Samuel A. Goudsmit – Session III

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ORAL HISTORIES
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Interviewed by
Thomas S. Kuhn and George Uhlenbeck
Location
Rockefeller Institute
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Interview of Samuel A. Goudsmit by Thomas S. Kuhn and George Uhlenbeck on 1963 December 7, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/4640-3

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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 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: Gladys Anslow, Robert Fox Bacher, Ernst Back, P. A. Boeser, Niels Henrik David Bohr, Hendrik Brugt Gerhard Casimir, Walter Colby, Dirk Coster, G. H. Dieke, Paul Ehrenfest, Albert Einstein, Enrico Fermi, George Hartwig de Hass, Werner Heisenberg, David Inglis, Edwin Crawford Kemble, Ivan Robert King, Oskar Benjamin Klein, Ralph de Laer Kronig, Alfred Landé, Otto Laporte, T. van Lohuizen, Hendrik Antoon Lorentz, Fraulein Mensing, Edgar Meyer, Robert Andrews Millikan, J. Robert Oppenheimer, Friedrich Paschen, Wolfgang Pauli, Linus Pauling, Isidor Isaac Rabi, Harrison McAllister Randall, Adolf Smekal, Arnold Sommerfeld, Thomas, Uhlenbeck (George's father), George Eugène Uhlenbeck, Albrecht Unsöld, W. van der Woude, Vry, John Wulff, Pieter Zeeman; Universiteit van Amsterdam, Rijksuniversiteit te Leiden, University of Michigan, Teyler's Museum, Universität Tübingen, and Universität Zurich.

Transcript

Kuhn:

What I’d like most to try to do is to try to go back to substantially the time that you two started working together. This is presumably the time when you, George, were back from Rome, and Ehrenfest had said that Sam should teach you what has been going on, particularly with regard. to models and spectra, and you start working together.

Gousmit:

That must have been in June, the end of June, because then the academic year was over.

Kuhn:

Now Sam’s impression and this adds something to what you’ve told me about this before, is that already at that time, he had been asked, presumably by Fokker, but it’s not clear, to do this review piece for Physica. [Paper No. 20] Have you got that piece there, Sam?

Gousmit:

Ja.

Kuhn:

And a lot of the basis of this discussion was sort of working out that article, or was about ideas to which this was in any case to be a review of somewhat the ground you were supposed to be going over together. He thinks that this piece probably provided a considerable vehicle.

Gousmit:

That was the one I was writing during that summer, and which Ehrenfest said, “if you help me with that, then you’ll learn at the same time all about it.”

Uhlenbeck:

I have no recall that it was in connection with it, because I certainly didn’t know anything about it.

Gousmit:

No. That’s what I had to discuss with you, I had to teach you that, and I’m surprised at this moment reading it again, that there are things in there which I am so convinced that I didn’t understand at the time; and why didn’t you become the co-author? I’m sure that several things are mentioned in there which were not clear to me at that time, but I probably learned from you to understand them or appreciate them. Like the Pauli-Rumpf paper, which I had forgotten that I knew about until the other night when I reread this old article.

Uhlenbeck:

All the sophistic difficulties. I remember that we talked about that; because this summer what Sam did was give me, all the time, little lectures in the afternoon. Then of course about this, then for spectra; then it was not only spectra, also about resonance and about the influence of the polarization on resonance. All these things which were done in the current literature. I suppose that probably many of them were discussed in colloquia in Leiden while I was not there. But I don’t remember that I helped writing anything, that I certainly didn’t. You wrote this all alone. I didn’t write anything.

Gousmit:

But the way it’s written, I could only have gotten some of the .ideas by discussing it with you. Because I didn’t know that much.

Uhlenbeck:

I don’t know, I don’t remember. I certainly didn’t know as much as you did about these things at that time, that’s for sure.

Kuhn:

You two are getting in the position now of trying to pass credit back and forth, and this is a useless occupation. This paper is, I think, particularly interesting because it’s written about as early as a paper which reaches these particular conclusions could have written, and sets up the whole problem to which you two in your joint papers immediately go on very quickly — it sets these up very clearly. If it provided the context, or part of the context for this teaching seminar for George, it has then a double importance, as part of the background for spin.

Uhlenbeck:

Did this appear before that?

Gousmit:

Ja, ja. No, it just was printed—.

Uhlenbeck:

No, that was this paper on the Opmerking—

Gousmit:

The hydrogen —

Uhlenbeck:

The hydrogen spectrum. That is the one—

Kuhn:

The hydrogen spectrum actually comes out just a little bit before this review paper comes out.

