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Interview of David Shoemaker by David Zierler on September 7, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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This is an interview with David Shoemaker, Senior Research Scientist at MIT, with an affiliation at the Kavli Institute for Astrophysics and Space Research. Shoemaker explains the relationship between LIGO, the MIT Department of Physics, and Kavli, and describes how these relations have changed over the years. He recounts his upbringing in Virginia, then Walla Walla, then Eugene Oregon, and then in New Jersey, where he spent his formative years, as his family moved to accommodate his father’s career. Shoemaker discusses his academic and social troubles in high school, and his undergraduate experience at Drew and then Tufts, where he majored in physics. He explains why he did not complete his undergraduate degree, and how he got to know Rai Weiss and the opportunity he offered to work as a technical instructor in the MIT Junior Lab. Shoemaker describes his decision to enroll in MIT’s graduate program, and he describes the Lab’s role in the COBE endeavor and the FIRAS interferometer project. He describes his work at the Max Planck Institute where he continued his focus on building interferometers, and he explains his decision to move to France to work with Alain Brillet. Shoemaker recounts his decision to return to MIT at the point that Weiss was becoming further involved in the LIGO effort and was forging partnerships with Caltech toward that end. He narrates the point at which MIT institutionally began to support the Lab’s work, and he emphasizes that the support predated any notion of LIGO’s success as a foregone conclusion. Shoemaker explains the early successes and promises of Advanced LIGO, and he provides a detailed account of the detection of gravitational waves, and the significance of this discovery. He describes the day of the Nobel announcement, and reflects on the impact of the attention LIGO received for the prize, for better and worse. Shoemaker discusses the post-Nobel life of LIGO and how, in many ways, the detection should be understood as a starting point for further additional discovery and not just the coda of a decades-long endeavor. At the end of the interview, Shoemaker muses on what lessons might be drawn from his experiences and the improbable nature of his successes in the field relative to the academic challenges he faced earlier in life.
OK. This is David Zierler, oral historian for the American Institute of Physics. It is September 7th, 2020. I’m so happy to be here with Dr. David Shoemaker. David, thank you so much for joining me this morning.
OK. So, to start, would you tell me your title and institutional affiliation?
I’m Senior Research Scientist at the Massachusetts Institute of Technology.
And what are the additional affiliations within MIT that you would be a part of?
I am in the Kavli Institute for Astrophysics and Space Research, commonly known just the Kavli Institute, which gathers together the astrophysics activities at MIT.
Right. So, can you explain a little some of the affiliations between—so there’s Kavli, there’s MIT Department of Physics, and there’s LIGO. How do these three boxes work together or not, as it were?
It sounds like a clear case of triangulation. You get different answers from every person that you speak to, right?
Some of the answer lies in the history of the group, which did not fit comfortably anywhere into the MIT environment when it first got going. It had been, in the early days, part of the Research Lab of Electronics. But it sounded to some administrators like the Center for Space Research, which is the predecessor of the Kavli Institute, would be the right place because we ultimately were going to be looking up into the sky to see what we could see. And that’s how we obtained our affiliation with the Kavli Institute, which is an interdisciplinary organization. Most people in it are from physics. There’s some AeroAstro people, Earth science, Mechanical engineering, etc. But it was the place where satellites were built, and where instrument scientists interested in research having to do with astrophysics and space research were gathered together.
That entity has had, I think, different levels of depth of interface with the physics department as the years have gone by. Clearly, most of the faculty members are physics faculty, and so that’s played a big role. And I think it’s become really much more the center for astrophysics at MIT over the years, and not just a place where satellites are being built.
All of these things, for me, are seen from a bit of a distance. I’m not a faculty member. I don’t teach. And until I’d say fairly recently, basically about until when we detected gravitational waves, when MIT got a lot more excited and interested in what we do—
—our group felt largely like an island. Part of that was—well, a lot of that was intellectual, having to do with the gap in the technologies we were interested in, and the seemingly unreasonable expectation that we might actually see gravitational waves. But then the other thing is that there were geographical separations on the campus. We require big spaces, require high bays, cranes, lots of laboratories, and so forth. And that held us at the edges of the campus, first on one edge when we were in Building 20 in the old MIT Rad Labs building, and then now at a different edge of the campus. So we don’t run into people in the hallways easily, unless one makes a real effort to make the incredibly long eight-minute walk from our laboratory over to the building where the Center for Space Research or now Kavli Institute is housed. And it’s not the kind of thing that I would’ve done often while I was trying to get an instrument built because it just would’ve been a distraction of some sort.
Thus, honestly, I don’t know an awful lot about these relationships—the specific relationships to the Kavli Institute. And, secondly, there’s been a great deal of evolution toward more of an integrated approach and more of a sense that we are really part of the Institute and a treasured part of the Institute. I think that’s taken seriously. It’s not just opportunism. We’ve gotten a lot closer in the last two or three years, but also gradually over the last five years, 10 years.
But this is quite clearly very much a post-2016 way of understanding these things. You would’ve had a much different answer earlier than that.
Yes, but a lot of what you would’ve gotten back from me was, “I don’t know.”
[laugh] I would have had to ask someone -- What does MIT do? What does the Kavli Institute do? What purpose does it serve? And I can tell you a bit more about that now. But you can get more of that from other people.
But, yeah, there’s definitely been a continuum of increased interest and commitment to the gravitational wave field over the last, well, 15 years or something like that. But the slope has not been linear.
And how much do you understand this within the context of this amazing narrative of Rai Weiss sort of toiling on his own for decades on end, without much institutional support from MIT at all? Do you understand that narrative as the sort of foundation for the way these things played out institutionally?
Yes. Now, in some measure, that’s because some of my knowledge is second-hand, and it comes from Rai Weiss—
—with of course my own observations at the periphery to understand it. And I think Rai sees himself as—how can I say this? He was slower to accept the fact that the Institute was ready to come around to the value of the research than he should have been, and I had less of a predisposition to suspect the worst of MIT than did Rai.
And so I could see, in a more continuous way, the fact that there were faculty who were making significant commitments of time and reputation to try and pull things for LIGO to the right place. And, there were some individuals from quite some time ago—the John Deutch story will be told by others —who were openly antagonistic. There were certainly a lot of faculty who thought, like most people in the world, that the instrumental goal was inaccessible. And I think there was a general lack of appreciation in the astrophysics community that this could actually be a tool that would be useful as more than a toy demonstration of general relativity.
All of those things changed gradually, but yet more quickly than Rai realized. And, I have my own complaints about things that have happened at MIT connected with my own career. But I think it’s actually gotten just continuously better with time.
And where is Caltech in all of this?
Well, I’m sure you’ve already heard three or four versions of the interactions between MIT and Caltech in the early years. It’s clear that Caltech, motivated by Kip Thorne, saw a great opportunity. I also think that the small scale of the institution, and the fact that they like to be strategic about where they put their resources, made it so that they could choose to make a unique commitment to gravitational wave observation and science early on that is just not MIT’s style, you know.
They have a very, very broad palette of interests, and they’re careful not to put too much focus in any one place or another. And, of course, [we would] have this problem if they were to suddenly shove a bunch of resources into gravitational waves, there are 100 other projects who say, “Why not my project as well?” Right. And so I see Caltech as having made a real commitment, a strategic commitment, motivated in some measure by the excitement about the science, in some measure about the prospect of garnering a Nobel Prize or two. That was not the approach at MIT, and so, as a consequence, there was a shift of the attention of the project from MIT to Caltech.
I really firmly believe that it was Rai’s very deep commitment to success of the field, to having a broad umbrella that would allow a lot of different people to participate, a recognition that it takes many, many people to do this, that enabled the field; he’s the person who drove that perception that was absolutely central to the success of the thing. But it was the leadership and the institutional resources of Caltech that made that vision possible. And, of course, as a consequence, Caltech has made a point of keeping the attention of the project on itself. And that’s been painful over the years in terms of getting recognition for MIT’s contributions. One of my favorite points of frustration has to do with Harry Collins; you must be familiar with Collins and his writings.
I don’t know if you’ve suffered through the books or not.
But he chooses data to support his theories from the historical resource, and he also chooses to make his stories engaging by focusing on aberrant behavior in science. That’s my—
—my probably naïve reading. I like the guy and I enjoy having a drink with him, but I don’t like what he does. And I think that one of the consequences of what he has done is to really focus the history on the activities at Caltech, and the things that have happened there. And, as a consequence, I think MIT’s very central role, not only Rai’s leadership but also the broader exceptional development of instrumentation, and the first attempts at upper-limits data analysis that took place in the MIT group, sort of fades into the background because it’s not part of Harry Collins’ story. And something that I’m very excited about is the fact that Dan….
Kennefick, Dan Kennefick?
Yeah, exactly, Dan Kennefick. He is engaging to start to work on a history of LIGO, and I don’t know how deep and how far he’ll get with it.
I’m part—I’m actually part of that endeavor, so—
Ah, OK, great.
—I’m very familiar.
So I must have exchanged emails with you in the past as we were trying to find a former memorandum of understanding—
—with like a scientific—ah, OK.
[laugh] How do you do?
[laugh] Yeah, that’s right.
Well, David, that’s great. Let’s take it all the way back to the beginning now. I’d like to ask first, tell me a little bit about your parents. Where are they from?
OK. My parents both grew up in the Northwest: Idaho and Washington. And my mother was the daughter of a very, very gentle pair of parents—a lawyer and a homemaker. And my father was the son of a civil engineer, and an extremely aggressive and ambitious mother—again, a homemaker. I’ll mostly talk about my father. He had a very strong influence on my intellectual thinking.
I think my mother’s gentle ways also have been important to the way I’ve navigated through life. But it’s just not something which becomes so obvious when you talk through the things that happen, especially in the domain of science.
My father was one of five brothers. They were all driven by their mother to succeed and to compete. And they I’d say all had fairly spectacular careers in their different chosen fields, all got doctorates, and went through a variety of different—I mean, there’s Frank Shoemaker, who was a physicist at Princeton, Sydney Shoemaker—
Oh, yes, yes.
Do you know of him?
I know of Frank Shoemaker, yes.
Yeah, a character.
Do you know, it’s a kind of—it’s not a very common name, but it’s a common enough name where you wouldn’t automatically make those connections, but, yeah.
Yeah, OK, good. So, yeah, Frank Shoemaker was one of my father’s brothers. He was the fiercest competitor, in fact, with my father. Sydney Shoemaker’s a philosopher at Cornell. Roy Shoemaker actually was a nuclear engineer at the Hanford Works.
And the family suffered health consequences. And, let’s see, who else? We have David Shoemaker, who was a chemist—a physical chemist—at MIT, and then went off to Oregon afterwards.
It was a group of people who were extremely driven. My father chose psychology, and was a faculty member at a couple different universities, bouncing around, looking for tenure. And then got an offer from Bell Labs, and a doubling of salary if he was willing to move from the West Coast to the East Coast.
I didn’t know Bell Labs employed psychologists. That’s very interesting.
