--> Display at 01:00:00:06. --> Display at 01:00:06:07 --> Erase at 01:00:10:27 Funding for this program is provided by Annenberg Media.

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1 --> Display at 01:00:00:06 --> Display at 01:00:06:07 --> Erase at 01:00:10:27 Funding for this program is provided by Annenberg Media. --> Display at 01:00:28:21 NARRATOR: String theory has been touted --> Display at 01:00:30:29 as the Theory of Everything, uniting physics at all scales, --> Display at 01:00:36:08 from the cosmological to the subatomic. --> Display at 01:00:40:22 While it is the only theory --> Display at 01:00:42:26 that mathematically works at all levels, --> Display at 01:00:45:07 currently, there is no observable evidence for it. --> Display at 01:00:51:03 But string theory is still helping to shed light --> Display at 01:00:53:24 on some unanswered questions in physics. --> Display at 01:00:58:16 Henry Tye, of Cornell University, --> Display at 01:01:01:08 uses string theory to explain the very beginning --> Display at 01:01:04:00 of our universe, the inflation that occurred --> Display at 01:01:06:22 in its first fraction of a second. --> Display at 01:01:10:21

2 Tye is looking for evidence in the form of "cosmic strings," --> Display at 01:01:14:07 infinitely long and extremely thin objects in our universe. --> Display at 01:01:18:25 If found, cosmic strings could be --> Display at 01:01:21:09 the first evidence for string theory. --> Display at 01:01:23:10 TYE: If ever somebody sees cosmic strings, --> Display at 01:01:26:20 that would be revolutionary. --> Display at 01:01:29:02 NARRATOR: Juan Maldacena, a string theorist --> Display at 01:01:32:25 at the Institute for Advanced Study, --> Display at 01:01:35:19 had been examining another enigma in our universe -- --> Display at 01:01:38:08 black holes. --> Display at 01:01:41:08 MALDACENA: It's one of the strangest predictions --> Display at 01:01:43:10 of general relativity, --> Display at 01:01:44:25 the theory that space-time can bend so much --> Display at 01:01:46:16 that it produces a hole in the middle of space. --> Display at 01:01:48:17 NARRATOR: While researching black holes, Maldacena uncovered --> Display at 01:01:52:15

3 an extremely useful relationship between string theory --> Display at 01:01:55:10 and the more familiar equations of particle physics. --> Display at 01:01:59:09 Physicists hope to use his model --> Display at 01:02:01:22 to answer questions in fields ranging --> Display at 01:02:03:17 from cosmology to condensed matter physics. --> Display at 01:02:07:09 SACHDEV: If someone had told me that string theory had something --> Display at 01:02:09:06 to do with condensed matter, like superconductors, --> Display at 01:02:11:11 I would have said that's impossible. --> Display at 01:02:13:17 NARRATOR: Both theorists --> Display at 01:02:15:00 are applying the mathematics of string theory --> Display at 01:02:17:28 --> Erase at 01:02:22:03 to decode some of the unanswered questions of our universe. --> Display at 01:02:35:16 NARRATOR: Henry Tye is a theoretical physicist --> Display at 01:02:37:16 at Cornell University. --> Display at 01:02:39:01 TYE: It's very exciting, you know, it's fun. --> Display at 01:02:42:26 For me, a lot of time

4 is thinking --> Display at 01:02:44:11 what's an interesting question to ask, --> Display at 01:02:46:14 what interesting things I can say. --> Display at 01:02:49:18 So it's, like, two limits. --> Display at 01:02:54:02 MAN: This is a much less important contribution. --> Display at 01:02:56:02 TYE: Sometimes we are arguing, sometimes we disagree, --> Display at 01:03:00:03 and then we try to resolve the disagreement. --> Display at 01:03:01:25 And you're resolving disagreement, --> Display at 01:03:03:09 usually, something new comes up. --> Display at 01:03:06:10 The distributor is right there. --> Display at 01:03:10:07 NARRATOR: Tye is currently grappling with string theory, --> Display at 01:03:13:01 which some believe to be the answer --> Display at 01:03:15:07 to one of physics' biggest inconsistencies. --> Display at 01:03:18:11 While the equations in Einstein's general relativity --> Display at 01:03:22:17 work for gravity at large scales, --> Display at 01:03:25:12 these equations cannot explain

