YouSaid · the spoken record

Cumrun Vafa

lines on the record: 172
first: 2021-07-26
most recent: 2021-07-26
sittings or episodes: 1
sources: podcast

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“Yes, more than that, he was my advisor, PhD advisor. So I got to know him very well and I benefited from his insights. In fact, What you say about them is accurate. He's not only brilliant, but he's also multifaceted in terms of the impact he has had in not only physics, but also mathematics. He's gotten the fields medal because of his work in mathematics. And rightly so, he has used his knowledge of physics in a way which impacted deep ideas in modern mathematics. And that's an example of the power of these ideas in modern high energy physics and string theory that the applicability of it to modern mathematics. So he's quite an exceptional individual. We don't come across such people a lot in history. So I think, yes, indeed, he's one of the rare figures in this history of this subject. He has had great impact on a lot of aspects of not just string theory, a lot of different areas in physics, and also, yes, in mathematics as well. So I think what...”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Which don't get any recognition, you know, yeah, you did this little work. Oh, yeah, you did this little work. Oh, yeah, yeah, five of you. Oh, yeah, this showed this pattern and then somebody else. Not fair. Me, those little guys, which kind of seem to do a little calculation here, a little thing there, which is not, doesn't rise to the occasion of this grandiose kind of thing, doesn't make it to the New York Times headlines and so on, deserve a lot of recognition. And I think they don't get enough. I would say that there should be this Nobel Prize for, you know, they have these doctors without borders, a huge group. They should do similar things, these string theories without borders. Kind of everybody is doing a lot of work. And I think that I would like to see that effort recognized.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“And they get identified with perhaps rightly with many of these new visions. But they are on the shoulders of these little scientists.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“There would be, but I think that part of this breakthrough prize was precisely the appreciation that when we have sufficient evidence, Theoretical as it is, and not experiment because of this technology lag, you appreciate what you think is the correct path. So there are many people who have been recognized precisely because they may not be around when it actually gets experimented, even though they discovered it. So there are many things like that that's going on in science. So I think that I would want to attach less significance to their recognitions. Of people. And I have a second review on this, which is there are people who look at these works that people have done and put them together and make the next big breakthrough.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Think it's possible that none of the living physicists will get the Nobel Prize on string theory, but somebody will. Because unfortunately, the technology available today is not very encouraging in terms of seeing directly evidence for string theory.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“With a big metal drinking champagne, I think to me the collective work is more exciting. And you mentioned my getting the breakthrough when I was getting it, I made sure to mention that it is because of the joint work that I've done with colleagues at that time. It was around 180 or so collaborators. And I acknowledge them in the webpage for them. I write all of their names and the collaborations that led to this. So to me, science is fun when it's collaboration. And yes, there are more important and less important figures as in any field. And that's true. That's true in String Theory as well. But I think that I would like to view this as a collective effort.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“How it gets recognized, I think, is secondary, in my opinion, than the appreciation that the effort is collective, that in fact that to me is the more important part of science that gets forgotten. For some reason, humanity likes heroes and science is no exception. We like heroes. But I personally try to avoid that trap. I feel in my work, most of my work is with colleagues. I have much more collaborations than solo author papers. And I enjoy it and I think that that's to me one of the most satisfying aspects of science is to interact and learn and debate ideas with colleagues because that influx of ideas enriches it. And that's why I find it interesting. To me, science, if I was in an island and if I was developing String Theory by myself and had nothing to do with anybody, it would be much less satisfying in my opinion, even if I could hit.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Other ideas that led to breakthroughs involving, for example, the example I told you about black holes and holography and the work that was later done by Maldacena about the properties of duality between particle physics and quantum gravity and the deeper connections of holography, and it continues. And there are many people within this range which I haven't even mentioned. They have done fantastic things.