Charles Baltay

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ORAL HISTORIES

Courtesy of AIP Emilio Segrè Visual Archives

Interviewed by
David Zierler
Interview date
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Video conference
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Interview of Charles Baltay by David Zierler on June 16, 2020,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/44764

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Abstract

In this interview, David Zierler, Oral Historian for AIP, interviews Charles Baltay, Eugene Higgins Professor of Physics and Astronomy at Yale. Baltay recounts his childhood in Europe as a refugee during World War II and his teenage years in Long Island. He discusses his education as an undergraduate at Union College and his graduate work at Yale, where he developed his expertise in particle physics under the mentorship of Jack Sandweiss and Horace Taft. Baltay discusses his first professorship at Columbia, his work with bubble chambers and CP violation, and his collaborative projects at Brookhaven and Fermilab. He describes his close work with Steve Weinberg, and his work at SLAC, where he conducted research on the SLC project. Baltay describes his decision to join the faculty at Yale and he describes his longstanding interest in Z decays. He shares his view on the rise and fall of the SSC, and at the end of the interview, he explains his more recent interest in cosmology.

Transcript

Zierler:

This is David Zierler, oral historian for the American Institute of Physics. It is June 16th, 2020. It is my great pleasure to be here with Professor Charles Baltay. Charlie, thank you so much for being with me today.

Baltay:

It's a pleasure.

Zierler:

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

Baltay:

I'm the Eugene Higgins Professor of Physics and Astronomy at Yale University.

Zierler:

OK. Charlie, let's now take it all the way back to the beginning. First, tell me about your parents. Where are your parents from?

Baltay:

From Hungary; my father was a lawyer, a judge. My mother was a housewife.

Zierler:

Where in Hungary were they born?

Baltay:

My father was born in Budapest, my mother was born in Western Hungary in a town called Sárvár. And they lived in a suburb of Budapest until 1945. When the Russians were coming into Hungary, my parents decided to go west. So we started out from Budapest and worked our way to first Western Hungary. We were there for a while. Then went on to Austria, then went on to Germany. And we ended up in Bavaria in a small town called Kempten in Bavaria.

Zierler:

Now, your family was mostly safe during the war itself?

Baltay:

Well, safe is a funny word. I mean, we were shot at, we were bombed at, but we survived.

Zierler:

Who was the greatest enemy? Who was the greatest threat to your family?

Baltay:

Well, first, in Western Hungary, we were in a house where Russian bombs came in, and our only luck was that they were crummy bombs. I was told that 13 bombs hit the house, but we were in the cellar and we survived.. The whole house collapsed but then we were dug out. Then, as we were in Germany, the Nazis were after us. For a while, we had a truck with the Budapest Justice Department, a moving truck the Nazis took. So we walked. And then the Americans started bombing us.

Zierler:

Why were the Nazis after you?

Baltay:

They saw a truck that moved so they took it. And, when my parents protested, they pulled out guns and said, "Just go away or we'll shoot you." So then we walked for, oh, I don't know, maybe a few weeks. And, as I said, then the Americans were bombing Germany and we were in Germany, so we were bombed. I remember when a bomb fell and made a crater, we would jump into that crater saying that two bombs are not going to hit the same place, which is pretty poor logic. [laugh]

Zierler:

[laugh]

Baltay:

But that's what we did.

Zierler:

What year were you born, Charlie?

Baltay:

'37.

Zierler:

So you have good, strong memories of the war?

Baltay:

Oh, well, it's hard to know what is a memory and what is stories told around the campfires.

Zierler:

Mm-hmm.

Baltay:

Yes. And my mother wrote a diary, so we have a pretty good idea of what happened. But, as I said, when we were moving west, the American Army was moving east. When we met the American Army, everything was frozen.

Zierler:

Mm-hmm.

Baltay:

And that was in a small town in Bavaria.

Zierler:

And how long did you stay in Bavaria?

Baltay:

We were there five years. So then our official title was "scheisse ausländer," which is German. I don't know if you know the meaning. And then they were pretty much telling us to move on someplace, so a lot of my parents' friends went to Australia, Venezuela, Brazil. My parents held out for the US, and in 1950 we were accepted to come to the US.

Zierler:

So you were essentially refugees from 1945 to '50?

Baltay:

Yes. DPs, displaced persons for five years—

Zierler:

Was going back to Hungary not an option?

Baltay:

It was an option. In fact, the Americans said, now that Hungary has been liberated from the Nazis go home. But they were occupied by the communists, which my parents had experience with from 1918 when there was a brief communist revolution in Hungary which was nasty, so they wanted to have no part of going back to Hungary.

Zierler:

Mm-hmm. Why did your parents hold out for the United States?

Baltay:

Well, my father thought that was a better place than Australia or Venezuela, and I think he was right.

Zierler:

Did you have any family in America?

Baltay:

No, nothing at all.

Zierler:

Uh-huh.

Baltay:

We arrived, and we borrowed 10 bucks from a friend, and that's how we got started.

Zierler:

[laugh] Where did you come in, New York?

Baltay:

We came to Long Island, so, yes, that's New York State..

Zierler:

And where did you go from there?

Baltay:

Well, then, my parents got various jobs. My father was a judge but then he got a job as a riveter in a bed factory, because a Hungarian law degree is not even worth the paper it's written on in the US.

Zierler:

Did he try to go to US law school to keep up his profession?

Baltay:

No. He was, I don't know, too old for that. He was in his 40s by that time, and we had to live. Going to law school was just not an option. So he got a job as a riveter, then, in that company, became a purchasing agent, and then he worked his way up and retired as the vice president of the company.

Zierler:

Did anyone in your family speak English before you got to America?

Baltay:

My father did.

Zierler:

Oh, he did?

Baltay:

Yeah.

Zierler:

And you picked it up pretty quickly as a boy?

Baltay:

Well, yes, we had to.

Zierler:

So you were 13 when you came to America?

Baltay:

Yeah, just about.

Zierler:

So I assume you had fairly limited education in Europe?

Baltay:

Right. Out of the first eight grades, I went to four, one in Hungary, three in Germany. And then, in the US, I opted to start high school, although I was a year ahead—I should have been 14 but, somehow, I got into high school.

Zierler:

So they didn't hold you back because you missed so many grades?

Baltay:

No. I don't know why, but that's how it happened.

Zierler:

Yeah, yeah. Probably because you were smart.

Baltay:

Well, I don't know. Then I applied to college and that's how it started.

Zierler:

[laugh] So where did you go to high school?

Baltay:

In a town called Sayville on Long Island, Sayville High School.

Zierler:

Public school?

Baltay:

Yeah.

Zierler:

Now, at that point, Charlie, were you already pretty good in math and science?

Baltay:

Oh, I wouldn't say pretty good. I mean, as a kid I read books in physics and math, so I had some idea, but pretty good is not the right word.

Zierler:

Did you know that you wanted to study physics when you got to college?

Baltay:

Well, I first wanted to be an engineer, but then, when I got to college, I realized that physicists tell engineers what to do, so I then switched to physics.

Zierler:

[laugh] Was that the influence of your father and his profession first as a riveter that influenced your desire to become an engineer?

Baltay:

No. I always liked technical things. And a lot of things in life happen in a funny way. When I got to college, I took freshman physics that was taught by the chairman of the department.

Zierler:

Where did you go to college?

Baltay:

In Union College. I was accepted at MIT, Princeton, and Union. And Union gave me the biggest scholarship, so that's where I went.

Zierler:

Uh-huh.

Baltay:

And so, I took freshman physics from Harold Way, and somehow the first exam I aced. I got 100 on the first exam. Then I joined a fraternity. I discovered beer. I discovered girls. My grades went from A to B to C.

Zierler:

[laugh]

Baltay:

And in the spring of my senior year, the chairman, Harold Way, came to me and said, "Charlie, have you thought of graduate school?" And I said, "Not really, but sounds good." He said, "What do you think of Yale?" I said, "Oh, Yale sounds good." He said, "I'm very good friends with Bill Watson," who was then the chairman at Yale. I don't know if you've heard that name?

Zierler:

Sure, sure.

Baltay:

Bill Watson was the chairman at Yale. He was a good friend of Harold Ways. He said, "There's a New York meeting of the American Physical Society every year and I always go and have lunch with Bill Watson. Why don't you come along and have lunch with us?" So I went along. We had a nice lunch. At the end of lunch, Bill Watson said, "OK, Charlie, you're in."

Zierler:

Wow.

Baltay:

So I never filled out an application. That's how I got into Yale Graduate School.

Zierler:

Did you bring your grades back up? I assume the chair of the department didn't have so much interest in a C student.

Baltay:

Well, but he remembered me from my freshman year, and Union is a bit of a party school. Don't say this publicly, but...

Zierler:

[laugh]

Baltay:

So he was probably used to kids doing what I did. And he and Watson had a deal where, every so often, Harold Ways said, here's a good guy, you should take him, and Watson took him. And they usually worked out very well. So that's how I got into Yale.

Zierler:

So you didn't even apply anywhere else, it just happened that way?

Baltay:

That's right. That was January of '58, I think.

Zierler:

Oh, wow. Right in the middle of Sputnik.

Baltay:

Yeah. So that's how I got into Yale, and then the rest is history.

Zierler:

[laugh] Did you know when you got to Yale what kind of physics you wanted to work on?

