Saul Perlmutter

I arrive at the corridor that leads to Saul Perlmutter’s office in the early afternoon as he wraps up a weekly group meeting with his research team. He is slightly built, wears a casual buttondown shirt, and has wire-rimmed glasses framing an effervescent pair of blue eyes. It is Thursday, the first opening he has to meet with me this week after being away on business. We exchange a quick hello before he hurries into downtown Berkeley for an appointment while I get the chance to speak to the members of his research group. Upon returning, he sits down at his desk for about five seconds in the hope of checking his email when Cathy Thompson, his administrative assistant, briefs him on the upcoming schedule. Several appointments still need to be met, there is a seminar scheduled in half an hour that he’ll want to attend, and then he leaves town again in two days. He glances at his watch and realizes he needs to meet with one of his group members before the day is through, and in order to squeeze in the interview with me he’ll have to settle for being a little late to the seminar. No time for email after all. Such is a typical day in the life of the University’s newest Nobel laureate. Last fall Perlmutter, who holds a joint post as Professor of Physics at UC Berkeley and Senior Faculty Scientist at Lawrence Berkeley Laboratory (LBL), was awarded the 2011 Nobel Prize in Physics along with fellow cosmologists Brian Schmidt and Adam Riess, officially “for the discovery of the accelerating expansion of the universe through observations of distant supernovae.”

The heart of the research leading to the prize was conducted in a pair of landmark studies that Perlmutter and his colleagues published in 1998 and 1999 on supernova explosions that occurred in galaxies in the distant past. A supernova is the explosion of an aging star, a cataclysmic reaction that emits so much light that a single event will outshine its entire host galaxy and can be viewed from Earth at a distance of even billions of light-years. These explosions— some of the most violent in the known Universe—have earned supernovae a place in popular vocabulary and imagination.

Credit: Lawrence Berkeley National Lab

Perlmutter became interested in the supernovae for a different reason. It turns out that a special class known as Type 1a supernovae, which originate from white dwarf stars, explode with surprising regularity in the Universe, and that every Type 1a supernova occurs with nearly the same brightness. Because of this, Perlmutter’s group here at UC Berkeley and LBL (formally titled the Supernova Cosmology Project), and the competing group of Schmidt and Reiss based mostly at Harvard (the High-z Supernova Search Team) were independently able to use Type 1a supernovae as “standard candles” in determining how fast galaxies were moving away from us across the universe. The brightness of a supernova’s explosion can determine its distance from Earth and, by extension, when it exploded. A supernova’s velocity can be determined by analyzing its redshift (that is, the shift in frequency that occurs in the supernova’s spectral features because of the Doppler effect), and together these two values can be used to determine the changing size of the universe over the course of billions of years.

Both groups expected to use the supernova data to measure the rate at which the universe is decelerating, a consequence of the fact that gravity as we know it only ever tends to pull things toward each other. Shockingly, they found the opposite. Not only is the universe failing to slow down in its expansion; it is actually accelerating. In order to account for this, it seems that there must be some new force at work, which scientists have cryptically labeled “dark energy.” The new finding has thrust us into a new age of ignorance, which is both irksome and exciting because dark energy comprises almost 70 percent of all that exists.

CS: So what’s it like to win the Nobel Prize?

SP: The day they call you up is one of these amazing whirlwind days. You’re woken up at 2:45 in the morning, and after I got off the phone with the Nobel Committee (though in this particular case I got off the phone with a reporter because they couldn’t find me), I looked at my wife and I said, “So, now what?” And I thought, “I guess I ought to take a shower, get dressed, and shave.” Because sure enough, within 40 minutes there are people at the door ready to start interviewing you, and there are trucks with TV crews outside. It becomes a nonstop day of interviews and celebrations, and the whole university and lab communities feel very much involved. It’s been such a product of these two communities for so many years that I think everybody felt like we were all doing it together, which is fun.

And then of course things got nice and quiet for a couple of days because the email was so overloaded that you didn’t know what you were missing! I had a few days to get around and talk to people. And then we started assigning administrative assistants to look through the mail, and we realized all of the things we had to do to go to Stockholm. There’s a huge amount of organization that has to happen there because it’s really set up for lone scientists to go to get the prize. In my case it was a team that did the work together, and so we were all going. It was like organizing a wedding remotely. In fact it was much bigger than the wedding we had in Berkeley when I got married. Out of the 31 or so people on the team, 27 came with their spouses, and my family was there. We were organizing banquets for 65–70 people.

