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Oral History Transcript — Dr. William Fowler

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Interview with Dr. William Fowler
By Charles Weiner
February 6, 1973

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William Fowler; February 6, 1973

ABSTRACT: Post-war career at Caltech, federal funding for research, relationships among Caltech, Jet Propulsion Lab and Office of Naval Research. Work through 1950 in nuclear physics, astrophysics, element synthesis in stars, influence of Bethe, Greenstein; Bowen/Lauritsen seminars, astronomical observations. Fellowship to Cambridge (1954ó55), beginning of collaboration with Hoyle and Burbidges; return to Caltech, further work on stellar element synthesis with Burbidges, personalities of G. Burbidge and Hoyle; contemporary views on cosmology.

Transcript

Session I | Session II | Session III | Session IV | Session V

Weiner:

Todayís the 6th of February and weíre resuming our discussion in Professor Fowlerís office. Weíre just looking at a notebook which contains your own notes of Oppenheimerís lectures on nuclear physics which we date, because it refers to fission and a few other things, as 1939 at least, and then the other side of the book, upside down, are the notes of 1946 starting I believe in January.

Fowler:

January 31st, I think it was.

Weiner:

31st, right, of the so called Bowen seminar, which provides an outline of the seminar, then the notes of the presentations of individuals, so weíll try to copy them. When we left off yesterday, we said we were going into a new period. A new approach. That is to talk about the developments not so much programmatically, but of your own work, the relationship to various visitors who came here. The first one we mentioned of course was Bethe, earlier, that was Ď47, but we didnít really talk about that -- and to talk about how the work gradually was enriched with visits, your own involvement -- talk of the period letís say starting off with Betheís visit, then Salpeterís visit, Ď51, in Ď53, your own going to Cambridge, in Ď54, and I said, just to repeat myself, we wanted to talk about those interactions, how it affected your work and the larger work here, and also your own observations of the growth of the field in a very rapidly developing period, the field of astrophysics, nuclear astrophysics, cosmology. So where do we start, with Bethe?

Fowler:

Well, Betheís visit was mainly because he was interested in the fact that we were measuring the reaction rates of the carbon-nitrogen cycle reactions and were right in the middle of it, and it was the first time that I had ever had any extended opportunity to discuss matters with Hans Bethe. I had met him during the war at Los Alamos, of course, but it was a very interesting few days. As I think Iíve said before, he stayed at the home of my wifeís uncle, and I went up to see him there several times, and in the garden[1] we talked over what I was doing and what new ideas he had. It was mainly, for me, an opportunity to talk to the great man, and to discuss with him the measurements that we were making. However, probably then the most significant change in direction of our work came in 1951, when Salpeter came to Cal Tech. I would guess he must have been on a sabbatical leave from Cornell. He introduced us to the problem of helium burning in stars. All that we had been doing on the carbon-nitrogen cycle and on the processes that take part in the proton- proton chain had to do with hydrogen burning in stars.

Weiner:

All right, you were telling about Salpeterís visit.

Fowler:

Well, Salpeter had become interested in how the helium, that is the product of hydrogen burning stars, how it finally is processed in stars. By that time Salpeter had interested himself in astronomical or astrophysical problems. Astronomers were aware that the hydrogen burning, when the hydrogen was exhausted, resulted in what they call a helium core in the interior of the star, and the question was, the red giant phase of stars should exhibit the properties of such a model, namely, a helium core surrounded by a shell of still burning hydrogen, surrounded by a large envelope that was still inert. So Salpeter was trying to figure out what happened when the helium began to interact, and he had come across or was thinking about a process that Bethe had actually mentioned in his carbon-nitrogen cycle paper, which actually included, if you go back and look at it, much more nuclear physics in stars than just the carbon-nitrogen cycle, which was the most famous part and the part most publicized.

Anyhow, Bethe had realized that two alpha particles bumping together did not interact to give nuclear energy because presumably the nucleus that it would form, berylium-8, did not have a stable ground state that was less massive than the sum of the masses of two Kellogg and Los Alamos alpha particles. So he had suggested that perhaps there would be circumstances in which three alpha particles could interact to form carbon-l2, and Salpeter had been thinking about that, and when he came here (summer, 1951) -- actually it may well have been that he came to think about it after he got here. He spent part of the time up at Mt. Wilson and part of the time here, and this whole question of what was happening in red giant stars and in their helium cores was uppermost in the minds of a great number of people. Nevertheless, from my own standpoint, I remember, I read Betheís article but I had read it mostly for the carbon-nitrogen cycle statements.

I had completely forgotten that Bethe had also worked out what would happen to helium, and so it was new for me when Salpeter said that he was working on the three alpha to carbon-12 process. So while he was here in 1951, he worked out the details of the calculation and showed that, essentially because the lowest state of beryllium-8, which is not bound, serves as a resonance in the kind of a two stage process Ė- first two alphas collide, amalgamate, to form the lowest state of beryllium-8, and then before it can disintegrate back into two alphas, a third alpha particle hits it with the emission of gamma radiation to form the very stable carbon-12, the overall result being that three alphas form carbon in helium burning. So Salpeter had worked that out, and that was our first, at least for me it was the first indication that what we had been doing in the hydrogen burning was just the very start of all this nuclear astrophysics, that here was now what happens next, and then one could begin to see, after the helium was burned and itís formed carbon, what does the carbon do? As a matter of fact, those more advanced problems remain with us to the present time.

As I remember, we didnít do anything about this three alpha process, although just after the war, we had made measurements on the beryllium-8 nucleus. We had produced it in the laboratory by bombarding beryllium-9, the known stable form of beryllium, with protons. Deuterons are given off, beryllium-8 is formed, it then breaks up into two alphas, and we had measured the breakup energy because it is a critical number in nuclear physics, and eventually it turned out in this process. We had done that before Salpeter came. Itís reported in a paper by Tollestrup, Fowler and Lauritsen.

Weiner:

Yes, thereís one by -- ďThe Energy released by beryllium in lithium reactionsĒ -- or is that an earlier one?

Fowler:

Yes, see, that had been done in 1950. But it may well have been the fact that we were working on that, was why Salpeter came out,[2] because he was working -- now that I think of it, thatís the way it was. He came out because we were working on this very first stage in his process, getting a number that he needed, and so that probably had something to do with his coming out here on a sabbatical in Ď51. But then the next step in the game was Fred Hoyleís visit -- I have 1953 here, and it was either 1953 or 1952. If I look at the papers here, we can soon find it. Anyhow, in -- I donít see it there -- in my recollection of things it was probably 1953.

Weiner:

You said Ď53 in the Engineering Science article.

Fowler:

And I would think that I would have looked up the date for the preparation of that article. So Hoyle came, was invited to Cal Tech to give a lecture, as I remember, on some aspect of cosmology, probably a lecture on the steady state theory, in which he was very intimately involved, very actively involved at that time. I remember that we anticipated such a large audience for his lecture that it wasnít held on the campus here, it was held up at what was then the Pasadena Junior College, which did have a much larger auditorium, and sure enough Hoyle filled it. I remember that after the lecture, for reasons that I canít recall actually, we had a -- no, it was before the lecture, we had a cocktail party for Hoyle and some of the members of the faculty. That was the first time that I recall actually getting to know Fred Hoyle. But then he stayed on after his lecture for a few days, and in fact the next day he came in to the laboratory and began asking us questions about the energy levels of the carbon-12 nucleus. Now, we havenít discussed that before in this transcript?

Well, this turned out to be a very exciting business, but at the time I remember being very skeptical of this steady state cosmology; even in those days in this area steady state cosmology wasnít very popular. But in particular I was very skeptical that this steady state cosmologist, this theorist, should ask questions about the carbon-l2 nucleus. What he wanted to know was whether there existed a second excited state of carbon-l2 around 7.6 MeV in excitation, there already being a state around 4.4 MeV excitation, the first excited state being well known. Well, Tommy Lauritsen was of course then and now the keeper of the records on excited states of nuclei. Heís had a long series of articles in Reviews of Modern Physics and in Nuclear Physics presenting the most up-to-date findings on the energy levels of nuclei. So we talked to Tommy (Lauritsen), and as I remember Charlie (Lauritsen) was in on it, and Hoyle kept insisting that there had to be a state in carbon-12 around 7.6 MeV, and we finally dug out of him his reasons for this. It turned out that he had become interested in what was by that time being called the Salpeter process, although as I said it was in Betheís original paper, at least mentioned there, namely the conversion of three helium nuclei into carbon-12. Hoyle had become interested in that because he and Schwarzschild had been working out previously the conditions, the temperature and density at the end of the red giant branch of stellar evolution in the Russell-Hertzsprung diagrams.

