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Courtesy: Peter Fritschel
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Interview of Peter Fritschel by David Zierler on September 2, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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In this interview, David Zierler, Oral Historian for AIP, interviews Peter Fritschel, Senior Research Scientist in the Kavli Institute for Astrophysics at MIT. Fritshel explains the historical connections between Kavli, Caltech, MIT, and the overall LIGO collaboration. He recounts his childhood in South Dakota, then New York City, and then back to South Dakota in support of his father’s academic career. Fritschel discusses his undergraduate education at Swarthmore, where he pursued degrees in physics and engineering, and he discusses his post-college work at Raytheon on CO2 lasers in its research division. He describes the events leading to his admission to MIT for graduate school where he joined Rai Weiss’s research lab, and he explains the progress that the lab had made on interferometers at that point in the mid-1980s. Fritschel explains the utility of his background in lasers for Weiss’s lab, and the significance of Caltech’s involvement in the LIGO project. He discusses the relationship between his thesis research on making an interferometer with a power recycling configuration in two arms, and LIGO. Fritschel describes his intent to leave MIT after he defended, and he considered opportunities more broadly in atomic, molecular, and optical physics, which led to his work in Orsay, France, with Alain Brillet and Adelberto Giazotto, the founders of the Virgo collaboration. He explains his decision to return to MIT, and how his work in France was useful for his return to LIGO. He explains how LIGO had advanced during his absence, he discusses his contributions to improving the sensitivity of the gravitational interferometers, and he describes how LIGO had made consistent progress over many years and not “all at once” with the detection of gravitational waves in 2015. Fritschel explains that the Nobel Prize given to LIGO’s principal scientists recognized the collaboration both as a theoretical and an experimental endeavor, and he describes the overall positive impact that this recognition had on the collaboration as it continues to push discovery in gravitational wave research and the advances in both physics and engineering that are required for LIGO to realize its future goals. At the end of the interview, Fritschel conveys the centrality of LIGO’s study of black holes and neutron stars in order to harness the collaboration’s ability to garner new insights on the early Universe.
Okay, this is David Zierler, Oral Historian for the American Institute of Physics. It is September 2nd, 2020. I'm so happy to be here with Dr. Peter Fritschel. Peter, thank you so much for joining me today.
Okay, to start, could you tell me your title and institutional affiliation or affiliations, as it were?
Yeah, I'm a Senior Research Scientist, specifically within the Kavli Institute for Astrophysics within MIT.
Okay. Can you give a little mapping of the affiliation or connections between Kavli and LIGO, and MIT Department of Physics? How do all of these things fit together?
LIGO was originally started as this collaboration between MIT and Caltech. Three main people involved in the beginning in terms of getting the project started were Rai Weiss at MIT. He was often thought of as the father of the field. Not the only person who came up with the idea of doing interferometric gravitational wave detectors, but one of the early ones. At Caltech, you had Kip Thorne as the theorist involved, and then Ron Drever was the experimentalist at Caltech. Those are the three that worked together to initially form LIGO. So, MIT and Caltech were the two institutions that created LIGO. The way it works at MIT is they have departments, like the Department of Physics and Department of Biology, or whatever, for the academic aspects of the institution- the student aspects, classes, and all that. Then, for the research parts of MIT, they have centers. Maybe that's done at some other institutions, I'm not quite sure, but they have these two different tracks, the departments for the academics, and what they call centers for the research areas. Actually, when Rai first started, he was in something called the Research Laboratory for Electronics, known as RLE. That's just the research center he was involved with when he first started doing LIGO stuff. Eventually, he moved into- at that time it was called the Center for Space Research. When I joined the project as a graduate student, it was within that Center for Space Research.
What year was that when you joined?
I started as a first-year graduate student in the fall of 1986.
Was this center part of the attraction for you to come to MIT for graduate work?
No, not for me. It was within the Center for Space Research because of its astrophysics, it was targeting astrophysical sources of gravitational waves. I was more attracted by- myself, I was more attracted by the technology and the concept of gravitational wave interferometers. I mean, I was interested, of course in the astrophysics, but personally I'm an instrumentalist, and I was attracted by this really cool concept of this huge gravitational wave detector that would be a more sensitive measurement tool than had ever been made. So, I was more attracted by the instrumentation. For me, it wasn't so important -- of course, I was enrolling as a graduate student in the Department of Physics at that time. Anyway, because the research was sort of split, the way MIT does things, at that time it was called the Center for Space Research. It's the same basic body, but sometime in the- I'm trying to remember when that transition happened. I'm going to say it was in the early nineties, it turned into the Kavli Institute for Astrophysics after a donation from the Kavli Foundation. I don't know if you're familiar with it. Maybe you know more about the Kavli Foundation than I do, but it was around that time they started establishing these different centers for astrophysics around the country, and around the world, actually.
Like Chicago, and Santa Barbara, this is all happening at the same time.
Exactly, and I think there are a couple others worldwide, too. Anyway, with the donation from the Kavli Foundation, it turned into the Kavli Institute. It was all the same group of people, but that's why it's now known as the Kavli Institute. I think it's actually the Kavli Institute for Astrophysics and Space Research.
In terms of your appointments and privileges, can you teach classes in the Department of Physics if you wanted to?
I think I could if I wanted to. MIT has a research track, which is the position I'm in. I'm not a professor. They have a research track. I haven't been teaching classes. I think, I could if I wanted to. Certainly, another member of our group who has the same position, a Senior Research Scientist, Eric Katsavounidis, does teach classes from time to time. So, I probably could.
What about graduate students? Do you take on graduate students?
Yeah, so, our group as a whole, does. I have not been the official graduate student advisor for any graduate students recently. It was quite a while ago now, but I think I was co-advisor for graduate students a while back- co-advisor with an actual professor in the group. I guess in both cases I was co-advisor with Rai Weiss for a couple of our graduate students in the early days of LIGO. Officially, I could. I could be the official, I think, as a Senior Research Scientist.
That's a great explanation of something that's sort of confusing to outsiders, so that's great. Peter let's go back to the beginning. Let's start with your parents. Tell me a little bit about them and where they're from.
My parents are both from the Midwest or western part of the country, my father grew up in Colorado. When I was growing up, my father was- most of the years that I was growing up he was a professor of religion at a college, kind of small liberal arts college in the town where I grew up, which was Sioux Falls, South Dakota. He comes from kind of a long line of Lutheran ministers. He was ordained as a minister, but most of my growing up, he was a college professor. He went back to the ministry a little bit later. So, he's from Colorado, and then my mother is from Kansas, and grew up on a farm in Kansas. They met in college. They went to a college in Waverly, Iowa. Why am I blanking on the name of the college? Wartburg College- good German name. There's an associated Wartburg seminary that was actually started by my forefathers on the Fritschel side. Originally, they came over from Germany and started churches, and started the seminary. So, anyway, yeah, on my father's side there's a long line of ministers. On my mother's side, she grew up on a farm. I forget now whether it was her father or her grandfather who came over from Germany as well and started a farm up in Kansas. So, she was a farm girl. They met in college, and then they moved to South Dakota where my father got a first church minister appointment in South Dakota. I think he was only there for a couple years, and then he took this professor job in Sioux Falls. So, most of my growing up was there, except for a couple years of my life, which certainly stands out. When I was in first and second grade, my father took a couple year sabbatical to continue to study. We moved from Sioux Falls to Manhattan where he studied at the Union Theological Seminary. So, we lived up in- I don't know if it was in or close to the border of Harlem, up in Manhattan, in 1968 and '69. I was just a kid, but obviously it was a very interesting time to be in New York City, especially moving from Sioux Falls to Manhattan. I remember just loving being in the big city.
Did your family go back to Sioux Falls from there?
Exactly, he was just there for two years for some graduate studies, and then we went back and stayed- I finished my schooling through high school in Sioux Falls.
Do you have sense of why your father went through this career transition?
It wasn't so much a transition. He went back to the same position, same job at the college.
No, I mean, coming up thinking about joining the ministry, and then becoming a professor.
I don't really know. I've never really talked to him about that. It's in the same basic field, right? Professor of theology rather than a minister. I think he was always sort of a theologian type of minister, as opposed to a- he was never a fire and brimstone kind of preacher, not that that's very prevalent in the Lutheran tradition. He was much more of a theologian and interested in the philosophy behind things. I think he just wanted to get some more study in that area with this New York trip.
Was the church a big part of your upbringing?
