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Credit: Johns Hopkins University
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Interview of Charles Bennett by David Zierler on June 10, 2020,Niels Bohr Library & Archives, American Institute of Physics,College Park, MD USA,www.aip.org/history-programs/niels-bohr-library/oral-histories/45438
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In this interview, David Zierler, Oral Historian for AIP, interviews Charles Bennett, Bloomberg Distinguished Professor in the Department of Physics and Astronomy and in the Applied Physics Laboratory at the Johns Hopkins University. He recounts his childhood in suburban Washington, D.C., and he describes the influence of his father, who was a physicist with the National Bureau of Standards. He describes his early interests in radio waves and telescopes. He describes his decision to attend the University of Maryland on the basis of its excellent reputation in radio astronomy, and he discusses his interests in instrumentation and his work at the Clark Lake Radio Observatory. Bennett describes the circumstances regarding his decision to attend MIT for graduate school, where he worked with Bernie Burke on analyzing radio observatory data. He discusses his career at Goddard at NASA and his involvement in some of the major missions of the time, including COBE and WMAP. Bennett describes his decision to join the faculty at Hopkins, and the ways in which his research changed in an academic setting. He discusses his current interest in the Hubble constant measurement and the importance in conveying scientific concepts to the broader public. At the end of the interview, Bennett shares his thoughts on how the scientific community can continue to progress in areas relating to diversity and inclusivity in the field, and he relates that his sense of wonder at what can be learned by looking at the universe remains much the same as when he was a boy.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is June 10, 2020. It is my great pleasure to be here with Professor Charles Bennett. Chuck, thank you so much for being with me today.
Okay. So to start, please tell me your title—and that might be a mouthful, I recognize—and your institutional affiliation.
All right. I’m a Bloomberg Distinguished Professor at Johns Hopkins University. I’m appointed jointly between the Department of Physics and Astronomy, which is really my home, and with the Johns Hopkins Applied Physics Laboratory.
Okay, and now let’s take it all the way back to the beginning. Tell me about your parents. Tell me about where they came from and their professions.
My father was born in New York. My mother was born in Washington DC. My father is a physicist, and a metallurgist. His research is on alloys, condensed matter physics, that sort of thing. He worked for what used to be called the National Bureau of Standards (now NIST), and my mother was at home with us three troublemaking kids. I grew up in Bethesda, Maryland in a neighborhood called Bannockburn.
Okay. All right. Tell me in greater detail about your father’s career. I love the transmission of physics from one generation to the other in the family.
Yes, I grew up around that kind of thing, although it wasn’t obvious to me at the beginning that I was going to go into that. But my father was always interested in math and physics. He was skilled in those areas growing up. He grew up in what you might call some tough neighborhoods in New York, and he was a nerdy kid.
He ended up doing some work for the Navy designing mines for the Navy because he was into metallurgy and magnetic fields, and while he was using his physics knowledge to do that, he was drafted by the Army. His father was a lawyer and so his father wrote a letter to the Army saying that “You can't draft him. He’s working for the Navy designing mines!” The Army basically said, “Well, he shows up or he goes to Leavenworth.” [Laughs]
So then he took a hiatus from designing the mines for the Navy to empty trashcans for the Army. He did that for a couple of years in Aberdeen, Maryland. He was married at that point, and my mother worked as a photographer there, basically I think taking pictures of the servicemen when they came in to the Aberdeen Proving Grounds. I think he also taught a course on binoculars: what they are and how they work.
But eventually, he benefited from the GI Bill and was able to go back to school and he got his master’s degree from the University of Maryland, and his PhD at Rutgers. There’s a great picture of him doing his physics work at Rutgers at his desk with me on one knee and my sister on the other knee. [Laughs] My younger brother hadn't been born yet, but yes, I grew up with physics.
Now in terms of your father’s, both his scientific style and his parental style, would he involve you in the world of physics on a professional level even as a kid? Would you learn sort of physics and his job from him, either directly or sort of through osmosis?
Well, I’ll give a couple of examples, He didn't sit down with me and say, “Let’s talk about physics and the work I do,” or anything like that, but he was very good at asking questions. You’d come across something in everyday life and he would say, “How do you think that works? Here’s how that works.” It was not like he said, “Here’s physics.” It was more like explaining things and explaining why the sky is blue and that sort of thing. It wasn’t really intended to be a series of physics lectures. I remember Physics Today magazine and other physics material sitting around the house, but I would never read it. Like I said, I didn't at that point have a particular interest in physics.
But what had more impact was that he sparked in me an interest in electronics. He would have stuff, some old resistors or something like that. He would teach me how to read a resistor color code and to know what the resistance values were. Then, back in the day, there was a company called Allied Electronics / Heathkit, and he’d get me their electronic kits and I’d put them together. So, this became a hobby of mine, to build a crystal radio or take apart something that was broken to see how it was supposed to work and that sort of thing. I was the kind of kid that would take a clock apart and then not be able to get it back together again. [Laughs] I think that was the path that was more consequential, other than the idea of rational thinking, something I didn't appreciate at the time, but also have since learned that not everybody thinks that way! [Laughs]
So electronics became a major hobby of mine. I became a ham radio operator and got a license to operate a station. That was another huge hobby of mine as a kid. I was always working on improving my radio station or using the radio to talk to people.
Now did you go to public school throughout?
I did, yes.
Were you a standout student in math and science?
Maybe standout, but not with the sign that you're thinking. [Laughs] I would say I was sort of, generally speaking, an average student with some moments of below average. [Laughs] At least up until the beginning of middle school. I started struggling in middle school, the first year of middle school, with science classes. My father, I still remember because this was a difficult time, asked me, “Can you just explain to me how you study?” I said, “Here’s what happens. There’s stuff I don't understand and we take a test and then with the graded exam, I would go back and learn what they meant for me to learn.” He said, “You know what would be more successful is studying before you take the test instead of using the test to learn the things you got wrong.” So we worked on that. That helped enormously, to actually study before the tests instead of using the graded tests as study guides. [Laughs]
Middle school was a real transition for me, from being just not that interesting in school and just wanting to get back to my ham radio, to me actually transitioning to being a good student. I did very well in math. My science improved as we went on. Other things I was never very good with. My French class teacher kicked me out of her class because I was so very bad at French. [Laughs] I speak some Spanish but to this day I still don't speak French! Nor do I try to! By the time I was in my last year in middle school and then into high school, I had become a pretty solid student. I would say A-, B+ at that point. Not a standout.
When it was time to think about college, it sounds like you were not specifically thinking about physics programs.
A sort of a life-changing moment came. My grandmother bought me a backyard telescope, one of these old Tasco refractor telescopes — not much of a telescope, but I was really interested in it. I think my father suggested to her that she buy that. But she asked a friend of hers whose daughter was an astronomer which kind of telescope to buy. That daughter was Vera Rubin. [Laughs]
That’s pretty good! Did you have any idea who Vera was in those days?
Only vaguely, but as we continue talking, you’ll see that she had a very profound effect on my life.
I would take the telescope out at night and look at things in the sky. I had developed these two hobbies, the radio electronics and the astronomy, and they both took my time and held my interest. My high school started very early in the morning, and I would get up extra early and I would read a little bit in the morning before going off to school. Early one morning I was reading a book by Isaac Asimov. He’s often known for his science fiction, but this one was a non-fiction book called The Universe: From Flat Earth to Quasar. It was fascinating. I was very interested in our solar system and what was out there, and somewhere, on page 300-and-something-or-other, I’m reading this book and there’s this part about how just recently the Bell Telephone Laboratory claimed that maybe they had seen radio waves from across the universe. Well, if you think about this, I was very interested in radio and was very interested in astronomy, and the idea that there was some possibility that radio waves were coming to us from across space – across the universe –… well, that was just completely fascinating to me.
Like radio waves might suggest that there’s life out there kind of thing?
No, not necessarily. Just that I could build radio equipment to pick up radio waves that weren't generated by us. Even just different objects in space generate radio waves was… To me, it was a meshing of my two interests. That moment in high school, or should I say outside of high school but during those years, that got me really interested in the idea of radio astronomy, that I could mesh my two hobbies, radio and astronomy with the telescope, and put it into one career. I decided I wanted to be a radio astronomer.
In high school.
In high school. Right.
Did you run this idea by your dad? Were you curious what he thought about this?
Well, yes, but he was not eager for me to become a physicist. I mean, he said that it’s nice to have a career where you're your own boss instead of somebody else telling you what to do. I still remember that advice along with other very important advice like not to take a typing class in school because I’m not going to be sitting in front of a keyboard all day or anything.
No, never! [Laughter]
But that has got to be the classic worst piece of advice I ever got. I still can't type! [Laughs] Anyway.
So with this sort of transition for you, then you were thinking about radio astronomy for undergraduate.
Absolutely. That was what I wanted to do.
Now Maryland had a solid program for you?
Maryland one of the country’s best programs in radio astronomy at that time.
Who were some of the luminaries in the field on the faculty at Maryland?
Frank Kerr, Gart Westerhout, Bill Erickson, … I’m trying to remember. I’ve got his face in my head, … Mukul Kundu.
There were others, too. There were some that were not in radio astronomy but were very good for me… One of them, Mike A’Hearn, taught me digital electronics. But I wasn’t sure at the beginning I was going to University of Maryland. I was considering other schools, but my father kept telling me that Maryland would be good for me because it was something like $500/year or something like that as opposed to the other schools that were thousands. It was what he could afford.
But there was a bigger point, which was that Maryland was actually was a powerhouse in radio astronomy. In going to other schools that I was thinking about, in retrospect I can see they really didn't make any sense.
So in the end I went to Maryland because I had no choice, but it was a very good choice for me.
What year did you start at Maryland as a freshman?
Okay, 1974. Tell me a little bit about the curriculum there. Was it the Department of Physics? Were you in the Department of Astronomy? How did that work?
That’s an interesting question because departments over the years, as you probably know, separate or combine. At the time, there was a Department of Physics and Astronomy, but they had an astronomy program and a physics program, and in fact the two were in two different buildings.
Right, which probably reinforced the false separation of the fields.
Yes. There was some conceptual idea that there was a department, but it was mostly separate. That meant that I had to decide whether I wanted to be in the physics program or the astronomy program, and I chose to be in both. You could satisfy requirements for one or the other, or as I did, just satisfy them all. There were recruiters that came to our high school from different colleges, and the recruiter that came from the University of Maryland happened to be an astronomer. This is like one of these freak coincidence moments. It could have been anybody, right, but it was an astronomer who came to recruit. I talked to her and told her about my interest in astronomy and she got very excited. Her name was Elska Smith. She wrote a textbook on astronomy and astrophysics. She really gave me the hard sell, “Oh, you want to be at Maryland. This is the place to be. I’ll be your personal advisor. I’ll guide you through the program as your adviser.” The whole bit.
Now Chuck, does radio astronomy from the beginning, does that imply an emphasis on experimental and not theoretical, or not necessarily?
To a large extent, yes, because in the early days it was largely experimentally driven. People built things. The radio waves were largely found accidentally just like with Penzias and Wilson. You could “see” there were signals coming from the Milky Way and Jansky did that work. So quite a bit of it was experimental… There was a lot of discovery space. Build something and see what’s there. There were some things that were predicted theoretically. The 21-cm line was an example. But mostly in those early days it was experimental. Build your own equipment. Jansky built his own telescope. Grote Reber built his own telescope. So that clearly was some of the attraction for me. And the University of Maryland had their own observatory at the time called the Clark Lake Radio Observatory. It was in the Anza-Borrego Desert State Park in Southern California, and Professor Bill Erickson at Maryland took me under his wing and sent me out there—again, hands-on radio astronomy work. So I had direct experience with doing that as an undergraduate.
How much lab work versus how much coursework was there for you undergraduate? I assume you were looking to be in the labs as much as possible.
Actually, I took the same curriculum as anybody else would have, so most of it was classwork. We did have labs, physics labs and things like that, but it was only by talking to some of the faculty that I was able to arrange to pick up some lab skills outside of classes. Professor Mike A’Hearn, who later became the PI of a NASA mission, was very knowledgeable about electronics and he taught me digital electronics, which I hadn't done before. I have to say the faculty were very giving, like Bill Erickson and Mike A’Hearn. I wasn’t doing so much that they benefited from, but I benefited a lot from the research opportunities they provided. The sort of summer or supplemental research (not part of the required program) are things that mostly fed my experimental interests.
