 Okay, folks, we're going to get started now with the next lecture, and it's my pleasure to introduce my colleague, professor of chemistry, Steve Miller, to introduce Alex Filippenko. First of all, I'd like to apologize, I'm not going to have any exploding rocket sleds. So, thanks, Josh. If you, like me, are a fan of the PBS program NOVA, you might well recognize Dr. Alex Filippenko, who has been a contributor to that show in recent years. I remember one episode in particular in which he was explaining Doppler shifts using the example of a car horn as the car drove down a highway. And as the car passes a stationary observer, the apparent pitch of the horn changes. I remember this instance, not for the lesson in Doppler shifts, but because of the two questions going through my head at the time. What kind of astrophysicist gets to drive a classic Ford Mustang down the highway for a TV show? And how can I get that job? It turns out that the answers to those questions are, respectively, Alex Filippenko, and I can't. Dr. Filippenko earned a Bachelor of Arts degree in physics from the University of California, Santa Barbara in 1979. And after that, he entered the PhD program in astronomy at the California Institute of Technology, where he graduated in 1984. He then accepted a Miller Fellowship to the University of California at Berkeley. And after the term of that fellowship, he accepted a full-time faculty position at Berkeley. And he has been there ever since. And he is now the Richard and Rhoda Goldman Distinguished Professor in the Physical Sciences there. He has done quite well in the intervening period. He was awarded a Guggenheim Fellowship in 2000. He shared the Gruber Cosmology Prize in 2007 and was elected to the National Academy of Sciences in 2009, among his many accolades. He's also one of the most prolific and widely cited astronomers in the world, having already published more than 700 publications. Dr. Filippenko's research largely focuses on identifying and studying supernovae, black holes, and other related objects or events. His group developed and operates the Robotic Katzman Automatic Imaging Telescope, or CATE, on the slide there, which has contributed to their discovery and characterization of more than 300 supernovae since it went into operation. The resulting data have contributed significantly to our understanding of the ways in which stars die. His group has also worked to identify possible black holes and study their relationships to other objects in the sky, such as galactic nuclei and quasars. But Dr. Filippenko is probably best known for his contributions to the work which will be the basis of his talk here today. In the mid-1990s, he was a member of both the Supernova Cosmology Project and the High Z Supernova Search Team. These groups used observed red shifts in distant supernovae to demonstrate that the universe not only continues to expand, but does so at an ever-increasing rate. This discovery was hailed by Science Magazine as the science breakthrough of 1998. It has since given rise to the idea of dark energy and resulted in the 2011 Nobel Prize in Physics being awarded to the heads of the two independent teams. Here's his picture. As impressive as his body of work as a researcher has been, a second talent contributes to Dr. Filippenko driving a classic convertible for a TV show while many others sit at home and watch. He is widely regarded as a great speaker, teacher, and ambassador of science. Among his many teaching accolades, he was named the Carnegie Foundation's 2006 U.S. Professor of the Year, and he has been voted by the UC Berkeley student body as their best professor a record nine times. And remember, he teaches physics. It is ultimately his place at the forefront of modern astronomy and his ability to communicate its ideas clearly to colleagues and lay audiences alike that make him a natural contributor to Nobel Conference 49. And so please join me in welcoming Dr. Alex Filippenko. There we go. Well, thank you very much, Steve, for that wonderful introduction. And I thank you all for being here. Wow, a full house. It's actually great that Gustavus Adolphus College is not shut down today, as is our federal government. I was a little bit worried there, yeah. So you all know where to be here to listen to all these wonderful presentations at the forefront of science. As Steve mentioned, the 2011 Nobel Prize in physics was awarded for the discovery of the accelerating expansion of the universe. And it was awarded to the leaders of the two teams. Saul Perlmutter in the middle there led the supernova cosmology project, and Brian Schmidt at right led the high redshift supernova search team. It was also awarded to Adam Reese on the left there, a member of Schmidt's team. He was my postdoctoral scholar at Berkeley in the mid to late 1990s when we did the research leading to this discovery. He was charged with analyzing the data. He was the first on the Schmidt team to realize what the data were trying to tell us, and I think it's appropriate that he received a share of the prize as well. I was the only person to have been, at one time or another, associated with both teams. And if you get me sufficiently drunk, I'll tell you the story behind that. It's unfortunate that there's a tradition among the Nobel Prizes in all fields other than the Peace Prize. They can be awarded to at most three individuals. And there were 48 others on the two teams that contributed to this discovery, and additional astronomers who did groundbreaking work in preparation for this discovery. And without the hard work of all these other people, these three gentlemen wouldn't have been so recognized. My colleague at Harvard, Bob Kirschner, likes to quip, it's not every day that you don't win a Nobel Prize. Anyway, these three gentlemen understood that without the rest of us working hard in the trenches, they wouldn't have been recognized in this way, and so they spent a good fraction of their prize money flying the rest of us out to Stockholm in December of 2011 to participate in Nobel Week. A nonstop, yeah, thanks, a nonstop set of parties and celebrations, receptions, all in the name of science. It was like the Swedish Super Bowl, actually, but for science. And I'm told that it was all televised, and in particular the Swedes love to observe the poor manners, primarily of Americans, at the Nobel banquet, so a topic of much discussion. Anyway, there's the Supernova Cosmology Project led by Saul. At the time, the high Z team, with which I was more associated, was having their team lunch, and I couldn't clone myself, and so I couldn't be in this photograph. So that's one team, and then the high redshift search is shown here, right after the awarding of the Nobel Prize to Schmidt and Reese on this team. And the rest of us like to say that we got to participate in nearly everything, all the parties, all the receptions, except for the handshake from the King of Sweden, the gold medal, and a share of one and a half million dollars. But that's the way it goes. All right, well, my talk today will be on cosmology, that subset of astronomy that deals with the structure and evolution of the universe as a whole. We're interested in some of the grandest questions. How big is the universe? Is it infinite, or does it somehow wrap around itself? What is its shape overall? What is its age? Is it infinite? Is it finite? This is a big time story. You see that big time story. When did the universe begin? Well, we now know that it began 13.8 billion years ago. A very long time indeed, but not infinitely long. And that's an amazing discovery, worthy of the cover of Time Magazine. And you know that these national magazines want to educate the public, of course, but they also want to make money. And they won't choose a cover story that they think will not sell. But astronomy, and in particular, cosmology, they sell. People are interested in this stuff. Cosmologists are also interested in the fate of the universe. Will it expand forever, or will it implode in on itself? This, too, was a big time story, how the universe will end. And back in 2001, when this cover story was written, we thought we knew how the universe would end. And so there's no question mark there. Now, a dozen years later, we've conducted more research, and we're not so sure how it will end. But I will tell you how we think it will probably end, the betting person, all right? How to lay your odds. Cosmologists are also interested in the fundamental building blocks of the universe. Those are galaxies, gigantic, gravitationally-bound collections of tens or hundreds of billions of stars. Now, our Milky Way galaxy would look like this if we could see it from the outside. This is not a picture of our Milky Way. If anyone has such a picture of the Milky Way, please see me afterwards. I'd like to purchase usage rights from you, OK? This is seen from up above. But it's about 100,000 light years from end to end. And light travels 186,000 miles a second, 6 million million miles per year. And it's 100,000 of those units across. So if you were on a planet orbiting a star here, and you sent a radio signal at the speed of light to an alien friend over there saying, hey, let's go to the Nobel conference, the 49th one, that is, it would take 100,000 years for your signal to reach that friend and another 100,000 years for their reply to come back saying, well, let's go to the 200,049th Nobel conference, OK? Roundtrip conversation of 200,000 years, hardly a stimulating conversation. I'm sorry, this is the way the universe is built. I'm just the messenger here. It's built out of these gigantic galaxies. And there are lots of them. Here's one of my favorite photographs from the Hubble Space Telescope, the Hubble Ultra Deep Field. The telescope stared at just one tiny part of the sky for the equivalent of two weeks, collecting light, seeing ever fainter objects. And this is a tiny but representative fraction of the sky. Imagine a grain of sand held out at arm's length. Imagine how small that looks. That's about the size of this picture here. And everywhere it's filled with galaxies. I could spend my hour counting