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Interview of Robert Marshak by Charles Weiner on 1970 June 15, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4760-1
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Childhood and early education in New York, undergraduate education in philosophy at Columbia College, 1932-1936; years of graduate study in physics at Columbia University, 1936-1937; influence of Isidor I. Rabi, the joint NYU-Columbia seminar in physics; transfer to Cornell University for graduate work in nuclear physics, 1937-1939; influence of Hans Bethe; thesis work on white dwarfs; first teaching position at University of Rochester, joint work with Victor Weisskopf in nuclear physics and particles; remarks on war years, astrophysics, cyclotrons, and other matters; Shelter Island Conferences. Formation of the Federation of American Scientists (F.A.S.) in 1946; Marshak succeeds Robert Wilson as Chairman, 1947. World Federation of Scientific workers, chaired by Frédéric Joliot-Curie, wants to enroll F.A.S. (1947, in Paris meeting). Marshak's work on two-meson theory. F.A.S. issues in the 1950s; the Emergency Committee and F.A.S.; Einstein's interests and views on relation of science to society; comments on J. Robert Oppenheimer; chairmanship at University of Rochester; Lee DuBridge; long-range plan and extensive development of physics department funded through AEC contracts; training of students from abroad such as Okubo, Sudarshan, Messiah, Regge. Last half of interview covers the Rochester conferences. Scientific work during the 1950s, the V-A interaction (George Sudarshan) theory (a.k.a. Feynman-Gell-Mann theory of weak interactions); books and works with graduate students. Travels to Europe and India (Tata Institute), 1953. Accepts City College (CUNY) presidency; reasons for leaving University of Rochester. Also prominently mentioned are: Robert Fox Bacher, Subrahmanyan Chandrasekhar, George Braxton Pegram, Julian R. Schwinger, Edward Teller; Lawrence Radiation Laboratory, and Massachusetts Institute of Technology Radiation Laboratory.
This is an interview with Professor Robert E. Marshak conducted by Charles Weiner, and today is June 15, 1970. We’re sitting in Professor Marshak’s office in Rochester. I’d like to start at the very very beginning and even before the beginning. I know that you were born in New York City in 1916, but I know nothing at all about your family background, where you lived in New York, your home life, family occupation, the kind of home, whether you had brothers and sisters, neighborhood experiences and, in a sense, your childhood.
Oh, that’s quite an undertaking. We all have a long childhood. Well, I lived in the Bronx. I was born in the east Bronx near a park called Crotona Park, and I believe that I was actually residing on Boston Road near Prospect Avenue for perhaps the first year of my life. Of course, I do not remember that. But we soon moved several blocks from that rather busy thoroughfare to a side street which was called Bristow Street. I believe it was 1384 Bristow Street. This was a quiet street with trees, about three of four blocks long, chiefly with private homes but with one apartment house sort of in the middle of the street and we lived in that apartment house. My parents were always broke. I remember that we had a six-room apartment in that apartment house and that my family, in order to make ends meet, had two boarders. Two of the bedrooms were rented out, and the two boarders — I think they were women — used to pay for the rooms and also eat dinner at night and so on. My dad came to the United States about 1907. It was a year or two after the 1905 revolution, when many Jews in Russia at that time decided that life would probably become more difficult. He had experienced the pogroms and the discrimination, and he thought that when Russia lost the Russo-Japanese War in 1905, the setting up of the Duma would lead to reforms. But it soon became clear that these hopes were short-lived, and there was a huge emigration in those years of Russian Jews. And my father and my mother, who did not know each other in Russia, left during that period. I think my father came to the United States in 1907; and my mother came in 1910. My father came from a town called Minsk in White Russia.
My father came at the same time from the same town.
Really? Maybe they knew each other. My mother came from a little town called Berezina, which is on the Berezina River not too far from Minsk. They met in the United States, and they were married in 1916 — January 1st, 1916. I was born October 11th, 1916, so I was the first son. My father learned a trade after he came to the country, after trying several other trades with some cousins who brought him here. As usual in those emigrations, some pioneering soul would come here first to try to get a job, earn enough extra money to try to pay the fares of brothers and sisters and start bringing in the family; and they in turn would bring cousins and aunts and uncles; and, in the case of my father, there were some cousins who came a few years earlier and went -into the fruit peddling business They tried to train my father in that type of job, but he wasn’t too good at it, and finally he learned how to be a garment cutter. Although I might say that during the Depression Years or whenever he was unemployed as a cutter, — even at the best of times the garment trade was seasonal, so there were many months during the year when there was no work even during a “good” year - he would go back, to fruit peddling with horse and wagon to supplement the family income. Well, my father never did too well in any of his jobs although he was a very hard—working person. [He is still living, age 83, and is now here in Rochester in the Jewish Home for the Aged.] That is to say, he was not in any way lazy. He just had not received sufficient training in Russia, where he was confined to the ghetto and could not go to a Russian school but instead went to a Hebrew school. So he was actually fairly well informed about the Talmud and so on; always had very great respect for learning and education; and always encouraged me to work hard at being a student. Just as an illustration, I remember that he would get up earlier than necessary, at four o’clock in the morning during the time that he was a fruit peddler to go to the wholesale market — he would get up fifteen minutes earlier to polish my shoes, because he argued that I would then have more time for my studies. Also, he refused to let me work during the summers as a child or even, say, work in a neighborhood grocery store to earn some extra money, because he argued that I should be a student. So in that sense I had very strong encouragement from my parents as far as school was concerned.
Did this result from your showing any early promise? Was that part of it?
Perhaps. There is a story, for example, about a cousin on my mother’s side who actually had gone to night school in engineering and had obtained a pretty good job as an engineer with the Board of Education in New York City. He was the educated man in the family, and apparently he told my father when I was very young that I had mathematical talent because somehow I could tell time or what have you. This was the story that my father told me. So I guess there was an early indication that I might do well at studies. And actually in elementary school I did do well in the sense that I did skip six times and did the eight years in five years; and I guess that led my parents to further do everything they could to encourage my studying, In that sense the home environment was not making the demands that it might normally make on a youngster whose, parents are extremely poor. That’s part of the early situation. Now, I have two younger sisters: one two years younger and another one six years younger. The older of the two was not a particularly good student, but the younger one was quite a good student. But the trouble was the Depression Years hit us as well as millions of other families in the sense that the normal seasonal work was reduced to zero say by 1929-’30 when I was 13 years old and my one sister was 11 and the other one was only seven.
And the only way then to start to develop some income was for my mother to go to work. Until that point she had been working hard as a mother with three children and taking care of a household with two boarders. But at that point there simply was no work for cutters. And the reason was that the ILGWU — to which my father belonged — had become quite a strong union in New York City and because of the Depression Years the owners of the small garment shops in New York City subcontracted in New Jersey for the material to be cut for sewing. And so the strong New York Cutter’s Union was bypassed by having the stuff cut in New Jersey and brought back to New York to be sewed. So those who were so-called operators, which meant they could sew, had some opportunities for work in New York. And this meant chiefly women. So there was a sort of general drift of women moving in and taking on jobs in the clothing industry in the Depression years, and that happened in our family, so that my mother became the chief wage earner, and my father was reduced to fruit peddling, taking care of the house and doing some of the cooking and so on. Those were difficult years, particularly for my younger sisters, and the youngest one always says that she remembers those years with considerable unhappiness. When the Depression started, I was 13 years old. In January 1932 I was graduated from high school. We’ll come to that in a moment. And so I entered the Depression years, went to college, and developed my own independent life as a student. But my sisters, and chiefly the youngest one, lived through a very dismal period at that time. Thus my years, you might say, as a youngster were rather happy years. When my mother started working, we moved to Crotona Park East, into a smaller apartment, because it was too difficult for my mother to take care of the large household in Bristow Street.
How old was she at about this time? I gather she was in her forties.
Let’s see: there was a seven-year age difference... She was seven years younger than my father. She’s 76 now in 1970. Let’s get back to 1930, 40 years ago. She was 36, 35.
What about your parents’ learning English? Did this take a while? Did you speak Yiddish at home or Russian or...?
We spoke Yiddish at home. I would say my mother made a greater effort to acclimate to the U.S. She was the one who, when she first came over, went to evening classes to learn English, and she knew English better than my father and could write in English — not too well but to some extent. My father to this day can hardly write an English letter. He writes Yiddish letters to me, but to my sisters he writes in very poor English misspellings and so on. My father claims that he had such a hard time trying to learn a trade that he had no time to study English, and that’s true. But I do feel that my mother felt that she should learn the language and felt more strongly about it than my father ever did. He thought he could continue living with his old Yiddish culture in the United States and not have to participate quite so directly in American society.
The old traditions were fostered in the community, I assume. Were you part of a Jewish community?
You mean where we lived?
No, actually, curiously enough, during the first 13 years of my life our neighborhood was not dominantly Jewish. It was about half and half. Many of the private homes were inhabited by non-Jewish groups. I remember many snowball fights between the Jewish kids and the non-Jewish kids and other evidence of petty antagonisms. Some blocks away, the main thoroughfare, Boston Road, was more predominantly Jewish. But this quiet street was mixed.
How would this reflect in the home as far as the reading materials around the house? Was there any collection of books that was part of your family reading?
Well, yes. My parents read Yiddish newspapers assiduously and kept well-informed on current events. They read Yiddish books occasionally. And I went to Hebrew school for a few years. But I was so interested in my own regular studies that I didn’t get too excited about the traditional Hebrew studies. I studied Hebrew for a few years and Yiddish. But when I didn’t want to devote a large chunk of my time to these studies, my father did not insist. He said: “Okay, you stay with your regular studies.” I did have a Bar Mitzvah, but by that time I was not going to Hebrew school, and so I had some months of instruction with a Rabbi to prepare for the Bar Mitzvah. But after the Bar Mitzvah there were no further “religious” demands made on me. As a matter of fact, in later years both of my parents lost much of their religious interest. They maintained their interest in Jewish cultural activities, and belonged to various fraternal groups in which they would hear Jewish concerts, and so on. But they did not go regularly to synagogue.
But you went at least in terms of special holidays?
I don’t remember really going very much, even on special holidays. This was additional beyond the Hebrew school, and I was busy with my studies, and my father never insisted. But I don’t remember very distinctly going with my father, say, to Friday evening services or anything like that, I had work to do.
I was thinking of Rosh Hashanah or something like that where there would be a kind of community activity.
There was substantial independence of spirit on the part of members of the family. For one thing, because of our poverty, my parents did not belong to a Temple, as middle class Jewish groups normally do. My father was more involved, and during my youth would go to synagogue on high holidays with his cousins - for a specified fee. My mother did not go since women were segregated at orthodox synagogues and she was not eager to go in view of her many household chores. Certainly there was no demand on the children to go.
You had sisters, but they were different in age; so that in the community you had friends either from school or from the neighborhood.
That’s right. There were kids on the block. You played with them.
Did anyone share your interests at all? You talked about your interest in work. That’s my next category of questions — you mentioned your interest in studies and the normal grade school work. But in addition to that, were you developing any special orientation? Were you developing any special hobbies that you recall?
Well, in a sense I guess my studies were really my chief and overriding interest. I found enough excitement in learning more and more about the “standard subjects” and that pretty much occupied my time. I know my parents made a short-lived attempt to train me as a violinist, because a cousin of mine was a pretty good violinist; and I could get lessons either free or very inexpensively. He lived at that time far away on 101st Street in East Manhattan. I remember making trips, to take those violin lessons. But I had two serious illnesses as a child which sort of cut out any special hobbies like that. I. think my first illness led to my dropping the violin lessons apart from the fact that I was not too talented. I had pneumonia when I was in the seventh grade; and then I had bronchitis when I was in the ninth grade. As a result, extra-curricular activities sort of died on the vine. I do not remember engaging in any extra-curricular activities in elementary school except keeping busy at skipping grades.
In spite of the sicknesses, you still were able to skip?
Yes. But in high school I participated in many extra-curricular activities.
Before we get on that, what about the summers? Did the family take vacations?
Well, there again, until the age of 15 when I finished high school, I did not have a summer job; and the general idea was that the family would go away for the summer and get very inexpensive accommodations. I remember my mother renting a cottage or a large room with some cooking facilities and the rent was $35 for the summer. My mother was a very adept housekeeper and could cook and could take care of housekeeping chores very well. And the idea was always to send the family off for the summer. It was healthful for the family and a very inexpensive set-up, and I was on my own to do my reading in whatever I pleased. And I spent most of the summer reading in either math or literature or philosophy or what have you.
Even at the grade school level?
Yes. My father would work during the summer. In my youth, up to the age of 13, he essentially had a steady job, and summer was the time when you worked in the clothing industry as a cutter. So he would work during the summer and come out for a few weekends, but the rest of the family would enjoy the great outdoors.
The Catskills or...?
Well, all over — wherever there seemed to be some pleasant and inexpensive arrangement. I remember being in Connecticut one summer, near Durham, Connecticut — or the Catskills, mostly the Catskills: Mountaindale, Ellenville, Woodridge, you name it: the Jewish Catskills.
The Jewish Alps. Now we’re getting to high school.
Well, the, high school was James Monroe High School, which was located in what was then a new section of the Bronx. James Monroe was in a neighborhood which had many good homes, private homes — a sort of suburban area in those days. It entered high school in 1929. Actually, the first year — my sophomore year — I did not go to the main building but was assigned to an annex situated on the sixth floor of an old elementary school building in the Hunts Point section of the Bronx. Many of us had to go to an annex for one year before we could come to the main building since there was not enough space. I would say that the exciting times started, which I remember with great pleasure, when I came to the main building of the James Monroe High School. There I would say my high school life was really very full, not just in terms of studies but also in terms of many extra-curricular activities. I guess it was partly through my mathematical aptitude in high school (I was getting pretty uniformly 100’s and 99’s in the math courses) that a teacher called Dr. Eugenie C. Hausle (in those days quite a few of the math teachers had Ph.D.’s — the chairman of the math department was Dr. Nathan Silberstein who, until his death a few years ago, always used to keep in touch with me) invited me to walk to school with her. She wanted company. She developed a fondness for me and encouraged me in every possible way. She was Faculty Advisor to the Service League, which did many things for the school. [pause in recording]
You were talking about walking with…
Dr. Hausle. I would say that she became my chief mentor and friend during high school. She was the Faculty Advisor for the mathematics team, and as I said earlier, she was also the Faculty Advisor for the Service League. Well, it is perhaps not surprising that I became Captain of the Math Team and President of the Service League. I do not know whether I really earned either one. But through the Service League I was involved in many extra-curricular activities other than just studies. Let me summarize the Mathematics Team. The Mathematics Team was a very interesting operation. It was a competition which I still think continues to this day among the New York City high schools. There would be five contests with five problems and five members on the team; and the contest would be given simultaneously in different parts of the city. The faculty supervisors just graded the answers because there wasn’t time for anything else. The contest was a test not only of understanding math but of speed. You might get one minute and 30 seconds for certain types of problems. You would train for the math team in the way you would for the football team — practicing many afternoons with trial problems or previous problems that had been given in former contests.
I joined the Math Team soon after I came to the main building and I did become Captain during my senior year; and when I was Captain of the Math Team, we did come out first in New York City and so we were awarded the gold cup. And also the Service League was extremely interesting. Maybe it was my connection with the Service League in high school that was responsible in later years for my interest in trying to be of service to society in a variety of ways. When I was graduated, at Commencement there were three major gold medals...I tell this story because it reveals an interesting sidelight on the existence of anti—Semitism in American universities in the 1930’s. I won the gold medal for scholarship because I was the first in average — I was valedictorian. I won the gold medal in service. I had been president of the Service League, and that was the usual reward. But there was a third gold medal, which was for “good citizenship.” Normally that was given to the president of the senior class, which I was not. But the Faculty Advisor to the senior class, Jacob Graham, was my history teacher. And I don’t know — he, seemed to feel that in terms of the various things I was doing for the school and for him (I used to grade his history papers) that I should get the gold medal for citizenship. So how he did it, I don’t know. But I was surprised at Commencement to find myself receiving all three gold medals apart from a few others in subjects like math, Latin and so on. Now, I might say, as far as the mathematics side of that experience was concerned, another person who played an important role in my life at that time was a Greek fellow whose name was Hippocrates Apostle.