5 gravity in the quantum world, --> Display at 01:03:29:19 at the scale of atoms and subatomic particles. --> Display at 01:03:35:04 We don't know how to merge general relativity --> Display at 01:03:39:13 of gravity together with quantum mechanics, --> Display at 01:03:42:16 and that was the outstanding problem that --> Display at 01:03:45:11 --> Erase at 01:03:49:25 had been plaguing fundamental physics for many years. --> Display at 01:03:53:16 NARRATOR: In the early 1980s, physicists believed --> Display at 01:03:56:26 an answer to this problem could emerge --> Display at 01:03:59:21 from the newly developing field of string theory. --> Display at 01:04:02:23 The equations of string theory --> Display at 01:04:04:16 are compatible with describing gravity in the quantum world. --> Display at 01:04:09:28 Mathematically, the gravity described by string --> Display at 01:04:12:10 is consistent with quantum mechanics. --> Display at 01:04:15:18 In fact, that's the only theory we know --> Display at 01:04:17:03

6 --> Erase at 01:04:19:00 that's consistent with quantum mechanics today. --> Display at 01:04:22:21 NARRATOR: String theory proposes that --> Display at 01:04:24:17 the building blocks of matter are not pointlike particles, --> Display at 01:04:27:29 but instead are vibrating strings. --> Display at 01:04:32:05 What string theory does is that we say that, no, no, --> Display at 01:04:35:02 all these little particles look like particles because --> Display at 01:04:38:06 we don't have enough resolution to look closely enough. --> Display at 01:04:42:14 They're so tiny that you really need --> Display at 01:04:44:19 an infinitely powerful microscope --> Display at 01:04:47:09 or a fantastically powerful microscope in order to see --> Display at 01:04:50:16 that maybe it's not a point, maybe it's not a point particle, --> Display at 01:04:53:10 --> Erase at 01:04:56:15 but it's a little loop or a little string. --> Display at 01:05:00:13 NARRATOR: String theory also proposes extra dimensions. --> Display at 01:05:04:09 While our universe consists of three spatial dimensions

7 --> Display at 01:05:08:14 and one of time, string theory has --> Display at 01:05:11:22 as many as seven extra spatial dimensions. --> Display at 01:05:14:20 TYE: So what happened to the other dimensions? --> Display at 01:05:17:25 The other dimensions are so small that we don't see them --> Display at 01:05:20:20 and we only see the three large dimensions --> Display at 01:05:23:09 and that's why we look like we live --> Display at 01:05:26:00 in a 3-spatial-dimension universe. --> Display at 01:05:27:29 NARRATOR: Over time, physicists realized --> Display at 01:05:31:22 that string theory contains more than just strings. --> Display at 01:05:35:17 It includes multidimensional objects, --> Display at 01:05:37:26 or "branes," for short. --> Display at 01:05:41:04 Our entire observable universe --> Display at 01:05:42:25 is made up of a 3-dimensional brane, --> Display at 01:05:45:10 represented here as two dimensions, --> Display at 01:05:47:11 that moves through

8 a higher-dimensional space. --> Display at 01:05:51:06 TYE: We realized that string theory contained --> Display at 01:05:53:13 other objects, branes. --> Display at 01:05:55:10 That means that things are 2-dimensional, 3-dimensional. --> Display at 01:05:58:14 They come together in a very neatly arranged package, --> Display at 01:06:01:18 --> Erase at 01:06:04:26 which, actually, opened new areas in mathematics. --> Display at 01:06:07:20 NARRATOR: While, mathematically, --> Display at 01:06:09:05 string theory appears capable of unifying --> Display at 01:06:11:18 Einstein's general relativity and quantum mechanics, --> Display at 01:06:15:09 this Theory of Everything has made few predictions --> Display at 01:06:18:14 that can be tested experimentally, --> Display at 01:06:20:12 and no evidence for string theory has ever been observed. --> Display at 01:06:24:00 In any case, the equation is not easy to solve. --> Display at 01:06:27:05 I mean, looking at it, I can't tell what the solution is. --> Display at 01:06:30:17 NARRATOR: But Henry Tye

9 is working to change that. --> Display at 01:06:32:13 TYE: The way to prove string theory, actually, --> Display at 01:06:34:26 --> Erase at 01:06:37:08 turns out the best way is probably cosmology. --> Display at 01:06:42:01 NARRATOR: Tye is using string theory --> Display at 01:06:44:01 to describe and explain the beginning of our universe. --> Display at 01:06:47:10 In the late 1970s, cosmologists proposed --> Display at 01:06:51:28 that our universe began with a period of rapid inflation. --> Display at 01:06:55:21 In its first fraction of a second, --> Display at 01:06:58:19 our universe expanded by a factor of 10 to the > Display at 01:07:02:21 that's 1 with 30 zeros after it. --> Display at 01:07:06:18 In this brief blip of time, --> Display at 01:07:08:21 our universe grew by a greater percentage --> Display at 01:07:11:01 than it has in the 14 billion years since. --> Display at 01:07:15:19 Supported by numerous lines of evidence, --> Display at 01:07:18:00 this period of inflation is now an accepted part

