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Oral History Transcript — Dr. William Fowler

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Interview with Dr. William Fowler
By Charles Weiner
May 30, 1974

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William Fowler; May 30, 1974

ABSTRACT: Work in realistic astrophysics in the 1960ís, continuing collaboration with Hoyle, position of Caltech and Kellogg Lab in physics and radio astronomy, work on government committees. Concludes with highlights of career.

Transcript

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

Weiner:

This is 30 May l974 and the beginning of the continuation of the interview with Professor William A. Fowler. Now, in our last session, before we went into the digression (which was very illuminating) on Fred Hoyle and his style and his interests and so forth, we were at the point where you were going to get into the story of the work with Hoyle and super massive objects. When you look over your career and your writing, this represents a departure from nuclear physics as applied to astrophysics and moves into an area of general relativity. Which is an area that, from what I can see on your reading list, you hadnít done anything in up until that time. But first how did that start? Was it a natural extension of the work you had done earlier with Hoyle?

Fowler:

It wasnít a natural extension in any direct way of work that Fred and I had done together. The origins go back to the very exciting developments in the decade of the fifties in the burgeoning science of radio astronomy. A number of radio telescopes were built and were used to investigate radio objects in the sky and this, coupled with the identification of these objects with optical objects led to revolutionary advances in our understanding of whatís going on in astronomy. Itís rather amusing that the first sources, as I remember, seemed to be what the radio astronomers called radio stars. But very soon there were identifications not with starlike objects but with galaxies and what one could call in general extended objects. And as soon as these identifications were made with galaxies, it was possible to determine the red shift optically; that could not be done by the radio techniques.

It was possible to determine the red shift optically, that meant, if one accepted the red shift as being cosmological in origin, that the distance to the radio source was given by the usual Hubble relation. So these so-called strong radio sources, once the distance was known and inverse-square law was used, indeed were very strong sources, in that they were putting out in the radio range, in some cases, even more energy than the optical luminosity of our own galaxy or of other galaxies. So physicists began to worry about the problem of where is this energy coming from, and thatís essentially how Fred and I got into it. You see, if you have the distance and if you have the amount of energy thatís being received here at the earth per square centimeter per second, you can calculate the luminosity. In some cases it came out as high as, if I remember the numbers correctly, 1046 ergs/sec. The luminosity of our galaxy in the optical range is more like 1043, 1044 ergs/sec. So we began to appreciate that there was a basic physical problem involved in what was the source of this prodigious output of energy. It soon became clear (and the radio astronomers in large measure worked this out themselves) that the primary, or the direct source of the energy, was synchrotron radiation.

Electrons, somehow or other in these sources accelerated to very high energies, relativistic energies, were spiraling around magnetic field lines and emitting synchrotron radiation, which turned out to be in the radio band. I think that model was primarily due to Shklovsky and Geoffrey Burbidge, I remember they independently suggested it. Although just exactly the origins of the synchrotron model arenít too clear to me. But, given that model one can calculate the amount of energy stored in the electrons and the amount of energy stored in the magnetic field. And when you look at the equations, you find that there is a minimum amount of energy required when the energy stored in the electrons and the energy stored in the magnetic field are roughly equal. I think thereís a factor thatís not quite one, anyhow, it was possible to calculate the total amount of energy stored in the magnetic field and in the electrons and that turned out in a few cases, to run up as high as 1062 ergs. When we began to hear about these claims on the part of the radio astronomers, we were skeptical at first. Of course Fred in part took the attitude, well, this just shows that these sources and the galaxies from which theyíre coming just canít be at cosmological distances. Because itís very clear that if one reduced the distances by a factor of ten then all the energy, the energy emission and the total energy stored, can be reduced by a factor of one hundred. And of course that led to the long period of controversy between Fred and Geoff Burbidge and those who accept the idea that the strong radio sources are at cosmological distances. We touched on that somewhat in the past in our discussions. On the other hand, as I think Iíve said before, Fred was always willing -- even though, for example, he didnít believe in the big bang -- he was perfectly willing with Robert Wagoner and me to look at what was the nuclear synthesis in the big bang. And so he was willing to look at the problem: What could the source of energy be if these objects were really at cosmological distances and were thus shining with enormous energy output and had to have a stored energy which was very great indeed? So then Fred and I did spend quite a bit of time both here and in Pasadena, and in the summer time in Cambridge, thinking about the problem. And of course all the time more and more information was becoming available.

The radio astronomers began to resolve the sources. Most of them or many of them are double sources. I remember Centaurus A is a kind of classical example. And of course here at Cal Tech there is a very active group in radio astronomy, Al Moffet and others, and so I had the opportunity to constantly discuss this problem with them. I remember Geoff Burbidge, because he had something to do with the synchrotron model, kept taking every case as it came up and doing further refinements of the model and always coming up with these very large numbers. For example, the rest mass of the sun is 2 X 1033 grams. If you convert that into the energy equivalent one get 2 X 1033 X 102l thatís 2 X l054 ergs. Thatís to say that if you could completely annihilate the mater in the sun, for example, you would get something some than 1054 ergs. So a radio source in which itís claimed that thereís 1062 ergs stored, means that somehow or other 108 suns, the equivalent of 108 solar masses have been converted into energy. So you can see immediately, just from those simple figures, why it was such a problem for us. In particular for me (for others of course, but in particular for me) there was the additional problem that if the energy had come from nuclear processes, by the conversion of hydrogen into heavier elements, all you get is 7/10th of a percent of the rest mass energy. Letís say one percent, so thatís another factor of a hundred. So if youíre going to get 1062 ergs from nuclear energy youíve got to completely evolve 1010 stars. Thatís 10 billion stars. There are 100 billion in our galaxy, that would mean that you would have to completely process, nuclear-wise, ten percent of the stars. And in some of these galaxies that were associated with strong radio sources there werenít even that many stars. So the problem was a very serious one, a very puzzling one, and a very interesting one. Iíve used rather extreme examples, not all of the radio sources went up to the extreme numbers that I have used. Thereís a wide variation downward of something like a factor of 104, 105, but there are these outstanding cases where one gets the most extreme numbers. So, Fred and I -- Fred was quite willing to think about the basic source of the energy: where did it come from, where did the electrons get their energy, where did the energy come from that produced the magnetic field? See, youíre going beyond what the direct interpretation of the observations indicate.

So in the early sixties we were puzzling over this and at some time or other we decided to look at what would be the properties of a single object that might be producing this energy. Now there again we were saying, well, letís not worry that itís got to be 1010 solar masses thatís going to produce this energy by nuclear processes. Letís just look at the problem anyhow and maybe we can understand the sources that donít require quite that much. So we started working out the structure of what we started calling a super-massive star. Stars in the range of up to 1010 solar masses. In fact we soon began to think of our super-massive stars as anything ranging from, say, 104 solar masses up to 1010. We were up against, again, a lot of skepticism on the part of our friends, because itís well known that the mass of ordinary stars cuts off around 100 solar masses, and in fact you can show on fairly reasonable grounds that stars over 100 solar masses are very unstable and just shouldnít form; if they do form they should immediately explode. We went ahead anyhow. We had been thinking about fairly massive stars for some time in connection with supernovae, and one of the basic properties of the super massive stars was already apparent in stars of the order of 100 solar masses. Namely that the ratio of radiation pressure to the total pressure is quite high, in fact that in part is why ordinary stars of around 100 solar masses are unstable. They have a ratio of specific heats (thatís the ratio of specific heats of radiation rather than of matter) and thatís pretty close to 4/3 that a system canít be found, that is it doesnít have a negative state, a state of energy that is bound in the sense that you have to put energy in, in order to completely disrupt it. But we went ahead and soon found, to Fredís delight and to mine, that actually the equations for super massive stars were extremely simple. Using radiation pressure as the main support against gravity we found that the structural equations were fairly easy to solve, at least in an approximate way.

Furthermore, we reasoned that the surface temperature would be quite high, that the main source of opacity would just be Thomson scattering, in which case itís possible to use some work that Eddington did many years ago to get the luminosity of a super-massive star. It turns out that for ordinary stars the luminosity varies as a fairly high power, the 3rd or 4th power of the mass. If one goes along the main sequence, which is merely a sequence in the masses that stars have, the luminosity rises quite rapidly. A star twice the mass of the sun has something like 20 times the luminosity. But when you look at the super- massive star problem, and this starts around 1000 solar masses, and itís in full effect at 10,000 solar masses, the luminosity is just strictly proportional to the mass. And thatís interesting because if luminosity is strictly proportional to the mass, the amount of fuel, nuclear fuel youíve got is proportional to the mass. That means all of these stars have a constant lifetime, and when you work it out itís the order of a million years. Well, this was lots of fun because we got the impression from our radio astronomical colleagues that they felt that the period over which a galaxy could be a strong radio source was something of the order of a million years. And we thought that just couldnít be a coincidence, so we decided to publish our results in 1963. We first sent off a fairly detailed paper. Well I canít quite remember, we prepared a fairly detailed paper for the MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY and we knew that that would take some time to publish, so we wrote a rather abbreviated paper and sent it in to NATURE.

Weiner:

You sent the one into the MONTHLY NOTICES in August of Ď62. How long prior to the writing up of this MONTHLY NOTICES paper had you been working on it? Prior to that?

Fowler:

I would say, now that you remind me of the exact date, we worked on the problem and brought it to a close during the summer of Ď62 when I was in Cambridge [England]. But we had been talking about it for at least two years before that time. It was in Ď60 or Ď61 that we came to be forcibly impressed with the problem that the radio astronomers had uncovered it. Iím fairly certain now that it was during that summer when I was there in Cambridge that we did the final blackboard work and the final arguing and looking up the literature and then writing the paper. Of course one thing I can say for sure is that the first draft was written by Fred, because according to our policy, our practice as Iíve told you before, is the one who wrote the first draft got his name on the paper first. And of course it was a field in which Fred had a lot more expertise than I had, because he had, as is well known, spent considerable time previously working through stellar structure problems. In fact he and Schwarzschild were the ones who were the first ones to give the explanation of the red giant phenomenon. But there were lots of nuclear problems involved, all of the interior temperatures are quite high, much higher than in the sun for example, by something like a factor of ten.