Not really. We went to church every Sunday, but again, it wasn't that big of a- I didn't think of ourselves as a church family, or very religious family. Again, it's just- the bent my father had was more of the philosophy behind religion, and the theology of it. He wasn't really pushing any of that stuff on us, on either me or my sister. I wouldn't say it was a big part of it, even though it was a big part of our tradition of the family, because my father's family came from that tradition. A big part of that, actually, also was the music part of it. One of my uncles was a- my father had two brothers, and one of his brothers was also a Lutheran minister, but much of his career was spent doing campus ministry in kind of an academic bent. His other brother was a musician, and he spend much of his career directing a choir at a college. It was, again, kind of a- there's a lot of religious music in the tradition in the family. So, the question was religion a big part? I wouldn't say it was that big of a part. It was there, but –
You must have been very aware of theological issues. Growing up, as you started to get interested in science, did you try to square that circle, or did you tend to keep those interests or identities separate?
I kind of left the religious part behind. I don't observe any religious traditions now. I just kind of left it behind.
Did you understand your parents to be believers? I mean, baseline stuff, in the existence of God, for example.
I guess they were, yeah. It never really came up as an issue between us. You know, am I a believer or not a believer, it was never really an issue.
Lutherans are kind of low-key about those kinds of things anyway, I suppose.
Peter, when did you start to exhibit strength in math and science?
Oh, I think, certainly in elementary school math, you start by doing math, right? Math was always easy and fun for me in elementary school. I remember starting probably at the end of like fifth or sixth grade, I kind of started doing my own stuff in terms of math, even within the school setting. You know, going to the college my father worked at and checking out books on math, and working on my own stuff in terms of math. So, I was always strong and interested in math from an early age. Not super math geeky, but just something that came easily and was kind of fun. I was always interested in science as well, and I was always interested in the side of- I was always interested in making stuff, like creating my own- a little bit like model airplanes, or cars, and stuff like that, not so much. More like trying to make stuff on my own, playing around with electronics, and making my own speakers for my bedroom. That kind of stuff. I was interested in making my own stuff, taking stuff apart and figuring out how it works, that kind of thing.
Did you have a strong science curriculum in high school?
No, not at all. I remember, particularly physics was really a bad class. It was almost a joke that the physics teacher, who was a nice friendly guy, I kind of liked him on a personal level, but he would just kind of read from a book in front of the class for a bit. There was really nothing very challenging about it. I don't even remember if we did much in the way of lab stuff.
Did you intuitively understand that there was way more out there than you were being exposed to?
Probably. It's long ago enough that I don't really remember that much more beyond the fact that it was just a terrible physics class. I had a couple of friends in the class that were kind of like minded. We were kind of interested in the stuff, and we knew this was a terrible class, and we joked about it and goofed off in the class.
When you were thinking about colleges, were you thinking specifically about physics programs?
No, not so much. I was actually more interested in engineering, and maybe architecture. That's getting back to the making stuff bent that I had. I was looking at engineering schools and, again, I was thinking about architecture. For example, one of the other ones I considered- I ended up going to Swarthmore College, and what's unique about that, I liked the idea of going to a small liberal arts college, but what was unique about it was that it had an engineering department, which you don't often find in small liberal arts colleges. So, that's what attracted me there. The other option I was also thinking seriously about was Washington University in St. Louis because of its architecture program. Anyway, so I ended up going to Swarthmore, and was imagining doing engineering. I started out doing physics, I guess, first year you don't really take engineering. You start with physics.
What year did you start at Swarthmore?
Fall of 1980. Class of '84. So, you start taking physics, and I guess I just stuck with that.
What was it about physics that you decided to go in that direction?
I guess, I just really liked getting down and being able to understand how the world works, understand physical phenomena, and being able to explain how things work at the level that physics gets to. I also did engineering. I think I minored in engineering, so I took some engineering courses. There was still that side, but I just decided to major in physics. Yeah, I think I just liked being able to explain why the sky is blue, and how electromagnetism works, and stuff like that.
I'm fascinated by the Department of Physics at Swarthmore. There are so many interesting people that you wouldn't necessarily associate with a small liberal arts college. People like Joe Taylor, for example. I'm curious what professors you might have become close with over your tenure as an undergraduate there.
One of the draws, I assume, about going to a smaller school, one of the things that's special about Swarthmore is without graduate students, and professors whose primary responsibility is teaching, is you probably have more opportunities there to develop those relationships than you would at an MIT, or a Stanford, for example.
Yeah, you may. I would say, actually, there were some- probably the closest relationship I had with a physics professor was somebody who came on relatively young- relatively to some of the other professors. What was his name? Frank Moscatelli, who came in as a starting professor while I was there, like when I was a sophomore. Maybe I first had him as a junior. I don't quite remember for sure. I think, since he was a beginning professor, I think he was little bit older. I don't think he was fresh after post doc, or something. I think he had done something at another institution before then. Anyway, he was a little bit closer in age to the age of the students than the other professors we typically had, so I think he made a little bit closer connection. Because he was starting out, and he was trying to figure out how to do it, and I think just kind of embraced the students a little bit more than some of the older. I think most of the other professors were quite a bit older, actually, at that time. There was a professor there- I'm trying to remember his name now who I did not have, because he left- I think he was there when I was a freshman, but left probably when I was a sophomore, or something like that. He was a professor who then went on to serve as a representative in Congress for a while in New Jersey. [Fritschel added later: This was Rush Holt, the CEO of the AAAS from 2015-2019.] Anyway, he might have been somebody else who was interesting, but he left before I ever had him as a professor. I think, I learned more physics just by the interactions with my peers. That's what I remember more about learning physics at Swarthmore is really just working on stuff and figuring stuff out with I would say either two or three, or four peers that I got along well with. We worked together and figured things out, starting by not understanding what this week's problem set was, and just kind of working through things. I think that's really the time when you gain an understanding of things, when you really have to work things out for yourself and doing it with other people who are working it out. You're all sort of bringing something different to the table, and I think that's when you really start grasping things and understanding it at a deeper level.
What kind of access to labs did you have as an undergraduate? Were there professors who were engaged in original research, and you could get a sense into what that was like?
Not really in those years. Things started to ramp up in that direction in the following years after I graduated, but there wasn't really much original, if anything, going on the years I was there. Again, most of the professors were quite a bit older. I think things just were starting to get going in terms of very general research a little bit later. We were doing mostly traditional lab stuff. When we had courses that had labs, they were kind of traditional. I don't know, Frank Hertz experiments, and stuff like that. Stuff that had been set up for you mostly, and you had to put things together and reproduce. I didn't get much out of it, I don't think. I don't think anybody gets too much out of those kinds of things. The lab aspect of things, I think, was kind of lacking. I do remember one- I think it was maybe one semester when there was more of a design your own kind of experiment, or not even necessarily experiment, but just lab project. I think that was more useful, even though there probably wasn't much of an outcome to it. I've got a hazy memory, but when I worked on it with one of my friends, it was some kind of magnetic circuit experiment, trying to understand- I don't exactly remember what it was, but we were trying to show something having to do with magnetic circuits. When you're not just reproducing some lab setup that's already been made, when you have to come up with everything yourself, that's again, when you actually start really having to learn things and understand things. The other thing that actually was very useful out of that whole process was I had an opportunity one semester to take a machine shop course. The physics department, maybe it was for the whole science department, but there was a machine shop that they maintained. They offered a machining course one semester, so I took that. Back to loving making stuff, that I liked a lot. That was extremely useful when I went to graduate school. One of the things that's been unique about our LIGO group is that we have our own small machine shop, with a couple of machines, and other things. Again, especially at that them when I was starting, graduate students were making a lot of our own stuff, so it was very useful that I had this training already, that I knew how to use the machine shop. Most graduate students typically don't do that. These days, that is very rare to find. We mostly just send things out to outside shops, but it's a very useful skill.
Peter, I'm curious if by the end of your undergraduate experience, your identity, in terms of your interest in physics, was well enough formed that you knew what kind of physics you'd want to pursue for graduate school.
No. I would say, not at all.
Even in terms of theory versus experimentation, were you wide open to everything?
Certainly, I was not. Certainly, experimental. I was not thinking theory.
So, you knew that much, that you wanted to do stuff, continue building things.
Well, at the end of undergraduate school, I did not- you might have guessed by now by the timing of the years that I've given you, I didn't go off straight to graduate school. At the end of my four years, undergraduate, I did not have any- some of my compatriots went off to graduate school, and to me, that was just not of interest at that time. I don't think I was even really thinking about it. But, definitely, experimental. What I did out of undergraduate is- what I wanted to do is, at that point in my life, I just wanted to get a job in doing some kind of research.
