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IRA FLATOW, host:

You're listening to TALK OF THE NATION: SCIENCE FRIDAY.

I'm Ira Flatow. This hour, we'll be talking about two seemingly different worlds, one the world of the super-big, like our universe, and the other world of the super-small, like subatomic particles.

One, we have particle physicists looking the tiniest bits of our world with their science-fiction-like names. You have quarks and leptons and bosons and things like that that sound almost made up and sort of are sometimes.

Cosmology, at the other end of the spectrum, looks at the big picture, the really big picture, how the universe, with its stars and planets, came to be. It also has some strange nomenclature. They talk about something called WIMPs, and they have dark energy, and they have dark. They're doing pretty well in making those kinds of interesting names up.

But these two fields, though, do have some things in common. You can't really know about one without knowing about the other. So this hour, we're going to bring them together for you and get an update on what's happened at the frontiers of both fields.

What parts of the puzzle are still missing, and what can the Large Hadron Collider tell us? We're waiting for that come online, possibly by the end of the year. Also, how does string theory fit into all of this?

We've got some of the biggest names in the universe here to talk about it at the campus of Arizona State University, broadcasting from the first annual Origins Symposium, and if you're here in the audience, I invite you to step up to the mike.

We have a microphone right here in the middle - to come down to the aisles on the side and wait for us to give you a little signal, you can come right up to the mike and ask a question.

Also, you can phone it in, 1-800-989-8255, 1-800-989-TALK. Also, you can go to our group that's Twittering us. That's Twittering at @scifri, if you'd like to send us a note, @scifri, or in Second Life or any other way that you think you can reach us, and we'd love to hear from you.

Our guests, let me introduce them. Lawrence Krauss is foundation professor in the School of Earth and Space Exploration and the physics department at Arizona State University. He's also the inaugural director of the Origins Initiative here at ASU. Good to see you again, Larry.

Mr. LAWRENCE KRAUSS (Foundation Professor, School of Earth and Space Exploration, Arizona State University): Nice to see you, Ira.

FLATOW: Thanks, Lawrence. Next to him is Michael Turner. He's professor in the departments of astronomy and astrophysics and physics at the Kavli Institute for Cosmological Physics at the University of Chicago. Welcome back to SCIENCE FRIDAY.

Mr. MICHAEL TURNER (Professor, Departments of Astronomy and Astrophysics and Physics, Kavli Institute for Cosmological Physics, University of Chicago): Good to be here.

FLATOW: Next to him is Brian Greene. He's professor of mathematics and physics at Columbia University in New York. He's also the author of many books and TV shows and stuff. You know, I'm sure he needs no introduction. Brian, good to see you again.

Mr. BRIAN GREENE (Professor of Mathematics and Physics, Columbia University): Thank you.

FLATOW: Also with us is Steven Weinberg. He's a professor of physics and astronomy at the University of Texas at Austin. He won the Nobel Prize in Physics in 1979 for his work in quantum mechanics. Welcome back, Steven.

Mr. STEVEN WEINBERG (Professor of Physics and Astronomy, The University of Texas at Austin): Hello, Ira.

FLATOW: Good to see how. Let me begin at that end of the table. Steven, let me begin with you. What don't we know?

(Soundbite of laughter)

FLATOW: Just a simple little question. What don't we - and we only have an hour to talk about it, so…

Mr. WEINBERG: We understand the way particles and forces work down to a certain scale of distances, maybe a hundredth or a thousandth the size of an atomic nucleus, but when you get to distances smaller than that, we just - for example, light waves with a wavelength less than that, we really don't know how they behave. The laws of physics are not well understood.

That's the sort of thing that will be explored at the Large Hadron Collider. It's also the sort of thing that you need in order to understand the early universe because in the early universe, times were very short.

The size of the universe doubled in a tiny, tiny fraction of a second. Light, in the time that the size of the universe doubled, could only go a very tiny distance, and you're getting into distances that small that are beyond our understanding and in fact even much smaller.

So in that realm of the very small, very short distances, very short times, very high energies, we don't know the rules that govern matter.

FLATOW: Brian Greene - but you - all four of you are theoretical physicists. You just get up there at the blackboards and write those equations, and there are a lot of stories about…

You were theoretical physicists versus experimental physicists, which we won't get into at the moment, but how do theoretical physicists then attack the problem that Steven Weinberg is talking about?

Mr. GREENE: Well, it's a really tough problem, and one of the approaches that we have been very successful at in the last 20 or 30 years is taking little baby steps.

So we have some well-established theories, Einstein's general relativity is the one that we use for describing the large objects, galaxies and the entire universe, the real big scales where gravity matters. And quantum physics, in various guises is the structure that we use to describe the small things that we've been talking about - the molecules, the atoms, the subatomic particles.

And we have been trying to increase the domain within which those theories can be made to work through various approaches known as quantum field theory.

String theory is, perhaps, the most ambitious of these approaches, which tries to whole-hog put together the laws of the big and the laws of the small into one theoretical framework that might be able to go way beyond the scales that Steven was referring to, and perhaps allow us insight into the physics of the very, very early universe, the physics of the Big Bang. So we try to go step by step.

FLATOW: Michael Turner, is it possible for us to test out these theories? I mean, we talk about the Large Hadron Collider coming on now. Will that help us examine whether these theories or particles exist?

