Eric Adelberger

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ORAL HISTORIES

Credit: Joe Belcovson

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

Interview of Eric Adelberger by David Zierler on June 5, 2020,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/44753

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In this interview, David Zierler, Oral Historian for AIP, interviews Eric Adelberger, emeritus professor of physics at the University of Washington. He describes his childhood as the son of German immigrants in the interwar period, his early interests in math and science, and a formative summer job at the National Bureau of Standards. Adelberger recounts his decision to attend Caltech for his undergraduate work, and the profound influence of Feynman on his understanding of physics. He explains his decision to remain at Caltech and his evolving interests away from high energy physics toward nuclear astrophysics. Adelberger describes his graduate work on a pulsed-beam neutron time-of-flight system under the direction of Charlie Barnes. Adelberger discusses his postdoctoral work at Stanford, where he did research on a tandem accelerator, and he explains the circumstances leading to his first faculty position at Princeton. He describes his ongoing work on isospin-symmetry breaking, and he recounts the recruitment process that convinced him to join the faculty at UW. Adelberger describes the diverse range of experiments he has pursued over the course of his tenure at UW, and the ongoing relevance of these experiments in theoretical physics. He discusses his work on gravity and general relativity, and he explains some of the philosophical considerations and intramural debates engendered by string theory. At the end of the interview, Adelberger describes what he sees as some of the open questions that have endured over the course of his career. 

Transcript

Zierler:

Okay. This is David Zierler, oral historian for the American Institute of Physics. It is June 5th, 2020. It is my great pleasure to be here today with Professor Eric Adelberger. Eric, thank you so much for being with me today.

Adelberger:

I'm really looking forward to this interview today.

Zierler:

Wonderful. So to start, please tell me your title and institutional affiliation.

Adelberger:

Yes, I'm an emeritus professor of physics at the University of Washington in Seattle.

Zierler:

Okay. Now, let's take it back right to the beginning. Tell me a little bit about your family background, your parents, where they came from, and their professions.

Adelberger:

Okay, my parents were both German. My father came to this country in 1929. At this point he already knew my mother. He had won a prize in Germany for interior architecture, and he used the money to come to the United States.

Zierler:

How old was he in 1929?

Adelberger:

He was born in 1905. So he was in his 20s. And he hoped to have a career here in interior design, but it was a bad time for that. He got here on Labor Day in 1929. And there were no jobs in his field for a fresh immigrant with no connections.

Zierler:

Did he suffer during World War I?

Adelberger:

Yes. Both my parents did. It was a pretty tough time. The embargo, you know, on food and everything continued to 1919. So there was malnutrition and economic hardship. But any rate, his family was pretty conservative. My father was a rebel. He had a very liberal and idealistic nature. He looked forward to starting a new life here, but it was a very tough time. But somehow, he kept on going back to visit my mother. And--

Zierler:

She was still in Germany?

Adelberger:

She was still in Germany. His English teacher in Germany had told him not to stay in New York, but instead go to Philadelphia or Boston where they spoke better English. On one of his trips to visit my mother my father met a very wealthy woman from Philadelphia who in essence treated him as a son. She arranged for him to collect art for her and allowed him to live at her Sweetwater Farm in Bryn Mawr, Pennsylvania. When FDR became president my father was very enthusiastic about the New Deal and held several different jobs. He was a craftsman as well as a designer and deeply believed that good design could produce better communities. He designed and built much of the furniture in the house I grew up in. At any rate, it was an exciting time for him and he did many New Dealish things, for instance, the interiors of the Green Belt housing project in Maryland. He was in a pretty liberal crowd. He knew people like Eleanor Roosevelt and Pete Seeger and many other people in that liberal environment. He convinced my mother to marry him and come to the US in 1937. She was from Cologne and very well read in literature and philosophy and concerned with ethical issues.

I was conceived in Germany before my parents came to the U.S. and I was born in 1938, in Sweetwater Farm in Bryn Mawr, where my father’s benefactor had allowed him and now his wife and baby to live. And so I grew up not feeling like an ordinary American at all. My family was obviously different. And--

Zierler:

Was German your first language?

Adelberger:

It was, actually. But of course, once the war started, there was no way that they spoke German in public. The only German I heard was my parents talking among themselves.

Zierler:

Right.

Adelberger:

And so I…

Zierler:

Did your parents feel conflicted in terms of their loyalty? Did they fully identify as Americans by the Second World War?

Adelberger:

Oh, they fully identified as Americans. I mean, they were both very liberal politically, and--

Zierler:

So they were horrified at what was going on in Germany?

Adelberger:

They were absolutely horrified at what was going on. Once the war broke out, my father had a whole series of jobs associated with the war effort. Designing cafeterias for factories producing armaments, etc. This job was not what he really wanted to do. He was a creative person. It didn't satisfy him artistically although it was needed. But one interesting thing, it was during the war, he went to Seattle to design some things for Boeing. And he thought Seattle was a wonderful place. But growing up, I never went west of Chicago. We were living in Arlington, Virginia, where my father had bought up a big piece of land, about an acre, and developed a wonderful garden. He was a tremendously gifted gardener. But I rebelled against his Germanic authoritarian ways. Fortunately I was very close to my mother. I felt she understood me and I treasured our discussions of ethical and philosophical issues. Here’s one example of her perceptiveness. In elementary math classes we were assigned “Learning Through Practice” exercises where one had to do, say, 30 long divisions or whatever, and I thought it was stupid to have to do these once you had the idea. My mother saw that that could turn me off of math so she did them for me once she was convinced that I understood the ideas. I grew up in a family where we felt that we weren't typical Americans at all and the neighbors around us were obviously different from us. After the war was over, my father got a job with the United States Displaced Persons Commission. He went back to Germany and helped to resettle the many war refugees and later privately arranged for Americans who wanted to adopt war orphans. We moved over there to join him in 1949, and I went to military school there. That was a new experience, all the other kids divided themselves into Rebs or Yanks. My father responded to the military simply by addressing everyone as Sergeant.

Zierler:

Who was his employer?

Adelberger:

U.S. Displaced Persons Commission. It was a U.S. government agency. And that time in Germany was an eye-opener for me and it also formed a lifelong belief in me that this whole idea of bombing civilians was a horrible thing. I remember going around just covering my eyes because it was so horrible. Both of my grandparents on my mother's side died in the bombing of Cologne, and so I've often felt this was among the many evils that we saw in World War II, this whole reliance on deliberate bombing of civilians. But any rate, we came back to the U.S. and I remember being afraid, because we got Life magazine then, and it was all about the blackboard jungle back in the U.S., and here we were in these military schools where there was no blackboard jungle (laughs), and I was going to come back and be in junior high, and I was worried what it was going to be like. But it wasn't as bad as I was led to believe. I went to a good public school. My parents didn't have a lot of money. We never had a car until after we got back from Germany. Didn't have a TV until much later.

But the schools were good. I went to Washington Lee High School. I thought it was an excellent school. I had some tremendously good teachers. I remember a Miss Garstens who taught geometry. And she said on the first day, "This class is going to be so fast-moving, if you drop your pencil and reach down to pick it up, you might miss something really important," And I love geometry, I just love geometry. She would have students go up and do proofs on the blackboard. And I would love to volunteer for that. And I wouldn't study them beforehand, I wanted the pleasure of working them out right there in real time. I loved that, I thought she was just a spectacular teacher. A very good physics teacher, Mr. North got me interested in physics. When I was little, I first wanted to be an engineer. I read a book about Isambard Kingdom Brunel, an English Victorian engineer, building marvelous bridges and big ships and all that. I wanted to be an engineer. Then I read a book, “The Stars for Sam” that was about astronomy. Then I wanted to be an astronomer because that seemed really interesting that we could learn so much about this enormous universe… I always liked machinery and making things. Mechanical things and stuff. And any rate after Mr. North’s physics class, I said, boy, this is what I want to do. I really liked it—it seemed like a very powerful way to understand the entire universe.

Zierler:

That one stuck with you.

Adelberger:

It did. My parents weren't religious, but after we got back from Germany, they thought that they should join a church for the good of their kids. They were both Lutheran. They didn't go to church before then, but they believed that we should now go to a church. It turns out that a member of the church, Harry Holmgren, was a physicist who worked at the Naval Research Lab. He could answer my questions about quantum phenomena that Mr. North could not. And he encouraged me as it was clear I really liked physics. After my junior year in high school I got a summer job building electronics for a man who installed Musak systems in stores etc. Now I am red-green colorblind and the resistors are color-coded (laughs) so there were some spectacular goof-ups. In my senior year in high school I got a summer job in the Nucleonics Section of the National Bureau of Standards. I had fun in this job which I continued through my undergrad years. They were making things, for example, that monitored the nuclear weapons testing in Nevada. They had a whole bunch of radiation sensors all around Nevada that would report on the fallout remotely, to the Bureau. And then there were instruments that monitored the explosions with super high-speed tape recorders. These instruments would record things until the detectors melted.

Zierler:

What year was this, Eric?

Adelberger:

This would have started in 1956. So I worked at the Bureau for 4 years and met some interesting people. Peter Bender, I don't know if you know him, but he's--

Zierler:

I do know Peter Bender. Yeah.

Adelberger:

Okay, so Peter was a young star there and we built electronics for him. There are some funny stories from my time at that job. When Eisenhower became president, he appointed a secretary of the interior named Sinclair Weeks. And Sinclair Weeks had it in for the Bureau of Standards, because Sinclair Weeks was trying to sell a battery additive to the army called ADX2 or something. I don't remember, okay? And the Bureau of Standards found it didn't do anything for the batteries and it was just basically Epsom salts and water. So Weeks was really unhappy with the Bureau. So the Bureau tried to mollify him, and turned to the Nucleonics division. They built this box, locally known as the Squeaks for Weeks box, which had a Geiger counter on a moveable arm and a radioactive source inside a nice walnut box with a glass panel. You could turn this Geiger counter down and it'd go [makes buzzing noises] like that. The box had a little engraved sign on it that said that when the battery runs down, return this to the Nucleonics Section for service. Okay? Well the guys in the Nucleonics Section had put a little mechanical counter inside the box so they could measure how many times Secretary Weeks moved this thing's arm down and back. Every time the box came in for service, there would be a little lottery pool to see how many times Secretary Weeks had turned the arm. It was always a very, very large number. (laughs). Anyway, it was a fun job. But I’d like to turn back the clock. During my junior year in high school, Mr. North told me to start thinking about colleges. My parents were very well educated but didn't know anything about the educational system in the U.S. And--

Zierler:

So at this point, Eric, you're thinking specifically about physics as a major?

