch jetzt, 323 00:23:24,228 --> 00:23:29,188 and finally, if we go a bit over a googolplex meters away, where - 324 00:23:29,188 --> 00:23:31,948 a googolplex is 1 with a googol zeroes, 325 00:23:31,948 --> 00:23:34,438 and a googol is 1 with 100 zeroes - 326 00:23:34,438 --> 00:23:40,428 then we come to a universe that looks exactly like this one. 327 00:23:40,428 --> 00:23:46,268 It sounds like fantasy, but this is exactly what the maths predicts. 328 00:23:46,268 --> 00:23:51,188 Somewhere right now, you're being attacked by aliens. 329 00:23:51,188 --> 00:23:54,518 Another you has just won Olympic gold. 330 00:23:54,518 --> 00:23:57,398 In one world you're behind bars, 331 00:23:57,398 --> 00:24:00,548 in another you've just been elected president. 332 00:24:00,548 --> 00:24:04,439 The possibilities are only limited by your imagination. 333 00:24:10,318 --> 00:24:14,868 An infinite multiverse with infinite copies of you 334 00:24:14,868 --> 00:24:17,678 is probably more than enough to be getting on with. 335 00:24:20,788 --> 00:24:25,327 But this is just the first stop on the magical multiverse tour. 336 00:24:28,998 --> 00:24:33,268 Anthony has a very different vision of the multiverse. 337 00:24:33,268 --> 00:24:37,548 It's a place of even more mind-bending diversity, 338 00:24:37,548 --> 00:24:41,097 where not even the laws of nature are the same. 339 00:24:43,469 --> 00:24:45,908 Imagine this lake is that inflationary substance 340 00:24:45,908 --> 00:24:48,168 that existed before our Big Bang. 341 00:24:48,168 --> 00:24:51,438 But this medium has the property that it inflates the universe, 342 00:24:51,438 --> 00:24:54,168 it doubles its volume in size every tiny fraction of a second. 343 00:24:55,599 --> 00:24:58,908 That's the inflating background, but then within that background, 344 00:24:58,908 --> 00:25:00,432 bubbles can form. 345 00:25:05,438 --> 00:25:08,358 And although these bubbles start small, they grow. 346 00:25:08,358 --> 00:25:12,368 They grow, in fact, infinitely big, and so within one of these bubbles 347 00:25:12,368 --> 00:25:16,599 could reside our entire observable universe and even a whole lot more. 348 00:25:16,599 --> 00:25:19,278 As this process goes on, you end up with a huge 349 00:25:19,278 --> 00:25:22,198 and infinite, even, number of these bubbles. 350 00:25:22,198 --> 00:25:24,878 Some could be our observable universe, 351 00:25:24,878 --> 00:25:29,167 some could be other universes with potentially different properties. 352 00:25:31,958 --> 00:25:34,188 And it's these different properties 353 00:25:34,188 --> 00:25:38,348 that mark this multiverse out from the rest. 354 00:25:38,348 --> 00:25:42,448 Unlike the others, in the inflationary multiverse, 355 00:25:42,448 --> 00:25:46,638 the laws of physics vary from one universe to the next, 356 00:25:46,638 --> 00:25:50,988 making it a very strange place indeed. 357 00:25:50,988 --> 00:25:53,798 What's fascinating about this sort of multiverse is that 358 00:25:53,798 --> 00:25:56,368 these universes could have incredibly diverse properties. 359 00:25:56,368 --> 00:25:58,599 Some of these might be like our universe. 360 00:25:58,599 --> 00:26:00,528 They might have very low energy, 361 00:26:00,528 --> 00:26:03,078 they might have electromagnetic force, 362 00:26:03,078 --> 00:26:06,108 they might have about the same strength of force as we have. 363 00:26:06,108 --> 00:26:08,308 Atoms, planets, stars, galaxies, 364 00:26:08,308 --> 00:26:11,368 everything we see could be in some of these other bubbles as well. 365 00:26:11,368 --> 00:26:13,878 But they could be radically different. 366 00:26:13,878 --> 00:26:15,278 For example, some of the bubbles 367 00:26:15,278 --> 00:26:17,188 might not have an electromagnetic force. 368 00:26:17,188 --> 00:26:19,349 Some of them might have an electromagnetic force 369 00:26:19,349 --> 00:26:21,878 but it's much stronger than ours and atoms wouldn't exist 370 00:26:21,878 --> 00:26:23,808 because they would all collapse or explode. 371 00:26:23,808 --> 00:26:24,988 In these other universes, 372 00:26:24,988 --> 00:26:27,318 there might be physics students taking physics class 373 00:26:27,318 --> 00:26:29,868 but as well as learning different things in history class, 374 00:26:29,868 --> 00:26:31,828 they learn different things in physics class 375 00:26:31,828 --> 00:26:33,548 than physics students in our universe. 376 00:26:33,548 --> 00:26:37,318 So these, these students might for example be going to class 377 00:26:37,318 --> 00:26:39,548 in five dimensions rather than four dimensions, 378 00:26:39,548 --> 00:26:42,628 or they might be talking about a whole different force, 379 00:26:42,628 --> 00:26:45,708 the blue force, that we don't have in our universe. 380 00:26:45,708 --> 00:26:46,988 They might not have atoms. 381 00:26:46,988 --> 00:26:49,878 They might have other strange collections of quarks 382 00:26:49,878 --> 00:26:53,479 that combine in some strange way and create more complicated forms 383 00:26:53,479 --> 00:26:55,678 that can form life in physics students. 384 00:26:55,678 --> 00:27:01,278 There might be... boy, I haven't thought about this very much. 385 00:27:01,278 --> 00:27:02,878 I'm just making it up! 386 00:27:02,878 --> 00:27:05,961 HE LAUGHS 387 00:27:07,438 --> 00:27:10,988 Infinite bubble universes bobbing around 388 00:27:10,988 --> 00:27:15,118 on an inflationary sea where the laws of physics run riot. 389 00:27:16,698 --> 00:27:18,118 Maybe it's making you feel like 390 00:27:18,118 --> 00:27:20,325 you've consumed too much bubbly yourself. 