Oral History Transcript — Hans Bethe
This transcript may not be quoted, reproduced or redistributed in whole or in part by any means except with the written permission of the American Institute of Physics.
This transcript is based on a tape-recorded interview deposited at the Center for History of Physics of the American Institute of Physics. The AIP's interviews have generally been transcribed from tape, edited by the interviewer for clarity, and then further edited by the interviewee. If this interview is important to you, you should consult earlier versions of the transcript or listen to the original tape. For many interviews, the AIP retains substantial files with further information about the interviewee and the interview itself. Please contact us for information about accessing these materials.
Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event. Disclaimer: This transcript was scanned from a typescript, introducing occasional spelling errors. The original typescript is available.
See the catalog record for this interview and search for other interviews in our collection
Interview with Hans Bethe
Hans Bethe; November 17, 1967
ABSTRACT: Natural radioactivity; ideas of nuclear constitution, size in 1920s; Gamow-Condon-Gurney theory of alpha decay 1928; discovery of neutron 1932; Cambridge as a center of research 1933; early theories of nuclear forces; analysis of short-range nuclear forces 1935-40; reasons for writing Rev. Mod. Phys. review articles 1935-37 and detailed review of articles' contents; beta decay and the neutrino hypothesis; application of group-theoretic methods to nuclear physics 1936-37; compound nucleus model 1936; nuclear models in general (compound nucleus, evaporation, liquid drop, direct interaction, statistical); contemporary knowledge of nuclear physics 1938-39; stellar energy production; energy limit on cyclotron; accelerators and theoreticians; nuclear physics at Los Alamos; post-war conferences; origins and development of the shell model of the nucleus; many-body theory in nuclear physics; current algebras in particle physics; origins and development of the optical model; of the collective model; autobiographical comments on political, social, scientific conditions in Germany and England in early 1930s ; nuclear studies at Cornell after the war; building the H-bomb; the Oppenheimer hearings; work as a consultant 1950-1970; involvement with PSAC 1956; views on disarmament; receipt of 1967 Nobel Prize.
Weiner:We're sitting in Professor Bethe's office this morning. This is the second part of an interview that was initiated almost a year ago. Today we're going to backtrack a bit to put things into the autobiographical mode, which should take us, I think, to your decision to enter the university and to seek a career in science. I'd like to know a little of the background of how you selected it.
Bethe:Well, my father was a professor of physiology at the University of Frankfurt, and very early he tried to interest me in his science, in biology. I wasn't very interested. I was not interested in plants or animals, which seemed to be the main subject of biology. I was always interested in the apparatus he had in his laboratory, which was mostly physical apparatus; and I was Interested from my early childhood in numbers. I played with numbers back much farther than I can remember. Do you want me to go into this in detail?
Bethe:I had a godfather who was then the actual professor of physiology at the University of Strasbourg. My father was an assistant professor there. My godfather, a very nice man, used to ask me questions about arithmetic. I must have been about four or five years old. I think one day he asked me (this, of course, I know from reports from my parents), "What is .5/2?" So I answered, "Oh, dear Uncle Ewald, that I don't know myself." Then it is reported that a few days later I had figured it out and ran across the street through the thick of traffic to tell him the answer. I was convinced he wanted to know. Another story that my father told me about my early experience with numbers is that he had a ceiling which had squares of some material on it, just like this ceiling, and he had moved to a new place, to Kiel. We moved from Strasbourg, where I was born, to Kiel when I was six. I looked at the ceiling in his study and said, "This has 72 squares." So he asked me how did I know that, how had I counted these so quickly. So I told him, "Weil, it's very easy. There are nine rows and each has eight squares." So these are two of the early experiences I was told about.
Weiner:Do you remember the age on this?
Bethe:For the second, I was six years old. This I remember myself: At the age of nine approximately I used to make big tables of the powers of numbers—any number to the third power or to the fourth power and so on, and I learned by heart the powers of two up through the twentieth, which I had figured out. So I always liked to play with numbers. Then a great discovery in school was when I attended boarding school—that was at the age of 11. In this boarding school each subject progressed at its own pace. I learned algebra there, which I thought was a wonderful science and really gave you much more power than you had Just doing numbers. Then later (I think I was 14) I found in my father's study a book which explained calculus, and I got hold of that and stole it and secretly studied it, and calculus has ever since been my favorite subject in mathematics. So I was mostly mathematically inclined, and mostly interested in the analytical side of mathematics, not in geometry. I am not very good at visual perception. So I knew I wanted to do something that had to do with mathematics. At the same time I was interested in natural phenomena, physics and chemistry. My father gave me books to read on physics and chemistry. Actually, the chemistry book interested me more than physics at the time. It was written, I remember, by a man of very controversial fame, Mr. Ostwald, who did not believe in atoms. I had then in the last two years of high school a good grounding in physics and in calculus, which was then taken up in high school. This was unusual in the German high schools. They were doing an experiment which had not been done before or after—namely, of giving us some electives in the last two grades, and we were excused from some of the Latin and Greek, which I didn't particularly enjoy. I wasn't really bad at it, but it didn't interest me. Instead we could elect to take five additional hours per week of mathematics—that's where we took calculus— and two or three hours of physics, which gave us quite a good knowledge, especially of mechanics and geometrical optics.
Weiner:This was all in Kiel?
Bethe:No, this was in Frankfurt. I should have mentioned my personal history. I was born in Strasbourg in 1906. In 1912 my father moved to Kiel, and in 1915 to Frankfurt. So the time in Kiel was very short, and the place where I really grew up was Frankfurt. And this, 1915, coincided with the time when I entered the gymnasium, so I went through all my gymnasium years in Frankfurt.
Weiner:One other question on the family: did you have brothers or sisters?
Bethe:I had no brothers or sisters. I was very much spoiled, by my mother especially, who spent a great deal of time with me and had a tendency to protect me far too much, protect me from any contact with other children, and I think this was very wrong. In the later years of my school, beginning at the age of 12, I had such contact and I had quite good friends. But it took me a long time to really get to know my fellows. She was terribly afraid always that I would catch cold, and she would keep me at hone. Generally she was afraid of all sorts of disease and other troubles.
Weiner:Was there religion in the home?
Bethe:No. My father was, I think, slightly religious. I was taught to pray in the evening before going to bed, and I attended the Protestant religious instruction, which was given in the schools in Germany. I was also confirmed, and the instruction which I got in this connection got religion out of my system completely. It was never very strong before, and the confirmation had the consequence that I Just didn't believe.
Weiner:As I understand it, your mother was Jewish; your father was not.
Weiner:So whatever religious instruction there was was Protestant.
Bethe:Yes, which was my father's religion. My mother really was not religious at all. In fact, one of the things I remember that impressed me greatly about my mother: she said, when I was nine or ten (this was in the midst of the First World War; I don't know whether she told it to me or to somebody else and I listened to it): "Here we are praying to God that Germany should win, and at the same time the French and the English are also praying to God that they should win. What is God to do?" A very direct approach.
Weiner:What was her family's background? What kind of occupations were there on her side?
Bethe:My grandfather, her father, was also a professor. He was a professor of ear, nose and throat diseases at the University of Strasbourg. He had been in Strasbourg already in the French time, but he was not a Frenchman. His family came from a palatinate by the name of Worms where they had vineyards. it must have been a rather prosperous vineyard; so his ancestors, as far as we remembered, were wine farmers. Her mother's family was a family of cloth merchants in Karlsruhe.
Weiner:I didn't want to take you back too far, but that would be part of the story.
Bethe:My father's family: My father's father was a medical doctor, a general practitioner, in Stäteen, and I think my father had a very strict upbringing. My mother had the opposite. My father's father must have been a very kind man. I did not know either of my grandfathers—they both died rather young. The family before that had been mostly educated people. Many had been Protestant ministers and some schoolteachers. My father's mother I don't know terribly much about. She was a somewhat disagreeable woman who was finding fault with everybody and everything. She had been a schoolteacher in her young days, but I know very little about her family.
Weiner:How about books in the home? Were there many?
Bethe:There were many books in the home. There was the usual German literature—Goethe and Schiller and novels of the 19th century and the 20th century. I read quite eagerly the German novels in the 1920s, which were beginning to show the dissolution of society, which was very strong actually in Germany in the inflationary period. I read my share of adventure stories, and that was about all. My mother, actually, was a writer. She wrote children's plays which were performed on the stage in Germany with some success. Some of the more exciting times were when her composer came and played the tunes on the piano and discussed the play with my mother.
Weiner:Did you ever develop an interest in music or dramatics?
Bethe:No. I am very unmusical, maybe not as bad as I thought I was as a child. But my mother, being very musical, thought that my talents were zero, and so she put no emphasis on this at all. I couldn't sing, I couldn't keep a tune, so I was not to be musically educated. I probably could have been under more normal circumstances.
Weiner:Her standards were rather high.
Bethe:Too high. She was quite a good violinist and also played the guitar and sang, and she compared everybody to her standards.
Weiner:How about the friends of your parents? Were there groups at the house? Do you remember discussions?
Bethe:They lived an extremely quiet life, and I think much too quiet. There were hardly any guests ever, and they hardly ever went out—maybe two or three times a year about the maximum. This was partly because my mother never was very well. She was given to depression, and she had intestinal upsets from time to time, but partly it was just by choice. So there were very few interesting guests at our house, if any. I had my social life much more with my own friends and their parents, which began at the age of 12, as I told you, and I made some very unfavorable comparisons between our house and that of my best friend, who had a lot of guests and quite a lot of interesting conversations.
Weiner:During this period, did you take any interest in technology, in little gadgets, in radio or anything of this sort?
Bethe:No. I was never very good with my hands. I did one thing, which was to build things with an erector set. That I liked. But this was not a very creative business. There are set parts which you put together. And that was about as far as my technology would go. My father was quite good with his hands, and in the year '23 he built a very elementary radio receiver so that we were among the first radio listeners in Germany.
Weiner:But you didn't participate in the building of it.
Bethe:Not to any appreciable extent. I participated slightly, and I did a little bit of wiring of simple circuits under my father's guidance, which I enjoyed. The radio was just one of the applications of simple circuits.
Weiner:But it wasn't something you had initiated.
Weiner:This is all by way of getting you back then to what you started to say about your interest in mathematics, and I think you were talking about the calculus book you had. That would have taken you in age to around 14 or 15. You mentioned also the electives at 16 and 17. From there where do we go?
Bethe:Well, I then entered the University of Frankfurt and was not entirely sure what I would study. I thought t would be physics. Unfortunately, the professor of experimental physics at Frankfurt was not a good man. His name was Wachsmuth. The reason he was there was that the University of Frankfurt was founded in a somewhat peculiar way. There were a number of learned institutions in Frankfurt before the University was founded in 1914, and he was in what was called Physikalische Verein. That being a second-rate institution, it had a second-rate professor. And when the University was founded, he automatically advanced to being professor at the University. I found his lectures very boring, and I mostly cut them. Occasionally Professor Wachsmuth had met my father on examinations of young medical students and then used to complain that I never came to his lectures.
Weiner:Was your father at the University?
Bethe:Yes, he was at the University. He was professor of physiology, but he was one of the people who Joined the University after it was founded, so he was not taken over from the previous establishment. There were much better people in chemistry, both inorganic and organic chemistry, so that for a while I thought I might go into chemistry instead of physics. However, I soon found that the experimental work in my hands did not succeed at all. I remember I took the chemical laboratory, and I went all right as long as we did qualitative analysis, but when it came to quantitative analysis I always came out with the wrong answer. I just couldn't do the experiments in a clean enough fashion apparently to have the right amount of materials left over. At the same time I took mathematics courses. 1 took one which was extremely good in the theory of numbers by Siegel, who was probably the most ingenious mathematician at the University of Frankfurt at the time. He spent quite a lot of time at the Princeton Institute later on. However, the course was really a bit too hard for me, and at the same time it seemed to me that it had very little to do with what I really wanted to know. it was very interesting, but it didn't seem to have any direct connection. I also took the university course in calculus, which would correspond to advanced calculus here, with lots of hexagons (?) and deltas and rigorous proof, and this bored me immensely. I found it very simple, but extremely uninteresting, and I really didn't see why one should go to such extremes for something which seemed very obvious and simple to me. I'm a little more lenient on it nowadays. So I think these experiences in my freshman year made it quite clear to me that I wanted to do physics after all and not chemistry and not mathematics. This was confirmed the second year. The second year I took theoretical physics with Madelung, who was quite a good theoretical physicist. He was not very productive. Perhaps he has done one good thing—namely, the calculation of the energy in a lattice of ions. The principal other contribution he has made is a very good book on the mathematical methods of physics. However, he knew theoretical physics very well. His lectures were interesting, and I was very convinced that this was the field for me. Then at the same time I took experimental physics, more advanced experimental physics, from the associate professor of experimental physics, Gerlach, who is quite a famous man for the Stern-Gerlach experiment, and he, too, was extremely stimulating. And that was one of the best courses I had at Frankfurt. And he was replaced very soon. He got a full professorship somewhere else. He was then replaced by Meissner, not the superconductivity Meissner, but the spectroscopist Meissner, who later emigrated also to this country and was for many years at Purdue University. He also was very stimulating, and he told me after a very short time that really the place for me to be was not Frankfurt but Munich. I should go to Sommerfeld. I had vaguely considered that before and certainly had considered going to a different university, and Munich was one of the most attractive choices. So Meissner said I should by all means go to Sommerfeld and wrote a letter to Sommerfeld on my behalf. So did my father, who knew Sommerfeld slightly from a chance acquaintance. So after two years In Frankfurt, I went to Munich.
Bethe:In '26. Munich was a wonderful place and was very fine just as a city and by its location to the Alps. I made great use of the Alps, going nearly every weekend with two of my friends hiking in the mountains.
Weiner:This was your first time away from home, wasn't it?
Bethe:Well, except for a period when I was 11 when I was sent to a spa because I had a slight case of T.B. and lived in a children's home. But it was the first time really away from home. I found it a little bit difficult. As I explained before, my mother had over-protected me. But I certainly liked the science at Munich. Sommerfeld's lectures were wonderful, and he very soon let me come to his seminar, partly on the basis of Meissner's letter, and I also quite enjoyed the advanced experimental laboratory and also some of the experimental courses and also the course in physical chemistry by Fajans, who also came to this country later. My best friend, the one who had such a good social life, Werner Sachs, had come to Munich at the same time, and we spent a lot of time together. He was continuing to study chemistry. I went into theoretical physics. Well, there was Sommerfeld's seminar—and this was in 1926, which was a very exciting time; Schroedinger's papers were being published, and in Sommerfeld's seminars these papers were being taken up one by one and with extreme care. He let the students discuss each of the papers in great detail, usually two students to one paper. I was given the assignment of reporting on the perturbation theory, which seemed very exciting and very plausible. I guess I've used Schroedinger's perturbation theory ever since. I had as a colleague in the perturbation theory an American who was not very clever whom I coached somewhat in presenting his part with no great success. I have forgotten his name. He has disappeared from the scene of physics.
Weiner:Had you heard of the developments in quantum physics in 1925 while you were still at Frankfurt?
Bethe:Not the modern developments. I had not heard of Heisenberg's papers. I had heard, of course, of the old quantum theory—the Sommerfeld quantum theory, Bohr and Sommerfeld. Madelung discussed that in some detail, but he did not mention the Heisenberg papers nor the Bohr correspondence principle and all the later developments of the early quantum theory. It stopped with the Sommerfeld atom.
Weiner:I see. And there was no discussion of some of these serious problems within...
Weiner:You didn't get it through the University, and you didn't get it independently.
Bethe:No. Once I was at the University, I guess I was fairly busy just doing the work for the courses, which I was taking, and I did very little reading beyond my courses. In high school I was always under-employed, and did a lot of reading beyond the immediate schoolwork.
Weiner:You were saying that in Sommerfeld's seminar you discussed this. How many students were there in the seminar?
Bethe:About 20, and then there were a couple of staff members. The most impressive staff member at that time was Wentzel. I remember in my second year there Wentzel gave a beautiful course on dispersion theory, starting with the old Lorentz-Drude dispersion theory and going through Thomas-Heisenberg and the dispersion theory as deduced from the Schroedinger equation. So we discussed Schroedinger's papers. In fact, I read Heisenberg's papers only about a year later. My first introduction to Heisenberg's theory was in Schroedinger's paper about the connection between his theory and Heisenberg's. And I read the papers leading up to Heisenberg's theory, like Bohr, Kramers and Slater many years later.
Weiner:When this was going on, this certainly didn't occupy you full time.
Bethe:Well, it occupied me pretty nearly full time. I took some mathematics and physical chemistry and experimental physics and theoretical physics and a seminar, and I read Schroedinger's papers, which were very nicely written but still required quite a lot of study. I was pretty well occupied except for my weekend excursions to the mountains. As I remember it, I worked pretty steadily some 10 to 12 hours a day during most of the time of my Munich study. I didn't work that hard in Frankfurt but I did in the Munich time. The German academic year, at least at that time, began in the spring. I started in the spring of '26. And I think some time In early '27, Sommerfeld suggested to me a topic for a thesis. This was on the basis of the experiments by Davisson and Germer, which I think were published in '26 or very early '27. He suggested to me that maybe I could do a theory of these experiments. And the first thing I looked at was that the diffraction maxima did not come exactly at the energies at which they ought to come according to the Laue condition. And so I puzzled a little about that, and then I had the idea that there should after all be a potential energy of the electrons when they enter the metal in which they are diffracted, and so this should change their kinetic energy and hence their wavelength, and so I suggested that there should be a refractive index entering the metal which depends on the potential in the metal. This I published. Sommerfeld approved it and I published in Naturwissenschaften some time in '27.
Weiner:It's interesting that In a list of your publications that's not shown.
Weiner:The first paper that's shown is in 1928.
Bethe:Well, it should be shown.
Weiner:This is a list that was sent to us by you earlier.
Bethe:Well, it is a sort of an important paper because it's the first paper, and t has the idea of the refractive index. This was I think within a few weeks of my publication: the same idea was published by Patterson in this country. I was a little bit unhappy that he got this simultaneously, but in the meantime I know that that happens. So then Sommerfeld suggested that now I should develop this further and develop a more complete theory of the diffraction, and that led to the first paper which is on the list, which is my thesis. Just this morning I talked to my father-in-law who happens to be here. Well, we had a celebration, a university celebration, yesterday of my Nobel Prize, and so my parents-in-law came here to celebrate. Well, my father-in-law just happened to talk about Sommerfeld and mentioned that he suggested to Sommerfeld while skiing (I presume it must have been the winter of '26 or '27) that it would be a good idea to extend his (Ewald's) old theory of X-ray diffraction to electron diffraction, and I presume this gave Sommerfeld the idea. Anyway what I remember is that Sommerfeld told me, "Now you go and look in the papers by Ewald on X-ray diffraction, and there you will find some of the basis which may help you do the electron diffraction." I didn't know until today that Ewald himself may have suggested that. Perhaps Sommerfeld had thought of it independently. Anyway I followed the lead and studied Ewald's papers and made a dynamic theory of electron diffraction by X-rays. it didn't contain terribly much new. It contained the idea of the refractive index which I'd already published and then one more important thing, namely, the form factor for the scattering of electrons by an atom, and I think that was the first time that form factor was given. Otherwise I tried to do a good job and got hopelessly bogged down in approximations which just didn't converge, and to a large extent the paper is a mess because it attempts to solve the problem of electron diffraction by quite insufficient means. Nowadays one would solve the Schroedinger equation directly, and I tried to do it all by perturbation theory. Well, you see, my first seminar talk took its revenge. So that was the thesis. I took half a year longer over it than Sommerfeld wanted. He wanted me to take my degree in the spring of '28, but I thought I wanted to polish the thesis a little more and study some for my oral examination, and so I took it in July of '28.
