Leonard Susskind

Zierler:

This is David Zierler. It is May 1st, 2020. I'm the oral historian at the American Institute of Physics. It’s my great pleasure to be here virtually with Professor Leonard Susskind. Leonard, thank you so much for being with me today.

Susskind:

You’re welcome.

Zierler:

To start, can you please tell me your title and institutional affiliation?

Susskind:

[laugh] I am Professor of Physics at Stanford. University, that is.

Zierler:

Let’s start right at the beginning. Tell me about your birthplace and your family and your childhood.

Susskind:

Well, I don’t remember being born, but I'm told that it was in New York City, in Manhattan. My family lived in the Bronx. Then, it was immigrants from Russia, Poland. My parents were born in the United States. I think they had lived all of their lives in the Bronx. For whatever reason, I think I was born in Manhattan, but I don’t even know where. In 1940.

Zierler:

Did you go to public school?

Susskind:

I did.

Zierler:

Through high school?

Susskind:

Public school, public high school, public college—CCNY in New York. And in a sense, I was extremely fortunate. The city of New York was very generous. Schools were good. City College was a free college, completely free. As a matter of fact, they paid me $1,000 a year to go there.

Zierler:

Really!

Susskind:

Yeah. Of course, I lived at home. It was a subway college; you went by subway. Free. Completely free. I went to graduate school at Cornell. Again the generosity of the federal government made it possible for me to go to graduate school. So I came along at a time which was a very fortunate time when education was publicly funded in a good way. I consider myself extremely fortunate for the generosity of the city and state of New York, and the American government.

Zierler:

What was your father’s profession?

Susskind:

My father was a plumber. I can tell you a little bit about the history of my family, if you want to go into it.

Zierler:

Please.

Susskind:

My mother’s family were not highly educated. They came out of Poland and Russia. Not actually Russia; my grandfather on my mother’s side came from Lithuania. He always told me he came from Latvia, but eventually he told me what city he came from, and it was Kaunas. Kaunas is in Lithuania. So I guess at that time, 1900 or whatever, [laugh] maybe there was no distinction between Lithuania and Latvia. It was a Jewish community there. My grandmother was illiterate in any number of languages.

Zierler:

[laugh]

Susskind:

They went to England sometime around 1900. They were both 15 years old. They hadn’t met yet. They met in England. My grandfather was a tailor. He was a gentleman’s tailor, which means he made suits. In London. They lived in London. That lasted, I think, for probably about five years until they came to the United States. They were simple people. My grandfather and my grandmother had lived almost all their lives in English-speaking countries, but neither one of them could fluently read or write English. My grandmother was totally illiterate. And she was a marvelous woman. She was very, very good with words. She could curse you out in the most incredible language, English or Yiddish. She had an extraordinary use of words. But she was completely illiterate. My grandfather could read and write and was very literate, in Yiddish but not English. They were not religious people. My grandfather probably did have a religious upbringing in Lithuania, but by the time he had passed through England and came to the United States, he was not highly religious. And at some point, he really got angry at the synagogue that he went to. He would go once or twice a year, when I was a very, very little boy. I remember him taking me. And then I remember he never went back. Apparently, it had something to do with him getting angry that the shul, that the synagogue, was charging poor people money to go there on the high holidays. And this offended him, and he never went back.

Zierler:

I have to share with you, my father had the same exact experience. Same exact experience, in Brooklyn.

Susskind:

Oh. Yeah, yeah. In Brooklyn? Oh, yeah, Brooklyn. OK. Brooklyn was the far end of the world to me. We never went there except once in a while for funerals.

Zierler:

[laugh]

Susskind:

We did have some family in Brooklyn. But it was the far end of the universe, as far as we knew. Anyway, my father’s family was quite different. They were from Russia. From the Pale, the Russia/Poland border. And my grandfather apparently was a house painter, but I don’t think he was an ordinary house painter. I think he worked on palaces and I think he was a fine craftsman who did elaborate plastering—I don’t exactly know. There’s no chance he was just a regular house painter. They were intellectuals in a sense. They had not gotten any education, but they were intellectuals. Widely read. And leftists. Leftists meant Marxists. This was the time of the czar. This was not the time of the Soviet Union. The czar was the enemy, and who was the friend? The friend was Rosa Luxemburg and the anti-czarist leftists. My grandfather was widely read. And both of them—apparently very fluent in English, widely read in English, Russian. They were anarchists. The family moved somewhat to the right when they became Stalinists. So my whole family on my father’s side were left. If they had any religion at all, it was the religion of social justice. But my grandfather was a gambler. I had always thought that there was a little bit of gangster in him. Turned out that wasn’t the case. I learned from my cousin that he was not a gambler with gangsters. He was a gambler in the union hall. He would go and play cards with his buddies in the union hall and lose all the money. So they were incredibly poor. Really, really poor. Poor to the point where they got thrown out onto the sidewalk when my father was 12. He had to leave school at the age of 12, and he became a plumber. He was a plumber all his life.

Zierler:

Did he inherit the family politics?

Susskind:

Yes. Oh, yes. If I had to characterize him, I would say he was a sort of classic Marxist. And it took him some time. Eventually he realized that Stalin was not the man to spread the wealth, and of course what he became was an FDR New Deal Democrat. But yeah, very social justice-oriented. And social justice for him tended to mean Black people. He lived and worked in New York, in the Bronx, in tenement buildings, and he was very torn by the treatment that Black people were subjected to. My whole childhood was very colored by that. And I myself was brought into the family business as a plumber when I was about 14 years old. So I worked first with my father, then when I got a little older—by the time I was 16, I belonged—illegally, because I was too young—but I did belong to the Local 2 of the Plumbers Union in New York. I was still in high school. And then when I went to college, I would say I spent at least half my time as a plumber, working for other plumbers, working sometimes for my father. Mostly for my father.

Zierler:

Did your father expect you to continue in a blue-collar future as he had, or did he expect other things for you, or hope other things for you?

Susskind:

No, he expected that I would go into business with him, and that we would run his plumbing company. His plumbing company was very small. It was a one-man operation. A one-man operation usually meant you hired a helper, a plumber’s helper. He was very good at educating young men to teach them how to become plumbers. He did that over and over again. So he had a following of young men, maybe about ten of them during the course of the time that he was in business, all of whom were very devoted to him because he had given them the tools to become something. Some Black, some not Black. Puerto Ricans. So those were my formative years, working as a plumber, going to school. I really liked mathematics. That was the only thing I was good at in school. I was not considered a good student, except by the mathematics teachers. And that continued right through college.

Zierler:

Not even the physics teachers?

Susskind:

There were no physics teachers. I didn't experience physics until I was close to 20 years old. I was maybe 19. The way I got to college was my father had an idea—he had been involved in working in tenement buildings in the South Bronx all of his life. At some point, he realized that all of their heating systems were going to fail. They were too old. They were 19th century. And he had the idea that he and I would go into business replacing the heating systems in big tenement buildings. These were big things with big furnaces and boilers. These were not small little houses. But he didn't know enough. He knew a lot, but he didn't know enough about technical things having to do with furnaces and heating systems, big heating systems. And [laugh] in fact, at one point, he and I were looking at some manuals, trying to figure out something about a heating system, and he saw the term “BTU.” You know what a BTU is?

Zierler:

Sure, yeah.

Susskind:

British Thermal Unit. He didn't know what a BTU was. He asked me, did I know what a BTU was? I said, “No, but I can probably find out. It’s a unit. It’s a unit of energy. It’s a unit of heat or power or something.” I didn't know. So he got the idea that I ought to go to school and become an engineer, a mechanical engineer. I did not like plumbing. I did not want to be a plumber. But there was no real other option. The only school we could possibly afford was City College.

Zierler:

So you weren’t a student in high school at a level where you were getting scholarship opportunities—

Susskind:

[laugh]

Zierler:

—where finances were not a problem?

Susskind:

No. It was quite the opposite. My letters of reference to college, in particular to City College, I'm afraid to tell you, said, “This man is not college material.”

Zierler:

[laugh]

Susskind:

I came from an ethnic area of all Italian, Irish Catholic. They were tough neighborhoods. I liked mathematics, and I knew I liked mathematics, but I was ashamed of the fact that I liked mathematics. I would go back to the neighborhood, and I remember I was carrying a mathematics book, and I just hid it away, because I didn't want any of the kids on the block to see that I was carrying a mathematics book. So, no. There was only one person in the family who had gone to college, and it was my father’s sister. She was a fine musician, very beautiful woman, and she lived and circulated among a community of artists, actors. She was a friend of Alfred Stieglitz. Whether that was a romantic connection or not, I don’t know. My father had supported the family from the time he was 12, and provided the money for her to go to college. I forgot how I got into it. Well, it doesn't matter. In any case, where was I? Before I mentioned that.

Zierler:

He wanted you to go into mechanical engineering.

Susskind:

Yeah. So he wanted me to be a mechanical engineer. I went to college. And for the first two years, I did very, very well. The first two years was where I encountered physics for the first time. Not mathematics for the first time; mathematics I was interested in. It was my first encounter with physics. Elementary physics for engineers. I liked it and I was so good at it. I mean, it was just so easy! Physics, mathematics, that’s what we were studying. I got all As. Then I got into the engineering side of things. And the first course in engineering that we took was mechanical drawing. Mechanical drafting. In those days, there were no computers. You actually sat at a drawing table with a fancy pen. It was an invention of the devil. It was called a ruling pen. Have you ever seen a ruling pen?

Zierler:

No.

Susskind:

OK. So a ruling pen, it has an active end—you see my fingers?

Zierler:

Yeah.

Susskind:

It had two nibs, and the ink was suspended by capillary attraction, and you drew with it. OK. If you were good at this, you could make beautiful drawings, beautiful mechanical drawings with it. If you were like me, you would leave blobs of ink all over the drawing.

Zierler:

[laugh]

Susskind:

And I couldn't—I simply was unable to make a full 100% drawing without leaving a blob of ink. This was not allowed. So the professor, who was a man called Harold Rothbart, who became a good friend of mine—Harold Rothbart came around, and he was watching me, and he said, “Susskind, this is not for you. This is the wrong subject for you.” He told me he would fail me in the class unless I dropped out of engineering. And I think he also knew that I wasn’t terribly interested in engineering. I said, “Oh my god, what am I gonna do?” By that time, I was married. I had a child. “What am I going to do? My father is waiting for me to go into business.” “I want you to drop out of engineering.” I thought, “Well, this guy really thinks I'm stupid.” And then he said something that really touched me. He said, “You're very, very smart. You should be a scientist. You should go into one of the sciences.” Well, I didn't know what that meant. To me, a scientist meant somebody in a white lab coat with test tubes. I really didn't know what it meant. He said, “In the sciences, you can try mathematics as a science, chemistry as a science, physics as a science. Why don’t you go around and talk to people in these departments and see if there’s any opportunity for you there?” So the first thing I did was go to the chemistry department. And they told me—this was two years into my education. They asked me, “Did you ever take a chemistry course?” “No.” “Do you know anything about chemistry?” “No, not really.” “Well, you can be a chemistry major, but you have to have an extra year, or maybe an extra year and a half.” Can’t do it. My father is waiting for me. My wife is waiting for me. I have a little kid. Can’t do it.

So I next went to mathematics. Now, there was a professor there whose name was Jesse Douglas. Jesse Douglas was the first Fields medalist. He was a cantankerous, extraordinary difficult character. He had been professor at MIT. He had been thrown out. Why? Because he never came to classes. He wound up at City College, where they tolerated him. But he took a fancy to me, and started to teach me what was for me advanced mathematics, a little bit of advanced mathematics. And I was good at it. He knew I was good at it. But he also told me that he thought I was made to be a physicist. I didn't know what a physicist was. So I said, “OK, I'm going to go to the physics department.” And I met a guy called Harry Soodak. Harry Soodak again became a close friend, or a lifelong friend, until he died recently. He took me under his wing and he explained some things to me. I had assumed that all of the problems of physics had been solved 200 years ago by a bunch of dead white Germans or Englishmen. He explained to me that it was a living science, that there were big, big problems, and that I could make a living, that I could become a physicist, a professor of physics. I started to learn it, and I would say within weeks, I knew what I wanted to do, there was no question. I was hooked. I was completely hooked. I started to learn classical mechanics. I started to learn quantum mechanics, general relativity. I was so completely hooked that I stopped doing anything else. I was still working, but I stopped doing all of my other courses. I failed everything.

Zierler:

When did you have to tell your dad that you weren’t going to go into business with him?

