Thomas Appelquist

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ORAL HISTORIES
Thomas Appelquist

Courtesy: Thomas Appelquist

Interviewed by
David Zierler
Interview date
Location
Video conference
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In footnotes or endnotes please cite AIP interviews like this:

Interview of Thomas Appelquist by David Zierler on August 28, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
www.aip.org/history-programs/niels-bohr-library/oral-histories/47181

For multiple citations, "AIP" is the preferred abbreviation for the location.

In this interview, David Zierler, Oral Historian for AIP, interviews Thomas Appelquist, Eugene Higgins Professor of Physics at Yale University. Appelquist recounts his upbringing in rural Iowa and then Indiana, where he attended Catholic high school. He describes his undergraduate experience at Illinois Benedictine College and explains his attraction to attend a small school for college. Appelquist discusses his decision to attend Cornell for his PhD, and recalls that, relative to others in his cohort who went to larger schools, he had the most catching up to do in quantum mechanics. He explains the development of his thesis topic under the direction of Don Yennie, which focused on aspects of renormalization theory using the Feynman parametric approach. Appelquist contextualizes some of the broader questions in quantum field theory and quantum electrodynamics at this time, and he describes the opportunities that led him to SLAC for his postdoctoral research. He describes his interests there as focused on theories of the weak interactions, and he describes his initial faculty appointment at Harvard where he joined the particle theory group led by Shelly Glashow and Sidney Coleman. Appelquist discusses his close collaboration with Helen Quinn on how to renormalize Yang-Mills theories, and he explains his decision to take a tenured position at Yale in consideration of the culture at Harvard, where the prospects of tenure were minimal. He describes the revolutionary discoveries of asymptotic freedom, QCD, and the “November Revolution” at SLAC and Brookhaven at the time. Appelquist describes his research and administrative activities to advance the particle theory group at Yale, and his overall efforts to improve the department as chair and in particular building up the condensed matter theory group. He discusses his tenure as Dean of the Graduate School and his long-term involvement with the Aspen Center. At the end of the interview, Appelquist describes his current interests in lattice gauge theory and explains why he expects that physics will see double beta decay in the next generation of experiments.

Transcript

Zierler:

Okay, this is David Zierler oral historian for the American Institute of Physics. It is August 28th, 2020. It’s my great pleasure to be here with Professor Thomas Appelquist. Tom, thank you so much for joining me today.

Appelquist:

My pleasure.

Zierler:

Okay. So, to start, please tell me your title and institutional affiliation.

Appelquist:

I’m Eugene Higgins Professor of Physics in the Physics Department at Yale University.

Zierler:

Okay, and when were you named to that chair?

Appelquist:

I was named to that chair in middle 1990s.

Zierler:

Okay, good. Alright, so let’s take it back all the way to the beginning, Tom. Tell me a little bit about your parents and where they’re from.

Appelquist:

I was born in a small town in Northwest Iowa called Emmetsburg. My parents came from that area. My father was of Swedish descent, second, third generation. His name was Leroy Appelquist. My mother was of Irish descent and came from Emmetsburg. So, it was an unusual marriage, a Scandinavian Lutheran and an Irish Catholic. It wasn’t without its problems, but it survived long enough anyway (laughter).

Zierler:

What level of education did your parents achieve?

Appelquist:

High school.

Zierler:

What did they do for a living?

Appelquist:

A variety of things. My father was a kind of self-taught Engineer. When I was young, we moved to northwest Indiana, Lake County near Hammond and Gary, the industrial area there. We lived in a small town a bit south of the industrial area called Dyer, and my father found employment with a small engineering company in Hammond that serviced the mills and refineries in the area. And little by little he self-taught himself a lot of electrical engineering and ended up with quite a good career. My mother was a homemaker for much of the time, but she had various jobs. She worked for a drug company in northwest Indiana for a number of years. It was kind of off and on.

Zierler:

Do you get the sense that with better opportunities your father would have pursued a higher education?

Appelquist:

Absolutely. I think he had all the talents, all the skills but that just wasn’t in the cards. He was born in 1915, so he was a teenager during the Depression, and more education just wasn’t possible. Maybe the same with my mother. It’s hard to know.

Zierler:

Do you get the sense from your father that he taught you a bit about engineering and physics?

Appelquist:

I’d say a little bit. Not so much physics. His engineering was more seat of pants. But certainly, he taught me some quantitative thinking and some of ways of approaching problems that were important for engineers.

Zierler:

And you went to public school throughout?

Appelquist:

No, for high school I went to a large regional Catholic school in Hammond, Indiana which is now called the Bishop Noll Institute. It serves the whole area, towns like Gary, Hammond, and reaching south into the small farming communities like Dyer, right on the Illinois-Indiana border. So, I went to that school. I commuted there. It was about a ten or twelve mile commute every day by bus.

Zierler:

What was the reason for going to a private Catholic school?

Appelquist:

The other option was to go to the public school in my small town and it just wasn’t very good. My parents took a look at it and thought I could do a lot better at this much larger regional school in Hammond. It wasn’t so much that it was Catholic although my mother’s faith was Catholicism and my father adopted it in a kind of pro forma way. It’s just that it had better educational opportunities.

Zierler:

Was the church a big part of your upbringing?

Appelquist:

No, it was a small part. We all went through the motions. My parents went to church on Sunday. Even my father who was a converted Lutheran did. But I’d say it didn’t go beyond that.

Zierler:

Mm-hmm. Tom, when did you start to get interested in math and science?

Appelquist:

In high school. I had a wonderful teacher of physics and chemistry. A nun actually. The teachers at this school were mixed. There were religious teachers, some priests, and nuns and also maybe about half the teachers were lay teachers. I can’t say that I was a really devoted student in high school. I was picking and choosing things that I like. I probably should have done better.

Zierler:

Were you thinking about physics specifically when you were thinking about schools to apply to?

Appelquist:

Probably. But my horizons were very limited in those days. Graduates of this high school would go to local colleges. Maybe a few would go to Indiana University or Purdue. A few with a little more money would go over to Notre Dame. So, yeah, I was thinking of it, but I wasn’t thinking beyond colleges and universities in that area.

Zierler:

And the idea of places like Caltech and MIT this was not in the cards for you at that point?

Appelquist:

That was just completely beyond reach. You know, you could have asked me if I wanted to go to Mars, I think.

Zierler:

Tell me a little bit about Illinois Benedictine College.

Appelquist:

So that’s where I ended up going. It’s about thirty miles west of Chicago, about halfway in between Fermilab and Argonne to place it geographically. I could have gone to the University of Indiana. I thought about doing that or maybe Purdue. I had those universities in mind. When I went over to IBC, saw the teachers there, it was a small college. At the time, they had a strong physics program. There was a wonderful professor there by the name of Rose Carney who impressed me greatly. It didn’t have much contact with research, although there were some possibilities at the University of Chicago. They seemed to be placing their graduates well in graduate school. Most of them in midwestern state university graduate schools but that seemed fine to me at the time. That was already a kind of aspirational. So, I ended up going there because the program was good, the track record had been good in recent years, and I liked the people. And I liked the idea of going to a small college. It was all male at the time, and it was associated with a Benedictine Monastery which is still there in Lisle, although it’s withering. The monks are aging and they’re not finding many replacements these days. They dominated the board of trustees and the officers of the college, but the teachers were a mix of lay teachers, priests, and brothers from the Benedictine Order.

Zierler:

But as a school without graduate students, you had the opportunity to develop pretty good relationship with the professors?

Appelquist:

Yeah, very good. None of them had active research programs, so we didn’t have the opportunity to get very involved in research, but on the other hand the courses were fine. I got a good introduction to all the mathematics that I needed up through various levels of calculus.