Mr. TURNER: I think so. When you asked our don't-know list, it's much easier to describe. We don't know what 96 percent of the universe is. That's the dark matter and the dark energy. And the dark matter - we think it's a particle, and we actually think that particle could be produced at the LHC and so if you're a cosmologist, you actually call the LHC the DMF, the Dark Matter Factory.

FLATOW: What particle would that be that you're talking about?

Mr. TURNER: Well, we think it's a particle implicated at the scale that Steven Weinberg was talking about, a particle that weighs maybe a hundred, maybe a thousand times what the proton does, and one name for is the neutralino, the lightest super-symmetric particle.

FLATOW: There's that name again. How did you come up with the name, a neutralino?

Mr. TURNER: Well, we're going to change that eventually.

(Soundbite of laughter)

Mr. TURNER: The focus groups don't like it so much.

(Soundbite of laughter)

Mr. TURNER: But I think the goal is - I think we've got a very good chance at the LHC to produce the dark matter particle. And that would end this 70-year-old mystery that started with astronomers, Fritz Zwicky, showing that there just wasn't enough mass in the stars to hold the universe together - going through this period where this connection between the very big and the very small came together, and dark matter was a central focus point, recognizing that there's not enough atoms in the universe - that's the four percent we do know about - and that implicating a new particle. And the LHC could be the place where we tie that story up, produce that particle and give it a better name.

FLATOW: Will we ever know what this dark energy is?

Mr. TURNER: So I think that's what gets everyone excited in cosmology. That's the next big problem. And there we feel like the solution may be a lot longer out, so we're not so focused in what it is. It might be something as simple, and I put this in quotes, as "the energy of nothing," quantum vacuum energy. Or it might be something as complex as the breakdown of general relativity. And right now, if you asked any one of the panelists, we could wax poetic about either solution.

FLATOW: Lawrence, do you want to wax poetic?

Mr. KRAUSS: Well, I did want to add that the neutralino is Italian, which is one of the reasons that we call it that.

FLATOW: You have to explain that a little bit.

Mr. KRAUSS: Well, it comes from - neutrino was actually - it's a long history. It was an Italian version of the neutron, when it was first invented - named by Enrico Fermi. But - and so we tend to follow those baby steps in general.

Our nomenclature isn't always the best, as we said, but the ideas are fascinating, regardless of the names. And dark energy is, as Michael said is - actually, I wouldn't say it's the next big problem. It's the biggest problem, I think.

I think we'd all agree on that, that the biggest mystery in particle physics and cosmology is why empty space appears to weigh something. That's literally the case. Most of the energy in the universe - you get rid of stars, you get rid of galaxies, you get rid of all the radiation, you get rid of dust. Empty space appears to have energy, and that's just crazy.

It's crazy if you think about it in a general sense, but from a physics perspective, it's kind of crazy except when you apply the laws of quantum and special relativity together, empty space isn't so empty.

So it's a bubbling, boiling brew of virtual particles that pop in and out of existence in a time so short you can't see them. So you might say okay, well that's fine. It's just due to them.

But the problem is when we apply our naïve ideas to that energy of empty space, we come up with a prediction, which is wrong by 120 orders of magnitude, which is probably the worst prediction in all of physics. And that's why we're excited because getting it wrong means there's a lot we have to understand.

(Soundbite of laughter)

FLATOW: I remember the last time I talked to Steven Weinberg about this, he said one of the great mysteries is that there should be a lot more of that stuff, right?

Mr. WEINBERG: Yes, exactly, and that's a problem that faced a lot of us for decades, and many of us assumed, well, we know it's 120 orders of magnitude smaller than we would naively expect. So clearly it's zero, for some reason that we haven't yet been smart enough to figure out.

And then in 1998, two groups of astronomers discovered it's not zero, it's just very small. And that compounded the puzzle, but the puzzle is not simply that there is energy in empty space, the puzzle is why there's so little of it and yet not none at all.

FLATOW: Does it mean we need new physics?

Mr. WEINBERG: Well, we don't know. It may be - oh undoubtedly we need new physics of some kind or other. The question is how new. How much of a revolution in physics will be required?

I can just say that a lot of very bright people have broken their heads over the years, trying to understand the dark energy. At first, we tried to understand why it was zero, when we thought it was zero, and now the problem is to understand why it is what it is, and there are no very good explanations. There are some that have been offered, but none obviously is correct.

FLATOW: Well hang on. We have a lot to talk about. We have a whole hour to do it. We have to take a break and pay some of the bills here. So we're going to take a break and come back and talk more with Lawrence Krauss, Michael Turner, Brian Greene and Steven Weinberg.

Our number, 1-800-989-8255. We encourage you to step up to the microphones here if you're here with us at Arizona State University. Also, twittering. Please send those twitters in, and phone number, as I say, 1-800-989-8255. Stay with us. We'll be right back after this short break.

(Soundbite of music)

FLATOW: You're listening to SCIENCE FRIDAY from NPR News.

