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Oral History Transcript — Dr. I. I. Rabi

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Interview with Dr. I. I. Rabi
By Thomas S. Kuhn
At his New York home
December 8, 1963

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I. I. Rabi; December 8, 1963

ABSTRACT: This interview was conducted as part of the Archives for the History of Quantum Physics project, which includes tapes and transcripts of oral history interviews conducted with ca. 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the 1920s. Also prominently mentioned are: Niels Henrik David Bohr, Max Born, Gregory Breit, A. C. Crehore, Peter Josef William Debye, Paul Adrien Maurice Dirac, Paul Ehrenfest, R. Fraser, Werner Heisenberg, Paul Hertz, Edwin Crawford Kemble, Earl H. Kennard, Ralph de Laer Kronig, Willis Eugene Lamb, Wilhelm Lenz, Maclaurin, J. Robert Oppenheimer, Wolfgang Pauli, Henry Augustus Rowland, Erwin SchrŲdinger, John Clarke Slater, Arnold Sommerfeld, Otto Stern, Phillip Subkow, Leo Szilard, John B. Taylord, John Hasbrouck Van Vleck, Wilhelm Wien, A. P. Wills; Columbia University, Cornell University, KÝbenhavns Universitet, New York City College, Universitšt Berlin, Universitšt Gottingen, Universitšt Hamburg, and Universitšt Leipzig.

Transcript

Kuhn:

I don't know what to tell you to concentrate on, but I think it would be worthwhile from our point of view if you would really start it out as a scientific biography. Leave it to later people to say how quantum physics developed; talk about it as you saw it, including how you got interested in it. One of the things Iím much interested in is when people first learned that there was such a thing as quantum physics and what sort of problems these seemed to be whether they were normal research puzzles or whether they were really projects for largeó scale reformulations. So it is really quite helpful on occasions to get people to go back to school, how they first got into the sciences and so on, and take it from there. I donít mean that first page to look just routine. If youíre willing to do it — not everybody is often this whole approach through sort of direct, fairly personal biography is thoroughly worth doing, particularly because the answers are often so different in, say, America and Europe, or in Germany and England - that sort of thing.

Rabi:

I was raised in a very orthodox Jewish family with a great religious influence on me, and it is my view, perhaps, that my scientific interest came from the religious. However, on the other hand, my religious interest, I think, was more concerned with the first chapter of Genesis than with the Ten Commandments, so you might say that my interest in science came from religion or that my interest in religion was more on the side which would interest scientists. On the other hand, my favorite reading and my best subject in high school, as a subject in which I got very high grades very, very easily and without any work at all, was history; history was, in that sense, my top subject, although my interest was in science which, I think, came about again from Genesis in a sense and the kind of thing they talk about: that the earth was flat, and things of that sort, My first reading of the Copernican theory of the explanation of the seasons and so forth left me with a scientific interest which never flagged and I can still contemplate the Copernican system with a tremendous amount of pleasure. So this was my essential background in this way. Actually, my readings in science as a kid, about age 11, led to a break-away from the religion in this orthodox family with the various difficulties associated with it, so throughout high school it was clear to me — I mean, I never thought otherwise — that I would go into science and I knew what science but did not know its name.

Kuhn:

Tell me what you mean when you say you knew what science? Oh, the basic structure of matter. How you get at that I did not know: whether you study electrical engineering, chemistry, mechanical engineering, or whatever.

Rabi:

As you note later on here, I did study these various things at Cornell ē It so happened that physics was badly taught at Cornell, very badly taught in my high school, although I did read a good deal about it. But the essence of physics never came through to me; it seemed to me to be the sort of thing where you measured the resistance of copper to another decimal point. Nothing duller than a physics teaching laboratory, nothing. Chemistry, on the other hand, was very interesting; there were things to do. You could experiment and so on, which appealed to my research instinct. Anyway, I went through the elementary schools in New York and to Manual Training High School in Brooklyn, which was not the best high school in Brooklyn or in the city, by any means. I chose it because it meant a different environment. On the other hand, as far as courses are concerned, I had enough courses there that I had credit way into my junior year at Cornell; as ]&aid, my best subject was history, but I was good in mathematics and, in fact, I was good in everything and had a high average, a Regentsí Average, among the first ten in the state or something of that sort without any attempt at all to study. I donít think I put in an average of ten minutes a day to this work, which left me with poor work habits; I probably would have done better if I had gone to Boysí High or one of those other places.

Kuhn:

What were you doing outside of school? You speak of having read some science and Iíd be interested to know whether there were any particular things you remember reading.

Rabi:

Quite elementary books. We did not have access to a good library ad no direction. Some history, history of science, some biography. What I did have was a wireless telegraph, as it was called then; I had a license to transmit; I made all my own equipment and so on, except for the earphones and the spark coil; I went in for photography in a big way and that sort of stuff, model airplanes, and all the things that a kid could do. Everything I did in this way I always enlisted a number of other kids in the neighborhood there in the far reaches of Brooklyn where we lived. I always had an organization. When we had a telegraph we had wires strung across the street I found some kid whose father was a junk man where we got wires which we strung high up from one building to another so the cops didnít see it, and we ran things of that sort. So I was a sort of center of a little group; in whatever I was interested in I would generate interest in others. When I learned to play chess somewhere I got other kids and we played chess - things of that sort — until I went to high school. I read vary widely, not only science but everything I could lay my hands on more or less systematically. In fact, I came towards science through all the books in the kidsí library, going sort of through Tarkington, etc., and then the next thing was the science shelf and I read astronomy; thatís how that other thing came about. Somehow I never cottoned to biology, never remembered reading biology. I read gardening and had quite a little backyard for awhile, but not biology. I did read a good deal, chiefly in things which concerned physics, as I realize it now, and astronomy, some chemistry, though not very much, and very little geology, except the outlines. I first heard of the quantum from a man Iíd really love to know what happened to at the end, a man named Phillip Subkow, who somehow or other had been in contact with a nut who wrote very widely and was very well known, an inventor by the name of [Albert Cushing] Crehore; he knew somehow about Planckís quantum h. This was in 1916. When I went to college I had this Cornell scholarship, the New York State scholarship, which more or less made it possible for me to go because we had very little money. Through my years in college I started in engineering and then took chemistry at the same time and graduated with a degree of Bachelor of Chemistry.

Kuhn:

If you doní t mind, before we really get too deeply into college, I would like to ask you somewhat more about the pre-college period. There are really two sorts of things: first of all, Iíd like to know, if I can, more about just how far you had gotten in the relevant subjects; the other thing, which is a very different issue, is that Iíd like to explore more the strength of the intention to be a scientist, the various things that seemed open to you as ranges of choice by the time you went — how you picked your major at Cornell, in other words - - and then something about family and attitudes toward this in your surroundings; was it encouraged, was it discouraged?

Rabi:

The family had no idea of it whatsoever; I think I was the first man in the family who had ever gone to college and they certainly had no idea of science whatsoever. They would have been happy if Iíd gone in for medicine or for the rabbinate, but as far as this was concerned, it was terra incognita with them and they had no views on it whatsoever.

Kuhn:

Neither negative nor positive?

Rabi:

I wouldnítí know about the negative because I had them completely intimidated; as the oldest child of two and the only son, I bad them completely intimidated and I donít think they would have dared to question me. I have no idea what their attitude was; I never did ask them, so itís as simple as all that if you can get the background of a Jewish family with the regard for the oldest son and a very verbal sort of oldest son. I got very little out of high school - - practically no contact with teachers or with other students of high quality; it was just a case of going to high school and doing my work, Outside I did a lot of reading, and thatís about it. I was interested in all sorts of other things; I was an avid, passionate newspaper reader. I went to high school during the period of the war; I entered in 1912 and graduated in 1916 so after the first year or so we were close to war and I followed that very, very carefully. I remember when war broke out I just couldnítí wait for school to open so Iíd have somebody to talk to about the war; I was so disappointed when I got to school that they werenít interested and didnít know about it; the other kids just didnít. So very early I had this whole interest that I have now in national and international affairs and in politics. I became interested in socialism at an early age through reading Jack London's The Iron Heel and I used to attend meetings, not of the junior socialists but of the Socialist Party. Iíd go there almost every night for two years and not once did anybody talk to me during that period, to this kid there. So I had all these other interests at the same time. I read very widely — novels; Iíd read science in an odd way, like a novel, as rapidly as a novel, not going through it with full understanding at all but in a broad way.

Kuhn:

Was all of this science reading at the level of semi-popularization?

Rabi:

Not necessarily. I picked upIŽ.P1 Steinmetz for electrical machinery — whatever happened to be available; if there had been good books available, I would have been quite far along, but there just didnít happen to be. I had nowhere to go for advice; I didnít really know how to get advice or what to ask about. I had no patron in that sense. I was a good student, as I said, in everything and in some things I was better than in others. For example, my highest grades on some exams were sometimes in English, but when handing in themes I never knew whether I would get an A or a C. But I was very consistent in the sciences, not especially in physics; in mathematics I had a very high Regent's average, about 91 or so, and you canít get that without being good all the way around; again, I did that without any trouble. Science was at a low level; the whole U.S., it must be admitted, was at a low level in that period of 1912 and so on. I went to Cornell chiefly to get out of town and again practically with no advice; I had a Cornell scholarship and there was the history of Cornell as a new, revolutionary kind of place in the way it was founded, instruction, mechanical arts, and so on. It was a very great mistake.

Kuhn:

Did you consider other places at that time?

Rabi:

Hardly. I was fixed on that one. Cornell put out a good humorous magazine, there was a great football team at Cornell; this was getting out of the ghetto, so to speak. It wasnít really a ghetto in that sense, but this particular environment was something else. It was a very great disappointment intellectually and a very low level, In the circle in which I moved at that time there were Carl Becker and other historians but I never got near them; it never occurred to me to take a course in history, something which I read for pleasure but which to take a course in was something else. There was the serious business of life and there, after the beginning, I concentrated on chemistry, chiefly mislead by a course in qualitative analysis which looked very much like research, I did very well, again without any work. I made it a principle never to read in the subject in which I was taking a course so if I were taking quantitative analysis Iíd be reading Shaw, philosophy or psychoanalysis. So I got a very liberal education in college — - but not out of the college —- by reading and talking to people. I didnít make any broad acquaintances but there are some interesting people that I continue to know. I changed to chemistry from engineering for reasons Iíve just said.

Kuhn:

Was it chemical engineering?

Rabi:

No, it was not, but it was chemistry, a concentrated course in chemistry; the only subjects I took outside of chemistry, physics and mathematics were freshman English and my senior year, when I had completed all the requirements add had no courses to take, I elected a couple of courses in philosophy, but that was all. Just a concentrated course in chemistry with the long laboratory hours and everything that went with it and very poor mathematics and, physics for a chemist. There actually (7??) (7??) for the book, for the course, and that sort of stuff.

Kuhn:

Was that really all the physics you did take?

Rabi:

That was about all the physics I did take.

Kuhn:

How much mathematics?

Rabi:

Just calculus and thatís all.

Kuhn:

A couple of years?

Rabi:

I think one year of calculus. Indeed, entirely a trivial kind of training. But I did read a good deal and my interest in history served me very, very greatly because I was one of the few who read history so I could anticipate what the subjects would be, how they fitted in, so there was no time when I didnít have a comprehensive view of what was going on; but I didnít have a modern view, in this sense, and I didnít know anybody there who did. It was true all over the U. S. Faculties were really—-to call them second-rate would be high praise. They had a physics department there, but somehow or other, you know, itís the luck of the game; you get section men who are stupid, you get the wrong people. There may have been good people but I didnít have them, so I never came in contact with a single first-rate mind in all the years I went from elementary school to secondary school to college. There may have been such, but I never ran into them, into this particular part of the faculty. In fact, it never occurred to us after awhile, to the brighter boys, to go to the faculty with any sort of question. You work it out.

