The Collected Works of Eugene Paul Wigner. Part A: The Scientific Papers, vol. II: Nuclear Physics

The Collected Works of Eugene Paul Wigner
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In Szilard enlisted Wigner and Teller to discuss the threat of an atomic bomb with Albert Einstein. They felt that only Einstein had sufficient prestige and influence to convey the urgency of the serious problem to President Franklin Delano Roosevelt. Einstein understood the problem at once and immediately signed the letter prepared by the Hungarian immigrants.

Though Einstein played no subsequent role in atomic bomb development, his message to Roosevelt is regarded as the catalyst that led to the massive Manhattan Project , which resulted in the successful development of the uranium bomb that devastated Hiroshima on 6 August and the plutonium weapon that struck Nagasaki three days later, ending World War II. Although Wigner, Szilard, and Teller had started the program and contributed importantly to technical phases of building the nuclear weapons subsequently used against Japan, they ultimately urged that the bomb not be used.

They expressed their objections to the Hiroshima bombing in the form of a petition written by Szilard that received the signatures of sixty-seven other Manhattan Project scientists. The administration of Harry S. Truman nonetheless decided to drop the bomb. From to , before returning to Princeton, Wigner was director of research and development at the Clinton Laboratories in Oak Ridge, Tennessee later to become Oak Ridge National Laboratory , a group of four hundred scientists and technical staff engaged in research and development under government contract.

At the time, the reactors at the site were the principal source of radioactive isotopes for use in fundamental atomic research and for human applications in medical diagnosis using tracers and therapy in the treatment of cancer. Hans D. Jensen for their separate discoveries in the theory of the nucleus and fundamental atomic particles.

Unlike most Nobel scientific awards, which are generally given for unique single discoveries or inventions, the award to Wigner recognized his contributions to many different areas of nuclear physics over a period beginning in the late s and extending for more than three decades. The parity law states that particles emitted during a physical process should emanate from the left and right in equal numbers or equivalently that a nuclear process should be indistinguishable from its mirror image.

In the s he pursued methods of protection against nuclear weapons effects which presumed that nuclear war might be survivable if suitable civil defense measures were taken. The advent of hydrogen bombs a thousand times more powerful than the atomic weapons employed against Japan made the defense measures advocated by Wigner questionable.

Robert Oppenheimer, the scientific head of the Manhattan Project, losing his government secret security clearance in In Wigner married Amelia Z. Frank, who died in That year Wigner became a naturalized citizen of the United States. They had two children. Wigner retired as professor emeritus from Princeton in He died of pneumonia at the age of ninety-two at the Medical Center in Princeton.

Along with the Nobel Prize, he was the recipient of honorary doctorate degrees from Princeton and twenty-six other colleges and universities in the United States, Europe, and Israel. In he received the U. Wigner Award. The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve. We should be grateful for it and hope that it will remain valid in future research and that it will extend, for better or for worse, to our pleasure even though perhaps also to our bafflement, to wide branches of learning.

See The Recollections of Eugene P. Kursunoglu, the point of view of one great scientist for another reveals much about the character of each of them. Richard P. Hewlett and Oscar E. Anderson, Jr. Also see G. Tributes to Wigner in the months after his death appeared in Current Science 69 : and Physics Today 48, no.

An obituary is in the New York Times 4 Jan. Doctors incorrectly diagnosed a childhood illness as tuberculosis. While Wigner was recuperating in a sanatorium, he pondered mathematics problems. Wigner attended Lutheran High School, Budapest — , and met the Hungarian-born mathematician and mathematical physicist John von Neumann who, he said, "was a much better mathematician than I was and a better scientist.

But I knew more physics. In Wigner obtained his doctorate under fellow Hungarian Michael Polyani, a physical chemist, economist, and philosopher. Wigner was invited back to Technische Hochschule as an assistant professor in the physics department. He immigrated to the United States in , joined the faculty at Princeton University , and devoted himself to the study of atoms and their applications.

He was naturalized as an American citizen in From to he taught at the University of Wisconsin and then returned to Princeton, where he spent the remainder of his career. He was named Thomas B. Jones Professor of Mathematical Physics in and emeritus professor in During his years at Princeton, he also spent time at the University of Chicago Metallurgical Laboratory and directed a civil defense project for the National Academy of Sciences and a similar project for the Oak Ridge National Laboratory — Wigner's statement "The problem of modern physics is now: What is the structure of the nucleus?

He helped develop the first nuclear reactors and the first nuclear bomb. For his detailed design of the reactors, Wigner was called "the first nuclear engineer. Killian, Jr. One of Wigner's favorite sayings was "The optimist regards the future as uncertain. As an early refugee from Nazi Germany, he worried, during the late s, that the United States did not take Hitler seriously enough.

Later he worried about Stalin's aims in the Soviet Union. During the s he seemed certain that nuclear war was imminent. Roosevelt of the threat of the Nazi's nuclear weapons. In Roosevelt established the University of Chicago Manhattan Project to construct an atomic bomb. Wigner worked on that project — and was Director of Research and Development at Clinton Laboratories — At Princeton, Wigner developed the ideas that eventually resulted in his receiving the Nobel Prize in physics.

His Nobel lecture on December 12— " Events, Laws of Nature, and Invariance Principles"—was a discussion of the general role of symmetry and invariance in modern and classical physics. Wigner supported his thesis that the laws of nature form the raw material in all natural sciences and said that the success of physics was its explanation of the regularities of nature.

