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Oral History Transcript — Dr. Walter Heitler

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Interview with Dr. Walter Heitler
By John L. Heilbron
In Zurich
March 19, 1963

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Walter Heitler; March 19, 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: Hans Albrecht Bethe, Patrick Maynard Stuart Blackett, K. Boehm, Niels Henrik David Bohr, Max Born, Georg Bredig, Louis de Broglie, Paul Adrien Maurice Dirac, Paul Ehrenfest, Albert Einstein, James Franck, Karl Ferdinand Herzfeld, Karisruhe Technische Hochschule, Ralph de Laer Kronig, K. Loewner, Fritz London, G. Rumer, Erwin SchrOdinger, Arnold Sommerfeld, Otto Stern, Gregor Wentzel, Hermann Weyl, Wilhelm Wien, Hideki Yukawa; Universitat Berlin, University of Bristol, Copenhagen Conferences, Deutsche Physikalische Gesellschaft meeting (Freiburg), Universitat Gottingen, Universitat MŁnchen, Zurich Eidgenoessische Technische Hochschule, and Universitat Zurich.

Transcript

Session I | Session II

Heilbron:

Well, if you would be so kind as to make a few remarks about Herzfeld --

Heitler:

Yes. Well, Herzfeld was in the department of theoretical physics with Sommerfeld; he was just the second professor there. He considered himself, by all means, a physicist and not a chemist. The only difference was that Herzfeld represented another field at that time - also very important or just as important as any other part of physics -- he represented statistics, thermodynamics, and the theory of liquids, solids and gases. As you may remember, he has written a handbook article on the subject which is still, I think, a standard work. ĎKinetic theory of gasesí would perhaps best describe his line. When I went to ask Herzfeld for a suggestion for a Ph.D. thesis for me, it was by all means so that I considered myself a physicist, but with an inclination towards this type of field. It was not because I thought I still was a chemist or something like that.

Heilbron:

Was Herzfeldís interest in quantum physics just a side line?

Heitler:

It was just as acute as anybody elseís, but, you see, he represented that line of quantum physics which originated from Planck, Boltzmann, etc. and, of course1 quantum phenomena there were at the time just as relevant as atomic spectra, I should say. I dare say one could get a great deal of information about quantum physics from the study of such phenomena. Well, just remember the historical role that statistics has played in the development of quantum theory and even quantum mechanics because the starting point was really the Bose statistics. At last they were the starting point of the Bose and Einstein, de Broglie and Schrodinger line, as we have discussed it yesterday.

Heilbron:

Did Sommerfeld and Herzfeld each have a seminar, or did they have a joint one?

Heitler:

No, no; there was a joint seminar, and another one who joined in was Wentzel. He had interests on both sides, but as I said yesterday, he also worked on statistical problems for a time. He gave a lecture which was really very good, and I derived a great deal from it -- the fluctuations in gases and so on.

Heilbron:

Did Herzfeld work with the students as Sommerfeld did, talking with them and so on?

Heitler:

Yes. Yes, he did. It was a very good atmosphere, and there was very good agreement between Sommerfeld, Herzfeld and Wentzel. Of course, Sommerfeld was by far the, what do you call it, more senior of the three, and so, of course his weight was a great deal more than that of any of the others as it is in every department1after all. But I should say theoretical physics was represented by these three people. Wentzel was Privatdozent, that is, lecturer. He was not a professor.

Heilbron:

Did students generally participate in seminars, give them?

Heitler:

Yes. Yes, the seminar talks were given by students as a rule. At the beginning of the term one made a program, and then the various subjects were distributed among the students. Occasionally also Wentzel or Herzfeld would give a seminar, I believe, but as a rule it was the students who had to give seminar talks on a prescribed subject, with prescribed literature.

Heilbron:

With prescribed literature?

Heitler:

With prescribed literature. They said, ďYou study this paper, and then talk about it at the seminar.Ē

Heilbron:

And would those be gentlemanly affairs, or was one criticized rather sharply?

