MS. DIANE REHMThanks for joining us. I'm Diane Rehm. A recent experiment at the South Pole appears to have picked up one of the most elusive signals from the early universe known as gravitational waves. These waves, ripples in the fabric of space-time, are said to have originated from the Big Bang during a period of accelerated expansion or cosmic inflation immediately after the Bang.

MS. DIANE REHMJoining me for this month's environmental outlook to explore implications of the discovery on understanding the origins of the universe: Mario Livio of the Space Telescope Science Institute, Geoff Brumfiel of NPR, and Paul Steinhardt of Princeton University. I'm sure many of you will have questions. Do join us, 800-433-8850. Send us an email to drshow@wamu.org. Follow us on Facebook or Twitter. And welcome to all of you. Thanks for being here.

MR. MARIO LIVIOThank you for having me.

UNKNOWNThanks, Diane, for having us.

REHMGood to have you all. Now, as you can well imagine, I am the one with the most questions simply because I think this is utterly fascinating. But I don't really understand it. So, Mario Livio, I'm going to start with you and ask you to briefly explain to us, what is meant by cosmic inflation?

LIVIOSo cosmic inflation is an event that we think happened when the universe was a trillionth of a trillionth of a trillionth of a second old. And at that time, our universe expanded at a stupendous rate, basically from dimensions that were much, much smaller than an atom to maybe the size of something like a grapefruit. So it is that event that actually, when we talk about, for example, the Big Bang, if you like, then that's what banged really in the Big Bang. It is this incredible expansion of the universe, very, very fast, which essentially produced everything we see later.

REHMSo, Geoff Brumfiel, there is something called the BICEP2 experiment, and that is how we get to this point of expansion, a trillionth of a trillionth of a trillionth second afterwards.

MR. GEOFF BRUMFIELWell, that's right. You can't obviously actually see the Big Bang happening. But what we can see is the afterglow of the Big Bang. It's called the cosmic microwave background. And to do that, scientists have built telescopes -- well, some are in space, and some are in Antarctica. There's very favorable conditions for looking at this faint glow that is all over the universe.

MR. GEOFF BRUMFIELThe BICEP2 is one of the most advanced of these experiments. And it is looking for tiny variations, polarization, actually -- kind of, if you've seen glare off water, it's something like that -- in this microwave background. And it uses those variations to infer what happened before -- well, not before the Big Bang -- but before the microwave background appeared.

REHMAnd, Paul Steinhardt, then comes something called gravitational waves, and that's why this discovery is such a big deal?

MR. PAUL STEINHARDTYes. So one of the traces of inflation -- one of the predictions of inflation is that it should produce a set of waves of different varieties. One set of waves produce concentrations of energy and matter -- what we call fluctuations in density -- that end up seeding the formation of galaxies and end up leading to the origin of our Milky Way and our stars and the like. Another set of waves are stretches in the fabric of space itself.

MR. PAUL STEINHARDTAnd they propagate as gravitational waves, waves of gravity itself, which, as they would move past you, would, say, stretch you in one direction and squeeze you in another. We've been -- we have seen for some time these hot spots and cold spots in the cosmic microwave background, which are signs of those density variations. But what BICEP2 has claimed is that they've now seen a second signal -- a signal of the second inflationary prediction, that of the gravitational waves.

REHMSo tell me the implications of their claiming to have seen this.

STEINHARDTWell, so the first implication would be -- it would be strong support for this idea of cosmic inflation. And there are...

REHMAnd the Big Bang.

STEINHARDTWell, and especially -- but the Big Bang generally, and especially cosmic inflation. We have lots of evidence of the Big Bang already, that the universe was hot and has been expanding. And we have evidence, as I said, of these hot spots and cold spots before, which were already consistent with what inflation predicted. But now there's another piece of evidence being claimed that adds another strong piece of evidence that points to cosmic inflation and points a way for, let's say, other competing ideas for explaining the origin of the universe.

REHMSo these are ideas out there, Geoff, and the question becomes: How many within the scientific community sign on to these or how many believe you need more and more and more evidence?