My father was a training psychologist. And I remember fondly visits to the University of Oregon laboratories to feed all of the animals that are used in the experiments, and the construction of mazes out of Masonite, and microswitches, and lights, and solenoids to drop bits of food, and so forth and so on. He was a Skinnerian, a builder of experiments, and wanted to find a simple linear scientific way of describing behavior of all kinds, including human behavior—a good old-fashioned psychologist.
He had been in the Navy, like so many other people of his age and time, and he cheated a bit to get in a year early. And an important element in this story, from my perspective, was that he trained to be and worked as a radar technician there, and learned electronics in the Navy, and left a couple of books about radar technology in the house. And that’s where I learned electronics. But he then went to Bell Laboratories to do research in training for the Bell System, which, of course, at that time, was this monolith, this wonderful monopoly that served us so well for some period of time, and discovered that he was very good at managing people who were working on training issues, and ended up at AT&T, the parent institution, as the director of training research for the Bell System.
As you can imagine they had at that time around 1 million employees who most all went through some training or education. They had universities across the US for training people to do different things like be operators, be telephone-repair persons, to put telephone equipment together, etc., because it was a soup to nuts organization at the time.
So there was a great deal of interest in quality education, which had a very specific objective of training skills. My father became one of the leading proponents of programmed instruction, the sort of thing where you open a book, and it says, “A transistor has three leads.” And you turn the page, and the question is posed, “How many leads does a transistor have?” If you got the right answer, then you turned to the next page. And if you got the wrong answer, you were invited to turn the page back again, and read the previous page.
And how—when I talk to a number of people, for instance my wife, about that way of learning things, she says, “That’s just awful—a terrible, terrible idea.”
But the fact of the matter is when you finished that little booklet, you would know how to build a transistor amplifier. [laugh]
This sounds very much like the Organization Man sociology approach of the 1950s and ’60s.
I don’t know the book, but he certainly was a man of that epoch. So, anyway, my father had this career in, first, Bell Laboratories, and then AT&T, and ultimately much of his career was spent managing large organizations. And that’s actually what I’ve ended up mostly doing, so there’s probably some contagion there.
[laugh] Now, did you grow up—were you close enough with your uncles who were scientists to sort of get a front-row seat to what that kind of a career and life was like?
I’d say that was not a strong formative influence. We saw Frank and his family sort of once every few months when my father and Frank were getting along. And when they weren’t, a year could go by. I also spent one summer with David Shoemaker and his family, on Lake Winnipesaukee, and I think I learned more there about how good citizen scientists comport themselves than I realized.
Now, you grew up in New Jersey?
I was born in Boulder, Colorado in 1953, lived there for 6 weeks, moved to Virginia, where my father was working for the government, and maybe in something which was a bit secret, having to do with training. We then moved to Washington—to Walla Walla, Washington—University of Washington—and then to Eugene, Oregon, where my father taught again, and then in 1959 moved to New Jersey, where my father was at Bell Labs nearby. And then when he was working in New York, we still lived in New Jersey. So, indeed, from, I don’t know, the age of 6 to 17 or so, I lived in New Jersey—in Northern New Jersey.
What town, where in New Jersey?
We were in—mostly in Scotch Plains. And Frank was down at Princeton of course, and it’s an hour drive or something like that. And so no, I would not say that I was close enough to Frank to have a sense of him as a scientist being a formative influence.
However, I can remember very distinctly one evening – I think it was probably a Thanksgiving that we were down visiting Frank’s family that he got a call sometime after dinner, 7:00 or 8:00 in the evening, that a large motor generator set in the laboratory had stopped working, and they wanted to know if Frank could come and fix it. So I went with him to Princeton to the labs where he was working. This huge concrete door against the radiation opened, he walked in, looked at this thing as big as a house, took out his Swiss Army knife, pulled out a couple of carbon brushes that were 6 inches across, scraped off their surface with the Swiss Army knife he always carried, put it back together again, and it worked.
I’m going to be a physicist.
[laugh] That got you.
And not just a physicist, but an experimentalist.
Absolutely as an experimentalist…basically as a car repairman in a different domain. And that was a key moment, but I wouldn’t say that was when I got the sense of what science is and what’s exciting about it, and how to think like a scientist, how to do troubleshooting; those are things I learned from my father—
Were you naturally—
—just because he was always fixing things and building things.
And so you were a tinkerer. You had that sort of in your blood?
Always, and certainly acquired from my father.
Right. And as a legacy probably of your paternal grandmother, you also had many access points to think about pursuing a terminal degree, and working in a—you know—at that level was definitely something that was—it was part of your purview?
In other words, like you said, like a car repairman. If you had grown up in a more blue-collar family, it might’ve felt simply more natural to direct those skills into a muffler shop, for example.
Absolutely, absolutely, or musical instrument building or something like that. I’ll add that my father was a formidable musician – cello, piano, organ, and conductor, and I also continue to play regularly. I think that the connection to academia, the notion that you should strive to learn and enjoy what you’ve learned was something that came from my upbringing, and particularly my father.
Now, in school, did math and science come easily to you?
School was a disaster for me from day one. I’ve never performed well in academic environments. I failed out of more programs than you can count. [laugh]
I almost didn’t finish high school because I missed so many classes because I was taking drugs too often. And then went to Drew University for a year and a half because I applied to a bunch of top-rank universities, and they all turned me down, but Drew accepted me. And then transferred to Tufts University. My sister was at Tufts University. She is two years older, a brilliant person, and much more focused and made a much more linear path through the academic life than I. And I was always two years behind her; the teachers would always say, “You’re not like your older sister, are you?” [laugh]
Now, despite your academic shortcomings, that formative experience with your uncle at Princeton when you knew you wanted to be a physicist, did that translate into you knowing you wanted to pursue a physics degree as an undergraduate?
It took a couple of years. The first year and a half, I was still recovering, I would have to say, from the excesses of my youth, and learned how to learn, and learned the joy of learning things that were tough, and for a while thought about linguistics after a couple of really good courses in linguistics at Drew, and also courses in music composition. But I also took a couple of physics courses, and really enjoyed those, and actually even did reasonably well in them. And so, by the time I left Drew University and went to Tufts, I was pretty sure that I wanted to have a physics major as an undergraduate.
And Tufts has a pretty solid physics program.
It was a good physics program. I didn’t do well in it, but it was a good physics program.
What year did you start at Tufts? What would that have been?
Let’s see, it must have been February ’73.
OK. So you’re really one generation after the Vietnam generation in college?
I finished high school in ’71, went to Drew ’71 to ’73-ish. And then from ’73 to ’75, I was at Tufts University.
OK. So you actually did catch the tail end of those era—that era?
I had a number in the final military draft lottery of seven out of 365, and Nixon ended the draft probably within days of the time they would’ve sent out the letter. So I was just indeed at the tail end of Vietnam; there was certainly a very big question in my mind what I would do if I’d received the letter, yeah. But I didn’t go, and didn’t have to seek a deferment or a vacation in Canada.
So, yeah, it was ’73 to ’75 that I was at Tufts University. There, I did pursue the coursework for a physics degree, and finished the course requirements. I also spent a year helping to develop experiments for an undergraduate teaching laboratory at Tufts. And that’s what I really loved doing. That was the thing that was the most fun for me in my work there. I never did get an undergraduate degree from Tufts. They had a language requirement, and I didn’t want to get myself to make those funny sounds in front of people. It is amusing that I ended up learning German and then more-or-less adopting French as a second maternal language.
So I never finished my degree at Tufts University. The next transition came when Rai Weiss was looking for a teaching instructor for the physics undergraduate lab at MIT. Rai called up Allan Cormack, the Tufts Physics Department chairperson, who subsequently won the Nobel Prize for his work in developing the mathematical background for X-ray tomography, and said, “Do you know anybody who doesn’t know what the hell they’re doing?” [laugh]
And so, with that, Rai got a recommendation for me and—
He was looking to add to his merry band of misfits?
I think that’s right, or take your choice of how you want to describe it. He was looking for someone who would capable of carrying out a task, you know. He didn’t want a loser. He wanted somebody who could actually do the work. But he was perhaps also looking for another soul to save. So, at any rate, he hired me to this physics undergraduate lab, the Junior Physics Lab, and that’s how I made the transition to getting to know Rai, and starting to be engaged at MIT.
Did you see this also as a back door to pursue graduate work at MIT?
I didn’t know what I wanted to do at that time. Honestly, I don’t remember whether or not I had ambitions.
But, certainly, you understood to be a physicist, you would need to pursue a terminal degree?
I don’t think I appreciated that so deeply as I did a few years later in Germany, which we’ll get to. But I cannot honestly say that I knew that further academic work was going to be something that was part of my vision of what was going to happen next. I wanted to do something. I wanted to work. The idea of working at MIT sounded really exciting. The job sounded like fun. I’ll do it.
What did he have you do there when you first got there?
Technical Instructor in the MIT Junior Lab. It’s an undergraduate teaching laboratory. At the time, and I think it’s still true, all undergraduate physics majors had to take two semesters of this laboratory, a series of experiments. And they varied between ones that you can walk up to and turn on, to ones where you really have to figure out what’s wrong with it, and not because I simply pulled out a resistor to see what the students could do but because it’s a complicated experiment, and takes some finesse to get it to go.
There were a lot of things in the experiments which had gotten sort of rundown or gotten out of date because they hadn’t had anybody young and motivated to try and improve it. They had a couple of old-timers who were great resources of experimental techniques of the ‘50s and 60’s, and invested in maintaining the infrastructure of the lab, but not more. And so I think the idea was to have someone young come in who could move things forward in terms of electronics, and ways of teaching things.
So I spent a summer, first off, just fixing equipment, and learning the physics, because I hadn’t learned very much physics at that time, learning the physics they were trying to teach via the experiments. And then during the semesters, it was an extremely intensive matter of going from experiment to experiment, and helping students past some technical difficulty or another. I didn’t know enough physics to teach them any of the physics, but I knew enough electronics and optics, and I knew how to fix a car, which was enough to look at the problem, and start to figure out what the problem was. And so, in that way, learnt more physics, was able to help a number of these youngsters through the difficulties they were having, and started to identify things that I thought should be improved.
It’s during this a two-year period, where I had summers during which I could just spend the entire time fixing experiments, making them better, and working on the write-ups for them. And then during the semester, there was a great deal of hands-on teaching time. They were making vacuum tubes, and you’d have to teach people how to be clean, and work with high-temperature furnaces, and a whole bunch of sort of strange stuff from today’s perspective.
So this was not a LIGO-type environment at this point?
No, this is a dedicated teaching laboratory that had a limited objective. It brought me into contact with a few of the faculty members who were experimentalists at MIT. And, in particular, Rai. For I think all the time I was working there, Rai was the teaching faculty responsible for the lab. He liked that because then he didn’t have to teach, and he could spend more time working on his own stuff.
Did you develop a mentor-mentee relationship with Rai in this context?
Yes, and it was very clear—it’s, in some measure, his personality. But then I was also hungry for direction in what I was trying to do, and he was always there with advice. And in fact, after a year of doing that, or a year and a half or something like that, he said, “David, you should go to graduate school.” And so, with that encouragement, I was willing to take a look at that possibility, and he really led me down that path.
So he was very hands-on with you, both in terms of—
—in the lab, and in terms of life advice?