Baltay:

Well, I knew I wanted to do something fundamental. Not better plastics for better radios but something—so particle physics at that time was just getting going in '58. And so, I joined the group of Professor Sandweiss and Taft. Horace Taft was the grandson of President Taft, was dean of Yale College at that time. So I worked with them and that worked out very well.

Zierler:

And what were Sandweiss and Taft doing at that time?

Baltay:

Well, we were doing what you call particle physics. Jack Sandweiss just came as an assistant professor from Berkeley where they just discovered the antiproton in 1956. Remember Owen Chamberlain discovered the antiproton in '56. So Jack Sandweiss said—the Brookhaven AGS accelerator was just getting going—he said, "Let's build a beam of antiprotons," which were then just discovered, so that was the hot stuff. So, as my thesis project, I spent a year at Brookhaven building an antiproton beam and that was my thesis experiment. So antiproton collisions—antiproton-proton annihilations.

Zierler:

Can you talk a little bit about the process of building an antiproton beam?

Baltay:

Well, the main equipment that we had to build is what we called a particle separator. You see, the AGS makes protons and you run the protons into a chunk of copper, and that makes all kinds of particles, pions, kaons, protons, antiprotons. You then somehow have to separate the antiprotons from all the other particles, so that you get a beam of pure antiprotons that you can then run into a bubble chamber and study their interactions. The antiprotons were a small fraction of what came out of the target, so we had to get rid of all of the other particles. So the beam separator was a crossed electric and magnetic fields which then picked out a particle of a certain mass. So I spent a year building that gadget. It was maybe 20 feet long and 6 feet across, so it was a big piece of equipment. But I was, as a graduate student, building that.

Zierler:

Now, why would this be done at Brookhaven? Was this a project that was too big to do at Yale?

Baltay:

Well, Yale had a small accelerator, but much too small. AGS at that time was the world's largest and highest-energy accelerator, and you needed that energy. You see, at Berkeley they had just built the Bevatron which was 6 GeV, just barely enough to produce antiprotons. But the Brookhaven AGS had 30 GeV, which is what was needed to make a lot of them, enough of a beam so that we could make a beam of them.

Zierler:

And what were the big research questions that his project was designed to answer?

Baltay:

Well, at that time, it was a big deal that there are antiprotons at all. Dirac predicted antielectrons, which were discovered, but then, are there antiprotons? That was a big deal. So just to study their interactions was the point. How do protons and antiprotons annihilate? Are they really the same particle, the same mass? So just studying the interactions of antiprotons was the point. We had discovered a few new particles on the way, a few antiparticles, so that was also interesting.

Zierler:

How closely related was your dissertation to the ongoing work that Sandweiss and Taft were doing?

Baltay:

Well, that was their experiment, so I was the student on their experiment.

Zierler:

Mm-hmm. Who else was on your thesis committee?

Baltay:

On the committee it was Allan Bromley, if you remember that name.

Zierler:

Mm-hmm. What year did you defend?

Baltay:

In '63.

Zierler:

In 1963. And then, what were your prospects after you defended? What were you looking to do next?

Baltay:

Well, again, it was serendipitous in the sense that Jack Sandweiss had friends. So I remember Art Rosenfeld, if that name is familiar to you—

Zierler:

Mm-hmm.

Baltay:

—came to visit Yale and offered me a job at Berkeley. And then, another friend of Jack Sandweiss's was Mel Schwartz. I don't know if that name is familiar.

Zierler:

Mm-hmm.

Baltay:

Mel Schwartz came and visited, and asked Jack, "Do you have any good students?" And Jack said, "Well, talk to Charlie." So Mel invited me to go to Columbia. I gave a talk, and then the chairman, who was Sam Devons at that time, said, "Are you coming?" Offered me a job, and I said, "No. I like Yale. I want to stay at Yale." Then Mel Schwartz said, "Charlie, come and sleep at my house overnight and I'll show you what you will live like here." So he showed me some of the mansions in Irvington, New York.

Zierler:

[laugh]

Baltay:

And I said, "Oh, wow. This is nice." So I said, "OK. I'll come." So that's how I got to Columbia. That was '64, I think.

Zierler:

And, at Columbia, this was a postdoc, or this was an assistant tenure line?

Baltay:

Well, I didn't want to be a postdoc, so they made a position called "instructor." So I started as an instructor, then in a year they made me an assistant professor. And, in another three years, they gave me tenure, so I had tenure in four years.

Zierler:

Mm-hmm. Did you take on graduate students while you were at Columbia?

Baltay:

Oh, yeah. Lots. But I remember when I first showed up at Columbia, T.D. Lee—you remember that name—was a big honcho, and Leon Lederman, Jack Steinberger, Mel Schwartz. I don't know if you know those names.

Zierler:

Of course. These are all luminaries.

Baltay:

Right. [laugh] So T.D. Lee invited me to lunch—every Friday, the department had a Chinese lunch. And then at 2 o'clock was a particle seminar, 4 o'clock was a colloquium. So Friday afternoons were very festive at Columbia at that time in the physics department. So T.D. invited me to lunch, and I remember sitting at a round table in a Chinese restaurant with eight bloody Nobel Prize winners. Starting with Rabi, Kusch—you may know those names.

Zierler:

Yeah.

Baltay:

Charlie Townes.

Zierler:

Uh-huh.

Baltay:

Willis Lamb. I don't know, did Lamb get a Nobel Prize? I think he did.

Zierler:

I'm not sure.

Baltay:

Madame Wu, Jim Rainwater who invented—I always laughed—the liquid-drop model.

Zierler:

Well, you have to if your name is Rainwater. [laugh]

Baltay:

[laugh] Right. And then there was Lederman, Schwartz, and Steinberger, who got their Nobel Prize later.

Zierler:

Mm-hmm.

Baltay:

So I remember Jack Steinberger saying to me, "Well, Baltay, you come highly recommended. What do you think we should do next?"

Zierler:

[laugh]

Baltay:

So, like a dumb jerk, I said, well, we should do A, B, and C. And he looks at me in front of that crowd and he said, "That's the dumbest thing I've ever heard."

Zierler:

[laugh]

Baltay:

So that was my introduction to Columbia. So I said, OK, I'll show these guys. And, as I said, within four years, I had tenure.

Zierler:

When you got to Columbia, was your plan to continue on with the research you had already done or were you looking to take on new projects?

Baltay:

Well, no. I wanted to take on new projects but still in a similar vein, I mean, still bubble chambers. Bubble chambers were just invented at Berkeley by Luis Alvarez and company. And Brookhaven had just built a bubble chamber, so I worked on bubble chambers, but in other topics like, just then, in '64, CP violation—Fitch and Cronin, if you remember, CP violation. So I proposed to do a K- experiment, separated K- beam in a bubble chamber, to look at CP violations. So the physics topic changed from resonance production and antiprotons to CP violations, but the same technique, bubble chambers.

Zierler:

Charlie, can you talk a little bit about bubble chambers? What did they allow you to do that wasn't possible to do before?

Baltay:

Oh, well, the way a bubble chamber works is you fill it with something like, let's say, hydrogen. And liquid hydrogen is just very cold. You heat it up until it should start boiling. So you have a piston on the bottom, you pull it down to reduce the pressure, then it just barely goes above the boiling point. And it says, where should I start boiling? And, just then, you put in a beam of particles, which then ionizes the hydrogen gas and that's where it starts boiling. So you form little bubbles along the track of the particle. Then you better push the piston up, otherwise the whole thing will explode. But then you take a photograph of these little tiny bubbles of hydrogen gas in the hydrogen liquid. That's why it's called a bubble chamber. But you get a beautiful picture of the whole event. I mean, the photographs—I don't know if you've seen bubble chamber photographs. They're just beautiful. And you usually take three stereoscopic views so you can reconstruct the curvatures. You have a magnetic field and you can reconstruct the whole event. So that's the beauty of the bubble chamber, and they were kind of king for maybe a decade. Their limitation is that you have to, by eyeball, look at the pictures.

Zierler:

Now, did you appreciate this limitation in real time or was it only when successor technologies came about that you realized the limitation of the bubble chamber?

Baltay:

Well, it came gradually in the sense that—let me maybe make one other comment, that a lot of people do a thesis, then get an assistant professorship, continue that work, then become experts at that field. I have sort of switched fields, I don't know, four times. I mean, I started out with bubble chambers looking at resonances, then CP violation, then moved on to neutrinos in the Fermilab 15-foot bubble chamber. Then moved on to e+e- collider at SLAC, which was not a bubble chamber but an electronic detector, which I spent 20 years at. I was cospokesman of the SLD Experiment at SLAC. I remember Panofsky asking me to do that. So I worked a lot with Burt Richter, Marty Breidenbach, Charlie Prescott. So that was not bubble chambers, that was e+e-, electroweak, Z decays. Then people discovered an accelerating universe, and that was just too much fun not to work on. So then I pretty much switched to astrophysics and cosmology. I'm now working on a space project, which was called WFIRST. It's now called the Nancy Grace Roman Space Telescope, and that's what I'm doing now.

Zierler:

Mm-hmm.

Baltay:

So I'm now doing astrophysics and—working a lot with Saul Perlmutter, if that name is familiar to you.

Zierler:

Yes. Yes, it is.

Baltay:

The other pleasure I've had throughout my career is working with very good people. I mean, Jack Sandweiss was first class. I wrote a couple of papers with Jack Steinberger at Columbia. Then worked with Nick Samios, is a name you might know.