Susskind:

Yeah, that was tough. My father was a very tough individual. I don’t mean tough in the sense of gangsters or that sort of thing. I mean he was a really tough-minded, strong-willed character. And while I admired him enormously—he has always been my hero—still, I was a little afraid of him, even at the age of—by that time, I was 21 years old. I was married. I wasn’t living at home. I had a child. I was still a little nervous about telling him. At some point, I told my wife, “Look, we gotta go over to my father’s house. We gotta tell him what I'm gonna do.” So we went over. I've told this story so many times that it has become a ritual to tell it. People ask, so I tell it. We went over, and he was in the basement cutting pipe. Cutting pipe for the next day’s job. And I went down and I said, “Benny—” I called him Benny. When we were working, I wouldn't call him “Dad.” In fact, I never called him “Dad.” Never knew what to call him. But eventually I wound up calling him “Benny.” “Benny, I'm not going to be an engineer.” He never, ever, ever used foul language. He didn't like it. But at that point he looked at me and said, “What the fuck do you mean you're not going to be an engineer?” And I said, “It’s not what I want to do. I want to be a physicist.” I don’t know whether he misheard or what, but he said, “You ain’t gonna work in no drugstore.”

Zierler:

Pharmacist. [laugh]

Susskind:

Being a pharmacist.

Zierler:

[laugh]

Susskind:

OK? He said, “You ain’t gonna work in no drugstore.” I said, “No, no, no. Not a pharmacist; a physicist.” He said, “Well, what the hell is a physicist?” And I didn't know what to say. He had no background in it. I finally realized—I don’t know if I realized; I finally said the key word. The key word was “Einstein.” I told him, “Like what Einstein does.” At that time, especially among Jews in New York City, Einstein was golden. It was something very, very special. Although [laugh] nobody knew what the hell he did. He was somebody very special. And my father lit up and said, “Einstein?” “Yeah, I want to do the kind of thing that Einstein did.” And he looked at me and he said, “Are you any good at this?” And I said, “Yes, apparently I am very good at it.” He thought and he looked at me and said, “OK. OK. If that’s what you're gonna do.” And then my mother came in, and my mother was with my wife. My wife had told my mother that I was not going to continue in engineering, and my mother was crying. She was crying, and she came in, and my father took a look at her. He was very kind to my mother. He was very much in love with my mother. But that’s the only time I ever saw him angry. My mother was—

Zierler:

Why was your mom so upset?

Susskind:

Because she imagined I was going to go hungry. The only thing we knew was to go into my father’s business. And he looked at her and said, “Shut up, he’s gonna be Einstein.” And that was the end of it. That was the end of it. He tried to learn physics. He was very supportive. And yeah, that was the end of it. Completely obvious that what I was going to do in life was become Einstein.

Zierler:

Big shoes to fill.

Susskind:

Yeah. So that was an incredible relief. I was so worried about that. So, at that point, I was failing out of college. The reason was because I was failing every subject except physics and mathematics. I failed history. I failed German. I failed everything under the sun. The physics department took me under its wing and managed to get me into Cornell graduate school, without a degree. I had no degree. And the people at Cornell were very—again, very, very supportive, but I felt so out of my element there, this academic world. It wasn’t true in CCNY. CCNY was full of kids like me. Lots and lots of working class kids. Cornell was something different. Cornell—Hans Bethe was very kind to me, and Ed Salpeter. They were extremely kind to me. They made it possible for me to do exactly what I wanted to do. But I felt so uncomfortable in this academic environment that I had never experienced. And I think that discomfort in the academic world lasted a long time. I always felt like an outsider.

Zierler:

Leonard, when did you start to think of yourself as a theoretical physicist? I mean, if you're coming from plumbing and engineering, why not experimental at the beginning, when you're just surveying your options?

Susskind:

[laugh] Well, first of all, I was no damn good at plumbing.

Zierler:

[laugh] OK.

Susskind:

Oh, I was good enough. I was good enough. My father was a master. He was a true master of his profession. I wasn’t interested, and I didn't like it very much. I did like building things with my hands. But building things with your hands, building with hammers and nails and screwdrivers and pipe wrenches—that’s a far cry from the kind of thing you need to be able to do to be an experimental physicist. A very far cry. I was always fascinated by the theoretical end. So as soon as I started talking to Harry Soodak, my professor at CCNY, and learned that there was this thing called theoretical physics and this thing called experimental physics, I knew what I wanted to be. There was no question. And my abilities up until that point were almost entirely just mathematics. So it was clear from the time that I started to think about physics altogether that it was theoretical physics, not experimental physics.

Zierler:

And did you start to think about the very deep questions that you had come to be known for, from the beginning?

Susskind:

I was trying. Let’s see. I was very interested in quantum mechanics and general relativity, so I guess the answer would have to be yes. But as far as I and everybody else were concerned, the questions were quite different than they are now. So did I see the future? No. I saw the past but I didn't see the future. One of the seminal things with the books—I never read physics books anymore. I never read physics articles anymore. I can’t. I just get bogged down in them. There were a couple of books that made a big difference for me. The first book that I read that I really got excited about was Goldstein’s mechanics book. Are you a physicist?

Zierler:

No. I'm a historian of physics.

Susskind:

[pause] You're a historian. Goldstein’s mechanics book, Classical Mechanics, was a standard, and I think it still is. Goldstein himself was not a physicist. He was some sort of chemical engineer or something. He wrote this very, very good book. It was the only good book at the time on classical mechanics. I read the whole thing, and I got very excited about the beauty of Hamiltonians and Lagrangians and Poisson brackets, and all these things. It was the first time I encountered what you might call “theory-theory,” building up ideas through mathematical structures. That really appealed to me. Then, I wanted to learn quantum mechanics. Various people told me books to read. The books were terrible at that time. They were bad. But Harry Soodak told me to read Dirac’s book. If I recall he even bought it for me. Dirac’s book was from 1933. To this day, I still think it’s the best book on quantum mechanics by a wide margin. So I read Dirac’s quantum mechanics book, and again, I saw this man building up a structure, building up a mathematical structure that in the end, after all the mathematics is done, it applies directly to physical phenomena. And that excited me, to no end. I also read Einstein’s papers. I think I still have it on my desk here. Yeah, I do! Yes! I didn't put this here for you. You know this?

Zierler:

Oh, wow. Yeah. Yeah.

Susskind:

Yeah. Why is it on my desk? I don’t know. It’s always—seems like it’s always on my desk. I read the special relativity papers, general relativity papers, and there was something there that I realized that just—I was thunderstruck by. It was the simplicity of the questions that Einstein asked. And they were questions that a 12-year—I wasn’t 12 years old, but if you told them to a smart 12-year-old, they would understand exactly what they were. If you move along on a train at the speed of light and watch a light beam, then the light beam is going to be static, because you're moving as fast as it’s moving. And that can’t be right, because the equations of electrodynamics say the waves travel, they don’t stand still. So that apparently was something he asked himself when he was 16. That’s not in his paper, but the first thing he says is if you move a magnet relative to a coil, you get a current. If you move the coil relative to the magnet, you get a current. There’s some kind of relativity going on, and the description of the two things is completely different. So there’s something wrong. We have to put these things together so that they are the same phenomena—moving the magnet or moving the coil. Or moving the magnet. I could understand what he’s talking about. That’s very simple. And then from that conclusion and a bunch of simple ideas, he came to these incredibly far-reaching things. Another example—the elevator experiment. If I remember, I don’t think he actually talked about an elevator. But gravity would be like being in the elevator, from which he concluded, if you were in an elevator moving up, and a light beam went across, the light beam would bend. He made this surprising conclusion that light, as well as everything else, gravitates, from something that a 12-year-old could understand. That to me was the way that I wanted to do physics. It wasn’t that I wanted to imitate Einstein. It just felt right. This is the way to think about physics. You start with very, very simple observations about the world, and from them, you draw far-reaching conclusions. Gedankenexperiments— I really, really fell in love with the idea of thinking about physics from a very simple starting point and building on that.

Zierler:

Did this inform the kinds of mentors that you gravitated towards?

Susskind:

No. By the time I went to graduate school, I was finished with mentors. Well, let me see; did I have mentors after that? Not really. People were very kind to me. Hans Bethe—they gave me the office right next to Hans Bethe. And Hans Bethe was very kind to me. He was kind to my wife. One day, he walked into my office and he asked—officially, I was supposed to be his student, so he asked if I would like to work on a problem with him. And of course, I would want to work on a problem with Hans Bethe. He was working on the problem of nuclear matter. The problem was to calculate the ground state of infinite nuclear matter. Of course you can’t have infinite nuclear matter because the Coulomb repulsion of the protons would blow up a large nucleus, but if you shut off the Coulomb forces between protons then you can have a state infinite nuclear matter. He wanted to calculate the ground state of it, its binding energy, and all that sort of stuff. There was a bunch of rules that had been constructed by other people for how you calculate many-body systems. It involved Feynman-like diagrams. And what he wanted me to do was to calculate a certain—basically, a certain Feynman diagram. Not relativistic Feynman diagrams; non-relativistic, many-body diagrams. I knew nothing about it. I was a little embarrassed to tell him I didn't understand what he was talking [laugh] about. So I went to my friend, Doug Rajaraman who was Bethe’s student, and asked him, “Can you explain to me what the problem is?” He said, “Yeah, the problem is easy. To explain the problem is easy. He just wants you to do an integral. He wants to get a number. A six-dimensional integral over some overlapping spheres, Fermi spheres.” Doug helped me figure out what the integral I was supposed to do was. And so I started to do the integral, and it was hard. I mean, I had to beat it down to a one—I had to eventually beat it down to a one-dimensional integral. And there were no computers; you had to calculate the integral, the number. And how do you do an integral? You draw the graph on a piece of graph paper, and then you count up the number of boxes that lie under—

Zierler:

[laugh]

Susskind:

—under the curve. And I did that. It took about three months. It was hard. And then at the end, Bethe—Bethe would ask me from time to time how it was going. He never pressured me. Eventually, he came into my office, and he asked if I was able to do it. And I thought to myself—by that time, incidentally, the people at Cornell had a good feeling about me. I had done other things. There was no danger of not coming up to par with them. And I figured, “Look, I have an alternative. Either I can tell him that I did it, in which case he would have me do another one.” Which I did not want to do. Or I could tell him, “No, I wasn’t able to do it,” in which case maybe he wouldn't ask me to do another one. I chose the latter. I told him I didn't do it. And he said, “Oh, that’s OK, no problem. You're working on interesting things. Why don’t you just keep working on the stuff you're interested in?” Which was connected to things I thought about later, and it was structure of hadrons. And so [laugh] he didn't ask me to do another one. It wasn’t until shortly before he died—I think he was about 95—well, it was five years before he died—he came to Stanford to give a lecture. He was 95 years old. Oh, what was he going to talk about? He was going to talk about the neutrino effect from the sun. The MSW effect and neutrino oscillations. He came over to my house for dinner. Just him. And I asked him, “Hans, do you remember the problem you gave me?” He did. He said, “Yes.” He didn't remember exactly what it was. He also remembered that I didn't do it.

Zierler:

[laugh]

Susskind:

I said, “Well, I did do it. And I even have the number.” And he said, “Why did you tell me you didn't do it?” I told him why. I told him—I didn't want to do another one. He started to laugh. He thought it was the funniest thing he ever heard. He said, “You did the right thing.”

Zierler:

[laugh]

Susskind:

But no, Hans Bethe would not have been a good mentor for me. He was much too practical-minded for me. I don’t know if that’s quite the term. He didn't like general relativity. And he was very computationally-oriented. He wouldn't have been the right person for me. If I had any mentor in that period after I went to graduate school, it would have been Feynman. But that wasn’t until a little bit later. Yeah, if there was any mentor—but even he wasn’t a mentor. By that time, we were friends. And I admired him enormously. Again, I admired his style of physics. But was he a mentor? Maybe in some way.

Zierler:

Did you see Feynman in the same mold as Einstein in terms of posing very elegant questions?

Susskind:

I guess I didn't think about that as much. Look, I didn't see him in the same way that I saw Einstein. I didn't know Einstein. I never met Einstein. Einstein was this Newtonian figure. He was in the league with Newton and Archimedes and Galileo. Feynman was a guy who was a terrific physicist. He was lots of fun. I enjoyed him. And I saw him as human. I didn't see him as a god. I saw him as a friend. So—oh, OK. What did I—I did see something in Feynman’s physics. He also had a certain simplicity of thinking. The two examples that stand out, and I've talked about these publicly on occasion—well, there were three. The first was his ability to cut through the great difficulties of quantum field theory and just draw diagrams. How the hell did he figure that out? And he didn't figure it out; he just made it up! People who tried to figure out what Feynman was doing could not get him to explain what he was doing. He just said, “Here it is. This is what it is.”

But later on, when he was studying helium, he decided to figure out how helium works. And at that time, the standard for studying helium was a method that they had been using—Feynman diagrams applied to many-body physics. And Feynman cut right through it. He never even thought about Feynman diagrams. He just pictured what the wave function would look like. He effectively closed his eyes, imagined what the wave function would look like, and wrote down a simple expression for the wave function. From that, he was able to derive everything in very, very simple ways. That, I admired. And I saw it again when he was doing parton physics. Everybody was doing, again, Feynman diagrams, calculating the complicated Feynman diagrams. And Feynman again just closed his eyes, pictured the proton as a bunch of little points moving along, the electron going the other way, and knocking out a quark, a parton. From that, he was able to derive a great deal of the way that the deep inelastic electroproduction worked.