And then the week itself comes, which happened fairly quickly because we were so busy doing all this organizing. It’s a whole eight days of activities and it’s nonstop from morning until late at night. They’re driving you around in a specially dedicated limousine, and they’re taking you to interviews, and to press conferences, and to filmings, and to your lecture, and then eventually you go to the big ceremony and then the banquet. They have these palaces and castles, kings and queens, and they really know how to use them to make it feel like a heightened event. And what’s striking is that Sweden really takes this stuff very seriously. People recognized you on the street. They would ask for autographs, and the awards ceremony and banquet were shown on TV as if it were a sports event or the Academy Awards. Everybody watches it.

CS: I noticed you were the first person to walk across the stage to receive the prize.

SP: Apparently the physics prize is considered the senior prize, I think because it’s the first one mentioned in [Nobel’s] will. And I was the senior member, I guess by age and by order in which they gave the prize. So I was always put at the front of everything, which was fun. But it also meant you had to try doing everything first before you got to see how it really is done. The nice thing is that the Swedes are very formal, and yet they have a nice sense of humor behind the whole thing. You get the impression that if you get it wrong, nobody’s going to be very upset.

CS: Do you see yourself differently now, and/or do other people?

SP: Well of course it’s still new, so it’s hard to know what will happen in the years down the road. But I’m still the same person. My friends and colleagues still have just as much respect (or disrespect) for me as they would have had to start with. There’s obviously a lot more that I have to figure out in terms of a nonstop stream of invitations for things that people want me to do now, and the real question is, how are you going to use your time? There are the things you feel are important to try to do, and some to which you feel that you can’t say no, but you also feel like you shouldn’t be traveling all the time. You should be getting some work done and you should be there with your family as well.

CS: How does your family feel about it?

SP: They generally have been having a good time with it. I think there were a few moments in which my eight-year-old daughter was a little bit nervous that maybe somehow I’d be taken away from her a little bit more. But I think she got over it quickly. To first order I’d say we’re still able to lead ordinary lives.

CS: I heard you don’t really like champagne.

SP: I’m not a big champagne person, but of course it’s nonstop for these celebrations. Everybody has to have champagne. So I always have a sip. So now I am a connoisseur of different sips of champagne.

CS: You’ve mentioned in the past that physics is a very social activity. Could you comment a little more on that?

SP: I think some people are lone scientists still, but in my experience the work that you’re doing is a reflection of a large group of people all contributing something. I like to think about problems quietly for a few minutes, but really I love to bounce the ideas off other people, and I come into work and I look forward to that. If there’s something I want to think through, I want to think it through with other people. And so we’re constantly getting the group together and asking questions. In general that’s the way in which most of the science I know works best. And so that fact that all those people came out to the Nobel ceremony was really appropriate.

Perlmutter’s team studies Type 1a supernovae like this one, supernova 1994D in galaxy NGC 4526 as captured by the Hubble Space Telescope.
Credit: NASA/ESA, The Hubble Key Project Team and the High-Z Supernova Team

CS: What is the hardest question that children ask you?

SP: There’s a whole family of questions that are premised on the [erroneous] idea that the universe expanding means that everything in the universe started at a point, and then expanded out from that point. I always try to correct that by saying that we shouldn’t think of it as an explosion of stuff into empty space (because empty space would be the universe, too). The picture that I think is much more apt is to imagine that the universe is infinite today, and that as far as you go in any direction there are galaxies, and the only thing we mean by the universe expanding is that all the distances between the galaxies are getting a little bit bigger. We’re pumping extra space between the galaxies. In that picture, as you go back in time it’s still infinite. It’s just that all these galaxies are a little bit closer together. Eventually, things get on top of each other, and once they get tight enough on top of each other our physics models don’t work anymore, and we call that the Big Bang. But it’s not a very great name. I mean really we should be calling it the Big Soup or something. I think in that picture many of the questions that people ask you about “what’s the edge of the Universe?” and “where was that center, where was it located?” go away.

