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Interview of David Bohm by Lillian Hoddeson on 1981 May 8,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Work on theory of plasma between 1946 and 1953. Initial interest in plasma at Lawrence Radiation Laboratory during World War II continued interest at University of California, Berkeley and then at Princeton University (especially in collaboration with D. Grass and David Pines). Also prominently mentioned are: John Bardeen, Albert Einstein, E. P. Gross, J. Robert Oppenheimer, Julian R. Schwinger, and Tor Staver.
This oral history interview will be focusing on your plasma oscillation work in the late forties and through the early fifties, but first, if I may, I’d like to ask you for some background. You were born on December 20, 1917.
You and I have the same birthday!
In Wilkes-Barre, Pennsylvania.
That’s right, yes.
What did your parents do?
Well my father had a furniture store in Wilkes-Barre, a small furniture store. And my mother didn’t do anything special.
I’ve had a younger brother. He became a chemist and eventually went to work for the Civil Service, but he died a number of years ago.
I’m interested in learning where your early interests in science came from.
Right. Well, I think I became interested in science when I was 8 or 9, when I read some science fiction stories. Then later, we had a book in the library, no a book in my fourth grade class, on astronomy which really impressed me with all these great things going on in the heavens, all the order, and so on. And then I had a few friends, and we went to the library to pick up some chemistry, I was around 12 or 13, and I became more and more interested in science, especially in physics.
Did you have a good course in science in high school?
Nothing particularly good, no. It was all right, but I was interested long before we got to their courses.
Were there any family influences at all?
Entirely friends and library?
I see. And then you went to high school during the Depression?
Were there any special influences in high school such as good teachers or —
No. I had a reasonably good geometry teacher, and I was very impressed by geometry and all, started proving various theorems, and when we took solid geometry, I think I worked out a four-dimensional geometry myself. I tried fairly extensively, just to go from three to four.
In high school?
Yes. Then I had a theory of trying to imagine the universe was four-dimensional, that we were sort of structures going through the fourth dimension, but we were only aware of three of them. I had one or two friends, and we used to talk about these things when I was in high school. And I used to like to study, also to construct model airplanes and small radios.
What about these friends, did they end up going into —
One was the son of a miner. I don’t know how he ended up. After he left school, he probably took some sort of job. I lost track of him. Another was able to go to college, and became an engineer.
Eventually, you ended up at Pennsylvania State College.
Was that a natural place for you to go?
Well, my uncle had gone there, he was an electrical engineer, and recommended it. People said it was a reasonable place. It turned out to be lucky, because the physics department was extremely small there, maybe two or three students, and the result was we could talk very informally and things went much better, I think, far better than they would have gone at a big place, although maybe they weren’t as advanced as a big place. I used to read for myself and talk it over with friends, I read other texts and books. The teachers were not anything special there. But, in some ways, in spite of all that, it was better there than at a big college, where there would have been pressure to compete, as I discovered later in Cal Tech where I went then as a graduate student.
Right. You decided while you were at Penn State or had decided already in high school...
Well, I had decided on physics long before, you see.
In high school.
Yes. It became clear I was interested in theoretical physics as I went along. And then I went to Cal Tech, I went out in 1939. And there I was rather unhappy because the atmosphere was very oppressive. They constantly were giving exams and competing and were not interested in what the subject was about. And once I met Oppenheimer in 1941 while he was down there, and he suggested coming to Berkeley, where I found the atmosphere more conducive.
Were there any other people at Cal Tech who influenced you besides Oppenheimer, who I gather at the time was going back and forth between Berkeley and Cal Tech.
He used to spend a few weeks at Cal Tech. I can’t think of anybody else. In general, I was rather glad to get out of Cal Tech.
Right. One thinks of Cal Tech as one of the major universities for physics in those days; of course it still is.
I mean, in many ways it was doing good work, but it wasn’t for me. And I’m not trying to say it was of no value. It was not what I was interested in.
I usually ask people about specific courses and professors, but they seem not to have been that important to you there.