Weiner:Do you remember your oral examination?
Bethe:I remember that very well. I was examined by Wien, the experimental physicist. That was the only examination which was hard. I had studied quite hard for it. I had spent some six weeks doing nothing but studying for the exam. I knew most of the questions he asked, but it was a hard exam.
Weiner:Because you hadn't been exposed too much to this kind of physics?
Bethe:No. He Just was a hard examiner. No, I think I knew experimental physics pretty well. The one question which I didn't know was the wavelength of cosmic rays, which were then believed to be light quanta. I gave him the answer he wanted—namely, that they were very short wavelength light quanta, but I didn't know the wavelength. Well, as a matter of fact, of course, they are not light quanta, so I was quite Justified in not knowing the wavelength. But he asked me all sorts of things about X-rays and canal rays, which was his specialty, and the determination of the electron charge—not unfair questions but ranging very much all over the field, and very little about quantum mechanics because that he didn't know. Then Sommerfeld's examination was very easy. As you might expect, he asked me some about my thesis, which was very easy, and then he had seen me study in his institute his lecture notes on crystal optics— double refraction and things like that—so he asked me about that because he knew I had prepared for that. I knew it at that time, but I've forgotten it since. Then perhaps the most pleasant was the examination by Fajans, the physical chemist. It was the custom to visit the examiner outside your special field—that is, outside physics—before you took the exam. So I visited Fajans, and he told me, "Of course, according to the bylaws of the University, I cannot Just examine you just in physical chemistry. I have to ask you some questions about general chemistry as well. But, of course, I won't ask you the chemical formula for something like indigo because I don't know that myself." So that was very nice. So I studied chemical formulae with a light touch, and he asked me something very simple like carbohydrates, and then after that he asked me some simple questions about mono-molecular reactions, which was physical chemistry, and it was extremely easy. Then I had mathematics. In mathematics there were four or five professors at Munich, some of whom had the reputation of giving very hard exams and one of giving very easy exams—that was Professor Peron. What you did as a student was to go to the factotum who arranged all these exams. He was an extremely fat university employee, quite uneducated, certainly drinking a gallon of beer every day. You gave him 20 marks and told him which examiners you wanted. And so I got Professor Peron as the examiner, and I visited him and told him I would like to be examined in differential equations and theory of complex functions, which were the only two fields of mathematics I had used in actual applications, and so he asked me some very elementary questions on the theory of functions, to integrate a certain thing which is very easy to do by the method of residues and I did that to his satisfaction and that was that.
Weiner:Were these done individually or were you all assembled?
Bethe:All individually. You made the rounds. There was a day set aside for my examination and that of several other candidates, and there were several offices set aside in the University next to each other, and that's where the professors sat, and you were told, "At 10:30 you go to Professor Peron and at 11:00 you go to Professor Sommerfeld. In the afternoon you go to Professor Wien." He held his exam in his own department. "And at 4 o'clock you go to Professor Fajans."
Weiner:Running the gauntlet.
Weiner:Now this was done in July at the time of...
Bethe:In July, yes.
Weiner:And by this time when your dissertation was completed and the orals, the procedure was to complete the dissertation. Did you defend that?
Bethe:No, you don't need to do this. The only time I had to defend something was later when I became privat-dozent. But for the dissertation, each of the examiners can ask questions, but only Sommerfeld did, and I think he did it as much for his own information as to quiz me.
Weiner:And then the orals did follow it, though?
Weiner:By this time you must have been making plans for the next steps.
Bethe:Yes. I would have wanted to make plans for the next steps, but at that moment it was completely dark. I had no job waiting for me, and I did not know what I would do. Sommerfeld was taking off for a trip around the world. It was just preceding his 60th birthday and he did not want it to be celebrated at home, so he took the occasion to take a year off and traveled for several months around the world. He did not provide a position for me. Well, he may have written some letters, but certainly I didn't know about them. After a few weeks, I got a letter from Madelung in Frankfurt offering me the position as his assistant, corresponding to research associate, at the University, which I accepted happily. In the meantime my parents had been divorced. That took place, in fact, in '27. My father lived in Frankfurt and still had his old job, so I went to live with him during the time I was with Madelung. A little later I also got a letter from Hund offering me an assistantship at his university, which was Rostock. These were very poor times really in German universities, so he did not have a regular position for an assistant, but it had to be put together from several sources. The salary was quite poor, and I was somewhat after money, so I stuck to the Frankfurt position rather than go to Hund. it would probably have been better for my development as a physicist to have gone to Hund who was a far more productive physicist. However, I went to Frankfurt, and the half year I spent there was very pleasant personally. I found Madelung a very agreeable man to talk to. However, he was not at all stimulating in physics, and I did very little during that time. I taught in the laboratory. The assistant In theoretical physics had as one of his duties to be one of the two or three instructors in the elementary laboratory, and my experimental facility was just sufficient for that. Then I wrote one more unimportant paper which is on the list. It I think was actually suggested by Madelung—that I look at that. Pohl had made a sort of lattice of wires about a millimeter apart which he charged alternately positive and negative, and then he let an electron beam go through the interstices between these wires and to his surprise it gave something which looked like two diffraction maxima In two directions, and he thought that was very strange because after all the lattice constant was a million times the wavelength. And so I showed that you should expect this. But that wasn't really physics.
Weiner:Did you have any other teaching responsibilities other than the laboratory?
Bethe:None. While I was there, I got an offer from Ewald in Stuttgart. I had been to Stuttgart on a visit to talk about my thesis, and my visit must have been in the spring of '28. I found this visit very stimulating, so I accepted this alternative position right away. I don't know whether it was ethical to leave Frankfurt in the middle of the year, but I did. And so I became assistant again but to Ewald. This was in the spring of '29. This was one of the best times I had until I came to Cornell. It was personally extremely nice. Mr. and Mrs. Ewald were extremely kind to me and had me at their house many times, and we went on walks together, and occasionally I was given the Job of taking the two older children out, one of whom afterwards became my wife—the other was a boy. In a personal way this was about the happiest time I had in Germany. At the same time it was very good scientifically. I had always been interested in the actual structure of complex atoms, and I had been very much interested in the papers by Hartree on the self-consistent field of atoms. I think that interest came partly from my interest in chemistry previously, partly from Sommerfeld's Atombau und Spektrallinien, which I had read avidly and in which the structure of complex atoms was quite a mystery. So I thought Hartree's paper was really a wonderful solution of our problems, and Hartree happened to give a talk on a visit to Stuttgart in the very first week when I was there. So that was the cause of my third paper, which was the comparison of electron distribution in helium according to various methods. I compared Hartree's method and Hylleraas' variational method and just taking hydrogen wave functions and so on. The same general line also led to this paper, which Is number five on your list. I extended Hylleraas' work to the calculation of a two-electron atom of the lowest nuclear charge, namely, the hydrogen negative ion. And this was the first calculation of electron affinity of hydrogen and I think the first time that anybody proved that hydrogen has an electron affinity. Hylleraas afterwards calculated it much more accurately, and it is now one of the important numbers in astrophysics, because in the cool surface region of stars there is quite a lot of H- and much of the absorption and emission of radiation is in fact due to the formation and destruction of the negative hydrogen ions. So that was a very satisfactory paper. The next paper is about the splitting of energy levels in crystals. The one suggestion that Madelung made to me was to learn group theory, and I spent probably the major part of my time in Frankfurt learning group theory. I can learn something only when I apply it to an actual problem, and Ewald then suggested to me to think what would happen to the energy levels of an atom when it is in a crystal. That was just the best possible way to apply group theory, and on that basis then I wrote this paper on the term-splitting in crystals. When I had got these results, Ewald suggested to me further that there were certain crystals which had very sharp spectral lines—namely, the rare earth salts—and the reason why they have sharp spectral lines is that the f-shell of the atom is deep inside the atom and therefore is not much disturbed by the neighboring atoms. The only effect of the neighboring atoms is that they make an electric field in the rare earth atom, an extra electric field, and that is exactly the condition which I had treated in this other paper. So he suggested to me to look at the Zeeman effect of these sharp lines of rare earth atoms, and that was another paper. Well, it was published only in 1930, but it was really conceived on Ewald's suggestion in the Stuttgart time.
Weiner:Did you have any similar collaboration with anyone else there? Any collaboration in the sense of having your interest called to certain types of problems?
Bethe:No. There were quite a number of other people In Stuttgart, of course. I got my first exposure to cosmic rays by Regener, who was an experimental physicist, but I didn't do any work on it. I talked to Hermann, who was the other assistant to Ewald, who was mostly interested in crystal structure determinations. But I just talked to him. It did not stimulate me to do anything in particular. There was another theoretical physicist there of whom I have lost sight completely. His name was Seyffart. We used to go to lunch together and talk physics.
Weiner:How about teaching? Bethel: No teaching at all. The only thing I did was to give some seminars. Ewald wanted to have some seminars on quantum theory and especially on the Hartree method, and I gave some seminars—maybe six during the whole semester—which were attended mostly by the staff and the students in theoretical physics.
Weiner:You were there in the spring semester...
Bethe:The spring semester of '29. in late May probably Sommerfeld returned and wrote a letter to Ewald: "I need Bethe and what are you doing with him? You nave no right to have him." It was Just about in these words. And so they fought over me. The upshot was that I returned to Munich in the fall, but Ewald was permitted to keep me for the semester. Sommerfeld offered me a bribe. He said, "Well, first of all, I can see to it that you can get your habitation, your privat-dozent position at Munich very quickly, and second I will get you a fellowship from the International Education Board." I was a little bit sorry to go back to Munich because my time in Stuttgart was very productive and most pleasant personally. However, the great man called and so I followed his call. So I returned In the fall of 1929.
Weiner:So you were actually at Stuttgart then only a little more than six months.
Weiner:And in that six months you did the work we've mentioned, and also you've indicated that it was an important personal experience.
Bethe:Yes. So then I went back to Munich, and in Munich I got interested (I may have gotten interested in it already in Stuttgart, but certainly I did the work in Munich) In applying the collision theory, which had Just been Invented by Born (I think Born's paper was '28 on collision theory), and extending it. It seemed to me that Born's method was very useful but that he had not done the application as simply as it could be done. There was a first application to the elastic and inelastic collisions in hydrogen that had been made by Elsasser in a rather straightforward manner. What I then did was to find a simple transformation which made it all very much simpler. In fact, it was similar to one that I had already used in my thesis, but I understood it much better in this paper. Essentially, what it was: In Born's theory you find that the scattering is given by the Fourier transform of the potential, and I showed that you could transform this into the Fourier transform of the charge of the electrons, which then connect much more directly with the wave function. And using that trick, I found it very easy to calculate both elastic and inelastic cross-sections, and I found a nice thumb rule for the inelastic cross-sections, which then permitted me to calculate the total energy loss in inelastic collisions. This, then, gives you the stopping power of a material for a fast particle, a fast-charged particle, a particle to which the Born approximation is applicable. So this paper, which I consider one of the four best papers I have written, is about the stopping power of materials for fast-charged particles. This problem I have come back to many many times, and I think we'll go through it chronologically, so I'll leave it to the later time.
Weiner:I'd like to know, though, without waiting for later times, what are the characteristics of this problem that were especially appealing to you? I don't mean in a detailed sense.
Bethe:I understand. Well, one was to apply some elegant mathematics. And the second was to get a result which was directly useful for comparison with experiment, and the comparison with really a gross experiment, not an experiment designed to probe into the details of atomic structure. it's really a gross property of matter. I like to get as far into the domain of the experimenters as I can, and to get something they can directly compare with a simple experiment. This was the paper that I used to become a privat-dozent at Munich.
Weiner:And this was in the fall of 1929.
Bethe:Well, I did the paper in the winter of '29, and I became a privat-dozent in, I think, May of '30—winter '29-'30. It took some time to do.
Weiner:And then you mentioned in our earlier session it was Sommerfeld's desire... Today you said it was an inducement—the International Education Board fellowship—but that's consistent with what you said earlier, come to think of it because you said that the whole thing was his idea, and he felt that this would be something you needed. Let me ask this: Were you aware of the tradition of Sommerfeld doing this with his students?
Weiner:Well, I have been looking into this, and I've discovered that the majority of the International Education Board fellows were supplied by Germany prior to 1930, and the greatest field was physics; and when you trace the institutions from which they came, you find that of the persons who recommended them, Sommerfeld probably sent more people for this fellowship than any other person.
Bethe:I should not be surprised. Of course, he had the largest number of Ph.D. students, certainly of any theorists, in the world; and he had just a wonderful school.
Weiner:Why do you think he had this large number of Ph.D. theorists?
Bethe:Well, one thing was that he always knew thesis topics to suggest. He was so much in the midst of the development of atomic physics that there were always a dozen things he wanted to have done. This is perhaps a trait similar to my own—he was interested in the application of the theory, and I think it's in the application of the theory that the largest number of problems exist that can be done by graduate students. This morning my father-in-law and I spoke about this very thing—why was Sommerfeld so successful. Sommerfeld could very accurately gauge the ability of the students, and he gave difficult problems to the abler students and simpler problems to the less able students, and he had a list of problems of various difficulty from which he just picked. And I think this was very different from most of the theoretical physicists in Germany at least. There's a story about Planck—that somebody came to him and asked him for a thesis topic, and Planck is supposed to have answered: "Well, young man, I would gladly give you one, but if I knew a good topic to work on, I would do it myself.
Weiner:Very interesting. I had someone tell me that once, not in regard to my own topic, but an American professor said that about one of his students.
Bethe:Now, another very productive person in Ph.D. students was Max Born. When he was in Göttingen, as soon as he came there, the students just flocked to him. He had, I think, ten Ph.D. students within a year. It was many more than he wanted. But these were about the only two of the older generation who had large numbers of students. Born, of course, was much younger than Sommerfeld.
Weiner:When you say this you're restricting it to theoretical physics, but you're not restricting it to Germany. You're saying this in general in terms of the world.
Bethe:No, I think in the world you should certainly mention Bohr. No, I meant in Germany.
Weiner:In 1930—I think we've discussed this before—going on the fellowship, the first was a combination of the Cavendish, and then you went to Fermi later.
Bethe:Let me look at the list of publications to see whether there's anything else that's interesting. I should mention this paper: "The Non-stationary Photo Effect." That was stimulated by Sommerfeld, who was interested in the photoelectric effect and did the fundamental papers on the photoelectric effect in 1930, using the solution of the stationary Schrödinger equation. He claimed at one point that it would be very difficult to do it in a time-dependent way. Weil, I found this a challenge, and so I did it in a time-dependent way, and my paper was published together with Sommerfeld's two papers. It's quite nice, because you can see that way what happens when you put an X-ray beam on an atom—namely, that then the photoelectrons don't come out before the beam gets there and come out later on and you can follow in time how they come out.
Weiner:Were you getting a feeling in doing this work, having your paper, for example, published along with Sommerfeld's, that you were making some good contributions and that you were being recognized?
Bethe:Yes. I knew I was being recognized. I was very doubtful, however, whether I could really compete. I saw people like Heisenberg and Pauli, who really were enormously more profound and really knew much more about quantum theory than I could ever hope to know, and I didn't know how I would stack up in the constant competition.
Weiner:Did you come in contact very much with a wider circle of physicists than those at your own university?
Bethe:Not very much. I remember one visit by Heisenberg to Munich. I was in great awe of Heisenberg, very eager to talk to him, but very apologetic for the applied quantum mechanics that I was doing. I met Pauli at a meeting of the German Physical Society, at a section meeting of that in Freiburg, where I went from Stuttgart and reported my paper on the term-splitting in crystals; and Pauli acknowledged my existence and said, "Now, Herr Bethe, I was very disappointed In your thesis. I had expected much better things. You really didn't solve the problem."
Weiner:I guess this is recognition when it comes from Pauli.
Weiner:These were, I gather, from what you say, individual visits. Munich itself was not the site of a seminar that attracted people regularly?
Bethe:Not from other places. There was the regular Sommerfeld seminar which attracted Munich people, including some of the members of the Technische Hochschule, so I knew the Technische Hochschule people, but none from outside Munich.
Weiner:What about visiting students—say, from America?
Bethe:There were lots of American physicists there. This, in fact, was great. One of the people who was there was Rabi, who yesterday at our dinner was present and got up and said that he had known me longer than anybody else present, longer than my family—longer than my wife, one year longer in fact—because he had been in Munich in '27 at the same time as Condon and Robertson. Those are the three I remember, and those were very remarkable people. I talked quite a lot to them. Rabi's recollection of that time was that in addition to me there was Peierls, with whom I developed quite a friendship in the Munich time. Peierls was a student simultaneously with me. He remembered that Peierls and I were constantly talking together and constantly laughing, and they, the three Americans, were very concerned about that, because they always thought that we were laughing at them.
Weiner:What was your relationship with them?
Bethe:Oh, friendly—not very close, but I know I liked all of them, especially Rabi. I talked to them maybe every couple of weeks or so.
Weiner:And from them you didn't draw any conclusions about physics in this country?
Bethe:No. I Just concluded that it existed, but that was about all.
Weiner:I think that covers the period.
Bethe:I think that covers the period before my fellowship. Well, then I got the fellowship and Sommerfeld wanted very much for me to go to Bell Labs, to Davisson and Germer. I wasn't terribly interested in that. I don't remember exactly why I wasn't interested. I don't think I was terribly interested in going to America, and I was more interested in going to a European country. I think I had some reservations about going to an industrial laboratory. But I think the main point, if I reconstruct this correctly, was that I thought that I had done about as much about electron diffraction as I could easily do, and there were other things which interested me more.
Weiner:What sorts of things?
Bethe:Well, one thing was the extension of the level splitting in crystals, to do more applications of that. I always wanted very much to do a theory of the cohesive forces in solids. Well, the two places were really chosen without regard to the subject matter. The two places were Cambridge and Rome. Rome was entirely the suggestion of Sommerfeld. He thought Fermi was a very remarkable young man and that I would probably profit from going to Fermi. I wasn't at all sure that that was the right place, but Fermi's papers seemed interesting enough, so why not go to Fermi? Then Cambridge was my own choice. I thought that was very much the seat of learning, and I think Rutherford attracted me. I worked much more with Fowler than with Rutherford, but I was just interested in England and in English life, and so this was my first choice. So I went to Cambridge. This was a cold place with bad food but very nice people, and I don't know whether I already described my impression of that.