So I had to look pretty carefully at what would be the rates of the nuclear processes in a temperature range, and thus an energy range, that we hadnít paid very much attention to before. So it looked to us that here was a source of energy. Now it didnít really in any way solve the radio galaxy problem because the energy that came out of this condensed object, the super-massive object, was light. Itís true it was quite blue light. The surface temperature as I remember depends on the exact mass but itís on the order of a 100,000 degrees rather than in the range of 5 to 6,000 for the surface temperature of the sun. So the light coming out, itís true, instead of being in the wavelength range of 5,000 Angstroms, itís going to be in the range of 500 Angstroms. But itís light nonetheless, itís not electrons, itís not magnetic field. But we were not put off by that, we felt, well, weíve done this work, clearly it canít have much connection with strong radio sources but itís kind of interesting, just from a theoretical standpoint, to have solved this problem. So we went ahead and published our two papers and then of course all hell broke loose. We had no sooner published -- our paper in NATURE came out one week and the next week, or a couple of weeks later, Maarten Schmidt announced his discovery of red shifts in what up until that time had been called radio stars which astronomers were observing at the same time as extended radio objects in the sky.

Getting back to the extended sources now, the radio emission comes from regions that are many times the size of the galaxy thatís usually at the center, or close to the center, between the two or more components of the radio source. But at the same time, astronomers had been observing radio sources that, when they made a proper identification with the Palomar plates, looked like stars. The radio astronomers would say, ďLook you optical observers, go look at this, these coordinates in the sky, see what you find.Ē There were sources that even the 200 inch telescope couldnít resolve so they were called radio stars. Now these stars, these stars that were radio sources, had very peculiar spectra. And I remember one time Jesse Greenstein came to me, and he had been studying the optical spectra of ďstarsĒ (in quotes now) that were associated with radio sources. And by stretching things, as he admitted, he thought he was able to identify lines of, I wonít say which ones, but some of the heavy elements. And so he wanted to discuss with me how in heavens name could these rather rare heavy elements, as I remember, have been produced in sufficient quantity to give the spectra that he was seeing. Well, I couldnít make any sense out of it and after some discussions he and I gave it up, we just completely forgot about it. Well, as everyone knows, historically Maarten Schmidt and others continued to work on the optical spectra of the so-called radio stars, and it was Maarten who finally broke it by noticing that in one of the cases, 3C273, a set of lines had the characteristic pattern of the Balmer spectrum, but was shifted considerably to the red. Once he recognized the Balmer spectrum, then he was able to recognize -- I donít know whether it was in the original source -- other lines, mostly of highly ionized carbon and so forth and so on. And this, then, indicated that these sources were certainly not stars.

They were given the name quasi-stellar object. Because although they were irresolvable in the telescope and thus could be classified in a sense as stars, one realized, when the red shift was known, they had to be very distant and thus the energies were far greater than one could get from an ordinary star. Immediately on learning about this discovery of Maartenís, Fred and I said, ďAh! thatís what weíve been working on all this time, our super massive objects are not strong radio sources, theyíre quasi-stellar objects.Ē Of course as everyone knows that terminology was contracted to quasars. So thatís about how it went. Itís still, I guess, one of the viable possibilities for quasars. There are again extreme difficulties. Itís true that the quasars put out much more energy in the optical band, in the blue, than they do radio energy. But whether or not the quasar is a single coherent object such as one would call a super-massive star certainly isnít proven. In fact I would guess that the majority of astronomers favor other models. Models for example which still involve an enormous amount of mass, but involve, say, a great number of smaller stars, the energy being generated in collisions between the stars or in supernova explosions of the individual stars. More and more (and now weíre coming up to the present time) there have been enough observations on similar violent events, as they are often called, in the nuclei of galaxies and the so-called Seyfert galaxies. The compact galaxies all show a kind of quasar-like properties in their very centers, in whatís called the galactic nuclei. In many cases where the active galaxy is close enough one can in some cases resolve the center into the individual stars, so clearly in those cases there is not necessarily a super massive object there, but there is a great deal of mass in the form of individual stars.

The one thing that seems almost inevitable, even if you start with that model of a galactic nucleus with an extended collection of say a hundred million stars Ė- extended in a sense, but so close together in another sense that there are frequent collisions Ė- then almost inevitably you get kind of a soup out of all these collisions. Once the gravitational energy begins to be dissipated and the kinetic energies of the motion of the individual stars begins to be dissipated by collisions, then the whole thing will coalesce into a single object sooner or later. Now people worked very hard to avoid that. If you use small enough stars, one can slow down the coalescence time. Itís still a very active field and one that I havenít played much of a role in, in the last few years, because Iíve gone back to thinking about nuclear problems in ordinary stars rather than worrying about these problems.

Weiner:

Can I ask a question on the early part of that? You published your paper in NATURE in February of í63, which was before the MONTHLY NOTICES paper came out I gather, and then you said that Schmidtís work came out very soon after that. Now yours was the only model on the scene, it seems to me, at that time. Was there an immediate link that people tried to make between what you had said, which was almost a prediction, and his findings? Did people regard it in this classical sense, ah, those guys came up with a model and a theory and here it is found in nature...? Was there any of that, first of all in the minds of you and Hoyle, and secondly in terms of a larger group?

Fowler:

Well, we certainly made that connection almost immediately, and I think itís true that a number of other people did the same. Because as I remember, very soon thereafter there was organized this first Texas relativity conference. Both Fred and I were invited to speak at that and in fact as I remember Fred led things off. There was a great deal of interest in this model generated once Schmidt came up with the discovery of the quasars. So there was a period where people looked on it, to a certain extent, as a prediction. The difficulty of course, as I have alluded to -- quasars just canít be that simple. As I say, there are alternative models that involve a great number of smaller objects rather than a single coherant one. And so, well, thatís about the way it was.

Weiner:

What about the response of the radio astronomers themselves to the model, putting Schmidtís work aside for the moment? Here youíre working with their data, trying to explain something that they had uncovered which had puzzled you. Was there a feedback from what you did to them? Were you in communication with any of the people in that field other than just using their information?

Fowler:

Well, there wasnít all that much exchange. Of course the radio astronomers at Cambridge under Ryle were very skeptical, and particularly before the quasar discovery, in attributing any connection between this model of ours and the strong radio sources. And they were quite right. How they reacted to the discovery of the quasars in connection with this model is pretty hard to say. I donít think the radio astronomers concerned themselves very much about the model. The discovery of the quasars opened up such a big area of observation for them that everyone became more concerned with getting on with observations and finding new quasars. It became quite a game to make a survey, find all the strong radio sources you could, and the radio astronomers then, for example like John Boulton, would try to make the identification themselves.

They were much more interested immediately in finding more of these objects and cataloging them and trying to get the optical astronomers to make more observations on the optical spectra. That was the name of the game and they really werenít too interested in any model. Particularly one that was so simple and in which you couldnít make any direct connection between this optical object and what the radio astronomers were seeing in the electrons and magnetic field and the radio emission. The next interesting thing that happenedÖand again my history may not be all that accurate. I came back from Cambridge in the fall of Ď63 to start teaching again. I bumped into Dick Feynman one day, and Dick said, ďWilly, you know those super-massive stars youíve been talking about?Ē ďYes?Ē He said, ďtheyíre unstable.Ē said, ďI know theyíre unstable.Ē ďAh,Ē he said, ďbut you donít understand, this isnít the classical instability, this is a general relativistic instability,Ē and I just thought Feynmanís talking through his hat, what can he possibly mean, what can general relativity have to do with these objects. The densities that one gets, the matter densities in a super-massive object, are actually quite low. Much lower than the central density in the sun.

How can there be any connection with general relativity. Dick gave a lecture on the instability of super-massive stars in his class. I didnít go to that, but I heard afterwards that he had given this and it was clear that he had something because he had convinced all the people in the class that he was right. And in fact Icko Iben was working in the Kellogg Laboratory at that time as a senior research fellow. Icko attended Dickís class. Dick had used the usual type of Feynman analysis, which got the right answers, but Icko decided that he would actually work it through, because he was an expert on stellar structure, all the detailed equations of the structure of a super-massive object. Of course he had access to the computer so he worked the whole thing through and sure enough he confirmed what Feynman had said. So, I immediately of course was interested in this. Because both Feynman and Iben used the full panoply of the relativistic equations, I just couldnít understand at all what was going on. And so I decided, well, why donít I get out my old notes from Tolmanís course, which Iíd had in general relativity thirty years before, and see if I can understand this.

Itís hard always to reconstruct, I decided that the only way Iím really going to be able to understand this is to stick as closely as possible to the Newtonian treatment of the problem, because that I know how to do from the work that Fred and I had done. And why donít I just look at the post-Newtonian, that is, take the general relativistic equations, expand them in an appropriate way, and only keep the Newtonian and what are now called the post-Newtonian terms. And sure enough, as is now well known the instability of super-massive objects arises, fortunately in a sense, in the post-Newtonian terms. So having found that I could do that in a fairly simple way, I kind of went off on my own during the winter of Ď63-Ď64 (because Fred was back in Cambridge) and worked out to my own satisfaction the post-Newtonian equations for a super-massive object. And ultimately published my results, I think for the first time, in the REVIEWS OF MODERN PHYSICS [36, 545, 1104 (1964)]; and later in PROCEEDINGS OF THE INTERNATIONAL SCHOOL OF PHYSICS, ďEnrico FermiĒ Course XXXV, Ed: L. Cratton, Academic Press (1966). Actually it took me some time to appreciate the instability because what I actually worked out.... [off tape] What I actually worked out was the binding energy of a super-massive star. That is, if you assume that the star is in hydrostatic equilibrium what its binding energy is as it evolves.