Yep, yep, still is. [laugh] I’ll add that just a few years ago, when I was 60-plus and he 80-plus, he came into my office and asked me what I planned to do with my career. But back to the 1970’s -- Rai suggested that I look at graduate school. I had not finished my undergraduate degree. He suggested I look at a couple different things at MIT. I told him I wanted to work with him. And at that time, it was a far infra-red stuff working on the Cosmic Background Explorer satellite COBE.
He got me into graduate school. It was an epoch when if a faculty member says, “Take this guy,” they didn’t look too hard, right. So here we have a major transition from being this junior lab technician after two years to starting as a graduate student in his laboratory.
Did you have to go back and finish the undergraduate degree, or that sort of got papered over?
It kind of got papered over, even though that was not at all my intention.
I stated in my application materials that I would be spending my free time in the summer working on coursework to complete the language requirement for Tufts University, and really did intend to, but that somehow never happened.
So sort of baked into the whole arrangement was you would really be in some ways aloof from the department of physics?
I didn’t mean to communicate that. I was a graduate student in the department of physics. I was subject to the requirements for a graduate degree in the department of physics, and was pursuing that. At the same time, I was in Rai’s lab working as a graduate student research associate, as most all experimentalists do, and that covered tuition and it paid for a minimal apartment and something to eat.
Yeah, I didn’t mean it administratively. I meant like where you were actually hanging out and spending most of your time.
Yes, and so, as I noted earlier, Rai’s lab was somewhat at the geographical periphery of the physics department. His attitude of course about the department was that it was a bunch of conservative administrators, and that they just sucked up time, and I shouldn’t waste any more time on coursework or associating with the rest of the department than was absolutely necessary. There were really exciting and important things to be done in the laboratory. And his attitude was contagious—
—and his enthusiasm too. I think that was an epoch before he took seriously the need to encourage, or force, I would say, graduate students to be engaged in the physics department and to write papers, in order to start to form for themselves a sense of career. He thought of the formal requirements of education, and the social aspects of physics, as distractions from getting research done, for himself. And because that’s where his focus was, and because he was such a very strong role model, that led a bunch of graduate students—myself included—down a rocky road in terms of success in the graduate career. And while some people succeeded, despite that, I didn’t.
And in terms of developing a dissertation topic, how closely did you orient the work you were doing in the lab with what you wanted to pursue yourself intellectually?
I had no conception of what I wanted to pursue intellectually. I wanted to build cool stuff, and help advance the research Rai thought important. [laugh] He’s a very, very strong role model here. And, as a consequence, what I did was what needed to be done in the laboratory, and what Rai thought I would be capable of.
There were a series of smaller projects that I got involved in early on, having to do with characterization of materials for filters and polarizers and so forth and so on in the far-infrared. When COBE got to the point that there was a design for the FIRAS interferometer, the Far Infra-Red Absolute Spectrophotometer that was used for measuring the background, and it was clear that a prototype needed to be built, Rai took that on as one of his tasks in the COBE project, and gave it to me as something that I should do. I received from designers a blueprint for how to build this instrument, and I built it with the help of a great machinist and technician Dick Benford, and with computing help from a very bright junior faculty member Ned Wright, and then characterized it.
And that would have been, I think, my PhD thesis. I’m not sure that that alone would have sufficed. I think I would’ve had to have complemented it, especially in those days in the department, with some observational results. It would’ve taken too long to wait for COBE to launch. But maybe that’s what I would’ve done.
But, by that time, I was screwing up in my academic work, and flunked out of the doctorate program. I passed the first part, but not the second part of the written general exam at MIT. And so, at that point, was told I should finish coursework for a master’s degree, and did that successfully.
I wrote up the work that I’d done for the COBE spectrometer as a master’s thesis, which is not a requirement at MIT. I have to mention that John Mather read it, I think mostly to inform the work going forward, but his copy came back absolutely covered in red ink – that’s a treasured souvenir of the epoch. After getting my Master’s degree in 1980, I started working as a technician in Rai’s lab on the gravitational-wave detector prototype for a year or so, reapplied to the graduate program, got back in. Still couldn’t pass the generals, and gave up on academic life at MIT at that point, and went back to working as a technician in Rai’s lab. By that time, I—
David, just at this point, it’s—you know, listening to you narrate how you developed the dissertation topic, it sounds like you took a highly technical approach to the problem that you were handed. In other words, your job, as your saw it, was to build the thing that they needed built. And it sounds like you did not very much involve yourself in the sort of broader research questions or the science underpinning the need for this instrumentation. And so it sounds like perhaps that approach was not very helpful to you. It didn’t serve you well to think like that when you would be going to take the generals because—
—you were not approaching science in that way.
That’s right. And that’s—that has been a consistent path for me until the last three or four years. [laugh]
I build stuff. I make it work. I help others organize to build stuff. I can do that for fairly subtle and complex devices, but I’m a builder and a tester, an organizer, and a systems person. I am not a scientist, I’d say, in the traditional sense of the term. I think you need people like me to make science move forward, so I’m not unhappy with what I’ve done. But you’re exactly right.
So, David, I mean, just ask the obvious question. There’s a name for people like you. They’re called engineers, right? Why is that not what you pursued?
[laugh] Engineers went through this terribly difficult transition —the fact of the rate of change of technology becoming faster than the period of time over which one has an education as an engineer. And so learning anything specific about engineering, learning about how any object works is a kiss of death. What you want to do to avoid this trap is to learn how to abstract things into systems, to learn how to deal with things in as abstract a matter as you possibly can. I don’t think that most engineers fix toasters, right?
But, I think, in some measure, I’d agree with you. I think actually the right term for it is technician.
And you absolutely need technicians, and as I learned so well in Germany—you need technicians who are involved in the experiment, who are really invested, who have a more or less profound intuitive understanding of the fundamental physics which is behind the design problems, the difficulties that one has in making measurements, and so forth and so on. But it’s an absolutely central part of making something happen.
And that’s the role that I played in my earlier career.
So is this to say that if you’re listening to somebody like a Kip Thorne hold forth on gravity, that this is sort of—you don’t—not that I would ask you to put yourself at his level as a peer, but you see this as more like you’re a member of the audience listening to a master in the field talk about this, as opposed to somebody inside that circle?
Specifically for gravity and the theory of general relativity, that’s definitely true. I think there’s this question—the term “imposter syndrome” comes up. There’s a point at which one learns enough of the surface features and their relationships that one can actually do science without actually having worked from a very fundamental level up to that understanding. And I think that’s tougher in general relativity than it is in, say, astrophysics, or instrument science which is—I mean—it’s a little bit like biology. There’s a whole lot of facts. There are a lot of relationships, functional relationships.
If you understand those functional relationships, and you start to understand the orders of magnitude, you get to the point where you can contribute, organize the effort, and pose questions, which in the end really helps facilitate new science. That’s a different thing than carrying through with a calculation that you might stimulate. So at this kind of level of understanding the tensions, and looking for relationships, and questioning them, contributing ideas, teaching people at that level, those are all things that I can do. But I’m not going to develop a new theory; I couldn’t teach general relativity to a student. That’s absolutely certain.
Now, just to tip the scales, I’m sure somebody like Kip would be the first one to say if you’re with him at the workshop, and you’re trying to explain what it is that you do, that allows him to create the theories that he’s doing, he would also say that you’re working on a level that’s outside his abilities as well.
I think that’s right. He wouldn’t say or need not think that it’s outside his abilities. He would say that it’s outside of his training and experience and interests. And I don’t know if I would have the same thing to say about his—
—studies of wormholes. Look, Kip is smarter than I am. But it is a similar sort of thing. You choose where to focus your efforts. There are people who are broad enough and smart enough so that they can cover all of these domains in real depth and—
And, necessarily, with LIGO, where there are—I mean, who knows what the—I don’t know what the exact number is. But if it’s over 1,000, right, however many people it took to make LIGO happen, by definition, you need a lot of different skill sets in that group.
And you won’t succeed if each one of those persons tries to become so broad–
—to be broad enough to be able to both develop new theories of gravitation, and fix the damn photodiode amplifier, right?
[laugh] Yes, that’s a very important point.
So you choose to specialize, and you choose the things that you’re excited and motivated to do. And then the nature in which you broaden yourself depends on your intellectual ability, the free time that you have, your discipline in broadening yourself, all of these things.
And I’d say that, as I’ve now mentioned a couple times, the freedom that has come with not currently carrying a big responsibility for making a bunch of stuff happen, and the fact that we now have gravitational wave results that are coming in, has vastly increased my interest in and thus slowly my knowledge of the astrophysics that one can do with gravitational waves. You know, someday I might call myself a card-carrying astrophysicist. I don’t know.
[laugh] David, to get back to the narrative, so, is this a low point in your career when the generals is like—it seems like it’s something that is not attainable to you? Are you sort of slinking back to the lab, or are you just having so much fun that you resign yourself to say, “This is where my contributions are. This is where I’m going to make my career”?
No, no, I definitely had a sense of disappointment—frustration that I either can’t or don’t have the discipline to learn this stuff and to perform as the monkey must in front of the faculty and answer their questions. So, no, it was a disappointment…it was a time of internal questioning.
And what is Rai telling you at this point? What’s his advice, given the fact that you’re so close to him, and you’re looking up to him for all kinds of advice?
Beyond his disappointment that it didn’t work, I don’t remember his reaction. I was certainly welcomed back into—
But, generally, he’s a source of—
Some of it was that I was good enough in the laboratory. The first thing Rai assured was that he had a way to give me money so that I continue to work. [laugh]
But he’s a source of support for you, not just financially. Like, he’s continuing—
He’s giving you confidence. He’s telling you to stick with it.
I honestly though don’t recall if he and I talked at that time about potential trajectories for me. And the next thing I did, I personally remember it as being of my own volition, was to write to a group in Germany that was doing this research, and ask them if they had any place for a visitor for a few months. And—
Yeah. What was this place in Germany?
What was the place in Germany?
It was in Garching—Garching bei München—a big research center of Max Planck, which is just to the north of Munich. To come back to a little bit earlier point in the story, Rai had applied to the National Science Foundation for support, probably in ’73, ’74, or something like that, ’72. The National Science Foundation, NSF—Rai must’ve told you this story—sent the proposal to a number of people for review—among them, to the leader of this group in Germany, Heinz Billing, who had been working on the Weber Bar method of pursuing gravitational wave detection for a number of years. And he and his group had built two bars well geographically separated, one in Frascati, and one in München, to test whether or not they would observe the excesses and signals that were coincident that Joe Weber thought he had detected.
And the group—a fascinating group. I could go on for hours about them. But, at any rate, Billing had become known as an expert in the field of gravitational wave detection, with these Weber Bars. As a consequence, he received from the NSF for a peer review this proposal from Rai for a gravitational wave antenna built around the idea of a Michelson interferometer measuring differential strain in the two arms. He thought it was a great idea, and immediately turned his entire group around to working on that approach to the problem. They had been very active for a few years in this domain by the early ‘80s, and I had actually visited them a year or so before writing without any forewarning.