So, graduate school was not a foregone conclusion for you by the time you were a senior?
No, absolutely not.
What were your motivations? Did you want to go out in industry and see what that was like?
Exactly. In the spring of my senior year, I was looking for jobs in industry. That's what I wanted to do, is do something- again, I wanted to do something hands-on. I didn't want to keep studying in books for the next several years. I wanted to get going on something hands-on. So, I looked for jobs in industry, and eventually, there was a job which I never really got an offer, but I interviewed for a couple times at a group in Bell Labs, which looked kind of interesting but didn't come through. So, I got a job working at Raytheon up here in Massachusetts, in the Raytheon Research Division. I don't know if they still have a research division, I mean, they do research, but I don't know if they have a specific research lab anymore. They had a research building in Raytheon here in Massachusetts. It was in Lexington, close to their actual headquarters building there in Lexington. It was right off 128, and this separate research building, which was basically the same kind of campus, but the research labs were a separate building. It was through a Swarthmore grad who was working there. I guess it must have been through the Swarthmore career office where I think I got the contact. So, I got this job working at that research lab, working on lasers, carbon dioxide lasers, which they were researching as use for laser radar, or lidar. So, that was the project. That was very- when I first heard about it, it was pretty appealing. There were a couple of jobs there in the research division that I sort of went up to interview for. One of them sounded really boring. It was something like researching -- it was more of like a material science looking into semiconductor device failures, or something. It sounded kind of boring, and on the other hand, you could work with CO2 lasers, which sounded kind of exciting. So, I took that job, and was there for a couple years. That was very important, I think, because that was back to very hands-on stuff. I was in the lab pretty much every day.
Was your sense that it was really a basic science kind of environment? In other words, you hear at Bell Labs that people would be doing research that had nothing to do with the corporate bottom line. Was it a similar environment at Raytheon?
Not so much. There was some of that, but not nearly as much as Bell Labs did.
Did everything have a defense industry feel to it for the research?
I didn't have that strong a feeling. Obviously, the projects that were defined, as the person doing the work in the lab, I was kind of removed from the strategizing about what we were going to do the research in, so I didn't really deal with that much. Obviously, everything had some relation to what they might- their defense interests. In this example, they were working on lasers for radar purposes, but I was really kind of just more doing the basic physics of the lasers and trying to understand the physics of the laser properties. We were trying to make these pulsed CO2 lasers that had- trying to stretch out the pulse lengths so that you could get more precision in the Doppler measurements you'd be making. The group that I was working in did have kind of an interesting background, they weren't working on it so much anymore when I got there, but they were one of the big groups earlier, probably in the early eighties, that developed the ring laser gyroscopes. That's a little more physics-y. Those had lots of applications, and very interesting physics that went behind those laser gyroscopes. There was that kind of tradition. I think there was definitely a couple members of the group that I could see more towards the basic physics of things. A couple of important things that job gave me was just more experience doing stuff in the lab, and finding that I really liked that, and doing things in the lab where you're trying to break new ground. You're trying to understand things that haven't been understood before and develop features of some technology that hadn't been developed for.
In terms of the hierarchy, Peter, would you be able to conceptualize projects and problems, or were those at your level essentially handed to you, and your job was to essentially figure them out?
More the latter, I would say. I wasn't there that long to be able to ever really do anything more than that. I was there for a little over a year and a half. The basic goal was kind of defined for me, but I kind of had free rein to explore within that. I didn't have day-to-day supervision. I would kind of be able to do what I wanted, and supervision was more like somewhat longer- week, or every other week kind of timescale. Basically, it was just me in the lab plus this lab technician. What was really great was this lab technician I was working with was kind of an older guy and had worked in these lab technology firms for two or three decades at that point. Raytheon, some of the other big technology firms around the 128 area, and a lot of it just in the laser area. So, he just knew a lot of the technologies. He wasn't a physicist. He didn't have that basic understanding, but he was a really good technician. I picked up a lot of good stuff working with him, just very practical lab experience. So, that was very important. It showed me that I like working in the lab, pursuing research where you're trying to understand things and push technologies in a new area. That was a big part of it. Wherever you're trying to push technology to a new area that it hasn't gotten before, it's interesting and exciting. The other thing I took away from it was, this is not something I think I would want to do for the rest of my life, because it is kind of- even though, like I say, you're pushing technology in a new area, it's a very niche area that is sort of fine-tuning. We weren't developing anything super new, like new laser systems. We were just kind of fine-tuning the properties of the CO2 laser system. I could kind of see that wasn't going to be a really strong motivator in the long run. So, in contrast, I think that's why I was really motivated by the whole gravitational wave enterprise. This is a really big picture pursuit-- it's hard not to be motivated by such a grand goal, discovering gravitational waves. So, that contrast was, I realized at that point that I kind of needed that contrast for something that would keep me motivated over a longer period of time.
What was the next move for you, as a result?
The next move was graduate school and choosing to go to MIT and start working in Rai's group.
Did you know of Rai beforehand, given that you were in the laser world?
This is kind of a vague memory, but I think- another nice thing about working in the Raytheon research group at that time is they would have weekly seminars where they would bring in people, like working at a university where you'd have a weekly seminar. They'd have weekly seminars, more technology focused than pure physics focused, but some of them were more physics focused. I can't say for sure that this happened, but I have a vague memory that Rai came in and gave one of those seminars when I was there. Sometimes I'm not quite sure if I'm making that up or not, but it definitely could have happened. Beyond that, when I was applying to graduate schools, I entered in fall of '86, so in the spring of '86, I'd sent out my applications and was waiting to hear. I think I'd gotten a couple of acceptances and was talking with some of the people at the institutions, University of California in San Diego, for example, was one of the ones I was talking to. I was trying to figure out what my options were, and I think I hadn't heard from MIT yet. It must have been that- I ended up just calling up Rai and said, it must have been because I remembered him because he had given this seminar. Like I said, this is a little bit vague, but I think that's probably the storyline. I think I just called him up and said, "Look, I'm waiting to hear from MIT. If I get in, I'd be interested." Or maybe I- it's all a little bit hazy. I think what happened was I called the physics department and said, "I haven't heard yet about my application." I think I was told, "Well, we're not quite sure if there's a group here that could take you. Here's one possibility." They might have given me a couple possibilities, and I think they might have given me Rai's as one possibility. So, then, I ended up calling up Rai and said, "This is my situation. I guess I'm not really admitted yet, but I'm looking for a place that might take me." Anyway, since I was in the area, and I was working at Lexington, I just came down and visited Rai at MIT. We had good conversation, and he showed me around the lab, and I probably talked to a couple people, and I was sort of sold on it.
Peter, I wonder if, in retrospect, you appreciated- for example, I talked to David Shoemaker yesterday, and I get the sense that when you go and work with Rai, you're joining a band of misfits, within MIT where it's this separate world. Did you have the feeling at the time that this was going to be- I mean, it is MIT, but it's really the Department of Rai, and all the crazy things that he's doing.
Right, right, right. I don't know if I had the sense like that particular- I probably didn't have the sense in that visit, my pre-graduate student sign-up visit, but I think at some point, yeah, probably.
So, the whole history of MIT not really believing in Rai and what he was doing, that sort of dawned on you in real time. You didn't get that all at once.
Right. I think that dawned on me over the first year or something. Right.
But he must have conveyed what a fun place his lab was.
Yeah, I think so. It definitely got conveyed, I think, just the excitement of what they were trying to do. I just remember talking to him and getting that spring of '86 visit and telling him about what I was working on at Raytheon in terms of the lasers. He picked up very quickly what the challenges were for me in that project, so it just seemed like this was going to be a cool, interesting academic research environment.
In terms of your connection to the Department of Physics, how much did you have to spend time there, at least in the beginning, taking courses and things like that?
I didn't really spend time, that's one of the things about, at least when I was a graduate student, I didn't really spend time in the Department of Physics. I mean, you went to classes. The MIT Department of Physics, at least at that time, there was a central physics office, and things like that, but classrooms, at least for the graduate student classes, they were kind of spread around, mostly in the main building, but spread around in different places. It didn't feel like you were going to the physics department. You were going to whatever classroom that professor happened to be teaching in, and then the fact that our labs were kind of separate from other physics labs. That was also a feature, and is still kind of a feature, again, because of these centers. It's not like all the people doing physics, it's not like their labs were near each other. So, I didn't really have a strong sense of being part of the Physics Department. I didn't do that many classes. There were certainly course distributions you have to fulfill, and I did that. I didn't do that many classes beyond that. I remember, I even kind of remember a transition in the second semester, like the spring semester of my first year, when I got- I really transitioned to thinking I should really spend more time working in the lab, and less time on these courses. Things might have changed, but at that time they were targeted to the physics students who were going to do theory. I wasn't getting that much out of them, so I just decided to do the minimum of the courses that I needed to do, but really try to spend more of my time on lab work.