391 00:27:22,718 --> 00:27:27,200 But this is nothing compared to life in the quantum multiverse. 392 00:27:29,548 --> 00:27:32,948 In a world where things can be in two places at once, 393 00:27:32,948 --> 00:27:36,190 there are multiverses lurking right under your nose. 394 00:27:40,678 --> 00:27:41,975 Great! 395 00:27:43,198 --> 00:27:44,238 Mmm. 396 00:27:44,238 --> 00:27:47,127 Pan-fried dumplings, my favourite. 397 00:27:48,359 --> 00:27:51,398 The quantum multiverse could be all around us, 398 00:27:51,398 --> 00:27:53,198 but we can't see it, because it operates 399 00:27:53,198 --> 00:27:56,964 according to the utterly bizarre laws of quantum mechanics. 400 00:27:59,988 --> 00:28:03,708 So the quantum multiverse is not separated from us by distance. 401 00:28:03,708 --> 00:28:05,888 It's not some place very, very far away. 402 00:28:05,888 --> 00:28:08,888 It's some place that's effectively here in space, 403 00:28:08,888 --> 00:28:11,528 but the complexity of the quantum dynamics 404 00:28:11,528 --> 00:28:15,123 prevents these different branches from talking to each other. 405 00:28:16,528 --> 00:28:20,238 The quantum multiverse comes from Hugh Everett's idea 406 00:28:20,238 --> 00:28:24,528 that every single event that can happen does happen. 407 00:28:24,528 --> 00:28:27,679 They just take place in parallel worlds. 408 00:28:28,798 --> 00:28:33,238 It's like an infinite garden of endlessly forking paths. 409 00:28:33,238 --> 00:28:36,988 How do we make sense of this wacky quantum multiverse 410 00:28:36,988 --> 00:28:41,068 in which all possibilities exist simultaneously? 411 00:28:41,068 --> 00:28:44,878 So every time I flip a coin, say heads or tails, 412 00:28:44,878 --> 00:28:47,548 that is just some little quantum accident. 413 00:28:47,548 --> 00:28:51,128 The universe is splitting into two worlds every time it comes up 414 00:28:51,128 --> 00:28:54,558 heads or tails, so our experience of this splitting 415 00:28:54,558 --> 00:28:59,448 is like the experience of walking through a garden of paths that fork. 416 00:28:59,448 --> 00:29:03,168 When we come to a fork in the path, we take one or the other, 417 00:29:03,168 --> 00:29:04,998 heads or tails. 418 00:29:04,998 --> 00:29:08,238 But both forks exist at the same time. 419 00:29:08,238 --> 00:29:10,318 We only experience one of them. 420 00:29:10,318 --> 00:29:15,188 Every time I flip a coin, the universe splits into two worlds. 421 00:29:15,188 --> 00:29:18,282 Heads I stick around, tails I'm out of here. 422 00:29:19,808 --> 00:29:21,888 OK, it's heads, I stick around. 423 00:29:21,888 --> 00:29:28,758 So in that other universe, where I got tails, the interview is over. 424 00:29:28,758 --> 00:29:31,841 Sorry, lady. HE CHUCKLES 425 00:29:32,878 --> 00:29:35,158 To understand what this might be like, 426 00:29:35,158 --> 00:29:37,428 imagine Seth's next few hours 427 00:29:37,428 --> 00:29:39,965 determined by the toss of a coin alone. 428 00:29:41,068 --> 00:29:43,548 I'd had enough of that interview. Let's see. 429 00:29:43,548 --> 00:29:48,599 I flip the coin again, heads I go left, tails I go right. 430 00:29:49,998 --> 00:29:53,168 Already, the universe has split into two, 431 00:29:53,168 --> 00:29:57,238 a Seth in a restaurant and another Seth wandering the streets. 432 00:29:57,238 --> 00:29:59,428 Maybe I should take a short cut over to the Bowery 433 00:29:59,428 --> 00:30:02,628 through this little alleyway here. Should I do it? Looks a little dark. 434 00:30:02,628 --> 00:30:04,835 Let's let the coin decide. 435 00:30:09,438 --> 00:30:12,998 Another flip and the universe splits again. 436 00:30:12,998 --> 00:30:17,401 In this one, Seth makes the fateful decision to walk down the alleyway. 437 00:30:31,708 --> 00:30:32,878 Hey! 438 00:30:32,878 --> 00:30:34,687 Hey, hey, hey, hey! 439 00:30:41,438 --> 00:30:43,158 But in another universe, 440 00:30:43,158 --> 00:30:47,049 the Seth who didn't take the short cut is safely taking a taxi home. 441 00:30:48,528 --> 00:30:53,038 So we can continue, so the me that went left went home, 442 00:30:53,038 --> 00:30:55,359 back to the hotel, good night's sleep. 443 00:30:55,359 --> 00:30:59,398 The me that went right said, "Let's see what Chinatown has to offer. 444 00:30:59,398 --> 00:31:02,798 "Here's an arcade. Shall I go in or not?" 445 00:31:02,798 --> 00:31:06,973 Another split, and one Seth decides to try his luck. 446 00:31:10,158 --> 00:31:12,558 MACHI NE PINGS 447 00:31:14,758 --> 00:31:17,204 Yes, yes, yes! 448 00:31:18,278 --> 00:31:21,268 The other Seth chooses to walk home, 449 00:31:21,268 --> 00:31:25,602 which results in the great New York coffee disaster. 450 00:31:45,609 --> 00:31:50,319 After a few hours, multiple Seths occupy multiple universes. 451 00:31:55,398 --> 00:32:00,973 Each one irrevocably separated, existing in their own reality. 452 00:32:02,038 --> 00:32:04,758 Quantum accident, like setting down this alleyway... 453 00:32:04,758 --> 00:32:07,807 Each with its own independent future. 454 00:32:10,318 --> 00:32:13,068 This bewildering quantum multiverse 455 00:32:13,068 --> 00:32:15,263 is what's known as the Hilbert space. 456 00:32:16,398 --> 00:32:20,528 It's a place of endlessly forking paths and parallel realities. 457 00:32:21,928 --> 00:32:24,888 A place where every version of every event 458 00:32:24,888 --> 00:32:30,360 for every living organism on Earth is happening, somewhere. 