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Elegant physicist makes string theory sexy

Telegenic string theorist Brian Greene talks about his life, the universe and the theory of everything in an extended Q&A with
Columbia physicist Brian Greene inhabits a multiple-perspective landscape modeled after M.C. Escher's artwork in a scene from "The Elegant Universe," a public-TV documentary based on Greene's book.
Columbia physicist Brian Greene inhabits a multiple-perspective landscape modeled after M.C. Escher's artwork in a scene from "The Elegant Universe," a public-TV documentary based on Greene's book.A. Cross / J. Dunn / Edgeworx for NOVA

If you're trying to impress the geeks, being a professional string theorist would have to put you pretty high up on the coolness scale. And if you're a string theorist with books, movies and TV shows to your credit, so much the better.

By those measures, Columbia University physicist Brian Greene has already achieved superstring stardom: His book about string theory, "The Elegant Universe," broke onto bestseller lists and spawned a "Nova" documentary series by the same name (which you can watch online). He has consulted with — and taken cameo roles in — movies ranging from "Frequency" to "Deja Vu" to "The Last Mimzy" (which opens Friday). He's made the talk-show circuit, from "Nightline" and Letterman to "The Colbert Report." And as if all that wasn't enough, he's also organizing a World Science Festival in New York City.

In fact, the biggest knock against Greene is that he's so busy with public outreach that scientists wonder whether he actually has time for string theory. Last year, for example, he was the subject of a meticulously plotted April Fool's joke having to do with a star on the Hollywood Walk of Fame.

Even though less telegenic physicists may turn up their noses, there's no denying that the 44-year-old Greene has managed to make one of physics' most arcane theoretical frontiers a lot sexier. (For the record, Greene is married with a 2-year-old child and another on the way.)

"The Elegant Universe" stoked popular interest in the concept that the fundamental building blocks of reality are tiny vibrating strings — and that such a paradigm could help explain the biggest puzzles of physics. In that role as an explainer of cosmological mysteries, he's following in the footsteps of Cambridge cosmologist Stephen Hawking, author of the similarly bestselling "A Brief History of Time" and occasional TV star.

Greene and Hawking are teaming up for the first time in a double-lecture series on cosmology in Seattle, presented by the Oregon-based Institute for Science, Engineering and Public Policy. Greene takes the stage first, on Monday, and Hawking is due to follow with an April 9 lecture. In a wide-ranging interview with, Greene previewed his lecture and talked about how he juggles his many roles in science and culture: So how do you feel about sharing a bill with Dr. Hawking?

Greene: Ah, well, it’s quite an honor. He certainly is the towering figure in the field, so I have no problem being the warmup act.

Q: Do you expect your perspectives on cosmology to differ?

A: I suspect that there’s much we agree upon. The place where we may diverge, if at all, is on the most modern developments: the role of string theory in shaping our perspective on cosmology, the possibility of testing string theory and other unified theories through cosmological observations. These are topics that I’ve been putting a lot of effort into and I will be emphasizing in my remarks. I don’t know whether Hawking will refer to any of those developments — nor do I know his views on them.

Q: So you feel as if you might be more optimistic than he might be on the testability of string theory?

A: Actually, Hawking’s quite an optimistic physicist. I’m not sure that I’d be more optimistic. But I think that my emphasis may be somewhat different in that this is the line of research that I personally have been pursuing the last few years.

Q: Can you give a preview of the particulars, because this is a pretty large question. Everyone is looking to the Large Hadron Collider and trying to figure out what specifics they might be looking for to prove string theory is valid.

A: Sure. I think that framing of the question is perfect, because indeed most people do think of the Large Hadron Collider, or accelerators, or atom smashers, or whatever you want to call them, as the primary tools for investigating cutting-edge ideas in particle physics and hopefully in string theory. But there’s another approach that has not received as much attention — which is to try to use astronomical observations to test some of these theories.

The way I like to think about it is, if I have a balloon that has no air in it, and I scribble a message on the outside of that balloon with a very, very fine-tipped pen, you can’t see the message because it’s too small. But then, if the balloon expands, you can take that tiny message, smear it out across this large balloon surface, and now you can easily see it.

It’s our hope that a similar idea might apply to string theory. Strings are very tiny, and that’s what has made them so difficult to test. But perhaps strings leave a little tiny imprint on the young universe, at the time just after the big bang. And then through 14 billion years of cosmic expansion, the universe gets bigger and bigger, and that little tiny imprint of string theory may get smeared out across the sky – just like my little scribble on the balloon gets smeared out across its surface. So the thought is, we may actually be able to test string theory through astronomical observations so long as we know what to look for.

We’ve been doing calculations that suggest that the place to look may be the microwave background radiation. And the thing to look for may be tiny, tiny additional temperature deviations from those that have already been seen, so small that they are a challenge to measure – but it’s not impossible that one day we will. That’s the basic idea.

Q: People have talked about the contribution of the Wilkinson Microwave Anisotropy Probe, and when WMAP’s initial results came out, people may have gotten the impression that those results were the be-all and end-all for study of the cosmic microwave background. But I suppose you’re thinking that there are other missions, such as Planck, that will bring more information to light?

