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In footnotes or endnotes please cite AIP interviews like this:
Interview of James Franck and Hertha Sponer Franck by Thomas S. Kuhn and Maria Goeppert Mayer on 1962 July 14,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
This joint interview with James Franck and Hertha Sponer-Franck 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 circa 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: Mrs. Bauer, Richard Becker, Raymond Thayer Birge, Max Bodenstein, Niels Henrik David Bohr, Max Born, Ode Clausius, Edward Condon, Dirk Coster, Richard Courant, Clinton Joseph Davisson, Peter Josef William Debye, Paul Drude, Dymond, Tatiana Ehrenfest, Paul Ehrenfest, Albert Einstein, Walter M. Elsasser, Paul Sophus Epstein, Enrico Fermi, Emil Fischer, Franck James, Walther Gerlach, Ladislas Goldstein, Fritz Haber, George Ellery Hale, Wilhelm Hanle, Werner Heisenberg, Herneck, Gustav Ludwig Hertz, David Hilbert, Johan Holtsmark, Hueckel, Christopher Ingold, Ernst Pascual Jordan, Martin Kamen, Felix Klein, Kunsman, Ferdinand Kurlbaum, Irving Langmuir, Max Theodor Felix von Laue, Philipp Lenard, Gilbert Newton Lewis, Frederick Lindemann, James Clerk Maxwell, Joseph Mayer, Lise Meitner, Robert Andrews Millikan, Rudolph Leo Bernhard Minkowski, Walther Nernst, Mrs. Nordheim, J. Robert Oppenheimer, Friedrich Paschen, Linus Pauling, Max Planck, Robert Wichard Pohl, Georg Quincke, Fritz Reiche, Heinrich Rubens, Carl Runge, H. Seeliger, Emilio Gino Segrè, Arnold Sommerfeld, Johannes Stark, Otto Stern, John T. Tate, Edward Teller, Woldemar Voigt, Otto Warburg, Victor Frederick Weisskopf, Wilhelm Westphal, Wilhelm Wien, Windaus, Robert Williams Wood; Berlin Colloquium in Physics, Berliner Physikalische Gesellschaft, Physikalische-Technische Reichsanstalt (Berlin), University of California at Berkeley, Universität Berlin, Universität Giessen, Universität Göttingen, and Universität Heidelberg.
I want to say why I went over to these studies of photo—synthesis. There are really several reasons why I did it. One of them was that when I came to Hopkins, where Wood always could work with practically no money, there were practically no apparatus, but leaves were around. I had already written a short note about something I read which was done by (Kautsky) in Germany. He studied the fluorescence of leaves and found that the fluorescence rose in the beginning and then went down again. This, which is often called the Kautsky effect, interested me, and we studied that a little bit more. And I said something about it, based on some information I read on photosynthesis by chance. I said one could improve somewhat the physics behind it. All that what I said was plain nonsense, because the data were not right, and the interpretations were naive and wrong.
And so I became more interested in it, but when I came then to Hopkins and found practically nothing there than a, few optical apparatus, I said now, we can do two things. And we did two things. Wood and I worked a time together, and Wood was always interested in fluorescence, so we studied the fluorescence of leaves in a different way than others have done it. And something came out of it. And on the other hand, I had a little vacuum spectrograph, a very small one, which was constructed in Gottingen by two of my co-workers. One was Cario and the other was (v ????). And with that we studied the absorption spectra of water and (??? lead) and a few other things. So more and more I went into the field of photo—synthesis. I saw that I had to go over into an entirely new field, and I played a little bit with the idea to go over to nuclear physics, and had also some ideas about neutrons. But it turned out that somebody else did the same thing. So I dropped that again, and went more into this field. And the more I went into this field, the more I saw that I had to learn a great deal more about it in a different way. [An extended discussion of photo-synthesis is here omitted.] I would like to say Libby, our friend Libby, got the Nobel Prize for his work, and I was quite pleased because I like Libby, and the work is excellent. On the other hand, I must say I think one should not forget that (Kamen) found C14.
It was really (Kamen) who found C14.
Yes, it was Kamen who found C14. And I must say he deserves the Nobel Prize, not only for that but for lot of other things. And finally he is now in the Academy.
I know, and at that occasion I heard that he had found carbon 14. I had always thought Bill Libby had.
I mean it is a scandal. It is really a scandal. How often in last time the Nobel Prize is given not in the right order. Libby deserves it, and I am very pleased that he gets it, but anyway, not quite correct to give it to him before Kamen. [More on photosynthesis omitted.] Look how wonderfully the plant arranged all these things. I have personally a great pleasure out of it to get an understanding of these things, but I have not succeeded to convince more than a very few people that there is something in it. Most of the people like to do the things in the way they are accustomed. This is too much physics. So I must say, a lot of things which I have said and published already, have proved to be true, but nobody read my papers and it will not be attributed to me. Now I don’t care, whether it is attributed to me, but I thought that the progress would be quicker if they would read it. And I will have even with my friend (Galfand) a discussion. He found a way out where he can do that still staying in the normal ideas that everything must be enzymatical1y done; thus the photo—chemical step must always be so that an enzyme is reduced, which then in turn reduces these things; which is of course nonsense. But the chemists and bio—chemists are so accustomed to the idea that everything must be a kind of reversal of respiration, which it is in the over—all reaction, But they say, “The essential part is that you reduce the enzymes. And if the enzymes are reduced, the thing goes backwards.” But it doesn’t go quick enough.