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Different people have been pushing it. And so, for example, the early epoch we just told you, people like Veneziano and Nambu and the Susquin and others were pushing it green and shorts were pushing it and so forth. So this was, or share and so on. So these were the initial periods of pioneers, I would say, of strength theory. And then there were the mid 80s that Edward Witten was the major proponent of string theory and he really changed the landscape of string theory in terms of what people do and how we view it. And I think his efforts brought a lot of attention to the community about high energy community to focus on this effort as the correct theory of unification of forces. So he brought a lot of research as well as, of course, the first rate work he himself did to this area. So that's in mid-80s and onwards and also in mid-90s where he was one of the proponents of the duality revolution in string theory. And with that came a lot of these”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“In the history of quite a lot of people, I mean, starting with Veneziano, who wasn't talking about strings. I mean, he wrote down the beginning of his strings. We cannot ignore that for sure. And so you start with that and you go on with various other figures and so on. So there are different epochs in string theory.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Were the key figures? I like the second version of the question because I think. Try to give a prize to one person in string theory doesn't do justice to the diversity of the subject. That to me is.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Doesn't allow you to pass them through each other. So the same techniques that work in higher dimension don't work in fourth dimension because 2 plus 2 is four. The same reason I was just telling you about strings finding each other in four. To classify for mathematicians as well. So there might be these things. So I cannot say that this is the reason that string theory is giving you 3 plus 1, but it could be a model for it. And so there are these kind of ideas that could underlie why we have three extra dimensions, which are large and the rest of them are small, but absolutely we have to have a good reason. We cannot leave it like that.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“That would be an explanation. That's a model we suggested with my colleague Brandenberger. But it turns out to be related to a deep piece of math. You see, for mathematicians, manifolds of dimension bigger than four are simple. Four dimensions is the hardest dimension for math. And it turns out the reason it's difficult is the following. It turns out that in higher dimension, you use what's called surgery in mathematical terminology, where you use these two-dimensional tubes to maneuver them off of each other. So you have 2 plus 2 becoming four in higher than four dimension, you can pass them through each other without them intersecting. In four dimension, 2 plus 2”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“So, if the dimension were too big, they would miss each other, they wouldn't be able to expand. So, in order to expand, they have to find each other, and three of them can find each other, and those can expand, and the other one will be stuck.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“In order to not put a halt, a string which is going this way and a string which is going that way should intersect each other and disconnect each other and unwind. So a string which winds this way and the string which finds the opposite way should find each other to reconnect and this way disappear. So, if they find each other and they disappear. But how can strings find each other? Well, the string moves and another string moves. A string is one-dimensional. One plus one is two. And 1 plus 1 is 2. And 2 plus 2 is 4. In four-dimensional spacetime, they will find each other. In higher dimensional spacetime, they typically miss each other.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Do strings do? Well, strings go around the box and move around and vibrate and all that, but also they can wrap around one side of the box to the other because I'm imagining a box with periodic boundary conditions, so what we call the torus. So the string can go from one side to the other. This is what we call a winding string. The string can wind around the box. Now, suppose you now evolve the universe because there's energy the universe starts to expand. But it doesn't expand too far. Why is it? Well, because there are these strings which are wrapped around from one side of the wall to the other. When the universe, the walls of the universe are growing, it is stretching the string and the strings are becoming very, very massive So it becomes difficult to expand. It kind of puts a halt on it.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Yeah, so we haven't explained that in string theory. Actually, I did write a model within String Theory to try to describe why we end up with three plus ones space-time dimensions, which are big compared to the rest of them. And even though this has not been, the technical difficulties to prove it is still not there. But I will explain the idea because the idea connects to some other piece of elegant math, which is the following. Consider a universe made of a box. Dimensional box, or in fact, if we serve in string theory nine dimensional box because we have nine spatial dimensions at one time. So imagine a nine-dimensional box. So we should imagine the box of typical size of the string, which is small. So the universe would naturally start with a very tiny nine-dimensional box.