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Interview of John Wheeler by Finn Aaserud on 1988 May 4, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/5063-1
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First part of interview focusses on Wheeler's work and relationship with Niels Bohr at the Copenhagen Institute in the 1930s; discovery of the meson, Delbrück effect, and resonance capture of neutrons; how the Institute worked; character of James Franck; Margrethe Bohr; origins of the compound nucleus model; Wheeler's first encounter with Bohr; pair theory; gravitational theory; Wheeler's philosophy of physics; Bohr's philosophy, the "open world."
We are beginning an interview that I hope will cover several things. Maybe I’ll say a little about the plan of the interview first. I would hope that we could start with your experience at the Niels Bohr Institute, beginning in 1934, and talk about both the period there then, and also the impact of Niels Bohr on your life more generally, and your later encounters with Niels Bohr. My main interest now, however, is in the relationship between physics and science advising and science policy in America, and very specifically the history and origins of Jason and the first fifteen years of Jason. So I would hope that we could talk specifically about your involvement in Project 137, your involvement in the pre-history of Jason and also your continuing involvement in Jason after that, but also more generally about your involvement in science policy and science advising, if not quite as detailed. That’s a big chunk, I have to admit, so I don't know how, to what extent you want to go into detail and how much time you want to devote to this plan. That will influence my questions, of course. So what do you think? I think maybe we could cover Niels Bohr this morning, if possible.
And maybe then we can go on from there to see how it develops. First of all, however, appropriate for this occasion, I would like to talk a little bit about archival material. We're going to have a meeting later today about that, and I have noticed that most of your papers, of course, are deposited at the American Philosophical Society in Philadelphia. There are also some papers with a finding aid, which I have seen at the University of Texas. I was wondering about the nature of that collection, for one thing, and for another, the fate of those papers, whether they also will be deposited at the American Philosophical Society eventually.
The papers at the University of Texas — some are in my office and are being shipped here. I have in these boxes which have just come, and that I haven’t yet unpacked, either books that I’ve written or, more numerous among them, books in which there's a chapter by me. So I need those to refer to, and so when we get a book case up here, I'm going to put them on it.
Your “autobiography case”, you mean?
Just a book case so I can refer to these things when I need them, right. And then there are other papers at Texas, some of which I let go to the archivist at the University of Texas, Frederick Birchstead. I’m a little embarrassed about that, because I would like really to have them all together at the American Philosophical Society, and yet I like symbolically to have some connection with Texas and they like to have some record of me. I would welcome your advice. It would be psychologically a little wrench to drag them out of their archives, now that I’ve let them have them, but I have not signed any paper. Because of the Nixon rule, you cannot give your own papers and get a credit for them, but you can give the papers to your family member and that family member can give it to them and get credit. The Texas archivist has just recently written to my son, asking him would he be willing to formally transfer them to the University of Texas, so the crunch is on, and therefore I’ve got to decide.
Yes. But of course Joan Warnow is the expert in this so we should probably talk to him. But my immediate feeling is that the main concern is to have them preserved. So if a chunk of your papers is at Texas, I can’t see any problem with that myself. I mean, it’s ultimately your decision, too. I corresponded with Zelda Davies and there seemed to be some interesting material there that might also pertain to our interview.
And I haven’t been out there, so, you know, that was what aroused my curiosity about this.
One more question about the archival situation. In my specific study about Jason, I have been given access to the Jason records which now are at the MITRE Corporation in Washington, outside Washington, DC. I have also seen the Charles Townes papers which are very extensive for Jason documentation. My main problem is that there is very little in the very early period, basically before 1966. After 1966, there are minutes for every steering committee meeting, for example, so it's very rich. Before that, it is much more scarce, and I was wondering, by any chance, whether you would have saved such material?
Well, right now at the American Philosophical Society Library in Philadelphia, there is an exhibit for Glass Window. I don't know whether you've seen that.
Yes, I’ve seen that.
You’ve seen it. And there is a letter in there about the early stages of Jason.
Yes, that I have. That I have. I know the material at the APS. I just was wondering whether there was something that was unprocessed.
I see. I honestly do not know what material there is. I have no memory I have a terrible memory of any specific file on that, on Jason. But there surely ought to be things, because Wigner and Morgenstern and I worked together at the beginning, making this proposal of a national defense laboratory, in reaction to Sputnik. And then we went on from there to the more immediate goal that was suggested to us by Killian. But you may have seen Herb York's autobiography.
And he talks about it.
Yes, I know that. I know that. I’m just chancing the question, you know, in case something should be in a drawer somewhere.
Yes. I don’t remember Herb York being at the surface of things, there at the beginning. I think it was to Killian that we wrote in the beginning.
Yes. I’ve seen that correspondence. I think that is the case.
Is that the case?
Yes, it is. I have the correspondence in my bag. We’ll get to that later.
I see. Right. Well, then, you know more about the beginning of Jason than I do.
Well, if I refresh your memory I’m sure that we can help each other. If you find something, by any chance, I’m just chancing this question to you in case you could help me. I know that correspondence. I’m thinking more about detailed meeting records and things like that for the early Jason meetings, which I’m missing. I’m not even sure whether they were prepared at that stage. But David Katcher, seemingly being a very orderly person, I would guess prepared such material.
David Katcher, oh good. He has some records, does he?
He has moved, and he threw out a lot of things. I haven't been very successful with him, in terms of finding records.
And he doesn’t remember either, you see, so I’m posing this question to different people.
Yes. All I recall is getting going on this, and then our meeting. But I don’t even remember the day of that, the year of that meeting. You remember the first 137 meeting?
Yes, that was in 1958.
The summer of 1958.
Summer of 1958, and it was at the National War College, Washington. It was about two weeks, if I remember correctly, and we were very fortunate to have Al Hill get hold of people who could brief us on problems.
Yes. Maybe we could get back to that, and now start with Bohr, because I would like to pull out some material on that when we talk about it.
I was just wanting this as an aside about archival material. If we now go further back in time, to the early 1930s, you finished your PhD at Johns Hopkins University in 1933. That was under Karl Herzfeld, is that right?
Karl Herzfeld, yes. I would be very interested to know whether it’s true that he was offered the special professorship here, which Wigner took instead, and whether Herzfeld turned it down. I have some reason to think that that was the case. Wigner mentioned to me at lunch last week that Van Vleck was offered it before he was offered it also. Do you know that?
Van Vleck was offered it, but he was by then in such a happy position at Harvard that he did not take it. And so they asked Van Vleck who they should get, and he suggested Wigner. But Herzfeld, my impression is, was asked also.
Even before Van Vleck, perhaps.
Well, it would seem the logical way to fit all these facts together, but I have no direct knowledge of that, and I think it's extremely interesting to know that, whether it's true.
That might be something that comes out of our discussion today on the longer term, to find papers relating to that. They should be here at Princeton somewhere, presumably, and I haven't seen any of that, I'm sorry.
Yes. So then I went to work with Breit. I had the possibility to go with either Breit or Oppenheimer. I had met both of them. Both of them were welcoming. But Oppenheimer was a man of too quick decision, and I’m a man of slow decision, and Breit was more my speed.
How were you aware of that, at that early stage in your career?
Well, from meeting them and talking with them.
That was a National Research Council Fellowship.
How did that come up? Was that fairly automatic or was that something that you had to work to get?
Oh no, I felt very lucky to get it, because there were very very few of them. That would be interesting to know, how many were awarded in physics that year.
Yes, that should be possible to find out. I haven’t done my homework that well. But that would be interesting to know.
Yes. But at any rate, then, about February of 1934, part way through my period with Breit, with his concurrence and support, I applied to have a second year and to have that second year with Bohr. And I remember writing on my form, “Because he sees further ahead than any man alive.”
Those were your words on the application?
Yes. As I recall them. I would like to get hold of the application to verify, because lord knows, one’s memory can easily be mistaken, but that’s the way I remember it.
Yes. So that was not something that you had from Breit. That was your words in the application.
Yes. I had met Bohr at the Chicago World’s Fair. I think that was 1932, but I don't swear to the date of that.
I believe it’s 1933.
I believe so, the World’s Fair, yes.
And he had spoken. Of course, it was not easy to understand what he said, but immensely impressive.
Was that a physics lecture? I think he was associated with the American Association for the Advancement of Science on that visit.
Probably so. I would like to know that. And if I remember right, my father was also there with me. My father encouraged my interest in science. He was always interested in science himself. And then of course it was necessary also to have Bohr’s approval, and I must have written him to get his OK. I cannot recall the correspondence. At any rate, then in September I did go. I had become engaged to this girl. It was the depths of the Depression. We were crazy not to get married right then and go to Copenhagen together. But no money, no go.
But she waited, fortunately.
Until I got back. But then I might have stayed longer in Copenhagen, which would have been a wonderful thing.
Was there an opportunity for that, do you think?
Well, the National Research Council Fellowship would not have been [holdable?] any longer, but I can believe that some money might have been scared up some way.
Local sources, for instance?
But there’s no use repeating Robert Frost’s poem, “The Road Not Taken.” At any rate, the freighter going over was very interesting.
There was no question in your mind about the Bohr Institute being the right place when you wrote that second application?
No, oh no, absolutely. It was a singleminded pursuit — no ifs, ands or buts, no doubts. That was the right thing.
So with Breit and Oppenheimer, there might have been a question, but you had no Oppenheimer that you compared Bohr with, when you made the decision.
