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Interview of Edward Kolb by David Zierler on July 21, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Edward “Rocky” Kolb is the Director of the Kavli Institute for Cosmological Physics at the University of Chicago and the Arthur Holly Compton Distinguished Service Professor of Astronomy at the University of Chicago. In this interview, Kolb explains how he acquired his nickname and he recounts his upbringing in New Orleans and his habit of spending time in the local library, where he developed his interest in science. He describes the financial constraints that compelled him to attend the University of New Orleans for college, and he characterizes his education there as broad but not deep, which caused him to consider a wide range of specialties for his graduate research at the University of Texas. Kolb describes working with his graduate advisor Duane Dicus in applying particle physics to cosmological questions, and he summarizes his dissertation research on the effects of axions in stars. He discusses his postdoctoral research with Willy Fowler at Caltech, and he emphasizes the influence of Allan Sandage on his decision to focus on cosmology. Kolb describes his second postdoctoral fellowship at Los Alamos where he joined the burgeoning astrophysics group in the Theoretical Division to work on Big Bang nucleosynthesis. He explains his decision to join the astrophysics group at Fermilab, where he collaborated closely with Michael Turner and benefited from the support of Leon Lederman. He describes his developing interest in supersymmetry and neutrino oscillations, he describes the impact of Alan Guth’s lectures on inflation, and he explains his increasing involvement with the astronomy and astrophysics department at the University of Chicago culminating with an offer for him to become chair of the department. He describes his objectives and achievements in that position, he explains how he maintained research interest in creating particles from the vacuum, and he describes how this research could be of value in the ongoing quest to understand dark matter. At the end of the interview, Kolb reflects on the different approaches that religion and science take to understanding reality, and he explains why he is most optimistic that understanding dark matter is the most likely major future breakthrough in his field.
OK, this is David Zierler, oral historian for the American Institute of Physics. It is July 21st, 2020. I am so happy to be here with Professor Edward Kolb, otherwise known as Rocky. Rocky, thank you so much for joining me today.
That’s fine, thank you.
So let’s start with the first question that’s raised from the very first thing I said, where and how did you get the name Rocky?
[Laughs] Well, I don’t know. It was the first name I remember having and I asked my parents, “Where did I get this name?” And they said, “Well, when you were three years old, one day you said ‘From now on, my name is Rocky. I won't answer to any other name.’” And I said, “Well, where did I get that?” They didn't know and I certainly don’t remember. But my kindergarten graduation certificate says “Rocky”. So, you know, there’s some physical evidence that it goes back at least that far.
And it’s official; you have a paper record.
Right, right. The big advantage now is if you’re in a physics or astronomy department, the user name “Rocky” is almost always available.
So it’s a big advantage.
Rocky, tell me what your most recent title and institutional affiliation is?
Oh, goodness. At the University of Chicago, we have a lot of titles. They give you titles rather than salary increases, which is typical in academia. So right now, I am the Director of the Kavli Institute for Cosmological Physics at the University of Chicago. And the Arthur Holly Compton Distinguished Service Professor of Astronomy and Astrophysics at the university. Prior to that, I was the Dean of Physical Sciences at the university for five years. And prior to that, I was Chair of the Astronomy and Astrophysics Department for five years. And then even before that for 22 years or so (1983-2006), I was at Fermilab in various roles in the Theoretical Astrophysics Department, the Center for Particle Astrophysics and things like that while on the faculty of the Astronomy & Astrophysics Department at the University of Chicago.
So to stay with your current affiliations, two questions: were you involved in bringing the Kavli enterprise to the University of Chicago?
I wasn’t the main player in that, but I was involved. Just about all of the senior people associated with the University of Chicago were involved in bringing the Kavli Institute there. And it’s been a really great thing for us.
Is there any particular institutional connection with other Kavli enterprises around the country?
Well, there’s a loose connection. Around the country and in Japan, China and in England, there are Kavli Institutes that are dedicated to cosmology or astrophysics in some way. It’s a loose affiliation, but we know what’s going on there and they know what we do. And often, students and postdocs, a Chicago student associated with the Kavli Institute here will go to the ones in Tokyo or Cambridge or Stanford. And there’s a beneficial interchange. So there’s not an official umbrella organization other than the Kavli Foundation, but there are a lot of interactions and it’s a really good, really nice organization.
And I suppose that it’s not controversial to say that it’s just remarkable the way that Kavli has supported physics and all the amazing work that’s been done as a result of that support.
Right, right. Fred Kavli was great. The Kavli Foundation’s been great. I wish we had another three or four or ten Kavlis to work with.
So the big advantage of the Kavli, is the unrestricted endowment fund which allows us to move rapidly into new areas and do things that it would be harder to do, at least at the beginning, through the support of federal agencies. It doesn’t replace the, I feel, generous support we get from federal agencies, but it gives us much more flexibility.
Not to put you on the spot, but the family whose chair you’re supported by, the Compton family, do you have any personal connection with the family or do they have a connection with physics?
Well, they have a connection with physics, of course. Arthur Holly Compton was a professor at the University of Chicago and he was a Dean of the Physical Sciences Division, Chairman of the Physics Department, and played such a huge role in the Manhattan Project in organizing the effort at Chicago. He brought Enrico Fermi to Chicago and Compton played a huge role in the Manhattan Project. Compton went on later to be President of Washington University in St. Louis. It was quite a remarkable family. He had two brothers I know of. One was President of MIT. The other was President of Washington State University. So they had three college president brothers. I don’t know if that’s been replicated anywhere.
It must have been a tremendous honor to get named to that chair.
It was, it was. And if you look at old photos of Arthur Holly Compton, he has a moustache. So I always think they had to have someone with a moustache as a Holly Compton professor.
[Laughs] Rocky, let’s take it back to the beginning. Let’s start first with your parents. Tell me a little bit about them, starting with where they’re from.
I grew up in New Orleans and they’re both from New Orleans. My father was older, 45, when I was born and older when he was married because his father, my paternal grandfather, died in the 1918 pandemic. The Spanish flu pandemic. And my father was 12 years old at the time; he was born in 1906. He was the oldest son with one brother and two sisters. When he was 12 years old his mother told him, “Well, your father’s dead. You have to support the family.”
Inconceivable at 12—
He ended up going to school at night to finish high school and later business school in what we would now call an Associate’s Degree, and he started working in a bank, riding a bicycle downtown delivering things, and ended up retiring 57 years later from the same bank as a vice president. So he worked his whole career at one place. Because of his responsibility in supporting his family, he didn’t get married until very late. So my father was maybe a generation or a half generation older than the fathers of most people my age. He never went to college, finished school at night, in business school. Not a Bachelor’s degree, an Associate’s degree in business school.
And so he didn’t receive a formal education, but I remember him working with me when I was a child. He was really good with numbers. Worked in a bank. You know, they didn’t have computers and things like that. And he was interested in numbers, and also cryptography. We used to write secret codes to each other and things like that, so I learned a little bit about mathematics from him. Nothing fancy, well, you know, when I was eight years old, it seemed fancy. It wasn’t algebra or trigonometry or anything like that. But I learned not to be afraid of numbers. So that’s sort of my father’s side.
My mother grew up in New Orleans. She went to high school and then started working after high school to help support her family in the Depression. Again, it was not a wealthy family. Her father—and I heard different stories--whether her mother had left her father or her father abandoned the family, so it was a single-parent household and she had to work to help support them. But she had an appreciation for education that she gave to me and she encouraged me in my education. And my father did also. Neither one of them was able to go to college, but they had a lot of respect for education and sent me to perhaps the best high school in New Orleans.
Where did your parents meet, Rocky?
They met in New Orleans and were married in 1939. Another reason I was born sort of later for my parents’ age is they had, you know, the Second World War come up and that delayed things. I never thought to ask why they waited so long to have children. I guess I just thought I was worth waiting for.
And your father was beyond draft age during the war?
No, no, no. He was in his late 30’s when drafted, now considered beyond draft age, but then they took anybody. He served in the Army in the South Pacific. So he was older, in his late 30s when he was serving.
Right. Rocky, did he talk about his experiences during the war to you ever?
No, never. Never.
Actually I overheard a few stories when he was talking with other WWII veterans. One story I remember is that his unit was lost in the jungles of New Guinea for a week . He talked a little bit to my son later, but he would rarely talk to me about it. I think that’s true of many veterans.
Yeah, I’ve heard that. I’ve heard that. You grew up in New Orleans up until 18?
I grew up in New Orleans. I went to elementary school and high school there. I also went to college—undergraduate-- in New Orleans. So I didn’t leave New Orleans until I was 21.
Rocky, I’m curious, even before your exposure to math and science formally in school, I’m curious if you can look back and recall any particular interests about how the world works, even before you realized your talents in math and science?
Well, I grew up in New Orleans and we didn’t get air conditioning in the house until I was in high school. Now, are you in Washington? Is that right?
You know, the Washington area—
New Orleans is warmer and more humid than Washington, if you can imagine such a plight.
I can’t, it’s too much. [Laughs]
The summers in New Orleans without air conditioning were pretty miserable. In the morning, I would go to a small park down the block and play baseball or something like that. In the afternoons, you just couldn’t be outside. And so there was one place I could walk to that was air conditioned. Actually, there were two places: one was a movie theater but I didn’t have money to go to a movie. That might have been 50 cents; that was way above my means. And the other was a little branch public library. And I remember it as large—of course when you’re eight years old, it looks enormous, but I’ve seen it since then and I couldn’t believe how small it actually is.