I think I learned some mathematics, things like that, which were helpful. I talked things over with friends, and I had a few talks with Tolman, but I think he was getting older and there wasn’t much chance of working with him. It wasn’t exactly what I wanted to work in his field anyway. There was a fellow called Epstein, a theoretical physicist, and he proposed some sort of problem to compute some sort of diffusion of light into gases in space, which didn’t interest me. I tried to do something with it, but it seemed finally just a computation.
Then you moved to Berkeley in 1939.
Excuse me, ‘41. Now you wrote several papers on scattering and also work on the theory of synchrotron with Foldy.
Yes, I have to explain what happened. When I got up there, Oppenheimer was just going more and more into war work, and I didn’t see a great deal of him. But I got started on this problem of scattering. And then Oppenheimer went off to Los Alamos and I stayed in the Radiation Lab. And I got this thesis out of scattering. And then worked in the Radiation Lab, but there wasn’t much doing there, in fact, for about a year or two. Until Massey and Burhop came along from England. And then they began to set up work on plasmas. You see, there was a serious problem there, how to understand this plasma in a magnetic field, which was very unusual. All during that year, I’d been studying plasmas, but on my own, you see, until they came.
What got you to start studying plasmas?
Well, first of all, because that’s what was going on there. But then it became interesting, because I could see the plasma as an interesting thing. First of all, it was a sort of an autonomous medium; it determined its own conditions, it had its own movements, which were self-determined, and it had the effect that you had collective movement, but all the individuals would contribute to the collective and at the same time have their own autonomy. Therefore, it seemed that there were a great many interesting things that you could think about in the plasma. And I became quite interested in it. The magnetic field complicated it in a large number of ways. Actually, we did some work there which came out later — I think Wakerling edited it — on plasma magnetic diffusion, and also sheaths in magnetic plasmas, and so on.
I noticed in your first note on the subject that the work was done under the auspices of the Manhattan district.
Yes, I was working for them at that time. It was aimed at using magnetic mass spectrograph separators for uranium.
So, it was directly related to the bomb.
Well, in a way it was, but it turned out it had very little relationship.
But it was thought that it might.
It was thought that it might, right. Yes, well, at that time, of course, everybody felt it was necessary to have this bomb. Then when the war was over, all the plasma work folded up. I worked for a while on these machines, the synchrotron, and so on.
Were you asked to work on the machines by McMillan, or perhaps by Lawrence?
Did he ask you to do some more work on the phase stability principle he had invented? While I was interviewing Robert Serber several years ago at Columbia University, he pulled out of his file a telegram that he had gotten from Veksler, I believe during the war, that suggested Veksler had actually come up with his version of the phase stability principle a number of years before McMillan.
I think that’s probably true. I mean, I can’t remember the details, but that sounds right.
So then you worked on the synchrotron —
— on the synchro-cyclotron. By then, I was thinking about the plasmas, but not doing very much on it, because the work wasn’t going on, and then I thought a little bit about more general problems in physics. I was interested in superconductivity, you know, things like that. Collective behavior in those circumstances. Then I went from there to Princeton, about the beginning of 1947.
Wait, before we move there, I want to ask you a few more questions about the plasma work. Was Berkeley one of the main centers for this sort of work in the U.S. at that time?
Well, it’s hard to say. During the war, they were using plasmas as sources of uranium ions, and therefore they were interested in plasmas. As soon as the war work was over, they were not interested in them anymore.
Was Berkeley the main center for this particular approach?
Yes, that’s right, for that approach.
Who else was working on it?
Oak Ridge, Tennessee was where they did the actual industrial application.
Who else was working on this at Berkeley?
Well, there were a lot of people. I can’t remember who they are, Lawrence was the head of it, and there was a whole bunch of people around him, I can’t remember what they were doing. There was a certain period of time, when Segre was there. I think he went off to Los Alamos. And Alvarez was around, but I don’t know if he was there during the war.
He also went to Los Alamos.
Yes, Los Alamos. There was a whole bunch of people whose names I can’t remember now, but who I know were working. The one I worked with was Massey. You see, it was fortunate for me that Massey came and we could get on this thing. Otherwise, there was very little to do then.
Now did you realize at that time that this work on plasmas would then have enormous implications for solid—state theory?
That came in Princeton, I think.
