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Oral History Transcript — Dr. Vladimir A. Fok

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Interview with Dr. Vladimir A. Fok
By Thomas S. Kuhn
At Palmer Physical Laboratory, Princeton, NJ
October 11, 1967

open tab View abstract

Vladimir A. Fok; October 11, 1967

ABSTRACT: Family background, early schooling; physics studies at University of Petrograd, Dmitri Rozhdestwensky. Introduction to Niels Bohr's atomic theories; Russian physical sciences tradition; Russian degree system. Stipend at the Optical Institute in Petrograd. Reactions to Werner Heisenberg-Erwin Schrödinger work, 1925-1926; to Göttingen University 1927 and 1928 (Paul Ehrenfest, Paul A.M. Dirac); life in Göttingen. Relationship with Bohr, Bohr's visit to Leningrad, 1934; visit to Copenhagen, 1957; philosophical aspects of physics in Leningrad. Also prominently mentioned are: Maurice de Broglie, Friedman, Goud, Samuel Abraham Goudsmit, Krutkow, Krylow, Liapunov, Hermann Weyl; Kazan V. I. Lenin State University, Leningradskii gosudarstvennyi universitet imeni A. A. Zhdanova, Moscow M. V. Lomonosov State University, Petrozavodsk o. V. Kuusinen State University, Proceedings of the Royal Society, and Universität Göttingen.

Transcript

Kuhn:

I would be very grateful if you would start out by telling me how you came to science in the first place. You know, we know now a good deal about how people came to physics and then to quantum mechanics in Germany, in England, in France, but very little about the situation in Russia, which brought so many people — a few in your generation and many more later — to begin to study modern physics.

Fok:

You know, in my case it's hereditary. My great-grandfather was already professor in the same region of science as myself. He was professor at a newly founded type of university since 1803.

Kuhn:

Did your father also continue to teach?

Fok:

My father was a scientist in forestry. He was at the same time in forestry and — something like topography — in both; so that it was quite natural in our family to continue this tradition.

Kuhn:

Was your father also at a university or was he at a research station?

Fok:

No. My father was at the Ministry for Agriculture in old Russia and remained at the same employment after the revolution.

Kuhn:

When you were at school, before you went to the university, was there a strong science curriculum in your school then?

Fok:

Yes, yes. There were several good teachers in different subjects. I remember the teachers in history. In physics we assisted at physical experiments. First of all we learned foreign languages. French and German I knew since my childhood, and English I learned in the school. That helped me very much, the knowledge of languages, in my scientific work.

Kuhn:

How much science did you study before the university? How much mathematics did one learn before going to the university?

Fok:

I don't quite understand your question. This was a very good school. There were elements of differential calculus and knowledge of geometry also; trigonometry we knew perfectly; some physics, some chemistry.

Kuhn:

Did you use your mathematics in the physics? Did you use the calculus in the physics in school or did that wait until you came to the university?

Fok:

When I was in the school there were separate subjects — mathematics and physics.

Kuhn:

In this country and the schools, you know, there are sometimes at the beginning two different ways in which one can teach physics. One can teach physics to somebody who does know calculus, or one can teach it to somebody who does not know calculus, and one teaches it very differently, depending upon whether the student can use his calculus or not.

Fok:

In my school, the teaching of physics did not require mathematical knowledge. It was a subject that did not require mathematical knowledge. But since at the same time there were some mathematical lessons, the pupils combined this for themselves — perhaps not all of them, but I tried to combine what I knew from the lessons of mathematics. But that is quite my personal approach.

Kuhn:

Did many students take the physics and the mathematics courses? Were they required for all students or was this a preference of your own?

Fok:

I finished school many years ago. That was before the revolution. In 1916 I finished school. So I speak of myself and not of the present state.

Kuhn:

When you finished school, did you know that you would be a physicist? Had you already decided what you wished to be?

Fok:

Not quite. I thought that perhaps I would be an engineer, but my father's wish was that I would first study at the university and then perhaps at some engineering institute. But in reality I chose physics at the university.

Kuhn:

If you had known that you were to be an engineer, you would then have gone directly to an engineering institution. You would not have gone to the university at all?

Fok:

No, no. Just my father's wish was that I had to know both mathematics at the higher level and engineering — first university science and then engineering. That was his wish.

Kuhn:

So at the university you took physics and mathematics from the beginning.