Weiner:I think you did. I think the important point there was the openness of people and the openness of discussion which you contrasted with the formality and compartmentalization of conversation in Germany.
Bethe:Exactly. Well, I thought I had covered that before.
Weiner:This does get us into an area that has been covered in some sense, so maybe you could just think about whether there's anymore...
Bethe:Where there's anymore to be said. Let me just mention the scientific work.
Weiner:Yes, I think what you mentioned last time was the style of work of Fermi and the impression that you had and the fact that you thought it influenced you.
Bethe:Yes, the scientific work at Cambridge: I was perhaps most impressed by Kapitza, who was interested in magnetic problems. This was the stimulation of the paper, "Change of Resistance in Magnetic Fields." Generally I was interested in solid-state physics. The next paper, "The Eigen Values of a Linear Chain of Atoms," I actually did in Rome, not in Cambridge; but it went on in the same lines. This latter paper of the linear chain of atoms has just recently been dug up again. People have become interested in this. It's known as the linear problem of the Heisenberg model, and in the last two or three years some interesting work has been done extending my work. Nobody in the meantime paid any attention to it. Well, in Rome, as you see from the subject, I was not really influenced in the subject matter very much by Fermi, but only in the style of work. I talked a lot with him. I calculated wave functions for some atom —I think it was the rare earth atom, which was the fashion in Rome, which was included in their treasury of wave functions. Otherwise Fermi and I talked a great deal together but didn't do any Joint work.
Weiner:Getting back to England for a minute... There were two trips to Italy and one to England.
Bethe:That's correct. The trip to Cambridge was four months, from October, '30, to January, '31; and then Italy was five months, February to June of '31, and then again four months, from February to May of '32.
Weiner:This one paper you mentioned...
Bethe:This came out of Cambridge, and only one paper came out of Rome. Now, I forget when I started writing my first Handbuch article. I think I started that only after my first time in Rome, but I'm not sure.
Weiner:How did that come about?
Bethe:People had noticed my papers about the electron affinity of hydrogen and the comparison of the three different methods to calculate the helium ground state. And so when Mr. Scheele wanted some quantum mechanics supplements to his Handbuch der Physik, either I was suggested to him or he thought of me himself. Anyway, he asked me to write on hydrogen and helium, which 1 was very happy to do. It interested me, and it was very good money. Springer paid 16 marks per printed page, which was a lot of money in those days, and salaries were very meager, so it was quite useful to have this additional money.
Weiner:You were back at Munich from June until the fall of '32. This was a hot summer in Italy.
Weiner:That was the second time you were back.
Bethe:The second time. The first time I was back from July '31 to January '32, taking off a long vacation in the summer. In August and September I was at home with my mother and in Switzerland in between.
Weiner:Where did your mother move to?
Bethe:Baden-Baden. But my work was in Munich, and while in Munich I was supported by the so-called Notgemeinschaft der Deutsche Wissenschaften, which gave fellowships much like the National Science Foundation, and such a fellowship I had already had in 1929 to '30 on my first stay in Munich.
Weiner:This is how Sommerfeld was able to get you to come back, because he had this particular Scholarship.
Weiner:And that supported you to the point of the fellowship, and then it picked up again after the Rockefeller fellowship.
Bethe:After the Rockefeller fellowship.
Weiner:I'm curious to know a little more about the first Handbuch article—how you worked, what approach you took.
Bethe:Well, I wrote down everything I knew. The beginning was fairly obvious, to derive the wave functions of hydrogen by the standard methods and then discuss the wave functions. I added a little bit, calculating various averages, which might be useful. On helium I put in all the work of Hylleraas, which was very excellent, and other methods, like the old Heisenberg method. I put in, as I said, everything I knew, starting with the early attempts of Heisenberg's perturbation theory and then leading up to Hylleraas' work, which gives much better values for the energy of the various levels. Then I discussed Stark effect and Zeeman effect, again using mostly the literature. I supplemented the literature on the Zeeman effect in talking more about the Zeeman effect of the fine structure. And 1 think also in the case of the Stark effect I calculated—that was really Just a simple exercise—how you go from the normal unperturbed Dirac state of the hydrogen atom to the Stark effect, which means a change of the quantum number. So I filled in wherever I thought there was a gap. Then I filled in a lot when it came to the optical transition probabilities. Many of them had been calculated. I supplemented the tables. I presented the tables in a different fashion, which made them a little more useful to the experimenters, giving tables of oscillator strength and transition probabilities, per unit time; and then I wrote down a number of conclusions from this: just how does the hydrogen atom behave when it is in an excited state? And I discussed the complicated questions about the intensity of spectral line and to find out Just how many atoms are in the excited state, and that's particularly difficult in the case of hydrogen because the excited states are degenerate, and so you have to know how many are in each of the degenerate states and each state of different 1-value. Well, I found a lot of things in the theory where the basis existed but where the material had really not been put in a form useful to the experimenter, and I tried to do that. Then, one of the original points I put in with regard to transition probability again had to do with the Stark effect—namely, the second state of hydrogen is quite a complicated state (it has a 2-s state and a 2-p state, and there is a fine structure between 2p 1/2 and 2p 3/2). Now, when you have an electric field, then the s and the p state get mixed but they start out at different energies. So I discussed Just how the mixture takes place in the presence of the fine structure splitting and also in the presence of the strong radiation probability, which exists in the 2-p state and not in the 2-s state. The 2-p state constantly decays in making the Lyman line, and the 2-s state is metastable. Now, this work later on was very useful to Lamb when he discovered the Lamb shift because it told you about the behavior of these states under the influence of all these forces. Then there were the problems of continuum radiation on which Sommerfeld had worked very much, and I took Sommerfeld's papers and other papers, Wentzel's and Stauber's and so on, and again tried to exploit them to get things useful for the experimenter. Well, there's the photoelectric effect, which is very important for X-ray absorption. How do you actually calculate X-ray absorption? What these people had done was to take the simple atom with just one electron around it in the lowest shell, in the k shell, and calculate the transition probabilities to the continuous spectrum where the k electron is removed. But that's not what a real atom is like. So I put in the corrections for the so-called screening; and discussed different kinds of screening, outer electrons and inner electrons and what effect does that have on photo-electric absorption. So this is the kind of thing I did with the existing theory. Then there came the collision theory. I should mention in this connection that in the theory of stopping power I was very much stimulated by Blackett at Cambridge during my Cambridge time and later. Blackett told me: "Look, here we experimented, especially in cloud chamber experiments, and want to know an exact formula for the slowing down of electrons or of protons or alpha particles in gas. Can't you, on the basis of your theory, give us an exact formula?" So in that way I got into the extension of the stopping power theory, trying to make it an exact theory valid for real atoms or gases like nitrogen or oxygen and even heavier atoms. And so that gave me the impulse to my next calculation on stopping power. Part of that is in the Handbuch article. This is in this article on the one and two electron problems, but part of it, the fall-out, in in the paper here, "Stopping of Electrons of Relativistic Velocities," which I did in Rome. I did write on the Handbuch article certainly during my second stay in Rome and maybe to some extent during my first stay. That I'm not sure about.
Weiner:How long of the total time period was involved and how much actual time did you put in on it?
Bethe:it was about one year for each of the articles, and the actual time was the majority of my work during this period. I did a little work on the side. But I would say two-thirds of my work during each of these years went into writing this article.
Weiner:So then it wasn't a question of Just an extra-curricular effort to make it understandable and to compile information, but it was actually your research, and it helped to mold and shape your research.
Weiner:Would you say that also characterized the review articles on nuclear physics?
Bethe:indeed, very much so.
Weiner:And yet there is a difference, I think, because on the nuclear physics review article you suggested it.
Weiner:You felt the need for it and you suggested it. In the earlier case, the assignment was thrown in your direction.
Bethe:Yes, right. And this was true also of the article on the theory of metals. in this case Sommerfeld had been asked to write it, and Sommerfeld told them, "I'll do it if 90% of it is done by Bethe," and I agreed to do the 90%.
Weiner:Again, did you recognize when you agreed on these first two papers that it would occupy you full-time?
Bethe:Probably not quite to the extent. I knew it was a big Job. think it was about twice as much as 1 thought it would be, and that has remained true whatever I have written.
Weiner:You get off easy if it's only twice as much. How about the reading involved in this? I would think that it would be a tremendous task to survey all of the literature? How much had you already gotten under your belt?
Bethe:I think about half. Now, on these articles, fortunately there wasn't terribly much literature yet. You will see that when you look at your references. There are not terribly many references. After all, quantum mechanics was young. Its applications had only begun, and so it was still a fairly easy task to read the literature. Then with the Reviews of Modern Physics articles, it was very different, but there most of the reading was done by Livingston, and I just needed to digest it. He just gave me a short abstract which I digested.
Weiner:He already, as I recall, had a good deal of the bibliography compiled on this.
Weiner:Three thousand articles is a number that sticks in my mind.
Bethe:That's right. But it was relatively easy on me. Well, that was the first article, and the second article was very similar, and I don't think I need to go into the details of that. It proceeded much the same way. I took whatever was there, and where I felt more needed to be done, I did it, if it was easy to do.
Weiner:The comment that is made on these articles is that 25 years later or more they are still the basic thing In the field, and in the case of one when you revised it yourself it needed only minor changes. Is that due to the structure and due, of course, to your insight and your ability, but in addition is it a question of the field Itself not having changed very much?
Bethe:It has not changed very much. The non-relativistic quantum mechanics has not changed, and not a great deal was done in that field between '33 and '55 or so when we published the second edition. In relativistic quantum mechanics, of course, a lot has been done, and there quite a bit of changes have been made. Salpeter added a lot of things to the relativistic quantum mechanics of helium, of the two-body problem. On the hydrogen relativistic quantum mechanics we had to add the Lamb shift, but that was the main thing.
Weiner:This was, I think, '59.
Bethe:No, '57. Well, we worked on it in '55-'56.
Weiner:As long as we're on that, what was the need for a new edition? How was this felt? Was it because of these changes you mentioned? Were they significant enough?
Bethe:Well, they wanted to have a new comprehensive edition of the Handbuch, which grew from I think 24 volumes to some 60 volumes in the second edition. So there were many new fields, and they wanted to bring the old fields up to date. Now, this was one of the old fields, and wherever possible they got the same authors to do it again. So that was it.
Weiner:I thought perhaps it was something internal.
Bethe:And at the same time we thought it would be useful to translate it into English since the center of gravity had shifted to an English-speaking country. So that was done.
Weiner:Let me recapitulate a minute on your whereabouts during the early '30s. We have just finished talking about the period of work on the Handbuch article. It started, you felt, during the second trip to Fermi's in Rome.
Bethe:I think it started before that. I'm just not sure whether I did it already during my first trip to Rome, but I'm sure I started it in Munich between the two trips to Rome and had written quite a lot of it by the time I went to Rome.
Weiner:This would be the one and two electron problem.
Bethe:Yes. I think it was just the one and two, and I must have more or less finished that in Rome, and then later in '32 I did the electron theory of metals.
Weiner:You were back in Munich from June of '32 through the fall, and it was at that time that you went to Tübingen. How did that appointment come about?
Bethe:I just received a letter one day: would I take this particular job in Tübingen. There was an experimental physicist at Tübingen who had several instructors working with him, but there was no theorist at all, and the theorist I think had been Lands until that time, and Land& had left for America, and I was to get this job on a temporary basis. I think even Lands had not been a full professor, but I'm not sure about that. And so this being a definite job, I took it, and In many ways I enjoyed it a lot because it was the first time that I really was responsible for the teaching of theoretical physics and arranged my own schedule of courses. I had quite a lot of contact with the experimental people there, and I had two young men working there as Ph.D. students. One I think had come from Munich to Tübingen to be with me.
Weiner:What sorts of problems were they working on?
Bethe:I believe it was something on the theory of 1 and 2 electron atoms. I think it was in connection with that.
Weiner:By that time you were finished.
Bethe:I had finished writing the article, but I now knew a lot of problems that had not been solved and thought it would be good to get a better solution on some of them.
Weiner:What were you doing on your own?
Bethe:I don't really remember. Looking at the list of publications, I think it's most likely that I spent most of my time writing this article with Sommerfeld on the electron theory of metals, because I don't find anything else that I have published, and I don't remember anything.
Weiner:This was a relatively short period anyway, from fall, which would have been... When does the semester usually begin?
Bethe:The semester begins on the first of November. I probably got there a little bit ahead of time. And then it ended at the end of February.
Weiner:March and April were vacation?
Bethe:March and April were vacation.
Weiner:And you were there then Just about six months if we include April.
Weiner:You mentioned in our session a long time back that you had first heard of your impending dismissal from a student through a letter, and I think you described the circumstances pretty well.
Bethe:Yes, I don't think I need to add any more to that. I probably mentioned also that Tübingen was really a very unpleasant place to live in at that time because it was a hot bed of the Nazi party. I remember they had any number of victory celebrations after elections and after lots of events in the early times of the Nazi government. They came to power on the 30th of January in '33, and I kept myself very much out of the main stream of the city.
Weiner:Did you take any side trips to Stuttgart or other places?
Bethe:Yes, I took a lot of side trips to Stuttgart. I'm sure at least once a month I went to Stuttgart to have some personal contacts with people I could talk to.
Weiner:You saw the Ewalds?
Bethe:The Ewalds particularly.
Weiner:You mentioned last time that you went back to Munich for two months on a fellowship. Was that the same fellowship from the Notgemeinschaft?
Weiner:And that you directed a Ph.D. thesis on electron scattering.
Weiner:What happened to the Ph.D. students at Tübingen? You never were able to follow through. They didn't get that far?
Bethe:They didn't get very far. One of them I saw again in 1955. I think his name was David. I don't know how he got his Ph.D. Anyway he seemed well established in Germany when I met him again. The other, who had written me that letter, I never heard from again.
Weiner:How about the student you directed on the electron scattering problem?
Bethe:There were two, and one of them, by the name of Hennenburg, was a very good man, and his thesis is still a good piece of work which is mentioned in the literature from time to time and in textbooks. He, I think, worked at Siemens later on on the electron microscope. He was one of the early workers on the electron microscope, and he was very highly regarded by his collaborators. He was also partly Jewish. I think he was one quarter, had one Jewish grandparent, and so I think mainly for this reason the Nazis thought they should put him into uniform and they sent him to the front and he was killed in the war.
Weiner:But he wasn't forced to leave.
Bethe:He wasn't forced to leave, and Siemens was very happy to have him, and the government did not put any pressure on Siemens to dismiss him, but quite a number of physicists who were considered unreliable by the government were purposely put into the infantry and sent to the front and the death rate was extremely high. Probably the most prominent of these was Euler, who was the great great grandson of the famous mathematician and worked with Heisenberg. He was one of the early contributors to nuclear physics. He did quite good work on nuclear physics In the mid-30s, and he had that same fate. He had no Jewish grandmother, but he was not a Nazi and showed it.
Weiner:In this period when Sommerfeld was attempting to find a place for not only you but for others, were you aware of any other effort from external sources to place people who were likely to be displaced? For example, I know that Bohr had been scouting around in Europe because of his concern. I understand that others were similarly concerned. Did you have any direct knowledge of this?
Bethe:At one time I heard through some friend that Bohr was doing this, and I remember I wrote him a letter. The rumor was that Bohr wanted me to come to Copenhagen, so I wrote him a letter that I would be quite happy to do so. But I had a vague possibility at Manchester. It was vague at that time and became permanent later. Bohr never answered, but Bohr never wrote letters anyway, so that didn't mean anything. I don't know whether I knew at that time of the activities in England of the committee.
Weiner:The Academic Assistance Council. It was Just starting up at that time.
Bethe:I knew that quite a number of us were placed in English universities. I may have known about the Academic Assistance Council, but I'm not sure. I may have learned about t only when I came to England.
Weiner:Then when the offer did come from Manchester, it came from Bragg. through Sommerfeld's writing to him?
Weiner:Do you know where else he wrote?
Bethe:Where Sommerfeld wrote I don't know.
Weiner:But Manchester with Bragg there seemed reasonable to you. It wasn't the question that it was the only possibility.
Bethe:It was the only possibility, but It also seemed reasonable.
Weiner:Fine. Then I'd like to proceed to that point. Did Peierls precede you there or did you follow him?
Bethe:Yes, by a very short time—maybe a few weeks.
Weiner:He also had been placed by Sommerfeld there?
Bethe:No, I don't know who had placed him there. Peierls had the very good fortune of having his Rockefeller fellowship Just in the year 1932 to '33. So he made his negotiations directly from Rome where he was at the time. And I don't know—quite possibly Heisenberg or Pauli wrote for him. I don't know how he got placed. But I am pretty sure it wasn't Sommerfeld. He didn't take his Ph.D. finally with Sommerfeld. He had two years, I think, at Munich, but then took his degree with Pauli, I think in Zurich.
Weiner:Then you went from Munich directly to Manchester or did you visit family or take any sort of a vacation that summer?
Bethe:I took a vacation that summer and saw my father and then my mother. In fact, I took at least two months of vacation and then went to Manchester.
Weiner:Did you feel at the time that you might not be coming back for a long time?
Bethe:Yes. In fact, I officially emigrated. That implied a statement to this effect to the German authorities, and it implied permission to take along some money—up to 15,000 marks, which at that time I think was $6000. I didn't have that much, but I had half that much from the Handbuch, and I got permission to take that out, and this was very useful to me. So I did officially emigrate, and I was quite convinced that I would not return. In fact, I did not then think that the Nazis would come to an end, so I was convinced that I would never return.
Weiner:How did your family feel about this? Did they agree with your judgment?
Bethe:My father I think agreed with my judgment very reluctantly. He I think was still hoping that the Nazis would reform. The only one I remember who disagreed was an uncle, my father's brother, who was a professor of Greek literature at Leipzig and who was an old conservative and one of the people who thought that the Nazis maybe weren't so bad because the Weimar Republic had been just terrible—all these terrible socialists. And so he wrote me a letter and tried to persuade me to stick it out and take a Job somewhere in industry, which was possible for me, and wait for better times in Germany. But he was the only one who gave me this advice. My mother really had no judgment and followed essentially my judgment on the matter: "If you can't get a university Job here and can get one in England, so you go to England. Too bad for me because I won't see you, but it's probably the right thing for you."
Weiner:Did she have any misgivings about her future in Germany because she was Jewish?
Bethe:None at ail at the time, and, as a matter of fact, in the first few years I came back to Germany regularly—I think I may have said that already. From England, usually two or three times a year; from America once a year in the summer.
Weiner:Up until 1939.
Bethe:Up until '38. In '39 it seemed too dangerous. In '38 it seemed quite dangerous to me already.
Weiner:What happened? How long did you stay?