Hippocrates was from an immigrant family from Greece, had gone to James Monroe High School, was good in mathematics and had worked himself up to being Captain of the Mathematics Team several years before I came along. But he was always very interested in the Mathematics Team and sort of was an assistant coach to Dr. Hausle, whenever he showed up. And he had won a Pulitzer Scholarship to Columbia College when he was graduated from James Monroe, two years before I was graduated. And he was the one who apparently took a shine to me as well and started telling me about the Pulitzer Scholarship at an early stage, so that I knew it existed, and encouraged me to apply for it; and also helped by giving me advice when I was captain of the Mathematics Team on how to become a captain. Another thing he did, which I considered very important in terms of my later college career, was that he had become somewhat interested in philosophy at college. So, here he was two years ahead of me, and he used to tell me about the great joys of philosophy and the exciting ideas to which he was exposed. And I remember he introduced me to the first philosophy book I ever read, namely John Dewey’s How We Think. And another book which he was extremely fond of, and which was an important book at Columbia College in the course “Contemporary Civilization,” was John Herman Randall’s Making of the Modern Mind, which opened up one’s horizons to Western intellectual history since the 12th Century — and both of those books I read as a high school student. I think there were others that came along, but I remember those very distinctly. So in many ways my last two years in high school were most pleasant and gratifying. I don’t remember getting 99’s and 100’s in most subjects in the ninth and tenth grades. But in the 11th and 12th grades, most of my grades were in that area — including English and the other subjects. And so it seems that in a curious way my academic performance was stimulated by my extra-curricular activities.
Was James Monroe considered one of the better high schools in New York in those days?
Oh, yes, in those days Monroe was one of the newer high schools. I think it opened about 1925 or ‘26, so it was relatively new when I entered it; and it had a very energetic principal called Dr. Henry Hein, who maintained high educational standards.
We were talking about the gold medals and you were relating it to the question of anti-Semitism in American college life. But then you got into the question of scholarships...
Well, those two were connected. Let me tell you what happened there. I was graduated in January, 1932, and the Pulitzer Scholarship was only available in September of each year. That is, Columbia College did not care to have people come into the system in the middle of the year. They admitted students on an annual basis. So I had those six months, and of course I wanted to have a college education, and even though the family was in serious financial trouble, still my father thought I must go to college. So I went to City College in February, 1932, but meanwhile was applying for the Pulitzer Scholarship. Since the Pulitzer Scholarship entitled you to free tuition at Columbia College for four years (which I think in those days was worth $400 a year) plus $250 a year in addition as a cash award, it was necessary to apply separately for admission to Columbia College. The Regents’ Scholarship in those days was worth $100 a year. I had received the Regents’ Scholarship, so I was assured $100 a year. I could go to City College, live at home in the Bronx, and try to earn extra money, which I was starting to do by tutoring to help support the family. But in order to go to Columbia College, obviously you had to apply for admission.
So I applied in the Spring of 1932, and in May of 1932 I was informed that I was rejected for admission to Columbia College. If I was interested, I was told that I could be admitted to Seth Low Junior College located in an office building in Borough Hall, pretty much for the Jewish kids, where, if they did well after a few years, they might transfer to the main college. Well, I replied I wasn’t really interested in Seth Low Junior College. I was then in a quandary as to whether I should take a batch of College Entrance Exams in June, part of the process of applying for a Pulitzer Scholarship. In 1932 I remember a figure of 500 applicants taking these College Entrance Examinations. The procedure was that the 30 highest in the exams would then be interviewed by the Pulitzer Scholarship Committee, and then 10 would be chosen. That is, 10 scholarships were given each year to the graduates of New York City public high schools, according to the will of Joseph Pulitzer. Since I was interviewed by the committee, I assume that I rated among the first 30. Now, a curious thing happened. Dr. Adam Leroy Jones, a reasonably well—known philosopher (he had written a book on logic; he was not distinguished compared to some of his colleagues like John Dewey and Frederick Woodbridge, but it was a good logic book used at least at Columbia College), was Director of Admissions and also Chairman of the Pulitzer Scholarship Committee. And so I wondered: if Dr. Jones, as Director of Admissions, had rejected a poor boy from the Bronx with all those gold medals, what chance would I have to be-awarded a Pulitzer Scholarship by Dr. Jones as Chairman of that committee.
I went ahead, in any case, with a personal interview by Dr. Jones. And believe it or not, I was awarded a Pulitzer Scholarship. How did this happen? For one, there was a member of the Pulitzer family on the Scholarship Committee. But most importantly I think from my point of view was the fact that Dr. John L. Tildsley, Associate Superintendent for High Schools, was on the committee. Dr. Tildsley was the top person for high schools in the New York City system. He had been commencement speaker at my commencement, and I had met him personally. More than that, after our meeting in January 1932, he became interested in my visiting him at his Spuyten Duyvil home during the Spring of 1932, Imagine a frightened 15 year old kid taking the trolley to the top of Spuyten Duyvil to meet with an important man like Dr. Tildsley. It turned out that he wanted to find out what I thought of the teachers at James Monroe; and I was a little naive and talked frankly about the performance of various teachers, their teaching style, and followed up later and made life difficult for the principal, Dr. Hein. Be that as it may, I was offered a Pulitzer Scholarship, and my guess is that Dr. Tildsley was chiefly responsible for the favorable decision. In any case, when I was offered the Pulitzer Scholarship, I had not formally been admitted to Columbia College as yet; and so I wrote back and said that since I had been turned down, I would stay at City College and just collect the money. You were entitled to go anywhere with a Pulitzer Scholarship, but you would not of course automatically get free tuition if you went to another college that charged tuition. But since City College was free, I could collect the $250 per year. However, a letter was quickly forthcoming saying a place had been found for me at Columbia College, and so I decided I would go there, because of the great opportunities in a university setup. I might say that of the 10 students who received Pulitzer Scholarships that year, I was the only Jewish youngster. This is very strange because I knew quite a few Jewish boys who were among the first 30, including Mort Hammermesh, the physicist.
He’s at Stony Brook now.
He was at Stony Brook — has now gone back to Minnesota. That’s the story of my trials and tribulations with regard to the Pulitzer Scholarship.
In the application did you have to indicate the field of interest you would relate to?
Yes we did, and in my application I believe I put down mathematical physics. In my yearbook — you know, they put little sentences about people — I remember that they put down for me: “So I sez to Al Einstein, I sez...” And so somehow because of my mathematics involvement, I sort of thought: well, that was the natural field I would go into. But as it turned out, there was an early, shift of interest to philosophy.
Before we get into that, let me ask you how the link between mathematics and physics first occurred. It must have occurred during your high school years. What had you known of physics during that period? What did you read or what courses did you take?
Well, frankly, I only took one physics course. I don’t remember it as in my senior year being a terribly exciting course. And I think mathematical physics was really conjured up by everyone telling me that I had a future in mathematics, and since Einstein was the great hero, I guess I put down mathematical physics. Of course, I read several of Einstein’s popular works at that time, but I do not remember spending a. lot of time actually on physics per se or on theoretical physics per Se. I think that it was sort of a childish…preference. Remember I was 15 1/2 years when I entered Columbia College. I was 15 when I graduated from high school, and I wasn’t very sophisticated in my understanding of mathematical physics, and I would say the physics side was only added on as a matter of form.
Apart from beginning math, what courses did they offer?
Actually only through solid geometry and advanced algebra. And I did not study calculus, say, because it was not offered in those days. I studied calculus at City College.
But I mean in high school.
In high school I did not go beyond solid geometry and advanced algebra in my own studies because the Mathematics Team required speed and expertise in those subjects and the other normal high school math subjects. The Math Team did not try to stretch your mind to go into, say, calculus or anything like that.
In other words, the Regents covered those subjects. I remember that the Regents went through — I guess advanced algebra and everything was geared to the Regents. Nevertheless, when you applied for the Pulitzer Scholarship and you indicated mathematical physics, there was this vague kind of linkage.
Now I think we’re ready, unless you think there’s some other important background, to continue with the college part of it. You indicated that you were at the point of going to City but then being accepted at Columbia, you went there. I guess that’s the next step.
I went to Columbia in September 1932.
But you attended City briefly?
Yes, I did for one semester, from February to June 1932. This is why it was claimed that I am a City College alumnus when I accepted the presidency of CCNY. I went to City College for one semester because Pulitzer Scholarships were only awarded in September.
Oh, you were a mid-year graduate.
Yes, that’s the point.
That had escaped me.
I’m sorry. I was graduated in January 1932. I, of course, didn’t know I would get a scholarship. It was very difficult to obtain one — I knew that — and so I went to City College, and if I didn’t get it, I presumably would have continued unless the financial situation at home would have become so bad that I would have been compelled to seek a job. But I figured that I probably would earn some extra money tutoring. I had the Regents’ Scholarship, which was worth $100 per year, and not to be belittled in those years. So it was after I received the Pulitzer Scholarship in August that I went to Columbia in September.
And at Columbia you started out with mathematical physics in mind?
That is correct.
Did you get to take any courses in that field that early, or were you taking a basic first-year course?
Well, what happened, as I recall, was that during the first year: I continued the elementary physics course which I started at City College. But when I came to Columbia, the horizons opened up in the sense that this represented the difference between Columbia College and City College. I mean City College has trained a fantastic number of outstanding people, but the curriculum was a pretty classical type of curriculum; whereas Columbia already was experimenting with new types of programs. One of the programs they were experimenting with at that time, which I found very interesting, was Contemporary Civilization, which covered the intellectual history of Western Europe starting with the year 1200. The chief text was John Herman Randall’s book to which my friend Hippocrates Apostle had already introduced me. I took that, and I took more physics, and I took calculus. But I also took a philosophy course in Aesthetics with Irwin Edman as a freshman. Actually, Irwin Edman was rather surprised that I was a freshman who had sneaked in. He had never admitted anyone into this course in aesthetics unless he was a sophomore. But, of course, to some extent I could argue that I had had a semester at City College and wasn’t a genuine freshman. In any case, I took a philosophy course and physics and contemporary civilization, among other subjects. And I would say that after that first year I became interested in philosophy and during my second year started taking more advanced philosophy courses — I think one with John Herman Randall in the History of Philosophy. Actually, that was a very exciting period in philosophy at Columbia.
They not only had some of the leading philosophers in the country — John Dewey was still around; he was not there full time but still giving occasional lectures — but they had others like Ernest Nagel, John Herman Randall, Richard McKeon (who later went on to Chicago), and Frederick Woodbridge who was a very distinguished philosopher. They also had some excellent graduate students - for example, people like Albert Wohlstetter, Paul Goodman and William Barrett. They were all graduate students in philosophy in those days. So I became very interested in philosophy and actually organized an undergraduate philosophy club. But even though I was becoming very excited about philosophy, I thought that every philosopher worth his salt should know one or two sciences well in order to be a serious philosopher. So I kept up with my math and physics. But after the first year I did not take any experimental physics courses. There wasn’t any time. And then a philosopher doesn’t really have to dirty his hands: I persuaded myself that one just has to know the conceptual structure of science. So I kept taking theoretical physics courses and as much math as I could fit in. But I also broadened my interests into other fields.
That is, I started taking economics, for example, and more history or political science. But I must say many of the courses were philosophy. Well, the result was that when I was graduated from Columbia I was the only one to graduate with honors in philosophy and mathematics - not in physics. It was only during the second half of my senior year that I decided to go into physics. And this was the outgrowth of a course given by Rabi in quantum mechanics. The reason I decided to leave philosophy after the first half of my senior year…I’ll come back to that. That sort of raises some new issues. Let me say that as an undergraduate my intellectual life was very full. I lived at home, of course, and used the $350 a year I obtained through the Pulitzer and Regents’ Scholarships to help the family and also did quite a bit of tutoring to add to the family income. And so here was this very poor boy delving into philosophy, a very impractical subject, but somehow I didn’t feel that I was being disloyal to the family, since I was contributing my share, I thought. And my father at that point did not try to exert any influence, because he realized that I was now beyond his intellectual depth and what I wanted to do was fine. He wondered sometimes whether a philosopher could earn a livelihood, but he didn’t really try to exert any serious influence.
As an undergraduate I became interested, as I say, in many things. I was invited, for example, by one of my friends to join him as a modern dance critic as a junior; and as a senior I was the modern dance critic for the campus newspaper, the Spectator. Also, I became the book review editor for the Spectator and then I became an editor of the Columbia Review, the literary magazine, so you see I had a great deal of fun. At the same time I was following up with physics. Five of us formed an undergraduate physics club, because somehow the course on relativity theory was not taught well. There was a Professor Wills, who was a fine gentleman and had written a book on relativity theory; but it was a rather formal book — the tensor analysis approach with very little physics. And we wanted to learn the “physics” of relativity. And these five “charter members” of that physics club are now all members of the National Academy of Sciences, five out of a hundred in the Physics Section. And the five were Norman Ramsey, Herbert Anderson, Henry Primakoff, Julian Schwinger and myself. We sort of egged each other on...
They were undergraduates at that time?
Yes. Schwinger came as a junior. That is, he had been at City College two years. He was in the same class I was at Columbia class of ‘36.
I thought he’d come in ‘36.
No, he came in ‘34. Lloyd Motz had discovered him, I guess. Lloyd Motz had been a City College student. He brought Schwinger to the attention of Rabi. Rabi quickly realized his talents, because Julian was writing some excellent papers as an undergraduate some of the prettiest papers, with physical insight, not as formal as in later years. Thus he came as a junior and we overlapped the last two years. Herbert Anderson was also in the same class. Henry Primakoff and Norman Ramsey were a year ahead — class of ‘35. So the five of us ran this little club and we taught ourselves relativity.
Was there no one on the faculty with the interest or the ability to give you this background?
No, because, you see, the only theorist on the faculty was Rabi, and Rabi by that time had become very interested in his atomic beam work, and was devoting himself to his experimental program. He was not particularly interested in relativity theory. But we discovered an early book of Richard Tolman’s on Special Relativity which was very physical. I remember we went through that book very thoroughly. Relativity theory was a natural subject to learn if one was going to be a philosopher. The other four students were physics majors.
And if you knew the math.
And if you knew the math.
Well, what did you do? Would you get together at one another’s homes or was it at the…?
No, at the college. I think there were some other people who came along for the lectures.
You lectured to one another.
Yes, we lectured to one another.
And you had regular meetings?
Yes, fairly regular.
Any minutes kept?
I don’t think so.
Did you have a name for it?
Undergraduate Physics Club.
In other words, although you focused on relativity, and that was your main purpose in getting together, it was established as a physics club, the way someone in another department might start an engineering club or a metallurgy club.
That’s right. I remember, for example, apart from relativity, giving a talk on “Laplace’s Equation in Physics,” because I was fascinated by the fact that the same equation was being used in so many branches of physics and so on and so forth. And I’m sure Norman Ramsey would remember some of the talks he gave. We had talks in other subjects in addition to relativity theory.
When you started it, it had not been in existence before. Did it survive after this particular group?
I don’t think so. There weren’t too many physics majors in those days.
Was there a journal club or any kind of a departmental colloquial set-up other than the one you established?
This was an undergraduate club. Later I spent a year as a graduate student at Columbia in physics after I decided to go for my doctorate in physics. And as a graduate student during that year, I attended a journal club or seminar, a theoretical seminar, which was a joint seminar of NYU and Columbia, because actually NYU had more theoretical physicists at that time than Columbia. There were Otto Halpern and a theorist called Johnson...There are some papers by Halpern and Johnson. It’s not the Johnson who was later at Bartol. For example, Primakoff, I believe, got his doctorate under Johnson. Anyway, there was this joint theoretical seminar, and Rabi used to come to it. But I would say that the theoretical “center of gravity” at that time was at NYU and actually was responsible for my leaving Columbia to go to Cornell.
You see, Rabi was the only one nominal theorist at Columbia and I had heard some dismal stories that he was preoccupied with his experimental atomic beam work, and it would take at least seven years to get a degree under Rabi. Perhaps it would be worth saying a word about why I decided to switch into physics. It was both a positive attraction, the excitement of quantum mechanics, which seemed to have all the ingredients that I wanted — it involved interesting mathematics and of course physics; and it had even philosophical possibilities, because it was at the frontier of science. But more, than that, I had taken the Philosophy of Mathematics course with Ernest Nagel the first half of my senior year, and I had worked very hard writing a term paper on the language of mathematics. I received an “A” for the paper, but I felt very frustrated by the end of that semester in the sense that I didn’t feel that I had really discovered anything terribly revolutionary in this branch of philosophy. My term paper was partly a regurgitation of old ideas, even though it sounded new. I had the feeling that philosophy was a sort of cyclic phenomenon intellectually in that you didn’t have a sense of continuous progress as seemed to be present in science.
