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Credit: David Mermin
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Interview of N. David Mermin by David Zierler on 2020 April 17,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/44328
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In this interview, David Zierler, Oral Historian for AIP, interviews N. David Mermin, Horace White Professor of Physics Emeritus at Cornell University. Mermin recounts his childhood in New Haven and his undergraduate work at Harvard, where he worked with Andrew Gleason and did his senior thesis on the Jordan Curve Theorem. Mermin describes his thesis work with on superconductivity with Paul Martin and the turn of luck that led to his fellowship at the Institute for Theoretical Physics in Copenhagen. He explains why his most formative physics education occurred during his time in Birmingham and describes many of his most important collaborations as a professor at Cornell. Mermin explains his delight in pursuing obscure areas of research in physics and why he is interested in the relationship between problems in quantum foundations and the nature of scientific knowledge. In the last portion of the interview, Mermin shares his view on the various categories that comprise scientific breakthrough.
This is David Zierler, oral historian for the American Institute of Physics. It is April 17, 2020, and it is my great pleasure to be here with Professor N. David Mermin. Dr. Mermin, thank you so much for being with me today.
Glad to do it.
We’re here virtually, of course, over Zoom, like so many things, due to the coronavirus. Professor Mermin, can you tell us your title please?
Horace White Professor of Physics Emeritus.
Now, let’s go right back to the beginning. Tell me about your birthplace and your early childhood.
[laughs] That’s a surprise. I was born in New Haven, Connecticut. Not into a family of Yale faculty. My grandfather moved to New Haven from Zhytomyr in the Ukraine in 1904 when my father was 2 years old. He had had it with pogroms. He was a shopkeeper in New Haven for all of his life. He had five sons and five daughters.
All but one of the sons, who was picked out to take over the shop, went to Yale, but none had any faculty connection with Yale. Women were not then admitted to Yale. The one thing that was clear to me when I was a senior in high school was that I did not, like almost all the top boys in my class, want to go to Yale. I wanted to get out of New Haven. So, I went to Harvard, where I majored in math. But that says nothing about my early childhood.
Well, tell us, what your father did for a living?
He was an engineer at the Southern New England Telephone Company.
And your mom: did she work out of the house?
She was a schoolteacher in elementary schools. While my brother and I were growing up she stopped teaching. After we both had left home, she resumed.
At what point did you start to demonstrate an aptitude for math and science?
I always liked math. The only sign of an aptitude for science, I guess, was I had a chemistry set for many years, in the basement. My view of chemistry was that the aim was to create dangerous chemicals using undangerous chemicals.
The catalog I ordered chemicals from had all dangerous chemicals unavailable to people under the age of 21. It never occurred to me that I could lie about my age, so I ordered only undangerous chemicals. My finest achievement was to make pure bromine out of undangerous chemicals, and also a few explosives. That was pretty much the limit of my scientific activity. I took physics and chemistry in high school, and breezed through them with so little effort that I found them both boring. And in college, I was a math major. I took practically no physics at all.
Now, to get into Harvard, you must have graduated near the top of your class, I assume.
I would have been at the top of my class if there were rankings, but there were not. I flourished in high school. I won many prizes in many different fields. I was editor of the high school newspaper, which took a huge amount of time. So I certainly enjoyed writing by the time I was in high school.
Did your parents emphasize the importance of education?
Not particularly. They didn’t have to. I took school very seriously. I did very well there. I read a lot, mainly fiction. But I also read many science popularizations like Eddington, Jeans, and Gamow.
And when you got to Harvard, did you start out majoring in mathematics?
That was the major I picked, I guess at the end of freshman year or the beginning of sophomore year. And what I discovered in college for the very first time was that the world had people who were much better at mathematics than I was.
This was a new experience for you.
It was a shocking experience. Nobody ever told me that Harvard was famous for having absolutely extraordinary mathematics majors as undergraduates.
So, you discovered that you had fellow students who were better at math than you were.
Yes. Immeasurably better.
Not only faster and smarter, but much, much better educated.
Coming from private schools?
Private schools or very good New York City schools.
So, like Brooklyn Tech and places like that?
Stuyvesant, Bronx Science, and also Fieldston.
That’s a private school.
And who were some of the luminary professors as an undergraduate in the math department, that you remember?
I wrote my thesis with Andrew Gleason, and I took several courses from George Mackey. Interestingly enough, Mackey had developed, just at that time, an interest in foundations of quantum mechanics, by which he meant giving a mathematically rigorous foundation to the subject. He did not consider Von Neumann to have done that. And he in turn interested Gleason in quantum mechanics, and Gleason proved the very famous result in foundations of quantum mechanics, known to this day as Gleason’s theorem. And he was my undergraduate thesis advisor. The thesis had nothing to do with physics or quantum mechanics.
What was your thesis on?
It was weird. It was producing an elementary proof of a famous result called, I believe, the Jordan curve theorem, that a circle divides the plane into an inside and an outside. And in fact, it was that thesis that made me realize that mathematics could be extremely boring, because everybody knows that a circle divides the plane into an inside and an outside. To have to write 50 pages to prove that rigorously seemed quite absurd. It was at that point, and only at that point, that I realized that I really did not want to pursue mathematics, in addition to the fact that I wasn’t as good at it as I felt I should be. The people who were smarter than me went on to win Fields medals and stuff like that, but I had no way of knowing that these were [laughs] among the best young mathematicians in the entire world. Anyway, I decided not to go to graduate school in math.
So, who did you talk to that encouraged you to make the switch to physics? Who were your early mentors? I mean, when you were feeling these frustrations about the absurdity of pursuing these mathematical theories, who did you talk to that was useful in guiding you to physics? Or, how did it occur to you to transfer over to physics?
I actually applied to graduate school in mathematical statistics. Physics was an afterthought. And the reason I did that was basically that my girlfriend was an undergraduate two years behind me at Harvard/Radcliffe. The reason it occurred to me to switch from mathematical statistics to physics was that Harvard had no program in mathematical statistics. It did have a program in physics. They had a rule that Harvard undergraduate physics majors could not enroll in graduate school at Harvard, but I was a math major, so it didn’t apply to me. And I wanted to stay in Cambridge, because that’s where my girlfriend was. So, I switched to physics. That was the main reason. And we got married, and we’re still married 63 years later. So it was [laughs] both personally and professionally the right thing to do. But I did take practically no physics courses as an undergraduate.
I want to ask: with such a strong background in math, entering the physics graduate program, what were some of the benefits and pitfalls of not having the physics background, entering into the physics graduate program, coming from a math background? How did that help you, and how was that a disadvantage?
It helped me in the sense that math was no problem. But I knew very little about applied math, which was more pertinent. The chief problem was, for example, that I had never had any course in quantum mechanics. The only physics course I had beyond introductory physics was a course in electromagnetic theory, which by sheer accident, was given by Edward Purcell, who was one of the best teachers in the physics department, and an utterly delightful man. He was basically the only physicist that I had any sense of. I doubt that he had any sense of me, since I just sat quietly, absorbing all the wonderful things he was telling me. So I got to Harvard in physics and discovered that the only thing to do there in theoretical physics was to take courses from Julian Schwinger. My first exposure to quantum mechanics was an utterly wacky course taught by Schwinger, in which he developed his own very strange approach to quantum mechanics, under the assumption that you knew all about it. I knew nothing about it, so I was probably the only person ever to learn quantum mechanics in the way Schwinger was then trying to formulate.
