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Oral History Transcript — Dr. Konrad Bleuler

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Interview with Dr. Konrad Bleuler
By Lillian Hoddeson
In Hirschegg, Austria
January 20, 1984

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Konrad Bleuler; January 20, 1984

ABSTRACT: In this interview, Konrad Bleuler discusses his memories of Wolfgang Pauli. Topics discussed include: Swiss Federal Institute of Technology Zurich; quantum physics; Werner Heisenberg; mathematics; Gregor Wentzel; Ernst Stueckelberg; Friedrich DŁrrenmatt; renormalization.

Transcript

Hoddeson:

Itís the twentieth of January, 1984, and this is Lillian Hoddeson, and Iím in Hirschegg speaking with Professor Bleuler about his memories of physics and Pauli in Zurich from 1932 up to Ď57, I guess. Is that correct?

Bleuler:

Thatís perfectly correct. So Iím glad to speak about my remembrances of the early days.

Hoddeson:

One point we should also clarify right on the tape, what the restrictions should be on this. Or would you prefer to do that later?

Bleuler:

Yes, we can do that later.

Hoddeson:

Okay.

Bleuler:

Letís see what comes out. Itís a great pleasure for me to speak about my early days in Zurich and all that I remember of my dear teacher, Wolfgang Pauli. I should first of all remind you that by now itís been only 25 years since Wolfgang Pauliís really early and untimely death in the year Ď57, on December 15th. You all know that Pauli was one of the greatest physicists collaborating in the very early days in the foundation of quantum mechanics and also taking part in an essential way in the development of general relativity. You all remember his great achievements, the Pauli principle, the introduction of spinors, the Pauli equation, the introduction of the neutrino, which was discovered much later, and just to give a very short summary [???], the foundation of quantum field theory together with his friend Werner Heisenberg. But it is not the point of this talk to speak about these scientific works which are well-known but to speak also about Pauliís personality, his life, his character and his deep thinking also in other domains. I met Pauli first when I started to study physics in 1932 at the Federal Institute in Zurich, where Pauli talked about theoretical physics. And already by that time, we heard a lot of well-known, interesting short stories about Pauli, stories which are to some extent well-known. But I should perhaps remind you from the very beginning, although there are a lot of pleasant — perhaps for certain people also unpleasant — stories about Pauli, he was known as a very sharp critic of everybody. I should really tell you that Pauli as a personality was very, very different from what you really think in general. And the personal contact with him led perhaps to a deeper understanding of his character, I might say to some extent of his tormented character, the problems of his life, and I might even say the tragedy of part of his life. So if youíll listen — and I will tell you some of the famous stories about Pauli — you will see all that already happened in the background of a man who sacrificed all his life to science. He also had enormous practical as well as personal, psychological problems. Perhaps some of the pleasant stories perhaps their outbreak [???] coming out of an enormous intention. But letís start with his young days. He was one of the young geniuses taking part in the very foundation, as I already said, of quantum theory. The average age of these great scientists — Heisenberg, Dirac, Jofgang [???], de Broglie, and Schrödinger — was at this critical period about 25. Pauli was the youngest and in fact the greatest genius because he was the only one who at this time knew as a body in fact all about the then-known modern mathematics, and that was the reason that he could create new developments which other people would not have created. I might just remind —

Hoddeson:

He was ahead in mathematics of Heisenberg and all the other people you mentioned?