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FLATOW: You're listening to SCIENCE FRIDAY from NPR News. We're at the campus at Arizona State University, at their Origins Symposium with guests: Lawrence Krauss, who is the driving force behind the symposium; Michael Turner, Kavli Institute for Cosmological Physics at the University of Chicago; Brian Greene, professor of mathematics and physics at Columbia; Steven Weinberg, professor of physics and astronomy at The University of Texas at Austin and winner of the 1979 Nobel Prize in Physics.

Our number, 1-800-989-8255. Lawrence, you wanted to say something.

Mr. KRAUSS: Yes. To jump in to what Steve was saying, one of the things we're actually going to have a discussion, if not a debate, at this meeting about is that one of the explanations that's been proposed is one that many scientists distasteful, but it may be true.

And that is this energy of empty space is such that if you added a little bit more, just a little bit more, galaxies wouldn't form, and if galaxies wouldn't form, then stars wouldn't form, and if stars wouldn't form, then astronomer's wouldn't form.

So the argument is the universe is the way it is because there are astronomers here to observe it.

(Soundbite of laughter)

Mr. KRAUSS: And that may sound ridiculous, and some scientists think it is, but nevertheless, it's become a possibility, and in fact, some string theorists in particular have argued that that may be the prediction of - well, if there's any predictions at all.

FLATOW: I'm having a senior moment about what's-his-name, the famous physicist who recently died who was the first proponent of that, in Texas. I'm forgetting what his name is.

But we're here because we see the universe.

Mr. KRAUSS: Yeah, and you know, the point is - well, many physicists find it distasteful because for 400 years, physics has tried to explain why the universe is the way it is rather than why it isn't, but at the same time, and for another reason, whenever we've gotten to a point where something really strange has come up, the anthropic principle has been proposed as an explanation.

But in this particular case, it's such a dramatic and difficult thing to understand, and it's also there are theories which provide a natural mechanism for many different universes, and string theory is one such possibility, that give that additional strength. And so there's a huge debate in the physics community about that.

FLATOW: Gentlemen, feel free to jump in at any point if you want to add something. Hey, I'm struck by what you said about the dark - the holy grail now is the dark energy because just a few years ago, we talked about uniting the forces of nature as the holy grail, you know, uniting gravity with the other forces, and that's sort of gone into the background, Michael, and it sort of faded a bit.

Mr. TURNER: You can't always choose the problems that nature gives you. So we're still very interested in looking at hints for the unification of the forces from the early universe, and one of our other big holy grails in cosmology right now is to test this idea of inflation, the idea that the universe went through a growth spurt and that this growth spurt, very early on, which explains a lot of the features of the universe today, including the galaxies and astronomers that we know exist, by blowing up quantum fluctuations, that would be or could be a big clue and piece to this unification.

And so that's one of the other major threads is, did the universe really go through this growth spurt. And thanks to the instrumentation we now have, particularly measurements of the microwave background, we're starting to test this idea. And what we might do in the next 10 years, probably more likely than solving dark energy, is to figure out when and if inflation took place. And if it really did take place, it could be a clue to this unification of the forces.

FLATOW: Brian, when the Large Hadron Collider does get up and running - what is it, slated for November or something like, somewhere around there, when they get it fixed - what particles - Michael mentioned a particle - what particles will it help you in your string theory ideas? What would you like to see come out of that?

Mr. GREENE: Well, there's a class of particles that string theory naturally gives rise to, that are called super-symmetric particles. I mean, the full name of string theory is super-string theory, and the super refers to this feature called super-symmetry.

And the idea is that for every known particle species - electrons, quarks and neutrinos - there is a partner particle that we haven't yet seen: for the electron, the super-symmetric electron or the selectron; for quarks, squarks; neutrino; sneutrino.

FLATOW: Is that because we think nature is symmetrical or likes to be symmetrical?

Mr. GREENE: Well, there are a number of pathways that lead to this idea, and one is this notion of unifying all the forces. So string theory is an approach that naturally does unify all the forces, but what comes along with that unification is this super-symmetric quality.

So, that's sort of one approach. There also are some experimental hints that this actually is a better way of describing existing data. So there are a number of avenues of thought that lead to this idea, and we'll look for the particles and see if they're found.

FLATOW: What about this thing called the Higgs boson?

Mr. GREENE: Higgs boson is another important particle that I'd say the majority of physicists think we will find at the Large Hadron Collider, and it's the particle that gives mass to the conventional other particles in the world around us.

So the reason why the electron has the mass that it does, according to this approach, is that we're all immersed in a kind of Higgs ocean, a Higgs field, a misty Higgs molasses, if you will, and as the electron tries to go through this Higgs molasses, it experiences a resistance to any acceleration, and that's usually what we call mass.

Now if this Higgs molasses is around, you should be able to hit it really hard, which we'll do at the Large Hadron Collider, and chip off a little piece of it. And the little piece will be a Higgs particle, and we'll look for that.

FLATOW: Steven, do you think we'll be more upset if we find it or more upset if we don't find it?

Mr. WEINBERG: Well, I think it'll be a lot more exciting if we don't find it.

(Soundbite of laughter)

Mr. WEINBERG: Some of us are dreading that what the LHC will find is a single, electrically neutral Higgs boson where it's expected with a mass of, oh let's say, 130 or 150 times the mass of the proton, and nothing else. I think that would be the worst possible outcome.

A much better outcome would be if they didn't find it at all.

