Hamish Robertson

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ORAL HISTORIES

Credit: Department of Physics, University of Washington

Interviewed by
David Zierler
Interview date
Location
Video conference
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In footnotes or endnotes please cite AIP interviews like this:

Interview of Hamish Robertson by David Zierler on May 6, 2020,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/44411

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In this interview, David Zierler, Oral Historian for AIP, interviews Hamish Robertson, Boeing Distinguished Professor of Physics Emeritus at the University of Washington. Robertson recounts his childhood in Hamilton, Canada and his experiences as an undergraduate at Oxford University and his early interest in working at Los Alamos Lab. He describes his decision to pursue graduate work at McMaster University, which had just built the first nuclear reactor on a college campus in Canada, and his intent to focus on atomic beam physics. Robertson explains his post-doctoral research at Michigan State and his shift from nuclear structure physics to neutrino physics and his formative sabbatical year at Princeton and his tenure at Los Alamos, where he worked on neutrino mass. He describes his views on the standard model, and the recruitment process that led to his decision to join the faculty at UW, where he helped to create a laboratory to continue research on neutrinos. Robertson talks about the major influence of John Bahcall, and he describes the issues in physics research that remain compelling to him.

Transcript

Zierler:

This is David Zierler, oral historian for the American Institute of Physics. It is May 6th, 2020. It is my great pleasure and delight to be here with Professor Hamish Robertson. Hamish, thank you so much for being with me today.

Robertson:

My pleasure, David. Thanks for asking me.

Zierler:

To start, tell me your title and institutional affiliation.

Robertson:

I'm presently retired. I'm the Boeing Distinguished Professor of Physics Emeritus at the University of Washington.

Zierler:

How did the Boeing chair come together?

Robertson:

That was a very nice honor that the department gave me in 2008, I think. Yes. It’s a chair that was originally given by the Boeing Corporation in honor of the Nobel Prize that went to Hans Dehmelt in 1989. Once Hans retired, it was given to other people. One of the previous holders was Norval Fortson, and then the department gave it to me. It was a huge honor. I was tremendously happy.

Zierler:

Was there any contact with Boeing at the time or since, as a result of this chair?

Robertson:

Boeing holds a so-called Boeing Breakfast once a year, which is a huge event. Boeing is tremendously supportive of the university, and they have many people—students with fellowships. There’s another Boeing professor somewhere else in the university as well. There are many things that Boeing does, and they have a breakfast at the University Club. There’s, I would say, probably two or three hundred people there, and the students give presentations. It’s quite an event.

Zierler:

Great. Now, let’s go right back to the beginning. Tell me about your family background and your birthplace and early childhood in Canada.

Robertson:

I was born in Ottawa in 1943. My father was stationed in Ottawa. He was an architect for the Navy, the Canadian Navy. Normally, we lived in Hamilton. And at the end of the war, my parents moved back to Hamilton, and I lived in Hamilton until I was about 16, at which time—so, I went to school there. I went to Hillfield, as it was called then—Hillfield School. It was a private school. And I did well in school. I finished with the Governor General’s Medal in Ontario, which was considered quite an honor, then. My mother thought it would be good for me to go to Cambridge, in fact. And that was on the plan, on the radar. I went over to England with my parents and interviewed at Cambridge, and actually [laugh] I can’t believe I had the chutzpah to say I didn't really like it. [laugh] I did like it, but they wanted me to do a number of things in the curriculum which weren’t of great interest to me. So I said, “How about Oxford?” And they said, “Fine.” [laugh] So I wound up going to Oxford.

Zierler:

Your mom must have been a pretty worldly person to think of Cambridge for her son as a place to go to school.

Robertson:

Yes. She had actually been to Oxford herself. She was at St. Hugh’s College. She had then gone on to a PhD at Radcliffe, which was the woman’s arm of Harvard University in those days. She was a scholar in Norse languages. She could speak ancient Norse. She could read Beowulf. It was wonderful to hear her do that. Immediately, you felt like you were going back a thousand years in time to hear this ancient language.

Zierler:

Was she an independent scholar, or she taught at a university?

Robertson:

She went back to Canada after her education and became a teacher in sort of middle school settings in Hamilton. And then once she got married, she gave up her external work, I think, partially to raise me. [laugh] I was her career.

Zierler:

In high school, did you distinguish yourself across all disciplines, or did you really stand out in math or science?

Robertson:

I was terrible at history. [laugh] So yes, no, my main interests were math and science. I had a mathematics teacher, Geoff Steele, who was absolutely wonderful. Normally, I actually hated school. I really would think of any excuse not to go to school. But Steele’s lectures were so good that I did not want to miss those. He totally inspired me to become something in the area of mathematics and physics.

Zierler:

Now, when you started at Oxford, was your intent to focus on physics from the beginning?

Robertson:

Well, I went into the natural sciences, yes. I was very interested in physics at the time. At one time, I wanted to become a chemist. It turned out that I really didn't have the memory for that. The nice thing about physics is that if you forget something, you can work it out. [laugh] You can’t do that in chemistry. You have to know. [laugh]

Zierler:

[laugh]

Robertson:

So my lack of really good memory steered me in the direction of physics. And I was already very interested in that. I was thinking recently that ever since I can remember being interested in physics, I wanted to go to Los Alamos. Oddly enough, I didn't go there right at the beginning. But I did eventually wind up there, which was sort of my dream location. I was so impressed and inspired at what Los Alamos had accomplished during the war. I was not of course conscious during the war of what was going on, but later, it was known throughout the world what had been done there. And to do what they did in the matter of two and a half years still amazes me.

Zierler:

That’s right. That’s the kind of national effort we could use right now.

Robertson:

Absolutely. [laugh]

Zierler:

I've heard many stories about graduate experiences at Oxford, but not many at all about the undergraduate experience in Oxford in physics. I wonder if you could talk a little bit about how the department was structured, the kinds of courses that you took, the interests that you developed?

Robertson:

Yeah. The Oxford and Cambridge schools are quite differently organized than in the U.S. You go to lectures. There are lectures, which are organized on a university-wide scale. And I remember I had lectures from Sir Denys Wilkinson—

Zierler:

Oh, wow.

Robertson:

—who was a noted nuclear physicist at the time. I think I can say this safely—that I found them pretty much incomprehensible. [laugh]

Zierler:

[laugh]

Robertson:

But he was a very amusing person, and was a wonderful person to listen to. But a little bit above my level, at the time. But I caught up, and eventually I got to really enjoy it. The main focus there as an undergraduate is you have a tutor, and you actually do most of your learning with your tutor instead of going to lectures all the time. The tutor would talk to you and assign you homework. It was a small group of people, perhaps—I forgot how many, but maybe three, four, or five, or something like that.

Zierler:

And the tutor was an upperclassman?

Robertson:

Which means?

Zierler:

Like just a few years older than you? A fellow undergraduate?

Robertson:

No, no. He was a professor. He was a full professor.

Zierler:

Oh, OK.

Robertson:

It was John Sanders, who was actually noted at the time, and still is, for the most precise measurements of the magnetic moment of the proton. He has written a very good monograph on fundamental constants. Unfortunately, he’s no longer alive. I worked with him later on during my undergraduate career as an undergraduate assistant in his lab. He was very interested at the time in the early development of the laser, and he wanted me to make measurements of the lifetime of a certain promising dye that could have perhaps shown laser action, pseudoisocyanine hydrochloride. And I developed a spark light source to try to measure the luminescent decay time of that. And I think if it hadn’t been for me, Sanders might have been one of the first discoverers of the dye laser.

Zierler:

Wow. [laugh]

Robertson:

[laugh]

Zierler:

Socially, did you mix in pretty well? I assume most of your fellow classmates were English?

Robertson:

Yes, that’s right. And I still keep touch with some of them, yes. They were a very friendly and supportive bunch. Coming from the colonies [laugh], I was not used to the ways of the more civilized world in England, I think, but they were very good to me.

Zierler:

How well prepared did you feel you were, relative to your peers, at Oxford?