And how was Schwinger trying to formulate it then?
It was crazy. It’s not worth going into, because it never caught on with anybody else. I enjoyed it, but realized after a year that I still hadn’t learned any quantum mechanics.
Now, it’s hard to get a sense of this in retrospect. Was Schwinger really a superstar, head and shoulders above all of the other faculty members at that point? What was your sense of his stature in the field?
Yes. I mean, not head and shoulders above all the other faculty members at Harvard, because it was an incredibly distinguished faculty. Almost every teacher I had at Harvard eventually got the Nobel Prize. At the time, I think it was only Purcell and an ancient experimentalist named Bridgman, who had one. But it was common knowledge that Schwinger had done extraordinary things in physics at that point. And there was also rumored to be somebody named Richard Feynman, who Schwinger didn’t like and never talked about, who was also said to be pretty good. Fortunately I had a good friend whom I met for the first time at Schwinger’s first lecture, named Gordon Baym, who had been a physics major at Cornell, and told me about this guy Feynman and showed me Feynman diagrams, which were anathema to Schwinger. They never appeared.
Yes, why is that? Why was that anathema to Schwinger — the Feynman diagrams?
There was a tension between Schwinger and Feynman, right from the beginning. I have no idea what it looked like from Feynman’s point of view.
You mean a personal tension, or a theoretical tension?
There was certainly a theoretical tension. I mean, their styles were totally different. And I had the feeling it was a personal tension, but I have no direct evidence of that at all. It’s one of the curious things about 20th century physics. I’ve never seen anybody write about the relations, if any, [laughs] between Schwinger and Feynman.
But each, as far as I can tell, behaved as if the other did not exist.
Did you have any contact with Feynman directly?
Not until I came to Cornell. Of course, at Cornell, he was somebody who had left within the last 10 years. Everybody called him “Dick,” and he paid frequent visits to see Hans Bethe and to give talks. He gave his famous lectures on the character of physical law the year after I got to Cornell. And he was clearly charming. Fascinating. Fun to read, fun to listen to, fun to talk with.
Coming from the mathematics background, do you think that guided you in terms of where you ultimately landed on the experimental versus the theoretical side of physics?
There was never any question that I would be a theorist.
Why is that?
Because that’s what I was interested in. I was interested in the structure of the subject and thinking about the nature of the world, and I knew I had no talent whatever for putting things together, doing things in the laboratory.
Oh, I see. So, as a tinkerer, that was not your strong suit.
I was never much of a tinkerer except for my chemistry set.
Besides Schwinger, who were some of the professors that you had a mentor/mentee relationship with at Harvard?
My thesis advisor was Paul Martin, a former student of Schwinger’s, who chose to do condensed matter physics rather than particle physics. I knew I didn’t want to be a student of Schwinger’s, because they spent all their time hanging around outside his office, waiting for him to show up. And the only other theorists were Wendell Furry, who was getting to be an old man, and Roy Glauber, whom I did not like. Then by sheer good luck, Paul Martin arrived as an assistant professor.
Where did Paul come from, when he got to Harvard?
He had been a graduate student of Schwinger’s at Harvard, and I think he probably went off to Copenhagen for a couple of years as a postdoc and then came back to Harvard.
And what was he working on? What were some of his projects that he was working on when you became his student?
He and Schwinger had just written a paper on the application of field theoretic methods to condensed matter physics, or more broadly low-energy physics. So, Paul had a lot of students applying this stuff to all possible problems in condensed-matter physics.
And was this the process that led to your dissertation?
Yes. My dissertation consisted of convincing Paul that what he suspected was a key to superconductivity actually had nothing to do with superconductivity. So, my thesis basically consisted in putting together an argument that Paul’s suggested thesis topic would not work. Probably one of the few Ph.D. theses in the history of theoretical physics that was entirely negative. [laughs] And it was bizarre. At some event many years later, probably Paul’s 60th birthday party, everybody did little talks about how wonderful it was working with him, which indeed it was. And then he got up and said he didn’t understand why people thought he was so wonderful a thesis supervisor, and then he went through each of us, one by one, explaining why he basically made no contribution to our education. And when he came to me, he said, “And David Mermin’s thesis topic exploded.” [laughs] That was his characterization of it.
What did he mean by that? What exploded, exactly?
It blew up! It turned out to lead nowhere. So, I emerged with a Ph.D., knowing virtually nothing about physics, and having written a thesis that was of no interest to anybody but Paul. And then, a wonderful piece of good luck happened to me. Everybody who got a Ph.D. in theoretical physics at Harvard applied to the National Science Foundation for a postdoctoral fellowship, and most of us got them. And then you wrote a letter to the Bohr Institute at Copenhagen, which was then called the Institute for Theoretical Physics. It was basically run by Aage Bohr, Niels’ son. And you said, “I have a physics Ph.D. from Harvard. I have a postdoctoral fellowship from the National Science Foundation, and I would like to spend a year or two in Copenhagen at your institute.” And for the first time ever, Aage Bohr replied in the negative. He said, “Terribly sorry. We have no office space left. You can’t come.” So, I went to Paul and said, “What do I do now?”
Were you crushed? Was this a big dream of yours to end up in Copenhagen?
It was not a big dream. It’s just what everybody did. I mean, two people who preceded me in getting Ph.D.’s, Leo Kadanoff and Gordon Baym were both in Copenhagen, and a whole bunch of people went to Copenhagen. Shelly Glashow, I think, went to Copenhagen. Shelly was probably two years ahead of me. It was just what you did, so I was at a loss. I said, “What do I do?” And Paul said, “Go to Birmingham. Work with Peierls.” So I went from this vision of Copenhagen, a magical paradise, a charming city — I had never been abroad — to Birmingham, the home of the dark satanic mills, a horrible industrial city.
[laughs] What was Paul’s connection to Birmingham? Whom did he know there?
Actually, now that I think of it, he knew Peierls. He spent some fraction of a year there at Peierls’ department, and realized that it was a wonderful department. So I wrote a letter to Peierls, basically the same letter. And he said, “Sure.” He said, “Come to Birmingham.” And in fact, he was visiting at MIT, or would be in a month or so. So, I met him at MIT, and we exchanged small talk, and I realized he was a lovely man.
Were you familiar with his work at the time?
I was very familiar with his book on solid-state physics. There were virtually no books on solid-state physics, and I knew Kittel’s book was awful. And there was a much smaller book by Peierls that I somehow came upon, which I realized was one of the best physics books I had ever read on any subject.
Why was it so good?
It presented the subject in a coherent, unified way. He wrote absolutely beautifully. His technical arguments were extremely well constructed, brief, coherent. It was a lovely book. So I had a very favorable impression of him. And he offered me a position, so off I went. And I basically learned physics by attending Peierls’ lectures. He was giving a course based on his book, and he just opened his beautiful world to me.
So, I have to ask: how is it that you graduated with a Ph.D. in physics from Harvard, and you had to go to Birmingham to learn physics?