And I mean there are a lot of things. But if one can do it, I may say, it is understandable, because the people who have done something about the chemistry of photo—synthesis always have done it with enzymes. They have so great results, that they therefore don’t want to give up this idea that it must be a photo—chemical act. They have not seen that there are two ways to use energy at room temperature for reaction. That we all don’t the whole time burn up and go up in flame come from heat of activations, because all our organic substances are instable in presence of oxygen. But there is the heat of activation. Therefore you need high temperature to do that. Enzymes on the other hand have lower heat of activation, and therefore one can get the ordered system of respiration. And this is so nice and so important, that the people say everything must be so, and forget that photo—chemistry is something else. There the quanta are big, and you have, so to speak, locally very high temperature. And therefore it is unspecific…
Let me ask one question about this, because this field is new enough to me, I find this immensely informative, but there are parts of it I’m sure I don’t follow. When you say that the bio—chemists are not paying very much attention to this, is it that they disagree over real substantive matters, or is it just that this isn’t the way a bio—chemist works?
I mean, the point is, that if now a bio-chemist sees an exp1artion about pi pi and n pi, he would say, ‘I don’t understand that method and I can’t criticize it, but why do I have to? Because with my way I can do it anyhow.’ And therefore, understandably, they say that to read that thing, to digest that, takes so much time. (Gelfand) is really a near friend to me, but he would say to me, just last time, “I was really very patient to understand what you had to say.” He finds that’s already one progress I made, that I brought him to be patient enough to understand what I am saying. But he didn’t understand it good enough to see that one is forced to these things, and to abandon the other things. And one is forced to it, because as a physicist I am accustomed to say that physical evidence is evidence too. And fluorescence and chemical kinetic and all these things should enter in it. So, that is the situation.
I’m very grateful to you for this.
And this is all I wanted to say about this matter.
I’m terribly glad you did…
Before the University you had been at Breslau, at least for a while. Yes?
Yes, because I had to prepare for the examination to go to a University, the (Abiturium). I had to make my Abiturium. And for that I went to Breslau, in order to make it fast. You see there is a lot of development before, but I don’t see that you need all this yet.
Oh yes. I think you don’t need to tell the details. But you have to say that you gave up the hopes to go to university when you were quite young, and prepared for some other work.
I was born in (Neisse) but we moved when I was about 10 years old or so (Sachsen). And in Sachsen there was a very poor school. They were so much behind the schools in Silesia, it was unbelievable. It was a whole year. I had to go back, for example, by a whole year, by taking the same book, but of a year ago. And of course it was very tedious, so I complained about it. I complained about it—but—[break]. The Professor was (Goodenoutz).
This was the cram school now in Breslau that you went to?
Ja, in order to get my preparation to make the Abiturium.
Now why Breslau?
Well, it is Silesia again. We came from Silesia. Secondly, it was the most highly recommended Presse by far and wide. There none in the neighborhood in Saxony, I believe. And Goodenoutz was very well known, and all the people from the nobility who were a little stupid went to the Presse, because if they got through, they were Einjahrige. So we were only two girls in the class; two girls, and they were all boys. Many from the nobility of (???) country; And I had decided to work as hard as I could in order to make it as fast as I could.
You made three years in one.
No, almost. Not quite. Two and a half years in one, I believe. After a year the next preparation was to come, because he gave the same thing over again. You understand? I think most of them took it twice. I forgot now, how it was. Anyway, when the next possibility to take the exam came at Easter time, I said, “I will try. I will try,” He said, “No, nobody does that.” He was afraid, because if I would fail, it would be against his—. So he said “No, you can’t do it,” and so on and so on. “You have to write a letter to your parents and say that they allow it.” And there I stood and said, “I have not to write a letter, I am majorenn. And so you see, you can’t do a thing. I am majorenn.” So the poor man, he was very angry, but what could be do? He could do nothing. So I sent it everything and so on, and the girl and I, we were sent to Neisse — the place where I was born, you see. The Real gymnasium in Neisse. And there I took the examination and everything came out fine. And my best examination I did in physics. The written. That was the best. And then there was an oral of course, and I missed one thing in oral. Namely I was poor in — how do you call it? Biology. And he wanted to know how the heart was working. Everything. And I got everything right except that I had only one chamber for the heart. And the man said to me, the teacher, he said, “Now look, don’t you know that everywhere in life you have to have ante-chambrieren?”