I was thinking of superconductivity, you see. But that was about as far as I was taking it at the time.
So solid state in general was really not at all your interest at that point. I gather that David Pines, and perhaps some other young people, became attracted to the idea of working with you while you were in California.
Well I knew David Pines fairly well in California so we talked quite a bit. There was a fellow called Hal Lewis, but he never got interested in this stuff, he did something else. I don’t know of any younger people.
So Hal Lewis and David Pines were the ones you talked to a lot?
Yes, I talked a great deal with them.
Did you have a feeling right after the war of finally getting back to problems that you weren’t able to work on during the war? One problem to get back to of course had been started by the war in a sense, the nature of plasmas.
Yes, I also wanted to get back to the problem of the nature of the elementary particles.
Did you immediately start discussing plasma work with David Pines?
No. What happened was he came to Princeton. I think we didn’t discuss a lot in Berkeley about this. But he came to Princeton as a graduate student when I was there. And he wanted to work with me and that’s how it started.
Where did you get the idea of separating the Coulomb interaction out by using a series of canonical transformations?
I got that from Schwinger. Schwinger had done this in quantum electrodynamics.
Right, that was just in ’47–8.
Yes. So I thought the canonical transformation could be used here. Of course, the problem is more complicated there, but it had an additional difficulty here that there were no plasma variables at all. You see, Schwinger had the electrodynamic variables, and merely had to renormalize them. Here you had to produce the new variables, and the question of how to get this clear mathematically took some time.
And this was then the problem that you gave David Pines for his thesis?
Well, I wouldn’t say it was exactly that way. I don’t give people problems. I know I said to look in this area. You see we were looking in the area together to see what could be done. I had two students at the time, one was Gross, the other was Pines. Gross, I think, began earlier, but more on ordinary plasma oscillations. Whereas with Pines I began to emphasize the solid-state aspects, the electrons in metals.
Gross started with you at Princeton as well?
As a graduate student?
So he came to talk to you, and you and he began to talk about plasmas. According to my notes, you were at Princeton from ‘46 to ‘51.
Just one or two institutional questions. I was wondering how the environment of Princeton felt to you after having been at Berkeley and earlier at Cal Tech.
Well, I thought it was better than Cal Tech, but I didn’t like it as much as Berkeley.
Well, for one thing, the environment was flat and uninteresting.
You mean the scenery.
Yes, and also the town was a bit staid, you know; it wasn’t really very interesting. I eventually could find interesting people, but in the beginning it looked pretty limited.
What about the physics?
Well, the physics was all right, yes, it was good. But the point is that — there was a fellow here who used to be in Birkbeck called Ehrenberg who said it didn’t matter how many people are in a department, the number that anybody knows is about the same no matter how big the department (laughter). You cannot actually get to know more than a few people, you see, I found that it had some good points and some difficult points; it was good that I could teach a course there in quantum mechanics and I wrote a book on the subject trying to clarify my understanding. I found having all these graduate students was good. Wigner and I were not hostile, but we’re not really close to each other in our way of thinking. That is, Wigner is far more formal. And Wheeler I could talk to a bit you see. I found the general atmosphere a little bit difficult in the same way as Cal Tech. There’s a lot of status consciousness, much more at the Institute than at the University. I felt that this status and security were often on people’s minds, you see. And this interfered with freedom of thought.
I’ve heard about this before, in other interviews.
Also, you see, I think there was a kind of pressure to think in a certain way, not that they were explicitly doing any pressure on you, but just simply by being there. If you talked to all these people, you must talk in their language. Now, David Pines and I had written a paper in which we looked at the plasma, the electrodynamic modes of the plasmas, where we would not have to invent new variables, but just renormalize as Schwinger did. That was one paper, you see. The idea was to start there. And then the problem was to find a clear way of doing this without having these variables to start with for the longitudinal modes.
You’re referring to the first of the four papers on the magnetic interaction.
The magnetic interaction, yes. So first, the idea was to just do the Schwinger stuff there, which is fairly straightforward. Just to cut your teeth on it right away.
(Pulls out the paper,) Will this help?
Let me take a look.