And from their theoretical models, they were able to calculate the central temperature and the central density at the tip of the red giant branch where, they felt, because there were no stars beyond there, that the helium burning must commence, and stop the evolution along the red giant branch. So Hoyle had ideas of what the temperature and density were and he had put these into Salpeterís calculations and found that the helium just didnít burn fast enough. It didnít give the necessary energy that his model required. So Hoyle, it turned out, we found out much later, had been trained in nuclear physics. He knew a great deal of nuclear physics, and he realized that the only way he could speed up the Salpeter process was to insert a resonance into the second stage of the three alpha into carbon-12, namely, when the beryllium-8 formed from two alphas, interacted with a third one -- that also had to be a resonance process. And so on those grounds he had calculated that this resonance should be equal, should be at a point where it just matched the mass of beryllium-8 plus the mass of helium over the mass of carbon-12, plus 300 kilovolts of thermal energy to really get it going. And on that basis he had calculated that this resonance had to be at 7.68 MeV above the ground state of carbon. Well, Tommy Lauritsen looked up the records, and indeed at one time or other in some of his very early diagrams, there had been a dash line which indicated an uncertain state around 7 million volts in carbon, but subsequently just after the war that state had been looked for by Buechnerís group at MIT and they hadnít found anything.

So, believing in Buechnerís results, Tommy had dutifully erased this state, and in the more recent publications there was no state in carbon-l2 around seven million volts. Well, Hoyle just insisted -- remember, we didnít know him all that well -- here was this funny little man who thought that we should stop all this important work that we were doing otherwise and look for this state, and we kind of gave him the brush off. Get away from us, young fellow, you bother us. So actually neither Tommy nor Charlie Lauritsen nor I did anything about it. As I remember, Fred talked to other people in the lab, and to it make a long story short, he convinced Ward Whaling, who was an assistant or associate professor at that time -- he was relatively new in Kellogg, had come here as a post-doc from Rice University and because of his obvious competence had been appointed an assistant professor. Anyhow, Ward Whaling decided to give it a whirl, and to make a long story short, he and the group working with him -- Dunbar, Wenzel and Pixley, performed an experiment of bombarding nitrogen with deuterons, producing carbon-12 and alphas and the alpha particles that leave the carbon-l2 in excited states have less energy than those that leave it in the ground state.

Thus by looking at a spectrum of the alpha particles from bombarding nitrogen-14 with deuterons, they determined the states in carbon-12 -- and sure enough they found the ground state, very strong alpha particle group leaving carbon in its ground state; they found a very strong group of alpha particles leaving carbon-12 in its first excited state, the one already known, and then at still lower alpha particle energy, they found a very weak transition, which nonetheless, weak or not, indicated that there was a third state in carbon-12, the second excited state, and the energy they got was almost exactly what Hoyle had predicted. We now know that the energy is 7.655 MeV rather than Hoyleís guess of 7.68. So it was really quite a tour de force, that a man who walked into the lab predicted the existence of an excited state of a nucleus, and when the appropriate experiment was performed it was found. And no nuclear theorist starting from basic nuclear theory could do that then, nor can they really do it now. So Hoyleís prediction was a very striking one. And of course when measurements of the properties of this state were attempted, then the old boys got in on it, and we spent a lot of time measuring, doing experiments measuring the properties of this state in carbon-l2, and when those properties were put into, by now the Salpeter-Hoyle formula (it had to be modified for this resonance) -- the Salpeter-Hoyle formula for the process, the agreement with the astronomical observations was fairly complete.

Weiner:

After a coffee break where we met Ward Whaling, we started digging in more. The paper in which Whaling was involved first appeared as an abstract, which he asked Hoyle to put his name on since heíd suggested the idea. Ward Whaling at the moment is looking in his files to see whether he has some further background. The actual publication then was in Phys Rev, volume 92, page 649 -- that was Ď53, and it was the 7.68 MeV state in carbon-12 by Dunbar, Pixley, Wenzel and Whaling. The results were announced at a meeting of the American Physical Society at Los Alamos and published in PR 92, 1095 (1953) with Hoyleís name the first on the abstract. Itís not clear to me how long the visit was for, did you ever work that out in our conversations?

Fowler:

Well, this is what we are now concerned to establish accurately, because Ward seems to remember that Hoyle came earlier. But I think itís -- at least in my mind itís fairly important that we get this with some accuracy. I donít know whether you want to turn that off for the momentÖTo get into the record the fact that Fred Hoyle was a visiting professor, let me read it again, carefully -- visiting professor of astrophysics during the academic year 1952-53, as indicated in the catalog for that year. Now, unfortunately, I donít have Ď51, Ď52. See, he may have come even earlier, which weíll have to check.[3] But in our conversation with Ward Whaling it developed that Hoyle was giving courses in astronomy, and that he, Whaling, had attended these courses.

Weiner:

He didnít say courses, he said lectures.

Fowler:

Lectures. Well, I think actually it was a course for credit. Iím fairly certain it must have been that, because I do not remember those lectures or that course. As I was saying earlier, my first recollection was having a party for Fred Hoyle before his lecture on the campus of the junior college here, which Whaling told us was in connection with a AAAS meeting in Pasadena that year. So from what we have learned, Whaling knew Hoyle from the course or lecture course that he had attended, and the upshot of the whole story is that Whaling was the man in the laboratory who took Hoyle seriously enough to do something about it. And as he was just telling us, he had just completed the construction of our low energy high current machine, which was designed for work in nuclear astrophysics, and as he said, he was looking for problems to work on with the machine, and so he found, showed the existence of Hoyleís state. And that is one of our triumphs in nuclear astrophysics, that a very complicated problem, the way in which helium burns, has been solved through a combination of theory, Salpeter and Hoyle, on the one hand, and an experiment, Whaling and his group, on the other hand, that showed that there was resonance in the second stage of this process.

We then took Hoyle very seriously, because of this triumph from our standpoint in predicting the existence of a nuclear state from astrophysical arguments. I at least then took him very seriously, and we did a lot more work on his state in carbon-12. We, for example, had to show that it not only existed but that it could be formed from three alpha particles. You see, the exclusion principle applies, and it could have been a state in carbon-12 which could not be formed by the combination of three alpha particles. Ultimately we and other laboratories showed that it had the proper properties to be formed from three alpha particles, and in fact we, the two Lauritsens and I and a graduate student, Charles Cook, showed that if you produced this state of carbon-l2 in the laboratory, that it indeed broke down into three alphas. We could actually observe them. Then by detailed balance we know that any state that can break down into three alphas can also be formed that way. So that was a very interesting series of events, and I became so interested in all of the advanced stellar evolution that Hoyle was doing that I decided that I ought to take a sabbatical year, the first one that would ever have taken, in 1954, the academic year 1954-55, and I found that at that time, there were the Fulbright lectureships available to Americans who wanted to spend a sabbatical year in England or Europe, and so I first applied for Denmark, actually, showing that I was somewhat ambivalent about what I wanted to do. I guess I figured that I could have the best of all possible worlds, I could go to Bohrís Institute in Denmark and then spend some time in England with Hoyle. And so it was somewhat out of my control, when you get right down to it, that was told that there was a position available in England in the Fulbright list but not in Denmark. The Bohr Institute was so popular that every physicist in the country wanted to go there. I suppose what happened -- and I later on was on the committee that chose Fulbright lecturers, and if a person gave a second choice, which I think I did, I made Cambridge my second choice, the person gave a second choice and if his first choice had many applicants, then he got his second choice. Well, thatís what happened to me.

Weiner:

Youíd have had to have made that application, that decision, already in Ď53 though.

Fowler:

I was singularly impressed by what Hoyle had done. And of course during Ď53 as weíve just seen Whaling and his collaborators had published their results, and so I made an application for the following fall, and in the fall of 1954, I went to Cambridge.

Weiner:

Let me ask a question before we get onto that phase of it. You mentioned that when Hoyle first came, the general local reception to the steady state theory was not an enthusiastic one, negative as a matter of fact?

Fowler:

Yes.

Weiner:

Then you talk about how impressed you were with the experimental confirmation of one aspect of his work, which turned you on to the subject in general. Ward Whaling downstairs also mentioned how the astronomers would constantly snipe at Hoyle during lectures and courses and how he would come back the next day with an answer to a specific question. Well, was there a turnabout in your overall view on the steady state theory? Did this mean that you were embracing all of Hoyleís ideas or that you were just curious about investigating them further?

