Howard Georgi

Zierler:

Okay. This is David Zierler, Oral Historian for the American Institute of Physics. It is June 26th, 2020. It is my great pleasure to be here with Professor Howard Georgi. Howard, thank you so much for being with me today.

Georgi:

You're welcome. I'm looking forward to it.

Zierler:

To start, would you please tell me your title and institutional affiliation?

Georgi:

I am the Mallinckrodt Professor of Physics in the Physics Department at Harvard University.

Zierler:

Let's take it right back to the beginning. Tell me a little bit about your family. Let's start with your parents. Where are your parents from?

Georgi:

Interesting. Okay, my mother is a Southern Californian, and a Stanford graduate. My dad was born in Chickasha, Oklahoma, and what he told the family was that he attended the University of Texas for six years and didn't graduate. He was a bomber pilot in World War II. I was born shortly after the people returned after the end of the war.

Zierler:

Did your father ever talk about his military experience?

Georgi:

Oh, yes. We don't know how much of it was true, but he was a very colorful character, and was shot down in Burma, and walked out through the jungle. As I say, to this day, we're not sure how many of the stories were completely accurate, but he was a wonderful storyteller, and a great salesman, which is what he did. He worked for Johnson & Johnson for many years. My childhood was interesting because he was working his way up to the office in the New York area, so we moved every year or so. I live in El Paso, Texas for a year before school, and having been born in southern California. I was born in San Bernardino, and then I went to kindergarten in Denver, before it was Denver. I went to first grade in Dallas, long before it was Dallas. Then we moved back to southern California for a while, and I lived in Pasadena and Covina, and then moved to Northern New Jersey as he finally got to the latter stages of his J&J career. I went to high school in the Morristown area of northern New Jersey, which at the time was just a gorgeous area with the old estates just starting to break up before the corporate headquarters moved out there.

Zierler:

Where did your parents meet, Howard?

Georgi:

That is a very good question, and I don't know the answer. As I say, my father was quite a dashing character.

Zierler:

Did your mom work outside the house?

Georgi:

She did not. I, in fact, learned a lot from my mom. She was quite attentive about trying to teach the kids, and me in particular, since I was the first one.

Zierler:

Looking back, was it disruptive for your education to move around so frequently?

Georgi:

I don't think so. Fairly early on, I was sort of self-educated. School was fine, and it was nice to have some validation of what I was doing, but mostly, I was educating myself.

Zierler:

Were you interested in chemistry sets, and nature, and things like that?

Georgi:

Absolutely. Chemistry sets, and back in those days, electronics was actually fun. There were vacuum tubes, and you could take things apart. Yes, I was extremely interested in all of that. Not very good at it, because I was always a theorist, and mostly was interested in the math, but it was really fun to see how things worked -- it's not fair to say I was only interested in the math, because I was always interested in the connection between the math and what was actually happening.

Zierler:

As a child, were there certain events that got you interested in physics, even before you knew it was physics, like Sputnik, or the Space Race, or things like that?

Georgi:

Obviously, the intense concentration on science in those days in the media must have played a role, but what I remember is a few books. There was My Friend the Atom, and there was a wonderful, wonderful chemistry book, which I can't find, which was basically a book about the periodic table, brilliantly done where the elements were described in terms of their position in the periodic table, and how that translated into their actual properties, and the industrial uses of the things. It was a great book. I'm sad that I can't even figure out what the title was or who the author was. That book, I think, really cemented my interest in the physical sciences way back. That was second grade.

Zierler:

You said your dad had settled down in his career so that you were able to attend one high school in New Jersey.

Georgi:

Yes, after some time in the junior high program in a little local school in Peapack-Gladstone, New Jersey, which was very amusing, but anyway, I went to Pingry, which at the time was in Elizabeth, New Jersey. It was a country day school, so I had a long train ride and car ride to school. It was a very good school. One of my good friends, who is a Harvard colleague, was the star student in my class. He's a man named Ken Wachter, who's now a famous demographer at Berkeley. I never had to worry about being in competition for grades because Ken was clearly the star. So, I could just have fun with my science and math and not worry about it.

Zierler:

This was a private school, or a public school?

Georgi:

This was a private country day school.

Zierler:

Did it have a religious affiliation?

Georgi:

Originally, yes. We sang a hymn every morning, but it wasn't really a chapel, and there was no particular religious affiliation.

Zierler:

Were the science and math departments strong in your high school?

Georgi:

They were. By that time, I knew a whole lot more math and science that the teachers, but still, they were very good. It was particularly good for me, because they sort of let me do my own thing.

Zierler:

How did you get so far ahead? Were you reading textbooks on your own? How did that work?

Georgi:

Yeah, I was reading textbooks on my own, watching TV programs. There was a thing at the time called Continental Classroom, which was a TV program that taught chemistry and physics. It was harder then. I learned calculus, originally, reading the Encyclopedia Britannica, which is maybe not the ideal way to do that, but it worked.

Zierler:

If not your parents, I wonder if there were grandparents or aunts or uncles that were really strong in math and science that might have had either a social, or even a genetic influence on your abilities.

Georgi:

Perhaps genetic. Certainly not social. I was definitely an oddball in the family from the beginning. They had no idea what I was doing or where it came from. My fraternal grandmother was very sharp and was a bridge player. Perhaps the one connection there was that I learned to play bridge at a very early age and played bridge with my grandmother. We went on a cruise when I was in the second or third grade, and we would play bridge with the adults. By that time, I had digested Goren's books. So, that was fun. My family was interesting, and had a somewhat turbulent history in many ways, and I could always retreat into my science and math. That was extremely helpful.

Zierler:

What schools did you apply to when you were thinking about college?

Georgi:

Harvard, MIT, and I guess I applied to Princeton. I wasn't really very interested in it. I had always assumed I would go to MIT or Caltech, because I was a nerd and that's what nerds did.

Zierler:

Were you aware of somebody like Feynman, even as a high school student?

Georgi:

Yes, although not as much as I am now. Some high school counselor suggested that I visit Harvard when I went to Boston to visit MIT, and I did, and I loved it. So, I was basically not interested in any place else, and was very pleased to get in.

Zierler:

I wonder if part of the factor was even though you knew you wanted to focus on math and science, a place like Harvard might offer a broader general education in the humanities as well, that you might not be able to get at a place like MIT or Caltech.

Georgi:

Yeah, in some sense, that was it, but mostly the kids were much more interesting. What I recommend to students looking at colleges is that they absolutely must spend a couple of days with the students during term time and see what the college life is like. That's what attracted me to Harvard. I was fortunate to come from a school where there were a few students that went to Harvard, and so I had a group that I could stay with in the dorms, and in the houses. That was great.

Zierler:

Was the plan to do a double major in chemistry and physics from the beginning?

Georgi:

This is an interesting story. Chemistry and Physics is not a double major at Harvard. It's a special concentration that combines the two. So, what happened was that I came in not knowing whether I was going to do physics, or chemistry, or math. I loved all of them.

Zierler:

Did you feel stronger in any one of them than the others?

Georgi:

No, not particularly. At the time, there was an absolutely fabulous series of chemistry courses. You had to apply to get into it, and it was a four-semester series of classes which satisfied all of the chemistry requirements for the chemistry and physics concentration. That wasn't what I cared about. I was just interested in the chemistry. In those four semesters, I had three teachers who would eventually win the Nobel Prize, and another who was the father of a Nobel Prize winner. I had E. Bright Wilson for physical chemistry, Bill Lipscomb, , Frank Westheimer (actually I guess he did not get the Nobel Prize, but he got every other possible award), and E.J. Corey. It was an amazing class, and a good group of people.

Zierler:

Were the professors for the special program co-located in chemistry and physics? There wasn't a dedicated department of chemistry and physics?

Georgi:

Not at all. They were all chemists.

Zierler:

So, you were getting your physics from chemistry professors.

Georgi:

Exactly. My first brush with quantum mechanics was from E. Bright Wilson. What I learned was that while I love chemistry, the part of the chemistry that I really loved the most was the physics. In the meantime, I had stupidly skipped the advanced freshman physics class, because I had done it. But it's stupid to do that, because the teacher was Ed Purcell, and it was a fabulous class. I enrolled in the third semester class, which was a modern physics class at the time, taught by Ken Bainbridge, a famous, aging experimenter, who read from a modern physics textbook. That didn't excite me very much. Fortunately, we had a great T.A. who noticed that I was bored and handed me Feynman's book, Theory of Fundamental Processes, and said, "Go away. Read this. Don't pay any attention to the course." So, that's what I did, and I was learning enough quantum mechanics in chemistry that I could understand what Feynman was talking about. That funny combination of events was what really turned me on.

Zierler:

I'm curious the faculty politics behind chemistry professors teaching physics. First of all, did they want to teach physics, and did the physics professors find it acceptable that chemistry professors were teaching their discipline? How did it work?

Georgi:

Well, sure. The courses were physical chemistry and thermodynamics and statistical mechanics, which are critical to both areas. So, from the physics point of view, there was no problem with that at all. From the chemistry point of view, it was a problem, and the course didn't last very long. This sequence of courses was eventually discontinued. I wasn't in the department, but I suspect that it was because most of the people that went through it ended up excited about the physics, and it wasn't producing enough chemistry concentrators.

Zierler:

At what point did you realize that it was the physics that you really wanted to concentrate on? How did that happen for you?

Georgi:

I think, gradually, over the course of that first semester. Certainly, by the end of my first semester, I sort of knew what I was doing, and because of the Feynman book, I was starting to fall in love with particle theory.

Zierler:

What was it about Feynman's work that was captivating for you?

Georgi:

I don't know if you know this book. If not, you should take a look.

Zierler:

I know it well.

Georgi:

Okay. I think it was the chapter on K mesons and the notion that superposition had this absolutely unbelievable effect and was real. That's kind of mind blowing when you first recognize it.

Zierler:

Did you realize at the time that you were living through a golden age in particle physics?

Georgi:

Sort of. In some sense I've been redoing the quantum mechanical treatment of angular momentum throughout my career. I realized that was something really special and I recognized that Gell-Mann had done something interesting that was related to this. I didn't know exactly what, initially, but shortly thereafter I figured out that what I should do is to take any class that Sidney Coleman gives, whatever it is. I had a wonderful group theory class from Sidney.

Zierler:

Was Coleman the luminary in your eyes in terms of the physics department, the person you gravitated towards the most?