Now did it occur to you, or did you get any advice that you would be well served by taking some engineering courses in terms of building instrumentation?
I thought about taking engineering courses, and generally I was advised not to. Part of it is the way engineering curricula are constructed, which is still the same today, which is there tends to be a sequence of courses that you need to take in order. So if you want to take that senior level course on electronics or whatever, you need to have taken seven engineering courses before it. I would see there were courses that sounded interesting, but were essentially impractical to take. So I didn't go that route, but of course, a lot of physicists are very hands-on. Surprisingly, I see that more and more engineers are not very hands-on. They tend to not do things with their hands. They tend to do only computer circuit design now—not like in those days when they actually built circuits.
Was there a senior thesis in your program?
Yes, it was completely optional, but I did a senior thesis. That was something I did out at the Clark Lake Radio Observatory. I took measurements and studied the change and the flux from the supernova remnant Cassiopeia A. It decreases in flux every year, and I made a measurement of that rate of decrease. I studied up on why it was happening, although I’m not the one that figured it out. So I did do that and I’m really glad I did. That was a great experience. Again, Bill Erickson taught me a lot about how to write up something like that. I’d never done that before, and that was a very useful skill to pick up.
Now did Bill essentially hand you a problem stemming from his own research, or you came up with this idea on your own for the most part?
You know, to tell you the truth, I don't remember exactly how that idea came up. He must have had a menu of things for me to pick from. It clearly had to be in his head because I didn't know anything about it. So yes, I’m sure he prompted it in some way.
And what were… I mean, just thinking about your undergraduate experience in total, what were some of the major questions in those days about radio astronomy? What was the research sort of looking for in terms of big questions to answer?
It was still very much a discovery period—what’s out there? One of the big accomplishments that had been made by people at Maryland was the determination of the spiral structure of the Milky Way using the neutral hydrogen 21-cm observations. That was one of the exciting new things at the time. Mukul Kundu was studying radio waves from the Sun. And then again, there was this Penzias and Wilson thing hanging in the background that I was interested in, although no one at Maryland was working on that at the time.
When you were thinking about graduate school, was staying on at Maryland something you had considered? Were you encouraged to sort of move on and see the wider world?
Let me back up a bit to answer that. There was an American Physical Society meeting at a hotel in Washington, D.C. I think it’s now an Omni Shoreham near the DC zoo -- but the APS typically held meetings at that same hotel. My father took me along because by that point I was interested in physics, and particularly he had in mind that they had the big, cavernous room with booths set up. You could see different demonstrations and books and things like that. He walked me through that hall. Well, first of all, there were some self-study books on physics that he bought for me. I was very eager to have those. But we also bumped into an old family friend, Vera Rubin, there. She was with her husband, Bob, and we were just chatting. She said, “You know, Chuck, you should fill out an application to come work at Carnegie Institution in the summer. We have a summer trainee program,” and so I did apply and I was hired to work at Carnegie in the summer! That was instrumentation work. Vera would go to the telescopes and observe spiral galaxies and their rotations, but the--
And this was sort of at the height of Vera’s sort of research powers, right?
It was. That time period definitely was. But supporting her was this very small group of people building the hardware to help her get good data, so they had their own hardware they would bring to the telescopes. There was something known as the Carnegie image tube intensifier, a big, strapping piece of hardware that gets attached to the telescope to basically amplify the light. While I was there, the group (which at that time was Kent Ford and Norbert Thonnard and sometimes Ken Turner who was a radio astronomer) was trying to make a transition from an image intensifier tube to solid state equipment for Vera.
I didn't work directly for Vera, but I was in the same part of the building that she was in. It was really fabulous because Vera would come back from observing trips and she’d be so excited about what she’d seen. She would say, “Chuck, come in here and look at this!” and she’d lay out her measurements and show me what it meant. Then, of course, that was a lot of motivation for making better equipment for her! So that’s the sort of thing I did there. I think I was there for three summers.
So you were asking about graduate school. I did the natural thing, which was talking to the people there about graduate schools and what they thought. Vera took out time to talk with me about the schools. They had a lovely little library there where they would meet with visitors. We sat in the library and I just asked her questions about different places. I was interested at the time in the Five College Radio Observatory at the University of Massachusetts, for example, because they were building their own telescope, and that appealed to me. I did take a trip up there to visit it. I asked her about that and other places. She gave me a pretty frank assessment of different schools.
Now were you aware of John Mather at that point?
No. Not at all. Vera was a positive person, so she didn't really say negative things about places, but you could tell which places she preferred.
What about Joe Taylor? Were you aware of Joe Taylor?
Well, let’s see. No, that came later. I first became aware of Joe Taylor when I was in graduate school in Green Bank, West Virginia where I spent a lot of time as a graduate student. I met Joe and his students there.
One day Bernie Burke from MIT was visiting because he used to work for Carnegie DTM. He made his big discovery in his youth of the decametric radio bursts from the interaction of the planet Jupiter with its moon Io. This was another observing-driven discovery, not a theory-driven thing. He was observing and he found these bursts and became very well-known. So while Bernie was visiting we were sitting in the library chatting and there were maybe five or six people around the table, Vera turns to Bernie and she says, “You know, Bernie, you should bring Chuck to MIT.” Bernie said, “Oh, that’s a good idea!” So I chose MIT!
Easy as that.
Yeah. It was later since I had to apply, obviously. Bernie told me to apply, and some time later he called me at home, which I thought was astounding. He said, “Would you like to come and work with me with a research assistantship?” That was my offer of admission. It didn't take very long for me to say, “I’ll do that!” [Laughs] So again, Vera was quite pivotal there.
What was Bernie’s work at the time? What was he doing?
Bernie was your classic radio astronomer. He was interested in anything having to do with radio astronomy. He was particularly connected with MIT’s Haystack Observatory. There was another professor, Al Barrett that shared the same office complex. They were in many ways opposites, but both very solid people, and they both used the Haystack Observatory. Al Barrett did molecular astronomy and Bernie was very interested in interferometry, which was a new thing at the time. He did very long baseline interferometry and aperture synthesis. He decided to build a little interferometer—he called it the miniferometer—out at the Haystack Observatory, and I worked on that as well. That was a big thing for Bernie at the time. But he was involved in all kinds of different projects. He would often go to a meeting or talk to a theorist or something and he’d hear different ideas and come back excited about something.
He typically had six graduate students or so in the group, and his technique was to very much drop the bird out of the nest. [Laughs] He would just tell us, “Do this,” without any background or anything. In fact, when I was moving into MIT, my parents drove up with me and the car was filled with my stuff for moving into an apartment. I stopped in to get my key so I could drop stuff off in my office, and at that moment, Bernie handed me some papers and said, “We have observing time in Green Bank in two days,” or tomorrow or something. “Go do it.” I had to learn fast.
There you go!
I literally threw stuff into my apartment, said goodbye to my parents, got on an airplane, and went to observe something where I had to read what it was I was supposed to be doing on the plane there, and I had never used the observatory before. [Laughing]
So it doesn't sound like Bernie struggled much in terms of coming up with research ideas and projects for his graduate students.
He did not. He had all kinds of ideas, and again, they were coming from all different directions. I remember right when I was finishing up, Bernie had talked to one of the Nobel Prize theorists at Harvard—Sheldon Glashow, I think it was—and Glashow had some idea of something that suggested a measurement, and Bernie said, “Oh, Chuck, this is perfect for you! Why don't you start building this?” and I’m thinking, “Because I’m graduating and leaving!” [Laughing] That kind of thing would happen all the time.
Typically, the radio observatories took proposals quarterly to assign observing time. Bernie had a lot of philosophies of life, and one of his little mottoes was, “You can't discover anything unless you're looking at the sky.” So his philosophy was that we graduate students were to submit observing proposals all the time. Remember, he discovered and got famous for these decametric radio bursts, not because he was looking for them, but because he was looking at the sky. Thus it was our job as graduate students to come up with ideas of things to observe and to write the proposals. He didn't do that; we had us do it. I don’t think he cared exactly what we were proposing, so long as we would be, “looking at the sky.” We graduate students would work together on ideas and bounce them off each other, and of course, we’re trying to pay attention to what’s going on in the world of astrophysics and radio astronomy. We would constantly be generating observing proposals. I learned some interesting lessons on proposal writing then. In my opinion, the most boring, uninteresting proposals were the ones that were accepted, and the ones that were really exciting were always turned down.
Chuck, another curriculum-style question. I’m curious if there were courses at MIT that you felt like you should take or ones that you were required to take based on your field of study.
Okay. First of all, there was a diagnostic exam they gave in those days which you would take in the summer before starting. It was on all areas of physics. It wasn’t in astronomy. At MIT I was in the Physics Department. There wasn’t an astronomy major. This was just a pure physics exam, and it tested thermodynamics, quantum mechanics, classical mechanics, and electricity and magnetism. The entire purpose for that exam was only to see what areas you have holes in and what courses you should take.
Based on that I took statistical physics. Also, other people were telling me there was a superb professor teaching the senior level undergraduate electricity and magnetism class. Everybody was saying, “That’s really worth taking with him because he’s really a superstar teacher.” I decided to take that senior level undergraduate class in electricity and magnetism and it was great.
I don't remember, but I’m sure there were required classes that I took, or at least they were standard classes for graduate students to take. I took quantum mechanics and statistical physics. I took two years of pretty solid classwork. Of course, I was going to the observatory for part of this time, which caused things to be a little more difficult since I needed to juggle the classwork with the research, but I think I did okay with that. There were standard courses that were basic physics courses and I took them all.
And looking back, what were some of the most relevant or important in terms of your intellectual development in radio astronomy?
That’s a hard question to answer because I feel like they’re all pieces of the same puzzle.
Mm-hmm [yes]. Nothing was irrelevant is what you're saying.
Nothing was irrelevant in understanding broad physics in different areas.
And this would include theory. Theory was important to you also.
Well, yes. I mean, these courses are not generally experiment versus theory, but they were more just, “This is how physics works.” Suppose you have a ball and it’s got some charge on it. Then what’s the electric and magnetic field? Suppose it’s moving. Suppose it’s moving relativistically. Then you have to know relativity. Suppose you kick the ball up. It’s all mastering the different areas of physics, and it was really a good feeling to do that, to master the different areas of physics. We took general exams. There was a part one and part two. Part one was a bunch of shorter questions. Part two, I think which was a year later, were longer more detailed problems. It was a great feeling to be able to sit down and just work these problems—you know, study for the exam and get really, really good at it and be able to sit down and just work the problems quickly. You feel like you really know physics, or as one of my fellow graduate students said at the time, “You’ll never know more physics than the day you graduate.” [Laughs] Because then you start forgetting everything that you studied. But just completely mastering the different areas of physics at that level was rewarding and important, I think.
How did you go about developing your dissertation topic?
The six graduate students put in proposals all the time and then when proposals were accepted for observing time, we would maybe pair up. The students mostly organized this ourselves: who was going to which project, and who was going to work together? Pairs of us went to observe based on who was interested and who was free enough from other obligations. So what happened was by the time I was most of the way through graduate school, I had worked on a number of different projects, and they were all in different stages of completion. When it came time, I felt, to leave I took a very pragmatic approach—I had my choice of many things that could have been my PhD thesis—and I decided to pick the one that I thought was closest to being done. So it was in some ways one of the least interesting ones, but I really…
But you could get it done.
I could get it done, and I wanted to get it done.
So what was that project?
I think that philosophy actually was very good because I’ve learned since then that everything takes longer than you think it will. I think that was an especially good way of making a decision. In terms of looking at the sky, we wrote a proposal to use the big 300-foot telescope in Green Bank, West Virginia to survey the sky, to do a big survey and just discover new objects, and that proposal--
How widely are you defining new objects? Is that literally anything that’s an object and that’s new, or were you focusing on anything in particular?
No, anything that’s there. You know, I can give you a coordinate, right ascension and declination, some spot on the sky, and we detected a radio source there that people didn't know of. We wrote a proposal to scan the sky and that was accepted and it was primarily my responsibility to carry that survey out. As I mentioned earlier, that meant I was in Green Bank, West Virginia for a lot of time. Quite a bit of time. But that turned out to be only step one because then when it came time for us to write proposals for the VLA (Very Large Array) in New Mexico, it occurred to us that, oh, we could take the sources that we discovered in the Green Bank survey and we could go see what they are by mapping them with the VLA. We created a bit of a pipeline of discovering new sources and then going to map them.