FLATOW: Why? If they're going to look for it, why is that…?

Mr. WEINBERG: Then we have to go to the theoretical drawing boards. I mean, there are theories that manage to explain masses and explain why the different interactions don't have the same properties, so-called broken symmetries.

There are theories that don't have a Higgs boson in them, and those theories might turn out to be right, although they have problems. They're not as popular as the theories in which the Higgs boson appears.

But it would be exciting to be sent off in a new direction, but it would be really boring just to find the Higgs boson.

(Soundbite of laughter)

FLATOW: Lawrence - I want to move back to you all in a second. Why - this is something I haven't heard from…

Mr. KRAUSS: Well no, but I mean, I think it's the biggest misconception about science is that somehow scientists are happy understanding things. In fact, if you're a theorist, you're happiest when you don't understand things because there's a lot more to understand about nature.

And in fact, that's the other thing that I think Michael was referring to. Nature surprises us, and that's the great thing. I mean, if we didn't - if nature wasn't more imaginative than we were, we could just sit in closed rooms and just come up with theories of everything.

But in fact, nature surprises us, and every time we put a new window on the universe, almost every time, it's surprised us. Dark energy just came out of nowhere, and so that's what makes science exciting, is in fact, the search - is not understanding.

And for many people, that's uncomfortable. For a scientist, that's the best. To be perplexed is the best state of mind to be in.

Mr. WEINBERG: Just to add to what Lawrence said. I think Steven is saying that particularly illustrates it because the Higgs particle finishes his story, his unification of the electromagnetic and the weak force.

And so here we have Steve Weinberg, instead of saying oh, all I want for Christmas is the Higgs from the LHC…

(Soundbite of laughter)

Mr. WEINBERG: …what he really wants is clues about where to go next and new puzzles, and I think that's what scientists are all about.

FLATOW: Brian, tell us a little bit more about it.

Mr. GREENE: Yeah, I mean, I think this is a really important point, but it's one that really even has an important implication for how we go forward with funding.

I mean, if you find nothing at the LHC, that would be really exciting to us, but imagine going back to the funding agency and saying you know what? Here's what we found: nothing.

(Soundbite of laughter)

FLATOW: I hate it when that happens.

Mr. GREENE: But if you have a public that really is attuned to what science is about, which is going into the unknown and not finding what you expected, and that's what really gets the juices flowing, then a result such as we didn't find anything at all and therefore we need to build the next machine, which will take us to the next frontier, that would be completely understandable.

FLATOW: Very interesting. 1-800-989-8255. Yes, sir.

GENE(ph) (Audience Member): I'm Gene. You know me as Genius(ph) on Twitter. It's starting to remind me of in Iowa, one day the wind stopped, and all the chickens fell over. So not finding…

Back in the early '60s, I learned - studied physics, and then I was told to get close to the speed of light, it takes a little bit more energy. A little bit closer, it takes a whole lot more energy. A little bit closer again, a whole lot and whole lot, a lot more. In other words, you never get there.

My question is with this idea of inflation, I see that as the universe expanding faster than the speed of light. Is it possible that, you know, under those conditions, if things really were sent out, wherever out is, to us faster than the speed of light and just that the light hasn't had time to get back to us?

Mr. GREENE: Actually, you have to be - we lie to you in school. We lie a lot, but you have to be like a lawyer and parse it a little more carefully. Nothing can travel through space faster than the speed of light, but as far as we know in general relativity, space can do whatever the heck it wants.

And in fact, inflation or not, there are regions of the universe right now that are expanding away from us faster than the speed of light. Locally - in fact, in general relativity, you can be moving at the speed of light and still be standing still. You're doing it now, in this room, you know? I'm moving -unless you had a lot of coffee, you're not moving very fast. But relative to a radio audience at the other end of the universe, which isn't moving fast in their local surroundings, we're moving away at the speed of light.

And that has profound implications, by the way. In fact, one of the biggest implications of dark energy - and I find it poetic - you ask me to wax poetic -I think one of the most poetic things is that it means the universe is speeding up.

And actually, in the far future, everything we now see, except for our local galaxy and a region of galaxies will have disappeared. The entire universe will disappear before our very eyes, and it's one of my arguments for actually funding cosmology. We've got to do it while we have a chance.

(Soundbite of laughter)

Mr. WEINBERG: What's a billion years here and there?

Mr. TURNER: That'd be the dark energy beyond.

FLATOW: Dark energy you can't see. All right, thanks for your question. 1-800-989-8255. And not to mention those things that - the spooky action-at-a-distance thing that people think - try to understand, right?

Mr. WEINBERG: The weird quantum mechanics.

FLATOW: The weird quantum mechanics.

Mr. TURNER: Quantum mechanics is, I mean, a lot of people have said it that if you think you understand quantum mechanics, you don't. I mean, general relativity is easy in a sense, and special relativity is easy because the mathematics isn't even that difficult in special relativity. But conceptually, quantum mechanics is just completely beyond our intuition. And it fascinates people. We can understand how to write down on a paper, but to truly conceptualize it is really where it ends.

There's a lot of fascinating experimental physics going on right now that try and use quantum mechanics for fancy things like sending messages and cryptography and all of that.

