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Robert Bacher’s Interview – Part 1

In 1943, J. Robert Oppenheimer recruited American physicist Robert Bacher to join the Manhattan Project as head of the experimental physics division at Los Alamos. Bacher directed the bomb physics division at Los Alamos from 1944 to 1945, helping oversee the design of the implosion bomb, known as “Fat Man,” that was dropped on Nagasaki. In this interview, Bacher recalls the initial conference of Los Alamos laboratory leadership in 1943 and describes Oppenheimer’s relationships with Enrico Fermi and General Leslie Groves. He recounts how Oppenheimer improved as a lecturer, and remembers the excitement caused in the physics community by the development of quantum mechanics and the discovery of the neutron.

Date of Interview:
March 29, 1983
Location of the Interview:


Martin Sherwin: This is Martin Sherwin. Today is March 29, 1983. I am going to interview Professor Robert F. Bacher – B-a-c-h-e-r – in his office on the Caltech campus in Pasadena.

Robert Bacher: Look, before we start on this, I want to talk a little bit more about things in general. If you are going to try to cover all of Robert Oppenheimer’s life, then one of the problems that you will run into is that you will get widely different views of Robert Oppenheimer from people who knew him at different times during his life. Of course, there are some people that knew him all the way through and saw a lot of him during this time. There are others that saw a great deal of him during some parts of this time.  But you will find a wide spectrum of opinion. Partly, this is a matter that Robert changed a lot during his life. He had an enormously difficult job to do at Los Alamos during the war. In the course of this, he became a quite different person. I do not think there was anybody else there that could have done his job. He despaired in the early days, as I think I mentioned in here.

Sherwin: What was your sort of sense of the change? How would you describe it?

Bacher: I do not think this is easy to look back on and see. I think he had strong feelings, as some of the rest of us did too, that if an atomic weapon could be made, it would be a problem to get it out in the open. I mean lots of people did not really think about that aspect of it until the end of the war. But I think he felt that what could be done in this area was extremely important to get out in the open.

Sherwin: Let me interrupt. Did he talk to you about this at Los Alamos?

Bacher: I am sure we discussed this at various times. But actually, most of my view on this is very largely a view I made up myself. My own personal view of this is one I made, and did not change before I went to Los Alamos.

Sherwin: And that was?

Bacher: Well, I think I have to go back and say something that puts this in some perspective, proper perspective before I say anything more, and that is that I had been doing some work as it may say in there. I was working at the [MIT] Radiation Laboratory. But also, I had been doing some work on the nuclear project at Cornell. In fact, we kept some work going on at Cornell for some time after the Radiation Laboratory started, and I came back weekends. In fact, I was in the laboratory at Cornell when Pearl Harbor happened, taking data. The whole question of whether one could do something in this direction of course was just a very, very something very far in the distance until [Enrico] Fermi’s pile in Chicago worked.

Even then, so much needed to be done in terms of getting materials and so on that it looked very, very far out. Robert Oppenheimer, as [Isidor] Rabi may have told you, came to the two of us because he had known Rabi ever since 1925. I guess I had met him in 1929 or thereabouts. Also, he was aware that we had both been connected with the Radiation Laboratory. He was very much interested in the problems that one would run into in setting up a new laboratory. This was why he came to us. We found immediately some problems that we thought were very serious problems in the way they were going at this.

Sherwin: For example?

Bacher: Well the principal thing I think was the military part of it, which we took a very strong view about.

Sherwin: I quote that in my book, where you say if you have to put a uniform on, you walk out the door that day.

Bacher: No, I did not say that. I said this was my resignation from the project on the day it became a military project, because I knew you could not run it that way. I think one of the things that you can say about [General Leslie] Groves in being a good manager was by the time that question came up – it was essentially postponed in the famous Groves-[James] Conant letter – as far as I know Groves never mentioned that subject again, because he came to the same conclusion. I went out forty years ago to the project to the two-week meeting that was held in the middle of April.

I guess it is probably true that Rabi and I were the only ones who were non-project members who were present at that meeting. I do not remember anybody else that was. We definitely were not. In fact, it was at this meeting that the question was brought up whether either or both of us would come out there. We became convinced – as it turned out, without adequate foresight into all the difficulties that might arise, because they just plain weren’t known. Our report to the Radiation Laboratory – to Lee DuBridge in private, I should say – was that we thought there was about a fifty-fifty chance of getting this in on the war. And that was a very much higher probability than most people who worked in nuclear physics outside the project would have put on it.