Zierler:

Tom, to fast forward for a second to Cornell. I assume much of your cohorts at Cornell were coming from schools like Harvard and Princeton and, you know, Caltech and places like that. So, I wonder looking back at Illinois Benedictine if you were fairly well prepared or you had some catching up to do?

Appelquist:

I’d say I had some catching up to do, but I think the basics were in place.

Zierler:

What did you have to work on?

Appelquist:

I had had very little serious introduction to quantum mechanics. I had a course in atomic physics but not a lot. So, when I got to Cornell, you’re absolutely right, my next-door neighbor at Sage Hall on the Cornell campus had come from Princeton and it became clear to me that he knew a hell of a lot more than I did about a much broader set of things. So, it was a little daunting. I looked around and said, “Well, maybe I’m as smart as these people but many of them know a lot more than I do.” They had much broader exposure, but I think in the end it didn’t hurt me that much because, you know, I got focused on the first-year graduate courses in mechanics, classical mechanics, E&M, the usual set of introductory courses, also a lab course. I had the tools I needed to do pretty well in those courses. So, I’d say little by little, by my second year at Cornell, I think that distinction kind of disappeared.

Zierler:

Right.

Appelquist:

Often it was little things that caught my eye. I mean they just knew things about the history of physics, famous physicists, what they had done that just hadn’t registered with me as an undergraduate. So little things were telling me pretty clearly that my classmates often knew a lot more than I did. Some from Princeton, Stanford, from Harvard, more elite small colleges.

Zierler:

To go back to undergraduate, Tom, I’m curious, you know, by ideology and geography I assume that college was a pretty conservative place even in the late 1960s. So, I’m curious if-

Appelquist:

Yeah.

Zierler:

-the Anti-war movement or the Civil Rights or the Women’s Rights movement if any of that touched on campus. If that was part of your experiences.

Appelquist:

Well, I graduated in middle sixties from college. Just a little bit before the sixties really started bubbling up, so the early sixties were quite a different scene for the most part across the country. No, none of that had any impact at all in those days at that college. And I think that was true generally.

Zierler:

Was the draft a consideration for you? Was that something you had to contend with?

Appelquist:

It’s something I had to contend with, but I had a student deferment right up until the age of what? Twenty-six I guess it was at the time. I don’t have the years so clearly in my head, but the student deferment also was important for me during graduate school at that point.

Zierler:

Right. Coming out of undergraduate how well defined were your interests in physics? In order words, when you were thinking about graduate school did you have sort of baseline distinctions about, you know, theory or experimentation or applied physics? Did you have any idea what you might want to pursue in graduate school?

Appelquist:

Not really. Probably tipping more toward theory just because I knew more theory and hadn’t had much exposure to experimental physics. But I’d say, no, I was pretty opened minded when I entered graduate school at Cornell. And you know, it took a while, a year and a half before I made a clear distinction about- a decision about where I wanted to go. There were a lot of opportunities at Cornell at the time. There was a very good high energy physics group in theory and experiment, a lot of astrophysics, and a huge amount of material science, condensed matter physics. So, no. I think it only kind of gelled for me after about a year or so. I was pretty open-minded going in. I wanted to feel my way in and size the situation up. See what I wanted.

Zierler:

So, in contrast from high school where, you know, going to a place like Cornell would have been like going to Mars what had changed by the end of your undergraduate that you thought you’d be able to get into a place like Cornell?

Appelquist:

Well, first of all, unlike high school I somehow decided when I was a freshman in college that the time had come to bear down and get good grades. So, I was basically straight A’s in everything. I had done very well in physics, in the GREs which I took. I had gotten an NSF Fellowship, so I was doing a lot better by all those measures and I thought I should certainly reach. So, I applied to some safety places in the Midwest, and I applied to Cornell and MIT. They didn’t let me in at MIT but -and I had learned a good deal about Cornell, about the people who were there. I had- I don’t think I had any professors who were trained there but for some reason I got to know it pretty well and it looked like a place that would be a good fit for me. And it turned out to be a great place in those days.

Zierler:

When did you start at Cornell? Was it ’64?

Appelquist:

’64, yeah.

Zierler:

And when you got there- I always- I’m curious. What was your sense of- like, what were the most exciting things that were happening in the physics department? Who were the, you know, the most luminous-

Appelquist:

Well, it was quite interesting actually. In the area that I eventually went into--if you think about the particle and nuclear physics people broadly, the luminary was Hans Bethe. He was then sixty-ish and he had been there for some twenty years. He had come after the war in the late forties, and he was still there, still quite active, although doing things that didn’t really appeal to me at the time. In particle physics, there was an experimental laboratory run by Robert Wilson who had been a student of E.O. Lawrence at Berkeley and who became the first director of Fermilab. He left Cornell at that point. The Cornell laboratory was called the Laboratory of Nuclear Science although it was mostly particle physics built around an electron accelerator. Most interesting to me is that the same year I came as a first-year graduate student, they hired Ken Wilson. Ken had been an undergraduate at Harvard. He got his Ph.D. at Caltech and then was a post-doc for a couple of years, at CERN and the Harvard Society of Fellows. So, he came and that was really quite an addition to the group. I can’t say most of us really understood what he was up to, but he was basically inventing modern effective field theory, for which he received a Nobel Prize in 1982. There were others. Ed Salpeter who had co-authored the book Bethe and Salpeter was on the faculty there. The person that I eventually worked with had also come in ’64. His name was Don Yennie, He had been at Stanford, then at the University of Minnesota, and he was recruited to Cornell in ’64.

Zierler:

And what was his research? What was he working on at the time?

Appelquist:

He was working on aspects of quantum electrodynamics. In particular infrared divergence issues. How to deal with infrared singularities and summations. Very detailed stuff, quite- technical. But a really good person to work for. Very good training working with somebody like that. He had been a graduate student at Columbia in the 1950s during a time when Yukawa was visiting Columbia. He was a student of Yukawa, so I’m always proud to tell people I’m a grand student of Yukawa.

Zierler:

How did you go about developing your dissertation topic?

Appelquist:

I started attending group meetings in the group that Don Yennie led (he had a post-doc that worked with him and a couple of--one or two more advanced students) and I got a sense of what was going on in the group and what his interests were. He had a kind of side interest that was a bit more formal than the calculational things. A new approach to renormalization theory. Kind of a new way of organizing Feynman graphs, identifying the divergences, separating finite part from the cutoff part. I got quite interested in that, so, I developed a dissertation along those lines that focused on aspects of renormalization theory using the Feynman parametric approach. It was before dimensional continuation came along. The other students were doing things that were a little more calculational and applied, and so I thought- let me try this. It’s something nobody else has focused on and he encouraged it and it ended up working out pretty well for me. I remember when I was a fourth-year graduate student, we went off to a conference at the Institute for Advanced Study. I drove with him down to Princeton and I gave a talk on this approach to renormalization that we had been developing. I was petrified because the audience consisted of Dyson, Schwinger, and other luminaries, and I’m thinking what could I possibly tell these people that they don’t already know.

Appelquist:

So, it was a kind of- it was a good awakening for me.

Zierler:

How’d you do at the talk?

Appelquist:

I think it went pretty well.

Zierler:

Good (laughter). Tom, who was on your committee?

Appelquist:

Oh, gosh! It’s hard to remember. Certainly Don Yennie. Some of the other theorists in the group at the time were Peter Carruthers, Tom Kinoshita, who was a master at large scale high-order computation in quantum electrodynamics, interests that were somewhat similar to those of Don Yennie but even more detailed and more computational. Another member of the group at that time was Kurt Gottfried. He spent quite a long career at Cornell and became--as you may know, one of the founders of the Union of Concerned Scientists.

Zierler:

Mm-hmm.

Appelquist:

That happened when he went off on a leave of absence in 1970/71 at MIT. That was the year that they began Earth Day.

