The Origins Podcast with Lawrence Krauss - David Gross

Episode Date: July 2, 2021

Lawrence Krauss recently had the pleasure of sitting down with David Gross, one of the preeminent theoretical physicists who has been involved not just in the development of the theory of the strong interaction, called quantum chromodynamics, but he is also one of the founders and developers of String Theory. In their discussion, they explore the growth and changes of physics from the 1950's all the way to current day discoveries and methodologies. Get full access to Critical Mass at lawrencekrauss.substack.com/subscribe

And you can calculate now to a precision of better than a percent the spectrum of all those particles that were being discovered at Berkeley. This was my dream. Hi, and welcome to the Origins podcast with Lawrence Krause. This week, I had a discussion with the theoretical physicist David Gross, who won the Nobel Prize in 2004 for his contributions to understanding one of the four fundamental forces in nature of the strong force, which set the basis and really completed. the description of the standard model of particle physics, a model that's so good, a fundamental theory that's so good, that not only can we use it to calculate certain processes to 14 dozen places of accuracy and compare them to experiment,

but it's also withstood the test of time for over 50 years, every single observation of the fundamental scales has been in accord with that theory. David is one of the preeminent theoretical physicists who's been involved not just in, in the development of the theory of the strong interaction called Quantum Gropodynamics, for which you won the Nobel Prize,

but also he's one of the founders and developers of what's called string theory, and we talk about that as well. Our discussion spanned physics from the 1950s to today, and David has a unique knowledge, not just of theoretical physics, but of the history of physics as well. I think he experienced an incredible series of episodes,

and we talked about those and his interaction with some other well-known physicists, It was a fascinating discussion, again, I think unique in illuminating aspects of the process of scientific discovery and potentially the future of science as well. I hope you'll enjoy the discussion as much as I did. With no further ado, here's David Gross. Well, thank you very much, David, for allowing me to virtually be with you in your study and have a conversation. It's great to talk to you. It's nice to see you.

We saw each other a few weeks ago. In reality, yes, and we've both been vaccinated. And so even here over Zoom, we can be safe. And it's nice to be vaccinated, and it's nice to see you doing so well. And it was fun to see in Santa Barbara. I want this dialogue to be kind of wide-ranging about probing many aspects of your many intellectual endeavors and ideas. But since it is the Origins podcast,

I want to usually begin. We like to begin with your origins. So I want to talk a little bit about what got you into science. You grew up in D.C. You were born in D.C. And did you grow up there? I grew up in a suburb in Arlington, Virginia. Ah, Arlington.

Were your parents' government work for the government? I worked for a variety of government agencies. the Senate staff and Council of Economic Advisors. Was he an economist? He was a self-taught economist. He was the English major. The best timed, I guess.

I know we both have views about economics that are similar. It's not particularly complementary in general. So where they both, they both, so was he, he was self-taught. He wasn't an academic in any sense then. He didn't have an advanced

degree or anything? No, he had a master's in English from Penn. And he, I think, really would have liked to have been a playwright if he had been able to do it. There's not a lot of, yeah, easy work in that field. It's harder than getting harder than being a physicist. What about your mother? Was she, was she? Remarkable woman. born in Ukraine, survived the war, the civil war, the pogroms, and came to this country at the age of six, and graduated with a degree in chemistry from Barnard. Wow. So she was a scientist?

Well, actually, she was a housewife at the end. Yeah, but she had scientific sensibilities, maybe, let me put it that way. Yeah, she definitely was interested in science. Well, okay, well, you know where I'm heading, which is where did your interest in science grow? Was it there as a young person or to develop later on? It developed rather early. So his family was very intellectual, but the dinner conference, which was fierce, mostly concentrated on politics and on events of the day.

As my father's career and interest dominated. Not unusual. There wasn't much science or interest in science at home. I think I got interested in science when I was in Israel. which we moved to when I was 12. Ah, he didn't know that. I knew, well, I was going to ask why on earth if you grew up and deced,

you go to University in Israel, but okay, well, you skip that part. You moved, you moved to, the whole family moved to Israel. Okay, interesting. My father, in a sense, was a refugee from the Eisenhower administration. So he had worked in Democratic administrations

and various capacities for all of his life. And when the Republican Revolution of 52 took place after 20 years of Democratic rule, at that time, there were no places like the Heritage Foundation or things, Brookings, and places which, and since he'd never got a formal doctorate in the areas in which he taught himself, political science, and economics and stuff. He needed a job,

and he got a bunch of jobs sort of advising foreign governments. They went to Korea, actually, and in a few or so to give advice to the struggling Korean government. That was just him. The family didn't go right. You didn't move there. But later, he, he got he was invited to join a rather distinguished group of ex-democratic people out of a job

to be the first u.s delegation to israel which came along with the first u.s foreign aid to israel oh and they the american government said well no give you a lot of money but since you obviously don't know how to spend it we'll send experts to teach Jihad expended since we have a lot of experience with a young country who's doubled its population from refugee camps in Europe and it's just fought a war with the Arabs and you know it's just beginning we can this was 50 this was 52

so this was the first U.S. foreign 80 I mean Israel was 40 wasn't Israel 48 or no was Israel was began in 48 but the U.S. was torn between oil and Jews still is

okay so they so we went to Israel got on a boat for those days and moved the four boys which was just beginning

poor is very poor still rationing food rationing We were kind of, since we had some kind of diplomatic status, but I was sort of thrown into school with almost no Hebrew. And, you know, in Israel at that time, Jerusalem, where we lived, the seat of the government, was a small town of 50,000 people, half of them crazy. But enormously interesting people from.

wall over. Yeah, yeah, I can imagine. So it was very exciting. And my father was an advisor to various ministries in the government was in the middle of it all. So it was an exciting time. But there was, you know, there was like one movie theater in town, no television, no nothing. So I really became an avid reader. And I got

hooked onto science by actually reading popular science books. Oh. as I am to a popular science writer. Well, no, that's, I mean, same with for me, and that's one of the reasons I write in return could have favor, because it was, you know, was everyone from Einstein, for me, Einstein and Asimov and Gamow

and even James Jeans. But what about, who turned you on? Sorry, Einstein and George Gamow's books and Eddington and, you know, anything I'd get my handle, which wasn't easy since, well, it was much harder than to get, especially all the books in a place like Israel. But, you know, I got a book, which I still keep close by. It was for my bar mitzvah, which was in Israel,

It was called The Evolution of Physics. By Einstein and Infeld. Yeah, a famous book. And the great thing about this was I was given this book by Leopold's brother, Heinrich. Wow. Wow. It was a promenzo present. And it was signed, as you're going to say.

Yeah, okay, signed, yes. By Albert Einstein. Wow, really? That's a real signature. Yeah. Wow. The only second time I saw a real signature of this was that when you go to the Nobel Prize Foundation at the end of the week to pick up the check, you have to sign the book. Ah.

And exactly the same signature. Yeah, I know. It's a very vid. I've seen the signature. I have copies of it because when I was chairman of the physics department at case. Western where Michaelson had had done

well it wasn't it wasn't that Einstein correspondent with Michelson but he corresponded with a nutty chair later on who spent 40 years trying to disprove relatively and

had come up with some and so and Einstein corresponded with him about what was probably wrong with his experiment so I have copies of those letters with his signatures but that's good

that book well guard that book it's worth something it was part of me so that really turned me on I think it's at the first it was at the first I mean I was wondering what the first book you for me it was a book about Galileo

when I was 11 or 12 or something but was that the book that really got you going yeah I don't know there were a bunch of books I still have a bunch of them one two three infinity yeah love that book well now but did your

your pay so you just but it was your So was Barmitsa present? Your parents didn't sort of encourage or, like, give you some science books early on or anything like that. It was just your, it was basically that and your own personal. Was it teachers? Any teachers turning on? No, it really was the books. And it was not just books.

I mean, the books about science, but it was really the books about theoretical physics. Yeah. Okay. Then you knew right away. You enjoyed. before we get to that, so were your parents obviously were inched in Israel. They were, you know, some of them had been, you know, immigrants who had been saved, you know, Jewish immigrants who had been saved.

But were they, were they secular? Were they religious? No. No. They were just secular Jews. But they obviously wanted to be there to support the formation of Israel. Yeah. Yeah. But also to get out of the U.S.

I can relate. I'm about to emigrate myself. It's an adventure. I mean, really. Yeah, it was an adventure, exactly. It must have been an incredible adventure for you, 12 or 13. At the same time, terrifying, as you point out, you didn't speak much Hebrew, and it must have been a little. But it was enormously exciting because everything was new, and my father would travel around the country and take me with.

with them off. And so it was very, very, very exciting and interesting, although very different than sort of suburban America. Yeah, yeah, yeah, yeah. Well, that's probably why it was interesting and exciting. Yeah, absolutely. Did you, so you knew you, so it was the theoretical physics that turned you on, you knew that right away. Was something about the, and maybe because of math and I love doing math problems. I had a neighbor who, in school, again, it wasn't very, it was too easy to get beyond the teachers. We would have an ongoing competition with doing integrals, which at that time was tough. Yeah, yeah, no, that's great.

Well, I was wondering. So you knew you enjoyed math, you had math aptitude, but again, it wasn't school. It was pure, you know, I had a few friends who were really good mathematicians. Oh, we never really, I wish in retrospect, we'd spent more time outside of school, pushing beyond the boundaries of school. We instead just enjoyed, you know, getting 100% and chatting and, you know, but never really. We, there were some math competitions, but yeah, I wish, I wish it was great that you had, you know, doing integrals. That would be neat.