So I did like that. By that time, I already had my own style, and it was very much like that. When I saw Feynman being able to do that and do it successfully, I was very encouraged. Because as much as I liked mathematics, my own style was never very mathematical. It was always, “Close your eyes, and see if you can see what the thing looks like.” In that sense, I think Feynman was a mentor. But it came a bit late for it to have really affected my own style. That already existed. I also admired Murray Gell-Mann enormously, but very different. Murray and I did not get along. In fact, I think we really disliked each other. But I could see his incredible ability to see patterns. To see patterns in nature. And that was something I wanted to be able to do, and I had no capacity for it. I had no capacity for symmetries or thinking about physics the way Murray did. So was he a mentor? Not a mentor, but—and if anything, somebody who I didn't get along with. But I did see him as having some extraordinary talent that I would have liked to have. I have mentors now, but they're all younger than me.

Zierler:

My big question about your time at Yeshiva University is I wonder if the religiosity of the environment—

Susskind:

[laugh]

Zierler:

—affected either the way that you taught or the way that you might have had to interact with students who might have come from a different spiritual background than you were coming from? Or administration. I wonder if those things affected your teaching style or the kinds of projects you were working on.

Susskind:

OK, so I'll tell you the way in which it may have had an effect. First of all, was I at Yeshiva University? I was at the Belfer Graduate School of Science. Which was a part of Yeshiva University, but it was separate. It was a graduate school of science. It was a very funny, idiosyncratic place. It was a marvelous place. It had some extraordinary scientists. Yakir Aharonov, Dave Finkelstein, Joel Lebowitz, Elliott Lieb. Freeman Dyson was on the faculty for a while. I was there for ten years. Wonderful mathematicians—Leon Ehrenpreis. And they were not all Jewish. Al Cameron, the great astrophysicist. James Truran, another astrophysicist. They were definitely not all Jewish. There was no religiosity there. In fact, most of the graduate students were not religious. A good fraction of them—most of the graduate students I interacted with were South American, and only a few of them were Jewish, Most not Jewish. I think there was a certain idealistic view to physics—the Aharonov view, the David Finkelstein view, the Joel Lebowitz way of approaching physics—a certain idealism about physics. I don’t mean political idealism. I mean—what should we call it? Love of Einstein, for a better word, although it wasn’t restricted to Einstein. And that may well have had to do with the origins of the Belfer Graduate School—from Rabbi Belkin. Rabbi Belkin was the president of the university at that time. Marvelous man. And he was the one who had the vision to create a graduate school of science. And I think maybe that sort of rabbinical tendency, whatever the right word is, may very well have influenced who the early faculty were. It was not a religious faculty, but it was idealistic in a certain way—depth of understanding is what counted. Is that a Jewish thing? I don’t know. Maybe—I don’t know.

Zierler:

As a matter of intellectual history, one of the things I really want to ask is, you know, it’s on your website, it’s all over the place—the idea that you're one of the fathers of string theory. So to the extent that that metaphor is meaningful, if we could make physics a family affair, to contextualize—

Susskind:

A what affair? Wait, say it again?

Zierler:

A family affair.

Susskind:

A family affair, yeah.

Zierler:

You're one of the fathers of string theory, and so that sort of begs the next question—to the extent that physics is a family affair and you're one of the fathers of string theory, it begs the question—who are your parents and grandparents?

Susskind:

[laugh]

Zierler:

Who are your children in string theory?

Susskind:

Yeah, OK. [laugh] Well, yeah. I'm not sure who my grandparents were, if grandparents mean, first of all, that they're older than you. Second of all, that you look to them as ancestors. But I do know where the ideas came from, and where the questions came from. First of all, they came out of the community of people who were studying hadrons, and this to a large extent meant the Berkeley S-matrix people, the disciples of Geoffrey Chew, who were studying the S-matrix of hadronic collisions. They had all sorts of peculiar religious beliefs. Well, not religious, but peculiar ideological beliefs. And what did they decide? They decided that the right way to think about hadronic collisions was through the S-matrix, and the basic principles were unitarity, analyticity, and Lorentz invariance. Now if you want me to say more words about those, I can. Unitarity is a basic principle of quantum mechanics. It says all the probabilities all add up to one. It’s much more than that. It’s the quantum version of information conservation—the rule that says that information is never lost. S-matrix is unitary and it’s analytic. Analytic in what? Analytic in the momentum of the particles that are scattering. And finally it’s Lorentz invariant. Chew and his disciples thought that unitarity, analyticity, and Lorentz invariance were enough—that’s all you really needed to get a unique answer for what the S-matrix should look like. That culminated, I think, with the work of Gabriele Veneziano, who just from those principles alone put together a mathematical expression for an S-matrix element. It’s famous. It’s called the Veneziano amplitude. And it’s just a mathematical formula that’s got two gamma functions in the numerator and one gamma function in the denominator. It’s a simple function.

I was already a young assistant professor when that happened. I was not really working on those things at that time. I was much more interested in quantum mechanics. But a fellow came to visit my friend Aharonov, his name was Hector Rubinstein. He was from Israel, and he was a friend of Veneziano’s. Veneziano was in Israel at that time at the Weizmann Institute. And Hector brought this Veneziano amplitude with him. He wrote it on the blackboard. I knew very little about it, but I saw it was a simple formula. I went home and thought about it and thought about it. It looked like it had the spectrum of states of a harmonic oscillator. Equally spaced levels. Equally spaced in energy squared, not in energy, but it looked very much like harmonic oscillators. And I started tinkering around with the problem of scattering of particles, photons, from vibrating systems. Supposing you had a charged ball on the end of a spring, and you scattered photons off it. I started calculating the scattering amplitude for that. And it had a very remarkable similarity with the Veneziano amplitude. It wasn’t right, not quite, but it had remarkable similarities. I wrote it down. I published it. It was called the harmonic oscillator analogy for the Veneziano amplitude. But it wasn’t quite right, and I kept thinking about it and thinking. Eventually I realized that it wasn’t a spring, but a string. That it had to have many modes of oscillation. That was the first inkling of string theory. It had been done simultaneously at about the same time by the great physicist Nambu. It was an interesting feeling for me when I discovered it. It all happened all at once. I suddenly realized, very suddenly, that it was a string, a harmonic oscillating string, and I thought I was the only one in the world who knew this. It’s a very exhilarating feeling to think all of a sudden I am the only one in the world who knows this. Later, I found myself a little bit disappointed that Nambu also knew it at the same time. But the compensating good side was Nambu was a very great physicist, and here I was, doing something that was the same as what Nambu was doing. So that was the origin of it. I wrote all these things up and then I did some mathematical work on it. That was the origin of string theory. There was another person who was very, very close to the same ideas, the great Danish physicist Holger Nielsen. I don’t know if you know his name. Nielson?

Zierler:

Mmhmm.

Susskind:

Holger Nielsen was the other person who had a little different take on it, but he was very close to the same ideas. And Nielson and I became friends and exchanged lots and lots of letters. So I would say the origins of string theory go back to Veneziano, but that wasn’t string theory. That was just a mathematical formula. And then the realization, the physical implementation of it as a physical system, that was myself, Nambu, and Nielson, quite independently, completely independently. None of us knew each other, and I don’t think any of us had ever even seen each other.

Zierler:

And in terms of where string theory went, in terms of—?

Susskind:

OK, so I knew at the time that the open string theory had a massless spin-one boson in it. That was a nuisance, because hadrons don’t have massless spin-one bosons. And after a little bit of working out closed strings—I think I was probably the first one to work out closed strings, but I didn't get them right. I had a mathematical mistake. But apart from the mathematical mistake, I knew that there were closed strings, and that the closed strings had a massless spin-two particle. I knew that a massless spin-two particle meant the graviton. I knew that a massless spin-one particle meant the photon. But I didn't want them to be there, because, you know, hadrons didn't have such things. And so I tried and tried to get rid of them, and I couldn't get rid of them. Eventually, I just said, “OK, string theory is a kind of model, but it’s a little bit too idealized, a little bit too mathematically idealized. It looks like the wrong thing. It looks like photons and gravitons.” And then other physicists came along. One of them was a Japanese by the name of Yonea, Tamyaki Yonea. And the other two were John Schwarz and Joel Scherk, a Frenchman. And they realized there was a huge opportunity there, and they all said, “This could be gravity.” They had some very beautiful ideas. And at that point, I said, “Oh boy, I missed the boat.”

Zierler:

[laugh]

Susskind:

I knew that gravitons and photons were there. I should have said it. And instead, I considered it a defect.

Zierler:

What boat did you miss exactly?

Susskind:

I knew there was a graviton in the system. I knew there was a photon in the system. But I was unwilling to say, “Oh, this could be the theory of the Planck scale.” You know, at that time, the subject of gravity was not considered a reasonable subject for grown-up physicists.

Zierler:

[laugh]

Susskind:

It was for quacks like John Wheeler, grown-ups didn't do gravity. OK? So I knew it was there. I sensed it. But I rejected it. But once they said it, I knew, “OK, I missed the boat, but this is really interesting, and maybe we should be thinking about gravity.” This was 1972. It was long ago. Then, I was still interested in hadrons. Ken Wilson had been thinking about these lattice gauge theories. I knew Ken a little bit. And I started thinking about his lattice gauge theory. His lattice gauge theory is what we could call a Euclidian lattice gauge theory. It wasn’t actually thinking of the system as a quantum mechanical system that evolves in time. I decided I would try to figure out how lattice gauge theory works as a true quantum mechanical Hamiltonian system. So John Kogut and I figured out what is now called Hamiltonian lattice gauge theory. That was a great success, and it really gave you a picture of how confinement works. The interesting thing about the picture is confinement worked by strings. The gauge field assembles itself into string-like configurations.

So I wrote papers on lattice gauge theory which are now considered classics. My main delight in it is that it connected together—the ideas of quantum chromodynamics and the string theory. I thought more about Yang-Mills theory, and I guess I was the inventor of the idea that the Yang-Mills gauge field, unlike electromagnetic field, has a kind of instability which causes the flux to assemble itself into these flux tubes, into these string-like configurations. So strings, lattice gauge theory, confinement—that occupied my attention for probably about five years between 1969 and 1974. And at the end, I think we have had and have a coherent picture of how quarks are confined and how hadrons work. That was satisfying. But I'll tell you, all during that period, I had a sense of very mild disappointment. Disappointment in the sense that I had not been there when the great revolutions of relativity and quantum mechanics were being discovered. I had come into physics a little bit too late. I would have liked to be there in the 1920s, in maybe the early 1900s. I felt the things I was doing were all outgrowths of the early era, marvelously interesting outgrowths, but not somehow as fundamental, or whatever you want to call it. When I started thinking about gravity, particularly in the light of Stephen Hawking’s major accomplishments about black holes and his very profound question about information, I began to think, “Wait a minute. There’s opportunity here for me to be in an area of physics which is as seminal—” or as deep as the early 20th century. And I still feel that way. I still feel that the second half of my career was more about things that I would have liked to have been involved in, than the first half of the career.

Zierler:

I want to ask two very basic questions about the deep questions that you've been involved in. One, just very bluntly, are you comfortable with the idea that the laws of physics suggest that the universe can create itself?

Susskind:

First of all, I don’t know what it means. And no, I'm not terribly comfortable with it. Partly because I don’t know what it means, and I think we're getting ahead of ourselves there. Or at least I would be getting ahead of myself if I were to make such a pronouncement. I'm not a great fan of the—what did Hawking call it?—his picture of the universe being created out of nothing. The “no boundary proposal.” I'm not a great fan of it. It’s not that I think it’s wrong. I just think we're getting ahead of ourselves. We're too ignorant, I think, to have any kind of clear idea of the origin of the universe. I think we need to think more. We need to experiment more, both real experiment and Gedankenexperiment. And we need to understand gravity and its connection with quantum mechanics better. Most of the explorations that are taking place today which are having the most profound effect I think are not about the real universe. They're about these model mathematical universes that come out of string theory. AdS/CFT or gauge/gravity duality or whatever you want to call it, which are really very much changing our picture of the connection between gravity and quantum mechanics. I can tell you more about what that connection is, but I really don’t think we're in a position now to accurately guess what the origin of things is. I just don’t think we're far enough.

Zierler:

When you say we're getting ahead of ourselves, does that suggest that after a certain period of time, technological advances, the next Newton or Einstein, that these are knowable questions?

Susskind:

Well, I don’t know. [laugh] I’d be getting ahead of myself if I tried to answer it. No, there are some things which I think I can foresee. Of course, I may foresee them wrong, but a certain distance that I think I can see ahead. But I would guess there’s going to be three or four major turns in our way of thinking before we get to those things.

