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Interview of Wallace Sargent by Alan Lightman on 1989 January 20, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA, www.aip.org/history-programs/niels-bohr-library/oral-histories/33966
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Parental background; influence and encouragement from mother; early schooling in England: technical schools versus academic schools; influence of reading The Children' 8 Encyclopedia at age 10; decision to go beyond trade school; influence of Fred Hoyle's radio broadcasts on astronomy in the late 1940s; Sargent's becoming antireligious; education at Manchester; early theoretical work at Manchester; ability at pattern recognition and recognition of spectra; early preference for steady state model and reasons for that preference; "dark-time" people versus "bright-time" people among astronomical observers; early interests in peculiar spectra: A stars and then Seyfert galaxies; influence of Fritz Zwicky and work on Zwicky compact galaxies; career at RGO and UC San Diego; work on high star formation in small galaxies and Seyfert galaxies; training of observational astronomers and recent lack of hands-on experience; specialization of abilities; Sargent's motivation in choosing problems to work on; criteria of observers in selecting problems; attitudes toward the horizon and flatness problems; change in attitude toward the flatness problem after the inflationary universe model; attitude toward the inflationary universe model; reaction to de Lapparent, Geller, and Huchra's work on large-scale inhomogeneities and importance of similar work done earlier by Gregory, Thompson, and others; belief in large-scale homogeneity by reason of the cosmic background radiation; work on Lyman alpha clouds; working relationship of theory and observation in cosmology; seriousness of theories of the very early universe; outstanding problems in cosmology: dark matter; ideal design of the universe; question of whether the universe has a point.
I wanted to start off with your childhood and ask you a little bit about your parents and what they were like.
Where shall I begin? Neither of them were well educated. In fact, none of my relations went to high school. I was the first person in my high school to go to [University]. When I was small, my father was a gardener at a large country house in England. My mother had worked as a shop assistant before she married him, and then she became a full-time housewife and stayed [as one] for the rest of her life except for one small period.
Were either of them interested in science?
No. But my mother was the one who pushed me as a child into trying to become educated. During the period she worked as a shop assistant, the son of the owner of the shop went to a decent grammar school in the village where [we lived], and then went to Oxford. Following that time, she had the view that her children would go to a university, preferably Oxford.
But you went to Manchester.
I went to Manchester instead. My parents couldn't give me any practical help about going through college, but they did let me stay on at school. First of all, when I was eleven, I took the exam that kids in England took at that time, which determined whether you would go to the grammar school or the secondary modern school. Roughly 20% of the population went to the grammar school, which was to prepare you for, or give you, an academic education. The remaining 80% would leave school at 14. I was the first person in my family to make the step of going on after 14. I was in a peculiar situation because, by this time, my father had been in the Air Force during the war. He was a gunner on an airfield near London, and then he trained dogs — Alsatian dogs — to patrol airfields later on. After the war, he didn't go back to gardening. He went to work on the steelworks in a town near the village where I was brought up. Because this town had a steelworks, there was a thing called a technical high school, which was intermediate between a grammar school, which was purely academic, and a secondary modern school, which was for the dim, the ones who were going to be drawers of water, etc. The technical school was supposed to prepare you for being a higher craftsman on the steelworks, that kind of thing — a draftsman, [for example].
Is that where you got interested in science or showed an aptitude?
No. I would say I started being interested in science before I even went to that school. For a brief period during and slightly after the war, my mother worked for a woman in the village who was crippled and couldn't do her own housework. They were somewhat better off than we were, so they could afford to pay somebody else to come in once a week. They had a set of encyclopedias [for] their children called The Children's Encyclopedia, which I read when I was around 10 or 11. [It] had several volumes and had articles about science and, in particular, about astronomy. I remember vividly one of the pages having a full-page photograph of the Milky Way with all these thousands of stars. On another page, there was a picture of the 100-inch telescope, which I was later to use. That turned me on to science. And then, when I passed this exam at the age of eleven, which meant I could go on to a better school, a traveling salesman came around to the houses of the few people who had passed the exam. I think it was six kids out of forty-four in the class. We were all in one class in this village school. Six were selected to go on to higher and better things. I suppose he went around to all of them. [He) sold my parents another set of encyclopedias, this time more advanced. There were courses of approximately early university level on physics, mathematics, biology, art, history — lots of interesting things. I read these when I was around twelve and realized that astronomy and physics were the things that I was interested in. But I didn't think I would be able to go on professionally. I thought the best I could do would be to become a lab assistant someplace, and that was my intention.