Bethe:In '38 it seemed quite dangerous. Munich was that fail, and so I arranged for my mother to stay in Switzerland after we had taken our vacation in Switzerland, and then she returned, however, and she returned before the particularly bad action of the Nazis in November of '38, but she was not arrested. At that time they didn't arrest many women—mostly men. She was left untouched, and then these events of November '38 finally persuaded her of what I had suggested to her very much in the summer of '38—namely, to come and immigrate to America. So after November she pursued that rigorously, and she had the good fortune of having been born in Strasbourg, which according to American law counts as France. She came under the French quota, which was empty, rather than the German quota which was full for three years to come. As a consequence she was able to immigrate in June of '39, which was just about in time.
Weiner:And she came directly to Ithaca.
Bethe:She came directly to New York, to Ithaca.
Weiner:Is she still alive?
Bethe:She died a year ago Just about.
Weiner:While we're on this line, how about your father?
Bethe:My father stayed in Germany. He married a second time in 1929, I think—the end of '29. I was first quite unhappy about this remarriage, but then learned to like my stepmother quite well, and now I'm on the best of terms with my stepmother, who is only ten years older than I. They had two more children, who live in Germany, and I see them whenever I go to Europe. The last time was in the summer of '66.
Weiner:Your father's alive?
Bethe:No, my father died In '54. He was then 82, which is a good age, and until about a half a year before his death he was very active and especially mentally very much alive and still did research and wrote papers and was editor of the main journal of physiology in Germany. It was only in the last half year that he deteriorated.
Weiner:Was he able to remain at the University throughout the war?
Bethe:He was and he wasn't. At the age of 66 he was dismissed. Now, this is a perfectly possible age to pension a professor in any case. On the other hand, a man of some prominence like my father would normally have been kept on to 68 or 70. So it did play a role, that he was too liberal, and I think this was made clear to him, and he took it very hard. But of course he got a full pension. After that he still continued to do some research at his old lab, which was permitted by his successor. His successor, I think, was formerly a member of the Nazi party but was not a violent Nazi. He stayed in Frankfurt until his house was destroyed by a bomb, which happened sometime in '43, I think. And then he went with his family to a small village about 50 miles north of Frankfurt. And there he was discovered by the American occupation troops. I don't know Just how it happened in detail, but they dismissed his successor and reinstated my father in the chair of physiology. He was then 73, and he taught as the only physiologist for two years or so, and then afterwards he got a few people to help him, but he continued active until about 77.
Weiner:I'm glad I asked you. I didn't know there was that much of a story to it. Let's get back then to coming to England. I think that's at the point we were, and then you had mentioned that Peierls had already gone and that you emigrated. You mentioned earlier that you lived with the Peierls family. By that time he was married and had a small family.
Weiner:What was your impression, your reaction, to things—psychologically or intellectually? You had been to England before but now you were coming as an émigré who had left Germany behind. Did you think that England would be your permanent home?
Bethe:Yes, I thought so. I felt that in some ways it would be difficult to be fully accepted in England. But I thought that I would want to stay in England permanently, and people were very nice at the lab. Bragg was very nice and especially his chief associate professor—you might say—James, an extremely nice man. There were several others there in the physics department whom I liked very much. Then there was Hartree, who was the theoretical physicist, and, as I mentioned before, I was very much attracted to Hartree's work, and we had quite a lot of discussions with each other. I also got to know some people outside of physics, and generally the English in Manchester were extremely hospitable and both the Peierlses and I were invited around to many interesting people.
Weiner:Yet at Manchester you knew it was only a temporary position?
Bethe:Manchester was only temporary, and I was a little concerned about what would happen next. 1 was fairly confident that something would show up. 1 was very happy then when Mott offered me a sort of research associate position, in Bristol for the next year.
Weiner:The next year—you came to Manchester In June, I gather...
Bethe:I came to Manchester in October, '33, and stayed there till the next summer, whenever it was—probably some time in July—or maybe in June, I'm not sure. Then the following October I started in Bristol.
Weiner:October 1934. Then did the Bristol position sound as if it would be a permanent one?
Bethe:No. It was not a regular staff position. It was a research associate position. Now, I knew that Heitler had been there in a similar position for one year and was now there the second year, so I presumed that I could stay at least two years also. And, well, I had to take whatever was offered.
Weiner:Was this position paid for by special funds in aid of displaced scholars?
Bethe:No, I think it was the fund from the government which gives such fellowships, and it may have been ICI, the imperial Chemical Industries. But it was, in any case, a normal English fellowship, not a specific one for displaced scholars.
Weiner:ICI did give some money also for displaced scholars, but you're saying that even if it did come from ICI, that wasn't the label on it.
Bethe:Yes. I think it was a government fellowship.
Weiner:Did you do any teaching at all at Manchester?
Bethe:At Manchester I did. I taught a course in quantum mechanics, a very short one. They have a very complicated system in England where a course Is broken up into small sections, and one instructor teaches maybe a month and the next teaches two months and so on. Well, I taught one month in a course for seniors, senior undergraduates, and this one month was devoted to quantum mechanics. I remember this course not very favorably because I got terribly much involved in the uncertainty principle and spent nearly all the month explaining the uncertainty principle, which was a bad thing to do.
Bethe:But apparently some of my students must have liked it because every now and then some Englishman I meet comes up to me and tells me, "I was in that course of yours In Manchester and it was very good."
Weiner:This was your first experience with undergraduates, although it's hard to distinguish the German university system...
Bethe:Yes, it was difficult to adjust. in the German university system it was about the same level as I had taught in Tübingen.
Weiner:Did you see any differences in the relationship of the teacher to the student or the attitudes of the students?
Bethe:Not really, no. The main difference in that particular course is that it was also attended by lots of the staff, and the staff somewhat swamped the students. I think even Professor Bragg came a few times, and certainly the younger staff members came quite frequently.
Weiner:How about at Bristol?
Bethe:At Bristol I didn't teach at all. I gave a couple of seminars, but that was all.
Weiner:Can you characterize what was new to you in England in terms of research or teaching or level of interest or methods of communication?
Bethe:The main difference, I think, was the closer association between experiment and theory. Bragg, after all, is an experimental physicist, and I was in his lab; and in Germany it had been well separated. it's true I occupied an office in Geiger's experimental physics department building in Tübingen, but it was a separate department, and I think this close correlation was new and, I thought, good. This was much more so then afterwards here in America.
Weiner:Much more so in England than here, or more so here than in England?
Bethe:Much more so in America than in England.
Weiner:And you liked this at the time?
Weiner:Did this call for any adjustment in the way you worked?
Bethe:Well, probably a little bit but not tremendously. That is, I always had been interested in theories useful to experimenters, and now this was more emphasized. It was a very good period scientifically. I think I have discussed already the work on nuclear physics which I did with Peierls. Also, I may have mentioned my paper with Heitler on Bremsstrahlung and pair production. But I'm not sure if I did because this isn't proper nuclear physics.
Weiner:Let me check on that. I don't see it. Let's get into the Heitler paper.
Bethe:Well I think this is perhaps the second important paper I have written. It is an application of Dirac's theory to a calculation of cross-sections for the electromagnetic interaction with electrons. And one process is the absorption of radiation, creating a pair of electrons, one positive, one negative, which follows directly from the Dirac theory of the positron; and Heitler and I calculated the cross-section for this process. Now, this was interesting in itself, and the results have been used very much by experimenters ever since. It's one of the important bases of the work here at Cornell on the synchrotron. But also t was very interesting because there were experiments by Anderson which seemed to indicate that electrons could penetrate large thicknesses of material, and our theory predicted the opposite. They predicted that they would emit radiation at a very great rate in such penetration, and so we did not understand how this could happen. Now, the first idea we had was that maybe this is an effect of the screening of the electric field of the nucleus by the electrons. The first calculation Heitler did—and, in fact, he did that all by himself without my help—was the emission of Bremsstrahlung by a fast electron in the field of Just one point charge, the charge of a nucleus. He found that this process increases with energy; so that the higher the energy of the electron, the more likely does it become that the electron loses, let's say, half its energy by radiation in one collision, which Is a very unusual way for any particle to behave, or at least so it seemed at the time. So then I set out to see whether this would be changed if you take into account that the point charge of the nucleus is screened by the electrons around it, and this was a fairly complicated calculation but manageable and I found the result—that it didn't really make very much difference. The only difference it made was that at very high energy this probability finally became constant—it reached an asymptotic value instead of continuing to increase. And this was definitely in contradiction to the work of Anderson. Well, several years later that work was then explained in terms of Anderson's having mesons rather than electrons, and the mesons, because of their much higher mass, do not emit much radiation—the radiation goes inversely as the square of the mass. But at the time we didn't know that, so we pointed out this contradiction, and concluded that electrodynamics must fall above a certain energy. In the meantime, by much more experimentation and distinguishing protons, mesons and electrons, we know now that electrodynamics continues to be valid up to much, much higher energies, and we still have not found any place where electrodynamics fails. This is over 30 years later.
Weiner:So far so good.
Bethe:So far so good. So our formulae were right, and our conclusion was wrong.
Weiner:Were you in correspondence with Anderson or Millikan?
Bethe:No, we Just had Anderson's papers. The only person I saw who was vaguely connected with these matters was Compton, and there's a paper here, a Joint letter to Nature by him and me, in which... Well, the origin of that paper was the following: Compton had somehow come to the conclusion that cosmic rays consisted of protons, and on that he had a terrible fight with Millikan, who maintained that cosmic rays consisted of electromagnetic radiation, which then made electrons. So Compton was very happy about our result—Heitler's and my result—that electrons should suffer very great energy losses when penetrating material—for instance, the atmosphere. And so he said, "The primary cosmic rays cannot be electrons but protons," and we wrote a Joint paper In which we gave arguments for this thesis.
Weiner:When did you see him?
Bethe:That was at that international meeting in London.
Weiner:The international Conference on Theoretical Physics, which was held in 1934.
Bethe:In '34, right.
Weiner:Do you remember anything else about that meeting?
Bethe:It was a very nice meeting. I saw some of the great people for the first time—for instance, Madame Curie and her daughter, Irene, and Joliot. I don't remember who all was there from America, but I think I met several of the American physicists for the first time. It was an excellent meeting. There were a lot of good papers, and in those days one could still understand all of physics and listen to all the papers and intelligently discuss them.
Weiner:Did you have any paper on the program? I think you did.
Bethe:I had a Joint paper with Peierls on the photo disintegration of the deuteron, which was quite a nice paper. And in this paper, in fact, I think we got the first idea of what is now known as the effective range theory—namely, that such matters as the properties of the deuteron do not depend sensitively on the shape of the interaction between neutron and proton but only depend on some overall behavior of the interaction. I think I probably covered that.
Weiner:I notice that in this period you were collaborating with people whom you knew in Germany. Had you known Heitler?
Bethe:I had not known Heitler before. I think I may have met him once casually at some meeting.
Weiner:Where had he come from prior to Bristol?
Bethe:I don't really remember.
Weiner:But he was there ahead of you. You knew he was there?
Bethe:Yes. He had I think come there when I came to Manchester.
Weiner:Do you think there's anything significant about the fact that you didn't...
Bethe:Collaborate with the English?
Weiner:...collaborate with the English? Was this a question of finding yourself in the same spot and therefore finding a natural affinity? Was it a question of theoretical as opposed to the experimental interest, or that the particular subject area was just one that you hadn't an interest in?
Bethe:I think it was a combination of all three. Certainly I felt more at home with my German refugee colleagues. The most important point, I think, was that there were not terribly many English theoretical physicists. The one with whom I might easily have collaborated was Nevill Mott, but he was quite busy, and while I knew Mott very well during my first visit to Cambridge in 1930—he is just about my age—and then again in Bristol. I certainly felt entirely comfortable with him. On the other hand, he was then interested in the theory of metals. I was then much more interested in what was then high-energy phenomena—that is, the high-energy behavior of electromagnetic radiation in electrons—and in nuclear physics. At some earlier date—namely, in 1930—it had been the other way around. Then I was interested in solids, and he was interested in high-energy collision. But I think that explains why I didn't write any papers with him. Apart from Mott, there was Dirac, who I think never in his life wrote a joint paper with anybody. There were not terribly many theoretical physicists otherwise. On the other hand, one of the things I remember very vividly and very favorably are the meetings that we had every two months or so with a small mixed group of theorists and experimenters. Did I talk about that before?
Weiner:No. You mentioned in a general sense some discussion group that Blackett organized.
Bethe:Yes, Blackett had organized this, and I think he considered it a discussion group of the refugees from the Cavendish Laboratory. It was mostly people who had formerly been in Cambridge.
Weiner:Oh, refugees in that sense.
Bethe:Yes. Well, this group met I think always in London, it being the easiest place to reach from anywhere else, and Blackett was extremely active. I think Kapitza was participating occasionally, only occasionally, I think. I am pretty sure it included such people as Cockcroft, possibly Oliphant, all these experimenters. And of theoretical people, it certainly included Peierls and Heitler and Nordheim and myself, all refugees. I don't believe Mott was included because he wasn't interested in this kind of physics at the moment. As I remember it, the group was about twice as big as I have told you—about 15 people. I think G. P. Thomson was a member of the group. When he was in the chair he insisted on calling on Heitler by the name of Hitler.
Weiner:That must have gone over big.
Weiner:What kind of procedure was followed at these meetings?
Bethe:It was extremely informal. I think there were just invitations sent out giving the time of meeting, and then there was maybe one talk prepared by one of the members of the group—for instance, by Mr. "Hitler," and then all the rest of the day was devoted to discussion.
Weiner:A whole day?
Bethe:A full day, one full day.
Weiner:At some quarters at Birkbeck College, was it?
Bethe:That was Blackett's place of work at the time. I don't remember where we actually met. He had very small quarters at Birkbeck, so I somehow doubt that we met there. It's more likely that we met at University College, but I really don't remember.
Weiner:Were there any records kept?
Bethe:We may have met at the Royal Society, but I just don't remember where we met. I do remember that on several occasions we went out to Mr. Blackett's house, which was an extremely pleasant place in a nice neighborhood. During the International Conference we also went to Blackett's house, and one of the participants was Roget, and another Leprince-Ringuet, both from France; and I remember that they played ball in Blackett's living room for quite a while with great virtuosity.
Weiner:Were any records kept of these meetings?
Bethe:I doubt it. There certainly were no official records, and I don't think I've ever seen any records.
Weiner:No minutes or list of who was there.
Bethe:So far as I know, none; but it would be a good thing to ask Blackett about.
Weiner:I talked with him on the telephone [in London). He was receptive to further discussion.
Bethe:Yes. He of course carried this on for many years and organized it, so he must know much more than I do.
Weiner:So it was a thing that involved no money, is that right?
Bethe:No money at all. We paid the railway fare, and we paid for our keep in London, and it was just for fun.
Weiner:There was nothing like this in Germany?
Weiner:How would you compare the group, in all respects, with what went on in Washington at the theoretical physics conferences?
Bethe:It was much the same idea. I think there was great similarity. The only difference was that the Washington conferences were several days, and I think a little bit more organized. There was a little bit more of a program, but not much.
Weiner:Any mix in the group of experimentalists?
Bethe:There were more theorists in the Washington meeting, relatively speaking.
Weiner:Again, were the theorists primarily refugees at the Washington meeting?
Bethe:Ii think at least half. I'm not sure about the exact distribution, but there were more Americans there like Condon and Rabi...
Weiner:Breit, I guess.
Bethe:Breit was certainly there. I don't know whether any of the Ann Arbor group came, such as Uhlenbeck.
Weiner:The reason I thought of this is that it seems that the occasion for Blackett's group was the presence of some refugee theorists, and the...
Bethe:I don't think so.
Weiner:...occasion for the Washington discussion was the presence of Gamow and Teller.
Bethe:That is definitely true of the Washington affair, but I think not of the Blackett affair. I think the Blackett meetings had existed before the refugees came. They were then primarily experimental people, and we were just added to an existing group. And the Blackett meetings were much more frequent, I think at least three times a year. Washington was only once a year.
Weiner:What would you say the main effects were of these meetings that Blackett held?
Bethe:Well, I felt very stimulated, and I learned about some of the experimental discoveries for the first time there. I think it was at one such meeting that I first learned about artificial radioactivity.
Weiner:That would have been just about the right time.
Bethe:Yes. That then gave food for thought for the next couple of months, and we tried out some of the theoretical ideas, such as our Bremsstrahlung and pair production results, and I think this stimulated the experimental people. Blackett was drifting more into cosmic rays and away from pure nuclear physics, and I think it gave him some ideas for experiments. Also, I believe that Heitler's and Nordheim's theories of cosmic ray showers were stimulated by these meetings.
Weiner:And it Is interesting that these were all people who were not at the Cavendish, although occasionally I imagine some of them were included.
Bethe:Some Cavendish people were included, yes.
Weiner:I wonder if there was some reason why it wasn't held at the Cavendish. Was this because of Blackett's role in it, do you think? Or was there a certain atmosphere at the Cavendish that wouldn't have been conducive to this kind of meeting?
Bethe:I think there was some atmosphere of self-sufficiency at the Cavendish. Other people really were not needed. I don't think the Cavendish would have objected to our meeting there, but my feeling was they wouldn't seek out anybody else's advice. There was the additional very practical reason that going from Manchester to London is very easy travel. From Manchester to Cambridge would have been very difficult.
Weiner:And you would have probably had to go through London.
Weiner:Down to London and up again.
Bethe:Yes. So it would have been much more of a problem.
Weiner:Let me ask you another general question about your reaction to England, that is, did you find, in comparing the experimental tradition in England to the experimental tradition in Germany, that there were significant differences?
Bethe:I never was sufficiently close to the German experimenters to really get the feeling. Whatever I did see—and this may be quite unfair—it seemed that the German physicists were really more interested in the apparatus than the physics and the English physicists more interested in the physics than in the apparatus. Now, this may be quite unfair, and, as I said, I didn't get close enough to the German experimental physicists.
Weiner:Well, talking about the apparatus, what about the general awareness, the level of technology in England compared to Germany?
Bethe:Well, in nuclear physics England was certainly way ahead of Germany. In other fields of physics there was not much difference, but, again, I don't have much evidence.
Weiner:I didn't mean so much that. By technology I mean the approach to experimental problems and to apparatus, to the handling of components and the building of—
Bethe:I'm afraid I am just not competent to talk about that.
Weiner:Then I'll drop it.
Bethe:A man who was a little of an outsider who could tell you a lot of the English approach is Goldhaber.
Weiner:Yes, he has. That's way I'm asking you—to get some corroborating evidence. He discussed it quite at length.
Bethe:I'm afraid I am not competent.
Weiner:Let me ask you another question: that is, do you feel that the experience in England changed you in any way—the overall experience? It marked a certain stage. You were by this time about 27 and had already established a certain style in physics, had come from a certain tradition, although you had come in contact with England earlier. But I want to know how you evaluate that entire period in terms of your own career.
Bethe:I think it gave me more contact with other physicists, especially of my own age, and it got me more in touch with the live problems of the day. There was much less of that in Munich and even in Rome, although Fermi of course read very avidly what was going on, it was still very far from the centers of research. So I think it got me much closer to the important problems.