Kuhn:

When had you actually made the transition to chemistry?

Rabi:

In my freshman year, at the end of 1916. I took both the first year; what moved me to chemistry was that I went up there with some roommates who were taking chemistry for some reason or other and I just took both.

Kuhn:

What sort of engineering were you thinking of when you - — ?

Rabi:

I wasnít thinking of engineering; I was trying to find out what made the world work. I didnít know what you could do. Itís hard for you to realize at your age and in this time, but all that time there was the overhanging problem of anti-Semitism and the possibility of earning a living. Indeed, although I was the top student and this should have been quite clear — Iím sure it was to the people in the department- I had not a single offer of a job when I got out. So when I got out, there was a possibility of staying on for graduate work but by that time I was so fed up by being in this isolated place at Cornell, just after the Russian revolution and after the war —- I was out in 1919 — so I came to New York and didnít go on for graduate work.

Kuhn:

What sort of jobs were being offered to gentile classmates?

Rabi:

As chemists —- various industrial companies; those are lousy, but it was something.

Kuhn:

Anti-Semitism was playing a real issue for industrial jobs also in many cases?

Rabi:

In all cases, not in many but in all cases. There were just no exceptions that I knew of, and also there were just no jobs within the university. It was an entirely different situation. So it was clear to me that somehow or other, if I wanted to pursue my interest, I would have to make money some other way; thatís the way it looked.

Kuhn:

You mean, pursue your interest on the side?

Rabi:

Thatís right, Iíd have to do something. I was very much interested; I mean, I wasnít out to make a name for myself but I just wanted to know. My first job outside was with the Lederle Laboratories which is now a part of some big company; I worked as a chemist analyzing mothersí milk and furniture polish, and there I met a young chap, a most extraordinary young fellow, by the name of Benedict Cassen he must have been about 17 or 18 who somehow or other had read very widely and who told me all sorts of things that I didnít know that I hadnít picked up at college.

Kuhn:

What sort of things?

Rabi:

Oh, about Maxwellís theory, quantum theory, and so on. He didnít know too much, but just suggestions elements of mathematics that I hadnít studied. 235 So I spent a good deal of my time in the next two years reading all sorts of stuff evenings in the New York public library.

Kuhn:

Was there more system than there had been previously?

Rabi:

No, just reading here and there. I spent some time in a business which was a sort of private banking business, discounting accounts receivable, with some friends of a friend of mineís relatives; I worked in that. I had a number of friends a roommate who had been at Cornell with me — and they were all at loose ends in this way for a number of years. Another fellow was a lawyer, another one had been a graduate of the Columbia school of journalism, and so on. I got to be about 25 - this must have been about 1923, Ď24, Ď25 and I said to myself, ďThis wonít do.Ē

Kuhn:

You also did newspaper work, didnít you?

Rabi:

That came just a bit later. ďThis wonít do. Itís either now or never. Youíre 25; youíve been doing your reading but youíre not getting anything.Ē It happened to all of us at once. We went off. One of us went to medical school and is a very good pediatrician now my roommate —- another one went to Harvard and got an advanced law degree, another, Ben (Ginsberg), went to Harvard and got a degree in philosophy; there were a number of us who dispersed in this way and I went to Cornell, simply because I didnít know any other place. It was, so to say, coming back, and I wanted to do advanced work in chemistry. However, Iíd taken all their damn courses anyway and physical chemistry, which I didnít have they didnít have, so I said to myself, ďIíll study physics; I know all the chemistry this place can teach me and Iíll put them together myself. What of it.!Ē So I went into physics.

Kuhn:

Were you supporting yourself on money you saved or were you under scholarship again?

Rabi:

No, my family had a little bit of money. I didnít have very much, but a little bit of money. So I went to register in the physics department and started taking some courses. This was a hell of a difficult time because this was now four years after I was out and had had very poor courses. I was too old to start with elementary courses, so I started with intermediate and advanced courses. By this time I knew a little something about the subject just from general reading. I soon realized that the part of chemistry I liked was called physics. If somebody had pointed that out to me before, it would have saved me many many years. I was charmed by Gaussí theorem, circuit theory, (maximum-minimum), effects, and that sort of thing.

Kuhn:

Do you remember what courses you took that year?

Rabi:

I took an enormous number of courses, I took electricity and magnetism, statistical mechanics, some mathematics courses, both advanced calculus and calculus of variations, something they called ďmodern physicsĒ; an enormous number of courses and much more than I could possibly digest and they were all advanced.

Kuhn:

Had you had the math for them?

Rabi:

No, I didnít have the math. I did something Iíve never done before or since. I made myself a schedule which began in the morning with the time Iíd get up until I went to bed, with even the meals all fixed. I knew I wasnít the kind of person to do it, so I carried it on rigorously; I knew if I broke it once it would be gone, but I carried it on for six months. Then somebody got me to take a walk on Sunday and that was the end of that for a long time. But I broke the back of the thing; I learned enough mathematics, sort of refreshed (further) and these other matters so that I was, in a certain sense, on the road to physics. Not elementary physics, though, and to this very day I donít know elementary physics. The sort of intermediate physics thatís taught, that stuff, I think they could probably flunk me in an examination on some of those latter problems in mechanics. But the back was broken; I was there and I had the feeling I was there. Thatís where I first heard about the quantum theory more definitely. I read a book the title of which I canít at the moment recall, although I tried to, and it sounded quite absurd to me. I was full of research ideas,

Kuhn:

Was it a book you read for a course or was it just a book 7

Rabi:

It was just a book. Courses never meant very much to me; courses meant I 285 went there and listened to the man. Thatís all. Guidance, what I might read, but I just went there and listened to the man.

Kuhn:

But the quantum was still not playing any role that you can think of in your course work as such?

Rabi:

Oh, no. That just didnít exist, either at Cornell or at Columbia where I went later, as far as course work is concerned.

Kuhn:

You mean, it didnít get into the statistical mechanics or into electromagnetic theory, both of which it might well have gotten into in a European university?

Rabi:

Oh, yes. Iím just giving you a measure of how incredibly low the standards were in the two major institutions; not that people werenít working in something connected with it at Cornell; there was (F. K. ) Richtmyer who was doing x-ray work and you had to have that, but it just didnít enter into the courses in a real systematic way. So when I got there I read some on my own. There was some man, a graduate student actually, who gave a few talks n the colloquium on Bohrís atomic structure, which all of us regarded with a very great skepticism I can give you an example which was while I was at Cornell —- when was that?

Kuhn:

Ď22-í23.

Rabi:

Sommerfeld came to lecture and I was sitting there reading in the library and Iíd see professor after professor sneak in and take a look at Sommerfeldís Atombau und Spektrallinien just to sort of refresh themselves in order to have something to talk about - not that they were actually working in this thing.

Kuhn:

Had you read that yourself at that point?

Rabi:

I had looked into it and that sort of thing; by that time I had a fair amount of general knowledge about the thing just from general reading which always was a take-off point for me to have ideas about it. For example, I remember I had the idea of the ring electron; then when I was here. (Columbia) I would have liked to do something with this. What sort of mathematics do you use for calculations of this sort? For this you need spherical harmonics so you go to the math department and try to find some book on spherical harmonics.. This was more in this haphazard, very amateur kind of way for which Cornell had a weakness; they required no examinations in course for the students and what happened in the end was that the students became lax and they actually had no advanced courses that really were required so therefore they were not given and the students regarded advanced courses just as mathematics.

The great men around there were people who may have been geniuses equipped with some (humorous) angle for their research. One man who had something of that sort was (jarl H.í) Kennard who was very much disliked by the others. He wasnít a great scientist but at least he was an honest man and he had the greatest influence of all because when he lectured, when there was something he didnít understand and which was a pitfall, heíd fall into the pit. And then it was interesting to watch him scramble out; youíd learn something. Well, I was a very active student and very talkative, with the result that when the end of the year came and I applied for a fellowship, I didnít get it; so I left and came to Columbia.

Kuhn:

Did you get a Columbia fellowship?

Rabi:

No, I just left: nearer to home, cheaper to live, and so on, and Iíd met a girl meanwhile who was there. At Columbia the atmosphere was immediately different. The Columbia faculty was not better than the Cornell faculty just as good, perhaps —- but there was a man, Professor A. P. Wills, whose one book of vector analysis you may have seen. He was no great shakes as a physicist but he believed in solid training, or as solid as he could give, and through his insistence everybody had to take a course in the partial differential equations of physics. No great shakes, Byerly Analytical mechanics: no great shakes either, but you had Hamilton, Hamiltonís canonical equations and things of that sort, Lagrangeís

Kuhn:

Did that get as far as things like Hamilton-Jacobi theory?

Rabi:

Not terribly far, but some — just on the fringes of it. (Interruption) Analytical mechanics, partial differential equations in physics, and so on basic stuff that one should have but which one really didnít get at Cornell. At the same time, looking toward the future, since I had to make a living, 333 I started this little newspaper, The Brownsville Bulletin with a couple of other people so I spent part of my time with this and part of my time there and I lived at home in Brownsville.

Kuhn:

When you said you had to make a living in the long run, do you mean you thought it perfectly possible that the physics would be for you but you wouldnít be able to make a living at it?

Rabi:

That right. I didnít it expect to. It may have been a very great exaggeration, but this was the atmosphere in which it was. However, somehow by accident, I met a man who was a professor in City College, I applied through him, and for the second year I was back, I had a job as tutor at City College at 800 dollars a year; that changed everything. I was on the road. I didnít have to worry and I dropped the other stuff, moved into a dormitory; I was on the road and had full time, so to speak, to devote to this without the other necessary distractions. So that would have been Ď2Ji. I taught at City College for three years and finished in the summer of Ď27, so that would make it Ď24. Anyway, I had this job at City College and at the end of the first year I looked around for a dissertation problem. My professor, Wills, had suggested measuring the magnetic susceptibility of alkali vapor, I mean the susceptibility on the quantum theory.

Most of his research was in magnetism. I thought about it very hard and it looked like, a very difficult dissertation thing to do; I told him I didnít want to do it. He was disappointed and had no problem, so I found a problem of my own, which was measuring the magnetic susceptibility of crystals; I picked the (Tutton) salt crystals which were all in the same system and differed very little in angle. I would measure the susceptibility and locate the ellipsoid of induction and, of course, there was a method for doing this, which was described by Voigt where with a cutting and grinding goniometry you cut out a section, hung it on a delicate torsion balance, and measured the homogeneity of the field. You have three sections and then measure the average and from these sectionsí average you could figure out the principal axes, the magnitude, and also could get the angle at which it was situated with respect to the crystal axes. That was a very, very difficult experiment and I was very slow to begin because I was chiefly interested in theory and at that time really began reading very widely in what was going on. As usual, I got together a group of students, graduate students, who were very brilliant people. It took a long time, more than a year, to get acquainted with anybody else but there was Ralph Kronig, S. C. Wang, Francis Bitter, Mark Zemansky; we stayed together and talked together about all sorts of things.

Kuhn:

This is really your second year at Columbia?

Rabi:

Beginning the second year at Columbia and on; I went to Cornell Ď22-í23, so Ď23-í24 was getting acquainted, and then Ď24-í27 was this period.

Kuhn:

Right, and already in late Ď24 you got your thesis problem.

