WEBVTT 00:00:00.000 --> 00:00:02.000 A few months ago 00:00:02.000 --> 00:00:04.000 the Nobel Prize in physics 00:00:04.000 --> 00:00:06.000 was awarded to two teams of astronomers 00:00:06.000 --> 00:00:09.000 for a discovery that has been hailed 00:00:09.000 --> 00:00:11.000 as one of the most important 00:00:11.000 --> 00:00:13.000 astronomical observations ever. 00:00:13.000 --> 00:00:15.000 And today, after briefly describing what they found, 00:00:15.000 --> 00:00:18.000 I'm going to tell you about a highly controversial framework 00:00:18.000 --> 00:00:21.000 for explaining their discovery, 00:00:21.000 --> 00:00:23.000 namely the possibility 00:00:23.000 --> 00:00:25.000 that way beyond the Earth, 00:00:25.000 --> 00:00:28.000 the Milky Way and other distant galaxies, 00:00:28.000 --> 00:00:30.000 we may find that our universe 00:00:30.000 --> 00:00:32.000 is not the only universe, 00:00:32.000 --> 00:00:34.000 but is instead 00:00:34.000 --> 00:00:36.000 part of a vast complex of universes 00:00:36.000 --> 00:00:38.000 that we call the multiverse. NOTE Paragraph 00:00:38.000 --> 00:00:41.000 Now the idea of a multiverse is a strange one. 00:00:41.000 --> 00:00:43.000 I mean, most of us were raised to believe 00:00:43.000 --> 00:00:46.000 that the word "universe" means everything. 00:00:46.000 --> 00:00:49.000 And I say most of us with forethought, 00:00:49.000 --> 00:00:52.000 as my four-year-old daughter has heard me speak of these ideas since she was born. 00:00:52.000 --> 00:00:54.000 And last year I was holding her 00:00:54.000 --> 00:00:56.000 and I said, "Sophia, 00:00:56.000 --> 00:00:59.000 I love you more than anything in the universe." 00:00:59.000 --> 00:01:01.000 And she turned to me and said, "Daddy, 00:01:01.000 --> 00:01:03.000 universe or multiverse?" 00:01:03.000 --> 00:01:06.000 (Laughter) NOTE Paragraph 00:01:06.000 --> 00:01:09.000 But barring such an anomalous upbringing, 00:01:09.000 --> 00:01:11.000 it is strange to imagine 00:01:11.000 --> 00:01:13.000 other realms separate from ours, 00:01:13.000 --> 00:01:15.000 most with fundamentally different features, 00:01:15.000 --> 00:01:18.000 that would rightly be called universes of their own. 00:01:18.000 --> 00:01:20.000 And yet, 00:01:20.000 --> 00:01:22.000 speculative though the idea surely is, 00:01:22.000 --> 00:01:24.000 I aim to convince you 00:01:24.000 --> 00:01:26.000 that there's reason for taking it seriously, 00:01:26.000 --> 00:01:28.000 as it just might be right. 00:01:28.000 --> 00:01:31.000 I'm going to tell the story of the multiverse in three parts. 00:01:31.000 --> 00:01:33.000 In part one, 00:01:33.000 --> 00:01:35.000 I'm going to describe those Nobel Prize-winning results 00:01:35.000 --> 00:01:37.000 and to highlight a profound mystery 00:01:37.000 --> 00:01:39.000 which those results revealed. 00:01:39.000 --> 00:01:41.000 In part two, 00:01:41.000 --> 00:01:43.000 I'll offer a solution to that mystery. 00:01:43.000 --> 00:01:45.000 It's based on an approach called string theory, 00:01:45.000 --> 00:01:47.000 and that's where the idea of the multiverse 00:01:47.000 --> 00:01:49.000 will come into the story. 00:01:49.000 --> 00:01:51.000 Finally, in part three, 00:01:51.000 --> 00:01:53.000 I'm going to describe a cosmological theory 00:01:53.000 --> 00:01:55.000 called inflation, 00:01:55.000 --> 00:01:58.000 which will pull all the pieces of the story together. NOTE Paragraph 00:01:58.000 --> 00:02:02.000 Okay, part one starts back in 1929 00:02:02.000 --> 00:02:04.000 when the great astronomer Edwin Hubble 00:02:04.000 --> 00:02:07.000 realized that the distant galaxies 00:02:07.000 --> 00:02:09.000 were all rushing away from us, 00:02:09.000 --> 00:02:11.000 establishing that space itself is stretching, 00:02:11.000 --> 00:02:13.000 it's expanding. 00:02:13.000 --> 00:02:16.000 Now this was revolutionary. 00:02:16.000 --> 00:02:19.000 The prevailing wisdom was that on the largest of scales 00:02:19.000 --> 00:02:21.000 the universe was static. 