Weiner:And yet one would think the circle around Sommerfeld and the various scientific groups in Germany would be in pretty close touch with important problems.
Bethe:Well, I think they were mostly self-generated problems. In the course of investigating quantum mechanics, you would come to the question of quantum electrodynamics, as Heisenberg and Pauli did, and then you would find in quantum electrodynamics that there are certain divergences, and then you would be interested in investigating the mathematical problem of these divergences. This is the kind of problem that I would have worked on in Germany. Or I worked on the electron scattering problem which was an extension of what I already had done. Then I would go out and look for experiments in which electron scattering was investigated and then use that in the theory. But it was not so much the style of working on something entirely new like nuclear physics. I doubt very much if I had stayed in Germany whether I would have gone into nuclear physics as soon.
Weiner:I think we discussed last time the fact that England was really a center of work in nuclear physics, while in Tübingen there was certainly nothing. And in Munich you said there was very little.
Weiner:What effect do you think the refugees had on England?
Bethe:I think they made theoretical physics somewhat more respectable, and this was against Rutherford's tradition. He was very much a pure experimenter. And the English mathematicians had of course paid no attention to the real problems of physics. And such persons as Dirac followed pretty much in the mathematical physics tradition; although he was extremely inventive in quantum mechanics, he did not come very close to experimental problems, and so the experimenters didn't feel that a theorist was of much use to them. There was one great exception to this kind of theoretician—that was Nevill Mott. The refugees theoreticians talked about the same problems as the English experimenters talked about and therefore were much more useful. And I think this had an effect on English physics.
Weiner:Something I don't understand, though: You said that one of the things that was new in England ...
Bethe:Yes, was that there was contact. That's true. But before us there had not really been many theoreticians who worked for the experimenters. Now, maybe I should mention the man 1 replaced—E.J. Williams.
Weiner:You replaced him where?
Bethe:At Manchester for a year. He was a very intelligent man, partly experimental, largely theoretical. He was very close to the experimenters—in fact, at least as close as we. But he didn't know enough mathematics. So many of the more difficult theoretical problems he would not have been able to solve, and the refugees, plus Nevill Mott, plus maybe Massey, were the only people who knew a lot of mathematics and at the same time wanted to be close to the experimental work. So I think there was a desire by the British experimenters to have theoretical help, but it was not fulfilled until the refugees came.
Weiner:And you feel the refugees had a predisposition towards areas of theory that had a relation to experimental problems?
Bethe:A relation to experiment—yes, I think so, I think that's very true, for instance, of Fritz London on the super-conductivity and the other people I have more or less mentioned.
Weiner:Where did this then come from and was it frustrated in Germany? You see, the thing that's difficult for me to understand is...
Bethe:A very good question. I was not aware of it in Germany, although I had always worked on applications which were somewhat close to experiment. It's a very interesting phenomenon, and I can't fully explain it. Sommerfeld certainly made a great point of getting results which actually could be compared with experiments. And, on the other hand, we hardly ever saw an experimenter.
Weiner:Well, you explained the circumstances of that. I think that it makes sense. I don't think we need put the pieces together now, but I think all the pieces are there to explain it. You were saying that at least in your case, at least in the case of Sommerfeld's students, the type of training received would help them fit in with a group of experimenters...
Weiner:...and that the opportunity to fit in was not really at hand in Germany, but was at hand in England, and that there was a particular gap in England because the theoreticians trained in England didn't have this relationship in their training to experimental work and couldn't fill the needs there. But there was a willingness on the part of the experimenters in England and there were no theoreticians to fill it.
Weiner:This makes a nice story. it is something to think about and to see if it holds up. It's a very good impression and interpretation and certainly is your story.
Bethe:It certainly is my story, and it's also that of Peierls, less so I think of Heitler, but I think quite strongly of Froehlich and London.
Weiner:In this period, really a brief period, did you become aware of the organized efforts to aid refugees?
Bethe:Yes, I was aware of them. I did not do much about it. I'm embarrassed that I didn't help much, but I knew of the effort. I knew, for instance, Szilard reasonably well. He was deeply engaged in this, and I met, I think, one or two people from the Academic Assistance Council.
Weiner:Do you remember more about Szilard and his role in this? When did you first meet him?
Bethe:I think there. I'm not sure. I may have met him in Germany, but I don' t remember. Well, Szilard was forever busy and always had dozens of scientists he wanted to place in one way or another. He traveled a tremendous amount, and he also did some experiments at the time on neutron capture. He was at Oxford. I don't remember much detail about him.
Weiner:It was Just a general question. Do you think that we have covered both the social and technical aspects of this period?
Bethe:Well, one more technical point. Bragg suggested to me that I work on the problem of order in metallic alloys. He had observed that, for instance, with a gold and copper alloy at a sufficiently low temperature that the gold and the copper atoms were regularly arranged, and then at a certain temperature this regular arrangement would disappear. So to speak, the ordered lattice melts while of course the alloy still remains solid. And he, with E. J. Williams, had made a rough theory of this based on the Weiss theory of ferromagnetism, and he suggested to me to look into this more in detail. I did, and wrote a paper which I think is quite a good one, which has been much quoted—that's it, "Statistical Theory of Superlattices." it has been much quoted and has been the basis of a lot of work by many people, to some extent trying to put on a rigorous basis what I did at that time somewhat intuitively; Onsager afterwards did some important work on this, and also Montroll. That was my main work in Manchester, at least the work which took the most time. The work on nuclear physics with Peierls took a little less time and gave many more publications. I don't know which was more important.
Weiner:I notice in this period there is a memorandum on cosmic rays published in the Carnegie Institution of Washington Yearbook. I wondered how that got in.
Bethe:I don't remember that at all.
Weiner:it says 1935. I wonder if it was after your arrival.
Bethe:It could have been after my arrival, I just don't remember. It may have been an extension of my paper with Compton, my letter to Nature, and telling once more that it should be protons, but I don't remember it.
Weiner:I was just curious if this was a sign of transition. You were at Bristol when you heard from Lloyd Smith about a job at Cornell. Now, did this come out of the blue?
Bethe:Yes. Lloyd Smith had been one of the Americans at Sommerfeld's Institute. I have mentioned only three of them, but there were at least a dozen while I was there. He came there, and Sommerfeld asked me to take care of him, so I invented a problem for him, which actually gave rise to quite a nice paper, and so he got to like me there. Then when he knew that I didn't have a job and Cornell was building up its nuclear physics, he suggested to the head of the department to invite me to come.
Weiner:Do you know how he knew that you were out of a job—that you were in a transitory state?
Bethe:He somehow knew that I had emigrated from Germany—I suppose probably from my papers—I had published enough—and giving as my address Manchester. I don't know how else he would have known.
Weiner:But you hadn't been on any of these lists that you know of that were being circulated around?
Bethe:I don't think so, but I don't know.
Weiner:Do you know where the funds came from for the position? Was it an existing position or was it newly created one on top of the existing structure?
Bethe:It was created on top but it was a regular university position. The department chairman, Gibbs, who had just come in as a department chairman—R. C. Gibbs—had successfully persuaded the administration that the physics department needed to expand and needed to get into the new field of nuclear physics. So they added first Livingston and then me and then the next year Bacher and I think the following year, Parrott, who is now the department chairman. He is in X-ray physics, not in nuclear. However, these were new positions given by the University, regular university positions.
Weiner:You mentioned last time that the salary was, I think, $3000, and the position was assistant professor.
Bethe:it was just acting assistant professor, of which they made the most yesterday at the dinner.
Weiner:This meant that the commitment was a temporary one.
Weiner:Was it for a year, did you think?
Bethe:It was for a year as an acting assistant professor. However, in the letter inviting me, which was very long—I think it was three pages single-spaced (Gibbs was a very careful gentleman)—
Weiner:Have you saved that letter?
Bethe:I think I may still have it, but it would take me a long time to find it.
Weiner:From my point of view it would be time well spent. I urge you some time to do that. In this three-page letter—
Bethe:He explained to me what the department was like, how they wanted to expand, how they wanted to do nuclear physics and do more theory, and who was there already, what they were doing, and that while this was only an acting assistant professorship, if I pleased them, they would be looking forward to a more permanent appointment.
Weiner:What was your reaction when you received this?
Weiner:There was no question in your mind.
Bethe:There was no question in my mind. My situation in England was so precarious, from day to day or from year to year, that I was very happy to get something which looked at least semi-permanent. Also, it seemed like a lot of money to me. It was probably nearly twice what I was getting in England.
Weiner:How did you get over here—on your own funds?
Bethe:On my own funds.
Weiner:What was the timing of that? The letter came...
Bethe:The letter came while I was in Copenhagen in August of '34.
Weiner:This brings us to another question: What were you doing in Copenhagen?
Bethe:I spent a month there. Well, everybody goes to Copenhagen. just wanted to see what Copenhagen was like, and it was a very nice month. I'm not sure whether it was July or August, but anyway it was interesting in one respect. I think I gave a talk on nuclear physics, or so it's told to me, and on nuclear reactions, and Niels Bohr listened to that and he claims that this talk convinced him that I was wrong, in that nuclear reactions must behave quite differently, and from this developed in his mind the theory of the compound nucleus.
Weiner:I've heard that, that he sat there shaking his head.
Weiner:Did you go by invitation to Copenhagen?
Bethe:I think so. I don't know exactly. I think probably.
Weiner:But it was your first trip there.
Bethe:My first trip to Copenhagen.
Weiner:Had you met Bohr earlier?
Bethe:I am not sure.
Weiner:And the letter came?
Bethe:The letter came and I immediately replied. It asked for a cable answer, so I immediately telegraphed back that I would be very much interested and would accept it with the condition that I come only for the second semester because I had an obligation to go to Bristol. I didn't just want to cancel that. This was before Bristol. So I said I should go to Bristol at least for one semester, and then I would come.
Weiner:This an interesting sidelight. I hadn't known that Bristol was a sort of lame duck appointment.
Bethe:It was a sort of lame duck. It wasn't very lame, because I had a very good time there. Well, it was a lame duck in the usual sense.
Weiner:You went to Bristol in October '34 and stayed through...
Bethe:I stayed till Christmas and then went home to my mother and got my visa straightened out and then at the end of January I left for the United States.
Weiner:And you proceeded directly...
Bethe:Directly to Ithaca.
Weiner:Was there any discussion, by the way, before you left—anyone who either encouraged you or discouraged you from taking the appointment?
Bethe:I don't really remember. I think I discussed it with Professor James Franck, who was in Copenhagen, and he strongly encouraged me to go, if I remember correctly. I didn't consult my parents but just informed them that this was what I would do. My mother was unhappy that I would be so far away but understood that I wanted a permanent job. I think Mott told me that he regretted this very much because he had looked forward to my staying there for a number of years and maybe giving me a more permanent position when he could, but he did this very mildly. I don't think there was very much discussion. Anyway there was not enough discussion to influence my mind.
Weiner:I guess because you recognized the limitations of the ability of the English to provide permanent places.
Weiner:Well, then, getting to the next part of the story, you came. I imagine you docked in New York and proceeded directly to Ithaca.
Bethe:Well, I spent a night in New York and I spent I think the afternoon or evening walking through the streets of New York to look at the city, which was very interesting. In those days there was not yet so much traffic that you would fear to be run over at every crossing. So I found it extremely interesting and walked all the way down from 50-odd street to the Battery and then took the subway back up. And then the next morning I took the Lehigh Valley train to Ithaca. I was very much astonished and a little taken aback by the desolate landscape west of the Hudson, the swamps of New Jersey, and I was astonished that so much of the land was not cultivated, because in Europe every square foot is cultivated. But otherwise there weren't many events. Then I came here and was received in a very friendly manner by Lloyd Smith, who let me stay at his house for about two weeks until I had found some other place to stay. Then I was immediately taken in hand by Professor Gibbs, who explained to me through many hours of conversation what I was to do and how I was to teach and what I was to teach and what it would be like and what they were trying to do. I met Livingston and started talking nuclear physics to Livingston. I found that there were very many things he didn't know, so this was the first germ of the Reviews of Modern Physics articles. Then I started teaching I think two or three days later and had I think two courses to teach, and there are still people around here who took the first course I gave. One is a professor here, Hartman. And then Gibbs said, "Well, there's Mr. Meyers here who is much more interested in theory than experiment. Can you take him on as a Ph.D. student?" So I had a Ph.D. student. He was quite intelligent, but I haven't heard from him for years. Then very soon—Well, that happened actually in a somewhat strange way. I met the visiting physical chemist. He was quite well-known at Wisconsin. I met him on a train going to Chicago. I visited Chicago to talk to Compton, and then I was also invited to Purdue by Lark-Horovitz, who was very much my protector for several years.
Weiner:Had you known him in Europe?
Bethe:I had not known him, but he knew about my arrival and invited me to talk there during our spring vacation back when all this happened. Well, what I wanted to say is that this chemist said, "Now, you are sitting there. Wouldn't you like some collaborators?" And I said, "Yes, of course I would." And I think he was instrumental in getting me a grant, probably from the National Research Council for a fellow to come here. And that was M. E. Rose, who Just died a couple of days ago. Then I got another National Research Fellow very soon after, and that was Konopinski. I think he came a year later. But he was actually sent to me having the National Research Fellowship. Uhlenbeck sent him to me from Ann Arbor. So very soon then I built up an empire and had these two very competent young theorists working with me.
Weiner:Did you have any funds to go with it?
Bethe:Well, I'm trying to remember what the first grant was. I have some idea that it was not a National Research Fellowship but something more private, particularly produced by my friend the chemist, but that lasted only for a year.
Weiner:Would it have been an industrial source?
Bethe:It could have been, if that exists, a fellowship from the Franklin Institute.
Weiner:The American Philosophical Society had funds. The AAAS also...
Bethe:I think the American Philosophical Society is quite possible.
Weiner:There are ways of checking that. And that brought a fellow there. Did you need much funds for your research?
Bethe:I needed just salary for these people. Otherwise I didn't need anything.
Weiner:Pencil and paper.
Bethe:Pencil and paper and that was provided, and a slide rule I had myself, and for some time I got every year at the beginning of the year a grant of $50 from the department to spend on research. I very seldom spent more than $10. But once I spent all the $50. I think I spent two years' allowance.
Bethe:I did some experiments on pushing pieces of metal through another piece of metal, and that was in connection with my first piece of war research on penetration of armor, on which I did the theory.
Weiner:But under ordinary circumstances, you had no need for funds?
Bethe:I had no need for money. Well, I spent long hours with Livingston talking nuclear physics, and I also went around the country and talked to people and found out they didn't know very much nuclear physics, and that I described before. So that was the start of these articles, which I think I started writing certainly in 1935 and probably only after the summer, but I'm not sure about that.
Weiner:Traveling around the country, you mentioned that within a few months after your arrival—that is, the first recess as spring vacation opened—you had been invited to Lark-Horovitz's.
Weiner:That means that you were in the swim rather early.
Bethe:Immediately. In fact, Gibbs saw to it that I got into the swim immediately. He suggested to me, when granting the delay of one semester, that I send in an abstract to the American Physical Society meeting in early February just a few days after my arrival so that I would get to be known right away. So I did and I gave a talk—that was, I think, a week after I got to Ithaca.
Weiner:That was at the New York meeting.
Bethe:The New York meeting.
Weiner:What paper was that? Does it show on this bibliography?
Bethe:No, I don't think so. It was the predecessor of this paper. It was on the same subject, but I gave a talk about t, and then afterwards...
Weiner:"Theory of Disintegration of Nuclei by Neutrons." So, in other words, the record of it would exist as an abstract.
Bethe:That's right. It was wrong as of that time and was then superseded by Bohr's compound nucleus, but it was then resumed by Weisskopf in the early '50s in his clouded crystal ball.
Weiner:He refers to that in the article in the Perspectives.
Weiner:it would be interesting to know what your reaction was to meeting the physics community at the New York meeting. You went a month after your arrival.
Bethe:Less than a month.
Weiner:I'm curious to know how you reacted.
Bethe:As far as I remember, I felt just fine, and I thought this was wonderful with lots of people to talk to. I really enjoyed that first meeting.
Weiner:Had you ever been at a meeting comparable in size to that?
Bethe:Yes, once in East Germany in Königsberg and that was a meeting of the German Physical Society, which was not quite as big, but nearly as big.
Weiner:Did you make any friends or establish any relationships at that first meeting in New York?
Bethe:I don't remember for sure. I certainly met a lot of people. How much actual friendship I established just then, I don't know. It's very difficult to tell when a thing like that starts. Probably I met Tuve and Hafstad at that meeting, and they became friends afterwards. But I wouldn't be too sure.
Weiner:When you made your contacts with people in America, through this meeting, through the invitations and travel, was there a characteristic pattern? Did you tend to be in closer touch with people from Europe who had come to America?
Bethe:No, not on the whole. Well, there were not many people who had come from Europe. There was Lark-Horovitz and there later in Washington there was Gamow. I don't think I was closer to Gamow than I was to most of the Americans. I was a little closer to Lark-Horovitz than to most of the American physicists I visited but not so much. I think I mostly met Americans and spent most of my time with them.
Weiner:What institutions did you go to mostly?
Bethe:Columbia quite frequently. Rabi was very good to me and invited me many times. I liked to travel to New York, and I gave talks in the colloquium there and talked to him. One day he told me, "Oh, there's a young student here whom you should meet and tell me what you think of him." That was Julian Schwinger. So I told him that I thought a great deal of him. And Rabi said, "That's fine, because so do I," and then Rabi made me write a letter about Julian Schwinger which he showed to some other people in the University who didn't believe in Julian Schwinger.
Weiner:Did that imply that you had already become...
Weiner:So that your word from the outside would have some weight at the University.
Bethe:So it seems.
Weiner:You mentioned Columbia. How about other east coast institutions?
Bethe:Well, the first year I think I must have been at least once at Harvard, but I'm not sure. Later on I went to Harvard a few times. Van Vleck always liked to invite me. Then there were the trips to Washington. This was not particularly to see any institutions but mainly in connection with these theoretical meetings and then Physical Society meetings. I was enchanted by my first visit to Washington, which was in April at the best time with the trees in bloom. I stayed at the then Wardman Park Hotel, which is full of flowering trees, and I thought that was just lovely. Then in addition—Well, I think in '35 we didn't yet have a theoretical meeting. However, in '35 already I think I visited the Department of Terrestrial Magnetism and Tuve and Hafstad. And this was presumably in connection with the Physical Society, but I'm a little vague in my mind just what the occasion was. Certainly I was very much interested in their experiments, in interpreting their proton-proton scattering, and for many years afterwards when we had the theoretical meetings, I always looked at the experimental work in Tuve's outfit.
Weiner:Did you get to California?
Bethe:I didn't at this early time. In fact, I didn't get west of Chicago and Purdue. In the first year still, I got to Minneapolis, again on a Physical Society meeting. For the first few years I went to nearly every Physical Society meeting and enjoyed them all. Physics was not so big yet. One could talk to most of one's friends and get a lot of new ideas.