Rabi:

Yes, late in Ď24 I started the thesis problem. I had a space in a room with another fellow and a magnet sort of to get started and that sort of thing. Naturally, the thing I did which was easiest was to start growing some crystals. Concentrate a solution, put it away, and then you could go to the opera and what, not, I taught at City College and that took an amazing amount of time; the first year I taught sixteen hours; the following two years twenty-five hours, day and night, but I seemed to have a whole lot of time.

Kuhn:

This was work in sections, or were you teaching?

Rabi:

Sections, and, in some cases, I had to lecture. In the evenings it was all my own —- nine hours in the evening, but I was making some money and was living on my own in that sense. Now, as far as physics is concerned, I had read in the quantum theory and didnít really know how to take it; there was no course in it. Professor Wills wanted to give a course on atomic structure and his idea of giving a course on atomic structure was to use someone like Sommerfeld and most of the course was taken up with how to do integration in the complex plane, (but no) physical ideas about it. There was research going on which was c1ose to important physics. Bergen Davis was doing very good research at that time with x-rays and [Harold W.] Webb was doing the life-time of excited states, but itís quite a different thing from (experiments of this sort) quantum theory. I was very far from convinced about quantum theory; in fact, I spent a lot of time thinking about models of atoms and so on. What finished me was when I read the Stern-Gerlach experiment; that was it, because I thought, ďWell, Iím a pretty smart guy; I can make models and so on, imagine things, but this is something quite different. This comes out of space and itís quantized —- nothing interior.Ē So I began to take it very seriously and to study books like Sommerfeld, Bornís Atommechanik.

Kuhn:

Where had you gotten the German for that?

Rabi:

I had studied German in high school and then I just read with a dictionary; thatís all. The German was not the hard part of it, no sir. I very soon began to hear about it more in detail and to discuss it with others. I preferred the correspondence principle because it was physical whereas the other was purely formal; somebody said, ďWell, D look at you and I establish an axis.Ē I said ďYouíre cockeyed; Iím looking the other way, now which axis is it that will be quantized?Ē And the other was physical. During this period while I was engaged in my experimental work

Kuhn:

What was the source of the correspondence principle? I donít mean historically; I mean where did y learn about the correspondence principle?

Rabi:

In the first place, itís hard to tell. People come through and give a lecture. Bohr gave a lecture here. Various lecturers that came through would talk about it. I began to look at the journals and try to read them. Then there was Bohrís little book. The journals and Bohrís little book.

Kuhn:

Which do you mean by the little book — the Cambridge lectures or the Quantum Theory of Line Sectra?

Rabi:

I donít really remember one of those; I donít really remember any more which they were. You know, you. just sort of browse around the library and read. Columbia had such great superiority over Cornell because weíd had Byerly, bad as it was, we knew Fourier Series and other functions of that sort. I remember when de Broglieís paper came out and the spinning electron. Working with susceptibility I used the spinning electron to make a calculation with the alkais.

You referred to this in your outline. This was a graduate student. And I said this was all wrong; in the paper itself I said if the Boltzmann statistics hold, t1t was all wrong. Herzfeld came through on a visit and I asked him about this. ďOh, itís got to hold,Ē he said. Iíd missed Fermiís paper somehow. After all, I was not a theoretical physicist or anything of that sort. I was supposedly doing experimentation and teaching twenty-five hours a week; Iíd missed it and if I hadnít, I probably would have been the founder of the electron theory of metals in this sense because I noticed it long before they did in Europe. I discovered later, interestingly enough, that Stern had pointed this out to Pauli when mine was a year or so before.

Kuhn:

But also itís not only Boltzmann statistics but itís a Boltzmann statistics over a special distribution in which everything is equally probable. Thereís no attempt to talk about space quantization of the electron axis.

Rabi:

This, of course, shouldnít make any difference classically. I havenít seen a reprint or looked at that for years; I donít remember what I did do on this. Iím quite sure Ďchat I did was right because there was discussion of the magnetic susceptibility of the alkalis and things of that sort; Iím quite sure that what I did was all right, that the calculation was O.K., but this was at reasonable temperatures and not at low temperatures. I read de Broglieís paper and was fascinated by it but didnít do anything with it. Then when. SchrŲdingerís paper came, which I read as it appeared, I said to myself, ďThis is it,Ē and closed my Bornís Atommechanik. I was still doing my dissertation and was just about finished. Kronig and I said, ďWell, letís just learn this thing by doing a problem.Ē We looked through Bornís book to see what problems were done and there was the rotating top, so we did this just for exercise. I can remember so distinctly how amazing this was that these energies came out because we had no idea nobody had any idea then what the wave function was or meant, but there it was, and only by analogy with the Heisenberg matrix mechanics could you find out the meaning of the matrix element or the quantum numbers.

Kuhn:

Had you paid any attention to matrix mechanics?

Rabi:

I read Heisenbergís first paper when it came out before his matrix mechanics and I think you referred to it as Born Heisenberg. I donít think Born had anything to do with the first paper; later on he pointed out to Heisenberg that these laws of multiplication were matrix laws. I read that and was absolutely fascinated by this crazy use of the Fourier series with these observed line frequencies in. We had a seminar a most interesting thing socially in American universities. We had a seminar of about four or five students, those people Iíve mentioned, who met Sunday mornings at 11:00; weíd go on perhaps until 11:00 at night, go out to eat together and so on. No member of the Columbia faculty, but the NYU faculty came to us Wheeler Loomis, I think (John Charles) Hubbard, (Durman), maybe (Richard T. Cox came four of those full professors (at NYU) came to our seminar. We had just an absolutely great time there, reading these things. Very exciting. Pauliís paper on the metals, paramagnetism of metals, was one thing; he used the grand ensemble which we didnít know. Zemansky said, ďWell, I think Iíll go to Europe next summer and ask Pauli about it.Ē That sort of thing. Well then, just to clean up my dissertation, by being lazy this way, I found the way of doing the problem which was much simpler and more accurate than anything that had gone before.

Kuhn:

And quite different.

Rabi:

Entirely different, entirely original thing. And I was able to do my whole dissertation. with more material than existed in literature up to that time in about six weeks.

Kuhn:

Really !!

Rabi:

I had the credit for doing a difficult thing, but actually I had no experience out of it whatsoever; all I needed was a balance, a magnet which existed, a switch which somebody else had built, a glass, little vessels or flasks of pyrex which somebody blew, and thatís all — and a telescope. It was a known method, extremely accurate, so it became no problem in this sense.

Kuhn:

Iíll be damned. When you say six weeks, you mean six weeks to put the equipment together and to —-

Rabi:

There was practically no equipment! There was a magnet; pole pieces. It was in a housing. On top of the housing I put a balance, and then I had a sort of torsion head on a piece of brass that went over the magnet like this— the torsion head; a glass fiber which I madeósimply put the glass in the flame and pulled it out - one end attached here and the other end attached to the crystal with a piece of shellac; I was oriented. Just had a slit in the piece of brass which I would look though and see the reflection of a face. I had it, thatís all there was to it. Identify the face, and then I looked at the side of this thing with a small telescope. And thatís what it was; I mean, there was nothing there, absolutely nothing there. I varied the susceptibility of the solution in which this crystal was dipped until there was no motion, sucked some out with a pipette, put it in a tube and weighed it, compared its weight with water in the same place and I had the various susceptibilities of the crystals. It was just sheer magic.

Kuhn:

Were you looking for another way to do the problem, or did this come out of a clear sky when you got it?

Rabi:

Not so much looking for another way —- the standard way of doing the problem was so boring to me and so difficult I just couldnít get down to it. I might never have finished my dissertation if I had had to do it that way because Iím not an activist in this sense. I like experimental physics, but Iím not an activist and I never was, especially at a time like that when the world was so full of theory and otherwise — I mean, a young man with the opera going on, plays, and so on. But there my wide reading was a great help. I just happened to be reading, for sheer pleasure, Maxwellís, which was something I knew but it struck me reading that that if you have something in one medium and in another, the effect is the difference between the two, So I thought now, ďThis is it,Ē because ordinarily the reason you cut it and grind it is that you have to have a particular shape because the end effects, but here if you have annulled them by a surrounding material you could use their original shape. Interestingly enough, I first found it experimentally and then proved it mathematically, that when you are at the minimum angle, there is a point of instability, and when youíre at the minor axis of ellipsoid, instead of moving in and out, you could move sideways, very violently; you could locate it just to a fraction of a degree so I could get the angle, which was always the worst thing to get out of that system of equations. It was all very great.

It also taught me a lesson. This paper was published; it was the first paper in that issue of the Physical Review; it was abstracted in Physikalische Berichte, Physics Abstracts and it was very well abstracted and nobody saw it. Absolutely nobody saw it. Van Vleck, who was interested in this field, learned of it some years later through a reference in an 484 Indian journal. It was seen by QCSJ Krishnan who started his whole career in magneto-chemistry using these methods, but else ever saw this thing; I saw no reference to it or anything. It shows that when you have something and you just introduce it on the world, they wonít look at it. It has to be brought in and gradually; it has to have backing. I hadnít read a paper on it to the Physical Society or anything of that sort; it was just written and there it was. More or less in this disconnected way I now have my Doctorís degree and weíre in 1927. Now weíd better go to some of your questions.

Kuhn:

Letís put it this way; I donít want quite yet to go on past 1927.

Rabi:

No, I mean to go back more specifically.

Kuhn:

In this group, your seminar group, what sort of sense had you of the state that physics was in? You were learning quantum mechanics. Iíd perhaps best do it by suggesting something to contrast it with. In Europe a number of people, but by no means everybody obviously, had been quite aware of quantum theories for some time.

Rabi:

For fifteen years.

Kuhn:

Yes, and they were relatively convinced. Now in the period youíre in graduate school in Columbia theyíre getting more and more discouraged about it. Itís becoming clearer and clearer that something they thought worked pretty well was not, when in application to particular problems, working any longer worth a damn. One of the very nice descriptions of this is the 499 description that Kronig himself gives in the Pauli volume; he calls it a crisis, developing very rapidly in Ď24, Ď25. How much sense of that sort of thing was there? What was the sense of the situation?

Rabi:

Iím now giving you a wormís-eye-view of this because I was a graduate student at a place where there was no theorist in this, but just what one graduate student learns from another. Sometimes maybe you get to a meeting, you listen to something, or you talk to another graduate student, and you have what you read in the journals and books. Now we, our group, very well knew that there was a crisis; in other words, we were quite familiar, although we hadnít done work in it, with quantum theory and the ideas of it. We were familiar with the paradoxes of space quantization, for example, with Einsteinís problems, with the difficulties of the light quantum hypothesis and things of that sort. We were familiar with difficulties that they had in quantization and the Stark effect, the difficulty in equal to 0, the thing falling in there. We also knew some of the successes, We knew something of Pauliís principle, which was a very strange thing at that time; it really wasnít what it is now. I certainly had been reading about the Zeeman effect and the anomalous thing, the fact that they liked to give the spin to what they called the Rumpf.

That we knew, arid we knew the whole thing was very odd; it was difficult in this way. So we knew there was a crisis and I think at that time we also understood very well in a certain sense that it probably could not work the difficulties that you had —- the radiation which did not correspond to the harmonics of the Fourier analysis but something else and therefore the mechanical interaction between the two electrons and the helium depended upon the mechanical thing where the mutual radiation could be something else. So it was not surprising this would break down. We knew that there had been calculations of the hydrogen molecular ion in this way, so that we knew there was a crisis. We knew a little bit about some of the methods used in calculating intensities, about the correspondence principle and some of those funny closure things where by means of an abracadabra thing you could guess that the end thing was closed and guess what would be in between. That sort of stuff. Of course, there were people who were much closer to this thing during that time who, although, I think were much younger than I was not having been out all those years, and more precocious, like Van Vleck and Slater were much more closely in it.