Robertson:

That’s a really good question. In fact, before going to Oxford, since I had done grade 13 in Ontario schools—in England, they do three years in university, whereas here in the U.S. and Canada, we do four. So I had to do an extra year of school, and I went to Winchester College for nine months effectively, to get that extra year of schooling. Which again was quite an experience. Winchester is a very old school, so-called public school—which here means private—in the south of England, and was founded in 1370 or something like that, with many of the original buildings still there. And that was also quite an experience, because of its ancient demeanor. I remember that they had just installed central heating, and I thought, “Oh, thank goodness.”

Zierler:

[laugh]

Robertson:

Otherwise I would freeze to death. So it turns out that their idea of central heating was this lukewarm pipe running around the middle of one room in the middle [laugh] of the building.

Zierler:

[laugh]

Robertson:

You’d wake up in the morning and there would be ice on the wash basin at the foot of your bed. It was something. But it was great! It was just such a wonderful experience. I made many good friends there, too.

Zierler:

In terms of your exposure across all of the subfields in physics, did you gravitate or take courses in any particular area?

Robertson:

At Oxford, you mean?

Zierler:

Right.

Robertson:

Yeah. I was very interested in nuclear physics. Oddly enough, I liked the courses in thermodynamics. Had an excellent lecturer in thermodynamics, J.T. Houghton. We had good courses in mathematics. So it was a very nice mix of topics from good people.

Zierler:

Was there a senior thesis requirement at Oxford?

Robertson:

There was not. No. It was done on an exam basis, so there was so-called first public honor moderations, which you take at the end of the first year, and then your final exam at the end of your third year. And I got a first there, which was quite unusual. I remember that John Sanders, my tutor, the other students asked him, when the results came out, “Who do you think got the first in your group?” He guessed everybody but me.

Zierler:

[laugh]

Robertson:

So I was happy with that. [laugh]

Zierler:

In terms of both your aspirations and your identity as a physicist at Oxford, at what point did you know that you were going to continue in graduate school in physics, and in what field did you want to specialize in?

Robertson:

Well, I wanted to come back to Canada. I guess maybe I was homesick, but I thought it would be a good place to be, anyway. I had considered going to UBC and to McMaster University, because those were the two schools that had nuclear physics programs that were really notable. McMaster had just gotten the first nuclear reactor in a campus in Canada. And in fact, my uncle, Peter Bell, was the architect who designed that reactor, which was a sort of incidental connection. So I actually went to McMaster thinking that I would do laser physics because of the interest that Sanders had instilled in me in that. But the person who could be my advisor there, Bob Summers-Gill, he had a laser group, but there were no openings in that group. I couldn't get into it. But he said, “I do have openings in the atomic beam physics group.” And I said, “Fine, let’s do that.” So I went to McMaster and did atomic beam physics with Bob Summers-Gill, who was a wonderful advisor. He’s somebody nobody has heard of, but he was an extremely good advisor. He wouldn't take any nonsense from me at all. [laugh]

Zierler:

I wonder, applying to UBC, if you were willing to go that far west, if you had ever considered Stanford, Berkeley, Caltech, that kind of thing?

Robertson:

I did, yes. In fact, I remember sending out applications to Stanford, and I got a cryptic response from them saying, “Please send more information.” But it wasn’t clear what they wanted, and I didn't follow it up. So I wound up going to Canada. I think I might have applied to some other U.S. universities as well. I don’t remember now. But my heart was in Canada.

Zierler:

And where was the program at McMaster, in terms of its development? Was it in building mode? Was it well-established at that point?

Robertson:

The atomic beam program was fairly well established by then. It was probably at least ten years old by the time I got there. The nuclear program was just starting up. And during the time I was there, an accelerator was proposed and successfully funded and installed. So halfway through my program, I moved from atomic beam physics, where we had been measuring magnetic moments and hyperfine structure, into accelerator physics, nuclear structure physics, as it was done in those days, and had some very enjoyable work on the Tandem Van de Graaff, measuring the structure of radioactive nuclei, the same nuclei that I had been studying in atomic beam method. So I had a very composite picture of a lot of the structure of these difficult nuclei, which was my thesis.

Zierler:

How was your time divided between course work and lab work?

Robertson:

Oh. That's hard to say. Well, it’s very much like it is here, I think. At the beginning, you spend quite a bit of time in course work, and then as time passes, you spend more and more in the lab. I think I tended to spend as much time in the lab as I could, because I enjoyed it so much. I had always had an interest in electronics from the very beginning. My father had given me, when I was, what, maybe eight, ten years old, what is called a crystal set. Do you know what a crystal set is?

Zierler:

Sure, yeah.

Robertson:

Oh, you do? Awesome.

Zierler:

Sure, yeah.

Robertson:

And boy, I struggled to get that thing going. And after that, I was totally hooked, and had an electronics interest ever since. And I found that being able to apply my electronics exterior kind of knowledge to physics was extremely useful. One of the first things I did in the atomic beam group was to build a new power supply. They had these big old vacuum tubes which were unreliable and unstable and hard to find, and so I built a transistor power supply for the atomic beam magnets. It worked, and I was happy with it.

Zierler:

Who were some of the professors at McMaster that you became close with?

Robertson:

I knew Carl Stager very well. He was engaged in electron paramagnetic resonance research. One of the things we wanted to do was to measure the magnetic moment of a certain nucleus which was quite long-lived, samarium 151. I proposed to Carl that we actually try to do this by electron paramagnetic resonance rather than atomic beams, and he agreed. And we were successful in doing that. I also worked closely with—well, not worked closely with, but was a good friend of John Cameron, who was doing perturbed angular correlations. And I remember Don Sprung very well. He was a theorist who was one of the really nicest people. During my final exam, I was so nervous. I thought I was just going to die. And so Don I think sensed this, and instead of saying, “Calm down, relax, it’s going to be all right,” what he did was to take off his shoes and put his feet up on the table, where the committee was sitting. He was wearing white socks, and he took off his white socks [laugh] and started checking his toes. [laugh] At that point, I thought, “OK, this is really going to be OK.” [laugh]

Zierler:

[laugh]

Robertson:

It was just a—who would have thought of doing that, you know?

Zierler:

[laugh]

Robertson:

[laugh] And I did fine. So there were many people at McMaster. They treated me very well. I was a very naïve young man, and you make mistakes, you do stupid things, and nobody ever gave me any grief. They just— “Please don’t do that again.” [laugh]

Zierler:

I always ask, for people who were in school around this time—had the counterculture, had protests come to McMaster’s campus? Was that part of the scene in the late ‘60s and early ‘70s?

Robertson:

There was very little of that at McMaster. There were of course people fleeing the Vietnam War, and we saw some of those and in general would support them. But that was our main exposure to that kind of turmoil that was going on then.

Zierler:

Was your sense that McMaster was a culturally conservative place?

Robertson:

Interesting question. Perhaps so. Hamilton was a steel town in those days, with a heavy industrial base.

Zierler:

And was McMaster pretty well integrated into the town, or was there a sort of town/gown divide?

Robertson:

It was pretty well integrated, yeah. It was located in town. It has a nice campus, but it’s not Harvard, not Yale. It was something that—very much the way the University of Washington is here, it was a hub of the creation of talent for the local industry and business. Students would be recruited directly. In fact, I remember that Westinghouse wanted me to go work for them. Westinghouse had a plant in Hamilton. And I gave it some serious thought, but I decided I wanted to stay in research.

Zierler:

What was the process of putting your dissertation topic together? How did that play out?

Robertson:

I actually thought I was going to be finished much before I actually was. I applied to Bell Labs to go to work in the U.S., and I didn't have a Green Card. It takes a long time, or it did even then—two years—to get a Green Card to go to the U.S. But it took me another two years to finish my thesis. And I remember I got extremely sick with something. I'm not sure what it was; some kind of respiratory thing that confined me to bed for a month. And during the time I was in bed is when I wrote my thesis.

Zierler:

Oh, wow.

Robertson:

So if it hadn’t been for that, I just—I would have never got it done. [laugh] But it was finally done, and I—

Zierler:

What was the topic? What did you work on?

Robertson:

The properties of the odd-odd cobalt nuclei—cobalt-58 and cobalt-60.

Zierler:

And were you thinking you were on a trajectory for a faculty position at some point? That’s what your aspiration was?