No. That was where the deep things were being thought about. But I had already received word, it must have been before I went, about this meeting in London. And therefore, after I had been in Copenhagen maybe only a month, I went to the meeting. That was absolutely wonderful, because so many great themes that were to develop were taken up.
What was your knowledge of the Bohr Institute before you went?
I remember one of my New York University colleagues who was working with Breit, Harvey Hall, said to me, “Well, that’s a great place to go to, but it’s generally for mature physicists.”
That was a compliment!
Well, I don’t know whether it was a compliment. Because he didn’t say, “And it's for mature physicists.” He said, “but it’s for mature physicists.”
Yes, it might have been the very opposite of a compliment.
But that didn’t discourage you. You said something about the trip over being interesting.
Yes. I could go into immense detail. But it was so interesting, this young German going back. Now Hitler was there, now there was an opportunity, now it would make sense for him to go back. It would be so interesting to know what happened to him in the war.
Yes, that’s probably difficult to find out.
Then, of course, Betty Schultz there was an enormous help in getting started, as a secretary.
She was the one you met first?
Yes. Bohr himself, of course, through the death of his son Christian, was really out of commission for a while.
Yes. You arrived in September and he had died in July.
Yes. I recall some years later — and it might well have been 1951 — in Copenhagen, I had a long walk and talk with Bohr in the woods north of Klampenborg. We talked about all sorts of things, but also about the great religious leaders. Maybe I mentioned that?
I’m not so sure. Go on.
How they won their leadership through their ability to console people in time of loss. [Telephone interruption] — 1951, if I remember correctly, was the occasion of the meeting of the International Union of Pure and Applied Physics, being held in Copenhagen. I was then vice president. Anyway, I was talking with Bohr in the woods north of Copenhagen, just the two of us, and he was commenting on how every great religious leader had won his status through his ability to console people in time of loss. I stupidly, stupidly, stupidly didn’t realize the background of his own deep grief about the loss of his son, because I learned later that he remained inconsolable until they arranged some kind of a memorial meeting for his son.
Years and years later, you’re saying?
It was some months later after the son’s death.
He gave the talk himself at the coffin, at the Carlsberg.
That talk has been printed. I have a copy of it somewhere.
Oh, you do? How soon was it after the death?
It was quite soon, I think. Well, I’m not sure. I would have to look back on that, but I think it was in connection with the funeral, so it must have been very soon.
Well. Anyway, I won’t go into all the story about Buddha and the ten grains of mustard seed and so on.
I think you have written that up.
OK, let’s go back to your early times in Copenhagen again. You have written about the main interests in Copenhagen when you were there. Maybe we should recapitulate a little bit about that. It was the prehistory of the discovery of the meson, you might say, and it was also the Delbrück effect, and of course it was also resonance capture of neutrons. Those three were the three main interests that you write about in your “Niels Bohr and Nuclear Physics” article in the October issue, 1963, of PHYSICS TODAY.
Is that also what I write about in that book edited by Roger Stuewer
You write about that there too, but a little differently, because in the Bohr article, you stick more closely to that period. Your method is a little different in the Stuewer article. But maybe you could say a little bit about the first two of those interests, and how you got into that, and to what extent it reflected the work at the Institute.
It was a great thing to have E. J. Williams there, because he had worked with Bohr quite a bit in the past, and was so deeply concerned about this issue. Bohr wanted to clarify whether quantum electrodynamics could be upheld at high energy, because Bohr was a defender of quantum theory, and here was an attack on quantum theory, that there was something wrong with it, and it was no small attack. I remember in this country, before I went to Copenhagen, the talk that Oppenheimer gave at an evening meeting of the American Physical Society — absolutely jampacked, people standing at the back and sitting on the floor and around the sides and the front — where he argued that it would not work at above 137 MC2. That of course meant that for the cosmic rays, you couldn't trust the predictions. Therefore that meant that when you got something going through 10 centimeters of lead, you had no reason to rule out the possibility that it was an electron, whereas if you upheld quantum electrodynamics as it stood, it couldn't be an electron. It was the difference between a new particle and an old particle, in the end. Now, Oppenheimer didn't bring that up in his talk, but that's when it became clear what the issue was. The reason I got into it was because I had worked with Breit and published a paper on the interaction of two photons to produce a pair of electrons out of a vacuum.
Yes, based on QED.
Yes. Right. And that to me was an exciting game, these elementary particle processes. So I must have absorbed the spirit of Bohr early, because I cannot remember ever consciously deciding, any more than I can remember consciously deciding that was the girl I was going to marry; it was just inevitable that I got into the game of this Delbrück effect. Well, that’s not really the right thing to call it; it was rather Gray and Tarrant anomalous scattering. And Jacobsen there in Copenhagen was working on that, and so that made a double interest. I had heard about the work of Gray and Tarrant at the London meeting. In retrospect, I would call the view was I had of the process as a minishower interpretation; it was not anomalous scattering at all, it was a minishower. I can’t really recall talking with Delbrück about this totally different interpretation of the effect, as contrasted to his concentration. Then we had Delbrück’s process of just simply elastic an scattering of a photon by a nucleus, which was certainly the hardest process anybody had treated in quantum electrodynamics up to that time. No wonder he switched to biology.
He wasn’t away already then, so maybe that’s part of the reason you didn’t discuss it with him?
You mean, he was already there before he got to Copenhagen; he was already talking biology?
Well, you know, the “Light of Life” lecture, which was in 1932, was the trigger to his interest in biology, and after that he slowly developed. He had some interest before that, too, that I’ve seen. He moved to Meitner in Berlin in part because there was also a strong biological program at the Kaiser Wilhelm Institute.
So that was on his mind, in fact, before 1932 also.
So there was something to trigger there when he read the “Light and Life” lecture.
That’s lovely. I told you, I presume, about going to Delbrück’s last lecture?
I’m not sure. No, I don’t think so.
At Caltech. I was there, and I had in the morning mentioned to somebody about Gödel’s proof of undecidability. Then in my own lecture and seminar I had talked about undecidability and indeterminism. Then I saw Delbrück there on the campus, and he invited me to come to his last lecture, retiring with all these graduate students of his there, and what did he talk to his graduate students about? Gödel’s undecidability. At any rate, so that meant an immense number of elementary particle processes to be considered. I had little diagrams for them. You might almost regard them as forerunners of the Feynman diagrams. And I had little notes on each process, and curves for their rate, and then I was doing number work. Why did I not finish that up?
That was in Copenhagen already?
Yes. Yes, this was in Copenhagen. Why did I not finish that up? Because I did an immense amount of work on it. The material is in the notes that I have still. And I think that it would be fun really to pull that together, and talk of the minishower, and its relation to all these issues.
Yes, yes. I enjoyed the observation that you never use a pencil but always a pen. That was done at DuPont.
Oh, DuPont Cement?
Yes, it was in THE MAGIC WITHOUT MAGIC. There is a reminiscence of you there.
Edwin Taylor, yes.
Yes. [actually, the recollection referred to is by Crawford Greenwalt, pp. 2-5]. That makes good historical source material, because you can’t erase it, when you have it on there.
And then there was Plesset there, and we got going on other processes. Now, why did we get going on other processes? Was it just make work or was there some big issue? In the cosmic rays there was that lovely paper of Bethe on the shower process. What would be the corrections to that, due to events taking place not in the field of the nucleus, but in the field of the outer electrons? That’s how come Plesset and I got going on some of these issues. Later on Lamb and I, Willis Lamb, wrote a paper on similar related things. But in that connection, Plesset and I did a paper on the dispersion theory as a way to estimate the rate of some of these processes, and especially nuclear processes. If you know the absorption, then you can calculate the scattering. And this was also a tool to predict the rate of the Delbrück process, because if you know the rate of absorption of gamma rays by a nucleus, you can predict the scattering. So we put together a paper on this, but Bohr was skeptical, and we never really published it. We should have published it, because it was really the first use of dispersion theory methods on relativistic processes. Toll and I later took that work up, and he did his thesis in that field.
You've mentioned two interests of yours at the Bohr Institute now. Neither of them led to publication. Is that correct?
Well, one at least. I would have to look. Some of the things did lead to publication with Plesset.
Yes, but we’re talking about the Feynman diagrams, or the precursors to the Feynman diagrams also.
I’m interested in how the mechanisms of the Bohr Institute were. One, whether taking up problems came naturally or whether it came through some direct or indirect guidance from Bohr. Also, how were the results disseminated? Bohr was a perfectionist and followed very closely what was published or publishable from his disciples.
So I don’t know if you have something general to say about, first, perhaps, how topics were chosen and started at the Bohr Institute. Was that something that came out of yourself or your own interests or something that came out of a general kind of agreement?
Well, I know that when I came there, the scattering of alpha particles by helium was what concerned me, because I had got going on that with Breit.
That was your dissertation basically?
No. It was just one of many things. I had given a talk in April of 1934, toward the end of my stay with Breit, before going to Copenhagen, at the American Physical Society meeting in Washington, about scattering, and how scattering was the great white hope to learn about forces, and how you could read back from scattering to forces. Arthur Ruark was there, and it was as a result of hearing me then that he invited me to come to Chapel Hill, at a time when it was very hard to get a job. So that when I left Copenhagen, I could know that I had a position. I had written numerous letters from Copenhagen to this and that place about a job. So this finally came through. But now, coming back, let’s see, where are we? We're still taking about these electron processes in Copenhagen, and about the choosing of topics. So how come I got off on that nuclear business, which really I stayed on with for some time? Well, I think I felt at that time that nuclear physics was the field that really held the hope of advance, that would tie into American physics, and tie in with experiment. That was the thing to work on, and this was an essential part of it.