So I would go there every afternoon. I’d walk there, wander in every afternoon to escape the heat, and I sort of, not with a plan, started reading books that were on the shelves and checking books out. I thought it was great. I never bought books, but I could check them out from the library. One day I discovered the science section and started sitting in the library in the afternoon in the air conditioning reading books on science. The librarian, who I remember as 120 years old—she was probably 30 or something like that—came up to me and said, “No, sonny. This section’s not for you,” and led me to the children’s books section. You know, Golden Books or whatever there was then--I guess it was the late 50s, early 60s.
So science was forbidden, which made it irresistible to me. When the librarian wasn’t looking, I’d run over to the science section, pull down a book, and sneak back to the table and hold it behind a children’s book to read the science book. And a couple of things attracted me—dinosaurs a little bit— but it was physics that pulled me in for some reason I don’t remember, and also space and astronomy. I found physics sort of by accident; it was forbidden, therefore irresistible.
So I kept an interest in that, read whatever I could, exhausted the library there. There wasn’t any online resources. But anyway, that’s how my interest in science began.
When did you realize in school that you were good at math and science?
Well, I would separate math and science. I was a B+, A- student or something like that in mathematics until I took physics. And I came to appreciate what math was about and how it’s used in physics. So, I was good, maybe the best person in math in the class, but not really exceptional (what I would now consider exceptional) in math until I took physics. And of course in science, in elementary school, I thought I knew more than the teacher and I probably did. I didn’t learn anything in science classes in elementary school.
In high school, I did not take any science courses until junior year. I took chemistry, and then physics. The high school I went to did not teach biology at the time. It was a Jesuit high school in New Orleans, and the reason they didn’t teach biology is that at that time, they thought biology wasn’t rigorous enough. It had nothing to do with evolution or Darwinism. They just didn’t think it was rigorous enough. So it was a 19th century high school education. They had two foreign languages when I started; a modern foreign language and an ancient foreign language. The modern foreign language was Latin.
The ancient language was Greek, the “modern” was Latin. It changed while I was there, Spanish was introduced, but for the most part it was a Jesuit, classical, 19th century education.
When you first realized you were good at physics in high school, what clicked for you?
Oh, I don’t think there’s any one thing that clicked for me. I guess I was good at physics in high school. There was an award for the top graduate in physics in the high school and I got that, but I just really loved physics. And I never thought of being really good at it. It was just something that was easy, almost. Well, I found it easy. Much easier than Latin or anything like that. So it was just—I liked it because it was structured and there was a way to get answers and I don’t know if I ever thought of it as a job—I just loved it and wanted to continue to do it. I didn’t quite know what that meant, but I wanted to continue to study it.
Where I grew up, there were no outreach activities or anything like that. So I never met a physicist, never met a scientist at all to really ask them, “What is science like?” You know, things like that. But I just decided I want to be a physicist and never looked back. I guess I decided it even before I went to high school.
Were there large-scale programs, like the Space Race for example, that sort of captured your imagination and might have led to your love for physics growing up?
Yeah. Well, the Space Race of course captured my imagination. In 1961 I was 10 years old, and I remember the big drama of every launch on television. Will the rocket lift off, or explode, and things like that. I remember being enthralled by that, but it had less of an impact. I think, on my interest in science since I had more of a theoretical bend, you know, how does nature work, what are atoms, things like that. So the Space Race was playing in the background, and I was certainly aware of it, but it didn’t drive my interest in science.
Did you think about going beyond New Orleans for undergraduate or you knew you needed or wanted to stay close to home?
Well, there were a couple of reasons. There was no way my parents could afford to send me anywhere else. At the University of New Orleans, which was part of the LSU system at the time, tuition was $130 a semester, and even that was a stretch to afford. I applied to a couple of places outside New Orleans. I don’t even remember where. I was offered a couple of partial scholarships, but there was not the money to send me anywhere else, and I had no desire to go anywhere else. Growing up in New Orleans, until I went off to graduate school, the furthest west I had been was Baton Rouge, Louisiana. The furthest north was Shreveport, Louisiana. And the furthest east was the Mississippi Gulf Coast. That was my world and I didn’t see much further—New Orleans at that time, and maybe still, was a very insular society.
For instance, in food, you know, they have great food in New Orleans, but I was maybe a junior in college before I had Chinese food or Mexican food, anything else other than Italian or Cajun/Creole. That was it. So I had a very, very narrow outlook on the world. To go someplace else was not something I ever really thought about, and it wasn’t possible anyway, so it wasn’t really pushed.
Did you declare to major in physics right away or going in did you know that you wanted to pursue physics?
Going in, I knew I wanted to pursue physics. I think you couldn’t declare a major until sophomore year, but I declared for a physics major as soon as I could.
Now looking back, Rocky—obviously at the time you didn’t have much to base it on—was it a strong department, as you look back on it?
As I look back on it, it was not a strong department. And, you know, when you’re an undergraduate, you learn through classes. But you also learn a lot through interactions with the cohort of students that you have. You know, working on problems together, talking to each other, and things like that. So skipping ahead a little bit, in 1973 I went to graduate school at the University of Texas, which was not at the time one of the very top elite places. I think it’s a fine place; it’s just not a very top elite place. And I was probably behind—I thought I was under-prepared when I went there compared to other people who had gone to more elite undergraduate institutions. But I caught up. I was maybe six months behind so I worked and caught up.
Looking back on it, I was not as prepared for graduate school as an undergraduate as I would have been if I had gone to MIT, Caltech, Chicago or someplace like that. But I had other experiences that made up for it. I did take a lot of liberal arts classes and humanities classes. I told my wife, who I met in a history class, that I only took those classes because there were no women in physics classes. And it was the 1970s so maybe sadly that was true. I don’t remember.
But occasionally high school students will come to me and ask where they should go to school. They want to be a physicist, they want to be a physics major, where should they go to school? How should they do it? And I always tell them, “Getting a good background in physics and mathematics is important, but also go someplace where you can get a good grounding in the humanities and liberal arts.” Because once you go to graduate school, that’s it. You know, you can absorb humanities on your own later once you get tenure, but I think that’s an important part of education that many people who go to technical schools do not get as good a foundation. I have no regrets—it worked out okay.
Rocky, I’m curious if the Anti-War Movement, the Women’s Rights Movement, the Civil Rights Movement, did that come to campus in New Orleans?
Yes it did. New Orleans—in terms of the Anti-War Movement and other social changes, was behind the times in everything except the Civil Rights Movement there.
Was it integrated when you were there?
No, the elementary school I went to in the mid-1960s (1956-1965), which was a Catholic Dominican-nun run school, was not integrated. My high school was integrated, but only with a smattering of minorities in my graduating class of 200. There might have been five or six African Americans, and a couple of Hispanics.
Who might have been bussed in. They were not there because they lived in the neighborhoods.
Well, it was a private school so there wasn’t bussing. Everybody was on their own getting there. In New Orleans there was a very big parochial school system and private school system. Because of the terrible racial prejudice in New Orleans, rather than integrate the schools, there was white flight from the city and public schools. Since there was white flight from the public schools, they weren’t supported as well by taxes because the people who were paying the taxes and voting didn’t send their children there, so public education deteriorated terribly. So the public schools in New Orleans at that time, with a few notable exceptions were poor.
It was a very segregated society. I graduated from high school in 1969. The Civil Rights Movement was certainly something I was aware of and supportive of, and it was much more important in New Orleans than the Anti-War Movement. Of course, when you’re a college student and you’re facing the draft and going to Vietnam, you know, it’s something that is certainly on your mind. But there wasn’t anything that I saw that were big Anti-War demonstrations on the scale of other places.
Did you have to contend with the draft personally?
Yeah. You know, I ducked it—didn’t dodge the draft, but I didn’t have to go into the Armed Forces because I had a deferment, a 2-S (student) deferment while an undergraduate. While I was in college they instituted the lottery system in the draft, and I lucked out because October 2nd in 1951 was a good day to be born. And also by 1973 when I graduated from college, the draft and the war were winding down. So I managed to get by without compulsory military service. I was lucky to get a high lottery number (#191—I still remember it).
Rocky, I’m curious if your exposure to physics was sufficiently broad during your undergraduate experience and you were advanced enough to have an appreciation for the kind of physics you wanted to pursue in graduate school?
My exposure wasn’t very broad, but I did a lot of reading on my own. And the faculty were supportive. I would, not for credit, do reading courses with faculty members who would say, “OK, read this book. Talk to me for an hour a week,” or something like that. So I did a few of those.
I had two interests. One I didn’t realize what it was at the time, but it would now be called particle physics, and the other was astrophysics. But always from a physics perspective. Not astronomy like looking through a telescope. It was always astronomy from a physics perspective. Those were my interests. And when I went to graduate school, I decided to go into a physics department at the University of Texas. Astronomy was done in the Astronomy Department and physics was done in the Physics Department, so that sort of directed me to particle physics. There was a Center for Particle Theory at Texas.
I’ve never really thought about working on experimentation or observation—I’ve always been theoretically inclined. You know, actually building things and experimental hands-on never appealed to me. Of course I had to take experimental courses in my education. It’s something I did and did OK at them, but it wasn’t really a passion for me as much as the mathematical and theoretical aspects of physics.
Now, did you go straight into graduate school from undergraduate or did you take some time off?
Yes. I went straight into graduate school. Gap years had not been invented at that time.
And what programs did you apply to and why was Texas the deciding factor?
