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Interview of Willy Haeberli by David Zierler on July 31, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Willy Haeberli, Professor of Physics Emeritus at the University of Wisconsin in Madison, Wisconsin. Haeberli recounts his childhood in Basel, Switzerland, and he describes his experiences as a student during World War II. He discusses his early interest in physics and his decision to pursue nuclear physics at the University of Basel under the direction of Paul Huber. Haeberli describes his graduate research on the ionization of gasses by alpha particles, and he describes the circumstances leading to his subsequent postdoctoral job at the University of Wisconsin, where he was attracted to work with Raymond Herb in accelerator physics. He explains some of the scientific and cultural adjustments in order to settle in at Madison, and he describes the central questions of the structure of atomic nuclei that propelled nuclear physics at that time. He describes his subsequent research at Duke University before returning to Madison to join the faculty, he describes his many research visits to ETH Zurich, the Max Planck Institute, Fermilab, Saclay, and at DESY in Hamburg, and he offers insight on some of the differences in approach between American and European accelerator labs. Haeberli reflects on his contributions to the study of polarized protons and deuterons and angular momentum assignments. He discusses his work developing gas targets of pure spin polarized hydrogen and deuteron atoms, and he describes the critical support of the DOE and the NSF for this research. Haeberli shares his feelings on being elected to the National Academy of Sciences, and he explains his preference teaching undergraduates to graduate students. At the end of the interview, Haeberli describes how the department of physics at Wisconsin has changes over his decades of service, and he explains how only with the benefit of historical hindsight can one distinguish the truly important advances in the field.
Okay, this is David Zierler, Oral Historian for the American Institute of Physics. It is July 31st, 2020. I am so happy to be here with Professor Willy Haeberli. Willy, thank you so much for joining me today. Willy, let's start first with your title, and your institutional affiliation.
Okay, I am Willy Haeberli, Professor of Physics Emeritus at the University of Wisconsin in Madison, Wisconsin.
Willy, let's go right back to the beginning, ninety-five years ago. First, tell me about your parents.
I was born in the city of Zurich. Of my parents, my father's name was Paul Haeberli, and mother, Claire Haeberli. At the time, they lived near Zurich, but while I was only a year or two old, we moved to the city of Basel in Switzerland. Basel being on the northwest corner, right adjacent to Germany and to France.
What were your parents' professions?
Okay, well, my parents- let me go back just a little bit. My parents grew up in a small farm village in the center of Switzerland, a little village of maybe 600 people near the city of Solothurn, Switzerland. In that city, my grandfather was not a farmer, but rather he was in charge of running a small steam engine train from Solothurn to a nearby city of Biel, about forty miles away. It was a very simple train, just back and forth, and he was running the steam engine. That's where both of my parents grew up, in that place. So, it was not a place of much educational opportunity, but rather, I said in one document that my father was a mechanical engineer. This is not a correct description, really, because my father was going to a nearby technical college; a two-year school where he studied engineering, but it was not a university. It was a community college. My mother, who grew up in the same village, often told me how she was crying for several days, because as a young woman, after eight years of elementary school, she was not allowed to go to school anymore, which she would have loved to do. Instead, she took an apprenticeship as a seamstress. So, that's the professional background of my parents.
Willy, what was your family's experience during World War II?
My family experience? Well, during World War II, I was most of the time in school. I wrote to you a bit about my complicated background in my schooling. I was, at the time, in a school called Gymnasium; Gymnasium being a prep school for a university. The particular Gymnasium I was in was the Gymnasium of Mathematics and Natural Science. So, we had a lot of instruction that would be considered rather advanced, if you like. We learned calculus, physics, chemistry, French, English, and it was at that time that already I knew that I was going to a physicist. As soon as I learned about physics in physics class, I just knew that was what I was going to do. So, living in Switzerland during the war, well, the war was, of course, changing the daily life in Switzerland a lot, because Switzerland was surrounded by the Axis by Germany and Italy. So, import of goods from abroad was very much limited. There was very little coal to heat the school. In winter, we were furloughed because there was no coal to heat the schools. As far as feeding the population, there was a big move away from the animal agriculture. The milk and cow economy was changed to total agriculture. Even in city parks were plantings of potatoes.
But your family was never in danger during the war.
There was never really any danger. There was bombing of the freight train station in Basel. American bombers were bombing the freight train yard. They claimed it was a mistake, but nobody believed it because it is true that to appease the Germans, the Swiss government allowed sealed trains to go from Germany to Italy, presumably with weapons. So, it was suspected that it was done on purpose that they were bombing that freight yard. So, stupid as young people often are, I was fifteen years old. We went to the roof to watch the bombers go overhead.
Willy, do you remember your reaction to the use of atomic bombs in Japan, and perhaps, did this spark any interest for you in nuclear physics?
No. That certainly had no influence at all on me, in that sense. The nuclear bombing, you see, at that time, news in Switzerland was rather limited, it was always difficult to know what was true and what was rumor. We were not totally aware of the destruction in Japan at the time.
When did you enter university as an undergraduate?
I entered university in 1944, just at the end of the war.
Did you major in physics? Did you know you wanted to study physics from the beginning?
Yes. I entered university, you see, university really was- there was no real undergraduate school. University was an educational institution where you get only a master's degree and a PhD. I entered university and recall my first laboratory session. The laboratory teaching assistants asked me what I was going to study. I said, "Oh, I'm going to study physics." They laughed and said, "Ha! You will find out how hard that is." I was presuming a little bit to claim that I was going to by a physicist. So, yeah, the answer is that in the very beginning I knew that I was going to get a degree in physics.
Why nuclear physics?