them. One, two, three, four, five. That would be pretty boring for you. But hey, it's a rather cushy job. They pay us to sit around and count galaxies. What could get better than that? Anyway, we've taken a number of such photographs, and we can tell that this is representative. So extrapolating over the whole sky, we can estimate that within the realm of today's great telescopes, there's something like 100 billion galaxies. And that's just in the parts of the universe that we can see. We now have very good reasons to believe that the universe extends far, far beyond the parts that we can see. And everywhere it is filled with these galaxies, the basic building blocks. How do they form? How do they evolve with time? These, too, are among the central questions of cosmology. So you can see what an amazing, vibrant, intellectually interesting field it is. And I feel very privileged to have been able to work in this field and contribute to the findings. Now, before I move on, let me point out that among the general public present company excluded because you're at this conference, you're interested, you're somewhat knowledgeable. But among the general public, there's considerable confusion between cosmology, the study of the structure and evolution of the universe as a whole, and cosmetology, the study of hairdos and facials. Now, I admit they sound similar as do astronomy and astrology, by the way. But they are different. They're spelled differently. In fact, if you write them down, you will find out that cosmetology is simply cosmology with an extra E-T in it, like the extraterrestrial. I don't know the cosmic significance of that. But nevertheless, that's how they differ. And they mean rather different things. Now, you might say, surely people don't have this confusion. Show me the evidence. Well, I'm a scientist. I will show you the evidence. Here is a copy of an ad that a colleague of mine placed in my mailbox some time ago. Make cosmology your career. Training and supervision in hairstyling, blow-drying, permanent waves, coloring and frosting. You laugh, but these are very important topics, OK? Scalp treatments, body and skin care, style cuts, basic cuts. For further information and interviews, call that number. Now, classes started back in March, so you missed the spring quarter. But I'm sure this will be offered at your local college or university in the next quarter or semester. So if you want to do, as I and many of my colleagues have done, and get to the cutting edge of this field, you need to take a course like this. Well, these guys need a course not only on their own profession, but a course on spelling and proofreading. Because in addition to foo-ther here, you see hair-slying, oops, hair-slying. See that? And coloring. Well, that's the British spelling, and my own thesis advisor was British, so I'll allow that one. Anyway, maybe their spell checker wasn't working or something, but they don't even know their own field. Actually, my father-in-law says, you know, Alex, the only real difference between your UC Berkeley course on cosmology and a course on cosmetology is that you don't give makeup exams. Oh, oh my goodness. See, my students have to put up with me every other day. You willingly came here. Puns are a highly underappreciated form of humor, but both my father-in-law and I like puns quite a lot. All right, well, the story of cosmology, in a sense, starts with Vesto Schleifer, the observational story of cosmology, an astronomer in Arizona who examined the light from galaxies before it was even fully understood that they were actually outside our Milky Way system. He passed the light of galaxies through a prism, producing a rainbow, a spectrum. From the spectrum, a scientist can tell all kinds of interesting things about the object he or she is studying. We can tell the temperature of the gases, the pressure of the gases, the chemical composition. For example, this line is due to hydrogen. There's neutral sodium. There's singly ionized calcium, that pair of lines. A trained spectroscopist can recognize the fingerprints of different elements and their ionization stages. But we can also tell whether an object is moving toward us or away from us and how fast. If it's moving toward us, the pattern of these lines produced by various elements remains the same, but shifted toward bluer colors, shorter wavelengths, higher frequencies. And if the object is moving away, then you get a redshift. So the audible version of this phenomenon is quite well-known. You hear the siren going like that, and that's because as it's coming toward you, in between the emission of two consecutive wave crests, the siren has moved toward you, making the distance between the wave crest smaller, the wavelength shorter, the pitch higher. Conversely, when it's moving away, during the time between the emission of two wave crests, the object has moved away, thus stretching the wave, giving a lower pitch. Now, if you hear an ee-ah, ee-ah, ee-ah, it doesn't mean that the driver is drunk and can't make up his mind which way to go. It just means you don't have a constant pitch siren, but you can hear that it goes from high-pitched to low-pitched. Well, Slyfer noticed that with few exceptions, other galaxies have redshifted spectra, but he couldn't do much else with this discovery because he didn't know the distances of the galaxies. Enter Edwin Hubble, after whom the Hubble Space Telescope is named. He measured the distances of relatively nearby galaxies, using a technique I'll describe in a few minutes, and he found something very interesting. They're all moving away, other than those that are so close to us that they're gravitationally bound to us, forget about them, so they're all moving away, but right now, at a given time, the more distant ones, which generally appear fainter and smaller in the sky, they're moving away faster, okay? So there's a greater redshift, a greater recession velocity at greater distances. Now, Hubble resisted this interpretation for a while, but we now know that in the case of the galaxies, the redshift is caused by a stretching of space itself, not by the motion of particles through a preexisting space. So in fact, it's not the classical Doppler effect. Basically, Earth and objects that are bound, that are solid, we're bound by electromagnetic forces, we're bound to the Earth by gravity. Anything that's bound to be strong doesn't expand. You may think you expand after a big lunch, but that's your fault, that's not the universe's fault. But the space away from strong gravitational fields does expand and electromagnetic waves, light, expands with it. And so you can see that you start out with a short wavelength blue wave and it gradually becomes longer. That's the cosmological redshift. It's an expansion of the universe and there are ways we can now distinguish that from motion of objects through a preexisting space. And it's definitely an expansion. So from our perspective in the Milky Way galaxy, a snapshot of the universe looks like this. All the galaxies are moving away and the more distant ones are moving faster than the nearby ones. Now let me pause here for a second because there's something kind of strange about this diagram as I've drawn it. What's peculiar about it? Yeah, a bunch of people said it, we're at the center. Why would that be? You know, do all these other galaxies not like us? Is it something we said or do we smell? Are all these other galaxies lactose intolerant? Get it? Milky Way galaxy, lactose intolerant galaxies. When I talk about cosmology to my introductory astronomy class at Berkeley, I say, what is it? Are we from Stanford or something? Big rivalry, okay, academic and athletic. No, I mean, first of all, with due apologies to those of you who might be Stanford alumni, it's an outstanding institution, it really is. Just not quite as outstanding as Cal. Anyway, we don't think we're in any privileged position. We think that this is a property of a uniformly expanding universe. Let me show you this little demo, which I noticed was on the slide that started the presentation that Steve had. Here's a hypothetical one-dimensional expanding universe where the ping-pong balls are the galaxies. They're gravitationally bound, they're not expanding, and the rubber is the space between them. So fix your attention on this ping-pong ball. All the others are moving away. But the same could be said from the perspective of any other ping-pong ball. And let this rubber be either infinite or wrapping around itself. The edges are irrelevant here. I'm not trying to fool you in any tricky way, all right? You get this apparent centrality in the universe without actually being the unique center. Notice also that the more distant ping-pong balls move faster than the nearby ones because every little bit of space stretches and the more space there is to begin with, the greater will be the stretching in a given amount of time. So this explains Hubble's relationship. It works not just in one-dimensional universes, works in three-dimensional universes. Here's an expanding loaf of raisin bread where the dough is uniformly filled with yeast. You let it bake for an hour. All the guys move away from each other. Again, imagine an infinite universe or one that wraps around itself. This one thinks that it's at the center, but all the others say that they're at the center as well. And in fact, there is no unique center, at least not in the dimensions that we can physically probe. There may be a center in a mathematically definable dimension, and I can discuss that later in the Q&A with, say, a balloon. Anyway, notice also that the more distant raisins move away faster than the nearby raisins. This one went from five centimeters to 10 centimeters. This one went from 10 to 20 in the same amount of time. That's because, again, every bit of space expands. The more there is to begin with, the greater will be the expansion factor. Okay, so that's the expanding universe. And with today's modern telescopes, we've measured pretty well the current rate of expansion. And you might think we're done. But we're not done, and this goes all the way back to