I think the things that I was painfully discovering, Van may have been teaching at Wisconsin and Slater at Harvard, but I donít think either of them had a strong feeling for that kind of theory. Both of them are more ďgive me that there slide rule and Iíll give you the numberĒ, so I think they were conscious of the crisis and unhappy, but I donít think they worried about it. Certainly nothing in Vanís subsequent career or in Slaterís. This Bohr-Kramers-Slater thing - Then they got frightened of this whole thing and never touched any fundamental stuff again, as far as I know, So itís a matter of temperament, I think.

Kuhn:

In this period, Iíd say I think your description of this thing fits Van better than it does Slater. It certainly fits Slater later.

Rabi:

Slater was there with Bohr and they had the Bohr-Kramers-Slater thing in which he thought Bohr quite misrepresented him, was too mystical, and he didnít do anything else at all, as far as fundamental physics was concerned; after that, except for means calculating methods, his matrix writing and things of that sort. But it was more problemÄ4solving than basic things.

Kuhn:

When you say he felt that Bohr misrepresented him, Iíve talked to him and Iíve had this also from him. How generally was that known? When do you suppose that you heard that?

Rabi:

I heard him say so in a meeting of the Physical Society in 1924 or 25.

Kuhn:

Right at the time.

Rabi:

Right then. He gave a talk. I was just a graduate student but heíd come back from Europe and had had this publication so I went and heard his talk and I heard him say so. Bohr had made it more mystical than was necessary.

Kuhn:

Was this something American physicists were prepared to believe? Was there any impression that Bohr might well in fact be —?

Rabi:

American physicists didnít know quantum mechanics; I mean, he gave this talk and I donít think they knew a goddamn thing about what he was talking about mostly. There may have been a few; maybe Van Check) knew, maybe one person here and there, but I doubt there were a dozen people in the whole United States.

Kuhn:

What Iím after here is something a little different from the technical content of the paper, which is more the extent to which the aura which surrounded Bohr extended to this country. Would one thing that if a man said ĎBohr has misrepresented me and Iíve really still got it rightí because Slater, after all, when he came back, did publish a paper on his own version of the thing - would they think, ďOh, he canít be right; Bohr must have it right.Ē

Rabi:

Some of that, I would say. On the other hand, there he is in the flesh, one of our boys, so to speak; that would have to shake one somewhat. I suppose different people were affected differently, depending on how much attention they paid to authority. Some did more than others. I really couldnít say. I thought the whole idea was rather silly anyway, myself, at that time. Not that I had a right to that opinion, but nevertheless I had it. I was too conservative: ďIím not going to give up the conservation of energy for anybody, Bohr or anybody else,Ē As a matter of fact, I was always inclined to disbelieve anything said by an older man. Just like that Itís awful. And Bohr to me was very old. Now let me see So we aware of difficulties, but not completely. When I got to Europe I discovered that with our group and our reading I actually knew much more physics than the Germans of comparable stage, but not as much, letís say, as some very special ones like Hans Bethe and so on, the darling of Sommerfeld. But if you take the run of even the good experimental physicists who were being produced in Germany, I had a much better knowledge, more knowledge, especially theory and so on. There was this very great bifurcation between theory and experiments there; itís beginning to happen here, unfortunately.

Kuhn:

What was it like at the time? Did you think of yourself as a theoretical physicist or an experimental physicist, or was it not a question that one asked?

Rabi:

Not in my mind. I thought of myself as a physicist and we didnít have any theoretical physicists around Columbia; Kronig did an experimental dissertation —- we all did —- we were just physicists, thatís all, and it never occurred to me otherwise. Iíd like to think of myself now as a physicist and not qualify it, the idea being that if you have an experimental idea that you want to do, you do it and if you have a theoretical thing, you try to work it out and see how you do it. Some people are more skillful than others at everything, or at one or the other —- there are differences. Of course, if youíre busy doing experiments, you havenít as much time to work out on mathemtica1 and theoretical things, and the same is true if youíre working on theory. If youíre busy doing calculation, the whole world can o by, even the theory, and you donít know whatís happening until you turn around and catch up. When I went to Europe I didnít go there to do an experiment.

The last thing in the world I wanted to do was an experiment; that came about quite by accident, I went there to learn, to be with the great masters. Iíd never yet met a first-rate mind, all the way through, until I got to Europe and then I began to see a new world. Not that I learned anything there, any specific knowledge that I wouldnít have had just as well at home. I always call it, in a mystical way, being immersed in the living oral tradition of physics, which, I think, is much more Important than people have credited it with. I use the image, ďYou know the libretto, but you donít know the tuneĒ; and thatís what I got out of Europe from those people, some development of judgment and some sense of proportion, as well as the social side, the social life. So there I was able to be with the greatest minds of physics of the generation in the century. The only one mistake weí made, actually, in our own estimate of what was going on when I went over was that we had underestimated the value of Diracís methods. They looked strange, these very abstract, symbolic methods. That we missed out on and I quickly learned when I got to Europe its value, its importance and its simplicity when you look at it in that way. But I did know all the business about the equivalence of matrix and the other methods and whatnot. That was all very clear; the whole meaning of the quantum theory in that sense I understood from our own talk fairly well before I went over —- transformation theory arid all that.

Kuhn:

With all this whole string of topics, starting as early in graduate school as you like and going right on up to the time you left for Europe, are there any of them which bring back to mind particular discussions or puzzles or things which may have gone on in your seminar or around the university?

Rabi:

Well, for example, the spinning electron, There was an infinite amount of discussion, particularly with Kronig. I mean, Kronig claims to have discovered it: I can say this: he mentioned that to me.

Kuhn:

Thatís very interesting.

Rabi:

And, you will notice, he published a paper against it and I published this other thing. I expressed myself, I thought, circumspectly about the thing. But that we talked about a very great deal, about what this might mean. Of course, space quantization was a fascinating thing which we would talk about —- the method and meaning of space quantization. This is before quantum mechanics as such, before you had the explanations which are current now about the states existing and so on. The Zeitschrift fŁr Physik was so fascinating, something new coming out all the time, that we talked about it all the time. But when I say ďweĒ now, Iím talking about this particular group of graduate students which were around here and not of the faculty. One of our best people, a chap by the name (Myron Schwarzschild) never did finish and get his Doctorís degree; it was very sad because he was probably the brightest. Then, of course, I taught at City College during this whole time and I talked about these things to people there. The highlights, as I remember them now—space quantization, the theory of the anomalous Zeeman effect. Some of these long papers —- . You know, there was a whole period for about six months or a year where everybody had given up and there were long papers in the Zeitschrift fŁr Physik that had no formulas: Der unmechanische Zwang and so on. Weíd talk about that a little bit. Then, of course, de Brogueís paper was very impressive to me, although my friends didnít cotton to it. We didnít talk about it enough, Iím very sorry

Kuhn:

If you people were talking about the de Broglie paper before the SchrŲdinger per there must have been very few who were.

Rabi:

Thanks to my brilliant dissertation I had lots of time; Iíd read these things.

Kuhn:

Did you follow the Annalen der Physik regularly?

Rabi:

Every journal; I looked at every journal that came in. When I was younger, then I knew the content of all the journals in this sense. I discovered, by the way, that thatís a part of provincialism. You find that with the Russians now whereas the Americans donít know it, the Russians know their papers better than the Americans do. But youíre isolated and you keep in contact with the world. Yes, oh sure, I read it; I found it very, very interesting. I often think if Iíd been in a stronger position somehow and not just at that time or when I had my dissertation and all this work to do, I might have really been fired by it to drop other things and work on it. I found it fascinating there and could have done something with it. And the same thing is true of the first SchrŲdinger paper; I was reading it right afterwards. So what you see now is a small coterie of little groups there, unknown to anybody else. I know when I got to Europe my dissertation had been published but also this; and nobody ever heard this man before and 617 there he is with these two things. Kronig, of course, had published earlier and he was better known so maybe it was considered as an appendage of Kronig or something. I think thatís what it probably was.

Kuhn:

How did the two of you work on that? Was there some distribution of function in the solutions?

Rabi:

It came about in this way. I think I was reading and Kronig said, ďLetís do something just to learn.Ē I said, ďFine.Ē Iíll tell you just what happened. We looked in the book and decided this is the thing, the symmetrical top. There was a formula given by SchrŲdinger of how you set up the equations, the Ji and so on. We set up the equation; there we had the equation. Then what do you do with it? We puzzled about it and suddenly we remembered that you introduced functions to separate the variables, so we separated the variables, got off the angular variables and got another equation, a differential equation. What do you do with it? Neither of us had the faintest idea, and it just so happened, in spite of the fact I was teaching 25 hours a week, I found myself sitting in the library reading, just for pleasure, Jacobiís works, the original works of Jacobi. By God, there was the equation: the confluent hypergeometric series.

So I came home: ďBy George, we have it! There it is The thing, the recursion formula, and so on. So we set up what we called a factory for the matrix elements and he did some, I did some, we set up the factory, and we got the matrix elements. There we had it. We knew the meaning of the quantum numbers from the analogy with the more classical thing and we sent the paper off to the Physical Review. Just independently at that time, Reiche and Rademacher had worked at the same thing, so Physical Review wrote back that they really wanted it cut down, that it was too long and something elseĒcou1d we cut it down?Ē Well, like good boys, we just chopped it; we gave nothing but the result. We didnít give the method, the recursion formulas, and so on, so we published this thing in, I donít know, four or five pages; Reiche and Rademacher published theirs in 101 pages in the Zeitschrift fŁr Physik.

Thatís what it was, just exactly that. Kronigís contribution was that he was an assistant in the department so he had more time and he slugged out more of the Well, we didnít have the integration; we had just the recursion formulas and things of that sort to set up the factory for all the matrix elements, and thatís what it was. The matrix elements had already been obtained by, I think, Dennison with the matrix mechanics and, I think, we were able to correct an error of so in that when this came out, or something of that sort. But thatís exactly what it was; I mean, you can see we did not know a heck of a lot about differential equations at all since we didnít even recognize this as a type of confluent hyper geometric series, We wouldnít have had it, we would just have had the energy levels, if not by the sheer accident of my happening to read. I read these things just for pleasure and that sort of thing and there was the confluent - .

Kuhn:

Very interesting.

Rabi:

It was really strange. Imagine coming there and having the equations

Kuhn:

To what extent did you people worry about the interpretation problem?

Rabi:

Well, everything happened so rapidly, we were worried. What is this wave function, anyway? But before you could really do a job of worrying, the answer came. The whole period between SchrŲdingerís first equation and the interpretation that-Born gave and his equivalents was only about a year, wasnít it?

Kuhn:

Well, it depends where you draw the line at the end of it.

Rabi:

Of course, transformation theory . All I know is this: SchrŲdingerís first paper was when, Ď25?

Kuhn:

No, Ď26. The spring of Ď26.

Rabi:

When I got to Europe in Ď27 it was practically all finished; we had transformation theory. So thatís one year. A couple of guys off here in America

Kuhn:

But this was a live issue at this point.

Rabi:

Oh, yes. What is it? Itís magic, but what is it? What does it denote?

Kuhn:

Was it easy to accept? You know SchrŲdinger had an answer to that. Were you disposed to take SchrŲdingerís answer seriously?

