 My name is Michael Robinson, so I'm chairing this lecture this evening. It's a great pleasure for me to do that. The Institute of Physics, Isaac Newton Medal, was established last year to recognize international physicists. It's already one of our most prestigious awards. The terms of the award are that the award should be made to any physicist regardless of subject area, background, or nationality for outstanding contributions to physics. And the 2009 award winner is Alan Gooth for his invention of the inflationary universe model. And it's a great pleasure to welcome him here this evening. Alan Gooth was born in 1947 and did his PhD at MIT. After postdoc positions at Princeton, Columbia Cornell and the Stanford Linear Accelerator, he returned to MIT as an associate professor in 1980. He's now a Victor F. Weisskopf Professor of Physics there. In 2004, he won the Peter Grover Cosmology Prize. He's offered several books including the inflationary universe, The Quest for a New Theory of Cosmic Origins. In 1980, working with Henry Tides, he realized that the standard cosmological model would produce catastrophic numbers of magnetic monopoles and that super cooling of the ground unified phase transition could suppress these monopoles. He went on to devise a detailed scenario for this, the inflationary universe. And in his famous 1981 paper, which has over 3,400 citations, he pointed out that this would solve two of the outstanding metaphysical problems of cosmology, the horizon problem and the flatness problem. And I'm going to leave it to Alan to explain what those are. In the abstract of this paper, he modestly wrote, unfortunately, this scenario seems to lead to some unacceptable consequences. So, modifications must be sought. Well, within a year, Lindy and Albrecht and Sinehart had come up with new inflation which solved these problems. Alan Goeth's inflationary universe received a tremendous boost from the detection of the CME fluctuations by Encovy and WMAP, which conformed to the predictions of the inflationary paradigm. One thing to say about Alan is he didn't just write the paper and submit it to the journal and leave it there. He spent two or three years trekking around to giving seminars, speaking at conferences, trying to persuade people that this was a really important idea. And I remember hearing him lecture at that time. And I think it's a great lesson for young physicists that you don't just write the paper, you actually have to persuade people that this is important. Tonight, he's tackling four of the grace imponderables, inflation, the multiverse, string theory, and the cosmological constant. So, it's a great pleasure that I invite Alan Goeth to give this lecture, this Newton lecture, on inflationary cosmology is our universe part of the multiverse. Thank you so much, Michael, for that warm introduction. I'm very pleased to be here tonight. I always enjoyed visiting England. I spent a wonderful day yesterday at Cambridge and tomorrow I'll be visiting Oxford. And it's really wonderful to have a chance to see so many of my old friends here in this country. The work that I'll be talking about is work that really goes back to 1979. When I got into it, I was really purely a particle theorist. I had never worked in cosmology previously. At the time, myself and a number of other people got sucked into cosmology, really through particle physics itself. This was the time when grand unified theories were first becoming an object of widespread interest. And what characterizes these grand unified theories, as you probably know, is the natural energy scale of about 10 to the 16 GEV. Now, by the standards of our local power company, that's not much energy at all. It's what it takes to light a hundred watt bulb for a period of about four and a half hours. But if you try to imagine putting that much energy on a single elementary particle, which is what grand unified theories are all about, it really is an extraordinary amount of energy. One way of seeing how much is to imagine trying to build a particle accelerator that might reach those energies. We can do it with present technology in principle kind of sort of. And what I mean by that is that if you build a linear accelerator, the output energy is proportional to the length of the accelerator and there's no real limit. You could just make the accelerator longer and longer. So you could imagine taking the largest linear accelerator in the world today, Slack, which is two miles long and reaches an energy of about 40 GEV. And you could do a back of the envelope calculation to ask yourself, how long would the accelerator have to be if it's the same technology to reach an energy of 10 to the 16th GEV. And you could all go home and check me. But when I did it, I figured that the length had to be 85 light years. Now at the time, many of us were very disappointed that neither NASA nor the Department of Energy seemed to be interested in taking up this challenge. So what it meant is that if we wanted to see the most dramatic consequences of these grand unified theories, we were really forced to turn to the only laboratory to which we had any access to at all, which has ever reached those energies. And that is the universe itself and its very infancy. According to conventional cosmology and inflation doesn't really change this, the universe would have had a temperature where the KT, the mean thermal energy, would have been 10 to the 16th GEV at a time of 10 to the minus 37 seconds after the instant of the Big Bang. So that drove us to be thinking about these unbelievably early times. And the results have been very interesting. It does seem to turn out that by combining ideas from particle physics with cosmology, new theories have been developed which seem to give a very good explanation for many of the properties that our universe has. And that's what I'll be talking about. Now, of course, the award is named for Isaac Newton, who's certainly, I think in the eyes of many, the greatest physicists who ever lived. Curiously, it comes