Was there anything about cosmology in those encyclopedias?
Yes. There was some discussion of the immensity of space. I remember being aware around that age of the possibility that space wasn't as simple as it looked, that it wasn't Euclidean. I don't know what the terminology was, but they used the word, "curved space."
But was it a geometrical idea?
Yes. I remember being aware of that.
Did you try to visualize that?
Yes. And, of course, I thought I could, as a kid. Later, I discovered I couldn't.
Can you visualize it now?
No. You may have seen some recent memoirs of Dirac in which Dirac asked somebody — was it [Abdus] Salam — how he visualized topological things. Salam said he thought of the equations and then interpreted what the equations were. Dirac said "Of course, you're from the Indian subcontinent. All Indians think through symbols. But I see four dimensional space quite clearly as a projection from five dimensional space down." I guess I don't think that way. I did well at this technical school, and by the time I got into the upper form — the school was streamed into four streams according to ability — I was the top kid in most subjects in the top stream. I realized at that point that I should have gone to the grammar school [where] you could study Latin and Greek, for example.
For the university?
For the university. But the school I went to did not prepare people for the university.
It was aimed toward trade?
It was aimed toward trade. You were supposed to leave at sixteen rather than fourteen. But gradually I became aware that I probably wanted to stay on longer. When you're sixteen, you take some exams in England called ordinary level to prepare you for more specialized courses in more restricted subjects, which you then take for the last two years from sixteen to eighteen. For this ordinary level, most of the kids only took a few subjects, but I took nine subjects and did well in all of them, including English and things like that. The teachers realized that I should go to the university, and there was a possibility of transferring to another school in the town. But, for some reason, I was kept on at the original technical high school, and they made special arrangements for me to study for another two years along with two or three other kids who wanted to become school teachers. For the last two years, I took physics in a class of one or two.
Did your parents support you in this change, this altered direction?
Well, I'll come to that in a minute. The teacher had been a coal miner in Nottingham until he was 28 and then had gone late to university. He didn't know all that much physics, but he tried. I guess the bottom line was that I taught myself a lot of the stuff I did in the last two years. I specialized in physics, mathematics, and chemistry, but I also took French and English as well, because I was really interested in humanities. I didn't know at the time that the real high flyers that were going to go to university concentrated solely on science in order to improve their chances of being accepted. Anyway, [about] parental approval, my mother was always keen for me to go on to the next step. My father was sometimes doubtful, particularly, because he was ill. He suffered from various illnesses from about the time that I was 12 or so until the rest of his life. He was often home from work, and we would have to draw some sort of welfare. Particularly when I was 16, it was pretty bad, because basically we had only potatoes to eat. I felt very guilty about staying on at school when I could have been working. But nevertheless — I was so stuck on being a scientist of some kind that I ignored this and continued. Light man: Tell me a bit about your undergraduate work at Manchester.
I would like to say one more thing, if you're really interested in the subject, about influences.
When I was 15 or 16, Fred Hoyle gave some lectures on the radio which became the subject of the book The Nature of The Universe. I heard those lectures, and first of all, the subject was absolutely brilliantly done. I learned, for example, that you could know about the temperature in the interior of the sun by measurements of the outside. It came as a surprise, although to some extent, it had been revealed in the encyclopedias I had read earlier. Then Fred had a quite strong Yorkshire accent, and I realized that people without standard English accents — BBC accents — could actually do that kind of work. That was a tremendous liberation.
That's wonderful. A lot of people from your generation were influenced by those radio talks that Hoyle gave.
The last talk he devoted, in some sense, to religion. I had been brought up as a Protestant. My parents were never very religious but made me and my brother go to church when we were young. I dropped out of going to church. But Fred made me violently anti-religious, and I got into trouble with the school because of it. You were supposed to read prayers in the morning, in English schools. It was a state religion, so there was a short religious service at the beginning of each day. So Fred got me into serious trouble. I had fights with some the teachers with whom I was on otherwise good terms because I was brighter than most of the other kids.
What is that he said that made you violently anti-religious?
I would need to go back to the book again to be sure, but he was propagating the view that a sort of personal god that we had been brought up to believe in was really not very likely to be the case. He might be willing to believe in a an all-embracing creator who took an eye on things, but Fred produced arguments that it was unlikely that God interfered in our lives — interfered is probably the wrong word — influenced by prayer, for example, [to move] blocks of stuff from one place to another, or anything like that. I think that probably I had this idea all along, but didn't recognize it. That was also liberating. I think now that Fred has gone back to some sort of cosmic intelligence, which I would have said he was against at that time. Anyway, Fred was a great influence, but I didn't meet him until many years later.