00:02:21.000 --> 00:02:23.000 But even so, 00:02:23.000 --> 00:02:26.000 there was one thing that everyone was certain of: 00:02:26.000 --> 00:02:29.000 The expansion must be slowing down. 00:02:29.000 --> 00:02:32.000 That, much as the gravitational pull of the Earth 00:02:32.000 --> 00:02:35.000 slows the ascent of an apple tossed upward, 00:02:35.000 --> 00:02:37.000 the gravitational pull 00:02:37.000 --> 00:02:39.000 of each galaxy on every other 00:02:39.000 --> 00:02:41.000 must be slowing 00:02:41.000 --> 00:02:43.000 the expansion of space. NOTE Paragraph 00:02:43.000 --> 00:02:46.000 Now let's fast-forward to the 1990s 00:02:46.000 --> 00:02:48.000 when those two teams of astronomers 00:02:48.000 --> 00:02:50.000 I mentioned at the outset 00:02:50.000 --> 00:02:52.000 were inspired by this reasoning 00:02:52.000 --> 00:02:54.000 to measure the rate 00:02:54.000 --> 00:02:56.000 at which the expansion has been slowing. 00:02:56.000 --> 00:02:58.000 And they did this 00:02:58.000 --> 00:03:00.000 by painstaking observations 00:03:00.000 --> 00:03:02.000 of numerous distant galaxies, 00:03:02.000 --> 00:03:04.000 allowing them to chart 00:03:04.000 --> 00:03:07.000 how the expansion rate has changed over time. 00:03:07.000 --> 00:03:10.000 Here's the surprise: 00:03:10.000 --> 00:03:13.000 They found that the expansion is not slowing down. 00:03:13.000 --> 00:03:15.000 Instead they found that it's speeding up, 00:03:15.000 --> 00:03:17.000 going faster and faster. 00:03:17.000 --> 00:03:19.000 That's like tossing an apple upward 00:03:19.000 --> 00:03:21.000 and it goes up faster and faster. 00:03:21.000 --> 00:03:23.000 Now if you saw an apple do that, 00:03:23.000 --> 00:03:25.000 you'd want to know why. 00:03:25.000 --> 00:03:27.000 What's pushing on it? NOTE Paragraph 00:03:27.000 --> 00:03:29.000 Similarly, the astronomers' results 00:03:29.000 --> 00:03:32.000 are surely well-deserving of the Nobel Prize, 00:03:32.000 --> 00:03:36.000 but they raised an analogous question. 00:03:36.000 --> 00:03:38.000 What force is driving all galaxies 00:03:38.000 --> 00:03:41.000 to rush away from every other 00:03:41.000 --> 00:03:44.000 at an ever-quickening speed? 00:03:44.000 --> 00:03:46.000 Well the most promising answer 00:03:46.000 --> 00:03:49.000 comes from an old idea of Einstein's. 00:03:49.000 --> 00:03:51.000 You see, we are all used to gravity 00:03:51.000 --> 00:03:54.000 being a force that does one thing, 00:03:54.000 --> 00:03:56.000 pulls objects together. 00:03:56.000 --> 00:03:58.000 But in Einstein's theory of gravity, 00:03:58.000 --> 00:04:00.000 his general theory of relativity, 00:04:00.000 --> 00:04:03.000 gravity can also push things apart. NOTE Paragraph 00:04:03.000 --> 00:04:06.000 How? Well according to Einstein's math, 00:04:06.000 --> 00:04:08.000 if space is uniformly filled 00:04:08.000 --> 00:04:10.000 with an invisible energy, 00:04:10.000 --> 00:04:13.000 sort of like a uniform, invisible mist, 00:04:13.000 --> 00:04:16.000 then the gravity generated by that mist 00:04:16.000 --> 00:04:18.000 would be repulsive, 00:04:18.000 --> 00:04:20.000 repulsive gravity, 00:04:20.000 --> 00:04:23.000 which is just what we need to explain the observations. 00:04:23.000 --> 00:04:25.000 Because the repulsive gravity 00:04:25.000 --> 00:04:27.000 of an invisible energy in space -- 00:04:27.000 --> 00:04:29.000 we now call it dark energy, 00:04:29.000 --> 00:04:32.000 but I've made it smokey white here so you can see it -- 00:04:32.000 --> 00:04:34.000 its repulsive gravity 00:04:34.000 --> 00:04:36.000 would cause each galaxy to push against every other, 00:04:36.000 --> 00:04:38.000 driving expansion to speed up, 00:04:38.000 --> 00:04:40.000 not slow down. 00:04:40.000 --> 00:04:42.000 And this explanation 00:04:42.000 --> 00:04:44.000 represents great progress. NOTE Paragraph 00:04:44.000 --> 00:04:47.000 But I promised you a mystery 00:04:47.000 --> 00:04:49.000 here in part one. 00:04:49.000 --> 00:04:51.000 Here it is. 00:04:51.000 --> 00:04:53.000 When the astronomers worked out 00:04:53.000 --> 00:04:56.000 how much of this dark energy 00:04:56.000 --> 00:04:58.000 must be infusing space 00:04:58.000 --> 00:05:00.000 to account for the cosmic speed up, 00:05:00.000 --> 00:05:02.000 look at what they found. 00:05:09.000 --> 00:05:11.000 This number is small. 00:05:11.000 --> 00:05:13.000 Expressed in the relevant unit, 00:05:13.000 --> 00:05:15.000 it is spectacularly small. 00:05:15.000 --> 00:05:18.000 And the mystery is to explain this peculiar number. 