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Interview of Michael Dine by David Zierler on April 14, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Michael Dine, Professor of Physics at the University of California at Santa Cruz. Dine conveys his provisional excitement over the g-2 muon anomaly experiment at Fermilab and he recounts his childhood in Cincinnati. Dine discusses his undergraduate education at Johns Hopkins, his developing interests in physics, and the opportunity that led to his graduate research at Yale. He describes working under the supervision of Tom Appelquist and trying to understand the force between heavy quarks within quantum chromodynamics. Dine describes his earliest exposure to string theory and his decision to take a postdoctoral appointment at SLAC, where he worked with Jonathan Saperstein on the next order calculation of the total electron-positron cross section. He discusses Lenny Susskind’s work on Technicolor and his subsequent appointment at the Institute for Advanced Study, his close collaboration with Willy Fischler, and the excitement surrounding supersymmetry at the time. Dine describes the impact made by Ed Witten when he arrived in Princeton and he discusses the origins of axion-dark matter research. He discusses his first faculty position at City College in New York and his reaction to the “string revolution” of 1984 and AdS/CFT a few years later. Dine explains his decision to move to UC Santa Cruz and his burgeoning interest in cosmology, he reflects on when his research focused to physics beyond the Standard Model, and he explains why it is possible to decouple the expectation that supersymmetry must be detected at the LHC. He explains why string theory is making strides toward experimental verifiability, and he reflects on the utility of being a theorist. At the end of the interview, Dine emphasizes his optimism about the axion as a dark matter candidate and why the field is moving steadily toward a greater understanding of physics at both the largest and smallest scales.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is April 14th, 2021. I'm delighted to be here with Professor Michael Dine. Michael, it's great to see you. Thank you for joining me.
You're welcome. It's good to see you.
Michael, to start, would you please tell me your title and institutional affiliation?
Yes, I'm professor of physics at University of California at Santa Cruz.
How long have you been at Santa Cruz?
Before that I was at the City College of the City University of New York.
Michael, a question we're all dealing with right now. As a theoretician, in what ways has the past year-plus in the pandemic been either beneficial or problematic for your science? Beneficial because, I say, perhaps you've had more bandwidth to work on long-standing problems that you otherwise might not have, or problematic because your work style might really depend on in-person collaboration with your colleagues?
Well, there's a little bit of both. So certainly, I am used to thriving on interaction with colleagues, especially postdocs, graduate students, undergraduates. And that's been more complicated. And I think like everyone, I've learned to meet and work remotely. So, I would say I've learned in some ways to cope or deal with it. I was, I think I mentioned before we started to talk in the interview, I was chair of my department for the first quarter of the pandemic period. So, I was dealing with a lot of things and at the same time was teaching a rather large class. And so, lots of challenges. So, on my desk at home, I have a, it's called a document camera, it projects things I write and also allows me to photograph them and record them. And so that was useful for teaching, but it's also been for me at least, different people have found different tools. For me it's been an important tool in collaborating when I meet with people and so on. So, I've gotten into a style of very regular meetings with postdocs, with students, and collaborators. So, as a theorist, it's probably in some ways, you know, with some discipline a little easier than for experimentalists right now. You know, if you can't get into your lab, if you can't get into the facility where you're working, it's obviously a much bigger obstacle. So, I think it's been a mix. And feel I've been productive in this period. Both in my service but also in my research. So.
Michael, an even more contemporary question: we have some wobbling muons at Fermilab right now that are causing a lot of excitement. Just a snap take from you, what is your take-away from the result so far?
Well I'm pretty excited. And this is a story that's evolved over the better part of two decades. So, when the result was first announced, it wasn't clear, by Brookhaven in the early 2000s, it wasn't clear how solid the result was, but we could come up with a lot of quite plausible explanations for the discrepancy. In particle physics, especially for example those of us who at the time were interested in supersymmetry would certainly have said, "Oh, maybe this is evidence for one of the new particles implied by supersymmetry." Over the intervening period, a lot of those ideas have been ruled out by the LHC. A lot of those new particles. And I was almost of the view that, well maybe, you know, with just a better experiment, the discrepancy would go away. And now it's clearly not going away, so in a sense it's more dramatic and exciting. We don't have a really good- I mean we have many explanations. There are lots of papers. But we don't have a really compelling explanation for what's going on. And so, I'm pretty excited. I'm also excited about, or looking I should say a little bit, at some of the underlying theory issues in making the Standard Model predictions and trying to make sure I really understand what are the uncertainties in the calculation and that they're really as robust as they seem to be. But I'd like to understand that a little better.
I wonder if you could compare this moment now as we're still coming to grips with what this discrepancy means, how this might compare to the run-up when there were starting to be real excitement that the Higgs would be found at the LHC? In other words, when the Higgs was found, it was in many ways a capstone, a completion to the Standard Model. But if I understand correctly, the best-case scenario now is that what we're finding at Fermilab might be physics beyond the Standard Model. If that's true, would this in some ways be an even bigger development than the discovery of the Higgs?
Well I think I might get in trouble if I say it's more or less dramatic. The issue is going to be where do we go from here? What is the next step? One thing that will happen is the experiment itself will acquire larger statistics, what's now a four-sigma deviation will likely become a five-sigma deviation. And it's, certainly, myself, I want to be more confident, the theoretical prediction. I mean we're really talking about a very tiny effect. And could there be something that we're not understanding properly in the theory? But that I would say, yes, in a sense it's- with the Higgs initial discovery, part of the problem is we- there could have been other things that happened. So, in line with what's happening with the muon, it could have been that the Higgs was there, but didn't couple exactly, didn't behave exactly as predicted in the Standard Model. And at this point of course we don't have that kind of precision on Higgs properties. But so far, it does look like the Higgs is very much the Standard Model Higgs and any deviations are very small.
As I said, the flip side of this is that you know, I think it's quite likely the ideas that we put forward to explain the muon anomaly might also predict things that we should see in Higgs. So maybe I should be saying that I see these experiments as potentially complementary. And I think at the moment we're sort of in the dark. Of course, if you look at the ArXiv, there are dozens of papers the last few days, the last two weeks rather, on the g-2 results. But I don't think anyone leaps out as obviously the correct one. And so, where we go from here is not totally clear.
Although that's also an exciting moment-
-when there's someplace where we know we're going; we just don't know where it is.
Michael, let's take it all the way back to the beginning. Let's start first with your parents. Tell me a little bit about them and where they're from.
I grew up in Cincinnati, Ohio. My parents, my father was from Cincinnati. He was I guess the second generation. His grandfather was an immigrant from Eastern Europe. My mother grew up in Baltimore and moved to Cincinnati when she married my father. My father was a physician. He was a pediatrician. He was active for many years. My mother had a background in biology but stopped working around the time I was born.
Is your sense that your mother, in a different generation, a more modern generation, would have kept up her career in the sciences?
Oh yes. And she- as her children grew older, she found work more in the social work area. But I think, had she come of age at a different time, she would have a career in biology.
Were you interested in your dad's profession at all? In the scientific relationship between medicine?
Yes, though I never really thought much about a career in medicine. But I admired my father. We discussed many aspects of science, including medicine, a great deal. He certainly was broadly interested and helped drive my interest in science.
What neighborhood did you grow up in in Cincinnati?
I grew up in a neighborhood called North Avondale. It was a very interesting, a lovely neighborhood. It was for its time somewhat unusual. It was a racially integrated neighborhood. Pretty self-consciously so. And schools I went to were integrated. There were a mix of people in professions, in business and doing other kind of things, among the adults. I'm still in contact with some of the kids that I grew up with. You know, I liked it a lot. It was a very kind of nurturing place.
Would you say that your interests as a boy very much foreshadowed a career in physics?
No. I was sort of all over the place, and I think when I, if I had any kind of crazy vision of what I was going to do, I was going to be a historian. I had an uncle who was a historian. I was very interested in history. Even at the time I got to college, I was thinking a lot about history. I studied science and physics and chemistry in particular in high school, but I only sort of got really excited about things in my college years.
Did you have a strong curriculum in math and science in high school?
Yes, we had a very- I went to a public high school called Walnut Hills. Which was a kind of magnet school. It's still a very fine school. And I had some very fine teachers across the board, but certainly in science and math. And certainly sustained my interests. I don't think I had from my classes, you know, a vision of what work in science would be like, or research in science. That came much, much later. But certainly, an interest in the subject, those subjects had developed. But I wasn't such a whiz kid, and I wasn't obvious that that was the direction I was going to take.
Between your family's financial capacity, geographic considerations, your grades, what kind of schools did you apply to for undergrad?
Well, so I applied to a variety of places. I had a pretty confused vision of what I wanted. I think as an undergrad, actually, I really wanted to go to Yale, and I wasn't accepted to Yale. I went to Johns Hopkins. I was quite happy there. And it's there that my shift to interest to physics really happened.
Did you still have family from your mom in Baltimore when you went to Johns Hopkins?
I did at that time, yes. Yes, I did. I had my grandmother who was still alive. I had some aunts and uncles and cousins in Baltimore in those days. So, I used to see them with some frequency.
Was the anti-Vietnam War movement significant at Hopkins when you were an undergraduate in the early seventies?
Yes, well I don't know what's significant. I don't know how we'd weigh as significant, but certainly it was there. I think that when I got to the university, that was actually just at the end of student deferments, and a shift into lottery. So that I think also kind of, you know, lit a fuse, lit a fire, under people. It wasn't- the campus was in some ways less radical than I expected. I was actually a little bit disappointed. I thought of myself as a kind of hick from the Midwest. And my high school was really much more, you know, my high school fellows were much more politically active, including the anti-war aspects and so on, than my college comrades were.
Now was it a professor or was it a course that turned you onto physics in college?
A little of both. It was a sequence of things; it wasn't just one. I think my first introductory physics course the professor was named Brad Cox. I think he may have retired recently. Well, suddenly I was exposed to a much more sophisticated view of the subject, and much more demanding view of the subject. I sort of came in thinking I was, well, I did take an AP physics, I knew this kind of stuff, and I really realized very quickly that there was an awful lot I didn't know. So that got me started.
There were some courses and teachers that were particularly memorable. My third-year quantum mechanics course was with Gordon Feldman. He was a theorist, an atomic physicist basically. And he gave a quite memorable course. I think that was certainly one moment, possibly a transitional moment. But I think even as I went through, I was constantly being reminded by my teachers that what I was learning in books is not the same thing as what it means to do science every day. Really learning that lesson took some time. And I also had different- you know, I got different, how should I say it? Advice from some of my professors. For example, on theory versus experiment. We were in the Nixon administration. There was a big shift from sort of a post-war boom in science funding to, you know, to something not as- I don't want to complain, but not as generous.
Not only that, but there was the additional controversy in Vietnam of the military funding of the sciences.