10 --> Display at 01:07:20:27 of our standard model of cosmology, --> Display at 01:07:23:03 --> Erase at 01:07:26:13 but how it happened is far from clear. --> Display at 01:07:30:01 TYE: Now, we know that inflation probably happened, --> Display at 01:07:33:18 but how does it happen, what causes it, --> Display at 01:07:37:01 what leads to inflation, that's still open. --> Display at 01:07:40:11 And that question, you have to answer --> Display at 01:07:41:22 only when you have a more fundamental theory, --> Display at 01:07:44:01 and the only more fundamental theory we have is string theory. --> Display at 01:07:47:02 NARRATOR: In 1998, --> Display at 01:07:51:24 while strolling through the Cornell campus, --> Display at 01:07:54:01 Henry Tye and fellow physicist Gia Dvali --> Display at 01:07:58:07 had a breakthrough idea for how they could explain inflation --> Display at 01:08:00:26 using the tools of string theory. --> Display at 01:08:05:01 Gia Dvali and I walked around Beebe Lake,

11 --> Display at 01:08:06:16 talking about branes, large extra dimensions, and, --> Display at 01:08:09:14 all of a sudden, we realized that the inflationary universe --> Display at 01:08:12:11 can be explained by having branes moving --> Display at 01:08:15:18 --> Erase at 01:08:18:01 towards each other, and that was the eureka moment. --> Display at 01:08:21:21 NARRATOR: According to their model, --> Display at 01:08:23:14 during the period of inflation, --> Display at 01:08:25:05 two branes were moving towards each other, --> Display at 01:08:27:12 and as they got closer and closer, --> Display at 01:08:29:23 the interaction between the branes drove the inflation. --> Display at 01:08:33:27 The branes are attracted to each other --> Display at 01:08:36:26 because one is a brane and one is an anti-brane. --> Display at 01:08:40:22 These branes would eventually collide. --> Display at 01:08:44:23 TYE: And when they collide, they annihilate, okay? --> Display at 01:08:48:10 And when they annihilate,

12 they release a lot of energy. --> Display at 01:08:51:03 NARRATOR: According to Tye's theory, --> Display at 01:08:55:22 this collision marks the end of inflation, --> Display at 01:08:58:13 and the vast amount of energy released --> Display at 01:09:00:26 in the collision gets converted to matter. --> Display at 01:09:03:23 It is the moment in the Big Bang when all the matter --> Display at 01:09:06:22 in the universe as we know it is created. --> Display at 01:09:10:04 And since strings are the fundamental building blocks --> Display at 01:09:12:15 in string theory, this matter is in the form of strings. --> Display at 01:09:16:25 These strings are created in various sizes, --> Display at 01:09:19:28 some large enough to stretch across our entire universe. --> Display at 01:09:24:08 These are called "cosmic strings." --> Display at 01:09:26:29 TYE: Because, in string theory, --> Display at 01:09:28:15 the only thing you can go to, at this stage, is strings. --> Display at 01:09:31:13 Some of them are tiny,

13 little strings. --> Display at 01:09:33:19 Brane/anti-brane annihilation will also produce --> Display at 01:09:35:19 excited strings or very excited strings or very big strings. --> Display at 01:09:40:15 So there would be a whole spectrum of them --> Display at 01:09:42:17 and some of them would be so big --> Display at 01:09:44:05 that they are larger than horizon-size, okay? --> Display at 01:09:47:19 --> Erase at 01:09:51:08 Or universe size. So those are cosmic strings. --> Display at 01:09:55:07 NARRATOR: Although, in 2010, --> Display at 01:09:57:06 cosmic strings have not yet been observed, --> Display at 01:09:59:25 they could be the key to providing the first evidence --> Display at 01:10:03:26 for Tye's brane inflation and for string theory. --> Display at 01:10:05:22 TYE: If the basic idea is correct, we would expect to see --> Display at 01:10:10:21 some cosmic strings in our universe, even today, --> Display at 01:10:15:07 and the question is how to detect them. --> Display at 01:10:18:16 NARRATOR: Physicists search for cosmic strings

