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Oral History Transcript — Sir Rudolf Peierls

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Interview with Sir Rudolf Peierls
By Charles Weiner
At University of Washington, Seattle, Washington
August 13, 1969

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Rudolf Peierls; August 13, 1969

ABSTRACT: Aspects of Peierls life and work in theoretical physics. Physicists and physics research in Manchester, Cambridge, Birmingham and other British institutions, beginning in 1933 after Peierlsí Rockefeller Fellowship in Rome and Cambridge. Observations on Russian physics, marriage to a Russian physicist, trips to Russia in the 1930ís. Attitude toward fission and his work with Frisch on the possibility of developing the atomic bomb; impressions of the U.S. in 1942 and his war work in atomic energy research. Other topics discussed are: Chadwickís cyclotron; Cherwellís accelerator at Oxford; Powellís discovery of the pion and development of photographic emulsion techniques; background of the Fuchs case; postwar experimental work at Birmingham; his role in postwar development of quantum electrodynamics; participation in conferences; effect of atomic energy on world politics. Postwar concern with broad-based issues in academic, social and political fields.

Transcript

Session I | Session II | Session III

Weiner:

Today is August 13th, and weíll go for about an hour this morning. Weíre in the post-war period now, and we just agreed that we would try to identify major themes in your work. Letís talk first about the academic physics theme. To start off, I think that one of the important events in the period was the work done by Powell and others in the discovery of the pion, and that leads to a number of questions about the circumstances of this, the reaction to it, and the more general question about the relation of that field -- cosmic ray physics -- to other fields in physics.

Peierls:

Well, starting with the work of Powell, which of course was a major turning point in that period, apart from the purely scientific content that started with the scientific aspect of it, there had been a growing mystery because it was believed, of course, that the mu-meson or the meson then found in cosmic rays was the particle predicted by Yukawa, and that didnít work. From this period of Yukawaís idea it was clear that such a particle should interact very strongly with nuclei, and it didnít. This was beginning to be realized from various cosmic ray experiments, and people were getting intensely puzzled, and I think in fact about the time or just preceding Powellís discovery, some people raised the question whether there might not in fact be two different kinds of mesons (this was put forward tentatively), and then Powellís discovery, in fact, settled that. Now, the background is that Powell was one of those people who surprised the scientific community by coming out with really big things when this was not expected of him. There are other examples. He had been regarded as a competent but not especially inspired man, and that was perhaps the reason why he did not stay very long in Cambridge but had to go out and get a job elsewhere -- he ended up in Bristol -- and he was a pupil of C.T.R. Wilson who had developed the cloud chamber, and in a straight line from that he got interested in the use of photographic plates for nuclear work, which other people had done, too, but he did it more thoroughly than anybody else. So it seemed useful, if not exciting too, and he went further in perfecting the technique for this than anybody else. Well, all right, it was worthwhile, but nobody expected anything very fundamental to come out of that. And he and his collaborators did some quite useful nuclear physics work -- I mean ordinary nuclear structure work -- where the photographic plate technique is still a useful tool; itís still used occasionally, though less so than at that time. And then he turned his attention to cosmic rays and developed ways of doing photographic plate experiments in cosmic rays. Then very fortunately it turned out that this was just the right tool for seeing the pi-meson and its distinction from the mu-meson. Itís a set of rather special accidents which result in the fact that it turns out to be much more profitable to look for it in photographic plates than with any other technique. Of course, nowadays one can do it by other techniques -- having accelerators and so on -- but that was the way to see it. This, of course, couldnít have been foreseen. I mean Powellís merit is first to have been so absolutely consistent in following that technique and with the hunch that something might come out of it; and then, when he got the evidence, to recognize immediately what was going on and to use methods of analysis and criteria which almost immediately the first tracks became available led him to the right answer, which was an extremely impressive piece of reasoning. So everybody was pleased first of all to see that somebody from whom one hadnít expected this turned out to be absolutely outstanding in his vision. Of course, this is not the only case. Lamb is another case who surprised everybody by doing much more than had been expected. The other thing was that this very major step was done with a relatively cheap method; that while everybody was worrying about getting funds for expenses and elaborate machines, here it was ideas that did it and not money; probably the 1st occasion when something as great as that in modern physics has been done at very little cost. The cost was not negligible because one did need fairly elaborate sets of microscopes, and also Powell and his group were working with the people in the photographic industry to develop special emulsions for nuclear purposes. This was assisted by government grant. I donít think the firms would have done it entirely on their own. So it did need government support but of course on a completely different scale from the accelerators. So that was pleasing. Well, now after that, of course, it was clear that physics was again in business in the sense that it was clear now that this was the particle that Yukawa had postulated -- that the pi-meson had a lot to do with nuclear forces. It is clear today that it doesnít account for them completely, and in any case the analysis hasnít been completed -- itís almost too complicated. But that it plays a fundamental part was clear. And this provided a stimulus to further experimentation on the one hand and to theoretical thoughts on the other. It also immediately made it clear what one was going to do with the high-energy accelerators apart from pursuing things like neutron-proton scattering from high energies, which one had always known was important and clearly remained important. The next thing was if you had enough energies to produce pions, you would then study their properties; and that was one of the next important things to do. I think probably the Chicago laboratory with Fermi was the first one to be in a position to do proper work, to generate enough pions to study their properties; and that again helped physics along. Of course, many of the accelerators had been designed before the existence of the pion was known, and some therefore turned out to be at convenient energies -- others less so. For example, the cyclotron at Harwell had the distinction of being the highest energy machine that could not produce pions. And itís going to retain that distinction, because obviously nobody is ever going to build a machine at exactly that energy again. I think with some improvements it either has been or could be turned into a machine which could just produce some pions but of course so close to the threshold that you would get a very poor yield. So in that case it would have retained the distinction of being the lowest energy beam which can just produce pions. But this is in the nature of chance. So from the theoretical end, as soon as the existence of the pions was known (and, in fact, a little before when according to Yukawa, its existence was postulated), one tried to fit that into the framework of quantum field theory and striking a lot of difficulties. Of course, quantum field theory had at that time got stuck just as the work was left at the beginning of the war. There was nothing but difficulties. And there were infinities in the theory which clearly were not very real. I mean in a sense nothing in nature could be infinite. And this was an unphysical part of the theory one had to get rid of somehow. It came into some problems where these infinities came up if you were careful enough in your calculation, but you knew pretty well what the answers should be in spite of that; and one got the habit of just leaving out some infinite terms that were unreasonable. But it was a bit messy. Heitler about that time just after the war proposed a theory, the so-called radiation damping theory, which was a systematic way of ignoring the infinities, which he set great store by, but which was a little controversial. Other people werenít quite convinced. And, of course, the later work then showed that it wasnít quite as simple as that. In a way it was simple, but it was different. Then I think Iím right that in time even before Powell the work of Lamb made an impact. Now Iím not clear about the relative dates, but I think Lamb was before Powell. I mean these two different lines eventually converged. Now, the interesting thing is -- this is a very general situation -- that an experiment which gives a quantitative answer which comes out with a number can have a remarkable effect on the theory, even when the number that you see by it doesnít reveal any particular information. The point there in the Lamb shift, of course, was a shift of the hydrogen fine structure lines relative to each other which disagreed with the theory. Now, it had been known for a long time that there were some difficulties. I mean the people had never managed to make the hydrogen spectrum check exactly with the Dirac theory. But the trouble was attributed to experimental inaccuracies. At least one wasnít sure that there was a discrepancy, but it looked always very suspicious. And, of course, Lamb had the merit of taking that seriously and realizing that it was important to pin that discrepancy down really and he developed clever techniques which made that possible. But, you see, there was no reason why years earlier theoreticians shouldnít have asked themselves: ďAre we sure that this should agree or can we think of any corrections which would make it disagree?Ē which was ultimately the answer; and what would we expect to find? But it took, in fact, a situation when actually an experiment had been done giving an answer that people sat down and said, ďHow can we really account for this?Ē It was this challenge. This very often happens in physics: that it takes a crucial experiment. You might sit down in advance and say, ďWell, now, this is an experiment which will either say yes or no; and what do we conclude if itís yes and what do we conclude if itís no?Ē And you might then by pure theoretical reasoning already get the answer. Very often this doesnít happen, but you wait until the experiments give one answer, and then you sit down and think about the implications. Sometimes what happens is a little more interesting. Once somebody starts doing the experiments but the answer isnít yet known but you know that there will be an answer next year, then you start sitting down and saying, ďNow, suppose the answer is yes, what do we conclude? And if the answer is no, what else do we conclude?Ē Peopleís abilities to think many steps ahead are always a little lacking. Anyway, so this stimulated people now into thinking how one could make sense Ö The main thing is here was a significant question you could ask and expect an answer to, which was mixed up with all the infinities. It wasnít just how you could talk yourself out of the infinities and then get the answers you had known for a long time, but how you could get something new. Thatís much more restrictive. Well, I wonít go through the whole history of this, because it started with Kramers being the first one to think about this seriously. It was picked up by Bethe, whether as a result of Kramers or independently, I donít know. And then, of course, this was rather more a physical picture, but it then met up with mathematical technique tricks that had been developed to carry out what we now know as renormalization by Schwinger and Tomonaga and others. And then in a very short time it became clear that in electrodynamics at least the infinities in themselves were no obstacle to getting sensible answers out of the theory, mainly, as you know, because what is infinite is the difference between the intrinsic mass of the electron, for example, and its real mass; and since we can never observe the intrinsic mass, which would require switching off the electric fields surrounding the electron, we donít have to bother whether the intrinsic mass should be in itself a finite or meaningful quantity. Whether thatís the last word, we still do not know; whether in fact the right answer should be that one should only think in terms of renormalized quantities and that the question of what is the mass of the bare particle is not a meaningful physical question -- is one view. And the other view is that since the coupling between the electron and the electromagnetic field is rather a weak coupling characterized by the fine structure constant of 137, we can get away with neglecting the complications and talking as if the intrinsic mass was not meaningful and the self-energy correction was infinite, although in fact it should be just rather large and finite. These are two alternative views and we havenít got the answer yet today. I think because of the way views have oscillated back and forth in the first excitement of making renormalization theory work and its various successes, including not only the Lamb shift but the anomalous magnetic moment of the electron and other things, one tended to the view that that was all there was to it and that renormalization was the answer to everything. I think today that more people would favor the thought that this is only an intermediate step and that physics wonít be finished until we have found some way of really never getting infinite quantities in the equations rather than having them there and ignoring them. That we donít know.

Weiner:

Can I take you back to the origins of the developments in the immediate post-war years? Were you at work on the subject, or was your attention drawn back to it because of the developments that you described?

Peierls:

Well, I was not working on this subject -- I mean on anything directly related to that. I was still chasing after possibilities of eliminating the infinities by having the finite electron. In fact, these new developments came to my knowledge just about the time in l948 when we had a small international conference in Birmingham, which we were rather pleased with. It was a little different from some of the conferences in that we had no program; we had no papers given; but for each session a subject and a chairman and an introductory speaker and then just free discussion. People had questioned whether this sort of method could possibly work. It worked very well, partly because it was the right time. People were excited about things and willing to argue. Partly it was because we were rather lucky in the kinds of people we got for the conference, which included Oppenheimer, Bethe, and Teller.

Weiner:

I think I have a letter here regarding the conference. But it was designed to be small and informal.

Peierls:

Not that small. I mean we had a lecture room with a capacity of about 300, and we just filled that, which wasnít such a small conference for the time.

Weiner:

I had the impression it was a small meeting. Who paid for it?

Peierls:

Nobody. It was all done on a do-it-yourself basis more or less. People paid their own fare or expenses or we got them from existing sources. The organization was very informal and didnít cost much.

Weiner:

The theme of the conference was ďProblems of Nuclear Physics?Ē

Peierls:

I donít remember whether that was the title.

Weiner:

The point is how did that bring these problems to your attention?

Peierls:

Well, I mean this included Bethe and Oppenheimer, who of course were up to date on what had recently been talked about, and so things like the Lamb shift and its implications were very prominent in the discussions. I probably had heard about them before, but this was really a way to get them clear. For example, to give you the climate of the thing, in the middle of the conference somebody had a letter from Dyson who was then at Cornell, summarizing the results he had just obtained in linking the Feynman and Schwinger approaches and showing connections and also in proving that the infinities could be thrown out not merely in the first order in which they appeared but to all orders, which was an important formal result, and so on.

Weiner:

This was a letter from Dyson?

Peierls:

He wasnít there.

Weiner:

Was Feynman or Schwinger there?

Peierls:

No. Was Feynman there? No, I think not. Certainly Schwinger wasnít. But I think it was a letter either to Bethe or Oppenheimer-Bethe probably because Dyson was with Bethe at Cornell.

Weiner:

As was Feynman, too.

Peierls:

Yes.

Weiner:

I do have the description of the conference, which was issued in March, Ď48, and signed by you and Oliphant. The topic was ďProblems of Nuclear Physics.Ē it was to be held from September 14th partially through September 18th. Hereís the thing that I wanted: ďThe subjects to be dealt with include, on the experimental side, accelerators and methods of detecting particles; on the theoretical side, field theory including hole theory and nuclear forces. Beta and gamma ray problems will be discussed both from the experimental and theoretical points of view.Ē Then you refer to informal discussion, ďto have few prearranged papers,Ē sessions devoted to one specific topic. The letter to Kramers was a little after that. You indicated you hoped he could come. And as far as funds, you say that there arenít sufficient funds to take care of expenses of all invited guests, but if thereís any difficulty, let you know.

Peierls:

Yes, I should make a correction on what I said about money. We had from some source a little money to help people, say, from the continent where there were currency regulations who couldnít bring even enough money with them to pay for their lodging or their living expenses in Birmingham.

Weiner:

What was the motivation? Was this a way of getting Birmingham into the center of things in physics?

Peierls:

Well, that played a part, of course, but generally we thought it would be a good idea to have such a conference, and we thought we could do it. You see, at that time there were no regular series of international conferences where there is essentially some kind of organization which decides where the next conference should be. It was more a matter of private enterprise, and we thought it was time to have one.

Weiner:

How many active participants do you think were there? I donít mean people who listened but people who were actually engaged in discussions.

Peierls:

Well, it varied from people like Bethe and Oppenheimer and so on, who obviously dominated the discussions, to people who would occasionally ask a question from the back of the room or make a point, intelligent or otherwise. Itís very hard to put a number to it. I mean obviously not everybody present spoke all the time. But I would say you could probably pick out some 20 or 30 people who were very active in the discussions and then a larger number of people who made a few remarks and then of course an even larger number who were more or less silent.

Weiner:

Was there any feeling that you had about whether the people were predominantly theorists or pretty well mixed?

