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Interview of Lothar Nordheim by Bruce Wheaton on 1977 July 24, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/5074
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Interview covers Nordheim’s life and career to 1976. Topics include family background, education at Hamburg, Munich, and Gottingen (grad. 1923, position 1928-1933), recollections of development of physical theories (1920s) and of schools and physicists; trips to Cambridge, U.S.A., Russia, Paris and Holland (late 20s and 30s): positions at Purdue (1935-1947) — secrecy and scientists’ political involvements; and work on H-bomb at Los Alamos (1950-1952). Concludes with opinions on postwar physics, Oppenheimer, and Carter’s Energy Program. Interspersed are discussions on Germany (culture, politics and economy) in 1920s through 1940s.
Today is July 24, 1977, my name is Bruce Wheaton and I’m in the La Jolla home of Dr. Lothar Nordheim. Dr. Nordheim, as I mentioned in the letter, I would like to expand somewhat upon the interview that you gave in 1962 for the SOURCES FOR HISTORY OF QUANTUM PHYSICS. Expand it both in terms of subject fields within physics that we discuss and also the time span. That interview pretty much ended in 1930. But I would like to know something a little bit more about your early family background. Information of this sort is of particular value in reconstructing one’s motivations within physics and understanding how physics as a discipline has changed. It has changed a great deal as I'm sure you have experienced.
You were born in 1899 in Munich?
You mentioned in one of the sources that I read that your father was a doctor?
A pediatrician. But the family was a merchant family?
That is correct.
Do you have any notion of how many generations back that was true?
The origin of the family was in Memmelsdorf, a small town in Bavaria. Then they immigrated to Hamburg and became merchants on a rather grand scale. Before the First World War the family was very rich. But that evaporated during the war and later in the inflation and so on and so forth.
There had been at least a generation or two before your father:
Oh, yes. There were actually two generations before my father. My father was a very intelligent man. He divorced my mother in 1920. In a way it was a disadvantage that he was from a rich family because he hadn't needed to complete things. He started many things for instance; there was a heritage from one of my granduncles who left a great deal of money for charitable purposes. On the urging of my father they founded a hospital for tubercular children, the See Hospital Nordheim Stiftung in Cuxhafen on the ocean near Hamburg. The name was changed during Nazi times. However, now the old name has been restored and its scope has been greatly expanded. Then he started a Sauglingsheim, that means a home for infants, and he had some theories but he never stayed with these things very long. After the war he had to take up his practice and make a living that way.
I see. He had not been practicing then when you were growing up?
Off and on.
Do you recall where he went to medical school? Where he studied?
How large was your family? Did you have siblings?
Yes, I have three sisters.
Younger or older than you?
One is just a little bit older and two are a good bit younger.
In this period of time when you were growing up you say your father was practicing on and off. Was it necessary for him to practice for a living as such?
We moved back and forth between Hamburg and Munich several times.
I see. This was motivated by his interests in his professional work?
Partly that, yes. As I said, he had studied in Munich and married in Munich but the family had roots in Hamburg.
So it was as though the family existed in two places and you just transferred back and forth periodically?
Right, more or less. I was born in Munich and then we had some years in Hamburg and then we returned to Munich. But we went back to Hamburg at the time I went to the Gymnasium.
I see. So your very earliest years were spent in Munich and then...
Back and forth.
Did your mother raise the children or did she do something outside of the home?
No. She raised the children.
Was there anyone else in the family who helped raise the children? Did you have help to do that? Did she have help?
The family was rich before the first war and we had a big house in Hamburg with the servants one could have at that time. Then when the marriage broke up, my grandfather bought a house with ample grounds near Munich (Schleissheim). Of course, then we had very hard times. I started studying in Hamburg and then went to Munich. That is described in my biographical sketch.
When was the family broken up?
So this was after you had completed the Gymnasium. The period of time that you went to the Gymnasium is of great interest to me. I was wondering if you had any exposure to scientific subjects or scientific methods of study before the Gymnasium. Did you collect anything as a young man?
I was interested in astronomy, also in science and popular accounts of these. I really did not have time to go beyond that. At the Gymnasium I was very good in mathematics and sciences. The old languages are not my cup of tea.
Was there anyone in your family who introduced you to some of these popular treatments in astronomy?
This you found on your own?
You recall any of the titles?
There was a yearbook for young people called NEW UNIVERSUM. It came out every year and it generally had quite a bit of material on a rather popular level, of course. Then I had some books on astronomy and so on.
So you had done quite a bit of reading in scientific subjects even before Gymnasium?
During my Gymnasium years.
You said at one point, I think, that your father was a very cultured person. You described him as cultured. Was that expressed in your home life in terms of art or music played in the home, or was this something that was largely restricted to your father who would attend concerts?
Ours was not a very musical family. But my father had a gift for languages. He had traveled widely and he had deep interests in history, the arts, and politics. He also had a fine collection of paintings of the classic Dutch masters. He wrote a little drama once and things like that. And he told stories. He was very good at that.
So in 1910 you went to the Gymnasium in the Gelehrten Schule des Johanneums?
In 1911. First we were taught at home by various tutors. Then I went for a quarter of a year to a Gymnasium in Munich and then we moved. I entered the second year in Hamburg and stayed through until the end of the war.
You had private tutors for a short period of time?
Yes. Then I entered a school in Munich which was a preparation for the Gymnasium.
I see. What sorts of subjects would be covered? Mostly ancient languages or all of the subjects in the curriculum of the Gymnasium?
No. It was mostly grammar and some arithmetic and history and culture and so on.
fairly simply mathematics, though? Really not mathematics at all?
Yes. Arithmetic. Again that came easy to me.
Could you briefly describe the general curriculum at the Johanneum?
Oh, yes. That was strictly althumanistisch. It’s the oldest protestant Gymnasium in Germany, founded in the l6th century. We had nine years of Latin, six years of Greek, and then six years of French, four years of English. During the war the teachers were generally very old. The young people, of course, had to serve in the army and so in that way it was rather fossilized at that time.
So there were modern languages in addition to the ancient languages?
Yes. I did somewhat better than in the ancient languages.
And the normal curriculum would call for you to stay there nine years?
Yes. At that time.
What about philosophy? Did you study any philosophy in the Gymnasium? Did you read Kant, for example?
No. I did that when I was a student at the university.
So this was not ordinarily a part of the curriculum?
No. Of course, we read the old authors. We read some Plato and Cicero.
But nothing fairly modern?
No. Nothing modern.
What about mathematics at the Gymnasium? What level of mathematics was expected?
That was through the simplest algebra. Up to quadratic equations and trigonometry. But no calculus.
What about analytic geometry?
Yes. Some of that started early with geometry based on Euclid. Later on also some analytical geometry, in particular the conic sections.
Any natural science at all?
Yes. There was some physics at the end for two or three years. And before that some biology and even geology.
Mostly natural history?
Anything that you could call a little physics?
Yes. They had regular physics courses on a fairly elementary level.
This would be gas laws?
And simple mechanics. I mean falling stones.
But you would not, for example, have been asked to read any of the analytical mechanical treatises of the late Enlightenment or anything like d'Alembert. Anything like that?
1911-1918, that was seven years?
I had started with the second year at Gymnasium, and I would have normally finished in the fall of 1918. But I served for a short while in the army.
I see. Right out of school before you had finished?
You got the Nothabitur. And I had to do that twice. [Laughs] Because I was in a way very lucky. My year would have been called in 1917 as an eighteen year old but then I had an injury in my knee and was not called for one year. Even then it was: not quite healed and so I was not fit to serve at the front.
Other than the fact that the teachers were mostly old in that period of time, were you aware of the fact that the normal course of study at the Gymnasium was being disrupted by the war? What effect did the war have on this school? Or did it have no effect?
It had no effect on the curriculum. Of course, as I said, many of the teachers were in their 70’s.
One last question about the Gymnasium. Was this something that your family paid for? Your father?
Yes. You had to pay tuition.
There was no problem about that before the war.
There was no problem.
Would you say that it was at the Gymnasium that you learned what physics was?
You stayed in Hamburg?
Yes, since I already had started my studies in Hamburg when my family broke up, and my mother and sisters moved to Munich.
And you went to the university which was, I guess, a new one?
Yes. That was opened early in 1919. They had in Hamburg quite a few scientific organizations. For instance, there was the Stats Institut fur Physik and there were some mathematicians and from one I learned calculus and theory of functions. He was actually a Gymnasium teacher, but he was very good.
This was Blashke?
No, that was before Blashke; the first year. Blashke came the second year and since there was no theoretical physicist yet, he gave a course on analytical mechanics on quite a high level.
I see. So you had had calculus that first year from this Gymnasium teacher?
So you were in a reasonably good position compared to most students confronted with analytical mechanics.
Yes. It interested me very much. Blashke gave a seminar on mechanics and among the things — as side reading was a first edition of Sommerfeld’s ATOMBAU UND SPECTRALLINIEN.
It must just have come out.
It had just come out. I volunteered for the talk on the quantum conditions. And that sold me on theoretical physics.
I see. So it was at that point that you felt you understood what physics was.
Yes. Also there came out some books at the same time on theoretical physics. One by Arthur Haas came out just at that time and on that I worked very hard.
That book, if I recall, is heavily historically oriented.
It was quite historically oriented but it was a general introduction to theoretical physics.
I was just wondering since you mentioned that, what place the history of science played in the education of a scientist in Germany at that time. One knows today it plays almost no roll at all in education of physicists. Would you say that that was not true in Germany at that time?
There was no systematic instruction, but in general, the professors gave some historical background. But it was not a discipline by itself.
You were at Hamburg for two years?
At Hamburg, I was a year and a half.
And then you decided to go to Munich?
Then I joined my family there.
I see. Your family had already gone to Munich and left you in Hamburg?
Yes. I stayed in Hamburg for the first year. My grand-parents were still living.
Was life difficult in that early post-war period?
Oh, yes, of course.
Were you protected somewhat from that by your family's wealth?
To some extent. For instance I got help during all the post war years from an uncle of mine who took over the family firm. He was a bachelor. That made things very much easier for me so that I always had a little help.
This was in Hamburg?
In Hamburg, in Munich, and later on also at Gottingen.
So there were family reasons for going to Munich?
…and there was Sommerfeld.
And there was Sommerfeld. Had you known of Sommerfeld before reading the book? Had you been aware at all of work that was going on in atomic physics before studying Sommerfeld's book?
Not really. But this came out during my first year. As I said before, it was the basis of the seminar of Blashke’s.
And it made quite an impression on you.
It made quite an impression on me. So I knew who Sommerfeld was.
You went to Munich with the hope of studying with Sommerfeld?
No, I tried first in Hamburg, something more practical. That is, experimental physics. But I’m very unhandy and I was not very good at it.
This would be with Wien?
With Wien in Munich. And it didn’t work. I went to Sommerfeld's seminar and gave a talk there and caught his attention.
When you say that experimental physics was somewhat more practical, what do you mean by practical? In terms of eventual professional position?
Would it have been more likely to get an academic position in experimental physics or an industrial position?
Yes. There was a possibility for industrial positions. At least I had vague ideas about that. However, my ideal was an academic position.
This wasn’t the first thought in your mind?
I also vacillated in my first student year between mathematics and physics. I think I chose rightly in that theoretical physics was the right field for me.
Do you recall what it was you were trying to do with Wien that didn't work out very well? Did he assign a problem?
Just some little things to do, actually more or less a practicum experiment. I should solder some platinum foils on electrodes. I could not handle that. [laughs]
So you moved over to the theoretical institute, caught Sommerfeld’ s attention and you were admitted into the colloquia that they have?
How many people would participate in the Wednesday colloquium at Sommerfeld’s Munich Institute in this period?
Oh, fifteen to twenty people.
And they would come regularly?
That was required if you were to maintain your position in the group?
Yes, of course.
Pauli was there at the time?
Herzfeld and Krutzer and among the students were Wentzel and later Heisenberg.
Pauli was no longer a student?
