 to welcome tonight for our first talk on the Dark Universe, Professor Sarah Tuttle at the University of Washington going to tell us about dark energy. So please welcome Professor Sarah Tuttle. Before I get started, here's what I need all of you to do. I need you to put on your clothes classes. Are you ready? Are you putting on your clothes classes? Yeah, putting on your clothes classes. But yeah, it's not that hard guys. If you don't need directions. You ready? So if you wear those, you won't know what's happening. Alright, so tonight, let me get my buttons. We're going to be talking about the entire universe. I think we can get through that in like 15, 20 minutes, right? You guys ready? Also, you've been primed by the quiz. So I'm assuming you all got that right. So we'll do a review in the middle because we're out for a visit and we have to do that one. So, hopefully you're ready. Dark energy, dark matter, and honors. Thank you. There's so many honors it almost wouldn't transfer. Alright. First of all, what is the universe made of? Honors. Honors, good. I like how you think. Anything else? Hydrogen. I see some people are taking this exercise seriously. Thank you. Yes, indeed. There are lots of things in the universe. Many of them you have mentioned. We have molecules and atoms and fear and honors. To be able to keep track of what you've noticed, and many of the things are things that we interact with on a regular basis, right? So if I were to ask you, like, make a list of the top 10 things you interacted with, I know, honors would be on the list, but, you know, it's like the table and my clothes and the ocean, right? So that's fantastic. We like counting things. That's one of what astronomers do best. In fact, you can think of us a little bit like the universal accountants. Doesn't that make us have even more exciting? That's right. It's not quite dark enough. Maybe we'll revisit this once the sun sets. We've got awful northern lands. But this is the universal energy budget. Now, you might think if you have, for example, recently done your taxes, your budget should be more complicated than this. It is not. It takes a pie chart. I know. I'm so sorry. So here you can see the three main constituents of the universe. We have dark energy. There's nothing there because we don't know what we're talking about. Chocolate cake, also known as dark batter, and honors. So honestly, I think I could stop the talk here because this seems like both adequate and everything we need. Dark energy is almost 68% of the universe. Now, if I were you, I would be concerned because I've just told you that most of the universal energy budget is dark energy and we don't know what it is. It could take more than 15 minutes. Dark matter, we can measure and observe, but we don't know what that is either. But we do have some honors. So that should be really good. So let's walk through what we're used to and what that means. And we'll talk a little bit about dark energy and dark matter. One of your key takeaways from this talk will be being able to differentiate between dark matter and dark energy. So the next time you're at a cocktail party and someone gets it wrong, you can come down on them like a ton of bricks. But even 5% of the universe, you know, the universe is big. There's a lot there. That makes a lot of room for honors, right? You're feeling retro and pretty good about it. You've still got like some honor space. You guys, there's not that many honors in space. I'm not actually my disappointment. So, I'd be making a few. There still could be space honors. I'm looking for graduate students. So if someone would like to complain me, space honors would be great. So what are we looking at in this picture? This is part of the Hubble Ultra Deep Field. I have a test for you. Are you ready? Now, not counting the stars that are in galaxies, but there's billions of stars in every galaxy. How many foreground stars, so stars that are in our galaxy, can you see in this fantastic image? How many? Oh, we've got hands up. You guys, I've got some zero guesses. What else? Two. Zero. That's not a four. There are two. Two. All of the rest are galaxies. All of them. Isn't that ridiculous? This is the size on the sky of a dime held out at your arm's length. You know, assuming you have like standard arms and not unusually T-rex arms. There's some air in there. But fall for it. Okay. So, for a second, we're going to delve into the honor portion of the budget. Since I have exposed the lack of otters so early on in this talk, but hopefully you've had enough fear that you're going to sit for a little longer. So here, oh, you can't even see that. That's tragic. Okay, good. Well, you'll never know what you're missing. Is there a missing baryon? I'm sorry. So, most of the baryons and the standard stuff in the universe isn't the stuff we're used to at all. Even in that little 5% otter sliver, it's mostly diffuse, warm or hot gas. This gas, which is so warm and so far apart from other stuff, it can't collapse to form things we're used to, like stars and galaxies. So that's most of it. There's a little bit of cold gas. It's like leaky refrigerator over here. And this is galaxies and stars and otters. And then there's the missing baryons. Okay, so we're like ten slides here. What I'm telling you is we don't have any idea what we're doing. I'm so sorry. That's not really true. We know some things. And it keeps us busy if we don't know things and that's cheaper than jail. So, when we say missing baryons, what we really mean is