Adelberger:

I was definitely thinking physics, as soon as I took that class, I decided this is what I really wanted to do, okay? And then after meeting Harry Holmgren, I got more and more interested in learning more about physics. About that time there was an article in Time magazine about pure science, and it featured Caltech and physics at Caltech. There was a picture in the magazine taken from Bridge Laboratory across Dabney Hall with the San Gabriel mountains with snow on them in the background. And oh man, that was just fantastic. And when I read about Caltech, it sounded really cool, okay? And so I said to Mr. North, "You know, I'm thinking about Caltech." And he said, "You know, those kids from California, they're going to be really smart and everything, and it’s going to be very hard, blah blah blah blah blah." And so that was sort of sobering, but any rate, I ended up applying to Caltech and Harvard and MIT and Chicago and got scholarships from all of them, but Caltech offered room and board plus full tuition so that made it even more attractive… And all I had to do (aside from keeping up my academic work) was to be a waiter in the student houses. And it was also about as far from Arlington, VA as you could get. Even better, Caltech sent the Dean of Students to Washington, D.C. to interview applicants from the DC area, and he told me about all the pranks that the Caltech students do and that with only 300 undergrad students in a given year they had opportunities to get to meet really outstanding scientists. And oh, this sounded like fun, fun, fun. And then the Harvard interview, I just really disliked it. You sat in a room and all these alumni were surrounding you, and I thought everybody was checking if my fingernails were clean or something. I thought it was all snobbery, while the dean from Caltech was telling us about the fun these people were having. So it was a no-brainer for me and I decided to go to Caltech. My father had a friend, Sarah Pollock, from when he was in Germany with the Displaced Persons Commission and she was with a Jewish relief group. And Sarah who lived in Beverley Hills offered to pick me up at the LA airport and take me to Caltech. When I got there it was smoggy. You know, I didn't have a clue about--

Zierler:

What year did you arrive there? Was it 1956?

Adelberger:

In '56. I was super naïve, it hadn’t registered that Pasadena was a suburb of Los Angeles. I had gotten the catalogue from Caltech that showed California Boulevard and San Pasqual Street bounding the campus, but I'd gotten the impression from Time magazine that this school was off in the mountains, with that picture with snowy mountains in the background. What's a California Boulevard and San Pasqual Street doing here? Well, maybe these are country lanes. And I really didn't know, I was clueless. I was truly clueless. So here it's smoggy and sprawling. Sarah drives me to Caltech and I get to Caltech and can't even see the mountains because of the smog. Woah. What, a downer. But Caltech had a freshman camp at the Capra Ranch out in the desert, and there I met a guy totally unlike me. Leroy Hood, I don't know if you know him. He's now a very well-known biotech star. He was later professor of biology at Caltech, and chair of the department, blah blah blah blah blah. Very famous guy nowadays. Lee was from Montana, and we hit it off. We couldn't have been more different, but we really hit it off, and we roomed together for four years. We've been friends for life. And I saw a whole new side of America, here at Caltech, and with Lee and I just liked pretty much everything about Caltech. It wasn't good for the social life. It was all males at that point. But aside from that, it was a wonderful place, and really pleased this rebel nature I inherited from my father… Caltech was an upstart irreverent place- a small place doing big things. And it was a no bullshit place. All of that resonated. I enjoyed it tremendously.

Zierler:

Eric, Sputnik happened right in the middle of your undergraduate years. I'm curious--

Adelberger:

That's right.

Zierler:

--what effect that might have had on you personally and the department in general?

Adelberger:

In retrospect, it was a very fortunate thing for me, because it put a big national emphasis on science. There was a lot of appreciation for pure science and many opportunities. I never had to think about a job. I grew up in a fortunate time. It's very different now. For students seeking academic jobs, it's a tough road now. It wasn't tough at all then. Was a piece of cake. Being in California, and having Lee as a friend, someone from Montana, got me started on all kinds of outdoorsy adventures. And I was a neophyte in a sense. My parents did lots of walks and things like that but, not mountain climbing and backpacking and all that stuff. That was not something I had been exposed to growing up in the East. And so it was, for me, a wonderful time. Exciting time.

Zierler:

Now Eric, who were some of the professors that you became close with?

Adelberger:

Actually, Dick Feynman, believe it or not. He would eat in the student cafeteria, the Greasy Spoon. And you could talk to him. He had this “class” called Physics X, where you could come in and ask any question you wanted to.

Zierler:

Yes.

Adelberger:

And I thought that was great. I idolized the guy. I just thought he was the ultimate, and a superb person.

Zierler:

Would Physics X go beyond physics? Would you talk about broader issues, or it was always about physics?

Adelberger:

It was always about physics. They had a YMCA at Caltech where students did a lot of talking about philosophy and other issues; they had brought in outside speakers of all kinds. I remember one event the Y had organized with a discussion between Feynman and some prominent theologian. They started out and Feynman asked the theologian, what exactly do you think happens when you pray? And then the theologian went on and on and then Feynman finally said, you know, "Arguing with you is like squeezing a balloon. You squeeze it down here and it pops up over there. and then you squeeze there and it pops over this way." But any rate, he was my hero, I admired him tremendously. I knew Murray Gell-Mann because I would meet him at a bookstore on the corner of California and Lake. It was a right-wing bookstore, and we would go there to sort of laugh at this stuff. But I had many outstanding people to talk to and many fun classmates. We were up to all kinds of trickery and nonsense, fun. It was just tremendous amount of fun for me. I also admired Bob Leighton, a very broad and talented experimentalist, and an excellent teacher. I’ll never forget complaining to him about an exam where it would have helped to have memorized numerical values for some fundamental quantities and explained to him that I liked physics because you could understand the big ideas and didn’t have to memorize all kinds of details and he said, “Look Eric, I’m trying to help you develop a crap detector so you can rapidly figure out if something makes sense or not.” I am forever grateful for that lesson that has helped me ever since.

Zierler:

So besides the mountain, it was exactly as the dean described?

Adelberger:

Yeah. (laughs) It was. And I couldn't have had a better time and I couldn't have been more grateful for the environment I had there. And when time came to go to grad school, I took the standard advice and applied all over, but I decided to stay at Caltech. It was just so much fun.

Zierler:

So Eric, before we get to that decision, I'm curious if you did anything during the summers that was relevant to physics?

Adelberger:

Not particularly. I kept on working at the Bureau, in the Nucleonics Section. My junior year I worked at the Bureau for half the summer, and then went on a big bicycle tour of Europe. I met my wife, Audra, in the summer of my senior year. She was teaching junior high in Maryland and she was living in Washington, D.C. and had a summer job as a lifeguard. I met her totally by accident. It turned out she grew up in Montana in a very outdoorsy, academic family. We hit it off very well and had lots of interests in common. Outdoors, classical music, general intellectual things. I don't remember all that much about the physics in the summertime except that I was working at Bureau of Standards. I was a GS1 employee, not a GS2 (laughs).

Zierler:

As low as it goes.

Adelberger:

As I said, I decided to do my graduate work at Caltech. The coursework was fun and Audra and I had great times in the California mountains. But I had trouble getting started in research. I didn't really know how to start (more of this naivete). Did I have to think of some topic and suggest it to a potential advisor?

Zierler:

Had you made a rough decision by that point about whether you were going to focus on experimentation or theory?

Adelberger:

I didn't think I was smart enough to be a theorist, but I enjoyed the theory and I enjoyed making things so it was pretty clear I was going to be an experimentalist. But I really liked the theory especially particle physics-the ideas of symmetry and symmetry breaking. So I told the particle people, I'd like to do something. Well, they had me polishing scintillators. I somehow acquired the feeling I needed to come up with a of a project I would like to do… I had to come up to an advisor, who was Bob Walker, and say, "Listen, I want to do this." And I wasn't prepared for that. So I was good at taking classes. Oh, by the way, as an undergrad I took a lot of philosophy and literature and history classes, because in fact, I got a very good liberal education, believe it or not, at Caltech. There weren't all that many requirements, so I had a lot of freedom to take non-scientific courses. And I enjoyed it, I thought that was really great. In fact, I thought I had got a better liberal arts education than my daughter who got her undergrad education at Amherst College and took hardly any science and math.

Zierler:

Eric, was the decision to stay on at Caltech influenced by a particular professor that you knew you wanted to work with as a graduate student?

Adelberger:

No. I obviously wasn't going to work with Feynman (laughs) and I didn't know so many of the particle experimentalists. It was really that I had a good time and Audra and I didn’t have any kids and did a whole lot of outdoorsy things that we became quite fond of. Especially the Sierra Nevada mountains… But it was a real problem for me, after two years of grad school, the courses went fine, but then I had real trouble figuring out what I wanted to do, and so I started out working in particle physics. Caltech had an electron synchrotron at the time and it was interesting but I was looking for something where I felt I could express my own self more. And the synchrotron experiments were necessarily team things. The teams were tiny by modern standards. But I wasn't happy because I couldn’t see how I could express my own style in that environment. And this was a big crisis for me psychologically, because I grew up being taught that if you start something, you finish it, period… But I obviously wasn't being fulfilled in some ways, in the job in the synchrotron lab. And so I had this--

Zierler:

Why not? What was it that you were not fulfilled about?

Adelberger:

Well, I wanted to have a feeling I was designing something or doing something rather than just being an apprentice, or just having a little piece of something. I wanted to have a feeling that this was mine. I don't really know how to say it, but I felt a little bit like a cog in a wheel or something. I can't say, but it was a real feeling. And so I went through this crisis, and then I decided I would not continue in high energy physics, and I went over to the Kellogg Laboratory, which was where Willy Fowler was and had a reputation among the students as a very friendly place. They were doing nuclear astrophysics and other important experiments in nuclear physics. I talked to Charlie Barnes, who led an experiment that conclusively showed that the weak interaction was a Vector-Axial-vector interaction… And Charlie was a wonderful advisor. I came and talked to him and immediately, he said, "Well look, here are some things you could do." And I picked one of them because it sounded like particle physics in a way. It had to do with breaking of isospin symmetry-a symmetry of the strong interaction that was broken by electromagnetic and weak interactions…

Zierler:

Now, was Charlie's work on weak interactions, was that ongoing by the time you connected with him?

Adelberger:

That had finished.

Zierler:

That had finished.

Adelberger:

V minus A was… But Charlie was involved in things with nuclear astrophysics or isospin symmetry and things like that. And--

Zierler:

So he gave you a problem to work on that you felt like you could make this your own?