Well, it is really hard to picture the limited size of the physics department. Like I mentioned in my documentation, there were only really two professors, one experimentalist in the department, and one theorist. Then, there were two extraordinary professors. One did optical spectroscopy. So, the only field of research at that time in the department was optical spectroscopy with this adjunct professor, or with the chairman of the department, who was only interested in nuclear physics. So, there was really only one area to choose.
Who was your graduate advisor?
Well, the chair of the department was my advisor, but also, one of the two alternate professors- he and the chairman both studied at ETH [HEH], so the two of them were basically my advisors. It was interesting, Huber, the big professor, taught also the introductory course in physics, a very large course for the time with about 200 students. Like I mentioned, I was chosen to be the lecture assistant to set up the very demanding lecture demonstrations.
As far as personal relationships to professors, the advisor was Huber, and the other was Baldinger. Huber, of course, was sort of off scale as far as any personal relationship was concerned. Huber was congenial, but rather distant Baldinger, on the other hand, was a very friendly person to the extent that during the last year of my graduate studies, he said he was invited to write a review article for a German Scientific Annual Review- it's called Ergebnisse Der Exakten Naturwissenschaften, the Result of the Exact Sciences. He was asked to write an article about electronics used in nuclear physics. Then he said, "Well, Haeberli, look, I have to write this article, but I would welcome you to be my co-author. However, we are under a deadline, and I have to write this article while I'm on a camping vacation with my family. Would you come along on my camping vacation?" You asked me at one time about personal relationships with professors, so that was a rather remarkable cooccurrence.
Is this what your dissertation was on?
No, no. My dissertation had to do with ionization of gasses by alpha-particles. The reason to do that is mostly it could be done without an accelerator by using a naturally radioactive source. The issue really was what happens when a gas gets ionized by the passage of other particles nuclear particles? So, the question that was given, how does that ionization likelihood vary when one mixes two gasses? I had to change mixing ratio of gasses and see how many ions get produced by other particles. The use of this activity in nuclear physics is very limited, but I understood that the use of this was mostly in medical physics.
Now, Willy, were you looking for a project that didn't rely on an accelerator because you did not have access to an accelerator?
That's correct. There was only one open air, 200 kilovolt open-air rectifier set that went all the way to the ceiling of a lab room. That machine was used to make neutrons by the DD reaction, deuterium ions hitting a heavy ice target. Because there were about eight graduate students, PhD students, in the department, and there were two post docs, the machine was very much in demand. That is why I did not use the accelerator.
What were the principal conclusions of your dissertation?
The principal conclusion of my dissertation was the following: when the ion goes through a gas and hits the gas atoms and breaks them apart, that's called ionization. The ionization in the mixture of gasses is not a linear relationship of the mixing ratio. Why not? My explanation, which was followed by calculations, was that the electrons ejected by one kind of atom being hit would ionize the other atom. So, there was a cross-interaction between them. I don't claim this was a very weighty discovery.
Willy, how did you come to the decision that you wanted to pursue a career in the United States? Why not stay in Basel?
Oh, well, staying in Basel would have had no immediate future. I gave you a picture of this being a very small department. So, there was zero chance of getting a position by staying on in Basel. I was quite highly regarded by my thesis advisors, and they presumed that I would pursue a career in physics, and said that to make me a scientist, I would best spend a year or two in the United States. In fact, my professor said, "Then, after that, you could come back to my institute and we would find a position for you." Well, I did the first part in the United States, not for a year or two. I did not go back to Basel, although, I must say I did get an offer years later for an associate professorship at Basel, which I was not inclined to accept.
What was the connection to Wisconsin?
Well, my professor, when he advised me to go to the United States, he knew a fair amount about science in the United States because he had traveled to the U.S. before the war, and of course, he kept up to date on current research in the U.S., in part my personal correspondence, but also by journal articles. So, he was familiar with nuclear physics research in the U.S. In his opinion, the two foremost institutions, as far as up to date, advanced instrumentation was concerned, were two laboratories. Hofstadter at Stanford had just built a linear electron accelerator, and for acceleration of protons, deuterons, other particles, by far the most advanced machine was the one built by Professor Herb at the University of Wisconsin. So, he wrote for me a letter to Hofstadter and to Herb, and they both made me a post doc offer.
Then, the hard part was deciding which one to accept. Well, I didn't have much to go on. In part, I listened to Professor Huber's impression of Campus life in the two places, and I decided to go to Wisconsin. He described Stanford campus as a quadrangle with Spanish architecture, and outhouses in the middle of the quadrangle, and in Wisconsin, he singled out the hills of campus with students walking around with books under their arms. Anyway, I just happened to choose that one. And of course, Madison is, as you may know, between two lakes. Does that answer your question?
Sounds like it was an easy decision at the end. Willy, how was your English at this point?
Oh, my God. This was difficult, yes. How should I say? In school, we had learned English for four years. But you know, it was school learning. We didn't learn to speak, really. So, I could understand English, I could read English, but I could hardly explain anything in English. So, that part was rather difficult. I do remember being teased by some of my coworkers at Wisconsin later on, when they said that after I arrived, I was described as "the mute" because I just listened. It was always a problem because at that time, when I tried to make a contribution to a conversation, it took me twenty seconds to make a sentence, and by that time, the conversation had passed on already. So, that is why I was mostly just quiet.
At Wisconsin, there was a professor named [Henry] Barschall, who was originally from Germany. I knew that he was from Germany, and when I came to Madison and I was introduced to Barschall, I immediately greeted him in German and he sternly answered "Here, only English is spoken." So, it basically was a good thing to get the message that I cannot speak German with him, because it would have sort of singled us out, and of course, he did not want to be reminded of his German background because he left Germany to flee the Nazis.