For example, as it gradually contracts it changes its radius from a very large radius to a smaller one and in the Newtonian approximation the binding energy goes quite simply proportional to the mass divided by the radius, with a gravitational constant coming in and a numerical factor that depends on the model. And because super-massive stars are fairly simple the coefficient can be derived analytically. We had known this, but what one finds when you put in the post-Newtonian terms is that -- if youíre solving for the binding energy and call it a negative quantity from the Newtonian, you get a negative energy which is the energy that had to be lost as the star contracted to a given radius. When you solve for the post-Newtonian term it turns out to be positive. And itís quadratic in the gravitational constant times the mass over the radius. In fact you can make a dimensionless quantity, GM/RC2, and the binding energy relative to the rest mass energy has a negative term proportional to the first power of this dimensionless ratio from the Newtonian calculation. And then a positive term from the post-Newtonian, proportional to the square of this number. So the upshot is that if you plot the binding energy versus one over the radius you get a parabola rather than a straight line, you get a quadratic curve rather than a straight line.

The binding energy goes to a minimum and then turns up again as 1/r, as the radius gets small and the quadratic term begins to become comparable to the first term. Not to go into all the details, the reason that it can be done in the post-Newtonian approximation is that the coefficient of the Newtonian term for a super-massive star is quite small. So the quadratic term doesnít have to be all that large, because its coefficient is of the order of unity, it doesnít have to be all that large until it matches the Newtonian term. Which would actually be zero for an object so massive that all of the pressure was due to radiation. So thatís how it worked out, and then it took me some time to realize that with the quadratic curve of this nature if youíre at the minimum, in order to further contract and be in hydrostatic equilibrium youíd have to put energy in. Well, if you donít have energy and the system is radiating then what is initiated is a collapse of the system, and this led to the use of the term gravitational collapse. It was on the subject of gravitational collapse that the conference in Texas was organized. And of course the other aspect of it is then, that once the system begins to collapse then youíre no longer dependent solely on nuclear energy but a fairly large amount of gravitational energy becomes available. Because the gravitational energy is converted in the collapse into kinetic energy. Now one is getting closer to a realistic model; this can by a number of processes be converted into, for example, the relativistic energy of electrons and perhaps even into magnetic fields. So we got into that part of it andÖ

Weiner:

Who is we? By this time you were picking up collaborators?

Fowler:

Yes. The difficulty is I canít remember exactly when thatÖ

Weiner:

Here is the bibliography, right here.

Fowler:

Let me see, when was that conference?... Ď65.

Weiner:

That was the first Texas Conference? What are they, every three years?

Fowler:

Yes, theyíve been heldÖ

Weiner:

Yes, because I was at the third one in Copenhagen in Ď71 when I was there.

Fowler:

Yes, yes. So by that time Fred and I were working together again. Another summer had certainly gone by. And I guess then, it must have been in in the summer of Ď64 that we worked mainly on the collapse problem. I have to say that although I had been working on this independently, it was clear that Fred understood all of this. He may have suspected the general relativistic instability but I know quite clearly that he never mentioned that specifically to me and I got it first from Feynman. And I might say just for the historical record that itís well known that when Chandrasekhar looked at what Fred and I had done on the super-massive stars, he also independently realized that one had to put general relativity in, and he independently found the instability that Iíve been discussing. And of course he did it in a very beautiful and elegant way. He was able to do it analytically and with the full panoply of the relativistic equations. Itís true he had to do some computing but it was a much more analytic treatment of the problem than Iben had done. In fact I think that Ibenís treatment was also essentially a post-Newtonian treatment.

Weiner:

Let me ask a question about this period after the Feynman lecture on it, when you said you went off on your own. Did you communicate with Feynman or with Hoyle during this period as your ideas were being worked out? Did you write or did you talk, depending on the case?

Fowler:

Not very much as I remember. I certainly had discussions with Iben. The problem for me was that I just couldnít understand what Feynman and Iben were saying. And I wanted to work it out in my own way, I wanted to see if I could get this strange result in my own way. And it was quite natural for me as a nuclear physicist acquainted with the binding energy of nuclei to look at that aspect of the problem. What is the binding energy of a massive star when you work it out precisely. And I knew from our previous work that the binding was quite small relatively speaking, that is the binding relative to the total rest mass energy was quite small compared to that for ordinary stars, just because the super-massive object is really a bundle of photons, in a sense. And if you had nothing but photons held together gravitationally theyíre in kind of neutral equilibrium, thereís no binding. Just to really try to understand it myself, I worked the whole thing through.

And then ultimately decided that once Iíd done it I might as well publish it and so I wrote the paper for the REVIEWS OF MODERN PHYSICS and gave lectures at Italy and elsewhere [Annual Science Conference Proceedings, Belfer Graduate School of Science, Volume I, Ed: A. Gelbart (1966)]. The collapse idea was very interesting. The next thing, as I remember, that interested me was, was there any possibility that the collapse could be stopped and reversed by nuclear processes, that is, could nuclear processes play a role in this? I was stimulated by the fact that there seemed to be periodic phenomena in some of the quasars, for example 3C373, which turned out to be a star that had been under observation, it was on plates in the Harvard files way back into the 19th century. Itís luminosity had varied with a period, some people claimed, of 13 years. I became interested in the possibility that a super-massive object had not consumed its nuclear fuel before it got into the general relativistic range, in the instability. It started to collapse, but then as it collapsed it raised the internal temperature, turned on the nuclear reactions, and they might then generate enough energy to develop enough pressure to reverse the collapse and expand the object, cool it off.

Then the nuclear reactions would turn off and the whole business would be repeated. And sure enough you can make a model, with some assumptions which may or may not be justified, itís awfully hard to know for sure. You can make a model of a super-massive object that oscillates. From a contracted state to an expanded state, the main difficulty isÖyou can generate the nuclear energy, but as the system is expanding, how can you radiate the energy fast enough? And there one just has to do some arm waving and say, well, the stop of the collapse will generate a shock wave, the shock wave going out through the tenuous atmosphere of the star will become relativistic and maybe thatís the way you can get the relativistic electrons and the large magnetic field. So, over the years I published a few articles independently and there was continued collaboration with Fred. In particular, Fred was still skeptical that the red-shifts were cosmological, and I had always felt and still feel that the best bet is that they are cosmological.

But the next stage anyhow, largely due to the fact that Fred was just stubborn possibility that the red-shifts were not cosmological in the quasars. I got interested with Fred in the question, could the red-shift be gravitational? And I realized that if you could bring light out of the center, directly out of the center of a super-massive object then it would have a considerable red-shift. And just like light even from the surface of the sun has a small red-shift. And just like light even from the surface of the sun has a small red-shift, if you could bring light out from the deep interior of the sun it would be greater, and in the case of the super-massive objects you could get red-shifts comparable to what one observes, namely red-shifts of the order of two or even more. In fact if the super massive goes to its Schwarzschild limit the red-shift will be, in the extreme case, two from the surface and infinite from the center. So I remember trying to build a model of a super-massive star that was so tenuous that light could come straight out from the center, and thus maybe the red-shifts were due to the fact that one was seeing light that was gravitationally red-shifted and not due to the cosmological shifts. Then of course if that were the case then we would have a chance of reducing the energy requirements down to the point where they would be somewhat more tractable. Well, I remember I was working on this and Fred, I think, had been down in La Jolla with Geoff Burbidge and he came up here to Pasadena to spend some time. And I told him about what I was working on. Almost immediately, although it may have been the next day, he came and said, ďYouíre crazy to try to do it that way.

The way to do it is to have a massive collection of stars and to have a source, a gas cloud, a source of energy at the center of this massive collection.Ē So there we went full turn from a single coherent massive object around to one that consisted of individual smaller stars. The idea being that although you had a lot of them, they were dispersed over such a large volume that light emitted by a source at the center, where thereís a big gravitational red-shift, could come straight out. We then spent some time working on that model. And itís still an interesting possibility. It turns out the stars have to be practically points, otherwise they will intercept the light. By points I mean they have to be more like neutron stars rather than white dwarfs or main sequence stars. So you have to have a hundred million neutron stars and in a small enough volume that it canít be resolved by the telescope and then you have to have all the debris of the collisions falling into the middle and there acting more as a coherent object, you see.

So you have both, you have a single coherent object thatís emitting light in the center, and itís surrounded by a great number of point-like objects that are producing the gravitational field, which in turn produces the red-shift. Well, the model really doesnít solve the problem too easily. It turns out that when you work it out and beat all the requirements that the observationists put on it, it has to involve something like 1011, 1012, 1013 solar masses. If thatís the model of a quasar then a quasar is more massive even than most of the galaxies we see by a factor of ten to a hundred. So, there are problems there and I have more or less concluded that there are so many difficulties with the model that the red-shifts, although in principle they could be gravitational red-shifts, almost certainly are not; and I think Fred agrees with that. Fred still is skeptical, and Geoff Burbidge is very skeptical about the cosmological explanation for the quasars. But Fred would be the first one to say that this model that we came up with would seem kind of cute. You see, I should have said that Greenstein and Schmidt had shown, very soon after the discovery of the quasars, that the red-shift could not be gravitational redóshift of light coming from the surface of a coherent object.

It couldnít come from the surface; you could show quite simply that the volume thatís involved in order to give, for example, the H beta line is so extended at the surface of a star where the gravitational potential is changing very rapidly, the gravitational red-shift for the outer part of the emitting region will be quite different than for the inner part. And thus there should be a very wide spread in the red-shift, and thatís just not the case. These lines are fairly sharp. So this model that we eventually came to, that the light was coming from the center of the giant object, is attractive at least in that sense. Because youíre at the bottom of a well, where itís rounded, a potential well, and thatís where itís varying the least. But even so when you put on the requirement that the gas could, or the coherent object at the center, had to emit a fairly sharp red-shift line, and work it all out, then the gravitational field has to be produced by some enormous mass. That gets into ranges of the order of ten to a hundred to a thousand times the observed galactic masses. The masses are comparable to galactic clusters. Cluster of galaxies, you see. But there it is. I think the main thing again is that the work weíve done has stimulated a lot of thought along, in the general area of the applications of general relativity to astronomy. In fact it led me to feel that here at Cal Tech we had to get back into the field of general relativity, in which Cal Tech had been preeminent when, first of all Tolman was here, and when H. B. Robertson was here. After Robertsonís death there had been a real vacuum in that area. In fact in order to even teach courses in general relativity we had to have Frank Esterbrook from down, from JPL and teach, from time to time, a graduate course in general relativity. And so that led then to bringing Kip Thorne here.