Adelberger:

Well, he suggested several things. The one that appealed to me most involved a pulsed-beam neutron time-of-flight system that a previous grad student had built and could be used for (3He,n) reactions which transferred two protons (carrying 1 unit of isospin) to make, at that time, exotic nuclear states that had one extra unit of isospin that could not decay via the strong interaction so that one could study isospin-breaking in nuclei. Charlie told me about this and said that I could have the whole system for myself to improve and exploit, Another no brainer. So I familiarized myself with the system, which involved high-power RF for the beam buncher and chopper, and nanosecond timing in the neutron detector, and began to make improvements in its performance. Charlie just let me be and I loved it. Often when I had beam time on the accelerator Charlie would come in, smoke his pipe, and tell me stories about the early days of nuclear physics. Sir Denys Wilkinson doing these experiments and on and on. Why the British call the pulse height analyzer a kicksorter; it's because the first pulse height analyzers were actually like pin ball machines. You had a bunch of steel balls, and the amplified pulse from the detector (a kick in Brit-Speak) would drive a solenoid that kicked the balls, The pin ball machine was tilted so that the balls would take parabolic paths whose heights would depend on the size of the kick, and fall into little channels arrayed along the bottom of the pin-ball machine. The number of balls in each channel would be counted by hand to determine the pulse height distribution, and that's why they're called channels today. They were actual physical channels in this pinball-like machine, and you'd see where the little spheres ended up in these channels. Well, this was fun, you know. And I was alone, and did some actually very clever things. I completely rebuilt this system and made all kinds of clever innovations turning it into a system for making very precise measurements of the energies of higher isospin nuclear states. and I really liked it. And then a younger grad student came along. His name was Art McDonald, who later won the Nobel prize for leading the Sudbury Neutrino Detector collaboration that conclusively showed that solar neutrinos changed the flavor as they traveled to the earth. Anyway we worked together. I was the older one, he was the younger one, we had a wonderful time working together making precise studies of the mass splitting of members of isospin multiplets and studying the details of the isospin-breaking decays of these narrow states. And so it ended up very, very good. I was fortunate to have more interactions with Feynman as he was on my qualifying exam and final exam committees.

Zierler:

Now, was he interested because of the helium aspect?

Adelberger:

Say it again?

Zierler:

Was he on your committee because he was interested in the helium aspect of the research?

Adelberger:

I don't know how the committees got picked. But anyway, Feynman was on my committees. They had oral exams, you know, candidacy exam, whatever it's called, you've got to pass. I decided to come into the oral exam, carrying this big cross I had made out of 4x4 timbers… And so I staggered into the room where the exam was carrying this cross. And so Feynman said, "Are you religious?" And I said, "No, it's a symbol." The exam started out very badly; I had blown the legendary Prof. Smythe’s opening question, asking me to calculate the force on a horseshoe magnet attracted to a sheet of iron. It turns out that I had always been confused about H and M inside magnetic materials, so the night before my exam I had gone over it again and thought I had it straight. But I hadn’t gotten it correct the night before so proceeded confidently and incorrectly. Feynman told me to look carefully at the boundary conditions at the magnet pole faces and I said, full of false confidence, don’t worry it will all work out. And then I suddenly realized my mistake. From them on nothing but magnet questions. So I was very glad when Feynman changed the subject and said, "I see you took a bunch of philosophy courses." and he started asking me questions about the intersection of philosophy and science. Then we got onto other areas of physics which I did understand correctly.

For my thesis defense I made a demonstration of my time-of-flight spectrometer. It had 2 aluminum U-channels-a slanted one that abutted a horizontal one. At the top of the slanted channel was a brass disk (a 3He ion) resting against a gate connected to a string that led to a hinged hourglass. A smaller aluminum disk (the neutron) rested at where the bottom of the slanted channel met the horizontal one. At the other end of the horizontal channel was a hinged flapper attached to a second strong that also connected to the hinged hourglass. The hourglass was originally horizontal with all the sand in the left hand side. I put all this under a white sheet in the examination room. When the committee came into the exam room, I told them that I had prepared a little demonstration to help the poor theorists understand the experimental tool I had developed. I whipped off the cover and pulled the string that released the gate (the chopper) and flipped the hourglass into a vertical position so that the sand began pouring out. The helium ion ran down the slanting channel and hit the neutron that then ran along the horizontal channel until it hit the detector flapper that pulled a string that flipped the hourglass back to its original position. This time there were no questions that I couldn’t answer. And any rate, I had a very fun, challenging and productive time at Caltech. After graduating, I stayed on for a little while as a postdoc and left in 1967-

Zierler:

'67. 1967.

Adelberger:

'67. Yeah. And I remember as soon as I passed my exam, Audra and I went backpacking in the Grand Canyon. While we were in the canyon the faculty office at Caltech called up to ask me some question about the postdoc or something. When they found out I wasn't at Caltech they postponed the postdoc for a month.

Zierler:

Oh no.

Adelberger:

Because I wasn't there. And I thought, that was a great tradeoff. (laughs) Any rate, my wife Audra and I did a l lot of backpacking in the Sierra Nevadas. Just basically climbed all over and had a wonderful time. The year before I left Caltech I met David Bodansky from the University of Washington who was on a sabbatical at the Kellogg Lab. After I graduated, the University of Washington called me up and offered me an instructorship. But somehow I didn't want to take that because I didn't know what it meant, so I took a postdoc at Stanford where they wanted me to build a time-of-flight system on their tandem Van de Graff accelerator. Stanford was a real change. Caltech was fun in a sort of irreverent and rebellious way. And Stanford at that point was very proper. I remember being taken on my first day there past the Tresidder student union and there was some Black Power speaker there.

Zierler:

Right. I mean, you got to Stanford in 1968. That's a pretty interesting time to arrive at Stanford.

Adelberger:

It was. At any rate, this Black Power speaker was saying, "And we're going to kill all you white [expletive deleted]." And all the overwhelmingly white crowd went, clap, clap, clap. And boy that disconnect was sort of weird, it seemed like a country club in a way, and something phony about it. At any rate, the atmosphere was not at all like the fun, irreverent one I experienced at Caltech. And so I wasn't thrilled, okay?

Zierler:

Were you working in a lab at Stanford?

Adelberger:

Yeah, they had a tandem accelerator in the basement of Varian Hall. And also there was a building right next door where there was a guard outside. Because they were doing classified research in it. At Caltech, that would never happen, okay? There were no buildings with guards outside because no classified research was done on campus—JPL was deliberately put off-campus. I didn't like seeing a guard outside a building you weren't supposed to go in. So it was an impedance mismatch. I wasn't really… I didn't have the same feeling that I did at Caltech, you know, what a wonderful institution, blah blah blah… So anyway, I didn't really like it.

Zierler:

Did you do any teaching at Stanford, or it was strictly research?

Adelberger:

No, just research, that’s what postdocs typically do. While I was a grad student at Caltech I met a very smart guy, Gerry Garvey, who was a nuclear physicist at Princeton University. He, together with a radiochemist at the Berkeley 88 inch Cyclotron had used a large and sophisticated apparatus to measure the energy of a higher isospin state that I had also measured with the little system I had built using (3He,n) reactions. Vastly more precisely than these people at Berkeley with this fancy thing had done. But the two results did not agree. So Gerry visited me at Caltech when I was still a graduate student to see who was correct. Gerry was a pretty young guy who also really had fun with physics, and he was instantly convinced that I was right and they were wrong. Then one day while I was at Stanford I got a call from Gerry Garvey and he said, "Look, why don't you come be assistant professor at Princeton?" And I thought great, it will be fun to be with Gerry.

So Audra, who was pregnant with our first child at this point, and I decided to see if we could be happy on the East Coast. We had our final backpack trip into the Sierra - where we climbed Mount Banner, got in our car and drove to the East Coast. I liked the Princeton physics department and the University. The department was pretty small with some outstanding people in it. I got to know Sam Trieman, Eugene Wigner, Bob Dicke and very much, David Wilkinson. I really liked David tremendously, I learned a lot from these people and I liked that. Audra had a job at Livingston College that she liked as well. But Audra and I didn't like living in Princeton. It became clear to me, even though I liked the department, that I probably wouldn't be happy there. In my first year in Princeton I climbed Mt Waddington (the highest peak in the British Columbia Coast range with Lyman Spitzer and Don Morton (both Princeton astronomers) and made a winter ascent of Black Kaweah in the Sierra with California buddies and the next summer climbed Huascaran, the highest mountain in Peruvian Andes, with Don Morton and a Harvard atmospheric scientist Richard Goody. But I realized there were more stores in Missoula, Montana, where Audra was from, where I'd want to buy something than there were in Princeton, New Jersey. I still remember clearly the day when I got a call from Seattle, and they said, "We want to offer you an assistant professorship." I, at this point, I'd been through Seattle on my way from Pasadena to British Columbia and Alaska for a climbing trip. And I remember what my father told me about Seattle, that it was a pretty place. So I said, "Hey, this sounds pretty good." And I went for an interview, and that point, Jim Bardeen, I don't know if you know him, but he's the son of John Bardeen and was a student of Feynman and a well-known expert on general relativity and black holes. I'd known Jim from Caltech grad school. He was on the UW astronomy faculty and liked living there. Yeah, this is a nice place. And the department had some very good people in it in atomic physics and nuclear physics and so on.

Zierler:

Eric, I'm curious, what was your research during your years at Princeton which presumably is what caught Washington's attention?

Adelberger:

Not particularly. I kept probing isospin-symmetry breaking, partly at Princeton University cyclotron, partly at the University of Pennsylvania tandem accelerator. It was more the whole thrust of my work up to that point, that line of symmetries and nuclei. There was a UW theorist, Ernest Henley, who was well-known for his work on symmetries in nuclei, whom I had gotten to know from my experimental work. I liked him a lot as a physicist and as a human being. Having Ernie as a colleague made a big difference in my research trajectory because, in addition to studying isospin-breaking in nuclear forces, Ernie was also interested in weak interactions in nuclei and parity violation in nuclei. And that got me thinking about, could I do some experiment here? These parity-violation experiments are really hard because weak interaction effects are tiny in nuclei. But Ernie had pointed out that there were simple and elegant cases of close-lying parity doublets in light nuclei when the small energy denominators and simple nuclear structure was expected to produce enhance effects. And I came up with a very clever, if I say so myself, way to do an experiment to measure the parity violation in the ½+-- ½-parity doublet in 19F. It used a horizontally polarized proton beam (we had such a beam in Seattle) to produce a polarized 110 keV 1/2- state using the 22Ne(p, alpha) reaction. A measurement of left-right asymmetry of 110 keV deexcitation gamma ray combined with the known magnetic moment of the ½+ ground state and the known lifetime of the ½ - state directly yielded the weak matrix element connecting the 2 states. A UW theorist, Johnny Blair, helped me to understand the dynamics of the polarization transfer in the reaction. And even better, I realized that the 22Ne(p,n) reaction produced a 0+ level in 22Na that decayed by emitting a 74 keV gamma that was necessarily isotropic, providing a rigorous null asymmetry allowing us to correct for polarization-dependence of the proton beam position.