He was, you know, a Wunderkind, and he had already written his encyclopedia article on relativity.
Was the official Wednesday colloquium the center of physics activity at Munich or did you have private group meetings amongst the students? A study group, people to get together to discuss literature besides the main colloquium?
One talked about physics. But mostly it was Sommerfeld and Pauli who were the real driving forces.
How would you characterize Pauli at that point? Or rather, what was your impression of him at that time? Can you recall that? When his impressiveness was still localized in a sense and had not yet spread over in so many domains?
He was a phenomenon. In a way it was a little bit discouraging because he was so much better and faster and knew so much more. He was about my age.
How would you characterize Pauli’s relations with Sommerfeld himself?
I think they were very good friends. Sommerfeld was very much interested in the young and promising people. He had generally a big school. Many of the future physicists went to study with him.
Did you feel that there was ever any animosity between the two of them? That Sommerfeld perhaps resented the success of his star student at that point or...?
No, I don’ t think so.
That wasn't part of Sommerfeld’s...
That was not in his makeup.
Were you ever aware in Munich at that time at the institute of any incipient anti-Semitism? Was there any hint of that?
I think that on the side of Wien. This was one of the reasons I didn't get any place with him. But not in Sommerfeld's group.
Would you characterize a little bit more what your feelings were for Wien's institute? Was it just a vague problem that you couldn’t quite define or were there more specific incidents that come to mind?
No, there were vague problems. I felt I didn't get anyplace. This was only a very short time, and then I switched over to Sommerfeld.
Was there any indication that this was also felt by other students in Wien's institute?
It was only a few weeks. I hardly got into contact with them.
You had no feelings of that sort at all in Sommerfeld's institute?
No, not at all.
Another question: this is right in the beginning of the inflation. I was wondering if that had any effect on your ability to do the work that you wanted to do there?
I went to Munich in 1921.
So things hadn't really gotten out of hand yet.
They were out of hand when I went to Gottingen in ‘22 and '23.
There was no particular effect that you recall in that early?
Life was not easy. The financial situation of my direct family wasn't very good.
You had then made a choice, when you left Wien’s institute for Sommerfeld's, that you were primarily interested in theoretical physics. What was you’re feeling about the split, if you can call it a split, between mathematical physics and physics based upon empirical studies? One is aware at that time that there was a certain growing animosity in some quarters, of empirical physicists against the purely theoretical mathematical work. Were you conscious of any of that? What was you’re feeling about it at the time?
Well, there was no contact between Wien and Sommerfeld, for instance. But later when I came to Gottingen, of course there was excellent contact. There were Born and Franck, who were very close friends, and worked together.
Could you say, in that period of time, was the lack of contact between Wien and Sommerfeld in Munich more characteristic of the situation in Germany? Or was Gottingen more characteristic?
I think the Munich situation was more characteristic. Generally, at that time, universities were built up around the professors. And each professor had his own little domain which he guarded very carefully. It was not, as in the American system, where you had an institute with many professors and so on. In Gottingen, it was more the other way around. There was much more contact between different branches, and often neighboring sciences and so on. That was in some respects much better.
I see. In saying that you felt that the situation in Gottingen was much better, did you feel that in Munich the lack of contact between Sommerfeld and Wien actually impeded progress?
Well, I was a very young student at that time, and Sommerfeld's circle was very active and so on, so I really didn't feel that very much.
Sommerfeld then recommended you as one of Hilbert's Hauslehrer?
On the basis of what work you had done at Munich, that he made that recommendation? Or were there a number of things that you did?
I think he had a favorable impression of me. I gave another talk at his seminar. And we talked about a dissertation. I think I have described it.
Yes, you have.
So, when Hilbert asked him whether he had somebody to recommend, he recommended me.
I see. Do you think this was because; from the very beginning, you took a strongly mathematical approach to the sorts of problems that were under discussion? More so than other students?
No, I don't think so. I didn't work out any problem of my own during the time I was in Munich.
There seems to have been a critical decision made, probably in Munich, perhaps shortly thereafter, that you would go on in physics, rather than in mathematics. You mention at a few points that you had, I think in response to a question in this interview of, “why did you write the article in the HANDBOOK ON MECHANICS?” that you were very much interested in the basic principles behind analytical mechanical systems. Hamiltonian formulations and what have you. I was just wondering, what was it that kept your interest alive in physical applications of mathematical principles of that sort? Why did you choose to stay in physics, rather than perhaps switching to mathematics? Or did you ever have an interest in pure mathematics?
I did during my first year in Hamburg. But I decided to go into physics when I went to Munich. I took some mathematics courses from Lindemann, who was a very famous mathematician, but he was quite old fashioned, and didn’t have much appeal to me.
What about, though, when you came in contact with Hilbert? Did you have any second thoughts at that point, that perhaps you would be happier in pure mathematics?
No. I was hired by Hilbert to help him in physics. This was in statistical mechanics, which always very much interested me. Then quantum mechanics, the old quantum mechanics. And then when the new quantum mechanics and wave mechanics came out — I was sold on theoretical physics, once I got into quantum mechanics — the old quantum mechanics.
And that was done to instruct Hilbert?
It started with Blashke, when I learned first about atomic theory Bohr’s theory.
I see. Did you learn the Bohr Theory from anything other than Sommerfeld’s book under Blashke?
It was mostly Sommerfeld’s book. This was the prime source at that time.
You said in your autobiographical notes that it was with some relief that you left your position with Hilbert in 1927. What did you have in mind when you said that? What was the problem?
First I must say, during the time I was his assistant, he was very sick. And not the genius he had been. He lived very much in the past in a way. His mathematical interest was logic, which was not terribly appealing to me. But he had the conviction that the best thing for a young man was to work with him. That was a reward in itself. And everything else, financial and family considerations, would be way down in importance.
Were there family and financial considerations in your case that you felt were not receiving enough attention in that period?
Yes. I felt it was, in a way, a dead end. For instance, Bernays, who was the mathematical assistant of Hilbert at that time, and a very nice person, he was Hilbert’s assistant and he was completely taken up by him. He was a good bit older than myself, and didn't seem to have any career, except being Hilbert’s assistant. Then, through Franck and Born, I got this Rockefeller fellowship which permitted me to travel around. With it came the prospect to become an assistant at Born's Institute afterwards.
I see. You had had close contact with Born in the years 1922 through '27 while you were with Hilbert, is that correct? Or could you say that, although you were officially with Hilbert, nonetheless you were interacting very closely with Born, is that right?
Not as closely as his direct assistants. Of course, there he had always a choice. I took my PhD with him. I think I wrote something in my vita about that. Also, in the interview with Heilbron.
Yes. Could you characterize the difference between Born's relationship with his group of students, and Sommerfeld's? Was there more interaction between a student and Sommerfeld, working on individual problems, or was it more of a group effort, compared to what happened at Gottingen under Born?
Born was a fairly reserved person, in his nature and in his makeup. He was an admirable person, but it was difficult to get really closely involved with him. Of course, he did some of his work, his creative work, in close collaboration. For instance, the beginning of quantum mechanics, with Jordan and Heisenberg, and I'm sure they had much closer contact with him than I ever had.
I see. One reads, for example, of Sommerfeld inviting students to come along on skiing trips, where a lot of physics was discussed. Would anything like that happen with Born?
Much less. There was some music in his home. And he was a good pianist. If he got someone, he liked to play pieces for two pianos.
And some of his students did that?
Yes. For instance, Heisenberg, although he wasn’t there very long. I forget which year that was. They played piano together.
Did you get the feeling at all that Born was somewhat dependent upon his students for ideas to develop, or not? Or was that work that he originated, and then had students help with?
Oh, yes, the latter. He originated many ideas. And he inspired people to do things. For instance, he gave me this thesis subject, but I worked that out essentially on my own; and he later suggested this work on collisions, according to the old quantum mechanics; and he sketched some ideas which I then worked out while he was away from Gottingen.
I see. Did you feel that you received as much credit as you felt you deserved, for the work that you did there? Or was it sometimes incorporated into other people's work, in a way that perhaps distressed you?
Not really distressed. Generally, Born acknowledged things. I think that the work on my thesis, the mathematical work, was really quite important at that time and laid the basis for seeing that the old quantum mechanics did one-body problems nicely, but failed in many-body problems. I really worked out the basic mathematical approach to that.
Had there been any other clear indications, before your thesis, that the many-body problem was not solvable?
Yes, Kramer worked out the ground state of the helium atom and got the wrong answers. Then later, Heisenberg studied the excited states of helium and found that what you got out of old quantum mechanics had nothing to do with what was observed. And that was all expressed in Born's first book on quantum mechanics.
The first volume. Explicitly called "The First Volume" because he expected that a second volume would be coming when the new mechanics was discovered.
What about physics generally, as it was seen in Gottingen in that period of time? There are a number of issues that are of interest to me. One is that the literature was growing very quickly. The number of papers that was appearing was accelerating.
Was there any problem? It’s nothing compared to the problems today, but were there any problems connected with just simply keeping up with work as it came out?
Yes. It was always difficult at that time.
Sommerfeld, of course, had connections, and found out new spectroscopic data before it appeared in print. Was that something that was also true in Gottingen? Was that one of the reasons for the close connections between Franck for example and Born? Or was that one of the products of the close connection? Was there a notion that physics would advance more rapidly if empirical work and mathematical work were able to keep very close contact with one another, and develop simultaneously?
I think that both Sommerfeld and Born had that very much in their minds. It required very close contact between phenomena and theories. So, the same with Bohr. And in Munich there was at that time nobody who worked in experimental atomic physics. Later, Gerlach came there, but that was much later, I believe.
In addition to the inflation of papers, what about the economic inflation at that point? Did that impinge in any way that you recall on one's ability to continue doing research work in physics?
Not really. I had a small stipend as Hilbert’s assistant. It wasn’t very big. But I got some additional funds from my uncle in Hamburg. That always took time, to mail things — he did that then every week — and as soon as you got your hands on some money, you went out and bought something to eat.
Something real. What about other students though, who were not in perhaps as fortunate a position as you in that respect? Were you aware of any other students in Gottingen who were impeded in their ability to do physics because of the inflation?
I don't think, really. That was, of course, over the whole of Germany, that these were very difficult years. But through all that time up to the Hitler take-over, culture, arts and sciences flourished in Germany tremendously. In physics of course, really it was one of the focal places. Not the only one, but really quite dominant. And it was the same in art and literature, the theatre and so on. So, in spite of the difficulties of living in the Weimar Republic, culturally, these were very good years for Germany!
Do you think it might be possible to say that it wasn’t so much a matter of "despite" as it was perhaps “because of”? Did you see anything that might tend to corroborate a notion that perhaps it was precisely because of the great difficulties of living there at the time, economically and in other senses that this tended to stimulate creative work in the sciences in particular or in the arts in general?
It may be. Also, it was a time of intellectual freedom, after the Empire and the war, though the Empire before the war wasn't so bad, after all. But there were no limits in any way, for cultural and artistic approaches during the Weimar years.
For example, it has been suggested that, precisely because there were no limits to creative expression, or seemed to be no limits, that this might have exercised some influence which made it more likely or more possible for physical theory to become less deterministic or less causal that one was no longer necessarily committed to seeking causal relationships in nature? Do you think there's anything to that generalization? Nordheim; I think it was rather the other way around. This state of affairs maybe helped the acceptance of the new ideas in physics, in quantum mechanics, that it was not as casuistic as people thought before. It might have helped. But it didn’t come out because there was this new feeling, but because to explain physics and the duality and so on, you had to go in that direction, to make any sense out of it.
Was that already clear, say in 1922?
No, not yet.
When did that become clear, that you had to go in that direction?
Only when the duality between particles and waves was recognized.
That is considerably later.
That started in '25, ‘26, ‘27.
I was just wondering if, in this period shortly before matrix mechanics, let’s say, or before Schrödinger, if there was any feeling that mechanics, as such, was failing? Not just in individual cases, but in general? That mechanical representation of microscopic systems in nature was fundamentally inconsistent?