Fok:

Yes, yes. At the university I took physics and mathematics from the beginning, yes. We had then a physical-mathematical faculty at the university, and I took this from the beginning.

Kuhn:

This was Petrograd?

Fok:

The University of Petrograd, yes. And then there was an interruption in my study because of the war, and after the war I continued my study at the university.

Kuhn:

At Petrograd when you were there, was there a strong division between experimental and mathematical physics, or were the two handled very much together?

Fok:

Perhaps the division was not as strong as now. First of all, the number of students at my time was a very small one, just because of the war and the revolution and all kinds of difficulties in studying. About this time, in 1918, at the end of this year, Professor Rozhdestwensky of the Petrograd University founded the Optical Institute. He knew all kinds of problems relating to optics, and what was most interesting to me, studied atomic physics in Bohr's theory.

Kuhn:

This would be already by 1918.

Fok:

Yes, yes, yes. There was very high-level staff at the University, in spite of the fact that the relations with the West were nearly interrupted during the war and the revolution, the scientific work continued in Russia; and when Bohr's ideas came they were easily accepted. They found comprehension.

Kuhn:

That interests me, because it is only really after the war in Europe in Germany that very many people take Bohr’s work seriously or begin to work on it. Of course the war interrupts there also. But except for Sommerfeld and also Ehrenfest, there are not very many —

Fok:

Yes, Ehrenfest was formerly professor at the Petrograd University, and Professor Rozhdestwensky of whom I spoke and others — Krutkov and Friedmann, Fredericks, Bursian, Krylov — were friends of Ehrenfest. There exist now at the Academy of Sciences letters or copies of letters or photos of letters between Ehrenfest and this theoretical group — Rozhdestwensky and Krutkov and others. The letters that I remember I read were between Ehrenfest and Rozhdestwensky. In that letter Ehrenfest expressed his admiration that in spite of all the difficulties, scientific research continued to develop in Russia and especially some ideas put forward by Rozhdestwensky concerning the influence of magnetic fields on atomic spectra which were in near accordance with what was done in the West; so that the level was very close.

Kuhn:

Was this particularly true at Petrograd because Rozhdestwensky was there, or would it have been true at other major universities in Russia also?

Fok:

You know, before the revolution, general theoretical physics developed first of all in Petersburg-Petrograd, because there was the site of the Academy of Sciences and the well-known, celebrated mathematical school, the so-called Petersburg Mathematical School that began in the 19th century or even earlier, Chebyshev, Liapunov, and others — Markov, Steklov. They were celebrated mathematicians who worked in theoretical mechanics, in celestial mechanics. Liapunov’s especially well-known in theory of equilibrium of celestial bodies. That was his most outstanding work so that all these great men had pupils. Most of them continued to live in Petrograd, so that I believe that at that time Petrograd was more advanced in this. Yet at the same time, we had a scientific tradition at other universities also. At Moscow University mathematics was very high and is now very high, and also at Kazan where Lobachevsky worked, and his tradition is still alive at Kazan. There is a special department for the physical application of geometry and Einstein's theory. We had no such special departments at Leningrad University. Leningrad is merged with theoretical physics. But there in Kazan there is a special department.

Kuhn:

Was it because of its special strength in physics that you had gone to Petrograd?

Fok:

No, I was born there, and I spent the whole of my life in Petrograd except travels.

Kuhn:

This was convenient for you then.

Fok:

Yes, quite natural.

Kuhn:

You heard I take it, of the quantum theory from Rozhdestwensky. It was he who told you of the quantum theory?

Fok:

Yes, yes. I was then quite a young man, and he invited me and other students from the physical faculty of the Petrograd University, about ten persons. Most of them later became scientists in physics and some of them members of Academy, and Rozhdestwensky himself told me once not long before his death that he thinks that one of his main deeds was that he helped these young men to develop into scientists.

Kuhn:

When you say he invited you — did he invite you to come to lectures or to his home?

Fok:

No. He invited me in the sense that the Optical Institute was ready to pay me a stipend and to make possible my study at the university, with some promise on my part to work at the Institute after the habilitation.

Kuhn:

This was when you had finished your first studies. When you became a graduate student you were at the Optical Institute.

Fok:

No. Even as what you would call an undergraduate student, this appointment at the Institute was already from the first semester of 1919. I was then a youngster, a student. I habilitated in 1922, and then continued to work for some time.