Zierler:

Mm-hmm.

Appelquist:

And the Union of Concerned Scientists grew out of that. He has been retired for a number of years but as far as I know he’s doing fine. So, there were a lot of interesting people at that time on the faculty. I liked Cornell a lot. I’m very fond of Cornell.

Zierler:

Tom, looking back what--how do you see your dissertation sort of fitting in with some of the larger questions in theoretical particle physics that were going on at that time?

Appelquist:

Well, I think it fit in in the sense that people at that time- and I can’t say in any way that we led the solution to this problem but a big issue at the time was how to think properly about quantum field theory. The best and most useful example of quantum field theory at the time was quantum electrodynamics. The quantum version of Maxwell’s theory. When it’s developed and applied it leads to lots and lots of integrals which seem divergent in the ultraviolet. There are so-called infinities all over the place and there was this issue about how you separate those affects, remove them, hide them. The phrase at the time was sweep them under the rug. It was considered a bit of mysticism. How you do that? How you separate that part of the calculations from the part that actually leads to something measurable? That’s the whole program of renormalization theory and people were trying to sort that out. In fact, there were people who simply didn’t believe in quantum field theory at the time because this hadn’t thoroughly been sorted out.

Zierler:

Tom and what-

Appelquist:

So, I-

Zierler:

-what were some of the experimental limitations that could have contributed to the so-called lack of belief?

Appelquist:

Well it wasn’t so much the experimental limitations because there were tried and true methods for separating the pieces that bear directly on experiment. And those experiments were being done and being refined in the 1950s. I’m thinking of things like the Lamb shift in atomic hydrogen that dated from the 1940s, and increasingly accurate measurements of the anomalous magnetic moments of the electron and the muon. Those experiments were underway, and the accuracy kept getting better and better. And that continues to this day, at a much higher level of accuracy than in those days but those issues are still with us. So, I don’t think it was the experiments that were being done that were forcing people to think more about this It was clear that there was a scheme that was working. The question was: did it make any sense and what were you really doing with all these infinities? Anyway, that’s a long-winded answer to the question. I’d say that the dissertation I worked on grappled with those problems to some extent. But I don’t think we nailed the solution. The real insight into that problem was developed by Ken Wilson and others. But Ken in particular led the understanding of how to think about quantum field theory in a very physical way. Observing that these so-called infinities were just reflecting the fact that you can’t take these theories and trust them to arbitrarily high energies even though they are virtual particles going around loops because nobody had ever done any experiments at these high energies. So, what you needed to do was to be modest and say you’re working with a theory that’s only effective up to some scale. And then you can organize all the dependence on the cutoff scale and see what it affects and what it doesn’t affect. It gets you thinking much more physically about renormalization theory and about how to use the quantum field theory. That became known as Effective Field Theory, the framework that all particle theorists work in these days. I had a hand in developing it through something called the Appelquist-Carrazone decoupling theorem. But the real hero, in my view, was Ken Wilson.

Zierler:

Sure.

Appelquist:

I only wished that I had understood Ken’s work better when I was a graduate student at Cornell. I’m getting ahead of myself a bit, but I only really came to talk a lot to Ken and be influenced by him when I was a post-doc at SLAC, and he came to visit for a year. Then I really started to talk with him.

Zierler:

Tom, what opportunities did you have after you defended? What did you want to do next?

Appelquist:

Well, I wanted to go on. I had started into these issues that were interesting me a lot in particle physics. Particle physics was in a very confused state at the time and a lot of people, by the way, had abandoned quantum field theory entirely in the late sixties. There was a whole school of thought led by Jeffrey Chew of UC Berkeley that said you just can’t use it for the strong interactions. You have to come at it in a new way. So, a lot of people had not been trained in the details of quantum field theory. I had, which was nice. I wanted to stick with that and see whether I could build on it and so that’s kind of where I was headed, and I applied for post-doc positions with that in mind.

Zierler:

What post-docs were most attractive to you?

Appelquist:

Well, it was strange. Nowadays people apply to God knows how many places. You apply to a central pool and are considered by dozens if not multiple dozens of places. I applied to five places and the two places that interested me most were the Institute for Advanced Study and SLAC. I got offers from both. I didn’t get offers from the other three places, but I was less interested in them anyway. But in the end, I had to choose between an offer from the Institute at Princeton and SLAC and that was hard. How could you possibly turn down an offer from the Institute for Advanced Study?

Zierler:

But it is a stark choice in the sense. I mean at SLAC even if you’re at theory, you’re in the middle of a very dynamic-

Appelquist:

Yep.

Zierler:

-environment.

Appelquist:

Right. It was a very dynamic environment. It was a fabulous time to go to SLAC. So, in the end it was an easy choice. I liked the people at the Institute. Steve Adler had just come, Roger Dashen, lots of other people. So, it was a nice environment but because of the breadth of activities and excitement at SLAC at that time, it didn’t compare. And I think I made the right choice.

Zierler:

It’s also an opportunity to live in Northern California for a while.

Appelquist:

I had the feeling we had just moved to paradise. It was a nice time to be in Northern California in the Bay Area. It was a time of political unrest but that didn’t affect Palo Alto much. It was very quiet in Palo Alto, but Berkeley was just brimming with political-

Zierler:

Right.

Appelquist:

-activity.

Zierler:

Right. And you were situated pretty much exclusively in SLAC? You didn’t have so much contact with the Physics Department?

Appelquist:

I did not. That was a time when there was very little contact between the SLAC people and the Physics Department.

Zierler:

Right.

Appelquist:

There was a history of that. I came in after the history was more or less over but there was still quite a lot of animosity between SLAC and the Physics Department that had a lot to do with the establishment of SLAC itself-

Zierler:

Sure.

Appelquist:

You probably know the history of that better than I do. So, that was still there and that affected the culture a lot. We would occasionally go to seminars in the department. Some of the faculty at SLAC had appointments there. Bjorken had an appointment in the department. But I would go down there only if there was a seminar in the department. They didn’t have much of a particle theory group in the department at the time. I’m thinking and nobody’s coming to mind. So, yeah not much contact.

Zierler:

So, that begs the question. Tom, how did you slot into what was going on at SLAC on the theory side of things?

Appelquist:

It was not so hard. There were a number of post-docs. Five joined the SLAC theory group the same year I did, so a lot of what I did was collaborative. I ended up collaborating on some papers with Stan Brodsky who had been a post-doc there a year or two before and was kept on as a long-term staff member at the time. And I collaborated a bit with (James “BJ”) Bjorken. These collaborations just build out of conversations that you’re having with different people. I started by collaborating on a short paper with Carl Carlson who had come from Columbia. A student of T.D. Lee’s. I think he’s still active and not retired at William and Mary College. I haven’t seen in him a while. It’s hard to know how these things happen. You get there and start talking, and see what the other people are interested in. I shared an office for two years with Martin Einhorn who had come from Princeton, ended up going to Michigan, and then toward the end of his career became the Deputy Director of the KITP in Santa Barbara. I think he’s retired now. I also ended up interacting a lot with Joel Primack, a graduate student of Sid Drell at time. He went on to quite a prominent career, shifting his interests into astrophysical things and spent his faculty career at UC Santa Cruz. I did quite a lot in two years.

Zierler:

Yeah.

Appelquist:

So, it was pretty successful.

Zierler:

Did you take this as an opportunity to work on new physics or were you looking to continue on and expand and refine your dissertation?