Heitler:

Oh, if it was bad, one was criticized, of course. Of course there was a discussion in between, and if you talked nonsense, then it was immediately criticized by one of the participants.

Heilbron:

You said you wanted to complete some remarks.

Heitler:

Yes. Well then, let us go back to the Gottingen period. After this paper with Rumer which I described yesterday there was one more paper which I think I ought to mention in this connection, and it contained the following result. As I said yesterday, in a chemical formula like the one I put on the blackboard there are several structures which cannot be omitted because they contribute very decisively to the energy. Secondly, they are necessary for the understanding of activation energies. Yet the finished molecule is represented by a wave function which is a superposition of all these. Now what remains to be seen is what justification the chemical formula has, and the justification lies in the fact that you can show that among all these structures, one structure is always dominant. And that is just the one which is described by the chemical formula. That is to say, if you take the whole wave function, you can regard the coefficients of the wave functions of the various structures as the probabilities for the occurrence of these structures. It turns out that the one structure which corresponds to the chemical formula exactly is the most probable one. And that was shown in a paper which I published in the Physical Review; I was in America then for a semester at the University of Columbus, Ohio, as a visiting professor.

That was in the summer of 1931. And this paper is published in the Physical Review, Vol. 38, 1931, p. 243. Well, then if you would like to make the list complete, there was one more paper in the Gottingen period with Gibson which is again on a statistical problem. It concerned the equilibrium of dissociation of a diatomic molecule; it happened that we had all the necessary data to calculate this equilibrium with great accuracy, and we did and found that it agreed 100% with the experiments. Now that is rather trivial from our present point of view, but was perhaps not quite so trivial then. This showed that when you have the molecular data, the quantum data, the quantum energy levels complete, and you have the dissociation energy, then the statistics is a perfect means of calculating with practically 100% accuracy the equilibrium. But, of course, this paper is perhaps no longer important; there are many more examples now. Well, then in the list of publications, Iím sure you know the Handbook article which is a summary of all the chemical work. Omitting a few minor papers which are not important, that completes this addition.

Heilbron:

When you were at Gottingen, you lectured on chemical questions and the quantum electrodynamics?

Heitler:

No, no, no. The lectures I gave in Gottingen were on various subjects. We were quite free to lecture on whatever subject we liked; there was no prescription in any way and no curriculum which had to be completed except that there was the main course of lectures on classical theoretical physics which was usually given by Born. Once or twice when Born was not inclined, or was away, either Nordheim or I gave the main course. I gave it once on optics, but in general the lectures I gave were on --. One was on statistics, statistical mechanics; another was on special relativity, and another on general relativity. And once I lectured on the theory of the electron -- Lorentz theory of the electron, and once on group theory, on the connection of group theory with quantum mechanics, and so on. But I never lectured especially on the chemical bond; I did that in America because it was especially wanted. Then there was another question about Gottingen. Yes, you asked whether quantum mechanics was included in the curriculum. It was not; not yet. The quantum mechanics was not part of the general education of a physicist yet; it was too new.

Heilbron:

Did Born give a general introduction to it? Do you recall?

Heitler:

I donít remember; I donít think he did. Not as far as I remember. He always gave the main course of lectures; of course we had it in the seminar. There was a seminar in Gottingen too; again, always on a variety of new publications, and there was of course Diracís theory -- Diracís relativistic equation, and so on.

Heilbron:

Was that a student affair too?

Heitler:

That was exactly the same as in Munich; it was a student affair in general, but it did not exclude professors lecturing. I remember for example that Weyl gave a seminar, or I think even two seminars, on the further development of this group theory method in the theory of chemical bonds. He added something to it, and in the first edition of his book this was included.

Heilbron:

Were the students expected to understand what one another were saying?

Heitler:

Yes, these were the senior students. The seminar was attended by students well, letís say who worked for their Ph.D., and of course the more senior people do. All the lecturers, the assistants, and so on were present. That was at that time the usual arrangement of the seminar. Students beyond the 3rd or 4th year attended.