Harvard was a weird place in those days. They considered themselves not only the most important department of physics, but in some ways, the only department of physics. Nobody read anybody else’s papers, as far as I could tell. I learned about being a scientist from a fellow student of mine, Pierre Hohenberg, whom you probably knew. We were undergraduates together at Harvard. We both loved the mathematics lectures given by George Mackey. And Pierre was also a graduate student at Harvard. It was he who told me that there were things called “journals” in physics, and that there was a place in the building called the “library” that had not only books, which I knew about, but also journals, and that people wrote articles in journals that were often relevant to the problem you were thinking about. It took a fellow student to tell me that was what I ought to be doing. Nobody in the faculty ever said, read this and that paper. It was a strange, inward-looking place.
Yes, with obviously no great weight put on teaching at Harvard.
No. They took teaching seriously and did it very well, but it was almost all self-contained courses. No reference was ever made to any current work that anybody was doing, except perhaps at Harvard. And most people who were graduate students had come from other places and knew that there was an outside world, but I didn’t, and I knew no physics, so I was terribly educated there. Birmingham was just an eye-opener. And there were a lot of other very good people on the faculty there. In particular, Vic Emery, John Valatin, Stanley Mandelstam, and, most importantly, Geoffrey Chester. At the end of my stay in Birmingham, I was putting together a list of places to apply to for a faculty position, and Geoffrey said, “You know, I’m going to Cornell. Why don’t you apply to Cornell?” So, I applied to Cornell. And Peierls must have said something good about me to Bethe and Geoffrey also spoke well of me. And almost by return mail, I got a job offer.
Before we get to that, I want to go a little deeper into Peierls. What was his style, and what was his breadth of knowledge that was so useful and important to you, in terms of it opening up your understanding of physics?
He ran a weekly theory seminar, and no matter what the subject was — it ranged all over physics — he knew about it, and he was able to ask questions about it that were designed to reveal to the students in the audience what it was that the speaker had been trying unsuccessfully to tell them. And the sense I got from him was that you don’t have to be a specialist in any field. It was clear that he was much broader than solid-state physics. I didn’t realize at that point the role he played in the development of the atomic bomb—his whole earlier history in nuclear physics. So it was two things. One, his insistence that everything had to be put simply and clearly, and two, that you shouldn’t specialize. Anything you were interested in, you should start thinking about, and you could have useful things to say about it, even though you weren’t an expert in the field.
And this was not the style at Harvard. It was a much more specialized and rigid —
I think so. It was very focused. Solid-state physics was not considered physics. In fact, it was taught only in the applied physics part of engineering. Yes. Harvard was awful in those days. [laughs]
Now, you got that offer from Cornell, but didn’t you have one more year as a postdoc in California?
Peierls said I should write to a guy named Walter Kohn. And Walter wrote back and said, “We have no faculty positions, but why don’t you come here as a postdoc?” When I got the offer from Cornell, I wrote back and said, “I got offered a postdoc at La Jolla. Is it okay if I went to La Jolla for two years before coming to Cornell?” And they wrote back and said, “One year would be very nice. Two years is too much,” which is obviously the right answer, since if I went for two years as a postdoc, the chance of my going back to Cornell would be greatly reduced. So I wrote back to Walter and asked if one year would be OK, he said fine, and that’s what I did.
Were you writing? Were you doing research during this time as a postdoc?
Yes, for a while I was filling in details of my thesis paper. I had managed to extract one result that I thought was interesting and more general, and of broader interest than simply persuading Paul Martin that he was wrong.
And what was that result?
It had to do with a considerable generalization of the mathematical structure that he thought heralded superconductivity. It was generalizing that to any phase transition. It was a sign of a phase transition, the thing that caught Paul’s attention. It’s just that he picked the wrong phase transition. [laughs] So, I wrote a more general paper about that, inspired by a paper that David Thouless had written that I also discovered when I got to Birmingham, since Thouless at that point had been a junior faculty member at Birmingham. He had gone on to Cambridge, but he left his paper as a residue, so to speak. So, I worked on that for a while, and then one day, Peierls popped into my office and said, “Isn’t it about time that you worked on some other expansion?” He told me that it was time for me to stop worrying about this thing I talked about in my thesis, which sent cold chills down my spine. What else is there to talk about? But then, I found a fellow postdoc, Eric Canel. Most of these people are now dead, by the way. Almost everybody I’ve mentioned so far is no longer with us — and I realized that I understood the problem he was worrying about better than he did, so I spent about a year collaborating with him on that. And those were basically the two things I had done. In retrospect, I don’t think either of them was really either interesting or important, but they got me faculty positions, partly because at that point, everybody was expanding like mad in that era, the early ’60s, and everybody was short of faculty, so there were jobs galore. But I didn’t really do anything of long-lasting interest until I got to Cornell. Well, I [laughs] wrote a paper in La Jolla for Walter Kohn. He and Pierre Hohenberg, whom he had met in Paris — Pierre had spent a postdoctoral year there — wrote a paper that led to density functional theory, for which Walter eventually got the 1998 Nobel Prize in chemistry. And when Walter got back — when I got to La Jolla, Walter wasn’t there --- from Paris he told me about the little theorem he and Pierre had proved, and asked me if I could generalize it from a theorem about the ground state to a more general theorem that applied at non-zero temperatures. So, I went off, thought about it, and realized that I had developed a funny way of thinking about thermal equilibrium that enabled me immediately to generalize the theorem Walter proved with Pierre. I wrote about this in my book of essays, Why Quark Rhymes with Pork.
What was your funny way of thinking about it? What was it?
It was a technical way of formulating thermal equilibrium, which nobody else used, which I kind of liked. And it was precisely the hammer I needed to crack open Walter’s nut. So, I went back to his office and said, “Here’s how you do it.” He didn’t believe me. It took me a day or so to persuade him that I’d solved the problem. And at that point, I realized this was the work he had in mind for me for the entire year. After that, we just became friends, and I did whatever I felt like doing. And the paper I wrote about it became very famous, particularly after Walter got his Nobel Prize thirty-five years later. I think it’s now my second-most cited paper.
What was Cornell like in those early days? Was it a department in transition? Was it a department that was exploring or emphasizing new fields of physics? What were the big changes that were going on at Cornell in those days?
They had just established something called the Laboratory of Atomic and Solid-State Physics, which still exists, and they were in the process of hiring many new people. The entire theory group, with one exception — Jim Krumhansl — consisted of people who had come within a few years of each other, including me. They were expanding both in theory and experiment. The low-temperature physics group that got the 1996 Nobel Prize for superfluid helium-3, were all hired at about the same time. And a lot of people had left in earlier years, so it was changing in character, almost completely. Less so on the high-energy experimental physics side, since Bethe had brought back a large number of experimentalists with him from Los Alamos, who were in the process of building a series of particle accelerators. That ended up being the last particle accelerator at a university, except for SLAC, which was hardly at a university. [laughs] And at least three high-energy theorists were hired in the mid sixties. So yes, it was in transition, a very exciting place to be. It was just getting underway. When I told Paul Martin I was going to Cornell he was surprised. “Why go there?”
Where was the funding coming from for all of this expansion? Was it mostly government?
You know, I’m not sure. The first thing I did when I got there was to apply for a National Science Foundation grant. So, there was a lot of government funding, and a lot of it through the Defense Department as well as the National Science Foundation. Where they got the money to pay all those faculty salaries, I have no idea. I just wasn’t interested [laughs] in such questions at the time.
When did you start taking on graduate students?
