Paul L. Schechter

Zierler:

This is David Zierler, oral historian for the American Institute of Physics. It is January 25, 2021. I’m delighted to be here with Professor Paul L. Schechter. Paul, it’s great to see you. Thank you so much for joining me.

Schechter:

It’s my pleasure.

Zierler:

Alright. So, to start, will you please tell me your title and institutional affiliation?

Schechter:

I am professor “emeritus” at the Massachusetts Institute of Technology, where I was the William A.M. Burden Jr. Professor of Astrophysics. William A.M. Burden Jr. was described by his granddaughter as being a part-time anti-Semite and a full-time alcoholic (laughter). He had a successful career as an investor in aviation, and his great grandfather made money — Henry Burden, I believe it was — made his money selling horseshoes to the Union Army in Troy, New York. This is a lot like Carnegie. I was at Carnegie Institution in Washington. Carnegie made his fortune selling steel plate to the Navy. Now, you know, the steel that one uses in ships is a very different thing from the steel one uses in rails. And so, he charged five times as much (laughter) per ton to the Navy as he did to the railroads. So, I am — that’s a bit of my background, or the background of people who supported my work. So, I retired at the end of — let me get this right; it’s been four years — at the end of 2016. I would have retired sooner, but my partner wouldn’t let me.

Zierler:

Paul, I’d like to ask a very in-the-moment question because of your ongoing activity, your pulse on the field in observational astronomy and cosmology. And that, of course, is about the pandemic. Theorists have it easy. Right? They’re doing great right now, with their equations. They’re doing well with the relative physical and social solitude. In terms of your work, your collaborations, generally your awareness of what’s going on in observational cosmology and astronomy: what have been some of the advantages, perhaps, in the world of remote data analysis? And what projects have really slowed down that require the physical presence to be there, day in and day out?

Schechter:

All the observatories closed down, and they opened slowly. And various considerations were: what fraction of their operation could be done remotely? What fraction of the instrumentation could be successfully run without somebody who really knew how to run it, on-site? So, when they reopened, they reopened with a limited complement of instrumentation. And then there were the issues of the safety of the staff of the observatories. So, reopening was actually much slower in Chile than it was in Hawaii, because the epidemic hit Chile much harder than it did Hawaii. And there was talk for a while of some of the observatories there closing down again. Some colleagues of mine are very proud of having been the first remote observer to get going on such-and-such telescope again. A lot of what people do these days follows on big surveys of various sorts. You know, survey work is the great work of astronomy. And then when somebody finds something interesting, everybody jumps on it. And that follow-up has been slowed down. So, people have lists of objects they want to observe and haven’t been able to get the time to observe them. They also have vast stores of data that they haven’t yet reduced (laughter). And they also have access to these various surveys that are being mined that they’re still working on, to change the metaphor, to low-hanging fruit, on these surveys.

So, since retiring, I’ve put more — I took my last trip to the Magellan telescopes on Las Campanas in Chile in November of 2019. And I had actually decided at that point not to ask for more telescope time. One reason I was continuing getting telescope time was that I, after retirement, remained MIT’s Magellan director. Magellan is a consortium. There are five partner institutions, each with a percentage of the time, and I was responsible for MIT’s piece of this. But at the end of 2019, I stopped doing that and therefore didn’t feel the need to visit the site and see what was going on and get a feel for what was going on. I hate doing that because I love serving so much. I love being there so much. But I actually had not been planning to observe in the spring of 2020. So, it has affected me less, and I still have colleagues who are getting data remotely, and so I’m still seeing data coming at a slower pace. The space telescopes are still working. That’s still coming in. Some of the surveys are going on, sometimes at a slower pace. So, it has been slower. This has been a lost year for everyone.

Zierler:

Yeah.

Schechter:

And that means not just physicists. It means everyone.

Zierler:

Absolutely.

Schechter:

You know, to varying degrees. So, who lost how much? How much did your kids lose in school? How much did — you know, maybe the physicians are making out better, but most people have seen losses – people who have lost family and relatives, people who have lost time that they would have spent doing things they couldn’t do. Everybody’s lost stuff. So, I’ve lost contact with people who I would have — you know, there are meetings I would have gone to.

Zierler:

Right.

Schechter:

So, we just had a remote kickoff session. One meeting was built around writing a book. So, it was to have been a kickoff week, and then we would break into groups and write chapters. So, we inverted that. We had the kickoff meeting, and we will congregate in Bern, Switzerland, perhaps in August, once the book is written, to discuss what we came up with, with the chapters. Everything’s been shuffled. But people just aren’t doing as — working as — producing as much. Let me say that. Now, you wouldn’t know that from looking at the stats on [arXiv.] You know, if anything, the numbers have been greater. It is, nonetheless, my impression that my colleagues have been less productive over the last — I think that’s not true for me, although it might be.

And I think I’m just particularly isolated. I have a partner who lives in another city. Instead of traveling, every other weekend, it’s been — you know, I’ve made three trips over the last eight, nine months, of ten days each. Was it two, or was it three? Three. And 10 days at a shot. And then there’s Skype. So, I’ve had more time, and I’ve been very happy. I’ve also been working. I worked with — I stopped taking on graduate students, because the graduate student is, at this point in my career, too big a commitment. But MIT has — I don’t know if you know — a fabulous tradition of incorporating undergraduates into research, and you know, they range from mediocre to pretty good to totally spectacular. And so, it is just enormous fun working with at least two out of those three (laughter). And you know, we publish papers. And you can give these undergraduates projects that are dicey, that may not pan out — you know, that are notions. And if it doesn’t go anywhere, you haven’t ruined their lives. They’ve had a good experience. Whereas, with a graduate student, if you get a project that’s a bad project, (laughter) it’s much worse. So, I enjoy working with the undergraduates enormously. I take on three at a time. I don’t have anyone between me and them, so I spend an hour with each of them for Zoom time. Zoom scheduled for an hour. Sometimes, it’s less than that. And that’s been good. So, you know, I miss my colleagues. I miss the face-to-face. The other day I said that Zoom is the geometric mean of telephone conversation and a face-to-face conversation, and it’s a good first approximation.

Zierler:

Paul, before we go back to your family background and your childhood, by special request, I know you wanted to talk about Simon White’s paper, “Fundamentalist physics: why Dark Energy is bad for Astronomy.” My first question there is: what is your connection to Simon White? Do you know him personally? Have you worked with him?

Schechter:

Jesus. You really don’t do much astronomy, do you? (Laughter) I’ll exaggerate a little bit. But when it comes to astronomers, the question might be: have you slept with that person? (Laughter) You know, and barring that, have you spent a night awake in a control room with that person? It was a very much smaller field. It’s a bigger field now. But we were working on roughly the same stuff at the same time. We came up at the same time. We corresponded. I don’t know if I’m on a paper with him, but we were — and I was a fan of his. You know you have, even in your cohort, there are people whose work you like, about which you are more or less enthusiastic.

Zierler:

Sure.

Schechter:

And I was enthusiastic early on about Simon’s work.

Zierler:

What is compelling? What is it about this paper that you wanted to talk about?

Schechter:

There is a phenomenon underway, a mass migration. You know, the great northern migration. It’s the great astronomy migration of physicists. And Simon is warning this smaller astronomical community, where everybody has been in bed with everybody, that things are changing, and you want to be careful about embracing this phenomenon in particular, because it’s going to change the way astronomy is done.

Zierler:

And what phenomenon is that? The convergence aspect of dark energy?

Schechter:

It’s not a convergence. You have major labs with great groups of people, and they’re kind of wondering what they should do next. And they look over into what astronomy is doing, and they say, “Hey! That’s pretty exciting.” And you know, someone like Mike Turner says: hmm, let’s call that “dark energy.” And then suddenly, it’s the Department of Energy. So, the Department of Energy is very happy to have Fermilab work on the Dark Energy Camera — the Dark Energy Survey and the Dark Energy Survey did a great job on that. They’re very happy to have Fermilab work on the camera. They were happy to have a Dark Matter Center in Berkeley back in the nineties that started the MACHO search. They’re happy to have SLAC building the camera for what’s now called the Rubin Observatory. They’re happy to have Lawrence Berkeley Lab working on DESI, on the Mayall Telescope. In each of the major labs — and I can’t quite point to something for Argonne that’s quite the same — but a major fraction of the effort in all of these is doing what people would call astronomy.

Now, when the Dark Energy Camera was just getting going, there was a meeting of interested people at Harvard in — I think it was 2003. I gave a talk there. And there were thirty, forty people in the audience. You know, it was a physics talk. And I don’t recall who organized it. I suspect Chris Stubbs was in there somewhere. Tony Tyson was probably in there. I asked people in the audience, “How many of you have ever called yourself an astronomer?” And maybe two of the people raised their hands. And I said, “Well, you might want to try that out for size, because for the next ten years, what you’re going to be doing is astronomy. It’s not physics.” And most of what they’re doing is astronomy. And then, there’s an overlay of physics, of course. There’s how many papers every day, with yet another variant of dark matter? If you searched for theories of dark matter, there’s a nice plot that shows (laughter) them all laid out, all the different kinds. And there must be — I’d be surprised if there aren’t a hundred kinds of dark matter. I wouldn’t be surprised if there are 300. I’d be a little surprised if there are a thousand.

So, there have been three great astronomical discoveries in the last — the last four great astronomical discoveries that have pulled physics towards astronomy, because that’s where the action is. And to a certain extent, it involved me. The cosmic microwave background; the deficit of neutrinos that were expected from the Sun — we now know why; the adoption of what astronomers were first calling “missing mass,” and then sometime in the 1970s and the early 1980s, it’s changed from “missing mass” to “dark matter,” as the name of the phenomenon. It’s a question of going from a name that describes a symptom to a name that describes the explanation. And then finally, the acceleration of the universe, which we’ve assigned some physics to and called “dark energy.” You know, if there were such a thing, then it would produce this acceleration. And people are flocking to this, because they’re finding it more interesting than the other options. And here, you have astronomers who are just doing what they were doing, suddenly having all these new friends wanting to use their telescopes. Now, in fact, Fermilab saved Cerro Tololo by building a new instrument for the Blanco Telescope and having it run on the Blanco Telescope. The national observatories are having trouble supporting the stuff that they built in the seventies, because there’s new stuff that they’ve built, and the way funding works — particularly with the NSF — is that construction, MREF or something like that, major research facilities — you get extra money for, but operations has to come out of your ongoing budget. And so, when you build something like Gemini and the new solar telescope in Hawaii, and ALMA in Chile, that’s fine. All the construction money comes — is extra. But then, you have to squeeze it out of everything else, the grants program, and whatever facilities you had built before. So, saviors. Fermilab comes along with a camera for the Blanco Telescope in Chile. Lawrence Berkeley Lab comes along with a new robotic fiber positioner to measure spectra for the Mayall Telescope at Kitt Peak. What could be better?

Zierler:

Paul, if I may — so, we’re describing a sociological phenomenon, where there’s a bandwagon effect of physics coming to astronomy.

Schechter:

Are we supposed to go there?

Zierler:

Well, let me ask the question, and we can pick whatever cliché we like: “Imitation is the best form of flattery”; “Let a thousand flowers bloom” — what exactly is the problem? And I understand you’ll be coming at this from the sort of turf perspective of: what’s the problem of all of these new people flocking to astronomy, if that’s where the action is?

Schechter:

Well, they do their science in very different ways. Best thing about being retired is not sitting on committees, and a lot of those committees involve promotions. Promotions for high-energy physicists are exceedingly difficult, because you try to get outside letters and figuring out who did what is really hard. And everybody on the inside: oh, yeah. He’s wonderful. So, there are these huge collaborations, and you know the size of the collaborations. You know, my work was done in ones and twos and threes, with people who were friends. Do you know Zipf's law?

Zierler:

Don’t know that name.

