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Oral History Transcript — Dr. Jean Ullmo

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Interview with Dr. Jean Ullmo
By Thomas S. Kuhn and Theo Kahan
At Ullmo’s home, Boulevard Malesherbes, Paris, France
January 7, 1963

 
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Jean Ullmo; January 7, 1963

ABSTRACT: This interview was conducted as part of the Archives for the History of Quantum Physics project, which includes tapes and transcripts of oral history interviews conducted with ca. 100 atomic and quantum physicists. Subjects discuss their family backgrounds, how they became interested in physics, their educations, people who influenced them, their careers including social influences on the conditions of research, and the state of atomic, nuclear, and quantum physics during the period in which they worked. Discussions of scientific matters relate to work that was done between approximately 1900 and 1930, with an emphasis on the discovery and interpretations of quantum mechanics in the 1920s. Also prominently mentioned are: Edmond H. Bauer, Eugene Bloch, Leon Bloch, Leon Brillouin, Louis de Broglie, Albert Einstein, Charles Fabry, Jacques Salomon Hadamard, Paul Langevin, Perot, Francis Henri Jean Siegfried Perrin, Boris Podolsky, A. Proca; and Ecole Polytechnique.

Transcript

Kuhn:

You have, seen now from [the questionnaire], I hope, the sort of thing we are after. I think you may have a very much clearer idea than I of how you can best help us elucidate the French situation.

Ullmo:

I have reflected on what I could tell you, and I must ask you if it does interest you. Of course, I have many memories of Langevin, who was indeed my master. I worked with him from all the years before the war. And I even wrote an article for Scientia in 1934, the title of which was “L’evolution de la notion du corpuscule d’apres M. Langevin.” In that article I summarized all the talks we had together for all those years between ‘28 and ‘34, so it’s a kind of compendium, a kind of resume of Langevin’s thoughts about mecanique quantique; it may be interesting for you perhaps.

Kuhn:

I would say there’s no question in my mind that I would be immensely interested in having you tell us of Langevin. I cannot ask you to go over all the same ground again. I would be particularly interested in having you talk about his attitudes towards corpuscles and some of the problems of quantum physics and something about his role in the, French, scientific scheme.

Ullmo:

Perhaps you’ll be interested by this — I’m sure you don’t know it — that’s a book I wrote four years ago on Modern Scientific Thought. In that book there’s a paragraph which I called “La theorie physique a l’oeuvre” — physical theory on the move — and in that special paragraph, I tried to resume the way in which I had lived, the appearance of quantum mechanics from the different points of views of Heisenberg, Dirac, de Broglie, and Schrodinger. And I tried to show how from being very far apart at first — they had not the same physical ideas and not the same philosophical ideas — in the end they came together. So I tried to give this as an example of the way the human mind functions. For the deeper part of what I know of these things, you’ll find it there. What I’m going to tell you now is more anecdotic, but the fundamentals of my insight on modern physics were expressed there. Let us go on with the anecdotes first, because, in fact, they are rather short, but they impressed me at the time because it was so new. I was not working but talking with Professor Fabry in 1928 just before Louis de Broglie got Le Prix Nobel. I had little habits of going to see him once a month and we had talks. Professor Fabry was interested in the first move in France of those new theories up to the point of publishing my first note in the Comptes Rendus, in which I tried to reconcile the idea of the photon with the idea of polarization, which, of course, is not so easy. I was twenty at the time. And I remember that one day he talked to me about the thesis of Louis de Broglie, and he was very ironical about it. I remember [his saying]: “Vous y croyez a ces choses-la, vous?” Of course, it’s not very kind to say these things of Professor Fabry, who was in his way a good scientist, even a great scientist, but he was very traditionalist-minded. He was not ready to accept new developments. I remember this because he told me this a few days before the Prix Nobel was announced for Louis de Broglie. So I could understand that that Nobel Prize had absolutely changed the outlook for French official teaching. From that moment, Louis de Broglie was projected into the front rank, and all honors were given to him. Quantum physics became respectable; but before, it had not been so.

Kuhn:

This story takes place then appreciably after the Schrodinger equation as well as after de Broglie’s own work, so that it really was the Nobel Prize rather than Schrodinger’s formulation

Ullmo:

Oh, yes; exactly because at the time I was a specialist of Schrodinger and Dirac’s equations. At M. Langevin’s seminar I was in charge of nearly all things which were published in the Proceedings — all of Dirac’s and Eddington’s things, and so I knew them rather well. And that was why Fabry was interested in talking with me, but from afar. He was just an outsider. That was a very strong event at the time.

Kuhn:

At this point, as an expert on the Schrodinger and Dirac formulations, did you yourself know of de Broglie’s work? I don’t mean, had you heard of it, but I mean would one who was now studying the more recent formulations in France around 1928, also have read —?

Ullmo:

Oh, yes, of course. In fact, all my vocation for theoretical physics had come from de Broglie — from reading the special article in the Journal de Physique while I was at the Polytechnique School in ‘24 and ‘25. It had seemed to me so interesting and moving; I told myself: “That’s my life; I must go in that way.” That was absolutely my starting point. But at that time, you know, pure science was very much despised in France. For instance, in the Polytechnique School which takes the cream of all the best French boys, who come from all over the country just to be Polytechnicians, exactly nobody at that time did pure science. They were all taken up by administration and business — all of them. Between the two wars, I can say, I was the only one who really went out of the Polytechnique School to do pure science. There’s another case of course; there’s Leprince-Ringuet.