Right. Though most of the people I was dealing with were not getting much of their money from the military. The money was coming principally from the Department of Energy and the National Science Foundation. So that wasn't such a big effect initially, but certainly there would be a realignment of funds, and the notion that the sciences were just entitled to certain kinds of funding changed. That, I think, in retrospect and in an appropriate way, kind of evaporated. Something that had existed in the immediate post-war years. But in particular, another thing that had happened is there had been a great hiring boom in academia right after the Second World War. And you know in universities, people were after a while, you get tenure, they're secure, and those positions were sort of locked. So, there was both a funding shrinkage and a tightening of the job market, even just for demographic reasons. And so, I was getting advice from my teachers. I sort of thought I wanted to be a theorist. I wasn't sure. And I was getting advice from faculty that you shouldn't be a theorist, it's too hard, there are too few jobs. And that was another sort of memorable aspect of that period. And you-
Were you any good in the labs? Did you default to theory because experimentation wasn't for you?
I was probably adequate in the lab. That was also true in graduate school. We'll cut to that in a little bit. I just didn't love it in quite the same way. But I do think my teachers were right, that I didn't have a realistic idea of what it meant, you know. Theory was to me something that I read about in books. What does it mean to practice it, to do it day-to-day? I don't think I really had a clue. I think I had a bit less of a clue than I realized at that time. And I think the other thing about experiment is that, and that people often get confused about, is that you know, some people in the lab or are brilliant machinists or maybe brilliant analysts or so on, often experimentalists aren't exactly one or another of these things, and they can still be quite successful and their work can be quite important and interesting. You don't necessarily have to be skilled at everything. For a theorist, your performance on exams is not necessarily a clue to your performance professionally, similarly for experimentalists, how you do in a lab course is not by any means necessarily the measure of how you perform in the world beyond. So, I don't think, and as I said, that I was afraid of experiment. We'll come to my graduate experience a little later. But I took to heart what this advice I was getting, it worried me.
There was a lot of stuff of course going on in particle theory during the time you were in undergraduate. Did you get a sense of that bigger world out there, or was your physics reality rather parochial and contained to Hopkins?
It was parochial and contained to Hopkins (laughter).
So, like Grand Unification, November Revolution, all of these things?
Well that happened actually when I was in grad school.
Oh right, because it's right after. It's the summer after.
But the lead-up- so I graduated, I finished- I basically finished just before the November Revolution. I was in graduate school in November of 1974. So, some of that wasn't there, but the discovery of asymptotic freedom was not on my radar. That happened in '73. That happened around the time I was a senior. The whole of all the developments around Yang-Mills theory, the Weinberg-Salam theory of weak interactions, these were not on my radar. And other things, other precursors to that. I was really not fully aware. So, I was really stuck in textbooks from ten years earlier. I would say, my professors were right. I didn't have a real view, any kind of realistic view of what the research world looked like.
But when you were thinking about graduate programs and professors possibly to work with as advisors, you were coming from the perspective of learning how to be a theorist in graduate school.
I was, but I didn't have a broad perspective of what the field looked like. So, if you want, I can go into that a little bit. So, I had- first of all, I had a big setback as I prepared for graduate school, which is I took the GRE. And for me, you know, one thing I had had in life, I had done well on was tests like that. I should say the menu of standardized tests that students face nowadays has evolved. But in those days, okay, when you went from high school to college, the SAT was the big deal. So, then that was something you just- in those days, people largely didn't prepare for these tests. You were advised not to prepare for the, in fact. Well I went and I took the GRE in much the same way. That was a big mistake. And I learned later that, you know, at all the fancy places, everybody prepared, especially for the GRE in particular subject areas like physics. So, I did very poorly in the physics subject GRE. And that affected my life probably profoundly and ultimately in ways that were fortunate. So, I had really dreamed of going- I was charmed by big names. I had dreamed of going to Harvard or MIT or something. I went to Harvard for a visit. I actually met with Shelly Glashow. He kind of said, "Why in the world do you think you should do this?"
What was the "this" that Shelly was referring to? Do you remember?
Theory, theory, theory. Theoretical physics.
Meaning you couldn't cut the mustard? Or that he thought everything was done?
Yeah, yeah. Meaning, why do you think you can cut the mustard? And it was the right question to be asking, and I found that quite discouraging, and with my GRE score, I didn't get into Harvard.
Did you know what you were getting into from having a conversation with Shelly Glashow? Meaning that he has a personality where he doesn't mince words.
Right, no, well, in that conversation, I certainly did not. I should say at that point I only had a, you know again, my view of the field was not very broad. I had a sense who he was, but not a real clear sense. And he certainly, his personality in that interview meshes with my experiences with him through the years. I'm of course a big admirer of his. But it probably was best for me in many ways that that my dream of getting into Harvard is not what happened. I went to graduate school at Yale. I had the good fortune that Yale didn't care about the GRE score.
I was going to ask.
And so, my grades were good, so they took me. In those days, many graduate programs, would just sort of take people on the theory that we'll kick them out later if, again, if they don't cut the mustard, if you like. This is not true of many places anymore. And I went, also not really understanding this. Graduate school is a kind of different experience than undergraduate years, high school years, and so on. But I think, I adjusted pretty quickly and did all right. I didn't get thrown out. And I actually had the good fortune that after a year, Tom Appelquist, who had been a junior faculty member at Harvard, did really important work leading up to the November Revolution among other things, came to Yale having not gotten tenure at Harvard. And so, after I'd been at Yale a year and a half, he agreed to be my advisor. And that was a spectacular experience.
What was Tom working on at the time you connected with him?
He was working- he was thinking about heavy quarks like charm (and possible heavier quarks, which would be discovered later). And we worked together, and actually that was one of the great parts of this experience. We worked together on trying to understand the force between heavy quarks within quantum chromodynamics, the theory of strong interactions. Understanding of the theory, at that point, was still at somewhat of its infancy and it was not clear how you might think about that problem within the theory. But there was a sense in which if the quarks are heavy enough, one knew how to, or thought one knew how to, calculate the force between the quarks. And that was sort of the thing we worried about, we worked on. We thought about extremely heavy quarks, how that might work.
So, I learned a lot of QCD, about quantum chromodynamics, but I really learned from that experience a lot of very basic quantum field theory, which was important to me later. And I think I also learned a certain approach to broad classes of problems, and it was very valuable. I should say that as I, to back up a little bit, you asked about experiment. I actually thought a lot about going into high energy experiment at the time, and I worked for a while, sort of half my time in theory and half my time in an experiment with a professor there named (John Sandweiss), a very distinguished high energy experimentalist. And we also worked- that was actually before the discovery of, or just before the discovery of particles carrying charm quarks. At that point, we only knew about particles like the J/psi which had been discovered in '74, particles which have a charm and anti-charm quark. So, the charm-ness just cancels out. So, particles which actually have some net charm have a charmed quark and some other kind of anti-quark rather than a charmed anti-quark. Those were a subject of search, and he was then designing an experiment and I worked on the design of that experiment to look for those. And I would say I was not a brilliant experimentalist, but I wasn't discouraged by the idea of experiment. I was a bit torn about what to do.
Would you say that your interests in experimentation were valuable as a budding theorist?
Yeah, I think so. And I think, you know, I like to think, not as well as I might, but I like to think I at least have some sense of what's going on in the world of experiment. I think understanding what the possibilities are, both what's likely to happen, what's feasible, you know. This story, which we talked about originally, is a very rich one experimentally. It's a very rich one theoretically, not just in the aspect of what new might it predict, but what goes into that extraordinary calculation within the Standard Model? And that has an experimental side as well as a theory side. So, one piece of that is, at least in part, extracted from experimental numbers. And sort of having some appreciation for that is- I think helps me.
Michael, was your sense at Yale, especially being Tom Appelquist's student and the circumstances of his hire at Yale, was your sense that you were there at a moment where Yale was very self-consciously building as a counter-weight to Harvard because of all of the amazing things that were happening at Harvard earlier in the decade, and Yale wanted to catch up, so to speak?
I don't think so. I don't think that's quite how it worked. I think- I'm not really sure. There were other theorists at Yale who influenced me a great deal. There was another young theorist who came at the same time named Itzhak Bars, who's now at USC. He was much more of sort of a pure theorist than Tom was. I mean, Tom was thinking a lot about experiments, about all the nitty gritty of connecting theory with experiment.
Itzhak was in sort of a different class, as were some of the older faculty there. So, a particularly influential person for me was Feza Gursey, who passed away in 1992. Feza was originally Turkish. He was also kind of a theorist's theorist. He was very mathematically inclined. He was both in some ways dreamy personality and at the same time he could be very hard-nosed, and I remember very well at a time when I was having this internal debate between theory and experiment, his taking me out to lunch and giving me some rather hard-nosed advice about what it meant to succeed. And he actually, in my conversations with him actually, did a lot to build my confidence that I could do this. It was the first time I'd ever heard a phrase which I've heard subsequently a lot. He spoke about "good taste" in science. Good taste in theory in particular. Which explained to me meant the ability to choose problems to work on that are both interesting and tractable. And tractable means tractable for you. You know, that you have the skills, the ability to deal with that. I think these days, you know, through most of my career, the epitome of good taste has always been Steve Weinberg, who in some way- of course, he's an extraordinary intellect, but he's not necessarily the flashiest.
But always through his career, had a nose for important problems, and problems that he could tackle. And he's clearly among the smartest people there is, but he's not perhaps the smartest. But his ability to choose things to work on, things to focus on, is important. And I believe that Feza actually at that lunch mentioned Weinberg. So, there was quite a mix, you know, at that time. People who were more theoretically inclined, more inclined towards following experimental developments. Another person who influenced me who actually left because he didn't get tenure was Pierre Ramond, who went to the University of Florida and has gone on to a very distinguished career. And he also, he was one of my teachers early on, who also influenced me profoundly. And he also tended to be on the more theoretical side of things. He tended to be kind of aligned a little bit with Feza, as did Itzhak. So, there were these different personalities and different styles, and I sort of knew what I wanted to do, but I really enjoyed everybody there.
On that point of having good taste, what was the intellectual process for you for developing your thesis idea, and what was really exciting in QCD at that time? What were some of the big unanswered questions to work on?
Well, I think to be frank, my thesis idea was very much shaped by my advisor, on this question of heavy quark physics. But the independent things I did were really kind of small off shoots of that. As a student. And I think-
So that's to say, Michael, that Tom's style as a mentor was very much, "Here's a problem, go work on it. Come back to me when you have something"?
No, no, it was actually very much we worked together a great deal. And then I went off and did a few other things. So, for example, one of the things I did independently was thinking a little bit about, not totally unrelated to the g-2, but to think about the spin of the quarks and the interactions involving the spins. So that's something I did independently. But I don't think, to be frank, I don't think at that stage I had a very clear vision of what I thought was most interesting in the field. So, at that point, I'd say I thought- I probably graduated feeling that understanding the aspects of QCD which were hard to understand in perturbation theory were important, but I didn't have, for example, an appreciation at that stage of lattice gauge theory, which has been one of the principle tools for dealing with this, and which was undergoing very significant development at that time. It started in the early seventies with Ken Wilson, John Kogut, and others. I only gradually developed an appreciation for that side of the field. And that has been a real tool. So, you know, I think as we go through this, our conversation, I think that some kind of vision, if you like, of what I thought was interesting and important in the field comes in my postdoc years.