Sherwin: What was the estimate for the length of the war?

Bacher: Well, both of these things were vague. Several years.

Sherwin: Several years.

Bacher: I mean two or three years or something of that size, several years. At that time, I think both Rabi and I had access to a certain amount of intelligence information from Europe. Let us skip that and say I had some access to intelligence information from Europe on technical matters. It was perfectly clear that the Germans had been cutting back very, very fast on lots of the things that they were doing of a technical nature. The worry that many people in the Manhattan Project had was that the Germans were going to develop the bomb, but that was something that considering what an enormous industrial undertaking it was, was hard to recognize.

On the other hand, the war in the Pacific looked like a dreadful thing. All of the problems of trying to really win a war in the Pacific looked really horrendous. I think this is a quite different view from the view that people had who mostly had European background. I think they mostly looked on – the war was the war in Europe.

Sherwin: [Leo] Szilard, Fermi.

Bacher: Yes. Well, I do not think Fermi had that view so much. A lot of people, and certainly [Hans] Bethe did not have any view like that.

Sherwin: Let me press you here just for a minute. Are you saying that the estimate in the spring of 1943 was that because of the intelligence information and because of what you knew it would take to build a bomb in terms of these huge plants and our ability to bomb Germany, that there was really not a very high percentage of chance that the Germans would build their own atomic bomb?

Bacher: Well, I did not think there was a very high chance of that.

Sherwin: Was this discussed?

Bacher: That is not a subject that I remember discussing. Or at least, I cannot think back forty years and think of a discussion on this subject. But my view was more or less that.

Sherwin: Well, they must have mentioned it to somebody.

Bacher: Well, I did. I certainly must have talked to Rabi about it because this was based largely on seeing what they were doing and cutting back all of their vacuum tube types that they were using in radar. This was of course picked up immediately. They cut back so much that if they were cutting so heavily, the question was why. We were very much interested in the why, because the why was related to their missile capabilities.

Sherwin: How did you find out about this cut down in vacuum tubes?

Bacher: It was part of the intelligence. I mean they picked it up from the radar sets that they found in planes and so on.

Sherwin: You mean the vacuum tubes were of an inferior quality?

Bacher: No, they cut back the number of tube types that they would do. They made a tube do a job that it really was not fitted to do. And you cut back very much on the capability of what you could thereby obtain.

Sherwin: Got it.

Bacher: If you take a policy to do that, you do it only in a very great emergency because it is very important that you cut back on that manufacturing.

Sherwin: Right.

Bacher: They were doing that.

Sherwin: I see.

Bacher: And they were doing it fairly early. They were doing that by 1943. Or starting to do it, I guess, in 1943.

Sherwin: At this conference on April 13, 1943, which you talk about in your piece, do you recall any specifics about that conference? This is the sort of first major gathering of Oppenheimer’s leadership more or less on site, because Los Alamos begins in the spring of ’43.

Bacher: Well, it was not only a gathering of that. Because, for example, Fermi was there and Fermi was not coming out to Los Alamos. But other than that, I do not believe there were people there who were not committed to the laboratory. I think everybody in one way or another was committed to the project. Now, there were some who left rather promptly thereafter who were present at that project. They did not stay very long.

Sherwin: Ed Condon would be one.

Bacher: Ed Condon.

Sherwin: Who else?

Bacher: Well, let us see. My memory is very bad on names now. Who is the man? Felix Bloch was there at that time. I am pretty sure he was there. I do not know for sure whether he was there at that conference. That I could not say, but he certainly was there very early in the project.

Sherwin: Did they have trouble with Oppenheimer or was it just trouble with the environment in general, the mountains, the isolation?

Bacher: Well, when you say these people have trouble, you could not say that—

Sherwin: Condon.

Bacher: Oh, Condon. With Condon I think it was a complicated business. I mean he and Groves were temperamentally orthogonal.

Sherwin: But there was no Oppenheimer problem there?

Bacher: I do not believe so.

Sherwin: I did not think so.

Bacher: I mean I am not aware of any Oppenheimer problem. I think Ed found that it was a very difficult place to work. It is very hard to know in going back and assessing Groves’ relation with people. I knew Groves pretty well over a number of years, because I saw a lot of him in Washington after the war and I saw quite a lot of him at Los Alamos during the war. Groves was a very astute man. He had a tremendous capability for getting jobs done on schedule. This of course, was not only just astuteness on his part, but he was really extremely forceful in getting things done. Some people found it just impossible to get along with him. Let me say he treated some people very, very badly. He treated [Ernest O.] Lawrence badly.