00:05:18.000 --> 00:05:20.000 We want this number 00:05:20.000 --> 00:05:22.000 to emerge from the laws of physics, 00:05:22.000 --> 00:05:25.000 but so far no one has found a way to do that. NOTE Paragraph 00:05:25.000 --> 00:05:28.000 Now you might wonder, 00:05:28.000 --> 00:05:30.000 should you care? 00:05:30.000 --> 00:05:32.000 Maybe explaining this number 00:05:32.000 --> 00:05:34.000 is just a technical issue, 00:05:34.000 --> 00:05:37.000 a technical detail of interest to experts, 00:05:37.000 --> 00:05:39.000 but of no relevance to anybody else. 00:05:39.000 --> 00:05:42.000 Well it surely is a technical detail, 00:05:42.000 --> 00:05:44.000 but some details really matter. 00:05:44.000 --> 00:05:46.000 Some details provide 00:05:46.000 --> 00:05:48.000 windows into uncharted realms of reality, 00:05:48.000 --> 00:05:51.000 and this peculiar number may be doing just that, 00:05:51.000 --> 00:05:54.000 as the only approach that's so far made headway to explain it 00:05:54.000 --> 00:05:57.000 invokes the possibility of other universes -- 00:05:57.000 --> 00:06:00.000 an idea that naturally emerges from string theory, 00:06:00.000 --> 00:06:03.000 which takes me to part two: string theory. NOTE Paragraph 00:06:03.000 --> 00:06:07.000 So hold the mystery of the dark energy 00:06:07.000 --> 00:06:09.000 in the back of your mind 00:06:09.000 --> 00:06:11.000 as I now go on to tell you 00:06:11.000 --> 00:06:14.000 three key things about string theory. 00:06:14.000 --> 00:06:16.000 First off, what is it? 00:06:16.000 --> 00:06:19.000 Well it's an approach to realize Einstein's dream 00:06:19.000 --> 00:06:22.000 of a unified theory of physics, 00:06:22.000 --> 00:06:24.000 a single overarching framework 00:06:24.000 --> 00:06:26.000 that would be able to describe 00:06:26.000 --> 00:06:28.000 all the forces at work in the universe. 00:06:28.000 --> 00:06:30.000 And the central idea of string theory 00:06:30.000 --> 00:06:32.000 is quite straightforward. 00:06:32.000 --> 00:06:34.000 It says that if you examine 00:06:34.000 --> 00:06:36.000 any piece of matter ever more finely, 00:06:36.000 --> 00:06:38.000 at first you'll find molecules 00:06:38.000 --> 00:06:41.000 and then you'll find atoms and subatomic particles. 00:06:41.000 --> 00:06:43.000 But the theory says that if you could probe smaller, 00:06:43.000 --> 00:06:46.000 much smaller than we can with existing technology, 00:06:46.000 --> 00:06:49.000 you'd find something else inside these particles -- 00:06:49.000 --> 00:06:52.000 a little tiny vibrating filament of energy, 00:06:52.000 --> 00:06:55.000 a little tiny vibrating string. 00:06:55.000 --> 00:06:57.000 And just like the strings on a violin, 00:06:57.000 --> 00:06:59.000 they can vibrate in different patterns 00:06:59.000 --> 00:07:01.000 producing different musical notes. 00:07:01.000 --> 00:07:03.000 These little fundamental strings, 00:07:03.000 --> 00:07:05.000 when they vibrate in different patterns, 00:07:05.000 --> 00:07:07.000 they produce different kinds of particles -- 00:07:07.000 --> 00:07:09.000 so electrons, quarks, neutrinos, photons, 00:07:09.000 --> 00:07:11.000 all other particles 00:07:11.000 --> 00:07:13.000 would be united into a single framework, 00:07:13.000 --> 00:07:16.000 as they would all arise from vibrating strings. 00:07:16.000 --> 00:07:19.000 It's a compelling picture, 00:07:19.000 --> 00:07:21.000 a kind of cosmic symphony, 00:07:21.000 --> 00:07:23.000 where all the richness 00:07:23.000 --> 00:07:25.000 that we see in the world around us 00:07:25.000 --> 00:07:27.000 emerges from the music 00:07:27.000 --> 00:07:30.000 that these little, tiny strings can play. NOTE Paragraph 00:07:30.000 --> 00:07:32.000 But there's a cost 00:07:32.000 --> 00:07:34.000 to this elegant unification, 00:07:34.000 --> 00:07:36.000 because years of research 00:07:36.000 --> 00:07:39.000 have shown that the math of string theory doesn't quite work. 00:07:39.000 --> 00:07:41.000 It has internal inconsistencies, 00:07:41.000 --> 00:07:43.000 unless we allow 00:07:43.000 --> 00:07:46.000 for something wholly unfamiliar -- 00:07:46.000 --> 00:07:49.000 extra dimensions of space. 00:07:49.000 --> 00:07:52.000 That is, we all know about the usual three dimensions of space. 00:07:52.000 --> 00:07:54.000 And you can think about those 00:07:54.000 --> 00:07:57.000 as height, width and depth. 