Zierler:

I'm talking to him next week, actually.

Baltay:

[laugh] So say hello to Nick. He's a good friend. So I worked with him for a bunch of years on the neutrino experiments.

Zierler:

Right.

Baltay:

Then Panofsky asked me if I would be cospokesman of the SLD experiment, so I worked a lot with Pief, then with Burt Richter—who is another name you are probably aware of—

Zierler:

Of course.

Baltay:

—Marty Breidenbach, Charlie Prescott. So we did the SLAC experiment. And now I'm working a lot with Saul Perlmutter, who is also as smart as they come.

Zierler:

Yeah, yeah.

Baltay:

So I've enjoyed working with smart people. That's been my pleasure.

Zierler:

So, in the early part of your career, when you were still working with bubble chambers, what other projects were you doing in those years?

Baltay:

Well, I mean, bubble chambers was the thing. I started moving from small—the 20-inch chamber at Brookhaven to—my thesis was on the 20-inch. Then I moved on to the—th 80-inch, was the next biggest bubble chamber. I built a few gadgets to—if you have a beam of particles coming in and they're all on top of each other, then it's confusing. So I built a gadget that spread out the particles as they entered the bubble chamber. So I did a few things of that sort. Also built some equipment to analyze the bubble chamber pictures. At that time, it was called a Hough Powell device that I worked on—the trouble with bubble chambers is that you had to physically look at the pictures, and that limited your statistics. So the idea was to build a machine that would look at the pictures automatically. I mean, this was back in the '60s.

Zierler:

What kind of machine could look at the pictures automatically?

Baltay:

Well, it had a laser beam which was made to move in a scan, and sort of digitized the picture and fed that into a computer. Nowadays, you see I have my printer here. I put a picture on it, it digitizes it. At that time, that was a big deal. But computers were much simpler in the late '60s, so it was a big deal to make computer programs that would analyze the pictures.

Zierler:

And were you splitting your time evenly between Brookhaven and Columbia?

Baltay:

No. I was fulltime at Columbia, but I did experiments at Brookhaven. So when you did a run on the accelerator, then you were at Brookhaven, but otherwise I was at Columbia.

Zierler:

Mm-hmm.

Baltay:

Then, when we did the neutrino experiments, that was at Fermilab.

Zierler:

What year did you start getting involved with neutrinos?

Baltay:

Oh, in '72.

Zierler:

What was it about neutrinos that attracted your interest?

Baltay:

OK. So I got to Columbia in '64. In 1972, Steven Weinberg came visiting Columbia, gave a colloquium on what's now called the Weinberg model, or the electroweak model, which is now the standard model of particle physics. And he predicted neutral currents. And one way to look for neutral currents was with neutrinos. So, in '72, I spent a sabbatical year at CERN working with the Gargamelle group. I don't know if that's familiar to you.

Zierler:

Yes.

Baltay:

That was a large heavy liquid bubble chamber. And we thought we saw neutral currents. So when I got back to Columbia in '72, with Nick Samios, we proposed an experiment at Fermilab. Fermilab was just getting started, so we proposed an experiment to look for neutral currents. And the gimmick there was that we wanted to look at a reaction which was purely leptonic. I don't know if these words mean anything to you.

Zierler:

Yes.

Baltay:

Leptons are electrons, muons, and neutrinos, while hadrons are protons, neutrons and so on. So we felt that, at that time—that was early '70s—we didn't know much about the quark model. We didn't know that much about hadrons. We said, we don't want to look at neutrinos interacting with hadrons because there the hadron uncertainties are bad. So we wanted to do a purely leptonic process, which was muon neutrinos scattering on electrons.

Zierler:

And when you say "we," Charlie, who were your main collaborators on this?

Baltay:

Well, Nick Samios and Bob Palmer. That's a name that might not be familiar to you.

Zierler:

Yeah.

Baltay:

But Nick Samios and the three of us were really doing that. Plus, a couple of people in my group and a couple of people in Brookhaven's group.

Zierler:

And why Fermilab? Why was Fermilab the best place to conduct this research?

Baltay:

Well, they were just coming on. They had high energy. Brookhaven did not have enough energy to really do that well. And Fermilab just built a 15-foot bubble chamber, that's a sphere 15 feet across. And, in a sense, that turned out to be one of the best things I've ever done. So, if I can diverge a little bit on that, the question then was, are there neutral currents? And Weinberg's model was a whole theory of the electroweak interactions. He united the electromagnetic and the weak interactions into what we call electroweak, and he made some predictions. Then, Gargamelle at CERN jumped on it, and we were competing, Fermilab and the 15-foot versus Gargamelle at CERN.

Zierler:

And when you say "competing," this was a race for the same discovery, who would get there first?

Baltay:

Well, for the same—yes, for the same leptonic process. That's the muon neutrino electron scattering. They beat us by a month but got the wrong answer.

Zierler:

[laugh]

Baltay:

They got an answer—they found too many events and they got an answer that did not agree with the Weinberg model. You remember, really the coin of the realm was the Weinberg angle, the weak mixing angle. And the sine squared theta Gargamelle got was bigger than 1, which is not physical. So Salam started alternative theories, and Weinberg-Salam was incorrect. So I remember Weinberg called me every other day, "Charlie, what are you seeing? How many events are you seeing?" And we got the right answer. We got sine squared theta to be 0.23. So that was really the first measurement of the Weinberg angle. And I remember the 1978 conference of particle physics that was in Tokyo that year. Weinberg gave the last talk, sort of declaring victory for the Weinberg model. I gave the talk before him saying that we got the right answer for the Weinberg angle confirming his theory. Charlie Prescott also did an experiment at SLAC, so those were the two experiments that really said Weinberg is right.

Zierler:

Did you see this as one of the great moments where experimentalists and theorists are working together to really move our understanding forward?

Baltay:

Yes, exactly. I remember in Tokyo I was at the same hotel with Steve Weinberg. We sat together every night, and, at that time, we were writing transparencies with ink.

Zierler:

[laugh]

Baltay:

That was the mode of giving talks. And we were sort of writing my talk, writing his talk. So I worked very closely with Steve that year. Then, years later, we did the SLD Experiment at SLAC.

Zierler:

How did you get involved in that?

Baltay:

Panofsky asked me to come and be the cospokesman for it.

Zierler:

Did you know Pief or he just knew of your work?

Baltay:

Well, when that thing with Gargamelle happened, then we got a bit of attention by saying that Gargamelle got the wrong answer showing that Weinberg model is wrong, and we came out saying the Weinberg model is correct. And I gave a talk at SLAC, and I even sort of explained what Gargamelle did wrong. Having spent a year at CERN on a sabbatical, I knew the Gargamelle people very well. In fact, I visited CERN later, and I said, "Show me your events." And I kind of figured out what they did wrong. So I remember giving a talk at SLAC that Panofsky and Burt Richter were at, and they kind of liked the way I analyzed the data, and they liked that I got the right answer. So I imagine that's why they then asked me to be the cospokesman, with Marty Breidenbach. I don't know if that name is familiar to you. So we were co-spokesmen of SLD, and we measured the Weinberg angle sine squared theta, and that is the best measurement even to this date.

Zierler:

Oh, wow.

Baltay:

So I can say I did the first measurement of sine squared theta, got 0.23. We did the best measurement ever. We got 0.23.

Zierler:

Can you explain, Charlie, why 0.23 is such a good measurement?

Baltay:

Well, yes and no. The theory does not predict the value of sine squared theta, but it wants it to be less than 1. And that number is kind of the most fundamental number in electroweak theory. From that number, you can predict all of the interesting cross sections, since all of the cross sections depend on that number.

Zierler:

So is any number acceptable? I mean, what if it was 0.02? What if it was 0.88? As long as it's below 1, is that what's most important?

Baltay:

Yes..

Zierler:

So what does 0.23 tell you that 0.88 wouldn't tell you?

Baltay:

Well, OK. How do I answer that? After we measured 0.23, theories came up for reasons why it should be, like, 3/8. What is 3/8? Comes out to be close to 0.23. But, to be honest, there is no good theory that predicts 0.23. That's like the proton mass. That's a number you measure and that's what it is. But, as I said, there are theoretical papers predicting it after the fact. But there's no real reason from the model itself that would predict that number.

Zierler:

And when you say that greater than 1 is not physical, is that another way of saying that it's not possible?

Baltay:

Yeah. I mean, if you say that I'm measuring the sine of an angle to be bigger than 1, you say that just cannot be correct.

Zierler:

Mm-hmm.

Baltay:

The sine has to be between -1 and +1. So, at that point, people said the Weinberg model is wrong and you need an alternate model.

Zierler:

What did Weinberg's model do for physics more broadly? How did it move the entire field of physics forward?