We have already skipped to the Bohm-Pines stuff —
Well, never mind, if you don’t want to go so fast —
It would probably be better to go in chronological order, perhaps to start with your first paper on plasmas, which seems to be based on a talk you gave when you were still at the University of California.
When was that?
This must have been 1947. I can check it in a minute. 1946. That’s early.
I was very interested then in the question of excitation of plasma waves, I tried to generate them by fast beams—the question of stability and instability.
By the way, was Oppenheimer interested in the plasma oscillations?
No, not really.
Was there, at Berkeley — the only person really was Massey?
Massey and Burhop, I used to work with. I don’t think there was anybody on the staff at Princeton who was interested really other than myself and the students I had.
Well, then I’ll start with the Bohm and Gross papers. The first paper is a letter to the Physical Review in July, 1948. [D. Bohm and H. P. Gross, “Plasma Oscillations as a Cause of Acceleration of Cosmic-Ray Particles,” Physical Review 74 (1948), p. 624.]
That was merely sort of a speculation.
The idea was to dust clouds with ion density.
I don’t know if that has ever turned out to be of any significance.
Was there any response to this?
It was merely a speculation, so I didn’t expect very much on it.
Then there are three detailed papers with Gross developing a whole theory of plasma oscillations. [D. Bohm and E. P. Gross, “Theory of Plasma Oscillations as Origin of Medium-Like Behavior,” Physical Review 74 (1949), pp. 1851—1864, “Theory of Plasma Oscillations by Excitation and Damping of Oscillations,” Physical Review 75 (1949), pp. 1864—1876, “Effects of Plasma Boundaries in Plasma Oscillations,” (1950), pp. 992—1001.] The first one is on the origin of the medium-like behavior. I was interested in the first paragraph, because it opens with a definition of plasmas, which suggests that plasmas were not familiar concepts at that time.
Oh, yes. Only a few people would have known about it. I mean those that worked on the subject.
I was interested in the fact that most of the references in that paper are to rather early material, e.g., Debye-Huckel in 1923, the Langmuir and Tonks in the twenties, the two Comptons’ book, J. J. and G. P. Thompson in 1933, and so on. The only two references which are a bit later are to Vlasov’s 1945 work and Landau 1946.
That was all the work that I knew. That is, people had worked on it, but I don’t think a lot had been done other than that, the work was more a case of working out details rather than making any further advance in principle. (Bohm’s wife sets up tea.) Langmuir was the one was developed the idea in the first place, obviously.
Do you know the background of the Langmuir work?
Not very well.
That would be interesting to find out. I believe it came from his interest in understanding discharge tubes.
The word comes from “plasma,” “to give form and shape,” you know. That has a sort of creative aspect to it, to make all sorts of forms and shapes out of itself.
Right. Did you go through the literature and discover the Langmuir work or was that something many people knew about?
I can’t remember. I must have known that at Berkeley. I found him in the literature evidently when I began to look up plasmas. He was one of the first places where it was to be found since he coined the word.
Was the fact that he coined the word something many people knew?
No, I found out from the literature. I think he stated it somewhere in the literature. [Irving Langmuir, “Oscillations in Ionized Gases,” Nat’l. Acad, Sci. Proc. 14 (1928), pp. 627-633, on p. 628 and Lewi Tonks and Irving Langmuir, “Oscillations in Ionized Gases,” Phys. Rev. 33 (1929), pp. 195—210, on p. 196.]
So it does seem that there’s really where it began. The Debye-Huckel stuff is earlier.
That’s earlier, yes, but it really wasn’t called plasma yet. It doesn’t have the dynamic character of a plasma, it’s more a static system, you don’t get much oscillation.
The key concept, I guess, is the ordering — this is the process that had the consequences. And this is also what hadn’t yet been taken into account in the theory of solids, thus causing a number of the old problems still to be around.