If you want to go higher up, you have to first go in the first room. Ante-chambrieren.
And of course I knew immediately the Vorkammer and made the correct heart out of it. And that was my only mistake. My lesson wasn’t so famous, of course, but I passed it. That was my fear.
You knew by then that you wanted to do physics?
Yes, yes. But, I cheated my parents. You see, I cheated my parents because I said if I have this Abiturium I now will go to a Lehrerinnen-Seminar and become a teacher for a high school for girls, Hohere Tochterschule. And now comes the thing which put me into the University. When I returned from Neisse to Breslau, and Goodenautz heard I passed, he put in the newspaper how good his Presse was because a pupil had done this and this and this and finished in such and such a time. I didn’t know it. I didn’t look at the newspaper. But a cousin of my mother’s saw it, whereupon she sent a telegram to my parents. I still didn’t know how to tell my parents. And she sent a telegram, whereupon both my parents absolutely were so astounded that they sent me a telegram, which I have kept, and on this was, “Studium erlaubt. Prachtkerl. Eltern.” This was my passport.
You mean up to that time, you had no encouragement from home?
I see, very different from mine. In my house…
They knew you were at the Presse?
They knew I was at the Presse because I wanted to use the examination for going to a Tochterschule. But they did not know that I would try so early, because I said I would try the regular way, of course. I mean, I wouldn’t give myself away. [A discussion of the large number of Jewish physicists from Breslau is omitted]
Why did you not go to Breslau while you were there, instead of to Tubingen?
This reason I hate to say. This reason was that I was hungry in Breslau. It was horrible. You see it was the war, and it was really horrible. Moreover, I had in Breslau got some skin disease which I thought may have to do with that awful —— what we ate, these awful things. And when I was through in Breslau, I said I want to go to a place where I can now recover physically. And I was told, go to Tubingen, go to the south. And therefore I went to Tubingen. And you have no idea. Tubingen still had everything to eat. There was wonderful things to be eaten.
It was a very small town in a rich environment.
Butter, you could have butter, real butter in Tubingen. Butter and honey, and everything. Meat and what not.
Now you’ve said that you had quite a few women classmates in physics at, Tubingen. Was that unusual?
I do not know whether, because I could not know it at that time. We were three or four.
They had a little bit better time during the war.
Ja, because two of them I told you went up to Seeliger in Greifswald, when we had to leave Tubingen, and two of us went to Gottingen.
Was there a problem in Gottingen? Because you were a woman?
No, there was no problem in Gottingen.
There used to be a ruling that any professor could object to having a woman in his class. When was that removed?
I don’t know, because I had never heard of it.
(It seems that it has been invoked occasionally). I know there was a regulation that any professor could refuse to have a woman in his class. When was that changed?
That is certainly true. It was. And the thing is that during the war there were no students, and therefore women could easier be accepted.
And not only this. After the war was over, they used Runge to arrange some courses for the Kriegsteilnehmer who came back from the war. The older students or more advanced students should take over all these classes, and go over with him in trigonometry and simple algebra and all these things. And I did too. I was kind of drafted. There were so few, so I was drafted for it. And Arthur von Hippel still tells me that he took a course which I had. Don’t you remember? So you see there was not this, because there were too few.
With other words, your question can be answered. One permitted women to be there when there was need of students, and one needed anyhow even a girl.
Yes, even a girl.
And later it was quite a difficulty for instance to get her to become Privatdozent in Gottingen, because one of my colleagues said he didn’t want to have a girl in the faculty. And there was another story which (Hilbert) tells of difficulty in the faculty. There was a mathematician, Emma Noether, who was excellent, and some old astronomer made great difficulty. And then Hilbert burst out and said “But the faculty is not a Badeanstalt!” Because at that time it was unheard of that women and men could go to the same swimming place.
How was it for you?
Easy. For some reason or another, it was always assumed, it was never really discussed at home that I would go to the University. I don’t really remember ever discussing anything else. Now there existed in Gottingen an institution called (Freies) Frauenstudium. I mean, a little school which took over from the Hohere Tochterschule for three years to the Abitur. It had its own house. But of course the inflation came, and it lost its house, and we were in the (???), I don’t know where — — But anyway, the unfortunate thing was that when I had been one year in that class, in that school, this school really lost all its money, and they said the last class, I mean the Ober-Prima they would take through. “But you in the Ober-Sekunda, you can go next year to the boys’ school.” I said: “No, I won’t. I am going into the Ober-Prima and will make the Abitur here earlier.” And they said: “Well, you won’t be able to do it.” I said: “I will.” “You won’t be able to do it, you are too young. You won’t be admitted.” I said: “All right, I’ll take my chance on that too.” And then I pulled all strings that I could to be admitted to the examination. I took mine in Hanover. There were five or four of us from our little school, and there were about thirty boys taking it as Extremer. And of course we were much impressed, because the boys were so much older than we were, and they seemed so mature, and they were very worried. And we did not appreciate at all of course, because they all had some (???) record for their career, or they would not take it as Extremer. Well eventually, one of the boys passed, and all four of us. We were really well-prepared.