459 00:32:33,489 --> 00:32:37,068 The number of possibilities is growing exponentially, 460 00:32:37,068 --> 00:32:40,078 doubling every time I flip a coin. 461 00:32:40,078 --> 00:32:44,558 There are literally gajillions of universes out there 462 00:32:44,558 --> 00:32:46,248 of which ours is only one. 463 00:32:46,248 --> 00:32:49,718 Actually, I calculated one day, that if you look at the total 464 00:32:49,718 --> 00:32:52,479 number of bits there could possibly be in the universe, 465 00:32:52,479 --> 00:32:56,798 so let's ask how many quantum coins could have been tossed since 466 00:32:56,798 --> 00:33:01,008 the universe began 13.8 billion years ago, a simple calculation 467 00:33:01,008 --> 00:33:04,518 tells you that the maximum number is ten to the 120. 468 00:33:04,518 --> 00:33:08,328 There have been ten to the 120 quantum coin tosses, 469 00:33:08,328 --> 00:33:11,798 which means that they're two to the ten to the 120 470 00:33:11,798 --> 00:33:13,728 different possible universes. 471 00:33:13,728 --> 00:33:15,518 It's a large number but it's finite. 472 00:33:15,518 --> 00:33:17,278 I just told you what it was. 473 00:33:17,278 --> 00:33:18,438 It's not infinite. 474 00:33:20,688 --> 00:33:23,878 The quantum multiverse feels like something 475 00:33:23,878 --> 00:33:26,119 straight out of a science fiction story. 476 00:33:28,248 --> 00:33:31,695 But, for some physicists, it's an inescapable reality. 477 00:33:33,788 --> 00:33:38,048 Whether you like it or not, the fact that we live in a multiverse 478 00:33:38,048 --> 00:33:41,233 is the dominant scientific paradigm. 479 00:33:42,518 --> 00:33:45,498 Suck it up, if I may say so again! 480 00:33:54,158 --> 00:33:56,158 This magical multiverse tour 481 00:33:56,158 --> 00:34:00,078 has taken us to some weird and wonderful places indeed. 482 00:34:00,078 --> 00:34:03,518 We've journeyed across an infinite multiverse quilt 483 00:34:03,518 --> 00:34:06,868 and dived into a giant inflating sea, 484 00:34:06,868 --> 00:34:08,848 and as if that wasn't enough, 485 00:34:08,848 --> 00:34:12,363 we've wandered through a thoroughly dizzying quantum maze. 486 00:34:13,278 --> 00:34:16,698 So, if you were starting to feel like you'd fallen down a rabbit hole 487 00:34:16,698 --> 00:34:20,805 into Wonderland, it's worth pausing for a moment to ask... 488 00:34:21,768 --> 00:34:23,599 Which theory is right? 489 00:34:24,968 --> 00:34:27,209 And can anyone actually prove it? 490 00:34:29,918 --> 00:34:34,008 For its most vociferous critics, the multiverse is unscientific 491 00:34:34,008 --> 00:34:36,283 because it can't be tested... 492 00:34:37,518 --> 00:34:39,008 ..even in principle. 493 00:34:44,398 --> 00:34:48,648 So, without proof, doesn't this make the whole idea of the multiverse 494 00:34:48,648 --> 00:34:50,377 simply a waste of time? 495 00:34:53,638 --> 00:34:56,118 Well, not necessarily. 496 00:34:58,868 --> 00:35:00,558 Exciting new discoveries 497 00:35:00,558 --> 00:35:02,868 now mean that evidence for the multiverse 498 00:35:02,868 --> 00:35:05,575 might not be as far away as we think. 499 00:35:07,048 --> 00:35:10,415 In fact, one scientist thinks she may have already found it. 500 00:35:13,158 --> 00:35:16,059 # She's a true original... # 501 00:35:24,408 --> 00:35:28,048 Professor Laura Mersini-Houghton has a radically new vision 502 00:35:28,048 --> 00:35:29,408 of the multiverse. 503 00:35:29,408 --> 00:35:33,798 It's bold and daring and, even by the standards of the multiverse, 504 00:35:33,798 --> 00:35:36,638 it's considered highly controversial. 505 00:35:36,638 --> 00:35:38,878 Truth goes through three stages. 506 00:35:38,878 --> 00:35:40,918 First it's ridicule, 507 00:35:40,918 --> 00:35:43,148 then opposed strongly, 508 00:35:43,148 --> 00:35:46,413 and finally, it becomes self-evident. 509 00:35:47,788 --> 00:35:50,928 Perhaps now we are reaching the stage of self-evident. 510 00:35:53,958 --> 00:35:56,998 Laura's major breakthrough was to take two big ideas 511 00:35:56,998 --> 00:35:58,698 and put them together. 512 00:35:58,698 --> 00:36:01,408 She combined the physics of string theory 513 00:36:01,408 --> 00:36:03,296 with those of quantum mechanics. 514 00:36:04,878 --> 00:36:08,208 The mathematics involved is fiendishly complicated, 515 00:36:08,208 --> 00:36:11,229 and Laura is probably one of just a handful of people 516 00:36:11,229 --> 00:36:13,288 who can even begin to comprehend it. 517 00:36:15,278 --> 00:36:17,588 But, for us mere mortals, 518 00:36:17,588 --> 00:36:22,639 one way to picture it is as a landscape and a wave. 519 00:36:26,229 --> 00:36:29,218 Before our universe went through the Big Bang, 520 00:36:29,218 --> 00:36:34,489 we can think of the pre- Big Bang era as a space which is abstract, 521 00:36:34,489 --> 00:36:38,058 it's an energy space, and various places on this landscape, 522 00:36:38,058 --> 00:36:42,131 on this energy field can produce different universes. 523 00:36:46,239 --> 00:36:50,808 We can think of these waves leaping over the rocks as the wave function 524 00:36:50,808 --> 00:36:54,808 of the universe, trying to travel through this landscape structure. 525 00:36:54,808 --> 00:36:57,848 If I think of the rocks as the energy field, 526 00:36:57,848 --> 00:37:01,598 and each pocket on these rocks representing an energy valley 527 00:37:01,598 --> 00:37:04,518 on the landscape, as the waves come through, 528 00:37:04,518 --> 00:37:07,078 many of them will be trapped in different pockets, 529 00:37:07,078 --> 00:37:08,807 rather than travel any further. 