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Credit: Thomas C. Blum
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Interview of Thomas C. Blum by David Zierler on September 11, 2020,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/45466
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In this interview, David Zierler, Oral Historian for AIP, interviews Thomas C. Blum, Professor of Physics at the University of Connecticut. Blum recounts his childhood in Reno, Nevada and he describes his early interests in math and science. He describes his undergraduate work in aeronautical and astronomical engineering at the University of Washington. Blum discusses his job focusing on computational fluid dynamics at Boeing after college and he explains his decision to pursue a Ph.D. in physics at the University of Arizona. He describes his graduate work in lattice gauge theory studying under Doug Toussaint. Blum discusses his postdoctoral work at Brookhaven, where he continued to work on lattice gauge theory, and he describes his decision to join the faculty at UConn. He describes his ongoing interests in chiral symmetry, g-2 and QCD research, and he conveys his excitement over possible future breakthroughs in hadronic vacuum polarization. At the end of the interview, Blum conveys how much fundamental work remains to be done in physics, and as an example he raises what remains an open-ended question: what is the real structure of the proton?
OK, this is David Zierler oral historian for the American Institute of Physics. It is September 11th, 2020. I’m so glad to be here with Professor Thomas C. Blum. Tom, thank you so much for joining me today.
Sure, it’s a pleasure to be here.
OK, so to start would you please tell me your title and institutional affiliation?
Sure, I’m a Professor of Physics at--in the Department of Physics at the University of Connecticut and also the Associate Department Head for Undergraduate Affairs.
When did you take on that second responsibility?
Oh, that’s probably been about five years now.
And I’m sure because of COVID it’s extra exciting and rewarding for you.
Right, well there’s a lot of new challenges but things seem to be going pretty well at UCONNN right now and including in the Physics Department, so I think we’re pretty happy the way things are going.
Is UCONN taking a hybrid approach? Is it all online?
No, it’s a hybrid approach. There are significant number of students on--living on campus and going to classes but also, you know, a lot of the teaching is still online.
But the labs are mostly up and running. Those that need to be--have an in person presence?
Yeah, the--especially the research labs have been actually--have been open again since probably May and certainly over the summer and, yeah, things are going well.
Well, Tom, let’s take it back to the beginning. Let’s start first with your parents. Tell me a little bit about them and where they’re from.
Sure, my family comes from the West Coast. So, my parents both grew up in Eastern Washington and Idaho and my dad, he grew up in Pullman, Washington. He wanted to be a farmer but he didn’t have any land to farm, so eventually he wound up as an accountant and then working for the IRS. So, he was a manager in the IRS for his career. You know, we--they eventually moved to California to the Bay Area where I was born in Mountain View and eventually we moved--
I hope they bought real estate in Mountain View.
Well, we did but [laugh] we moved to Reno early on like in the early ‘70s.
But later we found out that the little house that we sold in Santa Clara, California, you know, was, you know, essentially worth like, a million dollars or something.
Something ridiculous like that. And my mom she was a mother and a housewife for many years especially when I was young. But when I was probably in middle school she decided to go back to school and become a nurse and she eventually became a--she was an RN for a long time and then eventually became a surgical nurse for the rest of her career. And now they’re both retired and living back in Idaho, you know, back sort of in the roots where they started.
Now, you grew up in Reno?
Yeah, I grew up in Reno and when my--sorry, when--so, I have a twin brother. So, we were very close and he’s actually an astronomer now that I’m a physicist. And I have an older brother too. We are all very close.
--I’ll get to him later--
Where is he?
-- but -- He’s in Tucson, Arizona. Yeah, so we grew up in Reno. When we were seniors in high school my dad took a job again with the IRS in Alaska and so, we finished out our high school careers in Reno and then went to the University of Washington in Seattle. Again, there was a connection there. My mom’s sister lived there and we had lots of cousins there. So, we, you know, we were familiar with the area and University of Washington was a good school, so we ended up going there.
When did you get interested in science and math? Was it pretty early on?
Yeah, ever since I was a young kid, yep.
Same with your brother?
Yeah and, in fact, we were first engineers. We went to the University of Washington and became aeronautical and astronomical engineers and that was sort of from a love of science and science fiction. And, you know, space and space travel and all that kind of stuff. And we both worked at the Boeing company for several years before we decided to go back and I decided to study physics and he was gonna go into astronomy.
Now, did you have a competitive relationship with your brother in terms of achievements in math and science?
Yeah, we were competitive but I think as we grow--grew older and especially through college and so on we were actually very supportive. We were more like a team than competitors. We pushed each other but we also helped each other a lot.
Now, aeronautical and engineering in Washington it much have been such a big feeder for Boeing?
Right. Yeah, that’s--I mean they have a very strong aeronautics department because of Boeing, right.
How much physics was there in the aeronautical engineering program?
Well, there’s a good dose of physics, of course. It’s all classical. There’s no quantum but there is certainly a big dose of physics. But that was sort of the impetus to go back because I always, you know, I found myself still asking questions like why is this? Why is that? You know, how does, you know, how does turbulence work? You know, fluid mechanic’s very interesting but there’s a lot of questions and engineers, you know, they are very interested people and they do ask questions but at the end of the day it’s applied physics and I, you know, I kept wanting to go further for the explanations. And so, decided to go back--
What kind of--
--and study physics.
--lab work did you do as an undergraduate?
Lab work, so we had labs in, you know, aeronautical engineering, of course, where we, you know, worked in the wind tunnels and so on. Actually, it’s interesting that you asked because one of the few lab--actual science labs I ever took was an advanced physics laboratory when I was a senior because I needed, you know, some--I needed to fulfill some requirement of an upper division laboratory. And so, I took an optics lab and I was just fascinated. Again, it was more of the, you know, really fundamental science and the way nature works. Especially at the micro--you know, the atomic[??] level. And I just found that very, very interesting.
Did you have relevant summer jobs or internships toward this degree?
No, I didn’t actually. And so, I worked through college. I wish--I worked as a bank teller which was incredibly boring and I loathed going to work every day that I had to go to work [laugh].