Well, I applied to several programs, was accepted in several. I think I must have done OK on the GRE. My undergraduate grades were OK. I wasn’t as serious a student as an undergraduate as, looking back on it, I should have been. You know, that’s just the way it was. I had many other distractions. I actually chose Texas because it was the closest to New Orleans, and I could get there in a day’s drive. Again, my geographical horizon was very small.
Right, right. But you couldn’t stay in New Orleans to pursue a PhD in physics. That was not in the cards.
Well, it was possible, but I sort of slowly came to the recognition that there are better places that I could go to.
Yeah. Who were some of the professors that you became close with at Texas?
Well, my advisor Duane Dicus was a big influence on me and working with him was wonderful. We worked as collaborators rather than as a student and supervisor.
And what was Dicus working on when you met him? What were his projects?
Well, he was a particle theorist and he worked on quantum field theory and neutrino phenomenology. He was a phenomenologist when I started working with him. I took Quantum-3 from him, the first introduction to field theory, Feynman diagrams and the like. He was a really great teacher, and I really ate it up. I just ate it up. I just couldn’t get enough.
And probably you were exposed to a much higher level of physics than you ever got in New Orleans at Texas.
That’s right. And so I started working with Dicus and did a couple of problems. And he became interested in neutrinos and in neutrino implications for cosmology and astrophysics. And he was working with a collaborator, Vic Teplitz. At that time, Vic was Chair of VPI and he later went to the U.S. Arms Control and Disarmament Agency. Duane was a postdoc at MIT when Vic was an assistant professor, so they met there and we all worked together as collaborators.
So Dicus and I started a collaboration with Vic Teplitz, who I never met until much later. And we said, “Well, let’s think about what neutrinos can do in cosmology.” I had never taken an astronomy course. You know, I picked up astronomy on the streets. My first astronomy course was the first one I taught.
So together we learned cosmology, and I learned on my own general relativity, which was part of cosmology. And by reading books; in particular Steven Weinberg’s book Gravitation and Cosmology was a big influence—I read that cover to cover.
Rocky, looking back, was Dicus ahead of the curve in terms of applying particle physics to cosmological questions? Which became much more broadly adopted later on, but this is pretty early on, right?
Yeah. It was really in the first wave. And I think if I could speak for Duane—Vic Teplitz has passed away—we stumbled into it. I would love to say that with great insight I saw that particle cosmology would be an emerging field and I would be an early investor. But honestly, at that time I never thought, “Wow, this is going to be a great opportunity. This is going to be a field that will open wide and I’m going to get in on the ground floor.” So it wasn’t a strategic decision. It was “Hey, this looks like a neat problem to work on, let’s work on it.”
But it obviously had nothing to do with like the demise of the SSC and particle physicists looking for big answers elsewhere.
No, no. This was long before. And in fact, I would say until the mid-90s, maybe coinciding with the demise of the SSC, cosmology was frowned upon. It was not considered science. “Is it philosophy or is it science?” There are no predictions, and no experimental evidence. Well, there were predictions but no one did the experiments, so it was undervalued, I think, in hindsight.
But, you know, at the time, I just did what I loved—so the advice I give people like graduate students and postdocs who ask, “What should I do?” I tell them, “Do what makes your heart beat faster.” And planning, “This is going to be a great field to go in for the future, I’m going to go into that,” it may work out. It may not. But do what your passion tells you. Do what makes your heart beat faster. And in hindsight, that’s what I did. And I’d like to say, “Gee, you know, I had great vision and saw this field opening up,” but I can’t honestly say that.
How did you develop your dissertation? Did Duane give you a problem to work on that was related to his research or you developed this mostly on your own?
No. My 1978 dissertation was stapled together papers that we had written together. We were also the first people to look at the effect of axions in stars and in cosmology.
Were you calling them axions at the time or that’s a later adopted term?
No, I learned about axions the first time I had ever been on an airplane—actually the second time I had been on an airplane. My big journey in graduate school was to go to Fermilab to the Ben Lee Memorial Conference. So this must have been May ’77. And wow, I remember being blown away by Fermilab, never imagining I would one day work there.
And it was at Fermilab that Weinberg, and I think Wilczek, also talked about axions. It was sort of just coming out, and the name axion was there. So I went back and talked with Duane about it, “Gee, there’s this new thing, axions.” And somehow we said “Well, let’s see what happens in stars.” It turns out that it was again something we stumbled into. It was opportunistic.
Who else was on your committee?
John Wheeler. George Sudarshan. Charles Chiu, and Austin Gleeson. I was very close with Gleeson, although I didn’t actually write a paper with him until later.
And to the extent you were capable of such lofty thoughts or maybe your committee asked you this kind of question, what did you see as your contributions to the field with your dissertation?
Wow. I wasn’t asked that question and that’s a good question to ask. I’ll have to ask that. On Friday I’m going to be on a thesis to—
Uh-oh, I don’t want to get anybody in trouble.
I’ll blame you if somebody says, “Gee, that’s a mean question”.
But really it’s fundamental, right? Aren’t you writing a dissertation for the purposes of contributing to the field?
Yeah. So I had no great plan—I just wanted to do physics. I thought, “If I could write a paper, just one paper, making some incremental contribution, get a paper published, wow, that would really be something” I thought that would have satisfied me. Then I did that and then thought, “Well maybe I can get a PhD.” Well, then I did that. Then maybe I could do this, then maybe I could do that. I didn’t have any great plans or expectations. I sort of went along—I caught a wave somehow and sort of went along with it.
I said I caught a wave and was just swept along, but even if you catch a wave you have to keep your head above water. You have to stay on the surfboard or something like that. It’s not just, “Well, it just happened to me, I didn’t do anything.” It’s not just luck.
Well, another way of thinking about the question is what were some of the major questions in the field at the time and what did you see as your contribution in terms of answering them?
Well, one question had to do with dark matter and neutrinos. In graduate school we played around with massive neutrinos as dark matter. And also it was 1978 when I finished at Texas. The Weinberg-Salam Model was, to my mind, established, although it wasn’t really nailed down. Neutral currents were new. We wrote a paper on the effect of neutral currents in Type-II supernovae, again, as an opportunistic thing. So new particle physics was coming along, the Weinberg-Salam Model, neutrinos, and also the idea that finally people had accepted that quarks are real.
In cosmology before the mid-70s it was thought that there was something called the hadron barrier, and the temperature of the universe could never get above a typical temperature of hadron masses because the neutrons and protons and all these excited states of neutrons and protons were the fundamental particles, and as the temperature went up, the energy would go into making more and more massive particles rather than giving more energy to fundamental particles like quarks. So there was thought to be a hadron barrier, as it was known. So we realized, and other people did also, that there was no hadron barrier and you could talk sensibly about temperatures larger than the QCD scale.
What did you want to do after the defense of your dissertation? What were your prospects and opportunities?
Well, of course I had to find a job. I thought, “Well, I’ll go do a postdoc. I can continue doing physics.” I wanted to do whatever I could to continue doing physics because I loved it. I still do. There’s nothing I like better than doing physics. See, my wife’s not here to hear this [laugh]—but actually, there’s nothing I like better. I had applied to several places, and had a couple of postdoc offers Maybe a few people realized that what later came to be known as particle cosmology was an interesting thing.
I got a couple of job offers, but the one that was most attractive was from Caltech from the group Willy Fowler ran at Caltech in Kellogg Lab. Willy Fowler was a nuclear physicist who really was the person who started the field of nuclear astrophysics. Other people contributed, but he got the (1983) Nobel Prize for doing it, so another organization credited him with that. Willy Fowler is a person that I look on as the person who really did it. And, you know, I never really talked to him about it, but I think he stumbled into it the way I stumbled into particle astrophysics. You know, as a nuclear physicist, there were interesting applications of nuclear physics to astrophysics.
Hans Bethe had written his paper on the evolution on stellar energy, but it led to other questions, like where do all the elements come from? What happens in supernovae? Things like that. Anyway, Willy hired me at Caltech. Never quite sure why. And in those days, no one was mentored, at least no one I knew of was mentored. So I went in and talked to Willy my first week there and he said, “Well, yeah. Have a good two years. If you do anything, come see me.” You know, it wasn’t that cold, because he was a very friendly guy. Everybody loved Willy. And so at the time, I was interested in cosmology and interested in particle physics. Cosmology at that time—this was 1978 when I started as a postdoc—was disreputable. No real scientist did cosmology.
So I couldn’t decide whether to do cosmology or to really say, “Well, enough with cosmology. I’m going to concentrate on particle physics.” And of course at Caltech, Feynman was there at the time, and Gell-Mann. You know, it was a great place. So about the first month I was at Caltech, there was a series of lectures given by Allan Sandage, who was an observer. The great cosmologist Allan Sandage. He was the successor of Hubble. He was Mr. Cosmology I thought.
And he was out of the astronomy program.
Well, he was actually at Carnegie Observatories, which is also in Pasadena. The Carnegie Observatories had some official connection with Caltech at this time. Maybe he was on the faculty at Caltech, but he really was at Carnegie Observatories. So the great Allan Sandage gave a two-week series, maybe six lectures, on cosmology. And honestly, it was the worst lecture series I have ever been to. He wasn’t a great speaker, and I saw so many transparencies (young readers won’t know what a transparency is) that, to me, looked like graphs with random points scattered without error bars, and straight lines drawn through them. It was so empirical. Things like, the fourth brightest galaxy in a cluster is a standard candle, and so forth. It just seemed a mess. No real rigorous basis. It was all empirical. No understanding of anything. No real connection with physics.