Baltay:

Well, it established what we now call the standard model. So maybe one way to think of it is physicists are simple-minded folk. They want to understand nature to be simple. You say if nature looks too complicated, you're not understanding it. Originally, you had things like electric things, and you had magnetick effects (spelled with a ckat the end), lodestones in China, compass needles. That's two completely separate fields. Then, along came a guy called Oersted who saw that a current made his compass needle twitch. And there then came to be a theory which was culminated in Maxwell's equations, uniting electricity and magnetism. So that was a huge step forward in classical physics of the last—well the last before century by now. [laugh] So that was huge—that was the physics of the 1880s, to unite electricity and magnetism. Then Einstein said, OK, the next step is to unite electricity and magnetism and gravity, but even Einstein never succeeded doing that. And even today we don't know how to unite gravity with electromagnetism. But along that time, Madame Curie and other people discovered nuclear physics, strong interactions, and weak interactions. Weak interactions caused particle radioactive decays. So the force that mediated the radiative decays were then called the weak interactions. So, what the Weinberg model did is it united the weak interactions and the electromagnetic interactions in one theory, which we now call electroweak. So that's sort of an event like what Maxwell did in the 1880s. So that happened in the 1970s, almost exactly 100 years later. And that then gave the basis of all of what we call modern particle physics. Then along came QCD or the color force and the strong interactions being similar. To complete the job, we have to unite gravity with the other forces, which we still don't know how to do. There is no theory of quantum gravity, although some people claim they have a theory, but no one has a realistic theory of quantum gravity.

Zierler:

Who claims that they have a theory?

Baltay:

Oh, people like string theorists.

Zierler:

And when you say they claim to, would this suggest that you don't believe it?

Baltay:

Most people don't believe it.

Zierler:

Who would you say are the string theorists who are most vocal about making this claim?

Baltay:

Oh, I don't know. Let me not name names.

Zierler:

[laugh] OK. So let's get back to Panofsky. At what point does he contact you and how developed is the program before you get on?

Baltay:

Well, let me see. That must've happened in 1983. That's the year my daughter was born, and that's when Panofsky and Burt Richter approached me. At that time, they were just getting SLC going.

Zierler:

And what were the big objectives of SLC? What were they trying to accomplish?

Baltay:

Oh, the thing was to make and study the Z-zero bosons.. The charged current weak interactions were mediated by the W+ and W- bosons. What Weinberg predicted was neutral currents and therefore there had to be a new intermediate boson called the Z-zero. So that was the prediction that in addition to the W+ W- bosons, there had to be a Z-zero boson. And the W and the Z were discovered at CERN by Carlo Rubbia, a name you also probably know.

Zierler:

Yes.

Baltay:

I remember the New York Times headline "CERN 3, US not even Z-Zero."

Zierler:

[laugh] Ouch!

Baltay:

Yes. So that must've happened just around the early '80’s , '81, '82, something like that. So, in '83, Burt Richter started what they called a linear collider, an electron positron collider, at SLAC. And the first detector was called MARK II, but that was not a very sophisticated detector, so I think it was Panofsky and Richter decided that there should be a new detector for the new accelerator. And then they asked Marty Breidenbach and myself to run it, to be the cospokesmen, so that's how that happened.

Zierler:

Why do you think you? What do you think that was about?

Baltay:

Not sure.

Zierler:

Well, I mean, I'm asking because you had already been known at this point for making such excellent measurements.

Baltay:

Well, I've always had a good relationship with SLAC. Do you remember a guy called Joe Ballam—

Zierler:

Mm-hmm.

Baltay:

—who was the research director? When he retired, Panofsky or Burt Richter offered me that job, which I then declined because I was happy at Columbia at that time.

Zierler:

Right. Oh, so you're still at Columbia. What year do you leave Columbia?

Baltay:

'88.

Zierler:

OK, OK.

Baltay:

Well, this was '83.

Zierler:

So you were offered a professorship at SLAC or at Stanford?

Baltay:

At SLAC.

Zierler:

Uh-huh.

Baltay:

But which is part of Stanford.

Zierler:

Right, right, but not part of the physics faculty at Stanford.

Baltay:

No. No, that would've been a SLAC position.

Zierler:

Right.

Baltay:

So, anyway, then I imagine that what they said is, if we have a SLAC professor in charge, it would be good politics with the DOE to get a non-SLAC person. That's the way I rationalize why me. OK. So they said, let's look around for a non-SLAC person to be the co-spokesman with Marty Breidenbach.. I always got along very well with Panofsky and Burt Richter. A lot of people criticized Burt, but I always respected him. I think he was great. So that's how that happened, I think, that the motivation was to get a non-SLAC, an outside person, a university person.

Zierler:

And, when you agreed to take this on, what were your motivations? What were you looking to accomplish?

Baltay:

Oh, well, at that time, that was the hottest topic in physics. You asked me what were the goals of SLC and that new detector, which we called SLD, and that is to make zillions of Z particles and study the properties of the Z particle. And that, of course, was the goal of the LEP accelerator at CERN as well. You must be aware that that—

Zierler:

Of course.

Baltay:

—was the e+e- collider at CERN, for the same exact reason. They were both designed to be 90 GeV center of mass so that the e+e- just made a Z sitting there at rest in the lab, which is just beautiful. I mean, how can you have a nicer situation with zero background? You produced zillions of Zs just sitting there in the center of mass, and all you've got to do is look at them decay. At that time, nothing was known about the Z except that it carried the neutral currents. And that, in a sense, was the beginning of what we called precision electroweak theory. So, at that time, the Z mass was poorly known- it was just found in '82 by Rubbia at CERN, and not much was known about the Z. Theory predicted some things, but measuring what the Z was like was, at that time, the hottest topic. So I dropped everything I was doing. At that time, I had an experiment to look for the tau neutrino at Fermilab. I remember Lederman being very sore at me for backing out of that to accept working on SLD. In fact, SLD was competing for money with the Fermilab detectors CDF and DZero. You must've heard those words.

Zierler:

Sure, sure.

Baltay:

We were proposing to build the SLD detector at SLAC, and Fermilab was proposing to build CDF and DZero. And we were competing for money.

Zierler:

It was zero sum, either one project or the other was going to get funded?

Baltay:

Well, it wasn't clear. In the end, all three got funded. And all three were worthwhile so all three got funded. And we were a single detector at SLC competing with four detectors at LEP. And, as history has it, LEP had 10 times the luminosity, so we were wiped out by statistics, but we had polarized electrons, which CERN did not have. So, in the end, we got the best measurement of sine squared theta, the Weinberg angle, among lots of other things where we got the best measurements by virtue of having polarized electrons, which was Charlie Prescott's virtue. He built the polarized electron beam.

Zierler:

And what was the significance of this measurement?

Baltay:

Well, it was the most precise measurement of the Weinberg angle, so that's the most precise measurement of the fundamental parameter of the electroweak theory. So all cross sections were predicted in terms of the Weinberg angle. And we measured it to something like a part in a thousand.

Zierler:

How long did you maintain your association with SLAC?

Baltay:

About 20 years.

Zierler:

And what other projects did you do with them?

Baltay:

Oh, maybe I should even say 30 years because, at that time, SLAC had the 80-inch bubble chamber, which was moved from Berkeley to SLAC, and I did an experiment on that. And that was in the early '70s. So I did an experiment at SLAC, but that was not a major experiment, not a famous experiment. But, anyway, I worked at SLAC on that. Then I went to Fermilab, did an experiment with the 15-foot bubble chamber. And, as I said, that turned out to be interesting because we showed that Gargamelle was wrong and Weinberg was right. And I think that was one reason why Panofsky and Richter asked me to be the coleader of the SLD experiment.

Zierler:

Mm-hmm. And SLD was designed to do what?

Baltay:

To look at Z decays.

Zierler:

Mm-hmm.

Baltay:

The energy of SLC, the SLAC linear collider, was designed to be exactly the Z-zero mass, which we knew from the CERN discovery of the Z-zero. So the aim was to make a lot of Z-zeros in a clean way. Other people with hadron colliders were also making Z-zeros, but I always thought that proton-proton collisions are colliding garbage cans with garbage cans because a proton is made of three quarks, and so you have six quarks interacting making lots of background, while e+e- is just so clean. You have an e+e- making a Z-zero sitting there in the center of mass in the lab and just watching it decay. I mean, what could be more beautiful?

Zierler:

[laugh]

Baltay:

So that was the goal of the program of building the SLAC linear collider and CERN building LEP, and CERN building four detectors. SLAC could only afford one detector. The e+e- linear collider only had one interaction point, so it only had one experiment.

Zierler:

Did you work closely with Burt and Pief?

Baltay:

Well, let me see. When I started, Pief was the director and Burt was the research director. But then—dates are kind of hazy now looking back, but after a year or two, Pief retired and Burt Richter became the director. So I worked very closely with him. I met with him for a couple of hours every month, sometimes every two weeks.

Zierler:

And what was the arrangement? Were you on leave from Columbia during this time?

Baltay:

Well, I was on leave for one year, but, no, I commuted. I mean, I flew across the country twice a month. Essentially, we had three days of "SLD week," and then it became once a month, but we had sort of three, four days every month. At that time no Zoom, so we had face to face meetings for 20 years designing the experiment and then running it and taking data, and then analyzing the data. On American Airlines I now have two or three million miles.

Zierler:

[laugh] Did you ever think about just taking a fulltime job at SLAC?

Baltay:

No, I am a university person. . We started SLD in '83. We finished in 2003. I moved to Yale in '88. And I liked the idea of Yale. I liked coming back to Yale. I always liked Yale. It also happens that Yale is on Long Island Sound, and I like to sail, so we had a sailboat and that was attractive about Yale. Don't say that I said that to Yale.

Zierler:

[laugh]

Baltay:

But then, in '86 I spent a sabbatical year at SLAC. That was the height of the design and building the SLD detector.

Zierler:

And when did that start?

Baltay:

We started in ’83 and were ready for taking data in '89.