Kuhn:

Were there many courses on quantum mechanics or did you learn this by reading yourself and by talking with Rozhdestwensky?

Fok:

Not courses, but seminars — several seminars on quantum mechanics, and at the same time on Einstein's gravitation theory. So I had always an interest in theoretical physics, and I took part at their seminars so that I learned both quantum mechanics and gravitation theory from seminars.

Kuhn:

Who besides Rozhdestwensky on the faculty was involved with these?

Fok:

With quantum mechanics, quantum physics, theoretical quantum physics — Professor Krutkov. I wrote my habilitationschrift —

Kuhn:

In English we cannot say that. You did that for Krutkov.

Fok:

Yes, for Krutkov — quantum mechanics. Then on gravitation theory a seminar was conducted by Fredericks and Friedmann. You know Friedmann’s name?

Kuhn:

Yes.

Fok:

He found solutions of Einstein that were not expanding the universe and so forth.

Kuhn:

How many students were there usually in the seminar?

Fok:

In my time there were only very few, perhaps 15 or 20.

Kuhn:

At what point did you decide yourself to be a physicist; quickly at the university, before the war interruption?

Fok:

This was at the moment that I got an appointment at the Optical Institute, because this gave me the means to study —

Kuhn:

I talked to a number of the German people in Germany about this same time. It was always a difficult decision for them to decide to be physicists rather than, for example, engineers, because there were not very many jobs, and those of them who were not happy with the idea that they might finish by teaching in a gymnasium felt that it was a great risk to go into physics. Was this also true in Russia at this time?

Fok:

This time was an exceptional time. It is not characteristic for conditions in Russia at a later time; so that I don't know a definite answer to that question.

Kuhn:

What books or articles were influential in teaching people at your time how to do quantum mechanics? Was Sommerfeld —?

Fok:

What books?

Kuhn:

Or other things?

Fok:

We had first of all a Russian course of physics by Professor Chwolson in five volumes.

Kuhn:

I know that. This was his book, but he was not also at Leningrad?

Fok:

He was also at Leningrad.

Kuhn:

That would also help. Those are interesting books.

Fok:

Yes, very interesting books. The fifth volume, I believe, was published in 1915 and contained elements of Bohr’s theory of atoms and of relativity theory, which for the times was on a high level.

Kuhn:

I may say I don’t know all of those volumes. But there are two supplementary volumes which go from 1915 to 1926, I think, that were published later and that are very much a review of developments in the intervening period. They’re terribly useful to me.

Fok:

I forget when Professor Chwolson died — I believe in the early ‘20s.

Kuhn:

I may have the dates of the supplements wrong, but there is a supplementary volume that carries on from where the standard series left.

Fok:

Yes, the dates may be wrong. But, you know, perhaps not, because these supplementary volumes were written in collaboration with younger physicists, with other physicists; so that it may be that they are continued.

Kuhn:

Well, now, did you and did people around you use, for example, Sommerfeld’s ATOMBAU?

Fok:

Yes, we used his book — Sommerfeld’s ATOMBAU UND SPEKTRALLINIEN.

Kuhn:

Often in Germany and France, once it was translated, and with a few people in England, this was referred to as “the Bible.” Was it also a Bible in Russia?

Fok:

No, not quite a Bible, but we used it of course.

Kuhn:

Did you also use or care about the 1918 work of Bohr, THE THEORY OF LINE SPECTRA, I think it was called?

Fok:

Yes. I remember that Rozhdestwensky had given me especially this work of 1918 that I had to study, and I tried this, but I found very many statements that were not clear to me. Now it can be evident as to why, because at that time the ideas were not quite clear.

Kuhn:

It is still a very rewarding book, for the historian now. No physicist would now be likely to go back to it, but it is still very difficult. Some of the allusions —

Fok:

Yes, yes, yes.

Kuhn:

Was there anything else that you remember from this time as something that was particularly useful to learn your physics from? You know, things that were particularly influential.

Fok:

I remember that the subject of my habilitationschrift was on the adiabatic invariance for systems with commensurabilities between mean motions; so that I had to study then some of the celestial mechanics of Steklov, and I don't know —

Kuhn:

Charlier?

Fok:

Charlier.

Kuhn:

And Poincaré.

Fok:

Yes, Charlier, yes. That was for my personal study. And I wrote this in the autumn of '22.

Kuhn:

Was the habilitationschrift a second thesis for you? In Germany somebody would do a thesis for the doctor's degree and then after that would do a habilitationschrift, so there would be two things that had to be done.