Bleuler:

Yes. Might I just remind you that he wrote at the age of 19 a summary, a contribution to the famous volume of general physics, a contribution about relativity, special and general relativity, a contribution which later on it was his last contribution to science? It was published as a book which is even by now one of the best representations of general relativity. And itís just unbelievable that at the time mathematics used in this connection was generally absolutely unknown in physics. And he himself said, ďI wasĒ — if I might say the German word — ďa Wunderkind,Ē a prodigy. And perhaps that is also the reason that he was ... [???] to introduce this fundamental new notion of spinors because he knew of the existence of this mathematical concept in pure mathematics and you all know the fundamental importance of this notion on which then Dirac immediately afterwards built his famous equation. The same holds from his collaboration with Werner Heisenberg. I think the general agreement between these two — they were very friendly at a very young age — was that, so to speak, Heisenberg provided ideas, but Pauli worked out the mathematical structure and Heisenberg always thought, ďI need Pauliís help to work out things altogether.Ē

Hoddeson:

In what sense did Pauli need Heisenberg? Was it reciprocal?

Bleuler:

It was reciprocal in the way that Heisenberg of course was a man who had fantastic intuition. Heisenberg was, if I might complete that remark with my experience, I had also in much later years with Werner Heisenberg whom I knew very well in a later year after I went over to Germany, Heisenberg thought that one has just to have the right intuition how things should be in nature, what was the right nature of the thing. Then if the idea would be physically right, he thought mathematics will come around anyhow and put everything in order. Pauli put things in order but, as he revealed later, he did not always agree. He very often criticized the mathematics of a later year of his friend Heisenberg but also of many other scientists. And itís unbelievable how Pauli was really in full power of the mathematical structures to be used in physics. Itís a fact which at the time was absolutely not usual to a physicist to know all about mathematics which was known then. But after this scientific discussion, letís come back to our theme, what I remember from the early days and the youthful days of Pauli after the great discovery all these young peoples of course were very informal and did not apparently think at their young age about the distinguished German professors who were as you might well understand very, very formal people. So if I might present one of the pleasant Pauli stories it goes as follows: Pauli was known already to be most impractical, as I realized later on, already in his young age but was very well-known immediately — already at the age of 23, he was a great scientist — and he was invited in the house of a most distinguished professor. And he asked his host whether he would be so kind to explain to him how to find the place in town in order to buy something, I donít know what. And his professor, a very kind person, explained to him very much in detail knowing of course that Pauli was not very practical so everything seemed to work, Pauli went and came back and was kindly asked, ďPauli, did you find this place?Ē And Pauliís answer: ďOh yes, Herr Professor, it was very easy. Because if you do not speak about physics your explanations are perfectly clear.Ē And that was the way Pauli treated distinguished professors in the early years. It is in a way a tragic fact that Pauli, when he grew old and was one of the greatest scientists of his time, if he had now to discuss with younger scientists, kept on to make similar remarks and in this case of course these remarks against younger people were more or less dreadful. He forgot that he was no longer that young and that things were at the time accepted as the youthful humor of younger people. But letís come really to what I remember about studying with him in Zurich. His way of lecturing was very, very special. It seemed that when he had to lecture about the classical part of physics, like electrodynamics, thermodynamics that was his duty at the Federal Institute, there was only professor of theoretical physics who had to give all the courses, well these lectures were in fact for Pauli to check whether things also in classical physics were really in order. And he would turning his back to the students think looking at the blackboard and shaking his hands for several minutes to the formulas thinking ďis that really right?Ē One had the idea he had a discussion with somebody far behind or above him. I canít help thinking that, in the famous terms of Einstein, he was discussing not with the students who were completely forgotten, but he discussing with Him ďdoes it have to be like this?Ē And I remember, after thinking for several minutes on the blackboard, he eventually might turn around to the audience with a bright eye and say ďYes! Iíve got it. It must be like this.Ē Those were the explanations we had about how things had to be learned. But I also remember then as a research student later on taking part in the famous theoretical seminars in Zurich which were held together with a professor from the University at the time a well-known and unforgettable professor Gregor Wentzel who admired Pauli enormously and helped him I must say in practical facts and problems Pauli really had with the government.

Hoddeson:

Pauli had problems with the government?

