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Interview transcript

[Adam Smith] Hello, this is Adam Smith.

[Saul Perlmutter] Hi, this is Saul Perlmutter returning your call.

[AS] How very kind of you to call. Thank you, and congratulations on the award of the Nobel Prize.

[SP] Thank you, thank you. It’s a real honour.

[AS] So, as I think has been explained to you we record these very brief interviews for Nobelprize.org, so could we talk for just a few minutes?

[SP] Okay, surely!

[AS] Perfect, thank you. So, it’s very early morning in Berkeley. What were you doing when the news came?

[SP] [Laughs] We were sound asleep! And we got the first call from a reporter from Sweden, actually, who asked me how I felt. And I said “How do I feel about what?” And he told me that we’d won the Prize and my wife, of course, rushed to the computer to check to see whether this was a hoax!

[AS] And happily it wasn’t, yes! [Laughs]

[SP] Exactly!

[AS] So, taking you back to another moment of surprise, in 1998 you came up with this amazing result that the expansion of the universe was accelerating. Was there a sudden moment you realised that you’d come upon this, or was it a slower “Aha!” moment?

[SP] Yes, as I’ve been saying to people, I think this has to be the slowest “Aha!” in the history of science, in that nowadays, when you’re looking at data, it’s a very complex task to interpret it very carefully, and calibrate very carefully. And the first job we had when we saw the data coming in was to say “Ah, well, it looks like good data, and this should be nice, but right now it doesn’t make any sense. You know, the plots all look a little bit strange. I’m sure that once we finish all the calibration it’ll go away – it’ll all seem logical.” And of course, the more we calibrated it, the more the surprise sharpened up, and so by 4 months in, you really started to believe that this is a big deal. It’s a very different result than anything we ever expected. And, yes, by then, of course, you’ve been staring at the data for 4 months, so it’s hard to call it the same kind of surprise that people sometimes imagine.

[AS] Yes, yes. But there must have been a tension between wanting to be sure and wanting to be first, because you were in competition with the other team?

[SP] Yes, I think we still thought that we were very far ahead, in that we had many, many more supernovae that we had measured at that point. And so we didn’t – I don’t think we quite realised how close they were to seeing the same results. Because they were just working on this small data set at that stage. But we also felt very strongly the tension between wanting to announce an important answer, but also wanting to make sure that whatever you announced, people would believe it and that you would believe it, and that you had done all the homework necessary to make it make sense.

[AS] And did people believe it as soon as you announced it?

[SP] Well, I think that the first response would have been that it was harder to believe, but within 6 weeks the other team had also announced the same basic results. And so at that point, I think people started to believe it, because they knew that the two teams were fierce rivals and would have been very glad to prove each other wrong if it had been possible!

[AS] Yes. And so this accelerating expansion means that there has to be something, which has basically been termed dark energy, that’s pushing the universe apart. Is there any idea what that is yet, do you think?

[SP] No. Not only do we not know what dark energy might be, that would be making the universe expand faster and faster, we don’t even know whether really the answer will turn out to be a new energy in the universe. It’s possible that we’ve just discovered an extra wrinkle in Einstein‘s Theory of Relativity, and that that would be the real final result. But at this point, the job is really back in our court again as observers, and we have to come up with more data that will help narrow in on what the answer is.

[AS] Because the theoretical people have been proposing solutions at a great rate, but more data is needed to know which if any of these proposals is correct.

[SP] Exactly. I think the papers have been coming out on the order of one per day for the last 10 years, from the theorists. And of course, all these theories can’t be right! But the other thing is that the theorists themselves I think would tell you that they don’t believe any one of their theories. They’re just trying to expand the range of possibilities. And if it turns out that, you know … What they’re really looking for is for us – the observers and the experimentalists – to come up with some more data to help home in, help narrow in, on which range of possibilities could be right.

[AS] It seems to be one of the lovely things about physics; that sometimes it’s the time of the experimentalists, and then it goes back to the theorists, and then back to the experimentalists again.

[SP] No, no, it makes for a great tennis game of science!

[AS] [Laughs] And so what do the experimentalists have to do next? What is the next big challenge?

[SP] So our job now is to develop ways to measure this very subtle effect. It seems like a big deal, something that can power the expansion of the universe, but it only makes a difference over the timescale of a billion years, and billions of light years. So now we have maybe three different techniques that we could use to get at what’s going on. And each of them is a very challenging experiment that will require building new instruments, and perhaps even a new space telescope.

[AS] So in looking for these subtle effects, do we have to look at the fringes of the universe, or can we build experiments here on earth that will allow us to see it?

[SP] So far, nobody’s figured out any way that we could detect it locally. So far, as far as we know, it takes very large distances and billions of light years to be able to see enough of the effect.  But, who knows, it may turn out that there’ll be new ideas that we haven’t invented yet.

[AS] Splendid! When you come to Stockholm in December to receive your Nobel Prize, we happily have the chance to interview you at greater length, and we can talk more about this, so just a last question: when do you think you’ll be free to celebrate? I imagine you’re in the grip of the press now.

[SP] Exactly. I’m hoping that things will calm down by the end of the day, and maybe we can have a quiet evening and invite friends over to sit around and enjoy it!

[AS] Okay [Laughs]. And look at the stars perhaps!

[SP] Exactly! [Laughs] We’re having one of our first rains of the season, so we might not get many stars tonight.

[AS] [Laughs] Okay. Well anyway, congratulations once again, and thank you so much for speaking to us.

[SP] Well thank you, it’s a pleasure. Bye bye.

[AS] Bye bye.

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