Origins of Dark Energy with Adam Riess

This podcast is brought to you by Hotels.com. Make your next trip work for you. Hotels.com's new Save Your Way feature lets you choose between instant savings now or banking rewards for later. It's a flexible rewards program that puts you in control with no confusing math or blackout dates. Book now at Hotels.com. Save Your Way is available to loyalty members in the US and UK on Hotels with member prices. Other terms apply, see site for details. Welcome to Star Talk. Your place in the universe where science and pop culture collide. Star Talk begins right now. This is Star Talk. You'll be grasped ice in your personal astrophysicist. And I got with me co-hosting. What's up? How you doing man? I'm good buddy. Good to see you again. Professional comedian. You got your own podcast. Yeah. Inside out. Out and in. There you go. Giant burgers. Yes. Did they sponsor you? Yes. For those listening and watching, this is how not to host the show. Have a guess and not know anything about yes, it's called in and out burger. And the whole podcast is me interviewing people in the drive-through window. In the drive-through window. You want fries with that? So you're an astrophysicist. The guy was on my podcast. I was. Along with Alma Carnegie by the way. Oh, no, okay. All right. You know, that's all you say. Name dropper. Yes. But none of that impresses me as you got like a Peabody award and an Emmy award. I am. Yes. I'm writing you. I've been writing on the daily show. Yeah. And I've worked on the Colbert before. I love you, man. And I love you too, man. Thanks for spending some time with us here. Absolutely. Always great. You're making this happy. No, we're going to talk about the cutting edge of cosmology. Because everybody's talking about cosmology all the time. But who gets in there and say, where's the edge? Yeah. And where's where people at Fisticuffs? Yeah. We like to mix it up here. Where can we get people at each other's throat? At each other's throat. Because then that's actually, I mean, the history of science shows that's how discoveries emerge. Now, I have to say I'm doing a few of these with you. And this one has like, is really cool, really interesting because there is a lot of back and forth on this. And it's really, it's really cool. Yeah, yeah. No, it's good. And a lot of people contenders, I think, is the way to think about that. So we combed the universe to find who would be ideal in this conversation. And we found an old friend and colleague of mine, Adam Reeves. Adam, welcome to Start Talk. Thank you for having me. Welcome to my office here at the Hayden Planetarium. Excellent. Yeah. I mean, I was just wandering around the museum and you guys pulled me in. You were, he was with a bunch of children. He was, and his hand was being held by a teacher. Yeah. He might be a billion and have a Nobel Prize, but apparently he gets lost in large spaces, everybody. So you get to Johns Hopkins University. Yeah. The Bloomberg Distinguished Professor there. Bloomberg, he's a friend of my wife worked for him. He has a background in physics and engineering and came through Johns Hopkins. Yes, he did. And donated a whole building called the Bloomberg Center for Physics and Astronomer. Yeah. Yeah. And then he ruined everything when he created bike lanes in New York City. I'm telling you, let's spin it out on the mat. You said your Nobel laureate. Can we fix that? He says the man who does not ride a bicycle. Exactly. Okay. Many people don't know that the Space Telescope Science Institute is, which was responsible for receiving all the data from Hubble and other telescopes, Spaceborn, is co-located on the campus of Johns Hopkins University. That's right. So you also have a position there. That's right. That's where we have the joystick. Okay. I'm going to leave that right there. We have to add that you are a Nobel laureate. That's right. That's bad ass. Yeah. And I think if you have a business card, just say no, but that's all. You don't need anything else. No phone numbers. No phone numbers. You just think he want to talk to him. He's so smart, he calls. So, remind me, what year you won that? We won it in 2011. You won the Nobel Prize and that year was split three ways. Who are the other two recipients? Brian Schmidt and Saul Perlmutter. And Saul, I remember, was a West Coast guy. Right. Right. He led the Supernova Cosmology Project. Okay. With the same intent of making the kind of measurements you were making. That's right. With Brian Schmidt. Right. Right. Okay. And we were members of the HIGHZ Supernova team. HIGHZ would be high redshift. Correct. Supernova team. And it was given to you specifically for the discovery of the accelerating expansion of the universe. Which today we just called dark energy. Well, dark energy is, we think, the driving mechanism for the acceleration. Okay. There's still a lot we're trying to understand about the nature of dark energy. We'll get back to