 Hello everybody and welcome to our lecture today. My name is Zouan and I am a fourth year undergraduate student completing my degree in mechanical engineering. First, I would like to say a thank you so much to all of our donors we all benefit from and are immensely grateful for generations of your support. Moving on to logistics, please submit questions for today's speaker in the YouTube chat. And with that being said, I'd like to introduce our speaker for today. This is Alex Filipenko, professor of astronomy. He is a member of both the National Academy of Sciences and the American Academy of Arts and Sciences and is one of the world's most highly cited astrophysicists. Filipenko was voted best professor at UC Berkeley a record nine times. And in 2006, he was named the case Carnegie national professor of the year among doctoral institutions. Filipenko has produced five astronomy video courses with the great courses co-authored and award-winning astronomy textbook and appeared in more than 120 television documentaries. Please join me in welcoming Alex Filipenko. Well, thank you so much for that very warm introduction. And it's a pleasure to be here. I'm sorry that yet again, we can't hold a normal Cal Homecoming weekend, but at least this year is much more than we were able to do last year. So the trend is positive. The Delta variant cases are going down, especially in the Bay Area. And let's keep our fingers crossed that by this time next year, we can all be fully in-person, not just for the football game, but also for this series of lectures and also for the many, many events that are always held on campus for Cal Homecoming Day. This is one of the two favorite days we have along with the one in the spring when many prospective students come with their families to visit campus. So we hope to welcome you with open arms in the more normal way in future years, but this is better than nothing. So go Bears, beat Washington State. I'll be at the game tomorrow and I'm hoping that we'll do well. So I'd like to tell you today about an interesting discovery in astronomy, but more specifically in cosmology, that subset of astronomy that deals with the structure and evolution of the universe as a whole. So basically we're interested in, where the hell did it all come from? And this question goes all the way back to the cave person days. Here we are, thousands of years later, cosmology marches on. We still are trying to figure out where the hell did it all come from? And the story begins largely with Edwin Hubble, after whom the Hubble Space Telescope is named. He made a number of important discoveries about a century ago, one of which was that these so-called spiral nebulae in the sky, clouds of gas were actually bound, that is gravitationally bound collections of billions, even hundreds of billions of stars, and they collectively form these things called galaxies. We live in the Milky Way galaxy, and they're huge. They're like 100,000 light years across, and one light year is like 6 million million miles or 10 trillion kilometers. So imagine if this were a picture of our Milky Way, our own sun would be just one of the stars among a hundred billion, pretty amazing. But even more ones like this one are moving slowly, but the more distant ones, which look smaller and fainter in the sky, are moving away more quickly. So basically most of the galaxies, these giant collections of stars are moving away from us with the more distant ones moving faster than the nearby ones. So this led to the concept of an expanding universe. The galaxies themselves are gravitationally bound, they're not expanding, but the space between them is growing in size. Our universe is becoming bigger with time. This was actually a concept that Hubble himself resisted for many years. He thought that the interpretation of the data should be something different, but really it's that the universe is expanding, an amazing discovery. Well, there are a lot of cartoons about this, sorry I'm late, but how the universe keeps expanding. Again, I said that it's the space over millions of light years between galaxies that's expanding. Galaxies are not expanding, they're held together by gravity. Planetary systems like our solar system are not expanding, they're held together by gravity. Earth isn't expanding, you're not expanding, these things are held together by gravity and you're held together by electromagnetic forces. So a common misperception is that everything is expanding, that's not true. Only the vast spaces between galaxies are expanding. Nevertheless, there are a lot of cartoons that get this concept wrong. Here's another one, if the universe and everything in it is expanding, how come our budget gets shrunk all the time? Well, again, not everything is expanding, you're not expanding. If you expand after lunch, that's your fault, you ate too large a lunch, it's not the universe's fault. Okay, well with modern telescopes, we've figured out how quickly the universe is expanding and that's some number. I'll get back to that near the end of my talk, that's where the surprise is. There's a surprising new result about the expansion rate currently. But first I wanna tell you about how that expansion rate is changing with time. Now, how should it be changing? Well, centuries ago, supposedly Newton watched the apple fall from a tree, it didn't hit his head, that story is apocryphal. Nevertheless, supposedly he saw an apple fall and he wondered whether whatever it is that attracts it toward Earth and makes it fall is somehow related to why the moon retains an orbit around Earth and doesn't just go flying up into the cosmos. In other words, he tried to unite terrestrial phenomena