So when I took Rabi’s course, even though Rabi was not a good teacher and I have told him that — for one thing he was very busy working on the experiments which led to the Nobel Prize and he wouldn’t prepare his lectures very much — still he communicated a sense of excitement about the field, and the field itself was fascinating. And so I decided at that point to change to physics. Rabi didn’t take me seriously, because he thought I really was interested in philosophy. I’ve sort of kidded him in recent years, because he is the one who has become more interested in philosophy. In those days I remember many rides up and down on the Pupin Building elevator when I was trying to convince him that I really was interested in physics, and he kept saying “Well, you seem to be more of a philosopher.” Maybe this was Rabi’s way of telling me that he didn’t think I had any talent I should like to interpolate a little story about that philosophy of mathematics paper (this may be immodest, but I think it’s worth telling). When I went on to Cornell as a graduate student after a year at Columbia, I learned that a prize of $50 was offered to a graduate student each year who wrote “the best paper in philosophy” — whatever that meant. You were supposed to submit the paper anonymously. I just took out that old term paper that I had written for Nagel’s course and submitted it and won the prize against Charles Frankel. So I guess I might have made a go of philosophy, but I have no regrets. I think it’s good for a young man to go through some years of philosophical training if it’s possible. It adds a dimension to one’s interests in intellectual matters, but certainly my original notion that science is more of a progressive type of intellectual operation is certainly true, I think. [pause in recording]
We’re resuming now after a break for lunch. The first point I want to hear about is how you made the transition to physics.
Let me say just one thing about philosophy. I may have given the impression that I regretted my undergraduate experience in that field. I actually found that my interest in philosophy as an undergraduate greatly increased the level of intellectual excitement at college. And, as I indicated earlier, there was not only an excellent philosophy group at Columbia but some outstanding graduate students who have since become rather distinguished. So that I think that whole experience is not regrettable by any means. It in many ways influenced my own life in future years in terms of giving me, shall I say, a broader perspective about cultural and intellectual history, about intellectual pursuits in general. One must always balance off the specialized interest, which you must acquire if you want to become creative in a field, against the broader interest, which is, I think, difficult to pick up at an older age but is easier to pick up when you’re a college student.
So I don’t regret my undergraduate experience. I look back to it with great pleasure, but in any case, I did decide to make the change. Perhaps, things might have gone differently if Professor Randall’s efforts to secure for me the Kellett Traveling Fellowship to Europe, awarded to a graduating senior of Columbia College, had been successful. If I had obtained that desirable fellowship as a philosophy major at the end of my senior year, perhaps I would have felt committed to continue for a while in that area — I don’t know — but in any case his efforts failed for reasons I won’t go into, and there I was taking quantum mechanics and getting fascinated with it and deciding that I would like to do graduate work in physics. Now, for reasons indicated earlier, I was not very familiar with the experimental side of the department. I knew that Rabi was working on atomic beams, but I would say as a senior, the second half of my senior year, I hardly knew about the fact, say, that Schwinger was advising Dr. Goldsmith on neutron experiments. I think that I learned this first as a graduate student. Now, you see...I did not apply to Cornell as a senior.
I knew really very little about applying for graduate assistantships; and since I made my switch in the second half of my senior year, I had no sponsor in the physics department. That is to say, I could get any sort of recommendation in philosophy and perhaps in math, but there wasn’t much they could do for me in physics. And since applications were due, say, by February 1936 and I didn’t make my decision until late spring, there wasn’t much I could do except try to see what I could get at Columbia University for the coming year as a graduate student. And I was awarded a tuition scholarship, which was helpful, and I made up the rest of my support by even more extensive tutoring during that year. I think I heard sort of vaguely that it was extremely difficult to get an assistantship in the Columbia physics department, and in particular I think I heard that it was extremely difficult for Jewish students to obtain assistantships. Be that as it may, I didn’t feel that the fact I only was awarded a tuition grant and nothing more for the first year was in anyway reflecting a possible discriminatory practice, because I realized that I had just made the changeover and that was the best I could expect and was grateful for the tuition waiver. So I became a graduate student at Columbia for one year.
When was your graduation?
In June, 1936. For one thing at Columbia College, just as the entrance was in September, the graduation was in June. And I could have been graduated one year earlier after three and one-half years of college work — that is, three years at Columbia and a half year at City College — but my Pulitzer Scholarship extended for four years, and I was able to take whatever graduate courses I wished as an undergraduate. That was one of the great benefits of going to a college which was part of a university; indeed, in those days I pointed out to people who asked about the difference between City College and Columbia College that City College, as a college, had a greater variety of offerings than Columbia College, but after all Columbia College was part of Columbia University, and hence undergraduates could take graduate courses. Hence the combination was a much more powerful package than anything that City College could offer. And so I decided to spend four years at Columbia College. In this fashion I was able to build up a large reservoir of graduate courses in physics supposedly relevant to philosophy. When I transferred to physics, I was advised to make up certain deficiencies of, shall we say, the physics courses which were less glamorous to a potential philosopher — some of the bread and butter courses like statistical mechanics.
At the graduate level.
Yes. In other words, as an undergraduate I took courses, except for the freshman course, like relativity theory, classical mechanics based on the LaGrangian and Hamiltonian approaches, quantum mechanics — that sort of thing. But the more traditional electromagnetic theory and statistical mechanics were courses that I took as a first-year graduate student. So during my first graduate year, I tried very hard to learn the core curriculum for a person who wanted to get a Ph.D. in physics.
I have seen some letters from this period in the Pegram file at Columbia. There was one letter that Pegram wrote to Lafayette College in June of ‘36. It was about a faculty position that they had, and apparently you then followed through. I don’t know if you had a visit with them, but you wrote to them, I know, and it was a position you didn’t get. Do you recall this period?
Yes, I do. Professor Pegram had been my teacher in a classical mechanics course, either in my sophomore or junior year, and he had always been friendly; and of course I later realized what an important role he played in American physics. And he tried to be helpful when I made my decision to go into physics. He was chairman of the department at that time, I guess, and he told me I could have a tuition waiver but that was as far as Columbia could go. If I wanted a job, I would have to look elsewhere, and he was prepared to help. I remember the Lafayette expression of interest but I was never interviewed.
I’d like to have you remember the circumstances of the letter itself and the interest he took. In his recommendation he specifically mentioned you took advanced work in the department. Pegram wrote to them that the fact that they didn’t follow through on you was regretted by him. I had the feeling from the letter that he was aware of the anti-Semitic attitudes in the academic world.
Well, I think that Pegram was a very decent man and I think tried to be helpful. But I think it’s fair to say that in that period, in the mid-1930’s, we were aware of difficulties for the Jewish group in graduate work — and evidence I’ve since obtained after I became chairman at Rochester has confirmed that Impression. But there’s no point putting into history that unfortunate period. And I think Pegram himself, despite the fact that he was trying to help me, didn’t take any major measures to rectify that aspect of the situation at Columbia and probably felt that he had to move with whatever the climate was at the time. But I would not be surprised if the Lafayette situation did not materialize for that reason. I must say at this point it’s a little obscure to me what I would have done in Lafayette except to have a job. I could not have gone on for a Ph.D. This reminds me. I think I applied at that time...
You applied to Princeton for a Coffin Fellowship.
And I was turned down on that.
Well, the only record I have of it is that you applied for a Coffin Fellowship in mathematics. Condon was to be your sponsor. And I think Schwinger applied, too. I don’t know anything more. I don’t know if he got it either.
I think he did. Maybe that’s the reason. I’d forgotten about the Coffin Fellowship. I guess there were a couple of things that I tried to get during the second half of my senior year when I realized...
That would have come just about that period, in June.
I made a last desperate attempt to locate something in physics. I lived in New York City and I had the tuition waiver, and I decided for one year I’d better just see what I could do at Columbia and follow up from there. I’m not sure, but I think it was at that time possibly that I thought I’d better look into a high school teacher’s job in New York City and took the written exams. I think I did quite well on those, but I was failed in the speech test. My examiner, a Southern girl, decided that my Bronx accent was not appropriate for the job! So I failed to pass the total test for a high school teacher’s certificate.
Let me ask about Columbia. During that final year or earlier, what was your conception of relationships in the department, the different sort of groups, old and new? You mentioned your relationships with the four other students. But what else — for example, were you conscious of Rabi’s group and its relationship to others?
I was really pretty much of an outsider there. It just occurs to me: I think it was during the Summer of ‘36 that Fermi was a Visiting Professor at Columbia. And in order to bring myself into more intimate contact with physics, having made my decision to go on for graduate work in physics, I registered for his course in thermodynamics, I think it was. But after a week or so the temperatures rose to 105. I tried living on campus, but I found that I became rather ill under the extreme heat and the set-up of sharing a room with someone else who drank a good deal. Finally I dropped that course and left the city with the family as per usual. I think it was the last time I spent the summer with my family and studied quite a bit of physics and mathematics on my own. Well, during the year as a graduate student, of course, I got to know a little more of Rabi. I knew that he was one of the glamorous members of the department. His laugh, of course, was heard all over the building.
But I mingled a little. I used to get into the lab at night and see H.H. Goldsmith doing experiments, which I guess he had started with Fermi or before, but Fermi certainly had given him an additional impulse during the summer of ‘36 when he was a visitor. And the extent to which Schwinger would pass along suggestions to Goldsmith was pretty impressive. I think it was during his senior year or the year right after that Schwinger wrote a couple of very nice papers on the scattering of neutrons by ortho and para hydrogen. But I’m trying to think of who else was in the department. Quimby I knew as a professor and as a person who gave a very amusing course in the sense that he wrote up lectures and pretty much recited his lectures verbatim, but I didn’t know about any of his research work. There was Farwell; there was Severinghaus. Nothing very exciting in research. There was Wills. And Pegram by that time was becoming more and more the grand old man, although he wasn’t that old. And so perhaps the chief experimental programs that I knew about were Rabi’s and Goldsmith’s and Dunning’s. I guess officially Goldsmith was working for Dunning at that time. And Zacharias was working with Rabi. Zacharias used to come to the labs. And the theoretical contacts, as I indicated earlier, were through that seminar held jointly with NYU.
Who from Columbia participated in the seminar? I think you said Rabi used to come occasionally when you were there.
Well, Lloyd Motz used to come. Raritan used to come from Brooklyn College.
Wasn’t he a graduate student at Columbia?
When did he get his Ph.D.? At about that time?
I don’t have it with me He got a Ph.D. from Columbia in the late thirties. [M.A. ‘30; Ph.D. ‘37]
He got his Ph.D., but it took a long time and it was this example that persuaded me to try to leave the following year. I’ll come to that. I realized that Rabi was not the person through whom one should be trying to get a theoretical Ph.D., because he had shifted his Interest so completely. Motz also got a Ph.D. about that time on a subject related to certain theoretical aspects of Rabi’s work.
Kellogg was working closely with Rabi. Do you recall?
Yes, I knew Jerry Kellogg, of course. But I did not get into Rabi’s laboratory too much. I think my one contact was when Rabi asked me to do some theoretical computations in connection with his work just to see if I could apply quantum mechanics in the presence of a magnetic field and so on. I guess those calculations passed muster, but they weren’t very exciting or original calculations.
I started to ask you about the others who participated in the joint NYU-Columbia seminar.
Well, Schwinger, of course, came to it. Motz, Raritan...
These were experimental people.
John Manley came on the engineering side. Bacher was there in ‘34-‘35.
No, that was before.
And then you mentioned Primakoff.
Well, the fact of the matter was: first the groups were extremely small. You count them not in the dozens but in ones or two. And, as I indicated earlier, there was not a theoretical staff person on the Columbia staff other than Rabi. And the NYU input to those seminars — they had at least two senior staff people, Otto Halpern and Johnson, and they brought along their graduate students, of whom Primakoff was one.
And then Schwinger would have been from Columbia with you. Who were the others you mentioned earlier? How often did this joint NYU-Columbia group meet?
Oh, maybe once a month. It was not every week.
Did you alternate?
Frankly I don’t remember going to NYU. Maybe once or twice. I think there was alternation. But my impression is that I would always go when it was at Columbia — but not always when it was at NYU.
Did you have outside visitors In terms of visiting speakers?
I don’t remember any distinguished visitors like Oppenheimer. I don’t remember Bethe or any of those talking. But my memory is a little vague about that period. You see, for one thing I was only in a sense a first—year graduate student, and I would go to them, but I still felt I had a great deal to learn. I would go to the• seminar at Columbia and I think once or twice to NYU but I don’t remember those seminars as seminars in which I personally had any significant participation. I still was pretty much uneducated. The first original idea I got in physics was soon after I arrived at Cornell. That comes in the Fall of 1937 — in connection actually with Rabi’s work.
It was in nuclear structure.
No. It is true that my first published paper was with Gronblom on the alpha-particle model. But the first physics idea which had any element of originality in it was an attempt to explain the discrepancy which existed at that time between the two measurements of the magnetic moment of the proton by Rabi and by Otto Stern. Rabi was doing it by hyperfine structure, and Stern was doing it directly — through a Stern-Gerlach experiment — and there was somewhat more than a 10% discrepancy which seemed to be clearly outside the experimental errors of the two experiments. In the latter case…you measured the magnetic moment directly, and in the former case you measured supposedly the same quantity through the electron-proton interaction. So I hypothesized a new type of force, a non-coulombic force, between the proton and electron in order to explain the discrepancy. But I never published that paper, because by the time I finished the calculations, the discrepancy seemed to evaporate. I didn’t see any need to muddy the literature when the discrepancy had disappeared. But at the beginning it looked very genuine; it was way outside the experimental errors.
Getting back to Columbia, although that ties in: one other question about your conception of what was going on. How about the Dunning cyclotron group? Were you witness to any of their efforts to do the initial building? It started about ‘35, and by ‘36 it would have been in progress although Dunning was away in the spring of 1936.
Well, I’m trying to analyze why it is that I know so little about that year, about what was going on inside the department. I think there are several reasons. I think that the chief reason that since all I had was a tuition scholarship, I was not considered a very important member of the department. If I’d had a teaching assistantship, you know, I would have been brought into the inner councils more. At least I would have met many more people. In other words, I was really an outsider, and I think we were all treated as outsiders — those who had no assistantships. Secondly, it was the first year formally of graduate work for me, although I had had some graduate courses. Still it was pretty much a year of courses and not a year of any research activity on my part whatsoever; so that I was not watching out for those things. I was pretty much trying to show that I could master the material in this new field, which I had decided to go into, even though I had had some exposure. The courses were not very good indicators of whether I would become a creative physicist. Also, I think the department made me take some graduate laboratory work with that lady...
Right. So I took that graduate lab course and you know, you spend a lot of time in such a course. Now that I had said I wanted to be a physicist, they thought I should be exposed to some experimental physics. So I found the year pretty much full with the courses, and I was not invited to find out what was going on in the research labs and was not particularly shown around. But I did know about Rabi and a couple of times visited his lab, particularly in connection with that one problem that he asked me to compute. He asked me to come up to see him in his laboratory, so I saw where they were. And because Schwinger came at night, I sometimes joined him and Goldsmith and so I knew that there was neutron work going on. But other than that, it was more or less hearsay. Of course, there was a colloquium. I think I went to that and got some feeling for the department.
A graduate colloquium?
Yes, where they did have outside speakers. I remember one of my most exciting experiences was listening to an outside speaker at this colloquium when I was an undergraduate. I believe it was perhaps ‘34 when Dirac came to lecture at Columbia. That was one of the great experiences, to listen to him tell about the holes in the negative energy sea and so on.
Had you heard anything about this subject beforehand — anything relating to quantum electrodynamics?
Not too much, no. You see, Schwinger already knew quantum mechanics and was writing papers, but I didn’t really take quantum mechanics until the second half of my senior year. In those days the undergraduate curriculum was not set up in such a way that quantum mechanics came very early. It required a special effort to take quantum mechanics, which was officially a graduate course. So I would say that first year was a sort of warm-up period for me in terms of my own experience in physics. Since I had shifted fields, I had a lot to learn and felt pretty humble and worried a little about the future, what I was going to do after this one year to continue to support myself.
Was it that you had decided you didn’t want any more than a year there because you recognized the difficulties that you had and you really wanted to leave, or was it that there was a duration of one year only?
No, I believe they told me my tuition scholarship could be renewed. In other words, they could give me the same support but no more. So it was clear that I could not expect an assistantship from Columbia while I was a graduate student. And so the question was: should I continue at Columbia with merely a tuition scholarship and earn the extra money I needed to support myself and to contribute my share to the family income, through tutoring or any other jobs that I could pick up? Or could I get more substantial support elsewhere? But I must say, to me now, as I recall, the driving force for leaving Columbia was the realization that there was no future there in terms of doing a theoretical thesis because of Rabi’s transfer of interest. And if that had not dawned on me, I probably would have continued to try to get my Ph.D. with the help of a tuition scholarship and taking care of my support through tutoring, which I could do in many fields. I tutored not only in math but philosophy, physics and so on.
At what level?
All kinds of undergraduates (that is, students at Columbia University), and I used at one point to receive as much as $3 an hour, which in those days was a very handsome rate. So I could continue on that basis. It was not satisfactory, but I could do it. But when I learned from the hallway conversation of the trials and tribulations of Motz and Raritan and Rabi’s general disinterest in subjects theoretical, I started worrying about other possibilities. But my ending up at Cornell was a sheer accident. We can come to that whenever you want to.