How did you go about developing your dissertation? In other words, some people have a relationship with their advisor where their advisor is working on whatever they're working on, and they hand a graduate student a problem, and others are, "figure something out and bring it to me." Where were you on that spectrum?
I guess, probably somewhere in the middle. It takes a few years to figure out what your actual thesis is going to be on. Of course, the work that our group was doing was going through a lot of changes at that time. When I first started in the fall of 1986, the whole group was kind of focused on making a new, the group before those years had made a prototype interferometer. These prototypes are often described, or their moniker relates to how long their arms were. Ours was called the 1.5-meter prototype because the arms were 1.5 meters long. The sensitivity scales with the arm length, the important parameter is how long they are. Caltech had this much bigger prototype known as the forty-meter, because they have forty-meter-long arms. Prototypes are often known by how long they are. So, in the late seventies and early eighties, they had developed this 1.5-meter prototype. So, when I got there, the group was designing, and then intentions were to go to the next generation of prototypes, which would be the five-meter prototype. Still not the Caltech scale forty-meters, but bigger going up to five-meters. We were constrained by how much space we had on the MIT campus. Anyway, the group was focused on making- over the next several years we're going to build this new five-meter prototype as the next step towards the full-scale thing. Folks were working on different aspects of that. Some folks were working on the seismic isolation system you need for that. Some folks were working on the suspensions for the mirrors that you put on that. When I first started, I started working on the laser that we would need for that. I had this laser background at Raytheon and was interested in lasers. So, we were going to develop our own laser for that next generation five-meter prototype. Also, right around the time I started, this big new vacuum system was purchased for this five-meter prototype, with fairly large vacuum chambers. That was taking up space in this new experimental space, the high bay space in that building twenty at MIT. So, the whole group was focused on, okay, the project that we're working on is to make this new five-meter prototype. It got some ways along that path, but it didn't get carried through because also at that time, of course, the whole LIGO project was starting to get ramped up, the actual big observatory project.
You mean on all fronts. MIT is starting to get on board, the NSF is really behind this, the collaboration with Caltech.
Maybe leave MIT- other than our group, leave the MIT greater administration out of it. They had written a proposal to the NSF to get it started, to get it funded. You must have boned up on the early history of LIGO. That's when, at Caltech, Robbie Vogt was put in charge of the project. Are you familiar with that history?
Yeah. So, Robbie Vogt was put in charge probably when I was in my second year of graduate school. Rightly so, he saw that the two Caltech and MIT groups really needed to focus their efforts. Things were a little bit too, well, unfocused at that time. So, one of the things he did was to- we were working on this- like I said, what I started working on was this laser for the five-meter prototype. The laser was going to be a different kind of laser than what had traditionally been used. What had been used in the prototypes both at MIT and Caltech, and also in Europe up to that time, were these Argon ion lasers, which were green light lasers. But what we wanted to do, and this thinking had already been done before I got there as a graduate student, but for this new five-meter prototype, the decision had been made to move to YAG lasers, which is a near infrared one-micron laser. They're much more efficient lasers. They sort of have the promise of being lower noise lasers. So, that's what I was working on. Not that YAG lasers were super new technology, but to develop a type of YAG laser that was appropriate for gravitational wave interferometer was kind of a new thing at that point. So, that's what I started working on. Then, when Vogt came to be in charge, one of the things he said was that there were too many of these disparate efforts at Caltech and MIT. "We're going to use these Argon ion lasers that we've used for years, and we're going to drop that YAG laser program." So, the project that I had been working on with the YAG lasers was stopped at that point. I had spent a couple years on it at that point, so to just change course- oh, and another thing that was also sort of down selected at that time, early on there were these two methods of how you build up the gravitational wave signal in the arms. You want to make the arm as long as you can, but you still want the light to interact with the gravitational wave even longer than that. One way that was done, which was the way it was done in the first prototype at MIT, the 1.5-meter prototype, and had been done in a German prototype, was using what's called a delay line. You're just bouncing the laser beam back and forth between two mirrors many times, at sort of these discrete paths that were just going back and forth. The other method, and this is what they were doing at Caltech, was to put a resonant Fabry-Pérot cavity in the arms, which has a very similar effect, but rather than having these discrete beams going back and forth, effectively, they're all on top of each other, and resonating in this cavity. So, that was another decision that was made around that time, that the LIGO observatories are going to use the Fabry-Pérot technique, rather than the delay line technique. I think things were going that way already, because people were seeing problems with the delay line technique that would have been really hard to solve. So, that was a change that had been made. The basic configuration of the interferometer was being defined at that time, but there were aspects of it that hadn't been demonstrated yet. So, that's what became the project I started working on then, at that point, when the laser stuff ended. We also decided at MIT, because of the changes and because of probably also changes of people coming and going in the group, that the group was no longer focused on getting this 5-meter prototype going. Rather than putting together this prototype, we were going to focus on more individual components of it a little bit more. So, what I started working on then was, rather than a longer prototype where the mirrors are suspended from a pendulum, like you do with a real instrument, I started on working on what we called then a tabletop interferometer. The other term for it was a fixed mass interferometer. So, rather than making arms as long as you can in a laboratory environment, and with test masses that are suspended to have seismic isolation, it was all built on one optical table. So, it was a complete interferometer, but it's built on one optical table, and the mirrors aren't suspended. So, you're not trying to make an interferometer that has any sensitivity to gravitational waves, but you're trying to make an interferometer that has the same kind of optical configuration that we're designing LIGO for. That optical configuration hadn't been developed before. It was only on paper. Nobody had done it. So, rather than doing it on a larger scale prototype with suspended optics, we did it on a smaller scale, single bench prototype. I'm realizing this may be a good time to break, and then come back.
Okay, we'll do that. I'll stop it here. 200901_0285_D.mp3
Okay, so to pick up from session one from earlier today, Peter, just to orient us a little on the narrative from where we left off, you're still a graduate student through all of this, right? You still haven't defended your dissertation.
That's right. We were talking about how I got to what my thesis project was. As I was saying, the things that the group were working on were really changing in those times. The thing that was in front of the group when I started out as a graduate student was making this new 5-meter prototype. That project then got- abandoned is a little bit of a strong word, but it got morphed into other things. The project I first started working on, which was a new laser for that prototype, also got abandoned, I guess I would say. So, at that time, the actual configuration of the interferometer for the observatories was being crystalized at that point, but there were a lot of aspects of that configuration that had not been demonstrated before. So, my thesis project turned into sort of a two-stage project. The idea was to demonstrate some of these things on what I call the tabletop interferometer. Before that people had been working on what we called suspended mass prototypes. Suspended mass ones are the ones where the mass actually is suspended as a pendulum, like they actually are in our real observatories. So, what you saw in the early to late eighties were the development of these suspended mass prototypes around the world. So, again, there was the one at MIT, which was the 1.5-meter prototype, which was just being shut down in 1986. There was the Caltech forty-meter prototype. I don't recall exactly when that got started, but that was still in operation. There was a ten-meter one in Glasgow. The other big one was in Germany, in Garching. I don't remember exactly, ten- or fifteen-meter prototype. So, that's what was happening in the early to late eighties. Then what you started to see, starting in the late eighties, and then the early nineties, starting with the project that I did for my thesis, similarly, in the Glasgow group, and you saw this in a number of groups, they started working on these tabletop interferometers. The move was to demonstrate the particular interferometer configuration that was being designed for the big instruments. But, forget about trying to make any kind of sensitive instrument in the gravitational wave band, in the audio band frequencies. The focus was on demonstrating optically what the configuration was, and how you're going to control it. That kind of thing. So, you had my project, and there was a similar one that was in Glasgow in kind of a similar timeframe.
Would this be like a multiple independent kind of development, or were you in contact with these people?