Sherwin: Is that right?

Bacher: Yes. I saw this happen.

Sherwin: In what way?

Bacher: He just would take a very domineering view toward him. He certainly was very domineering with [Arthur] Compton and the same with [Harold] Urey.

Sherwin: Not with Oppenheimer.

Bacher: No.

Sherwin: Oppenheimer was what, just too quick?

Bacher: I do not know. I think very early in his association with Oppenheimer, he must have become convinced that Oppenheimer had qualities that he absolutely needed for that project out there. I think to some extent that the evolution, the very quick evolution that came over Robert was associated in some ways with this situation that Groves relied in him a great deal.

That did not mean that everything was as smooth as silk. When Groves was told things that were difficult for the project and hard to understand and crucial to the project by Oppenheimer, he would cope with them in a very, very definite way, a very responsive way. I think he had very great trust in Oppenheimer, which was a remarkable thing. I mean judging ahead of time, I think you would have judged that any one of the other laboratory directors would have been able to get along with Groves much better than Robert Oppenheimer. It did not turn out that way. Now Fermi was special. That is a different situation. Fermi was not a laboratory director and so on.

Sherwin: I have heard, and this is sort of an aside, but that Fermi was not a great Oppenheimer fan. Do you have that impression?

Bacher: When Fermi came to Los Alamos, he certainly worked very, very hard to try to make the project go. I think during the later stages of the war, he had very complicated feelings about everything. But I think that Fermi is a much more direct person than Robert Oppenheimer ever was ordinarily. They are completely different sorts of people. I was not aware of any conflict between the two.

Sherwin: Not conflict. I have heard from people who spoke to Fermi about Oppenheimer and a lot of people of your generation that when it really came down to it, Fermi did not—well that is the wrong word. It is not that he did not respect him as a scientist. He did not hold him in the same regard for his scientific abilities as I suppose most other people.

Bacher: Well, that is possibly very true. That is not a point that I saw much of during the war because that was not a point that really pertained to what we were doing at the moment. But I think I would put it a different way. Fermi almost always wanted to work on something that was closely related to what seemed clear experimentally. I think Robert probably established one of the foremost schools for mathematical and theoretical physicists in the United States. I think it is very hard to focus on just exactly the point you are trying to get at. That is not an easy thing to come to. It makes it too simple.

Sherwin: I am trying to understand from a variety of sources what the sense of Oppenheimer as a scientist was.

Bacher: Well, there was not any doubt that Oppenheimer was a very good theoretical physicist. He certainly did not have some of the absolutely penetrating and crushing ideas that others that you can name had.

Sherwin: Who would you name?

Bacher: Well, I mean [Paul] Dirac for example, [Wolfgang] Pauli, [Werner] Heisenberg. I mean each of these people at some time came through with something that was just absolutely overwhelming in the field. And there are others too. Now Robert’s contributions, I mean some of the contributions were really very important contributions. But there was not anything to it, anything like that.

Sherwin: What would you name as his major contribution?

Bacher: I am not well enough informed on that to really make an estimate of that. But he did some very good work before the war on various things having to do with cosmic rays and so on.

Sherwin: He did the black hole research that just became of interest again in the sixties.

Bacher: That is right. He suggested that. There were a good many things that are still extant that—

Sherwin: I want to ask another question and go back to that point you made about the German bomb and the war in the Pacific really being the vision of horror. Are you implying that for those people who thought the issue through, that the bomb was sort of seen as perhaps not necessary to win the war in Europe but even more necessary with regard to the Pacific war?

Bacher: I was not saying quite that. I mean you have extended what I said.

Sherwin: Well, I am trying to get a handle on it.

Bacher: Well, I think it is not easy to say in as accurate a form as that, because it is very easy to go back forty years after the fact and try to make everything absolutely crystal clear. That is not the way things happened.

Sherwin: Groves wrote a memo before the war ended. To [President Harry S.] Truman, I think it was. This might have been just after the war. In which he said, and I think this is an exact quote, “The target is Japan and always has been.” That is what he said.

Bacher: Now he is talking about the target for the—

Sherwin: The atomic bomb.

Bacher: For the atomic bomb. Well, when did he write that?

