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Interview of Fred Gilman by David Zierler on May 20 & June 10, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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In this interview, Fred Gilman, Buhl Professor of Theoretical Physics at Carnegie Mellon University discusses his career as a theoretical physicist and hopes for the future. He details his early passion for theoretical physics and his decision to attend Michigan State University for his undergraduate degree. He discusses attending Princeton University for graduate school and his thesis on Baryon Electromagnetic Mass Differences with his advisor Murph Goldberger. Gilman describes his time at Caltech as an NSF postdoctoral fellow. Gilman reflects on his involvement with the Snowmass Conference as well as his work on the High-Energy Physics Advisory Panel.
This is David Zierler, oral historian for the American Institute of Physics. It is May 20th, 2020. It’s my great pleasure to be here with Professor Frederick Gilman. Fred, thank you so much for being with me today.
To start, please tell me your title and institutional affiliation.
I'm currently Buhl Professor of Theoretical Physics at Carnegie Mellon University.
Now, let’s take it right back to the beginning. Tell me a little bit about your family background and early childhood.
Let me start with my parents’ generation. My mother was born in the U.S. Her mother arrived in the United States in 1900 at age 15, spent 50 years sewing coats — one of the original members of the International Ladies’ Garment Workers’ Union — and went through the full immigrant experience. She married another immigrant from Galicia, part of the Austro-Hungarian empire at the time. My father was born in 1911 in Pinsk, in what is today Belarus, but was then part of the Russian Empire. He had one of the worst childhood experiences one could imagine, in that both his parents died either from TB or flu coupled with malnutrition. It’s ironic that we're talking a century later in the midst of another world pandemic. In any case, my father was orphaned and he grew up with his mother’s family, in particular with his two uncles. The uncles came to America just after the First World War, and then went back and got the family. My father and his two brothers came to America in 1920, passing the Statue of Liberty and arriving at Ellis Island. He quickly caught up in school and graduated high school in the middle of the Depression.
My parents met and married in 1936 in Brooklyn, where they both lived.
And what year were you born?
I was born in 1940. Again, stop me if it’s a little bit too detailed —
Not at all.
Many events in my parents’ lives and my life seem like unlikely coincidences, most of them lucky after the terrible experiences of my father. Aside from being an orphan at age five, he went through the Russian Revolution and later the fighting between the Poles and the Red Army. He saw really awful things as a little boy. His life was much more normal once he got to America. After high school my father immediately went to work with his uncles. They had been furriers in the Russian Empire with special documents to travel and buy furs in the Urals, and they continued as furriers along with their cousins and others in New York. Quite successful, I think. At some point, a distant relative heard about a WPA project to look at parole and probation practices across the country. There was an opening in the Midwest, and my father took it and ended up in Lansing, Michigan. The whole project was overseen by a young lawyer named Wayne Morse, later maverick Republican senator from Oregon. So almost by chance, my father ended up in Michigan looking at probation and parole practices. The State of Michigan, at that time, had transitioned to a civil service system instead of a political spoils system, and after the WPA project, my father worked for Civil Service in some capacity and then took the exam to be statistician of the Department of Corrections.
What year would this have been?
’38, ’39. He got the job, and by the early ‘40s, he had become special investigator for the parole board, sometimes working with the State Police investigating gangsters violating their parole. Not long after I was born, he became assistant director of corrections of the State of Michigan. After the Second World War he established one of the first — I think California and New York were the other states — minimum security prison camps.
This is quite a career trajectory for an immigrant.
Yeah. But going back to his boyhood experiences, he had heard the screams of people being tortured by one side or the other in the fighting between Poland and the Soviet Union after WWI. It was fitting in a sense that he should end up trying to change the way we incarcerate people by creating minimum security prisons. These had actually been CCC camps from the ‘30s that had housed Hitler’s Afrika Korps prisoners during the Second World War. Afterwards, they were empty, and Michigan took them over. The prisoners would do work on trails and cleaning up state parks during the day. No walls, no guns, a few hundred men in each of these camps, of which there were eventually something like 13 to 15 in Michigan, scattered over the state. That's what he did. A very unusual trajectory. But coincidences all along the way that he even survived.
And then where are you in this narrative, being born in 1940? Is your family in Michigan?
Yes, my family was already in Michigan. My parents had bought a house on Milford Street in East Lansing, Michigan, and I was born in Lansing.
What language did your parents speak to each other, and what was the language in the house when you were growing up?
English. Very much English, with occasional words, usually interesting phrases, in Yiddish. And both of them could speak multiple other languages.
But it was important for your parents even to speak to each other in English?
Yes. Almost always in English. And I think if you had met my father, you would not have guessed where my father had been born.
Now, did your father’s career keep him in Michigan throughout your childhood, or did you move around?
No. He stayed there all the way until he retired in the 1970s. So 30-plus years. The only interlude to being assistant director of corrections was when we spent six months in Jackson. The state prison at Jackson was the largest walled prison in the world. There was a riot in April 1952. And I well remember the phone call to our house and my father literally taking his gun and heading to Jackson from East Lansing. The warden had taken cover in his office [laugh]. It was my father who appeared in the pictures in the newspaper the next day at a window of 15 Block — which was a maximum-security block that had been taken over by the inmates — talking to “Crazy” Jack Hyatt and Earl Ward, who were the riot leaders…with a guard with a knife at his throat standing next to them.
And I assume you have specific memories of these events?
Oh, yes. Obviously of my father going away and the next day, when I was in class in elementary school, my father came into the room, because he was back for a few hours to East Lansing, to assure me that he was still alive. He soon became deputy warden of Jackson Prison. In prisons in those days, the deputy warden was Mr. Security. There are many interesting stories from that time. The thing that I can claim that probably nobody else can is that I was driven to school by a murderer.
Really! Do tell!
We lived on the prison grounds outside the walls, and there were inmate trustees cleaning, cooking, and driving for the family. Each morning, I’d get in the car with Jimmy to drive to school, who had a life sentence for murder. Eventually, he was paroled, with my father bringing people to tears at the hearing for his actions during another riot where he sat on the steps of our house with a baseball bat to defend the family.
This is incredible. [laugh]
Yeah. Very unusual.
It’s a background not too many people have — with many stories of people, both good and bad. Before leaving this subject, I should tell you what my father learned from a hit man for the Purple gangsters, “Don’t never plead guilty to nuttin’!”
[laugh] It’s a triple negative. But you get the idea.
Sure, sure, sure. So Fred, to the extent that you had a normal childhood and you went to school and all of these things, at what point did you start to exhibit excellence in math and science?
In grade school, already. Toward the end of grade school, I was starting to read books on science, on nuclear energy and astronomy, and I was a very good math student from early on. By the time I was 13 or 14, I was convinced that I was not only going to be a scientist but a theoretical physicist.
That’s a very advanced kind of aspiration for a kid. First of all, how did you know what even theoretical physics was? And furthermore, how did you know that that’s what you wanted to do?
Mostly reading books and magazines on science and technology generally, and in physics particularly at a mixed level — from reading physics and biology textbooks, to reading popular expositions. A bit later, George Gamow’s book, One, Two, Three… Infinity played a big role, probably at age 14 or 15.
I wonder if Gamow would have been surprised that a 15-year-old would have been inspired by this book. Or you think that this is exactly the kind of person he was writing to?
I would say it’s the sort of person he should have been writing to. But I bet you that there were more than me who were changed by the experience of reading One, Two, Three…Infinity.
Fred, I wonder if growing up, if the Cold War at all played an influence in your intellectual development and perhaps your interest in becoming a physicist?
Yeah, I think the Cold War did. One of the things that I remember distinctly is Sputnik and then following very closely the Russian and American space programs, and literally seeing with my own eyes the first few Sputnik satellites. We had a cottage in the middle of Michigan on a lake, which was the place we spent the summers. I had a small telescope there, a reflector. I also had a chemistry set, and I built radios as a kid, including a short-wave receiver as well as other electronics. So hands-on, experimental physics, chemistry, electronics and astronomy were my interests from early on. It was much more than just reading books or doing a calculation. From the beginning for me there was the connection to observation and experiment.
Now I wonder if when you were thinking about what schools to apply to for undergraduate, if you were specifically considering what physics programs you wanted to apply to?
Yes, it was physics, although as you'll hear in a second, it was other things as well. I first applied to Michigan State. I walked to grade school, middle school, high school, and Michigan State, in different directions from the same house.
715 Linden Street.
So getting on a plane and going to someplace like Caltech or Harvard, that did not interest you at the time?
I applied to Michigan State, Michigan, and MIT. So MIT was the institution in the category you're talking about. And I would say several things led to my choice. An important factor was that there was for the first time at Michigan State the Distinguished Alumni Scholarship. It was based purely on merit. I took the exam, did extremely well, and was awarded the Scholarship. Living at home then made college costs minimal. Economic considerations certainly concerned my parents. Although I did have a scholarship also at Michigan, I don’t think I had one at MIT. So that’s partly what decided it. The second issue I would say, honestly looking back, is that I probably didn't have the maturity to really benefit the way I could have if I had been more mature and confident as a person. For me, it was a good idea to live at home and to continue to excel as a student and mature. As we'll discuss in a moment, Michigan State turned out to be a fantastic place for me. This was partly due to accidents. And partly, as my son-in-law says whenever I say it’s all luck, he says, “No, it’s not luck. It’s good fortune,” meaning that you were ready for an opportunity when it occurred and you took advantage of it. Let me give you a particular example. In the first year at Michigan State — in those days, there were four required core sets of courses that everybody had to take. The set in science was called natural sciences, with components in geology, biology, and something that was chemistry-related. That was also the first years of what was called the Honors College. Given the scholarship I had, I was in the Honors College from the start. And there was an inspirational person, Stanley Idzerda, who took on the leadership in creating the Honors College. Once you were in, you could develop your own curriculum, so to speak. At the end of the first term natural sciences course, I took both the final exam for that course and for the second term course as well. With an opening in my schedule for the second term, Idzerda recommended that I take genetics, which was a third-year course in biology. I did, and I fell in love with genetics. This is the era soon after the structure of DNA had been discovered by Watson and Crick. I had read a good deal about that, although the course mostly dealt with classical genetics. The teacher, Professor Fox as I recall, invited me to work in his lab during the spring term and repeat the classical genetics experiments with fruit flies. So I was breeding fruit flies and then anesthetizing them as they emerged as adults and counting recessive traits such as cut wings, short hairs [laugh] which led to standard distributions of what the progeny should look like. Now the luck. That summer — this is the summer of 1959, Cold Spring Harbor Laboratory for the first time had a summer undergraduate research program. Fox asked me if I wanted to go, and if I did, he would write me a letter of recommendation. I thought about it a little bit, with a little trepidation about going away for the summer to a new place, and decided that I wanted to go. They accepted me, and off I went to what was one of the formative experiences of my life. First of all, there was a set of other people, mostly from the schools that you mentioned before, including MIT, Harvard, Princeton, etc. Very, very bright kids my age. And I was assigned to work with Salvador Luria. I don’t know if you know this name.