Fowler:

Well, I wouldnít say there was a turnabout, because quite frankly I hadnít worried about the cosmological problems up until that date. It was not until I met Hoyle that I began to realize what was involved in the controversy, and of course once I became his close friend, which I did then during the year in Cambridge, I of course turned a very sympathetic eye on the steady state theory, although I think itís fair to say that even then and certainly now, I take the attitude that all of the cosmological models -- the steady state, the Friedman models, the ďbig bangí as itís popularly called, are all much too over-simplified, and none of them can be even a close approximation to what must be the truth. Now, this doesnít mean that I havenít done some work in the area; to come much further forward in time, the discovery of the microwave radiation -- which had, itís true, been predicted from the big bang models, but on quite erroneous grounds, as I found out by looking into it -- motivated me, and Fred Hoyle and Robert Wagoner, who was a research fellow here at the time, to look into nuclear synthesis in the big bang. In time we had to look into all the physics of the big bang, and so I did that, even though I didnít particularly think that this over-simplified homogeneous isotropic universe could at all model the real universe. And of course the same must have been true for Fred Hoyle, because he entered into the calculations with me and Wagoner, and made very real contributions to what has become a work thatís a very significant contribution to the literature, although all we did was in large measure confirm what Fermi and Turkovich had found many years before, that you could not make heavy elements in the big bang, because of the mass 5 and the mass 8 difficulties.

Weiner:

Which paper, what year was this?

Fowler:

Oh, thatís much later. Itíll be in the sixties.

Weiner:

Thatís when I heard you talk about it, I think.

Fowler:

It might be Ď66. Itís the Wagoner, Fowler and Hoyle paper on ďThe Synthesis of Elements at Very High Temperatures,Ē appeared in Ap. J. 448, April, 1967, and I notice it was received September 1, 1966, and Iím fairly certain that we started working on it in the fall of Ď65 which was when Wagoner came here as a research fellow, after getting his Ph.D. under my old friend Leonard Schiff at Stanford. Well, thatís jumping ahead of the game.

Weiner:

But thatís something we want to talk about some time in detail.

Fowler:

Yes. All right...

Weiner:

All right, I think youíve answered the general question about your attitude towards the overall cosmological theory, and I interrupted you at the point where you were about to go to Cambridge. Iíd like you to tell that story in detail, about your response to that environment, the differences you perceived, and the state of nuclear physics in general there, if you were able to observe it; and then of course in detail your relationship with Hoyle. Also, what were you doing/every day there?

Fowler:

Well, of course, Cambridge and England was really a terrific experience for me. It was something entirely different from any other experience in my life -- raised in Ohio, educated here in California, to go to a city of very old culture such as Cambridge was really a terrific experience. My wife went along and my two daughters, who were I guess 11 and 13 at that time, and I would say it was really one of the great years of my life. We rented the home of Denis Wilkinson, physicist. He had a year off to come to Brookhaven that year, so we lived in his house, on a very nice little court, Claremont Court, out on Hills Road in Cambridge. I had a bicycle, for example, and I rode down Bateman Way and Tennis Court Lane to the Cavendish. I had Denis Wilkinsonís office in the Cavendish. Tony French, who was -- is now professor of physics at MIT, was there. Nuclear physics was just about ended. Not entirely. There were research fellows, what we would call graduate students, like Neil Tanner, so there was some nuclear physics going on. They were still using the old original Cockcroft-Walton generator, and Kempton I remember at that time had plans to build a linear accelerator.

Weiner:

You were talking about Kempton and what he had in mind on the linear accelerator.

Fowler:

Yes. Kempton had collaborated with Rutherford in the early exciting days in the l930s, and had plans for building a linear accelerator, but these plans were quashed while I was there because Mott, who was the new Cavendish professor -- in fact 1954 was Mottís first year as Cavendish Professor in succession to Bragg who in turn had succeeded Rutherford -- wanted to go into other aspects of physics, primarily solid state physics, and so Kemptonís plans for building a linear accelerator never came into being. Now, there was one other accelerator there that had been built during Braggís tenure as Cavendish Professor, although it may have been started under Rutherford, but there was a Van de Graaff accelerator, a vertical Van de Graaff, pressurized type, that had been built by Shire who was one of the senior people in the Cavendish Lab. So there was, I must say, now that I think back on it, considerable low energy light nuclear work going on, and of course Ė-

Weiner:

-- there was a cyclotron there as well.

Fowler:

I guess there was a cyclotron, youíre quite right. I never made much contact apparently with the people working in the cyclotron lab. I mainly became friends with the youngsters who were working with Shireís Van de Graaff and with the old Cockcroft-Walton machine. And of course, oh dear -- the fission man, the Jacksonian professor --

Weiner:

Frisch --

Fowler:

Frisch was there, and -- but I didnít get to know Frisch very well, although he was very hospitable. For reasons that arenít completely clear, I didnít really get to know Frisch very well. He was concerned with what was going on in the cyclotron then, andÖ Of course, the other thing that happened and happened very soon was the fact that I met Geoff and Margaret Burbidge that year. I remember distinctly giving a colloquium in the Cavendish in which I discussed the experiments which had just been completed before I went to England in the fall of Ď54, the experiments that I referred to earlier with the two Lauritsens and with Charles Cook in which we had shown that Hoyleís state really could do the trick because it could break up into three alphas and thus it could be formed from three alpha particles. So I gave a colloquium on that and discussed the nuclear physics, and some of the astrophysical interpretations, which I had learned from Hoyle.

Well, the next day, Geoff Burbidge came into my office, I remember -- Geoff has, as everyone knows, very striking physical characteristics, very heavy jowls, looks for all the world, at that time looked like a very young Charles Laughton and in many ways acted like Charles Laughton, the great actor. Anyhow, Geoff Burbidge came into my office, introduced himself, said he had been at my colloquium, and that he found it very interesting, but he really couldnít care less about this complicated process by which helium is converted into carbon. He was interested in the nuclear aspects of the production of the heavier elements, the reason being that he and his wife Margaret had been making observations -- that is, Margaret had, because she was and is an observing astronomer -- on abundance peculiarities in certain types of stars, barium stars which have great over-abundance of barium and lanthanum and so forth. And he, Burbidge, a theoretical student who had gotten his degree the year or so before under Massey at the University of London, was trying to understand these rather strange observations that Margaret Burbidge and other observers were finding.

So that started an immediate collaboration between the Burbidges and myself, into which Hoyle, who was awfully busy at the time and was away from time to time, didnít enter. But anyhow in addition to being in this great wonderful atmosphere and still seeing Hoyle from time to time, really the very special thing that happened to me was that I met Geoff and Margaret Burbidge. We then began trying to understand how peculiar, how overóabundances of heavy elements could be produced and then observed in stars, and as a consequence while I was there during my Fulbright year, the Burbidges and I wrote two papers together -- Fowler, Burbidge and Burbidge. But Hoyle did not enter into that work enough so he did not join us in the publication of the papers. Now, the papers may have come out in 155 or even Ď56, but they appeared in Ap. J. in í55 Ė- ďNuclear Reactions and Element Synthesis in the Surface of Stars.Ē Thereís another one, ďStellar Evolution and the Synthesis of the Elements.Ē

Fowler:

Is that Ď55?

Weiner:

Thatís also Ď55.

Fowler:

Yes, well, you see I didnít get there till the fall of Ď54, so we started working together immediately. I gave this seminar early in the fall term, this colloquium, and immediately we began collaborating on this problem, which involves the production of neutrons in stars and then their subsequent capture by seed nuclei like iron to form the heavy elements such as barium which Margaret was observing. So that kept me then pretty busy that whole year, and again it introduced me to a new aspect of nuclear astrophysics. The Salpeter-Hoyle business showed me and others that there was something beyond hydrogen burning. There was helium burning. And in fact Hoyle in a very famous paper in l946 had analyzed, sketched out the charged particle interactions which go all the way up to the production of the higher group nuclei, iron and chromium and titanium. What I learned, when I started to work with the Burbidges, was that with charged particles, because the Coulomb barriers became so great, you couldnít go beyond something like iron or chromium or cobalt or nickel, and that to build the very heavy elements one had to envisage neutron processes.