530 00:37:10,088 --> 00:37:13,568 Each of these little pockets can be a potential birthplace 531 00:37:13,568 --> 00:37:15,422 for a universe similar to ours. 532 00:37:17,489 --> 00:37:19,598 Laura's idea was to represent space 533 00:37:19,598 --> 00:37:23,078 a bit like a mountain range of different energies. 534 00:37:23,078 --> 00:37:26,518 She thinks that our universe started out as a wave. 535 00:37:26,518 --> 00:37:30,048 As it crossed the landscape, some energy got trapped, 536 00:37:30,048 --> 00:37:34,052 creating different universes with different properties. 537 00:37:36,768 --> 00:37:38,963 It is without doubt a radical notion... 538 00:37:41,788 --> 00:37:44,948 ..but Laura also predicted a series of anomalies, 539 00:37:44,948 --> 00:37:47,438 which she believed could actually be observed 540 00:37:47,438 --> 00:37:48,848 in our own night sky. 541 00:37:50,369 --> 00:37:53,598 One of these would even reveal how our universe 542 00:37:53,598 --> 00:37:57,853 was once entangled with another, through a process called cross-talk. 543 00:38:02,008 --> 00:38:04,728 These universes are not only producing space time, 544 00:38:04,728 --> 00:38:07,369 but they are also separating from one another. 545 00:38:07,369 --> 00:38:10,088 Each one of those is taking its own identity. 546 00:38:10,088 --> 00:38:14,128 However, traces of that infancy, 547 00:38:14,128 --> 00:38:17,858 of that cross-talk between all the surviving universes 548 00:38:17,858 --> 00:38:19,848 and the landscape structure, 549 00:38:19,848 --> 00:38:22,998 those are imprinted forever in our sky 550 00:38:22,998 --> 00:38:26,616 because, after all, what we look at today in the sky 551 00:38:26,616 --> 00:38:30,056 is just a blown-up version, a re-scaled version, 552 00:38:30,056 --> 00:38:34,386 of what once was in our universe when it was in its infancy. 553 00:38:34,386 --> 00:38:37,936 Laura predicted that this cross-talk would leave an imprint 554 00:38:37,936 --> 00:38:41,646 on our early universe, a bit like a birthmark, 555 00:38:41,646 --> 00:38:47,300 and we could see this as a cold spot in the cosmic microwave background. 556 00:38:48,426 --> 00:38:52,496 The detection of the cold spot was one of the signatures 557 00:38:52,496 --> 00:38:56,296 that we predicted by tracing forward the quantum entanglement 558 00:38:56,296 --> 00:38:59,856 of our universe with all the other surviving universes. 559 00:38:59,856 --> 00:39:03,576 We predicted that there should be a large area in the sky 560 00:39:03,576 --> 00:39:07,136 of about ten degrees, and indeed that's what was observed 561 00:39:07,136 --> 00:39:09,946 about seven months after we made the prediction. 562 00:39:11,227 --> 00:39:15,186 Remarkably, all Laura's predictions have since been observed, 563 00:39:15,186 --> 00:39:17,416 including this cold spot, 564 00:39:17,416 --> 00:39:20,696 which she claims is a trace of another universe 565 00:39:20,696 --> 00:39:22,846 once entangled with our own. 566 00:39:24,506 --> 00:39:27,509 It's a discovery beyond anything she dared hope for. 567 00:39:29,136 --> 00:39:31,227 That felt incredibly good. 568 00:39:31,227 --> 00:39:32,746 It was unbelievable. 569 00:39:32,746 --> 00:39:37,217 I really got excited, and allowed myself for a moment 570 00:39:37,217 --> 00:39:40,266 to think that there might be something more to this idea, 571 00:39:40,266 --> 00:39:42,916 and when I heard the list of anomalies, 572 00:39:42,916 --> 00:39:47,116 I was so elated and happy 573 00:39:47,116 --> 00:39:48,776 and couldn't believe my eyes, 574 00:39:48,776 --> 00:39:52,936 that I allowed myself for a few minutes to jump up and down. 575 00:39:52,936 --> 00:39:54,626 I was jumping on the balcony. 576 00:39:54,626 --> 00:39:56,947 I wonder what the neighbours thought?! 577 00:40:01,736 --> 00:40:04,786 # She's a true original... # 578 00:40:04,786 --> 00:40:09,426 It's a thrilling thought, that somewhere up there in our own sky 579 00:40:09,426 --> 00:40:13,066 could be a clue to the presence of another universe. 580 00:40:14,626 --> 00:40:16,826 Laura's ideas are considered radical 581 00:40:16,826 --> 00:40:20,266 and she's yet to convince many of her critics, 582 00:40:20,266 --> 00:40:24,016 but it's a major breakthrough for an idea most people dismissed. 583 00:40:24,016 --> 00:40:26,217 Then, in 2014, 584 00:40:26,217 --> 00:40:30,746 scientists claim to have made another important discovery. 585 00:40:30,746 --> 00:40:33,426 NEWS REPORT: Space scientists hail a great advance, 586 00:40:33,426 --> 00:40:35,146 claiming the first direct evidence 587 00:40:35,146 --> 00:40:38,227 of what happened in the first moments of the universe. 588 00:40:38,227 --> 00:40:41,796 An international team of leading space scientists say they've 589 00:40:41,796 --> 00:40:45,786 found the first direct evidence of how the universe was born. 590 00:40:45,786 --> 00:40:49,066 Scientists had been scanning the sky, 591 00:40:49,066 --> 00:40:51,786 Iooking for evidence of gravitational waves. 592 00:40:51,786 --> 00:40:55,586 The news that they thought they had found them caused a sensation, 593 00:40:55,586 --> 00:40:59,306 because, if confirmed, it offered yet more tantalising clues 594 00:40:59,306 --> 00:41:01,946 to the existence of the multiverse. 