So, I really wish I had had some, you know, more experience outside of school but focused on science. And it turns out that, you know, I have two daughters or we have two daughters and they’ve gone into math and science and they have had opportunities like research experience for undergrads and so on that I think have been really helpful for them and enjoyable. I actually wish I would have had that opportunity when I was their age but, you know, I did OK anyway.
Now, Tom, when you went to get your masters was the idea that the masters would give you a leg up as you were gonna pursue a career in industry or were you thinking at that point that you might be on an academic type path?
Yeah, to be honest I don’t think I really had that much of a plan. I think it was more like inertia, like oh, you know, I’m not sure what I want to do. Maybe I’ll just keep doing what I’m doing [laugh].
So, Boeing was not a fore gone conclusion? You hadn’t--
--you didn’t have a connection there where a job was waiting for you at the end of graduate school?
No, no. I ended up working in a group doing computational fluid dynamics, so I did have a connection. One of the last classes I took is in the master’s program was on computational fluid dynamics and it was taught by--it turns out, I didn’t know at that time but one of the pioneers in CFD who actually worked at Boeing. His name was Hideo Yoshihara. And, you know, he was really good and he was sort of my in for an interview at Boeing and then I eventually got a job. But actually Boeing was never the plan it just--that just happened. I [laugh], you know, for reasons in my personal life I wanted to stick around in Seattle and so, that worked out. But I actually interviewed for other jobs too that weren’t for--that weren’t at Boeing.
What type of work did you do at Boeing?
So, I was in the computational fluid dynamics group, so it was actually interesting and, you know, I think there’s a lot of good work and a lot of good science at Boeing.
How much, Tom, was it a basic science kind of environment and how much of it was, you know, really directed towards, you know, what Boeing was there to do?
Well, the vast majority, of course, was engineering and directed at the bottom line for Boeing but the group that I was--the particular group that I was in and the person I was working for I actually had an opportunity to do more of, you know, basic, you know, research in numerical computation of fluid dynamics which was actually interesting. But I also learned [laugh], you know, ‘cause--so, Boeing had a computer division and they had a research group in the computer division that, you know, was responsible for a lot of the development of computational fluid dynamics in the company and I was actually surprised at first to learn but I--of course, I’m not surprised now that that almost that entire group was made of physicists not aeronautical engineers.
And so, I could see that the guys that were doing the really, really, at least from my point of view, interesting stuff, you know, they all had Ph.D.s in physics--
--not aeronautics. Of course, there were a few people in aeronautics who-- but also had Ph.D.s who were good but by and large the group was led by physicists.
This must have dove tailed nicely as an undergraduate when you were saying before about how the physics that you were getting, you always wanted to go deeper than that.
Can you explain a little, I mean I can take a guess, but in what ways is computational fluid dynamics relevant for Boeing’s bottom line?
Oh, it’s extremely relevant. I mean, you know, in many ways it’s like physics where we do experiments and then we compare with theory. And for Boeing it’s even more than that, right, because a lot of the design now is through computational fluid dynamics. You know, like, you--instead of putting a, you know, making a scale model of a wing or an airplane and putting it in a wind tunnel is extremely expensive. And if you can model that wing or that plane in a computer and, you know, compute all the various dynamics of the air flowing past the plane or the wing on a computer, it’s cheaper and in many ways there’s a lot of-- a lot more insight to be gained. So, you know, engineering is, especially for an airplane, it’s a lot of art and science and it used to be a lot more art and now it’s, you know, with the advent of huge computers and basic algorithms for, you know, computing the--solving the equations of motion for fluid around a plane it’s just--you can make a much more efficient plane. So, it’s extremely important.
I wonder, Tom, at what--at a certain point if you were looking at those physicists and you said, you know, this is what I want to pursue. I don’t want to sort of rise in the company here. Was that a gradual process for you or did you just sort of wake up one morning and say, you know, I’m going for a Ph.D. in physics?
I think it was always in the back of my mind to some point go back and get a Ph.D. It wasn’t clear what the Ph.D. would be in and, you know, I--like I said, I think Boeing was a very good company especially for engineers and especially if you wanted to build planes or, you know, do research in computational fluid dynamics. But in the end I decided that there was a lot--things that interested me more in physics than in, you know, aeronautical engineering. So, then I, you know, like I said, it was always sort of in the back of my mind to go back and get a Ph.D. and I think even in a place like Boeing if you wanted to advance to a certain level, whether it’s in management or whether it’s in, you know, the science and the engineering, it’s really the Ph.D.s who are, you know, who advance to the upper level and are able to do the things they really want to do. And so, I was gonna go back and get a Ph.D. and decided that physics was for me.
At that point did you have an idea? I mean given how strong you were on the applied and the experimentation side of things, did you give much thought to theory as, you know, as you were conceptualizing what graduate school would look like for you?
No, I was just interested in a lot of different physics. I really didn’t, you know, because I wasn’t a physicist, I wasn’t educated as a physicist I wasn’t thinking so much about theory and experiment. I was just thinking about different physics. You know, of course basic quantum mechanics. At that time the whole field of chaos was just starting and that very interesting and, you know, there’s just this--the whole field of high temperature super conductivity was just starting and those things just seemed like really fascinating to me.
And so, I was thinking--
Where did you apply for graduate school?
So, I--my choices were limited in the sense that I didn’t have a physics degree, undergraduate degree. So, I don’t think I had a really strong application and I actually ended up only applying at two places. One at the University of Washington and one at the University of Arizona because I had a friend down there doing a Ph.D. in Microbiology and I, you know, I liked Tucson. I thought the area was nice and this school was pretty good and I actually only got accepted at the University of Arizona, so that’s where I went.
[laugh] Easy choice.
Yep -- yep, but, you know, it worked out.
And so, in terms of refining all of your interests in physics how did you go about narrowing down in terms of what you wanted to focus on and who your advisor would eventually be?
