Physics Nobelists Observed An Accelerating Universe

In 1998, two teams of physicists looking at distant supernovae noticed something surprising—the supernovae were not only moving outwards but also accelerating. These observations have won three Americans the 2011 Nobel Prize in physics. Nobelist Adam Riess discusses how physicists are now looking at the universe.

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IRA FLATOW, host: This year's Nobel Prize in Physics has just been awarded to three American astronomers for their unexpected discovery that the universe is expanding at an accelerating rate. Peering into the depths of our universe back in 1998 with the help of instruments like the Hubble, they were looking for exploding stars or supernovae that were around way before our sun ever existed, hoping to trace the early evolution of the cosmos.

Joining me now to talk about it is our new Nobel laureate, one of them, Dr. Adam Riess, professor of astronomy and physics at Johns Hopkins University, senior member of the science staff at the Space Telescope Science Institute in Baltimore. Welcome back to SCIENCE FRIDAY, congratulations.

Dr. ADAM RIESS: Thank you, Ira, thank you.

FLATOW: I want to play back, in 1998, that little - when you were on SCIENCE FRIDAY, and you first published these results, here's how unexpected the observations were, according to your own words.

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RIESS: We fully expected that the expansion rate would be slowing down. I mean, that's what gravity does: It pulls on everything and causes something like the expansion to slow down. And we were very stunned to see that it actually appears to be speeding up, actually appears as though the universe is accelerating.

FLATOW: Did you know where you were headed with this, or that there was a Nobel in your future?

RIESS: No. I sort of chuckle when I hear those words because - so that was March of 1998. It was when - just at the time we were submitting this paper, and it was a very nerve-wracking time. And I think when I went on your show, it was one of the first times that we were sort of admitting in public that this is what we were seeing in the data, and at that point there's sort of no going back.

I feel for the guys who think that they've seen neutrinos faster than the speed of light.

FLATOW: You feel for them. Do you believe it?

RIESS: Well, I don't, and I don't think everybody believed us at the time. But what really helped, actually a big distinction I would draw between the two situations, is that there were two teams of astronomers competing with each other but coming to the same conclusion. And I think that all of us would love to see an independent measurement of the neutrinos.

FLATOW: Has anything changed in those years since you were on this show, anything about - any more ideas of what - maybe what all this dark energy might be?

RIESS: Right, well, first of all, the evidence that something funny is going on has gotten much better. I mean, it's not just observations of supernovae. There are five or six very critical and independent observations, observations of the cosmic microwave background, of features in the large-scale structure of the universe, of clusters, of gravitational lensing.

We have so many different tools in our toolkit now, and they all say the same thing, that it looks like there's something extra in the universe, that there's this 70-percent component that is dark energy. And we've even gone further than that.

In the last decade we've begun to measure a key property of the dark energy, the technical term is equation of state, but you could think of it as the kind of strength of the dark energy.

FLATOW: All right, I'm going to stop you there, and we'll get into that a little bit more, because we have to take a break, okay, so hang on. Everybody, we'll be right back talking more with Nobelist Dr. Riess here, who's going to come back and talk more about the dark energy, Adam Riess, astronomer and Nobel Prize winner. Stay with us. We'll be right back after this break.

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FLATOW: You're listening to SCIENCE FRIDAY. I'm Ira Flatow. We're talking with Dr. Adam Riess, who's just won the Nobel Prize, sharing the Nobel Prize in Physics for the discovery, I guess - would it be right to call it the discovery of dark energy?

RIESS: No, it wouldn't.

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FLATOW: Tell us what it really is.

RIESS: The Nobel Committee being, you know, wisely conservative, like a good court, took the sort of very narrowest statement that we can be confident is true, which is that these two teams of astronomers found that the universe is accelerating.

Now, that seems to be the smoking gun of dark energy, but we still don't understand what dark energy is or even - there's the outside possibility that we don't quite understand the laws of gravity and that there really isn't this dark energy.

So the fact that we see the university accelerating is really the tipoff that something interesting is going on, either on the gravity side or the content side of the universe. And so they stuck to what we could be sure about at this point.

FLATOW: Our number, 800-989-8255 if you'd like to talk about it, or you can tweet us, @scifri, @-S-C-I-F-R-I. Before the break, you were talking to me about the evidence getting stronger over the years.

RIESS: Right, so there's been a lot of independent evidence so that we're quite confident about our, I guess I should say our - we're confident about being not confident about what's going on, that there's something beyond either our simple understanding of even Einstein's theory of gravity or the less exotic components of the universe, that there's something like dark energy.

But we've gone even further in the last decade by measuring a key property of the dark energy. We've begun ruling out some of the alternatives of what it could have been. It could have been a kind of a topological defect in space that whenever you create space, you create more of this topological defect.

Right now it looks like, to within about 10 percent precision, it looks like just what Einstein had described back in 1917, that there could be what he called a cosmological constant, what we would call a sort of static vacuum energy.

FLATOW: And he called it the biggest blunder of his life, putting that constant in there.

RIESS: He did, but I guess it turns out even blunders for Einstein are still pretty good days for the rest of us.

FLATOW: I remember discussing this with Steven Weinberg years ago, and he said one of the interesting things about the dark energy is that - one of the mysteries of it is that there should be a whole lot more of it, right?

RIESS: Right, that's right.

FLATOW: And not only have you found it, but you didn't find enough of it.