with celestial phenomena. And he did so with his law of universal gravitation. Basically everything attracts everything else. And so extending this to the universe at large, all these galaxies, which you're seeing here, all these fuzzy blobs or galaxies, they should be pulling on one another over the vast distances of empty space. And so the expansion of the universe should be slowing down with time. Just like when I toss an apple, the proverbial Newtonian apple, you can't give a talk about gravity without having an apple. So when I toss it up, the gravitational attraction that Earth exerts on the apple slows it down. Well, so too, all these galaxies should be attracting all the other galaxies, slowing down the expansion of the universe. And if the universe is sufficiently dense, that is a lot of stuff for unit point. Then the slowdown should slow down so much that the universe eventually comes to a stop and then reverses its motion and ends up in a big crunch or a Gnab Gibb, which is big bang backwards, right? Big bang, Gnab Gibb. So if you were lying on your back, watching the galaxies, you'd see that they get fainter and fainter with time. You'd say you live in a well-behaved universe, but then you'd notice something peculiar, they're getting brighter, bigger, ah, you'd get nervous, goodbye cruel world. So you'd end in a hot, dense, big crunch. That's one possible fate for the universe. But it's also possible that the density, the mass per unit volume is sufficiently low that although the universe's expansion is slowing down with time, it never comes to a stop. That would be like an apple that I launch at a speed greater than or equal to Earth's escape speed. It keeps on going away from Earth forever, like a rocket that's launched greater than the Earth's escape speed. In that case, if you were lying on your back, watching the galaxies, they would get forever fainter and smaller in the sky, an eternally expanding universe that ends up cold and dark and dilute, a very different ending from the hot, dense, big crunch. So cosmologists would like to know what the fate of the universe will be, just because it's an interesting question. And the way we can attempt to answer that question is to measure the past history of the expansion in order to determine the fate. And again, let's go back to the apple. If I measure its speed at many different times and I show that it's slowing down a lot, then I can predict that it'll stop and reverse its motion and come crashing down. But if it's not been slowing down a lot, then I can predict that it'll keep moving away from my hand forever, okay? So that's the same idea with the cosmos. Look back in time and compare what the expansion rate used to be with what it is right now. Well, that's hard to do. How do you go back in time? We do it by looking far away. Light doesn't travel infinitely fast. It takes time to travel from there to here. You see the sun as it was a little over eight minutes ago because it takes a little over eight minutes for the light to traverse 93 million miles. You see even the nearest brightest stars as they were some tens or hundreds of years ago because they're tens or hundreds of light years away. And it took that amount of time for the light to reach us. And if you look at faint galaxies, they are say a billion light years away and four billion light years away. And that little smudge there might be nine billion light years away. So you're seeing them as they were one, four, nine billion years ago. And encoded in the light is information about how fast the universe was expanding one, four, nine billion years ago. So you can trace the expansion history of the universe. We get a movie of the past history of the universe. But we need to know the distances and thus the lookback times of these galaxies. How do we do that? Well, for nearby galaxies, we can find individual stars and study their properties. And let's say that that one there we determine is just like Betelgeuse, the left shoulder of the great hunter Orion. And that's a pretty nearby star. We know its distance. We know how bright it appears to be. So we can calculate its true intrinsic power, its oomph. And then we can compare that with the apparent brightness of this star and determine that star's distance. And we do that for other stars in the same galaxy. And if we get the same answer, then we feel pretty convinced that we've got the right answer. Now, this is quite analogous to how you judge the distance of an oncoming car at night. You look at the headlights of a car of known distance. Let's say it's two meters away, you say, whoa, those are pretty bright headlights. And then you look at fainter headlights and even fainter headlights. Your eye-brain combination almost intuitively judges the distance of the oncoming car by looking at how faint the headlights appear to be and knowing how bright they really are. I mean, if you're not very good at doing this, you shouldn't be driving at night, okay? Well, cars, stars, it's the same sort of thing. You just need a headlight whose true power you know. And then you look at its apparent brightness. Well, normal stars work for relatively nearby galaxies, but for the galaxies that are billions of light years away, you don't see any individual normal stars. They're too faint and they're blurred together. I mean, this blur here is like a billion stars that you can barely see even as one. So you might think you're hosed, but you're not because there is one type of star that becomes so brilliant, so intrinsically powerful that it can be seen even at distances of billions of light years. And that's the supernova, the exploding star. Now, this is a small minority of all