Zierler:

Would that suggest, then, that a physicist has no privileged position in questions about whether—

Susskind:

A physicist has no what?

Zierler:

That a physicist has no particularly privileged position in discussions about whether God exists or not?

Susskind:

[laugh] Oh, boy. Wow. Yeah, I don’t think he does have any privileged position. Yeah. He, she. I think I would subscribe to that view. That doesn't mean I don’t have my own view about it. OK, let me separate physics from science. Physics of course is part of science, but science is a bigger thing. Science includes, among other things, the theory of evolution. I think the theory of evolution is as profound in many ways. The original theory was not a mathematical structure, but it is a coherent theoretical structure which reminds me, in many ways, of physics. A basic simple idea carried out to its conclusions. Mutation and survival of the fittest. Its not physics but it is good, coherent logic applied to a puzzling problem. So if I were to say does a scientific way of thinking have a role in thinking about god—oh boy, that’s a hard question. I don’t think any scientist can answer the question of whether there was an intelligence that was at the root of the creation of the universe. That would also be getting ahead of ourselves. But still, scientists do understand the thing that we have to understand. They know what the questions are. I know when I think about the question of creation, I'm very influenced by my own scientific background. If somebody says to me, “Is there a god?” I say, “Well, I don’t really know, but you know, I'm very puzzled. If there was a god, and god did create the universe, is god susceptible to the same rules as ordinary matter? Does god satisfy the laws of quantum mechanics? Is he made out of particles?” And so forth. That’s the way my head works. I can’t help thinking that way.

Zierler:

Not the Jewish god. That’s a very easy answer. The Jewish god does not.

Susskind:

Yeah, I know. The Jewish god does not.

Zierler:

[laugh]

Susskind:

So what are the rules of the interaction between god and matter? I'm not seriously asking those questions now; I'm telling you that’s the way my head works. I get curious about things, and I start trying to build a mathematical model about how god would interact—that's crazy!

Zierler:

Leonard, here’s a much easier question, I think, because it’s much more rooted in the here and now. And obviously we can’t talk about all of it, but a very powerful theme in your career is your passion for communicating physics concepts to a broad audience, whether it’s through your popular books or through The Theoretical Minimum, or through your lectures to non-traditional students. What is the overriding passion behind all of these efforts? That you're really unique in terms of people at your stature generally are not interested in these kinds of things. They're much more sequestered, for the most part. What’s the motivation?

Susskind:

OK, I think there’s a number. This question has come up over and over again. So having thought about it, first of all, to some extent, it goes back to my early youth. My father and his friends were all plumbers. They were all intellectuals, although most of them had not gone past the fifth grade. They were all intellectuals, and I think a large part of my formative intellectual years was sitting at the kitchen table with him and his friends. I ultimately started to call it the University of the Kitchen Table, talking about all sorts of stuff. Science, among other things. Politics. History. And they were a little bit crackpotty. These were all people who were entirely self-educated. And the reason they were a little—particularly about science, they were a little bit crackpotty— I think the reason was because they had no way, no access to be able to find out what was real mainstream ideas and what was sort of off the wall. One of my father’s friends gave me a book; it was called World in Collision. Do you know that book?

Zierler:

Yeah, I've heard of it.

Susskind:

Yeah, OK. And I read it, and I was fascinated by it. But it’s crackpot! How would a person who had a fifth grade education, was curious, but had no access at all to science, to scientists, to the academic world—how would he be able to tell which was real and which was crackpot? And so they suffered that problem. When I got a little older, and already I knew some science, I would try to educate them. And they would listen to me. I think that was a part of it. I spent time trying to explain things to them. At some point, I got interested in doing that for a broader public at Stanford. Of course the public there was educated, but they had the same problem. They would come to me and ask me about something they read the newspaper, this or that particular new thing about physics. “Is it real or is it fake?” And I tried to figure out ways of—an algorithm for them to be able to tell whether something was mainstream or whether it was kooky. No algorithm I could think of ever worked. I thought of a number of algorithms. They all failed. And so I decided the only way to do this is to simply give people the tools to be able to decide for themselves. I'm not sure that works either. I don’t think it does. [laugh] And I began to enjoy it. Look, I've always enjoyed explaining things. I have a little bit of a Feynman in me. And what I'm talking about now is a love of being able to show people how smart you are. One way of showing people how smart you are is to show people how simple things are. What you're telling them is, “These things are really simple. At least if you're as smart as me, they're simple.” And so I do get a kick out of explaining hard, complicated, sophisticated, supposedly sophisticated things in very simple terms. A little bit of it is this ego thing that Feynman had a lot of, also. He got a great deal of joy out of showing how simple things were, if you thought about them the right way. And the right way meant to think of them as Feynman would have thought about them. I didn't get that from Feynman. I've always been like that. But even when I was a kid, I loved to be able to explain something in some way that showed how smart you were. So I think there’s a bit of that, too.

Zierler:

That gets me to my next question.

Susskind:

There’s another element. In learning to explain something—and this is really true—when learning to explain something, even to the most elementary audience, you always learn something about what it is you are explaining. And trying to figure out how to explain things in simple terms, your own understanding of that thing is enormously enhanced. That has been my experience—that almost everything I learned about physics, I learned by trying to explain it. So I'm very surprised that my colleagues don’t enjoy these things as much.

Zierler:

My next question is, your famous lecture—“What Worries Me Most”—it’s on YouTube right now, right?

Susskind:

What did I say?

Zierler:

If you go on The Theoretical Minimum, it’s the link right below. It’s the link there—“What Worries Me Most”—and this is in 2017. You're not talking in your capacity as a scientist at all.

Susskind:

Oh, oh, oh, oh.

Zierler:

You're talking about the orange Godzilla, as you called President Trump.

Susskind:

The orange Godzilla. Yes, yes, I do remember that.

Zierler:

Now, obviously we're talking from home.

Susskind:

It still worries me.

Zierler:

Of course, of course. But I wonder now—

Susskind:

It still worries me.

Zierler:

So now that we are in—however great this crisis that we're in the middle of right now, however we contextualize this in the grand sweep of history, the fact that you have poured so much passion into explaining scientific concepts to a broad audience—the things that you were talking about in that lecture seemed sort of—first, they're not scientific. You were worried about Mexico and treatment of the press and things like that. And now I wonder how you might update those concerns in light of where we are now and the administration’s response to coronavirus, and how that fits into a larger pattern of the president’s treatment of science and scientists, and the broader societal implications of that relationship.

Susskind:

I think I would like to think about that a little bit, and we'll get back together and I'll answer it.

Zierler:

OK.

Susskind:

Because I think this is a serious issue that I would like to think about seriously before I answer, and not just fly off the handle. If this is ever going to appear someplace—

Zierler:

It will. It will.

Susskind:

—yes—I want it to—

Zierler:

So we'll make this Susskind Part 1, and we'll reconvene. How’s that?

Susskind:

Yeah, yeah.

Zierler:

OK, so I'll cut it here.

Susskind:

I do feel you're correct. I do feel absolutely passionate about it. I am angry about it. I am upset. It occupies an enormous amount of my mental energy, my wife and mine. And my kids. And I would like to talk about this publicly, but I think I should not do it off the cuff.

Zierler:

Good. So I'll cut it here.

[End 200501_0086_D]

[Begin 200503_0087_D]

Zierler:

OK, this is David Zierler, oral historian for the American Institute of Physics. It is May 3rd, 2020. It’s my great pleasure to be here again with Professor Leonard Susskind. This is us picking up on our conversation from this past Friday. So, Leonard, where we left off on Friday—I asked you a question about your current political beliefs and concerns based on this YouTube lecture that you posted from a few years ago about your concerns about the Trump administration generally. Not just about science, but about a range of policies that you had concern with. And I thought, before we jump right into that, we might build out a little bit your intellectual history and development. One thing that jumps out at me is you very eloquently explained how your father’s family background influenced his own political identity and his concern, and his own version of social justice and concern about how African Americans were treated, and so on. We didn't really develop how that translated to your own political identity, what kinds of things you took from your parents that helped shape your own concerns about social justice and civil rights and things like that. So I wanted to build up a little bit about that from your upbringing.

Susskind:

Well, when you live with people and you learn from them and you interact with them, it’s always a little bit hard to say exactly how attitudes filtered through, where did my attitudes come from. They surely were influenced by my father and mother. There’s no question of it. But could I tell you exactly how and exactly when and exactly what circumstances? My father and I were close, but he tended not to talk about himself that much. The little bit I learned about my grandparents, about his—every once in a while, he would sit down and tell me some of his philosophical beliefs, which were pretty sophisticated. As I said, he had a fifth grade education, and that was it. He had to go to work when he was 12. That was 1918. And he did not have what we would today call an educated background. On the other hand, he must have read a lot. I don’t know where he picked up all his attitudes. He was a Marxist but also a Democrat. He was a union man, but I don’t think he was terribly active in politics in the union.

I'll tell you a couple of stories that I know, some of which I even remember. I am a person who doesn't remember what happened yesterday, but I seem to have some imprinted memories from very, very early. My father was a plumber, and he was a highly skilled plumber. He was a man of great integrity, and he was tough. He was very, very tough-minded. I don’t mean tough like a gangster. I mean tough-minded. At least in my experience, when he was working for other people on big projects, he was always the foreman. Just before the United States got into World War II—and of course I was born at this time, but I was only a tiny child. Roosevelt was firing up the war effort, and my father went south to work on munitions plants that were being constructed. I know we were in Louisiana, probably somewhere near Baton Rouge. We were in Tennessee, and my guess is that in Tennessee, we were in Oak Ridge, but I'm not completely sure. A number of other situations in the South where he was involved in building war plants. The first story that I remember he told me, he had a Black friend—he always had Black friends. He had a Black friend who was also a plumber, also involved in this project, also from the North. And he was working next to him and the Black plumber said something to the effect that he’s grateful to Hitler for only one thing—that he created work. A white, Southern cracker picked up a hammer, hit him over the head, and killed him, right in front of my father.

Zierler:

Whoa.

Susskind:

This was a formative experience for my father, I can tell you. Two other incidents come to mind that my father told me. One of them I actually remember fairly clearly and distinctly. While we were in the South, I think in Louisiana—and this, I do not remember; I was too young—an interesting thing was going on. Every night, they were building this plant, and every night, the pipe that had been installed would be de-installed and taken away. The plumbers thought the pipe was being stolen. It turned out that it wasn’t so much being stolen as being dismantled so that they would drag out and lengthen the time. And why? Because the local town was making money off the operation. So my father was concerned about it, and he actually did the worst possible thing that he could have done. Instead of getting to the FBI, he went to the local sheriff. This was a bad, bad move! I was told by my mother that what happened—in the middle of the night, his friends came to him and said, “They're coming for you. There’s cars coming, and they're coming for you.” My father realized what was happening. Apparently he and my mother grabbed me, pulled me into the car, and we drove off and never came back. We did go to other operations of a similar kind. So this also colored his view of [laugh]—let’s put it this way—certain areas of the country.

And the last thing I remember—well, no, there’s more. There’s more. There’s more. Plumbing in New York was a somewhat seasonal thing, so my father would take a job as a taxi driver on the off seasons. He was very good at it, apparently, and there was always a contest among the drivers who worked for this big company, who would bring in the most money. Invariably, my father would bring in the most money every—and the reason was, because he was the only taxi driver that was willing to work Harlem. But at one point, he was held up by a couple of young Black kids who tried to take his money. He just put the car in gear and rolled away, and in the process accidentally ran over one of the kids and broke his leg. This I do remember. I was probably around eight at the time. And I remember my father being terribly, terribly upset. He went to the hospital to see the kid.

Zierler:

Wow.

Susskind:

He saw the mother. And he was so upset by all of this that he gave the mother some money to take care of the kid.

Zierler:

Wow.

Susskind:

This was something unusual. And the last thing I remember along these lines is my father often he hired young men to be his assistant. It was a one-man shop except when I worked with him. Usually, it was myself, my father, and his helper. He had to have another helper besides me because I couldn't work full time; I was still in school. So I must have been about—this was before I was working, about nine years old, and a big, strong-looking, strapping, young Black man—mixture of Black and Puerto Rican—came into the shop, and he asked my father if he could talk to him. So my father took him—he wanted to talk privately. I went in the back of the shop with them, and I heard the conversation. The man wanted a job but he told my father that he had just gotten out of jail. He had been involved in some kind of gang fight in New York and somebody had gotten killed. He had been in jail, convicted of murder. He was let out. He told my father that he had no interest in that kind of thing anymore. Would my father hire him? My father hired him. He became a close family friend. His name was Ricardo, but we called him Richard. He became a mentor to me, And eventually a successful plumber himself.

This was the character of my father. He had this—I don’t know, this sort of real sympathy for the underdog. In that situation, the underdog was usually minorities. So I did come away with that, and with a tremendous admiration for my father. On the other hand, I also came away with plenty of anger toward my father. Plenty of anger. I was very, very angry that I was forced to work on the weekends. I was forced to—couldn't be with my friends. I was angry at my father for other things. But at the same time, he was this gigantic presence in my life, and my hero.