RIESS: That's right. On the other hand, if we had found enough of it, we wouldn't be here to find it because it would have accelerated the universe apart long before structures like us and our planet formed.

So you could say that the particle physicists always knew that there was a problem here, and we haven't - I wouldn't say we've made the problem - I would not say we've made the problem worse, but we've certainly shined a light, no pun intended, on this particular aspect.

FLATOW: Let's go to the phones, some interesting questions, to Kate(ph) in Chicago. Hi, Kate.

KATE: Yeah, hi, how are you doing? Thank you for taking my call. I think that I got my answer. I was going to ask if the dark energy was anything like aether that was discredited a while back.

RIESS: Right, well, that's a good question. You know, from time to time we do sort of imagine a kind of component out there in space that can do the trick of explaining a strange observation. We can't be sure, really, at this point that dark energy will always be with us, that, you know, it wouldn't eventually take on a sort of aether-like part of the story if in particular our understanding of gravity is wrong.

But right now the smart money says that we see something like dark energy, and the particle physicist always knew that there ought to be something like dark energy, and so it's really about trying to understand how those two become the same.

FLATOW: Thanks for the call, very interesting. Let's go to another phone call, Mindy(ph) in Rochester, New York, hi, Mindy.

MINDY: Hi, thank you for taking my call. My question is: Is it possible that the universe is expanding at an accelerating rate because there is dark - like a dark matter, like a halo surrounding the universe that is also pulling on the quasars so the quasars are expanding out faster because there's a gravitational pull by this halo surrounding our universe? Not only are they being propelled out by the dark energy within our universe, but they are also being gravitationally pulled by a dark halo surrounding our universe.

FLATOW: That's a good question. Thanks, Mindy.

RIESS: Right, that is a really interesting question. You know, at some level we can't be sure because we don't really see the whole universe. So we can only see out as far as the age of the universe, which is about 14 billion years, times the speed of light. And so it's always possible that there's a great surprise beyond what we literally call the horizon.

On the other hand, what we've seen of the universe, after a while it kind of looks like bad wallpaper. It repeats. We have seen the scale on which there are structures in the universe, and we haven't seen any kind of structure on the kinds of scales that your explanation for the acceleration would require. We haven't seen anything on the scale of a giant halo.

So while we can't say that, after you look at this wallpaper for a while, that last piece or part that you can't see looks completely different, it seems very unlikely.

FLATOW: Is there - are there any good candidates for what it is?

RIESS: Yes, well, you know, I think the best candidate remains our understanding of the vacuum in a sort of quantum mechanical sense, that there is what we call a zero-point energy to the vacuum, that is the energy - the vacuum is a much livelier and more interesting place than we learned about in high school chemistry - there are particles flitting in and out of existence - and that the sum energy associated with all those gives rise to, on a macroscopic scale, this thing we call dark energy.

The problem with this explanation is you start out using quantum theory to think about the vacuum, and then you switch gears when you get to this macro scale and switch over to another theory of physics called general relativity, which describes how energy or matter bends space.

And these two theories don't work together. We do not know how they interface. We treat them as sort of separate rulebooks. So what's so exciting about dark energy and this phenomenon is that this is getting to watch how the universe sort of works at that crossroads between these two theories of physics, and we hope it gives us a clue, it gives some bright person a clue on how to unify these.

FLATOW: And that's been sort of the holy grail of physics for the last...

RIESS: Yeah.

FLATOW: Right? To unify the geometry concept of, as Einstein put it, the universe in a geometrical form, and you know, its curved space and things, with a quantum idea, which is just particles and stuff.

RIESS: That's right. So you've heard a lot of terms for this like quantized gravity or unifying gravity with the other forces, and string theory tries to do this as well. And, you know, all we're saying as sort of observers is we're just watching how the universe does this or how it operates in that regime, and we're hoping that that's a clue.

FLATOW: Wow, so it's great to talk about this stuff because it's fun to speculate, isn't it...

RIESS: Yeah, it is.

FLATOW: Well, we wish you good luck on the prize ceremony.

RIESS: Okay, thank you. I want to give a sort of shout-out to my colleagues on the High-Z Supernova Team and the Supernova Cosmology Project, who have really enabled this work to be done.

FLATOW: And you're going to be heading to Stockholm when, December?

RIESS: December.

FLATOW: December? Make sure you take home some of the great chocolate coins they have.

RIESS: Oh, okay, I will.

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FLATOW: They've got pictures of Alfred Nobel on it. And where do you go from here? Anything that - you know, you're all theoretical physicists looking at stuff and thinking about it.

RIESS: Right, well, my fondest wish is that by generating these clues, we inspire, you know, sort of the next Einstein or, you know, really smart person to basically put all these pieces together. I mean, I think there are limitations to the degree to which observations can really, you know, crack this riddle, and it really does require a kind of theoretical synthesis that, you know, it's very hard to predict when that next great idea will come along.

FLATOW: Well, congratulations again to you, and good luck. We'll stay in touch.

RIESS: All right, thank you.

FLATOW: You're welcome. Adam Riess was on SCIENCE FRIDAY back in 1998, when he talked about the discovery of the expansion forces, expansion of the universe, and he's now a new Nobel laureate. He's astronomer and physicist at the Johns Hopkins University, senior member of the science staff at the Space Telescope Science Institute in Baltimore.

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