It was very elegant and classy. I could determine the 19F polarization by using Compton scattering to measure the circular polarization of the 110 keV radiation. It was like God had created this situation just for this purpose. But here I was, a young assistant professor, and this was a risky thing. And--

Zierler:

Risky in terms of tenure?

Adelberger:

Yeah. Would the experiment work? Could I get my colleagues to spend the money to build the stuff needed? Could I get enough counting rate to make a meaningful measurement? Fortunately, when I got to Seattle, I was given two excellent grad students to work with. I convinced my colleagues to let me do this, but it was a risky thing. But I thought it was just so beautiful. I didn't care about the risk somehow. So together with one of these students, Erik Swanson, and some postdocs, we did the experiment and it worked and made a splash, and that got me started in a whole new branch of nuclear physics.

Zierler:

What were the findings of the experiment and what were the implications of what you found?

Adelberger:

This was a case where the nuclear theory was very good; especially after the UW hired an excellent young theorist, Wick Haxton, who showed that one could calibrate the nuclear-physics dependence of the 19F parity-violating matrix element by measuring the decay rate of the first-forbidden beta decay of 19Ne, which we also were able to measure. This was an elegantly simple system, and you could calculate what you ought to see with small uncertainties in the weak interaction in physics as played out in real nuclei. This determined a combination of two coupling constants in the parity-violating weak nucleon-nucleon interaction… And then Ernie told me about another interesting case, which was in 18F, where there was a 0+, 0- doublet, where again the physics was very, very simple. In this case the observable was the circular polarization of the 1.08 MeV deexcitation gamma ray from the 0- state. Again, the observable was greatly enhanced by nuclear physics and there was an analogous first-forbidden beta decay to calibrate the nuclear physics. And so I, along with Erik Swanson, started working on that. We figured out the best reaction to use to make the 18F and designed and built a novel flowing water target to handle the intense He3 beams we would need to get the needed count rate. We designed and built circular polarimeters and electronics that could handle the high counting rates. We did the experiment at an accelerator at Cal State, Los Angeles which had a much more intense 3He beam than was available in Seattle or Caltech. This was a collaboration between us and Charlie Barnes and his student and people at Cal State LA including a former student of Charlie’s. But it was really a UW experiment. I mean, we figured out how to do it and build the kind of apparatus and everything. And so those two experiments together really allowed you to separately determine these two coupling constants. And they're still classic systems in the field. Other people, including Art McDonald, have done the experiments better since. But those two cases are the real benchmarks. I got the Bonner Prize of the American Physical Society for them. I started getting invited to be on program committees for nuclear physics, and reviews for departments and all of that stuff. And I got promoted rapidly.

Zierler:

Eric, why do you think this research got the attention and the traction that it did?

Adelberger:

Because these were very attractive, simple systems, and the experimental apparatus was elegant and so pretty. Aesthetics is important to me, okay? I inherited this from my father. And these were just lovely, beautiful things. I have to say so.

Zierler:

Did the research have theoretical implications?

Adelberger:

Yes, it remains an interesting area. People are still doing experiments trying to determine these issues. What it comes down to is, what you determine experimentally is something where the most respectable way to interpret the weak interaction aspects nowadays is by lattice QCD calculations. Because the complications of going from quarks to nuclei and all of that. But it's still going on. It's still a real thing. In 1986 I became interested in a new field: experimental gravity. The Seattle theorists had invited Ephraim Fischbach, a theorist from Purdue University for an extended visit. Ephraim had written a paper claiming that he had found evidence for a fifth force-an entirely new force in nature- that coupled to hypercharge (baryon number–strangeness) with a range of around a kilometer. I was intrigued by this. Ephraim made me realize that one needed to think about Equivalence Principle experiments in a new way, not the classical way where one asks if gravitational and inertial masses are identical, which at that point was best tested by Dicke and by Branginsky who compared the acceleration of different materials toward the sun, Instead, one should think of them as extremely sensitive ways to probe for possible new Yukawa phenomena that could be much weaker than gravity and therefore hidden from non-gravitational experiments by the irreducible gravitational background.

Fischbach’s force was based on reanalyzing old data from a famous test of the Principle of Equivalence by von Eötvös who compared the accelerations of different materials falling toward the earth. Fischbach combined this with his reinterpretation of CP-violation in kaon experiments and geophysical data studying the dependence of little g as a function of depth in a mine, to infer the existence of a new fundamental force. But drawing profound conclusions about a whole new interaction from a reanalysis of an old experiment is hardly convincing. So I started thinking about it more, and I saw inconsistencies and other problems in Ephraim’s analysis. But Fischbach said, oh, no no no no no no. But there really were problems and I was utterly unconvinced. But any rate, I said, we’re not archeologists, we’re physicists. We should really test this by doing a new, convincing experiment designed explicitly to test Fischbach’s claim. At this point, I was friends with a graduate student, Christopher Stubbs, a brilliant guy who took great pleasure in life and in science and wanted to do things out of the ordinary. He was intrigued by the idea of a new fifth force experiment. Christopher went on to direct the MACHO project that searched for dark matter using gravitational microlensing and is now an astrophysicist at Harvard. And I had a great colleague, Blayne Heckel, an atomic physicist who had done neutron parity-violation experiments that were related to the nuclear physics experiments I had done. And Blayne, Christopher and I decided to do a new experiment. That was the most fortunate thing that ever happened to me. In about a month of discussions about a field we knew nothing about, experimental gravitation, we came up with some really good ideas of how to do these experiments. Just super good ideas.

Zierler:

What was so productive about this collaboration, would you say?

Adelberger:

What was so productive about it is that first of all, we knew nothing about gravitational experimentation to start with, okay? We didn't know the lore so we and so thought about it from ground zero. And we were friends and full of enthusiasm. For me a chance to design something elegant totally from scratch. I liked elegant apparatus. I liked symmetry in apparatus. I loved geometry. We designed a torsion balance instrument that looked like nothing before. I knew about Bob Dicke's Princeton test of the Equivalence Principle where he compared the gravitational accelerations of gold and aluminum toward the sun. Mainly I absorbed the idea that Equivalence Principle tests are really difficult and subject to all kinds of subtle systematic effects…

So it wasn't truly ground zero, but we completely rethought it. We decided that the optimum materials to compare were beryllium and copper, and came up with the idea that the apparatus should be so symmetric that one couldn’t tell which test material was which. Dicke’s test bodies were 2 larger aluminum cylinders and a slimmer gold cylinder that was surrounded by 2 electrodes that applied a force to keep the pendulum from twisting in a classic Dicke feedback scheme. We decided to use 4 cylindrical test bodies, two of each material and that the test bodies should have identical outside dimensions and vanishing mass quadrupole moments. The beryllium test bodies were solid while the denser copper test bodies were hollow so that all bodies had the same mass. We monitored the pendulum twist with an optical system that didn’t favor any one test body over another. Because Fischbach’s force was supposed to have a range of order a kilometer we couldn’t rely on the earth’s rotation to rotate our apparatus as Dicke could, so we had to develop high-quality turntables that rotated the apparatus at a much faster period of our choosing.

I won’t go into more details, but we had a bunch of good ideas. In one month, we sat down and came up with the basic ideas how to do these. We're still profiting from them. We didn’t have any official support to undertake this, but fortunately I was a member of the UW Nuclear Physics Lab that had group funding, and had excellent infrastructure and technicians (especially machinists). Between borrowing stuff from other people and scrounging a computer from the senior lab we were able to make rapid progress. Eleven months later we had completed a definitive experiment and sent a manuscript to Physical Review Letters showing that the proposed 5th force did not exist. It just was absolutely exciting. And we cockily told ourselves that gravitational experiments were not so hard after all. (time was to prove this was a bit premature). And there was an important lesson there. Namely, that although Fischbach’s evidence was flawed the larger point that he raised, that there could be such a thing that would have profound consequences, was not wrong. And that wrong evidence actually started a new field. It turned out that many interesting theoretical speculations can be addressed by these super-sensitive "gravitational" experiments. Because you can look at things weaker than gravity. And so it was very fortunate that we tried to test it. Developed good technology for doing it. It has been exciting that repeatedly over the years, people have come up with suggestions for ideas that we could test. Unfortunately, so far, we've shown that all of them are wrong. (Both laugh) That, you know--

Zierler:

But that has value also, right, Eric?

Adelberger:

Say it again?

Zierler:

That has value also. Your--

Adelberger:

It definitely does. It has attracted a lot of attention because it addressed an important fundamental issue and it was persuasive. We did it right. We clearly didn't mess around. It's a beautiful thing. I mean these instruments are lovely things. And so it was a lot of fun. I also did an experiment where I tried to measure a parity violation in the hydrogen atom. It was an idea, again, go to a simple system, the hydrogen atom where there is a closely-spaced parity doublet, the 2s and 1p states, mixed by the neutral weak interaction. And it was a clever instrument, but in the end it didn't work for technical reasons. But it was a lovely idea. I got to know other famous people such as Val Telegdi because this was a lovely idea. It happened to have a practical problem with actually making it work, but it was fun. Went to lots of workshops and meetings, because this was clearly a clever idea.

Zierler:

What do you think there was-- What was it about this research that continues to elude success?

Adelberger:

So far, Mother Nature has hidden her secrets pretty successfully. In other words what's happening in physics right now, in my opinion, is we had all these wonderful, powerful and extraordinarily successful global concepts and yet there are major puzzles that we don't understand, such as dark energy and dark matter. We're clearly missing something big. And so people have gone back and thought that maybe some of these beautiful, powerful basic ideas of physics aren't really the ultimate reality. They're approximations. Is general relativity an approximation? Is Lorentz invariance an approximation?

Zierler:

But when you say, "Is general relativity an approximation?" An approximation for what? What does that mean?

Adelberger:

It means, does Einstein’s GR, a classical picture of gravity, break down. Most of us believe that gravity will eventually be described by a quantum theory that incorporates the uncertainty principle that will permit us to calculate what really happens at the center of a black hole… For instance, one possibility is that you can explain the huge conundrum regarding the cosmological constant, lambda, that drives the accelerating expansion of the universe. Einstein put lambda into his equations for a bad reason, to keep the universe stable and keep it from collapsing. After Hubble showed that the universe was expanding people just said, thank goodness that weird lambda is just zero. However the uncertainty principle of quantum mechanics makes a clear prediction -- the vacuum is not empty but filled with “zero-point” energy of all of the modes of fields of the electromagnetic weak and strong interactions. When you add up all this energy it comes up to a stunningly huge value. This doesn’t have any practical consequences in electromagnetic, weak or strong processes because it is always there-you cannot alter it and one only experiences changes in the total energy.