Almost immediately. There were students wandering around looking for faculty, and I found it a difficult process, taking on graduate students, because I was hardly aware of what I should be doing myself, much less what somebody under my tutelage should be doing. And I watched a lot of my colleagues — strikingly, John Wilkins — who had endless graduate students working on endless numbers of problems, and I just couldn’t do that. Every graduate student created a real puzzle to me. What on earth will I ask them to think about? Throughout my career, I found it a pleasure to work with graduate students. Most of the graduate students I’ve had, I liked enormously, and most of them have stayed in touch with me throughout my life, so they obviously enjoyed working with me. But I treated them the way Paul Martin treated me. That is, I’d bring them into my office and talk about what was bothering me, and ask them to think about it. I did tell them to read papers about it. And we’d start collaborating on something, and then after about a year of that, I’d pull out of the collaboration, so to speak, and I’d encourage them to go on and develop it further without me, and that would turn out to be their theses. And every time it happened, it felt to me like a miracle, that somehow, by God, I’d pulled it off again. And therefore, over the years, I became less worried about whether it would lead anywhere, this strange process. But I ended up with a fairly small total number of graduate students over my career: fewer than 20, which is unusual for a theorist. Well, that’s not true. There are two types of theorists: those that have a small number of students, and those that have armies of students, with whom they have group meetings, which I have never done in my life. Do you have a degree in physics?
No, I’m a historian of science.
Ah, right from the start.
Right from the start, yes. Can you talk a little bit about the collaborations that you pursued, like with Wagner and with Hohenberg? How did those collaborations develop?
I don’t think I ever published anything jointly with Pierre Hohenberg. I talked to him all the time, and I knew about his proof of the “Mermin-Wagner” theorem. By the way, you mispronounce “Wagner”. The W is pronounced V. Do you know the 9-W joke?
No, tell me.
“What’s the question to which the answer is ‘9-W’?” And the question is, “Do you spell your name with a V, Mr. Wagner?” “Nein, W.” The Mermin-Wagner theorem was a funny thing, because I heard about Pierre’s result on superconductivity and superfluidity from Geoffrey Chester, who had heard about it from Pierre. And it was then in the air that you might be able to have ferromagnetism in two dimensions, under circumstances where it was believed that you could not. And Wagner had just arrived at Cornell as a postdoc and was fluent in the paper from which Pierre got his idea --- a paper by Bogoliubov, which was then unavailable outside of Germany. But Wagner knew all about Bogoliubov, and it was the work of a day to generalize or to modify Pierre’s use of Bogolioubov’s result so that it excluded ferromagnetism in two dimensions. Wagner and I wrote a paper on it, which actually came out before Pierre’s paper came out. And it was a big hit. It was my first famous paper, and it was called the Mermin-Wagner theorem. And this was very unfair to Pierre. In recent days — well, not recent days — within the last [laughs] 40 years, I and Bert Halperin have been working to get people to call it the Hohenberg-Mermin-Wagner theorem. In fact, in my 1976 solid-state physics book with Neil Ashcroft, we mention the Mermin-Wagner theorem, and refer to it as a corollary of Pierre Hohenberg’s work.
What did Hohenberg do on his own versus what you and Wagner did? Was it sort of a multiple independent discovery kind of thing?
No. We would never have got the idea to do it — well, Herbert Wagner might have got the idea, because he knew about Bogoliubov’s paper. But it would never have occurred to me to make such an argument without hearing about Pierre’s argument.
And why was it such a big hit? What exactly was it about this theorem that made it connect?
Damned if I know. I think the reason it was a big hit was that it had applications in particle physics as well as condensed-matter physics, and it was at a time when the theory of phase transitions was just becoming big stuff. So, it had relevance to many different fields of physics. And it had a compact name.
[laughs] When you say “applications,” do you mean both theoretical and experimental applications?
I would have said more theoretical. It had experimental applications in the sense that it told you that certain kinds of phase transitions could not happen in thin films — that you had to have bulk matter for this kind of phase transition to take place. So, it had kind of negative experimental applications. But it caught on mainly because it just remained relevant for a very long time. I mean, it was a theorem. It was something [laughs] that you could prove. It’s by far my most cited paper.
Yes. When did you get to know Neil Ashcroft?
He came to Cornell as a postdoc the year after I came as an assistant professor. John Wilkins had met him when Wilkins was at Cambridge as a postdoc, and Neil was a graduate student. John thought very highly of Neil, and Geoffrey Chester had been on Neil’s Ph.D. exam committee, and also thought very well of him. Neil and I became friends almost immediately after he came to Cornell. He and John Wilkins and I decided we should write a solid-state physics text.
Why is that? Was there not a good solid-state physics textbook at that point?
There was Kittel, which we all thought was awful.
[laughs] Why? What was the problem with it?
It explained nothing. It had a lot of pictures and a lot of graphs and a lot of talk and didn’t teach you what the theory was underlying all this stuff. So, our idea was to write a book that had all the phenomenology that Kittel had, but that described things in a rigorous way, the way Peierls did. So, it was sort of combining the two books. We thought about it for a couple of years, and then we started trying to work on it. And it turned out that Wilkins had no patience for writing. He was too busy with his armies of graduate students. So, we suggested to John that this was not a suitable project for him, which he basically agreed to, although friendly relations basically ceased at that point between Wilkins and Ashcroft. For some reason, John did not blame it on me. He blamed it on Neil, which is peculiar, because it was a joint decision that John really did not belong in the project, which even John agreed with. Anyway, then Neil and I worked together for eight years, putting the book together.
Was the textbook aimed more at undergraduate students or graduate students?
Both. And it’s basically used in both courses, although we never knocked Kittel off his perch at the undergraduate level. And it’s probably viewed more as a graduate text than an undergraduate text, but it’s had an amazing life. I mean, it’s still going strong, although it came out in 1976. And in many ways, it’s old-fashioned. It’s focused on problems that were of primary interest 50 years ago. But there’s a large basic core of material that hasn’t changed at all, and nobody has managed to dislodge us from [laughs] our position of supremacy as a graduate textbook. It no longer sells anything in the United States, because a long chain of publishers took over the book from earlier publishers, and the most recent one raised the domestic list price to over $400. So, sales in the United States dropped to zero, probably 20 years ago. And they’ve now cut it once from $400 to $200, and then again from $200 to $100, but sales are still not picking up in the United States. Meanwhile, it’s been translated into French, German, Portuguese, Japanese, Russian, and Polish, and foreign prices were never very high, so it still sells 2,000 or 3,000 copies a year in Europe, mainly.
Have you been actively involved in revisions for new editions?
No. We have prepared no new editions.
That’s it. It’s just the same book?
Same book. Absolutely unchanged.
We both felt that eight years was enough time to spend on that particular project. The thought of going back into it and bringing it up-to-date was intolerable. But also, there were various highly favorable advantages in our original contract, very unusual provisions that made the contract both very lucrative for us and that no contemporary publisher would ever dream of offering. So, it would have cost us a fair amount of money to come out with a new edition. There was no incentive to do so, and a powerful incentive not to do so. And the book kept selling, so we left it the way it is. A few years ago a self-styled new edition called “Ashcroft, Mermin, and Wei” appeared in Asia, but we had nothing to do with it and would not have permitted it, if we had been asked.
When did you begin working with Asher Peres?
When I became interested in quantum foundations.