Weiner:

Thorne must have come just after his degree, didnít he? Was he brand new at that time, or what? When did he come?

Fowler:

Well thatís, it must have been in the middle sixties. That is something that we do want to find out.

Weiner:

When did he come?

Fowler:

Yes, he apparently spent one year as a research fellow at Princeton and then he came to Cal Tech, to Kellogg, as a research fellow in physics in 1966 and spent two years as a research fellow. I felt strongly enough about the need to get back into general relativity that having known Kip as an undergraduate -- he was really a brilliant youngster and he had done very well in his graduate work under Wheeler at Princeton -- I felt, and I remember that Carl Anderson felt very strongly, that we should get him. I thought that we could pay him as a research fellow under the Kellogg grant in nuclear physics, just because of the close connection, the competition in a sense, between nuclear energy sources in super-massive objects and the gravitational energy. I felt, if weíre really going to work out what role the nuclear physics plays, weíve got to do some really basic work in the general relativity. Not just with the post-Newtonian approximation that I had been playing around with.

So we got Kip and it is well known that itís had a happy ending, up to the present at least, and Iím sure in the future. He became an associate professor in Ď67 and a professor in Ď70 and has built up a school in general relativity that is really unrivalled in the world. Kip has had more students in general relativity, than I think all the other practitioners put together. He has played a role in general relativity very similar to the role of Robert Oppenheimer played in nuclear physics before the war. He has had a group of graduate students and research fellows that numbers up to around 20. Itís not quite so large right now, but over the past few years heís had a very active, very exciting group of youngsters. They have been able to find jobs, because of the excitement in the whole field of high energy astrophysics. Many universities have wanted to get back into general relativity, and so Kip has been able to find jobs for all the many graduate students who have gotten degrees with him. Itís changing a little now. And so he is not taking quite as many students as he has in the past. But thereís still, of course, an enormous amount of work to be done. Because, as is well known, the collapsed objects idea then went on into the black hole concept. Kip has played a leading role in that. Iíve been very proud of the fact that I played a role in bringing Thorne here. And that we were able out of our grant funds here in this nuclear lab to give him enough money to get started; it was kind of seed money. I had a special grant from the ONR which I used in large measure to support Kip and his group. And then eventually when Kipís work became recognized he was able to get a grant of his own. Thatís the way it goes.

Weiner:

Would the success of the group be also due to his personal style? Iíve met him a few times -- a beautiful style, which is very attractive, I think, to todayís students.

Fowler:

Yes, yes. It shows in many ways, in the graduate students who work for him and the undergraduates who play some role in their seminars and so forth. They just adore him and heís one of the most popular lecturers on the faculty, not only here, but outside. Heís done a great deal of lecturing, high schools, colleges, graduate schools. He just inevitably draws an enormous audience because heís quite well known for the clarity and enthusiasm that he brings to these lectures. Well, letís go get some lunch.

Weiner:

We are resuming now after a break for lunch. You said you wanted to fill in a few things on the super-massive story.

Fowler:

Yes. In a sense Iíll always be kind of grateful for the idea of super-massive objects, which Fred and I came up with in 1963, and worked on in Ď61 and Ď62. The reason being, there I was in the early Ď60ís, I was 50 years old and it was a whole new -- I shouldnít say career, but a whole new field of interest for me. The super-massive objects went on to general relativistic instability, gravitational collapse, gravitational red-shifts, and eventually led in part to the founding of what we now call relativistic astrophysics. There I had been for the previous 25 years working primarily in nuclear physics and in a very close offshoot, namely nucleosynthesis in stars. But here once it became clear that general relativity was involved, that delighted me. I didnít really know, when I was 50 years old, just how much more fun I was going to get out of my scientific interest, because in large measure the original excitement of the origin of the element game, of the nucleosynthesis game and the stellar energy game, was over and done with. So here was this marvelous thing that happened to me.

I really had to learn stellar structure, really had to know what Newtonian stellar structure, stellar evolution meant. And I had to learn a great deal about general relativity, which as you know can be extremely baffling. So, for ten years between the time I was 52 or 53 and a little over sixty it was really just a new breath of life for me. Now in recent years I have come to strongly believe that nuclear physics has a very important role to play even though it may not be the major role. We havenít touched on the whole pulsar development which shows that you can really get great quantities of gravitational energy out of condensed systems on a much smaller mass scale. But there are many similarities to the quasar business, and I havenít made any contribution in that field. But as the whole pulsar business and the neutron star business came along, I was able to appreciate it much more because Iíd learned some general relativity in the previous years. Now, as I was saying, Iím convinced that nuclear physics, nuclear energy sources have an important role to play along with gravitational energy and rotational energy and magnetic energy. In fact the interaction of all these divisions into which we categorize energy is a very exciting and interesting problem now.

So I have decided, and over the past few years have gone back into nuclear physics because always, in every model we worked on we eventually come down to the need to know nuclear reaction rates more accurately. We need to know them over much wider ranges of temperature and at less energy than we did in the past. So Iíve now gone back to the nuclear aspects almost entirely. But the almost ten years that I was involved in relativistic astrophysics were very exciting. And of course the field continues to be extremely exciting. One thing I did forget to mention, and it played a very important role in my enjoyment of the work. Shortly after Dick Feynman had his idea about the instability of super-massive objects he took on a young graduate student, James Maxwell Bardeen, the son of the double Nobel prize winner, John Bardeen. And itís true that Jim was Dickís student, but because at that time I got interested in the problem too, I worked very closely with Jim. Heís an extremely brilliant young theorist. And he came into my office, not quite once a day, but two or three times a week, and I learned just an enormous amount from him as he was learning the business. I had somewhat more experience and somewhat more knowledge of the observations than either he or Feynman and so I was able to help him too, in a way.

The production of his thesis, that I was just looking at now, itís true I wasnít his supervisor, but I played some role in it. And it was a real tour de force on the whole problem. He essentially did, as a graduate student, what Chandrasekhar did in making a very elegant and exact treatment of the problem. So while he was working on that I was pushing the post-Newtonian approximation, because he really understood general relativity, all the details, much more than I did, he was able to keep me from doing silly things. He then went on to the University of Washington. Now heís already a full professor at Yale. And a wonderful guy.

Weiner:

When was his thesis done?

Fowler:

Well, I noticed it was finished in Ď65, so he got right in, he must have started in Ď63. You see his introduction, the second sentence says, ďHoyle and Fowler proposed models of quasars in which, because of the predominance of radiation pressure, general relativity played an important role due to its effect on stability, even though the effect on the structure may be small.Ē And so his thesis was stimulatedÖthe references are to those two papers which I gave you.

Weiner:

Strong radio sourcesÖ

Fowler:

Reprints. His first reference is to Schmidt and references two and three are to the papers by Hoyle and Fowler. He must have started that fall when I came back, the fall of Ď63. I think itís one of the great theses that weíve produced here at Cal Tech. Ah, here on page 110, ďhowever Fowler (reference 48) has found that with non-uniform rotation the mass limit may be raised from a few times 105 solar masses to 108 solar masses.Ē Yes, gee, I forgot all about that. One of the ways to avoid the general relativistic instability is to rotate the star. Because a rotating star stores energy in the rotational motion and even in a very massive star you can get fairly large Newtonian binding energy that way. Yes, Iíd forgotten all about that, one of the ways we had gotten around the instability was to rotate them very rapidly. I wrote several papers on that. The difficulty is that the rotation has to be so great that the periphery is travelling with something like a tenth the velocity of light.

So youíre not going to get any sharp lines. Always when you play the game to solve one of the problems in connection with the observations, sooner or later you come a cropper on one of the others. And thatís why the observations are still so strange and wonderful that I think itís fair to say thereís no completely acceptable model of quasars. Nothing at all like the general agreement about models for pulsars. There are arguments about the details, but the pulsar as a neutron star, I donít think anyone seriously questions anymore. And that the pulses arise from the rotation of the magnetic field thatís associated with the pulsar. I did get into it a little bit, in that I used the model that I had, this rotating massive star model for quasars, I used it to make a pretty crude model for the pulsar in the Crab Nebula. I mainly wrote the paper so I could go to the conference at Jodrell Bank, and they invited me to give a talk. I had to do something so I wrote all that up. So it was a very exciting period and now Iím pretty much out of it, but of course, here at the Institute Kip Thorne keeps the pot boiling.

Weiner:

One thing I wanted to ask you about. Whether in fact, as this field developed from your first interest in it in the early Ď50ís, not your first interest, but your active involvement in the early Ď50ísÖ

Fowler:

Ď60ís.

Weiner:

Oh, not only this field, but the whole field of nuclear astrophysics. This led into lots of other fields of relativistic astrophysics and so forth. Was there a clearly defined separation of groups as the field got more specialized? I mean, youíre unique, I think, I may be wrong, in the sense of going from nuclear astrophysics into these other fields. Were there very many other people who did that? Now youíre saying youíve returned, but were there very many people who crossed over like that?