Gousmit:

Ja. But this was written earlier, the review paper was written earlier.

Kuhn:

Yes. Let me say one of them is pages 266-270—the hydrogen and helium paper—and 281-292 is the review paper. So that really doesn’t tell you anything about the order in which they were prepared. [#19 with G.E. Uhlenbeck: “Opmerking over de spectra van waterstof en helium,” Physica 5(1925), 266-270. No date. August/September issue. #20 “Iets over spectra en atombouw,” Physica 5(1925), 281-292. No date. October issue.]

Gousmit:

And the review paper has a footnote to our note in Naturwissensehaften “to be published”.

Uhlenbeck:

Already!

Gousmit:

So I’m sure, if I taught you anything, that that is the extent of my knowledge at the time, this review paper.

Uhlenbeck:

Well,I must say, I’m surprised about this Naturwissenschaften, because that I would have placed later, certainly after that one. About this hydrogen. I still remember about the hydrogen very clearly. That came also one of these afternoons, and it must be relatively early—if I recall correctly, it came about from the point that I was so dissatisfied about the fact that one had to learn the theory for the alkali atoms and then one had to still keep the old theory for the hydrogn atom. I thought that was terrible. There should be at least some relation between the two. And that’s the way it stood. At the end, when we discussed this, that it was clearly very unsatisfactory that there were two theories about things which should be similar.

Kuhn:

Did you know at that time that Sam’s first article, about four year earlier, had dealt in a sense with exactly this problem?

Uhlenbeck:

Yes, yes, I knew that. Of course we talked about that too. And then Sam went home and wrote that paper. That was the “Opmerking”.

Gousmit:

Which paper?

Uhlenbeck:

The hydrogen. That you wrote, very quickly, very quickly. And then we discussed it again. I think my contribution to it was mainly that I knew Kramers’ dissertation. I had looked at Kramers’ dissertation and found that line which Kramers simply passed over. Then it turned out that that was the line which was predicted by this scheme. That was a great satisfaction to me. And then also I told that to Sam, “look here, we have found this line which is already all the time in the books!” That was also mentioned then in the paper when it was rewritten a little bit about—. I would have placed that in the beginning of August, and I thought that the spin came afterwards.

Kuhn:

… George, there’s one missing element in this, or at least, one that looks like a missing element. In the hydrogen-helium paper, a lot of use is made of a paper by Wentzel.

Gousmit:

Yes. It was a vehicle, like rice is for certain meals. You see, it really had nothing to do with it.

Uhlenbeck:

No, but I remember that we discussed this Wentzel paper and we couldn’t make heads or tails of it really.

Uhlenbeck:

Well, it must be so that even at that time it took four or five weeks before these things appeared.

Gousmit:

In Physica?

Uhlenbeck:

Possibly. And in September, when I think the spin was discovered— Sam says it was in August. Then you perhaps put that note in in proof, you could have done that.

Kuhn:

Probably not, because it’s numbered consecutively, it’s note number 2. Maybe Physica is different from most, but usually you’re not allowed to make that sort of change in proof.

Gousmit:

May use this as exhibit A? This I just discovered. It has no precise date, but we may be able to date it.

Kuhn:

This is the letter from Ehrenfst to you [Goudsmit] in Amsterdam.

Uhlenbeck:

[Reads the letter] I don’t recall that.

Kuhn:

… It’s this letter which helps drive home the one discrepency. You remember you told me, George, that after getting the Lorentz paper or manuscript, the two of you went to Ehrenfest and said,we’d better withdraw it. Ehrenfest said, I’ve already sent it off.

Uhlenbeck:

That I stilI remember very clearly.

Kuhn:

But this doesn’t sound that way. And Sam’s recollection is that he wasn’t bothered by the Lorentz thing at all, and didn’t want to withdraw it.

Gousmit:

I probably was in Amsterdam.

Uhlenbeck:

Maybe I was alone; I don’t know whether we were together, but I remember that I talked with Ehrenfest. I talked, I think, with Lorentz alone, maybe Sam was not there.

Gousmit:

I don’t ever remember.

Uhlenbeck:

I still remember the manuscript that he gave me. But here [in Ehrenfests’ letter to Goudsmit] the Naturwissenechaften article—ja, that’s mentioned.

G:

. Ja. Apparetly I was writing it, and had sent a copy to Leiaen, and be [Ehrenfest] said, “don’t send it off until Wednesday night, because there are still some discrepancies.” Then there is on the side, it says, “oh no, you found you had made a mistake.”

Uhlenbeck:

But in this paper we didn’t say anything about the g sums, did we?