Kuhn:

I’m very much interested in the whole question of the attitude toward theoretical physics. When you say that the Ecole Polytechnique has turned out, in the period between the wars, very few people — almost none — would this be equally true of experimental and of theoretical [physics]?

Ullmo:

Absolutely; absolutely. No scientific people came out.

Kuhn:

What was the curriculum at the Ecole Polytechnique like when you were there?

Ullmo:

The highest possible mathematics were there, in fact, but as for physics, it remained exactly classical physics. We had at the time Perot as professor. And Perot was a very good man; he tried to put in a little new physics, but he knew nothing about it, so the, few pages he gave to Bohr’s atom were quite false. They meant nothing, in fact. The only, one who was really interested in the new physics was Becquerel, who was an examiner in the Ecole Polytechnique and who had been professor for two years between 1920 and ‘22. But these were on relativity theory. He made at the time a manual on relativity theory, which is very good. It is still one of the best —.

Kuhn:

But even relativity was not a regular part of the curriculum?

Ullmo:

No, absolutely not. Afterwards relativity and quantum physics were out of the question. We had a professor of mathematics, the illustrious Mr. Hadamard, who was of course a very great man, and he was interested in relativity. He even gave us something quite new, which I never found anywhere else, from which it was clear that the Lorentz transformation could be inferred from very simple considerations — a priori considerations — on group theory and the Fizeau-Fresnel experiment. That was very elegant, and I found this nowhere else. But, of course, that was just for elegance; that was really not our curriculum. Also, I remember that he gave in his lectures a very interesting idea about his work on Cauchy’s problem. He gave us a very interesting idea on the difference between mathematical determination and physical determinism. You could have mathematical determination on one side without physical determinism, if things diverge too quickly. That was very interesting, and so interesting that I’m taking this idea back in some of my recent publications. You know I’m, publishing studies on chance and such things. That was new at the time, and it is still. But apart from these special occasions, science was not at all on the upgrade in France. At that time, we were very materialistic in France.

Kuhn:

What sort of classical physics was taught? Was there good grounding in electro-magnetic theory, or not?

Ullmo:

Up to Maxwell’s equation it was well-known — but no further.

Kuhn:

But not really very much with solutions of the wave-equations even?

Ullmo:

No, no absolutely not.

Kuhn:

And what about mechanics? Would you do Hamilton-Jacobi theory?

Ullmo:

No; Hamilton-Jacobi was not taught at all, and we had to do it ourselves. That was our first revelation of new physics and mechanics, to Cauchy-Jacobi to Cauchy-Poisson. When Proca and I translated together the Dirac book, he had to add, if I remember well, an addendum on Cauchy-Poisson because they were not known, and that was in 1931. It was absolutely new. And even this has not made so much progress; it is one of my fights in the Polytechnique School that the mechanics professors cling to the ancient formulation and they give very little analytical mechanics, even now. That’s very scandalous.

Kuhn:

Is there any place that you might have been studying at this time other than the Ecole Polytechnique where the situation would have been significantly better?

Ullmo:

No. The place, of course, was with Langevin in the College de France, and there we had the most modern things. Of course, you know that Langevin’s lectures were something absolutely wonderful; all the people who were there had the impression of extraordinary claret and pushing forward. It was very beautiful indeed. But he was quite isolated at the time — quiet isolated. I can tell this fact, which is very significant of the state of things in France; the fact that Proca, who was one of my best friends — we worked together for all these years — was never really recognized. He never could succeed in getting a professorship; there were no professorships of theoretical physics and not one was created even for Proca. At that time he was absolutely illustrious, celebrated, well known. All people coming to Paris, like Pauli and such people came at once to see Proca, but in France Proca was still an outsider. C’est un peu severe, mais c’est juste, qu’il y avait-la une epoque de suffisance francaise. Les Francais s’etaient endormis sur leurs lauriers, ils ne voulaient pas vraiment suivre le mouvement modern. I remember also, for instance, that the two professors of physics were two brothers, Leon and Eugene Bloch, who literally knew nothing of theoretical physics.

They had good will; they tried to inform themselves. I remember that they came always to the seminar Langevin when I was talking because they hoped to get some information, but, of course, that wasn’t very serious. They were confirmed professors, and I was a young man of twenty-two; it would not have been in that order of course. But the fact that the Nobel Prize went to de Broglie began to change things. From that point on, respectability was conferred to the new quantum physics, but no chairs were founded. The teaching of physics was very, very, very reduced; so much so that aside from the group of Langevin and the group which formed itself around de Broglie, but which for certain reasons was never too eminent —. Broglie was too sensitive to personal relations; he had difficulties in getting the best pupils — well, I can’t insist on that. But apart from these two groups there was no physical theory here. When, for instance, Solomon was killed during the war, Langevin disappeared and others were dispersed, strictly speaking, there remained nobody for theoretical physics. I can give you a quite demonstrative example of this. When the war was finished, I was very keen at the time on teaching because I had been in the Resistance myself and I had seen the very great interest of the French humble people for ideas and for science. And that was quite in contrast with what I had seen from the French bourgeoisie during the twenty years between the wars.