Sherwin: That I cannot say if it was just before or just after—

Bacher: After what?

Sherwin: The war. In other words, May 1945 or September 1945. I do not remember.

Bacher: I do not think that would make a lot of difference because the war in Europe was over by May ’45.

Sherwin: In other words, he insisted that the target was always Japan.

Bacher: I do not think a lot of people who worked on the bomb in other laboratories than Los Alamos – I do not know too much about what people thought there. I do not think a lot of people really had that view when they went into the project in the first place. I went to work at Radar about a year before Pearl Harbor and it looked very grim. It looked extremely grim in Europe at that time. It did not even look good by the spring of ’43 when Los Alamos was started, but it began to look better.

Sherwin: It was better. The Russians had already turned the Germans around in Stalingrad and the Japanese had been turned around at Coral Sea.

Bacher: When was Midway?

Sherwin: Spring of ’42, May, June, something like that.

Bacher: Yeah.

Sherwin: I think that the fear, at least, had gone that they would be in California or anything like that. The concern was how was this thing ever going to be won. There is a difference between stopping them and beating them, of course.

This is a trivial point, but I am just curious. I am not familiar with this quote, where you say on the first page to quote his own words, he “almost came alive at Harvard.” Do you remember where you read that? In one of the books or something that he said to you?

Bacher: I do not remember anymore. But I think it is very likely if I put quotation marks on it, it is very likely something that he wrote in one of his essays.

Sherwin: It was not something he said to you?

Bacher: No, no. I do not think so.

Sherwin: You said that you met him in 1929.

Bacher: I think it was ’29.

Sherwin: Do you remember what the circumstances were?

Bacher: Oh, yes, I remember the circumstances quite well. I was a graduate student at Ann Arbor at the University of Michigan. They had these summer sessions there. George Uhlenbeck was in Ann Arbor and Oppenheimer was a great friend of Uhlenbeck’s. Oppenheimer came for a series of lectures to Ann Arbor during the summer of 1929. These were not very large sessions at that time. This was before the enormous expansion in physics. These summer sessions were where you sort of got to know people.

Sherwin: Are you talking about a dozen people perhaps?

Bacher: It was more than that because there were the graduate students at Michigan and there were the faculty members at Michigan who came. There were a fair number of visitors from the outside. I would not want to say how many there were, but the lectures were in what would be called a small lecture room that we would give a graduate course in today or something like that. I mean there were not enormous numbers of people.

But the way I got to know Robert and a good many of the other people too was in part because I grew up in Ann Arbor, and my family had a summer place at a lake about twenty miles away. My mother usually stayed out there in the summer. When it was terribly hot, I used to go out there evenings, back and forth, and was always there on weekends. Depending on the weather, sometimes she’d be in; sometimes not. But quite frequently, we sort of held an open house for people who came. We would have a group of a dozen or so out there who would come and usually stay for supper, a simple supper on Sundays. Inevitably, I got to know people much better this way than I would otherwise. I can remember the first time Robert came out there. With Robert’s luck on things, he was stung by a bee and he was allergic to it. It was really quite frightening.

Sherwin: What? I mean, he became short of breath?

Bacher: No, it was not that. If I remember rightly, it was on his leg or his arm or someplace.

Sherwin: What was the reaction?

Bacher: It was just enormous swelling and so on. I got to know Robert a bit more and especially because the group was rather small. Robert was at that time quite a difficult lecturer. In the summer of the year 1930 or 1931, I was a National Research Council Fellow here at Caltech. That was the first year I came to Caltech. He then spent part of his year down here. I was not working with Robert Oppenheimer. As a matter of fact, I was doing some work on spectra, atomic spectra.

I attended some lectures of Robert’s and they were extremely difficult to understand. They were incoherent. It is interesting that in the process of his later life, he came to the point of giving these absolutely magnificent lectures. I think this was something that he thought about very hard and worked at very hard. In fact, I know he did.

Sherwin: I suppose, in one sense, this was the first transformation. There was a whole series of new Robert Oppenheimers, or parts of him that are fundamental. Usually, if someone is a good lecturer, they are a good lecturer. If they are bad lecturers their whole academic career, they remain poor lecturers. He made this incredible transformation.