Bleuler:

To say the truth, Iím not sure whether Iím allowed to say this, but Pauli being originally Austrian — I should have said that then; I have just seen that the 25 years of his death were remembered by putting his picture on an Austrian stamp — but being nominated as a full professor at a Federal Institute in Zurich he eventually asked to become a Swiss citizen. When he first asked having filled in all the tremendous conditions — you might know from other sources itís very very difficult to become if you have not been present when the so-called the Rittley Oath was taken in the 13th century, you have no chance to become Swiss — he was not accepted, unbelievable. And eventually, if I might say so, he was then later on immediately accepted, that means Swiss citizenship was pressed on him, at the very moment he got much, much later, the Nobel Prize. But thatís just a side remark about how Gregor Wentzel helped him in all respects. And helped him very much when it came to the question of Pauli being abroad in Princeton during the war that he could keep his position. I must really say that Professor Wentzel, whom I knew very, very well also as my teacher and supervisor later on, was really a very upright man and took science very seriously, and he was one of the few people who realized at that time in Zurich who Pauli was as a scientific genius. So these seminars took place in a common seminar having also Professor Ernst Stueckelberg, then a Professor in Geneva, also Stueckelberg being a well-known theoretician, his work was very much, if I might remind you of that fact, acknowledged by Richard Feynman. For example, his idea of the particle going back in time being interpreted as an antiparticle came as far as I know originally from Stueckelberg and many other great ideas. I remember one special seminar in which, of course this seminar could be rather called. High Court, with scientific papers in the docket, sometimes really sentenced to death. From that one might record Pauliís classification of scientific papers. There were two classes or else there were old and right. Or the other class, new and wrong. But hardly anything intermediate. If it was even worse, Pauli would have said ďitís not even wrong.Ē That was the kind of atmosphere. But all what is written in physics is either understood or else itís thrown away, and not this half-and-half, what we see at present. But then in this connection it was a search for truth. And for Pauli, a lecture hall was a kind of a holy place where only truth was allowed. And a wrong statement was a sacrilege, and in that sense one should understand his rather extremely sharp remarks he might make to some lecturer who seemed not to present things in a quite logical way. But coming to that special, to another special seminar is the following: Stueckelberg always knew really special — I might say prophetic — ideas. He gave a lecture and of course Pauli — it happened very often — didnít agree. And said ďyou are not allowed to say such things.Ē But you see, Stueckelberg being a prophet, heís not so easily stopped uttering his prophecies. So Pauli in despair menaced Stueckelberg with a stick and it seemed — I was not present myself but I was told — that the seminar ended like the war of Troy, Pauli, rather corpulent, with his stick after Stueckelberg around the table in the lecture hall. That was the kind of attitude at this period. But let me tell you also in this connection, apart from Pauliís extremely sharp remarks, he might have said in a general colloquium of general physics, jumping up in the middle of a lecture of a somewhat clumsy younger experimental physicist, ďI have never heard such a bad lecture,Ē and breaking out in his most characteristic and boyish laughter. Well the effect was dreadful. All the audience was quiet for several minutes. Nevertheless, for this poor young lecturer it was dreadful but the result I think was very important. The result was when we as young collaborators or assistants had to give lectures we knew that we had to prepare things and that we really had to think things over before giving such a lecture. That was dreadful but, just to say what I was starting to say, as a personality Pauli was — and this is usually unknown — a most charming man and I remember that we went in the evening together to have a drink. He might say towards 6 oíclock or so, ďNow Iím ready for CampariĒ that was his special drink. And it might have been a Viennese custom that he very much liked music, not that he played an instrument or that he knew about the technique and the science of music, but I think the sense of music, the message which you find in beautiful classical music of some great composers, went deep to his heart and I think he needed that in view of the fact, without going into details, of all the troubles he had in his life and his tormented soul. And so there was the idea of Pauliís, very kind ideas, to go to good concerts, not alone but in company with young collaborators and younger scientists. To give you some details, his assistant — that was in some later years — was at the time Charles Entz, who is now a professor at Geneva, he liked Entz very much and he was very helpful to him. He had among his duties one very special duty that was to look at the newspaper — Pauli was not practical enough to do that — and to look for the announcement of the concerts. And