Rabi:

Not terribly, no, not terribly. There were no consequences of it that we could see that were useful. We liked it — I loved that thing, but there was nothing you could do with the wave function and the square of the wave function would give you density, but was it a real density? Well, what about the energy? (You donít integrate parts of it) interacting with one another so there was nothing to do with it, in that original SchrŲdinger interpretation. I will say this: he was always unhappy about the whole thing and I am, too, to the very present day, in the sense that I canít get myself to regard quantum theory as other than provisional in some way. Those were such exciting days with the issues of Zeitschrift fur Physik and Annalen der Physik one after another, bang, bang, bang - Diracís papers, which, as I said, we didnít appredate the full force and power of the method except of course, the spin, which was really grand.

Kuhn:

You were in Europe when the spin paper came out?

Rabi:

Letís see, when did it come out?

Kuhn:

Ď28, fairly early in Ď 28.

Rabi:

Yes, I guess I was there already. Wait a minute was that Ď28 or was it late in Ď27?

Kuhn:

I think the paper was submitted in December Ď27 or January Ď28; in any case it would have come out in very early Ď28.

Rabi:

I remember being somehow with Stern in Bornís office in Gottingen and Born said, ďPhysics will be over in six months.Ē He said: ďWe already have the electron. It wonít take much longer to have the proton and then, in principle, physics will be over.Ē I was really astonished, but I actually heard him say it. I remember in 1927 taking a walk. There was a meeting of the British Association at Leeds with Ted Kemble and Ed Condon. I met Ed Condon in Europe, a great friend. And Ted was just sad about all this. He had a nostalgia for the old days: ďThe mystery is out of physics,Ē he said; ďThese boys, theyíll this thing out and there wonít be anything left. The mystery is out of physics.Ē The mystery was out of physics. Well, as things went, all these difficulties that had been discussed and discussed were one after the other being resolved. Helium, all this business, half quantum numbers, whatever you have, one after the other, —- bang, bang, bang. The electron was no longer a mystery. No, the electron was not yet then, but still the spin was there even so. interruption

Kuhn:

Was there any sort of tradition at Columbia for these trips abroad?

Rabi:

Well, there was a fellowship, a traveling fellowship called the (William B) Cutting Traveling Fellowship for which I applied and didnít get. Some people had gone before, yes. Kronig had gone and another fellow, (F.G.) Slack, before me, but that was not the point in my view. I just wanted to get what things were happening.

Kuhn:

You were very conscious by now, I take it, of the fact that the things that were happening were happening in Europe?

Rabi:

I was more than conscious; I knew. Well, I applied for a fellowship, a small Columbia fellowship called the Barnard Fellowship, I think, which paid something like 1500 dollars out of which I had to support myself, my wife, and pay my fare. Thatís all I got. I was teaching at City College at the time and I applied for a leave of absence and I didnít get it. It was a severe blow, but I determined Iíd live only one life and I was going to do this, which I did. So I had to leave the job and I went to Europe. My general experience was an interesting commentary on the times which may never return again. I was very inexperienced and I didnít write a single letter; I knew where the people were, I bought a ticket, and the first place I went to was Zurich where SchrŲdinger was. I went there, I found a pension, settled down, and went to the seminar after finding out where it was. I went in and saw Schr8dinger -P— hadnít written to him —- and he was just leaving; in fact, it was the end of his time, and he was going to Berlin. Anyway, I went to the seminar and I didnít understand anything; I was very sad about this but I didnít know anybody.

Kuhn:

Was it the language?

Rabi:

Iíll come to it. I didnít know anybody but I looked around, and there were a number of people wearing shirts with the collar attached, which was the sign of the American, and there I found Jay (J.A.) Stratton who was there, I think, just out of Harvard or MIT, and Linus Pauling, and they reassured me that it wasnít so bad, that this wasnít really German but was SchwyzertŁtsch. I met a number of people there at that time; I think (Mason E,) Hufford was there, and Linus took me in to his house and gave me a drink, which was a great thing for an American then; this was prohibition then, 1927. Then I talked to Stratton about his problems, which were even more severe than mine; I think Iíd actually had more through our group. I stayed there for a few weeks and then things stopped because SchrŲdinger went away.

Kuhn:

When had you actually gotten there?

Rabi:

Oh, it must have been July, I guess, 1927. The next place to go was to Sommerfeld, so I simply went to Sommerfeld. One of the people told me of a pension where he had stayed; I went there, registered in this pension, came down in the morning for breakfast, and there was the most German-looking man I ever saw reading the American Mercury. It was Ed Condon, who had been there for a year already in Gottingen and had moved here. Then it turned out GLP.) Robertson was also there, so I made two very good friends there, good friendships. I went to Sommerfeldís institute, went in, and talked to the professo

Rabi:

ďMy name is Rabi, Iíve come here to work.Ē And thatís all there was. Iíd sit outside where they all were; thsold, sitting there, was an assistant; I think Bechert was Sommerfeldís assistant. The journals were in the Sommerfeldís library and if you wanted one youíd go there and knock on the door. My German was bad and I said, ďIst der Herr Professor vernommen?Ē, until he explained to me that that meant, ďIs he arrested?Ē Hans Bethe was a graduate student at that time, and Peierls was there. The professor would invite you out to have tea in the garden and so on he didnít pay for it, of course and then there might be some party to which you were invited; you were just a part of the crowd in that way and thatís how it went. I worked on some problem or other; I think I was chiefly interested then in trying to calculate the magnetic susceptibility of the hydrogen molecule. But then we bummed around, Ed Condon, Bob Robertson, and I. We had a really nice time t1 summer. Later on I went to England for a meeting of the British Association where my wife was supposed to meet me and she did.

Kuhn:

She had not come over?

Rabi:

She had not come over with me but came later. I took a ship with her and we went over the North Sea to Copenhagen in September. We got there, I bought a map of the city, checked my bags, walked over to the Institute, rang the, bell, and a blonde secretary opened the door. I said, ďMy name is Rabi; come to work here.Ē She gave me a key no letter1 now. I asked her the name of a pension where I could leave my wife. She told me, I left my wife there, came back and started to do some reading, trying to calculate this thing. Nobody was there; they were all away on a holiday. Gradually some people appeared and finally Bohr showed up. He was very nice. This was a surprise and, I think, they were quite shocked probably. Heisenberg showed up, and Kronig, who had by that time decided to leave America, came; heíd been at the Institute before. One day they told me that they had arranged for Nishina and me to go to Pauli. Bohr was tired and I hadnít made any arrangements; they kept only Kronig; Nishina had been there for a long time. So it was all set. Fine. I sort of got kicked out and went toí Pauli. Itís fantastic how a manís fate is determined in this way, I went to Pauli and I didnít know that Stern was there.

Kuhn:

How long was it?

Rabi:

Six weeks. I think I landed toward the end of October in Hamburg. Working with Stern were Ronald Fraser and John (B.) Taylor. John Taylor had been a chemist and so on, but had done molecular beams work and Fraser had come to work with Stern on molecular beams work. Well, afterí talking German all day, you really want to talk some English, so we became friends, and they had had very little theory so I could help them out and explain things. And I had read the molecular beam papers very carefully since space quantization made such a tremendous impression on me. So I was working with Pauli and Nishina and we published a paper, something about x-ray dispersion and so on. It was not published in a big journal but in the proceedings of The Deutsche Physikalische Gesellschaft. Then I had an idea for an experiment which was to gee over the difficulty of measuring inhomogeneous fields; I suggested it to Stern although I thought it was a rather trivial thing, and he suggested I do it.

They told me it was a great honor to be allowed to work in Sternís lab. I had no job, no position to turn down so I did it. I got to work and shared a lab with Taylor, who really taught mc the technique. I saw very little of Stern himself, during that time. I did the experiment. All the time Walter Gordon was there, and later on Jordan came, and, of course, there was Lenz who was the professor; there was Pauli, and Bohr used to come, and Born. It was a place where people were in and out all the time. And of course there was Stern. The seminars were marvelous and the colloquium was very interesting, very high level, in the sense that there were different kinds of minds; Lenz, for instance, had a mind like a steel trap. He could make up things on the spot, although he never accomplished very much. Then there was Stern with his marvelous physical intuition and point of view, and Pauli with his tremendous solidity. Walter Gordon and I got to be very close personal friends, in a sense. So all this was just great, all these wonderful people, and fortunately they were bachelors, so I had lunch with them every day. (Well, with Fraser and so on.) They got a good deal out of it, too, as is shown by the following. One time we decided their lunch was too expensive; it was 75 cents, which was a lot of money for me for lunch, a, very posh lunch at the Hotel (Espanada). So we moved away and went to the student place and after a few days they showed up with us, saying, ďCanít we keep together so that we can have some reasonable conversation?Ē And we compromised on another place, the (Courier House), in between.

I learned a great deal —- not only physics, but Besetzungsfragen; you know what those are, life in Germany, that kind of politics which they had and that sort of stuff. And I did my experiments starting from scratch because I really had no experimental experience because my dissertation thing was so simple. I did it in ďrecht timeĒ and Taylor and I introduced what Stern called the ďmechanische ArbeitsmethodeĒ. Theyíd worked before by the German method, with the laboratory opening at 7:00 oíclock in the morning and shutting at 7:00 at night; we couldnít come at such times; weíd come at 11:00 and want to work through and theyíd let us do it. Our wives would come around 11:00 and weíd make toast and sing. It just went —- bang, bang, bang; just like that, —- and that was it. We did the experiment and published the paper.

Kuhn:

This is over how long a period now?

Rabi:

A year. I started approximately in January and I probably finished around Christmas. Stern was very nice about the publication of it. He said, ďFirst, publish a letter in Nature; if you publish it in German, theyíll think itís my thing, and itís yours. Then publish the German paper,Ē I wanted to use, just for fun, a long German word, just one word, to make up the title, ďMolekularstrahlenablenkungsmethode,Ē but he wouldnít let me do it. So as soon as I was through, off I went to Leipzig with Heisenberg.

Kuhn:

Tell me a little bit more about that: that technique I hadnít known of before. Did it get followed up at all?

Rabi:

No, not much.

Kuhn:

You didnít use it further yourself either?

Rabi:

No, the interest changed from exact measurements in this way; the interest changed. It was a cute idea, but, I felt at the time, fairly trivial. This really was a sudden change in refractive index and the thing breaks in two rays but it was not really at the central part of the thing. When I was through, Iíd done it, I went off to Heisenberg and joined his theoretical seminar; again never a word before, but I joined right with it and it was very interesting there, too. There was Heisenberg, and among the other people there was Oppenheimer who was there for a short bit. Among the students there were Teller, Peierls, a whole raft of Americans [James H.]Bartlett, who is now at Illinois —- (Race) Otto Halpern, Guido Beck. And, of course, on the experimental side there was Debye. I finished 5t Hamburg/at the end of Ď28 and went there toward the end of Ď23; 1 was there about six weeks when Heisenberg left to go to America. I started some work there on quantum mechanical properties of the alkalis using superposition of the wave functions and so on. Heisenberg was interested in that and thatís the way I got my job at Columbia. He was on a lecture tour of the United States and they asked him at Columbia whom they should get; he suggested me. So I came to teach theoretical physics. Then, after Heisenberg left to come to America, I went back to Pauli who was by this time a professor in Zurich. This again was a very wonderful period. I donít think I published anything during that time I was just sort of talking to people.

Kuhn:

Did you publish something on the compressibility of the alkalis?