Now is string theory in its earliest form on your radar at all? Were you aware of John Schwartz and Michael Green and Veneziano? Were you aware of any of this early work?
Yes. Yes, but only in a very limited way. So, in particular, a couple of my advisors or mentors at Yale had an interest in them. I was not really familiar with Pierre Ramond's work at that time, but Pierre of course did extremely important work in string theory, you know, sort of what's almost foundational. Feza Gutsey was very interested in it and of course he talked about it a bit. There was another professor, actually, who I didn't mention. Charlie Summerfield. And actually he's an interesting name in the sense that he also did one of the early- he was a student of Schwinger's, and as a student he did one of the early calculations of the high order corrections in electrodynamics, quantum electrodynamics and g-2, to the muon electromagnetic dipole moment. But in a mechanics course that he gave, is he also taught us a little bit about string theory.
At that point, string theory was envisioned as a theory of the strong interactions. I remember feeling that I was fortunate to be in an age where I didn't have to think about string theory, that we had this quantum field theory, QCD, which described the strong interactions. In retrospect, I think that that's certainly true, but I certainly did not have an appreciation- I mean so this was on my radar a little bit, but it was mostly in the sense of relief that I didn't have to think about. The notion that it had something to do with gravitation was not something I was familiar with. It's around that time that people started thinking about this possibility, [Joel] Scherk and Schwartz in particular. But that was certainly not on my radar. That would only come later.
Michael, given how closely you worked with Tom, even collaboratively, how did you know, or how did Tom know, when you yourself had enough to defend?
Oh, that's a good question. I think my feeling is that Tom had more faith in me than I did (laughter). And that that was important to my career, certainly to everything that happened to me professionally subsequently. I think he could have taken it much more. If I look at what I accomplished in that period, he could have taken a much dimmer view than he did. I mean, I went on based almost surely on what things he said, I went on to a postdoc at the Stanford Linear Accelerator Center (SLAC). I was a little startled at getting that offer. I was not sure that I was worthy of that.
Now did Tom have any particular connections at SLAC at that time?
Yes, Tom had been there. I forget exactly which year, but he had been there as a postdoc. And he was well-connected with the faculty there. He'd worked with Sid Drell, he’d worked with Stan Brodsky. So, I'm sure whatever good words he put in for me was important.
Before we leave New Haven, who was on your thesis committee?
Tom was there, Jack Sandweiss was on the committee. I think Itzhak Bars was on the committee. What I do remember about my exam, it was a rather intense exam, and I do remember the night before, becoming very anxious about something in my thesis, which I realized I couldn't really justify. And I lay awake for a long time and got up and did some little calculations and thought about it a bit. Finally, I had an answer and thought, "This is really stupid, it's more important to be rested tomorrow than to think about this question." Well, I did get asked that question (laughter). And what I also remember is that the exam went on for a while. It was in the morning. And I felt I was managing pretty well. And at some point, actually, Charlie Summerfield I think was on the committee. Anyway, one of the faculty said, "Okay, it's good enough. Let's go to lunch." Over lunch, they told me the next round of questions. And I was thinking, "Oh my goodness." So, it was quite an experience. And so, I have a great fondness for... very fond memories, great fondness for all of my teachers, for that period.
Now, you got to SLAC when? The summer of '78?
I got to, yes, the late summer of 1978.
And what were some of the big things that were happening at that point?
Well, we were still very much in the sequence of things that happened after '74. We had the discovery of the tau lepton and the discovery of bottom quark. And on the theory side, the thing that was happening, it was something I was aware of already as a student, was there was a lot of progress in understanding how to relate, at least in certain circumstances, how to relate the theory of strong interactions to experiment. I should say that, back up and say what did Tom do prior to coming to Yale that was so impressive. Initially, the work of Gross and Wilczek and Politzer on the asymptotic freedom of QCD, there was a rather narrow range of things which it was understood you could calculate. The discovery of this thing called asymptotic freedom, meant that under certain circumstances, there's a small parameter, a weak coupling, that you can use to calculate. But initially in the circumstances in which these calculations were possible were very limited. So, on the theory side, what was happening when I got to SLAC in that world was that that was a lot of progress in extending that, and a lot of interest in going beyond that.
Now, Tom had already done some of that. That was part of what he had done that was so spectacular as an assistant professor who was describing how to do those calculations for the total electron-positron cross-section in QCD. He also worked out (with Politzer) how you might be able to use QCD for some aspects of heavy quark physics. And so that was the thing that drew my interest a lot. One of the first things I did with then-graduate student, Johnathan Saperstein at SLAC, was did the next order calculation of the total electron-positron cross-section. And this was something that was being measured at higher energies at SLAC at that point. So we did that calculation and then with postdocs, with (Larry Abbott and Murray Mclaren and Mike Barnett we did a lot of study of the experimental situation. And it wasn't perfect, there were some discrepancies. We tried to understand those. So that was kind of where things were when I first got to SLAC that first year, was sort of extending the range in which you could use QCD and trying to decide if we could really test QCD? Was it really the right theory?
Michael, as you say, it was only as a postdoc when you started to come around to where Tom was with you in regard to having the confidence in you that you eventually would have in yourself in terms of developing that good taste. How did that happen for you at SLAC?
Well, it only partly happened at SLAC (laughter). So another thing, so that first year, there was these two collaborations I mentioned, the one with John Saperstein and the one with Larry Mclaren and Mike Burnett and Larry Abbott. But there was something else that was going on there which also got me excited. Kind of affected my view of things. And this I actually have to go back to my graduate student days. So, as a graduate student, I think I was rather typical in the sense that I would go to seminars and so on and most of the time, I would be pretty lost. And there were certainly very few seminars I remember from my graduate student days. But actually, I probably could describe three. All of them at some level had a profound influence on my career, even though how well I understood what was going on varied. So actually [to] start with one, a seminar delivered by Helen Quinn, who later was a sort of mentor to me at SLAC. She was faculty at SLAC when I got there, but at the time, she was a postdoc at Harvard when she gave this seminar, and this was on the work she did with Roberto Peccei on the strong CP problem. And I struggled with Tom and on my own to understand that whole set of ideas around the so-called theta parameter of QCD, as a graduate student. So that's one seminar I remember. I remember a seminar by Steve Weinberg on the axion, basically the implications of the Peccei-Quinn solution of the strong CP problem.
But another seminar I remember quite well is a seminar that Leonard Susskind gave. Lenny at that point was on the faculty at Yeshiva University, this was just shortly before he went to Stanford, and he gave a talk on what he called Technicolor. And that one I kind of understood, and it really blew me away. Lenny came to Stanford that same year I got to SLAC, in '78. And we talked sort of more and more as time went on, and that whole idea of technicolor and the hierarchy problem. Prior to this, it hadn’t really occurred to me that one should even think about physics beyond the Standard Model. Lenny was already sort of advocating the view Standard Model is, as far as it goes, is right, and you should think about what comes next. And the second year I was there, I collaborated with Lenny. It didn't result in a publication, but I learned a lot. Mostly talking about this idea for understanding the origin of electroweak symmetry breaking, you know, what we now know with confidence is due to the Higgs. But thinking about this, thinking about field theories beyond those of the Standard Model. That happened with Lenny, and that I really took off with that, that happened for me only later, but this marked a really profound change for me.
Michael, what was Lenny's style as an intellect? How did he work through these problems?
Oh I- I have to think about that a bit. Well, first of all, he was a lot of fun. He was interesting in that he was on the one hand, somewhat iconoclastic, and on the other hand, he was a very careful and serious student of others. So, he learned well. He listened carefully. And he could be both a critic and he could tease you a great deal, and so on, but he was also very supportive of the people around him, and especially the younger people in those days. So, he was an interesting mix. He was a very delightful colleague. And you know, [he] certainly influenced me profoundly. Things I went on to do subsequently were certainly affected by this knowledge. And as I say, it was a combination of things ranging from crazy, wild ideas, but also to teaching me a lot of just rather technical but important stuff. So, there was just a great deal I learned from him. So, a lot of that happened my second year at SLAC. My publications in the second year were, eh, okay, but not all that remarkable. I still don't feel like I'd hit my stride. I was probably more confident, but not excessively so at that point. But the experience at SLAC, was a really wonderful one.
So, you were there two years total?
Two years total, which was sort of typical in those days. Nowadays, three years is more common.
And what was your sense of the job market at that point? Was it still as bad as it was eight, nine years earlier?
Well, I don't think I had a real sense of what it would be like to get a faculty job. I had certainly worried about would I get another postdoc job. You know, I should mention another person who was a postdoc with me, was Eddie Farhi. He went on to MIT. And Eddie was also a stimulating presence. Eddie had been involved also in certain ideas about things one could compute in the Standard Model in QCD. He had proposed something called thrust, and we had a lot of fun together. There were a whole group of us there. We both worried, we were both convinced at some point that we were part of a program of bringing some number of weaker people to SLAC, in the hopes that their careers will turn around or something.
But I think I had no realistic idea about what my future job prospects might be. I'd certainly worried a lot about what might lie beyond another postdoc. I was I think hopeful, but not certain that I would get a postdoc after this first one. That I did relied a lot on the support of, this time, people at SLAC, especially Sidney Drell, who was the director of the theory group, and the associate director of the lab for many years. He was a mentor to me theoretically and also in a kind of broader professional sense. And I think his support was important to this position I got. I had two offers when I left. One was at the Institute for Advanced Study. The other was at Lawrence Berkeley Lab. At that point, I had developed a two-body problem and that was the more workable solution to that one than a position at Berkeley. I think I was at that moment probably more excited about Berkeley. I was feeling it was more aligned with me intellectually. But the Institute turned out to be for me a very, very fortunate choice.
One thing people, when I was making this decision between the Institute and Berkeley, one of the things that was said to me was that basically the track record of postdocs, or what they were called, members, at the Institute in the previous several years had been very poor. That very few of them had gone on to faculty jobs. And that Berkeley was a more promising place for a career. In retrospect, when I tell that to people now, people don't understand that, because there are so many famous names that we associate with the Institute for the last forty years. But things were a little funny then. And it's really for a sort of a serendipitous reason I think that the Institute worked so well for me. Those first years I was there. It was also a great place for me. And it's there I feel I sort of found my stride.
What were you working on in that transition? In other words, coming from SLAC to the Institute, what did you know would remain on your research agenda when you got there?