Yeah. And is that friend, by the way, did that friend become a mathematician or a scientist or anything? Do you know? I lost track of him at some stage. Okay. Okay. But you chose to, but then you and your parents chose for you to go to Hebrew. University in Jerusalem instead of coming to university in the United States. Was that again a

at a time no actually I applied you know they were um the U.S. was a long way away I did apply to three universities the University of Cambridge Harvard and some other place and were affected by all okay well you shot high, but that's okay. You didn't have a safety school, except maybe Hebrew University. Was university free in Israel, or was it it was what? Essentially. Yeah. Okay. Like it was in Canada when I grew up. Okay. So, yeah. It was a continental style university where you majored. And they

admitted a lot of students and then threw away 90%. It was one exam a year at the end. It was very much of a continental. Ah. Now, and so was, okay, so that's when you really began to learn theoretical physics instead of math. And were there a lot of European emigre physicists teaching there? Or what was it? The head guy in Jerusalem at that time was Giulio Raqa of the Raqa coefficients.

Yeah. It was, you know, one of the second generation of quantum mechanics, scientists. He was a student of Fermi, and he taught quantum mechanics. And he was an excellent business, but there weren't many at that time in Israel. it was just beginning. You know, I am kind of jealous of students who are beginning to study science or whatever they want at this point in the world

because it's so easy to get access to everything. It's such a gift. Yeah, no, it really is. Definitely, when it comes to science, you know, I mean, I guess there is some misinformation. too so you can get hooked in craziness but yeah being able to have access to so much and that's one of the reasons why i do this too but yeah it's it is a it is a very the internet for all its flaws is an amazing resource for humanity created of course by physicists but anyway um or at least

yeah created in this special form by physicists but so so you did you um were you aware of so this was in the late 50s, early 60s then, is that right? Was I aware of what was going on? Yeah. Takedly, but not deeply. It was clear to me. I mean, so I was one of this kind of people who, you know, very early on, wanted to do theoretical physics at the frontiers of physics.

And I was well aware that that was in particle physics. but that hardly existed at all in Israel so directly again only through reading Scientific American Okay which used to be a good magazine It was a great magazine back then

The And I used to write for it a lot It's great magazine back then Now you did a master's degree there too Or was that a pro forma thing like Cambridge We just got that for being alive No I didn't do it masters. It says you do in your bio. I was just looking it up the other day.

Because you looked at Wikipedia, which is... Yeah. Well, it was the simplest thing to do. Okay, so I was surprised to see a master's degree. It wasn't something I would have expected you to do. But then I know in Cambridge, the way it works in Oxford, you get it automatically a year later just for being alive. Sure, sure. So as you know, Masters, which have almost disappeared in the U.S. So at that time, in Israel, that was the thing you did. You got a master's And then you went, you know, some people went on through a PhD, but most didn't. But I was totally uninterested and wanted to get out of there and get to a real place. Okay, well, that's the point.

So you had a vague notion. You knew you wanted to put fundamental physics. You knew it was particle physics at that time. You knew enough to know it was particle physics. You didn't know about the brewing, all the stuff's going on. And then you chose what was really the center, in many ways, the center, experimentally, at least, of particle physics. And so what made you choose Berkeley? Well, that time I knew I went off to apply to many places.

Yeah. The only place that accepted me, I only again applied to a few. Princeton, Harvard, Berkeley. You know, maybe Celtic. I don't know. You know, I could figure out by then where the action was. But, you know, I was nobody from, I don't think there had ever been anyone

who had graduated with a bachelor's degree from Israel at that time, who went on to study abroad. Those who did, they were just beginning. And those who did, first got their master's, but I didn't want to get a master.

Yeah, smartity. Yeah, yeah, yeah. So Berkeley was the only one accepted me. I'm, you know, that's, I, I, well, I, I, I, I, I, I, sure that. Well, I, you know, I grew up and I was in a small,

I went to a small college of Canada, and applied to, again, Harvard, Princeton, Caltech, Stanford, MIT. And I thought my safe school was Cornell. And I got accepted to MIT and nothing else. So that's why I went there. But I mean, to go to somebody like Rockout, one of my professors and get a letter of recommendation was almost impossible because nobody had ever done that. Yeah.

Oh, I see. Interesting. In my case, by the way, it was amusing. Two of, three of my professors went to Cornell, so that's why I figured for sure I would get into Cornell. But obviously, they didn't leave much of an imprint anyway. The book was a lucky because it really was the center of everything that was happening in every aspect of life.

And in fact, I was just recently speaking to our mutual friend Barry Beresh, who was, who went to Burr. Berkeley a few years before you, you graduated in 62, I guess. And Berkeley, you know, it was a great time experimentally in a sense that everything, in a sense it was great time, although it was beginning to get confused. There are particles being discovered up the wazoo. Every time you turned on an accelerator, a new particles, or many new particles were discovered, multiple resonances.

And it was wonderful, but theoretically, it was beginning to get really weird and, and almost depressing. And so you came there and I don't know how long it took you to your PhD. Must you come around 62 or 63 or something like that? I came in 62 and finished my degree in three years, but stayed on for another year. Sort of as a because my wife was finishing her. Ah, okay. Well, that's good.

But yeah, it was enormously exciting because in the realm of, you know, they just turned. they were the highest energy machine of the world 6G by God at the at the Bevatron on the hill and they were

discovering lots of adronic resonances so they were in the energy where you could you know PPP sorry proton fixed target yeah it was a six target you could produce particles

and so there would be lots of particles being discovered. And it was enormously exciting and that totally turned me on to understand the strong interactions. Which you eventually did. But it's a roundabout way. But, well, actually, I think, well, we'll get to that in a second. I didn't find, I don't think anybody who wasn't depressing. It was exciting. Well, it was exciting. But let's, well, let's, well, let's, I mean depressing in a sense that people were willing to throw out established theory. It was so wasn't depressing. Some people were so confused that they said,

well, our existing theory doesn't work, we'll throw it out. I look at it a little differently. There wasn't much existing theory. There was QED. Yeah. Great success of relativistic quantum mechanics. Feynman and Schwinger and Domitonaga and Dyson. 10 years earlier.

But, you know, that really hadn't changed anything. It wasn't anything new. It was just the earlier the rather technical difficulties of understanding relativistic quantum mechanics and and inventing, understanding the so-called normalization

or sort of beginning of understanding. Yeah, yeah. The way that you could do calculations. And since it was such a simple theory, calculations work, you know, could be done very precisely and they, and tested and they work beautifully. But then once you got into some real physics, dynamics and zillions of new particles and resonances and clearly non-perturbative can't be just understood as a simple. simple corrections to a classical theory which you understood very well, people were totally lost and all attempts to mimic the same strategy as QED completely failed.

So people were willing to try just about anything. Theorists, when presented with data for which there's no explanation or prediction, we'll try anything. And everything was tried. But there was a resistant, you know, a feeling that the golden path of just following the same path that led from Maxwell's theory to quantum electrodynamics wasn't going to work. That was certainly the prevailing theory of you and your advisor, Jeffrey Chu. It was actually attractive, you know, so to a young student like me, I mean, here you have. all this data, it's quite complicated and rich, and there's some interesting patterns,

but nobody understands really anything in a deep way, but lots of data. And Chu was one of those who said, okay, we need new ways looking at this, which are divorced from what has failed. And what by and large, people who tried to do quantum field theories to mimic QE quantum electrodynamics in the case of the strong interactions, failed so miserably that nobody was trying anymore anyway. Yeah, yeah. In front of the data, you needed something. Some people always were looking for symmetries and patterns.

As far as dynamics goes, which is much harder, just rely on very basic fundamental principles of nature. It's so hard to construct explanations that maybe just general principles will determine the measurable quantities that we confront with experiment. Okay, before we proceed with Chu and you, because I want to obviously go in this detail, there are two questions I want to ask. First, well, let me ask them both in. you can ask them.

The first, as an undergraduate, where you, or as a graduate student, were you in touch, because it was just up the hill, the Bevetron, with what was going on? Because I remember as a theorist,

and I was pretty mathematical when I was doing an initial part of my PhD, I really wasn't in touch strongly with the experimental groups at MIT. It was only the latter part of my, my PhD that I really did. But you were, A, were you in touch with them? And B, well,

You know, you say the strong interaction was these hadronic residences. There was also the weak interaction. Were you primarily interested in the strong interaction? I guess I'll ask three. And finally, did you choose chew or did he choose you? So those are three questions I want to go into. Yeah. So at Berkeley at that time, yeah, every, we're impossible to be a theorist off taking an account experiment.

And that was where the action was. And we had seminars, really exciting seminars up on the hill every week. And, you know, and Lab was up on the hill, but it wasn't that difficult. I had a Vespa. Ah, because, yeah, because Barry said he had to walk up or hitchhike. So you had a Vespa, so. Yeah. Just to get a ride sometimes with Steve Weinberg, or it would also take us up.

But, yeah, I had a Lombretta, and so I could make it up the hill. And, yeah, I'd go to all those seminars. It was enormously excited what was going on, not just by the way in experiment, but also in theory. I mean, I can remember some seminars that's still sticking my head. I remember Cabibo giving a talk. So this wasn't the strong interactions, a weak interaction, also. of giving a talk on the Cabeebo angle and his understanding of the weak currents.

Sure. And I remember actually Steve Weinberg asking the question about SU3 or why not SU8. And it's an interesting exchange. I remember famously a seminar up on the hill that Sidney Coleman, who spent one year while I was at first met him. He was visiting professor for one year, my last year as a graduate student. He gave a seminar on what was wrong with SU6, the attempt to, who, you know, which slides of the common. Yeah.

All was wrong with trying to construct an extended symmetry, included space time symmetries, rotation, invariance together. famous disproof until supersymmetry in a way, yes. It was an incredible, exciting theoretical seminar.

Well, yeah, he was a, he was a wizard. Yeah, he was wonderful. Professors at the time Bardacci

had just written a paper with some other, a lot of people wrote very bad papers about issue six. Yeah, they were famous. In fact,

in fact, didn't he just, and demolished them all with this one paper. And as you know, Sidney, very well, he enjoyed enormously giving this talk where he essentially, he was so sarcastic in a way. Yeah, yeah, he would have just demolished him with a smile.