Well, is it appropriate now?
Perhaps if it comes late in the story of your finding yourself, then let’s put it in sequence.
Well, I would summarize that year in Columbia as quite unspectacular. I was doing my work, and I think Rabi was beginning to believe I was a little more serious. I think I did get an “A” in statistical mechanics. But I don’t think he felt that that proved I was particularly promising as a theoretical physicist. I must say that the norm of comparison all the time was Julian Schwinger, which was a little rough.
Was he regarded as a star?
Oh, yes. Well, as a matter of fact, I could tell an amusing story in that connection. At Columbia College I was elected to junior Phi Beta Kappa. In order to be elected to junior Phi Beta Kappa, you were supposed to be in the upper 2% of your class. And Columbia had a system of inviting the junior Phi Bets to participate with the faculty in the election of the senior Phi Bets. And that would allow another 8% to be elected, but not necessarily the highest 8% in academic average. The rules were that everyone above a certain average — I think B+ average — was eligible to be elected as a senior Phi Bet. Of course, to push through someone down the list required special pleading. Now, Schwinger was eligible, but he had not gone to certain classes like chemistry and so on and had a small number of “F’s.” And so his average was not quite so high. I made a special plea and said, “If you do not elect Julian Schwinger, you’ll be very sorry because he’s going to win the Nobel Prize some day.” And he was elected to senior Phi Bet. Frankly I don’t know if Schwinger even had an assistantship. Maybe he did. He may have been the one exception.
I don’t know how it turned out. I know at one stage there were some letters written between Rabi and Bethe, who had sort of looked Schwinger over, to give his approval at Rabi’s request. The letters were written to Pegram, who used those letters in support of the idea of bringing Schwinger in from City College.
He came as a junior in 1934.
In ‘36. I don’t know if he did get an assistantship.
That would be very interesting to check that out, because if they didn’t give Schwinger an assistantship, one might draw certain conclusions. But in any case, so far as I was concerned personally, here was a philosophy student hoping to become a physicist who still had to take some basic courses as a first-year graduate student; and by that time Schwinger had written several important papers and had been practicing physics since he was a sophomore in college. So that even if there was one opening at Columbia for an assistantship, certainly Schwinger would have merited receiving it.
Perhaps it could be put this way. Of the theoretical physics students at Columbia at this time, you were in the lower 50% of your class?
Right. Which doesn’t make me too unhappy. But by the end of that first year, I started worrying about the following year. And then along comes a fellow called Sidney Siegel who was completing his doctorate in solid-state physics at Columbia and he was interested in securing a job as an instructor somewhere. This was in June ‘37. And he decided to attend a solid-state conference at Cornell which Bethe was running. Siegel said to a few of the graduate students: “Would you like to come up and keep me company? I’m going up to a conference at Cornell.” And I had never really been outside of New York City or the Catskills, and this seemed like a great opportunity to see the world. So I drove up with Siegel, and there were several others whose names I forget now. During the conference, Siegel inquired of R.C. Gibbs, the Cornell Physics Department Chairman at that time, whether there was an opening in the department. Gibbs told him: “No, there’s nothing for instructors. But there still are a couple of openings for graduate assistantships.” And so on the way back to New York, Siegel mentioned this in the car, and I started thinking about it: “Gosh, I don’t stand much chance, but maybe I should apply.” So in July, I applied, or it might have been the beginning of August. It took some time for me to muster courage to apply, because, you know, it didn’t seem too promising. But I did apply, and I guess Rabi must have written a reasonable letter on my behalf. By the end of the first year, I had some decent physics grades in my record but certainly no indication of any original thinking in physics. At first I was turned down. I received a letter after a few weeks saying: “Sorry, the positions are filled. But then a few days later a telegram came from Gibbs saying that if I was still interested, I could have an assistantship. Apparently one of the persons had withdrawn and accepted a Harvard assistantship. I was, of course, delighted and accepted the Cornell offer. And a completely new world opened up.
Had you any knowledge of Bethe’s work there?
By the time I came to Cornell, I had read his first article, which I think had appeared by that time —- the REVIEW OF MODERN PHYSICS article. But I didn’t know much more of his work. I knew that Bethe was a leading theoretical physicist.
But this wasn’t the major reason you applied.
Yes, it was. It was definitely a major influence in the sense that I knew Hans Bethe was a very distinguished theoretical physicist; that it looked pretty bleak in terms of staying at Columbia and finishing up with a theoretical Ph.D., and I didn’t think I had any experimental talent. So this seemed like a golden opportunity, if I could get in to Cornell.
That takes us to that period. This would have been the summer of ‘36.
Didn’t you take a course at City College in one of those summer periods?
No, that was later, after I had had my position in Rochester in 1940, when I wanted to get together enough money to buy a car. I took a teaching job for a summer.
Then you got the job in Cornell the early summer of ‘37.
No, the late summer, the end of August. It was just about two weeks before the start of the semester. It was really a deadline operation. Well, I could have continued at Columbia with the tuition scholarship for another year, and I don’t know what I would have done after that. But I had not applied any place else. I cannot understand at this point why no one took the trouble to advise me to apply to other graduate schools at the end of the first year. Perhaps I was reluctant to indicate that I wanted to leave. It’s not clear to me. Maybe there were very few opportunities. Of course, this was the spring of ‘37. But I don’t recall having applied to any other place except Cornell and very late in the year.
When you got to Cornell was it a question of signing up for specific courses in the field of theoretical physics or was there some kind of flexibility that you had? In other words, how much did you work on your own and how much did you work on a one-to-one relationship with a professor?
Well, somehow I guess Bethe seemed to take an interest in me from the start. I would say he was a friend all through my graduate student years. As I said earlier, after a couple of weeks I had an idea to explain the “Rabi effect,” as I called it and I guess Bethe thought that showed some originality. And so he sort of took a paternal interest in me and encouraged me to come around and talk to him about physics whenever I wished. Of course, I took some courses but not just with him. Another point was that he was not married at that time. He was not married until 1939. And so during the two years I was at Cornell — you see, I received my Ph.D. in 1939 — we went to lunch together on an almost daily basis. At lunch we would carry on scientific conversations, and we were joined by mathematicians, two mathematicians named Walker and Curtis. And then when Placzek came a year later, Placzek joined the group. So I guess I had the good fortune as a graduate student to be accepted at small faculty luncheons; and that, of course, opened up horizons even more. So in many ways, like in Grecian days, I was apprenticed to Socrates or something like that.
It’s a good thing you had a good appetite. I would think that would be a minimum requirement to lunch with Bethe.
Well, I had a pretty good appetite. I guess one reason Bethe accepted me was that he had received a very narrow education in Germany. He really knew little about philosophy or the arts or the humanities and, of course, American culture. Occasionally these matters were discussed, and I guess he found the conversations interesting. I think I gave him something in return, not much but a little, and also I kept on being pretty eager about physics and then astronomy. Within a year, I got very excited about astrophysics, and I actually did my thesis in astrophysics. We’ll get to that in due course.
I just thought of an observation about Bethe being new in this country. His relationship with you, an American citizen, might have contributed to his getting more acclimated to things, and in finding a new life. I say this because others who emigrated have said to me how important it was for them — for the first time they had graduate students — to have close relationships with their students in order to adjust more easily. I can think of several people who felt that this was very important to them if the age difference was not too great. It was an important transition for them.
I even recall several instances where I took a girl out to dinner and would invite Bethe along, because I thought he would enjoy it. He was pretty shy as far as women were concerned, and maybe he also appreciated that. There is a ten-year age difference between us. I was, say, 21 — and he was 31. He was still a pretty young man.
But he had no roots.
That’s the point. Then when I won the philosophy prize, he thought that was great and so on. I guess there were some non-physics aspects which compensated for all the time he did give to me. The almost daily luncheons meant I had an hour’s to an hour and a half’s exposure just about every day of the week with a leading scientist and with other faculty people. This developed a sophistication about what was going on in the world of science that was of course tremendous. And if there were visitors, I would be invited along and so on. He treated me as if I were a member of the staff rather than a student of his.
Who else was there as students?
Well, there were two post-doctoral fellows at that time, M.E. Rose and Emil Konopinski. They used to join the luncheons, too. They were his two post-docs. But I was the only graduate student. There were several other graduate students studying theory with Bethe but he didn’t invite them along. I guess we worked a little more intensely together. I was at Cornell for only two years, because I was able to finish up with the help of a President White Fellowship during the second year. Now, to some extent I guess I was relieved of the assistantship because the professor in charge, Professor Grantham, thought that as a theorist maybe I was not quite as valuable as an experimentalist assistant he would be able to get. Incidentally, our entering class of seven students included Joseph Platt, who is now President of Harvey Mudd College but who at one time served under me as Associate Chairman when I was Chairman of the physics department at Rochester.
That was your first teaching experience.
How did you like it?
On the whole I enjoyed it. It was a new experience. And I must say that when I look back, Professor Grantham insisted that we come a week before to go through all the experiments before we actually confronted the students. And I think that perhaps more of that should be done at the present time. We didn’t make as many blunders as we might otherwise have done.
What was the course?
Freshman physics. We were teaching the lab sections. We were assigned a certain number of labs per week — say three afternoon labs a week — and then we graded the reports. So this was a regular teaching assistantship.
Most of the undergraduate courses were handled by assistants?
Yes, at least the lab courses were.
Bethe had very little experience with undergraduates.
Well, he might have taught regular courses, but he never did any of this lab teaching.
I think he taught one one time and it didn’t work out.
He has taught undergraduate courses in recent years and been very successful. In those days, Bethe was needed pretty badly for the graduate courses.
You mentioned that after a few weeks you got involved with the Rabi effect problem. Now, when you tackled something like that, an idea that was in your mind from Columbia, was it stimulated in any way by conversations that you had at Cornell or by the environment? You said that it was the first piece of original physics research you’d done. I’m curious whether it was something that had been on your mind or whether it was something at Cornell that put you onto it?
I became aware of the problem at Columbia. At Cornell I started reading some papers where second quantization was developed and realized that I could write down a direct interaction between proton and electron and this could explain the effect. When I talked with Bethe about it, he quickly led me to an understanding of appropriate calculational techniques and the key consequences of the hypothesis. I always found Bethe extremely valuable in terms of trying out ideas on him, because refinements of the idea would move very rapidly in his presence. If I try to go back, I would say that for one reason or another, I think that Bethe never directly suggested the initial problem to me. When I generated ideas they were usually in a rather nebulous form, and he was always wonderful in terms of making me sharpen up physical consequences and the techniques of computation. For example, I chose the topic of my own thesis, but he was invaluable in terms of various stages. We’ll come to that.
How would you characterize his style? Was it a question of his trying to understand by asking a series of questions? Your responses would help to structure the logic of the argument? I was just thinking that he might perhaps have recognized that he didn’t understand what you were talking about until after the questions?
Well, I think that that’s a reasonable way to describe it. I think that he has a very logical mind and a very rigorous mind, although he, in later years, didn’t want to have very much to do with the very formal rigor of modern theoretical physics. But in terms of the old physics criteria, he had a very rigorous mind; and in trying to understand what you were telling him, he would make you sharpen up your statements. And from this interaction with him, I would begin to see certain aspects of the problem that I hadn’t before. Perhaps a good example was the two-meson theory where I had the original idea but the final paper included his name because of his contribution to the cosmic ray part, which material he had at his fingertips and enabled him to quickly see how the theory could be used to obtain an upper estimate on the lifetime of the heavy meson; this possibility had never occurred to me because I Just didn’t know the cosmic ray material. But the basic idea was suggested by me at the Shelter Island Conference in June 1947.
I want to get into that.
That’s much later. But it might be better to elaborate on this point in connection with my thesis. Actually, at Cornell, before my thesis, there was an unpublished paper on the Rabi Effect which I might say later received a later reincarnation in my meson-pair theory of nuclear forces.
We were talking about the abstract of the Rabi Effect paper.
You see, the title of that paper is “Electron Pair Theory of Heavy Particle Interaction and the Rabi Effect.” I didn’t realize that I had put Bethe’s name on it, but that’s characteristic. I always expressed my appreciation by adding his name to these papers. But throughout my scientific career, I always felt that one should not allow the alphabet to decide scientific credit. I still believe that one should order the authors to reflect the relative contributions to the particular paper; that is why with students who did much of the calculations you will find many Joint papers with the students’ names coming first. There were some papers published with only the students’ names because essentially I didn’t do much. But if I felt I did a significant amount, their names would generally come first. Well, in the case of the two-meson paper, I put Bethe’s name on in the same spirit, though not alphabetically. Anyway, in connection with the “Electron Pair Theory of Heavy Particle Interaction and the Rabi Effect” — it was the electron pair theory side of it which later became the meson pair theory, because the idea was to postulate a direct interaction between proton and electron and so we wrote down an interaction involving the two wave functions of the proton and the two wave functions of the electron, and took the diagonal, element. If you second quantize the wave functions, you have an electron pair theory of the proton-proton force. And so later on when I was looking into the meson theory of nuclear forces, I hypothesized that the mesons might be spin 1/2 particles and my “Rabi Effect” theory became a spin 1/2 meson-pair theory of nuclear forces. Wentzel liked this theory and developed a strong coupling version. And when Paul came through Rochester during the early years of World War II, he was very Interested in that meson pair theory; but I already had developed the weak coupling formalism in that first paper; and so could use it; the Rabi Effect paper did not go to waste in that sense.
When you wrote up the Rabi-Effect paper you only wrote up the abstract. You had made a presentation of it so you had to have some kind of a note.
I didn’t write up the paper actually because the Rabi-Effect disappeared experimentally. I just had notes.
Here’s a good question, I think. Did you preserve those notes? You were talking about your file.
I might have it. It might be up there in those blue green cases.
Well, that would be typical of a whole category of materials, because there’s no other record of that if it didn’t go into the literature except in cryptic abstract form.
What formal courses did Bethe offer that you took?
I think one was nuclear physics. I remember taking one with Lloyd Smith on scattering theory. I think I took a course with Bethe in solid- state theory.
In the nuclear physics courses, did he use any of the REVIEW articles?
Yes. Well, he knew all that material cold. I had read the published articles before the course, so I suppose I was amplifying and reading additional papers. That’s what led me actually to collaborate with Gronblom in my first published paper. Gronblom was a Finnish post-doc who had come...
I wondered where he had come from.
He came from Finland, and unfortunately he was killed the following year in the Russo-Finnish War. That’s why not more is known about him. But he was a very bright young physicist. He had his Ph.D. from Finland and came to work with Bethe for a year, and he was talking with me one day about the alpha particle model of nuclei and I made some suggestions which were helpful, so he put my name on the paper. But the paper was chiefly his idea.
Had you thought about nuclear structure prior to that time?
No, not much; and I think it’s fair to say that although I knew about the alpha particle model through Bethe’s article and from some additional papers about the discrepancy with the binding energy predictions of the model — that is, if you plot the binding energy as a function of the number of bonds, beryllium 8 is anomalous and so on — it was not really part of my scientific thinking. It was pretty much what Gronblom was thinking about, and he came around for help, and I gave him enough help, I guess, so that he thought we should be joint authors. I suggested a simple way to do the calculations once he told me what he was interested in.
Was Bethe interested in it?
No, I think Bethe just had a passing interest. I think Gronblom just probably told Bethe about it. I don’t think. Bethe participated much in that particular paper. I don’t think, it was very basic although it was interesting in the sense that it showed how skeptically you must treat simple nuclear models. There are many ways to “skin a cat” in nuclear structure. But I didn’t pursue further nuclear modeling beyond that original paper. During the war years I got involved in other work that you might say is connected with nuclear physics, like neutron diffusion, but as far as nuclear structure is concerned, I guess it’s fair to say that this subject has never really excited me — even to this day.
Later it would be of interest, I think, to find out how you characterized nuclear structure and why it didn’t happen to appeal to you as opposed to the things that did appeal to you. Maybe now is the time to discuss it.
Well, I think that in a sense all during my scientific career I’ve been interested in those problems that according to my judgment had a basic significance. Now, of course, each man’s judgment about this question is different. But somehow the nucleus was such a complex system that the answers you could obtain always seemed to be very limited in their applicability and I just didn’t get that much of a kick out of pursuing this field. So I sort of moved either in the direction of the type of physics where you are essentially thinking up completely new forces or new particles to interpret new types of measurements in the nuclear and sub nuclear domains. Of course, during the war years we were all trying to work very hard to achieve very definite objectives so far as the war was concerned. And there I became intrigued with developing better mathematical techniques to solve certain types of practical problems. That’s how I’ got into neutron diffusion where I think I did quite a bit of pioneering work actually.
