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Interview of Adam Riess by David Zierler on April 30, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Adam Riess, Bloomberg Distinguished Professor at Johns Hopkins, and Distinguished Astronomer at the Space Telescope Science Institute. Riess explains the value of his dual affiliation and his focus on calibrating the Hubble Telescope for cosmological experiments. He recounts his childhood in New Jersey and the “boot camp” style of physics education he received at MIT. Riess explains his decision to go to Harvard for his graduate work, where Bob Kirshner advised his thesis research on supernovae, while he worked closely with Bill Press on data analysis. He describes his field work at Mount Hopkins in Arizona and his use of the early internet to collect and share data, and he explains what we did not previously understand about supernovae and how that prevented an earlier understanding that the universe’s expansion is accelerating. Riess describes working closely with Brian Schmidt and Nick Suntzeff and how the High-Z team came together, and he explains the decision to use the term “accelerating” to describe the findings from the research. He describes being unprepared for the enormous reaction the High-Z team received after it published its findings, and he explains the opportunities that led to his staff appointment at Space Telescope. Riess narrates his sense of when the “buzz” for the Nobel Prize started and he related the sense of bedlam when the announcement was made and his immediate plan to make this a recognition for the entire High-Z team. He explains how the world of dark energy research has opened up since the discovery and he surveys advances in instrumentation that have propelled the field forward in the last twenty years. At the end of the interview, Riess discusses his current focus on the Hubble tension, he conveys his excitement for the launch of the James Webb Telescope, and he shares that he can’t wait to meet students that he has never seen in person after a year of pandemic-mandated virtual interactions.
Okay. This is David Zierler, Oral Historian for the American Institute of Physics. It is April 30th, 2021. I'm delighted to be here with Professor Adam Riess. Adam, it's great to see you. Thank you for joining me today.
Thank you for having me.
Adam, to start, would you please tell me your titles and institutional affiliations, and you'll notice I pluralize that.
Sure. I'm a Bloomberg Distinguished Professor at Johns Hopkins University, and Distinguished Astronomer at the Space Telescope Science Institute.
You got it. Now, Bloomberg. Who is, or was, Bloomberg?
Bloomberg is Michael Bloomberg, who was an alum of Johns Hopkins. He's been the mayor of New York City. He started the Bloomberg financial industry, and philanthropies, and he's been a big donor to Johns Hopkins.
Does he have any particular interest in astrophysics and cosmology?
He does seem to. I've met him on a couple of occasions, and he had some questions about quantum entanglement, and about the multiverse. So, he seemed genuinely, thoughtfully interested.
How far back does your dual affiliation go between Hopkins and Space Telescope?
Just to say briefly, I was an undergrad at MIT, a grad student at Harvard, and then I was a postdoc at UC Berkeley. And at the end of 1999, I came to the Space Telescope Science Institute and was exclusively there until around 2005 or 2006, and then I got the joint affiliation and became a professor at Johns Hopkins but maintained my position at Space Telescope Science Institute. And now, I basically go back and forth between the two. They're right across the street from each other, and basically every other semester, I'm either teaching formally at Johns Hopkins, or formally working on calibrating the Hubble Space Telescope at Space Telescope Science Institute.
Besides doubling your administrative responsibilities, I assume, in what ways is the dual affiliation beneficial for your science?
That's a great question. My science, in the last twenty years has really focused on using the Hubble Space Telescope for various cosmological experiments. So, having a deep understanding of the telescope's calibration has been crucial, even down to the level of knowing exactly when the data comes down, and how to access it. So, that was always very important, and around the middle of 2000s I also wanted to have greater access to graduate students and to be in a more educational environment. But Hubble remains very important to my research. Also, if everything goes well, in October, the James Webb Telescope will launch, and I'll maybe even transition to working on James Webb for my research and service work.
Adam, what opportunities do you have to include students with your work in the Space Telescope? In other words, can you bring undergraduates, graduate students there, or are there hard and fast boundaries in that regard?
There are no boundaries in terms of research work. So, I involve them in that a lot. Before COVID, I would have lunch with them every day at the Space Telescope Science Institute cafeteria, because the conversations you have with maybe engineers, or other calibration scientists are really invaluable. The actual calibration work that I do, generally, I do without students because that's sort of my service component of my work. It would not be appropriate for students to sign on to do that, though there may be some work that comes out of the work they do that is valuable for calibration.
What about grants and funding and things like that? How do you separate the way that you research is supported at Hopkins versus at Space Telescope?
They're very different. I guess, actually, formally, in my appointment, at this point, Space Telescope subcontracts me from Johns Hopkins. So, Space Telescope pays Johns Hopkins, and Johns Hopkins pays me, and like every other professor, I have nine months where formally I may be teaching or doing service work, and that could include the calibration work at the Space Telescope. I have grants as well that I can use for students, or I can buy back some of my time that can be used for research.
A question we're dealing with a year plus in the pandemic, how has your work been affected, either for better or worse? On the better side, perhaps, have you had more bandwidth to work on things simply by not having to commute, being at home, and in what ways has the lack of in-person connection with your collaborators really slowed things down for you?
Yeah. You know, I can do a lot of work-work, the technical work, the research work. I can interact with students in some way, but it's been a very, I would almost say, kind of bloodless way. I really thrive on the interactions, or give and take, the conversation. Sitting down with people and saying, "What do you really think about this analysis, or this data? What are you worried about, or what parts do we trust?" Those things are difficult to always put into a Zoom call or a paper. And I miss all of that. So, I would say, I have soldiered through, like everybody else has for the most part. If I were to have told myself, well this is the point my research is at, I told myself that two years ago, “Yeah, that sounds about right,” but it's a lot of the enjoyment of being in a science environment as rich as the one I'm in in Baltimore between Johns Hopkins and Space Telescope, a lot of that has been missing.
Just as a snapshot of where we are now, are you drowning in data? Is there more data than there is either computer power or people power to deal with at all?
I have a lot of data right now. I've been fortunate to get a lot of time on the Hubble Space Telescope in recent cycles. So, I wouldn't say I'm drowning, but I am satiated, and trying to get out a kind of final analysis of some project that I've been working on. It's challenging, but it's about the right amount.
I'd like to ask two broad questions before we go back and develop your personal narrative, because I think these will punctuate our entire discussion. They're going to be sort of nomenclature and sociology of science type questions. First, on the nomenclature side, the boundaries between cosmology and astrophysics as subfields, have those boundaries shifted over time, and with specific regard to your research, are they substantive differences, or are they really just about different people and different opinions at different universities?
In my view, there really is a boundary. I can't always promise that the words match up, but the boundary is very clear in my mind, at least. Which is, there are those whose primary questions are about the nature of the universe, forces in the universe, laws of physics that apply to the universe. And I would call that investigation cosmology. There are people whose primary interest is about the objects in the universe, and how they work. And I would call that study astrophysics. However, the cosmologist often uses objects in the universe as test particles, and so [he or she] needs to understand enough of the astrophysics to do that, and yet, at the end of the day, his or her questions are about the universe, not about the objects, and the astrophysicist more about the objects.
So, in my mind, I've always been squarely in that cosmology area. I use lots of astronomical objects, but at the end of the day, they are still black boxes, test particles, whatever you want to call them. I need to understand them well enough to know if they're telling me the truth about the universe, but the experiments that I devise are to understand the universe, not the objects.
Adam, as you know as well as anybody, the successful advance in either cosmology or astrophysics requires the interplay between theory and observation or experiment. Sometimes, historically, the observation leads the theory, and sometimes the theory leads the experiment. So, just in terms of where the fields are now, what's your sense of the state of play overall?
You know, it's been a strange period, and by period, I mean actually many decades. When you got to school and you study physics, you learn about primarily all the great theoretical insights. Basically, that is your grounding, as though physics proceeds by mathematical derivation and deep insight. And yet, the last 30 years, and in particularly my area of cosmology, has been, I would say, utterly dominated by observation and experiment, where surprises come out from the observation and experiment, and in my particular case, we can talk about the accelerating universe and dark energy of the cosmological constant.
We often reach back 100 years to Einstein, and say, "Well, you know, Einstein thought this might be a possibility," as though there hasn't been a great deal in the last 100 years to explain it. And the truth is, there has not been a great deal in the last 100 years to explain this. I'm not sure if I could visit Einstein in the 1920s and told him this was going on, and we had a conversation about the cosmological constant and dark energy, I'm not sure it would be all that different than a conversation I would have today with theorists, about why? Why is this? So, it's been a tough period in terms of the interplay between theory and observation.
Given the phenomenal advances in observation, and as you characterize it, theory is in many ways stuck, what does that tell you more broadly about physics, or about limitations in the way we can understand the universe?
You know, I guess my view is that theory can often proceed in more plateaus, and then big jumps. You know, you look at Einstein and general relativity, and you say, "What were the precursors to that?" And you might say, not that much. It would be hard to say you saw general relativity coming ten years earlier, and in the same way, the thrill of theoretical insight and progress is you don't see it coming. It's not like I can lay out an experiment, and I can tell you in five years we'll have the telescope, we'll have the data, we'll answer this question, the data will probably look like X or Y, and that'll be a step forward.
We don't have anything like that for theory, so what it tells me generally is we need to be always patient with theory. We don't know when the progress will come, who it'll come from, what direction. We don't know what will trigger it, which clues. Experiment and observation kind of methodically marches along, hopefully informing theory, and theory is more like the tortoise that you think it's way back there, and then suddenly it may be ahead in the race. So, I hope that one of these days we get this series of big theoretical insights, but it's been a while. Those of us doing observation, I think, have to mostly treat it like, great if it comes, but we need to chart a course that doesn't require the theoretical insight.
To the extent that patience is a virtue for physicists, perhaps string theory would require the greatest amount of patience, given the fact that it's doing such interesting and beautiful things that remain fundamentally disconnected from observation and experimentation. Would you include string theory, specifically, as one of those areas to be patient in that might produce one of those breakthroughs at some point?
You know, it has sort of been on a parallel trajectory to experiment, and I use parallel in the broadest terms, like maybe parallel in other dimensions. So, I can't even say the dot product with what we're understanding is necessarily even positive. I don't know -- I'm not steeped in it enough to say how much more patience we need to have with it or not. In some ways, it's unprecedented, I think that's fair to say, to go so many decades doing deep theoretical work that really smart people work on without coming to touchstones with experiment and observation. So, this is either the riskiest bet that will bear fruit, or not. I just don't know. I wouldn't tell somebody do or don't do string theory. It's certainly frustrating to not be getting the kind of input from theory that you would hope to get as an experimentalist.
Do you see experiments that are space-based that can operate on scales not possible on Earth as being potential areas of opportunity for string theory? In other words, string theorists would tell us one of the problems now is that there simply is not technological advancement that's capable of bearing out what our predictions are. So, how might space-based experiments yield some progress in that regard?
Right. I do not hear often of, or carry around with me a list, like I should, if it were the case, of the five-string theory experiments we need to do to validate string theory, to give them guidance. I hear things sometimes like, "Well, you know, now that string theory thinks about it, there could be 10^500 different universes." The most I hear about string theory from experimentalists often involves the multiverse. And as you know, that is something, by definition, we can't do an experiment in. So, I would not say so, that we're just lacking [that] quite [a] level of precision that sting theory needs. I would say, we're lacking experiments defined in this universe, and not other universes, to do. That's very tough.
Just to give you a specific example, the cosmological constant or dark energy it would seem to me is a great opportunity for string theory to say, "We've got that. We can explain that. We understand that. This is expected. This is the experiment to pursue." But it hasn’t turned out that way. As we try to measure dark energy, we're quantifying basically a number, which is the equation of state of dark energy, what we call w. For a cosmological constant, w should be -1. But for other types of ideas of physics, scalar fields and things like that, it could be another number. So, the question any experimentalist wants to ask a theorist is how, “Well, do I need to resolve this?” What is the precision with which I need to design my experiment to say something useful? For decades, we've been asking this question, and theorists can't tell us what an interesting precision is. Is it 10^-1, -2, -3? We don't know the precision with which we need to measure w to say, "Oh, it's still consistent with w=-1? That is profound." Or the distance to the next good theory is such-and-such a step size in w, so you need to resolve that at 5 Sigma.
