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Interview of Alfred Landé by Thomas S. Kuhn and John Heilbron on 1962 March 5, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4728-1
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This interview was conducted as part of the Archives for the History of Quantum Physics project, 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: Ernst Back, Niels Henrik David Bohr, Max Born, Constantin Caratheodory, Peter Josef William Debye, Paul Ehrenfest, Albert Einstein, Walther Gerlach, Samuel Abraham Goudsmit, Werner Heisenberg, Heinrich Mathias Konen, Peter Lertes, Fritz London, Erwin Madelung, Wolfgang Pauli, Max Planck, Erwin Schrodinger, Arnold Sommerfeld, Otto Stern, George Eugene Uhlenbeck; Artillerie Prufungs-Kommission, Universitat Gottingen, Universitat Marburg, Universitat Munchen, Universitat Tubingen.
I don’t at all want to bind you to this program that we’ve laid out here. It did seem to us that it would make a good deal of sense to stay fairly chronological. Perhaps on this first morning it would be a good idea to talk particularly about your own early years in the field, the years of your education.
I changed from Munich to Gottingen, back to Munich again and then to Gottingen. I began my studies at the University of Marburg, with calculus, with Professor Hensel. When I came to the University I thought I was excellently prepared, because in high school I always was, by far, the best in mathematics and physics. At the University I found out that everybody in the other seats were also the best, and some of them very much better. In fact, if these personal things interest you, in this course on calculus, I didn’t understand anything — what it was all about. There was a lot of talk about epsilons and deltas, but the whole idea I completely missed. This was in the spring semester. During the summer months I had a very good book — Serret — a French book translated into German. I then learned from this book.
Was that a widely used book?
Very much used, yes. It was recommended by Professor Hensel.
How much calculus had you had at the gymnasium?
Nothing, nothing at all… Trigonometry, yes. But, for instance, no spherical trigonometry, just ordinary trigonometry.
How much physics did one learn in gymnasium?
In the gymnasium there was very little. It was a secondary subject. But I happened to be in a separate course set up in the gymnasium for people who showed some inclination to natural science. There I had a very inspiring teacher who made experiments with us. He had experiments about Hertzian waves there in the laboratory, and all of this was very inspiring and interesting. He was my chief teacher at that time. In fact, do you know that when Einstein was asked, “What brought you to your interest in physics?”, he said, “Bernstein’s Naturwissenschaftliche Volksbucher.” It was exactly the same Naturwissenschaftliche Volksbucher which I read as a boy of 13 or 14. I became very much interested in physics and particularly astronomy — the planetary system and so on.
Did you intend when you went to Marburg to be an astronomer?
No, no. At that time already I was decided to go into physics. I spent only one semester of three and a half months in Marburg and then went to Munich. In Munich I began to study mathematics as good as I could. I had a course in algebra from Pringsheim. Lindemann was also there. I had crystallography from Groth, who was at that time the greatest authority in crystallography. I had physics from Graetz, although this was an elementary course in physics. And I had experimental physics with Professor Roentgen, who was so boring that it always began with the whole auditorium full and ended up with about half a dozen people. And I was not one of those half a dozen.
Was crystallography regularly studied by physicists?
Yes, it was among the required courses. Then, after a year and a half in Munich, where I had no contact yet with Sommerfeld, I went to Gottingen. There I really got into a more detailed study of physics. There my most impressive course was one in mathematics — differential equations and complex functions with Professor Toeplitz. In physics I had a very interesting course with Max Born who at that time was just a beginner. He gave a course on Maxwell’s theory — as far as I can remember — and also a little bit of relativity, which was his special subject. There were only three or four listeners — he was Privatdozent. You know that Born later became the most famous teacher of theoretical physics after Sommerfeld, but his first course was just abominable. He said a few words, then turned around, wrote something on the blackboard, and said, “Das Kommt so heraus”. Long calculations without much explanation. It was the first course he gave, maybe his second. Apparently I made a number of questions to him which interested him, because later on he remembered me and did one of the most decisive steps in my life by recommending me to Hilbert. In Gottingen I also made contact with a number of other younger people that were interested in physics at that time. In Gottingen mathematics and physics were very closely connected, very closely connected. I never found another place of such close cooperation. The main reason was that there was only one library for both together. People always met each other in the library and later on in cafes. The famous cafe of Kron und Lanz in Gottingen was a center of mathematics and physics in the afternoon. When the physicists had a question in mathematics, there was always a mathematician available right away to try to solve it. This is one of the things I miss very much here at Ohio State University. Mathematics in one building, physics in another, and the grad students don’t know each other. The teachers eat in the same faculty club but there is always one table where the physicists assemble and another table for the mathematicians. There was a very great advantage in Gottingen.