Fowler:

Well, in a sense, yes. Of course Iben, you would say that he was working in nuclear astrophysics, in fact thatís why he was here. Icko got involved and he always attended and made contributions to these relativistic astrophysics conferences. He on the other hand, even before I did, went back to what he had done previously, namely star evolution. Don Clayton, my student, got interested but he is primarily back into nuclear astrophysics. I think Dave Arnett was involved but heís now working almost entirely in nuclear astrophysics. The thing that I said that has guided my own trends in the last few years, has applied to everybody. This whole business of the observations on quasars, on the strong radio sources, on supernovae, on pulsars -- all of that has led to the realization that nuclear energy is not the only source of energy. Gravitational energy being transformed into rotational energy into magnetic field energy may actually dominate in very massive systems, as you might expect. Gravity goes with the square of the mass, nuclear energy only goes with the first power of the mass. It may dominate over nuclear energy. But nonetheless nuclear energy clearly plays a key role, maybe in just triggering, or in giving bounces. A gravitational collapse can bounce if you suddenly can turn on nuclear sources. So nuclear astrophysics has had a new shot in the arm from all of these discoveries. Even though I might turn the argument around, itís clear that nuclear energy may not play the major role in so-called violent events. So the practitioners of nuclear physics got into this, in the main found the realization that there was a lot of new nuclear physics needed.

Weiner:

Letís identify this as side 1 of tape 2 of the discussion with Professor Fowler.

Fowler:

The point we were touching on now was that -- to say it in a somewhat different way then I was saying at the end of that tape -- all of these discoveries in radio astronomy, and the correlated ones in optical astronomy, quasars, pulsars and so forth, completely revolutionized general relativity in this country too. For years, since Einstein, general relativity had been mainly in the hands of mathematicians. There didnít seem to be very much physics involved. There were the three classical tests. They all looked as though they agreed with Einsteinís theory of gravitation, so-called general relativity, and that was that. Well, with gravitational collapse and one thing and another, the whole field was revolutionized. And so physicists really got back into it. Chandrasekhar changed his whole life style, he had been working for years on rotating stellar systems. Iím sure than Chandra would tell you that this new idea, the instability of super-massive stars, changed his life too. Because heís spent a great deal of time writing in that area. And Johnny Wheeler got back into it, you see. And then young people like Kip Thorne and all of his students, like Bill Press. And of course with Wheeler there is Ruffini whoís a young physicist who got into the business. That, I would say almost the metamorphosis of relativity in the past decade, has been one of the most exciting things thatís happened. And I have found that being on the periphery of it is really quite exciting.

Weiner:

Wouldnít you call it the birth of experimental relativity?

Fowler:

Yes, it has led to that. Not directly perhaps, although there are theories of relativity, like Newtonís theory, which do not predict these instabilities. In fact one of the major enterprises has been to see how one can avoid arriving at instabilities in massive systems. Whether they be a single coherent object or a collection of many objects. It did lead to an interest in alternative theories of general relativity. And at the same time, of course, the space program came along, whereby much more precise tests of Einstein predictions, not just the three classical tests but many others, could be made. In fact Shapiro at MIT in collaboration with a group at JPL here is now beginning to give preliminary reports of all of their findings. Theyíve been sending radar signals both to planets and satellites and getting them back. Theyíve measured the change in the transit time of light past the lines of the sun, not the bending, which was the classical test. Itís beautiful microsecond timing techniques. In fact Shapiro gave a seminar here several weeks ago in which to the relatively large errors that are still intrinsic to their observations, Einstein comes out with quite high marks.

In fact their observations, among other things, measure the quadrupole moment of the sun, which is related to the oblateness. If the sun has a quadrupole moment due to rotation then it will be oblate. But itís that quadrupole moment that, Dicke has pointed out, also causes the perihelion of Mercury to process. An as you know Dicke has claimed to measure an oblateness of the sun of a few parts in 105 and thus part of the advance, 10 percent, something like that, of the advance of the perihelion of Mercury is due to that. So then the remainder is only 90 percent, and since Einsteinís value is the whole thing it looks like Einstein is wrong. Well, what Shapiro and company are finding (and there are also other observations) is that the quadrupole moment is very small, and that somehow or other Dickeís observations are either wrong or else theyíve been incorrectly interpreted, as many people are claiming. Then of course Kip Thorne with all of his young people decided at one stage of the game, well, letís really make a catalog of all of the suggested theories of general relativity.

Thereís a whole class called metric theories, and heís done that and he and his students have painstakingly worked out what these theories predict for all the experiments that have been proposed. See, many of the authors of particular theories didnít make any predictions about all these new things. So that all had to be worked out in a systematic way, and there his student Clifford Will has played a major role, and of course Bill Press. The fact that we got Kip here, gave him seed money until he was able to get his own funding, meant that when the space age came along in this same decade and these new observations could be made, that he had a group there which could then put the theory into a form where it could be applied. Thatís in the great tradition of general relativity here at Tech. Neither Tolmann or Robertson were interested in all of the mathematics, all the problems in general relativity you know, the great beauty and elegance of the mathematics.

They were much more interested in what the predictions were for observation. Robertson stressed that all the time. I donít know whether you ever knew Bob Robertson, but he suffered fools with great reluctance, and he made no bones of the fact that he thought most of the work being done in general relativity during his time was just nonsense. He worked with Hubble and the interpretation of Hubbleís Law. He was the first one to write down the effects of the deceleration parameter in a clear-cut way. So always thereís been this close contact with possible observations in astronomy or in physics. Tolman was very much interested in getting people like Kennedy and Thorndyke to work on their experiments. So Kip has carried on that tradition of really close contact with observation. And now itís a big field, relativistic astrophysics.

Weiner:

Let me ask just two questions on that. First on relativistic astrophysics. My experience in 1971 when I was in Copenhagen for the year, seeing that conference being held there, knowing many of the physicists personally and meeting othersÖ

Fowler:

Yes, I was there.

Weiner:

Yes, you were, thatís right. One night Alfred Schild had some of his friends over to our place and had a big party of about 70 people. I think you were involved in another competing party that night. Anyway, getting to talk with this group of people I felt a real sense of a new field that had recently come into existence. The people were really feeling a great sense of excitement, they were very self-conscious about their new existence as a field, as if they were just over the barricade essentially. I donít know if you sensed that, but it was as if there was a movement. But this was a clearly defined field, which was very, very hot, people felt they were on the brink of great discoveries. They were conscious that it had not existed more than six years prior to that time which dates right to the study that you were talking about. The super-massive object study, the instability study.

Fowler:

Yes, it dated back to that, but of course around that time there was also the new input, the new pulsars and the neutron stars. And wasnít it true that by that time [1971] the x-ray sources were beginning to be interpreted in terms of black holes? Wasnít the real excitement then the realization that these hypothetical relativistic objects that everyone had kind of pooh-poohed in the past could be real?

Weiner:

That was the issue at the meeting.

Fowler:

Yes, and of course at that meeting, as you say, there was such a thrust that the groundwork was laid for the organization of a society that has now been established. I forget the name of it.

Weiner:

Well, the Texas Symposium became something else didnít it?

Fowler:

No, thereís now an International Society in General Relativity. And it was started at that conference. People realized it had to be organized. Let me seeÖ

Weiner:

That would be something worth documenting the history of, just because it is so new.

Fowler:

It is extremely interesting because of problems with the Soviet Union. It was justÖ

Weiner:

I saw what happened there.

Fowler:

Yes, you see everyone else was willing to put up candidates to be voted on for officers on the council or whatever it was, but the Soviet Union wouldnít do that. They had to wait till they got their slate cleared.

Weiner:

They had wanted to appoint delegates rather than to have them elected.

Fowler:

Thatís rightÖthatís right.

Weiner:

I remember the other discussions that were taking place. I guess Peter told me about it, Peter BergmanÖ

Fowler:

Oh yes, it was apparent even on the floor of the meeting that there was all kinds of shenanigans going on. That was very interesting, but as you say there was a real thrust towards some kind of formal organization in this old field -- old in a sense, but brand new field in another sense. The Danish relativists played a leading role.

Weiner:

Christian Moller?

Fowler:

Christian Moller, I think without him the whole thing would have fallen through.

Weiner:

Well, let me ask another question. And that is relating to CalTechís tradition in this entire field of nuclear astrophysics and then later in the field that weíre talking about now, relativistic astrophysics. Is there a parallel to it, in other words are there other centers that have developed which are similar to CalTech, first of all in the nuclear astrophysics area? After all it was you who went over to England and the collaboration started in that way. Was there any parallel work that finally developed in Cambridge?

Fowler:

No, because by the time nuclear astrophysics came into full bloom there was no nuclear physics really, at Cambridge. You see under Bragg and Mott nuclear physics was essentially wiped out. Itís true that when I was there in Ď51i, on my first sabbatical, when Mott first became the Cavendish professor, the old Cockcroft-Walton machine was still being used and the electrostatic accelerator that E. E. Shire had built was being used. But Mott, I think quite consciously, and Bragg before him, had decided to turn things around. And you know in Europe the professor decides whatís going to be done. I know that there were great difficulties, because Kempton, who had worked with Rutherford, had grandiose plans for building a quite long linear accelerator outside of Cambridge.

Then Rutherford died, and Rutherford had encouraged this. Kempton was almost ready to start construction. I guess Bragg had permitted him to carry out all the design work, but when Mott came he just stopped it. This broke Kemptonís heart. Of course Frisch was there and the cyclotron was still being used, but not in any exciting or in any imaginative way. Frisch had so many other interests; eventually, for example, his interests turned to high energy physics and participating in a group that worked primarily at CERN. So low-energy nuclear physics, which is whatís involved in nuclear astrophysics, had died out at Cambridge, so there was nothing there. And no encouragement given. When I was there in Ď54 Wilkinson was a rising young staff member in the Cavendish, but he saw the handwriting on the wall and went to Oxford. He eventually founded the new nuclear laboratory there. Now Dennis is an extremely good nuclear physicist and his lab has made innumerable contributions to nuclear physics, but he himself has never been really interested in nuclear astrophysics. Sciama has gone to Oxford and is trying to turn things around. But I just suspect that he wonít be able to get a great deal of experimental work going on in the nuclear lab at Oxford, because theyíve got so many lines going into pure nuclear physics. No, I think that this lab is rather unique, Charles.