There’s even a difference between American and European, or Copenhagen physics involved here, perhaps.
Well, certainly, the people. I had not ever reflected on that point. But I can recall working with Breit in New York, having met and talked with some of the people I respected most. Breit had worked with Tuve at the Carnegie Institution of Terrestrial Magnetism on developing an accelerator to do experimental nuclear physics, and Breit himself was keenly interested in doing experiments, and not just theory. And the cyclotron was developing, of course, coming back to American physics. It took some time before Copenhagen had a cyclotron. Do you remember when that was?
Yes, it started working about New Year, 1938 going into 1939.
But the planning for it of course was way before. The planning for it actually started just at the time when you were there, and I would like to go into that too, whether that was something you were aware of or not.
I certainly don't remember that. That’s striking. There would have been Bjerge, Brostrøm…
No, that was later, that they came into it.
Yes. I wouldn’t have thought Jacobsen would have got in on that.
No. Actually, it’s very interesting, you know, when you came, James Franck had just arrived at the Institute.
He was a wonderful man, yes.
Yes, he was. Maybe you should say something about him or your work with him before you hear my specific question. I don’t want to lead you too much.
Well, he befriended me. I can remember, however, one day riding my…[telephone interruption]
We were beginning to talk about James Franck.
James Franck. And so here I was riding in to the Institute from Strandvænget 8 — where I lived — along Strandvejen, in the bicycle lane, when I saw him walking on the sidewalk. I slowed down to talk with him, and the bicycle toppled and hit him, and I knocked him down. He was very forgiving.
Did you know him at all before then?
Well, yes, I had met him there at the Institute. And then he several times had me out to his apartment, to supper, and also I remember his talking about how long it was going to take Germany to get over this disease that it had. But also, his talking to me about how he had changed fields in his life. It’s odd we should be talking about Franck here in front of a recorder, because I took a tape recorder, two tape recorders to talk with him when he was at Duke University, to get historical records for the Physical Society, just on general principles, and unfortunately both of them went kaput.
Did you get anything on tape?
No. But he’s a prince of a man. And then of course he would be invited to evenings at Carlsberg where I’d see him in a more informal way. Then there were the lunches at the Institute, and I simply do not understand why more institutions do not recognize that lunch is the way to make progress.
But at the Bohr Institute, they did.
Did you have any working relationship with him or was it just social?
No, we never worked on anything together. I recall talking with him in later life about his work on photosynthesis, and his ideas on that score. I gather nowadays that these ideas are again winning out, even though there was a time when they seemed to be eclipsed. He told me about his pro seminar where he got students to talk, in his own institution, before he had come to Copenhagen, and how valuable that was.
In Göttingen, yes.
…as a way of training students. Then he also told me about the invitation he had to go from Göttingen to Munich, and how the people at Munich were pulling out all the stops to get him — the minister of education, the rector of the university, and I don't know whether it was the burgermeister or who else, but there were three key people. He really wanted to stay at Göttingen, but how could he make an excuse not to go to Munich, when there was so much salary that came from giving the lectures, and so much salary from being the director of the institute, so much salary from being a professor? Well, he said, Now, that salary for giving the lectures, where does that come from. Well, that comes from the student stipends. “And how many students is that?” That’s 900 students. And then as he walked to the lecture hall, he said, How many students does this hall hold? 400. Then how can I conscientiously accept money from 900 students to give lectures to only 400? So on this basis, he had a basis to say, no.
When was this, do you remember? When was the offer?
Well, it must have been while he was at Göttingen, but I can’t be more specific.
Yes, that was a long time. He had to leave Germany, of course, in 1933.
Yes. I never got him to talk specially about his wartime experiences, but I recall he and I were taking separate flights back to America from some meeting. Maybe this was 1951, for all I know. And we were having breakfast. Maybe it was outdoors at the Angleterre? I don’t swear where it was. And I said to him, “But you’ll take all that long trip back to Chicago from Copenhagen by yourself? Suppose something happened to you?” “Oh,” he said, “we come into the world alone and we go out of the world alone.” And he must have seen so many people go out of the world alone, in the war time.
Well, he resigned, of course, from Göttingen. He didn’t have to go, because…
…he had the World War I experience and all that.
And the Iron Cross.
Yes. Did you get the impression that Frank was happy in Copenhagen? Were you close enough to him for that?
I always thought of him as a happy man, wherever he was. And not only happy himself, but one who gave happiness to other people. He’d have a lovely way in discussing things with you, to grasp you by the arm, or put his hand on your shoulder, so that he had a warm personal relationship with people, immensely supportive.
I’ve not heard anybody say anything bad about James Frank. He seems to have been quite a personality, quite a person.
But of course, when you were there he was just deciding to leave Copenhagen and go to Johns Hopkins University.
Yes, it was a way station.
And he understood it as that.
And it was so sad for me about Johns Hopkins. Wonderful people that they had there, and then this President Berry came along who seemed to have an antipathy toward the top people.
In physics or just generally?
Generally. And it took quite a time to bring that back. But Johns Hopkins — I have a great fondness for the institution. Steven Muller now is going forward beautifully.
Were there others in Copenhagen than Franck that you would like to mention?
Of course, Hilda Levi was there.
Yes, she’s a good friend of mine.
Yes. It always a bit colored my outlook on one of our good friends in the world of physics, that he ditched her.
Oh yes, I know that story. Yes.
Oh yes, and of course, Frisch and Hilda Levi — from them I saw counters at work, and Frisch was telling me about how this strange radioactivity he found. The activity increased with time, and then it decreased with time. How come? And finally he discovered the explanation. The counting rate was so high at the beginning that the counter was totally saturated, and only slowly would it recover enough to give a count so you have to be careful about what interpretation you draw. And of course that brings to mind also Hevesy…
…who came just after you, I think, to stay permanently. He came in October, didn’t he?
Yes, I think so, and he went to the same meeting in London.
Actually we didn’t talk about that meeting.
We were on the boat train, and here in the boat train was Hevesy, one Hungarian, and then Edward and Mrs. Teller, two other Hungarians, who had just been married, going from Copenhagen to London. But he had such a feel for radioactivity and such a feel for its history. The Vienna group, a group he had worked with.
Were you close to him at all?
Well, he was kind enough to invite me to his house once. It was a great treat to talk about history. And of course I remember the Tokay wine which came from his own place in Hungary.
That was memorable.
Yes. And his story about drinking heavy water — this made a great big splash in the newspapers, apparently.
That was the beginning of his biological research, that’s right.
I didn’t get an impression of what his overall program was, what great white hope he had. That’s interesting. These days I’m much more accustomed than I was in those days to ask one or another person, “What’s your great white hope?” In other words, what goal are you shooting toward?
Well, you see, that’s one of the things that I’m struggling with in my book too. Franck and Hevesy came as refugees, both of them, and they both had a higher degree of prestige than most visitors to the Bohr Institute; they were professors from before. And because of that, Bohr seemed to think that they should have some greater degree of independence in their work than other visitors. And of course they were experimentalists too, so they needed apparatus to work, to function. My impression is that this was part of what led Bohr to redirect his Institute experimentally to nuclear physics, and that was what made him think of installing a cyclotron and a CockcroftWalton installation, and that kind of thing. I think that was triggered in part by Franck’s and Hevesy’s appearance at the Institute, because he wanted something for them to do. And he was also aware that nuclear physics was coming into its own at this time. And he made this decision just before or at the time when you came there.
Have you been able to find some record of it?
Yes, yes. I found a record of that. Actually, it started with Franck and Hevesy doing an artificial radioactivity effort similar to Fermi’s in Rome — you know, bombarding the whole array of elements with neutrons. And in Copenhagen Hevesy and Franck were always a little bit behind, and I have Franck complaining in his correspondence at the time that whenever he had a result, somebody else had published it in NATURE already. So they were just a little bit behind. But that was the beginning of a nuclear physics effort at the Bohr Institute, as I understood it. And of course, I’m leading you now. I hate to do this, but that’s my impression, and I’m wondering whether you had some sense of these developments.
No, I was completely unaware of this. I suppose I was totally immersed in what I was doing. Why was I unaware of that? Of course, it would be no surprise to have a cyclotron. As a graduate student at Johns Hopkins I had this wonderful experience working with three experimental people, Feather and Diecke and Bierdon, and yet I think the conclusion I came away with was this: you can make progress so much faster in theory than in experiment, that it was a loss of time for me to get into that.
Yes. Well, it might be personal inclination also, of course; it was what you felt comfortable with. Yet, you felt that you could do either at that time.
Yes. I had worked with my hands a lot. I’d built a computer.
What was the relationship between theory and experiment at Bohr’s Institute, specifically, as compared to your experience with institutions in this country?
Well, I think I felt about physics some similarity with economics, in this sense, that Copenhagen is like a thermometer thrust into the body of nations. It does not itself have enough economic weight to influence things, but it can respond to things, as a thermometer does not influence the temperature of the object it goes into, but responds to it. And the Copenhagen Institute, in a certain sense, was more responsive to the wide world of physics than I had been accustomed to see either at New York or at Johns Hopkins. At New York or Johns Hopkins, yes, there were talks by other people, and from other places, about other things, but really to let your program be governed in a major way by that, I didn't see, in the way it was at Copenhagen.
Yes, OK, maybe we should stop here and continue after lunch.