Peierls:

Iím probably prejudiced, because on these kinds of things, which were then sort of hot news connected with field theory and Lamb shift and so on, obviously the theorists would be prominent. Of course, when the conference was planned, one didnít know the importance that experiments like Lamb shift and so on would have for the subject. Otherwise, one would have tried to get in people to talk about that. But they were not there. And so the experimentalists were either concerned with slow experiments where it took a long time to get the evidence, where there wasnít anything very acute and exciting; or they were talking about new techniques, new accelerators, new methods of detection counters and so on, which is very important but wasnít primarily my concern. So I remember clearly the theoretical side. If you ask Oliphant, he may have been more excited about the experimental part.

Weiner:

I should ask him some day.

Peierls:

Though itís possible that he would also say that the theoretical discussions were more exciting. I shouldnít try to guess that.

Weiner:

Were any of the proceedings published, either formally or informally?

Peierls:

No. think what we did was to have someone write up a short resume of the discussion but not attempting to either have a tape-recording, which in those days would have been difficult, or to get the speakers to write down what they had said and so on. We thought this would ruin the nature of the discussion.

Weiner:

Was this resume duplicated and distributed?

Peierls:

I think so. But I wouldnít know now where to get hold of a copy. It must exist somewhere.

Weiner:

How about your own files?

Peierls:

It might be somewhere amongst the old papers, but theyíre not in Ö

Weiner:

Thatís something Iíll look for. Iíll ask around among people who were there.

Peierls:

It was the custom for Nature to publish short reports on such conferences, and probably somebody must have written a page for Nature about the conference and saying a little bit about it. You might find some names there. Thatís easy. But thatís not a full account.

Weiner:

Do you think the significance of it was pretty much in sharing this new information and discussing it rather than any breakthrough in understanding that occurred at the meeting itself?

Peierls:

I donít think there was. In other words, it was different from these smaller meetings held at about that time in the United States on Shelter Island and the Cornell meeting and so on.

Weiner:

It would be a little hard to pin down as to what actually happened there, except for a clearing of the air.

Peierls:

Right. But there, you see, you had a large proportion of the people who were actually doing the work present. Our conference wasnít like that. It had a few -- well, I think probably Bethe was the only person present who was actually himself contributing to this development. Oppenheimer understood it very well and was very good in commenting on it, but he hadnít done much of it himself. I mean it was different from these working conferences. I mention it mainly because it helped me to learn a lot about this and no doubt some other people present.

Weiner:

Now, that brought you into it fully.

Peierls:

Yes. Now, I was then already worried about whether this would be the complete answer -- in other words, whether the theory that these hidden infinities could be made a consistent theory or whether sooner or later if you looked carefully enough, it would hit you back; and you would begin to come up against problems you could not solve. I tried to get at that by testing the effect of the theory on various problems where you might expect trouble. For example, the nature of the calculations one does is such that they lend themselves more easily to the analysis of scattering problems, collisions and so on, than of bound states; and so I tried to pose myself problems involving bound states to see what difficulties would show up there. This led, for example (this was work I didnít do myself but was involved with), to some members of the department looking at the problem of the relativistic corrections to the mutual interaction of two electrons in an atom -- say, either the corrections to the helium spectrum or the interaction of the K electrons in a heavy atom, which are much more relativistic, though the experiments canít be done as accurately, and to see whether the Ö There one already had answers. I mean Breit had given the formula how to formulate the relativistic corrections to helium, for example, or to any two electron problem. It was now interesting to see whether the somewhat intuitive way of Breit of writing this down, which seemed right, would in fact agree with what the modern method had to say about the problem. We got into some confusion because at first it looked different. And, in fact, rather excitingly, the difference seemed to agree with the remaining discrepancy in the helium spectrum until we then discovered that weíd made inconsistent use of the new techniques. One way this came out was when we discovered that if you applied this to hydrogen, where itís a two-body problem if you allow for the fact that the proton has a finite mass and therefore also moves, that if you took that result and then went to the limit of the infinite proton mass, so that the proton was just sitting still, you still wouldnít get the usual answer. So there clearly was something wrong, and then we found what was wrong, but at the same time it was also discovered that the disagreement had to do with some other part of the problem -- that the wave functions used for the helium atom hadnít been accurate enough. So both the apparent experimental disagreement and our theoretical correction both disappeared. This was the kind of thing one was trying at that time -- not to shoot down the new theories, but just to understand their limitations.

Weiner:

You were in touch with Kramers then on this as one of the people you were discussing these things with. Thereís one letter relating to someone that he had sent over. You said to Kramers in August of Ď49: ďIt was a great pleasure to have Gunther with us for one day and we were very interested to hear about the problems of the Lamb shift in helium. I had recently heard from Waller about ideas of one of his collaborators, who had considered the series of helium-like ions and had shown there a deviation which might be attributable to this kind of effect.Ē Then you refer to Wailerís group. And then you also say ďsome features of Guntherís work are similar to unpublished work by Feynman.Ē And ďFeynman has circulated typescripts of his paper fairly widely.Ē I guess you got this through Feynman or through Bethe.

Peierls:

Yes. Well, actually, this man Gunther, a Pole who was in Holland with Kramers and then came to us, was a very charming man but not very clear in his thinking. In fact, later he spent a year or so with us, and it simply developed that other people had done this helium problem which I mentioned, the two-body problem, and sorted it out eventually in a way that satisfied us. Gunther had another approach, and we had interminable arguments about that with him and we never believed that he would get anywhere; and in fact he didnít.

Weiner:

The interesting part of it was not so much him but the fact that you had developed by 1949 abilities in this field. You refer to several people at Birmingham who had studied closely these papers. You apparently were in touch directly with Feynman too?

Peierls:

Well, there was correspondence, direct and indirect; and what may be interesting: When you quote the phrase that Feynman had circulated typescripts of these papers, today we would say that we had Feynmanís preprints -- the same idea, but the word ďpreprintĒ wasnít in use at that time.

Weiner:

Itís much the same as the thing I have here of your Solvay talk, which was mimeographed.

Peierls:

Ah, but that was different because it was the procedure at the Solvay Conferences that papers were submitted in an appropriate number of copies so that people could read them before the conference. It was taken as a basis for discussion. So this was not meant for general circulation but was meant for the members of the conference. So I had a few copies made which went elsewhere. This was not in the spirit of the preprint.

Weiner:

Dyson was one of the visitors at Birmingham at just about this time, wasnít he?

Peierls:

No, that was a little later. That was interesting. Dyson was a pure mathematician originally, and in Ď47 he came to see me to ask my advice -- that he had got interested in theoretical physics; what should he do in order to learn that subject? I discussed various possibilities with him; explained, for example, that he would be very welcome to join us at Birmingham if he felt that would be profitable, but there were alternatives; and one of the alternatives we discussed, which seemed to me attractive and which he eventually acted on, was to go to Cornell and join Bethe -- which he did. Then somewhat later -- and I canít remember the year, probably 1950, I might guess; maybe í49 -- he returned from America and spent two years on a fellowship at Birmingham.

Weiner:

In this letter of August Ď49 you refer to him coming: ďDyson himself will be here next session.Ē So he must have started.

Peierls:

So he started October of Ď49, for about two years -- in fact, two academic years except he took one term off to go to Princeton.

Weiner:

Iíve been interested in the Shelter Island Conferences, first because of a remark Oppenheimer made to me that he felt that these were the last real intimate conferences of physicists that he recalled, and that they were looked back upon with nostalgia by a number of people who were present.

Peierls:

I would disagree with that, because I think the first few conferences in the Rochester series, which were later, were still very much in that spirit. In fact, if you look at the change of scale, the first Rochester Conference was called at Marshakís initiative as a meeting of I think a couple of days -- a very short one: one or two or three days -- of the people who were actively working in high-energy physics, mainly theoreticians but not exclusively (I wasnít at the first one, so I wouldnít know the number, but I think it was something like 30 people). And keeping the spirit of that thing, it eventually grew to a conference of a week or more with as many people present as the facilities would allow -- 300, 400. And one in the series, the Vienna Conference actually, was the first time that they simply abolished all restrictions on participation, and anybody came who wanted to; so it was over a thousand I think. And itís still the same thing.

Weiner:

Well, these three conferences I was referring to -- first at Shelter Island, the second at Pocono Manor in 1948, and then the third on the Hudson -- my question, though is: Were the results of these conferences communicated to you?

Peierls:

Not in any organized way. Many of these conferences -- I donít know whether all, but certainly some -- had some sort of duplicated notes, where some graduate students took notes on what was being said

Weiner:

John Wheeler did on the Pocono Conference.

Peierls:

Right. There wasnít one person doing it for the whole conference, but somebody would write up, for example, Schwingerís lectures and somebody else something else. I donít know how clear the original lectures were. Certainly by the time theyíd been written up and probably vetted by the speaker but not rewritten or anything, they gave some indication of what was going on but were not terribly clear. I remember the beautiful example where in one of Schwingerís lectures (I think that was at the Pocono Conference) he writes down an expression for the vacuum polarization or something like that, where he writes down a certain rather complicated four-dimensional integral and writes ďequals zero.Ē And then thereís a footnote: ďActually the integral is infinite, but it transforms as if it were zero.Ē Whether thatís the way Schwinger said it -- heís quite capable of that -- or whether that is how it came through whoever was writing it up, I canít say. It certainly doesnít help you very much when you read it.

Weiner:

What Iím getting at in all of this, with the Birmingham Conference, with the Shelter Island Conference, with the Solvay Conference, is the sense of community involved in a certain class of problems and the means of personal communication. There seems to be a rough clustering of these kinds of conferences in this period, and pretty much the same people -- if theyíre not present, theyíre certainly communicating the results in one way or another to one another.

Peierls:

Well, that is still the case. Of course, certainly the number of conferences hasnít diminished, and certainly at any conference the recent work of people who are not present is known and taken into account. That isnít changed.

Weiner:

I donít know if you had something in mind that followed this discussion which you started off on Powell and the other developments on Lamb and his work and how this led into your own work. If you have other comments on that, fine. If not, then I would like to talk about the shell model.

Peierls:

Well, just to finish that off, I donít think I initiated anything of importance in that field. I was very interested, of course, in trying to clear my own mind and trying to make some progress. But I think in this development, which really now becomes elementary particle physics, although one wouldnít call it that in those days until the discovery of strange particles and so on, I think Iíve been more a spectator and perhaps a teacher in trying to help other people to understand this. I helped with a few small things, perhaps clarified, and also I started some investigations which didnít prove fruitful. I mentioned earlier this hobby of mine to try and find ways of introducing something like a finite sized particle into the basic theory. The fashionable name for that now is nonlocal theory, but itís all the same thing. We put quite an effort into that in the post-war years. It carried more weight; of course, at a time when you thought that the existence of infinities just made it impossible to make any progress and a little less when the renormalization had shown that they neednít stop you from getting on. Then at least we managed to get the classical non-quantum picture of that formulated. This was done in work by McManus who was then at Birmingham, and then other people followed. But we never succeeded at that time in understanding how we could introduce quantum phenomena into this. Somewhat later, in the 1950s, I made some more progress with that, together with a young man called Chretien, who was then at Birmingham, is now at Brandeis. And the results were disastrous because they showed that the best way we knew how to do this resulted in a logically perhaps consistent theory in which, however, the infinities were not removed but were worse than they had been before. So that was not a success. I still have the feeling that something might develop along those lines, but at the moment I donít know how to do it.

Weiner:

How would you compare your role in this to others who have similar interests and are of the same generation, give or take ten years? -- you know, Bethe and Oppenheimer and others who followed pretty much the same themes in the Ď30s as you did.

Peierls:

Well, take Bethe. He made a considerable contribution, of course, to the discussions we have already mentioned. I mean he really saw that you could not only talk about the radiative corrections to the hydrogen atoms -- the Lamb shift or something -- but you actually could sit down and calculate some number, which was at his first attempt not terribly accurate, because various approximations had to be made which have since been improved on, but the idea was there. So that was very important and showed not only ability to calculate but very deep physical insight into what was going on? And that, I think, had a great influence. Later on he always kept an interest in this field, and one other major piece of work of his I remember is the Bethe-Saltpeter equation, which is a way of formulating in some approximation the relativistic two-body problem. I may have now forgotten a few other contributions, but mainly I think he has moved away from that in finding that the complications of the modern developments are a little beyond him. Iím not sure whether I interpret his attitude correctly, but think I do. And while heís very interested and understands to a large extent what goes on, he hasnít really participated in that lately, and thatís my own position, too. Oppenheimer was a little different, because although he did not make many direct contributions, there is some work by Oppenheimer and Wouthuysen, for example, how to do certain types of calculations, which is quite important. He didnít write many papers himself on this subject, but he was one of the people who understood extremely clearly what was going on and could help the people actually engaged in the work understand what they were doing. I mean this is a positive contribution even if you donít write any papers.

Weiner:

How about his role at a meeting either in synthesizing or obscuring. Iíve heard both views expressed of people who participated with him at meetings. Some say that he brought clarity to the subject, and others felt that he tended to obscure things by taking a point of view that muddied things up. I donít know if this is the difference in generations in the evaluation or not.

Peierls:

Well, my impression certainly is that most of the time he would help to clarify things. Of course, if you talk about a very restricted topic -- some calculation -- people who are interested in just completing that particular calculation and getting a number out of it might be upset because somebody raises doubts about the fundamentals and points to connections of things which are outside of that. This might therefore appear to obscure things. To my mind it doesnít. I mean in that sense you might argue that the presence of Niels Bohr at a conference would always completely muddle up things and get the discussion confused. And in fact about Niels Bohr it would be more justified than Oppenheimer, though I would still like to have Bohr present at most meetings. But, of course, he could be wrong. Anybody can be wrong, and there might have been occasions, although I donít know that I can recall any specific ones, where Oppenheimer was worried about some complication which was not in fact serious, and where therefore bringing in that particular point would retard things rather than advance them. If youíre willing to take part in a discussion, youíre bound to run that risk of going wrong. But I donít think he went wrong very often. And his main feature, of course, was the absolutely fantastic speed with which he could take in ideas. I mean talking with him individually, you never finished a sentence because when you said half of what you meant to say, he already understood what you were trying to say and would very often continue a sentence for you and say it more clearly than you were able to -- at any rate, then was commenting on it and pointing out the implications and so on. And he did the same in discussions, except that you donít interrupt people at meetings to the same extent that you do in private conversations. I would say that barring occasions when he went wrong, his presence certainly always helped to focus a discussion on the central points.

Weiner:

One final question just to follow this up. In addition to commenting as you have on specific personalities and how they reacted to this new period and the role they played, is there any way to make a generalization about this generation? In other words, the generation of theorists who made such contributions in the Ď30s? What kind of a role in general did they play in the later period; whether this new transition to elementary particle physics as a separate field really involved them as leaders or in a quite different role?

Peierls:

Well, itís very hard to generalize because you have to look at each case individually. Theyíre all very different.

Weiner:

I know you gave me different answers, for example.

