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Courtesy of Christopher Stubbs
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Interview of Christopher Stubbs by David Zierler on August 11, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Christopher Stubbs, professor of physics and Dean of Sciences within the Faculty of Arts and Sciences at Harvard, is interviewed by David Zierler. Stubbs recounts his life moving around as the son of a U.S. Foreign Service officer and the decisions that led his mother, as a single parent, to move to Iran where he attended high school. He explains the circumstances that led to his enrollment at the University of Virginia for college and his clear decision to focus on experimentation and the considerations that led to his graduate work at the University of Washington. Stubbs describes the excitement surrounding Ephraim Fischbach’s work on the Fifth Force, and working under the direction of Eric Adelberger on signal noise calculation for a torsion pendulum experiment. He conveys what it felt like to be at the center of research so fundamental that it was fair to ask, “was Einstein right?” Stubbs explains how a talk by Michael Turner motivated him to pursue dark matter research as a postdoc at the Center for Particle Astrophysics at Berkeley, where he pursued research in optical wavelength observational astronomy. He describes his first faculty appointment at UC Santa Barbara where he worked on the MACHO project, and the financial constraints that led to his decision to accept a tenured offer back at the University of Washington. Stubbs discusses his research on supernova cosmology projects and his happiness at being in Seattle, and he explains the pull that led him to accept a faculty offer at Harvard. He describes his work as department chair, he deflates the myth of the bottomless money well that is Harvard’s endowment, and he describes his shortcomings as chair in promoting diversity in the department while emphasizing the importance of this work in his capacity as Dean. Stubbs describes the circumstances that led to him becoming Dean, and he surveys some of the key challenges he has encountered in this role. He explains how he has been able to maintain a research agenda, and he reflects on his accomplishments as an undergraduate teacher and graduate mentor. At the end of the interview, in surmising his post-Dean life as a full time physics professor, Stubbs points to the need for a more complete intellectual framework of physics that is based on astronomical data as a broad-scale method to pursue the kind of research he hopes to accomplish.
OK, this is David Zierler, oral historian for the American Institute of Physics. It is August 11th, 2020. I’m so happy to be here with Professor Christopher William Stubbs. Chris, thanks so much for joining me today.
OK. So to start, would you tell me please your title or titles as it might be and institutional affiliation?
I’m on the faculty at Harvard university in the Department of Physics and the Department of Astronomy and I also currently serve as the Dean of Sciences within the Faculty of Arts and Sciences at Harvard.
When did you become Dean of Sciences?
This is year three.
This is year three. Are you beginning to regret this decision in our current time of pandemic?
Didn’t sign up for what we’re doing, never a dull moment.
OK Chris, let’s take it back to the beginning. Tell me a little bit about your parents and where they’re from.
My parents met when my father did a junior year abroad in the United Kingdom in the early 1950s at the London School of Economics where my mother was also a student. They eventually married. My father served in the US military in Germany. I was born in Germany in 1958.
Now your father’s American and your mother’s British?
Yes. My mother eventually became a naturalized US citizen. My father was a foreign service officer. My mother was a foreign service wife for many years. They were eventually divorced and she became a school teacher.
How old were you when you left Germany?
About three months old. I can cry in German.
And where did the family go after that?
My father did a few tours in Europe. They moved to Paris. He was still in the US military at that point. He eventually joined the US Foreign Service. They did many different tours in Asia. Given my father’s command of Hungarian—because when he was in the military, he was running spies into Hungary on behalf of military intelligence—given his command of that European language, the State Department sent him to Asia as a foreign service officer.
And so he did tours in Asia, in Cambodia, in Vietnam, and we were in fact living in Vietnam when the US government entered the Vietnam war militarily. So when the troops landed on the beach in Vietnam, all dependents were evacuated. And at age, it must have been eight, we moved to Bangkok and then Hong Kong. My father did multiple tours in Vietnam as a press officer and a propagandist for the US government.
Their marriage was eventually a minor casualty of the Vietnam War. They were divorced. My mother, at the time, was living with us in northern Virginia, and decided with her earning power, we’d have a better life abroad than in the US and she uprooted her young family and moved to Iran.
So my mother, my younger brother, myself—when I was around ten years old—moved to Iran and I attended the high school at which she taught, the Iranzamin International High School which had an International Baccalaurate curriculum. The language of instruction in the classroom was English, but the de facto language in the playground was Farsi. I had a remarkable adolescence in Iran.
I left there at age 17 to come to the US to attend university because interestingly, at that time, if you were born overseas with one foreign parent and did not reside continuously in the US for four years between the ages of something and something, you lost your US citizenship.
And since I was not born in the US, I didn’t have a birthright to US citizenship, you can’t be a German citizen if you’re born there. So I was running the risk of becoming a stateless person traveling on UN papers if I didn’t come to the US to go to college. My younger brother, the rascal, was born in the US and so qualified for a US passport, and by the time he turned 18, you could become a British citizen maternally. When I turned 18, I couldn’t. So he was gonna get two passports and I was gonna get zero, which although on average works out, I thought wasn’t quite fair.
So I had no choice but to come to the US for college and did that at age 17 and had a nearly terminal case of culture shock. It turns out if you parachute into the US speaking unaccented North American English, everyone thinks you know the culture. There were some remarkable culture shock experiences for me in that first year. I went to the University of Virginia as an undergraduate in Charlottesville.
Now, I want to go back for a second. When you said your parents’ marriage was a casualty of the Vietnam War, did your father want to continue living that life and your mother simply did not?
You know, I don’t know what the details of that break-up were. I think just—
Did your father continue in his career?
He did, yeah. He continued as a foreign service officer. In fact, interestingly, he was the press officer in Beijing when relations were normalized between the US and the People’s Republic of China. He continued as a sort of Asia hand in the foreign service for many years.
Now, what was your mom’s connection to Iran that compelled her to move the family there?
She was actually in DC, employed at the Iranian embassy as a secretary and had made sufficient connections to people there that I think she sort of schmoozed her way into a teaching job there.
I mean, that’s such a remarkable decision to make. She’s—just to be clear—she’s not Iranian herself. She’s British.
Correct, but I think she was one of those sort of hard-nosed Brits that was very determined, just a steely personality. And you know, she had lived in the UK, she had lived in Europe, she had lived in Asia, she knew what the US was all about, and I think the Middle East just looked like an adventure. And it sounds astonishing at this point to think that she was trying to decide between living in Beirut in Lebanon versus living in Tehran in Iran, but you have to remember, this was mid 1960s, right?
So the political situation was very different. The world economic situation was very different.
You could talk about Beirut in the mid 1960s as the Paris of the Middle East.
Absolutely, it was gorgeous.
Chris, where did you—with all of this moving around—how did you possibly—or did you not—get a sort of solidified education?
So I think I moved ten times in the first six years of my life or something, right? So to this day, if someone says, “OK, we need to move,” this like icicle of fear goes into my stomach. I have this just deep-rooted aversion to uprooting where I live. And my mom told this story once of—we were in transit somewhere in Asia and we were gonna overnight in some hotel, and apparently as I was going to bed, I was a little bit in tears and my mom was like, “Well, what’s wrong, honey?” And I said, “Well, don’t get me wrong, I really like our new house, but I think I’m gonna have a really hard time making friends here,” kinda looking down the corridor of this hotel ‘cause no one had bothered to tell me, “This isn’t your new home. We’re just spending one night here.”
So there was a lot of emotional scar tissue I think from those upheavals at an early age. My early education was kind of a patchwork of stuff. I was sent to the local Vietnamese School in the city of Hue for approximately second grade. And another family legend is that at one point—you know, the US was not militarily in the war at that point, but certainly there were tensions in that country, right?
And the local Viet Cong came to the school and had me sign my name on a piece of paper and went away with the piece of paper and when my dad heard that that had happened, he was like, “OK, you’re not going to that school anymore.” And I was home-schooled by my mother with some complicated correspondence program with some teacher in the US called the Calvert System.
So that was the first version of my being instructed by my mother was for sort of second grade reading, writing, arithmetic. I guess from there, when I went to Bangkok, I don’t think I went to school at all after we got evacuated. When we lived in Hong Kong, I did a year at a British school in Hong Kong. When we moved to northern Virginia, I went to a local public school. It turns out as my mother was making the transition to go to Iran, she had dropped me and my brother with her mother in the south of Wales for a year as she went to Iran to set up life and household.
So I did a year of schooling in a private school in Wales for what must have been approximately fifth grade at that point, and moved to Iran and entered sixth grade in this Iranzamin International School and went all the way through 12th grade through there.
How was your Farsi coming out?
My Farsi’s fluent and I have a high school diploma.
For all the good it does me in my day job, but—
It’s conversationally fluent. You know, reading and writing is pretty creaky at this point, but I think it’s a good thing. I think the broad perspective gained from that childhood experience in diversity is a good thing for sure.
And so what was your last year in Iran before coming back to the states?
I moved back here in 1975.
OK. So in 1975, there’s a sense that there are tensions building up with the Shah, but this is still far, far away from the rumblings of the revolution that would come four years later.
Right. Yeah, I mean I left and the place fell apart is my version of it. But actually my mother and my brother stayed in Iran through the revolution and through the hostage crisis.
On British passports instead of American. And yeah, if you think I have great tales to tell, you should talk to my brother who stayed in Iran through the revolution.
Were they unsafe at any point? Were they OK?
As I look back on that time, I think I was more apprehensive about their well-being looking at it from the outside than they felt on the inside.
Yeah, sure. You were getting all the scary news reports.
Right. But I think from their perspective—yeah. I don’t think I would wish on anyone living through a political revolution, especially one as lurching as the one that took place in Iran, but they lived an interesting sort of expatriate life there where my brother’s Farsi is better than mine, right? So they were pretty totally assimilated into elements of society there as opposed to going to the American school, never speaking Farsi, and being isolated from the local culture.
So at one point, my mother was having some neighborly dispute with some neighbor, who I think was hoping to exploit anti-American sentiment, and this was before the local government had really fully taken shape and the city of Tehran was largely ruled by these local “Komiteh” or committees, and when this neighborly lady started giving my mom a hard time, my mom went down to the local Komiteh office and said, “This neighbor of mine is giving me a hard time for no particular reason.”
They dispatched a bunch of investigators that came and interviewed everybody and the outcome of that was they went to neighbor and said, “Stop bothering the nice foreign lady next door. Quit giving her a hard time or we’re gonna be on your case.” So, I think my impression of what happened at that time is that people very much disassociated the American government from individuals and I think my family—that was home, right? There was sort of nowhere to go to if they leave.
