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Courtesy: Glennys Farrar
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Interview of Glennys Farrar by David Zierler on July 14, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
In this interview, Glennys Farrar, professor at New York University, discusses her career and shifting interests within physics. She details her time as an undergraduate student at University of California, Berkeley. Farrar discusses how she chose to attend Princeton University for graduate school to further her interest in particle theory. She discusses her thesis research which calculated the rate of decay for The Lambda under the mentorship of her advisor Sam Treiman. She describes the social isolation she faced within the physics department as the only woman. Farrar discusses her time as a postdoc at Caltech and details her research on the pion decay constant, as well as pioneering the field of phenomenological supersymmetry. Additionally, she speaks on the sexism she experienced while at Caltech. She details her experience at Rutgers University where she worked on Hadron Physics. Farrar discusses her time at New York University as Chair of the Department of Physics and her efforts putting together a strong faculty. She also details her growing interest in cosmology at this time and describes founding the Center for Cosmology and Particle Physics. She also speaks about her work on the stellar tidal disruption phenomenon. Lastly, Farrar notes her excitement for the increase in computation power in the future and reflects on the merging of different fields of physics.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is July 14, 2020. I am so happy to be here with Professor Glennys R. Farrar. Glennys, thank you so much for being with me today.
It's a pleasure for me too.
Wonderful. Okay, so to start, can you tell me your title and institutional affiliation?
I'm a collegiate professor of physics at New York University.
And what does the term "collegiate" mean?
(Laughter) It's a good question. I think they were just trying to bestow some modest recognition and didn't have enough named chairs to go around (laughter). And so, I think that's all it is. There was a small epoch when it entailed some sort of special seminars with undergraduates, but the funding for that disappeared but the title didn't.
I see. I see. Are there other collegiate professors at NYU?
Yes, there's something like twenty of us, I think.
Okay very good. All right, well Glennys, let's start, let's take this right back to the beginning. Let's start with your parents. Tell me a little bit about your parents and where they are from.
Well, my dad was in the army. He graduated from Purdue during the depression and was in the army reserve, and so when World War II came, he started——"enlisted" is not the right word since he was ROTC, but he joined in. He did his degree in electrical engineering, but due to the Depression he worked as a truck driver for a number of years before he could get a job using engineering. I realize that there are many things about me that reflect both my parents. My father was in the army for about twenty years, but was in the Ordinance Corps, so he wasn't involved with troops. We moved around when I was a child. We moved around every couple of years. My mother had four brothers and she was a really energetic, optimistic person. She didn't get a college degree because she had to stop after two years and work to try to put her brothers through school. She mostly, early in her life, worked at a newspaper, very small-town newspapers, and she did things like sell advertising copy. Then during the course of moving around the world with my father in the army, she didn't usually have the opportunity to have a job, so she'd volunteer and be involved in different activities. We lived in Japan and we lived in France. I was in high school in France, and then in a summer program at the Sorbonne, I met an American physics professor—from Boston University I think—who was taking the same summer program on French culture that I was, and we got acquainted and he learned that I had just gotten an 800 on my SAT that I took as a junior for practice. And he said, "Oh, you know, go ahead and apply for university, even though you still have your senior year ahead of you. You can just skip it." At that point, my dad was just retiring and we were going back to the States, but we didn't know where we were going. And the idea of going to high school for one year somewhere new was not so appealing, so I applied to Harvard and to Berkeley, in August, on his advice. I guess Berkeley had so many students, they more or less said, "Well, we can always fit in one more, come along." Harvard, however, said they didn't have any more room, but I could come in January when a space would open up. But Berkeley was right away, and it was going to be much cheaper, so that settled it. I moved to Berkeley, then my parents moved to Berkeley too, to keep an eye on me, I think. They got jobs, settled in, and eventually retired there.
Glennys, were you such an Army brat that you didn't really spend enough time in one place to consider that your place of formative growing up years?
Yes, absolutely. Typically, I’d be in a school for one year, maybe two years. I was in very tiny high schools in France. I was a tenth grader in Poitiers and an eleventh grader in Orleans. In my year I think there were maybe ten or fifteen students. So, it was a tiny school, but excellent teachers. I remember vividly the high school science teacher. But since I skipped my last year, when I got to Berkeley, I hadn’t taken any physics. Still, I decided I should take the physics course for physics majors. They were just developing the Berkeley Physics Course. And oh my gosh, I had so much trouble doing problems. I would think I understood the concepts, but I couldn't do the problems. I worked like a fiend and I did poorly on the midterm, I remember, but I had such a nice TA who was so patient and I spent so much time doing problems, that I eventually kind of got the knack of it and then it worked out okay. But I've always been very sympathetic to students. I think it's maybe improved my empathy as an undergraduate teacher, knowing how really non-trivial it is to get the knack of doing physics problems. But at a certain point, you do. If you do a lot of them, your brain… just some different wiring connects. And then you can do it. But why I wanted to go in physics is sort of funny. I had loved a book by Gamow as a girl. One Two Three... Infinity. And so, when people asked me what I wanted to do, I said, “be a physicist” and that produced so much astonishment, I think I stuck with it for that. It was the days when really women were very widely not encouraged to do science. I had my undergraduate advisor, freshman advisor in physics in Berkeley, recommend that I not do physics. And so, I took a double major in comparative literature as well as physics just to satisfy him.
Glennys, I'm curious—
But my parents were both really supportive.
Glennys, I'm curious if Mary Gaillard was helpful for you as a role model?
Not particularly. She was one of two women that I was sort of aware of. The other being Helen Quinn. It was an interesting time with respect to role models. I do remember the first time I encountered Helen Quinn. It was in a seminar that T. D. Lee was giving somewhere, probably at Stanford, and she asked him a question afterwards, and he was kind of putting her down a little bit, I would say. But she just stuck to her guns about her point. And I was so impressed at that. That had a real role model effect. I think when I was young—and I encounter this even now sometimes with students, depending on their background—I was really unwilling to admit that there were any prejudices in the field. That it would be relevant for me to have a woman role model. I just wanted to fit in and feel that people weren’t treating me differently. So, the fault might have been mine, but it just seemed normal that women didn't bond very much, and for sure not on account of being women. Mary K and Helen were both five-ten or more years ahead of me. I lose track a little bit.
So Glennys, among the men, per se, there was—
I just was never—
—who were some of the role models for you, men or women, at Berkeley?
Oh, at Berkeley? Oh, I didn't even know Mary K – She was not on the faculty at that point, and to my knowledge she wasn't a student there. She was mainly located at CERN, where her husband was on the staff. I don't know at what stage she became on the staff at CERN or not. But in any event, when I was an undergraduate at Berkeley, Stanley Mandelstam was on the faculty, and he was very supportive and another terrific and encouraging teacher was Eugene Cummings. I should add as relevant background that I married Stan Farrar while I was an undergrad. He was a law student at Berkeley. I married him after my sophomore year. I was really very young. We graduated at the same time, and he was trying to stay out of the draft for the Vietnam war. He was a conscientious objector but feared that he would never be able to get a job at a good law firm if he registered as a conscientious objector. But we found out about a program which sent professional students to India and a few other places for a year of post-graduate work, and his draft board gave permission to leave the country for that program, which kept him from having to get a physical for being drafted. He was protected for a year, and that was enough time that, by the end, the draft was sort of finished. Anyway, as a result I spent the year following my undergraduate years, in India—kind of working by a correspondence course with, remarkably, Stanley Mandelstam, who was a great theoretical physicist, you may know his name.
He would send me these long letters. I wish I had them. I might be able to find them if I could get to my papers, but things like that, I was not very—I've sort of not had sufficient reverence for some of the materials that were involved in my life. Anyway, I would try to do problem sets and write out questions, and he would write long, long answers as I was reading various field theory textbooks, and I studied Jackson and all of that all by myself. I had gotten admitted to Princeton and had to defer it to spend the year in India. At Princeton, you didn't have to take any coursework, so probably my education was always perhaps weak because I didn't have enough real in-person coursework at the graduate level.
Glennys, at Berkeley, did you have enough exposure to know what kind of physics you wanted to pursue in graduate school? Or you only made those decisions when you got to Princeton?
No, I would say that there's a funny cultural thing which was very strong, and it still persists. Namely, if you can do it, theoretical physics was considered the most prestigious thing in those days, and particle theory was certainly considered the most prestigious field, and I was a good student, and so that was the sort of work I naturally aspired to. It was of course extremely interesting. I mean this was really one of the glory periods of particle physics, and there was a huge ferment about how to do it in those days. But I just really didn't consider anything else very much. One of the things that strikes me as weird in hindsight is that as a graduate student at Princeton, I was totally unaware of the incredibly seminal work that Jim Peebles was doing in the department at that time. That isolation was pretty much the case for all the particle theorists who were on one floor, and Wheeler and Peebles and the group doing gravity and cosmology who were on another floor; particle people simply did not pay much attention to their work, as far as I know at least.
Was there someone at Princeton that you specifically wanted to work with, or you just knew that Princeton was a great place for theory?
The latter, it was just the latter. The general reputation.
And what was the process of finding a graduate advisor once you were at Princeton?
Well, that's an interesting question. Sam Treiman, who was my advisor, seemed somehow the obvious one. If you were doing particle theory, the main choices would have been Treiman or Goldberger. It's funny, as I think about it, I just can't imagine having wanted to work with anybody else. There weren't very many particle theorists. There were a number of assistant professors who then eventually did not get tenure and so on. People like David Gross and Curt Callan came as assistant professors after I was already underway with Treiman.
Glennys, I'm curious—
But the other people were much more formal than Treiman.
I'm curious culturally if being a woman at Princeton was in some ways more difficult even than at Berkeley? I heard that, you know, up until recently, they didn't even have women's restrooms in the physics building at Princeton.