Georgi:

This is a very complicated situation. When I arrived in 1964, the titular head of the theory group was Julian Schwinger, who got the Nobel Prize the following year, so that was pretty exciting. In fact, I did take Julian's relativistic quantum mechanics class in my third year, and that was source theory at the time. I was trying to learn quantum field theory, and I learned all the tricks, but without actually knowing the theory.

Zierler:

Was your sense that Schwinger was accessible to undergraduates? Could you talk to him?

Georgi:

He wasn't accessible to anybody. Certainly not his graduate students. No, no. He was an absolutely masterful lecturer. One student raised his hand in class once and Schwinger ignored him. Even more spectacular was that he clearly planned out the whole strategy of the blackboard, and he always ended right by the door of 256 in Jefferson Lab so that he could scoot out before any of the graduate students could get hold of him. I did actually communicate with him at one point. He had posed a question in class at one point, an integral that he had difficulty doing, and I did it. So, I think, I appear, not by name, but in one of his source theory books as the very conscientious student. That was a highlight of my college career, since he thanked me in class. My reaction to that was certainly unreasonable, because I thought maybe there's something there and I can contribute. So, I did spend some time the following summer trying to make sense of source theory, and eventually gave up, and decided that I would learn quantum field theory instead.

Zierler:

What was it about quantum field theory that you were more comfortable working in?

Georgi:

Well, the main thing was Sidney Coleman, I guess, . and that there were rules that I understood. Source theory, certainly at the time Schwinger was building it, was not something where you could write down a set of rules and the theory would follow. Quantum field theory was much more what we'd think of as a theory. It was clearly the right thing to do. Schwinger was not the leader of the theory group, but I didn't realize that initially. Perhaps one other amusing story from the time is that I also did figure out that in addition to Sidney, there was this interesting character, Shelly Glashow, in the department. I got up my courage and asked whether I could do a reading course with him in my last year.

Zierler:

What is a reading course?

Georgi:

A reading course is a course where you go in and the professor assigns reading, and you talk to the professor individually. It's an individual course rather than something that's prearranged. Shelly said yes, and fortunately, the deans wouldn't let me do it, because by that time I was concentrating a little too much on my physics classes. So, I took a course in abnormal psychology instead. That was, of course, very useful. You know, thank God, because I would not have been ready for Shelly at that point in my career.

Zierler:

You mentioned parenthetically that your identity as a theorist was cemented as a child, but you didn't truly know what that meant until you were in a proper physics program. As you're thinking ahead to graduate school, at the end of your Harvard time, did you know that it was theory that you wanted to focus on for sure?

Georgi:

Absolutely. It's a combination of several things. Partly, it's what you're good at. The mathematics and the connection of mathematics with physical science has just always made intuitive sense to me. That was really fun. I was good at it, and it was the fun part, and I was lousy at experiment. So, there wasn't really any question about this. I broke an NMR machine in the chemistry department early on. There weren't many of them back then.

Zierler:

And they said, "Don't come back."

Georgi:

That's right, exactly. So, it was clear from the beginning that I was headed to theory.

Zierler:

Did you have a senior thesis?

Georgi:

No. We didn't. I was actually never a senior. I graduated in three years for personal reasons. My wonderful wife of 51 years (who has been patient and supportive all the countless times I disappeared into what she and my kids referred to as “physics land”) was at the time a student at Vassar, and I was extremely tired of driving down to Poughkeepsie on weekends or having her drive up. I went to graduate school at Yale, literally, because it was much closer to Vassar than Harvard.

Zierler:

Oh, that's that question right there. To foreshadow a little bit, was the term "grand unified theory" a term that you could locate during your undergraduate years? Were people using that term specifically in terms of trying to find an all-encompassing theory for physics?

Georgi:

"Unified theory," yes, because Einstein made it famous, but "grand unified theory," no. We're not responsible for that crazy term. That was invented after SU(5), by others.

Zierler:

So, the term "grand unified theory" is externally applied and was not part of your world at all during your Harvard years.

Georgi:

Not at all. In fact, when I returned to Harvard and Shelly and I did start working together, what we were looking for was a theory that unified electricity and magnetism, because the SU(2) x U(1) model didn't. It was a partial unification, but not a complete unification. Shelly and I, recognized that a theory based on a simple group had lots of interesting features with our little SO(3) model. We were looking for a theory without specifically thinking about trying to incorporate the strong interactions. We started looking before we had any clue what the strong interactions looked like.

Zierler:

Did you have any physics relevant internships during the summers during your time at Harvard?

Georgi:

No, I taught tennis at a tennis camp, which was great. I'm still playing tennis.

Zierler:

Was the draft on your mind when you graduated early? Was that a consideration for you, what you had to do?

Georgi:

It wasn't what I had to do, but it was very much on my mind as it was. I was fortunate to have a minor medical problem which kept me out of it.

Zierler:

Did you get an official deferment, or you just knew you wouldn't be appropriate for service?

Georgi:

No, I didn't get a deferment. I just knew I would be inappropriate for service or hoped I would.

Zierler:

Besides the proximity to Vassar, what else attracted you to Yale?

Georgi:

Well, it was a good school. As you probably know, I worked for a student of Schwinger's, Charlie Sommerfeld.

Zierler:

What was Charlie doing during the time when you got there? What was his research?

Georgi:

He was thinking about the Thirring model, and scaling, and all of the things that we were all thinking about at the time, and trying to understand what Ken Wilson was doing, and what Sidney was doing with dilatation anomalies, and that sort of thing. He taught me about the Thirring model and the Sommerfeld model, which incidentally, I'm still thinking about. It's a fun toy. Again, I didn't work that closely with Charlie. There was actually a group of three students in our class who got together, and we educated one another. Itzhak Bars, and Sam Krinsky, and I had our little group. We went to seminars and talked to one another, and that was more the way I got educated. I could go to Charlie with questions about quantum field theory, which is what I was really trying to learn.

Zierler:

What kind of formal course requirements were there for theory physicists at Yale for the doctoral program?

Georgi:

That's a good question. There was a general exam, and I think there was not so much formal requirements for courses as a requirement that you take enough courses that you could pass your general exam. To be honest, I don't remember.

Zierler:

What was the process for you in developing a dissertation topic? Did Charlie essentially give you a problem to work on, or you more or less came up with something on your own?

Georgi:

It's a good question. He suggested that I think about this general area, and I got really interested in it. I still am. My first paper was actually with a post-doc, John Rawls, who was at Harvard at the time. The analogy between the Jackiw anomaly and the corresponding analogy in 1+1 dimensions. So, that was fun, and everything sort of developed from that.

Zierler:

On the experimentalist side, it's very easy to visualize the day-to-day of a graduate student. They're in the lab, they're working at the controls, they're refining the instrumentation. What is a day in the life of a theory graduate student look like? What are you doing on a daily basis that's moving the ball forward for your career?

Georgi:

You're calculating stuff. Theory is interesting because you spend almost all of your time going down blind alleys. You have some idea, or you're trying to understand some paper, so you're redoing the calculations in your own way. Then, eventually, you get stuck, or it doesn't work, but what keeps you going is that the manipulations themselves, just going from one step to the next and seeing how the math simplifies or works out is marvelous fun. That's what keeps you going. At least, that's what kept me going, and I still feel that way. When this is over and when I'm done working on my class for next semester, I'm going to go right back to playing with generalizations of one of these two-dimensional models, which is what I'm playing with at the moment.

Zierler:

During your time at Yale, were you paying attention to things that were going on in accelerator physics at places like SLAC? Was that compelling to you?

Georgi:

I didn't understand it well enough for it to be compelling, but I certainly was paying attention because I went to seminars. The nice thing about Yale was that it was a small, very, very friendly department, and not terribly hierarchical, at least in particle theory. The theory students went to all the seminars and were incorporated into the parties of the group, and what not. That was terrific. I remember the times when Sidney Coleman came and gave us talks, and some of the others. So, yes. We knew that there was something going on. I certainly didn't know exactly what was going on until I got back to Harvard in 1971, and things really started to happen.

Zierler:

Broader social question: your time in New Haven corresponded with major upheaval socially and politically. What is your perspective on all that was going on? Did you consider yourself a political kind of person? Did you involve yourself in some of those bigger issues, or did you try to stay away from all of that?

Georgi:

I didn't try to stay away at Harvard. I did go down to Montgomery to march, and I got to listen to Martin Luther King. That was interesting, but it was more trying to figure out what this was all about. I graduated from Harvard the year before Harvard was more or less shut down. My three roommates were still there and kept me apprised of what was going on in the meetings in the football stadium, and the fact that less education was going on than usual. Not much of that happened at Yale. Yale President Kingman Brewster was a master at coopting the students' passions. It stayed pretty calm, even though there were, of course, events that we were a little bit worried about. We were pretty isolated from this, because as I say, Yale was —

Zierler:

Cloistered?

Georgi:

Cloistered, and very quiet compared to other places. My second year, I actually was a freshman counselor in one of the Yale colleges on the old campus. That was wonderful fun. I've got to say, one of our best friends is a fellow that my wife and I got to know in his freshman year at Yale. So, I was pretty focused on the internal goings on at Yale. Then, when we got married, we moved into an apartment in the Black area across the tracks on Howard Ave, between the firehouse, the police station, and the hospital, down by Yale New Haven. So, we got to know the Black kids in the neighborhood, and they came and played with our dog. It wasn't a huge issue.

Zierler:

To foreshadow to very current events with shutdowns, STEM, and ongoing problems of representation and diversity in the physics community, I wonder if back in the late 1960s, early 1970s, when you were thinking about civil rights as a national issue, if you recognized that these issues did not stop at the door of science, and physics in particular.

Georgi:

Nowhere near as much as I should have. I was an oblivious nerd for a long time, not just about race, but about gender. It's astonishing how long it took me to figure out there was a real problem there.

Zierler:

Certainly, you're not alone in that. That's part of the issue.

Georgi:

Exactly. But I had some unique experiences that should have alerted me. I had several of the greatest women theorists as students. I had Helen Quinn as a fellow faculty member. When I arrived back at Harvard as a post-doc, Helen was there as a visitor because her husband Dan was working in Sam Ting's group at MIT, so Sidney and Shelly recognized a gift when she showed up at the department and said, "Hey, can I have a desk?" They said, "Ahh, yes." Helen was great, and we had a lot of discussions about this, but it just somehow didn't penetrate. It was obviously an issue. Helen, coming from Australia, recognized that we had a specific problem in this country, and it was worse here than in other places. So, we had a lot of discussions of this. It was an interesting time. Later, in my final days as a junior faculty member, a number of the junior faculty sat down and said, "Hey, this is really serious. We have to do something about it." That helped, but I didn't really get it until I became chair, and I discovered that we were torturing our women students. That turned me into a feminist.