Zierler:

OK, OK. And so, what were the decisions that led to you leaving Columbia and joining Yale?

Baltay:

Horace Taft and Jack Sandweiss were the professors that I did my thesis with. Horace Taft died very young. He was 57 when he died, They offered me his position, and that was too nostalgic to turn down. I mean, he was my thesis advisor, and I always liked Yale, even though I was very happy at Columbia. In fact, T.D. Lee tried to get me not to go, and I said, "T.D., do me a favor, just let me go." And he said, "No way." He then doubled my salary, offered me a named chair at Columbia, which was the best thing he could've done for me because Yale had to do the same, so that's why they offered me the Higgins Chair of physics with a double salary. [laugh] So T.D. knew what he was doing. He did me a huge favor by not obeying my request for a favor.

Zierler:

So it was really two things, it was the personal need to move and also this was a wonderful opportunity for you professionally?

Baltay:

Yes. And I liked the idea of Yale.

Zierler:

When you got to Yale, how had the department changed since your time as a graduate student?

Baltay:

Not a whole lot at that time. Well, Horace Taft had passed away. Jack Sandweiss, Bob Adair—I don't know if you know that name—was still there. Vernon Hughes was still there. So it was still very similar, but then the people I knew, my professors, started retiring. They asked me to be chair of the department in '95. And now the department is quite a different department. That's what happens in 30 years.

Zierler:

And you mentioned you took on a new project in 1989. What was that?

Baltay:

I'm sorry. A new project?

Zierler:

You took on a new project in 1989. What was that?

Baltay:

No. What did I...

Zierler:

In 1989. Something...

Baltay:

No. I continued with SLD at SLAC.

Zierler:

Oh, you continued with SLD. And how long were you with SLD?

Baltay:

Twenty years.

Zierler:

Mm-hmm.

Baltay:

So Marty and I were spokesmen—in fact, we were the longest lasting spokesmen for a major experiment. Most of the experiments had elections and they elected a new spokesman every three or four years. I remember Panofsky sat us down and said, "Charlie, there's no democracy in physics." He said, "Sixty-four clowns are not worth one Bill Willis."

Zierler:

[laugh]

Baltay:

[laugh] "So don't ever tell me that you did something wrong, because that's what the collaboration voted." He said, "You do the right thing. Your job is to motivate the collaboration to do the right thing."

Zierler:

Charlie, can you talk a little bit about how you stay on the same project for 20 years? What becomes new over the course of 20 years that demands your ongoing attention?

Baltay:

Well, the project had a very different nature as it moved along. I mean, for the first few years—let me see, from '83 to '89—oh, '89 we started taking data. Maybe that's what you referred to as a change earlier ….

Zierler:

Oh, right. OK. Right. And why were you starting to take data in 1989? What had changed in 1989?

Baltay:

For the first three, four years, we designed the experiment. And then we started building the experiment, and it was a very different trade, a very different job from designing. So in designing, you say, this is the physics we want to do, this is what the Z is likely to decay like, these are the kind of detector elements we need to see what the Z decays like. So that's sort of an intellectual, theoretical exercise. Then you decide how you are going to build a calorimeter, how do you build a magnet, how do you build various components of the detector. Following that starting to build the instruments is again quite different. We had at that time, a chief engineer, Bob Bell. Marty Breidenbach and I and Bob Bell went to see a major US company to build a superconducting magnet and we said, "We want a fixed price." And they didn’t want to give us a fixed price. They said, "We work on cost plus." And then Marty kept saying, "No. We wanted a fixed price." The guy looked at us and he said, "Let me tell you college kids something. You want a fixed price? We'll give you a fixed price. When we're halfway done, we'll then tell you what it really costs." And Marty said, "But we have a contract, we have lawyers" . and the guy responded, "Our lawyers are much better than your lawyers." That's when we decided to go to Japan to build the magnet. The detector cost 60 million dollars, or 100 million in today's currency, so negotiating the major procurements was a very different kind of activity—you don't get bored. Then when, in '89, we started taking data, that was a very different again. Then we started analyzing data. We started getting results. Then, in the '90s we were writing papers on physics results. And that was, again, a very different activity. And, by 2003, we were pretty much done, and we disbanded the collaboration in 2003.

Zierler:

And what had made you think that by 2003 the project had come to an end?

Baltay:

Well, we've pretty much analyzed all of the data. We stopped taking data in '97. So, by 2003 we had been analyzing data for six years, so that was enough. I mean, we pretty much did what we wanted to do, even though one or two papers came after 2003, we pretty much were done by 2003.

Zierler:

And, looking back over these 20 years, what had your research accomplished? How had it moved particle physics forward?

Baltay:

Well, we obtained the most precise measurement of the Weinberg angle, plus there were dozens of other results. The charm and the B quark were discovered, so one thing we did is a lot of B physics. Then we also did a lot of strong interaction QCD stuff.

Zierler:

Did you ever work with B.J. Bjorken?

Baltay:

Pardon?

Zierler:

Did you work with B.J. Bjorken at any point?

Baltay:

Quite a lot, and that was a very stimulating interaction.

Zierler:

On what projects did you work with him?

Baltay:

Well, I worked with Bjorken earlier when I was doing neutrino physics. The SLAC electron scattering experiments by Friedman, Kendall, and Taylor led to Bjorken scaling. Similar kind of effects were predicted to occur in neutrino scattering experiments, so we worked closely with BJ, as we called him, on checking out his scaling predictions which then led to the so called quark-parton model. You remember that in the '70s, neutrino physics was the hot stuff in particle physics. There were the Cline, Mann and Rubbia experiment at Fermilab, and Steinberger's experiment at CERN, but they were all huge, what we call counter experiments. They had steel plates where they could identify muons, but they could not identify electrons or strange particles. So, even though we were in a bubble chamber and therefore had much lower statistics, a factor of 100 less than the big experiments—I call them the big experiments—we had electron detection and we had strange particle detection, which they did not have.

So there were two areas where we did something that they couldn't do. One was the neutrino electron scattering to verify the existence of neutral currents and measure the Weinberg angle.. The only thing you see in neutrino electron scattering is a single electron, and they could not detect single electrons. A second area was a measurement of the rate of strange particle production. About that time Glashow predicted the existence of charmed particles, and we expected neutrino interactions to produce the predicted charmed particles, whose signature was their decay into strange particles. Our measurements of the strange particle production rates were consistent with the expectations and were thus a confirmation of charmed particle production in neutrino interactions. A theorist who gave us much guidance on charm and bottom production was Fred Gilman from SLAC, I don't know if that name is familiar to you.

Zierler:

Oh, yes.

Baltay:

He was a theorist. And the other guy we worked with a lot was Mike Peskin. So B.J., Peskin, and Gilman,. were valuable theoretical mentors, B.J. on neutrino physics, Gilman and Peskin during the e+e- days.

Zierler:

When 2003 came around, what did you know you wanted to work on next?

Baltay:

Even before that time the SSC was the big new project

Zierler:

You mean a decade earlier? You mean 1990?

Baltay:

Yeah. Well, let me see if I can remember. I was on the 1983 Woods Hole Panel that recommended the SSC.

Zierler:

Right, right. Do you remember what the big excitement was for the SSC for that panel in 1983?

Baltay:

Well, going to 40 GeV—40 TeV, I'm sorry. [laugh]

Zierler:

Right, right. Which would accomplish what? What would that accomplish going that high?

Baltay:

Oh, finding supersymmetry, finding new physics. It was a new high energy regime, and, historically, every time we made a jump in center of mass energy, we made new discoveries. So it was the mantra in particle physics that you must go up a factor of 10 in center of mass energy for a new facility. But the hot topics were, at that time, technicolor, supersymmetry. By that time, by '83, we had the standard model, but the standard model couldn't be the ultimate correct theory because it led to infinities in some cross sections, like WW scattering. So people knew in '83 that there had to be new physics. And, at that time, the theorists were pretty confident that it had to be at the TeV scale, that you had to have supersymmetric particles or technicolor particles at the TeV scale. So the goal of the SSC was to go to 40 TeV in the center of mass and discover all this new stuff. So that was in '83.

Zierler:

And were you involved in the cost planning for SSC? Were you involved in developing that initial number of 3 billion dollars?

Baltay:

Well, no, not 3 billion but 8.

Zierler:

Three billion was the initial figure. It came to be 8 billion, which was one of the problems.

Baltay:

Well it was 1.7 to begin with. At that time, Brookhaven was proposing to build a proton-antiproton collider called ISABELLE. That was in the late '70s, early '80s. So the '83 Woods Hole Panel was faced with the decision whether to proceed with ISABELLE at Brookhaven, or pursue another proposal by Bob Wilson, director of Fermilab—you must know that name, Bob Wilson—

Zierler:

Of course. Sure.

Baltay:

—who proposed what we called the Desertron at that time. In 1982, we had the first Snowmass meeting. You're probably aware of the Snowmass meetings?

Zierler:

Of course, sure.

Baltay:

I was chair of the Division of Particles and Fields of the American Physical Society that year, and I saw the labs doing their separate summer studies and fighting and competing, so I said, "Let's do a Snowmass independently of any of the labs." It was sponsored by the American Physical Society Division of Particles and Fields, and we did the '82 Snowmass meeting, at which Bob Wilson proposed the Desertron, which then became the SSC. So that was '82. The '83 Woods Hole Panel then said, let's not do ISABELLE but let's do SSC.