Peierls:

Right. I think few were actually leaders in the sense that lots of the ideas properly came from younger people. But the older generation took part in discussions and itís very hard to assess what their influence was in any of these things, when one is talking with people, trying to ask questions, helping to understand and so on. The one pronounced difference is that most of these people whose names that Iíve mentioned of that generation were still universalists in the sense that they had some knowledge of and certainly some interest in the whole of physics, the whole of theoretical physics, and therefore this means of course that itís difficult to get detailed knowledge of the technical details in any particular field as thoroughly as the person who concentrates on that, although, for example, people like Oppenheimer or Fermi went very far in knowing the job and in specific things. But it means that one is capable of making connections and seeing implications -- for example, in judging the validity of an approximation made because you know from a completely different branch of physics that thereís experience of this particular trick, either not working or working very well or working although it shouldnít -- things like that. And the present young people tend not to be theoretical physicists now but elementary particle physicists or nuclear physicists. In fact, even more so. In elementary particle physics they may be specialists in dispersion relations or in current commentatorsí or in group theory. And while you can achieve a lot more on the technical side, I think unless you have some people with a broader range of interests, you are in danger of the thing getting fractionated and losing in each field the experience thatís available from others.

Weiner:

Thatís perhaps a good point to stop on. [Pause in recording] Weíre resuming now after a break of several hours, and I think itís probably appropriate to get back to other developments within physics itself. In nuclear physics the significant thing was the shell model about that time in the immediate post-war years. Perhaps we could talk about that, about the reaction to it, how you reacted to it, what significance it had in terms of your own work. And how the shell model and other models competed or co-existed or for what limited purposes they were useful.

Peierls:

Well, starting with the shell model, I have already mentioned a couple of days ago that the ideas of Niels Bohr had led us to believe that there was no hope of doing anything like a shell model, and therefore all the wise people in that period knew that that couldnít work and stayed away from it. But there were a small number of people who were, as you like it, far-sighted or stubborn or narrow-minded, who persisted with shell model calculations. Now, some of those just did calculations because it could be done without caring much whether they had much connection with reality. After all, in those days there wasnít all that much detail known about nuclear spectra and so on. But some -- leading amongst them Maria Mayer -- really looked at the evidence with a view to checking whether there might be shell model features and showed that the evidence (simple evidence, not complicated calculations but just irregularities in the behavior of nuclei and so on) were such that you just could not ignore them. And whether theoretically you believed it or not, the facts were there. Now, this, of course, took some time to sink in; and the details that Maria Mayer herself and other people tried to fit the shell model to in quantitative detail, didnít work until Mayer and independently Jensen had the idea of the spin orbit force which sorted it out pretty well in outline. Well, it took some time, of course, before everybody was convinced; and then came a development Ö Well, there were two lines then following, of course. One was to exploit this model and see how far you could get in interpreting nuclear properties in detail. The other was to try and puzzle out why on earth this scheme worked although it shouldnít. I was not very much concerned with that first line, though I knew what was going on, and some people in my group were working on this, particularly Flowers and other people; but 1 didnít do very much myself on that. I was very interested in understanding this apparent contradiction. Now, independently of that, some people, particularly the Copenhagen group with Aage Bohr and Mottelson, had followed another line, and that was the collective model of the nucleus treating, very crudely speaking, the nucleus like a liquid drop. And this, of course, was stimulated by the ideas of Niels Bohr -- old ones -- because according to those ideas that should be the only possible treatment. Then there was a certain amount of -- I wouldnít say divergence of opinion as much as divergence of emphasis, just how much you should use the one model or the other. Again there happened to be an international conference in Birmingham, at that time in 1953, which for technical reasons was not as great a success as the previous one for our purposes, but was still an interesting discussion; and there we had some friendly arguments between Flowers and people like that on the one hand advocating the evidence for the usefulness of the shell model and Bohr and Mottelson taking the collective view, because there are certain facts that fit in clearly with the one model. Other phenomena were well described by the other. Then you have a sort of penumbra of things which you can try to fit in with one or the other, and you get different interpretations, but neither can be ruled out. So there was a certain amount of argument about that. And then in the course of time it became clear that the two things were not really contradictory but that when you had nuclei near the closed shells or near the magic numbers, then the shell model gave a very adequate description -- in general; I mean there are always corrections and complications. If you go far into open shells; if you have many particles outside closed shells, then the shell model simply doesnít give clear answers --because you have then a large number of states, which in the leading approximation of the shell model all should have the same energy, and the structure therefore has to be explored by taking interactions into account. And this leads then to a mathematical problem of enormous complexity which even the biggest computers cannot handle. And therefore then you need a point of view to simplify that and to bring out simple features, and thatís precisely what the collective model does -- so that there is now no conflict.

Weiner:

Youíre saying this in a way which synthesizes the elements of the two models into the overview. But was that apparent at the time of this 1953 discussion?

Peierls:

No, it wasnít. It was beginning to come out, but certainly one wasnít clear. I mean what was clear was that there were features which could be understood only in the one way and others which could be understood only in the other way. For example, the existence of magic numbers was unquestioned, and clearly when it was a shell model Bohr and Mottelson would never have questioned that. And that already makes it clear that when you are near the magic numbers, the shell structure must still play an important part. On the other hand, I donít recall now whether in í53 there was already clear evidence for rotational states. There was shortly afterwards, if not then. That clearly was a behavior which you couldnít get out of the shell model -- at least not easily -- but which just told you there was some distorted nucleus doing something like a rotation. So the fact that these models had to co-exist, because you couldnít do without either, was clear. Now, just how you treated the limitations of each model Ö I donít know whether that statement was made at the time. It is very hard to remember what you knew at what time. But I wouldnít be surprised if already it was then clear that the shell model was best near the magic numbers.

Peierls:

Iím not sure. But it could be that even in Ď53 it was evident that the shell model was good near the magic numbers, and the collective model was best away from magic numbers where you get quite different behavior. However, in any case, it was quite clear that there were phenomena which clearly called for one or the other approach -- you couldnít do without either.

Weiner:

Were people pretty adamant about their point of view in this 1953 discussion?

Peierls:

No, they were all good physicists and therefore open-minded, although I couldnít speak for everybody who attended the conference. But the people like Bohr and Mottelson. Mottelson was there. Bohr, Flowers and Lane and other people took part in these discussions.

Weiner:

But they came away unconvinced. None of them was willing to abandon the ideas they came with.

Peierls:

Well, the one side wasnít willing to abandon the shell model, and the other side wasnít willing to abandon the collective model. Nobody ever claimed that they should. Nobody claimed that the other model was wrong or useless or anything. Where there might be a controversy would be on just how far you could rely on one model and whether it was appropriate to treat a certain picture and what corrections you should allow in the model before it was realistic -- that sort of thing. And on that, one is always open-minded, of course.

Weiner:

Was this meeting similar to the first in that there were no formal proceedings?

Peierls:

Yes. However, it didnít work so well, partly, I think, because there was far more material available by this time, far more people anxious to talk about their work, partly because people had got wise to what the system was; so that you got the phenomenon of people getting up to make a contribution to the discussion and in fact reading a ten-minute paper; and sessions like that can become like a meeting of the American Physical Society, except you donít know whoís going to talk next on what, and that is not an advantage. Some sessions went all right, but some got a bit out of hand.

Weiner:

I see. How long did this meeting last?

Peierls:

I would guess about five days.

Weiner:

It was truly international in terms of people.

Peierls:

Thatís right. Again people did not get from us any help with their traveling expenses, and so it was left to people to come if they could. One had, as always, to limit the numbers. Mainly we could easily accept everybody from abroad, but in England you had to ration the places, because there wasnít room enough.

Weiner:

This was Ď53. Did you get other models about this time?

Peierls:

Well, I think the optical model was just about starting then. I remember that Weisskopf, who was unable to come to that meeting, sent us big drawings -- big pictures -- of the fits they had been able to obtain to neutron and I think proton scattering by nuclei with the optical model. It is now called the optical model. I think then Weisskopf called it the cloudy crystal ball. Itís the same thing. I think that its relation to other models was immediately clear; that this was not in conflict with anything but just a special situation where you could simplify life. That at least was clear to me pretty well from the start. This was not an alternative philosophy but just a nice way of exploiting the simple features you get at moderate and high energies. In simple terms, itís simply that youíre looking at a region where the compound levels are so dense that you couldnít see them individually or where in fact they overlap so that no structure is left. Therefore youíre interested only in the average behavior of reasonable energies. The uncertainty principle says that if you have an ill-defined energy, if you take a broad spectrum of particles, you can then get a definition in time; and, in fact, if you just take the straight energy average of the scattering amplitude, itís not quite the same as a scattering cross section -- there are technical complications -- but, broadly speaking, look at it: and at the average, you will look at short time behavior of the collision. That simplifies it because as the nucleon hits the nucleus, it will first collide with one other particle and then with another and so on until the whole complexity of it is built up. If you can find a way of looking at the short-term features, then you are back in the situation where you can think of one particle not very much perturbed by the others. That in a way extends the shell model, which also is basically a single particle description, up to the high energies. It wouldnít work directly, but it works with the aid of energy averages. Thatís essentially the relation.

Weiner:

Did the emergence of the shell model have any effect on the approach that experimentalists took to their work? For example, on the question of the collective model and the shell model, did they see it as their role to do experiments which would test one or the other model?

Peierls:

Yes. Well, the main thing, of course, is that these concepts are extremely helpful for experimentalists in sorting out the significance of what they are doing. And the experimentalists took immediately to the shell model, perhaps too enthusiastically and too uncritically, because they tended to apply it to situations where it might not be so justified. But it helped them a lot in discussing what was going on in their experiments and therefore gave them more orientation to the experiments. And that probably was a more important connection than just trying to check up on the shell model and seeing whether it would work. Of course, in the course of that, by describing your data in shell model terms, you would discover whether it worked easily or whether you got features which you couldnít fit in, and to that extent if there was a weakness or a need for corrections in the model. But I donít think that it was so much that they consciously set out to check the validity of the model. Of course, any experimentalist using a theoretical model is conscious of the doubts that may exist. But the main thing is that it allows them to think about the states or the reactions that were happening and therefore to plan new experiments that would throw light on things and so on.

Weiner:

How about theorists? Itís conceivable that a theorist could propose an experimental test of a model that he would feel is in dispute and that perhaps this would more often be a source of a proposal experiment.

Peierls:

Oh, that happens quite often, too. The way it does is that a theoretician, analyzing a spectrum that has been observed, says, ďWell, to fit in with what I expect, there should be another level of certain properties,Ē and he asks the experimentalists to look whether there indeed might be a level that had escaped attention or was outside the range of survey or something. Or he might say, ďTo fit in, the spin of this level should not to 1, as is most generally assumed. It should be 3. Letís try if one can measure that spin and see what it isĒ -- that sort of thing. That certainly happens all the time.

Weiner:

I think Bethe was one who proposed such a test, and I donít remember the exact circumstances. I think it had to do with the shell model. It was a test deliberately designed to disprove it. To see if Iím right, do you recall what his attitude was in regard to the shell model?

Peierls:

I donít remember what attitude he had. I donít know what period youíre thinking of.

Weiner:

Itís a vague thing in my mind, but it was a specific experimental test that he proposed, hoping that it would Ö

Peierls:

Well, thereís an interesting point. I donít know whether that is the one you have in mind, but it might be worth mentioning anyway. The difficulty Iíve mentioned -- that you couldnít understand how the shell model worked, against all the apparent theoretical arguments -- was so serious that it led people to look whether our fundamental assumptions about the forces might be quite wrong. In particular, Teller and Johnston then had a suggestion that perhaps the proper dynamics of the nucleus was not dominated by two-body interactions, as was our normal picture; but that the meson fields of all the nucleons would be so strong and would interfere with each other -- interact so strongly -- that you got as a result one quite strong field with which then all the other nucleons interacted individually; and that would then mean that the shell model was very much nearer the truth and was not even so much an approximation but an expression of reality; that each particle just saw a field of force, which is not just the average effect of all the other particles running around it but simply was established there by the presence of the others in the meson field they created -- now, this really found very little acceptance -- this suggestion. People didnít think it likely, and certainly Bethe didnít either. In that connection, he thought of what evidence we had that there were strong short-range two-body forces not merely in the two-body collisions that weíd seen directly, but even inside the nucleus. He then suggested that the experiments about capture of pions -- for example, positive pions, I think it would have to be -- would give direct evidence that this view was wrong. I donít know whether thatís what you have in mind.

Weiner:

Do you have any idea if he published the paper?

Peierls:

I donít remember. It may well be. I knew that was his suggestion. I think, in fact, he didnít suggest so much that the experiments should be done as that you could conclude that already from existing evidence. But this was not against the shell model. This was against the attempt to explain the shell model by making a revolutionary new assumption about the forces. And, in fact, since at that time already the evidence for the shell model could not be ignored, it implied that Bethe thought, as I did that somehow or other one must justify the shell model even on the basis of the existing current picture, which now is certainly assured.

Weiner:

The discussions in Ď53 and Ď55 and so forth were taking place at a time when elementary particles can be said to have taken a separate course in this sense, where the same topics werenít always on the same agenda of the meeting, where different groups met and people concerned with models and levels and so forth would meet together and read certain kinds of papers; and people concerned with the higher energy phenomena and with the elementary particles would be in a separate group.

Peierls:

Right. In fact, I canít think now of the date roughly for this change, but, for example, our Ď53 conference attempted to cover both sides but divided, of course, into sessions where we talked about nuclei and other sessions where you talked about particles or high energies.

Weiner:

Thatís a good way of comparing one conference with one five years earlier, where both were to be included.

Peierls:

True. But, there was not very much to talk about in Ď48 concerning nuclei at the level of such a conference. I canít remember now, but I think they want Ö

Weiner:

I remember now that your letter that I mentioned before didnít talk about that so much but stressed the accelerators and detectors. And that was symptomatic of what was going on at the time. Would you say that the difference between Ď48 and Ď53 was that you had enough experimental data to make this discussion of models more meaningful?

Peierls:

Yes. I mean there was plenty of experimental and of detailed theoretical material on nuclear physics. There was some, of course, in Ď48. There was also emerging a good deal of information about high-energy physics, but one still felt that it was appropriate to cover both in the same meeting.

Weiner:

The title of the Ď48 one was ďProblems in Nuclear Physics,Ē in which you classified as on the experimental side, Accelerators and Detectors, and on the theoretical side, Field Theory, Hole Theory and Nuclear Forces.

Peierls:

Right. Well, nuclear forces, of course, come into both. The knowledge is applied to nuclear physics, and its origin has to be thought of when you went into particle physics, presumably. But field theory we wouldnít nowadays classify as nuclear physics at all.

Weiner:

Well, what Iím getting at is the difference between Ď48 and Ď53. Was it possible in Ď48 for people to sit in the same room and discuss either of these, depending on their tastes, whereas in Ď53 the interests had separated enough and the sizes of the groups concerned with each had increased enough to make it necessary to have two simultaneous meetings?

