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Credit: David Giroux
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Interview of Gordon L. Kane by David Zierler on April 4, 2021,
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, David Zierler, Oral Historian for AIP, interviews Gordon Kane, Victor Weisskopf Distinguished Professor of Physics at the University of Michigan. He explains why came to hold a chair in Weisskopf’s honor and he describes his affiliation with the Leinweber Center for Theoretical Physics. Kane recounts his childhood in Minnesota and the opportunities that led to his enrollment in physics at MIT and his graduate work at Illinois to work with J.D. Jackson. He explains that the major topic in particle theory during his graduate work was understanding nucleon scattering and the significance of Geoff Chew’s bootstrap mechanism. Kane talks about his contribution to the discovery of the omega minus at Brookhaven and his research at the Rutherford Lab. He explains his decision to join the faculty at Michigan and his interest in group theory because of the advances made by Murray Gell-Mann. Kane describes the early work in the search for physics beyond the Standard Model, and he explains the value of string theory at the Planck scale. He discusses the possible new physics that would have been discovered at the SSC and why compactified M theory offers a plausible path to moving beyond the Standard Model. Kane explains why string theory is testable and why string theory predicts axions, he offers some possible candidates for dark matter and what compactified M theory offers cosmic inflation. At the end of the interview, Kane discusses his current interests in quark masses and charge leptons, he explains some of the advantages inherent in teaching at a large public university, and he describes why communicating science to popular audiences has always been important to him.
Okay, this is David Zierler, oral historian for the American Institute of Physics. It is April 4, 2021. I am so happy to be here with Professor Gordon L. Kane. Gordy, it’s great to see you. Thank you for joining me.
I think it’s a pleasure to try and do this. It’s fun to review and think about how things happened, which we don’t usually do.
Gordy, first things first. You’re known throughout the scientific world as Gordy. How far back does that nickname go?
Oh, that I actually know the answer to. I was a postdoc at Johns Hopkins and one of the professors was Gordon Feldman. (I noticed in scanning that you have a history from him also). So, soon after I got to Hopkins there would be- one of us would get a phone call and then someone would holler “Gordon.” The secretaries were getting the call and had to find us so they would holler “Gordon” and very quickly he said, “We can’t have a situation like this. Change your name.” And so, that was- Gordy was about October 1963 in Baltimore.
So, as a kid to your parents, to your friends, you were not Gordy. You were Gordon growing up?
No, it was- yeah, most- more Gordy, but Gordon. If I did something bad, I was certainly Gordon. And, yeah, to friends it was more common but not standard, whereas it became standard after that, and even people who didn’t know me. And actually, I noticed recently the-with the medical system being more and more computerized now, when they call me for an appointment or anything they- it’s Gordy, because that’s how my name got to be on the medical system, even if it’s a formal call.
(Laughter) Gordy, would you please tell me your titles and institutional affiliation.
I’m a professor of physics at the University of Michigan. I am a distinguished university professor of physics and that comes with a name and the name is Victor Weisskopf who is a wonderfully well-known physicist, first director general of CERN, professor, and department head at MIT. And through an accidental twist I got to know him extremely well. He was a mentor. If I go in order, I took a course from him when I was effectively a senior at MIT. That’s a slightly complicated story. But during that year I met him, and then it turned out that one day he turned up at the physics department in Ann Arbor after I was on the faculty and turned out that he had a son who lived in town, so he would come to visit the son. The son was on the faculty, in economics, and had a family. So, Viki came twice a year sort of to visit and whenever he got tired of relatives, I was his refuge in physics, so he would show up and we would talk physics many times. And that was a very- well, continually exciting and helpful accident that he was there, so I- and a very good mentor. So, that’s why I picked his name for the chair, the distinguished university professor chair. But then it turned out that there was a rule that it had to be the name of someone who was associated with the University of Michigan. He had spent a semester here, again because of the relatives, so we tried that out and hoped it would be close enough to the rules. The provost who was deciding whether I could use the title was Ernest Courant’s son, Paul. And Viki had grown up with Paul around. And so, when it came to him to decide whether I could use the name he simply approved it regardless of someone’s interpretation of the rules. And so, it came to be that that was the title.
Gordy, when did you go Emeritus?
When- January 1, 2020, a year and a quarter ago. I’m eighty-four.
Oh, so it’s still a relatively recent development?
Yes. I retired from teaching but not research. Michigan actually has a status called Active Emeritus.
What is your status? Do you retain an affiliation with the Leinweber Center for Theoretical Physics?
Yes. That’s a long story. It’s a center for particle physics and cosmology. Now, it’s gone through a couple of incarnations. But Larry Leinweber is a guy who- a great guy, who by an accidental path again, without any good plan, he sold his software company for a lot. He wanted to have a little closer connection to the university. He was interested in lots of things. It wasn’t that we found him. And actually, for a present for some holiday he was going take his family to CERN to see it just because it was an exciting, amazing place in the world. So, he had no special connection. So, we have an ATLAS group in the department, so one of them found the guy who gives tours at CERN, who happened to be a former ATLAS guy. So, that was straightforward. And arranged the tour. They loved it. And Leinweber talked to our department chair who pushed the Center as a place to fund and told him the sort of amount it would take to get the name associated with the center. And instead of the Michigan Center, it became Leinweber Center which is endowed now. I think I’m a full member. One of my PhD students is supported next year by the Center. The faculty cannot use that money for anything personal themselves. Not for salary or travel for faculty. But for students, to fund more, better students, for funding some post-docs, to bring in visitors; that’s what the money’s for. And we’ll talk a little bit about that later, but centers are a crucial thing in particle theory and cosmology, and all the top places have a center, one way or another. Places like Berkeley had a lab first and then the equivalent of a center and extra money that way. And there is a one-to-one correlation with requirements that might get named if you ask for a list of top places and whether they have a center. Historically that was something I started pushing for, and at one point in the nineties, I guess, I was on a dean search committee, so I had some connection with the person that ended up being the dean through their interview, dinner and all that. And I started working on the dean who was a woman from the English area and wouldn’t have thought of it. But I started working and kept saying every chance I got that we needed a center. And it was about her third or fourth year here when Tini Veltman, who was on our faculty from 1979, got the Nobel Prize, as soon as he got the Nobel Prize, our department chair went over and said, “Look, these guys can’t be as stupid as they look to you. You should really give them a center.” And I’d been pushing for it enough to fertilize the ground, I think. And the center emerged. Tini didn’t do administrative things, and I was on sabbatical in Santa Barbara when that happened. So, they made Mike Duff the first director. And then Mike left for a job in Imperial College, where he grew up, Provost, I think. And then I became the director after that for- the dean said six years maximum for positions like that in the university. So, for six years plus a year while we were looking, in case we could get an outsider- use it as a lever to get an outside person. So, then I was director emeritus of that. And now I just stopped teaching and became emeritus since a year and a quarter, January.
Well, Gordy, we’ll develop all of these stories as we go through the narrative. But first, let’s take it back all the way to the beginning. Let’s start first with your parents. Tell me a little bit about them and where they’re from.
My parents were both born in the U.S. of people who came from pogroms in Eastern Europe. They were non-German Jews, but the pogrom doesn’t distinguish. They were normal people in villages in the Ukraine, Lithuania and they moved a couple of times because of pogroms and then finally came to the U.S. My mother’s father became a contractor. I’m not sure what you call it. Guy who builds houses and buildings and stuff. And he was reasonably successful, not a big deal. And my father’s father was a typical story of immigrants. He didn’t speak English well and he was a tailor and worked at an old shop in downtown St. Paul where there were rows of stores and similar kinds of things. And my father then through- I don’t even know the story of how, but he ended up owning an auto part store in a town called Faribault, about fifty miles south of St. Paul, and driving down every day. And in auto part stores, you can’t carry everything you need for repairs, so whatever turned out to be needed, they would call suppliers in St. Paul, Minneapolis, where you could get anything, and my father would go get it and then bring it down the next morning. That gave him a nice lever to do something special. So, it was good. But he died, when I was a junior, 1950-something.
Gordy, do you know, is Kane an Anglicized version of perhaps Kohen or Kahan?
There may have been some earlier thing, but my father changed it from Kanevsky. And I’m not Irish. But when I meet strangers, it’s an Irish name.
Gordy, did your mom work outside the home at all?
Well, that’s a fascinating story too. She did get a bachelor’s degree at the University of Minnesota, actually in French, and never used it in traveling. But I was the oldest of four, so when my father died very prematurely, there were three to follow me who all wanted to go to college. So, my mother who was five feet tall and can barely see over a steering wheel started doing what my father did in a very heroic way, and she did it until the last one was through the university. And so, it’s many years driving down in the morning, coming back and making dinner, and really working outside the home. And this little, tiny lady would be going into all these auto part supplier stores. And they were pretty helpful to her.
And where did you grow up, Gordy? What neighborhood was it?
At first, we lived in Faribault, but only when I was too young for it to matter. Then we moved to St. Paul and I was probably eight or nine or ten. I don’t remember exactly. It was somewhere around that. And the reason we moved, I didn’t know at the time, but the reason we moved was because they were going to make me get a Bar Mitzvah, which they did. And so, we joined the temple and all that stuff. And it’s a social construct for people who arrive from different sources and it’s a very helpful thing. I’m not observant at all, but I did the stuff, and my parents did the stuff. And it’s a way to be part of a social group. And my friends and things were kind of readymade. We lived in a nice area called Highland Park.