I was going to ask you a little bit about your work at Manchester.
As an undergraduate, I took physics, and there I discovered that I'd been badly prepared, which was hardly surprising. I did well in physics, but I wasn't among the very top students. Part of the reason was I didn't bother too much as to whether something I was studying was for exams or not. I hadn't been brought up with this [approach]. Kids who go to certain kinds of schools are crammed and are taught not to waste time on things they're not going to be examined on. It produces a fine exam passing ability, but it probably is stunting in some other respects. Also, I was extremely interested in science, and a lot of the others weren't. They wanted a job being a scientist, but they weren't really interested. Nick Woolf, who's now at the University of Arizona, was in the same class as me. He and I used to spend a lot of time talking about various scientific things that had absolutely nothing to do with the classes we were taking.
Did you build anything at that time?
Only in labs, which I was not totally good at. Although I'd supposedly been trained at the technical school to be good at that sort of thing, in fact, my weakest accomplishments in the technical skill were building stuff or drawing.
Were there any professors you had that were particularly influential?
Yes. Maybe I should tell you a bit about Manchester. When I got there in the early 1950s, it had a very distinguished history in physics. [Ernest] Rutherford was there, followed by [William] Bragg, followed by [P.M.S] Blackett. All three got Nobel prizes. It was a wonderful period, which lasted maybe forty years. Just as I got there, Blackett was .leaving to go to Imperial College, and they didn't really replace him for a while. The place was drifting a bit. But, in the meantime, he'd helped to bring in radio astronomy and other kinds of astrophysical work. Blackett's own main interest was in rock magnetism, you might remember. I don't know whether you know that. He became convinced towards the end of his life that there was a connection between angular momentum and magnetism. Therefore, he devised methods for accurately measuring the magnetic properties of [certain] materials. As a result, very important work was done in rock magnetism, although his original hypothesis turned out to be complete rubbish. There was a guy called Wolfendale who worked on cosmic rays who's now a professor at Durham. The first few days I was at Manchester, we had to be told which classes we were taking. I remember going along and the man in charge said, "Dr. Wolf end ale cannot lecture until next Thursday because he's in Sardinia flying a balloon." This immediately changed my perspective, because I realized now that not only did you get to do science, but you got to visit Sardinia. That was pretty good. His lectures on cosmic rays were excellent too. They discovered the "V" particles there, the hyperons, just before I arrived. Manchester had been very strong in cosmic rays, but it was a dying field. Radio astronomy was strong through Lovell. Lovell and Blackett had Zdenek Kopal, brought in as professor of optical astronomy. In the last year that I was an undergraduate, there were some optional courses you could take, either in astrophysics, nuclear physics, or elementary particle physics, along with radio astronomy. I took a course with [Franz] Kahn and Kopal in theoretical astrophysics for one term. Franz Kahn is now a professor at Manchester. At the end of the first three years, I got an upper second class degree, which was okay considering the field. It wasn't brilliant. But they had a scheme whereby the better students from the second year could apply during the third year for a grant — like an NSF grant — to do research. So I applied for one, and I was one of ten out of a class of fifty-five who were selected to go on for a Ph.D. In those days, most people in England, and certainly at Manchester, stayed at the same place to do their Ph.D. Once you were given this grant from the government, you could do any sort of physics. You could shop around for different disciplines. I looked around, and I decided that Jodrell Bank, where the radio astronomy was, which was about 20 miles south of Manchester, was too isolated. And also [I felt] that a lot of the work was boring. Although I've built radios as a kid, I didn't think that was my [forte]. So I signed on to do theoretical astrophysics with Kahn, who at that time had just done a very important piece of work on the expansion of H II regions. I don't know if you've ever looked at this, but there's a very beautiful theory involving what kinds of shock waves are propagating, or under what conditions an H II region expansion propagates a shock wave. That was very nice work. He also was one of the first to study collisionless shock waves in connection with solar wind. Also Lighthill was a professor of applied mathematics at Manchester. It was a very strong school in fluid mechanics, and the bottom line was I decided to study fluid mechanics applied to astrophysics. I did one piece of work first on the radiative viscosity figures, which was published in Astrophysical Journal in 1959, which I did when I was between 21 and 22.
Why was the publication so delayed?