Heilbron:

When did you begin to select the topic which would succeed to your program of the chemical bond once you had completed --. When did you begin the quantum electrodynamics then?

Heitler:

Well, I began that immediately after this paper with Rumer was published. I thought then my job in this program was finished. Well, as I said, there were a few later additions -- this little paper with Poeschl and so on. But I had started in Gottingen in, I think, 1932 to change the subject and to work on quantum electrodynamics. Of course, quantum electrodynamics then represented the fundamental unsolved problem, and it perhaps still does. Well, then I thought that high energy phenomena would give some key to the further development of quantum electrodynamics, and so I started to work out the problem of Bremsstrahlung in Gottingen. Well, in my first paper about it I merely estimated the order of magnitude, and then I continued when I left Germany -- I continued my interests in England after I had to leave Germany owing to the Hitler persecution. Well, at the same time then Diracís Ďholesí theory appeared, and also the discovery of the positive electron whence it was clear that the Ďholesí theory was, after all, more or less correct. With the work of Bremsstrahlung on hand I could see -- that was easy enough -- that this was practically the same process; Bremsstrahlung and the creation of electron pairs. So I included the electron pairs and we could show them. Bethe joined this work in Bristol, but his contribution was mainly taking into account the screening effects which are quantitatively important. Then we could show that there was really perfect agreement between the experiment and the theory, thus proving Diracís holes theory to be correct. As a consequence of this I published a few more papers in Bristol all concerned with electron pairs, with positive electrons, annihilation, and various other processes. Well, I think that paper then proved the soundness of Diracís holes theory.

Heilbron:

Had you any clear-out program when you began the quantum electrodynamics, as you had with the --

Heitler:

Yes. I always followed -- and perhaps some critics would say I followed too long -- a definite program. And this program was then the study of high energy phenomena within quantum electrodynamics and within the theory of the positive electrons. Now the two subjects are always taken as one; at that time it wasnít quite so. In the hope of getting further information, I had one special problem in mind: ďIs there any breakdown of the theoretical predictions at high energies?Ē You see, if quantum electrodynamics is wrong, then there must be somehow a breakdown at very high energies. At first we believed that to be the case. In the paper with Bethe on pair-production and Bremsstrahlung there is really a statement which later on turned out to be false, namely, that this was a contradiction. The theoretical results were in contradiction to the high energy experiments derived for the cosmic radiation. The interest in high energy of course led me into cosmic radiation. The mistake was due to the following fact: there are very penetrating particles in cosmic radiation, and these are now known as mu mesons. But at that time nobody would think of a new particle, and the cosmic ray people themselves, including Blackett, believed they were electrons. Later on Blackett discovered cosmic ray showers. Now these showers were the next major step in my work.

These showers could be explained as series of successive pair productions, thus contradicting again our former statement that there was a breakdown of quantum electrodynamics at high energies. This was a paper together with Bhabha, who is now in Bombay, and simultaneously the same thing was done by Oppenheimer and (Carlson), I think it was. It showed that at very high energies you have the succession of pair creations when the photon passes through a thickness of material, and the cosmic ray showers were explained in this way. Blackett did not believe it at first; Blackett thought it was nonsense because of the existence of these penetrating particles. Blackett refused for a time to acknowledge the theory of cascade showers -- as they were called. Only when it appeared a little later, perhaps a year later, that these penetrating particles might just be the particles predicted by Yukawa and therefore not be electrons, only then he agreed that the interpretation of the cascade showers was correct. Well, there is a story, of course, about these penetrating particles.