Willy, you emphasized how small the department was at Basel. So, I'm curious what your impressions were when you first got situated in the Department of Physics at Wisconsin, which of course, was quite large. What were your impressions of how big physics could be in the United States?
It was, of course, a huge change, a huge step up in activity between Basel and Wisconsin. In Wisconsin, there were four professors in nuclear physics alone. There were about twenty professors in the department, compared to about two professors or so in Basel. So, it was very exciting for me to be there, particularly because I was given quite complete freedom to decide which research group to associate with. At first, I found it difficult because nobody told me what to do until I figured out that they expected me to make a choice and decide what research I wanted to pursue within that group of people.
Did you see this as an opportunity to continue on with the kind of work you did as a graduate student, or did you see an opportunity to go onto new projects?
Oh, totally the second. Yes, I saw opportunity to go on with a completely different, new direction. After all, this was the purpose of going to Wisconsin, where there was a substantial accelerator. So, yes, as it turned out, I really was rather poorly prepared, in some way, in learning nuclear physics and nuclear reaction theory, etc., because nothing of that kind was taught in my studies at Basel. Fortunately, my background in Basel, where I had learned that you don't need lectures to study something, you can go to the library and learn things on your own. So, I managed to develop some expertise on my own, while I was working there.
This must have been very exciting for you to have access to this new instrumentation.
Yes, it was. It was also rather illuminating to see how major activity is organized. It is not activity of one person alone, but it absolutely requires the collaboration of people. This accelerator, we used around the clock. That, of course, meant a group of people, usually one group of students under one professor, was using the accelerator for some two or three weeks, and then the use shifted to another group with the next professor. So, the idea, I guess, I wanted to work with lots and lots of the graduate students. In fact, the faculty wives rather enjoyed my presence in the lab. They told me that now the professor, their husband, doesn't have to go to work at night anymore to supervise the students. They can now rely on his post doc.
And of course, you say, "Faculty wives," because in those days there were no women on the faculty.
Absolutely right, yes.
Willy, what were some of the bigger questions that were being asked in physics, and in what ways was your research responsive to those bigger questions at that time?
Well, the bigger questions all had to do with the internal structure of atomic nuclei. As you know, nuclei are a complex construction that, in the most naive view, is made up of protons and neutrons, and the question is how do these neutrons and protons interact inside a nucleus? To study that, we would hit the nucleus with a fast beam of particles from the accelerator, and then study the result of the collision. I might liken it to hitting an instrument, and then listening to the vibrations emitted as a result. So, you hit the nucleus and it will vibrate, give off other particles, what was of the essence was the ability of this accelerator we had to marry the energy of the particles in tiny steps. Beam energy could be varied up to about four MeV, and the steps were as small as one KeV from one measurement to the next. Then, we would show big resonances at certain energies.
Was the experience at Wisconsin closed ended? In other words, did you know that you were only going to be there for two years, or could you have stayed on longer, but then the opportunity at Duke came up?
No, Wisconsin, to my chagrin, had a strict policy: to not keep post docs more than two years.
So, you would have stayed. You were very happy.
And my wife liked living in Wisconsin. To my chagrin, they didn't keep me longer. But in retrospect, I will say, it was a very good policy they had, because it avoided people hanging on, hoping for a permanent position that then never materializes. So, after two years, I had to find a new position, either to go back to Switzerland, or to stay in the U.S., but it was clear to me I was going to stay in the U.S. simply because going back to Switzerland without having a permanent position would really have not been a good career decision.
Willy, what about elsewhere in Europe? Did you look at positions elsewhere in Europe; England or Germany, perhaps?
No, that is a difficult question, because there really was absolutely no mechanism for me to approach German universities. I had no connection with any of them. I wouldn't have thought it appropriate or promising to just at random write to a German university: Dear Sir, do you have a professorship for me? That would not have seemed like a very good approach. So, instead, I decided to remain in the U.S. As I mentioned to you already in my documentation, I was at Duke University for two years, and found research at Duke quite satisfactory. Life in the south was not really much to my liking, and certainly, my wife Heidi did not particularly like living in the south. So, during my second year at Duke University, I had a conversation with Professor Barschall from Madison, at the American Physical Society meeting, the spring meeting which at that time was always in Washington D.C. He offered me a position as Assistant Professor at Wisconsin. My professor at Duke University, Henry Newson, used an expression that I hadn't learned. He said, "Oh, damn it! We were certainly caught with our pants down," because he would have liked to hire me, too.
You were very happy to go back to Wisconsin, and it sounds like your wife was as well.
Yes, that's right. I was very happy to be back in Wisconsin.
Did you feel that the time away allowed you to come back as an adult, so to speak? In other words, when you go as a post doc, if you never left, you wouldn't have had an opportunity to, sort of, grow up, right?
Absolutely, yes. It was also, you see, I totally, sort of, avoided feeling that I was still kind of a postdoc. Now, in the meantime, having been away for two years, was a separation. So, it was a new start that was more independent than I had before.
This was a tenure line position. In other words, you came with the intention of achieving tenure at Madison.
Absolutely, yes. Correct.
When did you achieve tenure?
Wish I knew. Maybe after four years, roughly.
Willy, can you talk a little bit about the impact of Sputnik, both on your career, specifically, and on the way the United States supported physics as a result?
It certainly had an effect on physics support in the U.S. But, David, you mentioned Sputnik. I can't help but tell you an amusing story about Sputnik. Does the name of Wigner mean anything to you?
Yes, of course.