Okay well, I'd gotten very friendly with a colleague named Willy Fischler, who's now at the University of Texas. He had then taken an assistant professorship at the University of Pennsylvania. And he was actually quite a close friend of Lenny's, and so I'd gotten to know him through Lenny. He actually was a friend of Tom Appelquist as well, and we had started a collaboration shortly before I got to Princeton, on a rather obscure but kind of nice little project. It's a project I remember quite fondly. And so, we continued that when I got there. He actually spent a sabbatical year at the Institute. I should say what was through at the Institute at that time. The senior faculty, very distinguished people, were Roger Dashen, Freeman Dyson, and Steve Adler. Steve was often a kind of remote area in physics. I have to say not all that interesting for me. Freeman was, you know, an incredible person, intellect, and so on, but not really working in particle physics at that point. And while Roger was actually doing a little bit of particle physics, he was really more interested in complex problems, often with military applications. He actually did a lot of consulting for the Navy. But Roger was an important mentor to me, even though we didn't collaborate. He advised me, quite intelligently, helpfully, about things I was actually working on. But really there was really no senior person that made sense to collaborate with. So, I started out, because of this two-body problem, I was doing something which in those days was very unusual. I was living in Manhattan and taking the train out to Princeton every day. And Willy was coming up from Philadelphia on the train. And our trains got in about the same time. And we had a car which we couldn't afford to keep it in Manhattan, and the parking in those days in the train station lot in Princeton was free if you left the car overnight. So, I just kept my car there, and I would drive it up to the Institute when I got off the train and Willy and I would meet.
We would drive up to the Institute together. And our days would start with very excited conversations about physics first, there about the project which we had initiated, and later other things. That was really important. Another collaborator who joined us was Mark Srednicki, who had been a student of Lenny's who had just started as a postdoc at Princeton University. And the three of us knew each other, and so we needed people to talk to, the three of us collaborated on a sequence of things. We had a very delightful set of collaborations that year. And then things evolved, and there were other collaborations. But at first, I certainly had very much this hierarchy problem on my mind, thanks in part to all of this brainwashing I'd had from Lenny about these questions. We'd already had some conversations even before getting to Princeton about, well, maybe we should think about supersymmetry as part of this, as a possible solution to this. So once eventually the initial thing we had been working on. We started to think about supersymmetry, and that was for us a big development, and it also led kind of serendipitously to our thinking about what we called the invisible axion. And so, you know, those problems were now all kind of on our minds. And within the collaborations, we each brought something. I think we were all essential to both developing the ideas and doing it.
Michael, to toggle back to the world of experimentation, particularly with supersymmetry, was there anything happening in either the national labs or at CERN where people were envisioning sufficiently high energies where supersymmetry was something that could be experimentally verified?
Yes, and you know, already experiments, there would be rumored developments at the SPS. I think actually there was more than we really realized in fact. In that initial period, we would have predicted that the lightest of the supersymmetric particles would be lighter than the Z, than the Z meson. And so, we're just in this period where the W and Zs were discovered. So, we would have sort of thought that things were in that ballpark. So, I think initially, we certainly thought about the phenomenology. I don't think we thought about it all that carefully, certainly I didn't think about it all that carefully. So, one certainly could have said precision, you know, one would have expected from the things we knew at that moment that it would be likely that you would see evidence of this as you did detailed studies of the Z. That happens in the late 1980s. T fact that the Higgs didn't show up in phenomena associated with the Z and in facilities that could produce the Z, should have been a warning, or was a warning that perhaps at least the initial ideas we had about supersymmetry were naive or overly-optimistic. I don't think we fully appreciated that (laughter). I mean certainly I didn't.
What was not known that in retrospect that you could say that these early ideas were to some degree naive or overly optimistic?
Well I think I would say at this point on the theory side, while I could refer- again, I probably would refer to Lenny again. The arguments about hierarchy- so, these are arguments due to Lenny, they're due to ‘t Hooft, due to Weinberg, due to others. These ideas are in some ways very compelling, and the fact that something like supersymmetry, the fact that we haven't seen at the LHC something like supersymmetry or evidence for technicolor or something else, this is a puzzle. But already, I think in 1979, Lenny also introduced me to. a bigger puzzle, a quantitatively bigger one, which is the dark energy, the size of the dark energy. And Lenny actually introduced me to this question in Aspen in 1979. And I think Willy was there with me too. And I remember this conversation pretty well. Where Lenny first explained to me kind of what the issue is, quantitatively a bigger puzzle, and we don't have supersymmetry, for example, or Technicolor to help. They don't solve this problem. So, the fact that there's another problem in sort of a similar class and more severe and we don't have good ideas to understand that, I think that's, if you like, one warning.
I mean, we'll probably come to more of this as we go along, since this has been one theme in a lot of my work, but I think this is part of it, and it's something that very quickly- I certainly remember Willy and I having conversations after- you know, we had our first, in the second year that I was at the Institute, Willy and I developed really what were the first sort of complete working models of supersymmetry, where all the particles had properties consistent with the experimental constraints. They weren't beautiful models necessarily, but where all the parts were kind of self-contained and controlled and you could calculate everything. And so, we had these models and we were pleased with them, and then we said, I remember saying, "Okay, we've solved everything except the cosmological constant problem. How do we deal with that?" And we did really sort of wrack our brains, and the problem is that supersymmetry doesn't really help it. It modifies the problem a little bit, but it doesn't cure it in any obvious way, and as that sort of sunk in, we worried, you know we'd worry then the fact we were somehow being naive, that there was some other way of solving this problem. And you know still the question, what is the explanation for that, and does that bring with it a solution to this problem of the Higgs. So, experimentally, the information was limited at that point. It's really in the early nineties with the program at LEP, at CERN that I think that the ideas of supersymmetry and technicolor and so on really come under threat.
How much time did you spend at the department of physics at Princeton? Was that part of your reality at all?
It was, in an interesting way. So, as I said, I had these two collaborators, and I sort of mentioned that at that point, the Institute, for traditional particle physics at the senior level was a bit of a backwater. But a couple dramatic things happened in 1980. One of them is that Ed Witten came to Princeton. And I don't know to what degree you've encountered Ed. Ed is an extraordinary intellect. Extraordinary person in many ways. I should say going back to this Baltimore raising of my mother, there's actually even some sort of distant family- I mean, not blood relation, but there was some connection of the families. I actually met Ed's father first. He was a general relativist. He came to the University of Cincinnati, actually, in the late 1970s as a faculty member. I actually met Ed when he had started graduate student school at Princeton, I was still an undergraduate being warned about how hard it was to do theory, and I met what must be, what I presume was the typical theoretical physics graduate student, and was just totally blown away. I was both- I was just awed, and I was like, "Well, maybe I don't belong in this field. This person is way beyond me"
And as I've often said, if there had been three Ed Witten’s, there wouldn't have been room for me in the field. But anyway, Ed came there that year, and certainly his coming had an influence on things I worked on directly and indirectly in a number of ways. He was thinking about supersymmetry already very deeply. Both from a perspective of how it might be realized in nature, but also from a more theoretical point of view. I would see Ed at seminars, we would chat. I think the pattern of my interaction with Edward in those days was often I would discuss an idea with him, and he would frequently criticize it, and I would have to- I couldn't always in real time address the criticism or think it through. And I had sort of the good fortune in some ways that I could go back to my office at the Institute, think for a few hours, say, "Yes, he's right, but…" Or something like this. And go back again. And that was a sort of pattern for a while in our interaction. I also was certainly a big admirer of David Gross, and learned a lot from David, who was there in those days, and Curt Callan. So, I think it was, as a young and somewhat shy and easily intimidated person, I think it was in some ways good that I could go have these conversations, come back and think a bit. And I learned a lot from all of them in those- all through those years there.
What was the overall intellectual environment at the Institute like? In other words, beyond just your immediate circle in physics, would you interact with people generally across the disciplines?
To some degree. You know, not perhaps to the extent I wish I had, but to some degree. I mean for example, people like George Kennan was there, And people like Michael Walzer, the political philosopher. So yes, to an extent. I certainly had interaction with people in astronomy, with John Bahcall, who certainly had an influence on me. I was sort of aware of people in math, at various times more than others. Let's say a little bit less so in social sciences and history, but there was some interaction, and I would certainly go to talks and I would go to lectures. So, it was an exciting place to be. Actually, the whole time I was there, I was a commuter. The first year I was taking the train up from Manhattan, and then the subsequent four years I was there, I was living in Morristown, New Jersey, and I had a carpool and drove with an architect actually, who had actually designed, been involved in the design of one of the buildings at the Institute. But so, I was kind of a nine to five person throughout my years there. And that also affected the way I experienced the Institute too.
Meaning that there was a dinner culture? There was socializing after hours?
There was a dinner culture, and only occasionally would I join that. And there was housing at the Institute, and a lot of the younger people lived on the campus of the Institute. There are cultural activities in the evenings and so on which I only participated in in a limited way. So, that probably also affected my experience and the extent to which I took in sort of the broader Institute. And to come down on weekends, you know, Morristown is a full hour's drive away, was a rarity.
Is four years, is that a long time? Is that a pretty long stint as a postdoc at the Institute, or was that standard at that point?
Yeah, no, no. So, I was hired for two years initially. After the developments with supersymmetry and the axion I remember a conversation with Roger Dashen basically offering me a long-term position. Postdocs have the title member, and there's something called long-term member, which is a five-year appointment. And after one year there, I was appointed a long-term member, so I had a five-year appointment. I was total there five years.
Were you in touch with Pierre Sikivie at all on the axion work at this point?
Ah, Pierre I should have mentioned. Pierre was a postdoc with me at SLAC, actually. But we did not discuss the axion. So the axion as dark matter work that my first summer, I guess, and a little bit into the second year at the Institute. The work on the axion, you know, that happened in stages. For the first stage, I have to give, in terms of actually raising some of the questions, Willy really deserves a lot of the credit and Mark Wise and I kind of figured out a lot of the details. Then in the summer afterwards, when we thought we'd solved this problem of the axion as discovered by Peccei and Quinn, and Weinberg and Wilczek, and we sort of saw this very generic sense in which the axion might be very weakly interacting and hard to see in experiments. So basically, to back up, in fact, this goes back to the seminar that Weinberg gave when I was a graduate student. You know, it was very quickly realized that the model for solving the strong CP problem that Peccei and Quinn had put forward predicted this particle, this particle was relatively light and would have been seen already. I mentioned Jack Sandweiss, this experimentalist at Yale, I remember Jack basically explaining to Steve [Weinberg] all the experiments which already would rule this particle out. So, we had gotten around this problem and this work with Mark and Willy. Other people had made similar discoveries. Some people called this the invisible axion.
We initially called it the harmless axion. And we thought, okay, this is the problem and then okay, what good is this? You can't see it. It was Willy who started to bug me about whether you would produce this in the early universe? Wouldn't there be too much? And we started to work on that. At that point, I had never done any work on cosmology. I really struggled and had to teach myself a lot. I remember actually, my wife was at a conference in Boston, and I hung out somewhere in Brandeis and taught myself a lot of stuff and these were days when you used the phone and you wrote letters. And so anyway, so Willy and I, we were corresponding, we were phoning each other, and it turned out that there were others working on this as well. Pierre Sikivie and Larry Abbott and Frank and John Preskill. And Mark Wise. And how should I say it? You know, we eventually learned that these other collaborations were going on. And then perhaps backing it up also again to say a little history, I go back to this calculation of the total cross section in e+/e- annihilation. You know, this was pre-internet, this was pre-email. Modes of communication are rather complicated. And so, when John Saperstein and I- so we did this calculation of this correction to the e+/e- to a cross section, and we learned then that there were other people working on this. So, in particular, one of the people working on this was Stephen Wolfram, who was at that point at Caltech, along with Tony Terrano and others. Anyway, and so we got somewhat anxious. And I don't know if you've ever encountered Stephen Wolfram?