You know, I have to tell you something. I don't know if I ever told you this, but when I taught at Yale, my colleague, Pfezergersey, I had been, who was a wonderful man and a good mathematical physicist, among other things. But, you know, he was once, apparently some journalists questioned him on this SU6 and all the hype that people were making about this. And he said, what does it imply to you? And he said, it applies to me that Fermi is that Pauley is dead,

because he would have taken the chalk out of their heads, which I thought was a good. I had a role with S use six. Anyway, there was very memorable seminars at that time. So those were the theoretical ones, but the experimental ones were, you know, the eight, mezzan, and this interacted with the theory because there was a lot of, this was a time where Gilman was riding high and finding patterns of free,

and then S use to sit down, that didn't work. But S3 was a flavor, was still being tested. That was his big success of, and the Bevetron, in fact, I guess. My professors at the time were Shelley Glashow and Sidney Coma was there for one year. Wow. They were working away at testing issues. And anyway, you had what I, the education I got, you know, one thing, I definitely got at Berkeley.

If I'd gone somewhere else, I might have. become more rapidly the kind of mathematical physics that I'm almost becoming became later. Yeah. Much later. But there, in Berkeley, the game was, you want to understand the data and make predictions. And that was, you know, if you'd asked me then, what's the goal of life is to make predictions? and then you'll ever guarantee that they're going to be, they'd be testing. I'm still a big fan of making predictions.

What I've learned later, you know, after some time, after, well, we'll get there. We'll get there. Predictions that I sort of made, or at least I'll make, but the, but nowadays is a little different. You make a big of 50 years. Yeah, yeah, it's a little different. Okay, now the second part of the second part of the question was, so there was confusion about everything except QED. There was confusion about both what we now think of as the strong and weak interactions.

Although, again, in my own side, when I wrote a book about it, for a long time, it wasn't clear how to separate those two things. And I don't know if you want to comment on that, but it was, I mean, to some extent, you're focused on the strong interaction, more or less for a long time. By that time, it was kind of clear what the difference was, although since one understood neither. The weak interaction in some sense were easier.

They were clearly, even though there was the only kind of effective theory that one had now understand the Fermi theory of the weak interaction an effective theory, that was a very successful effective theory. And I had a lot of arbitrary structure and parameters, but it was an effective theory and could be treated perturbatively and worked very well. The strong interactions were just a mess. There was no theory, period. The only thing one had were general principles, you know, of causality and conservation of probability.

and it's the consequences of those very general principles. Which is what Chu really focused on, although, and I don't know how much he influenced you, your view. That's just true. True, yeah, but if one goes back a bit, there was a period before that, maybe five years before, where all the leading juriditions were sort of trying to understand better quantum field theory. because in QED you don't really have to understand anything. You have these rules, you just calculate.

But that wasn't going to be enough for the strong interactions where the couplings are strong and you can't use perturbation theory. What is filter? So there's a lot of work, dispersion relations, general principles. You know, a lot of very important stuff was being developed. But much like it is today, and, you know, again, trying to understand and deepen our understanding of framework of theoretical business. But when the data started coming out like mad, and people started seeing various patterns and then it shifted. And the two essentially became a kind of profit for a kind of profit for a shift.

few years of this movement to try to understand the data and even construct a theory based on general principles that had been elucidated the years before without having a specific Lagrangian or Feynman rules and even not having necessarily field theory just the principles of observable that field theory illustrated as a relativistic quantum mechanical scripture. And then it went on to become almost a religion. It's certain, yeah. And it's amazing.

So, I mean, the essence of that religion were sort of two elements. One was one was nuclear democracy. which was the feeling that, you know, you don't really have elementary constituent of matter, elementary particles out of which you built everything else. It was very hard to identify what those might be in the case of the strong interactions. You had the proton neutron, which were discovered earliest.

But then what was special about them? Could you understand? You needed other the pyons, which were then discovered. But it wasn't at all clear what was elementary, what could be regarded as of one. And two had this radical idea that there were no elementary particles. Everybody was equally. Well, and what, you know, having come into a years later, the summary I got was that everything was made of everything else. And it started, you know, remarkably with a, there was a paper back in 1949, right after the work,

of Fermi and Yang, who must have been a very graduate student or just... Yeah, yeah. Which explained that the pion, which is very light, pseudo-scaler meson, could be regarded as a p.p. bar bound state. Hmm, interesting. So even the pion could be not elementary. But you could then regard the 3-3 residence. a rather narrow resonance that was discovered as a pyon-nucleon-bound state.

But then you could try to turn it around in regard to proton as a 3-3 resonance pie-on-bound state. I mean, and in the end, what Chu said is they're all bad, you know, you have no meaning to that. There are no meaning philosophically to the fields, which you never can observe anyway, just to these particles. And the way you determine their scattering amplitudes, things that you measure in these collisions, is just to impose general principles of unitarity, conservation of probability,

and relativity, which is a mathematical way of realizing causality. That was the big formal development of the late 50s. And you put all this together, and it's so hard. hard to find a consistent description that it has all these good features, so it's probably unique. This episode of The Origins podcast is brought to you by BetterHelp. We all have things that interfere with our happiness, obstacles that prevent us from achieving our goals.

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our sponsor at BetterHelp.com slash Originspod. Join over 1 million people worldwide who have taken charge of their mental health. Again, that's BetterHelphelp.com slash Origins Pod. That was the bootstrap. Now, so you, in fact, well, maybe that's what you're going to say by the bootstrap, because you said there were two principles of that religion. One was nuclear democracy. And the second was the bootstrap.

And the bootstrap is pulling yourself up by your boots, basically assuming nothing and just accept general principles and trying to find the answer without a specific dynamical model. Would that be a good way of describing the bootstrap? It really was the belief. It was just the belief. The belief, yeah. Belief founded on failure.

So, you know. Like a lot of religions, actually, but go on. So there were mathematical visits at the time who were working all on a corner. Unfortunately, there was very little communication between those guys. And people like me or my mentors, they were working on toy models of quantum field theory in lower dimensions. People like me felt two dimensions, who gives that? Yeah, which is famous because you've been famous for doing some things in two dimensions. But they didn't get very, I don't think actually tell you the truth.

the quality of the research in that field wasn't up to part. Then they were also working on general principles of quantum field theory, which had become highly mathematical, and some of them did some really good work. But they totally concentrated on totally uninteresting aspects of quantum filter. Now, were you interested? were you influenced well it's maybe a

totology to ask this but I mean were you influenced by Chu at the time I mean you were a new graduate student who's you know susceptible to or we you know you worked for him but did you buy it? Yeah no I got very excited by it for for about talking about a year it's sort of like communism

you have to get excited by such ideas but in fact I got so I attended a on the side, I used to like to go to other classes, not just physics. I went to a philosophy class, which was run by Paul Fierre, Abin, who was a mad German philosopher, a great professor. And he was very entran.

And I wrote a paper on the bootstrap, which I can never, can, I think I've lost completely, but on the bootstrap philosophy, which is really so I found a fascinating idea okay and what of course you know and it still is I'm amazed that today in the last few years there's been a total resurgence of bootstrappism within conformal field theory quantum field theory people are now using exactly the same ideas that true was postulating now of course they know very well that there's There's no unique S-matrix, no solution, even just if you're restricting yourself to four dimensions, there are infinite classes. So they know that.

But they still, enormous attractiveness to some people of this bootstrap idea of thriving all the consequences from a specific dynamical theory from general principles. Yeah, well, I mean... Modern computers and techniques are conformal filter today, you can do things that you would have... That school would have just found remarkable. Back in those days, in the absence... It's hard to, again, to remember,

it's like we talked about the Internet and the fact that everything is available at a keystroke. And the same is true of modern computers, and their impact on theoretical physics. So these people can do things to implement bootstrap ideas that were just beyond comprehension in those days. In those days, without the numerical power that one has today,

one could get almost nowhere. That was extremely frustrating after a while in that program. Yeah, I know. Then, you know, I realized at one point, and it was prompted by Francis Lowe, the first high-energy physics conference I went to, which was luckily held at Berkeley. In his summary, planetary talk, Lowe,

Francis Lowe was a great physicist. Yeah, I knew at MIT, yeah. Really. He said he was summarizing the bootstrap, S-Matrix approach to foreign interaction, and he said, yeah, but in the end, All it is, you know, is you take a general principle like Unitarian, you put in something on the right-hand side, you get on something the left-hand side, you bring some of the left-to-the-left-thous.

What have you learned? And it's stuck in my mind. And there were other things began to happen that were, gave one the hope of being able to do what I really wanted to do, most, which was to make predictions and have them work out. Well, you know, and okay, this is a great, it's kind of interesting. And I'm really interested in that it was Lowe in some sense who got you thinking outside of this job because, of course, well, it wasn't just. Well, I know, but what I meant is it's poetic to me because Gellman and Lowe's paper on

what we would now call kind of like the normalization group is sort of, we'll end up being very relevant to the work that eventually you want to. the Nobel Prize for. So we'll get there. We'll get there. Right. But at the time, at the, so in the last year or two, as a graduate student, I was beginning really to get tired of the bootstrap because it's a man. It's a man. It's not, okay. Now, so. Didn't learn anything fundamental. So you'd already begun to deviate from the true, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the, the beginning to become. So that's,

So that's fine. Now, you, so already by the end of your, of your PhD, that was the case. You moved, I assume you moved to Harvard right from your PhD, right, to be a junior fellow. Did you, did you go right to Harvard? Right. I wouldn't intend to go to Harvard. I got excited. I wanted to go to Princeton, which, and I.

Eventually you made it there. But then, then I was nominated by Chu for the society. As you know, this is where you were a junior fellow. you can't apply. And I hadn't even heard about it. I mean, and true didn't even tell me was nominated me. Oh, interesting. So I already more or less decided to go to Princeton,

but then I got this invitation to go to society. So I packed up. It was the kind of thing at that time, no one refused. Since then, people refused. But at the time, it seemed to me, that was kind of an offer you couldn't refuse. Well, yeah, I mean, it was so, for me, it was such an incredibly exciting, intellectually, and so sophisticated.