My very, very first memory—I don’t know if it’s my first memory—I seem to have very early memories, but the first thing I can remember was in the South. I don’t know where it was. I remember a place which was brown. It seems to me that it was a cabin of some sort, with a yellow or orange light hanging from the ceiling. I was being tossed back and forth or played with by two giants, two laughing giants. One was my father, and the other was his friend Joe, a Black man. A Black man with white hair. This is what I remember. Many years later, I asked my mother, “Did this take place?” And she said, “Yes, this took place.” She told me where, but I don’t remember where it was. And it was indeed in some sort of cabin they lived in, a thing that they lived in while my father was working on this project. That stuck in my mind. My father was no giant, he was a small man. He was five-foot-six. At the most in his life, he weighed 160 pounds, but that was unusual for him. Usually around 140 pounds. But I remember this big laughing giant. I asked my mother about Joe. Was Joe a great big man? No, Joe was a little guy. So that’s my first real visual memory that I can remember. So pretty much all of my life, I had this vision of my father as being an advocate for underdogs. It wasn’t politics. He didn't get into politics. He didn't have time for politics. But just in his own private life, this was his manner, shall we say.

Zierler:

The anger that you talk about, this amazing exchange where he realized what it meant to be a physicist and you said “Einstein,” when he got it, at that moment, this amazing story that you portray, was that an atonement for you, for the anger that you felt? Did that give you kind of a boost that kind of washed away the other stuff?

Susskind:

I never really thought about that, but yes, I think so! I would have to say yes. When I think about him and I think about the anger, yes, I also think about this other—I never really focused on it that way, to have that particular view of it, but I think probably yes.

Zierler:

What about the—I don’t know if favor is the right way, or inspiration, and certainly I wouldn't ask you to compare yourself to Einstein, but it would seem to me that in this dramatic moment where he tells you you're going to be Einstein, and then we fast-forward to what you've accomplished over your career, it would seem to me that there’s clearly some connection between the drama of the moment and how difficult it is for you to say this to him, and presumably probably somewhere deep in your psyche, you kind of owe it to him to become Einstein or however close you could get to that.

Susskind:

[laugh] You would have to ask somebody with a deeper understanding of human nature than me.

Zierler:

Something to consider.

Susskind:

That goes very deep, and—

Zierler:

Well, let’s continue with your own political identity. So in the late 1960s, you're already a professor at Yeshiva University, so you don’t have the undergraduate or even graduate story in the late 1960s, because you're already a professor. And yet I'm sure you're very politically aware. You're in New York. Tell me what’s going on for you personally in the late 1960s with regard to Vietnam, civil rights, the whole thing.

Susskind:

I was an enormous admirer of and an extreme opponent of Lyndon Johnson. Lyndon Johnson colored that period for me like nobody else. The good Lyndon Johnson was an incredible hero, and the bad Lyndon Johnson was an incredible villain. This was complicated. I had a couple of—well, I had just come from Berkeley when I went to Yeshiva. I had just come from Berkeley, and of course Berkeley was full of left…sort of infantile leftism. Especially among—well, most of my friends were probably—Most of them were probably Jewish, but they were Jewish extreme leftists. They were probably as leftist as my grandfather, except my grandfather had good reason for it.

Zierler:

[laugh]

Susskind:

These guys didn't have good reason for it. [laugh] I remember one of my crazy friends, when we came back to New York, decided they were going to stop a nuclear submarine. And they rowed out into the Brooklyn Navy Yard, where they got in front of the submarine, and the submarine didn't see them, and it started to move out and knocked over their rowboat and had to rescue them. They were political radicals but I would say somewhat infantile, even though they were very smart characters. I was not infected by that radicalism. My own politics has never been radical. It has never been—yeah, it has never been radical. It has never been extreme. If you asked me what my politics was, it was pretty similar to my father’s, absent the Marxism. I knew that Marx was not the right answer to things. What was it? It was Franklin Roosevelt, Lyndon Johnson. The presidents I loved. I was born during the Roosevelt administration, and I have very strong memories of my family’s feelings about Roosevelt. When I was I think seven years old—this was about two years after Roosevelt died—my grandfather on my mother’s side, who was not a politically active person as far as I knew, took me to Hyde Park. At the time, I didn't understand why he took me to Hyde Park. It was a pilgrimage! It was clearly a pilgrimage to Hyde Park to visit the home and grave of FDR. And I liked Truman. You know, I even liked Eisenhower a little bit. Kennedy. The good side of Johnson. And so my politics was mainstream Democratic politics. I even on a couple of occasions voted for Republicans. I was sorry afterwards, but I did. I never considered myself particularly radical. In this last year or so, in some way my heart was with Bernie and with Elizabeth Warren, but my vote went with Biden. So I'm very much—I wouldn't call myself a political moderate. I would call myself—

Zierler:

Pragmatic.

Susskind:

—fairly pragmatic, mainstream Democratic voter. My heart sometimes leans more left of the Democratic party. My brain says, “Don’t go too—you've got to win elections.” So I have never considered myself to be a radical or an extremist, and I don’t think I am.

Zierler:

So what was the scene for you in the late 1960s? Was there an anti-war sentiment at Yeshiva?

Susskind:

Yes, yes, yes, yes. Very strongly so. Very, very strongly so. I had a good friend—yeah, I still have that good friend. He’s ten years older than I am. I suspect you know his name. Joel Lebowitz. Joel Lebowitz was, in a sense, my political mentor at that time. Joel was a concentration camp victim, and he’s one of the few concentration camp victims that I've ever met that I thought came out whole, came out with a—what shall I say?—with his humanity completely intact. If anybody I would say at that period was my political mentor—I don’t know if that’s the right word—just my political ideal—it was Joel. Do you know Joel?

Zierler:

Not personally, no. I've heard the name.

Susskind:

But you know his name.

Zierler:

Yeah, of course.

Susskind:

Great man. A truly great man. And again, what was his politics? Mainstream Democratic, but with a very, very strong social justice side to it. So for me, what has been happening in recent years—more than anger—it certainly angers me—but disappointment, enormous disappointment in what’s happening. I saw the country getting better and better and better, in little, incremental ways.

Zierler:

You mean during the Obama years?

Susskind:

Well, even before. No. For the entire period up through the Obama years. I saw little incremental changes. Things were getting better for a wide class of people. In fitful steps. In little fitful steps. The arc of history bends but very slowly—whatever, that kind of thing. And that is what I saw. And then all of a sudden, this thing happened. What was my feeling? Well, anger, but just incredible disappointment.

Zierler:

In who? Disappointed in who?

Susskind:

Well, I would have to say in the country as a whole. But look, I won’t pretend there’s any kind of false equivalence. There isn’t. The country, or some part of it has allowed the election of a psychopath. I knew that I was going to talk to you tomorrow—that’s today—I did write something, because I want my feelings expressed in a clear way. So I wrote something, and at some point when you ask me, I will read it, to tell you what I think about what’s going on. And the reason I'm so intent on telling you that I never have been an extremist is because some people would think what I am going to say is extremist.

Zierler:

To build that up, I don’t know if you had a chance to review that video up on YouTube that’s on your blog, The Theoretical Minimum—“What Worries Me Most”—but the question there—

Susskind:

I went back through it. I did.

Zierler:

My question there is, is this something that you have done periodically throughout your career? In other words, like Reagan and Central America, did you give that kind of address? And so on and so forth. Or is this a unique kind of thing that you did in 2017?

Susskind:

It was unique in the sense that I had a platform, the platform being my own lectures. I've never had a platform. I've never tried to have a platform. So in talking to my students, in class sometimes I would do something like that. In semi-public situations, I would bring it up. Sometimes I would compose something to say. So it was not completely unique, but it was the one time that I did it in a situation where I had some kind of platform.

Zierler:

What were you thinking up to that point that built you to this place where you had this platform and you realized it would be bigger than what you were telling your immediate students?

Susskind:

I was beginning to think that I have to say something for my own self-respect, and I wanted to say something publicly to—I was thinking about my children. What do you say to your children afterwards? After this happened. Did I say anything? So I think that was part of it.

Zierler:

What’s remarkable is, in that address—

Susskind:

Incidentally, my children’s politics is just slightly left of mine.

Zierler:

[laugh]

Susskind:

Slightly. Not much, but slightly.

Zierler:

But what’s remarkable in that address is that you don’t lean on your status as a physicist. You're just talking as a citizen, like anyone else.

Susskind:

That was intentional. That was very intentional.

Zierler:

What was the idea there?

Susskind:

Somebody has to say something! Somebody has to say something! Somebody has to not walk on eggs, and say something! I felt everybody was walking on eggs. Everybody was—and somebody had to get up and say something! And I feel that way right now! I feel that way right now.

Zierler:

So I think before I get—so the line of questioning that wants me to get to my present question, which I'll get to in a minute, is as I noted when we talked on Friday, two things. One, the issues that you talked about in 2017 were not really scientific issues. And in light of where we are now with something like—where are we?—65,000 dead, a disaster of federal policy at every single level—in one sense, as devastating as the issues that you raised in 2017, it almost seems like those problems are kind of quaint compared to what we're dealing with right now, at least in terms of direct human tragedy. And specifically, with regard not only to your role as a scientist but in your humanitarian interest to democratize scientific knowledge through your publications, through your blog, through your teaching to non-traditional students, I wonder if you can talk specifically about the problems you see now as a crisis in science and communicating science with regard to who’s in the White House right now.

Susskind:

Right. Let me read what I wrote first.

Zierler:

OK, great.

Susskind:

Because some of this is addressed. And this is me speaking through—I don’t know whether it’s through my heart or through my gut or some other part of my body. But I'm not going to walk on eggs. I'm going to tell you what I really think.

Zierler:

Let’s do it.

Susskind:

OK. I'm going to read it. The country has been infected by a terrible virus, and I don’t mean the coronavirus. I mean the virus of hate, resentment, anger, bigotry, and ignorance. It’s the same virus that infected Germany in the 1930s. Right now, the United States is being tested. Tested in the same way Germany was tested in the 1930s. Germany failed the test. Will we? I don’t know. It took World War II, 40 million dead, six millions Jews, maybe 20 million Russians, five million Germans, British, Japanese Americans, before the Nazi virus was purged. Will the purge of Trumpism, formerly known as the GOP, be purged, and who will be there to pick up the pieces? In my 2017 lecture “What Worries Me Most” I expressed the fear that American institutions, in particular the security apparatus, was being taken over by Trumpian loyalists. I focused on Bannon, who as it turned out was dumped, but the lesson was broader. Today, we see the cabinet, the secretary of state, the secretary of defense, the national security advisor, the secretary of the treasury, especially the attorney general, and the entire Republican caucus of the Senate and House being crackpots and Trump loyalists. Not American loyalists but Trump loyalists. Maybe I overrated the Bannon danger, but the real thing I was worried about was Trumpification, and that has happened. And what about the Republican electorate? What has happened to it, that allows it to cheer on a man who has had a monstrous history of racial bigotry, discriminating against Black renters in his real estate days, wanting to execute five young Black men after they had been fully exonerated, and citing the vicious racist birther conspiracy. A man with a history of most outrageous misogyny. A record of promoting violence. You know, lock ‘er up. Second Amendment people. Admiration for a Republican congressman who had body-slammed a journalist. Associating with this deformed troll, Mr. Gorka, who has called for the execution of Hillary Clinton. A man who lies with every breath. In other words, a psychopath of extraordinary virulence.

And now we see another side of Trump—the incompetence of a very ignorant man who thinks he’s a genius. He knows more than all his generals. He is such a medical genius that all the doctors cannot believe how much he knows. A veritable prodigy with great suggestions like experimenting with Clorox injections. His own Dr. Mengele. From his own mouth—this is from his own mouth—I know more about ISIS than the generals do. I know more about courts than any human being on earth. I know more about renewables than any human being on earth. Nobody in the history of this country has ever known so much about infrastructure as Donald Trump. I think I know about it better than the Federal Reserve. About drone technology. I think nobody knows more about technology, this kind of technology, certainly, than I do. And along with Hitler, I alone can fix it. What has happened to half the voters? It happened in Germany and now in America. A cult of personality, which, like Hitler’s and Jim Jones’ cults, may very well follow their psychopathic leader to destruction. Am I exaggerating? God, I hope so. Red America, or at least enough of it, may come to its senses. Democratic president and congressmen may be narrowly elected. Congress, but in particular the Senate. COVID-19 will end. Some degree of normalcy may be restored in the United States, but I fear it will be a diminished America which will no longer be seen as a trustworthy leader of the free world. The diminishment of the United States will mean a diminishment of democracy. Europe is not strong enough and united enough to pick up the pieces and replace American leadership. That is what I worry about the most, and it’s worse than I thought in 2017.