So, my brother—four years younger than me—just after the revolution went to England to attend university, but my mother stayed until eventually the government closed the school at which she taught, and at that point, she relocated to the UK.
So she really would have stayed, given her preferences.
Yeah. And she lived a hard life. When we were evacuated from Vietnam, it was on eight hours’ notice with what you can carry. One of my early life memories is sitting in the back of a C-130 flying out of a US air base clutching my teddy bear and that was about all I had from that. So she left an entire life and household behind at that point, and similarly when she had to leave Iran, it was like one suitcase and we’re gonna inspect it at the airport and you can’t take anything of value out of the country. So she went through twice in her life of just completely divesting herself of all possessions.
Did you keep up with your father over these years? Did you stay in touch with him?
Yeah. So my brother and I would do annual visits to our father, so we got to go visit him in Asia, visit him in Hungary. The State Department did eventually post him to Hungary where he could dust off his Hungarian. And when I moved to the United States, he was posted to the State Department domestically. So ironically enough, when I attended the University of Virginia, I was an in-state dependent of his. So I paid in-state tuition at UVA and the little tag on the door said, “Christopher Stubbs, Arlington, Virginia,” and everybody who went to the local high school there were like, “We don’t remember you from our high school.”
And he and I bonded very much in that first undergraduate year, which was a really traumatic time for me just because of the cultural adjustment. And also I went to UVA at age 17, and not only that, but I was a really young and immature 17 year old with a pretty patchy set of social skills I would say.
Well, perhaps immature scholastically, but I mean you’ve seen more of the world than people three times your age.
Yeah, but it was very uneven. You know, I would say my preparation for undergraduate life was very uneven. Yeah, scholastically, it wasn’t until third year at UVA that I saw intellectual material that I hadn’t seen before, right? That wasn’t the problem. It was more just life in the US, adjusting socially, adjusting culturally, and just kind of feeling like a fish out of water.
So UVA was mostly about in-state tuition and being local to your father’s home base?
No, it’s much worse than that. So there I was in Iran in this high school, no understanding of the US higher educational system, and the version of guidance counsellor at that school was this lady called Mrs. Sahakian would get a book off her shelf and go, “Oh, here’s a good-looking college. Why don’t you go to this one?” OK? So in the international baccalaureate curriculum, it was incredibly fortunate that there were three years of physics.
So the first physics course I took was in tenth grade, and about two weeks into that class, I just latched on and thought, “You know, whoever does this stuff, this is the way my head is wired.” I mean, this exactly makes sense to me, what a great way to think about the world and I just latched on. The 11th grade physics teacher that we had was someone named Wilson Gilliam who was a graduate student who took a year of absence to go see the world and ended up as a physics teacher in the high school that I was at.
And he was spectacular. He would say, “OK, momentum is conserved but actually let me tell you why it’s is conserved- because there are these symmetries in nature.” And he’d kind of go a level deeper than normal high school physics and just absolutely had me hooked. And so when it came time to think of where to go to college, I thought to myself, “I should go where Wilson Gilliam is. Where did he come from? Something something something Virginia. OK. So what is there? There’s some University of Virginia.”
So I applied to the University of Virginia—to my astonishment, was admitted—went there, and I’m like, “Where’s Wilson Gilliam?” And they said, “Wilson who?” And I said, “Wilson Gilliam.” And they said, “We don’t know anybody by that name.” And eventually I sort of corresponded with him and it turns out that he was at Virginia Tech. [Laughing]
So I applied to UVA completely by mistake, but it turns out fortuitously, a distant relative of mine, named Bascom Deaver, who was a condensed matter physicist happened to be on the faculty at UVA at the time. And so he kind of took me under his wing. I credit Bascom Deaver and my father with getting me through those early years, but it gets even worse than that.
So at the time, I thought to myself—this is sort of [as a] senior in high school—I did a lot of outdoor activities when I was in high school. I was a photo safari guide, I guided fly fishing trips, I ran tours in the desert, lots of time in the outdoors, lots of time with conservation biologists. And I thought at the time, “I’m going to solve the nuclear engineering power problem for the world. I’m going to go to school, become a nuclear engineer, and along the way, learn all this great physics, solve the world’s problems, be intellectually satisfied, and have a good life.” Right? That was my plan at age 17.
So when I applied to UVA, I applied to the engineering school, to the nuclear engineering program. And in the original orientation for nuclear engineering at UVA, an individual came up in front of all the freshmen and said, “We’re very proud of the nuclear engineering program here because we teach you the civil engineering of how to pour the concrete to make reactors, and we don’t waste a lot of time on all that namby pamby nuclear physics.” And I thought, “OMG what have I done?”
So it took me a semester of not very good grades to get outta the engineering program and into the College of Arts and Sciences and become a physics major. So I would say those high school to early college transition was a succession of linked errors from which I managed to recover, most of them born from sheer ignorance of how the American system worked.
By the time you got to the end of your undergraduate experience in physics, how well-solidified were your interests in physics? Did you know if you wanted to focus on experimentation or theory for graduate school or that was still sorta wide open for you?
Yeah, so the other pivotal experience for me, as an undergraduate—and you know long overdue thanks to the mentorship of these people—there were three formative people in that period for me. One, who remains my lifelong best friend is Dr. Yorke Brown, who was a graduate student in physics at the University of Virginia, and he and I met because we both worked in a mountain rescue team in Charlottesville.
So we were both outdoors people and met that way, but then that relationship bridged into the academic side and he was a mentor and instructor to me in learning the field of physics and I would say fanned my interest very successfully. So he now teaches at Dartmouth and—not far from where we live here—and is the person I’ve maintained a relationship with I think the longest in my life.
I also got linked up with a laboratory run by Rogers Ritter who did experimental gravitation of various kinds and he and his group gave me the opportunity to do experimental science, and I found that just absolutely captivating. So building apparatus, making measurements, soldering things together, making apparatus work, doing systems engineering, just absolutely completely seduced me. To the point where my undergraduate grades—I’m relatively certain that my undergraduate transcript is the most horrific of all faculty members at Harvard, and I’m not exaggerating.
In fact, a few years ago I wrote off to UVA to get my transcript and they sent it to me and I opened the envelope and looked in it and I was like, “Man, I remember it being bad, but I don’t remember it being this bad.” [Laughs] And one of the reasons for that is in my upper division years at UVA, I spent all my time in the lab, I’d much rather build apparatus than do some quantum mechanics homework problem set, right?
So I never, ever, had any illusions of being a theoretician. From that point on, where I was an absolutely experimentalist. I’m not saying I was particularly adept at it, but it was immensely satisfying.
So when it came time to move on, I guess in the time when I applied for graduate school, it was a fairly—it’s not like by my third year I was absolutely committed to go to graduate school—I was kind of unclear on what to do, but by the fall of my senior year, pretty sure that that was the next good step for me.
So the young lady who’s currently my wife, we met at that point in Virginia and both applied to every program west of the Mississippi that had both a strong program in earth sciences, which is what she was gonna do, and physics for me. And went on a lobbying trip the Christmas of senior year so that I could look graduate advisors in the eye and say, “Please, please don’t look at my transcript, really, really let me into your program.” And that was the undergraduate to graduate school transition phase.
Where did you apply to graduate school? What did you think your prospects were?
I took the shotgun approach of just applying absolutely everywhere that I could possibly think of. All manner of schools. And the outcome of that was rather stochastic. There was one particular school that will remain unnamed where when I went, I really hit it off with an experimentalist. We really did well. It would be a great program for my wife. It was a great place to live.
And I left there with the understanding with this faculty member, that if I were admitted, I’d go straight into that person’s lab and we’d do great stuff together. It was, you know, one of those really good clicked kind of conversations. So, came back, thought things were good. I got the thin envelope from that place and my wife got the thick admissions packet. So I went to my mentor and advisor, my sort of undergraduate advisor, Julian Noble at the University of Virginia, and I said, “You know, I really thought I was gonna get in here. This is really weird.”
And he said, “Uh-huh. Tell me who wrote you letters of recommendation to that program and who did you talk to when you were there?” And I said, “Well I talked to person so and so and the graduate program advisor was such and such.” And he said, “Uh-huh. And who wrote your letters?” And I said, “A, B, C.” And he said, “OK. I understand. So the guy who was the graduate advisor there we turned down for a job in a really acrimonious search and the three letters that went out of here were the head of the search committee, the guy who got the job, and the department chair. So I think this is all political, OK? Which is why they turned you down.”
I had a phone call that week with the person who I thought I was gonna go and work with, I said, “Well I guess I’m not gonna come ‘cause I wasn’t admitted.” And he said, “Yeah, I saw that. It’s really weird. What are you gonna do?” And I said, “Well, you know, I don’t know. I got into Caltech, I might go there. I got into the following places.” He’s like, “What, what, what? OK. I’m gonna call you back.” So he hung up and he calls me back in half an hour, he says, “You’re admitted now, OK?”
And I said, “Well, you know, thank you. Appreciate it, but this really—this just kinda didn’t feel like the right thing for me to do. I don’t wanna come if there are factions of the department that kinda don’t want me.” So it was very—I think given my patchy strong letters, terrible grades kind of application, it was an interesting experiment to see by nominal rank of school where I was admitted and where I wasn’t.
So at the end of the day, my wife and I tried to make a choice that was some kind of life-optimizing decision, right? And we put a lot of stock in where we would be and what our lives would be like. And it sort of boiled down to a choice between Southern California with Caltech for me and USC for her versus moving to Seattle and going to the University of Washington, where we were both admitted.
And you were married at this point?
No, we weren’t, but we were clearly on track for that.
Yeah. What’s your wife’s field?
She went to graduate school in glaciology in Seattle. I think it was UCLA for her. UCLA for her and Caltech for me.
And to the absolute horror and chagrin of my mentors at the University of Virginia, we decided to go to Seattle for grad school. And that was a counter-cultural decision, right? I mean that wasn’t the nominal career-optimizing choice, but given the southern California commute that would be involved and how we’d live this kind of split life with commuting in different directions to different schools versus the just magnetism of the mountains and the life in Seattle and the University of Washington, we moved to Seattle in 1981 for grad school.
And of course Seattle in 1981 is a very different place than Seattle today.
Yeah. And it was great. I had a fantastic entering graduate class and learned a tremendous amount from my cohort. It was a really strong graduate program. I was extremely fortunate in the people that I eventually had a chance to work with, but similarly, I mean you know, the path through graduate school was not exactly a straight line to the finish line. Lots of bumps along the way, including a leave of absence to go off and do engineering for a while. It was a bumpy road.