work. Please. So, I'm going to say welcome to Start Talk. Thank you. Yeah. It's an honor to be here. Yeah. And so, you are co-discoverer of a... I guess growing up, I mean growing up as a kid. I mean, coming through school and graduate school. We always knew that there was this term in Einstein's equation that it referred to like a negative gravity or something. It was mathematically legitimate. But no one had... What is that? Nobody account. But no, no, no. It's just a math thing. So, every time we had a conversation about the expanding universe, you had to explicitly say, we're going to assume this is zero because we know what I'll be going to do. Expanding at a constant rate, basically. Or, or, or expanding only according to what the galaxies tell it to do. Got it. This would be an extra thing going on, okay? And you were just too lazy to explore them? No, I would have. No, apparently this gentleman was not too lazy to explore it. And he's saying, I wonder if that is a thing, okay? And there you go. So, first, catch us up on being co-discovered of the accelerating universe through these equations that I'm describing here. And you're getting data. What was your data? Sure. So, as you said, this term that Einstein had put in, which he actually put in for a good reason. At the time, he thought the universe was static. And so, this term was needed to balance the attractive gravity. Otherwise, the universe would just collapse on itself. Correct. And then, so astronomers at the time told them the universe was static, because they thought the universe was the Milky Way galaxy. They thought that was already everything. And, of course, it turns out there are galaxies out there. They're moving further apart. Hubble and others showed that. Hubble, the man. Hubble, the man. Yes. Hubble was a man before he was a telescope. I think that's right. He's more like the Robocop version of us. But he would be mistaken for a telescope, but a lot of parts. That's right. The shape of the body of the famous story is that once Hubble showed that Einstein that the universe was expanding, in which case, it was unnecessary to have this kind of repulsive gravity to balance things. And it was kind of dropped to the side. But as we know in physics, once something is possible, it is always there unless you have evidence that it doesn't exist. Right. Very important bit of scientific wisdom there. So, let's jump to the 1990s. And astronomers are looking for that. So, that was the 1920s. That was 1920s, yes. So, we're in the 1990s now. And astronomers think there's some matter in the universe. And the question is, is there enough matter to stop the expansion of the universe? Like, launching a rocket. Does it have escape velocity from the gravity? Is that matter? Is that matter? Something that would later be called dark energy? Is that sort of... No, this is what we call dark matter. That's right. We knew there was a lot of matter. Most of it was dark. We knew this because there was extra gravity, the rate at which galaxies stars-orbited galaxies. The stars would have flung out if there wasn't this extra matter. So, we knew all that. And then the question was, is there the critical amount, the amount that would halt the expansion? Or would the universe expand forever? And so, by the late 1990s, the best way to do this was to measure the... Expansurate of the universe in the past and compared to the expansion rate in the present. And see if it was slowing down enough to stop. And this is where the distance ladder comes in in terms of measurements. How do you know how far away... I mean, nearby... It's hard enough just nearby. I guess we can use parallax on stars. But these stars are sitting on our noses. That's right. We have whole galaxies nearby and beyond. So, what method... You had to really refine a method to do this. Yeah, so, you know, parallax is great having a tape measure and running it out somewhere is great. But these just don't work very long. You can get those at home depot. Yeah, I know, but not one that long. With your home depot tape measure, you can get to things that are walking distance of you. Right. But there are stars out there that, you know, you can't do, you know, radar beaming to them. Right. Because they're light years away. So, you have to use parallax a form of geometry that had its limitations because of the angles of the geometry. You just try to make up for getting some wrong a minute ago. I did. Pretty good. Yeah, but you did good. You did good. Yeah. You did good. So, if you have your two eyes and if you can put your thumb and you just look at your thumb with one eye and these switch eyes and then your thumb is like moving back to you. Hang on, I need a manicure. Let's use it. Wait, what am I doing now? Yeah, you're looking with one eye and a switch eyes and your thumb will shift back and forth as you shift. It turns out the amount that that shifts and the distance between your two eyes uniquely determines how far away your