What does Extremer mean?
Usually you take this examination regularly at your school. And your teachers give the examination. But the little school I was in did not have the right to take this examination. We had to go to a boys’ school, and this was in Hanover. So you see, you had the same fate.
But then you see, you may remember the one boy whom they let through. One of the teachers there said, “Well, he wasn’t really good, but he made the impression of an earnest young man.” He studied physics. And I once went home with you, and you said: “I don’t know where I got this dumbbell.” I mean you scolded about him. “How did he ever pass even the Abitur?”.... So I told you. And you said, “You know, he isn’t really an earnest young man, but he has such a deep voice he gives the impression that he is.” [There follows a German explanation to Franck.]
By 1923, a number of people were feeling terribly strongly what Bohr had clearly said earlier isn’t working. The combination of quantum mechanics and classical mechanics that we have worked out. There are problems now for which it will not work. There is going to have to be a basic change…But there were concrete problems also that some people were worried about?
Well look here. At this time there was a connection with these quantum ideas and the action integral theory, o to speak. This was taken over at that time, and worked fairly well.
And how soon did people feel this way? Do you remember when this talk of Heisenberg’s was?
It was in our colloquium, maybe a year or half a year before the first paper. He battled with it.
Do you remember how Max Born felt about this?
I think he felt the same way. But I am not certain that Max Born himself felt the difficulties as clearly as apparently Heisenberg felt. And whether he agreed with him, or whether he (independently felt that way) I have no way to know…
Let me ask one particular question that was on that sheet. In some places, one of the really bothersome problems for people was that you couldn’t do the two-electron problem, that is, helium. And it was pretty clear to some people by ’24 say, it just wasn’t going to work. You had worked on helium in 1920 with Reiche, and there in that paper you think it’s going to work out. Pretty clearly, you say the values aren’t good, but they should come in better. Did you follow that problem at all?
No, I didn't. I myself saw it was a difficult problem because the interactions would be influenced by quantum theory, and therefore it is not mechanically (lone), but what it would be I didn’t worry. I left that to (the theorists). But I believed that also these people in Norway or was that much later? The man who was a cripple and came — — Boaars… I know that these discussions went on very often, that there are difficulties.
Do you remember such discussions yourself, Mrs. Franck?
She came a little bit later.
I was too late.—No, of course not. I was in Gottingen.... I was very much together with Hund and with Heisenberg—no, Heisenberg not so much, but With Hund very much. And later when Teller came, of course, with Teller.
How about Jordan?
Jordan, I hardly knew him. Did you know Jordan very well?
I knew him.
Let me ask you about some things that happened in this period before 1925. Remember the Compton effect? What was this like? Did this come as a great surprise?
Yes, it really did.
And we immediately saw that it was a wonderful thing. And Debye had also thought on some similar things, but as often with Debye, he didn’t do anything about it…I can tell you something that Compton told me, and I have seen. I forgot the name of the men, a very well known man, who was professor in Harvard — — Duane. Duane had a battle with A. H. Compton in saying the experiments were not right. And so a lot of people in the United States, as Compton told me, did not believe it.
But how about in Europe?
We believed it already, that it was right. And we knew about photo effect, and we knew that if they are behaving quantized so far as the energy is concerned, they should also behave like that in respect to the momentum transfer. This was one of the things to which we said “fine, just fine”.
How about the Stern-Gerlach experiments?
That was —?
Ja, very early,
This we read in Sommerfeld’s book that we all studied, and we were not really too surprised. And I remember my own particular point why I was not surprised, because this thing was brought up in our discussion when we met during the war in Laon. You spoke a while ago about the depolarization in connection with Hanle’s experiment and with Wood’s experiment of the fluorescence. And you see, we always worked with correspondence principle on the one hand, and then that something could go slowly that would mean adiabatically or with the quantum process. And the quantum process was always a great riddle, and we didn’t ask further. So we were not so astonished about the Compton effect. After Einstein’s paper, 1916, we said why should it not be (always like that). With other words, so far as I am concerned, we went never deep enough. We said we are content; there is a great riddle; and. in one or another way it will be solved. But we did not make ourselves anything else than just used this bridge between the classical and the non—classical by terms ‘adiabatic’ or ‘quantum transition’, and so on. And as soon as quantum transition came I was not more astonished about this adjustment than I was about any other quantum transition.
What about electron spin?
That was just plain wonderful, and absolutely unexpected for — at least for — — people like myself.
You were, I think, in Berkeley in ‘25-‘26, which is just the time these things were happening in Gottingen. When did you leave Gottingen, do you remember what time of the year?
You didn’t leave till November. Well then things were already going on very very fast when you left. Do you remember them?
Do you mean in Gottingen or in Berkeley?
In Gottingen. Born left also, but that whole summer—
We were both on the same ship, the Borns and I. And when I went to Berkeley, Born was invited to Pasadena. And as far as I remember, the two went to Pasadena, and I went to Berkeley.