Weiner:Was this frequency of meetings and the liveliness of the life of physics significantly different than in Germany and England?
Bethe:Entirely different from Germany. In England there were the very nice Blackett meetings, but these were a very small circle, as I mentioned. There was essentially no large-scale meeting. So I very much enjoyed these more comprehensive meetings, and I spent many hours on the lawn of the Bureau of Standards, where the Washington meeting in the spring was normally held, discussing papers and nuclear physics with other physicists.
Weiner:Did you get the feeling then that there were a lot more physicists in this country than in either England or Germany?
Bethe:Certainly a lot more than I knew.
Weiner:A lot more than you knew in the other places?
Bethe:In the other places.
Weiner:That's the only way you had to judge unless you were comparing numbers.
Bethe:Well, I certainly got the feeling that it was much easier to get to know the other physicists here and get to know them from the entire country. I just liked it.
Weiner:You felt accepted.
Bethe:Very much so and from the very beginning.
Weiner:How about this other question that we had raised earlier in regard to the closeness that you felt existed in England between the experimentalists and the theorists (with all the qualifications involved)?
Bethe:This was even more true here, and it was here in a very personal way in the collaboration between Livingston, Bacher and myself and also when I went to Purdue I was asked to talk to the nuclear experimenters and make suggestions. I discussed many experiments with many people around the country. Similarly in Washington with the Department of Terrestrial Magnetism, and just a little less so at Columbia with the neutron group. I had a somewhat looser contact with them, but also some contact with Pegram and Dunning and those people. So there was even closer contact between theory and experiment and much much more direct contact between me and the people who actually did experiments which I was interested in.
Weiner:How would you characterize the other theoreticians who were already in this country as far as their closeness or lack of closeness to experimental interests?
Bethe:Well, there was Felix Bloch, who was quite close to experiment, so close in fact that he became an experimenter. Then Edward Teller, who came a little later, had very close contact, especially with chemists—not so close contact with experimental physicists. Gamow, I think, didn't have close contact with experimenters. Wigner I think not very close, although he did a lot of work that interested the experimenters. I don't think he came close to the experimenters until the Manhattan Project, and then he was very close.
Weiner:We were talking yesterday about when I asked him about this, that he felt that in his case there was a separation. Everyone you have mentioned (you mentioned four: Bloch, Teller, Gamow, Wigner)) were all refugees.
Weiner:Well, he was an émigré, but it's a question of interpretation. He was there a half year and here a half year, and things were decided definitely at about the same time that you had to leave. But what I really meant by the question was, what was the American theoretician like? Who did you know of as being a theoretician and how would you characterize them as far as their relationship to experimental interests?
Bethe:Well, Oppenheimer I think had quite a lot of influence on experimental work in Berkeley and in Caltech, both places, and while perhaps he was not quite as close to the actual day-to-day experimental work as I was here, he was certainly very close in a general way, suggesting experiments and interpreting and so on. Now, in the Ann Arbor group, Dennison was quite close to experiment. I think Uhlenbeck and Goudsmit perhaps not quite so, and La Porte was the fourth. I really don't know; I'm not sure about him. Well, who else?
Weiner:Breit, Van Vleck.
Bethe:Breit was very close to the Tuve Washington experimental group and later on to Herb's group at Wisconsin. Breit perhaps by nature is a little more distant than most of the others I mentioned, but he certainly worked very closely with these people. Van Vleck had, I think, strong interaction, not quite as strong as Oppenheimer or I, but had quite strong interaction with experimental physicists, and certainly the work he did was very directly useful.
Weiner:I just wanted to break it down into individual units and see how it added up as a total impression.
Bethe:Yes. Condon I think was more like Wigner and worked more on pure theory, although his work also was directly applicable to experiment. I think those are perhaps the most important people. I would say that among the people already here, about half were working closely with experimenters. [pause in recording, tape change] Well, I think there were very few theorists in this country who did extremely pure theory, hardly anybody who would work like Dirac on more or less abstract problems in quantum theory. Now there are lots who do this, but at that time there were very few. So I think there was more closeness between experiment and theory at that time than in Europe.
Weiner:I'd like to check another thing. Somewhere along the line (I forget where in my reading) there was some mention (maybe in our earlier session) about seminars at Cornell. What form did they take?
Bethe:Well, we had a regular weekly seminar in theoretical physics. Most of the time we discussed papers of other people, and we had somebody who would give a report on one or the other paper, similar to the seminars that Sommerfeld had had. And then occasionally if one of us discovered something, we would talk about that.
Weiner:These seminars here involved all of the physics department—experiment and theory people?
Bethe:I was talking about the theoretical seminars, and they involved just the theorists at the time.
Weiner:For example, Livingston would not...
Bethe:Would not participate.
Weiner:And this was similar to the Sommerfeld seminar.
Bethe:Yes. Then we had a general department colloquium also once a week in which reports might be given about a whole subject, not just one particular paper.
Weiner:What about the teaching here? You had already had experience with graduate students.
Weiner:So that part of it wasn't new. I would like to ask a few questions on that, but at this point I'd like to ask about undergraduate teaching. Was this significantly different than any prior teaching experience?
Bethe:I did only one semester of undergraduate teaching. No, that's wrong. I did two semesters of undergraduate teaching before the war. The first was a complete failure. I was given a section of sophomore engineers. Did I mention that already?
Bethe:And in order to make life easier for me, I was given a section which was out of turn. That is, in the first semester I was given a section in the work which normally would be done in the second semester. Most of these were repeaters, and most of them were football players, and they were not the least bit interested in physics, and I had a terrible time. It was no fun at all, either for them or for me. Then a couple of years later I was given a senior course (it's now a Junior course) in analytical mechanics, and that was very nice, and I did that with pleasure. This was not so very different from what I would have done, let's say, in Tübingen on analytical mechanics—just a little bit simpler because it was for undergraduates. Most of the time I taught graduate courses, but it was the first time in my life, except for the one semester in Tübingen that I really had to cover all of theoretical physics. In Munich I had just covered one very small area as a privat-dozent and so similarly in Manchester.
Weiner:How many graduate students did you have at first and then how did this number change? What I'm interested in Is the nature of your relationship with them.
Bethe:I think the whole department had about 30 graduate students when I came. We now have a little over 200. The number increased to 40-odd before the war. After the war I think we started at something like 80. That number after the war was dictated by the University administration, who put a ceiling on the number of graduate students because of the problem of housing. Now, quite frequently—in fact, every second year, 1 think—I taught the introductory course for graduate students, which was a complete course on theoretical physics, classical theoretical physics, no quantum mechanics at all. I alternated in that with Kennard, who was the senior theoretical physicist here, and this was a good stiff course. I think in many ways I wish we still had it. It has now been very much reduced in scope. We give fewer hours and cover more subjects in fewer hours and therefore much less thoroughly. Well, I found great variations in the ability and preparation of these people, but similar variations had existed in Germany. I found at least to begin with that I had to go more slowly than I would have done in Germany, mainly I think because the mathematical background was less strong. All that has changed in the meantime. In fact, one of the interesting things is that as time goes on the courses go faster and at a much higher level. The entering graduate students just know a great deal more than they did in 1935. Then I gave courses in quantum mechanics, various fields of quantum mechanics. I used to give a four-semester cycle in quantum mechanics, first on the general principles, and then theory of spectra, and then collisions, and finally theory of radiation in quantum electrodynamics. Now we do the same thing in two semesters, which means again that it's not covered quite as thoroughly. In this also I alternated with Kennard to some extent, and there was another man who was mainly an experimenter but who taught theoretical courses as well—Collins—who took some of this work. In the big course, the introductory classical physics, there would be, oh, maybe 20 students, sometimes 25—a very nice number just to have a nice class and talk to everybody. in the small courses—well, the first two terms of quantum mechanics were about the same size, but then some of the more special courses like collisions or radiation theory might have six people or eight or ten, and It was quite an idyllic life.
Weiner:How about the number of graduate students who were doing doctoral research under your direction?
Bethe:They started out very low. I had one the first year. I think I had two the second year. And then around 1939-'40, the number had increased considerably. I think I had something like four or five, which I think is about the right number.
Weiner:Then generally, when you got to that level of four or five, would they be working on the same general area?
Bethe:Some were working on nuclear physics. I think the majority were working on solid-state problems. I was no longer working on solid-state problems much, but I found that it was easier to get feasible theses in that subject than in nuclear physics—less competition and the problems could be more clearly defined.
Weiner:Did you consciously in your work with them—and I guess this is related to department policy—feel that students taking a degree in theoretical physics had to get a certain background in experimental physics?
Bethe:Oh, definitely. This was department policy, and I was in agreement with that policy. They had to do quite a lot of advanced laboratory and take quite a number of courses—lecture courses—directed to experiment rather than theory.
Weiner:Was this different than in Europe?
Bethe:Not different from Germany; different from England, however.
Weiner:Do you think the Cornell policy was probably in line with what other major physics departments were doing in this country?
Bethe:More or less. I think the other departments were somewhat more permissive and allowed the theorists to get away with less experiment and vice versa.
Weiner:I want to ask another question. In the interview you did in connection with Radio Bremen, you mentioned that you were impressed with the liveliness of the teaching—not necessarily your own teaching but of the teaching encounter. I wish you would expand on that a little.
Bethe:Well, it's customary in Europe to let the professor address the class and he talks and writes formally on the blackboard and leaves again, and the students listen and try to understand. Occasionally a few come forward at the end of the lecture to ask a question or two, whereas here whenever a student feels like it, he asks a question. I think it's much better.
Weiner:Were you prepared for this?
Bethe:No, nobody had told me. I think it happened right away, and, well, I Just answered the questions.
Weiner:As simple as that. How about the size of the groups that you were teaching here as compared to Europe? Was that significant?
Bethe:The Tübingen group was much bigger. I think my lectures there must have been to about 60 students. And so I thought the groups here were vary small. In the meantime, our groups are also 60 to 80 to 100 in theoretical physics.
Weiner:During the past ten years or so?
Weiner:Another question on your reaction when you came. It relates to research, and there are three aspects of it I think are interesting to consider. One is freedom in the choice of research area, the relative freedom that one has; secondly, the resources for research (for a theorist perhaps this is not a significant question, but it does have some interest); and, thirdly, the support for research, financial support, which also relates to what resources you have. But first anyway this idea of choice of a problem or freedom. In your discussions with Gibbs, for example, was it stated as a policy that they expected you to do anything under the sun or that they were hoping that you would pursue interests that they knew you had and that were also in line with the department's desires?
Weiner:I don't remember for sure. I think Gibbs may have expressed a desire that I work on nuclear physics primarily because that's what he wanted to build up. He probably said that he would like me to work with Livingston, which I wanted to do anyway. But there was very little pressure. I was essentially left to do what I wanted, and it just happened that I wanted to do nuclear physics, so that fitted into Gibbs' plans very closely.
Weiner:Did you get any feeling, though, in general, in your rapid assimilation into the larger physics community that there was any difference in approach and choice of research topics in this country than in England or Germany?
Bethe:I think there was no great difference in all three countries. People were left pretty free to work on what they pleased: of course, in the case of experimenters, subject to the available apparatus, but in the case of theorists, I think there was very little regulation.
Weiner:Those are rather general questions. I'd like to be more specific, if you like, and that is to see if there is anything In terms of the work that wasn't covered in the area of nuclear physics.
Bethe:I think there is probably nothing in the period before the war.
Weiner:I wanted to ask you if there is anything more about the energy in stars work?
Bethe:That I think I probably did not talk about, or did 1?
Weiner:Let me refer to it. Maybe it would be helpful to do that. You talked about the Washington Conference, and you described in detail, 1 think, who was there to the best of your recollection. Strömgren, Weizsäcker and others were there; you talked of the larger discussions that were held, and then some smaller discussions, which did not involve the people who had actual astrophysics experience; and you talked of some of the ideas that were advanced there. You said you remembered that at that meeting everybody talked about discrepancies, and everybody talked mostly about heavy elements. And then you described, 1 think pretty well, the day-to-day work that followed that and what led you to do your final carbon cycle.
Bethe:Yes, then that's that.
Weiner:it seems to be covered.
Bethe:Did I go on to the work with Marshak on the theory of white dwarfs?
Weiner:I don't think so because it wouldn't have come up in the context of what we were talking about. When did that start?
Bethe:Well, as I was working on the carbon cycle, I got a new graduate student, Robert Marshak, who came from Columbia and who was very much interested in my work; and so I gave him as a thesis to continue my work in a somewhat different direction and do a theory of the white dwarf stars. And he first of all found out that there couldn't be any hydrogen in a white dwarf and then could put limits on the temperature and the temperature distribution in a white dwarf star. And this was much more direct astrophysics than nuclear reactions in stars. This was really my only venture from nuclear physics farther into the stellar constitution. We also wrote a paper together which is in here, "The Physics of Stellar Interiors and Stellar Evolution," which is a progress report published in one of the yearly journals. So this was outside of nuclear physics. I did some work on the meson theory of nuclear forces in 1940, and I did some work on interpretation of cosmic rays—there is one paper on the measurement of neutrons in cosmic rays.
Weiner:Was one of those papers with Marshak something that led up to his dissertation?
Bethe:They were all connected with his dissertation. I think none of them can be said to have led up to it. They were part of the same general investigation. For instance, there's one paper, "The Generalized Thomas-Fermi Method as Applied to Stars," in which we developed the Thomas-Fermi atom, including elevated temperature. That had not been done by Thomas and Fermi. Another piece of work was that together we sponsored one of the WPA projects. There were two mathematicians, Blanch and Lowan, in New York who were out of work as mathematicians and had been hired by the WPA to produce some useful mathematical tables. Well, Marshak persuaded them to do numerical calculations of the temperature distribution inside the sun, including nuclear reactions, and we published a joint paper on that with these two mathematicians.
Weiner:How long was Marshak with you as a graduate student?
Bethe:I think through the fall of '41. It might have been '40. I just don't know. And then he went to Rochester. He was given a job and was told, "This instructorship will surely last only one year. There is no chance for a renewal." He has never left Rochester.
Weiner:That's a long time.
Weiner:Were you married in '39?
Weiner:And by that time the Ewalds had been moving around a bit.
Bethe:The Ewalds had moved to Cambridge by that time, and then they moved from Cambridge to Belfast just in the summer of '39.
Weiner:How did you renew your acquaintance with Rose Ewald?
Bethe:Rose had come to this country in 1936 independently of her parents. She Just couldn't stand Germany under Hitler. And some nice friends of theirs—two friends, namely: Landé and Courant—guaranteed her immigration. Land, I think, gave her the affidavit to immigrate, and Courant saw to it that she got a job. She got a job with another physicist, Miss Sponer, later Mrs. Franck, to keep her house and study half time at Duke University, so that's what she did her first year. And during that time there was a Physical Society meeting at Duke University. I told you I went to all Physical Society meetings except very few. To this one I went together with Niels Bohr, and each of us gave an invited paper about the compound nucleus, and Rose, knowing me, made a point of seeing me after the meeting and before the dinner of the Society. She wanted to ask me mainly whether I could find a job for her father. Her father in the meantime was still in Germany. This was in the spring of '37. She had immigrated in '36. Then I didn't know of a job for her father, but I fell in love with her, and then we met several times after that. I financed her studies in Smith College from then on and tried very hard to marry her, but she delayed this event for two years until in '39 she consented and we got married.
Weiner:Did her father visit for a while?
Bethe:Her father visited the United States twice—in 36 and '38.
Weiner:He went to the Michigan summer school and to Harvard Tercentenary although they told him he couldn't go.
Bethe:I didn't know that.
Weiner:He had only been given permission to go to the Michigan thing and wanted to stay on for the Harvard Tercentenary meeting.
Weiner:If my story is correct, he apparently didn't get permission but went anyway. I don't know what the consequence was.
Bethe:Nobody paid any attention, I suppose. We.., I know he was at the Michigan summer school, and so was I. But Rose I think was not around. I'm pretty sure she wasn't. He was there as a bachelor. And so I met him there. And then in 1933 he came again to the Michigan summer school, I believe, and he certainly came to teach summer school at Columbia. I'm not sure whether he came to Michigan also. And in '38 he had both his wife and Rose around him in New York.
Weiner:Let's go to something else in 1938. I saw a reference to the cyclotron here being used for the carbon cycle work. That's an interesting relationship.
Bethe:Well, in the carbon cycle there are certain nuclear reactions, the capture of protons by various carbon and nitrogen isotopes; and It seemed to us a good idea to check whether these reactions really existed and whether they had the cross-sections that I had predicted. And so there were a couple of investigations on this, of which I see one here by Holloway and myself, "Cross-Section of a Reaction N15 Going Back to Carbon 12." 1 think there must have been one or two other papers at the same time. I am not entirely sure because it's possible that our cyclotron was too weak to observe the pure capture reactions, the p-gamma reactions. it is possible that we could only observe the p-alpha reactions.
Weiner:How long a period did that work go on?
Bethe:About a year or so. Well, then came the war, and quite early in the war I said that I really should do something about the war, and I felt very strongly that way after the fast fall of France. I took two steps in this direction at an early time In 1940. One was to visit Dr. Von Karman in Pasadena. This visit was made jointly with Teller, and we asked Karman whether there was anything we could do about aero-dynamics, about flight problems, that would be of help to him.
Weiner:That was the way you thought science to be most effective, in your first impression?
Bethe:Yes. It was obvious that planes were the most important weapon in the Second World War, and that presumably not everything was known about flight. Weil, Karman said there wasn't very much to be done about planes. They were pretty well in hand. However, he was very much interested in shock waves, and aerodynamicists knew the general laws of shock waves, but they did not know what was going on in the shock wave itself in the short run. And in particular they didn't know this in case of chemical transformations. Now, a little milder than the chemical transformation was the question of what the molecules did when they went through a shock. The molecules—the normal nitrogen and oxygen molecules—don't vibrate. They only rotate and translate. And it was known that vibration Is very difficult to excite by collisions, and it is very difficult to transfer energy from translation to vibration. And Teller, in fact, had written a paper about this with Landau, the Russian physicist, about the speed of such transfer processes, and so Karman asked us: "Now, suppose you have a shock wave. It takes a long time for energy to be transferred. How will the shock wave look? How will the density and the pressure and the temperature behave behind such a shock wave?" So we did this jointly. it was a very interesting piece of work, and it has become the bread and butter of modern aerodynamicists. For instance, Dr. Kantrowitz, who was one of the great aerodynamicists, did his thesis, I think, on this problem at Columbia under the direction of Teller, an experimental thesis, in which he showed that indeed there is a relaxation behind the shock wave so that the vibrations get exited very slowly. He used shock waves then as a means of measurement of the speed of chemical reaction. And that work he perfected here at Cornell when he was professor here, and then afterwards at the Avco-Everett research laboratory, where he is now. And in this connection it played a great role in our understanding of re-entry phenomena of ? into the atmosphere. So this Joint paper of Teller and myself has had quite a lot of consequences. It probably isn't listed here because it never was published.