Schechter:

Z-I-P-F. Very, very crude — the biggest contributor to anything is as big as the next two contributors, is as big as the next four contributors, and so forth. Refine that, and the contributions are harmonic: 1/n, when you rank them. You know, what are we talking about? We’re talking about letters in the alphabet. We’re talking about dollars contributed to MIT. We’re talking about the mass contributed by stars in the universe. Everything, very roughly, harmonic distribution. What that means is that if you rank order the authors on a paper, the first three authors contributed as much as the next twenty. Nonetheless, you’re carrying this huge army. I’m now working with a group that’s — they’re not part of the dark energy collaboration. We are an external collaboration, so it’s like a green card holder. You’re not full citizens. We can work, legally, (laughter) on the data. I have a data green card. And when I started with this group, I was going to Magellan. I had some telescope time. “Paul, we’ve got some candidates. Could you check these out for us?” “Fine.” Went to Magellan, wrote the paper, ready to go, six days later. And it takes a month to go through the collaboration’s elaborate vetting process. So, the style is very, very different. You know, some of these telescopes — the Dark Energy Camera — Brenna Flaugher is her name. She oversaw that project. The Dark Energy Camera is fantastic. It’s producing fantastic data. And I’m delighted to have a shot at it. Unlike the NSF- and NASA-funded surveys, the Department of Energy is much less interested in how the data gets distributed to the larger community. They have a tradition of working on the data yourselves within your collaboration, and less so of making it available to the larger community. So, I’ve got a green card. I have some access to the data, but I have to be careful. And there are the major issues and the major issue is dark energy, naturally. So, my interests don’t run along that line, so I have to be —

Zierler:

Paul, let’s not take our terms for granted, because different people understand these terms differently. So, for you, where is the overlap, and where is the distinction, with astronomy, astrophysics, and cosmology?

Schechter:

I never call myself an astrophysicist. I don’t need the fig leaf of physics. I’m proud to be an astronomer. And people who use — my mother would never call me an astronomer. She always called me an astrophysicist, because that sounded fancier to her. And I think there are a lot of people who use the word for just that reason, taking their cue from my mother, which is a good thing to do (laughter). You know, it always served me well. So, they want to sound fancy. First of all, I have a degree in physics. Do I use physics? Yes. So, do you know the difference between physics and astronomy?

Zierler:

Well, I’m asking you the question, and I get many different answers from many different people, so what’s your answer?

Schechter:

That’s it. The right one (laughter). There are two people in my department who work on neutron stars. Deepto Chakrabarty is an X-ray astronomer, and Krishna Rajagopal is a theorist. Now, they’re both doing more administration and less working on this, but their interests are fundamentally different. Krishna is interested in neutron stars for what they can tell him about the equation of the state of matter at high density — at lesser temperature, but high density. Deepto is interested in physics for what it can tell him about the phenomenology of neutron stars. So, physicists are consumers of astronomy, and astronomers are consumers of physics. The goals are different. One is to understand the fundamental laws of nature, and one is to understand the manifold ways in which they play out in the universe — which, we discover new ones every day. And so, one primarily takes its excitement in the, “Well, who’d have thunk that,” and the other takes (laughter) yet another way in which nature comes up with a way to cook these things. And the physicists want to know the laws and how they play out as secondary. Now, you could say: how is this different from condensed matter physics, where you know the laws, and it’s just consequences? It’s not. You know? And by my definition, the condensed matter physicists are really materials scientists, but if they want to call themselves condensed matter physicists, that’s fine.

Zierler:

(Laughter) Well, I’m glad we know where you stand on these things. That’s quite useful as we develop this narrative. Paul, on that note, let’s go all the way back to the beginning. Tell me about your parents. First, where are they from?

Schechter:

The Cross Bronx Expressway (laughter).

Zierler:

I know it well.

Schechter:

Uh huh. Well, there’s a great book by Robert Caro that tells you about people who were pushed out of the way by the Cross Bronx Expressway, of whom there were a quarter million. And that’s where they’re from. My father had a degree in chemical engineering from City College. He had a last name which made him unemployable in the chemical engineering business.

Zierler:

Because he was Jewish?

Schechter:

That’s right. You know, he had friends who changed their names, from Rosenberg to Redmont (laughter). And similarly, from Cohen to King, and some of them got by with this, and he didn’t. He got a job after graduating from City College, first working with garbage in the New York City Sanitation Department — a sanitary engineer. And then around Binghamton, New York — he had done a paper in college on concrete, and so he got a job working near Binghamton upstate New York on a flood control project that had a lot of concrete being poured. From there, he was hired — he was drafted. He served as a tech sergeant in a toxicology unit in New Guinea, largely analyzing the blood of soldiers who were poisoned, most of whom poisoned themselves with methanol. When he got out, he got a job briefly working for a distillery in Philadelphia, but his family was in New York. So, he took over my grandfather’s business, which was a grocery-style deli in New York. And so, he ran that deli for twenty years. Long hours, weekends. He had a partner, and they were open from 8:00 in the morning to 11:00 at night.

I was born in the Bronx, Lebanon Hospital, now the poorest congressional district in the U.S. The center, in the early days of COVID-19. A very poor neighborhood, represented last year by Representative Serrano. Now, parts of it are represented by Alexandria Ocasio-Cortez. And that neighborhood has changed many times. You know, the number of famous alumni from that neighborhood is huge. But Molly Goldberg — I don’t know if you know who Molly Goldberg is. She was a fictional character on TV, very, very early on. And Molly Goldberg had a fictional address, which was around the corner from my father’s store (laughter).

When the Cross Bronx Expressway went through, anybody — you know, people left that neighborhood in droves. My parents moved to Queens. I was seven — very far from — well, you take the Flushing Number 7 line. You may know something about Queens. You may know something about Flushing — to the very end. Then you take a bus, from the beginning of that line to the very end. That gets you to the community in which we grew up. It had been a woods, which had been cleared for development. It was, in its way, quite nice, but it was hard to get into New York. I would go into New York, weekends, to use the Donnell Library, on 53rd Street, opposite the Museum of Modern Art, and to visit the American Museum of Natural History, where I took some classes, and I also loved the dioramas. I did well in school. Things were very competitive. That was fine by me. Everybody applied and tried to get into the best college they could, not very different from now, except for you were limited to just three. I got into Cornell, which in hindsight served me well, although at the time, I might not have thought so. I got a good education in spite of myself. I would have gotten a better education if (laughter) I’d paid more attention to my studies. I made some great friends. I learned a lot. And that —

Zierler:

Paul, what do you think the effect was of watching your father, who had a scientific background but did not work in that for the latter part of his career — what was the influence of that on you?

Schechter:

I can’t overemphasize it. I had to pull this off.

Zierler:

Was it always science for you, that as a kid, this is the area that you wanted to go into professionally?

Schechter:

I told people I was a double major in math and physics, and that isn’t quite true. I never did the paperwork for the physics degree. I did the requirements. So, (laughter) my degree is in math. And you know, I sent you a little anecdote, which I don’t know how you deal with such things in your oral history. But those words are the way I tell it, so if you just want to quote the paragraph —

Zierler:

No, please. You say it. I want to hear it from you.

Schechter:

I’m going to read it. Okay. So, this is something that I sent in an email to an advisee a few years ago. “On a cold and gray December morning, forty-nine years ago, in my senior year at Cornell, I ran into Al Silverman, who had been my research supervisor the previous summer. At a greasy spoon on College Avenue, he asked whether I was planning on going on to graduate school, and I replied that I wasn’t sure that I really wanted to. He then asked if there was something I would rather do, and I said, ‘No.’ He explained that a friend of his at Caltech asked if he knew any people who would be interested in grad school. He said that if there wasn’t something I wanted to do more—he thought I would make a pretty good physicist—and that he was going to write to his friend, saying I would apply. ‘Don’t make a liar of me,’ he said.” So, in fact, I did get in. They expected me to do high-energy physics. I deferred for a year, because the Vietnam War was underway, and they had eliminated student deferments. I taught in New York City schools for a year and decided to risk the draft. I flunked my draft physical because of eyesight. I don’t know if you know — the reason that they could flunk you because of eyesight is not because you couldn’t shoot straight, but people who are high [myopes] are at risk for retinal detachment, of which I have subsequently had two. And they just didn’t want to support blind people in the VA hospitals (laughter). So, I got out on eyesight and was able to go to graduate school after a year — the year teaching in New York was very, very interesting. I have many stories. They’re mostly funny, in a very sad way, and sometimes they’re sad without being funny, and sometimes they’re terrible without being funny (laughter).

Zierler:

Paul, were there any professors at Cornell who you became close with, or who gave a formative influence to your intellectual development?

Schechter:

Absolutely, Al Silverman. I have to be careful what I say, because there are people from his group who are still alive and active in the field. But he took a liking to me. And I’ll tell you how I met him. I had worked the previous summer on the Cornell synchrotron, which has had subsequent names. You know, building the very first one, on the construction — so, it was a forty hour a week job, 8:00 to 4:00. I wasn’t working for scientists. I was working for the construction crew, working on the magnets. And I was doing vacuum work and vacuum testing. And so, that was my summer job.

I saw Robert Wilson all the time. I would spend a day in the tunnel. You know, you would go in at 8:00 in the morning and leave at 5:00 in the afternoon (laughter). Was it light or was it not light — surveying in the magnet, stuff like that. The following year, I was looking for a summer job, and the building Newman at Cornell had a sub-basement. And the professors — and I was going to look for the professors — were on the top floor. It was three of two or three. Three, let’s say. And so, I started out in the sub-basement for some reason. You know, going to ask people if they had a job. I didn’t know if I was looking for someone in particular. I don’t recall. But I got into the sub-basement, and there was this guy in the sub-basement in the elevator, and the elevator was going up. It’s a freight elevator. It’s really slow. You know, so we go past the basement. We get to the first floor, and I look at this guy and say, “Would you happen to have a summer job?” And he said, “Well, who are you?” And it was Al Silverman. And he said, “Well, yeah. Sure” (laughter). “Let’s give this a try.” So, that shows how seizing the initiative matters. I worked in a little lab. There were some people working — I worked on a beam-spill monitor, photomultipliers. And it was mixed there, theorists and experimenters. So, my office — which was open and had a bench — was opposite Ken Wilson’s office.

Zierler:

Wow.

Schechter:

And Ken Wilson, whom I had seen at the folk dancing club there — Ken Wilson just leaned against his doorjamb for the eight hours that I was there. I don’t know how much longer he did that (laughter). Looking at me. And I was his inspiration, I’m quite sure. Yeah. Do you know that he was given tenure without having published a paper?

Zierler:

I did not know that. I know that getting tenure for Ken Wilson was a foregone conclusion, but I did not know that he did it even without a paper.

Schechter:

(Laughter) You know, I knew he was some kind of theorist. I didn’t know what he was working on, of course. So, let me tell you, while we’re on the subject, of Bill Press. When I get to Caltech, it was rough. It was rough. I told you I wasn’t a very good student, and they were pretty taken with themselves there, with good reason. I took a course in mathematical methods in physics. And the first problem set back — I remember precisely — it had sixty points’ worth of problems, and I got thirty of them. And I looked next to me, and the guy sitting next to me got sixty out of sixty. And I had worked hard on that problem set. And I was devastated. I didn’t know that the guy sitting next to me was Bill Press. [That’s the Press who also subsequently wrote the book on numerical methods in physics.] His mathematical methods in physics (laughter).

Zierler:

Right.

Schechter:

I think he didn’t know he was Bill Press (laughter).

Zierler:

(Laughter) That’s great.

Schechter:

But it turns out, things worked out okay for both of us.

Zierler:

Yeah.

Schechter:

But during the entire time there, you know, they talk about impostor syndrome. Who doesn’t have impostor syndrome?

Zierler:

Sure.

Schechter:

You know, I certainly had it when I was at Caltech. You know, I had it when I was at MIT. You know, there were all these great people at MIT. Who am I among all these terrific people? But you know, they seem to be fooled, so let’s just keep playing it.

Zierler:

Paul, what advice did you get about what kinds of graduate schools to apply to, who you might work with, what kind of career you wanted to pursue?

Schechter:

I just applied to the ones Al Silverman told me to.

Zierler:

Yeah.

Schechter:

And the only thing I had done — I actually did very well in a condensed matter class, but that was actually after the applications went in. I applied to the ones that Al told me to, and that was it. You know, I was not very engaged, the exception being that I did work for Silverman, and he liked what I had done for him. So, my grades were less than spectacular. My graduate record exams were pretty damn good, reflecting those two statements, both some weaknesses and some strengths of mine.

Zierler:

Did you have well-formed ideas about pursuing a degree in experimentation or even theory?