of course it was important to know Pauliís taste. As far as I remember, that meant that it was classical music from Bach to Schubert but by no means later. We sometimes made fun about this fact, Brahms was not accepted, although Pauli had been many years and he remembered sometimes his time in Hamburg as an Assistant to the distinguished Professor Lenz, you might remember his name from the Pauli-Lenz vector, or the Pauli-Lenz Runger [???] vector, from which Pauli gave before Schrodinger the first group-theoretic solution of the hydrogen atom which is usually not known. But coming back to music, the idea was that the concert program was studied and Entz had the duty to buy the tickets for Pauli and a small community of young collaborators, five or six, and so we went to the concert together. And I remember that upon hearing some pieces of music, some special pieces of music, that Pauli was deeply impressed, really deeply impressed; it was not just to listen to music of all the famous composers. I remember especially that we heard by a string quartet one of the late Schubert quartets — in fact a quintet with two celli — in C major with this wonderful long adagio which impressed Pauli tremendously. One realized that this music was part of his need for his soul, and it was a kind of medicine for all the troubles he had suffered from and I remember as a consequence of this concert, Pauli sat down and read a biography about Schubert written by Towngardner who also wrote about Mozart, and I think for Pauli it was of great interest to understand how that wonderful idea — in this case in music — could be created, how they come about, how it was possible that it has this effect to people who lived much later in a quite different society, and I think in this connection I should say that in a later period Pauli went also into study of philosophy, psychology, and to a certain extent, also in history of science in particular his study. Itís not the Kepler orbit that he was interested in but the general ideas of Kepler about harmonies in space, the Kepler spheres and geometric figures, and I think there are important letters of Pauli in his later years — unfortunately not yet published — where he discusses really the question of how fundamental ideas in physics were really created. What was the real origin, how is it related to psychology of the people and in that respect he was very much impressed by some ideas of the well-known psychiatrist Jung, although Iím sorry to say right away I donít have the feeling, itís not my impression that Jung very well understood Pauli and the importance of the relation between psychology and perhaps this notion of archetypes in scientific research because Pauli was not of the opinion that you could just create theoretical physics out of looking at all the experimental data. Pauli very much stuck to the data, they are there, but thatís not the only way to find the underlying fundamental ideas of the general laws which have I think a beauty in itself as an abstract mathematical and beautiful and natural structure and I think he was also realizing this problem why is it that fundamental laws exist in that extent and have such a natural structure if you look at this structure in an abstract way. He might say, because abstract thinking at the time was not very customary, ďmore abstract but simplerĒ and I think that is one of the greatest statements to tell all young theoreticians. But before coming to his really later — and as I should say rather tragic — years. I might tell perhaps a more pleasant sort of story about Pauliís relation with the well-known Swiss playwright, Friedrich Durrenmatt, who wrote as is perhaps well-known in the United States, The Visit (Der Besuch der Alten Dame), but also another play, the Physicists (Die Physiker). And I knew Durrenmatt quite well because we were both born nearly at the same place in the Emental [???] near Burm and I have a lot of personal contacts, and Durrenmatt was tremendously interested in the basis of science. He himself had a small telescope to observe the stars and I remember that Durrenmatt was the first who told me at the time of the existence of these clusters, of these new objects in the universe, and Durrenmatt had somehow the idea of extension and the greatness of the universe in large and extremely small dimensions and he had somehow the idea of what all the laws and ideas behind that could be, and on the other hand I think as a very critical writer he also realized the restrictions imposed on the human brain and so he was really interested to know that these great scientists who had made these fundamental discoveries. I donít know the English expression — itís a famous word in German — the Zauberlehrlingen (sorcererís apprentices), so at my friend Durrenmattís request, I brought some of the best specimens of these scientists to his home, among others Pauli and as far as I remember Professor Bardeen, Hans Jensen, Rudolf Mossbauer, and several others, and Durrenmatt was so very similar to Pauli. I think he should be considered as Pauli in literature, extremely sharp and critical, but personally very kind and very pleasant. Durrenmatt offered — and he was a specialist also in that domain — the very best wines, the very best French chateau wines, to his guests and got them to speak. I remember a contact between Pauli and Durrenmatt was immediately