You know, I was from Berkeley, which was a very different culture at the time. When I went to my interview, I had to buy a tie for the first time my life. And it was, so different, but enormously attractive. Oh, yeah, yeah. And then by the time I was junior fellow, it was the place that physicists, I mean, I was already

in Cambridge, but it was a breeding ground for physics. I mean, they were a large fraction of them were physicists. Students now, you know, rapidly know much more about the world than I knew about the world. Yeah. There weren't that many physicists in the society. And of course, Purcell was there. Yeah.

Great man. Great man. He was. You know, Adler had been, I guess, a junior fellow. But there were no... It wasn't the tradition that you guys helped create. When by the time I was a junior fellow was like, look at all the... You know, it was a tradition of physicists who had been junior fellows.

But it was... It was like one a year or one every other year. Ken Wilson, of course, the... junior fellow. But it wasn't as exciting a place. Harvard. By the way, I often think, thinking about you and your interview

makes me think, it would have been wonderful. I really wish they had recorded the interviews so that one could look over the years at these young whippersnappers like you or whatever. And it would have been fascinating to hear now. I was totally terrified.

Me too. I had spent, I realized that morning that I had forgotten my razor. All I had was a razor blade. Oh, no. Yeah. And I was all nicked up in suffering. They were all these very Harvard-e-Donyish fellows asking me questions. They were entranced over by the bootstrap.

Yeah, that would probably, yeah, I can imagine. Probably what got me in. But I enjoyed it enormously. Oh, yeah, yeah. Now, but the reason I'm asking, I mean, Harvard is a different place by the time. I mean, I was there many later than you. But was Schwinger still at Harvard then? Yeah, Schwinger was still King of the Mountain at Harvard.

But the year I went to Harvard, a whole bunch of people followed me, or vice versa. Sidney, Glashow, who was a professor at Berkeley, was hired back to Harvard. Sydney, who was an assistant professor at Harvard, was given tenure and came back from Berkeley to Harvard. And the third of my professors at Berkeley was Steve Weinberg, who moved to Harvard so his wife could go to graduate school and to law school.

And so the three of them moved with me. Yeah, or the other way around, as you say. So they sort of moved into the kingdom. And boy, that was fascinating to watch from the side as a mere nothing. Yeah, because they were the kings by the time I got there. But they were just the ponds. This place. So it was very similar to something I observed on a safari in Africa.

They took us and showed us what had happened the week before was a bunch of cubs or young lions had gotten together in a pack and came and killed their father and took over. And this was somewhat similar to who it is the king of the mountain, the lion on top of the heap, and all these young jackals came in and effectively drove him out in a few years. Yeah, and drove him out. And the famous story, of course, of him of Steve Weinberg getting his office and seeing that Schwinger had left his shoes in the cabinet to fill the ease. Yeah, anyway. But the reason I'm asking, let me just, I mean, it wasn't just a personality.

The reason I'm asking, and at least again from my studies, and you can correct me if I'm wrong here, is that the first person to really appreciate the usefulness of gauge theories, particularly non-abillion gauge theory, the theories that eventually became the theory of quantum chromodynamics, the strong interaction and the theory of weak direction, was really swinger. And so I'm wondering, A, if that's true, and B, if that had an influence on you. I think it's sort of true. It's a little more complicated. My reading in the history is that when, after Yang and Mills, which is the middle of 50s,

there were a bunch of people who found it very interesting. Now, they included people like Sakurai and others who were very much interested, and Salam and Ward and Naimad and everybody who was interested in a phenomenology, especially as it related to symmetries. Schwinger, you know, wasn't a symmetry man as such about, of course he, but he was much more interesting in dynamics and how to include non-a-belengaged theories in his formalism. Did he have any influence on me?

Yeah, his papers? Yeah, no, they're impenetrable, but I was thinking of classes or what? He didn't because it was rather impenetrable. And by the time I learned about non-abillingage theories, there were, no, he didn't have much. Because clearly he'd obviously had influence on Shelley and Glashow because, you know, he'd recommended that. Of the non-abillion gauge theories either. It was just, well, it was, you know, he gave him a thesis topic that turned out be pretty good related to. And eventually became non-abillion.

particular about the Ingalls theory that played in. Yeah. Now, but so, so were you more influenced by the young jackals then around you? Because they were, and as was Schroinger, by the way. So, you know, at the time, the big advances, the thing that got me out of the, you know, into, away from S-Metrix theory, was that big advances were happening with spontaneously, broken chirocemetery. you know, that was the big breakthrough of field theoretic techniques that, you know, understanding, spontaneous symmetry breaking. Yeah, and for the listeners, I mean, that's the fact that the underlying theory represents symmetry between left and right, but somehow the states that are manifest don't.

And that's the case in the world around you. I mean, both of your, if you look at you and me and our surroundings behind us, left is different than right, even though we kind of feel like there's nothing fundamentally different. But so the circumstances in which you find yourselves can violate that fundamental symmetry. And that was, that was obviously a very important central idea. And that was just developed around, around then, Banu and others. No, it went back earlier. But the big advance was to, one, understand that the consequence. of that, the whole, you know, which led eventually to understanding effective field theories.

And, you know, and Weinberg, I know at the time was writing lots of papers on, you know, using Carl, what we would now call Carl perturbation theory. Weinberg was in current algebra, so-called the behavior of currents that are the sources for these symmetries. That's, and there were, this was an understood. then the transition from understanding that as a product of symmetries, you know, to dynamics of the strong interactions. There were some rules that were being derived and compared to experiment, the Adler-Weisberger, some rule. This was directly learning about the strong interactions in ways that were trustworthy, but they weren't bootstrappy. And

So what was the most exciting work that you did, you think, while you were a junior fellow? At that time, was taking cognizance of this and trying to bring it into his framework. And these younger guys who were developing, working on this, including later me, were he was, it was a bit weird. But Springer suffered a lot because he was a recluse and had his own point of view and everything had to fit into that. And then he switched to trying to fit into his way of looking at it, which really wasn't different. It was just a recap of the same principles in different language, everything that other people had done. So it didn't Okay, but okay, it's not for Swinger now.

I want to talk about you. So what did you do, if anything, that you were proud of while you were in the society? So I was very interested in these, I was still working on Est matrix theory every once in a while.

And there was also a time where by the way, string theory began at some point. Yeah. I was also involved in the beginnings of that. But mostly I was concentrated on these currents. Because current, you know, partly because of my

upbringing, you were told, part of the true philosophy was you shouldn't discuss things you can't observe. You should really be a pragmatic physicist that only talk about what is observable. Yeah, well,

that's such a bad. It's very much principle in early days of quantum mechanics or many classical things you might talk about were not observable, they contradicted. But here was a different issue. Fields are not observable, only particles. That's what's observable in collisions. But currents were observable. So you could discuss their properties. And I got involved in the idea was to go beyond just using the charges,

the generated symmetries, those are integrals of currents to the local properties of currents, while we would call today operator product expansions. By making assumptions about those, you could derive some rules, which went beyond just testing for symmetries, which were going over and over again, symmetry, symmetries. And those symmetries, as we now understand, are kind of accidental properties of the strong interactions, and they don't teach you very much in the end.

But the currents could actually give you dynamics, So I studied those. Perhaps the most important thing I did at Harvard was explore various what we would call models. Today you would call theories of the torpories to different properties of the currents. But these currents are really observable, and there was an accelerator. being constructed, which among the rest could measure correlation, you know, these currents and at slack. And Callan and I are most famous what it was the demonstration by Calan and I of the polarization

of electron-proton scattering to... Was Callan and Harvard? Or, I mean, I would, I was an assistant professor. Oh, I didn't realize that. I knew of you at Princeton together. We worked a lot together at Harvard for some. Most importantly, we showed that you could easily distinguish between theories, models, like the cork model. Where the constituents of the proton were, had spin one half like quark.

or in one, it's been zero. Yeah. So that's the so-called Calum Grossworthy. And it was almost immediately tested because as the experiment came on, they did indeed discover that it looks like the proton is made out of quarks. Yeah, yeah. No, I remember I think being tested on. When I spent some time at CERN to, when I spent some time at CERN,

to show that the experiments, again, indicated that the things that made of the Roton didn't have just been one half. They also had color. They also had, they looked like quarks. Yeah, no, this hits home for me in an emotional way because... It was impacted me. But there were a lot of other things I did.

You know, I almost got the Venezuelanamo. Really? playing with, you know, along the lines that the people in Israel were doing as well, trying to construct functions. This is the bootstrap. Functions that were crossing symmetric. And I got very interesting in that when that happened, when Veneziano found the beta function, which did all that.

And the, and a bunch of other things. But that Callengross, what's interesting for me, because it is a way to try and connect the dynamics to look for fundamental physics. And it's emotional to me because after I failed my first PhD oral because I was too mathematical and not, I didn't know what was going on, I remember studying intensively to try and understand the phenomena, the physics behind the quantum field theories that I was interested in. and, you know, learning about, you know, what the experiments were that told you the quarks were, you know, I'd have colors, been a half, et cetera, et cetera. So, so it brings, it's bittersweet, well, it's sweet because I eventually passed. But, but, but, uh, but it was a traumatic time. But, but now, so that's, so did you move, you moved, you, did you spend a sometime at CERN while you were a junior fellow or did you move? Yeah.

Attracted me as a, you know, to go to, instead of Princeton was that you, you moved, you, you, get a year off. I took advantage of that I took half a year off at CERN. Yeah, I remember. Great place to be. And again, and this was already 68, you know. Yeah, so it's a great, great place to be. Very exciting place.

But then you finally made it to your Shangri-La. You finally got to Princeton where you'd always wanted to be from there, right? You became an assistant professor of Princeton. Yeah, right. And again, there was a choice, a lot of choices, but, and I was tempted to go back to Berkeley, where I had an offer, and that was always my dream to come back to California, which I finally succeeded. It took a while. But Princeton, you know, was really, yes, exciting for the physics at the time. And, yeah, so I went to Princeton.