What was it like at Frankfurt later?
In Frankfurt it was rather close cooperation… I was much further advanced in Frankfurt. Speaking of my student days, the center of mathematics was certainly Gottingen, but the great Sommerfeld in Munchen was a tremendous attraction. In my third year I went to Munchen and became one of the pupils of Sommerfeld — I became part of Sommerfeld’s circle. There were other young students and assistants. I was at that time one of the youngest who just listened in on the others’ talk. Debye was the chief assistant of Sommerfeld; Epstein was there. Ewald — the crystal optics — had his Ph.D. with Sommerfeld at that time. I remember in 1912 when Laue, Friedrich, and Knipping showed their first X-ray picture. We sat there in the theoretical physics seminar and clapped hands for five minutes.
Had the group heard in advance of this?
Oh yes, there was talk about it.
What was the attitude about the probable outcome of the experiment?
It is hard to say now. If I can talk of something quite different which just comes to mind concerning attitudes. I was in Frankfurt when Stern made his experiment, to which Gerlach also gave his hand in the last moment. First of all, Stern made this experiment with the prospect of showing there are no quantized states. He was more surprised than anyone else to find the division into separate beams. He thought to show that these quantum states are just some abstract stuff which helps us calculate things but are not real. He was more surprised than anyone else. Another instance: I was in Zurich in 1925. Debye was Professor in Zurich at that time, and Schrodinger was also. I knew Debye pretty well and spoke with him, and he said, “What do you think, Lande, of this crazy idea — Schrodinger thinks to solve the quantum problem by waves. Isn’t that crazy?” He used some German word of course. Well, these are just instances of what people thought beforehand. But about Laue, I don’t know anything. This whole group met every afternoon about two o’clock in the Hofgarten at a round table. The classes were almost exclusively in the morning, and the afternoons were always free of official duties. There all the problems of modern physics, particularly quantum theory, were talked through. Lenz was one of the group. Lenz was, I think, the first to give a … term analysis of the band spectra.
I wanted to ask one question in this connection with the transfer from university to university. When one went from Gottingen to Munich to join Sommerfeld’s group, was this something one did at one’s own pleasure, or did you need a letter to Sommerfeld? Were you recommended to him?
Oh no, not at all, not at all. One just went from one university to another for a change. Gottingen was a small town and people wanted to go to Munchen for various reasons. The chief reason of course was Sommerfeld. I was told, “Go to Sommerfeld. There you will learn more than you can learn anywhere else.” And in Munchen you have winter sport, and summer sport. You have mountain climbing. There was the Fasching in Munchen, which was very fine. There were theatres, I was always very much interested in music — I almost became a musician when I was young, very young. I had the idea, but fortunately I turned to physics. One didn’t need any letter of introduction, one just went to courses. After the course I spoke a few words with Sommerfeld. He was very professorial, as most German professors are very formal and so on — but less than most others. Sommerfeld was a great ski fan and almost every Sunday in winter went with some of his group into the Alps. All the time we were walking uphill and downhill, he talked of physics — nothing else, absolutely. And of course the great problem was the quantum riddle…
You mentioned a while ago a particularly valuable and highly recommended book in mathematics. Were there other books of this sort in mathematics or other subjects which one was particularly likely to have seen.
I learned my algebra from a textbook by Bauer in Munchen. Bauer was a very old, retired professor, but he wrote a very excellent book. I learned all my mathematics from books, never from courses. I can’t learn anything if someone is talking at the blackboard. I must sit at home and have a book before me so that I can go at my own pace, which was always very slow. I stopped when I came to anything which I didn’t understand. I simply couldn’t go on. Now at this time in Munchen I remember I was not the only one of this student group who wanted to solve the “quantum riddle.” To solve it meant to show some gap in the equi-partition theorem of the energy which allowed only selected energy levels. I had a model of a gas of atoms. They screened each other and so on. I spent a very great amount of time on this, and I remember there were other students who were also working on it. We almost raced to see who would solve the quantum riddle first. I also remember Sommerfeld telling us that this is absolutely futile and, that in his opinion quantum theory is something fundamentally new. We simply have to acknowledge this and give up this fruitless effort.
Do you remember how other people besides Sommerfeld felt in this period?