Robertson:

I never thought about that at the time. I never gave that any thought. Really what I wanted to do was to do research. So at that time, when I got into graduate school, you could have written your own ticket, because there was tremendous shortages of nuclear people and funding was abundantly available. By the time I got out, the situation had changed completely. The job market in the area had collapsed.

Zierler:

What was your sense? What structurally had changed? Was this the end of the Sputnik era? Is that basically what was going on?

Robertson:

It’s hard for me to associate a specific event. It seemed like it was more the continued decline from the end of the Cold War. Well, the Cold War was not over then, but from the—I'm sorry, from the end of the “hot war.” [laugh] There was a period following 1945 when nuclear physics and atomic physics was highly regarded and in great demand because of the work of developing the atomic bomb. And that ended sort of about that time. And perhaps it was associated with the new light that the industrial-military complex was being held in, about that time. But for whatever reason, in Canada, the funding sort of went away. There were just no jobs, not just in the area of nuclear physics but many areas. It was kind of a recession.

Zierler:

Now to be clear, your opportunity at Westinghouse was not Westinghouse Labs?

Robertson:

That’s right.

Zierler:

This was more work in the industrial setting.

Robertson:

Yes, right. They had a manufacturing plant in Hamilton. It would have been some kind of a higher-level job. They didn't want me to make lightbulbs. But I'm not sure exactly what I would have been doing there.

Zierler:

So what were your options when you finished at McMaster?

Robertson:

To get a postdoc. The normal trajectory. And I applied for some postdocs, and I got one, at Michigan State. And that was, at the time, considered to be quite an accomplishment, just to get a postdoc, because there were so few jobs, even like that. So I went to Michigan State at the time. I don’t think it was ever my intent to stay in the U.S., but once you get there, you know, life is what happens while you're making other plans. [laugh]

Zierler:

What was your work status? Did they sponsor a Green Card for you?

Robertson:

By then, I had one.

Zierler:

Oh, because it was the same process from earlier?

Robertson:

As it happened, I had one. And I went to Bell Labs and interviewed there, and they offered me a position. But to be honest, I didn't like it. It was a very difficult atmosphere. I felt that there was a lot of pressure there. The people that I talked to seemed to be under pressure all the time, and that, I could sense, was not going to work for me very well. So I decided to stay in nuclear physics and went to Michigan State.

Zierler:

What was your work at Michigan State? What were you doing there?

Robertson:

We had a 50-MeV cyclotron, so it was nuclear structure again, with very high precision. This was a world-class machine at the time, because of its high beam quality. So you could do very high-resolution measurements at high energies—proton, deuteron, alpha energies. So we worked on that. I worked with Jerry Nolen for a while on high-resolution transfer reaction measurements. Walter Benenson, I worked with everybody at the lab, really. And then in 1973, I went to Jülich for three months on an exchange visit, and worked with people over there. They had a very high-energy cyclotron, sector-focused cyclotron, 200-MeV alphas, I think. And, working with Willy Falk, another Canadian from Manitoba, I used that machine to make a measurement of the remaining members of an isobaric quintet. That was the first time that five members, all with the same isospin in the light nuclei, had been found, and we were able to make a test of the isobaric multiplet mass equation, something that Wigner had proposed many years before. But that was really nice. It was an exchange, and I went to stay in the apartment of Peter Turek, and I drove his car, which was an NSU rotary engine Wankel—

Zierler:

Wow.

Robertson:

—up and down the autobahn. So much fun. [laugh]

Zierler:

Wow, I bet.

Robertson:

Burned oil like crazy, but it was such a ball to drive.

Zierler:

Do you remember how fast you were going, at top speed?

Robertson:

[laugh] I'm actually not that crazy a driver, but I went to 100, of course, miles an hour. A hundred and sixty kilometers.

Zierler:

When you're writing your dissertation, of course you're very narrowly focused. You're not really sort of thinking beyond your immediate interest. But I wonder, with your postdoc and beyond, at what point you might have started to think about broadly what your contributions in physics were. What was the larger body of knowledge that you were contributing to?

Robertson:

And that’s a really good question, which in fact is what motivated me to turn from nuclear structure physics to neutrino physics. I felt that while the work was sort of interesting on a minute level of detail and I could do it well, it wasn’t satisfying in the sense of a long-term future. If you can’t explain to, for example, your mother, why it’s interesting, then you're probably not doing the right thing. Maybe that’s too strong a judgment, but I feel like what you do should be of relevance to certainly a wider group than just your local group.

Zierler:

Now is that because the field is so abstract, or because it’s so esoteric, or how would you describe that?

Robertson:

So esoteric, yes. It’s an important field, and it still is. But you want to be able to make a connection, I think, to certainly physics on a larger scale, if not other fields. The nice thing about—well, not nice thing—the thing that really got me about neutrino physics is that it plays a role in cosmology, astrophysics, how the sun works. I got immediately interested in the solar neutrino problem when I went to Michigan State. Sam Austin was there, and he was a noted practitioner of that area of physics. He was doing nuclear physics in support of solar neutrino studies.

Zierler:

What was your sense of the development of nuclear physics at that point? How well established was the field? What was your sense of the big things to discover on the horizon?

Robertson:

Well, at the time, the solar neutrino problem was the central issue in—maybe that’s too strong a word, but a central issue in nuclear physics.

Zierler:

And as a matter of intellectual history, where did this process build from to get to this point?

Robertson:

So that began way back in 1964, when Ray Davis decided that measuring the neutrinos from the sun was something that was actually possible and would be a check of the concept that that’s how the sun makes its energy, by burning protons to make helium. In the process, you make two neutrinos. So they could check that. And it was pretty ambitious, because it required what for those days was a huge detector, 600 tons of perchloroethylene fluid which had to be underground in a deep mine to keep the cosmic ray background down. He was successful in doing that. John Bahcall was the other person who was central to that business. And for many years, it was thought that the problem—as you know, the solar neutrino problem was that there are one third roughly as many neutrinos coming from the sun as you would expect based on the energy generation and the model for the neutrino spectrum. But it was commonly thought, certainly in the high-energy community, this was not a neutrino question; this was something to do with the astrophysical model, or maybe it was an experimental problem. But it turned out that it really was nuclear physics that was responsible for an extremely important new concept that the neutrinos have mass. Because that isn’t allowed in the standard model of particle physics.

Zierler:

Now were you generally aware of neutrino physics at McMaster, or this was brand-new to you when you got to Michigan State?

Robertson:

I think it was not until I got to Michigan State that I started to tune into that.

Zierler:

And what was your connection point to neutrino physics? Was it somebody you were collaborating with? Were you keeping up with the literature?

Robertson:

Yeah, I would say probably Sam Austin, who’s still active in research, was the person who really got me interested in that. I went to Michigan State, and when I got there, Sam was working on nuclear astrophysics. He wanted to see if there was a certain isotope, germanium-64, which could be produced by the alpha process after a supernova. The isotope was not known, and he was trying to make this isotope. And I pitched in on that, and figured out how to do it, and that was the first paper that I wrote there. After that, Sam and I collaborated on many things, and most of them with an astrophysical solar neutrino kind of focus. I wrote a paper on beryllium-7 production. Sorry, well, actually the boron-8 production in the sun. And that paper was reviewed by John Bahcall. I was, again, a very young guy, and John was an unusual reviewer. He did not review things anonymously. He actually called me up and said, “This is actually a really nice paper, Hamish, but you should make a couple changes here and there, and then I'll recommend that it be published.”

Zierler:

Now, what was John Bahcall’s stature in your mind at this point?

Robertson:

He was a giant. I could not believe he was actually going to call me up and talk to me. [laugh] And ever since—and the more I think of it, the more he has been, in some sense, a mentor in my life. He sadly passed away, I think in 2006, but he—well, one thing—I wrote a couple of papers which dealt with things that he had previously looked at, and he called me his most successful critic. And that is the most elaborate praise I've ever had in my life.

Zierler:

Yeah!

Robertson:

I could not believe [laugh] he said that. He was a wonderful man. He really—I miss him to this day.

Zierler:

Back on planet Earth, I'm curious about your status at Michigan State. To be clear, when you took the postdoc, there was no indication that this might have transformed into a tenure line position. Those were separate considerations.

Robertson:

No, and so naïve was I, I never even thought about that step. I was just doing my thing.