Writing it up took some time, but it wasn't too long. We also had to pay for it. I wrote it with another student, and we didn't have any money; eventually, the editor of the Astrophysical Journal published the paper for nothing. So I worked on radiative viscosity, partly because it looked like it might be important in some of the fluid mechanics problems I would want to do in astrophysics. Then I worked on the expansion of supernova remnants into the interstellar medium. I did work, which was later done again by Donald Cox and by Rosenberg and Scheuer. I never published my own work, but it was known to other people. It has been cited in other literature. I took one year over the radiative viscosity work and two years over the fluid mechanics. While I was doing the second part, Kahn came to Princeton for a year and spent part of the time in Pasadena. He recommended me to [Jesse] Greenstein, who was then running a thing called the abundance project in Pasadena, financed by the US Air Force. He had ten postdocs. Observations would be [carried out] at Palomar and Mt. Wilson, and would be [done] by this flock of postdocs. In those days, it was possible to join a thing like that without any previous experience. I had never seen a telescope.
These were abundances of stars?
Yes, only stars.
So this was a big shift for you, [since you] had done a thesis in theory.
Yes. In fact, the intention was that I would go on doing some sort of theoretical work with Greenstein, maybe on the abundances of elements. I knew no nuclear astrophysics, but I had taken a course in nuclear physics in postgraduate school, and a course in quantum electrodynamics. Neither were required. After I'd been at Pasadena for about two or three months, I went up to Mount Wilson to see the telescope that I had seen a picture of all those years before. They allowed me to guide for a few minutes, and I immediately decided that this was the thing to do. I quickly started to learn stellar spectroscopy, which I found amazingly easy. You know, different people have different natural abilities. I have a very good memory. I think I'm very good at pattern recognition. So when somebody presented me with a spectrum — you may have seen these old spectra with all these lines across it — I found it very easy to remember that this one must be strongly ionized silicon and this one must be europium. In fact, I can still remember the wavelengths. I last worked on them 25 years ago.
Before we continue with Caltech, let me just go back a little bit to Manchester. During your time at Manchester, say up to the age of 24; were you familiar with the big bang model?
Yes. I'd learned about it in Fred Hoyle's radio lectures — although, of course, the way he described it there was rather derogatory. In fact, I think he coined the term big bang.
Well, he was pushing steady state.
So I was very familiar from around the age of 16 with the steady state — big bang controversy. Then when I went to Manchester, the first radio counts were being talked about. I knew about that, yes.
Do you remember, during that period, having any particular preference for one type of cosmological model versus another?
Yes, I was definitely in favor of the steady state.
Do you remember why?
It's hard to remember, but I think one of the reasons was Fred's claim, which I now find to be specious, that having things created all at an instant put the act of creation beyond the scope of science. Whereas, if you're creating matter all the time, you could then study it. It seems to me that while that might be possibly true, it was nevertheless no reason to believe in one hypothesis rather than another.
That's the way you feel now. But at the time...
At the time, it seemed to be an attractive argument.
Any other reasons why the steady state appealed to you?
I think also because it did away with God, in what I would now regard as a very superficial fashion. You could regard creation, if it was going on all the time, as more of a natural process. I tended to think of God as a being, perhaps the creator of natural processes, but also the person who interfered in them from time to time. And doing away with that possibly [appealed to me], but I wouldn't have that attitude anymore. I don't think I treated very seriously the arguments having to do with the Hubble constant and the age of the universe and the age of the earth [as evidence for the steady state theory].
That didn't convince you?
That didn't impinge itself on me as being a very important argument. I can't reconstruct why. A sensible thing to say now is that one's knowledge of the relevant numbers was so poor that it wasn't the clinching factor. I think it was more aesthetic — the same thing that drives people now to think that omega is one.
That's something I want to come back to in a little while. Let me ask you about some of your early research work. You started off working mainly with stars, as you just described, and then in the mid-1960s, you began doing extragalactic work. Can you tell me a little bit about why there was that shift in direction?
Pure accident. In Pasadena, at that time, there was a division of labor — and interest — between dark-time astronomers and bright-time astronomers. The bright-time people were people like Paul W. Merrill, Jesse himself to a large extent although not completely, and Olin Wilson, who worked on the details of stars. The dark-time people were people like [Edwin] Hubble, [Allan] Sandage and Minkowski, who worked on galaxies. You were not allowed to switch between the two. In fact, if you were hired at Mount Wilson at Santa Barbara Street, you were hired into either the nebulae department or the stellar department, and you were not supposed to move from one to the other. There were fairly large pressures on young people at that time not to move from one thing into another. If you were hired into Greenstein's abundance project, you were supposed to slave away on stars. I tried to get out of that. For example, I was interested in Seyfert galaxies. Now the reason I was interested in Seyfert galaxies — I became interested before they became fashionable — was that they had peculiar spectra. My whole career has often revolved around peculiarities in things, recognizing peculiarities.