Rabi:

No, I never did. This was the period in Hamburg when Pauli was making the quantum electrodynamics which continued there; during the time in Zurich Slater was there doing some matrices; [F.] Wheeler Loomis showed up with his kids; just a lot of people of that sort. I made most of my friends —- Houston, [William W.] Watson all the people who are more or less my age; and most of all, Oppenheimer was working there that semester. And we got to know one another very well during that period, not just through science, but through lots of other things also — art, literature, politics, religion, and everything else. That essentially was more or less the European experience in this sense. At the end of that period I felt Iíd absorbed what there was and had had really a front seat for that period while it was happening. People came through; Dirac I got to know, and all the people of any significance in that time. Heitler, London, Szilard, Wigner, von Neumann,

Kuhn:

Were you at Gottingen at all?

Rabi:

Only for brief visits. All these were elsewhere. I know on my way back I stopped in Hamburg. They had a wonderful little session going on; theyíd invited Eddington, von Neumann, and Ehrenfest to talk about the fate of the universe in the sense of the thermodynamic death, and that sort of thing. Von Neumann visited in Leipzig, too; there was Eddington and his big (pipe); I got a tremendous amount out of Ehrenfest, a wonderful person. You know, something interesting happened to me. A year or two ago I visited Leiden again in connection with radio astronomy, but they were building a new theoretical institute. I thought that it was such a pity because I remember the other one so well and they said that on the wall Ehrenfest had physicists sign their names.

They said, ďYour name is probably there.Ē I said, ďNo, I donít think so; I was of no significance and I certainly donít remember it, but Iíd like to see it.Ē I went there to see it and right smack in the middle was my signature; you could take it off and bring it to the bank today. Itís a strange thing to see oneself of 30 years before and more absolutely right there. Among the people I met visiting Ehrenfest was Tamm. There was a photograph taken. After the war, Kramers came and brought me the negative of that picture with note from Ehrenfest. Apparently it was something be had written but hadnít mailed - the negative and this thing. It was really a shock to have a note from a dead man. When I visited Russia two years ago I showed Tamm this picture of himself as a young man. You can see it was, in this sense, a kind of voyage of inspiration, not actually of work.

I donít think I accomplished anything very much there. Oh, yes; I had one paper which was very useful to me and thatís the Dirac electron and the magnetic field. There were some other things I did which werenít really published or which Walter Gordon published, but thereís nothing very serious in that respect. One time I was in the library there in Hamburg and Lenz came in and said, ďHow are things?Ē ďOh,Ē I said, ďvery bad; I canít seem to get down to work.Ē His eyes lit up; be said, ďAh I have just the thing for you; Iíll give you a letter of introduction to Adler in Vienna and heíll help you.Ē That so scared the hell out of me that I really got down to work! It was marvelous therapy. I donít know if he intended it as such because heís always been sort of a hypochondriac.

Kuhn:

Was this group as a group at all concerned with psychiatry, psychoanalysis?

Rabi:

Oh, Pauli very much so. They knew a lot about it, yes. Iím talking about the Germans; I donít think either Fraser or Taylor was. It was interesting: Taylor was a real middle western American and Fraser a Scotchman and they could hardly understand one another, but a New Yorker could mediate between the two. An. interesting thing! Taylor thought Fraser completely absurd and Fraser thought Taylor was very limited.

Kuhn:

Tell me a little bit more about the Dirac electron paper. What got you on to that?

Rabi:

I thought that if I did it, there might be some property of the current which would show up some internal currents, some intrinsic thing. And also, if you did the electron in the SchrŲdinger theory, in the homogeneous field, you had a zero point moment. The Dirac theory turned out quite classically; the lowest state was zero. But this was the idea to do it in the homogeneous field and see if thereís anything of the current in that sense; otherwise you just had a plain wave and that was it. Yes, I think thatís the thing I did for (publication) before

Kuhn:

You got the confluent hypergeometric function again, didnít you?

Rabi:

The old confluent hyper geometric function again But there was no trace of that. It was a useful thing for me, though, to want to have done and to have understood. Itís been a useful concept to me since.

Kuhn:

Do you mean useful in the sense of having learned the techniques and having learned to deal with 7

Rabi:

No, no. The way of thinking, yes, but there was nothing in the technique just a set of differential equations.

Kuhn:

You run in there itís the earliest reference to it I do know to some rather odd properties of translational motion of the Dirac electron. That is, the main papers on the translational properties come a bit later than this.

Rabi:

No, I donít know what you mean.

Kuhn:

You have remarked about the currents at the end, some odd properties which lead you to the conclusion that, unlike classical mechanics, here one must not separate the translatory and the rotatory motions, you cannot take these apart.

Rabi:

Yes, because of the relativistic effect,

Kuhn:

I wonder whether that had any consequences for you or for anybody else?

Rabi:

It had nothing further than that in the sense of what the relativistic thing did and the doubling of the energy levels, the degeneracy there. I think I should at that time have carried that further, but Iíd gone through this experimental thing. Now when I came back I was working on theory, but whenever I sit down to think about great ideas all I could think about were solid state ideas, just as is there. And that has always bored me, and I said, ďWell, the hell with it, Iíll go back and do experiments,Ē having this technique, I was almost the only one except for the (W. H.) Rodebush group. Now I was, of course, very fortunate that when I came back Gregory Breit was at NYU. We took a liking to one another and we ran our seminars jointly; for many years, even after he left, there was a very close connection between NYU and ourselves. Their students who came got credit for it, ours didnít, but otherwise we ran it jointly. I ran the seminar and he ran the seminar and the colloquium and taught statistical mechanics and things of that sort.

Kuhn:

Let me ask you one question about this since itís already come up, and then try to take you at least briefly back to Europe for a little bit longer. You do a paper I guess actually itís a letter to the Physical Review [(38 (1931)p. 2082-3)] with Breit, outlining the possibility of getting nuclear moments by the use of molecular beam techniques.

Rabi:

Did we say that there? I donít remember that paper at all except for the formula.

Kuhn:

Yes. I donít have a reprint anymore, but I remember it, itís a letter that starts out by saying: ďTo date, the only ways of getting at nuclear moments are Ď It must be as specific as ďnuclear momentsĒ because itís about hyperfine structure and alternating band structure; you could do this also with molecular beams, and then you show why you will expect to get lines from which you ought to be able to analyze out the nuclear moment. Now I really wondered to what extent it had been the discovery that you could do that that took you back to molecular beams 7

Rabi:

No, I had to more or less start at first and the idea was to do something with meta-stable neon, I think, by deflection method. The nuclear moments were also very interestingly in my mind because Taylorís experiments in Sternís laboratory had been on lithium to see whether it had a Bohr magneto or whether it had something in addition 1ue to the nuclear thing. Taylor started this detection method, at Langmuirís suggestion, by the way, with the surface ionization, so we were interested in nuclear moments in this respect. It was in my mind, so I was interested in that. Gregory Breit and I, our talks used to roam over the whole field of physics and we would talk about this. He missed the great opportunity because he published a paper heís a real man to talk to — where he showed that penetration by protons would be much easier.

He did. I donít think he put real numbers into it; he was trying to make 200,000 volts which he couldnít up there, which was none too good and so on, but he could have done it with 20,000ílts if heíd had better support, if heíd had this integration. But weíd talk about all sorts of things and we were friends for the years he was here, so this just came along in our general conversation and I went after it immediately in a number of ways. The first were defleetion in a weakened homogeneous field tracing a regular Stern-Gerlach pattern. This I never published. There were some brief things read at a meeting but never published because what I had in the end was a curve which you had to fit with various things and you may have seen by this time that dull work like that is not my forte, If we had had computing machines if that had happened —- I would never have gotten the Nobel prize because we would just have fitted them in this way. I decided one day, ďGoddamn it, Iím going to do this my way; when the day is over Iíll know what the experimental result was,Ē and we did it with separated beams, the toughest way of all. Separated beams, single velocities — we broke it up.

The reason I picked sodium, first of all, was this question of the spin of sodium. (F. W.) Loomis and (R. W. Wood had done an experiment Phys. Rev., 1928) on band spectra and they said there was none; Harold Urey took the published spectrum, the printed thing, and photographed it, put it through the machine and you saw that there were alternating intensities. So I was going to do it to further convince myself that there was a spin, which we did; and then it went on from there, becoming more and more fascinating, as one went on. But thatís more or less how it came about.

Kuhn:

From that point on really, or from the early Ď30ís on, we can now look back and say you had made the transition to nuclear physics. Did you think of this as a transition at the time?

Rabi:

It was this way. The atomic thing was over.

Kuhn:

Was this clear? Did you deliberately say, ďThereís nothing more to do hereĒ?

Rabi:

Yes, I was using the atom all along, as I say, as my laboratory to study the nucleus and in whatever we did there were so many by-paths to which we could have devoted ourselves but which were more chemistry. For example, we had worked on scattering of atoms by atoms and so on, gas scattering, which was really fascinating in a way because of the difference between this and classical scattering which would show up. And, of course, when you do molecules, you go into all sorts of molecular properties so you have to really restrain yourself to keep your eye on the ball and keep on inventing methods and techniques to state what was the interesting nuclear property; you had to stay focused and most people Who started on it would wander off from the basic physical question. I felt at that time that that was the highroad for the important information of that time. I could do with this.

Kuhn:

You say when you first built the apparatus you were thinking about meta-stable neon or something of the sort?

Rabi:

Yes, the first experiments were for meta-stable neonís.

Kuhn:

Can you at all date the period in which you sort of said, ďThe atomís done; from here on we have to stick to the nucleus to keep from being dragged outĒ?

Rabi:

Letís see —- I got back in Ď29. When was that paper Breit and I published? I would say it was in that time.

Kuhn:

Ď31

Rabi:

That was it; I think it was then. We knew what was going on. Those were years of a lot of atomic stuff. I was never one like (Castler), for example, who invented this popping. And they keep on demonstrating one thing after another (???) theory, and I wasnít interested in that. I was interested in using this to find and to define things as r as we could. When I did lithium 877 I wanted both isotopes to see the effects, to see if I could get something with a different number of neutrons. I knew that this data must be useful; the theory wasnít there at that time. We had to accumulate data and look at it and see what it did. Of course, somewhere in between there, in Ď33, came Sternís experiment on the hydrogen, the proton with its anomalous moment, which really was a tremendous discovery, and then the deuteron, and then it was clear. It was clear anyway, but this really showed that there as really. hot stuff there.

Of course, I could have gone into another branch with neutrons and so on, but on the other hand, that was more or less preempted by Dean (G.B) Pegran and his group. Besides, it had a tremendous fascination for me and for everyone of my students who has been in it. Norman Ramsey and his crowd. Once you start this thing itís exact, the experiments are beautiful, there are tricks you can play; itís difficult in some ways, but it has a tremendous charm and so once youíre in it —-. But you do have to keep your resolution going not to be (pushed)off; it was so easy to turn that into chemistry —- surface chemistry, collision things and things of that sort whereas to stay with the nucleus you had a different sort of problem, so to speak, with each one.

Kuhn:

Let me take you back to Europe, briefly or not so briefly, I donít know how it will work. Iíd like it if you could talk impressionistically or with episodes about some of the differences you felt between the places you visited there, differences in the nature of the interest, the nature of the problems, in the emphasis on the relation of theory or experiment, what you will.

Rabi:

Yes, they differ so much from place to place. In Copenhagen I donít think I ever saw the experiment, but I never was in the in-group in Copenhagen.

Kuhn:

That was an important distinction, in-group and out-group?