Which was when?
In the early ’80s.
And what was your work with him on?
There is something called the Mermin-Peres magic square. It was all via email. I finally met Asher at a few conferences. Very nice man. I spent a couple of weeks at the Technion in Haifa, where I also spent a fair amount of time with him. But the “magic square” was mainly email. Asher had come up with what he claimed was a very simple version of Bell’s theorem that he sent me, and I wrote back and explained to him that it didn’t work as a version of Bell’s theorem, but it did work very nicely as a version of something else that was known as the Kochen-Specker theorem. So, I published the Kochen-Specker version of Asher’s argument, and Asher insisted on publishing — even though I still claim it doesn’t work — his own version of the argument. And those two papers together have since been called the Peres-Mermin magic square.
And what exactly is the magic square?
It’s just a way of writing down a bunch of data for a particular set of correlation experiments. At the moment, I couldn’t tell you exactly what it was, but if I looked up the pair of papers, I would first of all spend a lot of time trying to find them, and then significantly less time trying to figure them out. I could then tell you in detail what it was. But it just refers to a particular table of data that quantum mechanics predicts.
When did you first come up with the term “boojum”?
Oh, lord. That is described in enormous detail in a paper I wrote called “E Pluribus Boojum,” which you surely have seen.
What can I say about that? It was an impulse, in writing something up.
Does the term itself mean anything?
It refers to The Hunting of the Snark, by Lewis Carroll. And it has a specific reference to a phenomenon that I claimed took place in one of the phases of superfluid Helium-3. But again, it turns out that the term can be generalized to apply to many phenomena in liquid-crystal physics. So, it spread through the literature in both low-temperature physics and liquid-crystal physics, and therefore, it gained a lot of currency.
Why did these fields need a new term?
Oh, goodness. Science needs new terms all the time! I mean, anytime you come upon a phenomenon, a structure, you need something to call it. So, that’s commonplace.
What was the new phenomenon, or structure, that you came upon that required this new word?
It’s a pattern of lines which grow out of a common center, a so-called singularity. And when you have a singularity, you need a name for it. I don’t think it would be interesting to get into the technical details of it. And as I say, I’ve written an enormous paper on it that is easily available. It’s in my earlier book of essays, Boojums All the Way Through.
Were you surprised at how rapidly the term was adopted?
No, because it wasn’t that rapid. It took a couple of decades. And I haven’t actually done a search recently for how much it’s used, but it still is widely used today.
I understand the technical underpinning is quite complicated, but I wonder if you could provide a basic definition of what exactly a “boojum” is.
Well, the technical statement would be that in superfluid Helium-3 it’s a singular structure that exists on surfaces, and if you have a supercurrent flowing in a cylindrical pipe, if there’s a boojum on the surface and the boojum rotates in a circle around the pipe, then it can diminish the supercurrent. And in the Lewis Carroll poem, if a hunter is looking for a snark and finds a boojum by mistake, the hunter softly and suddenly vanishes away. The relevance is that if there’s a boojum in the pipe through which the supercurrent is flowing, that supercurrent will softly and suddenly vanish away by the action of the boojum.
Can you talk about your collaboration with Charles Bennett and Gilles Brassard?
A paper appeared arguing that Bell’s theorem provided a good basis for quantum cryptography. I read this paper and realized that Bell’s theorem had nothing to do with it, that it was just completely irrelevant. But on the other hand, the cryptography aspect of it remained valid and was interesting. And at that point, I realized — probably by looking at the references in the paper I objected to — that Bennett and Brassard had written a paper using quantum mechanics as a cryptographic device. So, when I wrote a paper pointing out what was wrong with the paper that used Bell’s theorem, I sent a copy of it to Charlie Bennett, who I had known for years, asking whether he could take a quick look at it and tell me whether I’d said anything foolish or stupid. And the next thing I knew, the phone rang early in the morning, waking me up. And it was Charlie Bennett, who was very excited by what he viewed as the way in which I had modified his work with Brassard. And he was calling to say that we had to write a joint paper on this. And since all joint papers he wrote on the subject were also joint with Gilles, it should be a paper by the three of us. So, we then got to work on a joint paper, and they wrote a very long paper, and I cut it down to a very short paper, and they expanded it back to a moderately long paper, and I cut that down to a somewhat less short paper. At one point in the process, I said, “The hell with it. We’re never going to agree on anything. Why don’t we just write papers of our own?” And they said, “No, no. We will write a paper together.” [laughs] And so, what emerged was a rather uneasy compromise. And then I started running into Brassard at conferences all over the place, and we also became good friends. And that’s the history of our joint work.
You said that earlier in your career, you had trouble advising graduate students because you yourself had trouble deciding what you should think about, so how could you expect to do this for others? As you developed in your career, were you able to refine your own identity and thereby make it easier to advise graduate students and give them ideas to work on?
Not really. I’ve changed my identity over the years. In a certain sense, I’ve never been sure what my field was, or what it was I was primarily interested in. As I say, I’ve gotten used to working with graduate students, and we get along together very well, mostly. And I started eventually being less worried about ruining their lives by [laughs] my collaborations with them. But typically, what I’ve done all my life is I’ve picked up some idea like the idea I picked up from Pierre Hohenberg through Geoffrey Chester, and the idea I picked up from Bennett and Brassard, and the idea I picked up from Walter Kohn, and just carried it off in a slightly different direction, and then found myself a well-known member of whatever field [laughs] the idea was developed in. And in that way, I changed fields frequently. The other reason I’ve changed fields is usually when that happens, it’s in a fairly obscure, tangential field of physics, which is terrific, because it means there are not many people working in the area. There aren’t many other papers you have to read before you can become an authority. And that’s the situation I flourish in, that I like best. But often, the field I tiptoed into then becomes a big field, and all of a sudden, there are conferences and huge numbers of papers, far more than I could read. And at that point, the field becomes, for me, much less interesting, much less pleasant, and so I look around to see if there’s some other [laughs] obscure field where I can make a small contribution.
So, you have a natural affinity for obscurity in physics. That’s where you’re most comfortable.
That’s where I’m happiest, yes.
And you’re saying that it just so happens as a matter of timing or dumb luck that those fields that you wade into sort of get more popular, and then you feel like you need to move on?
Yes. There’s some wonderful quote, I think from Newton, about wandering along a beach and picking up beautiful pebbles. And I’ve always liked that.
How much of a causative relationship would you be prepared to understand in terms of your interest in an obscure field, and your work in that field, having something to do with it, making it not so obscure and attracting interest from others?
As I become better known, it may bring attention to an area, but you know, I became interested in foundations of quantum mechanics in the early ’80s, and that was an extremely obscure field at that point. Very few people were working in it, and it was regarded as somewhat disreputable. And what brought that into prominence was the arrival of quantum computation and quantum information theory. And that was a rare case where I didn’t leave the field, in fact.
Because I was still interested in what are now viewed as philosophical aspects of it.
Can you give an example? What’s philosophical about this field?
My current view of the problems in quantum foundations is that the problems arise from a failure to understand the nature of scientific knowledge. Now, no practicing physicist worries about the nature of scientific knowledge. It’s the kind of thing that philosophers should worry about, but even they don’t worry enough about it. So, [laughs] that’s an obscure backwater in the currently raging field of quantum information theory.