Zierler:

Was there controversy over that? Were there some people who felt strongly about supporting ISABELLE?

Baltay:

Yes, very much so. It was a split vote..

Zierler:

And what were some of the strongest feelings in support of ISABELLE?

Baltay:

Well, they said it was immediate, it was at Brookhaven, it was sort of the next easy thing; 40 TeV at that time was pretty outlandish. I remember Maury Tigner—I don't know if that name is familiar—

Zierler:

Mm-hmm.

Baltay:

—was on the Wood Hole Panel, and he predicted a cost of 1.7 billion. That's what we voted on in '83. OK. Then it became 3, then it became 6, then it became 8, and it was on its way to 11.

Zierler:

And where did 40 come from as the goal for the energy? Why not 50 or 30? What was it about 40?

Baltay:

I don't know. It's a nice round number.

Zierler:

[laugh]

Baltay:

Something that Tigner thought we could reach. I mean, it's funny how, when you justify a project, you justify it from a beautiful scientific theory, but, basically, the machine people say, this is what we can build. You figure out why you want it and how you justify it.

Zierler:

Yeah. Right.

Baltay:

So 40 TeV was a nice round number, and Tigner thought we could do it.

Zierler:

Is there a theoretical limit on how high that number could go?

Baltay:

Well, it's limited by two things, mostly by money.

Zierler:

[laugh]

Baltay:

OK. If you build it with conventional magnets, which are limited to 20 kilogauss, then the radius has to be prohibitively large and therefore expensive. Superconductive magnets that could double the magnetic field to close to 40 kilogauss seemed like the answer, halving the required radius. Even so the cost estimate was 1.7 billion dollars, which sounded to us like insanely expensive. We said, it's so expensive that maybe it'll catch congress's fancy, and that was the proposal put forward by the Woods Hole Panel. Our attention then focused on designing the detectors to be built for such an accelerator. I was involved in proposing one of the two detectors with Bill Willis. I don't know if that name—

Zierler:

Mm-hmm.

Baltay:

He died quite a few years ago, and Barry Barish, you might—

Zierler:

Sure.

Baltay:

So Barish and Bill Willis were the spokesmen the second experiment. I don't know why first or second, but one of the two experiments. And then—when was it? In '93, the SSC was killed by congress.

Zierler:

Were you involved in the various debates about where SSC should be located?

Baltay:

No. That was way beyond my pay scale. That was beyond any physicist's pay scale. That was politics.

Zierler:

So, as far as you're concerned, physicists didn't really care if it was in the desert or if it was in upstate New York or Dallas?

Baltay:

Well, no, we would've loved it to be at Fermilab in Illinois.

Zierler:

Just because you have an existing infrastructure there?

Baltay:

Right.. But then, I think it was politics. The Texas delegation promised a billion dollars or something. So that was way beyond our pay scale, the choice of Texas as where to build it.

Zierler:

So, in 1993 it ends. And I'd love to ask this question. It's a bit of a counterfactual. What has particle physics lost as a result of SSC dying?

Baltay:

World leadership in particle physics for the US. That's a gross statement but that's what it is.

Zierler:

To what extent has CERN achieved world leadership as a result of what it has done?

Baltay:

To quite an extent.

Zierler:

Period?

Baltay:

Yes. Right now, it is the Large Hadron Collider (the LHC) at CERN that is the pre-eminent facility in particle physics.

Zierler:

Is your feeling—

Baltay:

Most American particle physicists work at CERN on the Large Hadron Collider.

Zierler:

And is your feeling that CERN has accomplished everything that SSC would have if it was built, or were things that SSC would have done that CERN, even to this day, would not be able to accomplish?

Baltay:

OK. The answer to that is not known in the following sense: CERN only built 7 TeV on 7 TeV, so 14 TeV in the center of mass, compared to SSC's 40 TeV, so three times as high. Now, CERN found the Higgs boson, which is their credit, but they did not find any technicolor or any supersymmetric particles. Now, who can speculate that, if you had built 40 TeV, you would have a reach for heavier particles? Maybe with 40 TeV we would've discovered supersymmetry, which CERN didn't because they only went to 14 TeV. But maybe there's nothing happening between 14 and 40, so we don't know because we didn't look.

Zierler:

Now, when you say discover supersymmetry, does that mean that there's a theory of supersymmetry and you expect that an experiment would confirm that theory?

Baltay:

Yes. I mean, supersymmetry predicts a supersymmetric partner (the jargon) , for every known particle. So it would double the number of known particles. But it does not predict the mass scale, so we don't know what the mass of the supersymmetric particle is. So we have the electron, then there's the supersymmetric electron. There's the W and there's the wino. So every particle has a supersymmetric partner, but we don't know the masses. Now, theorists are never stopped by ignorance. They write papers and they used to say, oh, they should be around 40, 50 GeV, a 100 or so GeV. So we were looking for particles in that mass range, and the large hadron collider at CERN, to this day, has not found anything in that mass range. So maybe when they increase their luminosity something might show up, but so far CERN has, as I said, found the Higgs, which is fantastic. That's a huge step forward. But they have not found any new physics. I'm calling the Higgs sort of old physics. The Higgs particle was predicted by particle theory, by the standard model some 50 years ago. but we didn't know the mass. But the large hadron collider did not find any new supersymmetry or technicolor or any other new particles. So who knows if we had built a 40 TeV machine we might've found something, or we might not. We just don't know.

Zierler:

Now, imagine, Charlie, in a perfect world where congress gave you 15 billion dollars to do SSC 2.0. Would you still recommend 40 TeV or would you go higher?

Baltay:

No, higher. People now talk about 100 TeV. You want it to be a pretty significant step up from the LHC. A factor of 10 would be nice, but 14 to 100 is a factor of 7, that's pretty close. And 100 is a nice round number.

Zierler:

So I won't quote you on this, but I'm curious, what would be the price tag, do you think, in today's dollars for 100 TeV?

Baltay:

Oh, I have no idea.

Zierler:

Far more than 10, 15 billion dollars, though, right?

Baltay:

Oh, yes. I mean, if you say it's linear in the energy, because the circumference would be linear in the energy—well, it's not even known what the Large Hadron Collider cost because CERN does bookkeeping in a different way. In US bookkeeping, when you talk about the SSC, 8 billion, that included the stuff, the copper, the magnets, the vacuum tubes and all that, plus the labor. In CERN bookkeeping, they don't count the labor because, well, these guys are working for us anyway. We don't count them. But LHC must have cost, I would guess, 5 billion. So I would guess 50 billion.

Zierler:

Yeah, yeah. And that is probably something that you'll never expect to see actually happen?

Baltay:

That’s right. I mean, look, we didn't get 10.

Zierler:

What do you think the end of the Cold War—what impact did the end of the Cold War have on the death of SSC? Do you think it was significant?

Baltay:

I don't see any connection.

Zierler:

You don't?

Baltay:

No. I don't see any connection. I think it was simply that we learned that 8 going on 11 is just not in the cards for a particle physics facility. And now people are pushing the high linear e+e- collider as the next project, and that is estimated around 8 billion, and people are not taking it seriously.

Zierler:

Where would this be located?

Baltay:

Well, we wanted to build it in the US, but now Japan is talking about building it. And even then, it's sort of dicey.

Zierler:

What do you think about China's prospects for becoming a world leader in high-energy particle physics?

Baltay:

Could be. They're very ambitious in science.

Zierler:

And is your sense that they're doing good physics in China these days?

Baltay:

Not so far, although I'm not an expert at that. But they don't have any of the large facilities. Right now, the US, Europe, and Japan are the only three places where big machines are being built.

Zierler:

So let's talk about your transition in 2003. This is when you get into cosmology?

Baltay:

Yes.

Zierler:

What was your initial interest? Did you feel like there was only so much more that you could accomplish in particle physics, you wanted a new frontier to work on?

Baltay:

No. It's more intellectual curiosity. I was reading a book by Steve Weinberg a book called The First Three Minutes, and I said, oh, my God, this is fun. The Hubble constant, expanding universe etc etc. So I just got turned on by the science. Then, the thing that really did it was the discovery in 1999 that the universe's expansion is accelerating. And you say it cannot be. All the laws of physics say that the expansion has got to be slowing down, which you can see by considering gravity. You have all these galaxies. They have gravity between them pulling them together, so if they expand, gravity has got to slow down the expansion. So all the laws of physics we know say the expansion has to be slowing down, BUT the universe is ignoring us physicists and it's expanding faster and faster. So that was kind of—I said, "Wow! That's the most exciting stuff." We still to this day have no good idea of what is causing this acceleration, but we have given it a name, Dark Energy!

Then, when you do a little general relativity, based on the measured rate of acceleration you conclude that this mysterious new component of the Universe must have repulsive gravity to be pushing the universe apart, and must be about three quarters of the energy density of the Universe. So you say, here is three-quarters of the universe and we have no idea what it is. It has repulsive gravity, which we don't have any idea of. I said, what could be more fun? The recently discovered Higgs boson is about a lousy few percent of the universe. The stuff you and I are made of, atoms, particles, are a few percent of the universe. So all of this particle physics I've been doing is about a few percent of the universe. What's three quarters of the universe? And it's got to be new physics.