FLATOW: A great compliment to the panel coming in on the Twitter from somebody who says - (unintelligible) says, I finally know what a Higgs boson particle is. Thanks.

Not many times we've talked about this, but you folks have.

Mr. TURNER: Every time I get out of the taxi cab, that's what the guy says.

(Soundbite of laughter)

FLATOW: There should be a TV show about stuff like - you know, like reality shows, where, you know, not just the CSI. We should have something with physicists looking for…

Mr. TURNER: We talked about that. I share this before the panel, we all be stuck in a house and people get to vote us off and…

(Soundbite of laughter)

Mr. TURNER: Yeah. Dancing with physicists.

FLATOW: Well, if The Woz could be on there, there's hope for anybody. Do we have another question from the audience here? Please, if you're asking a question, step up to the mike. 1-800-989-8255.

Let's go to the phone to see who's got a question there. Let's go to Steve(ph) in Modesto, California. Hi, Steve.

STEVE (Caller): Oh, hi.

FLATOW: Hi, there.

STEVE: My question is what happens when photons collide in deep space.

FLATOW: What happens…

STEVE: This is after…

FLATOW: Go ahead.

STEVE: After 13 billions years of - and almost infinite number of photons, I expect some of them have collided with each other. What happens to that energy?

FLATOW: All right. We'll see what we can do. Let me just remind that everybody that this SCIENCE FRIDAY from NPR News. I'm Ira Flatow here at Arizona State University. Michael, you had your hand up first then go to Lawrence.

Mr. TURNER: That doesn't happen very much anymore. So…

FLATOW: What do you mean anymore?

Mr. TURNER: The universe today is very, very big. And so, the space between photons is quite large. And so, the probability of two photons colliding is not very big. But if you go back to the past when the universe was much smaller, then the same number of photons occupy a lesser space. And so, the chance for collision was greater.

And in fact, we'll be talking about this this afternoon. This is one of the barriers to looking back to the very beginning. Because when we look at these photons in the microwave background, the most abundant photons, they haven't collided for the last 13.7 billion years. And that seems like a very long time, but they last collided when the universe was about 380,000 years old. And because of that, we can't look with our eyes any further back. And so it's one of the barriers we have to studying the earliest moments of the universe.

Mr. KRAUSS: But at the same time, it provides an opportunity because, in fact, that's what so wonderful about the universe is that the photons haven't collided, that the microwave background gives us a picture of what the universe look like almost 13.7 billions years ago. That's why two Nobel Prize - in fact, one of the people who won them is in this room.

FLATOW: Right.

Mr. KRAUSS: But that's why it's so important, because it gives us a baby picture of the universe.

FLATOW: Did you want to jump in, Brian?

Mr. GREENE: I like to say that it's also good to think about scale, though. I think when one says that the photons are very far apart, we need to have in mind how small the photons are. I mean, in any cubic meter of space, there are roughly 400 million of these guys running around.

So, there are a lot of them. They just interact so feebly that it's rare in those environments that they would actually interact much.

FLATOW: Mm-hmm. Yes, Steven?

Mr. WEINBERG: Well, I have to, though, support the questioner. Every once in a while, even now, a couple of photons in intergalactic space collide, but their energy is so low that the only thing that can happen is two photons go in, two photons go out.

(Soundbite of laughter)

Mr. WEINBERG: The different thing in the early universe is, when you go back to the very early universe when the temperature was something like 10 to the 13 degrees Kelvin, that when photons collided, electron-positron pairs could be produced, charged particles could be produced. That can't happen now because there isn't enough energy.

FLATOW: But don't we have photons in this room colliding all the time?

Mr. WEINBERG: Sure. Sure.

FLATOW: Yeah, because they're light particles.

Mr. WEINBERG: But not much - I mean, they collide and…

FLATOW: Right.

Mr. WEINBERG: …who cares?

(Soundbite of laughter)

FLATOW: If two photons collide out in the universe, is there anyone around to know it happens, you know, like the trees in the forest, they still make a noise. Yes, Lawrence, did you want…

Mr. KRAUSS: I was going to say that there is - there are, however, photons that do collide. And they're another one of our windows in the universe. There are objects out there, perhaps black holes colliding or stars exploding that are producing very high energy cosmic rays, which produce very energetic particles. Some of them may be very energetic photons, and they collide in the atmosphere and we use those photons which then produce particles in our atmosphere to try and learn about objects from extreme distances in space. It's a very exciting area of physics right now.

FLATOW: Mm-hmm. 1-800-989-8255 is our number. We - better than to get into another topic of discussion, let's get ready for a break because we have less than a minute to go. Let me reintroduce the panel: Lawrence Krauss with Arizona State University, Michael Turner, University of Chicago, Brian Greene of Columbia, Steven Weinberg, University of Texas at Austin. Our number: 1-800-989-8255. We're getting some of the best questions we've ever had coming in from the audience today. I'm just happy to sit here and not even look on my notes because your questions are better than ones that I would ask.

Also on Twitter at SciFri, and also in Second Life. Your avatars are hanging out there and sending in some good questions. We'll get to those. You can get free SCIENCE FRIDAY T-shirt for your avatar in Second Life. So don't be bashful. Stand up and put your hand in the box, pull out a T-shirt. We'll be right back after this break. I'm Ira Flatow at Arizona State University. Stay with us.