BRUMFIELRight. I mean, I think cosmology, which is what we're talking about here, the origin of the universe, it's a difficult field. And I'm sure Paul...

REHMYou bet.

BRUMFIEL...could say a lot more about that. The thing is it's very, very hard to find evidence of what happened very early on in the universe because, well, it was billions of years ago. So there have always been a lot of really interesting, competing ideas out there about how the universe got its start. Inflation has been one of the favorites. Paul's come up with a few others himself, in addition to inflation. He is instrumental in developing that. And so, yeah, I mean, I think that any sort of data you can get that points towards one of these theories is really important.

REHMWhat about so-called dark matter and dark energy? How does all that figure into what you're talking about, Mario?

LIVIOYeah, so these are different concepts. Basically, most of the matter in the universe is dark, which means it doesn't emit any light. But we see it because we see its gravitational effects. We see that, you know, that's what really holds galaxies and clusters of galaxies together and so on. So that's, in fact, you know, about a quarter of the energy content of the universe. Dark energy is a newer concept discovered in 1998 by two groups of astronomers.

LIVIOBasically, we all thought that the expansion of our universe should be slowing down because there is mass in the universe, and it has a gravitational force which is all-attractive -- everything attracts everything else. We thought the expansion should be slowing down, just like, you know, when I throw my keys up in the air...

REHMThey come back down.

LIVIO...the gravity of the earth slows it down. Instead, what we discovered in '98 is that the expansion of the universe is not only slowing down. It's actually speeding up. It's accelerating. And so there must be something that's pushing the universe to accelerate. And that something is the thing we call dark energy, which is some form of energy that is smooth, fills all space. And it exerts a repulsive gravitational force. It's a little bit like an antigravity. And by exerting this repulsive force, it actually pushes everything apart.

REHMWhat does this suggest about the possible creation of other planets, not just our own?

STEINHARDTWell, what we know about the universe is that it contains billions of galaxies, each of which contain billions of stars. And what we've been learning about the formation of planets and the existence of extraterrestrial planets in recent years is that there's many of them. And that's increased confidence that there are planets of all varieties, including terrestrial-type planets, planets like our Earth, existing throughout the universe.

STEINHARDTBut -- and the origin of those planets, stars, galaxies and all that would have its origin in this very first instance after the Big Bang -- these tiny variations in the distribution of matter that would be created by cosmic inflation. That's what their origin would come from.

REHMWhy is this so exciting, Geoff?

BRUMFIELWell, I mean, I think what makes it exciting is, you know, this is the -- really, this is the question, right, in science in a certain sense. Where did we all come from? And I think, as Paul was just saying, you know, inflation and the Big Bang is really at the root of everything else -- galaxies, planets, stars. I mean, all of it started -- if these scientists are right -- with inflation and the Big Bang.

REHMSo how does this tie in then to Einstein's Theory of Relativity and its relationship to inflation, Mario?

LIVIOSo gravitational waves are a prediction -- a direct prediction of Einstein's Theory of General Relativity. It predicts that there should be these ripples that gravity creates in the fabric of space. And, you see, you asked why this is so interesting. So the first thing you know, it's -- we're talking about the trillionth of a trillionth of a trillionth of a second of the universe, I mean, in the life of the universe.

LIVIOThat's exciting already. Plus this, if confirmed -- if this is confirmed, this would be the first time that we see the effects of these gravitational waves on matter, the way that they leave their imprint in this cosmic microwave background. Third, it would also mean that we can treat gravity with quantum mechanics, which has been something of a holy grail of physics. It's not -- it doesn't tell us what the theory is, but the effect that they're seeing is actually based on a quantum effect. So there are a number of reasons why this result, if confirmed, is truly phenomenal.

REHMMario Livio, he's an astrophysicist at the Space Telescope Science Institute. He's author of "Brilliant Blunders." Geoff Brumfiel is science correspondent for NPR. Paul Steinhardt is the Albert Einstein Professor in science at Princeton University and director of the Princeton Center for Theoretical Science. Your calls, your comments when we come back after a short break. Stay with us.