00:07:57.000 --> 00:08:00.000 But string theory says that, on fantastically small scales, 00:08:00.000 --> 00:08:02.000 there are additional dimensions 00:08:02.000 --> 00:08:04.000 crumpled to a tiny size so small 00:08:04.000 --> 00:08:06.000 that we have not detected them. 00:08:06.000 --> 00:08:08.000 But even though the dimensions are hidden, 00:08:08.000 --> 00:08:11.000 they would have an impact on things that we can observe 00:08:11.000 --> 00:08:14.000 because the shape of the extra dimensions 00:08:14.000 --> 00:08:17.000 constrains how the strings can vibrate. 00:08:17.000 --> 00:08:19.000 And in string theory, 00:08:19.000 --> 00:08:22.000 vibration determines everything. 00:08:22.000 --> 00:08:24.000 So particle masses, the strengths of forces, 00:08:24.000 --> 00:08:27.000 and most importantly, the amount of dark energy 00:08:27.000 --> 00:08:29.000 would be determined 00:08:29.000 --> 00:08:31.000 by the shape of the extra dimensions. 00:08:31.000 --> 00:08:34.000 So if we knew the shape of the extra dimensions, 00:08:34.000 --> 00:08:37.000 we should be able to calculate these features, 00:08:37.000 --> 00:08:40.000 calculate the amount of dark energy. NOTE Paragraph 00:08:40.000 --> 00:08:42.000 The challenge 00:08:42.000 --> 00:08:44.000 is we don't know 00:08:44.000 --> 00:08:47.000 the shape of the extra dimensions. 00:08:47.000 --> 00:08:49.000 All we have 00:08:49.000 --> 00:08:51.000 is a list of candidate shapes 00:08:51.000 --> 00:08:54.000 allowed by the math. 00:08:54.000 --> 00:08:56.000 Now when these ideas were first developed, 00:08:56.000 --> 00:08:58.000 there were only about five different candidate shapes, 00:08:58.000 --> 00:09:00.000 so you can imagine 00:09:00.000 --> 00:09:02.000 analyzing them one-by-one 00:09:02.000 --> 00:09:04.000 to determine if any yield 00:09:04.000 --> 00:09:06.000 the physical features we observe. 00:09:06.000 --> 00:09:08.000 But over time the list grew 00:09:08.000 --> 00:09:10.000 as researchers found other candidate shapes. 00:09:10.000 --> 00:09:13.000 From five, the number grew into the hundreds and then the thousands -- 00:09:13.000 --> 00:09:16.000 A large, but still manageable, collection to analyze, 00:09:16.000 --> 00:09:18.000 since after all, 00:09:18.000 --> 00:09:21.000 graduate students need something to do. 00:09:21.000 --> 00:09:23.000 But then the list continued to grow 00:09:23.000 --> 00:09:26.000 into the millions and the billions, until today. 00:09:26.000 --> 00:09:28.000 The list of candidate shapes 00:09:28.000 --> 00:09:33.000 has soared to about 10 to the 500. NOTE Paragraph 00:09:33.000 --> 00:09:36.000 So, what to do? 00:09:36.000 --> 00:09:39.000 Well some researchers lost heart, 00:09:39.000 --> 00:09:42.000 concluding that was so many candidate shapes for the extra dimensions, 00:09:42.000 --> 00:09:45.000 each giving rise to different physical features, 00:09:45.000 --> 00:09:47.000 string theory would never make 00:09:47.000 --> 00:09:49.000 definitive, testable predictions. 00:09:49.000 --> 00:09:53.000 But others turned this issue on its head, 00:09:53.000 --> 00:09:55.000 taking us to the possibility of a multiverse. 00:09:55.000 --> 00:09:57.000 Here's the idea. 00:09:57.000 --> 00:10:00.000 Maybe each of these shapes is on an equal footing with every other. 00:10:00.000 --> 00:10:02.000 Each is as real as every other, 00:10:02.000 --> 00:10:04.000 in the sense 00:10:04.000 --> 00:10:06.000 that there are many universes, 00:10:06.000 --> 00:10:09.000 each with a different shape, for the extra dimensions. 00:10:09.000 --> 00:10:11.000 And this radical proposal 00:10:11.000 --> 00:10:14.000 has a profound impact on this mystery: 00:10:14.000 --> 00:10:17.000 the amount of dark energy revealed by the Nobel Prize-winning results. NOTE Paragraph 00:10:17.000 --> 00:10:19.000 Because you see, 00:10:19.000 --> 00:10:22.000 if there are other universes, 00:10:22.000 --> 00:10:24.000 and if those universes 00:10:24.000 --> 00:10:28.000 each have, say, a different shape for the extra dimensions, 00:10:28.000 --> 00:10:30.000 then the physical features of each universe will be different, 00:10:30.000 --> 00:10:32.000 and in particular, 00:10:32.000 --> 00:10:34.000 the amount of dark energy in each universe 00:10:34.000 --> 00:10:36.000 will be different. 