Wigner's Nobel Prize was representative of the s' emphasis on quantum mechanics and its focus on the study of the microcosm.

During debates on the Princeton campus over the American incursion into Laos, Wigner argued that scientists should be advisers to the government. Others believed that scientists should rise above the political fray and keep themselves separate from political ends. Wigner, however, believed in a strong civil defense , and many liberals of the s saw his outlook as outdated and bleak.

Politically, he was a conservative, and he was accused of being a hardliner on the war in Vietnam. Hostile faculty and students attacked his views in Generally, however, his priority was physics, and he was largely divorced from social issues. Wigner's name was synonymous with scientific discovery: the Wigner-Eckart theorem in group theory; the Wigner coefficients in the quantum theory of angular momentum; the Wigner effect, the Wigner correlation energy, and the Wigner crystal in solids; the Wigner force and the Breit-Wigner formula in nuclear physics ; and the Wigner distribution in quantum chaos.

What Wigner called his "precious field" was the application of fundamental principles of symmetry in physics. He coauthored numerous books on nuclear reactors and nuclear structure, including more than five hundred papers published in eight volumes. Official recognition for his nuclear research included the U.

He received honorary degrees from more than twenty colleges and universities in the United States and Europe. Wigner was a member of the General Advisory Committee to the U. Atomic Energy Commission from to , was reappointed in , and served until Wigner married Amelia Zipora Franck, also a physicist, on 23 December She died tragically in , a few months after their marriage. They had a son and a daughter. Following Mary's death from cancer in , Wigner married Eileen C. Hamilton in and became stepfather to her child. In an article written by Erich Vogt for Physics Today December , Wigner was described as "always genuinely solicitous of people's feelings.

In Wigner said, "The enormous usefulness of mathematics in the natural sciences is something bordering on the mysterious. Abraham Pais, a fellow physicist, wrote, "He was a very strange man and one of the giants of twentieth-century physics. During an interview with the editor Andrew Szanton, he shared his belief in the duty of physics "to provide a living picture of our world, to uncover relations between natural events, and to offer us the full unity, beauty and natural grandeur of the physical world.

Wigner's memoir is The Recollections of Eugene P. Wigner, as told to Andrew Szanton For a biography, see F. Wagner, Eugene P. Wigner: An Architect of the Atomic Age Tyler Wasson, ed. The Hungarian-born American physicist Eugene Paul Wigner formulated symmetry principles and, together with group theory, applied them in atomic, nuclear, and elementary particle physics. On November 17, , Eugene P. In he entered the Technical Institute in Budapest, where, at his father's urging, he concentrated on chemical engineering although his principal interest lay in mathematics.

A year later he transferred to the Technische Hochschule in Berlin, still majoring in engineering. However, before long he was a regular visitor at the physics colloquia attended by some of the chief leaders in physics in Germany at that time, including Albert Einstein , Walther Nernst, and Max Planck. Wigner's doctoral thesis was on the formation and disintegration of molecules.

After a year and a half of work as leather chemist, Wigner eagerly accepted the offer of an assistant professorship at the Technische Hochschule in Berlin, where, in the late s and early s, his attention turned toward the exploration of symmetry principles in atomic physics. Related to this was Wigner's recognition that group theory, a branch of mathematics inaugurated almost years earlier, could be used to great advantage in accounting for the quantummechanical interpretation of atomic spectra.

His book on this topic, Gruppentheorie and ihre Anwendung auf die Quantenmechanik der Atomspektren ; trans. Wigner's stay in Berlin ended in when the Nazis came to power. His first post in the United States was at Princeton University , the second at the University of Wisconsin In he returned to Princeton as Thomas D. Jones professor of mathematical physics. During the s Wigner followed with keen interest research on neutron capture, and he was one of the first to realize its awesome and immediate potentialities.

She died the following year. After her death Wigner married Eileen Hamilton and had another daughter, Erika. Among his early efforts to alert the government of the United States was his visit, in the summer of with Leo Szilard , to Albert Einstein on Long Island. What happened made history.

At Wigner's and Szilard's pleading, Einstein consented to address a letter to President Roosevelt about the urgency of producing atomic weapons. In the actual production of the first atomic bomb , Wigner's role was crucial. Wigner not only took a most active part in achieving the first controlled nuclear reaction in Chicago in December , but it became his task to design the first large-scale nuclear reactor. His secret report of January 9, , outlined the details of the huge reactor, a million times more powerful than the first, to be built near the banks of the Columbia River.

The gigantic measure of problems to be solved can be gauged from the fact that Wigner's design called for tons of uranium and 1, tons of graphite. He also successfully argued that the cooling should be done by water running throughout the whole graphite structure in pipes whose central part contained the uranium. It is safe to assume that Wigner's feat saved about a year in the production of the bomb and also in the duration of the war. After the war he remained a leader in the investigation of the very essence of reactor theory, the neutron chain reaction , as evidenced by his authoritative work written jointly with A.

In the s but especially in the s, Wigner's attention increasingly turned to some fundamental questions of physical science and to their major philosophical implications. In Wigner received the Order of the Banner of the Republic of Hungary with Rubies from his newly democratized birthplace, Hungary. In , he was presented with Hungary's highest recognition, the Order of Merit.