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“The fact that we are in three or four dimensions is already strange. The fact that Strings's story, I cannot go beyond 10 or maybe 11 or something, the fact that there's this upper bound, the range is not from 1 to infinity, it's from 1 to 10 or 11 or whatnot. It already brings a natural prior. Oh yeah, three or four is, you know, it's just on the average. If you pick some of the compactifications, then it could easily be that. So in other words, Makes it much more possible that it could be theory of our universe. So the fact that the dimension already is so small should be surprising. We don't ask that question. We should be surprised because we could have conceived of universes with our predimension. Why is it that we have such a small dimension? That's number one.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“So there are these aspects that give further evidence for string theory, connections between each other, connection with the real world, but then there are other things that come about. And I can try to give examples of that. So, these are further evidences, and these are certain predictions of string theory. They are not as detailed as we want, but there are still predictions. Why is the dimension of space and time 3 plus 1? I don't know. Just deal with it. Three plus one. But in physics, we want to know why. Well, take a random dimension from 1 to infinity. What's your random dimension? Random dimension from 1 to infinity would not be 4. It would most likely be a humongous number, if not infinity. I mean, there's no, if you choose any reasonable distribution which goes from one to infinity, three or four would not be your pick.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“But still, logically, it is a prediction because really we didn't know that Graviton that we later learned that, oh, that's the same as gravity. So literally, that's the way it was discovered. It wasn't put in by hand. So there are many things like that that are different facets of physics, like questions and condensed matter physics, questions of particle physics, questions about this and that has come together to find beautiful answers by using ideas from string theory at the same time as a lot of new math has emerged. That's an aspect which I wouldn't emphasize as evidence to physicists necessarily because they would say, well, okay, great, you got some math, but what's to do with reality? But as I explained, many of the physical principles we know of have beautiful math underpinning them. So it certainly leads further confidence that we may not be going astray, even though that's not the foolproof as we know.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Why did it have to be this rich? The subject is very rich. It's not something we were smart enough to develop. It came at us. I thought I explained to you the development of string theory came from accidental discovery. It wasn't because we were smart enough to come up with idea, oh yeah, string, of course, has gravity in it. No. It was accident discovery. So some people say it's not fair to say we have no evidence for string theory. Graviton. Gravity is an evidence for string theory. It's predicted by string theory. We didn't put it by hand. We got it. So there's a qualitative check. Okay, gravity is a prediction of string theory. It's a postdiction because we know gravity existed.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“It has brought connections between part of physics all the way. Suppose you're just interested in particle physics. Suppose you're not even interested in gravity at all. It turns out there are properties of certain particle physics models that string theory has been able to solve using gravity, using ideas from string theory, ideas known as holography, which is relating something which has to do with particles to something having to do with gravity.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Want to learn. I want to know how the nature works, even though I cannot prove it today that this is it because of experiments Should not prevent my mind not to think about it. So that's the attitude many string theorists follow. It should be like this. So that's the unanswer to the criticism. But there's actually a better answer to the criticism, I would say. We don't have experimental evidence for string theory, but we have theoretical evidence for string theory. And what do I mean by theoretical evidence for string theory? String theory has connected different parts of physics together. It didn't have to”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“They would have every right to say what you're talking about is not science, because in science we will have to have experimental consequences and checks. The difference between string theory and something which is not scientific is that string theory has predictions. The problem is that the predictions we have today of string theory is hard to access by experiments available with the energies we can achieve with a colliders today. It doesn't mean there's a problem with string theory. It just means technologically we are not that far ahead. Have two attitudes, you say, Well, if that's the case, why are you studying this subject? Because you can't do experiment today. Now, this is becoming a little bit more like mathematics in that sense. You say, well,”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“First of all, the criticism for string theory is healthy in the sense that in science we have to have different viewpoints and that's good. So I welcome criticism. And the reason for criticism, and I think that is a valid reason, is that there has been zero experimental evidence for string theory. That is no experiment has been done to show that there's this loop of energy moving around. And so that's a valid objection and valid worry. And if I were to say, you know what, string theory can never be verified or experimentally checked. That's the way it is.