Zierler:

Serving as chair gives you a whole different perspective.

Georgi:

Oh, my God. You never recover.

Zierler:

Howard, how did you develop your dissertation topic? What did you ultimately work on?

Georgi:

It's not a very outstanding dissertation. I worked on the Thirring model, and scaling in the Thirring model, and had some right ideas and some wrong ideas. Just at the time when the importance of scaling and anomalous dimensions and all of that was developing, and anomalies — that's what the thesis should have been about. As I say, it's not a very interesting thesis, although it's about very interesting subjects, and I continue to think about them now.

Zierler:

What do you see as your primary contributions with your dissertation?

Georgi:

That's an interesting question. At the time, I think people were trying to understand things like the Sugawara model, which was a conjecture about building the energy momentum tenser as a product of currents. One of the things that my thesis was about was how that worked. I don't think of it as one of my big contributions.

Zierler:

Who was on your committee?

Georgi:

That's an interesting question. Probably Feza Gürsey, and Charlie, and who else? Maybe Sam McDowell. I don't remember.

Zierler:

Did you all have an outside reader?

Georgi:

I don't think so. I don't remember.

Zierler:

Was the opportunity at Harvard pretty much cemented before or after you defended?

Georgi:

Before, I think. I think Sidney Coleman had offered me a post-doctoral position. I was tremendously excited when I got the phone call from Sidney. I really loved Harvard, and I really wanted to go back.

Zierler:

Had you maintained pretty good contact with Sidney during your time in New Haven?

Georgi:

I wouldn't say that, but I attended his seminars, so we knew each other. I discovered later that I was Harvard’s seventh choice for a post-doctoral position. It was my good friend, Alvaro De Rújula, who found that out. At the time, it wasn't clear that Harvard was the right place to go, because it had been sort of a depressed time at Harvard. In that curious four-year period between when Weinberg's paper came out, and when people actually understand what it was about —

Zierler:

For the benefit of our readers, can you explain what Weinberg's paper was?

Georgi:

Oh, my goodness. Yes. In 1967, Steve Weinberg wrote a little paper called A Theory of Leptons, which was the first paper to put together the idea of a W and Z boson being part of an SU(2) group, with a U(1), with the Higgs mechanism. Ultimately, that turned out to be the right combination of things, missing still the strong interactions, but being dead on in the theory of the weak and electromagnetic interactions. The theory of the weak interactions was something we all understood at some level because Feynman and Gell-Mann had figured it out, and it worked beautifully, except that the theory didn't make sense. So, you did the calculations in a first approximation, and it gave you everything that you wanted to describe experiment, and then when you tried to refine the theory and go to the next level of approximation, the theory blew up. It was not renormalizable.

Zierler:

Why not? Why did it blow up?

Georgi:

The way we would say it now is that the W and the Z bosons, these massive bosons are not like the photon. The photon has only two degrees of freedom, an electromagnetic wave is polarized only transversely. So, it waves perpendicular to the direction of its motion. A massive particle can't do that because you can bring it to rest, and then there's no direction of its motion anymore. So, if it has spin, the spin has to be able to point in all three directions in space. That means that there's something more to the W and the Z than just the part that comes from the symmetry, which is the part that looks like a photon. That extra part was the source of all of the problems, because its interactions grow as the energy increases. Eventually, the interactions become so strong that, depending upon your point of view, you either can't say anything about them, or if you calculate naively, you get probabilities greater than one, and all kinds of bad things. So, we knew that the simplest version of the theory of weak interactions had this problem, and that it persisted even if you made the theory a little more sophisticated by having a massive W and Z mediating the weak interactions. That's something Shelly had done long before.

Zierler:

Weinberg's paper had an enormous impact immediately, but I'm curious, from your perspective, if you can talk about some of the long-range implications in terms of the questions that it raised, and all of the work that would be required as a result of what Weinberg had found.

Georgi:

First of all, let me disagree with you. In those days, this was before the archives, and we got papers in our mailbox and Physical Review Letters, which is where Weinberg's paper appeared. I recognized that it was a really interesting subject when I pulled out my Phys Rev Letters and saw this paper. I read through it, and I said, "Oh, it doesn’t look renormalizable to me," and I put it aside. That's what everybody else did also, including Steve. Nobody understood this paper for four years, and that's why Harvard was such a confusing and slightly depressed place.

Zierler:

But it wasn't forgotten. Just because it wasn't understood doesn't mean it was set to the bottom of the pile.

Georgi:

It was set aside. It was on the back burner. People didn't understand it well enough to do anything with it. It was maybe a partial motivation for the work that Shelly and company did on the GIM mechanism, but I don't think so. That was just as much from basic ideas about the weak interactions and Shelly's old theories. I wasn't at Harvard, but my friend, Tony Zee, who was a graduate student at Harvard at the same time that I was a graduate student at Yale, said that people were depressed because they just didn't understand what to do. That's why I believe the post-docs went elsewhere. It looked like the interesting things were going on at Seattle, Washington, with Lowell Brown, or Caltech, or someplace else, and that quantum field theory wasn't working. The recognition that this quantum field theory was really the answer was due to Gerard 't Hooft. That happened at the end of 1970, '71.

Zierler:

So, what happens then, at '70, '71?

Georgi:

Well, 't Hooft understood Weinberg’s paper. He understood many other things. Let me first back up and say how fortunate I was to finish my PhD and go off as a post-doc at exactly the right time, when 't Hooft had opened up an entirely new world. What he, and to some extent, his advisor, Tini Veltman, did was to understand first of all how to calculate more effectively in these theories where symmetry was the basic underlying part of the dynamics — non-abelian gauge theories. But then he understood why the Weinberg model of leptons was renormalizable. At some level, this is extraordinarily simple. He recognized that there are different ways of looking at the model. In one way of looking at it, it looks like a perfectly nice, renormalizable field theory where you can calculate corrections, and they come out perfectly finite. But the theory in this form looks like it has extra states with negative probabilities. In another way of looking at it, it looks like they're just these massive W and Z, and you get the weak interactions but it doesn’t look renormalizable. I should say that the way of looking at it in which you can calculate, it's not obvious that you don't get negative probabilities. It's not obvious that the theory is unitary. But in the other way of looking at it, it's unitary and it's not obvious that it's renormalizable. What 't Hooft said was, "Okay, I can show that these two ways of looking at the theory are equivalent. Therefore, it must be both renormalizable and unitary, and therefore makes sense." That was right. This was making use of some beautiful mathematics that had been done by Ludvig Faddeev, and others, but 't Hooft and Veltman really put it all together, and at the same time they developed this crazy, beautiful, new way of calculating things by changing the number of dimensions to something close to four, but not exactly equal to four. This collection of ideas was just a cataclysmic, monumental contribution. It all of a sudden opened up a completely new set of things to play with. Nothing could make a theorist happier than to have a completely new set of toys, and that's what we had in '71.

Zierler:

You said, of course, that this was terrifically good timing for you, personally, to be there at the right time and the right place. Did you see this as a departure from your dissertation work, or a continuation more generally on what you had been working on?

Georgi:

It was a complete departure. It was only much later that I recognized that there was some connection.

Zierler:

What was the connection that you saw later on?

Georgi:

The connection is scaling, and in particular, conformal field theory. What's funny about the Thirring model is something that I have since gotten quite interested in. All of the energy and the momentum that we've ever seen in the world is bundled into these things called particles that have definite mass. The mass may be zero, but it's definite. If you know what the particle is, and you know its momentum, you can calculate its energy. But there are quantum field theories, conformal theories, like the Thirring model that I was studying as a student, that don't have this property. The energy and the momenta are disconnected, and spread over all possible values in a curious, scale-invariant way. That's fascinating. It shows up, we now know, in many ways in different field theories. We don't know whether it has anything to do with the world, but I nevertheless find it fascinating. To get back to the story of what was going on, no, when I arrived at Harvard, I initially tried to continue along the lines that I was going, but then Shelly came, corralled me one day and said, "Hey, come on. Get into the model building game. This is a time when we should try to figure out what's going on. Weinberg's model is inadequate. Let's do something better." Fortunately, I immediately switched completely, and had to re-tool to try to deal with Shelly, which is wonderful fun.

Zierler:

What do you think Shelly saw in you? You're not yet a colleague. You're not a peer. What do you think he saw in you that he recognized you were up to the task for taking on this enormous project of improving upon what Steve had done?

Georgi:

Well, I think I was sufficiently self-confident that I could actually talk to him. When you deal with Shelly, you have to ignore certain things, like when he tells you to get out of his office, or that you're an imbecile. I was able to do that, and our skills were complementary in many ways, but similar enough that we loved the same kinds of manipulations. Early on in a discussion with Sidney Coleman, he described the fact that he and Shelly had twin minds. I think what he meant by that was that though they had completely different talents, they came at problems from the same point of view. Shelly was much more interested in the phenomenology, but coming upon a problem, their first idea was what are the symmetries? How are the symmetries organized, how are the symmetries broken? And that is my approach as well.

Zierler:

Why is symmetries the fundamental question?

Georgi:

I don't know that it is.

Zierler:

I should say, why is it the starting point?

Georgi:

It is one way of approaching a quantum mechanical problem in particular. Let me back up and say, when I say "symmetry" here, I'm particularly talking about a symmetry that normal people don't even know about. It's an internal symmetry. A symmetry not like the symmetry that we immediately think of, like the symmetry of a snowflake, which describes some change in the geometrical structure of an object. There are geometrical symmetries that we call space time symmetries, like rotation invariance, which we all knew about. But the original internal symmetry is something called isospin, which was a mathematical description of the sense in which protons and neutrons are alike. That was extremely useful. The tools already existed in quantum mechanics because formally it looks very much like rotation symmetry, but here you're rotating not in a real space, but in a purely quantum mechanical space. So, it's a nutty thing to do, but enormously useful in quantum mechanics. I don't know if I can say this in a way that will be understandable to anyone who is not a quantum mechanic, but what quantum mechanics do is to try to find quantities that have definite values. Mathematically, that means that they correspond to operators that commute with one another, where the order of the operators doesn't matter, because the operators in quantum mechanics, in some sense, represent measurement. It's not a very good measurement if you do one measurement and then another measurement, but then you get a different answer if you do the measurements in the opposite order. So, what quantum mechanics do is they try to find a set of operators that commute with one another so that you can do those measurements in either order and get the same answers and specify what's going on in terms of the results of those measurements. That doesn't work for something like angular momentum, because for rotations themselves, just the geometrical rotations, the order matters. It matters whether you rotate a book first around the X axis, and then around the Y axis, or the other way around. You get a different final state. Symmetry in quantum mechanics is particularly important because it allows us to deal with operators that don't commute with one another, but that fail to commute in this beautiful, simple way, determined by the symmetry. That was tremendously important in nuclear physics when people understood about isospin, and that gradually got translated into isospin in particle physics, and then Gell-Mann and others recognized that they could extend it to include the strange particles and enlarge the symmetry. Symmetries have been enlarging ever since. Why it is that that same symmetry turns out to be relevant to the dynamics of the strong interactions is one of the great mysteries, or accidents, or something, of particle physics.