So that was a whole new field that was opened up in my collaboration with the Burbidges. Now, if we can go ahead to kind of get the broad history of what happened, because I think itís interesting, and leave the Cambridge year for the moment. When the year ended, I realized that there was a great deal more to be done in collaboration with the Burbidges and with Hoyle, and it turned out that Geoff Burbidgeís appointment as a theorist in the Cavendish was ending that year, and he and Margaret were essentially looking for a job. So before I came back I began to make arrangements so that they could join me in Pasadena, and Margaret of course wanted to observe. That was the field for her. But the problem was that knew that it was very difficult for women to make observations at Mt. Wilson -- I think Palomar was completed by that time but there were longstanding prejudices in the astronomical community against women observers. The director then, Ike Bowen, my old friend, said, ďWe canít have women up there because we donít have toilet facilities for them,Ē and things like that. Astronomers call the place they stay on the mountain the Monastery, as you know. So we had to trick the Carnegie Institution people. We got Geoff appointed as a Carnegie Fellow. The Carnegie Institution did give Carnegie fellowships in theory, so Geoff Burbidge was appointed a Carnegie Fellow at Mt. Wilson, and then I arranged for Margaret Burbidge to be given a research fellowship in physics in the Kellogg Lab, paid for out of our grant funds at the time. So in the fall of Ď55 Margaret and Geoff came to the United States, and Geoff took up his Carnegie fellowship at Mt. Wilson and Margaret took up her research appointment at the Institute, and it just developed that whenever Geoff went to observe, which he decided to do after he got here, Margaret went along. So there was a happy ending in that regard, and Iím sure that Bowen was very soon aware of this, but he knew that Margaret had quite a reputation as an observer, and he knew she was doing good work, so Ike simply just overlooked the fact that maybe some silly rule was being broken.

Weiner:

Would Geoff Burbidge have known what to do?

Fowler:

Oh, Geoff wouldnít have had the slightest idea. Heís all thumbs -- and brains! So we immediately started further collaboration, and as I recall, Hoyle came in his by that time established position as a visitor, either in astronomy or in physics, and so the four of us were working together here, although it may actually have happened in Ď56. The time all passed very fast. Yes, we continued to collaborate. The Burbidges were certainly here, the next thing of major importance that occurred was the publication in 1956 of Ė- by Suess and Urey, of an article called, ďThe Abundance of the ElementsĒ in the Reviews of Modern Physics. We have been struggling to understand in terms of nuclear physics the abundances of all of the elements in nature, the so-called cosmic abundances of the elements. Weíve been trying to understand that but especially in the heavy elements. But the evidence prior to 1956, based on astronomy, spectroscopic observation and astronomy, actual measurements on meteorites, showed such a great deal of scatter that there was nothing in which we could really get a start in understanding the nuclear processes. Now, there was the general feature that the abundance of the elements falls off from hydrogen out to mass 100 and then flattens out, with a peak around iron, which we had come to understand as being due to the fact that iron is one of the most stable nuclei in nature, due to a combination of surface nuclear effects and Coulomb effects.

Some very broad general features were understood. But to know what was going on in the production of the heavy elements Ė- which by now we knew had to be made by neutrons and we were beginning to understand some of the nuclear rules for neutron production Ė- the scatter in the data was so great that all the essential features were obscured. And what happened in 1956 is that Suess and Urey made a review of all the abundance determinations, primarily the abundance determinations on meteorites, and in addition -- and think this was primarily due to Hans Suess with his great intuition, at least Harold Urey has told me so -- they had used the relative abundances of the isotopes of a given element. For example, tin has ten isotopes, so itís a rich feast of knowledge about abundances around mass 125. They had used the relative abundances of the isotopes of the elements as a guide in sorting out all these variations that were apparent primarily because you canít really say what is the abundance of xenon, which is a rare gas, relative to tellurium and the isotopic abundances of xenon, and adjusting those two segments of an abundance curve so that it fitted, and by doing that elsewhere, Suess and Urey took a lot of the scatter out of the data on abundances of the elements. In doing so they showed that at several places in the abundance of the heavy elements there were double peaks -- double peaks in the abundance relative to the nearby region. That is to say, if you plot the abundance versus the atomic mass or the atomic weight, there are double peaks around mass 90, and there are other sets of double peaks around mass 140 and 196, and so that we immediately realized then that the second of these double peaks in both cases was associated with nuclei with a magic number of neutrons. For example, in the peak around 90, the nucleus that makes that peak is zirconium 90, and zirconium 90 has 50 neutrons. It therefore is a closed shell of neutrons. It doesnít like to add the 51st neutron.

That means it has a very low cross-section for neutron capture. That means that if itís been built up in a neutron capture chain. Because it has a low capture cross-section, it has to build up a great abundance in order to keep the chain going. So we could see immediately -- and there was a corresponding peak corresponding to 82 neutrons. That for example is one of the barium isotopes, barium 138, I think, I may get this wrong, I should remember which barium. Barium is element 56, add 82 neutrons, you get 138 -- barium 138 sticks out as the most abundant isotope of barium, and when Urey and Suess had fitted all these around, it gives a peak, cerium 140. That was the neutron number 82, and then thereís another peak, the second of three, the second of a pair, that led to Pb208 which is doubly magic. So there were these three double peaks, and the second of each of these pairs, we immediately recognized as corresponding to what were called magic nuclei, with 50 neutrons, which is a closed shell, as Mayer and Jensen had shown -- 82 or 126. So that indicated to us that those nuclei had to actually be involved in the nuclear process that produced them.

You see, you could have the material made in a radioactive form which decayed down to these. But since these were more abundant than their fellows, clearly their special property of a small neutron capture cross-section must have-so they must have been involved in the process itself. That means that the process had to be a slow one so that any radioactivity could disappear during the process, and thatís the origin of what we now call the S process, where the S stands for slow. We then also quite quickly appreciated how making some sense out of the observations and getting the observations straight -- how important such a thing is. The first of these double peaks, we realized then, had to represent nuclei who were magic during the process in which they were produced, but had subsequently decayed. These would have to be then radioactive nuclei with magic numbers. Then when they decayed, they decayed down to something that wasnít obviously magic, yet its progenitor had been magic. Since such a process involves radioactivity of short lifetimes, it had to be a very rapid one, and so the first of these double peaks, and there are three of them, had to be due to a rapid neutron capture process -- the word rapid was abbreviated to R and thatís become the R process. Well, this stimulated us -- Hoyle was here by then and the Burbidges and myself -- to write an article that tried to cover the whole business of nuclear synthesis in stars, and we worked on it, oh, just night and day. Iíve never been so actively involved. There were lots of calculations to be made, lots of writing to be done. Margaret was asked to present, to accumulate as much of the observational evidence on these neutron processes, the R process and the S process, not only in numerical form, but to get some pretty spectrograms that could be reproduced. And the ultimate result was the publication of a paper on synthesis of the elements in stars in the Reviews of Modern Physics in 1957.

Weiner:

Meanwhile though you had published with Hoyle and the Burbidges on the origin of elements in stars, in Science.

Fowler:

That was a preliminary paper.

Weiner:

And the Californium paper with Christie as well.

Fowler:

Oh yes, Iíd forgotten. Everything went very fast. Thatís an entirely different story. There were all kinds of exciting thing happening that year. Thatís a different story. But the Science article is merely a brief statement of what ultimately appeared in the Reviews of Modern Physics article. Itís interesting mainly now historically in that it establishes a certain date of priority, if you want, because as is well known, Al Cameron quite independently and all on his own, when he saw the Suess and Urey paper, also appreciated the things that Iíve just been saying, and quite independently but somewhat later (primarily because he was working alone) published a Chalk River report that covered synthesis of the elements in stars in much the same way that we had done.

Weiner:

Where was he working?

Fowler:

I think Cameron at that time was at Chalk River. Iím fairly certain he was at that time at Chalk River, and he put out his ideas in a Chalk River bulletin, a progress report as it were, that came out sometime after our Science article, but his article then was published somewhat later[4] than our Reviews of Modern Physics article. We of course put out a preprint that was quite a thick volume, one of the very first of what we now call the ďOrange Aid PreprintsĒ that -- I remember we had to get it out in a big hurry because I had been invited to a Semaine díEtude in the Vatican with Fred Hoyle in Ď57. So we had to have a pre-print that I could take along to show people as well as giving a talk on it. But the thing that I think is actually worth repeating -- there we were, Hoyle and the Burbidges and independently Cameron and of course Salpeter and other, all with these rather nebulous ideas, about a nonetheless kind of grandiose scheme of how you could make elements in stars, which we felt was necessary because you couldnít make the heavy elements in the big bang. Even the most ardent supporters of the big bang, including George Gamow himself, had had to realize that you just couldnít get past this mass 5 and mass 8. It was just this other scheme, the synthesis of the elements in stars, which Hoyle had begun to look into because in the steady state he didnít have any big bang anyhow. He knew he had to make elements in stars.