So I said, “Well, enough of this. I’m not going to be a cosmologist. Now I understand why it’s so disreputable.” And then the next month, there were a few lectures on string theory. Now, this was 1978, maybe early ’79, before string theory was really established. I don’t remember who gave the lectures. It might have been John Schwarz.
Schwarz was one of the three people in the world working on string theory at that time.
John’s a great guy. Great lectures, very elegant, very beautiful. But I was not enthralled by the understanding of string theory at the time. And after one of the lectures, Murray Gell-Mann stood up and said, “String Theory is the future of particle physics.”
Gell-Mann said that?
Yeah, yeah. This was late ’78 or maybe early ’79. You know, I worshipped Gell-Mann and Feynman.
Was Feynman there also?
I don’t believe he went to the lectures. He was sort of skeptical of more formal things. So after my exposure to string theory, as it existed then, I said to myself maybe cosmology wasn’t all that bad. If this is my future in particle physics, I think I’ll stick with cosmology.
And yet, Rocky, what was it that sort of didn’t land home with you in terms of the lecture? In terms of string theory?
You know, it was a long time ago and I don’t really remember. It was very mathematical, very formal, and involved a lot of hand-waving. I don’t remember whether it was John’s lectures or not, it might have been a visitor.
But you might have sensed early on that there was a certain disconnect from physical reality, perhaps?
Yes, yes. So if I had been smart enough, I would have said, “This is the future of physics for the 22nd century,” and I would have worked on it in the 20th century. But it didn’t make my heart beat faster. So I think Gell-Mann was over-the-top (but perhaps correct) when he said, “This is the future of particle physics.” You know, there was the standard model, supersymmetry, things like that to do. But strings didn’t grab me. And is there a real logical reason why it didn’t excite me? I don’t know. It just didn’t. So I decided, “Well, I’ll stick with cosmology for a while.” And Willy Fowler, who technically was my advisor, was very supportive. Oh, and my neighbor in the office next door was Steve Koonin, who you know. So that’s how I met Steve.
Willy, Steve, and I were in the Kellogg Lab, a different building from the high energy physicists, who were in the Lauritsen Building, across the alley from Kellogg. And the Kellogg people were just incredible. Lovely, friendly, social. We had parties once a month. And there was a lot of singing, drinking; a lot of alcohol, and even occasionally something that is now legal in California, but at the time was not legal. It was a very social, open—and one of the things I learned from Willy Fowler that I think more people should learn; Willy had this idea that he could appreciate and value and really be proud of things that his students and postdocs did, even if he wasn’t involved in it.
Is that because he was a warm and generous person, just generally?
It had to do with his personality. We went to Dodgers games together and things like that. It was a very social place, it reflected Willy’s personality. Willy referred to us as “his boys”. Now, that’s not a phrase you would use now, and Willy actually was very good to Margaret Burbidge and other women; he did support women. But at Caltech, they had only just recently put a women’s restroom in the building.
It was ancient times. So he called us “my boys” and he was proud of us. And he valued and pushed us and inspired us. I wanted to do something good, but “Perhaps Willy will be proud of me”—you know, that kind of thing. And it’s something that is sadly not as widespread in our field as it should be. And there were many people who went through Caltech, through Willy’s group at Caltech. I could rattle off many names. John Bahcall, Bob Wagoner, Craig Wheeler, David Schramm, Gary Steigman, Dick Bond. There are many other names. Stan Woosley. I could continue to name people. George Fuller who’s now at San Diego.
And everybody loved Willy. And I remember one time when I was visiting the Institute for Theoretical Physics at Santa Barbara before it was a Kavli Institute. There was some program. And there was a lunch table and Stan Woosley was there, George Fuller was there, I was there, a bunch of Willy’s boys, and Gerry Brown, who was a professor at Stony Brook was there. And Gerry made the comment that, “Well, you know, Willy’s just done good things because he’s hired really good postdocs and students and it’s easy at Caltech. You get these great postdocs and students, that’s the key to Willy’s success.” And Stan Woosley stood up, red in the face. I thought he was going to punch him.
Shows how loyal people were to Willy.
Yeah. The rest of us just wanted to strangle him.
I’m sure Brown wasn’t prepared for the response he got. I didn’t really learn any physics directly from Willy. He was on so many committees and things like that in Washington that he wasn’t there all the time. But again, what I did learn from him is to value and appreciate and talk up the work of your students and postdocs.
And what were you specifically working on during that time?
Well, again, it was an opportunistic thing. I continued working on axions from stars. And then I went to a lot of seminars in the Lauritsen building, where the high energy theory group was. And at that time, people started talking a lot about grand unified theories, SU(5) and things like that. And one of the people I greatly admired was Steven Weinberg, and he had written a paper about grand unified theories as the origin of the baryon asymmetry, the asymmetry between matter and anti-matter, because baryon numbers violated the grand unified theories.
So somehow, I don’t remember how, I started working on this problem with Stephen Wolfram, who was the Caltech enfant terrible—you know, he was 16 or something like that, and a PhD student. I remember the atmosphere at Lauritsen among the theorists, the particle theorists, was very competitive, very—I don’t want to say cutthroat, but it was very competitive—"I have to look good for Gell-Mann and Feynman.” It was very competitive. Just sort of the complete opposite of the collegial atmosphere in Kellogg.
I was really happy. I was living in a collegial environment in Kellogg, although I spent most of the day in Lauritsen working with Wolfram and later with Jeff Harvey and David Reiss, who were graduate students there also. We became interested in grand unified theories and Wolfram and I wrote a couple of papers that were popular at the time on baryogenesis. This was a connection with Willy. What we did was to write down a reaction network for particles in grand unified theories, decays, scatterings, things like that, to produce a baryon number that was similar to what I was familiar with in nuclear physics networks. Like for Big-Bang Nucleosynthesis, there are nuclear reaction networks you write down where neutrons and protons produce this and that interacts with this. You put in the decay rates, the cross sections, and you put it on the computer and see what happens. Does that make sense?
And in fact, in graduate school I had written a paper or two with Dicus and Teplitz with Bob Wagoner, who was a professor at Stanford. Bob had written a code in the 60s for the Wagoner, Fowler, and Hoyle paper on Big Bang Nucleosynthesis. So I went to SLAC over the summer to go to the summer institute at SLAC and Dicus said, “While you’re there, talk to this guy Wagoner and see if you can modify his nucleosynthesis code with the effect of decaying neutrinos and massive neutrinos in cosmology.”
I went to Stanford. Again, that was a big trip for me, all the way to California. So to show you how travel naïve I was, this was August 1977 or something like that. You know, I’d only lived in Texas and Louisiana. In August in Texas and Louisiana, whether you think of it or not— I’m sure you do in Washington—when you leave an air conditioned building, you sort of brace yourself for a wave of heat and humidity. So I get to the San Francisco Airport in August and open the door to leave the terminal and it was colder outside than it was inside. It shocked me!
Mark Twain was right.
It shocked me. Anyway, I saw Bob Wagoner. He was very nice. And he gave me his deck of cards. This was when a computer program was an actual deck of cards—and it was in sort of a mess. He had run it in the mid-60s, I think in Cambridge. I seem to remember him giving me this deck of cards and random cards were falling out of the deck and the cards were out of order. Anyway, I finally got the code working, which I think impressed Bob.
I had worked with Bob Wagoner, and Bob Wagoner who had been a postdoc of Willy’s, one of Willy’s boys, so probably that connection helped me to get a job at Kellogg, because in hindsight, I wasn’t an obvious hire for Kellogg. Anyway, I had known about the nucleosynthesis code, the nuclear reaction networks, and told Wolfram, “Perhaps we can do the same thing with particle physics.” Actually, looking back on it, I did all the computer coding. I’ve written probably a dozen papers with Wolfram, who is a computer genius, and people are surprised that I did the coding.
Then to really get into the details of these elaborate grand unified theories that were being developed at the time, we talked with Pierre Ramond, who was at Caltech at the time, and tried to bring him into the collaboration. I’ll be facetious a little bit, Pierre said, “No, I want to play tennis. Talk to my student, Jeff Harvey,” which was the best thing to do. Jeff is really great. Harvey, and also another student of Pierre’s, David Reiss, Wolfram, and I wrote a bunch of papers. So that’s mostly what I did at Caltech. There were also other things that I did.
And what was your title there? Were you a postdoc or research associate? What was the affiliation?
I was a postdoc.
And it was a set term? Could you have stayed on longer?
Well, it was a two-year post doc. I didn’t think about staying on longer. When my time was drawing to a close I applied for a smattering of postdocs and faculty positions. Then, as now, it’s a couple of postdocs before you get a faculty position. But I applied to several places for faculty positions and ended up with three offers, which I was very happy about.
Rocky, I’m curious, as you’re on the job market and you’re thinking about the sort of niche that you would fill in the various departments, right, what did you see yourself as contributing in the way that you presented yourself for these admissions committees?
Boy, I wish I could tell you I had a grand vision. I just said, “This is what I’m doing. I think it’s pretty neat. I think there’s more to do in this field.” And at that time, and still a little bit now, there’s sort of an area between pure particle physics and pure astrophysics—particle cosmology--that has a foot in both camps. And I like doing both. So there was always the question at that time—not just in my case, but in other people’s cases—would you be hired by a particle physics group or an astrophysics group? Leon Lederman used to joke that I’m a “half-astrophysicist,” but that’s later in the story. In an astronomy department, an astrophysics group, would they hire you? “No. He’s a particle physicist.”