Then together with another graduate student, we looked for data from other surveys to see if we could get the spectra of the sources. Then I also went to Tucson where they used to have in the old days these glass plates from the Palomar Sky Survey, and we would use a measuring engine there and see if there were optical counterparts. As I said, we set up a sort of pipeline of surveying from Green Bank, finding thousands and thousands of sources, following up at the VLA, and then optical by going through archival data, and looking for other information. So when I did my thesis, I just stuck with the Green Bank part of the survey because that was the part that was furthest along.
Chuck, I want to ask you. It will be a recurring sort of question, so at the stage of completing your dissertation and really developing your sort of professional identity, I’m curious generally about your awareness of where technology is at any given time. In other words, what was available to you, and how good was that at helping you look and find the things that you were looking for? How much… How aware were you of the next advance in technology and what that would allow you to do? So in terms of establishing this narrative, at the end of your dissertation, as you're thinking about your next step, one of the questions must be, you know, well, what’s available for me to work with and what will that mean for my career?
So if you could just sort of answer generally about the state of technology at the time and how you saw that impact on what you wanted to do and where you wanted to go.
Right. So at least in those days—and I don't think it’s so much true anymore, but at least in those days as a radio astronomer, you were very aware of the instrument you were using because they were imperfect, and they shared their imperfections with you in all kinds of annoying ways. For example, I would be in West Virginia using one of the telescopes, using the receiver, and it would be misbehaving in some way or the other. There was always this kind of agonizing question of whether in the middle of the night to call the engineer and get him out of bed to see what was going on or just to live with it for the night. But you knew that this receiver has this idiosyncrasy, that it tends to oscillate, or gee, you really wish this receiver had bigger bandwidth so you could get two different spectral lines at the same time or make your observations more efficient. There was a constant awareness of the limitation of the instrumentation.
So the flip side of that there was also an awareness of things that were coming or might be coming. You knew what you wanted and you knew about things that were in development that might help do that. That’s a constant refrain. I think it’s true in science in general if you just look historically at the kinds of experiments people did very early on, and then more and more sophisticated versions of these experiments happened with new instrumentation. Computers themselves were a major change in what was possible to do. I think there was a constant awareness of the limitations. You didn't always know what was going to come far ahead of time, but you knew the directions people were doing research in and I tried to pay attention to those things and the people who were looking to be able to bring in new technologies. I do think that there are a lot of unsung heroes that worked on technology and that enabled all kinds of observations to happen. You know, the scientist that does those observations gets famous for discovering something, but the only reason it really happened is because the technology people made it possible!
Because they sort of developed this. Right, right.
You think back to the early telescopes like Galileo and back to like Carnegie going from an image intensifier to CCDs—even now, the development of far-infrared detectors to use in the x-ray. I mean, the advances are all really coming from the hardware, and a lot of the people that do the hardware don't really get the recognition that maybe they deserve for doing that. You look at new projects like LSST, now known as the Vera Rubin Observatory, and that project would not have been possible a long time ago. It takes an enormous amount of computer power.
…and most modern--
Right. So Chuck, I’m curious in terms of your acute awareness of the limitations and annoyances of the instrumentation, was that coupled with an appreciation or a faith that the instrumentation was going to get better?
Why would you have that belief? What was there to suggest that things were on their way to getting better?
So yes, I always that feeling. I still have the feeling everything is going to get better. [Laughs] I think it’s just because you see it all the time. You see it in non-physics instrumentation. You know, I remember 8-track tapes and cassette tapes. Just in everyday life, everything was evolving from the day my first car had an AM radio with a dial that you had to turn. I didn't mention before, but I worked at a radio and TV repair shop in high school. You know, literally the thing that would break in radios is the string that connects the knob that you're turning to the dial that goes across a display. You don't see those anymore. You see the evolution—the evolution from tubes to transistors, the integrated circuit. This was happening all before my eyes, right? I’d fix something, and then I would see the next generation of hardware, because things were evolving so rapidly. And I don't think it was just me as a physicist. I think people in society see this all the time. There are constantly new things coming out—you know, CDs coming out. You talk to family members when they’re really quite elderly and they tell you, “It’s amazing the things we have now that we didn't used to have! Every day there’s something new!”
There was that feeling that was palpable.
Right. Now I’m curious. As you're sort of assessing your next options, for what you did, was NASA the place to go or was it one of several options that you were considering? In other words, an academic appointment or another laboratory kind of environment. My question is could you have done what you wanted to do equally well at a different place than NASA, or was NASA like the spot for you?
I started my search for a job by not knowing. I didn't know really exactly where I wanted to be or what I wanted to do. By that time I had met the person who would become my wife, and we were kind of interested in ending up in the same city! This was in 1984 when I chose the PhD project that I could finish most quickly.
Is your wife in the academic world also?
She is. In political science.
The two-body problem.
Yes, exactly. So we decided to address the two-body problem by limiting the number of places that we would apply and we limited those to Boston, the Washington, D.C. area, and the LA area, roughly speaking. So those are three big population centers in both of our fields. But having done that, there was still lots of diversity of kinds of places that were out there.
In LA there was JPL, and I talked to them. There were also the aerospace companies doing high technology, doing research, and I talked to them, including the Aerospace Corporation, which is sort of a researchy place as well. These places all had a common theme of a hardware combination with science. Of course, in Maryland there was the NASA Goddard Space Flight Center. I wasn’t sure what I wanted to do, so I visited places and I talked to people, too, about what they thought of these places. For example, Bernie Burke was very much opposed to me going anywhere that wasn’t a university. [Chuckles] He made it quite clear that that was the success path and anything else would be a failure.
I interviewed at JPL and talked to them and I asked them, “Well, what would I be doing at JPL?” and they said, “Anything you want.”
But would that include anything that you would actually want to do with JPL?
Well, this was my puzzle with JPL. I kept asking, “What would I do?” and they kept saying, “Anything you want.” Yet I knew that wasn’t really true because they have to pay you and they have to get the money from somewhere…
More like anything that you want within the things that we offer you to do.
Or the money that you yourself can bring in. I think the real meaning was you can do anything you want as long as you can get the money to do it!
I did tour TRW when I was out in LA. They’re not TRW anymore. Companies keep merging. It was a large aerospace company largely defense related. I was very interested to see what kind of technology they were working on, so I told them I was mostly interested in the research and development of new technologies, particularly in the microwave area. They took me on a tour and showed me the things that they were doing, and then I learned an important life lesson that what they call “research” I call “development” and what they call “development” I call “building things”. [Laughs] So the whole scale was different, and I wasn’t so much interested in just building things that had been done before or developing things. I was more interested in the fundamental research, which was the part they really didn't do, although they called things research.
I went to a colloquium at MIT that one of our own faculty members was giving. I went to these seminars all the time. We were virtually required to do so. Bernie Burke would literally take attendance of his graduate students. This one was by Professor Rai Weiss. He and my advisor Bernie Burke were—there’s probably a contraction word for this, but frienemies or something? [Laughs] They played handball together; they were very competitive. Rai Weiss gave this talk about COBE. He was the chairman of the COBE Science Working Group, and he was talking about the upcoming COBE measurements of cosmology and I was in rapt attention. I’m listening to what he’s talking about and I’m thinking, “This is great! This is like wonderful!”
So I went up to him. Literally, I went up to him right after the talk after people finished their questions and I said, “Is there any way I can get involved with this?” It was really what I wanted to do, that kind of thing, back to the Penzias and Wilson kind of roots. Fortunately, he said, “I’ve got a Science Working Group meeting coming up at Goddard. We have two of the PIs for instruments at Goddard, but one is in California and we really could use somebody at Goddard because that’s where things are getting built and tested. Would you be willing to come down to the meeting and I can introduce you?” I said, “Yes, absolutely!” So I went down to the meeting and got introduced to people like John Mather. Mike Hauser was the another PI, and then there was a broad science team: Ned Wright, Sam Gulkis, Mike Janssen, etc., etc.
Did you feel, Chuck, when you started at NASA that you were riding the beginning of a really big wave?
I wouldn't say yes or no, but I would say I felt more like this was a very important measurement. I really didn’t know how well other people caught up with that. It was very challenging, and it’s exactly the kind of thing I wanted to do!
No, but I mean specifically my question is when you recognized that this was a very important measurement, how much of that work had already been done by the time you joined the project?
The COBE work started much earlier. I think maybe around the time I started at the University of Maryland, 1974. There was a proposal that John Mather led that was put in to NASA for a mission. Things were so different back then. It was sort of an informal few-page thing with no rules about all the stuff that they have now, but John and his team just put in the idea of a mission. Unlike the way these things work today, they weren't ready to just go do it. They wanted to study it. Today you have to study it already before you put the proposal in. So they got low level funding from NASA to flesh out the idea. That had been going on for quite a while, and then only a relatively short time before I got there did things really start ramping up into a real mission development. Basically, there was an IRAS satellite that was eating up the budget until it got launched, and COBE was in a hold mode until IRAS launched.
In the background, what had happened was there had been a bunch of different proposal ideas sent to NASA for all kinds of different things, but there was some common themes of cosmology. NASA literally selected people from the different proposals, which is very odd by today’s standard. I mean they didn’t just combine the proposal teams. They selected individuals from different proposals and made a new team out of them, a very unusual thing to do.
So they made this new team and they said to work together to come up with a mission, and mostly people had the idea of using expendable Delta rockets to launch these missions. But then NASA was going in the direction of the space shuttle and that everything had to launch off the shuttle, and so what the instruments looked like had to change. You know, you had to meet all kinds of shuttle requirements since there were astronauts involved. Basically, the mission grew very, very big and heavy. The shuttle was perfectly capable of putting up a 10,000-pound satellite. So COBE evolved, and most of that evolution had happened before I started.
But while I was there, the shuttle catastrophe happened. It was pretty clear quickly that NASA wasn’t going to be launching anything for a long time because they had put all their eggs in one basket and that Shuttle basket was faulty. That began a furious search for a way to keep COBE going. It was quite possible the whole project could have gotten canned.
Why? What would have been the connection in terms of…?
Just that it’s going to be years before we can launch. We’ve got this 10,000-pound monstrosity. We have no way to launch it. Let’s just give up. That was the concern.
Who in your view, Chuck, were the chief protagonists in ensuring that that would not happen?
I think it was a combination of our science team—Rai Weiss, John Mather, Mike Hauser especially—and also the project manager and especially the system engineer, Dennis McCarthy. He was very forceful in trying to figure out a way to keep things going. He at one point even had talked through channels to the Russians about their capability to launch COBE, and I heard by rumor that NASA told him that if he did that again, they’d shoot his kneecaps off! [Laughs]
Yeah. Right, right. So Chuck, in terms of making the case, how high up would the team have to go? Would this go beyond the administrator? Would this go to Congress, for example?
I don't think Congress, necessarily, although it might have gone there eventually, but it certainly was on the administrator’s plate to deal with, and certainly all the science leadership at NASA Headquarters. Nancy Boggess was there, a very strong pro-COBE protagonist. Charlie Pellerin I think was there at the time; I’m not sure that’s true. But the project leaders themselves were scurrying around trying to determine, what are our options? Let’s evaluate our options.
There were three instruments. The one I was most attached with was the DMR, the differential microwave radiometers, and there was some sentiment to throw that instrument overboard. You know, we have to make this thing lighter. The other two instruments were in a dewar. So you would have the dewar; you have those two instruments; you didn't need anything else. So I still remember going to John Mather and saying, “You have to stop them from talking like that. You just have to cut that off as an option,” which he did. He said, “No, we’re not talking about destroying COBE. We’re talking about saving it!”
In the end, the project put together a plan to get from a 10,000- to a 5,000-pound satellite without losing any instruments, and this plan was given to NASA Headquarters. Basically, the argument was, what a sexy mission with sexy science! Here NASA is down in the dumps. We need something to lead us back to restore our presence, and what could be better than this? That was basically the argument made, and NASA bought that argument. They said, “This is a sexy mission, and the important thing is that you have to promise us you can do it in two years.” Everybody swore up and down they could do it in two years, and it wasn’t a bad estimate. It was two and a half, but that was pretty close, actually, considering the enormous amount of work.