Fok:

No. The German doctor's degree is not the same as the Russian doctor's degree. The habilitationschrift — all the students must have it in order to obtain a diploma at the habilitated university. We have no division into undergraduate and post-graduate students; so that we have three degrees: first, habilitation at the university; then one must do some scientific research and write a scientific paper and give an exposition of the research before the faculty. I forget the special term —

Kuhn:

The defense of the dissertation.

Fok:

Yes, to defend — yes. Then one obtains the degree of “candidate,” not yet doctor. And then after several years' more work — and this time it must be quite original; the role of some consultant must not be too great — one may write a book or monograph about some subject. This opens the way to the doctor’s degree and to the professorship. Soon after my habilitation came the epoch of rapid development of quantum mechanics. We all read De Broglie's paper in ‘23 or '24 on waves of matter.

Kuhn:

I'm curious that you tell me that, and I want to ask you to say more about it, but let me say why I ask. In England and in Germany, almost nobody read that De Broglie paper until after Schrodinger. There were a few people that did.

Fok:

I remember quite well that it is just Professor Fredericks at the seminar on quantum mechanics read this paper, and I remember my impression was somewhat critical — it was so very difficult to believe: on waves of matter. But the paper was read and discussed.

Kuhn:

And it was not only presented but you all read it for yourselves also?

Fok:

Yes, after I heard it at the seminar — yes.

Kuhn:

This was the big one in the ANNALES DE PHYSIQUE, the very big long paper of De Broglie?

Fok:

I forgot which, but it was in ‘24; I forget which paper.

Kuhn:

The ‘24 paper is the ANNALES DE PHYSIQUE. There are little ones in COMPTES RENDUS also in ‘24, but —

Fok:

COMPTES RENDUS? No. Perhaps we did not —

Kuhn:

That's terribly interesting. To come back just a little bit before 1924 and the De Broglie paper, because there are other things, did one regularly read all the journals? I mean did you see the ZEITSCHRIFT FÜR PHYSIK, the ANNALES DE PHYSIQUE?

Fok:

Yes, ZEITSCHRIFT FÜR PHYSIK, ANNALES DE PHYSIQUE and COMPTES RENDUS.

Kuhn:

What about English and American journals?

Fok:

PROCEEDINGS of the Royal Society, PROCEEDINGS of the Physical Society.

Kuhn:

What about PHILOSOPHICAL MAGAZINE?

Fok:

PHILOSOPHICAL MAGAZINE also. I forget: since when is the PHYSICAL REVIEW?

Kuhn:

I don't remember exactly, but it very much existed at this time, the PHYSICAL REVIEW. It goes back before the First World War. Which of these journals would you follow regularly? They were in the library, yes, and if somebody said —

Fok:

Regularly the German, the ZEITSCHRIFT FÜR PHYSIK, and ANNALES DE PHYSIQUE.

Kuhn:

PHYSIKALISCHE ZEITSCHRIFT also?

Fok:

PHYSIKALISCHE ZEITSCHRIFT also but not so much. Then the Heisenberg paper of ‘25 made a great impression, and the Schrodinger paper of ‘26.

Kuhn:

I want to wait just a little bit before we come to Heisenberg and Schrodinger because there are some other things that happen in ‘21, ‘22, ‘23, and ‘24 that people in Germany saw as paving the way preparing the break, and I wonder what was felt about these same problems at Petrograd. What was the reaction and how did people feel about the Stern-Gerlach experiments?

Fok:

They were quite enthusiastic about this. (laughs)

Kuhn:

Had there been skepticism? Had people been doubtful about space quantization before those experiments?

Fok:

This I don't quite remember. The questions were discussed, but —

Kuhn:

Not necessarily a more difficult question, but a more difficult thing to accept was the Compton Effect, the evidence for the photon given by Compton.

Fok:

Yes. But that was so important evidence that it was discussed at the seminars. You know, in Leningrad, just in this narrow circle, we were rather prepared for this, because several years before our attention was drawn toward this question.