Newton, who considered gravity. And here's an apple. You can't give a talk about gravity without using the proverbial Newtonian apple. So here it is, boom. He supposedly watched it fall from a tree, and he wondered whether whatever it was that makes it fall is somehow related to what keeps the moon in its orbit. And Frank showed the interesting diagram from the Principia, imagining the cannonball fired at different speeds. Indeed, there is this deep connection, this law of universal attraction. So if we toss the apple up, the mutual gravitational attraction between the apple and the earth slows it down. And in fact, it comes to a halt at the top, and then comes back to my hand. So suppose you have a dense universe, a lot of matter per unit volume. Then every unit volume will be pulling on every other unit volume a lot, slowing down the universe quite quickly. In that case, the currently expanding universe would someday stop expanding and then collapse. It would implode on itself. So in this case, you could say big bang, big crunch. Starts with a big bang, ends with a big crunch, high densities, high temperatures again. Or you could say big bang, big nab gib, which is big bang backwards, okay? So that's what kind of universe you would have if it were a dense universe. If you were lying on your back, looking at the galaxies through a telescope, you would see them getting smaller and fainter, and you would say that's a well-behaved universe. And then you would notice something a little bit odd. They would get brighter and bigger again, and right around now you'd start getting a bit nervous, and then it'd be, ah, goodbye cruel world! And you would be crushed into oblivion, all right? That's one possible fate of the universe. But there's another possibility. Suppose I had eaten my Wheaties this morning. In that case I could heave this apple, forgetting about the technical difficulty of a ceiling here, I could heave it at a speed greater than or equal to Earth's escape speed, around 11 kilometers per second. And in that case, although it would be slowing down forever, it would never come back. It would either approach zero speed as time approaches infinity, or it would approach some constant positive speed as time approaches infinity. So that would be an apple that never comes back. In a low density universe, all the galaxies are pulling on all the other galaxies, slowing down the expansion of the universe, but not enough to ever have it implode in upon itself. That would be an eternally expanding universe, and if you were watching galaxies on a dark Minnesota night, you would see that they keep getting fainter and smaller, although at a progressively slower rate. So eternal expansion versus the Gnab Gibb. Which one is it? We want to know. Doesn't matter that we'll not be around to see what'll actually happen, we just want to know. That's what drives all scientists. How might we proceed to find out? Let's go back to the apple. Measure the speed of the apple at different stages of its path. See whether it's been slowing down a lot, in which case it'll stop and come back someday, or not slow down a lot, in which case it'll keep on going away from the earth forever. Examine the past history of the motion of the apple to predict the future. So in a similar way, examine the past history of the expansion of the universe in order to determine the fate of the universe. Well, to do that, we need to know how far back in time we're looking. Here, galaxies that are far away, say a billion light years away, four billion light years away, maybe that little blob there is nine billion light years away. You're seeing them as they were, one, four, nine billion years ago, because it takes time for light to travel from there to here. In fact, fun fact to know and tell, light travels about a foot per nanosecond, a foot per billionth of a second. So I'm seeing Steve, not as he is right now, but as he was maybe 25 or 30 billionths of a second ago. He may not even exist anymore. Oh, he does, good for him. He's still on this good earth. You see the sun as it was about eight and one third minutes ago, because that's how long it takes to traverse 93 million miles, okay, the light. You see the typical stars in the sky, the bright stars are some tens or hundreds of light years away, in a few cases, a thousand light years. So you're seeing them as they were tens or hundreds or thousands of years ago. So if you look at galaxies that are one, four, nine billion light years away, you're seeing them as they were, one, four, nine billion years ago. You're looking back in time. Telescopes allow us to look back in time. And encrypted in the light from those galaxies is information about how much the universe has expanded during the time that the light was traveling. That information is the red shift, okay? So if you know distances, hence look back times, and you can measure red shifts, then in fact you can reconstruct the past history of expansion of the universe. So how do we determine distances? For relatively nearby galaxies, it's pretty easy. This is the technique Hubble used. This is a Hubble space telescope picture. He didn't have those, but in such a picture you can sometimes see individual stars. Let's call that one Chuck, just for kicks. And let's say we know through studies of Chuck that it's the same kind of star as Betelgeuse, the left shoulder of the great hunter Orion in the sky, okay? And this is a relatively nearby star. We know how distant it is, we can measure how bright it appears to be, and thus we can calculate the true power. If we now say, well, Chuck is the same type of star, and there are different kinds of stars, by the way, you can figure out how far away Chuck must be in order to look this faint. And if you do the same thing with other stars, Tara and Frank and Lawrence and others in this galaxy, and you get the same result each time, well that builds confidence that your technique is correct. And in fact, Hubble used a type of star known as a Cepheid variable. Now this is the same principle by which you judge the distance of an oncoming car at night. You've calibrated how bright the headlights are of a car of known distance, six feet away. You say, ooh, those are pretty bright. And then you look at dimmer headlights, and you almost intuitively, almost instinctively, calculate the distance of the car. And if you're not very good at doing this, then you shouldn't be driving at night, okay? You get a consistency check through the angular separation of the two headlights. That gives your brain a consistency check because the angular separation decreases with increasing distance. Well, cars, stars, it's the same idea. Find stars of known luminosity or power or oomph, measure how bright they appear to be, and thus determine their distance, and thus how far back in time you're looking. Now you might say, well, that works fine for nearby galaxies, but what about these galaxies here? You know, how do you know that that one's four billion light years away and not five or a pi or something like that, billion light years? All the stars are too faint to be seen individually, and they merge together. So it sounds like you're hosed if you wanna look far enough back in time in order to really trace the expansion history of the universe. But you're not hosed. There is one type of star that's so brilliant that it can be seen at distances of billions of light years and separated from its neighbors. Anyone know what kind of a star that is? A supernova. Someone said a type 1A supernova. Ooh, boy, you know a lot, okay. Wanna come give this talk? Anyway, so yes, a supernova, an exploding star. Now, very few stars explode at the end of their lives, but those that do can become millions or even several billion times as powerful as the sun. And here's one in a galaxy where I've sped things up a bit, it typically takes a few weeks to rise and many months to decline. At its brightest, that supernova is about as bright as the central few billion stars in this galaxy. They're really bright. If our sun were to do this, and it won't, don't worry, be happy, but if it were to do this, sunblock of 50 just wouldn't cut it, folks. You'd need sunblock or supernova block of a few billion to protect yourself. But that's not gonna happen, all right. Okay, well, you first have to find a whole bunch of relatively nearby supernovae in galaxies whose distances have been measured through observations of relatively normal stars in those galaxies, because it's the combination of known distance and measured brightness that gives you the luminosity or power of a supernova. But you've gotta find a bunch of these things because there might be more than one way in which stars can explode. Indeed, there are several ways in which stars can explode. And even given a single physical mechanism, you have to measure whether there's a dispersion, a variation in the peak power. So you've gotta first find a bunch of nearby ones. Now, this is a bit hard, actually, because in a typical galaxy, a star might explode only once every 30 or 40 years. So if I were a really cruel advisor, I would have each of my students staring through the eyepiece of a telescope at one and only one galaxy, preferably at night. You see more stars and galaxies at night than during the day. Until that supernova, until the student finds a supernova, and then we would let the student graduate and move on to greener pastures. Meanwhile, I will have had decades worth of slave labor from said student. Now, there are some crimes that are so egregious that even a tenured professor can and should get fired. I mean, we can't take advantage of students in this way. But we can improve the odds by observing lots of galaxies. So let's say there's one supernova per galaxy per century. Statistically, that's the same as one supernova per 100 galaxies per year. Each of these 100 galaxies will produce a supernova sometime in the next century. Odds are that there'll be one a year. Maybe some years there'll be zero, some years there'll be two or three, but roughly one a year, okay? Or if you monitor 1,000 galaxies, there'll be 10, all right? So that's getting