So as early as Ď46, as I just said, as early as Ď46 he had laid out all the charged particle reactions up to the iron equilibrium peak, we call it. Then along came all this neutron business, which I might say the Burbidges and I more or less took the lead in. We had all of these ideas, but we didnít see how to use it until Suess and Urey made some sense out of the data. Iíve subsequently had many arguments with Suess and Urey, primarily about the amount of uranium and thorium produced in stars, but one has to say that it was their very intelligent analysis of the existing data, and just boldly changing in some cases what the geochemists said was the abundance, based on some measurements subsequently proven to be wrong Ė- boldly change it in order to make sense out of the isotope abundances, and keep a continuity in going from one element to the other on the basis of the fitting together of the isotopic pattern. For example, these peaks came because, I can think of one of them Ė- the tellurium isotopes on the low side of the peak are all rising in abundance, the xenon isotopes on the other side are all falling. So when you fit that together you get a peak. But everyone knows that xenon is a rare gas. Thatís not the abundance you find on the earth. Well, the earthís lost all its xenon, just because it didnít combine chemically with other things. So it was a very exciting time, and then as youíve just said there was also the discovery, the production of californium in a nuclear bomb test on Enewitok, and the measurement of its half life at 55 days, and the realization on all our parts that that was the half life also in the decay period of certain types of supernovae.

So Ė- but thatís another story that was very interesting now I think historically, although there are now so many other explanations, probably better ones, for the decay curve of type I supernovae that itís mainly of historical interest. It did encourage us in our analysis of the R process, because we realized at that time that the S process which is the slow one would stop when you got to lead and bismuth, because if you add a neutron to bismuth, 209, which is the last stable nuclear species in the parity table, you make bismuth 210 which I believe decays to polonium 210 by a beta process and that in turn decays by alpha particle emission back to lead 206. So the parents of the radioactive series, uranium 235, uranium 238 and thorium 232, we knew could not be made by this slow process. But here in connection with Suess and Ureyís double peaks we had hypothesized a rapid process, and that is fine because that rapid process builds through neutron-rich nuclei whose alpha decay is slowed down considerably. So then we saw that not only uranium and thorium could be made but all of the heavy nuclei could be made. When the results of the hydrogen bomb explosion were finally known four years after the test, we saw that even in a terrestrial explosion you could get a great enough neutron flux, and these neutrons in turn irradiated the uranium that had been used as an atomic bomb trigger and had by adding neutrons to the uranium built up very heavy nuclei. Californium 254 was one of the final products, which then fissioned. If such a thing could happen in a stellar explosion, the fission of the californium 254 with its great energy release would dominate the energy input into the expanding nebula. And we thought, wasnít it wonderful, the half-life of californium was 55 days as we jokingly said, Baadeís right-time observations on Type 1 supernovae showed a decrease with a half-life of 55 nights.

So that all seemed to make good sense. The problem now is that not all Type I supernovae show exactly that lifetime, and there are other suggestions, both nuclear-wise and otherwise, which may be better theories for the explanation of what one sees after a supernova explosion. But thatís not settled. I want to make it clear that I will not admit that itís settled until in the space program we get up and look with gamma ray detectors at a supernova explosion, hopefully in our own galaxy but it will probably have to be in another galaxy. But all of these various theories, the radioactive theories of energy input into supernovae, are characterized by a definite discrete gamma ray spectrum. We know, if itís californium and its radioactive products, what the gamma ray spectrum is going to look like. If itís due to nickel 56, and cobalt 56, which is another possibility, cobalt 56 has a half-life of 77 days, which is in the right ball park, as you can see. We will be able to tell by the gamma ray spectrum which is characteristic of these two points of view which it is. If there arenít any gamma rays then itís got to be some other explanation, such as Morrison and Sartori at MIT and Sterling Colgate at New Mexico Tech have given. But the main thing was that Suess and Urey paper, coupled with the hydrogen test results, showed that very heavy nuclei could be produced in an explosion or in a rapid process. This gave us the courage to go ahead with the publication of the paper that Iíve been referring to. And of course Walter Baade came into it because he had the best curve on a supernova, that he and Minkowski had taken in 1938. Thatís the curve which, when you plot the magnitude versus time as a straight line -- which is just like the logarithm, like the exponential decay of a radioactive nucleus -- by looking at that straight line weíve gotten this, the half-life, which apparently agreed with that of the californium. So Baade came into it. Christie came into it on the theoretical end. He was the theoretical physicist in Kellogg at the time. He got interested in what the Burbidges and Hoyle and I were doing, when he heard about the bomb explosion. So the very first paper on that subject actually included Christie and Baade as well as the Burbidges and Hoyle and myself.

Weiner:

You mentioned that the Ď57 work leading to the large scale Reviews of Modern Physics paper in Ď57, that Margaret Burbidge contributed the observational aspects. Where did the observational data come from? Was it some new information coming through or did she do a study of the existing data?

Fowler:

She did both. Margaret had been taking spectra since sheíd been here. I guess she was using the 100 inch at Mt. Wilson because she never used the 200 inch. And she also was getting time at Lick and at MacDonald. The Burbidges had spent some time in the United States some years previously. They had been at Yerkes for example. So they were quite well known, it turned out -- Margaret at least was quite well known to the American astronomical community as one of the observers in the business. Geoff of course is considerably younger, and he had just gotten his degree before he married Margaret, and he was not nearly as well known, but he jolly well became well known very soon because of his personal characteristics. Neither Geoff Burbidge nor Fred Hoyle suffer fools graciously.

Weiner:

Iím sure that this paper itself must have made a splash and Burbidge contributed.

Fowler:

Yes, but as I was saying, Margaret had been taking spectra. Some of the spectra that are published in that paper are ones that she had taken herself. In fact I think all the spectra that we put in the paper were ones that Margaret had taken. She especially went about the business, once we decided to get spectra which would illustrate helium burning, the E process, one of the other processes that we talked about, the alpha process, the S process, the R process -- she managed to collect I think primarily from her own observations -- maybe she borrowed some from other people, Iíve forgotten now, but anyhow, she primarily worked on the observational end of it. Geoff Burbidge primarily worked on the astrophysical models, the theoretical astrophysical background. I primarily worked on the nuclear physics calculations and Fred worked on everything. He always has been a Renaissance man. In fact, I consider him the da Vinci of our time because of his great breadth of interest, all the way from science fiction to theoretical cosmology and art and music. Heís really an incredible person in that regard. So out of it came this paper that, I guess itís fair to say, established all our reputations in a way, although Fred already had quite a reputation through the steady state theory.

Weiner:

Let me ask a question about the actual writing of the paper. With that kind of division of labor, did one person have the responsibility for writing it and was it criticized by others? Or did each one actually write a different section?

Fowler:

If you go back and look at the paper you will see clearly that the first part, which is primarily on nuclear physics, was written by me. The introduction was written by Hoyle and the section on nuclear physics, I wrote. The section on the astrophysical significance was written by the Burbidges and I think itís fair to say, primarily by Geoff, although Margaret could well have written the paragraphs of the sections on the actual observations that she had made. People have often asked me about this, about papers in collaboration. Iíve written quite a few in collaboration with the Burbidges, quite a few in collaboration with Hoyle, actually more by now in collaboration with Hoyle. The main thing is, the problem never seems to arise. Always itís quite natural for a group of people collaborating to know who is to write what. Drafts are prepared. These are criticized by the others. And then eventually one person takes over, kind of tying it all together, and I think that probably mainly is what Fred Hoyle did in that 1957 paper. Iím sure that I wrote my nuclear physics section and Geoff and Margaret wrote their business on the observations.

Fred may have written one of the sections too. But then I think he took that and wrote the introductory material and some material that made the transition from the nuclear physics details to the astrophysical details. Now, in my collaboration with Fred, itís not very often that we divide up the responsibility in recent years. Usually, since Fred is only here for a limited time, itís been the case that we spend all of that time in mutual discussion and arguing at the blackboard about what weíre going to do. Then when he leaves, one or the other of us accepts the responsibility of writing the actual paper, and in some cases I write it, in some cases Hoyle does. Then the person who writes it sends a draft to the other who then may change it considerably and add material that the first person had forgotten. But eventually -- thereís further exchange and further drafts and finally, out comes the paper. Now, in Hoyleís visit here recently this last fall, we got interested in the origin of deuterium. We felt that we wanted to actually publish or get the paper fully prepared before Fred got away, so after about a month of discussion of this subject -- which was triggered by the way by the discovery of the radio astronomers that thereís deuterium in the gas clouds in the galaxy; Penzias and his group found that thereís deuterated methane in whatís called the molecular clouds near the Orion nebula, and Cesarsky, Pasachoff and Mofett here at Cal Tech, Owens Valley Observatory, found evidence for deuterium in the center of the Galaxy -- and it was becoming very clear that we had to really face up to the production of deuterium, which can be made in the big bang but which is very difficult to make in stellar synthesis.