It's interesting to note how E. J. Williams got into theory. He’d been working on experiment at Rutherford’s lab, but Rutherford had that rule that you had to quit at 5 o’clock, and they locked up the lab. That drove him nuts, because he wanted to work late hours, so he switched to theory, and then he could work.
Just by pure necessity. Well, he must have had some aptitude for both.
How central was Williams at the Institute, and in his relationship with Bohr? You think that he was close enough that he would have some insight?
Well, Rosenfeld was closer, when Rosenfeld was around. But Rosenfeld wasn't around at that time, and Bohr always needed somebody to kick things around with. And Williams served that function excellently. Rozental, was it then or later?
He came later. He came in 1938.
Yes. I think Mrs. Schultz handled most of the business end of life; it was my guess, but I may be wrong on that. There are so many things one's not aware of in the beginning.
And when you come again of course it’s easy to mix up things too. Are there other people that we have missed out on?
Well, we've missed Bøggild? and Bjerge? and Brostrøm?
The three B’s, yes.
I always enjoyed talking with them, but I can’t remember getting into anything in a big way with them. And of course there was Plesset, who was my fellow postdoctoral fellow, from Caltech, and I think he’s retired now from Caltech. He got into engineering at Caltech more than in physics. I don’t really understand how that came about.
No, because you collaborated in Copenhagen.
Right, and he had a BelgianAmerican Foundation Fellowship for a while, later. On that basis, I stopped to visit him in Liège when he was there. I think he was working at Swing’s Astrophysics Institute. I do not know why he went there rather than staying. Well, where you get some money, that’s where you go, I guess. What about the mathematicians? Harald Bohr I met, but I never really got into any serious discussion with him.
Yes, he had just recently moved in to the new mathematics building adjacent to the Institute. That’s right. So there was a close collaboration between the mathematics department and the Bohr Institute?
Well, they were nearby, but I confess I could not point to anything of my own knowledge of collaboration between the two. That’s very odd, too, because the almost periodic functions are just what you’ve got in the old quantum theory, for the motion of the electron and the atom, almost periodic motions, superposition.
There were lunch discussions perhaps but nothing more.
And then of course there were the visitors who came. Oh, excuse me, I don’t know, why did I leave out Møller. Møller yes, of course. And what was he working on at that time? Was he doing his work on relativity? Because he did come out with a book on relativity.
Yes. You have an account that he returned from Fermi and Rome at some point.
Yes. That was in the Easter vacation, and that’s where the great thing happened about the collective model of nuclear reactions, so that was an exciting moment.
Yes. I don’t know if you’ve read Peierls’ introduction to Volume 8, is it, of the Bohr collected works?
I should have read it.
Where, you know, he questions Frisch and your reminiscences of the origins of the compound nucleus model because they don’t quite seem to fit in. I wondered if you have anything to say about that?
No, my memory’s so terrible that anybody, almost anybody could give reasons and I can’t confute him. I had thought the liquid drop model was there in the spring too. But he tells me that he thinks it was the collective model only in the spring, and the liquid model in the fall. But either he or somebody told me that in that early book of Gamow’s on nuclear physics, there’s a liquid drop model already before Bohr.
Yes, I think he published a paper even before that in 1929 or something like that. I don’t have that.
Really? A paper by whom?
By Gamow, right. So it must have been a feeling in the air. Noddack, I have never read her work. Did she talk of liquid drop?
I can’t really say. I’ve heard Gamow also, but I haven’t really studied it in technical detail, so I cannot say. Gamow is usually accredited with it.
Well, I wonder if Noddack(?) could have…
Ida, is that it? I wonder if she could have used that model in discussing fission. Have you read her paper ever?
No, I haven’t.
Neither have I. I have no idea. There was a student of mine at North Carolina, Katherine Way, I got going on the liquid drop model. You already have that.
Not her connection with you, no.
It was, looking at this and that property, and if you have a rotating liquid drop, then you have a magnetic moment associated with it, but when you got up to a certain speed, then she found that there was no longer any solution to the equations. So that really should have alerted us, already then, to the idea of fission.
When was this?
This would have been I think in 1937.
OK, so it was close. At this Slater symposium, needless to say, Slater’s experience with Bohr and his Institute was mentioned.
By the way, did you get a chance to talk to the Slater family at all?
No, I did not.
I did not either, and I felt badly that I had not. I’d meant to refer to them at the beginning of my talk, and I somehow was a bit flustered and did not, and I hope they didn't feel miffed.
Well, I have no idea. I wasn’t even aware who of them were there. It was a little awkward, I guess. But I wouldn’t think so. But what I was getting at was that you made some statements about the attitude in the United States institutions being democratic, whereas European institutions being more hierarchical. I don’t know if there is anything in that comparison or in that statement pertaining to the Bohr Institute.
I would think it’s like an American institute. But I’m in no position to comment, because I never really worked in a German laboratory, nor in a British one.
Yes. But you would not say that that applied to the Bohr Institute in any way?
What about being American at the Niels Bohr Institute? Were you treated differently than others, in some way?
No, the only handicap was language, because most people talked in German, and I had had three years of German, but still, it took a while to get up to speed.
Yes, of course. But you see, it seems to be mutual in a way, because here are a few pages of the guest book at the Bohr Institute. We have A. Proca from “Paris”, we have L. Landau from “Leningrad”, and Rosenfeld from “Liège”, and we have John Wheeler from “America”. So it seems to have been a faraway place; not only John Wheeler but even Professor Stern was from “America”. When people when came from as far away as the United States, it was just “America”.
And these are the dates.
These are the dates, yes. This is your date of arrival and your date of departure.
This must have been done after the event, not at the moment of arrival. It looks too neatly done.
No, I think it’s contemporary. I strongly think so. Isn’t that Mrs. Schultz’s work?
Because I can’t understand how else they could keep track of the exact dates, you know.
The 5th of September…
…the 29th of May.
Isn’t that something? I’ve never seen that before. Now I know something. 6th of September and the 29th of May. Well, that’s wonderful.
Yes. Maybe you could say something about your first impression of Bohr. I know you encountered him on the wall, wasn’t that right, wasn’t that the first time?
Working, pulling down these vines. I can’t quite communicate the feeling of very great intelligence, but not knowing just where I stood, and great kindness. I remember one discussion at the blackboard one time, and I was so flustered that I was erasing the board with the back of the eraser, and Bohr got up and he said, “You know, it would go more easily if you did it this way.”
That’s a nice little hint.
Yes, and then he always liked to make sure that just one person had the floor at a time. It made life go better. And holding the eraser was one way to hold the floor. And then this idea that when there was a discussion it was always better to have two or three people present, whereas of course, in contrast, in writing a paper, it’s better just to have two people present.
But that was the amount of it.
I can’t recall that we ever discussed what I would be working on. I somehow got into the swim of things there. I suspect that I hadn’t had any real contact with him until after the meeting in London, until I got back from that. And now I have to ask myself, was Williams at that meeting in London? It would seem he surely must have been, but I can't specifically remember it.
Did that conference have any implications or impact on your career in subsequent work?
Oh, absolutely, yes. Yes, because that conference got me into the question of the cosmic rays. I heard such good people talking about cosmic rays, and after the war, or as the war was ending, it became quite clear that it would be surely the simplest way to get high energy particles — to get them free of charge. So down the hill here we had this cosmic ray laboratory which we set up after the war, at my instigation. It was a building that had been used for wartime work, and we were able to grab it and get it without having to pay a big budget to get it — the way you and I would like to grab space in the library as a historian of science to handle things if it could be done likewise free of charge. So that was one impact. It’s odd, I can’t remember anything to do with gravitation physics there, but pair theory became so much clearer to me there, I would say, than it had ever been before. Pair theory, in the sense of having a feel for what electrons will do under this or that circumstance, polarization in a vacuum, and then getting started on this dispersion theory that John Toll and I went further with later, and then on this collective model, because really it fell to me in a way to be exponent and expounder of that in this country, when I’d come back. I gave lectures on the subject at summer schools in Michigan and Chicago. But the pair theory was of course inspiration for taking the idea of the electron very seriously, in contrast to Heisenberg, who regarded the discovery of the neutron as indicating the electron and the proton were not sacred fundamental there were more particles.
It was a gradual thing with Heisenberg, too, I think.
You think so.
Yes, I think so. In his first paper he has both things.
But Dirac was very much slower about coming to that position.
For him the electron was a simple thing. I have not found, maybe you have, the place where he says that, that the neutron isn’t a great thing.
It doesn’t come to me at the moment. [Interruption] We are back again. I think we ended talking about whether or not the electron was a constituent of the nucleus.
Yes, and I had the impression that Dirac was, like me, very late in accepting the idea that there was anything really other than the electron.
Was he late or did he ever accept it, basically, do you think?
Well, perhaps he never accepted the idea.
It’s a possibility, yes. There’s a friend of mine who is just finishing a biography of Dirac actually, so he might have a lot to say about that.
That’s wonderful, to find out.
He’s a Dane, actually.
I can recall with Breit, sitting around the table at lunch time talking of their idea. This was back in 1934 or 1935.
Or rather 1933, 1934, before I went to Bohr. The idea was that the nucleus is just electrons, and this word was recited as such a litany, almost as if it belonged to a religious creed or doctrine, that there are strong forces and there are electromagnetic forces. To me, a factor of 50 or 100 or 200 was not all that different, and I could believe that radiative forces had quite a different magnitude than electrostatic forces between electrons. It was, therefore, extremely interesting to see what electrons would do when they interact at high speed. But to discuss this, you had to have retardation, and you had to have a proper theoretical framework. Yet you wanted to be as simple as possible, and if you had a field — the electromagnetic field — it would have all these infinite number of degrees of freedom. So that’s how come I got excited about the electron idea, and kept interested in it, when I came here to Princeton in the fall of 1938 from North Carolina. I should look at my bibliography and see if I published anything on electrons during that period, 1935 to 1938, in North Carolina. I have a bibliography over there, but I won't look it up at the moment. At any rate, that's where I got onto this idea that there's just one electron in the world, an electron going backward and forward in time, although that idea, I learned later, Suckerberg had had earlier.