I was traveling around Europe, and I took a bus out to this idyllic research center in the middle of fields in Germany, and knocked on the door and said, “Can you give me a tour?” They were very warmly receptive of that visit. So they knew who I was when I wrote to them, I knew what it meant to be there, and I liked the idea of escaping my life in Cambridge. They accepted the notion that I would come for a six-month visit there in some kind of ill-defined role. My idea was just to work in their laboratory, and have fun there. Indeed I had fun [laugh], and ended up staying a year and a half.
And what—to the extent that you recognized those questions, even if you might not have been part of it—what were some of the main research questions that were going on at the lab when you arrived?
It was all about designing and building ever better interferometers and seeing how well they worked. They had built, first, a prototype with three-meter-long arms as a way of testing a number of things having to do with freely hung test masses being interrogated by laser light in a Michelson interferometer. They had, at the time I arrived, just finished the construction of a 30-meter prototype with the idea of increasing their sensitivity, and looking at some of the scaling problems that were due to its length.
This group had been together for many, many years—many decades. They started out by building computers, special-purpose computers, and writing the language from assembler on up for them to do automated scanning of bubble chamber tracks. And once they’d solved that problem, and delivered these computers, with all hand-built drum memories, and so forth and so on, they turned to these Weber gravitational wave detectors. This is the breadth of interest and expertise of both the leader of the group, Heinz Billing, and the group, which was just superb.
But then they turned to focus on these interferometers. They were in their mid-50s to mid-to-early-60s when I arrived, and they were maybe a bit bored. And they had just built this beautiful, beautiful machine. It was wonderful. They were engineering physicists, and so they built a machine with capabilities well beyond anything else in the world at at that time, but they didn’t have the enthusiasm to drive themselves to do what they could do with it.
I knew exactly what I wanted to do with that. It was quite obvious that the instrument worked well enough and was stable enough that one could use Rai’s 1972 article that laid out all of the different noise sources as a road map for testing the system, and understanding where the difficulties were. And so I leapt into that, and the machine was perfect for that research because of its stability.
For me, a wonderful aspect of the experience was that the Garching Gravitationwellen Gruppe members were all natural teachers. They all had a lot of excitement about the idea of doing the research, even if they didn’t feel so much the excitement of doing it themselves. But they were ready to teach me what I needed to know to work on the questions that were exciting to me, and they could and did critique what I came up with. It was a symbiotic relationship that worked really, really well for exploiting fully the technology that they’d developed, and to work past a number of the problems that were holding up the field. It was a really magical combination of conditions.
They also taught me how to take vacations. The first year that I was there, they would all come in on Monday morning, and I would tell them all the things I’d done over the weekend in the laboratory. After about a year of that, they said, “We don’t want to hear about that. [laugh] We want to hear about the trip you took up into the mountains.” So they were a strong influence in that sense. And they also taught me German—we started out in English, but then, after about the same period of time, they said, “We’ll do this now in German.” Typically we would be in the Lab making some measurements and I would try to explain something in German, and become completely lost. Roland Schilling would say ‘Halt!’ and some explanation of my errors along with a few verbal exercises would follow. Once mastered, physics took over again.
This was a good place for you? You were getting your footing here?
It was a great place for science.
What clicked for you personally that might not have at MIT? Was it an opportunity to get out of Rai’s shadow? Was that sort of holding you back to some degree, as good as he was for you?
I think you pose a really good question. I think that can be a part of it. I think I was completely—
Because you had to be your own person there. There was nobody for you to really lean on, right?
That’s right. I think another very important aspect of it was that I arrived as a blank slate; I came in with no history of poor performance. There was no expectation of any academic achievement. I was taken for exactly what I could do. And I think that freedom from all history allowed me to work without the burden of wondering whether or not I was doing what I should be doing.
It was a very clean start, and then a very supportive environment. If I needed anything to do this—the work that I was doing, someone to do a calculation, someone to build me a piece of electronics, someone to teach me how something worked, there were five people there to do that—well, actually more because there were the workshop technicians and the electrical engineers. And that’s where I learned this notion of a vocation of being a technician in Germany is something that—well, it’s taken very seriously. You train well, and then you get respect for what you do, and you’re part of the research team. And it was a really, very, very nice environment for doing that sort of work.
And where did your skill set specifically fit into these bigger collaborations, these bigger projects?
A bigger project in what sense?
I mean, what was going on there overall?
Oh, OK, good. I think there were a couple different things. There was having the vision of the systematic exploitation of the performance of the instrument. And then there was the ability to troubleshoot, the ability to look at each thing as a problem to assemble a set of tests that would illuminate where the problems were, to decide to make modifications to repair the thing, or get it to work better, or reconceive of how it should be done, and to move forward with it. So I think “synthesis” is a good general term for it.
How long did you stay there?
A year and a half, year and three-quarters, something like that.
And did that experience sort of help clarify what your next move was? In other words, was this sort of a—I don’t know—sow your wild oats? Was it an opportunity for you to…Maybe, I mean, there was a sort of a stultification at MIT where you really would know not what your next move is until you get out and see what else is there.
And so I want to know when you’re thinking about, like, six months out of leaving Germany, that might help you figure out what your next move might be in a way that you might not have ever been able to do that, had you just continued grinding it out at MIT?
Right. Again, the German group’s history here is crucial. There were two persons in the group who had PhDs: the most junior person and the most senior person. But the contributors who were in informal leadership roles due to their formidable capabilities as scientists had effectively an equivalent of a master’s degree, a Diplomarbeit. And, as consequence, they were held back in the Max Planck system. When Heinz Billing, the initial head of the group—the Max Planck director, retired, a transition was needed.
Normally, what happens in a Max Planck society, at least in that epoch and I think in some measure still today, the group is terminated, and the permanent employees of the group are spread around to other groups that need members. Sometimes, a leader designates a Nachfolger, a follower, the next person to lead the group. And sometimes the Max Planck Society adopts that recommendation. In the case of this group, I’d say Heinz Billing did a poor job of thinking about that question. I think he avoided it.
But then, more significantly, the people who had the intellectual capability and stature to take on that role didn’t have PhDs and couldn’t take on that role, rued the fact that they did not have that level of education, and were very firm with me that I must not be held back by that arbitrary measure of accomplishment. So they really pushed me; they made it clear that if I wanted to continue in physics, I needed to have a PhD. One option was to apply to a doctorate program at Max Planck. A new director had just been installed with the retirement of Heinz Billing. He tried to fit in as the leader of the group. The group did not think he was the right person for that role, and so they rejected him, which is something you don’t do in Max Planck, right.
But well before he chose to leave, I asked him if he would take me on as a graduate student, at the Technische Universität in München, but he didn’t want to do that. About that same time, Alain Brillet, who was working in Orsay, just to the south of Paris, was starting up a group in this field. There were starting to be discussions within Europe between the various different groups in this nascent field of interferometric detection of gravitational waves to look to see where things were happening, to try and form a—how can you call it?—a nexus of people who were working on it. Alain Brillet wanted to strengthen his group to be able to move forward in the field. He was starting to work with Aldaberto Giazotto in Pisa, and starting to think about building a kilometer-scale detector in Europe.
Alain offered to take me on as a graduate student in Orsay, with the condition that I write my thesis and defend it in French. He offered me the opportunity to make most of the research that was represented in my doctorate thesis the research I’d already done at MIT and in Germany. This sounded like a really wonderful arrangement to me, so I jumped at that opportunity. In 1986, I left the German group and moved over to Alain Brillet’s group in Paris.
There was a specific thing that he wanted me to work on. We had been, up to that date in the field, using an old gas argon-ion laser approach for illuminating the interferometers. It was extremely energetically inefficient—many, many electrical kilowatts to get out a watt or two of light power. It was unreliable. It was expensive. At that time, Neodymium YAG solid-state lasers were just becoming feasible. And, in particular, the diode pumping of those lasers was just becoming feasible. And he asked me to develop —as it turned out to be—the first of the frequency stabilized diode pumped neodymium YAG lasers as a prototype for what one could use to illuminate gravitational wave detectors.
I worked on that, and then also worked on writing up my thesis of previous research, which involved doing more analysis than I had done before. It also involved writing my first paper—by far, the best paper I’ve written—which is about the Garching instrument characterization. And so, in that way, I actually continued to work closely with the German group. There was just starting to be email at that time, and then a certain number of trips back to Germany to work through things.
There were no course requirements to finish the doctorate in France, given the fact that I had a master’s degree from MIT. It was a pretty straightforward matter to work my way through writing the thesis, and publishing a couple of papers. There was work still to write and present my work in French but that was fun work. I’d learnt how to learn German, and enjoyed learning that language. And so learning French was more straightforward. I’ll remind you that I never received my undergrad degree from Tufts because I did not finish the language requirement!
The subtext here clearly is also there’s a lot of intellectual maturity happening at the same time.
Yeah, indeed, a lot of the other half of the effort, understanding in a more quantitative way the work, and starting to think more strategically about how to plan things, doing more design work – all of those things were also stimulated in the French group, again, a place where I was given both good mentoring by Alain, and also given a lot of room to try things out. So it was a very rich experience in terms of my intellectual growth.
And in terms of—to get back to this idea of previously you might have been sort of—you might’ve separated yourself intellectually from the kinds of research questions underpinning the instrumentation and the building, did you feel like you had sort of crossed a Rubicon where you were now able to complete a thesis because you were able to be involved in those questions? In other words, you weren’t writing it. Your dissertation was not simply a technical manual of an instrument.
It’s true. I had made some kind of adiabatic transition toward greater capability to do more of the things that most physicists do. I think I’m still a neophyte on that side, for what it’s worth. But, at any rate, it certainly was possible for me to do enough so that science advanced. It was a complete enough exposition, a complete enough understanding, so that I could feel comfortable that I was really making science happen, and I was perceived as such by others.
What was your next—?
I still think I have a really weird skill set for a physicist.
But that’s a different matter.
What was on your horizon at this point? You successfully defend. This is a major milestone for you in your life intellectually. What did this experience—besides just sort of checking the box, and now being sort of eligible, what did you see as what was newly available to you beyond just the administrative angle of things?
Well, certainly, I was becoming more ambitious in what I wanted to do. I could see that I was able to contribute to making this field move forward, and the field continued to excite me for its technical challenges. And I needed a job! [laugh] I wanted to apply this in a very practical way to making the field move forward. I’d met my wife. That, along with all the other ways it made life richer, was instrumental in me being able to write a thesis that could be understood in French.
She also had taken a doctorate in physics, nuclear physics. So we made a list of the places that we could go next, and pursue what we wanted to do. She had wanted to move to music performance, and I wanted to continue in this field, so we made lists of cities where you could do these things. The only place where the two careers lined up was back in Boston. I wrote Rai a note, and he offered me a job, and oh by the way helped interface my wife to the music scene in Boston. [laugh] And so we came back to Boston in 1989.
Were you in—did you keep in close touch with Rai during your years in Europe?
“Close” is not quite the right description. We certainly had exchanges at least every six months or so; sometimes a little bit more frequently. He came over to visit once.
Did you feel like you wanted to sort of keep up with what was going on at MIT because, in the back of your head, you might’ve considered had you kept up, you would be able to jump back into things pretty easily?
