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In footnotes or endnotes please cite AIP interviews like this:
Interview of Max Born by Thomas S. Kuhn on 1962 October 18,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Part of the Archives for the History of Quantum Physics oral history collection, which includes tapes and transcripts of oral history interviews conducted with ca. 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the 1920s. Also prominently mentioned are: Niels Henrik David Bohr, E. Bormann, Louis de Broglie, Cauchy, Peter Josef William Debye, Paul Adrien Maurice Dirac, Albert Einstein, James Franck, Josiah Willard Gibbs, Werner Heisenberg, David Hilbert, Huang, Ernst Pascual Jordan, Felix Klein, Alfred Landé, Max von Laue, Erwin Madelung, Albert Abraham Michelson, Hermann Minkowski, Wolfgang Pauli, Max Planck, Venkata Chandrasekhar Raman, Erwin Schrödinger, Arnold Sommerfeld, Otto Stern, Toeplitz, Woldemar Voigt, Theodore von Kaman, Norbert Wiener; Como Conference, Universität Göttingen, and University of Cambridge.
If it's all right with you I would like to start out by asking how you got interested in the sciences in the first place.
Well, I've written this in my Recollections.
If you feel that that simply goes over ground that is extensively covered in your Recollections, then we can go on. I should particularly like to ask you in connection with your interest in science and with pro-university education in science how many eminent and productively active figures have come from Breslau? There is yourself predominently, but also Otto Stern —
Well, there were a number and in Goettingen we formed a real group. There was a mathematician, Toeplitz. He was quite well-known at this time. He worked also on quadratic forms of an infinite number of variables and such things — integral equations. Then there was another one, Hellinger, who was, of course, in Chicago later. Toeplitz went, I think, after the 1933 catastrophe to Jerusalem. Then there was Courant who is still in New York. And I think there were still more, but I have forgotten who they were. Ladenburg was in there; and Reiche. The whole Minkowski family — Hermann Minkowski and his nephew Rudolf. Hermann's brother who was well-known in medicine; you know he was one of the precursors of insulin discovery.
flow that is not as a university one of the great centers of the period. But it perhaps produces at the pre-graduate level a larger number of the people of importance than any other.
It just came to my mind that they all were Jews. That was the part of Germany to which the Polish Jews, when they avoided the pogroms in Russia, went first and settled. And they were very interesting people. They were poor first, but very quickly they rose and became quite wealthy (They settled, and believed after a few years) that they were German, and from such families they came. My family was much older in Germany. My family from my father's side came from Goerlitz which is a little corner on the Oder-Neisse line between Brandenburg and Silesia. And my mother' s family was Silesian, a very old Jewish family there — I don't know where they come from originally. But all the others were certainly of Polish, Jewish origin.
What sort of a Jewish community was the community in this area? Was it one that was quite conscious of being Jewish?
Oh, there was a very orthodox part with several synagogues — one of the synagogues was just opposite the house where I was born, and I could see it. But my father didn't take part in all that at all; he was a scientist and didn't make use of that. He didn't come from Breslau; he was a student there, but he came from Goerlitz and his family lived in Goerlitz all those years. When his father died, he took them over to Breslau. And he had a brother who studied medicine in Breslau, and he helped him very much. And then he had two sisters and they married in Breslau. My mother's parents were great industrialists — textiles. At the top of their development they had about five or six factories in various parts of Silesia.
Several people to whom I've talked about interest in science in and around Breslau have pointed to one man — I think no one has yet remerered his name — who was particularly a good and inspiring teacher of science at one of the gymnasia.
Well, that I'm not sure of.
Well, we had a very good teacher in the upper forms. His name was (Maska); it's also in my recollections. He was really a very good teacher in mathematics and physics. And it was around this time when Marconi's first experiments were known, and he imitated them at once — repeated them. He took two boys, myself and another one, as helpers, and we learned these things at once. This was quite attractive.
You think this had something to do with increasing and sustaining your own interest in the sciences?
Yes, it certainly made me interested in these things.
In curricular terms how far had you gotten before you entered the university? In mathematics —
Not at all as far as today; I mean we had nothing of infinitesimal calculus. We just made algebraic equations of the second order, and we learned plane analytic geometry — hardly anything in space. And we had trigonometry of a stupid kind; I wasn't interested in mathematics at school.
How about physics and chemistry?
Oh, we had very little. I think we had one or two hours a week for the whole of science, and this was divided into the organic sciences and the inorganic ones. They didn't count much on each of them. It was a so-called humanistic gymnasium. The Greek and Latin were foremost.
Were you entirely clear when you left the gymnasium and went on to the university that you wore going to be a scientist?
Well, you see, my father told me that I should try everything. I heard lectures about every possible — and impossible — thing. And I was attracted mostly by astronomy because it had such a romantic aspect. There was an observatory in a little tower on the roof of the very old baroque building. And they were old instruments, and not a single modern one. And the teacher was very funny. But I have written this in the article, you know. And mathematics interested me also because it was so clear. One could understand everything. The other subjects need much memory and I hadn't —. Chemistry never attracted me at all. There was so much memorization in it. Even now when my son, who is a very good chemist, though he is a medical man, would explain to me things in a chemical formula I can't understand them. They're very difficult.
I know what you mean. I was very concious of that contrast in my own education. Though I think there is vastly more theory now in many parts of chemistry than there was when you were a student. How one thinks often of mathematics as being one subject, theoretical physics being almost another, and experimental physics being almost a third. On the other hand, Planck writes that when he first went to Berlin, nobody there knew what a theoretical physicist, as codred with a physicist, was. Particularly this whole question of the conception of the man who decides to go into this field and of the curricular relations between mathematics and theoretical physics and experimental physics interests me a great deal.
Well, I can't say very much about it. When I came to Breslau and started in Breslau there was a young man, who was only a few years older than I, Clemens Schaefer. He is living still; he's over 90.
Have you seen him at all?