Appelquist:

I’d say a bit of both. I was getting very interested in theories of the weak interactions. How you could develop a quantum field theory of the weak interactions. It was still very puzzling, very problematic. It looked as though you could do it by introducing fields for the W and Z bosons and writing Feynman diagrams. But there were divergence issues that were new because the W and Z had mass. It was very puzzling. So, part of my interest shifted in that direction to see if we could get that sorted out. I pretty much understood what was going on in quantum electrodynamics by that time, but to apply that to the weak interactions was still very puzzling and I worked on that for a while. Once again, I can’t say we really solved that problem. Two years later it was more or less solved by a Dutch graduate student by the name of Gerard ‘tHooft, and that really ushered in the new era of gauge field theories in the early seventies. So, I’d say I was trying to do things that I knew would expand out in different directions.

Zierler:

Was joining SLAC as a faculty member- was that an opportunity that was available to you-

Appelquist:

No, that was not available at the end of my postdoc. They were not hiring faculty members. And post-doc jobs were just two years at the time.

Zierler:

Right.

Appelquist:

They are much more typically three years now. So, you were encouraged to apply elsewhere for faculty positions.

Zierler:

What were the opportunities available to you?

Appelquist:

I applied to Harvard, Yale, UC Santa Cruz and maybe some other places that I forget now. But those are the ones that I focused on.

Zierler:

With that record, the job market was pretty solid at that point then?

Appelquist:

No. It was starting to get weaker. It was the beginning of the seventies, so the big bubble of job opportunities of the sixties was starting to decline. But there were still some opportunities available. It was on its way down into the years of the 1970s when things got pretty bad for a while. But most of the post-docs at SLAC did pretty well, getting faculty jobs of one kind or another after a two-year postdoc. I got offers from those three places. I could have gone to UC Santa Cruz or Yale, but Harvard looked a lot more interesting at the time. Even though it was very clear that faculty jobs in those days at the elite universities were all temporary. There was no relation between junior faculty jobs and tenured faculty positions.

Zierler:

In other words- you knew that-

Appelquist:

-I was fully aware of that.

Zierler:

You knew going in that tenure was almost certainly not going to happen?

Appelquist:

That it was very unlikely.

Zierler:

Although it did for our mutual friend, Howard Georgi?

Appelquist:

It did, but that was like five years later. So, I picked Harvard and- well, there’s a lot to say about that era. Do you want to jump to it now or you do you want to talk more about SLAC?

Zierler:

No, no, no. We’ll catch it in time. That’s good.

Appelquist:

When we left Palo Alto, I really missed California. We went to Boston in awful winter. And-

Zierler:

I wonder if you rethought Santa Cruz during that winter?

Appelquist:

Yeah. I thought maybe we had made a mistake. My wife Marion kept saying, “What are we doing here? Why are we here?” The situation at Harvard was a lot more complicated than SLAC. At SLAC, everything was upbeat. The deep inelastic experiments were being done. If I can just dwell on that for another minute, we saw a good deal of Feynman. He would occasionally come up from Caltech to talk about his parton model. So, we saw him a lot. The other post-docs were Martin Einhorn who went to Michigan, and Tung-Mow Yan who went to Cornell. He worked with Drell on the Drell-Yan process which is still often referred to even these days. Carl Carlson went off to William and Mary and John Pumplin went to Michigan State. So off I went to Harvard. Shelley Glashow and Sidney Coleman were the core of the particle theory group. Julian Schwinger was just departing for UCLA. There were other theorists in related areas. Arthur Jaffe, a mathematical physicist had just come from Princeton. Some other names will come to mind. Then about three years after I got there, they recruited Steve Weinberg over from MIT. So, he joined the Harvard group. This was now about 1974 and there were no other positions available there. In ’75, I got an offer from Yale for a tenured position. So, I looked at the situation at Harvard and I thought I’d better grab this (laughter). So, I moved to Yale at the end of- at the very end of 1975, started teaching here in the Spring of ’76.

Zierler:

Tom, before we get to Yale-

Appelquist:

Alright, let’s backtrack to Harvard.

Zierler:

Yeah, to go back to Harvard, were you working with Shelly and Sidney? I mean was there sort of a cohesive group that you were a part of?

Appelquist:

That’s a complicated question for that place and those personalities. The first year I was there, both of them were on leave and I didn’t see them. I did see quite a bit of Julian Schwinger that year, but nothing approaching a collaboration. And then at the end of that first year Shelly and Sidney came back and I certainly interacted with them a lot, but I never wrote a paper with Sidney. I did end up a couple of years later writing a paper with Shelly, but I’ll come to that in a bit. So, no, not a lot. We hired Howard Georgi as a post-doc the second year I was there. He came and he immediately started collaborating with Shelly.

Zierler:

Right.

Appelquist:

He became Shelly’s main collaborator for a number of years. You couldn’t go into Shelly’s office without seeing Howard. He was always there. That worked very well for both of them. So, no. In fact, the person that I ended up collaborating with a lot in the beginning even in 1970 was Helen Quinn.

Zierler:

Mm-hmm.

Appelquist:

Helen had been a Ph.D. student of Bjorken at SLAC, left the year before I went there as a postdoc. So, I didn’t meet her there.

Zierler:

Oh! So, you didn’t know her from SLAC at all?

Appelquist:

Not at all. She had gotten her PhD in ’67 and had gone off to Germany with her husband who was in experimental high energy physics. They went to DESY in Hamburg. She then came back to Boston because he had gotten an offer at MIT working with Sam Ting. And she just came along. They were living in Sommerville and she was unemployed. She showed up at the Harvard Physics Department one day and said, “I live in the area now. Could I- “

Zierler:

Yeah.

Appelquist:

“-get an office.” We said, “Sure, take an office.” So, she came in everyday, usually with her daughter who was about a year old or less. And she and I collaborated quite a lot. I wrote several papers with Helen and that was a lot of fun.

Zierler:

And what were you working on with Helen? What was the research focus?

Appelquist:

Well, by this time ‘tHooft’s papers had come out on how to renormalize Yang-Mills theories and deal with the divergences. So, we picked up on that, very much influenced by his work. We wrote some papers on some model field theories and then on the full electroweak theory which actually had been proposed by Steven Weinberg some years earlier in 1967. But not really taken very seriously I think even by Steve until the work of ‘tHooft in ’71 which really showed that these theories were tractable in a way that all the cut-off dependence could be organized in a systematic and sensible way. So that kind of blossomed around 1971 and Helen and I picked up on that and started writing some papers. It also turned out that Joel Primack, with whom I had collaborated at SLAC also moved to Harvard at the same year as a member of the Society of Fellows.

Zierler:

Ah-huh.

Appelquist:

So, he joined our little group. Helen, Joel, and I were collaborating quite a lot in those days. Shelly- no. Shelly is an interesting, mercurial character and it was not so easy to collaborate with him. Howard figured out how to deal with Shelly. And they got along pretty well. The rest of us, we’d talk to him, but I couldn’t imagine collaborating with him.

Zierler:

Howard is the Shelly whisperer. He knew what to do.

Appelquist:

He did. It was fine.

Zierler:

And where is Steve Weinberg in all of this?

Appelquist:

For the first two and half or three years he was still at MIT and then he came over to Harvard in ‘73 or thereabouts. Steve was a solitary figure research-wise. He didn’t, and still doesn’t, collaborate much. He came over and was working very hard on theories picking up on his famous paper, “A Model of Leptons”, which won him the Nobel Prize. He was also working in the same general area with a small number of students. He never had many graduate students. So, among the senior faculty at the time, there were three separate islands. There was Sidney Coleman and the people he influenced. A lot of students circled around Sidney. There was Shelly and Howard and then there was Steve who was more of an island unto himself. There was not a lot of interaction between these three centers of activity.

Zierler:

Was there bad blood or it was just people doing their own thing?

Appelquist:

There was some bad blood between Shelly and Steve for reasons that I don’t fully understand.

Zierler:

Well that probably goes back to the Bronx.

Appelquist:

It goes back to their high school days, right. Steve often used to say, “When I went to high school, I felt like if I wanted a career in theoretical physics, I should at least be the smartest person in my high school class.” And he looked around and it wasn’t so clear that he was.