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FLATOW: You're listening to SCIENCE FRIDAY from NPR News.

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FLATOW: You're listening to SCIENCE FRIDAY from NPR News. I'm Ira Flatow here at Arizona State University, talking with - talking about physics, cosmology, particle physics, all kinds of stuff. Gone into interesting side trips. And I mentioned before, I couldn't think - I had a senior moment. I couldn't think of the name of the person I was trying to think of before. It was John Wheeler who had mentioned that - his idea was that the reason the universe exists is because we are here to observe it. It needs the process of observation to create the objects in the quantum world.

Also with me is Lawrence Krauss of Arizona State University; Michael Turner, University of Chicago; Brian Greene of Columbia University, also he's head of the Science Festival in New York. It's happening this year, right?

Mr. GREENE: Yeah. June 10th to June 14th, the World Science Festival, yeah.

FLATOW: World Science Festival. Great. Also, Steven Weinberg, professor of physics and astronomy in University of Texas at Austin, and winner of the 1979 Nobel Prize in physics.

Steven, was I right about John Wheeler? From another fellow Texan - I know you came, like, to Texas pretty late there, but…

Mr. WEINBERG: Yeah. Well, he - yes, you are right about his views, but his views were very different from those of most astronomers and physicists today. John really thought that things - the only things that can exist are things that we observe, and they exist so that we can observe them.

I remembered, he had an argument, the universe will live forever. It has to be eternal, because otherwise there wouldn't be time for us to observe everything. Now, John, was a great physicist and he was my professor at Princeton, but I think that was sort of crazy.

(Soundbite of laughter)

Mr. WEINBERG: And most of us take a very different point of view. For us, this whole anthropic business only makes sense if what we call the universe, the Big Bang, the galaxies expanding out to billions of light years in all directions is just one part of a much larger multiverse.

FLATOW: Mm-hmm.

Mr. WEINBERG: And in which the different parts have different values for constants of nature, like the dark energy. Then, the anthropic idea just becomes common sense. It's just like trying to understand why water is liquid on the surface of the Earth.

If the Earth was the only planet in the universe, then it really would be amazing that with just the right business from the sun to make water liquid and how intense life to be possible. And John Wheeler might say, well, it has to be that or else we wouldn't be here.

But most of us would feel a bit, you know, that was kind of theological. On the other hand, if there are countless planets which we now know there are, then -and many of them are not close - are either too far from their planet for water could be liquid or too close to it…

FLATOW: You mean, there sun.

Mr. WEINBERG: Yeah. I mean, I actually mean from their respective stars.

FLATOW: Right.

Mr. WEINBERG: In that case, it's natural that we are on one of - the minority of planets which are at the right distance from this star. It's just common sense.

FLATOW: Yeah.

Mr. WEINBERG: That's what where we would be. And there's nothing in the formation of planets that has anything to do with us.

Mr. TURNER: And it's not - it's also, and Steve forgot to mention something very important. It's not theological. A lot of people think that somehow the anthropic principle suggests the universe is fine tuned so we could exist, and that's evidence for - but it's exactly the opposite. It's just like evolution. It's, you know, why does a bee so fine tuned to be able to see the flowers? Because if it wasn't, they wouldn't survive. And in this case, it's cosmic evolution.

M: Yeah. But John Wheeler probably did think it was fine tuned.

Mr. TURNER: Yeah. Yeah, he did, I think. And that's why we disagree in stuff.

FLATOW: Speaking of fine tuning, Michael, Did you…

Mr. TURNER: Some of us chaff at using the word anthropic and common sense in the same sentence.

FLATOW: I can see that.

Mr. TURNER: And when we have so much in front of us to try to understand about the universe - I mean, if you - the metaphor for cosmology right now is that we know a tremendous amount about the universe. And we understand a lot less. And so, some of us feel like we ought to concentrate on our own universe before we imagine a multiverse.

FLATOW: Well, let's go to our own universe, and a question right here in the front row, yeah.

Unidentified Woman: You guys briefly mentioned the importance of public understanding of the value of scientific discovery, the idea that a non-finding can be equally as important, if not more important, than a tangible discovery. This is something that's clearly important to you, gentlemen, because you're participating on a public forum. How do you feel that academics in general are addressing this issue in terms of funding and also in terms of just increasing public understanding of science?

FLATOW: Can you be more specific and give us an example of what you're talking about?

Unidentified Woman: Well, specifically, you guys were talking about the Hadron Collider.

FLATOW: Right.

Unidentified Woman: And you can read in scientific articles that people think that scientists, in general, will be creating a black hole and kill us all.

(Soundbite of laughter)

FLATOW: Mm-hmm.

Unidentified Woman: And that this is not good for anybody.

FLATOW: Well, we all hate it when that happens. Yeah. Yeah.

(Soundbite of laughter)

Unidentified Woman: So how do physicists in general address this question, that I think has - it has its roots in public - the public not understanding what you physicists are doing in general.

Mr. KRAUSS: You really hit a really important point that I think the scientific community is partly responsible. We tend to sometimes hype things so much. And we have to be aware. You know, we've got to be careful about saying what is likely to happen, and we want to promote things. After all, the Large Hadron Collider costs a lot of money and we try to convince people to spend money to do something. And we often like to say it's going to recreate the early universe. It's going to - and sometimes that comes back to bite us.