But gravity is different, Einstein told us that gravity is sourced by the total mass-energy so it should respond to this enormous energy by blowing up the universe. This is and was a huge contradiction, why should something so huge be zero? This was the classic “cosmological constant problem”. The modern “cosmological constant problem” came with the discovery that the expansion of the universe seems to be speeding up so that an incredibly tiny, but definitely non-zero, value of lambda fits the data right now, but people wonder if it is truly constant or is a dynamical field that varies as the universe evolves. But if it is a constant and we don't understand it, then there are no more experiments to do, so to speak. The problem will be up here in our heads. People speculate that Lorentz invariance could be an approximation, that it breaks down? Is it an emergent symmetry? These huge problems that we cannot understand from our accepted ideas have sparked many creative speculations for ways to get around the problem. Some of these ideas could have implications for things that you can test with super sensitive mechanical experiments. Not all of them of course. It could be, for instance, that string theory ideas are untestable. If everything happens at the Planck scale it's not really testable in any direct sense. But maybe things don't all happen at the Planck scale. Maybe there are things that happen at more accessible regimes. Obviously, it would be revolutionary to find evidence for such breakdowns. But it may be forbidden so to speak. Mother Nature has just hidden it, that she won’t reveal any breakdowns in a regime you can get to. But the thing is that these tests are interesting to smart, thoughtful people because right now we don’t have a clear path forward. And that's a rewarding thing.

Zierler:

What have been some of the most important and even vexing questions in physics that motivated you to design the experiments that you did?

Adelberger:

Well, I'll just give you one example. Again, it was stimulated by a theorist. Nima Arkani-Hamed, who's now at the Institute of Advanced Study, but at the time a grad student at Berkeley and later a professor at Harvard. He had the idea that some of the extra space dimensions in string theory could actually be much larger than anybody had suspected. That they weren't curled up at the Planck scale, but they could be curled up at a much larger scale, and that this could explain why gravity is incredibly weak compared to the other 3 forces. Nima and his co-workers imagined that that these extra dimensions would manifest themselves only with gravity. You couldn't see it any other way, but only by studying gravity itself because the graviton is a unique particle that couples to absolutely everything. The graviton’s string is not tightly stuck to a string theory brane (string theory contains higher dimensional structures, called branes, as well as 1-dimensional strings) as are the strings for all non-gravitational phenomena. As a result gravity can expand into the extra dimensions which could explain why gravity is so weak compared to the rest of physics which is confined to the brane. Nima gave a UW colloquium in June 1989, and pointed out that a bomb-proof test of his idea would be to test the gravitational inverse-square law down to the shortest attainable distances and see if gravity began to get stronger than expected. If so, you would finally be seeing the true strength of gravity… This was terribly exciting. Up to that point, we'd been doing Equivalence Principle tests that became the most sensitive and general probes of this important principle. We knew that the inverse-square law of gravity had only been tested down to the millimeter scale but we hadn’t had a good reason to test it at shorter distances. But Nima provided a wonderful motivation for us to begin such tests… Again, we started from ground zero and built an apparatus that looked nothing like the other ones that had been used before. It was much more symmetrical, much more sensitive, blah blah. In fact it was beautiful and very successful. Now, 3 generations of apparatus later, we can say that any extra space dimension must be curled up with a radius less than 30 micrometers (about 1/3 the diameter of a human hair). A number of other ideas for solving current problems in physics could also have violated the inverse square law, so that we also could constrain those with our super-sensitive and convincing tests. I have a poster someplace that shows the graveyard of all the theoretical speculations that have been strongly constrained or decisively ruled out by our work.

Zierler:

So what have been some of the most significant theoretical speculations that have been wiped out as a result?

Adelberger:

Well, any large extra dimensions now have to be smaller than 30 microns or so. That's like a fraction of the width of a hair on your head. The string theory partner of the graviton, called the dilation, or a possible massive graviton must have masses greater than 5 meV. But of course, one can always say that’s not so interesting because the dilation could have the Planck mass, but that is a theoretical prejudice-the dilation starts out massless like the graviton and quantum corrections that give it a mass. But I’m an experimentalist and am confident that if we did find convincing evidence for a low-mass dilation, lots of theorists would suddenly be able to explain it. But there is a very interesting and serious conjecture that string theory and black-hole stability require gravity to be the weakest force of all. Well, experiments we do can look well below gravity. So it's one of the few ways than one could find a potential violation of string theory. One of the very few ways. It may not happen. But I'm saying there is a very serious statement that current understanding of fundamental physics requires that gravity be the weakest force of all. And we have a way of looking for things that are much weaker than gravity.

Zierler:

Is there--

Adelberger:

What interested me was just--

Zierler:

I'm just curious. Sorry to interrupt. But is there a particular physicist that you most-closely associate with that assertion about gravitation?

Adelberger:

Yes, Nima Arkani-Hamed, was the one that first told me about that.

Zierler:

So surely someone like him, he's aware of your work. What do you understand is his response to your research?

Adelberger:

Oh, he likes it. (laughs) and appreciates the work of our group. I think we have a great relationship. By the way, we named our little experimental gravity collaboration the Eöt-Wash group. It's a pun because Baron von Eötvös was the brilliant Hungarian scientist who did the first torsion-balance test of the Equivalence Principle and we’re from Washington.

Zierler:

I was going to ask you about that, so that's good then.

Adelberger:

But so I don't want to make it sound like it's only me-the other PI’s and our students and postdocs have done much of the work. But I think founding this group was a real accomplishment. We’re a very small group that has had an outsize impact.

Zierler:

Right. So I don't want you to, of course, to speak for your colleagues. I can ask, you know, members of that team so to speak, but why then, as far as you understand, why then does string theory persist?

Adelberger:

You know, there's an interesting question. Now we're getting to the side of me that also likes philosophy.

Zierler:

Please.

Adelberger:

I'm concerned that physics is, in a certain sense, in a dangerous period. If we get too enamored of things that are almost in principle untestable, that's a bothersome thing to me. One thing you learn from philosophy is that there's a huge difference between philosophy and science. Philosophers are still arguing the same questions they'd argued a long time ago. Science can get past that. But if we're going to talk about theories which we don't have any way to test, that's a potentially dangerous thing, nothing to keep us on the right track in physics.

Zierler:

It's dangerous because it sounds like science but it's not really science? Is that the problem?

Adelberger:

It is a new kind of science, I'll have to say. Consider the anthropic principle, for instance. I'm an old curmudgeon, and I think that's just an excuse for not trying hard enough to understand why the universe is the way it is. Take the cosmological constant problem. I’m not a bit satisfied by the notion that there exist universes with all possible values of the cosmological constant and we just happen to live in one with a very tiny positive value. I hope we can find a deeper reason. So I have some problems with the way things are evolving… I think it's unhealthy, when so much emphasis is spent on things that aren't testable. It is turning natural philosophy (the name for physics in Newton’s time) into actual philosophy.

Zierler:

But when you say, Eric- say, "not testable," is that settled in your mind? Do you leave open some possible future advance where string theory can be testable and it might, you know, some amazing things might happen as a result? Or as far as you're concerned, you're beyond what can be conceived of as a testable theory?

Adelberger:

Well, if everything happens at the Planck scale, then I cannot see any way to test it experimentally. The evidence in favor of it would have to be that it resolved a very important theoretical conundrum the way Planck’s quantum solved the black body problem. But that led to an outpouring of new theoretical and experimental findings that stimulated one of the greatest intellectual flowerings of all time. But in the string theory scenario we just discussed I cannot conceive of what this outpouring would be. Nevertheless, a consistent theory of quantum gravity would be a great intellectual achievement, even it didn’t make any testable predictions. It would be a monumental accomplishment, but also a monument-it wouldn’t have as much impact on the future as if it made testable predictions. It would be very good for the health of physics if we could somehow translate ideas into things you can actually test.

Zierler:

Not because-- It bothers you, just so I understand, it doesn't bother you because you've closed off the possibility that it could be true, it's that there's no way of testing whether it could be true and therefore, our energy should be spent elsewhere. Is that a fair summation of what you're saying?

Adelberger:

Well, David, that's probably a fair summation. I--

Zierler:

Or no, you can be more blunt. Do you just think that multiverses are absurd and that doesn't, you know, it just doesn't exist?

Adelberger:

It’s not absurd, I just don’t find it satisfying. Let me broaden the question. There are very smart people who talk about the collapse of the wave function in quantum mechanics. And they explain it all, again, with a multiverse picture. All possible outcomes of a measurement occur, either in our universe or, if not, in alternate universes. To me, that seems like the most egregious violation of Occam’s Razor. The principle that you don't want to drag in millions of things that you can't test to explain one thing that you do not understand… I know there are many very smart people that don't agree with me. That this picture should be a central issue in theoretical physics, But that’s not the point here. We're not really in science at this level, okay? That's why respectable people can have so drastically different views. But I agree with Feynman, whose attitude was encapsulated in his remark that “You can’t teach quantum mechanics to a dog”—meaning that maybe humans are not smart enough to truly “understand deeply ” quantum mechanics, but are smart enough to use it.

Zierler:

I'm curious, Eric--

Adelberger:

And it hasn't been translated into science, mind you.

Zierler:

I've had remarkably similar conversations with other students of Feynman, and what you're expressing right now, I've heard in similar ways. And some people have directly credited Feynman and what they learned from him intellectually as sort of one of the sources of having that sort of visceral reaction that you have about these things. And I wonder if you feel the same way in terms of how you learned how to be a scientist from Feynman.

Adelberger:

Yes. I told you about the debate at the Caltech Y, with the theologian. Another memorable thing that influenced me was the… A lot of "woo-woo" physics/philosophy that was supposedly based on what we have learned from quantum mechanics. Feynman always poo-pooed that. He said, "These people don't even understand what they're talking about." So yes, absolutely. By the way, I want to tell you a story. Feynman had some interest in the things I was doing until his death, I went back to Caltech shortly before Feynman died and we went to lunch at the Athenaeum, which is the faculty club. Feynman he was still teaching a class. So I went and listened in on the class, and after it was over, Feynman had to sit down for about 15 minutes before we walked over to the Athenaeum for lunch, he was that weak. But the thing was, he was weak physically, but mentally he was exactly the same person-the same boyish enthusiasm. And many people describe it that way "boyish" is not a negative, it's tremendously positive. He was still interested in all these kinds of things. I was extremely impressed by that. That he still had this thing I admire so much. I don't like it when people get old and they suddenly become religious or something. That bothers me. But Feynman stayed Feynman. He did not cave in. It was a remarkable thing to me. He was a great person.