Yes, I saw him when I arrived. I came to see him, and I had a nice hour with him. And the next time I came I was in touch with the present physicist in Cologne, and he said, "Oh, it's not worth while to see Schaefer, he's a disagreeable chap." So he dissuaded me from seeing him, but I found out later that it was perhaps that there was a quarrel between these two because old Schaefer has tried to interfere still in the running of the department, or something like that. Then I have regretted very much that I haven't seen him again, but I have had some correspondence with him. He was the only man who knew anything of Maxwell theory. He gave a lecture on Maxwell theory — it was the first one I heard on it. I found it terribly difficult. Also the experimental teaching was very primitive and not very good. Later it was better... A few years later came Lummer, who was a good experimentalist and had a very good lecture. When I came, the professor's name was Meyer, and he had certainly quite a good book, for that time, on the kinetic theory of gases. It was still used in Germany many years later. Oscar Meyer. And then he became old; he couldn't continue his lectures and there was a young man asked to give his lectures — he was a mathematician named Neumann, and he came from a very celebrated family. There is the well-known mathematician Neumann, and, his father a minerologist — one of the founders of minerology. Minerology came from a few men, and one of them was Neumann. And his grandson was this Neumann. He died only a short time ago; he was later a professor in Marburg, and there I visited him. He was a nice chap. And he did this physics only to be nice to the faculty — he had no particular attraction to it. He made it very dry. And he gave lectures mainly, I think, on the potential theory. This was very stupid, I think — very trivial from the standpoint of today. It is a special case of partial differential equations. Quite a small section in Courant's book.
Under these circumstances, did you then find important things in your development at Zurich and at Heidelberg that you were not finding at Breslau?
Well, at Heidelberg there wasn't much. There was an old mathematician, Königsberger who has written two very good biographies, one of Jacobi and the other of Helmholtz, and he gave a lecture on the theory of surfaces — on differential geometry in general. And this taught me a lot, for at Breslau I had learned Mathematics with all the epsilons, and so on — very carefully and logically. And Königsberger did it in the most crude way with d's — dx was just a small quantity and so on — but it gave the essence of the thing much better. And there I learned a lot. If you want to see, I have got all my lectures in detail — many of them. I have saved some of them; most of them I have given to my son.
Do you mean that he had used, this particular set?
No, no there were several copies of it, and other people had it. But I worked out all my lectures in this way. And, therefore, I did take only one or two lectures a term, but I did it very carefully, and then I knew that stuff. I wrote it down in my own kind of shorthand and then at home I took an hour or two to work it out every day, and then it was bound together.
I noticed you also have notes on Hilbert's quantum theory lectures. Presumably those are not your own — No, they were Hilbert's. In Göttingen it was the rule that one student was chosen to work them out in this way. Then they were copied by some secretary and then one copy was put in the reading room of the institute, and the second could be kept by the man who did it, and the third one could be kept by the professor.
You say your son also has a number of volumes — I save him most of mine. I have only kept those which I still can use. They are quite modern mathematics; not very modern, but the kind which I still understand.
The Hilbert quantum theory lectures interest me a good deal because they show him just at the period before the new quantum theory. Those in particular, I would like it very much if we could make a microfilm of.
You can have them, yes.
You were telling me a little bit about what Zurich and Heidelberg may have added in the way of educational dimensions that were not at Breslau, and you keep speaking of mathematics there particularly. Where did the physics really enter? There was nobody who excited you about physics while you were at Breslau?
When I came to Göttingen all the time I was thinking I ought to do mathematics. It was really the influence of a friend, this man I told you about,Toeplitz. He had a great influence on me. He was a very self-assured fellow, and his father was a mathematician, and he considered all people who were not mathematicians kind of minor stuff. And so he persuded me to be a mathematician. And only when I came to Göttingen and saw other things, I became doubtful about it.
What sort of things at Göttingen then began to make you think of physics rather than mathematics?
Well, Hilbert himself. It was like this when I arrived in Göttingen: I had an introduction from my step-mother to Minkowski because my step-mother and Minkowski were both born in Königsberg and they got together at the dicing lessons — they knew each other. So she gave me an introduction. Bat before that I went to Hilbert's lecture, and in the first lecture he said that he wanted to have the students who wanted the position of Ausarbeiter to work out this first lecture. And at the next lecture there came about four or five with this lecture worked out as a test — one was mine. Then he came back the next lecture and said that mine was by far the best, and so h took me. So I knew him — I saw him every day. After the lecture he talked about it, and he told me how to write it. I worked it out in this way, and I came to his house to fetch it and we talked and I saw him every day. Then he gave me about a year later a doctor's thesis on the proof that the roots of the Bessel functions were (consonental) numbers — it wasn't known at the time. And I tried it hard for a few months, and then I told him "I can't do that." Then he laughed and said, "Oh, of course, you are much better in physics, you should concentrate on that." And he pushed me a little in this direction. Then came the accident of his prize work with Klein. This is written of quite extensively in my Recollections. I was rather pushed into that by Klein — Felix Klein — but I found it very attractive in the end. So I came to mathematical physics. At that time there wasn't much distinction between experimental and mathematical physics; most of the people knew both. I think Planck was the only one who couldn't experiment.
What interests me particularly is that you speak of Klein and Hilbert as people who pushed you toward physics. Of course, today one would think of them immediately as mathematicians and not as physicists. Who were the physicists? Did you at this time know at all the people who were the physics teachers?
Oh yes, I had a course — several courses — in the physics department. There were two physicists, Adolph Rieke — he has written quite a well- known German textbook — and Waldemar Voigt, Voigt is almost forgotten now, but I think he was quite an important man. He really was the who applied the idea to organize the research according to group theory. And his book on crystal physics, which I have here still, is systematically ordered according to the group properties of the space groups, and so on, of the crystals. I think this is quite a feat. And I had several courses — most of which I have forgotten — but one remained in my memory because it was a course on optics given by Voigt. We made all the elementary optical experiments on the diffraction interference, and so on, with our own hands. And this was a very good course — very well-prepared. To every experiment belonged a sheet where the experiment was explained, and one had to fill out lines about what one was doing and then to write down the measurements and so on. And it was awfully well-prepared, and I learned a lot there. This was my only real contact with practical optics; why, I've written two big optical textbooks, and I'm always ashamed that I haven't since those days seen these experiments. Well, I have seen all those in the books, but many very long.