So, again, like I said I was interested in many different topics and--but--and, you know, because I really didn’t have an idea of what I wanted to do when I started, I was just interested in everything and I think that--for me that turned out to be an advantage because I was able to focus on not just the topics but the people who were teaching the topics and the people that were really good and that I could see myself working for. And that, you know, that I admired because I could see that they were very talented and they were, you know, very helpful and they loved physics. And so, that’s really how I decided in the end what field to go into. I mean, you know, I did want to at some point I thought, you know, taking advantage of my computing background would be helpful but that was never the, you know, overriding thing. But that may have steered me a little bit towards my eventual Ph.D. which was in, you know, lattice gauge theory. But I have to say that the, you know, the really important aspect was that the people there doing high energy physics were really good. So, you know, my first advisor was Anna Hasenfratz. She was a young professor at Arizona and, you know, I was--I really enjoyed working with her and--
And what was her research at the time?
She was doing lattice gauge theory. She was actually studying the electro-weak theory not QCD. And I was just starting to work with her when she got an offer to move to Colorado to Boulder. And she decided to go to Boulder and she said, you know, “You can come to Boulder if you want. You know, I’d be happy to have you come with me” and I said, “No, I have to stay in Tucson.” You know, I had other commitments. You know, I had family commitments and so on. And then, it turns out that the other person there doing lattice gauge theory, Doug Toussaint who I had taken classes with for quantum field theory, you know and I thought he was spectacular, he had a position open and so, I was able to move over to work with Doug. And that was really, really good for me. And not just to get my Ph.D. but for my career down the road.
What was Doug’s style as a mentor?
Doug was pretty laid back. He was pretty--Doug is, you know, his brilliance shines through and he’s always ready to explain things and work things out and he was always willing to talk and communicate. But he was never, you know, really pushy or put a lot of pressure on me. It just kind of worked and you know, like I said he was just a really--he’s really, you know, one of the smartest people I ever--had ever met and it was just fun being around him.
Now, did you develop your dissertation topic as a sort of problem that Doug was working on that he handed it to you or were you more sort of developing it on your own and you would bounce ideas off of Doug?
Yeah, so it was very much more the former. You know, he--I can remember in the beginning he’s saying, “You know, well, here’s this proceeding from the last--from last year’s lattice meeting” you know, “Go ahead and look through this and see what’s interesting.” And, you know, there was so much stuff, you know, it was hard to get my head around. Eventually we decided on a topic that was very, you know, sort of fundamental to the whole enterprise at the time that was computing something called the beta function or how the coupling constant in QCD runs. You know, an issue of renormalization in quantum field theory but non-perturbative not in perturbation theory and it’s something that he was working on. Actually, he wasn’t working on the beta function but he was interested in QCD at finite temperature and you needed to know these kinds of things to do some of the calculations that he wanted to do. And so, he suggested that topic and I thought it was interesting and then we went from there.
What do you see as some of your principle conclusions in your own research as a graduate student?
So, the calculation we did of the beta function was the first ever calculation of the beta function non-perturbatively in QCD. So, that was with QCD with two flavors of light quarks and it was really a breakthrough in the sense that it allowed us to calculate for the first time the equation of state for QCD at finite temperature which is, of course, very important property of QCD at high temperature because, you know, the whole idea was people were interested in searching for the quark-gluon plasma. This idea that quarks would become de-confined at some high temperature and, of course, that was eventually found at RHIC at Brookhaven, you know, probably a decade later. Maybe not quite--yeah, probably about a decade later. So, this was a very important topic and it was the first time that would--that people were able to calculate the equation of state in QCD with dynamical quarks.
Right. Who else was on your committee?
Oh, boy [laugh]. Let’s see. So, Mike Schupp was an experimentalist on Atlas I believe. So, there was a large--see there was a large group of high energy experimentalists at Arizona at that time because they had come to Arizona to try to get the SSC in Arizona. You know, they brought this guy in, Pete Carruthers, who was very highly regarded theorist. You know, sort of in the time of Feynman and those guys and he was a very smart guy and they brought in all these people to try to get the SSC to come to Arizona. And, of course, it didn’t work out. It went to Texas but there was still a very good group there to do high energy--experimental high energy physics and Mike Schupp[?] was one of them. And so, he was on the committee. Let’s see, who else? The other-- it must have been that Ina Sarcevic[?] who was also a theorist was on the committee. Man, I’m blanking right now. There was-- I guess the reason I’m blanking--oh, one was probably my advisor when I first got there who wasn’t Doug, was John Donoghue who was an AMO experimentalist. And then there’s one more whose name eludes me at the moment. Adrian Patrascioiu.
We can come back to that when we edit the transcript. That’s fine.
Now, when you finished obviously Brookhaven was quite relevant. Is that definitely--
--where you wanted to go?
[laugh] No, again I didn’t really have a plan. Doug said, “Well, you know, in this game you’re gonna have to make--you’re gonna have to apply to a lot of different places and you just see what happens.” So, I basically applied to every place in the U.S. that had a lattice gauge theorist.
And Brookhaven, of course, was one of the very best places. Not just for lattice gauge theory but for high energy theory in general. But they also had, you know, Brookhaven’s a very historic place. You know, Mike Creutz was there, sort of the founder of the field at least in practice. You know, after Wilson, he’s probably the biggest guy who, you know, who started the field. But they had a strong group in lattice gauge theory, so that was definitely a very good place and I was, you know, I didn’t really know all that much about Brookhaven at the time. You know, again, not coming from a physics background there’s a lot of things I was very naïve about and--
--didn’t--just didn’t know. But Brookhaven was, in retrospect, it was another one of those things that, you know, really helped me in my career by going there as my first post-doc.
Tom, if we could just zoom out for a second. If you can describe sort of the broader state of play in lattice gauge theory in the mid 1990s, what were some of the major questions that were going on and what were some of the frontiers of research at that point?