Yes, there were problems in the theory of solids. I can’t remember, but Bardeen had some problem calculating the self-energy, I recall, which really involved this implicitly. I think he was working with Wigner, but had left Princeton already. The point was that each particle because of long-range interaction affected all the others, and one had to understand why the effect wasn’t bigger, you see. And it was basically because of screening that it wasn’t bigger. And why the mobility was what it was, and so on. And so one got the idea from Debye-Huckel of a screening cloud around each particle. But the thing had to be extended to the idea of screening which moved with the particle; you see, Debye had a static idea of screening. But when the particle was moving, you had to have a cloud that moved with it, and it gets distorted, and so on. It gets a lot more complex. And so that was really basically the same as renormalization in elementary particle theory. You see the actual charge on the electron is infinite, according to that theory, but it surrounds itself with a cloud, which makes it finite.
Was it completely clear to you after reading Schwinger’s paper and the Debye-Huckel that these were really different forms of the same idea?
Oh yes, that was fairly clear. The same thing, yes. Only I think that it was Schwinger, actually. I heard him talk; we went to a conference up in the Pocono mountains in the forties, late forties. And he gave a long talk of eight hours. It took eight hours, in which he expounded his theory, which overwhelmed everybody. And after thinking that over, it was clear to me that it would be the thing for the plasma work.
Returning to Bohm and Gross, the first paper develops a theory of an unbounded plasma, and the mechanism for such oscillation. The second one includes the collisions and instabilities produced by part of the sharply defined velocity, and excitation and the damping of oscillations. The last one is on boundary effects. This then laid the basis for the work you then did with Pines.
Yes, it helped there. It helped lay a basis. It wasn’t a complete basis, but it helped clear up quite a few questions that had to be cleared up in order to do this other work about what we meant by a plasma, and so on, and how it all worked.
Do you think that if Schwinger hadn’t given that long, eight-hour talk, you would have come to this anyhow?
I couldn’t say. At that point, it did produce the result.
That’s very interesting.
I mean, maybe I would have come there anyway, but it would have taken longer.
Meanwhile, you were working on the basis of the quantum theory. Was that something you worked on much of the time?
Well, I was constantly working on it — I can’t say how much, but a fair amount of time.
How closely did you work with Gross on the plasma theory?
Well, we worked together, you know. It’s hard to say.
Say once a week?
No, it was much more informal than that. You see, the point is that we would meet whenever we felt like it to talk things over. I mean, it was a case where we would go somewhere and talk about other things as well, and so on. I mean in those days, I didn’t meet people at specific times or anything like that.
And the fact that you were in trouble just in this period with the House Un-American Activities Committee, did that have any impact on the way you were doing your physics?
Well eventually it did, you see, but in the beginning it probably didn’t. You see what happened was that I didn’t testify, and apparently the whole issue was dying away, and then, it was revived, and they indicted me along with a lot of people for contempt of Congress. So, the minute the indictments came out, the University suspended me on pay. My contract had the rest of the year to run.
When did this happen?
It was late 1950 when it happened. They said I wasn’t to come to the University, you see. Of course, I met whoever I wanted to meet, but, I went to the Institute sometimes.
The Institute was off—
It was off somewhere else about a mile away. And during that time, of course, a number of things were happening. First of all, I finished the quantum theory book, and I sent a copy to various scientists including Einstein and Pauli, who liked it very much. Einstein wanted to discuss it with me, and we had several discussions on this and on several other topics. But I’ll come to that later. Now, what happened was that, not being able to go to the University, I had to work at home. I felt that in some ways it liberated me. I was able to think more easily and more freely, you know, without having to talk the language of other people. And therefore, I was able clearly to confront the question of how to define this variable. We hadn’t gotten to how to make a canonical transformation, but how to define this variable that would be self-maintaining in a self-oscillation of all the particles. I think I can find it in one of these papers here (looks through papers). I remember puzzling, trying to find out how to formulate the formula for the collective variables that would take all this into account. It’s easy enough to have them when the particles are moving slowly and are nearly static, but if the particles themselves are moving, then you have to have a different function to describe the collective motion, and that was the one we got. Now, the next stage was to go on to make a canonical transformation using those, to find a canonical transformation. And that was as far as I got when I was in Princeton.
Let’s see, I think that was already in the first paper.
Here’s the canonical transformation, yes.
This approach eventually provided a way of calculating the interaction energy between the electrons in a solid, which Wigner had tried to do in 1934 and improved on a bit in 1938.
Bardeen was involved in that, too, but in some way I can’t quite recall. But Wigner was the main one.