And Dirac to some extent?
An electron going forward and backward?
Well, maybe not, but he had a theory based on electrons.
Yes. But I confess that also here I like to talk about the idea of the an action at a distance picture. It was considerably later, after the war, that I was still deeply in love with that idea. That was a period, 1949, 1950, I went to Paris. I would normally have gone to Copenhagen, but it was not, I thought, so useful for my three school age children to learn Danish as to learn French, and so I took the train back and forth to Copenhagen. But in writing up my proposal for the Guggenheim Foundation, because they gave me the grant, I took as my central point electron theory doing similar ideas for gravitation theory. But with Bohr, the interest was more on these nuclear things and trying to reconcile the many particles features and single particle feature. That paper of Hill and mine would have been a paper jointly by Hill and Bohr and me, if there had been more time, but I was taken up by then in this Project Matterhorn here, and that was so demanding, that I had to do this work at night, in 36 hour stretches, no let. And Bohr wrote back that he thought the best thing to do — or maybe he cabled back — was to send it in ourselves. Well, I remember speaking to Mrs. Bohr the year or so before she died, about all the ideas that Bohr had contributed to so many people and people didn't know about it. And she said, “Yes.”
But you must have discussed this in Copenhagen too when you were there.
The pair theory?
Well, the more specific question of the electron in the neutron, for example.
Because Bohr was a little late in coming to that conclusion too. A lot of people were, you know, late in coming to the conclusion that the neutron is a fundamental particle.
And of course that’s understandable, because you didn’t have too many fundamental particles at that time.
So to what extent was that discussed in Copenhagen?
We really worked entirely on nuclear structure, not on these more general questions.
But wouldn’t that come up even with nuclear structure?
Well, it’s odd, but no. We were trying to reconcile these collective properties with individual particle properties, and one thing is enough at a time. Bohr had this wonderful power to be able to concentrate. And if we weren’t concentrating, then we were talking on much wider issues, and not that.
Because before the discovery of the neutron, Bohr was using the dichotomies of the nucleus, you know, in beta decay and all that, as an argument that quantum mechanics did not apply to the nucleus as such and that the nucleus had a deeper kind of physics than the atoms surrounding it. Isn’t that correct?
No, I didn’t know that. There was his Faraday Lecture. That was in the thirties, before I got to Copenhagen, if I remember correctly. And there he talked about the problem of localizing an electron, and how you would not be able to localize the electron within nuclear dimensions because the very potential you would need to localize it would create new electron pairs. This business of how a potential could create electron pairs always fascinated me, and also the question, what kind of a potential would it take to localize an electron? It’s a very interesting thing, because if it’s too deep, then it produces pairs, so you haven’t managed to localize the electron that you hoped for. You have to have it just the right depth. But there are still untreated questions there, and you know this present day work that's occasioning so much excitement of Gentner and colleagues in Germany. I’ve forgotten which place it is, but at any rate, it’s about producing pairs. I had predicted with Fred Warner the idea of two heavy nuclei coming together being able to produce a pair, and now the striking thing has been seen that there are resonances in this process, and that's not explained yet.
But you were saying that…
…that when I went to Copenhagen, I wanted to go on with this idea that the interaction between electrons was the great thing, and also, in the same idea, to take out the field in the space between the particles — the gravitational field — and that’s quite a deep thing. And I would still like to come back to that, although I don’t regard that today as the great white hope. You've heard that old phrase, “Somebody who is a reformed drunkard gets religion more strongly than anybody,” and so I became more strongly field theoretic after that. So that’s how come I moved into gravitation. That’s a field theory that, at that time at any rate, that was the master field.
But that was much later.
That was 1951, 1952. The work with Bohr was 1949, 1950, and during Matterhorn I got the paper finished up on the collective model, published with David Hill. I would really like to take that paper and redo it. The PHYSICAL REVIEW just stuck all the pictures at the end, instead of putting it in the text the way it should be done.
Oh. That was unusual, wasn’t it?
Yes. Well, I don’t think they’d ever had a paper with so many pictures in it. But I think it would help. But at any rate, then, at that point, I came back here and started to teach, and the first course was a graduate course in relativity, where I could get onto gravitation theory, and that’s how come I started this long period of involvement, and the very first year it became clear that the number one issue was, what happens when you’ve got gravitational crunch, whether of a star or a cosmos? And I suppose I had absorbed from Copenhagen days the idea that you try to sort out what’s the biggest issue, and then you go at that, hoping to learn something new. And so all along the way there have been new things to be learned. I’m giving a talk at Maryland a little bit later this month on gravitational crunch.
Do you consider this a complete turnabout or just a complementary way of dealing with the world?
The issue as I see it now may be totally preposterous. I’ll give you a copy of this paper of mine, maybe you have it already, called “World as System SelfSynthesized by Quantum Networking.”
I don’t think I have that one, no.
Anyway, the idea is that the world is created by observer-participators. There isn’t any machinery. And there are billions of years yet to come and billions upon billions of people, living places yet to be inhabited, and the communication back and forth between these people is what establishes the whole show.
To what extent do you consider that an extension of Bohr’s philosophy?
Yes. Well, I think so, yes.
Did you discuss such issues during your first visit at all?
No. I never had such a preposterous idea before.
No. But I was thinking of..
Observer participancy? Oh, always. Always. Oh yes. That always came up. Bohr was always talking about examples, there were discussions and debates and points that people would bring up and his replies. Oh yes. Oh, absolutely. So that is so to speak the meat and drink, like your mother’s milk.
Yes. So you hooked onto the Copenhagen spirit, so to speak, from the beginning.
Yes. And contrary to what Harvey Hall said to me, that you should only be a mature physicist where you’re going, I think it’s very wonderful to grow up not yet a mature physicist, observing this atmosphere at a good impressionable age. But before I forget it, I’ll give you a copy of that reprint.
No, I haven’t seen this.
Well, at any rate, there is the crunch. We got onto this because we were talking about gravitational crunch, and as you approach crunch, simple cosmologies do not permit you to communicate back and forth between everybody. Your domain gets more and more constricted. But I’m prepared to believe in this. Something I’m more excited about than anything right now is that these Kalatnikov-Balinsky Lifschitz mixmaster oscillations in space offer the opportunity to get signals back and forth, in a way you would never be able to in a simple cosmology. And crunch is part of the game.
Well, in some of your later articles, you have thoughts, I saw you refer to Wooten's work for example, he was your student, right?
You’re establishing the concept of distinguishability as the wellspring of the quantum principle, as you say, kind of making some more basic explanation for the quantum. Is that something that you think Bohr would have agreed with?
I think he would have wanted to ponder it and ponder it and ponder it before he published about it. And I don’t think he would have been ready to publish it. That’s a good question, how would he react to this? Well, no, I think he would like this, in a way. That’s a very good question, because here a complementarity is accepted — the idea that you can’t get an answer until you ask a question — and that gives you the complex part of it. But on the other side of it, you’ve got to be able to distinguish the answer, and for that you need a probability amplitude to measure it. That, I think, he would have been very pleased by. I feel he would have wanted to grab it and run further with it, but I'm too stupid to see how to run further with it.
Well, of course we’re just talking hypothetically now. “We are inescapably involved in bringing about that which appears to be happening.” That's another Wheeler quotation.
I try to be very careful about how I put these things. We don't create the past. Some people try to say it that way. That's not true.
Yes, but that is also something that would be in line with the Bohrian approach.
Yes, right, absolutely. This very cautious way he had to state things. Absolutely central.
So you don't see any disagreement between your present approach to cosmology and philosophy of physics, and his approach.
It’s a continuum there.
As a matter of fact, you might have overheard a phone call earlier today from this postgraduate student at Columbia, coming to hear this talk that I give on Saturday the 14th or whatever the day is, maybe it’s the 13th of this month, at the New School for Social Research where I’m talking about this very topic to a group of philosophers. So it will be on a different level than a physics meeting, but also Zorack is going to give a talk there, for whom I have a very high regard. Anyway, I’ll be interested to try it out, because that's my way to learn, is to speak.
That’s to philosophers.
Have you tried your thoughts out on philosophers?
No. No. No, I was invited to do this, and I thought that I’d see what they had to contribute.
Well, Bohr wasn’t too fond of philosophers when they were too dogmatic. I mean, he thought that philosophy was more of a developing field than a set discipline, so to speak. I don’t know if he said that in print, but he said that more informally, I think.
And also today I think many people feel that philosophy has become a school of argumentation.
Sophism, yes. I’m not up to date on modern philosophy, I’m sorry to say, but yes.
Quine, since Gödel died, is perhaps the greatest logician. I was sitting in front of him a year and a half ago or a year ago, and at a break in the meeting, I said to him, “Ben, how come you never sound interested in the problems of physics, how is the world put together and so on?” “Oh,” he said, “I used to worry about it, but I solved that problem so I’ve gone on to these things.” So I said, “What do you mean?” “Well,” he said. Well, I quote his words here in this article.
As his words, you quote them.