To get it done that fast required some special things that wouldn't have normally happened. The center had to make the COBE work a priority in a big way. When we needed something, we needed to get it, and when we needed to order something -- everything was on paper in those days, but they would slap a paper on top of every procurement that we put out that said, “COBE Emergency.” Everything that we ordered was streamlined through the system. Then they relaxed a lot of the more formal management style, into what we called the “skunkworks”. “Just figure out what to do and do it!” So that all helped enormously in making things move faster.
It occurs to me to mention that in going from MIT to Goddard was for me a big culture shock in a technical sense. If we graduate students at MIT were asked to evaluate something, to me that would mean doing the calculations and writing up a memo that says, “Here’s what we’re assuming. Here’s what we’re doing. Here are the calculations, and here’s our conclusion.” And yet working on COBE at Goddard, when somebody asks about something, there was none of that. You're just in a meeting and somebody asserts something and then, okay, that’s the way it is. I’m thinking, really?! I’m thinking, “Do we have anything to back that up?” Some of it I understood because you had to move fast, but I was surprised at the lack of rigor in the calculations and considerations of many things, that they were more gut feeling assertions. It’s just a different way of working. It took some getting used to.
Chuck, can you explain a little bit about the makeup of the team and what… You know, when you have a team that’s this big, it’s sort of hard to get a sense of who is doing what, and is a particular person contributing in a particular way because of their expertise? Or it’s just a matter of this is convenient for a given person to be working on a given part of this at a given time? Can you just give a sense of the overall sort of division of labor and where exactly you fit in on COBE?
It’s a bit of a difficult question to answer. First, I should say you call it a big team, but by today’s standards it was a small team. [Laughs]
Sure. Right. Fair point.
I mean we scientists could all fit in a little conference room together! So I personally was--
I meant a big team in terms of brainpower, essentially, you know.
[Laughs] So first, there was an essential idea that this was not a space mission with three instruments. This was a space mission with a science goal.
And that everybody on the team was participating in all the instruments, even if you weren't specifically working on it, that the science goal involved all of the instruments. We were going to use all of data and that we were all in this together. Then they had named what they called the PI, which was maybe a slightly different usage than we use in other cases. The principal investigator, again, doesn't make sense from that science point of view, but it does for developing the hardware. So there would be a person assigned to each instrument to be the person in charge of making sure it gets done. Those were what we called the three PIs. My interest was on the differential microwave radiometer, in particular. Because it used microwave hardware, while the other instruments were more far-infrared. So my background was more matched to the microwave radiometers.
I started working on that at the beginning. Then when I was there maybe a year, or something like that, when it had been proposed that I be made the Deputy PI of that effort. Originally there was a PI for each of the three, and then they decided that it would be a good idea to have a Deputy PI for each of the three. I was, in a sense, elevated from being a science team member to being Deputy PI of that instrument development. Again, the PI who was George Smoot was out at Berkeley, 3,000 miles away while this instrument was being built and tested at Goddard. I was there every day.
Chuck, I’m curious with this step up. To what extent are you relying on your sort of general education in radio astronomy and relying on both your coursework and the lab work and all the research that you did as a graduate student? How much of it is you're just sort of like learning on the job and sort of figuring out new things in a very different kind of environment?
I think it’s a combination of the two. I’m going in with all the background knowledge that I had, which of course was enormously useful, and yet I was dealing with things that I hadn't dealt with before. I did have to learn some things on the job and other things I had the background for. I needed my knowledge of physics and my technical knowledge -- the combination of the two. The way it was, I still remember, there would be something that would come up that I didn't know about and I would have to stop and study up on it so I understood what was going on. You know, I was able to talk to John Mather or Rai Weiss or other people if I needed help understanding what something was all about.
And in terms of as a… Did you view Rai and John… Was it a mentor relationship? I mean was it like a quasi-colleague, quasi-mentor relationship that you had, or did you feel like…
It was. That’s…
Well said. Yes. These people were my mentors, including Mike Hauser. They were both my colleagues, but you know, I was the new kid on the block and they were relatively senior people, so yes, very much the combination of mentors and colleagues. It was nice. I mean it was nice to have very good, smart colleagues to learn from.
Were there things that you understood or were able to do that were a real asset to the team? In other words, you were able to do things or know things that nobody else could?
Well, I’m not sure that there were things that they couldn't do, but there was too much to do for everybody to be everywhere at the same time. To give you an example, late in the game, I pushed to allow the COBE radiometers to be passively cooled so the instrument would be more sensitive. This required the front-end detector systems to be re-designed and re-built. I led that effort, which made it possible for the anisotropy to be discovered.
For another example, we were in a meeting with the project manager and the system engineer and John Mather and other people were there. They were talking about the launch at Vandenberg Air Force Base, and they were showing the launch complex. As the rocket goes up, it will be tracked by these radars and blah, blah, blah. I became immediately concerned and I said, “Well, how powerful are those radars? We have very sensitive microwave equipment!” They said, “Oh, it’s not a problem. It’s never been a problem before.” I said, “Wait a minute! You never launched a COBE before!” This was an example of not having things written down in a technical way. The managers don't want problems, so they try to dismiss them.
After I left that meeting and I calculated… Well, first I got a hold of the information about the radar, which was non-trivial since it was mostly classified, but I found out about the radars from public sources. Then I calculated how many volts per meter would be on our detectors from those radars, and then I wrote up a little technical memo and I gave it to John Mather. Of course, John, being a very smart guy, looked at this memo (in MIT style) and said, “Yes, we’ve got a problem here.” So he and I went back to the project and said, “I know you want to dismiss this, but it won't look good if you launch COBE and blow out its detectors!” In the end, we got them to kind of agree not to point those radars at COBE when it’s within a certain distance from the launch pad. It was funny because they actually refused to categorically agree to that arrangement, but you could tell they got the message and they didn't want to be blamed.
Right, right, right.
So here was something where I had never done that calculation before, but it’s something you can figure out how to do. And anybody could have done that. I had the idea that that there could be a big problem. I didn't know for a fact until I did the calculations. So that’s just an example of anybody could have done it, but I was there and I did it.
Sure. Now Chuck, this might be as much a sociological question as a scientific question. You know, it’s funny you mention when this idea began quite informally in the 1970s. I’m curious, you know, your perception of when this becomes a (capital V) Very big deal. There’s the germination of the idea. Then there’s the “This is growing and we’re really on to something,” and then at some point it’s “Whoa. We really have something here.”
What’s your sense of when that transition happened?
John Mather did this research as a graduate student and a post-doc, so he was pretty much following the path that he was already on. The research he had done largely had not worked because the stuff was difficult. But you learn lessons that way, and that’s the difference between an expert and a non-expert. The expert is somebody who’s made every possible mistake already (and learned from them). I think what John was doing was already a very big deal. It’s just it had to be thought through in getting it above the atmosphere and solving a large number of technical issues. Then the other ideas that came in that brought the other two instruments were also big ideas, and putting them together was a big idea. Other team members also had previous experiments that were important.
When Rai Weiss gave this talk at MIT, I instantly thought, “This is a really big deal!” I understood it as a big deal right away from that point. It was already a big deal before I showed up on the scene, in my opinion. It was more of a question of when the rest of the community really started to appreciate it and what it was going to do. You know, I don't know… It’s hard for me to say what the community at large was thinking during this time. It’s quite possible in the early days they were barely were tracking what was going on—not that they wouldn't be excited about it, but they may not have known much about it – it was far in the future until it wasn’t. I really don't know. I was just a kid then.
Did that change the nature of the work or the nature of the team? In other words, did that realization, the very big deal realization, sort of change the character of the work or the motivations at all?
Yes, I think so. Well, certainly the science team, I think, understood that they were working on something really important. I think there were different levels of appreciation through the greater number of people, engineers and technicians, both--
You mean in terms of institutional support that NASA gave the project.
Right. Yes. I mean, so it’s hard for a technician in a lab somewhere at Goddard to know what’s a big deal and what isn't a big deal. You get some of the sense of it when you know you then have emergency orders go through and things like that, but what’s really valuable for these things is when the scientists give talks for the technicians and engineers and people working on things to convey to them directly that what they’re doing is important. I think that’s very effective. John did a lot of that, and just skipping ahead, I did a lot of that on WMAP both to people at Goddard and at our contracting companies just to say, “This is not just your job. You're working on something really important.” It’s very effective. People want to work on something important. They want to understand that what they’re doing is important.
How long did you work on COBE? Was there a clean break at some point in terms of “We are done and we are now moving on to other things”?
Yes, I think pretty much for me. We had our initial scientific papers from the DMR instrument in 1992, and then we operated for additional time and published, if I remember right, the final data analysis papers in 1996 or so. This was the exact same period of time that I started transitioning to what became WMAP. So yes, it wasn’t a complete sudden transition, but it was pretty sharp within those couple of years where I was more or less finished up with COBE and really ramping up my focus and time on WMAP.
How did WMAP come about?
After COBE detected, discovered the anisotropy of the CMB, there were obvious next questions to ask. Up till then it was a detected or not detected sort of thing, and--
So intellectually there was a really clear transition from COBE to WMAP.
Yes. Once you knew that there were temperature fluctuations at a known amplitude, studying them was a no-brainer.
That’s like the obvious next question.
Yes, the obvious thing to do, and everybody in the limited community that does that kind of thing knew that. I mean, there was no secret about that.
And the same kind of technological question. Was it immediately apparent once we know that these things are here, it’s obvious that we want to measure them, but in terms of assessing the available technology, was that feasible right away or was there a catching up process?
There was some catching up and there was also some disagreement about which direction the technology should take.
Oh. What were the parameters of that debate?
There are fundamentally two different directions to go, and loosely I can call them coherent and incoherent detection. COBE DMR was coherent. That basically means relying on phase information as opposed to just having a bucket collecting photons where you don't rely on phase information; you're just collecting photons. There were relatively new devices being used called bolometers which just count the energy that falls on them versus the more radio kind of design that I had been working on. Actually, bolometers themselves weren't that new an idea. They were actually transition edge sensor bolometers and they were discovered at The Johns Hopkins University back in the 1940s. But there’s a difference between conceptually might such a thing work to where you can actually make things useful out of them?
So there was this debate going on. Everybody understood, I think, the basics of the tradeoff in the sense that the bolometers could be much more sensitive, and on the other hand, the more radio technique, the coherent technique we had more experience with and potentially could have a lower systematic measurement errors. There was what I think was an incorrect sense that if you were below 100 GHz frequency you would use one, and above 100 GHz you would use the other. I think that kind of thinking was a little bit sloppy. I think the question is not just what the detector itself is, but how you're coupling the radiation to the detector. You can use a coherent coupling technique with an incoherent detector. So I think it was a little more complicated than some people were saying at the time.
But when it came time to propose WMAP, there were three proposals to do basically the same science measurement. There were two that were coherent and one that was incoherent. So one drawback, you might say, of the bolometer approach is that you need to have a cryogenic dewar, because they have to operate at very low temperature. COBE had bolometers in that dewar, so it had been done, but the COBE cryogenic dewar was a major technology development item. There wasn’t a company that sold five versions of off-the-shelf space-qualified cryogenic dewars! [Laughing]
So it was very much custom made and raised a lot of issues about its technology readiness level and risk. So there were--
How did the debate about the technology also inform the research questions that the people who were participating in that debate were asking? Was that relevant, the technology as it related to the big questions that WMAP begged?
I remember we had a meeting at Goddard with our fledgling team…whatever we had of it at the time. We really had a nice discussion that day of the different techniques and what to do. There were strong arguments on both sides, proponents on both sides, and one of the things I really like about groups like the WMAP team was the ability to have quality arguments—I mean, not personal arguments, but you know, “What about this? What about that? Flip side,” you know, really high quality arguments about the considerations. So I would say that nobody on the WMAP team had any illusions or misunderstandings about what was going on or what the situation was. It was a question of, which would we better off doing? Do we want to just optimize our sensitivity to be as good as we can get it, or what about our systematic measurement errors? What about the cost? What about the complexity? So real life is messy. [Laughs] One of my sayings is, “Everything is a tradeoff.”
So Chuck, to situate yourself within this, where are you landing in terms of both the technology and the research questions that WMAP poses?