One felt that the old quantum mechanics, which was based on classical mechanics, was not the real answer. That was the theme of Born's first book on quantum mechanics, and we talked about that. One had the feeling [that] the superposition of quantum conditions on classical mechanics was something unexplained and unnatural. This was the feeling one quite strongly had. But one didn't know the answers. But they came with Heisenberg and Schrödinger. And experiments, of course the Franck-Hertz experiment and Stern-Gerlach, and Compton and Davisson-Germer and so on, which showed up the duality.
Would you say that in 1922 the duality as such was recognized? I mean, that there was incompatibility?
No, not quite. Then one tried still to work with the old quantum mechanics. One found that the old quantum conditions selected out the periodic solutions in mechanics. But for the many-body problem they are not stable. So that was an unnatural thing. The periodic solutions exist, but every small deviation would make them go away. One had the feeling that that was an unnatural thing, and that it didn't work. You could not get any good results, except in the direction of the correspondence principle for large quantum numbers, where you got the right answers.
One was seeking a new mechanics — but still mechanics.
Yes, right. To see how far one could go with the old mechanics, and then, of course, you needed new ideas.
You say there was de Broglie; what about de Broglie's work?
It was not recognized at once, but rather was considered as a curiosity. Then Schrödinger took it seriously, and that was the beginning of his wave mechanics.
But even just a little bit earlier than that, let's take the Compton Effect. What was the reaction to the Compton Effect? Was this looked upon as something impossible to explain, without throwing out well-accepted ideas? Was it something that made a big impression? Or was it just one in a continuing series of recognitions that there were serious problems that somehow had to be dealt with?
I think it was recognized. I don't know when I heard about that first. I think it was probably not in Munich.
December, '22, I believe, is when it was announced. It would have been the spring of ‘23 that it was discussed.
But then, in Gottingen, it made quite an impression. It showed that the light quantum was actually something tangible. Just as the Franck-Hertz experiment showed the existence of discrete atomic states.
What about the photoelectric effect?
Of course the photoelectric effect was explained in quantum terms by Einstein in 1905.
People, of course, knew of the paper, but did people take it seriously? It was based upon a hypothesis that asked a lot.
When I became conscious of physics and its principles, I think it was generally acknowledged. You knew there was a quantum — a light quantum — and first, of course, there was Planck’s explanation of the black-body radiation. Then Einstein's photoelectric effect. And then Bohr's atom. Then came all these others, Franck-Hertz experiments, and later, they were somewhat later I believe, Stern-Gerlach and others. And then the diffraction of electrons in the Davisson-Germer experiment.
Would it be possible to say that there was a distinction made, in the early 1920s, before matrix mechanics, between the light quantum, as a spatially localized unit of energy in radiation with a momentum that you can define [on the one hand], and the quantum of action, in collision phenomena on the other? Did one separate those two concepts? Was one more accepted than the other?
No, I don't think so. I think that the quantum was accepted, that is the light quantum, and also, after the Compton Effect, that it had momentum. But the trouble was, on the other hand, you have diffraction of light, the wave nature of light. That was cleared up only by the development of quantum wave mechanics.
There is a conflict there, between diffraction and interference phenomena on the one hand, and the quantum relations in the photoelectric effect and the Compton Effect for radiation on the other hand. But when you look at the quantum of action in this period of time, you didn't have that much of a conflict. You didn't quite understand why things should be quantized, but there wasn’t this internal contradiction that you have in the case of radiation. If my reading of those papers gives me any indication. Of course, I wasn't there. I don't know. I'm interested in knowing whether you felt at the time that these two notions were really combined into one idea, of “the quantum” that carried the light quantum with it — or whether the light quantum really was a separate issue, and was resisted precisely because of this internal conflict? What do you do with interference phenomena — in 1922, I mean, before Schrödinger?
Yes, that was the dichotomy which existed at that time, and which one more or less felt, and couldn't explain. It was not very many years later, then, when these things became clarified.
There were two people working on photoelectric phenomena at Gottingen at the time: Robert Pohl and Bernard Gudden. Was their work widely discussed?
Pohl’s work was always discussed in seminars and colloquia. But I'm not quite sure what, in these early days, Pohl’s work was about.
I was really wondering if you recalled Pohl's reaction to the Compton Effect. Pohl's in particular.
I can't recall anything about this. I did not have much direct contact with Pohl and his group.
But you felt that Einstein’s work was, at that point, 1922, early 1923, was fairly well accepted, both the 1905 paper and the 1917 statistical treatment of radiation?
And that one just said, "Einstein is borne out by the empirical relationships that we find, and that conflict that is inherent in his idea, we simply must accept”?
Yes. Both. The photoelectric effect was generally accepted; that's a quantum effect. And also, since the 1917 paper on radiation, that you needed, for instance, forced emission. Of course memory may play a deceiving role in matters that are now so generally and easily accepted.
You feel that at the time it was accepted?
So in what sense then was de Broglie's thesis a curiosity? He wasn’t to be taken seriously? Why?
It appeared first as a curiosity, that you could explain the hydrogen atom — the states of the hydrogen atom — as a kind of standing wave.
I think that isn't in the thesis. That was a later reformulation of the theory, I think, if I remember correctly… What about the notion of pilot waves as such? Was that what made it curious, that nobody understood what a pilot wave could be?
I'm at the moment not quite sure what was in de Broglie’s thesis.
Well, I was wondering what it was about it that made it a curiosity. I mean, in that context, it would seem that Einstein’s work would also be a curiosity; it seemed to give you some useful data, but it did that at the cost of insisting that you accept the notion that a particle could be diffracted in some sense. It would seem that if de Broglie's thesis was a curiosity, that Einstein's would be a curiosity, too.
The first recollection I have of de Broglie’s work was not the thesis, but it was his notion of the standing waves in atoms and this is the first real recollection I have of his work. Then, of course, Schrödinger took it seriously, and developed his first theory, which gave really the mathematical description of the electron waves.
Was Schrödinger’s wave mechanics the development that convinced you personally that some serious step forward had been made here, in late ‘25, early ‘26?
The full conviction arose when it turned out that Heisenberg's quantum mechanics and Schrödinger’s wave mechanics were identical — that they were different aspects of the same thing. And that didn't come so very much later.
Yes, but before that came, how did you think of atomic problems? In terms of matrices, or waves?
I tried to understand both. Of course, wave mechanics has its origin in Gottingen itself, and so, one tried to…
You mean matrix mechanics?
Yes, matrix mechanics. And so one tried to understand. One had to learn to operate with matrices, which one didn't do before. Schrödinger came about the same time; and about a year later, it was found that they were two sides of the same thing. And that was the clincher that convinced practically everybody.
You mentioned at one point that the treatment of collisions by the old quantum theory was never fully developed. Given the fact that matrix mechanics came along, one can understand why not. But you said at one point, I think, that had it been developed further, it might have led to many of the developments that then came out of matrix mechanics.
The work on my long paper on collision processes based on the old quantum mechanics was started before Heisenberg and Schrödinger showed the way to the new one, but it was published afterwards. However, it foreshadowed many results of later work, as was generally recognized.
Did you think at that point there was a purpose to following up and doing more work on it?
No. That should be done on the basis of wave mechanics and quantum mechanics.
When it had been shown that Schrödinger’s and Heisenberg’s approaches to atomic theory were mathematically equivalent, which way did you prefer using for yourself? In terms of your own conceptualizations of problems, were you more comfortable dealing with wave mechanics, or with matrix mechanics? You said you had to learn matrices. A number of people were in that position, in 1925, of all of a sudden having to go back and learn linear algebra and matrix theory. But which way felt more comfortable for you?
That depends on the problem. You need for instance, matrix mechanics to deal with such things as spins and angular momentum. It's a natural thing to do in that field. Of course, you can get some of it out of wave mechanics, but it is much more convenient to superpose some matrix mechanics on that. And if you have spin, then you have a discrete variable, and the spin variables, and the continuous position variables, and your wave function becomes a matrix itself. So you really cannot say “I prefer this or the other.” They are connected.
Coming back to the wave-particle duality that hadn’t quite yet been formulated at the point we’re talking about, what did you think of an electron then? What was an electron, in your mind? Had it become something that was dissolved completely into the mathematical formalism, or did it still retain some physical vestige, and if so, was it a particle or a wave, or neither or both? In that very difficult transition period, how did one think about physical problems? Or did one just not think about them?
Well, one felt that duality, that there is something not quite recognized, and that one could work with wave mechanics and get right answers, but that there were still difficulties in the interpretation. That was the concept of duality and so on. And that didn't come so very much after that, I think that was all sorted out by ‘27.
Yes. But in moving up toward that sorting out period, how widespread was concern over the issues that ultimately had to be resolved in terms of a probability interpretation of a wave function, or an uncertainty principle? Were there just a few people who were concerned about that — Born, Jordan, Heisenberg — or was it generally felt, at least at Gottingen, that here was a real serious problem, almost a philosophical problem?
Yes, that certainly was the general feeling?
It was? Did people discuss this, this philosophical problem that had popped up in the middle of physics? Did anybody give colloquia on how you might go about approaching this from a point of view quite outside of physics?
The problem was there. And you would probably not talk about it unless you had some way to go ahead. I personally was concerned at that time with the general transformation theory as initiated by Jordan and much more elegantly by Dirac.
[You wouldn't need to worry] unless you were confronted with an unsolvable problem in your own research, that depended on it?
That was not the case. Very soon, first Born got the “probability interpretation” of the wave function, and many people didn’t like that, of course.
Did he discuss this interpretation as it developed in his own mind?
Not with me. I was not then in his inner circle. He might have discussed it with Heisenberg.
But there was no public discussion of it.
I am not quite sure, I think that came also fairly early in the game. I’m not quite sure exactly the date.
Yes, I think it was early in ‘27. So what was the reaction to the probabilistic interpretation of wave mechanics then, when it was put forth by Born? Was this seen as the solution to a problem?
That depends on, on which side you sat. It was accepted in Gottingen and Copenhagen from the beginning, and people of that circle the Copenhagen circle that was rather wide. But Sommerfeld didn't like it. Schrödinger didn't like it. Einstein didn't like it.
But in Gottingen it was quickly accepted?
This was because of Born's influence in Gottingen, or because people were really convinced that this was the way to solve the problem that had come up?
In Gottingen, I think it was accepted at once. As I said, other people had difficulties in accepting it.
What was the reaction to the negative opinions of it — Einstein's, for example, or Schrödinger’s? What was the reaction in Gottingen to Einstein's reservations?
I think Gottingen people and Born himself felt that people might have difficulties accepting it, and understood it. For instance, Born and Einstein were very close friends, and they corresponded about that. It didn't hurt their friendship, I am sure.
Did people in Gottingen think that Einstein was raising valid issues? Or that this really was a subject that was not physics, that this was something that should not really be the concern of a physicist but was really more philosophy? It didn't really matter how you interpreted a wave function; you could calculate it?
That's a very pragmatic point of view. You want to have a consistent system of thought about it, and this was a philosophical question, possibly one just accepted it, but —
Was that recognized in Gottingen at the time, that it was a philosophical issue and not really in physics?
But you have to have a modus operandi. You know how to solve the problem, but not how to interpret it. I think it was recognized that it was quite a deep philosophical question, and therefore of great importance for the development of human thought.
Its profundity, you feel, was recognized in Gottingen at the time.
Yes. In my opinion, quantum mechanics is one of the greatest revolutions in human thought, both in its practical applications and philosophically. Practically, we now know how to calculate atomic effects and molecular effects, and it goes even into chemistry and biochemistry. We know the rules. Not that it can do everything, and it took a very long time to explain many things, for instance superconductivity. But the tools for normal matter are there. And therefore, it had tremendous practical effect. I think the philosophical effect is as profound. You get away from causalistics, strict causalistics, as the only possible way to think scientifically. That has been mostly expressed by Bohr — most profoundly.
But the recognition of that, it seems to me, takes a certain amount of time.