to be pretty good. I could have my students scanning thousands of galaxies until they find several dozen supernovae. Then we let them graduate and move on to greener pastures. But this would be considered, you know, terrible punishment to the student as well, right? This would be an egregious crime and I would probably get fired. Because, you know, students need to study and sleep and most importantly, party, all right? Fortunately with modern technology, we have a better technique. We attach digital cameras, like your little CCD camera, to the eyepiece end of a telescope and we take photographs of thousands of galaxies throughout the sky and we simply look for arrows. And where there's arrows, there are exploding stars. You see, it worked once, twice, three times, four times, five times. By rigorous mathematical induction, I conclude that this technique works every time. Well, obviously it can't be quite that simple, otherwise we wouldn't give degrees for this kind of work. A number of teams, including my own, have developed largely robotic telescopes that do the work for us. And here's the telescope that my team runs at Lick Observatory, the Katzman Automatic Imaging Telescope. It's been expertly programmed to look at over a thousand galaxies a night, nearly 10,000 in a week. And it compares the new pictures with the old pictures and it finds supernova candidates. Here's an example. Waitong Lee, my close associate, expertly programmed it. Here's a before a picture of a galaxy and then here it is again and there's something new. There's this arrow here. Well, the arrow was put in with Adobe Photoshop or something. The new thing is this little guy there. And that's a supernova candidate. It's not necessarily a supernova. It could be a cosmic ray, a charged particle that interacted with the detector in a way that looks like a star. Or it could be an asteroid flying through the field of view with Earth's name written on it. Astronomers will someday save humanity by finding the asteroids decades before they hit. And then physicists and engineers will figure out a way to deflect them so together we will save humanity. Anyway, one person's garbage is another person's gold. We don't care about the asteroids. We screen out most of the several dozen candidates that are found automatically by the system each night and focus on the one or two that appear interesting. And this is done by slaves, I mean undergraduate students who through their superior eye-brain combination examine the candidates at the end of each night and determine which ones are likely to be genuine supernovae and worthy of further consideration. And I'm very proud of my team. For about a decade we actually found more nearby supernovae than all other teams in the world combined. And actually Steve, our current count is closer to 1,000 exceeding 900. So you saw an old reference. I should update that. Let me know where you found the 300, okay? Cause that sounds a little bit embarrassing compared to 900 or 1,000. Anyway, I'm very proud of my team. And this fellow at the left is kind of interesting. There he is. I like to say that he's the cosmetologist in our group, okay? Maybe he's trying to get a date or something. And then I realized I teach at Berkeley and so this is not at all unusual. Every week I have a pizza lunch for my group. I bring them pizza and they justify their existence for the past week. Anyway, through studies that we've been doing and many other teams as well. And by the way, the studies with Kate did not lead, did not contribute to the Nobel Prize winning work. Other studies had already calibrated supernovae pretty well before that, but we've been refining the technique since that time. And a number of groups have been working on this, okay? Nevertheless, we've contributed to this and we and many others have found that when you pass the light of supernovae through a prism and produce a spectrum, you find that they come in two main types. They're now many other types, but they're called type one and type two. Now we could have called them Fred and Jean, but we call them type one and type two. Astronomers are kind of boring people. Type ones don't have any evidence of hydrogen in their spectrum. They have everything else, calcium, magnesium, iron, sulfur, silicon, oxygen, but no hydrogen. This is important because hydrogen is by far the dominant element of the universe. By the way, these supernovae produce and disperse into the cosmos the heavy elements of which we are made. So the carbon in your cells, the oxygen that you breathe, the calcium in your bones, the iron in your red blood cells, all of these elements were generated in stars prior to and during their explosions and ejected into the cosmos, making them available as raw material for the formation of new stars, planets, and ultimately life. And this is what Sagan meant when he so eloquently said, we are made of star stuff. He did not discover this, but he popularized the notion. Quite literally, the heavy elements in your bodies were created by stars many billions of years ago. So you are not just within the cosmos, but part of the cosmos in this very direct way. If that does not grab you, you were either brain dad or you were momentarily thinking about something else, like the government shut down or how the football team did or something. I know it happens to me all the time, so let me not accuse you of being brain dad. But anyway, type ones know hydrogen, type twos they do have hydrogen. Okay, the type ones in particular have a subclass called type 1A, which is thought to come from a weird kind of a star, kind of like what our sun will turn into at the end of its life. It'll be what's called a white dwarf made out of degenerate matter, not because it's morally reprehensible, but it's very, very dense, and this is the term that quantum physicists give to it. And if you're a part of a binary system, which our sun is not, then the white dwarf can steal material from the other star, grow in mass, and become unstable at some point and explode. Or it can merge with another white dwarf to which it's gravitationally bound. And that gives rise to a type 1A supernova. They are very luminous, they're nearly all the same, there are some differences among them, and we have to generate ways to read the label on the light bulb, but I won't go into those details. All right, so because of the work of many, many people, by the late 1980s, early 1990s, it was already recognized that type 1A supernovae are excellent cosmic beacons with which to determine distances of galaxies and hence lookback times. So two teams set off to find distant examples of type 1A supernovae and to measure them. And a given supernova is used in two ways. Its apparent brightness is used to determine the distance and hence the lookback time of a galaxy using the inverse square law of light, which I described before. The recession speed or the redshift due to the expansion of space is measured from the spectrum. So the supernovae are critical for these two reasons, measuring distances, hence lookback times and redshifts. And it's the relationship between lookback time and redshift that traces the expansion history of the universe. The teams found the supernovae using telescopes primarily in Chile equipped with wide angle cameras that could survey thousands of galaxies at a time. This is a picture roughly the area of the full moon. Now the full moon is not rectangular in shape, but this house about the same area. And nearly every little blob you see here is another galaxy, not a star in our own Milky Way galaxy. There are thousands of them. You know, with your naked eye, the sky is dominated by stars in our own galaxy. But when you take deep photographs with big telescopes, the sky is dominated by other galaxies, okay? So if you take a bunch of photographs of different parts of the sky like this and then repeat the process three weeks later, some of those roughly 100,000 galaxies will have produced a Type 1A supernova. They're pretty rare. They're once per galaxy, per several centuries actually. Nevertheless, with 100,000 galaxies, any sample examined three weeks apart will reveal a dozen or so of these things. You can do the math. So they're found by digital subtraction. Here's part of an image taken on the 7th of April, 1997. Another one the 28th of April. You subtract the earlier one from the later one. You get a bunch of noise. That's okay. Every measurement process necessarily has some noise associated with it. But here, cleverly placed in the middle of the square, is something that looks like it might be real. And a Hubble picture of it a few weeks later reveals it as well. And it's marked with an arrow. So it's gotta be a Type 1A supernova, right? Well, it's not that simple. You have to get the spectrum, the fingerprint to be sure. And you need the spectrum in order to determine the redshift. And that was my main role on both teams. I'm a spectroscopist by training. I've studied supernovae since the mid-1980s, and I have access to the world's greatest optical telescopes, the twin 10-meter Keck telescopes in Hawaii. These are gigantic light buckets with which we can collect the data and disperse the light into a spectrum. These are amazing machines to use. 36 hexagonal segments structured in a honeycomb pattern, acting in unison like one mirror, but much, much cheaper to make. And this technique was invented by Jerry Nelson when he was at Berkeley. He's now at Santa Cruz. Here's Fred Chaffee, a former director of Keck, showing, for perspective, the size of the telescope. And he usually wasn't there when we were taking data. The extra light-gathering power provided by his pupils is dwarfed by the glass here. So this is just a PR shot. Anyway, I would get spectra of the supernova candidates that my colleagues got. And they would look sometimes something like this. Here's a nearby Type 1A, brightness versus wavelength, a lot of squiggles, and one at redshift 0.455, which means it's roughly five billion light years away, has the same squiggles, some small differences due to noise and stuff, but no great differences. And when we got data like