Weiner:Originally because of the war it wasn't published, but later the knowledge became...
Bethe:Yes. It actually was not classified. It was published as a pamphlet by the Aberdeen Ballistics Laboratory, but it never was published in any journal. On the other hand, t is always quoted.
Weiner:You don't recall the exact title at this time, do you? If not, we can look for a reprint later.
Bethe:I don't really know, and I don't know if I can find a reprint, but there exist reprints.
Weiner:The thing that I would like to ask is: where was Teller at the time that the two of you got together to go to Pasadena?
Bethe:Weil, he was a professor at George Washington University. He was for some reason out in California at Stanford. Why, I don't know.
Weiner:They had a summer school at Stanford, I know.
Bethe:I was teaching at that summer school. He was not. What he was doing there, I'm not sure. Maybe he was just there on vacation.
Weiner:But from there, since you were both in California, then you took off for Pasadena.
Bethe:Then we took off for Pasadena, and in fact we then drove home together, as far as I remember.
Weiner:When did you do your work on it—out in California that summer?
Bethe:We started it out there, but mostly we did it by correspondence between here and Washington.
Weiner:That's another reason to preserve correspondence. it would be interesting to see the stages in this development.
Bethe:I'm trying to remember the exact sequence. It may be that we went down to Pasadena together, and then still stayed together. I know he was with his wife vacationing in the Sierras, and I know that Rose and I went to visit them, and we talked together at the time on this subject. But I think most of the work must have been done later on at home.
Weiner:About how long a time was involved in that?
Bethe:Six months roughly.
Weiner:Was that the main piece of work that you did during the six months, other than your responsibilities for your job?
Bethe:I guess about half my time was spent on it, half my research time.
Weiner:But this was not an organized effort, It was a spontaneous thing.
Bethe:This was a spontaneous thing. After this spontaneous thing, I then went on to investigate shock waves in general. What are the conditions for shock waves to occur? And I found some quite interesting things, and this also was published, and von Neumann found this very interesting.
Weiner:Now, in the first case resulting from the discussion with Von Karman, you undertake to do something spontaneously; you recognize from him that there was a need, and you do it. Then how does it get used? How does it get applied?
Bethe:Well, we sent it to Karman and the Aberdeen Ballistics Lab. distributed it to some people who might...
Weiner:It was through him. He was the one who had the tie?
Weiner:You didn't have any tie-in with any government agency?
Bethe:No, none at all.
Weiner:It was Just an unsolicited contribution?
Bethe:That's right. Then at the same time, a little later, I thought that another interesting problem might be the penetration of armor by projectiles. And so I read the article in the Encyclopedia Britannica on armor penetration and had some discussions with a very good friend of mine here, George Winter, who is a civil engineer, and he gave me directions as to what engineering book to read. So I read a book by Timoshenko on the theory of elasticity, and by putting these together I produced a theory of penetration of armor which was published as a confidential report by the Frankfort Arsenal through the offices of Professor Seitz, who was one of the consultants to the Arsenal. Once it was published, it had a confidential stamp, and I couldn't see it anymore. I had a copy for myself, which was not stamped, but that was really illegal.
Weiner:And yet, of course, you had done this on your own and not under any request.
Bethe:Right. But it was legitimate that it be confidential. Then the third thing. I talked to a physical chemist here, Kirkwood, who had some connection with the government agency, the Office of Scientific Development.
Weiner:The Office of Scientific Research and Development.
Bethe:OSRD, right. I couldn't be cleared because I wasn't a citizen yet. However, he gave me some work that he was interested in on shock waves in water, and that is listed somewhere here I think. I am not sure, maybe not. Anyway it was published by the Navy after the war in a collection of papers on underwater explosion. This was fairly successful, as good as you could do it without having modern computing facilities. It was all analytical. And I learned quite a lot doing it. Kennard was also in this small group led by Kirkwood. Kirkwood asked for my clearance. in the meantime, the Radiation Laboratory at MIT was being founded, and some people from here went to the Radiation Lab, particularly Bacher, and Smith at the same time went to RCA, also to work on radar and similar problems.
Weiner:This was Lloyd Smith?
Bethe:Lloyd Smith. And I was very much interested in the Radiation Laboratory's work and wanted very much—it was clear to me from what Bacher said that this was the real thing and more important than explosion waves. Almost as soon as I got my clearance (I got my clearance on Pearl Harbor day, which was a few months after I became a citizen) I was approached by the Radiation Lab to work for them, and I first worked here at Cornell on some problems of interest for them. And In this connection I did some published papers, namely...
Weiner:There's a break between pre-war and post-war right here in the bibliography, unless they're published after the war.
Bethe:Yes, this is it. It was still declassified during the war, `Theory of Diffraction by Small Holes." I followed Sommerfeld, who had always been interested before quantum theory in diffraction theory. And so I worked on the transmission of electromagnetic waves, radar waves, through a relatively small hole in a metal sheath. That is, you have a wave guide, and at one point in the wave guide there is a metal plate separating one part from the other. Well, if you do that, then nothing will go from one part to the other. Now you make a small circular hole in the metal plate and then something will go from one to the other. I found ways to calculate this. It had been entirely empirical until then. Then Schwinger afterwards improved it further and made it quite a fine art. Well, in this manner they were then able to understand a certain device in the wave guide, which was known as a CR box, a transmission reflection box, and they could understand how to couple one wave guide to another. I invented a way to couple two wave guides to each other in a particular way—namely, in such a way that if the wave from one guide was going in both directions, then the wave in the other guide would only go in one direction; and that was rather fun, and that Is being used as a technical device. There was a patent on that. I never got any money, not even the one dollar that they were supposed to give me. That is being used to the present day to find out the mixture of waves in a given wave guide—how much initial wave and how much reflected wave there is.
Weiner:This was done on the premises here?
Bethe:The first part was done on the premises here. By that time I spent I think all my research time on this and on the Kirkwood project and nothing on pure physics anymore except I may have had a Ph.D. student, but I'm not sure. I had a heavy teaching schedule because Lloyd Smith had left and had left me his course in addition to my course, but what was left I used for this work.
Weiner:Were you at Columbia? I had some notes that you were visiting at Columbia.
Bethe:I was visiting at Columbia in '41. That was before the time now talking about. The visit at Columbia was the spring of '41.
Bethe:it was the spring semester of '41. At that time I had many extremely good students who afterwards became well-known physicists and I worked at that time on the armor penetration theory and also on the shock wave theory and on the general shock wave. But this was before the time of the Radiation Lab.
Weiner:Through 1941 anyway.
Bethe:Well, the Columbia visit was the spring term of '41, so it went to June. And through 1941 I did this kind of work and maybe in December or certainly in January, '42, I started working for the Radiation Lab.
Weiner:You mentioned the students who became well known for some work in physics. Would you like to name them?
Bethe:Well, there was Julius Ashkin, who is now the head of the department of the Carnegie Institute of Technology. There was Bernard Feld, who is a quite prominent nuclear physicist at MIT now. And there was Nirenberg, who is now director of the Scripps Institute of Oceanography. These are three I remember. I think there was a fourth who was of similar stature.
Weiner:And Marshak was earlier.
Bethe:Marshak was earlier, yes.
Weiner:This was '41. I wanted to ask another question before you go on. That is, did other physicists share your concern with the implications of the impending war and the role of science in it?
Bethe:Oh, very much so.
Weiner:Well, certainly by this time, but I mean at the time of your trip with Teller to see von Neumann, for example.
Bethe:I think the fall of France was a great shock for most physicists, and very soon afterwards the OSRD was organized and became very lively. Very soon afterwards also the Radiation Lab was organized. I think that must have been in the fall of '40, but I'm not entirely sure about that. Certainly many people felt concern, and most of the science organizations and the war work of the scientists was on a voluntary basis. Well, I know that Bacher felt very much concerned and joined MIT's Radiation Lab as soon as it was open. Rabi, DuBridge, and lots of other people—Purcell, Alvarez.
Weiner:I guess Ernest Lawrence did a lot of recruiting for those laboratories, too.
Bethe:Yes. At the same time, of course, there was the effort on uranium fission. I had very little contact with that until much later. Then I thought that couldn't possibly have any influence on the war.
Weiner:Was there a particular feeling that people who had been involved in nuclear physics had something special to contribute to the Radiation Lab at MIT?
Bethe:I think only insofar as nuclear physics used the most advanced technology in electronics. And they were generally intelligent people.
Weiner:When did you go there?
Bethe:I went there only in May of '42, but before I went I had assembled a group of younger theoretical physicists to help me in the problems assigned by the Radiation Lab. They included Julian Schwinger and Julian Knipp, both of whom were at Purdue at the same time; Frank Carlson, also then at Purdue, Marshak of Rochester. I think these were the main people in the group.
Weiner:And they were assembled...?
Bethe:Well, we met occasionally at Ithaca—I think only twice—and talked about the work, and we met in my home and talked about the work and distributed the work for the next couple of months and then disbanded again. And then we all agreed that we would go to MIT for the summer. I think I went a little earlier than the rest, and soon afterwards—I think in June—the others came and rented one big house for all these bachelors, and there was some scarcity of room in that house, and I remember they had one room that had to be doubly occupied—namely, by Carlson and by Schwinger; and that did not do any harm because Carlson was a farm boy and was used to getting up at 5 a.m. and Schwinger was used to going to bed at 5 a.m. So they had a very happy time together. Carlson would get up and prepare a meal which was breakfast for him and supper for Schwinger, and then Schwinger would go to bed. Likewise in the afternoon: At 5 o'clock when everybody left the Radiation Lab, there was one lone figure braving the stream coming out from the Radiation Lab, and that was Schwinger, who was just coming in at 5 p.m.
Weiner:Has that always been his characteristic style?
Bethe:It was at that time until he got married. When he got married he shifted his time to getting up at noon.
Weiner:A compromise. It seems to me that the way you describe it, there was a minimum of red tape.
Bethe:A minimum of red tape.
Weiner:Because here you assembled your group, you met when you wanted to, you'd decide to go there for the summer—
Weiner:Was this because the military wasn't too interested in it or was it the result of the management of the project itself?
Bethe:Well, I think mainly the latter. Of course the MIT work itself was secret, and we couldn't do secret work here, even though we were cleared, because we didn't have the right kind of safes and so on. The work which we were given, which was the work on the transmission of apertures in metal plates and some wave guide theory and so on, was sufficiently innocent and sufficiently removed from application so that we could do it in an unclassified manner and do the calculations unclassified, and then when we finally wrote t up, I think the final report was then made confidential, so that we couldn't take it home. It could only be read at the Radiation Lab.
Weiner:To just backtrack for one minute to something quite different: You mentioned that from the time of your arrival, you got into the swing of things right away and that also your reputation in some sense had preceded you and was growing steadily. This probably led to job offers.
Bethe:It did. Essentially only to one, one important one. That was in '37. I was offered a full professorship at the University of Illinois by Professor Loomis, who was a very good friend of Rabi, and I think perhaps was instigated to this by Rabi. I considered this quite hard because Loomis was a very remarkable and intelligent man, with whom I would have been happy to associate, and I think the department had a lot more money than our department here for research, and it was a bigger department, bigger staff. Then of course I got a good increase in salary. But when Cornell matched the salary, I decided to stay here—I think mainly because of the advantages of scenery. Illinois is an awful place to live if you like the hills, and I felt some tie to Cornell by then but not a very strong one. I think I felt a strong tie to American physics in general but not in particular to Cornell. I think I decided it mainly because Cornell is prettier.
Weiner:I've come across some correspondence of Loomis's inquiries and Loomis's attempts to get you. I think the letters were written just after he learned that you weren't coming. Then he was on his next hope.
Weiner:I didn't see it in his papers; I saw it in another collection. His papers have been deposited at the University of Illinois library. That was something on my mind. That's why I asked that. We're back at the summer at the Radiation Laboratory.
Weiner:This was all business, I gather. There was no physics discussed that was unconnected with these problems.
Bethe:No physics unconnected, no.
Weiner:And all the physics you did was pretty much applied theory to problems that had been suggested to you. This was certainly on assignment.
Bethe:Entirely on assignment. Well, I was encouraged to go around the lab and listen to people and see what might be interesting, and then I would do it; for example, somebody would suggest to me to think about the junction of semi-conductors to a little wire, a so-called cat's whisker, as they called it then. I tried to understand that theory and got maybe a quarter of the way to a transistor in this connection. I understood pretty well how this junction worked. I unfortunately stopped there. I didn't see that this might be useful.
Weiner:There was a history of the Radiation Laboratory written by Henry Guerlac. You might be able to tell me: How did he come to write that? Was he there?
Bethe:He was asked to come there for the specific purpose of writing the history.
Weiner:While the project was going on.
Weiner:He was sort of a staff historian for the government?
Bethe:For the government, yes.
Weiner:I'll have to talk with him and get it from his point of view. I haven't read that history. It hasn't been published, but it is available at the Library of Congress and Susskind at Berkeley in the electrical engineering department is trying to do a history of radar and electronics up to the present, and I think he has intentions to revise that and do something with it. I don't know if you want to go from there to Los Alamos.
Bethe:Yes, I think so. Already in the summer of '42 (I had only been at the Radiation Lab I think for six weeks or so), I was called by Robert Oppenheimer to Join him in a group at Berkeley to discuss the possible assembly of an atomic bomb. Now, over the telephone he obviously couldn't tell me very much, and I learned only in the last few days among my congratulatory letters that apparently Van Vleck, who had been in the know for a long time, explained to me in detail what the uranium project was about, and this seemed fascinating, and so I went. We had, I think, two months in Berkeley, from some time early in July to early September, and had a very intensive discussion. Teller was involved and I think I probably described that before.
Weiner:I think there was a section on it. You mentioned this group at Berkeley—Konopinski, Serber, Van Vleck, maybe a few graduate students, and, of course, Teller and Oppenheimer. You discussed it in a small sense, I think.
Bethe:I think I would just as soon not enlarge on that, because I have talked about that in other connections. I have talked recently about it to a historian of the AEC.
Weiner:I was thinking of Hewlett who did the published history of the AEC.
Weiner:What I would be most interested in, if we were to plan an agenda for the remainder of the time, is what I call the social history of Los Alamos, the things that went on in this unique assemblage of unique people under special circumstances.
Bethe:I should mention, just to keep that clear: After the summer work I returned to MIT to the Radiation Lab, and in fact the longer period of my work there was after that summer—from September to March of '43. And then in April of '43 I went to Los Alamos.
Weiner:Did you take your family with you when you went the first time?
Bethe:Yes. Well, my family was only my wife at this point. The first child was born in Los Alamos in February, '44, and so we were very mobile at that time.
Weiner:Did anybody else come from here? Bacher by that time...
Bethe:Bacher came a little later. From here came Greisen, who was then just a young Ph.D. just finished and is now a professor here; Mc Daniel, who I think had in the meantime taken his Ph.D. and gone with Bacher to the Radiation Lab but then came to Los Alamos very soon. And then there was Holloway, who on my recommendation had gone from here to Purdue to work with several Purdue experimental physicists on the reactions between tritium and deuterium. They had found a lot of interesting things, cross-sections. And this whole group then shifted to Los Alamos, I think already in April of '43. Well, the social life.
Weiner:What I mean by that is not necessarily the parties, although that's interesting, but, in addition, you had a particular responsibility. You described already some of the relevance of the work done there to the theory of nuclear physics. But I mean some of the problems in working with such a diverse group—how you handled things, how you reacted personally to the entire experience and having a child born there—in whatever form you think it's best to treat it.
Bethe:Well, it was really a very enjoyable time for all of us. The place was full of people we were friends with, and so we had really a very close social life, probably the most intense social life that we have ever had In our life. There were some people that we particularly liked. Very soon, for instance, the Weisskopfs moved there and the Bachers. We also saw a lot of the Wilsons already then. We saw the Serbers and sometimes the Oppenheimers. The Peierls moved there much later, but we saw a great deal of them. The Tellers lived very close to us and were close to us. The Blochs while they were there though that was only for a short time. After a short time he decided that Los Alamos was not the place he wanted to be and moved to some radar lab in Cambridge—not, however, to MIT, to a lab directed by Termer. There were dozens of people that we saw quite a lot of and we would call friends, and there were many dinner parties at the various houses. I should certainly mention Cyril and Alice Smith, whom we got to know there and got to like very much, and Flanders, the mathematician. Flanders, Smith, Bacher and I went very frequently on Sunday hikes up the mountains. So we had really quite a gay time. It was a very strenuous time. I don't remember when I usually went home, but probably about 7 o'clock in the evening. We were to some extent confined to Los Alamos by the gasoline shortage. That is, it was not easy to go for a long drive and to get anywhere you would have to drive. So most of our recreation was going into the mountains directly behind Los Alamos, which meant a drive between three and ten miles. That was compatible with our gasoline rations. Rose went fairly frequently to Santa Fe, which was of course a nice place to visit, and for any purchases other than food you had to go to Santa Fe. There was nothing to be had at Los Alamos except food. Our supply of food was quite good with one exception—namely, in the early days the restaurant which existed for all of us and where most of us had to eat because we didn't have our own houses yet, believed in very small food rations. The lady had fed the boys of the Los Alamos ranch school, and somehow—I don't know—she apparently thought that boys don't eat very much, and we never got enough to eat. It's the only time in my life except during the First World War when I didn't get enough to eat.
Weiner:That must have been difficult to take.
Bethe:It was very difficult and all of us lost tens of pounds. Apart from that, we really had no want. We were, as you know, restricted in our movements to a radius of 50 miles around Los Alamos except by special permission. Rose and I very much enjoyed hiking in the mountains. We did quite a bit of that until she became too pregnant. Somehow the good air of Los Alamos stimulated us to get our first child. We had tried for a year or two before. To have a child at Los Alamos was very comfortable. There was a government hospital, with uniformed doctors who were very nice people. We are still in touch with the pediatrician, Dr. Barnett, who lives now in New York, and so you just moved to the hospital—that is, my wife did—and the child was delivered, and it was all as simple as could be—much simpler than it would be here. Also, it was free of charge. You just paid—I don't know—a dollar sixty-eight a day for room and board at the hospital.
Weiner:And the place of birth on the birth certificate was given as a post office box.
Bethe:Right, given as a post office box—Post Office Box 1663, Santa Fe, was the official address. That, however, was only in the later times. In the earlier times, our first child was born in Sandoval County, Rural.
Weiner:What does that mean?
Bethe:it means not in any village.
Weiner:Oh, I see.
Bethe:And Sandoval County was the county in which we were, somewhere on a ranch way in the country—that was what it was meant to imply. Well, having children had a great advantage because you got a bigger apartment. The size of the apartment was determined by the number of children, and there was a rule that you had one bedroom if you were Just man and wife and two bedrooms with one child and three bedrooms if you had two children of different sexes. If they were of the same sex, it was still two bedrooms.
Weiner:And If you had a larger family?