Who are some of your standout graduate students over the years — people that you advised who really impressed you as graduate students and then you’ve been really proud of where their fields and their career went after studying with you?
Well, there’s Jason Ho, who has spent most of his career at Ohio State University, who worked with me on something called the Mermin-Ho relation when he was a graduate student in the field of superfluid Helium-3, and I’ve been very close to him for many, many years. We still talk to each other several times a year. A wonderful man and very creative. Highly original. There’s John Rehr, who is now retired from the University of Washington, who is a much more nuts-and-bolts kind of physicist, currently interested in phase transitions. And his thesis was in the area of phase transitions. There’s Anupam Garg. I spoke to him just a few weeks ago. He’s at Northwestern University. He’s the first student I had who wrote a thesis on quantum foundations. For many years, I’d warned students not to work with me on that, because it was too dangerous. [laughs] There were no opportunities to get jobs afterwards. Then there are David Wright and Lisbeth Gronlund who both got Ph.D.’s with me and went on to leave physics entirely to work at the Union of Concerned Scientists, where they’ve had very distinguished careers in issues related to science policy for several decades.
We talked about when you arrived at Cornell, how the department was in a period of expansion and transition.
You’ve been there so many years. How has the department changed over the course of your career? What new directions has it taken? How has it continued to grow? Where do you see it standing, relative to other departments over the many decades you’ve been there?
Well, you have to bear in mind that I retired in 2006, so my awareness of the current status of the department is weak. I really retired, and moved into the internet world of physics and out of the Cornell physics department, pretty much. The glory days of the department, from my perspective — I got there in ’64 – were from the late ’60s to the late ’80s, when I would argue that we were, at least in theoretical condensed-matter physics, the best department in the world. We had wonderful, wonderful graduate students, postdocs, and visitors. It was just an amazing place to be. Michael Fisher was doing phase transitions. Mitchell Feigenbaum was doing Feigenbaum-esque things. John Wilkins was doing bread-and-butter, nuts-and-bolts condensed matter physics of all kinds. Ken Wilson, who was nominally a particle physicist, moved into condensed-matter physics with the renormalization group. So, we had all those absolutely first-rate, highly original, unique figures, all conducting seminars, holding classes, giving talks, attracting visitors. And on the experimental side of condensed-matter physics, the low-temperature physics group of Dave Lee, John Reppy, and Bob Richardson were famous – also the best in the world. And then every one of the theorists I mentioned left Cornell [laughs] in the late ’80s, lured away to other places. And that ended the period of world eminence.
During this golden period, what was the culture among the faculty? Was there a real spirit of collaboration?
And would this take place — I mean, was it one-on-one in people’s offices? Would faculty gather just among themselves? How did you communicate generally with other faculty members?
It was everywhere. We all had lunch together — there was no formal luncheon or anything like that, but we’d all go to lunch at the faculty club, hang around afterwards, talking about things. There were three or four weekly seminars to which everybody – faculty, postdocs, graduate students – went. Everybody on the faculty knew everybody else. We all got along well with each other, and we all found each other to be interesting. Postdocs and graduate students knew and interacted with us all. And the students were very engaged. The focus was the seminars. They were very well attended. Probably fewer than 100 people, but more than 50. And it was just a very close community. There were no private corners. Paul Martin came to Ithaca on a visiting committee to investigate the state of the Physics Department. I ran into him after the committee had met with our graduate students. I asked him how it had gone. He said “They all think they’re in Valhalla!”
When people started leaving in the mid- and late ’80s, given the department’s reputation, why was it not able to replenish with the next generation of leading physicists? Or was it?
We got some very good people, but they were not up to the level of the ones who left. The people who had left were the ones I mentioned. Fisher, Feigenbaum, Wilson, Wilkins — although Wilkins was not as famous as the others — were all unique. They were irreplaceable.
Yes. And was there a common theme that drew them to other places? Was it generally more money, more prestige? What was the common theme, if there was one, that pulled them away?
It was different in every case, and in many cases, I tried very hard to prevent it. With Ken Wilson, it was basically — well, I have to begin with John Wilkins. John Wilkins decided he wanted to go somewhere where his talents could really be put to good use.
Why not at Cornell? Why couldn’t they be put to good use at Cornell?
There were too many other people of very high quality. I think he wanted to go somewhere where he was clearly the elder statesman, and could put together behind the scenes a really world-class department. And he did it, primarily by luring Ken Wilson to Ohio State. And the reason Ken Wilson was willing to leave was that his wife wanted a higher position in computation at Cornell. This was at the time when computers were just appearing on the scene, and she wanted to be in charge of how the Cornell faculty got online, and the whole introduction of the internet into university life. And there was a lot of resistance to that. Wilkins found her a job at Ohio State, where she could do precisely what she wished. So, Wilson left, mainly because of Allison. I never really understood why Michael Fisher left us. I think he was tired of the small town of Ithaca. He wanted to live in the Washington area, being part of a bigger, more urban community. He traveled a lot, and the Ithaca airport was a horrible place to travel from. Washington had serious airports. He was quite unpersuadable. Feigenbaum found teaching painful, and he left for Rockefeller, where you don’t have to teach, as you did at Cornell. He found it painful, not because he didn’t find it intellectually interesting, but because it was too much of a drain on him. He worked too hard on it. So, in each case, it was a highly personal motivation that was very hard to compete with. You couldn’t really offer them the usual kinds of things — you couldn’t offer them titles or higher salaries. They didn’t need titles. They were all world famous.
What about you? Did you ever think about leaving?
No. Never did.
You felt loyalty to Cornell.
My wife was a Professor of English at Cornell. And it would have been hard for two people to go somewhere together. And we liked it here. I never encouraged anybody to offer me jobs anywhere else. And Ithaca’s a wonderful place for children to grow up. That kept us occupied from the middle ’60s until almost the ’90s. So, for all those reasons, it never really occurred to me to think about leaving.
What was your reaction when you learned that you had been elected a member of the National Academy of Sciences? What was your reaction to that news?
Great pleasure and surprise, both. I was at a conference in Spain and got the news in a phone call from Bob Richardson. I phoned my wife in Ithaca to tell her. She had already heard from Bob.
What is it that you felt you were being recognized for? Was it something specific, or was it the summation of all of your work?
I doubt that it was anything specific. I don’t believe there was any particular citation that went with it in back in 1991. I always had the feeling that it had a lot to do with my name being well known. And the reason my name was well known was: one, I was co-author of a famous, widely-used textbook, and two, I had a lot of columns in Physics Today that were funny, [laughs] as you remarked, and got a lot of attention. And the process of election to the National Academy of Sciences is a very time-consuming and intricate one, as I learned after I became a member, which goes on practically for a year — indeed, many years. And members are required to vote on proposed members in all fields, whether you know anything about the field or not. You have a minimum number of people you have to vote on in other fields. And it therefore is helpful to have a name that is familiar to people from a large range of scientific fields. I find myself, when I vote in these elections — as I feel duty-bound to do — that if I’ve actually heard of somebody in another field, then I vote for them, because I figure that if I’ve heard of them, they must really have accomplished something. [laughs] And I think other people may think that way.
Are there any practical benefits to being a member of the National Academy of Sciences, or is it merely a nice thing to be recognized at that level?