REHMAnd welcome back. We're talking about a recent experiment at the South Pole that appears to have picked up one of the most elusive signals from the early universe known as gravitational waves. We've got three outstanding commentators here with me. Mario Livio, he's an astrophysicist at the Space Telescope Science Institute. Geoff Brumfiel is science correspondent for NPR. Paul Steinhardt is at Princeton University.

REHMHere's our first email from Bob in Charleston, Ill. He says, "If the Big Bang initiated the cosmic inflation, which took place a trillionth of a trillionth of a second after the Big Bang, that seems to suggest that the speed of light must have been exceeded by the constituent particles. If so, how was that possible? Or was it that that incident obeyed a different set of rules from the ones that nothing can exceed the speed of light?" Paul Steinhardt.

STEINHARDTWell, the speed limit dictated by Einstein's Theory of Relativity is that particles can't travel through space faster than speeds equal to the speed of light. And that law's obeyed, so far as we know, during the Big Bang and during cosmic inflation. However, there's no rule in Einstein's General Theory of Relativity about how fast space can stretch.

STEINHARDTSo even though a particle may be moving through space at speeds less or equal to the speed of light, the space in front of it or behind it can stretch at rates so great that light can't catch up. So, for example, if the space between you and I were inflating right now, after a short period of time, we wouldn't be able to see one another because so much space would be created that light would not be able to traverse that huge distance.

REHMMario, you want to add to that.

LIVIOJust maybe one metaphor, if you like. I mean, imagine points painted on the surface of a balloon. And those points don't move on the surface, right, because they are just painted. But the balloon itself can stretch.

REHMExpands.

LIVIOYeah, and that can stretch faster than light. There is nothing to prevent it in Einstein's Theory of Relativity, even though the points themselves, or if you like, the matter in this case doesn't move faster than light.

REHMThat's a great analogy. Thank you for that. I'm going to open the phones -- because I know our listeners want to be involved -- first to Ryan in Houston, Texas. Hi there. You're on the air.

RYANHi, Diane. Thanks for taking my call.

REHMSure.

RYANCan you hear me OK?

REHMCertainly can.

RYANOK. My question was for Mario because I heard him make this reference. He was saying that the universe -- in respect to the universe accelerating, he likened it to throwing your keys up into the air, and then the force of gravity pulls them down. My question is, how do we know that we aren't just at a relatively early spot in the wide span of the universe where the keys are just leaving the hands and they haven't really gotten the opportunity to slow down yet? And who knows if they can slow down many, many billions of years from now?

LIVIOSo, basically, the gravity actually decelerates the keys even just as soon as they leave my hand. It is -- they have not been decelerated to the point where they return and moving the other direction, but they are being -- they feel the gravity of the earth throughout the whole time and are being decelerated throughout the whole time. What we are seeing is that our universe right now is actually accelerating.

LIVIONow, actually, earlier in the life of the universe, more than about 6 billion years ago, believe it or not, our universe was decelerating because matter within the universe had the upper hand at that time and gravity dominated. This dark energy started dominating over gravity only about 6 billion years ago because of some peculiar property, which is the following: As the universe expands, the density of matter continuously goes down.

REHMHmm.

LIVIOLike, you know, if you expand something, it dilutes it and dilutes. But the density of dark energy stays constant. So what happens is, as the density of matter goes down, down, down, about 6 billion years ago, it finally dropped below the density of dark energy. And that's when dark energy took over and started accelerating the universe.

REHMGeoff.

BRUMFIELI realize I'm on the panel, but I have a question for the other panelists.

REHMGood. Be my guest.

BRUMFIELSo dark energy is this force accelerating the expansion of the universe. Inflation was accelerating the expansion of the universe quite quickly in the early universe. Do people think there's any relation?

STEINHARDTProbably not, just because the timing and the energy scales are so different, different by a factor of, you know, a googol, 10 to the hundred or so, in the density. So there's no particular reason why one event should be closely related to the other caused by the same fundamental physics. In fact, this kind of leads to a bizarre picture of the history of the universe where there's a period of inflation, if you like, or accelerated expansion at the beginning.