Eugene Wigner was a regular summer professor visiting in Wisconsin. He and Gregory Bright had been at one time in Wisconsin, but they did not remain on the faculty. But Wigner was visiting every summer. Wigner had the reputation being super polite. I remember meeting him at afternoon tea in the physics department. When I was introduced to Wigner, he said- this was just when I came as a postdoc, fresh from Switzerland. Wigner, "Oh, yes, Mr. Haeberli, so nice to meet you. You know, Mr. Haeberli," he had this Hungarian accent, "every time at Princeton University, when a difficult problem comes up, we have to ask Haeberli about that."
So, that same Wigner was at a dinner party at Ray Herb's house with me, and Ray Herb was fascinated by the idea of space travel. Wigner said, "Well, look. An organism, a living thing, a person, an animal would never be able to survive the weightlessness in space." The next morning was the news in the paper, Sputnik had circulated overhead while Wigner pronounced it impossible.
It goes to show, even smart people can have wrong opinions.
Willy, when did you start to take on graduate students?
Immediately when I started my assistant professorship. My colleagues were anxious when there were new students applying to grad school that they would to all of us, including me, so that I would have a chance of getting research going with graduate students. So, immediately this happened.
Who have been some of your most successful graduate students over the years?
Oh, my God.
Don't be scared, if you forget anyone, you can always go back in the transcript and add names later on.
Yes, well, one of my most successful graduate students was named Steve Vigdor, who eventually became director of all research at Brookhaven National Laboratory. So, from that sense of success, as far as getting a very much advanced position, he certainly was one of them.
Willy, how interested were you in working, either on a sabbatical, or to visit at national laboratories, such as Fermilab, or Brookhaven, or perhaps a little later on at SLAC? Did you work at any of these laboratories? For example, your colleague, [Lee Podrom], he would go back and forth from Fermilab to Madison all the time. I'm curious if you did something similar.
I was slow in responding because I have such an extensive history of working at other laboratories. I always was interested in keeping in contact with other laboratories in many different ways. My first sabbatical, I was at ETH in Zurich, and started a research project there which lasted about eight years. I went back and forth, and it had to do with a study of parity conservation. There is this fundamental law of physics that there is no difference between left and right. In other words, if you looked at the laws of physics in the mirror, they would be totally the same. This can be tested with an experiment that I started at ETH in Zurich. In addition, I was given a Max Planck Fellowship to be a visiting professor at Max Planck Institute in Heidelberg. That always led to other projects, yet. I did experiments at the French Laboratory, Saclay, where they had a cyclotron that made polarized beams, which I needed to study nuclear reactions at higher energies than I had available at home. One big experiment was the one at Brookhaven National Laboratory, where we provided a target for the large- you know about the collider at Brookhaven. I worked at the laboratory, DESY, in Hamburg, the electron accelerator.
So, anyway, there was a lot of interest I had in working at other places, and I always felt very much welcome to contribute my technology. I had this wonderful scientist working with me, Tom Wise, who helped me build a polarized target, polarized beams, and he was a wonderful person to help in setting up the experiments, like I say, at DESY, and so on. So, yes, I much profited from going to many different international laboratories. My other activities, internationally, was to be on the advisory board of various laboratories: Kernforschungszentrum in Karlsruhe, I was chairman of the advisory committee. Also, in Switzerland at the Swiss Institute of Nuclear Research, I was chairman of the program committee.
In what ways did working in the major laboratories in Europe differ from working in the major laboratories in the United States?
You know, in the small laboratories, there were the big differences. But on the world scale, these huge accelerators, of course, require huge engineering efforts, huge financing, huge staff, huge collaborations. It's always a little disconcerting to find that there may be 200 collaborators, 300, on a given experiment. In that respect, I found no difference between working in the U.S. or working in Europe on large projects. They were organized much in the same way.
Willy, can you talk generally about your work studying polarized protons and deuterons?
Well, it is difficult to do that, but generally speaking, David, the work could be divided into two groups of things. One group is to make beams of particles in accelerators that have the spin all in one direction what's called a polarized beam. So, that is one activity that evolved, in my case- my students and post docs were amused to remember the various devices I invented, one after the other, everyone getting a big improvement in intensity. Polarized source number one, two, three, four. In fact, there was an incredible history over ten years of improvement in the intensity of these beams.
Now, I was not the only one in the world who worked on improving those beam intensities. The biggest other project was a project at Brookhaven National Laboratory. One thing is to make polarized beams and use them to study how the spin of the particles, beam spin one way or the other, how that affects nuclear force, what's called the spin dependence of the nuclear force. So, these in-house research activities with my graduate students extended over twenty years. That was followed by a second activity of providing not just a beam of particles spinning all in the right direction, but also a pure hydrogen gas target that was spin oriented. The targets I made were of a special kind. Polarized targets had been made, in particular, for high energy experiments by polarizing protons inside certain solids, the polarization being produced by flipping the spins all in the same direction by microwave irradiation. But those targets were useful only for beams at very high energy, because to penetrate a solid block that is polarized, takes very high energy beams.
My idea was a completely different one of making pure hydrogen atoms polarized as a very dilute vapor. But that has a problem that these targets would be so dilute that only with huge beam intensity would they be useful. That just plays into the advantage of so-called storage rings. You know there are these rings where particles keep going around and around, and these particle intensities can be built up to very high intensities. In those rings, if you were to put a block of polarized matter in the way, would destroy the beam immediately. So, what that calls for is a very dilute vapor. So, that is what my idea, my proposal was. The proposal, actually, was made way back at the conference in 1962, but only became practical twenty-five years later. What I developed is a tube containing polarized atoms through which the beam circulates. Then, from a side-arm of the tube, we will inject spin-polarized atoms. These so-called storage cell targets have been used in the meantime, extensively. We built a target that was used for many experiments at DESY in Germany. That is, DESY, the accelerator, is this six-mile electron accelerator.