If I want to be grandiose about it, I say in the late 1880s, 1900s, people thought they understood physics. They had Newton's gravity, they had Maxwell's electromagnetism. People said, we understand physics. Then they looked at atoms, and atoms did not do what you predicted from classical physics. So atoms did what they were not supposed to do according to the current laws. So that made us invent quantum mechanics and relativity. In a sense, 100 years later, in 1999, we came to that point where we thought we had the standard model of particle physics, of all of physics, we understand physics, we can predict what the universe will do. And the universe is not doing that. So there has to be new physics. So, in a sense, if you want to be grandiose about it, we are at that point 100 years later where we say we don't understand gravity, we don't have a quantum theory of gravity, something new has got to happen. I mean, when we say three quarters of the universe is something new, that's pretty new.

Zierler:

And when you say "new," does this mean dark energy and dark matter?

Baltay:

No. Dark energy is three quarters, dark matter is about an additional one quarter. And I distinguish between the two, to me dark energy is much more mysterious in the sense that dark matter is invented to explain the motion of galaxies and it has attractive gravity. So it could be regular stuff. It could be the next super symmetric particle we find at the large hadron collider. It's not unusual stuff. It has attractive gravity, it has pressure, it has all the usual properties. Dark energy has to be different in kind from anything we know of. So they're really quite different. They're both called dark matter, dark energy just because we ran out of names.

Zierler:

[laugh]

Baltay:

We had to call them something different. Physicists learned a little public relations. Instead of calling the New York Times and saying, we spent zillions of dollars studying the universe and we have no idea what's going on. Instead, you say, we discovered dark energy. Isn't that wonderful? What is dark energy? We have no clue. We have no idea what it is. So, to me, that was just mind blowing. What is dark energy? So then I got into that, and it turns out that you cannot study dark energy with particle accelerators or any ground-based study.

Zierler:

Was this a surprise to you? Did you think that particle accelerators at some point would be relevant to studying these things?

Baltay:

No. You see, the acceleration was discovered in astrophysics in the properties of supernova explosions in outer space beyond our galaxy. So it was pretty clear that you could not touch it with particle accelerators. So that's when I started talking to people in the Yale Astronomy Department. They said, "What do you know about supernovas?" I say, "Nothing, but I'm learning fast." And then I hooked up with Saul Perlmutter, who I sort of knew, and then we are working now very closely with Saul on this WFIRST space experiment. Saul and I designed a supernova survey with this space experiment. We decided we had to go to space to study it, so that's what we are doing.

Zierler:

Charlie, what do you think all of your experience in particle physics, what does that bring to the table in your new interest in cosmology?

Baltay:

Oh, everything, in the sense that the physics, the math—I mean, supernova explosions are physics. There's iron that decays, there is oxygen, there is silicon, so it's nuclear physics. The explosion itself is physics, mass. And just an attitude of looking at things carefully and analytically and critically, and designing—I started out saying that I, in my career, went from bubble chamber physics to CP violations to neutrinos to e+e- interactions. At each step, I had to learn a new trade. At each step I had to learn new physics and new technology. So, to me, that transition from particle physics to cosmology is not that big a transition. It's the same critical thinking, it's the same putting together a collaboration, it's the same making a plan, figuring out how you can do it, how can you afford it. I mean, WFIRST now is a 3-billion-dollar project. So cost is a big deal of how you design the measurements. So, to me, it's really quite similar, and it just a transition in my career. [laugh] And, also, if I say, what am I really scared of? I'm scared of being bored. So you say, how did I do SLD for 20 years? Well, it was kind of time to quit.

Zierler:

Right.

Baltay:

And now I work with a new group. I now work with NASA, I work with different people, different customs, different culture. So, to me, it's now fun. I feel like a graduate student learning a new trade.

Zierler:

How did you connect with Perlmutter for this project?

Baltay:

Oh, I don't know. He was at Berkeley. He's a physicist. He's not an astronomer, he's a physicist. I sort of knew him. He was at Berkeley. I hung around Berkeley some. Then Saul is the one, you obviously know, who discovered the accelerating universe, got the Nobel Prize for that. Then he proposed SNAP, a space experiment. That was Saul's proposal. The whole WFIRST started with Saul. And, at that time, I was talking to the Yale astronomers of what is the next step, and I said, "Supernovas." But you wanted to look further and further back in time, which means further and further away in space. Is that connection familiar to you, then?

Zierler:

Mm-hmm.

Baltay:

The velocity of light is slow, so something that happened far away takes a long time for light to get here. So if you want to look further back in time, you have to look further away in space. And further away in space by Hubble's Law is redshifted. So the light from the supernovas are redshifted into the infrared. Infrared is heat, and the earth is hot relatively. Space is cool. I mean, the earth is like 300 degrees Kelvin, space is like 3 degrees Kelvin. So Saul Perlmutter proposed to go to space to do the next experiment on supernovas and I said, "Oh, my God. That's the thing to do." So then I called Saul, I started talking to him. Saul went to the DOE to propose this SNAP space experiment. And DOE put me on a panel to review that. And I remember sitting there reviewing Saul's proposal and I said, "Oh, my God. That's what I want to do. That's the next fun thing." I mean, one thing I learned early at Columbia from T.D. Lee and Leon Lederman is to look for the cutting edge. Look for the frontier. And I said in the 2000s, the frontier is cosmology. Now particle physics has a long range planning survey every 10 years, it's called P5 survey (Particle Physics Project Prioritisation Panel). I don't know if you've heard of that.

Zierler:

P5, of course.

Baltay:

Yeah. So I chaired the 2008 P5, and one thing we did is, at that time, Dennis Kovar was the Department of Energy particle physics guy. And he said, "Cosmology has nothing to do with particle physics. Particle physics is something you do with accelerators." And one of my jobs was to convince him that dark energy is at the very heart of particle physics. Because I said, particle physics is not defined by a tool, like an accelerator, but by an intellectual question. What are the fundamental constituents of the universe, and what are their forces or interactions between them? Here is three quarters of the universe. We have no idea what it is. That's the heart of particle physics. What are the fundamental constituents? The most prominent is dark energy. It has repulsive gravity. So I convinced Dennis that cosmology, dark energy is at the heart of particle physics. I don't know if you've seen that Venn diagram of three circles.

Zierler:

Sure.

Baltay:

So I made that up.

Zierler:

Oh, you made that up!

Baltay:

Yeah.

Zierler:

For what? What did you make that up for? Was that for an article?

Baltay:

No. I was chairing the 2008 P5 panel, and that was the cover of our report. But that one picture summarizes all of particle physics, and it had three circles. The top was the energy frontier, the large hadron collider; one of the lower circles was intensity frontier, neutrino physics, which is the Fermilab program; and the third was cosmology, dark energy, dark matter.

Zierler:

Charlie, can I ask, is it a two-way street? Are advances in cosmology—will they be helpful for advancing particle physics, as well? Does it work both ways?

Baltay:

Yes. To me, that's one of the wonderful things, that, initially, you had people, then you invented telescopes and went to astronomy, to bigger and bigger things. And you invented particle accelerators and you went to smaller and smaller things. And the two fields completely separated. Now they have come back together. Astrophysicists want to know, gee, have you guys found a couple of particles we could use as dark matter? What about dark energy? But it goes both ways. For example, another experiment I'm working on at Kitt Peak is a galaxy survey where I think we can get the best neutrino mass measurement. So that's really a strictly classical particle physics measurement, what are the neutrino masses? You must have heard about neutrino oscillations?

Zierler:

Of course.

Baltay:

They measure mass differences but not absolute masses of neutrinos. So we believe now—not everybody believes, but some of us believe—that you can get the best measurement from cosmology of the neutrino masses. So that's a straight particle physics measurement from cosmology, so it goes both ways. If the large hadron collider finds a supersymmetric particle, maybe that's what dark matter is. So, to me, it's wonderful that the two fields come together. And, in fact, I believe that I have not left particle physics, I just moved on to dark energy, which is part of the heart of particle physics.

Zierler:

Understanding dark energy, will that help create the grand unified theory that incorporates gravity?

Baltay:

If I knew I would publish immediately. I mean, we have no idea. Could be.

Zierler:

It's possible, though?

Baltay:

Could be. I mean, look, right now, we don't have a quantum theory of gravity, but, all of a sudden, gravity is up for grabs. Maybe there is repulsive gravity.

Zierler:

Charlie, how do we know that we need a quantum theory of gravity?

Baltay:

Oh, because physicists are simple-minded folk.

Zierler:

[laugh]

Baltay:

There's no better reason. It's just that, oh, there has to be a quantum theory of gravity. I'm exaggerating a little bit, but that's basically it.

Zierler:

I'll share with you Michael Turner—I'm not sure if you know Mike Turner?

Baltay:

Oh, I know him well.

Zierler:

So he gave me a great example about discovering dark energy. He raised the question, how do we even know we're looking in the right place? In other words, the metaphor is, when you're looking for a ring that you lost on a dark street, you're only going to look under the streetlamps 'cause that's where it's light.

Baltay:

Yeah.

Zierler:

So what do you think about that? How do we know that we're looking in the right places?