this, well then, I was a very happy camper. And now you see the real reason we build observatories in Hawaii. I find San Francisco Bay Area water to be too cold for swimming without a wetsuit. Well, here are three examples of Type 1A spectroscopically confirmed supernovae marked with arrows. And the punchline is they're faint. They're really, really faint. And you might say, well, big deal. They're in these scrawny, pathetic-looking faint galaxies that are obviously far away. I mean, here, look, you can't even see the galaxy there. I mean, it's there, but you can see the supernova. So these are obviously very distant galaxies, so you expect the supernovae to be faint. That's true, but these were fainter than they have any right to be. They imply greater distances than could be accommodated in a well-behaved universe. Distances that were greater than expected based on their red shifts in any well-behaved universe. Let me give a simple example. Suppose I go back to the apple and suppose I toss it and I assume the universe is just one second old, okay? I can measure the distance of the apple from my hand after one second. That's some distance. But the apple has slowed down in its upward journey. If the mass of the earth were less, then for the same toss, there would be less deceleration, and in one second the apple would go farther. Now, I can't make the mass of the earth less, but I can do the next best thing. I can toss the apple faster, and it's the same desired effect. It goes farther in one second. Now, suppose the earth didn't exist at all, and you ignored Jupiter and the sun and all those other things. Would there be any reason for the apple slow down? Hey, physics students, any reason for it to slow down at all? No, that's just Newton's first law of motion. It would keep on going in the same direction with a constant speed. So in one second, it would traverse an even bigger distance, right? But that's the biggest distance you can get under the influence of gravity or no gravity. What we found was that the supernovae, the galaxies in which they're located, the apple, so to speak, were at greater distances than you could have reached in the amount of available time. And we had to rule out other possibilities for what might be going on, like maybe there's fog in the way making the supernovae look too faint or something, but we had, you know, we ruled all that out. So the natural interpretation is that they're at a greater distance. To achieve that greater distance, what must you have? Acceleration, that's right. If I attach a rocket to this apple and it goes, zoop! Then in one second, it can cover a greater distance than that, which is covered with no deceleration, just no forces acting upon it. Now you might be wondering, well, wait, wait, wait. You know, your argument depended on an assumed age of the universe. What if it were two seconds old, then obviously the apple goes farther in two seconds. Good try if that's what you were thinking, but the detailed argument is independent of the assumed age of the universe. Really, the measured distances were greater than expected, given the red shifts in any decelerating or constant expansion universe. And so the implication was acceleration. And I was privileged to be able to announce this result at a meeting in the Los Angeles area in late February 98. The headline that came out was astronomers see a cosmic anti-gravity force at work. We use this term anti-gravity hesitantly because people ask us, can we gather this stuff, whatever it is, and attach it to our cars and levitate over traffic jams? And the answer is no. It's either a property of space that cannot be harnessed or there's so little of it that it'll never be harnessed with any reasonable amount. Nevertheless, it has an anti-gravitating-like effect, all right? In that it accelerates the universe rather than decelerating the universe, a very strange thing. And no one would have paid attention had there not been two teams that came up with the same result at about the same time. This forced other physicists and astronomers to take the results seriously. The HIZ team submitted their paper in March of 98 and it was published in September of 98 and the Supernova Cosmology Project submitted in September of 98 and it was published in June of 99. And so because there were two teams that got the same result, people had to take notice. Maybe the technique is flawed. That's still a possibility. And so every scientific result has to be verified through independent techniques, for sure. But at least there were two teams using the same technique that got the same answer. That probably meant that neither one of them made some really stupid error like a programming error, two plus two equals five, which is a huge embarrassment and causes you to lose your funding. Well, by the end of 1998, no one had found any obvious flaws in the methods by which the data were collected or analyzed or interpreted. So the editors of Science Magazine proclaimed this to be the single most important discovery in all sciences in 1998. And the caricature of Einstein is surprised here. You might think it's because he's blowing multiple universes out of his pipe. Now, Lawrence might talk about this later, the fact that we think that there are multiple universes and they come from the pipes of famous theoretical physicists. Well, the first part of that statement might be right. There may well be multiple universes. I'm actually pretty convinced that there are, but I have no definitive evidence. No, he's surprised because this one universe is expanding faster and faster with time rather than more and more slowly as a well-behaved universe would. He's doubly surprised because he has a sheaf of papers here where there's an equation. The Greek letter lambda equals eight pi G, Newton's constant, times the density of the vacuum. Now, you might say, whoa, the Nobel conference organizers have sunk to new lows. Inviting this bozo from Berzerkli who's talking about the density of the vacuum, you were taught on your mother's knee that the vacuum is sheer emptiness, nothing at all, zilch. How can it have a non-zero matter or energy per unit volume? Well, again, I'm just the messenger here. This was Einstein's idea. He was a lot smarter than I am. He came up with this possibility when in 1917, shortly after developing the general theory of relativity, he realized that the universe should be either collapsing in on itself because the gravitational force between galaxies should be causing them to implode on each other, or maybe the universe started out in an expanding state in which case it should keep on expanding, but there was no evidence for anything but a static universe. The sky didn't appear to be falling, there was no evidence for change. He and many others found a static universe to be aesthetically pleasing. So he introduced an idea, the cosmological constant, an effect of unknown physical origin which acts in a direction opposite to that of gravity and has a magnitude exactly equal to that of the attractive gravity. That would prevent a collapsing universe. You know, it's like this apple. It all goes back to the apple. If the net force is zero, the apple doesn't move, or at least it doesn't accelerate. If the net force is non-zero, then it accelerates. You know, George Lucas said, may the force be with you? No, no, no, may the net force be with you? He has to go back to freshman physics, okay? The force may be with you, but if some other force is against you, then you're gonna lose. May the net force be with you, okay? Here the net force would be zero. Einstein didn't like this because it appeared to be a mathematical fudge factor that did not make the equations mathematically wrong, but it made them look less aesthetically pleasing. There had to be this fine tuning between the size of the upward arrow and the downward arrow, for which there was no real physical reason. And there was certainly no experimental evidence in a laboratory for this effect. And this effect implies that the vacuum energy is non-zero and that it's repulsive. And many physicists found that to be a repugnant idea. So Einstein never liked the cosmological constant. And when Hubble, 12 years later, discovered that the universe isn't static after all, the whole physical and philosophical motivation for the cosmological constant vanished, Einstein renounced the idea supposedly as having been the biggest blunder of his career. Because had he not introduced it, he would have predicted, as some theorists did do, that the universe is likely to be in a dynamic state, either collapsing or expanding. He could have been famous had he not introduced this idea. So here he is, sad that he ever introduced the idea. Now, I don't know that that's what he's thinking, but it could be what he's thinking. What have we done the better part of a century later? We've reincarnated the idea, not to have a static universe, but one which over the largest scales is accelerating, is expanding faster and faster with time. So here in this room, the down arrow dominates everywhere in our solar system, down in our galaxy, down in our local cluster, our local group of galaxies, down. But as you get to sufficiently large scales of order 100 million light years, the up arrow dominates and the universe expands faster and faster with time. And if Einstein were around now, he would see that maybe his biggest blunder was actually his greatest triumph, the idea of such an effect. The only blunder was the small mathematical, the arithmetic error of giving an equal magnitude to the two arrows. And so maybe Einstein's reaction would have been something like on the cover of Science Magazine. Well, the discovery that was initially made with supernovae that were four or five billion light years away, that meant that in the last four or five billion years, the universe has been accelerating. If it's being accelerated by something like the cosmological constant, whose effect per unit volume is always the same throughout the history of the universe, then there's a clear prediction. Long ago, when the universe was denser, it should have been slowing down in