They went first to M.I.T., and only later in the year did they go to Pasadena.
This could be.
I think Mrs. Born didn’t go to Pasadena actually.
Maybe she didn’t then, but we were on the same boat, and he went to Pasadena.
Do you remember anything about him then, or about the month just before?
I was not so much with this theoretical group, because it was not the time when Teller — — Teller was not in Gottingen at this time.
No he wasn’t. Teller and I didn’t overlap. He came in ‘30 when I left.
And I worked more with Teller later, so I was not so much on this end.
But did you know what was going on? I mean did this get the whole —?
Oh sure, yes, but only in colloquia or so. I had not many discussions with any of them. That was not the case, because I myself was very much interested to go out. I went to Berkeley, because they were doing some molecular work and I had quite a few things to get clearer about and so on. And I went. You see, that was the time when it began to be possible to analyze these spectra, and also to single out whether you took one where you had polar binding, or whether you took the one with the homo polar binding etc., and all that was of interest at this time. In reality, the measurements, or the determination, of dissociation heats came at that time. And I told everything to Birge. It was not Birge’s idea. I brought it with me from Gottingen. But we were working together on it.
What did you find the situation at Berkeley to be? Did people know quantum mechanics at Berkeley?
No, very little. It was this way. Now here is something here for your history, right now. When I came, I told a little about it. I told also about his thing for the Faraday Society. With other words, I explained the Franck principle. There was only a Franck principle. And I explained this in all details when I came to Berkeley, particularly to—not to Birge—to Condon. And Condon had not yet any subject for his doctor’s thesis, so this became his doctor’s thesis. And he worked on it, and wrote this paper, and from then on it was the Franck-Condon principle. That happened at this time.
Did Birge propose it as a dissertation or did Condon want to do it?
No, no, Birge did not. It was really that Condon began to understand the whole thing. So as far as I know, it was more Condon than Birge; much more.
How did you happen to go to Berkeley in the first place?
Ja, how did I? Oldenberg had been in where had Oldenberg been? He was there before in Pasadena? Was he in Pasadena?...I was a Rockefeller Fellow and I was among the first five.
And we came into contact with the Rockefellers.
I don’t know which one it was, third or so, it was just in the beginning of it.
You don’t remember why you chose Berkeley?
We all believed that if somebody from Gottingen would go, the best place - would be Berkeley, because Berkeley had first excellent men, like Gilbert Lewis. It was furthermore the old Eldorado, where it would be very nice to go. I am sure that the Rockefeller people were consulted also but I don’t know the details. What would be a good place? Anyway, Berkeley seemed to be, with the Golden Gate, and with San Francisco, and with everything, and with the total change in surroundings, the most interesting also from personal reasons. And then they had —
No, they wanted someone also.
We had often gotten pupils in Gottingen from Berkeley.
No, Condon came later. They came all later.
I’ll tell you why I was so much interested too in Berkeley now.
The secret mystery of quantum mechanics. The black magic of quantum mechanics, was brought by Oppenheimer to Berkeley.
Tell me what that means.
Well nobody in America knew anything about quantum mechanics at that time. And Oppenheimer came to Berkeley—
Condon didn’t know anything. Not a bit.
No, but Oppenheimer brought it. And (Joe) was there you see.
When was that?
‘27, when he went back, I think....
Right, and Condon knew nothing, I know now. Condon knew nothing about it, and as I say, I told the whole story and he started his thesis. He did it really almost all by himself, had very little help.
You worked with Birge.
Ja, we wrote that one paper, but I worked myself alone. And they had a new vacuum spectrograph, I remember that. A new vacuum spectrograph. And Hopfield was there, and he had just set it up, but it wasn’t finished and had to be adjusted and so on, and so on. I said I would do it, and work with it afterwards. So I worked with it and took the nitrogen spectrum, in this spectrograph, and took it with me. And there is that funny thing, that I analyzed it, and Birge wanted to be the first one to analyze it. So what he did, he analyzed it, sent it to me in an envelope: “Don’t look at it, don’t look at it before you arrive”, or something of that sort. But I had already done it on the way, so that was a little bit difficult situation. Do you know Birge?
Birge is a really decent and nice men, but a little bit narrow.
No, not only narrow. He was terrifically egotistic.
But he didn’t know it.
No he didn’t do it purposefully, definitely not, really not.
I mean I must say I have very warm feelings for Birge, in spite of the fact that in his own memory these things have changed a good deal, and not absolutely correct.
But he was very nice.
The vacuum spectrograph I take it just happened to be there. It had nothing to do with your picking—?
Yes, just happened to be there. No, no, no, it just was there, and they had nothing - they were not very good in experimental setups at that time… They just began to buy things, etc. It was a new building when I came; it was a new building. But where I went often, and had a great pleasure, was to the seminars of Gilbert Lewis. That was really very nice…And there I also could have quite often a good discussion with him.