Well, it was a pretty good place for you to go. You, now this was 68 between. Yeah. So I was, at the time, you know, there were two things that totally obsessed me. One was this,

this deep and elastic scattering, which was the way to test the properties of these products of currents. Which, again, let me just say for the listeners, was really just a way of trying to look at the scattering of particles like electrons, which would scatter up a proton and reveal facets of the proton. Yeah, I mean, this was very energetic,

using the electron as a microscope to probe the structure of the proton. And an experiment where people didn't expect much to happen, the proton would be smeared out object, and okay, you'd see it smeared out, big deal. Very much like what people... Motherford. He Thompson thought Rutherford. Yeah.

I never bothered to ask him what he was doing. But Rutherford found protons inside the nucleus of atom. Yeah. I know, because I've heard you talk about this, you were, at least as you said then, I assume you're going to say the same thing now, is you were trying to disprove that any simple quantum theory would work and instead. So the main thing is I just thought this was,

absolutely fundamental measurement discovery of this point-like structure. So, or what looked like point-like structure. And not only that, it was quarks because that I was wedded to not so much. But the experiment, experiments and the strong interactions were never clean, as they are in the case of the weak interactions, which is why many of my theoretical colleagues avoid would just concentrate on the weak interactions because it was a lot cleaner.

But if you looked with a biased eye, if somebody had written down, managed to put forward some conjectures, which were then more or less plus or minus 20%, verified, convinced me that this was a theory of quarks. And that was just crazy because there weren't any real quarks. So what was it going on? And then point-like behaviors.

So I was convinced this was essentially enormously important. And that was shared by a lot of people, but not totally. partly because there was no way of thinking about it. There was no framework in which you could understand any of this in a fundamental way. And partly because, you know, experiments when they, when the discoveries are first make, they're big errors. Yeah. It could easily be wrong and it could be.

So, but I was obsessed and at that time, I, I, I, I, I, I, I, I, I, you know, I, I, I, you know, I, was influenced by a lot by Ken Wilson, who I met at Harvard, partly because Roman Jaquif, who was somebody I worked with, was a junior fellow with me, was his student. And his ideas were just enormously exciting. And the renormalization group, which at that time had been developed, you know, Proterative Renormalization Group by Callan and Simonsic, which I knew very well because of Callan, and even more so by Wilson's Renormization Group. So you learned about the Renormalization, so his ideas on renormalization influenced you.

I was going to ask. I knew about him before there were papers because he would come often to Cambridge where his family lived. His father is a professor there. And he would come by and Roman and I would talk. to him. Nobody else would. We would. And then I, you know, famously I brought him, he was on sabbatical at Princeton in 71, where, again, when he was just writing, developing these ideas, and I famously got him to give a course, which became a physics report. I got John Kogan through.

lot. Ah. I didn't know that's how that physics report forced him to take

that. Wow, I didn't know that. I knew their physics report, but I didn't realize the

etymology of that. So, and those, those lectures that Ken gave were very important historically because that's

when his ideas became public. Were they important to you, though? I mean, you know, so basically, I was very close

to Ken at the time. We were playing games. you know, we, again, you know, numerical, we were looking, studying the structure we normally, looking for limit cycles, looking for all sorts of things. But it was all based on, you know, old-fashioned computers where you get the cards. He was very good at that, and I just went along. But it didn't lead anywhere. Again, you know, modern computing has truly changed the way theoretical physicists are able to, to work.

But anyway, so I was, but that gave me a plan to deal with this thing. I really wanted to see whether I could, well, to understand esendotic, what we now call ascendotic freedom, which is a way of getting point-like behavior. Did you, well, did you know, I mean, hold on a second. So I was going to ask you about this being, but it's interesting, I don't think I've ever talking about it. So did you, in advance, you knew that the only way to get asked, that they got the, the behavior that was seen in diplomatic gathering was to have something like acid product freedom, or did the realization occur after you discovered asymptotic freedom?

No, it happened along the way. To be totally obvious, and most people didn't think it was obvious. Ken Wilson didn't think it was obvious. Sure. But he thought of it. Well, one, you didn't take the experiments, again, weren't, as I said, so you couldn't have to believe them. There could be anomalous dimensions. They could be small. They could be, you know, whatever. Experiments were conclusive, and the few people who understood how to ask the question of this type were divided. And there's certainly no proof of it.

And so my main goal was to show, well, it was a way of narrowing the kind of theories. And it really meant quantum field theories and there were no other theories. Except the string theory, which had been developed already in 68, 69. and which I was enormously interested in and spent a lot of time and did a lot of work on that with Schwartz and Nouveau and Shurk. At Princeton, it was for a year, so I was totally just doing that one. It was very exciting. But I did realize that that could, you know, string theory is worse than quantum field theory. very soft at very high energy. It doesn't give point-like structure after all.

Strings aren't point-like. They're extended. Yeah. And by the way, again, I'm just going to interrupt just for the listeners, because we're talking to things. I mean, just, I'm assuming most people, many people listen to this, know what asymptomatic freedom is, but with the, but it wasn't what was, what was fascinating about the Slack results,

which were recognized for a while. I think maybe Bjorkane was probably one of the early people to recognize this. But, but, but was it not just that there were point-lides objects inside the proton, but what was really weird was they acted like point-like objects that were not interacting very strongly with one another, whereas the whole point of the strong interactions were the interaction is strong. So how could you have something made up of particles

that looked like they were relatively freely banging around inside the proton? And that's what appeared to be the result of the Slack experiments. Anyway, I just wanted to preface that for people. So you could, one way of describe, describing that would be to say that you have protons made out of quarks, point-like objects, and they interact very weakly. But that, of course, is crazy because then if you hit the proton with a hammer or another product, those quarks are going to escape, just like electrons escape, get ionized,

escape from the atom when you smash something into it. And they never did, no matter how hard you hit him. So something was very weird. Anyway, one explanation could be when we realized that how particles interact depends on how close they are together. That can change. There are ways of understanding how the strength of the interaction between particles changes with distance.

That's its normalization. group approach. And with that tool, I realized, OK, well, I could, one, try to understand whether you really need to turn off the interaction as you go to short distances to explain the phenomena. And if so, then you could examine using weak coupling techniques, whether that happens in any theory one

could write down. And the list of theories that are sensible, I knew were the finite, well, not a finite, but a denumerable set that one could maybe get a handle of all possible theories. Anyway, that was the plan, which I started to work on maybe at the end of 71. And one aspect of that, which I thought, you know, was probably the hardest, was to sort of see whether asymptotic freedom was necessary. And there'd been some partial work on that by Parisi in a class of theories, and Callan and I worked on that and extended that to all theories except these not-a-being-engaged theories.

And then the other part of the program was to see whether there were any theories which had this property of Assamdata Freedom. and that I worked on alone, but at some point I was dealing with a nasty integral inequality I couldn't prove and Sidney Coleman helped me and we wrote finding their paper showing that there were no such theories. Once again, excluding these complicated, you engage theories. That was sort of the last, you know, in hindsight there was no, there wasn't the intuition that one could have had, saying, okay, well, most theories have, the coupling gets weaker when you move particles apart because the force is screened by other particles.

And then maybe if I want for the force to get stronger when I go to pull them apart and thereby weaker when I pull them together, I want something like anti-screening and how can I get anti-screening. So, anyway, that is not the way. In retrospect, that's how we now explain it, but you're right. The intuition was never there in advance. Well, the intuition wasn't there, and not being engaged theories were not discussed directly in either of these elements of this program because they were too unfamiliar and difficult

to do. Nobody at that time. you know, Ed Hooft and Veltman famously developed that formalism so that they could argue that theory was normalizable. But nobody was calculating these higher order quantum effects, which would be necessary to get this phenomenon. So what I had to lose, you know, and that was the final part of the story, which led to. So indeed, it's correct that I suspected that there were. no such theories, that even non-a-beal-engaged theories would be again not be asymptotically free. And this was sort of back to Chewy and days, if you want, I would show.

You know, this would be an experiment that I could show, implied that no field theory could explain. And as somebody would grown up with that, you know, had been interested in that to begin with. And also was fascinated by string theory, which couldn't do it either. Anyway, I was, my expectation and kind of hope was that I could kill quantum theory. Instead, you saved it, of course. But, well, that's an issue. I'm really happy to hear this. We've heard, we've talked and I've heard, you know, little bits.

but this it's nice to, I don't know whether deconstruct as I were, but to probe in detail what it's hard. And again, again, after the fact, it's always hard to remember your thinking exactly the time. But you decide to work on it.

And it was a formidable calculation to do because the theory was new, the kind of theories hadn't, the techniques that were developed later on to make those calculations simpler, weren't yet there. And you had to do this incredibly complex calculation. And is that the reason you,

well, I'm going to want to ask you. So you did have a graduate student that you brought on at the time. Frank was my first graduate student. Which is a good beginning. And my problem. I said, besides which, you know, my strategy was always, graduate students were sort of controllable collaboration. all my students always worked with me

I mean I didn't yeah problems so but yeah come out and work but it was tricky so for example one of the tricky businesses was that we were

calculating this function this beta function that controls how physics changes as you scale things upward And it has to be independent of the, you know, this theory has a big symmetry, gauge symmetry, and anything you observe has to be independent, invariant under the symmetry transformations. So really just reformulation or not. But intermediate steps aren't, and it's how it ends up being gauge invariant,

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Indeed.com slash origins. Offer valid through September 30th. Terms and conditions apply. So because, though, it was a complicated calculation. And it was great. I mean, it was lucky for Frank to come at the right time. But you were lucky. I mean, Frank was a pretty good student to it. And, and, but you, you know, when you finally, when you came up with the answer, as we would say technically for the physicist, the beta function was negative,

but for the rest of the world that this concept of asymptotic freedom, that the specific set of theories had the property that was necessary. First of all, were you skeptical? And second, I mean, how much back and forth did you go through? Because this is quite a statement to make. You have to be pretty certain you're right. Yeah, it's quite a statement. In our paper, first paper, the discovery paper,

actually wrote down the Lagrangian and said, this has to be it. See, it wasn't just that, but the thing, well, there were two aspects of that. One was, when you, together with these other things, these other elements that work with Coleman and Gallant, you know, there was a unique theory that could explain, have this property, and that was based on this generalization of Maxwell's theory with many charges, with more than just one electric charge. But then once you look, you know, try to apply this to the real world with quarks, then you said, well, it has to be a theory of quarks interacting with this

this generalized electromagnetic chromodynamic field. And what are the charges? Well, already people had identified that these quarks had to carry a label, a charge, can't play any role, necessarily, but it had to be there to account for how you count combination of statistics. Statistics of the proton, for example. So one already had three colors that had to be there for SU3. And that is about it, aside from the mass of the quarks, there are no other parameters in the theory.