established without any problem. Well but of course what these great scientists did not realize was then when Durrenmatt wrote his play The Physicists he was a kind of Swiss Dante. As is well known, Dante [???] the greatest of his contemporaries, also the highest in literatureís hierarchy, into the inferno; so Durrenmatt had the scientists played in the madhouse, in the asylum. Nevertheless, this play was sometimes criticized as being slightly dreadful. Nevertheless, at the basis a very interesting I might say from the mental standpoint about the definition of what could be called a real scientific discovery, a statement which goes like this: first of all a real fundamental statement must be formulated in one relatively short sentence, and the point is, if this sentence once came out of the mouth of the one who discovered that, if it was his idea and it was understood, it turns out it is absolutely impossible to take it back. That means if you say ďitís wrong, I never meant this, please forget about it,Ē you will never take it back, and that was the original idea of this play, that the idea is Einstein wants to take his idea about energy and matter, producing all this enormous energy; thatís real, but that sad fact is not usually understood. And in this connection, we had also — itís a pity we had no tape recorder at this time; that would have been much better — when I organized a conference on new developments in physics, we had Durrenmatt giving an after-dinner speech, about his ideas about physicists. Well that is all very pleasant but with that I think we come to the latest years of Pauli that means to the year Ď56, actually itís the year before he died really an untimely death. It was related to an idea, going again back with all intensively to scientific research. All of a sudden, he took up some much earlier idea, which he had never agreed with before, of Heisenbergís to make, to produce a model of particles — we would now say hadrons but that was not the notion — in which Heisenberg had been convinced already as early as Ď46, known in a well-known article, that all these particles — it was then at the moment of the discovery of the pion by Okialidi [???] — are not elementary and should have an internal structure and he drew up a model and a model which unfortunately at the time was called by some journalists who were present at the seminar with a dreadful German expression (Weltformel) that means more- than-absolute, universal formula, but in fact it was a model to say how the inner structure of a particle could look like and how one could obtain the mass of the energy eigenvalue of some more fundamental interaction. If you look at this model — it was, as you all know, heavily criticized — itís very similar I might say what you call the bag model. But Pauli suddenly got hold of this, although he had rejected it many times, and Heisenberg who needed Pauliís help for the mathematics was really enthusiastic that eventually after having tried many times for several years, that Pauli dreamt [???] on that and thought with this idea or structure of Heisenberg showing what was absolutely new at that period, a new inner structure of the fundamental heavier particles that with that model, with an enormous of course generalization of fundamental concepts, he might get around some problems he always fought in field theory. To tell the truth he never quite agreed with the so-called renormalization, he might say ďI donít want to renormalized, please.Ē So with an enormous effort, he went into that research, and one had the impression that he must have somehow felt, although he didnít know the reason, that little time was left for his research, which actually was realized a year later. I have the feeling, I know I donít have definite signs that this lethal disease — it was a cancer — had already developed I donít know how far but and Pauli thought although all his achievements are well- known I have to get first the things are not in order as they are by now and itís absolutely needed to go to a first step and so he worked practically day and night for several weeks and its well-known and I remember during that period that Pauli sometimes after having been depressed he was really enthusiastic and he had moments where he thought that everything was understood; he might stop in the middle of the road and say ďIíve understood everything.Ē But of course the world was not to be renewed in such a short period and as far as I see and that is generally not known that this period of about two to three months ended practically with a nervous breakdown in that state of being worn out to a large extent for reasons mishaps in Zurich not being understood he accepted an invitation to the United States and left in this state of depression and of course during all that period the collaboration between Pauli and Heisenberg of course [???] because they were the best-known scientists, and people wanted to know what really had happened and what about this world formula which unfortunately went to all the newspapers, so it was technically not the final idea by any means and Pauli didnít want to have it published. And so Pauli, people said that might be the new theory, and this great old man will again renew physics, he was as far as I heard invited to give a seminar I think in Columbia where all the young famous scientists had assembled to ask questions.