But that work on neutron diffusion wouldn’t have been something that would attract you under normal circumstances. You wouldn’t have selected it as a kind of fundamental problem.
No, I think not. That is, I quickly became interested in astrophysics and did my thesis in that something that was new and fundamental; gaining insight for the first time into the energy sources of the stars was of course terribly intriguing. I’m willing to do additional, shall we say, dirty computational work in order to pin down what I consider a novel phenomenon, as was the case with the problem of the white dwarf stars, where I had to do some pretty nasty calculations to develop the equation of state under white dwarf conditions of a degenerate electron gas (we’ll talk about that later) and to identify a new process called conductive opacity — that is, the transport of energy through a star via the electrons rather than by the radiation, which also occurs in neutron stars. And I had to learn solid state theory for the white dwarf paper and apply Bethe-Sommerfeld methods and do a lot of numerical work. But the motivation was to understand a completely new state of matter. But in nuclear physics somehow… Let me say there’s one exception where I have worked in nuclear physics but at the same time perhaps it illustrates the point I am making. Through the years, I have been interested in nucleon-nucleon scattering, and a student of mine, Peter Signell, and I in ‘57 for the first time really explained high-energy nucleon-nucleon scattering — in the several hundred Mev region — by adding a spin-orbit interaction to the Well-known tensor interaction. And again I’ve been willing to do a lot of nasty work, particularly when the students do most of the calculations, in order to pin down the properties of the nucleon-nucleon interaction. But then to move on from that, say, to study many-nucleon systems, I have not been interested in that aspect…At least as far as nuclear structure was concerned. I’m sorry to state this prejudice, because in other ways later on I became interested in superconductivity even though that is a many-body problem but again it reveals a completely new type of phenomenon. Of course, there is a superconductivity model of nuclear matter. [pause in recording]
You were talking about superconductivity attracting you even though it’s a many-body problem.
It isn’t just the many—body side. It was a sort of a new type of phenomenon, where you’re getting qualitatively very different effects. Also, its possible connection with theories of elementary particles was a factor. I suppose if I knew more about modern theories of nuclear structure, I could be turned on. I think my colleague, Bruce French, has done very interesting things, in nuclear structure in applying group theoretic methods and so on. In any case, to stop this digression, the paper with Gronblom was a very brief paper, and was not indicative of any major trend in my own scientific work.
When did you pick up the interest in astrophysics? Well, starting with the work that Bethe was doing...
Well, what happened, of course, was that Bethe came back very excited from a George Washington University conference organized by Gamow and Teller.
The spring of ‘38?
The spring of ‘38. That was towards the end of the first year I was at Cornell. Bethe worked out the carbon cycle, and he had asked me to please do some calculations for him to see whether it quantitatively gave the right answer for the sun using a realistic model like the point-convective model, which I did, and he refers to that in a footnote in his paper. It was also at that time that I learned about the New York Academy of Sciences Astronomical Prize, which was being offered, all of $500, and told him about it, and he submitted his paper and won the prize in ‘38.
Did you get a finder’s fee on that?
Yes, I got a 10% finder’s fee, but I gave him a 20% return when I won the prize in 1940. So at one point in late Spring of ‘38, I said to Bethe: “Gee, that looks very interesting. You ask me to give a seminar on some astrophysical problems and I may end up doing a thesis in this field.” He readily agreed. I don’t know whether I actually talked about the white dwarf stars in that first seminar, but I became aware of their existence and the fact that they were much more dense stellar objects than the sun. And so I suggested that I would like to figure out the energy source of the white dwarf stars, although the first part of my thesis was a further exploration of the carbon cycle and proton—proton reactions applied to main sequence stars. But the most interesting part of my thesis was certainly the part on white dwarf stars. There I sort of had to dig in. And the problem was the following: Chandrasekhar had written his book, AN INTRODUCTION TO THE STUDY OF STELLAR STRUCTURE, and that book was published...You have it there?
By ‘38 and ‘39 it was a classic text.
He must have written it...
It was earlier. [Chandrasekhar’s Preface is dated December 1938, and his book was published in 1939 by the University of Chicago Press.]
Maybe the book came out just as I was finishing my thesis, although I had read his papers. The point is, what had happened is this — and by the way this is an interesting story because it’s not finished yet. Something decisive should occur in the next few years. As I said, Chandrasekhar had written several papers on the white dwarfs. He became involved in a fierce battle with Eddington during the middle ‘30s regarding the correct equation of state for a degenerate relativistic electron gas—that is, where the Fermi energy is so high compared to the electron mass that you must apply special relativity formulas to the various energy levels. But Eddington didn’t believe that this was a correct application. Chandrasekhar was following the standard beliefs in the ‘30s about relativistic electrons, and rightly argued against Eddington, who seemed ignorant of the Dirac-Pauli work.
Well, anyway, Chandrasekhar considered a stellar mass at zero temperature with a degenerate electron gas inside and computed what the predicted mass would be for a given central density. Or conversely, if you knew the mass of the star, how much matter you must accommodate, you could predict the radius and the central density. There are actually two parts to the calculation. One is to predict the radius as a function of mass, and Chandrasekhar showed that there was a critical mass above which the white dwarf would not be stable and that is called the Chandrasekhar limit. But this limiting mass depended critically on the amount of hydrogen in the star.
The reason is that for hydrogen you have one electron per nucleon, while for any other element in the white dwarf state, you essentially have one electron for every two nucleons. In contrast, in main sequence stars, the pressure connected with nuclei is an important contributor to the total pressure; so you also have to know the separate abundances of helium and heavy elements. But where the pressure of the nuclei is unimportant compared to the electron pressure, the distinction must only be made between hydrogen and everything else. So all you have to know is the amount of hydrogen. Now, the Chandrasekhar limit (in units of the solar mass) is 5.6 divided by the square of the molecular weight. If you have only hydrogen, u = 1; so the critical mass is 5.6 solar masses. But if you have no hydrogen so that, u = 2, the critical mass is 1.4. And similarly you can make predictions about the radius of the white dwarf from a known mass. For Sirius B, the best measured white dwarf—it’s the companion of the brightest star in the sky, Sirius A—the observed mass is very close to the solar mass; and you can then predict its radius if you know the hydrogen content. The second crucial point is the extent to which the finite temperature inside a white dwarf star would change the prediction about the radius as a function of the mass. In summary, Chandrasekhar could predict the radius of Sirius B as a function of its hydrogen content, assuming a completely degenerate electron gas (i.e. zero temperature). But the important point was you had to know the hydrogen content. And in order to know the hydrogen content, you had to know the internal temperature, because the proton-proton reaction, which Bethe and Critchfield had calculated, would depend sensitively on this temperature.
Well, to make a long story short, I examined the conditions inside the white dwarf stars in much more detail than Chandrasekhar, computing inward from the surface where the energy transfer was radioactive; but I found as I proceeded to integrate the equations of stellar equilibrium—after about 1% of the radius—that this was no longer true and that a new regime took over, which I called conductive opacity, where the electrons transferred the energy through elastic collisions with nuclei, This was a new effect and the calculations required the use of solid-state methods. And this was another example of where Bethe was extremely helpful. He knew solid state physics thoroughly and he was an excellent consultant for my thesis. Once I derived the internal temperature—ten million degrees for Sirius B—it turned out that the proton-proton reaction is so copious that it yields too much luminosity for Sirius B unless the hydrogen content is essentially zero. So that pinned down one parameter. And then knowing what the temperature was, I could also calculate the effect of that finite temperature on Chandrasekhar’s prediction of the radius from the observed mass. So I could then make a completely sharp prediction for the radius of Sirius B. Well, the observation of the Sirius B radius had been made by some famous astronomers in the mid-l92Ws—Adams and others. You can measure the radius of Sirius B first from the red shift, where you measure (M/R) (M and R are the mass and radius of the star), and secondly by measuring the luminosity and effective surface temperature of the star. And it seemed in 1939—when I finished my thesis—that those two measurements were agreeing although both disagreed with the theoretical prediction by a factor of 2.5. And so my thesis argued for a gross contradiction between theory and observation. And in those days Henry Norris Russell was the great dean of American astronomy.
He was at Princeton, and I visited him and explained my work. He thought I had come upon a serious discrepancy and even conjectured that there might be a companion of Sirius B, a third star which could explain the effect. However, the mysteries of science are usually unraveled. Within the last few years, after a lapse of 30 years, my Sirius B prediction has been verified. The point is that the period of Sirius B is in the order of 60 years and since Sirius A is very bright, you have to wait until Sirius B is sufficiently far from the much brighter star that you have a chance to separate the light of Sirius A from Sirius B. Well, last year, 1969, was a fairly good time to study Sirius B. Of course, you can do it a few years earlier and a few years later. Actually, around l963-64, Jesse Greenstein and Oke started performing the measurements and were finding a result much closer to theory, but they never published it. They presented their result to a AAAS meeting but they never published the paper. Apparently, these two astronomers got interested in quasars and other glamorous new developments and never followed through on Sirius B. To me this is very upsetting, and I’ve been pushing in the last year or two to try to get this measurement done, because to me it is as critical a measurement for the white dwarf regime as, say, the sun is for the carbon cycle and proton-proton reaction and as the crab pulsar is for the theory of neutron stars. Especially so since in a white dwarf star, the core is degenerate electron gas and the envelope duplicates the gaseous state of matter in a main sequence star. The neutron star, as we know it now or think we know it, has a neutron core, then a crust, which is really the white dwarf state, and then the atmosphere, which is really a “main sequence” regime. So we have three basic states of matter. It is even more fascinating in the sense that a star whose density goes up to about 10 grams per cubic centimeter, which is the white dwarf regime—is basically stable, You go above 10, up to about 1014 g/cm3, you can show the star is unstable. And it is only when you come into the region of 1014 to 1016 neutron star regime—that the star is again stable. So in terms of our understanding of basic forms of matter, stellar matter, it seems to me that the Sirius B measurement is very important, because there is no other white dwarf on which a serious measurement can be made. And then in those days there were only seven white dwarfs and now there may be hundreds, but very few are binaries. Essentially, the material on the binary stars, where you can measure the mass of the white dwarf component, has not increased in 30 years.
Why is that?
You see, you cannot measure a separate mass unless it is part of a binary.
But you said the material has not increased in 30 years. Is this because of the measurements? People have just neglected this?
No, the material has increased. Many more white dwarf stars have been identified, but to know it is a white dwarf is not the same as testing out this theory. You can know it is a white dwarf from the spectral type and from the low luminosity, say, but you don’t need very great accuracy for that. And you have no knowledge of the mass. And what we’re trying to test here is the theory of degenerate configurations which connect the mass and the radius. So you have to know the mass. Now, in order to know the mass, it has to be part of a binary system. And there are very few binary systems—that’s a very accidental type of situation. So essentially the number of white dwarfs about which we know the mass has not increased in 30 years. Perhaps the number will increase in another 10 or 15 years; my astronomer friends tell me there are some possible cases where the data can be worked up. And with Sirius A being the brightest star in the sky, this is the most favorable case to study. And this is why when I was down in Texas a couple of weeks ago giving some lectures, I talked with some of the McDonald Observatory astronomers urging them to make the measurements. I’ve now become almost a missionary on this, because I hate to see the next five years pass by without a good measurement of the radius of Sirius B. Anyway, that was my thesis at Cornell, and the interesting thing is that 30 years later I am still eager to have the main prediction checked.
Did this equip you in any way in your own mind for your attitude against, say, the nuclear physics approach? In other words, with this discrepancy—and its lack of resolution to this day in terms of the testing of the theory—would this mean that you could still choose sides and identify with this approach or against this approach depending on how you viewed the problem?
The answer is really no but I should amplify. I mentioned just a little while ago that a crucial point in the prediction for the radius of Sirius B was to know the hydrogen content. And the crucial point for that was to use the equations that Bethe and Critchfield had developed for the energy production due to the proton-proton sequence of reactions. Now, the initiating reaction is proton plus proton giving deuteron plus positron plus neutrino. And in calculating that you have to know whether you have Gamow-Teller selection rule or Fermi selection rule. Now, it was generally believed that the Gamow-Teller selection rules were valid, but remember this was 1939, and the crucial test of it was the helium 6 to lithium 6 transition, which seemed to require the Gamow-Teller selection rule. But we weren’t absolutely sure. For instance, we weren’t sure that helium 6, whose spin had never been measured but only deduced from nuclear physics—that its spin was zero because it had four neutrons and two protons—that this was strong evidence for the Gamow-Teller selection rule. And therefore this test could have become a test of nuclear physics versus astrophysics, because if the Gamow-Teller selection rule was not true, the proton-proton reaction would have a much smaller transition probability rate; and therefore the amount of hydrogen permissible inside the white dwarf would be very substantially greater—and therefore you could change the prediction in my thesis. If you have hydrogen in Sirius B, you could have a larger radius, and that would move in the direction of the early astronomical observations. So that in a sense, and in my published paper in The Astrophysical Journal in 1940 I highlight this point, there is a major clash between nuclear physics and astronomy. But, of course, since then, the evidence for the Gamow-Teller selection rule has become overpowering; so I don’t think the astronomical observations will be testing any nuclear physics—it will be testing astronomical theory.
Well, how about in your own mind? It seems to me that you then picked up this kind of question in your own beta decay work in later years and the Gamow-Teller selection rule applies to that work.
I guess you’re right. When I think about it, I guess that this is the first time that I became intimately concerned with beta decay and the Gamow-Teller selection rule. And it then became a very important theme in my scientific work in the sense that in a few years I was working out the theory of forbidden transitions, forbidden beta decay. Before turning to forbidden beta decay, I should relate an amusing story in connection with my thesis. When I came to Rochester as an instructor in 1939 after receiving my degree, I wanted to publish my paper on the white dwarf stars in The Astrophysical Journal, and the cost of publication—it was a rather long paper—was $250. Well, I asked Lee DuBridge, who was then chairman of the Rochester physics department and who had hired me, whether it would pay the publication charges. He consulted my colleague, Victor Weisskopf—Victor later told me this story—who was rather dubious about astrophysical calculations. Weisskopf told DuBridge, “After all, you have no experimental handle on what goes on inside stars, in stellar interiors.” So DuBridge was not so sure one should invest that amount of money and came back and said, well, Rochester would pay half of the cost if I got Cornell to pay the other half, and I appealed to Bethe, and he persuaded the Cornell physics department to pay $125. Well, a few years later, at Los Alamos, when Weisskopf was a group leader and I was his deputy group leader in the theoretical division of which Bethe was head, we started talking about atomic bombs which could have temperatures much higher than the suns temperature—50 million degrees rather than 20.
My astrophysical papers became rather useful to the Los Alamos Theoretical Division and Weisskopf no longer questioned the value of astrophysical work. One other bit of gossip. When I finished up at Cornell, I remember that summer Bethe had received an invitation to write a review article for the Reports of Progress in Physics of Great Britain and made an offer to me which he said Sommerfeld had once made to him—namely, if he would write the article he would receive the money for it and it would be published jointly, because the original invitation had come to the professor and not to the student, And this is what happened between Hans and me. I remember that the honorarium for that article was 8 guineas, which was about $40 at that time, and I spent most of the summer of 1939 writing that article. Bethe read it over and made a few changes and we published it together as part of this Progress Report article. The review article is interesting in terms of indicating the state of knowledge in astrophysics at that time, because it tries to cover not only main sequence stars and white dwarfs but also some aspects of stellar evolution.
In respect to publication, this review article turns out to be your second publication, and yet this wasn’t exactly your thesis, although parts of it were in it.
Well, you see, the reason is that my thesis was not published until 1940, because it was a long paper; and The Astrophysical Journal took a longer time to publish. Also, I think actually the review article was not published until 1940, but it was dated 1939. The paper “Generalized Thomas-Fermi Method Applied to Stars” was an outgrowth of my thesis.
How about paper #l0?
No, this is something else. This paper is “Forbidden Transitions in Beta Decay,” which, if you wish, had something to do with my interest in beta radioactivity, but it was really quite independent of astrophysics. But where astrophysics had its impact…Well, first there was the review paper published with Bethe in the British Reports on Progress in Physics, Then this “Generalized Thomas-Fermi Method Applied to Stars” was an attempt to calculate the equation of state and other stellar parameters when you started getting pressure ionization and became the basis for an important paper during the Los Alamos years by Feynman, Metropolis and Teller.
This uses an analogy from the theory of metals, doesn’t it?
Yes. In my white dwarf paper, I used solid-state theory to work out the conductive opacity and in the Thomas-Fermi paper I drew on solid state physics.
This explains the length of your thesis.