So immediately one could say not just has to be a theory like this. had it be this specific theory, period, nothing else. Yeah. Furthermore, once you said that, everything, just about a lot of things that made sense, you know, that were part of the lore of trying to build understanding of the phenomenology of Hadrons of strongly interacting particles fit in naturally to this theory. That's on the one hand, my God, that is a real, more.

I never forget. But second was immediately, if you're going to take that this seriously and say this has to be the strong interactions, I can write down the equations with just the masses of the quarks as parameters, period, that's it. Then somebody says, well, where are the corks? So immediately, first, you know, problem was, where are the corks? the corks? How are the quarks? Why don't they ever get out? Now, people who had believed in quarks, you know, it was hard not to believe in quarks because it looked like there were corks, said, okay,

well, they're corks, but you can never see them. They're confined somehow. They can never get out. And it was enormously exciting to realize that if the force gets weaker at short distance, it gets stronger and large distances. And maybe that, and keep the quirks from ever escaping. Maybe. One, we didn't have, you know, understanding of asymptotic freedom and its physical origin. Two, there were no models of confinement, no examples.

There are analogs that are quite known in physics, like magnetic monopoles. But nobody had made that connection either. So at the beginning, it's really scary. And so this discovery, which happened very rapidly, realization there's only a unique theory, it could explain, yeah, everything fits in,

everything we know about chiro symmetry breaking patterns, of course. But on the other hand, there's this totally weird phenomenon of confinement. So to contain both of those emotions of exhilaration and fear, your time is really strange. Was it, was it a eureka moment? I mean, did you feel like when you got the result and you were convinced it was right? I mean, I'm sure there were some time when you really, as you say, where there was, you know, a lot of finagling and saying, did we get it right?

Do you just say this is amazing? Did you realize it was going to, I mean, I hate to put it in this terms, but did you realize it was a Nobel Prize winning moment? Well, as I said, yeah, there's the exhilaration. part. But you knew it was significant. I mean, you knew it was really going to change things. But, yes, yes. Okay, but you had this fear, and it's your perfect semific, because I was going to go from that to confinement, I was going to go. We still, there are many, and I must admit, I actually, when I first met you, I have to admit, it was at a time when you were with several colleagues at Princeton had been working

on an idea that might explain confinement. And it was the, it was the, it was the, it was the, it was the, it was the hot thing at the time. And I went to attend to the summer school, which is where I met you. And all three of you talked and were very excited because you were pretty sure you're on the verge of another breakthrough. And which didn't happen. And we still don't have a fundamental proof of confinement. So I wanted to ask you, I mean, every, no one, no one doesn't believe it's confining. It's one of these things.

But an analytic proof doesn't exist. And I think there's a, there's a big probably. a million dollar prize maybe for it. Do you think there will be, I want to get to Laosucceed in a second, but do you think there will be a, there will be ever an analytic proof of confinement? Well, you know, I'm not sure what that means.

There are so many things that we, in physics that haven't been rigorously proved. Yeah. Our confinement is sort of at that level now. So, for example, I mean, anyway, that became my next obsession. I haven't gone to be. Sure. The first goal, of course, was to you use this theory to do what I really wanted to do.

Prediction. That beautiful series of papers with lots of predictions came out by you after. The deep question was confinement. And what I wanted was not so much a rigorous proof of confinement. that clay millennium prize, a million dollars in QCD,

but a physical argument. Well, physical argument, physical understanding, and a controllable way of calculating properties of hadrons.

Now, today we have, as far as understanding this phenomenon where you have a theory is to have big arguments with Vigner. At tea time, we'd say, can't have a theory based on particles that don't exist as

asymptotic states. You can't take out of the bottom. It makes no sense. They're unobservable. Anyway. But we do have an understanding of confinement through many analogs or models that confine that can be solved exactly. I mean, it's not a strange phenomena anymore.

It's standard. It's ordinary, it's explainable. But QCD is a complicated theory, and it's unlikely they will ever have analytic solution of anything in QCD. It's conceivable there'll be well-dvised approximation methods, and that's what we were really certain. What I really wanted was a way of making pretty good calculations or arbitrarily improvable calculations. That to some extent has been achieved by use of modern computers. It's called lattice QCD. You truncate the solution to a finite dimensional thing,

and then you take the limit where you cut up space into individual points, a lattice, and you take the spacing of those points to zero in a way that the theory tells you how to do, and you can calculate now to a precision of better than a process. percent, the spectrum of all those particles that were being discovered at Berkeley. This was my dream. It has been achieved. And in that formalism, quarks are confined.

So if you want that formalism of QCD, which in this way of doing it exhibits confinement, also that has, you know, as many tests as you want of complicated spectrum and scattering face shifts of hadrons. Let me jump back and as a devil's advocate and say to what extent it exhibits confinement, but to what extent is it an input in lattice gauge theory? In some sense, confinement is a

input into lattice gauge theory in terms of... You could see it, Phil. You could pull these corks apart instead of getting... You can measure the... Within this formalism, it is verified. Now, if you ask,

Okay, well, you haven't taken the lattice basin to zero. You haven't taken the core continuity. It doesn't matter to me. Yeah. At the level of the kind of rigor, which is wonderful, physics should always try to do. But it's never been my life goal to prove rigorous theorems. And the physical understanding of confinement is, to me, quite clear.

The method we were trying, which was based on semi-classical, approximations thought us a lot about insinons and non-classical saddle points to these complicated integrals but didn't lead to a controlled

approximation in the real world for QCD with three colors and so on. All other analytic tools have so far failed. There's still some hope. Okay, well I want to ask you I'm glad we, well, we got the last case

there, Eric, a lattice QCD like I wanted to. And I wanted to ask you a very topical question in that regard, your opinion, because I just prepared a little public explanation of the muon G minus two anomaly, which is, which if true, is very exciting because it points to physics beyond the standard model. But what is equally interesting is a new calculation using the, and it's wonderful to see lattice QCD come into its own in this sense, which is accurate enough to be able to apply to this problem where you need to know the result to one part in a billion, it tends to disagree with the other ways of using it,

which is to use experiments and plug them into perturbation theory and try and estimate what happens. This direct lattice QCD appears to agree with the experiment. So I wanted to ask you what you thought about that and whether you think that'll be the result or whether the G-minus 2 is really signed something new. I don't know. I don't know either, but what's your gut feeling?

So the lattice QCD calculation that was done that is somewhere between the previous, you know, collective calculation, which uses experiment, but then it requires analytic continuation to get it. So it's, you know, it has errors as well. Yeah. Yeah. But it, but it is interesting that it, that it's close to experiment. So, you know, it's hard to know. I'm agnostic about it to some extent. I'd like it to, I'd like it to represent something fundamentally new and beyond the standard model,

but I don't know for sure. No, so, but this is something under our control. This doesn't require a machine. This requires more calculation on both sides, which is being done, of course, to try to narrow that theoretical. But it is a lovely situation where the discrepancy is, in both cases, even taking the lattice, that lattice QCD calculation is in disagreement with the experiment, just not by 4.2 sigma. Yeah, yeah, but not by enough to be a gold.

Yeah, it's intriguing. And the good news is the experiment is going to only, I think they've only analyzed 6% of their data. so the experimental uncertainties will go down. Theoretical uncertainty will go down. So should we make a bet, whether it's new physics or not? This theoretical calculation is only one group is done. Yeah.

And so since they were able to do it, I mean, it's an extraordinarily impressive calculation. It really wasn't, will be done again for sure because of the importance. It's fascinating. It is, it is an, I mean, since I've been, it is the most exciting little bit of particle physics that's happened in a long time, I think. But remember, you know, for going back, in my younger days, I was interested in trying to calculate the electron proton-mass difference. Electron, proton neutron mass difference, yeah.

which now on the lattice has been calculated to less than a percent. It is amazing. It is remarkable. Again, and this is... That is not as exciting as an you know,

an analytic calculation. But it's still, it's fascinating to see, you know, it's something I've lived through. You know, it's something I can appreciate seeing the change

from when I was a graduate student to now. Well, okay, so we've now done QCC, We talked about it. But now, and we've gone on so long that, well, I find it fascinating. But I want to, it would be a shame not to get to string theory, which we'll get to briefly. But one thing I want that did intrigue me if I think about you.

So the fads, I don't know whether you want to call it fads, but the focus of the herd was sort of on the strong, ultimately the standard model and the strong interaction. and then it moved to grand unification for a while. But I don't think you, I don't know of you working on grand unification directly. Did you work on grand unification? So I was, you know, after GCD was totally obsessed with trying to develop. Understand QCD in detail. But yeah, no, I, towards the end of the 80s,

I was 70, beginning of the 80s, definitely, I was not so much focused on grand unification originally, Georgia, I, Glashow, et cetera, et cetera. I actually didn't have much faith on such a simple extrapolation. But it was a striking fact that the couple, you know, that the indications were that there was this enormous scale. But I think I turned to it partly, you know, I was more interested in supersymmetry and string theory. Yeah, but even at that time, the late 70s, early, I mean.

Yeah, early 80s especially. Yeah, but the heyday of sort of the classical heyday of the string of guts was sort of mid late 70s. And, you know, the initial models of discovery of the fact that, hey, the coupling consens seem to come together if you made this wild extrapolation. I was discovered quite early. That was more... In 74, 75, I think.

