How did it all start? An awesome questions certainly. But it appears there really was a beginning. Some scientists refer to this as the Big Bang. I like to call it the great flaring forth. Imagine the universe beginning like this. Fourteen billion years ago everything in the universe, all the bright matter of the stars and galaxies, as well as all the dark matter no one has ever seen. All of it existed in a single point. So energetic it was trillions of degrees hot. Instantly, this micro universal rushed apart even faster than the speed of light. The discovery that the universe has expanded and is still expanding is one of the greatest of human history. The common understanding had been that the universe is simply a vast space, a vast space in which things existed. Large things like galaxies and small things like atoms. Scientists knew that matter changed form in the universe but everyone assumed that the universe as a whole was not changing. But no, universe is changing and has changed dramatically. The universe has a story, a beginning, a middle where we are now and perhaps in some far distant future an end. In the 1920s, the cosmologist Edwin Hubble trained his 100-inch telescope at the night sky. He was trying to determine if our Milky Way was the only galaxy in the universe. Not only did he discover the universe is filled with galaxies, he also determined that all of them are rushing away from each other. With Hubble's work, humanity learned that the universe began with a massive explosion that has been carrying the galaxies apart for billions of years. Another special quality about the universe is the rate of expansion. If the rate of expansion had been slower, even slightly slower, even a millionth of a percent slower, the universe would have recollapsed immediately. That would have been it. After a million years, the universe would have imploded upon itself and formed a massive black hole. On the other hand, if the universe had expanded a little more quickly, even slightly more quickly, even calculations show one millionth of one percent more quickly, the universe would have expanded too quickly for structures to form, it would have simply exploded. There would have been no galaxies, no structure, no life, nothing but dust for all time. So what we've discovered is that we're living in a universe that is expanding at exactly the rate necessary for life and structure to come forth. It could be then that even though we can't call the early universe alive, we can understand it as life generating. One of the physicists who was reflecting on this is the celebrated Freeman Dyson. He mused that the more he reflected on the structures of the early universe, the more he became convinced that in some sense, the universe must have known from the very beginning that life was coming. The light from the beginning of time has been traveling for 14 billion years. Meanwhile life has been evolving. With the recent emergence of advanced technology, we were at last able to see the story these photons tell about the birth of the universe and where we ultimately come from. So welcome. It's so good to see you. I'm glad to be here. Can you give us a feeling in your studies of the early universe and its emergence over a billion years, what are some of the major phases in that emergence? Well, going chronologically and starting at the beginning, we're essentially certain that the universe started with something that we call cosmic inflation. There are several different versions of cosmic inflation and we're not sure at all which version is the right one. But cosmic inflation is actually a fairly simple assumption that fits naturally into our modern picture of particle physics. The first stage is a very brief period of exponentially increasing expansion. So two points that are very close start flying apart faster and faster and faster and quickly are flying apart faster than the speed of light and then can communicate. This goes on and on for a very brief period lasting perhaps 10 to the minus 38 seconds. But during that brief period, there's been as much expansion as much increase in size by a factor of about 10 to the 30 as is likely to occur in the whole future of the universe. So it's an amazing brief period. During that brief period, another thing that happens besides this expansion is that there are quantum fluctuations that get created and then greatly expanded in size. The quantum fluctuations are the seeds for the formation of all the structure in the universe, galaxies and clusters of galaxies and large-scale structure superclusters and so on. It all seems to have come out of this brief period of inflation. So that's step number one. Step number two is after the era of inflation, the universe has to fill very quickly with particles and radiation. Particles that are moving very very rapidly nearly at the speed of light. So it's a very hot dense early universe, very uniform except for these tiny fluctuations that were caused by these quantum fluctuations. Then, the next thing that has to happen is that some physical phenomenon causes a slight asymmetry between particles and anti-particles, matter and anti-matter. A little bit more matter. We know of several different mechanisms that could naturally lead to this. We don't know which one or ones or actually the right ones. The next stage is that all of the antiparticles annihilate with almost all of the particles so that for every billion anti-quarks, for example, they annihilate with a billion quarks and there's one quark left, that happens at about 10 to the minus four seconds. For every electron and positron that annihilate, there's a billion annihilations and one electron is left and we are made of that remnant. Amazing. The next thing that happens during the first three minutes is the first elements form. Initially the universe starts out with a lot of dark matter, and protons and neutrons and electrons, and the protons and the neutrons join together. They make deuterium, the heavy