Yeah, so to understand you have to remember or know that, you know, the theory of the strong interactions that is QCD, Quantum Chromo-Dynamics, which was, you know, basically came into being in the early ‘70s with the deep inelastic scattering experiments at SLAC and other places. It was the fundamental theory of the strong interactions but at low energies it was completely intractable. And by low energies I mean, you know, around the scale of the proton mass, one GeV or so because it’s completely non-perturbative. The coupling constant is large unlike in QED. So, in QED you can use, you know, the fine structure constant is one over 137. It’s a very small number so perturbation theory worked very well. But for QCD that’s not the case and even more importantly QCD has a property known as confinement, so, you know, hadrons are strongly interacting particles. Particles that interact via the strong force or QCD only come as neutral objects. I mean neutral in the sense of QCD not electric neutrality. And--which means that, you know, they’re made up of quarks and gluons that are bound together. They’re confined and in nature we don’t’ believe that a quark or a gluon can exist freely by itself. It always has to be bound together with other colored particles in a neutral state. And so, these two things make QCD extremely difficult to solve. And like I said, you know, people like Mike Creutz started doing simulations in QCD even without quarks, just gluons in say the mid ‘80s and they show that it had a lot of promise to be able to, you know, tackle this non-perturbative[?] regime of QCD. And so, by the time you get to the ‘90s there’s still a lot of promise but people are starting to realize man, this is a lot harder than we thought. And, in fact, you know, Wilson famously, you know, Ken Wilson, the father of the field, the father of lattice gauge theory, you know, he famously said that it’s just, you know, it’s just too hard. The computers are not big enough to do this problem and it’s gonna take, you know, I don’t know what he said, 50 years or something. And, you know, by the mid ‘90s people were starting to say, yeah, you know, it is really hard. So, the big questions were always sort of the big questions in strong interaction physics. You know, what’s the structure of the proton? How do quarks and gluons, you know, interact to create hadrons? And, you know, how does the, you know, how does QCD work at finite temperature. Again, this whole idea of a quark gluon plasma was a huge question that would--we were spending hundreds of millions of dollars on it at--RHIC and so on to, you know, to demonstrate experimentally. And then there was, you know, there was just a lot of hard work in the field to improve algorithms, so, you know, we couldn’t just depend on computers getting faster and bigger and better at a rate that would allow us to do the kinds of calculations we wanted to do. So, we had to make--we had to do our calculations, you know, smarter and smarter and smarter and that worked. And people did it and, you know, by the early 2000s people were doing realistic simulations of QCD. And now, you know, this is sort of the cornerstone of being able to search for new physics at large hadron colliders and in precision calculations like muon g-2 and flavor physics. You know, without the lattice we couldn’t do the comparisons. We couldn’t do the standard model calculations.
Tom, I wonder if you can talk about, you know, working in a theoretical group at a national laboratory in some ways you could be anywhere. You know, you could be on a college campus, you could be at a research institute, and in some ways it’s really important for you to be, you know, in a national laboratory environment where there is a very strong and cutting edge, you know, experimentation sort of, you know, environment. So--
--in what ways were--was the theoretical group--in what ways did it benefit just from physically being situated in the same area?
So, there--you know, there are several ways. Some were, you know, like directly beneficial. Like, you know, Brookhaven because there was a large group of lattice gauge theorists, you know, post-docs, and senior staff members that was an incredibly helpful environment, right? You saw these people every day, you could talk and collaborate and so on which is not necessarily true in a university setting. You know, on a university setting if you have two people doing lattice gauge theory, that’s already really good, right? I mean two faculty people and also at Brookhaven, you know, you had big super computers. You know, we were very fortunate when I first came to Brookhaven maybe a few years after I got there, you know, TD Lee started the RIKEN Brookhaven Research Center which had a strong component to do lattice gauge theory. And because of TD Lee and people at Columbia like Norman Christ who came along and Bob Mawhinney[?], we were able to get special purpose super computers for our--for lattice QCD at Brookhaven National Lab and that was incredibly important. So, you know, having the resources both computational and in people around us was very good. And then broader than that, you know, just being in a large theory group that you got to interact with every day. You know, we used to eat lunch together every day, the whole theory group. You’d have seminars several time a week, colloquia, you know, all sorts of things, so it was fantastic to
Who were some of your key collaborators both at the post-doc level and at the senior scientist level?
So, when I first got to Brookhaven and, you know, ever since I’ve worked with Amarjit Sony, so he was very important collaborator for me. And like I said, you know, the people that made up the RBC--well, so we were--I was at the--eventually I was in the high energy theory group at Brookhaven to start with then I moved over eventually to the RIKEN BNL Research Center. We were all in the same area, so it didn’t really matter. It was just sort of a, you know, who was paying you at the time. But --
Were you working with Sam Aronson at all at that point?
No, Sam’s an experimenter and later became the head of the RBRC and then, of course, the Director of Brookhaven. So, I knew Sam but I never really worked with Sam.
So, you know, Mike Creutz was also an informal colleague and collaborator, so I used to talk about lattice gauge theory all the time with Mike Creutz especially in the early days when we were thinking about doing Domain-Wall Fermions. I mean, Mike was a huge resource ‘cause he was also interested in chiral fermions in the lattice. And like I said, my colleagues from Columbia Bob Mawhinney and Norman Christ and then there was a bunch of post-docs that came through that were really good collaborators for me. Of course, Taku Izibuchi who was a post-doc there and then later came back to be a staff scientist. I continue to work with Takuto this day. Kostas Orginos was a post-doc at Brookhaven. We worked together a lot. There was--one of the nice things about working at Brookhaven in the RBRC was there was this steady stream of young researchers coming from Japan who would do post-docs and then, of course, they would go back, so another important colleague was Shoichi Sasaki. So, he did a lot of really neat stuff that we worked on together on nucleon structure and nucleon spectroscopy. You know, there’s so many other people that--Yasumichi Aoki was one. I didn’t work with him but Rob Pizarski was always fun to talk to. I mean he’s a staff member who was in the high energy theory group and then moved over to the nuclear theory group. Dima Kharzeev, Raju Venagopalin, Peter Petreczky, Frithjof Karsch. There were just--like I said there were so many people and so--
It sounds like you had a great time overall there too?
It was very good, yep. Yeah--
Now, when you became associate physicist, was that sort of dipping a toe in the water about perhaps pursuing a career at Brookhaven?
No, it was--my career was very tenuous at that time, so I’d finished a five year fellowship at the RBRC and I was still looking for a faculty position. And so, that was kind of a stop gap that they provided me and then eventually I got this faculty job at the University of Connecticut. And by the way, oh, I should mention Larry McClarren. He was then the director of the RBRC. He was immensely helpful especially in, you know, boosting my career at that time.