At that particular time, it was more independent. There wasn't as much contact amongst groups around the world as there is these days. It was much more independent. There would be conferences where you would come together and talk about things, but it wasn't the type of much more close contact that you have these days, both because of the communication abilities you have these days compared to back then, and also just because the field was that much smaller back then. Things were much more independent and more isolated than they are now. So, my project was sort of a two-step thing, and I guess the first, the thing is that the design for the LIGO interferometers at that point had converged to this configuration where you have the basic Michelson interferometer, and then you have these resonant Fabry-Pérot cavities in each arm, and you're going to have power cycling, which is adding another mirror at the input to the interferometer. So, that configuration, what we call a power recycled Fabry-Pérot-Michelson interferometer, was the design that we were going to go for LIGO. That was known by sometime in the mid- well, probably late eighties. That particular configuration hadn't been built anywhere. None of these earlier suspended mass prototypes had actually built that configuration. So, the project was to build that configuration not in a larger suspended mass type scenario, but in a more compact, tabletop interferometer. So, that's what my thesis then became. So, I actually made the first ever interferometer which was that configuration where we have the Fabry-Pérot cavities in the two arms, and you have a power recycling configuration. That was the first demonstration of that actual configuration. Then, like I say, there was that period of time, roughly a decade, where we're doing these tabletop demonstrations. After my thesis, that got other graduate students at MIT and at other groups around the world continued to do that kind of thing to further demonstrate other aspects of the whole system. For example, at MIT, it developed into another thesis. For example, one of the next ones was Nergis Mavalvala, using that same kind of tabletop interferometer to develop and demonstrate how you control the alignment of the interferometer. So, my particular project didn't really look at that. You had to be aligned, but there was no automatic sensing or control of the alignment. So, she did that aspect. There were others, like at Caltech there was a graduate student thesis that on a tabletop interferometer did the next iteration, a more realistic implementation of the control system, of the way that we control the different degrees of freedom. There were certain aspects of the way that I built it that wasn't going to be practical for the final, big instruments that we made. So, there was that period of time, stretching over about a decade, where other groups around the world were working on these tabletop interferometers to demonstrate different aspects of the configuration. That period is sort of over now. It sort of had its decade, and then people don't really do that type of experiment anymore. Now those types of questions tend to be answered just by modeling things. The simulation and modeling capabilities of the instruments have developed over the years, which we didn't really have at that point.
Is the advance in modeling really a statement about computational power, and its growth over the years?
I think it's a statement both about computational power, and about the field growing in people. I think back on the early days-
Meaning there's just more people to look at the data and make sense of it.
It isn't so much the data. I'm talking about modeling interferometer. Nothing to do with collecting gravitational wave data but modeling the interferometer. How is the interferometer going to work? How are you going to control the interferometer? Now that there are more people involved, you can have people that are just dedicated to that. If, in the early days, all you were doing is modeling, you'd never build anything. You just didn't have enough people to do all that kind of stuff. People tended to focus on just building things. As you say, along with probably the computational infrastructure, and computational power wasn't really there back in those days either. So, I guess it's both.
How closely are you working with Rai, in terms of- there's your project and what you're working on, and of course, there's the broader LIGO effort. How much are you working exclusively toward that broader effort, and how much of this is your own project, what you're interested in, and you'll plug that into LIGO where you see fit?
As a graduate student, it was more the latter, I think.
So, you never felt any specific pressure to be like a company man, or anything like that, that your research needs to be exactly what LIGO needs when it needs it. It wasn't like that.
Not quite, I guess, but there were those changes that the group had to do when Robbie Vogt came in charge. MIT as a group had to be the company man. In other words, we were giving up two things that the MIT group was trying to pursue in the late eighties. So, we gave up those new lasers we were trying to develop. Interestingly enough, six or seven years later, we returned to developing these YAG lasers, and trying to shift the operating wavelength of the interferometer from green light to near infrared. So, from half a micron to one-micron light. We stopped that effort but then came back in 1994, I think it was. The project actually changed. We realized those YAG lasers at one micron are actually much better lasers. We made the switch when the real official LIGO project was getting started, after, when Barry Barish was put in charge of the project, that was one of the early changes that was made in the technical design. We're going to use these YAG lasers, that's the future. I'm not trying to justify or anything, but I think we did have that kind of foresight. Unfortunately, we had to give it up, and it probably was the right decision at the time. And we did have to give up this pursuit of the five-meter prototype. So, there were things that we had to give up as a group that we were working on in order to go on with, like you say, the company- what Vogt was defining at that time. We had to coalesce the efforts at MIT and Caltech.
Who was calling the shots in terms of those strategic decisions about the direction of the overall collaboration?
I'm not sure that I- again, as a graduate student, I'm not sure. I didn't have a lot of visibility into that. I saw the outcomes of it.
But it's not like it's Rai just by himself.
No. He agreed to go along. I think he agreed that the Caltech-MIT partnership that was happening wasn't coalescing well to get the project off the ground. I imagine he recognized that was true. He agreed with these decisions that Vogt made, for example, to stop the laser project, and stop some of these other projects that we were working on, and to decide to just go with the Farby-Pérot scheme in the arms rather than the delay line scheme. I wasn't involved in the particular discussions they had about it, but I saw the results of those decisions as a graduate student.
Who was on your committee?
Who was on my committee? Let's see.
It's amazing to me how fuzzy people's memories are about these things.
Yeah. The committee wasn't that big of a deal at that point. Certainly, these days, they tend to be more- I think current graduate students tend to meet with their committee regularly while they're doing their thesis. Back in those days, at least for me, it wasn't that formal. I think at the beginning I said, "This is what my thesis topic is going to be, and here's the abstract." As a committee, we didn't meet again until I had an actual defense. One of the members was Shaul Ezekiel, otherwise known as Ziggy. He had been one of, maybe the first student of Rai's when Rai was a professor. Good friends with Rai at MIT. He did a lot of stuff with lasers. Who was the other one? Richard Milner, as I recall. It's not a crystal-clear memory of whether anyone else was on the committee. Anyway, that was my thesis project. The other aspect of that, I think, worth pointing out that at that time -- I wasn't really working with Rai on my project. At that time, he was involved with getting the LIGO project off the ground- those were also the days when COBE, the microwave satellite was getting going, and he was heavily involved in that project as well. He had a lot of other things going on. I think I would usually meet with him once a week, or maybe two, just to let him know how things were going. But on a day-to-day basis, it was basically me and the other scientists in the group, either post docs or other research scientists. There were also a lot of changes in those years of people leaving and doing other things. A significant person that came in during that time when I was getting started on that thesis project was David Shoemaker. He had spent some time in the European groups, both at Garching, and then the one at Orsay. Garching had one of those early suspended prototype interferometers. The group at Orsay, in France, outside of Paris, was one of the two lead groups that formed the Virgo collaboration. So, he had this experience in Europe, and then he came back and joined the group at MIT probably around 1989 or 1990. He worked quite a bit with me on that thesis project that I did. It was pretty much the two of us working on that.
After you defended, did you think about leaving MIT? Was that part of a plan, or did you know this was your spot, and this is where you wanted to stay and make a career?
No, I did leave MIT. I had no intention of sticking around. Didn't even necessarily have the intention of sticking in the gravitational wave detectors field. I looked around a little bit at other groups. I actually did my thesis in the area of- it was not in astrophysics. It was in atomic, molecular, and optical physics. I was more interested in the instrumentation side. We weren't really doing atomic or molecular physics, but optical physics. When you do a PhD thesis, you do it in some area of physics. So, mine was in what they call AMO, atomic, molecular, and optical. It was a little bit different within our group to do your thesis in AMO. I think, maybe, up until that time, I might have been the first one. Up until that time, the graduate students did their thesis in astrophysics, even though they were working on developing this instrumentation. Often, what they would do as part of that thesis is, even though most of their work was doing some development on these detectors, they would do some aspect of the thesis looking at some astrophysics, looking at the prospects for detecting some astrophysical source, for example. But since I was doing my thesis not in astrophysics but AMO, I didn't have that part of my thesis. My thesis really was just on detector design. So, I was looking around at other groups in that area, AMO, atomic, molecular, optical physics. Definitely considered going out to one of those groups. What I ended up doing was I went to that group in Orsay, outside Paris, which was the group that was run by Alain Brillet. So, the two founders of the Virgo collaboration were Alain Brillet and Adelberto Giazotto in Italy.
Were you aware of their work as a graduate student, or was this after you started looking around and seeing what you wanted to do next?
I was aware of their work as a graduate student. Some of it from the papers, and much of it from just learning about it from David Shoemaker, because he had just come from there. He actually did his PhD thesis there at that group. So, it was mostly through him. I ended up deciding to go there, and much of that decision was not even so much that I wanted to stay in this field, and this is great, it looked like a fun experience to live in France for a couple years. I had some desire to do some world travel, so that was really as much of what made the decision for me as anything else. When else am I going to do that in my life? It just looked like a good opportunity to try that.