Well, again, I didn't disagree with anything anybody on our team was saying. I was concerned that, unlike COBE which was quite expensive, we were going for a cost-capped lower scale mission. The bolometers needing a cryogenic dewar and bolometer technology and all was, maybe OK if you were doing it out of a university lab -- you would take those chances -- but for a NASA mission that was cost-capped, my opinion was that it was very risky to propose to do that, and that in a review, we would have to convey confidence in the cost and speed of making it work.
Why the difference? Why emphasize the difference between an academic setting and a NASA setting?
Just in terms of cost and visibility. You know, if some person at a university tries to do something and it doesn't work, it may not have used that much money and it may not be very visible. But if NASA tries to do something at a significant scale and in the public eye, failing is a much bigger deal. I remember for years there were people that said, “NASA should just do more smaller things. Then some of them fail and some of them succeed, and it’s much more cost effective than making sure that everything works.” There’s something real to that argument, but the thing that’s missing is the political aspect. You know, the article in the newspaper that says, “NASA failed,” and…
So you appreciated as somebody who was sort of policy aware that a failure at NASA was, by definition, a much more high profile affair.
Yes. It was going to be high profile. One of the things that happens is because NASA doesn't want to fail, they spend extra money to be more careful, and…
And where is Challenger in all of this? Is that like front and center to this sensitivity?
Well, I mean certainly that was a huge black eye for NASA. It just reinforces this thing that I’m saying, which is that failing has consequences, more than just losing that particular investment. So if Rai Weiss’s group built a bolometer and a dewar and put them on a balloon and sent them up and it didn't work, nobody would know the difference and it wouldn't cost as much because he didn't spend the money he needed to make sure that nothing could possibly fail!
I mean, keep in mind the cost of a launch itself is enormous.
Yeah. What’s the budgetary environment? If we could just have a broader context, were you sensitive to the idea that “We have to spend our money wisely”? Is this not a period in NASA’s history where it’s blank checks all over the place?
My impression, although I wasn’t directly aware at the time, is that sort of in the 1960s, scientists could really try different things and do different things and there wasn’t tremendous grant pressure. You had a good idea; you could try it. That’s my impression. Maybe that’s too rosy; I don't know. But certainly space missions cost a lot of money. The NASA budget is limited, and the idea of this program was to do cheaper missions where you really had to do things that were technology-ready to be cheaper. You couldn't just stop for five years to fix the technology you didn't prove ahead of time and pay a marching army while you're doing that. And you had to hit some kind of cost scale. WMAP had a strict cost cap.
I should say that I actually campaigned for these kind of smaller missions within NASA. At some point all of NASA’s missions were big and expensive, and that wasn’t true of the initial days of NASA, which were much more like I was describing of the ’60s. But together with Steve Holt, who was then the head of science at Goddard, he and I got together and said, “It would be much better for science to do many more smaller missions than just these big ones.” So we held a little conference and invited people to present ideas for smaller missions, and we invited the managers from Goddard to come and hear these ideas.
There was substantial opposition, especially from what we called the Projects Directorate, which managed these things, to the idea of managing smaller missions. One of them I think literally said, “Why would I want to manage something small when I could manage something big?” So we pressed on our idea.
There was a program called the Explorers Program. COBE was an Explorer, but COBE was undoubtedly in excess of $1 billion, and the question is how about something that’s much smaller than that? Maybe you’ll take a little more risk, but not crazy risk, and then you can have more of these things and not have the whole NASA science program riding on very few missions.
In the end, we won this argument. The MIDEX program was put in place. WMAP was one of the two first MIDEX missions. I gave presentations on a couple of different science ideas that you could do with these smaller missions, including what we ended up doing. In the end we did make progress in that argument, and that enabled WMAP to happen because otherwise there was no opportunity for it at all.
As WMAP matured, did the research questions change as well?
Not fundamentally, but WMAP was built quickly. There were things around the edges and a better understanding of some things, but fundamentally, we had the detection from COBE and that was at very large scales in the sky. You're basically testing what happened with gravity in the beginning of the universe.… At issue here is whether you're measuring spots on the sky that are causally connected or not, whether there was time for different spots on the sky to interact with each other. If you measure big enough distances on the sky, there’s not time enough for them to interact in the history of the universe, so we call that “primordial” and that’s what COBE measured. COBE had a seven-degree beam on the sky, so many, many times the size of the moon—so it had very coarse focus.
When you get down below the size scales where all kinds of physics can happen, you might think that, oh, that’s going to get very messy then and you're going to need to untangle the cosmology from all these physical interactions of the gas that’s there. But it turns out that that’s not really true. The physics is solvable, and there are important signatures about the universe from that. So this was the whole idea of going from COBE to WMAP. We wanted to go to smaller angular scales to actually see the signatures that we thought should be there. Theorists had already worked it out. We knew what we would look for, and we did calculations estimating, given a certain sensitivity, what can we detect? We saw for ourselves that we could determine the density of atoms in the universe and the density of cold dark matter in the universe. The fundamental numbers of cosmology could be determined, which COBE had not done, by seeing the patterns of the hot and cold spots across the sky with enough resolution and sensitivity.
So that was the guiding principle, and that didn't really change during the course of the observations, although I do still remember when we were writing the proposal I asked the question, “What happens if we don't see those things?” [Laughs] So we actually put a line in the proposal that said that not seeing the signature of these things that we expected would be even more revolutionary! [Laughs] So again, this idea wasn’t a secret. Everybody knew that this was the thing to do, so the question really among three proposals that went in to NASA was which was going to be most convincing for NASA? [Interruption]
Chuck, another question I have is it’s clear to me how WMAP is the obvious next place to go after COBE, but that doesn't necessarily tell me if you think that the discovery…the things that were discovered as a result of WMAP should be understood as an addendum to COBE, albeit a very important addendum, or they are essentially fundamental and should stand on their own.
Oh, I definitely think WMAP’s contributions were fundamental and stand on their own. As I said, COBE didn't measure the things that WMAP measured.
The thing that COBE measured, at least in this regard, is the detection, the discovery of the level of the anisotropy of the cosmic microwave background. But that left a lot of open questions like, What is the model of cosmology? What’s out there? How much of what constituents are there? What’s the shape of space? What happened at the very beginning? What’s the ultimate fate of the universe? Those questions were not addressed by COBE, and so WMAP was not a repeat of COBE so much as it was a next step to learn much, much more about the universe. So COBE discovered the anisotropy. WMAP established the Standard Model of Cosmology with 5% atoms and 70% dark energy, which was an astounding thing, and 25% cold dark matter. We didn't know those things before—and things about the nature of inflation, ruling out some inflation models, but seeing other signatures that were consistent with inflation predictions. None of that was done by COBE.
Sure. I talked to Mike Turner just yesterday.
I asked him basically the intellectual history of dark energy and why you named it that, and did you realize that it would be so fundamentally mysterious, not just like, “Let’s start thinking about this now,” but it might always remain mysterious. So I’m curious intellectually how the development of this idea of dark energy—beyond naming it, right?—just the idea of what dark energy is, how important was that for WMAP?
At the time we wrote the proposal for WMAP, that was before the supernova discovery of the accelerating universe. But what we said in the WMAP proposal was that we could measure the curvature of the universe, which means adding up all the forms of mass and energy and seeing what was there, and so that would include dark energy as well. When the supernova teams announced the accelerated expansion of the universe, I’d say that raised the stakes on what we would see.
Because accelerated expansion is one thing, and you could posit that it’s due to some dark energy, but if it’s due to some dark energy then it should show up in the WMAP data as part of the mass-energy of the universe. So if we didn't see that, that would mean something else was going on that was causing the accelerated expansion. As it turned out, they’re two sides of the same coin, but they didn't have to be. They’re not redundant measurements; they’re completely different kinds of measurements. One measures dynamics (acceleration), the other mass-energy.
So with the cosmic microwave background, we are saying the geometry of the universe appears basically what we call flat or Euclidian, and the matter is only 30%. The only way that can happen is if there’s some dark energy that’s 70%. So we said there must be 70% of something else there, and the other experiment is saying something—we don't know what, but something -- is causing the accelerated expansion of the universe. Well, you put these two together and you have a consistent picture that there is something like a cosmological constant that we see in accounting for the total mass-energy by the cosmic microwave background, and we see the effect of it in the supernovae data as driving an accelerated expansion. It was funny to me after we had WMAP results and the accelerated expansion results that people were still questioning the reality of it because we had measured two completely different aspects of the same phenomenon. I thought, “How could that not be right?”
Yeah, yeah. Now I’m curious. You have, of course, a very big career change right in the middle of WMAP, right? This is when you head over to Hopkins, and I’m curious, first of all, if you saw your ongoing work with WMAP as essentially a smooth transition or this would affect your participation in the program. How did all of that work out?
Well, we made our big initial WMAP splash in 2003. We had already launched the satellite and it all worked, which was one of the most stress-relieving moments of my life. We did the scientific analysis; provided the world with sets of cosmological numbers -- the things that people wanted to know cosmologically -- and we went on to working on the next parts of the data analysis and improving results, bringing in the polarization and other aspects. But during that time, I would say during 2004 while work was continuing—and it was clear this work was going to continue for some time—I was wondering what was next for me in the sense that I literally went to Goddard to work on COBE. I didn't go to Goddard because it was my dream to go to Goddard; I wanted to work on COBE.
And then the WMAP flowed really naturally from that, so there was no reason to do anything else. Just stick with it and do my thing. But by 2004, I’d built and launched WMAP So what am I doing next? I’m looking around to see what was around to work on. What are the opportunities at NASA?
So Chuck, that raises a very interesting question. It was clear… I mean, the transition from COBE to WMAP sort of like you didn't have to look very hard. It presented itself, right?
So that begs the question was that not the case for the next big thing that WMAP might present to you? Was that not so clear?
Okay. At the time, there was a DOE push for a SNAP satellite. This was the SuperNova Acceleration Probe. The Director of Astrophysics at NASA personally asked me my opinion of it, and I said, “I don't really know that much about it. I’d have to study up. I’ve been doing cosmic microwave background work.” One thing led to another, and I remember saying, “There are different ways to measure the cosmic acceleration. It’s not clear this is the one way. They had a fairly large mirror and it’s not clear to me how the price is going to scale the mirror size. It’s all not clear to me.”
In the end, I was appointed to be a co-chair of a committee that had DOE and NASA people on it to consider the broader question of characterizing dark energy. This became known as JDEM (the Joint Dark Energy Mission) and people on that committee were arguing all kinds of different ways to measure dark energy, not just the supernovae, but baryon acoustic oscillations and clusters, gravitational lensing, etc. We had an open series of discussions about this. I learned a lot.
Then I was on a different committee with a bunch of meetings at Goddard under a project office that continued these discussions, which were sometimes quite hostile. Quite a bit of time had gone by, and it wasn’t clear to me where all of this was going. I talked to people at NASA Headquarters. There was this new satellite in Europe that they were working on, called Euclid. Wouldn't it be more sensible just to join in with a bigger and better Euclid? But NASA put all kinds of conditions on that and the Europeans weren't anxious to have NASA join in on it in a big way – to the point of changing the design. This was all very different from my experiences on COBE and WMAP.
Yeah. So that sort of suggests in terms of your research on the early universe and things like that, was it not so immediately apparent what the next big project was because perhaps that’s not what WMAP lent itself to?
Once WMAP established a Standard Model of Cosmology, we could ask the same question we asked with COBE: What didn't we know that we still wanted to know? Well, there are things that we didn't know that we want to know. What is this dark energy? What is the dark matter? And what actually did happen at the beginning of the universe? Well, we found several indications in the data very much in support of the inflation idea, but we also put constraints on specific models of that idea that that one couldn't have happened.
And I’m curious on that point. Were you ever in contact with Alan Guth? Did you ever talk to him about these things?
Oh, yes. Sure. Yes, absolutely.
What was his reaction to your research?
He was excited about the measurements that we made that really are hard to explain other than with something like inflation, and he was excited at the fact that we could start to pick between inflation models. You know, inflation is more of an idea than it is a specific model. It’s a paradigm and within the paradigm you can have all kinds of specific models. The basic question is, what is the shape of the inflation potential? WMAP put limits on what that shape could be. It couldn't just be anything. So that was exciting to Alan and to many of us that we could now say that even a textbook example of inflation called ??4 was ruled out, That model may have seemed very attractive, but that isn't what’s going on in our universe.