We don't have that information. They haven't provided that. They don't have any other ideas. So, as an experimentalist, that's where it's most frustrating. I've been on teams where you invite on a theorist to guide you with that, but in this case they say, "I don't know. Just do what you think is possible, because we can't tell you." I understand that, and I'm not blaming them. I'm just saying that is specifically where the lack of theoretical input has been painful on the experimental side.
If not string theorists, where else might you look for a breakthrough on understanding quantum gravity?
The best thing I can say is experiments. Different kinds of experiments. At some point, what you're looking at is either a great experiment that does that, or you're looking to pull together lots of little tensions with the Standard Model, or vanilla Lambda-CDM, and hopefully knitting those together. I sometimes think in this mode that what you're hoping to do is provide clues that sparks theorists to think of solutions. The solar neutrino problem comes to mind. We don't see the right ratio of neutrinos from the sun, and theorists think about that problem and they're drawn to it. They're drawn to solve it, and that sparks an idea. So, I hope that happens with Dark Energy.
Well, Adam, let's take it all the way back to the beginning. Let's start first with your parents. Tell me about them and where they're from.
Sure. My dad was born in Berlin, Germany, in 1931. It was a very, as I understand, assimilated Ashkenazi Jewish family, meaning they were not practicing, but that was their background. As you know, that was a place in time you had to flee from. So, in 1937, my dad and his mom fled Nazi Germany, and got --
Was his father not in the picture?
So, his father, Curt Riess, was a well-known author and writer for newspapers in Paris. He was writing a lot of anti-Nazi pieces and he had to leave a couple of years earlier than the rest of the family, because his work was really not welcome in Germany. There was also a divorce, I think, that occurred around that time. So, at that time, I think it was just my grandmother and my father.
Where did they go?
They came to the United States. At the time, the story goes, or what they told me is that it got to a point in time where you couldn't liquidate your assets and bring them over, but you were still able to take a vacation-style trip. I think they bought tickets to go around the world as though on a vacation, or leisure trip, and got off in the United States and cashed in the rest of the trip to have some money with which to start new lives in the US.
Did they have family here, or someone to sponsor them?
My grandmother's sister, my father's aunt, Margot [Posnanski] was already here in New York. So, she met them in New York, and I think there was a little bit of movement around the country, and they may have gone between California and New York. There aren't many people around from that time to let me know. My father was an only child.
What about your mom? What was her story?
My mother was born in New York in 1938, also to a Jewish family, not very practicing, and grew up in and around New York City. So, at some point, they were both in New York.
That's where they met.
What were your parents' professions?
My mom became a clinical psychologist, and my dad, for a while, was an aeronautical engineer, and then he migrated over time to individual commercial businesses. He had a delicatessen in New Jersey, kind of a Jewish-style deli. He had a frozen food business. He had various sort of small-scale business enterprises.
And you grew up in New Jersey?
Where in New Jersey?
I grew up in Warren, New Jersey, Somerset County. Its in the middle of New Jersey. But you know, everything in the upper half of New Jersey is kind of in the shadow of New York City.
Right. Adam, when did you start to get interest in science?
That's a good question. I would say the key element of my interest is my curiosity. I was the kid that always asked why, and how, and why, and wanted to understand how things worked. My parents were relatively patient answering some of those questions, but at some point, it became clear that science is the discipline that does that for a living.
Were you a tinkerer? Did you take stuff apart, build it back together?
I took stuff apart, put stuff together. I remember when I was a kid being fascinated by the outlet in the wall, and the two plugs that went in, and how everything worked after that. I remember it seemed important to have the two prongs separate. So, I remember laying a wire across them while they were plugged in just to see what would happen. Of course, I shorted out the circuit breaker in the house. You know, stuff like that I would do just to see what would happen.
Was your family Jewishly connected at all growing up? Were you members of a synagogue? Were you bar mitzvahed? That kind of thing.
No. We were descended from Jews and shared many cultural links, but we were atheists when I grew up. We were areligious. I married a woman who's practicing Jewish, and we raise our kids Jewish, and we belong to a synagogue. I take it as a cultural thing. I'm not particularly religious in a religion sense, but I am --
You see the value of it, sociologically.
Yes, I see the value of it sociologically. The traditions are very heartwarming. There are values and morals that are important to share with children. It's a good forum for that. It's a good social outlet.
You went to public schools throughout?
I did. I always went to public school.
And your high school, was it particularly strong in math and science curriculum?
It was good. Watchung Hills Regional High School. It had strong AP courses. It had good math. I took up to BC Calculus there. The amusing thing, considering what I did, is that it had horrendous physics. There was a physics teacher who was a year or two away from retirement and was completely uninterested in teaching physics. Completely uninterested in talking about physics. So, he would just sit there and tell us stories about his life. It was actually an AP physics course, but it was modeled on this famous course that MIT had come up with back in the '60s, PSSC Physics. So, we got these old textbooks, and we got these tests that seemed so hard, but there was something compelling about the tests. It was the way the questions were asked. What would happen if you shined a light through a pinhole like this? Would it look like this or that? I wanted to be able to answer those questions, and I spent a lot of time reading the PSSC textbook. The only time in my life I had a tutor, a physics graduate student from Rutgers, came a few times to talk to me about physics. My parents arranged it because they knew I wasn't getting any actual physics instruction. I was maybe the only kid in the course who actually tried to learn physics.
Another big driver, without a question, was the summer between junior and senior year in high school, I got selected to the New Jersey Governor's School of Science. The way it worked was that your high school picked you if they thought you were strong in science, something like 100 students across the state were selected. And we went to Drew University as rising seniors. For a month, we lived there, and we took advanced courses. I got to take a course in special relativity from Jim Supplee at Drew University, and I was enamored with it. I was in love with it! I was utterly fascinated when I learned special relativity. I remember, for a while, as we talked about it, the first time learning about it, just thinking this was a trick, like just an optical illusion, but not real. Like, it will just look to you like moving clocks age slowly, and moving lengths contract. And then I came to understand at a deeper level that this was real and suddenly it was like Star Trek is real! And that was when the bit flipped in my brain and I was like, I have to go into physics!
Between your family's economic capabilities, between geographic considerations, between your grades, what kinds of schools were within range for you to apply to?
That's a good question. I was an academic late bloomer in high school. I came into high school probably in the top 15 or 20 kids in terms of grades. I was still quite serious about playing soccer, so I had to split time. And then, around sophomore year, I became very much more engaged in science and school and I became one of the highest achieving kids in the school. But still, it was unclear where I should go to college. So, I applied to a fairly large range. My desire was to go to Princeton, but I did not get in. The best school I got into from a physics standpoint was MIT. So, that's where I went.
So, it was 1988 you arrived at MIT?
And it was physics from the beginning. That was the plan.
What were your impressions of MIT when you first got there?
I thought it was very hard. When you look at the level of difficulty from the standpoint of--how much do I have to “up my game” to be here and do the tasks? That year, from senior year of high school to MIT, was definitely the biggest jump in difficulty I had ever experienced. I used to do all my math homework in front of the TV while I watched Monday Night Football, with half my brain while I was watching the game. And then suddenly, I was like, “I don't know how to answer these questions. I just don't know.” I would sit down and think about it, and I'd talk to somebody else in the class, and I’d find out that they don't know either. It was just crazy hard.
But they created the environment where it was the work that was hard. It wasn't like they were being mean to you. I had to think hard, and I had to study hard, and I had to learn -- and this was maybe the key skill that I had to learn -- I had to learn how to carry around hard problems in my mind while I went to dinner, while I rode my bike across the Mass. Ave. Bridge, because the funny thing about hard problems is when you don't know the answer right away, it's not like looking up a fact where -- I don't know the year Grant was born, but once I look it up I'll know. It's more like, I have to have a new idea. I have to have a creative insight. I have to kind of wander around in the wilderness a little bit and you need to keep varying your perspective until the idea happens.
There's an intuition that you have to learn.
There's an intuition. And intuition is great, but it changes throughout the day. I know that sounds weird to say, but it changes with what you're thinking about. I can't tell you how often I'd be sitting there playing soccer in the intramural league at MIT and go, "Wait, okay! That's where I'm going to go." And that was -- I just had to learn how to think in that way. I think of it almost like -- I've described to students, it's like an oyster with a grain of -- who makes pearls? Oysters? Clams?
Oysters. You know, you need that irritating piece of sand in there to keep irritating and to stay with you until eventually it becomes the pearl. If your mind works in that way, it's unsatisfied until -- you just don't feel okay until you have an answer to this. That is very much my nature. So, I learned how to think in that way at MIT because I had to.
Adam, what were some of the standout classes or professors in the department of physics that were really important for your intellectual development?
Yeah. That's a good question. Ed Farhi at MIT whom I took quantum mechanics with was certainly one of those. And Ed Bertschinger, whom I took advanced quantum mechanics from was another. Also key was an experimental lab called Junior Lab -- it's this very famously hardcore course at MIT. It's the hardest thing you do there. It's two semesters, but you get triple credit because it’s so much work. You're doing these famous experiments from Nobel laureates and the foundations of quantum mechanics from the 1930s and '40s. The equipment kind of sucks, and it's meant to. It's not state of the art. You have to kind of get things to work.
What I really loved was the data, and it was the only time in my life where I'd really gotten data. This process of going from data to answering a simple question kind of fascinated me. Like, how do you say something about the quantization of charge on the electron by watching these tiny little particle things float up and down in a Millikan experiment? And like, you take data, you make measurements, and all the things that go well or wrong during the experiment comes down to, how can I answer this from this pile of numbers? And how do I go from a pile of numbers to yes or no and with what confidence? We call it data reduction, but if you think about that idea, data reduction, it's like saying I have many, many pieces of information. We all sort of know there's a potential to lose information when you reduce it. And yet, we're all reductionists. We all want to answer a question. We don't want to have just a pile of data. We want to have a yes or no. It's like this or that. So, I love that process. I think it's so interesting.
Adam, did you have any summer internships or laboratory opportunities that were relevant for your studies?
I did, but none of them were very good, I would say. I'm just being honest. I did a summer project with the plasma science instrument group at MIT that ran the plasma science instrument on Voyager II, that was shortly after Voyager II had passed Neptune. There was some problem with the instrument, and it was one of those things where nobody really paid attention to me as an intern to give me an introduction to that. I did one educational project with Taylor of Taylor and Wheeler, who wrote the special relativity book on calculating orbits around a black hole with general relativity in a way that could be visualized. So, those were okay, but they weren't very inspiring. They never felt like I was doing research or inspired me to do research. It wasn't until I started graduate school that I actually had research experiences that were compelling.
In undergraduate, were there any cross-registration opportunities at Harvard? Were you involved at all with what was going on at Harvard as an undergraduate?
I believe that there were some cross-registration opportunities, but I didn't avail myself of any of those. Partly, it felt like, why would I do that when at MIT -- I mean, there wasn't a science course that didn't seem like it was there. I knew students who went over to Harvard for more liberal arts opportunities from MIT, at least when I went.
Were you solidly in the experimental camp from the beginning? Did you ever dabble with the idea of pursuing a career in theory?
You know, the idea of a career never really --
Or at least, I should say, for graduate school.
Yeah, right. I would say, not really. I would say I was focused on the courses when I was in them, with very little thought about what would happen after that. And to be very honest, I didn't really see myself as staying, necessarily, in physics for very long. As my dad would say, "What does a physicist do?" I didn't really know, or I often thought -- I know there are a few people here at MIT who are really brilliant, more brilliant than I. Those must be the ones who actually will do physics. But I thought, this is just so interesting, and it's probably good training for learning how to think. And I thought there must be lots of areas where this background would be good. Even at the time I was applying to graduate school, I had thought about going to work at the CIA in some kind of image analysis, or working on Wall Street in some kind of data analysis.
What kind of advice did you get, if at all, about where to go to graduate school, what programs would be good for you, who you might work with?
To be honest, not very much. It wasn't the orientation or focus of the advisors that I had. There was probably one exception. There was one professor that I liked quite a lot, Steve Meyer, who was my junior lab professor. He was at MIT and working on the cosmic microwave background and ended up going to Chicago. But he spoke to me and my junior lab partner, Jeff Jewel, about opportunities. But for the most part, I felt like, when I was there, MIT wasn't that focused on your career development. It was focused on teaching you physics.