Most significantly, in , is Wigner's award of the Nobel physics prize for "systematically improving and extending the methods of quantum mechanics and applying them widely. This marked an unusual departure for the Nobel Committee, which normally awards the prize for a single discovery or invention. Wigner, who retired from Princeton in , was also active on behalf of other scientists. His dedication to the defense of America's freedom, and of freedom everywhere, constitutes indeed a major aspect of his life and activities. It was the same unconditional appreciation of freedom, whether threatened by dictatorship from the right or the left, that determined Wigner's position amidst the debates on nuclear armament and civil defense.

His philosophy is best evidenced by his insistence on the crucial importance of the role of nonscientists in the modern scientific world: "The struggle for men's minds continues and it is quite possible that the conflict between democracy and dictatorships will be won not by armies, not even by scientists, but by philosophers, psychologists, and missionaries who articulate and communicate our ideals. Wigner's Symmetries and Reflections: Scientific Essays contains a selection of his less technical papers on a wide range of subjects.

There is no comprehensive account of Wigner's life and work. A profile of him appears in Robert H. The history of modern physics, of which he was a part, is entertainingly given in George Gamow , Biography of Physics Wigner was born in Budapest and was one of a small number of extraordinarily talented Hungarian-born physicists who contributed to the transformation of Newtonian physics.

Wigner obtained his doctorate from the Technische Hochschule later Universitaet in Berlin in , where his contacts with physicists of equal standing were established at colloquia of the German Physical Society. He worked at a Kaiser Wilhelm Institute, followed by the University of Goettingen, until his recruitment by Princeton University in , a move precipitated by his early perception of the Nazi menace. In —38 he worked at the University of Wisconsin before returning to Princeton. He moved to the University of Chicago —45 to contribute to the Manhattan Project , before becoming director of research and development at the Clinton Laboratories later Oak Ridge National Laboratory — However, from preference for teaching and research, he returned to Princeton for the rest of his career.

His main interests in theoretical physics concerned quantum mechanics and nuclear reactions but later became more philosophical. He was awarded the Nobel Prize in jointly with Maria Goeppert-Mayer and Hans Jensen for the invariance principle, which concerns the rules governing observable physical events.

Wigner, Eugene Paul 1902-1995

He was also a practical engineer. His involvement in the Manhattan Project arose from his fear that the Nazis might develop nuclear weapons , and he helped to prepare Einstein's letter to President Roosevelt. He contributed to the design of the first experimental fission reactor in Chicago and the first reactor for plutonium production at Hanford.

His honors included the U. National Medal of Science In he was elected a fellow of the Royal Society and other learned societies, including the National Academy of Sciences and the American Academy of Art and Sciences. He was a member of the General Advisory Committee to the U. Atomic Energy Commission from to , was reappointed to the Committee in , and served on it until Denman, Michael " Wigner, Eugene Paul. Denman, Michael "Wigner, Eugene Paul. Hungary, grad. Technische Hochschule, Berlin, He was a professor at Princeton from to and again from to In he became a U.

After beginning his association with the Atomic Energy Commission in , he served as a member of its general advisory committee from to and from to He shared the Nobel Prize in Physics with U. Jensen for work on the structure of the atomic nucleus. Wigner, Eugene Paul —95 US physicist, b. He was the first physicist to apply group theory to quantum mechanics.

With this technique, he discovered the law of conservation of parity. Eugene Paul Wigner All Sources -. Updated Media sources 1 About encyclopedia. Budapest, Hungary, 17 November ; d. Complete Dictionary of Scientific Biography. Learn more about citation styles Citation styles Encyclopedia. Wigner, Eugene Paul gale. Wigner, Eugene Paul b. The Scribner Encyclopedia of American Lives. Eugene Paul Wigner gale. Eugene Paul Wigner The Hungarian-born American physicist Eugene Paul Wigner formulated symmetry principles and, together with group theory, applied them in atomic, nuclear, and elementary particle physics.

Wigner, Eugene Paul columbia. Probably I knew 95 percent of what was in that paper. But to have it all together, to have it printed, was very, very useful, nevertheless. It is difficult to explain, but if one knows that 3, 5 and 7 are prime numbers, it means more than to know that 3 is a prime number, 5 is a prime number, and 7 is a prime number. And even if you knew every single thing—which I did not, probably—but even if you did know, the fact that it was put together was useful. No, excuse me. I was just going to say about the period leading up to this, that you had been in contact I assume with Bethe when he came to this country, and were you in contact with him during the period of his writing this three-part paper?

You know, my correspondence at that time was very meager. First of all, I wrote out every letter in longhand, and hence wrote very few letters. Now I can answer one of the questions you asked before. One of the half years spent in Manchester, when I did not know what to do. It does seem so. But I was in Manchester.

As I said, my future was uncertain, and Polanyi wanted to help me out and invited me for half a year to Manchester. So of the unaccounted half years, perhaps two or three, this accounts for one, Wisconsin accounts for a second. So I think I have accounted for my life. He was here. You must have visited, instead of corresponding. Was he then part of your widening circle at the time?

Or you part of his? You had no intimate contact with him at that time? I would like to ask about still because meson theory was formulated around Would you recall in what practical manner did it affect nuclear theory?

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This was one of my great errors. But you understand, that was my thought. Was this question discussed here in Princeton about nuclear forces and the origin of nuclear forces? That was part of it. Breit and I were the ones who were interested in it. Breit shared this view about meson theory, but we never discussed it. The question of nuclear forces had already come to exist in , when Heisenberg proposed that the nucleus consisted of neutrons and protons.