00:10:36.000 --> 00:10:38.000 Which means that the mystery 00:10:38.000 --> 00:10:40.000 of explaining the amount of dark energy we've now measured 00:10:40.000 --> 00:10:43.000 would take on a wholly different character. 00:10:43.000 --> 00:10:45.000 In this context, 00:10:45.000 --> 00:10:48.000 the laws of physics can't explain one number for the dark energy 00:10:48.000 --> 00:10:51.000 because there isn't just one number, 00:10:51.000 --> 00:10:53.000 there are many numbers. 00:10:53.000 --> 00:10:55.000 Which means 00:10:55.000 --> 00:10:58.000 we have been asking the wrong question. 00:10:58.000 --> 00:11:00.000 It's that the right question to ask is, 00:11:00.000 --> 00:11:03.000 why do we humans find ourselves in a universe 00:11:03.000 --> 00:11:06.000 with a particular amount of dark energy we've measured 00:11:06.000 --> 00:11:09.000 instead of any of the other possibilities 00:11:09.000 --> 00:11:11.000 that are out there? NOTE Paragraph 00:11:11.000 --> 00:11:14.000 And that's a question on which we can make headway. 00:11:14.000 --> 00:11:16.000 Because those universes 00:11:16.000 --> 00:11:18.000 that have much more dark energy than ours, 00:11:18.000 --> 00:11:21.000 whenever matter tries to clump into galaxies, 00:11:21.000 --> 00:11:24.000 the repulsive push of the dark energy is so strong 00:11:24.000 --> 00:11:26.000 that it blows the clump apart 00:11:26.000 --> 00:11:28.000 and galaxies don't form. 00:11:28.000 --> 00:11:31.000 And in those universes that have much less dark energy, 00:11:31.000 --> 00:11:33.000 well they collapse back on themselves so quickly 00:11:33.000 --> 00:11:36.000 that, again, galaxies don't form. 00:11:36.000 --> 00:11:39.000 And without galaxies, there are no stars, no planets 00:11:39.000 --> 00:11:41.000 and no chance 00:11:41.000 --> 00:11:43.000 for our form of life 00:11:43.000 --> 00:11:45.000 to exist in those other universes. NOTE Paragraph 00:11:45.000 --> 00:11:47.000 So we find ourselves in a universe 00:11:47.000 --> 00:11:50.000 with the particular amount of dark energy we've measured 00:11:50.000 --> 00:11:53.000 simply because our universe has conditions 00:11:53.000 --> 00:11:57.000 hospitable to our form of life. 00:11:57.000 --> 00:11:59.000 And that would be that. 00:11:59.000 --> 00:12:01.000 Mystery solved, 00:12:01.000 --> 00:12:03.000 multiverse found. 00:12:03.000 --> 00:12:08.000 Now some find this explanation unsatisfying. 00:12:08.000 --> 00:12:10.000 We're used to physics 00:12:10.000 --> 00:12:13.000 giving us definitive explanations for the features we observe. 00:12:13.000 --> 00:12:15.000 But the point is, 00:12:15.000 --> 00:12:18.000 if the feature you're observing 00:12:18.000 --> 00:12:20.000 can and does take on 00:12:20.000 --> 00:12:22.000 a wide variety of different values 00:12:22.000 --> 00:12:25.000 across the wider landscape of reality, 00:12:25.000 --> 00:12:27.000 then thinking one explanation 00:12:27.000 --> 00:12:29.000 for a particular value 00:12:29.000 --> 00:12:32.000 is simply misguided. NOTE Paragraph 00:12:32.000 --> 00:12:34.000 An early example 00:12:34.000 --> 00:12:37.000 comes from the great astronomer Johannes Kepler 00:12:37.000 --> 00:12:39.000 who was obsessed with understanding 00:12:39.000 --> 00:12:41.000 a different number -- 00:12:41.000 --> 00:12:45.000 why the Sun is 93 million miles away from the Earth. 00:12:45.000 --> 00:12:48.000 And he worked for decades trying to explain this number, 00:12:48.000 --> 00:12:51.000 but he never succeeded, and we know why. 00:12:51.000 --> 00:12:53.000 Kepler was asking 00:12:53.000 --> 00:12:55.000 the wrong question. NOTE Paragraph 00:12:55.000 --> 00:12:58.000 We now know that there are many planets 00:12:58.000 --> 00:13:01.000 at a wide variety of different distances from their host stars. 00:13:01.000 --> 00:13:04.000 So hoping that the laws of physics 00:13:04.000 --> 00:13:07.000 will explain one particular number, 93 million miles, 00:13:07.000 --> 00:13:10.000 well that is simply wrongheaded. 00:13:10.000 --> 00:13:12.000 Instead the right question to ask is, 00:13:12.000 --> 00:13:15.000 why do we humans find ourselves on a planet 00:13:15.000 --> 00:13:17.000 at this particular distance, 00:13:17.000 --> 00:13:20.000 instead of any of the other possibilities? 