thumb is. Which is then used. So, try this. Put your thumb here and do the same thing. So, now it separates even more. Yes. So, that's an angle. You can measure the angle. We know how far your eyes are. You know, exactly how far away you're from. You did this with my hands, but I don't have to look at you. Well, that worked either way. I'm blotted both ways. So, what are our eyes? How do we do this with astronomically? Well, you can take a picture of a star and if there's a background star is behind it. And then six months later, take another picture of that same star. Now, the width of your eyeballs is the diameter of Earth's orbit. Now, that's a good. Now, you can measure it. Now, you get that and you see how much it varies. You know how the diameter of a orbit, about a being, we get the distance to it. And we have sent telescopes into space to measure this exquisitely far beyond what's even possible from Earth's surface. Hubble and then Webb. Very reliable. No, no, no. It's a telescope called Gaia. Gaia, G-A-I-A. So, now we trust these because it's like geometry. We got this. Right. But now you have to go beyond that and you don't get to use parallax. Right. Right. So, then you have to use another method. Okay. There are methods that we use here on Earth like a lighthouse. So, if you're a ship captain, you want to make sure you're far from shore, you want to make sure a lighthouse, which you know is very luminous, looks very faint. And it assures you, wow, it's, I have to be far away. And we can actually do that quantitatively by measuring how bright the lighthouse actually appears. So, in the past... I like that analysis. It was a good one here. In the past, there was a class of pulsating stars called sephid variables that have this wonderful property that they tell us whether they're a very luminous lighthouse or not very luminous lighthouse, depending on how frequently they pulsate. And there are about 100,000 times luminosity of the sun. So, the big advantages, if you want to measure far, you better have a very powerful lighthouse. Right. So, they were good for a while, but we had to go out much further. Just a second. Is that the second wrong of the distance letter? Yeah, I think so. It is. It's the third one after the Home Depot tape was taken. So, you said something important there. 100,000 times brighter than the sun, which means the sun at those distances, we would just never even see it. Right. That's right. It's not useful. Right, that's right. So, the name of the game at this point is to be able to measure truly cosmological distances very far out. We're really just in search of an ever more luminous standard candle, something that you can just see far away. If you can't see it, you can't measure the distance. For me, explain the standard candle and that my understanding is that we don't really know what that luminosity is. So, what standard candle is any object whose luminosity is uniform? So, when we see a standard candle and its uniform, when it appears dim, that tells us it's far away. Right. And we know that there, we know why they're uniform. That's been correct. We know we have, we start out with very good theoretical understanding and then ultimately we have empirical understanding. It shows us that. So, by the 1990s, these sephia variables are just not luminous enough. We really need things that are billions of times more luminous than the sun. Because we now want to look so far back that the universe has changed, that the universe is younger, that it was expanding at a different rate. So, this requires us to go back billions of light. So, it's like when you're a kid, you shoot up when summer, kneels like... In high. Ford, yes. Oh, shoot up. You dropped it. No, no. It's you. I don't know what you were doing in that summer. No, I don't know what you, I don't have what kind of chastisers. I'm from the streets, everybody. I grew up on the streets. No, you shoot up in height. Like in one summer. You go from four, nine to five, nine. Okay. But then as you get older, it's progressively. So, that's sort of the idea here. In very rudimentary terms, when you're going back in the early stages of the universe, you're looking... You're going back to the younger. The younger, where the expansion is faster. No, we don't know that yet. Well, it could be. It could be slower. Right. So, let's not jump the gun. So, by the late 1990s, we had known about Supernova. You got to going back to the ancient Chinese. A star would suddenly appear where you had saw nothing. And we came to realize that these are exploding stars that are billions of times illuminosity of the sun. In fact, a very word, Supernova. Nova means new. It's Latin. And so, a really bright new thing about Supernova. And only we would later learn that they start dying at the end of its life. Right. My wife calls me a Supernova. Dying? I have to fill back that. Anyway. You're still in therapy. We'll let him sit there. And it means looking your eyes when