(Laughter) Yes, it really was. More so even than I understood. I was the only female in the Physics Department other than secretaries. Actually, I was the first woman to get a Ph. D. in physics at Princeton – having women undergrads came a few years later – and when I applied for grad school I had to write them a special justification for why they should consider admitting me given they ordinarily would not take women. (I wrote that it should be obvious and that if they wanted to pat themselves on the back about their excellence, they should do it for themselves and not ask me to do it for them.) It was odd culturally anyway because of the Vietnam War, so the number of male colleagues in my cohort was somehow really depleted. I was almost the only theory graduate student at the time. And so, there was a very small group of people that you might kind of socialize with. There were a couple of students doing really formal theory. People like Barry Simon come to mind, just a couple years ahead of me. But later I learned something that was really interesting. It was at a—I think it was a memorial for Sam Treiman—I remember hearing all these people giving talks about what a wonderful experience being his student was, how warm Treiman was, and how he brought them to his home for dinner and stuff, but he was absolutely never like that with me. Treiman and I would have a one hour a week meeting, pretty much every week, and apart from that I was just completely isolated socially within the department. I never went to lunch with anybody. Anyway, back to that event: Treiman had really famous students. His first two students were Steve Weinberg and Nick Khoury, and Nick was sitting next to me at this event and I said "What's going on? I had such a different experience than people are describing!" And he said, "Didn't you realize? You were considered a real hot potato. Everybody was so worried about appearing to be, you know, too friendly with you." And therefore, the kind of interaction that Treiman and I had was apparently really different than for other students. His advice was well-meaning, and he gave me a lot of advice. But much of it was not good. I mean, for instance, I didn't apply to postdocs in a timely way because he told me, "Oh, there's no rush." Well it turned out later he'd considered there was no rush because he assumed I would stay in Princeton or New York, and he arranged with Columbia and the Institute for me to get a postdoc there, so the fact that I actually would have loved to have gone to SLAC and was too late to apply because he told me there was no rush, and I should go ahead and finish my thesis first... But also, things like telling me that you don't have to ever pay attention about recognition because your work will speak for itself. You know, there's some truth to that, but it's a terribly over-simplified view. I still have a—I used to until pretty recently have a—two-page CV because he said, "Oh, your CV should never be longer than two pages." So, I just kept cutting stuff out and now have trouble reconstructing what I’ve done! But anyway, on the other hand, I so admired and learned so much from Treiman in terms of intellectual approach and rigor. He was a real phenomenologist in a way that many people weren't in those days, and—especially in retrospect—I’m very grateful to have had him as my advisor. I love his kind of phenomenological but rigorous approach. But it wasn't very valued then, at least in the places I was finding myself, like the Institute for Advanced Study. So I think that the biggest problem I had in terms of finding my way professionally was—well, maybe I was encountering it to some extent as a result of being a woman—but I think the real problem was not finding out what my strengths were and learning to appreciate them. There seemed like such an atmosphere of tearing people down and belittling them and (laughter) when I went to Caltech, where I had my first postdoc after the Institute, I remember meeting Gell-Mann, and he said, "Oh, you're the new postdoc. Remind me where you're from." And I said, I was from Princeton. And then his face got all into a horrible, like, prickled up scowl in the way he would do, and he said, "Oh, I've been to Princeton. Ooh! Ooh! First time you open your mouth somebody says, “You’re wrong.” Then the next thing, “It's obvious.” Then the third thing is, “I thought of it first." Well, I may not be remembering the order... But anyway, that was so true of my experience—that you couldn't open your mouth without people jumping on you that your idea was no-good, obvious or inadequate. I wouldn't say Treiman was like that, but in general. And somehow the kind of stuff that I was doing wasn't really appreciated in Princeton and IAS. As I said, I am much more phenomenological—observation oriented—by nature. So, in fact, I would have been really happy at Stanford, which had a much more phenomenologically-oriented experimentally-oriented outlook. Anyway, it took quite a while till I got over feeling kind of a disconnect between things that I would do, which I felt were important, but the rest of the world wouldn't appreciate them. It was really many decades, I would say, before I learned that other peoples' judgment about what was important was not in general right. A thing that was a very sore point for me for many years, which I guess I'm only coming to grips with, is that in the time I was at the Institute, I had a really deep insight into how form factors of hadrons—that is to say, how hadrons respond when you scatter them elastically at a large momentum transfer—reflect the existence of three quarks inside protons, or two quarks if it was a meson, if the fundamental coupling constant of the interaction is dimensionless. It was radical because in those days, people did not know whether quarks were real, and many people thought they were just mathematical constructs. Everything that we now attribute to quarks, at the time people had derived as a mathematical current algebra result. Apart from the observed behavior of form factors that I had understood directly depended on the physical existence of quarks. So, to me it seemed like it was really an important insight, but when I would talk to people about it, they would all poo-poo it. Then in the summer after I’d understood that, I went to Stanford on my way to Caltech, not having written it up because all the constant negative feedback made me fear I was wrong for some reason, and I explained it to Stan Brodsky. He was very enthusiastic, and said we have to write this up together. I’m still sad about that—I think he should have instead said, "You should write this up and we can write a follow-up paper together.” Instead of, you know, we must write it up together. Its among our most-cited works for both of us and the foundation of his later work with Lepage trying to formalize the connection to asymptotic freedom (which had not been discovered when I figured out about the scaling laws). From the beginning I understood that the scaling behavior results from the absence of an intrinsic scale in the theory and isn’t just a phenomenological prescription. Anyway, for many years I blamed myself for not having ignored all the negative comments in Princeton and just written it up when I figured it out.
Glennys, let's not get too far afield.
Okay, but can I just go back? Let me just go to what I was coming to, which was how important it is to feel somebody appreciates your work. When I got to Caltech and explained this thing to Feynman and to Gell-Mann, they both thought it was really important. So, in hindsight I think it was just too bold an idea for most people to accept coming from me.
And it was such a curious experience for me that really good people could see that it was important (laughter) [BJ] Bjorken was another one who really appreciated it. So anyway, sorry, I went on for too long about that.
No that's okay, the audio delay just makes it—I don't want to sound like I'm interrupting you, but you don't know when I'm asking a question, so that's fine.
Yeah, yeah, sorry about that.
That's fine. I didn't want to get too far afield, because I'm curious first, let's go back to Princeton. I want to hear a little bit about how you developed your dissertation. Was Treiman, did he essentially give you a problem to work on? Or did you come up with something more on your own?
No, no. He gave a problem and it turned out that the first problem I started working on, there was enough to it that he considered it a complete thesis, and that was that. I finished in only two years and a couple months.
And what was your dissertation? What did you work on?
There’s a particle known as the Lambda, which is made of three quarks like a proton, but one of the quarks is a strange quark. The Lambda is a neutral particle, and one of the decay modes is into neutron and photon. And I calculated the rate for that. It hadn't been calculated before.
And what was the significance of this calculation to the field?
Oh, I would say middling. I've never checked—I should go and look at how many citations the paper has! In those days, people were just attempting to see if they could understand various processes. Calculating things involving hadrons was difficult. They're still difficult. People now have a formalism called effective field theory, which basically formalizes and kind of legitimizes the calculations that people did in those days. But back then it was really just attempting to see how much can we understand? How well can we explain various measurements within the framework of these sort of simple models?
What were some of the experiments that were going on in particle physics that may have been relevant to your research?
The problem that Treiman had given me had to do with weak and EM interactions, but as it turned out, all of the important stuff that was going on back then—it was just at the very beginning of the period when people were discovering partons and deep inelastic scattering—had to do with hadron physics. Up until the discovery of scaling laws and deep inelastic scattering, all of the evidence was that hadrons were really complicated, squishy things. Then, suddenly, evidence emerged that they were made of constituents that were eventually recognized to be quarks. Do you know what deep inelastic scattering is? I don't know how...
Well, I'm a historian of physics, so I'm not a physicist myself, but I'm tracking with you.
Right, right. But anyway, you remember that in SLAC, people developed the Stanford Linear Accelerator, and what they did with it was to scatter high energy electrons off hadrons. What they discovered (for which they got a Nobel prize) is that when they break the hadron apart and don't pay attention to what it breaks into, but just look at what the electron does, that it behaved almost like elastic point-particle scattering. That result gave Feynman the insight that there are point-like constituents he called partons, inside hadrons and that's why it looks like the scattering of two-point particles instead of the scattering off some very squishy thing. Now, we understand in fact that there really are quarks inside. But at that time, there were two competing pictures: the one of Feynman with partons really being point particles inside the proton, and the other being the current algebra approach of Bjorken and Gell-Mann. In any event, these experimental discoveries were just revolutionary, and it was a very, very exciting time. In those days, SLAC was the center of the world, as these discoveries were getting made.
So Glennys, I'm curious, you ended up at the Institute but was your preference in terms of where the most exciting stuff was going on, was your preference to have gone to SLAC right after your dissertation?
Yes, that's what I was trying to say earlier. The deadline for postdoc applications at SLAC was in early December. I was scheduled to defend in mid-December, and Treiman said, "Oh, wait until after you've defended to apply, because there's no rush." And I just believed him and didn't apply. And then by the time I applied, it was too late. And Treiman said to me, "Oh, but your husband is working in New York, of course you have to stay in the Princeton, New York area, and it never occurred to me you might want to go to SLAC." So anyway, that's what I was referring to.
Right, right. How did you make the best of your time while you were at the Institute? Who were some of your key collaborators and what were you looking to accomplish while you were there? Do you have any special recollections?