Did you think about what this new force might be? You see, now we believe that there are four or five types of forces, but at that time, things were quite different. The existence of four or five types of forces is a recent discovery; this discovery had not been made at that time. People thought that there were 55 different kinds of forces which someday would be explored and so on. However, we did not feel that this question was ripe for discussion,.

But, and this is very odd: I discussed that once with Teller, and I told Teller that I think at short distances the nucleons repel each other just as atoms do. But of course, again, that was a very strange thing to say, and to think that that was the origin of saturation. You can say such things, and you have no support for it, no support against it, it is a rather useless thing to say and I never did do anything about it.

It turns out, and this is the strangest thing, that it is true. But I assure you I never claimed any credit for it. I felt that this idea of exchange forces may be very artificial, but we explored it, and I came to believe in it more and more. Yes, it did. But you see, I also wrote a number of papers pointing out that it is very difficult to explain the total binding energy, if the ratio of Majorana to ordinary forces is 3 to 1, which is the necessary ratio for saturation. You referred to your guess about short-range, what would happen at short-range between nucleons.

May I ask, when was the short-range character of nuclear forces recognized, and when did charge symmetry and charge independence come to be recognized? Let me answer the questions one by one. The short-range character of the nuclear forces I think was obvious to everybody. It is often said that I recognized it. Everybody knew that. But the very short-range repulsion was recognized much later.

You know, now the nuclear forces are considered to be essentially attractive outside of a radius of 0. This is what I meant. This very short-range repulsion is what I thought, and mentioned to Teller, that this is probably the explanation. It was put forward and given good arguments for by Jastrow. The other question was…. The charge independence was the only one which I ever felt to be important, and that was due to the analysis by Breit and Present, I believe, of the experiments of Milton G. White and some other people in California. But the way we learned about it was through the experimental work of Dr.

White and some other people, and the analysis of the experiments was due, I think, to Breit and Present. I hope I am not misquoting Breit. Then a paper was also written by Breit and Condon. I remember that very well. And then Feenberg and I realized what this really means, that there is charge independence. I think that was in collaboration with Feenberg. That was in That is when you introduced the symmetric Hamiltonian and its application to the theory of nuclei. I would like to ask about your collaboration with Feenberg, and your use if isotopic spin.

The concept of isotopic spin was also, I believe, introduced by Cassen and Condon, was it? Cassen and Condon. Cassen and Condon did not introduce the concept of isotopic spin. They introduced—but should look that up—I think what they introduced was the isotopic spin variable, but not the quantum number.

But this is isotopic spin as a quantum number similar to total spin. Not introducing formally a variable to distinguish proton and neutron. That was done in the very first paper of Heisenberg. He wrote the one which I mentioned. Certainly not at this time. In fact, an erroneous belief of mine was that in the heavier nuclei when the ratio of proton to neutron number changes, there are electrons and neutrinos in the nucleus which are emitted in the beta decay.

This is the false theory of beta decay which I mentioned. And I thought that the first two are added at chlorine, the first time it happens that the neutron number exceeds the proton number, chlorine But this was an erroneous idea. And the picture—at least never heard of it. This raises a question. Now you say it is an erroneous idea.

At the time when the paper was published was there any comment on it, any criticism of it? That was a hidden remark in one of these papers, perhaps in the paper on the mass defect of helium or some paper of that sort—a rather early paper. I can find it, perhaps. You are right, here is the paper. In that paper I said that, and the conversation with Teller was very soon after that.

But what I was getting at here was more of a point about criticism and discussion through the literature. Was this the case? Did you get reaction to your papers when they were published? Or once it was in the literature, did people just assume that that was…. Did they let you know whether they agreed with it or not?

People on the whole agreed. It is not a derogatory statement, I was questioning it, as you realize, because my ideas were different. I discussed it with him. Well, we will see how experiments will turn out. What about outsiders? Because you normally would be in touch with Bethe, whether it was through a published paper or through private correspondence or personal conversation.

But what about others? I think it was. I remember Peierls and Bethe wrote articles, and they still wrote in Manchester, and they knew the paper which I had written on scattering of neutrons by protons—in They must have known it because they criticized it, in my opinion incorrectly. There was also at that time a question of time delay. People used to write letters. One notices from various correspondences that letters served the purpose of reprints.

And what was happening in Europe, if my impression is correct, is that at the more important centers—say Copenhagen, Leyden and Zurich—one morning Pauli would be in Copenhagen, the next morning he would be in Leyden, the following day in Zurich, and the whole thing would be passed around like gossip.

Not to the same extent. One of the first impressions which I got in the United States is that people here worship solid work much more than they worship it in Europe. Therefore ideas counted for less. I may have been a little bit mistaken, because my principal contact was Breit. And Breit is a little addicted to this. What about the experimental centers here? You mentioned that in the mids, by this time, experimental results began to be important, but earlier they were more of a qualitative nature. When was it that they first began to be a serious factor?

Secondly, where did you look for these results? At what centers of research? I remember that the paper on the mass defect of helium was much influenced by the measurements at Berkeley, which incidentally were—not wrong, inaccurate. And also, the mirror nuclei that you mentioned, the isotopic-spin multiplets were discovered to a large extent at Caltech. Is that correct? May I ask a question still about the ls? You had done extensive work in atomic physics, and you were one of the first people who introduced group-theoretical methods.