That name I don’t know.
OK. Max Delbruck was a theoretical physicist who was the first to calculate the scattering of light by light. He turned to biophysics in the mid-1930s and did the founding experiment of bacterial genetics with Luria in 1943, for which they won the Nobel Prize. Cold Spring Harbor in those days was the place where — a little bit like Brookhaven on Long Island was to the physicists — you came in the summer with your family, did research, talked with your colleagues from around the country, and attended the very good conferences that were held there. In the same building as Luria was Jim Watson, who had been a PhD student of Luria’s. Down the way — in another lab was David Baltimore. Most of all, it was the experience of interacting with both my peers and the superstars of biology, of genetics in particular. Luria gave me an experiment to do that was at the frontier and amazingly simple. We were trying to understand, when the genetic material from a bacterial virus gets incorporated in the DNA of the host bacterium. The idea was to have a modified virus bring in the gene to “digest” sugar, whereas the bacteria were bred not to have the enzyme to digest sugar. I'd infect the bacteria with the virus, and then allow them to multiply. Every 20 minutes or so over several hours, I'd take out a sample and plate it out in many agar dishes. If the bacteria could “digest” sugar, they would leave a clear plaque, empty of the colored sugar mixed in the agar. We looked for the onset of the exponential rise in plaques once the gene was incorporated in the genome of the infected bacteria. That experience convinced me of two things for the rest of my life. One was the value of undergraduate research, which I strongly advocate to this day. The other was the brilliance in finding an insightful experiment — especially done in a clever way — at the right time.
Fred, I have to ask you — did you seriously consider pursuing biology instead of physics at that point?
Yes, I did. Because Luria said, “Why don’t you come and work with me at MIT?” I really seriously thought about that and eventually decided, no, I still wanted to be a theoretical physicist.
So what was that fork-in-the-road moment for you? How did you make that final decision?
Looking back, I think some combination of the spark of interest in math and theoretical physics, and maybe a bit of hesitation in making too big a jump to leave Michigan State, change fields, and go to MIT. Too high of a jump for me in those days. As you know, later on, I was able to find things to do and make much bigger jumps —
— maybe even in the wrong direction. Not in my opinion wrong, but at least wrong compared to how it all worked out.
Sure, sure. So at what point, then, did you start to settle on physics programs for graduate school? As a junior?
As a junior to some degree, but definitely in the fall of my senior year. Here’s more about my undergraduate career. Even the very first semester, because I had taught myself calculus in high school, I didn't take the usual freshman physics or math courses. I took electricity and magnetism, the course I'm teaching this year — a junior course. And I took a junior linear algebra course in math. After the first two years at Michigan State, it was all graduate courses. In addition to research with Hugh McManus on cyclotron design, that meant electricity and magnetism, mechanics, quantum mechanics, and math courses at the graduate level as well. With the guidance of a math professor, Leroy Kelly, I took the exam each year for the William Lowell Putnam Mathematics Competition. The highlight of my senior year was to be on the three-person team from Michigan State that placed first in North America. Most important in leading up to grad school was taking quantum field theory, where I benefited a lot from the books by Feynman on Quantum Electrodynamics and Fundamental Processes in addition to the text by Schweber. At the advice of my professors, I applied and got into Harvard, MIT, Princeton, Stanford, and Berkeley.
Those are some hard choices that you were facing there.
I chose Princeton. And I think looking back, that was very much the right choice.
Now, were you looking to programs specifically with theoretical physics in mind and the kinds of professors you would work with?
Yeah. Specific people. In Princeton, it was Murph Goldberger, who ended up being my thesis advisor, in fact.
In those other schools, who were some of the other professors that you might have worked with, had you gone there?
Schwinger at Harvard. But the vibe I got was that he had a huge number of students and spent relatively little time with each of them. And that Caltech — and I think I verified this myself when I got to be a postdoc there — was the best place, maybe, in terms of both Feynman and Gell-Mann being there. It was, in fact, the best place for me as a postdoc, — but —
Not a controversial statement to make for sure.
— but while some people had a great experience there as grad students, they could be unkind to some of the graduate students.
[laugh] Right, right.
In any case, I thought that Princeton was more friendly — and it had more people I was interested in working with. There was not just Murph Goldberger. There was Eugene Wigner, Sam Treiman, Arthur Wightman. John Wheeler. A lot of great people.
What about Berkeley? What attracted you to consider Berkeley?
Less a specific person as much as general reputation. It was clearly one of the most prominent universities. And the presence of the Rad Lab.
That’s why I wanted to ask. I'm curious also how much you had considered what lab opportunities there would be for you at these given institutions.
At this stage, not so much, but some. As we'll discuss, later on, it was almost everything in the decision to go to SLAC as a postdoc, rather than a faculty position — it was the place to be because of the new domain opened by the physics experiments.
Right. OK. So my first question with Princeton is, when you get there, I assume most of your cohort had gone to schools that were more like Princeton and less like Michigan State. Is that a fair assumption?
Correct. A more than fair assumption.
How well prepared do you feel that you were relative to your cohort as you began the program?
Very. Because of the very special attention and opportunities that I got at Michigan State. I got super attention from individual faculty members who acted as mentors and advisors as well as teachers. Here is another example of a major undergraduate experience. After the summer at Cold Spring Harbor, during the next academic year an experimental particle physicist named Joe Ballam came to Michigan State. Joe was a bubble chamber physicist, and I wandered into his office one day, started talking, and ended up scanning bubble chamber pictures from Brookhaven. The following summer — so it’s between my sophomore and junior year — I was at Brookhaven working in the bubble chamber group. This was another wonderful research experience. Again, there were a lot of young people from Columbia, MIT, and other universities — and I met Nick Samios, and Ralph Schutt, who was the head of the group at the time, and many others.
What was Samios’s position at that time?
He was, I think, already a rising star, but Schutt was in charge of the group. When the omega-minus was discovered, I recall he was very involved in the discovery and was known as a major figure. So let me add — I'm sorry that I have many stories —
Sorry? Fred, this is what I'm here for! It’s all about the stories!
[laugh] I told this story at T.D. Lee’s 80th birthday celebration. You can find my talk on the web, but it doesn't have some of what I'm about to tell you. There was a seminar that summer about an experiment to see whether there were one or two kinds of neutrinos. The seminar speaker was Mel Schwartz, then an assistant professor, and I was at the seminar, sitting with some of my young colleagues. At some point toward the end, there was a question about the theoretical side of things. The issue was what motivated two kinds of neutrinos? What if there was only one neutrino? Then a muon could virtually become a neutrino plus a charged W, which would emit a photon and then recombine with the neutrino to form an electron. The net process is mu decays to e gamma. How do you calculate the decay rate and would it happen often enough to be detected? Suddenly, the question was referred to somebody sitting behind me, and I looked over my shoulder quickly and said to the summer student next to me, “Who’s the kid answering the question?” And he said in a serious whisper — “T.D. Lee.” [laugh]
T.D. was of course already one of my heroes. Much later, I spent interesting times with T.D. over the years, including telling that story at his 80th birthday celebration. Afterwards, T.D. told me his own story about how young he looked. He arrived by air at Stockholm for the Nobel Prize ceremony — those were the days when the plane stopped on the tarmac, you went down the ramp from the plane, then walked across the tarmac and into the terminal. As he was walking towards the terminal, a man came running up and said, “I'm a reporter from the Stockholm paper.” “Is your name Lee?” T.D. said, “Yes.” The reporter replied, “Oh, good, your father must be on the plane,” and ran on.
[laugh] That’s great! [laugh]
[laugh] OK. All right — I'm sorry for the diversions.
Not at all, not at all. So I'm curious — at what point did you start to work closely with Goldberger?
OK. Back to your question about preparation. I thought I was very prepared. Although when you get to this level, there are people around you who you think are one hell of a lot smarter than you are. The first year was not difficult for me. At Princeton, the Ph.D. qualifying exam in physics was called the general exams, which were a pretty fearsome set of exams — when I prepared for them, I knew more physics than I knew at any other time in my life. [laugh]. Three days of written and two days of orals, in that era. The normal time to take them was in the spring of your second year. I studied over the summer after my first year and I took them early in the fall of the second year. I did very well and as soon as I knew the results, I got my courage up and marched myself down the hallway to Murph Goldberger’s office and asked him if he would be my thesis advisor. And so we started —
Was he the kind of person where you needed to get your courage up? Was he imposing? Or this was just more a reflection on you, would you say?
It’s more me. He was not unfriendly. He was brilliant and had established himself at a young age as one of the leading theoretical physicists in the world. I was just a student hoping that he would take on the possibility of being my PhD advisor.
What do you think compelled him to agree to take you on? In what ways had you demonstrated your worthiness?
At that point, I think the only way he could have known me is either from other faculty or the results of the general exam. I never asked him how he decided. Of course, it didn't have to work out after I had done some practice problems, but obviously it did. One of the things about Murph was his humanity, although he was not the gentlest person in the world, and he had some pretty strong opinions at times. But for me, he was an extraordinary advisor. Let me tell you another couple of stories. One day, we were standing working at the blackboard, relatively early on, and the phone rang. In those days, I think he was scientific advisor to the Air Force and on the President’s Science Advisory Committee, and he was always coming back from Washington having “saved the nation.” The phone rang, right in the middle of Murph writing an equation, and he whirled around and took the chalk and winged it across the room and hit the phone. That’s one Murph story. He also had his sayings that his students sometimes adopted. In Watson’s treatise on Bessel functions ‒he could quote the page where some obscure identity was to be found. He would say, “It can be shewn — "
There were many “Murphisms” like that and he also could be somewhat of a jokester. More seriously, Murph was a leader of the S matrix approach, and particularly of using the analytic properties of amplitudes to derive dispersion relations. Arthur Wightman, his office was next door to Murph’s, emphasized from the beginning of his course on quantum field theory that the basic question facing particle physics was whether relativistic quantum theories could be formulated in a mathematically consistent way that would describe nature. There were a lot of people who thought there was not a strong interaction theory analogous to Quantum Electrodynamics that was renormalizable, and even if such a theory could be formulated you could not solve it.
Would you say that Murph’s research was in part geared towards helping answer that question?
Indirectly. Rather, Murph led a whole alternate approach. While not precluding quantum field theory being applicable, his approach started with the observed physical states, writing down the S matrix connecting incoming particles that scatter to outgoing particles, and then looking at the analytic and other properties of particular S matrix elements. That led to dispersion relations that were exact, but it also provided a framework for physically motivated approximations. This was a fairly successful program in many ways. The successes included the Goldberger-Treiman relation, relations between scattering amplitudes, and some understanding of specific processes like pi nucleon elastic scattering or photoproduction. At the time that I was Murph’s student, the rage was Regge poles. They gave a systematic understanding of the energy dependence of two body scattering amplitudes in terms of amplitudes corresponding to poles in the complex angular momentum plane. It gave you insights into scattering amplitudes at very high energies.