Yes. You see the reason I got involved In Thomas-Fermi paper was that people had worked out the equations of stellar equilibrium which required a knowledge of the equation of state—the pressure as a function of temperature and density for a mixture of elements—and a knowledge of the opacity—that is, how the energy propagates outwards from the central part of the star. These determine the equilibrium conditions, the temperature-density distribution, for a main sequence star. On the other hand, in the core of a white dwarf star, the pressure is determined by electron degenerate gas. However, you start with the same boundary conditions in the white dwarf star as you do in a main sequence star—namely, essentially zero temperature and zero density. But as you move through the envelope of the white dwarf star, where you first start out with a perfect gas equation you have to go through a transition region. And so you have to work out an equation of state for the pressure as a function of density and temperature in the intermediate region. And that gets rather complicated and you start groping round for another method; and that’s how I developed the generalized Thomas-Fermi method to derive the equation of state in this transition region. This paper is now forgotten because the Feynman-Metropolis-Teller paper is a much more complete calculation but I think they refer to this paper as the basic starting point.
And you wrote this up after you left Cornell in 1940, and yet this is another one which you did jointly with Bethe in the same sense as the earlier ones.
Here again I discussed the paper with. Bethe and he was very helpful. I felt his name should go on the paper, and he did not object—and I think rightly so. And he never once raised the question of what order I ever put the names or anything like that.
When was it apparent in your thesis work that you really had a problem and had reached the point where you really could complete a thesis? You said already that you thought of this problem and went to Bethe with it and then he agreed. As a matter of fact, this was an outgrowth of some of the papers that he had been working on, but you had defined the problem. That’s one stage. But when in the course of the work did you really feel you had something that was appropriate for a thesis?
Well, I think in those days there weren’t so many students, and I had continuous contact with Bethe, and at a certain point I sort of went to him and said, “What do you think? Should I try to finish up this year or not?” and told him where I was, and he thought it seemed reasonable to finish up. For example, paper number 8 in my bibliography is really part of my thesis. So strictly speaking, my thesis led to three papers: “The Generalized Thomas-Fermi Method,” the long paper, “The Internal Temperature of White Dwarf Stars,” which I might say—I hope not immodestly—is the key paper that is used, for example, by Schatzman in his book on the white dwarf stars. He quotes many results directly from my paper. Actually, Schatzman in later years was trying to argue that the energy of a white dwarf star originates from its atmosphere which contains quite a bit of hydrogen, but that has not held up. I had another idea of where the energy was coming from. But this paper here: “The Radiative and Conductive Opacities under White Dwarf Conditions,” was published in the Annals of the New York Academy of Sciences.
This was the first time that the transmission of energy by electrons is pointed out as a major mechanism. But I also had to extend the formulas for radioactive transfer because of the transition region between the envelope and the core of the white dwarf star. And the reason that it is published in the Annals of the New York Academy of Sciences is interesting. You see, Bethe’s winning the 1938 A. Cressy Morrison prize brought prominence to the New York Academy of Sciences because it was an important paper, and of course, later on it was the paper which led to Bethe’s winning the Nobel Prize. And then in 1940 the New York Academy offered the prize for the second time. The Cressy Morrison Prize had been offered about ten years before Bethe won it on the same subject of the sources of stellar energy. As a result of Bethe’s winning it and a sense of the new excitement in the field, it was offered a second time in 1940. And I won it then for my white dwarf paper. I think in the submission for that prize, Bethe’s name was added—Marshak and Bethe—because he had been involved to the extend indicated.
I was assuming that this was the paper, though—the one that was published in the Annals.
That won the prize?
No. It was really paper number 6, Henry Norris Russell might have been a member of the jury, but in any case he has a lovely article—he used to write regular articles for Sky and Telescope, and I ran across the one recently where he summarizes the results of my paper and was pleased that it had won the prize. Whether he was a member of the jury, I’m not sure. My Paper 8 contains the detailed calculations for the opacities.
Paper number 8.
Paper number 8. And the reason, as I say, it was published in the Annals is that the New York Academy of Sciences ran a special conference on stellar interiors in 1940 because of the excitement generated by Bethe’s paper. And Bethe suggested that I be invited to this conference. I think Harlow Shapley was actually the chairman of that little conference. In 1940 I was exposed to the important people in astrophysics; and, for example, in 1940—the first year I was at Rochester—I was invited by Chandrasekhar to give a seminar at Yerkes Observatory where he was at that time and where I first got to know him. I was also invited to be Visiting Lecturer at the Harvard Observatory during the summer of 1940.
Did you feel at this time that that was your field?
No, I still felt that this probably was not my number one interest, that it was my number two interest, because I soon turned to the problem on forbidden transitions in beta decay. The first year I came to Rochester I started working on other problems which were more directly connected with particle physics broadly interpreted. And this number 3 paper, “The Heavy Electron Theory of Nuclear Forces,” employed some of the methods I had developed for the Rabi effect paper. But the idea developed when Bethe wrote a paper showing how he could derive certain properties of nuclear forces—e.g. the tensor character—from a neutral meson theory. You see, the problem at that time was the following: Yukawa had suggested his meson theory of nuclear forces, but it was known that there was an equally strong force, between two neutrons and two protons as between a neutron and a proton. And so you needed neutral mesons. But neutral masons had not been observed. So I guess Bethe wrote his paper with the thought: “Well, maybe these charged mesons that are seen have nothing to do with nuclear forces. They’re not the Yukawa mesons.” And I guess in a fundamental way Bethe was right in 1940—that the muons observed by Anderson and Neddemeyer in 1937 were not really the Yukawa mesons. “Since you’re not seeing neutral mesons, these unobserved neutral mesons may after all be the only ones which are responsible for nuclear forces. Let’s see what I can do to calculate the properties.” So he wrote a paper calculating those properties. And he made certain interesting predictions for the quadrupole moment of the deuteron in terms of the amount of tensor force and so on and so forth. So I turned the problem around and said, “Well, we do not see neutral mesons. We see charged masons. Maybe they’re the only ones. Then how do we develop forces between two like nucleons?” Well, we could have a meson pair interacting with the nucleon. But if a meson pair is involved, it is natural to assume that the mesons possess spin 1/2—and that’s how my Rabi effect calculations could be used. All I had to do was to change the mass of the electron to the mass of the meson, and I would be able to derive pretty quick answers. And that paper...
So it becomes a heavy electron.
It becomes a heavy electron. That’s why I called it that. I consciously called the meson a heavy electron because I was dealing with spin 1/2 masons.
Wasn’t this the term which Bethe deliberately said he didn’t like. He had opposed calling the meson observed by Anderson and Neddemeyer a heavy electron, since he thought it had practically nothing in common with the electron.
That’s right. And actually later in the two-meson theory that raises a very interesting point. I think Bethe always felt that the mediating particle for nuclear forces should be a boson. And he really didn’t care for any theory which postulated spin 1/2 particles as the mediators of the nuclear force. Because clearly if you brought in spin 1/2 particles, you had to do it in pairs and Bethe felt that was rather clumsy. And so in that sense it turned out that he was right. Of course, he was wrong about the particle observed by Anderson and Neddemeyer; their particle was a muon which is basically a heavy electron. Later on, when we come to the two meson discussion, this point will come up again. Well, there was another point which explains the paper with Weisskopf.
Paper number 7 you mean? [“On the Scattering of Mesons of Spin 1/2 by Atomic Nuclei,” Phys. Rev. 59, 130, 1941.]
Yes. Well, I was telling Weisskopf about the result with spin 1/2 mesons. In a moment it might be interesting to tell you about Weisskopf’s hope that I would work on quantum electrodynamics when I came to Rochester. We’ll come back to that in a moment. But I decided to go my own way. And I showed that I could duplicate Bethe’s results with his neutral meson theory with my charged meson pair theory except for the r dependence; however, I could replicate the spin dependence, the isospin dependence of the nuclear forces. Then there seemed to be a large discrepancy arising from the fact that if the Yukawa mesons were the same as the ones discovered by Anderson and Neddemeyer, the scattering cross-section for these cosmic ray mesons seemed to be too low by a factor of 100 or more. And so it seemed interesting to try to see whether or not one could explain the low scattering cross-section that was being observed for spin 1/2 Yukawa mesons by taking advantage of the meson pair interaction with nucleons. Now, here one of those curious things happened. Actually, the calculation with Weisskopf is incorrect. We found a small cross-section but we made some numerical mistakes. But later on when Wentzel took over this meson pair theory — and did strong coupling calculations with it, he was able to derive a reduced scattering cross-section. This was about 1946. But Weisskopf and I did a weak coupling calculation and I do not claim that we had an inkling of Wentzel’s effect in our calculations.
You indicated that in the paper with Weisskopf that this question of meson scattering involved taking it to higher approximations as crucial. Did you yourself do it?
No, we just had made some (2π) mistakes (the bane of a theoretical calculation!) and so we had computed a low cross-section. We realized, of course, that the perturbation calculation was terrible. We didn’t know at that time how to do it better. So I would say that the conclusion, that the meson pair theory could explain the low scattering cross—section, is not correct in the weak coupling approximation. If you work out the weak coupling theory correctly, you will find a large cross-section, and actually I must say that there was an exchange of correspondence between Weisskopf and Oppenheimer on this matter. Oppenheimer was extremely interested, and Weisskopf got quite excited at one point — became interested in my work even though he had wanted me to do something else — but Oppenheimer expressed considerable skepticism about the result. But, as I say, it did turn out later that Wentzel was able to do that very thing with the meson pair theory in the strong coupling approximation.
What was the response of others? You mentioned Oppenheimer’s skepticism, but how about other physicists?
Well, I recall that Pauli came through Rochester in those days after the first paper. Pauli’s taste was such that he did not care too much about explaining this experimental discrepancy with the scattering. I remember his telling DuBridge at a party at Weisskopf’s that "that's interesting work”— in reference to the concept of using meson pairs as the mediating particles for nuclear forces — which was the biggest compliment I could expect at that time. In that lies a little story about my Rochester appointment for one year.
Just getting back, before you talk about how you got to Rochester and then the whole sequence of events, I have some further questions about the astrophysics work at Cornell. One question is on the white dwarf work, which you at one point decided with Bethe would be appropriate to submit. What followed from that? Was there anyone else who had to be consulted in terms of accepting this, and was there a formal or informal examination?
There was a formal final oral examination. There were also written qualifying examinations along the way. But we have passed that point already. The final oral examination committee had Bethe on it and Bob Bacher, and a mathematician, Curtis. These are three members of the committee that I remember and probably one outside chairman. What would you like to ask about that?
Was there anything memorable about it? In other words, was there any particular hard time or was it routine?
Actually I think Bacher did give me a hard time and I think tripped me up on the operation of a bubble chamber.
No, I’m sorry cloud chamber. See how much attention I paid! I didn’t really know the detailed operation of a cloud chamber, but Bacher decided to vote to pass me, I guess, anyway on the basis of the thesis. The first part of the thesis was not very deep, just deriving some implications of Bethe’s carbon cycle about energy production in the main sequence stars, The second part was the more substantial work, but Bacher himself was not following astronomy, so I guess it turned out that Bethe was the only one who could pass judgment on the merits of the thesis and I guess he decided it was worth a Ph.D., because I received my Ph.D. in June of 1939.
While you were at Cornell did you have any association with the cyclotron work?
Not directly. I did enter somewhat into the total life of the department and was aware of the various experimental programs, because I consistently attended colloquia and seminars; and I recall being perhaps a little forward in that I would frequently ask questions at colloquia and try to get a broad education in physics. And I was aware of the work of Livingston and Bacher and there were some solid-state programs, and Lyman Parratt was interested in X-ray work and so on. Lyman Parratt was the one who forced me to take a physics laboratory course for one year, the first year I was at Cornell, which I do not regret. It did bring me closer to experimental aspects of physics, And indeed I think throughout my scientific work in physics I think on the whole I’m a theorist who likes always to confront theoretical predictions with experiment. I’m interested in this confrontation. It’s part of the fun — seeing whether the theory works out — and I try to work in theoretical areas where I can make fairly clear cut predictions so that I either win or lose in a definitive way.
Except in most cases you have to wait 30 years.
That’s an exception. In astronomy you can only observe while in physics you can experiment and set a more rapid pace if you wish. Of course, Weisskopf is even more extreme in that sense. You might say he’s a phenomenological theorist who likes to work with experimentalists. I think he would agree, certainly in our war experiences together, that I have more mathematical expertise than he does, although clearly I don’t have as much as Dyson and some of the other particle theorists. And where I wanted to exert myself in exhibiting mathematical prowess, I could use rather rigorous mathematics. For example, during the war years, in connection with my neutron diffusion work, I developed some fancy methods, which we can get to. But I must say I generally liked to be close to experiment and perhaps this experience at Cornell, of being forced to get my hands dirty in at least one graduate laboratory, may have had some influence.
You didn’t become involved in any of the other work that was going on?
No, I was not a research assistant on any of the experimental programs.
How would you characterize the relationships in the department? You met several new people. You worked with Bethe, an accomplished, well-known person out of the European tradition; and at the same time you studied with Bacher and Livingston with fresh Ph.D.s in hand in the department, where Richtmyer at one time...
He had retired.
And Gibbs certainly...
He was the paternalistic chairman of the department. I think an important name to mention is Kennard — of “Kennard packet” fame — and Lloyd Smith. Now, a few words on the flavor of that department. It was clear that Bethe was the distinguished scientist in the department. It was also clear that Bacher and Livingston in nuclear physics just worshipped him. I mean Bacher very early established an extremely friendly relationship with Bethe, and the Bachers and the Bethes have remained very close friends ever since. It was evident that Livingston, Bacher and their students all looked to Bethe for theoretical guidance. And, of course, there was the Bethe-Bacher article and the one with Livingston in the famous Rev, of Modern Physics series. Now, as I said, Gibbs was the administrator, who I think was very proud of having captured the plum that was Bethe. It seems that the only conflict in the department was between Kennard and Bethe in the sense that Kennard did not believe in quantum mechanics, even though if you read some of the textbooks on quantum mechanics, they talk about the "Kennard packet.” So at an early stage Kennard was making some original contributions to the new field of quantum mechanics. But apparently he never fully believed in quantum mechanics and used to constantly argue about it with Bethe. Actually, the second year I was in Ithaca, I rented a room at the Kennard’s, and had a few conversations with Prof. Kennard. I don’t think that Kennard harbored a personal jealousy against Bethe and that he was rationalizing his personal animus. I think that on intellectual grounds he was constantly taking issue with Bethe and Bethe was probably getting a little annoyed after a while, because he thought Kennard’s questions were not very perceptive. As far as Lloyd Smith was concerned, I think that Lloyd Smith had been brought in before Bethe as the promising young American theorist, because he had a history of having worked with Sommerfeld, he had an NRC Fellowship and so on.
That’s where he met Bethe, at Sommerfeld’s lab.
Yes. I think Smith suggested Bethe for the Cornell job. Looking back, there was a little sadness in that recommendation. Smith was sporting enough to bring in Bethe, but it was clear after Bethe came that he overshadowed Smith. Some later developments in the Smith career the fact that he left university life to go into industry and so on — are probably connected with the fact that he came out second best at Cornell. But that is conjecture on my part.
How would you compare the attitudes in the department to the attitudes in Columbia regarding, say, anti-Semitism, in terms of relationships, recommendations for jobs?
Frankly I think there was not much difference. And I sort of learned later passingly that the reason that I was first rejected for a Cornell assistantship had some element of that but I don’t know how much. Again, I was one of seven graduate students who entered the Cornell Physics Department in 1937 (at Columbia in 1932 I was one of ten Pulitzer Scholars). But, of course, in New York City it was clear that statistically 10% was wrong. I must say it is not clear to me to this day whether statistically one out of seven was wrong at Cornell, because it could have been right in terms of relative numbers. But there was some talk that there was some problem originally in getting Bethe accepted — he is half-Jewish — but once he was appointed and he did so exceedingly well — I mean he was the pride and joy of Cornell — he certainly, in contrast to some other refugees who worried about a superabundance of Jews in university life — did not worry about the problem at all. He would not let any quota get in the way. So he may have been a positive influence. But that has something to do with my job at Rochester, which we’ll get to perhaps.
Let me ask one other question about Bethe’s other graduate students. I didn’t ask it directly, but you did tell me of others in terms of solid state. Do you recall how many there were? I remember that a number of them did work on solid state because — I think Bethe put it this way — that it’s easier to find a thesis problem for someone in solid state physics. But did you get a feeling of the relative balance among graduate students in terms of how many of his students were in solid state as compared to other fields?
Well, as I recall, there were some graduate students, like Mike Baroody — I think he went to Battelle Institute and has been there ever since in solid state — and then there was Eugene Parker from the South. My impression is that the theoretical graduate students (all four of us) worked in one large room. I think Parker was in nuclear physics, and there were two in solid-state physics and I was in astrophysics. In addition, Bethe had two post-docs, Konopinski and Rose, who were both interested in nuclear physics, although Rose at that time was working with Bethe on limitations on the size of cyclotrons due to the problems of focusing. This latter work played an important role later in cyclotron development. M. E. Rose passed away a couple of years ago while a professor at the University of Virginia.