Schechter:

No. I actually kind of liked the idea of theory more, but that was fantasy. I had no idea what either meant. The first year, I got a sense of what experimental physics was. I worked in the basement of the Kellogg Lab, where I forget what it was we were bashing into what, you know, nuclear astrophysics. And I wasn’t liking that. So, here we go on to some interesting stuff — you’re going to find more interesting. I actually mentioned that I enjoyed folk dancing. There was a folk-dance café in Pasadena, that I frequented. And a guy who I knew there — I liked him; he was a friend — had a copy of Scientific American, and in it there was an article by Joe Silk. And he showed me this thing. It was on galaxy formation. It was shortly after the Silk mass was discovered. And I thought: this is really cool. And I knew we did astronomy at Caltech. I had a friend there, Judy Cohen, and she said: you know, there’s this new professor, Jim Gunn, who’s just arrived, an assistant professor. He does interesting stuff. Maybe he would take you on as a student. And he did, and that was great.

And so, while I was officially a student of the physics department, I was working for Jim Gunn, who was a perfectly good physicist working in the astronomy department. He was a triple threat. He was an observer, he was a theorist, and he was an instrument builder, and he has done all of those ever since. So, on the recommendation of my friend Judy Cohen, the result of my friend the folk dancer showing me an article in Scientific American, and Joe Silk’s very, very nice article, I switched over to being a physicist supervised by an astronomer. This was easy at Caltech, because they had a Division of Physics, Mathematics, and Astronomy, and so there was a fair amount of flexibility across them. Jim — I said he was a triple threat — was a co-I on a grant on which Kip Thorne was the PI. And so, I sat in Kip Thorne’s group for a year or two, in Kip Thorne’s group, because astronomy actually considered itself more exclusive than physics, and I wasn’t one of them. So, there was a space for me in their building, which was named after a guy who, in the last few weeks, has vanished — has been cancelled at Caltech. Caltech has cancelled — Caltech has “millikancelled” somebody (laughter).

Zierler:

Paul, this flexibility at Caltech, with the fluidity between astronomy and physics — this was a new community. This was a new way of looking at things from what you were exposed to at Cornell.

Schechter:

No. It was administrative. The small place, and you know — so, the executive officer from each department was not a full-time job. It was a part-time job. And maybe the executive officer had a secretary. Maybe not (laughter). The real power was the division head, which at that time was Bob Leighton, who was the “Leighton” of “Feynman, Leighton, and Sands,” and the Leighton textbook, and actually the Leighton telescopes on Mount Wilson.

Zierler:

What did you want to work on? What were the things that were most compelling to you as you sort of —

Schechter:

I didn’t know. I thought, you know, I liked doing math and physics. I was good at it. I liked some of the courses I took. And I read this article, and it was good. And Jim was doing interesting stuff. He wrote a terrific and highly regarded paper with Richard Gott — Gott and Gunn — on spherical collapse. Spherical collapse is a code word. The idea is you have a homogeneous, uniformly expanding universe, critically bound, so it expands forever as a parallel, as boring as you can get. You take a small region of this — spherical, naturally — and produce a little bit of overdensity. And by virtue of that overdensity, it slows the down the universe, it becomes more overdense, and so forth, and you have gravitational instability. And the spherical calculation produces objects that Gott and Gunn mapped into clusters of galaxies, and it kind of hung together. So, I was interested. And I made notes before talking to you. I hope that’s okay — papers that influenced me — Gott and Gunn was certainly one. Silk was one. A book that influenced me was — it was called Problems of Extragalactic Research, and it was the proceedings of IAU Colloquium 11. I think current IAU colloquium numbers are in the 400s or the 500s. It was in Santa Barbara, and it was basically all the people who were working on galaxies and clusters of galaxies at the time, and they could all go to one meeting with about thirty authors (laughter). And that was, you know, a book that Gunn had told me to read, and I read it cover to cover, and it influenced me enormously. McVittie was the editor of that book.

And so, I was interested in how one might apply the spherical collapse model to galaxies rather than clusters of galaxies. And there were at least two problems with this. First of all, the clusters had the long-standing problem of missing mass, which was, of course, a misnomer. The mass was there. We couldn’t see it. Now, we call it dark matter, but even “dark matter” is a bad name. Really, “invisible matter” would be better, because the light doesn’t interact with it, and that’s actually key to what makes our universe work in ways that I will return to. But we didn’t know that at the time. It was just missing matter, missing mass. But if it was there, the clusters would collapse, and you could figure out how much of this overdensity, this excess density, was needed to have clusters form in the time available — the Hubble time. So, once you had this model, you would say: how much of the density perturbation was needed to produce a cluster? Galaxies were older than clusters. You know, they’re more dense, so they must have formed sooner. So, they would have needed bigger density perturbations. Again, we don’t know what they were. And my notion was that if we had galaxies, then we would have to have clusters, because there would be — if the galaxies were Poissonian — and that was the view I took at the time — there would be regions that, by accident, had extra galaxies. And so, they would form clusters. The big problem with that — we didn’t know what caused the density enhancements that caused galaxies, and Joe Silk had actually made life a lot more difficult for us, because he had determined that if you had perturbations in the early universe, which would be composed of — we had had the cosmic microwave background, which started all of this thinking.

So, it started Joe on this thinking, which started Jim Peebles on this thinking. You know, if you had these — you know, a perturbation, it yearned to condense and become a galaxy or a cluster. It would undergo acoustic oscillations. We now call them baryon acoustic oscillations. And on mass scales smaller than what has come to be called the Silk mass, they would damp out. And so, you could barely make clusters, let alone individual galaxies. So, I had one thought. I thought if there were black holes seeding this, they wouldn’t participate in this. So, that’s kind of dark matter. It turns out it wasn’t the dark matter (laughter) that was — and they could see these things. But the required density perturbations, the mass over density, if you like, was just too much to do it.

So, I was kind of stuck with this, and I got stuck on the mathematical aspect of the problem. And I gave you a paper, and I’m not going to tell that whole story, but I do tell the story in the paper — Bill Press knew about my problem, because I was working in the same area. I have the note that he left on my desk that says, “Paul, I’ve been thinking about your problem, and I have an idea.” And so, what he added was the notion that it was a possible spectrum perturbation that wasn’t necessarily Poissonian. He still couldn’t solve the fundamental problem — what I called the “fundamental swindle,” but then he was able to add the fifty-cent word “self-similar,” because in a bound universe, things would evolve in a self-similar fashion, and that won you something, if you could have something you called “self-similar,” like similarity solutions. And we published the paper. Bill did what was the first cosmological N-body simulation. Jim Peebles had simulated an N-body as a cluster, but he had seeded that by making it overdense, like Gott and Gunn. Bill just sprinkled them with a power spectrum, and I think it was, in fact, by Poissonian power spectrum of white noise. And we saw what evolved in that. You know, so today, you can do trillion-point masses. He did a thousand. It was done with computer time that was available at the end of the year. The call went out: if there’s — you know, you used to have [“accounts”] with a finite amount of time on the one computer. If you got projects that need doing, that was the time. So, you’ll seize that. And we wrote our paper, never solving the fundamental problem. It’s been addressed since then. What do they call it? Enhanced Press-Schechter? Extended Press-Schechter? Then that’s better, using an “excursion” set. But that’s how that came about.

But there was a second problem, and the second problem was that it wasn’t, much as we would have wanted — even if we took the dark matter into account, it wasn’t a marginally bound universe. All evidence — putting all the mass and clusters you could — was that the cosmological density as we knew it, even with this dark stuff, was only a fraction of what was needed to bind the universe. And that made forming these things that much harder. So, Silk says, you can’t form any masses smaller than 10¹⁴ or 10¹⁵ solar masses, which is a very big cluster of galaxies. It’s not even a cluster of galaxies. And it only gets worse, if you think the matter density is less than cosmological, because you’re fighting that deficit to get to marginally bound before you’re actually bound. So, this was a real problem. The theorists hated the astronomers for not finding the stuff that they knew was there. And well into the 1990s, Alan Guth just couldn’t believe that that stuff wasn’t there. And they had respect for us, but we were just missing something. It had to be there. Or omega, if you know what omega is, had to be 1. So, omega was a big problem. Let me tell you how dark matter made things very much better, which is something that a lot of people, a lot of physicists, don’t understand.

Zierler:

Yeah.

Schechter:

I’m sure you do. How dark matter saves this story is that the baryon acoustic oscillations — as we call them now, because we understand them better — are exactly that. They’re oscillations in a fluid of baryons and photons. The pressure in those acoustic oscillations is the pressure of the photons interacting on the baryons, and the baryons feel that pressure, because the light interacts with them. The dark matter doesn’t feel that. So, as far as the dark matter was concerned, it’s pressureless. It’s free to collapse. So, the baryons are oscillating on top of this dark matter perturbation, but the dark matter is happily condensing underneath that, and can rise to the levels needed to produce clusters of galaxies and even galaxies, because you don’t have the Silk damping. I think that Jim Peebles was the first person to appreciate this, and he should be the next person you interview, even if he’s already done an interview. And the question you should ask him is, “When did you first realize that having invisible matter would make it possible to form galaxies and clusters?” He’s written a cosmology book. You might want to buy yourself a copy of it and see if he addresses that in that. But it is actually the best argument for dark matter. It’s not galaxies, Vera Rubin. It’s not clusters of galaxies, Fritz Zwicky. It’s — you can’t get galaxies or clusters without that dark matter condensing early on, even while on top of it, the icing on the cake, is oscillating. So, if you were to do a power spectrum [paraspectrum] of the dark matter, as opposed to the baryons, you wouldn’t see these oscillations. It’s not oscillating, and it’s much bigger amplitude. How do you like that? That was a question. How do you like that?

Zierler:

I like it very much (laughter). Paul, let me ask, on the personal side of things, or the sociological side of things, your collaboration with Bill: what did you bring to the table, and what did he bring to the table, in terms of knowledge, in terms of creativity, in terms of different areas of expertise? How did that all come together for this collaboration?

Schechter:

So, I brought the idea and a very imperfect notion about what a fluctuation spectrum might look like, and a calculation of how that would translate to a mass function. He extended that to non-Poissonian, non-white-noise, noise spectra, power spectra, the fluctuations. And we now know that it’s not white noise. And he brought some fancy words to it, which helped a lot. And he brought N-body experiments which showed, to the extent that you can do this with 1,000 masses, that it wasn’t crazy. So, he brought — you know, first and foremost, he brought a physical sophistication, a physical maturity, that I just didn’t have. He had been a good student as an undergraduate, and he had been a good student as a graduate student, and better than I was. So, he understood much more, and was able to bring what I was doing into a context that the world would understand. I worked for a year, trying to get the mathematics of that — what are the fluctuations of a Poissonian distribution — and I was stuck on the problem that my answer would work the same in one, two, and three dimensions. And it seemed to me that was crazy. If you had an answer that told you what the clusters in clustering galaxies looked like, it shouldn’t look the same on a line, a plane. So, I went and searched in literature. I went to talk to a guy who worked at Bell labs, who worked on the clustering of telephone calls, because he had tried to solve a problem (laughter). And I got hung up on this, and Bill said, “It’s good enough. Forget it.” “What you’ve got is good. We’ll add different power spectra. We’ll add N bodies. This is good.”

Zierler:

And he was assistant professor, or he was still a postdoc at this point?

Schechter:

He was a grad —

Zierler:

I mean, you’re basically the same age.

Schechter:

Oh, no. Absolutely not. He’s seven days older than I am (laughter). So, there’s no date on that message that I have from Bill, but he was probably still a graduate student.

Zierler:

Aha.

Schechter:

No, he wasn’t a graduate student. He was, by then, a postdoc. His then wife — his present wife, describes her as “Bill’s first ex-wife.” His present wife is his second wife. But she describes her (laughter) as “the first ex-wife,” who I really like, and Bill — his wife was working on a degree in linguistics on a vanishing Indian language [Native American] at UCLA, and so he had to stick around. So, Caltech was happy to give him a postdoc, and he had a postdoc for a year. And then they were happy to give him an assistant professor job, because people were — you know, he was really okay for an assistant professor job. But they said: this is strictly temporary. You’re going to have to go someplace else. A year after that, Bill went to Princeton. So, he went to Princeton in 1974, and a couple months later, I followed him to Princeton, to the Institute for Advanced Study. By then, our paper had been — two papers, actually — had been published, and we weren’t working together, but we were still friends in Princeton. He was an assistant professor at Princeton in the Physics department, and at the end of those two years, my postdoc was up. Postdocs were hard to get then, but I got myself another postdoc. We can talk about postdocs being hard to get then. And I went to University of Arizona as a postdoc, and Bill went to Harvard as what was then the youngest full professor appointed at Harvard.