So I came back from the Resistance with the idea that we had at first the call to help and promote French teaching. That was the time of the Langevin-Wallon project which was not exactly applied at that time, but which is still the push behind the French reformation of education … At that time, in ‘44 and ‘45, I came back to the Ecole Polytechnique, and I had a seminar of theoretical physics for my pupils, which in fact is impossible, ordinarily speaking, because they have too much to do during their curriculum. But it was just after the war, and they were more nature because many of them had been in the Resistance or in the war, so we could have such a seminar. And in that seminar I had very brilliant pupils, like Horowitz or Leon Bloch or Messiah and others. I just taught then once a week the elements of theoretical physics. When the Commissariat a l’Energie Atomique was constituted we had to have a section of theoretical physics — that was a first necessity. The only people we could find for the first people there were my pupils — that group of Bloch, Messiah, Horowitz; there was no one else in France to get into the Commissariat. That proves the absolute rupture between before the war and after the war, because before the war all was concentrated around Langevin. When Langevin disappeared there was nothing left.

Kuhn:

Contrast this, if you will, with the situation in experimental physics.

Ullmo:

I don’t know experimental physics so well, of course, but in experimental physics the tradition was maintained. Of course people like (Trillat) and like (Rocard) were half experimentalist and half theoretician, were very good physicists. They maintained the tradition of French physics. All this, I understand, had a social basis. C’est tout un expose — un long expose — a faire, ca nous entrainerait très loin —. La France entre les deux guerres s’est endormie, endormie dans la prosperite, endormie dans le Malthusianisme, puis qu’il y avait très, très peu de naissances, donc très peu de competition pour les situations; et endormie dans l’orgueil historique; parce qu’elle avait gagne la guerre de 1918, elle pensait que personne ne pourrait jamais l’egaler. D’ou — très peu d’attention portait a ce qui se passait a l’etranger, très peu, et une grande facilite de carrière pour le peu de gens qui se tournaient vers la science mais a condition qu’ils faisaient la science traditionnelle ou ils etaient compris, ou ils etaient recus. C’etait l’Ecole Normale qui fournissait les savants. Il y avait autant de postes que de jeunes Normaliens -– a condition qu’ils ne se fassent pas remarquer, qu’ils ne soient pas eccentriques. D’ou reellement, cette impression que nous avions, nous dans le groupe de Langevin, constitue essentiellement de Langevin, d’Edmond Bauer qui etait tout-a-fait l’animateur du laboratoire de Langevin, l’impression que nous avions d’etre tout-a-fait en dehors de la science officielle. Nous avions des antennes; quelqu’un comme Joliot-Curie venait travailler au laboratoire — venait demander des renseignements, venait exposer ses resultants; mais la Sorbonne nous ignorait, et nous ignorions la Sorbonne. Les nouveaux movements de la science etaient Presque volontairement ignores par la science traditionnelle. Et alors, l’autre anecdote que je place maintenent, c’est Leon Brillouin — alors je me souviens bien de la date, ca devait etre en janvier ou Mars 1925, a fait un expose au College de France sur les matrices d’Heisenberg. Eh bien, justement, la reaction etait une reaction d’ahurissement. Stunning! We were stunned, absolutely stunned; everybody in the audience was stunned.

Kuhn:

How large was the audience?

Ullmo:

Well, it wasn’t very large, and I don’t suppose there were many official professors there. I remember perhaps thirty people, and most of them were young. Probably Brillouin had sent invitations to the important people in the Sorbonne; certainly he had done so, but I can’t remember whether they were present or not. But I remember the general feeling of astonishment and even of being stunned: “But what does this mean? What does this mean? What’s in this?”

Kuhn:

In many places, of course, I think the reaction to matrix mechanics was one of astonishment and total wonder at what it could mean, but at many of those same places, people were not surprised to find themselves reacting that way, because they had been so terribly clear before that things were all wrong. Was that same consciousness here?

Ullmo:

No. At the time I think the general French scientific community was not in a state of crisis. They were exploiting well-known domains. Someone like M. Edmond Bauer, who had put before himself the question of understanding the quantum, because he had made his thesis on the question, was absolutely unique. The consequence was that he never made any career. He was perhaps the most brilliant of the young physicists at the time, but they never offered him any chair, and he had great difficulty in having a career at that time. He had to stay as Adjoint de Langevin because his interests were outside the general routine. That was exactly the atmosphere at that time; it was very stuffy. The general French course of teaching clung to the nineteenth century, and eventually, of course, the discoveries of Rayons X,(Becquerel) and Curie [changed that] but on the experimental side [only]. They were not ready to feel the impact of the theoretical crisis. I can say this with great assurance, parce que j’ai tout a fait vecu ca en 40, je me souviens aussi de son premier expose chez Langevin, etc. C’etait très curieux.

Kuhn:

What about Langevin himself in this?

