Jim Gates: What is String Theory, Its Status, Its Open Challenges?

00:00:00.000 | - We have to talk a bit about the magical,

00:00:04.920 | the mysterious string theory, super string theory.

00:00:08.280 | - Sure.

00:00:09.120 | - There's still maybe this aspect of it,

00:00:12.320 | which is there's still, for me,

00:00:14.880 | from an outsider's perspective,

00:00:16.440 | this fascinating heated debate

00:00:19.040 | on the status of string theory.

00:00:21.660 | Can you clarify this debate,

00:00:23.640 | perhaps articulating the various views,

00:00:25.720 | and say where you land on it?

00:00:27.800 | - So first of all, I doubt that I will be able

00:00:30.200 | to say anything to clarify the debate

00:00:32.720 | around string theory for a general audience.

00:00:37.720 | Part of the reason is because string theory

00:00:40.760 | has done something I've never seen theoretical physics do.

00:00:45.680 | It has broken out into consciousness

00:00:47.920 | of the general public before we're finished.

00:00:50.480 | You see, string theory doesn't actually exist,

00:00:52.880 | because when we use the word theory,

00:00:54.200 | we mean a particular set of attributes.

00:00:57.160 | In particular, it means that you have

00:00:58.600 | an overarching paradigm that explains

00:01:00.960 | what it is that you're doing.

00:01:03.000 | No such overarching paradigm exists for string theory.

00:01:07.000 | What string theory is currently

00:01:08.880 | is an enormously large, mutually reinforcing

00:01:11.880 | collection of mathematical facts,

00:01:14.480 | in which we can find no contradictions.

00:01:16.520 | We don't know why it's there,

00:01:18.680 | but we can certainly say that without challenge.

00:01:21.800 | Now, just because you find a piece of mathematics

00:01:23.560 | doesn't mean that it applies to nature.

00:01:26.260 | And in fact, there has been a very heated debate

00:01:30.240 | about whether string theory is some sort of hysteria

00:01:34.280 | among the community of theoretical physicists,

00:01:37.040 | or whether it has something fundamental

00:01:38.480 | to say about our universe.

00:01:41.440 | We don't yet know the answer to that question.

00:01:44.960 | What those of us who study string theory will tell you

00:01:47.560 | are things like, string theory has been

00:01:50.320 | extraordinarily productive in getting us

00:01:52.240 | to think more deeply, even about mathematics

00:01:55.200 | that's not string theory, but the kind of mathematics

00:01:57.960 | that we've used to describe elementary particles.

00:02:00.800 | There have been spin-offs from string theory,

00:02:02.600 | and this has been going on now for two decades almost,

00:02:05.560 | that have allowed us, for example,

00:02:08.000 | to more accurately calculate the force between electrons

00:02:11.320 | with the presence of quantum mechanics.

00:02:13.600 | This is not something you hear about in the public.

00:02:16.120 | There are other similar things,

00:02:17.880 | that kind of property I just told you about

00:02:21.680 | is what's called weak-strong duality,

00:02:23.680 | and it comes directly from string theory.

00:02:25.920 | There are other things such as

00:02:28.800 | a property called holography, which allows one

00:02:34.000 | to take equations and look at them

00:02:37.280 | on the boundary of a space, and then to know information

00:02:40.000 | about inside the space without actually

00:02:41.720 | doing calculations there.

00:02:43.400 | This has come directly from string theory.

00:02:45.040 | So there are a number of direct mathematical effects

00:02:49.520 | that we learn in string theory, but we take these ideas

00:02:52.320 | and look at math that we already know,

00:02:54.280 | and we find suddenly we're more powerful.

00:02:56.440 | This is a pretty good indication there's something

00:02:58.240 | interesting going on with string theory itself.

00:03:00.120 | - So it's the early days of a powerful

00:03:01.960 | mathematical framework.

00:03:03.000 | - That's what we have right now.

00:03:04.200 | - What are the big, first of all,

00:03:06.720 | for most people, probably, which as you said,

00:03:10.440 | most general public would know actually

00:03:12.360 | what string theory is, which is at the highest level,

00:03:15.900 | which is a fascinating fact.

00:03:18.480 | - Well, string theory is what they do

00:03:20.040 | on the Big Bang Theory, right?