Zierler:

Paul, perhaps as you organize these things in your memory, it sounds like the actual thesis research was more of an afterthought. That was not the central experience of yours at Caltech.

Schechter:

Oh, no. The thesis was, you know — there was a piece on the clustering of galaxies, describing the formalism I had developed for the Poisson stuff. There was a piece on the luminosity function for galaxies, which was what originally interested me. I was actually not interested in the luminosity function for galaxies. I was interested in the mass function for galaxies. And so, I became interested in measuring the internal velocity dispersions of the stars and galaxies, which is something which is addressed in McVittie’s book. And then there was a piece on isolated galaxies, because once you have this idea of galaxies and galaxies in clusters, how is it that you sometimes have galaxies that don’t seem to be accompanied? It was easy enough to do the calculation. What would isolated galaxies look like, and how would they be different from galaxies that had lots of friends? Because clearly, the more massive ones would attract friends. They were popular.

Zierler:

Who was on your thesis —

Schechter:

Other galaxies just gravitated to them. You know how that works?

Zierler:

Yeah. Who was on your thesis committee?

Schechter:

Jim Gunn was my thesis supervisor. It’s hard to remember who else.

Zierler:

What about Bill? Did he serve as an outside reader?

Schechter:

No. He was actually gone by the time I defended.

Zierler:

Yeah.

Schechter:

You know, I sort of lingered into the summer, I believe, and a little past. And he was gone. Bob Leighton may have been on the committee. Irwin Shapiro sat in on a preliminary presentation of it, but he was just a visiting professor. Jim’s approach to thesis supervision was benign neglect, and so, he wasn’t really into it. So, I’m sure Jim read it, and someone else may have read it, but my reaction coming out of it was: what was I worried about? (laughter)

Zierler:

Paul, as you note, the job market, even for postdocs, was quite difficult. This being the mid-1970s, there are obvious macrosocial realities behind these trends. But I’m curious. Specifically in your field, what were some of the problems that were holding back more offers forthcoming, as you were thinking about your next move?

Schechter:

The amplifier. So, the way it works is that A tells B: I’ve got this student. He’s pretty good. B tells C: I hear that this student is pretty good. C tells A: I hear your student’s pretty good. A says: Oh, I was right, and cranks up the volume. And that keeps going until the volume hits eleven, and you have an enormously loud shrieking sound, over which nothing else can be heard. So, I will not name the individuals, but there were — you know, I would apply for the same jobs, and I could point to individuals who got offers at five different places who worked on the same thing I worked on, and got five offers and I got none.

Zierler:

And who would have been your initial amplifier? Jim Gunn? Would he have been the one doing that for you?

Schechter:

He would have been, and there was a point at which he finally was. But you’re going to like all this. It was actually Peter Goldreich who got me my first job. There was, when I was at Caltech, an evening seminar organized by Jim Gunn and Peter Goldreich, which was called the “Russian Roulette Seminar,” and I believe they originated it. They have had them since — and the idea was that there was a topic was picked for each trimester, of which there were three, and they would pick out important papers in the field. And the graduate students taking this seminar, and the professors, would all read the papers. It was held at their houses. They had cookies and coffee. And the names of everybody who showed up were put in a hat, and whoever’s name got pulled out of the hat would present the paper. And I did six semesters of that, and learned a hell of a lot from Jim Gunn, but yet more from Peter Goldreich, whose title was Professor of Geology, Astronomy, and Physics, and Assistant Wrestling Coach (laughter). When Peter graduated from the Bronx High School of Science, he didn’t have to go to Cornell. He could have gone to a Yankee farm team (laughter). But idiot that he was, he went to Cornell, and the die was cast. Peter has a style of thinking which he may have — I don’t know whether he adopted it from Feynman or just that they co-evolved — but it is this, get to the point, boiled to the essentials, that I have in the course of my career tried to follow and found enormously helpful, because it turns out, most of what you want is in the fine stuff. So, we were talking about Joe Silk, weren’t we?

Zierler:

Yeah.

Schechter:

Joe, you’re reading this? That first paper, you published in Nature on the Silk mass, really is brilliant. It really is fantastic. The twenty-page paper you published in the Astrophysical Journal, that it took me more than a month to go through, going from there to the works by Misner, papers with Misner as one of the authors — the guy who died in the Texas tower was one of the authors, too — on spherical collapse and general relativity, that didn’t add very much, but it took a hell of a long time for me to get to the point when I realized it was all in the Nature paper in the back-of-the-envelope calculation. And whatever factors of pi you might have introduced in that paper, I’m not even sure you got them right (laughter). And so, if you can get there first with something simple, take the money and run, because it’s mostly in the simple — and Peter was fantastic at taking things apart and saying: this is what’s at work. This is at the core of this.

So, Peter was good buddies with John Bahcall. I also ran with Peter, around San Marino. It’s a bit of an exaggeration. He would run circles around me, as we ran (laughter). I kid you not. So, John Bahcall was visiting the campus. I was looking for postdocs. I spoke to John Bahcall, and — see if I can get the quote right. Peter? You’d spoken with Peter? And John said something like, “Why don’t you finish your degree and start living?” You know, today he would say, “Finish your degree and get a life.” And I mean, I don’t have that exactly right, but that’s basically what he said. Well, I’ll do the best I can. And then I spoke with Peter, and he said, “Well, you’re going to take the job?” What are you talking about? “He didn’t offer you the job?” No, he had offered me the job (laughter). I think what he said was, “Why don’t you finish your degree and start living like a human being?” Neta, if you read this, you know I loved John, in part because of this (laughter). That was the way he was. So anyway, I went to the Institute for Advanced Study. Probably the most distinguished person in my class was Roger Blandford. John didn’t understand what my thesis was about. Oh, understanding what my thesis was about — we’re allowed to loop-de-loop, aren’t we?

Zierler:

Absolutely.

Schechter:

So, I’d done this work with Bill, and there was a meeting of the Astronomical Society of the Pacific. I don’t know if the name means anything to you. Bu the session at which I gave my talk was chaired by George Abell, clusters of galaxies, UCLA. He found them all using the Palomar Schmidt. Sitting in the front row was Jim Peebles. Have I described his work, which has subsequently attracted some attention? A bunch of us went down there in a car together. It was held at University of Southern California, so we just got on the Pasadena freeway and drove down there in a car, a bunch of us. And after the talk, George Abell said, “Oh, thank you for this very, very interesting talk. And are there any questions?” And Jim Peebles is right there in the front row, and Abell was looking at Peebles. Crickets. You know, so it didn’t register. And in fact, the paper barely registered in ten years. It had maybe seventy-five citations in its first ten years. So, John didn’t quite appreciate that, but he trusted Peter Goldreich. And while I was at the Institute for Advanced Study, Ray Weymann was on sabbatical there, and he liked me, so he got me the job at University of Arizona, my second postdoc. I went on this second postdoc, and I was applying for faculty jobs, and I was encountering some of the same amplifier effect that I described to you. I was getting to the point where saying that Jim played an important role. Four of us had applied for a job at Harvard. I don’t know how much you know about Harvard’s hiring practices in that era.

Zierler:

You were doomed.

Schechter:

They were called “folding chairs.” (Laughter) But four people were on the short list for that, all of whom are now members of the U.S. National Academy, and Jim Gunn knew them all. And for whatever reason, Jim had told them, “You should probably hire Schechter.” And so, not understanding or knowing my work, they nonetheless did. I had, I should say, during the four years as a postdoc, done a lot of work first with Wal Sargent of Caltech, then with Jim, measuring these internal motions in galaxies, these velocity dispensions. Why are these important? I’m talking to physicists here, so I’ve got to make it sound like physics. Okay? (laughter)

What keeps a star from collapsing? Well, it’s pressure. You know that. What keeps a galaxy from collapsing? It’s got stars, but it’s a collisionless fluid. That collisionless fluid — nonetheless, there’s a Vlasov equation. You could do moments of it — the Jeans equation — there is, nonetheless, what is effectively a pressure exerted by the stars, and it depends upon the RMS velocity of those stars, just as if it was a temperature. kt is equal to mv2 over 2, except the m’s are kind of big. The v’s are kind of big. So, the point was to measure the v2, the temperatures of these things, and these galaxies are temperature supported, and that’s the way you determine the mass, because there is something called the virial theorem, which in its simplest form says that the gravitational binding energy is twice the kinetic energy. So, that was the way you measured the masses of these things, which was very interesting, because you wanted to know how galaxies formed, and to know how they form, you needed to know what their masses are to figure out how they collapsed.

So, that was why I got interested. And I started observing in these velocity dispersions even while I was at Caltech. I used the Palomar sixty-inch, which was referred to as the Pig Eye, as opposed to the 200-inch, which was the Big Eye. And I didn’t get anything done on the Pig Eye, but while I was there, while Sargent was there with Alec Boksenberg’s machine — and he was interested in the question. He said, “Give me your observing list.” And he observed all my objects. And two years later, after he couldn’t reduce the data himself, he came and said, “Well, you know, I observed those objects two years ago. So, I wrote a paper, and it’s Sargent, Schechter, Boksenberg, and Shortridge. And that was a pretty good paper, and that got a lot of attention. And then with Jim Gunn — could I just say something? Yeah. With Jim Gunn, we worked more on the internal rotations of the galaxies, getting a better idea of what the kinematics of the galaxies were — of elliptical galaxies. Spiral galaxies, everybody knew. You know, Vera Rubin. They were rotating and flat. Spiral galaxies are cold. That’s what makes them flat. The velocity dispersions are small compared to the ordered motions. Elliptical galaxies are hot. That’s what makes them round. The disordered motions are large compared to the ordered motions. And I want you to know I’m an astronomer. I’m not a physicist.

Zierler:

Yes. That’s clear.

Schechter:

So, I worked with Jim on this, and that went very well. And we had some instrumental problems, and I helped to correct for those. And so, he said — he told Harvard that — Harvard hired six assistant professors that year. And I’m sure that they didn’t order them as to who they wanted to keep, because they didn’t want to keep any of them. But if they had, I would have been the last, and I was gone in fourteen months. The handwriting was on the wall. I got an offer from Kitt Peak National Observatory, as it was called then, which was assistant astronomer and tenurable. I went to speak to George Field, and he said, “Take it.” And I did. Maybe not in exactly those words, but that’s the way I heard it.

Zierler:

What do you think Field’s advice was about? Stability? This is where the exciting science was? You would do well there? All of the above?

Schechter:

“You would do well there,” is the nice way to put it (laughter).

Zierler:

Yeah.

Schechter:

And it was great, and I liked being near the telescopes. And there was a lot of astronomy. There was a lot of observing. It was great for observing. It was culturally — George Lake, a contemporary of mine — actually a little younger — now the late George Lake, who would have been fun for you to interview — said, “What should one think of a town whose cultural veneer is so thin that its main drag is called “Speedway”?

Zierler:

That’s great (laughter). That’s great.

Schechter:

But boy, you know, winters were wonderful. Summers, for some reason, I found tolerable. The telescopes were there. I did a lot of observing.

Zierler:

I can’t help but wonder, Paul, culturally this was probably a fairly purely astronomer kind of place. You must have really been in your element.

Schechter:

Oh, yeah. You know, so all sorts of astronomers would come and — you know, I had a home. People would stay and would be my guests. I would pick them up at the airport, and they’d stay at my place, and I’d drop them off at the airport. So, it was great. They were coming through all the time. It was wonderful. It was a crossroads. My “functional responsibilities” were light, and so I wrote some papers that were good. And we’re moving on in my career. Is that okay?

Zierler:

Absolutely. What year is this now? Just so we’re rooted in the narrative, what years are you at Kitt Peak?

Schechter:

1979 through the end of ’82.

Zierler:

Okay.

Schechter:

Late ’79 through the end of ’82. I did want to tell you one thing about getting the job. I told you Jim Gunn said I was the guy to hire.