its expansion. That's because galaxies were closer to each other, so attractive gravity was bigger than it is now, and moreover, the amount of volume between them was smaller, so the cumulative effect of the repulsion would have been smaller. So in a sense, gravity dominated over anti-gravity, and as the universe expanded, one declined, the other got bigger, and at some point in the past, they crossed each other. So the prediction was that early in the history of the universe, it should have been decelerating. So Adam Rees was the principal investigator of a project using the Hubble Space Telescope, with which we found more distant examples of supernovae, six, seven, eight, even 10 billion light years away, and we found that indeed, for the first nine billion years of its history, the universe was slowing down, and it's only roughly in the last five billion years that it has started speeding up. This transition from slowing down to speeding up mathematically is known as a jerk. So in a sense, we measured the cosmos to have gone through a jerk, and the New York Times headline that came out was a cosmic jerk that reversed the universe, and there's my former postdoc, Adam Rees. Now I start getting all these phone calls, hey, who's this jerk you work with who reversed the expansion of the universe? And Adam's mother was not very pleased with this juxtaposition. All right, well, what is the stuff that's causing it? It's not the visible matter in the universe. Visible matter always pulls. Even anti-matter, we think pulls. It's a positive, regular form of energy, although I don't disagree with Tara. It should be measured before we can completely claim that, but everyone believes it pulls. So anti-matter's not gonna do it. Dark matter doesn't do it either. By the way, there's dark matter there. There, it's not that hard to detect Tara. There, you know, what's the big deal? Now anyway, we know that there's a bunch of dark matter there precisely because this cluster of galaxies is gravitationally bound. The galaxies are moving around so fast, you can measure that with spectra that it would quickly disintegrate unless they were bound by extra matter. Indeed, it's the extra matter that causes those speeds. And that argument was actually first made by Fritz Zwicky in the early 1930s. One of my heroes, an astrophysicist at my graduate alma mater, Caltech, he was decades ahead of his time on a number of issues, but he wasn't believed very much and he wasn't well liked, in part because he was arrogant and abrasive and didn't think highly of the intellectual capacity of his Caltech colleagues. Now, he might be showing you here what he thinks of the typical brain size of one of his faculty colleagues. And again, I don't know that that's what he's thinking, but it could be what he's thinking. And he is on record as having referred to his colleagues as spherical bastards because, you know, they're bastards any way you look at them. A sphere is the only object that looks the same from all directions. I do not encourage you to start referring to your friends as spherical bastards. You will quickly end up friendless. But anyway, Zwicky came to the idea of dark matter in an oblique sort of way I mean, that's the genesis of it. And then decades later, Vera Rubin came up with the same explanation for the fact that spiral galaxies, which are spinning quickly, don't appear to be disintegrating. And just as Zwicky was ignored for a long, long time, Rubin and her colleagues were ignored as well. But now, as you heard earlier this afternoon, dark matter is like the big thing in astrophysics. It's eclipsed only in a sense by dark energy. The term that has been dreamed up for whatever it is, it's causing the acceleration. You know, it's not luminous matter. It's not dark matter. It's not antimatter. It's something. It's some form of energy, but we can't see it. So it's dark and it's mysterious. So it's dark in that regard too. Dark energy, a term coined by Michael Turner at University of Chicago, a theorist. It's regrettable in a sense, because if there's one equation people have heard of, what's that equation? E equals MC squared, right? Most people have heard of it, even though the actual understanding of it is actually pretty profound and subtle. But I'm continually being asked, are dark energy and dark matter just two sides of the same coin? And the answer is almost certainly not. Dark matter pulls, dark energy pushes. They appear to probably have very different physical origins. But in honor of the discovery of the accelerating expansion of the universe and the implication of dark energy, my wife Noelle made the following t-shirt which was distributed to members of the Nobel winning teams. Dark energy is the new black. A limited edition. By the way, the other possibility for explaining acceleration is that Einstein's general theory of relativity is incorrect on the largest scales. That's an amazing conclusion as well, if correct. Most theorists seem to be focused on dark energy being the explanation rather than relativity being wrong. But in the, in interest of completeness, let me just mention that. What is the dark energy? Well, we don't know. I think it's probably the vacuum energy. In other words, these little things, virtual particles are created in pairs and live for a very short time. We know that that happens. Their presence affects the measured energy levels of the electron in a hydrogen atom, for example. But they're fleeting and it was always thought by physicists that in a sense for every positive energy fluctuation, there's a negative energy one and so the total ends up being zero. Mostly as you heard during the discussion because if you do the back of the envelope calculation, you actually come up with an infinite vacuum energy and you can get it down to 10 to the 120th power with a little trick or maybe 10 to the 55 power with another little trick. But the point is it's a real problem and everyone had assumed that it's zero. But if there's a slight non-cancelation with a positive net energy density, this has the desired effect of expanding space away from gravitational fields like that of Earth faster and faster with time. And all the evidence seems to be consistent with that. But another idea is that dark energy is some new kind of energy associated with a new field, kind of like the Higgs field about which you heard from Tara, but different from it. And it goes by the generic name of quintessence like the Aristotelian fifth essence, but there are hundreds if not thousands of different models. Now you might say, well, wait a minute. Before I close, you know, I've only presented to you evidence from supernovae. What if the technique is flawed? Could be flawed. So as I said, it's important in science to have other independent techniques. And I won't go into them, but let me just say very briefly that there are now many other techniques. In part, measurements of the microwave background radiation, and I believe my colleague George Smoot will be discussing that tomorrow. But a number of different ways of studying the microwave background radiation and the little tiny temperature fluctuations which are associated with density variations in the early universe, they give rise to the same conclusion. And one piece of evidence is that if you take those little tiny density variations when the universe was just 380,000 years old and you let gravity sculpt the universe for the next 13.8 billion years, and you ignore dark energy and you do your computer simulations, then you find that the formation of galaxies and clusters of galaxies and voids doesn't quite end up resembling the observed universe now. Whereas if you include dark energy plus gravity and rerun these simulations, then the growth of galaxies and clusters of galaxies and voids ends up now at redshift zero, giving us a structure that actually looks like the observed structure of the universe. And there are other arguments as well. So in the end, when you put everything together, we come up with this pie chart, little bit updated using the Planck results which George will probably discuss, little bit updated pie diagram compared with what Tara showed. For years we'd been saying dark energy is 73%, but it's more like 70 to appears. So the dominant stuff of the universe averaged over billion light-year diameter volumes, okay, not this room. Let me emphasize, okay, but giant volumes filled with what we thought was empty space, well, it's not empty, it's got this dark energy. When you add it all up, it dominates and we don't really know what it is. For the youngsters among you, if anyone tells you that physics is dead, there's nothing left to be discovered, you tell them, what about 70% of the universe? Nay, what about 95% of the universe? Because most of the remaining is this dark matter and we don't really know what that is. I think it's probably a wimp, but I'm not sure, okay? So we don't really know what 95% of the universe is. We know pretty well, 5%. And in fact, the stuff that easily shines, stars and planets and stuff, is only 0.5%. That's the only part we understand well. So in a sense, we're the debris of the universe. We're the afterthought of creation. That's not to say you're not important. You are, to yourselves, your family, your friends, your loved ones, but you're not made of the dominant stuff of the universe. The dominant stuff is the dark energy and we don't know what it is followed by dark matter and we know only a little bit more about what that is. And dark energy is also important because it is widely thought to be a quantum scale phenomenon that acts everywhere and thus dictates the dynamics of the universe overall. So it's the one or one of very few observational tests of quantum theories of gravity or string theories, those theories that are attempting to unify the two great pillars of modern physics. Quantum physics, the physics of the very small and general relativity, the physics of the very large. Any such theory that's incompatible with dark energy or a failure of general relativity can be ruled out as not being a viable candidate theory. So the implications of the acceleration