Hoddeson:

Including Gell-Mann?

Bleuler:

I donít exactly, but most of the now very well-known great theoreticians were there and asked all kinds of questions: how does it really work? And to say the truth, Pauli gave in. He was sincere to say openly that although in his state of mind — it was absolutely not known to all the members of this seminar that Pauli had practically worked too much and practically suffered a breakdown. He gave in and said, ďI cannot answer.Ē What I do not understand even now and I should really explain that — of course it was a great misunderstanding — that seminar was considered a kind of victory of the younger generation over the great old man. And I had seen Pauli afterwards, occasionally in California. He was very depressed, and thought ďwell, no I donít see any further,Ē and still went looking at the development. Now, a quarter of a century later, one could ask and friends of my mine asked what are you ... [???] Because in relation to this discussion, most of the concepts or some of the most fundamental concepts which are now really at the basis of modern theory like degeneration of the vacuum, the Goldstone particle, the S-matrix, and the fundamental idea to calculate masses as eigenvalues from a new kind of a system, that was all there. And at this time, the official theory was completely different, it was all built on analytic continuation or sometimes called californiazation of physics to find everything as singularities in the complex plane, the then theories by now are completely forgotten, but as I just said, these fundamental concepts, especially the degeneration of the vacuum — Heisenberg was dreadfully criticized for this idea as I remember in some conferences — are now the basis. Pauli nevertheless was very depressed and I remember meeting him, he had to make a contribution to a conference on field theory and his contribution was not a scientific one, but it was a short but very impressive and as far as I see, never-published verses. And I just remember, it was to a German conference so I have to say it first in German and I will try a translation because it has a classical rhythm of classical German poetry Herrlich entstrůmet dem Mund der gelehrten der Hamburg [???] ilber dem Grund der Physik erscheint er wie bleuliche Dunst. That was his contribution to the then-famous field theoreticians. That was his final comment about field theory because his idea had been that field theory in the conventional form doesnít work altogether. If I might try an English translation but that will lose this classical rhythm, itís the form of some Schiller poetry. Wonderfully flows out of the mouth of the learned of Hamburg [???] always the ground of physics appears it as bluish as dust I think that was his last scientific contribution which really showed how depressed he was. In this kind of a depression he also because he thought it was really a mishap of all this correlation [???] he terribly attacked in an official conference that is well-known, Werner Heisenberg for having seduced him into this work, but I canít help thinking it was one of his kind of boyish reactions as I have told you in an earlier period. I should really say that he met later at the Lake Como in this wonderful place, Larenna [???], he met Heisenberg again — He felt, not knew, that it was very late in his life — ďletís make friends again. Look Werner you have young collaborators to go on, I am not able any longer to contribute much.Ē And there we come to the last moment I met Pauli on the occasion of a small conference taking place on beautiful Jura [???] mountains with wonderful forests and occasionally we went on long walks through the forests of these mountains, Pauli starting not a discussion it was in fact remembering and criticizing his scientific life, saying essentially that well what he had done in the twenties that might have been quite all right, but all the later work in this later period after the war it was not the right thing. I have not achieved what I really wanted, he was convinced that a new decisive step as important as the development which took place in the twenties should occur again that the deeper understanding was absolutely needed and I remember that walking so — it was not prepared — for hours through this forest, we came through a place where there was an old chapel in the middle of these woods and Pauli went in and remained still and quiet for several minutes. A few weeks later, he left us forever. I think you should remember Wolfgang Pauli, in spite of mistakes he might have made, as one of the most devoted scientists and a sincere scientist and a fighter for truth.