Kuhn:

Again, I tell you a little bit more about why I ask this question in particular, and it's different from the Stern-Gerlach question. In many places, but not in all places — and it is interesting to know which places are which — the whole problem of the photon and of the Einstein development of a photon theory were not taken very seriously. In some places they were. This was part of the question as to who read De Broglie and who did not read De Broglie. Now, for example, we have the minute books or a copy of the minute books of the Kapitza Club at Cambridge. When Compton's discovery is first announced there — and this is an informal minute book — they write in the minute book, "Compton is right,” "Compton is wrong,” and then the members of the Kapitza Club sign their initials according to which they believe, and many people are sure that Compton is wrong. Now, elsewhere, people thought that must be right. But it was a key issue, the Compton Effect — and it did divide the profession in many places.

Fok:

You know, at that time I was still in contact with Professor Krutkov, who was my teacher in quantum mechanics and with Frederichs, and they accepted this without any doubt. At the time they were themselves very young, and young men accept more easily such discoveries. You know? (laughs)

Kuhn:

Yes, yes, yes. Another question about this period — and it may be impossible to answer — in the years 1923, 1924, in certain places in Germany (and perhaps more than anywhere else, in Göttingen) people thought that the situation had suddenly gotten very difficult, and you remember Born when he writes his book, ATOMMECHANIK, calls it Volume I. He says in the preface that “What I am doing is trying to push the old quantum theory to the limit because we must have a new atom mechanics, and I think it is going to come soon, and I will write the second volume about the new quantum mechanics.” There were some people who felt that now for the first time they had used up the possibilities of the old quantum theory; that there was now a deep crisis in physics which there had not been four years earlier, and that the whole picture had to change. Was there that sort of sense at Leningrad? Is my question clear?

Fok:

Yes. It was felt then that it is very difficult to do something, to have real progress on the same lines as indicated by interpretation of this quantization rule. But at the same time one did not understand sufficiently the underground of Bohr's ideas, who always thought that one must have, so to say, deeper reasons for progress in physics. So that I believe it was the same as everywhere. It was felt then that something must happen in order that real progress may be possible and this sense of relief came with Heisenberg's and Schrodinger's papers.

Kuhn:

Were there particular problems that you remember from this period as being problems which were not working — you know particular focuses or particular places where there were difficulties? I asked Dirac this question, and he said “the helium atom.” Was one aware of the helium atom as a particular problem?

Fok:

Well, you know, as early as 1920 Academician Krylov whom I mentioned, applied his knowledge of celestial mechanics to the helium atom and introduced a conception of average charge for the nucleus and inner electron, so that since the outer electron moves much more slowly than the inner one, it would be a good approximation to introduce an effective charge in the sense of averaging over the motion of the inner one. So that such problems were considered, but at the same time one felt that it is difficult to reconcile the instability of such a classical system with what one knows from observations of atoms.

Kuhn:

Was the dispersion problem of particular concern also to you in this period?

Fok:

Yes. At that time, so far as I know, the physicists continued the study of the influence of magnetic fields on atomic spectra. Landé’s factor and so forth.

Kuhn:

Were they excited by Landé’s results?

Fok:

Yes.

Kuhn:

I remember Goudsmit talking about the reception of the magic RKJ. In 1924 there was also a strange paper — a very interesting paper and for some people a very influential paper by Bohr, Kramers and Slater.

Fok:

Ah, yes, yes, yes. This paper was doubted from the beginning because non-conservation of energy even in elementary processes was presented as not satisfied. Yes, this paper was discussed but rather skeptically.

Kuhn:

Well, you spoke about the sense of release and relief that was produced by the Heisenberg and the Schrodinger papers. Those two of course came close together, but they did not come at quite the same time. Did matrix mechanics, the Heisenberg paper, the Born-Jordan-Heisenberg paper make an impression before you knew of Schrodinger?

Fok:

You know the Schrodinger paper made the Heisenberg paper easily understandable. The matrix by itself was felt as something perhaps artificial. But very soon, when Schrodinger's paper appeared and Schrodinger demonstrated the equivalence of the points of view — perhaps different physicists took different positions at times, but as to myself, I fully accepted this since the advent of Schrodinger's paper.

Kuhn:

Before Schrodinger had you tried to learn matrices or to do any problems using matrices?

Fok:

Before Schrodinger I attended a course in mathematics by Professor Tomarkin, who came later to the United States. It was a course in the theory of linear operators, and he spoke on the spectrum of proper values of operators. That was about ‘23, this mathematical course, perhaps in the winter of ‘23-‘24. I remember that I expressed my opinion — that it may be that the mathematical spectrum of proper values of operators may be connected with the optical spectrum. I never published this. And when I read the paper by Schrodinger, “Quantisierung als Eigenwert problem,” then I thought that this is very near to what I expected.