Now, Fred, how did you go about developing your dissertation topic? Did Murph hand you a research question that was related to his work, or did you come up with your topic mostly on your own?
More the latter. But before that, let me go back to an important earlier event. During my first year at Princeton, the American Physical Society met in New York in early 1963. From Princeton, a group of grad students took the train into New York and went to the APS meeting. I was coming out of a session and ran smack into Joe Ballam, who had been my undergraduate research advisor at Michigan State. He had just moved to Stanford to be the research director of the Stanford Linear Accelerator Center. He said, “Why don’t you come out this summer? They were just beginning to build the linear accelerator tunnel and the experimental halls. Everybody is gathered in a warehouse on the Stanford campus. You'll be in the theory group and learn about the physics we will be doing.” So I said yes on the spot, and in the summer —
That was an easy “yes,” for you, I take it?
Yeah, a very easy yes. The lucky coincidence was running into Joe, who had made the transition from being at Michigan State to Stanford, and as head of research he could just issue the invitation to come out for the summer. I crossed the country on the train, and stayed in a hotel in Palo Alto, and rode a bicycle each day to the warehouse on campus. It was then still called Project M for “monster.”
What year would this have been?
Summer of 1963.
And are you interacting with Pief Panofsky at this point? Did you have that option?
I worked with Sam Berman, a theorist who was a student of Feynman, on photoproduction of particles with spin 3/2, as part of a panoply of calculations on producing secondary particles by running an electron beam into a stationary target. There were to be experimental searches to observe new particles, as well as secondary beam lines of pi mesons, K mesons, etc. They played big roles in the initial experimental program at SLAC, although the central element was of course using the electron beam itself to do elastic and inelastic electron scattering off protons. I did meet Sid Drell. And I met Pief Panofsky plus several of the other experimentalists as well. It was the first time I went climbing in the Sierras, with a theory postdoc who was an experienced climber. It was my first time in San Francisco. An absolutely great summer, at the end of which I gave my first theoretical physics talk, at Stanford of all places. Not a very impressive talk, I have to say, with simply the formalism and the results of the calculations and what it meant for the production of spin 3/2 particles. Little would I have believed that in four years, I’d be back in a different role.
[laugh] Now Fred, it’s hard to parse these things out looking back, but was your sense at the time that this relatively fledgling organization was about to burst onto the scene as SLAC, or no?
How? How did you have that sense?
Of course, that sense also grew with time. But I already understood that this was going to open a new energy domain for interactions of photons and electrons. Electron-proton scattering had already been used to measure the size of the proton at Stanford with a much lower energy linear accelerator. That won the Nobel Prize for Bob Hofstadter. Electrons were a different and interesting probe. You should understand that the people who were at SLAC felt the rest of the country thought they were wasting their time with the lower energies available with electron beams compared to proton beams. This was particularly true of the East Coast physics establishment, who thought that SLAC would make secondary discoveries, if not be almost irrelevant. But as long as frontier proton accelerators were built, their attitude mostly was to let them have their toy and be out of our way.
Fred, I'm curious how you divined this tension, if you will, in terms of the East Coast establishment belittling what was going on at SLAC. Were you hearing this as somebody who was coming from Princeton, or were you hearing this in Palo Alto about what they were saying in places like Princeton?
That summer, I didn't hear it. After I arrived in 1967 and afterward, I heard it from my faculty colleagues, particularly Dick Taylor. You can find it in the account of SLAC’s creation in Panofsky’s autobiography, Pief Remembers. It was stated publicly in Pief’s welcome talk at the beginning of the 1975 International Symposium on Lepton-Photon Interactions, which was appropriately at SLAC.
OK. That’s it? He lays it all out there?
Yes: The lack of appreciation of what could be done with electron beams versus the string of discoveries that had transformed physics. While it was not said in an unkind way, you could imagine somebody else giving the talk and openly celebrating his triumph and the naysayers defeat.
But I imagine Pief in 1975, this is — not that it’s perhaps the best choice of words, but that it’s a victory lap, right?
That was my feeling at the time.
Because in 1975, he had proved them wrong.
They were wrong multiple times. The revolution in particle physics starting with inelastic electron scattering in the late 1960s through the mid-1970s came very largely from electrons, neutrinos, and electron-positron annihilation rather than proton beams.
So not that I needed any more reason to appreciate what a visionary Panofsky was, but the way you're telling it really makes it hit home.
Incredible, incredible man. Unbelievable as a physicist, instrumentalist, and director. But now let me go back and resume the 1962 to 1965 timeline. When I first worked with Murph, the subject was Regge behavior in field theory, which is the topic he was working on with Gell-Mann, Low, Marx, and Zachariasen.
It was an interesting time and era, but looking back, of course, people could say that while it gave us insights into scattering amplitudes, it was a diversion from the central question: “What are the fundamental constituents and interactions?” Incidentally, Murph had little patience with people who relished making the math extremely formal or unnecessarily complicated, regarding it as mathematical masturbation.
I've heard a very similar quote from Feynman — remarkably similar about mathematics.
At the same time there is the deep paper by Wigner on the incredible efficacy of mathematics in describing physics. I think more and more that it is unbelievable how a few simple symbols — as Feynman said when he got the Nobel Prize, “some marks on a piece of paper” — will give you a description of all of quantum electrodynamics, let alone general relativity and the gauge theories that are the language in which we express the standard model.
Fred, during your first stint at SLAC, what was your day-to-day? What were you working on?
In the summer of 1963? A good part of it was learning the formalism of how to treat spin 3/2 particles and their electromagnetic interactions. A resonant state of the proton with spin 3/2 had been discovered in the ‘50s, so we knew such particles existed and we wanted to calculate their production rate. But we were more generally interested in particles that had never been seen, and to understand what the discovery potential for such objects would be at SLAC. Very mundane in a way, but very speculative and exciting in another. It was an introduction to the world of thinking about future accelerators and experiments opening a new domain that would play a big role later in my life.
Fred, I'm glad that we had this interlude with SLAC, because obviously I leap-frogged my question about developing your dissertation topic.
OK that we covered it now.
No, that’s good. So when you got back to Princeton, I'm curious, how well-defined was your plan in terms of the kind of dissertation you wanted to write before and then after SLAC? How formative was SLAC to the kind of dissertation you wanted to write? The kind of research you wanted to be engaged in.
I didn’t know what my thesis topic would be. It was Murph who first took my experience during the summer and married it to something he was interested in about Regge poles at that moment. Soon we moved off to other topics. How did I get to my dissertation? A totally different way. David Sharpe, a student of Murray Gell-Mann, came to Princeton as a postdoc. David told me about a new calculation by Roger Dashen, a student of Steve Frautschi, of the neutron-proton mass difference. The magnitude of the measured mass difference between the proton and the neutron is 1.3 MeV. It was natural to attribute this to electromagnetism, and with the charge distributions of protons and neutrons as then-measured by Hofstadter and others you could implement a calculation. There was a problem: naively, the electric field of the proton will give a positive contribution to its energy and hence to the mass of the proton, a contribution that is not there for the neutron, and would make the proton heavier than the neutron. That’s opposite of what nature does. The early field theory calculations at the time also had the proton heavier than the neutron. If these calculations were correct, the proton would decay to a neutron plus a positron and a neutrino. There would be no nucleus of hydrogen, and we wouldn't be here.
Forget about calculating the magnitude; let’s at least get the sign right! Many people tried to find ways to make the neutron heavier, but nobody really succeeded, at least not without charge or magnetic moment distributions that were very implausible. Roger Dashen found a method using dispersion relations to potentially flip the sign because of the strong interactions. It involved a crucial assumption about the effect of the strong interactions. I started looking at what would happen with other particles besides the neutron and proton. For example, there were the positive, neutral, and negative sigma particles, whose mass differences had just started to be measured accurately.
As a result of what, Fred? How were they now being able to be measured accurately? What advances had occurred that allowed for this to happen?
The growth of large bubble chamber experiments at Brookhaven and Berkeley is what I recall gave the data sets that provided sufficient statistics to measure those mass differences. My thesis was to extend Dashen’s method to the strange partners of the proton and neutron. Within the experimental errors at the time, I found that the Dashen approach was consistent with the data. There was “No red flag from experiment.” In addition, there was a section of my thesis which was done with my fellow grad student, Henry Abarbanel, where we applied Dashen’s formalism to calculate a mass difference in a simplified field theory model where you could calculate everything exactly. Dashen’s method gave the correct answer. The problem was that in the simplified model the answer came from the diagram with a photon being emitted and then absorbed, the analog of the proton’s electric field adding to its energy and mass! Dashen’s method worked, but the source of the resulting mass difference would have made the proton heavier than the neutron. It made us suspicious, although our model theory was hardly as complicated as strong interactions. What I tell [laugh] my children and others is my thesis was wrong.
That’s pretty blunt.
Yeah. I can soften the bluntness by saying it wasn’t wrong because I made a math error or that the data was wrong, but that I was focused on the wrong explanation. A few years later we knew that the mass difference is not primarily due to electromagnetism. Rather, the mass difference is mostly due to the difference between the masses of the down quarks and the up quarks that are constituents of the proton and neutron, With the down quark appropriately heavier than the up quark, the electromagnetic contribution is overpowered by the contribution from the quark masses, making the neutron heavier than the proton. Why is the down quark heavier? We don’t know. The difference in mass of the down quark and up quark remains one of the fundamental parameters in particle physics which determines the nature of our whole universe, but we do not know how to calculate it. Perhaps its particular value is just given randomly at the beginning of our universe, and we will never be able to calculate it.
This also brings me to a philosophy about theses. Murph learned it from his advisor, Enrico Fermi. Fermi told Murph, and Murph told me, and I've told it in turn to every one of my grad students.
Now, was your sense — did Goldberger tell you that he got it from Fermi? Is that the intellectual tradition?
Yes. He told me — and it’s about the purpose of theses in general, Fermi said a thesis was like a driver’s license, in the sense that it was a certification that you could do frontier research which could be published and put in a form that other people could use in their research and add to the progress of science. You didn't have to write a thesis that was brilliantly transformative, but rather it could simply be the jumping off point to a career in science. Fermi then had a one-line statement which summarized it, which is what I tell my students: “You don’t have to show your thesis to your grandchildren.”
You don’t have to show it. While you are not forbidden to show it, your thesis does not have to be a highlight of your life contributions to science.
Who else was on your committee, Fred?