But he didn’t get that logarithmic term.
This whole screening business, yes. The logarithmic thing came out of screening.
I was wondering whether Wigner was interested in your work on plasmas when you were doing it?
You see, I have to explain about Wigner; we get along quite well, but we have a different way of thinking. You see, I’m interested in the principles of the collective motion and self-maintaining variables in the plasma, and so on, the autonomy of behavior. I think Wigner thinks more mathematically. He may think physically as well, but he wants primarily to put the things in terms of equations and formulae. And therefore, we probably didn’t have a lot of contact.
Was this Wigner calculation something that was on your mind in the beginning? Or was it something that occurred to you later. It doesn’t really get done until the fourth Bohm-Pines paper, which is mainly David Pines’ paper.
Well, this was not the main stuff on my mind. No, we were aware of it, but it wasn’t the main point. You see, I’ve never been interested in calculation as the main point.
In the third Bohm-Pines paper, I see that you’re in Brazil.
And so you did this work by correspondence.
Yes, but unfortunately, my memory of the period is poor. I mean, I’m sure we corresponded about it now that you say so. I think a great deal of the work had been done before I left, you see. But it was necessary to organize it, and I think David did a lot of the organization.
In that paper, you also relate the work to Tomonaga’s one dimensional treatment of a degenerate Fermi gas. How did you get the idea that your approach might apply to electrons in metals?
Well, it became very clear that metals were a very dense electron gas and all the particles were free, so they would satisfy the conditions for a plasma. The question was, how can it be done quantum mechanically? It was clear that a canonical transformation was needed for that. I mean, I would have known about canonical transformations before, and eventually they might have turned up, but the thing was on my mind because of what Schwinger had said.
Is there anything more than we ought to get down on tape? As I said before, the papers stand by themselves, but the connections aren’t obvious and they are what I’m trying to record in this interview.
Connections with what?
With ideas and circumstances, for example in the hope of learning where the ideas came from. And who was working on what and who was talking to whom — things that are not in the papers.
It’s hard for me to remember that. You see, I remember I read the various papers, you know Vlasov, and some of the earlier papers which provided the basic principles. And then there was a great deal of thinking, you see, I’d been doing during the war about how these particles move and so on. How they move collectively together. The idea of collective motion occurred at a certain point, but I can’t remember how — collective coordinates to describe the state of the whole system.
Before we move on to the next subject, which will be the Bohm-Staver work, I want to go back to two points. First, did you have conversations with Oppenheimer having to do with your situation vis-a-vis the House Un-American Activities Committee? And what was your conversation with Einstein about?
Well, I never really discussed my suspension much with Oppenheimer, except that he helped me to get this job in Brazil as far as he could. He wrote a letter in my favor, for which he was criticized later. But beyond that, I should also add that while I was very impressed by Oppenheimer in the beginning, when we got to Princeton, we didn’t get along so well. He wanted me to do calculations on renormalization; he thought that was the big thing in physics, and that I was wasting my time writing that book and playing around with plasmas. And so therefore we weren’t all that close, you see, scientifically speaking, that is. I think that he helped me as far as he was able to. But beyond that, we didn’t have very much contact.
You also mentioned a conversation with Einstein.
Well, I had several conversations with Einstein. After writing this book on quantum mechanics, which I wrote to try to understand it (based on my graduate course), I sent a copy to various scientists including Einstein. He wanted to discuss it with me, and we discussed it. He felt that the book was as good as you could present the ordinary point-of-view, but he still didn’t accept it. So we discussed it for a while, and meanwhile I myself had been feeling that it wasn’t all that clear, and that therefore these two things together made me feel that the interpretation of quantum mechanics was not satisfactory. So I began to think about it, and I produced another interpretation, which came out in two papers in Phys. Rev, in 1952, two papers, using a particle and a wave, the causal interpretation I called it. And I discussed all those things with Einstein; we also had correspondence afterwards when I was in Brazil.