And live in France for a while.
Yeah, so that was great. I'm glad I did it. The actual work there wasn't all that satisfying. Some aspects of the work environment weren't all that great. I was married at that time, so my wife and I went over there, and it was a great couple of years for us. I was very fond of that time that we spent there. I think it was useful to get to know some of the people in Virgo, and some of them were still there, and I keep in contact with them, and so on. But the actual work I was doing, I wouldn't say I got a lot out of it the way the group was-
Was Virgo sufficiently different, where you felt that you were learning new physics?
Interesting. I wouldn't say I felt like I was learning new physics. I was learning a little bit- well, some different ways of doing things, I guess. One of the things that characterized the Virgo project that was different is that they never had- that project formed a little bit later than the LIGO folks, and they actually never had one of these suspended mass prototypes. So, for LIGO, and also the GEO group, they all started with these suspended mass prototypes and then went from there, whereas the Virgo collaboration was more of a collaboration of several different groups that brought different things to it. But none of the institutions was doing everything and doing a full prototype. What do I mean by that? For example, the Italian side, what they were bringing to it was the mechanical design of the suspension system. They had a much more elaborate design for the test mass suspension than we did in LIGO, at least in the first stages of LIGO. Then, on the French side, the Orsay group brought in the optics experience with lasers and optics and precision measurement. That was kind of what they brought in. Then, they brought in other institutions within France and Italy. A lot of times they're bringing in groups from high energy physics that might have experience in electronics, and stuff like that. So, to form the Virgo collaboration, they're bringing in these groups that had different expertise, and then try to synthesize into the whole, whereas on the U.S. side, we started Caltech and MIT, each group did everything on their own to make a prototype. You have to do the lasers, the seismic isolation, the electronics, and all that. So, each group kind of had knowledge of everything, and some level of expertise in the whole system, whereas the way the Virgo project formed you have these different groups, each of which have their much more limited expertise which we're trying to bring together. So, you can see that before they made the big Virgo machine, they never really had a prototype to synthesize everything together. So, it was just a very different approach. So, I saw that part of it there, and the other thing is they had a stronger -- in particular, that Orsay group had a strong modeling group -- modeling of the interferometers, so doing optical modeling of the interferometer. So, I was able to see how important that was. They had gotten into that and spent more of an effort on that in the early days than on the LIGO side.
What was your next move after the work at Orsay?
Yeah, so then, at Orsay, I was just there for a little bit under two years, and again, wanted to come back to the U.S. It wasn't a foregone conclusion that I would come back to work on LIGO, although I think it was probably, coming from Europe, hard to look at other areas. So, I tended to look at, or make inquiries into places that were very closely related to LIGO. What I ended up doing when I came back to MIT- this is the story. I was kind of interested in going to Caltech to work on LIGO, as opposed to MIT. I think, at that time, it just wasn't -- I don't remember exactly how it went. There wasn't really an option, somehow. I don't remember exactly why. But there was an opening at MIT, so I just came back. I figured I'd come back for a maximum of five years.
Maximum. That's it.
Yeah. Of course, I'm still there.
Coming back, did you know you were going to be coming right back to LIGO, or were there other projects you were considering?
No, that was the job. I was coming back to work on LIGO.
I'm sure you appreciated the opportunity to get away and broaden your perspective. I'm curious what had changed in the interim, with a fresh pair of eyes that you were coming back to.
Well, let's see. What changed? In LIGO as a whole, that was when -- I was blissfully away from all this at that time, but that was when there was a lot of turmoil in the LIGO project, particularly at Caltech, having to do with Ron Drever. You probably read or caught on to some of this history. That's when Ron Drever was sort of pushed out of the project, during the years when I was in France. When I came back, there's still the aftermath of all that stuff going on. He had been kind of pushed out. It was still before- I think when I came back, Robbie Vogt was still in charge, but it was very close to the transition when Barry Barish was brought on. Certainly, within the first year that I was back, that transition also happened, that Barry Barish was brought on as the leader. So, that was happening. I was brought back, actually, to work on a very specific project, which we did. So, back to a suspended mass prototype interferometer. We're finally going to get to use that new- not so new anymore, but this five-meter vacuum system to make a five-meter prototype. It wasn't quite the same design that it was originally conceived for, but it was similar. What I was brought back for, in those days, it was seen as very important to demonstrate in the prototypes that you could get close to the sensitivity that we're claiming the big interferometers are going to get. You're not going to get the same strain sensitivity, of course, because that strain sensitivity comes because you're making the thing really long. But you can get the sensitivity in two other ways. You can split up the sensitivity and think about it in two ways. To make the gravitational interferometer as sensitive as it is, you have to do two things. You have to make the test masses really, really quiet. Really, really low vibrational noise so that when the gravitational wave comes through, the effect of the gravitational wave is larger than the inherent motions of the test masses. You have to make the test masses really, really low noise. Really quiet.
How do you do that?
You do that with a combination of- the mirror suspension is part of that. You have both passive and active means of isolating the test mass from the surrounding ground vibrations, or just acoustic vibrations. That's why you put things in vacuum systems, so they're isolated from the acoustic noise, and then you have these elaborate suspension systems, or seismic isolation systems. So, you can isolate them from the vibrations pretty well. Then you also have internal, thermal noise, which is the fact that because the thing has some, unless things are at absolute zero temperature, the fact that something has a temperature means that its elements, or in this case, the atoms have a random motion to them. That's what temperature actually means, sort of the average motion of a group of particles. So, since our test masses are not at absolute zero, they're at room temperature, there are some internal motions that they have as well. So, you can't eliminate them, but what you can do is you can make them smaller by making the mechanics very low mechanical loss. If you tap on a wine glass and it rings, how long that ringing decays, or how long it takes for that ringing to decay has to do with how much mechanical loss there is in the glass. So, you can make the thermal noise smaller by having systems that have very low mechanical loss, or another way to put it is they have very high Q, quality factor. So, that's another aspect of designing it for low vibration. Anyway, so that's one aspect. In order to make a gravitational wave detector, you have to make the test masses be very low vibration, very low noise. The other aspect is, okay, if they're low noise, you have to be able to measure that. You have to have a measurement system that's capable of measuring these very low-noise objects. So, you can kind of separate the problems in those two ways. Not everything is separable like that, but to a large degree, you can separate the two challenges. In those days, it was seen as important in order to demonstrate the fact that we could design a system that had a low vibration noise, we call it displacement noise. It had low displacement noise. That was actually the goal of what they were doing at the Caltech forty-meter prototype. Their goal was to say, okay, we can demonstrate that we have the very low displacement noise that we need in the LIGO interferometers. It's not going to have a good strain sensitivity because it's one hundred times shorter than what we're going to build for LIGO. But we can see that there's nothing preventing us from making the test masses as quiet as they need to be. So, that was their goal. Then, if you look at the other half of the problem, now we need to design the interferometry so we can actually measure that. So, that was the goal of this new prototype at MIT, which is what I signed on to do when I came back to MIT. We call that the phase noise, because you have to measure the relative phase of the light as it comes back and interferes at the beam splitter. So, we built what we call the phase noise interferometer at MIT in those days, in the early 1990s. The idea, again, was to demonstrate at the level that we needed for the big interferometers, that we could make an interferometer that had the phase sensitivity.
Peter, just to zoom out for a minute on the career track, is this like the equivalent of a tenure line position that you're signing on for, or is it a totally different world?
This was in the research track.
Is there a tenure process on the research track?
Well, sort of. It's not quite tenure. So, the MIT research track has three levels. Research Scientist is the starting level, and the next level up is the Principle Research Scientist, and the third level up, which is what I am now, is the Senior Research Scientist. The Senior Research Scientist position is actually seen as sort of an academic position. To get promoted to the Senior Research Scientist position, the process is somewhat similar to getting tenure, in the sense that you have to have a lot of recommendations from collaborators around- not just collaborators, but from people in the field, not just MIT but from around the world. You have to be a recognized contributor to the field.
What about in terms of job protections, and soft money versus hard money?
Yeah, so in job protections, it's not like a tenured professor. In terms of job protection, if you're at the Senior Research Scientist level, there's a commitment that if you lose whatever soft money, you're on, MIT will support you for one year. There's some soft landing, but it's not a tenured position. So, yeah, I was brought back in the Research Scientist position. There really weren't new professor positions being opened up in the field at that period of time. Again, at this particular time, I think MIT was not as supportive of the whole project and the goal as Caltech had been. So, that took a while yet. Anyway, I was brought back as a Research Scientist.