I said that. So, what we came to really realize in the 1990s is there's two completely different ways nature produces this kind of Supernova explosion. And that's very important. One way is you have a very massive star that loses its ability to produce energy. And producing energy was the way produced pressure that held back gravity. And so, it's a very dangerous thing for a star like this to lose the ability to do that. It's basically lost its structure. And so, it will implode, followed by an explosion. And those are very bright. They're great. But the problem is they come over a wide range. That could have been a very massive star or a medium star. Or that could have been a star that when it collapsed turned into a black hole. In which case, we'll see almost nothing. So, that's reliable as a standard camera. So, it's not going to be a good standard camera. But it's not a good standard camera. And then we realize hiding in this distribution of all kinds of different exploding things was a subclass that were all the same. And that is a completely different mechanism. It's called a Type I A Supernova. And that occurs when you have the core of an old star like our sun will become called a white dwarf, which is in a very special state. It's holding itself up against gravity because of quantum mechanics. And it can only be stable up to a certain mass known as the Chandra Seikar limit after the famous Indian astrophysic physicist Chandra Seikar, who in the 1930s showed that a star could only sustain itself up to about 1.4 times the mass of the sun. So, now imagine this. You have a white dwarf star sitting there. It's less massive than this Chandra Seikar limit. Maybe it's in the mass of our sun. And money is on business at this point. It's doing nothing. And it would be happy that way. It would just cool off and live its whole life that way, cooling, cooling, radiating. But what if it has a friend and you know with friends like these who needs enemies? These are a star orbiting that star. And they get you close, we think. And mass starts to transfer over, we think. And the details of exactly how this occurs are debated. But somehow the mass transfers are not clear. Whether it's like they actually merged or it was a gradual process. And I just say something between Einstein and you guys, you seem to leave a lot of stuff off to the side. And we're not sure, but we'll just go whatever. Well, because he's after the consequences. That's correct. That'll be clear in a minute. So anyway, so somehow mass transfers over. And when it reaches that Chandra Seikar limit, it's like, boom. A thermonuclear explosion runs through the star. Okay. And what's so great about this is they always blow up at just about that same mass. Very close to that. So this is a standard candle. This is something you recognize it far away. And how do we recognize it? It has a certain spectrum and has a certain chemical fingerprint. And this was observable within the Milky Way because that was a distance that we could observe this. Oh, we could observe these beyond that. We could observe these at some of the most distant gavel. Because of the telescope. Now, they're incredibly rare. There's only one in a galaxy like ours per century. But there's no real limit of galaxies. So if we can take a wide enough image that contains hundreds of thousands of galaxies, and then come back a month later, you know, what turned out to be, oh, so unlikely to happen is like guaranteeing to happen. It's like winning the lottery because you buy all the lottery tickets. Ready? Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie because we listen to Star Talk every night and support Star Talk on Patreon. This is Star Talk with Neil DeGrasse Tyson. And you began this in graduate school for a member correctly. And that whole group, that whole group. Who's the head guy on that group? Brian Schmidt, Bob Kirschner, the Chilean group for the Colontololo, which you know very well. And so what changed the game was in the 1990s. We both came to realize this class was special. It wasn't like the other supernovae and the advent of large cameras by those standards on telescopes that had a big enough field of view that you could simultaneously stare at 100,000 galaxies and actually have a chance to do this experiment, actually find supernovae on demand. Right. So you don't have to wait around for one to show up and then look at it. Right. You would like to see the whole group of stars in the world. And you would see the whole group of stars in the world. Right. So you don't have to wait around for one to show up and then look at it. Right. You would like, we're going to find three supernova tonight. Right. Right. And it was actually quite amazing because back in the day when the Hubble spell based telescope was a new thing and it was incredibly valuable to get time, we would propose for time and say, we'll tell you exactly where the supernovae is on Tuesday. So you could start observing