Gordy, when did you get interested in science? Was it early on?
Yeah. I had the typical kind of interest that many children have. You know, occasional questions about what the universe was all about and the kind of things that a lot of children discuss, I think. But there was a specific thing I got as a present, as a Bar Mitzvah present. I got a book by a journalist. It was called The Universe and Dr. Einstein. I have to admit I looked it up. By now, I wouldn’t remember the name. And Lincoln Barnett was the author, was the journalist. And there was this book with this Einstein guy who I- maybe I heard of him, but I certainly didn’t know anything else. And he was working on the kinds of questions that were kind of exciting. You know, you could get a job doing it, which is not something I’d known but it gave me goals and thinking, you know, quite a bit. But St. Paul was a really intellectual dessert and so- let me change the story slightly. My junior year at MIT, my father was dying. And it took him a long time to die, so he needed to stay at home and have care. I had gotten through high school easily but had no special standout qualities- a guy like Wilczek who works puzzles at the breakfast table. Or dinner. But it was pretty easy for me. So, when I got to MIT, I didn’t know what I was doing. I was this kid from the Midwest who had no idea what classes were like and what anything was like. And I by accident had an aunt and uncle who were tournament bridge players for relaxation, and they taught me how to play bridge well very early. As I was leaving high school, I was at the level of a tournament bridge player. So, my first year to MIT, I assumed I could keep raising my status by winning in bridge tournaments and do school as easily as I had been. But that wasn’t the way it worked because of course at MIT, to get good grades you have to work full-time. So, my grades weren’t as good as they should have been. And then my junior year my father was dying, my mother was driving to the store, not staying at home, and my grades weren’t as good as they should have been. And so, I took a year off. I also got- had bad medical issues. I got psoriasis all over my body which is scary. There’s was no cure for it then. It’s completely different now but there was no treatment of any kind for it then. And for a teenager, that’s a really scary thing. So, I dropped out of school, stayed home, and took care of my father, then started at one point going to the University of Minnesota since it was there, and I could take some courses. And actually, I got a degree from there quickly- yeah, the degree was in philosophy, bachelor’s degree because all those courses were not so hard. But it was actually helpful because I was getting more and more interested in courses about how the universe worked and what we’re made out of. And that was before we knew- that was before the Standard Model and before any of the cosmological successes except there must be a Big Bang but that was it.
Gordy, if life had not gotten in the way, was your sense you would have stayed at MIT and gone straight to graduate school from there?
I think the answer’s yes. After my father died, then I got married and it gave me some support system. And I did go back to MIT for a year. So, during that year, I applied for graduate schools and got into University of Illinois, PhD program. It turned out that I learned later that Francis Low- did you interview him before he died?
Okay, so Francis had called Dave Jackson at Illinois said, “Accept this guy.” Because I’d been asking questions and talking, and it showed enough to make it interesting. I got to know Francis, really pretty well, on the physics side. And he facilitated getting into graduate school which, one will never know, but I might have had big problems because of the poor performances earlier. But anyhow, that answers your question because I did it and I got into graduate school in Illinois. Illinois then was a very well-known school. It had- Dave Jackson had gone there, who was my adviser. And Nishijima who invented part of the Standard Model. And I was trying to think of his first name. John Bardeen was famous in condensed matter, and Bardeen and Schrieffer were working on superconductivity, and writing those famous papers. So, Illinois, besides my getting into a good place, it was a well-known school during that time.
Gordy, what year did you start at Illinois? Was it ‘58? ‘59?
’59. And I got my PhD in ‘63.
And did you know it was theory? That you would pursue theory for your thesis research, or you were open to experimentation as well?
I can change a light bulb and that’s about it. And I didn’t enjoy it and I wasn’t good at experiment. I enjoyed theory, and hope I was kind of good at it.
Gordy, was anybody talking about cosmology or even astrophysics at that point?
Not very much. ‘64 was the Princeton guys finding out about the cosmic microwave background radiation, which took time to settle in as a concept. Jim Peebles was writing cosmology papers at Princeton and so there was some work. I don’t remember too clearly. I didn’t work on it at first at all. But it was starting. And inflation entered in 1982, so it didn’t have that crucial concept to make it something that we could understand.
Gordy, what were some of the big things going on in particle theory when you were a graduate student?
The biggest- well, they didn’t teach field theory in the departments because it had a bad reputation because it was strong interactions and we had no idea how to do that until QCD appeared, which was in the beginning of the seventies. That kind of concept had simply not existed before. So, the big fashionable thing when I got my degree was understanding nucleon scattering, and the new particles. And indeed, my thesis was on that kind of thing, so I had- nobody today has any interest in it.
Gordy, how did you develop the relationship with Jackson so that he would end up being your advisor?
Well, it turned out he- because Francis had called him, it turned out he was set up, and then I took his course, then he was writing the first edition of his famous book. And so, well, this was already after I was a student, but I worked all the homework problems in that book, of which there were many, that helped solidify him being an advisor, because I could do that. Also, we had the same birthday, a good omen. So, I did the kind of research first mostly that he did, which is calculations and ways to describe data systematically. But there was no big progress or real interest in that stuff unfortunately. After the discovery of the J/psi, he moved to describing systems like that and applying what we knew about atomic physics to those kinds of systems. And I mostly didn’t want to do that. I wanted to go to beyond the Standard Model of, whatever it was after the early seventies. That was complicated too. Michigan didn’t have an expert in the Standard Model. A lot of places didn’t. It didn’t exist in 1971, and it was completely in place by 1973. But it wasn’t long and drawn out at all, so one had not learned it before it became relevant in terms of theory, working on things. We worked on dispersion relations and analyticity, too- a big field in String Theory today involves analyticity and unitarity, and they’re doing the same things we already did in the early sixties. So, it’s interesting
Gordy, was there anything going on in the world of experiment that was relevant for your research as a graduate student?
Yeah, well, let me mention one other theory thing first. That was Geoff Chew at Berkeley was pushing the idea of a bootstrap mechanism where things had to settle out because they had to and try to make a theory that does that. So, that’s the first thing I worked on as an assistant professor. I wrote a couple of papers there that were certainly publishable but not breakthroughs. and that area was not- it was just past its peak at that point. So, that was what was the main fashion in theory, and I wrote some papers on the description of scattering and did pretty well there. And working with Regge poles, which was the way of- in that domain, the way of taking some different states of increasing mass and unifying them into one idea. That, along with the pole on the complex plane. And that was a big sub-field in which I worked on some. And- but a variety of things. One- actually a paper of which I’m rather proud is during that, the omega minus was discovered at Brookhaven. And Murray Gell-Mann had just at that stage predicted it. So, the omega minus was predicted and then found. But it was- it’s an unstable particle that decays very quickly and it was hard to study. So you could deduce a little bit about it from its production, but I figured out from its decay modes that you could actually measure it’s parity which was important also because it had to have the same parity as the other members of the decouplet that Gell-Mann worked out. And testing that was important. That’s one of the few papers that I wrote alone because I just figured out how to do it and wrote this paper. It’s completely different from other kinds of things like dispersion relation analyticity and were projects with grad students or postdocs.
Gordy, besides Jackson, who else was on your thesis committee?
I don’t remember very well. I saw you asked Frank that question. I-
I always like to ask that question.
Yeah, so I anticipated it and I couldn’t even remember who it was. There was a guy whose name was Roy Schult. And I didn’t know how to- I don’t know how to look up who was on the faculty then. But he had just come on the faculty three, four years before me and was working in the same areas, so he was the guy that I really interacted with. Nishijima was a brilliant Japanese and he invented strangeness and filled out the big part of the Standard Model. He wasn’t the only one, but he wasn’t- he was Japanese, and he didn’t communicate well. So, I can’t remember. He would have been probably on the committee, but I can’t remember, and I’m not sure. There were guys like Rudy Haag who was- he would have been a string theorist today. He was an analyticity theorist and, but he proved theorems about scattering amplitudes and what you could do with them. And he was as famous as Arthur Wightman at Princeton, for example. Jackson historically had always interacted a lot with experimenters in interpreting data, so that was what I was trying to do also. And [he] certainly talked with the experimenters a lot about what needed interpreting and then putting it in a form that would be ideas that could enrich it. So, if you- but if you look at the literature in that era, we have nothing remotely like today you have nothing like the Standard Model then. But new particles were being discovered, that’s what was new, all the time. And sort of the history of particle after particle turning up and that’s what the experimenters were searching for. And that got systematized first by Gell-Mann with the eightfold way, and then after that got systematized by the Standard Model and solved. So, the whole idea of quarks didn’t exist when I got my PhD and all that other stuff, gauge theories. I had a sabbatical coming, and in the first few years when you get a new job, you spend a lot of your time teaching because you hadn’t ever taught and written lecture notes and stuff. So, you do less research. And so, in the sabbatical I thought- I went to a joint sabbatical with Oxford and Rutherford lab. Rutherford at the time had a theory group which was strong and large, and they had funds doing particle physics and experimental groups based there. So, we lived in Abingdon, which is a small village in between Oxford and Rutherford. Actually charming. Lots of good memories of living there. But a guy named Graham Ross, who was a postdoc from Oxford and Rutherford too, had just shown up as a postdoc at Rutherford one year- just a new postdoc. And Graham has learned the Standard Model getting his PhD. I guess from John Taylor in Oxford. And he taught me the Standard Model, which was a great help. You know, he understood it perfectly. And it’s a different way of thinking and doing, totally, but over that sabbatical year, Graham taught me a huge amount. So, that was lucky, running into him, and him liking him very much being able to know more than a young faculty member when he was postdoc. All that was very fortunate.