We also made a target for the Brookhaven heavy ion collider to use as an internal target to study the interaction of polarized particles, protons hitting protons. The ideal experiment, I like simplicity. I was never much of a fan for so-called heavy ion physics, because it's what I facetiously call, that's like linoleum on linoleum. That's too complicated. I like protons on protons, ideally both of them spin polarized. So, we accomplished that kind of experiment in a number of cases. One case, I had a wonderful, long collaboration with a former post doc of mine, who was professor at Indiana University, where they had a 200 MeV storage ring, for which we built an internal target. The person's name is Hans Otto Meyer. He was a post doc who I invited originally to come from Switzerland. He was actually from the University of Basel, where I was also studying. So, he, then, became professor at Indiana, and we had these experiments, which met this ideal of having protons on protons both spin polarized.
In what ways did your research contribute to understanding new methods of angular momentum assignments?
Well, yes. With unpolarized beams, we could determine only the orbital angular momentum of particles in the nucleus, but not the spin direction relative to the orbit. So, spin orbit coupling refers to the idea that an orbit of particles couples with the spin of particles either parallel or opposite to the orbital angular momentum. That is what our devices allowed to determine: the total angular momentum. It was interesting to me that after we developed these methods, a whole industry developed in Japan where two laboratories did nothing but these experiments, on and on for years and years. That was never my style. I'd have a method developed, and then when it was well established, I would turn to some new idea, rather than repeating the same thing over and over.
Willy, can you talk a little bit about your collaboration with -- I don't know how to say it. Is it ETZ Zurich? Is that how you say it?
ETH Zurich. Eidgenössische Technische Hochschule.
It's where you worked on the polarized beams, and you were studying symmetry violations.
Yes, well, actually, the actual accelerator was not available at ETH, but rather the associated research institute called the Swiss Institute of Nuclear Research, abbreviated SIN. Anyway, at SIN, that is where we did these experiments.
Was it there that you were searching for time reversal violation in the beta decay of polarized nuclei?
Yes. There were two fundamental experiments. One was a time reversal experiment, and one was a parity conservation experiment.
What years was that collaboration?
I'm looking here. I made some notes. 1970, roughly.
Willy, I'm curious if in your return to Europe, and Switzerland in particular, if you saw that there were now more opportunities in physics than you had when you left in the early 1950s.
Well, yes. There would be much more. I think now the picture has changed very much, in the meantime. As I left Switzerland, the science establishment in Europe was still recovering from the long war. The war was maybe not so long, but it certainly was extremely destructive, particularly for science in Germany. So, at the time, opportunities for young people to do science was very limited in Europe. Now, I would say, the situation probably is the reverse. I think now there are better opportunities in Europe than in the U.S. At the moment, as you know, science support is not at its best in the U.S., while in Europe, the support- it only started with the big laboratories like CERN, and people got used to the fact that to do modern science does take a lot of resources. In central Europe, certainly, this was provided, and they still provide it now. So, I would say, overall, the opportunities are better now in Europe than in the U.S.
Of course, much of that has to do with the fact that the SSC was never built.
Were you involved at all in the planning of the SSC?
No, I was not involved in the planning at all. This was in some way a sad story, at least a sad story for the research in high energy physics. But the SSC never developed and now I think it still is true that CERN activities are at the forefront of high energy physics research.
Was the energies that were going to be possible by SSC, would that have been relevant for your research? Would you have done research at SSC?
No, but it's an interesting question, because on the one hand I did work on high energy accelerators, but I never considered myself a high energy physicist in the sense that the physics results have excited me for most of my career were not specific high energy physics experiments.
Willy, let's talk about some of the work in the second half of your career, more recently. Can you talk a little bit about how your group developed gas targets of pure spin polarized hydrogen and deuteron atoms?
Yes, that has an interesting history. The idea to make polarized gas targets, I may have mentioned that already, I proposed that based on the work of Kleppner. Kleppner made spin polarized atoms for the purpose of the hydrogen maser. Kleppner found out that one can put polarized atoms in a vessel, the surface of which is coated with Teflon. The reason to coat the vessel is that when a polarized atom collides with the surface, it may lose its spin orientation. But Teflon, he found, had the property that the spin was preserved in the collisions. So, that gave me the idea to say, "Well, if that worked for Kleppner for the maser, maybe we could make a vessel like this as a target. A vessel with an opening for a beam to go in and out."
Indeed, we tried this. The pilot experiment we did was in- let me see, I have the notes here someplace. 1981 was our first test of such a target. We tested it in our local laboratory with our beam from the accelerator, and found that, indeed, one can make such a target, and it survives the ion bombardment. Which, of course, Kleppner did not have to worry about for the maser. So, in '81, we tried this first, but it was only a whole decade later that we produced a real, useful target for a storage ring. That was done in a test in Heidelberg.
I mentioned already that I got a Humbodt fellowship to work in Heidelberg, and that was the pilot test that I was able to do using their storage ring. See, at this point, starting in 1991, the scenery in nuclear physics had changed a lot in the sense that the low energy accelerators that were typical for university laboratories were no longer supported by DOE. At Wisconsin, we had support from DOE way back to the time that Ray Herb- oh, I didn't mention that the accelerator in Madison that Ray Herb built actually was shipped to Los Alamos during the war to measure neutron cross-sections for the Los Alamos project. When that accelerator was returned to Wisconsin after the war, the Department of Energy issued the first research grant to Wisconsin, to Ray Herb. Ray Herb told the story that the question was what to name that contract. So, it was called the DOE Contract GEN1- Generator Number 1.