Did you ever think about staying at MIT, or was that not encouraged, that you should go elsewhere?
That was not encouraged. And the truth was, it felt like such a bootcamp experience that I felt like I really would like to go somewhere else. The only people who seemed more unhappy and miserable than the undergraduates were the graduate students. I'm just being honest. It seemed like a joyless place in terms of people having well-balanced lives. I thought four years of bootcamp was enough.
So, absent any guidance, or negatively defined by where you didn't want to be, did you just apply by reputation? Did you have any well-formed ideas about what programs would be good for you specifically?
You know, as I started getting to the end of my physics education, the one thing people would tell me is, you need to figure out whether you like condensed matter, particle, astro, molecular, atomic, and you need to figure out whether you're an experimentalist or a theorist. These seemed like really hard questions to me, but the more I pursued them, the more I realized that there was a lot to learn by the process of elimination. My feeling about condensed matter came from people at MIT building refrigerators to get down to one degree kelvin, and that didn't seem that exciting to me. Particle physics seemed like these big colliders and big teams and I didn’t know how I could fit in there. And I decided, I am probably not smart enough to be a theorist and I also I liked experiments.
In a summer program at LLNL I learned about a particular experiment, the MACHO project, that was trying to see whether the dark matter was black holes by looking at micro lensing and that sounded really interesting. And I'll admit, there was a fair bit of reputation. I thought, I'll apply to graduate schools and see what happens, and when I got into Harvard, I just thought, still thinking a little bit like an undergraduate, that will look good on my resume when I want to go to the CIA and do image analysis, or to Wall Street to do data analysis and anything else. I always thought this graduate school thing may not even worked out. I may not get to the end. I looked at places where I could still get a terminal master's and still have something to show for it. I was not committed or convinced that I would continue in this field.
And to go back to the nomenclature question, circa 1992, were you thinking specifically astrophysicists to work with, or cosmologists to work with? How refined were your thoughts?
That's a good question. So, as I said, what led me initially was "astro". The question of what's up there and out there raises that feeling of basic wonderment and curiosity.
Adam, just to interject there, would you also throw astronomy into the mix at that point?
Sure, yes. Absolutely. When you went to Harvard in astro, you were required to read a book by Frank Shu called The Physical Universe, and to pass a basic test of competency on it. I had not really had any astro courses, or cosmology, or anything like that when I was an undergraduate. So that summer I went through the book page by page. It was so interesting, the different kinds of objects resulting from weird physics. But when I hit the chapter on cosmology, in particular on the expanding universe -- I didn't realize other than in a pop culture way that the universe was expanding, or even what that meant. And again, it threw me back to when I learned special relativity. Like, you mean real -- not like optical illusion expanding, but really expanding? What would that even mean? Those kind of framework questions were exciting to me, and I wanted to work on that, or in that somehow.
So, as soon as I knew about it, that's when I knew I wanted to do it. I don't think I knew the word cosmology before that, and then once I read that chapter in Frank Shu's book, that's what I wanted to do. So, when I then started speaking to different professors about possible projects to start research in grad school, one of the first ones I spoke to was Robert Kirshner, who was chair of the department at the time. He was very gregarious, charismatic, so he was appealing as somebody to interact with on a daily basis. Most of the physicists I knew were somewhere on the social disorder spectrum, so it could be difficult and not much fun to interact with them.
You will always have a good time with Bob. There's no question about it.
You will always have a good time with Bob. But in particular, some of the things he was working on seemed to hit right down the strike zone that I was interested in. He was studying supernovae but had this interest in using them to measure the universe. He had done his thesis work using Type II supernovae in this way, which are seen expanding after a core collapse event. And he said to me that there's another supernova type that's starting to get refined, Type Ia, and this guy Mike Phillips has started to look at whether they would be good standard candles, and I'm thinking there's something more rigorous or sophisticated to do with that data by collaborating with Bill Press at Harvard, who was an expert on data analysis. He wrote the book Numerical Recipes. So, the subject matter, the area absolutely spoke to me as yes, that's what I want to do.
So, you got to Harvard, and then who ultimately became your advisor?
Bob Kirshner. Bob Kirshner was going to be the advisor on issues related to supernovae, and Bill would advise on issues related to the data analysis. And the question about the universe seemed obvious. How fast is the universe expanding?
So, between the Observatory and the department, where did you spend more of your time?
In the department. Sorry, the Observatory is in the department. The Center for Astrophysics, the CFA, 60 Garden St. was the place I went.
Did you recognize in real time what a fantastic moment this was in observation, in astrophysics and cosmology?
No, not at all.
When did that dawn on you? I mean, like COBE, for example. Was that on your radar as a graduate student?
That's a great question. I remember when the COBE results came out. It was my last year or two at MIT, and everybody said, "Go to the auditorium. We're going to hear a talk about COBE." I think I went, and I didn't understand it in any real detail, but that seemed exciting. I also remember when I was in junior lab, and one of the professors won the Nobel Prize that day, and they said, "Go to the colloquium and hear about quarks." So, it was vaguely on my radar screen. I will say, something else impactful was when Voyager passed Neptune. That was very exciting to me. So, I would say my tastes, my interests seemed to go in this sort of cosmology-astro sort of direction, but until I went to graduate school and spoke about doing an actual project, it was not something that I was reading books about, was thinking about very much, other than this one Physical Universe book that was our required reading.
What was Bob's style as an advisor? Did he give you problems to work on? Did he tell you to go out and figure stuff out and bring it back to him?
That's a really good question. Bob's style, I would say, was to get a big clan together. He had a big group and it had about 13 people in it that was kind of his posse, his clan. He brought us all out to lunch every Friday and has us go around the table and say briefly what we had done that week. But the real style of working, I would say, was a ladder, where there was anything from graduate student neophytes, to postdocs, to people who really were like one foot into assistant professorships. What you really did was -- you would talk to Bob in the beginning about the general idea of your project, and he was very fast on his feet, but he was not a detail guy who would sit there and explain how to do stuff. You would have to find somebody, a mentor in the group, who actually knew the nuts and bolts of how to make observations or work with data.
So, for me, that was Brian Schmidt, who was my co-Nobel laureate. When I went to graduate school it was my first year and for him it was his fourth year and final year. So, he sort of took me under his wing and taught me how to make measurements, went with me to the 1.2-meter at Mount Hopkins, showed me how to make observations, how to reduce imaging data. Everybody sort of had somebody in the group that they would go to on a day-to-day basis to find out how to do stuff.
Had Brian already defended his thesis by the time you first connected with him?
So, he was still in the middle of his research. Which was what specifically? What was he working on for his thesis?
He was working on Type II supernovae and using them to measure the expansion of the universe, and I was going to work on Type Ia supernovae and measure the expansion of the universe. So, we had different kinds of supernovae. He was at the end stage of his graduate school time; I was at the start of mine. He was working a little bit more with observations, but also with the models of the supernovae, whereas mine was going to be much more empirical, data driven. I gravitated towards that. But I learned a lot from Brian about how to collect and analyze imaging data.
How much time did you spend away from Cambridge, in site at various observatories that were relevant for your research?
Initially, I went out to Mount Hopkins out in Arizona to make measurements maybe four or five times. And then, it quickly became clear that to do the project that I wanted to do required making an observation every two or three nights to follow a bunch of supernovae, and that I would have to live out there, or we'd have to come up with another way. Also, I was not such a night owl that I really enjoyed staying up all night all the time. I found that my enthusiasm for the research I was doing plummeted around 2 or 3 in the morning, when I just really was very tired and wanted to go to bed.
So, I was able to put together a new kind of protocol at Harvard to get the data. We would ask various observers for an exchange, "We just need 20 minutes of your time somewhere in the night to re-observe this supernova. just point at it, take a picture in these filters at these exposure times, and we’ll pay you back when we're on the telescope." So, I coordinated that new protocol so that I was basically -- it was the early days of the internet, FTP, calling a lot of people on the telephone, and getting observations every couple of nights, so that by the end of my thesis, I was able to put together an observation set of 22 Type Ia supernovae in the north, that was the first northern dataset. There was a southern dataset from Calán/Tololo survey. And each of these had 20-25 SNe, so required like 400-500 individual nightly observations, which would have been very difficult to collect for an individual, unless they moved and became nocturnal.
So, Adam, I'm sensing at this point there's a turning point in the narrative, where up until now, the dominant theme is cluelessness, naïveté, you're trying to get your footing, you're figuring things out. So, now that you're getting deep into the data, you understand supernovae. At what point are you starting to connect your narrow field of research -- graduate students are super focused on what they're doing. At what point are you starting to make the bigger connections with fundamental questions about how the universe works; the bigger questions in astrophysics; the bigger question in cosmology? Was that part of your intellectual development during your thesis research, would you say?
You know, it's funny. Up until midway through graduate school, I would have said that was more ambitious than I think I was. I was trying to figure out how to make sense of this data. How do I make this project work? Initially, the project was to understand that Type Ia supernovae were not perfect standard candles. Some are brighter, some are fainter, some have dust in front of them. And it was to get these points to line up on the Hubble diagram. Why weren't they lining up? What was different about each one? What clues or empirical information was in their light curves? So, initially, like you said, I was focused on how to make these better distance indicators. It wasn't until I made some serious progress on that -- it was like okay. Let's get back to the real question about the expansion rate of the universe. It wasn't until maybe my third or fourth year where people would say to me, "Hey, you're making these into really good distance indicators. Seems like you can really say something about the Hubble constant, or you can really say something about our motion with respect to the inertial frame of supernovae."
At some point, that lightbulb went on. I've done the spadework now. Now, I can go to the payoff. But it was slow coming to that. It wasn't until, like I said, my third or fourth year. You get so burrowed in on, you know, am I getting the signal to noise I need to measure the shape of these light curves? I was initially working with some old photographic data before I realized the photographic data just wasn't good enough to make the measurements that we were trying to. So, like I said, it was back to the mode of junior lab, where you've got this pile of data, and you're trying to reduce it. Initially, I was disconnected from the big question. That didn't come until toward the end.
So, to foreshadow to the discovery of the accelerating universe, what was not understood about supernovae, and how did that inform our ignorance about a non-accelerating universe? And what did you learn in the course of this thesis research that would ultimately lead to this massive discovery?
Yes, okay. That's a good question. So, I would say, it was the refining and empirical understanding of Type Ia supernovae. Up until that point in time, you have to understand that supernovae was a broad class of things that explode. The idea to say, I'm going to look at an explosion, and from how bright it is, tell how far away it is -- ignores where you have to deal with the enormous variance of the explosion, the enormous variance of the line of sight to the explosion -- of how much dust you're looking through; in another galaxy; in our own galaxy; whether that was a dim or luminous explosion -- would really challenge the ability to say how fast the universe is expanding. Or even harder -- I remember I was asked this in one of my first research exam questions -- to measure q-naught, the deceleration parameter, would be to say that you knew the explosions you were looking at much further away, much further back in time, were the same as the ones today.
Now, they don't have to be the same, but you have to be able to standardize them or normalize them in a way. So, until you could tackle that problem, it seemed pie in the sky to us working on the supernova side. Now, there's a bit of a split development here, in that the other team that ultimately makes this discovery with us, the Supernova Cosmology Project, Saul Perlmutter's group -- they were approaching it from the pure physics side of interest in this question of the deceleration of the universe and knowing that supernovae were objects that were bright enough to do this. But we would have said, back in the early '90s, when I was working on my graduate work, we still have to understand which ones are dim, which ones are dusty, and which ones are distant. Until you can separate those three, you can't make that measurement. And they were going after making the measurement, and doing the hard technical work of how do we find them that far away? Whereas we were working on the refining part.