It takes perhaps a whole generation of new physicists, to confront this problem from the very beginning, so that they can then understand it or convince themselves that they understand it. It would seem to me that you would be dealing with a group of people who had been raised in fairly mechanistic and deterministic theories, who were then all of a sudden confronted with a very successful formalism, which was very difficult to interpret physically because it couldn’t be interpreted mechanistically. It was throwing out causal relationships that had formally been at the heart of physical theory, and I would expect that there would be a certain amount of resistance to that.
Yes, and there was. And there still is. And always, some people try to amend quantum mechanics, to get back to a mechanistic goal.
What is your feeling about that now? Do you think that there’s anything to that?
I don’t think it can be done. You have to change your way of thinking about many things.
Well, that was just in the period then when you left Gottingen, with the support of the Rockefeller Foundation.
So in 1927, with the help of the Rockefeller Foundation International Education Board, you were offered funds to travel. Could you go any place you wanted to?
No. Most of the physicists wanted to go to Copenhagen. So it was suggested that I should not go there, at the beginning. I was interested in statistical mechanics, and so it was a natural thing to go to Cambridge and seek connections with Fowler. Of course, the person to whom you went had to agree to that.
I see. Did you give any thought to coming to the United States at that time?
Not as a student, so to speak. There was very little in the matter of theoretical physics going on, of course. There were some people of my age group that were developing well — such people as Van Vleck and Slater and Pauling. Most of these people went to Europe to study the new quantum mechanics.
Can you characterize the general attitude in the German physics community toward American physics at that time? It was clear that there was not much going on in theoretical mathematical physics. What about experimental physics? How America was viewed say in 1927?
I think the general attitude was that it was still some out-of-the-way place. There were experimental people, like Michelson and Millikan, and Rowland and others who were recognized as first-cl ass experimentalists, but one still thought of America, at that time, as an outlying district.
Certainly with respect to theoretical physics.
So your first choice then was to go to study with Fowler in order to develop your interest in statistical mechanics. Where did you develop that interest in statistical mechanics?
I had always had it. I read first, and then very soon after I arrived in Gottingen, Hilbert gave a lecture on statistical mechanics, and I had to prepare him.
How far back did you go in your studies? Back to Maxwell's distribution function, or to Gibbs or the Ehrenfest paper?
Yes. The Gibbs and Ehrenfest papers had influence on me, and to some extent, Boltzmann. I had never really read Maxwell’s paper. Of course, Maxwell's work was at the basis of all statistics.
What was the general attitude about statistical treatments of mechanics? Not just about kinetic gas theory, but the use of statistics in physics? When you were first learning it; when you were preparing it for Hilbert?
You don't mean quantum mechanics?
No, I want specifically to keep separate from that. Once that came along there was a new motivation for statistical treatments. But before then, was this considered to be a perfectly legitimate way to do physics?
Oh, yes. Yes. It was considered to be quite legitimate at that time. You cannot avoid it when you desire to have an atomistic underpinning of thermodynamics.
And you chose Fowler because he appeared to be the most knowledgeable foreign expert?
Yes, and Cambridge was a good place to go. And, of course, living there, I learned English which was developing into the international language of science.
Did you already feel that to be the case in 1927? That it was becoming an international language?
Yes. For instance, I went from Cambridge for a few months to Copenhagen, because the English academic year was over and there was still some time left. There, the discussion was divided between English and German. So if you really wanted to take part, you had to know some English.
You had studied English at the Gymnasium. Is that right?
Yes. But that was not directed at speaking English. It was reading Shakespeare. Which was not so easy?
It's not been easy for me. What was the general feeling about British physics? Having already discussed American physics from a German perspective, was British physics considered to be second class? I don't just mean Fowler's work in statistical mechanics, I mean generally.
No, and particularly Cambridge was considered as one of the centers. There was Rutherford’s Laboratory.
But would that also be true in mathematical physics? I don’t think of too many people in Britain, at that time.
Oh, Eddington was still living, and Larmor. I’m not sure. At least he was not active. I'm not quite sure. But there was Jeffries. I mean, they are applied physicists. Oxford was one of the leading places in Europe in physics, in that subject.
Do you mean Cambridge?
Did you feel that your relations with Fowler were successful? Did you learn what you came to learn?
I learned how to work by myself, to put my own problems in order. He was very busy and very nice, in many respects, but I didn't have really very much close contact with him.
Who were your contacts while there?
In Cambridge, most people worked for themselves. But I played chess with Kapitza, and I saw quite a bit of Dirac. Kapitza had a private club. There were very few university-wide colloquia. He had a private club, the Kapitza Club, which generally took place in the chambers of Thomas. There were Hartree and Dirac and Kapitza and some younger people, and that was quite stimulating. But there was no general university picture — and that was quite different from where I went next — Copenhagen. There, the physics people in the Bohr Institute were one big family. One had all kinds of seminars and talks, and so on, so that it really was a most stimulating place at that time. Of course, many people loved to go there, to Copenhagen.
Did you feel that this isolation in Cambridge was detrimental to your work?
It was for me a very creative year. I had good ideas at that time. As I have not had at all times. So it was stimulating. And I made scientifically good progress, and learned English.
Did you have any contact with Rutherford at all?
Not directly. I think Blackett was there at that time, and he came also sometimes to the Kapitza Club.
What sorts of papers would be discussed at the Kapitza Club? Experimental work?
Yes. Kapitza himself was an experimentalist. Of course, very widely read.
So in ‘28 then you came back via Copenhagen to Gottingen?
Did you habilitate at that time when you came back?
And then became Born’s assistant?
Yes, all at the same time.
Someone once said that one of the reasons that Gottingen was able to produce so much good work in physics was that the physicists and the mathematicians shared a library. Is there anything to that? Did you think that there was especially close contact between mathematicians and physical problems at Gottingen, compared to other places?
I think there was closer contact with the mathematicians than at most places. Hilbert, of course, took up the physics side; he only could do one field at one time. In the course of his life, he took up most fields in mathematics and physics. About physics he said, “That’s much too difficult for the physicists." Then there was Courant, who was a good friend of Born and Franck, and who had interests in applications. He wrote the right book at the right time, the first volume of Courant-Hilbert when it appeared it seemed to be uninteresting, but then it gave the mathematics you needed for wave mechanics, and all the details that were known.
Were you conscious of a difference in the acceptance of the probability interpretation of quantum mechanics, between Copenhagen and Gottingen?
There was no real difference, I think. There may have been some differences but the principles were the same.
Were you aware of any difference in the way these issues were being discussed at Gottingen when you came back in ‘28, compared with when you left in '27?
Things had developed quite a bit since that time. The development was furious. I don't know whether from memory I can get all the dates, when the various things were developed, and the connection between quantum mechanics and wave mechanics, and the uncertainty principle and Bohr's interpretation of it and all that.
I wasn't so much concerned with the chronology of it as I was with just the general feeling. Whether or not people were now discussing non-deterministic theory in a more accepting way, when you came back than when you had left? Is there any general statement you could make about how well or in what way people were coming to grips with the changes that had occurred in physics?
In Gottingen, that was generally accepted. I think that Born’s interpretation of the wave function, in the statistics fashion, had been [accepted] already before I went away. Then with the general interpretation of the so-called transformation theory in quantum mechanics, you can look at all the things in a much unified way, which was partly due to Dirac. That was already going on before I left. All these things were completely accepted when I came back.
Were people already looking around for new fields within physics to apply the new formalism?
Yes. The advent of quantum mechanics made so much accessible, that it was very easy to be a good physicist at that time. You could almost tackle any problem and get a new point of view on it. Most of atomic physics, molecular physics, solid state physics, really the foundations were laid in the late twenties and then in the thirties.
Right in the middle of that period, you traveled again. Within a year, a year and a half of coming back to Gottingen, you went to the United States?
Yes, I came to the United States.
Why was that?
I got an invitation as a visiting professor at Ohio State University.
Who did that come from, do you recall?
They wanted to build up their physics department, and they invited Lande and Thomas, who stayed there, and then Heitler and me, as visiting lecturers.
Did this correspond to a particular point of development in your own work? Were you particularly receptive to this invitation? Or did you accept it because you thought that this would be an interesting experience?
To go to the United States — everyone liked the idea. In some respects, I had hoped maybe that there would be a career for me over here. In Europe the physicists were very abundant, compared to the number of places available to them.
You would have had a number of years to look forward to continuing as a Privatdozent?
Without much thought of advancing for a while?
1930 that was also the year of the summer Michigan Symposia. Did you have anything to do with those, since you were in Ohio?
No, I left at the end of the regular academic year. I was there for the second half of the academic year, which went to June, as it does now. Then I left for back home again, so I was only there for a limited time. And not for the summer. I went to the Michigan seminars later, when I came back to the United States.
Was your decision to come at all motivated by the events of the depression? You say that al so affected your family's money.
That was not directly connected with that. Of course, you like to go to the United States, and you got a comparatively good monetary reward for that. It was welcome.
Events had transpired that put you in a position where things like that were now welcome, whereas in the past they might not really have been necessary.
Then you went back to Gottingen. Is that right?
Yes. That was only one semester in Ohio. And then in Gottingen we had quite a nice group. There were Heitler and Teller and we were very close to each other and talked about many things.
The three of you?
Yes. And we had a joint luncheon place, where very often we asked foreign visitors to come.
Did Born participate in that?
But if somebody would visit, that person would participate?
I guess Ehrenfest came a few times in that period?
Yes, he did.
What was your impression of him?
He was a very stimulating person. Somewhat queer. He was a Socrates. He asked questions, and tried to get people to answer, to think and to answer. The Socratic Method. He also came to Copenhagen, and I visited Copenhagen several times during that era.
Did you ever go to Leyden?
Yes. I gave a talk there.
Yes, you mentioned that at one time; writing your name behind the blackboard.
So then you were back in Gottingen for another year and a half or so, before traveling again?
Yes. Then I got an invitation to come to Moscow. That was arranged by Tamm who invited successively Heitler and me, and there, I went for the experience.
Did Heitler go?
He was there before me.
What kinds of research were they primarily interested in at the Moscow Institute?
They were interested in statistical mechanics, and theory of solids I was asked to see if I could work together with Blokhintsev who was a student at that time, and soon became a fairly prominent person. We wrote a paper together, and I gave a course on statistical mechanics, and so, that was very nice. But otherwise it was very disturbing. I think I wrote about that in my biographical sketch.
Yes, you did mention that it was a period of famine.
Was that the primary cause of your discomfort?
And the living conditions. One should not be too explicit in that respect. I wasn’t quite well at that time, due to the difficult conditions, and certain facilities were simply beyond description.
What about the facilities for physical research at the institute?
They were very difficult. They didn't have anything. They couldn’t get anything in Russia itself at that time, and if they had to import it from the outside it took endless difficulties. So it was really very remarkable that some people were able to do good experimental work. Also, there was [very little] in the libraries and things came in only belatedly and so on. So it was a very difficult time that the Russians had.
How many people do you remember working at the institute? Tamm and Blokhintsev?
And Dorfmann in this period. I don't know whether he was at the same institute, but I talked with him on physics and I met a number of younger people.
Was Joffe there?
He was at Leningrad, and I visited Leningrad in vacation time.
Can you contrast the institutes at Moscow and Leningrad at all? Did you get enough of a feeling to do that?
I really don't. I was in Leningrad only a very short time.
Were you aware of any particular differences between the theoretical preconceptions in physics in the Soviet Union at that time, compared to the West?
Not at Tamm's institute.
What sorts of differences did you see?
From the people that I talked with in Russia, there was no difference in outlook. Of course, at times they had difficulties. But if you talked with them, there was no difference in outlook really, with respect to physics.
Were you conscious of any attempt to reformulate theory on the basis of dialectical materialism? Or did that have any effect?
No. Not the people I came in contact with. I know that there were attempts there. For instance, in Leningrad I met Frenkel who had also visited Gottingen before. He wrote one of the first acknowledged good texts on quantum mechanics; it had a universally accepted outlook. Politically, people accepted the Soviet regime and the state saying, "it may not be the best but it's much better than the times of the Czar.”