Gordy, was your sense- was Rutherford an exciting place to be at this time?
As exciting as any place that didn’t have a particle physics lab. And a little more exciting than that because it had a big physics lab in many areas they had. But no senior gauge theory people. So, the experimental groups had the back-up of a lab to help make equipment and stuff. It was a little better funded and supported, more visitors, and stuff like that as well. But particle physics wasn’t its main mission, so within a few years it started to go downhill from lack of support- a conscious funding decision by the British. So, it is- now it’s probably not- well, I don’t know if there’s anyone left doing particle theory.
And did you head to Michigan straight after Rutherford or there was another stop in between?
No, Rutherford was a sabbatical. So, I was on the faculty at Michigan and the seventh-year sabbatical.
Oh, I see. I see.
Yeah, so places didn’t have money for visitors in those days the way they do now where you just bring someone. There were few centers. So, we would go places in summers a lot. Our first trip to Europe was- I got on the faculty in ‘65 and then the first trip to Europe was in ‘68 to give lectures at a school in Finland. The guy arranging it had been at a summer school with us in Wisconsin, Pekka Tarjanne. But he was arranging a school, and so he invited me.
Gordy, tell me about the faculty when you first joined at Michigan. How- was it a large department even then?
Yeah, a large department. It was as big as any department except MIT and Berkeley. Fermilab didn’t exist then. The University of Chicago wasn’t big. And Illinois had at least guys I mentioned like Haag and Nishijima and Jackson. They were very well-known people. And everybody knew who Bardeen was, even not in this field. And David Pines was there and enriched the department. He didn’t know about particle theory so much. But there weren’t so many visitors, in which case you didn't have a seminar every week. But there was a coffee break and most people connected to particle physics came and so you talked to people there.
Gordy, as you say, during this time, it seems like there’s a new particle discovered every day.
How did this affect your research? What were you working on by the mid- by the late 1960s and early 1970s?
Learning group theory because of Gell-Mann, and working on the bootstrap calculation where you break down something where you exchange the same particles in the t channel that you might get in the s channel and following the kind of path that a number of people- not a large number but some people had gone down with Geoff Chew’s enthusiasm. But Jackson was not a fan of such things. So, after I came to Michigan, I thought about it and I decided it would be exciting if it were true. So, I did a bootstrap calculation, and it worked but was clumsy. The department was big it’s always been- outside of the top private schools, it’s been a good university and at that point it had a number of famous people in particle theory. I wasn’t going to do formal field theory, but most people still enriched the discussion. I had another fortuitous helpful thing at Hopkins. There was a graduate student during the time that I was on the faculty in Michigan. I overlapped with him one year at Hopkins, but he was doing-looking for a thesis problem and Gordon Feldman and Tom Fulton who were the senior guys, were a little behind being caught up in the exciting fields at that point. So, I ended up as this guy’s advisor and we did a more ambitious bootstrap calculation which technically worked but was so clumsy that it couldn’t have been a way to understand the world. Bill Palmer. Later he got a faculty job at Ohio State. But we worked on a lot did a huge amount of computer work. So, I got him going and then I moved on to the faculty at Michigan and he spent two more years finishing his thesis but stayed at Hopkins for that and we got together one summer to do some work.
Gordon, what was going on at the national laboratories in the 1970s that was compelling to you?
Nothing that I knew was compelling. Berkeley had a bubble chamber and was discovering more particles. Fermilab didn’t exist. SLAC didn’t exist. They were building SLAC.
No, I’m saying in the 1970s. SLAC, of course, is already well underway by the 1970s.
In 1974 the J/psi was discovered. And I have to check the date, but in the 1970s, I was already well enough known to be elected a fellow of the American Physical Society in ’76 I think. During the time that the Standard Model was being discovered, so, the Standard Model is compelling and needed some tests but it falls into place so cleanly that you just know it’s not- it has to be right. And so, but there were a lot of calculations to do to check things and predictions made by the Standard Model. I don’t remember too cleanly. I was connected to a lot of experimenters then. The first Snowmass meeting occurred. And Marty Perl and I were the leaders of the Beyond the Standard Model session group- group. So, all the stuff that I was involved in thinking up and pinning down and getting a working group going and so forth about all the Beyond the Standard Model things, in particular Higgs physics, which had become my area in the seventies. That’s another complicated story. In 1971, when the Standard Model was being written down, and finished in ‘72 and ’73- in ‘71 I had a difficult back surgery, was completely knocked out for a semester at the crucial time, and we also bought a fixer-up big old house near campus and moved in then, which required time. So, I missed basically the day-to-day excitement of the Standard Model. I was well enough connected with people at SLAC, which was the center of everything then. I was well enough connected so that I could talk to them and learn stuff, but I didn’t have time to do things. Then by the mid-seventies the thing I focused on were the single Standard Model Higgs as well as something called supersymmetry that was occasionally talked about in this seminar. Nobody knew much about it. And I kept asking how one could test it and no one knew the answer. So, I worked on that. For example, I wrote a paper with the first Feynman rules for producing a gluino pair and stuff like that. And so, I was working on extending the Standard Model. But my first thesis student in those areas was Howie Haber, who is now a Distinguished Professor in Santa Cruz. And I think he’s retiring. No, I think I beat him on teaching. But he was my first student and that was working on Beyond the Standard Model physics. I got him working for his thesis on two Higgs multiplets theories.
Gordy, in the 1970s, the very early days of String Theory, was that on your radar at all? Were you aware of Green and Veneziano and Schwarz at all?
That was 1986.
Well, but it starts earlier though.
No, there’s a couple of papers. But the crucial paper was by John Schwarz and Mike Green. And the thing that they did was prove that if you- if the world is ten dimensional then there are no anomalies in your theory. Before that every theory people had written down that included gravity and quantum theory had anomalies, and so, couldn’t have been right. And the thing that was exciting and burst on the world and changed directions for 500 people was the derivation of the absence of anomalies if your world has ten- nine space dimensions and one time dimension. And then Green and Schwarz wrote that paper. And then right after that, a lot of people jumped on it. They proved many things that were crucial and- well, let me come back to that too later ‘cause now I do work on that. But the history of getting there is different in some ways. But back before 1985, there was no String Theory in the modeling sense, and nobody working on anything relevant.
Gordy, let’s go back to 1982, in Snowmass. So, when you’re thinking about new physics beyond the Standard Model, does that automatically mean searching for projects where you’re operating at higher energies, or is there possibly more to it than that?