Zierler:

And your naiveté, I assume—were you single at this point? You weren’t thinking about a family to support, nothing like that?

Robertson:

No, no. I was single and I was not short of money. So that was not an issue. Well, I didn't have a lot, but I had enough to—

Zierler:

A single guy doesn't need that much. [laugh]

Robertson:

That’s right. I remember having to decide whether to buy a pillow for my apartment or to get the front end of my car fixed.

Zierler:

There you go! [laugh]

Robertson:

I think I decided I could sleep without the pillow for a while. [laugh]

Zierler:

[laugh] And so when did that work transfer into a tenure line offer?

Robertson:

So it came completely out of the blue. I had been a postdoc for one year, and Walter Benenson, one of the faculty members, came up and said, “We're going to make you an assistant professor.” They were really pleased with what I had done. I said, “OK, what does that mean for me? What do I do?” And of course it’s a teaching position.

Zierler:

Was your sense that they saw in you an opportunity to make a mark in neutrino physics, where there wasn’t one before in the department?

Robertson:

I think not so much in neutrino physics at the time, but in physics in general. The kind of physics that they were doing, which was low-energy, nuclear structure, cosmology applications, astrophysics—neutrino physics came along a little bit later, apart from the solar neutrino work. The focus on the solar neutrino problem was, are there nuclear structure processes that had been overlooked? Are the cross-sections right? Have we got all of the i’s dotted and the t’s crossed? So actually turning to look at the neutrino itself came later. That started in—well, so, one thing that was very influential in my life was the year I spent in Princeton. After I became an assistant professor at Michigan State, I asked for a sabbatical to go and work at Princeton for a year. It was much earlier than I should normally get one, but they allowed me to do it, because it was clearly in their benefit and mine as well, for me to learn how to do this stuff. Gerry Garvey at Princeton had arranged for—I don’t know how this happened, but it was one of these amazing things where you have a year of—’75 to ’76, I think—where a bunch of people spontaneously gathered together in one place, and we had the most wonderful time. Garvey was the center of it, and we spent an entire year learning and laughing, is the way I look at it. He was, again, one of those people that just was a magnet for good people. And of that group that worked at Princeton, many of them, you will know their names. Bob Tribble was chair of the APS Division of Nuclear Physics. Stuart Freedman, who passed away, sadly, was there. Eric Adelberger is a member of the National Academy. And Bob McKeown was there. Tom Bowles. Art McDonald wasn’t there at the time. He came a little bit later to Princeton. But it was really a very exciting year to spend there. What we did was not so exciting. I mean, we did some work on isospin conservation in nuclei. But from that, we developed—I think you'd call it a network nowadays, which did lead to much more significant results later on. That’s where I really got to know Tom Bowles, for example. And Tom later was the person who recruited me to Los Alamos, where we worked on the neutrino mass there, the direct measurement.

Zierler:

Before we get to Los Alamos, one of the questions I wanted to ask you—the context of my question about the circumstances of your offer and what it represented at Michigan State was—I'm curious—you always hear about how Berkeley and Stanford were always very aware of each other. And I wonder if Michigan State and Michigan had a similar kind of relationship, in so far as physics might have been concerned.

Robertson:

They did, yes. They were quite competitive at the time. Michigan had a cyclotron, not as—it was an older machine, without quite as much resolution, more current to produce radioactive isotopes in abundance. But Henry Blosser, who was the director of the lab at Michigan State, was a formidable force. He developed the superconducting cyclotron. And eventually all of nuclear physics in Michigan sort of coalesced around the Michigan State program. And it still is. It’s still the number one nuclear physics laboratory in the country. They have the facility for rare isotope beams just coming online.

Zierler:

Now, by 1981, you were a full professor at that point, at Michigan State?

Robertson:

I was associate professor, but tenured at that point. I became full professor in 1982. At the time—so Michigan State was making its transition to heavy ion physics at that point, and Henry and I had a talk. He was very supportive of my work in neutrino physics. I told him that I wanted to do this measurement of the mass of the neutrino. He was very supportive of it. But I could see that if I stayed at Michigan State, the competition for funds would be difficult not just for me, but for him. I would be more of a problem for him. He needed every nickel in order to get this new high-energy cyclotron going. And so I had to decide what to do. And Tom Bowles, as I said, “Well, look, why don’t you come to Los Alamos?”

Zierler:

And Tom was at Los Alamos at that point?

Robertson:

Yes, he had been there for some years. I'm not sure when he went there; probably in the mid-‘70s. But he was there at the time. And we remained good friends. So I went down there and interviewed, and he took me out to the Rancho de Chimayo, and we came back; it was a dark, cloudless night. He stopped the car, and he said, “Get out. Look up.” And I was hooked! [laugh] That was such a beautiful sight. Just the stars everywhere over the sky. And I loved living in New Mexico. I still think it’s the best place I ever lived.

Zierler:

You're still single at this point, in 1981?

Robertson:

No, I had just been married. So I got married to Peggy Dyer in 1980, on July 4th, actually, in Canada.

Zierler:

Was that an easy sell, moving to New Mexico?

Robertson:

I think it was, yes. She had been a postdoc and research assistant professor at Michigan State, but I think she felt like she wasn’t able to really pursue the kind of research that she wanted to there. There was kind of I guess a culture that made it difficult for a woman, at the time. I don’t think there was anything really intentional there, but it was just the sort of historical kind of thing. Henry Blosser was very old-school, and he was a wonderful guy, but he had sort of a male focus, I guess. Nothing inappropriate, other than just kind of neglect. But she was happy to set foot on a new path at that point, too.

Zierler:

And the basis of the interview at Los Alamos was—this is not a fellowship. This is not a visiting kind of thing. This is—if you take this, you're leaving Michigan State and you're starting on a new path?

Robertson:

Oh, yes. They tried to keep me there. That’s when they made me a full professor, in 1982. But I still had decided that I was going to leave at that point, and I went to Los Alamos, fulfilling, I might say, a long, lifetime goal, to get to Los Alamos.

Zierler:

Right, right.

Robertson:

Something I had sort of forgotten about, I guess, and then it came true.

Zierler:

What was the job title that would have made this I guess minimally a lateral move, to Los Alamos?

Robertson:

In those days, it was technical staff member, I think. No, it was just staff member, at Los Alamos, yes.

Zierler:

And is there a tenure type process or assurance, or how does that work?

Robertson:

No. The two weapons labs, Los Alamos and Livermore, did not have that kind of system. Brookhaven did. But you were basically a scientific employee. So there was no tenure, but there was certainly an understanding that it was a permanent job.

Zierler:

So besides the clear skies and the new opportunity, from an instrumentation perspective or a budget perspective, what were the real draws to Los Alamos?

Robertson:

Well, the reason I went there was to do this neutrino mass experiment.

Zierler:

I mean, I'm asking—that could not be done at Michigan State? Is that the idea?

Robertson:

Right. One thing that they have is the ability to handle huge amounts of tritium, because that’s what’s used in a hydrogen bomb. They knew all about how to do this. I remember when we started the project, we worked out how much tritium we were going to need, and it seemed like a huge amount. Like 5,000 curies, as I recall. And we went to the people who handled tritium and said, “Is this going to be feasible for us to handle this?” And there was this old guy; I forgot his name now. He wore a ten-gallon hat. And he came down and said, “Son, we lose more than that every day.” [laugh]

Zierler:

[laugh]

Robertson:

I don’t know if that was true or not, but [laugh] it was very reassuring. So they did help us a lot on that score, and it was not a problem. So that was one of the main reasons—

Zierler:

What was the end point? What was the end goal in your mind in terms of what this experiment would achieve?