Even with the famine and all, and the living conditions. Do I recall that when you left the Soviet Union you went through Rome on your way back to Gottingen?
No, I didn't go to Rome.
I see. I had picked up somewhere in the literature that you had visited Fermi briefly in the early thirties.
No, I haven't.
You had met him in Gottingen?
[Yes] while he was in Gottingen, and we were quite friendly.
I see. He was only there a short time, though?
Yes. He was only there for one semester, or so.
And he didn't like it very much?
He didn't like it particularly. No.
Do you remember why?
He didn't find much relevance. Of course, he was always a man with ideas, but at that time they were rather half-baked. He didn't get much relevance from Born.
I guess he was searching at that point for the proper area to concentrate his interests; doing a number of things.
So you returned directly to Gottingen from Moscow? That would have been in —
Yes. I first saw my family, and I went to Gottingen, and of course it was just when Hitler took over.
Relative to your statement about incipient anti-Semitic tendencies that you perceived in Wien’s institute in Munich, was there anything like that in Gottingen that you were conscious of? I expect that there wouldn’t be in the Physical Institute, with Born and Franck.
There was none in physics and mathematics before the Hitler takeover. There was certain tension between, I think, Pohl and Born and Franck, always. But from the outside they got along quite well.
What about outside the physics institute, in the university generally?
There may have been some, not really in the sciences, from people I had contact with.
What about just living in the town?
There was nothing, really. Long before Hitler, one was conscious, [but] one really did not talk about that. I mean, I really didn't feel Jewish. I'm only half a Jew. My mother was from Austria, and was Aryan, and I was baptized as a small child. I can't do anything [about that] and my family hardly ever talked about it. They were a fairly famous family, and one didn't feel any difference, before the Hitler time.
This was true right up to January, ‘33?
In Germany, Hitler came gradually to ascendancy. That worried people quite a bit. Hitler, of course, talked against the Jews from the beginning. There may have been some anti-Semitism at the Gottingen University. However, at the departments with which I had close contacts, physics, mathematics, astronomy and physical chemistry under Eucken, you never felt it.
What was the reaction then at Gottingen, when Hitler came to power?
This was devastating. From the beginning, I: don't think anyone had any illusions. At the beginning people thought maybe one could do something. There was the famous instance, Franck's resignation first, before the dismissals came.
Was it a surprise when Hitler came to power?
No. One always hoped maybe it could be avoided in the long run, but everything went in this one direction. Once he came to power, became Reich chancellor, people were very much afraid that that would be permanent. Then came these things, like the Reichstag fire, and so on, and I think most of the people I talked [to] felt from the beginning that they would all have to leave, and that the Hitler regime would ultimately lead to war.
From the very beginning?
Yes. And, of course, it killed the university life in Gottingen and the scientific life as well. During the Weimar Republic that flourished. That was stopped entirely, and has never been completely resurrected since.
So you feel it was clear from the time Hitler came to power, even before the race laws were officially enacted, that you would probably be leaving? Before it was made illegal for persons of Jewish ancestry to teach at the university, were there reactions in the university? Were people told to stop teaching, even before the laws were enacted? Or did that wait until the legislation passed?
The first hints of the legislation came rather early. First they were in somewhat minor form, for the summer term, which in Germany started in May. All people with Jewish antecedents were inactivated. They got their salaries paid, but they weren't allowed to teach. That is the first thing. Landau, who was one of the mathematicians in Gottingen, and who had been appointed professor before the First World War, he did not fall under this law because he was so early getting his position. But when he started to try to teach, there was a demonstration.
Student demonstrations and so on. Also, it is clear that they were pushed by the Nazis, people who led them. And he could not teach.
You mention in a few places the great help that Franck was in this period of time in Gottingen.
Would you elaborate a little on that? Just what did he do that was helpful?
First, of course, there was enormous correspondence all over the world, to find places for the people who had to leave. And then for these people and a few others he held a seminar where we talked about physics mostly. That was very stimulating and held the people together, so to speak, and made them partly forget. There was enormous activity in finding places for all who had to leave.
Positions were sought in any country outside of Germany?
In any country.
Including the Soviet Union?
In the Soviet Union, in Turkey, the Turkish government offered to take some people at that time. Some people went.
Dessauer I guess went to Turkey.
In a way, I was lucky, because I was young and had just made my name and was promising, but not so old that it would take very much money to get me. Also, as a former Rockefeller fellow, the Rockefeller Foundation always helped out. If someone wanted me, the [Rockefeller Foundation] paid at least half of it. In that way, I had some anxious times, but I was never out of work, or didn't know where to go next.
When did the offer from Brillouin come to go to Paris?
I don't recall exactly when it came. I had some contact with Brillouin before, and he liked very much the paper on the theory of metals that I wrote. I went to Paris, largely with Rockefeller Foundation money.
This was in the fall of ‘33?
It was in the fall of ‘33.
But that time there was no question in your mind that you had to leave.
There was no question, whatsoever.
What were your feelings on leaving about physics? Did you feel that this was the passing of an era of German physics, that this would end that?
Yes. That was quite clear, from my experience in Gottingen. We were a very flourishing group in physics; it was at once dismantled, and disappeared. That was more than at any other place — Born, Franck, Heitler, Teller, myself — all had to go Pohl stayed with some of his assistants. Dr. Herta Sponer, who was very close to Franck whom she later married, would certainly go in course of time, though she was Aryan.
What was Hilbert’s reaction?
At that time, I didn’t have contact with Hilbert anymore. There's a book, HILBERT, by Constance Reid, which gives some information on this topic. Apparently he didn’t quite understand things.
Were you able to do some work the year that you spent in Paris?
Oh, yes. But I worked on my own. I corresponded with Heitler about some things, and I wrote some papers. But in France at that time the structure was set. It was very difficult for outsiders to get into it, and it was quite clear that it would not be a permanent solution.
Not because you felt that whatever trouble was going to develop in Germany would spread to France?
No, certainly not. However, the possibility of a war, to be later initiated by Hitler, could not be discounted. The French scientists are a closed group, and you have either to be related to one of the old professors, or have married their daughter to get in.
Where had Heitler gone?
To Bristol. And later to Dublin, the Institute of Advanced Studies.
So you then went to Holland?
I then went to Holland. I got invited by Fokker and I talked with Brillouin about that, and he said, "Yes, you should take it,” because of the feeling he had that it was very difficult to get accepted into the [French] academic circles. Because [that is how] they were, not because they were anti-foreigners.
Did you feel that this enforced wandering disrupted your own output in physics? Or did it act to make you find solace in the physics that you could do?
Yes, I think the latter is the case. I didn’t have anything else, didn't have to teach, and so I could concentrate on physics.
But you felt that these were not going to be permanent positions, either one of them.
So you came back to the United States again.
Yes. I was invited to Purdue University where Lark-Horowitz was very active. I got a recommendation from Fowler, I think. There was the hope that this could develop into a permanent appointment, but there was hostility on the part of the faculty — the non-physics faculty. Also, the climate of opinion in the town, apparently, was against foreigners.
It wasn't so much anti-Semitic as it was anti-foreigner?
I think so.
And you were married at that time?
Yes. On the basis of the appointment at Purdue, I decided to marry.
Your wife had studied physics?
You mentioned at one point that you had taught her?
I taught her a course. Actually, she got her doctorate working with Heitler. That was on the theory of polyatomic molecules, following the Heitler-London line, quite complicated then. We worked together on some papers later.
She completed her degree before ‘33?
Yes, that was a hectic time. She took her examination in January 1933, and then we married and went away to America — all in about one month's time.
Did she find it difficult living at Purdue?
In Lafayette. No. She was very young and flexible. And she had been in Bristol with Heitler, to finish her thesis, so she also spoke English quite well.
I see. Did this anti-foreign atmosphere in the town make a difference?
Again, it did not make a difference in the physics department. There was Lark-Horowitz, who was himself of Jewish parentage. The second year we were there Hubert James came, with whom we became very good friends. They were, of course, 100 percent Americans, he and his wife.
It was at that time that you began to become seriously interested in nuclear physics?
Yes. My first paper on nuclear physics appeared at that time. I think it is paper 28 on my list of publications — on the nuclear matrix element in the Fermi theory of beta decay. That was one subject nobody had given any thought to before. I thought that was an essential point, and I discovered the difference between normal-allowed and super allowed transitions by an analysis of these things. I think that was a good paper, an important paper.
Do you think your growth of interest in nuclear physics had anything to do with the fact that you were also at the same time looking for a permanent position some place?
No. I think that [one] had nothing to do with [the other]. I worked also on problems in cosmic radiation at that time, and that gave me contacts. When it turned out that I could not stay at Purdue, I got two offers: one from the Carnegie Institute in Washington, the Institute of Terrestrial Magnetism, a purely research position; and [one] from Duke. Both were interested in my cosmic ray work. And I decided on the academic position, because then I was really part of the American academic world.
Yes. And that was a permanent appointment.
Yes. The position at Carnegie Institution went to Forbush when I declined. He also worked in cosmic radiation.
Why cosmic ray research at that time? What was it that got you interested in that?
I started to work with Heitler on what then was called high energy physics. I was interested in the phenomenology of cosmic radiation, and worked quite a bit on that. I wrote several papers from the Institut Poincare in Paris, and through Duke University on cosmic ray particles and cosmic radiation.
Were you interested in the phenomenology of cosmic rays as such, or was this a way of studying nuclear physics without having a cyclotron?
Nuclear methodology was quite different at that time. You had counters and cloud chambers for cosmic ray research. I was interested in nuclear physics too, but this one paper was the only one I actually wrote in this field. There was not much nuclear physics in Duke at that time, but fairly active cosmic ray work.
Was there any talk about building some kind of high energy machine? Some kind of accelerator?
No. Not in the pre-war times. Later, after the war of course, they did. Henry Newson, whom I induced to join the Duke faculty, built machines.
Did you actually do experiments to get cosmic ray plates?
No, I did not. There was a cosmic ray group mostly under Walter Nielsen, Chairman of the department, who brought me there, and I helped interpret their results.
What was your reaction to Millikan's work on cosmic rays at that time?
When I met Millikan at my first visit to the U.S. in 1930, he had the idea that it was all gamma rays. By 1937, it was quite clear that that was not true, because there were geomagnetic effects.
He missed all of those.
Was you’re feeling about American physics, say in 1938, substantially different from what it had been when you had looked at America from Germany before?
Oh, yes. There was tremendous development since that time. I think it was in part due to the Americans themselves, and the people of my own age group, who grew up with quantum mechanics and atomic physics. They also came to prominence at that time. And then, of course, there were many refugees who came to the United States and took up a good part — some very excellent people, of course — and they helped, too.
It was a joint effort?
I think so, yes. There was a tendency in the United States itself going strongly up in the sciences, and this was helped by the importation of some very good scientists from abroad.
Do you have any feeling for when that curve began to rise for American physics? Had the second and third derivatives been positive for a number of years?
It had already started when I came first to America in 1930. We discussed at Ohio State University the importance to physicists of having visiting professors, this idea of upgrading their institution. Michigan did the same. They got Goudsmit and Uhlenbeck, and of course they had — what was the third one?
Yes, right. And, of course, Dennison. They had Crane and some fellows. And this was not due only to the influx of foreigners. There was definitely the tendency here in the United States, there were Slater and Pauling and Van Vleck and some more people of the same generation.
What was your reaction when the war began?
I was not surprised. I expected this. We anticipated ever since the Hitler takeover, that it could only end in a war. The main question was: when will America be forced to join in with the Allies?
Were you able to take any active role in encouraging America to join with the Allies?
No, I don't think so. I didn’t feel that I could. I was not yet a citizen. I felt it would not be my task.
What was your reaction to the discovery of fission?
That was a fabulous discovery. I was not a participant in the group that acted behind the scenes, but I was very much interested in what they did. There were quite a few publications in 1939, but that suddenly stopped. Then I didn’t know what happened.