hydrogen, that's a proton and a neutron. Then the deuteriums quickly get bound together into helium, two protons and two neutrons. Tiny amounts of other things form, for example, a tiny bit of lithium. But basically, the universe is expanding so fast at this early stage that the production of the elements stops with these very light elements and incidentally almost all of the helium in the universe which is about a quarter of all of the mass of elements of atoms is made in the first three minutes or so. So the universe is basically a hydrogen bomb. Among other things it's fusing and making helium and releasing a lot of energy. Then, the universe basically just expands and cools for about 300,000 years. The next stage is that atoms form. We've had the nuclei and the electrons and as the universe cools down, atoms can actually form. That is the nuclei can grab an electron or two electrons in the case of helium and forms stable atoms. Once that happens, the universe becomes transparent. The light of the Big Bang can start on its way to us and we are continually observing the light that was released at the time of the Big Bang. Of course, we were observing light as time goes on that's been traveling greater and greater distances. But we're continuing to observe the light of the Big Bang. In fact, we can see evidence of these tiny fluctuations, slight differences in density and temperature from one direction to another direction. We have wonderful satellites that are observing this, the American Wilkinson Microwave Anisotropy Probe, WMAP for short. The European Planck satellite which will be telling us next year what it's been seeing. After this few 100,000 years when the universe becomes transparent, the next big event is the formation of the first little galaxies. The dark matter halos form, we call them dark matter halos, they're just clumps of dark matter. The way they form is that if a given region has a little bit more mass than nearby regions, then it expands a little bit more slowly. The whole universe is getting less dense but these regions are getting less dense slower. So compared to other regions their size, they're increasing their density. When they have about twice the density of an average region their size, they stop expanding. The rest of the universe continues to expand. They fall together a little bit and that's how the universe forms the dark matter clumps or halos as we call them, that will host the first galaxies. This process continues on bigger and bigger scales. Meanwhile, in these first galaxies, the ordinary matter, the atoms can continue to fall toward the center. The dark matter doesn't interact with light, it can't radiate away and even Synergy. So it's flying around with a certain amount of velocity and that prevents any further collapse. But the ordinary matter can fall to the center. When it does, it forms the first stars. Now, these first stars are very dramatic, they're probably even be very massive, and they're going to explode in gigantic supernova explosions. The heavy elements that are formed in the centers of stars will be released for the first time into the universe and will start to get elements like oxygen, the most common of the heavy elements after hydrogen and helium, and carbon, that's the second most common, and nitrogen, silicon, and eventually Iron, lots of elements. These are only formed in stars. Of course, that's what we're made of. The earth and the rocky planets are all made of these elements that form only in the stars. So these first stars start this process of what we call the enrichment of the universe with heavy elements. In addition, these first stars should produce the first massive black holes. When the supernovas occur, the centers of these stars will become massive black holes with masses perhaps a 100 times the mass of the Sun. These black holes will then start to accrete ordinary matter. That atoms can keep losing energy and get up close to the black holes and as they fall toward the black holes, they will glow very brightly. These will be the first quasars, many quasars. All of these things occur in the first billion years and in fact, these little galaxies with their first stars will continue to agglomerate and form bigger and bigger galaxies. By the end of a billion years, we already have very bright quasars and as bright as any that have ever existed in the universe, and some pretty massive galaxies with these early galaxies having fallen together. So by the end of a billion years, the universe has changed drastically. It doesn't look like the present-day universe, these early galaxies don't look like modern present-day galaxies. But a lot has already happened after just a billion years. It's now almost 14 billion years since the Big Bang. So the first billion years is a very busy period. It's an extraordinary breathtaking story really. Isn't it? It is. So Primack, you're one of the originators and developers of the Cold Dark Matter theory? Can you explain it to us? Well, first of all, we now know that almost everything in the universe is invisible. All the stars and all the galaxies, the planets, the gas, the dust, everything that we can see with our telescopes adds up to about half of one percent of what's actually there. The vast majority of the matter in the universe is made of some mysterious stuff called cold dark matter. We know a lot about its properties, but we don't know what it is. The cold dark matter is crucial for forming and then holding together the visible galaxies. So dark matter is the backbone of the structure of the universe. It's what makes galaxies form, it's what holds galaxies together. We know where it is, we know roughly how much of it there is, and we hope sometime soon to find out exactly what it is. How thrilling to be part of modeling this and investigating and now coming perhaps to an even further understanding of it? What about dark energy? How does that fit in? Well, dark energy is even more mysterious than dark matter. Einstein, back