Zierler:

Yeah. So I guess my first question is, where do you place the crisis of public trust in science and in scientists among this broad array of crises that you bring to bear? Particularly with regard to your own role as a scientist with a deep and abiding interest in communicating and democratizing scientific understanding.

Susskind:

Look, my science is—I don’t think it’s at risk here, and I don’t think—it’s too small and it’s too special and it’s too esoteric for anybody to care very much. Well, there’s a public out there that enjoys it and wants to hear about it. One of the things I worry about a lot is what has happened—I think it’s because of the internet, because of the blogosphere—what has happened to communication to the public of science, in particular my kind of science. It has gotten sensationalized. It has gotten really silly, sometimes. Every day in my news input that comes to me, there’s another revolution in science, another revolution in physics, another screwball revolution in physics. So I kind of worry that there has been a degrading, a very bad degrading of—in the old days, Scientific American was pretty good. You got pretty much the real stuff that came from the people who were doing the real stuff. Now, it’s not Scientific American which is so bad. It’s not what it was. But there’s just too much out there which in order for it to survive in the world, it has to produce a scientific revolution once a week. Well, there isn’t a scientific revolution once a week. And so I'm a little bit unhappy about the degradation of the communication of science to the public. And that happened a while ago. That happened a long time ago. It was part of my reason for trying to get into the public physics education. But my main approach to it was just to teach physics. It was not to give people any kind of ideology about it. It was just to teach physics in order to give people the tools to be able to come to their own conclusions. It never worked, incidentally. It never worked. I'll give you some examples. People would come to me with news articles. I'm talking about my students in my continuing studies classes. They would come to me with news articles. What did I think of this? What did I think of that? Sometimes they were good. Sometimes they weren’t good. But I tried to find an algorithm for them. How do you decide if something is mainstream? How do you decide if something is reliable? I had various suggestion—I told them, “Look, there are some institutions which are better than other institutions. If it comes out of the Institute for Advanced Study, it’s probably pretty good. If it comes from a Nobel Prize winner, it’s probably pretty good.” All of this backfired. All of this backfired. Somebody came to me with—I won’t name the crackpot Nobel Prize winner. He’s British. And said, “Oh, is this thing about ESP reliable? It comes from a Nobel Prize winner.” That failed. As far as the IAS went, the Institute for Advanced Study, another student came to me and he said, “Look at this.” And it was about how you can tap the vacuum energy. Well, you can’t tap the vacuum energy. It’s silly. And I looked at it, and I saw it—it was from some guy whose name is Hal Puthoff. Hal Puthoff was a nutcase. He, together with Russell Targ, did ESP research, remote viewing, which was really, really silly. He’s a crackpot and a charlatan. But I see that it says that he is the director for the Institute for Advanced Study. Well, I knew he wasn’t at the Institute.

Zierler:

[laugh]

Susskind:

I knew the director of the Institute for Advanced Study. He was a friend of mine. And then I looked more carefully—oh, the Institute for Advanced Study in Austin, Texas. Which turns out to be a one-room operation in some—

Zierler:

[laugh]

Susskind:

—yeah. So everything I tried, every rule of thumb I gave them to try to give them some rules for how to tell, didn't work. There was no rule of thumb. My conclusion in the end is all you can do is try to teach them physics.

Zierler:

So, I wonder—it seems to me that whether we're talking about “Fire Fauci” or not believing in climate change or things like that—it seems at the heart of that—and it has been growing in recent decades, recent years certainly, and probably been accelerated by the current administration—is the suspicion that scientists are actually capable of getting after the truth. And now I want to contextualize that with your debate with Lee Smolin, because it seems to me that—let me ask you, but the debate basically got—I mean, it’s a very narrow debate with regard to your field, but if you really break it down, it’s an argument about how scientists can achieve truth and what truth even means. So my first question is if you can define exactly what the anthropic principle is, and then sort of contextualize how this debate happened and whether you saw it primarily as a scientific debate or a philosophical debate.

Susskind:

Well, we were not debating over the anthropic principle. We were arguing about something else. We were arguing, again, about his approach to communicating with the public, and sensationalizing, and capitalizing on the distrust among the public of science. That is what it had to do with. It did not have to do with the anthropic principle or really any particular scientific thing. It had to do with what I saw as his capitalization on the American mistrust of science, and sort of using it to promote himself, frankly. To promote himself and his own ideas, which I thought were not good. I thought he was substituting this trick of—basically of writing books, but writing books that I did not think were good, but using his own—he’s very—he’s a powerful communicator, and he writes well, and I felt he was using that and the public mistrust of science to substitute for doing some good science himself. That was my feeling. And I got very angry and annoyed. Would I do that again? I'm not sure there was any value to it. I think in the end, it probably just—it was he says, she says, he says, she says, and—

Zierler:

Now, the fact that he singled you out for comment—do you think that he was baiting you because he knew the kind of person you were? Because he wanted to have this kind of debate?

Susskind:

No. At a personal level, Lee and I have always been friends, and I think he’s a great admirer of mine. That has always been the case. I don’t think he was doing any trolling of me. No, I don’t think so. I was the origin of that debate. I got very angry and I publicly said so.

Zierler:

What exactly got you so upset?

Susskind:

That he was using the public mistrust of science to promote himself. It again had to do with this public mistrust of science. Which I had been starting to feel worried about, and it was partly the origins of my continuing studies efforts. So I saw him just undermining all of the trust that should have been placed in the mainstream scientists. It’s not always the case that the mainstream is right, but in this case—and I don’t even know if the mainstream was right in this case, but I do know that what he was selling was snake oil.

Zierler:

And what was it that he was selling?

Susskind:

[laugh] Loop gravity.

Zierler:

Please, explain.

Susskind:

Well, I'm not going to try to give you a technical explanation. What I can tell you is that what he was doing and what his colleagues were doing didn't work. And so instead of doing what did work, he—not all of his colleagues, but he in particular, instead of doing the right thing, which was to try to build more good physics, he did this other thing, which was write this book which I thought was incendiary. I thought it was misguided. And I thought it was opportunistic. So I was annoyed. Now, if it happened today, I would just let it go, because these things tend to disappear anyway. I don’t think it had any particular good effect—the argument. And science will go its course. Look, I was partly worried that if there was enough public sentiment against what I thought was good physics, and enough public sentiment in the other direction, that it would affect hiring processes at universities. It to some extent did, but only a very limited extent. For example, in my own department, many of my colleagues who did not know the subject, began to ask, “Should we hire one of these people? Should we hire one of them?” Them, I don’t—should we hire a person doing loop gravity, or whatever it is. I tended to keep out of it, but my colleagues eventually pretty much figured it out themselves. And when I say my colleagues, I don’t mean the people in theoretical physics. I mean the people in experimental physics and so forth who had listened to this, were puzzled. “Should we hire one of these people?” And somehow, they managed to figure it out themselves. So in the end, I think good science will rise above bad. And I'm not sure that my—those particular efforts have any good effect. I think the main good effect of my lecturing and my courses is that I constantly keep on meeting young people, people just coming into the field now, who said they were inspired by the lectures. This is almost every day, a new graduate student or even more than graduate students, young faculty, tell me they were inspired by my lectures. OK, that’s a great feeling. It’s very nice. Did it have the effect of being able to educate a broad public and give them the tools to sort out the reliable from the unreliable? I don’t know. Probably not.

Zierler:

Well, to the extent that you're capable of reaching as many people as you have—I mean, my question is, when your concern is restoring this trust in science, you've given yourself a very tall order, because your field is—I mean, it’s basically as esoteric as it gets. It’s like you and maybe two or three other people that really understand what you're talking about.

Susskind:

Oh, no, no, no, no. No, no, no no, no.

Zierler:

[laugh] Well, whatever it is. Whatever it is.

Susskind:

It’s not two or three. [laugh]

Zierler:

[laugh]

Susskind:

No, no.

Zierler:

Whatever the number is, it’s a highly rarified group, right?

Susskind:

It is. It is.

Zierler:

My question is then, how do you lean on your own expertise to explain that scientists are capable of getting after truth? Capital “T” truth. And how do you communicate those truths to the public with the intention of using that as a means to restore their trust?

Susskind:

I haven't analyzed it in the depth that you want me to analyze it. What I know is what I like to do. I like explaining. Some of it is this Feynmanian ego trip thing.

Zierler:

[laugh]

Susskind:

I love to show people how clever I am. I love to show people how easy things are if only you were as smart as me. But I also get a lot of pleasure in seeing people understanding something they didn't, particularly if it’s easy to understand if you think if you think of it the right way. There’s a certain visceral pleasure in it. I like doing it. And at the same time, I also have done something for somebody. I did get very interested in trying to educate the public. I decided to concentrate on a public who had a bit on knowledge—a bit of scientific literacy—but wanted to know more. That wasn’t quite the point. The point is that’s what was available. So there was all these people in the Stanford community, many of whom had some technological scientific background, all of whom had learned calculus at one point in their life. If they didn't use it, they probably remembered it. And were interested—a lot of them were people who may have wanted to be physicists in some earlier phase of their life, got frustrated, wound up doing something else. These were mostly older people. There was one lady, Jane, I remember, who was 95, I think. She participated and asked good questions. Yeah, so I had this natural public out there. I'll call them the Palo Alto crowd, which means somewhat knowledgeable and somewhat frustrated in their inability to learn anything. My first attempts were more or less at the Scientific American level. And they came to me and said, “This is not what we want. We want the real thing.” And I said, “Well, if I give you the real thing, the next time, there will be half as many people, and then a quarter of many people, and then an eighth.” And they said, “No, don’t believe—that’s not true.” And they were right. They were right. So while I tended to give them a much simpler version of things than I would have to a graduate class, I think it was honest. And in that sense, it was the real thing. I know you cannot really learn physics without mathematics, so I told them, “Look, we're going to do mathematics.” They said, “That’s OK. We'll do it.” And it apparently worked. It worked quite well. Anyway, it was fun when I was doing it. I enjoyed it.

Zierler:

So the problem, Leonard, obviously it’s bigger than your efforts, right? But what is it going to take long-term to restore this trust in—oh, you can’t hear?

Susskind:

No, I hear you now.

Zierler:

So I said the problem obviously is bigger than whatever your efforts are to deal with it. But what is the long-term solution from scientists in general, in terms of restoring trust in science? What do they need to do? I mean, as opposed to just wishing away the president. What do scientists themselves need to do?

Susskind:

I think it would be good if more scientists would take up the challenge of communicating with the public. My colleagues in my own field don’t do it. They're too busy doing physics. I have often—

Zierler:

And do you think that’s because many of them simply don’t care, or the pressures of the job simply don’t allow that for most people?

Susskind:

I think it does allow it. I organized some lectures, not by myself, from Stanford faculty to continue my own lectures, and the people enjoyed it. When I say the people enjoyed it, I mean the faculty members that I had do it enjoyed it. Incidentally the lecture about what I'm most worried about, that took place at the end of one of these lectures which was given by somebody else. I think it may have been Eva Silverstein, but I'm not sure.

Zierler:

Yeah.

Susskind:

I think they probably don’t feel as comfortable about communicating as I do. But when they do it, they do it well.

Zierler:

Right, right. I want to ask you, Leonard—getting to some specifics about your career. And the first one is, on a range in terms of—I'm curious, in terms of your reliance on technology to accomplish what you have. So, you know, the range from the abstract mathematician who can sit in an office with a pen and a pad, to an astronomer who needs better imaging to see what’s going on with a given exoplanet—where are you on that range, looking at your work as a whole, in terms of your reliance on technology?

Susskind:

When you say technology, do you mean experiment?

Zierler:

I mean advances in technology. Advances in technology over the course of your career to come up with the ideas that you've come up with.

Susskind:

Certainly in the early parts of my career, I was reliant on experimental physics and the technology of building accelerators. My early career was particle physics and the experimental data about hadrons, protons, neutrons, their excitations, their spectrum and so forth played a very, very big role in the invention of string theory, the invention of lattice gauge theory, all these things. My thinking about cosmology—which I'm not a cosmologist, and I've only done a very little bit of—was certainly very heavily influenced by the cosmological discoveries that began sometime in the early 1990s and which has evolved. So, very, very strongly in that respect. On the other hand, the main things that I have been involved in, in recent years, which I find extremely exciting, are questions which could have been asked in 1930. They could have been asked, and they were asked. How do you combine general relativity together with quantum mechanics? How much technology has been necessary in order to create the ideas that we now have? Not very much. Very little. The invention of modern quantum field theory was inevitable starting with Dirac’s discussions about quantum electrodynamics in the ‘30s. The early ‘30s; maybe the late ‘20s. So that was an inevitable development, a development of modern quantum field theory. It had to happen, assuming people continued to study it. And the questions and how it connects to gravity were also inevitable and had to happen. And it did not happen as a consequence of technology. Now, I've gotten into—well, I and my community have begun to realize that there are powerful connections between computer science, in particular quantum computer science, and the things that we're doing. And so the existence of quantum computer science, the questions that quantum computer scientists ask—questions about complexity, entanglement, and all those things—while the technology has not yet borne fruit as technology, it created a subject whose purpose is technological. I think it has had an enormous impact on me and my colleagues. So the idea that quantum mechanics can be used technologically and how to think about that technology, how to think about entanglement, how to think about complexity and so forth—yeah, that has been a big deal for me.