14 --> Display at 01:10:22:13 in different ways. --> Display at 01:10:24:13 One way is through the lensing of faraway objects. --> Display at 01:10:28:27 TYE: Lensing's a way to do it -- if a cosmic string tension --> Display at 01:10:32:12 --> Erase at 01:10:35:26 is big enough, then you can lens a galaxy. --> Display at 01:10:38:27 NARRATOR: Gravitational lensing occurs when a dense object, --> Display at 01:10:42:25 such as a massive star, bends space-time and causes the path --> Display at 01:10:46:25 of a light ray from a more distant cosmic object --> Display at 01:10:49:22 to be deflected around it, producing a distorted image. --> Display at 01:10:56:26 Therefore a massive cosmic string --> Display at 01:10:59:08 would also cause the light of a galaxy --> Display at 01:11:01:10 to bend around it, resulting in a double image. --> Display at 01:11:05:28 In 2004, physicists thought they might have found evidence --> Display at 01:11:10:19 of a cosmic string through gravitational lensing. --> Display at 01:11:14:14 TYE: They find something which is, like, two galaxies

15 --> Display at 01:11:17:28 are very close to each other, same color -- --> Display at 01:11:21:19 which means the same spectroscopy -- --> Display at 01:11:23:02 same luminosity, and same distance from us. --> Display at 01:11:28:09 So this is very much what you expect --> Display at 01:11:31:12 if you have a cosmic string between one galaxy and us --> Display at 01:11:35:22 and the light will bend around the cosmic string --> Display at 01:11:38:09 and you can bend left side and right side --> Display at 01:11:41:00 and so one galaxy will look like two galaxies, --> Display at 01:11:44:23 but those two galaxies would be identical, so people think --> Display at 01:11:51:20 --> Erase at 01:11:55:12 that maybe this is a signature of cosmic strings. --> Display at 01:11:59:07 NARRATOR: To look at these galaxies in finer detail, --> Display at 01:12:01:24 they turned to the Hubble telescope. --> Display at 01:12:05:22 TYE: In January 2006, the Hubble space telescope --> Display at 01:12:10:04 looked at it very carefully

16 and found that it so happens --> Display at 01:12:14:15 that there would be two very similar-looking galaxies --> Display at 01:12:17:24 next to each other, okay? --> Display at 01:12:19:18 But they are not a single galaxy --> Display at 01:12:22:12 due to cosmic strings providing double image. --> Display at 01:12:26:15 If it's a cosmic string, then what happened -- --> Display at 01:12:29:03 these two images would have, clearly, a line between them, --> Display at 01:12:32:18 that one is shifted a little bit from the other one --> Display at 01:12:35:00 and that line would be a very, very distinctive line --> Display at 01:12:38:10 and that would be a signature of cosmic strings. --> Display at 01:12:40:28 So this is an example which turned out not to be the case, --> Display at 01:12:44:18 but it's this kind of detection and continued searching --> Display at 01:12:48:15 for these kind of events that, hopefully, one day, --> Display at 01:12:51:10 --> Erase at 01:12:54:24 will show that cosmic strings exist. --> Display at 01:12:57:25 NARRATOR: Tye is hopeful that

17 he will find cosmic strings, --> Display at 01:13:01:21 which would provide the first hint of evidence --> Display at 01:13:04:11 for string theory. --> Display at 01:13:08:12 And by measuring these distinctive signatures --> Display at 01:13:10:10 and showing their existence and showing that they are --> Display at 01:13:14:15 really part of superstring theory --> Display at 01:13:16:16 will be a fantastic triumph of theoretical physics --> Display at 01:13:20:19 or fundamental physics or physics, in general. --> Display at 01:13:24:04 NARRATOR: While Tye uses string theory to understand --> Display at 01:13:28:27 the beginning of our universe, Juan Maldacena has uncovered --> Display at 01:13:33:19 an extremely useful relationship between string theory --> Display at 01:13:37:07 and the more familiar equations of particle physics. --> Display at 01:13:41:00 Physicists hope to use his model to answer questions in fields --> Display at 01:13:44:29 ranging from cosmology to condensed matter physics. --> Display at 01:13:49:05 Juan Maldacena is a theoretical physicist