I must say that it was the last place I wanted to go.
[laugh] And it was not because I didn’t like the idea of working again with Rai, but I think there were a couple different things. My contact with Rai made it extremely clear—I’d also met Robbie Vogt, a name you must’ve heard already—that the situation in the US was extremely frustrating at least for those at MIT, and that the whole scene there was fraught with danger of failure. And clearly also that it was an unrewarding place to spend time at that moment in the field. It was just awful—just awful. But that was, I think, just a piece of it.
The other more important thing was that I wanted to stay in Europe. I liked living in Europe. I was all ready for another language and another country, and the idea of going back to the States and kind of falling back into Jello land was not something that appealed to me at all. So, when we came to the States, my wife and I were very clear we were going to stay till she finished her master’s degree in vocal performance, then we’d go back to Europe. [laugh] That didn’t happen. [laugh]
And so when you got back—
When you got back to the lab, I’m curious, what had changed and what had remained the same? And, of course, the bias in there is that you had changed—
—in your years that you were gone.
Well, the group had gotten larger. There was of course this engineering and strategic evolution toward building LIGO. The notion that while there were prototypes yet to be built and problems yet to be tested on the laboratory scale, that the goal that Rai had laid out was to move directly to kilometer-scale instruments, and not to continue with ever larger prototypes, which many in the field had been considering.
That was one change – in attitude, the growth of the group, the increased level of planning and strategy and coordination. And then the other huge transition was the close relationship that had been forged with Caltech—close, not forcibly friendly, and not forcibly comfortable. But one where it was clear that the fates of the two groups were very closely linked, and effectively the groups were being forced to work together, more or less productively. And in the case of MIT, what that meant was that we flew out to Caltech once a month, and spent a week there, and tried to make things happen that way.
There were also a whole new set of graduate students, among them Peter Fritschel, Nergis Mavalvala, Joe Giaime, Brian Lantz, Nelson Christensen. I spent a great deal of time with Peter early on. There was a vacuum tank which we did not use for a vacuum but simply to form a quiet environment acoustically in which to make experiments. And he and I spent a great deal of time sitting together on the large horizontal vacuum flange, working through various problems in optics in this vacuum tank.
Fun memories. My focus, initially, was still principally on building things, and making experiments work, but then more and more in planning what experiments needed to be done to demonstrate what would be convincing to the National Science Foundation of our ability to build full-scale instruments, starting to do more modeling and computational work in understanding optics constraints—these kinds of things. So moving more into analytical stuff, and more into strategic planning.
Was there a sense of momentum, like things were getting bigger and more exciting, and closer to fruition than when you were there?
Definitely, although the times were so initially fraught with concerns of failure sense that any day NSF could just say, “No more.” But also the very difficult situation with the leadership at Caltech being—I don’t know what words to use here— completely wrong for the phase of the project, and morally bankrupt. It made it so that it was hard to focus on real work. Rai was so completely invested in making things work that he completely prostrated himself before these false gods [laugh] and told them to tell him what to do, and he did it. And he wasted years of his life doing this. “Spent” I think is probably a better term [laugh] because all that work ultimately led to success, right, but it was a very, very, very difficult time, you know. But we all had, in some measure, a bigger sense of the future that drove us on.
And what did you do? How did you plug back into the lab?
I first off just worked with Peter and others on experiments, and made them work. More and more, I became the person who made presentations at the Caltech meetings about what experimental work would be needed and how we would do it. I was the right person in some measure because I’d been thinking about it, but in some measure because I was very good at that, and could carry across ideas in a way that navigated carefully the mixture of the need to be convincing scientifically, and to be clear about what we wanted to accomplish, but not to push buttons, and not to seek to correct past ills.
But, anyway, it was possible for me to push the program forward for MIT in a way that was really useful for MIT and for the project. And so that was something I spent more and more of my time doing, and continue to do that to the day. [laugh]
As a result of having the degree, were there new opportunities both within the infrastructure of the lab and the infrastructure of MIT that were not available to you previously?
An interesting question. I mean, the position into which I was hired was one which is—I don’t know if it’s quite reserved for people with doctorates but it would’ve been very strange to give it to someone who didn’t have a PhD, and I would’ve been quite limited by ability to advance through the very nice system at MIT for people who are not faculty members –from research scientist, to principal research scientist, and ultimately to senior research scientist. It’s a well-defined hierarchy, one which involves more and more responsibility, more privileges in the institute, and more salary too. And that was only possible because of the PhD.
There was an opening for a faculty member; I wonder when that was? It was probably around ’95 or so, to which I applied. And my application actually went very far up the chain of command, and there was an individual who didn’t like me. Actually, it was an individual who had taught me quantum mechanics when I was a graduate student—a failing graduate student. It was an undergraduate course in quantum mechanics, which I failed miserably. And that person who’d become the dean of science remembered me, and said, “That person is not going to become a faculty member at MIT.” [laugh] And so he made it impossible for me to become a faculty member at MIT. So you ask did new opportunities open up? Yes and no.
In retrospect, it was probably best for me that the faculty position did not work out. I can’t say that I would have designed the path that I took to remaining as a research scientist. But it’s definitely a much more appropriate position for me than a teaching faculty would’ve been, because as teaching faculty, I would’ve been incredibly constrained about what I could do and time—use of time, my ability to travel, etcetera.
Now, in terms of privileges, if you wanted to teach a graduate seminar, could you?
And that’s just something that you’re not—you haven’t been interested, or you haven’t had the bandwidth for?
It’s a combination of several things. I think I would have to be motivated to put a lot of time aside, and that time would be initially to learn the material well enough so that I could teach it to students, and then to actually carry through with the teaching of the course. There are the constraints of not being able to travel freely during that period of time.
On the other hand, it would have been rewarding to do. Something that I very much enjoyed doing early in my time at MIT was teaching graduate students how to be good experimentalists. Just a different kind of instruction, but it’s instruction nonetheless. I found it very rewarding to see people grow, and to be able to answer their questions, and to pose them challenges and see them succeed. So all of that part of teaching appeals to me a lot. But the constraints of doing—performing—doing a formal course that didn’t appeal to me, it doesn’t appeal to me.
Can you narrate sort of—you know—to foreshadow to 2015 and 2016, right, when does the narrative shift from MIT is not really believing in what’s going on at the lab? There’s problems with the NSF. When does the narrative shift from this is an impossible dream, and it’s not going anywhere, and nothing is happening, to, holy smokes, gravitational waves, and then separate from all of the awards that happen as a result of that? I’m just talking about the narrative of the science. And we can talk about how society recognizes the discovery later. But if you could develop a narrative of when—you know—when that threshold is crossed from this impossible dream to, oh, my goodness, look what we’re now seeing.
Well, the way you pose that question, I think, I’m going to answer a slightly different question.
That is to say, what was the arc of the change in MIT’s attitude about this as a scientific endeavor?
But wouldn’t that be beside the point? I mean, once LIGO starts to do what it did, isn’t it sort of beside the point what M…I mean, MIT is going to come around regardless if the science is there.
It was before the actual discovery that we started to feel much more support within the Kavli Institute and at MIT.
OK. That’s an important question. So, the institutional support is not reactive to the discovery?
Not exclusively reactive to the discovery by any means.
OK, OK, that’s [??]
MIT made a significant contribution to pulling LIGO through the management difficulties in the 80’s and early 90’s; Claude Canizares, then the director of the Center for Space Research, really invested time and effort to save LIGO then. I am not sure how convinced he was that it was going to work, but it was not going to fail for that reason! Then Rai made a deal to retire as an active faculty member in—I wonder when it was? It was 2001 that he became emeritus, with a deal that they would hire two faculty—junior faculty—members in the field to compensate for his retirement. And they hired Erik Katsavounidis early on, and then, shortly thereafter in 2002, Nergis Mavalvala. And MIT did not really support Erik, who was pursuing the astrophysical science.
Nergis, on the other hand, really caught fire. She immediately came up with a concept of quantum studies, quantum sensing, quantum measurement as a field that would be exciting, would be sufficiently mainstream so that the rest of the faculty could understand it. It still bore a strong impact on our field. And we started to see at that point much more support from the physics department for the success of the endeavor, at least in part because they wanted her to succeed.
And about the same time – this is 2002 – we had a new director of the Kavli Institute come on, Jackie Hewitt, and she also really cared about the physics as did the new head of MIT astrophysics, Deepto Chakrabarty, a neutron star specialist. So we started to see in younger faculty, as older faculty moved out of positions of leadership, in the various different places in the department, excitement starting to grow.
Peter Fisher then also took on the leadership position at the department of physics. One by one, the old school moved out as the new school moved in. That new school tended to be younger than I am, actually, by 10 years or so, all really, really understood the potential in our field , and saw the progress that was being made. By this time, the NSF had already invested its hundreds of millions of dollars, and so it was clear that it was something that had real life to it. It must be said that MIT didn’t help as they might have to get those hundreds of millions of dollars.
But by the time funding was in place, MIT understood that it was something of stature. I’d say it was by around 2010 that MIT really ‘got it’. And by the time we made the discovery in 2015, we had close colleagues who’d been following our work, who anticipated this could happen on the timescale of, for instance, their responsibilities in the department who, when we told them about it, they understood what had been accomplished and who had made it possible. I would say the growth really was after they made the commitment to this new faculty member, Nergis, and they saw how things were progressing in terms of the success of the Project and the growth of a field.
I have to say that Caltech does everything it can to make it look like a Caltech project. But had it failed, MIT and Caltech would’ve shared responsibility for the catastrophe. And the people at MIT understood the great responsibility they had to keep it from failing, which it sounds like a rather negative statement but it’s an important element, you know. MIT’s a conservative undertaking because of its scale; it manages risks for a business.
Yeah. Now, in terms of the science behind the first detection of gravitational waves, in your memory, how dramatic a moment is this in terms of, like, before and after? Is this a process? Is there one day where it’s we don’t see gravitational waves, and then the next day we do? How does this play out that ultimately makes LIGO this incredible success story that it would ultimately become?
We knew as Advanced LIGO came together that the instrument would perform far better than the initial LIGO detectors, and there had already been months of experience with commissioning or tuning the detectors in both Observatories before we started the fateful O1 observing run. So we knew we were treading on new ground. But, of course, we did not know to orders of magnitude the rate of any of the sources. We were optimistic but thought that there was probably a long slog ahead of us of observing, incrementally improving the detectors, and then starting to see hints of detections. That’s not the way it played out, happily!
There are a couple different layers to the recognition of the first detection. There’s the question of instrumentation, there’s the question of the data analysis, and there’s the question of the collaboration and sociological structure. From the perspective of the instrument, it was, I’d say, almost immediately clear to the people who were most closely connected to the instrument— I count myself among those at that time—that it almost certainly had to—well—it had to be a gravitational wave. We knew enough about the instrument and the way it behaved, we knew enough about the other signals that were present at the time, and the kinds of issues we had with data quality, that we could say—I would say intellectually—we could say, well, that we’ve seen a gravitational wave. And that was instantly gratifying in terms of the feeling that what we’d done actually did make sense, that we had understood what we were doing, and that it was going to be judged as worthwhile by our scientific peers, which is a really nice thing.