His personal papers are now deposited there.
Yes. On the whole M. E. Rose has written many more papers since 1939 than Emil Konopinski, although Konopinski in those early years had a national reputation as a result of his work with Uhlenbeck on beta decay. But Rose was a very hard worker and moved around among several fields through the years and made some fine contributions to science.
There’s one comment about Cornell, where in the astrophysics work there were a number of very detailed computations, numerical computations that were involved. They were done by a WPA project. How did this come about?
Well, actually this work was not done at Cornell, but later at Rochester. Interestingly enough, I asked one of my NYA students at Rochester, Herbert York, to do these computations. York later became head of defense research for the DOD and then Chancellor at La Jolla; he is still at La Jolla at the present time. What happened was that as a result of having done my thesis, I realized that there were some interesting problems that we could still get information about if careful numerical computations were carried out. And one of the problems was to try, by determining the temperature — density distribution inside main sequence stars more accurately to learn something about the helium content of these stars. I mentioned earlier that for main sequence stars you really had to know the hydrogen concentration, the and everything else — usually called the Russell mixture, because there was a certain combination of heavy elements: carbon, nitrogen, oxygen, iron and so on, which corresponded to the average spectral observations on main sequence stars. And so when I came to Rochester, I kept this possibility in mind.
I was awarded a Sigma Xi grant-in-aid about 1940 to pursue this work. I think it was that during Christmas of 1940 that I tried to use the University of Pennsylvania computer to do a better job on the integration of the equations of stellar equilibrium for main sequence stars. Well, this experience was a big disappointment. Penn had an analog computer with gears, many gears were involved, in my computations, and the accuracy turned out to be very poor, of the order of 10%, which was no great improvement over what you could do with an ordinary hand computer. So I decided that was a thankless task. But I kept my eye on the problem and I had some connections with the NYC WPA Mathematical Project; I knew the director, Dr. Arnold Lowan and he was always eager to do jobs for scientists. And so I submitted a proposal to compute more accurately the equations of stellar equilibrium for two typical main sequence stars, the sun — yes, that’s paper number 9 [“The Internal Temperature-Density Distribution of the Sun”]. G. Blanch was Lowan’s chief assistant, and she was so helpful, she didn’t know anything about astrophysics, that I put her name on the paper. So the WPA project computed the sun and Sirius A. These calculations led to conclusions about the need to introduce a substantial amount of helium into the chemical composition of main sequence stars. And it was those calculations, I think, which were the basis of Schwarzschild’s later approximations to the equations of state, which enabled him to do more analytic integrations to determine helium contents for a wide range of stars. In other words, he used these accurate calculations as check points, and he is well known for being involved in the helium content problem. But I think my “WPA” papers were the first to demonstrate that you really have to become serious about the large helium content of main sequence stars.
Your papers justified the use of the point convective model?
Right. The WPA computations also tried to show what the realistic model was for main sequence stars rather than Eddington’s “standard model.” Eddington’s model was just a shot in the dark in the early days in order to find simple heuristic solutions of the equations of stellar equilibrium. I don’t wish to criticize. This is an illustration of the progress of science. Until we had more knowledge about the thermonuclear reactions which were responsible for the energy production, it did not make much sense to try to work out more carefully the temperature-density distributions in the main sequence stars operating in accordance with carbon cycle and the proton-proton reactions. And I think as early as 1939 I gave a paper at Princeton of which there is only the abstract available, in which I said that probably in the sun the proton-proton reaction may be as important as the carbon cycle. It has now settled down to being chiefly the proton-proton reaction in the sun and the main sequence stars less luminous than the sun; the more luminous stars like Sirius A shine by virtue of the carbon cycle.
That came up in one of your papers –
Maybe I’m putting them together, but it was the early work that you described in the Perspectives in Modern Physics, the Bethe Festschrift. You were talking about Bethe’s work there, and then that when you picked it up, you were able to demonstrate that the proton-proton reaction predominated in the less massive stars.
Yes, this was way back. Everyone immediately jumped on the carbon cycle as the chief reaction and started forgetting about the proton-proton reaction. It was important at that time to point out that one should not, especially if one pays attention to the helium abundance in main sequence stars. Now, the Herbert York computations were published after the war. There’s a paper here I think with York that came out much later when we finally got around to publishing it. I think it was published with Phil Morse because when I got interested in the stars before 1940, Phil Morse got interested in the opacity question. And I made some trips in 1940 to Cambridge to talk with him about some of these astrophysical questions. And after the war when I published the paper with York, I think that Morse...
This is 1950, number 31, right? [“Equation of State of Hydrogen, Helium and Russell Mixture at High Temperatures and Pressure”]
Yes — Morse did the opacity computations. He published very elaborate calculations on the opacity — he got interested in that problem because of his atomic interests. And I needed better equations of state for my thesis, and so I got together with Morse. But this was all done about 1940 but I didn’t get around to publishing the results until 1950. And York, while an NYA assistant to me as an undergraduate student, helped with the detailed computations.
I’m not sure I know how that worked. Was he subsidized?
Yes, the National Youth Administration provided stipends to poor undergraduates for doing assigned jobs by the professor. So I had an NYA assistant, and I used him to help compute the equation of state. He did it quite well. But the war came, and there wasn’t time to write up the material, so it just hung around until after the war, when I finally got around to writing it up.
Now I think we’re ready to get you out of Cornell as a graduate student. I’d like to start at the point where you began to think about what would happen when you got the degree, what alternatives you had in mind, and whether you were thinking of the fact that you would be a professor at some university or whether you had anything else in mind.
I must say when I try to recall that period, I must confess that I had no career options clearly in mind. I guess the situation sort of developed naturally as I got more and more interested in astrophysics and in physics and wanted to have a career involving research. Now, the question was: what job was available? Here Bethe took complete charge. He was the one who worried about what job I would get. And to some extent I have taken over that attitude from Hans. I have accepted the responsibility of trying to place my students and have tried to keep my ears open as to possible positions. I think some professors don’t feel that responsibility, and the students scout around, make their applications and then say, “Please write a letter of reference.” Certainly in those days Bethe did concern himself with my welfare and wondered where he could take care of me. Now, what happened was that an instructorship became available at Rochester. And I don’t really remember now how many possibilities Bethe considered in his own mind. But before I had given it much thought myself, he told me: “Well, there is an instructorship for one year at Rochester, and I think it will be good for you to get this experience, and I’m driving to see my friend Weisskopf." And I think Rose Ewald — she was not then Rose Bethe came along for a picnic, and we met at Keuka Lake where I met Weisskopf, The next day I was interviewed by DuBridge in Rochester and was offered the job, Bethe said that even though this job was only for one year, he thought that it would be a good idea to take it; and he would try to get me another job, perhaps a post-doctoral fellowship, after that year. I think one other job opportunity became known to me. There were not too many openings in 1939. The other job was an instructorship at Smith College, and I was turned down. So after I was turned down there, I don’t remember any other positions for which I applied, and I accepted the Rochester offer.
You were talking about the conversation with DuBridge and then coming for one year. In that kind of conversation, when it’s only for a year, you would not have gotten into any very deep considerations of what was expected of you when there’s not a long-term basis in mind. I assume that they had in mind that you would teach some courses and that’s all.
Well, essentially the situation was that the Rochester physics department at that time had seven or eight staff people. I mean Van Voorhis was a post-doc and Kurti was another post-doc. The professors (of various ranks) were DuBridge, Sidney Barnes and T. Russell Wilkins; about five experimentalists and there were two theorists, Weisskopf and Plesset (whom I was replacing). DuBridge had been trying to get some theorists ever since he came to Rochester in 1934. The 7 Mev proton cyclotron had been started about 1935, the third cyclotron in the country. The Cornell cyclotron had been finished, a smaller one, when Livingston came from Berkeley to Cornell. And DuBridge, always attuned to developments, thought that to build a cyclotron for 7 Mev protons would be a major achievement. And so he worked very hard to secure $10,000 from the Research Corporation and with some second-hand generators from the Rochester Gas & Electric Corporation, a fine accelerator was constructed at Rochester.
I have a note that it was nearing completion in 1936.
Yes. There’s a paper that DuBridge and Barnes wrote in 1936 in which they say that it was nearing completion. In other words, it may not have been in full operation...
This is quite consistent. It may have gone into full operation about 1937, the year that Weisskopf came. That’s what I was going to say. After DuBridge came, he came as a solid-state physicist, well known for his book with Hughes on photo-electric phenomena. He had done experiments in that area. But the excitement of nuclear physics was evident when he was brought in as chairman to build up the Rochester department. He replaced Russell Wilkins, a Canadian who had studied with Rutherford but was not a broadly-based physicist albeit a great gentleman.
He was in alpha particles.
Yes, in that area he was a pioneer. But in terms of a broad knowledge of physics, DuBridge was brought in to supersede him. And so DuBridge obviously made the decision that while he would have some solid state going, he would also have the department get into nuclear physics, the wave of the future, and carried out negotiations soon after he arrived to build the small cyclotron. But at the same time he decided to build up the theoretical staff. The first theorist he brought to Rochester was Fred Seitz. I think that was 1935, and I believe Seitz stayed until 1937. And then I think somewhere around 1936, he added a second theorist called Milton Plesset, who was a student of Oppenheimer’s. He had written several nice papers with Oppenheimer on the application of relativistic quantum mechanics to electrodynamics. Well, when Seitz decided to leave in 1937 to go to Pennsylvania, Weisskopf was brought in to take his place. But apparently both Weisskopf and DuBridge were not satisfied with Plesset’s performance in the sense that he was shifting his interest, because indeed later on he went and joined the engineering school at Caltech.
And so DuBridge wanted someone to take Plesset’s place. DuBridge really wanted Charles Critchfield to replace Plesset for many reasons. But Critchfield, who was finishing the same year I was, in 1939, as a student of Teller’s at George Washington University, received a fellowship to Copenhagen, so he was not available for a year. Hence DuBridge simply wanted a theorist for one year. And I was recommended, I guess, sufficiently well by Bethe to be offered the job for one year, and the letter of appointment said, “This appointment is for one year with no possibility of renewal,” I mean in the most unequivocal language possible. Now, what happened was that the war broke out September 1st, 1939, and I arrived in Rochester about a week after World War II broke out. And a few days after I arrived, an assistant professor, J. Stuart Campbell, In the Institute of Optics, which was a separate department at the University of Rochester, committed suicide.
Naturally, everyone was terribly upset. And, in particular, the question was raised of how to get someone to replace Campbell at that late date, and I remember suggesting to Weisskopf that perhaps Critchfield had not gone to Copenhagen and that he might want to recommend Critchfield’s name to DuBridge as a last-minute replacement. And I remember Weisskopf saying to me: “Well, you’re cooking your own goose, because DuBridge wanted to have Critchfield here,” and I replied, “Let the best man win.” DuBridge was pleased with the suggestion and offered the job to Critchfield; I was right — he had not gone to Copenhagen — and he accepted the offer. So Critchfield and I were together in Rochester. Through a series of circumstances, I sort of published more papers than he did that year. But the other point was — he’s a very intelligent physicist; he’s now at Los Alamos — It turned out that he was not top successful a teacher. I guess I was considered a better teacher. And as a result Weisskopf and DuBridge decided that I should be kept and Critchfield should be released. And so DuBridge helped Critchfield get another post-doctoral fellowship after one year. I forget now just where he went. So that’s how I happened to remain In Rochester.
That was a good move, suggesting that he come at that time.
Well, I didn’t know that he was DuBridge’s candidate when I suggested it, and I am not surprised that I gave the gentlemanly reaction when Weisskopf said, “You’re cooking your own goose.” I know for a fact that after another year or so that Weisskopf, like most other people in the country, was eager to attract Schwinger to Rochester, as a replacement for me. But Schwinger decided he didn’t want to come to Rochester and I guess Weisskopf didn’t have any other candidate. C'est la vie.
That’s the story of the last 30 years and of your involvement here. Was it clear in your mind once you were here more than a year that this would be the kind of environment you had in mind?
No, I would not say it was clear at all. I was told by Professor Boothroyd, who was the chairman of the astronomy department at Cornell when I finished there: “Well, that’s a fine place, and I think you’ll be staying there for a long time.” I’ve always remembered that, because I must say that certainly at the beginning I only expected to stay for one year. And even after my appointment was renewed, the war reached the U.S. and it was very difficult to know what anyone’s future would be. Well, we can go on from there. Actually, Weisskopf was not treated too well in Rochester in spite of his international reputation. He was only an assistant professor and was not promoted. I was an instructor for four years and was promoted to an assistant professorship just before I left for war work in April, 1943 — the day I was married. We can go into that, if you want, very quickly. You will recall that Pearl Harbor occurred In December, 1941. DuBridge had left in December, 1940 to head up the Radiation Lab, as a precautionary move, to get into the radar game. And he started to try to persuade scientists throughout the country to help with the research problems of the Radiation Lab. Hans Bethe took on a major theoretical project for the Rad. Lab. I’ll talk a little about that in a while. And then he asked some of us to join him, as the leader of this university group, to help the Radiation Lab at a distance, so to speak. And, of course, summers we went to Cambridge. But meanwhile, we were supposed to stay at our universities and complete the training of as many students as possible. So, in Bethe’s group were Schwinger, Henry Hurwitz (now at the G.E. research labs), who was a Ph.D. from Cornell, J. F. Carlson and Julian Knipp, two students of Oppenheimer, and myself.
And these were all theorists.
Yes, these were all theorists. Several were Oppenheimer’s students, because he was the chief source of American Ph.D.s. And I guess Bethe was trusted...He was a citizen by that time, I guess.
Bethe was involved even in the early bomb work.
This is earlier. So anyway we worked on the radar project, even before Pearl Harbor. But after Pearl Harbor, it was clear that we had to be thinking more seriously about joining different war projects on a fulltime basis. We really put aside any other research after December, 1941, and for another year or so finished up with our students. For example, Herbert York finished a master’s with me at that time. By the spring of 1943 all the research physicists had left Rochester. The department was left in the hands of the old man Fairbanks, who was just a teacher and could not do any research. And he took care of the physics teaching of cadets — all the various programs — V-12 or whatever the programs were. But in terms of my own career, I guess by that time DuBridge and Weisskopf felt that I ought to be kept on and be promoted to assistant professor, effective September 1943. But in April 1943 I left for the Montreal Atomic Bomb Laboratory, and President Valentine of the University of Rochester decided that it wasn’t necessary to promote me after all. He had accepted DuBridge’s recommendation at the beginning of 1943 but since I left in April, he proposed that my appointment take effect after the war. And DuBridge was ready to acquiesce until I pointed out to Weisskopf that this was rather unreasonable, and so the promotion went through. We can go on to the war years, but that’s up to you. Shall we do that? Or the Rochester years.
The pre—war Rochester period. Some of the papers started coming with Weisskopf.
Only one paper really.
Well, I thought...
The one on the...
That’s right. You’re perfectly right: Paper number 7. But the earlier ones we were talking about — the heavy electron paper I started to ask you before when we took a break about how Nordsieck came into the story, since you thanked him for discussions along with Weisskopf. If I remember, I suggested before that he was in Europe on some kind of fellowship in 1936 and then came back and got his position at Columbia. Where did you cross paths with him?
Well, I must have crossed paths at some meeting at Columbia. I thanked him for teaching me how to cut off divergent integrals by means of a procedure which he had adopted in one of his papers. It was a mathematical point.
There was no real relationship.
No real relationship. It was just a mathematical point. I said earlier that Weisskopf had hoped, when I was first interviewed for the Rochester job, that I would be interested in working on quantum electrodynamics, because he had written a rather important paper on the subject. That is to say, by hindsight we realize that it was important, where he calculated the self-energy effects of electrons and showed how the electron pair theory led to a more tractable logarithmic divergence. And perhaps if I had accepted Weisskopf’s challenge, some of the post-war quantum electrodynamics might have seen an earlier birth — I don’t know. The fact remains that my failure to pick up that challenge did not lead Weisskopf to proceed any further himself. He was more interested and acted as the chief consultant on the nuclear physics program at Rochester at that time. And that’s how his interest in nuclear physics developed, because of the cyclotron here and the new types of reactions they were discovering. I instead wished to develop ideas of my own, and so I didn’t jump at that opportunity, I somehow was not interested in quantum electrodynamics. I think partly due to the fact that because I had devoted so much of my thesis work to astrophysics, I had not sharpened up sufficiently the tools for calculation in quantum electrodynamics to make me feel at home in that field and partly, I guess, because my style is different I prefer to look at fresh problems instead of digging into something that someone else had already started in a serious way. In any case, I did not pick up the challenge and Weisskopf and I have sometimes chatted about the fact that maybe if we had joined forces in 1939, we could have...Because Weisskopf had realized some basic things. He didn’t know about renormalization, but he had been able to identify the types of divergences and the extent to which the pair theory helped to reduce them. There is a crucial paper published by Weisskopf in the Physical Review in 1938.