So it wasn’t always clear, but there were some organizations who either said, “Well, let’s take a chance on this” or “This looks like something to do.” After Caltech I also had a couple of postdoc offers, but the thing that for some reason attracted me most was to be an Oppenheimer Fellow at Los Alamos. It seemed exotic. People say, “You turned down three faculty positions to take a postdoc?” I wouldn’t advise my student to do that or my postdoc to do that, but again, I had no plan.
Was there really exciting stuff that was going on at Los Alamos at that time?
Yeah. The theory group at Los Alamos at that time, I don’t quite know about it now, was really good. Dick Slansky was there, who I had known from Caltech. Slansky was working with Gell-Mann. Geoff West was there at the time. And Terry Goldman, who was at Caltech at the time, had a permanent position at Los Alamos, so I knew him and wrote a paper with him at Caltech. So I’d known people there. And it seemed like a very friendly atmosphere. A little bit isolated, but a very collegial, friendly atmosphere that may be friendlier or more collegial than a typical academic department.
I went to Los Alamos and it was a strange thing to do because at that time, I was married and had two children. And job security was a concern. You know, I have to feed my family. My wife Adrienne was not working full-time. And for some reason, they don’t pay historians and archivists the way they should. I know you think it’s wrong, but they’re undervalued economically.
[Laughs] Thank you, I appreciate that.
And so it was, again, maybe not the most logical career choice. But I went to Los Alamos as an Oppenheimer Fellow. When I arrived they were just starting an astrophysics group in the Theoretical Division. This was all “in front of the fence.” No classified work or anything like that. And the person who was chosen to head this new group was Stirling Colgate, with whom I really hit it off. He was another mentor of mine, sort of a hand-off from Willy to Stirling Colgate. So I went there as a postdoc, and continued what I was doing. It was a very welcoming, collegial atmosphere where people appreciated what I was doing. And, like at Texas and Kellogg, there wasn’t the competitive cutthroat environment that is in many other places. And I liked that.
Did it feel like an academic department or did it feel like a national lab from your vantage point?
At that time, from my vantage point, it seemed like an academic department. There wasn’t a lot of bureaucracy and burden of administration that I think national labs are dealing with now. And I like the idea of national labs, although I enjoy teaching and I always thought, “Well, one day I’ll be teaching more.” I wanted to do physics and I think that’s the reason I went to Los Alamos as a postdoc rather than start teaching in a standard faculty position.
And did you continue working on axions or was this an opportunity to move on to other areas?
I moved on to other areas, other areas in sort of particle physics and cosmology. I don’t think I continued to work on axions. I continued to do some work on neutrinos and did some more technical work in radiative corrections to rates in Big Bang nucleosynthesis. Once Big Bang nucleosynthesis was very important and people really were leading the next generation of improvements on the calculations essentially that Wagoner, Fowler, and Hoyle did in the 60s. So this was sort of a complicated—radiative corrections through a bunch of rates. And it involved particle physics and cosmology, so I enjoyed doing it.
How long were you there?
Well, let’s see. I started there in 1980 and sort of landed there, we found a place to live, and then immediately went off for six months to Santa Barbara, to the Institute for Theoretical Physics. Then went back to Los Alamos, and I was an Oppenheimer Fellow for another year. And then Stirling Colgate said, “We’re going to demote you and make you a permanent staff member.” I said, “OK.” Because, you know, I was sort of wondering, “Do I have to look for another job?”
Rocky, who brought you out to Santa Barbara? What was the connection there?
Oh, there was a workshop on cosmology. I forget what it was called.
Would this have been a Jim Hartle connection?
No. Jim was there and I met Jim there, but it was more in cosmology. So the people who were there were Gary Steigman, Dave Schramm, and I met Mike Turner there for the first time, although we had been in communication before. Alan Guth, Paul Steinhardt. You know, it was this new generation of people working in cosmology.
That must have been a pretty exciting time for you.
Yeah, it was exciting. And in hindsight, maybe I didn’t appreciate—I thought this was the way things always happened, right? [Laughs] I didn’t have a ten-year plan. I didn’t really have a five-year plan. I was lucky if I had a five-week plan on what I was going to do next. So then I went back to Los Alamos and became a staff member and—
So you accepted that right away.
Yeah, because my wife and I were having a third child, and with three children, maybe a permanent job, a long-term job, is not such a bad thing to think about.
Rocky, did you see that as possibly meaning that going back into academia proper was not in the cards? Or did you see this more as a temporary opportunity? To the extent that you planned for such things.
Yeah, but I took the job and I thought there was some chance I’d be in Los Alamos for the rest of my career and that would have been fine with me.
Right, because that was a perfectly acceptable place to do high-level physics.
Right, right. And again, the theory group, my collaborators at the time, in my cohort, were Wick Haxton, who you may know, now at Berkeley and Stuart Raby. The Center for Nonlinear Studies was just pushing into nonlinear dynamics. That was very exciting. I didn’t work in it, but to see what they were doing, it was a vibrant place in the theoretical division. And I think I would have been happy there.
How long did you stay a staff member at Los Alamos?
Until September 1983 when I went to Fermilab. Sometime in late ’82 Leon Lederman came through Los Alamos to give a colloquium, and I met him and he talked about starting something in astrophysics at Fermilab. And that sounded interesting to me. Now, I had known David Schramm—my first paper that I wrote with Dicus also included Schramm. Schramm had left Texas for Chicago and I don’t think he ever read our paper, honestly. I had interacted with and known David Schramm and Steigman and Turner and people like that, the people at Chicago. So I guess they whispered my name into Lederman’s ear as someone to get to Fermilab.
So I met Lederman, talked to him, and it wasn’t immediately, “Oh my God, I have to be there.” But it was something like, “Hmm, you know, that sounds interesting.” And later on as it developed I got an offer from Fermilab to come start a group at Fermilab doing particle physics and cosmology and astrophysics.
Now, I was 32 years old at the time, and in hindsight, I would have said, “Lederman, what? You’re going to give the keys to a 32-year old to start this group? Are you crazy?”
And Rocky, had anything similar been started like that at Fermilab before or this was really new territory?
It was really new territory and it was not without some—not resentment---but some trepidation among more mainline particle physics people who thought particle physics is accelerators, and if you don’t use an accelerator, you’re not doing particle physics. People would remind me that the A in FNAL is Accelerator, not Astrophysics. But I always thought an accelerator is a tool. You don’t say, “A carpenter is a person who uses a hammer. If you don’t use a hammer, you’re not doing carpentry.” You know, there are other tools that you can use to get to the physics.
In the first year at Fermilab, Michael Turner—my partner in crime at Fermilab and thereafter-- took a leave of absence from the University of Chicago where I think he had just gotten a faculty position. We all lived out in the village at Fermilab—have you been to Fermilab? It’s about 30 miles west of Chicago and the University.
No, not yet.
There are some old white farm houses onsite that were put together into something called The Village. I lived in one, Turner lived in another, Dave Schramm lived in another. Roy Schwitters was in another because he was starting CDF at Fermilab. Paul Grannis from Stony Brook was starting D0. He was in another. And it was, again, I guess I responded to very friendly, open, welcoming environments. It was really an exciting, wonderful time.
And it’s really the beginning of a lot of fundamental work that was going on then.
Yes, yes. And it was fun. It was fun. I couldn’t wait to get to work every day.
Rocky, did you have a mandate? Did anybody sort of lay out what the expectations for you were? Or it was entirely—you made it up as you were going along?
We made it up as we were going along. Turner’s two years older than me. I guess he was 34, I was 32. We were hiring postdocs, remodeling offices, and building offices, doing this, doing that. And I kept waiting for someone to come around and say, “OK, you kids aren’t in charge, I’m actually in charge.” But we were left alone.
And the institutional support was there? They gave you what you needed?
There was great institutional support.
Where did that come from? Who set the tone from the top in terms of the environment and support?
I think it was Lederman. You know, it was Leon’s vision and Dave Schramm was involved in focusing his vision. But you know, it was mostly Leon. At National Labs in 1983, it was a softer time, and the director had a lot of discretion. And Fermilab had a huge budget compared to what we spent in the theoretical group on salaries and little bit of travel and visitors. It was infinitesimal compared to mounting an experiment or something. So it’s not like it was a choice, “Are we going to discover the top quark or do astrophysics?” You know, it never came down to that. We also has support from NASA.
But Leon left us alone and provided inspiration. And the life in that period at Fermilab was wonderful. My wife and I hit it off with Leon and his wife Ellen. We had many dinners at their home. Leon would invite a lot of people. Passing through Fermilab were senators, cabinet members, artists, professors here and there, various famous people. And Leon would entertain them at his home very often for dinners and cigars. I used to smoke cigars then. A lot of alcohol. It was just a great time filled with jokes, physics stories, and history.
What were some of the major research questions that you and your group were involved with at that time?
We sort of pushed into supersymmetry. More into dark matter. Phase transitions became a really pressing issue. Magnetic monopoles, cosmic strings (not fundamental strings).
Were you following string theory at that point? Was that still relevant for your work?
Modern string theory was just starting when we went to Fermilab, and it was something about which I scratched my head and said, “Hmm, that’s interesting. What can I do?” But I looked on it more as an opportunity. Are there things that are being discovered in string theory that I can apply to astronomy and astrophysics? There were a couple of things I did, but not very much. Perhaps there’s still not very much that comes out of string theory, but maybe there is. Anyway, that came later. And again, in the 80s, string theory was just finding its footing and was not as established as it is now.