18 --> Display at 01:13:54:02 at the Institute for Advanced Study in Princeton, New Jersey. --> Display at 01:13:58:09 Growing up, Maldacena was always interested in how things work. --> Display at 01:14:02:19 MALDACENA: I was interested in how the TV works, --> Display at 01:14:04:20 how the radio works, how technological things work, --> Display at 01:14:08:14 and then I was interested in reading --> Display at 01:14:10:03 about the basic laws of physics, in the sense of what are --> Display at 01:14:13:23 the smallest things that govern the behavior of bigger things. --> Display at 01:14:18:13 NARRATOR: In the 1990s, Maldacena began studying --> Display at 01:14:23:29 the dynamics of one of the most surprising predictions --> Display at 01:14:27:05 of general relativity -- black holes. --> Display at 01:14:30:09 MALDACENA: A black hole is an object that forms --> Display at 01:14:33:23 when you put too much matter in a small region of space --> Display at 01:14:38:13 so that the gravitational forces become so big that, essentially, --> Display at 01:14:41:10 nothing can escape -- not even light can escape,

19 --> Display at 01:14:44:03 and that's why it's called "black." --> Display at 01:14:46:03 It's one of the strangest predictions --> Display at 01:14:49:21 of general relativity -- that space-time can bend so much --> Display at 01:14:52:21 that it produces a hole in the middle of space. --> Display at 01:14:54:11 NARRATOR: According to general relativity, --> Display at 01:14:58:17 once something crosses the surface or horizon --> Display at 01:15:01:08 of a black hole, it is lost forever. --> Display at 01:15:05:18 But in the 1970s, --> Display at 01:15:07:13 physicist Stephen Hawking proposed a radical new idea. --> Display at 01:15:13:01 He realized that, according to quantum mechanics, black holes --> Display at 01:15:16:18 are actually continuously emitting tiny amounts of matter. --> Display at 01:15:20:20 This is known as "Hawking radiation." --> Display at 01:15:23:09 KLEBANOV: In a classical black hole, nothing escapes from it. --> Display at 01:15:27:15 What Hawking realized, which was an amazing discovery, --> Display at 01:15:34:23

20 was that, if you actually consider quantum mechanics --> Display at 01:15:38:23 --> Erase at 01:15:43:05 in the vicinity of the horizon, actually, things do get out. --> Display at 01:15:47:21 NARRATOR: Because a black hole is constantly emitting --> Display at 01:15:49:28 Hawking radiation, it slowly evaporates over time --> Display at 01:15:53:24 and will eventually disappear, like water in a tea kettle. --> Display at 01:15:58:16 This has led to another scientific quandary, --> Display at 01:16:03:10 called the "black hole information paradox." --> Display at 01:16:06:02 MALDACENA: Since a black hole would form --> Display at 01:16:07:17 and then emit this radiation and completely disappear --> Display at 01:16:10:28 because it's losing mass to this radiation and, --> Display at 01:16:13:05 in the end, you would be left with nothing, --> Display at 01:16:15:03 you would have a situation where you would form --> Display at 01:16:16:23 the black hole in many different ways, --> Display at 01:16:18:24 they always evaporate in the same way,

21 --> Display at 01:16:20:09 and therefore you would have different initial states --> Display at 01:16:23:01 that would lead to the same final state, --> Display at 01:16:24:20 --> Erase at 01:16:26:12 and this is not allowed in quantum mechanics. --> Display at 01:16:30:07 NARRATOR: In quantum mechanics, --> Display at 01:16:31:27 if you have different initial states, --> Display at 01:16:33:21 you should get different final states. --> Display at 01:16:36:28 But with black holes, --> Display at 01:16:39:09 although they are formed from different objects, --> Display at 01:16:41:16 they all end up in the same final state, --> Display at 01:16:43:27 --> Erase at 01:16:48:10 so there is no information left about how they were created. --> Display at 01:16:52:01 This became an important paradox for string theorists to solve. --> Display at 01:16:56:18 If black holes violate the laws of quantum mechanics, --> Display at 01:16:59:24 this would be devastating for string theory. --> Display at 01:17:02:18 MALDACENA: Due to the results of Hawking,

22 --> Display at 01:17:04:05 people had the suspicion that perhaps black holes violate --> Display at 01:17:07:28 the laws of quantum mechanics, and if that were the case, --> Display at 01:17:10:21 that would be dramatic for string theory, and so on. --> Display at 01:17:14:00 That would be a way to disprove string theory. --> Display at 01:17:19:17 NARRATOR: Many physicists were struggling to solve --> Display at 01:17:21:27 the black hole information paradox, --> Display at 01:17:24:21 and, in 1997, Maldacena had a breakthrough --> Display at 01:17:29:11 when he uncovered a mathematical relationship --> Display at 01:17:31:07 between two seemingly unrelated theories, --> Display at 01:17:33:01 one with gravity and one without, --> Display at 01:17:36:29 that could provide insight into different problems --> Display at 01:17:39:21 in physics, including this paradox. --> Display at 01:17:43:20 It is commonly known as the "AdS/CFT correspondence." --> Display at 01:17:50:12 Maldacena's remarkable contribution has developed