Other places, Michigan State, Pennsylvania, Texas, have at one time or another spent a great deal of time and effort in their laboratories on nuclear problems, on nuclear synthesis or on energy generation. But I donít think there is any other place that has carried on a continuing program at the scale that we have here. In many of the other places, the interest developed because my students have gone there. Or people have come out here. At Pennsylvania, Bill Stevens was a graduate student with me. A year ago he took a sabbatical, came out, and went back and started using their Van De Graaff for some heavy ion measurements in nuclear astrophysics. Thatís mainly been the way itís gone. My student Cary Davis went to Michigan State and started some nuclear astrophysics there. Heís now at Texas, but Sam Sutin has continued the work. In fact Michigan State is doing some very interesting work in nuclear astrophysics. Clyde Zaidens was our student. I forget whether he worked with Tombello or Kavanagh, it doesnít matter. He went to the University of Colorado and now the University of Colorado has a very active program in nuclear astrophysics. Davis has gone to Texas and he started a program there. So I think itís fair that Kellogg is the only nuclear laboratory that has had a major program in nuclear astrophysics.

Weiner:

Well, itís unique, because in addition to the tradition here, the individuals, with Lauritsen, Fowler, and their descendants, thereís the link with a large observatory. This is something that is very rare. Here you are combined practically under one roof, not in the laboratory but the links are there, from Bowen on.

Fowler:

Yes, I donít know whether in your discussions weíve ever mentioned that sometime early in the 1960ís we started what was called a sins seminar, S.I.N.S. The standard joke was that we were all sinners. We chose the name just so we could have that awful pun. But what it was, was an acronym for Stellar Interior and Nucleo Synthesis: SINS. It met every Friday, astronomers came and the nuclear physicists and some of the relativists and a lot of the space physics people would come. Meet Gerry Neugebauer for example. And we still have a SINS seminar which attempts to bring together the astronomers and the physicists who are interested in nuclear astrophysics. Itís not quite as active as it used to be. One of the things is that seminars here at CalTech have really proliferated, we have to put out a calendar of all the physics seminars. And itís always a full page like that.

Weiner:

(looking at calendar): For any particularly day, practically, thereís several things going.

Fowler:

Yes, you see thereís the Astrophysicistsí Journal Club, the Infrared and X-ray Scaling Seminar, the High Energy Physics Seminar, Applied Physics Seminar, Physics Research Council, Gravitational Research Seminar. The standard Kellogg seminar. On this one there doesnít happen to be a SINS seminar. But we have them about once every two or three weeks now. But it relates to what you say, in that because we were in an astronomical atmosphere as it were, we were always encouraged. Iíve told you in the previous sessions that a great role in the direction that we took was played, first by Ike Bowen and then by Jesse Greenstein, who kept pointing out problems. Ike got us started, Jesse is the one who -- because he was interested in stellar abundances, thatís his field, among many other things Jesse does -- always kept bringing up problems you see. And encouraging us to study this reaction or that reaction to see what was going on. So youíre quite right, if we are unique itís in part because we were at a unique place.

Weiner:

Looking back though, on the decision that you took with Charlie Lauritsen at the end of World War II to stay in low energy nuclear physics with particular application to astrophysics, this is what you carried out. I wanted to speculate, if you had merely stayed in low-energy nuclear physics you might have been in the doldrums here. In other words if it wasnít with that link. Because low energy nuclear physics in many places in fact became not the growing exciting field but a relatively stable field that didnít attract so many people for a certain period.

Fowler:

I think youíre quite right if it hadnít been for the astrophysical aspects of low-energy nuclear physics I am certain that Charlie Lauritsen would not have remained in it. In fact thereís one aspect of this point that I donít think we got around to discussing. Itís true that Charlie decided to stay in low-energy nuclear physics but at the same time he realized that the future in nuclear physics was to go to high energy. So he took the lead in establishing the synchrotron laboratory. I donít know that we ever mentioned that, but Charlie was the one who essentially got Bob Bacher here. To head up what eventually became the synchrotron lab. But even before Bacher came Charlie had brought Robert Langmuir here to start the design of -- I remember it was a very modest thing -- a seventy million volt synchrotron. When Bacher came, Bacher realized you had to go even beyond that and the thing would up, eventually, at a billion volts. Largely due to the fact that they were able to get the big magnet structures from Berkeley. I think it was the model of the bevatron they brought down here. So Charlie didnít leave CalTech in the lurch insofar as high energy nuclear physics was concerned. He insisted that CalTech get into the field. But it meant starting a new lab and getting new people. I remember I was kind of upset at the time, because he felt that the only way to convince the power that be Ė- which included Millikan even then, this was after the war, but mainly Watson and Houston as I remember Ė- that we had to show that we could get some money for this new field. So Charlie insisted that I write a proposal for this seventy million volt synchrotron.

I remember I had to take a couple of weeks off. I went up and saw Ed McMillan, learned how synchrotrons worked, how much steel, how much copper and how much power and then how much staff was going to be needed. So the original proposal for a seventy million volt synchrotron, I remember writing it. At least I wrote the first draft. Then Robert Langmuir came out. It really was something, how we operated in those days. We were still Ė- the dates now -Ė we were still very closely connected with Inyokern and Robert Langmuir. You may well call him Joe. Heís the nephew of Irving Langmuir, his father was Dean Langmuir, Irvingís brother. Bob was at Schenectady. He had been a graduate student here, got his degree under Houston, I remember. He was at Schenectady with General Electric. Charlie decided that he was the guy we needed to get started in building a machine.

Because Joe had been building a seventy million volt machine at GE. His group had gotten the go-ahead from General Electric. I forget who was the leader, but Joe was one of the major designers and Charlie found out about this. So Charlie said, listen, youíve got to go back there and talk to your friend Joe Langmuir and tell him you want him out here and weíll make him an assistant professor. I remember I had a trip East with plans for something in connection with the transfer of Inyokern -- whatís now China Lake -- from CalTech to the Navy. Chick Hayward, who was experimental officer at Inyokern, had to get flight time, so he was going to fly back. It was one of the big navy bombers. I remember we had a crew of about ten types. We stopped in Nashville for some reason, maybe itís Memphis. Some big naval base. I remember Chick having to arrange for quarters and chow for his crew. Chick Hayward eventually became Vice Admiral and Deputy Chief of Naval Operations and all that. So I said to Chick, look, on this trip I want to go to Schenectady. He said, ďOh thatís great, weíll fly into Schenectady.Ē Itís this great big bomber, ten feet of snow on the ground and all they had done was scrape the runway. Down in that bomber into this 100 foot gap -- Iíll never forget it as long as I live! If we had skidded a bit the wings would have gone right into the damn snowbank. Iíll never forget, I can see it now, the snow going back, the side of the snow wall going by at a hundred miles an hour. So Joe Langmuir was there and he was just incredibly impressed by my pal. What was Chick by that timeÖhe was a captain by then.

So thatís how we hooked Joe Langmuir on coming out here to build the synchrotron. But the whole point of this story, thatís taken longer than it should perhaps, is that Charlie had enough vision to see that at the same time as his lab stayed in low-energy nuclear physics that CalTech had to get into high energy. Not on the Berkeley scale, but on a scale appropriate to CalTech. And of course over the years the synchrotron grant grew to be equal to the grant we have here in Kellogg and eventually exceeded it by about fifty percent. Now, of course, itís mostly a users group. And this is the reason why, when the new building was built for the high energy physicists, it was called the Lauritsen Laboratory. Because Charlie was the one who had the idea of doing this.

Weiner:

You said that JoeÖyou probably have other things to do so we ought toÖ

Fowler:

Yes, because I do want to go to the seminar.

Weiner:

You have other things before that. A couple more things which I think will wind it up. About the relative position of the Kellogg laboratory and the work being pursued here, which is not all nuclear astrophysics by any means anyway. And the relative position of the Kellogg group in the total CalTech physics scene. At one time you would have said it would have dominated it, because it was the most active and the most continuous group as far as I know. But Iím not clear about the total picture, when you talk about the synchrotron laboratory. How large did this loom in the total physics picture at CalTech?

Fowler:

I would say that the high-energy physics group that grew out of the synchrotron lab (as they now call themselves, high energy), that group dominates the physics division if any group does. But Kellogg is a very substantial part of the activities of physics. So large, in fact, that weíre jokingly referred to as one of the dukedoms in the business. Sometimes jokingly, sometimes there are real worries about laboratories of this type. Even though Charlie and I and Tommy (Tombrello) never wanted Kellogg to be an institute of nuclear physics or a laboratory independent of the physics division. Nonetheless just because we had our own funds we have been very very independent. And it has, as a consequence, caused problems with regard to those who were perhaps less fortunate in that regard. On the other hand I think anyone on the campus will agree that we have played a role in seeding three of the most active groups on the campus now. You could even say four.

We seeded Kip Thorne. By seed I mean that we took money from our grant for nuclear physics and paid a young man in relativity to come start a group. Some years ago Jerry Wasserberg was offered a position at Harvard. Well, we had been working a little bit with Wasserberg because of his interest in nuclear chronology and in dating. And I was a very close friend of Jerryís, I just thought, my God, we canít let Jerry go to Harvard. One of the reasons why he was going to go there was because Harvard was going to give him enough money to build a type of lab he wanted. So I said, ďJerry, if youíll stay weíll give you a hundred thousand dollars a year.Ē And we did. It took some doing to modify the proposal in such a way that we could still get money from the nuclear physics desk. If you want to do geophysics, why donít you go and get the money from the geophysics section of the National Science Foundation? Well, the geophysics section didnít have any money in those days, and didnít have enough money to do a lot of dating. They were more interested in much more practical things, in a sense. After all plate tectonics was just coming along, and oceanography and all that sort of thing.