So, I would say, going back to my own work, until we refined them and standardized them, until you got all these points pretty on a line, you couldn't say, or we wouldn't have any confidence in saying, that we were measuring the change in the expansion rate of the universe, and not just the change in the mean amount of dust in the universe. Or the evolution of the supernovae -- maybe they were fainter in the young universe and now they've gotten brighter. How would you know which was which? So, I would say, for the local group around me, we became so impressed with both the work I was doing, and the work that was being done in Chile at the Calán/Tololo survey. We were two groups within a group that were working on refining and finding such sharpening of the Type Ia supernovae. By the time I was done with my graduate work, we could measure the distance to a supernova with 5% precision, with no, as far as we could tell, dependence of that residual on anything about the circumstance of the supernova.
So as I was finishing my graduate research, people in our local group -- Brian Schmidt and Nick Suntzeff --were starting to say, "Why couldn't we do what the other team is doing now but better, because we now understand the supernovae well enough to tease out the measurement?" So, this is the sort of backstory of how our team, the people who studied supernovae, got to the question of using them for cosmology. I was always interested in cosmology but had spent my time immersed with supernova people, learning how to standardize the explosion to get a precise distance measurement.
Given how phenomenally exciting this observation was, what was Bob's reaction when you would bring this data back to him? Did he realize in real time what a big deal this was?
I think he did. Especially by the third or fourth year of my doctoral thesis, I would show him this progress in group meetings. He and other people -- it was very compelling as scientists to see this large scatter of points come together. Can I share a slide with you?
Let me just show you, because this is really a great example of that. It's just going to take me one second to pull this. [pause] Alright, yeah. This is the slide I want. Let's see, can I get permission to share screen?
Alright, I got it. Can you see this?
So, here I am in graduate school. Here's Bob; colorful vest. Here's Bill Press, expert on data analysis.
You look like you're about 11 years old.
Yeah, I am 11 years old. No, I wasn't. But anyway, this is the essence of what I was doing. And these were already new measurements. This data didn't exist before I started graduate school. Half of this came from the Calán/Tololo survey. Half of it came from the observations I acquired at Mount Hopkins. But basically, being able to refine the use of the colors and the light curve to correct individual supernovae. Learning that a fast-rising, fast-declining light curve meant that it was intrinsically dim, so you were overestimating the distance. An intrinsically red-looking supernova meant that there was dust in front of it, and you were also overestimating the distance. The opposite could bring it the other way.
So, going from this to this for the same set of measurements was essentially the essence of my thesis. The people around me who initially knew the field much better that I saw this ability to standardize SNe is a powerful tool for measuring the cosmology. So, I was the clueless kid who was starting to understand through this work, I had built a much sharper tool that we could do surgery with.
That's great. Adam, when did you first connect with Nick Suntzeff?
That's a great question. My advisor, Bob, was -- let's see. I guess, I was just going to show you this. This was our first Hubble diagrams. The green points came from the Calán/Tololo survey, and the red points from my thesis. So, Nick was a member of the Calán/Tololo survey. This predates me some, but there were good, strong relationships between my advisor, Bob, and many of the supernova people who worked at Calán/Tololo: Mark Phillips, Nick Suntzeff, Bob Schommer. So, you just sort of understood when you started graduate school that your research group was friendly with another group, so there was a lot of “prisoner exchanges” going on between them. So, Bob invited out Nick one time, and Mario Hamuy another time. You know, in 1993, I remember him pulling something off the fax machine and saying, "Mark Phillips sent me this preprint." A preprint is a thing where before you submit the paper, you might circulate it. I got a chance to read that, and that's where we understood they're using something about the decline rate, and it's improving the type on the supernovae, but Bill Press knows better ways to use the data that uses all the information, not just the decline rate in a certain interval. That was the idea of my original thesis.
So, Nick Suntzeff visited, and he was an expert in observations of supernovae, particularly on calibration of observations. He visited, and over lunch or something, I think I got to chat with him a little bit. He seemed like a smart, thoughtful guy. What I really learned from not just Nick, but all these people around me, it really seemed like everybody knew some area really well. Everybody really was a master of a niche of this project. If you really wanted to get the fundamental calibration of a supernovae right, you went to talk to Nick. If you really wanted to understand how to use a pile of numbers and tease out a particular signal, you'd go talk to Bill Press. When you wanted to understand how to make observations that night on the telescope, you'd talk to Brian, or maybe for how to get some software working.
So, I grew up in an academic family, of sorts. It wasn't like a lone advisor and his or her graduate students. It was like a clan that seemed to nucleate around Bob as this charismatic person. And from each of them, you would learn some key thing and I absorbed and synthesize all of that towards the goal I had of collecting the data and saying what the Universe was doing. There was no one aspect where you say, if I did that aspect well, I didn't have to know anything else. That was graduate school. Graduate school was -- I'm going to learn to do this aspect of this thing that nobody has been able to do this and that’s enough. But to actually do the measurement of what turned out to be the acceleration of the universe, you had to get all your ducks in a row. The points had to be along this line well, but they better be calibrated well, and you better have gotten deep enough signal to noise while you got your galaxy subtraction software to work -- all this stuff.
So, being in this group and learning from people who were really knowledgeable about one of these things, I would just constantly flit around talking deeply to these different people about the part they were so knowledgeable about. So, at the end, this was the fun part. It was like, in some ways, you almost felt like a master contractor working with subcontractors, going off and speaking to them about how we get the bathroom floor laid, because the electrical has got to come in and meet here. To me, what I learned, at the end of graduate school to being a postdoc, was okay, now I have to care about that the final measurement is right, and there are all these subparts, and they all have to be on good foundation.
Were you staying in touch with Brian by the time he had left, and you were still at Harvard?
He moved to Australia, which was tough because Australia is not around the corner, and we didn't have Zoom and things like that. So, it was emails and the occasional phone conversation. But it was very important that I had established such a good rapport with Brian that we could communicate very efficiently, and we sort of knew what each other knew and how each other thought. In many ways, we thought in the same way about how to do the science. We rarely argued about how to do the science because we understood what needed to be done. We met sometimes. We had a very formative meeting in 1996 at the CFA, where everybody from what ended up being the High-Z team, met and we talked about the project. We voted, actually, on choosing a leader, things like that.
And then, again, in 1997, where the young people -- we called them Indians -- we always joked that there were Indians and chiefs. Brian was a bit of a chief and an Indian because he ended up leading the team, but the chiefs didn't know what the Indians did, and how to do that kind of work anymore. There was a big divide amongst the people who coded computer programs and those who didn't. It was a generational thing. The people who knew how to write the software to do data reduction, and those who didn't. As I said, it was very generational. Anybody over the age of about 35 or 40 didn’t know how to do these things, and the people who were under that age did. We were in this transition from photographic to digital astronomy. What I mean is, yes, the older astronomers had used CCDs and gotten digital images, but we were doing much more sophisticated analysis of the pixels. We weren't just summing the pixels.
The big breakthrough in our field that allowed us to find the supernovae, and make such precise measurements, was image registration, convolution and subtraction. So, you could essentially remove -- let me see if I have an image here. You would have an image of a supernova. Here's the supernova. Here's its host galaxy. Our ultimate coin of the realm was the measure how bright is this spot here? And of course, it's sitting on top of other bright pixels from the galaxy. We want to measure this bright spot with respect to the background, to the nothingness. So, what you needed was an image -- here you see, it's not quite late enough, but a year later, this supernova is gone. And now, you need to take an image like this, and you need to digitally match it, align it, register it, convolve it, match the seeing, match every aspect so that essentially it could have been observed the same night as this observation, just without the supernova, and then subtract this image from this image. That was cutting edge capability in the early 1990s that Brian Schmidt knew how to do that, while a senior person like Bob Kirshner, he understood the concepts that were being done, but he couldn't sit down with you at the terminal and figure out how to do it. So, that became this generational divide for us between the chiefs and the Indians. I was an Indian, Brian was leader of the Indians, and at that point, people like Bob and Nick, to some degree, were a little more on the chief side.
Now, as your co-advisors, were Bob and Bill basically on the same page in terms of when your data was ready to be written up and defended?
They were, because it was one of those theses where the results spoke for themselves. Once you had this, people were like, “Oh, that's really something.” This is like from Science magazine in November 1995. So, people were talking about this technique and these tools and how they were going to be important. So, whenever you have a student who has moved the field in some way forward a little bit, that increment is enough so that they can graduate. So, I actually finished in just under four years, which is very short for an observational thesis. So, that must have been the case.
Adam, do you have any specific recollection of feeling lucky or privileged in real time that you sort of fell into this amazing collaboration, and you had this ability to be at the right time at the right place to gather this phenomenal data?
Right. I certainly did by the end of graduate school. Initially, it felt like hard work, and it didn't seem obvious. What I'm not telling you is there were trials and tribulations where I applied these same techniques to a pile of photographic light curves where nobody had properly subtracted the galaxy background. So, the supernova light curves -- these were the things on the right that I measured in my thesis -- were not good enough. They had large systematic effects in them, so that when I made this diagram, it didn't improve things. It made things worse. So, there were rounds in the beginning where it was like, oh my god, this project isn't going to work, I'm not going to make it through graduate school. I don't feel lucky. I also spent a lot of time studying Bayesian probability and the statistical determination of confidence at a level beyond the typical astronomer or cosmologist was learning at the time which later proved invaluable.
So when things came together by the third and fourth year, then it was suddenly like, “This is so much fun! This is so exciting! This is really great!” My advisor would come by each day. Bob would always sit down in your office on the way in. Maybe he rode his bike in, and he'd go, "Any breakthroughs?" And you know, from Bob, that always seemed like a sarcastic joke. Like, “Any breakthroughs?” “What, since Tuesday?” But it suddenly changed to, "Yeah, let me show you. Here's the new supernova. Look, you can see it's a fast decliner, so that means it's faint. Look, it started out over here, and now it's coming to the line." It felt like, yeah, these are breakthroughs. As I began making progress I developed and implemented some new ideas about how to use supernova colors to account for dust and dimming which really propelled the tools forward by 1995-1996.
What postdoc opportunities did you have available to you?
That's a great question. You know, it's interesting. In hindsight, you would have thought a lot, but not really. I applied for postdoc positions, and I got on the waiting list from the Miller Fellowship at UC Berkeley. I was not the first choice, but there was the possibility of offering more than one. Alex Filippenko, who as at Berkeley, wanted me to come to Berkeley, and was trying to get this fellowship for me, and helped me get that, but I did not come in number one. Saul Perlmutter and Gerson Goldhaber, who were doing their competing project, offered me a postdoc position at LBNL, and I got no other offers besides those two. I didn't have any other opportunities. The problem was -- there were two competing teams at this point, but I only had one solid job offer from the other team, and one waitlist opportunity.
How much interaction did you have with Saul as a graduate student, before you were thinking about postdocs?
Really, none. I really did not interact with him. Interestingly, I met him briefly during the summer before graduate school. I did a summer internship at the Lawrence Livermore National Lab, just a summer job. And when I was there, I was working in the MACHO group, and I was characterizing defects on their CCDs. So, it was not very exciting work, but they had a couple of team meetings, and this guy, Saul Perlmutter, was on the MACHO project team, so he came to a couple of those. But it wasn't anything related to supernova, or anything we would do later. Other than that, I didn't meet him again until the end of graduate school when I went to a meeting in Spain at Aiquablava in 1996. Maybe that was the first time I actually met him related to supernovae in some way.
Just to set the stage for your work with Brian --
Oh, sorry. Just to finish one thought I do want to say is, I think things would have proceeded quite differently, the history of this discovery, if I had taken the postdoc position in Saul's team and had left our team. What ended up happening was I got off the waitlist for the Miller fellowship, and ended up staying on our team, because by that time Alex Filippenko had switched from Saul’s team to our team. That was my desire. I was working with Bob and Brian and all these people, but you know, you've got to have a job. But I think, as I said, it would have gone very differently, because I was a key Indian on our side, actually doing the analysis work and I had developed a lot of the critical tools we ended up needing by 1997-1998 to analyze the distant supernovae.
To set the stage scientifically for the origin story for the High-Z Supernova Team, what was the state of play in the study of the expanding universe? How were advances in the expanding universe relevant as a -- I don't know what you would call it -- a starting off point, an intellectual foundation? What was going on at that point?