595 00:41:01,946 --> 00:41:04,016 So this has been a really exciting time 596 00:41:04,016 --> 00:41:06,066 to be studying the theory of inflation 597 00:41:06,066 --> 00:41:09,186 because inflation predicts that there would be 598 00:41:09,186 --> 00:41:12,556 gravitational waves formed during the inflationary process, 599 00:41:12,556 --> 00:41:14,866 these are ripples in space time. 600 00:41:14,866 --> 00:41:17,776 It turns out that those gravitational waves 601 00:41:17,776 --> 00:41:19,586 Ieave a telltale signature 602 00:41:19,586 --> 00:41:22,266 in a pattern on the microwave background radiation, 603 00:41:22,266 --> 00:41:24,986 and that signature has been searched for for a long time 604 00:41:24,986 --> 00:41:27,227 because it's a prediction of inflation. 605 00:41:32,496 --> 00:41:35,511 The data in 2014 turned out to be a false alarm. 606 00:41:36,856 --> 00:41:38,585 But the theory is solid. 607 00:41:40,706 --> 00:41:43,736 The idea is that the violent nature of inflation 608 00:41:43,736 --> 00:41:45,556 created gravitational waves. 609 00:41:46,906 --> 00:41:49,706 These waves would have warped the fabric of space 610 00:41:49,706 --> 00:41:52,626 and produced a particular pattern of ripples in the cosmic 611 00:41:52,626 --> 00:41:57,359 microwave background, enabling us to observe them, even today. 612 00:41:58,796 --> 00:42:02,107 The hunt is still on for evidence of gravitational waves. 613 00:42:02,107 --> 00:42:05,227 But, if they're discovered, it would be a huge leap forward 614 00:42:05,227 --> 00:42:07,036 for the idea of the multiverse. 615 00:42:08,576 --> 00:42:10,576 Gravitational waves, I think, 616 00:42:10,576 --> 00:42:14,626 makes the multiverse more likely in two ways. 617 00:42:14,626 --> 00:42:18,906 The first is that the multiverse is a prediction really of inflation, 618 00:42:18,906 --> 00:42:21,426 and so because this makes inflation more likely, 619 00:42:21,426 --> 00:42:24,146 it then makes the multiverse more likely. 620 00:42:24,146 --> 00:42:27,716 Second, I would say that the sorts of models, 621 00:42:27,716 --> 00:42:30,856 the simple models that people have been thinking about for 30 years 622 00:42:30,856 --> 00:42:34,786 that give rise to eternal inflation, are precisely the sort of models 623 00:42:34,786 --> 00:42:37,376 that are compatible with these theories. 624 00:42:37,376 --> 00:42:41,456 Scientists are still looking for proof of gravitational waves, 625 00:42:41,456 --> 00:42:45,381 but if found, it will be a major step forward in cosmology. 626 00:42:46,626 --> 00:42:49,816 So, this really makes me feel excited to be a cosmologist 627 00:42:49,816 --> 00:42:51,716 and be alive and working now. 628 00:42:51,716 --> 00:42:53,316 This is a spectacular time 629 00:42:53,316 --> 00:42:55,796 that we're never going to have in human history again. 630 00:42:55,796 --> 00:42:58,906 We've learned what the history of the universe is, 631 00:42:58,906 --> 00:43:01,826 and now we're learning where the universe came from, 632 00:43:01,826 --> 00:43:04,706 how was it born, were there other universes born? 633 00:43:04,706 --> 00:43:06,636 And we're actually making progress. 634 00:43:06,636 --> 00:43:09,436 We're not just talking, we're learning real things, 635 00:43:09,436 --> 00:43:13,566 and we've come incredibly far in that quest. 636 00:43:15,796 --> 00:43:18,586 These new ideas have given great support 637 00:43:18,586 --> 00:43:21,196 to theories of the multiverse, 638 00:43:21,196 --> 00:43:24,196 and to those critics that suggest the idea of the multiverse 639 00:43:24,196 --> 00:43:29,111 is a waste of time, it's given them something to think about too. 640 00:43:48,266 --> 00:43:50,856 While some scientists are looking for evidence 641 00:43:50,856 --> 00:43:53,866 for the multiverse in the distant regions of space, 642 00:43:53,866 --> 00:43:57,357 others believe our best hope of detecting the multiverse 643 00:43:57,357 --> 00:44:02,706 might lie much closer to home in the dizzying world of quantum computing, 644 00:44:02,706 --> 00:44:08,155 where today this team at MIT have switched on their latest machine. 645 00:44:09,376 --> 00:44:12,986 The type of evidence we can get for the quantum multiverse 646 00:44:12,986 --> 00:44:15,636 is much more immediate than that that we get 647 00:44:15,636 --> 00:44:18,786 for the inflationary multiverse, for instance. 648 00:44:18,786 --> 00:44:20,946 So, for the inflationary multiverse 649 00:44:20,946 --> 00:44:24,107 we're never going to actually have access to these other worlds, 650 00:44:24,107 --> 00:44:26,826 so we're just going to have to believe in inflation 651 00:44:26,826 --> 00:44:29,347 and thereby believe that these exist. 652 00:44:29,347 --> 00:44:33,186 But, we could indeed do some quantum virtual reality experiment 653 00:44:33,186 --> 00:44:37,357 which demonstrated the existence of the quantum multiverse, 654 00:44:37,357 --> 00:44:40,237 at least in the context of virtual reality. 655 00:44:40,237 --> 00:44:42,466 In the quantum multiverse, 656 00:44:42,466 --> 00:44:46,186 each universe that splits apart is permanently severed, 657 00:44:46,186 --> 00:44:49,736 but quantum computers might have an extraordinary ability 658 00:44:49,736 --> 00:44:51,237 to access them. 659 00:44:52,506 --> 00:44:54,946 So, a quantum computer is like a regular computer, 660 00:44:54,946 --> 00:44:56,709 but really, really small. 661 00:44:58,266 --> 00:45:01,176 That is to say, the bits of the computer, 662 00:45:01,176 --> 00:45:04,066 so the places where you store information, 663 00:45:04,066 --> 00:45:05,866 are individual atoms, 664 00:45:05,866 --> 00:45:10,996 or individual elementary particles, like photons or electrons. 