No, not necessarily higher energies at all. One of the most interesting measurements is the muon magnetic moment, the g--2 for the muon. So, that’s one thing I worked on calculating during that era to see what happened. And it had supersymmetric contributions. So, then you get a prediction that depends on the slepton masses. It’s interesting because it’s an indirect probe of something like supersymmetry which will contribute at the three percent level to the value of g- 2. Their experiment is being repeated now and they moved the big Brookhaven ring to Fermilab. They put it in the ocean at the East Coast, went around and up the Mississippi as far as they could. And then they put it on a truck. It was wider than the full two-lane road, so they stopped all of the traffic and brought it to Fermilab. And it is—it has been taking data and it is scheduled to report blinded results on April 7th now. That’s three days from now. So, that’s an example of something where there’s predictions where it wasn’t just higher energies. But that’s a sum rule kind of thing and you don’t really know everything then. So, let me introduce the main character in the rest of things, and that’s what’s called the hierarchy problem. So, if you want to be ambitious and make a real theory, the theory can’t- it has to depend on objects which you write down because it’s a theory of something. And there’s no alternative that’s always good except the Planck scale. Right? You have to write the theory at the Planck scale, or you have to introduce, as far as it’s known, you have to introduce some other stuff that depends on how lengths are measured in France or something. So, you want to write a theory at the Planck scale and String Theory is naturally a theory at the Planck scale. But then you have to figure out how to get predictions from it. And the main thing is that the Higgs boson mass is sensitive to quantum corrections. So, if there’s physics at the Planck scale, the particles of the Planck scale will go into intermediate states and amplitudes involving Higgs bosons. And in the Standard Model they do. Then because the mass scale of the Planck scale is 1018 GeV so there’ll be particles of masses in that region. There might be 1017 GeV crazy high masses. And if you’re going to describe the world by relativistic quantum field theory, which you certainly want to be able to do, because it works, and we know a lot about it. So, there’s something wrong with the Standard Model, because it’s got a single Higgs, and that leads you to this- what’s called the hierarchy problem, that you can’t keep the Standard Model scale separated from the Planck scale in regular theory. So, there has to be something new and supersymmetry is the new thing that comes in. And super-partners can cancel the contributions of the Standard Model particles for general reasons with minus signs in the Feynman rules and so forth. We can’t understand the world until we solve the hierarchy problem, meaning preventing this coming together of the scales. You can cast it in other forms but that’s what it is. And soon after- well, not so soon, within ten years after Green and Schwarz and no anomalies, people had been studying how to take a theory that is a String Theory in ten dimensions and how do you make predictions if the world were four dimensions. And of course, that was the big thing for everybody in those eras. And people were more ambitious than anybody had a right to be. But you know some of our leaders. So, they wrote down- they found there were different types of strings and string theories, and that depends on how you can compactify. That means-compactify means taking your theory and projecting it into four dimensions where we live and with luck finding one that works our way. So, quite a lot of people dropped everything and worked on that. And what they found was that there’s several kinds of string theories which will give you different compactification results. And they didn’t find- they found a lot of things. For example, you have quarks and leptons in the string theories. When you write down the structure of the theory, the Lagrangian, predicts there are quarks and leptons. And those are masses in the String Theory at zero modes, but they then get mass by the normal Higgs mechanism so that could be legitimate and that solves the problem. The hierarchy problem is then solved by the super-partners and the Higgs mechanism all can work. So- but two things. One is that they found out that there apparently wasn’t a unique thing. And they’ve been saying, “We’re going to find the unique theory in the world, and it will be out next week.” And it didn’t work. And the- well, I guess that’s just the way to characterize it, that they were too ambitious. When it failed, then they backed off a lot. They were, again, being, they shouldn’t have been. For someone like me coming from the phenomenological side- at that point I wasn’t a string theorist at all. I gave a talk at one conference where I had a section entitled “Predictions from String Theory” and I just put a blank transparency. But- well, there are things to go back to, I guess. But let me introduce the rest of my life there. The point is what happens is that what I had Haber study was two-Higgs theories and see if that would stabilize things in interesting ways and what predictions there were. Then in the late seventies, we learned that supersymmetric theories, in order to have no anomalies, need two Higgs states for sure. So, suddenly in a supersymmetric world, suddenly you have to have two Higgs-es doublets, in theory. And so, it isn’t like putting them in an ad hoc way, even though the initial study had been somewhat that way. And that solves the hierarchy problems. A way to see it is the following. If you look at the Standard Model the way when particles get mass, then the Higgs mass at tree level in the theory, no loop diagrams or quantum corrections is tree level. And there’s an upper bound of the Z mass on the mass of the lightest Higgs particle. It can’t be heavier than the Z. And then there are necessarily going to be radiative corrections. And soon after the thinking on that, Haber got his Ph.D. in about ’77- ’78- I’m not sure exactly. But he and independently a couple other folks calculated the quantum corrections to the Higgs mass. And they’re not divergent, or sensitive to higher mass scales. You get top loops and top squark loops. And the combination of them is finite and calculable. At that point, the top mass wasn’t known, but had an entered, of course, but only logarithmically. And so, the value doesn’t change that much. So, one could see that there was an upper limit of the lightest Higgs mass of about 130 GeVin the supersymmetric theory. And then the other supersymmetric partners, you have two doublets, we have one doublet and the Higgs gives mass to the Ws and the Z, and then that leaves one scalar physical scalar states because there’s two doublets would be two complex doublets. So, four scalars in the Higgs sector. And you’re still only using three of them to give mass to the W and Z. So, you’re left with five particles. And one of them is gonna be that lightest Higgs. But not the others. The others don’t have to get heavy. But that gives you an approach to the Higgs sector where you can really quantitatively calculate it. So, I worked a lot on that stuff. And already from talking with people at summer schools from—I had—well, I was going to write a review, I recall, on a lot of different Higgs stuff that I’d been involved in and make it more complete. But it ended up being a book. I had more—I had publisher contacts. The book was co-authored by myself, and Howie Haber and Jack Gunion and Sally Dawson. And we started out writing a review and it slid into being a book, which is thick. But some different- in different models, you pick different ways of finding the Higgs. And BJ, we had at some meal, we were sitting and talking about this stuff-
BJ, Bjorken, you mean?
Yeah, Bjorken. He said, “You guys got away with writing a book which at least ninety percent is wrong.” And it’s true, so-
Gordy, to go back to 1982, in Snowmass, just so that I understand, so, you’re saying that physics beyond the Standard Model does not necessarily mean operating at higher energies. Is that also to say, just to establish the intellectual origins of what would become the SSC project, were people- were you part of discussions in 1982 that did lead down that line to the SSC where obviously higher energies was the whole name of the game?
Yeah, absolutely, to get the squarks or whatever solved the hierarchy problem.
So, then square the circle for me. On the one hand, you’re saying, we don’t need higher energies to move beyond the Standard Model. And yet the SSC is all about achieving those higher energies.
So, the answer I gave you is misleading. There are a few observables that require- that would require beyond the Standard Model of physics where all you would know is if there was something beyond the Standard Model of physics. You wouldn’t know what it was. You wouldn’t know most of its properties. So, I was giving the answer that to go beyond the Standard Model, almost everything of interest is at higher energies, and higher energies are required to solve the hierarchy problem. If you find the g-2 result, that doesn’t solve the hierarchy problem for you. It just can encourage you to think there’s other stuff. There’s one “other stuff” that is interesting, so I’ll mention it. Later, I’ll come to how we wrote the compactified M Theory that is very successful. And it would solve the hierarchy problem. But in there- in that compactified M Theory, we can calculate electric dipole moments of particles there. So, that’s not higher energy, it’s coming from loop effects in the electric dipole moments of a Dirac particle, the one loop result that was first done by Schwinger for photons in the loop, alpha over two pi correction, which is famous. But it’s just a thing that would be again like the sum rule of many loops of different things coming in and some dominating and getting an answer. So, we actually did predict that the electric dipole moment of the electron should be about a million times smaller than the naïve estimate from super-partners of arbitrary mass because of big cancellations and because when you take the existing limits on masses, we just suppress the electric dipole moment which is at zero energy. So, it doesn’t like heavy things in loops. But we can calculate g-2 and the electric dipole moment, we successfully predicted that people who reported a year or so ago would not find one at one order of magnitude smaller still than what the experimentalist can do. But no other- all other predictions far larger than ours are already wrong. So, I think a good example of how string things can work but we had to work in the compactified M Theory and learn how to do those calculations for that to work. They’re not string theory predictions, they’re compactified string theory predictions. So, that is stuff, again from the nineties, that part. But the SSC story is that it’s absolutely clear that to solve the hierarchy problem, which must be solved if we have any chance of a deep understanding of the laws of nature, you can’t- even if you can write them, without knowing how to separate the Planck scale and the electroweak scale and zero energies, scale and so forth, without knowing how to do that, you can’t have a deep understanding of the underlying laws. So, you must go to high enough energy to test ideas. The first Snowmass was in 1982. So, my influence was mainly toward higher energy and working out ways to detect things so you could find them if they were there. And many people were doing that. And the meetings by fancy panels to establish Snowmass and the SSC took place after that and were totally influenced by that. And the only other person who was equally involved with that and also on some of those committees was Mary K. Gaillard, who was- who did- who understands and can deal with the theory and can deal with all that. And she was effective in that role. But the need for higher energy couldn’t overcome the political-
-situation then. And as you know, the SSC was canceled in ‘93.
Gordy, were you involved in one way or another with the SSC all the way through 1993?
Yes, I was on some committees. I’m not a very good committee member because consensus is less important to me than getting it right. I haven’t learned yet. When I grow up, I’ll be quiet when I'm on committees.
(Laughter) Gordy, the autopsy report of the SSC is something of a history in and of itself.
When did you first detect either budgetarily or scientifically or politically that this might not be a viable project?
I did predict it, right. I predicted what would happen when- so, when they started to build the lab, it was in Waxahachie, Texas. They hired a few people. I went- I spent every summer for three months there the moment- as soon as they had a building. And my main job for which they paid me, was to help Roy Schwitters, who was the director, answer questions and deal with things. So, I should have a one-page memo about every possible question. Or if he knew he was going to get a call that was scheduled from a reporter, he might tell me to come and I could answer all the theory questions that reporters or other people might ask and set Roy up to be able to answer them all. And I was there I guess four summers. But also, one of the people they hired was Frank Paige. So, he accepted the job there and moved. There was the thing called the Drell Panel, which was the big panel which laid down the consensus recommendation of the field and brought it to the Department of Energy for funding. And there was a technical committee before the Drell panel that I was on about what you needed to do, and how much energy you needed, and various things. And Frank Paige was on that also. And when he cleaned out his file cabinets as he was leaving the SSC after it was dropped, he found a copy of a letter that he and I had written, urging that it be staged and that an energy like ten TeV instead of forty TeV looked to us, through all that we had learned, between 1982 and 1990 with a great deal of work done in that time. We knew much more. We knew that- we were pretty sure ten TeV was enough with high luminosity, or fifteen TeV. And I still think that. And we certainly knew about all the troubles of the detector and the beam pipe. And it’d all be solved if it staged- if we built at ten TeV machine that would more or less be like today’s LHC. We knew we should find the Higgs, and we might find other stuff. And Frank found a letter that strongly recommended—that he and I wrote, saying “Don’t go to forty TeV, and build this ten TeV one instead, and then we can’t fail.” And because of funding getting out of control ‘cause the price was- some very nasty things were done in the accounting. Like they always quoted the budgets and then-year dollars, but if you bought the machine and paid for it all at once, then you would not use then-year dollars. And, the extra cost of gaining safety to have a slightly larger beam pipe, so the beam didn’t touch the walls. People were nervous about that. What the accelerator physicists were nervous about that, But, if you only have a ten TeV, that’s not a problem. So, Frank and I were right, and scientifically it was right but there were a lot of well-known people on the committee. So, a couple of other people on the committee said that CERN can reach that sale, so don’t bother us with staging and such things. The committee was headed by Sid Drell, who was a very smart guy, but he had worked on arms control full time for fifteen years already at that point. He was a fine physicist, but things change. And so that was- one could understand why what happened. But the energy was the whole thing because of this issue of the hierarchy problem. That’s what we knew we have to solve. And from the amount of opposition to the SSC that was visible in the physics community, it wasn’t a consensus thing; even in particle physics- and because Congress was getting more and more difficult.