Exactly. Yeah. No, I guess I just didn't have much faith in that. I can understand it. It was a big extrapolation. Not as big an extrapolation is made for string theory, but it was a big one. Just a big extrapolation. population, it just sort of didn't, I mean, it made a lot of predictions like proton decay.

Yeah. But it didn't have anything new in it. Okay. The other thing that I became more and more than this was, you see, QCD was a truly remarkable theory, which I always was very proud of, was essentially no parameters. Yeah, yeah, yeah. It's a complete theory. Whereas the standard model, the Higgs sector, the standard model, as well as QED, had, you know,

was a synthetically free. And there had to be some new physics at the ultra-mobile. Yeah. You know, so grand unification was clearly a lorry. The companies did seem to come together. Something was happening. But just putting things into a SU5, SOTN group with, didn't. solve that problem.

Well, and I don't know if you felt the same way. As a graduate student, that was the kind of thing to work on. I didn't work on either. I kind of, by that point, what happened was that, yeah, you had this sort of kind of natural theory called SU5, which looked like it was the simplest possible way of. But then it wasn't clear that that worked experimentally. And then it became a matter of finding more and more complicated groups. and that to me just didn't attract me at the time.

I mean, inventing the wildest, craziest, largest groups to do things. It just seemed... What? Like E6 or E8? Yeah, exactly. Like E6. It just seemed like frantic, you know, just an excuse to...

Well, it was an excuse to get PhDs, I suppose, but I didn't... It was very interesting. There were lots of... There were other issues in the standard model that you might have hoped if you unified things, you'd get some insight into, like the

spectrum of flavor and masses and mixings. But it didn't happen. Yeah. It wasn't much coming out of this. And again, I was always more interested in dynamics, and there was

still, you had this problem of or we call it an ultraviolet completion. So you, so. Then there's another thing that motivated me and many others, but it certainly was also happening at Princeton, remember, which was interest in gravity, quantum gravity as a part of nature. It's something field theory you should think about, you know,

Hawking's idea is Euclidean path integrals and super symmetry. and string theory. Because, you know, I never lost my interest in... I was going to say, you never lost your interesting theory, it's dynamics. So even before the heyday, you were fascinated by it. Yeah. And I always had a connection through John Schwartz, who was always, you know... So string theory was developing very slowly.

Because you and Schwartz had worked together and other things early on, is that right? And we worked on string theory together. With Nevo and... Yeah, others, okay. So I always, and John would, his mother lived in Princeton, would always come to Princeton once or twice a year. Ah. And I would meet with him. And Ed Whitten also was very interested, kept interested in string theory at that time.

So, in fact... Did Witten push your own interest at all? Did he reinforce your own interest? Not particularly. Well, more in thinking of it. about unification with gravity, anomalies, that whole story. So it was clear from the unification of the couplings that something interesting has happening very close to the plankland.

So it became clear that you have to think about gravity. And I'd worked a lot on solitons, insinthons, and played around with those ideas, you know, did some nice work. Yeah, you did some nice one. The decay of hot, flat space. Anyway, there are all sorts of interest. So it was learning about thinking about quantum gravity. But these were, I'm inside,

but they got more and more out of, you know, tired of not succeeding to get a controllable calculational tool for QCD. and not willing to do that, not my cup of tea, but I got more and more interested in unified theories with gravity and their problems and string theory. And you quickly became, I mean, you certainly quickly became not just,

not just did your work become central to making a quote-unquote phenomenological, at the time, phenomenological theory of string theory that looked like it might be a theory of the world. But you also became a zealous advocate for the approach, would you say? So in 1983, I went on sabbatical to Paris.

I remember I met you there for lunch once, but anyway, it doesn't matter. Anyway, my plan there was to get back into string theory, seriously. And I was going to work with Andre Nevo. but Andre had they got a job offer from CERN and was not in Paris so I did other things but I was also thought you know

burning up on what had been done in string theory not much over that 10 years it's been very slow only a few people working on it but still it was impressive and and then the year after this explosion happened. So I was in a good position. And there weren't very many people who knew anything about string theory. And I was teaching a special topics course at Princeton that year. And I'm not sure what I would have taught, but I decided to teach string theory. And boy, that was just about

everything. There were everybody. And teaching, of course, is, I don't know for you, but for me, teaching is the one way to really understand things. Yeah. So that was a very exciting period. Yeah, I mean, 1984 was the string revolution and looked like all the problems in fundamental physics be solved and were people. And I don't know if you were one of these people, but there were people who were saying, yes, you know, the future is here now. now and we're on the thrust crux of knowing. Yeah, so one of the most exciting elements of string theory is, remains,

to some extent, is that every parameter, so you know, in physics we write down equations, we have Lagrangians, we have Hamiltonians that dictate the directions, dictate how things work. And there are all these parameters that are in these equations, like the charge of the electron or the mass of the electron. And in quantum field theory, by and large, those are free parameters. And it's always annoying because physicists like to calculate everything. They have free parameters that you could adjust or somebody got to adjust.

You don't understand how to calculate is very annoying. The great thing about string theory is that in some sense there are no three parameters sense that every parameter you might insert into the solutions of the theory is dynamical, has dynamics of its own, and might be determined by some dynamic. And so that was enormously appealing. Going back again, bootstrappy, if you want, this is better than that. him put strong. Now,

go on to that. Very close to that. Throw away the core. So that was enormously alluring. And of course, we've understood things are slightly more complicated to say the least. But at that time in 84,

there was a feeling. There were only five theories. And all possible parameters, that we observe at low energies in our standard model could be calculated. It was incredible hubris, incredible excitement and incredible hope.

That hope hasn't obviously materialized. And it engendered lots of sharp discussions, and I don't think it's necessary to go into those, nor can we do spring theory justice now anyway. But let's go, where 30 years later, more than that, almost 40 years later, which is weird to think, isn't it, David, almost 40 years after 1984. And the, it is, would you say it's a success or failure or neither? Of course, it's success. I mean, success. I knew your answer, but I just

wanted to hear why you'd say it. Right. What? When you're climbing a mountain in the dark, which is the way I picture physics, you know, exploration in physics is climbing a mountain I've ever seen and is covered with clouds and it's dark. Okay? As long as you're going up, it's good.

So you think we're going uphill? Do you think we're still going uphill when it comes? The focus has shifted a bit. So there are no parameters in the basic discussion of strings, but they've sort of reappear as boundary conditions. Yeah. Choose particular solutions. But the main breakthrough, the main advantage change of attitude

is that string theory is no longer separate in any way from field theory. It's not like it's a different. part of a bigger framework and it includes them both. So, you know, back in 84, it was operating under a traditional point of view. There would be a theory which you could write down, just like you do in quantum mechanics, or you do in quantum field theory. You write down a specific theory, like QCD, and then you solve it. or test it.

But you never had that in string theory. You just had ways of constructing solutions of something, not a theory, but solutions, which were consistent with general principles, a few want bootstrap. And it was somehow different. It certainly is different. Let me make a statement, which I,

You probably won't agree with, but let me make it anyway, and you can refine it. Is it fair to say that string theory has not succeeded in achieving the initial claims and goals of the theory, but it's been incredibly useful to the physics community in developing a new way to think about many aspects of physics? Would you say that that's a true statement? Yeah, that's sure. That's certainly, I wouldn't say that's all, that's much more. Yeah, I don't think, string theory isn't a theory. Yeah.

And that's why I never thought it should be called a theory. It was a mistake. But anyway. But quantum field theory isn't a theory either. Exactly. That's the reason. But people don't realize that. The public doesn't.

CCD is a theory. Yeah. CCD is a specific theory in the framework of quantum filter. By the way, QCD is also a string theory. We now understand that there are these dual descriptions. That's one of the fascinating parts. In all sense, when you confine quarks, they create flux tool, behaves like a string. And in cousins, close cousins of QCD are undeniably string theories in hyperbolic, bigger space, ADS, anti-decidious.

Right. We now know that string theory and quantum field theory can often be different ways of looking at exactly the same phenomenon. So quantum field theory is a lot richer than we ever imagine. Yeah. And theory is taught, is an extension of that framework. What that framework is, the framework of theoretical physics, the fundamental framework, is something we do not know how to describe at the moment. But it certainly contains both what is called string theory and quantum field theory. And what the rules are, we don't know either, to tell you the truth, especially since some of these descriptions and the ones who are most interested in contain quantum gravity,

contain gravitational physics, which the quantum level is really demanding of a forcing us to confront some of our most basic notions of space and time and even causality. And like happens at any exciting time, I suppose, if it is exciting, that always happens at the frontier physics, which you never get a sense of when you read the history books, because it's all described as if it was logical, coherent after the fact. It's confusing. And I think it's fair to say that what reigns right now is a lot of confusion, a lot of claims, a lot of of confusion and we'll see where the dust settles. Would you think that's a fair thing to say? Well, you know, there's just no, so there were people, some of my good friends who would

argue that string theory, which they thought was a normal theory, is a wasted time and a failure because one can't calculate the mass of the electron. And it doesn't, it isn't motivated directly by experiment. But string theory, as I said, you know, is the standard model. There's a question about it that, in fact, I just got a paper from one of my students, extant, who was making big advance towards constructing the dual string theory representation of QCD itself. I think that will happen. I'm not sure how useful it will be as a calculational tool, but it will happen.

I think, you know, but it's fair to say, look, when can go back and forth? Structure of theory, string theory, is part, parcel. Yeah. Okay, I'll accept that, but I think part of the reaction was simply, you know, the claims that the expectation was appeared as if 1984, like we will calculate the mass of the electron and therefore just wait. And that was unfortunate. You're close. But yes. And so what's missing to be able to do that is totally unclear.