Is there any point in this period that strikes you as the point at which you definitely began to think of yourself as a physicist and not a mathematician, or was it a slow, gradual, and imperceptible transformation.
It was quite slowly and gradually; no, I can't remember I (felt) more and more that I wasn't good enough in mathematics, and then began to study nysics. I think — strangely enough — I studied Gibbs first, when I went to England. Only before that I had the elastica problem with my thesis. ...
I take it that when you began that problem, it was a problem that you did not think of yourself as interested in.
Not in the least..
Did you then get interested in work of that sort?
Yes — or no, I was never interested in this kind of problem, but only in the mcthods to solve it. It was like this: There was the seminar of Klein together with Runge, on elasticity, and I attended it. I made the decision not to take part, only to listen because there was another seminar by Hilbert and Minkowski on electrodynamics of moving bodies which interested me deeply. There Minkowski's first ideas about relativity were already worked out and shown. And in Klein's seminar I didn't take one of the lectures to give — the students had to give lectures. But there was another fellow called (Haas) — I think he was later quite well-known as a physicist and he got this problem of the stability of the elastic line. And I was just called a co-referee, and I had to jump in if he were ill, or something. And he became ill the week before, and he came to me and said, he couldn't do it — that he was quite ill. I think he was unable to do it; he didn't want to do it and so he wanted to avoid it, and, in this way I came into the thing. And I had only a few days to prepare myself. And I saw that there was such a lot of literature — impossible to read in a few days — so I thought I'd better do it myself. And so I sat down, and the problem was clear. I had learned quite decently the theory of varia- tions, so I worked out a new method to determine, with the help of the mathematical criteria of the minima, the stability of such lines. I spoke about it, and Klein was very favorably impressed by it and wrote me a letter that I should do this as a prize paper for the faculty. This was very rare and a great honor, but I declined it. When I came back to Göttingen my friends said, "Your career is lost; Klein is so angry about your letter declining to do this that you have no chance to get any pro motion in Germany at all." And so I went to Klein and asked this favor, and so on, and he wasn't very nice. But I did the paper; I wrote it out. And in doing this work I found out how nice it is to calculate the angle where it would turn over and to try out how it fit with experiment. I made some very simple instruments — I wrote in (my paper that it was done by my hand), but I have found in my Recollections that it was done by a mechanical firm — well-known, (Spindler and Hoya). They made a very good microscope. I had a friend there amongst the mechanics, and he did it for me — made this apparatus. I made the experiments in my room on a table, and they gave, excellent results for the elastic constants — much better than you get pushing and pulling and, this sort of thing. So therefore, I was very proud of this. And then I wrote to Felix, (and I said), "Perhaps I am quite gifted for this kind of thing." And then I went to Breslau, and there I met Ladenburg. These people were really physicists, and there I learned first the real problems of physics — the optical pnblems of coherence of waves and such things that I had, never heard before. Voigt was only quite formal.
From whom at Breslau then did you particularly begin to get these problems?
By Ladenburg mainly. But also Schaefer who gave a lecture on Maxwell's theory, and Lummer a little in his lecture — I saw very brilliant experiments in lecture.
But from the point of view of learning the problems of modern physics, that this was not Lummer's strong point.
Well, from Lummer I heard of Planck's formula, for he worked on this. And, he — and perhaps Pringsheim his colleague — put me on this problem with the black-body which was connected with the Planck formula. It was to test a little piece of the curve.
You think then that it is really at that point, which is 1903, that this is really the first real awareness —
Yes. And then Ladenburg and Waetzmann and Reiche and we decided to read modern physics papers. And there one day we discovered the 1905 paper of Einstein. Reiche knew it already from Planck, and he told us we must read that. And there I became excited; I found this marvelous. And then I bean to work on my paper on the electromagnetic mass of the electron. And when I had the misfortune with Lummer — with my apparatus — I sent the paper to Minkowski. And he reacted very nicely; he asked me to come and finish this in Göttingen. And so I did.
At the time you left Göttingen to go to Cambridge do you think Minkowski was still unaware of the Einstein paper? You had not heard it from him?
Well, I don't know whether he knew that, but he was very familiar with all tricks of relativity already. And I think he had exactly the same ideas as Einstein, only he had not this way of expressing them in the most simple and impressive way. So I'm not sure. I asked him later once what he thought of Einstein — for Einstein was his pupil in Zurich — and he thought Einstein was a lazy fellow. He hardly ever came to the lecture. He hadn't a high opinion of him. He was very astonished when his papers came out.
But he saw their value?
Oh, yes. But I don't think he mentioned him very much in his big paper of 1908. I'm not sure.
As you were then in these years becoming a physicist, what belief did you find on — for example — the reality of atoms?
I think we took them all quite as a matter of course, and we made fun about these people like Ostwald who didn't believe in them. I don't think we ever doubted them, although there were very few real proofs.
What about Boltzmann's work in statistical —
Well, this I learned in connection with Gibbs. I came — I don't know why first to Gibbs and then to Boltzmann.
Did you learn this largely by yourself?
Yes, quite alone. I think I must have heard of Gibbs somewhere, or I got a paper of his in my hand, and when I went to Cambridge, I remember only that I bought in a shop two volumes of his papers on thermodynamics and statistics. And I read them. Oh, there was another connection. At Göttingen at that time was Zermelo. He was really a pure mathematician and worked on the theory of sets. I heard his lecture and was quite impressed by it. But apart from this he had a terrible controversy with Boltzmann on the foundation of statistical mechanics. And I heard a lot about it without reading the papers. I knew only that there was something like that; I didn't take part in it at all. I knew of Boltzmann via Zermelo, and then I must have heard the name Gibbs, also. Therefore, I bought these books by Gibbs just by chance in a shop. And I read them and was fascinated by them, and I studied them every day in Cambridge.