Well, one thing I remember vividly was learning that I was being paid only 2/3 what the men postdocs were and when I talked to the Director about it, his saying that was because I was married and my husband had a salary, too. I said I had no problem if they wanted to make means-based salaries, but in that case, they should inquire about need and not make assumptions based on gender. (That was sort of on a par with Columbia proposing an unpaid postdoc to me around that same time.) Another recollection from IAS was the time at lunch when I was sitting opposite Steve Adler at the long table the physicists always occupied in the IAS cafeteria, and he was telling about some new idea he had. I made some comment about it, and he looked directly at the man sitting to my right and exclaimed “Wow – that’s a really interesting observation!.” It was so strange, but unambiguously he had actually perceived that my neighbor and not me had made the comment. It was only many years later, that I was able to make sense of it when a senior woman in the NYU administration nonchalantly alluded to what she considered a well-established phenomenon of men frequently not hearing a point made by a woman in a meeting, and its being ignored, until a few minutes later a man makes the identical remark and then everyone jumps on it as a great idea. Her theory was that men learn as boys to tune out their mother, and that habit carries over to all women! (Laughter) But back to your main question: basically, I didn't collaborate with anyone very much. My insight about the quarks explaining the form factors came toward the end of my time at IAS—Ken Wilson spent a year or a semester at the Institute that year, and he was talking about renormalization group and anomalous dimensions and that was very important and profound for me. I didn't collaborate with him, but that gave me a lot of insight and is how I came to understand the scaling relation of the form factors. The other person I worked with was Jon Rosner who was a visitor briefly at IAS. Again, I had had an idea—the thing that happened over and over in that period of my life is I would have an idea, I would mention it, and most people would be so critical of it, I would be ready to give up, and then one person I would tell it to would be enthusiastic, and then we would write a paper about it. I just didn't have the confidence to decide on my own that something was worth writing up. In any event, I had understood that there was a flaw in an argument that Feynman had advanced, about how to prove experimentally if there were quarks and what their charge was. (At the beginning of the fall term postdocs were giving talks about what they had learned in the summer. One of the postdocs had heard Feynman talk about his idea at a summer school, and then reported about it to us at IAS.) I saw a flaw in the argument but figured, "Well, [the guy giving the report] clearly has not understood or reported Feynman’s argument properly because here's a counter-example." and didn’t give it any more thought. Then I went to a little workshop at Fermilab a few months later, and Feynman gave a talk about his idea. He was really pleased with it because if you could prove there were quarks inside protons it would be so important. And so I raised my hand after and said, "You know, there's a counter-example to your idea, so there must be some extra assumption that's needed. I'm not sure what's wrong with your argument, but this counter-example seems pretty persuasive." And I explained the counter-example, and he said, "Oh, you cute young thing. Come up and talk to me afterwards." And that was amazing, even in those days. The entire audience kind of gasped. People in the audience were exclaiming about it later, and it's even written up in a couple of people's memoirs. But I went up to the podium after and explained my counter-argument, and he was quite respectful actually, and then that was the end of the day. Then, the next morning, so many guys came up to me and said, "Ooh, you can't believe it." and “Feynman was so upset—you know, he's upstairs from me and he was pacing the floor all night!” Then immediately when Feynman got in, he came right up to me and said, "You know, I have to apologize. You're right." I don’t remember if he made a public apology (laughter). But at least he was very gentlemanly. I learned much later that in fact the way I got the job at Caltech was because Gell-Mann, who was so competitive with Feynman, had heard that I showed Feynman was wrong (laughter). Anyway...
That's a very interesting story about Feynman. Of course, much has been made about attitudes towards women, and the cavalier way in which he addressed you during this talk, but it sounds like beyond that, beyond that one exchange, he was actually quite respectful of you?
Oh totally. I absolutely admired his regard for me. He treated me with the utmost respect. Although he would always refer to the Fermilab story and make jokes about it and introduce me to people later when I was at Caltech as, "This is the person who revealed my only mistake in my entire science career." But I felt that his respect was somehow not just due to that incident. I think he was respectful of people – actually, much more respectful of people than most others are—in a profound way, that is to say, of really delighting in people’s ideas. I don't know, maybe I just had a lucky experience.
Glennys, when you got to Caltech, I mean you alluded to this a little bit before when you were talking about Gell-Mann. I've heard often that there was, you know, in those days there was an East Coast way of doing physics and a West Coast way of doing physics. Perhaps no better exemplified than Princeton versus Caltech, so you're very well positioned to reflect on those distinctions. How did you see those differences when you arrived at Caltech?
Gosh. That's an interesting question. David Gross came to Princeton toward the end of when I was a student. Pre-Gross, the world view at Princeton was pretty pre-seventies, let me say; people as far as I knew worked on fairly formal topics like dispersion relations and current algebra. (With the caveat that due to my own isolation, my impression may be way off the mark.) Whereas at Caltech with Gell-Mann and Feynman, there was much more of a ferment of new ideas and approaches. The activity level was also quite remarkable at SLAC because the experiments were right there and had such a big impact on people and there were a lot of visitors. But in all the places, I mostly worked by myself. You’d go to seminars and you'd talk to people that way. And I was lucky because I was an early riser and usually first to arrive at my office, and Feynman was usually the second person arriving and he would pass right by my office as he walked from the stairs to his office. He would always plop down on a chair in my office to visit, because he had had lots of ideas on his half hour walk from home that he wanted to share. So that was wonderful, but we never did any real research together. But overall, at least in the particle theory group, it was not especially collegial—not in the sense that people were nasty to each other or anything, but the environment just wasn’t very…
Yeah, right. Right, right. There were people like Willy Fowler and that group, and the astronomers were very collaborative, but not the particle theorists. At least not from my perspective.
So Glennys, what were you working on? What were some of your major research projects during your early years at Caltech?
Well, the first things I did were following up on the understanding about the quark constituents—writing the PRL and then a long paper with Brodsky, laying out how to try to formalize that theory. I also worked by myself and with a student, Darrell Jackson. We derived a fundamental relationship on the pion decay constant—a remarkable connection between the decay constant and the pion form factor—and we understood how quarks that are carrying a large fraction of the momentum of a fast-moving hadron behave—how they share the momentum and spin of the nucleon, and stuff like that; that work has been very influential. I also did a number of nice follow-ups of that, but then the idea of supersymmetry came along. Gell-Mann was very engaged in supersymmetry, and he invited Pierre Fayet to spend a year or two at Caltech. Fayet had worked with Iliopoulos and developed one of the early models that could potentially have been a realistic extension of the Standard Model. At the time nobody had a clue of how to discover supersymmetry apart from trying to find particles with the same quantum numbers as known particles but differing by ½ unit of spin—e.g., something with a negative charge that had spin-0—and then try to measure its interactions to see if it had the right strength coupling to be the scalar partner of the electron. Among the many problems of that approach is that it’s usually hard to measure the spin of a particle. But I realized there is an indirect way to find evidence for supersymmetry, namely that essentially any supersymmetric particle made in a collision would decay to what's now called the lightest supersymmetric particle, the LSP. The LSP is generically a weakly interacting neutral particle which escapes undetected but can be inferred due to the imbalance of the visible momentum and energy. And so, I really pioneered the whole topic of what is now called phenomenological supersymmetry, laying out the signatures to study supersymmetry that are very, very widely used now—really, the workhorse(s) of that whole field. I like to joke that if I had a penny for every event searched using that approach, I would be a very wealthy person.
Glennys, I'm curious. You know, during the early 1970s, these were some of the most exciting years in the beginning of string theory. I'm curious if you were paying close attention to string theory and if you found any of that work relevant for your own research?
I paid attention in a sort of distant sense. Another person whom Gell-Mann brought to Caltech in that time period was John Schwartz. And there were many visitors too. But somehow, I never felt I could make a big contribution to problems that are formal or mathematical or entail deriving consistency conditions and such. Problems that are connected more to experiment are where I feel like I can make some contribution. So, while I am interested in string theory, it seemed very unlikely to be pertinent to anything we could study experimentally for the foreseeable future, so it was not where I wanted to put my focus.
And what were the circumstances leading to you joining the faculty proper at Caltech? Was there a particular person who championed that promotion for you?
Not that I know of. I think that what happened is that the work on the scaling laws came out just after I arrived, and they must have promoted me based on that. But it was always a mystery, you know, who was actually responsible for things like promotion decisions at Caltech. Feynman was famously not an activist and he wouldn't take students mostly, and he wouldn't write letters for anyone, and so on and so on. On the other hand, I'm sure if he had expressed a view, he would probably have been really influential. Gell-Mann... maybe. Probably that’s most likely. Or it could have been someone else, sort of in the background. But anyway, I don't know where that came from.
And in terms of diversity, what women were on the faculty at that point?
Oh, there were none. Not in physics. There was one woman faculty member -- in Humanities -- named Jenijoy La Belle who came up for tenure and didn't get tenure, although she had a lot more professional achievements than her (male) contemporary assistant professor, who they did tenure. She actually sued them and that went on for a long time, and eventually she was granted tenure. Apart from Jenijoy, there was Anneila Sargent, who I think was a graduate student during most of the time I was at Caltech. Later she became a faculty member in astronomy—maybe the first woman—and had a very distinguished career. Another woman in astronomy at Caltech then was Catherine Cesarsky, a postdoc back then, who also had a very distinguished career including being the head of the European Southern Observatory. But in physics, there were simply no women except the occasional student (and none in particle theory). I mostly knew other women from the locker room at the swimming pool.
Now, were you spending time at SLAC in the mid-1970s? Were you there for all of the exciting things that were going on?
Not particularly. I spent a month or two at SLAC a couple of times. I spent the summer between the end of my postdoc at the Institute and when I started my position at Caltech at SLAC. Besides that, I went up to give a seminar now and then or make a short visit for the SLAC summer school, but basically, I didn't go there very much. I met a couple of people who became good friends I still cherish. One experimentalist friend I made that first summer, a few years later when they discovered the J/psi particle, called me up in Pasadena on a Sunday evening and said, "Oh Glennys, I'm so excited. We've made this discovery. I can't tell anybody. We're going to have a press conference on Tuesday. But I know I can trust you, so just don't tell anybody” (laughter). So anyway, that was fun. When the J/psi particle was discovered, that was an amazing period because so much was being discovered. So, I was pretty much in touch in the way that people were in those days, by writing letters and using the phone. And visiting occasionally. But I certainly wasn't spending extended time there.
And what other projects, what else were you working on by the time that you were on the faculty full time at Caltech?
At the beginning, I was really focused on the corollaries and consequences of the insights about the particle content governing the behavior of exclusive scattering, where particles don't break up, e.g. made the discoveries I mentioned with Jackson. But then after maybe a year and a half the supersymmetry stuff came on the stage, and then that's what I worked on. Those were the two areas that I mainly worked on. I did one project later with Steve Frautschi. I could have just done it by myself, but he was a really fine person and hadn’t been very active, so it seemed like a good idea to try to draw him back into doing research more actively.
And what were some of the really exciting developments with supersymmetry at that time?