CS: Hmm, it’s really hard to wrap my mind around that.

SP: Absolutely. These are all mindboggling ideas. Although as I point out to everybody, any model of the universe is hard to wrap your mind around.

CS: Who is your favorite Nobel laureate or scientist?

SP: It’s probably easy to choose Einstein, just because he captured so much of what we like to think of as the prototype of physics, which includes a strong humanist component amidst this amazingly crazy scientific picture that turned out to be true. Similarly, the playfulness of people like Feynman is very attractive to me, and that translates down to the diverse capabilities of people like Luis Alvarez.

CS: Have you gotten a chance to enjoy the Nobel laureate parking space?

SP: Yes! So far I’ve parked there maybe ten times. I definitely appreciate it every time, and I’m hoping that I’m providing a role model rather than just taking up space.

CS: If you had to pick out a single greatest challenge to the work that led to the prize, what would it be?

SP: You had to find a way to get a whole bunch of things to all work all at the same time. We would be using maybe a half dozen telescopes around the world simultaneously, but they’re all controlled by completely separate entities, and they’re scheduled by different people, and you have to be able to talk to everybody and get them all on the same page together so that they’re actually scheduling them in a coordinated manner, and you have to get all of the people to work simultaneously together in a coordinated manner, and your software has to succeed all at the same time.

It’s an interesting logistics problem, which is not at all what you expect to be the hard part of a science project. I always thought the science itself was going to be one of the simplest experiments I knew. There were sophisticated parts of it that took some ideas that we had to invent to make it work, but as bad as those difficult science parts were, the most difficult parts were the social and logistics parts, getting the story to work with all those humans.


In the 13 years since the original findings of the Supernova Cosmology Project and High-z Supernova Search Team, complementary techniques have arrived at results that are in striking agreement with the original findings of the supernova studies. Yet despite mounting evidence of dark energy’s existence, no one really understands what it is or why it behaves the way that it does. The simplest way to account for an accelerating Universe is an idea known as the cosmological constant, due to Albert Einstein, which postulates that dark energy can be incorporated into the intrinsic fabric of spacetime. Unfortunately, theoretical estimates of the value of this cosmological constant are 120 orders of magnitude (a factor of 100 quintillion googols) larger than the experimental evidence indicates, a spectacular failure of understanding that has been described as the largest discrepancy in science between theory and experiment ever.

Current research efforts in the Perlmutter group have proceeded along two fronts in the effort to better understand dark energy. Part of the group is continuing to push forward along the Supernova Cosmology Project’s original efforts, searching for ever more distant supernovae and using them to obtain smaller error bars on the Universe’s expansion. In tandem with this, Perlmutter and colleague Greg Aldering run a complementary study called the Nearby Supernova Factory, which is an effort to characterize supernova events that happen much closer to home. Graduate student Hannah Fakhouri said that the study of nearby “twin supernovae,” supernovae with nearly identical temporal features, could lead to a better understanding of intrinsic supernova processes and the eventual identification of a more stringent class of standard candles than the Type 1a subset. According to Fakhouri, the new prize and fame has only slightly cut into Perlmutter’s involvement with these efforts, and thankfully so. “Saul has an amazing ability to be excited and it’s infectious,” she said. “Sometimes when I’m frustrated and things aren’t really making any progress, he’ll come and he’ll stand by my desk, and he’ll ask what the status is. And I’ll say what’s working and what’s not working, and somehow he’ll manage to take whatever is said into a very positive light. And somehow it becomes exciting and possible to solve the problem.”

Saul Perlmutter’s Nobel Prize will mark him as the ninth laureate from UC Berkeley in physics. Previous recipients include Ernest O. Lawrence, Emilio G. Segre, Owen Chamberlain, Luis Alvarez, Donald A. Glaser, Charles H. Towns, Steven Chu, and most recently George F. Smoot. It is a select club with one of the strictest academic membership requirements on earth. In Perlmutter’s case, the academic qualifications appear to have a personality to match. “He’s really great as a person, and he’s just really humble about it. He doesn’t flaunt the fact that he’s won the prize,” Fakhouri said. “I would say it couldn’t have happened to a better guy.”

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