Zierler:

It must have been interesting to watch Helen hold her own in this otherwise boy’s club, right?

Appelquist:

Yeah, and she did. The two of us collaborated by ourselves for about a year and so that helped. She had not been very active for a year or two before coming to Harvard, and, in all modesty, I think I played some role in pulling her back in- in a collaborative way. She went on to quite a fine career. As you know, she went off to SLAC, originally a glorified post doc of some kind and stayed on at SLAC. Eventually she became the President of the American Physical Society, and then SLAC started to think “we better treat her a little better.” It took a long time.

Zierler:

Yeah. Now, in terms of the transition over to Yale were you reading the writing on the wall in terms of your tenure prospects? Were people sort of giving you a clue it was time to start thinking elsewhere?

Appelquist:

Yeah, especially with the arrival of Steve Weinberg. By that time, the Harvard particle theory group was pretty full and none of these people were older than their forties at the time. There was Sidney and Shelly, and to some extent I viewed Arthur Jaffe as a member of that group although doing more formal mathematical physics. And then Steve came over and that led to a full house at the time. And I thought this does not look like it’ll work out for me here. There weren’t any open senior positions, and the way Harvard and Yale were structured then was that there was no connection between junior and senior faculty positions. They were just counted differently. That remained the case at Yale all the way through to the 1990s until we finally got rid of that system. So, I got this nice offer from Yale, I liked the people there, so I decided I’d go. I’d say that it was all done on friendly terms.

Zierler:

Now, did you have graduate students at Harvard?

Appelquist:

I did. I had a couple of graduate students when I was at Harvard, one of whom became a fairly prominent senior member of the theory group at Los Alamos. His name is Terry Goldman. I haven’t been in touch with Terry for a few years, but he had quite a successful career there. I had another student at Harvard. His name was Jim Carrazone, and he and I developed this Appelquist- Carrazone decoupling theorem. He took a post-doc position at Fermilab and then left high energy physics and went to work for Exxon Research in Houston. He has had a great career doing applied physics, applied mathematics, and studying inverse scattering problems. I haven’t seen him for a while.

Zierler:

Now, Yale recruited you or you were applying? You were-

Appelquist:

No, I was recruited. I was approached by the Chair of the Yale Physics Department at the time who said, “Would you be interested in an offer of a tenured position here?” And I said, “Well, yeah.”

Zierler:

(Laughter) And who was chair at that point?

Appelquist:

Allan Bromley.

Zierler:

Oh, okay. And it was Bromley specifically? He was the one who reached out?

Appelquist:

Well, the full department was behind it, but he was the one who approached me, encouraged me to come, and hosted me and my wife when we came for visits. So, he clearly played the lead role although even at that time there was a particle theory group here and they were pretty enthusiastic about it too. But he was the leader of the department.

Zierler:

But in reaching out to you the idea was that this would be an opportunity to build up that group?

Appelquist:

Yes, the idea would be to strengthen the department in general and to build up that group which had been somewhat quiet in recent years.

Zierler:

Right.

Appelquist:

And he wanted to bring somebody in who could bring modern ideas to the-

Zierler:

Yeah, so you felt that you had sort of a mandate to do that? To get to Yale at the center of these conversations?

Appelquist:

I had a mandate to try,

Zierler:

Yeah.

Appelquist:

with encouragement from Bromley and others in the department at the time to do that. I knew it would be challenging. It wasn’t going to happen overnight because of the people that were here, and the personalities but I decided to take a stab at it and so, I moved to Yale.

Zierler:

Now when you joined that group, or you created your own group?

Appelquist:

I had an office in the same part of the department where they were, shared seminars, and in a sense joined the group because there was an established grant then called a contract with the Department of Energy. The DOE doesn’t have contracts anymore. They have grants. I came in, put in a new expanded proposal, and it led to some expansion of the level of funding to the group. So, yeah in a sense I joined the group.

Zierler:

I’m curious, Tom, just to go back one year. Were you paying attention to the amazing things that were happening at SLAC in 1974?

Appelquist:

Of course. In fact, it led to one of my most important pieces of work. I’m glad you backed up since it brought to mind a name that I should have mentioned. I talked about a lot of other people but maybe the person that I collaborated with most prominently when I was at Harvard was David Politzer.

Zierler:

Oh.

Appelquist:

So, now let’s go back to 1973. David was a second-year graduate student of Sidney Coleman, and Sidney put him on to the problem that led to asymptotic freedom. He got him computing the renormalization group beta function that determines the evolution of the coupling strength in a Yang-Mill’s theory as opposed to quantum electrodynamics. It was a problem I had through about with Jim Carrazone and we had plunged into it the year before but got ourselves confused about gauge invariance and whether the calculation would mean anything. And unfortunately, I abandoned the problem. A year later, David was put onto it by his advisor, Sidney Coleman. Why Sidney didn’t get involved directly himself, who knows? Looking back, of course, he should have. He would have shared a Nobel Prize, but he didn’t.

Zierler:

But that pre-supposes that Coleman would have known where asymptotic freedom was going absent Politzer’s research.

Appelquist:

Yeah, that’s true.

Zierler:

It might not have panned out to anything.

Appelquist:

When David started working on the problem, I can remember I said, “This is interesting, David but, what’s it good for? And how do you know the answer will mean anything? How do you know it won’t be gauge dependent?” And David said, “I have no idea whether it’s gauge dependent or not. I have no idea what it’s good for, but it looks like an interesting problem and I’m going to calculate the beta function of the Yang-Mills theory.” And he did.

Zierler:

Tom, the-

Appelquist:

He got it right.

Zierler:

-unlikeness of all of this makes it even more fascinating how this was happening in parallel with David Gross and Frank Wilczek at Princeton.

Appelquist:

That’s a big story in itself. I’m sure if you talked to different people, you’ll get different versions. David Gross and Frank Wilczek were working on the same problem at Princeton at the same time. I think David Gross had a much better sense of what the physical consequences might be. By that time, he was already a tenured professor at Princeton. Frank was his student and they did the calculation and I’m sure the story that you’ve probably heard is that they got the wrong sign. The whole question is just the sign. Is it positive or negative? Is it positive like every other quantum field theory that we had ever investigated including electro-dynamics or could the sign be negative? And if the sign is negative was it--did it mean anything? Was it gauge dependent? David Politzer didn’t know the answer to that but my memory of all of this is that from the very beginning when he had finished the calculation David Politzer knew it was negative. The story goes that he went down to Princeton and maybe Sidney was on leave at Princeton at the time and that David Gross, and Frank Wilczek had, in fact, gotten the wrong sign, that they had made some kind of a mistake, and once they saw Politzer’s result they revisited what they had done and corrected their mistake. That’s an apocryphal story that permeates the field.

Zierler:

Right.

Appelquist:

I don’t know for sure just how true it is, even though I was pretty close to David Politzer at the time.

Zierler:

What are the red flags that jumped out for you on this?

Appelquist:

David Politzer himself was always very quiet about it. When I would ask him in the year that followed, is this really true? He would kind of waffle. He was a very mild-mannered guy at the time, so that may have been part of it. So, I don’t know if it’s true or not. At any rate in the end they both got the same sign. It was negative and it revolutionized the field.