--was the job market like in the, you know, the early 2000s? I mean it’s always terrible. The answer is it’s always terrible. The question is how terrible was it?
I don’t know. It’s hard to say. I mean, you know, for me it seemed terrible [laugh]--
--‘cause it was very hard to get a job. I interviewed at many places but was just very hard to get a job. I think now in some ways it’s a little bit better for lattice gauge theorists because I think there are more faculty positions designed for lattice gauge theory and not just high energy physics in general which is a testament to how, you know, sort of important and mature lattice gauge theory is now as a field. I don’t know. I don’t know if it was any worse or any better than in, you know, other times, but like you said, I mean it’s--there’s a lot of people. There’s a lot of smart people out there and not that many jobs so…
Tom, I know you’re gonna say again that there was no grand plan. I get that.
But I wonder to the extent that you would think of bridging your Ph.D. work with your coming academic work at UCONN in what ways did your time at Brookhaven sort of make you switch gears from your dissertation topic and in what ways was it sort of, you know, one smooth track to what you’ve been doing, you know, over the past 15 years as a professor?
So, there’s a couple of things. One, of course, I still do lattice gauge theory, so, you know, I’m still in the field of lattice gauge theory. But my interests have changed a lot. You know, like I said, early on in the Ph.D. and even when I arrived to Brookhaven, you know, finite temperature QCD was a big topic and I was interested in that and I did work in that. But I pretty quickly got into this idea of chiral fermions. You know, chiral fermions on the lattice was always a big thing for several reasons. One, the conventional ways of discretizing the Dirac operator, so this fundamental operator that describes fermions that, you know, we use in quantum field theory, it breaks this fundamental--the way you do it when you take it from the continuum and put it on a discrete lattice breaks this fundamental symmetry in nature called chiral symmetry. And chiral symmetry has a lot of important consequences for QCD. It’s why pions are light and, in fact, if quark were massless, pions, you know, there would be massless hadrons in the world. That’s why pions are almost massless but not quite massless. So, there’s incredible consequences from chiral symmetry and our simulations in QCD at the time were defective in some ways. I mean it’s not that they couldn’t be overcome but it was difficult to overcome this breaking of chiral symmetry. And if you could come up with a formulation where the chiral symmetry was preserved even when the lattice spacing was non-zero, that would be a big advance. And so, that really interested me. Not only that, there was some very deep theoretical issues involved with chiral symmetry and especially as it pertains to chiral gauge theory which would be like a fundamental theory of nature like the weak interactions. So, there was a lot of interesting stuff going on and this idea of Domain-Wall fermions just came about, you know, was published by this guy David Kaplan at the University of Washington. He was also a very prominent high energy nuclear theorist and I actually worked on this a little bit when I was still a graduate student, sort of at the end after I’d sort of finished my thesis with one of the post-docs who was at Arizona, Leo Karkkainnen. And we had a great time working on this, you know, this--I mean, you know, it’s kind of interesting because this chiral--this formulation added an extra fifth dimension, right? I mean that sounds really cool and, you know, in some ways you can think of this extra fifth dimension as physical, in some ways it’s just a trick to, you know, maintain the chiral symmetry. But it was very interesting and so-- at some point Soni and I published our first papers on the Domain-Wall fermions and it sort of just exploded at that point--
--you know. And so that was one thing. Another thing towards the end of my tenure at Brookhaven I got interested in, you know, the hadronic contributions to g-2 mostly because, you know, people at Brookhaven were working very hard on the measurement of g-2 and the hadronic contributions represented the most difficult part of the theory calculation the part that was most uncertain. And so, that also took off and that sort of led--that actually helped a lot I think getting my eventual faculty position at UCONN. You know, the--‘cause this was a very important topic.
When you started a Connecticut what was the ongoing appointment with Brookhaven? In other words, was this like a 50/50 appt? How would you --
--split your time?
Yeah, so this is another great thing that TD Lee started at the RBRC. You know, soon after the RBRC was founded he started this program that they called the RHIC Fellow’s Program and it was basically a bridge program where RBRC would pay half the salary for the faculty member at another institution and the idea was to seed faculty positions in non-string theory positions around the country because, you know, he felt and others felt that, you know, at the time string theory was like, you know, completely taking over the theory landscape and he didn’t think that was right. He thought that there should be positions available for people doing other things. And, you know, one of the things was strong interaction physics which was, you know, very-- a huge challenge and still is. So, he stared this program and every year since probably 90, I don’t know, ’97 or maybe ’98 or ’99 there have been several of these fellows that are half time at Brookhaven or the RBRC and then half time at some other institution. And so Connecticut just became one of those and that’s how I got that, you know, I got that position. So, for five years I was half time between UCONN and Brookhaven and then the idea is that after the five years you come up for tenure in the institution and then you become full time at the institution.
Was this a unique arrangement that you put together or there were others who had this similar kind of appointment?
No, it was something that, in fact, Brookhaven or RBRC is still doing.
So, now we have another junior colleague at Connecticut, Luchang Jin, who’s on the same deal and like I said other places not just UCONN and the RBRC but other places like UCLA, University of Arizona, Stony Brook University, Iowa or Iowa State, you know, many places.
What are if any the teaching and publishing expectations during those first five years?
Well, the expectations are very high [laugh] just like--
-- so you’re teaching?
-- just like any other--
You are expected to teach when you’re on this five year plan?
Yeah, but you have a half load, so instead of, you know, you have half load but you are expected to teach and the research expectations are very high just like they would be for any other faculty member to publish and get grants.
Did you take on graduate students right away?
Yes, it was a big challenge [laugh].
[laugh] Tom, I’m curious what your impressions of the Department of Physics at UCONN were when you first sort of got your sea legs there.
I think my first impression it was a very collegial department, that everybody got along and you know, it was just a nice place to work. And to be honest [laugh] I was just very thankful that I had a position and at a good research university and, of course, you know, here, you know, Storrs is a dairy farming town. You know, sort of halfway between Boston and New York and I just thought it was a great place to be both to do physics and a raise a family and, you know, just live.