I’ve come to know University of Washington physics program quite well, as you know of course I interviewed Eric [Adelberger], I talked to Larry Yaffe last week, Hamish Robertson, Lillian McDermott, I’m talking to Marshall Baker, and it’s really such a phenomenally strong and special department and it’s one that’s sort of out of the way and you wouldn’t normally associate all of these powerhouse physicists being concentrated in this one place. So it’s really quite remarkable what the program has accomplished over the years.
I completely agree. When I had a chance to go back there and join the faculty, I leapt at it.
Yeah. Did you have a sense, Chris, when you joined, that it was in building mode? That it was a place that was situating itself to really be in that upper echelons of physics programs? Or had that transition already occurred by the time you got there?
So my recollection of that phase of my life is I was not conscious of those kinds of institutional issues. I was just worried about passing the qual. [laughs]
When did you connect with Eric? Right away or that came later on?
No, that came later. So let’s see. It’s complicated. I made it through the introductory graduate courses. I always knew that because of my weakness in formalism and mathematical ineptitude that getting through the written qualifying exam was gonna be the big hurdle for me in graduate school. I wasn’t the least bit worried about making some experiment work. And the qualifying exam at the UW was a substantial exercise.
So a lot of focus on course work and apprehension about the qualifying exam. In parallel, my wife’s research group was building instrumentation to install in glaciers in the Arctic, and we would have conversations at home where I would say, “Oh, well, you know you might think about a circuit that does X, Y, Z.” And before you knew it, I was in their group meetings. And before you knew it, I was helping build instruments. And I very nearly switched into geophysics at that point because I felt like with my skill set and knowledge at that point, I was closer to the research frontier in that domain than I was in what I saw in a lot of the research programs in the physics department.
So I had some great times with her advisor, Bernard Hallet and working with my wife, we’ve written papers together, we’ve built Arctic instrumentation and installed it together and it was sort of—my spending a lot of time doing that drew me away from paying full attention to what was going on in the physics department and that led to a kind of period of disillusionment and reassessment that led to my taking a leave of absence and kinda thinking through what is it that I wanna do?
So I spent a year doing consulting engineering, building geotechnical instrumentation for water tables and methane in landfills and acoustic emissions and cracking rock and sorta said, “Yeah, OK. So I’m a competent engineer. I could feed my family being an engineer.” And I think the empowering part of that was from that point forward, I never felt like my livelihood was in jeopardy. I always felt like I had a fallback career path as a decent engineer and I didn’t have to worry about it.
And that let me take a path in physics that was not as risk averse as some of the decisions that some of my colleagues made, right? It let me sort of go into things and say, “I’m gonna go big or go home and embark on risky projects,” because I always felt like I had this vocational fallback I could turn to.
Now when you say disillusionment, were you disillusioned with yourself? That you were sort of taking a safe path in academic physics and you wanted to shake that up? Or were you disillusioned with academia more generally?
Yeah, good question. I think it was a confluence of factors. It was not being sure I could deal with the deferred gratification of arriving at the research frontier after years and years of investment. I think I was craving wanting to get there sooner, right? So there was some frustration with that. And I have to honestly say also a sense of I don’t wanna do some boring thing, and worried that I’d get trapped in some project that I didn’t think was really fundamentally interesting.
And what was interesting to you? When you say fundamentally interesting, that’s of course very subjective. What was fundamentally interesting to you?
Yeah, so my tastes have always drifted towards—let me back up half a step to put that in context. When I was at the University of Virginia, in about my third year, I very seriously considered trying to do a dual major in physics and philosophy. And I really explored that quite vigorously and eventually came to realize that it would extend my time as an undergrad because the overlap of requirements was so small that it was almost like I’d have to do those two degrees in series rather than in parallel.
And when I had to kind of make a down select choice, I thought, “You know, I bet if I’m a physicist, I can read philosophy papers, but I’m not sure the converse is gonna be true. So if I’m gonna pick, I’m gonna pick the physics path.” But when I look at myself now and my intellectual priorities, I often wonder what aspect of my physics education beat out of me my passion for philosophy? Because at that early time, it was really quite strong.
And so by the time now, fast forward to graduate school, I was looking for things to do that I thought would be profound in some way, right? This is audacious to think that some junior graduate student is trying to find some world-shaking experiment to work on, but that was very much the attitude that I had.
I started working with a particular faculty member at the University of Washington whose outlook was very similar to that, but that relationship was not productive in the sense that while we had a similar outlook, we had similar intellectual weaknesses. And when I got stuck, that person couldn’t really very well help me get unstuck and was, on the personal side, someone who managed by guilt and manipulation, which is something to which I’m extremely susceptible.
So I would kinda come home and kick the cat and be miserable and my wife would say, “You know, you’re not happy with what you’re doing. You should rethink your plan. There are elements to this that are not working for you.” And so that—
How was her program? Was she doing fine? She was not experiencing any of these kinds of questions that you were going through?
No, she was actually thriving in her program. Her group was incredibly socially functional, great group of people. They were doing great. She, I think, sort of lost patience with the academic shtick and after a master’s degree, went off into the corporate world and worked for software companies and I think found that to be more satisfying than the academic track and mindset. So I think she just kinda decided a PhD wasn’t for her and went off to do something different along the way.
So how’d you come back into the fold? ‘Cause you did, of course.
Yeah, so I spent that year doing consulting engineering and then decided I just wouldn’t forgive myself if I didn’t go back and finish a PhD. So that was a leave of absence and—
Was there a dead end, Chris, in consulting engineering that you would plateau pretty quickly, that there wasn’t—in terms of weighing these grand ambitions you had with what a field such as consulting engineering could offer you, whatever the pinnacle of that looked like, over the course of the year did it sort of dawn on you that you’d get there quicker than what would be satisfying to you?
That was a consideration, but the perspective I had at the time was, “OK, I’ll have a nine to five career and spend every weekend skiing on the side of Rainier and have a good life.” So I think my overall plan there was to lead a satisfying life by having a big outdoors component to it, had I gone down that track.
Yeah. Probably focusing that much on what would be enjoyable to you beyond a career is suggestive of the fact that you needed something more out of a career itself.
I guess. Yes.
Not to put you on the psychiatrist’s couch or anything.
No, that’s OK. Yeah, it’s hard to see these things from within. So I went back and sort of expressed to my academic advisors at the time this kinda craving to do some fundamental thing and I was fortunate that I got linked up with Blaine Heckel, who at the time was working on a project with Los Alamos to measure the lifetime of the neutron, the sort of fundamental weak interaction cross section, if you like.
And it also had a bearing on nucleosynthesis. And so that felt to me like the right kind of project, right? I mean it had a link to cosmology, it was an important measurement to make, and we were headed down the track of doing that experiment when two things happened kinda simultaneously. One is, in some budget move—I’m guessing at the Department of Energy or something—they terminated the support for that experiment. So that was thing number one that happened.
Thing number two that happened was Ephraim Fischbach and colleagues published a paper about the fifth force in Phys Rev Letters that caught my attention because of my previous connection to experimental gravity as an undergrad. And Ephraim Fischbach was, at the time, visiting the University of Washington. So that kinda caught everyone’s attention. It was like, “Holy cow, where’d that come from?”
And just to briefly recap what that was about was by doing a reanalysis of old, archaic data from a torsion balance and looking at data from gravimeters going down mine shafts, there was a self-consistent picture of there being a new interaction with a range of a few kilometers about part per thousand gravitational strength coupled to baryon number. And there’s a deep connection between conserved quantities and interactions, and baryon number that could serve as a conserved charge, so it kinda made sense. And there was, interestingly, no experimental data that disagreed with that hypothesis.
The fifth force idea was quite topical at the time and I think it was around sort of December that it came out and my recollection—although I haven’t dug up any notes here—is that kind of over Christmas break, I did some chicken scratching calculations of hey, you know, what kind of experiment could you do to see this. I went to a kind of brown bag, “what are we gonna do about this?” meeting of UW experimentalists and I couldn’t remember this, but my recollection is that I actually had the temerity to speak out at that meeting and say, “Well, here’s what I sketched out.”
And Eric Adelberger and Blayne Heckel were there and rapidly came to the decision that we’re gonna do this experiment. We’re gonna test this idea.
What did you share exactly? What were your calculations that were compelling to them?
I think I actually sort of did some signal noise calculation for a torsion pendulum experiment, as I recall. It’s like, “How strong are these forces, what are the background, and what can you see?” kind of a thing. Like literally just back to the envelope stuff, right? But I my senior thesis at UVA was a torsion pendulum speculative paper, right? So at least I knew what books to pull off the shelf to look at signal to noise in torsion balances.
Eric and Blayne invited me to join an effort to do that project, I had had enough experience with experimental gravity to know that PhDs took 13 years in experimental gravity. So I said, “OK, look, you know, we’re gonna try this for a year and then we’re gonna reassess it and see where we’re at.” They’re like, “OK, no problem.”
So within a year, we had a Phys Rev Letter paper out that refuted that hypothesis, right? I mean we busted our tails. It was a highly competitive, highly charged, high stakes—and in many ways, exactly the project I was craving. Was Einstein right? Is there a new force? What’s up with this? It was tailor-made for me.
And when you say it was a race because lots of people all over the country were interested in this and it was a question of who was going to get the answer first.
Yeah. It was highly competitive.
And what was the experiment like during that year? What were you doing? What was the day to day like during this time?
Super intense, working every weekend, working long hours, putting together as rapidly as possible an evacuated rotating torsion balance on a turntable, which is like a crazy idea except it was the right thing to do, and a handful of four or five people working intensely together and hammering through technical problems at an amazing rate in a environment at the nuclear physics lab at the University of Washington with machine shop and infrastructure that could support that kind of endeavor.
Now, the instrumentation was sort of ready to go or it needed to be modified or created anew from this experiment?
We made it all from scratch. I mean, we learned how to hang things on tungsten wires. We learned how to crimp tungsten wires. Fred Raab was a postdoc at the time, helped engineer an optical readout system with lateral effect photo diodes, wrote a bunch of A to D converter code, a really talented undergrad helped with that part of it, and we just sprinted to put together an apparatus—I mean, the signal here was not small, right?
By the standards of equivalence principle experiments, this was a pretty strong effect. So moderately crude apparatus should have been able to see it, and Blayne Heckel was a key part of that endeavor. He’s a very talented experimentalist who’s extremely good at calculating and understanding things. Eric is a super-talented physicist and devised elegant devices and measurement schemes. So Blayne and Eric and Fred and eventually others—and I think the other part that was great for me was to be the first graduate student doing that in what has become a succession of incredibly impressive experiments that continue to this day.