in 1916, realized that his original version of the theory of general relativity are modern theory of space, time, and gravity created by Einstein at the end of 1915, Einstein realized that this theory requires that the universe be dynamic. It has to be expanding or contracting, it can't be static. He asked the leading astronomers of the day whether there's any evidence that the universe was doing these things, and the answer was no. There was no evidence. So Einstein asked himself, is there something that he could add to the original version of the theory that could possibly prevent it from having to change? He came up with something called the cosmological constant. It would be a property of space itself. The more space the more of this cosmological constant. The cosmological constant would make space repel space, so that you'd have space causing expansion and then more space would cause more expansion. So the expansion would speed up. What Einstein guest was that if you could balance this expansionary force against the attraction of gravity, you could get a static universe. Well, it turned out that it didn't work, it didn't work theoretically, but also it turned out not to be the universe that we actually live in. Later on, Edwin Hubble, the great American astronomer, discovered that there are distant galaxies and that the galaxies are flying away from us at a speed proportional to their distance. In other words, the universe is expanding. Einstein then said that this cosmological constant he invented had been his greatest blunder. In fact, it was one of his greatest achievements because it turns out the cosmological constant or something very much like it called dark energy is actually what fills most of the universe, it's most of the energy in the universe. In fact, because as space expands there's more of it, it's increasingly becoming more important. The matter which is mostly where the galaxies are, is becoming more and more dilute as the universe expands and the galaxies get further apart. But the dark energy associated with space itself is becoming more and more important. Now, it's possible that the dark energy is just Einstein's cosmological constant. In other words, just a property of space that doesn't change. Of course, the more space the more of it there is, but the amount per amount of space would then be exactly the same. It's also possible and this is something that was discovered since Einstein, but using the basic general relativity formalism, that the dark energy could be changing with time. The natural way that it would change is that it would decrease. There'd be more dark energy per unit of space at early times and it would be decaying away. If that's the case, then that has great implications for the future of the Universe. It can completely change the way the future of the universe would go. If the dark energy is just a property of space, the universe is going to thin out and every galaxy or small group of galaxies that's bound together by gravity would become an isolated island universe, ultimately with no sign that they're any other galaxies around except the little nearby galaxy you get group. On the other hand, if the dark energy changes its nature, decays away, then the distant universe might not entirely disappear. So we'd love to find this out, but the only way we can find out is by doing very careful studies of how the dark energy has changed through time. So the best studies we can organize from the ground are now being organized, there's something called the dark energy survey. Very likely, it's going to require a new spacecraft or maybe several to do studies from space that allow us to look without having to look through the atmosphere and all the complications that entails. But instead, look above the atmosphere and get an unimpeded view of the distant universe and study very carefully the expansion of the universe in the past. That's how we're going to try to figure out what the nature of the dark energy is. Fantastic. This research is so exciting clearly and we'd love to hear more about this wonderful opportunity you have now for Hubble Space Telescope research. Can you tell us about that? Well, I'm involved in a couple of Hubble projects. One uses many of our resources in space and on the ground to study just one little area of the sky. That's a particularly good area to look at because it's a very clear view of a distant universe looking out of our own galaxy. That particular region and essentially all of the other main regions that have been studied already with Hubble Space Telescope and other telescopes, we 're going to get a chance to record images of with the new camera, the Wide Field Camera 3 that was installed on Hubble Space Telescope in the last service mission by the astronauts, and this new camera gives us the opportunity to see images in the ultraviolet and especially in the infrared, light that doesn't penetrate the atmosphere and that we can only really see if we can get above the atmosphere. There are at least 50 major scientists involved in this from around the world and all of them represent groups that are somewhat larger than that. So it's a worldwide group of scientists that are working on this. My own role is to provide some of the theory that will help us interpret these observations. My group has done the world's largest simulation, the highest resolution large simulation of the evolution of the universe about a billion light-years across, and all of the dark matter halos that could host galaxies that we can see. About 10 million halos are being followed at any given time, about 50 million halos during the entire evolution of this region of the universe. We're also doing high-resolution simulations of the origin and evolution of galaxies. We're hoping that if we're clever enough, we're going to be able to tell from those images and comparison to the simulations, just how it is that the galaxy is formed so that we can really fill in the details of the picture.