…It was the time in which there was a very thorough revision of statistical mechanics, certainly initiated by the quantum riddle. Something must be wrong with statistical mechanics. It was the time of Zermelo and of investigations about ergodic systems. My friend Paul Hertz, a nephew of Heinrich Hertz, spent many years — his most productive years — on a thorough critique of probabilistic mechanics. He wrote many articles, but he simply didn’t go with the times. He couldn’t get out of the classical idea. But on the other hand, it was necessary to investigate whether really there was no gap in classical statistical mechanics at all. Other people simply took the new quantum rules, and tried to improve on Planck’s proof of the radiation formula. You know there were several other approaches — Einstein’s derivation, Debye’s derivation — in order to reduce everything to the most elementary things.
In this period before the Bohr atom, was the black body radiation law seen as the only source of the quantum riddle, or was the specific heat theory and the photo-electric effect part of the riddle also?
No. Black body was of course the starting point of it all… It was always really the quantum riddle of non-equi-partition of energy and selected energy levels. How to interpret this — even Planck changed his mind, several times. If I am not mistaken, the origin of the specific heat theory going beyond Einstein in terms of proper vibrations — quantized proper vibrations of matter — came first from Debye. Debye gave a derivation of Planck’s radiation law, which was a forerunner of his specific heat theory. Now I must find out what is the difference between Planck’s derivation and Debye’s derivation of Planck’s radiation law. Planck had the Jeans proper vibration, and let each of them have only select energy levels. In Debye’s derivation it was different. I am not quite sure what was the difference.
You were actually at Munich when Bohr’s paper, the Bohr atom paper, came out, were you not?
No, I was in Gottingen again. I began to write my thesis in Munich about quantization of vibrations in a medium… just some question which Sommerfeld wanted to clear up and it was of no great concern to anybody. But at that time, Professor Hubert in Gottingen became very much interested in theoretical physics. Since he didn’t know much of physics, he engaged an assistant. His first assistant was Professor Ewald, Sommerfeld’s pet student. Sommerfeld and Ewald were very close… Sommerfeld had recommended Ewald to be Hilbert’s teacher in physics. In Gottingen he was called “Hilbert’s Hauslehrer” — the implication is: a poor young man who needs some money and gives lessons to a rich boy. Ewald was there for one year and then in 1912 I got this position. I went from Munich to Gottingen on the recommendation of Max Born, who remembered me from his first course. This was very decisive, because as Hubert’s Hauslehrer in Gottingen I certainly had official status in the scientific community and became a member of the group of young mathematicians and physicists… This, in fact, was the beginning of my scientific career. Every morning and afternoon I had to report to Hilbert on new literature in quantum mechanics, on ideas about the behavior of solid bodies at low temperature, on spectroscopy, and the like. Hilbert, at that time, had the ambitious plan to find what he called “the world formula” — a formula in which you just put in the initial conditions and then the world develops, a la Laplace. Of course quantum mechanics made a big crossing out of this idea. It was a combination of optics, of relativity — special relativity at that time. He tried also to put in a little bit of quantum mechanics. Of course not very much came out of it except that there were always very lively discussions.
Did Hilbert also feel, as Sommerfeld had, that the quantum effects were absolutely fundamental, or did he hope to find, a semi-classical derivation for allowed states?
I don’t know. I don’t think that anybody had definite ideas about that. There were always hopes that maybe there is a way to explain and understand the quantum phenomena. Hilbert said, “Physics is too difficult for the physicist. Only a mathematician can do it.” And he had a number of similar bons mots at that time.
Was he partly responsible for the strength of the liaison between the mathematicians and the physicists at Gottingen?
Max Born was a pupil of Hubert… In that group at Gottingen at time was Max Born, von Karman, Courant, Weyl, Erwin Freunlich, and Becker. Hecke was a mathematical assistant of Hilbert, and there were a number of other young physicists who always came and went again. There were meetings, and seminars, and in one of the seminars a young Danish physicist, Niels Bohr, came, and gave his first report on the frequency condition in the atomic model. This must have been in 1912.
Before it was published?
At the same time as it was published.
Do you think you heard it from him before you saw the paper?
Yes. You see, it was published in the Philosophical Magazine in English. The Germans at that time — I exaggerate a little — didn’t believe anything before it was published in a reputable German journal. In fact, only a few people read English journals because in the gymnasium, English was not taught — only Greek, Latin, and French. Many people simply didn’t understand English.
Did people in Germany by and large read French journals, or did they restrict themselves to a great extent to German?
Not too much besides German. Anyway, I remember this first meeting of Bohr, which must have been after publication in English. He spoke rather poor German with his usual very soft voice, and in the front row were all the big wigs. They shook their heads and said, “If it’s not nonsense, at least it doesn’t make sense.” I spoke with Max Born after the lecture, and he said to me, “All this is absolutely queer and incredible, but this Danish physicist looks so like an original genius that I cannot decline that there must be something to it. This was the attitude.