23 --> Display at 01:17:51:29 into what's called the AdS/CFT correspondence. --> Display at 01:17:56:09 That's quite a mouthful, but what it ends up doing is --> Display at 01:17:58:10 relating two theories which are seemingly unrelated. --> Display at 01:18:03:01 NARRATOR: This relationship is an example of a duality. --> Display at 01:18:06:24 KLEBANOV: His paper got people tremendously excited. --> Display at 01:18:12:14 Duality, it's a very familiar notion in theoretical physics. --> Display at 01:18:15:04 It's basically that the same physical system may have --> Display at 01:18:20:00 two different descriptions, and, usually, they're complementary. --> Display at 01:18:26:17 NARRATOR: AdS/CFT equates a string theory with gravity --> Display at 01:18:32:16 to a particle theory without gravity. --> Display at 01:18:35:16 Within a given space-time, represented here as a sphere, --> Display at 01:18:40:06 the string theory lives on the interior --> Display at 01:18:43:17 and the particle theory lives on the boundary. --> Display at 01:18:46:12 Additionally, the string theory has

24 --> Display at 01:18:48:03 one dimension more than the particle theory. --> Display at 01:18:51:04 Juan Maldacena explains --> Display at 01:18:54:13 that what I'll call a conventional theory -- --> Display at 01:18:57:09 a theory of ordinary elementary particles, but without gravity, --> Display at 01:18:59:26 can actually be equivalent to a theory --> Display at 01:19:01:24 that does include gravity, but there's a trick, which is --> Display at 01:19:05:01 that one theory is in one dimension --> Display at 01:19:06:26 and the theory with gravity is in one dimension more. --> Display at 01:19:09:22 MALDACENA: The duality's a relationship --> Display at 01:19:12:18 between a particle theory that lives on the boundary --> Display at 01:19:14:25 and a gravity theory that lives in the interior. --> Display at 01:19:18:13 So you could have a space-time --> Display at 01:19:20:12 which is, let's say, the surface of a sphere --> Display at 01:19:22:20 or, let's say, an apple or an orange. --> Display at 01:19:24:24 Then the surface,

25 or the skin of the apple, --> Display at 01:19:28:05 would be the boundary and the rest is the interior. --> Display at 01:19:31:04 And then you can either have a theory that lives only --> Display at 01:19:33:08 on the boundary -- that's the particle theory -- --> Display at 01:19:36:02 and an equivalent description would be, --> Display at 01:19:38:12 well, the gravitational theory living in the interior. --> Display at 01:19:41:00 There is a lot of mathematical evidence --> Display at 01:19:42:26 that the duality is true. --> Display at 01:19:44:25 Since it relates two theories, you can calculate --> Display at 01:19:48:04 in two theories and you find that the results are the same. --> Display at 01:19:52:22 NARRATOR: This duality is the first concrete example --> Display at 01:19:56:17 for a realization of what physicists call --> Display at 01:19:58:23 the "holographic principle," which relates one set --> Display at 01:20:02:10 of physical laws on the boundary of a region --> Display at 01:20:04:10 with a set of laws for the interior.

26 --> Display at 01:20:06:28 MALDACENA: It's called "holographic" because the idea --> Display at 01:20:08:24 is that all the physics that occurs in the interior --> Display at 01:20:11:20 is encoded on the boundary of some region. --> Display at 01:20:14:18 And in a hologram, an optical hologram, --> Display at 01:20:18:24 you have a 3-dimensional image is stored on a 2-dimensional --> Display at 01:20:22:17 photographic plate, so you have --> Display at 01:20:24:21 the whole information is encoded in these two dimensions, --> Display at 01:20:28:00 but when you look at it, you see a 3-dimensional image. --> Display at 01:20:30:18 NARRATOR: Along with contributions --> Display at 01:20:35:26 from other physicists, AdS/CFT also led to a resolution --> Display at 01:20:40:18 for the black hole information paradox. --> Display at 01:20:43:29 According to Maldacena's model, a black hole --> Display at 01:20:47:03 within a certain space-time is mathematically equivalent --> Display at 01:20:49:26 to a gas of particles on the boundary of that space-time.