Zierler:

I'm curious, Eric. I mean, given your strong views, have you engaged in debates on this, or have you decided mostly to let your research do the talking?

Adelberger:

I haven't engaged in debates, but I have given public lectures. I was a Phi Beta Kappa Visiting Scholar in 2008-2009 where I spent time in 9 different institutions ranging from small liberal arts colleges to UC Berkeley meeting with students and giving public lectures. I do talk to non-scientific friends that are intrigued by things they read about physics in science. And I make my strong (and often disappointing to them) views perfectly clear. Somehow people like to tie their new age philosophy or whatever to physics. It gives it respectability, and I give no quarter there. (laughs)

Zierler:

Eric, you have a long record of service in the profession. And there's a lot of influence that you can wield depending on the committees that you're on, or the editorial boards you serve on. I wonder if you saw those opportunities as a place, perhaps in a quiet way, to further the views that you believe in?

Adelberger:

Yeah, let me give you an example. I've been on many review panels. But two of them were especially interesting to me as I was in a definite minority. One of them was the NRC Beyond Einstein Program Assessment Committee for NASA. And the other was NRC Committee for Gravity Probe B also for NASA. My opinion of Gravity Probe B is that the main scientific issue it actually was addressing was, “does the Earth define a preferred frame?” That's all that it was asking.

Zierler:

What does that mean? What does that question mean, a preferred frame?

Adelberger:

Okay. I'm glad you're asking. What it means is, suppose you said Coulomb's law is correct, but there is no magnetism. The only way you could hold that opinion is to say that the laws of physics apply in only the special frame where the charges are at rest. If a charge isn't at rest your theory breaks down. You need magnetism to deal with a moving charge. In order for 2 different observers in relative motion to both explain a given setup of charges you need to have magnetism-it is a basic requirement of special relativity. There's a lovely textbook by Ed Purcell on electromagnetism where he introduces magnetism exactly as a consequence of relativity. If you have Coulomb's law, you've got to have magnetism. So that different observers will agree on the facts. And now, there's a similar thing in gravity. If you have a relativistic theory of gravity there’s going to have to be an analogue of magnetism, called gravitomagnetism simply so that different observers in relative motion will agree on the facts. And so if you say I'm going to test gravitomagnetism, what you're really testing is, is it true that different observers have to agree on the facts? Is this an important issue on which NASA should be spending billions of dollars? There were a lot of famous people on the panel and invited to testify before the panel who did not agree with this view. I won't embarrass them by telling you their names, but they swore up and down that this was a great experiment. Very important. Now, in my opinion, it's really testing if different observers have to agree on the facts. And thank god at least one person out there at that committee, Francis Low from MIT understood this point. But a lot of others either didn't or chose not to. And that was for me a big disappointment.

Zierler:

Why? What was so disappointing?

Adelberger:

That we couldn't state the simple facts. Nobody would have believed the results if they disagreed with GR. But panel members said things like “they shut down the SSC and we don’t want to give them ammunition for shutting down another project”. I was in a small minority on the panel and wanted to write a minority report but that was not accepted.

Zierler:

"We couldn't" or "we chose not to"?

Adelberger:

We chose not to. And that bothered me quite a bit. It really soured me in a sense on these larger issues. The other panel where I had a problem was the Beyond Einstein Program Assessment Panel that was asked to prioritize which mission in its palette of major projects NASA should support with a “funding bump” that was expected to appear in the near future. There were many missions to consider including a large x-ray observatory, LISA (a low-frequency gravitational radiation detector in space) and the Supernova Acceleration Probe favored by Michael Turner from Chicago that would study dark energy with a space telescope that would observe type 1A supernovae (the objects that provided the first evidence for dark energy). And again, a lot of smart prestigious people on the panel, but the charge to the panel was slanted so that you had to assume that the project was ready for funding in this supposed window between two other major missions. In my view, by far the most interesting and only unique thing on that menu was LISA, as it could study low-frequency gravitational waves that you couldn't possibly do except by going out in space and where many, many interesting objects were predicted to radiate in this band.

But the charge to the committee was slanted towards the supernova probe, because it said, "Available for a funding window between so on and so on and so on." But it was not competitive scientifically, especially since there are a lot of ten meter-class telescopes with adaptive optics here on the Earth and a lot of clever astrophysicists who already exploiting newer ways to probe dark energy such as baryon acoustic oscillations… And they can figure out ways to do this physics from Earth in a short time and respond promptly to any new discoveries. Whereas LISA was unique. None of the other missions were in the category of LISA. Namely, potentially, a real breakthrough thing. The panel report said nice things about LISA but recommend the Supernova Probe because it was “ready” and fitted into the size of the funding window… But I felt strongly that our report should have been more skeptical about this charge, because it turns out that window never developed in the first place. But that wasn't as bad as one about with the Gravity Probe B, which I thought was really dishonest.

Zierler:

And you were vocal?

Adelberger:

Was I vocal?

Zierler:

Yeah.

Adelberger:

Take a guess, I was very vocal.

Zierler:

And who was your audience? Mostly allies or people that disagreed with you?

Adelberger:

Well, I wanted to file a minority report on GPB, and they didn't want that. So the audience was all the other members. And there was a small group that felt as I did, although I was by far the person that felt that the whole premise was wrong. The argument I just gave you, if you think that different observers have got to agree on the facts there is little point in that expensive mission

Zierler:

So what did that suggest to you about where the field was headed? What had crept in that allowed for this framework to be unfolding as it did?

Adelberger:

Dare I say money? (laughs) You know, there were political arguments like "Well, they shut down the SSC, I'm not going to shut down this thing." In fact I think NASA wanted to shut GPB down because it was years behind schedule and fantastically over budget. I believed they were asking for our help… But anyway, those kinds of arguments are not science arguments. Those are political judgements. And I believe these panels are supposed to be providing scientific advice, not political advice. And any rate, it was an eye-opener for me. So it's interesting reading Artie Bienenstock’s account of the panels he served on. He had quite a different take and experience. He was able to do really a lot of things. I felt on these panels, I was outgunned by the other (laughs) concerns.

Zierler:

So I'm curious in what ways, you know, your reaction to this, how that influenced the kind of research you continue to do? Were you self-conscious about that, that there were things that you felt were important to undertake? Not just because of their scientific value, but because of the message that you wanted to send. Were you also interested in using that research to send a message about your beliefs about, you know, where the field was headed?

Adelberger:

I was not trying to send a message. I was doing it because it was consistent with the message. And the message is that physics is an empirical science, that it is very important to test our beautiful and “sacred” principles as deeply and thoroughly as we can-to understand the limits of what we know for sure. It is disturbing to me how much press is devoted to these, I'll just call them "untestable", but it's maybe not the right word, “speculations” may be better. It just seems to me, as I say, it's a way of avoiding the hard work. That's another thing that Feynman did. He said it takes hard work to really understand physics. (laughs) You know, you've got to work at it. And I believe that Feynman wouldn't have had much use for some of this stuff.

Zierler:

In what fields of physics do you feel like you've made the most significant contributions?

Adelberger:

Well I think it overlaps it's some combination of nuclear/particle physics and gravitational and astrophysical physics. And I--

Zierler:

Is there anyone--

Adelberger:

As I say, we haven't discovered any breakdown, which I dearly would have loved to do. That's why I'm still pursuing these issues, hoping that Mother Nature's going to give us a hint. But I do feel, we really set a standard for how to do convincing experiments. I don't know if you know this, but there's recent discussion about dark matter, for which there is much observational evidence, but for which we have good reason (nucleosynthesis) to believe cannot consist of any particles we already know. The current belief is that the “dark matter” phenomena are evidence for new elementary particles. The focus was on weakly-coupled very heavy fermions (WIMPS) that some theorists love because they could support their love of supersymmetry. But another possibility is that the dark matter could be extremely low-mass bosons that form a coherent field. Instead of having little bullets flying around, you have smooth waves because it takes huge numbers of the super-low mass bosons to make up the required amount of dark matter. These bosonic waves would have a frequency determined by the mass of the bosons. One particularly attractive candidate for bosonic dark matter is an axion or axion-like particle that couples to the spin of a fermion such as an electron. In the last two years we analyzed a long series of data we'd taken with a very clever gizmo. This clever gizmo is a solid state gyroscope, basically. It fits inside my fist. But it has angular momentum. It's a lovely trick, where you combine two different kinds of permanent magnet. One kind where all of the magnetization comes from electron spins, while the other permanent magnet is a rare Earth magnet (samarium-cobalt5) where half the magnetization comes from orbital angular momentum.

So if we put these things together in such a way that the object has no net external magnetic field, but it does have a net spin and net total angular momentum. So this little thing is really, truly a gyroscope. Its net electron spin would experience a torque if the bosonic field is axionlike, (couples to spins) that oscillates at a frequency determined by the mass of the bosons that make up the wave. Furthermore, the gyroscope’s net total angular momentum allows its sensitivity to be inferred from the steady torque applied by the Coriolis force of the Earth’s rotation. We analyzed a long series of data that we'd taken with this gyroscope and obtained constraints that extended to axionlike masses so small that their quantum wavelength would have implications for the galaxy. Our sensitivity was far, far worse than that needed to detect the most interesting case of the Peccei-Quinn axion. But we did show how to analyze such data rigorously and correctly. Other people, who are getting all kinds of money from Heising-Simons Foundation et cetera for doing related experiments, don't understand how to do it right. And so I feel this is an educational service. Unfortunately, some people are resistant to education. So I saw this work setting a good standard for how to do these things.

Zierler:

You emphasize the overlapping nature of your research and its impact on astrophysics and gravitation and nuclear. I wonder if there's a particular experiment or research endeavor you were involved in that really exemplifies that overlapping nature of your research?

Adelberger:

I can't cite a particular experiment—I’d like to think that the "Eöt-Wash" experiments all fit in that category. Another thing I was involved with Christopher Stubbs and Tom Murphy, was laser ranging to the moon for doing gravitational tests. In particular, we wanted to make a precise test of the non-linear property of gravity by seeing if the Earth’s gravitational binding energy (less than a part per billion of its mass) falls toward the sun with the same acceleration as the moon (a much smaller fraction of its mass is gravitational binding energy). Einstein predicts that these should be identical, while other metric theories allow for differences. That was fun, again we started out from ground zero and developed a lovely, very successful instrument. But its sensitivity to the gravitational properties of gravitational binding energy has now been outclassed by a beautiful triple-star system that consists of a super-close neutron star-white dwarf binary system orbiting a second white dwarf, This allows one to test if the neutron star (a millisecond pulsar) and the nearby white dwarf fall toward the second white dwarf with the same acceleration simply by precisely timing the radio pulses from the neutron star which is a pretty good clock. Because the gravitational binding of a neutron star is huge (more than 10% of its mass) this system is inherently extraordinarily sensitive. It has a simple elegance that reminds me of the parity-doublets in light nuclei that so pleased me in my nuclear physics days. We knew we had been outclassed.