So we seeded Jerry Wasserberg. Mercereau in the high energy group wasnít able to get all the money he needed. There, we at one time felt we wanted to build, we at least wanted to look into a superconducting linear accelerator such as the one that Fairbanks is still trying to build at Stanford. So we go Mercereau a couple of hundred thousand dollars a year. And then Jim Mayer in engineering wanted to do channeling and ion implantation. One of the very first groups to do that. So we gave him practically half time on one of our accelerators. Didnít charge him a thing. In fact we got some funds for him. So I think in that sense weíve been pretty generous and in a way may have justified our existence. But in more direct response to your original question. One other thing you must realize is that here at CalTech, for reasons that arenít too clear to me, radio astronomy was in physics, not in astronomy. Now in part that was due to, as you well know, a common situation in this country. Optical astronomers just didnít think that radio astronomy was ever going to be anything. They thought it was all nonsense. Bacher had the vision that radio astronomy was going to be something, and so he put it in the physics part of the Division of Physics, Mathematics and Astronomy so he could keep it right under his own thumb. Bob did it. Now itís true that over the years the radio astronomers are in the same building as the optical astronomers and very closely associated. But theyíre still in the physics part of the division. That may all be changed in the next few years, but thereís a very interesting thing that someone ought to follow someday.

The -- what should I say -- the inertia in the astronomical community to radio astronomy. So much in contrast, you see. Ike Bowen encouraged us to go into nuclear physics, that related, because he could see that. I think Ike was one of the least enthusiastic about having a group in radio astronomy here. Itís just a fantastic thing. There he could be so far sighted in one area, blind in another. Now I may be doing Ike an injustice in putting it too extremely, but itís just true as it has been in many places, radio astronomy got its impetus mainly from physicists. I think physics can be proud because it just wouldnít have gone as fast. Of course it took physicists. The instrumentation is so entirely different, so there are lots of reasons for this.

Weiner:

The whole microwave field is strictly a physics field, strictly from a generation that grew out of World War II.

Fowler:

Thatís right. And Bacher knew all that, you see. But we are reminded of all this because you asked me about relative size of Kellogg in physics. You must also remember that in this time the whole business of radio astronomy grew up. And in recent years applied physics has come into existence. But I think that our grant and the high energy physics grant are still -- theyíre both in the million dollar class -- and theyíre several times what any other group has. Three times what any other group has.

Weiner:

On your outline that you drew up two years ago when we started all of this, do you feel that youíve covered that final point here on the low-energy accelerator or do you want to say a little on that?

Fowler:

Well, as you said just a few moments ago, nuclear physics at many institutions went into the doldrums because nuclear physics became in large measure nuclear spectroscopy, and had the same history that atomic spectroscopy had. The cream was skimmed off the milk. Nuclear spectroscopy was a lot of detail about the angular momentum and parity and other properties of excited states of a given nucleus. It may have 100 excited states and there are lots of nuclei so no matter what beautiful work people did in nuclear spectroscopy, no matter how clever they were in measuring short lifetimes, and angular distributions, and developing instrumentation for it, there just wasnít any excitement in it. So as a consequence the National Science Foundation and the AEC wound up with a lot of low energy accelerators at various places around the country which just werenít being used. I was asked in 1968 to chair a committee on possible new uses of low energy accelerators. I guess I mentioned that because I think itís one of the other significant contributions that this laboratory has made. We not only went into nuclear astrophysics, but Professor Whaling went into beam foil spectroscopy, Jim Mayer has done channeling and ion implantation, and Tom Tombrello-of course all this is continuing -- Tom Tombrello has been analyzing lunar samples with our accelerators. Itís a nondestructive method and you can analyze the surface to find out where the solar wind is implanted. Itís an extremely exciting thing. So, I was able, with a committee that consisted largely of my friends and my students, to put together a little booklet that essentially told people of all the exciting things you could do with a low energy accelerator if you were willing to go into kind of the applications aspect rather than to stay in the pure nuclear physics. So thatís why I put that down there. Itís had some influence.

Weiner:

You know, that reminds me of the original application of the low energy accelerators, which was in the field of biology and medicine.

Fowler:

Right, right.

Weiner:

Now that is something that we havenít talked about, and thatís essentially -- it did fade out after the war didnít it?

Fowler:

Yes.

Weiner:

Once the program was turned to nuclear astrophysics the source of funding was not tied to any possible medical use. For example the Navy funding was strictly as we discussed in that grant proposal that we looked at if you remember -- l946 grant proposal -- which said for the fundamental studies in nuclear structure, with some relationship to the astronomical program. So essentially there was very little of what youíd call nuclear medicine or applications of it, here at CalTech.

Fowler:

You see that was all wiped out during the war, because the building was turned into a rocket ordnance laboratory. All of that was wiped out, and another decision that Charlie made when we came back to peacetime activities was not to restart the nuclear medicine. And I think he was very wise in that. Actually he had pretty much lost interest in it even before the war. In fact Charlie really lost interest in it in Ď32 when Cockcroft and Walton showed that you could disintegrate nuclei, you know. He had built all these machines as electron accelerators to produce x-rays. He immediately took one of them and reversed -- well, he didnít even have to reverse the polarity because they were AC machines. He just put a positive ion source instead of an electron source in the thing and went to work in nuclear physics. Itís true that we did all the x-ray therapy here before the war while I was a graduate student. But by the time I got my degree in Ď36 it was largely being phased out, even then. Still Charlie had essentially solved the problem to his satisfaction, that in x-ray therapy there wasnít much point to going over something like 400 kilovolts. And in fact that played a leading role in practice in this country. General Electric built a 400 kilovolt machine, they were used all over the country in hospitals. Eventually cobalt and so forth came along. And now thereís renewed interest in neutron therapy and in meson therapy. But weíve never played any role in that at all.

Weiner:

Weíre going to run out of tape and out of time simultaneously. Are there any other major things that you think that we should be covering that we havenít, whether for now or for sometime in the future? Weíve gone through the outline, thatís pretty clear, but I was just thinking, reflecting backÖ

Fowler:

Maybe, I know this one point here that I ought to make.

Weiner:

This is Side 2 of tape 2.

Fowler:

The point I wanted to clarify was in my discussion of the quasar red shifts and what I call the discovery of the quasars. I only mentioned Schmidtís name -- of course it was Maartenís discovery of the Balmer spectrum in 3C273 that I think most people would call the fundamental discovery. But nonetheless one has to realize that the radio astronomers themselves knew even before Schmidtís discovery that there was something very special about these pointlike sources. They definitely were not stars. In the very same issue with Schmidtís paper is one by Hazard, Mackey, and Shimmins [Nature 197, 1037 (1963)] -- Schmidtís article followed this one in the same issue [Nature 197, 1040 (1963)] -- which pointed out this fact that there was something very special about these radio stars, as they were still called then. I donít want to give the impression that the optical astronomers did the whole thing. Because Iíve got a lot of friends in radio astronomy and they quite rightly can say thatÖin fact in that reprint in that paper you showed me Iím sure the radio astronomers will put forth the claim that Hazard and company really discovered quasars. It was again one of those beautiful things in science where from two directions you come to substantially the same conclusion. Maartenís was just that much more dramatic, in a sense. But thatís another story. No, I donít see anythingÖ

Weiner:

Well, let me say that one thing we havenít mentioned, just to show that weíre both conscious of it, is another dimension of your career, which has to do with national advice in terms of various boards, including the National Science Board, and adviser to various government agencies. And including professional positions, including your coming presidency of the American Physical Society. But maybe thatís something just to refer to; maybe in a couple of years we can get a better perspective too.

Fowler:

Yes, since just last month I retired from the National Science Board after six years, the normal term on the Board. Perhaps itís too soon to evaluate what that has meant to me personally and what Iíve been able to do. Oneís reaction at this stage always is one of great frustration. I frankly feel that although I did the best I could as a member of the National Science Board I didnít really accomplish what I would have liked to have accomplished. Which, quite frankly, was to substantially increase the amount of funding for university astronomy in this country. All of my colleagues on the board will tell you, almost jokingly, well, Willy Fowler was always plugging for astronomy, in particular radio astronomy. Because I think it is just scandalous that in our country a field that has been so exciting and has contributed so much as radio astronomy is still only practiced in six or seven universities. Itís just as though there were places that didnít have chemistry departments. I just find it almost incomprehensible, and I donít understand why we canít have more funds for the places that have gotten into the field. You see, one of the real tragedies has been that because of funding difficulties the Foundation has stopped funding two of the seven places, namely Ohio State and Illinois. And theyíve cut Stanford back to practically nothing. Now, the trouble you get into in all this is that youíre self-serving. Well, if somebody doesnít support areas in which theyíre interested I donít know how else it can be done. But at the moment though, you can see thereís a great deal of frustration in my feelings about the National Science Board.

Although I must say I enjoyed it. I got a much deeper appreciation on how the staff of the Foundation works and the, what I think, the excellent job they do. And I also enjoyed working with the other 24 members of the Board. But itís a very frustrating business. There are so many conflicting demands on the resources that this country will allocate for science that inevitably some fields, and unfortunately the new fields, suffer. Here astronomy has gone from the little optical window that was available twenty years ago, and now we have radio astronomy, and infrared astronomy, and ultraviolet astronomy, and x-ray astronomy, and itís just incredible that weíve not been able to fund more activity in astronomy. Of course astronomy doesnít have any practical application and I suppose thatís where the real rub is. Iíve also been on the Space Science Board. And now Iím going on the council of National Academy of Sciences, and so I have played some role and will continue to play a role. I have to say that donít feel Iíve been very effective in that role. I really wish I could have done more. But maybe on the other hand, what efforts I have made have held the line at where it is now.

Weiner:

In a difficult period.