But it's not like a five year or ten-year commitment. It's sort of, "let's see how this goes."
No, I mean, in terms of whatever assurances you were offered in taking this position.
Yeah, no, the assurances are just- on the one hand, there was no defined timeline. So, as long as the LIGO project kept going and kept getting funded by the NSF, that job would still be there.
Right. I'm curious also, obviously there's benefit to leaving and working on a different project like Virgo, but I'm curious what you might have brought back intellectually, with skills, things like that, that might have advanced your work that you might not have been able to do if you had just gone straight through.
Interesting question. I haven't thought about that too much but let me see. Well, one of the things I worked on, back to the lasers, when I went to the group in Orsay, some of the time I spent working on the YAG lasers. The folks involved with Virgo, and the Orsay group, which was the group bringing lasers and optics to the project, they didn't have this baggage of having worked with Argon ion lasers for years and years. They clearly saw the benefits of moving to these YAG lasers. They were working on that, and I worked on that project there. So, I gained some more experience working with the YAG lasers, which is funny. When I first came back to MIT, LIGO was still wedded to the Argon ion lasers. And then it was, like I say, one and a half to two years after I got back that we finally made the switch. I think I got more experience with those other lasers in France, so that was useful. Let's see. There were aspects of the way the group was run in Orsay that I just did not like. A number of my direct colleagues I was working with one-on-one I liked, and we had good relationships and all that. But it was more the direction of the group that I found problems with. It was the first time that I'd been working in that size of a group where I didn't really like the way it was managed. It was certainly one of the reasons I didn't consider sticking around longer that I did. Sometimes, it's good to have a bad experience to teach you what not to do. Bad experiences are as good examples as good experiences. So, I think I can take away from that aspects I don't think a group should be run this way. So, in that sense, I learned something in that style as well. I think otherwise, just making connections with the folks in Virgo, which are still there. Some of those folks are still working on it. I think that was the positive stuff that came out of it.
Peter, at what point is- I mean, just to foreshadow what LIGO would go on to accomplish, there's this long history of it's in survival mode, people doubt it. It's that big narrative. From an outsider's view, it seems like, amazingly, all these things come together and happen really quickly. Is your sense from the inside, is that really how it happened as you see it also?
No, not the latter part. We were spending many years before that making progress. There's the whole period of making the initial LIGO detectors. I'm not talking about the prototypes now, but the ones at the observatories. From the late nineties up through the late 2000s, that's when we were actually constructing the facilities and making the very first large-scale interferometers. We were making progress- I mean, the progress was very hard to come by, in terms of the sensitivity, but we were making progress. Eventually, the interferometers performed with the sensitivity that we designed them to. That sensitivity didn't happen to be quite good enough to detect anything, at least in those data taking runs we did with them. But that was very satisfying to get to that level. We actually got them working as well as they were designed to be. That was just a lot of hard work, and a lot of unforeseen problems that we came across and had to solve. That whole thing was rewarding in that sense. Then with advanced LIGO, we're making all new detectors and it felt like we sort of had the chance to do it better this time. Everything that we got wrong with the initial detectors; we could now do it right the first time with the advanced LIGO. In many cases, that was true. Of course, not everywhere. There were new problems that came up that were unforeseen, but to a large extent, we really did do much better with the advanced LIGO detectors. That period was much shorter, in terms of when we started working, and putting in the advanced LIGO detectors, making them work, and then getting our first detection, relative to the initial LIGO experience was certainly much shorter, but it was on the heels of all those years of experience before that. Not sure if that quite answered the question, or what the original question was, but –
Yeah. When did you get the title that you currently have now?
Oh, good question. I probably should look it up. It's something like- what is this, 2020? I was supposed to send you a CV, wasn't I? I'll do that. It was something like- I'm going to say it was less than ten years ago. It was somewhere between five and ten years ago. I should know it better than that, but somewhere in that region.
And this would be Principle Investigator?
No, Senior Research. I got promoted to Principle Research Scientist, that would have been more like a dozen years ago, I guess. The Principle Research Scientist is the first level of promotion, and that also has some- you have to have some external letters of support, kind of thing. So, that's also a certain threshold. I would say that's more like twelve to fifteen years ago, and then the Senior Research somewhere between five and ten years ago.
In terms of putting the history together for what the Nobel actually recognized, when is that science happening? How far back does that go? Obviously, the Nobel is not recognizing Rai Weiss for what he was doing forty years ago. That's a buildup, but what's the history in terms of the actual science that's going into this incredible recognition?
The history of the actual science- let's see here. There are a lot of ways to answer that, I guess. I mean, what they were recognizing, I think, it's one of those things that's- what they were recognizing, I guess, there, was Rai being sort of the father, or founder of the field. Like I said, he's not the only person, but one of the people who first conceived of the idea of going after gravitational wave detection with these interferometric style detections. He then basically committed the rest of his career to that. Not completely, because he conceived of it in the early seventies, and then he continued to work on cosmic microwave background stuff, maybe equally as much, up until the mid-1980s, or so. But after the COBE project, he really was dedicated to LIGO.
It's an interesting question, because when the Nobel is awarded in theory, there's a much longer lag time, because the committee wants to make sure that the theory actually plays out experimentally. But the idea is, I guess, that in the world of experimentation, you don't have that lag time, because if the thing works, and it's giving us this incredible data, these images and things like that, the turnaround is actually much quicker. So, I guess, the basis of my question is how far back the Nobel committee might have gone in terms of this decades-long collaboration, scientific pursuit, in actually saying this is what we're actually recognizing. Here's the science where we're saying this is what's worthy of a Nobel Prize.
Yeah. Well, because part of it was for the theory, right? Because Kip was one of the awardees as well, which is the theory side of it. So, it was both the experimental and the theory aspects of it. I would say both of those go back to this- in terms of their contributions, it goes back to the early seventies, both on the experimental side, in terms of the concept first came into being, at least with Rai. I'm not a complete expert, but I think that's also when Kip Thorne started to work on the theory side of gravitational waves. Sometime in the early seventies, a paper that he wrote was called Gravitational Wave Astronomy. That's an interesting one to look up. It's just, what might gravitational wave astronomy be, if we could actually detect gravitational waves. That's an interesting historical thing to me. I think, both sides, theory and experiment, it would go back to the early seventies.
Is there a time when you sensed the buzz before the Nobel announcement? Like, this is for real. This is really happening now. We're really going to get recognized for this.
Well, I mean, we were all expecting, with probably at least fifty percent expectation that the Nobel would be given in 2016. We made the announcement earlier that year. Our detection was in September of 2015. We announced it in February of 2016. We thought, maybe fifty/fifty. Actually, the whole group at MIT, when the announcement gets made, it's usually like 6 a.m. east coast time. So, in 2016, actually, the whole group gathered in our office area at MIT for the 2016 live announcement. We were, like I said, maybe half expecting it to be that year, and of course, it wasn't. We did the same thing next year, and I think we all had much greater than fifty percent expectation in 2017. It was awarded the Breakthrough prize the previous year, at the end of 2016. I think actually the first time, for me, that it hit me how much of an impact this made to the general public, to people outside of our community, was the day of the announcement, and how much of a big splash it made in the media the day of the announcement. I think that probably would be the first time- I always expected, over the years, when people would ask me at dinner parties, cocktail parties, "What are you working on, and what are the applications? Why is this important?" I think I would often say, "When we actually detect gravitational waves, it might be front page news, maybe. Maybe second or third page." I underestimated the actual attention and interest that it actually got.
As you know, of course, Rai has lots to say about the disconnect between how complicated the endeavor is. All of the people that worked on this project, and how narrow the recognition is in terms of who actually gets the prize. It's an imperfect system, of course.
An imperfect system. It was designed one hundred years ago when things were much more individualistic in terms of those achievements. That's what was nice about the Breakthrough Prize. They recognized the collaborative endeavor, the whole group.
In a perfect world, how many people should have gotten the Nobel Prize, just in terms of- it's at least in the hundreds, right?
Yeah, it's probably- I'd put it maybe at around one hundred. I don't know if I'd put it at hundreds. Certainly not the thousand that's on the author list. But, yeah, maybe one hundred.
And this would be recognizing that it's not just the vision that somebody like Rai had, but actually- I mean, the vision is amazing. You're not getting anything without the vision. But there are still a lot of people doing a lot of hard work over many years, without which LIGO doesn't happen.
A lot of hard work, a lot of clever work. A lot of little visions within that big vision that needed to happen. So, yeah, exactly.