Gousmit:

No, no, no. But you were checking up whether the idea would fit it. You thought you had found a discrepancy.

Uhlenbeck:

This. I have completely forgotten; I don’t know what this is. I didn’t even know that I did something about the g sums or found some errors.

Kuhn:

Regardless of the date, do either of you have any particular recollections of the point at which spin enters? Not as to whether it comes in August or September, but where it comes relative to the development of ideas. What, for example, is its relation to the hydrogen-helium paper?

Gousmit:

I have a recollection.

Uhlenbeck:

Ja, I also have a recollection of how it came. In my recollection, it came on an afternoon that we talked about. Then it was always this question of the 13 quantum numbers, and I still remember that I said, if there are 4 quantum numbers, there must be four degrees of freedom. Do you remember?

Gousmit:

See, it checks, that’s exactly what I said, and it came when I was trying to explain the Pauli principle to you, how you get these terms with the four quantum numbers.

Uhlenbeck:

And if there are four degrees of freedom then there must be some kind of internal—. And that was really the starting point. But, and you must remember too, Sam, that we did not think of publishing that at all at the moment when we said that. Because I still remember that you. said—I think I even have a letter from you —- wouldn’t it be nice if one could write such thing down, but they are clearly too speculative.

Gousmit:

I’d like to see that letter.

Uhlenbeck:

And then on1y after having talked with Ehrenfest, I think, we were encouraged to write something down. But I remember this discussion with Ehrenfest very clearly, that he immediately was, so to say, convinced. Ehrenfest was immediately convinced. /

Gousmit:

He said to me, “you have no reputation to lose yet, go ahead.”

Uhlenbeck:

“Beide sind jung, genug, um sich eine Dummheit leisten zu koennen.” That’s what he said. I don’t remember about these g sums. And it is also clear, we wrote afterwards a paper on spectra, and that was about g-sums and so on.

Gousmit:

We wrote it afterwards but it came out of the summer discussions.

Uhlenbeck:

Ja, but that was really spectroscopy. That was these different coupling schemes. That was later really. And the spin — after the Naturwissenschaften paper—stood for a while without further consequences, so far as I remember. It was not so that we continued with it, until, really, the Heisenberg letter came. Then came Heisenberg’ s letter. You may have that still.

Kuhn:

It’s here.

Uhlenbeck:

And that put us onto it again. There was, of course, this factor two, the Thomas factor two that he said, ‘how do you avoid it?’ And then it is also so that he had, of course, derived the—.

Gousmit:

But he didn’t give the derivation, he just gave the result.

Uhlenbeck:

That’s the way I remember it. And we didn’t know how to derive that. That was not clear to us. Then we worked like a dog. And there I think that’s the only place that van der Waerden is approximately right. Einstein was at Leiden at that time. I remember still that one Sunday Einstein once said “you must go take the co-ordinate system in which the electron is at rest. Then you get it. Then immediately for circular orbits it came out directly, without—. Then for elliptical orbits—I had to study perturbation theory. I did that very hard out of Born’s book, and then finally with the fomulas there, you did it also for elliptical orbits without any difficulties afterwards.

Of course I didn’t know that, and even Ehrenfest hardly knew that sort of thing because we were educated in such a qualitative way, always qualitative, and always with simple models, never long calculations. Then, of course, we had the same factor two, but then at least we could answer Heisenberg that we also didn’t know how to get a factor two, [laughter].

Gousmit:

You might read this sentence here: that’s a letter of Bohr to Kronig [26 March 1926]—that one sentence down there near the end. [Einstein’s remark that the coupling between the spin axis and the orbital motion was a consequence of the theory of relativity was a “revelation”]

Uhlenbeck:

Ja, that was with Einstein, ja. This letter, has this letter. Ja, it’s a very dark one why that is a revelation. Because if you thimk of it, it is so you don’t need relativity theory, although I remember that we used these formulas for the transformation of the electric and magnetic fields. Although it was just Biot-Savart. But it just shows that everything was so strange. Why Bohr was so impressed by it—.

Kuhn:

That’s very hard to understand.

Uhlenbeck:

Very hard to understand. One would have thought of Bohr that he would say it right away he didn’t understand. And Bohr was then—that was December, I’m sure—that was the Lorentz festival. He came then to Leiden and he talked at length with us.

Kuhn:

Presumably he and Einstein were there at the same time.

Uhlenbeck:

Yes. But when he talked with us, I don’t think Einstein was present.

Gousmit:

Yes, several times. I remember that drawing the diagram on the blackboard of the hydrogen structure, and that Einstein and Bohr were sitting there, but Einstein did not understand it, he did not know enough about details of spectroscopy.