It would be fun to talk to you about that although it’s a completely different subject. I must tell you that when I was a graduate student I was very moved and impressed by your writings on quantum mechanics and spent a lot of time over them. But I think it would take us too far afield to discuss them right now. Okay, finally, before we move on to the Bohm-Staver, which is a slightly different application, namely, to the theory of superconductivity [D. J. Bohm and Tor Staver, “Application of collective treatment of electron and ion vibrations to theories of conductivity and superconductivity,” Physical Review 84 (1951), p. 836], I would like want to take a few minutes to review historical highlights in calculation of the interaction between electrons —
—and the ions?
Well, between the electrons and the electrons. It seems to me, the first important step was the invention of the Hartree-Fock method, which then enabled Bardeen in 1936 to calculate the second-order contributions in perturbation theory. He got the log divergence, suggesting that the electron interaction can’t be treated as weak. It was clear one needed to find a better way of taking care of the long-range nature of the Coulomb interaction. Wigner’s calculations in 1934 and 8 were based on a combination perturbation-variational calculation, he didn’t get the logarithmic term, he interpolated between the high and low density limits. As far as I can tell, except for one paper by Macke which is of some importance, the next important step was the Bohm-Pines theory. There was a gap of about 15 years in this development. Is that correct?
As far as I know; my memory doesn’t serve me very well for that. It must be right. I don’t think a lot of progress was made. Don’t forget that four or five of those years were war years, and then there’s a dislocation. I think that you couldn’t have gotten very far without bringing in something like a plasma. Since nobody brought in a plasma, there was not very far you could go.
Was this the first time you made the analogy between a metal and a classical plasma? Was this a completely new approach?
As far as I know.
The approach changed solid—state physics. After your work, the next important step doesn’t seem to be until the Gell-Mann-Brueckner work of 1947 [M. Gell—Mann and K. A. Brueckner, Phys. Rev. 106 (1957), p. 364]. Does that agree with you too?
Yes, as far as I know. I didn’t follow it very much after I got to Brazil. You see, when we finished these papers, my interests began to go in other directions. So I couldn’t tell you very much about it from there on.
Before we go to Brazil, let’s talk about your work with Tor Staver, which was done in Princeton back in 1951. Who was Staver?
He was a graduate student of mine, a Norwegian, and he got started working with me you know just about the time I was in trouble with the Un-American Activities Committee and had to leave. I corresponded a little with him, but he finished the work largely on his own. I think that David Pines organized it then.
I see, David acted as a sort of an advisor?
No, he was away from Princeton. But he organized it when Staver was killed in a skiing accident in Massachusetts. David took on himself the business of organizing what Staver had done and putting out a thesis.
I didn’t know that.
That’s my memory of it.
Did the idea of applying the collective treatment of the electronic and ionic vibrations to the theories of conductivity and superconductivity come out of your general reading and interest in super-conductivity? Or was it inspired by some particular person?
Well, I had been thinking about superconductivity for a long time starting in California, so it was always interesting to me.
And this was then a natural area to apply the theory to. You were also undoubtedly familiar with the work of Bardeen and Frohlich.
Well some of that came later, didn’t it? I mean I can’t remember the timing of that.
This letter that you and Staver wrote to the Physical Review. [David Bohm and Tor Staver, ‘Application of Collective Treatment of Electron and Ion Vibrations to Theories of Conductivity and Superconductivity,” Physical Review 84 (1951), pp. 836-7.]
Yes, that was just before I left, you see.
It has a reference to work by Bardeen and Frohlich. [H. Frohlich, Phys. Rev, 79 (1950), p. 845; J, Bardeen, Phys. Rev, 80 (1950), p. 567.]
Oh yes, of course, that’s right. Yes, I was familiar with that.
—work on the electron-lattice vibration interaction. And then this led to the concept of a randomly fluctuating part associated with individual particles, causing screening. In this work Staver and you did, who was responsible for the main idea?
Well, I suggested it to him and he worked it out.
I see, the idea of a wake which captures the electrons. Were there any responses to this?
Well, it would have been hard for me to know because I left in upheaval. You see, I think that I could have seen better if I had stayed there, but I wasn’t aware of responses. When I got to Brazil, I began to get more interested in the causal interpretation, so I didn’t follow this as closely.
So in Brazil, your main work was on the interpretation of quantum mechanics?
Quantum mechanics and statistics, and so on.