How had people felt about the Rutherford atom before the Bohr paper?
It was known, but only a short time after it was known, Bohr came already.
The Rutherford model wasn’t given any particular priority?
No, no. I remember that at that time there was a little book on the structure of the atom completely in J. J. Thomson’s line. There were pictures of corks with iron pieces in them floating on water. In the middle was a magnet. It showed how they arrange in fours and fives and sixes and so on, and even in various “shells”. This was the main idea at that time. The only regret was that you could have these models only in two dimensions instead of attractions and repulsions in space.
You were just starting to say you were giving a seminar.
Yes. I had to give a seminar talk about my long calculations, fruitless calculations, on finding a gap in statistical mechanics which would allow selected energy levels. I gave this talk and wrote the whole blackboard fall of formulas, and during that time it came to me, “This is all nonsense. I must believe Sommerfeld, who told me there is no solution this way.”
Was this when you were back in Munich?
Yes, before I became assistant of Hilbert. I went to Gottingen already a convinced quantum theorist… By the way, I forgot this. In my first Gottingen period, before I even came to Sommerfeld, I wanted to begin already preparations for my thesis. I went to the laboratory of Professor Riecke, who was at that time the chief experimental physicist in Gottingen. Just like everybody else there, I was given some problem about cathode rays. The first job was to have a little wire in the empty space of the cathode ray. I put in an electrode or something. I pumped out the tube and every time next morning there was air in it again. I did this for about two or three weeks, and always dirt or air or something. I became so disgusted with experimental physics that I decided to become a theoretical physicist.
When, do you suppose, did the Bohr, atom become generally accepted, or did it ever become generally accepted.
It never became generally accepted… The older people, as always, simply couldn’t follow the times. It was too complicated and too upsetting. It is the same with nuclear physics. I myself simply couldn’t follow all the very difficult mathematics involved in nuclear physics. I also know of Max Born, who simply stopped when nuclear physics began. He said on several occasions that he understands nothing of it. Whereas the younger people find themselves in their veritable element. Quantum theory of radiation and all these things, for another generation are as the semi-classical theory of quantum mechanics was before.
I asked this question particularly because here is a new idea announced in 1913 and ten years later people including yourself are writing that it can’t be done that way.
There were people who from the beginning said, “This is all nonsense, it is just a cheap excuse for not knowing what is going on.” Then others said that there must be something to it, and others after a rather short time just took it for the only truth, took it for granted. And this attitude lasted until 1926. Even Bohr himself spent quite a time going through the whole periodic system and explaining by orbital pictures how the qualities of the various atoms changed with one electron after the other built in.
It’s often said that Bohr himself felt well before 1926 that the model was wrong.
Yes, he was very dissatisfied with this model… It was makeshift. I think he always had the idea that it was makeshift and something provisional. By the principle of correspondence he tried to make it a little bit more coherent with classical mechanics, and in fact the development of the new quantum mechanics came partially through the correspondence principle.
Did Stern’s choice of this particular way of shoving the non-existence of quantum states — I mean through the examination of total angular momentum — at all relate to the work you were yourself doing at that time on quantization of angular momentum?
No, very little.
Then he really started on this before you got to Frankfurt.
Yes, I think so… Many people worked on the same problems at that time.
Had you known him at all before you got to Frankfurt?
No. I became acquainted with him only in Frankfurt when I came there. I learned about his beginning experiments with atomic rays. By the way, Stern’s main interest before that was thermodynamics. He wrote a paper together with Einstein on statistical thermodynamics. How he came to make these experiments I don’t know.
How did research go on, to the extent that it did, during the war?
First of all there were the oldsters who simply went on in their research. Sommerfeld’s relativistic orbits came out in 1916. Einstein was not touched directly by the war and his general relativity also came out in 1916. Then my own work during the war began about 1917 or so. In the first few years I was in the Red Cross and also in various army units, where it was found out that I was pretty useless as a soldier. In 1917 there was a special set-up in Berlin. A scientific board for war research — the Artillerie Prufungs-Kommission — had a big building in Berlin. Technicians and physicists and mathematicians were called back from the armies in the field, back to Berlin, to form this very large group of scientific research. Max Born was there from the beginning, and he achieved the very difficult feat of calling me back from some army outfit. I was in training at that time. Then began very close cooperation between Born and myself. We had the special project on sound detection — of canons and so on. The psychologists Wertheimer and Hornbostel were also involved. A number of physicists, at that time, were in uniform working in Berlin at the Artillerie Prufungs-Kommission. One of the main spirits was Ladenburg.
Was there no systematic attempt to call the older physicists to this sort of duty also?