How if at all did your research change when you moved over into full-time after those five years? In other words just simply by virtue of not being at Brookhaven half of your time?
I don’t think the research changed so much because of the move. The research I think naturally changes as you progress between more of a, you know, a manager. You know, I still do a lot hands on stuff but not like when I was a post-doc or a graduate student, right? I mean there’s just so many other things to take care of between teaching and advising graduate students and post-docs and service. You know, there’s a lot more things, you take on more responsibilities including various different physics projects and--but, you know, research wise it’s-- it hasn’t changed a lot because, so we have this thing we call the RBC collaboration which stands for RIKEN BNL Columbia collaboration which started when we started the RBRC at Brookhaven. And it’s just a group of lattice gauge theorists who work together on similar problems to develop-- and develop our own code and so on. And so, I’ve continued to work with that same group of people, the people of Columbia, people of Brookhaven and now people at UCONN. So, in that sense it hasn’t changed so much.
And if you could give sort of a broad overview over the past 15, 20 years what’s the state of play in quantum chromo-dynamics nowadays? In what ways has it changed from when you first got involved and in what ways are the same fundamental questions still being pursued?
So, it’s much more now just a tool in our, you know, toolbox to do the kinds of calculations that we always wanted to do. So, you know, it’s really become a tool where we can do realistic simulation. So, we can have, you know, physical quark masses, we can have big boxes and small lattice spacings, we can take the continuum limit, we can take the infinite volume limit and that allows us to do things like compute the hadronic contributions to g-2. Which are, you know, for the hadronic vacuum polarization we have to get errors in our calculations that are on the half percent level to be relevant to compare to experiment and to find new physics. And we’re actually not quite there yet. We’re more like at that one or two percent error level but we’re gonna get to that half percent level in the next year or so. And that’s just incredibly important because it’s the difference between yeah maybe there’s something going on and yes, there is new physics or no, there’s not new physics. It’s just the standard model.
What’s gonna happen in the next year or year and a half? What advances are sort of on the cusp?
So, we’re just getting, you know, it’s just a lot of straight forward work to make smarter and smarter measurements that are happening. We just have to, you know, we have to finish the analysis. Computers are still getting bigger and still getting faster so that helps. And it’s just, you know, it’s just a lot of, you know, keep working on the problem until the errors get smaller. It’s not like there’s a big--there’s a lot of innovations but there’s no, you know, giant change between one way of doing things and the new way of doing things.
Tom, I’m struck by an analogy that you wrote on your faculty page where you say that, you know, in principle QCD describes all of nuclear physics in the way that quantum electro-dynamics describes solid state physics. Can you flesh that out a little bit what you mean by that? It’s very intriguing.
Yeah, so I mean, you know, nuclear physics if you like could be, you know, you have these things called protons and neutrons, right? And protons and neutrons are made up of quarks and gluons just like atoms are made up of nuclei and electrons, you know, that are stuck together by the electromagnetic interaction. Well, protons and neutrons are built from quarks and gluons and, you know, the gluons bind the quarks together into this object we call a nucleon. Either a proton or a neutron.
And it’s their binding quality that’s why, of course, they’re called gluons?
Yep, exactly, and then you can take all these protons and neutrons and you can start stacking them up together, right and you get nuclei. And you can get, you know, you can go from a deuteron, say a proton and neutron. Sort of the most simple, non-trivial nucleus we have except for the proton, you know, for a hydrogen atom and you can go all the way up to these very heavy nuclei, right? And so, that’s sort of the analogy. That’s like, you know, putting atoms together to make some material or atoms together to make molecules and so on. So, it’s just another level of, you know, it’s just another regime but it--you know, if you go to a small enough distance scale everything’s quarks and gluons not protons and electrons.
Now, the work that you do on super clusters at Fermilab and Jefferson Lab what’s the difference between super clusters and the work that you do on super computers at Argonne and Brookhaven?
So, there’s not a lot of difference now.
Where did those names comes from? What is a super cluster?
I’m not sure that--I [laugh] don’t use the terms super cluster but I could imagine what you mean. A super cluster would just be, you know, a bunch of, you know, basically nodes that are maybe, you know, in your laptop you have one or two nodes, right? A computer, CPUs and a cluster is just a bunch of them where they’re all connected with very high-speed network, right? And if you put enough of them together you get a very powerful machine but that’s sort of the idea behind today’s super computers. You know, it used to be that a supercomputer, like when I worked at Boeing, Cray made super computers but they’re very different from the super computers we have today. They concentrated on making one node very, very powerful and very, very fast or a few nodes, right? But you did your calculation only on a few nodes that were very, very fast. Then the idea started growing that well, you don’t need really fast nodes. You just need a lot of nodes that are pretty fast. But once you have a lot of nodes that are pretty fast and you want to break up your problem then you have to make sure they talk to each other in an efficient way. And so, then you had to have these interconnects that were very efficient and, you know, people develop those. And so, then, you know, sort of these things have sort of--there used to be a sharp-- a more sharp division between what we would call a supercomputer and a cluster. They’re now kind of blurred and now, you know, now you have things like GPUs which are even faster, you know, computing elements or nodes or CPUs but they’re called GPUs ‘cause they’re, you know, gaming processor or graphical processor units that were supposed to be really fast to do real time graphics for gamers, right? But again, if you have a lot of these they don’t have to be very smart. If they’re just fast, [laugh] you can do a lot of calculations on them. And so, you know, now there’s clusters of GPUs or, you know, there’s -- you have CPUs and GPUs on the same chip and then you have many of them that you have enough of them, you know, you have a supercomputer.
Tom, while we’re defining terms with super clusters and super computers where is quantum computing? Where is that in all of this?
[laugh] Well, computing is another whole thing entirely and you know, I’m not expert on quantum computing.
Is it relevant for your work?