STEINHARDTAnd then we're heading towards a new period of acceleration in the future. And the universe, as we know it, the universe made of matter, galaxies, stars and the like, is a brief interlude between these two periods of accelerated expansion. Going into the future, which is what Ryan's question was about, we really don't know what happens.

STEINHARDTThe common view at the moment -- just because it's the simplest picture -- is that we just accelerate forever, and the universe just becomes emptier and emptier of matter as we know it. We don't know that that's true. That dark energy could decay someday. It could be, as Ryan suggested, just the -- you know, act one in what it will be a more complicated story about the universe in which the dark energy itself decays into a new form of energy. And the universe goes through a new stage of evolution.

REHMGo ahead, Mario.

LIVIOI just want to add that if the universe actually will continue to accelerate the way it does today, then about 2 trillion years from now, we will actually not be able to see any galaxy. I mean, all of them would be out of view for us. And if a new civilization is born then in, you know, what remains of the Milky Way Galaxy, then it would just not see any other galaxy. So, as Paul just said, we live in this peculiar intermediate time where we see all these hundreds of billions of galaxies all around us. But this may be just when, speaking in terms of the universe, may be just a short interval.

REHMAll right. To Randy in Elkhart, Ind. Hi there.

RANDYHi, thank you. One quick point in honor of today's date, a trillionth of a trillionth of a trillionth of a second. All the markets on Wall Street just shut down while everyone ran to buy the biggest telescope.

REHMAll right. Go ahead, Randy.

RANDYThe second point is they were talking earlier about the matter stretching along one dimension and shrinking along another. That sounds to me very much like gravity in action on the tides. When the earth is between the moon and the sun, the high tides are on the line between the sun and the moon. And the tides are lowest, therefore the water is shallowest, on the parts of the earth 90 degrees from that line.

REHMPaul, does that make sense?

STEINHARDTWell, the source of the waves we're talking about here that we see in the microwave background aren't from some force like a moon pulling on space. They come from this much more subtle and beautiful effect that Mario referred to, that the universe, as we know it, was at some point before inflation on a subatomic scale, occupied a size much smaller than an atom.

STEINHARDTNow, when we think about energy and matter, we're used to -- or let's say the matter in this room. We think of it as being at rest with respect to us and just sitting still. But we know on subatomic scales matter never is at rest. It's constantly vibrating and fluctuating around. We don't notice it because it's on such a tiny scale.

STEINHARDTBut inflation takes those tiny vibrations and stretches them to scales which are, you know, sizes which end up occupying the observable universe and beyond. And so what we see is a frozen snapshot of what those vibrations and waves were like created by what was originally these quantum vibrations, stretched and then frozen out.

REHMRather than moving backwards, what I'd like to understand is, how do we know for certain that the universe is continuing to expand? How do we know that, Mario?

LIVIOSo there are many, many lines of evidence that show that the universe started from a hot and dense state. And let me just point out a few. One of them is simply the microwave background itself. The microwave background, which is in what we see -- the signature perhaps that has been observed by this experiment, BICEP2 -- this is radiation that fills all space.

LIVIOAnd the universe started with a situation where it was in what we call a thermal equilibrium. Everything was in equilibrium with each other. And we have very, very direct evidence that tells us exactly, you know, how the radiation emitted should behave at every single wave length. And we see that.

REHMI see.

LIVIOWe see it very, very clearly. There are other pieces of evidence that come from all the atoms that we see around us. We call this Big Bang nuclear synthesis, how the light elements were formed when the universe was in this hot and very, very dense state. And finally we see the expansion itself because we look at very distant objects, and we actually see that they are receding from us by the fact that the light from them is actually stretched to redder wave lengths.

LIVIOIt's a bit like, you know, when an ambulance passes you by. When it comes towards you, you hear a higher pitch. and, when it goes away from you, a lower pitch. You hear this as it passes by you. The same happens with light. And everything moves away, shifts the lights towards the red, which is what we call the red shift.

STEINHARDTJust -- but your question, Diane, was about the future. How do we know it's going to continue into the future? The past is certain, but the future we don't know. So if the dark energy is there forever -- it's just going to be some constant form of energy that's going to be there forever -- then it will just be expansion, acceleration, and an emptier and emptier universe going forward in time. But...