at a time when my own wife Susan has made analogies between me and Isaac. I think the sign of my wife's comments were a little bit different from the IOPs. It came about when I was explaining to her about the multiverse and how I was working on this and talking about other universes and things. She looked at me very quizzically and then she sort of smiled and said, well, I guess it's OK. Newton worked on alchemy. So to begin, I want to begin by talking about the standard Big Bang theory. The theory that existed basically before inflation was discussed. The theory is basically the theory that the universe as we know it began some 13 to 15 billion years ago. And now, in fact, we think we have a very precise estimate of that age, 13.7 plus or minus 0.2. I suck in these words as we know it for good reason because the 13.7 billion years comes from extrapolating backwards the universe that we see. And 13.7 billion years ago reaches some kind of an incredibly hot dense state, which now easily looks like an actual singularity. But we don't really understand that singularity. The further back you extrapolate, the less reliable your extrapolation. So nobody claims to know for sure that the universe actually began 13.7 billion years ago. And in fact, I'll later be telling you in today's talk that inflationary models strongly suggest that the event that happened 13.7 billion years ago was not really the beginning of all of existence, but rather just our own local Big Bang in a much bigger multiverse, which existed previously. In any case, though, 13.7 billion years ago, we are firmly convinced that the patch of matter that we now see was in the form of an extremely dense uniform soup that filled space uniformly. This filled space uniformly part I'd like to emphasize, there's a common cartoon notion of the Big Bang as a tiny egg that was sitting in empty space and suddenly exploded. That is not, never was, the scientific description of the Big Bang. As far as I could tell, there's nothing illogical about the exploding egg theory compared to the normal Big Bang. It just doesn't agree with what we see. Because if you had an egg that exploded, unless we were right at the center, which seems highly implausible, if we were over here and the explosion was there, well, obviously when you look towards the explosion, you'd see an explosion. If you look the opposite direction, you'd see essentially nothing. And that does not resemble our view of the sky. When we look around in different directions, what we see is an essentially uniform distribution of matter. And we also look at the cosmic background radiation, which we view as the leftover heat of the Big Bang. And that's measured very precisely in this unbelievably uniform in its intensity in all directions. It's uniformed to about one part in 100,000. The egg theory would predict that the sky should look very non-uniform because when you look toward the egg, you'd see a hotspot. Opposite direction, you'd see a cold region. But that's not at all what we see. What we see is things look completely uniform. So in fact, the Big Bang theory posits that the initial space was uniformly filled with matter, no localized egg in empty space. And this uniformed distribution of matter was all expanding. All the bits of matter were moving away from the other bits of matter. And that's the scientific version of the Big Bang theory. And this is a very successful theory. It has very important abilities to explain features of our universe. In particular, it explains how the early universe expanded and cooled. And you could actually calculate how fast that expansion and cooling should take place in a very simple way. You can calculate how the light chemical elements formed because this model started when the universe was so hot that even the nuclei of atoms would not have been stable. So the nuclei have to form later as the universe cools. This work was started by George Gammoff and his collaborators back in the 1940s. And they, at that time, became very disappointed in the results and eventually gave up on it. And the reason was not that their calculations were wrong, their calculations were approximately correct. But they were assuming that all of the chemical elements had to be made in the Big Bang. And they showed that it was not possible, which was correct. Our current point of view is that most of the chemical elements around us were not formed in the Big Bang, but rather were formed much later in the history of the universe in the interior of stars. And then when stars explode, they spew these heavy elements out into space, ready to recollect into later generation stars like our sun. And only the lightest chemical elements were produced primarily in the Big Bang. But that still gives about five different isotopes or so that one can measure and predict. And the predictions for the abundances agree very, very well with the measurements. Finally, the classic Big Bang theory allows us to describe how the matter in the universe congealed to form stars, galaxies, and clusters of galaxies. That's certainly still a work in progress. Nobody claims that we completely understand that. But it certainly seems to fit with the basic Big Bang picture. But what I want to talk about tonight is going beyond the conventional Big Bang theory. So let me move on to comment about a few of the things that the conventional Big Bang theory does not describe. In particular, in spite of the fact that the theory is called the Big Bang, which might make you think that it describes a Big Bang, the one thing that the theory literally says absolutely nothing about is the Big Bang. It says nothing about what banged, why it banged, or what happened before it banged. It says nothing about the bang. It is literally the theory of the aftermath of a bang. When the theory begins in the scientific description, it assumes that all the matter already exists. All the matter is already hot. All the matter is already expanding outward. The explosion of the Big Bang had already happened before