I would say it was the consequence of my thesis, and of the Calán/Tololo work, a series of papers by Mario Hamuy, that basically turned just what I'm showing you here in this plot, a bunch of points that obviously are correlated, distances and redshifts, called the Hubble diagram, to those same points precisely on the line. So, the state of play was to say, “Wow, we can measure these distances well!" We can do this further out. If the ones at high redshift, when the universe was younger, had more mass, or were born dimmer, that won't fool us because we will be able to distinguish those with these techniques and do this. So, the idea of measuring q-naught, the deceleration parameter, became very compelling. The backstory was the cosmology community was struggling to understand whether Omega Matter, the mass density, was low or high. Whether it was 0.3, as astronomers were seeing, or whether it was close to 1, for which there was a theoretical preference from Inflation, that the universe have that higher, critical mass. So, there was, I would say, a kind of missing mass problem--missing between theory and observation.
The thought was, if you go to larger scales, maybe we haven't seen the matter yet, but if you go to the largest scales and see the effect on the whole expansion of the universe, you will find it strongly decelerating. You will see a strong deceleration of the universe that will tell you if q-naught is -- let's see, Omega Matter over 2 is equal to q-naught – so if q-naught is 0.5, that will tell you that Omega Matter is 1, and we've been missing most of the matter. So, the desire was the extend this Hubble diagram that you see to the largest scales. Now, measuring the Hubble constant, the actual rate of the expansion of the universe, was a different question or challenge. That really relied on being able to calibrate the true luminosity of any of these Type Ia supernovae to get absolute distances, absolute measurements. That was, in many ways, less of our interest or issue. Even though we studied it, we tried to do it at some level, other people were doing that problem. Other groups. Our group became focused on extending the Hubble diagram.
There was a key moment-- I guess, I should add this, too. It's an important part of the story. Bob Kirshner used to go out to use the MMT, the Multiple Mirror Telescope, on Mount Hopkins in Arizona. It was one of the bigger facilities at that time for getting spectra. On one of those trips, I was with him as a graduate student, and Pete Challis too, and I think that was it. While we were observing supernovae, we got a telephone call from Saul Perlmutter on the phone, saying, "Oh, we think we may have found a supernova at redshift 0.4." We were pretty stunned by that! That would have been about the highest redshift Type Ia supernova known at that time. He said, "Could you take a spectrum of it to see if it’s a Type Ia?"
Saul was well-known for doing this. He had to, sort of. He couldn't always count on when he would find supernovae. And we were supernova people, so we took a spectrum, and unlike a lot of observers he might have called, who would have just looked at the spectrum and said, "Okay, I don't really know supernovae. You tell me if this is what you were looking for." We looked at it and went, "Holy cow!" I mean, I remember fitting the spectrum, and saying, "Oh my gosh. This looks like a Type Ia supernova at redshift 0.45!" And we gave the spectrum to Saul, but when we took that spectrum, we said to ourselves and to other people on our team, "We could do this!" We thought we could do this better than them. They're finding them, but we know what to do with them when we find them. We know how to put them precisely on the Hubble diagram. Maybe it's arrogance, but they came to it from a different angle. They were working on the hard problem of finding them. We were working on the problem of understanding them well enough to measure their distances. When we got a glimpse into finding them by seeing them do this and us being involved in this way, that was even more reinforcement. We could do the finding part, too.
Between the scientists themselves and the observatories, the High-Z team was a truly global collaboration. There were people and telescopes literally all over the planet. What was the value of that, both in terms of the sociology of it and the science?
Right. There was the reality of it that these were people who had gone to school together or had been postdocs with various people in the group. So, you stay connected to people. And it's natural for people to become far-flung. It is astronomy, after all, so it's all over the world. So for practicality it became very valuable to work with people who are going to be making measurements at different telescopes around the world at the same time, or who have access to different facilities because of their appointments in different places, that became very valuable, and very powerful.
What would ultimately become, of course, your publication in May 1998, what portions of that were directly from your thesis research? What advances had happened since your thesis research? And what did you rely on from your collaborators that you had nothing to do with?
That's a very good question. What was interesting about our work, and this is probably true on the other team as well, but I can't be as sure, is there was the constant churn of every semester, we were back on the sky looking for supernovae. We had time on telescopes all over the world to use, and we needed to find and follow up supernovae. Supernova observations are very demanding. You can't go, "You know what? I'm going to focus on the data reduction, and we'll get to observe that supernova next week when I have time." You have to find the supernova, so you get images, you have to analyze them right away, because you may have Hubble Space Telescope time, as we first had, that is targeting a blank part or dummy coordinate in the sky so you need to update the coordinates in a few days. You have people at other telescopes ready to take spectra, and this all must be done before the supernova fades. So, what was happening was once we started collecting data, a lot of the energy, focus and effort of the group moved to the assembly line sort of that time critical work.
The spectra need to be taken, the images need to be taken, they need to be subtracted, we need to identify the candidates, we need to get the coordinates to Hubble. So, I would say my area of interest and expertise really was much more on turning the data into measurements of distances and what we could say about the expansion history. I would say, I was focusing more on that by 1996 and '97, while the group was largely focused on collecting new data in this kind of way with no idea we had enough data and were close to any breakthrough as the data was mostly sitting on tapes. I also would go to the Keck Observatory with Alex Filippenko to take the spectra, but then I would go right back to work on measuring and analyzing all of the light curves.
So, getting back to your question, I had in my thesis developed a process and procedure for going from telescope images to points on that line that you see on the Hubble diagram, and some of those were directly from my thesis, like fitting them with the multi color light curve shaped method -- what we call MLCS. That was the core of my thesis. The group in Chile had their own methodology for doing that, but MLCS was more advanced at that moment, using Bayesian likelihood to incorporate knowledge about dust. Once I had reduced the light curves for what became our paper, I would analyze them with MLCS but also send them to Chile, and they would give me their results from that as well. So, in that way, it was still interacting with other parts of the team that had other techniques and methods for this. There were a few things that were brand new that we had maybe never done at this level. Things that astronomers call K corrections, or relativistic corrections, that needed to be calculated for supernovae with particular colors at particular redshifts.
One of the innovations of our time, that I think Brian and Nick had come up with were specialized optical filters that we had built to our specifications that corresponded to the redshifted light of normal rest frame filters that we had produced and sent to the different observatories. So, to answer your question, there were a lot of techniques that I had just brought forward from my thesis, because that's what I knew how to do. There were a few things that had to be developed on the fly that were new in terms of measurements and analysis. And there was a lot of energy distributed around the need to observe new supernovae. And I have to say, the most important thing that you have to really remember when you're looking back on this is we didn't know we were about to make a discovery. We didn't know the universe was accelerating. This seemed like it would be a slow burn of progress. This didn't seem like, “Oh my gosh, what's this going to turn out to be? Quick, quick, crunch the numbers.” It was like, “Well, we're going to have to collect data for many, many semesters, and we're going to have to tease out whether the universe is decelerating a lot or a little, and that's not going to be a sudden moment, because the confidence intervals will shrink, but we aren't going to suddenly know something.” So, in the fall of 1997, when I was first looking at the reduction from our first decent-sized set of data, that was a total surprise.
I'm curious, Adam, if there were any internal deliberations about the use of the word accelerating. Of course, inflation, expansion, these are all just words, and they're highly imperfect at conveying the concepts behind them. Were there any competing candidates to accelerating? What questions or answers did accelerating fail to grasp?
Right. So, I'll tell you, the way it actually started, and this is just the technical reality-- if you could see here on my screen, this is the key page to my lab notebook. I'm showing you this to really focus on, to make this point. Initially, we thought the universe would be decelerating, and that would be telling us what the mass density of the universe. So, if you look in the upper right here, it’s very simple looking, but in this expression lies a lot of cosmology, the equation: q-naught equals Omega Matter over two. And that just simply says, cosmologists have defined their terms and their units in such ways that they've redefined the variables so that they become very simple, and that is just to say that the deceleration and the mass are directly proportional, in fact, equal to each other, with this divided by two number, and so we'll observe the deceleration. That'll be the left-hand side. But the physics is the right-hand side.
The physics is what the mass density is of the universe. That’s what's everybody was asking about -- what is the mass density of the universe? Is it low, or is it 1? That it only seemed natural to always think in terms of, okay, so what is the mass density of the universe we get? So, before we thought about acceleration, because we didn't know we were seeing that, the punchline was to say, what is the mass density? So, when I first analyzed this large set of data in the summer and fall of 1997, I started out writing my computer program to fit the data after it was all reduced and the light curves were analyzed with MLCS, and just spit out what the needed mass density was, because after all, that's the punchline, without having yet noticed that the universe was not even decelerating.
The initial result, the first time I looked at it and saw something that ended up being the thing, was just seeing a negative mass density, because I'd written a really simple compute program that didn't cut off below zero mass. It didn't say know anything below zero makes no physical sense. It was just this equation, at some level, allowing me to fit anything to the mass density, and not noticing that the deceleration had changed sign to become an acceleration. So, initially, it was, “Hey guys, we're getting a negative mass density. That doesn't make any sense!” So, initially, it was in the terms of Omega Matter, and then -- this was like a little while later on my lab notebook, the initial thing that I introduced when I thought about what could make physical sense, it was the cosmological constant as the alternative that could fit the data.
So, initially, it was, oh my gosh, the Universe needs a cosmological constant! That's the only way to not be seeing something crazy like negative mass density, which is not even valid physics. So, it wasn't until that and working on that, and talking with my colleagues, and I think it was Nick Suntzeff who said, "Well, you know, another language for this is a kinematic term, as though you were doing a Taylor expansion, and after h-naught, there's q-naught. So, why don't you fit it that way?" And we struggled a bit because the equations are not as obvious with q-naught because h-naught and q-naught are both expansions at redshift zero.
So, they're not exact-the approach to describe the data with q-naught doesn’t explain or model the physics that dictates q-naught. They're only exact when you put them back in physics language of Omega Matter, Omega Lambda. So, initially I said I could use Omega Matter and Omega Lambda, and I could convert it exactly to q-naught. And when we looked at the result, we were like, right. Of course! We were in the accelerating phase, and that's what it means to have a cosmological constant bigger than Omega Matter over two, but it wasn't our initial way of thinking or looking at it. It was initially, oh my gosh, there's a cosmological constant! Or something like that. I was recently giving a talk about this.
This is why I pulled this up on my screen here. The initial email chain from me and my colleagues all talks about the cosmological constant. It says –
Alex writes to everybody on January 10th, "Adam showed me fantastic plots before he left for his wedding. Our data imply nonzero cosmological constant. Who knows? This might be the right answer!"
Bruno Leibundgut, "Concerning a cosmological constant, I'd like to ask Adam or anybody else in the group if they prepared enough to defend the answer. There's no point in writing an article if we're not very sure."
Brian Schmidt, "I agree, our data imply a cosmological constant." So, you see, all of this is about the cosmological constant.
Bob Kirshner, "I'm worried. In your heart, you know the cosmological constant is wrong, but your head tells you, you don't care, and you're just reporting the observations. It would be silly to say we must have a nonzero cosmological constant only to retract it next year."
Mark Phillips, "As serious and responsible scientists, ha! We all know it is far too early to be reaching firm conclusions about the value of the cosmological constant."
John Tonry worries about magnetic monopoles.
Alex Filippenko, "If we're wrong in the end, then so be it.”
Then I wrote, “The results are very surprising. Shocking, even. I avoided telling anyone about them because I wanted to do some crosschecks, and I wanted to get further into writing the results up. The data require a nonzero cosmological constant. Approaching these results not with your head or heart, but with your eyes. We are observers, after all."
Alejandro Clocchiatti, "If Einstein made a mistake with the cosmological constant, why couldn't we?" This was all in the course of a day.
Nick Suntzeff, "I really encourage you, Adam, to work your butt off on this. We need to be careful. If you're really sure the cosmological constant is not zero, my god, get it out. I mean this seriously. You probably never will you have another scientific result this exciting coming your way in your lifetime."
So, you can see, in the beginning, it was all talk about a nonzero cosmological constant.
Adam, this might be a question better for your wife than you, but how distracted were you during your wedding?