Ullmo:

Well, Langevin was the most progressive and enthusiastic of men, but he was a rationalist, and so he was very much in reaction against the new philosophy — if I may say so. He took the same position that Einstein took. In that little article you’ll find his ideas, and he was very strong about this. He thought that the way of putting things as Jordan and even Dirac himself had done at that time, the choice of the electron, the liberty of the electron, etc. was, as he called them, “un devergondage intellectuel.” And he had an idea, which I consider very profound, and which is still, I suppose, the truth of the future, if it’s not the exact truth now, that the difficulties we got into on the complementarity principle and in the determination principle were caused by the fact that the problem was wrongly put. His formula was: It is not a crisis of determinism; it is a crisis of mechanism. It is because we keep much too naively to representations of points and forces and such things that those images, those representations don’t fall in the new domain, in the new part of things of the world we have got into. And he thought that the real images were to be taken from membranes tendues.

Kuhn:

Did he work at this? Did he try himself —?

Ullmo:

No, at that time he was too tired. In fact, he couldn’t work anymore himself; he was already very tired and ill from ‘28 on. It was for him a very great effort even to give his lectures. But if he had been younger, he would have done it because he thought it was by stretched membranes and Jeans’ parallelipipede. He says, in the Jeans parallelipipede we know that only certain wave-lengths are possible, and that a certain number of quanta are attached to each of them; that was a nombre d’occupation, which has been taken again by (Costa de Beauregard) recently. That was for him the physical reality — kinds of ondulations compatible with the limited conditions of the box of Jeans, of the stretching of the membrane. And in those possible vibrations a certain number of quantum of energy are attached to one. And if we went profoundly in such images we would find again a new determinism, but not of the kind of points and corpuscles — that was absolutely his idea, and I still think he is right.

Kuhn:

Now, again, in France, there are people working very hard, I believe, on this point of view. Has that tradition endured in the intermediate period; I mean, one knows of Vigier now, for example. Have there been people also trying to bring this point of view forth in the interim?

Ullmo:

No, not in the interim. I can tell you with some affirmation, no, because I was the only one who maintained that idea, and except for teaching, I didn’t do any real physics from the war on for personal reasons. So the only way in which I expressed those ideas was on the philosophical way when I fought against le theoreme de von Neumann. I wrote things on mecanique quantique, et la causalite and on le theoreme de von Neumann, and I think I succeeded in showing the contradictions inside those theories. But that was only a logical and philosophical point of view; that was not real physics. And at the time I knew I was quite alone, and that was, of course, one of the reasons why I didn’t do physics, because it’s very awkward to be the only one with these opinions in physics. When Vigier and de Broglie and Bohm came back to that point of view, they admitted that I had been the precursor, or let us say someone holding those views while no one dared to hold them for some time. But, of course, at first I don’t approve of the way in which Bohm, Vigier, and de Broglie are trying to reinstate those theories because they are too mechanical, I think; they are too much attached to that point and corpuscle point of view. And I even go so far as to say that the contestation against the Bohr views are much better done from the inside, because if you attach the contestation to those new theories which are themselves very contestable, you leave a ground for that kind of positivism. I said this in that book.

Kuhn:

Coming back to Langevin, when did you begin working closely with him?

Ullmo:

Exactly when I came back from a trip in America in January, ‘28.

Kuhn:

Had you known him or talked with him before that at all?

Ullmo:

I went to see him when I went out of the Polytechnique school to tell him that I intended to do theoretical physics. And so I had my military service to do, a trip to America, and during that trip I had made some work, and I brought it to him. From that moment on, he was very, very kind. I can tell you an anecdote — something quite apart. [recorder switched off here]

Kuhn:

What about the role of Leon Brillouin in this?

Ullmo:

Well, Leon Brillouin was very brilliant. And he had the strength of being his father’s son, and being the most brilliant boy coming from Ecole Normale. So from the beginning he was sure to make a brilliant career. And the same was true of Francis Perrin; they were the two cardinal’s sons, if I may say so. And both of them being very clever, they understood that the new science was important, and so indeed Leon Brillouin did very interesting things himself all the time. But by mischance he was not a very good professor, and he did not know how to have students and pupils. The only one he took wasn’t valuable (???). Brillouin did really excellent work for all those years, but without influence. As for Perrin I remember the first expose I heard from him, which was very brilliant, and which was a little later, perhaps in ‘32 about spins isotopiques; I remember. And his father was present — I knew his father rather well — and he told me, “Isn’t he brilliant, my son!” And also I can tell — I don’t know if someone else has told you this — someone who was very important for promoting that new science was Solomon because Solomon had not been in the ordinary careers; he had not been at the Polytechnique school, and he had not been at the Ecole Normale because I think he had begun by working to be a doctor, a physician, if I remember well. I don’t remember at that time how he came to do some physics, and he married the daughter of Langevin. But he was soon very brilliant; he went to Copenhagen and he worked for his thesis with Rosenfeld. He made a very brilliant thesis, and he came back from Copenhagen absolutely full of those new ideas, but he was absolutely in advance of all the French people. The same fact [applied to] him as to Proca, he couldn’t find a job. He was the most brilliant, the most advanced of young physicists and even the influence of Langevin could not put him in the official [circles]. And the same was true of Jacques (Vintair). Of course, (Vintair) is not a first class physicist, but he knows his job — I would say he was a very good one - but he never succeeded in being nominated to the French University. Absolutely all those who did new physics were outcasts.