Peierls:

No, no. We had no parallel sessions. It was still the same people Ö Well, some people may have stayed out of some meetings -- I wouldnít know -- but it was basically the same group discussing both, but they divided them neatly. One morning or one afternoon you would talk about one thing, and it wouldnít get mixed up with the other.

Weiner:

There was no need for it to get mixed up. There was no advantage at that point.

Peierls:

Right, except that on a subject like nuclear forces and so on, there would be overlaps. There are still overlaps today.

Weiner:

Iíve tried to date approximately this clear division, and I felt that it perhaps was at the beginning of the Rochester Conferences.

Peierls:

That is probably a good point, because those were the first organized conferences. The others were very informal, like the Shelter island one and so on. Those were people getting together to talk about specific problems. But as a conference trying to survey the field, those were the first ones devoted entirely to particle physics -- what we now call particle physics.

Weiner:

This takes us into another area -- two areas. One is the general description of what happened in particle physics as a separate field as it developed and its implications for the rest of physics. And the other is what happened when you saw the same thing happening in the departments that you were involved with. We can get into both of those if you feel that weíre through with the things that we wanted to talk about -- the pion, the cosmic ray work, the models, quantum electrodynamics we touched on, all those.

Peierls:

Well, thatís a fairly arbitrary selection. One could go on and on, of course, but one has to stop somewhere.

Weiner:

Well, I would like to go on with things that you felt were central themes during that period and that figured in this transition--where, in fact, you saw a very clear branching off into separate very large fields.

Peierls:

Well, it was a gradual transition. Now, as far as my department or my group in Birmingham was concerned, I always tried to keep a coherence between all parts of it; so that while, of course, each person at any one moment would work on a specific problem, it had to be in one or other of those fields; that I tried to maintain a general interest in all of these problems and tried to educate particularly the graduate students so that they would understand a technical discussion in any one of those fields. Now, there was a certain segregation gradually forced on one, because there grew up in the department more and more people whose work was in the elementary particle area and for whom the information they had to discuss became so extensive and so specialized, that you needed to have at least meetings of that group talking only about their problems, other people being allowed to listen in if they wanted to, of course, and many did; but where you got that becoming almost a separate group in the department.

Weiner:

Of what size over the years?

Peierls:

Well, by the time I left Birmingham in Ď63, it was, I think, over half the department. Well, toward the end of that period I had Stanley Mandelstam as the senior person in that field, who was a man of outstanding ability and who, of course, collected around themselves a group of other people -- some postdoctoral visitors, some graduate students who started working with him and so on. So that formed a very substantial part of the department. After my departure, this became even stronger, because, as it happened, there werenít many people on the nuclear side left -- just a few -- and not many people on the solid-state theory side; so that now there in Birmingham the main strength of the department is on elementary particles.

Weiner:

The size of the department from the time of your return after the war to the time you left -- what kind of rate of growth was there?

Peierls:

Well, it was much greater than anyone could have possibly foreseen. I canít recall the numbers, but we were about 15 people when we started in Ď46 and I think there must have been about 60 when I left.

Weiner:

And that compared to about two, three or four before the war.

Peierls:

Before the war -- well, yes. It depends on how you count. I was there, of course, and there was one student at the time that was aiming at the Ph.D. There was one other student in what I would properly call applied mathematics. He stayed for a year after his degree trying to help me build a little homemade analogue computer, which we then completed but abandoned after the war because it was obsolete. But thatís hardly part of that outfit, so I think a maximum of two before the war is an accurate number.

Weiner:

Now, during the post-war period, the synchrotron that Oliphant had wanted going -- I guess it was Ď48 or Ď49.

Peierls:

No, much later. I think in fact, it first got the beam about the time of the Ď53 conference.

Weiner:

What was going on before then?

Peierls:

Well, this was an extremely difficult project. Again, in Oliphantís tradition, it was entirely homemade, but again, I donít think that necessarily in itself slowed it up. What did slow it up was the post-war situation in England where materials, labor, industrial effort and so on were very short, and everything took a long time. There were still priorities in the supply of certain materials and components, and you had to struggle to get allocations. The other thing was that it was quite impossible to get a new building, and therefore Oliphant decided to build that synchrotron inside the cyclotron building, so that these two machines were practically sitting on top of each other, making life very difficult. So this meant that although the design of the synchrotron was started at about the same time or perhaps earlier than the cosmotron in Brookhaven, it got completed very much later. I think the concept of that machine antedates that of the cosmotron.

Weiner:

You mentioned that it was immediate post-war.

Peierls:

Thatís right. Well, it took some time before Oliphant actually formulated his plans enough for approval and so on. I canít pin down that date. But my impression is that it was before the cosmotron, and then, of course, they exchanged ideas and information between Brookhaven and Birmingham. But it took a long time to get it finished, partly because of the just practical difficulties of the post-war period, partly because of the space limitations which made everything difficult, and also shortage of money, which meant doing everything in the most economical way, which is not usually the fastest way. Actually, Oliphant did not see the completion of that machine. He had left Birmingham for Australia by the time it got working.

Weiner:

What about the cyclotron? Was it immediately finished after the war?

Peierls:

Yes. I donít remember the date, but that didnít take long.

Weiner:

And that was put into use.

Peierls:

Yes.

Weiner:

What could a cyclotron do that was relevant in those first years?

Peierls:

Well, it was a beam on which you could do nuclear reactions. It produced 15 mev protons, I believe, which at that time was not the highest energy available but was not out of proportion with what other people had. So that was a useful machine, and quite some good work on it was done. I would have to refresh my memory before specifying any particular items. And it was revolutionary, because it was one machine doing work which many other people in the world were doing, too, and so you have to look at details to pick out individual contributions, but it was a serious machine.

Weiner:

During the period that your group increased so rapidly, did you have close links with the experimental work being done at Birmingham?

Peierls:

Oh, yes.

Weiner:

Did this take a formal organization or were there regular meetings?

Peierls:

There was a regular physics colloquium run by the physics department mostly but not always concerned with experimental topics. We, in general, attended that. We had a theoretical seminar, to which some of the experimentalists came if they thought they could follow. We had some ad hoc meetings. But mainly it was individual conversations between people. Of course, the limitation was that for so many years the experimentalists were preoccupied with building that synchrotron -- I mean the more senior ones were on that rather than working with the cyclotron -- and didnít have the time or the interest in keeping up to date with what was going on in physics. We couldnít help them very much with the practical side. Very occasionally there were problems about how to compute magnetic fields or something where we could usefully talk with them. But generally it was separate. Then when the time came for the machine to be completed and to start experiments with it, it took some trouble to reestablish a common ground and common language.

Weiner:

Was this similar in any sense to the pre-war period when the work on the machine in fact was machine physics rather than doing experiments with it? Were all the energies devoted to that?

Peierls:

That was never so much the case in England.

Weiner:

But you did say that in Birmingham this was the case for a number of years.

Peierls:

Oh, that was strictly temporary. I mean that was for the first year that Oliphant got where he was concerned with hardware and so on and had very few students. But, generally, in established laboratories in England, that was not the case. It was very often the case at that time, pre-war in the United States.

Weiner:

In Berkeley you mean.

Peierls:

Berkeley, I donít know. Certainly I think Lawrenceís interest was far more in the machine than in its applications. It was probably true of Berkeley, yes. But particularly it was true of other smaller departments, who then, when the cyclotron had been proved to work, got funds to build themselves a cyclotron and really were too interested in that as a machine rather than what you could do with it.

Weiner:

What was the exact title of your department?

Peierls:

Mathematical physics.

Weiner:

That would be the post-war title.

Peierls:

Yes.

Weiner:

And differentiated from the department of physics.

Peierls:

Right.

Weiner:

Thereís an interesting comparison, because in U. S. universities itís generally a single department.

Peierls:

Right.

Weiner:

Now, does this imply any differences in relationship between theoreticians and experimentalists in England than existed between those two groups in the United States?

Peierls:

Well, the structure varies very much in England. I mean there are many universities where theoretical physics is, like it is here, in the physics department. I think thatís probably true of the majority of cases. But I think the separation into departments by itself does not affect the working relationships of the theoreticians and experimentalists. What does affect it is that the theoreticians usually or very often come from a mathematics background. For example, Birmingham has an undergraduate course in mathematical physics, which is theoretical physics except that we use it as a training ground both for people who want to do normal theoretical physics and those who want to do other branches of applied mathematics, letís say -- hydrodynamics. Most in Birmingham went into proper theoretical physics. Anyway, this course was distinct only after the first year, and you could enter either by joining the physics school in the first year or the mathematics school. And then if you passed certain tests, you could after the first year transfer into the mathematical physics course. The structure of the physics course was subsidiary mathematics, or the mathematics course was subsidiary physics; such that you could have this double entry. But the vast majority of people we got came from mathematics. Now, this gives a bit of emphasis, and itís still a hangover from the old Cambridge system I mentioned, where theoretical physics is simply regarded as a branch of mathematics. This makes communication somewhat harder for people with that background. This is aggravated by the fact that, in general, the training course of the physics undergraduates is deficient in mathematics and in theory. This is hard to avoid in a system where you have only a three-year undergraduate course; and even at that itís supposed to be the completion of your professional training. I mean itís not like here where anybody who wants to be a professional physicist will at least go on to a masterís degree. Itís not the case in England. Itís possible, of course, only because thereís much more specialized training at school, as you know -- high school -- but that is not always so modern or so well balanced that it really forms a proper foundation. So as a result of that, thereís a lot to learn in three years, and it means that you cannot learn both theory and experiment adequately in this division. And that does make the communication harder. This is improving, partly because the senior experimentalists have now acquired a lot of theoretical knowledge. Itís absolutely necessary for their professional work. And itís partly because there are now more and more post-graduate lecture courses and organized instruction, which tends to make up for any deficiencies in the undergraduate course. So it is improving.

Weiner:

Did you find in the early post-war period any significant difference in the type of student who was coming into physics, first of all in numbers? There were more, of course. And you pointed out that this was a pent-up demand, too.

Peierls:

Right. But not only that. I mean the increase in numbers was not just the backlog, but physics had become more glamorous. Of course, that in part resulted in some people trying to do physics that were quite incapable of it and had to be discouraged. They were just attracted by the glamour and didnít really know what it was about. But generally -- well, I think an important factor was that it was clear that there was and would be a demand for trained physicists. I still remember Ö My father was in industry when I was young, and one of his colleagues asked him, ďWhat is your son doing now?Ē And my father said, ďHe is studying theoretical physics.Ē ďOh,Ē he said, ďso he doesnít want to earn any money.Ē That was in the Ď20s. Well, he was probably right, because I have never earned money on the scale that he would have regarded as satisfactory. But certainly before the war a physics student who wasnít outstanding in ability could look forward to the choice of going into high school teaching or possibly some job in industry, but they were very few and many of them very routine and dull. And only if he was outstandingly bright could he expect to end up in an academic career. And, in any case, if somebody started at Birmingham, he would start with the feeling that, well, he hadnít managed to get into Cambridge and therefore he probably wasnít bright enough to be a university teacher or do research. Now, part of the post-war pressure of numbers results in evening out that sort of class distinction, because as the numbers at Cambridge and Oxford couldnít be increased by an enormous factor, it meant that more people had to go to other universities whether they liked it or not. At the same time some work in the other universities raised their prestige, and so on the research side -- I mean somebody who after the war got a Ph.D. in Birmingham would not feel in any way second rate as compared to somebody who might have got a Ph.D. at Cambridge. That, of course, helped a lot.

Weiner:

What were the emerging centers of theoretical physics in the late Ď40s? -- Birmingham certainly.

Peierls:

Cambridge continued but somewhat handicapped by this mathematical emphasis and also by a rather complicated organization, lack of space; and there was really never any very great coherence in the group. Oxford started under Maurice Pryce. Bristol never was a very strong theoretical school -- Manchester certainly.

Weiner:

Who was at Manchester?

Peierls:

Fairly shortly after the war, Rosenfeld came there and started quite an active group.

Weiner:

Oh, in other words a group started around him. I knew he was down there, but didnít know that he was to be the nucleus of a large group.

Peierls:

Yes, I mean he had a number of graduate students and had some senior collaborators.

Weiner:

Was there a feeling that he was going to stay there or was it only temporary?

Peierls:

I think it was a permanent job, and whether he had any reservations, I donít know; but it looked as if he was going to stay.

Weiner:

So it was Manchester and Birmingham and Cambridge and Oxford.

Peierls:

Edinburgh, where Max Born went -- I canít remember exactly when. It was during the war. But, of course, during the war he couldnít build up much of a school, but it developed a bit more after the war. Bristol was quite active, Iím forgetting. Of course, Heitler and Froehlich were there at the time and of course Mott until his move to Cambridge. I think that was about it at the time. Then Froehlich went to Liverpool and started building up a group there. Iíve forgotten when that was. It must have been in the early Ď50s.

Weiner:

Letís talk at this time about the experimental things, except that I wanted to get some information on Cambridge. Who was the main person in the theoretical group?

Peierls:

Letís see. Fowler had been away during the war. He came back. He was at one time at the National Physics Laboratory. That was just post-war, I think. But then he fell ill, and the job of running that laboratory was too much, and I think he returned to Cambridge. Then he died. Now, who actually succeeded Fowler? Anyway, the main thing was that probably the person doing most to hold the theoretical group together there was Kemmer.

Weiner:

Who had been there many years, right?

Peierls:

He had been there during the war to work with Halbanís group. That was nothing to do with the University. Then he went to Montreal during the war, and then returned to Cambridge. So, essentially that was a fresh start. He is a curious man in that he did excellent work, which we have mentioned, before the war; and then hasnít really done very much since. Heís encouraged some people and sort of helped in organization and so on, but hasnít really given quite the leadership one would expect, although he is extremely knowledgeable and has very good judgment. But somehow something was lacking. But certainly he was the most influential probably in developing things at Cambridge. And he in a general way, though not in technical things, guided people like Salam and Matthews.

Weiner:

What about the experimental centers as long as weíre making this rundown? -- keeping in mind that weíre talking about the immediate postwar period.

Peierls:

Yes. Cambridge was beginning to run down in nuclear physics at that time.

Weiner:

Would you date that from the time of Rutherfordís death?