Were you aware of more than just a potential? Did you wonder, or did you understand why things stopped being published?
I must confess [I knew] nothing. I was quite busy at that time. And as soon as the war started, I tried to get into something on my own.
You mean, as soon as America entered the war?
Entered the war, yes. I went to the National Defense Research Committee, and was assigned to arms and ammunition. I did some very good work there. It was quite interesting. It was a big applied problem, and I solved it. The question was whether melting occurs, and generally how hot it gets, at the inner surfaces of guns.
These are big guns — cannons?
It can be applied also to small weapons. I gave the complete theory of how much heat is developed and when melting occurs for guns of any type. There were experiments in which propellant gases were sent through vents; those showed melting. However, it turned out that melting never occurred in the guns of that time. We calculated the actual temperatures which are produced in complete agreement with all experimental evidence. We also finished extensive numerical tables. We had a small group of people, a student, my wife, and a young girl who became quite adept with electric calculating machines.
Mechanical machines? Electric assist, but they were basically mechanical?
Was this the first time that you had ever done anything like applied problems of that sort?
Yes, that's right. I could see where you can have an analytical solution, where you can have numerical solutions, and they were complementary in this case. Unfortunately, I don't have any copy of that work myself. My student, H. Svoulak, who collaborated on that, wanted to write a publishable paper on that, and he lost his own copy and squeezed my copy out of me, and I never got it back. It is probably in some archives.
That was about a year? Then in '43 you were approached by the people in the uranium committee?
I don’t know if they called themselves that.
It was already the Manhattan Project.
And you had been picked to —?
— go to Oak Ridge.
Do you have any idea of how that selection occurred? It was just out of the blue, as far as you were concerned?
Yes. Of course, I didn’t know.
Didn't even know it existed?
[I didn't know] that it existed. I think most people who had specialized in fission and nuclear physics were already on established projects; in Chicago and at Hanford. They just looked for people who might be available.
But you were approached with a position of substantial responsibility.
Yes. I was a fairly well-established physicist.
I would expect, in looking for a physics director for a new project that they would have tried to get somebody who was already in the project, rather than going outside. How did they represent what it was you were to be doing, when they first talked to you?
I was not yet appointed the director of the physics division, but as a senior theoretical physicist or principal physicist in charge of the theoretical physics work at the X-10 lab, which later developed into the Clinton Laboratories and finally the O.R.N.L.
This was to produce plutonium?
This was to act as a pilot project for the Hanford reactors. Of course, in Oak Ridge there were all sorts of separation processes going on. But that was quite separated. We didn't know about them, during war time. Only after the end of the war were the barriers between these things removed, and I visited and talked about problems at the other projects.
I see. So you didn't even know that the diffusion process was going on at all.
No. My contribution to the O.R.N.L. REVIEW (fall '76) was for a memorial, for 25 years and all the people who were there were asked to give contributions, generally in a light vein. I sent you what I wrote there. That gives a little bit of information about all kinds of activities there.
Of course, it doesn't go into technical things. You were more or less forced to work out things for yourself. In a way, that was very healthy.
How did you reconcile the kind of universally accepted scientific values of openness in research and making the results of your research available through publication, with the kind of controls that were in effect? Of secrecy and compartmentalization of effort, and your inability to discuss certain things with certain people? Did you find that was a conflict?
No. Of course, it was wartime. We felt the importance of the project. And it was very interesting at the same time. One could talk to people. Even when I was in Oak Ridge, we had regular monthly meetings with the Chicago group, information meetings, and I could talk to Wigner, Weinberg, Fermi, and Creutz and so on. So that was stimulating. Of course, later on, even during the last year, during wartime years in Oak Ridge, we felt that our work would be ultimately very important for peacetime applications, and our thoughts were very much directed toward that.
In power generating, neutron diffraction, and, of course, the use of isotopes and so forth, at which the laboratory was strong. [It's] not my personal field, but you heard quite a bit about it. And then, we hoped that after the end of the war, some of these things would be publishable.
But the primary purpose of the X-10 was to act as a pilot project for plutonium production?
Yes. Physics, chemistry, and biology, radiation protection and so on.
When you went to Chicago, did you find that Fermi had changed from how you had last encountered him?
Yes. I was quite friendly with him many years earlier in Gottingen. But he was rather cool to me, when I joined the Manhattan Project. One could feel this. That I went to Oak Ridge, I think, disturbed him. That was under DuPont and he really had not much to do with design of the reactor there. He was invited to direct the start-up, and he did. But that was in a way competition to him.
I see. Even though you hadn’t really picked that — it was thrust upon you.
How was that expressed?
Oh, it was not directly expressed. At that time he was a famous man and a Nobel Laureate, and had constructed the first reactor pile. In Gottingen, it was before he really became well known and did his remarkable work.
I’m surprised, though. He was well aware of the purposes of the reactor development project in the Manhattan Project. It would seem that there would be no particular feelings of resentment or competition from the development of a prototype for the Hanford reactor.
Yes. I don’t know. But there was certain coolness from him toward me. Not that he was uncivil or anything like that, but —
Just kind of a resistance to help? So you didn't know anything about the diffusion processes that were going on in Oak Ridge. I wanted to ask you about that.
No, I didn’t know in war time. There were barriers between the various organizations of the Manhattan Project, though they were removed pretty early after the war.
But they were certainly in effect during the war. It's probably also the size of the. Manhattan Project, at least by '43, that distinguishes it from, for example, the work at the Radiation Laboratory at MIT on radar. The people that I’ve spoken to have indicated that there wasn't anywhere near as much compartmentalization of the effort [there]. There was some, but they were generally able to cross over the different section groups and discuss problems.
Yes. And that, of course, was the military that insisted. General Groves. Compartmentalization! Oak Ridge was actually a military reservation.
Were you aware for example of Lawrence’s attempts to do isotope separation, using the cyclotron?
No, not in wartime. We didn't talk about bombs at the lab during wartime. But I think it was in our minds.
I see. You were just producing plutonium. That was all the X-10 was officially supposed to do, and you didn’t know quite why you were doing that, officially?
Unofficially, did one know? When were you officially aware of the fact that bomb production was the point of the whole business?
I think I wrote this here, in this little article. When I learned about plutonium and production of plutonium in reactors in Chicago, I tried to get something out of Wigner. I asked him what would happen if one assembled a large amount of pure plutonium. He answered, “So?” and shrugged his shoulders. That was enough for me.
Was there any official indication of the purpose of your work on the X-10, before the actual bombing in Japan? Were you aware of the test, for example?
No, we were not informed about the test. I remember, there was some rumor in the newspapers about some event in New Mexico, and I thought it maybe was something. But then, of course, I was quite surprised by the announcement.
Where were you when you heard that announcement, about Hiroshima?
When the announcement was made we were on a holiday in the Carolina Mountains.
Can you remember your reaction?
We were not 100 percent surprised. We sort of suspected what the Manhattan Project was all about.
What was your own personal reaction to the news that there not only had been a bomb, but it had been used?
That was, of course, mixed. We understood how terrible that stuff is, and [pause] and maybe we got some slightly more information than the general public, I'm not quite sure. You look tired.
No. I'm just interested. In that article, you mentioned that the Smyth Report gave out a lot of information. You didn't explicitly say this, but I got the impression that [you felt it] went farther than it should have. Is that a correct assessment of your feelings about the Smyth Report? Did you really think it was necessary? Certainly something was necessary.
We were so trained in keeping things secret. That was hammered in all the time. It just came as a complete surprise that they opened the door that wide.
In retrospect, do you think that that was a proper level of disclosure?
Yes, I think so. We were then impatient that so many things remained on the secret list for so long. On the practical side, it really was opened up only with Eisenhower's Atoms for Peace announcement in '53. When we tried to do politics, which we of course did, in these scientists' organizations, we always were for opening up the field.
When was the Oak Ridge Association of Scientists and Engineers formed? Was it immediately in the wake of Hiroshima? Or had there been indications that it would be formed before?
No, it was not before. It was subsequent to that. I am not sure about the actual date when we got together.
Do you remember who else was involved in setting it up in the first place? Not so much the names as what kind of representation among the technical staff at Oak Ridge was involved? Was it just top administrative people, with administrative responsibilities such as you? Or was there a cross section?
There was a cross section. I think that the chemistry department was very active in it, besides the physicists. And my recollection of how this started in Oak Ridge is slightly hazy. We soon had a working group and then contacts with other groups in other laboratories. At the beginning it was mostly only those within the Manhattan Project. They were the only ones who were in the know and felt that the public needed more information, and that there were peacetime appellations that would be important to disclose and so on.
How long was it before the groups in the Manhattan Project, the various groups, got together and formed the Federation of American Scientists?
I think that was fairly soon, sometime in '46, but I can't tell you the exact date.
Was its primary goal at the beginning to make certain that civilian control was established over fissionable material? Or were there other goals stated at the beginning? Was there supposed to have been a more active role taken by the Federation in establishing policy relative to radioactive material?
Yes, I think also active in lobbying, at least for the United Nations. You know there were attempts from the. American side to internationalize atomic energy — the Lilienthal and Baruch Plans. From hindsight one can say, it could not have succeeded. And the reason, the Russians had a project of their own which, as one knows now, went quite well. We didn't know about it. Thus they would not accept an internationalization where they played the second fiddle, but would be able to get the essential technology themselves.
Had you ever had serious thoughts that the German bomb project was well along?
There was quite a bit of worry about that. But we didn't know. And it turned out later that they were far behind.
But there was that fear always?
Was there opposition due to security regulations, or to anti-German tendencies and feelings, in the United States toward the formation of your lobbying group either at Oak Ridge, or the Federation itself? The Federation always seemed to me to be treading on very thin ground, because it was of necessity made up only of those people who had some inside knowledge. There were tight security regulations that had to be maintained, and that’s a difficult position to be in. You have your position, for which you are lobbying, and you have the information that would give you the advantage of your position, but you would always feel that there were restrictions that prevented you from divulging that. Is this a conflict that you had to confront?
Yes. And so we lobbied for more distribution of information, for freer information. That was one of the main points. But we were very well trained, so that I don't think there were any sensible leaks from the project.
Even after the war?
Even after the war. Of course, as we discussed, the Smyth Report gave quite a bit of information on many of these things.
Yes, probably sufficient for your arguing purposes.
Let me come back to that question I asked you a moment ago, but now about the postwar period: this idea of maintaining silence with respect to research results that under ordinary circumstances would have been published. Once the war was over, was it possible simply to continue the wartime feeling that this was legitimate, that it should be restricted? Or was there growing resistance?
I think scientists lobbied continuously for declassification of many things. But that was not done very soon. For that reason, since the basis of knowledgeable people was comparatively small and restricted, Wigner proposed this one-year crash course for people outside. But that was still handled under security regulations.
The public speaking tour that you mentioned in one of your articles, one that you took on behalf of these lobbying interests, was that your first political activity of that sort? Or had you had other experiences of that kind before?
No. That was the first public thing. Of course, we had our own sessions within the Federation or within Oak Ridge, where we discussed what we should do, and organized these field trips. Of course, we had essentially to confine [ourselves] to the Smyth Report, and the implications one could draw from it. But the public was largely not informed.
You mentioned that Clinton Lab was put under the control of the Monsanto Company, and that there were difficulties that you encountered. What are your feelings about the relative merits of private and public support for basic research? Based both upon that experience, which was basically a negative experience, I guess, and also you’re subsequent experience which has been more positive. Is it possible for a private company to sponsor what you consider to be valid basic research?
Yes, but it is very difficult. Monsanto was not really interested. Though, of course, their chairman, Charlie Thomas, had some interest in it. Their attitude was: "This is not a public laboratory, this is Monsanto.” And everything went under the name of Monsanto and so on. They only administered the existing lab, which was for a definite purpose, of course.
Did they take over control of everything there, the diffusion plant?