Kuhn:

Clearly, if one was doing theory, one was doing the new physics; but did the jobs go to men who were doing classical theory, or did they go to men who were doing experimental work?

Ullmo:

They went to men who were doing classical theory, well, experimental work, of course, but for the posts which were considered to be in theoretical physics, they were still physique-mathematiques they had been in the elder Brillouin’s time.

Kuhn:

But there were jobs that went to people to do mathematical physics?

Ullmo:

There were jobs, absolutely, absolutely.

Kuhn:

It’s not a question then of there not having been mathematical physicists?

Ullmo:

There were but they were the ancient ones.

Kuhn:

What sort of chairs were those? Who took them? Who was getting the chairs that Solomon and some of the others might have had?

Ullmo:

(Rocard) did get it, of course, and (Trillat) aussi, n’est-ce pas, et Nell aussi a ete nomme I think, a ce moment-la. Thinking hard I’ll find others, you know, but they were far from me; I don’t know them well because they were very far from my physics. (Citron) aussi. Je pense aux gens de la Societe Physique. Je les connaissais bien tous ces gens-la.

Kuhn:

I ask about the names more to identify the jobs which these other people should have had. With the elder Perrin — how did he feel about the revolution in physics? To what extent did it have an impact directly upon him and upon his work?

Ullmo:

Well, at that time, he didn’t work at all anymore. He had become a political figure; he was minister a short time afterwards, and I can say he lived on his glory. He was not making any lectures anywhere, and he was not publishing anything; no, I don’t think the new physics was something in which he felt involved. He left it to his son, but, you know, his son being far from him he said “Just look at the boy who is doing such extraordinary things!” He hadn’t kept in the mood as Langevin had, no, not at all.

Kuhn:

The reason I have kept pressing this point about experimental versus theoretical physics is that when I talked with Leon Brillouin, he made this point that he felt that when he was a student, the image of the physicist was of the experimentalist not of the theoretical physicist.

Ullmo:

That’s true.

Kuhn:

And he said people used to say to him “You’re mad to do theoretical physics!” Now this after all, was still at a period before wave mechanics, before matrix mechanics so that it wasn’t the total novelty of those ideas that was involved. But he spoke of the extent to which anybody who wanted to do theoretical physics would wind up doing mathematics, and not doing even classical theoretical physics.

Ullmo:

That’s quite true, because the tradition did not distinguish, in fact, between experimental and theoretical physics up to 1914. Being a physicist meant being in a laboratory, and if you were clever or keen enough, you did some calculations about this, as Langevin had done for magnetism. But the idea of someone absolutely concentrating in his office, in his cabinet, and doing theoretical physics was new at the time.

Kuhn:

Well, was it new, or was it that that was what a mathematician did?

Ullmo:

No, because the French mathematicians are always very pure mathematicians, and so they didn’t consider themselves at all like physicists.

Kuhn:

Well, what about Poincare?

Ullmo:

Well, that’s a point, of course, but Poincare etait l’exception qui confirmait la regle parce qu’il etait le plus pur des mathematiciens, absolument le plus pur. Ce qu’il avait applique a la physique, ca paraissait descendre de l’Olympe. Mathematiques, ce n’etait pas du tout quelqu’un, comme (Schwegard) qui apprend des mathematiques pour resoudre son probleme, c’est quelqu’un qui se dit, “est-ce que je vais appliquer mes connaissances sur les equations aux derives partiels ou sur la theorie des ondes, a tel ou tel probleme,” voila. I can give you a very simple example which will show you the fact. At that time in ‘30 when I began working with Langevin, it was nearly impossible to classify me because I didn’t want to do any laboratory work. I felt too clumsy, and I didn’t want either to do pure mathematics because I thought they were a little dusty at the time. So I wanted to do only theoretical physics. But at that time, that was not a recognized job, and when Langevin wanted to have me helped by the state, he had to intervene near the Caisse Nationale des Sciences which was the first form of the Centre National de la Recherche Scientifique, and he asked that there be created for the first time a scholarship for theoretical physics. I was the first one to have one, and it was created for me in 1932. That’s very definite as progress.

Kuhn:

There were scholarships in physics, but they would have gone to people with laboratory interests?

Ullmo:

Exactly. And there were scholarships in pure mathematics; I was only the first one. And it required all the influence of Langevin to obtain it.

Kuhn:

To what extent was Langevin himself isolated because of his views; I mean, to what extent did his own rather special sorts of interests or at least for France, keep him apart and keep him in a non-central position in the [physical community]?

Ullmo:

He was very much admired, and he was considered to be the best French physicist at that time. But he was a little of an outsider for many reasons which were confused. Being a Communist, not being in the Sorbonne, but in the College de France, and being at the head of the Ecole de Physique et Chimie — that is a special high school, so it was permitted to him to be in the general flow. “For Langevin it was all right.” He was a most wonderful man indeed, on the intellectual and on the moral sides.

Kuhn:

By the time you were working with him he was lecturing, but he had pretty well stopped doing research?

Ullmo:

Yes, he had stopped doing research.

Kuhn:

Do you know to what extent papers of his own lectures have been collected and exist anywhere?