665 00:45:10,996 --> 00:45:15,596 An ordinary digital computer processes information 666 00:45:15,596 --> 00:45:18,746 by busting up the information to its smallest pieces 667 00:45:18,746 --> 00:45:22,636 which are called bits, so a bit is a small chunk of information. 668 00:45:22,636 --> 00:45:26,436 It only has two possibilities which are usually called zero or one, 669 00:45:26,436 --> 00:45:29,386 but they could also be yes or no, heads or tails, true or false. 670 00:45:29,386 --> 00:45:33,227 So, a quantum computer also divides up information into bits, 671 00:45:33,227 --> 00:45:34,896 but now they're quantum bits, 672 00:45:34,896 --> 00:45:37,456 so if I'm an electron that can be over here, 673 00:45:37,456 --> 00:45:40,746 we call that zero, or over here we call that one, 674 00:45:40,746 --> 00:45:42,666 so this quantum bit or Q-bit, 675 00:45:42,666 --> 00:45:46,536 in some weird funky quantum way that nobody really understands 676 00:45:46,536 --> 00:45:49,506 registers zero and one simultaneously. 677 00:45:49,506 --> 00:45:52,516 And this gives quantum computers a power 678 00:45:52,516 --> 00:45:55,186 that ordinary classical computers don't have. 679 00:45:55,186 --> 00:45:57,826 Because quantum computers have the ability 680 00:45:57,826 --> 00:46:00,186 to operate in many states at once, 681 00:46:00,186 --> 00:46:04,636 performing a staggering number of calculations at the same time, 682 00:46:04,636 --> 00:46:09,666 some believe these calculations are taking place in parallel worlds. 683 00:46:09,666 --> 00:46:12,866 Some people believe that quantum computers already prove 684 00:46:12,866 --> 00:46:14,786 the existence of the multiverse. 685 00:46:14,786 --> 00:46:16,506 They say that the quantum computer 686 00:46:16,506 --> 00:46:19,866 is doing all these different computations in different worlds, 687 00:46:19,866 --> 00:46:24,066 and then to get the answer to the question, it recombines all this 688 00:46:24,066 --> 00:46:27,081 information from these different worlds to give you the answer. 689 00:46:28,716 --> 00:46:31,306 And there's one famous maths problem 690 00:46:31,306 --> 00:46:33,956 that if a quantum computer could solve, 691 00:46:33,956 --> 00:46:37,906 could one day prove the existence of the quantum multiverse. 692 00:46:37,906 --> 00:46:42,666 The killer app for quantum computers is factoring large numbers, 693 00:46:42,666 --> 00:46:46,896 so factoring is taking a number and dividing it up into its factors 694 00:46:46,896 --> 00:46:49,156 so four is two times two, 695 00:46:49,156 --> 00:46:51,367 15 is three times five, 696 00:46:51,367 --> 00:46:53,546 21 is three times seven. 697 00:46:53,546 --> 00:46:55,716 Now that's pretty easy to do, 698 00:46:55,716 --> 00:46:59,276 and you and I can factor small numbers pretty easily, 699 00:46:59,276 --> 00:47:03,586 but when the numbers get very, very large, so I have a 512 digit number 700 00:47:03,586 --> 00:47:09,076 that's a product of two 256 digit numbers, it starts to get very hard. 701 00:47:09,076 --> 00:47:13,186 And, in fact, there's no known method on a classical computer 702 00:47:13,186 --> 00:47:17,516 to factor such numbers without taking a very, very large amount of time, 703 00:47:17,516 --> 00:47:19,227 maybe the age of the universe. 704 00:47:19,227 --> 00:47:23,596 However, a very small quantum computer with only a few 705 00:47:23,596 --> 00:47:26,956 tens of thousands of quantum bits could, in fact, 706 00:47:26,956 --> 00:47:31,006 factor a 512 digit number very rapidly, 707 00:47:31,006 --> 00:47:32,826 and how does it do that? 708 00:47:32,826 --> 00:47:35,646 It basically breaks up all the possible ways 709 00:47:35,646 --> 00:47:37,476 of factoring the number, 710 00:47:37,476 --> 00:47:41,836 and then all of these different parts get tried out together, 711 00:47:41,836 --> 00:47:45,546 and then recombined to give you the answer to the problem, 712 00:47:45,546 --> 00:47:47,798 to give you the factors of the number. 713 00:47:49,367 --> 00:47:53,357 These colossal calculations would take a classical computer 714 00:47:53,357 --> 00:47:57,186 more than the age of the universe to arrive at the correct answer, 715 00:47:57,186 --> 00:48:00,367 but a quantum computer could, in theory, 716 00:48:00,367 --> 00:48:02,367 tap into the multiverse, 717 00:48:02,367 --> 00:48:05,796 doing all the calculations in different universes 718 00:48:05,796 --> 00:48:06,831 at the same time. 719 00:48:08,156 --> 00:48:12,107 We're on the verge of a quantum computing revolution. 720 00:48:12,107 --> 00:48:15,546 The fact that these engineers might be building the first 721 00:48:15,546 --> 00:48:20,386 machines to access these hidden worlds is a spine-tingling thought. 722 00:48:20,386 --> 00:48:21,996 I am excited. 723 00:48:21,996 --> 00:48:25,996 I am, now that the thing is up and running as of this morning, 724 00:48:25,996 --> 00:48:28,726 I am going to come up with all kinds of fiendish 725 00:48:28,726 --> 00:48:32,756 and nefarious uses for this beautiful quantum computer. 726 00:48:32,756 --> 00:48:34,121 Wa-ha-ha! 727 00:48:37,956 --> 00:48:42,598 The multiverse is, admittedly, more than a little bewildering. 728 00:48:45,237 --> 00:48:47,987 A dizzying array of inflating bubbles, 729 00:48:47,987 --> 00:48:49,466 split personalities, 730 00:48:49,466 --> 00:48:51,514 and undulating landscapes. 