His interest I think had started even earlier than that. This is a theme in his work I think dating from the early thirties. Just one career detail: You were a visiting lecturer at Harvard in 1940. What was that?
That was connected with my work on the white dwarf stars and winning the A. Cressy Morrison Prize in 1940. In fact, I guess Critchfield and I were the first young generation of physicists to stumble into the field of astrophysics. Our teachers, Teller and Bethe, had been introduced to the field by Gamow; but we were the first physicists to receive Ph.D.s on astrophysical subjects. So it was not a big community. There was this New York Academy of Sciences meeting, to which I referred earlier, where I was introduced to the “astronomical establishment,” if you will; and so I received an invitation to give some summer lectures at Harvard, where, of course, I had a wonderful opportunity to meet many of the later leaders in American astronomy. I think it was during that summer that I met Leo Goldberg, who’s now the Director of the Harvard College Observatory. I think that’s the summer that I met Martin Schwarzschild. And Henry Norris Russell was there at the time. Of course, I had met Chandrasekhar because of the invitation he gave me to Yerkes, and Harlow Shapley had presided at the New York Academy meeting; so I really got to know the leading astronomers. And it’s quite possible that if the war had not come along, I might have continued in astronomy. Certainly the appreciation which the astronomers showed for my rather modest contributions was very conducive to continuing in that field.
How long did you stay at Harvard?
That was just during the summer. They had a very interesting summer program, and I was asked to give some of the lectures in that summer program.
Was that Harvard College Observatory?
That was under Shapley’s wing.
Right. Some of the other lecturers were Henry Norris Russell and so on. I was in very good company as a young man.
That was an interlude that I wanted to cover. Now, I’d like to get back for a minute to the heavy electron paper. You said a few things about it before. I’m curious as to what Bethe’s reaction to this was, because, after all, you tackled a couple of things here, using the heavy electron terminology, which was not a natural thing for him to use and which he objected to; but also you came to a couple of conclusions. I think you said specifically that your paper “established that the existence of unobserved neutral masons is not indispensable to a theory of nuclear forces.” That seems to me very diplomatically worded. And yet it’s directed at Bethe’s papers. I’m curious as to whether there had been discussions with you on this, whether there were substantial disagreements and whether there were reactions from him on this before, during or after.
Curiously enough, I don’t think we really conversed very much about that paper. First of all, you have to realize that in Bethe’s own career he did not ever spend a lot of time on the meson theory of nuclear forces. In a sense, his own paper was a rather isolated one. I don’t remember. He wrote some other papers too where he was trying to understand beta decay—with Nordheim—on the basis of meson theory. He did write several papers about 1940, but I don’t think he ever returned much to that subject. So he was not himself quite so deeply committed to any point of view. And I think he must have taken the attitude that he was exploring one point of view and I was exploring another, and I think he felt: “Well, it’s interesting that you can get similar results,” I frankly don’t think either one of us thought that we had written terribly important papers. You know, sometimes you develop a theory and you sort of are convinced that you’ve really hit on something, you’ve understood the language of nature, and that’s it. I’ve had such feelings along the way — like the two-meson theory. I was really sure of that. But in this case, he used a neutral meson, and only the charged mesons were the observed particles. I was treating the charged mesons as the mediators of the nuclear force and using a pair theory. Each approach was defective, but each of us was trying to explore the problem a bit further. I think it was just interest and curiosity so far as he was concerned and also as far as I was concerned.
It wasn’t something that was much in the air at the time with a lot of people suggesting new kinds of mesons?
No, this was still very early. This was 1940. The only mesons that had been suggested and for which there was any evidence was the Yukawa-type meson to do the nuclear force job and by indirect deduction you said you needed charged ones to explain the exchange forces and neutral ones to explain the ordinary forces. It is true that various types of Yukawa-type mesons were postulated (e.g. Moller-Rosenfeld mixture) to modify the radial dependence of the nuclear force but there was no premonition of the two-meson theory. Let me say, though, that the experiment which was crucial in establishing the existence of an exchange force — that is, where the proton changed into a neutron and the neutron into a proton in a collision — was done at Berkeley a decade later via high-energy nucleon- nucleon scattering. One found in this experiment that the cross-section for scattering had maxima for small momentum transfer and for large momentum transfer. For a normal force the differential cross-section decreases monotonically as the angle increases, as the momentum transfer becomes bigger; because it’s harder to have large momentum transfers.
But if you exchange the charge, then what was a small momentum transfer becomes a simulated large one. And that experiment was only done when the synchro-cyclotrons were ready after the war — beginning with Berkeley. So the direct demonstration of an exchange force came only in 1949 or 1950. Until then the evidence for exchange forces which had been postulated in order to explain the saturation of nuclear forces was indirect. And therefore you could not be sure whether you really needed exchange forces — and therefore charged mesons — to explain the saturation. And the reason my heavy electron theory was picked up by Wentzel and also by Teller was because they saw in it possibilities which I only vaguely perceived — namely, Wentzel in terms of a strong coupling model, which would lead to desirable reductions in cross-sections; and I think Teller because he argued that if you have Fermions as the mediating particles, you can produce saturation effects even for an ordinary force. Bethe himself did not dig so deeply into the meson theory of nuclear forces. So the answer to your question is that Bethe and I each in our own way only touched the surface of the nuclear force problem in 1940 and did not make a big issue of our differences.
And you weren’t the one to pursue it anyway?
That’s right. I sort of dropped the heavy electron theory.
At that point and picked up a new thread in your work.
True. Later on, the heavy electron paper came back to haunt me in connection with my two-meson theory in 1947 as we shall see.
On the paper with Weisskopf, the one you did with him in 1941, did the experimental results involve the cyclotron at Rochester in any way?
No, because the small cyclotron was not producing mesons.
No, you couldn’t have with that machine.
That was a low-energy accelerator. There were two cyclotrons at Rochester after the war — the small one which DuBridge and Barnes had built, and the large one which was built after the war: again started by DuBridge and built by Barnes (but that was the 240 Mev machine, which was not ready until 1949).
In your theoretical work, did any of these ideas involve the kinds of thinking that would be affected by that first cyclotron?
No. Weisskopf was the theorist for that small machine, and I was not interested. He was taking good care of that experimental nuclear physics program. In a sense I was pulling him out into another area by...
Into the next generation of machines.
And the cosmic ray field. I was interested in the high energy cosmic ray evidence.
By the way, on the original cyclotron at Rochester, they indicated that it was based on calculations of Bethe and Livingston. That would have been before Weisskopf came.
Oh, sure, because it was started before Weisskopf came. DuBridge must have consulted Bethe frequently.
The next point I want to take up gets into the forbidden transitions, which you commented on before very briefly. A couple of questions about that. I guess that you’ve already answered the point about getting into that through astrophysics and the earlier work. And then you talked of having discussed this with Weisskopf, and I wanted to know what his contribution was in this discussion. And then did the question of the tensor interaction have anything to do with your interest in nuclear forces?
The tensor interaction? What do you mean?
Well, where you were talking about your results. First of all, they supported the Gamow-Teller rule and then you discovered that a tensor reaction was required to explain the beta lifetimes and the energy spectrum.
First, I must emphasize that the tensor interaction in nuclear forces is not the same as in beta decay. The beta decay could have been axial vector — as far as the Gamow-Teller rule is concerned — except that one was arguing for tensor from some other evidence, perhaps. That is, maybe I had some additional evidence for the tensor versus the axial vector interaction. I’d have to check back on that.
You were talking about the tensor interaction being required to explain the beta lifetimes and the energy spectrum.
Is that quoted from my paper?
No, it’s summarized right here.
Well, let me say a little about it, and then we can look at that paper.
We’re talking now about paper number 10, this 1942 paper. [“Forbidden Transitions in Beta-Decay”]
Well, certainly beta radioactivity was very relevant to the nuclear physics experimental program that was going on at Rochester, because radioactive isotypes were being produced in (p,n) reactions. My interest in it, however, again was more from the direction of trying to pin down the nature of the interaction rather than, say, learning about spins and parities of nuclear states. So I would say that the more important influence emerged out of the astrophysical work in that I was interested in Fermi versus Gamow-Teller selection rules. And I had the idea that perhaps I could demonstrate the presence of the Gamow Teller rule by studying the highly forbidden transitions. In other words, when you go to the highly forbidden transitions, you1re really testing beta decay theory in much greater detail; in allowed transitions you replace the crucial interaction operator in the nuclear matrix element by 1; whereas when you consider forbidden transitions, you really have to expand to much higher powers of that operator — and you then can get unique predictions about the forbidden spectrum which are different from the allowed spectrum. In Paper Number 10, I examined in elaborate detail the implications for the fundamental theory of beta emitters like K40 and Be10. I was struck by the very long lifetimes of these radioactive nuclei. And I reasoned that if I could show that I must have Gamow-Teller selection rules to explain these highly forbidden beta emitters, then I would predict unique forbidden spectra — which were different from the allowed spectra — depending on the spin change in the beta decay. Let me put that another way. In the case of K40, the spin is known to be 4, and it decays to Ca40, which has spin zero.
So we have a spin change of four units which is a large amount of angular momentum change and really probes the theory. Now, if three units of the four came from orbital angular momentum and one unit from the spin operator (Gamow-Teller rule), then I could predict a unique spectrum. If, however, all four units came from orbital angular momentum (Fermi rule), then there would be great ambiguity, because you could have many different matrix elements contributing to the final beta spectrum. The uniquely predicted beta spectra for K40 and Be10 were later confirmed by experiment. K40 was easy but Be10 was more difficult. At first, Don Hughes (who has since passed away but before then was at Brookhaven), claimed to measure an allowed spectrum for Bel0. Madame Wu then redid the measurement and came right on the nose with the predicted forbidden spectrum. Apart from the theory of forbidden transitions in beta decay, I computed in this paper the prediction for forbidden orbital electron capture. That is, I developed the consequences for the capture of orbital electrons, which is the inverse of beta decay, for forbidden transitions. Moller had developed a theory of allowed electron capture right after the original beta decay theory was proposed by Fermi, In extending the theory to forbidden transitions, I established certain subtle points about whether the capture was from the LI or LII election shells, which enabled one to say something about the spins and parities of the nuclei. And while in those days — in 1942 — these nuances were too early for experimental confirmation, after the war this approach developed into a very fruitful area; and M. E. Rose is the one who sort of cleaned up my calculations in the sense that he put in screening for the electron wave functions and so on.
That was much later.
Oh, yes, in the l95Os. Because it took quite a long time for the development of experimental techniques before these types of measurement could be made. So paper 10 covered several subjects. In one sense, while I started out being interested primarily in the nature of the weak interaction, I ended up by indicating how the theory could serve as a probe for learning more about nuclear states. Now, the question you asked about the tensor interaction in beta decay. The point was that Konopinski and Uhlenbeck, in their own paper on forbidden transitions, by analyzing a large number of spectra of allowed transitions, had come to the conclusion that you had to have a combination of tensor and vector interactions in beta decay. Now, for allowed transitions, the scalar and the vector interactions yield a Fermi selection rule; while the tensor and the axial-vector interactions yield a Gamow-Teller selection rule. So in allowed transitions you cannot tell the difference between scalar or vector on the one hand or between tensor and axial-vector on the other. As we know now, the correct theory is vector and axial-vector.
But, for example, in 1956 when Lee and Yang presented their parity-breakdown hypothesis, they thought beta decay was governed by a mixture of scalar and tensor, and that the neutrino was right-handed. But in the early l940s Konopinski and Uhlenbeck were giving arguments that the beta decay interaction was tensor and vector, which was a combination different from the two I’ve just mentioned. So what I was saying, through the train of arguments connected with the highly forbidden transitions, that I had established the existence of the Gamow-Teller rule; and since Konopinski and Uhlenbeck were arguing that other data required a combination of tensor and vector, I had to conclude that the tensor interaction was responsible for the Gamow-Teller rule. But, of course, if they had come out for a combination of axial-vector and scalar, I would have been compelled to conclude that the axial-vector was present; because as far as this prediction was concerned — the unique spectrum for a highly forbidden transition — it works equally well both tensor and axial-vector. Now it’s axial-vector, and this is equally correct. The Konopinski-Uhlenbeck argument was a gratuitous input, and we now know that the Gamow-Teller rule is the consequence of an axial-vector interaction with a left-handed neutrino.
We were looking for possible links with other works. The other point I’m interested in is the nature of the conversations with Weisskopf.
As I recall, one of his contributions was to help check out my method of calculation. I discussed this with him to be sure he couldn’t detect any flaws in it. He agreed that it was correct, and then he reminded me about Moller’s work on allowed orbital election capture because he had been in Copenhagen when it was done. And then in discussing what one might learn about some of these nuclear states, I certainly benefitted from his knowledge in this regard.
You didn’t have a chance to pursue this work because of the war, and I notice that in 1942 you were visiting MIT as a visiting lecturer. Was that in connection with the stint at the Radiation Lab?
Yes. You see, as soon as Pearl Harbor occurred, in December 1941, I was just finishing up this paper, and so I took another month to complete it; and then I suspended my unclassified research. I immediately plunged into the Bethe project. I think this project started somewhat before Pearl Harbor, but it’s quite possible it started just after. Everyone was mobilized after Pearl Harbor as rapidly as possible. I know that after January 16, 1942 I was working on the Bethe project; and that meant exclusive attention to radar problems; diffraction through small holes, wave guides and so on and so forth. And in the summer of 1942, I was at the Radiation Lab the entire summer, and Jay Stratton was then chairman of the physics department, and he asked me if I would teach a summer course in mathematical physics to give MIT a hand while I was at the Radiation Lab, which I did. So I taught during the summer of 1942 while I was continuing research on radar. [pausing]
We’re resuming now after a break for a very pleasant dinner.
That dinner is recorded for posterity. As far as the radar work was concerned, perhaps some comments might be in order. Bethe devoted his time chiefly to developing a rigorous theory of diffraction through small holes because in the radar game we were talking about 10—centimeter and 3-centimeter waves where the wavelength is comparable to the dimensions of the objects we are talking about; and therefore the old approximations like Huygens principle are no longer valid, and one had to develop more rigorous methods. Bethe tried to develop such methods. But Schwinger really started blossoming forth in his formal approach to these problems, and in this context he developed Green’s function methods to solve these electromagnetic problems, which I think did have an impact later on his approach to quantum electrodynamics.
I was more interested in direct applications of the theory to the design of practical radar instruments. And I always was proud after the war of having designed a TR box in the 10-centimeter range to transmit and receive signals, which was a crucial component of a radar system adopted and used throughout the war. I wrote a series of published papers, as did many of the other members of the group. And I also worked on such problems as the transmission of electromagnetic energy through bent wave guides and I applied methods like the WKB method to these problems.
This led to an amusing incident during my stay in Canada about a year or so later when Lord Appleton visited the Montreal project and asked me if I could help him solve the problem of the reflection of electromagnetic waves through the earth’s atmosphere. I suggested that probably the WKB method could be applied. He hadn’t heard the term WKB method and asked if I would please write him a memorandum. And I had a hunch that Lord Rayleigh probably had solved that problem as well as many others in electromagnetic theory. I might say that I remember one seminar at the Radiation Lab where Bethe had proudly developed a method for diffraction through small holes, and Otto Halpern stood up and said that Lord Rayleigh had solved the problem by the same method. So I had been sensitized to Lord Rayleigh’s prowess in solving classical electromagnetic problems. And sure enough I discovered that Lord Rayleigh had invented the WKB method before WKB (Wentzel, Kramer’s and Brillouin) about 1907 or 1908 precisely in connection with the problem of the reflection of electromagnetic waves through an atmosphere of varying refractive index. And I wrote to Lord Appleton and referred him to Lord Rayleigh’s paper, for which he expressed great thanks.
But the WKB method is a very interesting technique and certainly was very useful for the problem of bent wave guides. That was one contribution. There were other theoretical contributions, but I would say that during the year one of the things that I remember best was the design of the TR box based on all the parameters that were required, using a combination of optimizing the theory and the needs of the engineers.
There was a device used in radar work called the “black box.” That wasn’t it?
”Binding Energy of 4n Nuclei on the Alpha-particle Model,” with B. O. Gronblom, Phys. Rev. 55, 229, 1939.
”The Internal Temperature of White Dwarf Stars”