You mentioned earlier that this was not very popular because people did not want to learn group theory. When you went into nuclear physics, did you consider employing group-theoretical methods right away? You see, I thought that it is a useful tool; and that if there is a need for it, fine. If there is no need for it, not. Now when it turned out that protons and neutrons are similar, and I thought for a long time that the spin-dependent forces were weak, then of course it was a wonderful opportunity to introduce a type of group-theoretical results which I considered much before I really understood atomic spectroscopy correctly.

And I used that. But it was a very powerful tool. The important problems of symmetry in atoms and in solid state had been explored using group theory. Did one worry about the questions of symmetry in nuclear physics? That is very old. That I can tell you. The quantum number experimentally, as you know, was introduced by LaPorte and Russell. Then I started working on the symmetry of atomic wave functions.

That was done in What number is that on your bibliography? That the mathematical deduction was correct, was pretty obvious. But the fact that it is conserved was obvious. Nobody could contradict it. They may not like to hear it. Well, really not; because I thought that the rotational symmetry was so powerful, and ever since I have found that it is really beautiful how the spatial symmetry, which plays no role in pre-quantum mechanics, now suddenly explains so nicely the transitional properties.

I thought that that was a really remarkable accomplishment. Let me quote Jordan. Pascual Jordan. Jordan said to me once that it is very good that you worked out the symmetry of group-theoretical considerations because, had they not agreed with experiment, this would have been the last occasion to introduce changes into quantum mechanics. Because, you see, suppose the helium ground state did not come out right, what would you have done?

It would not have given a hint what to do. It just would have stood there. Something would have been wrong, but with no indication how to change it. But if something with the structure of the spectra—with the group theory had been wrong, you would have had an indication how to change it. This leads me to ask a question about the fact that at what state of the development of wave mechanics were you able to discern that it was not just a theory of atomic spectra, but it could completely describe all atomic phenomena?

Yes, I had that. This is it. You refer to your excitement about the paper by Heisenberg, Born and Jordan, in the Kuhn interview, that it meant very much to you. You discussed it with your friends in Berlin. So I assume that it was already at this point that you recognized that wave mechanics was the theory that would describe these phenomena. This was not wave mechanics. It was quantum mechanics. But you see, the paper of Born, Heisenberg and Jordan was a paper which only gave stationary states and transition probabilities.

The fact that more can be obtained was valid when Schrodinger published his paper. And that was a greater step. So was the observation of Ehrenfest, which nowadays seems trivial that the wave packet moved according to classical mechanics. He compared the motion of wave packets according to classical mechanics and quantum mechanics and found that their centers of mass move in the same way.

But it really solves things. That was conveyed to me. Bohr published a paper saying that he thinks not; that it is not the right way, that quantum mechanics did not give a proper description of nuclei. This was not said in so many words, but if you read the article, you gain this impression. I did not know what the situation was, and thought that I would try out what one obtains from quantum mechanics.

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I was not convinced that Bohr was wrong. Not at all. Does that answer your question? The important thing is that a certain amount of doubt had already been introduced, almost 30 years ago, that quantum mechanics may well not be the theory to discuss the forces between nucleons. I thought people believed it to be the theory to discuss the forces between nucleons. About the nucleons I should like to ask a question: Was it always apparent that the nucleons inside the nucleus behaved like the free nucleons? No, Bohr said no, and he said—well, the way people read Bohr… Bohr is not so easy to interpret.

He speaks so that the statements are not clear-cut. But from this, how does one conclude that Bohr is saying that the nucleons inside the nucleus are going to behave in the same way as when they are free? People are reasonably successful in explaining nuclear structure by quantum mechanics.

Now, if I think of the nucleons packed in the nucleus, and when they are free outside the nucleus, whether they have the same electro-magnetic and nuclear properties and so on? This he questioned completely. You see, Bohr spoke only in great generalities, and not in clear cut definite sentences, but he expressed doubts in his very intuitive and very charming way. He did not say, to my recollection, anything concrete. Some concrete statements on this were made, in particular by Sachs, who investigated the nuclear magnetic moments, and he thought, and many other people thought, that the magnetic moment of nuclei in the nucleus may be different from what it is outside.

I think experimental work was decisive. The discovery of the neutron. The discovery of the deuteron. I remember a conversation with the physicist whom I esteem as highly as anyone, Dirac, and I told him, how nice that a deuteron has been discovered. And he said he was skeptical of it. But that was what started me, and the knowledge of the great difference between the deuteron binding energy and helium binding energy. However, also very important was the paper of Heisenberg, which I mentioned.

The next great step was again an experimental discovery, I would say, namely, the proton-proton scattering. I think you probably can get better historical evidence or historical records of this than my recollections. Well, I learned about it from Milt White who came to Princeton after having made these experiments. I had heard, of course, about the experiments already. Then, the important theoretical work, in my opinion, was that of I think it was Breit and Present. But surely I have quoted that several times.

This opened up the way to look at nuclei, nuclear structure, from a different point of view. Now, the next thing was—I did not mention it because you put it further back—the very important work of Gamow and Condon and Guerney. But that, of course, was very important, very important. Next came the slow-neutron experiments, with artificial radioactivity, which convinced me that all that about the electrons in the nucleus was nonsense; that chlorine entering that was a personal reaction.