No, only the X-10. X-12, which was devoted to the magnetic separation of isotopes, was then united with X-10, while the gaseous diffusion plant was under a different management. I think, you need both government support of research and private research. I was myself surprised when I accepted the job at General Atomic. But de Hoffmann and Creutz were very good friends of mine, and were essentially research scientists. John J. Hopkins apparently had really far-reaching ideas on this. And I was getting on in years, relatively speaking. So it was agreed that I would not have to retire before finishing my 68th year, which gave me 12 years, and I thought General Atomic will last about that long. And so it did. It was conceived as a real research laboratory, with many things. I don't know whether I should continue with that. About my activities here, before and after the formal retirement.
Well, let's go back a little bit. You left and went back to Duke, then. You resigned your position?
Yes, from Oak Ridge.
From Monsanto-Oak Ridge, and went back to Duke. Then you had a period of a couple of years of very creative work on shell theory. That was a period of time when other people were also doing that.
Yes. I had become much more involved in nuclear physics during the Manhattan Project, and so I was very much interested in that. At that time I also cleaned up some work which was done immediately before the war in cosmic radiation, and then I went into the shell business.
Did you ever find it difficult to change gears in physics? You seem to have done a number of different things, and done important work in all of them. Was there an underlying link that put them all together? Or was it difficult to change in that way?
No. I think that is so with many people; that sometimes you have to change the line of your work. You get stale if you stay too long in one field. Though the field goes on, of course. I started my career in quantum mechanics, and the first thing I took up really with the new quantum mechanics was solid state, electron theory of metals and quantum statistics in general. Then, after a while, I felt, maybe you get stale, and I went into high energy physics: radiation theory and cosmic radiation. Then I found nuclear physics became interesting. That was enhanced by joining the Manhattan Project. Of course, you learned new things in reactor-physics, on which I am now an expert.
Applied nuclear physics.
And so it was quite natural that I continued to work in nuclear physics.
Was that one of the reasons that you went to Heidelberg in '49?
No. The family of my wife lived in Karlsruhe which is not very far away, and we wanted a reunion of my wife with her family: her parents and her brothers. My father-in-law was at that time director of the Institute of Technology in Karlsruhe, and he arranged that I be a visiting professor in Karlsruhe and Heidelberg. Of course we were interested in how things were going on in Germany. In Heidelberg there was one person, a very intelligent person, Bothe, who was involved in the German effort during war time, but he never talked about it. He was an expert in neutron physics. But that was not the chief reason I went there.
Jensen wasn't there yet, but he came there later?
No, he was in Hamburg at that time.
What were your feelings on going back to Germany?
They were mixed. At that time conditions were still rather poor. If you want to know more about it, you can ask my sister. She lived through that in Germany, through the wartime, and the first postwar years. You always had an ambivalent feeling in Germany. Are there good Germans and bad Germans? You know, of course, it was a kind of · schizophrenic affliction of the whole culture, or of a large percentage of it. So we always felt you were on uncertain grounds.
Are you speaking now of your feelings before you went, or having had these feelings corroborated after being there for a while?
We wanted to see. You don't talk so much with people about that, but you feel it.
Did things seem quite different to you than they had before? Obviously a lot of things had happened and the circumstances were quite different.
Yes. Science was more or less dismantled. There were a few people, who still practiced it, but it was a slow process building up again and it was still far from complete. The importance of Germany in science had been reduced very much from the pre-Hitler times.
So the kind of physics that you were familiar with, that had been done in Germany, just didn’t exist anymore when you were there in ‘49?
Yes. One can say that. I don't know whether it was on this visit or another, I visited Sommerfeld in Munich. This was very nice, but he was quite old then and not active in any respect.
Did he say anything about his experiences during the war?
No. That could have been unpleasant for him. Otherwise, this was a very pleasant visit I had with him He was very cordial. He always was, and I admire him.
You later expressed great concern about the public and semipublic discussion about the development of the hydrogen bomb. Were you conscious of this discussion before there was any indication that you might become involved?
Yes. Actually I went to Los Alamos several times, before there was work on that. I went to Los Alamos in the fall of ‘45 on a recruiting trip for Oak Ridge, because many people at Los Alamos didn't know whether they should stay there, if Los Alamos would be maintained, and so on. Then I went there in summer of ’46. There was a session on Teller's idea of the so called “super,” the potential hydrogen bomb. There I got my first information, real information, on the subject; what it physically might be, and so forth.
How well developed were his thoughts at that point?
It was frustrating. Teller had worked on this during the war years, and it seemed to be an enormously difficult job. It was questionable whether anything ever could be done. Then I went in '49 on a scientific trip about the shell model. Of course, there was Maria Goeppert Mayer there, and several other people. We had a kind of symposium on that. So I knew Los Alamos fairly well all ready before I went there for a longer time.
When was that?
That was in 1950
That was a full time position for two years?
Was this same principle of compartmentalization used on the "super" project; keeping other people from knowing exactly what all the other parts are doing? Or were things more open?
No, I think that was not at Los Alamos. In Los Alamos during the war time people could talk to each other. That was one reason, I think, why that project was successful. Because you had so many things coming together. You need the neutronics; you need facts on explosions, shock waves, electronics and what not, chemistry, metallurgy.
Do you still feel today that the decision whether or not to develop the "super" should have been made in private? That it should not have been discussed as openly as it was?
Yes. It was blown up as a political football. I think that was not good. Of course, my reasons for going to Los Alamos were again not quite simple. I needed at that time a change of scenery very badly. My wife had died in an accident on our first visit back to Germany, and I was very nervous and depressed. Here was something quite different then, something one had to work hard on, this specific project. And then I felt, "you have to know whether there is anything in it.” Herb York wrote a book on that, that it would not have been necessary, might not have been necessary. But that one should again have tried to get accommodation with the Russians, that no one should develop it. But I think that, again, was a wrong speculation. It wouldn’t have led to anything, because it still was the time of the Cold War. Then the Russians were trying themselves to develop it. So I think negotiations on that would have been as fruitless as the ones at the United Nations on the internationalization of the atom bomb, just after the war. And so it was.
York is talking about whether or not it was the right decision to have made at the time. What about the issue of how much the public has a right and a responsibility to know in a democracy? It’s a very difficult question. What was your feeling in this particular case? Do you still feel it was not proper for this issue to have been discussed as openly as it was? Regardless of what decision was made?
That only divided the country. This was started really before one knew what could be done. Now, in ‘51, one knew it would go, and even comparatively easily. That would have been the time when it should have been presented for public discussion and decision. But probably not as long as one didn't know whether it would work at all.
Can you tell me what your responsibilities were in that period of time?
Yes, I can. There are several ways you can construct hydrogen bomb, and I worked on an alternative scheme, which was also originally proposed by Teller, and which is neurotically very complicated. I got that project as my main task; I should see what one could do. And I did solve it. I got a very elegant method of calculating the stuff; one was built and later successfully exploded. But it was much more complicated than the regular bomb. I went to the Marshall Islands to see this test, but it was postponed and postponed and I could not stay that long, unfortunately. But then, you know, that ordinary H-bomb goes something in three stages: first, an atomic implosion; then, a thermonuclear reaction; and then, the neutrons should go into the uranium tamper and again produce more energy.
More fission and energy. I worked out the neutronics for this part.
But you never saw the test?
I saw one ordinary test in Nevada. And I went to the Marshall Islands to see one of the big thermonuclear tests, specifically of the device I designed, and could not stay there. I was then back at Duke University and could not stay away forever.
Is this still physics? In the course of your career, and through force of circumstance, it seems as though, with the exception of the occasional moments when you got back into an academic environment, you were coming closer and closer to real applied problems.
That is true. That was partly why — force of circumstances and so on — that I wanted to do something positive. My contributions in these instances were that I learned to know where neutrons are going and what they like to do and what they don't like to do, and to be able to treat very complicated neutronics problems. And in treating these things, I have been generally very successful. It's the same thing in reactor physics, at least the beginning of reactor physics, in that you have to find out what the important things are, how they behave, and so on. Today it is less physics, but engineering. The fundamentals are well established, one knows what to do, and people have learned to make more and more complicated calculations on machines.
Actually my question is a larger question that we were talking about at lunch. What did physics become in that period of time? I was wondering whether or not the experience that so many American physicists had during the war — working on large scale projects like the Radiation Laboratory at MIT, or at Los Alamos or Oak Ridge — whether or not that might not have had some very profound influence on how the community defined physics problems thereafter. After the war you're confronted with large machines and cooperative efforts of the same kind. How did that compare to the physics that you grew up with, that you learned when you were a student? It's a different sort of endeavor.
Yes, that is quite true. One has found the power of collaboration in large projects. That is for instance typical in the big accelerator problems and high energy physics. It takes a team effort to build a big machine like that, similar to the Manhattan Project nearly. And then it needs many people to make experiments with these machines, and to interpret them. And you know that in high energy physics there may be 20 names as the author of one paper, but they are all needed. In some things it's really necessary. It does take a big team to build a rocket, a space satellite, a communications system, space lab, and things like that And that is not a thing which a single person or a small group can do.
Do you think that this has changed the complexion of physics and physical research in any fundamental way? Or is it just something that's characteristic of the new kinds of problems that people are confronting? You don't build a 200 million dollar accelerator like the one at Stanford without doing a lot of work, and convincing a lot of government officials, in a way that you never had to do before to do research in physics. I wonder whether that doesn’t change the kinds of motivations that go into the work that is done?
Yes. Certainly. And such big efforts, they can only come about with government assistance. That’s the only source that can provide money on the scale necessary for such things.
Is that kind of research necessary?
Yes. It is. Of course, the theorists profit by it. There have to be people like Gell-Mann, Feynman and others who really interpret the results. Of course they may not get the right idea at once, but one of these days one will combine ideas, for instance, as people do in trying to unify various field theories, and now gravitation and quantum mechanics. That is very difficult. And one doesn't see quite what it will be. Things become very complicated. But then you need also idea men.
How would you characterize the changes that have occurred in the profession of physics, over the span of your career?
In my time, to choose physics as a field of work had to be an avocation. You had to be really interested in the field, and hope that you can make a living that way. Now, it is a profession, like anything else. Until a few years ago it was very easy to find jobs in physics. That has changed now. And so people simply took it up as a line of work that promised a fairly good living. So it's a profession. Like lawyers or doctors. Of course, there are still people who like physics for itself.
But are the basic motivations the same? Aside from young people coming into a field that might look upon it as a kind of ready-made professional field where they can expect to get a good job, are there any more profound differences in motivation, and in the kinds of problems that are treated and discussed?
Yes. The trouble is that physics has branched out, and there are so many specialties which no single person can really command and study by itself. When I was younger a young theoretical physicist was supposed to be able to work in any field of physics.
And you did work in quite a few of them.
For instance, Born was not only the leader in solid state, crystal structure and quantum mechanics, but he also wrote a big book on optics. And people with whom he had contact were asked to help him and to write chapters of this book, in a field in which originally they were not quite familiar. And so on and so forth. That is hardly possible anymore. Now, an electronics expert, he works in electronics. He maybe worked with a high energy team on a big accelerator, but he had his special field, electronics.
What is the effect of that kind of specialization on physics? And on the sort of work that gets done? When you’ve got a group of 20 people, each of whom specializes in a different aspect of some field, can they produce as meaningful or more meaningful a piece of work as one person?
There has, of course, to be a leader who can take a broad view of things, and he says, "Now, over here, one needs an electronics man, there. I need a mathematician to work up the data.”
But to what extent is that leader a physicist or an administrator? More and more, he's taking on the role of administrator.
If he’s only an administrator it won’t work. He has to be a physicist. And keep track of the ideas which underlie the experiments and so forth.
He would be an administrator whose working capital is theory?
Not necessarily. He has to have a feeling for physics. Not all good physicists are theorists. But he has to have an idea. For instance, Franck was an outstanding example of an experimentalist who had a very deep understanding for physics in every respect. He would not do the calculation himself, but he understood what was going on.
What about Teller?