He was against quantum mechanics still?...
Yes, he was still then, correct, be was. And he did not discuss it actually. He just brushed it off.
Did you argue with him?
Ja a little, in the beginning, but I gave up.
Do you remember how you felt when you first heard of matrix mechanics and wave mechanics?
When I first heard about it, if you are young enough, you accept it very easily. And once you know how the photon behaves, now why shouldn’t the electron behave the same way? That was something that you take — if you are just a few years younger in your stride.
Now how about matrix mechanics? How about p x q being different from q x p?
That was wonderful. In fact, I was a mathematician and I became a physicist when I bad my first course on quantum mechanics, because this was wonderful. I liked the mathematics in it.
But to this equation I understand Pohl’s aversion. I had that tool. I accepted it, but I had that aversion too, that a x p is not p x a. Because I didn’t learn enough mathematics.
What did Pohl say?
Oh. I meant Pohl’s aversion was more general. Pohl had an aversion for instance against all of Dirac’s ideas, negative energies and what not, and all these symmetries and things, he disliked it. And I could feel like Pohl in this particular case.
Were the students terribly excited to know that this was going on around them?
Most of them knew nothing about it, except the ones that were fairly well advanced. I knew a little, because I heard from Wigner and from Johann von Neumann, what was going on. But I think the average of the young students was somewhat unaware of what was going on. For the older ones were not.
My whole life has showed me that it is very difficult to change one’s mind, but that if one wants to be a scientist one has always to be willing to change one’ s mind and forget. What (Madelung) called “what do I care what nonsense I thought yesterday.” One has to.
I totally agree with you, but it makes it terribly hard for a historian…
You know, by the time I had quantum mechanics, I met Vickie Weisskopf for the first time. There was be and I and Stobbe. I don’t know where Stobbe is now, he is somewhere in America…There was a group of us who would discuss things together. Born was away, Born was sick. And so we had one semester of quantum mechanics from Born, and then Heitler and Nordheim took over the second semester. But there was a group of three or four students who would talk together, and eat together. In spite of the fact that I ad to come home for dinner, I quite often had supper with them in town. And we talked about quantum mechanics and learned a lot by talking with each other, seeing each other’s troubles and straightening them out. So it was at that time a small group of vastly interested students. Oh Delbruck was in it too.
What sort of problems?
We tried to understand what we’d been taught, largely. And then of course we all were on our theses. I don’t know how much I discussed with Vickie Weisskopf about this (Lyman Spectra), and I know it in and out because it was discussed between us a great deal.
Weisskopf was a man who impressed me very much quite early, because he was a man who could talk both languages, the language of a theorist and the language of an experimental man. We understood each other. Arid the same happened with Teller. Teller was excellent in talking to an experimental man in a way in which he could understand. On the other hand, always willing to take up things which came from experiment.
Most of the students of Born were not able to do it at that time. Certainly I was not.
Most of them were not able. Ehrenfest helped, and later a large number of contacts with Teller helped, but at that time, we sat behind equations to a large extent.
Maybe if you asked me what the great advantage of G3ttingen was, it was just that. This interaction of both sides. And not one person. I remember the time in which we had a party and. everyone made jocular poems. And there was (Rubinowicz), who worked with me a time, and he wrote “Von Theorie wird man nicht heller. Gott geb’ uns taglich einen Teller.”
It was (Rubinowicz.) I thought it was you.
No, no. It was Rubinowicz.
How about in this interaction Professor Born himself? Could he talk sufficiently in the experimentalist’s language so that your interaction—?
No, not so very well.
Born, when I met him right now —— and we are really old and good friends — said that I sometimes drove him mad. He gave me an idea or so — I don’t know what it was — and I said “I don’t know what to answer about it. I have to think about it. But I also would like to know what Bohr says about it.” And he regarded that as not too nice. And I didn’t know that I made him sorry. I found Bohr was one of the men who sometimes — yes — he could really discuss things with an experimentalist. And Bohr was really something different from the group you speak of. Namely, Bohr was an amateur, and if such men like Wigner or so, or other people, came with too much involved mathematics, he even left, and said “I can’t understand this.” Max Born, on the other hand, was a man who knew more mathematics than most of the theoretical physicists I have met. He had the school of Hilbert, and all that. He had all shades, and therefore it was not here a theory, there an experiment, but —.
How about Bohr and Born? Could they interact?
Not so well I think.
I have never seen them together.
Not so well. Because so far as Bohr is concerned, I believe Born was to him too much of a mathematician, and so far as Born is concerned, he liked to be — Born was only content when he could get these things in a real clear mathematical language. And they were a little bit different, but this attracted me to both.
That is why Ehrenfest was so important; made such a great impact on this group of students, Weisskopf and myself, because he was so different from Born.