have been extreme, that's why it was awarded, the discovery was awarded the Nobel Prize. And finally then, let me go back to the question I asked, how will the universe end? Well, it's pretty clear that if the dark energy continues to be repulsive, then the universe will expand faster and faster and faster with time as the dark energy dominates more and more over attractive gravity. A runaway universe, so to speak. So if you want to actually see galaxies like this one with your very own eyes through a telescope, you'd better go and look pretty soon in the next few tens of billions of years because beyond that time, galaxies will have been whisked away to such great distances that they will be too faint to see and the universe will be cold and dark and empty. That's what we thought 12 years ago, but theorists like Andre Linde at Stanford and others have pointed out that we don't really know what the dark energy is and there are models, theoretical models of dark energy in which the sign changes in the future from one of repulsion to one of attraction. There's a historical precedent for that in the inflation of the early universe. That's something that acted like dark energy when the universe was a tiny blink of an eye old but then it reverted to an attractive kind of gravity. But maybe today's dark energy will do that someday. If that's the case and if there's enough of it, then it turns out that despite accelerating right now, it will someday start decelerating and maybe even will come back and so there might be a big crunch after all. But I think the data are compatible right now and best with eternal expansion, the cosmological constant and that we will live in a universe that is a runaway universe effectively. Well, to close, let me point out that the famous American poet, Robert Frost, in 1920 certainly didn't know about anti-gravity in the accelerating universe. He didn't even really know about the two possibilities of an eternally expanding and a collapsing universe that hadn't been studied in great detail by cosmologists yet. But in the context of, I guess, Dante's Inferno or some say in the context of a conversation he had with Harlow Shapley, an astronomer who said the sun might blow up or the earth might someday freeze, he came up with a poem that in retrospect is relevant to what I had to say right now. It's called Fire and Ice. Some say the world will end in fire. Some say in ice. From what I've tasted of desire, I hold with those who favor fire. But if it had to perish twice, I think I know enough of hate to say that for destruction, ice is also great and would suffice. So you see, in the context of what I discussed today, Frost would prefer a universe that ends in a big crunch, hot and compressed like fire. Hot like fire. Fire isn't compressed, but whatever. But if the universe and he had to perish twice, then eternal expansion and an ending in ice would be okay with him and that's perhaps appropriate given his name, Robert Frost. Thank you for your attention. Thank you, Professor Phillip Panko for that mind-expanding lecture. We will take a few minutes to gather our panel up front and at the same time, our ushers will begin to pass out pieces of paper for you to submit questions. Thank you. Okay, folks, please find your seats. We'll get started in just a minute, one minute now, okay? All right, let's begin our questions with members of the panel. Does anyone have a question? I'm not very hopeful about experimental clarification either. We'll see. Do you want me to go ahead? All right, so first I wanna make a comment about the dark energy and you can tell them about how wrong it is, but we were there at a small meeting when Mike Turner and we were discussing what should we call it? And the answer that we said, we can't call it the cosmological constant because all the grad students assume we have the correct answer, right? So we have to give it a new mysterious name so people will actually investigate and understand. And so we tried several different names. I can't remember all of them, but at the end, Mike Turner says, we have to call it dark energy because it's clearly an energy. And besides, we want the department of energy to pay for part of it. And if it says energy in the name, they will certainly think of it. And so he's a far-thinking guy and that's why he's now becoming the president of the APS. He's been very active in not only the theory, but in also making the field progress and being head of many committees. And it's certainly on one of those commissions, he said the study of the acceleration of the universe, which is, we label the dark energy problem, is a really key and critical problem. So you talked about where we are now, but you didn't talk about what we might be doing next. Do you have, I mean, I have my own ideas on this, but. So, right, what to do next? Well, it's a combination of many different measurements that allow us to set constraints on the dark energy or whatever it is that's causing this acceleration. From the supernova perspective, if you measure the expansion history of the universe in greater and greater detail, then you can rule out some ideas for what dark energy is because they will not agree that the predictions for how quantitatively the universe expanded with time will not agree with the observations. So that's one way of doing it and that's the technique that I and my colleagues are pursuing, we're trying to measure through supernovae, the expansion history in more detail. Of course, we have to combine that with measurements of the microwave background and the Planck measurements about which I think you'll be talking tomorrow are certainly very interesting. I'm not sure what's beyond Planck in terms of microwave background, but we need to make those measurements more carefully. We need to do other things like, you know, as you know, measuring the so-called integrated sax-wolf effect. That's an effect where you can see microwave background photons going through superclusters of galaxies and if the supercluster, if there were no dark energy then it turns out that the photons would gain energy on their way in because they're falling into a gravitational field and then they would lose exactly the same amount of energy coming out. So you get a net gravitational shift of zero. But because the supercluster expands due to dark energy during the time of flight of the photons across it, the blue shift coming in is a little bit greater than the red shift going out because the cluster has expanded more, you know, on the way out. And so there's a net blue shift, the radiation looks a little bit hotter, you know. So measuring that is another constraint. Measuring X-ray clusters of galaxies provides additional constraints. So it's many, many different constraints that give you this concordance cosmology, as we now call it, to ever greater precision. And one of the interesting things to me is that there are certain tensions that are appearing. The Planck data give a Hubble constant, this expansion rate of the universe right now, which is significantly lower than what we have measured using, you know, the Cepheid variables in relatively nearby galaxies. And so not everything is rosy, and this is actually good. It's a little bit like Tara said, that if you find things that are unexpected, that might lead to a whole new discovery. So we'll see as the data get better and better. But in the dark energy, the JDEM mission and, you know, all these things, I guess now it's called W First, if it ever gets built, given the state of the economy will help. And there's a European mission called Euclid that'll help measuring gravitational lensing of galaxies in another way of getting additional constraints. So there are many different types of observations that we hope will let us home in on whether this really is the cosmological constant or something else. Yeah, I think that these, they're all, it's really exciting when they're a little discordant results, but again, I wanna go back to my result that some of the results are wrong there. They're all, you know, the Hubble constant itself, as you know, if you look at history, was measured to be 100 with 10% accuracy and 50 with 10% accuracy and instead it'd be 75. We think we're better than that. No, exactly, so I wanna be careful about this, but it's, what is a little, what may happen, and while I don't like to predict anything that's less than a trillion years from now. It could be a little like particle physics, as Frank Kitar was saying. I mean, the standard model works just too well and that's been a big frustration in particle physics for many, many years. And this picture of a cosmological constant, unfortunately everything seems to be coming down to it, but unfortunately that's the one value where you really can't say what it is. And it could be that it's quite possible that while we've had this incredible period of discovery that we have this model that we can't understand that explains all the data and it may continue, my bet is that we'll see that everything is gonna be consistent with this model that isn't explainable for the foreseeable future. Yeah, it could become so difficult and so expensive to show a difference from the prediction of the cosmological constant that effectively we can't reach that kind of precision. It would have been easier if it hadn't been, because then it would be easier, but it looks. Well, that's right. It looks like one and walks like one and make back like one. Right. So I actually think that this is another reason for the multiverse idea that the vacuum energy can be pretty much anything. Well, we'll talk about that. And we don't live in a universe with a high vacuum energy because stars and galaxies wouldn't have formed. But we don't live in a universe with zero vacuum energy because out of the continuum of numbers, zero is a very unlikely number, as is any other single number. But the point is we live in a low vacuum energy universe and that was conducive for the development of complexity. So I'm okay with that, but I can't prove it and it leaves me in a dissatisfied state. It should. Yep, it does. Good. We're in