stars. Our sun won't do this, but those that do become millions or billions of times as powerful as the sun. And here's one exploding in a galaxy of 100 billion stars and that one star there at peak brilliance is as bright as the central billion stars in this galaxy. This takes several weeks or months. We've sped up the process here, so it's not to bore you. But that's a billion suns there, but it's one star. So again, if our sun were to do this folks, sun block of 50 just wouldn't cut it. You need sun block or supernova block of a billion or so to protect yourself. But don't worry, be happy. We've determined that our sun isn't gonna blow up. If it does, you can tell Carol Chris to fire me from Cal. Believe me, the least of my worries and the least of your worries will be me being fired from Cal if our sun explodes. But don't worry, be happy, it's not gonna happen. All right? Well, by finding nearby exploding stars like this one, in a galaxy where we can also see relatively normal stars like these, and so we've determined the distance of that galaxy through normal stars, that's like knowing the distance of a nearby car. And then you look at how bright the supernova, the headlight is and knowing the distance, you can figure out how powerful it really is, okay? So this is like the nearby car. But you have to do this for a bunch of exploding stars in a bunch of nearby galaxies because they might not all be the same, like car headlights and bicycle headlights and big semi-truck headlights. So we first need to find a bunch of these exploding stars and we can do that in principle by looking through the eyepiece of a telescope at one and only one galaxy. I could have my students do this. And then when they find a supernova, we let them graduate and move on to greener pastures. Meanwhile, I will have had decades of labor from them because a typical galaxy produces a supernova once every 30 or 40 years. But there are some crimes that are so egregious that even a tenured professor can and should get fired. I mean, students need to sleep and study and go to the parties, right? Not necessarily in that order. This would be considered cruel and unusual punishment. So with modern detectors and telescopes like the cameras you have in your phone, we have a better technique. We can attach these cameras to the eyepiece end of a telescope, take photographs of thousands of galaxies and simply look for arrows. You see that wherever you see an arrow, you see an exploding star. By mathematical induction, I conclude that this process must work every time. Well, obviously I'm joking here. The universe doesn't paint these arrows in the sky for us. We have to find the supernovae some other way. And the way we do it is with a robotic telescope at Lick Observatory, which is owned and operated by the University of California. I run a telescope here called CATE, the Katzmann Automatic Imaging Telescope, which is not a big telescope by today's standards, but it's been programmed to take photographs of about a thousand galaxies a night. And then it repeats the process the next night and it compares the pictures. And usually there's nothing new in the new picture, but occasionally there is something new and then we mark it with an arrow and that's a supernova candidate. And there might be a dozen such candidates out of a thousand images over a night. So then I have Cal undergraduates who look at those candidates and using their superior eye-brain combination, they determine which ones are likely to be genuine exploding stars because there are other things they could be. And these students get their hands dirty with research at an early age. They learn how to, you know, computer program. They know how to deal with statistics, with data analysis. They get the thrill of discovery of a supernova and this serves them well no matter what field they go with. STEM fields that are much more immediately useful to society like, you know, applied physics or medical physics or engineering or computer science. But the bug that bites them is often astronomy and the chance to do research of this sort is a real thrill for them. And it launches them on their course of action. And, you know, some become professors of astrophysics but only a minority. They also get to use other telescopes at Lick Observatory to monitor these exploding stars, how bright they get, how they fade with time. They also use a bigger telescope to study the supernovae in greater detail. And they can do this now from campus because we have these observing rooms set up. They don't have to go to the observatory, which is great because, you know, students typically don't have cars and they have, you know, classes to take and all that. But now they can do it from these observing stations at each of the UC campuses. And during the pandemic, we've even made it possible for everyone to observe using their laptop computer at home. So it's just, it's like we call it pajama observing. So all this has led to a big increase in student involvement. I now have 12 to 15 undergraduates in my group at any given time, not to mention the grad students in the postdocs. There's also a thing called the Automated Planet Finder at Lick, which searches for planets going around other stars. On other homecoming days, I've talked about that research. But anyway, Lick is an amazing place with a lot of student hands-on opportunities. It's also our base for astronomy, education and research for the University of California system. And we attract in a normal year, not during the pandemic, but in a normal year, over 25,000 visitors per year. We are beginning to open up to the general public in limited number gatherings where people are