And so to some extent, what's happened for the last 30 years or so now, almost 30 years, 25 years, has really been just exploring the framework and the connection between different ways of looking at the same phenomena to enrich our understanding both of standard model or. ordinary physics, the innermove of the headstring and gravitational physics, if you want. Okay, well, look, you know, this brings us to the present, which is, as you say, I think

puts it in perspective. Obviously, we could go on about that, but right now we just, yeah, as you say, we're hoping and where people are working and there's lots of areas. And we'll see what the future is. But, well, I don't want to interrupt you if you want to say one thing before I move

something else. There are great successes, you know. Oh, sure. You know, deep paradoxes in trying to apply quantum mechanics to gravity, which I've been around for 100 years. And there, the combination of this enlarged framework is solving a lot of those problems. Well, it's giving us new ways to address them. I guess I'm not as optimistic that it's solved them, but it's certainly giving us new ways to think about them.

Well, I'll give you an example. famously claimed quantum mechanics fails in when you marry Einstein and okay

and that isn't true and one can demonstrate that without any question in simple examples of black

whole physics yeah simple examples but let me ask you a question I don't think we have resolved the fundamental paradox of black hole information law. So it's clear, I think people are optimistic, but I don't think there's a clear what? If you announce a paradox, you say,

okay, a black hole violates quantum mechanics. And of course, there are lots of black holes, including the big ones that are in the standard. And then you have this theoretical framework, which we all believe in, all in the aspect, different, and which for certain black holes that I can construct in my mathematical lab do not violate quantum mechanics for sure,

then I have shown that the arguments of the paradox are simply invalid. And in that case, and in presumably every case, since we have good evidence for quantum mechanics, You know, the responsibility here, much like in trials, is prosecution, not the defense. Okay. I didn't come here to pray string theory or bury it. In the early stages of the application of duality to the information paradox gave up. Yeah, yeah, I know, I know. But, you know, physics isn't done by democracy or voting. by raising a question mark and saying these two are incompatible, you know, you have the responsibility.

That's universally the case. It's not just maybe it's in ballot because you haven't in every possible case. Come on. Absolutely. I agree. No, no, look, I think the point is clear, and I agree with you. Let me ask you two more, two or three more questions to end this. I want to talk about the future a little bit, but not the future related to string theory. But I do have to ask you something I've never asked you about, I don't think. So Wilchek and Witten were both your graduate students. And I think most people of my generation would say that they are among the two of the most preeminent theoretical physicists in the generation,

but sort of semi-generation after you. Yeah, I mean, but they're certainly among, the top. Oh, absolutely. And is that is that just luck? Well, I don't know. I don't mean,

I mean, look, what's clear to me in having been a faculty member and a student is that students moved to the people who are doing the most interesting work. So it's not surprising that perhaps they chose you. What? What?

Artist. What was that? especially the smartest students. Yeah, the smartest students tend to know what were the interesting people and try and work with them. And sometimes the people agree to let them work with them. That's not always the case. But I think I remember you famously, and I think this is true, and I can't help but say this story, because it relates to the Society of Fellows where both you and I and Ed was a member,

is I think you wrote to them a single line recommendation, Didn't you say something like, this guy is smarter than me and he's smarter than you? Take him. Is that true? I heard that somewhere. About who? About Whitten? About Whitten?

It's true. Everybody's different. So I'm often asked questions of this sort, although you've been much clever than most. It's a question. You know, ordering people on a straight line. Yeah. That I don't buy anyone. One of the amazing, well, you know, I mean, you meet a lot of interesting and smart, creative people.

And I don't do a hierarchy myself. I don't, I generally don't do that. 78 dimensional space. So there's no order points in, and, you know. such a space. And anyway, the amazing thing is that each, everybody is so different than everybody else in so many ways, which is what makes it so wonderful. Yeah. Yeah. Characters in life, but especially these extraordinarily talented creative colleagues, because they're all exceptional, but in different ways. In different ways, yeah. And that's, by the way, that's something I tell young

people too who have, they tend to have this stereotype of the, of the brilliant theoretical physicists or the great scientists. And I try and say, me, it's not true. There's a thousand points of light. I know people have made great discoveries who are not the best mathematically in their class or, you know, I mean, it just, it's just, it takes all, when science is healthy, it takes all kinds to really make it go. But it's not just in science, of course. It's true in everything. In everything, literature if we had novelist work along some line you know okay well let's let's go to the future i mean one of the i know you've written about this or talked you've had a few positions institutionally that have offered you the opportunity that i wouldn't say pontificate but at least to think

about this as you were head of the cavley institute which is an institute of theoretical physics at santa barbara which part of whose job in some sense is to look at the future and try and decide where interesting areas would be for research. And then you were also president of the American Physical Society, which perhaps isn't as interesting a deal. It's more sort of a, you know, administrative. It doesn't itself govern the future of physics in any real way. But it caused you at least to be, to think about all the different areas of physics, probably.

So where, how do you see the, it's the future bright and where do you think the, both in particle physics and in other areas of physics are the brightest? Where do you think are the most exciting areas? And of course, this is always, you know. There's many. Yeah. So there are really two, well, first of all, I'm a theorist. And most of what defines the future of science is mostly defined by experiments,

experiments and by experimental opportunities and technological advances that allow you to see even further. So that's true in most areas of science. It certainly was true in particle physics from its beginning. And there, you know, there are unbelievable opportunities all over the place from the instruments that now allow us to look back almost to the beginning of the universe and to study black, cold, mergers, and collision. I mean, to condensed matter, you know, the structure of ordinary matter and control over the ordinary matter, including its quantum mechanical. The quantum mechanical properties of ordinary matter. Quantum computing, do you think, are you as optimistic as some?

I'm more optimistic about quantum phenomena, including construction of quantum computers. But, yeah, I mean, computing is, remember, is a goal, theoretical goal. So if you develop a quantum computer, you would think that its main purpose would be to enable you to do these calculations a lot better. Yeah.

So it'll have some impact on physics in that way. It certainly might have impact on society. I mean, Feynman thought that it would help him understand quantum mechanics better if there was a quantum computer. It was interesting quantum computing by his quantum simulation. Yeah. Of course. And he liked to calculate, as I do.

You know, it's nice to have these powerful instruments to simulate and calculate. But I think much more interesting for physics is the control and deeper understanding of quantum mechanics of the, quantum mechanics of systems with many degrees of freedom, like in quantum field theory or many-body theory. And that is becoming more and more powerful, you know, possible, both with theoretical tools, but experiment is again the driving force. There is another part of physics, which I'm now more engaged,

which is more exploring the erratic, the frontiers of theoretical knowledge. And that can proceed without, with a slower pace of experimental, luckily. Although they're dangers, I think we have such a solid base in the framework that produced the standard model, which is this unbelievably amazing theory, to allow us to continue in that way.

Who knows what the boundaries are. So you would say to a smart young student now that physics is a good field to go in, not biology, or, I mean, not to dissuade them from biology, but it's, but if you're, but it's still, it's still worth. Absolutely. Good. And, and there are different kinds of people. You know, you really have to find out what you really love.

And physics education enables. you to do some of these approach other areas which traditionally have not been part of physics, but physics is very imperialistic, such as the physics of living matter. So physics is not a bad way to do fundamental biology. It's becoming, yeah, there are two fields emerging in ways that, I've said this before publicly, but one of the many times I got depressed as a graduate student and wanted to quit physics, I thought of doing a joint PhD MD because they had that at MIT and my mother would have been very happy. And doing biophysics.

And I went actually to speak to the uncle of a friend of mine who was chair of cell biology at Harvard. And he said, don't do bio physics because it's not of interest to physicists and it's not an interest to biologists. And that was true back then. But it's now it's the two, it's hard to distinguish the fields. Well, it still is quite different. Biology is still young, exploding experimentally with new techniques, but their problems are deep and enormously exciting. But it's a little different. So it really depends on what you like.

But physics is amazing and is going to continue for a long, long time. I mean, there's a lot to be. Yeah, absolutely. Well, look, that's a good way to end. I hope that, I mean, physics is amazing. The store and your participation in physics has been amazing and fun to go through and been always, it's fun to discuss it. I hope we have a chance to discuss in 40 years from now how these things have proceeded. But it's been a pleasure and it's been actually a really special pleasure because you and I know each other for many years.

But what I like about this is it gave us a chance to talk about some of the, some things we haven't really ever talked about together before. And the other thing for young people who are thinking, it's also fun, although very different, to build institutions and to contribute back to this incredible scientific culture and community that enables us to do science. Yes, absolutely. And it's a fundamental part of our culture.

Intellectually, some of the most interesting ideas people have ever come up with. And it's a pleasure and privilege to be able to do it. It's a privilege that we both had. And that also takes me back because I will say that I've enjoyed this conversation now. The first formal conversation we have not formal. Yeah, well, the first formal, not informal conversation we ever had was the very first lecture I ever gave. I never gave a lecture as a graduate student was when I'd gotten into the Society of Fellows and you decided at Princeton that therefore I must have something to say

or Latin essay you, but I got invited to give a seminar and I was terrified beyond belief because you were in the audience. And I remember at the time, you know, there were not any really difficult questions. And I remember asking you why afterwards. He said, well, you told us this is preliminary and you invited us to ask questions and that disarmed us. What did you talk about? Do you remember the title? I think actually it was probably related to my PhD, which was on black holes in the early universe,

an idea I had about black holes in phase transitions in the early universe. But it was very speculative and ill-defined. Well, it wasn't quite ill-defined, but it was enough to make me worried. worrying about primordial. I'm hoping that my paper, which I now understand has 10 citations based on my Pitchie, that'll be one of these things that in each of five years it'll become discovered. But anyway, either way, thank you, David, for the time and patience. And it's been a real pleasure.

The Origins podcast is produced by Lawrence Krauss, Nancy Dahl, John and Don Edwards, Gus and Luke Holwerta, and Rob Zeps. audio by Thomas Amison, web design by Redmond Media Lab, animation by Tomahawk Visual Effects, and music by Ricolus. To see the full video of this podcast, as well as other bonus content, visit us at patreon.com slash origins podcast.