No, it was a constant struggle between scientists and the military. The military authorities wanted cannon fodder — indiscriminately; and the scientists were of the opinion it was better to save some lives and to make them work on scientific problems.
But was there no attempt to bring older physicists to Berlin for war research?
A few were in this outfit. There was old Professor Kurlbaum, who had worked on black body radiation… I don’t know what else Sommerfeld did. I had no personal contact with him at that time… Max Born was at that time particularly interested in crystal structure, his old pet subject. At the same time he was a really trained mathematician. A pupil of Minkowski and Hilbert, he was trained very thoroughly, quite in contract to myself. I picked up mathematics only here a little bit and there a little bit. I never became expert in it, to the great regret of Max Born, who always blamed me for my lack of a solid mathematical basis.
Was there not much emphasis except in a few places in Germany on giving physicists a really sound training in mathematics. I mean, was Born the exception, or were you the exception, or did it vary from university to university?
In Germany, there were only two or at most three centers of — where you really could learn mathematics and theoretical physics thoroughly at the same time. Whoever had a really burning interest went either to Munchen or to Gottingen. Not to Berlin, because in spite of Planck’s great scientific prominence, Planck was not a teacher. He worked on his own problems. He was a one-track mind, he didn’t look side-ways. This was just his way. So the centers of teaching were Munchen and Gottingen only. And connected with it was a great idea of self-importance. We in the group in Munchen looked down on the other universities. It is something like Harvard here, maybe. It must have the stamp of some Harvard man, otherwise it cannot be worth much. In fact modern quantum physics was not treated in any other university as far as I know. In most other universities were specialists in regular physics — the coefficient of refraction of this kind of glass from the temperatures -15 to +75, and so on. They simply did not follow modern developments. Every young man who was interested in modern theoretical physics just went to Gottingen or Munchen. There was no other way.
That I take it, was not as true of experimental work.
No, not in experimental physics. There was, of course, the Stark effect and many other important things were done elsewhere. But mathematical physics and modern theory you could learn only at those places. Then there were of course centers in Holland. There was the one person, H. A. Lorentz, and then Ehrenfest.
Did people from Germany characteristically spend any time in Holland?
No, very little.
Did most of the people who did go to Munich and Gottingen learn more mathematics, get a more thorough training in mathematics than you yourself did?
Yes, most people had a very good training in mathematics. Look, just to take an example, at the Ph.D. thesis of Ewald, who was a very good friend of mine. It was very mathematical — complex functions and all very high mathematical methods — applied to relatively simple physical problems.
How did your own work with Born on crystallography, and the attempt to apply the Bohr atom to crystals start?
You know that Born was the first who proposed that the atoms might be space models, instead of all in one plane. I think Bohr stubbornly held to the idea of planetary systems, and then, since the planets are all in one plane, the idea that it might be in space simply didn’t come to anybody. To talk about times a little bit before this, the problem of helium came directly after hydrogen. There you have two electrons and why should they not be in one plane… Now this is of course the real history of physics. Sommerfeld found out that it would be a more stable system if you have one electron here and the other in an orthogonal plane. I think he wrote a paper on this, quoted by Born. I think I wrote some notes on this development on these papers which I sent you. Apparently Sommerfeld at least had the idea that there might be space models, but it didn’t come to anything. Nothing could be proved, there was no experimental approach, until Max Born from his crystallographic point of view found out that the elasticity features of crystals cannot be explained by a plane system… But again Born thought only of the symmetry elements in crystals — thought only of crystal structure. The symmetry had, therefore, to be cubic or octagonal. I think it was myself who really tried to set up a model in which electrons can run on a polyhedric model. I wrote several papers on “Electronen im Polyheder-Verband.” Born was more or less in sympathy with this, of course always with reservation. Everything was done with great reservations. I remember at that time in Berlin I was already in the Artillerie Prufungs-Kommission. Born and I went together to Einstein’s home, and Einstein also seemed quite interested in these space models. He only asked, “How can they remain stable?” “The slightest perturbation will upset the whole clockwork.” And the usual answer is that there are quantum conditions and they take care of that.
Has anyone asked about stability conditions for coplanar models?
There is always this question in the air, but the quantum conditions took care of that. This was my first personal contact with Einstein, and he of course made a great impression on me personally. From that time on I always thought of space models, and a little bit later I wrote my first paper on the helium atom in which calculations about mutual perturbation under quantum conditions were considered — I think for the first time. I tried to explain the two spectra of helium. I don’t remember the details. One was coplanar and one was in mutually inclined orbits, and at that time I studied one of the astronomical works on planetary perturbations very thoroughly.