But this was not a subject which in these days would automatically have been a standard one?
No, no it was quite a new thing and nobody did it. A different thing was kinetic theory of gases, the ordinary elementry things — they were done everywhere.
But without doing anything as elaborate as Boltzmann's approach to the subject?
No, no. Well, we heard from Zermelo about this controversy about the foundation of the second theorem — whether this could really be reduced to a probability theorem or not. Zermelo didn't believe that. I have for gotten what he believed, I only knew that he was against Boltzmann.
But you think, on the whole, there was not much question in the minds of physicists that the atom was there to stay, that there really were such things?
Well, in Germany we didn't discuss it much at all. But only when I came to Thomson in Cambridge and he showed us the experiments. Of course, there was no doubt that there were electrons in the atoms.
Was this, do you think, a characteristic difference between England and Germany during this period?
Yes. Oh, I think England about that time was far ahead of at least all the provincial German Universities. Perhaps Berlin was different. In Berlin there were Rubens and quite modern physicists. But it was also not quite on top at all.
But do you think Cambridge was ahead generally of the German universities, or ahead with the respect to the problem of atomic structure?
Well, it was the central problem at that time, and the Germans didn't know it.
What would have been seen in Germany about 1910 as the central problems of physics?
Oh, that's much later. Then already there were known the Einstein papers on specific heat. And Kármán and my paper was 1908 — no '12. But Einstein papers were certainly known, and there was the controversy about Planck's quantum theory already going on. No, the period which I mean is the period of my student times — from 1900 to 1905 or '06. I at least didn't come in touch. But with Franck it was quite different. Franck was in Berlin and worked on gaseous charges in the line of Thomson's book. And he knew all these things on the collision of atoms and ions, and so on — the idea of excitation or ionization. That was already quite familiar to him, but not to me.
On this subject of the belief about atoms, what about the crystallographic question? There was a lot of work on elasticity and some on crystallography at Göttingen did people suppose that these were real space lattices with atoms at the corners, or was this much a mathematical device?
Well, Voigt, my teacher, made no use of it; he always did it with continuous media with certain symmetries, but he mentioned that it could be reduced to the idea of a lattice. And when I started my work with Kármán, we tool: it for granted that there are real lattices. I saw it from the point which I looked up only recently. The first paper — our first paper on specific heat — was a few months before Laue's discovery was known. And the second paper was a few months later, and in the second paper Laue's discovery was not mentioned, which shows clearly that we didn't regard this as more than just an ordinary verification — a taking of a known fact. We didn't take it as a surprise at all. I remember that I — at the same time as Laue — was thinking about using X-ray diffraction to prove the lattice structure. There were these experi ments going on by Pohl and somebody else. They made a very narrow slit of wedge shape and thought in the narrowest part of the wedge there would be broadening due to diffraction. And they had estimates of the wave lengths from that. And. I thought one should take other particles which were much smiler than one could make in an artificial wedge, for instance, the colloidal particles in a gold solution. I knew they were not molecular, but a hundred molecules or something of this size. I thought they should give a diffraction of proper wave lengths, and I worked it out theoretically — the rings — just as Laue did. And I was so busy with that, and then suddenly appeared Laue's paper with the crystals, and I dropped this idea. Of course, I wouldn't have gotten it, for the X-rays in use then were much too short forthe colloidal particle. They were perhaps wave lengths 10 times smaller than the size of the particle. Oh, but this is very private, I mean I've never told anybody about this because I did not publish the theory, nor did I do the experiment. But I contemplated it — I remember 'it very well. So you see I took these things seriously.
What about the ether? Was the ether still felt to be a real physical bearer of electromagnetic waves?
No, I think I followed always Einstein in these things. At that time he thought ether was a consensus concept .but later he took it up again and said it was quite a useful word for expressing the properties of empty space.
But that's a very different ether than the one that people were trying to build with Gyroscopes —
Oh no, this I never believed.
Was the physical reality of the ether still an issue during your education?
Well, there was a lot of talk about it, but I can't remember.. But just how backward. Germany was at that point can be seen from the following: when I came to Göttingen, I heard a lecture of Voigt on optics, and it was a good lecture. He used the electromagnetic theory. But I was told by other students that this was the first time — he gave this lecture every second year — the first time that he hadn't used the elastic theory of ether. That was about 1904 — '03 or '04. So late as that. The Maxwell theory hadn't penetrated so far as to be accepted for such things.
I'm interested in and surprised by your references to backwardness. But still what transformed this situation in German physics?
Well, I don't know. It was a slow transformation. I think it was partly our own work.
I think that this is one of the things that one must immediately say.
But there were other things, which went on quite without our influence — went on since radioactivity. I didn't take part in that at all. When I came to Göttingen, there was a lecture by Johannes Stark — the Nazi professor later. He was the Privatdozent, and he gave a lecture on radio-activity. And I didn't even understand the simple things. I remember quite well that one day there was a colloquium where one of the young Privatdozents named (Bestelmeyer) gave an interesting lecture on new experiments by Rutherford — I think the alpha deflections by the atom must have been happening at this time — 1905 or '06. And I was quite fascinated by it and after the lecture I went to him, and we went home together. I asked him about the simple fundamentals of radioactivity — I knew nothing about the, the —
Yes, the displacement law.
Of course that was, to some extent, characteristic of Germany. There was a little in Berlin, but Germany was late. Paris, Vienna, and England were all centers for radioactivity in senses that Berlin also later became one.
But there was here in Brawnschweig this paper by these two school-masters — they did work right from the beginning. Aster and Geitel ... And in Göttingen Stark was a very bad lecturer, but he was quite good in this thing. He did the experiments in radioactivity.
I didn't realize he had done much with radioactivity.
He didn't publish much, but he was interested in it. He gave a lecture on it.
Because his gas discharge work, and so on, I do know, but I hadn't known of his radioactivity work. Was there a change in the attitude of the students, or of universities, or of the government, toward science that helps to account for this increasing up-to-dateness?