27 --> Display at 01:20:53:28 And while it is very difficult to solve --> Display at 01:20:56:11 the black hole equations, understanding --> Display at 01:20:59:16 how the gas of particles behaves is relatively straightforward. --> Display at 01:21:04:21 Studying these particles on the boundary --> Display at 01:21:07:00 reveals a clearer description --> Display at 01:21:08:15 of the black hole and its Hawking radiation. --> Display at 01:21:13:09 In this description, information about --> Display at 01:21:14:22 how the black hole was created is not lost. --> Display at 01:21:19:21 MALDACENA: The duality helps us understand the fact that --> Display at 01:21:22:04 black holes respect the laws of quantum mechanics, --> Display at 01:21:24:22 which was something that was called into question. --> Display at 01:21:27:24 It says that Hawking radiation is an approximation --> Display at 01:21:29:23 to the exact answer, so the exact answer is, well, --> Display at 01:21:34:07 given by this gas of particles on the boundary

28 --> Display at 01:21:37:09 and it allows you to compute things precisely --> Display at 01:21:41:08 and in a way that information is not lost. --> Display at 01:21:44:23 So I think this convinced a lot of people, --> Display at 01:21:46:26 including Hawking himself, apparently, --> Display at 01:21:49:16 but it's still a little bit abstract, --> Display at 01:21:52:01 I think we still have a lot of work to do. --> Display at 01:21:54:26 Any gauge theory will have --> Display at 01:21:56:04 some kind of instability at finite R charge. --> Display at 01:22:00:08 NARRATOR: While the duality has been successful in helping --> Display at 01:22:02:12 to resolve the black hole information paradox, --> Display at 01:22:05:10 the duality is based in a hypothetical universe, --> Display at 01:22:08:26 one not found in nature. --> Display at 01:22:11:24 KLEBANOV: So the models we can solve -- --> Display at 01:22:14:02 I'm afraid that, literally, they are not realized in nature, --> Display at 01:22:17:24 but they can be used

29 as kind of schematic models --> Display at 01:22:21:18 --> Erase at 01:22:24:12 for things that are realized in nature. --> Display at 01:22:28:11 NARRATOR: As a model, AdS/CFT has been a useful approach --> Display at 01:22:32:10 to understanding theories in the real world. --> Display at 01:22:35:25 It has been used to analyze --> Display at 01:22:37:22 --> Erase at 01:22:40:29 or to get some intuition about theories in nature. --> Display at 01:22:43:18 NARRATOR: One area where it has been applied is --> Display at 01:22:47:04 in condensed matter physics. --> Display at 01:22:51:12 Subir Sachdev is --> Display at 01:22:53:11 a condensed matter theorist at Harvard University. --> Display at 01:22:57:01 SACHDEV: My field of physics is called condensed matter physics --> Display at 01:22:59:15 and we study the motion of electrons and crystals. --> Display at 01:23:03:18 So the challenge of the field is, knowing what we know --> Display at 01:23:06:04 about quantum mechanics, can we predict the quantum state --> Display at 01:23:09:11 of trillions and trillions

30 of electrons? --> Display at 01:23:11:18 Given the structure of a crystal and, say, --> Display at 01:23:16:02 something about the density of electrons in it, --> Display at 01:23:17:27 can you tell me is it going to be a metal --> Display at 01:23:19:26 or an insulator or a superconductor? --> Display at 01:23:22:14 NARRATOR: Currently, Sachdev is investigating superconductors. --> Display at 01:23:30:17 While standard conductors conduct electricity --> Display at 01:23:33:11 with resistance, superconductors do so --> Display at 01:23:36:12 with zero resistance, at extremely low temperatures. --> Display at 01:23:41:00 For Sachdev and his colleagues, the goal is to find materials --> Display at 01:23:43:28 that superconduct at relatively higher temperatures, --> Display at 01:23:48:23 allowing for practical applications, such as --> Display at 01:23:50:13 ultraefficient power grids that could transmit electricity --> Display at 01:23:54:05 over great distances without energy loss. --> Display at 01:23:57:20 SACHDEV: What we'd really like to do is,