00:13:20.000 --> 00:13:23.000 And again, that's a question we can answer. 00:13:23.000 --> 00:13:26.000 Those planets which are much closer to a star like the Sun 00:13:26.000 --> 00:13:28.000 would be so hot 00:13:28.000 --> 00:13:30.000 that our form of life wouldn't exist. 00:13:30.000 --> 00:13:33.000 And those planets that are much farther away from the star, 00:13:33.000 --> 00:13:35.000 well they're so cold 00:13:35.000 --> 00:13:37.000 that, again, our form of life would not take hold. 00:13:37.000 --> 00:13:39.000 So we find ourselves 00:13:39.000 --> 00:13:41.000 on a planet at this particular distance 00:13:41.000 --> 00:13:43.000 simply because it yields conditions 00:13:43.000 --> 00:13:46.000 vital to our form of life. 00:13:46.000 --> 00:13:49.000 And when it comes to planets and their distances, 00:13:49.000 --> 00:13:53.000 this clearly is the right kind of reasoning. 00:13:53.000 --> 00:13:55.000 The point is, 00:13:55.000 --> 00:13:58.000 when it comes to universes and the dark energy that they contain, 00:13:58.000 --> 00:14:02.000 it may also be the right kind of reasoning. NOTE Paragraph 00:14:02.000 --> 00:14:05.000 One key difference, of course, 00:14:05.000 --> 00:14:07.000 is we know that there are other planets out there, 00:14:07.000 --> 00:14:10.000 but so far I've only speculated on the possibility 00:14:10.000 --> 00:14:12.000 that there might be other universes. 00:14:12.000 --> 00:14:14.000 So to pull it all together, 00:14:14.000 --> 00:14:16.000 we need a mechanism 00:14:16.000 --> 00:14:19.000 that can actually generate other universes. 00:14:19.000 --> 00:14:22.000 And that takes me to my final part, part three. 00:14:22.000 --> 00:14:25.000 Because such a mechanism has been found 00:14:25.000 --> 00:14:28.000 by cosmologists trying to understand the Big Bang. 00:14:28.000 --> 00:14:30.000 You see, when we speak of the Big Bang, 00:14:30.000 --> 00:14:32.000 we often have an image 00:14:32.000 --> 00:14:34.000 of a kind of cosmic explosion 00:14:34.000 --> 00:14:36.000 that created our universe 00:14:36.000 --> 00:14:39.000 and set space rushing outward. NOTE Paragraph 00:14:39.000 --> 00:14:41.000 But there's a little secret. 00:14:41.000 --> 00:14:44.000 The Big Bang leaves out something pretty important, 00:14:44.000 --> 00:14:46.000 the Bang. 00:14:46.000 --> 00:14:49.000 It tells us how the universe evolved after the Bang, 00:14:49.000 --> 00:14:51.000 but gives us no insight 00:14:51.000 --> 00:14:55.000 into what would have powered the Bang itself. 00:14:55.000 --> 00:14:57.000 And this gap was finally filled 00:14:57.000 --> 00:14:59.000 by an enhanced version of the Big Bang theory. 00:14:59.000 --> 00:15:02.000 It's called inflationary cosmology, 00:15:02.000 --> 00:15:06.000 which identified a particular kind of fuel 00:15:06.000 --> 00:15:08.000 that would naturally generate 00:15:08.000 --> 00:15:10.000 an outward rush of space. 00:15:10.000 --> 00:15:13.000 The fuel is based on something called a quantum field, 00:15:13.000 --> 00:15:16.000 but the only detail that matters for us 00:15:16.000 --> 00:15:19.000 is that this fuel proves to be so efficient 00:15:19.000 --> 00:15:21.000 that it's virtually impossible 00:15:21.000 --> 00:15:23.000 to use it all up, 00:15:23.000 --> 00:15:25.000 which means in the inflationary theory, 00:15:25.000 --> 00:15:28.000 the Big Bang giving rise to our universe 00:15:28.000 --> 00:15:31.000 is likely not a one-time event. 00:15:31.000 --> 00:15:34.000 Instead the fuel not only generated our Big Bang, 00:15:34.000 --> 00:15:40.000 but it would also generate countless other Big Bangs, 00:15:40.000 --> 00:15:43.000 each giving rise to its own separate universe 00:15:43.000 --> 00:15:45.000 with our universe becoming but one bubble 00:15:45.000 --> 00:15:48.000 in a grand cosmic bubble bath of universes. NOTE Paragraph 00:15:48.000 --> 00:15:50.000 And now, when we meld this with string theory, 00:15:50.000 --> 00:15:52.000 here's the picture we're led to. 00:15:52.000 --> 00:15:54.000 Each of these universes has extra dimensions. 00:15:54.000 --> 00:15:57.000 The extra dimensions take on a wide variety of different shapes. 00:15:57.000 --> 00:16:00.000 The different shapes yield different physical features. 