I remember I watched a YouTube of Rai giving a speech at MIT maybe the day after, where he's just so flustered. He's just so extraordinarily gracious to emphasize, this is everybody. This is not me; this is really everybody. So, it must have been really gratifying for everybody there to at least have him convey that so clearly.
Yeah, definitely. That was not a surprising message to hear from Rai.
Yeah, just in terms of who he is. Can you talk a little bit about- there are a lot of prizes to go around? The OSA, the Charles Hard Townes medal. Can you talk a little bit about how LIGO would be connected to the OSA? I mean, there are so many different societies that could and have recognized LIGO. That's one of the brilliant things about LIGO is that the physics go in so many different directions, that there's hardly a society that wouldn't have an award to give out. I wonder if you could talk a little bit about the significance of the Townes medal.
Right. Well, the Optical Society of America encompasses a lot of the technology. Optics, the lasers, OSA is where laser physics research would be in the domain of OSA. The lasers, the optics, the precision measurement to some degree, interferometry in general is sort of a field of optics. So, much of what we do is within the domain of the Optical Society of America, and we'd certainly go to OSA conferences over the years. So, I think that's where that would come from. Townes himself worked both on- I'd have to go back and look up a little bit more to remind myself exactly, but I think he worked both in lasers and interferometry in his career. So, those two aspects tie up nicely. I'll look up his biography again to see more details, but he was involved in both of those aspects, so that kind of makes sense.
I've talked to many people who have won the Nobel Prize, and a theme is that in many ways it hurts their research agenda. They're pulled in so many directions, and they're involved in so many new things, and they have all this new visibility, it's kind of hard to get back to the science. So, I can sort of reformulate that question to you as a member of the collaboration. In what ways did- after that amazing rush of this recognition, in what ways, good or bad, did it sort of change LIGO's direction, or what it was doing?
I can't think of anything bad in my perspective. It seems all good.
There weren't people that sort of got sidetracked or pursued other interests as a result of this? That really didn't happen.
Oh, like you're thinking, okay, we've achieved this and now I can go do something else, kind of thing?
No, actually, I can't think of many people who did that. I think most people thought of it- I mean, I think, myself, this is- a lot of people ask that question, actually. You've gotten there, you've detected gravitational waves, now what are you going to do?
But that presupposes, of course, that there isn't so much more to learn exactly in this same track, right?
Right. And that's the way most of us think about it, that it's just the beginning. There's a lot more to learn, just in detecting more things. We've obviously seen that since the very first detection. For myself, and people like me working on the instrument, there's still a lot more –
Just as you indicated in our email exchange yesterday, finding a two-hour block of time for you suggests there's really a lot to do every single day.
Right, right. So, there's just more to do on the instrument side in terms of improving them. There's actually just a lot of interesting physics and engineering in the detectors. That's just fun to work on.
Does the result of detecting the gravitational waves open new pathways of inquiry that were not even possible before? I mean, that was the goal, right? So, that part of the goal was achieved, but just by virtue of achieving that goal, does that now unlock new questions to pursue?
It does, yeah. There are certain aspects of the physics, in both the astrophysics, and then the physics of let's say general relativity, that will be- I'm not the best person to explain all this, or to know as much of this as others, but the question of both the astrophysics and the physics, by which I mean general relativity, that will be explored more and answered further as we get more detections, not just a greater number, but also different types of detections. For example, detections of- you were trying to understand more, as we detect more and more of them, we're trying to understand what the population is of the black holes, which you can't say much about with just detecting one merger. But, as you detect more and more, and you detect them further and further away, which means earlier in time, then you can start to say more about the history of the universe. What we're looking at now is we're trying to design the next generation detectors, where one way to make another big leap in sensitivity is to make them, again, much longer. So, right now we have four-kilometer detectors for the ground base detectors, and going up to ten times that, so forty kilometers long. With the forty-kilometer-long detector, you could detect black hole mergers that are happening throughout the observable universe. The ones that we've detected so far sound very far away, but they're still what, in cosmological terms, you'd call the local universe. But, if we make them ten times more sensitive, we can see ten times further away, and really probe things that are happening much earlier in the universe. So, that's a whole line that we're hoping to get into.
What are the technological advances to make the next generation possible? What's available, or will be available in the future that wasn't for the previous generation?
Well, one way of advancing the sensitivity is just by making them much, much longer. That's what we're working on now. There are some technological advances that would have to be made to scale some of the compliments up. As you make it longer, things have to get bigger. But it's not like any real fundamental new technology that you have to develop. There's actually an engineering aspect of it. If you're making the thing ten times longer, the challenge is to get such a thing funded, because it's going to be expensive, and then much of the cost of the whole thing is going to be just in- that whole forty kilometers has to be evacuated, like we have now, but a ten times longer tube starts to get very expensive. So, the whole project is dominated by these tubes that are running forty kilometers. So, it's an engineering problem. How can you make those tubes much cheaper than what we did the first time around with different materials, different vacuum handling, different vacuum procedures? So, that's one challenge that's more of an engineering challenge. It's important because unless you can bring the cost of that down it might never get funded. But in terms of the detectors themselves, there are challenges involved in just scaling things up, but it's not like we need to necessarily invent a new piece of technology. There's another way of going about trying to make a significant improvement in the observatories that we already have. That is where we need more technology developments. The path there is to start cooling the detectors to cryogenic temperatures, or at least below room temperature. The thing there is we'd probably be using different materials for the interferometer, the test masses. Right now, we use fused silica, glass. It's a special high-grade fused silica glass. For that, you'd be moving to use crystalline silicon, and you'd be changing- you'd need to change the laser wavelength from one micron to two microns and outbreak them at cryogenic temperatures. So, that is a lot of technological changes that we're working on right now. There are sort of these two routes, and the second route involves a lot more technology challenges of the detector components themselves. So, there's a lot more uncertainty there on whether we can get there, and we can make those advances. But the other route, in terms of making a longer detector, in that sense, technologically is less risky and more assured. There, the question is can we get such a big project funded.
Well, Peter, I think for my last question, I want to ask you both in terms of where LIGO has been and where it's going, can you talk a little bit about the differences in terms of discovery of the universe in a historical stage. In other words, what does LIGO tell us about the early universe, the Big Bang to 400,000 years after, or whatever that benchmark is, and what does it tell us about the universe as it currently exists, and how might those distinctions change as LIGO really. I mean, there's no end in sight. LIGO can go maybe for another century, theoretically, right? So, long term, what might it tell us both about the current universe and 13.6 billion years ago?
Yeah. Well, right now it's not telling us much about the early universe. We're not yet sensitive enough to see black holes from the very early universe. We have to get to this next generation.
But that's a goal.
That's a goal, absolutely. There are other things in the early universe that, again, would be a goal, but we're not detecting anything or seeing anything in terms of gravitational waves that might come from the very early universe, like the inflationary period of the universe producing gravitational waves, or other cosmological events. Again, these are goals. They're possibilities. We're not there at the moment. So, more in terms of the current or more local universe, one of the things that it showed was- the first thing you'd say is that we showed that there are black holes out there that exist that are in the mass range of tens of solar masses. Before that, we knew about massive or supermassive blackholes, which are typically in the centers of galaxies, including our galaxy. So, we knew that those existed, and we also knew from X-ray binary measurements that there were black holes of smaller masses, like five to ten solar masses in size. Before our first detection, and then many subsequent detections, we didn't know of the existence of black holes of fifty solar masses, in that kind of range. Certainly, we knew that they would be possible. There's no reason they wouldn't be possible, but we just didn't know of their existence at all. They were sort of filling in that- what is the population of those black holes. So, that's the big thing on the black hole side, and then with our big discovery with the neutron star - neutron star merger in 2017, again, that was always something that was sort of suggested, that neutron star - neutron star mergers are the cause of rayshort gamma-ray bursts - things that have been seen in electromagnetic observations for many years, it was thought that those might very well be caused by a merger of two neutron stars. Until we solidified that theory with our combined detection of gravitational waves, and the electromagnetic observations from that source in August of 2017. That's the other big thing that came out so far, some people thing that's a more important discovery than the first black hole-black hole merger.
What you said just a few minutes ago really stands out, that what the Nobel Prize recognized was really just the beginning. So, with that, there's a lot to stay tuned for, and I'm so glad that we were able to do this and get your perspective on all that's been accomplished so far. So, Peter, thank you so much for spending this time with me.
Oh, yeah, I wasn't sure we'd go for two hours, but it went for two hours.
There you go.