You don’t mean just at UW, you mean first graduate student in the country?
Well, I think other people were—there was a whole community, at the time, of experimental gravitational physicists with whom we were competing at Irvine, at Colorado at Boulder, and so there were people who already viewed that as being their subfield in addition to others, who like us, were drawn into it from other subfields because it was so seductive an experiment to do. So I would say there were half a dozen groups nationwide that were engaged in that at the time.
And you’re year involved in this, this is totally an in-house UW project? There are no outside collaborators, it’s all within the department?
That’s so cool. Were people like Eric in contact with Ephraim during this time?
Was there any—you just want the experiment to tell you useful things, but were there things that were exciting beyond just the science about, you know, having this opportunity to think about whether Einstein was right or not? Did you give much thought to that at the time?
Yeah. And so what exactly were your findings in this publication a year later?
So I think we pretty convincingly showed that if you ran an experiment with beryllium and copper—I mean, we don’t need to go into the details here—but the key thing is that the baryon number to mass ratio would be different in the two different test substances, and I think Eric brought his genius of experimental physics to this problem and innovated a bunch of elements of torsion balance technology that—despite that apparatus being, by then, centuries old—I think were pivotal to the experiment working as well as it did and I came away from that with a deep appreciation of differential measurements, symmetries in apparatus, crafting a careful experimental question that you ask of nature, and paying fastidious attention to systematic errors. And that training that I got at that graduate stage has stood me in good stead ever after.
And in terms of the role of this experiment on this fundamental question, in what ways did the experiment help to answer is there or is there not a fifth force?
It remained controversial for quite some time. There were other hints and indications from gravimetry and other domains of having a positive signal. And so you know, science worked its way forward with a reconciliation of inconsistent results that led to, as you might imagine, theoretical speculation to try to accommodate all the data by invoking ever more complicated models, right? Well maybe a force that couples to baryon minus lepton number. Maybe it’s some other attribute of materials.
That led to a succession of experiments to try to hammer out parameter space constraints and at the end of the day when all the dust settled, the overall consensus arrived at a null result, no indication of a signal. Likely what Ephraim and company saw was some element of systematic error that afflicted the Etovos data in some way that I have some speculations about, but I’m not sure we’ll ever know.
Was this the work that led to Eric becoming your advisor in what would become your dissertation?
Oh yeah, absolutely.
And how closely related was your dissertation to this specific experiment? Was it one in the same?
My dissertation was this experiment.
Right. Who was on your committee?
So I remember Eric and Blayne—I’m sure there was a committee member—I’m not sure who that was. It may have been Norval Fortson. I don’t exactly recall, I’m sorry.
But it was an exciting ride, right? The very first time we turned this thing on and started to take data, there was an indication of a signal. And Eric was off giving a talk in Michigan and I remember talking to him on the phone and I’m like, “Hey, I ran all night long. There’s a sinusoiudal modulation of the position of this thing’s equilibrium position, and you know, this could be really true.” And he’s like, “Oh my God, you gotta be kidding me.”
But we eventually figured out it was a systematic of when the apparatus rotated, if it wasn’t exactly rotating about vertical, and there was tilt, and it turns out there’s a cross term that if the torsion pendulum tilts back and forth, it also rotates, having to do with the way that you support it, so it was actually a systematic but we had thought ahead where we could rotate the vector of composition within the torsion pendulum with a rotator on the top.
And so by 48 hours later, we had shown that it was actually locked to the tilt and not to the composition vector and it was a systematic error. We detected an earthquake in Alaska because this thing is a magnetometer, a seismograph, a thermometer, a tilt meter, in addition to being a fifth-force-ometer. So it was the standard cycle of experimental physics. It’s like take some data, figure it out, fix what’s wrong, iterate.
But that cycle was quick and there was a lot of rapid iteration: try this, didn’t work, try something else kind of vibe. It was exciting.
And this is obviously to just go back to when you were a bit unmoored previously in your graduate career, this was exactly what you needed to sort of jazz you up and get you really where you needed to go.
This is what I craved. And I think it was also moderately high profile at the time, right? As a graduate student, I went places and gave talks. The meetings at Moriond that happened in the January, as I recall, of every year, were a central part of the intellectual development where that community would kinda get together and thrash things out. You know, we tried different compositions, different materials, built very elegant distributions of lead in the laboratory to flatten gravitational field gradients in the vicinity of the apparatus. Figured out how to measure that with a gradiometer configuration.
You know, things just got better and better and better and more and more and more sensitive as the years went on. And I’m immensely proud and impressed with my colleagues at the University of Washington continuing with that vein of experiments that now is at the 10 micron scale of testing gravity, which is a relevant thing to do.
Just to fast forward, how far has the field progressed from that original year doing these experiments, really you know, in uncharted territory?
Many orders of magnitude of sensitivity improvement.
Yeah. Which tells us what, beyond the lab in terms of gravity in general, how has our understanding of gravity changed as a result of this enhanced sensitivity?
I’d say there were—I’d bin it into three different epochs. The first epoch, which was my dissertation, was testing a hypothesis of there being a concrete target of an anomalous interaction. When that gave a null result, I think people came out of that with a renewed appreciation of the extent to which testing the equivalence principle is a foundational thing to do and it really probes the nature of gravity in a very deep way.
And so the intellectual motivation shifted from “is there a fifth force?” to “let’s go test the foundations of gravity using the equivalence principle”, and in the post-dark energy era, a sort of dimensional analysis that you can do on the back of an envelope about the energy density of the dark energy suggests a length scale of order 100 microns. And testing the nature of gravity on that length scale is I think the more contemporary motivation for doing some of those experiments.
Now when you graduated, when you defended your dissertation, you were involved in this fundamental research. I assume that you had a lot of options available to you in terms of departments and institutions that would be more than happy to take you on board and provide a home for you to continue with this kind of research. Was that your experience?
It didn’t feel that way. [Laughs] It was a time of, “What am I gonna do next?” apprehension. My recollection of my mindset of the time was, “OK, that was immensely satisfying, enjoyable, and great. What is the next big unsolved problem in physics and where can I go to work on it?” And I had heard a remarkable colloquium by Michael Turner describing the dark matter problem and I decided the dark matter problem was the next big thing, and essentially talked myself into a postdoc at the Center for Particle Astrophysics at Berkeley.
I encountered Bernard Sadoulet at a meeting in Germany where I gave a talk on the fifth force and I took him aside, with the help of some French competitors, who I think told Bernard to take me seriously, and bless his heart, he created something called The Center for Particle Astrophysics fellowship, to which I then applied, and lo and behold, I was appointed to it. And so I moved to Berkeley to work on dark matter and started in Bernard’s group working on cryogenic hockey pucks of Germanium to detect wimps. This was a complete change of technology and problem set in the graduate student to postdoc transition.
Chris, just to get a sense of your mindset, did you see a clear transition from your dissertation research into dark matter or did you develop a taste for really exciting, fundamental research and you saw dark matter as the next obvious thing to sort of continue to excite that which you had been craving all along?
More the latter. It felt like a complete switch of vocabulary, topic, technology, and colleagues.
So in what sense, when you were getting your sea legs in this new field, what was the new kind of stuff that you needed to learn?
Astronomy, particle physics, cryogenic dilution refrigerate technology.
Cosmology? Is that a word that’s being used in these circles also?
Yeah, sure. Sure. And back in that time, there was this stark discrepancy in galactic rotation curves that had really gained traction by then, right? There was strong evidence for dark matter on the scale of galaxies and there was just complete confusion about the average matter density of the universe, and you know, is omega matter one or not and strong theoretical prejudice about that.
The WIMP hypothesis was reigning supreme that you could reconcile the inferred dark matter density if there was some relic that had a weak interaction cross section in the early universe and the Center for Particle Astrophysics was a National Science Foundation Science and Technology Center established to go after the dark matter problem in many different ways, and was a great blend of physicists, astronomers, cosmologists, experimentalists, and theoreticians and it was a heady time. It was great.
Now I’m curious, obviously if you knew perfectly how to integrate your research in gravity into this new field, we’d have a grand unified theory and we’d be all set, right? But I’m curious to what degree was your background in gravity useful as you were learning astronomy and cosmology and dark matter?
Not, but I think my background in systematic errors, in experimental design, in electronics, the kind of foundational toolkit of experimental physics was useful.
Yeah. What were your impressions generally of Berkeley? Just physics in general at Berkeley coming from UW?
I was terrified. I felt like I was going to the big leagues. I was worried I wouldn’t measure up. I worked my butt off. It was an incredibly stressful time. We had a young family, we had no support network, and I was absolutely intimidated. And later on top of that, I was asking all the stupid questions at all the seminars because I didn’t know the material. So insecurity was high, apprehension was high, and it was stressful.
I think the intellectual environment was absolutely vibrant. Bernard Sadoulet had collected and herded an intellectual effort that was just nothing short of remarkable between microwave background experiments, cosmological measurements with supernovae, the direct detection projects, the indirect detection projects. So the Center for Particle Astrophysics was a real force multiplier for that effort on the west coast at the time.
Who were some of your most important collaborators at Berkeley?
So I worked—The Center for Particle Astrophysics fellow position was a kind of do what you think is best position. So I could pick what I worked on. So I started working—and this’ll end up being moderately hilarious in retrospect—on two projects. One, the supernova cosmology project with Rich Muller and Saul Perlmutter and Carl Pennypacker to look at type one A supernovae to map out the history of expansion and then in parallel, Bernard’s group working on WIMP detectors in cryogenic Germanium.
And a few months in—and when I looked at thinking about working on the cosmic microwave background, my assessment was that those experimentalists were better than me and I had a little to add in that domain. So I looked away from the CMB at that point, and I think that assessment was accurate. And decided I was splitting my time too much, I was too fragmented. I dropped the supernova thing, put all my effort into the direct detection experiment, so the PIs were Blas Cabrera and Bernard Sadoulet, with involvement from UC Santa Barbara with David Nelson and company.
The graduate students and postdocs and theoreticians at the Center for Particle Astrophysics all felt like one big intellectual community all knit together by this common objective. So we’d go to the astronomy talks, the astronomers would go to the direction talks, it was great. And I guess I had probably been there for about six months when this prospect arose of looking for chunks of dark matter in the outskirts of our own galaxy, the Milky Way, using dynamic gravitational lensing using gravitational microlensing.
And I went into Bernard’s office one day, and my recollection of how this went is I said, “That’s a really elegant project. It uses about the dark matter the one thing that we think we know, which is that it gravitates and it seems like it’s a very broad-reaching project, if this can be made to work, and the Center for Particle Astrophysics should support this and we should put effort into that project.”