But I became interested in other aspects of dark matter, neutrinos, neutrino oscillations, and I spent quite a bit of time with Michael Turner writing a book, The Early Universe. It just was the right book at the right time. It turned out to be a good seller—I’m not retiring on the royalties, but [laugh] at the time it was very influential. People still buy it for some reason I don’t understand. It was just opportunistic. Wherever we saw something that we could do we did it.
What were some of the really exciting things about the early universe at that point in terms of what was being discovered both on the experimental side and the theoretical side?
So going back—inflation was big, of course. I first was exposed to inflation back when I was at Caltech. Alan Guth came through and gave a seminar. And I said, “Hmm, that looks pretty interesting. I wonder what I can do there.” And later on I wrote several papers about it, Supersymmetry and Inflation and things like that. And I became interested in the idea that— motivated by inflation—the expanding universe can lead to creation of particles from the vacuum.
I later learned that this was first pointed out by Schrödinger in 1939, and then ignored. It wasn’t referenced for 20 years, in fact 30 years, until the late 60s when Leonard Parker started working on it. The idea is that the expansion of the universe affects the virtual particles in the vacuum, and the virtual particles can be caught in the expansion of the universe and become real particles. That’s sort of the hand-waving way I describe it. That interested me since it has an application that it is one way to understand the origin of the density perturbations produced by inflation.
It brings quantum field theory in particle physics into general relativity in cosmology. The three things I’m interested in are general relativity, cosmology, and particle physics. I’m just lucky that I live in an era where the three can work together.
Again, going back to 1970s or so when I was in graduate school, there were people in general relativity who wrote papers on cosmology; but that was more from a general relativity perspective—and there were some astronomers who worried about cosmology from an astronomy perspective—but particle physicists really did not. And the first person who sort of legitimized the field of particle cosmology I think was Steven Weinberg who did both. And it was—“Well, if Steven Weinberg can do it, it can’t be too bad, right?” It’s respectable if respectable people do it.
For sure. Rocky, was your sense that—was general relativity undergoing a renaissance to some degree at this point?
No, I think general relativity at that time, that time being the 70s and 80s— as I look back on it, was in a sort of a mathematical, dry, dusty period. Very formal and mathematical. It wasn’t until recently that people really started taking general relativity into other fields—looking at gravitons and the quantization of general relativity, and string theory’s played an important role in that. So I think general relativity is different now than it used to be.
Chicago has a great tradition of general relativity, going back to Chandrasekhar, Bob Wald, Bob Geroch. But now the idea of hiring someone who only does general relativity is not something that people do. You hire someone who does general relativity and black holes, or general relativity and gravitational waves, or general relativity and string theory. So general relativity is now more enmeshed in other fields of physics than it was in the 70s. I don’t know whether that made sense to you or not.
Absolutely. Absolutely. And so what happened next? Where did the field go from there?
So general relativity?
I mean in general. The work that you were doing at Fermilab.
Oh, phase transitions was something that we worked on and were very interested in. These were cosmological phase transitions where symmetry is broken, producing topological defects like cosmic strings, magnetic monopoles, or domain walls. Texture could be produced in cosmological phase transitions. It was a huge industry then and I think it was really centered at Fermilab. I think Fermilab became, starting in 1984 through 1990 through sometime later, the center for particle physics in cosmology. We, I think, had the largest group and I think we were the most influential. I tried to follow Willy Fowler’s example and value the work of others. We had many postdocs and students, and I really appreciated and valued and talked up and enjoyed their accomplishments. So enjoying the accomplishments of others is something that many physicists find difficult to do.
[Laughs] Rocky, when did you know it was time to move on from Fermilab and pursue other opportunities?
When I went to Fermilab in 1983, it was always with the idea that I would have a connection at the University of Chicago.
Right. That was built into the arrangement.
That was built into the offer. It started out as a part-time professor at the University of Chicago and then—
And you were teaching, Rocky, right from the beginning?
Yes. A reduced teaching load, of course, because I had other responsibilities at Fermilab, but I started teaching in 1984. I started teaching the usual things. At that time if you’re a new person, you teach a special topics course. Then I became interested in teaching core courses, cosmology for non-science majors. Cosmology for Poets, or whatever. And it turned out I really enjoyed that.
And sometime probably in the mid-80s, late 80s, I made the transition between a part-time professor and a tenured position—so the part-time was removed. I had tenure at Chicago and tenure at Fermilab, but it didn’t really make any day-to-day difference in what I did. But my engagement at the University of Chicago continued to sort of adiabatically grow. I had students from Chicago and postdocs. Some postdocs were hired jointly at Chicago and Fermilab. By this time, Michael Turner was no longer officially on leave at Fermilab. He had returned to the University of Chicago, but he would still occasionally come out to Fermilab and we’d work together. Our idea was if you fly over Chicago at 10,000 feet, you don’t really know whether this person is at Fermilab or the university? We were just one big Chicagoland group.
And I went into the Astronomy and Astrophysics Department. Maybe I’d just always gone where I thought it would be a welcoming, collegial environment ‘cause—
Yeah. There’s a theme that’s developing here I see.
I hadn’t really thought about that until now, but it really was and still is a very collegial, friendly place. And not competitive. People appreciate the work of others. In some departments, I don’t want to name any institution in particular, you know there are wars between the condensed matter physicists and the high energy physicists. There are wars between this group and that group. There’s nothing like that in the Astronomy and Astrophysics Department at Chicago. It’s smaller and it’s really a wonderful group.
So I started teaching more—I started learning astronomy by teaching it, which is a great way to learn things. And my involvement at the University grew adiabatically. My research center before around 2006 was really at Fermilab. Our home was close to Fermilab. I would drive in to Chicago to teach or for faculty meetings and things like that. That got a little old. I was spending too much time in traffic. It wasn’t a productive way to live. I was also involved in external committees for NASA, NSF, and DOE, in addition to a lot of travel to speak at various places.
At some point in early 2001 or so, my wife Adrienne and I, together with Leon and Ellen Lederman, went in together and bought a little pied-à-terre in downtown Chicago. Leon was living at Fermilab but still doing a lot of things in the city. He wasn’t officially at Fermilab, he was at IIT, Illinois Institute of Technology, and he was driving back and forth a lot. Leon, when he was young, was a terrible driver. His driving skills did not improve with age. The idea of him driving back and forth between Chicago, between the university, IIT in this case, and Fermilab, made Ellen nervous.
Anyway, we bought this place downtown together, and if I had to teach, I would wait until after dinner at home in Warrenville, and when there was no traffic drive in and spend the night there and then just jump to campus the next morning. That led to a little bit more engagement at the University of Chicago.
Then in 2006, I got a call from the Dean of Physical Sciences, who said, “Your colleagues and I want you to be Chair of the Department of Astronomy and Astrophysics.” I thought about it for a while. And you know, again, this was not a long-term plan of mine, but there were a couple of reasons to do it. One reason is our children had gone off to college, and we were spending more time in Chicago…the symphony, opera, theatre, dining, things like that. The western suburbs were great places to raise a family. You know, when people say that, it means you really don’t want to live there unless you have a family. So the city of Chicago had some allure for us. And maybe we decided we wanted to live in Chicago. It was clear that I couldn’t be chair of the department—when you really have to be there—and live near Fermilab.
So I transitioned to Chicago—it wasn’t much of a transition. I was already a tenured faculty member, so I just took my toothbrush and went to Chicago and started there as chair of the department. And so that’s been my academic home since 2006.
Was that an interesting transition, going from part-time right to running the department?
There’s an expression in New Orleans around Mardi Gras--where there are parades with elaborate, expensive floats. The floats are recycled and appear in different parades because they’re so expensive to build. So there is a phrase, “Same floats, different parade.” Well, you know, I was mired in some administrative position almost my entire career. Director of this, head of that, always leading something. So the administrative thing wasn’t a big change. I wasn’t teaching anymore because there is teaching relief when you are chair. And my administrative work was then at Chicago rather than at Fermilab. It was “same floats, different parade.”
What did you see as some of your key opportunities and challenges running the department at Chicago?
There were a couple of things. One was access to optical telescopes. Through its history, Chicago either has had access to front-line optical telescopes, or not. I thought about it and asked, “What do we have to do at Chicago to really improve the department?” The department at Chicago is very physics oriented, but it is an astronomy and astrophysics department, and we did not have access at that time to really top telescopes. So our optical/infrared observing was really not very strong. I wanted to build that up. To do that, you need access to telescopes. In astronomy, optical telescopes are run in a different way than particle accelerators. The access is really through privately owned telescopes.
There are various consortia that operate these large telescopes. So we would have to spend money to buy in to have access to a large telescope. If you don’t have access to a telescope, you can’t hire faculty members, you don’t get students, you just can’t do it.
Part of it was building the case to the University administration for a large investment in optical astronomy. And I was successful doing that, raising some external funds, getting some funds from the university, getting the president of the university excited about optical astronomy. So that was something that I thought was an accomplishment. And now we have a very good, very active, optical astronomy program.
Another thing has to do with our building. The astronomy and astrophysics department in Chicago started in 1893 at Yerkes Observatory, which is 90 miles away on Williams Bay in Wisconsin. That was the home of the astronomy and astrophysics department where they built Yerkes Observatory in the late 1890s, at the time, the world’s largest telescope. And so there was never a real building as home for astronomy and astrophysics on campus.