I have gone through his papers at the Library of Congress. It would probably interest you. Each of the lectures has three folders. One folder is correspondence, another folder is notes, and the third folder is usually the transcript that somebody has taped, transcribed, and sent back to him. The notes are a yellow sheet of paper like this. It sort of looks like this, you know, a couple of lines here and there, maybe a quote or two. But just absolute fragments. Then you read the transcript and it is crafted prose, beautiful. This is not what he has edited now. This is the transcript. The published version is generally a few commas, a word taken out. He developed this ability to speak in the clearest and most rhythmic way.

Bacher: Sometimes when he was particularly concerned about something, he wrote his talks. He did that occasionally. Sometimes he would have a subject, which he would lecture on a number of times, and you would find an evolution of a talk.

Sherwin: This sort of disastrous lecturing ability when he was young is extremely interesting.

Bacher: It was fantastic. He was very difficult to understand. And this was not just because he was incoherent, but you could not read what he wrote on the board very easily. And he would start to write over here about something, and then he would pace up and down and talk for a while then continue writing on the other end of the board or something. It was all very disorganized.

Sherwin: It is another thing to take this and sort of absorb it so well, and reorganize it in your own head so that it will come out clearly. Was that part of the process?

Bacher: Gee, how do you know? I mean I do not know. My feeling is that it took him some time, and it took some incentive to get him around to a point of extraordinary clarity.

Sherwin: Do you think self-confidence has anything to do with this?

Bacher: I do not believe that was it. I really do not. Is that story about [Paul] Ehrenfest in this thing?

Sherwin: Oh, yes, when he is banging on the table because he could not hear you on the telephone. Yes, that was a very good story.

Bacher: That is just typical.

Sherwin: When you are talking about Oppenheimer coming to this area – Berkeley and Caltech – with the new quantum mechanics, could you briefly tell me what the excitement of quantum mechanics was for the physics community?

Bacher: In the first place, there were just a host of problems that could not be solved, and that had not been touched before.

Sherwin: For example?

Bacher: Essentially the problems of atomic spectra. The Bohr theory could give you a hydrogen atom. The Bohr theory almost bogged down at trying to do anything quantitative beyond that. A great deal had been done at the classification of spectra. A lot of that occurred here at Caltech and the Mount Wilson Observatory laboratory, which existed here because they had a very good spectroscopic group there. [Ira] “Ike” Bowen, later director of the observatory, operated one of the leading spectroscopes in the country at that time and made great contributions, especially in the spectra of the light elements, which were particularly important in the energy of the stars, the sun, and so on. He did a great deal of work in this area.

In terms of trying to understand this in the mid-twenties before quantum mechanics, the techniques of classification were well known. In fact, some of that goes back long before even the Bohr theory. But there was not any way of connecting it with a real theoretical understanding. It only came out of quantum. Now the same thing is true in a lot of other areas, too. The same thing was true in terms of particle physics. Remember that in 1932 both the neutron and the positron were discovered. They were there in enormous quantities too, and [James] Chadwick’s work on the neutron was unbelievable.

To give you a little feel for that, I spent the summer of 1932 in Cambridge, Massachusetts. This was the second year of my National Research Council Fellowship. John Slater, who was the principal theorist at MIT then and the head of the department, had a small group there. Ed Condon came up during that summer, and Phil Morse was there. Jay [Julius] Stratton, Will Allis. I have forgotten some others too. We had a seminar once a week, which was mainly to go back and sort of read up things.

Slater came around to me and said, “There is something I think we should hear about in the seminar.” He said, “It is not in your field and close to what you work at, but I think it should be reported. It is probably not true; it is probably nonsense and so on.”

I said, “What is it?”

He said, “There are two papers by Chadwick on the neutron. They came out in April in the Proceedings of the Royal Society.” I do not know if I was aware of them or not. Anyway, sometime in June he asked me if I would report them.

I said, “That is not my field. I do not know very much about it but I will go take a look at them.”

I went to take a look at them. I had read a little bit just for general education in radioactivity. But I did not know much about particle physics. In fact, I knew practically nothing about it. I started to read this stuff, and I read through it very carefully. I said, “Goodness, this is true. This is really true.”

I went down to see Slater and I said, “I think you should get somebody more experienced than I am to report this paper in there. I think that paper is correct, and this is a very important report and a very important discovery.”

“Oh,” he said, “you report it.” So I went in.

Copyright 2005 Martin J. Sherwin. This transcript may not be quoted, reproduced, or redistributed in whole or in part by any means except with the written permission of Martin J. Sherwin. Rights granted to Atomic Heritage Foundation.