Robertson:

Ah, yes. So I had gotten very interested in neutrino mass. So the history is that in the late ‘70s, the standard model was being developed, and also the observations from cosmology were starting to show that dark matter was a major component of the universe. Vera Rubin had recently discovered the velocity profiles of galaxies and clear evidence for dark matter. And the question came up—could neutrinos be that dark matter? And so the goal was, can you measure the mass of the neutrino to the level where you could decide yes or no, that it was? The catch of course in those days was that there was really no way to measure the mass of the mu and the tau neutrino. You could measure the mass of the electron neutrino if you were really clever and figured out how to do it. So that was our goal, was to try to at least measure the mass of the electron neutrino to decide if it was the dark matter. And later on, it would be found through neutrino oscillations that that’s enough. All you have to do is to measure the mass of the electron neutrino, and neutrino oscillations and mixing then tell you what the masses of the other neutrinos are. That you don’t call them the mu and the tau anymore because they’re all mixed states. But this started up in quite an interesting way. I was invited to give a talk at the Erice conference in 1980, which was on the parity violation work that I had been doing in nuclear physics at Chalk River and Michigan State. So I agreed to give that talk. And this was a really important conference. To be invited to give a talk like that, certainly for a young guy like me, was a very big deal. The problem was that my wedding had been arranged at that time. So I had to tell my mother, who had done all this work to schedule—

Zierler:

Oh no. [laugh]

Robertson:

—yeah, really! And my wife—you know— “Would you mind if we put this off for a couple of weeks?”

Zierler:

[laugh]

Robertson:

I still [laugh]—I get these looks.

Zierler:

Never recovered from that one, I'm sure. [laugh]

Robertson:

She still married me. I don’t know why. [laugh]

Zierler:

[laugh]

Robertson:

But I went to this meeting, and it was really crucial, because Tom was there, and Art McDonald was there, and we had discussions about neutrino physics and neutrino mass.

Zierler:

What was Art McDonald working on at that point?

Robertson:

He was still at Chalk River, and he was working on parity violation, too. He was working on measuring circular polarization of gamma radiation in the capture of neutrons on protons. That was the focus of that particular meeting. It wasn’t really neutrino physics at Erice at that time. But we got together, and over a lot of gelatos, we started to hatch a plan, at least—I don’t know if Art was part of that plan to measure the mass of the neutrino. I don’t think he was, at the time. But Tom and I said, “Is there a way to do this?” And Stuart Freedman was there, too. He had spent some time thinking about that. And the last person who had done this was Karl-Erik Bergkvist in Stockholm. And you should read his papers. Everyone should read his papers. Stuart even said to me, “Have you read his papers? Are you crazy? [laugh] Can you think of any way that you could do better than that?” Well, Bergkvist had actually shown that you could get down to about 50 electron volts on neutrino mass, which wasn’t quite enough to answer the question of the dark matter. But he said in order to do better, you have to understand the molecular structure. That was the key. So I thought, and Tom also thought, that the only way to beat that is to work with molecular or atomic gaseous tritium. So that was the goal, was to develop a source where we could actually measure neutrino mass using molecular gaseous tritium. And that meant we had to develop a recirculating source, which we did. We started with some really crazy ideas with jet sources. Because—I actually built a jet target at Chalk River for a different experiment, but that didn't go anywhere here. And Dan Kleppner—I don’t know how we got in touch with him, but he had some very good comments on how long atoms would survive in a tube. You know, a metal tube. And that was the genesis of the source. We never actually got to use the atoms. We're still thinking about that one. But we used molecules, and that was good enough to do the measurement. Then we started—I went to Los Alamos, and a couple of weeks after I got there, Jay Keyworth, who was the director of the physics division—he later become presidential science advisor—called me into his office. And he said, “I'm really glad to see you here. I didn't realize Peggy was coming, too, and I read her CV, and I think I'm even gladder that she came than you did.” [laugh] Then he said, “So what do you need to measure this neutrino mass thing?” And I hadn’t even thought about it at this point. I had no clue. So I think I said $750,000. And then he said—

Zierler:

Was that just a number you made up, or was there any basis in reality?

Robertson:

Pretty much the number I made up. Well, you have some idea, I guess, but we didn't really have that much of an idea. So I said that, and he said, “OK, fine.” And that was it! [laugh] He gave us the money, and off we went. The good old days, you know? You can’t do that anymore. But he was very supportive. It turned out that was not enough money, and it got a little harder as things went down the road, but we eventually were supported through to the end.

Zierler:

In terms of dark matter and dark energy and thinking about these things at that time—so nowadays, that’s still—like that’s the standard question, you know? Like what remains mysterious now? And you know, that dark energy and dark matter. So I'm curious—does that surprise you, if you sort of take where we are now and sort of rewind back to the 1980s? Did you think that dark energy and dark matter would be better understood by now given what you were involved in at the time?

Robertson:

Well, of course dark energy was not even on the horizon in those days. That came along much—

Zierler:

So it was only dark matter that you were thinking about.

Robertson:

Yeah. I think there was a general feeling in cosmology that the universe ought to be flat. And actually shortly after we got there, not more than six months after we got to Los Alamos and started to do this work, the result came out from Lyubimov’s group in Russia—the Soviet Union at the time—that they had measured the mass of the neutrino and found it to be 30 electron volts, which was right on the button for closing the universe gravitationally. So the project that we had proposed to do by pure chance suddenly became world-visible. Everybody wanted us to get on with it. And of course it was hard to do, but we did. And other people got into the mix, too. But we were only thinking about the dark matter at the time, and whether neutrino mass was enough to close the universe. The Russian number catalyzed a lot of research in that area. We now know that neutrinos probably couldn't be the dark matter, because they're hot dark matter, and they don’t have the right structure in galaxies to give you that kind of—what we understand to be the profile of dark matter in galaxy clusters now.

Zierler:

When did you start thinking about the implications that this research had on the standard model?

Robertson:

That was also known at the time. I think the standard model, however, was thought to be something that could be viewed as having made a prediction that the mass would be zero purely on the basis of convenience. There wasn’t a good explanation for why it wouldn't be as heavy as the electron neutrino, for example, if it wasn’t zero. It was set to zero by depriving the neutrinos of right-handed fields. You can put those back in, but you do face the problem of what prevents the neutrino mass from being much heavier. That’s still an issue. There is no good solution to that. That’s why we think neutrino mass points to something beyond the standard model. But in those days, there had been a long period before we had started working on this, where nobody was looking at neutrino mass at all because neutrinos were known to be left-handed particles, which violate parity. And it was thought that the neutrino, although nobody actually said this but everybody thought—the neutrino is what’s responsible for parity violation. If that’s true, the neutrino must be massless, because otherwise it can’t be always left-handed. Then when the neutral current was discovered and confirmed—the standard model prediction that the neutral current would be there—that meant that the left-handedness was not a property of neutrinos; it was a property of the bosons. So you could have neutral current interactions which don’t involve neutrinos at all. And in fact, the neutral current doesn't violate parity maximally. So that was an argument which said that the old thinking, somewhat naïve thinking that the neutrino mass had to be zero because it was responsible for parity violation, that went away. We were still left with the issue of why the standard model doesn't get the neutrino mass right. And that remains a central question for the standard model and future models.

Zierler:

I wonder if you could explain that. In terms of the fact that the standard model can be contradicted, does that make it sort of not so standard? [laugh] What are the larger implications there?

Robertson:

[laugh] Well, that’s what we live for. If we actually found the ultimate theory, of course, we’d be out of business. [laugh]

Zierler:

You mean the grand unified theory?

Robertson:

If that’s what it is, yes.

Zierler:

So just so I understand, up until neutrino physics, the standard model could have been thought to be some kind of version of a grand unified theory?

Robertson:

Yes. I mean, it was very predictive. Everything that it would predict and that you could measure was confirmed. There were certain things that were not in the standard model, and long even before the standard model was created, the fact that gravity is not a part of it was and still is an issue. There were other things—there’s a strong CP problem which is not really understood, and that’s a very active field of research today, too.

Zierler:

And where is string theory in all of this?

Robertson:

String theory is one of the efforts to try to come up with a theory that is beyond the standard model and predicts many of these things that are not presently either included or not correctly given by the standard model. There are other approaches. Supergravity is one of them. I'm not a theorist, and I don’t know what the state of the art is, in that, but no one has come up with a convincing model yet.

Zierler:

Of course you're not a theorist, but I'm just curious if you were thinking about these things, because of the clear impacts of your research on theory.