Zierler:

Yeah.

Schechter:

But I don’t know if you know this, but Alan Guth had five postdocs in that era.

Zierler:

That’s a busy time for him.

Schechter:

(Laughter) Spent ten years in the desert before he found the Promised Land. It was tough. And you know Alan Guth, and I know Alan Guth. Right. So, after my second postdoc — I want to tell this story, because it points to how wonderful a certain person is. I applied for faculty positions, and I also applied for postdocs — third postdocs, because they were two-year postdocs in those days. You know, like Alan, you might have to take another postdoc. I wrote to Martin Rees, and Martin said, “Paul, you’re ready for a faculty position. You let me know if you don’t get a faculty position, and we’ll find something for you here.” What a guy. You know? How can one not think fondly of such a guy for the rest of one’s life?

Zierler:

Yeah.

Schechter:

“Just let me know.”

Zierler:

Paul, what was the most exciting work you were involved with at Kitt Peak?

Schechter:

Exciting to me, or exciting to you?

Zierler:

Exciting to you.

Schechter:

The infall of galaxies toward the Virgo Cluster. I was very lucky at the time to have, within ten feet and within one hundred yards, Jeremy Mould and Marc Aaronson. You know Dennis Overbye’s, Lonely Hearts of the Cosmos?

Zierler:

Sure.

Schechter:

So, Aaronson, Huchra, and Mould were the guys who were challenging Allan Sandage on the Hubble constant. They were getting distances to galaxies using the infrared Tully-Fisher relation. And so, not only could one get the distances to the galaxies, but in the case of galaxies around the Virgo Cluster, the distances were good enough so that you could look to see whether their velocities were what you would expect from this spherical infall model that I told you about. And so, it was — moreover, far out in the spherical infall galaxy. There are three interesting radii. There is, first of all, a turnaround radius, and that’s perhaps the most interesting, where the expansion has stopped and it’s just now beginning to collapse. And that depends upon what the mass density is. It’s closer in or further out, depending upon what the cosmological mass density is. And so, using — there’s a paper: Aaronson, Huchra, Mould, Schechter, and Tully — and we come up with a cosmological mass density of 0.29. Nobody believed us. It’s got a lot of citations. I won’t say nobody believed us. The infall into Virgo is a beautiful thing. And we did a lot of interesting things in that paper. That was my single biggest effort there, and I’m very proud of it, and I’m proud of the fact that we got the right number, you know, that I couldn’t persuade the Alan Guths and Mike Turners of the world that we got the right number. Well, that was a disappointment, but we got the right number. The uncertainty was ridiculously small.

Zierler:

What was the disconnect with the Mike Turners and the Alan Guths of the world?

Schechter:

These things are not easy to understand, and there are lots of places you can make errors. The single biggest place that we could make an error would be in our estimation of the overdensity, because after all, the infall depends upon how overdense it is. And so, we made an estimate of the overdensity based on the numbers of galaxies in Virgo, and in numbers of galaxies spread out beyond Virgo. So, it represented a density enhancement to such-and-such, producing a velocity field of such-and-such, and the connection between the two is the mass density. But you could easily get it wrong, and that was, in fact — contributed the most to our uncertainty—the uncertainty in that. Then the calculation of the velocity field — I’ve described it as being the location of the turnaround radius, and I think that is a fair way to describe it, functionally. So, they don’t understand the — you know, it’s complicated. How do you get the distances to these things? Is it on this side? Is it on that side? What do you do about groups? What do you do about weird guys, you know, that turn out to be streaming through Virgo like a bat out of hell, you know, because — early on — you know, there have — Haldane, I think, had four stages of new results, [Four stages of acceptance (see below)] the last of which is, “I always said so.” So, you can look that quote up. [https://www.goodreads.com/quotes/78634-the-four-stages-of-acceptance-1-this-is-worthless-nonsense ]

So, people didn’t want to believe it, and basically they didn’t believe it until we were vetted by cosmic acceleration. They just couldn’t see. So, there was this awful paper by Mike Turner, and I accused him of betraying the astronomical community. He said, “Well, we can fix everything, if the Hubble Constant is thirty.” (Laughter) Here, you’ve got a whole bunch — you know, tens, twenties — of very smart people who you know personally to be very smart people — working on the Hubble constant, and you know, yes, they’re arguing. Is it sixty? Is it seventy? Is it eighty? But nobody’s talking thirty, Mike. You know, to just throw that out is a betrayal of a community of which you claim to be a part. But theorists, of course, allow themselves that luxury, and observers allow themselves the luxury of saying: yeah, I’ll do some of those observations when you’ve got a little more reinforcement for that. But knowing that there wasn’t a chance in hell it was that, it just seemed so incredibly crazy. Told them so. So, where are we? So, Kitt Peak. The other thing I did was that working with Bob Kirshner and Gus Omler and Steve Shectman. This business of the luminosity function that I worked on, that was kind of interesting. So, we were working on doing that, and the business of large-scale clustering was interesting. And so, we undertook a survey first, just to study the luminosity function, and then to do large-scale clustering. And we found what we called, and what was called, the Boötes void. And that was, by far, the biggest void that had been found to date. Can I show you something? I don’t know how you’re going to get this into what you do, but this is what appeared in a paper just last month [arXiv 2012.03511], and this is great. So, you see something that says “reference” down the middle?

Zierler:

Mm hmm.

Schechter:

So, if you look on the left — I’ll bet you recognize this. This is one of these cosmological n-body simulations, and it’s bigger than a thousand. And what you see marked are some knots of points that are what they call clusters of galaxies. So, let’s go back. Zeldovich was very big on the idea of clusters forming first, a top-down scenario. And the reason was the Silk mass. He knew that smaller mass perturbations [would be damped], and so the idea was that big masses could form. They would collapse and fragment into small masses. Now, we know now that was wrong, because the dark matter could collapse on the small scales first, and those are the points here. So, this is a cosmological n-body simulation, and we talked about the spherical collapse model. Something I teach in my advanced undergraduate and graduate classes is small deviations from the spherical collapse model, and if you have something that’s elliptical, ever so slightly ellipsoidal, it collapses first along one dimension, and then along another dimension. So, it pancakes, and then when it collapses in the other direction, it makes a filament. So, you have knots where the filaments merge. You have filaments where the walls merge. And between the walls, you have voids, where there’s nothing. So, there are — the technical word is a “shipload” — a shipload of points, on each of these here. And what they’ve done is something clever. This evolved out of initial conditions. They made the baryons, the galaxies that these points represent, just tracers. And they took the initial conditions, and they reversed the sign, so that what was positive density perturbations would be negative perturbations and vice versa. So, you see these red points here?

Zierler:

Mm hmm.

Schechter:

In that mirror, those are all the things over here. The blue points, they’re in here. These blue points, they’re over in here. So, slightly oblate things collapse to form pancakes and filaments if they’re over-dense. If they’re under-dense, they expand to form spheres. They all asymptotically go to spheres. And so, voids are intrinsically spherical. And are they perfectly spherical? No, but they’re a hell of a lot more spherical than the filaments are, or the walls (laughter). So, we discovered, in the course of this, the Boötes void, which was the largest known region in the universe without a McDonald’s. And that was a big thing. Walter Sullivan, dean of science reporters — not just in the New York Times, but dean of science reporters — got wind of this, and he thought it was pretty important. So, he told his editor: this needs to go on the front page. Now, this is 1981. Bob Kirshner is at Michigan. He’s got tenure. Gus Omler is at Yale. He’s got tenure. Steve Shectman is at Carnegie Institution in Washington, which is effectively tenured. Paul is assistant astronomer at Kitt Peak National Observatory. So, even though we did comparable work of different sorts in our survey — I can just stop this sharing. Isn’t this a wonderful picture?

Zierler:

It’s amazing.

Schechter:

No one has done this until now. It’s just fabulous as a teaching tool. Jim Peebles is very interested in what goes on in the voids. Again, reason to talk to Jim. So, there was going to be a press release, and he knew this was good. And we agreed that since Paul didn’t have tenure, he would front this effort, even though Kirshner was the first author on the paper. So, when Walter Sullivan called somebody up, he called me up, and there I was, on the front page of the New York Times and in a lot of places. You know, a lot of press. It made my mother very happy. Made my father happy. And there used to be, when I was in high school and thereafter, ads in the New York City subway. Do you know New York at all?

Zierler:

I do. I do.

Schechter:

Ads in the subway that said, “I got my job through the New York Times.” And I got my job through the New York Times (laughter).

Zierler:

(Laughter) That’s great! That’s great. Who was reading The Times that day that was really instrumental?

Schechter:

Bartlett Giamatti (laughter). Not quite, but I got an offer from Yale. I got an offer from Carnegie Observatories. And Kitt Peak Observatory, which was at the time headed by Geoffrey Burbidge, grudgingly made me an offer to counter after I had those two offers. And when Yale saw that it was going in the way of Carnegie — because Carnegie had the glass. Carnegie had access to Palomar. It had the telescopes in Las Campanas, and I had to go with the glass, even though I knew I wasn’t a west coast person. I was leaning that way. Pierre Demarque said, “Well, would it help if Bartlett Giamatti called you?” You know, then he was only the president of Yale. He wasn’t yet the commissioner of baseball (laughter). But no, it wouldn’t have. The attraction of the glass at Carnegie took me to Carnegie. So, you asked what work I liked when I did Kitt Peak? Both of those. The in fall to Virgo was the stuff that I’m proudest of, but the void was fun. And when I was thinking about the void, I understood a lot about voids. I came to understand what I told you about voids being intrinsically spherical, which I don’t think people understood, in the way I’ve described it to you, at least. Jerry Ostriker started thinking about this stuff, and then I met him — you know, I told you, you meet all sorts of people in Arizona — and we were out for drinks, and he was explaining to me this stuff, and I had already understood it, but he (laughter) needed to explain it to me: “Yes. Yes, we should definitely write a paper on this. Yes.”

Zierler:

Did you see this as — were you getting off of a more traditional academic track, or you weren’t thinking in those lines?

Schechter:

I would have preferred the academic track, because I liked the idea of being a professor. But the access to the glass is just hard to say no to.

Zierler:

Yeah.

Schechter:

You know, Yale subsequently got into telescopes, but it didn’t have telescopes. You know, if I wanted to suddenly do — you know, if I wanted to become a theorist and return to the more theoretical stuff, Yale would have been okay. But for an observer, no, it wasn’t right. And I became yet more of an observer, and I started doing instrumentation stuff when I got to Carnegie. I couldn’t be everything. I couldn’t be as good as Jim Gunn in any one of the things he did, and I wasn’t. But the balance of my career shifted more toward instrumentation, starting at Carnegie and then at MIT.

Zierler:

Paul, what was your initial title at Carnegie, and how might that have reflected your relative seniority in the field at this point?

Schechter:

“Staff astronomer.” You know, but that was the same title that Allan Sandage had.

Zierler:

Very broad. Doesn’t tell you much, actually.

Schechter:

Carnegie is a sinecure, and it was much sought after.

Zierler:

Yeah.

Schechter:

You know, you had almost no functional responsibilities. There was research money. There was money to travel, to observe. You had telescopes. Actually, in those days, we had access to the 200-inch. It’s hard to say no to that.

Zierler:

If you wanted to teach, and if you wanted to take on graduate students, was that available to you?

Schechter:

Caltech was very jealous of its graduate students.

Zierler:

Right. Right.

Schechter:

Once in a while, if there was a graduate student who they weren’t guarding quite so jealously, they’d let that student work for someone at Carnegie.

Zierler:

What was your initial project at Carnegie?

Schechter:

One that didn’t go very far, and I won’t talk about it much, except to say that in the course of doing it, we began — I turned to the study of the Milky Way and did that for about six years, and that turned out to be altogether, in terms of getting citations, a mistake. Although, in terms of intellectual development, it wasn’t a loss. Astronomy has undergone an enormous revolution since I got to Caltech. And in rapid succession — so, we’re getting to what I worked on at Carnegie, but we’re getting there slowly. I think if we make this long enough, no one will read it (laughter).

Zierler:

(Laughter) Perfect.