So this idea that we were now ruling out specific inflation models and yet had measurements that indicated something like inflation must have happened. But still, what is the dark matter? What is the dark energy? What happened at the beginning of the universe were unanswered questions. So the idea of JDEM at the time was to try to learn about the dark energy. But it wasn’t clear that if you made these measurements that you would solve the problem.
The focus of a lot of these measurements was to determine what we call the equation of state parameter of the dark energy. If it’s a cosmological constant, it would be equal to -1, so how close is it to -1 and is it, or is it changing with time? That’s basically what the JDEM mission was about. But you can imagine that no matter how tightly you make your measurements, you still haven't ruled out that it’s not -1 or that it’s not changing with time.
Then you ask yourself theoretically, if it is different than -1 or if it is changing with time, what level would I expect that to be happening on?
Yeah. So Chuck, that makes me think. As you were starting to think more systematically about dark matter and dark energy, did these concepts become more mysterious as a result of you thinking about them more?
I don't really like the word mysterious. I mean it’s…
Or poorly understood. Was your appreciation of how poorly we could understand it?
No, I think I always understood that! Take dark matter. I find it hardly surprising that there are kinds of matter out there that we didn't necessarily predict. Why should it be surprising that there are different kinds of matter out there, some of which don't interact with light? I personally don't find that surprising at all. The only question is not that we see such things, but exactly what it is? And to a large extent, knowing the answer to that may not change cosmology at all. It’s more about its properties. Is it decaying or annihilating? That will change cosmology. But if it’s just gravitating with no other interactions its identity may not make any difference for cosmology. The dark energy is more uncertain, though. It was more unexpected. Particle physicists were calculating how big would a vacuum energy be? They would get some ridiculously big number that clearly wasn’t true, so they figured that to get something much, much smaller than that, the only natural thing is to have some reason for it to be exactly zero. It turns out, well, it’s not zero if this is vacuum energy. It’s not zero; it’s just very close to zero. It’s not huge like they would naively think, and that’s odd. That’s very odd. So that indicated that there was something going on that we really didn't understand as opposed to the dark matter, which I felt like, okay, we still want to know what it is, and it may be something surprising, really. But I find the dark energy to be more of a central physics question. They’re both important physics questions, but…
So can you set the stage for your arrival at Hopkins, right? I mean, coming from Maryland and then MIT, you're very well aware of what academic physics looks like, and as a result of your tenure at NASA, you know what NASA physics looks like.
So I wonder to what extent did you look at this change as an opportunity to change your own research focus? Or did you look at it more as an opportunity to sort of continue on the trajectory of the things that you were working on, albeit in a new environment?
Let me back up just a step from that. If I don't get back to it, you can lead me back. After our big WMAP splash in 2003, which was all over the newspapers and magazines and media and everything, I started getting phone calls from different universities asking would I be interested in dean positions and faculty positions, heading centers, etc. I was receiving quite a number of queries. I would look into the places and try to learn about them and ask myself, “Is this interesting to me?” Then of course, the two-body problem remains.
At some point decided I was going about this the wrong way. Instead of being prompted by any individual place, I ought to ask myself the question what is it that I want to do next and worry about the place separately. I was looking at the horizon at Goddard, and I knew that this dark energy mission debate was going on, but I was getting frustrated by it. There were a lot of players. It was contentious in a way that COBE and WMAP were not, and there was a lot of discussion that wasn’t framed the way I would frame it. I couldn't control any of that, and it was not clear to me whether there would be a mission, what it would look like, and even how compelling it would be in the sense that we were just talking about.
By the way, I should tell you as an aside back then, Mike Turner had called me and said, “Chuck, how do we say how well we have to measure the dark energy? How do we frame that?” because he knew as well as I did there was no specific sensitivity level to meet -- it could be anything! How do you pick a number? If you're going to fly a space mission, you have to say, “I’m going to determine something at some level,” but how do you keep that level from being completely arbitrary?
I had already thought about this a lot before he called, and I had realized that the measurements are difficult and we can't do arbitrarily better. We can only do so much better, at least given technology or money, and so I told him that I thought the best way to set a level is measuring what I called “to the knee of the cost curve”. You can measure to the level where the cost is somewhat reasonable, and then it gets really expensive fast for not much gain.
He liked that answer, actually. Paul Steinhardt had his perspective on this, and I think it’s a hard argument to refute, is that since the dark energy, if it’s not w = -1 could be within 10-2 or 10-4, 10-10, 10-20, 10-100 of w=-1 and none--
Were you in contact with Paul, or you were just aware of his work?
I was talking to him. He said, “The thing is that we have no reason to pick any of those over any others, and yet we can't measure all that much deeper.” So effectively he was arguing this was a waste of time.
What was your response to that?
Well, I thought he was making a good point. I don't think it’s a waste of time because I think we should measure to the knee of the curve, and maybe in the future the knee of the curve will change. But my feeling was that we should do what we could reasonably do, but I think he had a very sound argument that without any prediction that the next order of magnitude is where we would see something, it really is a bit of a crapshoot. This is very different from the WMAP mission where we knew what we were looking for. We knew what it should look like, more or less, and we knew how to estimate what we would see or do.
So this bothered me. A lot of things about this bothered me about the way it was being carried out. Experimentally, it just wasn’t the way I like to do things. So I was looking around, asking myself, “What would I do next?” The CMB is one thing, and this dark energy is another, but there’s no CMB mission on the horizon. Yet there’s a lot of ground-based CMB experimentation going on, which I’m not allowed to do as a NASA employee. It had been 20 years since I’d been at MIT and I missed being at a university. I missed the students. We didn't really have academic things at NASA. I thought, I didn't come to be at NASA. I came to do COBE and stayed to do WMAP. If there’s nothing keeping me here, then maybe I should try something different.
So in light of the excitement and offers and universities reaching out, why Hopkins?
This was partially the two-body problem. My wife was quite happy and wasn’t anxious to move and I wasn’t anxious to uproot her. It was also partially because Hopkins had a rich experimental history in the Physics department and a history of involvement in space-related research. It was reasonably close by. It was a combination of these things.
So when you say reasonably close by, you saw value in also not being so far from Goddard also.
Well, it wasn’t so much distance from Goddard, although I would agree with the statement. I thought it was a plus to be within commuting distance of Goddard. It wasn’t clear to me how much I would stay connected, or not. That was a plus, but I really meant in terms of being able to commute from our home in Bethesda. As it turned out, I did commute from our home in Bethesda for two and a half years, but then Hopkins offered my wife a faculty position, and now my commute is a lot shorter!
That’s a slog, Bethesda to Baltimore.
[Laughs] Yes – a big slog. I listened to a lot of audio books!
Yeah. So to get back to my--
So as I said, I flipped the problem the other way around and asked myself, “What will be helpful for me? What do I want to do? I’m not seeing a NASA mission I’m really excited about being involved in right now. I have no idea what the dark energy mission future is, and by going to a university, I can get NSF funding and build ground-based experiments to do important research.”
So in terms of the ongoing work of WMAP, you felt good about where it was and the people that were--
I should say I didn't drop WMAP by coming to Hopkins. I continued doing the WMAP work, much the same way as I would have if I were at NASA.
Right, but when you say you're not so concerned about being in commuting distance to Goddard because you weren't sure, that just suggests obviously you were able to continue WMAP from afar, essentially.
Once we were in the data analysis stage and not building and testing, it wasn’t such a big deal. We already had team members that were in different places. It wasn’t that big a deal from a data analysis point of view.
Right. Sure. You can do everything through Zoom now. [Chuckles]
So to get back to that question that you wanted to provide some context to, getting to Hopkins, to what extent beyond WMAP did you look at this as an opportunity to work on new things?
Oh, I very much thought about that. I thought I had been at Goddard for 20 years and there’s a certain sameness to something after 20 years and I was wondering about it being kind of reinvigorating to be in a different environment and see things differently. One of the things on my mind was there was so much in cosmology that overlapped with particle physics—like inflation, dark energy questions, non-Gaussianity questions, etc. But we didn't have any particle physicists at Goddard to talk to! I thought that would be nice to have people down the hall that I could talk to about some of these things. I thought it would be nice to have students and post-docs. Looking back at these thoughts that were in my mind versus reality, I realized after I arrived at Johns Hopkins that that reinvigoration was even more important than I thought. I really felt like it was a very healthy thing to do -- to shake things up a bit and think fresh about things in a different environment.
Where did radio astronomy rank in terms of the things that you wanted to continue to do?
Well, I was definitely interested in what should be the next CMB experiment.
Why? Why was that obvious that there should be a next experiment?
The initial results of WMAP were all from data that had to do with the intensity or the temperature of the signal. It was a hard slog from that to our second result that actually was the first time there was a serious measurement of the polarization and we needed to figure out how to handle doing that data analysis. We had to invent the data analysis along with getting the results.
It was clear that our polarization measurements were limited. As a kind of quasi-humorous aside here, when we wrote the requirements for WMAP, they were all on the temperature signals, but we designed to keep the polarization signal, even though there was no requirement for it. Every time some question came up about some design change that would ruin the polarization signal, I was against it. Even though there was no requirement, I thought why would we give that away? I don't think the importance of having that polarization signal was fully understood early on, so the satellite wasn’t optimized to measure polarization. It came along with what we had. I thought that ground-based polarization observations were needed and in fact, people were gearing up to do that. There was ACT and SPT and other experiments already looking at that sort of thing. So that struck me as an important frontier where, again, I could in principle join a team from NASA, but when you work at NASA, you're not supposed to be doing ground-based astronomy.
Upon joining the faculty, where did you see your own interests and expertise fitting in with the overall scope of what the department was doing at that time?
When I visited Hopkins with the idea of seeing what I thought of the place. I did talk to the particle physicists and it was great discussion. I talked to other people there about their research, and again, it was reinvigorating. To me these were new and different people to talk with. I went back home and I’m thinking, “That was a pleasant visit.” I’m looking at the webpages of the department and I’m saying to myself, “Oh! They have an instrument development group. I wonder why they didn't mention that to me!” So I called back up to the chair and said, “Is there some reason I didn't see this instrument development group while I was up there? Or, the machine shop.” He said, “Oh, we didn't think about it! You should come back up.”
So, I went back up and Hopkins has this group that’s quite unusual, within the physics department there’s a group that designs and builds instruments. They have a huge machine shop. These things used to be fairly commonplace in universities, but they started disappearing a long time ago. In fact, Bernie Burke—when I was still at MIT—wrote a little piece for Physics Today called “The Quiet Shops of Academe,” complaining that all the academic institution machine shops were going away. I remember that they didn't have the resources to keep their machinists. Yet here at Hopkins you have engineers and machinists and technicians building instruments. In fact, Hopkins does this for other universities. We do it for Berkeley and Princeton and other places. So I thought that was an extremely attractive thing to have, a very active and capable instrument development group.
So there were a combination of things: Hopkins had the theorists; it had the instrument development group; it had people doing things that were not my particular interest, but interesting things to learn about and be educated about. So, I found it exciting. Even the mundane things offered a change of scenery, a different office, and taking a walk around the campus that I wasn’t familiar with and seeing new and different things. Like I said, it was a pleasant kind of shakeup from 20 years at the same place.
Did you take on graduate students right away?
I started to take on some graduate students early in my time at Hopkins. Just be clear, my early time was mostly focused on WMAP data analysis. The last WMAP papers that we published from the team were in 2013, so there was quite a long time there where WMAP was still a major focus of what I was doing.
And why 2013? What happened at that point where you knew it was time to sort of wrap up that project?
Every two years NASA held what they called the “Senior Review,” deciding on whether or not to continue operating missions, and how much money to put toward satellites to continue to operate them, and to continue the analyze data. The different satellite teams would come in and give a presentation of where they are with their science, and where they see things going, and they try to justify why they should continue operating and do data analysis. They need to justify the costs. We had done this with WMAP every two years, and then it was pretty clear to us on the team that there were diminishing returns in continuing the observations. You get less and less for your money as time goes on, and the point had come where we decided that we weren't going to go to the Senior Review to ask for a continuation. We didn't need them to tell us that we were done. We could figure that our ourselves.
There was also a nice timing that I intellectually liked with the European Planck mission: the idea of publishing our final WMAP papers before the Planck results came out so that there would be no bias on our part from anything that Planck was finding. The conclusion of WMAP in 2013 was basically from the amount of time it took after the end of WMAP observations for us to analyze the data one last time, go through the whole process, and get the final papers out. That was the end of the project at that point.