Ullmo:

They were considered to be very precious and rare because I remember that I had taken very precise notes about them and for many years those notes were requested of me by people wanting to get inside physics. They asked me whether they could have them. By mischance I lost those notes during the war when the Germans took my things. I was considered to be an enemy of the Germans, so they made requisitions on my house and I lost everything. So for those last years of Langevin’s lecturing I suppose they are difficult to obtain. Mais je me souviens tout-de-meme qu’un livre avait ete publie vers ‘33/34 qui s’appelait quelque chose comme L’Introduction a la Physique quantique ou La Mecanique Quantique dans une collection bleue.

Kuhn:

Ce n’etait pas le bouquin de Proca, non?

Ullmo:

Non, ce n’est pas Proca, non. Et ce livre reproduisait en fait le cours de Langevin.

Kuhn:

Et ca etait sous le nom de qui?

Ullmo:

Je ne m’en souviens plus, mais je sais que c’etaient des gens qui assistaient au Seminaire, et au fond ils n’avaient fait que reprendre le cours de Langevin. Alors la, au contraire, il y avait une presentation tres elegante de la mecanique analytique et de la mecanique statistique parce que c’etaient les deux grands — et puis les premiers modeles qu’avait construits Langevin justement pour le magnetism —.

Kuhn:

Did he teach quantum mechanics also in these lectures?

Ullmo:

Oh yes. D’une facon tres originale. Parce que quand il parlait mecanique analytique et mecanique statistique c’etait comme introduction a la mecanique quantique, il ne faisait plus de cours classique c’etait — il faisait vraiment un cours de (???). I’ll give you the notes.

Kuhn:

Oh very good; I’m extremely grateful. I just want to be sure I have the year of this.

Ullmo:

It’s ‘34.

Kuhn:

It is perfectly true, also that except for a few particular episodes what in France interests me, I think, more than anything else, is exactly the situation which we have been discussing here. It’s then really the question as to why were so few French people involved? Why did it never become, in these key years, as much a French occupation?

Ullmo:

J’ai tache de vous donner le contexte social. Il faut ajouter que la France avait ete saignee a blanc par la guerre. Reellement, tout ce qu’il y avait de plus brilliant avait ete tue pendant la guerre de ‘14-‘18. Et c’est ca qui rendait les autres des survivants ayant la carriere trop facile. En meme temps c’etait les gens des generations les plus maigres, le depeuplement etait a son maximum en France. Alors, enfants uniques, plus de concurrence du fait des morts de guerre, et des postes très nombreux et très imminents a remplir puis qu’il y avait encore tout le prestige de la science francaise du l9ième siècle, c’est a qui rendait des carrieres trop faciles et des individus trop pretentieux. Quand on est le successeur de Poincare ou le successeur de Curie, ou le successeur d’Hermite ou de Jordan, on se considere comme quelqu’un de très important, on n’a pas envie de se mettre a l’ecole de M. Heisenberg ou de M. Dirac. Et l’exemple meme de de Broglie est demonstratif; de Broglie a fait quelque chose, parce que lui aussi c’etait un outsider, an outsider absolu. Singularite totale. Les seuls physiciens que je viens de vous citer Proca, Solomon, de Broglie et, disons, moi, sont des gene qui avaient absolument refuse le jeu social, le jeu de l’arrivisme, le jeu de l’Academie, le jeu des situations. Nous etions des gene qui preferiont notre vocation a nos interets. Eh bien c’est un peu exceptionnel, n’est-ce pas?

Kahan:

Tell me, to what extent is an unwillingness to go to school to Germans also a part of this story?

Ullmo:

Oui, oui. Pendant la guerre de 1918, il s’etait developpe un très fort sentiment anti-allemand et une tentative d’abaisser le prestige intellectuel des Allemands. Ceci jouait sans aucun doute, un peu inconsciemment, mais ca jouait dans la bourgeoisie francaise et meme dans les intellectuels francais. Je n’en ai pas des preuves directes, mais c’est certain.

Kuhn:

But would you think that this had been true not only in the last war, but also perhaps in the Twenties?

Ullmo:

Oui, ca a dure au moins dix ans, ca a certainement jou un role entre 1920 et 1930, certainement. Quand Einstein est venu a Paris dans son fameux debat avec Painleve, les Francais avaient un peu l’impression que Painleve devait “river son clou” comme on dit en argot — a Einstein. Il y avait un peu ce sentiment que la raison francaise, la rationalite francaise n’allait pas se laisser emporter, deborder par le romantisme brumeux des Allemands. Ca a joue, assurement. Mais surtout il faut voir dans cette France d’entre les deux guerres, une tres grande eclipse de la France. C’est un moment d’affaissement pour les raisons que j’ai dites tout-a l’heure, demographiques-historiques, et c’etait le moment ou les bourgeois sont riches mais ils sont Malthusiens, ils ne cherchent plus a justifier leur position privilgiee; ils se contentent d’en toucher les dividendes d’honneur, d’argent et d’avantage. L’idee qu’il y a un devoir social n’existe pas. L’idee du progres economique n’existe pas. C’est un point que j’avais vu tellement fortement parce que je m’interessais aux questions sociales et economiques quand j’ai cesse de faire de la physique a partir de 1934, c’etait pour essayer do reveiller l’interet des Francais dans l’ascension, dans le progres. Alors, je l’ai fait au Centre Polytechnicien d’Etudes Economiques, n’est-ce pas, qui est un grand levier, et c’est la que nous avons re-appris aux Francais le progres, l’expansion, d’aller de l’avant. Nous l’avons appris et maintenant les Francais sont redevenus jeunes, et ca remarche. C’est un peu personnel ce que je vous dis la: moi qui ai beaucoup souffert entre les deux guerres de cette affaissement de la France, au contraire maintenant je suis tres heureux parce que je vois le redressement de la France selon les voies memes que j’ai souhaitees, redressement scientifique et redressement du progres economique. Entre les deux guerres je me suis evertue a preparer les moyens du redressement scientifique, par exemple — j’ai negocie beaucoup de choses: pour que l’Ecole Polytechnique, pour qu’on puisse faire de la science en sortant de L’Ecole Polytechnique. Et maintenant it has come to fruition: in ‘50, ‘60 every year into pure science, and even the others are really feeling the usefulness of what we have taught them, and so the general level of scientific technique has grown up immensely everywhere. I feel this in my pupils, and every day I have a token of progress of that fact. That’s why I’m rather happy, as you see.