Schechter:

So, photocathodes had already come to Caltech and to astronomy, so people would use an image intensifier to — it was a type developed by Kent Ford at Carnegie’s Department of Terrestrial Magnetism. And the idea was, a photocathode, electrostatic acceleration, focused either magnetically or electrostatically — and finally, a phosphor. And then you’d put a photographic plate behind the phosphor. But you then got the quantum efficiency of a photocathode, which is on the order of twenty percent, instead of the quantum efficiency of a photographic plate, which was two percent at best, more like a percent or a half a percent. So, of course, these things look like hell, because they were fried by the phosphor. Then, people started reading those phosphors electronically, and centroiding on the flashes for each electron, so you could recover the spot. That was the Boksenberg machine that Sargent used at Caltech and took that great data. Shectman at Carnegie made a version of that, that was one-dimensional, the Reticon^TM, the z-machine. About 1979, charge coupled devices started being used in astronomy. At first, they were tiny. And everybody was trying to get their hands on them, and nobody could. But the silicon had efficiencies of fifty percent and more, but they were very noisy devices. They had to be run at liquid nitrogen temperatures. They were small. And there was a lot of black magic associated with producing them.

So, everyone was struggling to get their hands on one of these things, or two. So, we had one of these at Carnegie, and I needed to do photometry of stars in large regions. You know, so like the surveys that are going on today. And so, I did a survey — I can’t tell you for sure that it was the first drift scan survey, but like the Sloan Digital Sky Survey, the idea is: you take the telescope. You put it — you know, Jim Gunn. And then you let the thing — Jim did some drift scanning at Palomar with his device, and he may have preceded me in that. I’m not sure. The idea was current. Everybody knew about it. But I started doing drift scanning using the Las Campanas forty-inch, the Swope Telescope, the one-meter telescope, on which we had a charge coupled device. And the width — the number of pixels across was 330. You know, these days we talk about 10,000. Gunn’s gadget had 5 times 2,048. So, that was 10,000 for Sloan. But we had 330. You know, I really wasn’t going very deep, so I wanted to go faster. And so instead of turning off the telescope — this telescope was made commercially by Boller and Chivens, and they had replicas in the north. They had replicas in the south. If you wanted to run it in one hemisphere or another, you just switched the leads on the motors. So rather than turning the telescope off, I ran its sidereal time counter to the rotation of the Earth, so that we could cover twice as much sky.

And then, because I didn’t want the objects to saturate, instead of tracking exactly at the sidereal rate or twice the sidereal rate, or anti-sidereal rate, I let the objects spread out, so they covered more pixels. That, on the one hand, kept the device from saturating. On the other hand, it provided more pixels and lower — you know, average out over the read noise. So actually, the photometry was better that way. So, then I wrote a program to analyze this, because nobody had ever seen data that looked like this before, these things that were — had the PSF of a star in one direction, and basically a boxcar in the other direction. And I wrote a program to analyze such data, but it was more general. It could analyze any such CCD data, and that became something called DoPHOT, and that is now my third most highly cited paper. And you know, it was available — and its virtue was that it was fast. I did everything — covering a lot of territory, computers were slow. We were filling tapes so fast. We would ship the data back in crates — with tapes in crates. In the early days of very long baseline interferometry, those guys who you would see at Caltech — you know — Marshall Cohen and Al Moffet. They did VLBI, and they would have stations all over the country, and they’d come back in a truck loaded with TV video tapes — big two-inch TV video tapes — full. And then all the students would go out and help them unload their truck full of tapes, because the truck had the — there was no internet. So, we shipped tapes — you know, 2,400-foot, half-inch tapes in boxes back. And we analyzed the data. We published our photometry. It wasn’t wonderful, and it was subsequently surpassed by — but you know, we did this drift scanning early on.

We also did the same drift scanning — Kirshner, Omler, and Shectman and for a follow-on to the Boötes Void. We did the Las Campanas redshift survey, and we used drift scanning as well. So, it’s almost certain that they started — they, we — started drift scanning for the Las Campanas red-shift survey, which was the first — which, in another way, was a prototype for the Sloan Survey. It used aluminum plug plates, and those were Shectman’s idea. And Gunn was interested — Gunn was Schectman’s thesis supervisor — Gunn was interested in doing a larger redshift survey, and at first considered robots, and in the end went the Shectman route. Shectman used — fibers are very fragile. Shectman was a bicycle enthusiast. And so, he used bicycle cables’ cladding. First, he used hypodermic needle as cladding for the fibers, then he used bicycle cable as cladding for the hypodermic tubing. And then, they would go out there and plug in the plates. And it became a matter of pride who could plug in the plates the fastest, without their arms falling off, because holding your arms over your head for half an hour actually was not very comfortable (laughter). You know, try it for three minutes, and you’ll get the idea. So, I was part of that effort, but it wasn’t my focus. We were a team. We were buddies. And so, I was part of the effort, and so I did my share. You know, I don’t think I did less than my share. But I wasn’t — you say: who was pushing it? Who motivated it?

Zierler:

Yeah.

Schechter:

You know, who said, “Let’s do another round”? It wasn’t me. You know, surely — sure, why the hell not. Let’s do it. But it wasn’t me. Kirshner, Gus, Steve, they all wanted to do it more than I did, I think. But I did it because I so enjoyed working with them. Which, you know, again is different from this huge collaboration. This was as much a bunch of guys doing something because they enjoyed doing it, as it was doing science, and could afford to do science for the pleasure of doing it with their friends.

So, I wrote this software when I was at Carnegie. That was good. And I also built a spectrograph to do spectroscopy of carbon stars, which was another way of studying the structure of the Milky Way. That’s a sleeper. That data is sitting in the literature, and one of these days, we’re going to — maybe tomorrow — we’re going to look up the Gaia proper motions for these things, and we’re going to get the world’s best rotation curve for the Milky Way, way the hell out there, using carbon stars. So, I was working on that as well, and I built a spectrograph to do that, under Steve Shectman’s guidance. And so, those were the things I did. I wrote a program, and I built a spectrograph. And there were some papers, which frankly — if you look on the — if you know about the Astrophysics Data System Abstract server?

Zierler:

Mm hmm.

Schechter:

You look on that. Don’t sort by citation count. But if you look in the years, you’ll see the papers I wrote from that time. My galactic structure work had some interesting byproducts, but it wasn’t science.

Zierler:

Did you think at one point that you’d spend your whole career at Carnegie? Was that the track you were on?

Schechter:

Yes. But Carnegie is a really small place.

Zierler:

That cuts both ways.

Schechter:

So, with apologies to my very good friends at Carnegie, it’s not a place where people grow old gracefully. And it was riven with rivalries, because you couldn’t escape these people. And injuries not forgotten, and after six years there — I told you I was not a west coast person. I wasn’t very happy, and I thought MIT was now part of a one hundred-inch — on the one hand, Palomar had — Caltech had stopped cooperating with Carnegie. Carnegie was founded by Hale. Hale attracted the now-disgraced Robert Millikan to Caltech because of its grating engines, because the ruled gratings. A lot like Rowland at Hopkins. I mean, these grating engines were really rare. There were just a few in the world. And so, he attracted Millikan to Caltech. And Rockefeller, as I understand it, couldn’t give the money for Palomar to Carnegie. There was a joke when I was a kid: does Macy’s tell Gimbel’s? (Laughter) And you know, a saying — and the corresponding saying was: does Rockefeller talk to Carnegie? No. But Rockefeller needed astronomers, and Caltech didn’t have them, except for Fritz Zwicky, who you could call an astronomer.

And so, the arrangement was that the Carnegie people would help in the building of the 200-inch and participate in its exploitation. And Hubble was there at Carnegie, not Caltech. He was the person who was going to use the 200-inch to solve cosmology. And then after Edwin Hubble, Allan Sandage, his designated successor, was going to use the 200-inch to solve the problems of cosmology. And Caltech was happy with this arrangement. You know, they got an astronomy department, so to speak, for free. And when they finally had an astronomy department of their own, and Carnegie had its own one hundred-inch in Las Campanas — well, whose telescope is this, really? And I wasn’t party to this, but eventually the Carnegie people lost access to the 200-inch. At that point, MIT had a role in a one hundred-inch telescope, and that looked interesting enough to me. I hated leaving Las Campanas, but I wanted to be on the east coast. The west coast wasn’t resonating. So, Alar Toomre sidled up to me in a meeting and said, “Would you be interested in coming to MIT?” And I said, “I’ll think about it.” And then while he was on vacation, he says I left at least half a dozen pink “While You Were Out” notes on his desk (laughter).

Zierler:

(Laughter) That’s great. Had you let it be known that — were you putting out feelers that you were thinking about moving on?

Schechter:

No. No. It was just a — things weren’t quite right for a number of reasons, and the west coast wasn’t working for me. And as I said, I looked around me, and this was a place where the people grew grumpier and grumpier as time went by. There have been exceptions. George Preston, I love you, but people grew grumpier and grumpier as time went on.

Zierler:

What was the initial appointment at MIT?

Schechter:

Full professor.

Zierler:

Physics department?

Schechter:

Yeah. The appointment at Yale was full professor, so the job I got through the New York Times was a good one.

Zierler:

What were your feelings about joining a physics department?

Schechter:

I was happy. I didn’t want to teach freshman astronomy. Teach physics. That’s a good thing to teach. You know, I teach upper division of astronomy and graduate students in astronomy, but if you’re going to be teaching a 101, make it physics. That’s real stuff. That’s great.

Zierler:

Why? Too much fluff for freshmen in astronomy?

Schechter:

You know, I have friends who have made a career of teaching astronomy 101. And they’re well known, and they have gotten much praise for it, but I can’t do that. I spent a sabbatical at one of these institutions, where one of these friends works. And the friend went off for a week, and I covered 101. So, I taught 101 the way I would teach it. Students said: gosh, this stuff is so different (laughter). You know, if I had given a course like that for a semester, I would have been lynched, because it was demanding. But I could give it, you know, as — because it was nothing great. I was just expected to babysit, and so teaching it at a somewhat more interesting level for me was not a great crime. I was supposed to — if I had showed some pictures, I had done my job. But you know, that was just not something I wanted to do, but teaching physics, teaching undergraduate classes in physics, is something I like. And teaching undergraduate classes in physics at MIT is yet more fun.

Zierler:

Did you see any particular opportunities for collaboration with the faculty at MIT? Was that part of the draw?

Schechter:

No, and I haven’t, in all my time there. No, actually, there was one person, John Tonry. How can I say this? And John and I were very close, but he left for Hawaii in 1997, I think, he finally closed the door. Certainly ’96. No, John was a great attraction to me, and we worked together for six or seven years. John subsequently did Pan-STARRS. He has been part of the supernova efforts, and now he’s got something called ATLAS has been quite successful. He’s done very, very good things. John was a real pleasure, because he was somebody who loved the physics and who looked at the physics angles and brought good physics to astronomy.

Zierler:

I was thinking, it is notable the lack of collaboration for you with your fellow faculty.

Schechter:

At MIT.

Zierler:

At MIT.

Schechter:

So, I continued to collaborate with Kirshner, Omler, Shectman. And then I started working on gravitational lensing, and I found a new bunch of collaborators.

Zierler:

And what was your entrée into gravitational lensing? What was the initial contact there?

Schechter:

Are we having a second talk?

Zierler:

We can. I’m going strong. We can take an intermission now.

Schechter:

No, let’s — because we don’t have too. So, I told you that one of the two things that really has made astronomy different is charge coupled devices. And we’ve gone from that 330 by 512 CCD, with which they did this work that I described to you in drift scanning — to the Rubin telescope, which will have a three gigapixel camera, where it can cover — and Shri Kulkarni is doing fantastic work at Caltech, and you always give credit to the more senior person, and you shouldn’t. I’m forgetting her name. I’m embarrassed. Mansi Kasliwal.

Zierler:

One hundred percent.

Schechter:

Right. So, Shri Kulkarni is leading this project called the Zwicky Transient Facility, and Mansi Kasliwal — I want to say- and that’s not quite right either. [Looks like Shri Kulkarni is the PI and Mansi Kasliwal is a Co-PI. https://www.ztf.caltech.edu/page/team-members ] Anyway, Zwicky Transient Facility, and they have silicon which is bigger than the fourteen-inch photographic plates that the Palomar 48-inch was designed for. So, as big as those things were with which you did the Palomar survey, with which George Abell did the Palomar Sky Survey, the silicon is now bigger than the photographic plates. That is quite amazing. You know, the silicon in your camera is bigger than thirty-five-millimeter film or can be.