No, I don't think so. In the First World War, which began in 1914, there was no exceptional treatment of scientists, as reasonably, in the last war it was done in all countries . And I think Ins the only one who didn't go to the front. My friend Ladenburg was an officer of the reserve army, and he went out with the first cavalry regiment in the field, and had rather wild experiences in the fighting. But he was wounded a little and sent back. Then he had the idea of this sound-ranging — other people had it too, but he was an officer, and, therefore, could get through with it. He started a sound-ranging department in one of the administration buildings, and there he called me in — I was in the airplane department at the time.
When you say in the airplane department — what sort of work were you doing?
Well, I mean I wasn't flying; I was in a camp where a group of physicists were trained to teach the crews of the airplanes to use the radio for communication. And. I got ill there and was in bed at home. My wife was clever enough to call in a professor at the university that we knew, and he gave me a testimony that I was very ill and couldn't go back to the camp. And during these days I was called to this other bureau where I had to work — this office. And there I worked for several years — during the whole war on these problems.. There were a great number of physicists collected.
You yourself then managed to call some people back from service.
Yes. And then it was my main interest in the war to save people from being killed, and I had quite a success. But in a few very sad cases I had no success. One, in particular, was our best Göttingen student in mathematics, (Hartner). He was in an infantry regiment. I tried and tried to get him back and then at last I got permission and, sent him a telegram — to his regiment — and in the night before it arrived, he was killed. And then I had the impudence to write an anti-militaristic article in one of the physics papers about this case, and it will be printed in my Collected Papers.
If you follow the papers on quantum physics from 1906 and 1908 on, there is far less discontinuity during the war in Germany than there is in other countries. There is less disruption ...
Well, the reason, I think, is that in England they put all the scientists into some war service, systematically. Later I had a discussion about this sound-ranging with young Bragg. I knew that he was in it. I knew reports from our front that the British had a much better one. I asked him why it was. And it turned out that they had much more money, much more power and influence to do the right thing. For instance, we were not allowed to build (an electric registering apparatus for timing the sound.) This was a quite simple thing to do, and we had all the plans made, but we didn't get permission. But the English did it, and they had a very nice apparatus. On some attacks these were found, but we weren't allowed even to imitate them.
Really. Even after they had been found during attacks?
No. The German officers were so stupid; they didn't understand the importance of that.
But this meant on the whole that a man like Sommerfeld, say, who was over age, and, therefore, not subject to call, would not have been asked to do science for the government, for the war effort?
No. He could do what he liked. In Britain I think they were much more patriotic and —.
All right, Sommerfeld could go on doing what he liked, but perhaps an experimentalist would not be able to because he couldn't get the equipment any more.
That may be, I don't know.
I wondered whether this may have made German science more theoretical after the war?
I don't know. I think it was more that the German mind at that time was more philosophical and theoretical.
And certainly was prepared to bring usually better, more powerful, mathematics to bear on physical problems.
I find also that there was some other difference in mathematics. It was perhaps better, I don't know; the British mathematics was awfully good. The difference was another one; it was a more philosophical one. The British have an inclination to two extremes — that's my impression. Either they are terribly abstract and then they are beyond all experience and work only with the most abstract ideas, or they are purely empirical and don't like the way of applying theoretical things to the empirical facts. I don't know whether you have the same impression.
Tell me more about what you mean — who you think of for the category that is terribly abstract? Certainly I know the empirical.
Well, Eddington was — Jeans and this kind of people who philosophize about quantum mechanics in a way which we don't like at all. They try to show that it is a priori — that it couldn't be different, that it's a consequence of the construction of our brain and such things.
This jumps way out. When you first knew of his wave equation, would you have thought Dirac's wave equation was in this same category? How did that seem when it first came out?
Dirac was quite in our line. That was another generation already.
Well, how was Dirac's relativistic electron theory received? Did this seem durchsichtig from the start?
Oh yes, we grasped it at once. You see, Pauli was very close to it. Pauli missed only putting these two-two matrices together into a four- four matrix. Why he missed it I'm not quite clear. I think that Pauli altogether was by far the most gifted of all of us including Heisenberg and Dirac. He missed the quantum mechanics. But perhaps he missed it only because he knew that Heisenberg and I were working on it, and he didn't want to interfere too much. But otherwise, I.think his ideas were always correct, and he had always the most powerful method of taking things.
Where would you place Einstein in this whole group
Well, Einstein — it's very difficult to compare him at. all because he was a universal genius. He had exhausted himself with the general relativity and the cosmology and these things, and when it came to quantum theory and quantum mechanics, he was perhaps too old to follow. But all the foundations of it are due to him nearly all of them. The idea of transition probability.
Were you at the meeting in Salzburg in 1909 of the Naturforscherversammlung?
I think I was; I'm not quite sure.
This is the place where he read his famous paper on statistical fluctuations.
I can't remember. I was once at one of these meetings with him, and I have written in my Recollections how it was. I spoke about relativity, and he was already beyond it and spoke about quantum theory or something. But I don't know whether it was in Insbruck, or in Salzburg.
You don't remember that fluctuation paper or how that was received at the time?
Oh yes, if it's me personally that you mean. I don't know how other people received it. I have given a lecture on the occasion of the fifty years anniversary of Einstein's 1905 paper — that was in 1955 — in Berlin. And this was centered around this paper. I thought this was the most important —.
You mean the 1905 paper?
No, the fluctuation paper. You know this lecture of mine?
I ask particularly about that meeting and about that paper partly because of the curious history of the photon and the photon idea. ... There seemed to be lots of places that were very much up to date on what was going on, but paid very little attention to the photon. They thought this was an aberration, or if not an aberration at least pushed it aside. Do you have any recollections yourself of discussions or of attitudes toward that problem?
Well, I can't remember, but I have the feeling that I took it very seriously after Compton's experiment — where it shows the collision laws are holding. And then also after Einstein's fluctuation consideration where it showed that you get the correct fluctuations considering a photon gas. There are, of course, the '24 papers — the photon gas paper.... But you think it may very well be that this range of ideas was not taken terribly seriously earlier than that?