Spectra, in particular.
In particular, spectra. I worked on peculiar A stars, for example, at least in part, because that's what Jesse happened to be doing when I got there. But I was really attracted to the field by the peculiar nature of the spectra, rather than by the intrinsic scientific interests. Other people were working on the spectra of the oldest stars of the galaxy, which I think is more interesting from a fundamental point of view - just because you want to know what matter was like early on. But I was absolutely interested in the peculiar A stars because they were peculiar. I read about Seyfert galaxies — I probably read Seyfert's paper and became aware that there were these galaxies with very unusual spectra. That seemed reason enough to investigate their properties. I've been trained in physical analysis of things, so I'm reasonably well equipped to try and do something about the temperatures, densities, etc. I got spectra on NGC 4151 and NGC 1068, I think, in 1961. I observed first on the spectra of bright stars, learned the trade, then I was allowed to use the nebular spectrograph. The bottom line was that it took years to figure out anything, and really the measurements I had were not very good. I eventually persuaded [John] Oke to get some observations on the [nucleus] of NGQ 4151, in particular, which we then wrote up together in 1968. I have often worked on things like that where I got initially interested and seven years later or so, something comes out of it. I guess the course of my career was that gradually I became interested in more and more fundamental problems, while at the same time having an interest in the peculiar. I gradually moved from bright stars, peculiar A stars, to stars in the galactic halo that I studied with Leonard Searle in the late 1960s, and stars in globular clusters — things like that. By the end of the 1960s, a little less than 10 years after I started as an observer, I switched completely to working on extragalactic things. The first major piece of work I did was on the Zwicky compact galaxies, and again, the reason was that they were peculiar, that they were a class of things that were outside the normal accepted body of things that [people] were investigating. It seemed to me that there was a good opportunity to find out something, although it was not entirely clear what it was going to be. My interest in that started, I vividly remember, in 1964 in the Hamburg IAU meeting, where [Fritz] Zwicky gave a talk about his compact galaxies. I had known Zwicky while I was a postdoc earlier. I had talked to him in the basement of Robinson while we were both measuring things. He was measuring his pictures, and I was measuring my bright stars. I'd realized he had lots of interesting' views. Then I left Pasadena to go back to England. As I recall, Zwicky gave the first talk that I'd heard on the compact galaxies. He showed some pictures, and I remember Margaret Burbidge asking the question, "Are the spectra emission line or absorption line or continuous?" And Zwicky said "Everything." That indicated it was a rather broad class of objects. At the end of his talks, Fritz left out on the desk some lists of the positions of his compact galaxies. In fact, the first list is in his book. Not very many people took copies, but I took two and took them home. By this time, I'd been at the Royal Greenwich Observatory for two years. After three years as a postdoc with Greenstein, I had to find a job. I wanted desperately to go back to England. I went to the RGO [Royal Greenwich Observatory], which I disliked intensely. The only good thing I did there was to get married. But I left, as soon as I'd spent the two years that you had to spend outside the United States in order to get back in again. After I'd been at the RGO for a year, I met Geoffrey and Margaret Burbidge at a conference on peculiar A stars in Germany, and I said I was miserable and needed to be rescued. They appointed me to San Diego, where I went as an assistant professor of physics in 1964. So in 1964, I came back to the United States with Zwicky's first list of compact galaxies. Then I was able to observe at Lick. To begin with, I worked on the stars because I was still supposedly a stellar person. I only stayed at San Diego for two years. I'd only been at San Diego for a year and two months when I was offered a job to go back to Caltech again, which I immediately jumped at, particularly since, when I told Geoff, he said "Well, you'd better take it then." All this business about place A maneuvering with place B to keep somebody did not work out. Then at Caltech I was still supposed to work on bright stars, but after a year I was asking for dark time.
You were transgressing the order.
Yes. By that time, it was beginning to fold up. Various sociological [processes] led to its demise. I was very lucky, [since with] Zwicky's compact galaxies I wasn't trespassing on anybody's territory, because most of the nebular department people said they didn't exist. So I could hardly be accused of treading in their territory by studying the components of the universe that didn't exist. That got me into two subjects of interest. One was very high star formation in small galaxies and the other was Seyfert galaxies which were very much more luminous than the classical Seyfert galaxies that Seyfert had studied. In fact, they were intermediate between quasars and Seyfert galaxies. There was a small papersomewhere in the Astronomical Journal in which I think I used the term "missing link." Incidentally, at that time, [that work] convinced me that quasars were at cosmological distances. I'd been prepared before about 1968 to believe that there was some possibility of these very high redshifts — being due to some other mechanism. The fact that there were Seyfert galaxies which were at small redshifts made it easier to believe that there were similar objects at bigger redshifts, and some (the quasars) so bright that they drowned the light of the galaxies that they were in.