Stephen Wolfram never suffered a low opinion of himself. And he assured us over the phone and in a meeting, we had that his collaboration had better techniques than ours. They were going to get the result faster and it would be more reliable. And they had automated it, we had some limited computer element in this, but we were also doing a lot by hand, and in rather mechanical and mindless ways. Once you decided what you had to do, the calculation was just sort of tedious and it was a question of, so what's the most efficient way to do it? So, we had this competition. We actually had a result first. They had a result; they didn't agree with us. We had a meeting. Couldn't decide what the problem was. Then we learned that there was a group in the Soviet Union that was doing the calculation and was about to publish. And Johnathan and I just said, "Okay, we'll take our chances. We can't find anything wrong with what we've done. We've done a lot of checks. We'll publish." And I think we actually communicated with them [The Soviet Collaboration] by telegram, if I remember correctly, and after putting our paper out, we learned that they in fact had the same result. And in fact, the other group had some error, which was never quite straightened out. Of course, Wolfram went on to truly automate, you know, inspired by his vision of them automating these kinds of calculations. You know, develop, first it was something called SMP at Caltech, and then there was Mathematica. So, in the end, his results were in some ways more interesting.
This is just to say, in terms of the modes of communication in those days, a lot was more complicated. So, I said, we also learned eventually that there were these other groups looking at what became the axion of dark matter story. In the same spirit of communication, I mentioned that Willy and I, then the subsequent year, developed these models for supersymmetry. This is something that later comes to be known as gauge mediated supersymmetry breaking, something I worked on also with Ann Nelson. But a sort of more primitive version of that. But in that story, also, there's an interesting communication element, in that Willy was from Belgium. He was still a Belgian citizen at that time, and he had an obligation for military service, which he hadn't yet fulfilled. So, he was drafted that second year, so he was still at Penn, but he had to go to his service. I don't remember what the nominal term was. I think it was probably two years, and I think he may have only served one. I don't remember exactly.
But in any case, he went off to Belgium to do his military service. He was offered the opportunity to be an officer, which meant somewhat cushier job, but a longer term of service, and he declined. He was a runner. He and Lenny, in fact, ran quite a bit. So, he was a bit older, he was older than me, older than the typical solider at that point. But he was quite physically fit. And so, they said okay, and they sent him to the Commandos. To some kind of Commando unit. He was eventually relieved of that and put in an office, and we collaborated long-distance, truly long-distance, and this really meant mailing letters. So, we would send long letters with calculations and so on back and forth. Occasionally we would have a phone call. This was actually a very delightful collaboration and quite successful. But it was a mode that's unimaginable now. And we had some competition there too, and again you know, generally didn't know until later. But Joe Polchinski was, and Mark Wise, were particularly relevant in that whole work also.
To go back to the job market, when did you finally decide to leave the Institute and see what else was out there?
Well, that was again driven by my two-body problem. I wasn't exactly sure what I most wanted to do, but I really didn't have that much control for what was going to happen (laughter). So, my wife was in a position in Morristown, and at some point, that ended. She needed to move, so I needed to move, and she had no certainty where she would be, so I had no certainty where I would be, and so we were both kind of applying various places in the country. And in the end, she landed in New York. She was in a sort of situation where there was a lot of difficulties for women. Their choices weren't that extensive. She ended up in something in New York. I had an offer from City College, and so I accepted that. That was one of the rare occasions where we worked in the same area code, at least for a while until the Brooklyn area code changed from Manhattan. So still, so I commuted then.
So, I went to City College. City College was also very nice for me in ways that were in some ways also somewhat unexpected. City College has, as you know, an illustrious and interesting history. But in physics in particular, the Department was particularly strong, as a result, in part, of the efforts of one of its past Presidents, Robert Marshak [Himself a distinguished physicist]. In particle theory in particular, there was a physicist originally from Japan named Bunji Sakita. Who for me was again, turned out to be a very important mentor. Really delightful person. And it's actually from him I first actually learned a lot of string theory, I learned a lot of field theory, all of which had been valuable to me through the years. We had a couple collaborations. There were several other high energy theorists. There was one high energy experimentalist. There were sort of very distinguished condensed matter theorists and experimentalists. Myriam Sarachik actually I've been in touch with recently. She recently won the APS award for research, in her career in research.
And had that amazing profile in the Times, too.
Right. Right. So, she was there, and there were several other condensed matter experimentalists and theorists, Herman Cummins, Joe Birman. So, it was a very, very interesting place to be. And interesting student body, both graduate students and undergraduates. And one that evolves. It was different than it had been a decade earlier, and it's evolved since. So, I was there for five years. Five very delightful years. And the next move was also in part driven by the two-body issue (laughter).
So, what happens? What's next?
So, I should back up, and I should back up to the time at the Institute. Particularly important for me at the Institute, again, were these younger collaborators, and a particularly important one for me was Nathan Seiberg, who came in my third year there. And who I sort of went from being my mentee to being my mentor rather quickly. But we had a series of collaborations while there and first understanding field theory, aspects of supersymmetry, and then understanding aspects of string theory. Often using some of what we'd learned in field theory and applying it to string theory. So, string theory is something that sort of really reemerges on the scene that final year when I was at the Institute.
One might even call it a revolution!
Right. So, the work of Green and Schwartz in '84 was the summer before my final year. And Ed had, Ed Witten, had long been a proponent of string theory as something interesting.
Not just interesting, but something that he encouraged others to work on because he was so bullish on where it was headed.
Well not exactly. It was a little complicated. Prior to '84, he thought it was really interesting, but he worried- a way to describe it was he said it was like it could be one of the great problems in mathematics that takes hundreds of years to solve. So, I'm not a faculty member yet, I'm in this kind of glorified postdoc position. Okay fine, Ed, but hundred year-long problems, that's not necessarily the best career move. And Ed actually put forward some of the obstacles. His work on the anomalies in particular which inspired the work of Green and Schwartz in this revolution was actually a sort of statement that maybe it doesn't work. Maybe it's a problem. And then you also had work on compactification of higher dimensions, which would be essential to string theory, and which also seemed to pose obstacles. And so, Ed both laid out the obstacles and then the work of Green and Schwartz and then his own work with Candelas, Horowitzand, Strominger sort of cleared those away. And so, starting in the summer of '84, and certainly that fall, he became quite an advocate for string theory and Seiberg, and I basically said, "Okay, we've got to learn this." And at that point, the literature wasn't kind of easily penetrable. What was important, what was not, was not clear. So, we started studying on our own, started some review articles and papers and things, but what was probably really important that fall was that David Gross gave a course on string theory at the University, and we went.
How long was he involved in string theory at this point? What was your sense on that?
Well my sense was that as a postdoc when he was at Berkeley, he'd been interested in string theory. he'd worked on it in those early days, and then he'd gone on, most dramatically to discover asymptotic freedom and make important contributions to QCD. But he was primed. He was sort of ready to go. And so he gave this course, which I think for him was probably a way of, you know, bringing himself back up to speed, remembering how things worked and so on, and while he was doing this, he was working on this heterotic theory with Harvey, Martinec and Rohm. But you know, he had this classroom full of both young people and senior professors who were trying to figure out what was going on, and so it was quite a wonderful course. And he managed to combine things that were deep with things that were mundane. He launched a lot of us in this topic. And Seiberg and I realized that there were things that we had been thinking about that had applications to the things that were going on and we were able to find out niche in this story. That was my last year at the IAS, and I was also applying for jobs and each of us had a young child, so it was an awfully busy, but quite an exciting period.
And what was in these early, even perhaps naive moments, what exactly was the excitement about what string theory could do? And of course, we say this from the vantage point of history, where we might be asking some of the same questions today.
Right. Right. So, at the time- so, I think what I- well one thing I remember quite closely is when Ed was doing the work with Strominger and Candelas, and Horowitz, we would hear about it. Bits and pieces of results. That fall, I was still rather resistant to this idea, even though I was, you know, I was taking the course and I was talking with Seiberg, but I there was a question related to the hierarchy problem, which had been long lingering. And I remember on a Friday afternoon asking Ed, "Well, how are you going to solve this problem?" As if, "Ha ha ha, you can't possibly." And Monday, just before David's class, Ed comes up to me and says, "By the way," and takes me over to a black board and explains the solution to this problem (laughter). And I just remember thinking, "Oh my goodness, everything is going be solved in a week or two and I will have missed the boat." So, at that point, I became much more highly motivated. I should say now, you know, leaping forward to twenty-five, thirty years or so, retrospectively, there's a sense in which string theory hasn't delivered certain things. And I'm an expert on that. I've made some part of my career on, you know, what are the challenges? But that said, it has delivered a lot. There's a lot that we've learned, a lot we've seen about, and so it's a complicated story. I mean, for example, you know, we talked about axions a little bit. It's really only in string theory that we have a sensible understanding of how axions might work and why they might work. And that's just one of many successes. The point that Witten made to me that day is still an extremely interesting one and profound one. That we don't have necessarily mean that the theory describes nature. As an example, we haven't seen an axion yet. We don't know for sure that that idea's right. Many of these things are in that class. But yeah.
But what was the optimism? What was the sense that these things could actually be solved? And not just solved, but from Ed's point of view, in the short term?
Well, for different people there were different points of view. So, there were people who had been long focused just on how do you make a quantum theory of general relativity. There were people like me who were focused on things like the hierarchy problem, also understanding for example, you know, we talked about the muon a little bit. You know, why are there generations of quarks and leptons? Ed basically over a period of a couple weeks gave answers to those questions. So, for example, supersymmetry. you might have argued that supersymmetry as we proposed it was kind of contrived. But in this construction of Horowitz and Strominger and Witten, it was there. It was there just as we'd talked about it. It kind of fell out. This solution to the hierarchy problem sort of fell out. The axion fell out. So, from my perspective it was as if all the speculations about the questions that had been bothering me had some dramatic kind of realization there. I mean when Ed took me to the board that day, I think it's in that conversation I said to him, "Okay, now you've got me convinced that I have to work on this." And he looked at me and said, "You needed this?" Because the other things for him, the fact that it was this quantum theory of gravity, that was for him already compelling.
So, for different people there were different drivers. And certainly, one of the things that Seiberg and I realized pretty quickly was that there are also obstacles. But there were reasons why these problems, you know, there were sort of things that were really interesting, but there were also intrinsic obstacles. And those are still there, but the exact form, the way you phrase them, has changed. Has evolved. But those problems are there. So, the fact that you have this structure that's theoretically really interesting and has some aspects that are very promising, that remains the case. That there are hard problems in the way, possibly intractable, that also became clearer at some early stage.
But at this point, you're thinking string theory from a career perspective, this is looking good at this time?
Yeah, at that moment, I'm sort of thinking- I'm almost worried that, you know, one better get on this train. It's less obvious as time evolves. It becomes more complicated.