Zierler:

And Tom, just to back up a little further-

Appelquist:

And if I can just add that when you do a calculation in quantum field theory, you must, as phrase goes, pick a gauge. You have to decide what gauge you’re going to work in. And then at the end you have to show that it doesn’t depend on that. When he did the calculation, he just worked in a particular gauge, got an answer, put it out there and wrote a paper. It was only in the following year or so people started to demonstrate that it was a gauge invariant answer. So, he didn’t know when he did the calculation but his answer to my questions was how do you know what you’re doing will be gauge invariant? He said, “I have no idea. I’m just going do it.” Damn, I wish I had had that attitude at the time. So, that’s the story on asymptotic freedom. Anyway, in the wake of the development of asymptotic freedom, David and I started collaborating, asking the question of what would happen if you apply this theory to the c-cbar threshold. What would happen at the threshold of charm and anti-charm (c-cbar) production, which was being looked at SLAC at the time and also by Sam Ting at Brookhaven. We were studying that in the summer of ’74 into the fall of ’74 and we were writing up a paper. We had come to realize that when you pass through a c-cbar threshold, the perturbation expansion would break down and bound states would form. We coined the term charmonium for the bound state that would be formed. And we were writing a paper with the word charmonium in the title, but we hadn’t put the paper out. We were not writing it fast enough and David had gone off on a visit to Brookhaven or Stoneybrook. Then one weekend in November the discoveries were announced of the J/psi particle. And we rapidly wrote our paper up and put it out--within a week and so. That turned out to be very nice for us. I just wish that we had gotten it out about two weeks earlier. I ended up writing that paper and several other papers with David Politzer and then we went on to look at more details of the spectrum of states in a c-cbar system analogous to positronium, and ended up writing a paper with Shelly Glashow and a new post-doc Alvaro DeRujula. You asked me earlier whether I had collaborated with Shelly. Yes, I wrote one paper with him.

Zierler:

Tom, were you involved in QCD at all during this time?

Appelquist:

Oh, yes. Once asymptotic freedom was discovered it was the basis for QCD. Until asymptotic freedom was discovered the idea that you could develop a gauge theory of a strong interactions by gauging color was kind of bubbling around. Gell-Mann had thought about it with his post-doc Harald Fritzsch, but nobody was taking it very seriously because it wasn’t clear how you would calculate with it. The feature that one had to explain was Bjorken scaling, the fact that the quarks looked like free particles at very short distances inside the proton. But once asymptotic freedom was discovered people said, oh my god. This is it. Asymptotic freedom means that the interaction gets weak at short distances. It means the quarks are just rattling around like free particles deep inside of the proton and that turned out to be the case. Once asymptotic freedom was in place, people really started to believe tin QCD.

Zierler:

And when you were thinking about QCD did you see the initial excitement over string theory as having flamed out essentially?

Appelquist:

Yeah, I did. I thought that it was a curious model for holding quarks and anti-quarks together. It led to a kind of confining potential. But I didn’t understand it as a quantum field theory. I was totally wedded to quantum field theory, and my view was that once we developed QCD and we learned how to deal with it and learned how it could even lead to strong forces and confinement at larger distances, we didn’t need string theory anymore. We had discovered the key to the universe and string theory was just a kind of phenomenological model. But things changed a lot in 1980s once people realized that this is really a theory of gravity. So, yeah. I was surprised.

Zierler:

That’s exactly what I was going to say.

Appelquist:

Yeah.

Zierler:

Tom, let’s get back to Yale. So, how did you go about, you know, to the extent that you felt that there was this mandate that Yale needed a shot in the arm in terms of theoretical particle physics, right?

Appelquist:

Yeah.

Zierler:

There are sensitivities about, you know, Yale has a certain stature in the world and there’s a need to meet it and there might be expectations. But there might be people who think that things might just be fine the way they are.

Appelquist:

Mm-hmm.

Zierler:

So, I’d be curious if you could talk a little bit about navigating those waters.

Appelquist:

It was not as difficult as it might have been because of some of the personalities. When I came to Yale the department was big and broad. It still is. In a way it seems broader. We had a big nuclear physics group led by Allan Bromley with a lot of people there including some theorists who worked in nuclear theory. Most prominently, Francesco Iachello came shortly after I did, and just retired last year. There was also atomic physics. The senior member of that group and leader was Vernon Hughes for many years. Vernon had been Chair before Allan Bromley. So, there was a lot going on in the department in different areas. Some real strengths on the experiment side. Bob Adair had a group in experimental particle physics at Brookhaven. But the particle theory group consisted at the time of three senior people and a couple of junior people who had been left over from an earlier time. Among the three-senior people, Feza Gursey was a very mathematical theorist, He was very active at the time, writing papers in mathematical physics and gauge unification idea. I really treasured his presence. He was a wonderful man. The other two members were not as active as I had hoped and as the department had hoped. But they were very nice people and so easy to work with. One was Charlie Summerfield who had been Howard Georgi’s mentor at Yale.

Zierler:

Right.

Appelquist:

I’m sure Howard must have mentioned Charlie to you. And Samuel McDowell. Sam had come from Princeton some years earlier. Despite the Scottish name he was Brazilian. He’s still alive. He lives in a suburb here. Charlie is still alive too. He retired maybe fifteen years ago and moved to Gainesville, Florida and has an office in the particle theory group there. It was Charlie and Sam who had become relatively inactive, but they were both very nice people and were not about to retire or go away for sure. They continued to do some work at some level and were quite supportive of trying to build up the group. They were not resisting it in any way. I don’t think they knew what to do exactly or how to do it but they weren’t fighting it. I liked them personally and I still do. It was a benefit that there were no difficult personalities here in the group. So, what did I do? I started by finding the funds to recruit other people. I should mention that there were junior faculty here at the time, and like Harvard there was no connection between junior appointments and senior appointments So they would spend some time at Yale and then leave. One of the persons who was here and had left the year before I came was Pierre Ramond. Pierre went off to work with Gell-Mann at Caltech for a number of years and then became one of the very first recruits when they started building up the physics department at the University of Florida in the 1980s, and he’s still there. And there were a couple of other people on the junior faculty. One was Itzhak Bars who had been a student of Gursey, and whom they kept him on for a while until he left to go to the University of Southern California. The number of junior faculty had dwindled to very few --and they were about to leave. So, one of the first things I did was to try to recruit some other people. We managed to hire a young theorist from Harvard whom I’d gotten to know. He had come to Harvard as a junior fellow, had been a student of Geoffrey Chew at Berkeley. His name is Shankar. He’s quite famous for his quantum mechanics books and others.

Zierler:

Right.

Appelquist:

So, I recruited Shankar from Harvard. A year after he got here, he left particle physics and switched into condensed matter physics and he has had a long career. We collaborated a little bit. Also, I got additional funds from the Department of Energy to hire a senior research scientist by the name of Alan Chodos who had been at MIT. We were one of the creators of what’s called the MIT Bag Model of confinement, a phenomenology that we didn’t need much once QCD came along. But it was quite influential work. So, Alan came and stayed here for about twenty years as a senior research scientist. Eventually he left because his wife moved to Washington, D.C. Then slowly we started hiring other junior faculty here. It was difficult because the system was still such that there was really no tenure process so to speak. Nevertheless, we got some very good people who came and flowed through the group at the time. Maybe, the most high-profile person I hired, and the most fun, was Lawrence Krauss. We brought Lawrence from MIT and he really livened the place up. Say what you want about Lawrence and his issues and his problems, he was a ball of fire.

Zierler:

Yeah.

Appelquist:

He interacted with all the experimentalists, and he and I got a nice grant from the State of Texas when the SSC was being developed. So, he was quite a presence here for a number of years, wrote a lot of papers then left us to become Chair of Physics of at Case Western. He went on to Arizona State and has had his problems at there.

Zierler:

Yeah. Tom was there still also a generational shift? I mean were there the right retirements happening at this time also?

Appelquist:

Not for a while. That was the problem. When I came Feza Gursey was in his fifties, and Sam and Charlie were in their forties. So, they were not on the threshold of retirement. That’s one of the things that made it difficult. San and Charlie didn’t end up retiring until the early 2000s. I had to work around that.