Let’s see. Dick Blankenbeckler, who was at Princeton and later at UCSB and then SLAC; Uriel Nauenberg, an experimentalist later at Colorado; Roy Cook, a young theorist; and Murph. I had heard that after you got done with the usual presentation and questions on your thesis, the final orals committee tries to teach the student that they don’t know everything. They start asking questions across physics in mechanics, electricity and magnetism, and so on. I was told that Murph would always ask to write the equations of motion of a rocket. I was so ready! They didn't ask me!
Probably because he knew you were ready for that one. [laugh]
This is June of ’65, and I came to Murph’s office with my thesis on Baryon Electromagnetic Mass Differences. I had two copies, one for him and one for the department. Murph looked out the door and then he looked from the hall into Blankenbeckler’s office, who wasn’t there at the time. Then he said to me, “Tell” — I've forgotten the lady’s name who was the department secretary — the secretary that “they read the thesis instantly.” “Just put it on her desk and get a date for your oral defense.” [laugh] Just Murph. Pure Murph.
That’s great. Fred, to the extent that you thought about such things, and in light of your comment about not having something to show to your grandkids necessarily, what did you see as your primary contributions with your dissertation, either retrospectively looking back, or at the time?
As per Fermi, it really was not such a great contribution to knowledge, as it turned out. I learned a lot of things. I published my first papers, one of them a collaborative paper. And for several years afterwards, until quarks were understood to be there — this subject didn't die, and calculations of the electromagnetic contribution to the proton-neutron and other mass differences continue to this day. More importantly, I learned a lot of physics, doing calculations, and testing your theory in models or where you have a known answer in a limiting case. It also gave me a bit of skepticism that I was on the right track and not missing something important at times.
At what point did you put together the opportunity to work with Gell-Mann at Caltech? Was this before you defended, or did you defend, and you were pursuing various opportunities?
OK, another interesting story. We had already decided at the beginning of my third year that I’d try and finish that year. Murph agreed that the work with Henry Abarbanel and the calculations I had done would be — by Fermi’s definition — a suitable thesis for a PhD. For all three years at Princeton I was supported as an NSF predoctoral fellow, and I applied to be an NSF postdoctoral fellow. In the meantime, Murph was in contact with many physicists both professionally and because of his work advising the government. He interacted a lot in those days with Norman Kroll. At some point, in the fall of the third year, he must have run into Kroll somewhere and mentioned that he has a student who will be getting his PhD. Norman, who was just in the process of going to the new campus of UC at San Diego — more or less, the founding —
Right, he was just getting started, then.
And so Murph — I guess; I wasn’t there — with me graduating had raised the possibility of my being a postdoc at UCSD. I vaguely remember meeting Norman at the American Physical Society meeting and talking to him about the new campus in San Diego, how big the department would be initially, and the plan for its future. In the meantime, I got the NSF postdoctoral fellowship, and I went and talked to Murph and told him that the things that I've done and interested in make it much more interesting for me to be at Caltech. This was true in particular because of Murray Gell-Mann at that time. As it turned out, I interacted as much or more with Feynman as Gell-Mann, including Feynman’s lectures to a few postdocs on his work on Yang-Mills theories. But in any case, Murph — it was not right then in front of me, but it was within a day or so, had phoned Murray, and it was all arranged. I would go to Caltech as an NSF postdoctoral fellow, and Murray would be my postdoctoral advisor. Done.
Just one of these things that probably took a few minutes and changed my life.
Amazing, amazing. And you must have been in the clouds when this all came together.
Absolutely. Let me come back to two world events that took place during this time. One was the Cuban Missile Crisis in the fall of ’62. That was very scary. You're too young to have lived through it.
No, but I'm a historian, and I know it well.
Sitting in Princeton, especially at night, you could hear the airplanes, the transport planes in groups, flying southward toward Florida, and you understood they were preparing for a potential war. Every few hours, there was a convoy headed southwards. That was a very scary time. I lived in the graduate college, which is where most of us lived — of course. Princeton undergraduates were totally male at the time; I think there were one or two women graduate students who lived somewhere else. In my last year, with a group of my friends who were almost all in political science, I lived in a house on Madison Street in Princeton. During the Cuban Missile Crisis, we sat in a room in the basement of the Graduate College — all glued to the TV screen. Standing room only. It was true again in the fall of ’63, that day of all things there was a seminar on scattering theory that Murph gave at the IDA building, whose headquarters was in or very near campus. He had just finished his book with Ken Watson on scattering theory. .
Let’s talk about when you arrived on the scene at —
As we were standing outside the building before Murph’s talk, someone arrived and said, “I heard that the president has been shot.” We stood around outside for a while, and somebody went to listen to their car radio, but there was no new information. We stood there debating — “Should we leave? Should we go in?” In the end, Murph decided to give the talk. Of course, when we came out, we got the word of Kennedy’s death. One of my friends was Ralph Roskies — he had come as a math grad student, but was a student of Wigner, and I got to know him quite well. Ralph and his wife Dodie plus others from his family and me drove to Washington and arrived in the evening, parked, walked, and then stood in line to go through the rotunda of the Capitol. At three or four in the morning, I don’t remember exactly — I was too dead tired and didn't think I was going to ever make it to the Capitol. So I dropped out and fell asleep in a chair in a hotel lobby. The others stood in line until they walked through the rotunda, past the casket.
Those were the times that we lived in. Let me mention a few words about other people, before talking about the physics breakthrough that was going to be very important in my life. In my graduate class — and who became a lifelong friend — was Jon Rosner, who became a fellow theorist at Chicago, Kip Thorne who has now won the Nobel Prize, and Jim Russ, much later my colleague at Carnegie Mellon. In the class a year earlier, were a number of leading particle experimentalists and theorists including Stew Smith, Curt Callan, and Steve Adler, lifelong friends as well. Now let me return to the spring of 1965. Just as I'm finishing my thesis. Steve Adler, who had been a student of Sam Treiman and became a junior fellow at Harvard, had discovered how to derive a sum rule starting from the algebra of currents proposed by Gell-Mann. He came to Princeton from Harvard to talk to Sam and show him what he had done. Steve, Curt Callan and I gathered in Sam Treiman’s office, and Steve went through the details of the calculation of the sum rule. I don’t know how much time to devote to what the sum rule was —
Murray Gell-Mann had proposed that you could use quarks not only as constituents of the proton, neutron, and other strongly interacting particles, as originally proposed by Murray and by George Zweig, but as quantum fields and form currents, much as you would form the electric current from the fields of electrons in quantum electrodynamics. The currents in this case were those that appeared in the theories of electromagnetism and the weak interactions. The order in which you formed the product of two currents mattered, so that if you formed the difference between the two orders, the commutator, the result was yet another current. Altogether, the set of these currents formed a closed system, a current algebra. That current algebra had been written down by Gell-Mann in 1964. Gell-Mann backed away from quarks as observable particles but proposed that the current algebra could still be true, putting aside its original derivation. If the set of algebraic relations between the currents was true, perhaps we might finally have a piece of a long-sought theory even if quarks themselves were not physical particles.
Adler took one of the current algebra equations and converted it into a sum of measured, physical quantities in place of the commutator on one side and a pure number on the other side. The resulting sum rule had measured quantities of differing sign that had to all add up to one. And the sum rule worked! I still remember where I stood watching Steve derive the sum rule and putting in the numbers coming from experiment.
And you knew this at the time? You knew just how momentous this was?
I did feel this was very important — this was the first time, instead of guessing, instead of waving your hands, instead of making approximations, you had something that could be an exact law of nature and had testable physical consequences.
What did you see as the broader implications for this? Does this change everything as far as you were concerned?
Not yet. The big thing that was still to be settled is the nature of quarks. Perhaps the current algebra would end up being correct even if the quarks were not observable. Many people were very cautious in that regard, as Murray Gell-Mann was at that time. Others were antagonistic. In Princeton, the word “quark,” when I was there as a grad student — was not uttered by the faculty in my presence. It was regarded as total bologna by many. Harry Lipkin came to Princeton in those years and informally discussed his work regarding quarks. People told him that he’s crazy. Murray, to his great credit, very much pushed onward to see how much physics you could derive starting from the commutation relations.
Fred, was it a one-year postdoc that you renewed for another year because things were just so incredible? Or was it supposed to be a two-year program from the beginning?
The NSF postdoctoral fellowship was potentially renewable for a second year, but I didn't realize when to reapply until too close to the deadline for the second year.
Caltech just picked me up for the second year.
Is that right?
Now, you said that you actually had more contact with Feynman than you did with Gell-Mann.
Yes, I did.
How did that play out? That certainly was not the plan.
No, that was not the plan. Let me go back in history again. We talked about the period just before graduating, with Steve Adler visiting and current algebra sum rules. That summer, I went to the Les Houches summer school. Within a week and a half of my final oral in June, I was on an airplane for the first time in my life on the way to London, first, and then to Paris. I gave a talk at Oxford, arranged by David Bailin who had been a postdoc at Princeton. There weren’t very many people there, but I met Dick Dalitz for the first time. After London, I went on to Paris and then got on a train to Chamonix, and finally by taxi to Les Houches. Once again, luck in some ways — I met a bunch of people who were the lecturers. Among them, lifelong friends, Dave Jackson and Maurice Jacob, who was the director of the school. There were also fellow students like Michel Della Negra, who later was a postdoc at SLAC and much later the spokesman of CMS at the LHC. During that summer, the paper of Adler and also that of Bill Weisberger, who had derived the sum rule in a different way, appeared in Physical Review Letters. There was a bunch of people at Les Houches trying to understand these papers — and so I got to give a seminar — the third seminar in my life — to students and faculty of the school. I included some other things that I had been thinking about and it was the first time in my life I really felt I was at the frontier, so to speak, and had something to add.
Were you giving a job talk, perhaps, and you didn't know it?
No. I already had my job. I was going to be a postdoc at Caltech. I wasn’t going anywhere except straight to California once I got home. [laugh] Perhaps I was giving a talk for 20 years later or 30 years later and didn't know it.
So back to the question on Feynman. More contact with Feynman.
I arrived at Caltech, ready to dive into sum rules, at the right place, at the right time, with the right people around. Murray was at that point mostly working with Roger Dashen on trying to extend current algebra to a bigger domain — trying to make the basis of a dynamics. There was another class of sum rules that were called super-convergence relations. They involved scattering amplitudes which decreased rapidly with increasing energy. Using dispersion relations, you could turn them into equivalent sum rules. By combining current algebra with super-convergence relations, one could derive additional constraints. Before any paper associated with my thesis was published, I had written a couple of short papers with my fellow postdocs at Caltech. When I arrived at Caltech in September after driving across the country, I very rapidly met the theorists including Feynman, Gell-Mann, Fred Zachariasen, George Zweig, and Roger Dashen. I also met many of the experimentalists, including Alvin Tollestrup and Bob Walker, who had been at Los Alamos and led photoproduction experiments with the Caltech electron synchrotron. And there was a young assistant professor, Barry Barish, who became a lifelong friend. All the postdocs were in a single room, which Fred Zachariasen called “the pig pen.” Among the pigs was yours truly, Chris Schmidt, Mahiko Suzuki, an Indian physicist who used the single name Babu, and Joe Dothan, who was an Israeli, who had just gotten his degree in Israel. That was the pig pen. I also met John Bahcall, who was a postdoc but very shortly became an assistant professor, and John Faulkner, who was also in astrophysics. Bahcall was already thinking about neutrinos produced in the sun, and Faulkner worked on stellar evolution. Chris Schmidt, Joe Dothan, John Faulkner, John Bahcall and I would often all go to dinner together. We were all bachelors, but by 1967 we were all married.