Zierler:

An ongoing mystery, as well.

Georgi:

Absolutely, an ongoing mystery. It's completely crazy. The string theorists think they know the answer, but who knows. Maybe they do. To those of us who are just using them and playing with the symmetries, it still looks mysterious that Gell-Mann's SU(3) and the color SU(3) are based on the same structure. That's just nutty.

Zierler:

At what point in your collaboration with Shelly did you land on SU(5)? When did you realize that you had this SU(5) that you were dealing with?

Georgi:

Oh, goodness. That's a long story. The first thing we did was a trivial but somewhat influential little paper on SO(3), which was a version of Weinberg's model of leptons. A wrong version, but we didn't realize it at the time. Fortunately, there was some data that turned out to be wrong. There was some data that suggested that the Z that Weinberg, and earlier Glashow, had predicted didn't actually exist. The neutral currents that it would need to mediate didn't actually exist. So, we set about to construct a theory that didn't have such a thing. That was easy, because Shelly had thought about it long ago when he was thinking about SU(2) x U(1), and it was just a matter of updating what Shelly had done to include the Higgs mechanism in the appropriate way. So, that was one of the easiest papers ever to write. But we recognized that there was something important about it, or several things important about it. The most spectacular one was that electric charge was quantized. One of the amazing facts about the world is that we don't see any fractional electric charges. We now say that we see one third integral electric charges, but we don't see an electric charge of Pi, or the square root of two times the charge of the electron. That quantization is critical to the way the world works, and it came naturally out of this theory. Of course, the addendum to that is hilarious, because Dirac had a different explanation of the quantization of electric charge having to do with the existence of magnetic monopoles. He showed that in a quantum mechanical theory, if a magnetic monopole exists anywhere in the universe, then electric charge is necessarily quantized. 't Hooft and Polyakov realized that in this trivial little theory of mine and Shelly's, which predicted quantization of charge for a different reason, the monopoles were there as solitons. So, that's a beautiful story of how theory works in complicated ways. Anyway, soon the neutral currents were discovered, so we had to give up on SO(3). We begin to nail down what the standard model actually looked like. We spent a lot of time exploring ways of trying to unify SU(2) x U(1) without SU(3), without the strong interactions. Frankly, at that point, we still were not at all certain what the strong interactions looked like.

Zierler:

What's standing in between you and understanding what those strong interactions look like?

Georgi:

We had no idea how they worked. This was initially before asymptotic freedom. One key idea was asymptotic freedom, which didn't exist at the time.

Zierler:

Were you aware of what David Gross and Wilczek were doing at the same time?

Georgi:

No. I was aware of what various other model builders were doing, and I knew what Sidney Coleman, and Eric Weinberg, and David Politzer were doing. One of the really important papers from the period was a paper by Sidney, Eric, and David called Radiative Corrections as the Source of Spontaneous Symmetry Breaking, or something like that. It's a paper about a version of Weinberg's model of leptons, but where the Higgs mechanism is not forced on you but generated through corrections to the lowest approximation to the theory. The paper was not very interesting, or rather the subject was not very interesting, but the paper was brilliant. This was the place where Sidney and Eric explained to the rest of us that in a renormalizable theory, what you think is a dimensionless parameter is actually a dimensional parameter in disguise. This is dimensional transmutation, which Sidney wanted to call dimensional transvestism, but never mind. They settled dimensional transmutation, and that's an enormously important idea. The paper was also enormously important because it really taught people a lot of mathematical tools for dealing with these quantum field theories. Sidney, Eric, and David were all working on this class of ideas, and they divided it up so that David wasn't on that paper. The paper was just Coleman and Weinberg, but he was very much working on it. They divided things up so that Eric was on that paper and David would continue working on finding the beta function in QCD. That turned out to be rather important since he discovered asymptotic freedom.

Zierler:

Were you working on the SO(10) model at the same time? Was this a separate project that was happening concurrently?

Georgi:

I'll get there. We're still a long way from SU(5). So, Shelly and I were all over the place. We just learned lots of group theory in order to try to find unified theories, and nothing worked. Meanwhile, asymptotic freedom was discovered. David and I were working on applications of this, and Tom Appelquist, and we realized that it was essentially right. But we still had the wrong — at least, I still had the wrong idea that one had to break the SU(3) gauge symmetry in order to give mass to the gluons, because we didn't see any massless particles. The key was was when some number of people, and I don't know who's really responsible for this, ultimately, recognized that you don’t have to break the SU(3) symmetry of the strong interactions. Things confine and the particle masses get generated that way, and this is an instantiation of dimensional transmutation. Then, the light dawned, finally. I think Shelly and I learned about this from Steve Weinberg, but it was an idea that was very much in the minds of a number of people at the time. Then, basically, things happened in one day. Shelly and I spent the rest of the day saying, "Okay, maybe the strong interactions are not strong because the coupling constant is big, but just because of confinement." That's wrong. We didn't have the right idea, but it allowed us to say, "Well, okay. Why don't we try to unify color SU(3) along with SU(2) and U(1)?" So, we tried that for a while, and nothing happened, and then I went home for the night. That evening, I discovered first the SO(10) theory, and then the SU(5) theory. The reason that it went that way is that the group theory of the SO(10) theory, once you learn about spinnor representations of the orthogonal groups, you know exactly where to put the quarks, and the leptons, and the antiquarks, if you want to do that. So, to make a long story short, after first reminding myself about the Pati-Salam model, which is a beautiful picture of lepton number as the fourth color, I realized that the SU(4) Pati and Salam's SU(4) x SU(2) x SU(2) model had the same structure as rotations in a six-dimensional space, and SU(2) x U(1) could be imbedded in SU(2) x SU(2), which has the same structure as rotations in a four-dimensional space. While I couldn't add two and three and get five, I could add four and six and get 10. The reason is that I knew what to look for. I knew where to put the quarks and the leptons. It had to be in the 16-dimensional spinnor representation of this group. So, I did that, and it worked beautifully. The problem that Shelly and I had been having was that we didn't think of putting quarks and antiquarks together into the same representation. That's crucial. I didn't think of it either, but SO(10) did it for me automatically. I was just drawn to that by the group theory.

Zierler:

So, you brought this to Shelly, SO(10), and you said, "Let's try to put these together?"

Georgi:

No, the evening is young. At that point, I realized that I wanted to know something. 16 fermions are required in the SO(10) theory. That's one more than you need for the first family of the standard model. The extra one is what's called a right-handed neutrino, which doesn't have any interactions under SU(2) x U(1) or SU(3). I knew from the Pati-Salam model that if I took SU(4) x SU(2) x SU(2), the Pati-Salam model (which is equivalent to the SO(6) x SO(4) that I put together into SO(10) ) and said, "Okay, what is it that leaves the right-handed neutrino invariant?" that I got the standard model, SU(3) x SU(2) x U(1). So, it was natural to ask, if I take this beautiful 16-dimensional representation of SO(10) and ask what is it that leaves the right-handed neutrino invariant, what do I get? I should have known immediately how SU(5) was embedded in SO(10), but that wasn't at my fingertips at the time, so I did a very boring and tedious calculation, and just enumerated all the states that were left invariant. Then, I could count them, and there were 24, which is 5 squared minus 1. Finally, the light dawned, and I said, "Okay, 2+3=5." So, that's where SU(5) came from. Then, I was very happy. By that time it was 2 or 3 o'clock in the morning, and I'd had a glass of scotch, but something was worrying me, which is the fact that I remembered why it was that we didn't put quarks and antiquarks into the same representation, and that's proton decay. So, at that point, I drew the relevant diagram in SU(5) that allows three quarks to turn into a positron, which gives proton decay. I was very depressed, because I knew the proton was stable, so I went to bed. Then, the next morning, I explained to Shelly about SO(10), and SU(5), and proton decay, and of course, being Shelly, he was much more excited about proton decay than about anything else. He said, "Idiot, this is the way we see it." So, that's the story. The one thing I'm somewhat annoyed at myself about is that I didn't include SO(10) as a footnote in the SU(5) paper, because that's where it belongs, or as a separate note. It's a very beautiful theory, but we liked SU(5) because it didn't involve any extra fermions at all. So, that's why we wrote the paper that way.

Zierler:

How was the paper received initially when you had it published?

Georgi:

My favorite reaction was from James Bjorken – known to everyone as BJ one of the early heroes of the parton model and the author of a well-known book on quantum field theory, who described his evolution in reading the paper. He got more and more excited as he went through it, and it was beautiful, and then he got to the discussion of proton decay, and he said, "Oh, this is crap," and threw it out. Everyone recognized it was beautiful. A few people recognized that proton decay was an opportunity rather than a problem. As I say, notably, Shelly. Otherwise, nobody knew what to make of it. Of course, people were quite naturally bothered by the fact that we need enormous gauge boson masses to slow down proton decay — this was before Georgi-Quinn-Weinberg, so we didn't know how to estimate the mass of the scale of the symmetry breaking in SU(5). So, what Shelly and I did was we just looked up the experimental limits on the lifetime of the proton, which at that point were not very good, but good enough that we knew this mass was enormous. The other thing that people didn't like about it, quite reasonably, is that we were extrapolating over many, many orders of magnitude in mass to get from where we are to where things look beautiful.

Zierler:

What year does the paper come out?

Georgi:

It was the beginning of 1974. The work was done at the end of 1973.

Zierler:

During this time, you're at the Society of Fellows. Is that really a big difference between your initial post-doc?