the theory begins. In a similar vein, the theory just says nothing about where the matter came from. It simply assumed that all the matter already existed and existed in a particular state. In the conventional form of the Big Bang theory, for every particle that exists in the universe today, there was some precursor particle that existed right from the instant of when the theory begins to describe our universe. Now, you might be surprised that one can even talk about where the matter came from. But it turns out that in inflationary models, one can actually explain where essentially all of the matter in the universe came from, although not quite all will be getting there soon. So, let me move on now to describe how cosmic inflation changes our picture of the Big Bang. Inflation is a modification of the Big Bang theory. It does not throw away the Big Bang theory, because as I've told you, the Big Bang theory is, in fact, a very successful theory for describing many features of our universe. But inflation modifies the standard Big Bang theory. And the nature of the modification is, I think, well described by a word that I believe originated in Hollywood. It's the prequel. It's what came before the description of the Big Bang that was already part of the standard theory. And in particular, inflation can explain what I would refer to as the bang of the Big Bang. And by that, I mean it explains the repulsive force that drove the universe into this period of gigantic expansion, which we call the Big Bang. And it does that in the form of what I consider to be kind of a miracle of physics. Now, of course, scientists have to be careful when they talk about miracles, because scientists, I think, aren't supposed to believe in miracles, or at least they're not supposed to admit that they do. But when I talk about a miracle here, I'm not talking about anything supernatural. But the way I look at it, there are certain properties of the laws of physics which are so surprising, and so novel, and so different from what most of us learned when we were in school, that I think they just naturally seem to be something that you would want to refer to as a miracle. And inflation is really based on two of these miracles. And the first is the miracle of repulsive gravity. Gravity is not always attractive, but gravity can act repulsively. And this is known in the context of general relativity. Einstein himself made use of it in his earliest model of the universe in which he introduced this cosmological constant to produce a repulsive gravitational force, which would prevent his universe from collapsing. Einstein believed that the universe was static. And he discovered that if you just had ordinary gravity, as described by general relativity, the entire universe would collapse. And not believing that that could happen, he introduced this repulsive gravitational force, all within the context of general relativity, to hold the universe up. And that repulsive force is something which can exist in many ways in general relativity. General relativity allows both kinds of forces to be produced as gravitational forces. In particular, according to general relativity, you can get a repulsive gravitational force if you have a material with a negative pressure, a material which actually has a pressure less than zero, which you can think of as a suction. And furthermore, particle theories tell us that you can create states of negative pressure. But in particular, states for which the energy is dominated by the potential energy of a scalar field are states that will have a negative pressure. And that's basically how inflation works. It's based on states where it's dominated by the potential energies of scalar fields, producing negative pressures, which produce repulsive gravity, which cause the universe to rapidly begin to exponentially expand. So inflation proposes that at least a patch of this repulsive gravity material, this negative pressure material existed in the early universe, it doesn't have to fill the early universe, it just has to have a patch of it. And we don't really know what energy scale inflation happened at, but a likely place at which it might have happened is at the scale of grand unified theories. And just to give you some sample numbers, I will use grand unified theories for my sample numbers. So if inflation happened at the scale of grand unified theories, this initial patch can be unbelievably small, it could be only about 10 to the minus 28 centimeters across. And that's enough to produce our universe from it. And it can be in the midst of a bigger space, it does not have to fill the space. Now since any such patches in large fantastically by the inflation, one doesn't really care about the initial density or probability of such patches, as long as one thinks that there's at least some possibility that at least one of them existed. And then our universe would come from that one patch. Once you assume that such a patch exists, the gravitational repulsion created by that patch becomes the driving force of the Big Bang. The patch starts to exponentially expand. The time constant of the exponential expansion would be only about 10 to the minus 37 seconds if we're talking about inflation at the grand unified theory scale. So every 10 to the minus 37 seconds, this region of space would double or multiply by e. This accuracy doesn't matter which of those you say. And we'll keep doing that again and again. And to make it work, what you need is a total factor of about 10 to the 28, which only requires about 65 time constants. e to the 65 is about 10 to the 28. Now you could have much more. You don't need to fine tune the amount of inflation you have. It's perfectly okay if there's much more inflation than that minimal amount. But to make the theory solve the problems it's intended to solve, you need at least 65 time constants of this inflation. And that means that inflation needs only last for about 10 to the minus 35 seconds, or 100 times the time constant which was 10 to the minus 37 