Fowler:

itís been a very difficult period, very difficult period. I was appointed to the Board by Johnson so I served for part of Johnsonís administration. Then in the early days of the Nixon administration, it was there that the great difficulty was that the Bureau of the Budget, and what became the Office of Management of the Budget, just took over the reins. The group under Nixon, that we all know about now, were not only high-handed in their handling of political matters, they were very high-handed in everything they did. Watergate has done one thing, that is it has relieved that situation greatly. I think Guy Steverís got much more responsibility and power, if you want to put it that way, now than he had before. There are people who question this, but they point to the fact that PSAC [Presidentís Science Advisory Council] was demobilized and there is really no presidentís science advisor. But they donít appreciate the fact that Stever has a much greater hand now, than Ed David, or Lee DuBridge ever had. So Iím frankly very encouraged about the future prospects.

The last few years weíve turned the Science Foundation budget around. You know it reached a peak in Ď68, then flattened out and then actually dropped a bit. Now itís beginning to turn around again. I think itís been in large measure because the National Science Board has really supported Guy Stever. Heís very popular with the members of the Science Board, Guy is quite a fellow. So I think that in that regard the future is quite bright. The difficulty is that inflation has hit laboratories extremely hard. We consume a lot of power here and the power bill is just getting out of hand. And every piece of equipment costs five times what it used to cost, and salaries are up, but all the grants are level. And Iíve seen one of the other, one of the main frustrations on the Board was to see good proposals from good institutions declined for lack of funds. You know the Science Foundation has to decline a great number of the proposals to them. Many are actually withdrawn, people donít want to have it on the record that their proposal to the Foundation was declined. There are those that are declined for lack of merit and those that are declined for lack of funds. And that category has been increasing over the period while I was on the Board. Itís just heartbreaking, in a way, to see some of the ideas that we just canít afford to support. And at the same time outside of the basic sciences thereís been the increased support of applied science in a way through the RANN program, Research Applied to National Needs. As a member of the Board I supported that, because I think there are problems in society that science has got to take seriously and work on.

But what I had hoped, and what I suppose most of the Board members had hoped was that the funding for Research Applied to National Needs would be entirely on top of the normal basic funds. It hasnít turned out that way. Now itís all bound up with the fact that even though the funding in the SRPS, ďserps,Ē the Science Research Program has increased, it just hasnít increased enough to keep up with inflation and to keep with the fact that science is growing. Particularly a field like radio astronomy is just incredible now compared with what it was when the Science Foundation started, you see. Those are the problems that weíre up against. I make no bones about it, I think science has a great role to play in our society, we canít turn our backs on science and technology. We have to live with them, but on the technological end weíve got to be more selective. I donít feel badly at all about getting off the Board and not being reappointed, as one could be, for another term, because I think that someone else should take a crack at it. Maybe theyíll be a little better at it than I have been.

Weiner:

How has this affected your research work here, your involvement in national policy?

Fowler:

Well, you see before I was on the National Science Board I was on the Steering Committee for Controlled Thermonuclear Research in the AEC. That was a job that took me away at least once a month. And then thatís continued while Iíve been on the Science Board and on the Space Science Board simultaneously. And the main thing that has happened is that it essentially just took me out of the laboratory. You see, I worked in the lab every day essentially until, well, it must have been Ď66. Let me just see, thatís an interesting thing that we never touched on. Bardeen wasnít my last experimental student. But essentially around Ď64 or Ď65 when I got involved in National efforts, primarily with controlled thermo-nuclear research, I just had to quit working in the lab. And then of course, right at that same time I got interested in the general relativity, and that was a purely theoretical effort. And the time that I have been on the National Science Board, that has taken me away. For income tax purposes you have to figure out how many days youíre away each year and I have been away from Pasadena more than a hundred and eighty days each year for the last four or five years.

Part of that is because I spent the summer in Cambridge. But the summers in Cambridge were at the most ninety days, so Iíve been away during the school term something like a hundred days. So it meant I just couldnít work in the laboratory any more. Iíve continued to have experimental students, but largely due to the fact that Charlie Barnes, my colleague here in the lab, has been willing to share supervision. So weíve had several students, Toers and Lyons I remember have been joint students of Charlie and mine. Charlie spends most of his time in the lab. So thatís been the main affect on my professional career of being involved, and Iím sure thatíll continue now. In fact itís been a decade so Iíve completely lost touch with all the details of the detection techniques that we use in the lab. The whole damn business has been revolutionized by -- if nothing else, by the solid state counter. The lithium drifted germanium counter and the lithium drifted silicon counter. So thereís a whole new game in the lab and I just wouldnít be able to get back into it. But up until I got involved on a national scale I worked every day in the lab. That was true of Charlie, he went toÖ

Weiner:

Charlie Lauritsen?

Fowler:

Charlie Lauritsen. For almost ten years before he died he was spending a great deal of time in Washington and on the East Coast and he just didnít come in the lab anymore. Although once in a while heíd come back, and Tommy and I would be working and he would come in and pitch in. Particularly if there was something we needed that had to be made in a hurry, Charlie would. He never lost his knack at the lathe. He got a great deal of satisfaction out of that. Nope, thatís been the main difference.

Weiner:

Let me ask you a sort of a wind-up question. You mentioned the term satisfaction. When you look back over your career, from your student days at Ohio State right up to the present, is there any period of time where you think back with special pleasure, in terms of the content of the work and the satisfaction of doing it? Any period that stands out more than any other?

Fowler:

Of course I was incredibly happy as a graduate student. That was such an exciting time. The positron had just been discovered, the neutron had been discovered, deuterium had been found. Cockcroft and Walton had found that you could disintegrate nuclei with low energy. That was really just terribly exciting. In my career as an adult I think Iíd have to say the most exciting time was when Fred and the Burbidges and I were working on the REVIEWS OF MODERN PHYSICS paper on the synthesis of the elements in stars. That was so exciting because as things began to fall into place you just really got a lot of satisfaction. The fact that something worked, the work on the S process and the work on the R process. It didnít all just come overnight, you know. We had to go through all the nuclear aspects of the nucleo synthesis game, and one by one these things fell into place. You see, as I told, Seuss and Urey came out with their rationalization of the so-called cosmic abundances, really the solar-system abundances, and with that as a firm base to work on it, you had one little conquest after another in applying the nuclear results to the abundance correlation.

I would say that was the most exciting period. And then working with a real bunch of characters there. Margaret Burbidge is a sweet, wonderful woman, Geoff is difficult at times; FredÖ you wouldnít call Fred difficult, but he was always picking up the ball and running with it. Fred was the smartest of the four of us. There is never any question about that. But boy, that was exciting, what a gang it was. Then we got Walter Baade into the act, I remember him. I love Walter, Iíve known Walter for years. He lived over on Michigan Avenue and I used to go over there and talk to him about supernovae. He had this enormous lore, you know, just incredible, all he knew about supernovae. Now thereís no doubt, Charles, that that was the most exciting thing. The super-massive star stuff, super-massive objects, that was exciting too, but it was nothing like the years Ď57, Ď58, when the nucleo synthesis stuff was breaking.

Weiner:

Does that coincide with your own estimate, if you had to assign importance as to your most important contribution. Where would you put that? The most important contribution.

Fowler:

Oh, I donít think thereís any question but itís the most important. In my mind I think itís the most important. True, it was a group effort, but nonetheless, I anticipate that if I am remembered in science it will be as the F in B2FH [Burbidge, Burbidge, Fowler & Hoyle]. Thereís just no getting around it. Fred, you see, is different in that regard. I think if you ask anybody about Fred, the first thing theyíll mention is steady state. And although there again there are three names, Bondi, Gold and Hoyle, that was quite independent work. Bondi and Gold worked together. In fact I never have found out from Fred the whole story there. Have you interviewed Tommy Gold?

Weiner:

No, I donít know himÖI mean I know him, sort of.

Fowler:

Yes, of course you maybe think of him as an astronomer. Actually Tommy is a physicist, and soís Fred really. Theyíre thought of as astronomers, but theyíre both physicists. You see, Fred was trained as a nuclear physicist, worked with Peierls. And thatís why heís been so knowledgeable in nuclear astrophysics. So I would say that I think of the nucleo synthesis as the most important thing. In nuclear physics itself, I like to think that the discovery that Charlie and I made of the internal pairs from oxygen was the single most exciting thing we did. The most lasting thing, of course, was my thesis, out of which the mirror nuclei came. Thereís no question that the idea of the mirror nuclei, and the fact one could say that the nuclear forces were charge independent (or charge symmetric, I can never remember now) was the biggest thing that we did. I suppose there are those in physics, or those in astronomy, who are still skeptical about nuclear synthesis in stars. They would probably say that mirror nuclei is the most lasting thing. Of course we never really talked about the mirror nuclei. That came out of my thesis, from the beta decay energy between mirror nuclei. After the war in addition to the nuclear astrophysics we pursued that, you know. We realized right away that mirror nuclei should have the same level structure. We never went into it in an extremely systematic way. Typically of the way weíve always done things here, we picked a particular case to concentrate on. I. remember, for example, we had found the excited state in lithium-7 at 478 kilovolts, so we knew there had to be a similar state in beryllium-7 or else there was something wrong with the mirror nucleus concept. So one of the first experiments we did after was to look for this excited state in beryllium-7, sure enough there it was. And then, of course, Tommy Lauritsen continued a lot of that as you know, because he continued in the study of the energy levels of the light nuclei.

Weiner:

Well, maybe we should check this out a couple of years from now and see how your estimatesÖ

Fowler:

Yes, it might be interesting to listen to what I had to say about me. Yes, weíll see how I feel a couple of years from now.

Weiner:

Iíd like to do that.

Fowler:

As you know there are lots of problems in the Academy too nowadays, and Iíve just, among other things, been elected to the Council and it begins to look kind of rough.

Weiner:

I guess it has. Letís agree that weíll do it several years from now. Weíll sit and just bring things up-to-date, just for a personal pleasure if nothing else.

Fowler:

Iíve certainly enjoyed this, Charles, and I must say, even for the record, that I hope somehow or other, that even though youíre going to MIT that you could continue to do this. I would love to hear some tapes like this from other people. Is it possible just to go to your shop?

Weiner:

Let me just turn this off.

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