Then, by 1990 or so, after DOE had supported the research program at Wisconsin quite generously for years, they terminated that contract. They made a policy decision that DOE was no longer going to support small university accelerators. So, at that time, the support for Wisconsin research shifted to NSF. Well, I was fortunate enough that they made an exception for me because they wanted to support the kind of research, I told you about polarized sources and targets. They saw a use of these devices in high energy physics. So, the DOE continued to support me in that. By and large, by 1990, there was very little new ideas that people had to do low energy nuclear experiments with the small accelerators at universities. So, the whole development with the targets was no longer carried by my grad students but was entirely done with post docs and with my senior scientist, Tom Wise, who was just an excellent resource in technical developments.
Did you welcome this transition?
Yes, I did, in a sense. But, you know, when you are in a situation when you have no good ideas anymore to do experiments with your local facility, then I don't see- some people were hanging out and doing the usual things out of habit. That is not what I wanted to do. So, yes, I welcomed the change.
In what ways did the transition to NSF advance the science in a way that would not have happened with ongoing DOE input?
Well, it advanced the science only in a sense that it avoided the destructive effect of no longer funding what still was good research done at Wisconsin. At the time, there was still quite an active program. My well-known colleague, Heinz Barschall, did wonderful experiments in neutron cross-sections. Without the NSF support, that would have died instantly. So, in that sense, I think it was a very satisfactory, smooth transition from one agency in the federal government making a policy decision, but not in a way that left people out in the cold.
Willy, who have been some of your most important collaborators over the years, not just institutions, but individuals that you've worked with?
Certainly, I will say, the work I did would not have been possible without the collaboration with my senior scientist, Tom Wise. Let me give a little bit of background. Tom Wise was a graduate student, and at one time, thirty-five years ago, teaching assistant in one of my courses. I encouraged him, of course, to go out for a PhD, and Tom Wise said he loves doing physics, he loves working with me, but he hates taking courses. In particular, he said he never enjoyed taking all these required theory courses. So, he refused. He said if I will have him without a PhD, he would be happy to just be my scientist. So, for thirty years, we have been working together, and he has been just absolutely instrumental in his work on both, polarized sources and targets. So, that is one collaborator I have to single out.
A second one would be the collaborators at ETH, Professor Lang, and Dr. Simonius. They both were rather happy to have me there because I was able to solve a fundamental problems they had in one of these experiments. Another collaborator who was of much importance was Erhardt Stephens, who was at the time at the Max Planck Institute where we did these first tests with the storage cell targets, and who later was Professor of Physics at Erlangen. I already mentioned Prof. Hans Otto Meyer at Indiana University. Then, of the local faculty, a most important collaboration I had that was enjoyable was the work with Professor Anderson, who was in atomic physics. What did I have to do with atomic physics? Well, David, let me tell you that to develop these ideas, how to spin polarize atoms, it involved atomic interactions. One idea was to use cesium interaction with hydrogen to make beams of negative ions. So, to measure those fundamental atomic collision cross-sections, I did together with Anderson. Anderson was most happy to have this impetus to his program of measuring atomic collision charge exchange cross-sections. Charge exchange, referring to transferring electrons from one species to another as they collide.
Willy, what did it feel like to be elected as a member of the National Academy of Sciences?
I must tell you that I was delighted but was not totally taken aback. My dear colleague, Heinz Barschall, urged me at one time to become citizen, and mentioned that some important honors require citizensip. He had been a member of the academy for years. As was Ray Herb, the builder of the accelerator. I delayed citizenship for a long time, and in fact, became a citizen only after Heinz died.
Why, Willy? Why did you delay citizenship?
Inertia. It took work. It took work to become a citizen. But it is much to the credit of the United States, but I never felt any pressure. I never felt I was being discriminated against, never felt there was something wrong with me because I was not a citizen. So, I just avoided it. Eventually, I became a citizen because-
What year did you become a citizen?
Just before I was married. 1990. The reason was that the woman who was my life partner for many years was denied a permanent visa. She had lived in this country for fifteen years, and we lived together, but she was still on her student visa. Eventually, she was told to leave the country because her expired five years ago." She left but was unable to get a new visa. So, it was a real struggle to get her to come back. To make a long story short, eventually the American consulate in the Zurich relented and said, "Okay, you can go back to the U.S. for one month to pay your taxes, and to pack up and leave the country." Well, interestingly enough, at customs, when she entered immigration, the immigration officer said, "How long are you planning to stay?" She said, "Well, my visa is only for one month, but I'd like to stay longer but the Consulate won't let me.", "The consulate does not decide. I decide. The State Department decides. You can stay for a year." So, then, we made an urgent effort during that year to get her to be a permanent resident. But I had to become a citizen so that she could be my dependent.
So, finally the force of inertia was overcome.
Yeah. So, then we were speaking of membership in the academy. So, after I became a citizen, two years later, I was told that I had been elected. I must say, I was very gratified. I was very grateful for that honor. In the meantime, I learned just how complicated it is to become a member of the academy; how many steps there are in the election process. So, I was very grateful to become a member.
It also is recognition by your peers. In other words, the people who know your work well are the ones who have a very important role in making this decision.
Yeah, that's right.
Willy, when you went emeritus in 2005, in what ways did you see that transition as an opportunity for you to concentrate on things that you might not have had time for as a full-time professor? I ask, because physicists never retire; they just focus on different things.