Now, the big bang explanation may very well be the correct one, but Hoyle and I decided that weíd better get on the record, and this is typical of the way we operate, what possible mechanisms there were in the synthesis in stellar explosions of deuterium. So we worked together for about a month during November and December, and I had made some extensive notes on the nuclear physics. This is an example of how we work together. In this case, since I was busy teaching a class and Fred wasnít, Fred just sat down actually, usually in the living room of my home, and drafted the paper. Then when weíd get together, weíd argue about this and that, and so forth and so on, and finally in the middle of December we sent it off to Nature and Iíve just received the proofs in the last few days. Now, one thing that I think is interesting -- Hoyle never looks at the proof. Once the draftís gone in, once a manuscript has gone in to the publisher, then Iíve always had to do all the proofreading and stuff like that, because Fred is thinking about something else by that time. He wouldnít want to waste any time reading proof on a paper that we wrote two months ago, you see.

Weiner:

Thatís the experimentalistís job.

Fowler:

Thatís right. But itís typical of how Fred operates.

Weiner:

Let me ask you how the name ordering is decided on your papers.

Fowler:

Well, the first papers that I wrote with the Burbidges had my name first, and I canít quite remember why both of them did. I guess looking back on it, although Geoff and Margaret acquainted me with the problem, those papers were basically nuclear problems. It was the very first time when I had appreciated that neutrons had to be used, and so I guess my name went on first because they were basically nuclear rather than astronomical papers. When it came time to publish the big paper, I realized that it would be the third in which I had collaborated with the Burbidges, so I realized that it would be fair to put their names first. Then there was the question, should it be the Burbidges or Hoyle? Finally on the paper we sent to Science we put Hoyleís name first, but then on the big one we just decided, letís make it alphabetical and let it go at that. So again itís kind of, it always just comes very naturally. Fred and I have, more or less, the rule, that whoever actually does the most of the writing will put his name first. For example, this last thing we did together, Fred did all of the final writing, so itís Hoyle and Fowler. But on our paper some years ago on nuclear synthesis in supernovae, which I did on a second sabbatical in Cambridge in Ď61, Ď62, I did most of the writing so thatís Fowler and Hoyle. Itís always very clear whose done most of the work in the actual writing, so the name being first has more to do with who did most of the writing, not with who had most of the ideas.

Weiner:

Let me ask you another thing about that paper, since itís a big one and also symbolizes your important contribution. Was it invited? Did the editor of Reviews of Modern Physics ask you to do it? How did the idea come to write that kind of a review paper? Was Condon editor at the time?

Fowler:

Condon was editor, and now that you remind me, Iím fairly certain that Condon had asked me in general, Edís a very good friend of mine, at some time or other Ed had said, ďWhy donít you send a paper to the Reviews of Modern Physics?Ē Now, that brings up a point that I really think should be clarified. The paper was published in the Reviews of Modern Physics. It did in some ways review the whole field of nuclear synthesis in stars, but on the other hand, more than half of it was completely new. All of the business except for this previous publication in Science that we had just sent off because we were so excited about the whole business, and which didnít give any details -- all of the stuff about the neutron processes and much of the nuclear physics of the earlier stages of stellar evolution, was brand new. It was strictly a review article. But it was a pretty long article, and Condon had said heíd be glad to publish something in this general area and so one thing led to another. We sent it to him. He accepted it, published it very quickly and thatís how it came about. I donít remember Condon asking me specifically for it, knowing that we were writing it, although he may have. He may have seen the article. But I do know that Ed had told me at an Academy meeting or something, or at some kind of a meeting, that heíd welcome a paper in nuclear astrophysics. So he got it.

Weiner:

At the same time a year earlier you wrote an article for Scientific American -- you were giving other talks. It seems that this was a red hot subject, a great deal of interest and need for public exposition of it. This was the first time that you started expressing yourself to a popular audience, wasnít it? Iím not saying the reader of the Scientific American is exactly the reader of the Pasadena Star, but still itís a different kind of an exposition.

Fowler:

Well, that was the one with Greenstein?

Weiner:

No.

Fowler:

Thatís still earlier, before?

Weiner:

The article with Greenstein is Ď56, thatís ďElement Building, Reactions in Stars;Ē thatís for the Proceedings of the National Academy.

Fowler:

Yes, that was invited. We were invited. I know now that we were at that time both candidates for election to the Academy, and some of our friends who were supporting us I guess asked us to publish in the National Academy. In fact, it was Paul Merrill who asked us to do that, and quite shortly thereafter both Jesse and I were elected to the National Academy, so Iím pretty sure thatís what Paul Merrill was up to. On the Scientific American articles, sure, the whole subject was becoming very popular and I started writing articles there.

Weiner:

Scientific American comes first, then Scientific Monthly.

Fowler:

Scientific Monthly eventually became Science, didnít it?

Weiner:

That was absorbed by Science -- then were you invited on Scientific American, did Flanagan or someone ask you?

Fowler:

Yes, Flanagan invited me. Again, it was kind of a standing invitation, and of course Flanaganís invitation is very nice because he pays something. So when I began to see I had something to say that was appropriate for the Scientific American, I just took him up on his generous -- you know, Flanagan goes around, at least he used to, to find out what the hellís going on and talks to everybody and gives them the general invitation, in a way, and then when they have something appropriate to do, they respond. On the one in the Scientific Monthly, I would guess I was also invited to do that. Iím fairly certain. Let me just say that in my mind at least, the next big thing that happened was the work between Hoyle and myself on super massive objects. Now, thatís a pretty long story, and we might want to let that go until some other time. Again, for me that was essentially also a major change in direction, because it had very little to do with nuclear physics, and gave me an opportunity to study some general relativity and learn what it was about, and to really make an application in an original way on stellar structure, in this case these very massive stars. So thatís a story, we can get into that or we can continue.

Weiner:

Iíd like to use what time we have remaining to fill in some details.

Fowler:

Right. I wonder too if we shouldnít talk a little bit more about Fred Hoyle and the reaction to all of this at the time, because I think you expressed an interest in that.

Weiner:

That I was just about to get to. Let me ask you a brief question about the Cambridge years. You talked of the work with the Burbidges, of the beginning of your relationship with Hoyle, told about the seminar you were giving. What about other people there in nuclear physics? You mentioned there was not much going on, but other people with a similar interest? Didnít the Burbidges have any other persons to relate to, or Hoyle anyone to relate to there, who could do the kinds of things that you were beginning to do?

Fowler:

Well, the Burbidges were pretty much working alone. Margaret did not have a position, as far as I remember. She may have had some funds from the Royal Society or something but she did not have a position in Cambridge. And Geoff ostensibly had some kind of a fellowship or grant. He was ostensibly the theoretical physicist for Ryleís group. Well, it became very clear right at the outset that -- and I donít want to be unfair -- that Ryle and Geoff just didnít get along. Whether this is because Geoff was too independent or whether as Ryle might say, he just thought Geoff was talking nonsense and wasnít a good theorist, which Iím sure he believed -- I donít know. But very clearly, Geoff did not work into the Ryle group. The blunt fact is that Ryle and his group like to do their own theory. So Geoff has told me that Ryle just wouldnít make available to Geoff the observational results on which Geoff could so some theoretical calculations. But one way or another, of course he started to work with me on this element abundance problem, and so he spent full time on that.

Now Geoff and Margaret knew all the younger people. There was the D2V Club (Delta squared Vee Club) and they introduced me to that. However, I think they spent most of their time working on these two papers that the three of us ultimately published. Actually, there was a great deal of numerical calculation to do, and somehow or other they found a little calculation machine, incredible little business with levers -- I often jokingly say, it was probably made by Babbage himself. Margaret went through the neutron capture processes which involve a differential equation for the production and destruction of every one of the nuclear species that you want to include in the chain. So there was something even in those days like 50 species involved, and those differential equations had to be integrated step by step, and Margaret did it by pulling the levers on this machine, which would then spin and add up things. So they were very busy. We were all very busy in the preparation of these two papers. I donít know if Iím answering your question?

Weiner:

Yes.

Fowler:

Now, I got to know the young fellows and the senior people, Shire and Kempton and Tony French and Neil Tanner and the research fellows. I got to know them very well. My wife and I had them to our house frequently. And although Iíd go down and talk to them in the lab, I didnít work very closely with them because I too got so thoroughly involved in this work I was doing with Burbidges. And of course Fred was there from time to time, took part in the discussion, and Fred and I were still carrying on discussions about the somewhat older stuff, the details of the helium burning and details of subsequent processes. That collaboration with Fred during that year didnít come out immediately in a paper, but that came to full fruition in the publication of the Reviews of Modern Physics article. But it was apparent to me even then in Cambridge that Fred Hoyle and Martin Ryle did not see eye to eye.