There was an excuse for Blackettís not believing that the cascade theory was correct because there was a remark in our paper saying that these penetrating particles are probably protons, and Blackett could show then that they were not, but they had this intermediate mass. Well, the whole thing was cleared up when Yukawa published his first paper on his theory; you know it was a very short paper in which there was practically only text and no formulae, but which contained all the essential ideas. Then the identification of these penetrating particles with the Yukawa particles was almost evident. Well, later on this bad to be modified; the Yukawa particles became the pi mesons and the penetrating particles were the results of the decay of the mu mesons. With this paper by Yukawa now becoming so to speak true (???), I mean it was clear that the essential ideas were correct -- my own research program also became clear once again. As I was predominantly interested in high energy, and believed that this was the key to the future, which probably it still is, I of course started work immediately on the mesons theory which kept me busy right through the war until 1946 or 1948, when we worked out the theory of the atomic mesons simultaneously with Yukawa and his collaborators. I worked with Kemmer and with Frohlich, and there were a few things which I think were contained first in our paper. That was the explanation of the anomalous magnetic moments for protons and neutrons.

Heilbron:

Was Yukawaís paper immediately known?

Heitler:

It was not immediately noted, not quite. The first paper appeared in 1935, and it was not taken in by European and American physicists, I believe, until the situation in cosmic rays became such that there was a great deal of probability for this paperís containing some truth. It took three years before it was really acknowledged. It appeared in 1935, and only in 1937, 1938 was it continued and worked out into a reasonable theory.

Heilbron:

Do you know how it became known at all? Wasnít it published in a Japanese journal?

Heitler:

It was published in a Japanese journal, and I donít quite know how it became known, but I heard it from somebody. I read it immediately after I was convinced that there was a problem concerning the penetrating particles in cosmic radiation. I became convinced that it was correct because these penetrating particles could not be electrons and could not be protons -- where Blackett was right. Then there was a rather exciting conference in Copenhagen where the whole business was then explained and cleared up.

Heilbron:

It was agreed to let a new particle --

Heitler:

It was agreed, and Blackett agreed, and everybody agreed that there was a new particle. Then this was also the starting point for the work on meson theory.

Heilbron:

Were the Copenhagen conferences just irregular affairs?

Heitler:

During a certain period they took place every year, and they were at Easter. I remember when the first conference took place. After I had come to Gottingen and after the rather unfortunate position I had in Copenhagen as a Rockefeller Fellow, I had a desire to go to Copenhagen once more and talk to these people and to learn about their point of view at this time -- not as a guest -- but as a proper member of the Institute, if only for a few weeks. So I wrote and asked Bohr, ďMay I come?Ē And I got a letter saying that I would be welcome, and shortly afterwards I received a telegram saying that they had decided to hold a conference. That was the first of a series of conferences which went on -- I donít know when it was, 1927 or 1928 or so every year at least right up to 1933. Then there was a bit of an interval owing to the political complications, and they were resumed again later on until the war broke out.

Heilbron:

These were by invitation? People were invited to attend these conferences, selected --?

Heitler:

It was always the same people; they were delightful conferences. They were small -- perhaps 20 or 30 people and it was just the people who would be interested in modern theoretical physics and quantum mechanics. Dirac was often there; Rosenfeld and Nordheim were there; Klein and Heisenberg -- well, these people. Jordan was often there; Ehrenfest was (a regular member). They were delightful conferences -- always very fruitful; there was always a fresh idea which came out from there.

Heilbron:

Was Ehrenfest the leading spirit of those?

Heitler:

Yes. Not as a research scientist -- that he never was. But be was leading with his clear and profound understanding, and he was leading with his criticism, and his wit. Kramers was also a very frequent member; Lise Meitner was also there and Kronig.

Heilbron:

Could one notice that Ehrenfest was getting more and more disturbed about the --?

Heitler:

No. No. The last conference before the break until after Hitlerís power was in the spring 1933. He attended the conference, was lively as ever, and he even said to me -- I was on my way to England then as a refugee -- as well as to Nordheim, to come to Leiden again and so on. He went back after the conference to Leiden, and there it happened. It was not to be noticed in Copenhagen. I got the news immediately when I arrived in England, a few days later. Well, perhaps his closer friends would have noticed something. I donít know. Well, you know he had a child who was a mental defective, or something like that; I think this contributed as well as the political developments. Perhaps various other reasons gave him the -- made the decision for him.

Heilbron:

How did you get to Bristol?