So you saw a continuous progression.
Yes, I saw a continuous progression — which strictly speaking isn't completely fool proof. But always in science, you have to place your bets on what is most plausible, not on what you’re sure of.
Especially in astronomy.
Yes, that's right.
Let me ask you a more general question. Do you think that the training of observers in astronomy has changed since your own student days, or your early days?
Well, I guess I got no training at all. I was merely shown.
Well, the experience you had.
I think there are two factors which are working in opposite directions right now. One is that the equipment is becoming sufficiently standardized that people trained as radio astronomers can use optical telescopes and vice versa — as long as it's routine measurements. In: that sense, it's more and more possible to do synoptic studies. On the other hand, people don't now get the hands-on experience that you really require to get the very best out of the observations, in many cases.
Why is that - that people don't get the hands-on experience that they used to?
Because there isn't the opportunity. If you're a graduate student, you have a choice of what you do, but if you're a postdoc like I was, and you want to work in some other subject, it's very difficult. The advertisement says "Wanting somebody with expertise in this, this, and this." And that's what you do, and you go there. I think that's bad. I think that [one of] the best things that could be done for science nowadays [would be] to have postdoc [positions] that are sufficiently broad in their scope [that] people can do anything as long as the equipment is available.
Do you think that would allow them to get more hands-on experience?
They would discover what they were best at, because often the first thing you do is more or less by chance. I think people's abilities are quite specialized. I know in my case that I'm terrible working with pictures, and I think probably better than most people working with spectra, even as an observer. And I'm quite sure there are people who are sort of hum-drum theoreticians like I was and would be much better as observers. Not necessarily, because I don't subscribe to the view that observing is an easy activity for anybody who is good at theory. There are more factors involved than mathematical intelligence. The ability to see what are the problems you can do doesn't seem to me highly correlated with mathematical ability. Light man: That leads to this question. Do you think that your view of astronomy has been affected by the particular fact that you're an observer as opposed to a theorist?
Well, remember I started out doing theory. I think I still look at questions from a more theoretical standpoint than most observers do. I would have said I was a schizophrenic person, [in that] I'm driven to choose topics that are peculiar — often not because they have any obvious potential theoretical impact. But, on the other hand, I think the way I tackle questions is more that of a theoretician. I think I know more about mathematical physics than a lot of observers do.
Well, you certainly work a lot with observers. Suppose I generalize the question and ask you whether you think observers as a group have a different view. I know there are many levels in which you can answer the question.
Yes, I guess in selecting a problem, an observer's viewpoint is fundamentally different. That is, you often select problems because they're in some sense do-able or observationally attractive to do rather than [because they have] a deep significance.
I'd like to get your reactions to some fairly recent discoveries both in theory and observation. Do you remember when you first heard about the horizon problem?
Not clearly, but it was almost certainly hearing Kip Thorne talking about such matters at Caltech when I was an assistant professor. [In particular, I recall Kip giving colloquia and Journal Club talks on, for example, the "Mixmaster Universe," which was an early (unsuccessful) attempt to show that an initially anisotropic Universe would become [isotropic.]
Kip is a little younger than you, isn't he?
Yes. He and I were junior faculty together in the late 1960s. That's almost certainly where I heard about it.
When you first heard about it, did you regard it as a fundamental problem in cosmology?
No. I didn't really think much about cosmology until quite late in my career, because of this business where I stepped from bright stars to more distant stars to nearby galaxies to further away galaxies.
So you didn't worry about it too much?
No. Also, I had a view, until quite late, that we didn't know enough to extrapolate the expansion of the universe back very far. It wasn't until probably a year or two after the microwave background radiation was discovered that I finally concluded — what everybody else had concluded long before — that[the background radiation] gave you a very good excuse to extrapolate back the expansion of the universe by at least a factor of 1000. Therefore, one ought to start taking seriously, shall we say, deeper questions.
Of course, for the horizon problem to make sense as a problem, you have to extrapolate back much further than z equal 1000.
Right, but — how shall I put it?
That made you begin putting some credibility in extrapolating backwards in time?
Yes. Light man: Do you regard the horizon problem as a fundamental problem today?