I’d say there are practical un-benefits, in that you are constantly being asked to be on various committees, to advise in various things, to attend annual meetings, which are not really very interesting. Many of my friends who are members have become very actively engaged in Academy activities. I’m thinking of Pierre Hohenberg and Gordon Baym, primarily. I’ve never enjoyed that sort of thing. I don’t enjoy scientific administration, which is what most of the activities involve. I had a six-year term as director of the Laboratory of Atomic and Solid State Physics, and that was quite enough administration for me. So, in a way, the benefits aside from glory are, from my point of view, negative. One exception: When my wife and I visit London we are entitled to stay at the Royal Society, which charges very little and is a five minute walk from the National Gallery.
You mentioned the Physics Today columns as being possibly a reason behind your election to the National Academy of Sciences. And I want to talk about — how did the “Reference Frame” column begin? How did that start?
It was an idea of Gloria Lubkin, who was the editor of Physics Today for many years.
She reached out to you?
How did she know you? Were you known for publishing funny things before this column started?
Well, the boojums essay appeared in Physics Today before the “Reference Frame” columns started.
That got a lot of attention, and I’m pretty sure that was why she asked me to become a columnist. And it took me a long while to agree to do it, because – the usual thing — I couldn’t imagine what I’d write about.
It’s also a very unique thing, because you are — I mean, you’re doing something that not many of your colleagues are doing, in terms of engaging a broader audience in a very humorous and relatable way. I just wonder if this is a talent that you sort of developed in real-time, or you sort of always had an interest in writing and conveying scientific concepts to a broader audience.
Well, I always had an interest in writing, going all the way back to being editor of the high school newspaper. So I always enjoyed that, and the columns — well, you have seen all the columns in one place in my newer book of essays, Why Quark Rhymes with Pork.
They developed as they went along, and they all have a similar tone to them, in a way, even the more technical ones. And I found as I traveled around giving physics colloquia and talks at universities that I was best known for those columns in Physics Today. Everybody wanted to know who “Professor Mozart” was.
Yes. I wanted to ask you about that. Where did Professor Mozart come from? In your mind, of course. Where did he come from?
He gave me an opportunity to say things that I was reluctant to say myself. That’s where he came from.
[laughs] And yet, obviously, everyone knew that he was you. You’re Professor Mozart.
No! Most people thought he was Neil Ashcroft. [laughs]
Yes, which is really strange. People in physics were very surprised to hear that he wasn’t Neil. And I refused to say who he was.
One of the themes that recurs in all of the columns is this idea that you shouldn’t take things so seriously. That’s a real theme that comes out in the columns. And I wonder if you could talk a little bit about that, about your interest in taking a lighter view of things. You seem to say that there’s a lot of self-seriousness in physics, and you wanted to shake that a little bit.
Very much so, yes.
So I guess the two questions there are: why do you think there is an abundance of self-seriousness in physics, and why is it important to challenge that — gently, but still to challenge that a little bit?
Well, it isn’t just physics. It’s a problem with academics more generally, that they tend — with many exceptions — to take themselves much too seriously, and therefore they have less fun. [laughs] Fun is important. It has to do, I guess in part, with my distaste for scientific administration and all the kinds of secondary non-intellectual aspects to the field that one is constantly being asked to do.
I think another thing that comes out from the columns that’s more implied is that you bring a sense of humility to your field as well, that that’s really where, I think, a source of your interest in poking a hole at that self-seriousness comes from. Right?
Yes, I agree. I’ve never taken myself that seriously, or at least not that seriously as a physicist. I’ve never regarded that as a major part of my identity, and many people do.
One thing that you do take seriously in these columns, it seems, is that you’re very interested, and you’re very good at, conveying very technical concepts in understandable terms. So, it seems like in a certain sense, you’re interested in perhaps democratizing physics a little bit, or at least making very difficult concepts to understand a little more comprehensible.
Yes. Well, that — I wouldn’t call it “democratizing” so much as — how shall I put it? I have always had trouble understanding physicists and physics talks. I think physicists lack a sense of how obscure, and therefore uninteresting, what they’re doing can be. And I’ve always maintained that if you can’t fairly easily get other physicists interested in what you’re talking about, then it’s probably not worth doing at all.
Aha. And what about conveying these concepts to a non-technical audience? Where do you see value in that, beyond the physics community, in terms of the larger world?
My books on relativity, for instance?
Right. What’s your motivation there for conveying these concepts to people that are not working at physics at your level or at a graduate level?
My practical motivation was that for years, I’ve taught courses for non-scientists, and the reason I like doing that is I like trying to extract what’s really interesting about a subject from the formalism – the network of abstractions that physicists generally erect around it. And it’s a serious intellectual challenge to do so, and there are not many things that you can actually do it with — and I think quantum mechanics and relativity are rare in that sense, in that you can extract things that ought to be of much more general interest.
So, what is it about quantum mechanics or relativity that does make it extractable, so to speak?
Well, with relativity, it’s that the subject is basically something simple that everybody feels they understand — space and time — and what makes it really fascinating is the fact that their understanding about it is wrong. And that’s always wonderful, when you discover that something you thought about all your life is wrong.
And is that because relativity goes against common sense, in terms of how people assume space and time work?
Yes. I mean, we have a very naïve sense of what space and time are, and when you look at it harder, you discover that in fact it doesn’t really work that way at all. But I like the idea of pointing out to people that they’re wrong about things. I mean, the most odious thing about Donald Trump is that he’s never wrong about anything, and in a certain sense, that was what I disliked in George W. Bush. But W, in fact, turns out to have been such a minor version of the problem compared to what we have now that I’m ready to forgive him. But there’s something genuinely evil about not ever being able to acknowledge that you’re wrong. It goes against everything I believe in. It’s, in some ways, the most immoral of all Trump’s immoralities.
Is that a hallmark of a good scientist?
Not just acknowledging that you were wrong, but enjoying the fact that you were wrong.
Would you say that it’s a hallmark of a good scientist.
It’s crucial for a good scientist always to consider the possibility that you’re wrong.
Can you relate any dramatic circumstance in your own life when you were proved wrong about a particular thing, and when you derived enjoyment from it?
Interesting point. I mean, in a sense, that’s what learning relativity was all about, and to some extent, learning quantum mechanics too. I’m trying to think of something more technical that I was wrong about. You know, usually by the time that it gets to be a finished work that appears in a paper, it’s right. The worst thing that can be said about it — and it’s commonly the case — is that it’s not very interesting. [laughs] Now, it’s peculiar. I can’t think of any case where I published something that turned out simply to be wrong, other than minor errata, which I try conscientiously to correct.
But you have seen this happen among your colleagues.
Well, it’s happened in fields. I mean, in any field that people are actively engaged in, there are many possible ideas that are not all mutually compatible, and therefore, some of them have to be wrong. And one that’s been going on for years, that I finally stopped paying attention to, is high-temperature superconductivity, where there just have been raging disagreements.
What about — you mentioned both relativity and quantum mechanics in terms of — what is it about quantum mechanics that makes it so suitable for conveying to a broader audience?
A lot of it stems from Bell’s theorem, the fact that you can distill the strangeness from some very simple experiments that can be black-boxed. And the data in those experiments are basically just yes/no answers to certain questions, and you don’t really have to know how the yes/no answers are arrived at. You just have to know that it’s possible to make these black-box devices to behave in such a way. Before I learned about Bell’s theorem, I didn’t think you could really do it with quantum mechanics. I mean, you can do certain things. There’s the famous Feynman lectures about two-slit diffraction, which are also very nice and very surprising. But it’s rare that you can do it without getting technical.