Zierler:

Eric, you said before, you know, talking about your earlier research and how it knocked down so many theoretical suppositions. I'm curious if you can reflect on any aspects of your research that might have really strengthened or confirmed some theories?

Adelberger:

Well, to confirm a theory, rather than to provide additional support for it, you'd have to observe something that the theory predicts and that no one has seen before and confirm it. In a sense, I was the first to have found or placed limits on the parity violation of these systems. But I wouldn't make too much of it. The "Eöt-Wash" experiments have supported our current paradigm by proving that it successfully accounts for the facts in regions where it was possible to believe it could no longer apply.

Zierler:

(laughs) Okay.

Adelberger:

We clearly haven’t made any Earth-shaking confirmations, where something that nobody really believed before is now accepted because of what we did. It’s too bad but it’s a fact. But that doesn’t mean that we wasted our time.

Zierler:

So maybe, Eric, to give the readers a sense of the scale you're working on, what might be an example of an experiment that did just that? You can speak about others, perhaps, more easily than you can speak about yourself. What might you be comparing yourself to in establishing this standard?

Adelberger:

When Feynman, Gell-Mann came up with V minus A for weak interactions there were some wrong experiments there that stood in the way of coming up with V minus A. But V minus A looked very attractive to Feynman and Gell-Mann. Just on theoretical grounds. But it seemed to disagree with experiments for a while. So the first experiment that really convincingly agreed with V minus A was an important thing. I'd say that's--

Zierler:

Okay.

Adelberger:

Okay. The detecting of the solar neutrinos. Ray Davis detected the solar neutrinos doing radio-chemistry on his tank of cleaning fluid. That confirmed that nuclear reactions were taking place in the sun, but I don't think anybody doubted that, okay? What SNO (Sudbury Neutrino Observatory) got the Nobel Prize for was to show that the neutrinos had a non-zero mass and oscillated from one flavor to the others. Now that was a big deal. I was a fellow at CERN in 1992-93. There was a colloquium on solar neutrinos, and all the big-gun particle physicists sitting in the front row were badmouthing the idea of neutrino oscillation. The only thing they could see as really important was finding the Higgs boson, okay? Well, in fact, we learned more from neutrino oscillations than we did from the Higgs. The eventual discovery of the Higgs confirmed something we basically knew. But neutrino oscillations we didn't know. Discovering the apparent accelerated expansion of the universe was a very big thing. It's interesting that a lot of these really big discoveries lately come from astrophysics. In fact, I chide my particle colleagues, or chided them since I no longer engage in these sort of discussions, that the most important and exciting things we have learned in their field in the last 30 years or so have come from astrophysics and not accelerators: Dark energy, what the heck is that? Dark matter, that's even older than 30. What the heck is that? Neutrinos oscillating.

Zierler:

Why is--

Adelberger:

These are all particle physics questions and we have a fantastically interesting universe where you can look and see something that you didn’t know before (laughs).

Zierler:

Besides the fact that the big guns were there, and they were all convinced that it wasn't true, why is it such a big deal to discover neutrino oscillation?

Adelberger:

The standard model didn't permit it because its neutrinos were massless. Now you can say the standard model was modified to give the neutrinos mass as a result, but here's my take. We have no idea of where the neutrino masses come from, they are complete outliers. We learned that the quarks are mixed-- the mass eigenstates are not the interaction eigenstates, okay? For a long time, people believed that leptons were not mixed. And there are experiments you could do to test this, you could see if a muon ever turned into an electron plus a gamma-ray, for example. If the leptons were not mixed, that rate is very low. It only happens by very indirect processes. The general belief was that leptons were not mixed. Then, when I was in grad school there was a rumor out of an accelerator in Switzerland that this thing was happening with a branching ratio of about 10 to the minus 9. Well, it turned out not to be true, but it caused people to rethink. Why should we assume that the leptons have no mixing? Now the question is really, why aren't they mixable? Well, the neutrinos are leptons also. People assumed those weren't mixed, but in fact they are. Neutrinos are mixed. In fact, the question now is trying to understand the mixing in all of that. Perhaps neutrino flavor mixing could provide the missing source of CP violation needed to explain why the universe has a net baryon number. Are neutrinos actually fermions, like in the modified standard model, or are they different combinations with Majorana masses and so on? So these fundamental questions about neutrinos are very important. So those, all of the experiments I talked about that made a big difference have to be done on a scale which is much bigger than what I'm involved in.

Zierler:

You mentioned before you wanted to emphasize that the Eöt-Wash Group is more than you. So I'm curious if you could talk a little bit about your collaborators in this endeavor. Who else was involved in getting it started?

Adelberger:

Okay. Blayne Heckel, an atomic/neutron physicist and I got it started. Jens Gundlach, who was a nuclear physics graduate student at the time, worked with us beginning with our second paper. He later became a permanent faculty member and co-PI, For the last 3 years or so he has been the PI. Jens now also leads a major effort in biophysics.

Zierler:

What have been some of the objectives of this group?

Adelberger:

Our objectives are to test whatever issues in fundamental science are accessible to very sensitive techniques of experimental gravity. That's our agenda-to develop wonderful instruments and exploit them to test current open issues in fundamental physics… And we’ve been very fortunate that we've had a long string of cases where people know what we can do, and they first check if their ideas disagree with our constraints or not? Or other people tell them that those ideas are not consistent with what we find, or sometimes we tell them. I'm very proud of the innovations and the standards we've set in doing these things. You know, I love geometry. And--

Zierler:

We started with geometry. Way back.

Adelberger:

We started with geometry, right? Einstein’s gravity is a theory of geometry, right? I like to think that our instruments exploit geometry and its symmetries to test these theories. In fact, I like to think that there are two kinds of physicists. There are the geometricians and the algebraists. I'm definitely a geometrician. (laughs)

Zierler:

Eric, one thing we haven't talked about yet is your career as a mentor. And I'm curious if there are any stand-out graduate students or postdocs in terms of productivity in collaborating with you over the course of your career?

Adelberger:

As I said, Christopher Stubbs was an outstanding example. I have had other students who have done well in the academic world: Tim Chupp at the University of Michigan, CD Hoyle at Humboldt State University and recently Will Terrano at Arizona State University. Some of the students that we get at Washington want to stay in the Seattle area, by the way. That's another (laughs) limitation. Of my first graduate students at the University of Washington, one of them, Ross Mars, went on to Livermore National Lab where he invented the electron beam ion trap EBIT. The other student, Erik Swanson, returned to the UW where he is now an important player in the muon g-2 experiment at Fermilab. Some students have started companies, others work in high-tech industry. One very interesting case, one of my early students was from Bangladesh. I had a prejudice that most people from that part of the world didn't get their hands dirty on experiments and only wanted to do theory. But not Zafar Iqbal, he was a great experimentalist. When he came to the University of Washington, he was the second most popular author in Bangladesh. He wrote science fiction. The most popular author was a famous poet. Zafar had made a word processor for Bengali. As my student, Zafar worked on the ultimately unsuccessful hydrogen atom parity-violation experiment. This was a sophisticated, high-tech experiment that involved a lot of different technologies. Zafar was amazing-he could do anything without breaking a sweat. He went on to Caltech as a postdoc working on a double beta decay experiment, and then to Bell Labs where he held a record at the time for some communication speed that I no longer recall. He had already decided to go back to Bangladesh and Bell paid enough so that he could sock away funds needed to support a professor who earns very little in his home country. And he's a professor of something. But he's also a great proponent for human rights there. I ran into his son a couple years ago. He was at the Institute for Theoretical Physics in Santa Barbara, and so the family tradition is being continued by him. I've had quite a variety of remarkable people, is what I'm trying to say.

Zierler:

Yeah.

Adelberger:

And I think they all got something valuable out of their grad school experience. Including, I’d like to emphasize, how to write clearly and well. That skill will be of immense value to them whatever they do in their subsequent careers… When it is time to start writing a thesis, I tell them the first thing to do is to read Elements of Style by Strunk and White. Unfortunately most students today have not been educated to write well.

Zierler:

Yeah, yeah. Eric, I know you're emeritus now. I'm not sure if you have contact with graduate students currently, but I'm curious--

Adelberger:

Yes. I'm still doing experiments in the labs.

Zierler:

Oh that's great, that's great. So then it doesn't have to be an abstract question. I mean, given, a recurring theme in our talk has been, you know, where the field is headed and trends in the field and things that people are thinking about. What advice do you or would you give talented young graduate students now as they're developing their identity? What do you think, over the course of a career that's just starting out for a 25 year old, what are some of the most exciting areas in physics to work in?

Adelberger:

Okay. I think astrophysics, definitely. I think gravitational physics, LIGO, LISA and precision tests. I think that modern atomic physics is an area where a talented person can have an enormous impact; where you can still do a small scale experiment that's very impressive such as exploiting clocks that have a part in 10 to the 18th stability and so on. There's a man I really admire in Vienna, Markus Aspelmeyer, who combines tremendous skill in atomic physics with an interest in gravity, he's now working toward detecting the gravitational entanglement of a pair of tiny particles… These are areas where a young person can really set his or her own agenda assuming you're interested in that. Now that's not everybody's cup of tea. But if it is, recent technical advances have made it practical to exploit quantum mechanics in new regimes. I think, for example, of optical techniques that allow one to cool macroscopic mechanical systems down to their quantum ground state and so on. There are many interesting things you can do there; many with practical applications. This is one of the places where DARPA's money has been well-spent. There's a lot of nonsense that DARPA has funded as well… But DARPA support helped that whole field flower.

Zierler:

And for you, what are you personally excited about in terms of your own work, in terms of the things that you look forward for advances and discoveries?

Adelberger:

I'm not going to be doing it, but I think there are probably some very wonderful fundamental issues one can probe with these ultra, ultra-stable clocks. I'd like to somehow collaborate with Markus Aspelmeyer exploring new ideas for testing gravity. I was scheduled to go to Vienna in early March, but the COVID-19 outbreak prevented it, which was unfortunate. But I'm sure we'll have more interactions.

Zierler:

What do you see as the mysteries in physics that have been there since the beginning of your career and which remain today and for which you're not so optimistic that they'll ever be understood?

Adelberger:

That I'm not optimistic they'll ever be understood?

Zierler:

Yeah. You said before a few times that, you know, there's-- Sometimes it seems like maybe Mother Nature just doesn't want to tell us or show us.