No, it could be eventually and there’s a lot of people now in the field of lattice, you know, there’s a lot of lattice gauge theorists studying the kinds of algorithms that would allow us to work with a quantum computer. So, there is a lot of promise. I mean, if we did have a real quantum computer, we could do a lot of things, lot of calculations that we at the moment we cannot do. Like, I said--like we were talking about before this idea of computing all of nuclear structure from the quark-gluon level. That’s extremely difficult right now with the computing resources we have. But if you had a quantum computer, you might actually be able to simulate, you know, a very massive nucleus from the quark and gluon level. I mean but that’s a very difficult problem right now. But, in fact, it’s, you know, except for maybe something like helium or you know, you get beyond helium and it’s really, really hard to do a lattice QCD calculation. But if you got a quantum computer, that’s possible. Things like QCD at finite density. So not where you’re sort of simulating the vacuum and what happens when a particle goes through the vacuum but if the particle actually goes through matter. You know, nuclear matter that’s extremely difficult to calculate and, in fact, we don’t really have a way of doing that at the moment. But if you had a quantum computer, maybe that becomes tractable.
Tom, another very broad question and I’ll narrow it to your field in your research in general. We all know, of course, that the standard model can be and needs to be improved upon. How might QCD provide that pathway and what’s particularly exciting about your research, you know, in that pursuit?
So, first off the possibility that we find new physics in QCD is not very likely. Where QCD comes into play is it’s an integral cornerstone of the standard model, right? You have QCD, QED, and the weak theory. So, those three out of the four fundamental interactions.
Where’s gravity, of course, that’s the big question.
Well, so gravity at the level of, you know, say experiments going on at the large hadron collider gravity just doesn’t play a role. You know, you have to get to very small distance scales around the Planck scale before quantum gravity becomes important or you know, maybe inside a black hole or something like that. But--so QCD is a fundamental part of the standard model. So, if you’re looking for physics beyond the standard model first you have to know what the standard model is. You know, what does the standard model say when I do my experiment what I should get out. Well, there’s a definite prediction from the standard model and QCD plays part of that. So, our job is to be able to do calculations in QCD with such accuracy, such precision that we can compare the standard model to experiment and hopefully the errors are small enough that if there is a difference, we’ll be able to detect it. And that’s really what’s going on, for example, with this--with the nuon anomalous magnetic moment. The experiment that’s going on right now at Fermilab to measure this quantity--this thing called-- that people call g-2 but it’s really the magnetic moment of the nuon. If we calculate that very, very precisely, there--you know, there’s a hint already that there’s a discrepancy between the standard model and experiment. The two don’t quite agree. They’re off by about somewhere between three and four standard deviations. That’s the [laugh]--that’s just on the cusp. That’s not enough to really say you discovered something but it’s enough to say this is interesting. This might be a place where there’s new physics and so, the experiment is gonna reduce their error by a factor of four and we need to reduce it, or we need to make it smaller. And like I said earlier the leading, you know, the most--the dominant errors, the biggest uncertainty comes from these hadronic contributions and the only way we can calculate them from first principals is using lattice QCD. That’s not the only way we can get the answer. We can also use experimental data from other experiments to figure out what the contribution is. And those two ways of doing the calculation are completely different and if they agree then we have real confidence in the standard model result and then we can compare it to experiment. And if they disagree, we can really believe that it’s new physics and not just that we didn’t know how to do the calculation. So, that’s the exciting thing. I mean it’s a hunt for new physics. We--if we find it that’s great. That means it is some new physics. Either somehow different but we know--we would know that there has to be something new that we don’t’ know about yet.
Tom, what are some of the --
But that’s a whole other--
What are some of the broader--
OK, go ahead.
--theoretical basis for searching for these new physics. I mean in other words you have to have a pretty good hunch that there’s new physics out there to discover, so to step back a little bit what are some of the theoretical basis for, you know, that underpin all of this research?
So, there’s lots of different ways to look at it. One thing that people have thought for a long time is, you know, so, quantum field theory is the fundamental language we use to describe nature. Our most fundamental theory of nature which is the standard model but we know that the quantum field theory will break down at a high enough scale, at a high enough energy scale. So, you know, that already tells us that there should be--if the theory works the way we think it works, there should be some new physics at a certain scale and that scale is maybe a TeV somewhere around the scale of the large hadron collider right now. There are other things like, you know, dark matter, dark energy, you know, the matter, anti-matter, asymmetry of the universe. I mean these things we can’t explain with the standard model. You know, we can’t--there--we think there must be new physics to explain those because we can’t explain with the standard model. So, there are sort of these issues that we know will occur at high enough energy scale that cannot be solved by the standard model. So, to have a consistent mathematical picture that all hangs together there has to be some new physics.
Now, when we’re talking about higher energy is this a case where it would have been great for you if the SSC was completed or if the ILC remains on track?
Absolutely, if the SSC had been built, you know, we would have these things earlier. Either discovered new physics or we’d be moving on to other--you know, to even higher energy to find new physics. So, you know, the LHC has done a super job. They discovered the Higgs particle and that was the capstone of the standard model. But that would have been done already, many years before if the SSC had been built. Fairly have gotten to much higher energy than the LHC has now. I don’t think we would have known, you know, more than we know now but assuming that we don’t see anything new at the LHC in the next couple of years then we would sort of be in the same position. But, you know, if they do discover, you know, if they discover a heavy super symmetric particle at the LHC in the near future, well, if the SSC had been around, you know, we would have already discovered that.
Right. Tom, can you talk a little bit about, you know, just to bring the narrative up to the present who are some of your key collaborators, you know, in the last five years? Who have you been working with on a sustained basis?
So, the key collaborators have been--some of the collaborators again that I’ve been working with my whole career. So, Soni, Christ, Taku Izibuchi. One of the key collaborators especially in the nuon g-2 work has been a new colleague at UCONN, Luchan Jin. with Norman Christ at Columbia and then went to Brookhaven briefly and then to UCONN. So, he’s been incredibly--he’s been an incredible collaborator. And Christoph Lehner. Let’s see we, you know--
Tom, I’m not sure if you could hear but you cut out. Oh, there you are.
Yeah, the connection’s not so good. So--
The last thing I heard was tremendous collaborator.