There’s a question of the data analysis, and that took a bit longer for people to acknowledge—“acknowledge it” sounds like sort of condescending or something—for the people who had been looking most carefully at the data to come to the firm conclusion that it had to have been a gravitational wave, and to start to have the change of mindset for the transition from ‘before’ to ‘after’. For a number of detailed reasons, there were questions whether or not it could be an injection of a signal, questions whether or not it could be a statistical outlier, these kinds of things.
It took a bit more time—more like weeks to a month—before people started to get that sense that we were in a post-detection epoch, and that we were going to have to start thinking differently about our data analysis, and no longer see it as an upper-limits effort, but to start looking at the parameters of the signals, and understanding which astrophysics you could extract. Then there’s the impact on the collaboration, which continues, I’d say, to unfold. But the collaboration had made a unanimous, coherent effort to reach the point where one could confidently detect a gravitational wave. In making that first step, it succeeded in that core mission, the mission around which a lot of the activities were focused, and around which a lot of the sacrifices were focused.
We are still understanding what a collaboration means in the context of many gravitational waves. Before the detection, a lot of our activities got equal and relatively small attention in the scientific world. You could write a paper about the photodiode amplifier or about the statistical noise characteristics of the instrument, or about the software that you wrote for a pipeline, or about the potential scientific interpretation one could make of a gravitational wave. And all those papers would have a certain audience, and a certain amount of attention, and a certain influence on one’s career.
After detection, the papers about the astrophysical interpretations got (and continue to receive) an enormous amount of attention. And by ratioing, you can see that everybody else and their efforts have become less visible and harder to motivate. This has caused incredible difficulty in maintaining—oh, in redefining, honestly, is what we need to say—redefining what the collaboration should be.
What are its goals now? How do you reward people in the collaboration for doing things which don’t lead to astrophysical papers? These changes started taking place soon after the 2015 discovery, and evolution continues. But we had a very strong delta function from that discovery experience.
Can you narrate the day when—as we were saying before—when society the broader scientific world, really starts to pay attention to what’s going on, and starts heaping about as much praise onto a scientific collaboration as is possible? Does that happen suddenly, or is that also sort of process?
Well, let’s see. First, there was the effort at secrecy in the collaboration, which worked pretty well. But there were a number of people—Rai among them—who broke that vow of secrecy, and told selected individuals. There were also people who made guesses. And maybe there were a couple of accidents, although I can’t actually think of a specific one.
The bottom line is that there’s a period of time between the initial detection and its announcement, which I think—yeah, I can’t tell you exactly how many months it was—five months, something like that—while we were assuring ourselves that there was a signal, understanding what our confidence was in it in a quantitative way, and then extracting the astrophysical information that we could from this thing, which is not only the first gravitational wave signal but also the proof of—“proof” is too strong a word—a demonstration that black holes are likely to exist and that stellar black holes of this mass range exist, that there’s a number of them and there are a whole bunch of astrophysics that comes out of this one discovery. We were preparing all of that, and it was a time of tension because of the effort to hold back on the information until we were very sure of it. I think that was actually overdone, and a difficult thing for us to live down. The collaboration still has a reputation for opacity.
But then we got to the point where we could plan an event and prepare people for ‘something’. I’d say within days of the date that it was announced, people were pretty sure that LIGO was going to announce the detection of gravitational waves. But I don’t think that it was appreciated how obvious it was that we had done it. It must be said also that we spent years and years telling people that the first signals might really be difficult to identify as gravitational waves instead of instrumental artifacts, and that we may have to wait for a handful of detections before we could say with confidence that we’d seen something. And, instead we had a signal that really hit us over the head. And as a consequence, it was—I think—it was more dramatic than one might have expected.
So, the day of the announcement in Washington, D.C., was really a signal even I think for the scientific community, and certainly also for us. I went through several different phases of personal integration of this as a change in the phase of life. I mean, there was the first day or so when I felt it just had to be a real signal based on what I knew about the instrument but could not quite say I believed it. After a month or so when I saw more studies, that made it look like it was coherent astrophysically.
When I saw the first draft of a paper, it took on a new sense of meaning and significance. And then at the announcement, when it was something we could talk about openly and subject to the critique of our peers in an open way, all of those things were steps forward in getting a sense that it was a real event for me. But I think for the scientific community, it was something that had a huge step function on that date when people saw that paper, and read it.
What was the day like on the Nobel announcement?
And, in fact, for me there isn’t too much more to say than that unburdened pleasure. The day of the Nobel announcement, we all got up at 4 a.m. for the second year in a row, got ourselves down to MIT, and piled ourselves around the projector, and waited with bated breath and, well, had an incredible moment of pure joy, right. [laugh]
So the second year in a row, meaning that that first year, there was a distinct possibility that it was going to happen?
Well, we knew that the Nobel Committee did not like to give awards shortly after significant events because they want to be sure of them. They’re a conservative organization. And so while we were convinced that it was a discovery that was worth a Nobel Prize, and we were convinced that the Nobel Committee would see that sooner or later, we weren’t sure whether or not it would happen the first year.
We thought because it was so exceptional that they might make a quick decision, but they did not. That first year the Nobel was instead something having to do with the topology of doughnut holes and handles on coffee cups. We were quite disappointed. But then the year after that, it was the right interval, it was the right time in the cycle for an astrophysics announcement, and so it was there. So I can’t say that we were sure of it, but we thought it was pretty likely that it was going to happen, and we were all primed for it, and we all had our extra bottles of champagne around.
To what extent did Rai set the tone for—even though the Nobel Committee can only award three actual Nobel Prizes, right, to what extent did Rai set the tone that, as you convey, everybody was there with excitement because there was this feeling that, even though three people are specifically being named, it’s really a recognition for the entire collaboration?
Ooh, interesting question. I know that Rai and Kip worked very hard to try and convince the Nobel Committee to the point perhaps of saying “We’re not going to accept it unless you do make it an award to the Collaboration,” but the Nobel committee operates under a set of rules that currently won’t allow that. But I think the thing is, the collaboration felt appreciated.
The collaboration knew that it had made this possible.
But my question is, did they feel appreciated because Kip and Rai—and, of course, there’s Barry Barish as well as the third Nobel Prize winner. Is it that Kip and Rai are setting the tone for demanding that the entire collaboration is appreciated, or is it the Nobel Committee insinuating, saying in some way, conveying in some way, “Look, this is how we do it, but we recognize that LIGO is more than these three individuals”? Like, that’s really what I’m asking in terms of how you felt appreciated.
Right. The Nobel Committee said that, but they didn’t use the word “but”. They said, “We award three. We recognize that the collaboration was an absolutely central part of what happened.” But I think that the more important truth is that Rai in particular communicated this truth. Kip has not been an active participant in the collaboration for quite a few years. Barry has been distant for quite a long time too. Rai continues to be extremely engaged, and was up to the moment of the discovery and beyond.
But Rai has always set the tone that the whole team – the Lab, and the collaboration, is what matters. So we didn’t need a message from the Nobel Committee to tell us that. And when you hear the words the Nobel Committee says, you know the committees that that went through to have the language formed were sensitive to this fact. It was nice that they said some words—I don’t remember what they were now—but nice that they said some words having to do with the collaboration, but that’s not where the reward came.
This observation—I’m not sure where it came from, but it’s certainly not original to me—but it does really bring into stark relief that the Nobel Prize originated at a time when there wasn’t big science like there is now. There was no concept of a collaboration where 1,000 or more people were involved in it. And, yet, they have not adapted at least insofar as actually who gets the award.
Right, right. I think one of the things that became clear to me that it was a very fun contrast to make. Another award was given, in fact, before the Nobel Prize was named. The LIGO Scientific Collaboration, along and Rai, Kip and Barry – were awarded the Princess of Asturias Award for Technical and Scientific Research. This is an award given by Spain yearly. There’s always one given for science, and one given for sports, and one given for philosophy, and so forth and so on. They chose the collaboration explicitly, along with Rai, Barry, and Kip well before the Nobel Prize Committee made their award.
It was a very interesting thing, first off, when I was first contacted by my handler. Because of my role in the collaboration, being the spokesperson at that time, they want to have me receive the award. I asked my deputy, Laura Cadonati, to take the lead role, but they said, “Well, why don’t you come along?” I said, “Sure.” [laugh]
The handler, when we spoke, said “You know, I think you’ll be going to a Nobel Prize ceremony celebration soon too. I think you’ll find we do it better than they do.” And they did. And the difference was intrinsic to the two institutions—the Nobel Prize is this self-perpetuating, self-aggrandizing endeavor.
It’s about keeping the Nobel name in the news. The Asturias award is about rewarding the achievers.
Yeah, not only that but I’ve interviewed many Nobel Prize winners, and a recurring theme is that the research suffers because now they are signing letters to the secretary-general of the UN, and they’re dealing with interview requests and all of these things where it’s very unlikely that it has a good effect on the science. So that’s certainly true.
The other thing, just as a—you know—just to include this as well, is that the problem of recognition is not limited to major collaborations. There are big problems in terms of an individual who gets an award where two or three other people were closely involved in that project as well. It doesn’t have to be a thousand-person collaboration. It could be two or three people, and there’s a lot of contentiousness about who gets it and who doesn’t.
Penzias and Wilson is a classic example. You have a couple of very good nerdy engineers who got it when they had no idea of the significance of their discovery. [laugh] I mean, it’s good. Nerdy engineers are good. [laugh] Don’t get me wrong. [laugh] But there are lots of cases, yes, where both the taste of the Nobel Committee, which actually tends toward theory, although they’ve done a couple of good experimentalist awards now, but—and also to the numbers of people they’re willing to include in their roster, provide severe constraints. Their culture is firmly attached to the past – look at the number of women who receive Nobels. And then, as you say, the research suffers afterwards.
It also suffers beforehand—not so much in our case because we were so deliberately conscious of it. But you look in biology, and the way that people are cutthroat—you hear about people being sabotaged and so forth because of the competition for that reward—that’s awful. But in the case of the award and the ceremony in Spain, it was perfectly clear that the activities and the structure were all set up to give the winners of the award pleasure. And the Nobel Committee and the processes and all—were all about aggrandizing the Nobel name.
And in the latter case, you feel like a pawn. And in the first case, you feel like a king. [laugh]
It was dramatic.
That’s great. Well the question to ask for you is, I wonder to what extent did you manage to extract the best out of this recognition, and keep the worst of it at arm’s length? In other words, because of Rai, not because of the Nobel Committee, but you must feel a tremendous sense of pride in being a part of a collaboration that was recognized at this level, even if you are not individually in possession of the prize itself?
Absolutely, yeah, and between—and I think the other part of it which is crucial—I keep coming back to it again—is the way that Rai and the others—but Rai’s really the one who matters because he’s the one who’s still really engaged now—the way that he absolutely—he was—I’m searching for the right words—selfless. It was clear before and after the award of the prize that he thought the team had achieved this, right.
And in what ways has—you know—on the flipside of individuals who are awarded with the Nobel Prize, and how their research suffers, at the sociological level, at the grand collaboration that LIGO continues to be, has the Nobel Prize and all of the other awards, has it had that similar effect, or has it gone in the opposite direction?