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Makes the point by a triangle Called blowing up a point, and then this triangle is what they call P2 projective two space. But these pictures are very physical and you feel it. There's nothing amazing. I'm not talking about six dimension. 4 plus 6 is 10. The dimension of string theory. So we can visualize it, no problem.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“The cube is a rendition of this six dimensional space to a sphere times another sphere times another sphere where three of the circles I'm not drawing for you, for each one of those directions, there's another circle. But each time you get to the boundary of the cube, one circle shrinks. When the boundaries meet two circles shrinks. When three boundaries meet all the three circles shrink. So I just give you a picture. Now, Mathematicians come up with amazing things. Like, you know what? I want to take a point in space and blow it up. You know, these concepts like topology and geometry complicate it. How do you do? In this picture, it's very easy. Blow it up in this picture means the following. You think about this cube, you go to the corner, and you chop off a corner. Chopping off the corner replaces a point.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“You just take an interval and it's another interval that's just going to be a square. Square is a four dimensional space. Yeah, why is that? Well, at each point, On the square, there's two circles, one for each of those directions you drew. And when you get to the boundaries of each direction, one of the circles shrink on each edge of that square. When you get to the corners of the square, all both circles shrink. This is a sphere times a sphere. I have divine interval. Just described for you a four dimensional space. Want the six dimensional space? No problem. Take a corner of a room. In fact, if you want to have a sphere times a sphere times the sphere times a sphere. A cube.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Now I can describe the sphere in the following way. I can describe it by an interval, which is think about this going from the north of the sphere to the south. And at each point, I have a circle attached to it. So you can think about the sphere as a line with a circle attached with each point the circle shrinks to a point at end points of the interval. So I can say, oh, one way to think about the sphere is an interval where at each point on that interval there's another circle I'm not drawing. But if you like, you can just draw it, say, okay, I won't draw it. So from now on, there's this mnemonic. I draw an interval when I want to talk about the sphere and you remember that the end points of the interval mean a strong circle. That's all. And then you say, yeah, I see. That's a sphere. Good. Now we want to talk about the product of two spheres. That's four-dimensional. How can I visualize it?”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Exactly, exactly. And this comes brings me to the next example I want to mention, which is fear. Let's think about how do we think about the sphere? Well, the sphere is a sphere, you know, the round, nice thing, but sphere has a circular symmetry.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Exactly how the planes meet, for example, what's the dimension of their intersection, and so on. So, how do we come up with intuition? We borrow examples from lower dimensions, build up intuition, and draw the same pictures as if we are talking about 10 dimensions, but we are drawing the same as a two-dimensional plane because we cannot do any better. Our words change. Not our pictures”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“This is an example of how we come up with intuition. Let me give you more examples of it because I think this will show you that people have to come up with intuitions to visualize that otherwise we will be a little bit lost.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Okay, we're beginning to see pattern. Okay, now come to the question. We're in 10 dimensions. Now we have the intuition. We have a seven dimensional plane and an eight-dimensional plane in 10 dimension. They intersect on a plane. We draw the same picture as two planes, and we write seven dimension, eight dimension, but we have gotten the intuition from the lower dimensional one, what to expect. It doesn't scare us anymore. So we draw this picture. We cannot see all the seven dimensions by looking at this two-dimensional visualization of it, but it has all the features we want. So we draw this picture, which is 7, 7, and they meet at the five-dimensional plane. It says five. So we have built this intuition now.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Okay, so plane and the line intersect at the point in three dimensions. How about the plane and a plane in 3D? Well, plane is two, and this is two, two plus two is 4. In 3D, 4 minus 3 is 1. They intersect on a one-dimensional line.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“But if you have a one dimensional line and another line, which is 1 plus 1 on a plane, they to be intersect at a point. Typically means if you are not parallel, typically they intersect at a point. So 1 plus 1 is 2. And in two dimension, they intersect at a zero-dimensional point. So you see two dimension, one, and one two. 2 minus 2 is 0. So you get point out of intersection. Okay, let's go to three dimension. You have a plane, two-dimensional plane and a point. Do they intersect? No, two and zero. About the plane and the line? A plane is two dimensional and a line is one, two plus one is three. In three dimension, a plane and a line meet at points, which is zero-dimensional. 3 minus 3 is zero.