Born could have been a mathematician, and a good one. But I like them both, Bohr and Born both. Both have a strong feeling for the outer world, that one has an obligation to the outer world, and furthermore, both are very educated people. This is also something. I must say I always, when I see something which Born wrote, it is so nice, and. so good. While Bohr, on the other hand, battles with the language, because he must make his own language, otherwise he cannot do it. Bohr told me that when he went to school and his brother especially, the mathematician, told me — that Bohr had so great trouble to write little essays one has to write in school about everything, that finally he became always ill and stayed home when the day came to write essays. Because it didn’t work. It just didn’t work. He could not write an essay. He told me about the story, when he should write a story about the harbor, and the ships which came in. And Bohr wanted to say so much about it, that he could not start. And in all his writing, it is so difficult. If one makes a statement and then tries to tone it down, and again and again be careful that you don’t say too much, it must be very difficult or Bohr to write. So they are so different people. And I think Gottingen was quite good, because of tolerance to every way of thinking. Don’t you think so too, Hertha?
Oh yes. [Unenthusiastic agreement]
You started to talk the other day, and I wish you would say more now, about your own work, and particularly about the work convincing the chemists....What was it like trying to show chemists quantum mechanics, and how to handle—?
I did not really show them quantum mechanics, but I showed them what comes in a binding, or the difference between one binding and another binding. What are the properties of let’s say polar molecules? And what are the properties of strictly atomic binding? For them it is very astonishing that you could, for example, dissociate with light. What happens then when you do it. Or, for example, from fairly simple experiments that you carry out you get let’s say an ionization potential out of it fairly correctly, or you form it in such a way that you get your dissociation heat, again fairly correctly. These things the chemists did not know. And it was new to them to do it in this fashion. This is what they usually wanted to know when they invited me to give talks talking on these different kinds of molecules. Of course we said different names for them—molecular arid ionic—but the chemists knew what was meant in each case. So they learned about this and how one could use a lot of things to get unknown properties out of them with only a little spectroscopy or so. For that matter, they also should learn about the spectra themselves and how to present them and what they bad and so on. All this you see I gave in these talks, more or less.
Did you have trouble with them because they were trained as chemists, not as physicists?
No, I’ll tell you why not. I had from the first year realized that I should take chemistry. I took a full year of chemistry in Tubingen, and there was Wislicenus at this time in Tubingen. And when I came to Gottingen there was Windaus. I listened to Windaus lecture in organic chemistry, this had actually some effect on me not only on me but on what I was doing. Because I took a great delight in organic chemistry. Whereas before inorganic chemistry was for me a very tedious subject and I didn’t like it a bit. I just learned it, but without my heart. I learned it with my brains, but not really. The organic, however, fascinated me. And so when I had heard it once I went afterwards. I was so interested that I felt I did not know quite enough about it. So I went to Windaus and asked him whether I could perhaps take it a second time by helping his assistant to set up the experiments; which he allowed. So I helped to set up the experiments with his assistant, and listened then for free, so to speak, to the lectures. And then when it came to the doctor’s examination, Windaus had forgotten about it; I visited him —. You know it is customary, you make the ‘Besuche’. He said “Well, I know already what you want. I know what the physicists always want. You want inorganic chemistry and that’s all, and a little physical chemistry.” I looked at him and said. “No, I like much better organic chemistry.” And he was very much surprised, and I told him what I had been doing. So in his examinations be asked me only about organic chemistry, which was fine, which went fine. “Except,” he said, “I have to ask you one question out of inorganic chemistry. I think that’s best.” You see, we all sat around the table. So he said. I should talk about porcelain manufacture. Manufacturing of porcelain. And I just flunked that, completely. And he laughed, because it really was the only question I couldn’t answer. But he was so amused that I really said the truth. Inorganic chemistry does not interest me. And I really learned a lot from him, I believe all my liking today for the aromatic compounds has something to do with that old training.
How to tell my chemist, that’s not your only art. You had also given a talk in America when you came, when Fleck, was there, and what was that?
Oh yes, that’s right. This actually was the beginning of my benzine. When I came to America in 1936 1 was invited immediately to give a talk at the next meeting for the Advancement of Science. And this was in — oh that dirty place, where it is so dirty, a lot of soot and — Pittsburgh, it was Pittsburgh. And I had really nothing ready. I didn’t know what to do, but then I hated to say no. So I sat down and thought over “what in the world can I really say and do for this?” Well, then it occurred to me, I had some copies of the Journal of Chemical Physics, and there were some papers in it by (Kistiakowsky) and by someone else all of them on benzine. “Oh,” I said, “this is easy, that is easy.” I know so much about spectra that it will be easy for me to analyze that spectrum.” Here is the fluorescence; you have an absorption,” and so on and so on. I just began to analyze that spectrum. I had to give a survey of latest developments of this and so. And I said is a later development, this will take no time to do this. I sat down, I sat down all day. I sat down also part of the night, and that was a great puzzle to me. I went so far — I dug out Wilson’s paper, you know, on the symmetries of benzine. Well, I just did the symmetries. And then I looked up things on the vibrations etc. It was a tough time. So I thought well, this is really an awful thing.