00:03:21.600 | (laughing)

00:03:23.360 | One, can you maybe describe what is string theory,

00:03:28.240 | and two, what are the open challenges?

00:03:32.160 | - So what is string theory?

00:03:34.440 | Well, the simplest explanation I can provide

00:03:38.940 | is to go back and ask what are particles,

00:03:43.000 | which is the question you first asked me.

00:03:45.520 | - What's the smallest thing?

00:03:48.640 | - Yeah, what's the smallest thing?

00:03:50.920 | So, particles, one way I try to describe

00:03:55.920 | particles to people to start,

00:03:58.640 | I want you to imagine a little ball.

00:04:00.800 | And I want you to let the size of that ball

00:04:03.560 | shrink until it has no extent whatsoever.

00:04:05.960 | But it still has the mass of the ball.

00:04:08.720 | That's actually what Newton was working with

00:04:12.720 | when he first invented physics.

00:04:14.200 | He's the real inventor of the massive particle,

00:04:17.080 | which is this idea that underlies all of physics.

00:04:21.400 | So that's where we start.

00:04:22.360 | It's a mathematical construct that you get

00:04:25.000 | by taking a limit of things that you know.

00:04:27.200 | So what's a string?

00:04:29.800 | Well, in the same analogy, I would say,

00:04:32.240 | now I want you to start with a piece of spaghetti.

00:04:35.200 | So we all know what that looks like.

00:04:37.160 | And now I want you to let the thickness of the spaghetti

00:04:40.760 | shrink until it has no thickness.

00:04:43.520 | Mathematically, I mean, in words this makes no sense,

00:04:46.120 | but mathematically this actually works.

00:04:49.040 | And you get this mathematical object out.

00:04:51.440 | It has properties that are like spaghetti.

00:04:53.400 | It can wiggle and jiggle,

00:04:55.160 | but it can also move collectively

00:04:57.680 | like a piece of spaghetti.

00:04:59.480 | It's the mathematics of those sorts of objects

00:05:02.040 | that constitute string theory.

00:05:03.620 | - And does the multidimensional, 11-dimensional,

00:05:09.920 | however many dimensional, more than four dimension,

00:05:13.920 | is that a crazy idea to you?

00:05:15.840 | Is that the stranger aspect of string theory to you?

00:05:20.040 | - Not really.

00:05:21.600 | And also partly because of my own research.

00:05:24.280 | So earlier we talked about these strange symbols

00:05:28.560 | that we've discovered inside the equations.

00:05:31.080 | It turns out that to a very large extent,

00:05:33.040 | a dinkers don't really care about the number of dimensions.

00:05:35.380 | They kind of have an internal mathematical consistency

00:05:38.300 | that allows them to be manifest

00:05:39.920 | in many different dimensions.

00:05:41.800 | Since supersymmetry is a part of string theory,

00:05:44.280 | then this same property you would expect

00:05:46.200 | to be inherited by string theory.

00:05:48.340 | However, another little known fact,

00:05:51.380 | which is not in the public debate,

00:05:53.160 | is that there are actually strings

00:05:54.720 | that are only four dimensional.

00:05:56.720 | This is something that was discovered

00:05:58.440 | at the end of the 80s

00:06:00.800 | by three different groups of physicists

00:06:02.720 | working independently.

00:06:03.840 | I and my friend Warren Siegel,

00:06:06.400 | who were at the University of Maryland at the time,

00:06:08.520 | were able to prove that there's mathematics

00:06:10.640 | that looks totally four dimensional,

00:06:11.940 | and yet it's a string.

00:06:13.520 | There was a group in Germany

00:06:15.120 | that used slightly different mathematics,

00:06:17.720 | but they found the same result.

00:06:19.520 | And then there was a group at Cornell

00:06:21.280 | who using yet a third piece of mathematics

00:06:23.520 | found the same result.

00:06:24.360 | So the fact that extra dimensions

00:06:27.400 | is so widely talked about in the public

00:06:30.680 | is partly a function of how the public

00:06:32.680 | has come to understand string theory

00:06:34.240 | and how the story has been told to them.

00:06:36.520 | But there are alternatives you don't know about.

00:06:38.920 | (silence)

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