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Ten dimensions. Yes. So I will explain how some of the analogies work. First of all, we do a lot of analogies. And by analogies, we build intuition. So I will start with this example. I will try to explain that if we are in 10-dimensional space, if we have a seven-dimensional plane and an eight-dimensional plane, We ask typically in what space do they intersect each other, in what dimension that might sound like how do you possibly give an answer to this? So we start with lower dimensions. We start with two dimensions. We say if you have one dimension and a point, do they intersect typically on a plane? The answer is no. So a line one dimensional, a point zero dimension, and a two-dimensional plane, they don't typically meet.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Resolving a puzzle in four dimensions. The puzzle was where are the degrees of freedom of the black hole hidden? The answer, hidden in the extra dimensions, the tiny extra dimensions. So then by this time it was beginning to, we see aspects. That extra dimensions are useful for many things. It's not a nuisance. It wasn't to be kind of beamed off. It was actually in the welcome features. New feature, nevertheless.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Were hidden somewhere, so later in string theory, the work that we did with my colleague Astrometer in particular showed that these ingredients in string theory of black hole arise from the extra dimensions. So the degrees of freedom are hidden in terms of things like strings, wrapping these extra circles in this hidden dimensions. And then we started counting how many ways like the strings can wrap around this circle and the extra dimension or that circle and counted the microscopic degrees of freedom. And lo and behold, we got the microscopic degrees of freedom that Hawking was predicting four dimensions. So the extra dimensions became useful.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Quantum arguments Heuristic quantum arguments led to this entropy formula. But then he didn't answer the following question. He was getting a big entropy for the black hole, the black hole with the size of a horizon of a black hole is huge, has a huge amount of entropy. What are the microstates of this entropy? When you say, for example, the gas is entropy, you can't where the atoms are, you can't this bucket or that bucket. There's information about there and so on. You count The black hole, the way Hawking was saying, is there was no degree of freedom. You throw them in and there was just one solution. So where are these entropy? What are these microscopic states?”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Hawking. Hawking had been studying black holes in mid-70s following the work of Beckenstein, who had predicted that black holes Have entropy. So Beckenstein had tried to attach the entropy to the black hole. If you throw something into the black hole, the entropy seems to go down because you had something entropy outside the black hole and you throw it. Entropy was, the black hole was unique, so the entropy did not have any, black hole had no entropy. So you seem the entropy seemed to go down. And so that's against the laws of thermodynamics. So Bekenstein was trying to say, no, no, therefore black hole must have an entropy. So he was trying to understand that he found that if you assign entropy to the to be proportional to the area of the black hole, it seems to work. And then Hawking found not only that's correct, he found the correct proportionality factor, a factor of a one quarter of the area in Planck units is the correct amount of entropy. And he gave an argument using quantum semi-classical arguments, which means basically using a little bit of quantum mechanics because he didn't have the full quantum mechanics of string there. He could do some aspects of approximate”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Learn that these extra dimensions actually solve problems. They weren't a nuisance the way they originally appeared. First of all, the properties of these extra dimensions reflected the number of particles we got in four dimensions. If you talk to these six dimensions to have like six, five holes or four holes tend to change the number of particles that you see in four dimensional spacetime. You get one electron and one muon if you had this, but if you did the other J shape, you get something else. Geometrically, you could get different kinds of physics. So it was kind of a mirroring of geometry by physics down in the macroscopic space. So these extra dimensions were becoming useful. Fine, but we did need the extra dimension to just write an electron in three dimensions. We wrote it. So what? Was there any other puzzle? Yes, there were.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“But still, was this skepticism? You're putting all these things that you want me to imagine, there are these extra dimensions that I cannot see. And you want me to believe that string that you have not even seen the experiments are real, uh-huh. Okay, what else do you want me to believe? So this kind of beginning to sound a little funny. Now. I will pass forward a little bit further. A few decades later, when String theory became the mainstream of efforts to unify the forces and particles together,”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“It's beginning to sound a little bit funny. Similar feeling to the way perhaps Dirac had felt about his positron plus or minus. You know, it was beginning to sound a little bit like, oh yeah, not only have to have 10 dimension, but I also have to this. I have to also this. And so conservative physicists would say, hmm, you know, I haven't seen these experiments. I don't know if they are really there. Are you pulling my leg? Do you want me to imagine things that are not there? So this was an attitude of some physicists toward string theory, despite the fact that the puzzle of gravity and quantum mechanics merging together work.