Having been the spokesperson during the period of time when a number of awards were given—
Right, you’re very well-positioned to reflect on this. [laugh]
—I can say that only a limited number of people -- around 10 to the minus two or three of the people involved in the undertaking, or thereabouts – can be recognized in prizes, and also announcements of key events. And so many, many more people are looked over—and overlooked, I should say—than get a chance to be in the limelight. You can only do wrong in selecting individuals because you’re deselecting other individuals. And there are people who don’t get on the stage who are marked by that for their lives.
And back to the phase transition after that first detection: If you’re somebody who’s responsible for bringing the astrophysical results to the public, then you’ll be remembered, and if you’re somebody who toiled endlessly to build a stable control system for a 37-degree-of-freedom control system for a LIGO interferometer, you could be forgotten. Right. And that happens at all levels in institutions, grants, tenure, and the stories you can tell your children about your experience in Stockholm.
So the whole prize thing, and, more generally, the fact that the scientific community and the public, I think, because of the way science is brought to the public and even to the greater scientific community, focuses on exceptional characters who often are those who skim the cream off the top of the effort. That’s deeply problematic for maintaining a sense of collaboration, coming back to this earlier thing I was saying. The collaboration doesn’t know how to function now. The collaboration has lost its egalitarian reward structure. And I don’t know how it can be reconstructed. I think maybe we should blow the thing up, and start over again.
[laugh] Well, perhaps such a precise illustration of the deleterious effects of all of these prizes is look how long we’ve been talking about the prizes during our talk, and not about the science. So let’s get back to that, right.
Forget all the Nobel stuff and all of that, right. What do we now understand—and specifically for you, right. I could ask Rai this question. I could ask Kip Thorne this question. But, for you, what do we understand about the universe and the instrumentation as a result of detecting gravity waves that we didn’t know when that was not a foregone conclusion?
From the combination of all of the other confirmations of Einstein’s theory of general relativity, and the Hulse-Taylor observations, the decay of the pulsar orbit, our understanding of the phase sensitivity of a Michelson interferometer, one could say that it was already a foregone conclusion before the detection that the instrument that we had built would be sensitive to gravitational waves and that a detection after some number of years of observation would be likely at our level of sensitivity. But we could’ve forgotten something. There could’ve been something about the interaction that we’d missed.
I mean, there’s the age-old question. If the interferometer arms change length, and the light changes color, do not the two effects completely cancel out? That kind of thing. So, there’s the confirmation that we understand the instrument and its basic interaction with spacetime in a way that gives us confidence to move forward, and propose bigger and better things.
There’s our understanding of the—it’s starting to sound sort of pedestrian, honestly, you know—the fact that you can do data analysis, and extract parameters, and have confidence in them. You see a coherent collection of events, and you can gain confidence that you understand how to do that sort of extraction, right. I think all of those things, just as I was saying before, are hard to wrap a soundbite around, and have it sound like they are really spectacular steps forward. But they are.
It’s hard to wrap a soundbite around those things to make them sound like they’re significant steps forward for science. But they’re enabling for future science in a way which is really key. This patina of scientific knowledge that I have allows me to speak with great assurance and enthusiasm about the importance of the fact that we now know that there are stellar-mass black holes, that we’ve confirmed the kilonova model for the emission of electromagnetic radiation around the inspiral of a neutron star, that we understand the first things about neutron star equations of state, that we start to see populations of black holes. We see even more massive black holes in our most recent observational run, which likely are the product of previous coalescence events, and that opens up a path toward the hierarchical development of the supermassive black holes. I can repeat all those words that you’ve heard from all these other people, or you can read about in the summaries of our papers. But it’s really good stuff, and it is possible because the photodiode amplifier doesn’t have parasitic oscillations, that the vacuum system does not leak, that the data were transferred without error, that the bad data were identified, and so forth.
But the big point to emphasize here—and this is really—again, this is one of the problems with the recognition is that a lot of people assume like LIGO is, well, we can wrap up and go home now. And, really, it’s just the tip of the iceberg in terms of discovery.
Absolutely. I think that while Alain Brillet and Adalberto Giozotto had a pretty clear vision of where they were going, most of the people who joined the Virgo experiment early on did it as an experiment. They thought they were going to build Virgo, and they were going to build it better and faster than LIGO, and they were going to be the first to detect gravitational waves, and then they’d move on and do some other interesting experiment. Some number of LIGO people certainly also saw it that way. That’s completely changed now, happily.
But Rai really saw this as an observatory from the very first moment, and the first step of an ongoing science. And I have to talk about the NSF here. The National Science Foundation is phenomenal, right. And they shared in this vision and conspired to make it a success.
That’s so nice to hear. [laugh]
[laugh] I just hope they can hold onto it for a few more months [laugh]—
—and, if not, for years or the rest of our lifetimes. At any rate, they really got the observatory notion, and the fact that this is the tip of the iceberg, back in 19…I don’t know, ’72 or ’73 or something like that. And as a consequence, they gave this very continuous support, and also I think have helped communicate that to people in science policy. Lastly, had we just seen one event, and it had then been quiet for years, it would’ve been much, much more difficult to paint the picture of growth.
But if you look at the number of events versus time, thanks to the ability to improve the instruments, and the growth in rate as the cube of the sensitivity of the instruments because of the volume that you encompass, we’ve been able to draw a curve of the number of events versus time, which has grown very much as we projected some years ago. We’ve had enough new events, events which differ from each other enough so that the person in the street who likes to read about science can have a sense of differentness, of variety. That’s wonderful news for communicating this vision of this being a new observational science, and not simply a flash in a plan.
And to refine the question just specifically on this point, right, it’s a two-way street, how the instrumentation allowed us to detect gravitational waves. But, going the other way, what did we learn about the instrumentation when it confirmed that gravitational waves could be detected, and how might that be useful for building the next generation of instruments?
It’s hard to know what to call out there. The way that the imperfections in the data stream influence our ability to make precise inferences of the astrophysical parameters is something that we’ve only learned through the trial and error of having real signals buried in real noise. And that has heightened our attention to certain aspects of the design, going forward. The obvious thing is that we want more sensitive instruments. We want longer instruments. We want brighter light. We want less seismic noise.
All of those things are things we knew already, and we haven’t really learned anything about from the instrumentation. Ok, I’ll call out two things. One is that the nature of imperfections in the data stream, the way that those imperfections can mimic gravitational waves, and the way in trying to trace that back to specific sources of noise in the instrument, we have new motivation to look at the time series in a critical way. Whereas before, we may have only looked at time averages of the best data to see how we were beating down the fundamental noise sources when, in fact, the non-stationary noise characteristics in fact have a big influence on how much you can do, and when.
I think the other thing especially this most recent announcement of very massive black holes brings to light is the fact that there really is a continuum of gravitational wave sources toward larger and larger masses, which translates to lower and lower frequencies of where the coalescence takes place. You’re probably familiar with these spectrograms that show an increase of frequency with time, ending with a coalescence that depending upon the mass of the thing, some hundreds of hertz, or, in the case of our binary neutron star, up around a kilohertz or so. This last big black hole event appeared as this little, tiny bit of a spectrogram between the point at which we could start to observe at around 40 hertz, and the time the coalescence took place at around 80 hertz. There were only four or so spirals of the two black holes before they coalesced, because of the frequency at which we start to observe. If we could move that starting frequency down by a factor of two, we could’ve extracted much more information from this source, and we we now know that there are 150 solar mass black holes out there because we just saw one being created.
There are certainly 300 solar mass, 600 solar mass black holes made from further hierarchical coalescences. The further down in frequency we can look, the more astrophysics we can see, the more different varieties of black holes we can draw out, and the better we can understand for example, the assembly of supermassive black holes.
So we can pull out more astrophysics if we can look at lower frequencies, and we need new observatories to do that. We’re just at the point now where the Einstein Telescope in Europe is about to put in its application for recognition as an element on the major road map for the next decade in Europe. And in the US, we have a program to develop a concept for a ground-based instrument called Cosmic Explorer which will be a factor of 10 more sensitive than the ones we currently have. The objective of the two proposed projects is similar, but, in particular, there’s a different philosophy about the lowest frequency you want to try to detect.
In Europe, they’re burying the detector some 300 meters underground to move away from a noise source we call the Newtonian Background. When a seismic wave passes near a detector, one’s familiar with the notion that the ground actually moves. And if that causes the test mass to move, that’s going to mask the gravitational wave signal. You need seismic isolation.
The other effect though, when a seismic wave passes, is that the earth is being compressed and rarefied, and compressed and rarefied. So the density distribution around the test mass is changing with time. And if you think about Newtonian gravitational attraction, the test mass points toward the sum of all vectors. You say toward the center of the Earth. What it’s really doing is pointing toward the weighted sum of all of the mass that’s nearby. And if that mass is moving, if the density is moving with time, that vector is going to move around, and the mass will wander.
That motion of the mass, again, can mask a gravitational wave. But this is something which you can’t reduce by engineering. I can reduce the direct mechanical seismic coupling to nothing if you give me enough money and time. I can’t mask Newtonian gravitational attraction to the changing Earth. If you go underground, you can reduce that because the seismic noise is lower deep underground.
That is the low frequency limit to instruments on the Earth’s surface. And the Europeans have targeted that as something that’s so important to them that they’re going to spend, who knows, something like an extra billion dollars to put their instrument underground. That’s not currently the philosophy of the instrument that’s being conceived of by the US folk, which prioritizes other science targets, in particular the signal when two neutron stars coalesce – which is at higher frequencies, where other technical limitations dominate.
Is that a budgetary conclusion or a scientific conclusion?
It is a balance of considerations – scientific, technical, and budgetary. We can go on for hours about the trades that go into this on both the science and the technology fronts. And they’re really interesting, the way the elements come into tension. Would you rather have one detector that can detect to lower frequency and resolve polarization, or two that can better resolve position? If we can convince the world’s funding agencies that it is worth it, we could build three, then we can do triangulation. We can better localize sources, and better communicate with the electromagnetic community.
You’d like to have different kinds of detectors for different kinds of science goals, in the end. So maybe the differences in the European and US concepts will be best for science. We’ll each build our concepts, we hope; maybe we’ll build two, or we can get Australia to build one. I don’t know where we are going to get $1.5 billion; this would be quite a call on the NSF alone. But, at any rate, there’s different science to do. Coming back to your question, we learned that it is important to be able to detect at low frequencies because of the science that we now know is there.
Now, of course, none of us knew with confidence what gravitational wave sources we would see first. And we really don’t know what sources will be revealed with instruments ten times better. We’re confident that there are some. But the really important reason to build these things is what we don’t know yet, what we’ll discover by accident by having an instrument that’s there at the right time and right place, and has the right sensitivity. That was a huge bet by the National Science Foundation for the current LIGO Observatories. And it worked. [laugh] So we can hope that that will be true also for this next generation of instruments.
What are some of the long-term technological limitations that you continue to see? In other words, you have lots of exciting ideas about what the next generation of instruments is going to be able to do. What are some of the technological limitations that might be achievable in 50 years but are—you know, even with all of this support, all of this interest, that are just sort of out of reach now?