Kuhn:

The Heisenberg paper came out in the last quarter of 1925. The Schrodinger papers did not begin to appear until 1926. Now, in that period in late 1925 you must have been aware of the Heisenberg, Born and Jordan work. Did you try to see whether you could use matrices yourself for physics the way that Born was using them?

Fok:

No, I believe at that time I did not try. When Schrodinger's paper appeared, then very soon I published also two of my papers on the same subject — the first “Generalization of the Schrodinger Equation,” for the magnetic field but for particles without spin. This was not yet known at that time. And a second one on “The Relativistic Form of the Schrodinger Equation;” I used their five dimensional space-time. And later there were very often attempts to use this five dimensional space-time. This was not for the first time. The terrestrial physicist Mandel also operated with five dimensional geometry, but he did not apply it to quantum mechanics.

Kuhn:

Was he the person you were trying to remember? There was somebody else also.

Fok:

Yes, there was somebody else also.

Kuhn:

I've forgotten the name. Oscar Klein was also much interested in this same man whose name I cannot remember.

Fok:

Yes, yes, yes. And my paper was published a little later than Klein’s paper, but was written quite independently.

Kuhn:

What led you to take these two problems?

Fok:

Simply my interest in realization, so to say; of my own idea of the connection between operators and mathematics in spectra. I thought that Schrodinger found the key to this.

Kuhn:

I see why you were so quickly convinced by Schrodinger’s approach, but there were many problems that one might have taken up, being convinced of Schrodinger’s approach. You picked two, both of them generalizing the field equation, one to include magnetization and the other a relativistic form. Why is it, do you suppose, that those were the first two things you did with it?

Fok:

You know, there was an attempt by Weyl, not connected with quantum mechanics, but an attempt to introduce Goud’s difference in relativity. And there Weyl used a linear differential form with vector potential as [???]. And I tried to use this same form for quantum mechanical problems, so that I was inspired also by Weyl’s work; but I said it was the face of the wave function that was influenced by Weyl’s form. The right place for Weyl’s differential form was just the exponent — the face of the wave function — and not the Goud's. Perhaps this is one of the reasons.

Kuhn:

Yes. You told me — and it is interesting — that your seminars had been both on relativistic problems and also on quantum mechanical problems. Now, that would not always have been the case elsewhere. In other places one might have done a lot of quantum mechanics without ever doing gravitation theory. You know, there were many places that were not that much interested in the general theory. Now, had you yourself gone on between 1922 and 1926 working on both of these sets of problems? Later you do both. You said you did your habilitationschrift on adiabatic invariance. What other topics did you work on before 1926?

Fok:

You know, I had different subjects of investigation. I have published at that time a paper on integral equations, a mathematical paper, and also a paper on the theory of illumination, Lambert's Law — that, one, it was possible to introduce the vector potential of illumination. I was young then and I worked in different lines. (laughs)

Kuhn:

Did you do other things in quantum mechanics or other things in relativity before 1926?

Fok:

No, I believe nothing to be mentioned. You know, these papers of 1926 were well accepted by Ehrenfest, and he recommended me to the Rockefeller Foundation so that I had the possibility of a stay in Göttingen during ‘27 and '28 — from August ‘27 to August ‘28. But at that time I attended Born's Lectures and thought over all this, and what I made myself then was something on the collision problem. Soon after I returned to Leningrad I wrote an investigation on what is now called The Hartree-Fok method. That was soon after I returned.

Kuhn:

Did you find the atmosphere of physics in Göttingen very different from the one you had known in Leningrad?

Fok:

Heisenberg was no more there at that time.

Kuhn:

No, he was in Leipzig.

Fok:

He was in Leipzig. I met him then in Leipzig. Then I met for the first time Dirac in Göttingen, and I believe that I attended his lecture in Leipzig on his equation — the Dirac equation.

Kuhn:

How did that seem to you — the Dirac equation? You, after all, had done a relativistic wave equation.

Fok:

(laughs) It was quite new for me, and this introduction of new degrees of freedom of the electron seemed to me of particular interest. I found that it was quite, in the German sense genial. (laughs) How do you say it in English?

Kuhn:

There is no good English translation. “Appealing” comes close, but really it does not translate well.

Fok:

Yes.