agreement, Lawrence. Professor Shears has a question. So, Alexi, you also mentioned that it might be possible that Einstein's theory of general relativity might fail at these really large distance scales that we haven't been able to test. Yeah. But you said that people didn't really like that. Yeah. The failure of general relativity is a possibility, but general relativity is such a beautiful theory. It's based on this most simple assumption. I mean, beyond special relativity, which just assumes that you can't tell if you're moving at a uniform speed and the speed of light is independent of your motion or the motion of the emitter and that's an experimentally testable fact. Those two things lead to special relativity and then the principle of equivalence, the idea that you can't tell whether you're in an elevator accelerating upward or in a gravitational field pointing downward and any of you who have been in an elevator kind of feel heavier when it first starts accelerating. How do you know the Earth's mass didn't become bigger for a bit? That's the principle of equivalence and that is such an obvious and measured thing from which all of general relativity falls. And then the mathematical framework that comes out of that is so pretty that many of us just are reluctant to abandon general relativity, but it's definitely a possibility that it may be wrong. It's just that I think most theorists, if you look at the numbers of papers that are written, there are many, many more papers exploring the possibility of dark energy versus those exploring the possible failure of general relativity. General relativity is very difficult to modify in a consistent way. Most attempts fail with very gross confrontation with experiment. So most of, I think many people, many theorists have tried to modify general relativity, but most of those attempts never leave the desk drawers in the end, they don't go public because they're obvious failures. There's another reason. Not only indeed, in fact, most of those modifications are far uglier than the possibility of dark energy, I think, for most theorists. There's two other things. We think that really at small scales, at very small scales, that general relativity probably will change when we have to introduce quantum mechanics, but so it's not just that it's hard to change theoretically. The question is, why does it suddenly change on a scale of galaxies? And that sort of seems kind of arbitrary. If you put fundamental physics constants together, it's not a natural scale to change. Now some people have argued that, well, there is one other scale, which is the size of the universe, and maybe there maybe some, you know, it could be evidence of something outside of our universe, and you make those hand-waving arguments, but from a fundamental physics perspective, it's not a, you wouldn't, if you locked a physicist in a room and asked her what scale would general relativity change on, she wouldn't say the scale that we measure it to be. So I think that's another fact. Nevertheless, just as a final point on this issue before moving on, I must confess that occasionally at three in the morning, I wake up screaming, my wife can attest to this, because I'm concerned that dark energy and dark matter may be our modern day equivalents of Ptolemaic epicycles. Remember Ptolemy had the idea based on Aristotelian physics that essentially everything circles the earth, but to get the observed, to get the predicted positions of planets to match the observed positions of planets, you have to have these little extra little epicycles, these little orbits, and if he added epicycles on top of epicycles, he could have achieved arbitrarily good agreement with the data, because in fact, any periodic function can be decomposed into a sum of sines and cosines of different amplitude and phase. This is for those studying mathematics, you may recognize this as being Fourier analysis, okay? So in a sense, he was inventing Fourier analysis, but it was mathematically brilliant and arbitrarily good agreement with observations, yet we now know fundamentally wrong. So I do worry sometimes. I would also like to add a bit of historical perspective. In the past, there have been theories that look extremely well-established, and far better established than our current cosmological standard model. Like Newtonian gravity, Newtonian gravity went from triumph to triumph, among other things, solving an earlier dark matter problem when the gravity acting on the planet Uranus seemed to be wrong, and people used that to predict the new planet, Neptune, which was subsequently found. Similarly, the wave theory of light in the 19th century was a great triumph and had much mountains of experimental evidence and even a profound theory with Maxwell's equations and electromagnetism. Nevertheless, it was drastically modified in the 20th century. Both of those things were drastically modified in the 20th century. Newton's gravity eventually gave way to Einstein's and the wave theory of light had to be generalized to incorporate quantum mechanics. So we may be in a situation like that, but what I think is true is that a modification of gravity will have to be profound. Little tricks and ugly fixes are not worthy and are unlikely to agree with the vast body of data that is acutely. I wanna add one thing, Frank, just because I worry, but because I get lots of letters, you probably do too. From people who say, you know, everyone thought Einstein was crazy, people think I'm crazy, therefore I'm Einstein. Great logic. But the idea is that some people think that, okay, all these fundamental theories have been overthrown and I can show everything's wrong. And the really important thing for people to realize is that Newton's law of gravity isn't wrong. It's right. It works very, very well and NASA uses it a lot. And intercontinental ballistic missiles depend on it and all sorts of stuff that affect our lives. And similarly, the wave theory of light isn't wrong. We modify our understanding at some level, but those explanations which have satisfied the test of experiments still are valid and that's a really important part of the continuity of science. Yeah, I also'd like to say that when we can, we try to tweak things and add things rather than considering radically different changes in successful theories. So certainly in the case of dark matter as opposed to dark energy, it's very plausible that it's just a new kind of particle of some kind, either an axion or a WIMP or some other kind of new particle. And although there have been attempts to mimic the effects of dark matter by changing gravity, I think those are widely regarded as silly at this point. If there's a more conservative fix, that should certainly be explored fully. I think Professor Ting has a question. Yeah, I was just wondering, would you like to make a comment? Why happened five billion years ago? Yeah, why did it happen five billion years ago that this rough equality between gravity and anti-gravity, if you will, occurred? So that's one of the big cosmic questions. It's part of the reason many theorists don't like the cosmological constant. First, the fact that it's a very small value but not quite zero, that's very weird. And then the fact that there's this rough equality, 0.7 versus 0.3, that's roughly 50-50. It could have been 100 to one, it could have been a quadrillion to one, it could have been a Google to one. Why is it 50-50? And I don't know, you know? It's the why here, why now problem that Eichel Turner talks about. Yeah, I'll talk about it. The Tanya Harding problem, some of you are old enough to remember that, right? We'll probably hear about that from Professor Kraus tomorrow. Yeah, but we don't really know. But we do know it couldn't have been a very large cosmological constant if that's what it is, because then stars and galaxies would not have formed. And it's a pretty small value, it could have been smaller, but zero is simply unlikely, you know, out of the continuum of numbers. So an anthropic type argument, which Steven Weinberg actually did make in the late 1980s, he made this argument that clearly the cosmological constant isn't more than 100 in some units, the units I've been using, because otherwise we wouldn't be here. And he was right, you know? Yeah, good. But zero is a much more beautiful number. Zero is more beautiful, except that no theorists have come up with the exact cancellation. But everyone thought it was, and we should point out that a universe in which it was zero would be nicer than the universe in which we live in. I had this debate with several fundamentalists, and maybe I'll get into it. There's a coin, there's a question. Yeah, why do all type 1A, supernova, more or less, have the same energy output? Yeah, the type 1A's are all more or less the same, because... Especially considering it's very cataclysmic exchange. Yeah, it's cataclysmic, but it occurs at or near the same mass that's trying to say car limit each time. It becomes unstable at that point. You get a runaway set of nuclear reactions. Now, to be fair, we're finding all kinds of weirdos supernovae recently that don't seem to fit in that paradigm. So there may be ways in which the surface layers of a white dwarf can explode more than they do in what is called a nova explosion. This would be a supernova, as opposed to a supernova, or a nova, right? Anyway, in between a nova and a supernova, we're getting into the fine details here. But it appears that many, if not most, of the white dwarfs that do explode with a high luminosity do so at or near the Chandra limit. Good, thank you. No time. Okay, folks, I think we'll have to cut it off at this point. I know there are a lot of questions. We took a lot of questions from the audience, and I know your folks are gonna be disappointed that we're not gonna be able to get to those. I'm going to offer that we will make copies of the questions and try to answer them on the internet, so watch the Nobel Conference website in the near future for answers to some of those questions. And at this point, I think we should adjourn and reconvene at 6.30 for Professor Ting's talk. Thank you.