Yes. Well, you know, maybe what is a bit unusual is just how long I was still teaching. After I retired, I was already eighty years old. So, I really cannot claim to have started any new phase in my life. I still haven't done my cookbook. For many years, I loved to cook dinner. I kept a log- I have two logbooks of dinners I cooked, and I'm always planning, yet, to make a cookbook out of it. It might happen; we don't know. David, one thing we have not touched upon is another phase of my personal life that is quite an important part, in my view. That is my teaching.
Yes, yes. That is actually what I wanted to get to next. We talked a little bit about your career as a mentor to graduate students, but I wanted to ask you a few broad questions about your career as a professor. The first one about teaching is, what have been the most enjoyable classes you have taught undergraduates?
I must say that I seem to be an exception, odd man out, in that I love teaching undergraduates. I much prefer undergraduate teaching to graduate courses, and I much prefer teaching introductory courses for beginners. Of course, the department was always glad to have volunteers to teach the large, introductory courses. So, for many years, I taught algebra-level and calculus level introductory course. What I loved about it was to have a big audience of students who were predisposed to think that physics is a pain in the neck. It's something they have to pass because of what the rules say, but they doubt that that they will understand or even enjoy it. So, I made it a mission, if you like, to see to it that students would not only just have to take the course but would actually get to like it.
One of the methods I used was to have well thought out lecture demonstrations that would be added as an explanation of the material being presented. The other thing I tried to do was to prepare my classes ahead of time so that the blackboards would be legible from the back rows of the lecture room. The lecture room had three blackboards that could be moved up and down. So, I made it a policy to have these blackboards prepared ahead of time in my head so that they would show an evolution of ideas. The other thing that I considered extremely important was to teach the students how to think about solving problems that they are typically given as homework problems, and as problems in the examinations. To show them on the blackboard, step by step, how one thinks about applying the fundamental laws to arrive at the solution of a particular problem. Not only that, I think what often frustrates students is that they feel unfairly treated in their written examinations. I made it a policy to try to let the students know ahead of time exactly what the criteria were on which their grade was based. I would give them exam questions to practice on ahead of time, and I would give them a formula sheet ahead of time, so they knew exactly what to expect in an examination. So, overall, I enjoyed the interaction, because my approach was really very well received by the students.
Willy, teaching at a major public research university, like the University of Wisconsin, is very different from teaching at a smaller elite school, like a Princeton or a Stanford, in that the range of aptitude and the range of background that the students came from would be much larger. So, I wonder, in what ways did that range of background and aptitude present opportunities, and in what ways did it present challenges as a teacher?
Well, it certainly presents challenges, because as you imply, many of the students we get in Wisconsin come down from the north woods, from farms, and are not always well prepared. So, yes, that is one challenge, like I said, that I try to overcome by being careful in giving them, at least, the opportunity to do well in a course. At the same time, this did not prevent the better students from an appropriate learning experience. That is because at the large university, the undergraduate courses are of different flavors. There is a calculus level course, that is really quite advanced, and it is a challenging, good experience for the better students. Then, there are the algebra level courses that are much more amenable, much more acceptable, to the less ambitious students.
The other thing I have to add is that I was, at some point, dismayed by the observation that many students in the lower level introductory courses would take only one semester of a two-semester course to satisfy some general course requirement. To me, it did not make much sense for a student of that kind, say a liberal arts student, to take only one semester that was related to mechanics, motion, and thermodynamics, and that was the end. So, it occurred to me to start a quite different course for liberal arts students: a course that we called Physics in the Arts. Now, you might ask, and of course my colleagues asked, what does physics have to do with the arts? Well, you can use, I believe, the arts as a vehicle to interest students in physics. Take, for example, visual arts. Color, color perception, or lenses, photography, all have physics aspects. Obviously, to understand these area, color, or image formation by lenses, you have to learn some physics laws. You have to learn about wavelength, about law of refraction, and so on. So, we use that vehicle to build up a new course that was based on visual arts and on sound. Sound perception, vibrations, what is frequency? What is harmony? What is a musical scale? And so on.
So, together with my colleague, Ugo Camerini, we started a new course called, Physics in the Arts, which started out small with twenty students, but in the meantime, has become a big success. It now requires two big lecture courses. It now has 300 students, but we always insisted in having small laboratory sessions for these kinds of students, on the argument that they need more assistance than the physics courses would normally have. Thus, we limited the laboratory attendance to twelve students per section. So, in the laboratory, it was amusing to me that if you take liberal arts student and put them in front of an oscilloscope, you can teach them to look at sound waves on an oscilloscope, and to study the concept of frequency, and amplitude, and wave form, and you can get across the concept of a Fourier spectrum, and so on. So, this course has become quite a successful new course that I take some pleasure in having started it together with my colleague, Ugo.
Introductory courses with a large enrollment were usually taught by two professors. Often, we alternated teaching the lectures to allow us to follow our research projects elsewhere. After Ugo retired, I was very fortunate to be able to team up with a young new faculty member, a charming lady from Rome, Italy. Gelsomina de Stasio and I, maybe because of our European background, we had an easy rapport, she was known as an enthusiastic researcher but was not looking forward to her teaching duties. She however not only joined me in teaching “Physics in the Arts” but came to love it. She devoted much of her energy to the course and kept teaching it after my retirement. Along the way, she wanted is to write a textbook for the course. She overcame my reluctance and eventually we agreed that she would write the part about visual arts and photography, while I would do the sections on music and sound. After her marriage she changed her name to Pupa Gilbert. The book has been used at other Universities to initiate a similar course. It has been translated into Chinese, and Pupa is in the process to write a second edition.
Willy, have you ever experienced the pleasure of converting a liberal arts student into a physics student?
No, I don't think so. I think I let them be happy to be in the liberal arts.