Going back to Copenhagen, to an entirely different and more concrete thing, of course you came there in the middle of the problem of the refugees from Germany.
I had the impression, without being privy to the conversations, that Bohr was all the time working hard to make places for people, writing letters and what not, not only to England but to America. And I have no idea of all the things that went on. He had that wonderful way of taking the person he was talking to and walking up and down the garden somewhere.
No, I was thinking, at the Institut. Of course he would do it also at Carlsberg, but as a way to really have a one on one discussion I've never seen that rivaled. Somehow, that's more a Continental habit, it seems to me, than an American habit.
Well, I don’t know. Yes, I think you’re right. Just walking is more of a European habit. They’re driving cars here. Maybe that’s part of it. But you weren’t involved in helping the refugees or in helping him help the refugees?
Well, I had no position myself.
No, but conceivably you could have helped drafting letters, or something to that effect. Did that have any effect on the character of work or the atmosphere at the Institute?
Well, I do remember his speaking of the crisis, when — I think it was the spring of 1935 — when Kapitza, going back to the Soviet Union, was denied permission to leave, and Bohr doing everything he could at the time. The discussion was at Carlsberg. It was at dinner time, or after dinner. I think maybe Franck was around during the discussion. But of course in the end there was nothing that could be done.
But it seems to me that the working atmosphere at the Institute wasn't really affected by that. I mean, there came a lot of refugees, but they were of the same…
…the same interest in physics, yes. It didn’t feel as if you were running a refugee camp. No, not at all. Not at all. It was never a lot at one time.
And of course Bohr was able to get support for most of these people through the traditional channels, with the traditional argumentation, you know, from the Rockefeller Foundation and the Carlsberg Foundation. [Telephone interruption]
I was about to start on…
…whether there was anybody in particular to mention among the refugees.
Of course there was Frisch, who, within one month of his arrival at Copenhagen, gave a talk in Danish.
Without having any previous experience with the language?
Yes. Then, and I was too stupid to be tuned in to nuances, in encounters between Heisenberg, when he visited in the spring of 1935, and other Germans who had had to leave Germany, and who were also at the Institute — what kinds of relationships were there there. I could not tell you. I was not tuned in on that.
Of course, there were Franck and Hevesy. And there were several others. I have a list of them somewhere. But I guess my question is, whether there was anybody you had a particular relationship with.
No. I would say not. I always enjoyed Placzek. Was it then that I met him? Placzek was wonderful.
It was then that you met Teller, wasn’t it?
Yes, Teller and of course Delbrück. I used to talk with him regularly at lunch. That was the beginning of a long relationship. And with Frisch, of course, over many years, and we still keep in touch with his wife, although not as much as we would like to. Then also I can recall that Massey visited, the atomic physicist from Britain, and it was a great treat to come to know him.
Yes. He didn't come all that often, I think.
No. He was not a regular visitor, and I had the feeling that for him it was a very special occasion, rather than a routine visit. Of course, Rosenfeld then and many many years, had been great, and I see Mrs. Rosenfeld when I go back to Copenhagen.
Yes. Talking about papers, I think his papers are going to be deposited at the Niels Bohr Institute now, which is good.
That should be a very rich collection.
Oh, yes. He was such a scholar of the subject of physics, and so historyminded. It was just a joy to talk with him on any part of the history of the subject.
Yes. What is difficult to reconcile, I think, is, you know, the kind of continuous discussion of the central topics that took place at the Bohr Institute, and the redirection from say quantum physics to nuclear physics that took place. Did you sense some kind of transition while you were there, either in terms of discussion or in terms of activities in general?
Of course, I had not been there for a long enough period to sense the discontinuity in the method of treatment there.
And I think most people find it hard to realize, especially the ones who go there today, what a small place it was at that time. You could go to the library in the morning, and you and maybe one other person would be there — maybe two people in addition to yourself.
Which makes fluctuations highly likely, of course, and it makes it an easier place to handle.
Yes. It’s amazing that a place like that… Oh, there’s a question. Did Kramers visit during that period? I cannot recall.
I can’t tell you. Actually, I could have brought the whole list, of course, and then we could have taken it visitor for visitor, but that might be taking it too far. I think that list there contains most of the people who came during your period. But that might be too much detail.
Well, let’s see. Oh, yes, I met Weisskopf there. Delbrück, Hevesy, Hilde Levi, Proca, yes, I had to give a talk after Proca's death in Paris, on him and his work.
How much later was that?
That was, I think, 1951.
So he died early.
Yes, Klein, I wonder if I met him there? Because I’ve certainly known him for many years. Guido Beck, oh yes.
He was one of the refugees.
Yes indeed, I've known him for many years. Von Hippel, wonderful person. Kopfermann.
Yes, Kopfermann you must have met.
Yes, indeed. Delbrück, Bethe, Weizsäcker, Heisenberg, Rosenblum from Paris, yes. Von Laue — I do not remember meeting him. Ladenburg, of course, came here to Princeton afterwards, but I confess I don't remember meeting him there.
No, it may have been a very quick visit.
Yes. It’s written “dead.” He must be dead by the time this was written.
No, I'm sure that was put in later. They just maintained this book. The names and dates were put in at the time, and then the death date was put in later.
And Placzek, Rausch von Traubenberg and Gamow, oh yes. That was great, to know him. And of course I continued to know him over the years, and I feel sure he was at that London Conference.
Yes, I'm fairly sure he gave a paper there, didn't he?
I think so. Chandrasekhar was at Copenhagen for a long time. I've left out Strømgren in all this.
Bengt Strømgren and his father. And the parents had me to dinner at their place along with Chandrasekhar, and I can remember afterwards walking and talking with Chandra, as we walked back to our places of living.
Were they close to the Bohr Institute? Were they often there, the Strømgrens?
Not very far away. Lise Meitner, yes. Rosofsky — oh, I would have forgotten his name completely, because I went to visit him in Warsaw after the war. I saw him in 1947. Placzek again. Hertha Sponer, yes.
You remember her.
Oh, yes indeed, very much so. As you know, she married Franck, and became Mrs. Franck, and I learned from her some of the things I would not otherwise have known about molecular transitions. Teller. Here, he’s come from London, so he’s been established in England evidently during that year. Now, that’s odd, but I don’t see Teller back in the fall, when I came myself.
Yes, it could have been on an earlier page, if he was there for a long time, of course.
But I don't think of him as having been there when I came. October of 1934 was the time, and here I arrive in September, 1934, and then we get to Delbrück and Bethe in September, and Heisenberg. Well, there are a lot of people here in September and October, Hevesy, Frisch, Placzek. I’d like to know what the date is of that London conference. You don’t happen to remember it, do you?
It may have been in October.
It was October, but I don’t know which day.
Oh, the date exactly. No, that I can’t tell you.
Yes. I probably can find that out, because it would help me in telling whether these were people who were coming in the aftermath of the London conference, or on their way to the London conference.
Yes, because that’s an important point. Well, I have the Proceedings at work.
Yes. I have a place I could probably find it, but I won’t take time to do it now. Well, let’s go on, because I don’t want to hold this up.
Yes. Well, we should probably end this about Bohr, because we have to go to other things too.
You have to go somewhere else?
Well, not I, but we should go somewhere else in our discussion.
Oh, yes. There’s an article, where I did the best I could at that moment to discuss the Copenhagen Institute and what it was like. This article where I did the best I could is in a volume published I think by Reidel edited by three of our colleagues, one of them I think Ulfbeck. Yes.
I should definitely look at that.
And more about it, of course — at the people who made it go. Mrs. Niels Bohr was so vital in the whole thing, and it’s not fashionable for some reason to talk of such things, but really I think she did have a powerful influence. She kept up a certain standard.
Well, that’s something that really hasn’t been appreciated and looked into. I agree with that.
Yes, and people somehow seem to believe that scientists are lone creatures, but they aren’t.
And she was not just a passive protector of her husband either.
No. No. She was a woman of real principle.
Yes. Maybe you could talk a little about that, if you have some story or some experiences to that effect.
Well, I can recall calling on her in Copenhagen, oh, I think she was about 90, after 90, and she invited me around to lunch, but what was the lunch about? Primarily it was people raising money for some benefit in Copenhagen that she was pushing.
Oh. At 90.
At 90. That’s what I call principle.
That was typical.
I did not see the interview, but I heard there was a great thing, on Danish television with her on her 90th birthday.
I just heard about that also.
It would be, I think, really wonderful to get that translated, and have the same sound film but with the words.
It should definitely have her own voice, yes.
Yes. But now, what else about that? “All kinds of people,” she once said to my wife, “come to the Institute, and you don’t have to make all of them your best friend.” But she felt that she always had to have them at least once to her house.
What role did she play in interaction with physicists? Was she just a hostess that withdrew, or was she more of an active person? Did the physicists learn to know her, in other words?
I had the feeling always that she talked about these things with her husband, afterwards, rather than talking with the individual at the time.
Yes, that was the role of the woman too, to some extent, of course. They had a fairly traditional approach to things that way, did they?
Yes. I wish my wife were here to comment a little bit more. She believed in standards.
Yes, they both did.
She was shocked by some people. And she believed in putting all her heart and energy into something that was important. And it must have taken a lot to have her husband away so much, as he was.
Did she ever try to set physicists straight, or somebody that didn’t live up to her standards? Are there any examples or stories about that, that you can think of? I’m just fishing.
Yes. I’m trying to think. I know that, or I was told by various people, that it happened to young artists, young painters, young musicians, the Bohrs befriended and helped out.