And during this time you wrote your next book, on causality?
That’s right, yes.
So, in a way, you left all of these problems on plasmas quite abruptly, at least for a while.
Yes, well I never returned to them fully, but I returned a little bit when the work with Carmi in 1960 on trying to develop ways of describing collective motion. [D. Bohm and C. Carmi, “Separation of Motions of Many-Body Systems into Dynamically Independent Parts by Projection onto Equilibrium Varieties in Phase Space. I,” Physical Review A133 (1964), 319—331; II, Physical Review A133(1964), 332—350.]
You stayed in Brazil for four years. What was it like there in comparison to the centers that you worked at before?
Well, it was fairly isolated, of course. I didn’t really have too many people to talk with, the situation was one of general chaos. I mean, you can get used to that. I did some work there, but it was difficult for me.
Did you keep up with the literature?
Well, I was reading the literature on my own interest but I didn’t follow the plasma work any more to any great extent.
Were you aware of the work that David Pines was doing, applying the concepts you two had developed to all sorts of problems?
Yes, he sent me papers and so on, you see. But at that time I had ceased to work on the subject.
As a final question, when the BCS theory finally came out, did you have a feeling your work had been a step?
I hadn’t thought of it; I suppose I could have thought of it that way. Well, it might have been. But, I can’t recall that I had any strong feeling. I was just sort of keeping up with it. I mean, I wasn’t really putting a lot of attention in at that time.
The work that you had done with Staver, and then carried out later by David Pines (see interview with Pines by Hoddeson) clarified the electron-electron interaction, which was quite a necessary step.
Well, I think I would have understood that at that time, yes. But you see I think that my interests really began to go in other directions, and possibly I began to feel when I got back to Europe that people were not interested in the physical or the general concepts but wanted primarily to have a way of calculating things, you see. I felt it was fortunate that in Princeton I had David Pines there; he was ready to talk about these things, you see. Gross was ready to do it too. And Staver to some extent. But you see it’s not common that you find people that want to even talk about these things. I remember getting to a conference in Holland on this plasma work, and I felt that there was no physics there at all, they were just putting formulae on the board. They were not really interested in questions of what is the collective and what is the individual and things like that, you see. And I remember having an argument with a fellow called Braut, and I said, “I don’t understand what’s going on here,” and he said, “I don’t understand what you mean by not understanding.”
I remember that too.
It was lunchtime.
And it was such a funny thing to say, “I don’t understand what you mean by not understanding,” and he couldn’t see how comical it sounded.
In that direction, I feel that the way of thinking is this: that people feel the truth consists of mathematical formulae which agree with experiment, and that any physical ideas are useful in so far as they will lead to these formulae, but otherwise, they have no significance. That’s the attitude I picked up. I did try to read some of the papers on the subject, and again I felt the same thing, you see. So I couldn’t maintain a very strong interest. It would have meant a big effort to go back and find out all that had gone on in between and give up some other things that I was interested in.
Is there anything I should have asked you that I didn’t?
What did you discuss in your interview with David Pines?
We went over the papers in some detail, including some of the subsequent papers in which he applied certain of the ideas to the passage of charged particles through heavy materials and to superconductivity. Soon I’m going to sit down and see if I can write part of the story.
How long a history do you plan for this subject?
Do you mean in pages?
Maybe 30 or 40 pages.
Is it part of a larger book?
Yes, part of an 800 page volume that Oxford University Press will be publishing.
On the history of solid—state physics. (PAUSE)
One of the problems that seemed very important was to get in between the domain of the collective and individual. You see, each was a limit, and that was one of the things that I wanted to go on with, but it seemed very difficult mathematically. But I didn’t have any very clear idea of how that could be done you see. It would have required some very intensive work. I tried to come back to it in Bristol with Carmi, and we got a little way, but on the whole, I don’t think my interest was strong enough to go on with it.
Well, maybe one day, you’ll get back to it.
Well, not likely. It’s a very difficult point.
I’m not a physicist, but David explained a little bit to me about plasmas, and I find that it’s such a beautiful thing. There’s something rather lovely there. So maybe he’ll see it from another point of view from this other work he’s doing.