But anyway, the neutron experiments were then very important. I think the explanation of that was given by Breit and me. Now, the next—you see, from there on the discoveries did not change everything. They changed part of the picture, but not everything. So it was still the same type of problem you were confronted with, and it was just a question of changing a little emphasis here and there. Not little, perhaps. The next thing was, of course, the fission discovery, which again was an experimental discovery, and in some ways furthered physics enormously. Can you guess where I found out about it?

In that building there—it is the infirmary. Because I contracted jaundice and was in the infirmary for six weeks. They fed you on potatoes, beans, and everything boiled in water, and the food was not good. But the rest and the detachment were wonderful. In addition to that, Szilard was in Princeton, and he came to visit me every day, and we discussed fission problems and this and that. Well, the theory of Bohr and Wheeler of course occupied us very much, and I think it contributed to the development of our ideas about nuclear structure a great deal.

In some ways, unquestionably. Not in an obvious way. Were these regarded really as part of nuclear physics—the fact that it was believed that a meson had been discovered? Or was it thought that this was somewhat of a separate phenomenon? Well, he was at Caltech where the work was being done, and evidently had discussed this in The Harvard Tercentenary had discussed a lot of things in relation to penetrating radiation. Then we can go back and fill in. To get you in the frame of mind where you are thinking of the sequence.

Then we can fill in. Obviously there are going to be things left out, and then we can go back to these things in a few minutes. I think the shell model was really a tremendous progress, and it is a most successful model. But nobody understood it. It was an indication which stuck in my mind, and there were several other indications which stuck in my mind, but they were parts for the formation of a picture, but not yet a picture.

And the picture was formed by the discovery of the magic numbers. You know that Elsasser discovered them much before; nobody believed it. The next one was of course the rotational levels. The order. And I think I would stop here, at present. This was the last of real importance. I mentioned the rotational states. The phenomena attendant to the rotational levels. The fission work did. To the interest. You know, people got excited about it. Johnny von Neumann said that the trouble with nuclear physics is that it started at the wrong end of the periodic table.

We interrupted you? No, no, not at all. I meant to recognize there a very important peak. One of the first things to come out after the war was your work with Heisenberg, the Wigner-Heisenberg theory of the R-matrix. Was it not the most complete attempt to define these pi-nuclear reactions? Yes, Yes. I think also the mathematics which is attendant on it is fascinating. Similarly the peripheral reaction theory of—was it Salpeter? Who discovered the peripheral reaction? But, Stewart Butler Well, I would like to inquire about this question, what was the—and still is—a complete, consistent description of nuclear reactions, in the low-energy range, of course?

But that is true. I think that the R-matrix theory is very nice and very interesting. In other words, it reduces the whole continuous dependence of the cross-sections to a number of parameters. There is Mr. Rosenfeld in Manchester. He is opposed to it. Yes, the same Rosenfeld. You see, nobody suspected. The article of Feenberg and myself had rotational levels in beryllium 8, and Hund pointed it out again. And that was a real discovery that shook my belief in many of the older theories.

May I ask about these two peaks you mention, the discovery of fission and the discovery of the rotational levels in nuclei. In the case of fission, the liquid drop concept proved to be extremely successful. It showed that the characteristics could be defined in terms of the liquid drop, the deformation of the nucleus, and so on. Not very well. It gives a beautiful picture, but if you look at the details of this picture, they are very inadequately fulfilled. You see that the spontaneous fission is strong in those nuclei in which one would not expect it to be strong.

The many resonance levels in uranium were an enormous surprise. In fact, so much so that even I was amazed at it, although I was not one of the main believers in the liquid-drop model. But it was a nice picture and a beautiful picture. With apologies to my friend Charles Weiner, may introduce a metaphor which would like to know whether you think it is correct: that Bohr was often an impressionist in his physical theories, in broad strokes. And this was the description of the fission process as a liquid drop. In details it would not bear intent scrutiny, and yet the broad strokes were somehow correct.

It is correct that liquid drops also separate, if they are electrically charged. In the case of rotational levels, one finds that the nucleus behaves more like a rigid body than like a liquid drop. Yes, and there the experimental support is massive. Look at the Hafnium spectrum. One level after the other, within I think 2 percent, const. Have you completed the filling in? Here is a question on that. Meson theory was proposed in , and until the shell model came along, I would think there were many people who were common to high-energy nuclear physics, mesons and nuclear forces, low-energy physics.

There was not much compartmentalization. There was a certain fluidity, and people thought that they were somehow working on common frontiers of physics. Now, this question is as much a question of opinion as of physics. I would like to inquire from you how this fluidity helped matters, in looking at physics.

This is a very difficult question, as I am sure you know better than do, I think it gave physicists an elation, that they know physics. Now this elation-do I pronounce the word correctly? Thank you. That elation has largely disappeared. Nobody knows physics. You know, I knew physics on the whole reasonably well. However, I did not know electromagnetic theory, for instance, as well as I should have: I felt embarrassed by this and wanted to learn it.

I know that I will never learn, let us say, the present thoughts on high energy physics, that a large part of physics will always remain a closed book to me. I know the Feynman diagrams, but I am not as at home with them as I would like to be.

Advancing Research: Nuclear Physics

And perhaps I can learn that. But as to the whole of physics, I certainly cannot. Now, this illusion, to be able to know physics, or that one would like to know physics, has disappeared with the tremendous development and fragmentation of physics. And that is a sad thing.