I think it's very important that scientists try, of course, to get people interested in what we're doing but not over-hype the situation because it's always bad. And in fact, it's exactly that if we say we're guaranteed to discover all these new particles of Large Hadron Collider and we see nothing, then how can we come back and later say, you know, that was what we really wanted. Okay.

Mr. GREENE: Although I might just add one thing to that, I don't think it was by design but this notion of creating a black hole that could eat up Geneva and the rest of the world was perhaps the greatest PR ploy that one could ever have imagined for the Large Hadron Collider.

(Soundbite of laughter)

Mr. GREENE: I can't tell you the number of television and radio shows I did where they ostensibly said they wanted to talk about the physics of the Large Hadron Collider. The only reason they had me there was to discuss black holes eating up the Earth. And it was actually a wonderful opportunity to then jump off from that and talk about the bill signs and how exciting it is.

But getting back to your question more generally, I think there was a time when there was a resistance on the part of the scientific academic community to be out there talking about ideas in the public setting. And when I was writing my first book, there was definitely a fear that I don't know how my colleagues are going to respond to this. But I was really pleasantly surprised, there was great support among the people who - at least in my face - there is great support.

And I really get a sense from doing this World Science Festival and other activities that there's a willingness and even an enthusiasm on the part of so many scientists to try to get the real message of science out there. So I think things are going in the right direction.

Mr. TURNER: And I should say that, you know, for programs like this there's some perception of some people in media that people aren't interested in science. But lots of people listen to this program and we have an event associated with this meeting, yesterday at a high school, 1,000 teenagers spent two hours in the afternoon, and there was no basketball players there. There's you know, three physicists. And it was really gratifying.

I think the public really is interested. And probably the people we have to commit the most maybe are from the media people because I think the public is fascinated by what's going on in front of science.

FLATOW: Yeah. We have 12 million downloads of our Podcast, so it's pretty - you've given them the opportunity to listen to it as much as they can.

Mr. WEINBERG: This is an old story when Galileo wrote his dialogue concerning the two chief systems of the world, in which he presented his discoveries about astronomy. He wrote it in Italian rather than in Latin. Latin was the language that would reach scholars throughout Europe. And Italian was a language that would be read by ordinary people. And he wanted it to be read by ordinary people. Unfortunately, it got him into some trouble.

(Soundbite of laughter)

Mr. WEINBERG: But we don't face that problem at least.

FLATOW: While we have a large audience here, Brian, let me ask you about string theory and what do you think is happening with it. It's been many decades now, old - are you still is confident in it as you've always been, or what - about answering everything?

Mr. GREENE: Sure. Yeah. That's a great question. And I think it's worth just clarifying what confidence means. I'm often asked, do you still believe in string theory. And I'm glad you didn't frame it that way because my response to that question would have been I don't believe in anything until it's experimentally proven. I have confidence that this is the best approach currently on the table for answering this deep question of putting together Einstein's theory of gravity, general relativity and quantum physics. If there were a better theory on the table, I'm sure all of these string theorists would turn their attention toward it. It is the best thing we have. And over the last few decades, the math has come together in such an incredibly compelling way. The pieces have locked together in a way where as you work on it, you feel that it has to be leading me toward a true, deeper understanding of the world. But that is not how you judge a theory. You judge it whether it makes predictions that are going to be confirmed by experiment, and we are working hard in that direction. So, yes.

Mr. TURNER: I suspect Lawrence maybe wants to…

Mr. KRAUSS: Yeah. Brian and I have talked about this publicly in the past. But, yeah, it's been, I think, however, unfortunately, the direction has demonstrated that it's less and less likely they've be able to predict anything. In fact, instead of a theory of everything it would be a theory of anything in that sense that, right now it looks like that it predicts a multitude of possible universes in which almost anything can happen. And science is sort of based on falsifiability, and if you could predict anything, then you really predict nothing. And so it is still promising, although I see my friend Frank Willcheck(ph) in the audience and he says it's been promising and promising and promising. So, we'll see.

FLATOW: Okay. Did you want to get a rebuttal in, Brian?

Mr. GREENE: Well, the only thing I would say to that is, you know, when you're trying to answer questions that are this deep; questions that are in one form or another we've been asking for thousands of years, questions that could indeed lead to resolutions of how the universe began, where it all came from, the origin of time - these are big issues. And if you're working on a theory for a few decades and it matures in various unexpected ways, you go with it and you try ultimately to extract some predictions from it.

So, I would say that trying to judge string theory today is like trying to judge a block of wood that hasn't yet been turned into a violin. You know, it's in an infant stage. It's a very difficult problem. The progress has been astounding. There are questions that we've resolved in the theory that I, 20 years ago, and I think my colleagues would agree, would think we would never get this far in certain domains. But we've not made enough progress in the other direction which is making the experimental predictions, and that's just the state of being at the cutting edge.

FLATOW: Well, and it also looked to me as a journalist and as someone who'd deal with the public, it goes back to the question you were saying before. Whatever you say just spell its name right. You know, the fact that there is a controversy about it and gets people to talk about it, you know, and even think about the controversy of it. And they begin to talk about it and there can't be anything wrong with people talking about science.