Chuck, to bring the narrative up to the present, what have you been involved with in recent years?
Lots of different things, actually. There’s an experiment we call CLASS. It’s a ground-based experiment that we’re operating in Chile now. That started with conversations I had while I was at Goddard. We sat down and had a discussion about the question I just mentioned, about the future of polarization measurements from the ground. What are the design criteria for what you would build? What are the decisions to make? What are the key arguments? We wrote down some key governing principles, one of which I think was wrong, but the others I think were good. The main impediment was a lack of the necessary technology development to make them happen, and so I and others started putting in proposals to develop the technologies that one would need. You never win all your proposals, but generally speaking we got enough of those funded that we were able to build and develop instrumentation.
We had one proposal to the National Science Foundation that was kind of somewhat humorous because we proposed to build a polarization modulator, and the proposal was turned down with the review saying that it couldn't be done. We went ahead and built it anyway. Then we put in another proposal to the NSF saying that we wanted to calibrate it and measure it and see how it performed, and that was turned down, too, the reviewer basically saying, “No, it will never work.” But it did work! We did get enough funding on the detector front and on other fronts to try to make progress.
I’ve also built up a group—group is probably the wrong word, but a structure at Hopkins called [email protected]. Once I got to Hopkins, I learned more and more that there were a lot of people at Hopkins doing space-related activities across the university, not just in the physics department, but one thing I learned pretty quickly was that faculty interactions are mostly with your department and you barely see people from other departments. So you don't even know what is happening at your own university. I decided that it would be useful to the university for people to know each other and to hear what others were doing and maybe form collaborations if they wanted to.
Careful. You sound like a dean in the making. You’ve got to be careful about that.
Yeah, yeah, yeah. [Laughs] I’ve turned down every dean offer that I’ve ever gotten. [Laughs] No, when I was asking myself what I really wanted to do, the big punch line was I really like being a scientist and doing science. [Laughs]
I did direct the WMAP space mission, and directed it on budget and on schedule and all of that, so it caused some of these dean inquiries, I’m sure. But that’s not what I really love. It’s the doing the science and instrumentation.
So anyway, I got permission from the provost, funding from the provost to figure out how to make a [email protected] operation and to get people together, and that’s been quite successful. I now know a lot of people across the university I wouldn't have known otherwise. There have been collaborations that have been formed, and I think slowly (and only slowly) people are starting to realize what is going on at Hopkins in the general space arena—and I’m talking about everything from doctors working on astronaut health, to making better batteries for spacecraft, to better materials for spacecraft, to how the sands on planets charge up. Broadly speaking, there’s a lot going on. So that’s been on my agenda as well.
Also, because the Planck mission started putting out data, I had an obvious interest in what that looked like and how compatible it was with the WMAP data. So a small group of us started doing research looking at those things. We’re doing all kinds of different analyses and writing papers on what Planck is seeing, and what’s going on more generally with cosmology.
If I had to summarize my key interest at this point, I would say WMAP established the Standard Model of Cosmology – by that I mean the percentages of makeup of the universe. I mean the fact that the universe is indistinguishable from flat/Euclidian. That all is the Standard Model of Cosmology with an inflationary beginning of some kind. Now I’m interested in testing that model. Does it really hold up, or are there cracks in the model?
Chuck, I want to ask. Is the decision to call it the Standard Model of Cosmology… How self-conscious is that to the other use of the term standard model?
It was very self-conscious! I mean it was deliberate, yes.
What was the thinking there?
For the first time, instead of debating whether the Hubble constant was 50 or 100 or the universe is open or closed, we now have a Standard Model. We have a model with a set of parameters -- detailed numbers -- just like the standard model of physics. We know the standard model of physics is not correct – or at least not complete. For example, we know neutrinos have mass. We know the standard model of physics needs to have modifications, but it is the standard model that everybody works from. So we felt the cosmology model was a comparable situation, that we now have a set of numbers and an idea of inflation and the expansion of the universe and the role of dark energy and dark matter, and this was a Standard Model of Cosmology that we all refer to. So yes, we thought it was an analog to the physics model.
Right, right. So I guess this is a good segue to the last part of our discussion where I want to ask first some sort of broadly retrospective questions about your career.
Can I just put in one more thought before we go there?
Oh, yeah. Absolutely!
I was saying that I see now testing the Standard Model of Cosmology is maybe the thing that I’m most interested in doing now, and I’m not sure how widely appreciated this research is. It’s been kind of a slog convincing people, but I think that there is definitely something wrong with the model.
Mm-hmm [yes], and this is motivating to you. You see something wrong and you see an opportunity to fix it.
Well, yes. I mean, to me when you see something wrong, something that doesn’t fit, this is where you have discovery space, right?
Up until, I would say 2013-ish, everything was holding together. One of the things we always said in our papers and in our talks was we have a Standard Model of Cosmology and all the measurements agree with it, but that’s not true anymore.
So in particular, look at the Hubble constant measurement. You measure the early universe from the CMB and you get a value, 67, 68 km/s/Mpc, but you measure more locally in the late universe you get something more like 73 or 74 km/s/Mpc. What’s happened in the last few years is that the errors on those measurements are getting smaller and smaller, so they’re getting into more and more conflict with each other. We saw that tension a little bit on WMAP, but it wasn’t significant. But now it’s quite significant. Now it’s 5.5?, and that’s at the level where something is clearly wrong. Further, you cannot throw out any single measurement and make it go away, so for example I can choose not to use Planck data at all and the tension is still there.
You're saying you have to continue to do science.
Yes. Well, I think it’s more than that. I think there’s something very important going on here. I think it’s not just another problem; I think there’s something major that we stand to learn from this. I think maybe there’s a bigger target… To me it might be a bigger target than dark matter and the dark energy question, although it may be related to them.
So in terms of the bigger questions, in terms of the retrospective questions that I want to ask, first is do you see your work specifically as contributing to the broader effort of establishing a grand unified theory? Do you think about that at all? Is that something that’s interesting to you?
Definitely, yes, yes.
How so? How do you see your work contributing to a grand unified theory?
It’s a basic view of physics that we don't really want to have a theory for everything that happens separately. You have the feeling that you're on the right track when you have a theory that explains multiple phenomena, so the idea of a grand unified theory basically is the ultimate example of that where everything is tied together within a single framework.
You think it’s achievable? This is an achievable endeavor?
I don't know. In principle, yes. There’s no obvious reason why we couldn't, but I don't think we’re going to be there soon. You could view the Standard Model of Cosmology as a subset of that question. Do we have a model that explains all cosmological observations? You know, just like Einstein knew that there was something screwy going on with the advance in perihelion of Mercury, he didn't say, “Oh yeah, you guys have to just make that measurement a little better.” He said, “Oh! Maybe it’s telling us something really important,” and it was!
So that’s why I feel like these areas where results are surprising are exactly what you want. That’s where your clues are.
So I have a fun question, but I also think it’s important because if there was one term that the broader public knew about physics, it would probably be the Big Bang, right?
So what do you like about the term the Big Bang and what do you not like about the term the Big Bang?
There are actually a few terms that kind of bug me, but I’m a loner in this. [Laughs] My issue with the “Big Bang” name started when I got lots of emails from just ordinary people, with the WMAP results in the press, in the media. People would send me all kinds of questions by email, but there was a recurring theme to many of them, which is “Dear Dr. Bennett, This Big Bang idea just doesn't make sense to me… if this and that and blah, blah, blah.” I realized that what was going on is people were not understanding what the Big Bang theory was, so of course it didn't make sense to them. What they thought it was wasn’t right! Then I realized they think that wrong way because we professionals talk that way. We say things we don’t literally mean.
So why shouldn't they have the wrong idea of what the Big Bang theory is? We all say—and I try to avoid it, but I still say it by accident sometimes—that the universe started with a big bang, but that’s not right. What is really a statement of the Big Bang theory, and I teach this in my class at Hopkins, is the Big Bang theory is a theory that explains the evolution of the universe. That is to say, it starts hotter and denser and it gets less dense and cooler as time goes on. So over the course of 13.8 billion years, the universe is expanding and cooling. That’s the Big Bang theory. It’s not an event at the beginning; it’s a process of evolution. If you ask what supports the theory, well, what supports it is the fact that there’s a cosmic microwave background that’s 3 degrees and that we’re seeing the expansion of the galaxies, etc. None of that has to do with an initial condition. That all has to do with the expanding and cooling. And the same thing with Big Bang nucleosynthesis, which isn't until 3 minutes. There’s a lot of time before 3 minutes.
So the thing that could be sort of disappointing or deflating to students or the broader public, right—the Big Bang is so satisfying because it connotes a beginning, right? What you're emphasizing is there is not that historical narrative that is so easily applied to what actually the Big Bang is. So my question is then how do you convey what time even means when we’re talking about the Big Bang?
During most of the period of the evolution of the universe, the time is fairly well defined. But it’s not well defined when you get into the earliest times. To me it’s actually a more exciting thing to say not, “Hey, we understand everything,” but that we don't understand. We don't understand what happened at the beginning. Saying, “the Big Bang happened” is not an answer because what does that mean? What happened at the beginning? We really don’t know.
But that does suggest that there is such a thing as a beginning.
Not necessarily. The Big Bang name was made up by an opponent of the theory, of course, as a way of criticizing it, and the idea that we all talk about it is that the galaxies are expanding and you play the movie backwards in your mind and eventually they’re on top of each other. That’s fine in a coarse way, but in a detailed way, you can't keep playing the movie backwards because at some point it’s not just gravity, but quantum mechanics that plays a role. And now you're not quite sure what time means. You're not quite sure what the quantum processes are. You know, this is easy. You just apply our quantum theory of gravity and you can tell what happened. That would be great if we had a quantum theory of gravity! [Laughs] The truth is that we don't know what happened. We have the inflation model, but we also have models where the universe can be viewed as collapsing and bouncing or as brains oscillating through each other. There are all kinds of ideas about this, but the thing is that we don't know.
Right. So when we say we don't know what happened, right, what is the response to… How does physics explain, then, how the universe creates itself at the beginning, because the easy out there is a religious response or a spiritual response that there is something metaphysical at play here.
How do we respond in a scientific manner that while we don't know today, somehow someway physics will explain how something can be created out of nothing?
Physics already has explained that. There’s no problem in physics creating something out of nothing. In fact, Stephen Hawking wrote a book about this and gave talks about it, and indeed, he was criticized for taking a scientific point of view of the fact that you can get something from nothing. In fact, Alan Guth — you may remember what he calls inflation — he calls it the ultimate free lunch, right? [Laughter]
You basically are getting a universe from nothing. We know as physicists that you have a vacuum. You have nothing, right? But even when you have nothing, you can have virtual particle pairs created. Not only can you, you must. That’s the nature of quantum mechanics. Mike Turner will sometimes refer to a definition of dark energy as how much does a box of nothing weigh? So obviously nothing isn't nothing; there’s no such thing as nothing in quantum mechanics. It’s not fundamentally a problem to create something from nothing, but it is exactly what happened at the start of the universe that we don't know.
More of a sociological question. I certainly would not want to go through every prize that you have won, but I am curious if there is one that sort of is most special to you, either for the work that you were recognized or the organization that gave it to you or the person that is the namesake for the award. Is there any of all of the awards that you’ve been recognized for that sort of is most personally or professionally special or satisfying to you?
That’s a difficult question to answer. The first thing that comes to my mind—and it may seem odd to you—was one of the early ones that was the recognition of becoming a member of the National Academy of Sciences. It’s not one of those big prize awards. You know, I got the privilege of paying them annual dues (!), but the reason that was meaningful to me is for one, of course it came before all of these others, but more importantly, you're elected to the National Academy by your colleagues, fairly broadly. I felt that being recognized by a broad swath of my colleagues was quite a high compliment, and that was very meaningful to me.
Of the other awards and prizes, they all have their own flavor and character and for me, my memories of particular events and of the interactions with people. It is difficult to compare one against the other. I can tell you in dollar amounts some are bigger than others. The Breakthrough Prize was the biggest prize and the Shaw Prize was also a big prize. The Breakthrough Prize was sort of out of my comfort zone with the glitzy movie star environment. I don't mean that in a negative way. It was just very different from any previous life experience! But it was fun doing a completely different kind of thing there. Yes I would say that each of them has their own unique flavor. I remember all of these different events warmly and fondly.