Ryle was convinced even then that his observations in radio astronomy were incompatible with the steady state theory -- that he was seeing even then evolutionary effects that could only be explained in terms of a Friedman-evolving universe. Hoyle took the attitude that insofar as he could get his hands on Ryleís data -- which of course eventually Ryle had to publish -- Hoyle always had some way of making a result compatible with the steady state. And that general disagreement has lasted until this day, but even in 1954 it was very apparent that there was no love lost between Hoyle and the Ryle group. Now, Ryle, you see, even then had a fairly large group of young radio astronomers working with him. Fred Hoyle has always been a lone wolf. In Ď54 when I was there, I donít believe he had any graduate students working with him. Now, I may be wrong but they certainly werenít very obvious. When I went back in Ď61 and Ď62, he had by that time transferred from the math faculty to the newly formed department of applied mathematics and theoretical physics, DAMTP itís called -- and that year, which was also a very inspiring and productive year for me, he did have a number of students. Narlikar and Chitra were there and Roxburgh was there, Roger Tayler, who was not a student, was there. But by that time in the department, Hoyle had built up a group that were all essentially working under him, and there were the people in hydrodynamics under the director whose name I canít remember.[5] Dear me.

Weiner:

Taylor?

Fowler:

No, not Sir Geoffrey Taylor, oh dear, Trinity man. Anyhow he and Hoyle didnít see eye to eye either, and eventually Hoyle broke away from the department and formed the Institute of Theoretical Astronomy.

Weiner:

Letís do that -- bring you back to your first observation of Hoyle in his own environment. I think this is the thing we decided we would talk about. Where do you want to start? How the Ď57 work was received, which is important in terms of your own career as well? Or how Hoyleís relationships to his colleagues in the overall field developed, something about his style, as a possible explanation of this?

Fowler:

Well, I think basically one has to point out that Fred is a very independent worker. He, in addition to the collaboration with the Burbidges and with me, was carrying on quite independent work in cosmology at one and the same time. Now, he did finally find a collaborator in that area, and for a number of years he has written papers on cosmological problems with Jant Narlikar, and so Fred has demonstrated that he can collaborate readily with a number of people. But basically I would say that Fred is a lone wolf, and this probably is the reason why he just didnít become a house theorist for Ryleís radio astronomy group. Fred has to be in the forefront. Heís got to be the leader. He has many of Gell-Mann and Feynman characteristics, and his whole background I think as a youth was as a Yorkshireman with all the antipathies they have toward the English in the south. So I can see that both personality-wise and other-wise, there were plenty of reasons why the radio astronomy group at Cambridge and Hoyle should have diverged. Now, as to how the paper was received, I think itís fair to say that it was very well received. Whether thereís any immediate connection, I donít know, but shortly after the publication of the paper in Ď57, Fred was made the Plumian Professor.

Now, because of the great controversy over his work on cosmology, it might well have been that this very solid piece of work on nuclear synthesis in stars swung the balance. Iím sure there were other candidates. So Fred was made the Plumian Professor. Once he had that chair and the responsibilities that come with it, then he was willing to start developing a group of research fellows and students, and thatís how the department formed. Then he found that he wasnít the boss. So he decided around Ď64, Ď65 that if he was to continue to have an active group in the field, that he wanted a new institute of his own. The Burbidges and I encouraged him in that, and as a result, he almost singlehandedly built the Institute of Theoretical Astronomy, from which heís just recently retired. But always -- the other thing I think that has to be integrated -- always in the background of Hoyleís relationship with the rest of the astronomical community is the controversy over the steady state theory. There are many astronomers who just congenitally believe in some kind of a big bang universe -- as I quite frequently say, the old Bible story -- and they just cannot accept the concept of the steady state universe, and denial of a beginning, as it were. So that has always and still is something that marks Hoyle as a very special individual in the astronomical community. Itís true that Bondi and Gold were in on the start of the steady state theory, but Bondi is now a bureaucrat in the English scientific establishment. Tommy Gold has gone on and gotten into a thousand and one other controversies, including whether the moonís covered with dust. But Fred is the person that everyone thinks about in terms of the steady state theory, because he stuck to it. Bondi and Gold havenít really done anything on steady state theory for a long time. And Fred has oscillated, as you know. There were a few years -- a few years ago he was finally convinced that Ryle really had the evidence which would rule out the steady state, and there was the famous interview in which he essentially, letís say, recanted. But then shortly thereafter, the Australian results contradicted the Cambridge observations, and Fred got back onto the steady state bandwagon.

He and Narlikar had modified the steady state, oscillations in the steady state, which they felt at one time or another were necessary to accommodate the theory to the observations, but which detract from the very great simplicity and elegance of the theory, I think. As Iíve said, I donít think either the steady state of the big bang can be the ultimate correct explanation. But I would say, if I had to bet right now which one would be closer to the truth, I think I would have to bet on the big bang. But I donít have the strong feelings about it that many people do who would say, ďWell, the discovery of the microwave background radiation, which the big bang theory predicted and which is so consistent with the cooling off of a fireball down to the present low temperature, 2.7 degreesĒ -- theyíd just say, ďThe big bangís the correct theory, thatís all there is to it.Ē That I do not agree with. And I donít think itís because of my close association with Hoyle. I think Iím just very skeptical of such oversimplified models, and in particular ones that are based on an original singularity. For me the thing thatís anathema in physics or astronomy is the singularity. For others, itís the lack of a beginning, or the lack of a singularity. This will just have to be resolved by more and more observations or more theory. Actually Fred is now, with Narlikar, working on a theory that is neither big bang nor steady state. This is a theory in which the mass of every particle grows. It is in a sense an evolutionary theory, because as time passes, a particle, a single particle can interact with more and more of the universe, because of the light travel time. Fred is very Machean in this theory (from Ernst Mach) in that the mass of the particle is due to its interaction with the rest of the universe, so as its horizon expands, its mass can increase, and thatís the theory heís off on now, and it has many attractive features. But the people--if you think people hate steady state, they hate this new theory of Fredís even more. Even more firmly.

Weiner:

Just on the basis of philosophical treatise positions, you mean?

Fowler:

I think so. And partly because itís another one of Fredís wild ideas, as they think. There are people, for example Murray Gell-Mann, Murray just doesnít think thereís much use to working on cosmology. Astronomy has great possibilities, but he thinks Einstein and Friedman solved the cosmological problem so why do these crazy guys discuss it anymore? Itís all been solved. All youíve got to do is measure the proper parameters and see which one of the Friedman universes is it, and thatís it. And Fred just takes exactly the other attitude. He says ďNo, thereís something really to be learned by understanding the universe as a whole; we havenít got the right answer yet,Ē and heís been willing in the last few years to give up the steady state entirely and work with Narlikar on this new one which is kind of an outgrowth of work that Wheeler and Feynman actually started. Feynman carried it pretty far and then gave up on it, and whenever Fred comes here he always tries to engage Dick in conversations about what new developments Fred has come to. And of course, one of the interesting parts of his theory is that you can put it into a form, where the simplest way to look at whatís going on is that the gravitational constant is decreasing. This has then, some similarities to the Brans-Dicke cosmology.

Weiner:

I donít know how much time you want to take now but it would be really interesting to talk about your impression of Fred Hoyle in terms of his total being, his personality, his intellect, the way he expresses it. Because, as youíve expressed to me in the past, itís all of a piece, the science fiction and everything else sort of relates. It might be nice to have a sketch of him as youíve known him over the years and as you interpret him.

Fowler:

I suppose Iím the person whoís been closest to Fred, except for his wife and immediate family; I donít think thereís any question about that, that Fred and I have become very close friends. And of course in addition to our scientific collaboration, weíve done a lot of walking and climbing together in the English lake district and the Scottish highlands, and then we both share a great interest in spectator sports, professional sports. The one thing that I did religiously that first year I was in Cambridge was go with Fred in the fall and winter to the rugby matches. I had never seen a rugby game before in my life. Actually that year, Ď54, Cambridge had a winning team. They won all of their games, and Fred and I went out on Saturday afternoons or whenever they played at Grange Road to watch the rugby team. So he taught me the finer points about rugby and soccer. I guess Iíd seen a soccer match before but I never appreciated what it was all about. Then in turn when he came to the United States we frequently then and even now go to baseball games or to professional football games, and when heís here, like last fall, we watch the Monday night football games and the Saturday college games, and the Sunday professional games. But when weíre watching the television, weíre at the same time discussing what weíre working on. In fact, this fall, itís just typical -- on Sunday afternoon weíd watch the Rams play. Iíd set up a card table in the living room where I could have some work in front of me and still watch the television. Fred would sit on the couch with a big pad in front of him, and weíd watch the game and heíd do some writing or Iíd so some calculating -- thatís the way it goes. Back on Fred as a man; of course, in addition to being a close friend I really admire him very greatly. Iíve read all of his science fiction books.