Kuhn:

Yes, I know what you mean. Had you made any attempt before this to put spin into your own wave equation? You said when you did it, you did not know about spin. And of course you might have known —

Fok:

I knew that this relativistic wave equation that I proposed did not agree with experiment because of the magnetic influence, because of the non-conservation of the spin, but I did now know how to make this, and only Dirac has shown this.

Kuhn:

Of course that was a very different approach.

Fok:

Yes, a very different approach. Perhaps it would be promising to try to combine Pauli's results concerned with the spin, since they were the first concerned with the magnetic properties of the electron, but. I did this. (laughs)

Kuhn:

Was there more activity in Göttingen when you were there than there had been in Leningrad? Did you find people —?

Fok:

I don't have the impression that there was more activity.

Kuhn:

I know when Americans went to Göttingen in 1927, often, though not always, they had the impression that they had not known what was really going on in physics. Now, they had been reading about quantum mechanics, but suddenly the whole level of conversation changed for them. That would not necessarily be true coming from Leningrad, but I wondered whether there was any of that same sense.

Fok:

You know, I had the impression that the maximum of the activity in Göttingen was perhaps earlier, before I came there — perhaps.

Kuhn:

Was von Neumann there while you were there?

Fok:

Yes.

Kuhn:

And Wigner also?

Fok:

And Wigner also.

Kuhn:

Because I did not know that you would be here, I did not have a chance to prepare. Often I try to find out who was there the same year that you were there so that I can ask you, but I must now rely on your memory.

Fok:

Yes. I remember some people: Born, Professor Courant, then Wigner, then Rosenfeld; then Hylleraas, who died some years ago and Heitler.

Kuhn:

Was Weisskopf there then? Or did he not come until a little later?

Fok:

I knew Weisskopf several years later when he was in Russia.

Kuhn:

One thing that was an issue for many people but most of them in Copenhagen after the Schrodinger equation is, of course, the whole problem of the interpretation of the Schrodinger equation.

Fok:

Yes, but that was a later period, a later period after '27.

Kuhn:

Not really; not there, it was not. ‘Twenty-seven is the Heisenberg indeterminacy principle.

Fok:

Yes. This is the beginning of the true interpretation.

Kuhn:

But when I say people were worried about it — See, it was Heisenberg's feeling in ‘27 or the beginning of ‘28 that really after the Como Conference and the Solvay Congress at the end of ‘27, that it was all finished; that they finally had the right interpretation. But in 1926 and earlier in 1927, there had been deep worries about it. Now, did you encounter these?

Fok:

You know, in 1926 I believe there was no true interpretation of quantum mechanics because the ideas of Max Born were often interpreted in a statistical way, as if there were particles in the classical sense, but the statistics of this classical particle is governed by the wave equation; and this is not the correct interpretation.

Kuhn:

No.

Fok:

I became more concerned with the interpretation mainly in the '30s. I published a book on quantum mechanics, and that was the first book published in Russian on the subject — in '32. And at that time I did not know the true interpretation of the wave function, but nevertheless when I read this book now, I find no mistakes. I simply expose such formal part of the quantum mechanics, and then I give some remarks on the superposition principle, and these remarks turned out to be correct in spite of the fact that at that time I did not know the correct interpretation. Then I remember a visit of Professor Bohr to Leningrad. That was in 1934, I believe. I spoke with him on the physical meaning of the wave function. Then I expressed my opinion that since a wave function is connected with a state, then there must always be some wave function. Bohr was skeptical about this — he did not agree but, as he always did, he expressed his disagreement in a very delicate way. And I felt this. Since that time I thought over and over this question, especially after the appearance of Einstein, Rosen and Podolsky's paper and after the publication of Bohr's answer. I then translated this into Russian, and it was published in the USPEKHI, the Russian review, with my own comments. Well, I took fully and completely Bohr's view. You know, at that time there was a discussion, quite a philosophical discussion, in Russia on this subject. Some papers were published against Bohr and against me, since I defended Bohr's views. Now it is all in the past, but at that time it was not so easy to defend this point of view. Now, since that time I wrote several papers in which I tried to give a more convincing explanation of the true interpretation of the wave function and the quantum mechanics in general. I did not alter the basic principle, but I found some more appropriate expressions and so forth. It was in 1957 that I spent a whole month with Professor Bohr at Copenhagen, and then I had the possibility of discussing with him, and I first tried to discuss what we are now discussing. But it was not easy, because Bohr wanted to express his ideas, so for the man who spoke with him — it was nearly impossible to react to his ideas; so that I prepared such a memorandum or a paper with the expression of my point of view. I criticized some of Bohr's expressions, like uncontrollable interaction and also symbolic character of quantum mechanics. And with some of my remarks Bohr agreed, and this can be seen from Bohr's paper entitled "Quantum Physics and Philosophy.” He sent me in English — and I translated this into Russian — and this was published in the USPEKHI PHYSICS NAUK, the Russian journal. So that it was my great satisfaction that Bohr accepted some of my corrections. It did not alter anything substantial. Then later I made the translation, and published in Russian, Bohr's book. You remember —