Yes, more among that group than among the visitors at the Institute.
Well, of course they had such a responsibility for really the whole intellectual community, by occupying that house of honor. That’s a heavy burden to carry.
Yes, but they really took that seriously too.
Yes, and I gather she was quite a friend of the Royal Family. But she explained to my wife how in every court there is always intrigue inside.
How did she and her husband supplement each other that way? Was he equally conscious of standards and form at the Carlsberg and otherwise?
I don’t know what he would have done if somebody had come with blue jeans and no necktie to a formal dinner at Carlsberg. I never saw that happen.
No. So it was informality with some formality. Not everything wasn’t allowed.
Yes. And I recall a dinner at their place, a Sunday midday dinner at their place at Tisvilde with the singer, I should remember her name now, but distinguished American singer, that they were looking after. Then of course, all their trips to other countries. She played a distinguished part in that. She really looked like a queen, acted like a queen, and yet was very warmhearted. Well, where do we go from here? We were talking about the Copenhagen Institute.
Yes. Maybe we should wrap up. I’m sure we could go on forever about this, but we were talking a little bit about the impact of Bohr’s philosophy on your own work and on your own philosophy. One aspect of that perhaps, triggered by the war, was his open world approach.
Yes, he worked at the sculpture out in the courtyard of this building. It’s a Pevsner piece. “Composition in the third and fourth dimension”, it’s called, and at the foot of it it’s dedicated to Niels Bohr.
Oh, is it?
And his words about the open world and so on. I worked them out in consultation with Aage Bohr, and Aage Bohr was here with me for the dedication of the sculpture.
I see. Was that just after Bohr's death?
I don't know whether it was 15 years ago. But anyway, there are the words about the open world there. Speaking of philosophy, Aage Bohr, in a long walk and talk with me, said that his father would never have had the same dream I have, that we could get to the answer some day, and find out how the world is put together. Rather he would have felt that we would go on and on and on and on, world without end, unraveling things.
Yes. It was the process, rather than the goal.
And I would be extremely interested to know anything that would speak for or against that analysis of Niels Bohr's way of thinking.
Well, it seems to me his whole person, or his whole approach to discussion was like that.
This is the tennis, the one person and two person tennis games that you talk about.
But then, to take everything apart — you take evolution and Darwin. There was a broad idea: natural selection. Well, you could say that everything else since has been filling in the details. A lot of details. DNA was a detail that was pretty important. So it’s in that sense that I would think of the hope of seeing how things are put together that we can work toward, still recognizing there’ll be things like the DNA that have yet to be filled in after that.
Yes, but you can expect what is to be filled in. You see the holes.
You see the broad pattern.
Yes, the structure is there.
Yes. So I have that optimistic sense. It might well be that Aage Bohr is right in his analysis of his father’s thinking, because if Niels Bohr had been as optimistic as I about understanding how the world is put together, then I would think he would not have spent so much time on other things, his other responsibilities. And he would have had the feeling, which is at least the feeling I have, that nothing that man can do for other men is greater than giving them an understanding of where they fit in the scheme of things. And that’s so big a goal that that would have pushed other things aside, that in his case were not pushed aside. On the other hand, he had such a sense of responsibility that my interpretation may be wrong. Rather, he may have felt, out of loyalty to his country, to the position he occupied in Denmark and so on, that he had to do all these other things.
I think that is right.
And so, it might not have been that he regarded less the great white hope that I talk about, but regarded more his obligations. But that’s a guess.
Yes. How do we resolve that?
It’s a very interesting issue, how high did he ever hold these hopes? I can’t recall his ever speaking at that level. And I quote in this article I gave you the words of somebody who had a great influence on Bohr. That’s Rutherford, saying, “When a young man in my laboratory uses the word universe, I tell him it’s time for him to leave.” And I had the feeling, that Bohr never quite got into these questions of cosmology, and that he didn’t resonate. I gave him the little book called GEOMETRODYNAMICS and I knew he would never have a chance to look at it because his life was so busy. But he seemed to like the title of it, as a better word for general relativity. But that is the closest I ever came to finding out how he resonated to or responded to concepts of cosmology.
But on the other hand, of course, he was more than willing to expand on the complementarity concept and complementarity to him was, well, if not a religion, it was as far as he got to religion, I think.
And the pedagogy of it. I mean, the realization that everything can be seen from two sides. To the extent that that is the opposite of dogmatism, that was what he wanted his philosophy to say, even to school children. I mean, he was very dedicated to giving talks on the school radio, for example, to that effect. So that’s not cosmology, but it is certainly a dedication to the lesson of physics.
But it may be more important.
Yes. It reaches more people. I don’t know. But certainly he was philosophically oriented also. Complementarity wasn’t merely a pedagogical principle, it had more substance than that.
Yes. Yes, you’re right. And I speak in this article that I referred to, about Bohr’s interest in that. The Gamow business — or Alpher and Gamow — about creating the elements in the Big Bang — I can’t recall any discussions with him on that. But he must have regarded that well because that was a definite application of nuclear physics. I would love to find out more on that score. These questions — you wanted answers and I give you only questions. I told you, I guess, about the story of Dirac, going to Copenhagen as a postdoctoral fellow recommended by Rutherford. Bohr was back in London for a brief visit, after Dirac had been in Copenhagen for a few months. Rutherford wanted to know how that young man had been doing. “Oh, we don’t really know. He doesn’t say very much.” You know this story?
No. I don’t remember it. I probably haven’t heard it.
And Rutherford told him, “Well, that reminds me of the story about the man who bought the parrot at the store, and took it home and he worked on it week after week and he couldn't teach it to talk, so he went back to the parrot dealer and said, ‘I want a parrot that’s guaranteed to learn to talk. So the parrot dealer gave him this parrot and he took it home, and he worked on that for two weeks with no result at all, and he took it back. ‘You told me it would work and it didn’t.’ ‘Oh, how terrible, you wanted the parrot that speaks, and I sold you the parrot that thinks!’”
Terrible mistake, yes.
Well, anyway, that was the relation of Bohr and Rutherford. I can recall Bohr working on the talk on Rutherford. It was a tremendous exercise for him. And I recall his wanting me to work with him on something on quantum theory, and he even also invited me to accept a professorship at Copenhagen, but I did not want to give up my children.
Yes. Had it been earlier even, it might have happened — had it been in 1935 perhaps, as you said before.
Yes. But to work out something with him would have been of course a wonderful result, but an infinite work. That love of getting things straight and making a comprehensive treatment, not just a few splashy details, that was characteristic.
But he must have been very difficult to work with. I mean, he was all-consuming in some sense. I spoke for example to Weisskopf about it. Of course he loves Bohr, but also I got the impression that he could only be there for a little because, you know, it takes your own independence out of you, because it's so demanding and you become a part of Bohr in the discussion process, in a way. I don’t know if that’s the way he put it, but isn’t that true? Or do you think that you could work as equals?
Well, I can recall, in the paper on nuclear fission, the formula for example for the rate of fission. I came with that to Bohr, and I had to argue it and persuade, but he accepted it. But he wouldn't take anything just on somebody’s say so. He wanted to understand it through and through.
Was that different by virtue of your being at Princeton then? I mean, then you were more equals?
Yes. Perhaps so.
I mean, the visitors at the Bohr Institute had a very different role, of course, and I don’t know if Bohr saw himself more as a mentor for them, than with you in Princeton at that time.
It’s odd, I never thought of him as a mentor at all.
No. I thought of our not facing each other, but facing a common difficulty, to try to understand something. And I’m not sure that it would have made any difference to be in Copenhagen. Well, after all, the paper on the collective model of the nucleus, which eventually just David Hill and I published, we worked out… [Telephone interruption]
It was interesting what you said about Niels and Aage and optimism and pessimism.
Yes, that’s an absolutely fascinating topic, and I would like to explore it more. I’d like to have another long walk and talk with Aage, to get his slant on that.
Yes. I would think that Niels was the eternal optimist.
Yes, exactly. I don’t know whether Aage but of course, everybody has his own attitude too, that colors things.
And optimism and pessimism aren’t necessarily correlated with world views like that. I don’t know. It’s hard to define these things. I don’t know to what extent it comes out of that or is a reflection of that. It’s very tough. I don’t think we’re going to resolve that question tonight, but it’s just fascinating.
It would be interesting to ask other people who have talked with Bohr about that. Weisskopf would be somebody, although I don’t know whether he’s talked that much with him about it. Who would be another person?
I don’t know if Rozental is somebody who has gone into that kind of thing.
Yes. Perhaps not to the same depth. One could ask also Mottelson.
Yes. And the sons, I suppose. I don’t know how much they were exposed.
Yes, the other sons, of course, a perfect thing, and then Teller. Teller would be a good person to ask about that.
They were so close?
But so many others have gone. Delbrück, for example.
He would be excellent, yes. I don't know about Danes, other than the family? I don't know if Lindhard(?) for example is close enough.
Yes, that’s a good point. Lindhard would be one. And Sven Gösta Nilsson.
Yes, the Swede. That’s a whole project in its own right.
Yes, oh yes. About whether the mystery is soluble, that’s it in brief. Can we ever know?
Whether the question is meaningful too.
Well, that’s a part of it. That’s part of it.
That’s the question and answer. The answer necessitates the question, yes. — [Telephone interruption] — Well, this whole discussion started out with my asking about the open world. Did that kind of issue arise in your conversations with Bohr before the war?
Understanding the world, hope of understanding the world?
No, you know, Bohr’s open world, what developed into the open world.