Heitler:

Well, there was always some connection between Gottingen and Bristol; the young scientists often spent a year in Bristol; it was a sort of fellowship. In fact it was more for junior people -- people just after their doctorates. And well, there was this difficult situation after Hitler many scientists had to leave. Born wrote to Bristol to say that they must take one of these displaced scholars, and, of course, then that was my first job in Bristol. Then later on I got a better position.

Heilbron:

Was it clear among those who were leaving that they were going to be leaving essentially for good?

Heitler:

Well, I should think the majority knew, some of course hoped that Hitler would be a temporary affair, but there was little hope that it would be over soon.

Heilbron:

Were there a series of increasingly disagreeable incidents at Gottingen or was it just the coming to power of Hitler that [brought on animosities]?

Heitler:

[It was only concerned] with Hitler coming to power. The trouble in Gottingen started immediately after Hitler came to power, not before. There was nothing, really nothing before; well, at least not in the science faculty. We never noticed anything before, but probably there were a great deal of Nazis, perhaps in other faculties,

Heilbron:

And that was probably true of Munich as well?

Heitler:

Oh, surely it was. But Sommerfeldís department was clean, even after Hitler came to power.

Heilbron:

I also wanted to ask you about the relations between the schools here [in Zurich], between the E.T.H. and the University. Are there many joint themes?

Heitler:

Yes. In physics the colloquium is jointly and the theoretical seminar is jointly.

Heilbron:

Has that always been the case?

Heitler:

That has always been the case, well, at least for a very long time. I donít remember if it was the case when I was here with London and Schrodinger; I donít remember. But at any rate it was the case when I came here; it was the case when Pauli was at E.T.H. and Wentzel had my chair here. There are, of course, discussions between the members of the two departments.

Heilbron:

Is there any particular reason why a student in theoretical physics would now choose one or the other?

Heitler:

Well, the lines represented are somewhat different. I often get students who have started in the E.T.H., get their diploma there, and then come to me for a Ph.D. These are students who would like more, well let us say, a subject more on physical lines, rather than on formal lines. The two professors now at the E.T.H. represent the more abstract line of field theory, which is not what I am doing, and vice-versa at (???) too.

Heilbron:

How long have you been preoccupied with the sorts of issues that you discuss in your little book about science?

Heitler:

Oh, the new philosophical book; oh, I see, you want to come to this. Well, a very long time in fact. The purely philosophical thoughts were really on my mind for 10, 20 or 30 years, more or less. But the decision to publish this now came in connection with the rather dangerous situation in which we find ourselves now, and which, I think, everybody agrees has something to do with science, to put it mildly. Probably without this situation I would never have thought of publishing this, but of course it is also true that when I decided to write something about these things that I had to think it through thoroughly once again. It wasnít just all prepared before.

Heilbron:

I was wondering whether part of the reason that you had written it was not only the political situation of the sciences but also the fact that, at least to us, physics appears to be a much different thing socially now than it was in the Twenties and early Thirties?

Heitler:

Yes. That is true.

Heilbron:

How great do you find this difference?

Heitler:

I think there is an enormous difference. The scientific life right up to the war was completely different from what it is now. Well, Iím talking about my own subject; it may have been different in chemistry; I donít know. But in my own subject, the atmosphere is completely changed. Science was done on a small scale; it was usually done by people who had, not the obligations to technology, or any other obligations in mind. The number of theoretical physicists was small, and the amount of money available to them was also small, and the number of jobs for them was very limited. It was not easy for a young scientist to enter the University career. He had really to be very good or to be very lucky in order to manage; and especially in the years of the great financial depression, 1929 to 1933 there were just a few possibilities. Thatís all very different now.

Heilbron:

Were there many people at that time who were desperate for chairs? Were there many people despondent about it?

Heitler:

There were quite a number of second class physicists who did not manage; that is certainly true. Well, I remember in Gottingen there was some difficulty. Born had two assistants and they tried to eliminate one; the government tried for reasons of economy, and only after a severe fight could Born succeed in keeping the two positions. So it was that quite a lot of people waited for a chair for instance, myself.