we're getting better at measuring them all the time. That's the optimistic way to look at it. And what you can imagine is that since we're used to finding things that are bright and perhaps nearby as in clumps, looking for stuff that's diffuse and often faint and far away is much, much more difficult. So this is really, just imagine, this pie is slowly getting more filled in as we get our ship together and build better telescopes. So have faith with us. We're working on it. Okay, it's time to play a game. Some drink in should be ready to run around. So can I have like two volunteers? I need runners. Who's going to come up here? The best part about this quiz is that many of these are overlapping answers, but you don't know what the answers are, but you might get them right. So I need people to run prizes. So can I have two volunteers up here? Yes, ma'am, and a white shirt and a white bag. Yes, representing the standing room seats. Come on back. The titles will be back there. Well done. I know, I'm so proud to have made it. Okay, what's your name? Thank you for joining us, Leana. On a scale of 1 to 1,000, how's your astrophysics knowledge? One. Perfect. Danielle, nice to meet you. 1 to 1,000, astrophysics knowledge? Negative. We're going to explore in our space here. Here's how this is going to work. Some of my students, they know. So, here's how this is going to work. We're going to run around, but wait until they answer the question. So we are going to play a quiz, Dark Matter, or Dark Energy. You ready? You've got to be psyched. Is this Dark Matter or Dark Energy? Shout it out. Otherwise, this is just cheating. Okay, good. Here's the bullet cluster. It is one of our favorite demonstrations of Dark Matter. Well, you can't entirely tell there is here. Can you see the purple? Yeah, good. Okay, stick with me. So this is demonstrating the hot gaps and the concentration of matter from the bullet cluster. The bullet cluster is actually two clusters that are passing through each other. One is that more standard matter, like gas and stars, is kind of electromagnetically sticky. So it kind of sticks together when the clusters crash together. And the Dark Matter is like, see, you sucker. Which you can see demonstrated in this slightly blurry and not very bright video. The book. And then here is the Dark Matter. That's the only appropriate response. Now, this is useful because we're observing Dark Matter, and a tricky thing is that we don't actually know what Dark Matter is made of. I'm telling you, there's so many questions. Okay, Dark Matter or Dark Energy? You have to yell out loud. We're the loud people. All right, so this is a Dark Matter detector from an experiment called Mop Ground. We have various undergrounds. If you don't get suspicious, we're trying to blow stuff up. We're totally not trying to blow stuff up. Probably. So part of those come in, they mix around, they get detected in the detector, they shoot potters out. It's all very exciting. Okay, Dark Matter or Dark Energy? Keep that powder dry. Okay, this is Apple, they're fiber optics. Use an experiment I'll talk about that is for detecting Dark Energy. You have to take a little shouty break and drink some beer. Dark Matter or Dark Energy? I don't know. Dark people in a bar would be good at shouting. All right, those of you who said occasional lensing. This is the actual model of the distribution of the matter. If you have a very keen eye, what you'll see here are these kind of blue, skinny, stretched out galaxies around the edge. That is a distant galaxy that is behind a giant cluster of galaxies. And that galaxy is being lensed by the giant blob of matter that is distorting space-time. I hope you notice that. It's kind of the same as if you hold your glass and look at the water, except not at all, and giant, and it's space-time. All right. So, our conclusion from the end of this part of the talk, there are many, many positive particles for Dark Matter. This is a lovely demonstration from Symmetry Magazine that I enjoy a lot. So we know a lot about particle physics, particle astrophysics, but there are still many suggested particles from the process of measuring them and trying to figure out what it could actually be that is Dark Matter, how it's interacting with everything around it, because it is the dominant form of matter in our universe. Okay? You ready? It's probably not an honor, by the way. Okay. Now we're getting to the serious portion. You can tell because there's a lot. There may be as many as two more plots in this talk. So stay strong. I know. I know. You're going to make it. I have faith. So, one of the tricky things about Dark Energy is trying to convince you that we are not total lunatics for telling you that Dark Energy is a thing even though we don't know what it is, nor that we can measure it. Which, you know, might test even the most enthusiastic of you. So, what I'd like to demonstrate is that there are a variety of observations that are extremely different. They might cover different distant ranges. They'll cover all different sorts of astrophysical properties. We are able to pin this that the universe is expanding and accelerating and we're not yet quite sure how to explain that. So, this plot just shows us constraining some cosmological parameters with three different experiments. The cosmic microwave background, there was a question on that. Did you get it right? Type 1, a supernova, that one too, and the baryonacoustic oscillation. No one asked about that because it's already