I want to ask you, for the final series of questions for our conversation, some more introspective questions that would ask you to think about your career spanning from the beginning to the present. And the first is [about] your main contributions: what do you see them as, and in what fields do you see them as having the greatest impact?
Oh, lord. I’ve worked in so many fields.
Not all of them. I mean, you have worked in so many fields, but obviously you’ve made bigger contributions in some fields than others. Right? And so, what are those fields, and what are those contributions that really stand out in your own mind?
The work that gives me the greatest pleasure is my semi-popular expositions of quantum mechanics and relativity. It’s peculiar, because nobody thinks I’ve contributed anything to relativity.
Among your peers.
My own view is that my 2005 book on relativity, It’s About Time, has ways of looking at special relativity that I’m not aware of anybody else ever having suggested. But I think I’m probably the only person in the world [laughs] who thinks that way about the book — possibly a couple of people who wrote blurbs for the dust jacket [laughs] feel that way about it. And those two are, by far, the most important to me. It’s kind of funny, because neither of the subjects is anything I’m officially known for. They’re both kind of hobbies. Well, the quantum mechanics, I’ve been writing about that for such a long time that that’s becoming more of a part of my scientific identity. But by far, the most important thing I’ve done in condensed-matter physics is writing the textbook with Neil Ashcroft. The other things I’m well-known for and that are most highly cited are almost all things I spent maybe a day or two days thinking about, then maybe another day writing about. It’s peculiar, looking back on my career. [laughs] There’s no great body of stuff that has altered the direction of the field. You know, like Ken Wilson’s work on phase transitions.
Would the word “dabbler” apply for you?
Not quite. Dabbler suggests a certain superficiality, and I don’t regard my work as superficial at all.
But it is unique in the sense that you have moved around to the degree that you have. Most of your peers have not done what you have done.
I suppose that’s right. What I regard as unusual in me stems from the fact that I have a lot of trouble understanding what other physicists do, and therefore one of the rules of thumb I’ve had over the years is that I when I write a paper I want it to be something that I can read 15 years later and understand. And partly because of how hard I find it to understand things, that is a non-trivial constraint on what the paper should be like. And I’ve now been writing papers for long enough, and people have been asking me questions about old papers that are decades old, that I find in some cases — to my dismay — I have trouble [laughs] understanding what I was saying. Not often. Usually, I’ve written them clearly enough that I can still understand them if I have some reason to look back at them.
That leads me to my next question, thinking about how many fields you’ve been involved in. Are there fundamental concepts in physics, or laws, or theorems, that are especially close to you that you feel an affinity toward, that you learned and have always stayed with you, and inform your work, how you see the world?
I’m not sure. I’ve never really thought of it that way. These questions you’re asking me are all the kinds of things that earlier in my life, I could have thought of for a year or two, coming up [laughs] with some formulation — but anything I said now would be quite superficial.
What do you understand now — or what do you feel like you understand now — that you didn’t understand when you started in your career?
Oh, my goodness. I don’t think I can answer that question, partly because I can’t remember what I was like [laughs] when I started my career. But again, it’s too broad a question. I still regard it as a miracle that I produced as many as 18 graduate students, many of whom are still in physics and have had successful careers of their own. I still don’t understand how I managed to do that.
Well, maybe you’d have an easier time answering the flipside of that question. What do you not understand today that you didn’t understand at the beginning of your career? In other words, what was mysterious to you in 1965 about physics, about the way the world works, that remains as mysterious today?
Well, at the moment, I’m under the illusion that I understand quantum mechanics, which may well stay with me for the rest of my life. I’m already 85!
Is that a humble way of saying that possibly no one understands quantum mechanics?
I would say that at the moment, I and a few close friends understand quantum mechanics, [laughs] and we’re trying to explain it to the rest of the world. And we’re making a small amount of progress.
Who would you include among this small circle of friends?
Chris Fuchs, who is a physicist at UMass-Boston; Ruediger Schack, who is a mathematician at Royal Holloway college in London; possibly Ulrich Mohrhoff, who writes about physics from the Pondicherry Ashram in India; a few of Chris’s students, postdocs, and collaborators. Hans Christian von Baeyer recently wrote a whole book about it. That’s about it. I have a few sympathizers of my own — or I had; some of them have died — but we haven’t persuaded many people. But there’s so much noise in this area. There’s so much talk, so much nonsense, that it’s very hard to sound a fanfare and say, “This is it. Listen.” Nobody really reads anybody else’s papers anymore. I wrote what I thought was a ringingly clear explanation of our way of thinking about quantum mechanics. I posted it on arXiv and published it in Reports on Progress in Physics, which is a leading English scientific journal, and I got basically no reactions, no responses, positive or negative, from anyone. People are too busy writing papers to read other papers. So am I, although I’ve pretty much stopped writing for the past couple of years.
And that’s a problem in terms of the future of the field, if no one is reading anyone else?
Yes, it is a problem. There’s too little communication. Most of the communications I’ve had with other people are like my communications with Asher Peres. They’re personal communications by emails. And that’s my main source of scientific stimulation these days: emails with other people.
Well, I’d like to ask — I think my final question is one that’s forward-looking. And that is: what are you excited about for the future? What are the breakthroughs that you see on the horizon that would really — you know, you say with quantum mechanics, there’s a lot of noise. Right? So what would be a breakthrough that you can envision, in your lifetime, in the next generation, however long it might take — what might be the breakthrough that quiets the noise, that really moves the ball forward in your field in a way that it hasn’t over the course of your career?
One of the breakthroughs that had just come to my attention recently is high-temperature superconductivity. It looks as if there may actually be room-temperature superconductors, which would be an astonishing breakthrough on the technological scale.
What makes it a breakthrough?
If you can have usable room-temperature superconductors, the world will be transformed, technologically, in all kinds of ways. It would be as big a breakthrough as the computer breakthrough of the last 30 or 40 years.
What would be an example of how the world would change?
Oh, transmission of power, the kinds of devices one can have in one’s houses, powerful magnets. Everything would change. Machines would be different. Motors would be different. Everything electrical would be different. It would be wonderful, but I would be dead [laughs] by the time it happens.
Well, I said that was my final question, but I can’t help myself. This is a subset to that, and that is on the nature of breakthroughs. You know, when you read about this breakthrough, how much of the breakthrough is about —
I didn’t read about it. I was told in confidence.
I repeated it to you.
Probably I should not have. [laughs]
When breakthroughs happen, either you being witness to them, you causing them, or you envisioning them in the future, how much are breakthroughs about technological advance, and how much of it is about the individual and the intellect and the moment of insight? How do those things interact with each other to form those breakthroughs?
They’re separate. I mean, high-temperature superconductivity is mainly a technological breakthrough. Bell’s theorem was a conceptual breakthrough in foundations of quantum mechanics. Bell’s theorem, from my point of view, was the biggest breakthrough during my career. But very few people [laughs] would agree with me. For me, it was the most eye-opening thing ever.
Well, Professor Mermin, it’s been a delight spending time with you, and I really appreciate you sharing your insights with me.
Rather to my surprise, I enjoyed it.