Heilbron:

Were there, many people who, expecting careers had gone through the doctorís degree and then couldnít get them?

Heitler:

Oh, I think there were many. Yes, I think that was true; some went into industry, and so on. There were not many people who got a doctorís degree in theoretical physics with the intention of starting a university career. I think a doctor in theoretical physics was rather rare, perhaps one a year or so, not much more.

Heilbron:

You said yesterday that only with great bravado could one look toward a university career without some considerable family financial support, and soon.

Heitler:

Well, in the years before the First World War, and the years following, it was really so. You could only start a university career if you had money to keep yourself in life. After the war this changed gradually by the fact that you could be assistant to some professor; a number of assistantships and a few fellowships were created. (I think some of the) Academies established some fellowships and so on, other organizations too; and then you could start the university career by becoming an assistant to some professor and then becoming Privatdozent and so on. I donít know if it was possible in all subjects, but it certainly was in theoretical physics. So the first thing you had to do was to get an assistantship, in some department. Then if you were good, you were saved, so to speak. If you could produce enough new ideas and publish something, then it was all right. It was good to publish something.

Heilbron:

One could live on this system?

Heitler:

Oh, yes. Yes, one could live; not very lavishly, but you could live, you could live.

Heilbron:

And that was the first rung; once one had got on that, if it went reasonably --

Heitler:

Yes, well, you could become Privatdozent, which had no financial advantage, but then if you had published a lot, you could hope for a professorship sooner or later. Sometimes it took a long time. And there was one, perhaps somewhat tragic, type of person -- those who had gone to the stage of Privatdozent, and never got a chair. Never got a professorship. The eternal Privatdozent with a small income, lecturing, and so on, and this was a somewhat tragic affair.

Heilbron:

Were there many who --

Heitler:

There was one in Gottingen; he was called Hertz; I have forgotten his Christian name.

Heilbron:

Paul?

Heitler:

Paul, yes, Paul Hertz; you are right. He was quite an elderly man, and he never got a chair. There was that danger, you see.

Heilbron:

Were part of the sort of dimensions you want to put into physics contained in the outlooks of people at that time?

Heitler:

Well, I really canít say much about that, at least as far as the time a few 10ís of years back is concerned, but I can tell you something now. I didnít discuss this sort of thing much with physicists, but I did discuss it now [recently] with some scientists, a few physicists, a few biologists and so on and it seems to me that at the present, starting a few years ago, the interest in such questions [has] increased enormously. And I have the feeling which arises simply from the reaction to this book that ideas of this sort are spreading fast in Europe, amongst doctors, amongst biologists, amongst some physicists; for example, Born wrote to me essentially agreeing and so did Lise Meitner.

Heilbron:

What about the younger physicists?

Heitler:

Some of the younger physicists do undoubtedly agree -- for example, those in my department, but that is perhaps not so surprising. Some others [do] too. Well, I canít say how many it is, but there are certainly a number who have inclinations in such directions. But very probably it is true that this was not so perhaps 30 years ago.

Heilbron:

Has there been any opposition to it?

Heitler:

No, not to my knowledge. There have been countless reviews. Some are rather colorless; one or two are in opposition, but not very violently, and the majority are more or less in agreement. I have not had any violent opposition, any significant violent opposition, I must say. But that was quite a surprise; I had expected it, of course.

Heilbron:

Yea, surprised to hear it.

Heitler:

Yes, Iím quite surprised myself, you see, but what surprised me most was that there was a lot of agreement from the medical side. Even here in Zurich I can tell you perhaps this; there were at least three members of the medical faculty who spoke to me or wrote to me saying that they agreed and that they were very glad that this book had appeared. And there are also a few from Germany and especially from Scandinavia who wrote in a favorable way. There was one psychiatrist, even someone from the veterinary faculty, and one or two philosophers who agreed. And all together I think I can say that Iím surprised.

Heilbron:

Yes. Well, I am too. Would you say that you think some sort of a difference in the recruitment of physicists would be necessary before any change of the science itself would be possible?