Robertson:

Oh, to be sure. Yes, absolutely. The dual interest in neutrino mass comes from A, cosmology, and B, theory. One wants to know—and we still want to know—what is the mass of the neutrino? We now know that they do have mass. But understanding what the pattern of mass would be is very key. For example, we know that neutrinos are now—there’s three states, and they have mass splittings, or splittings of the squares of the masses, that have very well-measured results from neutrino oscillations, at well-defined numbers. So what is that pattern? Is there a symmetry involved there? If you look at the quarks, you see that the pattern is quite similar. If you choose the normal hierarchy of neutrinos, you see a similar kind of pattern in the mass of the quarks. So it seems like maybe there’s something going on there that we should try to understand. And we don’t. Cosmology wants to know the actual number. The theorists are more interested in the pattern. Theory is not terribly good at predicting the masses of fermions at all. And that is still a work in progress. But what has been very illuminating in theory is symmetries. And so people want to know, you have a small gap and then there’s a big gap, and we see that everywhere. Why? In the neutrinos and the quarks. But maybe the neutrino pattern is not that way. Maybe it’s inverted. That would also be indication of a symmetry but something different.

Zierler:

I'm curious—your time at Los Alamos, how well integrated were you with the broader academic community? Were you attending conferences? Were you publishing? Or in a national laboratory setting, you're sort of just there in your own world?

Robertson:

Oh, no, very much. We would be definitely going to conferences and publishing papers, and a lot of interaction. We had in those days not so much in the way of external collaboration on the experiment, but there was a lot of interest in what we were doing, and we were very interested in what other people were doing, and we would get together regularly at meetings. I was not doing classified work. And I actually did not have a clearance until I—well, I would have had a clearance had I stayed at the lab, in 1994, but left before that happened.

Zierler:

Did you need citizenship to work at the lab?

Robertson:

No. But you do need a good hand at paperwork.

Zierler:

[laugh] Right. Yeah.

Robertson:

I did a lot of that. [laugh] So eventually that got burdensome. And I had been living in the U.S. for so long I should become a citizen anyway, so I became a citizen in 1993. In May 1993.

Zierler:

And when was your last year at Los Alamos?

Robertson:

1994. We were recruited by University of Washington in ’94. Wick Haxton and Eric Adelberger and Derek Storm came after me, and us.

Zierler:

Oh, Wick was at Washington at that point? I didn't know that.

Robertson:

Wick was at Washington. Yes, he was at Washington, then. Yes. And he and—well, the physics department thought that it would be really good to have us come there. There were—well, I'm starting to remember what the—there had been some departures before that, but I can’t remember exactly who. So they had the ability to make a targeted hire. They actually were prepared to make three professorships, and John Wilkerson and I became state-supported faculty, teaching faculty, and Peter Doe became research faculty. We all went to University of Washington at that time.

Zierler:

So clearly Washington is making big moves for itself here. How did you understand in general what the physics department was trying to achieve with these offers?

Robertson:

It was a very strong department in fundamental symmetries, and they were very keen to try to build that strength. Dehmelt’s Nobel was not that old at the time. He won that in ’89. So there was really strong support for keeping the activities present there. The laboratory had, however, been focused on nuclear structure physics for quite a while, and we talked a little bit about that—that that kind of research was getting to be difficult to support through the Department of Energy. And so they were looking for redirection, and we were able to provide that with SNO. And then there was still a lot of very strong work going on—the work of Adelberger on non-Newtonian gravity that was still very notable. Theory predicts many kinds of contributions to that, but especially, for example, from extra dimensions. And there was the parity violation work of Adelberger. There was nuclear astrophysics work going on. Kurt Snover was there doing work on nuclear structure. So there were a number of people, but I think there was a sense that it was time to make a change.

Zierler:

Was part of that lifestyle? Were you looking forward to getting back to an academic environment, teaching, taking on graduate students, that kind of thing?

Robertson:

You're asking this about me and not about the lab or the department?

Zierler:

Correct.

Robertson:

Yes. I was actually not keen on going. I loved Los Alamos, and I was never an enthusiastic teacher, I think, I would have to say. I'm too slow. [laugh] The students are always faster than me. [laugh]

Zierler:

That reminds me about your initial impression with Bell Labs, too, in terms of the pressure that you sensed, and how that environment was not for you.

Robertson:

Yeah, yeah, right. Yeah, I mean, Los Alamos is really—it certainly was—a dream environment for somebody who wants to focus on research. I like having time to think about things.

Zierler:

So it sounds like this was a group decision, like either you were all in, or none of you were going?

Robertson:

Sort of, yes. Actually Tom Bowles was invited to go, but he decided not to go. And so it was just the three of us went. And it was a group decision. I think my wife Peggy was quite keen on moving, too. She had been a postdoc at University of Washington in 1977 or thereabouts and liked it very much. She loved Seattle, and she encouraged me to consider doing that.

Zierler:

I mean, Los Alamos, in terms of living, there’s not much in the way of civilization there, right?

Robertson:

Well, that might be true, but there are compensations. Santa Fe—we had this beautiful house on the mesa overlooking the lights of Santa Fe and the Sangre de Cristo Mountains. And every time I would drive home at night, I’d see the beautiful blood-red light on the mountains, and I would say, “Wow, they actually pay me to live here.” [laugh]

Zierler:

[laugh] So you weren’t looking to leave, either lifestyle or research-wise?

Robertson:

Yeah, I'm not a big-city guy. And so for me, it was an ideal environment. But Wick Haxton saw very clearly that there were changes coming that would make it more difficult for the kind of work that I was doing at Los Alamos to continue in that carefree mode. That there was—already, we had had visits from so-called Tiger Teams at Los Alamos. The environment was changing. There were I thought somewhat artificially trumped-up security scares at Los Alamos. I had the feeling that somebody in Washington was trying to make it difficult for the lab. I have no basis for thinking that other than paranoia, but there was a change afoot. Wick was very perceptive in making that clear to me, and so I realized that he was probably right, and it was a good time to make the move.

Zierler:

Now in terms of the investment of all of these new hires, what about their commitment in giving you the kind of lab environment you needed to continue with your work?

Robertson:

At the time, the university was building a new physics building for the department. It was like they built it for us. They didn't really, but it felt like that. And out of that, there’s always some money that is available for equipping the labs and teaching environment in the building. And so they were able to make available for us a huge laboratory for building the detectors that we used in the Sudbury Neutrino Observatory. The neutron detectors.

Zierler:

Was it also an opportunity to start from scratch and figure out what it is that you really needed?

Robertson:

Yeah. Not to say that we weren’t being well-supported at Los Alamos; we were. But it was an opportunity to have students, which was always a problem at Los Alamos. We had some students. One of the best students I ever had was Dave Knapp, who is now at Livermore as a staff scientist. But he was Art McDonald’s student, actually, at Princeton, but his family lived in Los Alamos, by chance. His father was the director of the accelerator division. And so Dave worked for me as a student, and we did work on the neutrino mass experiment together on that. Well, that’s kind of a rare thing. There were very few opportunities like that. We had some undergraduates over the summer, who were excellent. But as I say, having graduate students long-term at the University of Washington made all the difference. In 1998, I started working with Karsten Heeger. He was a student who joined me, then. Or actually, before that. But we worked on the solar neutrino problem at that time. We were already working on SNO. And we wrote a paper, which was in Phys Rev Letters, where we showed that it was very unlikely that there could be an astrophysical solution to the solar neutrino problem. That even if you allowed all of the neutrino fluxes to be free parameters, there was still at the two-sigma level at least, a problem, that made it look like it was more likely neutrino oscillations than astrophysics that was causing the solar neutrino problem. And Bahcall reviewed it. And again, he calls you up and, “Here’s a couple of changes to make,” says he likes the paper, and publishes it. And later on, he told me that it was with that paper that he first became confident in his own mind that this really was a neutrino physics problem and not an astrophysics problem.

Zierler:

And had Bahcall been following your work at Los Alamos this whole time? Were you in contact with him during those years?

Robertson:

From time to time, yeah. Not closely, but yes, from time to time. We would go to conferences and meet there and chat. We always had a warm relationship.

Zierler:

When you got to Washington, did you overcome your reservations and embrace teaching, or did that never really happen?

Robertson:

To some extent. I actually wound up teaching the undergraduate big lecture series for a while, and I actually got to like it. It was done in sort of a collaborative group environment.

Zierler:

This is a Physics 101 kind of class?