And Bernard said, “I don’t disagree with you, but who’s gonna drop what they’re doing, go learn all that astronomy, and help make it work?” And I said, “If you let me do it, I will.” And he said, “OK.” And to this day, I’m indebted to him giving that vote of confidence to someone who was then a junior postdoc. And I teamed up with Charles Alcock at Livermore and other colleagues and we made the MACHO Project work.
So as a postdoc, I started into optical wavelength observational astronomy, had to learn, yet again, a whole new set of vocabulary, right? Second time in a year. And don’t tell anybody, I’m a Professor of Astronomy at Harvard and the number of astronomy classes I’ve ever taken in my life is goose egg zero. So it was all basically self-taught from that point forward. And I think that kind of I’m going to say intellectual fearlessness I credit Eric Adelberger with imprinting on me at an early age. Like, “You can figure this out. You can make it happen. You can make a difference.”
And that project consumed me for the next 10 years I would say, and we spectacularly basically failed to find dark matter in the Milky Way but the constraints from the MACHO project span over six decades in mass. I think it was incredibly successful from the perspective of excluding possibilities.
Was Santa Barbara particularly exciting to you because of all of the things that were going on there?
Yeah. So, along the way, I guess two or three years into being a postdoc at Berkeley, it was time to start looking at faculty jobs. And another wave of apprehension and self-doubt in that when I would read ads in the back of Physics Today that were all kinda very subfield specific, I would say, “I’m not one of those. I’m not one of those. I’m not one of those either.” I mean, I felt like very much a floating around between the pigeonholes of physics kind of a person.
I mean, to this day, it’s kind of hard to describe what kind of scientist I am. I would say my interests are at the intersection between particle physics, gravity, and cosmology. Well what does that make me? I’m not entirely sure. So at the time, when applying for entry-level faculty positions, I called Phil Lubin at UC Santa Barbara who was one of the microwave background scientists associated with the Center for Particle Astrophysics, and I said, “Hey, you guys have a faculty opening. Should I apply?”
And his initial answer was, “No, no. We’re looking for a something.” And then he kinda paused and said, “Actually, you know, yeah. You know, actually, yeah. Why don’t you apply?” So I applied to UC Santa Barbara and I had not yet clearly completely rectified my ignorance of American geography, and especially in the state of California ‘cause I actually thought Santa Barbara was some deeply embedded part of LA. No, I really did! And this is after living in California for a few years.
Northern California though, different world.
That’s right. So I got on the airplane at like Oakland or something and flew to Santa Barbara and the plane landed, I look out the window and I’m like, “Whoa. Hey, this place looks really cool. We could actually live here.” And then I suddenly thought, “Gee, I better rewrite my whole talk,” which is on transparencies, right? So that I do a good job.
And I remember I got so cranked up about this, I called my wife and was like, “Hey, you know, I wasn’t really sure that this would be of interest to us but it’s really quite livable here, in this place called Santa Barbara.” And I was so worried that I slept so poorly the night before I went onto campus that I had this incredible crick in my neck from sleeping poorly, and my first appointment of the day is with Mike Witherell and I kinda went in and I tried to be, you know, friendly and gracious. He asked, “What’s wrong with your neck?” And I said, “God, I don’t know, it’s just killing me.” And he gave me an Aspirin, a kindness that I will remember to this day that got me through the day of interviews.
And it was great. So my first faculty job was in the UC system after being a postdoc in the UC system and I, to this day, have a incredible fondness and respect for the University of California. Our son’s a graduate student there now. I think it’s a fantastic system. Started a research group at UC Santa Barbara that pursued the MACHO Project vigorously, with a succession of graduate students working on that at UC Santa Barbara, I sort of decided that this idea of using telescopes to go after fundamental physics where the signal for anomalies is non zero in the astronomical domain, using astronomical tools and techniques to do fundamental physics was a good place to be.
Was the Kavli Institute, was that part of the equation as well at this time?
Yeah. So the ITP was there at the time and I guess Doug Eardley and Tony Zee were probably the people who I remember the most as being on the faculty. I can’t remember—I think it may not have been called KITP at that time. I think it was just ITP, but I don’t remember. And while there at Santa Barbara, I guess my version of events is the following—and again, this is a little hazy, this was as long time ago—but my version of events is when I got to UC Santa Barbara, all the cheap faculty housing was gone and we had to buy a house on the open real estate market in Santa Barbara.
And on a junior faculty salary in that scenario, I was having a hard time making ends meet. So I went to the department chair at the time and I said, “I don’t wanna go find a competing offer from some other school, but you gotta pay me enough money to feed my family and I just can’t close the gap financially.” And he said, “Well, you know, we have all these salary ladders and we’re highly constrained, but let me see what I can do.”
So he called me back a few weeks later and said, “Well, you know, we’ve met, we’ve deliberated and given how promising you are as a junior faculty member, we’ve decided to aware you a raise of I don’t know, 200 bucks a month or something.” And I said, “OK. Thank you.” And as I had my hand on the door handle on my way out the door, I said, “No hard feelings, but you basically leave me no choice. I need to feed my family and I need to respond to the job feelers that I’ve been getting from other places.”
And he’s like, “Whoa, whoa, whoa. Tell me about that. What kind of job feelers?” And I said, “Well, you know, Caltech, Berkeley, lots of places are asking me to apply for a job.” And he said, “You didn’t tell me that.” And I said, “Well, you know, I think I kind of, in an indirect way sort of did.” And I did that. I responded positively, and applied to other jobs. And the fickle spotlight of fashion had shone upon the MACHO Project at that point to where it was a pretty high profile undertaking.
I had played a central role in making that project work and so lo and behold, I got tenured faculty offers from lots of places, and among them, the University of Washington. We elected to move from Santa Barbara back to Seattle, given the opportunity to go back to the intellectual environment that you described at the UW, that was the choice that we made.
Wow. That says so much for the University of Washington that you made that choice again. It really does.
And over some big name alternatives.
That, again, would have been the kind of conventional, normal choices, right?
Now your wife was still in software? The two body problem was not such a concern? She’d be able to find work obviously in Seattle, of all places?
So, yes. Short answer yes, but we had made a counter cultural choice of her investing her time and effort in our two young children. So we were a single income family. And that was a critical part in why we couldn’t make ends meet, right? And at the end of the day, move back to UW in—what year must that have been,’93 I guess—and one of the things that was attractive was it was a joint position split between physics and astronomy, which is kind of intellectually where I was at. And had a delightful time, went back to Seattle. Craig Hogan was there at the time, Eric was there, Blayne was there, and had wonderful graduate students, a great ambience and just a real hardnosed spirit of experimental physics that I think in some ways it’s no surprise that I found intellectual satisfaction in the department that trained me, right?
In some ways, that shouldn’t come as any surprise. It’s a selection effect because they had branded me to think their way, so no big surprise that when I went back there, I found it immensely satisfying. But even that transition was not without its moments. I think, to this day, I believe my grade in advanced quantum mechanics in graduate school at the UW is an incomplete and I was petrified about going to faculty meetings and facing the faculty member whose course I didn’t complete when I was a graduate student, even many years later.
I’m sure both you and the faculty members got over that soon enough, though.
I don’t know. You can see I’m still worried about it! And it was a great time. And one of the things that we did at the time was start a series of brownbag seminars about vacuum energy and started asking ourselves, “You know, with the tradition of precision measurement at the University of Washington, what experiments can we do in atomic and molecular or experimental gravity or something to try to get a handle on this whole vacuum energy thing?” ‘Cause that’s like really kinda strange, right?
And we had theoreticians come and talk to this brown bag experimentalist lunch telling us, “Don’t bother. The vacuum energy is identically zero because if it weren’t, it would require a remarkable lack of cancellation, blah, blah, fermion, boson, this, that, and the other, you know, omega-Lambda has gotta be zero and here’s, why. And omega mass has gotta be one, and here’s why.”
So incredibly strong theoretical prejudice in that direction. We beat our brains out to try to think, “Can we run the LIGO gravity wave antenna in some way to get a handle on this? What can we do? And what about Casimir effect type experiments?” And we eventually—at least Craig Hogan and I—kinda convinced ourselves that any laboratory apparatus kind of experiment that you tried to do was just swamped by the Newtonian gravity of the constituents of the apparatus. That it was just really hard—other than a Casimir effect type thing—it was hard to think of an experiment that you could do in the lab and that you just needed to do cosmology to look at vacuum energy.
And so right about then, there was a breakthrough in type Ia supernovae as distance indicators led by my now friends at CTIO in Chile, about correcting the peak brightness of supernovae based on their rate of decline and their color. And I had known of the supernova cosmology projects way back from my time at Berkeley at the Center for Particle Astrophysics, but this was the key technical breakthrough that shifted that to being a really incisive measurement.
So Craig and I joined one of the two supernova cosmology projects, the one that was at the time led by Brian Schmidt, and embarked on a project which the astronomers on the team were going after it to measure the deceleration parameter and the average matter density, but at the time, Craig and I—from that early time—were kinda motivated by, “This is the way to look for vacuum energy, cosmological constant type things.”
So that endeavor proved fruitful, right? I mean as you may know, in the late 90s, those two teams, ours and the group led by Saul and company at Berkeley, both basically came out with evidence for accelerating expansion and the discovery of dark energy. So I could tell this tale in a way where it looks like I did a whole bunch of completely disconnected random projects, but I prefer to tell it in a way where there is some sort of integrating intellectual thread that runs through all of this, it’s just that particular instantiation of each individual project might differ.
So what is that thread? What do you see as that narrative through line?
It’s this sort of collision point between gravity and particle physics, and like you said, at the very outset, why don’t we have a quantum mechanical theory of gravity, right? I mean, it’s a place where things really kind of grind in terms of the framework that we have theoretically in physics and I think I’m just remarkably fortunate to have had a career in a time when we were able to carry out experiments that were incisive in that domain.
Now, Chris, operating at this level, did you feel—just sort of foreshadowing ahead at Harvard—did you feel like Seattle was a bit too out of the way in terms of the things that you were working on?
You never did?
I was involved in big international collaborations and it didn’t matter where I was.
OK. So I’m just trying to piece together here, Seattle—I think you used the term yourself—it has this magnetic pull on you and your family, right? So you obviously not once, but twice, turned down offers to go to more quote unquote prestigious places, both as a graduate student and as you were thinking about faculty jobs. And so even Harvard being Harvard, what happens in 2003 where you say, “You know what? There’s actually something that I’m willing to consider leaving Seattle for.”?