Yeah, well, that's a funny story because I knew this result just before my wedding. I got married on January 10th, 1998, and it was tremendously exciting, and I knew this was a really great result, but I was also concerned about it. About all kinds of stuff. But you know, your wedding is a really big deal, too, so I headed off to that. And when I got back, we were packing our bag for our honeymoon when basically this email chain broke open, which was the first broad communication to the rest of the team. Again, we were very, at that point, siloed because some people were observing new supernovae. We were spread all over the world. We weren't all sitting together.
But Alex Filippenko was in the same building as me, just down the hall, or on another floor down the hall. So, he knew this stuff. And Brian knew it because he and I were doing a lot of crosschecking, but not a lot of other people knew it. So, this email chain basically starts the dialogue, or shares the dialogue. So, when I saw this broke up, I came back from just getting married, just repacking our bags to go on our honeymoon. I was like, "Honey, I need to answer this." And she was like, "Oh god, are you going to be like all the time with work? I mean, we're going on our honeymoon." And I said to her -- we always joke about this -- I go, "This is a really important email." And her response is, "Yeah, yeah, they're all going to be important." So, every time I show this in a public talk, I always show it to her, and I go, "See, that was the important email!" with a wink.
Adam, given how exciting these results were, and the need to publish them, what consideration was given to periodicals? What magazine, what journal, what was the best place to share this data with the world?
That's another great question. Here's the funny backstory about that. Ordinarily, in astronomy, in physics, in science in general, people are very big on a Nature letter, or some sexy, short announcement. And our team felt very strongly that extraordinary claims require extraordinary evidence, and we could not say that we were seeing a cosmological constant, or the universe was accelerating, in 1,000 words, limited to two figures, or such requirements for a letter. We wanted to show, as I think is the right thing, we had the goods. We had the goods, we had the data, we had the tests, we had the crosschecks. All that stuff.
So, our group shortly after broke out into an argument about, should we go for the exciting, Nature thing, or should we write what we called “the War and Peace” version. What resolved this discussion was that before discussing with the team, I had already written a lot of the War and Peace version. So, for the people who wanted to go for something quick, the War and Peace version would actually be just as quick because it was mostly done. And the truth is, having worked in a lot of collaborations, it sometimes takes longer to write something short, because you basically can't answer everybody's questions, or satisfy them. You keep saying, we're up against the page limits. We're up against the word limit.
The beauty of a longer paper, once you realize that, is you could answer everything. People have a concern; you could show something. So, quickly, once we realized it wouldn't slow us down because I had already written most of it, and we could use it to answer everybody's questions, then everybody agreed. And then, we just didn't care where it went at that point. It was like, people will see and hear about this wherever we publish. This whole notion seems moot-- I think when you look back on discoveries, you don't think, now what journal was that in? You know?
As the email thread conveys both excitement and caution, how important was it for you to replicate that in the publication itself? In other words, what was like the bullhorn moment for you, and what was the place where you wanted to protect you and your team because some things might have still been provisional at that point?
Yeah. You know, it was really great to have the team we had. We have a lot of skeptics and cautious people, and they provided great sounding boards. You talk to Nick, and he would go, "Well, how do you know the atmosphere is gray, and that when you have non-photometric observations which means cloudy weather that you can really measure light curve points?" And you'd go, "Yeah, how do I know that?" And you would go and do these little research projects that were instigated by these very smart people who knew just what question to ask. So, you never really drank your own excitement or Kool-Aid. You would always be like, "First I've got to convince Nick, or I've got to answer Mark's question," or whatever.
So, I quickly switched into that gear by having these people asking me the tough questions and still being a very young guy in the field. It was like, yeah, got to answer their questions. I quickly switched into that mode, and the paper, I think, very much reads like that. Like, here's three caveats, and why they're not a problem. And here's four concerns and the tests we've done as a result of that. And you might have been worried about X or Y, but here's what we have to say about that. I would say, the paper ended up being a very methodical walk-through FAQs.
To what extent were you prepared for how the paper was received?
Not at all.
I mean, this is a fire hydrant that opens up. You're just not ready for this.
Yeah. And you know, there's scales and there's scales. When you're a graduate student and a postdoc, you're like, "Hey, we're going to say a little something. We're going to add a little word to the great book of science." That's exciting. That was already excitement to me. And looking back on it, my gosh. What I really think about it is I had no idea. And I'll tell you, the best example of this was we're having the email dialogue in January. Somewhere along the way, in February, this reporter from Science magazine who later wrote for the New York Times, Jim Glanz, got wind of this story. It may have been when Alex and Saul talked about it in a very preliminary way at a February conference or it might have been from Don Goldsmith who haunted Berkeley and was an astronomy writer himself. But basically, Jim Glanz contacted us -- me and other people -- and said, "I'm going to write about this. I'm going to write a story about this in Science Magazine." But we didn't quite have the paper done! This was in February and was very uncomfortable because we wanted to have completed our documentation.
But this is sort of the way the media works, right? They were like, "We're going to talk about this anyway. We're not waiting for you to have your official paper." This was shocking to me as a first, second-year postdoc. Like, “A media person is going to talk about this? That's so weird! Why would he do that before we say so ourselves in our paper?” And then, he put out a story in Science magazine, and I came into work the next day on my bike, and my phone is ringing when I open my office door. And it was unusual for anyone to call me in my office except for my fiancé. When I opened my office door, it was ringing. I picked it up, and it was CNN. They were like, "We have a crew on the San Francisco Bay Bridge. We can be to your office in 15 minutes. We'd like to talk to you about this accelerating universe." And about what we would call dark energy, or the cosmological constant. I forgot which word they said. And I was like, "What?" I'm a postdoc. I've never -- you know, what? This was crazy! And CNN came and filled the halls with media folks and interviewed me and that immediately appeared on TV.
And then, later that day -- and by then, I'm just getting tons and tons of calls from the media and stuff. And later that day, I got a call from the MacNeil/Lehrer Newshour on PBS. "We'd like you to come in and talk to us about this live." Where for their live show they have many millions of viewers. You can probably find it online. This was just completely bonkers to me. Completely bonkers! Anyway, that was the paper. So, all I could say is, I was completely unprepared for that. Unprepared for how to talk to the public about it, even how to think about it in that way. Certainly, that this would become like a household sort of thing. This became the Breakthrough of the Year for Science magazine in 1998. A breakthrough that at the beginning of the year, or late the prior year that I didn't even know about.
Now, in 1998, of course, Michael Turner coins the term, "dark energy." Does that register with you right away?
You know, Mike Turner had a way with words. I don't think, initially, I understood why that was a good term in the way that the history of cosmology has gone, but in hindsight, I think it is a great term. I don't think I appreciated it. I just thought, well, the cosmological constant. But Mike talked about this -- the idea of it was a more general phenomenon that it could be more of a fluid, it could be more of a field. Really, what it is, is most likely, energy in space. But what is the origin of that energy? That's the question. And in cosmology, there's a history of, you just call anything dark that doesn't produce photons of light that you can see. So, it was most literally dark energy, as a kind of yin and yang to dark matter. And of course, it makes perfect sense, but again, not having enough perspective on the field, it was like, "Oh, okay. Mike Turner says it's dark energy. Okay, yeah. Well, I guess a cosmological constant would be a dark energy." But I really like it, and I think it's perfectly correct and appropriate.
Now, when does Chris Stubbs enter the picture?
Well, Chris Stubbs had been on the team since 1995. He was leading a research group in Seattle, Washington, at the time, where he was a professor. He had a couple students, and they were working on measuring some light curves, and interested in Type Ia supernovae. Somehow, when the team nucleated, he joined, probably through a connection with Brian, or maybe Nick, I'm not sure. And then, he was on the team, and he had his students, Al Dierks and David Reiss -- no connection to me, different spelling of the last name -- who had done an earlier, very small, like two supernovae analysis that didn't get any definitive results. So, they were on the team. He was more of a chief at that point as well.
What were some of the advances, either in the instrumentation or even computers, that allowed the so-called Higher-Z team to do things that the High-Z team could not?
The Higher-Z team was a follow-up project that I led, starting in the early 2000s, to find more distant supernovae at redshift greater than one using the Hubble Space Telescope and its Advanced Camera that was installed in 2002. The big concern still on our minds, even after the discovery, was what if there was some kind of gray dust in the universe that filled space between galaxies, and made distant supernovae look fainter? Or what if supernovae were born with less luminosity in the past. Now, we had an important test even in our 1998 result, by comparing Type Ia supernovae in old and young galaxies, but nearby, we saw that the light curve and color standardization worked pretty equally well. So, it was like, the Type Ia supernovae didn't know or care, once we standardized them, whether they had come from an old or young galaxy. The concern when you're measuring acceleration is you're comparing supernovae when the universe is young to when the universe is old. So, it was a reasonable proxy for what we were trying to do, to check special locations where the galaxies were young and old. But the concern was still, what about gray dust? What about something else?
So, the concern was, when we were looking at distant supernovae, we were saying, "Oh, they look faint. They must be far." And the conclusion was the universe is accelerating. But what if when we were looking at faint supernovae, they weren't really far. It was just clouds of intergalactic gray dust, which is an idea that theorists invented in 1999 just to explain what we were seeing.
So, this is a problem with both land-based and space-based telescope. This is not ozone atmosphere stuff.
No, no, no. This is in between the galaxies. So, the idea would be relative to a low-mass universe, or relatively empty universe, that the supernovae we were seeing at redshift .5 or so were fainter, and we thought it was because the universe was accelerating. This reddish brownish curve you see here is trending up here. That's what happens because of an accelerating universe. That supernovae at redshift .5 will look relatively faint. But what if instead it was dust or chemical evolution, these orange curves you see here? Well, the key distinction was, go to even higher redshifts where these curves part from each other, because the reason this happens is, for the real cosmology, when the universe is more compact, when it's younger, it's more dominated by the attractive gravity of dark matter. So, it will be decelerating before it began accelerating some 5 billion years ago.
Instead you're looking through longer and longer paths of gray dust, or supernovae are just born fainter and fainter in the early universe, the curve will continue to rise like this, just looking fainter and fainter. So, we had to find supernovae at redshift beyond 1, and the problem is that they're just so darn faint that you can't really do that from the ground. Here's a ground-based observation of a distant supernova and its host galaxy, and the same thing seen from Hubble. And you can see how well you can separate the light of -- because Hubble has better resolution, it allows you to find the supernova here, and it was just too hard to do that from the ground over here.
So, what happened was in 2002, the astronauts put a wide field camera onto Hubble, the advanced camera. And I led a project, joined with another team called the Goods Team, which wanted to use that camera to mosaic large parts of the sky, to do that every 45 days to search for supernovae. So, for the first time we were using Hubble as the actual supernova search engine, and that allowed us to find Type Ia supernovae at redshifts beyond 1. So, we tiled two areas of the sky every 45 days, digitally subtracted the images, found the supernovae, measured their spectrum to make sure they were Type Ia supernovae, measured their light curves. So, here are some of those supernovae. And ultimately, when we returned to this diagram, we were able to extend it to higher redshifts and see the turnover in this Hubble diagram, which in my mind, and in a lot of people's minds, ruled out the possibility that it was some kind of astrophysical dimming -- some dust or evolution -- but was actually a decelerating followed by accelerating universe. Of course, around the same time or so, cosmic microwave background observations started coming out showing that the sum of all energy densities in the universe, matter or dark energy, was 1. Therefore, that was very strong support for seeing what we were seeing, the 0.7 in dark energy.
Now, we've been so strictly on the science side of things. To go back to the job/career side of things, of course, in 1999, you joined Space Telescope. So, I'm going to guess, and you can tell me how off this is, by 1999, you are a hot commodity. There are lots of people who are interested in you. Are you specifically not wanting to take a faculty position because being in a research environment allows you to fully focus on the topic at hand?
No. The truth is, I was not such a hot commodity in 1999.
Wait a minute. How is that possible? How can that be? You're not getting overtures from like Caltech, Stanford, Princeton?
Nope. I'll tell you why, I think, is the same phenomenon I said earlier, when I didn't get tons of postdoc offers, is I'm still working with a large team of people, and everybody from the outside, they're never sure who's really doing the work there. They're like, I know Bob Kirshner. He's really good. I know Nick Suntzeff. He's really good. I know Alex Filippenko and Mark Phillips. They know the chiefs, but they don't really know the Indians. What happens on big teams is people know the chiefs, but they don't really know the Indians. So, people aren't saying, "Wow, that was great work you did." They're saying, "That was great work from the team." I'm not often getting invited to give the talks about the work. So, when I apply for jobs, I got an offer at Rutgers, I got an offer at Brown, and NYU, and at the Space Telescope Science Institute. I didn't get on the shortlist for some of the places that admittedly are more like the top 10 in our subject.