Georgi:

Yes, but not so much for the physics. I mean, the Society of Fellows is amazing, and I got to have dinner once a week with the great philosopher Willard Van Orman Quine and poetry critic Helen Vendler, many more luminous characters, like Andy Gleason, the brilliant mathematician who played a large role in winning World War II by breaking German and Japanese codes. These are just remarkable characters, some of them now historical, unfortunately, but some, like Helen, still around. It was wonderful. It also had a fabulous history in particle theory. Steve Adler, David Gross and Curt Callan had been junior fellows, so I knew this was a good thing. But no, the physics was not going on the Society of Fellows. The physics was going on in the department. It was wonderful when David Politzer joined the Society the following year, and many others followed. It's a wonderful institution, but those are sort of two separate parts of my environment.

Zierler:

Did you get a sense that being part of the society of fellows was grooming you to become a Harvard professor? Was that part of the process?

Georgi:

Yeah, that was definitely part of the process. In those days, we had a terrible system where our junior faculty, our assistant professor positions were glorified post-docs.

Zierler:

It was almost impossible to get tenure from that starting point.

Georgi:

Exactly. I, and David Nelson, and later Cumrun Vafa, who went through the Society of Fellows, were hired immediately as associate professors.

Zierler:

But that's still not tenured. That's just tenure line at Harvard.

Georgi:

It's still not tenured, but it was clearly a signal that something was good. It was a terrible system, and we've since fixed it. We really have to be very careful not to — I shouldn't say that, because we're maybe about to do it again, but we recognize that if at all possible, we should hire faculty as assistant professors, and really support them very well so that we have more young people around, and that they can grow into people doing fundamentally different things.

Zierler:

Were you recruited by other schools? Did you ever give consideration to leaving Harvard?

Georgi:

I was recruited by other schools. Michigan, in particular, had a grand plan to hire Frank Wilczek, Tony Zee, and me. I took that very seriously, because that was fairly early in the process. It fell apart partly because it began to look like I would get tenure at Harvard, and possibly for other reasons as well. That was interesting. It would have been interesting. What would have happened? But I loved Harvard, and if there was any way I could stay, I was going to do it.

Zierler:

When did you start thinking about supersymmetry, and when did you meet Savas Dimopoulos?

Georgi:

Oh, goodness. Now, this I can't exactly remember, except that when Savas initially came to Harvard — I should have tried to figure out the date exactly.

Zierler:

He came as a visiting professor? What was his initial appointment?

Georgi:

No, he came, I think, initially, as a post-doc. I'm pretty sure he came as a post-doc, because he came first to visit us, and he stayed with my wife and me, and he had a toothache. The process of trying to get Savas to actually go to a dentist was extraordinarily complicated. He's an absolutely wonderful character. I love him dearly. So, I started thinking about supersymmetry. I thought a little bit about the field theory earlier, but not about the phenomenology, and it was Savas that really got that jumpstarted.

Zierler:

How did this develop into this major collaboration on supersymmetry?

Georgi:

Well, it was an obvious thing to do.

Zierler:

Obvious, after the SU(5) work, you mean?

Georgi:

Not just the SU(5) work, but the difficulties in breaking supersymmetry. The key idea of the supersymmetric SU(5) paper was that, at low energies, it should look as if supersymmetry has been softly broken. Nowadays, there are different ways of thinking about this, but the point is we'd been thinking enough about supersymmetry that we knew that the conventional ways of breaking supersymmetry that were analogous to the Higgs mechanism just didn't work. Spontaneously broken supersymmetry is in the same sense — well, it doesn't work in any way that's at all similar. In fact, nowadays, there are ways of doing this where you spontaneously break it in a hidden sector and it gradually filters down, but we were not so much interested in that as what it looked like at low energies, and how the symmetry from high energies would translate.

The key idea was really the soft breaking — and this goes back to renormalizability. If you have a theory that makes sense — let me go back and talk in one more way about renormalizability, which is really the way I like to talk about it. The infinities that show up when you try to do calculations in a non-renormalizable theory are perfectly natural, because the way quantum field theory is defined, you assume that interactions between the fields take place at space-time points. You do that because a space-time point is a relativistically invariant object. It looks the same in all reference frames. But if you try to make the theory sensible by extending the point to some extended object, except for string theory, which is much more complicated and different, you have problems with unitarity. The probabilities become negative, and all sorts of bad things happen. But if you break the symmetry explicitly, but with masses, say, then as you go to shorter and shorter distances, eventually the masses become irrelevant, because the energies that you require to probe those shorter distances get larger and larger because of quantum mechanics. Then you see the underlying symmetry before it's broken by the masses. So, that was the idea. We'll break supersymmetry with terms that go away at very short distances. Then that will allow us to maintain the beauty of the supersymmetric theory, and its advantages without the problems that we were having with spontaneously broken supersymmetry. That was the motivation. It was one of many things going on at the time, I must say.

Zierler:

For you personally, you mean?

Georgi:

Yeah, exactly.

Zierler:

What else? What other research agendas were you pursuing at this time?

Georgi:

A big part of it was understanding whether QCD was really right, and whether you could calculate. David Politzer and I spent a lot of time, and also Keith Ellis, who has since become a great expert in this, on the underpinnings of what's now called the QCD Parton Model and understanding how you can actually calculate things at very high energies. Of course, that is now a very important and much more difficult field, because at the LHC, it's crucial. You don't see particles anymore. You see jets. You measure the particles, but what you're actually looking for in the high energy collisions is the underlying properties of these very high energy quarks which show up as jets. David Politzer had always believed, from the early days of asymptotic freedom, that this kind of calculation was the really important thing about it. I think that's the sense in which David had the right idea much more than any of the other people that are responsible for asymptotic freedom.

Zierler:

What did David have right? What did he understand that others did not at the time?

Georgi:

He understood that it should allow you to actually make sense of scattering processes at high energy. He had a very "seat of the pants" approach to this. You just calculate and see what happens. The other part of this that was going on was something called infrared safety, which was due to various people, including probably mostly Steve Weinberg. There are things that you can calculate using QCD that are insensitive to the details of how the quarks get confined. There are other things that are sensitive, so you say, "Well, okay. Experimenters, please go measure these things that we can calculate, and don't worry about the fact that we can't calculate other things." David was a little more ambitious, and said, "Okay, let's try to figure out what's really going on." In the long run, while infrared safety is an important part of all of this, David was right. We really need to understand what's really going on in high energy scattering. What's really going on is how to get from those underlying events where the quarks and the gluons are coming off at enormously high energies, to the lots and lots of particles that we see. That was a tough transition, because when we started in this business, the particle data book was a booklet that you could put in your back pocket because there were a handful of particles, and they had a handful of decay modes, each. The transition from that to what goes on at the LHC where the particles are not the important thing, but it's the underlying quark and gluon events that are the important thing, took a while. I think David was really one of the great heroes of this.

Zierler:

You said before, Howard, that the term "grand unified theory" was applied externally. I'm curious, after SU(5) was out there, and people were really playing around with it, when did you start hearing this term? Where was it coming from, and what was your reaction to it?

Georgi:

I believe it was invented by John Ellis and may have first appeared in a paper by Ellis, Ross, and Gaillard. I'm not sure. I'd have to look that up. It seemed fine. I didn't have a particular reaction because when it first showed up, I was almost entirely thinking about other things.

Zierler:

Was your understanding of what Ellis was proposing was that this was truly a grand unified theory, that we would be able to incorporate gravity, that it would all come together, or was it more limited than the term "grand unified theory" actually —

Georgi:

Initially it was more limited. The point I wanted to make was that the SU(5) and SO(10) came out way too early. We had no idea that the standard model was right, that the pieces were SU(3) x SU(2) x U(1). It was one of many possibilities. The same was true of SU(2) x U(1). I think one of the great ironies in particle physics history is that Steve Weinberg got the Nobel Prize for a specific theory, because if you've ever read any of Steve's papers, most of them start by writing down the most general possible gauge theory. Literally, what happened to me at least was we wrote down these beautiful theories SO(10) and SU(5), and then I went on to all of the other things that were going on at the time, which was understanding how to actually calculate things in QCD, understanding how QCD might tell us about the masses of actual hadrons. One of my favorite papers from the post-SU(5) period was the paper with De Rújula and Glashow on hadron masses, which is simple. Understanding why the sigma baryon was heavier than the lambda baryon in an understandable way was fantastic. We loved that, and then we applied that to calculate the masses of the charmed particles, and they came out right. This was before they were actually seen – but we were confident and we were right. That was good. There was all this stuff to do because the experimenters were discovering amazing things. In fact, I sat on the sidelines for some of the charmonium papers, because I was working with David on other things. There were too many interesting things to do in those days.

Zierler:

When you say in the early days, when you were working on QCD initially, and you were wondering even if it's right, it's an existential question. At what point did you feel like you got a better handle on what QCD was and what its promises were for the field, generally? How did that play out?

Georgi:

Well, it developed gradually from '74 to '76, by which time it was beginning to become clear. It actually started before that. The beginnings were the idea that something like this had to be right in order for the Parton model to work as well as it does. A more detailed understanding of that developed very gradually, at least in me. I suspect other people may have understood it much more clearly. I was always a field theorist at heart, although I spent my time model building and doing things like De Rújula-Glashow paper where we were doing much more phenomenological things. I really wanted to understand how this showed up in quantum field theory, and at some level, that's the right approach, but at another level, it's just too complicated. You have to just wait. There are still things that we don't understand that eventually computers will get good enough to tell us from first principles about QCD. At what point did we know enough to say, "Okay, I'll bet my house on QCD."? Somewhere in that period between '74 and '76.

Zierler:

Howard, can you explain what the impact of supersymmetry is on the standard model?

Georgi:

Nobody knows.

Zierler:

But we do have a supersymmetric standard model, even though nobody knows.

Georgi:

That's correct, and we've hypothesized that supersymmetry says there's a fermion for every boson, and a boson for every fermion, because supersymmetry is a symmetry that connects things like the Higgs boson, and things like the quarks and leptons. Unfortunately, it doesn't connect the Higgs boson to the quarks and leptons, because they're very different objects. Nothing that looks like the supersymmetric partner of the Higgs has ever been seen. Nothing that looks like the supersymmetric partner of any of the quarks, leptons, or gluons have ever been seen. Nevertheless, supersymmetry says they exist. If they exist, then once these things start to show up, then the theory starts to look simpler and more elegant in the same way that the SU(5) theory starts to look simpler and more elegant once you get to the enormous masses associated with the symmetry breaking.