Oh, wow. [laugh]
Within a year and a half. Additions to the pig pen were Steve Adler as a visitor from Harvard in the spring of 1966 and the next year came David Horn as a postdoc and Howard Schnitzer on sabbatical from Brandeis. I wrote a couple of papers with Steve Adler and one with Howard Schnitzer as well. But the most important series was with Haim Harari, who was a postdoc at SLAC. He and I wrote three papers in 1967, two of which were Phys. Rev. Letters and one was what we called our century paper, because it was a 100-page preprint that was a giant overview of sum rules, how to derive them, their consequences, and the classification of the physical states in terms of the algebra of currents. Murray, because he was required to teach, taught one course, which was a “what I did yesterday” course. Literally, it was out of his notebook of recent calculations, making it an unbelievably valuable course for me to watch in real time the advance of the frontier of physics. There were very few grad students who dared to sign up. It was mostly the postdocs and the faculty, including Feynman and others.
They would attend?
Oh boy, would they!
And Feynman from the back of the room would pick on Murray. [laugh]
Anyway, it must have been — I think it was December; maybe January. But somewhere in the middle of the year, Murray was going to be out of town. He said, “Why don’t you teach my class and talk about sum rules?”
So I did. And the biggest questioner was a student named Feynman.
Who I had already met, of course, and interacted with somewhat. We had a big conversation at the blackboard after my talk about different ways of deriving sum rules, and where and how we might be able to derive new sum rules. Afterwards, he told Julie Curcio, the secretary, to make for me a copy of a dozen or so pages from his own 1965 notebook. I still have that, today. It is mostly Feynman’s derivation of the Adler-Weisberger sum rule. It starts with “Murray says” followed by a current algebra equation. One of the interesting questions from this period, whose answer may never be known for sure, arose when Steve Adler arrived in the spring. Feynman gave me his notes before Adler arrived, so my copy must have been made in November or December, rather than later. Adler also had a conversation with Feynman, and his recollection, which he wrote in a 2005 memoir, is that he also saw a part of Feynman’s notes with a calculation where he recalls Feynman had inexplicably written a zero rather than a one on the right-hand-side. A year and some ago, I sent my copy of Feynman’s notes to Steve, but those notes date from just after Adler’s paper and don’t shed light on an earlier calculation. It remains possible that Feynman could have been first in deriving the sum rule — were it not for the mistake.
What did Feynman say about it?
I only know that once Adler’s calculation came out, he did his own derivation of the correct sum rule. Of course, he went on to use his way of thinking to develop his version of understanding inelastic electron scattering in terms of point constituents which Feynman called partons. Murray called them put-ons.
Why? Why’d he call them put-ons?
Because it’s a jab at Feynman, I suppose. They were always —
It was just Murray and Feynman. Also, Murray always showed his command of words and languages and would refuse to recognize certain words or names if it wasn’t his term for it. This was the case with the W boson. If you were talking about weak interactions where the weak force was mediated by a vector particle as the photon mediates electromagnetism, and labeled that particle by the letter W, Murray would give you his quizzical look of complete consternation — a look you can see in some of the videos of him being interviewed. “What are you talking about?” After you defined its function in a theory of the weak interactions, he would finally break into a look of revelation and say — “Oh, you mean “ooks” or something sounding close to that.
Murray would explain that “ooks” was a word in a Mayan dialect for “weak” and that since he had proposed the concept first
“he had the right to name it.”
Murray would come into the pig pen and talk for an hour or more at a time describing how to look for patterns in languages and trying to see whether there could have been one language many thousands of years ago. There’s a story that I heard when I came to Caltech, which was presented to me as a true story from a few years previously. A set of graduate students and postdocs was having lunch in the cafeteria, the ‘Greasy,’ and Feynman and then Murray joined them. The subject of clocks came up, and Murray recited verbatim the Encyclopedia Britannica article on clocks. His obituaries note that Murray memorized the whole Encyclopedia Britannica as a child. After Murray finished reciting the article, Feynman looked at him and said, “But Murray, how does a clock work?”
[laugh] Did he have an answer?
I assume so. But the story illustrates their difference in personality as well as their interaction. They were both geniuses. Like the greatest artists, they both changed how we all perceive the world around us.
Fred, let’s move on to the transition to SLAC. How did that come about? Was this the clear choice for you in terms of the best place for you to go next? Were there a range of considerations that you had? Or was it always SLAC from the beginning?
I should add here a very, very important piece of my life. In December of the first year at Caltech — so that’s the end of ’65 — Henry Abarbanel’s parents, who lived in LA, invited me to dinner. After I left, unbeknownst to me at the time, Henry’s mother called a close friend of Henry’s sister and of Henry, Barbara Weiner, and asked if she could give me her phone number? I called in early January 1966, and we started to date. By October, on my birthday, we were engaged, and were married in March of ’67.
[laugh] At the end of October, I wrote a letter to Sid Drell. And at that point I knew —
Now, Drell — what was his position? Was he the executive head for theoretical physics at this point?
No. He was deputy director. Pief Panofsky was director, Sid was deputy director, Joe Ballam was head of research, and Pierre Noyes had taken on the job of head of the theory group at SLAC. So officially the offer letter would come from Pierre. In any case, at the end of October, I sent a letter to Sid and I got a very prompt answer that they were in the process of thinking about postdocs for next year, and to send my application and have letters of recommendation sent. At the end of November, one month later, I got a letter from Sid followed by Pierre’s official letter offering me a postdoc at $950 a month, which I promptly accepted.
And how well-delineated was the offer? In other words, was it clear that your work was going to be in theoretical physics at SLAC, or it was more open-ended than that?
Not broader. It was to be a postdoc in the theoretical physics group. Incidentally, I had given a talk at SLAC early in 1966, probably January or February, I drove up and gave a talk on sum rules. It was the first time I met Haim Harari, whom I later worked with, Myron Bander, and a bunch of other postdocs and laboratory staff. By then of course the laboratory was just about to turn on the electron beam. The theory group was located where it was to be for the next 40 years on the top floor of the central laboratory next to the director’s office. In any case, I re-established my relationship with Sid as well as with Sam Berman, whom I worked with in the summer of 1963, and I met BJ [Bjorken], and others.
How did you feel about entering into a major experimental facility as a theoretical physicist? Did you see that there were any issues in terms of where you fit in, in the grand scheme of things?
No, not at all. If anything, the opposite.
After Caltech, I thought about being an assistant professor. There were informal offers of positions at UC Santa Barbara and UC Irvine, and my alma mater wrote me a letter saying that they would love to have me come back to Michigan State and offering a faculty position. I didn't try very hard to look beyond being a postdoc at SLAC for a couple of years. I made a slightly risky decision, although there were lots of new academic jobs opening up around the country, so the likelihood I wouldn't end up somewhere with a faculty job was quite small. But SLAC was where I thought the physics would be.
In particular, one of my papers with Steve Adler in 1966 focused on how a family of sum rules derived from current algebra could be tested using high energy electron beams. The sum rules were true for all values of the momentum transfer from the electron to the proton and could be written as an infinite sum of measurable quantities being equal to the number one. We showed that the then-available data indicated that the sum rule was indeed correct for small values of momentum transfer to the proton. However, the bulk of the sum rule came from contributions from the proton and a few other particles nearby in mass, and these contributions each fell off rapidly with increasing momentum transfer. At high momentum transfer−yet unmeasured at that point−an increasing number of high-mass states might contribute to the sum, but if they all fell off with momentum transfer like the first few terms did, the sum rule would fail miserably. What kind of conspiracy involving the high mass terms could not only keep the sum from going to zero as the momentum transfer increased, but could continue to keep the total sum equal to one? The abstract of our 1966 paper indicates that with electron beams of 5 billion electron volts “it is reasonable to start trying to check” whether the sum rules continued to be valid. SLAC, with up to 20 billion electron volt beams, would be the first place where the sum rules were seriously tested. As Steve Adler says in his memoir, we were too cautious in not pushing further in 1966 into how the sum rule could be satisfied when the momentum and energy transfer were arbitrarily large. In addition, after enjoying interacting with Bob Walker on photoproduction data as input for testing sum rules, I knew there were many people at SLAC whom I would enjoy interacting with on a broad range of particle physics experiments.
How closely did you work with Drell?
I collaborated on several papers with Sid, along with Henry Abarbanel, on very high-energy proton-proton scattering during my first couple of years at SLAC. Let me also add one more thing about the transition to SLAC. We moved to the Bay Area in July, August.
Yes, 1967. By then, the accelerator was up and running. The people doing inelastic electron scattering on proton targets were starting to collect data. In the midst of the beginning of the experiments, the International Symposium on Lepton-Photon Interactions at High Energies was held at SLAC.
What year is this now?
This is summer/fall ’67.
Oh, so right when you arrive?
We arrived mid-summer. BJ was getting married. He gave a talk at the Symposium, a very important talk, and immediately after that he and Joanie went off on their honeymoon. I was assigned the job —
To the mountains, right? I bet they went off to the mountains.
I was assigned to listen to the tape of BJ’s talk and transcribe it, so that when he got back he could more easily convert it into a manuscript for the Proceedings.
Oh, wow. [laugh]
So I was pushed into transcribing — although I was happy to do it, of course — the talk in which BJ sketched a big bump in the inelastic electron scattering cross section that corresponded to elastic scattering of the electrons by point-like quarks inside the proton. It had the beginnings of the idea termed scaling. If quarks were point particles, there is no dimensional quantity coming from the quarks and therefore the underlying process could only depend on the ratio of two kinematic quantities such that the dimensions of each of them cancelled out in their ratio.
And this is still all in 1967?
Yes. It is in terms of insight into what to look for in the data. Once you removed the factors that had to do with the kinematics and the electromagnetic nature of inelastic electron scattering, dimensionless quantities called structure functions encapsulate the physics. They generally depend on two variables with dimensions, but with point constituents, which have no dimensions, they can only depend on a dimensionless ratio rather than each variable independently. That’s the crucial insight.
Fred, I wonder the extent to which this particular avenue of inquiry played into Pief’s speech in 1975. How large did this particular project loom in terms of the kind of idea that he wanted to convey in 1975?