Rabi:

I rather think so; I mean, they were at Bohrís house or at his summer place and that sort of thing, so I canít speak very much about it, except of a certain spirit which I felt there, which wouldnít dare to be trivial. Somehow or other one just want to work there and you had the feeling Ďif you stayed there you had to think of really significant things. At Hamburg

Kuhn:

You were there in the fall of Ď27, right after the Como Conference, right after the Solvay Conference, where the interpretation issues were so alive and Bohr must have been deeply involved in measurement problems.

Rabi:

Well, it was over, and I think (I saw not very much).

Kuhn:

You saw nothing of that?

Rabi:

Well, it was done. I knew the results and so on. I had no problems in connection with it; they came earlier. Bohr had wonderful ways of putting it, this way and that way, but it was —- maybe I donít understand it to this day well enough to feel that it needed all that amplification that Bohr gave it and he certainly did. Actually I didnít know anybody in Copenhagen. Kronig behaved very badly to me because he paid me no attention whatsoever, I think I was an ugly duckling; here Iíd showed up without anything and heíd been there, he was known, and he was afraid somehow that Iíd give him a bad name although heíd been to our house and we were good friends at Columbia. I saw no trace of him at all while we were there; he didnít call on us or anything nothing. Bohr himself was much nicer.

Oskar Klein, again, was not in the least friendly. I think I was just barely tolerated and then shipped off and it may have been Well, Kronig was very bitter about America and he used to speak of it in the most derogatory way, lie said, ďI once was a professor there and it doesnít mean anything,Ē and that sort of thing. And, of course, there was such a feeling in Europe. In GŲttingen they subscribed to the twelve issues of the Physical Review but waited until the end of the year to get th1em all at once so as to save postage. Unsold had a fellowship to go to Caltech and he was inquiring in German fashion about what he should wear, where he should live, how he should behave, whom he should see, and on and on. And Sommerfeld finally said, ďNehmen Sie das nicht so ernst; das Leben in Amerika ist gar nicht so schwer. Da wird jeder junge Mann eim Assistant Professor.Ē Weíd had a very dumb guy from Columbia, (Cranford), who had some private funds and went and hung on to (Kronig) and gave Americans a bad name. We were not highly regarded, I must say, nor was there any thought that America would amount to anything as far as physics was concerned. There were a few people, certainly, but one looked down their noses on Americans. Oh, there were a few exceptions, in favor of Americans here and there, but mostly they were looked down on.

We felt very bad about this. Ed Condon and I talked about it and we said, ďWeíre going to really do something, very definitely, in our generation,Ē and we did because ten years later the Physical Review was the leading journal in the world. But nobody would have guessed in 1927 that this would happen because we had a latent time bomb. We had a lot of students in these universities, all getting a lot of education but no leadership; and when we came back, my generation, Condom, Robertson, Oppenheimer, myself, and then people like Van, sort of mature enough to get students, we just sort of changed the whole works in this short time. I had half the graduate students in the department at the time I was an assistant professor. We sort of brought back the white manís magic, so to speak. Thatís the kind of spirit there was. Of course, when I came to Hamburg that was different. I already had, in a certain sense, this introduction: I was with Nishina, I got along quite well with Pauli, which is remarkable, and there were Fraser and Taylor; so things were much better there and, of course, there was Walter Gordon who became very friendly. These were bachelors and it was a different thing, so I really got into the swing of things more there. Now, about comparisons. There was no question that any student of physics could get a hell of a lot better education at Columbia up to, letís say, final work for the Doctorís degree, a much better education at Columbia than you could at Hamburg or any German university.

Kuhn:

Even Munich?

Rabi:

I say up to latter part of graduate work. At Munich they had Sommerfeld and the seminar, Sommerfeld was a wonderful man, very slow witted, beautiful lectures, grand lectures —- slow witted so that by the time he understood it, everybody else did. This was really pretty solid. Of course, it was smaller; Sommerfeld had only two or three graduate students. The lectures were marvelous. The full professors gave marvelous lectures. They were paid for it with extra pay and I think it worked very well. But I would say in physics, of the students I saw around Stern, any one of our better students could have run away from them, in experiments, in certain difficulties in technique and what not, and in basic education. They didnít quip know what to do, so to speak, but, of course, these boys didnít either; Stern told them what to do. I think the same thing was true in Gottingen. In America we had the absence of great men, of leaders of this sort, and some of those we had were kind of primitives like Bergen Davis, who was brilliant in some ways; he knew very little physics, but he used a lot of it and, so on and he did some very important work. He made some awful mistakes, too. But it was already clear to me then that our system was a lot better for us as a system; what we needed were the leaders. The general democracy which we had allowed young people to come forward, and you couldnít say it had the tinges the French had with French physics: there wasnít the kind of back-biting and fighting for position that there was there. In Leipzig there was the great Debye who was just a prima donna and would show off to his seminar because he was good in theory and so on, and brilliant, and the rest —- I donít know whether they were repressed or just not very good —- would sort of nod their heads. The theoretical one run by Heisenberg was a delight. There was a real free camaraderie; he had a seminar where a paper was presented and after that, there was ping-pong, coffee and cakes; it was a real friendly thing. But to show the example of what had already happened to German physics in 1928, the seminar in Berlin had invited the seminar in Leipzig for a visit. This was fully supported by the Saxon government, since Leipzig was in 939 Saxony, and they paid for the fare and for hotels in addition to which they gave each man 10 marks extra to have a good time. We were received there one evening in Berlin-Dahlem at the Kaiser-Wilhelm Institute: Poland, Haber, and so on. Of the group that went from Leipzig there was only one German, Heisenberg.

Kuhn:

Really!

Rabi:

Only one German, Heisenberg himself. Otherwise there were Americans, the largest number, and then there were Austrians, Hungarians, — Teller was there —- a Bulgarian, a Chinese, and some others, maybe 10 or 12, and only one German.

Kuhn:

Why is that? What had happened?

Rabi:

The intellectual interest in Germany was going down very rapidly. There at Hamburg, with Pauli and everything else, there was only one graduate student who is now Prof. Jensen. and just got the Nobel prize; he had just come along, just a beginning graduate student. Only one! All these great men there!

Kuhn:

This I hadnít realized. It comes as a great surprise to me.

Rabi:

I donít think itís generally known somehow, but this is what I saw. In Gottingen, now, I donít know; I wasnít there so I donít know how many they had, but very few. In other words, they were producing a few people; those who went through and were refined became good, very well educated. But we sent through a whole mass of people and itís true our tops were not as good as theirs, but we just had a hell of a lot and in time our tops were better. There just wasnít anybody in Europe after that as good as Julian Schwinger, for example, or Feynman and so on, who came Out of our general system, so we had the makings of it, given the leadership. And the leadership had to be American. You couldnít get ĎHasenpfefferí and so on; you had to have somebody who could say, ďNow look here, old sock, itís this way; one of our boys can do it,Ē and so on. It was true in the Ď30ís that the people, the refugees, didnít contribute very much, except for their own persons; Hans Bethe had no students, nor did Weisskopf, and Teller, I think, had one man. It was after the war when they had become fairly acclimatized that they made a great contribution, but we had already had the numbers before. Thatís a very interesting point in the sociology of it. Another point is that there was a complete separation between the experimenters, letís say under Debye, and the theorists working with Heisenberg. They didnít see anything of one another and there was practically no cross- fertilization. There was a little more connection in Zurich because Scherrer and Pauli were good friends, a little more; they used to go out on picnics together and things of that sort.

Kuhn:

How about Hamburg?

Rabi:

In Hamburg there wasnít a heck of a lot in experiment except Stern; Sternís experiments were very close to theory. Stern himself had been a professor of theoretical physics; prior to this he had been a professor of physical chemistry. Actually his professorship in Hamburg was physical chemistry but he didnít care much about titles at that point. He was an expert in thermodynamics. So that was the interesting physics in Sternís place and, of course, altogether with Pauli and so on, there was no question; there it was completely integrated, there was no difference. The other kind of work that was done there was a kind of spectroscopy, chiefly exact spectroscopy, intensity measurements by [Peter Paul] Koch kind of straightforward pedestrian work, good, solid. Heíd been a Roetgen assistant. I never did stay in GŲttingen long enough. In Munich I never even saw a sign of an experiment or even heard of it.

Kuhn:

That had classically been bad and apparently for some years the relation between Wien and Sommerfeld was very bad.

Rabi:

I met Willy Wien and he told me an extraordinary thing; he said that [H.A.] Rowland had solved the problem of radiation from the dipole before Heinrich Hertz in a clumsy way, he said, but heíd done it. Iíve never seen a publication on it but thatís what he told me; he may have been anti-Semitic or something, I donít know, but I doubt it. Those are about the only universities I can comment on. I never stayed at Berlin for any time. I had many ideas for experiments which I would discuss with some of the theorists around, fantastic people who had no idea what experiment was. Youíd tell them about something which might be extraordinarily difficult and which one could do in five years, and three weeks later youíd see someone and HeĎd say, ďDo you have any results?Ē

Kuhn:

Do you think that situation was better over here, the relation between theory and experiment?

Rabi:

Oh, yes. We had no theorists because we were more unified. Itís more the Anglo-Saxon tradition which we changed. It depends on what you work on; I mean, even Maxwell was not so hot in experiment, but he was doing them all the time, or J.J.[Thomson] all of them, in that sense. Dirac was a great exception, but he was just so preoccupied. I think this sharp separation we see now is the disaster of the German infiltration; of course in Germany one could characterize it almost by saying that the theorists could barely We were talking about coming to Columbia.

Kuhn:

Well, letís do just a little bit more with Europe first. You were in Europe two years, and during those two years I would say really, except for the problems that grow into field theory, most of these problems, from a modern point of view, get pretty well solved, as to basic principles, right during that period.

Rabi:

Yes, the quantum electrodynamics, the outlines and so on, was basically done; the molecular structure and the atomic structure, helium and so on and the resonance, were done; the Dirac theory of the electron was in; the holes were not fully understood.

Kuhn:

The whole idea hadnít been suggested yet.

Rabi:

Well, around that time. I think it had been, yes, surely.

Kuhn:

The problem of negative energy states was there; I think the hole theory you donít get until later.

Rabi:

No, natural hole theory didnít come till later but that the holes were positive was understood. It wasnít clear whether they were protons or electrons. Then it was thought that it might be the protons; in other words, the positron as such was far from understood; it was not really understood, I think, until after it happened. Letís see, what else was there?

Kuhn:

Well, theory of solids also, the theory of conduction and the theory of solid states.

Rabi:

Yes, theory of solid states had been well started beginning with the rudiments of the theory of conduction by Sommerfeld, the further advance by Bloch; those functions had been done. Yes, some of the elements of what held solids together; the ferromagnetism in a certain sense had been in principle sort of put down by Heisenberg. Yes, I think itís fair to say that this was clear and everybody was beginning to think it more or less. The uc1ear physics, the nucleus was the next thing. Even before I left, Heisenberg and so on were getting after the people working with nuclear physics, Meitner and so on, beginning to press them and question them, and others.

Kuhn:

You spoke before of Ted Kembleís saying at the British Association meeting, ďTheyíre just going to grind it out; it isnít exciting anymore.Ē Iíd be grateful for any sort of an elaboration, recollection of conversations or of things that were being said about ďitís washed up; letís get to the nuc1eus or about people who didnít feel this way.

Rabi:

I couldnít give you chapter and verse at all. I do know that people like Heisenberg and so on were beginning to talk about the nucleus around 1929 and late Ď28, even though they might still have been working on something else, and to say that this was coming. Sternís experiments were preparation, you see, for something of that sort. Just a bigger interest was developing in that direction; the mystery of the beta was beginning to sink in, the mystery of the beta spectrum.