Yeah, good question. I do have to say, one element in our decision to return to Seattle was the sense that the values—it sounds funny to over generalize here—but the value structure and the way people live their lives or the typical person on the street in Seattle felt like where we belonged as a family. It felt like the kind of place we wanted to raise our children.
And so moving from California to Seattle, that was a big ingredient in that decision. And so, yeah. So what about the shift to Harvard? So while I was in Seattle, I would occasionally receive phone calls of inquiry from various institutions and I would give them the answer that I just gave you, which is, “I can do what I do from here living a great life. Why would I move?” I mean, not feeling like I’m missing anything.
And I never—I think the following statement is true; I was never attracted by the kind of prestige element of allegedly more illustrious institutions, right? That was never an issue for me. We had a great time in Seattle, it was a great time for our children. We thoroughly enjoyed living there. By the time the opportunity to move to Harvard arose, a number of things had happened.
One was, by that point, I was a full professor in my groove, you know, had been there for 10 years, and was a little bit worried that I was kinda starting to lose my edge, that I had kinda settled into a rut. And I could see this kind of failure mode of—I wouldn’t call it intellectual stagnation, but more I would call it intellectual satisfaction and just kinda settling out and not quite being as forceful and hungry. So that was one apprehension.
The next one is going to sound hilarious, given my current position, and that is I could see in my future being asked to become a department chair.
And I was extremely apprehensive about what I was gonna do if someone twisted my arm to be a department chair. Third, we became apprehensive about some of the elements of the public school system that our children were attending in Seattle as they were moving through middle school into high school kind of age and didn’t have the wherewithal to send them to private school for an extended period of time.
So we had some apprehensions about the education that our children were receiving. In the midst of all of that, I got a call from Harvard. It was their initiative to call me on the phone. My now good friend, Bob Kirshner, who was a colleague on the supernova team, said, “Hey, you know, we’ve been talking over here and we’ve been thinking it would be good if you thought about coming to join us at Harvard.” And I said to Bob, my stock answer to this question is—
Oh yeah, I know the other thing that happened is I turned 45 and when the odometer rolled over, I did a harsh self-assessment of what’s reality, what was the plan, what’s holding up, what isn’t holding up? So in that moment of sort of psychological weakness, Bob had the foresight to call me on the phone. And I said, “My stock answer is I don’t need to move, but you’ve caught me in this moment of psychological weakness such that I will go home and raise this prospect with my family and then day after tomorrow I’ll call you and say, ‘No.’” And he said, “OK. Sounds good.”
So went home, after dinner at the dinner table things kinda quiet down and I said, “So, got this phone call today,” and my wife looks at me across the table and says, “Yes, go on. You know, which is it? Is it Pasadena, is it Berkeley, what’s our future here?” And I said, “Well, astonishingly I get a phone call from Cambridge Massachusetts and Harvard University.” And my wife said, “Well, kinda knew this was likely to happen. Tell me more.” Our son said, “I’m never leaving Seattle. You’re gonna have to pry my dying fingers away from Mount Rainier.” Our daughter said, “Huh, sounds interesting. Tell me more.”
So we thought long and hard about it and it was a razor thin decision as to what we would do. For all the reasons that I mentioned, Seattle’s a great place, it’s still near and dear to my heart, love the people that are there and had a great life. Worried about the school system.
What did they want—what did UW try to do to get you to stay?
I would say UW made clear their desire that I remain there. My colleagues, I think, were supportive of whatever decision we would make, but—
It usually goes the other way, right? It’s that you’re an assistant professor at Harvard and you don’t get tenure, even though you’re doing incredible work, and the University of Washington comes and offers you a job and that’s where you spend your career. You were kind of going in the other direction.
Yeah, all those things happen. I think the way I understand this from my current perspective is that the physics department here decided they wanted to diversify, that they wanted to embark on a sort of non-accelerator particle physics element and a biophysics element. And so they went out looking for, you know, both open ads and targeted opportunity hires to strengthen the department in those two domains.
And so at the end of the day—and interestingly—and this is really kind of amusing—I had never visited Harvard up until that point in my academic career. I never came and even gave a talk here, right? It was kinda sight unseen for me. So we actually made a decision and moved in a remarkably short period of time. Like within a period of months, we had decided and moved house. It was a quick turn of events.
And had some serious apprehensions about moving to Harvard. You know, I didn’t feel like I would necessarily feel at home in a really kind of elitist sort of institution. I had real apprehensions about whether it was a good match for me intellectually. But on the other hand, the astronomy element of Harvard with the Center for Astrophysics is a powerhouse intellectually with a tremendous amount of telescope resources and knowledgeable people, which has no peer nationally.
I mean, the Center for Astrophysics has 300 PhD astronomers doing science here. It’s a big thing.
I wonder, Chris, how much of a parallel you might see looking back to your experience in 1989 coming from Seattle to Berkeley and feeling the way that you felt there and then in 2003, coming from Seattle to Harvard and assessing where you might fit in in this much bigger environment.
Yeah. I would say by that point, maybe inappropriately, I had some sense of not worrying like I was intellectually inadequate—
Well, you weren’t teaching yourself astronomy at this point either.
True. Yeah, no, I mean I think it was more whether I was a good match to the institutional culture I think was my biggest apprehension.
And obviously you are at this point, right, or you wouldn’t still be there. How did that match come about? How did you figure out how to make yourself fit in?
I’m not sure that’s what happened. I would say more what happened was I came here and had surprises, both positive and negative. And the people here are extraordinary. It’s a fantastic intellectual environment. On the other hand, there’s a sense of complacency and self-satisfaction that I find terrifying.
Complacency that if you’re at Harvard, you’ve made it and there’s no place else to go so the research suffers?
No, more complacency that as an institution, we’ve made it and we don’t need to worry about adapting and evolving and improving.
And just a rip from the headlines kind of observation, nowadays with remote learning and coronavirus, I’m sure even a place like Harvard is facing existential questions of what exactly are we offering and what’s of value if everybody is just sitting home on their computers? What does Harvard even mean at that point?
Absolutely. I mean if we pride ourselves in the residential liberal arts undergraduate experience, that is in diametric collision with public health considerations. You’re absolutely right. So then ironically, you know, having come here and shared my perspective of the sense of complacency, before you knew it, I was a department chair.
[Laughs] It’s a very unique position to be in when you’re department chair because it’s Harvard and it’s physics and so much of what happens at Harvard sets the tone and reverberates around the country. So in any number of areas, when you became chair, what did you see as the most important items to work on that would be fundamentally important for moving not only physics at Harvard forward, but sort of how academic physics was moving in general at that time.
You know, questions on how graduate students got funding or attracting students or issues of diversity and inclusivity, both among students and the faculty. What did you see, coming into the chair position, as the most important things that you would wanna work on?
So the way I framed that at the time was I kinda made myself a list of stakeholders in the department from undergrads to staff to graduate students, postdocs, junior faculty, senior faculty, and said to myself, “I’m gonna make things better in some tangible way for every single one of these groups that are stakeholders in the enterprise.” And had pretty much fired up a good head of steam when the 2008 financial crisis hit and just completely knocked the legs out from under it.
So I seem to have a knack for taking on administrative jobs that two years in are derailed by some national crisis. So never let me take another position. It’s not in the national interest, clearly, right? So that rapidly devolved to, “Oh my god, how are we gonna get through this?” And just kinda survival level crisis management.
Meaning that even with the gargantuan endowment that Harvard has, the 2008 crisis really did have budgetary impacts on your department?
So, minor digression.
There’s an impression that the Harvard endowment is this monolithic bank account that, you know, like all the money’s in one big account and you can just write a check and get through it. That is emphatically not the case. Harvard has endowments, plural, like thousands of them. The overwhelming majority of them, highly restricted in order to carry out the wishes of the donor.
So for example, long after the nation of Ukraine has been absorbed by whatever transformation occurs in Europe, Harvard will have a professor of Ukrainian studies because there’s constrained money that just can’t be used for any other purpose. So a lot of it is crystallized and not fungible. And highly constrained in the ways that it can be expended. So our managerial discretion to transfer resources is far, far, far less than you might imagine.
That’s a very sort of good public service announcement for what so many people think to be, you know, this is how Harvard works. That’s quite interesting. So even in terms of the physics department, there are constrained endowments that you didn’t necessarily have access to that would have allowed you to float the situation easier?
So what did that mean in terms of decisions on staffs and decisions on laboratories, on graduate student funding? I mean is it really all of the above? Did you have to take a hard look at all operations coming out of the physics department?
Sure. Yeah, I wrote a memo that’s enshrined in the minds of some of my managerial colleagues that basically said, “No more strawberries.” We just cut back on everything. We suspended hiring. But I’m proud to say we got through it with no layoffs in the department.
Yeah. Obviously, you must have had to make some difficult decisions, but I wonder if you also saw opportunity to trim the fat a little bit so that really, the best and most significant research was what would be supported and recognized?
Yeah, so I mean it’s certainly true that you know never let any crisis go unexploited, and that’s true for sort of at the five percent budgetary level, but the system has evolved—and look, as with all big institutions, there are plenty of things that you inherit that maybe you wouldn’t have done that way starting from a blank piece of paper and times like this are an opportunity to make those changes and adjustments for sure.
Can you look back at your period as chair and be proud of your contributions to making the department more inclusive for underrepresented groups?
No, I don’t think I was successful in that regard and I think if you look nationally as a field, despite the effort that has been expended to address pipeline and participatory issues in our field where we face major challenges, we had made depressingly little headway relative to what I think we need to do.
And in my current job, that’s a top priority element for me—across now all of science and engineering—to identify effective steps we can take to make meaningful, lasting, substantive change in the participation in these technical fields. It is the top of my list of things to do.
And so let’s just jump right into that, so #ShutdownSTEM, of course if that just becomes a day on the calendar that we used on that day, but we don’t keep that conversation going, we sort of miss the point of the whole effort, right?
And so you have this amazingly unique and powerful position to really change the nature of so many of the ways that we think about these things. And so from your perspective, what are some—I guess to begin with, what’s some low-hanging fruit that you see that these are easy wins to increase diversity and inclusivity in STEM? Let’s start just with that. What do you see is some low-hanging fruit to change where we are?
So some of our departments had done this already, but people are taking a really hard look at what are the predictors of success in graduate admissions and how should we bring those to bear on who we decide to invite to come here for graduate school. So the traditional indicators are grades, GRE scores, but I think there’s by now really compelling evidence that GRE scores indicate a lot more complicated factors than just likelihood of success in graduate school, right? Socioeconomic factors and others.