Oh, by ’75, much, much more had happened, of course. This is ’67. This is the very beginning. And nobody knew yet that you'd get anything deep and quantitative out of this. The experimentalists themselves had mostly developed analysis programs for the case where nothing interesting occurred! If the actual physical cross-sections all fell off rapidly with momentum transfer, the measurements would be totally dominated by a sea of bremsstrahlung photons emitted by the incoming electron, reducing its energy, and then scattering from the proton in a regime of lower energy and momentum transfer where the cross sections would be much bigger. By early 1968, there was nothing to show anybody yet, nor did it unambiguously tell us where we were headed. But the cross-sections were big, compared to what some had projected based on a rapid fall-off with momentum transfer.
Now for your first two years as research associate, you had not yet determined at this point that you were really going to make a long-term career at SLAC. Or was this sort of part of the plan from — ?
In fact, I expected the opposite.
I went to SLAC thinking I’d be there two years as a postdoc, and where the action was, so to speak, and then I’d find a faculty job.
Right. So then what happened in 1969 when you were named associate professor?
So before 1969 is 1968. [laugh] The International Conference on High-Energy Physics was held in even years. In ’66 it was in Berkeley. I was there as the scientific secretary for the current algebra section. I have a wonderful picture taken at the beginning of the conference, which is the only international meeting that I know of where there was a one-hour talk at the beginning that should have been the summary talk. That’s because there was one person who was so dominant in driving the whole field of high-energy physics, Murray Gell-Mann. He laid out the key questions, and what we had to do to answer those questions, both experimentally and theoretically. In that picture, in the first row there’s Murray, and sitting right next to him is Murph Goldberger. Many rows back you can see Feynman.
It’s all coming together for you.
My two advisors, one for my PhD and the other as a postdoc, waiting for Murray to get up and provide the summary of what you're going to hear for the next five days.
In ’68 the International Conference on High-Energy Physics was held in Vienna. Barbara and I — it was her first trip to Europe, my second, went to the U.K. and especially to London, then on to Paris, and finally to Vienna. I was for the first time a delegate, which was by invitation in those days. This is the conference at which the first results on inelastic electron scattering were announced. Panofsky was the rapporteur. An important talk, and I’ll come back to that. Early on the first day I saw Sid Drell. We talked about the terrible situation in Czechoslovakia and then about the presentations from SLAC. He then told me that given I was beginning my second year at SLAC, I would be looking for a faculty job. The SLAC faculty had met, and they wanted to be sure that when I got an offer, I would give SLAC a chance to respond.
So I have to ask, Fred — did you bother looking for other offers to compel SLAC to reply?
I wasn’t interested in compelling but did want to explore my options. I applied to Caltech. When I visited, Murray wasn’t there and again it was Feynman who asked the most questions during my talk. I recall that I also applied to Santa Barbara. And I thought a little bit about other places. But very quickly after I visited Caltech and I think Santa Barbara, I was told that a faculty offer from SLAC was going to be made. At the time, SLAC didn't have any assistant professors.
You were going to be the assistant professor?
No. Later, they did have assistant professorships. I was not —
Oh, you mean as a category of employment, they didn't have?
Right. Because the original laboratory, which had relatively recently been established, had hired tenured people as associate and full professors. They just hadn’t yet gotten into the usual mode. Within a few years, the category of assistant professor was established, and the first appointments were experimentalists, starting with Elliott Bloom and Michel Davier. I became an associate professor.
And that was a tenured equivalent kind of position, associate professor?
Tenured associate professor at Stanford. You maybe don’t know the history of SLAC. SLAC faculty were Stanford faculty.
Right. No, no, I understand that. I'm saying, though, if there were any curiosities — I mean, what you had done essentially is you had skipped over the whole tenure process by going from postdoc to associate.
So I didn't know if that was a unique arrangement, but obviously it was not.
I believe that it was unique, just because of the timing near the beginning of forming the SLAC faculty. After me, assistant professor was the normal first appointment for somebody who was a postdoc or sometimes even an assistant professor elsewhere.
Fred, in weighing various opportunities, like thinking about Caltech or Santa Barbara, obviously a difference with SLAC is that it has some level of remove, given that you're at SLAC and not at the physics department. I'm curious how that weighed into the constellation of decisions that you were making at that point.
Not at all. I don’t think anybody else on the SLAC faculty thought that they were at a disadvantage. They just didn't have to teach!
So that was a plus, meaning that you didn't have —
Yeah, for most people. Not for me, so much, but for many people.
Right. So I ask that because I know that you did take on graduate students.
So that’s sort of a natural signal that there is something about being in a traditional physics department that was probably attractive to you.
Yes, and to almost everybody else on the faculty as well, starting with Pief. I don’t want to get into a long story, but when SLAC was going to be established, Pief in particular, and then other people with him, insisted that there be a faculty. Pief felt that to attract the quality of people he saw as necessary for SLAC to be successful, you needed to have a set of faculty at SLAC with appointments at Stanford. Naturally the people in other areas of physics within the Stanford physics department at the time thought that given the number of potential appointments Pief envisaged, the SLAC-associated faculty would dominate the department. There was a terrible fight inside the department. People who had been long-term friends stopped talking to each other. You can find personal accounts in Pief Remembers and the memorial volume for Sid Drell in his recounting of science contending with bureaucracy.
Barbara and I, who came years later from outside and weren’t part of the war, were able to be good friends with people on both sides. The Stanford provost, Fred Terman, known as the father of Silicon Valley, made the decision that there shall be a separate SLAC faculty in addition to the faculty of the physics department. Terman also set down the guidelines that the SLAC faculty would not teach undergraduates, but that Stanford graduate students could have PhD advisors at SLAC.
Fred, let’s get into your work in the early 1970s. What were some of the things you were doing at SLAC during those years?
Let’s back up a bit, because I stopped you by saying ’69 is preceded by ’68 and discussed my faculty appointment. Let me pick up the story there. I'm sorry we're taking up time.
No worries, no worries.
Let me go back to August of ’68 in Vienna. I gave my first talk at a conference in a parallel session on current algebra, and the first data was presented from the SLAC/MIT collaboration on electron scattering. It was of course early, with a big rush to get the data out before the conference. There was just one plot presented in which the data from different electron energies and scattering angles was tested as to whether it was consistent with being a function of a dimensionless ratio of variables as proposed by Bjorken. And, if you look at the plot and disregard the points from very low energies, you do see that at high momentum and energy transfer, the data points do fall within error bars along a single curve that depends on the ratio of variables, just as expected for scaling. However, it was presented by Panofsky briefly toward the end of his talk. He didn't emphasize it and most people didn't pay attention. Nor was the SLAC/MIT collaboration ready yet to say, “Hey, look at what we’ve discovered.” But it was presented — and in retrospect, this is cited as the debut of a great discovery.
After the conference, I was going to give talks on sum rules using my handwritten slides from Vienna in Geneva, then at Frascati outside Rome, and finally at the Weizmann Institute. In the talk that I gave in the conference and later elsewhere, I talked about my work with Harari and others, and then, near the end, reviewed my earlier work with Steve Adler and showed that once you were in the regime where there was scaling, the sum rules could be cast into a form where they could be true at very large momentum transfers. I probably have not explained it for the non-experts.
In 1966, there remained the crucial puzzle of how a family of sum rules Adler and I found to be valid at low momentum transfer could still be true when the momentum transfer becomes large and the low mass contributions have died away. We now had the answer. Scaling was exactly the “conspiracy” between contributions at high mass and high momentum transfer needed to make the current algebra sum rules work. Things had come full circle in a sense: Hypothetical quarks in currents had led to current algebra, which in turn resulted in sum rules; now, in Vienna, the sum rules looked like they could be valid at large momentum transfer given the scaling found in the data, which in turn was due to real quarks inside the proton. I took my transparencies and borrowed Pief’s slides for my talks after Vienna. In my office, I still have Pief’s and my slides that were shown in Vienna and afterwards in 1968. I plan to send the originals to the SLAC archives.
Around the time I was in Vienna, Feynman visited SLAC (his sister lived nearby), saw the data, and developed his parton approach. While a number of people at SLAC understood the implications of the data, starting of course with Bjorken who had proposed scaling if there were point constituents, Feynman’s very physical language involved “partons” in the proton each carrying a fraction of its momentum that was equal to a value of the scaling variable. It became the most common language for interpreting the data. In the year that followed the Vienna Conference, there was an increase in the momentum transfer in the SLAC experiments by going to bigger electron scattering angles. By the spring of ’69 the evidence for scaling was spectacular. That summer, the International Symposium on Lepton-Photon Interactions was held in Liverpool. The experimental talk on inelastic electron scattering was given by Dick Taylor, representing the SLAC/MIT collaboration, and I gave the corresponding theoretical talk. My talk began with inelastic electron scattering on atoms with the constituent electrons knocked out of the atom, and then electron beams with millions of electron volts of energy hitting nuclei with protons and neutrons being knocked out of the nucleus. The new experiments at SLAC now showed us the constituents of protons.
So what year does this take us up to?
We are now in September 1969. In fact, on September 1st, 1969 — I recall the date because I thought at the time that it was 30 years since the beginning of World War II — Barbara and I got on an airplane at SFO to fly to the U.K. and on to Liverpool. A couple of questions that I was asked in the discussion period after my plenary talk reinforced something that I was already thinking about. How do the excited states of the proton, the nucleon resonances, produced in inelastic electron scattering behave as the momentum transfer increases and scaling sets in? I already had a suspicion that the behavior of the resonances was tied into scaling in some way. In 1967, just after I arrived at SLAC, I extended the work I had done with Adler by evaluating a current algebra sum rule at a momentum transfer of one GeV and found it could be satisfied largely by contributions from the resonance region. By 1969, we also knew that scaling was setting in around one GeV. How could we be in a regime where scaling is relevant, but also where resonances make quark-based sum rules work? Suspicious, but not conclusive. The top issue that I carried away from Liverpool was to do more work on this. When I got back to SLAC, I told Elliott Bloom and other experimental friends to look in the resonance region in the SLAC data and compare it to deep inelastic scaling. With lots of other important things going on for everyone, not much happened on this for many months. Meanwhile, I worked with graduate students and postdocs on dispersion relations and sum rules, while also continuing to devote serious effort to my other major research area, the phenomenology of strong interactions. Duality for the strong interactions was all the rage, including for me, where I co-authored a duality based paper with Harari and Zarmi.
My first PhD student was Inga Karliner, whose thesis was on photoproduction sum rules. Jumping a few years ahead, in addition to Karliner, I also wrote several papers with Frank Close, then a postdoc at SLAC, and with Kugler and Meshkov on the implications of quark currents for photoproduction, electroproduction, and strong interaction processes. There were several other groups doing related work and getting similar results using explicit quark models, including Feynman, Kislinger, and Ravndal. In fact, my last physics encounter with Feynman was in my visitor’s office at Caltech in the spring of 1973 as he stood drumming his fingers on the empty file cabinet, while he, I, and Meshkov discussed the strong evidence emerging for quarks coming from the relative signs of amplitudes for almost twenty photon and pi meson transitions. Of course, by then, there was hardly anybody who wasn’t convinced for other reasons.