Well, the most exciting development was simply realizing that one could do experimental searches. At first it was just an interesting formalism, but after discovering that you could search for it (which is my contribution, of showing how you could study it experimentally) Fayet and I wrote a number of papers looking at the consequences. After that I did a lot of work on supersymmetry, considering different possibilities that maybe gluinos were very light, and how would you be able to exclude that, and so on. For many decades—I guess you could say for four decades from the early seventies—people thought SUSY had such promise. It's somewhat out of favor now, just because SUSY has not been seen at the LHC and theories have become mostly very artificial given the experimental constraints at this point. So, I quit working actively on SUSY pretty much in the early nineties just because it didn't seem like it was a very attractive theory anymore, given the experimental constraints. You sort of had to stand on your head to design models which would not already have been excluded or had unnatural parameter choices. Then, I started moving into astrophysics and cosmology, not particularly consciously, but I just wound up doing that. So, there was a period when I was mostly learning and wasn't making that many important contributions, but by the 2000s I had almost entirely shifted to astrophysics and cosmology. There was an innovative paper with Jim Peebles on cosmology, and I did a bunch of phenomenological stuff in astrophysics that's been important, like figuring out what the magnetic field is of the Galaxy. That work is something I'm really proud of. I did that with a graduate student—realized how one should approach the problem, and what data you could use, and sure enough, we were successful. We discovered the existence of a directed, poloidal component that nobody had imagined. And then another thing along those lines, with another graduate student, was discovering tidal disruption events. I’d figured out earlier that stellar tidal disruption events might be the source of ultra-high energy cosmic rays—just in terms of sort of general argumentation—but the existence of TDEs hadn’t been confirmed. Then I realized that you should be able to find evidence of such events in archival Sloan data, if you looked at it properly. And so, with a student, we did that, and sure enough, we found the first two clear examples. And so on. So, I did a bunch of different things, but it's only in the last five years I would say that I got back to really doing mostly particle physics on this dark matter. This sexaquark dark matter that I sent you the paper on.
Now, were you thinking about astro—
But now I'm back to doing particle theory.
Were you thinking about astrophysics at all during your time at Caltech, or that only came later on?
Oh, astrophysics came much later on. Back then, particle theory was so divorced from astrophysics and cosmology… It was really only in the late ‘nineties and early 2000s when the two started to come together.
Oh, I was going to ask, what were the circumstances leading to your transfer to Rutgers in the late 1970s?
Well—as I was told afterwards—although they admired my work, in my third-year review at Caltech they decided they didn't want to take the risk that I would come up for tenure after three more years in the normal course of events, and that they would want to choose not to tenure me. They felt like I might sue them like Jenijoy La Belle had, and they just didn't want to take that risk. (laughs) And so it was a really weird thing. A very kind person there—Do you happen to know Judith Goodstein? She's the sort of historian of science for Caltech.
Oh no, I don't. That's a good person. I should know that name.
Yeah. I should get in touch with her again! She and her husband invited me over for dinner. He was on the faculty in physics. And they said they just wanted me to know that, you know, that was the decision, but that both Feynman and Gell-Mann had advocated for me to be continued for three years, like would have been pretty normal. And said that I was really good and all of that, but that the rest of the department really, in effect, said, you know, we can't trust their judgement because she's probably turned their heads. I believe, David and Judith Goodstein were sort of scandalized by that and decided to tell me what had happened because they felt bad. It was really lucky for me that they did, otherwise I would have been horribly demoralized by that experience and most likely left physics. But you know, maybe it was for the best, because the social atmosphere is pretty difficult at Caltech. Rutgers was not a wonderful option, but I loved New York, and it was the best thing going, among of the other places that I had an offer from. Gell-Mann actually organized an offer from the University of Florida, but I didn't particularly want to be there, and I loved New York and so on. And then, my environment improved hugely two decades later, when I went to NYU to be chair and in effect renovate the department; that's a long story. I got to build a department that just suits me so wonderfully. Everybody is really congenial, there's a big intellectual diversity—from string theory to the SDSS—and so there's people to talk to about all sorts of things, and I just love the atmosphere. If I had stayed at Caltech, I wouldn't have had this wonderful last two decades of an extremely wonderful environment.
Glennys, of course, you couldn't have known that at the time of course, how well things would have turned out. I'm curious. Were you surprised at this news that you got from Caltech? Did you think that you were on your way to tenure, and did you think that the circumstances were such that you were treated fairly or no? In terms of this, how you left Caltech.
Oh no, I absolutely didn't think I was treated fairly. I thought it was really outrageous. I think in those days, people didn't really feel like they had very many rights, and so for my side, it was—I mean, it was such a weird situation, that they were so kind of unapologetic. I mean, they apologized in a way, because they said, you know, in effect, normally you would stay on and you'd have a crack at tenure. I don't think anyone ever thinks they're on their way to tenure at that stage, at that intermediate stage. But to simply not even be allowed to continue and in effect compete, was a shock. And for them to feel so much like it was a fine reason! That they thought of it not as a particularly negative thing—that they just didn't want to have to make a decision… as if they weren't! (Laughter) but anyway… So that was, you know, pretty upsetting, and I even talked to Jenijoy La Belle about it—she was encouraging me to bring some kind of action. But I just figured, you know, if I did that, it would be… I would wind up being consumed by it for who knows how many years, and even if I were to succeed, it would be really… There was no good outcome. It would be hard feelings if I succeeded. If I didn't, or whatever, I would have a horrible reputation in the physics world. So, it just didn't seem something that one should fight.
And Glennys, there's obviously no way to know this for sure, but do you feel like being a woman contributed to how these decisions played out?
Oh totally. I apologize if I didn't make that clear. The reason explicitly was that they were afraid that if I came up for tenure and was denied it, that I might sue them—precisely because I was a woman. Because Caltech was in that moment midway through a multi-year lawsuit with Jenijoy La Belle, the woman in English who they didn't give tenure to originally. And then she sued and eventually got tenure as result. So their position for me was “We want to avoid creating a situation where we will be forced to decide about tenure for you, because we don't want to create the possibility that we would make a negative decision on scientific grounds or whatever grounds, and then we would be vulnerable.”
So, it was absolutely, there's no—
Right. Glennys, you did make that clear. You did make that clear, I guess I'm just having trouble wrapping my head around, you know, exactly what it means, what you're saying. Because essentially, if this was the message coming from—
If this was the message coming from Caltech, how does that not destroy their reputation in terms of being a place that's known to be, you know, just toxic to women in general? Why would any woman, knowing what you had just gone through, why would they ever even think for a second about coming to Caltech if this is what was going to happen?
Well, I mean, this was in the sort of late-ish ‘seventies, and that's, well, it's more than forties years ago. I think that peoples' attitudes were really small. They couldn't care less in those days if it seemed toxic to women.
And I think that there was a real ethic in those days that decisions would always be made to benefit the institution. I think that concerns [about equity] just simply weren't there. And you know, the decisions a person in my situation would make have really changed. I think now, a woman in a similar position without a doubt would bring some action, just because it so clearly… (laughter). It's so funny what you said about getting your head wrapped around it. It's so funny to think that they thought their course of action was legitimate. Their view was that if it ever came to making a tenure decision, then they would be more on the line than just letting me go then. Also my husband, Stan Farrar, was a lawyer and they said that that actually gave them more reason for pause than they would have had otherwise.
And were they so clear? I mean, so brazen about the gender issue, that they wanted to assure you that substantively, your contributions and skills as a physicist, that was not the issue? That if you were, you know, a man and you had made these contributions, there wouldn't have been any concern about giving you tenure? Were they really that brazen about narrowing this down to being a woman thing?
No, no, no. [audio breaks up] David?
I mean, let me try to [inaudible] This was not the [inaudible] tenure decision. It was common practice that after someone's been an assistant professor for three years, they get reviewed and then the decision is made: do they continue? And then at the end of five years, you get reviewed for tenure. And most places, a three-year review is more or less a pro forma thing. It's essentially never done now, to not continue someone after three years. Instead, what we do when people come up, we take the opportunity to tell them, okay, these are the weaknesses in your portfolio that will be judged when you're up for getting tenure -- when you're being evaluated for tenure. You need to do more in the way of this or that, you know, publish more or give more talks at international conferences, or that sort of thing. The third-year review is an opportunity to identify, to review someone's work and identify how they can better prepare for the tenure review. But it's still technically the case that they don't have to continue you at that point. And very, very unusually, Caltech chose not to. And then I was simply told that I wasn't going to be continued, but that I could stay as a senior research fellow. And then this kind couple, David Goodstein—who was or had been effectively the department chair, called division head I think in those days – and his wife. They just privately wanted me to understand that there had not been any criticism, and only support for my science. So that was what I was trying to explain earlier. It was very important personally, because otherwise I think I would have been really very demoralized.
Yeah. And I see that at Rutgers, you achieved tenure quite quickly. You were associate within one year of you going there. I'm curious, was that either informally or formally, was that sort of part of the process when you went there, that you were, the expectation or the understanding was that you would get tenure quickly?
That was it exactly. Right. But they didn't want to bring someone in from outside with tenure who didn't already have it, but you're absolutely right. They agreed to review me right away.
And what was your experience like at Rutgers? Did you look at this as an opportunity to pursue new research? Was it a fresh start? Or were you simply looking to continue the work you had done at Caltech?
My work naturally migrates around, so I’m pretty flexible about my surroundings, but there was nothing about the particular science people were doing at Rutgers which made it intrinsically a scientific boost for my own work. It would be more accurate to say that it was a respectable job and a reasonable location, since it was well-connected to New York and Princeton and so on.
And so, what were some of your significant research projects during your Rutgers years?
Well, I went back to doing hadron physics mostly. Some of the insights I'd had about how asymptotic freedom works in elastic collisions turned out to have implications for various experiments in nuclear physics. But overall, I would say that my work in that period was not phenomenal. I sort of “went along.” I had gotten divorced from my first husband while I was at Caltech, and after a couple of years in New York married my present, final husband Anthony Terrano. And then we had kids. Our first child was born in 1984 and second one in 1987. I was actively working on various things, but there was nothing super-noteworthy in retrospect. Sort of a respectable level of activity. Then I started moving into cosmology, and then in '98, I went to NYU as Chair of the Department of Physics. I had a mandate to refurbish the department and create a completely new kind of department. I thought it should include a center for cosmology and particle physics, because those two fields seemed absolutely headed toward a kind of union, with cosmology becoming a major source of inspiration for particle physics. And it should include not just cosmology but also astrophysics, because astrophysics and cosmology are inextricably intwined—that’s even more clear now than two decades ago. It's called the Center for Cosmology and Particle Physics, because fitting in “Astrophysics” would have made the name too long. Anyway, since going to NYU my work has been really very productive—in effect, I could bring the world to me, unlike in the first places I worked, where I was working pretty much in isolation.