Gordon, it’s a difficult question because it would ask you to predict something that didn’t happen. But given what you were thinking about with supersymmetry and the Higgs in the 1980s, best-case scenario, everything was up and running, ‘93, ‘94 the SSC was in full swing, best-case scenario, what would you have found? What was most likely going to be there at those energies?
Certainly, the Higgs that was found was going to be there, and some super-partners. Now that we know- so, every particle in the Standard Model has a super-partner. It turns out that for good reasons, good theories predict the partners of gluons, so gluinos, and the partners of W and Z, so their super-partners will be detectable. They’re spin one half, because the W and Z are spin one. Those almost certainly will be- those particles naturally come out in the TeV region. And with a 10 TeV machine, you get enough energy to see them and enough luminosity, it’s pretty straightforward at that point. So, we would have known by 1995- they would have known about the Higgs and about supersymmetry and we’d be studying supersymmetry the way that the LEP collider at CERN studied the Standard Model. The Standard Model was formulated but it produced ten to the seven Zs and lots of other particles and scattering. Lots of Ws. And basically, solidly confirmed the Standard Model. And you can learn a lot from the decays. For example, very likely in the decays of super-partners, it gives the particle which forms the dark matter. In almost all theories, that’s true. So, you don’t- that particle’s stable and neutral so it doesn’t interact with the detector. But you can see its absence in some cases. It might be hard. But theorists have figured out ways to do it. So, you can do everything learning something for ten, fifteen years at the LEP collider.
Gordy, given that we’re still in the Standard Model, as it were, what are some of the theoretical propositions that would suggest that there’s something there, given how relatively little we’ve seen after 2012 at the LHC?
It’s the things I’ve been saying. We’ve worked on the compactified M Theory and so we have concrete examples. And if the super-partners were a few hundred GeV for the electrically charged but not colored, and if it were about two TeV or heavier for the colored ones, which is very reasonable. The lightest we could get our colored gluinos, for example, would be one and a half TeV. They naturally have mass like that. You’re starting at the Planck scale and giving these guys mass and it’s not zero. But the theory always brings them down enough so you can get some of them at these stages. So, you would see them. And so, I’m not the least bit worried because the theories turned out to be basically right. And so, whatever it is that solves the hierarchy problem will be found. If you look at CERN’s programs now, it’s got luminosity (basically intensity) frontier. And those are things like g-2 and a few other things. But you have the energy frontier trying to move to be like one hundred TeV. And that’s because if you make a bigger tunnel at all, which you have to do- we can’t just make the LHC better. We have to make a new tunnel. Then you might as well make one that’s at one hundred kilometers and so, there’s been a lot of talk about that. And if you also make your magnets better than the existing ones and put those magnets in a big tunnel, then you get to one hundred TeV for the total energy. So, now that is- that wasn’t at all on anybody’s agenda five or six years ago, but now it’s the leading CERN alternative after the LHC is done running. So unfortunately, they’re not just canceling the LHC and building a new one, which they should do, but they’re going through the whole running of the LHC, upgrading once more after the current upgrade, to get higher luminosity still because the tunnel size is fixed. The Chinese have been talking about the same thing. It would be a spectacular thing for them and put them on the map as leaders in this fundamental field if they built it. That’s a controversial thing for reasons we probably don’t have time to explain. But Steven Hawking and I wrote an essay on why that one hundred TeV machine is needed for science because of the hierarchy problem, and also for cultural and economic reasons, and why objections that were being raised some people were not valid.
Gordy, when would you say you- when would you say you became really fully involved in cosmology?
Hmm. So, 2008. And that’s because we had been writing down the compactified M Theory and had made definite predictions for the cosmology and how things work. And there had been inflation required by the theory, and all that stuff. So now I’ve written as many- in the last fifteen years I’ve written as many papers on cosmology as not. And I’d finally solved the problem of knowing the origin of inflation. What physical object is the inflation? For cosmologists it isn’t a particle. It’s just a concept. They don’t have any physical candidate. But we now think we know what it is. In the process of compactification, you get particles called moduli. The simplest way to think about them is that they specify the size of the Planck scale region. So, the Planck scale region when you go back to that M theory is seven dimensional. And then you find that there’s a manifold with the symmetry of the G2 manifold, which lets you say a great deal. One way you can think of moduli is that, for example, each of the seven dimensions has a diameter. And to have laws of nature fixed, where everything is described by moduli so each of those diameters is described by moduli and every other aspect of the Planck scale theory is. Two planes are formed by some moduli where the particles will cross in various ways. By the time you’re done, you’ve probably got one hundred moduli to describe the seven-dimensional region. And the moduli have to be stabilized, or else the laws of nature will change. So, if those diameters are different then it’ll mean the Ws get a different mass or something like that. So, they all have to get fixed. And that has- the theory has to do that automatically, and the compactified M Theory does. And then the way those moduli work is shortly after the release of energy with the Big Bang, then those moduli feel a potential from interacting with all the other moduli, they interact, and they feel a potential, just like the potential energy in any system. And they roll down to a minimum of their potential. It can be complicated, but they will finally roll to the minimum. And rather quickly and stabilize at the values which you can then calculate in some cases. It’s hard—you can’t do everything, but you can calculate a lot. But in particular, then, we calculate their lifetime and we calculate- we check that the quality of decay by nucleosynthesis so you don’t screw up the calculations for the amount of helium and hydrogen and other things in the early universe. And their galaxy formation will look a little different from the moduli making galaxies than it does if you have the traditional way. The moduli decay: that gives us the particles. All the particles that we know, and love have come from the decay of the last moduli which is the lightest one because their decay rate is proportional to the mass. It may be a little more complicated, with some particles left from decays of the heavier moduli. And so, the Big Bang, for example, is now understood as the decay of a known modulus, and it gives us all the Standard Model particles plus dark matter plus axions if they’re there. Well, maybe they’re the dark matter, too, but it gives us all those. So, they occur in calculable ways and we can talk about them and study them from theory that we have. So, all the work I’ve done with the compactified M Theory comes from a nice story. It’s been with the guy name Bobby Acharya. The name is Indian but he’s English, got a PhD at Imperial College in London. He’s now a professor at King’s College, London, and also faculty at ICTP, the International Centre in Trieste. So, he’s holding both positions. He’s an amazing guy. He totally understands all the things we’ve done. I started working with him fifteen years ago and I guess we’ve probably written seven or eight, nine papers together. And then each of us has separately written half a dozen in that time scale. But the theory can get mathematical. He understands it. And it turned out- a totally amazing thing, the Simons Foundation funded a study which went for four years, and was just ended, and gave ten million dollars for that study. And there’s an executive committee that leads it, and you know, Simon Donaldson who has a Fields Medal and was important to get Simons to fund the thing. And then guys who know some physics like Dave Morrison. And Bobby, who knows both and is sort of the leader. And Mark Haskins. I've gotten to know them all. The main thing they study is the G2 manifolds we compactify on. But the reason I mention it is that it turns out that I’ve gone to some of their meetings, even though I'm not mathematical enough, really. But Bobby turns out to be the guy who answers all the questions at the meetings that they have. And those are all mathematicians in the audience and Bobby knows the mathematics that are related, and he knows the physics and he is astonishing. So, it’s very lucky for me to be able to work with him. The way it happened is that the String Theory world, at each of their meetings has typically one phenomenological person and you could think of it as to provide entertainment. But when they get criticized about not having such things, they can point to one speaker at their meetings. So, I have been trying to make sense of String Theory and get predictions. I wanted somehow to get testable predictions which they don’t generally get. Out of forty talks in their meetings, thirty-nine do not come close to mentioning prediction. And one will mention it but not actually do it. So, I was working on it. You have to stabilize the moduli and we can do that. But it was unclear from the other methods if they stabilized moduli. And there is a fashionable approach labeled KKLT. I don’t know if you've been to seminars and heard about KKLT. So, I was trying to use it to make testable predictions and I couldn’t. So, I think in about 2004, I got invited to be that guy that gives a different talk for amusement at the Strings meeting. And part of it was I explained why I couldn’t make any progress at getting predictions out of KKLT and they should all do it. And the reason I couldn’t get predictions was finally their world is full of what is called fluxes, that are generalizations of electric and magnetic fields when you compactify. The fluxes are just fields that they’re equivalent to electromagnetic fields in the four-dimensional world. But you get lots of other fields that end up being around and they’re all fluxes. And their fields have dimensions just like electric and magnetic fields have dimensions. And all the fluxes in KKLT have and are at the Planck scale basically. They have mass dimensions, but their masses are big- to make predictions, you have to get down to our TeV world, and nobody had done it then. So, I complained and said, “Help me out. I'm not smart enough to do this.” And at the end, in coffee break, this guy who I hadn’t met walked up to me and said, “I know how to do what you want in M Theory.” He said, “I did it in my thesis.” And I literally brought him a ticket to Ann Arbor, and we worked together. He spent one semester in Ann Arbor after a year or two plus visits, and I went to Trieste and London a couple of times. And it does all the things. It actually explains in the- for sort of fun, I made a list of about twenty questions. So, you suppose we could find beyond the Standard Model theory where it took us beyond the Standard Model and explained the world. I’m not very interested in explaining the Black Hole information paradox. It doesn’t affect observables and there’ll be an explanation and I’ll be kind of interested and I don’t think it’s as important as explaining the real world, but string theorists think the opposite. Here is the list of what needs explaining: [ed. note: Kane added this list subsequent to the interview] * Origin of matter (quarks and leptons) * Origin of quark and lepton mass hierarchy? * Origin of weak CP violation * Origin of forces (strong, electroweak, gravity, unified?)? * Origin of electroweak scale (Higgs mechanism, allows quark and lepton, W and Z masses)? * Origin of supersymmetry (or its absence) * Origin of supersymmetry breaking? * Origin of the Hierarchy? * Origin of complete moduli stabilization? * Origin of scales (supersymmetry breaking; electroweak symmetry breaking; µ; gravitino)? * Origin of super-partner masses, values? * Origin of electric dipole moments * Origin of strong CP violation? * Origin of cosmological history? Matter, moduli, or radiation dominated? * Origin of inflation? What is the inflation? * Origin of De Sitter vacuum? * Origin of matter asymmetry? * Origin of flavours, why 3 flavours in nature? * Origin and nature of dark matter? A few are there for technical reasons for experts. Most are clear to lots of readers. Several have calculations.