Peierls:

Thatís part of it. Rutherford died. Everybody expected Chadwick to succeed him. However, Bragg was chosen. I at the time regarded that as a tremendous error, because Bragg had already shown that he had already once ruined a department that was in good shape when Rutherford left it behind. And his interest, of course, was in solid-state physics. He quite rightly built up that side of things at Cambridge. Perhaps it was in the end a very good thing, because as an indirect result of that they got into the business of modern X-ray crystallography in a big way, and that eventually came out with things like Crick and Watson. Yes, they were directly under Bragg. I mean thereís nothing wrong with that. But about nuclear physics, certainly Bragg wasnít encouraging that too much. Cockcroft had taken the second chair in experimental physics, but was, of course, away all during the war and then took over Harwell, so he never returned to Cambridge. And Frisch was appointed to his chair, who himself had, of course, made very great contributions to nuclear physics. Well, perhaps I shouldnít say very great contributions, but he has made at least one very great contribution in connection with the sorting out of fission and other not quite as big things, but who I think was then past his most productive period, and certainly hasnít exerted any kind of leadership at Cambridge. And then it was a sort of vicious circle, because as there were no outstanding nuclear physicists at Cambridge, nobody pressed for facilities for building accelerators or anything, which would have been possible in the post-war period. And then later that got more difficult, and finally it became impossible, and then of course as a result no nuclear physicist would go or stay there. Thereís one episode worth mentioning perhaps with Wilkinson, who was a very bright nuclear physicist though you may not know his name, who was at Cambridge, and they were anxious to keep him. He was willing to stay provided he got some equipment. He had a particular plan of what he wanted, a big Van de Graaff accelerator. Application was made to the DSIR to provide funds for proving this accelerator. He had simultaneously an offer of a chair in Oxford, but heíd said he would stay in Cambridge if he got his equipment; otherwise he would move to Oxford, which first of all was a more senior and established position and also he would be close to the Rutherford Laboratory and be able to do some work there. Now, people tried very hard to get this and it took longer and longer, and he finally set a deadline and said if by that time the thing wasnít approved, then he would go -- which he did. However, the application did not thereby stop, because it was not an application to provide a machine for Cambridge, but it was an application to provide a machine for Wilkinson. I mean it was a personal application. And the wheels went on turning, and finally the machine appeared, and is now in Oxford.

Weiner:

Itís interesting that it should have followed the individual.

Peierls:

Yes, because the nature of the grants is that they are grants made to a particular person. It needs the approval of the university. Oxford neednít have accepted it, but of course it accepted it.

Weiner:

At todayís pace it means a permanent handicap for Cambridge.

Peierls:

In the subject, yes.

Weiner:

Well, that was the first on our list of experimental institutions. That was a negative comment.

Peierls:

Right. Birmingham we have already discussed. Liverpool became quite strong in both nuclear and later meson physics.

Weiner:

Chadwick left there about Ď48. Was it prior to that time or afterwards? He left to become Master of his old college.

Peierls:

Yes, Iím surprised it was that early. Well, under Chadwick, there was a solid group of intelligent people; and under the influence of Chadwick, of course, the standard was high. But it was a small group and originally had rather limited equipment -- a very small cyclotron that had worked during the war that was then rebuilt after the war to make it a little less temperamental and so on. It still wasnít an outstanding research tool. And then I think it was Chadwick who started the plans for getting a big cyclotron, but, of course, didnít stay to see it completed. Then Skinner took over and Chadwick left. Skinner had been at Harwell and was used to running a large group and handling people. He was very good with people and got things organized. And so that group grew to a good size and surprised everybody, because it came into operation considerably after the Chicago machine and had low energy or not much. And people said, ďWell, all these people can do is repeat experiments which have already been done.Ē However, it soon became clear that if you have skillful experimentalists, that isnít a fair judgment; because for one thing, repeating experiments which had already been done, they found that quite a few of them were inaccurate or quite wrong or perhaps misleading. So they started off by re-measuring things which were established in the literature and found that they were different.

Weiner:

Thatís not quite the same as getting great glory for doing something.

Peierls:

But very important.

Weiner:

I know, but in terms of prestige.

Peierls:

Well, they certainly had considerable prestige. One reason was that they developed on the machine side a highly efficient method for extracting the beam from the machine. Up to that time people either bombarded targets inside the machine, which was for certain purposes adequate, or they had extracted a beam but losing most of it and getting a rather poor intensity and definition; and this method developed at Liverpool revolutionized that technique, and it was almost immediately copied in other machines. So, at any rate, that became and has remained a strong center. Now, Manchester under Blackett had been Ö I mean when Bragg went to Cambridge, Blackett succeeded him at Manchester and really restored the spirit of the place; built up cosmic ray physics, which was his main interest at the time; and that was first class. It wasnít, of course, nuclear physics as such. How they acquired prestige in the modern field particularly was by the discovery there of the strange particles by Rochester and Butler -- the first examples of the new particles. I donít know actually whether that was done at Manchester or by some operators at high altitudes in the mountains. There were probably expeditions going off, but anyway it was done by people on Blackettís staff. Manchester is still a good center, although itís got a little bit complicated. There was a complicated history, because when Blackett went to London to Imperial College after some years he was succeeded by Devons, who made some decisions about machines, including in particular one accelerator meant for accelerating heavy ions, on which there were varying opinions how exciting a tool that is. But he didnít stay very long, and very suddenly left to go to Columbia. He had then persuaded Flowers to come as a theoretician. He was successor to Rosenfeld, I donít know whether directly or with a gap. And when he left, Flowers took over as director of the laboratory. Now Flowers has gone.

Weiner:

Devons was not a theoretician.

Peierls:

No; nor was Flowers. Sorry. Flowers was a theoretician, but he took over nevertheless the directorship of the laboratory.

Weiner:

And you lost Flowers then.

Peierls:

Oh, no, no. He had been with us only a couple of years.

Weiner:

I see. He was already gone.

Peierls:

He was in Harwell. The point is he had during the war got a rapid training in experimental physics, but was basically interested in theory and therefore arranged to come to us for a couple of years on Harwell funds to get retraining, and then returned to Harwell and almost immediately became the head of their theoretical physics division because they just had lost Fuchs.

Weiner:

What about Bristol?

Peierls:

Bristol was, of course, an important center in cosmic ray physics, particularly exploiting photographic plates. Now, that at one time made them, of course, the center of interest in particle physics; but with the development of high-energy accelerators, the importance of cosmic rays as a source of information about particles tended to diminish. I think nowadays the interest in cosmic rays is largely to find out about cosmic rays, which is a fascinating subject in itself and has relations with cosmology and so on, but is a subject quite separate from particle physics.

Weiner:

There are some people who are attempting to save money by going back to cosmic rays. Iím thinking of what Alvarez was doing for a while at Berkeley. Maybe he still is.

Peierls:

Well, I think the total amount of informationÖ [Telephone Interrupts}

Weiner:

You might just tell what that telephone call was about for the record. Who had read this?

Peierls:

My wife had just seen the London paper.

Weiner:

A recent one?

Peierls:

Yes, Sundayís.

Weiner:

This reported that Powell, whom we were just discussing, died.

Peierls:

Near Milan. It isnít clear from that whether -- I know that he was on a continental trip -- he fell ill there or whether it was an accident.

Weiner:

How old was he?

Peierls:

Sixty-five.

Weiner:

Well, we were just talking about Bristol and about Powell.

Peierls:

Thatís right. So Bristol really now has been mainly a center of cosmic ray physics, with the exception that with now a change toward people doing research work not with machines on their own premises, but by machines serving many people, like the CERN machine, the Nimrod accelerator at the Rutherford Laboratory, which serves all the British universities and so on, and therefore you find in many centers people starting experiments -- mainly visual type of experiments: cloud chamber, bubble chamber, photographic plate and so on -- which need relatively short exposures and then long-time data analysis, which people do in their own places. So there is also a team at Bristol doing particle physics using machines elsewhere.

Weiner:

Was Powell involved in that consistently?

Peierls:

I do not know. He was lately the head of the department and therefore was no doubt responsible for that work and encouraging it. How much interest he took in detail, I donít know. Certainly he himself was not a cosmic ray or photographic plate specialist. He served on many of the committees that looked after work at CERN and also after the UK relations with CERN. And from that point of view he was very interested in machine physics and in cloud chamber work and all these kinds of things, as well as in photographic plate work, which is still a useful tool. But he certainly was very interested in all that. He was until a year or two ago the chairman of the Nuclear Physics Board of the Science Research Council, which has succeeded DSIR. So he was interested in a general way in backing particle physics and nuclear physics. But how far he was interested and participated in the detailed work going on in this department, I donít know.

Weiner:

Of course, something that you havenít really mentioned in any of these places is solid state as a separate field. Was there any particular institution other than Cambridge where solid state was strong?

Peierls:

Oh, yes. Well, first of all, we traditionally group all low-temperature work together with solid-state physics including liquid helium, which is about the least solid substance I know. First of all, the Mond LaboratoryÖ [Interruption] Well, I was just saying Cambridge, of course, had the Mond Laboratory always involved in solid state and low temperature work. So had Oxford. Nottingham had a strong group on magnetism, originally under Bates and now Stevens and Iíve forgotten who else. Leeds had some solid-state work. So this was fairly widespread. Of course, you donít get these very shapely defined centers, because youíre not concerned with very big equipment, and you donít have to have research groups of the same sort of size that you need in particle physics. Iíve certainly left out things, but I think it would go too far to enumerate them all.

Weiner:

I really didnít want to go into detail on solid state, but just to get a feeling. I think your last point was the important one; that when you talk of centers in that field you get a somewhat different meaning, unless youíre talking about very large low-temperature laboratories.

Peierls:

Yes, but the helium liquefier nowadays is not an expensive piece of equipment. It was at one time. And there are certain extreme things. For example, there is now a tendency to want to use bigger and bigger magnets. There are some very large installations in the United States. There was talk about a big national magnet laboratory in England, which didnít come off but may still be created some day. By and large, itís a field for cheaper equipment.

Weiner:

Getting back to the enumeration you were making before, we covered Cambridge and Oxford and Birmingham and Liverpool and Manchester and Bristol. Does that take care of the major centers?

Peierls:

I may have omitted something. There was a somewhat smaller group in Edinburgh under Feather. I should mention Glasgow under Dee.

Weiner:

That gives me a picture of the distribution. It was certainly different than before the war when there were just one or two centers, say, in nuclear physics. There was the Cavendish, and then when the Cavendish students would go elsewhere.

Peierls:

Yes. Well, you see, from about the early Ď30s on, Rutherford I think quite deliberately encouraged his senior collaborators to move and start new groups. I mean he encouraged undoubtedly Blackett to leave Cambridge and go to Manchester Ö No, sorry, he first went to Birkbeck College in London and then later to Manchester. He encouraged Chadwick to go to Liverpool, Feather to go to Edinburgh and so on. Well, Iím not sure but that some of these moves might have taken place after Rutherfordís advice, who would have recommended these people for the appointment and so on. I think that was deliberate policy.

Weiner:

Was the group pretty well scattered before his death?

Peierls:

Well, I wouldnít say scattered. Some of the senior people started their new teams, but there were younger people growing up.

Weiner:

Well, the older group anyway.

Peierls:

Yes, but I mean the Cavendish was as active on the day of Rutherfordís death as it had been. It was just full of bright young people.

Weiner:

Chadwick left in Ď35 for Liverpool, and by that time Oliphant had left.

Peierls:

Dee left a little later, I think, for Glasgow but not much later.

Weiner:

Well, this takes care of a point that I had in mind -- of postwar distribution of interests at various British institutions.

Peierls:

That doesnít, of course, describe the whole of physics, but the main fields.

Weiner:

Well, itís not appropriate for us to try and do it. There are other ways of getting at it, too.

Peierls:

And I shouldnít do that really without sitting down with some lists and bits of paper to run up Ö

Weiner:

Well, what you have done is to give an interpretive evaluation of how things developed at specific places and what the strengths were with relation to the overall development of the field. This brings us to a point about the second theme, if you think weíre ready for it, in your work; and that is the organization of physics in the university in terms of your own efforts, relating to the organization itself and educational innovations. And I think this also has national implications in terms of allocation of resources vis-a-vis panels on which you sat and Ö

Peierls:

Right. Well, letís try and get going on that, perhaps not very systematically, because I havenít thought it out for the purpose.

Weiner:

And youíre still very much involved in it.

Peierls:

I mean I may bring things up in the wrong order, but that doesnít matter. Well, one thing is that since the end of the war, really my main activity in physics has been training students rather than contributing to the subject itself -- well, training students in a broad sense, including also encouraging some younger postdoctoral people and so on. And obviously Iíve been very interested in that -- I mean to the extent even, as I told you, just to bring that up again, that I tend to think of problems in connection with students; that a problem really gets going when I allocate a student to it, and from then on itís a Mr. So-and-Soís problem. And I think, ďWell, I must talk with him and see what we can do about that.Ē Now, I was always very conscious of the fact that the purpose of physics departments -- and particularly of departments training theoretical physicists, with which I was finally concerned -- could not be just to produce more people to do research, academic research, because the need for that would always be limited. And I remembered the pre-war years where at least some people (I remember particularly Mott in that respect) had been reluctant to accept students because it was a lottery. If they couldnít get into an academic career, they werenít very well set up. Now, I knew always that there was room for theoretical physicists provided they were adaptable and broad-minded in a lot of activities. One of my favorite stories about this is that when I was in Manchester there was a young man who had been trained by Hartree in applied mathematics, which was near to theoretical physics. I donít even know whether he got a Ph.D. or just his first degree and then looked for a job. He was offered a job in the laboratory of the biggest railway company in England, which then was still a private firm. It wasnít yet nationalized. And the director of this place took him on and said, ďLook, I have no idea what applied mathematics is or what you can do for us, but weíll give you a year. Weíll employ you for a year, and during that year you go around and look at our laboratory and look at other activities in the organization. And at the end of the year, youíll come back to me and tell me what you think you can do for us. And if we like that, you will stay.Ē This I always regard as the sort of classical model of an attractive job for a theoretical physicist. Of course it worked out, and of course he stayed -- until the war. And he got along fine. Now, this conviction got confirmed during the war, when all theoretical physicists got involved with other things, war work of some sort. And now some of that was simply work on atomic energy or, to some extent, radar, where their specialized knowledge was essential, and they had to be used for that reason. But it developed far beyond that, because while you were on these things you get involved with all sorts of practical problems, almost engineering problems, but where the ability to formulate a problem from first principles and think it out comes in very handily. Some wouldnít take to that, but then they didnít generally go into that kind of work. But all those whose outlook was suitable and who were good physicists in their own right, did very well in that: people like Bethe or Fermi. So I knew that clearly there was room for such people provided one could persuade them to take an interest in that kind of work and provided one could get the prospective employers interested. The second was very difficult in post-war years, because there was a desperate shortage of such people, and they were just not available. What I did always was when research students came to us, I insisted strongly that they should not regard this training as necessarily automatically leading to an academic career -- first because the field was limited and also because it wasnít everybodyís cup of tea. Not everybody is happy in that sort of occupation, and I explained to them why and tried to get them to keep an open mind about work in industry or other organizations that could use this -- with some success. A number of people did in fact go into jobs outside the universities, though because of shortages, I think probably most of our people in fact got into academic work. Then in about the l950s this little speech I made to people tended to lose conviction, because that was a period of rapid expansion of the existing universities and the foundation of new ones, together with very tempting jobs abroad -- as a result of which there was such a shortage and all the good people were really needed in academic jobs. So knowing perfectly well that all these people would in fact go into academic work, there wasnít much point in trying to persuade them to keep an open mind. I knew always that this would stop. I didnít appreciate how suddenly and completely it would stop. The position is completely different now, because of a combination of circumstances: the economic position in England, which has suddenly and completely stopped the further expansion of universities -- for a time at least -- the fact that there are similar difficulties of a somewhat different nature in the United States, and therefore people no longer as easily can get a postdoctoral appointment in the United States, together with the fact that efficient schools of theoretical physics have got going and turning out people who are looking for jobs, together with the people who are coming back from a few years of postdoctoral work in America and are looking for jobs; so that now there is an acute oversupply and a shortage of jobs. We havenít yet had anybody not getting a job at all, but whereas effectively for any new Ph.D. there was a wide choice of jobs he could have -- now one has to work pretty hard to fit them in somewhere; and sometimes they donít get the kind of job they would like to have. So this would seem the time to develop the idea of making use of them in industry, because this is absolutely necessary in the long run for a healthy relationship between the universities and the community, a system which feeds its own output back into its own system wouldnít be of any interest to the community. Why should they maintain training schools and universities if they never see their product?