Well, of course, nobody could be unaware of the motto over the entrance hall of the Institute, where this grant was acknowledged from the Rockefeller Foundation that had let the Institute get started in the first place: “to promote interchange among people from all countries.” So there the ideal was expressed at least in the scientific sphere, but that's before it had got to this other sphere.
It’s the expansion of that I’m thinking about, of course.
And Bohr’s visits to other countries. Of course, I remember the account I get from E. J. Williams of their trip to Russia, making contact with the people there.
The first trip? That was when?
I’m not sure what would that have been 1934?
I believe so, yes.
That’s odd, because in 1934 I was there, and I would have thought I would have known it. But there’s that picture, and Williams telling me about them going to visit the Kremlin, and the Museum associated with the Kremlin. This was closed to the public at that time, so it was a very great privilege to be let in, and to be taken around by a guide. Williams was really upset because Bohr was not showing any interest in all these things the guide was showing. And then they came to this stage coach with the springs on it and the mounting. Oh, you couldn't drag Bohr away from it. He was discussing it — how it operated, the principles of it, and how you could write when you were traveling and so on. So it's an all or nothing tension.
Yes. I guess that's needed for that kind of concentration.
A couple of hundred feet down the way, Hadley Cantrell — was it Hadley Cantrell had set up a perceptron. Was it a perceptron? I hope I've got the word right. It was a building which had a strange shape, proportions all cuckoo. But if you looked into it at a certain angle, it looked just like a normal room, simply because of optical illusion, and people’s sizes were totally out of kilter. So Hadley Cantrell had taken the psychologist down there who was visiting, Kohler, the psychologist, with a couple of other guests, to show them this. Then somebody brought Niels Bohr down, at the same time, and neither of them had been planned to meet the other. These two great people were introduced, but they didn't say very much to each other. Then they got looking. Then pretty soon Bohr would say, “Oh, come over here, look at this, see this.” And then the other would come and like that, and then Bohr said, “Let’s sit down somewhere.” So they found a room and they talked for about half an hour about it. As you say, it was all or nothing. Totally taken up. And then, do you know the story — and I would like to get it correct, Magnus Magnusson from Reykjavik told me of how Niels and Harald had gone to Iceland? They’d read the Icelandic sagas and were taken up with them and thought they really should see them. They were going around from one place to another in the country, and word spread around about how enthusiastic they were. So the Icelandic newspaper people were following them and getting their comments. And word of all this got back to Copenhagen. So when their plane came into Copenhagen bringing them home again, here were all this group of Danish reporters with their notebooks waiting for comment about it. Have you heard this one?
And so Bohr talked about half an hour, and they couldn’t get it at all. They all had their notebooks but got nothing in writing. One of them finally got a bright idea. He turned to Harald Bohr and said, “Could you give us just a brief summary of that?” So Harald Bohr gave a nice crisp five minute summary, and then he turned to Niels and he said, “Is that all right, Niels?” “Oh, Harald, you were much too clear!”
Well, that was the difference between the brothers, wasn’t it, or part of the difference? That was why he went to his brother often, I think. They were so close.
By the way, did Harald have any children?
You’ve got me. That’s a good question. I’d really have to look into that. Well, the open world again. My question is, did that influence you in your own work during the war and after the war, in terms of your social engagement? Because I remember in your article in the Stuewer volume — your large article there — I think you say that you regretted after the Second World War that you hadn't entered those kinds of questions earlier.
And I was wondering whether Bohr and the open world and all that had anything to do with that, or how these things interconnect.
Well, I think it was a much more immediate issue. I think it was simply my feeling that I just couldn’t stand all these people who said, oh, what a crime it was, the nuclear weapon. To me, weapons are weapons and policy is policy, and peace is determined by policy, not by weapons. I mean, what’s right and wrong is a matter of policy, not of weapons, and so my feeling was that every month lost meant a half a million to a million lives that would have been saved. And I had not appreciated at that time how much difference one person could make, how much difference he could make.
Yes, and that of course has figured strongly in your career since then, I would say. Maybe we could run through your subsequent collaboration with Bohr, after that first approach, just to get that straight.
Yes. In 1937 he came to the States.
That was on his trip around the world, yes.
Was that it? And there was a conference held at the Carnegie Institute for Terrestrial Magnetism. I have a picture of Bohr and myself and Breit and Gamow and so on there. And then I was talking to him about the alpha particle model on which I’d also been doing some work. He listened carefully, but he did not express himself pro or con. That was a very interesting, that was typical of his reaction to a new idea, to listen without expressing himself, but reflecting. I had come on that, really because year after year I’d been plugging away at that problem of the scattering of alpha particles by helium, which I’d started with Breit, which I carried on at Copenhagen, which led ultimately to this socalled resonating group structure method and to the S matrix — that was about 1937. So that was a topic I talked with him about at that time.
Yes. That was a brief encounter?
Yes. It seems to me also that then, there had been Bethe’s big article. When did that come out, the one that's often called Bethe’s Bible?
It's in REVIEWS OF MODERN PHYSICS.
Yes, the three articles. When was that? Was it 1936?
It must have been about that time, because I know Bohr felt a bit that his thunder had been stolen in that article.
Oh yes, the compound nucleus.
…and that it was useless to go and publish some of the things he was doing.
Could it have been between the NATURE article and his article with Kalckar? I guess that may make sense.
There were to be more articles with Kalckar.
Yes, but I was thinking that the first compound nucleus article with Kalckar may have come after the Bethe Bible. Because that came out, obviously, after the NATURE presentation of the compound nucleus.
That was not due to any discussion of yours? You had left.
No. But I found myself being an expositor of the method of the compound nucleus, discussing all kinds of problems in this country, and giving lectures as I mentioned at Chicago and Michigan summer schools of physics.
You took that up immediately after Bohr had published it.
Yes. So then it was very logical, when he came in 1939, to apply the same methods of the compound nucleus to the fission of uranium.
It was logical but it could not have been predicted, because he brought the fission with him here.
So that was not the thing you had set out to work on.
Did you have plans to work together before he came, at any rate?
No. He was giving lectures, you remember, on quantum theory and measurement.
So the fission was the reason for your working together at all that closely in 1939.
Well, we probably would have been close together on the measurement business too. But Rosenfeld was really his official companion on that topic. But Rosenfeld had not been occupied in the same way with the nuclear physics.
Even though it was he who broke the news. Yes, did Rosenfeld go back or how was that?
No, he was here.
Oh, all of you were here.
Yes, indeed, and stayed at the Nassau Club.
That's how it worked, yes. Was that the first time you had a real one to one collaboration with Bohr?
Had you had that kind of collaboration before?
No, I had not.
No. So that took most of your time. That was a very intensive thing during the period.
Well, of course I had my courses here at the university; I was teaching courses. Our house was being built, and the architect would often come in, so I introduced the architect and Bohr to each other. The house got finished September 1, 1939, the same day that our paper was published, the same day the war broke out. Well, anyway, we used to be at the other building, that we aren't in now. Sometimes we'd work in Bohr's office but more often in mine. I think he felt that he was safer from being found in mine. Also, in his office there was a list of things that had to be done, written in chalk on the blackboard, and if he could get out of that room, then he could be with a free conscience.
So that went on for the whole semester?
It went on until shortly after the meeting of the American Physical Society, and then he had to go back. That was the end of April. I wish I knew the exact date he had to go back. But the paper wasn't finished then, and Peierls and Weisskopf told me it was a great honor — they don’t know anybody else had it — of being allowed by Bohr to finish a paper without his being there!
He didn't even have to clear it before it was published?
It went in.
It just went in.
I think that is very unusual, yes.
But there was a change in the proof. There was a factor 2 on the penetration exponent, if I remember correctly, because I of course sent him the manuscript and there was time enough for him to respond before the proof came back, so I could correct that in proof.
Well, of course you have described the details of that collaboration in other places, so I don’t know if you have anything to add in particular to that.
And then the next time, was that in 1949 or was there something in between? Of course you were together in Los Alamos, right?
Well, Los Alamos — I was never there at the same time that he was. But I would visit from time to time there, on this question of criticality of a plutonium processing plant, because if you by accident gather too much plutonium in the chemical processing plant, why, it would be a very bad thing. The plant would be put out of operation. And should a second plant be built, for 200 million dollars more? That was quite a question. But I was talking to him in Washington during that period. That was just after he had seen Roosevelt, and I think I’ve written about that somewhere.
So that was the discussion of the open world more than physics?
Yes. Let’s see, the Danish ambassador had a dinner, and there was Bohr and Frankfurter and he was kind enough to invite me, so that was an interesting occasion.
Yes. And then it was 1949 that you met again.
Yes, 1949. I can’t remember anything in between.
Right. And then you were called back to the Matterhorn Project.
I do not know when I began to keep my notebooks, and whether I already was keeping them at that time. I suspect not. I suspect that I didn't begin in a big way until the Matterhorn Project.
Actually I cannot tell you that. That’s one of the few things I should look up at the APS still because the notebooks are there, right?
Yes, right. I, as you see, am still working on more notebooks.
Oh yes, continuing volumes. Is there any collaboration after 1949 with Bohr? Were there other things?
I think I would remember that. I honestly can’t remember any.
OK. Well, after this I think we should go back in time again, and talk a little bit — not now, I think we don't have the time for it — about your war experience, as the introduction to your getting interested in and exposed to science policy and science advising matters, because that must have been a watershed for you personally, as well as for physicists.
Oh yes, my wife did call. Yes, I think we should stop here.