Gordy, given your interest in making String Theory testable, what would that look like? What is a successful test to verify String Theory?
First, you have to understand that its compactified string or M-theories that have predictions and tests, not string theories. Okay, I’ll go through a lot of them. Compactified String Theories have complications and things that are hard to do but you can calculate some things and make predictions. So, we predicted the Higgs mass before it was found in a couple percent, few percent accuracy. Then we actually predict the whole spectrum of particle masses. We can write down a theory which now predicts the whole spectrum, the squarks and sleptons and the gluinos and charginos. So, there’s as many particles as there are in the standard model, and we can predict each of their masses. And we can calculate how each of them decays. And we can look at the moduli and we can calculate what happens in their decay. So, having moduli earlier in the universe, they populated it with particles, but then the next lighter modulus in mass decays, then you get lots of collisions with the other particles and a lot of them go away. So, it’s a pretty complicated system. But it’s possible. Bobby wrote one paper about it with a PhD student. And I’m working with one graduate student where we write a little bit about it. Our stuff isn’t fashionable, so it’s not picked up by twenty-five people because they are doing the Calabi-Yau studies and not predicting observables yet.
Gordy, why would it not be fashionable? What does that even mean?
You- I mean, you know what fashionable means in particle physics. You’ve seen fashions-
-come and go. And that’s kind of what it means. But it’s a job thing, and momentum. So, string theorists who are working at all on real-world stuff are very few. So, they are- they were all trained to work on strings like the heterotic string and Type IIB and so forth. So, they work in those theories. They build on what they’ve done. That’s normal. And the Calabi-Yau manifolds are much better understood mathematically. And so, you can do things there you can’t do in our case of g-2 compactifications. That’s one thing I’m hoping is somewhat fixed by the Simons Foundation grant, because it’s defined as manifolds of special homology. But in practice that basically only leads you to G2 manifolds. So, we’re going to know much more about /G2 manifolds than we did five years ago. We already do. And they’ve just been extended for three years. So, it’s a big investment in our compactification, sort of the only one of their programs. So, all this works in our theory. It started as a full 11D quantum theory, so it has a “UV completion” automatically. The universe around the time of the Big Bang and the particles that come out include dark matter. There are several candidates for the dark matter. There would be a whole lot of cosmology that can be worked out there. And then these sum rule things like g-2 and the electron and nucleon electric dipole moments and the production cross sections for squarks and charginos at the new collider that isn’t funded yet. And the production cross section for gluinos. Think about how the Standard Model was verified? It was production of e+e- to quark, anti-quark with one of them radiating the gluon to give you a third jet. And that was measured at DESY in 1979. And at the new big collider, we’ll have to separate the production cross-sections for stop squarks and bottom squarks and the decays of those guys, or which one’s decay into few particles or a lot. And in most of the decays, the lightest super partner will occur. And it is likely to be either the dark matter or to decay in the dark matter. I think it actually decays into dark matter. But all those things have to come out right. To make the theory right you have to get the list. Close enough. One thing, Morgan and Claypool and IOP wrote- asked me to write a little book. They had a program of little books. I’ve been using that title for twelve years. I wrote a Physics Today article with this title, String Theory in the Real World in 2008. And what I’m really excited about is that IOP now said they didn’t like their little book program. But they wanted me to write a new edition which is quite a bit longer. So, I just finished about a 200-page book with this title, and it’s at the publisher, so it should be out this spring.
So, String Theories also predict axions. Basically, what happens is that in the underlying theory, moduli and axions pair up, so effectively moduli are the real parts and the axions the imaginary parts of some equivalent complex fields. They predict something about their mass. They solve the strong CP problem with its approach to axion. Bobby and two postdocs wrote a long paper on that. I didn’t work on much, but I’ll be working on part of it for dark matter. There’ll be a proton decay prediction which we haven’t worked out yet, but we will. It just takes time and people. So, I’ve given you a list of a long number of those.
Gordy, on the question of dark matter, it’s fascinating to see how so many physicists from so many different subdisciplines are working on this. From your vantage point, what are some of the most promising avenues to solve this cosmological mystery?
The dark matter? The big detectors. So, there are two ways to solve it. There’re three big detectors in the world. One in the Gran Sasso, which is more NSF funded. And a couple DOE ones. But the biggest DOE one is going in the Canadian mine now. And those are both- it’s been actually an amazing, wonderful thing that we long had predicted certain particles with dark matter. Those have been excluded experimentally pretty much. But a whole new field that I haven’t contributed to has emerged. All- basically all young people, all young theorists. If the dark matter wasn’t what we thought it was, then you still have to use the detectors to have the dark matter scattered. That’s what you've got to find out. So set up a big detector, and dark matter particles will bounce out, and something will recoil. Or if you had a superconducting system, it will make the current flow, and we’d know something was there, and destroy the superconductivity by making or dumping some energy when it’s scattered. The key thing is the dark matter, the universe is made up of the dark matter and we’re moving through dark matter. Think of the dark matter as more or less stable. Maybe some around galaxies. Maybe it’s uniform, everywhere; maybe it’s some around galaxies more than in between. But you can set up a detector and then if the thing you can detect, which instead of nuclei has turned out now- the exciting thing, what you’re asking about in part, is the electrons in the atoms can make. That wasn’t done at all before a few years ago. It was the nuclei that was being studied. And then we’ve gotten together with condensed matter physicists and looked at phonons recoil. But anything- if there’s a recoil in the process, then something can be detected if you claim the backgrounds are negligible Then you can set up a beam and wait for a recoil and see what you’re sensitive to. The masses, the ones that we expected with older analysis, those masses were a few GeV and more. And most of those regions have now been studied and haven’t found a signal. So, people immediately- smart young people started looking at electron recoil and condensed matter physics. Now there are ten or fifteen nice ways to look for recoils or other stuff from the dark matter. And both detectors, particularly the Gran Sasso one, which is the leader I think, it’s in the Gran Sasso tunnel. There is a big U.S. detector which is coming soon. Actually two, I think. So, something will find it. And these detectors are for the first time sensitive enough to find almost anything, rather than the older ones which could only work in limited regions. So, it’s pretty likely they’ll find something. The string theories predict that the dark matter is either made up of axions and of hidden sector particles. Hidden sectors are- you can think of it simply that live in a visible sector which we call the visible sector, the whole universe. And we’re not finished even measuring its properties yet and solving the hierarchy problem, but we will. Then there are other sectors which are like ours but somewhat different. Their moduli got stabilized at different values and then probabilities of certain things happening change in those universes. And we know, given that the supersymmetry solution is right, then we know for a fact that there is at least one other hidden sector. Because we know you can’t break supersymmetry in the visible sector itself, but you can break it another sector and then transmit it to our sector and break supersymmetry with that. So, hidden sector particles are candidates for dark matter. And if you look at hidden sectors, quite a few of them have some stable particle in them. It can be different kinds. It can be a color multiplet which is electrically neutral. And it can be like an electron. So, I think hidden sector particles are likely to make up the dark matter and axions qualify, and it can be both. It would be easier to detect if one of them is most of it, and other is a smaller amount. But we just don’t know enough yet to calculate the relic densities.
Gordy, given your optimism on where dark matter research is headed, I wonder what impact all of this might have on the search for dark energy?
Unrelated. The dark energy searches- dark energy is not stuff that clumps like matter or that interacts with stuff. Nothing will scatter off it. It’s a different cosmological thing which makes space. Simply it has constant energy density. That’s what dark matter is. It’s energy that’s from the gravitational fields. And the experiments for those are basically the ones you know, where you leave a standard candle. So, you count supernovas of a certain type and then you look at whether they’re expanding. They’re unrelated to axions or hidden sector particles. So, dark energy is certainly there, and that’s kind of interesting, but it doesn’t help you understand our world, so I'm less interested in dark energy. Now we know, with dark matter- we do probably know that dark matter is one of those types that are hard to see but possible to see. And we’ll find out, in your lifetime, maybe not mine. But it fits- the dark matter helps us understand the whole world, because it fits in the theory, and we need to know why it’s there. It will help us understand the hidden sectors- to see which ones give stable particles. So, it won’t be an a priori thing with someone smart enough to write down what a hidden sector particle is unless we get people who work enough that the compactified String Theory hidden sectors. So, if enough postdocs are funded in compactified M Theory, then we’ll have a shot at that. But it works like normal physics does, and it’s going along well. And the dark matter detectors are fifth generation and amazing detectors that detect things we never have imagined could be detected.