Zierler:

Tom, I wonder when you were named chair, did this provide new or bigger opportunities basically to continue doing the things that you were already working on or maybe another way to ask that question is, is the fact that you became chair, was that a signal from a critical mass in the department that these changes really needed to happen?

Appelquist:

I think that it was a signal to some extent that these changes really had to happen. On the other hand, it was an era where the system was still the same. That is, we were nowhere near a tenure track institution. We still had the system that had long been in place at Harvard and Princeton and Stanford and Yale that junior faculty positions were flow-through positions. It was too early to change that. I was chair in the 1980s, and this system was so engrained at the time that I had to live with it. I did a lot of recruiting but what we did is we just slowly started bringing in more senior people with tenure. There were some notable successes, so we did the best we could given the system at the time.

Zierler:

Tom, I’m curious, you know, the 1980s in many regards feels like a very long time ago. Was-

Appelquist:

Yeah.

Zierler:

-diversity even on your radar? Was anybody even talking about diversity? Did anybody raise flags with the fact that, you know, a woman had never achieved tenure in the physics department at Yale?

Appelquist:

Not nearly as much as it should have. We had a number of women on the faculty, but they were all in junior faculty positions and they would flow in and out and go on to other positions. There was no pressure at the time. Diversity was not nearly as prominent as it should have been. It wasn’t that we that we were in anyway opposed to hiring women. When I was chair, we certainly thought about the possibility of recruiting prominent women and we would have, had we seen some really good opportunities. But we didn’t at the time, so no, we ended up not really addressing that issue and not really being pressed to address it by the university and society. It was a different era.

Zierler:

Right, that’s why I prefaced it with saying, you know, sometimes the 1980s doesn’t feel like very long ago and sometimes it feels like eons ago.

Appelquist:

Sometimes it feels like eons ago. Just to jump ahead a bit to 1992, there is a volume sitting on my desk over here that always stuns me every time I look at it. In 1992 after I finished being Chair, I was asked to serve on a Faculty-Trustee Search Committee that picked the next president of Yale. It ended up picking Rick Levin, an economist who stayed on as President here for twenty years. When the search was all over, everything that was done as part of the process was put together in a summary volume. All the interviews, all the opinions, etc. I got it out a couple of weeks ago just to look through it, and it’s quite interesting. It’s a 1000-page report. The word diversity does not appear once.

Zierler:

Yeah.

Appelquist:

Not once. It was 1992. Times have really changed.

Zierler:

They sure have. Tom, looking back, you know, within the culture that you were working in what do you see as some of your key accomplishments as chair?

Appelquist:

As chair I did a number of things. If I could point to one thing it was building the condensed matter theory group. We built up a group that became quite prominent. It became even more prominent as it evolved the years after I was Chair, but we got it started. A bit like Stanford we had both a Physics and Applied Physics department and we still do. And there were some animosities between the two departments at the time. Things like material science and solid state were banished to Applied Physics. The Physics Department itself did nuclear physics, basic atomic physics, particle physics. Those were the cores, and a growing amount of astrophysics later. In Applied Physics, there was a fair amount of experimental condensed metaphysics. But we had no theoretical condensed matter physics and so, one of the main things I focused on that during the time was building a condensed matter theory group. We also started to change the direction of the experimental nuclear activity, although that was not easy. Despite my fondness and good relations with Allan Bromley, he was not keen on that. But slowly it changed and it’s now much more focused on dark matter detection, neutrino physics, etc. We are mainly using the Wright Laboratory as a staging area for off-campus research. At that time, the retirement of Feza Gursey was on the horizon, so we had the opportunity to make an appointment in particle theory. We made a move into string theory, hiring Greg Moore from the Institute for Advanced Study in the early 1990s as a kind of replacement for Feza. But we didn’t have the resources to expand much in this area and he became pretty frustrated here. He left at the end of the 1990s and went to Rutgers where he has stayed. I made three outside tenured appointments when I was chair. One was Greg, and another was Charles Baltay, recruiting him from Columbia. He is still with us, not retired and quite active. He’s eighty-four and going full speed.

Zierler:

A great example of a particle physicist going into cosmology.

Appelquist:

Indeed, and he chaired the department in the 1990s as well. So, we did that. The other senior recruit was a very distinguished addition to the atomic physics group by the name of Serge Haroche. He’s French, originally from Casablanca, Morocco. He was a great addition to the experimental AMO group. We shared him with the Ecole Normal in Paris for a decade. Eventually his split life got to be too much for him. He went back to France and he won the Nobel Prize after he went back. So those were my three outside senior recruits when I was chair. And then building up condensed matter theory. After trying for a couple of years to recruit some prominent senior people whom we didn’t succeed in getting, we re-targeted at the junior level and brought in a couple of people who have become leaders in the field. Two of whom we’ve kept, one of whom, Subir Sachdev, we lost to Harvard about five years ago. I recruited Subir, Nick Read, and Doug Stone. They formed the beginning core of the group, and at that time as I said before, Shankar’s interests were changing into condensed matter theory. So, by the end of my time as chair I think we had quite a nice, condensed matter theory group and it has evolved. We lost Subir but we gained Steven Girvin a few years ago. Doug Stone is still here, and we have a couple of young, condensed matter theorists.

Zierler:

Was it nice to go back to being a civilian after your time as chair?

Appelquist:

Yeah, but then I ended up taking on an even more onerous job a few years later.

Zierler:

Right (laughter).

Appelquist:

So, I ended my chairmanship at the end of the eighties and then did various things for a couple of years. And then became Dean of the Graduate School in ’93. I did that for five years.

Zierler:

Was that something that you were looking to do or how did that play out?

Appelquist:

No, I wasn’t looking to do it at all. As I mentioned, I had served on this faculty-trustee search committee picking Rick Levin (my neighbor by the way, just down the street) as the next President. He had been Dean of the Graduate School for two years. And so that position had opened up and he asked me to step into it. It’s not something I was looking for. Not at all.

Zierler:

What were you looking to accomplish as dean? What was sort of the state of play at the time?

Appelquist:

That’s a complicated question. At the time, and up until about five years ago, there was no dean of the faculty--most universities have something called dean of the faculty looking over all of the faculty in the arts and sciences. Yale never had that. We had a dean of the undergraduate college and the dean of the graduate school. So, being dean of the graduate school was partly being a dean of the faculty, looking over faculty recruiting and faculty development and partly overseeing the graduate school and all of the graduate students. So, it was a complicated job with these two roles to play. Really a full-time job, much bigger job than being department chair. I did it for five years, restricting my research mostly to Saturday mornings. I had some great post-docs at the time, so I managed to stay active in research. But it was a very consuming job. The biggest issue at the time was that our graduate student teaching fellows were trying to unionize, and we had to fight it and we did, successfully. They’re still not unionized to this day although I think they will be eventually. That was one hat, overseeing the Graduate School. The other hat was sharing the duties of dean of the faculty with the Yale College dean. He was Richard Brodhead who went on to become President of Duke University for a number of years. So, Dick and I shared dean of faculty responsibilities. I handled the science departments. He handled the humanities and we split the social science division down the middle (laughter). It’s a little more complicated than that but roughly speaking that’s the way we ran things for five years.

Zierler:

Tom, over these many years of administrative service how well were you able to keep up with you own research?

Appelquist:

When I was chair I could do it pretty well because I stopped teaching. I made that decision and I had some good post-docs and good grad students and kept going full speed through the 1980s working on a variety of things that I’m still pretty proud of. It was much harder as Dean. My days were consumed by administrative details, and as I said, what I did was to devote Saturday mornings to meeting with students and post-docs. So, it was much harder, and it is one of the reasons that I decided not to go on with administration. I had some opportunities both here and elsewhere, but it just wasn’t what I want to do, so I managed to get out in 1999. I got back into research pretty well, but it was hard. If you’re in an upper-level administrative position at a university, it’s really a career change.