To me itís just fantastic that he has more than matched my publication rate, in the professional field -- and no point in being falsely modest, I have published 10 papers a year now for some years -- but Fred more than matches that, and at the same time, he finds time every year to write a book of science fiction. Now, itís partly because heís just so terrifically organized and because this is a feature of Fredís whole life. He doesnít do a useless thing or a trivial thing. He never does a trivial thing. When he decides -- and he must think about this during the year -- to write a new science fiction story, he goes off in a caravan that they have. They can put it any place they want. Sometimes itís down in Cornwall, sometimes itís up in Scotland. He spends six weeks, walking during the day, when the weatherís good, part of the time, but also just writing out in longhand on legal sized paper the whole darned thing. He gives that to his wife, Barbara, and from then on he never has anything to do with it.

She sees that it gets to the publisher. She sees that itís proofread. And itís in that way that he can be so effective and so efficient. Then the other amazing thing is that he is competent enough in music and in writing lyrics that he has written an opera with Leo Smit and that again was done at the same time that he was here on one of his visits. While he and I were working on something, he went out on the desert with Smit on a camping trip for about a month, and they came back with this opera composed. To me itís just Ė heís the only person that Iíve ever known who had capabilities in such a large number of fields. Another thing about Fred is that when discussed with him in the early days work that I was doing in the laboratory myself, or when I discuss with him work thatís being done by the staff here, the younger people, Fred really understands. He has an incredible intuition about experimental work. So in my sense, I really think that Fred Hoyle is a very great man, that heís a Renaissance man if there can be such in this day and age. And the other characteristic in our work together that Iíve noticed, whenever we get into a new problem, my immediate reaction is to go and start looking through the literature for some kind of a solution. Fred will never do that, never do that. He immediately, when some new problem comes up in our discussion, goes to the board and starts working it out for himself. If he canít work it out at the board, then when we terminate our discussion, he sits down and a day later comes back, ďIíve got that solved.Ē And I know he will not have had any recourse to a text book or to literature.

The only thing that Fred ever uses help for, is for experimental numbers. Heís very contemptuous, even of me, when I want to look up how someone else solved this problem. For example, in this paper that we just wrote while he was here last term, we had to have some equations about how a shock wave propagated through the medium of an exploding star. The picture we had was that in making the deuterium, which was the idea of the paper, that a very massive star collapsed and exploded, and the explosion sent a shock wave out through the outer envelope, which had been left out there in a very tenuous form by the collapsing inner core, and as this shock wave came out through the tenuous medium, it spalled all the helium into protons and neutrons, and the subsequent capture of the neutrons by the protons made deuterium. Well, we had to do all this shock wave physics, and I wanted to immediately go and look at the paper that Sterling Colgate had written on the subject, or go talk to some of our experts over in aeronautics about shock waves. Gerald Whitham is our great expert on shock waves. Fred would have none of it. He just went to the board and wrote down all the proper equations, which turned out to be correct. But the funny thing was, I didnít realize, it wasnít until Tommy Lauritsen read the proof, that we had -- that Fred in his derivation had changed the convention about what you call upstream of the shock and what you call downstream. It just shows how independent the guy is. He had apparently vaguely heard that people working in shock wave physics thought of-in fact I canít even get it straight now--of material coming up into the shock as being downstream and material back of the shock as being upstream. Well, some way or other Fred got it all turned around, so ours is the only paper in the literature -- we of course specifically define what we mean, but Tommy Lauritsen pointed out that it was absolutely in contradiction to the convention.

Thatís typical of Fred Hoyle. He knows enough physics by now that any problem that Iíve ever seen come up, he makes an independent solution of it. Now, he gets himself into a lot of trouble actually just that way, because he frequently then, in his own papers -- I always try to, in spite of the fact that Fred does it independently, I always try to give references to previous work. Fred doesnít do that. He says, ďLook, I did this all myself, I worked it all out, just because someone else did it ten years ago, thatís none of myÖĒ Thatís one of the things thatís gotten him into a little bit of trouble, some carelessness about -- well, not carelessness, he just never thinks, because heís done it himself, to go back and look in the literature as to who did it first, see. Well, that invariably gets you into problems with other people, you see. And then overshadowing the whole business in Fredís life, it again comes from his independence of thinking, he just will not accept the Friedman cosmologies, in part because he didnít do that first. He canít independently discover that, you see. And I really think that Fred has a terrific motivation to understand what he calls large scale physics, the cosmological physics. Heís just driven by the desire to understand what the red shifts and what the quasars mean. He will not accept the conventional point of view, and as a consequence, heís kind of a maverick or heretic to everybody else. That colors the whole relationship between people and Fred, the fact that hereís a guy who for some reason or other just wonít knuckle under as to what looks like, to them, overwhelming evidence, that indeed we do live in an evolutionary universe, with the quasars being at cosmological distances. Hoyle and Burbidge have been the main protagonists on the other side.

Hoyle and Burbidge to this day donít believe that the large red shift observed in the quasi-stellar objects is cosmological. Part of it may be, but that part would be similar to the red shifts of the most distant galaxies, which run about 30 percent, whereas in the quasi-stellar objects, you see red shifts almost up to a factor of 3. So there again, they are in conflict, with people like Ryle and Maarten Schmidt here, and Alan Sandage, all of whom are convinced that the correct cosmology is the Friedman picture, the evolutionary cosmology, and that in particular the quasi-stellar objects are extremely distant. But you see, itís again characteristic of Fred, heís not unwilling to adopt a point of view that he didnít believe in, and to work out the consequences. When we decided that it was important to really see whether heavy elements could be made in the big bang, even though Fred just thought that the big bang had no connection whatsoever with reality, he was perfectly willing to go along with Wagoner and me, take that model, see how far you could go. Now, you might say, well, in that case he could be pretty certain that the conclusion was going to be that the big bang couldnít make heavy elements, but Fred worked as hard as Wagoner and me trying to find ways to build elements heavier than helium in the big bang. We tried quite a few new ideas that Fermi and Turkovich did not have to get around the mass 5 and the mass 8 gap, but with all the new data and all the new theory we could put in, we just werenít able to do so. And in a similar way, he and I started a few years ago to think about, if the quasars are cosmological, theyíre extremely luminous then, where do they get their energy? Fred went to work on that problem, even though he thinks that theyíre essentially local, and thus that the energy requirements are much smaller than on the cosmological point of view. So -- but heís a very great man.

Weiner:

Let me ask you one more question, I know you have other things to do. You mentioned that some of the resistance to his ideas could be due to philosophical predisposition. In addition to the things youíve described, which I think I understand, is there some element of that, in terms of his view of what the universe should be like, the way you want it to come out?

Fowler:

I suppose there is a certain element of that, but itís not on a very obvious level, and itís certainly not -- oh gee, what is the word? Itís certainly not a very simple thing with Fred. If he is biased by some kind of a philosophical prejudice, itís at an extreme level of sophistication. I think that many of the people who firmly support the big bang evolutionary cosmology is just because it has -- it can be understood in a very intuitive and very naive way, itís kind of built into us. Fred has gotten in his thinking far beyond elementary concepts in this regard. He really has thought about it at a very high level of sophistication, much beyond the mathematics that he does with Narlikar. So exactly -- of course, weíre all biased by what we believe, but frequently when Fred is talking to me about it, I realize that heís always done a lot of thinking about the ďarrow of timeĒ problem, for example. In that regard, many times in walks, Fred talks on such a level that I donít even know what heís talking about. Then I manage to change the subject back to ďwhat do you think about neutrons and the synthesis of barium?Ē There are many fields in which Fred has extremely sophisticated ideas that tie in with his general attitude about cosmology and his desire to understand really whatís going on, and his refusal to accept the picture that looks so obvious to other people.

Weiner:

I guess one would have to do an analysis of his science fiction work, to look for this thing youíre getting at.

Fowler:

Yes, you could see it in a way there.

Weiner:

Itís certainly a very sophisticated view of the universe and of peopleís relationships within it, I think, that comes out of his work. Well, thereís probably much more, I know thereís much more, but I think we shouldÖ

Fowler:

All right. I think Iím kind of running down anyway. I promised my wife Iíd do an errand for her, so letís call it quits.

[1]Ardiane (Ardy) and I were married in this lovely garden in August, 1940.

[2]See S. E. Salpeter, Ap J 115, 326 (1952) mentioning summer work in Kellogg (1951)

[3]He came in 1952.

[4]In retrospect, I am not sure Cameron's Chalk River Report was ever published.

[5]G. K. Batchelor -- some question about initials?

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