Zierler:

So I wonder if technology is something that you specifically have in mind with your very heady response when we spoke on Friday in terms of when we talk about is it possible for the universe to have created itself. And you say, “Well, we're not even close to being there yet.” So buried in that sentiment, I think there is an idea that maybe we can get there, that these are not necessarily unknowable issues—

Susskind:

Yeah. Yeah.

Zierler:

—and maybe things like computational power will allow us to get there. Is that fair?

Susskind:

Yes, maybe. I think it’s fair. I think it’s fair. But I also think it’s unpredictable. For me, anyway. Look, the rule of thumb, which always works, is expect surprises. But you cannot know what those surprises will be. By their very nature, surprises are surprising. So I would guess between now and then, there will be a good number of surprises and changes—not 180 degree changes in direction, not even 90 degree changes in direction, but significant changes in direction that we can’t really predict now. Now, there may be some very bright young person out there who sees some change that hasn’t yet been communicated to the rest of us. But from the look of it now to me, there will probably be a number of surprising changes possibly from experiment and observation. There are these observations now which are claimed not to agree with the standard cosmology. Universe acceleration rate has been accelerating up. That can’t be. It’s impossible. But who knows? Maybe they've discovered something that will impact and surprise us. My guess is that at least two or three major surprises from pure theory will be involved before we can answer the next set of questions. So it’s in its very nature that surprises are surprising, and I can’t predict them.

Zierler:

[laugh]

Susskind:

If I could, I would have published them.

Zierler:

Do you accept that one of those surprises might be the answer to another question you raised on Friday, which is if there is a creator of the universe, is that creator beholden to the laws of the universe?

Susskind:

[laugh]

Zierler:

And my response there was—and again, I'm coming from—I'm an observant Jew, and I'm coming from the perspective of the Jewish god, it’s very clear—when we say the Shema, when we say, “Listen Israel, god is one,” the oneness refers to the uniqueness. That there’s nothing like god, and by definition, the creator is not beholden to the laws of the universe. So maybe that’s right, and maybe that’s wrong. Who knows?

Susskind:

It reminds me of another thing. People are all constantly talking about multi universes and things. But the word, the very word “universe” means that there’s only one.

Zierler:

[laugh]

Susskind:

So they're misusing language.

Zierler:

[laugh]

Susskind:

Right. Now—

Zierler:

So the oneness there is—I ask that because by definition, if one is—so we say god is holy, right? The word in Hebrew is kadosh. Kadosh does not mean holy like you're a monk on a mountaintop. It means separate. It means by definition unknowable.

Susskind:

As little as I knew, yes. As little as I know.

Zierler:

[laugh] So I can’t help but asking—if there is no creator of the universe, then that answers the question in and of itself. But if there is, is there a way to ever truly know if the creator of the universe is beholden to the laws that it has made?

Susskind:

[laugh] I have the feeling that no matter what we discover, what agency we discover that may have had agency in creating the universe, you'll then ask what created it.

Zierler:

Yeah.

Susskind:

Is it turtles all the way down? Or is it—

Zierler:

Right.

Susskind:

It’s not that I'm not curious about it. I am curious about it. I am curious. I'm not an observant Jew. I didn't have that background at all. I do not dismiss the possibility that there was –let’s call it an intelligence—that was involved in the creation of the laws of physics and the universe and all that. I do not dismiss that. But then I get myself into a logical paradox. Who created it? I don’t think this is the right way to think about it, but it’s the only way that I have available to me to think about it. So my own mental makeup is to be curious. I am a very curious person. I would like to know how the uni…and I would especially like to know, was there an intelligence? But I don’t see a way of getting at the answer.

Zierler:

Yeah. So I want to share with you—you know Irwin Shapiro at Harvard? We had a similar line of questioning, and he shared with me when he was eight, he realized that there was no scientific evidence for god, and he never let go of that, right there. And so I pushed him on that a little bit, because the problem with that line of reasoning is, you're applying a scientific standard to a non-scientific entity. In other words, you have to leave open perhaps the possibility that there’s something outside of the laws of science and the laws of nature. Right?

Susskind:

I don’t know. I once had this conversation with a Vatican advisor, a Jesuit. We agreed about absolutely everything, and in particular I asked him, “When you speak of god, do you speak of god the creator, or of god the intervener?” And he said, “I only mean god the creator.” And I had to admit, then, that I had no particular reason to believe that there was no god the creator. But then we started talking about god the intervener. And once god can intervene with the world and affect the world, then if we believe in science, we have to give it a set of rules, and those rules have to conform to what—well, they both have to conform to what the reality is, and they have to conform to what we call science. So does god have to satisfy a set of physical rules? Not if he doesn't intervene. If all he did was create—OK, he created. But if he’s also allowed to poke his finger into it and change things and stir them up, then we have to have rules for that. If there are no rules for it, it means the world has just an element of random, incomprehensible randomness. And even randomness is a rule. Even randomness is a rule. But I'm getting way—

Zierler:

I'm bringing you there. It’s my fault. I'm bringing you there. So let me reverse engineer the question in terms of in your own career. What is no longer mysterious now that was mysterious at the beginning of your career? What is really understood now that was a big question mark 40, 50 years ago?

Susskind:

Forty, 50 years ago—well, look, just at a very mundane level, we've understood a great deal about elementary particles. When I was a very young physicist, the electron was known. The photon was known. Protons and neutrons were known. Neutrinos were known. There were beginnings of thinking about how to unify these things. In my opinion, they've never been unified. But we now have this thing that we call the standard model of particle physics. We now understand hadrons. We pretty much completely understand hadrons. Quarks, gluons and all that. I would say we pretty much understand it. We understand renormalization. One thing when I was very young—this was just at the very beginning of my graduate school days, I would say nobody understood what renormalization was. It was this cookbook peculiar recipe where things come out infinite, and then you do some things to it, subtract some infinities. There were some rules for it, but the rules didn't make a lot of sense. During the course of the next ten years or so, Ken Wilson figured out really what renormalization is, how it works. And so that was monumental. Yeah, elementary particles, critical phenomena. I think you're probably looking for a broader kind of answer, and a more far-reaching kind of answer than that. And then in more recent years, I think we have begun to very much uncover the relationship between quantum mechanics and gravity. But it’s still—if you asked me to summarize it in five words—well, I can’t summarize it in five words. But in a few words, I would say in the early days of my career, it was thought that what you have to do is quantize gravity. Like quantizing electrodynamics. Classical theory, a given classical theory, you apply some rules called quantization, invented by Dirac. You apply those rules to a classical theory and you get the quantum version of it. That was what was thought had to be done. I think from all that we've learned in the last 20 years, people like Maldacena, myself to some extent, other people—Joe Polchinski—the picture is very different now. Quantum mechanics and gravity may be manifestations of the same thing. It doesn't make sense to separate them and then quantize gravity - that gravity is a manifestation phenomenon. Quantum mechanics—that every gravitational phenomena has its reflection as a quantum phenomenon. And this is this connection between quantum information theory, entanglement, complexity theory—that I don’t think the picture will wind up being: Take a classical theory and then quantize it. That to me is a very, very deep lesson that has been learned in the last 15 years, I would say. Fifteen, 20 years. How it will all play out though is still not clear. How it will play out in the real universe is not clear.

Zierler:

At the beginning of your career, when you mentioned on Friday that grown-ups didn't pay much attention to gravity anymore—

Susskind:

Yeah.

Zierler:

—and now you're saying like what a big deal it is in terms of what we're just starting to understand. What was that, at the beginning of your career? Did they totally miss the boat?

Susskind:

Not everybody, of course. John Wheeler was excited about gravity from the get-go. But—OK, so Feynman said that he thought that an understanding of gravity, any new understanding of gravity, is 500 years in the future. So it was too esoteric. It was too far in the future. It was too outside the framework of what could be ever experimentally measured—the quantum mechanics of gravity. I wouldn't call LIGO having—LIGO’s great; don’t get me wrong, but I don’t think it has directly impacted the quantum mechanics of gravity. Feynman thought it was just too far away and there was plenty of other stuff to do. There was particles to figure out. And so grown-ups who were distinguished by their practicality, by their recognition of what real-world physics could possibly do—they kept away from gravity. Not everybody. Steve Weinberg was interested in gravity. I think what really made a difference—[laugh] it may be that the bogging down of particle physics—particle physics is bogged down. It hasn’t changed significantly since, I don’t know, 1980.

Zierler:

Wow.

Susskind:

Yeah, no, it’s really bogged down. Restless minds had to go somewhere. And I can tell you—the best of the theoretical physics community are very restless. They're not called high-energy physicists for nothing.

Zierler:

[laugh]

Susskind:

They are a very high-energy group of people. And they are restless. So where do they go? String theory gave an opening. It gave an opening to think about. They were restless. Particle physics bogged down and there only was one thing left. How did it all fit together with gravity?

Zierler:

So I'm going to share with you what one of your colleagues—I asked this question about—I don’t want to say his name, because I just want to leave it like this. I want to get your reaction to it, though. Because I asked him a similar question to you, which is the extent to which he sees his work as contributing to the grand unified theory. And he said, “Well, we have a grand unified theory.”

Susskind:

We do?

Zierler:

[laugh] So he said, “We have a grand unified theory. It’s called string theory. The problem is that it hasn’t been proven yet.” So I want to get your reaction to that.

Susskind:

I believe that string theory is a powerful guide and has much to teach us about gravity and quantum mechanics but I am far less certain than my colleague, whoever she or he is, that string theory is a final answer.

Susskind:

Yeah, no, this is fine. All right. So what I said was that people went the only place they could go. They had run out of things to think about, about particle physics. It’s not that the subject is finished by any means, but it got stuck. And restless people are not going to stay stuck in the same place for years and years. And they went to the one big major problem that was left over from the Einstein revolutions—how to put Einstein the quantum mechanicist together with Einstein the relativist. And that was the, I don’t know, the big elephant in the room. And so the opportunity that might have arisen, that may have arisen out of the bogging down of elementary particle physics, is that this community just bypassed the question of elementary particles and jumped straight to what may wind up being more fundamental. But we'll find out.

Zierler:

When you say bypass, is that problematic, or we don’t know yet?

Susskind:

I don’t think we know. Particle physics just got to be a big mess. It got to be a big mess, a lot of confusion. And there are very, very fundamental problems. One of them is called the gauge hierarchy problem. There are other problems. And we just got stuck. So, I would say in some people’s minds—to some extent me, and people like Witten and other people—we decided that the thing to do was to try to bypass it, go around it, jump to some more distant way of thinking about a remote set of phenomena, and that meant gravity and quantum mechanics and string theory and all that sort of stuff, and hope to come back to the problems of particle physics from the other end. The other end meaning people talk about bottom-up and top-down; well, bottom-up had failed to get past a certain point. Can we jump to the top and come down? And so far, I would say we have not. But at the same time, we have learned an immense amount about the connection between quantum mechanics and gravity. So again, surprises are a thing to expect, but you can’t expect to know what the surprises are. And a lot of surprises have been coming out of thinking about gravity and quantum mechanics. And maybe the biggest surprise is that we may be able to do experimental physics with it in the laboratory, but not experimental physics on real black holes, but experimental physics on quantum circuits, on quantum computers, on cubits. There may be an interesting opportunity to use our tools.

Zierler:

I don’t know if you heard before or if I cut out—this idea that string theory might be the grand unified theory if it’s proven correct. What is your response to that?

Susskind:

First of all, I have a response to it that annoys and angers my string theory colleagues. And it begins with the question of, “What do you really mean by string theory?” OK, so let me tell you what I mean by it. What I mean by it is a very precise mathematical structure that was put in place starting at a certain period. It involves super symmetry. It involves a certain amount of sophisticated mathematics. And it’s a highly precise thing. Mathematicians have won Field Prizes for contributing to it. It definitely exists. It definitely is mathematically consistent. But it is not the real world. The real world doesn't have supersymmetry. The real world is a more complicated place that does not conform to the rules of this very, very precise mathematical structure. So then the question is, what can you mean by string theory that might be broader? Some sort of generalization of string theory, some sort of expansion of the ideas of it, which would include the real world. And I don’t think we have that. So you might call it string-theory-inspired ideas, and we don’t have them yet. So if I were to make a very precise statement, I would say the real world is not governed by string theory. Could the real world be covered by something a little bit broader, an expansion of it, a pushing of its boundaries in directions that it hasn’t been fully defined? I think that’s very, very possible. In fact, I think it’s probably more than possible. My guess is the answer is yes. That would be my guess. But we do not have that version or that expansion of string theory at this point. So I would say at the present time, the answer is strictly speaking, no, but with some expansion, some generalization of the ideas, maybe, and in my view, probably yes.