seconds. And at the end of that time, the region that will be destined to become our observed universe would still be small. It would be about the size of a marble, but vastly larger than the 10 to the minus 28 centimeters that it started. Now inflation will end because this negative pressure repulsive gravity material is fundamentally unstable. So it decays much like some radioactive substance decays. And when it does decay it ends inflation. And furthermore, it releases energy when it decays. And that energy produces a hot soup of ordinary particles. And that hot dense soup becomes the primordial soup of standard cosmology. So when the repulsive gravity material decays, it produces the initial conditions for the conventional Big Bang theory. The prequel ends and the main movie begins. However, I should qualify this. There is a caveat. This decay that ends the inflation and we'll be coming back to this point happens in most places, but it does not happen everywhere. And the tiny regions which are left, which remain inflating, the rare regions that are left that remain inflating turn out to be very important and we'll come back to that. Okay, now a peculiar feature of this expansion driven by the repulsive gravity is that the energy density of this negative pressure repulsive gravity material is not lowered as it expands. If you had any ordinary gas expanding by this huge factor, it would thin out. It would allude to zero energy density or incredibly small energy density. That does not happen during inflation. For the expansion driven by this repulsive gravity, the energy density actually remains constant as the expansion takes place. So even though more and more mass energy is appearing in this enlarged region of the repulsive gravity material, the claim is that total energy was still conserved because total energy does have to be conserved. That principle is not going to be violated by anything that I'll talk about. And the way that works involves what I'm calling miracle number two of inflation. And miracle number two is the fact that although we are accustomed to the idea that any energy is a positive number, energies do not always have to be positive. energies can be positive or negative. And in particular, the energy of a gravitational field is negative. And that's a statement that's true in Newtonian mechanics. And it's true in general relativity. Although in general relativity, there are some ambiguities about how you define it. But if you find it the way I'd like to define it, it's true in general relativity as well. In Newtonian physics, it's actually pretty easy for you to see it. Probably everybody knows how to derive the energy density of a coulomb field at the standard calculation in freshman physics courses, and done in more sophisticated ways in graduate courses. And the energy density of an electric field some positive number times the square of the electric field strength, the value of that positive number depends on what units you use, of course. If you compare Newton's law of gravity with coulomb's law, at first glance, they're sort of the same, they're both inverse square laws. But if you look a little more closely, you realize that they actually have opposite signs, two positive charges repel each other, two positive masses attract each other. And if you just do the same calculation that you would do for coulomb's law, for Newton's law of gravity, you can calculate the energy density of a Newtonian gravitational field, and the whole calculation is identical, but this minus sign carries through at each step. And you'll end up proving that the energy density of a gravitational field is actually negative. And intuitively, what that corresponds to is simply that if you were comparing this with electrostatics, to build a large electric field, you have to push charges together. And as you push them together, they repel each other, and you have to do a lot of work to push a lot of charges together. If you're trying to make a large gravitational field, you're pushing masses together, and you don't have to do any work to push masses together. They attract each other. You can actually extract energy as the masses bolt towards each other. So you can create a strong gravitational field and take energy out at the same time, and that implies that the energy of the gravitational field must truly be negative. And that means that as the universe undergoes this huge expansion at a constant energy density, so more and more energy is appearing in the form of the matter that fills this region, it can be compensated by having more and more negative energy up here in the gravitational field, so that the total energy remains constant, incredibly small, and possibly exactly zero, which I think is the most likely energy given this picture. So the positive energy of the false vacuum was compensated by the negative energy of gravity, and the total energy of the universe may very well be zero. And false vacuum just means this repulsive gravity negative pressure of material that we've been talking about. Okay, so that describes the mechanism of inflation. I think I'm done describing everything I want to describe about the mechanism of inflation. But so far, I think all I've best convince you of is that inflation is a possible story about how the universe could have begun. But I want to do more than that. I want to try to convince you that there's a lot of evidence that our universe actually went through this history, that this really does describe the universe that we live in. And I want to in particular talk about three crucial pieces of evidence that our universe underwent this process of inflation. So the first is the large scale uniformity of the universe. And in particular, the large scale uniformity is indicated very strongly, observationally, from the cosmic background radiation, the radiation that we view as the afterglow of the heat of the big bang. That radiation, as I think I mentioned in my introduction, is known to be uniform in its temperature, as one looks across the