REHMWhat does that mean, an emptier and emptier universe going forward?

STEINHARDTSo the universe is expanding today, which means all the galaxies are moving away from us. They will be moving away from us at an accelerated rate. You recall that we discussed inflation. I said, if you and I were in the room and the space between us were inflating, we'd eventually lose sight of one another. The same will happen in the future. We'll lose sight of those galaxies because we are going a kind of slow inflation now. And so we will eventually lose all sight of them.

REHMPaul Steinhardt, he's Albert Einstein professor in science at Princeton University. And you're listening to "The Diane Rehm Show." All right. Let's go to Patrick in Utica, N.Y. You're on the air. Go right ahead.

PATRICKAll right. Thank you for having this show. We need at least a month's worth of this to get this explained.

REHMI fully agree with you.

PATRICKI think of myself as being reasonably intelligent, and the things that they're saying, I -- makes me wish Carl Sagan was still alive to be able to explain these things in a way that I can understand it. Here's my question. Now, if the -- well, the farther away an object or galaxy is, the more red shifted it is. And so this is seen as evidence for the acceleration of the expansion of the universe.

PATRICKBut what I'm wondering is, if the universe, when it's accelerating much more quickly during its infancy -- and supposedly I've heard that it was actually accelerating faster than the speed of light (unintelligible) gradually slowed down to another level which -- I mean, I guess we don't really know how fast it is. But what I'm wondering is, how do we know that this increased red shift of the most distant objects is not attributable to the speed of the expansion a very long time ago?

PATRICKIn other words, we're looking at the old stretched out light from when the universe was expanding more rapidly. And as a secondary, I guess, add-on to that, when Mario was explaining things, I really wish that the scientist communicators would explain how they know, you know, these things that they're saying because, a lot of times, they tell us these amazing mind-bending things, but they don't really explain how the heck they know these things.

REHMI'm glad you called. Mario.

LIVIOSo let me start with the second half of how they know. So how do we know, for example, that there is expansion? So we actually observe these galaxies that are, you know, billions of light years away from us. And we see the light from them being stretched, being red shifted. And by measuring that red shift, we can actually tell how fast everything is receding from each other, you know, every one of these galaxies receding from each other. And plus we actually find the relation that relates the distance to the speed of recession.

LIVIOAnd that relation, which is called the Hubble law, you know, when you know a distance and when you know a speed, you can tell time because, you know, if I know that the distance from here to there is 200 miles and I know I'm traveling at 50 miles an hour, I know it will take me four hours to get there. So we can basically, like, rewind this expansion and see, you know, when did it all start? And that's how we get, for example, an age for the universe, which is about 13.8 billion years.

REHM13.8 -- I love that. Geoff, how do you, as a science correspondent, put all this together for NPR listeners to know and understand?

BRUMFIELOh, my goodness. Well, to be honest with you, I just take my best shot and quote these guys. I mean, I think, going back to what Patrick was just saying, the measurements themselves can be very complicated and very nuanced. Another line of evidence we have for this accelerating expansion is super nova explosions, the explosions of dying stars. We look at those in far-off galaxies, and we measure how bright they are. And that tells us something about where they're moving and how they're moving.

BRUMFIELBut these measurements are really, really tricky. I mean, people are devoting their whole careers to them and, I think, going into a lot of depth about those measurements. I mean, I certainly get lost pretty quickly when we do. But I also think there's a valid point which is, you know, there are a few lines of evidence for what's happening. And it's very, very hard to tell.

REHMAnd the more you hear about it, the more it sinks in, and you begin to understand. Geoff Brumfiel is science correspondent for NPR. We'll take just a short break here. More of your calls, your email when we come back. Stay with us.

REHMAnd welcome back. Here's a great email from Mike, who has B.S. in physics from Purdue. He says, "I'm familiar with previous attempts to detect gravity waves from black hole collisions, et cetera, and the instruments used to detect them, which have been unsuccessful, as far as I know. How does the instrument used for this experiment differ from previous instruments? Why was it able to detect this probably much weaker signal?" Paul?