Zierler:

Yeah.

Appelquist:

You just have to decide if that’s what you want to do. And I did it for five years and then I said that’s just enough.

Zierler:

You rang the bell. You were done.

Appelquist:

I think so, yeah. Walked out the door.

Zierler:

Tom, how did you get involved with the Aspen Center?

Appelquist:

Like a lot of people, I started going to the Aspen Center in the summer as a young person. I first went in ’74. That’s where I started working with David Politzer. He and I were both in Aspen in the summer of ’74 and we started working on the application of QCD and asymptotic freedom to charmonium. We started working on our first paper there, trying to finish it up in the fall of ’74 but not quickly enough as I said before. So, that started in Aspen in the summer of ’74. I went there just like lots of other people to do research and interact with other people, three times during the 1970s: ‘74, ’77, ’79. And then, for various reasons I stopped going. We had another child, a daughter, born in 1981, and that made summer travel a little more difficult. So, we restricted our summer visits to nearby Brookhaven Laboratory. I then went back to Aspen in ’86 and ended up going every year from ’86 to 2017. I got hooked into it. In ’86, I was coming to the end of my chairmanship, getting close to it. Then in ’87, I was asked to join the Aspen Center board- the General Members do various things. So, I became a little more involved in its administration. And in ’93 I was asked to become president of the Center.

Zierler:

’93, ’96 you were president.

Appelquist:

Right, it’s a three-year term. So, from ’93 to ’96 I served as President of the Center and that was a lot of fun. The physics center was changing at that time too. By the way, diversity was becoming quite an issue at the Center.

Zierler:

Right.

Appelquist:

One of the best things we did was to build diversity among the General Members and the attendees. and I think we did a fairly good job. It’s continued, developing a lot more in the years since. But we started into it. We devoted a special week to it in the summer of maybe ‘94, called the “Week of Women” or something like that. We invited every prominent female theorist we knew. The Center is mostly a place for theorists. Not entirely but mostly. So, we invited everyone we knew and brought them all together for a week of both physics and just general discussion about how to improve the field of physics for women. That was quite a big event that time, and I think it went very nicely. In fact, I think it had a good effect on the field broadly and certainly on the Physics Center itself. Have you been to Aspen? Do you know the Physics Center?

Zierler:

No, I have not.

Appelquist:

One of the things we did was to mount a big fundraising campaign to build a new building on the campus. It’s a five-acre campus. That was quite successful. I did all of that work together with David Schram. Dave had been president and was chair of the board at the time, so Dave and I led the fundraising effort to build the new building, known as Smart Hall. I enjoyed working with Dave. He unfortunately died in an airplane accident in the late nineties, flying himself to Aspen from Chicago. Then I kept going as a member, a trustee and, you are doing various things. In the early 2000s I was asked to chair the Board of Trustees which I did for five years. I just I liked the place. I liked the interactions that were there. It was good for me as a young physicist. I thought I could give back to it a bit. I should also mention that in ’86 when I started to go back to the Physics Center, we had a teenage son at the time and a young daughter. We decided to buy a condominium in Aspen at the time. We brought a unit at the Gant, a nice Aspen condo complex, which we kept for thirty years. So, that kind of locked me in, hooked me into the Aspen community. I have not been going to the Center for the last two years but for almost thirty years it was quite a run. Met a lot of people, made a lot of friends. Did a lot of hiking in the mountains.

Zierler:

Well Tom, to round out our conversation I want to ask two last questions. First, I want to know what you have been working on in recent years just to bring a narrative up to the present. Then I want to ask you some sort of a future facing questions about where theoretical physics heads from here.

Appelquist:

I’ve worked on a variety of things over the years. But most recently starting about ten years ago I began a collaboration with a lattice gauge theorist by the name of George Fleming. George is the spouse of Bonnie Fleming, a prominent neutrino physicist. So, George came to Yale as a senior research scientist and he’s still here. I got quite interested in the behavior of quantum field theories other than QCD, theories that might have something to do with physics beyond the standard model. Not supersymmetric theories because they’re hard to deal with using lattice techniques but other kinds of theories that have conformal symmetry. Lattice techniques had by then evolved quite a lot and were producing exquisite results for QCD. So, we thought it would be good to apply these methods to other kinds of theories, more hypothetical theories, theories for physics beyond standard model. So, that’s what we started into. We began looking at a variety of different quantum theories, similar to QCD but mixing in various numbers of fermions to see what kind of behavior would emerge and using lattice methods to study these theories. That’s what I’ve been doing, along with some related things over the last ten years. Our work led to the formation of a multi-institution collaboration. We call it the LSD Collaboration which stands for Lattice Strong Dynamics, and it continues to this day, making use of large-scale computing facilities to explore various quantum field theories that just might have something to do with physics beyond the standard volume. Do they? The jury is still out. I am not a lattice professional. I describe myself as more of a consumer of lattice methods than a producer. So, that’s been my focus. Thinking about theories that might have something to do with physics beyond the Standard Model. They could be the basis for the formation of composite dark matter particles. They could even have something to do with explaining the Higgs boson and why it’s so light. One hundred and twenty-five GeV is quite light compared to what people thought it might have been. So, that’s the sort of thing I’ve been doing. Still focusing on quantum field theories but using lattice methods to study these theories where they get strongly coupled and where traditional Feynman diagrammatic methods don’t work.

Zierler:

So, Tom, for my last question because you were part of- you were a witness to and part of so many of the- you know, fundamental and exciting times in theoretical particle physics in the second half of the twentieth Century, using your powers of extrapolation where do we go from here? What are the most exciting things that you see in the future? Maybe, you know, when you give advice to younger people in the field about the things to focus on what do you see as the, you know, the top line stories in theoretical physics going into the rest of the twenty-first Century?

Appelquist:

That’s a tough question. Lots of papers are being written by theorists, and fewer by experimentalists because it’s difficult to do experiments these days. I’d say that there have been no major discoveries since 2012 when the Higgs boson was produced. Lots of work but no major discovery. I’m extremely interested in the question of whether the neutrino is its own antiparticle, whether it is a Majorana particle as opposed to being a Dirac particle. To this end, there’s a whole set of neutrinoless double beta decay experiments being mounted all over the world. That’s a really important issue. It’s a yes-no question about the nature of the universe whose answer will help provide important guidance. Will it open up a whole new era? I don’t know. My guess is that it’s a Majorana particle and that we’ll see double beta decay in the next generation of experiments.

Zierler:

But what’s it going to take to get there?

Appelquist:

It’s going to take large detectors, it’s a matter of scaling up the experiments that will be done and this work is underway. There are collaborations all over the world for these. That’s a very exciting frontier. Beyond that there is the high energy frontier. What’s going to happen at the LHC, and at higher-energy, higher-luminosity versions of the LHC? For a long time, the ideology of super symmetry dominated particle theory. People were convinced we were going to be seeing super symmetry, --so called low-energy supersymmetry and super particles. It hasn’t happened. No evidence for it so far. Will something open up beyond the standard model at the LHC at accessible energies? I hope so. But I don’t know.

Zierler:

It’s an interesting time because-

Appelquist:

So-

Zierler:

-there’s so much that’s still needs to be figured out and no clue of how to get there.

Appelquist:

There’s so much we don’t understand. We have this theory that involves nineteen adjustable parameters when you put it all together. And we have no clear understanding of how these parameters are related. I’d say the theory by itself doesn’t directly show us the way- I think it’s going to take experimental guidance. I really do.

Zierler:

Well, Tom, on that note I want to thank you for spending this time with me. It’s been a lot of fun talking with you and getting your insights and recollections over the years. So, thank you so much for this.

Appelquist:

It’s been very nice talking with you.