I think there—speaking of things I could talk about for hours.
But there are two key things that come to mind to me. One is—and, actually, they can be flowed down from science goals, since I’ve turned into a systems engineer of sorts. We would really, really like to be able to look in great detail at the final coalescence moments of a binary neutron star because it reveals things at interaction energies and densities which are beyond anything we can ever build on the ground. It’s a place to examine exotic states of nature in neutron stars. It’s completely inaccessible otherwise. It’s a particularly difficult frequency range from about 700 hertz to 1.5 kilohertz, or something like that, to make an instrument that is not limited by quantum noise.
And so, in fact, there’s a lot of work to be done in improving this use of squeezed light, of making light which allows us to play with the Heisenberg uncertainty principle. It allows us to look more at either the momentum or the position of our test masses, and not at both simultaneously, and to interpret that in terms of a gravitational wave strain. There’s work to be done there, not only incrementally in making light which is initially more ‘squeezed’ and having lower optical losses in the instrument to preserve that squeezing, but certainly also new topologies of the interferometer which will allow us to use light in a different way to look in more detail at those high frequencies. I think that’s absolutely certain to be something that will be a focus. It’s a challenge which is really easy for a lot of the physics world to attach to now. The quantum initiative is the big, new thing. And it’s also a place where you can really make a change in the gravitational-wave science one can do.
The other place is thermal noise, effectively the Brownian motion of our test masses. And, more specifically, the thing which dominates now in our detectors is the thermal noise due to the mechanical losses in the optical coatings on the mirrors. This beam of light traveling over a multi-kilometer distance comes in, and hits our mirror. And the first thing it sees are 50 layers of subwavelength-thickness alternating index materials that makes a highly reflective coating. And a thing called the fluctuation-dissipation theorem tells us that where that light touches the lossiness—effectively, if you push on that surface, and if pushing on it makes heat instead of making it bounce like a lossless spring, that’s where the thermal noise expresses itself. And to reduce that, one obvious thing to do is to reduce the temperature. This is an effect which goes as the square root of kT – Boltzmann’s constant times the absolute temperature – and that’s what KAGRA, the new Japanese gravitational-wave antenna is trying to do. It’s reducing the temperature to 10 Kelvin or so with great technical difficulty.
Another approach is to change the nature of the coatings in a way which reduces their losses either incrementally, by changing the means of putting down the layers and the materials that you choose, or moving to completely different reflective objects like crystals or waveguides of some kind. But we’re at the point where either we confront really burdensome problems of cryogenics, among them the fact that you’re throwing laser light, perhaps megawatts, at the surface, and you have to get the heat out without introducing thermal noise in other ways. Or we need to resolve really messy materials science problems. Very few of us in our field now are materials scientists. So we’re gearing up on that. But I think both of those are projects that will see progress for decades to come, and could very well still be very strong foci of development efforts to make yet better gravitational wave detectors on the Earth.
The other thing to do is to throw our detectors up into space. And that, of course, is something that’s happening with LISA, with the gravitational wave antenna in space, which is planned to launch in 2034 – let’s hope that schedule sticks.
If you can get three spacecraft up into space, working as well as they do on the test bench on the ground, then there’s absolutely stupendous science that will be done. The frequency range accessible to a space antenna will allow the observation of the coalescence of much more massive systems, black holes with the mass of a million suns spiraling into eachother, and expand our understanding of the large-scale structure of the universe.
And then in the further future, there certainly should be follow-on space missions. I think the holy grail for gravitational wave detection is to see the time varying amplitude of a cosmological primordial background.
The analogy to the cosmic microwave background is a cosmic gravitational wave background. There’s already been efforts to detect that through looking at the polarization of the B-modes of the cosmic microwave background. There was, in fact, an announcement and a retraction of the effect; sadly, some dust was masquerading as signal. That technique may yet yield something—which could be called evidence of a primordial gravitational wave background.
I think there’s a nice analogy to the Hulse-Taylor observation of the pulsar where it was very clear when they won the Nobel Prize that they had shown that Einstein’s theory of gravitational radiation was making correct predictions. But it wasn’t an observation of the time-varying amplitude of the gravitational wave. That was what we did in 2015 with LIGO. And in the same way, an interferometer detector measurement of the primordial gravitational wave background would be extremely exciting because it goes to the very earliest moments of the universe, and the specific time evolution of the signature would carry more detailed information than a snapshot. At high frequencies, you’ve got LIGO and Virgo, and at low frequency you’ve got LISA. At even lower frequencies there is pulsar timing – using the naturally distributed high-precision clocks we call neutron stars, and searching for coordinated shifts in that timing as indicative of the presence of a superposition of many slow-motion galactic coalescences. This might be the next domain where a clear signal is seen, by the way.
But there’s a middle band between LIGO and LISA which may be a place where there’s a minimum of noise from other gravitational wave events which would allow you to see that primordial background. And so I think in 2050 that there should be a mission flying that will have that as its objective, and will build on all of the technology and the science that came beforehand. And that will be a really, really exciting time. I just have to watch how much I eat, and how I exercise so I’ll still be around then. [laugh]
[laugh] Well, David, on that note, for the last part of our discussion, I want to ask you a broadly retrospective question about your career, and then to continue on for the last question, a more forward-facing one. And, in your case, it’s a unique kind of question. And I want to emphasize that one of the great values of our oral history collection is that it is one that students access to learn not just about physics, but how people made their way, how they achieved their successes from all of the diverse backgrounds that they came from. And so, for you, of course, there’s a certain unlikelihood to the successes that you’ve had in terms of where you came from, some false starts, how you persevered, how you changed it up. What do you see as some of the major narrative through lines that a young kid who has some raw talents, but doesn’t necessarily have either the academic discipline or the mentorship or the direction to actualize those talents, right?
You took away my major weapon, which is mentorship.
You did have that. You did have that, but that—
I took that away because I’m not going to allow you to sort of put this—all of your successes or a vast majority of your successes on Rai. You did this on your own as well, right. And so what are some of those narrative through lines for that kid who might be reading this oral history next year, 10 years, 30 years down the line when LIGO’s doing amazing things, right? What do you see as some of the big lessons learned from your life that allowed you to achieve what you did?
It’s tough. I think an obvious thing, and it’s advice that almost everyone always gets, which is to pursue your passion, and I think to really strive to work on something that you just can’t resist. You can’t keep yourself from working on it because you’re so excited about it. Now, not everyone will choose a passion which can either have a long arc or which can earn one enough money to live comfortably. But I think that that’s a key thing, because I think it allows you to work through challenges.
I think the other thing is to try and maintain a level of optimism. And, in fact, to look—it sounds so trite—to look for ways in which setbacks and the constraints that appear can be used to reform one’s vision of what the future could be, by exclusion of maybe some of the most obvious or desired paths, and to cause one to seek alternatives. I think another thing that has served me very well is to let my attention wander, and to not be monolithic in my interests. I went to Germany because I wanted to live in Germany. [laugh]
And I thought I could get a job that would let me live in Germany for a while. But obviously I’d chosen a job that I thought I had some skill in, and where I thought I would be interested. But a lot of it had to do with a sense of wanderlust, a desire to try things out. That also led me to France, right. [laugh] I can’t say that it was wanderlust that led me back to the Boston again but [laugh]…
But also in there is your sort of keeping careerism at arm’s length, right, that the opportunities came because you were pursuing the things that you wanted to pursue, and not the other way around.
That’s right. I have a son who’s currently in between undergraduate and graduate school and is a physicist, and he and I talk about these things from time to time, of course. What I sincerely hope is that there are still avenues for that sort of meandering path, and for that more casual approach in what is certainly a much more competitive environment now.
Competitive and also more bureaucratized and corporatized.
That’s right, and where measures of success—I mean, I don’t think that Rai could get a student without an undergraduate degree into the graduate program today, right?
[laugh] “Sorry, Professor Weiss, we don’t do things that way.”
And so I think there are a bunch of things that make my advice potentially irrelevant for young people, and I find that depressing because I think a lot of the things that made my career possible was a sense of flexibility, a sense of shared risk-taking on everyone’s part. I don’t know. But it’s hard to say.
Or it can be that just expectations have changed?
That it’s not that maybe you coming in without an undergraduate degree. The next generation might not be coming in with a master’s degree. It might not be so fundamental a shift. It might be more incremental.
It may be. It may be, yeah, maybe.
Well, David, for my last question, I want to ask you—it’s—you know, you’ve conveyed so beautifully what all of the potential excitements are surrounding where LIGO is going for the next 30 years if not beyond that, right. But to bring that back to a personal level, right, you want to eat well. You want to be around for all of it. What are you most excited about personally in terms of your contributions to this endeavor where, quite literally, the universe is the limit?
I see the expertise that I developed over the years of working in leading Advanced LIGO was in a combination of seeing how systems fit together, and the trades involved in synthesizing a complete detector from ingredients; and in finding ways to communicate to funding agencies and the scientific community, the feasibility, and the realities of making those instruments come into existence. There are two things that we’ve talked about, which still are in that formative stage – that is the ground-based, next-generation instruments, the European ET and the US Cosmic Explorer, and then LISA. And those are the places that I’m putting my time.
In both cases, the timeline for realization of the projects is mid-2030s and 2040s or something like that, which is not so far away that I’m sure I’m going to be dead by then. [laugh] And so there’s some level of an anticipation of a personal reward in seeing that instrumentation work, and then seeing the science that comes from it. In all of those cases, there’s another generation, a younger generation of people who are taking the leadership, and who want that leadership. And so I don’t want to interfere with that, and I don’t need that role. I don’t know if I have the patience and focus to do it anyway. But, at any rate, I’m not going to do it because somebody else is.
Instead, maybe it’s a little bit like having a grandchild. What I can do is to try to keep in contact with those groups to offer help in oversight committees, in reading documents, and correcting them, and trying to catch things I think would be distracting to people who will read them critically. Just use the skills that I’ve developed which made it possible to get Advanced LIGO together to try and make these next-generation instruments succeed. I have to say that the level of satisfaction that I get is variable. [laugh] It’s no longer a limelight satisfaction. It has to be a more subtle thing. But I think I’m willing to give that up—I had my fair share, and so it’s good. That’s the thing that I’m doing now and I’m enjoying doing.
It’s a little bit odd given my role as a research scientist because I have a job. I’m not a faculty member. I don’t pursue good science for good science sake. I’m paid principally by the LIGO Laboratory and the NSF to work on LIGO. And so there’s a bit of a tension there. But the LIGO Laboratory tries to do the right thing in that way. And I’m able to contribute at a reasonable level to the stuff that I really care about.
There you go. Well, David, it’s been an absolute pleasure speaking with you today. You gave me a truly valuable and unique insight on this collaboration, and on so many other things about your journey to get where you are now. So I’m deeply appreciative of this time together, and this is really going to be a really special edition to our oral history collection. So thank you very much.
Your closing paragraphs are extremely well-polished and—
—[laugh] and have all the right words.
But I mean it. I do mean it.
I really do.
[laugh] That’s good. That’s good to hear. [laugh] I enjoyed it too.