STEINHARDTWell, first of all, I should say that we already have evidence for gravitational waves prior to this BICEP2 data. It was observed many decades ago by observing the rotation of stars -- known as pulsars -- about one another.

STEINHARDTWe could, from Einstein's General Theory of Relativity, which predicts gravitational waves, predict the rate at which the stars spiral around one another and slow down and confirm with high precision that they were emitting gravitational waves. BICEP2 is looking for something different. It's not looking for waves produced by stars rotating around one another but by these events of cosmic inflation, which stretched quantum vibrations or fluctuations to large scales.

STEINHARDTAnd, unlike previous experiments that have been looking at this cosmic microwave background radiation and observing primarily the variations in temperature or the intensity -- the hot spots and cold spots -- this is looking at that same radiation with something you can think of as like polaroid lenses, polaroid glasses, which screen out some of the light and only allow light in which has a certain polarization, only a certain way in which the electric field is vibrating from that light as it comes through your glasses.

STEINHARDTAnd that pattern can be used to discriminate different sources that are producing hot spots and cold spots. In particular, it was designed to pick out the gravitational wave contribution from simply the variations in density. And that's what they're claiming to have found.

REHMGeoff?

BRUMFIELSo I think what your listener had there was there's actually a different set of experiments that are trying to directly measure the expansion and contraction of space right here on Earth from events in our own Milky Way Galaxy or relatively nearby. It is, in principle, possible to measure tiny, tiny variations in the space we're living in. This experiment, BICEP2, doesn't do that. What it's trying to do is pick up a subtle signature in the after-glow of the Big Bang. And that signature was made by gravitational waves.

REHMNow, if the universe is continuing to expand, could there be another Big Bang in which our own universe would burst its own balloon?

LIVIOSo it is possible -- still possible from an observational perspective -- that the acceleration that we are seeing now will actually, in itself, start speeding up. If that happens, then various scales will start to be torn apart. You know, galaxies will be torn apart. At the moment, the acceleration that we're seeing is not going to tear out galaxies. Just the distance between them increases.

LIVIOBut if this acceleration will increase in itself, it could tear apart galaxies. It could tear apart stars, planets, humans, even atoms and nuclei eventually. So that would be a situation that, you know, we refer to as the Big Rip. We still don't know that that is actually happening. And most of people, I think, would bet against that. But, in principle, that's still possible.

LIVIOThere is another thing that is somewhat related to the question that you ask, and that is the concept of the multiverse, which says that, just like our universe is out there, there can be a huge ensemble of universes, all of which, you know, start with some sort of an inflation of the type that we're seeing in our universe and so on, so it's not, if you like, our own pocket universe but other pocket universes that can pop up, you know, in this large ensemble.

REHMAll right. And to James in Roanoke, Va. Hi. You're on the air.

JAMESThank you, Diane. My question has to do with the nature of the initial conditions that we're looking at with this experiment. And I'm asking you a question: Is it not true that with this experiment that we are looking at essentially conditions, you know, within, like, the Hawking limit where we are actually looking into or out of -- it's hard to look at the perspective that way -- of a black hole from the inside?

REHMPaul?

STEINHARDTNo. I don't think that's the right way to view what's going on. I think we're -- first of all, we're looking at a period in which there isn't enough matter and radiation in the universe or energy in the universe to form a black hole. And the universe is expanding, unlike a black hole, which is fixed. So I would say no.

LIVIOMaybe just I'll put a slight twist on that, which is there is something of the effect that the listener is talking about in the sense that the gravitational radiation that maybe we see its effects now on the cosmic microwave background is sort of a quantum effect, a bit like what we refer to as Bekenstein-Hawking radiation, which is similar to an effect that we see with black holes. The way this gravitational waves are being emitted has something to do with that.

REHMHmm.

LIVIOBu it's certainly not quite a black hole that we're talking about.

REHMAll right. To Jeff in Cleveland, Ohio. You're on the air.

JEFFHi. I have a two-part question.

REHMSure.