Robertson:

Yeah, sort of. And you have a lot of pre-engineering, and some pre-med students in there. Some of them don’t want to be there. It’s kind of a weed-out course for some people. But I never really felt that, so much. These are big classes with 200 people or so in them. And what I think I enjoyed most was the action of getting together with the other instructors who were doing similar introductory lectures, and trying to figure out how to get this stuff across in the best way. I was moderately good at it. I was never a great teacher. But I could do the job.

Zierler:

And who were some of your most successful collaborations with grad students and postdocs?

Robertson:

Oh, well I had many, many grad students that I enjoyed working with. Karsten is one in particular, who’s now at Yale. Let’s see. Charles Duba is now Associate Dean at Digipen. Noah Oblath is staff scientist at PNNL. “Wan” Wan Chan Tseung is an accelerator physicist for the Mayo Clinic. I had a nice collaboration with Laura Bodine, now Laura Minter on the experiments we've done recently. She has been involved in the TRIMS experiment. Alan Poon was a student that was actually working with Chris Waltham at UBC, and so we co-supervised Alan, and Alan and I remain very good friends to this day. He’s now at Berkeley. My most recent student, Eric Martin, is now a postdoc at UNC. So there were many students that I worked with and enjoyed and benefited from greatly. They're a good group of people.

Zierler:

Now, did you feel like your research focus remained essentially on track going to Washington as you would have, had you stayed at Los Alamos? Or do you feel like you changed directions a little bit simply by virtue of being in a new environment?

Robertson:

We brought the solar neutrino work with us, the Sudbury neutrino work with us. And then once that was—not completely finished; sort of halfway through—we joined the German experiment on neutrino mass getting back to the old problem of, “What is the mass of a neutrino?” That’s the experiment called KATRIN in Karlsruhe. And we're still involved in that, and that’s now finally taking data after some 17 years of construction. And we were also involved in a new project here called Project 8, which is another novel idea from two guys at MIT, Joe Formaggio and Ben Monreal, of how to measure the mass of the neutrino. So I remain engaged in the same basic issues. The same questions are still very motivating to me. And we've had a lot of success. I mean, the solar neutrino problem is now solved. That was a wonderful time. I still remember in 2001, at Queens University, we had the analysis meeting, closed room and all, and the first results came out, and we just sat in stunned silence as we saw it was obvious that neutrinos were oscillating.

Zierler:

What does it mean, that it’s solved? What does that mean both in terms of the science and its implications more broadly?

Robertson:

So the old issue of why there are not as many neutrinos coming from the sun as you would expect is conclusively solved. They're all there, and we showed that they're all there. They just change their flavor. And so the old experiments that were measuring them were not sensitive to those other flavors. So you get perfect agreement now with the prediction of Bahcall’s model, and the measurements of Davis are absolutely correct. They're measuring the electron neutrino components of the neutrino flux. So the other thing that comes out of it, of course, is that in order for neutrinos to oscillate and change flavor, they have to have mass. So the solar neutrino problem shows that the electron neutrino is involved in this mixing process. Two years before that, the Super-Kamiokande experiment had shown that mu neutrinos are involved in mixing. And so mu neutrinos mix with tau neutrinos. That also shows neutrinos have mass. And with the SNO experiment, it shows that all three are now mixing with each other, and you have tightly constrained numbers on the differences between the squares of the masses. So that says the standard model is deficient in some respect, and we have to try to figure out what it is.

Zierler:

And what’s the future? Where does it go from here?

Robertson:

Well, so the solar neutrino problem, having been solved, actually means that there isn’t a lot of research going on, on solar neutrinos, right now. The Super-Kamiokande experiment is sensitive to solar neutrinos, and it’s still measuring them, and the Gallium experiment in Russia is still running. And Borexino is still running. But the big issues there are more can we understand the details of how neutrinos are made in the sun. What is the relevant role of the CNO process compared to the p-p process. Because that’s still not understood very well, how much is one kind of chain of nuclear reactions versus the other. But the neutrino issues are well sorted out, and most of the neutrino physics now is focusing on long-baseline neutrino oscillation experiments, the new experiment at Fermilab, DUNE, and the experiments in Japan are looking at that kind of physics, HyperKamiokande.

Zierler:

I guess the most concrete way I can pose the question is, if a graduate student expresses interest in pursuing neutrino physics, what would your advice be? Is there still work to do? Is this still an enriching field to go into?

Robertson:

Come work with me on finding the mass of the neutrino. We have to figure out what that is! [laugh] So yes, the central issues in neutrino physics are we still don’t know the mass. We know that they have mass, but we don’t know how much. We don’t know if neutrinos violate CP, although it looks like now there’s a three-sigma indication that they do, from the T2K experiment in Japan. We don’t know whether neutrinos are their own antiparticles. This is a really central issue in physics. Neutrinoless double beta decay is the way to find out. Why do we want to know that? Well, neutrinos, if they are their own antiparticles, it means that lepton number is not conserved. And that gives you a mechanism for creating the universe, essentially. Why is there matter in the universe and not antimatter? You need some mechanism that, A, violates CP, and B, violates Baryon number and, by inference, lepton number. So those things were laid out by Sakharov in 1967 as the conditions for creating the matter asymmetry of the universe. Still one of the central questions in all of physics. So there is no shortage of exciting physics to do on these things.

Zierler:

What year did you decide to become emeritus?

Robertson:

2017, I decided to retire. I guess I don’t know why. Just seemed like a good time. [laugh] I'm still staying active in research. I've had a few minor health issues, and I thought, “Well, maybe I should get out before it’s getting worse.” But actually they turned out to be so minor they're gone, and then I'm fine again. [laugh]

Zierler:

Wonderful. [laugh] That’s great to hear.

Robertson:

Thank you.

Zierler:

Now in terms of our current crisis and social distancing, are you able to continue your work remotely, or do you really need onsite access to equipment to continue on?

Robertson:

I'm very much an experimentalist, so yeah, we're building equipment. In this Project 8 experiment, actually the laboratory where the prototype experiments are being developed, the final site decision hasn’t been made. That’s a long way off. And in KATRIN, of course, the experiment is actually in Germany. I don’t go to Germany very often. I go there about twice a year for collaboration meetings. But that work—we completed our obligations to deliver the detector system for KATRIN in about—when was it?—2012, I think. So it has been running successfully since then. And we of course have an obligation to keep it going, and we're involved in analysis. Analysis, we can do without having to go to Germany.

Zierler:

At this point, we're essentially—in terms of the narrative, we've built up to the present day. So now I’d like to ask you some sort of more broadly conceived questions that will ask you to assess your career as a whole. And so my first question is—and this gets back to questions about dark energy and dark matter—what are things now that are truly understood that were not at the beginning of your career, that you were specifically a part of?

Robertson:

Yeah, well I would say that the fact that neutrinos have mass, that has been a question since 1930 when the neutrino was first proposed by Pauli. That is conclusively answered. We know that they do. We know that that’s not something that is explained by models that we have today. And so it’s a window to the larger model or physics description that must be out there. Hopefully, it’s a valuable clue for theorists. It’s also a constraint for theorists, that what they predict must include this in order to come up with something that really is an advance in theory. That’s the main thing, I think, that I've been devoting my life to. But there are smaller things that I could point to. One of the things that I really enjoyed was something that Sam Austin mentioned was that we don’t know where the lithium-6 in the universe comes from. We were at the time working on an experiment to measure parity violation in lithium-6, but it turns out that that physics for the experimental physics was ideally suited to make the measurement of the cross-section for producing lithium-6 from helium and deuterium. And we made that measurement at Chalk River, and we could show that the cross-section was too small for lithium-6 to have been made in the Big Bang, and most of it must be being made by cosmic rays or perhaps by stellar processes. I think the details are still up in the air. It’s not really known where it’s coming from.

Zierler:

To flip that question on its head in terms of ongoing mysteries—so the fact that the mass is still unknown of neutrinos—I wonder, sort of building off of that, what does that say about like larger questions about things that physicists, experimentalists, really still don’t understand, beyond neutrino physics?