So looking hard at what we do in graduate admissions—because that’s something that if we change it, takes effect immediately, and the turnover in the graduate population is every six years. And so in five years, we’ll have a completely different demographic distribution in the graduate students.
I think another place where we can have a high impact on the national scale is to better train and educate the postdocs who come through here who often go on to faculty jobs at other institutions to help them be effective agents for change in the places that they go. And that’s very high on my list because postdocs are at a complicated professional stage where they are neither faculty nor students, and as with many places, Harvard is similar in that it’s not entirely clear who sort of owns the education and training of postdocs institutionally.
Is it a departmental function? Is it a divisional function and who’s looking out for their welfare? You know, it tends to be more kind of PI-focused in the sciences, but we’re trying to appropriate ownership of that problem at the science division level and working in partnership with the postdocs that are here, put in place a professional training and preparation program that will help them both understand these challenges and be effective in helping to solve them nationally. And I see that as a leverage point for us.
The standard response is going to be doing something about faculty hiring. Yes, we’re gonna do better in that domain, but the problem is that the time scale for turnover in that cohort is measured in decades. It’s hard to achieve a high pace of change if we do it through the mechanism of hiring new faculty.
I think the most substantive undertaking that I foresee in the coming year is actually going right to what I think is the heart of the problem, and that is climate and culture issues in science departments. I think that we need a university where people feel like they’re welcome and they feel like they’re respected and where they feel like they can thrive. I don’t feel that’s universally the case in the departments that we have in the sciences and I think we need to take steps to address that.
What about issues about changing the culture, specifically at a place like Harvard where—I certainly won’t name names—but where there are graduates of the program—both undergraduate and at the graduate level—where obviously we are light years away from the overt or even casual racism of decades ago, but there are still many, many memories and instances where people were made to feel not welcome, were made to feel like they didn’t belong there, were assumed that they were support staff, things like that.
Now this is getting into the not so low hanging fruit, but some of the really more difficult ways of changing the culture or tone of an institutional environment. Are these things where—from your vantage point—there’s concrete change that can be made or is that sort of beyond what can happen within any given campus?
So my personal answer to that is that’s what we have to do. I don’t have a knob on my desk that I can crank that says ‘improve departmental culture’. Right? It’s very hard to bring about that kind of change, and furthermore, I think we talk about this in three elements, with diversity, inclusion, and belonging. The diversity part is demographic metrics, right? That’s kind of easy to track. And I think it’s easy to fall into the trap of thinking that success in this domain is achieved by demographic representation. That’s not the case. That’s not the goal.
The goal is that people feel next step included, and then they feel like they belong. The middle school dance analogy is diversity is that you get to go to the dance. Inclusion is that someone asks you to dance, and belonging is when you have no hesitation of going up and asking someone to dance. And we need to get to that latter state. And we’re at the early stages of this transformation.
And I think one of the challenges is balancing the national and institutional and individual appetite for rapid change with what it actually takes to make lasting, systemic change in an academic institution, right? And finding a path that, as you say, picks up the low hanging fruit or fruit that’s on the ground, sure, let’s take those opportunities, but let’s put our effort into lasting substantive institutional change that actually addresses the core issues.
And part of the thing that’s hard about that is it’s difficult to identify performance metrics, but I think we’ll know we’re there when we get there, that’s for sure. And we are not there now.
Chris, in terms of the motivating factors that are most important to you, there’s the broader social justice issue of anyone and everyone who has talent and interest in the sciences should be encouraged to pursue a path of success, no matter who you are, where you come from, or what you look like. Right? So that’s sort of the social justice aspect of it.
But then there’s the more qualitative and quantitative aspect of diversity is good for science, you know, in and of itself. Do you see those two—are those two items integrated or do you see them as separate in terms of the motivation that you have to be a part of this change?
I think it’s all of the above. I mean, one of the ways I phrase it here—yeah. So bear with me. One of our fundamental problems at this institution is if ever there were a place that were viewed as elitist, snooty, and exclusionary, it’s where I work, right?
So how do elite institutions get that way? Answer; by rejecting people. We pride ourselves on how selective we are for undergraduates and what fraction get admitted. We pride ourselves on how selective we are and what filters we apply to people, so we become elitist and self-congratulatory by rejecting people. And at the same time, out of the other side of our mouth, we say, “Oh, we wanna be inclusive and welcome everyone to come,” right? So those are just fundamentally in collision.
So my way of phrasing it is it’s in the vital interest of the excellence of Harvard that we cast as wide a net as possible, identify the most excellent people, and have them come here, emphasis on have them come here. So I have had colleagues tell me that they explicitly advise scientists of color to not come to Harvard.
Because it’s not seen as an environment where they can thrive and succeed. That cannot sustain itself. We cannot remain the magnet for people to come and do their best work under those circumstances.
It’s also just an embarrassment that that’s sort of the word that’s out there about Harvard.
Right, and that’s a recipe in the long run for us becoming a mediocre institution, and so even amongst—and I have to admit, there are colleagues that I work with who view this elitist Harvard out of date self-image as what they aspire to retain, and my argument to them is even if that’s your motivation, it’s important that we do this because if we don’t, the Harvard that you want will not persist.
Chris, in what ways did your tenure as department chair prepare you for your current work and in what ways was this simply a quantum leap and you had to learn on the job?
Yeah, so, when I stepped down as department chair in the physics department after a three year stint, I told myself, “Well, that was an interesting and valuable experiment.” If I look at the results of that experiment, I don’t wanna do academic administration, but it’s the sort of satisfaction to emotional toll ratio is not a good thing. And I became deeply involved in this big survey telescope project called LSST and my plan was to go for a sabbatical year to Chile and commission LSST.
And the project, as is the case with big, expensive, hard projects kinda slid to the right in terms of its timetable. And the year that I was gonna go on sabbatical was not the right year to go to Chile and commission LSST ‘cause there was nothing there to commission. And that happened to coincide with a big turnover in Harvard leadership. So new dean of the faculty of arts and sciences, new university president, total turnover within the system.
And the staging of those different appointments was not exactly optimal. And so the outgoing dean of the faculty of arts and sciences called me to his office—and I thought he was gonna chew me out for not having offered a general education course—and he said, “Hey, we’d like to ask you to serve as interim dean of science as we go through this transition.”
And I thought to myself, thought number one, my previous conclusion was never wanna go back in academic administration, however, I do kinda have this little hole in my professional life and yeah, you know, maybe I could do that for six months and do some good and then bail out.
So thought about it, talked to my wife about it, and said sure, but only for six months because that way, your successor is going to be forced to appoint my successor in short order and we can just kinda get along with things. And the new dean of the faculty of arts and sciences was appointed, Professor Claudine Gay from the Department of Government, and the first thing she did in the first meeting that we had was to say, “Please, please, please, do more than six months. Do the whole year ‘cause you gotta help me out here and keep doing what you’re doing.”
So I said, “OK.” And by that point, I had come to two surprising self-realizations. One was this job is more interesting than I thought it was gonna be. It’s really actually a profoundly interesting and challenging task. And second, even more surprisingly, I was a little bit better at it than I thought I was gonna be. And so I relented, agreed to do the full year, and as that year unfolded, struck up what was, from my perspective, a really great working relationship with Dean Gay.
And that relationship between my position as a divisional dean and the overall dean of the faculty of arts and sciences is an absolutely key relationship to the institution functioning well, and I’d like to think that both of us came to an appreciation of doing business well together and when I was asked to remove the word ‘interim’ from this title, I sorta thought, “You know, I can continue to be, I would hope, impactful in my own subfield and advance the scientific enterprise and teaching and do what I can to make the world a better place from that standpoint, or maybe I should take seriously the notion of trying to make Harvard better and do what I can to raise all boats in the scientific and educational enterprise that we have here.”
And when I put it to myself that way with a serious dose of apprehension about whether I’m the right person for this job and whether I’m up to it and whether I’m of the caliber of leadership that I think Harvard deserves, eventually thought I’d give it a shot. So in some ways, it’s actually an easier job than being department chair emotionally because there’s a level of clinical detachment from the faculty that makes it easier to say, “I’m the dean and I don’t think you made a good judgment call here and I’m calling you on the carpet for it.”
It’s easier to do that from this vantage point than being a department chair where they’re like your friends and your colleagues and a year later you’re gonna be back in the faculty meeting with them. So I would say the sort of stomach churning emotional part of it from that standpoint seems easier, but at the same time, the stakes are higher and especially now, the stakes are really high.
So significant elements of apprehension, significant elements of hoping that I have my priorities straight and that I can do things that are impactful in a collegial, consultative fashion, to help Harvard make the world a better place.
How long do you see yourself in this role?
I think I’ve got two years to go.
And then the plan is—
It’s a five year position.
And then the plan is just back to the physics department, that’s the idea?
That’s my current plan.
Now on that note, how, in recent years, perhaps specifically between 2010 and 2018, how well have you been able to keep up with the research over the years?
I think I’m doing fine. I think it’s actually, for multiple reasons, I think it’s really important that someone in this dean position maintain an active research group, be sending proposals through the system, be living the life of a PI because otherwise I think you just kinda lose touch and become ungrounded with the reality of the system.
This whole fundamental cosmology domain remains a vibrant and interesting scientific subfield. We’re pushing forward on addressing the fundamental systematic errors that afflict these type Ia supernovae as distance indicators. A student of mine wrote a paper—being the sort of cosmology police—showing where some other authors, we think, strayed from the road to truth and took them to task as a result. We’re using solar cells as ways to calibrate astronomical apparatus. A bunch of fun stuff going on.
Chris, one aspect of your career we haven’t yet talked about is your work teaching undergraduates and serving as a mentor to graduate students. So over the years, if you can reflect back, what have been some of the most enjoyable courses you have taught undergraduates? Perhaps those who also might never think about physics again after leaving your class.
Yeah, so I taught a great course at the University of Washington, which was a little bit the sort of how things work kind of class for non-science majors. And that was great. It was sort of demystifying technology, teaching them some scientific method along the way. Every single day we’d have students submit questions, you know, an example question is, “I was in the library and I tried to call my friend on my cell phone and I could see her, but her phone didn’t ring. How can that be?”
So everything from sort of the physics of your toaster to technology and its scientific underpinning and so that was a great course. I thoroughly enjoyed that. I think one of the courses that Eric and I did together in Seattle for graduate students was us experimentalists got a little worried that the introductory graduate sequence was all about second or partial differential equations and Ylm’s and not quite as grounded as maybe we would have liked and so we did a graduate course on interferometer in all of its different domains. Everything from matter wave interferometry to gravity wave antennas and had students read fundamental papers and discussion group to sort of ground them in an experimental physics outlook. That was a great class that I thoroughly enjoyed doing with Eric.