sky, to the extraordinary accuracy of one part in 100,000. Now I might mention just to be complete here, that when you just look at the radiation, you actually see deviations of about one part in 1000, not 100,000. But those deviations that you see at the level of one part in 1000, we associate with the motion of the earth through the cosmic background radiation. And that motion produces a particular pattern. We have no other way of measuring the velocity to this kind of accuracy. So when it fits the motion of the earth through the background radiation by looking at the pattern of radiation, it gives you a dipole. So when it fits the best dipole, and that determines the velocity of the earth through the radiation, you compensate for that. That's introducing three parameters, the three components of the velocity. And with those three parameters, you then ask, what are the residual fluctuations? The residual fluctuations you have to attribute to actual anisotropies of the radiation itself. And those residual fluctuations are what's at a level of one part in 100,000. So we believe the radiation itself really is uniform to this level, but we see a deviation in excess of that due to our motion through the radiation. Now to understand what this means about the universe, I need to say a few words about what we think is the history of this radiation. And in particular, we believe the radiation was released at about 400,000 years into the history of the universe. And by released, what I mean is that prior to this time, the universe was so hot that it would have been a plasma. And plasmas are incredibly opaque to radiation. Roughly speaking, the photons constantly scatter off of the free electrons, which have a very high cross-section for scattering photons. So during the first 400,000 years of the history of the universe, the radiation was frozen with the matter. Even though each photon was moving at the speed of light at any given instant, each photon was constantly colliding with an electron and scattering in changing directions. And the net effect is that the photons really didn't go anywhere during the first 400,000 years of the history of the universe. But then at 400,000 years, the matter cools enough to become neutralized and suddenly, or at least rather suddenly, the universe becomes transparent to these photons. And from then on, the photons just move on straight lines. And when photons move on straight lines, they form images, just like you see my face from the photons that travel along straight lines from my face to your eyes. Similarly, when we look at the cosmic background radiation, we're essentially seeing an image of what the universe looked like at 400,000 years after the Big Bang. So the conclusion then is that if the radiation looks unbelievably uniform, that means that the universe itself was unbelievably uniform by 400,000 years after the Big Bang. Now, what does that say about explanations of this uniformity? It says a lot, because when you do the calculations, and they're fairly simple calculations, what you find is that if within the context of this conventional Big Bang theory, you try to explain how the universe got to be so uniform, you have to explain how it got to be uniform by 400,000 years. And the point is that there's just not nearly enough time for information to travel from one piece of matter to another by 400,000 years to allow this uniformity to be established. So if you believe that the universe did not start out uniform, if you believe it started out uniform, I should specify that then everything is okay. You could just put all of this into your assumptions about your initial conditions. But if you want to explain this uniformity, then you really cannot do it in the context of the conventional Big Bang theory. And the reason is simply that in the conventional Big Bang theory, the matter moves away, moves outward so quickly, that there's not time, given the limitations of the speed of light, for the matter that goes this way to have communicated in any way, for the matter that goes the opposite way. So there's no explanation for why they should be at the same temperature at the same time, which we know they were to this extraordinary accuracy of one part in 100,000. And to allow them to communicate would require the transmission of energy and information at about a hundred times the speed of light. And nothing that we know of in physics allows that to happen. So within the conventional Big Bang theory, unless you start the universe out completely uniform, there's no way to explain uniformity that we see. That's the problem. However, in inflationary models, that problem goes away completely. In a very simple way, inflation modifies this prehistory of the universe. And in particular, because inflation gives an acceleration to this expansion, it means that the universe can start out small and essentially hang out that way for a little while before inflation starts. And during that early period before inflation, there's plenty of time for the region that's going to become our observed universe to become uniform by the same kind of processes that a slice of pizza gets cool when you take it out of the oven. Things just come to the same temperature if they have enough time. And this region is small enough so there is enough time. Then inflation takes over and produces the accelerated expansion and magnifies this tiny speck to become large enough to include everything that we observe. So inflation provides a very simple and natural explanation for how the universe got to be so uniform. So that was item number one, the first piece of evidence that our universe actually underwent this process called inflation. The second issue I want to talk about, there are three I want to talk about. The second is what is usually called the flatness problem for reasons that you'll see shortly. It's basically the problem of explaining why the early universe was so flat. By flat I, of course, do not mean two-dimensional as sometimes audiences assume that I meant. By