00:16:00.000 --> 00:16:03.000 And we find ourselves in one universe instead of another 00:16:03.000 --> 00:16:06.000 simply because it's only in our universe 00:16:06.000 --> 00:16:09.000 that the physical features, like the amount of dark energy, 00:16:09.000 --> 00:16:13.000 are right for our form of life to take hold. 00:16:13.000 --> 00:16:16.000 And this is the compelling but highly controversial picture 00:16:16.000 --> 00:16:18.000 of the wider cosmos 00:16:18.000 --> 00:16:20.000 that cutting-edge observation and theory 00:16:20.000 --> 00:16:24.000 have now led us to seriously consider. NOTE Paragraph 00:16:24.000 --> 00:16:28.000 One big remaining question, of course, is, 00:16:28.000 --> 00:16:31.000 could we ever confirm 00:16:31.000 --> 00:16:34.000 the existence of other universes? 00:16:34.000 --> 00:16:36.000 Well let me describe 00:16:36.000 --> 00:16:39.000 one way that might one day happen. 00:16:39.000 --> 00:16:41.000 The inflationary theory 00:16:41.000 --> 00:16:43.000 already has strong observational support. 00:16:43.000 --> 00:16:45.000 Because the theory predicts 00:16:45.000 --> 00:16:47.000 that the Big Bang would have been so intense 00:16:47.000 --> 00:16:50.000 that as space rapidly expanded, 00:16:50.000 --> 00:16:52.000 tiny quantum jitters from the micro world 00:16:52.000 --> 00:16:55.000 would have been stretched out to the macro world, 00:16:55.000 --> 00:16:58.000 yielding a distinctive fingerprint, 00:16:58.000 --> 00:17:00.000 a pattern of slightly hotter spots and slightly colder spots, 00:17:00.000 --> 00:17:02.000 across space, 00:17:02.000 --> 00:17:05.000 which powerful telescopes have now observed. 00:17:05.000 --> 00:17:08.000 Going further, if there are other universes, 00:17:08.000 --> 00:17:10.000 the theory predicts that every so often 00:17:10.000 --> 00:17:12.000 those universes can collide. 00:17:12.000 --> 00:17:14.000 And if our universe got hit by another, 00:17:14.000 --> 00:17:16.000 that collision 00:17:16.000 --> 00:17:18.000 would generate an additional subtle pattern 00:17:18.000 --> 00:17:20.000 of temperature variations across space 00:17:20.000 --> 00:17:22.000 that we might one day 00:17:22.000 --> 00:17:24.000 be able to detect. 00:17:24.000 --> 00:17:27.000 And so exotic as this picture is, 00:17:27.000 --> 00:17:29.000 it may one day be grounded 00:17:29.000 --> 00:17:31.000 in observations, 00:17:31.000 --> 00:17:34.000 establishing the existence of other universes. NOTE Paragraph 00:17:34.000 --> 00:17:36.000 I'll conclude 00:17:36.000 --> 00:17:39.000 with a striking implication 00:17:39.000 --> 00:17:41.000 of all these ideas 00:17:41.000 --> 00:17:43.000 for the very far future. 00:17:43.000 --> 00:17:45.000 You see, we learned 00:17:45.000 --> 00:17:47.000 that our universe is not static, 00:17:47.000 --> 00:17:49.000 that space is expanding, 00:17:49.000 --> 00:17:51.000 that that expansion is speeding up 00:17:51.000 --> 00:17:53.000 and that there might be other universes 00:17:53.000 --> 00:17:55.000 all by carefully examining 00:17:55.000 --> 00:17:57.000 faint pinpoints of starlight 00:17:57.000 --> 00:18:00.000 coming to us from distant galaxies. 00:18:00.000 --> 00:18:03.000 But because the expansion is speeding up, 00:18:03.000 --> 00:18:05.000 in the very far future, 00:18:05.000 --> 00:18:08.000 those galaxies will rush away so far and so fast 00:18:08.000 --> 00:18:11.000 that we won't be able to see them -- 00:18:11.000 --> 00:18:13.000 not because of technological limitations, 00:18:13.000 --> 00:18:15.000 but because of the laws of physics. 00:18:15.000 --> 00:18:17.000 The light those galaxies emit, 00:18:17.000 --> 00:18:20.000 even traveling at the fastest speed, the speed of light, 00:18:20.000 --> 00:18:22.000 will not be able to overcome 00:18:22.000 --> 00:18:25.000 the ever-widening gulf between us. 00:18:25.000 --> 00:18:27.000 So astronomers in the far future 00:18:27.000 --> 00:18:29.000 looking out into deep space 00:18:29.000 --> 00:18:32.000 will see nothing but an endless stretch 00:18:32.000 --> 00:18:36.000 of static, inky, black stillness. 