I don't know this lecture of yours, and I obviously should. [Break while paper is looked up.]
I can't tell you whether other people did; I didn't work on it. Well, I think from the beginning that I thought that Einstein's explanation that the electromagnetic field is a probability field for photons seemed to me the only possible one, and if a photon appeared I always regarded it from this side. This seems to me quite possible; I wouldn't say it was so, but I think it might have been so.
Is that an idea you think that he published or that came to you in conversations, perhaps in Berlin during the war? The notion of the electromagnetic field as a probability field for photons.
No, this is just printed in one of Einstein's papers. I can't tell you where. Of course, this is very vague. I have just now come over this with my collaborator on our latest optics book where we happened to make a new edition. And there the question' arises how to bring in the new discoveries in optics, like the maser and the laser, and so on. There comes the question of the coherence and all that from the modern stand-point — which is quite changed. And then the problem was how is the probability aspect of the electromagnetic waves connected with the Ψ function? For the electromagnetic field as such is quite a different thing. Now I haven't worked on it for years, and so I have quite forgotten it, but I reconstructed it roughly that one has to take E + iH where E is the electric vector, i is the square root of minus 1, and H is the magnetic vector. E + iH is a kind of Ψ function with three components, and that I think does the trick; it behaves just like a quantum mechanical Ψ function for a single particle at least... [Phone call breaks into the interview here]
I started to ask you about that work with Landé and about trying to place the Bohr atom in a crystal lattice and calculate forces. It's fascinating work to look at now, and, of course, very strange as one watches these ring models manipulated — the computation of potential functions. And yet it's quite clear that at least in Landé's development that work had some very real importance.
Well, it had some for me, but it had a very strange history which is not expressed in the published papers, namely a mistake we made. We calculated the mutual energy of these rings — the sum over the energy of a pair — and we worked it out. And we forgot that one has to write one-half of that. If you write the sum of Eik one counts every pair twice — the ik and ki. We forgot this and we worked it out and these ring models fit it beautifully, and gave us the correct values for the compressibilities. So we thought this was wonderful, and we gave it to Einstein for publication in the Berlin Academy. And the next morning I came to my military department, and there was Landé sitting quite depressed, and he said you must destroy the paper — it is quite wrong. And he told me that he had found this mistake.
That he had found it or that Einstein had found it?
He had found it, I didn't. I saw it at once, and I said, "You are right, this is awful. There is no other way; I'll run at once to Einstein, in spite of my service hours here, and ask him not to put it before the academy, for it must be changed." Well, I ran to Einstein, and he laughed — I have never heard him laugh so much. And he said, "This is so marvelous that you have made a mistake; I thought you would never make one. You mustn't destroy it. Of course, we'll not submit it at once — I will give it back to you. But I expect to have it in a week or two again in an approved form." So I took it back. Of course, we were very dejected, then we began to think about it, and the idea came up at once that it meant that the things are not rings. In the potential function the exponen must not be two, as for the rings, but eight. Then it came out right. And I said, well, we'll write it again and we'll just turn it around! We'll calculate this and say that it doesn't fit by a factor of 2, which means definitely that the atoms are not plane, but are cubic, at least, and perhaps spherical shape. And so we wrote it again, and this way it came out. And then Einstein was very content. He said, "I told you so — that it would be all right, and would lead to some progress." And this was so much more convincing Just because of this error that it meant a higher symmetry, not plane, but a cubic thing. That we were quite happy about. This I have never written, even in my Recollections, I think.
What this leaves me with is perhaps the impossible question: in order for that sort of series of events to leave deep conviction that the answer is, "It must be a higher symmetry," one presumably had to take the initial atom model itself quite literally. You have to have quite deep convictions about at least something very like the Rutherford-Bohr atom. Now was this model that firmly established? ...
Oh yes. I think that was quite established. But, of course, there was no way of explaining other symmetries than plane ones. It was a quite artificial thing if you would make two crossed circles, and you could never get a cubic symmetry at all, I think, In this way. And so I saw at once that it was something quite new. But the convincing thing was that for the four or five crystals that we had — all the combinations of the alkali with the halides — for all of them the figure was correct apart from the factor two within quite a small error. And this was so convincing. It must be a general property of matter. For all ions this was coming out — for positive and negative ions — they must all have this higher symmetry.
Well, now you go on from there for a bit with the whole question of cubical atom models and others, and then seem not to go very much further.
Well, we believed that from the beginning that such static cubical models are only models and nothing more — they had not much content of truth. And then we had to wait until quantum mechanics was developed far enough. Then I didn't go into this anymore because (???) the s state of an ion is spherical. I have never taken part in calculating energies from the atomic models.
This same period, in Berlin, is the time of Einstein's probability coefficients paper, which was, I think, 1917. Did you talk to him about that paper at the time that it was coning out or being prepared?
You mean the derivation of the Planck law from the transition probability? Oh yes, that we talked over very carefully. That was most impressive. Particularly the symmetry law which came out; that the probability of the up-down and down-up was equal — this was quite surprising.
How about the idea of the induced radiative transitions?
Well, this was quite surprising, but not so much for me, for Einstein had explained to me that if you translate the ordinary classical formula into quantum language, you must have the symmetry — the up-down equal to the down-up.
I think with the little time that left what I should like most of all to ask you is about he period when you and Professor Franck both go to Göttingen and really — I think one must say — transform physics at Göttingen. Did you both set out from the start to really make things over again at Göttingen?