Glennys, what were some of the big questions or people that served as catalysts for your transition and interest in cosmological issues in the late 1990s? What explained that transition for you?
Well, I guess a couple of things. In the mid-nineties, in '92 I think it was, I took a sabbatical year at CERN where Misha Shaposhnikov and I started working together on baryogenesis. This is the question of how do baryons come to be in excess of anti-baryons in the early universe. That was some of the first bit of cosmology I did, although it's almost more particle physics than cosmology. And then there was a period when, in the late nineties especially, there seemed to be a real mystery about ultrahigh-energy cosmic rays: they seem to be observed at much higher energies than would be expected according to certain logic, and so therefore maybe the UHECRs were a completely different kind of particle. As you can imagine, that had a lot of particle theorists excited and I started working on it, and that very much started to draw me into related problems of astrophysics. That's why, for example, I became interested in the Galactic magnetic field, because it deflects cosmic rays and therefore has to be understood to figure out where they are coming from. So, I was looking at the models in the literature for the magnetic field, and I thought, "This analysis isn’t rigorous by particle physics standards—I can do better than this." (Laughter) So, anyway, it was a “one thing leads to another” kind of a proposition. And then with my students and others we started placing direct detection and indirect detection constraints on dark matter coming from astrophysics… All of that came really naturally, because by then I had a knowledge of astrophysics adequate to start using it for these purposes. Now it's a big industry and lots of people are doing it.
What were the circumstances leading to your switch to NYU? Were you recruited? Were they specifically looking for somebody to lead the department?
Yes. NYU had been one of the very top physics departments for years and years, but in the 80s, the university became very over-extended financially, with big loans to do a lot of building, when interest rates went up to like 18%, and they had taken the loans thinking rates were going to stay 4%. And so, the university really went into a tailspin. They had to sell their uptown campus and get rid of everybody who didn't already have tenure and merge many departments. So, they went through a period of a real contraction until toward the mid- to late nineties, the professional schools like the law school and the Tisch School of the Arts—you know the famous film school—and the medical school said themselves, you know, our reputation is being weakened. We're amongst the best in the country. Right up there with Harvard and Stanford. But our reputation's weakened because the Faculty of Arts and Science is so weak because of this pre-history. So, the professional schools put money into FAS, and there was a really smart dean who decided rather than spread the resources overall, he would focus in on individual most promising departments and try to really bring them up. He had all the different departments make proposals as to how they would use the resources, and then the ones that had the best idea, he’d give resources to. As I understand it, Physics basically made a proposal that everyone will hire one of their former graduate students and keep doing the same thing as they had been, and you can imagine the Dean [of the Faculty of Arts and Sciences] didn't like that idea, so Physics got nothing for another few years. At that point they decided to try again to get a chair, only this time their plan was to make Physics essentially part of the Courant Institute doing numerical simulations. Somebody called me and said, "Don't worry, there's no chance that you would be offered the job, because they definitely don't want a particle theorist. But how about letting us put you on the list of people to be interviewed?"—they were looking for people who could present a different perspective. And so, I interviewed with the Dean, and I explained to him exactly why making Physics into a simulation center was a terrible idea—because the value that Physics really has lies in the fact that while it’s mathematically rigorous, you have to reconcile with external facts. This is the crux of the discipline, and it's different from what you do in math. And it's different than in a descriptive science. So, I told him that they should either decide to get rid of the physics department or just keep it to, you know, teach a few courses, or else they should be serious and actually have a good physics department. I told him what you should do is this and that; if you want to do it, you should start a center for soft matter physics, and a, you know, center for cosmology and particle physics and really jump past the rest of the departments that are just sitting there doing stuff from thirty years ago. Anyway, half an hour later, he called me and said, "You've just got to take this job!" (Laughter) So, then the rest is history. Because I always thought it was a shame that there hadn't been a really good department in New York for some time. And I think it's really worked out, it's a wonderful department.
So. that's pretty remarkable, that based on this conversation, you have this department that is essentially, you know, there's the support there to build it from the ground up.
Well, it was so enlightened of the Dean. And I totally give him the credit for taking this point of view, of giving adequate resources to initiatives that could really make a difference. He was terrific.
And so, with this support—
And I do think it was a correct assessment. Because I was quite disheartened about the prospects of physics at that juncture, because so many departments were just doing the same old-same old: old fashioned condensed matter physics, old fashioned nuclear physics, old fashioned particle physics. And completely unreceptive to the parts of physics that were fermenting but disconnected, like the whole field soft matter research. It didn't even used to exist as a field then. Or certainly there was very little place for it. There was a huge bifurcation between astrophysics and cosmology and physics. And biological physics, for example. I thought physics should embrace these areas that were new, which were going to regenerate the field, rather than saying, "Oh, if it's alive, it can't be part of physics.” That worked out. I was just extremely fortunate that I did have a kind of very—at that time—way ahead of the time understanding of the situation, but normally the potential for doing something about it would just have never come to fruition. I was just really lucky that the circumstances to act on the idea presented itself thanks to that Dean and the circumstances at NYU.
So Glennys, I'm curious, with this expansive vision that you have for where physics should be headed, not just at NYU, but sort of generally, plus this material support from the dean, what was your game plan to actualize this vision at NYU?
Well, you know, I started with searching for people. I brought immediately one really, really good particle theorist, Gia Dvali, who has been just pre-eminent through the years since then. We finally lost him fairly recently to the Ludwig Maximilian University in Munich. This was starting in '99 (I went to NYU in ’98). So, I was going down to the Institute [for Advanced Study] and listening to talks and getting acquainted - a person whom I really admired was John Bahcall, and in fact all the entire Princeton astro faculty is amazing. So, I was learning a lot of astronomy. (Actually, the way I got into doing so much astronomy and astrophysics myself was that I had to learn a lot in order to be able to hire people in this area. And then I wound up just working on it myself.) But in any event, I realized that there was a group of terrific young people who were all postdocs at the Institute. There were four of them that I proposed to hire. I don't know how well you know these names, but it's a really impressive list: Matias Zaldarriaga, Daniel Eisenstein, David Hogg, and Andrei Gruzinov. And so, I called up the Dean—this is something like 8 pm on December 23rd—and said, "I'd like to hire these four people." And within a couple of hours, he had gone to the president and gotten permission. (laughter). And so, I made them the offer, and we attracted them all except for Eisenstein (he’s subsequently done great work - he's at Harvard now); we instead got Scoccimarro who's also an excellent scientist. Bahcall tried to convince them to stay longer at IAS and then go to a more established place rather than accept at NYU, but I think it actually wasn’t a fluke that they accepted and came to join in creating this entirely new thing. You know, young and ambitious people can be a little bit reckless in a certain way, but those are exactly the kind of people who you want – they are going to be the most daring and courageous scientifically. We've since lost Zaldarriaga, who is now a permanent member at the Institute for Advanced Study. So overall that's not such a bad track record. We've in the meantime hired a bunch of terrific other people, so we have a very, very strong department now. But anyway, the circumstances of identifying this group of really excellent young people and having the support of the dean who was ready to go to bat for that pretty bold move of hiring four people right in one chunk gave us a wonderful momentum, and now the Center for Cosmology and Particle Physics has nineteen faculty.
And Glennys, I'm curious, you spent three years as chair, and then you founded the Center for Cosmology and Particle Physics in 2001. Had you felt that what you had accomplished as chair in those three years had established its own momentum, and that you would be able to sort of step down and enjoy the fruits of your labor and to concentrate on the center at that point? Was that the idea?
Well, that was partly the idea. But there was also an issue that the dean for science in that interval was a real micromanager. It was so exhausting and unpleasant trying to deal with that—I mean, there's so many demanding aspects of being chair without adding to it. First of all, I was doing a huge amount of effort in recruiting, but also, we were trying to improve the graduate program and create lots of staffing, infrastructure, etc. But that DfS wouldn't tell me how much funds there was going to be for the graduate program, he wanted to make up his mind at the end, depending on what he thought of the applicants and stuff like that. And in terms of space for hiring people, he wouldn't tell me—he kept saying, "The space that you think of as yours, I'm now going to call Dean for Science’s, and you have to make an active case for using a space”, and so on. And so it just seemed like he was tripling the effort involved (laughter), I remember discussing it with him, I said I feel like this is as much work as three jobs, because I have to do each one of these extra things which are completely unnecessary. Just give me a budget. I'm not asking that it be any bigger. I just want to know what I'm trying to work with. And let's agree provisionally on space— if we haven't used it well in two years, we can negotiate it again, but for now, I want to know I can try to recruit people and be able to offer them lab space and stuff like that. He just said, "No, this is the way I operate. I hope you'll stay on as chair for another three years, but I can't do things differently." And at that point, I really felt like continuing as department chair was not the right return on my efforts. And I'm very happy I did that, because I was able to get the Center for Soft Matter research going without being chair. I contacted the key people and so, and while it actually got officially started a little bit later, I developed the concept of what it was going to be, made the case, and identified key hires. So, I think that worked out fine, because in fact the effort of getting the CCPP center started and really on the map was pretty big. But I probably would not have made the correct decision if it hadn't been for that dean, who was (laughter), you know, exasperating.
Glennys, what were some of the biggest and most exciting issues in cosmology at the turn of the century for you? What were the ideas and some of maybe the technological advances that compelled you that, you know, this was the right time to establish this center for cosmology and particle physics?