confusing. Okay, that's what you'll notice. What you'll notice here is that those overlap actually in an extremely narrow part of the supply. So, that should be telling you something and it's not just that people are good at drawing. So, first, we're going to talk about the cosmic microwave background. So, how many people here have observed the cosmic microwave background on a tube television or are such a committed hipster on a tube television? When you turn on your television in between channels, you get snow. And about 1% of that snow is the cosmic microwave background. It is a less over-graduation from clearly beginning of the Big Bang. So, there you go. Next time someone gives you grief, just be like, I'm an observational astrophysicist in the Big Bang. It seems like I'm just surfing channels but it's an experiment. So, the cosmic microwave background is exciting for a bunch of reasons. One reason is this really fantastic cartoon that hopefully everyone here has experienced. But the plot that spawned it is amazing because see how there's this really nice curve? There's dots on that curve? The error bars on those dots which are observations are so small, they're basically the size of the line which is the theory. So, for one time, our measurement and our theory lined up smack on. Shocker, people want a Nobel Prize. It spawns sassiness, science, it works, bitches. You know, sometimes. So, the cosmic microwave background is seen here so we've set up many satellites to measure and map the cosmic microwave background. Here we have slices from codees which went up in the 90s that really gave us this initial confirmation. WMOP in 2003 and Plunk in 2013. What you can see here is we're getting better sensitivity and more spatial resolution. The fact that the colors are different over here is just because your hands don't follow direction as well. The cosmic microwave background is interesting because it lets us know that the universe, in fact, is expanding. Which, if you think about it for just a second, it's kind of weird. It's weird that the universe is expanding. I think it's weird. It came up with a big bang. They expanded the universe and surprised it. It's also a good place for my favorite observational astronomy story. So there was a brave and intrepid theorist who bought up the cosmic microwave background. He was like, we're going to find it. They start building an experiment. We're going to find it. Down the street there are some good-for-nothing astronomers and they're trying to do an experiment with a radio telescope. And the radio telescope was hosed and it wasn't working, which was a bummer. And they tried everything. They went below the switches and they turned it on and off and they plugged everything in and they looked it and it didn't work. So finally they went out to the telescope. It was a radio telescope so it's a big horn. It's a big giant horn. And the horn was filled with pigeons. You guys, pigeons are not good for science. I mean really any science as far as I can tell. So, they shot the pigeons. They cleaned up the pigeon food. Then they were just really sad about it. They lay on the floor and then eventually they were at a bar much like this, chatting. And someone said, oh, it's weird that you measure that because the guys down the street thinks that's the beginning of the universe. And then they wanted to oppress. Totally how it happened. So, roughly 30 seconds to be okay with the idea that the universe is expanding. And like maybe you can talk yourself into that. Right? There's an explosion at the beginning. So, unsurprisingly, people were a little mixed on that. And so, they started making other measurements. This is a measurement using supernovae. Take one in supernovae. They're interesting because they're standardizable candles. That means we know when they go off, they're sort of like 100 watt light bulbs. We know how much energy is coming from them. So, if I took some brave soul here and handed you 100 watt light bulb and said, walk away. You could walk away. And then we could take images and figure out how far away you were by how dim that light bulb was. You know, and how mean we were by how long we let you walk. So, you can do this with supernovae. And so, of course, in the 90s, we've been working on it, but it's hard because if you look here, these are great supernovae. People did this. Huzzah! Everything looks fine. These lines that are super faint that you can probably barely see because we're in a tent. These straight lines are predictions to confirm the expansion of the universe. And there were several teams working on it. And what they found was that it wasn't fitting their predictions, which is awkward, especially since the last people won a Nobel Prize for fitting predictions, you know. You don't want to go too far astray. But it turned out, and here you can see, these are galaxies before and after supernovae. But it turned out when these measurements were confirmed that the universe is not just expanding, but is expanding and accelerating. So, I think that, like, you probably need more of this to make sense. The idea that the universe is expanding and accelerating means not only that everything is moving far away from everything else and faster. So, sometimes, people talk about dark energy like vacuum energy. Like, something is pulling from the outside because it's really difficult to understand what might be causing this kind of acceleration. Now, I know, isn't that the cutest? You can imagine a balloon. The author doesn't have to imagine