I revamped the introductory physics sequence for engineers here at Harvard and inserted a big numerical component, both for data analysis and for numerical modelling of physical systems. And I think that was a good class. Had a great time teaching a sort of trade craft of optical astronomy and observational techniques, everything from the science of detectors to image reduction methodologies for undergraduates here, that was a good course. So, I don’t know, lots of fun stuff.
And for graduate students, if you want to talk about any standout graduate students that you’re particularly proud of and the kinds of things they’ve gone on to do, I’d be interested in hearing that. Additionally, if you could talk more generally about among your most successful graduate students, what do you see as some of the attributes that they share and how much of that might be related to the kinds of things that really energized you when you were a graduate student, particularly as you got excited in this year-long experiment on the fifth force?
Yeah, so that’s a great question. I have, over the years, had the privilege of working with a large number of outstanding junior colleagues as graduate students and postdocs, and I’ve always viewed my role to draw out of them some articulation of where they see themselves in the future and try to use their time in graduate school as a transition to equip them to move into that future in a successful way.
And I would say rather than rattling off the graduate students who are on the faculty at different places and claiming them as the trophies on the shelf, I would say what I am the proudest of as a mentor is the instances where they moved into something different and did something that they found interesting.
So a number of students that got their PhD with me moved into biomedical instrumentation or the life sciences in some way. Another student that I’m extremely proud of moved into the sort of public policy domain and has been very effective in that regard, initially with stints in DC and eventually in the kind of philanthropic private sector.
So I think that element of intellectual agility, I would like to think, I encouraged. And I think that’s the connective tissue to my intellectual heritage is to—what I try to tell people is to just have some opportunity radar scanning that’s looking broadly at opportunities and needs and not being apprehensive to move in that direction. Some kind of thoughtful assessment of if given the chance to educate yourself, what can you bring to bear on solving that problem?
And on top of that, because of the nature of the work that we do, it’s intrinsically collaborative in teams and helping people navigate the human factors of successfully addressing hard problems as a collective and harnessing the mentality of a group and bring that collective to bear on a problem I think is another hallmark of the experience that students get working in our group.
Chris, now that we’ve brought your work really up to the current day, I think for the last part of our talk I want to ask a few sort of broadly retrospective questions and then a forward-facing question. So the first is what advantages do you see, if any, to the very unique career path that you’ve taken? Particularly I’m struck by your interest in diving headfirst as a postdoc into a field that you had to teach yourself as if you were a freshman essentially. And so what advantages do you think that approach confers long-term as you might give advice to a graduate student?
I don’t want for a second to imply that the choices that I’ve made and the decision-making template that I brought to bear is necessarily right or better or even necessarily good, right? I mean, I think it’s an entirely fair question to ask am I just the guy who walked away from the airplane crash, right? I mean how much of this is serendipity and how much of it is incredibly shrewd career management? I have no idea. I have no way of knowing.
And I do think though that a graduate education in sciences ought—above and beyond everything else—oughta equip you how to teach yourself things and how to teach yourself new things. And I think you can find lots of examples of mid to late career scientists who have stagnated by virtue of not having kept up and taught themselves new things. So I think that element is essential to professional success and in my case, essential to personal satisfaction, right?
But each person has to find their own path and different people find different things satisfying. I think maybe the harder part is understanding what it is you do find satisfying and understanding how to seek it. And I think also—look, there are many projects that we haven’t talked about that were not successful. There are many times where things didn’t turn out as planned. Not surprisingly, we’ve emphasized the ones that did, but I could rattle off failures.
You mean scientifically successful, but of course there’s always value in learning from what didn’t work.
Yeah, that’s right. And I think one of the hardest lessons I learned from Eric Adelberger as a graduate student was we talked about the fact that this torsion balance had a tilt problem, so I made a tilt meter that had some optical thing that had some interrupted beam that was supposed to be able to tell when this thing was tilting, it just didn’t work. I mean, it just failed and it failed spectacularly.
And so I went into Eric’s office and I’m like, “Well, you know, I got the data from this thing and it really sucks, comma, but,” and I started making all these excuses of how I was gonna get better and Eric’s like, “Didn’t work. Drop it.” And I was, “No, no, but I spent months making…” “Didn’t work. Drop it. Move on. Didn’t work. Drop it. You hear me? Drop it.” And I craved like, “Oh no, if I just, if I just…” And that willingness to recognize the need to let it go. Not only did it not work, it ain’t gonna work.
And so having that judgment of when to relinquish things is just super hard, but boy, I tell you, I came away from that lesson with Eric and try now to say, “OK, so here’s the palette of things that we’re doing. Which of these things should we set aside and which are the things that we’re gonna move forward with?” I think that’s a hard thing to learn. I don’t know how we got off on that track.
No, it’s great. That’s a good track to get off on. Very broad question, in what ways—and I guess I’m specifically thinking about just in the way you describe it, that exciting year of doing the research on the fifth force at UW, it seemed to me like not a particular high tech enterprise.
No, it wasn’t.
Right, exactly. And so my question is in what ways has the phenomenal growth in both computational power and technology changed over the years and what impact has this had specifically on your research and your view of the research in the field generally? And so I wanted to sort of situate that year at UW because it seemed like really fundamental work can happen even without a 50 million dollar multi-laboratory effort. So I wonder if you could just sort of reflect broadly on the role of computers and technology in moving the field forward in fundamental ways over the past 20, 30 years?
It is true that the initial fifth force experiment that we did was almost a kind of Home Depot kind of experiment. I mean, that’s being a little bit uncharitable, but you’re right. A team of six people in one year did it, how hard could it have been, right? And it just required understanding what the right question was to pose of nature and it was such new green field intellectual terrain, that Home Depot technology could allow you to make a state of the art contribution.
That’s not common. It’s not common that something comes out of left field and you just go, “Whoa, hey, we can do this.” So I feel fortunate that that happened right at that particular career stage. It’s certainly true that in cosmology, there’s been—over the last two decades—a progression of consolidation and I think maybe the best example of that is in the microwave background domain where, at the time at the Center for Particle Astrophysics, there were lots of single PI group level microwave background projects. People in Antarctica, people in high dry deserts, small aperture, you know, ground-based, lots of projects.
That led to let’s call it 10 year ago efforts where it was bigger apertures, the South Pole Telescope with John Carlstrom in Chicago was a convening point for that. That and the Atacama telescope with the group at Princeton sort of shook out that field to where there are now fewer, bigger experiments. And now the microwave background endeavor has kind of focused on CMB S4, which is a kind of like all hands on deck, here’s the next thing for us to do and there’s gonna be one project.
So I think that’s illustrative of what’s happened across a lot of this field of observational cosmology and the LSST project that I mentioned is another such example. It’s an end to end billion dollar endeavor that has drawn an international participation to engineer an optical survey system optimized to go study dark energy, as opposed to using telescopes that are as old as I am.
So that, I think, in all cases is a consequence of the measurement frontier becoming more challenging. By the time you’ve scraped off the easy thing to do at a factor of 10, then you get down to a factor of 100, now we’re gonna do it at a factor of 1,000. You know, the root N statistics that you need, the attention to systematic errors, the level of complexity that’s necessary to achieve the measurement objective necessitates more money, more people, and more time.
And the only time that kind of gets a reset is if there’s a whole new different flavor of question that you can ask, and then you start with the Home Depot level projects and it eventually evolves to these much harder, much more sophisticated, much more complex endeavors. On the computational side, yeah, sure. I mean, I would say the three enabling technologies for the kind of stuff I’ve been doing are optics, detectors, and computers in equal measure.
And I remember during the MACHO project, we got our first few megabyte hard disks and we thought we were in paradise. I mean the empowering evolution of computers—both from the data collection and analysis and simulation side—has been transformational. There’s no question.
Chris, I think for my last question I wanna ask the forward-facing question. Obviously, it’s very clear what your goals are in your current position and I wish you a lot of luck in all of the above because like you said at the beginning of our talk, this is certainly not what you bargained for, particularly with the corona virus, but in a couple of years when you get back to the physics department and you can throw yourself sort of fully back into that world of research, what are the big open questions that are most compelling to you in your field?
What are the things where this is where you wanna pour your energy into, this is where you feel like the field is on the cusp of fundamental discovery, and how might you recreate that magical year at the University of Washington where you recognized that there was this race, there was this intensity, there was really opportunity to move the field forward in fundamental ways? What do you wanna accomplish in that realm as you look toward the rest of your career?
So I think it remains the case—as has been true for some time now—that three big indicators of our lack of a complete understanding of the intellectual framework of physics come from astronomical data, right? Evidence for inflation, indirect though it may be, evidence for dark matter and evidence for dark energy. And those three remain unresolved, despite my having committed a lifetime of effort to try and figure ‘em out.
And I think I’ll look hard at where is the opportunity to make a substantive step forward in that domain? Historically, the inflation piece has been the domain of my friends in the microwave background as the way to look for, you know, evidence of primordial imprint on the CMB. I’ll probably leave that to them. I think it’s a little late in my career for me to turn into a CMB person.
The prospect of using 21 centimeter radiation to make a three dimensional map of large scale structure looks interesting to me. That’s radiofrequency technology. I’m a HAM radio guy, I can imagine moving in that direction. The dark matter/ dark energy pieces remain thorns in our side, and I’m a little apprehensive that after the LSST, I don’t know quite what the successor project is gonna be to go after dark energy and I think we need to be more creative instead of looking at large scale averages, start looking for more subtle pieces of how to reconcile is this, you know, quantum fluctuations in the vacuum or is it really the classical cosmological constant that sits on the GR side of the equation in motion?
On the dark matter side, it’s interesting that those projects—again, another example of a lot of consolidation, moving from lots of mom and pop experiments to gargantuan vats of liquid xenon or whatever, right? Again, those big projects have had yet to find scattering evidence for WIMPs as the constituents of the Milky Way halo. So look hard at both direct and indirect detection experiments in the dark matter domain and try to find a place where I can make a difference.
Well, Chris, it’s been so fun talking with you today. We’ve covered an amazing amount of ground in a relatively short time together. What a compelling life story from the beginning you’ve had and, you know, it’s just been a lot of fun to listen to you and to get your perspective on all of these things, so I’m really quite honored that you were able to squeeze me into a very busy time in your calendar and I wanna thank you very much for that.
And at the right time, this is going to be an interview, a transcript that is going to be tremendously valuable in our collection for people to access from any number of areas. So I’m really so glad we connected. Thank you so much.
No, my pleasure. Thanks for your time and interest.