Yes. I've worked on the microwave background angular fluctuations for the last few years. So therefore, yes, I do regard it as a big problem.
Let me ask you about another problem, the so-called flatness problem. Can you remember when you first heard about that?
About why omega's so close to one? Probably late. It's very hard to reconstruct this. My tendency is to work in subjects observationally and l get to know what things are out there before I bother to find out what people think about them. I'm a sort of bottom-up, not top-down person.
I think history has shown that that's frequently a very fruitful approach. Well, do you remember approximately when you heard about the flatness problem?
I know it was before Guth because when Guth made the first attempts to [solve] it, the problem didn't come as a surprise.
You knew about it by then?
Did you know about it long before then?
I would have said so — maybe ten years before then. But that's only a guess.
Do you remember when you first heard about it, whenever it was, did you regard it as a fundamental problem, as a serious problem in cosmology?
No, I didn't. I cannot give you a rational reason why. I was much more taken with the apparent homogeneity of the universe than I was with the actual value [of omega].
So the horizon problem impressed you more than the flatness problem?
Did your view of the flatness problem change any after Guth — after the inflationary universe model?
So you still don't take...
Oh! Excuse me, I regard it as a very important, serious problem, after Guth, but my view as to whether omega is one has not changed. I belong to the class of people who say, "I don't know. It is a problem to be determined by observation."
Do you think that you took the flatness problem more seriously after the inflationary universe model? You said initially you didn't worry too much about it. Did you give it more credibility later?
Do you have any idea why you gave it more credibility later on? I know that's a very difficult question.
It's a difficult question. I suppose the fact that there was a potential explanation gave it more credibility. That's the only reason I can think of.
How much stock do you put in the inflationary universe model itself? Do you think that it's likely to be true or that it's very speculative? How do you regard it?
Well, this is perhaps tangential, but the thing that's come out of it that I didn't know before was the possibility of having a physical explanation or a physical accounting for the cosmological constant. I'd read for years about the fact that Einstein didn't think it was a very good idea to have introduced the cosmological constant. Other people are claiming that it came naturally out of general relativity. I'm not sufficiently well up on general relativity to know whether that's true or not. But I was very impressed with the idea that you could get negative pressures out of physical situations, and therefore, measure the [effects of] the cosmological constant. So that part of it stuck. Now, of course, examining what the value of the cosmological constant is, is another question. I think that's the main intellectual thing I got out of the inflationary universe model. For the rest of it, I would prefer to see what nature's actually like.
And see what omega actually is.
Do you remember how you first reacted to the results of de Lapparent, Geller, and Huchra on the large scale structures that they found?
I would have to dig a bit deeper. I was already familiar with the idea that there appear to be voids and narrow structures. So that confirmed views, or pictures, of the universe that I had for a while. But I have to say that that whole field has been the biggest observational surprise to me. When I started on extragalactic astronomy, the absolute word was that there were field galaxies that were spread more or less uniformly and then clusters, and there was practically nobody who entertained the idea that there were voids. I think that's been one of the biggest surprises in our view of how the universe is [arranged]. I think the work that you mentioned has pushed that to the extreme, but it was already [on the scene]. Gregory and Thompson had done it and others.
Oemler and Schechter and so forth. Has that work and those surprises, beginning in the early 1980s, shaken your faith in the big bang model at all, or not?
No. Because I don't see how it can contradict the idea that the microwave background radiation is coming from large redshifts. Therefore, I think the universe has expanded by three orders of magnitude or so. It doesn't strike me as being all that surprising that it shouldn't have been expanded by some more. I think the topology is very surprising.
Besides these examples that I've just mentioned, have any of your other major perceptions of cosmology changed in the last decade or so as a result of other developments that I haven't talked about?
I guess the thing that I thought a lot about is the Lyman alpha clouds, which I worked on for some [time]. I can't say they've changed my perceptions of things, but they've sure as hell made me worry about what they could be and how they would fit into the kinds of schemes that are now entertained. Most likely, they're objects which – at least at the time when we observe them — fill the voids. That seems to be the canonical idea. But what happened to them and why there were things like that in the voids is an intriguing and completely open question.
Do you think that theory and observation have worked well together in modern cosmology?