Gordy, another speculative question. What do you think all of these developments mean for cosmic inflation?
In the compactified M Theory we’ve been able to write down linear combination of moduli that give inflation, so I think we understand it! It’s actually the linear combination, which is like the Planck scale volumes, so if a modulus can do things, so can a linear combination of moduli. So, I was working with a postdoc named Martin Winkler who visited Ann Arbor. And we figured out what the inflaton is. So, the inflaton is approximately the linear combination of moduli that describes the Planck scale seven-dimensional manifold. And then it- that is the scalar field that makes the expansion occur that the cosmologists have been talking about forever. So, we look at its potential, and its potential has a shape that leads to inflation in a slowly varying region. And now we can look at its decays or its connections to other stuff. So, again it’s gonna take time and writing down things, but we’ll be able- we understand inflation now I think completely in principle. We know what its physical field is in our theory. We know it’s capable of describing the observed inflation. That it can make some predictions for some subtle things. But in my view inflation is a solved physical problem that we understand. And if some other hidden sector is going to inflate, then it could lead to a universe. But lots of hidden sectors that exist do not inflate, and we can figure out each one by one. So, we understand inflation. We haven’t had time to calculate much more. I’m still somewhat funded. DOE won’t fund me because I retired. The university very generously gave me some funds for travel and visitors and computers, etc, for a few years if I stay active, more or less anything else for research, for five years. So, I haven’t been able to use that for the last year, unfortunately.
(Laughter) Gordy, just to get your pulse on where things stand today, your pulse on the overall sense of the field, this goes back to a question we discussed right at the beginning of your career, and that’s your sense of where observation and experimentation drives theory and when theory drives observation and experimentation. So, overall in cosmology right now, what’s leading what?
Well, so, we have a lot of cosmology experiments which look at galaxy stuff, and those are dark energy experiments. And there is no theory that gives dark energy explicitly, but that’s wrong. People say there’s no ideas. That’s wrong. I was going to say that there’re ideas about dark energy every month, but I went and looked and there were ideas submitted every week about dark energy. People are working on it, and it’s hard. And you have to have a huge amount of confidence to take the time to work it out, and people don’t do that in general. If calculations can’t be done in the lifetime of a graduate student, they won’t try. But I think dark energy will be figured out. Dark energy is driven by experiment first, but Einstein’s equations allow a cosmological constant. We just don’t know how to calculate its size. The dark matter, I think we know what it is. It’s some amount of axions and some hidden sector stable matter. Dark matter was driven by theory for decades, but its driven by experiment now. But the theory has progressed a lot. And we’ll know right away how to interpret. So, it’s a mixed theory and experiment, really. I guess there’s very few things left to measure. We know how much dark matter there is pretty accurately. We know- we can make a list of the measured things in cosmology and in particle physics. We know almost everything. So, once we get the mass of one or two super-partners, we'll know we’ll know right away at a higher energy that that tells us something about it. So, in a sense, we just need to measure a few things. Then we’ll have a theory of our world complete.
Gordy, on that point, talking about String Theory as a testable notion and the interface between observation and theory, to what extent do you think that the multiverse is a testable proposition?
It’s not String Theory that is testable; it’s compactified String Theory. So, because of that, compactified String Theories are, in fact, testable, and I've given you a bunch of examples and stuff. There are no experiments, not in four dimensions. Doesn’t mean anything when you talk about testable as such. We know that if inflation occurs in a hidden sector then you have a potential universe. Inflation doesn’t occur in the world automatically. So, all of- many of the multiverse worlds don’t exist. My favorite example is that in the 10500, that world that Mike Douglas found, none of those theories had an electron. I don’t know whether they could be in hidden sector worlds. And any theory that doesn’t inflate doesn’t matter. It may be ninety-nine percent of all multiverse worlds don’t inflate. Now, how do you know- why should you think about them? Because when you write down the compactified theory, then you should get a possible world, and you could see that you could get some others. So, if you get compactified and if the theory gives a number of other correct predictions, you’re testing the theory very well, it makes many predictions, and the fact that there are other universes that have different moduli stabilizing the values and different values for things, those are predictions of the same theory. If that prediction were correct, then other predictions should be correct in a full theory. If those predictions were wrong, the whole theory would be wrong because they’re tied together, and these are real theories. They’re not just a bunch of conjectures. If you really write down one, then see—the multiverse is its other solutions. Suppose you write a Lagrangian in normal physics. Then the Lagrangian leads to a lot of solutions. Then there would be boundary conditions, for example, to see which ones are physical for the problem you are studying. Right? It’s familiar. Lagrangians have huge numbers of solutions in general, but only a small part apply to a problem that you’re working on. So, if a multiverse is arising more solutions from an existing theory which already had confirmations, then it’s right. You can’t have part of it be wrong. But we don’t know much yet about which worlds of the multiverse do more than fluctuating briefly into existence. The way you can tell is do they inflate? If they don’t inflate, doesn’t matter. And that’s it. But some will inflate, and any given theory you will be able to figure it.
Gordy, just to bring the narrative up to the present, after retirement particularly in this year of the pandemic, what are some of the things that you’ve been working on? What’s been most compelling to you in recent years?
This stuff. So, I finished that book a few weeks ago and spent a lot of time on that. But one thing that hadn’t been done in any String Theory and that we are doing- we had one paper that’s posted and another one that we're writing, was the masses of the quarks and the charge leptons and neutrinos, understanding those masses and why there are three families. So, I have been working with two PhD students on that and I’m happy with the progress. For the first time, we’ve written down some organizing and predictive things about the masses of the quarks and leptons, and we can say why there’s a hierarchy of quark masses, etc. So, the top quark and the bottom quark are in a doublet, they should have the same mass. But we can do- the reason why they don’t have the same mass in the theory and more or less predict the ratio. And we’re currently working on the second, the first paper we wrote said you could make some sense of the quark masses and the charge leptons, and now we’ll do the neutrino masses, and making some sense of them, and finding the seesaw mechanism, constrained in certain ways. And that paper we are working on right now. So, I spend a fair amount of time on that and working with my two PhD students. And they’re both working on that stuff. Then we- the other thing is the hierarchy problem question. So, I keep looking at alternatives to look for is there anything different. And several years ago, with a PhD student, I did a calculation, we did a calculation of the spectrum of super-partners, and what masses they should have. And that’s where I- that’s where more or less the argument that no gluino should be lighter than about 1.5 TeV. And could be and that there’s no interesting limit. The LHC limits come from experimenters by assuming a model which makes them the biggest whereas if you look at how gluinos decay in our theory, our mass prediction wouldn’t get within two or three TeV. And it’s just the way our predictions are different. And they don’t use realistic. But it doesn’t matter, what matters is the signal. So, it’s okay. So, it could be that the-well, so I spent a lot of time thinking about the hierarchy problem and is there some other solution that isn’t just some new chunk of physics to stabilizes like supersymmetry does. And supersymmetry does it. It’s the only known thing that does it. We more or less understand why this stuff is much heavier than Standard Model stuff and it’s a little presumptuous to say we completely understand it. So, we more or less understand it, but not well yet. With data we will. Most of the super-partners will have masses like thirty or forty TeV, and a ten TeV machine can’t check them but there is a small chance of an associated production like a gluino plus a quark, gluon plus a squark. And you might be able to do- you can do that for sure at one hundred TeV. So, you can check most of the spectrum at one hundred TeV. And if the luminosity weren’t a big deal, once you see one super-partner, then we have a shot at some others. But also in my head, most of them are tens of TeV that. But you get three of them right, then your predictions for all will be.
Well, Gordy, now that we’ve worked our way right up to the present, for the last part of our talk I’d like to ask a few broadly retrospective questions about your career and then we’ll end looking to the future with one final question. So, one thing we haven’t talked about so much is your long-term affiliation with University of Michigan, right? It’ll be sixty years in four years that you’ve been with the University of Michigan. Just a very broad question: In what ways has being at a very large public university, right, on the other side would be, you know, like a Caltech. Very small, very private, right? In what ways has being at such a large public university influenced you? Either by the students that you interact with or your fellow faculty members or the collaborations that you’ve been a part of. Do you see your work at University of Michigan being particularly influential in the kind of research you’ve done over your long career there?