No, as I have said — I don't know whether you have heard it or read it — when I was in Frankfurt I got a call to Göttingen to take over the whole department — experimental and theoretical. And there was only one associate professor, Robert Pohl. Now, I decided at once that I couldn't do that, because I wasn't good enough in experimenting and I had not enough ideas to keep a whole department working. So I went to Berlin and I went to the minister end was discussing this thing with one of his officials hours. I said, "I can't do that; you must at least nominate one other physi cist as my helper." But he said, "There's Pohl, why don't you work with him?" And I said, "I hardly know him, and I have had no personal contact with him; and it's very difficult for me — can't we do anything else?" And then he came with this enormous ledger where all the details of Göttingen University were contained. And then I found, after a long the following: Voigt, who had retired about a year before his death, had transformed his full professorship into an Extraordinarius with the personal rank of a full professor, but with the intended remark that it was to be canceled with his death. And then Pohl's professorship was of the same order, and by the mistake of the writer of the ledger these two remarks were exchanged, so the canceling was at Pohl's death and not at Voigt's. And this I discovered, and I was very proud and said, "Now you see we have the professorship, for Pohl is still living and the other professorship is not canceled." "It may be a mistake, but what have I to do with your mistakes? I insist that it is done."' And they laughed, and said, "It can't be done; this is apparently a mistake." And I said, "No, no, I insist on this." And so we went out and cane back with the minister himself, Becher); this was in 1921 shortly after the Revolution. And he also laughed very much and said, "We are still in the process of rebuilding, and in a Revolution anything can be done. You are right; we'll make it as you propose. We'll accent this as written in our budget. And you have only to tell us a name, and then we'll call him." So I thought very hard a few days about whom — there was Ladenburg and Franck and. Hertz and, a few others — Baeyer. I decided for Franck, for he was my close friend, and also I knew him — knew that he was a yery gifted man. And so Franck was appointed. And then we were three. But the condition was that the two others, Pohl and Franck were appointed first only as Extraordinarius — not the full professorship. But a year later they were promoted to full professorships. And it was just in time, for this year Franck got the Nobel prize, and then I was completely justified — that was a great triumph for me. And in this way we got there, and there was hardly anything to change. The courses were all quite decently organized. Franck wasn't interested in teaching at all, and Pohl did all that — he did it until he retired a few years ago. And. I built my department up as I thought right; not very much chance compared with Voigt. So we had not the feeling that there was anything new.
It really was then just the individual impress of your own work and per- sonalities as teachers. Almost immediately you start to get, from the beginning, really first-rate students. I think particularly of the speed with which Pauli comes up.
Pauli was my first assistant. I wrote to Sommerfeld and asked him whether he knew a young man who could be my assistant there, and he. recommended Pauli, and I accepted him. And I was, from the beginning, quite crushed by him. v wife expected a baby and couldn't go for a summer holiday and waited at home, but I was very tired and went away to a little place in Bavaria. Pauli visited me there to make my acquaintance. And then he came with me for all my walks, and it was not at all any recreation because he talked physics all the time — very heavy physics. He was a man of enormous energy. But he was a very pleasant fellow. And then he came to Göttingen, and when he left, after two years, I think, he recommended Heisenberg as his successor. But I think Heisenberg was not really his successor — his successor was, I think, Hund, or somebody else between.
I think Heisenberg perhaps came to you before Hund.
Yes? I don't know who was there, but Hund knows all that. But we had a friend, an industrialist in Westphalia. We are still very great friends with their son. My wife was there for a few weeks for recovery at their country home. He gave me the money to have a private assistant. And I think Heisenberg had this post, but I'm not quite clear. But these things are known to Hund; if you want to know that, Hund can give you every detail.
Is the industrialist you speak of Henry Goldman?
No, Henry Goldman was quite a different man. Henry Goldman's acquaintance we made in a very funny way. When I was still a professor in Frankfurt there was an inflation, and the money had no value at all, and I couldn't buy any apparatus. And. I wanted to have some dollars, and so we wrote to a friend of my wife's, a young businessman in Berlin, — no I didn't write him, but I met him by chance in the road in Berlin. And I said, "Where are you going?" And he said, "I'm going to America; I'm engaged to an American girl, and I want to marry her." And I said, "Oh, when you go to America, you must find a German-American — a rich man — who can give me a few thousand dollars to continue my work." And he said, "I will do that." And a few weeks later I got a postcard from him where he wrote simply, "Your man is Mr. Henry Goldman." And he gave me an address on Fifth Avenue. "Write him a nice letter. He's coming to Berlin and will be in the (Adion) Hotel." So I wrote to the (Adion) Hotel, and I got a very nice reply and a check for some hundred dollars at once for my department. And then I went to Berlin to thank him. He was an elderly Jewish man and he told me his story. He was the founder of one of the big financial institutes — banks Sachs and Goldman. It was one of the big ones of the time, comparable with Carnegie and such things. He was a friend of Carnegie's — they called each other by their Christian names — or Jewish names, as the case may be. And Goldman said, that he was always on the side of Germany. He thought that the Americans and French and English were quite wrong to give all the guilt for the First World War to the Germans. He didn't believe that it was quite equally distributed, and he wanted to help the Germans, and, therefore, he came over. He wanted to know how he could do this, apart from helping me. Making use of the occasion, I said, "By helping me more." I got quite a lot out of that — not quite a thousand dollars, but that was an enormous sum for that time in Germany.
Was that only in the Frankfurt, period, or did that go on in Göttingen also?
No, later also. Later he sent big parcels; I think one day there came forty such big boxes with clothes and shoes for poor people in Germany which my wife had to distribute, and it took her weeks and weeks. And also money for my department. And he visited me once; he came to see Einstein; I introduced him to Einstein. He was very keen to see the celebrated man. And he came with Einstein in his car to Göttingen and stayed with me. And later when the Nazi's came, I met him in London. He was completely broken down, for he had such a faith in the Germans, and now there was an anti-semitic movement and he couldn't understand it at all. He died a short time later as a broken man. But at the end of the First World War he told me that he had retired from his business because his sons and brothers who were also in it didn't share his good opinion of the Germans — they were on the allied side. So he retired and spent all his money on collecting pictures and works of art. We were in his home on Fifth Avenue — it was a remarkable estate — incredible pictures of the first-class masters. And he was almost blind at the time, but he could describe every picture in complete detail. Once when we were there, for example, the bell rang and there came two men from the Harvard College of Arts, and they wanted to see these pictures. And he showed them around and he explained everything to them in detail — the pictures and also the statues. As they were leaving, he ran his head against the door; he couldn't see that it was half closed. He returned and I helped these people out with their coats and so on. They said, "What is wrong with Mr. Goldman? Doesn't he see well?" I said, "He sees nothing." And they said, "But that is impossible; he has explained all the pictures to us. And I said, "Yes, he knows them all by heart — he loves them so much." I don't know what has become of them. I think he intended to give them to the Metropolitan Museum. He was quite an interesting man.