Now, supersymmetry does a little more for you than SU(5), or does something orthogonal to what SU(5) does, because it's got one foot in space and time, in the connection between spinless particles and particles with spin. That involves rotations, and that means that space-time has to get into it. So, it's not a purely internal symmetry, but it's nearly so. The field theory is extraordinarily beautiful. So many beautiful things come out of the theory of supersymmetry. One of Ed Witten's favorite tricks is to think hard about the quantum field theory of supersymmetry and then predict that various things are going to happen.

Zierler:

The rest of the world is waiting to catch up to Ed Witten, right?

Georgi:

Correct. That's another amusing story. When I became an associate professor, in 1976, associate professors normally had an office to themselves. I worked very hard with this. I said I'd just as soon move in and share an office with this post-doc that we just got, who's really a pretty smart guy. So, I spent a number of years sharing an office with Ed. That was an extraordinary experience.

Zierler:

Was he talking about string theory in those days?

Georgi:

Not in those days. That didn't happen until the early '80s.

Zierler:

Was he moving in that direction, if you can tell looking back?

Georgi:

Yeah, he was moving in that direction, but in those days, he was just absolutely the best in applying effective field theory ideas to complicated questions in quantum field theory. There are lots of other people that deserve lots of credit, like Fred Gilman and Mark Wise, but Ed was a guru. David Politzer and I were thinking about similar things, which was one reason we were so interested in having Ed come to Harvard as a post-doc. We wanted to pick his brain. We did some fun things, but Ed really had it nailed. He's a very smart guy.

Zierler:

In terms of the advances that were going on in the experimentation world, obviously the large electron-positron collider would be a big deal in terms of supersymmetry and the standard model. Were you paying close attention to what was going on at CERN? Were these the kinds of developments that, as at theorist, were important for you to pay attention to?

Georgi:

Very much so, particularly in the '70s when we began to learn about the structure of neutral currents, and its connection with what people were seeing. It was a complicated experimental situation because the disentangling of neutral current phenomena and QCD phenomena from the phenomena involving the production and decay of heavy quarks and heavy leptons was very complicated. There was so much that happened all at once that the phenomenology was absolutely fascinating. Also, it was a little more accessible in those days. You could go to CERN and look at the big bubble chamber. My favorite part of visiting Gargamelle was a chain that they had that just hung horizontally in the magnetic field. You didn't have to connect it to anything, it just hung there. Nowadays, it's on such a vast scale that you can't see it. It's almost beyond anything that a human can comprehend, but in those days, you could imagine what really went on in those experiments a little more easily. I was very involved in trying to understand what the experiments were doing.

Zierler:

In terms of your involvement with what goes going on at CERN, were you closely following the developments of SSC, and what that may have promised for the field, and for your research in particular?

Georgi:

Yes, very much so. I was on the SSC policy committee and was kind of hoping to have more excuse to visit Waxahachie. For one thing, I had family in Texas, but also, I knew that this was the way to find out what was going on with the W and Z.

Zierler:

Was your sense that part of the excitement about the SSC was simply not ceding leadership to Europe, besides the energies that were being considered at SSC? Was there a national, patriotic component to it as well?

Georgi:

I know that's part of the politics. I don't think it was part of the physics, honestly. I'm sure there were people who thought that way, but the people I hung out with just realized that this was the best way to get at the physics, and they were very concerned that the LHC wouldn't work. I think the mistake that we made in thinking about this, looking back on it, is not understanding, or not predicting properly the dramatic advance in detector technology, and computer technology, and all the rest that now allows us to make some sense of this basically impossible machine. The LHC is a crazy, impossible machine. It's not something that you would build if you were at all rational, except for the fact that there was a possible political and economic path to it. The SSC people, I believe, genuinely thought that it wouldn't work, and that it wouldn't do the things that it promised to do. It did, not as much as we would like, but a tremendous amount. A lot of that is due to the geniuses that construct these machines and detectors. Advances in silicon detectors, and all the rest that goes into this machine, and triggering. It's an amazing story, and I hope that someday all of the gory details get the adulation that they deserve.

Zierler:

That's one of the things that we're doing right now. That's the idea.

Georgi:

Yeah. It always drives me crazy to listen to experimental talks at colloquia, because they jump in and start talking about the theory instead of these gorgeous machines and trying to explain what an impossible thing they're actually doing in disentangling the rare events that they're looking for from all of the other stuff that goes on.

Zierler:

Given the fact that you were involved with SSC planning, in what ways, from your vantage point, did you see planning for the SSC as something that needed to be complementary and not redundant to what was going on at CERN?

Georgi:

That was certainly part of the problem. It would, I think, have made the LHC sort of unnecessary. In that sense, maybe there was a patriotic component, but I think more so on the other side. CERN said, "Okay, here's a cheap and dirty way of doing this. If it works, it'll be fantastic." Turned out they were right. It was, but it didn't look like that at the time. It really looked like the LHC was a high-risk machine, and that there was a good possibility that you would build it, and you just wouldn't be able to disentangle, and wouldn't be able to see the physics that you were interested in. That turned out not to be the case, for various reasons.

Zierler:

Can you explain dimensional deconstruction, and where did that come from?

Georgi:

Oh, goodness. Can I explain dimensional deconstruction? Sure.

Zierler:

Or, would you, I should say.

Georgi:

Dimensional deconstruction is something that all physicists learn about in their first waves class. You know that you can model a massive string by taking a massless string with masses on it and appropriately taking the limit as the masses come closer and closer together. Dimensional deconstruction was basically the same idea applied to quantum field theory. The analog of the string, here, is a dimension, but instead of the dimension, the degrees of freedom in a massive string are continuous, like a continuous dimension. But the degrees of freedom of your massless string with masses on it, there are a countable number of them. I should say that my contribution to this was mostly understanding the high school physics very well, or the college physics very well.Nima Arkani-Hamed and Andy Cohen were definitely pushing on that idea, and I was a technical consultant in many ways.

Zierler:

Did you see your work in heavy quark effective theory as a logical progression from QCD? In other words, what unanswered questions in QCD leads you to heavy quark effective theory?

Georgi:

Heavy quark effective theory is one of my favorite things, but the hard work was done by people like Shmuel Nussinov and Misha Voloshin, and David Politzer, , and Mark Wise, and Nathan Isgur, who identified the underlying physics, which is that if you have a very heavy quark, the most important thing just turns out to be the color electric field. In the limit that it becomes infinitely heavy, that's all there is that's left. So, the heavy quark effective theory, I liked because of the symmetry. Almost everything you can do with the heavy quark effective theory, you can do explicitly the way the Russians did things long ago. Russians are very good at this. But it was too complicated for me. The heavy quark effective theory was a way of making a lot of things trivial. It took me a while to convince people that really the symmetry was all that was left, and that that's where all of the juice came from, or the symmetry plus the effective theory technology.

So, it was a very fun period, because convincing Mark Wise that this was all that was necessary was a fun process. At one point, he finally sent me a little paper in which he said, "You know, there's not much that's really terribly interesting about this paper, but it has one thing that you will like: it uses the heavy quark effective theory." So, at that point, he gave up, and decided this is the right way to go. So it was a technology that made things easier, but the brilliant physical ideas were developed by these other characters, who are wonderful. The one thing I added was this notion of velocity super selection rule, which allows you to turn it into an effective theory in a simple way.

Zierler:

I have so many questions about unparticle theory, but the first is, did you mean that term seriously? Did it sort of begin as a joke and then it took on a life of its own, or you literally meant unparticle theory when you started developing these ideas?

Georgi:

Oh, I absolutely meant it, and this is actually what I discussed at the very beginning of our chat. these are the theories in which energy and momentum is not bundled into particles. This is something that has puzzled me since I was a graduate student. I'm not sure what it was that possessed me to try to think about it from a more modern effective field theory standpoint. I think that I was searching around for something really interesting to do, and I realized that I didn't have the faintest idea what this stuff would look like if it existed in the real world. That's what the unparticle physics is supposed to be. If there really is a sector of our world in which there's this stuff that is not particles, and not in any sense decomposable into particles, what do we do with it?

Zierler:

Does this brush up into dark matter and dark energy? Are these similar kinds of ideas?

Georgi:

Probably not. It would be nice, but it doesn't seem that the scale invariance that is part of the unparticle physics idea is compatible with what we know about dark energy, and dark matter. I've got to say, I don't know what it will do, to this day, even though there have been some interesting calculations. The other part of this was that I had, in some sense, been working on conformal field theories off and on for fifty years, but the mathematics is much too hard for me. My hope was that unparticle physics would be a way of giving some physical insight into this mathematics. I don't think that's happened very much, but maybe a little bit.

Zierler:

What is the theoretical basis for understanding that unparticles is a thing?

Georgi:

Well, I don't know how else to say it other than saying that we have this beautiful picture of the standard model in which everything is associated with fields, which are in turn associated with particles. We understand that very well. That's quantum field theory. The Thirring model is a quantum field theory, but it is different. The Thirring model is this 1+1-dimensional model, which is the original model in which Ken Wilson developed the idea of a non-Lagrangian approach to all of this, and anomalous dimensions, and all of that. It's a model in which the energy and momentum is simply spread– it is continuous. There's no discontinuous relation between the energy of the stuff and the momentum of the stuff. The stuff can have any energy and any momentum. I'm interested in it because it's just odd. It doesn't look like the real world, yet it emerges from quantum field theory, which is the mathematical structure that we use to describe the world. That's why I think it's fascinating. I hope that it's there somewhere, because I'm just genuinely curious about what it would look like and what it would do.

Zierler:

Do you think discreet scale invariance will help you get there?

Georgi:

I don't think so. I had some fun with that, but I don't think it's going anywhere.

Zierler:

But maybe.

Georgi:

Who knows? You never know.

Zierler:

When did you start working with Aneesh Manohar?

Georgi:

Well, he was only a graduate student at Harvard for two years, so we had a rather intense collaboration over that period, and then he was a junior fellow. So, that five-year period.

Zierler:

What was your work with him? What were you two working on together?

Georgi:

What we got started working on was extending an idea of Steve Weinberg's about how to estimate things in a strongly interacting theory. Steve's idea was basically that in a strongly interacting theory, if there was something like dimensional transmutations, and this dimensional transmutation idea is operating, then that's got to be built into all of the calculations that you do in the process, and that in a strongly interacting theory there is no small parameter. So, if you do a calculation, and then try to do a more accurate calculation, you somehow ought to get at least roughtly the same answer. They ought to be consistent. In a way, it's kind of a field theoretic instantiation of the old "bootstrap" idea. So, we just thought about how to formalize this in more general theories, and use it, and to apply it then to the effective chiral theory that describes the pi-mesons, the lightest mesons, as approximate Goldstone bosons associated with the breaking of a chiral symmetry, and lots of other things. It became sort of an industry.