masked and all that kind of stuff. So it's really an amazing place. And we do a lot of technology development there and all kinds of stuff. A year ago, last August, Lick almost burned down. I was up all night, the night of August 19th, 20th because one of the fires that ravaged this part of California actually came to the observatory grounds and you can see as night falls in about an hour or so, it'll get dark. Now you can see the flames really well. My Cape Telescope is right there. I at times during the night thought it had burned down, but it turns out it was just smoke enveloping it and the smoke was reflecting fire light, but it survived. And the three meter telescope survived and the automated planet finder survived. And it was just, you know, we owe an enormous debt of gratitude to Cal Fire and the other firefighters. I mean, we were fortunate that they set up a base at Lick Observatory because it's high up, it's 4,200 feet and it has a few roads leading from it. So they could monitor the progress of the fire and go to the hotspots, but, you know, they saved us and it was just amazing. There were millions of dollars worth of damages. Most of those insurance is paying for, not all of them. As you know, it's hard to get the full amount of money from insurance. So we're definitely down as a result of the fire. We're also down because of the COVID-19 and all the restrictions that, you know, universities have now found themselves under. So we're suffering this additional cut to our budget of 15% because of COVID-19 on top of the fire. So unfortunately, despite all this great stuff that we do at Lick, especially for the students of the University of California, UC funding is definitely in a precarious state right now. And, you know, we know that there are a lot of worthy causes and many worthy causes within the university itself. So, you know, we're always grateful to any gifts to the university, but in particular for Lick Observatory, I was able to get a gift through Google and we're now trying to raise matching private donations. And I'm writing a renewal proposal to Google and they've told me that, you know, getting matching donations to the degree possible would help them see that their gift actually made a real difference. So if you feel so inclined, go to the usual Berkeley website, give.berkeley.edu. And if you put Lick in the search box, it'll dump you to the UC Berkeley Lick Observatory Operations Fund. And those monies will go into helping preserve Lick as a research institution and an institution where students, especially undergraduates, can get real life research experience and get motivated to pursue STEM fields. So all gifts, no matter how small and large, are very, very welcome. So thank you for your consideration. Now, back to my story, we've now found lots of these nearby headlights, these nearby cars. And so then we wanna find similar distant headlights in these distant galaxies. And the way we do it is by using bigger telescopes like in the Southern Hemisphere in Chile, and we take wide angle pictures of the sky. And there are thousands of galaxies in such a picture. And when we repeat the process in the same parts of the sky a few weeks later and digitally subtract the earlier images from the later images, occasionally you'll get something that looks like it might be real among the noise. And my job on both of the teams that early, in the early 1990s, set out to measure the fate of the, or the past history of the universe, my job was to use the world's greatest optical telescopes, the Keck Observatory, which University of California also has a ownership stake in. And so I would examine these supernova candidates in detail and figure out which ones were genuine supernovae. And so we would study those. And the punchline was that they appeared very faint. They're really faint. And you might say, they're in these pathetic scrawny looking galaxies that are obviously very distant. Here you can't even see the galaxy before the supernova exploded. So it's obviously very distant. And that's true. But the point is that the exploding stars appeared so faint that the inferred distances of the galaxies were greater than they had any right to be. They were farther away than in any well-behaved universe, one that's slowing down, or even one that's not slowing down but expanding at a constant rate. The galaxies couldn't have gotten that far away without having sped up. If they had sped up, then they could get that far away. But that wasn't the anticipated answer, right? It's as though there's this cosmic anti-gravity force at work. And I was privileged to be the first to announce this to the world at a meeting in Los Angeles in February of 98. It was a real thrill to have a chance to do this. But, and we use the term anti-gravity hesitantly because people say, well, can we use this stuff, whatever it is, to levitate over Bay Area traffic jams or LA traffic jams? And the answer is no. This stuff is either a property of the universe, of space itself, or it's some sort of energy that's flowing through space but has a repulsive effect. But there's so little of it that you'd have to collect it over millions of light years before you see a measurable effect. So we're never gonna use this, but never say never, I suppose. Anyway, so Einstein looks sad here because over a century ago, he actually proposed that such an effect might exist. But he renounced this idea as being just kind of outlandish and there was no evidence for it. If he were around right now, his reaction might be something like this because we now have evidence for this idea that he renounced possibly, well, he renounced it as his biggest blunder, but it could have