Zierler:

Wow.

Schechter:

So, that has been — so, you’ve gone from quantum efficiencies of 1 percent, to quantum efficiencies of 1, and you’ve now got the whole area, you know, with everything the telescope can deliver. And the challenge is getting the telescope to deliver. So, MIT was part of the Michigan-Dartmouth-MIT Consortium. They had just commissioned the Hiltner Telescope, and I had, when I was at Carnegie, worked on an instrument, and I thought I knew something. And when we started using the Hiltner Telescope, it was producing terrible images. And the reason it was producing terrible images? We were told that the telescope was — by the guy who figured it and measured it — was as good as the Hubble Space Telescope. Turned out he was right, and that was when the Hubble Space Telescope had its spherical aberration (laughter).

So, the Hubble Telescope had a mission to fix it, and we had a mission to fix it. So, first, I learned how to measure what your mirror surface looks like, using Hartmann testing. And after much effort, I was able to persuade — you know, taking the mirror out, rotating it [mirror], showing people that the pattern of aberrations rotated when we rotated the mirror, and it wasn’t the mirror support. You know, because people didn’t want to hear this, that the mirror was bad. When the seeing gets good, when you look at a star in the guider, you see it scintillate. You see its size change. It’s called seeing. It expands, and contracts, and goes up. These images were frozen. They were frozen because the seeing was better than the image quality in the telescope. It’s something the telescope couldn’t do. So, we had a mission to repair our mirror, just the way they had a mission to repair the Hubble Space Telescope. We packed our mirror into a van. We shipped it across the country from Arizona to Pittsburgh. It got figured. It got returned to the telescope, and it produced fabulous images. It produced images better than any telescope on Kitt Peak, by a lot.

Zierler:

Explain, Paul. What’s a better image? How do you know this is such a better image? Just the resolution?

Schechter:

Yeah. You know, I could show you, but I have images that I show people for the Dark Energy Survey that are just the same object, seen with — instead of talking about arcseconds, I’ll talk about pixels, and full width half max. The difference between four pixels full width half max and five pixels full width half max is huge in terms of the sensitivity of the telescope. You take the diameter of the image, whatever that percentage increase or decrease is — that’s the equivalent of getting that telescope bigger by that percentage in diameter. You know your figure of merit is the area of your primary mirror times the solid angle of the sky you cover, divided by the area of your image. The smaller the area into which you can fit your image, the lower the noise when you’re reading it out, and the more you get, the fewer pixels you have to waste.

And so, good image quality — and the second great realization of — this is mostly in the seventies the twentieth century — was that telescope sites could deliver much better images than people thought was natural seeing. And the first place that this was demonstrated was with the Multiple Mirror Telescope at Mount Hopkins. And the reason both — and Michigan-Dartmouth-MIT, and first at Mount Hopkins — it’s first because the mirrors were good. I told you that. But more importantly, both on Mount Hopkins and Michigan-Dartmouth- MIT, there was no concrete. The structures were steel, and they were very well ventilated. So, you didn’t have — if you go to Palomar, the dome rides on these wonderfully thick — on this wonderfully thick — it’s a stubby cylinder of concrete. What is it, three feet wide? You know, and that stays hot. Stays hot for days. And hot air boils off, and you never get great seeing. And the more concrete you’ve got, the longer it stays hot. And so, you want to build these things with the lowest possible thermal inertia, and you want them well ventilated, so that they cooldown to the ambient as quickly as possible. And you want to monitor your image quality so that you can take advantage of it. And people just weren’t doing that.

And so, what was — there was a paper on arXiv a day or two ago. It may have just been last night — talking about — probably last night — the image quality on the Mayall Telescope for the DESI instrument built by Lawrence Berkeley Lab. You know, and guess what? If you work hard at measuring the image quality, you can do better. And there were a lot of things you can do. Your primary mirror is this big thing, and one of these telescopes, your primary mirror, order of magnitude, weighs ten tons. And it might be a meter thick or a half meter thick, depending on the telescope. But it doesn’t matter whether it’s a meter or a half meter, or honeycomb, or not. It is not sufficiently rigid to maintain a surface. So, you take that thing and tip it over on its side, it’s going to flex. You know? I don’t want to break a pencil, but this thing flexes. You don’t see it, but it’s flexing when I — you know, and the mirror does that under gravity, also under thermal stress. So, you need to monitor what the surface of your mirror is and compensate in the mirror support for those changes in the surface. That’s called wave front sensing.

We did very crude wave front sensing at Michigan-Dartmouth-MIT, and we got better images than anyone else’s the telescope. And people who were building — Matt Mountain, who was in charge of making Gemini work, came to look and see what we were doing. He said, “You’re doing everything we’re talking about doing for Gemini.” You know monitoring the wave front, correcting actively in the course of the observations. Don’t wait until it goes bad to focus. Proactively make good images. You know, and the measure is whether or not you’ve got a differential image motion monitor outside, measuring the scene, and whether what you’re measuring at the telescope is the same as what you’re getting outside or not. The differential image motion monitors work. And if your telescope isn’t producing images that are as good as the ones out there say you should be getting, you’re screwing up. So, astronomers were bathing in their own heat and have continued to do so into the 2000s, 2015s.

When I was twelve, I fell off a bicycle. I chipped my front tooth. It wasn’t so big. So, I just spent thirty years with a slightly chipped front tooth. When I moved, actually, to Cambridge, I went to a dentist, and he said, “You know, I could fix that for you.” And he did, and he did a very nice job. It’s great. I see other people’s images, and I tell them, “You know, I could fix that for you.” Did you get that? They don’t listen! Not invented here. They don’t listen. It is not rocket science. You can make better images. We have better images at Magellan, without adaptive optics. Other people get their images with adaptive optics. But just by controlling the primary and secondary mirror, we do better than anyone getting on any telescope in the world, in terms of not having — we’re talking about correcting on a timescale of thirty seconds, not on the timescale of thirty milliseconds. And all we’re doing is delivering what that differential motion monitor outside is saying we should be getting. All we’re doing is not screwing it up. So, I became a seeing nut when I went to MIT. By God, we’re going to produce great images. We’re going to do everything we can to produce great images. And when we got into Magellan, we’re going to do everything we can to produce great images. And so, working with the late Matt Johns — I’m sorry to say — we produced a very good system for monitoring the image quality and instantaneously updating it. Dare I say, the best on the planet.

Zierler:

Paul, the pursuit for better images: to what extent is there an aesthetic component that you just want to look at better images? To what extent is this because there are specific questions you want answered for which only better images are available? And to what extent is it just because when you see an opportunity to do better work, you go for it?

Schechter:

So, I’m going to show you something. It might take a minute. Do you need to get a cup of coffee?

Zierler:

I’m fine. I’m great.

Schechter:

Alright. Let me do a little searching here. You know, I could show you all these things. These things are so beautiful. These gravitational lenses. Okay, here we go. Let me find you — let me share. There’s something else I wanted to share, but we’re not there. Okay. Can you see a bunch of — three rows?

Zierler:

Yeah.

Schechter:

All of those are gravitationally lensed quasars. What you see in the top row — I’ll lie a little bit — are images taken with the Dark Energy Camera on the Blanco Telescope. And these are the discovery images. Looking at those things, we said, “You know, that thing actually is quadruple.” You know, when they make the catalog, it all gets smushed into one object. This particular case, it got split into two objects. Otherwise, it all got smushed into one object, because how do you tell if it’s one object or not? What you see on the bottom are Hubble Space Telescope images of the same things. Are those things beautiful? The better the image quality, the more beautiful they are.

Zierler:

Yeah. Yeah.

Schechter:

And what you see in the middle is Magellan. Magellan is a hundred miles north of Cerro Pachón, where these images were taken. The atmosphere is the same. It’s the same the entire length of Chile.

Zierler:

Wow.

Schechter:

The local windshear isn’t much different. Their differential image motion monitors produce the same that ours do. In 2000 — I think it was 2003, maybe 2005, I wrote to the then-director of National Optical Astronomy Observatories, who were then planning the Dark Energy Camera, and I said, “You know, I could help you make your images better.” And: oh, yeah, yeah. So-and-so is taking care of that. Ten years later, the then-director of NOAO, with the Dark Energy Camera then into its fourth year of operation, said, “Paul, you’re going to have a heart attack, but we finally started controlling the primary mirror.” (Laughter) And it just didn’t seem a priority to them. Look at this! How could this not be a priority? And the fact that people don’t hear you just makes you get more strident. You know, The Rime of the Ancient Mariner, and the guy starts out, and the first line is, “There was a ship!” He’s grabbing people by the lapels saying, “There’s this story. I’ve got to tell you! You could do better.” I had somebody from ESO visiting, checking out our telescope, watching our images come in, kneeling in front of the guide camera, jaw dropped. I won’t say “drooling,” but transfixed at the quality of our images. And this is not rocket science. Anybody can do this. This is just not hard. The ideas are simple. The instrumentation is more than adequate. You can control what your telescope is doing and deliver what the atmosphere is delivering. So, I became a seeing nut and an image quality nut.

Zierler:

But aesthetics is part of it. It’s clearly part of it for you.

Schechter:

Oh, these things are beautiful.

Zierler:

But does beauty automatically translate into: better science can happen as a result?

Schechter:

Oh, sure.

Zierler:

Or is beauty just sometimes the end goal?

Schechter:

You see that one?

Zierler:

Yeah.

Schechter:

This is all Magellan images again. So, Tommaso Treu is using gravitational lenses to measure the Hubble constant. You’ve got something called the Hubble tension. These gravitational lenses, the ones we discovered, are among the ones he’s measuring to produce the Hubble tension. Now, that isn’t my particular science. I use them for something else. But they’re incredibly useful for a bunch of different things, and they’re useful, and they’re beautiful. How could you not work on these things? Okay. Stop share. You know, I tell students at MIT, our job is to help you find something you love. You work with me for six months. See how you like the kind of stuff I’m doing. Then you go work for someone else for six months. See how you like what you’re doing with that person. Find something you love. If you leave here having found something you love, we’ve done our job.

Zierler:

Yeah. Has that borne out with some of your graduate students? Have you experienced that pleasure?

Schechter:

I have not been very good with graduate students. I’ve been much better with undergraduates.

Zierler:

Would you self-assess as to why that might be the case?

Schechter:

Well, for one thing, I haven’t brought in shiploads of money. So, I’ve had relatively few. MIT does not have an astronomy department. And so, people back into astronomy at MIT, starting out thinking they’re going to do physics or astrophysics. And so, we compete for graduate students who are interested in astronomy. We don’t get them. They go to the places that radiate — “We’re astronomers here.” And so, in a respect, it was a mistake. And after twenty years, I realized I had made a mistake, that a physics department was not what I needed, because I wasn’t getting the graduate students, and to a certain extent, I wasn’t getting the postdocs, and to a certain extent, I wasn’t getting the fellow faculty. We kept losing people who would just be more comfortable working in an astronomy department. I don’t have to name names. People who know who was where, who was an assistant professor at MIT and went some other place — you know, they would prefer being in an astronomy department, and I understand that, because the physicists have this notion of what the right physics is, and astronomers are much more accepting of the different things that might pan out. So, when we have tenure cases, we’d have to make cases to physicists, and sometimes it’d be damned hard. In some cases, I couldn’t get appointments through, because — first of all, the physicists just didn’t see the cosmic significance, the cosmic frontier. They didn’t understand that astronomy bubbles up from funny things that you wouldn’t expect it to bubble up from. So, we find things that are gravitationally lensed. Who would have thought that? Well, actually, you know who would have thought that. Bill Press and Jim Gunn, who we’ve talked about, in 1972 wrote an enormously prescient paper on gravitational lenses, seven years before the first one was discovered. If I keep circling around to the same people, there’s a reason.

Zierler:

Yeah.

Schechter:

The only people I know. Well, that too.

Zierler:

Paul, looking back with the Magellan telescopes, given how central you were to their development and —

Schechter:

We look back twelve billion years.

Zierler:

Yes. Yes. But let’s keep it physically in Chile. In terms of the goals from the starting point, what has played out, more or less, as you expected? What have been, perhaps, some disappointments? And what have been some triumphs that you might not have even seen coming?