Weiner:

Which of course was true during the boom period of theorists -- but it seemed effective.

Peierls:

Ah, but that seemed a temporary phenomenon. I mean if you have an agricultural problem, the first thing you set aside is the seed corn to keep going; and similarly, if you have a shortage of people, the first thing you must make sure is that your universities are well staffed so that they can turn out more people. Of course, with that goes the fact that your high schools should have good people, and that has never been taken care of as effectively.

Weiner:

Iím thinking of a similar problem in the Ď30s when the solution in England and the United States was to convince industry that it needed physicists and then to convince those training physicists to motivate their students so that they would be useful. Lindemann, for example -- in his papers there are several eloquent pleas to industry. That was the same in this country. But of course times changed and the situation appeared no longer to require that kind of pressure.

Peierls:

Yes, now it goes again. Now weíre back. Weíre back in that situation. Iím very interested in that, in trying to see how one can get a crack into this situation. Now, itís quite true that many students are willing to look at such possibilities and not merely as a sort of emergency measure because they have to live, but there are some who are willing to recognize that it might be interesting. I had quite an interesting experience. One of our students in Oxford, who was getting a doctorís degree this summer, a bright young man, in solid-state theory, had as his first choice the idea of going to Illinois with a postdoctoral fellowship if he could get one, and his supervisor wrote to Illinois, who were encouraging but couldnít make any promise, and so clearly he had to look for alternatives. And so he looked at jobs in industry and liked the look of several of them, with the result that when finally the offer from Illinois arrived, he turned it down and decided to take a job in industry.

Weiner:

Thatís unusual.

Peierls:

Thatís unusual, but itís an encouraging phenomenon in the context that weíre talking about. I mean it would be terrible if everybody took that view, but if you get some people taking that view, itís healthy. But the main trouble there is that industry doesnít seem very good at taking in such people -- the physics-based industry. The chemical industry has learned this very well. Thereís no problem if you have a good chemist whoís willing to take a job in industry; thereís no problem in placing him. Itís not only that a firm will have him, but theyíll give him something worthwhile to do, because probably the chemical industry has known for a long time that chemists are essential for everything. The physics-based industries are not nearly so good -- in England. I donít know about the United States.

Weiner:

The situation is very much the same. The complaint may be the same, too -- that is, that they find people too narrowly trained. Industry finds that the new Ph.D.ís are too narrowly trained and too specialized to really be of use and to think physics in a general sense.

Peierls:

Yes. Iíll come back to that. Thatís an important point. Thereís, however, another difference. In the physics-based industries -- things like electronics or what have you -- there are many jobs which could be done either by an engineer or by a physicist with some adaptation. Iím told that in the United States they have an adequate number of engineers, and they figure if they do this work, why use physicists? In England theyíre desperately short of engineers, so itís different. Theyíre crying out for the engineers to do this work.

Weiner:

For the physicists to do the work that engineers should be doing?

Peierls:

No, theyíre desperately short of engineers for their work. I donít quite know, of course, how they want to employ those engineers, but they certainly canít say that they donít need the physicists because they have a plentiful supply of engineers to do the same work.

Weiner:

This relates to specialization, which Iíd like to relate to what was going on in physics. We touched on it. Thereís another thing: that reminds me of another point that I donít think we really got the answer on, and that is the motivation of the entering student, the type of student that was coming in after the war. You talked of differences in numbers, and you talked of the glamour of physics attracting people.

Peierls:

There was some, yes.

Weiner:

Well, it seems to me that when you can build up an entire laboratory around a large machine, where youíre involved with machine physics and problems of this type, youíre apt to get a different kind of physicist than in an earlier period when first of all jobs werenít guaranteed and where you just wouldnít have this kind of physical hardware engineering project to work on.

Peierls:

Right. Well, in experimental physics thatís certainly true. Now, thereís a very strong tradition in England: that the right employment for an experimental physicist is to do things with his hands, or at least to get things done, to be concerned with hardware -- so much so that there is an overemphasis on laboratory training, I mean on practical laboratory classes. In my view too much time is spent on that out of the three years available. For example, in Rutherfordís days the development, with some exaggeration perhaps, was that people would come into the lab and start doing a job and wouldnít do an awful lot of reading but essentially would learn from experience on their own experiments and know perhaps what the other people around them in the Cavendish were doing. Now, that in those days wouldnít give you a complete view of even nuclear physics, but it came pretty close, because the Cavendish was the center and certainly you would learn a lot. Nowadays, of course, there is no place in the world where you could work in that way. So itís true that many people come in because of their liking for gadgets and for equipment -Ė machinery -- and playing with them. But there are also many others who have an intellectual interest in physics, and some of these might turn to the theoretical side, but not all. And we do get quite a good selection of people who are quite suited by ability and temperament for research, including theoretical research. One should, of course, bear in mind that of the undergraduates that we take in, only a very small proportion stays on for post-graduate work; and we couldnít take anymore because of the numbers of grants and all that.

Weiner:

Weíre resuming now after a brief intermission for coffee. I think we had touched on the question of specialization in the post-war period.

Peierls:

Yes. Well, this, of course, is a continuing problem in education and in peopleís ways of working. I have always been on the side of maintaining some breadth of knowledge and of understanding and of interest, although, of course, one has to work in one field at a time, at any rate, and most people stay working in one field for most of their careers; but at least they should have an open mind for the general area to which their field belongs; and I think in the case of the theoretical physicist, that must mean the whole of theoretical physics as well, of course, as experimental facts in many branches of physics. Now, at Birmingham I tried to maintain that spirit with varying degrees of success. In spite of these efforts, some people ended up being more specialized than others, of course, and having less patience for breadth, itís perhaps interesting to remember how this appeared when I moved from Birmingham to Oxford. For example, in Birmingham we had a policy Ö Always our accommodation was short, and people had to share rooms -- even senior people, but particularly students. I always arranged the distribution, apart from such factors as not putting fresh air fiends together with people from North America who liked a temperature of 80 in their room or something or smoking habits or things like that, to mix people so that people would share rooms who worked in different fields -- on the grounds that they would meet the other people in their fields anyway, but it seemed healthy to me for them to be exposed to the company of people who were doing something else and who might occasionally ask their advice about some information or method or something, and you would get some contact. How much this achieved, I donít know. But, of course, I moved to Oxford, where there was a going department containing a lot of senior people whom I didnít want to push around, and it turned out that most of them had the tradition and quite strong preference for their pupils being all together, and I didnít feel it would be right to push people around, and so thatís the way it is in Oxford now. We have one section of the department Ö I mean physically thereís one side of the building containing all the solid-state people and another containing all the elementary particle people, and across the road or around the corner are all the nuclear theorists. Iím a bit unhappy about that, but when you have existing groups of people and they like to work in a certain way, one canít prescribe how they should do it.

Weiner:

But in a sense is your approach regarded as an anachronism, as a holdover from a period when physics in fact was one, and now these people feel that the reality of it is that physics is divided?

Peierls:

No, I think itís not quite that. I think everybody realizes that there are conflicting requirements, and that you have to balance the requirements for expertise in a given field with the breadth and generality. And they probably just feel that they lean more in one particular direction than I do. If they associate that with my being too old, they are too polite to say that.

Weiner:

But how about the training itself? You talked about your desire to have a Ö

Peierls:

We have a similar problem arising in the training. Our system is now that we have post-graduate lecture courses for research students. We didnít do that in Birmingham, but in Oxford we have an examination there that they have to take at the end of that year in order to encourage them to take those lecture courses and the associated work seriously. Of course, thereís always the danger if there is an examination that they take it too seriously, particularly having come from an undergraduate course and essentially thus concentrating on working for the examination, which is the last thing we want. These are courses covering all the fields in which the department is interested, and theyíre encouraged to go to as many as they can. The examination is so devised that you can in fact pass it by concentrating on a narrow front, provided youíre good enough at it. I mean you have to do a certain number of questions, and if you limit your choice, then if youíre unlucky and donít know the answers to those particular questions, youíre really in trouble. So there is some pressure applied to keep their interest general, but at least through that year, to get them started. But itís flexible, and people do get away with a rather narrow line. Similarly, I maintain the practice of having a theoretical seminar every week in which there are talks on all branches of the subject; and we try to encourage speakers to present them in such a way so that people in other fields are not completely out of their depth, at least starting off by explaining what their work is in aid of, which with outside speakers doesnít always succeed. They donít always get the point, but on the whole I think the standard is good. But only a very small number of the students come to it. Itís a pity: sometimes you go to the trouble of getting a really first-rate speaker giving an excellent talk, and in fact the only people there are the people who already know what he was going to talk about, because they are in his field and the others are absent. I donít know what we can do about that short of making attendance compulsory, which I think would be unreasonable at that level. Thatís a common problem that happens everywhere, not only in my department.

Weiner:

Wouldnít you say this is common to physics in general?

Peierls:

Yes.

Weiner:

For example, the meeting that was held in Trieste -- was it two years ago? -- when they were organizing the meeting, I talked with Oppenheimer about it, and he said this was an attempt to once more bring unity to physics -- to bring together the various elements -- and to make it deliberately smaller, not quite as small as Shelter Island but to go back to a smaller set-up. And I talked with Marshak at a later stage of planning for it, and it became apparent how impossible even this goal would be.

Peierls:

I was interested in the idea and hoped it would work, but I never expected it to. I was unable to come for other reasons. I was busy or I would have come. But the point is: they admitted defeat from the beginning. Salam was the organizer essentially, and what he did was to run a number of periods in succession -- a few days on this and a few days on that -- and he invited speakers to come for a particular period in the hope that they would stay on for a few days and listen maybe to the end of the previous period or the beginning of the next. But that is really admitting defeat from the beginning.

Weiner:

I wonder if there were very many people who stayed for the whole thing.

Peierls:

Some did -- I donít know how many. Well, you see, the point is: if people are already specialized, then to spend two or three weeks listening to a few talks in other subjects isnít going to remedy that.

Weiner:

Thatís the point. Thatís the way physics is set up.

Peierls:

Actually there was a recent meeting. But, of course, you were there. I think on the whole the Florence meeting was an extremely useful one, and its strength was that it was not specialized; that it gave people the opportunity of hearing good talks in other fields.

Weiner:

I know I talked with a number of people about their reactions, and it was very interesting. The sessions they wanted to hear were generally not in their own field.

Peierls:

Yes. You probably talked to more people than I did. I had the impression that most of the people liked this approach and enjoyed it. Was that your impression too?

Weiner:

Yes. First of all, because the talks were deliberately geared for this kind of meeting -- this says something about organizers of the program. Because they could have just presented their very specialized thing, and therefore there would have been reasons for only the specialists to come. But they apparently recognized that there would be a broader audience.

Peierls:

Yes. My main complaint was that half the time was spent in parallel sessions. I mean after the meeting I realized that I would have enjoyed it even more if it had all been general, because what happened was that even in the specialized sessions; people went to a lot of trouble to present their stuff in an intelligible way. But when you have five meetings to choose from, you tend to end up in the one thatís closest to your field. Many people did that, not all. And so a lot of this effort was really wasted.

Weiner:

The general point on specialization is that this is the fact of life in physics and it has developed over a number of years, and any efforts to counteract it have to be contrived, have to be artificial in some way; and in some cases are successful. I wonder if in England, in the high-energy physics community, if there is such a thing that can be defined as that (I think someone has given me a list of 200 names of people who are in particle physics in England today and has apparently just completed a sociological study of this entire group). I wonder if they are a very similar group to their counterpart in the United States, no matter how much larger the United States group might be.

Peierls:

I think so. I can judge best on the theoretical side, of course. There are differences. It is still true, although itís improved in England, that the gap between the theoreticians and experimentalists is still greater in England. Some people attribute this to the trend that I think in most universities here itís common that even the graduate courses are not divided between theory and experiment. Everybody takes the same graduate courses. Maybe there are variations in different departments. This doesnít strike me as a very good idea, because the future experimentalists are forced to sit through very high-brow theoretical courses which they canít really absorb. They learn the okay words, but they really havenít got the interest or sometimes the ability or background to get to the bottom of that. And I donít think that is responsible for the closer mutual understanding there. Itís much more that the senior experimentalists themselves know more theory, regard it as important, and discuss their work in terms of theoretical concepts, which then of course affects the younger people. I think thatís much more how it does. But apart from this slight difference, which is improving in England (I mean the amount of theoretical tools at the disposal of the experimentalists and the understanding of experimental factors by theoreticians is growing), I think they work in pretty much the same way. Now, that way is to me not very satisfactory. I think there are far more, both here and in England and in other places, theoretical physicists working in the field than the field can take. You see, in experimental physics you are limited by facilities. There are only so many machines, and there is only so much room around them. Anybody else who tries to get into the business without access to a machine is just lost. In theory thereís no such limitation. The numbers are getting out of hand. You see, itís depressing to think that any slight new idea, some new way of doing something, is immediately picked up by dozens or maybe more people throwing themselves into that, trying desperately to be the first to get some new point there. Now, itís perfectly clear that there are many other people sitting in other places doing the same thing. Itís a question of who gets out of it first. Pauli always used to say: ďI canít understand why people have such strong feelings about priorities. If something is so obvious that somebody else is doing it at the same time as you are, then itís not worth doing. Itís the ideas that occur to you and that nobody else has thought about that are really satisfying.Ē

Weiner:

But heís neglecting perhaps an important dynamic in what might be called the social system of science, and that is that there is a drive for recognition and a normal one.