--also have some collaborators in the UK. Yeah, that’s Luchang and that’s true. Another really important collaborator is Peter Boyle. There’s a whole host of my RBC colleagues and RBC is a pretty big collaboration now and Antonin Portelli. I actually started a collaboration separate from the RBC collaboration for some of these calculations for nuon g-2, so Martin Golterman at San Francisco and Santi Peris in Barcelona, Christopher Aubin in--at Fordham in New York, working with some people in Mainz in Germany. Hartmut Wittig, Harvey Meyer were other, you know, they’re prominent lattice gauge theorists in Europe. I hope I’m not forgetting anybody. Like I said, the--you know, I’m still very much a part of the RBC collaboration. Oh, I did start working also with people at Fermilab. Andreas Kronfeldand a post-doc there named Will Jay recently. So, the big thing in the U.S. now as far as the DOE is concerned and really the high energy theory community is the neutrino physics, right? I mean the big experimental program in the U.S. is the neutrino experiments especially this thing called DUNE which is gonna be built at--it’s a deep underground neutrino experiment where they’re gonna build this big neutrino beam at Fermilab and fire it off to South Dakota. And so, that’s a big thing in the U.S. and so, I’ve started working on some nucleon physics. Again because it’s nucleons and how neutrinos interact with protons and neutrons, you know, lattice gauge theory can be informative. So, we’re working with people at Fermilab on that.
Tom, I want to switch over to mentorship and teaching for you. First, on the graduate side of things who have been some of your most successful graduate students at UCONN?
So, I haven’t had a whole lot of graduate students. One of my first graduate students Ran Zhou he did well. He went to--sorry, he went to Indiana to work with Steve Gottlieb as a post-doc then he went to Fermilab post-doc. And now I think he’s working at a software company in Silicon Valley. And I just had another graduate student Chung Tu[?] who after he graduated and he had a job at a software company in Atlanta. And then another graduate student Dan Hoeng[?] who is actually, he did part of his Ph.D. with Taku and me at Brookhaven and he stayed as a post-doc at Brookhaven for a year and now he’s taken a post-doc in lattice gauge theory with the Michigan State group. And I guess that’s it. I had another grad student when I first started, Shaumitra Chowdhury who did some of the original work on the hadronic contribution to g-2 who was teaching Connecticut and I think now he’s somewhere in Brooklyn or Queens I think, you know, teaching at a four year college. Are you still there?
Oh, OK. You weren’t moving.
And on the undergraduate side of things, Tom, I’m curious what kind of courses do you like teaching the most to undergraduates?
I guess I like teaching quantum mechanics. I--because I’ve been the associate department head I haven’t done a lot of teaching. I teach a half load, so I don’t do as much teaching and for whatever reason I’ve been teaching graduates. Actually when it comes to teaching graduates or undergraduates I like teaching quantum mechanics and I like teaching statistical mechanics. Statistical mechanics has a lot of overlap with lattice gauge theory actually. Just the mathematical formalism is very similar. But I also think statistical mechanics and thermodynamics is very interesting. But physics. I like the--I like teaching, you know, I like teaching them all really.
It harkens back to when you were thinking about graduate school and you wanted to take it--
--all the physics.
Right. Yeah, it’s--yeah, it’s just interesting. It just interests me in the--you know, the question, you know, why are we here? Where did we come from? How does it work?
Tom, on that note of, you know, really big questions since we’ve gotten to, you know, right up to the present in your research I want to ask for my last question how much appetite you have personally for, you know, pursuing a grand unified theory? If you see your research contributing to that effort, if you think that that’s a realistic effort and if not, how, you know, how do you bound your research agenda in terms of keeping it broad enough so that it’s exciting and it naturally goes wherever it goes but not so broad that, you know, it’s impossible to define your parameters and, you know, conduct experiments or conduct, you know, theoretical work that’s-- it’s simply too all over the place to actually, you know, achieve something concrete. I wonder if you could comment on all of that?
Yeah, so unfortunately half of that was garbled in this poor Ethernet connection but I think I got the jist of the question. You know, how do I focus my research so it’s, you know, not too narrow so it’s not interesting and not too broad, so I don’t get anything done. And, you know I--
And the beginning part of that was just how much appetite you might have for thinking about a grand unified theory and whether or not you see your research as relevant to that or even if such a pursuit is worthwhile.
Certainly, I think the pursuit of that is worthwhile because that goes back to the, you know, the heart of the matter. You know, how does it all work and why are we here. I think my research touches on that a little bit in this whole idea again of searching for new physics because the, you know, the more new physics we find it’s going to warm the question of, you know, is there a grand unified theory or not and if there is, what is it? Where is it? You know, what energy scales and so on. So, that’s certainly relevant. I mean just the search for new physics. I mean the search for new physics is sort of a way of asking the question in a different way, you know, but it’s still asking the same sort of question. What is--how does the universe really work at its most fundamental level? On the other hand, you know, there’s a lot of interesting physics that doesn’t have to ask the very fundamental questions. Even just, you know, how does the world work in a more mundane way or not necessarily mundane but you know, again, how do we get nuclei? You know what is the real structure of the proton? You know, these are very interesting questions too and just trying to figure out how do I do those calculations. You know, not just asking the question but then the question is how can I actually answer the question. And that’s also very interesting, you know, that--and can be very rewarding. So, you know, in a broader sense I think one of the--I think and I’m not the only one, you know, thinking about the more broader questions is something we all like to do and something that we don’t have enough time to do, right, because our days get filled up with all sorts of other things.
You know, like today literally I’ll be talking on Zoom the entire day starting with you and then we had this thing called Snowmass. Do you know what Snowmass is?
So, I’m very involved with Snowmass. I have a Snowmass talk or call right after this then I have a thesis defense right after that, then I’m talking to a, you know, I’m--I agreed to mentor a high school student for this semester. So, you know, so the whole day literally will be zoom. They’re all important, they all, you know, they’re all things that need to be done. But that means it’s less time to sit around and think about, you know, grand unified theories.
[laugh] Well, Tom, on that note the last thing that I want to do is contribute to your Zoom fatigue and I’m glad we were able to wrap up with that last question. It’s been a lot of fun talking with you and I want to thank you so much for spending a little bit of your precious time with me.
Sure, it was my pleasure. Thanks for inviting me and, you know--