In the spring of 1970, I had returned to thinking about the behavior of resonances and scaling. Elliott Bloom showed me the plots that I wanted, including those made using a slightly different, but equivalent, dimensionless scaling variable found by a graduate student. It made the data converge faster to the scaling curve, and also made the peaks and valleys due to the resonances, which wigged back and forth across the superposed scaling curve, clearer. As someone who lived in both the worlds of scaling in deep inelastic scattering and strong-interaction duality, the question of their relationship was settled. Resonances were not only related to scaling; they formed a dual view (in the sense of strong-interaction duality) of inelastic scattering. At low energies, one can see the individual resonances and they average to the scaling curve. At high energies, there are many overlapping resonances and their contributions merge to form the scaling curve. Phrased in physical terms, there are two complementary or equivalent ways of viewing electron scattering off protons and neutrons. In one view, the kick given to a quark by the electron yields scaling and a snapshot of the distribution of charges inside. A dual way is to think about what happens to the proton or neutron because of the energy and momentum transferred; it becomes combinations of nucleon excited states, the resonances. Late one night, I derived consequences of that duality and remember, without much sleep, catching Sid and Pief as they came into SLAC the next morning to show the result to them.
With Elliott Bloom, I wrote a Phys. Rev. Letter proposing what became known as Bloom-Gilman duality. Later generally termed quark-hadron duality, it was used over the years in other contexts to equate a sum of contributions of resonances to a calculation done at the quark level. We completed the paper quickly because Barbara and I were expecting our first child, Michelle, who arrived near the end of June 1970. A year later, we wrote a much longer, detailed Phys. Rev. paper. They have become my 2nd and 3rd most cited papers. A gap of thirty years ensued before dedicated experiments at Jefferson Lab and DESY began examining Bloom-Gilman duality in detail using polarized beams and targets to isolate individual amplitudes. In the last two decades, duality has been verified impressively in multiple ways by comparing resonance region data to theoretical predications that include the logarithmic corrections to scaling due to QCD, the theory of strong interactions that was discovered after our papers.
In the 1969-1970 timeframe, the SLAC-MIT Collaboration was completing measurements of electron scattering on neutrons versus protons. Thinking in terms of quarks, the proton has two up quarks and one down quark, while the neutron has two down quarks and one up quark. The scattering rate is proportional to the square of the charges, so the scattering off up quarks should be four times that off down quarks. Given their quark content, inelastic scattering off protons should be larger than off neutrons. The data was presented in 1970 at the International Conference on High Energy Physics in Kiev, my one and only time in the Soviet Union. The neutron to proton ratio varied from close to unity down to about one-half. After that, the doubters almost entirely disappeared.
That was it. So what had changed? What had been so convincing even to the doubters at this point?
First there were much more data, including at much larger momentum transfer, that showed scaling. Second, was the newly measured neutron-proton ratio. Third, one could extract information on the spins of the constituents and that was consistent with quarks which have spin ½. Finally, alternate theoretical ideas had failed to make correct predictions, in some cases spectacularly so.
Allow me to jump ahead, because for me the capstone of the inelastic electron scattering experiments occurred in 1978 with the use of a polarized electron beam to see the parity violating asymmetry (due to weak interactions) between the rates for electrons with their spins opposite their direction of motion (“left-handed”) and that for electrons with their spins in their direction of motion (“right-handed”). The beautiful experiment, led by Charles Prescott, had a sensitivity at the level of a couple more left-handed electrons scattering compared to right-handed electrons out of 100,000, and verified the theory unifying the weak and electromagnetic interactions. At the conclusion of Prescott’s presentation of the results in the SLAC auditorium, there was dead silence in response to the request for questions, Instead, the audience spontaneously rose in a standing ovation. A couple of days before that, I went to Dick Taylor’s office to discuss the results of a calculation done with Bob Cahn related to the experiment. Dick was on the phone, but near the end of his call he motioned me into his office. He was talking with Glashow or Weinberg, giving a rundown on the results, and he concluded the conversation with “You can buy your ticket to Stockholm.” The next year, Glashow, Salam, and Weinberg did win the Nobel Prize. Eleven years later, Dick Taylor bought his ticket together with Jerry Friedman and Henry Kendall.
Fred, let’s reorient ourselves back into the narrative. What year were we in now, roughly?
Well, ’70 is the Kiev conference — but I've also described my path to a large degree in ’71, ’72, and even ’73. The next big event is the so-called November Revolution, in November 1974.
Please, let’s talk about that.
OK. Although we're getting pretty far along in time, —
Fred, on that point there, I just want to say, I think let’s for tonight — we're going to make this part one. And then the move to SSC, we'll pick this up for part two at a later two.
So let’s bring the narrative through your time at SLAC, and we'll pick up the part two at another time.
OK. There are lots of pieces, and I'll skip over a bunch. The November Revolution is the weekend of November 9th and 10th, and Monday, the 11th, 1974. The seminal precursor event for me was in the summer of ’74, at the International Conference in High-Energy Physics in London. I was the plenary speaker on the deep inelastic scattering and the structure of hadrons. Almost everything was in place of what we soon called the standard model. We already had the theory of strong interactions as quantum chromodynamics. Electromagnetism and the weak interactions had been unified into the electroweak interactions. Quarks and leptons were the fundamental, point constituents of matter, and we had recently understood that quantum chromodynamics acted like a free field theory at very short distances, so-called asymptotic freedom, and confined quarks from appearing as free particles at large distances, infrared slavery. All was beautiful. Even more spectacular was that we could do calculations in each of these quantum field theories and, for example, calculate the strong interaction corrections to the electromagnetic or weak interactions. Its almost 50 years later, and the standard model not only remains unscathed, but after many more stringent experimental tests. Back in the summer of 1974, along with its great successes there was a huge problem‒‒ the electron-positron annihilation data from the SPEAR colliding beam machine at SLAC.
Why was that such a big problem?
Because in the standard model the rate for electron-positron annihilation into final states with strongly interacting particles (hadrons) was easily calculable as electron-positron annihilation into quark − antiquark pairs. The quark-antiquark pairs then manifest themselves as strongly interacting particles. Further, the rate for electron-positron annihilation to a quark-antiquark pair is the rate for a muon-antimuon pair multiplied by the square of the quark charge in units of the muon charge. The sum of the rates for up, down and strange quark-antiquark pairs, including a factor of 3 for the three “colors” of quarks, should have been equal to 3 (4/9 + 1/9 + 1/9) = 3(6/9) = 2 times the rate for muon-antimuon. Instead, the early SPEAR data was much higher, although with relatively big error bars. This is a quark-theoretical calculation you can literally do on your fingers. However —
However — [laugh]
However, the SPEAR measurements at that time seemed to say you were wrong. that the data were about twice what we expected! You had a stack of theory papers several feet high, each with a different explanation. Burt Richter himself had a good time jabbing the theorists with provocative statements that “maybe the electron is like a hadron.” [laugh] One speaker at the conference, John Iliopoulos, who gave the plenary talk on the theory of the electroweak interactions, advocated a different proposal. From his work with Glashow and Maiani, he asserted that there was a fourth type of quark, a charmed quark. Furthermore, at that international conference every plenary speaker was promised a bottle of wine if they finished their talk on time. It was very good wine.
I still have my bottle!
I wouldn't dare let anybody drink it, this many years after 1974. But John, being John Iliopoulos, had brought along a corkscrew and a glass, opened the bottle, and started drinking as he was answering questions.
Did that count? [laugh]
Did that count? Was he OK?
He was very OK.
He not only asserted that there was going to be a fourth quark in addition to the up, down, and strange quarks, but he would bet any taker a whole case of wine that in two years at the next International Conference on High-Energy Physics, charm will have been discovered experimentally. There were lots of stories and jokes about the bet. That’s July 1974. Now we'll come back to November 1974. That fall, I was on sabbatical at the Institute for Advanced Study. Back at SLAC, the experimentalists had gone back to look at anomalies in measurements at SPEAR that had been made during the summer when there was a strike. The usual accelerator and SPEAR operators were gone, and various physicists took on running SPEAR. There had been considerably higher rates of events in one particular energy region, and they had gone back in November to check more carefully again. I was told you could literally hear the great discovery, in that as you changed the energy of the machine in tiny steps, you could hear the spark chambers dramatically increasing their snapping as you hit the resonance, which was given the name psi. I got a call to expect the announcement on Monday. Sam Ting, who had led an experiment at Brookhaven observing electron-positron pairs produced by smashing protons into a target, had found the same particle. There was a joint press conference announcing the November Revolution in particle physics. After that, SPEAR, or rather the SLAC-LBL collaboration, cleaned up. Within a few weeks, they had found another narrow resonance, the psi-prime. I came back to SLAC in January and had one of the great times of my life engaged both with my fellow theorists and daily conversations with multiple experimentalists on getting physics out of the gold mine that nature had conveniently placed at SPEAR energies. In the spring, they found three states that had masses between those of the psi and the psi-prime. If the psi was the ground state with no angular momentum of a charm-anticharm quark system, these three states corresponded to adding one unit of angular momentum.
In the late spring of 1975, another great discovery was made, starting with the realization that the electron and positron beams at SPEAR were polarized because the bremsstrahlung from different spin states is not the same and the tiny difference builds up the polarization with time. Since there is more bremsstrahlung at higher beam energies, the polarization increases more rapidly. When the polarized electron and positron collide, they annihilate into an electromagnetic field that is polarized perpendicular to the plane of the storage ring. If the electromagnetic field becomes a muon-antimuon pair, they have a characteristic dipole angular distribution. The muon pair events produced at SPEAR exhibited this distribution and the polarization grew with time in accord with the calculations. It was discovered at the same time that when the virtual photon becomes a quark-antiquark pair, while one does not observe quarks directly, the quark and antiquark leave contrails of strongly interacting particles along their direction of motion, called jets. The highest energy data from SPEAR not only showed indications of quark and antiquark jets, but that the jets have the same angular distribution as muon-antimuon pairs. Quarks evidently must also have spin ½. I remember talking to Burt Richter at the time, and how taken he was with this result. Even though most of the physical particles that make up the jet have no spin at all or have integral spin, the jets obey the angular distribution determined by their parent quarks which have spin ½.
Is this to say that Burt was among the doubters before this time?
No. He wasn’t a doubter at all. He thought the psi was a charm quark-antiquark bound state. It was spinless final particles exhibiting an angular distribution revealing the non-zero spin of their unseen parent quarks and antiquarks that struck him.