Peierls:

Well, up to a point. I mean you can see that if a young man wants to establish himself, wants to write a thesis and wants to get his name known, then itís important to publish something; and he can publish it only if heís first because otherwise it will be turned down. That is a sad necessity. But it goes much further than that, because people with a perfectly established reputation are in just as much of a hurry in being first to get their latest piece of work out, although itís more or less a routine development of somebody elseís idea or some idea that is in the air. I donít think itís wrong of young people to feel that they would like to be first. But if in fact that many people are competing to do essentially the same job, it does suggest there are too many people at work in this. Now, how you can remedy that, I donít know. Iím not in favor of rationing or limiting the number. It also very easily results in fashions. Because people are so much aware of what everybody else is doing at the present moment, that thereís a tendency for everybody to chase after the same idea. Thereís this very dangerous thing: If somebody invents a crazy hypothesis or a wild hypothesis without very strong foundations, thereís some resistance in his mind to publishing this because it might not be sufficiently well-founded. Once heís published it or sent out a preprint, then of course it encourages other people to use the same assumption or the same model or the same approximation and then write a paper to show either what would happen if one adapted Dr. Jonesís hypothesis to another problem or alternatively showing that in some cases Dr. Jonesís hypothesis would give the wrong answer. You get a vast literature devoted to it -- from just some foolish approximation. You see a lot of that.

Weiner:

You mentioned the problem of coping with this and talked of rationing as something that you wouldnít be in favor of. But in the immediate post-war period, it seems to me that there may have been discussions in England and elsewhere on what you wanted to accomplish on a national scale. Iím not talking about the military or defense but in basic physics, what your needs were. As a matter of fact, in some of your papers at the time when you were asked to talk on such a topic, you said what were the important experiments to do and so forth. Was similar attention being given on an organized, informal basis to problems of education, to the training of students, to work that would be needed, the types of specialization?

Peierls:

No. Iíve always been very afraid of these speculations, because the recent history of such efforts has shown that all the committees who get to work and say how many scientists or doctors or what-not will we need in 10 or 20 years time -- they have always been wrong. You canít let things grow at random. To some extent, limitations of resources come in. I mean the number of, for example, experimental people is limited to some extent by facilities, although not that much, because I think until quite recently any promising student, provided heíd done well enough in his examination (and there is a loophole there that not every bright man is necessarily good at exams, and we might have missed people) -- but there are fairly firm rules. As you probably know, our university degrees are in classes. You would like, if possible, to get a first class degree to do research. If you get an upper second (the second class is divided in most universities), you are still eligible for grants, although you are somewhat handicapped in the competition, if they are short. Below that, nobody would give you a grant. That might miss some people, although on the whole correlation is not too bad between ability and the examination. So with that limitation I think itís been quite true until recently that anybody who had at least the minimum degree necessary and had in somebodyís opinion the right ability to do research would in general get in somewhere. And if he wanted to do, let us say, nuclear or elementary particle physics, and if he was keen enough, he would get that. This is changing. In other words, there were enough facilities to provide for the people who wanted to do this, and there were enough grants. Now the authorities, the Science Research Council, has decided that the manpower in nuclear physics, which in their terminology covers both nuclear and elementary particle physics, is getting too big, and there must be a limitation; and theyíve therefore put a ceiling from this summer on the number of their studentships, which are the main source of support for graduate students, that can be held in those subjects.

Weiner:

Thus by a reallocation of resources you redirect manpower.

Peierls:

Yes. We hope, of course, that if they are refused a grant to work in these fields, they might turn to applied physics or other problems more useful to industry, which one wants to encourage. The total number of grants hasnít been diminished, but they have been reallocated so that itís easier to get a grant in other fields. Now, thereís also the factor that if you have people who want to work in applied physics or engineering or something, you should give them grants. But to ration the department and the number of students they can take on in certain fields is a little difficult. Iím not disapproving, but it does create new problems. This is the first time it has been tried.

Weiner:

A specific question on the immediate post-war period regarding such discussions: Were there attempts then to come to grips with this or to anticipate problems?

Peierls:

No.

Weiner:

Not just the problem of oversupply.

Peierls:

No, there were no discussions that Iím aware of, except insofar that when a university was starting a new department, decided they might start a new theoretical physics department, built in the decision of whether to do that or not, and also, if so, whom to appoint and what field to favor -- the people in that university would have such considerations in mind, and they might also consult people outside and get general guidance. But this was entirely private enterprise, and there was no body at work or no committee that I know of. There may have been groups discussing this in a systematic way, but there was no effect. I mean Iím not aware of any impact of such a group.

Weiner:

Do you think we should move now to this other area on scientistsí responsibility? Iíll start off by asking whether this feeling of responsibility about the uses of science came as a direct result of the war, or whether there had been in your own mind feelings about it or reasons to think about it earlier before the war?

Peierls:

I donít think so. I donít think I had thought about it earlier, except in a very general way. If you are a scientist, of course, you think occasionally whether or not your work is of some usefulness to anybody other than yourself and how it could fit in, whether you have a duty to the university or community to do things that might not be the ones you would have spontaneously chosen. So these things do come up, but not in any major way, and certainly not in any way relating to military questions.

Weiner:

Well, then, when did you start thinking about it?

Peierls:

In a general way, of course, as soon as we got involved with atomic energy. I think this was implicit. We werenít really conscious of the problems, and that was probably because the answers were at that point so obvious to us. So they werenít even worth stating. I mean, for example, there was never any question that it might be wrong to think out -- and not only think out, but agitate for more work on -- atomic weapons, for two reasons. The most obvious one was that we were involved with Nazi Germany. There was quite a possibility that they might be at work developing similar things. We didnít know from the start how big the necessary effort would be. And the thought of Hitler being in full possession of such a weapon was, of course, terribly frightening. There was no question that that must be prevented. Beyond that, we also felt that we were living in a country -- certainly the United Kingdom and we also thought in the same way about the United States -- where, while one might not approve of everything the government was doing or the principles they were using in any single thing, they were on the whole responsible and humane. Once you made the techniques of that kind available to them, you could safely leave them the decision of what to do with them. This obviously depended on other factors in the military or in the national situation that we didnít have the information on. I donít think we consciously went through these arguments at that time, but if youíd asked me at that point, I would probably off the cuff have made the same answer. So to that extent we were aware of the problem. Then, one was left with the post-war situation.

Weiner:

What about before that -- when the weapon had been completed. We were discussing it over coffee. You used the phrase: ďthe decision to drop the bomb.Ē Did this problem present itself in different terms at that time?

Peierls:

It should have done probably, but it didnít to me. Again, I had the feeling that what to do with it was out of my reach. The first thing to remember was that there was a war going on, and in war many things happen that are cruel and cause damage and injury. One didnít like war, but we were in it. We didnít see the atomic bomb as something morally different from anything else -- different in scale perhaps, and has become more clear since, in the ease with which you can make a decision to press a button and drop it. But, as has been pointed out, the number of people who perished in Hiroshima, for example, was smaller than the numbers who were killed in a single fire raid on Tokyo. That was one point. Also, the other thing was that the decision had to be taken by people who had more access to relevant factors and information than we had, and who we felt essentially were people whose judgment could be trusted. Moreover, our contact -- we had no direct access -- with them was through people like Oppenheimer, in whom we had confidence. We didnít know to what extent he would be consulted about this decision. In fact, itís not clear today how far in fact he was. But if it was a question of making quite sure that the military knew what they were doing, what it meant to drop that thing, then we could trust Oppenheimer surely to explain it to them. That Iím sure he did. I think if someone had asked me: ďDo you think one should drop this on a city of Japan or not?Ē my own reaction, I hope (I mean itís hard to know how far one is influenced by a thought that came later) I would have said, ďNo. Thereís no reason one cannot demonstrate its power by dropping it on some relatively sparsely inhabited place and then use it as a threat, and perhaps follow it up if that wasnít enough.Ē But I think the arguments used at the time for turning this down now look incredibly foolish looking back.

Weiner:

Were you aware of the discussions going on at the time with the Franck group for it and the petition and so forth?

Peierls:

No.

Weiner:

Do you think that was because you were part of the British group?

Peierls:

No. As far as I recall, the Franck memorandum was not widely circulated at Los Alamos. It was sent to one or two individuals who took it straight to Oppenheimer and so on, and accidentally some people heard about it, but I think it was not widely circulated, but I didnít happen to see it. I think this probably had nothing to do with my being British.

Weiner:

You started to talk about the post-war situation, which was different.

Peierls:

Well, first of all, the subject had become public. One could talk in the open about it. And therefore also it was important that public opinion should be influenced in the right direction. It was immediately clear that scientists had a job there, because you canít have a reasonably intelligent public discussion without some understanding of simple technical facts; and it was up to the scientist to explain them. There was a great demand for technical lectures on the subject. And also we felt that we were in a good position to participate in public discussion because we had lived with the implications of this problem for considerably longer than the general public and therefore could help with that. At the same time we, as scientists, were being blamed for having started up this very dreadful new weapon, and in simply defending oneself and explaining that this was not such an unreasonable thing to do, you had first of all both to explain why it seemed necessary to go ahead and secondly why the existence of such weapons might not be an absolute disaster but might also have opened a way of improving the international situation, which leads you straight into thinking of what is the right way of living with that. The frustrating thing was, of course, that you could think of many nice academic solutions, which however would clearly not be implemented without the participation and approval of a lot of people on whom you could not possibly have any influence -- in particular, the Soviet Union or the Soviet government and the United States government. The Soviet government we obviously couldnít influence in any way. The United States government -- it wouldnít have been profitable to appeal to them directly. What we could do, of course, was to agitate within the U. K. for as enlightened as possible an attitude of our government, who then in international discussions would pass this on. Well, that is complicated. And also, there were no particular issues on which we had any disagreement with the British government, who seemed to us to take a more or less right line on the subject of nuclear power, except possibly over the question of whether Britain should itself have an atomic weapon, which was a very complicated question which you could argue, but itís also not quite obvious which way one should argue.

Weiner:

You mentioned one issue was the secrecy issue, which had double implications not only in an international sense but in terms of hampering research at the universities in England.

Peierls:

Well, that was really a rather technical point, because we had no intention of arguing against secrecy about atomic weapons as such. It was clear that that work would be secret. It was also quite clearly recognized by the government that there was no point in imposing any secrecy on purely academic research -- I mean on nuclear physics and so on. The question was only where do you draw the line and how far can new discoveries in nuclear physics or any other parts of physics have any possible bearing on new weapons and should therefore be kept secret? So it was really the question of how best to implement a generally accepted principle. That was the issue.

Weiner:

You described how that took place.

Peierls:

Right. There our complaint was not that they had the wrong views but that they didnít understand how nuclear physics and physics generally operated and therefore had written down rules which didnít do what they should have. Thatís a rather small issue; and, as Iíve explained, itís quite dead. It died immediately.

Weiner:

One of the forms that this sense of social responsibility took was the British Atomic Scientistsí Association.

Peierls:

Yes. We called it the ASA.

Weiner:

We agreed that we could dig into other sources for exact details of when it went out of existence and so forth.

Peierls:

Yes, there was a little journal published that Iím sure can be got at.

Weiner:

Iím curious about Bohrís role in this and his role in the international sense. I know of it in general, but as it affected you in your work.

Peierls:

Well, the main thing about Bohr, of course, was his Memorandum on the Open World, which was written during the war and published just after the war, and made some extremely powerful points. We were, of course, in great sympathy with that but trying to discuss how one might on that basis arrive at some more practical points. I mean he didnít propose any kind of scheme or agreement as to how one might get further within the spirit of that. I donít think otherwise Bohr came very directly into what we were doing.

Weiner:

I remember one of the things in the Bohr letters was a letter that he had written to the Manchester Guardian in 1950 which they had commented upon editorially and then you had replied to them, saying that they had missed the point.

Peierls:

I remember our correspondence in the Manchester Guardian. I canít remember that this arose from a letter by Bohr.

Weiner:

We were talking about Niels Bohr, and I had commented on that correspondence with the Manchester Guardian. Here is the letter that you wrote.

Peierls:

[reads letter] This reads to me as if the Manchester Guardian had written a leading article about Bohr but not based on a letter by Bohr to the Manchester Guardian, except that he might have sent them a copy of his memorandum.

Weiner:

Well, Bohr had made a proposal apparently to the UN.

Peierls:

Wasnít that his Memorandum on the Open World?

Weiner:

Thatís right.

Peierls:

This started really, as far as the Manchester Guardian goes, with a leader, which shocked us as being very misleading and really failing in understanding what the problems were; and for the leading liberal paper of England this seemed to us disastrous. So I felt compelled to write to them about this. Iíd forgotten this particular letter, though I agree with what it says. But there was another incident when the Manchester Guardian came out in a leader opposing the free exchange of scientists attending international functions and traveling back and forth. There were no western scientists going to the Soviet Union or vice versa; and when it started up again or at least was discussed, the Manchester Guardian came out pointing out the dangers of this. Then I think this time we wrote a reply for the ASA. I think this was the time when I was president or acting president and Moon was secretary or something like that -- maybe vice versa -- in which we therefore signed the letter as Officers of the Association, which was a device of bringing the Association into it without necessarily speaking on their behalf, because that would have meant calling a meeting and getting everybodyís approval, which would have taken too long. Iím quite sure that what we said had the approval of the members.

Weiner:

In the background of this what influence did the Fuchs case have in terms of the argument that the Manchester Guardian and others advanced?

Peierls:

That would be brought in. In general, it had remarkably little effect on public opinion in England. The more responsible papers -- and unfortunately the Manchester Guardian was not amongst them in this context -- and the general public, as far as you could tell from talking with people, took the line that this was unfortunate and just a hazard; that unless you really lock up everybody and supervise at every step, which would just not be possible, this was the kind of thing that was bound to happen. That was that. I was most impressed by the sanity and maturity of the British publicís reaction to this, excepting only certain sensational newspapers which tried to make a dramatic story out of it and bring up wider implications. Also, rather amusingly, many of the refugees took this rather as a personal danger for themselves and sort of (some of them) began to pack their suitcases, thinking that this would end up with a general xenophobia and so on. But it didnít.

Weiner:

They didnít, in other words, anticipate it. They were pretty much on the defensive in the sense of thinking that people will just stereotype them Ö

Peierls:

If youíre interested, I have a number of typical stories which impressed me at the time. When Fuchs was arrested I got the news from a newspaper, one of the evening papers in London wanted my comments. I wasnít willing to comment but asked them for detailed information on what they knew. So I discovered that at the first hearing when Fuchs was arrested, he had mentioned, when he was asked whether he had a lawyer, that he didnít know where to get one. And whatever the merits of the case, it seemed clear that he ought to have a lawyer. So I got the next train to London and tried to see him and see what I could do. I phoned up the head of the special branch of Scotland Yard who was responsible for political cases to get his permission to go to the prison to visit Fuchs. I could probably have done it without asking his permission anyway. But he was very nice and said, ďCertainly, by all means; but if you go, would you mind coming to see us first because there are some points we would like to discuss that might perhaps influence him in a certain way. Weíll be glad to discuss it with you.Ē So I went. The main point was Fuchs had then, although he had changed his mind and allegedly or at least claimed not to be pro-Communist anymore, he still out of a sense of chivalry was refusing to name his contacts and so on, and they thought this was foolish and they expected I would think it foolish too, and they wanted me to urge him to do that -- which I tried. I donít know whether this was a success. Anyway, in the course of this conversation, Commander Burt of Scotland Yard, asked me what sort of man Fuchs had appeared to be and whether we realized what his views were. I said, ďNo, he didnít say much on political things, but he gave the impression of agreeing with everybody else, being perhaps a little to the left of most of us but not drastically.Ē Of course, I knew that as a young man he had been mixed up with a Communist student organization in Germany, but that was understandable and this was very common with young people. It didnít mean very much necessarily. And he laughed and said, ďYes, I know. My son is the same.Ē At that point I was just trying to picture a senior official of the FBI making a remark like that.