Hoddeson:

Excellent, excellent. I wonder if I can ask one question which wonít delay us too much. Since you knew Pauli for so long, and Heisenberg also, if you could comment a little bit more on the changing relationship between those two from the period of the 20s which was before your time but of course you know about it up to the late 50s. As I understand it, the relationship was a purely scientific one; they were friends, but it was mainly in science where they met.

Bleuler:

It was mainly in science.

Hoddeson:

They had quite different personalities.

Bleuler:

They were completely different personalities. But I knew also of course several of these well-known scientists also, Professor Jofgarten [???], I still remember Niels Bohr a little bit, and also great scientists like Christian Muller and old Professor Manne Siegbahní [???] and I have seen Fermi although I did not know him personally, all of these scientists had perfectly different character, and as characters Pauli and Heisenberg were exactly opposite. Heisenberg was a most correct man, who made everything in perfect order, he was correct, and could do everything. He was a perfect car driver, in contrast to Pauli; there are fantastic stories about his driving cars for example. Heisenberg was also interested in music, he was a perfect piano player, he had a great family, and his children were very kind and very talented. And that was lacking with Pauli. He might, and Heisenberg told me once that Pauli — because they had lot of personal contact because they were together in Copenhagen with all that young generation — made to him a kind of a confession, he said, look Werner, my life is dreadful. Iím sitting around in pubs, and have no real life. And Heisenberg made a very interesting analysis, and said ďwell everybody has to live his life.Ē So they were absolute, opposites, but I think it was a great friendship. Perhaps for this reason, because they were so different.

Hoddeson:

Were they friendly personally although they were so different?

Bleuler:

They had to work together in a very intense way, and I think in Copenhagen, all the young generation of great scientists was together to a large extent in Copenhagen and they all knew each other. They had very personal contact.

Hoddeson:

The other part of the question has to deal with whether the nature of the scientific relationship.

Hoddeson:

The way you painted the relationship, Heisenberg was the more intuitive person who offered ideas and Pauli was the one who was more rigorous —

Bleuler:

And criticized all those ideas.

Hoddeson:

Criticized and worked them out, thought about them deeply, and so on. And had the mathematical facility to do that.

Bleuler:

Heisenberg had definitely not.

Hoddeson:

Yes. Is this characterization true throughout their scientific working relationship or was there a change?

Bleuler:

No, absolutely throughout. Thatís the reason when in these latest years this new collaboration started, it was again the same. Pauli worked out the mathematics and Heisenberg knew that he needed the help of Pauli and I remember that Pauli often said ďwell, I have to brush up Heisenbergís mathematics.Ē All in the later years, and also when the new development came about, renormalization, by Schwinger, Dyson and Feynman, Pauli looked in a very critical mathematical way at these methods and improved these methods by trying to make a more rigorous mathematical representation of the renormalization process, the so-called Pauli-Wheeler (?) renormalization and he very critically looked at it, and when renormalization was new, Pauli rejected it, he said ďitís not rigorous, I do not believe it.Ē I remember it was a special moment when Professor Rabi suddenly appeared in Zurich together with Julian Schwinger for a private seminar, not an official seminar, to try to explain to Pauli the success of the theory. So Pauli well agreed I could say as a working hypothesis, but he was not convinced in his deep thinking that it was the final solution. And I think that will be remembered. I would by no means criticize renormalization, itís an enormous success. But itís another question about the fundamental theory.

Hoddeson:

One moment. This as far as release of this tape, itís mainly to friends.

Bleuler:

Itís all to friends.

Hoddeson:

Yes, because of some of this.

Bleuler:

Itís of course very personal and should not be used, at least not for the moment, for publication in this form.

Hoddeson:

Okay thatís good.