A: Absolutely. So Planck is one mission, and then there’s CMB-Pol – the polarization measurements. All these experiments have a possibility of giving us more refined data, which will provide a sharper image of just what the universe looked like about 370,000 years after it was born. That kind of precise data has a chance of showing imprints of exotic physics. And among the candidates for that exotic physics, a prime candidate is certainly string theory.

Q: I remember at the time that the WMAP results came out, people were talking about the “second peak” or the “third peak” in the curve showing data about the cosmic microwave background. Is that the sort of thing you’re looking at?

A: That’s part of it. But in fact those features are, from our perspective, the gross overall features. We’re suggesting that on top of those peaks there may be little wiggles. And those little wiggles of a very tiny size could reflect the physics of string theory operating in the early universe. So it’s a difficult measurement, because it was a heroic feat to measure those peaks – now we’re saying hopefully we can go further and measure additional features on top of those.

Q: Hawking has said that there could be a “theory of everything” produced in the next 20 years, or by 2020. Do you get that same sense? Or will there ever be a theory of everything?

A: Well, I always find it difficult to make predictions that are tied to a specific time frame, because as we all know, one of the exciting things about science is that you don’t know when the big break is going to happen. It could happen tomorrow, it could happen 10 years from now, it could happen a century from now. So you just keep pressing on, making progress, and hope that you reach these major milestones — ideally in your own lifetime, but who knows? So I don’t know if 2020 is the right number to say. But I would say that string theory has a chance of being that unified theory, and we are learning more and more about it. Every day, every week, every month there are fantastically interesting developments.

Will it all come together by 2020, where we can actually have experimental proof and the theory develops to the point that it really makes definitive statements that can be tested? I don’t know. I hope so. But hope is not the thing that determines what will actually happen. It’s the hard work of scientists around the world.

Q: One of the things that’s come up is this idea of all the possible solutions for string theory’s equations — that there’s a landscape of 10500 possible scenarios, and how can we possibly narrow it down? Some have even made this a feature of their theories – the idea that we’re just one blip on a whole spectrum of possible universes. That could be a daunting prospect, if you look at it that way, in order to actually arrive at the one truth out of 10500 possibilities.

A: I agree. … I would say that it’s an interesting framework that people have started to take seriously as a possibility. If it's true, it rewrites the way we think about the universe. Rather than thinking about one universe, and seeing our goal as explaining its unique charactistics, we’re going to be thinking about a universe that has many different characteristics in many different regions. Our region may happen to have its particular properties by historical happenstance, by accident, or by virtue of the fact that we can’t exist in any of the other regions.

My own feeling is that even if this large mega-universe picture is the right one, there are still detailed features of our universe that we can make headway in explaining. We’ve made tremendous progress without this idea, in terms of explaining how particles interact, how atomic nuclei are formed in cosmological evolution. So it by no means says that we can’t answer deep and important questions, but it does frame them differently. It puts them into, as the language of the trade indicates, a much larger landscape.

Q. It was once said that only two or three people in the world understood relativity at the time that Einstein came out with his theory. And I suppose the same thing might be said today about string theory. It’s a very popular subject for lay people such as myself, but it’s hard to wrap your brain around it. How do you think people will be able to wrap their brains around string theory, as they have over the decades in the case of relativity?

A: Well, I think string theory in many ways is much easier to understand than relativity. Relativity challenges your basic intuitions that you’ve built up from everyday experience. It says your experience of time is not what you think it is, that time is malleable. Your experience of space is not what you think it is, it can stretch and shrink. These things are so counter to experience that it is very difficult even for professional physicists to take these ideas on board in a deep, intuitive way.

When it comes to string theory, though, it’s a very natural idea. It’s saying that those particles that we imagine making up everything in the world around us, that we previously envisioned as being little dots — now we’re saying if you examine them with a sufficiently powerful microscope, that dot will actually not be a dot. When you magnify it, you'll say, "Oh, it's actually a little filament, it's a little string."

So from that point of view, it's not a difficult idea to grasp. Of course, there are features of the theory that are hard to grasp, like extra dimensions of space and things of that sort. But from a rock-bottom standpoint, I think string theory's easier to grasp than relativity and also easier to grasp than quantum mechanics.

Q: I guess one of the problems is that we're talking about a length scale that is so small that not even the greatest microscope could reach that scale. So you have to look at the inferences from that conception of strings and see what you can find in the macroscopic world that can reflect that unseen, or unseeable, world.

A: That's certainly the case. But that was the case also in the early days of quantum mechanics. Now we have technologies that allow us to probe directly to the small distances where quantum mechanics really comes into play. But in the early days, you were trying to find indirect signatures of this strange picture of the microworld.

Now the difference here is that I don't think we'll have equipment that can measure these tiny distances in 30, 50 or 100 years. It could be 500 or 1,000 years, or maybe we'll never be able to probe the tiny distances that string theory shows as the relevant arena for its new ideas. But that's the framework of science: You put forward fundamental ideas, and you try to work out their consequences in a manner that can be accessed with the equipment that you have.