Weiner:

One thinks of the transcript of the Oppenheimer case -- the lack of humor.

Peierls:

Yes. At the end he said, ďWell, itís really a shame we have to lock up a man like that, an able scientist and a man of his convictions.Ē I mean he knew that obviously he would be convicted and go to jail. ďWhatís the point of that really? But itís the law; it has to be done.Ē

Weiner:

Thatís remarkable. And this was not a put-on for you.

Peierls:

I donít think so.

Weiner:

So you heard of it from a newspaper then. This must have been quite a shock.

Peierls:

Yes, indeed.

Weiner:

But you say that the impact on public opinion wasnít a major one and you feel it didnít affect policies.

Peierls:

Only indirectly, because it had a much stronger impact in the United States, and that of course reacted back.

Weiner:

What about the Pugwash movement? I think thatís an interesting thing. Did you get involved from the start?

Peierls:

No. I think I could have. I canít remember now, but think I was asked whether I wanted to go to the first meeting, but probably I couldnít manage it from the point of view of time, and also I was too pessimistic. I didnít really see that anything would come out of that. So I didnít go until the meeting in 1960, which was held in Moscow. I was extremely surprised about how much could be done. The effect it would have was another question, but how far you could have a rational discussion in that sort of group, and bearing in mind the rule that of course no statement could be written down even as an internal report, let alone a publication, unless it was agreed by all people present or substantially all. There was no voting, in other words. Maybe I came to it with great pessimism and reservations and therefore was completely staggered how far you could talk rationally and agree on certain things -- not very far and not on everything, of course; you never expect that. And since then I have participated fairly regularly. I missed only a few of the conferences since then.

Weiner:

What about the role of the physicists? Itís not limited to physicists, of course, but in general you get the feeling that physicists have tended to take a leading role.

Peierls:

Yes, thatís a very interesting fact. Itís clear that physicists dominate Pugwash very largely. Theyíre probably the largest single group amongst the members. One should certainly ask why. I think there are two factors. One is the rather minor one that physicists have a stronger motivation because they feel very much more directly involved with nuclear weapons and similar things. It is still true, I think, that a considerable proportion, though not by any means the majority of the physics members of Pugwash, are people who at one time or other were either directly personally involved with atomic energy. But I think thatís only a minor factor. Another factor is that it turns out that physicists have a particular qualification to take part in this kind of work, in this kind of discussion, partly because what helps is that they can speak so easily a common language with their foreign counterparts. They have many personal acquaintances -- say as between the United States, Soviet Union, England and many other countries. Thatís true in other disciplines, too, but physics is a much more closely knit community, even with the present increased numbers. And, of course, itís much easier to talk with people you know as persons and respect. In addition, I think it is the particular training of physicists. I mean it arises from the fact that physics is a science where you cannot have controversy for long. If people disagree about something, about a fact or theory or something, it usually isnít very long before itís settled who is right and who is wrong. So we are all used to keeping an open mind and also to distinguish between what is fact and what is conjecture. We canít live without conjecture, but we must distinguish it from what we know, and therefore we never object to listening to arguments by other people who have different views, because if we are right, then this will sooner or later show up, and this is fine, and weíve only strengthened our position by justifying our case. If we are wrong, we have nothing to gain by refusing to listen, because obviously before long weíll be shown up. Itís hard to describe. I mean this is true of other sciences to a large extent as well, but not to the degree that it applies in physics. Niels Bohr once put this very nicely -- this was long before the war -- when we were talking about the difference in attitude toward general problems of physicists and others. He said, ďWell, you see, if you are a physicist, you must have gone through the experience of having asserted something as a firm fact or the truth and then being proved wrong. Thatís very important. If you are a philosopher or a historian, this might never happen to you.Ē

Weiner:

Thereís always a way to weasel out of it.

Peierls:

Right. I think a historian, if heís honest, will probably have that same experience. It depends on how you work. I mean if you research on detailed facts, itís almost the same situation. If you make historical theories about trends and so on, then you canít go a long way without being exposed to that. Of course, a lot of the problems we discuss at Pugwash are not scientific problems at all. In fact, the majority are not. In fact, itís quite essential to have people around who are experts on military strategy and on political trends and on international law and so on. And we do have them present. But there have been some attempts to organize other groups based more on people like that and containing no scientists or very few scientists, and theyíve never got off the ground. I wouldnít say that all these groups havenít. Some groups I know never really got properly organized or found a proper working basis and it seems to be true that without scientists and particularly without physicists itís much harder to do that kind of thing. One detail: Pugwash had a study group on European problems, problems of Europe, which of course are exciting and interesting -- about how one might get over the tensions over Germany and European security and so on. This was a group which was not very successful. I attended one meeting of that group because there was some question of linking it up with some conference, and I was more or less representing the central office in that. On the whole I was very disappointed with the level of the discussion. It was a small group. It may just have been accidentally a question of individuals, although there were some very sensible people. And then it suddenly dawned on me: This group didnít contain a single scientist.

Weiner:

Well, you were there.

Peierls:

I was attending one meeting.

Weiner:

Thatís an interesting observation. It raises a question about post-war cooperation among scientists who were politically divided and at war. The significance, many of us feel, of Pugwash is that the Russian and American scientists were together. But the question I want to ask now is: what about the relationship with German physics and British physics or American for that matter?

Peierls:

Not in Pugwash but in physics?

Weiner:

In general. How the war affected the relationship. What was left in Germany, how they emerged from the war in terms of physics, and then how relationships were reestablished?

Peierls:

I probably donít know all the facts there. German physics was in rather poor shape after the war, because so many people had left before the war. There were, of course, some very good people left, but they were a little disoriented by the general disaster, conscious of the part they had played during the war and pre-war, and so morale wasnít all that good. Also, there were physical difficulties --laboratories destroyed and so on. The restoration of the physical equipment didnít take very long. Then, of course, young people came to take the places that had been left. I donít think Germany has recovered the position she had, say, in the l920s, but there is a lot of very sound physics still going on.

Weiner:

How long was it before German physicists were again in close touch with colleagues in other countries? How long after the war did it take? Was it a question of reluctance to reestablish close contacts, or was it a question of the fact that there wasnít much going on there?

Peierls:

A bit of both, but the first factor disappeared quite quickly. The first person to be invited formally to come to England, for example, to give a lecture was Heisenberg. I was a little bit upset about this. In fact, I corresponded with various people about this, because Heisenberg, of course, had been rather close -- he wasnít a Nazi -- but he was rather too tolerant of the regime. I didnít mind too much what he did during the war, because in wartime once you are in a country, you have to participate. Well, one can do what Von Laue did and just sort of disappear in the background and not say much in public, but that wasnít Heisenbergís attitude. But it was before the war when he could have got out or tried to fight things, or at least, if he wasnít able to fight or wasnít able to succeed, he could have got out, and he certainly chose not to. And I did not believe that one in the long run should bar Heisenberg from contact. After all, all scientific contacts are based on scientific merit, and he certainly is a great physicist. But it seemed to be wrong as a gesture that he should be the first person to be invited. But he was. I canít remember the date. I would think it was around Ď49, maybe earlier.

Weiner:

Laue I think came to some international meeting of pure and applied physics around Ď48. Ewald told me the circumstances of his talk at such a meeting. I donít know if it was Ď48 or Ď49.

Peierls:

Well, in that case, Heisenberg must have been just before.

Weiner:

This was not a meeting in England anyway. The one Iím talking about I think was in France.

Peierls:

Then he also came to England to the Royal Society where I remember meeting him. He was, of course, a charming and extremely decent person; had absolutely remarkable integrity. I mean I mention that incident only sort of to pin down the period. I donít know exactly when it was, but after that I think quite soon people started to get invitations for visits and conferences and so on in a perfectly normal way, limited only by the normal considerations of whether they were the right people to contribute to whatever was the purpose.

Weiner:

I have a final question, just asking you to reflect back on certain things that you might want to identify as especially important over the years. But before that, I want to know if in this last section where we tried to identify three major themes in your post-war work -- academic physics, the organization of physics in the university, and the international aspects -- whether you can think of something very important. Well, I donít want to use very important, because then you may be modest and say itís not important, but something that you think might be relevant that we have left out.

Peierls:

You mean any one of those Ö

Weiner:

Thatís right, and whether you feel weíve covered as best as possible these areas at this time or whether you can think of things that we might have.

Peierls:

Nothing comes to mind immediately. I mean obviously one could go on filling in details on this for ages. But nothing especially significant comes to mind that we havenít covered. Probably when Iíve had time to reflect and possibly when I read the transcript, I may think of things, but I canít think of anything now.

Weiner:

Well, then Iíd like to ask this question relating to your entire career, your entire life and work: whether you can identify a period or an event or a clustering of events that gave you the most personal satisfaction.

Peierls:

Well, thatís a complicated question. In judging just the scientific work, I think probably the early years, sort of from Ď28 to the early Ď30s, were the most exciting simply because it was in physics a very exciting period. It was a time when quantum mechanics had just been developed and had brought the key to what was up till then a lot of confusion, and suddenly almost everything fell into place. People who were fortunate enough to be working in that period just had to look around and pick up any problem in atomic physics, solid-state physics, anything like that, which had been giving trouble, which had been a mystery, and to which nobody else had yet had time to apply the new ideas, and just looked at it, and there was the answer. Everything fell into place, with some exceptions, of course. There were some problems that remained insoluble. So that was an extremely exciting period. I mean also, of course, just the time when one is in the middle twenties and beginning to feel that one can make a contribution -- this is personally the right time to get satisfaction out of what youíre doing. But it also happens that the period of physics was right for that. Of course, there had been exciting things going on in physics all along, but they didnít have this dramatic impact, this sort of final resolution of things. I mean now, of course, weíre discovering things almost daily in elementary particle physics, but every new discovery brings with it new problems and new mysteries. We havenít found the keystone yet in the sense in which one had quantum mechanics at that time. And also Iím not in the swim of that today. Of course, satisfaction comes in various ways. I wouldnít deny that the sort of recognition one gets later and external signs of having established oneís position gives one a certain amount of satisfaction; the feeling of confidence that you can run a department, that you can take on a student interested in some field in the confidence that you will find something for him to do even though you havenít a clear idea to start with what to put him in. Thereís always in principle that difficulty. You know the old remark by Planck to whom a student came asking for a problem and he said, ďMy dear sir, if I knew of a problem, Iíd solve it myself.Ē You always have a bit of that. But this sort of feeling of confidence that you will be able to handle this gives some satisfaction. I think I derived a lot of satisfaction from writing a popular book in the l950s.

Weiner:

We havenít discussed that at all I realize now; satisfaction from having written it or while writing it?

Peierls:

Both. That it could be done. I enjoyed the process of formulating things. I donít know whether you know the book, but itís an attempt to set out the content of theoretical physics in entirely nonmathematical language or jargon, not using a word that wouldnít be familiar to the general reader unless you explained it, but nevertheless taking the whole thing seriously -- not glossing over things but presenting the arguments honestly. I thought this could be done and was gratified to find that indeed it could be and that it wasnít very difficult.

Weiner:

And it didnít matter at that time Ö Well, this was personal satisfaction.

Peierls:

Well, I was probably conceited enough to think that if I made a good job it, other people would like it. But certainly it was gratifying to see that they did, and, for example, that a substantial number of copies were sold and that it got translated into a number of languages and so on.

Weiner:

What led you to write it?

Peierls:

I think it was this. I had previously given many popular lectures to all sorts of audiences, and these were mostly on atomic energy and things like that. But I found that some of the questions asked were on atomic energy, and were mostly questions like: Could there be a bomb doing that? Or, could one stop the Russians doing this? But then there was also a number of questions from people with very little background asking about the nuclear forces or things like that. The typical question was: Why can mesons be responsible for holding a nucleus together when there isnít nearly enough energy in the nucleus to create a meson? And so on. And you tried to answer those questions as best you could. It was obviously worthwhile to satisfy their curiosity. But if you have only a ten-minute discussion period, or even if you have an hour to talk about something like that, you canít get very far, because the story is a continuing one; and you canít explain one thing without having told the background to it. Therefore, I felt there was a need for telling the whole story, but in the sort of spirit in which I tried to answer simple questions by simple means and not piecemeal.

Weiner:

Was it very long after you made up your mind that you went ahead and did it?

Peierls:

I canít remember how long the idea took to grow. There was, however, a much more practical motivation. That idea was in my mind. But at the time also there was a very considerable financial need to do something like that, which is characterized by a phrase with which I was rather pleased on the dedication page of the book, which says: ďTo the Treasurer of Somerfield College, Oxford, and the Bursar of Caius College, Cambridge, but for whom this book would not have been written.Ē You get the point. My children were then students. So that probably triggered the decision to go ahead and write something.

Weiner:

Well, thatís a different realm of satisfaction.

Peierls:

I know thatís not really what you were asking for.

Weiner:

No, I was probing. I wasnít looking for a specific answer. I wanted you to answer. All of these things are important and interesting. If you had to evaluate the importance in terms of lasting contribution of the work you did, other than how much satisfaction you got out of it, would you again identify the same things?

Peierls:

That is very hard. I mean I feel I havenít really sufficient distance to make that evaluation. I think my published work as distinct from what I might have done by influence, giving ideas to others or helping others find some right approach, consists of not very great peaks but a general plateau of contributions, some of which are actually wrong or obsolete by now, but generally contributions which are worthwhile, often on points of detail and some on rather technical points of method, but I think few of them really sticking out above the background. So I think itís hard to identify anything as being of special importance.

Weiner:

Taken as a whole in specific fields, you donít feel that any in one field has made more of an impact than some in other fields?

Peierls:

I donít know. I think probably the work on solid-state problems has stood up better than on other things, though there are some bits of work on nuclear physics which I still like. In field theory I was trying very hard to get somewhere but didnít really succeed.

Weiner:

I think the fact that you were so versatile and were able to pick up top problems in each area as they came up and to say something significant about each is in itself a peak -- you know, just this process of being able to do this and do it consistently in addition to the particular merit of a number of the contributions. Well, I think weíve covered a lot of ground, if you think that weíre through for the moment.

Peierls:

Yes. Good.

Session I | Session II | Session III