flat I mean Euclidean because according to general relativity, space-time is fundamentally non-Euclidean. But our universe is incredibly close to Euclidean and why it's so close to Euclidean is basically what this flatness problem is all about. Now according to general relativity there are three possible geometries if you assume that the universe is homogeneous and isotropic, same in all places, same in all directions. And there are closed geometry which is like the surface of a sphere, an open geometry, or a flat geometry, where flat is the Euclidean case and that's the case that we're very close to in what we're now trying to explain. According to general relativity, the flatness of the universe is related to its mass density and cosmologists talk about a quantity called capital omega which is the actual mass density whatever it is divided by what's called the critical mass density. Where the critical mass density depends on the expansion rate. It's not a constant but for a given expansion rate there's a certain critical mass density and the critical mass density is just defined as that density which makes the universe the flat case which is the boundary of the two other cases. So if omega is equal to one, it means the universe is flat, if omega is greater than one is closed, if omega is less than one it's open. And the key point that makes this a problem is that omega being equal to one turns out when you look at the equations of motion is an unstable equilibrium point of the evolution of conventional cosmology and that means it's like a pencil bouncing on its tip. If it stays exactly straight up that's a solution to the equations of motion. It can in principle stay exactly straight up forever talking about a classical pencil. But if the pencil is leaning just a little bit in any direction it will rapidly start to fall in that direction and that's the same way that omega behaves with respect to omega equals one. That is if omega is exactly equal to one it will stay exactly equal to one forever. But if omega in the early universe were slightly below one it would rapidly fall towards zero and no galaxies for example would form. Lots of other things would be different too. The universe would just dilute to zero density very quickly. On the other hand if omega in the early universe were just slightly greater than one omega would rapidly rise towards infinity which would mean the universe would reach a maximum size turn around and collapse and all that would happen rather quickly if omega were greater than one in the early universe. To be as close to the critical density as we measure today if we go back to say one second after the big bang omega must be equal to one at one second after the big bang to an accuracy of 15 decimal places. And that is the heart of this flatness problem. Conventional cosmology can only work if the initial value of omega was equal to one initial meaning at time one second. It could only work if omega at time one second was equal to one to 15 decimal places but there's nothing in the theory that causes omega to have that value. You just need to put that value in by hand if you want the theory to in the end describe our universe. So if you're going to just assume it started that way there's no problem if you want to just make up initial conditions in a fine-tuned way you can make this work but if you want to have any explanation for why the universe looks the way it looks this conventional big bang theory doesn't work. It just tells you that you need omega to have started out extraordinarily close to one but it doesn't give you any reason why it should have started out incredibly close to one. The inflationary model solves that because during inflation gravity behaves very differently it behaves repulsively and that turns all kinds of things around and in particular it turns around the behavior of omega. So instead of omega being driven away from one during inflation omega is driven towards one and it's driven towards one with incredible rapidity. So a very short period of inflation like the one we talked about 65 e-folds is all that you need to arrange for omega to be as close to one as it needs to be even if it started out rather far from one. So omega can start out being two or ten or one-tenth or ten to the five or ten to the minus five. The further you start from one you need a little bit of extra inflation to drive you to one sufficiently but because the effect is exponential you don't need a lot of extra inflation to drive omega to one. Now this turns out to actually give a prediction. You could avoid this prediction if you arranged for inflation to end at just the right time but because omega is driving excuse me because inflation is driving omega to one so quickly unless it ends just at the right moment it will drive omega very very close to one much closer than it needs to be to just explain current observations. So the prediction is that omega today should be one that even today we should have a critical density that the mechanism which drives omega to one overshoots and produces not something that just approximately one but should really be almost exactly one even today. Now for much of the history of inflation that was a problem because some years ago the astronomers thought that the value of omega was 0.2 0.2 or 0.3 and that made it very difficult for example when I had dinner with astronomers they would say things like well you know inflation is a pretty theory but it just doesn't fit the data because it predicts omega is one and we know omega is not one it's only 0.2 or 0.3. Fortunately all that changed it about 10 years ago and the latest number which comes from data from the WMAP satellite combined with the two-degree field survey and the Sloan Digital Sky Survey and the supernova data to put all this together to get the most precise estimate of omega that people know how to make and that's it and this is an experimental number not a theoretical number and now omega is one just like inflation predicts so it's a big success.