The question there that Aneesh and I got puzzled by is the quarks. In the chiral theory, when you write down the theory, you have this breaking that comes from the quark masses. The quark masses that you need to make that work are tiny, the U and the D quark masses of the same order of magnitude as the mass difference between the proton and the neutron, or the K+ and the K0. Whereas, in a picture like the picture that Glashow and De Rújula and I had of the hadrons being built out of quarks, the quarks have roughly a third of the mass of the proton. Our idea was that somehow the constituent quarks of the constituent picture have to be related by some spontaneous symmetry breaking to the underlying quarks. So, that's sort of our picture, and it's now been taken up by people who do nuclear physics, and what not. It's a popular idea. I never figured out how to make sense of it. We had the idea, and it was fun and interesting. Maybe there's some germ of truth there, but to my knowledge, there's still no consistent calculational scheme that allows you to really be sure that things work that way. Ultimately, I like things that I can be a little more sure of than that.

Zierler:

What is the flavor puzzle, and when did you get involved with that? What does that mean?

Georgi:

Oh, gosh. That's easy. We're built out of up quarks, and down quarks, and electrons, and neutrinos are kind of important to us, because they allow the sun to shine, but for the most part, everything that we do only involves that first family. Why do these other things exist? Why do they mix it up the way they do? And now, what are neutrino masses? That's part of the modern version of the flavor puzzle. All of those things are just totally mysterious. More practically speaking, it goes back to the GIM mechanism, the Glashow-Iliopoulos-Maiani mechanism. Flavor changing neutral currents are not there. At least, we've never seen anything that looks like a fundamental flavor changing neutral current. That's automatic in the standard model because of the GIM mechanism, but it's still amazing. What it means is that the theory tells you absolutely nothing about what flavor is. There's nothing that distinguishes the flavor, except these parameters that determine the masses of the individual quarks and leptons.

At some philosophical level, that's unacceptable. That means the theory is incomplete. So, you then ask, where do we look for physics that distinguishes the flavors? Of course, the answer is you look around the corner, because that's where you can see at the next accelerator. But you keep building higher and higher energy machines, and it doesn't show up. So, the question is, where is it? The string theorists say, "Well, okay, maybe it's hidden up there at the plank scale, and you'll never seen it." That would be sad. I would love to see the physics that distinguishes the down quark from the strange quark show up at some energy at which we can do some experiments.

Zierler:

What are some of the possibilities in terms of ongoing work with strong coupling models for the Higgs boson? Where might that lead?

Georgi:

I'm not sure it'll lead anywhere unless we get some experimental data. It's easy to build models in which the Higgs is not fundamental. David Kaplan and I did it long ago. As long as you have a parameter that you're willing to tune and push the scale at which the new physics shows up beyond the scale of your accelerator, that's fine. They're ugly, these models. The fundamental problems with these models are not so much that you can't build them as that no one has come up with a beautiful way of coupling the dynamical Higgses to the fermions to give the fermion masses. There are ways we can do it, but they're not compelling, and there's nothing pretty about it. I think that people will only get interested if there's some actual data that shows there's something that's not right about the Higgs boson. That is one of the most important things that we hope LHC, or the next machine, will tell us, since it looks increasingly like it's going to be very difficult or impossible for the LHC.

Zierler:

Howard, what are some other research endeavors you've been involved with in the past few years?

Georgi:

Let's see. In the past few years, I spent a lot of time on an idea that didn't go anywhere, which is the idea that somehow you could view a high-energy event as stuff going on an expanding shell, moving out at the speed of light from the event. I thought it was a good idea. It didn't work. That happens. It was maddening because it kept giving us indications that something interesting might be going on, so I kept slogging away at it for several years. I probably spent much too much time on that problem. I'm having wonderful fun, at the moment, for the last year or so, returning to my youth. I'm actually exploring generalizations of a model that Julian Schwinger wrote down back in the '50s. This is not complicated, and it may or may not have anything to do with the real world, but I'm hoping it'll teach us something about unparticle physics, because these are explicitly solvable models that have unparticle physics, and have enough other structure so they actually have ordinary physics, ordinary particles, and unparticle physics, and you can see how they fit together. Admittedly, this is in a rather oversimplified world where there's only one space-dimension. That's what allows us to solve the theories explicitly, but it's great fun. I'm enjoying the exercise. It's enough out of the way that I can do it at my advanced age without worrying about all of the other things that are going on. It's not a problem that's close enough to the mainstream that I have to compete with all of the young bucks.

Zierler:

Howard, one aspect of your career that we haven't touched on yet is your work as both a teacher to undergraduates, and a mentor to graduate students. First, I want to ask, what have been your favorite courses to teach undergraduates?

Georgi:

I have two favorite courses. The first was waves. Partly, that's because the first physics course I took that was so terrible was partly a waves course. So, I enjoyed teaching that course for many years, and wrote a little textbook which is now free on my website. It's a brilliant book that has changed a number of lives, but it's too hard for most undergraduate classes. For the last 20-some years I've been teaching Physics 16, which is the latest version of the course I skipped when I was an undergraduate. It's a mechanics class for students with at least AP level preparation in physics and math. It's just marvelous fun. I love the kids, and I get to follow them through their Harvard careers. My goal is to get to know every one of them well enough to write a letter for them. So, that's just terrific fun.

Zierler:

In terms of your career as a mentor for graduate students, how would you describe your style? Are you mostly hands-on or hands-off?

Georgi:

Mostly hands-off in the sense that I let the graduate students do their own thing, but just try to talk to them and treat them as collaborators. It works when I'm throwing out ideas, and when I'm getting the best graduate students in the world, which I did for a period in the '80s. This was rather wonderful. That was a time, you will remember, when Steve Weinberg and Shelly Glashow were both on the Harvard faculty. So, we really got our pick of all of the top students who wanted to do particle theory. When they got there, they realized that both Steve and Shelly were essentially impossible to work with, so a lot of them worked with me.

Zierler:

By default, they came to you.

Georgi:

Exactly. Yeah, it was either me of Sidney Coleman, so Sidney also had brilliant students.

Zierler:

Howard, I don't want to put you on the spot by asking you to name your most successful graduate students. Inevitably, you might leave off one or two, but I'm curious if you can think about some of the shared characteristics that your most successful graduate students have had. What are the things that they shared that suggested to you that they would go on and do important work in their own right?

Georgi:

It's not that I refuse to answer that because it might cause friction. I refuse to answer on the grounds that I think it's philosophically the wrong question. One of the things on my personal webpage is a little talk that I gave, an after-dinner speech for our PRISE program, our undergraduate summer research program. I described the fact that one of the really fun things I've done in my career is people watching. I've had this wonderful experience of getting to know Feynman, and Gell-Mann, and Glashow, and Weinberg really, really well, and learning how their minds work – and Sidney Coleman, and Helen Quinn, and David Politzer, and Ed Witten, and my own students, Lisa Randall, and Ann Nelson, and David Kaplan, and Aneesh Manohar, and the whole bunch. What I believe strongly is that the differences between any two of these people, the way they think about problems, are absolutely enormous. So, I just think that no two great physicists think in the same way, and that convinces me that there are probably lots of ways of being a great physicist that we haven't seen yet.

This is why we need diversity – not just for fairness but we don’t know what great new ways of thinking we will be missing if we just keep training people who look like us. So, what I see in my graduate students are people who are incredibly talented in all areas compared to normal people, but you never quite know what it is that's going to make them truly special. There are a few cases where I could really see it. My three students who have been elected to the National Academy were clearly special right from the beginning, and many others like Aneesh. I don't want to leave them off because I've got about 20 that I could name. They're also really special. But that's kind of the way it works. I think people do not realize the enormous range of talents that are possible with the human brain, and just how many different ways there are of thinking about things. So, yes, all of these people are good at all of the usual things compared to normal people. Enormously so, so they appear like magicians to normal people. But each one is so different from each other one. That to me is the real miracle of my career in physics, that I've had the opportunity to see all these characters.

Zierler:

Howard, now that I think we're at the point in our discussion where we've covered everything in a narrative sense, I want to ask you for the last part of our talk a few broadly retrospective questions about your career, and then maybe a few things looking forward to the future. The first thing that I'd like to ask is: I'm sure you're well aware of this idea that theoretical particle physics had a golden age, and it ended at some point. There are many different ways that we can locate this. The late '70s, the early '90s. And yet, in hearing about the work that you've done after that time, it sounds like either you think that we're entering into a second golden age, or we're still in that first one. So, I'm curious to hear your broad perspective on where particle physics has been since the 1980s, when you got this beautiful crop of graduate students, and where you think it might be headed in terms of what can be accomplished next.

Georgi:

I don't know entirely how to answer that. I'm hoping there will be a second golden age. I don't think we're in it. I had high hopes for the LHC, and they may still teach us something revolutionary, but it's becoming more and more difficult to imagine that. I'm embarrassed to say that I'm not really participating in all of the revolutionary things that are going on on the boundary between cosmology and particle physics. That's not because I don't think these are fantastically important. It's just that it's not the way I like to do science, and it's not the way I'm really good at doing science. Deep down, I can't get over the fact that when I was growing up and first learning about this, it was still a creation myth. So, I'm hoping that experimental rather than observational science is not dead at short distances, but for that to happen I think that some sort of miracle will have to occur. That's one reason I like the idea of unparticle physics. There may be something there that shows up in precise experiments that are not necessarily such high energy, or something else that we haven't thought of yet that would make it a new golden age. But who knows? Meanwhile, I love all of physics and will continue to try to get students turned on to physics in general, not particle physics in particular.

Zierler:

What do you think it will take to get to that second golden age in terms of technology, or the next Feynman, or the hard work working out the calculations? What do you see is the right mix that would lead to a second golden age in theoretical particle physics?

Georgi:

I think partly it depends on what you mean by theoretical particle physics. What I mean is very narrowly defined. That would take data. I don't think we're going to figure this out theoretically. The golden ages in theory are always associated with golden ages in experiment. That doesn't mean that they're not incredible contributions all by themselves. 't Hooft's discovery, explication of non abelian gauge theories is an amazing example that was fabulous, and incredible theory, but so many experimental pieces went into the underpinnings of that that you can't imagine it just existing in a vacuum. At least, I can't imagine it just existing in a vacuum. So, I'm not a great believer in mathematical elegance as a way of making progress. I could be completely wrong. The string theorists may find their way out of the swamp land and come up with the right answer. That's not impossible. It's not that I don't do that because I think it's not the right approach. It's just that I'm not particularly good at it, that I prefer to do things that I can really make a contribution to. So, the answer is I don't know, but I hope there will be.