been his greatest triumph actually. So it's kind of an interesting story. But again, there are many cartoons about this that are not quite right, okay? The universe is expanding at an accelerated rate. That should be good for housing starts. Again, this is not a local effect. You see this over tens of millions of light years, not here. Or the universe is expanding faster than ever and I don't even feel a breeze. Well, that's because it's not expanding here, all right? All right, well, we don't know what it is that's causing the accelerated expansion. So we call it generically dark energy. It could be a property of space itself or it could be some weird energy like light flowing through space, but not light itself. Light doesn't have the right properties but it's an energy flowing through space rather than being a property of space itself. Do you see the somewhat subtle distinction there? So we're trying to figure out what it is and that's important because it's 70% of the contents of the universe and we don't know what it is, we just know it's there. That's kind of disconcerting. 25% of the universe is dark matter and we don't know what that is either. That's the stuff that holds galaxies together. There's not enough gravity associated with the visible stars to hold graphics galaxies together. They would go flying apart and there's not enough gravity to hold clusters of galaxies. These are all galaxies that are bound together and they would go flying apart unless there's extra gravity and that gravity is attributed to something called dark matter and that's something that one of my heroes Fritz Zwicky came up with in the 1930s and he wasn't taken very seriously even though he was brilliant and I think he wasn't taken seriously in part because some of his ideas really were kind of crazy but mostly he was arrogant and abrasive and he didn't think highly of the intellectual capacity of his Caltech colleagues. And Caltech is a pretty brainy place like Cal. Okay, I did my graduate work at Caltech and his colleagues didn't think kindly to his view of their intellectual capacity and here he might be showing you what he thinks of their brain size, right? Well, I don't know that that's what he's thinking but he might be and he is on record as having referred to his Caltech colleagues as spherical bastards because you know, they're bastards any way you look at them and a sphere is the only object that looks the same from any direction, right? Now, I'm not suggesting you start calling your friends spherical bastards. You will quickly end up friendless but Zwicky is one of my heroes. So he came up with dark matter and we don't know what that is. Maybe it's black holes, they're dark but we think it's mostly little particles left over from the Big Bang. Just things called WIMPs, weekly interacting massive particles or other particles called axions or something like that. So we don't know what they are. Yeah, I've got my time clock. Thank you, Brandon. Okay, so dark energy makes the universe expand faster and faster. We don't know what that is. Dark matter keeps galaxies and clusters of galaxies bound. We don't know what that is. So we don't really know what 95% of the universe is. So there's a lot of room for discovery open out there. And if there are any students or youngsters listening to my talk, if someone tells you astrophysics is dead, there's nothing left to be discovered. You tell them, what are the origin and nature of 95% of the universe? We don't know. But we've been trying to find out and this brings me to the last part of my talk. What is the physical origin? We don't know. It's important because it's 70% of the universe's contents. It might provide a clue to the unification of quantum physics and gravity. So it's an important problem. And just to show you how important it is, in 2011, the discovery itself, not the explanation for what dark energy is, but the discovery itself was honored with the Nobel Prize in physics to the team leaders, Saul Perlmutter here at Cal, Brian Schmidt at the Australian National University and Adam Reese, who was a postdoctoral scholar, a Miller fellow supervised by me in the mid to late 1990s at the time we were doing their work. And the rules of the Nobel is that it can't go to more than three people, usually to the team leaders. And I'm glad it went to my postdoc Adam Reese as well. But these gentlemen understood that without the rest of us working in the trenches, the discovery would never have been made. So they spent a good fraction of their prize money flying the rest of us out to participate in Nobel week. And that was a lot of fun. Here's the actual awarding of the prize. And there's one of the teams right after the awarding of the prize. Here's the other team. I should have been in that photo, but I wasn't because the main team I was associated with was having its celebratory lunch at exactly the same time. And I felt a greater closeness to the Schmidt team. And at that meeting, my wife, Noelle, revealed her consolation prize to all of us who didn't technically win the Nobel Prize. It was a limited edition t-shirt, Dark Energy is the New Black, okay? So anyway, she made this t-shirt kind of funny. Then a few years ago, everyone won this breakthrough prize, which was nice, but we don't really do this for the prize as we do it for the thrill of making a discovery in science in contributing to humankind's understanding of the universe. And when I was a kid growing up, never did I think that I would be involved in such an important discovery. I have to pinch myself that I was at the right place and at the right time. Okay, so what is the Dark Energy? Well, a crucial thing is whether it's...