Certainly this difference is felt by physicists who have been in physics for a full generation. Do you think that the new entrants to the profession are aware of the difference and if they are, are they bothered by it at all? I think that is similar to the question of whether the children who grow up in Russia or in China or in Hungary are missing freedom. Probably not, consciously, but their outlook on life—I think you know of it. Os homini sublime dedit, coelumque tuere inssit et erecta at sidera tollere vultus. Something has been said. Now, this type of elation is smaller in present day physics.

Similarly, I did not miss not knowing all the physiology that could have been known, all the biology and so on. Newton did know all the science of his time. In a sense I missed it, but just as the Russian child…. May I ask, you said that earlier on you were not interested in meson physics, but later on you became interested in meson physics, did you not? Critchfield, Teller and I did write one paper on it, which was unsuccessful. But yes.


I never worked on it seriously. You learned of it here. Is that agreeable? You learned of fission through Bohr, as did everyone else, on his arrival in this country. Then what type of discussion ensued at Princeton? Most of it I heard indirectly because I was in the infirmary. Szilard and I discussed it very much. And we also knew about the ideas of Bohr and Wheeler. I think we drew their attention to the fact that the calculation can be done by the so-called transition state method.

You probably knew about that, the so-called transition method? Two of the people who developed it were Pelzer and myself, for chemical reactions, and of course I knew the method, because everybody reads his own papers very carefully. We drew their attention to that. I think it was a very interesting time and quite exciting. They are neutron rich but in the first moment making an error of sign, I thought they were neutron-poor. But he came to me with that idea one morning.

He was, at that time, in the United States. There was an enterprise similar to the enterprise which he founded in England and this supported him. Do you know the Academic Assistance Council? There was one in America also, but it was not formally organized. The way I remember it, K. Herzfeld collected the money, and he was here along that line. I see. He could do things which I surely could not do.

Were you at the subsequent Washington meeting? At the Washington meeting, there again it was talked about. Was the only difference that it was a more formal presentation of it in Washington? At the Washington meeting? You see, here, there was a seminar in that little room, and Bohr spoke in that seminar. My recollections are not terribly clear on the details. I think I was in Washington, but I could not swear to it. That brings another question before I proceed with fission. It fixed something. It made it public opinion. It crystallized it. When Gamow and Teller spoke about the Gamow-Teller selection rules, altogether about the theory of beta decay.

May I ask a question on beta decay? As you have done before, Professor Wigner, could you point out the major peaks in the discussion of the universals of interaction? In the theory of our understanding of beta decay, and—there was a time when Yukawa introduced mesons, that he thought it might also be the data for explaining beta decay. Maybe it is. That had overwhelming significance.

Critchfield and I thought that there is a universal beta decay and that it is an anti-symmetric interaction. Wait a minute. It would be that, scalar and tensor? We proposed that it is anti-symmetric, and now—what does that mean really? We proposed that it is—no that was—it would have been vector. Now, our great work was that the experimental results were wrong, and indicated that it is tensor, so we abandoned it, which was lucky, because it is not right, even though the interaction is vector. This had no significance. Now, what was the next thing?

And the subsequent discovery of the V minus A interaction, which is now very well established. It was about that time, through your discussions with Szilard, that you realized the potential implications of fission. Have you ever really expressed yourself on this and given an historical account of it? If not, this might be a good time. I hope that you will preserve this, under whatever circumstances you think are best. Well, it may be interesting. No, it would not. Somebody who does not want to believe that Hitler wants to attack France will not believe it, no matter what you say or do.

But if somebody does not want to believe that civil defense can be established, he will find some reason, however idiotic. It is incomprehensible. It gets out of the realm—it gets into an emotional state. Let me ask a question, beyond that period. What do you think was the effect of the war on the development of the field of nuclear structure?

There are several factors of course to consider. You can consider that it accelerated the work in the field, or sort of left everything pending, or provided a thinking period, or brought people together to communicate. There are many things that one with no knowledge of it might suggest as possibilities.

They became, so to say, ingenious developers. And nuclear physics was delayed. Now, occasionally it is good if you go away from a subject and let it settle in your mind. You forget your prejudices and this and that. But the favorable effect was only that way. You mentioned before the R-matrix theory; the beginnings of the R-matrix theory were conceived at the end of the war, and I wrote it as we finished. Our work had become entirely of an engineering nature and calculated how thick an 3-beam has to be, and such things which are not usual for theoretical physics.

Also, the considerations on the so-called radiation damage—that turned out to be very important for solid-state physics. And finally, of course, the theory of material under very high pressure which was developed at Los Alamos. Those were very important things. Also, people learned about shock waves. Did you know that there were shock waves before? You were a baby, perhaps, at that time. But the whole knowledge of shock waves.

What about the effect of bringing large numbers of people together—including a number of people from Europe—together with the younger generation? One factor was bringing people who had been in Europe before together with people who have been in America for a long time, who were native Americans. Secondly, bringing together people from various parts of the United States, and thirdly, bringing together senior men and the younger men.

Was it effective? Did it mean anything? I made a great many friendships at that time which have lasted very well, Alvin Weinberg, whose name is probably familiar to you—is one of my closest friends—I met him through the uranium project. Young is an easy name to spell, Weinberg is probably familiar to you. There was much friction there, as you probably also know. Well, the environment itself was quite different. It was an artificial ,contrived environment, whereas Chicago was a university atmosphere.