Teller also was very universal, and very fast. He is, of course, a theorist, but he can look at experiments. A theorist must be able to look at experimental material. I had to do that myself. If, for instance, you look at the shell model [of the nucleus] enough to know what there is, what we have to explain, and study the experimental material from all sides, and you suddenly start to see things. If you have a good physicist, he may be either theoretically or experimentally gifted, but he has to know the other part too. There are very few who can do both parts. Fermi was one of those.
And these days he has to be a good bit of an administrator in his own right.
Yes, to bring people to work together, this is a gift in itself.
Can you say a few words about the estrangement between Teller and the physics community? How did it come about? How did you see it?
Teller, apparently, from the beginning — that is how I have to reconstruct it — was fascinated by the idea of thermonuclear reactions. Either as an explosion or as an energy source. During the war at Los Alamos he pushed that. There's a big book written by various people, the HANDBOOK OF THE SUPER; that was a wartime thing. Then, he fought for continuation of that work, and he encountered all kinds of obstacles. People said, “We have the ordinary bomb, what shall we do with more of the same?" There's no money. That laboratory [Los Alamos] had to struggle to exist, to survive the postwar slump. Then he was the first open advocate of continuing the work, as answer to the Russian bomb test. Then there was this public debate which you know about. It always went too slow for him. Finally, he had an idea which worked. One can reconstruct how it goes. Then, everyone thought it was not so difficult, after all. However, he was restive, and he wanted a place where he could work for himself. So there was the idea, shared by some others, by Lawrence for instance, to have a second weapons laboratory. So that was founded, and he went over to Livermore. He always had the feeling; I think I wrote something in this vita which I think expresses it better than I can extemporarily.
On the bottom of page 25.
This sums it up better than I can do talking, because one has to be somewhat careful how to word such things.
You were fairly close to him in this period of time?
Yes. We were very good friends in the old Gottingen days.
And that was still true here?
He had always this conviction, which was not shared by physicists in general, that the way to confront the Russians was to always stay ahead of them.
Do you share that view?
Not quite. I think one has not to forget that, but it is very necessary to come to an understanding with the Russians. Here sit two great powers — which both have the power now to blow up the world, not only they, but the whole globe.
It doesn't really matter anymore who is superior?
In some sense, that's true. Only, the other side has to feel that they cannot do anything. Even if they have more bombs or better bombs, that they can’t use them without destroying themselves.
You said at lunch that you had gotten more and more interested recently in energy production and problems that we are running into with expendable resources. There, too, of course, there has to be a large input from the physical sciences.
Uh, yes. That is very important. But it's not only physics. It's very much politics, economics, and public relations, and so on. In order to realize big changes, there has to be a definite determination. Physics cannot tell you too much about how to do this.
Have you always felt that way? Or is this a fairly recent change in your viewpoint? Are you more optimistic now than in the recent past, or are you less optimistic, particularly about American society’s ability to solve some of the serious problems that involve technology?
I think I have become somewhat less optimistic. That is a change which is worldwide. I guess I would call it, from what one thinks is rational for people to do, and what they do. For example, in this New York blackout a few days ago, that triggered looting of such tremendous extent. That demonstrates on a small scale that people are willing to be violent. In war this has always been the case, but in peacetime, at least in the democracies, it was in general not so. But it has now become prevalent all over the world. People have become more violent than they have ever been. Of course, there have always been addicts of violence. Nazi mass murders. That is something I hope will not recur. But it will occur on a smaller scale in many parts of the world. And this is what makes me less optimistic. People sometimes don't think; they are very emotional. For instance, foes of nuclear energy go on vague things, not on real technical grounds. They are emotionally so concerned that they see [only] the one side. There is a possibility that there may be an accident sometime. And that must be avoided under all circumstances. So they are not rational. And it’s so in other problems.
Do you see any global cause for this growth of irrationality in the world?
It goes similarly also in the countries like Britain, France and Germany. And, of course, in the less developed areas — hijacking of planes, arson, bombs, and so on and so forth. That is really a change in peacetime living. I lived through the last days of the German Empire, in postwar Germany, then through pre-war, pre-Second War, and in the United States of America, and through the wartimes and after wartimes In these former times in the United States — at least in the smaller cities — you didn't think about having to lock your doors, and nothing happened. Of course in Chicago it was unsafe to leave your doors unlocked and so on, but that's now generally the case. People attack problems not on a rational basis, but on a preconceived opinion of, so to speak, on faith, which has formed somehow in their heads.
Have you ever seen anything like this before? Different culture, different time, in your experience?
You might say that the coming of the Hitler regime was a kind of popular insanity.
Do you see similarities?
Not quite. Hitler's ideas were much more directed. He wanted his Third Reich and his German nation to be the foremost and to dominate the world. There is a little bit of that in contemporary Russia, of course. But I think they're still quite a ways from the way it was in Germany.
Well, is there anything else you can think of that would be profitable to mention, based on your vast experience? You've touched so many bases in the development of physics in this century, associated with many influential and important people in physics.
I don't think so. I am still moderately active and did quite a few things at General Atomic which are useful but not of world shaking nature. If I may, I don't know if you want this, I could say a little bit more about Oppenheimer.
All right, I would like that very much.
In practically everything I have told so far I have said nothing against anybody. If I make some remarks on Oppenheimer, I’m not quite sure.
All right. If you feel free to make them, I can assure you they will be treated with respect. You will see them before anybody would have the opportunity to look at them, and you can put a partial restriction on some of the material if you wish; it will be held for however long you wish.
Oppenheimer, of course, was a man with great charisma. He was eloquent and literate; unfortunately, he was also ambiguous, and not always logical, and ideologically confused. [He] was not always very good in personal relations. Of course, he apparently did a great job at Los Alamos during the war. He kept that together. But after that I think he thought he was the only one that could guide scientific politics, and I think that was wrong. I remember during the time of the Super — I was at Los Alamos in 1951. There was a conference on the super (bomb}, after the principle was clear that it would work. And he agreed with that. Before he had been very much against it. But afterwards he gave the impression, "Yes, now I will guide the thing.” And he actually managed to be the most influential advisor in scientific polices, for the arms question for the government, as chairman of the AEC Advisory Committee and so on and so forth. He had adopted the grand manner. For instance, he arranged a scientific conference at a plush resort in New England and had all participants conveyed there by limousines. I think he was wrong on several points and I distrusted him. Apparently, as one learned from the proceedings of the hearings, which you probably have seen, he has had leftist ideas and friends, but this I don't hold against him. But it showed, he did not quite distinguish between personal things and technical things. I had one very unfortunate experience with him. That was in '38. I was invited to give a colloquium on cosmic rays at Stanford University. It was Felix Bloch who arranged that, it was a summer trip. Oppenheimer, who was at that time at Berkeley (it was before the war started, of course), appeared. And he did not let me talk. I said a few words, and [he interrupted,] "Yes, we have found that a long time ago and much better!" He repeated that from time to time, and so on. I really could not [continue]. Finally Bloch cut it short and said that he’d better stop this discussion, or something to that effect. I had analyzed the cosmic radiation in the atmosphere into its main two components, a hard part (later identified as u-mesons) and a soft part, electrons and photons. This work I published later in some papers. However, there came never a publication on this matter from Oppenheimer and his school. But he did not let me talk but said, “0h, we have done that much better.” Since then I was not his greatest friend anymore. I had known him for a long time. He was in Gottingen in 1926 and I knew him from there, and later met him several times in the United States. So this was an experience. I think he sometimes saw himself as a demi-god. And with that, apparently, he ranked other people, and that may have been the reason that many people were against him. In a way I found it a relief that he was removed from the position, so to speak, as the foremost scientific advisor to the government. But the way it was done, I thought wasn’t the right one. People felt that there could have been a different way. You don't have to do it that way. Does that seem to make my position clear?
Yes, I think so. Do you have any notion of his motivation for his opposition to your statement of your results?
Oppenheimer has died quite some time ago.
Yes. But in '38, when you were giving this talk, did you understand at the time?
No, I didn't ever. [I thought he'd] apologize later. He never did. Maybe he thought here was someone who might diminish his glory. Of course, he had just developed with Serber the theory of cosmic ray showers; cascades of electrons and gamma rays. That was very good work. (It was also done independently by Heitler and Bhaba.) I used the Oppenheimer method in my analysis, and maybe he considered this as trespass on his domain. That's the only way I can think of it. He was a man of great power and great vanity.
What about your present interests in energy problems?
It’s anti-climactic. Scientifically, I am still interested in nuclear physics, and try to follow it as much as I can. [Just] more slowly. I have particular interest in the fission process; in the material I gave you there are some hints of that. On the other hand, I consider that the energy problem is one of the foremost problems which civilization has at this time. It is, of course, closely linked with the population problem, about which I personally don't think I can do anything. In energy, I am an expert in physics, particularly nuclear energy, and know what it is. I can understand when people talk about solar energy and so on, and have a fairly good idea what can be achieved on these lines. To get a long-range solution, one has to follow a definite path, which is very difficult. One has to see the problems and so on. For the short range, one has to take energy anywhere you can get it. And there are several things [President] Carters program is less than even that. It's temporizing, at best.
But then again, as you said yourself, although there is a heavy technical input, they fundamentally are social problems. They are problems that require political and social and economic solutions, as much as, or perhaps even more than they require physical solutions. One doesn’t doubt the technological feasibility of extracting solar energy, if you throw out economic considerations. Or of conserving oil resources, if you throw out the social problem of people's felt need which is increasing for consuming energy.
Yes. But the Carter program cuts out the one thing where there's a proven large amount of available energy, at prices which are not too far different from the ones you have now.
You mean nuclear energy?
That's nuclear. This is a proven technology. You have to work out many details, but it is a very large amount of energy, much larger than fossil fuels, if you can burn all the uranium and thorium. If you can do that. And if you know the techniques. And to throw that out! This is the farthest advanced of unconventional energy sources. The light-water reactor, L.W.R., forgetting about the burned fuel is a proven solution of atomic energy. It is the farthest developed, but it is wasteful of uranium, and the uranium will not last very long, if you only rely on that and throw away the burned up fuel. There is geothermal. Where you can have it, it's good, but it will be a secondary source. It will never be [primary] so far as I can see. Like hydro, this is also a finite source, which yields only a small fraction of today’s energy consumption, so also geothermal. Solar energy might be very good to heat and cool houses when the technology is a little bit more developed, I have no doubt. But as to separate electricity generator, I have my doubts. And it is very expensive. So with all the sources. You can think of other things, like reflecting sunlight from satellites and transmitting it by microwaves, that is more or less absurd. And so are thermal gradients of the ocean, because that stuff would foul up in no time, and one doesn’t know what to do about it.
The same with tidal gradients, too?
Tidal gradients will be also a secondary source, possibly. In a few places, but not universally. Wave motions may be better. Wind is a good secondary source.
But in addition to whatever the program is, there has to be some realization on the part of American society, that their energy consumption rate is out of hand. That it can’t grow as quickly as it has been growing in the past.
Yes. That is true. Most people apparently don't feel the urgency of this. Carter has some idea but he talks of the equivalent of war, and that alone is not sufficient. That’s more rhetoric.
Well, I'm sure we'll all hear a good deal more about it in the near future. Perhaps people will come to their senses when it begins to come a little closer to home. As long as it doesn’t come too close to home, then people don’t take it too seriously. I have enjoyed this a great deal. I'm very happy that you were able to give us all the benefit of your experiences. I think it's been very helpful.
At least I have lived for quite some time.
Yes, and you’ve experienced quite a bit.
 Lately the Carter Administration and its Department of Energy have changed their position to some extent. Their greatest fear is that of nuclear weapons proliferation, and the easiest way to that is through plutonium. Thus, there is still a moratorium on reprocessing and fast breeder demonstration plants. Limited research on these topics is to be continued and also on alternate fuel cycles. The implicit hope is that the uranium reserves will be sufficient for the present LWR technologies will a political solution for the plutonium problem can be found. What is not fully weighted is that reprocessing is required to simplify the waste disposal, for improved reactors, and that the best way to get rid of plutonium is to burn it up in reactors. Also, inevitable, the U.S. will fall behind other advanced countries in technology.