Baltay:

You don't. I mean, I think his analogy is right. You look where you can. In a sense, you say, what are we going to learn about dark energy? And the answer is, at the moment, we have limited aims. One thing dark energy could be is Einstein's cosmological constant. And that makes a prediction about the ratio of the pressure to the energy density of dark energy. Einstein's general relativity says, if it's a cosmological constant, that ratio has to be -1.0000. So that's the first thing we want to measure, the ratio of the pressure to the energy densities of dark energy. If it's exactly -1, then we say that's Einstein's cosmological constant, whatever that is. [laugh] If it's not -1, it's something else. So that's really the first thing we are trying to measure. Now, that's only a small corner of what you could know about dark energy, but that's what we know how to do, so that's what we're doing. We cannot do what we don't know how to do. [laugh]

Zierler:

Do we know what our limitations are?

Baltay:

"Our limitations are," in what sense?

Zierler:

When you say we only know what we know how to do, do we know what we don't know how to do?

Baltay:

You're getting to be like Rumsfeld now.

Zierler:

[laugh]

Baltay:

[laugh] There are known unknowns and unknown unknows. And I don't know how to answer that. I mean, we just don't know what—

Zierler:

It's the same as my question about the bubble chambers. Do you know the limitations of bubble chambers as you're working on them, or do the limitations really only become apparently retroactively when you're aware of the next technology?

Baltay:

It's the latter, I think, in the sense that, when bubble chambers were invented, it was the cat's meow. That was the new technology. And you started studying it and as you started, you were delighted with the low statistics because low statistics were better than no statistics at all. Then, as time goes by, people are saying, gee, I want more events, I want more statistics. I cannot do that with bubble chambers. So people like Fitch and Cronin invented spark chambers, wire chambers, other technologies. At first, we looked down on those guys. I said, "Look at this crummy picture you're getting. You're getting a bunch of sparks and no resolution. You don't see the event. You guys don't know nothing." But then they got more and more statistics and they started outclassing bubble chambers. And there was maybe a 10-year period when both were pretty current.

But then, with time, bubble chambers went out of fashion because they were limited in the statistics they could get. And the other techniques got better and better, and now what they're getting, for example, in liquid argon spark chambers looks almost like a bubble chamber picture, but they can get infinite statistics, or a lot more statistics. So it's that way, when a new technology is born, it's the exciting technology. And then, as time moves on, you find its limitations and you invent new technologies to get around those limitations.

Zierler:

Charles, you said before, one of your challenges is not becoming bored, right?

Baltay:

Yeah.

Zierler:

What are you most excited about in the future in terms of not becoming bored, about the things that will continue to engage your imagination and your interests?

Baltay:

Well, right now, I'm very excited about space, working with NASA on this WFIRST project, learning, what's an L2 orbit? How do you fire a rocket? How do you avoid single point failures? You have a camera, you say, I have a shutter, and the NASA engineer says, what if the shutter gets stuck? You have 3-billion-dollars-worth of space junk. So you better not have a shutter on your camera. So you learn a new trade. You learn a new technology. I remember when I was first reviewing some space projects, they said, well, we're writing the program to launch this thing, and it's 30-million dollars to develop that program. And, like a dumb jerk, I said, "I could write that program with a graduate student over the summer." And then, they said, then what? And then we debug it. He says, "Look, if the thing doesn't work in the first two seconds, it's all over." Right? You launch a rocket, if it doesn't work in the first two seconds...so NASA has a completely different culture. So, to me, that's exciting. I'm learning a new trade. I'm learning a new culture. And so I'm looking forward to it. I have been quite involved with Saul Perlmutter about designing the mission, and we are now at a point that NASA says, OK, you guys write a design report and you go away and we'll build it. In five years, we'll give you a call that it's ready to launch. But, in the meanwhile, what we're doing is developing the software, developing the data analysis algorithms, so this is all new stuff to me; all new stuff to anybody. So that's exciting.

But it's very similar to when we designed SLD. At first, we didn’t know what we were doing, and then we started studying, and we learned. We worked with a group of 100 people. Now WFIRST is working with a group of maybe not 100, but 30 or 40 scientists—maybe it's 100. So, to me, that's exciting. It's a new business. It's a new trade. But it's sort of, to me, a succession to particle physics. And, as I said, my big contribution was convincing the department of energy that it should be part of particle physics so that they're now supporting a lot of cosmological activities.

Zierler:

Charlie, when you say that particle physics concerns itself with one or two percentage points of all the matter in the universe, and then dark matter and dark energy make up the vast majority—

Baltay:

Yeah.

Zierler:

—is that another way of saying that, proportionally, understanding dark matter and dark energy is much more significant?

Baltay:

Oh, I don't know. No. That's a big statement. That's a big statement. And most particle physicists say, gee, I wish you guys wouldn't be taking our good money playing with astrophysics and cosmology.

Zierler:

[laugh]

Baltay:

Although, if you look carefully, on particle physics PR publications, increasingly, they have pictures of galaxies and stars on the cover. So I think that, even particle physicists are beginning to see that dark matter, dark energy are exciting, and that they're part of particle physics. But, as I said, right now, there's still some differences of opinion, but now DOE has accepted those three circles in that Venn diagram. And even the Office of Particle Physics now has three subsections, the Intensity Frontier, the Energy Frontier, and the Cosmic Frontier.

Zierler:

Well, Charlie, now that I think we've gotten right up to what you're doing up to this very day, I think I'd like to ask you one last question. It's a very big question and it's one that will ask you to consider both your career retrospectively and these things that we've been talking about in terms of what you're excited for the future. And it seems like one of the big themes in our talk today has been advances in technology and how that's helped you, in your work, advance the field forward. So I'd like to ask you, both in terms of your past accomplishments and what you hope to achieve in the future, where do you see technology among all of the things that are required to make for successful research? In other words, there's hard work, there's technology, there's some luck, there's the people that you work with, there's the budgets. Where do you rank technology among the things that are most important for making the next big discovery, both as a matter of what you've accomplished in your past and what you hope to accomplish in your future?

Baltay:

Well, if you want to catch a bigger mouse, you gotta build a better mousetrap. So, when you want to address a question like dark energy, you need technology to build the instrument to do that measurement. If you didn't need new instruments, the experiment probably would've been done before. So most big steps forward involved new technology. If you only had your eyeglasses on your nose, you couldn't see a supernova and you couldn't see a quark or an electron or anything, right? So astronomy started taking off when Galileo built a telescope. That technology moved astronomy forward. When we learned how to do space missions, that moved astrophysics an incredibly giant step forward. You now have the Hubble space telescope. We can see further. We can look further back. So technology enables science.

So, to me, science and technology are two different but complimentary parts. You cannot do science without technology. If you want to measure the size of this table, you need a meter stick. You can't get around that. If I want to measure it more precisely, I need a more precise meter stick. It's as simple as that. If I want to measure atoms, they're so tiny that I need an accelerator and bubble chambers to look at what's happening. So technology is required to do science. Well, unless you're happy to do what's been done before. But, if you want to keep making steps forward, if you want to work at the frontier, you need to invent new technology. For the astronomers, you need to build bigger telescopes. When CCDs were invented, silicon devices, they replaced photographic plates. It was a huge step forward in astronomy. Computers are enabling us to do statistics we couldn't have dreamed of before, so technology is just absolutely crucial. And doing new physics, new frontier physics, involves building new instruments, new technology.

Zierler:

Charlie, are you optimistic that society will continue to support these new technological endeavors?

Baltay:

Well, again, the answer is yes, but with a limit. In a sense, with the SSC, we learned that limit to be around 10 billion dollars. We did the experiment, that congress said 10 billion is too much for a particle physics experiment. We are now building WFIRST for 3 billion, and that looks like that's gonna fly. So I think I'm optimistic that society will support basic science up to a limit of billions of dollars but not tens of billions. So that's sort of a short answer. But predictions are hard, especially about the future, so who knows.

Zierler:

If you were given an opportunity to speak before congress as being a scientist who was part of that ask for this level of support, what would you tell them?

Baltay:

Well, I did that. After the 2008 P5, we visited congress and told them that, in a sense—you tend to make the historical analogy, that back in the early 1800s there was this guy, Faraday, who kept dropping frogs' legs into vinegar to see it twitch, and then started learning about electricity and learned about electrons, and who could care less, right? Well, that led to electromagnetism, which is your life today. When the electricity goes off, you're dead in the water, right? Your car won't work, your house won't work. I mean, right now we live in an electromagnetic society. And that took maybe, what, 50 years, 100 years? From basic research to where it is a way of life. Nuclear physics, quantum mechanics, relativity started early in the 1900s, 1920s. Atomic energy is just now beginning to be significant in reducing carbon emissions by building nuclear power plants; another 50 years, 100 years.

But the historical precedent is that, whenever you learn something basic about science, which most people couldn't care less about, it changed your way of life. I remember I was at a cocktail party talking to people. I was talking to a Wall Street broker, and I said, "I'm all excited about the age of the universe." And he looked at me and said he couldn't care less. "You tell me what the stock market will do Monday morning, that's important. The age of the universe, who could care less?" So basic science is esoteric, egg headed, few people do it. But eventually, understanding about nature leads to a way of life. And I don't know which particular endeavor will lead to a life-changing thing. Thermodynamics led to the steam engine, locomotive, cars, Carnot cycle. Many, many examples of irrelevant basic science leading to hugely important consequences. And, if history is any precedent, what we are doing now is going to shape the future.

Zierler:

Well, Charlie, from what you say, I'm excited. That sounds good to me!

Baltay:

OK, good. [laugh]

Zierler:

Charlie, I want to thank you so much for your time today. It's been such a pleasure talking with you.

Baltay:

OK, good.