Kahan:

Have you some recollections about the connection between Louis de Broglie and Langevin?

Ullmo:

Yes, yes.

Kahan:

Do you know the reaction of Langevin to de Broglie’s ideas?

Ullmo:

In my recollection they were absolutely one with another; in fact, Louis de Broglie was a pupil of Langevin. Before he received all those honors and became an independent professor, he lived in the shadow of Langevin. For those years when I worked with him, we worked together as two pupils of Langevin. There was not a question of his being the professor and my being the student; we were pupils of Langevin. And Langevin admired him and considered him absolutely in the rational tradition he hoped for! The models and ideas of de Broglie were absolutely congenial to Langevin, absolutely. De Broglie came absolutely regularly to the seminar de Langevin, absolutely. He was exactly like a pupil.

Kuhn:

To come back for a moment: you spoke of going to hear Brillouin’s lectures on matrix mechanics. Do you remember more than the sense of shock? Do you recall things that people said?

Ullmo:

I remember more, but of course in a very elusive way. It was the arbitrariness which was so surprising. It was presented — I think it’s quite true for Heisenberg’s ideas –- as something which is an ordinary function and which becomes a non-commitative thing. You know, a matrix coming from nothing, and that matrix being justified on the shortest possible way by the fact of the Balmer series.

Kuhn:

I take it that perhaps no one in France, except Brillouin himself, ever did anything with matrices at the start?

Ullmo:

Oh yes, yes; there was a good thesis which was published only later, but which was begun at that time, mais j’oublie le nom — nous allons le retrouver — by one of the best pupils of Langevin and Bauer, who was perhaps the most important in the Langevin laboratory at that time. Just at the moment. I don’t remember the name, but he was working on matrices specifically. He even gave some ideas on matrices which I never found anywhere else; it was absolutely special. Comment est qu’il s’appelait?

Kahan:

Celui qui est mort tragiquement?

Ullmo:

Oui. C’est celui qui a fait une these sur les matrices (anti) commutative, etc. Enfin, Mr. Bauer will give you the name. Oui, ca va me revenir parce que je connais tres bien enfin c’etait la fils de —.

Kuhn:

Well, now, was it very different with the Schrodinger equation, I mean, when the Schrodinger equation was announced?

Ullmo:

I know the Schrodinger equation was accepted; I know it was absolutely — the fact that it came from de Broglie’s equation was satisfactory, and the fact that it came in the general line of theoretical physics. … Of course the Congress Solvay and the Born interpretation gave quite a debate, but the Schrodinger equation itself was absolutely accepted. If I may recall a quite special personal remembrance — in France I had introduced the Dirac equation, and I myself had written something on the Dirac equation in which I deduced it in a much more rationalistic way than Dirac himself. And at that time I received a visit it was in ‘31 — from Boris Podolsky. He came from America, he told me, nearly on purpose to see me and tell me that Einstein himself had much approved the way in which I had deduced the equation. I think I have the letter somewhere, but I don’t know if I can find it. He gave me a letter in which he put all the points for which he supposed that my way of deriving it was better than Dirac’s. Well, that’s personal, you know, but that was the end of, let us say, of the rationalist approach.

Kuhn:

As a student of theoretical physics, once it has become clear to you that this is what you are going to do, what journals did you follow? What would you read?

Ullmo:

Essentially Proceedings and, accessorily, The Physical Review. I could not read German well at that time, but my father spoke German very well, so I had him translate for me the most important papers of Heisenberg and Weyl and afterwards von Neumann, but I read especially in those two [journals] I’m talking about.

Kuhn:

You say you did not read German very well; would this have been fairly typical of the few people in your position — not to be able to read even scientific German easily?

Ullmo:

I suppose so. In fact German was rather learned by French boys who were considered to be good pupils. But there were so few of us, so few, so few; I can’t give a statistical answer.

Kuhn:

Was German taught in French schools?

Ullmo:

Yes. It’s even a tradition that the best boys at that time did learn German, but perhaps at the time, because of the war of 1914, German had subsided. I can’t assure you, but perhaps. It was a moment where English had been quite predominant because of those memories of the war, but I can’t assure you.