Zierler:

But you're not a definite skeptic that string theory has failed to produce promising results, and it won't likely in the future. You think that it may well.

Georgi:

Sure. Obviously, I feel that it's distorted the field a little bit because it's so pretty, and it has such an unbelievable guru in Ed Witten, that perhaps people that might have made major contributions in other areas have gone into string theory, and that's not necessarily helpful. But they've done amazing things, and they've created a lot of amazing mathematical technology. So, I'm an admirer of string theory even though I don't do it myself. If I had to guess — well, I don't have to guess. I don't know. So, let me leave it at that.

Zierler:

You've used the term "mysterious" throughout our conversation. What are some of the things over the course of your career that you feel like you truly understand that were mysterious, say, in the late 1960s, and what are some things now that are as mysterious as ever, and you might have been surprised thinking back 50 years plus, that these things are still mysterious?

Georgi:

50 years plus — K mesons were mysterious then and are mysterious now for different reasons. Back in the '50s, they were completely mysterious when they were discovered, and have gone through a remarkable evolution. Just the saga of the K mesons would make a great story, because there have been multiple stages of unraveling mysteries that have then led to more mysteries. That's the way I like to see these things work. The flavor puzzle that is still with us, and in some sense, it was with us when the muon and the K were first created. In some sense, they're less mysterious, and in some sense, they're every bit as mysterious now. Nobody talked about what we now call the strong interactions in the '50s. There were people thinking about nuclear physics trying to figure out what was going on there. That must have been a terribly exciting time as people began to see inside the proton and the neutron and see this incredible zoo which I fell in love with after it had already been described experimentally. Nowadays, we don't think about particles anymore. We theorists think about other things, but I still love the particles. There are lots of mysteries in QCD that I'd love to understand better, but I don't have the mathematical tools. It'll be interesting to see whether, as computer technology develops, we find mysteries in QCD as we really understand better how to get from the underlying theory to the actual things that we see. That's very possible. It's a tough business, so I don't do it, but it's an important business. It will be interesting to see what machine learning and other technologies do to that.

Zierler:

You said you personally have not moved into cosmology yourself, and yet, there have been many people in particle theory who have moved into cosmology. I'm curious if you've thought about the way that some of your work has influence cosmology, and how it might be useful in terms of ongoing advances in that field.

Have you thought about the ways your work has influenced where cosmology is headed, even though you personally are not involved in those transitions.

Georgi:

Not really very much. I follow it a little bit, in particular, thinking about the connection between cosmology and the hierarchy puzzle in particle theory, which is related in some way to a lot of my work. I don't know what to say about it. It just seems to me to be — it's not my taste. It's too remote from actual experiments, and I think, to some extent, I have to get used to it. If I were a young scientist coming up today, I'd certainly be fascinated by what's going on in astrophysics and cosmology. I've probably guessed wrong about astrophysics and cosmology more than most other people in the field. In particular, a well-documented case is neutrino masses. I was just astonished when it was discovered that neutrino masses were really at the root of the absence of observation of neutrinos coming from the sun.

Zierler:

Well, you were in good company on that.

Georgi:

It's true, but what can I say? So, I don't think I'm a very reliable source here. I do hope that there continues to be an experimental component of really fundamental physics. There's so much stuff going on in other areas, like condensed matter theory, and what not, that I don't think we'll see again a time when particle theorists are on the pedestal that they were in those days, because there's just too much other interesting stuff happening.

Zierler:

But that's not to say that all the mysteries have been solved.

Georgi:

I'll say! The question is whether all the mysteries WILL be solved, or whether there will simply remain things that we're frustrated by our inability to address. I'm sure that's true at some level. Well, really I'm not sure of anything, but I strongly suspect that's true at some level. I don't believe that somebody's going to write down the ultimate theory on the back of an envelope someplace and all our problems will be solved.

Zierler:

So, is that to say you've become — what are your thoughts on the achievability of a true grand unified theory? Does that seem more remote to you, or less since you've first started thinking about this post-SU(5)?

Georgi:

I hope that I got across the point when we were talking about SU(5) that we weren't looking for a grand unified theory.

Zierler:

Right, but it was external right? It was applied to your work, right?

Georgi:

But more than that, what we were looking to do was to unify the stuff that we saw. It wasn't a grand plan. In fact, we were explicitly ignoring gravity because it was so weak that it didn't have any effect on the stuff that we cared about. So, it's a different kind of unification. It was unification from the ground up, not unification by writing down the ultimate answer. I think that's an important distinction. Yes, we want to make things simpler. Yes, we want to understand what's there and how it fits together into something beautiful. Do we think that we can intuit what's there because it's beautiful and unified? Well, some people do, and I don't.

Zierler:

We talked about this a little in the beginning of our talk. In terms of your current interests, I know that you are dedicated to correcting the issues of representation among underrepresented groups in physics, both in terms of minorities, and women. Can you talk specifically about what you've done in terms of helping to correct those historical imbalances?

Georgi:

As I say, in some sense, while I don't think of myself, and never have thought of myself, as a misogynist or a racist. I was definitely an oblivious nerd for much of my career.

Zierler:

Part of that is just as a white male, you don't have to be aware of your identity. It's not a factor.

Georgi:

It's not a factor, but neither is it an excuse, because when you look around and notice the dearth of women or minorities in your field, you ought to, as a scientist, think about what is causing that. I'm embarrassed by that, but I hope that I've, to some extent, made up for it with my efforts, with women, particularly. There, I really had no excuse, having had some of the unbelievably outstanding women graduate students, who just taught me a lot, for still being clueless. It was really the undergraduates, ultimately, who convinced me that there was something seriously wrong, and that I needed to start listening more carefully to what they were saying. That's the main thing that I've done, is to listen more carefully to what they're saying, and to try to convince other people to listen more carefully to what they're saying. It's an interesting experience being in a committee where you're the only man. That's an experience that I've now had multiple times, and it's something that all men should feel, because you get definitely more of an understanding of what it's like. I like to tell my colleagues, and this is true, I no longer get called on as much as I used to in meetings because I don't react quite the same way that I used to. I'm less inclined to interrupt someone.

The minority issue is just such an intractable puzzle that it's very frustrating. I'm delighted that everyone at the moment is so energized. There will certainly be a little pulse that will improve things here. How we maintain that energy over a long period of time will be what really tells the story. It's tough, because there are so many related issues that we have to solve that are political and economic. I'm an optimist, but boy, you really have to be an optimist to spend all of your time working on that.

Zierler:

I want to share a fascinating perspective as it relates to these questions. I spoke with Dave Weitz yesterday, and he was telling me, one of his motivations for coming to Harvard when he was recruited away from Penn was that he realized that, Harvard just being Harvard, this would really be his opportunity to cement the status of soft matter physics. It really landed home the point that Harvard, deserved or not, really still sets the tone in a broad way in terms of physics. I wonder if we can apply that concept to what we were just talking about. How might Harvard take a leadership role in these questions of shut down STEM and underrepresented people in physics, how might he department of physics at Harvard, looking to the next 20 or 30 years, really take a lead role in correcting some of these imbalances?

Georgi:

It's a great question. We are working on it. I think we have the model of women in physics to help, because that's a place where I think we really did make a difference. We, for a long time, worked very hard to maintain a reasonable group of women in our graduate program. It makes a huge difference at many levels. Each year we work a little harder on the minority question, and I'm hoping that this will really push us. We just voted to eliminate GREs. That's a good thing. I've been saying that for a long time, but it's nice now that there's some momentum, and that it's actually going to happen.

Zierler:

On the basis that there's a bias inherent in the GREs.

Georgi:

Well, on the basis that there's a bias inherent, and also that it doesn't really tell us what's really important. Both are necessary. I do believe the tests measure something. They just don't measure something that is the most important thing to me in my students. In fact, in some cases, it can actually be counterproductive, but that's another story. All I can say is that we're working on it, and it's wonderful to have a real group in the department that's very excited about it and working hard. I just hope we can maintain that enthusiasm and that momentum for a while. It will make a difference.

Zierler:

That's great to hear. Howard, for my last question, I want to ask you something that's a little more forward looking. It's obvious that you uphold the fundamental law of physics that physicists never retire. You love what you do too much, and there's still so much work to be done. So, I want to go back to this idea in the '70s, in this particular golden age, when you were just overwhelmed with all of the amazing things to work on. It certainly seems like this spark has never left you. Time is limited, resources are limited, graduate students are limited, so how are you going to pick the most impactful research projects to focus on for the remainder of your career? What are those issues where you feel like you have both the perspective and the connections to make the longest and biggest possible impact for your future?

Georgi:

I have to say that at this point, research is only one of many components to the way I think I'm contributing. I don't want to hang on, as much as I love what I'm doing, I don't want to hang on if I'm not contributing. I think in recent years, my primary contribution has been much less in research, and much more in both undergraduate teaching and in helping to encourage the whole department to focus on undergraduate teaching, and women in physics, and other things. My students who have gone on to wonderful things include not only people like Lisa Randall, and Ann Nelson, and David Kaplan, and Aneesh Manohar, and all the others, but also people like David Morin, who is now my co-head tutor at Harvard, and writes these wonderful textbooks. I don't know if you know his book on classical mechanics, but that's sort of the standard study text for the Physics Olympiad teams around the world. That's a fantastic contribution. So, one of the things I hope I can do is to continue to help my colleagues see multiple contributions to the field, not just people who sit in their lab, or their closet doing fabulous research. My research, I suspect, is going to continue to be in sort of off-the-wall areas that are high-risk and fun and may not go anywhere. But that's okay with me. I'm having fun.

Zierler:

Maybe something will stick.

Georgi:

Exactly, maybe something will stick. That's the goal.

Zierler:

Well, Howard, it's been so fun talking with you today. I really want to thank you for spending the time with me.

Georgi:

Well, thank you. This is a wonderful thing you do, and I know a little bit about it from the time I spent looking at Sidney Coleman's contributions.

Zierler:

Wonderful.

Georgi:

I had the sad task of writing his Biographical Memoir for the National Academy, and Sidney’s oral interview was very helpful.