a balloon because they've already got one. We use balloons to invoke this idea of centralist expansion, although balloons have centers and you can draw galaxies on them, but that doesn't really make sense because it's still really weird. What's even weirder when you think about centralist expansion and acceleration is that it's not always the way that the universe has been. So, the universe, not only is misbehaving, but is changing with time. So, we can't make a measurement here and assume that that's what happened in early times. And in fact, looking at this, so this is the big bang, isn't that clearly illustrated? This is time. So, initially, the universe painted like you intuitively might expect. It exploded. There was a bunch of stuff in it and it was going outward, but it was slowing down a little bit because, like, you know, that's how gravity and stuff and things works, right? And then something happened and it started to accelerate and that's where we live now. So, we call this in the matter-dominated time and energy-dominated time. And something that Ethan is going to talk about in the next talk is what happens next? You guys, we can't even find the otters, so who knows. But Ethan is going to try and give us some guidance about what happens next. That's one of the reasons we study cosmology because we want to know what might happen next. This is just one more illustration of the difference between matter and energy-domination. So here you can see the balloon is losing and the anvil is winning and then the balloons are winning. So if you remember nothing else, just remember, the balloons are winning. Okay, we're almost there. Who has played Guess Who? All right, you guys are heroes. Someone has Guess Who in the back. Jesus. Someone write an otter, you have Guess Who. Oh my God, I don't even know. I don't know these people, I promise. So, I use Guess Who as my example for how observation and theory work together. Okay? Sit with me, it's totally a stretch, but also I could fit in an otter so it's worth it. So, we know some things about the universe. Right, we've made some measurements. We can measure supergum, we can measure these things, and we've got all these theories that make predictions. And so what we do is go back and forth and we ask the universe, do you have glasses? Are those glasses red? Do you have long hair? Are you an otter? Things that don't work. We eliminate theories that don't work and we add in new theories that might match our observations. So in fact, when the plump results in 2013 came back, there was an entire field of theory that just stopped being good anymore. There was a whole bunch of people that were like, I guess I'm going to go think about something else. So it's a brave life, being a theorist. And you have to be able to explain things like this. So for example, initially people thought that the cosmic microwave background would be homogenous. It would be flat. But what you can see here is that there's actually huge temperature variations. I mean really not that huge, but pretty big difference to what we're expecting. So if you would like to be a theoretical astrophysicist, please remember to explain this whole spot. Thanks. Last but not least, hence you think that all we do here is honors, I'm going to talk for three minutes about head-decks and experiment I'm involved with to measure dark energy just so you know that we are making a really good effort. Really good effort. Head-decks is the Hobby Everly Telescope Dark Energy Experiment. It's on this 10-meter telescope out in West Texas. There's not a lot, there's a sneak museum out there. They tell us that we should be astronomers to go to exciting places, but I've made some poor life choices. So this survey, well this is the focal plane. This is where the image from the telescope is projected. When it is completely filled every image will take 35,000 spectra from 35,000 fibers. Those of you that have been lucky enough to win the little wooly goodies, can you look through them right now? Do you see the rainbow? That's what a spectrum is, but it doesn't fit on your face. It's fine. So these are each fiber bundles with hundreds of fibers. They sit in the telescope and it's working, much to my excitement after six years. It's taking now about 8,000 spectra instead of 35,000 spectra. It's 35,000 spectra, but it's trying. It's making good effort. Detecting lime and alpha emitters. These are faint, but young galaxies that break just between two to four. And we're using them to try to detect the barrier acoustic oscillations. Now barrier acoustic oscillations are a standard ruler. Remember we have standard gambles. Now we have standard rulers. We like to make it sound like we know what's going on because we have somebody start this and missing that. So the easiest way to think about standard rulers is we're using the clustering of galaxies, a particular kind of galaxy to measure the distortion space-time. So here you can see these galaxies and otters are equally distributed. And if you have a very sharp eye, see how they're... Imagine if you just had a grid of lights and you threw them over a 3D object like a bush or your toddler. They would change how far away they are from each other. And I know, well you have to sometimes, you have to make your own thumb lock. And it would show you the shape of the thing underneath. So we use these galaxies to show us the shape of space-time underneath to expose how their energy changes with time. Okay. Also there's a lot of wrenches involved and