Well, I hope the work is influential, but it’s funny the way fields work. The physics community, the theory community, the particle physics community, now knows about the work Bobby and I have done with the compactified M Theory. But we’re not being very influential because we haven’t made a clean dramatic prediction that comes true, like, we predicted the electric dipole moment and nobody else did. But there aren’t any string theorists who really know how to calculate it. So, they don’t care much about it. They don’t know whether it’s interesting. If a super-partner is discovered I will have been very influential. Being at Michigan has been good, but not completely. I’ve had good students, but not postdocs because of how the funding works. But I’ve collaborated a lot with Bobby, and also with Malcolm Perry from University of Cambridge, and I’ve been able to have funds do bring them a lot. So, the way a lot of fields get built up is that people have postdocs. So, I've had several very good students, and all of them have ended up with a two-body problem. So, they usually get some job offers, but not at the top ten places because their string theorists don’t do phenomenology, and if they do it’s Calabi-Yau instead of G2. No one should plan on work at a place without a center. And so, my postdocs have had to leave the field and move to a place for their spouses’ job. They have very good jobs (Google, etc), just not string phenomenology. Most of them, not all but, it’s a bit better with students. One student who was on the faculty and got tenure at University of Chicago and we hired one of the other top students, but he isn’t working on this yet. So, we’ve done- Bobby and I have done enough that people will pick it up as time goes on, eventually. People go- ninety percent of string theorists only study string theories. They don’t study the real world. They don’t objectively say that. They don’t think the real world is interesting compared to their theories. And theories are, in a sense, much easier to study. The real world is an unyielding, often unfriendly place. Whereas following the mathematics of string theories is, for anybody who can do it, it’s easy to do.
Gordy, you’ve contributed an enormous body of literature to the field over your career, some of which has been geared more towards popular audiences or lay audiences. Between your writings or lectures that you give geared toward that audience, what are some of the things that are most important to you to emphasize about your work? About physics? About science in general?
The work- I do talk in the work about how science works. I talk about it a lot. One thing that I’m sort of proud of and is amusing is a book called What’s the Matter and it was put out by the Great Books Foundation, 2007. So, it’s just- so, it’s for a course at any university that wants to have original material for the students to read. And we, so, let me read you the list of authors of chapters in this book. So, there’s a chapter by Feynman. Chapters, a couple by Aristotle. Galileo. Newton, Faraday. Maxwell. Planck. Einstein. Heisenberg. Weinberg. Hawking. And me.
That’s pretty good company (laughter).
So, it’s delightfully amusing to me. And so, the chapter is taken from the third chapter of the book I call Super Symmetry which talks about how physics is done, how science is done. And it includes saying things like, pointing out things like effective theories work. And what happens in physics in particular is that the world separates, so you study quarks without studying atoms or planets, and you study stars without studying galaxies, etc. The world breaks up into various effective theories which all join on to one another. We do physics, and then you solve that, and it ties into other things, but you don’t have to pay attention to most of the world. Whereas in biology, almost everything affects what you do, and you need evolutionary or comprehensive description. So, physics is the easiest science, for sure and that’s what that chapter is called that was reprinted. It explains why. Another measure of impact – on inspires they give some examples of how to ask questions, and the three names they use are Witten, John Ellis, and Kane. So, there’s a pattern in the books then. First book was written during the sabbatical at CERN in 1986. I enjoy writing, so I taught a course, an undergraduate course and so I wrote a textbook about particle physics. Most of the books up until then had been historical. It has no logic to it, and you don’t get to understand things. So, the first book I wrote was called The Particle Garden. My wife made up the title. Particles are the seeds from which the universe and everything emerges and works. That was the idea. And the book was about the Standard Model and mentioned- and some things were beyond the Standard Model, but they were in the framework of stuff that was sort of understandable and a few other things. So, that book was mainly what we understand about the world for people who were curious about it. And it isn’t-I’m not very good at- I mean, I like writing, I think I’m good at explaining, but not at for example, anecdotal stuff and, and I didn’t- I forgot to collect lots and lots of cool stories to put in the book, so it doesn’t have very many. But that was the first book. The second book was on supersymmetry by the time we were confident we understood it. That’s 2007, I think. Well, I wrote the Particle Physics textbook at CERN in 1986. If you study electrodynamics, you are given basically Maxwell’s equations pretty much, and you solve them. It’s a deductive field. Sometimes there’s a little bit about the input in Maxwell’s equations and where it came from, but mostly it’s a deductive thing. And particle physics to the Standard Model was ready to be a deductive course. So, I wrote that textbook as a deductive thing. You write down the equations of the Standard Model and then you look and see what they tell you and what they describe. And that’s how I thought it should be taught. So, there’s that book and it’s just had a second edition. Cambridge asked for a second edition of it. And I made it even more readable, so it’s actually rather good conceptually and for readers, the Standard Model for anyone who had an undergrad course in quantum theory and has seen spin. The Standard Model can be understood, and that book can be read on an airplane or in the bathtub. but it’s still conceptually I think the best description of how the Standard Model works. So, you need to know what wave functions are and what spin is, and that’s all. Any physicist or chemist, lots of such people can read it. Then I followed that path of the textbook level and at the public level. The public level- the second book is the supersymmetry one, and it’s the opposite. It briefly summarizes the standard model but then talks about what you can do. And the hierarchy problem useful, practical variants but not much of that. But the second one, stuff mostly still coming stuff. Then I- I guess it’s because I had some contact with people in the publishing field, so I edited a whole bunch of books. One is called Perspectives on Higgs Physics, so I just asked a dozen people to write a chapter with it, ranging from experimental detection to theoretical things. And I was doing it so I could try interesting things. So, I know from interaction with him that Howard Georgi doesn’t like Higgs because it’s too fundamental. So, I asked him to write a chapter and I gave him the title “Why I would be Unhappy If the Higgs Were Discovered.” So, you can do things like that. Now, the perspectives on supersymmetry and perspectives on LHC. And those don’t take much time because chapters are written by others who are experts.
Gordy, looking back over your long career all of the papers that you’ve written, all of your collaborations, all of the large-scale research endeavors you’ve been a part of, is there anything that sticks out in your memory that stands out above the rest as being most intellectually satisfying for you?
Theory work is not particularly satisfying because long calculations are needed, except that sometimes things work out okay which is exciting. And the Standard Model itself is great. And supersymmetry is beautiful. But I think the most exciting for me was the year I started working the problem of really writing down the compactified theory that stabilize moduli and everything we tried worked. The year that I worked with Bobby, the first year that we succeeded with stabilizing the moduli in the compactified theory, which no one else had been able to do up to that time. And then if you look at what might be possible in that theory, then it looks like maybe you can make a complete theory describing our world. And so, I got very impressed by myself and Bobby, and quite excited about it. And I think we’ve now succeeded in that. We’ve written a version which does describe our world in the following sense. So, make a list of twenty or so things which must be in any explanation, in any theory (as I did above). So, you must predict the masses of the- predict or explain the masses of the particles and things like dipole moments and cross sections and the strong CP problem. In QCD you’re allowed to have complex amplitudes and you don’t, and why is that? Big mystery. Somehow it doesn’t happen. seventeen years that it took to do that. But I didn’t see any obstacle to that. After one year, we stabilized the moduli, calculated different things. It has felt really good. And nothing has gone wrong. It will be interesting to see how the muon g-2 works. Two different ways of doing the theory, both should work, but disagree. One disagrees with our prediction, the other does not. Several people have suggested additional contributions we neglected.
Gordy, for my last question looking to the future, of course, you have a tenure in the field where I certainly wouldn’t ask you to predict the future but perhaps you can extrapolate based on all of your experience. And I’d like to focus specifically on the question of mentorship. If you look back at the work that you did with Howie Haber, right, if you had a graduate student now of that caliber, are you optimistic that the next generation of particle physicists, cosmologists, astrophysicists are working in a time of equally foundational possibility? That the things that are going on today can yield the kinds of discoveries, the kinds of breakthroughs that you’ve been a part of as a young person in the field yourself and as a more senior person, as a mentor to excellent graduate students?
Yes, the fact that we can write a theory that solves all these things at once still leaves huge room for working out substantive details. So, I think there will always be a certain number of people who want to work on this—want to work in this kind of field. Not so many. You know, when string theory came along, it induced a lot of people to come in who would rather not have. Things like that. But there’s always going to be people who can’t resist it. The kind of things to solve for twenty years, twenty-five years and questions to deal with like multiverse and what it means and why some things are true of the compactified theory that aren’t obvious. Why the theory has hidden sectors with the properties that it has. It’s not obvious what all those properties should be. So, working- in quantum theory, the way to say it is that in atomic physics and in quantum theory, there are still some exciting things, still some challenging things. And eventually there won’t be. This is a great, exciting time to enter particle physics and cosmology, both on the theory side and the experimental side the discoveries may be made that let us deeply understand the world, and complete that understanding, after centuries of the quest. We can be hugely proud that people evolved who can complete the understanding. They’re still be applications to commercial things, smart phones, etc. But exciting things theoretically will run out there. And I think the same thing is going to happen here. That’s kind of sad. And some people say we won’t be able to understand the world, and test multiverses. But I see no reason for that. The progress we’ve made is wholly amazing. That the funding has built the machines that it does is amazing. Countries that would do the research needed and build a one hundred TeV collider might not have existed, but they do. CERN will build it. The U.S. would never build it. Be grateful for WWII. Universities help support- universities give us money for centers. Give us half a million dollars for a center at some point. That a dozen universities would do that. Wow. It’s a statement about the culture that might not have existed. So, for quite a while I think, people won’t be frustrated about opportunities. But then I have to believe that ultimately, in a few decades, they will be writing books, finding analogies. I’ve tried to find analogies for a lot of things, and it really gets hard. So, that will be the next stage, after we have the theory.
(Laughter) Next stage indeed. Well, on that note, Gordy, it has been an absolute pleasure listening to all of your stories, insight and perspective over your career. I’m so glad we were able to do this, and I really appreciate you taking the time, so thank you so much.
You’re welcome. It’s been fun.