Uhlenbeck:

I have not an impression that Einstein took part in the discussion very much.

Gousmit:

No, but he was present, I remember that, at some of the discussions. We went there many times, remember?

Uhlenbeck:

Many times, ja, many times. -

Gousmit:

And the blackboard was not allowed to be erased, everything was on there.

Uhlenbeck:

And Bohr insisted that now one should look, at hydrogen again. He did not know this paper.

Gousmit:

And that I told him at the time.

Uhlenbeck:

He did not know this paper. It was in Dutch of course, too.

Kuhn:

Why did you bury that paper in Dutch?

Uhlenbeck:

I don’t know. That was the easiest language to write, and it was also the quickest to publish for us, I think. No real reason for it. The Naturwissenschaften, that wasn’t, that—. .

Kuhn:

Ja. Your doctoral exam was in December. So Einstein was there in December, and Bohr was there too.

Uhlenbeck:

Ja, that’s right, Sam had not done his doctoral examination. That was right. I had done that of course.

Gousmit:

You see how he signs that little note, (in Dutch) or whatever it is. [chuckle]

Kuhn:

It doesn’t look to me as though you two are going to succeed in recreating—. Maybe we should get Sam to go to the board and give one of the lectures he gave you—.

Gousmit:

We had no board, that was one of the troubles.

Uhlenbeck:

We did it all on paper. We sat next to eachother, and he did it on paper. I don’t have these things anymore. It was—.

Gousmit:

But it was the Pauli principle.

Uhlenbeck:

The four quantum numbers; that was for sure. All the further developments were, so to say, after Bohr had it accepted, so to say. There was no doubt for us, of course, anymore, although we didn’t know the factor two still, at all. No idea.

Kuhn:

What is the date on that Heisenberg letter, the first of the Heisenberg?

Gousmit:

November. It was right after it appeared. I think a day after the date of Naturwissenschaften.

Uhlenbeck:

It was very close anyway.

Gousmit:

Immediately after.

Kuhn:

Yes, November 20 was the issue of Naturwissenschaften.

Gousmit:

[checks letter] And this is November21.

Uhlenbeck:

Ja, it was very quick.

Gousmit:

Immediately. Then I wrote him two letters, I don’t know what’s in them, and then he wrote again in December, the 12th. And that’s a most interesting letter, December 12. About his own work. I think this is historically more interesting, where he says what he is doing.

Uhlenbeck:

And you went to Copenhagen I think in January?

Gousmit:

Ja.

Uhlenbeck:

And after that I didn’t do spectroscopy anymore, except that we wrote this paper.

Gousmit:

But that was really written during the summer, or at the end of the summer.

Uhlenbeck:

No, this was later; it was the review paper.

Gousmit:

Oh, the review paper!

Uhlenbeck:

Then you wrote the review paper.

Gousmit:

I thought you were thinking of the Opmerking paper.

Uhlenbeck:

No, no, the review paper, that was in that spring that we—. There is nothing that one can say.

Gousmit:

There is one discrepancy, or credit. I claimed that I was the one who knew that helium Paschen line so well, and the forbidden component. You claim that you are the one.

Uhlenbeck:

No, I found that in Kramers dissertation, I didn’t know that line, of course.

Gousmit:

I knew it, I had seen the—you see, the first thing I ever saw was Paschen showed me that line, and I had studied, of course, these things in Sommerfeld’s book. I still—I got a Paschen reprint that I had had for a long time, with the different lines.

Uhlenbeck:

But then it must have been so that because it was in Kramers dissertation it was discussed for the Stark effect, and also a lot of it was understood, all right, but this line was standings there and was not in his calculation, and that made an impression on me.

Kuhn:

Except that in one respect at least, I think, you don’t remember this quite right, George, —because at least in the paper you point out that Kramers has explained this line—I forget how—but by some sort of interaction with other electrons, and then you point out that if that were the right one, then there would have to be two lines, one of which is not observed.

Uhlenbeck:

Ja, ja, something like that. So, it’s perfectly possible that Sam knew the line, and that what you did was to take the thing in Kramers’ thesis and do the further analysis as to what was wrong with the way Kramers handled it.

Gousmit:

I don’t see it as discrepancy.

Uhlenbeck:

That was one line which stood out.

Gousmit:

Ja, we’ll have to look at it. [They look it up]

Uhlenbeck:

I would have to study this again. But the point was this, that if one tries to explain it by an accidental presence of an electric field, then necessarily also component (3D) should occur — and even with greater intensity. See especially figure 10 of the dissertation of Kramers.