sometimes things don't fit together. And the students are very, very brave. And many of them have stayed in astronomy against all odds. In the end there were about 150 of these built. And I know it was tiring. And they installed on the telescope. There's all the different pieces coming together. And so what I wanted to point out here is that, you know, I can make lots of jokes about dark energy, but these are huge international collaborations and they only do a small part of the work, right? And so our collaboration was many continents and we're only doing dark energy from wrenches of two to four in a particular way. There are many other experiments on going including E-boss, which is using the Sloan telescope at a packing point and the South Pole Telescope to see where the otter is going to play in the snow. Making different measurements. So what's important here is that we use a lot of different techniques to try to figure out what we're doing to expose what dark energy is. All right, so what is dark energy? Well, it turns out it's going to take more beer and more time before we can answer that question, but I will just leave you with this defensive otter Hopefully the next time I'm back to talk we can discuss how the universe has changed in the following years. We're going to take your questions. Please speak as loudly as you possibly can. So, Sarah, I can hear you from here. And if I can ask Sarah, would you please repeat the question when you hear it so that everyone online can hear the question too? Ooh, there's people. Are there more than 15 people online? More than 15? Wow, exactly. So, some low-online people are brave people. You don't even have to be wearing pants. Yes. So, he asked that video of two things going through each other. What's that? So, that was two clusters of galaxies crashing into each other. And the part of the galaxy clusters that you're used to like galaxies and gas, they slow down and interact. And so, they stay together and the dark matter doesn't interact so much on the outside. Yes. Good. So, with two further question one, does dark matter interact with seeing gravitational light as other matter? And, dark energy can we measure how it's actual rate of acceleration? So, the first, second part, we can't measure the rate of acceleration. It's a thing people like to fight about a lot. Scientists need something to fight about. This is a good one. And, differently, gravitationally. Which is part of the different particle issue. All right. Yes. I see a hand. Go. The question is, can I explain how my experiment works in a slower and dumber fashion? I can't answer it. Well, I have to get in the zone. Space time, yeah, is flat. Dumber. Exactly. We expect it to be flat. If it's distorted, we can measure it. So, we use galaxies to measure how space time is distorted. Because of, because of the initial conditions from the Big Bang and just after. So, here's something to think about, because everyone needs an extra thing to think about. Is the universe smooth or bumpy? Bumpy. Right? It's bumpy. We're not smooth. No, no smoothness here. Bumpy. So, from something that's smooth at the beginning, because something that's bumpy at the end, and the answer is, for some reason, the universe started out bumpy. And so, trying to make those measurements over time is part of what we're doing. Yeah. Yes. Why does it stick together in the clusters before they go through each other's? Yes. That's a good question. If dark matter is hoping you guys have had more to drink, the same, gravitationally, why is as it crashes through each other? The short answer, and I want to leave some excitement for Ethan, will also be talking about these things. Yeah, I'm just drinking, so that should be good. It's a smart man who drinks a flask. The answer is, it interacts with itself, because it's selfish that way, probably. And it does, it interacts differently. This is one of the running issues with dark matter, is, for once, the same way that we see dark matter come. Why doesn't it occur in the same places? So this is my theory and I hope this is this fight. Yes. So the question was, since we know so little about dark matter, couldn't it be, shouldn't there be lots of kinds of dark matter, couldn't there be dark matter, people and galaxies and things, or so that makes the second part of that question harder to answer. There could be certainly different kinds, right? We're discovering new things about the universe and, you know, as we improved the way of asking, I feel like dark matter people would be a little complicated. I could take the astronomy quarter and go here. There are some fundamental issues with the way dark matter that we observe it. And I feel like it would make life tricky. But if it was different, anything is possible. So, you know, I'm not going to vote down dark matter people today. I'm not going to be on the internet and vote that down. I don't need that to be my only one. One more question. Yes. Yes. Okay. Explore. If space time is expanding and accelerating, is, is time you can, like, everything going slower while we sit here. And it feels that way. So, what's going on in the time Oh, it's in it. We're everywhere. So, so, the way to think about, I don't know, you can do a good shield for the expansion in time. Yeah. Good. I'm going to pass that question to you because I think that you'll have a better ratio than I have on the fly. I mean, so, for example, it's so exciting, you guys. All right. Well, thank you so much. I will be around later if you have questions.