And of course, to return to our good friend Shelly Glashow, this is well before his famous, you know, crusade to make departments string-free, because there were too many string theorists as far as he was concerned.
Well it's a little, yeah, it's only a little before his little piece with Paul Ginsbarg. You know, the Desperately Seeking Superstrings that he wrote in Physics Today. Which I have revisited occasionally. If you've not read it, you should read it. It's quite a clever piece. And you know, it's not without its points (laughter). You know, there are things he was right to be worried about, certainly.
What about your work in elementary particle physics? Are you still involved? Are you sort of totally two feet in with string theory at this point?
Oh no, no. I'm very involved. And my own work has evolved through the years. Through the second half of the eighties, I would say probably not everything, but a good fraction of my work was string theory related. In the nineties, I returned to the phenomenology of supersymmetry and did a variety of things. Particularly with Ann Nelson I thought about the problem of breaking supersymmetry. Supersymmetry, if it's a symmetry of nature, has to be broke., I thought a lot with her, spurred by questions she raised, about the breaking. I should back up and say that the early nineties saw work on the theoretical side of supersymmetry, the whole program launched really by Nathan Seiberg and then Seiberg and Witten realizing that supersymmetry was a tool for understanding quantum field theory. So, that certainly caught my attention and I did work in that area, and then with Ann we thought about taking what had been learned, what could we say about the breaking of supersymmetry? And this led us back to thinking about phenomenology, what it might look like, and led us to this idea of so-called gauge mediated supersymmetry breaking. And there was a period where it even looked like there was some experimental evidence for it.
Is supersymmetry breaking a very logical conclusion in terms of where the field is headed to work on?
Well, it was (laughter). At the moment, you know, I was thinking we can come to that in a little bit, but just to say that- just to finish this digression, so certainly you know this was one set of questions that- a lot of other kind of phenomenological beyond the Standard Model questions, both in technicolor and in supersymmetry, occupied my attention. More recently, I'm actually thinking a lot about aspects of strong interactions and aspects of cosmology and axions. And my thinking about string theory is lately focused on the questions of how do you understand the dark energy, and how might you evade these problems that Seiberg and I discussed early on? And so, a lot of my work in string theory is sort of in those areas. And string theory here is broadly defined as whatever quantum theories of gravity look like. I have not been part, too much part of some of the questions which have preoccupied a lot of the practitioners of the information problem. And AdS/CFT for me has been kind of a tool or a model for exploring some of these questions that bother me, and I haven't worked that much directly on that. So, I'm only sort of a semi-string theorist.
(Laughter) Michael, to go back to axions, were you thinking along the lines of, even in the early days, that this was a possible solution to dark matter?
Well certainly by the time that I did the work with Fischler. It was initially not on my radar. This was prompted- I the first problem we had was, you know, Willy's first question was really, "Isn't there too much of it?" And it was only once you said, okay, if you just adjust things so there's just enough, then it's perfect. But it took us a while to get to that. The dark matter is a problem, as an issue, was not something completely in the forefront of my conscience, at least at the time when we started that work. You know, more recently obviously more so. The whole story was not so convincing in 1981 as it became subsequently. So, it was kind of something I was vaguely aware of initially, at that time.
We've been so focused on the issues; we have gotten away from the Institution. So where are you at this point in the chronology?
So, in that, in the work on axions, I was at the Institute.
Right, you're still at the Institute, but then working afterwards.
So, well, do you want me to go longer timeframe, or…
Yeah. Okay so I mentioned my transition to City College. Then leaving City College, again because of these two body issues for Santa Cruz.
But you were happy at- City College was good for you? You would have stayed longer?
City College was good for me; I could happily have stayed there.
And there was a strong physics department there?
Yes, so yes, yeah, so as I said, there was Bunji Sakita. Also, Michio Kaku, Stuart Samul, and Ng Pong Chang. And this whole group of condensed matter theorists and experimentalists. And you know, New York is an exciting place. The commute was a little grueling. And things were complicated in other ways, and I received an inquiry about UC Santa Cruz. We actually went- my wife and I actually went through a job process twice. I was offered the position, she was going to be offered a position, then that fell apart, then we came back basically the subsequent year. We missed the Loma Prieta earthquake as a result of this. And she was offered a position. And mine was reoffered. And so, we came here in 1990, so I've been in Santa Cruz since.
Now Santa Cruz was for me exciting, actually, on a few counts. Both for some things I knew and some things that I only learned later. Santa Cruz, I did know at the time I went there, had a very strong high energy experimental effort headed by a colleague of mine named Abe Seiden. Abe remains a leader in the high energy experimental world in the U.S. And I had a theorist colleague, Howard Haber, who I knew from before who had actually been a postdoc at Berkeley when I was at SLAC. And then was at Penn for also some of the time I was at Princeton. He was a phenomenologist and was doing work that was very interesting for me, especially on Higgs and on supersymmetry. And so, it was an exciting place for me to come intellectually. It turned out to be even more exciting than I realized. Santa Cruz has an extraordinary astronomy effort.
Yeah, I was going to say, did you know about the astronomy program before you got here?
Only vaguely. Santa Cruz started as this alternative sort of hippie-dippy school in the mid-1960s. The vision, Clark Kerr had this vision for the campus. He was president of the UC system at the time, and he had this vision basically of a humanities-oriented school with a kind of residential college structure and so on. But for, again, for reasons that are not so hard to trace, it became a very strong school in the sciences as well. The SLAC accelerator started around the same time. So, people came in order to be near to SLAC. Astronomy happened because of, in my understanding, at the time the campus was established, the UC regents were complaining that the UC observatories, which were on Mount Hamilton in San Jose, were not affiliated with one of the campuses. And so, they wanted it to affiliate with one of the campuses, and my understanding, at least at that time, there was some bad blood between Berkeley and the people at the Lick Observatory, so they said, "Okay, we'll go to Santa Cruz."
And the stories I'm told, I think of Santa Cruz as a pretty laid-back sort of place. I think of astronomers as a laid-back group of people. In those days they wore suits and ties. Santa Cruz was a little weird for them, but still they came to Santa Cruz (laughter). And you know, there are others that are obvious things. The Bay is there, so it's rather natural to have strong efforts in ocean sciences, and obvious place to do earth sciences. So, all these things developed. A strong chemistry effort developed. So, it was a very rich environment scientifically. I thought of it as this kind of laid-back place, but the expectations were really quite high, and the standards quite high. So, it was quite a sort of rich experience. My wife had a position in Los Gatos, which is twenty-five miles away. I had immediately a carpool with several colleagues, including Abe Seiden, who I’ve mentioned. What happened is several of the high energy experimentalists lived in the San Jose area because they wanted to be midway between SLAC and Santa Cruz. George Blumenthal, one of my astronomy colleagues who eventually became chancellor, lived over here because his wife taught in San Francisco and it was a way of living in between. So, we had a rather spectacular carpool. (laughs) Which continued basically through my time here. Some of the membership changed, but my mornings began either with sort of gossip about our kids or discussions of the latest things in the news. But I learned about things like extrasolar planets and the dark energy problem, for that matter, in my carpool. And I learned a lot about radiation-hard electronics for accelerators and so on (laughter). So, a lot of things I learned in this carpool.
Michael, is this also around the time when you start thinking specifically about string theory's value for cosmology?
I have to think a little bit. I should say, at Santa Cruz, also, I had another important colleague, who was Joel Primack. Who with George Blumenthal and Sandy Faber, another astronomy colleague, and Martin Reese, put forward the cold dark matter paradigm. And I learned from him all sorts of things.
You know, one story I tell is the story of the dark energy. I first heard in the mid-nineties that there was a puzzle about the age of the universe and the age of globular clusters. Measurements of the Hubble constant, of the expansion rate of the universe, seemed to suggest that the universe was younger than some of the stars we knew. How could that be? I remember hearing about in my carpool from George Blumenthal. But from my colleague Joel Primack, I really heard a solution, which to me initially didn't seem credible. So, at that point, there was no direct evidence for dark energy, and most of us sort of believed that there shouldn't be any. That this cosmological constant should be zero, and that that was the mystery we were trying to solve. That maybe there was some principle that would explain that. And Joel said no, maybe if it's just right, so that it's taking over the universe now. This would explain some of these puzzles. And it would also explain some issues in formation of structure in the universe. I was quite skeptical. Why should the cosmological constant have this peculiar value? This is one of many instances of my not being right. In fact, over the years, from supernova measurements, CMB measurements, and studies of structure formation, we know that the cosmological constant is there. We know how much there is. We know it with some precision, and that certainly has had a profound influence on my thinking about how we should approach problems in cosmology. For example, and in my thinking about string theory, over the last ten to fifteen years, landscape ideas have figured a lot. Many of the ideas that I have developed were strongly influenced by colleagues in Santa Cruz and elsewhere, but especially in Santa Cruz.
Were you thinking specifically about all of the iterations that inflation had gone through, even from 1981 to where it was by the time you got to Santa Cruz?
I have to think when I get really more serious about inflation. I think it's probably in my Santa Cruz years that I got really kind of serious about it. It’s not that I hadn’t learned about it. Alan Guth spent some time at SLAC when I was a postdoc there and he was thinking about these issues and as I was hearing about it from him, but my understanding and appreciation was sort of slow to come about. Certainly, we had lots of conversations about inflation in my years at the Institute. But it's later. I'd say a lot is probably thanks to concerns that were raised by string theory and thanks to my exposure to Joel Primack and others. That I get more serious. Willy Fischler had a lot of influence in my thinking on these issues. So, there's a range- I'm not sure I know exactly where to date my sort of conversion to being a kind of inflation theorist.
Here's another really broad question that'll be tough for you to pin on the map chronologically, but you know, the overall pursuit of physics beyond the Standard Model. Of course, it's very clear the excitement with the so-called first-string revolution or superstring revolution in the 1984 -1985 region. And then if we bound that by your earlier comments about the significance of discovering the Higgs, you know, in 2011-2012. When for your research agenda was the specific motivation of physics beyond the Standard Model, where roughly would you locate that as an intellectual or a scientific motivation?
I would say that, again, to pinpoint is a little tricky. But I think that the work on supersymmetry really leads to that. And that becomes a theme for me in my work at that point. And so, when I make my first grant proposal of my own when I get to City College, I give it that title. And that was not such a common thing at that point. So, calling my proposal whatever I called it, but something along the lines of Physics Beyond the Standard Model, was not so typical at that stage. Subsequently, a good fraction of my work is thinking about such issues, and not just in string theory but with ideas like supersymmetry, technicolor, and so on. But at the same time, thinking about issues in the Standard Model itself. So, and these things somewhat overlap. So, for example, I turning to the present moment, one of the things I've been thinking about quite a bit over the last year or so is the question about the masses of the quarks. What do we know about them? And in particular, the masses of the lighter three quarks, the up, the down, and the strange. Unlike the case of the electron or proton, which you can run through some kind of accelerator, or mass spectrograph and measure its mass. The quarks we don't have access to in the same sense. We can't separate an up quark by itself, put it on a scale, and ask what it is. So how do we know these masses? And it turns out there's a complicated story related to the subject of so-called lattice gauge theory from which we obtain the up, the down, and the strange quark masses. And one question, which lingered for a while, is could the up quark mass be zero?