Slowly, faculty started migrating from Yerkes to campus, because the telescope was basically useless for research. We mostly occupied a building that was originally built in the 1950s to house a computer. We really didn’t have adequate building space. We were spread out over 4 buildings on campus. So Bob Zimmer, who was president—and is still president of the university--was ambitious in building, and we worked together to start and to end up finishing a large building that now houses astronomy and astrophysics along with aspects of the Pritzker Molecular Engineering Institute.
Getting 21st century facilities for our department was very important. And it was, not a struggle, but you have to keep your eye on the ball about how much space you get, where the rooms are, and things like that. I didn’t become an architect, but I did a lot of worrying about the right kinds of space.
Also, I started fundraising for fellowships, for lectureships, and things like that in a department that hadn’t really done that before, and was pretty successful. And we expanded and did a lot of hiring. At a university, every department feels they need three more faculty members immediately. I managed to do it.
What were the strong points or weak points in the department that may have informed the faculty hires?
Well, I think a weak point was optical/infrared astronomy. And it’s a combination, it’s a chicken and egg thing. You need the facilities to get the faculty, then well why do you need the facilities if you don’t have faculty? But Zimmer’s a smart guy and he was able to grasp this immediately.
So optical infrared astronomy was weak. And probably every department will say, “You know, our graduate students aren’t as good as they should be. We should be getting better graduate students.” I think we started recruiting graduate students whereas before, Chicago had this attitude, “Well, we’re really good. If people don’t apply or don’t come, that’s their problem.” No, it’s our problem. I hopefully changed that mindset.
And were you seeing that top graduate students who might otherwise have come to Chicago were going elsewhere? Was that part of the issue?
Yes. So every student we really want also has offers from one or two or multiple other competitive institutions.
And so what’s the hook? What does Chicago offer that you would tell those kinds of students?
Well, part of it is trying to get the students to get the idea that we want them. It’s recruiting, right? The idea that, “Oh yeah. You can come here. Good.” That doesn’t work. “Come here and it’ll be great.” It’s a slow thing, right? You don’t immediately change things overnight. And also advertising the department. Not taking out ads in USA Today or anything like that, but becoming more visible. And also getting optical/infrared access is something that attracted more students. We can also use the allure of the vibrant city of Chicago.
It’s something we continue to work on. We’re still not where we want to be. I don’t think anybody should ever feel that they are where they want to be, but we’re continuing to work on it. Another thing that’s helped us recently is having a new, modern building rather than an old tired building. You try to recruit someone doing precision optical physics—optical, solid state, something like that. And you show them the lab that they’re going to have to do their precision experiments, and they ask, “Well, what’s that in the corner?” And you say, “Well, that’s the rat trap.” It doesn’t give a good impression. “Yeah I’m going to go there and do precision experiments in a lab that has rat traps and the paint’s peeling off the wall, the plumbing doesn’t work.” So I think the building’s important.
And also we’ve recruited some pretty good faculty, starting from when I was Appointments Committee Chair and Department Chair and Dean. I’ll mention two. We recruited John Carlstrom and Wendy Freedman. Wendy Freedman has really given exposure to our optical astronomy program.
Rocky, to the extent you were able to keep up your research as Chair and then afterwards, what have you been working on in more recent years?
I have continued to work on this idea of creating particles from the vacuum and I think it’s a very rich phenomenon. Right now I’m interested in the idea of making dark matter that way. I think this is really a good time to do it because dark matter has not been detected at the LHC. It has not been detected in underground experiments—the direct detection underground experiments—and many of us, myself included, sort of expected it to be.
So people are scratching their heads and then the question comes up, since the only thing we know about dark matter is that it has gravitational interactions, what if it only has gravitational interactions? How would you produce it in the early universe? I think the most promising way is through this idea that Schrödinger came up with in 1939. Now of course he didn’t talk about dark matter, but that’s really what I’m spending most of my time on.
Rocky, do you see your investigations into dark matter as yielding promising results for the future of dark energy as well? Or do you tend to think of them separately?
I don’t see a direct connection now with dark energy, but you know, the vacuum is something that we don’t understand. The vacuum’s involved with dark energy, we think. And creating particles from the vacuum may—if we learn more about the vacuum, we may learn something about dark energy. So I don’t see a direct connection now, but eventually hopefully they’ll be tied together.
Do you tend to think of what’s most important in terms of making these discoveries as a combination of theory and advances in instrumentation and experimentation? Or do you think of those separately also?
No, I think it’s very healthy, of course, when there’s an interplay between theory and observation. And the observations and experiments depend upon instrumentation. And right now in cosmology, as opposed to what it was in the 70s when I started, are tremendous instruments and facilities being built for cosmological research. Large telescopes like the LSST, the Vera Rubin Observatory in Chile that will be mapping dark matter and dark energy, and these incredibly technically advanced dark matter detectors that people are putting underground. And all sorts of satellites—JWST, Hubble Space Telescope—all doing astronomy that’s connected with dark matter distributions. What can we learn about dark matter from astronomy? Accelerators also, what can we learn about dark matter from them?
So it’s really, right now, the culmination of things coming together in ways that, if I had been really smart, I would have dreamed about in the 70s or 80s, but I didn’t imagine then how remarkably broad and deep cosmology would become.
Yeah. I wonder, Rocky, if you can reflect on—we talked earlier about how in many ways you were at the vanguard as a graduate student with this early dual approach to particle physics and cosmology. How has the field changed when that became a lot more—I don’t know what the right word is, fashionable? More common to think of it in those lines? How has the world changed where we had this influx of particle physicists, you know, particularly in the 1990s and going forward—how has the field changed as a result of that?
I think it’s really healthy now because of that influx. And I think that there’s a migration going on now from collider physics, which is still very active and important, to cosmology as the place to test new ideas in particle physics. We just went through an exercise in Chicago of hiring someone doing particle physics and cosmology. We had, of course, many, many applications. And after reading 200 some odd applications, I came to the conclusion that every particle physicist, at least every phenomenologist, does cosmology. It’s part of their tool chest now. And the idea that “I only do accelerator physics” or something like that is just very rare to find now. So cosmology is really now mainstream in particle physics.
Sometimes I feel like maybe I was at the head of the wave before; now suddenly I’m being run over by a wave of particle physicists, because so many more people are doing it now. When we started this in the late 70s, 80s, in times like that we could have a meeting of a hundred people and have everybody who works in the field. Now it would be thousands.
We’ve talked about it going in one direction, but in what ways has cosmology advanced particle physics in terms of the advances that have been made in cosmology?
Yeah. So in terms of—I’m sorry, which ways have particle physics advanced—
No, we’ve talked about the ways that which particle physics have advanced cosmology, but going in the other direction, in what ways has that advance proceeded?
Well, I’ll give one example (about astrophysics more than cosmology): solar neutrinos and neutrino oscillations and things like that. The first indications of neutrino oscillations came from astrophysics. Either cosmic neutrinos or neutrinos from the sun. And that has sort of opened up a new range, a new mass scale in neutrino physics.
There are also many limits from cosmology on the properties of particles, lifetimes of particles. Axions are an example. The limits on axions, both from axions from the sun or stars, emissions of axions from stars, or axions in cosmology not producing too many axions to exceed the dark matter density, really limit the range of masses and interaction strengths of axions. So people who build laboratory experiments to look for axions are guided by cosmological and astrophysical limits on the mass and lifetime and interaction strength of axions.
And there are other examples I can point to, but maybe neutrinos and axions are simple examples of how astronomy, astrophysics, and cosmology have influenced particle physics.
Rocky, have you been involved or following neutrino projects like AMANDA or IceCube?
Yeah. I follow them. I don’t work in that field now. I’ve written a couple of papers about it, various things that I’ve forgotten about. I was on an advisory board for IceCube for a while. I may still be, I don’t remember. So I’ve been following that. That’s something that’s interesting but hasn’t impacted my work directly yet. But you know, I got into cosmology through neutrinos and neutrinos are still pretty interesting in astrophysics and cosmology. And of course in particle physics.
Right. In many ways, it’s sort of the glue that binds them all together.
Rocky, one aspect of your career we haven’t talked about so much, particularly during your time at Chicago, is your work as a teacher to undergraduates and as a mentor to graduate students. So first, on the undergraduate side, what have been your most enjoyable courses to teach undergraduates?
I teach, maybe every other year, a class that’s a course people can take to satisfy a core requirement at Chicago. They are undergraduates who are economics majors, whatever, you know, the whole gamut. And it’s also the first course for an astrophysics major. It’s essentially a course about the Big Bang. And our students in Chicago, the undergraduates in particular, are really good. So I can do some things that are pretty advanced. I enjoy doing that, trying to reach audiences that I think need to be reached.
My motto for the class, particularly for those who are not going to be science majors, is “It’s your universe too.”
[Laughs] That’s great.
So I love it, I work on cosmology for a living, but it’s your universe too. You can understand it.
Whether they pursue a career in physics or not, you want to convey that.
I think that every educated person should have some idea of the age of the universe. How old is the universe? How do we know the age of the universe? Why is there a universe? What’s in the universe? What it’s made of? How do we measure the universe? These are things that every educated person should know. Just as every educated person should know concepts in physics. People should have some idea about the Second Law of Thermodynamics.
In the course I talk about relativity. Of course relativity, particularly general relativity, can get very technical and mathematical and difficult very quickly, but understanding the Equivalence Principle is something anyone can understand with a little effort. Understanding the two postulates of special relativity is something that does not require mathematics. It can be understood by most people. What is quantum mechanics? It’s something every educated person should know. My goal in this class is to reach this audience of very smart people who may not have a great understanding or love or appreciation of science and to try to get them to come to the conclusion that it’s their universe too.