Well, the observational discoveries were snowballing – Hubble Space Telescope was just making so many discoveries on every front, and there were many satellites that were exploring x-ray astronomy and radio astronomy and the CMB discoveries, and then of course in the late 90s there was the discovery of dark energy through the supernovae studies. So, it really was a no-brainer. And at the same time, while I was very fond of particle physics, there had been no major new discoveries, and new accelerators were pushing up the energy frontier with nothing new on the horizon except the Higgs. My feeling was that particle theory had become sort of tiresome. People were working on the next-to-next to minimal supersymmetric model with breaking in the octagonal sector, or whatever. Theorists were being very creative but without major new experimental puzzles to think about, pure accelerator-based particle physics just was less compelling. Meanwhile, in astrophysics, like I was saying, there were so many new telescopes and of course now we have all the Keck telescopes and the Europeans are making huge developments with the ESO telescopes—like the GRAVITY experiment that's looking at the orbits of the particles around Sagittarius A*, the Milky Way’s central black hole, and there's the EHT—Event Horizon Telescope—that's imaging the black holes in M87 and our own Galaxy. And the gravitational wave detectors and Atacama Cosmology Telescope. Really, almost all of the exciting driving things in particle theory are coming from puzzles that have gotten raised and measurements that are getting made in astrophysics and cosmology. Like, for example, is dark energy really just a static cosmological constant? That is a perfectly fine description empirically of the data, but very odd theoretically. And new measurements are on the horizon, which will much more accurately establish whether it's actually a constant, or whether it might be evolving. I can just go on and on. There's a huge number of things. Really, my conviction—also for the Soft Matter Center—is that the key is focusing on fields where there are big observational discoveries or new technical breakthroughs that will continuously rejuvenate the field. And of course, nature has cooperated because so many different interesting things have come out of all these observations, unlike in pure particle physics where the observations have been admirable, and the energies have been going up and up, and the experimentalists are going a phenomenal job, and there are of course many non-trivial advances coming and some intriguing tensions with the Standard Model. Another interesting area is heavy ion collisions. But in any event, there have not been comparable new major insights coming from particle physics experiments. …So anyway, that's why – but I guess I'm not being too responsive to your question about "why cosmology?"
Well, Glennys, I'm curious, you know, as a sort of overview, you mentioned earlier that you got interested in some ways in cosmology because you had to learn about it in terms of the people that you wanted to hire. I wonder if I can flip that comment around a little bit and ask you, in what ways did you use your formal education in graduate school, in your post docs, in particle physics—In what ways was that advantageous to your transition to some degree into cosmology? What was it that you understood about particle physics that would be useful in cosmology as a basis for understanding these big questions?
Of course the wonderful thing about physics is that, or a wonderful thing, is that there are so many fundamental principles which appear over and over, like issues of statistical physics, that are crucial to understanding many things in astrophysics, and yet it was also pertinent for understanding, e.g., collisions with lots of particles in the final state in particle physics. One could go on and on about how the fundamental knowledge of physics manifests in many places. As it’s turned out, especially in this recent work on sexaquark dark matter, it's been my intimate understanding of particle physics which let me realize that this particle could exist. People had not predicted a mass that would make it stable enough to be the dark matter, but if it's a little bit lighter than people's expectations, then I realized not only would it be stable, but it would not have been discovered. My own view was we couldn’t be confident that it can't be light enough, and so then I started pursuing it. What's amazing, as it turns out, you can actually calculate its relic abundance with no free parameters—using statistical physics, by the way—in the early universe, when the universe was ten millionths of a second old. Earlier than that, at the really, really early part of the big bang, there was just a quark gluon plasma. But as the temperature cooled below about 150 MeV, which is the temperature at ten millionths of a second, the plasma transitioned to the known particles like protons and neutrons, instead of just being a soup of quarks and gluons. Our understanding of the properties of the quarks like their masses and the temperature of the transition between the quark, gluon, plasma, and hadrons, is knowledge that's been derived from particle physics—it’s been studied with lattice gauge theory and experiment and so on. So that's very well-established particle physics, and I realized that I could use that knowledge along with statistical physics to calculate the dark matter relic abundance. And you simply get the right answer. It's astounding. There are no free parameters, and you find out that the prediction is that the ratio between dark and ordinary matter is somewhere between around four and six, and lo and behold, the observational value is 5.3 +/- 0.1. With other theories of dark matter, getting the right answer is a matter of tuning parameters, and you're lucky if you can get in the right few orders of magnitude of the ballpark. And here it just simply comes out. So that's why I'm so excited about it. Even if it turns out not to be the right explanation for dark matter, it's a beautiful example about how all the different threads of my expertise had to come together. Like my early knowledge of particle physics and then the study of cosmology and stuff. And what's really fun, the thing that I was working on over the weekend and why I was not responsive to your messages, was that I realized that dark matter, in a very interesting and you might say likely range of parameter space, would actually bind to nuclei in the Earth at a level that should be detectable, and I was in fact in touch with a geochemist at Caltech who on Monday next week, he's going to start searching for it. It's amazing. It could be that we would just discover it in a few weeks. (Laughter) It's kind of mind boggling. So, you've caught me in a period of being on a high. But one of the things I often tell my students is a criterion for being a theoretical physicist, is you have to be resilient, because of the frequency that you have a great idea and then it turns out not to be right, or it's not what nature did: that's the generic situation (laughter).
Glennys, can you talk a little bit about your work on the stellar tidal disruption phenomenon? When did you start working on that?
The reason I started working on it and thinking about it was because I was interested in these ultrahigh-energy cosmic rays. I joined the Pierre Auger Observatory actually in order to be able to use the very high-energy showers that these things (UHECRs) make in the atmosphere. They are quite rare, very, very high-energy nuclei, we now know, and how they're created is not known. And their flux is extremely small. There's one per square kilometer per century that hits the Earth. So, they're very, very rare. But there are experiments—sampling detectors—covering many, many thousands of square kilometers that have mapped out their behavior. Anyway, in those days - very early days – given their high-energies (hundreds of thousands of times higher than the LHC), people had thought it would take—it seems pretty obvious that it would take— a really exceptional situation to produce them. Maybe like a supermassive black hole with an active galactic nucleus or something. Only, you could look around and you could see and count these things. They're so visible. And so that was very paradoxical—it was like you should be able to see UHECRs coming from these particular sources, because there are so few of them, but in fact, people could see that they seemed to be coming from all different directions, not any particular direction. And so, I was trying to think, how could you explain this fact. One possibility I thought of was that the sources were short-lived, so there could be very intense emission of some really high-energy particles, but lasting so little time that when you took a random look at the sky, few or none would be “on”, and so you wouldn't see them. It would reconcile this puzzle, that it requires a powerful source to accelerate to that energy, but there were no powerful sources close enough to be associated with them. Anyway, in thinking about what the source could be—thinking about all the different options—I realized that it might be a stellar tidal disruption event. These had been hypothesized but they had never been seen at the time, except for a few conjectured examples detected in X-rays. And that was the situation. It was Rees, I think, who first proposed stellar tidal disruptions should occur. There is a supermassive black hole at the center of more or less every galaxy, and some star’s orbit gets tweaked a bit, because it has a perturbation from some other star near its orbit and happens to be directed in closer to the black hole. And then there's a phenomenon called tidal disruption, which is basically that because the force of gravity falls like 1/r^2, it means that the force on the nearest part of some extended object, like the moon for example, is much greater than the force on the far side... To make a long story short, the force gets big enough to actually tear apart a star if it gets close enough to the black hole. And then you have all the material that previously was forming the star, making a plasma that crashes in on itself. At the time, the theory wasn't very well-developed, but I reasoned that it might produce an event sort of like an AGN, which was the source that people thought could create the highest energy cosmic rays. Anyway, with this in mind, I wrote a paper with Gruzinov in which we showed that the whole idea could work, and then I did the estimate of how often these things should be happening and realized that they should be visible in the Sloan Digital Sky Survey archival data. I had a terrific graduate student—he was a masters student coming for a year from the Netherlands—and he was open-minded and smart and ambitious, and we said, "Well, let's look." Because I had talked to the people on SDSS, and they all said, "Oh, that sounds too hard. We're working on something else."—so they hadn't done it. So, with Sjoert van Velzen we looked and he did a beautiful job, and lo and behold, there were these two events that are now listed as the first two secure examples of TDEs. But most importantly, we established the right way to study them—reducing the 100-times higher background from supernovae, without introducing theoretical assumptions about what the flares are like. So now people are using our method. There are lots of dedicated searches which are looking at the sky every two days or more. (In the SDSS data set that we used only a small stripe in the sky was repeatedly looked at, once a week for three months every year, for eight years.) And now there are dedicated efforts to look for transient events and there's an alert network so if somebody sees some flare go off, then other telescopes look at it if its promising. Now there are several dozen of these tidal disruption events that have been observed, which have been quickly followed up to actually watch their evolution over time. So, the whole field has really blossomed. It turns out to be very interesting because it gives you insight into all sorts of phenomena. TDEs can be used as a tool for cosmology and testing general relativity and so on. And what I'm proud of is that the methods that we developed are the gold standard methods that people use to get an unbiased assessment of TDE properties, frequency, etc.
Glennys, what have been some of your most productive collaborations with graduate students during your time at NYU?
Well, that was certainly one of them. Another that I can point to is a collaboration with Ronnie Jansson, with whom we uncovered the structure of the large-scale Galactic magnetic field. Another one is with Jeff Allen—both could well have stayed in the field. Jeff wanted to stay in New York, and he works for Facebook now I think, and Ronnie went back to Scandinavia. With Jeff we worked on ultra-high-energy cosmic rays and we proved from the data from Auger observations that there's something wrong with particle physics models at very high energy because there were discrepancies in the descriptions of their atmospheric showers that can’t be attributed to measurement errors. Ultra-high-energy cosmic rays hit an air nucleus high in the atmosphere, carrying ten times the center of mass energy of the LHC, and that energy just keeps getting broken down into more and more particles with less energy as the subsequent particles collide and start new sub-showers. We developed a new approach to analyzing the data and showed unambiguously that there was a real discrepancy in the theoretical models using data from the Pierre Auger Observatory. That came out as an Auger PRL. That was a really productive piece of work. People are still trying to figure out how to fix the particle physics models. And right now, several students are working on different projects with me relating to Dark Matter and cosmic rays. I wound up with a fairly large group.