For string theorists, it's very hard to do, for exactly the reason you're saying — because the strings are operating in a realm that is fantastically small, even by the scales of quantum theory. Nevertheless, people are working very hard to find indirect signatures. The LHC has a chance of seeing the extra dimensions of string theory, has a chance of seeing the vibrational patterns of strings, has a chance of seeing the supersymmetric particles that string theory requires. And as I was saying, these astronomical observations have a chance of seeing the effects of string theory in the microwave background radiation. So all of these are indirect signatures of string theory that we at least have a chance — a long shot — but a chance of seeing.

Q: When people talk about what the LHC could contribute, they talk about Kaluza-Klein particles, supersymmetric particles or quark jet suppression. ... Are there particular candidates that you favor for what we might see with the LHC.

A: Well, the most conventional answer to that would be the supersymmetric particles. This is an idea that people have been developing for decades, and it actually emerged from string theory: this notion that there should be more particles than the ones that we know about, and the reason we don't yet see them is because they're so much heavier and you need a more powerful machine to conjure them up. People are really having great hopes that the LHC will be able to see those supersymmetric particles.

But beyond that, to me, the exciting possibility is seeing evidence of extra dimensions of space. One of the most bizarre features of string theory is that it doesn't work in three dimensions of space. It needs more dimensions, all the way up to 10 dimensions of space. And the idea that we don't see them because they're very small is an attractive one, and potentially testable if they're small but not too small. If they're not too small, the LHC may be able to, in essence, pump some energy from our dimensions into those other dimensions, and we would see that by virtue of energy being lost from our dimensions because it's escaping into the others. That would be a wonderful thing if that experiment turns up a positive result. We could actually see evidence that the dimensions that we have for thousands of years thought to be all there is are actually a small part, because there are many more dimensions. That would be so exciting.

Q: Tell me what's up with the World Science Festival, and the movie "The Last Mimzy," which I think you have a role in.

A: Well, yeah, "Mimzy" is coming out this month, and surprisingly, I saw the trailer just by chance the other day — and was shocked to see that my tiny moment in the film is actually in the trailer. My students happened to see it, too. Apparently the trailer ran during their favorite show, "Desperate Housewives." They said to me afterwards, "Wow, you must have a really big part to make it into the trailer." And I said, "Actually, what you saw in the trailer is it. There is nothing else. That is my part."

Q: Well, who should we be looking for? Are you the sage professor?

A: Yeah, there's a scene when they call in an expert scientist to examine a doll — I won't give away the story, but it has some mysterious qualities. So that's the role I play. I give my assessment of the situation, in three sentences, and then I'm done.

But the science festival is going extremely well. It will launch at the end of May 2008 — I think the dates are May 29 through June 4. There's excitement in the city and beyond, including the cultural institutions like the Met and Lincoln Center and the Guggenheim, and the universities like Columbia, Rockefeller, NYU, Cooper — the whole shebang. Everybody is just so excited about this prospect of having a real national event focusing on science for a number of days in New York. So I think it's going to be a very exciting extravaganza.

Q: How do you strike a balance between those public engagement activities and your own research? People always complain that scientists aren't engaged enough with the public, but I'm sure no one ever said that about you. I suppose they could say, "He's spending so much time on this science festival, what's he doing in terms of research?" How do you strike that balance?

A: Well, it's a tough balance to strike, and it's one that I'm constantly aware of. Luckily, in the example that you mentioned, there are now six full-time people working on the science festival, so I don't have much day-to-day involvement. I'm involved in the big decision-making stages and the big meetings, but not in the day-to-day stuff.

What I've been doing for the last couple of years is, I typically don't do any outside activities in the morning. I keep 8:30 to 1 o'clock completely free. I typically don't even go into the office. I go into a little corner of one of the Columbia libraries where I have a full computer hookup and all my stuff, and I do my work there.

Even when I wasn't doing much "science for the public" stuff, I found that four or five hours of intense work in physics was all my brain could take on a given day. So now I try to focus that in the early morning hours, so that when I meet with students or I have to do some writing, or I have to do some interviews, I typically try to do that only in the afternoon.

Q: I guess it's different for a theorist - it's more of a solitary activity, and you don't have to worry so much about going into the accelerator or the experimental lab.

A: Totally, yeah. It's a matter of sitting with paper, pen, computer and other people's articles and trying to make headway. Then, in the afternoon, my students are typically working on projects with me, and we can convene and discuss progress and kick ideas around in a more informal way. But I like to have my dedicated, concentrated hours in the morning, when I can just clear my mind and only work on physics.

Q: It's fascinating how we have all these high-tech devices — the Large Hadron Collider, the International Linear Collider, the Supernova Acceleration Probe — but when it comes right down to it, the human brain is still the premier instrument for doing physics.

A: Oh yeah, no doubt about that. And luckily, it doesn't crash as often as some computers do.