Schechter:

First of all, I wasn’t there (laughter). Actually, I was there at the start, and that actually had some influence on my leaving Carnegie. It started at Carnegie, and I figured: oh, hell. This is going to be ten years of hell building these telescopes. It’ll be total chaos. Everything is going to be sacrificed to building the telescopes, and I don’t want to do that. So, that was part of my leaving for MIT. Then eight, nine years later, they were looking at partners, and we got in with a fantastic deal at the last minute, not having earned any of the sweat equity. The sweat equity was Steve Shectman, my collaborator on the sky surveys; Matt Johns, project manager; and a bunch of other people. Al Hiltner, early on. Frank Perez. Steve Gunnels. Engineer. Absolutely crucial. The people at L and F Industries did a fabulous job on building those telescopes. And at the last minute, because somebody left MIT for Caltech — thank you. I don’t want to say that, because he was a good colleague, but thank you. I said, “If we don’t have a big telescope, they’re constantly going to be leaving us for Caltech.” So, that guy who left got us into Magellan. You know, MIT was not used to using its own money to buy into telescopes. MIT was used to using the government’s money to do things.

Zierler:

Right.

Schechter:

But it found $7.2 million of its own money to get us into Magellan. By that time, most of it had been done. But Shectman knew what I’d done at Michigan-Dartmouth-MIT for the image quality, and he said, “Okay, Paul. The active optics system is yours. You do that.” Fine. So, I did that, and that was just the last — two years from discussions to having something working. And the first night, Steve Shectman had — fabulous. Steve was the guy who was the astronomer, and when he got a CCD onto this thing, he sent me an email the next day. This is even before the dedication. He said, “Paul, you’re not going to believe this.” And he sent me images that were 0.35 arcsecond seeing. There’s a white board, or was a white board, at the Blanco Telescope that had a record of the best seeing images ever at the Blanco Telescope. And the very best one on the board the last time I was there, which was 2000, was 0.68 arcseconds. The first images Steve saw at Magellan were half that. You know, part of that was luck, of course (laughter). But you know, we had done something right.

Zierler:

Paul, as you are getting closer to retirement —

Schechter:

As I was being restrained from retirement.

Zierler:

(Laughter) Well, therein lies a story. What’s that?

Schechter:

You know, my partner didn’t want to have to worry about what trouble I might be getting into at home.

Zierler:

Yeah. Yup, yup, yup. As it was coming, what were your considerations in terms of — you know, retirement in your world means there’s just more time to work on the stuff that you wanted to work on. Right?

Schechter:

You just answered the question.

Zierler:

So, what was that stuff? What did you want to work on to get away from the committees?

Schechter:

Finding gravitational lenses. I’m using them to measure the — okay, so this will sound good to you. It isn’t what interests me. But we set very good limits on primordial LIGO mass black holes. Whatever’s producing the LIGO signal, it ain’t primordial black holes. We set very good limits on that. You know, that’s actually not what interests me. What interests me is the stellar content of the galaxies. We can measure, like nobody else, the graininess of the gravitational potential. So, other people, they measure the light and they multiply by some number, and that gives them a mass in the stars. We measure the graininess in the potential, the microlensing, by the stars. And we can assign — tell you how much graininess there is in the potential, and therefore how much stellar mass there is. Now, were there LIGO-mass black holes at a cosmologically significant density, we would see those too. But no, there aren’t. But what really interests me is the stellar mass in the galaxies because to this day, the question of how much is dark, and how much is stellar, is poorly known, because we’re always measuring some light and multiplying by a number. You can get the total mass from the rotation curves but dividing it between stuff you can see and the stuff we can’t see requires a measurement of the gravity, if you’re interested in mass on that scale.

Zierler:

Paul, let’s go to the big retrospective questions now for the last part of our talk.

Schechter:

John Torvy evidently stole it from Hal Abelson. Someone I know at MIT says, “If I have seen less far than others, it’s because giants are standing on my shoulders.”

Zierler:

(Laughter) Ah, that’s great. What a great disclaimer.

Schechter:

So, I am not the big picture guy.

Zierler:

Yeah, but in terms of what you’ve accomplished and who you’ve been around, you have insights to the big picture. So, let me ask it like this: in your world, it’s a world of gradations, in terms of what’s understood and what’s not understood. So, I wonder, to really boil it down: going back to Caltech and when you really started to come into your own professionally, academically: what was totally not understood then, that is really well understood now? And what was mysterious then that more or less remains as mysterious today as it was then?

Schechter:

Allan Sandage was not a nice man, but he did great science. Allan wrote a paper in Physics Today, 1970, “Cosmology: A search for two numbers.” And today, people ridicule that paper. “Oh, ha-ha-ha-ha, cosmology, a search for two numbers. Everybody knows that we get so many numbers out of the cosmic microwave background.” You know, there’s much more to cosmology than that. Allan said the two numbers were the first and second derivatives of the cosmic expansion: the Hubble constant and the acceleration, which we now give a bunch of different names. In those days, it was called q₀ [q naught] and it was strictly an acceleration. Today we have the third derivative. If you can find it, if you have access to the New York Times paper, go look for “Cosmic Jerk [Disarmed].” [https://www.nytimes.com/2003/10/11/us/a-cosmic-jerk-that-reversed-the-universe.html] ” And my friend Adam Riess has his photograph under that headline. You know, “jerk” is the third derivative (laughter).

Zierler:

Yeah. Yeah (laughter).

Schechter:

So, they played a very nasty trick on Adam.

Zierler:

Ah.

Schechter:

I tried to get a copy of it, but the New York Times wants a phenomenal amount of money for copies of their pages. It’s not criminal. It’s what the traffic will bear. The people who want those pages are willing to pay — have the money to pay it, but I didn’t buy him an electronic copy of that. Those two numbers that Allan Sandage spoke about have been measured. We know what they are. That was the holy grail, and they have been measured. So, in that regard, it’s done. Now, what about all these other numbers? That’s mere physics. Those two numbers are on one side of Einstein’s equation, and they describe the geometry, and everything else is the stress energy temperature — tensor. Will you tell me what goes in there? What kind of particles you got? Fine, you tell me the physics. We’ll put in the stress energy tensor. That’s not interesting. The only two interesting numbers are the scale — the Hubble constant — and whether it’s open or closed. Have you been to Cambridge in the last few years?

Zierler:

No.

Schechter:

The area around MIT doesn’t look like it did when I got there. When I got there, it was factories that were disintegrating. It’s now biotech.

Zierler:

Yeah.

Schechter:

It’s said to be the third hottest real estate market in the country. The city of Cambridge is rolling in money. My property taxes are half what they would be in the next town over because of all the biotech and other tech that’s around here. But biology is a big deal. In the late — mid-1990s at MIT, they decided to add a biology requirement. And the biologists, because they wanted to endear themselves to us, said: No question. Physics was the subject of the twentieth century. Biology was the subject of the twenty-first century. So, look. You know, when you come up, you have questions. The questions I had were mostly answered. There were some interesting ones that remain. The gravitational lenses A, can help answer them, and B., they’re beautiful, so that’s what I do. But all these guys who are fussing about whether — the power len, index of the equation of state — you know, how much does this — you know, how big a difference is it to you? I mean, yes, if it is precisely 1, that’s something special. At what point do you say: yes, it’s precisely -1.

That’s a good question to ask people when you talk to them. You know, or is it -1? -1, plus or minus what? Will you say, “Okay, uncle. It’s -1”? Interestingly, on the curvature, they were all willing to say that when you added the dark energy to the matter that the curvature was flat. They were willing to do that when it wasn’t established to within five percent, because that so coincided with what they wanted. But on the cosmological constant: oh, no, 1 percent isn’t enough. They’ve got to push further than that. You know, when is good enough? I’m very fast to correct people when they say I’m an astrophysicist. The hell I am. They want to call me a cosmologist. Well actually, I’m not a cosmologist. I heard a great talk by Paul Steinhardt, in which he said that the difference — the cosmologists work on things that are in the linear regime, and the astronomers or the astrophysicists, work on things that are in the nonlinear regime.

Zierler:

Hmm. That resonated with you.

Schechter:

Yeah. You know, they like the CMB, because it’s in the linear regime. You know, we like galaxies because they’re beautiful and nonlinear things.

Zierler:

Paul, I wonder if you could reflect broadly over some of the technological advances in telescopes over the course of your career. What’s possible now that wasn’t forty years ago?

Schechter:

Well, for one thing, it helps to have a hundred times the quantum efficiency. For another thing, it helps to have twice or three times better images. And you know, there is more money available, because this stuff is interesting. There’s more money available because DOE is going to put money into it. So, you can — you know, we build instruments now. Is it fair — it probably isn’t fair to say — what fraction of a Palomar is going into the camera for the Rubin Telescope? In terms of man hours, equivalent man hours. You know, inflation’s been a factor of 20. It’s hard to say. But that telescope was built — there’s a book by a guy named Florence, The Perfect Machine, that describes the Palomar Telescope. You know, I think it was built for what was then $10 million. So, multiply by twenty. That’s $200 million. The camera for the Rubin Telescope is $200 million. So, we have, until now, been willing to put more and more money into this, and we astronomers — and also physicists who are now doing astronomy — are the beneficiaries of that excitement (laughter). And do they get good value for their money? I think we tell a good story.

Zierler:

Paul, last question, looking forward: what are you most excited about? What are the things that you think the field has —

Schechter:

Lunch?

Zierler:

(Laughter) A little bit beyond that.

Schechter:

Dinner? (laughter)

Zierler:

What do you think are the most fundamental discoveries waiting to happen, and who’s going to do it? What do you think will happen in your lifetime?

Schechter:

That’s precisely the kind of question that — where I see less far than others. That’s precisely the kind of question for which I am the least good.

Zierler:

You could take a stab at it.

Schechter:

It’s not the stuff that everybody thinks about. It’s stuff that somebody’s not thinking about. So, you’re asking me: what are other people not thinking about? Alright, I’ll tell you (laughter).

Zierler:

That works.

Schechter:

No. I won’t tell you what other people are not thinking about (laughter). You know, if you just address the questions that are currently interesting, there’s a good chance — because the universe is so wonderfully complicated — that it will show you — that it will present you with things you weren’t expecting. So, go ahead and tackle those things that are questions that are relatively interesting normal science questions, and if you’re lucky, something exciting will grab you. You know, we were looking for the luminosity function of galaxies. We found the Boötes Void. Thank you very much. That’s great. Kirshner and his students were fully expecting to find deceleration. It didn’t happen. That’s good. Ray Davis was expecting three times as many neutrinos as he got, and for years, people said he — didn’t know his own experiment, and they told John Bahcall that he didn’t know how to calculate (laughter). So, there’ll be people doing things that are interesting, and you know, measuring cosmic structure. Trying to measure cosmological parameters to a percent is not crazy. It’s the only universe we’ve got. We might as well know it as well as we can.

Zierler:

And for you, you remain part of the field. What do you want to do, personally?

Schechter:

So, I want to find the stellar mass fraction in galaxies. That translates into something called the initial mass function and where it ends. You know, how far — people model the spectra of galaxies by saying: I take so many stars of this mass, and so many stars of this mass, and so many stars of this mass, and I put them together, and I synthesize the light that I get from the galaxy. And then I add up all the mass that it took to make, and that’s how much we have — mass bringing that light we have. So, you ask the guys who do this, and they say: well, you know, those very low-mass stars, they don’t produce much light. What’s the lowest mass star for which you think you’re seeing some light? 0.15 solar masses. Oh, that’s pretty good. And what fraction of the stellar mass in the galaxy is from stars that are less massive than that? seventy percent, he says. So, they have no idea what the stellar mass is. There’s something happening that they can’t see, and they make guesses. They make guesses based on the solar neighborhood, which may or may not be representative of the universe. They make guesses based on how they think stars form. They just don’t know. So, I want to measure the stellar mass fraction in galaxies. Is that boring? Yeah. Is it fun? Well, I get to have a lot of fun in the process. Got to find gravitational lenses. Got to observe them with telescopes. Sorry to end on a down note.

Zierler:

Not at all. And I didn’t hear a down note. I heard “fun.”

Schechter:

Well, there you go.

Zierler:

Paul, it’s been great spending this time with you. I really appreciate it.

Schechter:

Okay, good.

[End of Recording]