Robertson:

Well, yeah. I mean, the origin of the universe—it’s hard to think of a bigger question. So this is something that I think drives a lot of physics today, is to try to understand, what is the actual origin of the universe? What has led to the fact that we have matter in the universe today? In fact, I believe Ann Nelson used to say that you think that you don’t know where 95% of the matter or the contents of the universe comes from. In fact, it’s worse than that. We don’t even know where 99% of it comes from. Because we don’t know where the normal matter comes from. We don’t have an explanation for that. So there’s dark energy, there’s dark matter, there’s the matter asymmetry of the universe. And the neutrinos are maybe the things that we understand the best. [laugh] But they're a very small part of the universe, less than 1% by mass.

Zierler:

In terms of understanding best, in terms of getting to the deepest questions, do you believe that the laws of physics allow for the universe to have created itself? And obviously that gets into, to some degree, a philosophical or a spiritual question. But just to keep it within the realm of theory and your entrée in experimentalism, could the universe have created itself without some external factor?

Robertson:

That’s certainly well above my pay grade.

Zierler:

And everyone else’s, I should mention. But still, I want to hear what you have to say.

Robertson:

I think it’s quite likely that it is something like a vacuum fluctuation that just got away. Having said that, I can’t tell you even what that means.

Zierler:

[laugh]

Robertson:

But it has all the characteristics of almost like a thermodynamic fluctuation, but just that something has created a chaotic sea of energy, in a very condensed state which then expanded. There’s a lot of interest in whether it’s just one of an infinite number of such universes. And I don’t know of ways in which we could address that question experimentally, but there may even be ideas on how to do that now.

Zierler:

By infinite number, would those be universes that exist sequentially, like before our universe there was one prior? Or are you referring more to multiverses?

Robertson:

Multiverses, yeah. Universes that are perhaps evolving contemporaneously with ours, but are no longer in contact with ours, that we can’t see. And they may have very different conditions. But one of the real questions is, the universe seems so finely tuned. It only works that we are in it because it has been so finely tuned. You can imagine all kinds of universes where, for example, the zero-plus state in carbon-12, which is one that I studied, is in a slightly different location. Then the triple-alpha reaction doesn't work, and then you don’t make heavy elements anymore in stars, or not the right number. And so then you don’t get the opportunities for people and planets and so on, in the same way that we have in this universe. And there’s many, many aspects—fine-structure constant—all of these things seem very finely tuned. We don’t really have a good understanding of why that is. And one of the I think quite compelling explanations of why that is is that it is that way because we are in that particular universe where those numbers happen to work out that way.

Zierler:

Which would include the presence of the human mind that is capable of perceiving such things.

Robertson:

Exactly, yeah.

Zierler:

Different question. Particularly with you, who has been involved in such a satisfying narrative in terms of understanding neutrinos, which is really kind of unique in physics, right? To have that—like, “We really get this now,” right? So in terms of assessing the relative components that go into mode of discovery, there is advances in technology. There’s the grunt work, day in and day out, of the lab. There is luck of being at the right place and the right time talking to the right people. And then of course there’s insight or genius or whatever you want to call those moments where it’s really just marveling at what the human mind is capable of perceiving under the right circumstances. So in very broad terms, how do you see those different factors all playing a part into this narrative of advancing discovery and knowledge? What’s the most important, just reflecting on your particular career and experiences?

Robertson:

I found that where you really make advances is by bringing together the boundaries of disjoint fields, and where they touch, that’s where you suddenly see a new flowering of information, opportunity, and advance. It’s hard for me to quantify that, but I think maybe the solar neutrino problem is an example of that. The motivation there initially was not neutrinos at all; it was simply to study the way the stars work. So you bring those two things together, and suddenly you see something which you would never have been able to see if you were only studying neutrinos or only studying astrophysics. There are lots of other examples, I'm sure, better ones that I could think of. But I'm always trying to be alert myself to developments in fields which are neighboring to the one I'm working in, to see if there is an opportunity to bring into our field information from those other fields. I don’t know much condensed matter, but I recently read a paper where they're using NV diamonds to build maser amplifiers, actually oscillators. So now I'm very interested in whether that has an application to the Project 8 experiment that we want to do. So that kind of thing is stimulating. It takes you into areas that you don’t know much about to begin with, and may have opportunities. I'm not sure if that’s the question you're really asking, or whether you want a broader picture on this. I think it does translate to an overall picture of how physics works. Nobody that I can think of is so broad that they can really be acquainted with all of physics now, certainly not all of chemistry or biology as well. But where you see people working at some boundary which is close to the boundary of another field, that is often where you find the action, the discoveries.

Zierler:

You don’t see any one of those factors particularly driving it any more than others. It’s really just a combination, and it’s hard to quantify.

Robertson:

It’s opportunistic, I think. Yes. I think there’s certainly a focus on trying to solve certain problems, but the path there is always sort of a fractal kind of path. You can’t get there without taking side roads to other areas, bringing back with you the fruit of that little exploration, and taking it down the road to the next one.

Zierler:

So in terms of advancing knowledge and getting closer to however close we can get to those fundamental questions, do you see experimentalists and theorists in a real yin and yang relationship? Is it a real partnership in terms of reliance on each other to advance knowledge and to get closer to answering those basic questions?

Robertson:

In my experience, very much so, yeah. We would never have gotten anywhere without the interactions with theorists. I mentioned a few already. John Bahcall, Ann Nelson, Wick Haxton. So yeah, my own personal experience is yes, and I think that would be an experience with almost everybody. Could we take a short break now?

Zierler:

Actually, I only have one last question, but I'm more than happy to take a break if you want.

Robertson:

Let me come back, and I'll talk to you in a second.

Zierler:

No problem. [pause]

Robertson:

I'm back! It’s really getting warm here. The sun is shining, and I had to take off my sweater.

Zierler:

Yeah, I see the light coming down.

Robertson:

Oh, yeah.

Zierler:

So Hamish, I think for my last question—and it’s such a beautiful thing, always, because I've never met a physicist that truly retired. There’s nobody that has ever—even—so yesterday, I spoke with Pier Oddone, who was the director of Fermilab for a long time.

Robertson:

Right.

Zierler:

And he now is a grape grower for wine in Sonoma County. And so even him, he’s not even fully retired. He’s still on advisory boards and things like that. And so it’s just such a beautiful thing, because the obvious answer is always, I mean, the people I talk to, and their stature in the field, the initial wonderment and drive never goes away.

Robertson:

That’s true.

Zierler:

So with that context in mind, I want to ask you, because you're certainly a part of that pattern, what continues to drive you? Why do you remain active in the field? What are the things that still motivate you that you want to know personally and what are the things that motivate you to continue to be productive and contribute in ways to the field like you have your whole career?

Robertson:

I'm still working 24/7, basically. My wife just can’t understand what is wrong with me.

Zierler:

[laugh]

Robertson:

But I sit there in the dining room, typing away. I'm writing papers. I'm on conference calls. It’s just—it’s actually wonderful to be retired, because you're now free to think and focus on all of these problems that have sort of consumed you all your life. And they still do. I enjoy working on the neutrino mass problem, which I'm still working on. I have hopes that before I kick the bucket, I will finally know what the mass of the neutrino is.

Zierler:

So that’s a knowable question. You think it’s possible to get there.

Robertson:

We have an idea that—it’s a stretch, but I think we have an idea that will get us there. There’s an idea that I mentioned earlier— from Joe Formaggio and Ben Monreal, using microwave radiation from the betas to measure the electron energy. So it’s a lovely idea. I wish I had had that idea. It’s so beautiful. It’s one of these things that you just say, “Well, we have to try this.” It might not work. It’s hard. We can tell that. But there are so many interesting problems associated with it that every day I'm cracking some new thing, which I like to work on. I enjoy the comradeship of working with my colleagues on this. We have a wonderful group of people. I meet with them regularly. By Zoom today, but [laugh] it still goes on in a very nice way. It never gets old. The problems are always new and stimulating. So you really—I find I just can’t put it down. It’s addictive. [laugh] Just can’t stop. I love it. [laugh] So I hope to keep on working. You know, you only get a certain amount of time to do these things, and I am not going to waste any of it. [laugh]

Zierler:

Wonderful. Hamish, it has been an absolute pleasure talking with you today. I really want to thank you for your time.

Robertson:

David, my pleasure. It was nice to talk to you. Thank you very much.