00:18:36.000 --> 00:18:38.000 And they will conclude 00:18:38.000 --> 00:18:40.000 that the universe is static and unchanging 00:18:40.000 --> 00:18:43.000 and populated by a single central oasis of matter 00:18:43.000 --> 00:18:45.000 that they inhabit -- 00:18:45.000 --> 00:18:47.000 a picture of the cosmos 00:18:47.000 --> 00:18:50.000 that we definitively know to be wrong. NOTE Paragraph 00:18:50.000 --> 00:18:53.000 Now maybe those future astronomers will have records 00:18:53.000 --> 00:18:55.000 handed down from an earlier era, 00:18:55.000 --> 00:18:57.000 like ours, 00:18:57.000 --> 00:18:59.000 attesting to an expanding cosmos 00:18:59.000 --> 00:19:01.000 teeming with galaxies. 00:19:01.000 --> 00:19:03.000 But would those future astronomers 00:19:03.000 --> 00:19:06.000 believe such ancient knowledge? 00:19:06.000 --> 00:19:08.000 Or would they believe 00:19:08.000 --> 00:19:11.000 in the black, static empty universe 00:19:11.000 --> 00:19:15.000 that their own state-of-the-art observations reveal? 00:19:15.000 --> 00:19:17.000 I suspect the latter. 00:19:17.000 --> 00:19:19.000 Which means that we are living 00:19:19.000 --> 00:19:22.000 through a remarkably privileged era 00:19:22.000 --> 00:19:24.000 when certain deep truths about the cosmos 00:19:24.000 --> 00:19:26.000 are still within reach 00:19:26.000 --> 00:19:28.000 of the human spirit of exploration. 00:19:28.000 --> 00:19:33.000 It appears that it may not always be that way. 00:19:33.000 --> 00:19:35.000 Because today's astronomers, 00:19:35.000 --> 00:19:38.000 by turning powerful telescopes to the sky, 00:19:38.000 --> 00:19:41.000 have captured a handful of starkly informative photons -- 00:19:41.000 --> 00:19:44.000 a kind of cosmic telegram 00:19:44.000 --> 00:19:46.000 billions of years in transit. 00:19:46.000 --> 00:19:50.000 and the message echoing across the ages is clear. 00:19:50.000 --> 00:19:53.000 Sometimes nature guards her secrets 00:19:53.000 --> 00:19:55.000 with the unbreakable grip 00:19:55.000 --> 00:19:57.000 of physical law. 00:19:57.000 --> 00:20:01.000 Sometimes the true nature of reality beckons 00:20:01.000 --> 00:20:04.000 from just beyond the horizon. NOTE Paragraph 00:20:04.000 --> 00:20:06.000 Thank you very much. NOTE Paragraph 00:20:06.000 --> 00:20:10.000 (Applause) NOTE Paragraph 00:20:10.000 --> 00:20:12.000 Chris Anderson: Brian, thank you. 00:20:12.000 --> 00:20:14.000 The range of ideas you've just spoken about 00:20:14.000 --> 00:20:17.000 are dizzying, exhilarating, incredible. 00:20:17.000 --> 00:20:19.000 How do you think 00:20:19.000 --> 00:20:21.000 of where cosmology is now, 00:20:21.000 --> 00:20:23.000 in a sort of historical side? 00:20:23.000 --> 00:20:26.000 Are we in the middle of something unusual historically in your opinion? NOTE Paragraph 00:20:26.000 --> 00:20:28.000 BG: Well it's hard to say. 00:20:28.000 --> 00:20:31.000 When we learn that astronomers of the far future 00:20:31.000 --> 00:20:34.000 may not have enough information to figure things out, 00:20:34.000 --> 00:20:37.000 the natural question is, maybe we're already in that position 00:20:37.000 --> 00:20:40.000 and certain deep, critical features of the universe 00:20:40.000 --> 00:20:43.000 already have escaped our ability to understand 00:20:43.000 --> 00:20:45.000 because of how cosmology evolves. 00:20:45.000 --> 00:20:47.000 So from that perspective, 00:20:47.000 --> 00:20:49.000 maybe we will always be asking questions 00:20:49.000 --> 00:20:51.000 and never be able to fully answer them. NOTE Paragraph 00:20:51.000 --> 00:20:53.000 On the other hand, we now can understand 00:20:53.000 --> 00:20:55.000 how old the universe is. 00:20:55.000 --> 00:20:57.000 We can understand 00:20:57.000 --> 00:21:00.000 how to understand the data from the microwave background radiation 00:21:00.000 --> 00:21:03.000 that was set down 13.72 billion years ago -- 00:21:03.000 --> 00:21:05.000 and yet, we can do calculations today to predict how it will look 00:21:05.000 --> 00:21:07.000 and it matches. 00:21:07.000 --> 00:21:09.000 Holy cow! That's just amazing. 00:21:09.000 --> 00:21:12.000 So on the one hand, it's just incredible where we've gotten, 00:21:12.000 --> 00:21:16.000 but who knows what sort of blocks we may find in the future. NOTE Paragraph 00:21:16.000 --> 00:21:19.000 CA: You're going to be around for the next few days. 00:21:19.000 --> 00:21:21.000 Maybe some of these conversations can continue. 00:21:21.000 --> 00:21:23.000 Thank you. Thank you, Brian. (BG: My pleasure.) NOTE Paragraph 00:21:23.000 --> 00:21:26.000 (Applause)