Willy, to go back to earlier in our conversation, when you were young, and you realized right away that you loved physics and you wanted to be a physicist.
My first inkling that I liked mathematics was in elementary school. In elementary school, we had a lazy teacher who was teaching us arithmetic, and he gave us like ten blocks each of ten arithmetic problems. Whoever got all of them done first could run to the front to his desk and have the answers checked, and if the answers were all right, he got a piece of candy. That was in elementary school. Well, it was such that I got so much candy that the teacher stopped the practice. I just loved doing arithmetic, and my mother, later, often reminded me that as a seven- or eight-year-old boy, I would always come home with my backpack from school, and as soon as I was at home, I would sit down and start doing my homework. I loved doing homework, and I loved doing calculations. So, that was my first inkling that maybe that was the right thing for me to do.
Do you still think, Willy, that applies today? The things that you loved to do, the things that you were interested in, do you think that's the same today for young students who spark an interest in physics?
Well, it really sparks the interest in physics, specifically, for me in Gymnasium, because it was this mathematical Gymnasium, we learned calculus at the same time as we learned physics. I just knew I was going to be-
One big difference from when you were a student in physics to students today is that there were no computers, and now there are. How do you think that has changed the student experience in physics?
I don't really know. I do not believe that it has helped the students in learning or appreciating physics. In some respects, David, I think it has had a negative aspect to it. Before calculators and computers were readily available, as a student, you always had to have developed a sense of magnitudes to understand whether a given answer made any sense. Now, people put numbers in computers, and they believe whatever answer comes out without having the experience and facility to mentally make a rough estimate. So, it is good, in a way, to have to avoid the hard work of doing long division, etc. That certainly was of no particular use, but to have learned to have an estimate of something was a good thing.
You're so well-positioned, given your long tenure at the University of Wisconsin at Madison. In what ways has the physics department changed over the years, and in what was has it stayed the same?
It has changed a lot over time. At first, I saw the changes as positive in that we were able to add new faculty. We could search for good people from good universities for junior appointments, and that was of benefit in expanding the department. Now, in later years, I must say that I am concerned that less actual experimental physics gets done in the department. respect. So, I'm not all too happy about the changes.
Willy, for my last question, I want to ask you a very broad question, that makes you think back on your earliest interest in physics, throughout all of your research, to today, really, and looking ahead. In your area of research, what were things in the 1940s and fifties that were really mysterious, or really unknown, or not understood well, and how has your research contributed to truly understanding things that used to mysterious, or poorly understood? What do we really understand now, that sixty or even seventy years ago, we did not understand well at all?
What strikes me is the fact that what seemed important at one time, in later years, seems unimportant. Do you even look at the experiments we did forty years ago, fifty years ago? At that time, there was much excitement in my field. At conferences, when you reported about experiments that had to do with elucidating the structure of a given nucleus, that was an unsolved problem. In my area, there is something called the Fermi-Yang ambiguity. Fermi and Yang pointed out that the interpretation of nuclear processes always has an ambiguity that has to do with the spin ambiguity, not knowing which way the spin is pointing. So, the Fermi-Yang ambiguity, at that time, was a mystery. How do you resolve that ambiguity? That we did manage with polarized beams, and reporting on that at conferences, at the time, was causing some excitement in the sense that, well, here was a problem we did not understand, and now we have an answer. But nowadays, looking back, David, who cares about the Fermi-Yang ambiguity? So, it is maybe a negative statement that what was considered important and fundamental at one time, has lost its luster.
What kind of wisdom have you gained over the years in determining what is actually important, and what is of, at best, passing relevance?
For instance, studies of the laws of symmetry in nature has remained important. I much enjoyed an experiment we did at ETH, having to do with mirror symmetry. The question, is if laws of nature are left and right symmetric? We studied this question for the special case of strong nuclear interactions at ETH, where we detected a tiny difference between left and right, and the interaction between polarized protons and protons. Now, years later, do we care about that? No, because in the meantime, that has made progress way beyond what we did at the time. In the meantime, one knows that in weak interaction, there is a violation of parity. So, what we laboriously worked to detect in the proton-proton interaction, has later been interpreted as a weak force contribution between strongly interacting particles. So, I don't see that any of my work has survived in a way that is still, now, appreciated as having answered a question that has been of lasting importance.
But that's part of the scientific process. You cannot have subsequent research to supplant previous research, without the previous research.
Yes, that's right. I don't get dismayed by the fact that progress happens. I'm pleased to observe that progress happens, and that what once was a big mystery now turns into a small one. What has been of importance to me is that through this work, many of my students and associates have been able to build on the experience they gained to build their own productive research programs.
Willy, the second part of my question would ask you, if you will, to use your powers of extrapolation to think about the future. Thinking about all the things that you've been involved with over the decades, where do you see your field headed into the future? What are the things that, if you have opportunity to provide advice to young nuclear physicists, where are the most exciting avenues in the field, going into the future from today? I ask the question on the basis of, of course, extrapolation. All of the things that you've learned are relevant for where the field goes next.
It's hard to answer your question, because I don’t venture to predict the future. If indeed, a young physics student asked me what areas of research I would find most exciting, I would find it hard to tell. When I now read the research papers, like Physical Review, or Physics Letters, most interesting are the recent gravity wave experiments. Gravity wave experiments are certainly a remarkable accomplishment with the interferometers and correlating gravitational wave observations in different locations on the Earth.
Willy, it's been absolute pleasure speaking with you today. I know we've both been looking forward to this day, and it certainly did not disappoint. I want to thank you so much for sharing all of your insights and memories with me. This will be a tremendous addition to the historical record, and I'm quite honored by our time together, so thank you very much.