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“So, this was a conundrum. It was elegant, it was beautiful, but it was very specific about which dimension you're getting, which structure you're getting. It wasn't saying, oh, you just put the equals to four, you'll get your space-time dimension that you want. No, it didn't like that. It said, I want 10 dimensions. And that's the way it is. So it was very specific. Now, so people try to reconcile this by the idea that maybe these extra dimensions are tiny. So if you take three... Like tiny spheres or tiny circles, then it avoids contradiction with manifest fact that we haven't seen extra dimensions in experiments today. So that was a way to avoid conflict. Now, this was a way to avoid conflict, but it was not observed in experiments. A string observed in experiments? No, because it's so small.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“It was a kind of a natural kind of a question to try to kind of unify because in physics we love unification. Now, gradually string theory was beginning to show signs of unification. It had graviton, but people found that you also have things like photons in them, different excitations of string behave like photons, and another one behaved like electron. So a single string was unifying all these particle into one object. That's remarkable. In ten dimensions though, it is not our universe because we live in three plus one dimension. How could that be possibly true?”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“So theoretically, the first place that this was observed when you were describing these fermionic strings. So that was the beginning of the study of supersymmetry, was the Via string theory. And then it had remarkable properties that this symmetry meant and so forth that people began studying supersymmetry after that. And that was the kind of a tangent direction at the beginning for string theory. But people in particle physics started also thinking, oh, supersymmetry is great. Let's see if we can have supersymmetry in particle physics and so forth. Forget about strings and they developed on a different track as well. Super symmetry in different models became a subject on its own right, understanding supersymmetry and what does this mean? Because it unified bosons and fermion, it unified some ideas together. So photon is a boson, electron is a fermion. Could things like that be somehow related?”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Now, there are different versions of strings, but the version that ended up being related to having particles like electron, what we call fermions, needed 10 dimensions, what we call super strings. Now, why super, why the word super? It turns out this version of the string, which had fermions, had an extra symmetry. Which we call supersymmetry. This is a symmetry between a particle and another particle with exactly the same property, same mass, same charge, etc. The only difference is that one of them has a little different spin than the other one. And one of them is a boson, one of them is a fermion because of that shift of spin. Otherwise, they're identical. So there was this symmetry. String theory had the symmetry. In fact, supersymmetry was discovered through string theory theoretically.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Everything was working beautifully for particle physics. And so that was the shining golden age of quantum field theory and all the experiments, standard model, this and that, unification, spontaneous symmetry breaking was taking place. All of them was nice. This was kind of like a sideshow and nobody was paying so much attention. This exotic string is needed for quantum gravity. Maybe there's other ways. Maybe we should do something else. So anyway, it wasn't paid much attention to. And this took a little bit more effort to try to actually connect it to reality. There were a few more steps. First of all, there was a puzzle that you were getting extra dimensions. String was not working well with three spatial dimensions on one time, it needed extra dimension.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“Exactly. It got exciting, but at the same time, not so fast. Namely, it should have been fast, but it wasn't, because particle physics through quantophilia was so successful at that time. This is mid-70s, standard model of physics, electromagnetism, and unification of electromagnetic forces with all the other forces were beginning to take place without the gravity part.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source
“So it took a few more years to get to that point. They noticed that physicists noticed that whenever you try to find the spectrum of strings, you always get a masses particle, which has exactly properties that a graviton is supposed to have. And no particle in hadronic physics that had that property. You are getting a massless graviton as part of this scattering without looking for it. It was forced on you. People were not trying to solve quantum gravity. Quantum gravity was pushed on them. I don't want this graviton. Get rid of it. They couldn't get rid of it. They gave up trying to get rid of it. Physicists short said, you know what? Strength theory of quantum gravity. They changed the perspective altogether. We are not describing the hadronic physics. We are describing this theory of quantum gravity.”
2021-07-26 · Lex Fridman Podcast · #204 – Cumrun Vafa: String Theory · IDENTIFIED FROM THE TRANSCRIPT · source