Kuhn:

The collection, let's say.

Fok:

Yes, the collection. And then Bohr wrote a preface for the Russian edition, a very kind one. He mentioned me as an old friend of him, and I was very proud. For the last time I saw Bohr in ‘61 when he came to Russia. That is nearly all about my views on the interpretation of quantum mechanics. Yesterday I had a lecture here on the same subject.

Kuhn:

It's partly I did not know you were to be here, but unfortunately, my seminar is Tuesday afternoon, so there was no possibility for me to attend. I wanted very much to. You know, in this country there are some physicists who are very much interested in the interpretation problem, but not very many. In general physicists, most particularly the younger physicists, are impatient with this subject and think that either the problems are solved or if they are not solved, they should be left to the philosopher — that doing physics is now something else. Is that true in Russia now also or are Russian physicists still (I know of your own concern and I share it) interested or are they also impatient of these more philosophical problems?

Fok:

No. Most of them accept Bohr's views and mine also. But some of them try to make something else, something like Bohm in your country, but they are of no influence. Also it is different in different places. In Leningrad University, where either I teach or my pupils are teaching, they expose of course Bohr's views and my views. But at the Moscow University there is some misunderstanding of these views. They always are very glad when somebody like De Broglie or someone writes against Bohr.

Kuhn:

Who represents that position in Russia? Who are the figures at Moscow who particularly approve of the De Broglie or the Bohm or the Vigier position?

Fok:

Perhaps Blokhintsev. But among the philosophers, I believe that mostly my point of view is accepted. One of the leading philosophers, Omelianovsky, does accept. If you are interested in these questions, I may refer you to the American journal SLAVIC REVIEW, the number of September ‘66. There is a paper by Loren Graham, a paper with comments by myself.

Kuhn:

I have not read Graham's paper, I have it sitting on my desk in an offprint, but I did not know about your comments, because though they are in the journal, they are not part of the offprint, so very good. I'm much interested to know that you did comments on that paper. You spoke before of the period in which it had been difficult to talk about the issues in Russia. Was the effect of that period largely or entirely on discussions of problems of the interpretation of quantum mechanics, or did it also affect the practice of mathematical theoretical physics in a more central way?

Fok:

You know, most of the physicists kept their opinions for themselves and ceased to discuss; and they worked as before.

Kuhn:

So they worked on the same problems, and —

Fok:

On the same problems, yes.

Kuhn:

— the same things they would in any case have done. It was not then like biology today.

Fok:

You must excuse me. I must soon go to New York.

Kuhn:

Good, Listen, you have been immensely kind, and I am very grateful to you, and it has been very interesting for me.

Fok:

How do you intend to use this information?

Kuhn:

What we will do with this, what we have done with all these other interviews that we have conducted (at least if you will permit us to) is: We make a transcript which I then edit to get the spelling, to get the names right, to take out some of the repetition, but leaving it as nearly as is possible so that it can be read with the original conversation. Then this is put in the library at the American Philosophical Society at Berkeley and usually a copy also in Copenhagen.

Fok:

Could you send me a copy to the Leningrad University?

Kuhn:

Of course we could. There is no publication —

Fok:

There is no publication, but —

Kuhn:

They are there for the use of students of the history of modern physics, of the quantum theory.

Fok:

I know that there is no publication.

Kuhn:

Yes. So the only thing that the project has published is the thing you have seen, which is a list of materials. Other people will publish, but if they want to quote they must ask. Let me say it will not come to you immediately. It is hard to get these things typed up and edited, but I will make very sure that you get a copy. Do not expect it next week. I would say it may be two months, particularly because…

Fok:

I would also like to remember your name.

Kuhn:

Would you like to write it or shall I write it; would you like the address also or just the name?