Did you feel that Space Telescope was specifically a good home base for you?
Of the options that I had, I thought it was. I thought the work with the Hubble Space Telescope seemed very exciting. When I went there, it felt like they had a real mission. I liked the whole kind of NASA mission kind of world. So, that seemed very appealing.
What was the environment like there? Was it collegial? Was it intense?
It felt collegial. It felt mission focused. It felt like everybody was for a purpose to run and feed this telescope that's the world's most advanced science instrument. That felt like something really exciting to be a part of.
Obviously, it's very difficult to separate what you were sensing at the time versus what ultimately would happen, but when did the buzz start to build that the Nobel Prize is coming?
That is tough to say. I would say, after the confirmations. So, the cosmic microwave background that I talked about, very important. This turnover in the Hubble diagram that we saw at higher redshifts. Then, it became clear that this was true. So, the first step, is I would say, that point. I think, in 2003, the breakthrough of Science magazine was cosmological consensus. So, I would say, it took five years after the discovery, or so, plus or minus, to say, everybody pretty much thinks this is right. And then, there was discussion, well how could there be a Nobel Prize? We don't understand what dark energy is. But some people pointed out that acceleration is so fundamental it’s a basic discovery no matter what explains it.
And then, of course, there were a lot of various people involved. So, people would say to me things like, "I think you'll win the Nobel Prize," or "I think this will win the Nobel Prize," or something. And there were a few earlier recognitions. Probably one of the biggest ones in 2006 was the Shaw Prize, which was a new Hong Kong prize. That went to myself, Brian Schmidt, and Saul Perlmutter. When that happened, that was maybe the first time when it was like, gosh, I guess these prizes really exist, and recognition like this really could happen. But until then, I had heard so many things like, "It's crazy dark matter never won the Nobel Prize. It's crazy inflation never won the Nobel Prize." You just didn't know whether it's a complete fantasy to ever even talk about that. There's nothing official. Nobody ever says, "So-and-so was up for the Nobel Prize, and then they got it, or didn't get it." Everything is very secretive and mysterious.
Although, Adam, I'm not sure if dark matter or inflation are fair comparisons because the question marks that were there from the beginning remain there. There's no more question marks with the accelerating universe.
Yes, and no, on the side of dark matter, what you might actually say is something like flat rotation curves in galaxies would be the equivalent fundamental discovery. For flat rotation curves we know the luminous matter we see wouldn't explain that fact. Therefore, there is something else matter-like causing extra gravity. So, you could draw an analogy to the acceleration and say it’s like seeing the universe is accelerating and matter of any sort wouldn't do that. It's something else, something energy-like. It's beyond the attractive gravity of stuff that we're familiar with.
So, it could have been the case that you would have recognized the empirical evidence that leads us to believe there's dark matter in the same way of the empirical evidence that leads us to believe there's dark energy. It’s not quite the same for inflation, that is trickier because the discovery is quite theoretical. And of course, I saw the paper we had written was getting more and more and more citations every year. It wasn't falling off. It was thousands and thousands of citations. So, then there were people who analyze citation statistics saying, "This is our shortlist of Nobel Prize possibilities," and they would put us on their list.
And then I got invited to go to Stockholm a few times for various reasons, like to be on a defense for somebody's PhD defense, or I was invited to give a talk. And one time when I went a professor there invited me into his office and said, "Okay, I'm the secretary of the Nobel Prize physics committee, and I have a few questions to ask you." And he asked me some questions about how the science was done, and what were we thinking at this juncture or that juncture. And he also said, "This is the way this works. I'm going to ask you some questions, but you can't ask me any questions." And he took careful notes, and he came to my talk and took some more notes. And that was it. Obviously, he was just collecting knowledge and information. So, a number of things like this happened. Other prizes, lists of citations, conversations with colleagues who would say that we should win the Nobel Prize, and all this put it on my radar screen as something that could happen, but also might never happen, or might not happen for 40 years.
I'll ask this question kind of out of chronology, sort of as a foreshadowing, but I'll just share with you, when I was talking to Nick Suntzeff inevitably about who won the Nobel Prize, who didn't win the Nobel Prize, the problems associated with this, I shared with him that in my job, I'm very privileged. I have interviewed almost every living Nobel Prize winner, and a theme that comes up is the way that this level of recognition can derail the science because of all of the distractions. He interjected right away and said, "Well, it hasn't slowed down Adam. It hasn't slowed down Saul." So, as a way to foreshadow your reaction post-2011, did you do a good job in the run-up to 2011 to try to not let these prizes and things like that be a distraction to the science and the most important things at hand?
I would say, in hindsight, yes. I can't say that was deliberate in any way, because obviously I didn't know that was going to come. But it was just simply, the more I worked on these areas of cosmology, the more I thought, “This is great! This is amazing! This is what I should be doing! This is so compelling! I love this stuff! The science is fascinating, the process is great, I love it.” So, it was just natural to me. I guess, if anything, I would say the success in these projects just convinced me that I should keep working in this area. This was what I was good at, so the idea of getting distracted or doing other things, was like, distracted doing what? You know, what was I better at doing at that point than just keeping on keeping on? In particular, we were creating new questions to try to answer. When you would find a result, you would say, "You know what we should have done? We should have gotten the data this other way." Or "Now, we should do this experiment." And then, that's what I wanted to do. So, it just seemed natural. Like, you ask a kid at Disneyland at noon, "Are you ready to leave?" They're like, "No. This is fun." So, that's really why I didn't get distracted, because I was in my heart still an Indian, and I was doing what Indians did. It was fun.
Where were you when you got the call from Stockholm?
Well, I was in my bed. It was 5:30 in the morning. The night before, I had had kind a Johns Hopkins meeting. It was a dinner at the president's house. I was with Chuck Bennett, who was P.I. of WMAP. We joked with each other, because at that point we were getting these annoying calls from the university press, always the week before. "We need to work on a press release just in case you win the Nobel Prize." We'd say to each other, "This is so stupid. We shouldn't be asked to do this. Nobody should write a press release about something that didn't happen." And they'd just do it for both of us. So, we'd joke, like, "Oh, well, hope you win the Nobel Prize tomorrow," because we knew what day it was. And one of us said, "All right, if you do, I'll bring in donuts." We were just joking.
And we went to bed that night, and at the time I had a 1-year-old and an 8-year-old, and my wife and I were lying there. It was 5:30 in the morning, and I heard my 1-year-old kind of making noise in his crib. I was wondering as parents do, is he going to stay asleep, or do I have to get up? Anybody's who's had young kids, there's that careful transition moment, where if you don't disturb them, they just might go back to sleep. And then the phone rings. And I was like, "Oh my god. This is ridiculous. What jerk is going to tease me and call at 5:30 in the morning the day when they call for the Nobel Prize?" Because, as I said, for a few years, I was on alert because the Hopkins press office insisted on vetting pre-press releases with me. And that's where I was.
What did it feel like when you got the call?
It felt like a dream sequence, or not anything like reality. It just seemed bananas, and it was bananas. Not only was it bananas on the phone, the moment I hung up the phone it was bananas. Everything was bananas. My phone was ringing, media people came to my lawn, Hopkins sent over a press person. I did come into work a couple hours later, and there was a giant banner across the building. I don't know how they got that printed up. There was champagne flowing. My office was filled with reporters. It was utter bedlam. And of course, we immediately thought about the team -- Brian and I made radio contact. We told each other: “We’ve got to make this a team thing! Got to involve the team! This has to be a team thing!” So, we began coordinating that.
Now, the collaboration, obviously, the problem of who gets recognized and who does it, it's not nearly as acute as, say, LIGO, where there's orders of magnitude more people. I mean, High-Z is big, but it's not as big as LIGO, right? So, the sensitivity is perhaps not as extreme, but still. Nick is first and foremost among them. It's highly problematic that some get recognized, and some do not. Emotionally, how did you deal with that?
You know, I'm a sensitive soul, so I knew how certain people felt or would feel. That was easy to know.
You mean, empathetic. You feel what other people are going to feel.
Absolutely. I'm an empathetic soul, and so I knew that, and it was clear to me from the beginning. I mean, this is the hard thing, I was sensitive right away, and I had thought about it. There are different ways this could go, because you're not in control of it, and will it be okay or not? There is a feeling, look, everybody may not be okay with it, in the sense that they wish it had gone a different way, but there may be a difference between what people are okay with, and what is right, in some way, what is reasonably fair. I think Brian and I understood, or speaking for myself, that what they did wasn't crazy. The way they did it involved a fair bit of thought and research, and if you looked at how the work went down, this was probably the best they could do within the framework of their rules. Thus, severely limited by these rules -- three people. The best would have been to recognize the two teams straight and flat out. But as trained physicists you learn early about the byzantine and strange rule of the three.
So, if that is really a hard limit, then this probably wasn't crazy. As I said, we had seen some other prizes and things like that that had been similar. There was one prize that recognized Brian and not me. There was something that recognized me and not Brian. Saul was always recognized which is what we expected. And then, there were people who had been chiefs who had trained us and educated us who were very instrumental in starting the project or had given really critical advice in different parts of it. So, we reached out to those people right away and tried to make it as broad and celebratory a moment, and yet, understanding that some people would still feel bad about it. We did get feedback in the beginning that there weren't people who felt like it should have been them instead of us, let's say. I think it was mostly like, they would have liked to have been included, and it sucks that these rules are such that that doesn't seem an option. But that seemed quite out of our hands.
I'll share another piece of wisdom from Nick, and one that's really quite magnanimous, and that was his recognition that ultimately, this science is supported by taxpayers. And taxpayers need to have a visceral connection with a face. So, awarding something on the magnitude of a Nobel Prize, you don't establish that connection with a team, an anonymous team, but you do with individuals. People that you can see, who you can see speaking, and things like that. Does that resonate with you at all?
I have never thought of it that way or heard that. That's very interesting, and I would agree with it that I think that is true. But I would also add that you have to remember that the person, or people, who create these prizes are philanthropists, benefactors, but mostly captains of industry in some way who have created something. So, I don't think that is what they were thinking when they limited the number. I think they're thinking of themselves. I think they think that in many cases they were heroic, special characters, and they created something, and they want to find the versions of themselves that if they'd gone into science or done something else that is who they would want to recognize -- that's the way I've often thought of it. You're this philanthropist, and you want to find the people who you think of yourself like.
Alternatively, and this is closely related to that, is they may think they want their prize to be so special and famous, and they don't want it diluted by -- let's just say for argument's sake that the LIGO team won the Nobel Prize, and it's 1,000 people. And now there are 1,000 people walking around saying, "I'm a Nobel laureate." And after ten years, you have maybe 10,000 such people, and after a while, it's very common. And then it might lose its specialness. That might have been an unappealing thought to a philanthropist who starts a prize. They don't want it to be common like a participation prize. I mean, none of these are great reasons, in that I would much rather have prizes recognize teams, because teamwork -- not only is it important. I mean, you take out critical pieces of a team, who says whether the thing ever occurs or not? So, we shouldn't focus so much on who did more than other people, or whose contribution was more critical, because "more critical" is an oxymoron. Many pieces are critical. So, that would have been the best thing, and the right thing in my mind. It's just not in the way they do it.
As I'm sure it dawned on you at the time, your Nobel lecture would give you essentially the biggest platform there is for a scientist. What did you want to convey in this very special opportunity about your work, about science, about the nature of collaborations, about how the universe works? What were the kinds of things that were most important to you?
It's funny, this might sound very unambitious because when these things have come along, they've always been much more than I expected. So, my ambition of, like, when I'm a Nobel laureate, I'm going to tell people the way things are or should be isn’t on my mind. In each of these moments where I feel a bit overwhelmed by it all, I fall back on trying to be as accurate as I can, and I just want people to know what actually happened, as though anthropologists or historians are going to be scientists themselves, and I want them to know this is really what happened. They may someday be trying to put together a great theory about how these things happen, and I better explain the experience correctly so they can do their study. So, that's what I've tried to do.