Bethe:Well, up to two of each sex would still keep you at three bedrooms. And then afterwards it was not really provided for. In fact, it occurred I think only once or twice.
Weiner:it was Just not permitted.
Bethe:Just not permitted. Well, General Groves was not at all happy about the large number of children meaning that larger apartments had to be built, and so he told Oppenheimer at one time that he should see to it that there were not so many children. Oppenheimer answered that was hardly the job for the director of a laboratory.
Weiner:How about attempts at local self-government?
Bethe:Yes, well, there was not terribly much of that because the Army ran the place pretty tightly. There was a so-called town council, of which Weisskopf was for some time the chief. The town council heard some special complaints about non-functioning stoves and overheated houses or under-heated houses and things like that, and it heard occasionally, I think, a case of a traffic offense. But I don't think it was concerned with the two or three crimes that were committed at Los Alamos. We had quite a wild lot of machinists because machinists were very rare, as they were all busy In under-heated the defense industry, and so it was very difficult for Los Alamos to get them. And so they were induced to come to Los Alamos from the most unbelievable corners of the country, and mostly they were drunkards or otherwise not very reliable people. And so they very frequently had fights with each other, and one machinist slit the throat of another machinist from cover to cover, and it Just barely was possible to put him together again. But these cases were not heard by the town council. I don't know who did anything about it—maybe the military.
Weiner:You mentioned your friends, the people you had known earlier, people who had been in your circle professionally or personally before. What about coming into contacts with new people?
Bethe:Well, Cyril Smith was one such. Another such person was Captain Parsons of the Navy, who was directing the engineering division.
Weiner:That's not the same one that was referred to as "Admiral Parsons"?
Bethe:He was afterwards Admiral, yes. Some nice people we met were the Kennedys. He was in charge of the chemistry division. Then the doctors, Barnett and Nolan. Then some physicists that I hadn't known like Julian Mack of Wisconsin.
Weiner:Was there much of this coming into contact with physicists in fields other than your own or who were really good physicists that somehow you just hadn't met?
Bethe:Quite a lot. Robert Wilson, for instance, I had not really met. I had met him at Princeton for a few minutes, but I didn't get to know them until there.
Weiner:When you met him was he there because of the war situation? Was that in the early '40s when he was in charge of a group?
Bethe:Well, when I met him he was still doing pure physics research at Princeton. He measured stopping power of protons. That was one of my theoretical subjects. So I think the majority of the people we saw were people whom we met at Los Alamos, but only just a majority.
Weiner:What about discussions of problems in physics other than those directly connected with the project?
Bethe:There was not terribly much because we just didn't have the time and energy. It was a very absorbing time. 1 at least felt that I should spend my whole effort on this. I think one or two—well, a few people, I suppose, were doing a little bit of pure physics on the side, but I think very very few. Now, the experimental nuclear physics division, of which Wilson was in charge, was one division which did work very similar to what they had done anywhere. But the rest of us did very different things, and there was very little point of contact.
Weiner:You sort of put everything on the shelf, and I think so did 90% of the people there.
Weiner:I think last time we discussed some of the implications of the technology and the ideas for subsequent development of nuclear physics, so I won't go into that. I don't remember if I asked you about the planning there when it was apparent that the end of the project was in sight for post-war work, whether there were any discussions, seminars. I know we did talk about job recruiting.
Bethe:Yes, there was a lot of that—placement.
Weiner:What about discussions of plans for the future and attempts to really do some mutual education through seminars or anything of that type?
Bethe:Well, there were many plans for the future; and there was a group specially set up by the government for this purpose, the so-called interim Committee, of which Oppenheimer and Fermi were members, and they called in many of the rest of us and we did discuss what should be done with atomic energy. We all were agreed that one ought to have research reactors and probably one could do very interesting research with neutrons, crystal diffraction, monochromatic neutrons—to see what their properties are, absorption properties and so on. That was one kind of thing we discussed. We discussed further work on cross-sections of nuclear reactions, including deuterium and tritium. We thought that certainly nuclear physics as a whole should be much more emphasized. I may have told you that four of us from Cornell went back to Cornell at that time.
Weiner:I don't think so.
Bethe:That must have been in the early fall, September or October of '45. We went back to Cornell: Bacher, Rossi, Parrott, and I—to discuss what Cornell would do in nuclear physics, as we were very much interested in having nuclear physics more emphasized, having more machines going to higher energy and having a much larger part of the University funds used for nuclear physics, getting more positions and so on. And we found a very receptive administration here, which promised to give us a separate division of nuclear physics—that's this laboratory of nuclear studies with Bacher as the director—to give us more Jobs, to give us financial support. This was before such support was promised by the government.
Weiner:Where was the University going to get the support?
Bethe:Well, President Day thought he would get it somehow. I don't know what he had in mind.
Weiner:Why was he so receptive?
Bethe:He thought it was exciting, what we had done and that probably nuclear physics would continue to be exciting.
Weiner:Do you mean what had been done with the bomb?
Bethe:With the bomb.
Weiner:But he was thinking of peacetime research.
Weiner:Did you use any implied threat that since others also recognized what had been done, that if Cornell didn't come across, perhaps you would be received well elsewhere?
Bethe:Well, I happened to have an offer from Columbia at the time, and this was part of the inducement to Cornell.
Weiner:Now, this was in early '45.
Weiner:I mean late '45. You were back...
Bethe:We came Just for a visit for this purpose, and then we went back to Los Alamos.
Weiner:With an authorization to recruit?
Bethe:Yes, indeed, and we recruited a considerable number of people who are still here. Some of them our own good graduate students, like McDaniel and Greisen. Then we recruited Corson, who is now the provost of this University. One of the interesting features in his case was that there was some hesitation on the part of other members of the physics department: was he really a good enough physicist? Then we got De Wire who had been at Princeton and came with us after the war.
Weiner:And you got Feynman, too. You got Feynman before you got the authorization, though.
Bethe:Feynman we got before. I think I got Feynman appointed by writing a letter to Professor Gibbs and telling him that there was a marvelous theoretical physicist here, could I offer him a Job? And Gibbs got that authorization from the administration, so Feynman had a job here I think beginning in '44.
Weiner:He also got some raises.
Bethe:He also got some raises before he got here, right. Did he tell you that?
Weiner:Yes, he did, because he was getting other offers.
Bethe:Yes. Sure, that was very nice. Well, one of the good people we had—namely, Rossi did not return to Cornell but went to MIT. 'MIT was very active at the same time. They also got Weisskopf from Rochester In the same recruiting campaign.
Weiner:Do you know if MIT had made a similar commitment?
Bethe:I think they made a commitment to support nuclear physics very strongly. in fact, they offered very high salaries to research associates without any teaching obligations—so high that we couldn't compete.
Weiner:Was this Just because they were richer?
Weiner:In each case, there was as yet no definite government support.
Weiner:I wanted to go back just a minute unless you feel you've answered this question too many times, but let me ask it and you can tell me—about your reactions, psychological and intellectual reactions, at the first successful test at Los Alamos? What you were doing and how it appeared to you and how you felt.
Bethe:Well, 1 have answered that many times. Well, 1 felt rather over-awed by what I saw, because it is still a great deal different to see it from just having calculated it. We had calculated quite carefully the effects in light and the fireball rising in the air, before the test actually took place. And we had calculated the energy release in various ways. It was the biggest number that any of us had calculated. I was very much overawed by it, and yet it was a confirmation of what we had done. I did not feel like Oppenheimer that I was like God destroying worlds, but it was a most impressive sight. One of my questions, of course, before the test took place was whether the initiator would work which would provide the first neutron, and I was very largely responsible for the design of that initiator, and I wasn't entirely sure that it would work. The rest of the device I was sure would work once it was assembled. I think that sums it up pretty well. Then in the subsequent weeks our greatest interest really was to press for international control of atomic energy, and almost immediately after Hiroshima and Nagasaki we went out and tried to persuade people to agree to such international control.
Weiner:Was this through the lobby in Washington?
Bethe:Yes, through the lobby, Higginbotham in particular.
Weiner:I think this is a logical end to this section, because I think that for me to get anything new on the political side, I will have to make a very thorough study of all the good stuff that has been written—and Alice Smith's book.
Bethe:Alice Smith's book is extremely good, and I also want to recommend to you for the Los Alamos atmosphere the book by Groueff, Manhattan Project.
Weiner:Yes, John Wheeler told me about it. I started to read it.
Bethe:It's extremely accurate.
Weiner:Even though he puts quotes around conversations that you know he didn't hear but somehow he captured it.
Bethe:He captured it. He talked to 200 people, I think, all of whom he names in the beginning, and absolutely everybody who had been in the Manhattan Project and whom I have talked to, agrees that his part of the Manhattan Project was pictured just incredibly accurately.
Weiner:That's interesting. It's a good test of some of these techniques, which doesn't mean that the whole thing comes off necessarily.
Bethe:The whole thing comes off very beautifully, too.
Weiner:it's well written, I know.
Bethe:it's very well written, and the characterization of General Groves is just marvelous.
Weiner:It's sensitive and accurate.
Weiner:Well, that's by way of saying that I don't think there's any point in getting into that unless I felt that there were some vital things missing from it. I don't know that there are.
Bethe:And Alice Smith has done such a good Job of the scientists' political movement, that really I could only detract from it and not add anything to it.
Weiner:I would like in the remaining time to just skip to the present with the hope that with proper preparation on my part and review of everything you've done we can perhaps sit down, if we both think It's worthwhile, to do something on the in-between time, not neglecting 20 years of history.
Bethe:They are less interesting than the years we have covered so far as my person is concerned, but they are still quite interesting.
Weiner:But I think that's almost a separate project. What I'd like to do is get to the recent events, and that is your receipt of the Nobel Prize in Physics for 1967, and to ask you this question: whether you had thought in previous years that the prize might come to you.
Bethe:I had thought it might, but I had also thought that it was rather unlikely. The reason for this was that generally the Nobel committee rewards one great discovery rather than a large number of less-great discoveries, and I think my scientific life has mainly been a large number of medium great discoveries. The only thing I have done that the world has considered a real discovery is the energy production in the stars, and this I thought was rather disqualified because there is specifically no Nobel Prize for astronomy, and of course the main question in this theory was an astronomical question and not a physics question. And so I thought that by a combination of these two facts, the chances of my getting it were not very great. They were not zero, but not very great. The Nobel committee has gradually, I think, changed its attitude on these matters, and they have now in more recent years given a few prizes which are apparently more for the lifetime work of a person than for one particular thing. I'm thinking of Wigner, for instance. It is true that one of his works—namely, the group theory of nuclear symmetry—had to be singled out, but I think it was evident that the prize was primarily given because he's a great physicist and not for one particular discovery. So there has been a tendency in that direction, and I would think that in my case it was primarily given for my lifetime work more than for the particular discovery.
Weiner:Were there years in the past when you thought despite these feelings that you might get it through what other people had said?
Bethe:Well, I am sufficiently well convinced of myself that I thought I was as good as some of the other Nobel Prize winners in a general way, but In contrast to them I have not made any specific discovery. Well, I just didn't know. I thought that while I didn't scurry every October to the newspapers to see Just who had got the prize and complain if I was missed, it certainly seemed possible to me that I might get it. It seemed to me to become less likely in recent years because since about 1950 I have done a lot of government work and done pure physics much less than before. And what I have done has been less in the frontier of physics than my earlier work. So for these reasons I thought that the likelihood was decreasing.
Weiner:Had other colleagues expressed their views to you on their feeling that you should receive the Prize?
Bethe:Yes, I guess occasionally people had said so. Some people thought that I should have got it together with Lamb for the explanation of the Lamb shift when he got it for the discovery of the Lamb shift. Some people thought I should have been added to the trio of Schwinger, Feynman and Tomonaga. Some people thought I just should have got it. But, well, this is never very serious—one would just play with t. It never was a matter of great excitement to me until it came.
Weiner:How did t come? This year In particular had you given any thought to t?
Weiner:How about others? Had you thought of who might get it?
Bethe:I didn't even do that this year. I was very curious who might get it until two groups of people got it who were very close to my heart. One was the Wigner-Mayer-Jensen group, and the other was the Schwinger-Tomonaga-Feynman group. After that I thought that the people who really ought to get the Prize now had the Prize.
Weiner:Justice had been done.
Weiner:And were you even aware this year that the time was coming?
Bethe:Well, I was aware because I had read the Nobel Prizes in medicine. Chemistry was simultaneous with mine, but medicine, which included Professor Wald of Harvard, whom I know slightly, and we were just talking about that the night before I got the announcement. I was talking to some friends here, who also knew him.
Weiner:And how did the word come to you?
Bethe:Well, at about quarter past six in the morning the telephone rang, and I said to myself, "It's impossible that anybody would call me because everybody has better sense than to call up at 6:15 in the morning." And so I just let it ring. Then it stopped ringing, and then half a minute later it started ringing again, so the second time I thought, "Well, maybe he really wants us." So I went to the phone, and a voice with a slight Swedish accent at the other end said, "Dr. Bethe? I am happy to tell you that you have won this year's Nobel Prize in physics." I said, "What?" And so he repeated, and he told me that I was the only winner and introduced himself as the representative of the Swedish government TV and broadcasting. He had been given orders to come to Ithaca the night before and spend the night here and then to wait for instructions from Stockholm. And then he had been told to keep a telephone line open to Stockholm to get the news from the Swedish Academy as soon as it came out. So he did. His job was to tell me. Only four hours later did I get the official telegram from the Academy.
Weiner:Did you doubt it at all?
Bethe:I did not doubt it, no.
Weiner:You thought it was authentic.
Bethe:Yes. He seemed authentic. And then about a minute after he had hung up and was just trying to run a bath in the bathroom, the phone rang again and the first radio network called me and asked me questions, and from then on there was an uninterrupted flow of telephone calls from radio networks and from the various press agencies, Associated Press and United Press and whatever press, and finally the Swedish newspapers. Then around half past seven my wife took over some of these duties and answered some of the calls, and she called the University. Well, that was a little later, after eight. She called the University press office and asked them what they wanted to do about it. They said they would arrange a press conference for me at 11:30. But it all sounded pretty authentic, so I didn't really have any doubts.
Weiner:After you were through with the telephone, how did you explain to your wife what the telephone call was about?
Bethe:She came in from another room about 7:30. I was Just on the phone explaining where my son is and where my daughter is, and she was very puzzled by these explanations.
Weiner:She didn't know all this time while you were on the phone?
Bethe:No, she did not. She was sleeping. So then I hung up and then I told her I got the Nobel Prize, and so she Just burst out in a big beam and said, "Oh, darling!" and embraced me. And by that time the next telephone call came.
Weiner:You weren't allowed any private Joy.
Bethe:Not for very long. And about eight o'clock, those two Swedes, the reporter and the cameraman came to the house and explained to me the further proceedings while I was having breakfast, and then it went on all day.
Weiner:I guess the culmination of it in a sense was the ceremony here last night.
Weiner:What did that involve? Was it an evening dinner?
Bethe:It was an evening dinner given by the University. They invited the full professors of the physics department and the leading members of the administration here and then a list of certain friends whom we had suggested. Well, we had invited, for instance, Bacher and Feynman from Caltech, but it was too far for them to come, but Doctor de Hoffmann came from Southern California, with whom I had published a book and worked very closely; then Berjun-Keeny came from Washington. He is the man who is executive director of the committee, the sub-committee of the President's Science Advisory Committee, and I have been on that committee for many years. Then Robert Wilson came from Chicago specially for the occasion to give an after-dinner speech, and also another man De Wire, who is on leave at the Chicago project. Rabi came up from Columbia and Dyson from Princeton, and Weisskopf would have come if he were well.
Weiner:Were the proceedings recorded, do you know?
Bethe:No, no recording. No, it was quite informal and very nice. It was like a revival meeting. Every now and then somebody stood up and said, "I want to drink a toast," and said one or the other thing about me.
Weiner:How would you compare this demonstration of appreciation and affection with the Festschrift occasion last year about this time?
Bethe:Well, it was a little bit similar. In my response I said, "Well, I'm somewhat at a loss what to do next year." it was somewhat similar. It was full of warmth with lots of my old friends. It was a little different because it was a much smaller group of people. Last year I think there must have been 150 or so. This year there were maybe 60, and this year they were very specially selected by the University, whereas last year everybody was invited who wanted to come. But it was the same kind of demonstration of affection, which I really appreciated very very much. And I also had an enormous number of telegrams and letters. I didn't know there were so many people who liked me.
Weiner:You mean since the announcement?
Bethe:Between the announcement and now.
Weiner:Were many of them like the Van Vleck one recalling earlier instances?
Bethe:Quite a number. There were quite a number of letters from friends from high school in Germany whom I had never seen again and some from people I knew in my student days at the university.
Weiner:Let me ask another question then. You mentioned what the Nobel committee standards were in regard to your own feeling of whether or not you would get the Prize. Forgetting those standards, if you had to judge the most significant single piece or series of work that you have done in terms of its significance to science, what would you have selected?
Bethe:Well, probably in significance to science and as to the piece which had the most influence on the future work of other people, the stellar energy was the thing. It was not my best paper as a personal effort, I would say. it was a good paper, but I would say there are at least three which are as good or better as a personal effort. I mentioned already the stopping power theory. I would also mention the explanation of the Lamb shift, which was after the war, and then the articles... [End of Side 1 of tape]
Weiner:The Reviews In Modern Physics articles.
Bethe:Then I would mention finally the paper with Heitler on pair production and Bremsstrahlung and then maybe a little lower down, the term splitting in crystals and the order and disorder in alloys. So these are six or seven which I consider about equally great as the stars.
Weiner:This is in terms of significance to the field.
Bethe:In terms of the significance to the field and, in terms of personal effort, I think some of them were more.
Weiner:How about the one that was the most fun?
Bethe:Well, I think maybe the Lamb shift was the most fun, mainly because it was the quickest and because it was a problem that had confused many people and in a field in which I had not thought that I could do something—namely, relativistic quantum mechanics.
Weiner:In other words, it was like a challenge.
Bethe:Like a challenge, yes.
Weiner:I remember last time I think you described the stellar energy work as the most exciting.
Bethe:Well, I think it's very difficult to compare these nuances. The stellar energy work was certainly the most exciting, and I think t went over a longer period than the Lamb shift. It was perhaps more fun altogether because it lasted longer. I think these two probably were the most fun and most exciting. Some of the others were I think , as scientific work, Just as good, but perhaps not quite as much fun.
Weiner:Perhaps some time in the future we'll talk and I'll ask this question, which you needn't answer now, and that is how you think this new recognition will influence you and your relationships in Cornell.
Bethe:I don't think it will influence me very much. I've always done what I wanted to do, and I'll continue to do what I want to do, and I don't see any reason why I should change my field of work. And so I think I'll Just go on the way I was.
Weiner:You're fully involved in an entirely new problem now. Judging from our earlier discussion, you feel you are getting results from that.
Weiner:Well, I think we've covered a lot of ground.
Bethe:We sure did.
Thank you very much.