731 00:48:53,906 --> 00:48:56,796 But, if you're struggling to choose 732 00:48:56,796 --> 00:49:00,156 which multiverse model you are actually in, 733 00:49:00,156 --> 00:49:01,987 you might not have to 734 00:49:01,987 --> 00:49:06,276 because we could exist in all of them at once. 735 00:49:15,367 --> 00:49:19,087 Max believes all the multiverses could happily live together... 736 00:49:20,746 --> 00:49:25,604 ..in one extraordinary, humungous mathematical multiverse. 737 00:49:30,626 --> 00:49:34,506 The idea that all of this is completely mathematical 738 00:49:34,506 --> 00:49:38,357 sounds pretty nutty at first since it doesn't seem mathematical at all, 739 00:49:38,357 --> 00:49:43,386 but actually, when we look closer, there is mathematics everywhere. 740 00:49:43,386 --> 00:49:47,916 Here we see some beautiful mathematical circles forming, 741 00:49:47,916 --> 00:49:51,166 and whose spreading over the water is perfectly described 742 00:49:51,166 --> 00:49:54,158 by a mathematical equation called the wave equation. 743 00:49:55,626 --> 00:49:58,836 This tree here doesn't look very mathematical at first sight, 744 00:49:58,836 --> 00:50:01,446 but if we look really closely at this bark, 745 00:50:01,446 --> 00:50:03,876 it's made of cells, that are made of molecules, 746 00:50:03,876 --> 00:50:05,516 that are made of atoms, 747 00:50:05,516 --> 00:50:08,076 that are made of quarks and electrons, 748 00:50:08,076 --> 00:50:09,516 and as far as we can tell, 749 00:50:09,516 --> 00:50:11,946 neither the electrons nor the quarks, 750 00:50:11,946 --> 00:50:14,987 nor any of the other particles that make up all of this 751 00:50:14,987 --> 00:50:19,083 have any properties at all, except for mathematical properties. 752 00:50:21,186 --> 00:50:24,516 Understanding how our physical world of stuff can come from 753 00:50:24,516 --> 00:50:29,526 something as intangible as maths, is hard to get your head round. 754 00:50:29,526 --> 00:50:32,677 But we experience worlds of numbers all the time. 755 00:50:52,836 --> 00:50:54,756 Hi, my name is Shawn Robertson. 756 00:50:54,756 --> 00:50:56,977 I'm the animation director at Irrational Games, 757 00:50:56,977 --> 00:50:59,445 and I'd like to introduce you to Elizabeth. 758 00:51:01,266 --> 00:51:03,626 She's curious about the world, I mean, you know, 759 00:51:03,626 --> 00:51:06,756 from a personality standpoint, so she wants to touch everything, she 760 00:51:06,756 --> 00:51:10,066 wants to take a look at everything, she wants to see everything. 761 00:51:10,066 --> 00:51:13,806 Elizabeth's world is a representation of our own, 762 00:51:13,806 --> 00:51:17,719 but look closer and it all boils down to sets of numbers. 763 00:51:19,596 --> 00:51:23,636 So, here we're looking deep under the hood at just one of the objects 764 00:51:23,636 --> 00:51:26,266 that's in the game. So the initial, look at it, it looks 765 00:51:26,266 --> 00:51:30,237 fairly realistic. It's got shape to it, it's got textures to it. 766 00:51:30,237 --> 00:51:34,196 But if you look at what this is really built out of at its barest 767 00:51:34,196 --> 00:51:37,956 Ievel, it's just a bunch of vertices and polygons and, you know, we can 768 00:51:37,956 --> 00:51:42,446 go in and we can manipulate these as artists and really change everything 769 00:51:42,446 --> 00:51:46,997 that's, you know, that the end user is going to see in the game. 770 00:51:46,997 --> 00:51:51,166 The only properties left here that this object has is a bunch of 771 00:51:51,166 --> 00:51:56,546 numbers, an X, Y and a Z coordinate here for each of your points. 772 00:51:56,546 --> 00:51:58,906 It's like you can put in some more numbers here 773 00:51:58,906 --> 00:52:01,056 and they would specify colour and texture 774 00:52:01,056 --> 00:52:05,476 and so on, but ultimately both this world and our physical world 775 00:52:05,476 --> 00:52:11,266 seems really at the bedrock level of description to be just numbers. 776 00:52:11,266 --> 00:52:16,166 Max believes our world, like Elizabeth's, is also made of maths. 777 00:52:16,166 --> 00:52:18,839 Maths is as real as the ground under your feet. 778 00:52:20,756 --> 00:52:23,906 And he also believes that equations are the foundations 779 00:52:23,906 --> 00:52:25,999 on which the multiverse is built. 780 00:52:29,036 --> 00:52:32,556 If we accept that our physical reality is actually 781 00:52:32,556 --> 00:52:36,997 a mathematical structure and nothing more, then we have to accept 782 00:52:36,997 --> 00:52:43,466 that any mathematical structure is a physical reality and nothing less, 783 00:52:43,466 --> 00:52:47,276 which makes me wonder, what about all these other mathematical 784 00:52:47,276 --> 00:52:51,166 structures that mathematicians have discovered and classified, and can 785 00:52:51,166 --> 00:52:54,909 make a whole atlas containing one after the other, what about them? 786 00:52:59,436 --> 00:53:02,706 This is Max's mathematical multiverse, 787 00:53:02,706 --> 00:53:04,492 home to all the other theories. 788 00:53:05,886 --> 00:53:09,066 These weird and wacky worlds have all been given life 789 00:53:09,066 --> 00:53:11,956 by the equations that describe them. 790 00:53:11,956 --> 00:53:16,426 Every equation is a multiverse in its own right, 791 00:53:16,426 --> 00:53:20,522 and each is a part of one giant mathematical structure. 