And speaking of which, this is SCIENCE FRIDAY from NPR News. I'm Ira Flatow here at the Arizona State University as part of the - excuse me - as part of my - I have to drink a water - as part of symposium we're having here. And we're going to go to audience - a question? Go ahead right there. Every week I have this same part of the show, I need a glass of water. Go ahead.

Unidentified Man #5: I wanted to say come back. You've mentioned about the expanding universe and then the cosmology and how your, Lawrence, your pun that eventually we won't be able to see anything at all because of the rapid expansion of universe. And I want to know, like, in your professional opinion, whether we're misinterpreting this and that is it all possible that 96 percent that we don't know right now could be explained by it's too far away for us to see, it's moving too fast and we're in a localized universe now?

Mr. KRAUSS: Well, I mean, all right, your question went in different directions than I thought it would. I think the answer is no to that particular part. I think - I mean what we're measuring things we can see here now. We're measuring the acceleration of galaxies away from us. We're watching them speed up. And so we're seeing things in our universe. But what it does point out to me - and I think this is really - maybe we should be humble. Because one of the things we've recently discovered, which I think is fascinating is that in the far future - because these dark energies persist, than astronomers in the far future will come up with a picture of the universe which is completely wrong. There every bit of the evidence will suggest they live in a static, empty universe, exactly the universe we thought we lived in the 1900.

And so I'd like to say we're living in interesting times. Maybe the only time in the history of universe when we can - when we know we're living in interesting times. But the more important point is, it suggests that if we're - if they're missing something then, maybe there are key parts of the universe that we're missing now. And while we have this incredible picture that there maybe things that are out there that are going to change it completely. And really that's what makes science so exciting.

FLATOW: Now, Lisa Randall was on the program a few weeks ago and she talked about the fact that the reason why gravity is so weak here is that it may be a part of another universe sitting right next to us, and was just leaking into here. What do you think? Is that…?

Mr. KRAUSS: It could be. I wouldn't bet on it. But it could be.

(Soundbite of laughter)

FLATOW: It may not - but there could be other universes that are around us that we don't know about?

Mr. KRAUSS: Well, if she's talking about, in that context, they're talking about a possibility comes from string theory in which extra dimensions…

FLATOW: Right. Right. Yeah.

Mr. KRAUSS: …not other universes in our space, but other universes in extra dimensional space which is sort of one of the requirements of string theory. And it's certainly possible. I don't personally think it's a very attractive picture, but we'll see. And we may… And there's some people who hope there may be evidence for it at the Large Hadron Collider. If the extra dimensions are large enough, maybe we'll be able to bang things together so hard that some of the energy leaks in extra dimensions. Again, I wouldn't bet on it.

FLATOW: Brian?

Mr. GREENE: Yeah. Which is a good point just to emphasize, we're talking about string theory in the fact that we've not been able to put on the table, do this experiment and find these results that theory is giving a result that's confirmed. And if you don't find that, the theory is ruled out. We can't get to that stage.

But it is possible with the Large Hadron Collider, long-shot possibility, that some of the features of string theory could be approved(ph). It is idea of extra dimensions, you know, slamming these protons together at very, very high speed and some of the debris gets jammed in other dimensions and you recognize that by having a little bit less energy in our part of the universe, and it's leaked away. That would be great. Finding these super symmetric particles, that'd be great. Creating a little microscopic black hole, again an idea that really has its origin in string theoretic ways of thinking about things. That would be spectacular.

FLATOW: Yeah.

Mr. GREENE: So, all these little pieces of the puzzle, where they to happen - again, I consider it a long shot - but where they happen again, you would have much great confidence that this set of ideas was going in the right direction.

FLATOW: Michael, you can go about 30 seconds.

Mr. TURNER: Okay. I was just going to get to the question asked, which sort of was, could this cosmic acceleration go away? It's such an extraordinary thing - we haven't used the word.

FLATOW: Do we know why it happened?

Mr. TURNER: Well, we…

FLATOW: Why it kicked in at that point?

Mr. TURNER: We would say that dark energy has repulsive gravity. And so, I think the question is an interesting one. And that's an extraordinary thing, Carl Sagan used to say extraordinary results require extraordinary evidence.

And 11 years ago, when this discovery was made, I don't think the evidence was there. And I think today I could tell the questionnaire that cosmic acceleration is not going away. The observations that have been made over the past 10 years have really nailed it. The universe is really speeding up and we have to deal with that. It's a big, big mystery.

FLATOW: All right. And there's your take-home for tonight, talking around the dinner table, and well the universe is expanding and it's not going away.

I want to thank our guests: Lawrence Krauss of Arizona State University; Michael Turner of the Kavli Institute for Cosmological Physics at the University of Chicago; Brian Greene, professor of mathematics and physics at Columbia University, and also headed the World Science Festival coming up in New York this June; also Steven Weinberg, professor of physics and astronomy at the University of Texas at Austin, and winner of the 1979 Nobel Prize in Physics. We'd also like to do a shout out to KJZZ, our local SCIENCE FRIDAY Public Radio Station, right here in the neighborhood. And thanks also to Arizona State University and the Origins Symposium for their hospitality and bringing us here.

I'm Ira Flatow in Arizona State University.

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