Why is this interesting? Howard Georgi and others pointed out that this would be an alternative to the axion solution of the strong CP problem. Now we think we know definitively the answer to that question from lattice gauge theory, for over a decade. Lattice gauge theory seems to say that the up quark mass is not zero, and with some high level of confidence. And I've been trying to understand those statements a little bit better. It's a little bit of my being a bit, I don't know, ornery or something, because obviously my personal interest is, well, it should be the axion, that's the solution I like. But maybe because it's something in my nature, I say, "Okay well, let's really look at these others. The other proposed solutions. Could they, are they viable? And so. I, for example, had been thinking about some issues related to the systematic errors, if you like, in the determination of the up quark mass. These are very hard calculations. Having the computer power to do the calculations, having the suitable algorithms which are adequately efficient, that took a long time. And those are also very complicated. And to what degree are there subtleties, are there uncertainties, in these computations? There are some additional checks, consistency checks you can do, but this also sort of characterizes I think a little bit the kinds of things that drive me. I have a beyond the Standard Model question, but it leads me back to think about, with some pleasure, about some physics that's more rooted in the Standard Model and our understanding of the Standard Model.
Michael, I'd like to- I'd like to ask a nomenclature question that might actually get to some questions about sociology in the string community.
So, your emphasis on string phenomenology, right? It suggests to some degree, and people really need to understand this better than they do, that string theory isn't a thing. It's a lot of things and a lot of people approach it from different perspectives. And there's a range from people who are operating in something that touches on a purely mathematical basis, all the way to, for example, compactification. People like Gordy Kane that really approach it in as testable a way as possible, right? So, your emphasis on string phenomenology sort of scientifically but also in terms of your intellectual sensibilities. What might that tell us about your approach to string theory?
Okay, so yes, when I say this, I mean different people mean different things by all these things.
So, for example, for me, string theory is, and I think for large numbers of people who you might describe as string theorists, string theory is not exactly just the study of these objects called strings. It's really the study and the question, "What is the theory of quantum gravity?" Of which string theory is some kind of corner perhaps of some broader structure. And we don't know exactly what that is. Because how can you do phenomenology with this thing? People mean various things by that. So people sometimes mean as, say, Gordy Kane does, let's take some particular construction of string theory, we're not quite sure why this one is important, what you should do, because there are many, many such things, but let's see if this one looks a little bit like something we see, whether if we take this at face value, it predicts something else.
I'm actually after a little something broader, which is what might be a generic output of string theory? An example is low energy supersymmetry, of the sort contemplated for the LHC. For example, could it be that supersymmetry is there, and is it perhaps just a scale, an energy scale a little bit higher than we're looking? Could there be some reason for this? And so a type of question I've asked is, in the sort of landscape framework that people discuss, might supersymmetry be an expected outcome. People have complained of course that a landscape is not predictive. I'm not so sure. What do we mean by this landscape? A picture is that the underlying system can be in many possible states. The universe, some kind of metaverse, can be in many possible states.
I'm sorry, did you say metaverse or multiverse?
Well, it can be either.
Okay, so we've got to stop there for a second. How are meta- How does metaverse and multiverse, how are they interchangeable? That's just a fascinating idea.
Yeah, I don't know if I have a thoughtful answer to that. Let me use multiverse.
Let me use multiverse. Just so there are these many universes, but-
The philosophers are going to jump all over that one!
Right (laughter). But a kind of question is the following: If a multiverse picture is correct, then we're sitting in a universe with some level of energy which is nearly-zero, and then there are states with more energy, less energy, and the problem is the ones with less energy. In this picture, we're not the lowest-energy state, so why don't we decay to this lower energy state? I thought a lot about what could be the answers to that question, and I claim there's really only one very robust answer that we know about. And that's if nature is in some sense approximately supersymmetric. It turns out that if nature is approximately supersymmetric, that the universe we live in, even if it's surrounded by many of these lower-energy states, lower cosmological constant states, can be very- is automatically, very stable. If it decays at all, it decays after very long periods of time, exponentially longer than the observed age of our universe.
So that, I have to confess, I've been saying this for a few years. I don't know that anybody's really paying much attention. But then the question for me is, okay, this argument by itself doesn't say if the supersymmetry has to show up at the LHC. It really only requires that the new particles implied by supersymmetry should be somewhat lighter than the highest energy scales you might imagine. The Planck scale or something. Is there more than that? Does that observation lead to some prediction for the energy scale of supersymmetry breaking? So, when I speak of string phenomenology, I'm not really thinking in the sense that Gordy [Kane] does other people do, asking about precisely which particular states you see. But just this very sort of softer question of, okay, if nature is approximately supersymmetric, how good an approximation, at what kind of accelerator should the super-particles show up? And is there an argument that we've just barely missed it? Or is it just far away? For me, this seems to be a more primitive kind of question. Rather than looking at, say, Model X7925 and twelve more digits attached, and asking does that model happen to describe what we see? Instead asking in this sort of generic way what might be the scale at which we see new phenomena?
And there are other questions like that. I think the axion question is also an interesting one, and also raises immediate issues, because what it suggests, if the axion as it emerges, sort of seems to emerge naturally from string theory, then you expect that the axion will be lighter than is predicted by, for example, these old arguments of Fischler, myself, Abbott, and Wise and so on. You predict that things would be too light to see with ADMX. Possibly visible to other kinds of experiments that people are thinking about. And certainly, this is something I also view as a kind of phenomenology. So, the issues I'm kind of focused on are things that are sort of generic in some sense like this. It's some sort of broad class of the things we see in string theory or quantum gravity. There are these axions, and most of the time they're very light. Can we see them? What's required? These light axions require that cosmology be different, for example at very early times than is often assumed. That the universe, for example, was in its past not so hot. Not much hotter than the temperatures of nucleosynthesis. What would that tell us? What kind of evidence would we have for that? What do those cosmologies look like? So, these kinds of things that look generic then applied to broad classes of the things that we see in string theory are the things that sort of preoccupy me.
Another sociology question, given the fact that you identify as a "semi" string theorist, right? As you well know, there's a range of perspectives regarding patience. How much patience should the broader physics community accord string theory, going from all of the original excitement in the mid-1980s to where the field is now. And that range, of course, you know, on one end is: "Amazing stuff is happening right now. And you should stay tuned because it's worth it and we're building up to something incredible." All the way to: "Guys, you've been at this for forty-something years now. When are we going to see something that's experimentally verified? Where are we going to see that string theory actually defines how nature actually happens?" So, where do you see yourself roughly on that spectrum, given the fact that you've approached these things in a pretty unique way?
I'm very much of the view that, well, I think I've sort of described what I think is kind of the experimental direction and its limitations. My view is that we have to go after generic things that we might learn-
And has that changed, I guess? That's the real question. Has that optimism changed in terms of the promise of what string theory could uncover from those heady days in '84 and '85?
Oh no, that optimism has changed, I think. I think I mean in terms of the things were just around the corner, I think that lasted for me just a few months (laughter). But that said, I see two elements of this. I see that first, string theory has already provided us with some ways of thinking about issues in physics beyond the Standard Model.
Meaning we're already there, to some degree, you're saying?
We're already there to some degree. I think of the proposals to look for very light axions are very serious. There are experiments, there are prototypes. There are things happening. There are, you know, there are some arguments that, yes, that supersymmetry might be there and around the corner, in a sense. The problem is of course that "around the corner" has a dollar price tag attached to it, or a euro price tag, or some price tag attached to it. That is very high. I'm not optimistic that, say, something along the lines of Calabi-Yau manifold number XYZ will be the right one and we will predict exactly certain things, and we'll measure exactly those things. I'm not an optimist in that sense. On the other side supersymmetry has proven to be an extremely valuable theoretical tool. It's taught us lots of things about quantum field theories, about how such theories work, and all these things about QCD. So, there are lots of things that we've learned from this, and string theory is similar in the sense, even in some ways in a bigger sense. It's provided us insight in terms of how a quantum theory of gravity might work, how larger theories work. And it will continue to do that. So, I'm quite enthusiastic about all these things and what we'll learn. I do think that in terms of how we'll translate some of this into our understanding of phenomena in nature, I think those problems are hard, and the payoffs may not be quick. It may be very long term.
And to what extent is your overall research agenda simply hamstrung by the fact that experimental facilities, specifically with supersymmetry, even the LHC, the SSC that never was, they're simply not operating at the energies that might verify some of these things.
Well I turn that around and say we're discussing, you know, as a community we're discussing future generations of facilities. And of accelerators. And the question is where do you want to land? So, I could turn this around and say the following. You can look at the Higgs mass, and you assume that there's supersymmetry, just what does that tell us? And this actually goes back to a calculation really done by my colleague, Howard Haber, some years ago. He realized that with supersymmetry, in a simple-minded way, the Higgs mass should not be greater than the mass of the Z, which is 91 GEV, and instead it's 125. So how did that happen? He said, well that can happen, if you have supersymmetry, but supersymmetry has to be a pretty high scale. It has to be at an energy scale about twenty to thirty times as large as the energy scale that you could probe with the LHC. So now you can say, "Ah, good, okay, this gives us a target energy.” But that translates into the energies of the quarks that you collide in the collider? They have to be very large. So, the price tag associated with getting to that scale is very high. So, for me, one of the questions is: What can we do to be more precise about this? That energy scale is rough. It could very easily by factors of a few in one direction or the other. And those factions of a few translate into billions of dollars in price tag. So, can we be more precise about where we want to land? And that's something that certainly drives a lot of the things I think about and work on. Because of the science policy implications, I would certainly be reluctant to just make some random statement. And I personally don't feel like I have a clear answer to that question.
What about even more fundamental questions, like figuring out a way to integrate general relativity and quantum mechanics?
Well, I do think those questions- I mean, that I think is sort of where a lot of the activity in string theory is, and I think there is real progress. And there are also challenges. And this is- it's not where, except sort of peripherally and sort of thinking about some of these issues of landscape and some of the inflation and other issues bear on this, it's not really my focus, but the focus of people who are thinking, for example, a lot about quantum information and general relativity and so on. This is where I think a lot of the energy should go. The things that string theory and its extensions have taught us, things like AdS/CFT and the construction of the resolution of the entropy problem from black holes. String theory is clearly telling us things that are interesting about how quantum field theory of general relativity works. But there are a lot of things that we don't understand sort of in our guts. We have various sorts of specialized situations where we can do these calculations. What's really going on? And I think these are kind of big questions.
Does John Schwarz's famous dictum that string theory is smarter than we are, does that resonate with you?
What does it mean for you?