792 00:53:22,636 --> 00:53:25,992 By his own admission, it's a radical idea. 793 00:53:32,686 --> 00:53:36,266 Whenever in the history of physics someone puts forward an idea 794 00:53:36,266 --> 00:53:38,706 which sounds kind of radical, 795 00:53:38,706 --> 00:53:41,556 a lot of other people are going to jump up and say, "Oh, this is nuts, 796 00:53:41,556 --> 00:53:44,046 "this is crazy, I can't believe our world is so weird," 797 00:53:44,046 --> 00:53:49,076 but our job as scientists is not to tell our world how to be to conform 798 00:53:49,076 --> 00:53:53,316 with our aesthetic preconceptions for how... 799 00:53:53,316 --> 00:53:54,997 For how it ought to behave. 800 00:53:54,997 --> 00:53:58,266 Our job is to simply follow the evidence wherever it leads us 801 00:53:58,266 --> 00:54:04,036 and try to, with an open mind, determine how our world actually is. 802 00:54:04,036 --> 00:54:07,036 And I think it's abundantly clear already from the history of physics 803 00:54:07,036 --> 00:54:11,826 that the world is vastly stranger than we ever thought it was. 804 00:54:16,346 --> 00:54:21,166 So, on another world in another universe, could there be 805 00:54:21,166 --> 00:54:25,364 another Hugh Everett who is finally getting the recognition he deserves? 806 00:54:27,606 --> 00:54:31,396 One who is witnessing how the ideas once dismissed as the ramblings 807 00:54:31,396 --> 00:54:36,083 of a crazy eccentric are now part of the scientific mainstream? 808 00:54:37,716 --> 00:54:43,356 There are still many more questions for future generations to answer... 809 00:54:43,356 --> 00:54:46,316 but these ideas, and the people advocating them, 810 00:54:46,316 --> 00:54:48,967 are bringing about a scientific revolution. 811 00:54:51,066 --> 00:54:53,443 It's a truly thrilling place to be. 812 00:54:55,636 --> 00:54:59,076 Now we've come to a remarkable time where observational 813 00:54:59,076 --> 00:55:02,436 evidence about the universe combined with our theories of what's going on 814 00:55:02,436 --> 00:55:05,556 at the most microscopic quantum mechanical level 815 00:55:05,556 --> 00:55:10,646 give very strong evidence for the existence of these other worlds 816 00:55:10,646 --> 00:55:13,615 and these other universes in the multiverse. 817 00:55:16,606 --> 00:55:18,494 We used to think we were unique. 818 00:55:20,606 --> 00:55:23,247 We believed that the Earth, our home, 819 00:55:23,247 --> 00:55:25,795 was at the centre of the universe. 820 00:55:27,566 --> 00:55:30,486 But little by little, we've been forced to change 821 00:55:30,486 --> 00:55:34,997 our perspective, learning that we are just one planet revolving 822 00:55:34,997 --> 00:55:39,707 around the sun, which is just one star amongst countless others. 823 00:55:43,636 --> 00:55:48,146 Now it seems we may have to give up the long-cherished notions 824 00:55:48,146 --> 00:55:50,476 of the universe altogether, 825 00:55:50,476 --> 00:55:53,406 accepting instead that it could be just one 826 00:55:53,406 --> 00:55:56,606 of an infinite number of others, 827 00:55:56,606 --> 00:56:00,975 just a humble part of a truly infinite multiverse. 828 00:56:04,686 --> 00:56:10,636 When I think of our universe as a humble member in the vastness, 829 00:56:10,636 --> 00:56:13,396 I can only marvel at the beauty of nature. 830 00:56:13,396 --> 00:56:17,926 I am not surprised because, of course, nature always has new 831 00:56:17,926 --> 00:56:22,127 and beautiful surprises in store for us that are out there to be 832 00:56:22,127 --> 00:56:27,406 discovered, but I also feel very fortunate that I am 833 00:56:27,406 --> 00:56:31,966 at the right time and place where I can take part in that discovery, 834 00:56:31,966 --> 00:56:35,788 even if it's just one small step beyond what's already known. 835 00:56:37,146 --> 00:56:40,636 And there is an awe inspired by that beauty, 836 00:56:40,636 --> 00:56:43,480 complexity, and yet simplicity of nature. 837 00:56:48,836 --> 00:56:50,956 Some people feel that when they think about 838 00:56:50,956 --> 00:56:53,596 how big even the observable universe is, it makes 839 00:56:53,596 --> 00:56:57,486 them feel tiny and insignificant and that's right, physically - 840 00:56:57,486 --> 00:56:59,926 we're just really specks - 841 00:56:59,926 --> 00:57:03,156 but mentally, when you think of our understanding of the universe, that 842 00:57:03,156 --> 00:57:07,436 we have been able to conceive of the laws that govern the evolution 843 00:57:07,436 --> 00:57:11,916 and creation and complexity of the universe, we're huge. 844 00:57:11,916 --> 00:57:13,796 We're giants in that sense, 845 00:57:13,796 --> 00:57:17,406 and I feel excited to be a part of that process and it makes the 846 00:57:17,406 --> 00:57:21,558 universe, the interior universe, the mental universe, feel vast to me. 847 00:57:25,997 --> 00:57:29,696 Some people don't like multiverses cos they say it makes them 848 00:57:29,696 --> 00:57:33,966 feel insignificant, but I think it's actually good news, 849 00:57:33,966 --> 00:57:37,516 because we humans have again and again and again underestimated 850 00:57:37,516 --> 00:57:40,877 not only the size of our cosmos, realising that everything 851 00:57:40,877 --> 00:57:44,926 we thought existed was just a small part of a much grander structure - 852 00:57:44,926 --> 00:57:50,046 a planet, a solar system, a galaxy, a universe and a whole hierarchy 853 00:57:50,046 --> 00:57:54,396 of parallel universes - but we also repeatedly underestimated the power 854 00:57:54,396 --> 00:57:58,926 of our human minds to understand our cosmos and that's a wonderfully 855 00:57:58,926 --> 00:58:02,999 empowering thing, which shouldn't make us feel insignificant at all.