If we could go back to your work with Jansson for a second, what does it mean that you discovered something new about the magnetic field of the Milky Way? What was it exactly that you discovered, and what were the surprises that led to this discovery?
Prior to our work, people had been trying to look at the magnetic field of the galaxy and also other galaxies observationally, with the main technique being Faraday rotation measures. There, polarized light from some distant object like a quasar—when it comes through a medium where there are free electrons and there's a magnetic field—the direction of the polarization rotates and the amount it rotates is frequency-dependent, so you don't have to know the original direction, because if you measure it at many different frequencies, you can map out the different amounts of rotation for the different frequencies. That lets you extract what's called the rotation measure. This theory was all worked out by Faraday. The rotation measure is sensitive to the product of the electron density times the magnetic field integrated along the line of sight. And so, people had done measurements of RMs of distant quasars, especially in the Galactic plane, and there was pretty clear evidence that there was a magnetic field along the direction of the spiral arms, and it was sometimes reversing directions in different arms. But RMs have a sort of limited utility, and at a certain point I realized, listening to a talk about WMAP… You know what WMAP is, right?
Yeah, okay. So WMAP was measuring the microwave radiation. They were intending to look at the CMB, but in the direction of the Galactic plane, they were dominated by emission from the Galaxy, and they could actually measure that and subtract it. Part of that emission from the Galaxy is called synchrotron emission. That is produced when relativistic electrons—they're cosmic rays accelerated in supernova shocks—when those electrons are spiraling around the magnetic field, they emit radiation called synchrotron radiation. It turns out that synchrotron radiation depends on the transverse component of the magnetic field, weighted by the cosmic ray electron density. So, the rotation measures give you the longitudinal component of B -- the line-of-sight component -- and the synchrotron emission can give you the perpendicular component. Anyway, hearing that seminar when WMAP announced that they had detected the polarized synchrotron emission, I realized, ah-ha! Because I had been reading, like I said, the papers about the Galactic magnetic field, trying to use them for UHECR cosmic ray deflections, but it was a mess. I thought the GMF models that existed then were totally rubbish, to be honest—(laughter). We can delete that from the interview. But anyway, people were picking and choosing which rotation measures to use to fit their pet model of the spiral arms and so on. But anyway, so then I said to Ronnie—again, I was so fortunate to have a student who was both smart ready to be daring—I said, "Look, we can write down a functional form of the field, which includes spiral arms and it includes a halo." We could already tell from the RM data that some sort of toroidal component was needed; you could imagine that maybe the spiral arms just extended vertically. And then just for good measure, I said let's include a poloidal component because in external galaxies, it looked like there might be some evidence of that. By poloidal component, I mean a component that extends somewhat vertically out of the plane, way out—like a dipole magnet, if you remember the experiments where you use iron filings to get the shape of the magnetic field of a bar magnet. A poloidal component has that general kind of shape—It flows out of one side and in the other. In a bar magnet, it comes around and it flows back in at the other. In the Galaxy it might be self-contained or connect[ed] to other galaxies.
So that's called a poloidal field. Anyhow, I said, "Let's put that in, just because maybe it's there" even though a directed poloidal field was not predicted. And so, we had this rather general model. Maybe the reason nobody had tried to do such a complete job before, was because when you start to count the number of free parameters that you're going to need, it's quite large. For every spiral arm, you would need a field strength. For the toroidal component, you would need its strength and how it falls off vertically and radially. If there's a poloidal component, you need to have a model of how that is distributed radially—so when you count up the parameters you need, something like 22 parameters is sort of a minimum. And so, people's reactions would have been, well, that's hopeless. You have too many parameters. But first of all, there are 40,000 different lines of sight for which there's excellent data. And what I reasoned was that if there's a global signature, even if there's a lot of noise from various Galactic foreground things like supernova, that you could still in principal pick up a residual that could tell you about this large-scale field. The great thing about working with students on a project like this is that they're going to get a good education whether or not in the end the project works. So, one can just be adventuresome and give it a try. In fact, we developed a really quite good model, and nobody has been able to make significant improvements even though nearly 10 years have gone by. I've been working with somebody for a few years now to improve it. He's in Germany, and we both are doing other things - him especially - but he's very talented, so I believe that we're going to come out with an update to the Jansson-Farrar 2012 model. I hope that we get it done this year. But it's amazing, JF12 has been so durable because it's really not easy to do much better than we did. It's been very influential because there are so many applications. And there's this entire large-scale structure that hadn't been anticipated, which is by the way very interesting from the galaxy evolution standpoint – especially how the poloidal field can come about. I'm talking about a field that's actually a directed field. It goes from South to North. And it's quite strong. It's as strong as the random field. It's easy to understand how random fields can get generated—just from turbulence and supernovae explosions and dynamo effects and so on. But the existence of a large-scale poloidal field has got to be telling us something deep about galaxy formation, which people haven't tried to think about before. So that's another project I’d like to work on trying to understand, with new students. It's wonderful having students and teaching. You kind of keep rolling along from one thing to another. And then there's this dark matter project—it turns out to be making use of all the astrophysics I learned along the way. With another student we placed wonderful limits in general, not just on this particular dark matter particle, but other kinds too, using a dwarf galaxy 400 kiloparsecs from the Milky Way, which we happened to learn about, that proved to be a perfect tool for the particular test, and so on.
I was asking Glennys, no no, that's great. I'm curious, just a sort of broad question, if you can reflect over the past few decades, what have been some of the major technological innovations, either with telescopes or computational power. What have been some of the major technological developments that have spurred the field generally and your research specifically?
Well, certainly the increase in computational power has been tremendous. It means that there are things you can do with a realism that just wasn't possible before. That's a huge impact. A related recent development that I'm quite excited about, is the potential for convolutional neural nets and machine learning tools to be very powerful scientifically. One example would be trying to interpret the signatures from cosmic rays, which are so hard to… Let me try to start again. There's some background noise, I hope it goes away, that's distracted me. There are many instances, and the Galactic magnetic field is a little bit like that, where the data looks very complex, and yet you can tell from physical understanding that there's got to be information embedded in it because there's some underlying phenomenon that is—coherent is not exactly the word I want—but it's obeying physical laws. So it might be that there's turbulence, for instance, or some other effect that makes the patterns complicated. And yet there's information embedded in that. So, I think this is going to be a really powerful new direction that I'm working on—just started with students to work on—a couple of projects. How to exploit machine learning when you don't know what the phenomenon is you're looking for, that's the interesting challenge. It's one thing if you're trying to model something like events at the LHC, where you know your theory is perfect and it's just that they make complicated signatures; there it's relatively straight-forward. But when you don't know what the physics is that you're trying to model, and yet you believe there's information imbedded in the data, that's certainly very challenging. And then of course the powerful telescopes—the whole ensemble of astrophysical information coming from ground-based and space-based telescopes of all different wavelengths plus gravitational waves. So definitely the data has been phenomenal and had a huge impact.
You mentioned earlier that you have, in some ways, you've circled back to particle physics. Can you explain sort of broadly what compelled you to return to your intellectual roots, so to speak? And in what ways have you worked in particle physics in more recent years?
Well, primarily it's through this hypothesis about the possible identity of the dark matter particle being the sexaquark. So, it's a very specific thing that drew me back. Because otherwise I was doing more empirical, phenomenological studies—for instance, trying to characterize the magnetic field of the Galaxy, or characterize the way ultrahigh energy cosmic rays are formed, or things like that. But anyway, what I realized some years back was that there's a particular bound state of quarks, namely two up, two down, and two strange quarks, which can combine in a way that's extremely favorable energetically—because of the way the Fermi exclusion principle works. And the idea that this particular configuration of quarks could be deeply-bound came to me... that it could be enough lighter than two Lambdas to be stable. (If you could separate the quarks into two baryons, each of them would have one u, one d, and one’s quark—just like the Lambda particle that I was studying for my thesis; I never thought of that connection before!) But anyhow, the naïve idea is that this state is only moderately bound; that hypothesis was put forward by Jaffe in the ‘80s, and there were lots and lots of experiments searching for it. It would decay in a billionth of a second or so. That's now pretty much excluded by experiment. Or maybe there’s a weakly-bound short-lived state something like a deuteron but made of two Lambdas which decay; I believe now there may be some evidence for that. But neither of those cases would be interesting for dark matter. What I realized—actually, it was thanks to Feynman. There were a few principles that Feynman loved and kept talking about over the years that I was in Caltech. One of them being that when particles have a particular quantum relationship, the attractive force is especially strong. I won't go into the technicalities. But anyhow, this particular configuration of quarks obeys that principle. And so, it occurred me, maybe they're just a lot more bound than people's simple-minded modeling is showing, because—in my opinion—our understanding of how quarks bind to make hadrons is so inadequate we would never get the answer right if we didn't already know the answer (both laugh). And then we struggle to make models that agree with data. So, if this set of uuddss quarks happened to have a special character because of this extra force, that isn't so important in all the other particle states we’ve tried to describe, then of course our models won't incorporate that. So anyway, I said to myself, I should explore this possibility. And the reason why I started thinking about it is that people are always saying the way we know there's physics beyond the Standard Model is because there's dark matter. And of course, also dark energy and inflationary cosmology, but if you put aside cosmology and inflation and neutrino masses (which might be a trivial extension of the Standard Model), the evidence that people give for BSM physics is that there's dark matter. And I thought to myself, well, you know, is that really true? Could it be that dark matter could be made of sexaquarks? I call the deeply bound uuddss state a sexaquark. Six quark states or -- usually -- three quark, three antiquark states, are commonly called hexaquarks. But this state, if it exists, is so special, I want to distinguish it from all of the rest. Plus, the Greek prefix hexa- should logically be reserved for a triple q-qbar, following tetra- and penta-quarks. Plus, the letter H is used for the Higgs, so I wanted a different letter; the letter S wasn’t already taken. And so, I chose sexaquarks. I'm used to the name now, but it's very funny, it really does cause some people to get distracted or embarrassed or something. (laughs) But anyway, I don't notice it anymore because I'm used to it. It is logical and apart from the "sexa-" aspect, it would be a perfectly fine name and I thought why should one be deterred by such puerile considerations? Anyway, if you make the hypothesis that this particle is 10% more strongly bound than its mass scale, then it becomes lighter than two protons and then it's absolutely stable. So I worked out a few years back, whether it would have been detected in particle physics experiments. I looked at all of the around 20 experiments that had been searching for Jaffe’s H-dibaryon, and each of them made an assumption of some kind or other that, as it turned out, would have prevented them from seeing a long-lived sexaquark. And then I started looking at other constraints that one could place on such a particle from nucleosynthesis, and whether if it were the dark matter, would it interact too strongly and be detected and excluded and so on and so on? I worked out that it passed all of the conditions. Then I started thinking, well, how could I calculate its relic abundance, and I worked out all of the standard scenarios that people use and realized they wouldn't be valid for this hypothesis. I was stymied for a while, and then I realized, oh, I can try to do it with statistical physics, and then I did the calculation, and it came out to be right. So, then I was really sold. However, the whole thing has an interesting sociology. The first paper I wrote—about the fact that a stable S below 2 GeV wouldn't have been ruled out—I wrote in 2017 and I submitted to PRL. But the referees were very negative. One said, you know, people have been talking about the H-dibaryon for 40 years. Why is this new? This is not timely. If the author really believed in this, she should have followed in up sooner after she first pointed out the possibility in around 2004. Therefore, it shouldn't be a Phys Rev Letter. Well, I was really burned up because it was a completely new proposal that it was stable. The referee said, well, everybody's always known that if the mass were light enough it would be stable. Of course! The fact that that's obvious doesn't mean anyone actually thought through whether stability was allowed by experiment or followed up on its consequences. So, I was pretty upset—I thought that it was a pretty ridiculous point of view, to say that it shouldn’t be published because it was not timely... And the other referee gave me the only referee's report in my life that has been genuinely belittling—it was so dismissive and pejorative. It was horrible. I even protested to Phys Rev Letters, but they were pretty indifferent to that aspect and didn't respond to my complaint. So I decided I didn't want to publish it somewhere else; if it turned out to be true and it got the Nobel prize, then I was going to publish these referees' reports and let Phys Rev Letters be ashamed of themselves for (laughter) not doing a better job. Because they should not accept somebody's referee report as—how should I say, as… A person who writes a sexist and demeaning referee report is not being objective enough that you can trust their scientific judgement, I would say.