JEFFIs it possible, and can we detect, that the expanding universe is curving back on itself? And then the second question is that, is that accelerator in Europe revealing anything about the origin of the universe?

REHMPaul?

JEFFThanks.

STEINHARDTSo at the present time what we see is that the expansion of the universe is speeding up and that there isn't enough matter in the universe or energy in the universe to cause it to curve back on itself. Now, if you're looking about the far future, we can't really tell. It really depends upon what is the nature of this dark energy.

STEINHARDTIs it an energy that's going to remain small and positive forever? Or, for example, could it decay into another form of energy that would cause the universe to maybe undergo contraction and a bounce and a new bang? All these things are logical and scientific possibilities.

REHMHere's -- go ahead.

STEINHARDTAt the accelerator in Geneva, at the Large…

REHMRight.

STEINHARDT…Hadron Collider, there is potentially some interesting results that they -- insights that accelerator can give us about this question. For example, if one takes what we observe today at the Hadron Collider, the particles that we actually observe and assume there's nothing else to be found, then what the Collider is telling us about the nature of our current vacuum, our current state of the universe, is that it's not going to be there forever.

STEINHARDTIt will eventually undergo one of these decays I described, bringing the universe into a phase of contraction. One of the reasons for pursuing new experiments at the accelerator and going on to bigger accelerators is to test that idea because it will give us insights into what will be the future of the universe, the future fate of the universe.

REHMHere's an email from Chris, who says, "I've heard this discovery potentially helps the argument for a multiverse. Is this true? And please explain." Mario?

LIVIOSo it helps the discussion in an indirect way, in the following sense. Let's suppose that this discovery is fully confirmed. Then this would mean that very probably we had cosmic inflation. We had this period of incredibly fast expansion and so on. Now, inflation is not one theory. It's actually -- there are many models of inflation. But in many of those models, it is almost inevitable that, you know, while our universe at some point decayed into a more leisurely type of expansion, other parts continued to expand like crazy.

LIVIOAnd then other parts can decay into other pocket universes and therefore forming a multiverse, you know, this ensemble of many, many universes. So I would say the following: The fact that if we confirm inflation for sure, then it strengthens the case for a possibility of a multiverse. But in no way does it actually prove that the multiverse exists.

REHMPaul?

STEINHARDTWell, there are two embarrassments about the cosmic inflationary theory. One of them is that it's extremely difficult to start this inflation. It requires very special conditions, which we don't know how to have naturally obtained. And the second problem is this multiverse. So Mario was being kind in saying that there's a chance this multiverse occurs. It's really hard to avoid producing multiverse if you have inflation.

STEINHARDTAnd if you have a multiverse, what it means is the universe breaks up into patches, in which every conceivable physical possibility occurs, universes that are like ours and universes that are patches or universes that are completely different. Which means that the theory makes no clear predictions of anything, since anything, literally, can happen in this theory.

STEINHARDTAnd this has been a fundamental problem in the cosmic inflationary theory that's been around for 30 years. Both these problems -- the how do you start it and how do you get predictions out of it? -- we haven't figured out how to resolve them. The evidence from BICEP2 suggests that maybe we really have to figure out how to solve them, but, until we do, we can't really be that sure about this explanation.

REHMGeoff?

BRUMFIELI'd just say the one other thing that I think annoys scientists quite a bit about multiverses is that our universe is, almost by definition, everything we can observe. So there's no way to prove it. There's no way to find one.

REHMSo these experiments will continue because this one has not been confirmed?

LIVIORight. So, you know, they provide some very intriguing suggestions that this is what has happened. But, you know, they observed in one patch of the sky…

REHMRight.

LIVIO…in one radio frequency and so on, there are some anomalies in their data which need to be clarified. There is always the possibility that dust in our own galaxy and so on produces these signals and so on. The experimental group is excellent. And they did their best to try to eliminate these other possibilities, but we will need more experiments.

LIVIOAnd the good news is that there are at least about half a dozen experiments right now, both at the South Pole -- you know, there is the (unintelligible) at the South Pole. There are experiments with balloons from the South Pole. There are experiments in Chile. There is the Planck experiment, which is a big, big experiment on the cosmic microwave backgrounds.