How can I make head or tail out of it? I think we have to make an experiment. So I started on benzine, and this was the reason why I began to work on the benzine spectrum. And then when I had all the spectrum and so on, the Nordheims had come by that time, and Mrs. Nordheim had done with Heitler her dissertation: She knew something about quantum mechanics, and so I asked her if she could help me with the analysis. However actually I learned very quickly all what has to go in. You know, to multiply these things etc., and we got an idea. I mean I had found the spectra, I had taken the spectrogram. All that was a headache was the difference between the first excited band in benzine and also a band in absorption. We did get it with much trouble. But experimentally I could manage it. On the other side, you see, from a vibration in the ground state, which was much weaker and so. I had all this. And then there was unfortunately a vibration which fitted exactly in the benzine with that difference.
Now, this I put also in that talk, in Pittsburgh. And then I gave some others, and so on. It was not only on benzine that I talked. I gave a general survey what he wanted. And afterwards, Fleck came and said, “Oh you gave an excellent talk, and this was really a nice survey,” etc., etc. But I in my heart knew that there was one fraud about it, that the benzine was probably not quite right. They didn’t know. None in the audience knew anything about it. So then afterwards I went back to it, and then I saw, (Sklar’s) dissertation in the Chem. Phys., I sent him this note…I had money from — I forgot now which foundation — Pennsylvania somewhere. I’ll ask Herzfeld whether he can send him on loan for two weeks, because this is a matter of two weeks. And Sklar came. It wasn’t a matter of two weeks. And we tried and so on, and it was still very difficult. So were now three you see. Then I said, well, we could ask Teller about it. And we asked Teller about it. We were now four on that problem. We had everything, but the last tip was given by Teller in reality, and then we had the whole benzine. After that I made a complete analysis of the benzine spectrum, with all the symmetries, every one of them, for all the vibrations, which one could be taken and so on. Which were allowed. Which were not allowed. And it was really the first complete analysis of that thing. I made one person angry, and this was (Ingold). He was furious. After we had it, I took a trip to Europe, and I saw him in England, and he was furious. He had done some work on benzine before — on fluorescence — but he had done it wrong. I was still too young to understand his deep hurt feelings, you see. Deeply hurt, that someone worked on benzine where he had some paper before on benzine. And ever since, our relationship is not very good. Not too good.
But he repeated your work.
He repeated afterwards our work. We published in when was that? I don’t know now the year. But then, Ingold had some pure heavy benzine, which he sent to Baltimore. In Baltimore in the chemistry department they had this. And he sent them six or seven or something cc. of heavy benzine. And I begged them, because I wanted to make certain our theory by taking heavy benzine; by taking the heavy benzine spectrum. And I aid I am doing this heavy benzine by myself. Nobody is going to touch the apparatus. I fill it. I got one cc. from the man in I forgot now the name — in Baltimore. I got one cc, from him. Took it, sealed off, brought it back to Durham. Nobody wanted to touch it. I said I am going to break it off. I am going to seal it on. I am going to take the pictures. I did. And then I will recover the sample, which I did. When I brought the sample back, they had broken ail what they had had from England. It was the only one left, that 1 cc. I had, from this benzine. And then I went and did this analysis again, ail over, all over. And Mrs. Nordheim has really taken differences and so on. We have worked hard on it. And now I think the benzine problem is solved. I consider it completely solved.
But there are many people who ascribe it to Ingold.
Ja, ja. Ingold repeated in l94. We got it out in ‘39, I know now. ‘38 or ’39.
Did he quote you at all?
I doubt it. I haven’t looked. If so be would do it in such a way that it is not so conspicuous. But anyhow, he redid it. But I feel much more honored that the Russians have now recognized it… Now we are doing the spectra of substituted benzines in the solid. Which is extremely interesting. We go down to actually a liquid helium temperature, and come out with some astonishing and some nice results. For example we found photo-chemistry — oxidation at low temperature. And this is a real and a nice thing. We were the first ones, and nobody had it before.
For the chemist it was a great surprise that the photo—chemistry could happen at low temperature.
Ja, it was a surprise.
But if the quantum is there, you were not surprised.
No, no, I was not surprised. We went down to four degrees. We got the genuine phosphorescence; that is from the lowest meta-stable state down to the ground state. And, as soon as this could be measured, and it had all the vibrations — Now that’s one thing, you see, which my people have to learn; to do a decent analysis by having the correct symmetries with the electronic transition etc. All right, we took this, and then we took a spectrum at 77 degrees. At 77 degrees there was another spectrum, which was at much longer wave-length. We measured it again. I wondered and wondered and wondered. And I still remember when I got it, looking out of the window. I had a l6O vibration in it, and this is a CO. [Franck and Sponer competing for the chance to explain these result] Well, do it, or don’t do it at all. Do it right or don’t do it at all; that’s my point. Let it go if you can’t do it right.
Do you have questions?