Kuhn:

Well, it’s at least a lead; it’s something we can look into further, because I do find it terribly interesting that you would follow the Physical Review and the Proceedings and not, on the whole, German, except where you knew there was a particular paper.

Ullmo:

Exactly.

Kuhn:

Where would you first have learned of the Schrodinger equation? Not from the Annalen der Physik?

Ullmo:

I’m trying to remember: probably I first learned of Schrodinger’s equation in Langevin’s courses, yes, certainly. Eddington and Dirac — I was the first one to know them in France. I was bringing them to Langevin, but for the German things Langevin had another source, and I waited for his courses to give them to me. At that time there was a book of Birtwistle. Birtwistle was important for the first translations of several important articles. I suppose they were considered English, but we read them in English from the German in Birtwistle. It was considered important in that time.

Kuhn:

And that generally was a quite influential book in France, was it?

Ullmo:

Yes. I consider this [to be true,] yes. And I remember also qu’il y avait eu un livre de Hartree, c’est un peu vague mais —.

Kuhn:

But the early German books on quantum mechanics would not have had the same influence here?

Ullmo:

I suppose not. Of course, I must say that Sommerfeld was widely read. I remember that Langevin had advised me to read Sommerfeld, when I went to see him in ‘27 or ‘28. That was considered to be the very important book, but probably I read it in English because there was probably an English edition at that time because certainly I did not read it in German. Oui, c’est une reedition francaise probablement, c’est ca. I certainly did not read it in German, and I read it, so it must have been in English or in French. Et alors le livre de Hermann Weyl sur — a ete traduit de bonne heure par Proca d’ailleurs, si je me souviens bien, et a eu beaucoup d’influence en France.

Kuhn:

Was Born’s Atom Mechanics much read here? Were the books of Born and Jordan read?

Ullmo:

Non, surement pas. Nous connaissions la theorie des transformations de Born et Jordan, mais c’etait par Langevin, c’etait a travers Langevin. Le livre, n’ayant pas ete traduit, n’etait pas diffuse, n’etait pas connu. Par contre le livre de Dirac a tout-de-suite ete traduit, a tout-de-suite eu une grande extension.

Kuhn:

This point seems important enough to me to press you on — I wonder to what extent this difficulty in handling German at that time affected things? Do you know of anyone else who had it? Were there other people working with Langevin who would take the German sources from him?

Ullmo:

Surement, I’m absolutely sure of that. Je doute meme que de Broglie sut l’allemand.

Kuhn:

He may well not have. He surely knew some; he cites some German papers, one or two of which are quite obscure. But he could perfectly well have been put on to these by someone else. In any case, this is a point that had not occurred to me before; it’s certainly something to ask about — this actual command of German as a language.

Ullmo:

Francis Perrin, lui, certainement savait tres bien l’allemand, parce qu’il avait fait sa these avec Sommerfeld; done il avait travaille en Allemagne. Oui, c’etait a l’epoque justement un des points que je me souviens le mieux: le fait, tout-à-fait exceptionnel, d’aller travailler a l’etranger pour un Francais. Moi, c’est entendu, j’etais marie de bonne heure, j’avais des charges de famille et a cause de ca, je n’ai pas pu aller travailler a l’etranger. Mais enfin l’obstacle etait grand, ce n’etait pas quelque chose qu’on envisageait facilement. Je me souviens que quand (Vintair) qui etait un des mes camarades a l’Ecole Polytechnique,a ete en Angleterre, je crois a Cambridge ou a Oxford, c’etait vraiment tout-à-fait nouveau et exceptionnel. Le cas de Perrin ou de Solomon, c’etait vraiment du a ce qu’ils etaient le fils ou gendre, comme je le soulignais tout a l’heure, et que leur pere ou leur beau-pere savaient qu’il fallait les envoyer la-bas.

Kuhn:

There were no fellowships available?

Ullmo:

No, there were absolutely no scholarships in France. There were no scholarships for communication. You couldn’t do any career if you were not always on the move. You could not have time to go somewhere, or have time to work for yourself. Those scholarships did not exist, in fact.

Kuhn:

When you spoke earlier of the special subvention that Langevin had made for theoretical physics in ‘52, you said there were such things for experimental physics, and also for pure mathematics. Now, were those scholarships to enable you to study, or were those teaching positions?

Ullmo:

No, they were scholarships to study, specifically. But they were associated with the ordinary career. You went to a laboratory in the Sorbonne to make a thesis and so you were helped for a few years. It was the same thing if you could find a special [program] of mathematics and even mathematical scholarship — I don’t even remember if they did exist. I didn’t want to be too boastful, but I think I remember that having that scholarship for theoretical physics gave the lead for all kinds of theoretical scholarships. And mathematicians’ scholarships came only afterwards, but I’m not absolutely sure of this.

Kuhn:

So the typical scholarship before would have been to support a piece of research under the guidance of a professor in a laboratory in France as a part of getting your degree?

Ullmo:

Exactly, exactly; that was it. And even that Caisse Nationale des Sciences at the time was very new; I don’t know how many years it had been in existence, but it was perhaps three years. So probably there were not even mathematical scholarships in between.