Now everything came together in a rush. Returning to the question that was so troubling at the time of the London conference, the contribution from production of charm quark-antiquark pairs added to those for up, down and strange quark-antiquark pairs still was not big enough to match the SPEAR measurements of the total rate for electron-positron annihilation. In the summer of 1975, Martin Perl came forward with another set of events from SPEAR, which had a muon and an electron or had a few other particles, plus unseen neutral particles, potentially neutrinos. These events seemed to behave like the decay products of two parents, which Perl called “U” for unknown at first. The U did not appear to be consistent with charm. Rather, it was consistent with being a heavy relative of the electron and the muon, a third lepton. There were many doubters, including in the SLAC-LBL collaboration itself. Aside from detailed questions about detector efficiencies and the like, it seemed unbelievable that nature would put yet another major discovery in the SPEAR domain, let alone have Perl, who had been searching for such a particle, find it. I had lots of discussions about further tests to see whether the signal was real or not, and later conversations with Marty Perl and Gary Feldman about what to name this particle. In the end, it was all up to Marty and he chose “tau.”
Now that we had a third lepton, we had to take into account the production of tau-antitau pairs. Although the basic process was electron-positron annihilation into tau-antitau, those pairs decayed mostly into strongly interacting particles plus unseen neutrinos and had been counted as if they were hadronic coming from quark-antiquark pairs. The total annihilation rate was now consistent with the data, and the crisis of understanding in 1974 turned into a triumph after 1975.
At the 1975 Lepton-Photon Symposium at SLAC, the pieces of the standard model of particle physics were fully stated. I regard the standard model as one of the great intellectual achievements of the 20th century. In Haim Harari’s plenary talk, he had six leptons, the electron, muon, and tau together with their respective three neutrino partners. They were matched by six quarks, up, down, strange, and charm, plus two quarks that were yet to be discovered, although they already had the names top and bottom (or truth and beauty). It took only two more years to find the bottom quark, but twenty to find the top. In my plenary talk on electron-positron annihilation, the features were the emerging agreement between theory and experiment for the total annihilation rate and the discovery of quark jets. I remember noting that while impossible to pull out of the background at low energies, the shape of the quark jets at the highest SPEAR energies −their ‘sphericity’ in momentum space −were already similar to my then-still-slim sphericity in ordinary space. This was the only time that I ever witnessed my experimental colleagues being pleased that there were no more major discoveries just before a conference. The 1975 Lepton-Photon Symposium was the greatest conference that I ever attended.
Fred, I wonder if at this point in the mid-1970s, given that SLAC had won these arguments, had proved itself, if its self-identity as a brash upstart had started to mature into something else.
Yes. It had, and I think it thought of itself at that time as the particle physics laboratory in the world, and a place of great discoveries which had trained and would train many future leaders in the field.
Let’s move into the later 1970s.
OK, let me finish the story of charm. After the 1975 conference different teams of people in many labs went to work to try and find charm‒‒particles with a charm quark and an up, down, or strange antiquark. In the spring and early summer of ’76, it was found. At first, a group at Berkeley, and then one at SLAC found both the neutral charm meson and the charged charm meson in the SPEAR data. I called my friend Haim Harari at the Weizmann Institute to give him a heads-up about the coming announcement. When I called, his daughter answered. “Can I talk to your dad?” “No, we have a visitor, John Iliopoulos, and they're out playing soccer. They'll be back later.” She asked me if I wanted to leave a message, and I said, “Just tell them they found it.” John Iliopoulos had won his bet.
“They found it.”
For me, intertwined with all of this history, is the growth of our family and our life at Stanford. In addition to our daughter, Michelle, Barbara and I had three sons, David, Jonathan, and Daniel. Like Barbara and I, all our children had red hair, and the family was called the Red Army by some of our friends. I also — in ’80, ’81, got much more involved in the Jewish community because our synagogue in Redwood City burned down. I became president and led the building committee —
— to rebuild the synagogue. I was also involved in many Jewish community activities on and off campus, including chair of the Stanford Hillel board and of the Stanford Jewish Federation campaign. As head of the Jewish Cultural Arts Council, the most moving and singular event was Elie Wiesel talking at Yom HaShoah and being a guest in our house.
Wow. Now, Fred, as we move into the 1980s, I want to ask you — how and when did you get involved in the leadership of the high-energy physics field, culminating in your decision or you being asked to chair the APS Division of Particles and Fields (DPF)in the late 1980s? How did this develop?
I just turned the page of my notes and that’s exactly the next topic.
We're literally on the same page!
Right, we're on the same page. In the late ‘70s and early ‘80s, I worked especially with my graduate student, Mark Wise, applying the now-known theory of strong interactions in order to study corrections to all the weak K meson decays and other processes, especially those involving CP violation. The papers with Mark, one is my most highly cited paper, are some of the most important that I’ve written, along with my work with Elliott Bloom on Bloom-Gilman duality. More generally, in the 1980s I was working on CP violation and heavy quark physics. My work with Mark Wise helped inspire competing experiments, KTEV at Fermilab, led by Bruce Winstein −who became a close friend, and NA48 at CERN to measure the CP violation from the decay amplitudes of neutral K mesons. These incredibly difficult experiments were refined over two decades and converged on a value consistent with the standard model. In the mid-80s, Kleinknecht, Renk, and I became the authors of the section on CP violation of the biennial Review of Particle Properties. Panofsky pulled me into helping make the science case for the electron-positron collider in Beijing and my first trips to China. At the same time, I was a proponent of building experiments at both proton and electron-positron machines to measure the decays of B mesons (containing a bottom quark) where many decay modes were likely to have large CP violating effects. The culmination of this period was presenting to a DOE review at the end of the 1980s the physics case from my work with Dib, Dunietz, and Nir for building an electron-positron collider−a ‘B factory’−at SLAC that would provide precise, redundant measurements of CP violation as predicted from the standard model.
In this same timeframe, I was elected to be the vice-chair of the DPF for the year 1988. As vice-chair, I presided over the Snowmass ’88 Workshop on US High Energy Physics in the 1990s which was centered on the Superconducting Super Collider (SSC). But my involvement with the SSC starts years before, to late ’83 when Jim Cronin invited me — it was the first time I had thought much about the supercollider — to give a theoretical summary talk at a workshop in Chicago in early 1984 on a proton-antiproton option for the collider. Later that year, I was the co-leader of the working group on electroweak interactions and Higgs bosons at the Snowmass Summer Workshop. Then at Snowmass ’86, I co-led a group on B physics and CP violation at the Supercollider, plus continued the work on finding the Higgs boson. Late in the 1980s, I was deeply engaged in workshops to delineate physics at the SSC, aside from leading Snowmass ’88.
In the fall of 1989, I was in Dallas, Texas, for a meeting of the High Energy Physics Advisory Panel (HEPAP), because as chair of the DPF I was ex-officio on HEPAP. At the same time, the SSC Board of Overseers was meeting in the same hotel in Dallas. My friend and colleague from his time at SLAC, Roy Schwitters, was already the Director of the SSC Project. During a break in the HEPAP meeting, I encountered Roy Schwitters, who said he had something important that he wanted to talk to me about.”
He told me that the SSC Board of Overseers had discussed me as head of the Physics Research Division of the supercollider project. Which was dumbfounding.
This was a pile of bricks for you? You had no idea this was coming?
No idea. Usually such a job is done by an experimentalist, especially someone who has built detectors and managed big experiments. It was an honor to be asked, especially as a theorist. A set of hard questions soon sunk in and I did a lot of soul-searching. I understood that this was going to be a huge change in my life in every way. But the challenge also became intriguing and even exciting with the opportunity of working with a whole new set of people, learning new skills, and most of all the chance to change physics. In the end, I decided to take it on. And I knew, even at that time — that the project might fail. This was taking a big risk, much bigger than going to SLAC as a postdoc rather than taking a faculty job. In addition to that, I would eventually have to give up my tenure at Stanford. Since our two oldest children would be off to college, it wasn’t quite as big a transition for the family as it might otherwise have been.
So Fred, for the next interview session, we're going to pick up on this point. And let’s put down in our notes the first question that I'll ask you for round two is going to be — and we'll discuss it then, but I'm intrigued — the autopsy of the SSC is a remarkable history in and of itself. And so I'm intrigued by the idea that you saw risk in this from the beginning. So let’s just make a mental note of that. The last thing I want to talk to you for our session today is the 1988 Snowmass Conference, OK?
The question there is, what was your involvement with the Snowmass Conference? Why was it so important? And fast forwarding a little bit, in what ways was it similar and in what ways was it different as a result of it becoming linked to the P5 process that happened in the 2000s? That will be my last question for today, and then we'll pick up for round two.
I was chair of HEPAP when P5 was created and an ex-officio member of the first P5. I wouldn't tie P5 so directly to the SSC experience.
No, no, no, right. It’s its own question. It’s its own thing. I'm talking about where your involvement in the 1988 Snowmass Conference was, with regard to your role in HEP. And then the follow-on to that is, how did it change as a result of the linkage to P5?
OK. As we discussed, I was elected to be the vice chair of the DPF, which implied becoming the chair of the DPF the following year Over the years before that, I had become increasingly convinced that the SSC was the next giant step in high-energy physics world-wide. The SSC Laboratory would have also been the natural place for a linear collider or other future machines. Incidentally, in 1989 Burt Richter, made me the chair of a committee to consider options for the future of SLAC. Sadly, most of those involved on the Committee are now gone —
In the medium term, there were three main alternatives for SLAC: a tau-charm factory, a B factory, or participation in a major way in the SSC. In the longer term, the ambition was to build a linear collider that would complement the SSC. It’s a long, interesting story in itself, with the eventual outcome for SLAC being the choice of a B factory, even though Burt started out terming it “boutique physics.” In the 1980s more generally, from being on program advisory committees all over the country, Snowmass meetings, etc., I think that I became recognized in the community as someone interested in the future of the whole field, not just a narrow advocate for their home institution or married to electrons or protons. And then it was natural as part of being the vice-chair of the DPF and taking on organizing Snowmass ’88 to represent all of particle physics. It was very delicate, because it was at a time where clearly most of the community was aiming to be involved with the SSC, but definitely not everybody. That was one tension. The opposite tension was voiced by Maury Tigner, then-head of the SSC Central Design Group, and worried that if you talked about any other physics besides SSC, people might get the idea that we were not fully behind the SSC. We're the only field I know of where the science advisor to the president called us “a bunch of greedy bastards.”
[laugh] Which advisor was this?
I hesitate to say! [laugh]
OK. [laugh] We can do the math.
[laugh] In this general era, with the SSC plus the ongoing program, maybe more than one thought that.
In short, I just took Snowmass on naturally and it became my meeting to organize and to make it a success. However, in ’89, when I was chair of the DPF and got the job offer to actually go to the SSC, it was totally unexpected. I thought somebody else was going to do this great project. Not me.
So Fred, that’s a great place — I'm going to hit end of the recording here.