Cyril Smith I think I met first after the war. Because we did not go along with the standard ideas. Is the standard interpretation in terms of the scientific work or in terms of the administrative procedures? No, in terms of the technical possibilities. We thought that the heat transfer agent should be water. We felt that people had been using water for cooling for many years. On the other hand, the engineers wanted to use helium cooling, which we thought would delay things unreasonably, and would introduce problems which are difficult to foresee and difficult to master, and we also felt that we knew how to calculate a heat transfer coefficient, which of course was considered by some of the engineers as interference in their prerogatives.

I want to know something about the conference and whether it was significant. It did assemble a large number of people, young Feynman at the time and Dirac was here, and people from all over the country. Oh, yes, and all over the world. We made every effort to get Russia to cooperate. It was a very interesting experience, actually. We felt we should get into equilibrium with this fact that science contributed a very important new weapon, and that this new weapon should be somehow controlled, that war should be discontinued, if that is a good word.

But there were technical papers at the meeting dealing with theoretical developments with quantum electrodynamics perhaps. As a matter of fact, Shelter Island I think I missed, but there were several conferences, principally organized by Oppenheimer, which were very important and very successful, and at those I learned a great deal. You said just now that you learned a great deal. Was this different from other conferences that you attended?

You know, I think you are right. I am not consistent. The fact is that I happened to learn about quantum electrodynamics at these conferences, and in that way for me it was different. But these conferences were small and were a select invited group. Now, did they represent the beginning of a new stage, or the end of an old one? The beginning—well, you see, he felt that physics should be kept together. I think he will give you a more eloquent motivation for that.

Part A: The Scientific Papers

But he was a natural leader, and he somehow organized them. But the point that I was getting at is the developments after the war. If we take your statements about the effect of the war, then the next question is, what happened after the war? You mentioned some theories, some ideas developing during the war.

What were the major events then that characterized the development of this field of nuclear structure? Evidently these were important years. The number of physicists has increased very much. They have much more money. Physics has expanded greatly. Well, yes, more or less. You know, I remember a conversation with Franck, James Franck.

After this rapid development which has taken place before the war, there will be a time to settle all this, and the progress of physics after the war will be much less rapid. Because I kept up with physics much better than I expected. I did not keep up well, but much better than expected. But people in high energy physics lost interest in nuclear structure. Nuclear structure became something that you had to learn.

And the high energy physicists and a number of physicists were not interested in that, and they said that fundamentally new discoveries will come at high energies. Oppenheimer was one of them. So he did not remain—you know what Bismarck said? Was this the general pattern of the older group? Would you say that this was a mass movement over into high energy? Can I suggest a final few questions, to bring it to a logical close?

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First let me ask my colleague if anything glaring has been left out. I would like, if I may, so far as physics is concerned, to complete the picture to mention, on the nuclear structure, one or two minor points. The wine bottle model—I have a high admiration for Feenberg—but this was essentially an error, similar to many errors which I mentioned, by Bohr and by myself.

The magic numbers were known and he felt that that was the easiest way to explain them. Another question which occurred to me was that nobody has successfully given a connection between the nucleon-nucleon force and the binding energy of nuclei. You know, that is so, and I mentioned that this was a problem which was always on my mind, and I wrote several papers. I pointed out that we still do not understand the magnitude of the nuclear binding energy.

I understand this situation changed a short time ago, and you should be familiar with it, because Bethe says he developed…. So, you see, that is very nice, but is it what we ask nuclear physics to explain? It has no color to it. You see, it has no color. Yesterday I listened to somebody explaining the analog states. Well, the analog states was a beautiful discovery also. Isotopic spin, what I call isotopic spin multiplets in very heavy elements. The clouded crystal ball model is a very useful model, which I also participated in. The many-body theories—Brueckner, Bethe, Goldstone—were very important and significant discoveries.

For the record I should make a minor correction in my statement about the d, p reaction, direct reaction. I think Oppenheimer and Phillips had predicted first of all in the case of light nuclei, and later on it was Guth who predicted it for heavy nuclei, and it was Stewart Butler who verified that that was so. Guth—Oak Ridge, yes—and I see him very often. No, I did not know that, thank you. That Oppenheimer did it, I did know. I would like if I may ask one question, and it is the following: This is a remark attributed to Professor Wigner, and I always have believed it to be correct.

Here is the opportunity to verify it. It quotes you as saying that you have always wanted to work in significant problems, and that you have always followed a path which led to significant problems. Also, a contribution is not really a contribution, because it has antecedents; it is exploited then by others and they add to it, and that gives it more life and content, I was happy, interested in it; enjoyed it. Whether it was significant or not is for others to judge. May I ask from which of the major pieces of work that you have done have you received the most personal enjoyment?

I think the R-matrix theory gave me very much pleasure. It was great fun. Isotopic spin introduction gave me much fun. That gave me a great deal of fun. One should not work in a field if the work, the down to earth work and thinking about it, even unsuccessfully, does not give you pleasure. The great weakness of Szilard was that he had no pleasure in work, and he did not draw the consequence of this, not to be a physicist.

He went into biology because he did not want to learn mathematics, the mathematics which was necessary for continuing physics. He liked to contribute ideas, but to work on them did not give him pleasure. They have their own foolish ideas. A final question. Well, it is on a plateau. I hope that it will come off the plateau, but it is difficult to expect it. Critchfield and E. Wigner, Phys.

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Abstract Arrival in the U. Wigner: I never have seen as much money in one heap as was offered at that time. Weiner: When you translated it into German marks, I think it must have sounded like a tremendous amount. Wigner: Well, it was. Weiner: You mentioned coming here in