LIVIOAnd all of these in the coming months and years will actually repeat the experiment with different frequencies, other patches of skies, different type of equipment, better models for the dust, you know, and so on. So I think that within, possibly even as short as a year, we will actually know whether these things are confirmed or not.

REHMSo, Paul, this race that -- I'm sorry. So, Geoff, this race that people are talking about, different scientific labs going at it really, really hard.

BRUMFIELYeah, absolutely. I think there's been -- I think there's a lot of competition in this particular field. And…

REHMBecause…

BRUMFIELWell, I mean, Paul will get upset with me, but I will say the word Nobel Prize. I think people do think about Nobel Prizes when they think about these big theories. But I did speak yesterday with John Kovack, the head of BICEP2. And he said, you know, they release their results to the public not because they're interested in a Nobel Prize necessarily -- although I'm sure they wouldn't say no -- but because they're interested in their results out to the scientific community quickly and having people verify it and, I mean, getting the scientific process rolling.

REHMInteresting. And you're listening to "The Diane Rehm Show." Paul, you wanted to make a comment.

STEINHARDTI just wanted to say, so, over the next 18 months when these various experiments come in with more data and BICEP2 will actually produce their paper so we can actually study them more carefully, it's a very exciting period. We shouldn't diminish that. It's a very exciting period of uncertainty, which I tell my students they should all enjoy.

STEINHARDTIt happens very rarely in science where you, you know, you know a result is coming, you see some tantalizing hints of it, but you're not quite sure which way it's going to go. And whichever way it goes, the risks and what's at stake is really high. It's going to really determine how we think about the universe in the century to come. So you can -- we know this is going to resolve itself in the short period of time.

REHMBut that's the question: Will it really resolve itself? Or will there be really ongoing discussion and disagreement, Mario?

LIVIONo. I think that this actually the best example of how the scientific process really works. You know, we had a number of puzzles about the universe. Then this theory of cosmic inflation was suggested, which, in one blow, suggested answers to many of those puzzles. But like any good scientific theory, it actually provided very clear predictions that can be tested by further experiments. One of the predictions was of these gravitational waves. Now we have the first claimed measurement of these gravitational waves.

LIVIOAnd now other experiments are going to try to confirm or refute these gravitational waves. So this is exactly the way that science really progresses. And this is one of the most fantastic examples that we've seen in recent years, how all these steps, you know, follow one another. I strongly believe that we will know, one way or another, you know, whether this particular detection is correct or not. And, yes, we will be able to determine whether cosmic inflation is a correct theory.

REHMPaul?

STEINHARDTI didn't mean to imply, Diane, that this would be the end of the story of cosmology. It will set the direction. In other words, one direction would be keeping with the current paradigm, the idea of a Big Bang followed by cosmic inflation. Verification of these results would probably drive most theoretical ideas in that direction and knock off competing ideas.

STEINHARDTSo, on the other hand, if the results were to change, we might find ourselves pointing towards a whole different concept of how the universe originated and where it's going. So it's going to set the direction for the next century. It won't answer our questions entirely.

REHMAnd when you think about the age of the universe, where does God step in?

STEINHARDTWell, I like to avoid questions about religion myself when talking about cosmology because I think that, however I answer that question, I think it colors the way people view my scientific view. So I view my feelings about religion to be personal, and I don't like to discuss it publicly. But maybe others have…

REHMMario?

LIVIONo. I feel about the same about this. I mean, you know, we are trying to pursue scientific methods to answer these questions. And, you know, Galileo, 400 years ago, said that the scriptures were for our salvation. They were not written as a scientific theory. And he mentioned the fact that even the planets were not mentioned by name in the scripture, so I sort of follow Galileo in that respect.

REHMMario Livio, Geoff Brumfiel, and Paul Steinhardt, thank you so much for being here.

STEINHARDTThanks for having us.

BRUMFIELThank you.

LIVIOThank you for having us.

BRUMFIELIt's been a pleasure.

REHMMy pleasure. Thanks for listening, all. I'm Diane Rehm.