You speak of this initial impression that Pauli made on you. What was it like as the year went on to work with him — to have him for an assistant?.
Well, it was very difficult to work with him. He never would do what you told him to do — he did it his own way, and generally he was right. But he didn't help me very much with my routine work, and that was the difficulty. I had people who wanted to get a doctor's thesis — an ordinary one and not a very high-brow one — and for this he had no interest. And then I was suffering from bronchitis very much and had sometimes to stop my lecture and he had to give it. The lecture was at 10:00, and at half past 9 I always sent my maid over to his house which was in the neighborhood, and she always found him still in bed snoring and had to wake him. He had quite a regular life — he worked deep into the night and slept all the morning.
Did the range of problems that Sommerfeld had introduced him to interest you more through him than they had previously?
Well, I think not. I knew all that Sommerfeld did also from his publications. But he was just at that time finishing his celebrated article on relativity in the Encyclopedia. And this I admired very much; it is a marvelous piece of work — still one of the best presentations.
Was Heisenberg very different as an assistant?
Oh, Heisenberg was quite different; he was like a little peasant boy when he came, very quiet and friendly and shy. My wife tried to make him a little more worldly. Very soon I discovered he was just as good in brains as the other one. But he was much more helpful. He helped me with all my routine things in a very conscientious way.
Was the contact with Copenhagen that becomes quite important in the twenties maintained by Heisenberg, or did Bohr visit often?
No, Bohr came only to these lectures. I can't remember that he ever came another time. And I was once in Copenhagen for a few days, but was not a member of his team at all. But Heisenberg was there for a long time and. Pauli also and Hund also.
In that terribly important article "Ueber Quantenmechanik", you speak of long conversations with Bohr, that have been quite rewarding in the formulations of the paper.
What did I say?
You speak there of the use that you have gotten from some conversations with Bohr.
I think perhaps we met somewhere, or perhaps he came to Göttingen another time, I can't remember — or it was my visit in Copenhagen.
Do you remember when that visit would have been?
Let me see if I can find the point in the paper where you say this — yes. It's in that first footnote.
"A favorable chance has led —." It must have been a chance meeting somewhere, but I can't remember where. Which year is it?
'24? No, I can't remember that.
Did Heisenberg play an important role also simply as someone who was closely associated with both Copenhagen and Göttingen, keeping the two groups informed about what was going on at the other place?
Yes, certainly. You asked yesterday about our philosophizing. I mean the philosophy of the thing was always coming from Copenhagen at that time, and I didn't like it very much at the time. The way that Bohr considered all these things from a philosophical standpoint seemed to me premature, and didn't fit to this. I always thought mathematics was cleverer than we are — one has first to find the correct formalism before one should philosophize about it. So I saw the importance Of the Correspondence Principle, but I didn't think it was the absolute center of everything. And it was a kind of philosophy which seemed to me not righht. At least that's what I remember about it.
In some ways that attitude though, probably even more strongly, would be close to the attitude that one thinks Sommerfeld probably took toward the Copenhagen approach. He was clearly not even impressed with the Correspondence Principle, as you very clearly were.
Yes, but Sommerfeld was always very content to have some prescription to do a calculation, and he never thought about deviating from it in a some- what courageous way. And I was quite convinced that one had to; that there must be something new behind it. And, therefore, I think I did much more experimenting with such things — and Heisenberg too. And Heisenberg was really ahead of me in this sort of way. Though I'm not so sure that he was much ahead, for I once had a talk with Jordan about it — or was it a letter from him — and he said that the idea of replacing the differential operator by a difference operator, which I did in this paper, didn't satisfy us, and we considered earnestly the possiblity that there was a kind of multiplication law behind it, as Heisenberg then really did. But we didn't find it. So this multiplication idea was certainly in the air at that time.
Surely; the steps there are in some respects so close.
And that was certainly not in Copenhagen. Even if Heisenberg started this work in Copenhagen it was (???). And Bohr has never claimed anything.
Though the Kramers dispersion theory is such a key step in this development that the question I ask particularly is how close these personal connections through Heisenberg may have been. The intellectual connections through certain of the published papers are very important. Certainly the Kramers dispersion paper which is a Copenhagen paper is one of the terribly important ones that both you and Heisenberg build on in the next steps. But you do feel yourself, at least to the best of your recollection, that you were somewhat distrustful of the explicit extent of philosophy in the Copenhagen approach?.
Well, I always thought if one always considers only the correspondence case it means the limiting case. One can never extrapolate to the other extreme, and one has to have some new idea. And I didn't see in the Copenhagen approach any suggestion of this; therefore — except this Kramers thing. But that came over from Holland, not from Copenhagen. Or was Kramers still in Copenhagen at this time?
Oh, I think Kramers was in Copenhagen. You see because that comes immediately after the Bohr-Kramers-Slater paper which was done in Copenhagen. Just let me ask you one more thing. Your sense that there was something missing in the Copenhagen view, and that it was perhaps premature to be this philosophical — how did you feel that Heisenberg stood on that problem? Did he share very much the Copenhagen view, or did he have also some of your distrust?
No, I think Heisenberg was just the buffer of both. I mean he saw the importance of both — the approach from the correspondence side, but he also appreciated my view that one ought to have some new invention — new calculus instead of the old one. And that's what he tried. ertain I insisted in the presence of Jordan and Heisenberg and Hund Eund was there already, I think — that there must be a new calculus, and what (I) tried here in this paper was just to show that there is a kind of calculus. It's not a calculus, but an analogy.
Indeed it is, and it's exactly the sort of thing which Heisenberg himself does in what's really he next paper in that series.