Yes, in the following sense. It's very rare in astronomy that you have, as you have in physics, clear predictions about what to do. In that sense, I regard present-day astrophysics as being an ideal subject for somebody like me, because I would be bored and uninterested in just going out and checking that some number that somebody had predicted was corrected. It's much more interesting than that. My business is to find out things, [and] have some theoretician say "Well yes, this is what we expected or could have expected on the basis of such an idea. Now maybe this will be true if we do this." It's more of an interactive process. Occasionally, of course, it happens in physics too, where somebody almost accidentally discovers high temperature superconductors. Then there is the theoretical interplay in trying to understand why the mechanism works, and that inspires other observations. But, in high energy physics, in particular, it seems to me that the interplay is all in one direction. Astrophysics, until recently, has almost been too much in the other direction, whereby observers accumulated fairly unrelated facts, [and] then a picture was put together by theoreticians. But the observers could often do damn all about verifying the picture. Maybe by the time the picture was produced, all the evidence that you could have accumulated had already been gotten. I really like subjects in which there's interplay. It seems to me there is a good deal in cosmology now.
Do you think that the theorists are justified in extrapolating backwards in time in this early universe work that has been fashionable?
You mean back to Planck time?
Or a hundred times the Planck time — back that far.
I'm sure that ten years ago I would've said no, and now I would say yes. Because just as the history of actual discovery has been far more surprising than expected, it seems to me — just because of that — one ought to treat wild theories with more seriousness than one would have done. Everything we've learned indicates that we can actually know more about the universe than one would have suspected at the time when a particular point of view was formed. For example, when the expanding universe idea was put forward, I think there was no clear view that you could, in fact, look back to the microwave background radiation… Of course, as we know, the calculations [were done, which] would have enabled you to have said clearly, "If you point a radio telescope, [you should detect this radiation]." But nevertheless, that didn't happen until 30 years after. And there are things like the primordial abundances, which I also worked on, where it took years for it to be realized that there was an actual connection with the observed world with something that one would have said was beyond our knowledge. Therefore, I am fairly sure that there will be other examples of that. Whether that [allows us] go back to a hundred times the Planck time, who the hell knows? But at least it's worth trying.
What do you think are the outstanding problems in cosmology today? Where are the frontiers?
I occasionally think, being a keen reader of Watson's The Double Helix, if I were Watson and Crick working in astrophysics, what would I regard as the problem to try and solve. I think the dark matter problem is unquestionably the most interesting, and the one that is most likely to be solved, and the one about which I have no idea at all. I would be interested to know what other people think. For example, I am not particularly interested in knowing what the value of the Hubble constant is. I'm not all that interested in knowing whether omega is 0.2 or .99. But I would really like to know what the major constituents [of the universe are].
This is a question I meant to ask you earlier, and then I'll finish up. One of the things that we're interested in is the extent to which scientists use metaphors or visualization in their work. Do visualization and images play any role in your scientific work?
I would say no, but they may be playing such a fundamental role that I just don't recognize it.
For example, have you ever tried to visualize the big bang? Has that ever been important to you?
Only when I'm trying to explain to a class — or to rich people whom I'm showing around Palomar — how you are inside the big bang, and how the big bang can be in all directions. In that sense, yes.
For pedagogical purposes.
But not for my own research.
I want to end with a couple of philosophical questions. With the first one, you might have to throw aside your natural scientific caution. If you could design the universe anyway that you wanted to, how would you do it?
Well, that question could be dealt with on lots of levels.
Do you mean in its large-scale structure?
Let's take the universe as a whole, and not answer the question on the level that you'd like the Yankees to win every season.
I don't think I'd want anything different to what we have here. It's sufficiently complicated. It's sufficiently complicated to be interesting. Are you interested in answers like whether one would like a completely chaotic universe or close to the edge [of a closed universe]?
Well, I don't want to guide your response. I'd like you to free-wheel a bit. Of course, if you don't want to say anything, you don't have to. You said that you wouldn't change anything because it is sufficiently complicated. Is that what you meant?
Yes. I wouldn't want omega to be one for some aesthetic reason, for example.
If it turned out to be one, you would be satisfied?
I would be more satisfied at having understood why, than in the actual value.
So you would be just as happy if it were .93, if you understood why it was .93?
Well, let me ask you one last question. There's a place in Steve Weinberg's book The First Three Minutes, where he says that the more the universe seems comprehensible, the more it also seems pointless. I was wondering whether you ever thought about the question of whether the universe has a point.
I've thought about it occasionally. I have essentially zero religious impulses. Therefore, I don't see any reason why I should expect the universe to have a point. One wasn't asked at the beginning, "Do you want it to have a point or not want it to have a point?" And so you should just take things as they are. I certainly wouldn't belong to a class of scientists who have an endless striving to find a point that would lead them to believe in God or anything like that.
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