Adelberger:

Right. (laughs)

Zierler:

So that's what I'm asking. What are those things that you're thinking of?

Adelberger:

My nightmare scenario, so to speak, is that there is a cosmological constant and it's truly a constant just like Einstein said and not a dynamical field. There is no supersymmetry, but well, that's already pretty much true, okay? Let's see, what else was it? I don't quite remember what other one-- But these are things where if they are true, it's hard to think of what a follow-on is. Okay? The idea that physics is an onion and you peel off layer after layer after layer after layer. You know, it's possible that we've peeled off all of the layers of the basic laws of physics, and all that remains is working out the quite fascinating details of what you can do with bunches of matter. I remember hearing a physics colloquium from a big guy in Bell Labs, a number of years ago, and he basically said that in the future, industry will have no use for young people studying physics-- . Everything is really computer science from now on. There are no new things we need to know. Well, I mean, that was not true and we've discovered some things which are actually interesting. But--

Zierler:

To stick with the metaphor of peeling back layers of an onion, would you include the origins of the universe or the early universe as among those layers?

Adelberger:

Oh yeah, we've learned an amazing amount. What's really amazing is that this simple picture of inflation, which seems like such a weird idea, explains the data so well, although it has lots of problems theoretically, but gosh, does it do a good job of explaining some beautiful data. So yes, we learned a lot in cosmology. But there is still a lot to understand.

Zierler:

Who do you most associate in terms of being impressed with inflation?

Adelberger:

Impressed with it?

Zierler:

No, what physicist are you thinking of when you're admiring inflation? For what it's doing, the data.

Adelberger:

I really admire the people who made all of those spectacularly precise measurements of the cosmic microwave background (CMB) that told us so much about the early universe. I admire Jim Peebles at Princeton who is the father of the now standard cosmology and also Paul Steinhardt at Princeton who is trying hard to develop viable alternatives to the standard cosmology. It is important for some smart people to rebel against the perceived wisdom of the time-to go against the prevailing wind when there are big things we do not understand. . . Those CMB measurements are really described very well by a simple inflationary model that requires one to accept a fundamentally fantastic phenomenon. If it is not basically correct, how come it explains so many things? That, to me, is a real puzzle. I hear Paul’s arguments why it is inconsistent and can't be right. And yet this darn simple thing works. It's a marvelous thing.

Zierler:

Can you explain what it means, that it works?

Adelberger:

You mean what are the ingredients of it that seem to be working? Well, that the universe is flat, that the density perturbations in the early universe are nearly Gaussian and seeded the formation of the structure we see today, the cosmological helium to hydrogen ratio… All these details are predicted by the very simple picture that relies on cosmological inflation. It's not confirming inflation, but it sure is consistent with it, right?

Zierler:

Right, right.

Adelberger:

Many people get into physics because it's simple, although as Gel-Mann said, he has a hard time explaining to his mother how it’s actually simple (laughs). But basically, that is the appeal, how much you can understand from a few basic laws.

Zierler:

Do you think ongoing work in searching for a grand unified theory, is this a promising prospect to you, do you think?

Adelberger:

By that, do you mean string theory or do you mean something different than that?

Zierler:

Going right back to Einstein, you know, the unified field theory.

Adelberger:

Right, as long as string theory is an outgrowth of that.

Zierler:

But I'm saying, but I guess what I'm asking, because we already know your opinions about string theory. I'm saying, does that endeavor, is that something that's useful to continue working on, absent string theory? In terms of continuing to work on the problem within the testable confines that you've referred to.

Adelberger:

Okay, I see what you're saying. I think, it's worth working on. Are we going to see breakthroughs there? I don't know, but clearly it's worth working on. First of all, I want to go back. I'm not dissing string theory, okay? Because as a mathematical discovery, it's been very, very unexpectedly fruitful, okay? Such as discovering relations between theories that seemed utterly unrelated before. I'm not putting any of that down, it’s spectacular.

Zierler:

Right.

Adelberger:

Not at all. The only thing I'm putting down is the anthropic multiverse idea. String theory started out with the hope that we would find that the world is the way it is because that's the only way it could be self-consistent… That was the original motivation and it’s a beautiful idea. Okay? Then theorists discovered that there are 10 to the 500th power different string theories, or something like that. This led to all of the anthropic principles and multiverses, etc. It wasn't bad that people did that, but it just seems to me that it's not a fruitful way to go. I think it's a cop-out. There are hard problems here, understanding why. Just saying that everything possible occurs in some multiverse and we just happen to live in a preposterous improbable one is not satisfying to me. I think it is a convenient exit-a way to stop worrying about the problem,

Zierler:

Exit from what, Eric? When you say it's an exit, exit from what?

Adelberger:

An exit from trying to understand why our universe is the way it is. It’s not obvious to me that a satisfactory theory can't have parameters that one simply has to measure. Of course the fewer the number of these parameters the more powerful the theory. But the idea that there is no point in understanding the relation between the experimental parameters, to find some pattern, because there is no fundamental reason behind their values, all values are realized somewhere in the multiverse. To me this is sad and defeatist. Now I must admit we may ultimately find I am utterly naïve, old-fashioned and profoundly wrong. But in the meantime, I think it is better to struggle to find patterns in Nature than to simply admit defeat. To me the latter seems like a cop-out.

Zierler:

Have you thought about the role of computational power and machine learning and the effect that it might have in terms of pushing the ball forward in the future?

Adelberger:

I've seen the dramatic impact of increasing computing power on experimentation… It's inconceivably different now from my grad school days. Powerful AI techniques are beginning to be applied. I can't believe it will not be a game changer for certain kinds of science. Computer power certainly has been a game changer in experiments. When I was working at the Bureau of Standards years and years ago, they made their own pulse-height analyzers with vacuum tubes, and the biggest one had 256 channels. It had to go into the electronics shop every week or so to replace failed vacuum tubes. The failure rate, even for the best tubes, prevented the device for working more than a week or so. Think how different this is now, a modern desktop computer has billions of transistors and it works for years. When I first learned electronics, the ethos was to reduce your component count as much as possible. Blah blah blah. When I first started learning to code you had to conserve memory so you used memory locations over and over. All that stuff is irrelevant now, Things have changed enormously during my lifetime and I suspect that the changes will continue into the future in ways that it is difficult to imagine now. AI techniques are beginning to be applied to data analysis. Surely those methods will be a game changer for so-called big-data science. It is not clear to me how large an impact AI will have on high-precision experimentation or on the big theoretical issues.

Zierler:

Yeah, yeah. So Eric, on that note, I think, you know, now that we're right up to the present day. I want to ask you one last question that's a pretty broad question. And it harkens back to another theme that you've brought up repeatedly, is really hard work and the value of doing the work, right? Day in and day out. So, I'm curious in terms of, you know--

Adelberger:

By "day in and day out" I don't mean plodding, I just mean focus.

Zierler:

Yeah, right. Exactly.

Adelberger:

It's only a focused effort.

Zierler:

Right, right.

Adelberger:

And trying to really understand it.

Zierler:

Exactly.

Adelberger:

And when I talk to undergrads, I always tell them. Look, it's not like I can inject physical understanding into you. Okay? I can teach you the seeds of very powerful ideas, but you've got to internalize them, and you've got to work them out for yourself and understand them in your own way. It is not so different from music or sports. A teacher or coach can help you, but you have to do the work to become a successful musician or athlete.

Zierler:

Right, right. Exactly. Exactly. So my question is on the nature of discovery and the way discovery happens. And I guess, you know, I said it's a broad question because I want you to think about it retroactively in terms of the discoveries you've been involved in. And then also to think ahead. You know, about future possible discoveries. So you know, to the extent that there's a pie chart that you can understand what makes discovery happen and one component is that hard work and that focus. And another component is technological and computational advances. And another component is, you know, those eureka moments. Those moments of brilliance or genius or insight, right? I wonder, you know, to the extent that it's possible or worthwhile to rank those things, what do you see are the most important components, both retroactively where you can look at a given discovery and you can say, "That was mostly about this, and then this, and then this." And then thinking in the future about, you know, is it really going to be about genius, or is it going to be about artificial intelligence? Do we have limits to our technology? You know, so I wanted you to just sort of reflect on that as my last question. Both retroactively and what you might think the future might hold.

Adelberger:

You know, one element of the pie chart you didn't mention, but it's important, is luck.

Zierler:

(laughs)

Adelberger:

I'm serious, alright?

Zierler:

I was hesitant to include luck, because I wasn't sure if you'd accept luck as a scientific concept. (both laugh)

Adelberger:

That's a very profound question.

Zierler:

That's why I saved it for the last. (both laugh)

Adelberger:

This isn't an answer at all, but it's something that concerns me. It is common to hear that that it is important to have the huge inequalities in incomes that characterize the US these days because it stimulates innovation. If a person doesn’t have the opportunity to make billions and billions of dollars from his or her work there will be much less innovation. This argument is made by many economists, and it's also made by people that have made billions and billions, and it's somehow in the US culture. But I think it is wrong. The really innovative people innovated because it was fun and challenging and satisfying. They didn't innovate in the hope that one day they could be in the top 0.01%… So I think it's very important for our society to encourage young people to appreciate the deep satisfaction that can comes from scientific work-where one can pick one’s own problems and challenges and contribute to human’s understanding of the world. I worry that so much focus today is just on these money issues. This isn’t directly responsive to your question, but it's something that's relevant to the kind of people that are attracted to science.

I see how fortunate I was that to grow up in a time when I didn't have to worry about money issues. I'm not rich, but on the other hand, I didn't have to worry about supporting myself and my family… And that allowed me to follow my interests and have the deeply satisfying pleasure of innovating… It doesn’t seem as easy for young people today as it was when I was young. So that's my worry. You weren't asking me about worries.

Zierler:

No, but you're answering it to the extent that the discoveries that you contributed to came from that basis of joy. Of wanting to do it.

Adelberger:

Right.

Zierler:

And that those discoveries would not have happened--

Adelberger:

And the satisfaction that comes from having done it.

Zierler:

Right. And those discoveries would not have happened if you didn't have that joy to get yourself involved in it in the first place.

Adelberger:

Right, right.

Zierler:

So I think, actually, that really is a quite elegant answer to my question. And what it really sounds like you're saying, in terms of thinking toward the future, and your concerns about money, is that the world needs more people like that dean from Caltech who was so formidable during your high school years.

Adelberger:

(laughs) Yes, well. That's true. And I hope lots of people grow up and enjoy geometry classes. (both laugh)

Zierler:

Eric, it's been so nice to talk to you. I really appreciate the time you spent with me.

Adelberger:

Well, thank you very much, David. I enjoyed talking to you.

Zierler:

Okay.