I take out things like my lab notebook, or the initial paper, or the words that were used in the emails. Like, when you asked me, when did accelerating universe become part of it? So, I went back to the words, like, oh look, everybody is saying cosmological constant. That's the fact. That's important. You wanted an answer to that. I don't know whether it'll fit into your theory, but I have to get the story right. So, what I was mostly thinking at that time was I want to tell this story as the story happened. Where the data came from, how we thought of it at that moment. I want to get it right for people, historians, or whoever else wants to put together the story. We're still just one discovery in many discoveries. People want to know how discoveries happen, and then they want to collect the data on discoveries with all the anecdotes and pieces. I better get that right and not aggrandize it or tell you the way I think discoveries happen. How would I know? I've only been involved in this one.
Did you ever have a sinking feeling as the excitement started to dissipate immediately around that, but you recognized the intensity of interest is not going to go away for the long term, did you have a sinking feeling that you would be distracted from the science?
You know, I've always felt like I had the ability to say no to things if I needed to. I didn't feel -- and maybe, again, this comes from not feeling like I'm some superior human being that I need to be now stepping on greater platforms. I've always heard the remark about Nobel-itis -- this disease of either losing the ability to do work after that because of this, or drinking your own Kool-Aid, and thinking, “Now I know everything! Now I'm super smart and wise, and people will ask me things.” And they do ask me things, but I remember I'm really knowledgeable about a specific something, and I'm good at doing some specific things. So, that's what I'm good at, so not to start to become something else, or to claim I'm now wise about how we cure, I don't know, certain problems in the world. I'm more likely to give bad advice on that because it's not in my wheelhouse.
On the question of platforms, have you ever involved yourself in any of the things that Nobel Prize winners do in terms of being a signatory and talking about things beyond your wheelhouse?
Yeah, sure, sure. I'm very interested and concerned about climate change, so I've been involved in that. I've written letters, and signed letters, and talked to people, and done events to publicize that. I describe it as; this is a critical problem. It's scientific in nature, in that we can study it like a science problem, and we can find solutions in a science way, and the conclusions can be first drawn scientifically before we decide on policy. Let's stop stopping that process. It's been horrifying to me to see the politicization of many problems. I often joke, if dark energy had political aspects to it, nobody would believe in it. It would be highly controversial, because, you know, sure, people could get in there and go, well, if I throw out this data, and I don't look at this, and I choose this, and then the evidence is gone. That’s where we are with lots of modern science problems that have become highly politicized. So, I feel sympathetic about that. I worry about that. Education is also very important to me as well. And the usual set of things that come along to Nobel laureates, where they're asked to sign this letter, or that letter, or give their approval on this. I do that as well. But I still spend most of my day doing the kind of research that I do.
Another problem with “Nobel-itis” is the public misperception that the discovery means we've wrapped it up, we've figured it out, we can all go home now, when the reality is we're now just getting started because we can now ask questions that weren't even possible. To that end, just to bring things up to date, the past ten years, how has the science changed? What new opportunities are available?
Ironically, we've reached this consensus, but the consensus was a more phenomenological or empirical one, like yep, this is the way it looks. And that was in the early 2000s. Then we undertook ever more precise measurements and tests, some of which have reinforced that. Others, more recently, have indicated tensions with that. I think the reason that other kind of Nobel-itis problem you talked about where, the, “Yep, it's all wrapped up,” is not an issue for us is because even from the beginning we knew it wasn't wrapped up. We created more of a question than an answer. What is dark energy, was a question nobody had before the universe was accelerating. It became more like, “Why is the universe accelerating?” Dark energy. “What's that?” I don't know. I mean, that became an immediate boom, boom, and there was no chance to do be smug. It was always, “Whoa, we've seen the tip of an iceberg.” “What's the iceberg?” So, that was never a problem, and I would say, it's continued to be very compelling to try to answer those questions. The pace hasn't always followed -- you know, 1998 was watershed, but it's still been very exciting.
What have been some of the advances in the telescopes, in the world, broadly, of observation, that are allowing things now that wouldn't have been possible or even conceivable in 1998?
Yeah. So, since 1998, specifically for the work I do it would have to be the new instruments that were put up by the astronauts on Hubble. The Advanced Camera; the Wide Field Camera 3; the new infrared capabilities; wide angle surveys all over the sky; surveys like Pan-STARRS or ZTF, that basically can observe the whole sky every week to find transient objects, supernovae; other satellites; the Gaia European Space Agency mission to measure parallaxes; the cosmic microwave background satellites; WMAP and Planck; of course, LIGO. So, there's been tremendous amounts of improved measuring and observing capability for the universe. That's why I said from early in our conversation about theory versus experiment, I could talk all day about the tremendous experimental breakthroughs or progress, and what they're teaching us, which has been a lot. When I make that parallel for theory, it's very small.
Just because I talked to Joe Silk recently, it's on my mind. He's excited about moon-based telescopes in craters at the South Pole of the moon. Regardless of feasibility and budgeting to make it happen, is that something that would be particularly exciting and relevant for you?
You know, I'm not saying you couldn't do anything interesting there for what I do. It would just be like an interesting telescope sight, which would have the natural advantage of the kind of resolution we get from space, but it would come along with lots of complexity. Not just the dirt and debris that would get kicked up on the moon by the people working on it, but at the end of the day, anytime you're doing a big project like that, it comes down to the politics of the financing, and who's for it and who's against it. You would quickly become the tail wagged by the dog. The efforts and interests from the astronaut side, and the capabilities, and the rockets, and whatever, would trump whatever your -- you would become kind of window dressing, I think, for that. So, my concern is, I can't read those politics in the long term and know whether it would be worth putting time and effort and energy and passion into that. If they were saying, "We're absolutely going to the moon. It's absolutely happening. You give us the payload, we'll put it there." All that stuff, then I'd get excited about it. But when I look at it from what I think is more, in my mind, realistic --
On the budgetary and administrative side of things, of course, at least peripherally, you were witness to the DOE's transformation into becoming an agency that supported astrophysics. I'm curious, what are some of the long-term implications of having the DOE, and not just the NSF, as a prime source of funding opportunities for the next generation of observations and experiments?
Right. It hasn't been much of my focus, because I've always been on the more, I'll say, the NASA side, or the NSF side. So, I've never directly really had a DOE grant, or leveraged DOE assets, or anything like that. I mean, I certainly welcome and am glad they've come into the field. I see it more as the coming of fundamental physics to cosmology as much as anything, that DOE people are interested because they recognize the physics you do with particle accelerators is informed by the physics you do in cosmology, and that cosmology has become a serious, quantitate, and rigorous subject, so that it interests them now. It's not just like looking at pinwheel galaxies and speculating on whether the universe is expanding.
So, I've appreciated the rigor they bring, the interest they bring, and it sort of has solidified to me in my mind the way cosmology has changed. I have witnessed the transition to what we call the era of precision cosmology. To me, that goes hand-in-hand with the proposition that, “if you build it, they will come.” If precision cosmology is a real thing, then the DOE will be interested, and they are. So, to me, what's had more of the impact is the changing of this field that I've gotten to participate in to become precision cosmology.
To return to an earlier comment you made, I'm glad you hear that you're satiated, and you're not drowning in the data right now. But if I understand the trend lines correctly, what's coming in the pipe, in terms of all of the experiments and observations? Where do you see AI as a vital tool in dealing with all of this data? Is that going to be part of the mix, or is that only going to be an imperfect and temporary solution?
You know, AI will be, probably, good and important for sifting. But especially when you're drowning in data -- you should never drown in data. What you should be able to do is figure out which parts are the most important and how to find them. When we were looking for supernovae, it was a needle in the haystack problem. The danger is to not get infatuated by the haystack, but rather, keep figuring out where the needles are. Okay, you've got bigger haystacks. That's a chance to find more needles. But I hope we don't drown, because I hope we're smart enough to stay focused on what it is that we need to get out of that data. Not every pixel on the sky is important to study, but it is important to sift. So, AI can help with that, but AI is not going to tell us what we should be doing, or why we should be doing something. It'll just be a tool, I think, to help us sift faster.
Just to bring our narrative right up to the present, in the past two years, what's been most important to you? What are you most focused on these days?
I'm focused on something called the Hubble tension. The Hubble tension is basically an inability to connect today's expansion rate seen from the early universe from the cosmic microwave background, in concert with the cosmological model which includes dark energy, to what we empirically measure to be the expansion rate today. This value called the Hubble constant, there's a disconnect I've been seeing on the work I've been doing, about a 4-5 Sigma difference between what you would predict together with the early universe, and the cosmological model as we understand it, and what we actually see. It tempting to think that it may be a clue to something missing in the cosmological model. So, I've been working on refining those measurements to see if it points to that or not.
Now that we've worked right up to the present, Adam, I'll ask for my last question -- it'll be a really big question that's both retrospective and forward-looking. It'll touch on one thing we haven't yet talked about, and that is your role as a mentor to graduate students. So, as opposed to a graduate student who's thinking about pursuing a career in particle theory, where that might be a very iffy proposition based on what's possible and looking out a decade or two into the future.
Obviously, in the world of observational astrophysics and cosmology, you can correct me if I'm wrong, but my sense is that's not a problem in terms of exciting things to work on. Whether there are going to be jobs, that's an administrative question, but in terms of the science itself, there's no question that there's fundamental work to do. So, to the extent that you can extrapolate your own luck, your privilege, your talent, being in the right place at the right time, being so well-served by Bob and Bill, what are some of the things that you bring from your own experience that you can transmit to your graduate students, because in all likelihood, one of them, many of them maybe, will have the same magical moment that you did in the mid-late 1990s to take things to the next level, just as you have?
I don't know why, maybe it's just more my nature, but I've taken less of this sort of chief vs Indian role, like I just need to tell students how to do things and then they go forth and do them.
Maybe that's because you haven't accepted that you're a chief.
I think that's correct. I guess I’ve always preferred the “player-as-coach” model, like how in baseball there were certain players who were also coaches, and they played on the field. I like to be more like that, where I have research projects I'm working on to gel with research projects I've suggested to my students and postdocs. And we kind of work together in some ways, and I talk to them at a finer grain level of, “What are you stuck on? What is hard? Where should we go with this?” I enjoy that. I enjoy the teaching of how you actually do detailed steps to how you draw scientific conclusions. So, I think I've worked in that mode.
And largely, also, because I feel like I can model being a scientist by being a scientist. It's a different way, I think. One isn't better or worse, but they are different experiences. I've had a number of graduate students, postdocs, and whatnot, who have graduated all the way to professor. All I can say is, like any of us who have kids, we always say, "I'm not going to raise them the way my parents did me. I'm going to do some different stuff." So, I would say I'm in that mold, and maybe the next generation will swing back the other way. I like to be, as I said, much more doing science side-by-side with my charges.
Just as a follow onto that, for you personally, what are you most excited about? What are you most optimistic about for however long you want to be active in the field?
Well, some of the new projects and experiments coming along. The James Webb Space Telescope is going to be the largest change in my area in 20-25 years. That's supposed to launch in the fall, and I was awarded time on it for the first cycle.
And that's on schedule? Fall seems feasible.
Yep, October 31st. At this point, we're getting so close, and it's packed up and everything. There may be launch delays, but they're not like, “Oh, we need to build something that took longer.” So, instead of October, maybe November or December, but it's close. And then, some of these really large-scale facilities coming online, that if you know what you're looking for could be very powerful. Science questions, of course, still, what is dark energy, to more fine-grain, what is causing this Hubble tension? I still can't wait to see, when LIGO goes back up, what else is out there in the dark. They were up, now, seems like a long time ago, and a short time, and I feel like there's way more there.
Of course, I can't wait for COVID to end, and get back to meeting with my colleagues, going to colloquia, and going to conferences. And meeting with my students, I'm working with students now for almost a year that I've never met. It's just not the same, especially for my model of advising where I'm much more of a player-coach. I want to be there with them. So, just getting back to normal will feel like tremendous progress.
Adam, it's been fantastic talking with you. Thank you so much for doing this.