If they're somehow so overwhelmed by what their feelings are. And so, to me, the fact that the editor accepted that as a basis for rejecting the paper, was scandalous. He should have said, okay, I have to get another referee because this person obviously is not objective enough. Or at least, I think it should be taken as an obvious evidence that it wasn't objective. Anyway, so I said to myself fine, it'll be one of these famous papers that isn't published. Or else it'll turn out to be wrong and then it won't matter. Not wrong, but that the sexaquark isn't that light. And so, then I wrote the paper in 2018 with the calculation of relic abundance and finding the answer was around five times the baryon abundance, as observed. I again submitted to PRL and I got similar kinds of objections. A paper came out by Kolb and Turner, who are very well known in the field, whose title was, "A dibaryon cannot be the dark matter." Their argument was based on making an assumption that this thing is like a deuteron, it's loosely bound. I had even mentioned, in passing in my paper that, because of its special structure, it didn't have this character, which was really important in why the thing didn't disintegrate after it was made. But I guess they wrote their paper without understanding it. They sent it to me, and I pointed this out, and what they did is they added a couple sentences at the end saying, "Of course, this argument is invalid if, in fact, it doesn't disintegrate." But they didn't change the title and the entire paper, and they didn't change the abstract, they didn't change anything except for few sentences acknowledging this caveat which in fact completely falsified their blanket claim. (The right way to have used their analysis would have been to derive an upper limit on the dissociation amplitude, needed to preserve the DM to ordinary matter ratio produced in the quark-hadron transition.) But later Mike Turner said to me, "Well look, we'd done all that work of writing the paper. We didn't want to have to rewrite it." Anyway, they submitted it, it was published, and I've had a hard time since, getting grants to work on it and getting related work published... So I decided what I'm going to do is I'm going to take advantage of the fact that the new Phys Rev X claims to be cutting-edge, but it doesn't have such a short page limit, and so I could really cover all of the different aspects at once. (I don't want to just publish it in a sort of archival journal, because I think it's really important.) The point is, it's so radical an idea, that you have a huge number—I mean, any reasonable person would have a huge number—of questions, and you can't just address them separately. So anyway, I'm very excited because I think the paper is terrific. And I'll see what happens. Of course, it may not be what nature has done, or it may be that it is, and we'll find out in a few weeks by discovering the bound states (laughter). When I reflect about all this now, I’m asking myself – why do I continue to work on this topic when it’s so traumatic? (The insulting referee gave as one reason the first paper shouldn’t be published, that experimentalists might waste their time searching for it. But if the sexaquark conjecture is not right, it would be my own time more than anyone else’s that you could say has been wasted!) I think the answer is mainly because of a feeling of obligation to the field – somebody needs to be sure we don’t unwittingly overlook something of such fundamental importance, and my career is secure so I can afford to do it. But another reason is my conviction that one should not dismiss something based on preconceived ideas about whether it seems “likely.” It occurs to me now, that maybe I sort of identify with the sexaquark, and don’t want it to be dismissed out of prejudice…
Well, Glennys, now that we've sort of brought the narrative up to your very current work, I want to ask you one last question that's, it's a very broad question that's sort of, you know, it will draw on your retrospective thinking about your career and also I ask you to sort of consider where things are headed. And first, you know, I was struck when we were talking about your days at Caltech, how you emphasized that you know the world of particle physics and cosmology were really quite separate. And you know, obviously, your career, you've sort of been at the vanguard of bringing these two fields together. So I wonder if you can first reflect on what role you played and how you sort of rode that wave of more inclusive or a more multidisciplinary approach to physics in general, and what that might mean for where both, you know, particle physics and cosmology is headed in the future? Both in terms of thinking about them as discrete disciplines and thinking about, you know, the broader effort in physics to unify as many of these disparate fields as possible. So, I wonder if you can just reflect a little retrospectively about how the field and how your own work has brought us to where we are, and where this is all headed in the future.
Oh, I think there's absolutely no doubt that the major part of each field is kind of merging. I mean there are certainly important parts to particle physics and astrophysics and astronomy that aren't influenced by each other. E.g. people who are doing nuclear physics or low-energy hadron physics, or perturbative QCD, or there's plenty of parts of neutrino physics … but even neutrino physics is influenced by astrophysics, and neutron stars are providing important constraints for nuclear physics! And while certain kinds of astrophysics seem to just be doing their thing, understanding how supernovae work and so on, what's interesting is that even those areas are influenced too. I organized the sessions from the Division of Astrophysics at the last APS meeting, and it was so much fun. Every single session, even about things that were superficially pretty much pure astrophysics, had particle physics implications and connections. And you see it in the postdocs. They're all learning… all the very best ones are really straddling both areas. They write papers on — I'm talking about people doing particle physics constraining dark matter, writing papers about supernovae and how they emit radiation. And somebody else using white dwarfs and their x-ray emission as a way of testing axions. And so, the commonalities are just pervasive, and the astrophysicists have to know (at least should know!) the particle physics connections too. First of all, there are many very well-motivated astrophysical studies whose motivation is the fundamental physics it might reflect. For example, if there are interactions between dark matter and baryons, more than just gravity, as there is in the sexaquark model, then that influences the early formation of structure as the material gathers up, e.g., in making really early galaxies. The presence of those interactions will tend to wash out the production of really small-scale structures. And so that motivates astronomers to look and see, well, how well do we understand the small-scale structures in the universe? There are just innumerable examples. Another example is trying to get limits on the mass of neutrinos. It's almost the case, you may know there's a major particle physics/nuclear physics experiment taking place in Karlsruhe called Katrin, trying to measure the mass of one of the neutrinos by the end point of tritium beta decay. And they are going to achieve a mass limit with untold hundreds of millions of dollars spent and decades of work, which may turn out to be not as good as the limit from astrophysics. Of course, the really interesting thing would be if it turns out that Katrin finds a mass that's bigger than the upper bound from astrophysics (laughter). Then we know for sure there are things we don't understand! But anyway, I just mean it's an example. There's just no end of interplay. The reason is, I think, because the kinds of theories that are beyond the Standard Model are so hard to detect with ordinary, let's say, lab-based experiments. So, the connections between fields are partly because we've been driven there. People have looked and looked and looked for problems with the Standard Model, though the LHC and so on, and mostly they just confirmed the Standard Model. People look for signatures in the electric dipole moment of a neutron or mu’s decaying to electron plus gamma, etc., so in many, many experiments people have searched for ways that the standard model of particle physics could be not right. And then of course, particle physics is very much driven by some—or I should say, very aware of some—really abiding puzzles, probably the most important one being why is there any baryon asymmetry at all in the universe? Why aren't there equal amounts of particles and antiparticles. In which case, everything would have annihilated, and there would just be radiation left, and there's no place for us. No matter to form us out of. So that's clearly a major question, and that question doesn't have an answer in the Standard Model. So, in the search for explanations – oh, here's an example of the axion, speaking of Helen Quinn, she's associated with the axion. That’s a hypothetical particle. It may be that its major effects are astrophysical, if it's light enough then its wavelength is so long, it's extremely hard to see evidence of it in laboratory experiments. And yet, it may play a role on a cosmological or astrophysical scale. So, it's really because of these deepest puzzles in particle physics… even apart from the possibility that sexaquarks explain the dark matter, there are still many other puzzles that point to new physics and really the cosmos as a whole is the best laboratory for that.
Well, Glennys, it's remarkable to hear all of this because there are many particle physicists who doubt the idea that there remains much fundamental work to be done. So, it's quite interesting and exciting to hear your take on these things, particularly in all of the innovative ways that you have taken this multidisciplinary approach with cosmology. So, it's been an absolute delight speaking with you today. I'm so glad that we were able to connect, and I'm really quite honored that you've spent this time with me. So, I really want to thank you so much for it.
Well, thank you! As you advertised, it was fun! I’ll be really interested to see what comes of it, because it's so long and meandering. I don't know what you'll do with it.
(Laughter) Well, I'll cut it here.
[End of Recording]