Zierler:

So maybe as a prelude to the question of how do we get there, perhaps we can talk about how we've gotten to where we are now. And so if you look broadly at all of the discoveries that have been made over the course of your career and you want to break it down into how much of it was advances in technology, how much of it was just the daily grind of working out mathematical problems, and how much of it was whether you want to call it strokes of genius or true insight, how do you break down the source of all of the advances that have been made by you and by your colleagues over the course of your career?

Susskind:

Yeah. It seems to me that very little of it came out of advances in technology or technology or even experimental physics. The evolution of it—OK, so we talked about this I think was it yesterday, or—?

Zierler:

Friday.

Susskind:

Yeah, we did talk about it. And I told you that the origins of, for example, string theory were in hadron physics. Hadron physics is a subject that goes back to the ‘60s. On the experimental side, it went back to the ‘60s. Lots and lots of experiments on collisions of hadrons, creation of new particles, mesons, excited states, protons, protons with higher angular momentum which made them look like they're some sort of rotating objects and so forth. That all goes back to the 1960s. The very early ‘70s, there were deep inelastic experiments where protons were hit by high-energy electrons, and quarks revealed and so forth. Those were the heyday of technological or experimental advances that contributed to things like string theory. After that, I think to a large extent, it has been almost completely independent of experimental developments. And it has not relied in any significant amount on the technology of computation. In other words, Mathematica. And as I say, some of it was the grunge work of doing calculations, calculations which—lots of them—the calculations all together sort of contribute a kind of—what shall I call it—a kind of data. A kind of data which you mine for ideas. So some fraction of it was lots and lots of calculation by lots and lots of people over the world, and some of it was just, as you said, stroke of genius. A stroke of insight. For me, I never did lots and lots of heavy calculation or not for many years. Other people have. My friend Steve Shenker, for example, is a master of using output of calculation as data to generate new ideas or brilliant ideas. I never did a lot of calculation like that, or at least not for a long time. I did at one time, but not for a lot of time now.

Zierler:

It sounds like to the extent that we can extrapolate these experiences into the future, it really sounds like we're waiting for a genius to come along.

Susskind:

Well, maybe.

Zierler:

It’s not about the computers, necessarily. It’s not about the technology.

Susskind:

Yeah. My approach to physics—this was not done by design. My natural inclination is to focus on clashes of principle, on paradoxes, on Gedankenexperiments through which we view clashes of principle, and then eventually debug and understand what resolves the clashes of principle. So that’s a way of thinking that—I think it’s fairly rare. I don’t think any of my colleagues tend to do that.

Zierler:

Now is that because you believe deeply that any clash of principle just demonstrates a limitation of our knowledge and not an understanding of how the universe works that would allow for such paradoxes?

Susskind:

Yes, that is because I [laugh] fundamentally believe that there should be a consistent mathematical or logical picture of the universe, and that it’s intolerable to have a clash of principles, both of which you believe in. A clash of principles requires that you believe in both principles, but they seem at some level to be inconsistent with each other. And that’s intolerable. It’s also wonderful. It’s also wonderful when you have one of these things.

Zierler:

So I guess that would put you squarely in Einstein’s camp with this legendary argument that he had with Niels Bohr.

Susskind:

Absolutely. Absolutely. Well, first of all, Bohr and Einstein were both very great thinkers. It’s generally—it used to be thought by most physicists that Bohr had won the argument. I think today, many of my colleagues would say that Einstein won the argument, at least in so far as the questions he asked were deeper than the ones that Bohr tried to answer. In particular, the question about entanglement. The story about entanglement very much encapsulated, I think, Einstein’s discomfort with quantum mechanics. Bohr refused to think about it. When Bohr was confronted with the ideas of entanglement, he tended to dismiss it and say, “Look, I have my rules. Here’s my rules. Here’s the Copenhagen interpretation.” And I think today we’d probably say that things were deeper than what Bohr was allowing for, and the depth was really illustrated by Einstein’s thinking about entanglement. So yeah, I would certainly fall into the Einstein camp in many ways.

Zierler:

That all leads to—it must be your belief that there is a grand unified theory, whether or not we can ever achieve understanding what it is.

Susskind:

Well, yeah, I do think there should be—that there is. I do think there is. But what I do on a day-to-day basis is mostly controlled by my own instincts of the moment. And I said I'm instinctually drawn to situations where there appears to be a conflict of principle, and to try to unravel it.

Zierler:

So would that be the through line? Of all of the areas that you've made major contributions—quark confinement, holographic principles—

Susskind:

OK, quark confinement was very much an issue of conflict of principle, at the time. It was thought that every quantum field has a particle associated with it. And—right. It was very much a conflict of principle. So I think almost everything I thought about, at one level or another, traced back to some such conflict.

Zierler:

So that’s really the through line. That’s my question. If you look at all of—the massive contributions you've made in so many different areas, it would seem like the through line that connects all of them, which could be understood as disparate research questions, is really your quest to try to harmonize these paradoxes.

Susskind:

Yeah, very much so. Very much so.

Zierler:

So what’s your batting average?

Susskind:

Almost perfect. Trumpian!

Zierler:

[laugh]

Susskind:

[laugh]

Zierler:

No, seriously. I mean, of all the things—I mean, if you—

Susskind:

It has been good. It has been rather good, I think. [laugh]

Zierler:

If the overriding principle is that you've—first of all, part of the job is identifying the paradoxes, too. You're not just handed these paradoxes on a platter.

Susskind:

Right. It wasn’t always me that identified them. Steven Hawking identified a very, very fundamental paradox, and I've spent the last 30 years thinking about it.

Zierler:

But he was comfortable with that paradox, where you were not.

Susskind:

Yeah, yeah, yeah.

Zierler:

That’s the idea.

Susskind:

That’s right. That’s the difference. That’s right.

Zierler:

Now, part of that—and again, I don’t want to pigeonhole you, but wasn’t part of Hawking’s comfort with the paradox was the fact that he was an atheist?

Susskind:

[laugh] I don’t think so.

Zierler:

No?

Susskind:

I don’t think so. No, I don’t think so. I don’t see what the connection was. Why was Stephen Hawking comfortable? Look, I have to tell you, my biggest frustration with him—and I was often very frustrated by him—you know, we were friends. To the limited extent that we interacted, I think we admired each other a lot. Certainly I always had that feeling from Stephen that he admired me, and I always admired him. But my biggest frustration with him is, “Stephen, how can you not see the opportunity that this thing has opened up? The opportunity that your own question has opened up. How can you not see it?” And yet he couldn't see it. I think he probably thought of his legacy as the idea that quantum mechanics broke down in black holes. I don’t think that was his legacy. His legacy was asking one of the very deepest questions, and despite the fact that he didn't answer it correctly, it has dominated physics for 40 years now—well, 30 years—the question about Hawking radiation. So I found it very frustrating. I wanted him to see that what he had done was leading someplace different than he thought.

Zierler:

And he never did?

Susskind:

Well, I think in the very end, he did. Yeah. At the very end, he did. But sort of reluctantly, and always trying to say it in his own personal way, which I think probably wasn’t helpful.

Zierler:

Leonard, I think for my last question, I want to ask what you want to accomplish personally. What work you still have to do.

Susskind:

Well, OK. That’s a day-to-day thing. I've been very, very involved in the questions of connections between complexity theory and black hole physics. I want to finish that. Now, it has gained a lot of traction in the community, but generally speaking, my colleagues would say that it is still ill-defined. That the whole notion of computational complexity, how it affects the interior of black holes and so forth is still somewhat undefined. It is not as crystal clear as entanglement, for example. It’s a very subtle and difficult topic. And I want to finish that. I want to have a very crystal-clear understanding of how the growth of complexity in quantum systems reflects itself as the growth of the interior of black holes. More broadly, I want to understand the interior of black holes, and how the interior of black holes is encoded in the basic quantum structure that AdS/CFT or string theory and so forth—the interior of black holes is very mysterious. And complexity theory comes into it. Complexity theory is a deep mathematical subject which came out of computer science. I do want to finish that. It is identified with me; that’s nice. I would like to finish it, and see it through. I doubt very much whether I'm going to do that alone. There’s enough people now who have caught on to that subject that I think it will happen.

Zierler:

What’s it going to take to get there?

Susskind:

Oh, I think just a lot of clear thinking. I think just a lot of clear thinking now. A lot of clear and ingenious thinking. What’s going on now is rather spectacular. What has been going on for the last year or two. And one of the things that has happened incidentally—maybe 15 years ago, I was very worried by the fact that the people who were dominating physics, including myself, were the same people who had dominated it 30 years ago and 40 years ago. Ed Witten. Juan Maldacena was already getting to be pretty mature. And it did not look like there was a new—I couldn't see a new generation of young physicists coming and replacing them. Over the last few years, five years, something like that, there has been a whole new generation who have come and largely left the older people in the dust. And that’s exciting. That’s really exciting.

Zierler:

If you're willing to name names, who are some people to look out for?

Susskind:

Oh! Well, my current colleague, Douglas Stanford. I don’t know if you know his name.

Zierler:

Yeah, I do.

Susskind:

You know the name Stanford, but I don’t know if you know the name Douglas Stanford.

Zierler:

No, I do know his name.

Susskind:

My other student, Harlow. But lots and lots of others. Young people who—there’s a young person now that really seems quite extraordinary. His name is Henry Lin. He’s a student of Juan Maldacena’s. There are other students of Maldacena’s who have made big impacts. And the surprises. The surprises have tended to come from this younger group of people. I won’t try to name—I won’t try to name them right now, and if you like, I will send you a list of what I think some of the real—oh! There’s Geoff Pennington. A major contribution was made in the last year, I think it was, by Jeff Pennington, also at Stanford. But Almheiri—Ahmed Almheiri at the Institute for Advanced Study. All these people are very young. And we're beginning to see the old pattern of very young people generating the cleverest, most brilliant ideas. And that I find very reassuring. I was very worried about it. I like being in the middle of things, but I don’t want the subject to die when the current generation of senior leaders dies out. So it’s dependent on young blood, and for a long time, I was concerned. That has turned over. That was something that did happen.

Zierler:

Why do you think it was dormant, and what exactly changed where now there’s a lot of promising work?

Susskind:

OK, opportunity comes in waves. People flourish when there’s opportunities. There were incidentally during this period lots and lots of very, very bright young people. Very smart people. But you need two things. You need very, very smart people and you need opportunity. Opportunity comes in waves. It seems very much to me like at a certain period, enough was known to create a new opportunity for a new way of thinking, and those young people who were there simply took advantage of it. So I think it was a combination of lots of smart people who have always been there, and all of a sudden, an opportunity arising, or at least things reached a certain degree of maturity where there was a big opportunity to make some big advances. And they did.

Zierler:

So it sounds like you're pretty optimistic about this new generation.

Susskind:

Oh yeah, very much so. Very, very much so. I'm a little disturbed by the fact of my own inability to keep up with them. But yes, it’s good.

Zierler:

[laugh] Well, Leonard, it would be an understatement to say how special it is to have spent this time with you. I really identify—I mean, the stories that you tell about your father, I hear—my grandfather was like that. He was a taxi driver in New York for 50 years. So I really—I know exactly where you're coming from.

Susskind:

Probably the same generation as my father, probably. Roughly.

Zierler:

That’s right. That’s right. It’s obvious that you don’t just have an amazing mind; you have a really big heart. That’s really obvious as well.

Susskind:

Well, thank you. Oh, that’s nice to hear. Look, is this thing going to be available to—? My wife wants to see it.

Zierler:

Of course. So what we're going to do—next steps is I'll get this transcribed. We'll clean it up in terms of where we cut out here and there, so we'll clean it up a little bit. I'll probably make it two separate transcripts, since it has been two separate discussions. And then I'll send it over to you. And then the two things there are we might need some help spelling technical terms and also possibly some names that are not easily available to us. But then the big thing is—it’s going to go in the Niels Bohr library. It’s our honor to include this where—you said you're on the Einstein side of things, so that’s really [laugh]—that’s great for us. The written transcript is really what the researchers are going to go to. So when you're reading it over, and you feel like you can explain a concept maybe a little more accurately or elegantly, you're more—the transcript does not need to be a verbatim record of the discussion. You can clean it up as you see fit. And then I can send you the audio to this, tomorrow or Tuesday, if your wife wants to listen to it right away. Otherwise I'll have the transcript to you in a few weeks.

Susskind:

Well, she wants to hear what I had to say about politics.

Zierler:

[laugh] Good. And a lot of people will. Leonard, thank you so much. I really appreciate it, and we'll be in touch.

Susskind:

All right, David.

Zierler:

Take care. Bye-bye.

Susskind:

Take care. Bye-bye.