I think it means exactly that. I think of something like this entropy puzzle, where one does the Strominger-Vafa computation of the entropy... it's a beautiful thing and it's a dramatic thing. Of course, it's been around for a while now too, but exactly what's going on, in a way that we could describe in some very general way, we don’t really know. It's some very specialized situation, and a lot of supersymmetry and where you have some so-called duality which you can hang this computation up. What a quantum theory of general relativity is in a general, a sort of generic sense, are there many of them, or are all of the manifestations we see part of the same thing? Whatever it is, how this calculation looks, how this result works in this away from these very special corners is something that we don't understand that deeply. And we have some inklings too, and I think some of this work on things like quantum information and so on may hold keys to it.
Does the statement that string theory is smarter than we are, does that beg then the possibility that we might need to outsource our limitations to things like quantum computing, if that ever happens? Or even artificial intelligence?
Conceivably. You know, in a sense, you know we have a sort of model for that sort of thing. Where you're going back to quantum chromodynamics and lattice gauge theory. So, the things we understand like these quark masses, only by doing very elaborate simulations, the guts of which we have relatively little intuition for. So, could that be the way we understand the problems in quantum gravity, perhaps? I tell my students in the classroom when I teach them about quantum chromodynamics, I say there's this problem and it's one of the Clay prizes. And it's unclaimed. And it's basically just derive this result in a way that you could see on a piece of paper rather than with, just somebody reporting to you what they did with this incredibly complicated computer analysis. So, could it be like that? I don't know, I don't know that i have any particular insight, but certainly that's a model for a case where there's something we'd like to understand in our guts, and we only understand it in this sense of you could do, you know, give me a supercomputer, come back, and I'll tell you the answer.
Michael, what did it feel like when it was announced that you were the winner of the 2018 Sakurai Prize?
Oh, that felt nice (laughter). And I was very pleased to get it with Ann. And I felt gratified to be considered in that class- I mean, my advisor received it and many others who I admire; I felt sort of privileged to be part of that group.
Did you feel that you were being recognized for one particular aspect of your research? Or more of an overall achievement award?
No, I thought of it as a kind of career recognition.
Though nominally the prize is used for youthful contributions, if you look at the wording (laughter).
(Laughter) Michael, just to bring our conversation up to the present, one thing we haven't talked about is your work at Santa Cruz as a mentor to graduate students. Who have been some of the significant people who have worked with you?
Well I want to be a little careful here because, you know, there are many and I don't want to single them out. I'll just say I've enjoyed my work with students, and it's been important to me and valuable to me in a lot of ways. Hopefully I've been valuable to them. Certainly, in terms of kind of metrics of success, there are variation as some are in academic positions, some are in research positions, some have gone on to industry or finance. I think what I have often felt about working with students and from my perspective, the selfish thing I gain is I get to think about questions which you know in some sense might be beneath the dignity of a senior researcher, but now okay, let's look at this because I need a problem for a student. And I get to ask all kinds of questions which might otherwise be embarrassing. And I think that's been very valuable. And I certainly have, I think, I've followed the model of my own advisor, of trying to have a very collaborative relationship with students.
To return to the question of your interest in the world of experimentation, right now the general feeling is in cosmology and astrophysics that, you know, observation and experimentation is really leading the field in many ways because the theory is so good. It doesn't really have so much to move on at this point. What are some of the things in experimentation, in observation, that are most compelling for you? That might really move the needle on the theoretical issues that you've been working on for so long?
Well, I think on the table right now there are a few things. We talked at the very beginning about g-2.
And I think that one is, as I say, I don't want to say what I hoped for and didn't hope for, but I think the fact that this isn't going away is surely telling us something important. So, either there's something new and it's pretty close by. It's something that in an energy range that you know you might well have thought you should see evidence for in colliders. And so that's really dramatic. Either that, [or] the alternative is that there's something significant we are missing in our understanding of Standard Model theory. And that would also be dramatic. I think that on the cosmology side, I think the story of dark matter, the story of dark energy, the question of whether there is, you know, whether the acceleration is truly a cosmological constant or conceivably something else. I think these are really huge things. At the moment, there are also some anomalies in B physics, in the physics of particles containing B quarks. And how seriously to take them, that's an interesting question. But perhaps, if the g-2 is telling us something, maybe this is related. So, there are a group of directions. I mean, I think I mentioned my own interests, current interest, now in light quarks. This is not unrelated to questions involving g-2 and the Standard Model side of those computations. So, all those things are driving me. I think that I would like to have a stronger argument one way or the other about what the, for a target for an extremely high energy accelerator.
Which would tell you what? Which would tell the field what best case scenario?
Best case scenario is you tell the field that, ah, there's some new strongly interacting particle at a few TEV, which you should be able to see. Or I'm not really, you know, as a science-- there's a sort of science policy aspect of it, how compelling would the case have to be to justify a ten billion dollar class facility, a new ten billion dollar class facility somewhere in the world? That's a tough question. But I think it's a kind of target for theorists. For example, if there's a particular candidate for the dark matter, and that's heavy. Can the story of dark matter, in that framework, point to a particular energy scale, which we should be looking at?
Michael for the last part of our talk, I'd like to ask a few broadly retrospective questions about your career and then we'll look to the future. So, the first one, it begs the question, because the narrative through-line of all of your research is, you're working on, like, really the hardest stuff. The stuff that's not so simple, cut-and-dry research. Is that a fair summation of the work that you've been involved in, would you say?
That's not sort of the way I think about it. I think it at some level probably goes back to the lunch with Feza Gursey. A lot of it gets to a question of sort of, what's the utility of a theorist? And there are different sorts of things one might do. I've always thought of this as, you want to ask the questions that are going to be just beyond our current experimental or theoretical reach. So ideally the questions aren't too hard (laughter).
Well maybe I would ask like this. I mean, the way I look at it, the metaphor of open loops and closed loops. What over the course of your career, either in your collaborations, the stuff you've worked on yourself, do you feel like these are things where the science is settled? We understand this now. We can now apply it to a broader framework. What are those things where you were involved in something? I get it. We understand it now. Now it's time to move on. And what are the open loops in your career, where the things that you were working on, certainly you've made contributions, certainly the field is advanced, but perhaps those fundamental, those existential questions, they remain?
I think they divide into categories. I think the questions that are sort of purely theoretical, some of these are settled. I mean I think there are things about quantum field theory that are settled. There are things about string theory as a theory that are settled. The questions that have to do with nature are largely unsettled. All these issues associated with the hierarchy problem; these are largely unsettled. The dark matter, I think that as I said, I think the axion, for example, as dark matter, looks very promising. That said, whether the axion as dark matter is readily detectable is another matter. It's clearly not easy, in any case, but whether it's detectable in your lifetime is a tougher question. And I think that, for example, as I said, these ideas about hierarchy, I think clearly some of our initial thinking on this was naive. But I think it's sort of an open question whether we were completely wrong, and that gets to some of these issues I mentioned about whether the scale of supersymmetry breaking, for example, might be slightly larger than we anticipated, and could it be some explanation for that? Or are we completely off the mark? And there I don't just think we know.
Have you ever experienced a eureka moment? When you didn't understand something and then it clicked?
Well there are different sorts of eureka moments, and at some levels, sure. About things that are purely theoretical questions, frequently. Some of this reflects the fact that I'm just not all that smart, and sometimes things I should have understood suddenly become clear, and that's really nice. In terms of nature, things are harder. Most of the eureka moments have been, "Oh it might work this way." As opposed to, "It does work this way." And you know, I think in terms of Feynman. Feynman, I remember reading at some point, [was] saying something to the effect that there was only one case in which he really guessed a law of nature as opposed to developing theoretical tools to better explore things that we sort of knew. And this was with relation to something called the conserved vector current, a feature of the weak interactions. And he described also his frustration to realize that other people, Marshak, who I mentioned in connection with City College, and Sudarshan had also had realized the same thing. So really having an insight, a eureka moment, about nature is something that even for great figures like this are rare. So, I said, my eureka moments I think tend to be more, "Oh, I understand some theoretical things. So, like I think in the more distant past, some of the things with applicants- Seiberg for example, in supersymmetry, there were moments where some theoretical thing just fell into place. It's something I'm doing now. It's not as dramatic, but something that's more like quarks, there are moments where, oh yes, there is something one can say. So those kinds of things, yes, I think that's with some frequency and kind of what gives pleasure in the day to day work. Nature is a bigger challenge.
To go back to this question about patience or not with string theory, more broadly for your overall research, what are the things in your career, the things that you've worked on, where you've been rewarded with patience, where it was good that you stuck with something for as long as you did, and where would you look at and say, "Perhaps I was involved in something that I should have dropped earlier than I actually did"?
I feel like, well, I mean it gets back to this question of, these different kinds of accomplishments. So, I certainly can, you know, I think what I've tried to do from thinking in terms of really explaining features of nature, I think there I've tried to think about broad sets of issues in the hopes that throwing enough darts occasionally, something will be right. And at the moment, I hold onto the things that look at least promising or not obviously wrong. I think I've managed both thinking about nature and thinking about theory to have a set of questions which have been rewarded by development of long-term bigger pictures. As to string theory itself, I think, you know, there are several things I could point to. They're not necessarily imminently going to be involved in explaining some feature of nature, but I can't help but feel they're part of human understanding of how nature, our ultimate understanding of how things are put together. And this applies also to a lot of the ideas about supersymmetry, and certainly the ideas about cosmology. You know, I think, take inflation as an example, I think I have put forward ideas there which, while we don't have necessarily got the ultimate theory of how inflation works, or what it's about, you know they may be part of that story. So, I think as a theorist, one has to be satisfied in some sense with that. With adding to the structures with which we gradually understand more and more about nature itself.
Michael, last question looking to the future. If you were to isolate simple curiosity about how the universe works, even a child-like wonderment, and you were to separate all of the issues of papers and administrative duties and all of the side work that comes involved with an academic life, what are the things you want to be most focused on? What are the things that you don't currently understand that time, being a finite resource, you're most curious about and also most optimistic about learning or understanding for however long you want to be active in the field?
Well I think every question I've raised in this discussion is in that category. I mean I don't think I would do it otherwise. And I think my level of optimism varies a bit. I think I'm ultimately optimistic that I'm contributing to some kind of broad human understanding that will gradually resolve some of these kind of questions, and so I would say dark matter and the dark energy, the workings of the laws of nature at the shortest distance scales, and generally this kind of movement towards understanding the very large and the very small. You know, I should say I'm in the midst of writing a popular book at the moment, and it's really focused on this question of looking at things on both the smaller scales and the larger scales. And so, when you ask this question, I think it's not quite the same point, but I mentioned Sandy Faber, one of my very distinguished astronomy colleagues here. When I first came here, we were both in an event at a fancy dinner on account of our spouses. Her husband is an attorney. It was a very large event. The organizers were clearly trying to figure out what to do with us, and they stuck us together at the same table, and it was a very memorable conversation. What I remember her saying about this sort of question was, she said, "The great thing about astronomy is you get the answer. You ask the same questions you asked as a kid, just with more and more sophistication."
And I'd say I'm asking questions I asked as a young theorist with greater sophistication and you know, and with some experience of successes and failures with some of these.
Michael, this has been a fantastic conversation. I'm so glad we were able to do this.
And you had the opportunity to share all of your insights over your career. So, thank you so much.
Thank you for having me. This was fun.