31 --> Display at 01:23:59:10 once we have a complete theory, is predict -- --> Display at 01:24:01:11 Aha! If you went to the laboratory --> Display at 01:24:03:14 and you put together this element and that element --> Display at 01:24:06:07 and this element from the periodic table, --> Display at 01:24:07:25 you'll get this beautiful superconductor. --> Display at 01:24:10:15 --> Erase at 01:24:14:25 We are very far from that goal, but that's the ultimate aim. --> Display at 01:24:18:16 NARRATOR: Sachdev realized that the complicated mathematics --> Display at 01:24:23:21 he was using to understand superconductors is closely --> Display at 01:24:26:24 related to the particle physics without gravity in AdS/CFT. --> Display at 01:24:32:07 So in order to gain insight into his own work, --> Display at 01:24:35:15 he began exploring the other side of the duality -- --> Display at 01:24:39:02 string theory that includes gravity. --> Display at 01:24:41:28 SACHDEV: If someone had told me that string theory had something --> Display at 01:24:44:03 to do with condensed matter, like superconductors,

32 --> Display at 01:24:46:13 I would have said that's impossible. --> Display at 01:24:48:21 In some sense, these fields are about as far --> Display at 01:24:51:03 as any two fields of physics could be. --> Display at 01:24:53:07 And then I learned of Maldacena's correspondence where --> Display at 01:24:56:04 he and others realized that there was a connection between --> Display at 01:24:58:21 the type of theories we've been looking at without gravity --> Display at 01:25:02:28 --> Erase at 01:25:05:25 to theories with gravity and one-higher dimensions. --> Display at 01:25:09:15 NARRATOR: Maldacena's ideas have helped Sachdev --> Display at 01:25:12:00 get a better understanding of phase transitions --> Display at 01:25:14:19 of certain materials -- the temperature at which --> Display at 01:25:17:08 a solid changes to a superconducting state. --> Display at 01:25:20:21 SACHDEV: So, at that point, there is a phase transition --> Display at 01:25:22:23 in the quantum nature of the electrons --> Display at 01:25:25:00 and what we've realized, in the last few years,

33 --> Display at 01:25:28:27 is that these critical points are exactly the type --> Display at 01:25:31:08 of quantum state that's easily described --> Display at 01:25:33:28 by Maldacena's duality, and, somewhat amazingly, --> Display at 01:25:38:10 this dual description allows you to get at --> Display at 01:25:40:06 certain properties of this critical point --> Display at 01:25:44:04 --> Erase at 01:25:47:01 that you couldn't get at by the traditional methods. --> Display at 01:25:50:03 NARRATOR: These phase transitions involve --> Display at 01:25:53:01 strong interactions between particles --> Display at 01:25:54:27 that are extremely difficult to calculate, but mapping --> Display at 01:25:58:02 this system without gravity to a system with gravity, --> Display at 01:26:02:00 surprisingly, makes things easier. --> Display at 01:26:04:22 So in physics, it's useful, many times, --> Display at 01:26:06:19 to simplify your systems. --> Display at 01:26:08:04 The nature of the duality is such that, when the particles

34 --> Display at 01:26:12:16 on the boundary are very strongly interacting, --> Display at 01:26:14:25 the gravity description is relatively simple, --> Display at 01:26:19:18 so you can use this duality to be able to solve --> Display at 01:26:22:15 or to understand how at least certain cases --> Display at 01:26:25:12 --> Erase at 01:26:27:20 of strong interacting particles behave. --> Display at 01:26:30:17 NARRATOR: Along with Sachdev, there are a variety --> Display at 01:26:32:27 of research groups using the AdS/CFT correspondence --> Display at 01:26:36:29 to provide insights into unanswered questions --> Display at 01:26:39:26 in diverse areas of physics. --> Display at 01:26:43:21 Somehow, this subject has had a lot more spinoffs --> Display at 01:26:45:17 than, I think, anyone had the right to anticipate, --> Display at 01:26:49:28 particularly, these rather effective connections --> Display at 01:26:52:23 with nuclear physics, with other types of physical systems -- --> Display at 01:26:57:12 condensed matter physics and cosmology.

35 --> Display at 01:27:01:28 It goes way beyond, I think, what I could dream of. --> Display at 01:27:07:09 NARRATOR: In the past, --> Display at 01:27:10:12 science has not been able to successfully explain --> Display at 01:27:13:07 the beginning of our universe or black holes, --> Display at 01:27:16:10 but both Henry Tye and Juan Maldacena --> Display at 01:27:22:06 have used string theory and extra dimensions --> Display at 01:27:24:09 --> Erase at 01:27:27:25 to gain a better understanding of the physics of our universe. --> Display at 01:28:06:07 --> Erase at 01:28:11:17 Funding for this program is provided by Annenberg Media. --> Display at 01:28:14:23 For information about this --> Display at 01:28:16:08 and other Annenberg Media programs, --> Display at 01:28:19:03 call LEARNER --> Display at 01:28:21:06 and visit us at --> Display at 01:28:24:19