Yeah. So this question is like it’s geared towards… It’s like a sound bite kind of question to sort of summarize all of the things that you have learned over the course of your career, and that is simply looking back to your time in graduate school all the way up to today, what do we understand now fundamentally with cosmology that we didn't understand 30, 40 years ago?
I think we’ve learned an enormous about cosmology! I think we knew next to nothing back then. Modern cosmology begins with Einstein’s general relativity. That’s the basis for everything, and Friedman’s interpretation of it in terms of the metric of the universe. Those are the underlying equations that govern everything. Then it’s a question of accounting for what’s in the universe and that comes from measurement. We had early measurements from Zwicky in 1930s that there was dark matter, but nobody paid any attention to it. We had debates about the Hubble constant value for decades, but it’s only in the more recent period that we’ve collected just an enormous amount of information to take us from these kind of broad debatable ideas into having this ultra-specific model of the universe. I think virtually everything we’ve learned has been in this recent time.
And I should say also the rate of development is just stunning, but also the rate of technological development has been stunning. You didn't directly ask the question, but what we are able to do now, specifically in cosmic microwave background measurements, if you had asked me when I was graduating MIT, “What do you think? You’ll be able to measure this?” and I would have said, “No way! That’s not possible!”
But you did say you were an optimist when I asked that question about instrumentation, that there’s always room for improvement.
Yes. There’s always room for improvement, but I am stunned by how much improvement there has been!
Really, when I was in graduate school, I was watching the measurements of the temperature anisotropy ?T/T. The temperature anisotropy upper limit was 10-3, or so. It was coming down very slowly. It was very hard. Now we’re many orders of magnitude down from that and it’s just amazing.
If you had told me that it would go that fast…
I’m really stunned, not that it happened, but by how quickly it happened.
So that leads me what will be my last question, which is sort of a future, forward-looking question. But before that, as we discussed earlier, on as we both know today is #ShutDownSTEM, I think it’s a very beautiful thing that the physics community recognizes the social import of today and Black Lives Matter and how science and physics is not…that science is a human endeavor, and the foibles of humanity affect us in the physics community as well, issues of underrepresentation, issues of how systemic racism is not sort of… It doesn't stop at the door in terms of sociologically the way that science and physics is done. So I’m curious. I’d like to hear your perspective on not so much the issues of how we got to where we are now, but as an eminent physicist, as a leader in the field, as somebody who has the voice and a platform to shape the conversation in a productive way, what do you think are some of the ways that physics as a community can respond as positively and productively to this historic moment that we find ourselves in?
That’s a great question, and I’m not sure I know the answer to it. It’s been obvious for forever that there’s a problem, and I should say today we’re talking about a problem with a lack of black people in physics, but for many years the lack of women in physics was also a problem. It still is a problem.
Not to mention black women in physics.
And black women in physics! But just to reflect a bit, when I was a freshman at University of Maryland, we started with 120 physics majors, and one was a woman. A couple of years ago, I taught my first physics class at Hopkins where most of the class was female.
And to me, that was fabulous. It may not always feel like it, but we can make progress. That problem isn't done and over with, but we have definitely made progress, and I think we’ve made progress in black America, too—not fast enough, not enough by any means, but we did have a black president. You know, there are things that happened that would have been unthinkable a while back. Unfortunately—this is partially because the problem is so pervasive in society—I think there are limited amounts physicists themselves can do, but we should do what we can. There are questions of how many students come to a university wanting to do physics, and it’s quite low.
You mean across the board.
Across the board. You should ask, “Well, why is it so low?” Well, that’s the question. And then the universities will fight over the top black students and try to get them, so in that regard it’s not “We don't want them;” it’s more the opposite. And then what about the black students who are not at the level of white applicants? Do we accept them too or not? There are some serious questions to ask, but the big question to me is why we’re not seeing a lot of black students coming in. You could view some of that as sensible because who in the hell would want to go into physics?
Including your father!
Yeah, that’s right.
With his advice to you!
Exactly! So obviously some of this has to do with role models. Do young black boys and girls see role models and say, “Gee, I’d like to do something like that”? I think it’s very important to make sure that we’re establishing role models, and making sure that there’s a welcoming message there. But it doesn't take long in these conversations before you get to scenarios that are actually quite difficult to know what to do with. The good news is people have tried various initiatives, and we get some view of what functions and what doesn't function and what’s effective and what’s not. But as long as there’s a huge societal problem — as there is — there’s a limited amount physicists by themselves can do. Our society as a whole needs to be doing much, much better. There are bridge programs. There are outreach programs. There are all kinds of things that physicists have tried and can try to do. Some are highly successful; some are only so-so; some don't work at all. Some have negative consequences that were not intended. And I’m not an expert in this, but certainly our professional organizations are able to survey some of the things that have been tried to understand which are the effective things to do. It doesn't really help overall when universities go after the same students. If you have one bright black kid and one university gets him and the others don't. That doesn't really advance anything, which university they go to. The question is not that one university won out over others, but how do you change the population? I think that the role models can make a big difference, and hopefully we’re making progress in creating some—again, too slowly. But the systemic problem is so severe—society is literally keeping blacks in poverty, imprisoning young black men—it’s hard to see how we can have a healthy physics community with black students and physicists while that’s going on. I’m not an expert in this, but that’s my view of it. Our society must do much much better, and the physics community needs to do its part.
Yeah. That’s a powerful statement, though, to recognize that. How can we have a healthy physics community if the larger community and those problems are unhealthy, so to speak? I think--
That’s why I feel a frustrated that there’s a limited amount I think we can do. We should do it, but I don't think we can solve the problem by ourselves. I think it is a societal problem and has been since blacks were brought to the country in chains and since we had a civil war and since we’ve had housing discrimination, voting discrimination—voting discrimination continuing to this day.
And the huge imprisonment of young black men. I just don't see how university X doing so-and-so is going to make a world of difference, even though they should still do what they can.
Right, right. Maybe they should do what the idea is-- What you’ve emphasized is that the initiative of any single university is not going to move the needle, but if everybody recognizes that it should be done as a concerted effort, maybe that will move the needle.
I think that’s probably correct from what I know, and I do take some comfort in the fact that even though we’re not at parity with women yet, that situation has changed enormously.
You know, in my own department which I’ve now been at for 15 years, when I arrived we had no black faculty and now we have two. So is that wonderful? No. Is that progress? Yes. And there are things that I’m not going to talk about where I do try to make a difference. But I’m familiar with Twitter and other social media, and I find the attitude not terribly useful for real life if you really want to make a difference. I’m frustrated by virtue signaling, and even today I feel like a lot of what’s going on is virtue signaling as opposed to actually doing the real things that people can and should do. I tend to prefer doing things behind the scenes to make a positive difference without saying, “Hey, I did that!” There are definitely occasions where doing things behind the scenes can be more effective than being in people’s faces or telling other people what to do.
I won't corner you, Chuck, on saying specifically what the things you do, but are the activities that you're involved in more in your capacity as a good citizen or as a scientist?
I meant as a scientist. I do think that there are things individuals can do. You can weigh in at key moments and you can press on important things even when it’s unpopular to do it. I’ve seen some of those things make real changes. I just don't think that being on Twitter and calling someone out on something is effective. In the end, does that really cause anything to happen other than just saying, “See how great I am that I called this out?” I just feel frustrated that there are too many people doing that and not enough people actually doing real things.
Yeah. Well, let’s get back to the universe and not to the unhealth of our society for my last question, and that is… You know, it’s a forward-looking question. I want to pick up on what you said a short while ago about just how blown away you are with the quality of the instrumentation today, and so I want to ask-- It’s a very broadly conceived question, but to the extent that discovery, particularly in your field, if we can look at it as a pie chart of there’s the grunt work in the labs day in and day out and analyzing the data, and there are those flashes of insight or eureka moments or brilliance or whatever you want to call it. You throw in a little bit of luck, right—the right people, the right funding—and then of course, there’s the technology, right? So in terms of looking forward in terms of the next big things for cosmology to consider and to discover, in assessing that pie chart—not getting exact, of course. I’m not looking for any kinds of exact numbers. But what do you see as the most important factors for the future, particularly in light of just how amazing the technology is now and how there might be diminishing returns on what a forever line of improving technology can actually show us and teach us?
Well, of course I don't know the answer to this, but my sense is that there have been many points in history where people have said, “Well, we’ve learned almost everything that’s possible to learn.” There are books, like The End of Physics and that sort of thing, but people used to also say that before quantum mechanics was invented. You know, we pretty much understand electricity and magnetism and mechanics. What else is there? So I take a pretty dim view of saying, “Yeah, hey, we’ve reached this magic point in history where everything that we can know, we will know.” I would definitely bet against that being correct.
I still feel like technology drives everything. You know, there are bright people that do great things, but most of those things would be done anyway by a different person if the technology is there to get the measurements. So, I can't predict about future technologies, but there is a tendency to project technologies in terms of today’s knowledge. It’s like with magnetic tapes. “Oh, we can double the density of storing on magnetic tapes,” or “Oh, look. If we do this, we can actually triple it.” But you know, we’re running into an end of how much we can possibly improve magnetic tapes. Well, maybe magnetic tapes aren’t the way to go at all! People would probably say, “Oh no, no, no. That’s the only thing there is.” So yes, there are technological limits to specific things, but I think the there’s just been no evidence in history ever that we have hit a limit, and I don't know why that should be right now.
Okay, so we’re optimistic. So that begs the question what do you see… Again, it’s a projection; you don't know. What is on the horizon? What are the major advances in cosmology as you see them from today looking forward?
Well, in cosmology itself, I do think that there are these key questions we mentioned before that I think are the ones we want to answer. What happened at the beginning of the universe? What is the dark matter? What is the dark energy? Is the dark energy changing with time? And now I would add to this why is there this 5.5? problem? Something is clearly wrong. So those are the questions we definitely want to answer.
In terms of the technology… Just let me say a word about computers. It’s funny to think of computers as instrumentation, but in many ways they are. One of the transitions that happened that we’ve already passed is that it used to be if I wanted to know how to design a circuit, I would mock it up in my basement with resistors and other things like I described earlier and see how it works. Now if you go to any engineering school, you’ll find that the engineers have no idea how to mock up a circuit because that’s not the way they do it. They do it on a computer. They put in the virtual resistors and transistors and the computer will tell them what the circuit does, or the computer will even tell them how to put together the resistors and transistors to make the desired outcome happen.
So computers have become part of instrument development, and in fact, much of WMAP was something that I had never done before in the sense that we tried things out in the computer during the design. What if we did this? What if we did that? We’d simulate what would happen, and that’s become a norm in the field to simulate things on the computer. But now, again, we’re seeing experiments that would not have been possible without computer power and we’re seeing experiments that are limited by computer power. I’ll tell you a little story.
You know, NASA has been building rockets for years, and if you tell NASA to build a new rocket, the first thing they’ll do is get out their blueprints of their previous version and they’ll modernize it—and Lockheed Martin is the same way. But if you go to a place like Blue Origin, which had never built a rocket before, and you get people in a room and say, “Let’s build a rocket,” they don't have any blueprints to go back to. They have to invent something new, and so they ask themselves—and this actually happened—“What’s new about rockets that’s different from all those years ago?” and they all say, “Computers!”
And they say, “So why are we sending commands from the ground to the spacecraft to tell it what to do? Why doesn't it tell itself what to do?” So they design the Blue Origin rocket to basically program in the objective and have the computer figure out what it should be doing. So they reached a point in Blue Origin where they had to do a test where they would explode the astronaut capsule (without astronauts, obviously) and make sure that the capsule would land safely. But what shocked them was that the rocket came back and landed safely, too. They thought that was going to be a loss, but the rocket had all the computer power it needed to say, “Where am I? Where am I pointed? What do I have to do to get back home?” I mean, that little story (whether it’s true or not!) I think illustrates the difference between trying to continue and rehash existing technology versus having the foresight to look ahead. But it also illustrates how important the computers have become as part of the instrumentation.
So that’s clearly a trend that’s going to continue as the computers keep getting smaller and lighter and more powerful.
A lot to be excited about.
There is. I’m still excited. I feel still like a kid about it. All of this stuff is just great!
Well, Chuck, on that note, it’s been an absolute delight speaking with you today. I really want to thank you for your time.
Thank you very much. Take care.