Kuhn:

Where did you hear that talked about?

Rabi:

I canít really tell you. We knew, we talked about it wherever I went, but I canít tell you who in the sense of assigning particular credit.

Kuhn:

I had less a question of credit in mind than sort of where these issues were live.

Rabi:

I was moving only in the very top circles at that time, from being a lowly graduate student at Columbia who was even turned down for an assistantship, and then going to Europe and being around with the top people; and thatís what they would be doing, and people would be coming through. Some of these things, one just knew, thatís all. It was part of the general gossip. Letís see, when was Condon-Gurney? Wasnít that Ď28-í29, or was it after that?

Kuhn:

I think itís a little later but Iím really not quite sure. Itís all sort of confused for me when it happened; I think it happened while I was there.

Rabi:

Things were coming that way. There was that sense that the mystery was going out of it; all sorts of stuff was happening. I myself, I must say, never felt that we were nearing the end of anything but that was always because of my philosophical orientation, not because of these events. My philosophical orientation had always been that physics is just the end of the road, the borderline between all the rest and philosophy. If you think of the philosophical problem of matter becoming conscious of itself, that canít come to an end unless it comes to an end because of paucity of means of further investigation. And that I donít believe either — that we will essentially be stopped because we havenít got the means. So these other 087 statements of Bornís and so on I only felt were a lack of cultivation. But Iíll tell you this: almost without exception the greatest scientists Iíve known have felt that it would come to an end, that there would be a closure. I believe itís even true of Einstein.

Kuhn:

I didnít know heíd felt that. I knew of a number of others who had.

Rabi:

Yes, and thatís what they were looking for, a comprehensive theory. Well, if youíre looking for a comprehensive theory, of course, thatís got to end it, but I just donít think that will ever happen and itís only a theoretical physicist, a man who concentrates on that, who gets this megalomania; I donít see how an experimental physicist could ever believe it.

Kuhn:

I think the thing to do now is to come back to Columbia about which weíve already talked a good deal concerning the period which most interests me. You talked about talking in Europe with Condon about this sense that ďweíve got to change the American situation.Ē You havenít really told me how you got back to Columbia. Were there other places?

Rabi:

No, I didnít have any job at all. It was in April and my father was in the real estate business, he owned some houses, and I expected that I would come back, I had no job I hadnít written a single letter -, and I would join him in this and continue as well as I could; because more than most I was also interested in physics, whether I did it or somebody else. And one day, like a bolt out of the blue, I had the offer of a lectureship from Columbia for $3,000., which was a sum beyond the dreams of avarice to me at that time. They said, ďDonít bother to telegraph, just writeĒ; well, I telegraphed. This with a baby coming too. So thatís what happened; thatís all there was to it. Actually what I think happened was that it had been offered to Kronig who turned it down; he left America because he didnít find it inspiring enough: heís a man who sold Xerox at five. And then Francis Slack, I think, didnít want to live in New York and went to Vanderbilt, so I was next. They could have offered it to Ernest Lawrence who made a bad impression somehow; he was too bombastic for them. So then I came to teach theoretical physics. I had no other offer so that was that. Iím quite sure, from the friends Iíve made, although I didnít realize it, that I nevertheless would have had a pretty good job after I came back if I werenít caught by the depression at that moment, you see. A year later Iíd have been out of luck. There just werenít any jobs. There was an intent to bring the department up to. European standards; they made offers to Einstein and to all sorts of people.

Kuhn:

Who led in that?

Rabi:

I think probably [George B.] Pegran; there was nobody else to lead in it.

Kuhn:

Well now, Pegran was by no means new there, so this is really a transition in general awareness of Columbia thatís occurred in the years youíve been away.

Rabi:

No, no; theyíd tried before through the years. Columbia had for years tried to get a theoretical physicist and never succeeded. Way back they got ?4ac1aurin who was a New Zealander; Pegran brought him actually and he was a professor of thoretica1 physics, but he was promised that he would not teach Ďundergraduates but then when some professor was away he was asked to do it and he got into a fight with [Pres. N.M.] Butler. When the presidency of MIT was vacant, one day they got a letter from Professor Maclaurin applying for the position. This was a joke, but it was followed up by some pretty strong testimonials, Since MIT was about to close anyway because of lack of funds and otherwise, he got the job. The reason he applied was that in British countries you apply for jobs. But thatís about the last attempt they had, Then there were the famous Lorentz lectures on theoretical physics which were given at Columbia and from which the theory of the electrons came, and others. They tried but they never succeeded in getting a theoretical physicist actually until after the war. They had Fermi, of course, but Fermi didnít do theory, he did experiments, and itís true of almost every theoretical physicist weíve had here. I brought Willis Lamb, a pure theorist, an Oppenheimer student, and he got the Nobel Prize for experiments. Itís only recently that we Ďye had enough of them so that they sort of worked on one another, but they turn experimenters.

Kuhn:

Why is that? I mean, thatís not been typical everywhere.

Rabi:

No. Well, first, a lot of it is my influence. I just donít believe in the bifurcation, During the Ď30ís Szilard was here; Szilard used to come to my office almost every other day with an idea of an experiment for me to do, and I determined that I would never do an experiment that Szilard suggested Why shouldnít I have my own fun? I said, ďNow look here, Leo; I will get you all the apparatus you need; I will get you an assistant, space and everything you want. Do this experiment. Itís a beautiful thought.Ē But, of course, he wouldnít, and a lot of things he suggested then were later done by others. He was a very bright guy, but he just wouldnít. Now Willis Lamb had this idea for this experiment and I said, ďO.K., Willis,Ē I got him an assistant, a really very highly paid man for then, a man who had worked with me and we paid him the same salary as we paid an assistant professor, $6,000. That was Retherford, who worked together with him. Yes, itís a special Columbia knack. Our experimental people didnít need any theorists to help them and I always stood strongly against employing theorist just because he might be useful to experimenters. Ever since then Iíve said: ďWhat you fellows really are talking about is getting a man who will be a director of research without getting credit for it. What sort of physicists are you anyway, if you have to go to a theorist to tell you what to do in some places and after youíve done it, to have to go to the theorist to tell you what youíve done?Ē So we were specials in that way, really.

Kuhn:

To what extent did you have yourself, coming back from Europe, some feeling that reorganization was needed, effort were needed, or were you simply there now to do your own job?

Rabi:

Oh, no. I was all over the place as soon as I came back; you see, thatís the kind of person I am, and it made a very big difference. Suddenly the whole damn department started working hard whereas they hadnít before. They said, ďGoddamn it, Rabi, before you came here we used to have three hours for lunch and play bridgeĒ

Kuhn:

What sort of things did you try to do?

Rabi:

Just talk to people who were there all the time; I think I made life interesting from the scientific point of view. It was interesting these wonderful new ideas then began to be ventilated; Iíd give a course, Iíd talk about them to students and professors and so on; just that. No, I didnít reorganize anything. Of course, I had the great protection of (Pegran). When I came back I taught two hours a week and some full professors taught fourteen: I taught standard stuff. I gave statistical mechanics and then in the course of time I gave quantum mechanics and every course in the place. But it was that sort of thing polling what the ideas were, possibilities, talking about physics just for fun in this way, what one may do, what we would find out, ideas for experiments, meanings, how paradoxes are explained, what quantum theory means in this situation or that situation. People just got very interested.

Kuhn:

Who else were the particular participants in this new vitality?

Rabi:

Oh, just the new people that they had made except that old Professor [A.P.] Wills suddenly began to come and work nights and it pretty nearly killed him; he got sick, Then there were the people that were produced and the new students, John Dunning, a new graduate student when I came back. We had a seminar. We didnít have any new people for a time o the result was that at one time I had half the students in the department and half the money. Oh, we just had a great time, the students and I. We worked every day of the year with the exception of three or four days, New Yearís Day and Christmas day and so on. It was just real fun. To show you the difference in styles, Jerrold Zacharias was an assistant professor at Hunter College; he was an instructor, an assistant professor, and taught the regular sixteen hours a week plus the committee work that a man does. In addition to that, as a privilege, he put in about sixty hours a week at Columbia. That sort of thing.

Carl Frische, now the president of Sperry Gyroscope, was my research assistant, whom I got some money from later, $1500 bucks, married and a child. People just worked. There was Jerry Kellogg. It was just great fun. In experiments the meaning just has a novelty and charm of its own, no matter how many times you you've seen them and itís great. We didnít have any new appointments at Columbia for some time. If I wanted to talk physics afterwards, it was either with Gregory Breit or Iíd go to Princeton and speak with Ed Condon and Bob Robertson. We went back and forth a great deal; that is, theyíd come here and so on, and a number of us began to form a coterie; we would come and go and so on. Itís the kind of clique that hits a field, you know; we were so to speak. We were young people. We may not have had much in the way of grade, but we were it. There was no question/about it?; thatís where people came. So we were kind of a self-appointed elite just communicating with one another, but people knew what was happening. true I didnít publish anything —- I told you about that other work but that was the great thing about Columbia; there was no such thing. I know I was offered a promotion. The first year I didnít publish anything and became an assistant professor; then they wanted to promote me and I said, ďNo, please donít; wait until I do something!" because I was having a big influence within the department, that was clear, and on other departments. Urey just came at the same time from Johns Hopkins and we had a group of people that could talk about things and keep it alive and exciting. Yes, thatís Ď31. No, I think there was something before Ď31, maybe, but I donít remember. You ask here [in the questionnaire] whether the quantum theory was worked out. I did not feel and donít feel now that itís worked out and it really

Kuhn:

You did feel, though, that the quantum theory of the atom was worked out.

Rabi:

Not that it was worked out but that it required the further kind of work which was not the kind of work I wanted to do and I think itís a very rich field now for a certain kind of fellow. Because ever since Thomas and Fermi quit the atom for some of this other work with machines, we havenít gone further in understanding the atom, which is a great pity. Became if you regard the atom as a laboratory in which to do experiments you can get electrons in close contact for a long time, for example, investigate nuclear properties and things of that sort there is a tremendous amount of information still available. We donít have this theory yet of a single atom, not even hydrogen quite, and certainly not41euterium, so it isnít worked out by any manner of means. Oh, yes, Diracís hole theory and Pauliís neutrino hypothesis, Pauliís visit to the United States. We went to this little Chinese restaurant on Broadway down the street there and he told me about this.

Kuhn:

125th Street?

Rabi:

No, itís about 121st, 22nd or 23rd, before the Jewish Theological Seminary was built. I donít remember where, but it was around there in a basement. The question was whether to publish this or not. ďI think Iíll be cleverer than Dirac,Ē he said, ďI wonít.Ē He meant Diracís magnetic pole theory. H donít think Iíll publish it.Ē I urged him to publish it. He gave a talk about it but I donít think he ever did publish it; he gave a talk about it in Berkeley.

Kuhn:

Did you get involved with these pob1ems hole theory — at all yourself?

Rabi:

No, never, only by following. I was close to it in the sense of following it and seeing that papers on it were given in the seminar. I had a little paper, hardly more than a letter, on neutron scattering in the Physica1 Review in the early thirties, I think. I had something of the 1ectroa-neutron interaction post-war. Gregory Breit and I published a letter on nuclear structure, a premature letter. He had a tendency to close off a subject and turn to something else before it was closed off and thatís been his great weakness all along; otherwise he would really have had the recognition for much more than he has. No, I donít think so. No, I was really very busy; once I got going on those experiments, this was a day and night job, all the time. I had about fifteen students to keep going.