Heitler:

Yes. Well, I almost think so. I think two things are necessary. One is easy, or fairly easy, that physicists should no longer represent their results as an over-all world-picture, and that they should recognize their own limitations. That I think is fairly easy, and then I think sooner or later fresh lines of research will have to be opened in the directions which I have mentioned. And by the way attempts in this direction have been made. For example, in the school of von Weizsacker who was a theoretical physicist before he is now a philosopher. There has been quite good work done in his department on the theory of colors. There is a book by (Heimenthal) on the theory of colors; it is a continuation of Goetheís theory.

Heilbron:

I didnít know about that at all.

Heitler:

Itís quite recent, yes, quite recent. Well, the [my] book is now being translated; the English version must come out very soon. I expect it any day; it should have been finished long ago, and Iím sure there will be some fun then.

Heilbron:

Yes. That should stir some of them up.

Heitler:

But then to my surprise there will also be a Danish translation and a Norwegian one, and an Italian one so far. Iím very pleased; I never expected that. What I had expected, quite frankly, was a violent reaction against it from some quarters, or that it would be ignored.

Heilbron:

You have as you finish the book some vague remarks about Plato and Pythagorus and so on.

Heitler:

Thatís deliberately vague; I didnít want to commit myself in any way. I still donít want to commit myself, but these are just vague indications.

Heilbron:

Do you see any indications of how one should try to get back the sort of thing that Kepler was trying to do? The case is much clearer in biology, I think, but in physics --

Heitler:

No I donít see that one can get -- no, I think biology is much clearer; in biology it is easy -- not easy, but it is easier than that. I think that if there is any truth in the Kepler business at all, of which I am not at all sure, it is very, very difficult to (gain) access (to it). I think we are not (ripe) for that yet. This was merely meant as an indication that one should be careful in discarding such things all together, especially things we know so very little about. We know so very little about Pythagoras and yet we have every reason to believe that he was a most serious investigator and really a great man.

Heilbron:

In your analogy that present day physics should be considered as a projection of --. Do you feel that physics should continue to explore the dimension in which it is now engaged as well?

Heitler:

Oh, yes, I think physics should be continued; well obviously it is not the idea that I mean physics should be stopped. But what I think one can ask of physicists now is at least to think about the limitations of their own work and of their own results and, too, to think a little more of the moral implications of their work. There has been a lot said and written about that already, so thatís not new, but I think one ought to be a bit more aware of what one is doing in physics and to what (obligations) oneís results can lead, and be a bit more careful about it. There is, for example, the example I mentioned in my book. I think this subliminal influence, this (extolling of the short) pleasures of life -- I think such things should not be done by a (???).

Heilbron:

No, I think thatís one of the (worthy) forms of persecution that one could --

Heitler:

Yes, and there are a good many such inventions. Chemistry of course is leading, perhaps. And I think thatís all I ask the physicists -- I mean, thatís the intention of the book, to ask the physicists these two things for the time being. Iím not an idiot and think that (now) the physicists should all change and regard Keplers harmonies as tools and go on working on this. I mean that would be foolish. That will probably be a very long time before weíll be getting any certainty about that, but I think in biology, changes may be more imminent. At least that is my impression. And in medicine too there is a lot going on in the direction leading away from the purely mechanical view of the functioning of the body and toward an appreciation of, well, let us say that the illness belongs to the whole personality of the person, and so on. Well, Iím not a doctor, I canít give you any details, but that is my impression Ė- that a lot is going on in this direction. And, therefore, received a lot of favorable comments on it just from the medical side.

Heilbron:

And. no physicists proclaimed this was subversive of the --

Heitler:

No, they didnít; well, I think a lot ignored it. Iím quite sure a lot didnít like it, but there were very few reactions from physicists. As I said, Born was one of them, and Lise Meitner was another, and [there were] a few younger people. But most of them didnít react. Well, that means nothing; thereís no reason why they should especially write to me, but I havenít seen any reviews either in physics periodicals, perhaps not yet.

Session I | Session II