Rocky, in what ways is the metaphor Big Bang useful in teaching undergraduates and in what ways does it cause sort of more confusion than you’re prepared to try to resolve?
[Laughs] I think it causes more confusion among scientists than among undergraduates.
I went to a talk a decade ago by a mathematical relativist and when he spoke about the Big Bang, he meant the initial singularity. What happened at temperature of 10 to the gazillion degrees, he didn’t really care about. He meant the Big Bang in a different way than I did. I think it’s a good name. It’s a sexy name that gets people excited. There are misconceptions that undergraduates have, in fact most people have, even some scientists, perhaps many scientists, that the Big Bang happened at a point, and it’s an explosion of galaxies into space. That’s not the Big Bang. It’s an explosion of space between galaxies, not an explosion of galaxies into space. To get that concept across to non-science majors is a challenge, and I enjoy that.
What about the challenge of explaining how, you know, for somebody that might be inclined to think that the universe implies a creator, how might physics offer a counter-narrative to that?
Yeah, it does offer a counter-narrative. I’ve never—surprisingly---in 30 years of teaching this, at Chicago at least, really run into the, “What about the creator?” question. I’m sure some students have that question and are maybe too shy or intimidated to bring it out publicly, but even privately, it hasn’t come up. I keep waiting for it to come up. Sooner or later it will.
Well, pretend it just came up. What’s the answer, in your mind?
I see a division between science and religion, as many people do, and once you start saying, “Well, I don’t understand this. It was the creator. That’s the way God wanted it,” it ends your investigation into that subject. And I object to what’s called “the God of the gaps.” You know, “We don’t understand this, therefore there’s a God.” That, I think, is a very dangerous path for a scientist to take.
There are words that I think scientists should not use. I wish I could say I never use them. One word is “believe”. “I believe this.” “Belief” is, I think, a word that we should not use. Another word is “I know”. “Know” is a word we should use very sparingly.
I give a lot of public lectures, sort of inspired by public lectures by Leon Lederman, who I think played a large role in the community in legitimizing public outreach and public lectures. And occasionally in public lectures I’ll get a question, “What about God?” And I’ll say, “Well, no one asks the Pope about quantum gravity, why are you asking me about God?”
You know, it’s not an answer, but I often do that to get a laugh and try to get out of it. So you didn’t mention just now, sort of skirting around it, the idea of public outreach, which has been a big activity for me. In the 70s and 80s when I was just starting, the idea that if I would be interviewing to be hired as an assistant professor and somebody said, “What do you want to teach?”—and I said, “I want to teach non-science majors. General physics and non-science majors,” I would have never been hired. The correct answer would have been, “I want to teach graduate students special topics and this and that. The most advanced things.”
It used to be thought that if you spend effort and time in public outreach, it’s a waste of effort and time and you’re over the hill—it means you can’t do science anymore. And I think Leon Lederman was very important in changing that perception—and other people too—Steve Weinberg I mentioned—have been really important in changing that. Carl Sagan going back before that, but that’s a little bit too early.
Yeah. I might suggest that now, where we have a crisis in science communication with regard to the coronavirus crisis, generally the importance of conveying scientific concepts is quite high, maybe as high as it’s ever been.
Yeah. You see on the television every day people talk about exponential growth. How many people know what an exponential is?
Right. [Laughs] Exactly.
So I think public outreach is now generally valued and honored in our community. It wasn’t before. That doesn’t mean everyone should do it or has to do it. Frankly, there are some people who shouldn’t do it, but people who can, should. And they should be respected and appreciated for what they do.
Well, Rocky, for the last part of our conversation, I wanna ask you a few sort of forward-looking questions, and the first is, what do you want to accomplish personally with your research agenda going forward?
Oh, I want to discover dark matter, understand dark energy, and come to understand the particle physics behind inflation.
That’s all. Yeah. I have no great ambition. If I could just do those three little things, I would be happy.
Of the three, what are you most bullish on?
Dark matter at the moment.
Well, I sort of got into the game with neutrinos as dark matter. And about every other year I propose a candidate for dark matter. And now this idea that dark matter comes from the vacuum by the expansion of the universe excites me. Makes my heart beat faster. I’m looking for a way—it’s certainly plausible—to find an experimental handle or observational signature of it. So that would make me pretty happy.
[laugh] And we talked a little bit about this before, but what needs to happen in dark matter, both on the theoretical side and the experimental side, for this to get closer to where you hope it’s going?
Some evidence for dark matter would be really amazing. Ten years ago, when I gave public lectures about dark matter, I would say, “We’re looking for dark matter at accelerators. We’re looking for dark matter underground, direct detection. And we’re looking for dark matter by something called indirect detection, looking for the annihilation products of dark matter say from the center of our galaxy.” And 10 or 20 years ago, I would say, “We’re really going to discover it—it’s going to be a great time. We’re going to see evidence from all three techniques and it’s going to be a great time trying to figure out how to put together these three pieces of evidence into the real answer.” Well, none of those pieces of evidence have, so far, shown through. Which surprised me, disappointed me, but I keep calm and carry on.
Do you see the ongoing mysteries of these areas as speaking more broadly to our inability to come up with a grand unified theory of physics?
Yeah, or at least a theory beyond the standard model. One thing that would really be a big break in cosmology is the discovery of physics beyond the standard model. We had hopes when LHC started operations that they would discover supersymmetry. Physics beyond the standard model that would open up an incredible number of applications in cosmology from inflation to dark matter to dark energy. But so far, there’s been no indication of supersymmetry or any other physics beyond the standard model.
If the ILC ever came online, do you think it’s possible that supersymmetry would be found there?
There are two approaches. One is to increase energy, say to what the SSC would have had, and another is to do precision experiments at lower energy, and that’s sort of the ILC plan, or what they’re planning at CERN or at least what they announced at CERN. Lower energy, more precision measurements. I don’t know which one would be more fruitful. In the past, I think it’s been higher energy, but maybe that path has stopped now.
And also, CERN has discovered the Higgs. It still is sort of the missing piece in the puzzle of the standard model, but it’s an odd piece. Its mass is telling us something because it’s right on the borderline of vacuum stability. What is that telling us? It’s telling us something, but I don’t know what it is. Other people are trying to figure that out. I’d like to know what it is. So doing precision experiments with the Higgs is something that’s an opportunity for the future.
So there are future opportunities. All of them are big and expensive and I don’t know whether we’re going to be able to do all of them.
Now, Rocky, on the mentoring side of your career, I wonder if you can talk sort of generally about what are some of the shared characteristics of your most successful graduate students? In terms of their attitude, in terms of their interests, in terms of the way that they approach physics?
Oh, I don’t know if you could just narrow it down, say “these are the three things you have to have” because they have been different. But first of all, they all have to have passion. They have to have the fire in the belly to do science. If it’s something like, “Well, am I going to do physics or am I going to do this or that?” that’s probably not good—you know, it has to be a consuming passion. And I’ve had students who have been more on the phenomenological side, I’ve had students who have been more on the theoretical side, and it takes both and I’ve had students who have been successful doing all of them.
And some of my students have gone on and concentrated on teaching. In addition to students, I would also include postdocs in that because, I don’t know, I lost count, but we must have had 30 or 40, probably more postdocs come through Fermilab when I was there. Many of them have gone on to populate cosmology. And I’ve tried to mentor them by encouraging them, and again, appreciating and valuing what they do, what they have done, their accomplishments. And you know, I have been surprised. There have been students I thought had really all of the tools and never really built anything, and some students I didn’t think would excel and end up being great.
So it’s really hard to judge. It comes from the consuming passion inside and it’s hard to look at somebody and tell—looking into someone’s soul is something I have difficulty doing. First of all, I don’t think there’s a soul and I don’t know where to look for it. I think that’s really the thing. And I really try to see if people are really consumed by science.
Yeah. Well, Rocky, that’s a great segue into my last question which is a lot of our talk in the more recent minutes has been on the enduring mysteries in physics and what you hope to discover, but reflecting over the course of your career about those things that have risen your own heart rate, that have inspired your own passion, what—and this is speaking personally and as a representative to the many fields that you’ve been involved in—looking back over the course of your career going all the way back to graduate school to today, you know, on the opposite side of mystery is true understanding and discovery, what jumps out at you as something that physicists really understand about how the universe works today that might have been a mystery in the mid-1970s?
Well, I would say the standard model of particle physics. The fact that it explains so much, that gauge symmetries seem to be fundamental and symmetries in general, that we may have the fundamental particles that are most responsible for making the world around us. I don’t know if in the mid-70s people would think that—I guess this was in place by the mid-80s; this was a really rapid advance—that we’d have such a deep understanding. That doesn’t mean we can calculate everything, in particular, quantum chromodynamics at lower energies, lower mass scales, becomes very difficult, non-perturbative and things like that. That doesn’t mean we can calculate and understand everything, but we have the conceptual framework.
And the fact that except for dark matter and dark energy and inflation, except for these three things that come from cosmology, there’s nothing in our world that we think cannot be explained by the standard model.
That is pretty remarkable. It’s also a curse.
[laugh] In what ways is it a curse?
Much more effort in getting beyond the standard model, that’s important.
Right. Well, Rocky, on that note, it’s been a great pleasure spending this time with you. I wanna thank you so much for sharing all of your insights with me and to state the obvious, this is gonna be a truly important addition to our collection as the Niels Bohr Library, so I really appreciate it and I’m so happy that we connected.
Thank you. It’s been really great talking to you.