it Thursday. And they were like, you're going to what? Like you're going to tell us where a supernovae is on Tuesday. And we're like, maybe Monday night at the computer's operating fast. And then like, you know, I got a dinner. Can we roll that off? But it was, you know, if we had bad weather, something it was scary too, because it was like, and if we don't just stare at blank sky, which is no astronomer, wants to use the most capable facility to just like stare at night. You're right. This type 1a supernovae are visible halfway across the universe. That's right. But they're only useful as a standard candle once you can calibrate those that are closer than have some overlap, maybe with the sephiyids. Is that right? For the discovery of the 1990s, that the expansion of the universe, and here's the big spoiler alert, that it was accelerating, not decelerating, you don't even have to calibrate them, because you're only using them as relative measures. You're saying, you're saying how much was the universe expanding back then relative to how much it's expanding now, even if I don't know an absolute device out. It's not even there. So Neil is handsome, but relative to me, not so much. Okay. So I've forgotten that that's important. That's very important. So the two stories we're going to tell disconnected in that way. And so by the late 1990s, even if I didn't know the absolute, the true luminosity, was it 10 billion solar luminosities or 8 billion solar luminosities? What I could say is, oh, that distant one was so faint that it is 10 times further away than this one, whatever the true luminosity you've got a history or an experience. So you've got a whole string of pearls. That's right. That's right. And space. So that was super sleuth and away. It's like you're a detective using evidence. But within the distance ladder, you have these three rungs, and what strikes me is four rungs. Four rungs, sorry. You have rest. But this is to be clear, this entire discovery of the exalering universe only dependent on one rung internally to itself. But if a severe is a sort of got a, you know, okay, say it does affect its brightness. So now that rung is sort of there's some weakness in that rung which can propagate through the rest of the distance ladder. So how are we accounting for there's so much we don't know dust, right? Or other components that could sort of affect one rung of the ladder could then sort of throw off the entire calculation. Even in your relative comparisons, the dust would give you the wrong distance. Right. So when I was a graduate student, this was the part of my thesis was to figure out how to contend with dust in these type when it was supernova observations. So it turns out that dust makes things dimmer which would fool you into thinking it's further away. That's very bad. Okay, but it does something else too. It makes light look redder when the light passes through it. So look at a sunset, right? Not only does the sun look dimmer, but it also looks redder. So if you're seeing the red, then you know that's, there must be dust. Exactly. But then how do you determine how much dust you look at some supernova where there is no dust like it's way far out of its galaxy or it's the bluest one you've ever seen or something like that. So the power of the red, the redder it is, the more dust. And in fact, if you really do this right, differentially, all you need to know is it's so much redder than other ones. And then that affects how much difference it is. Oh, yeah. It's like that you're sort of, you're getting these pieces of evidence and building that's fascinating to me. Right. So much science happens that way. People think it's just one question you're wanting to answer in one experiment. Yeah, no. Oh, my gosh. Well, it's striking me in all of what you do. Not so much Neil, but you. But you hit a roadblock and find a way around it. Right. That's all for all of the brothers. We need clever people. That's exactly on the team. It's fascinating. Okay. So now, if I remember correctly, the goal wasn't so much to measure this Einstein term, wasn't it? No, I did. No, it wasn't even on my radar screen. It was just to lay it out. It's just to see what's going on. It was just to measure how much the expansion was slowing. Okay. Right. And was it slowing enough to equations? Yeah, yeah. Tell me what you, you wrote stuff. I wrote stuff down. Yes. Yes. Okay. So I wrote down some standard equations of what should have worked for the data, which is a question anyone would know just. Yeah. And you thought you were thinking it was slowing down. And not only that I was so sure it was slowing down because that's what everybody told me. And I was in graduate school at the time. That I said, I said, okay. So the supernovae will measure the slowing and I'll immediately convert that to what is the mass density of our universe? This famous number called omega M. And then apply that to our universe. And it's rapidly. Well, right away, yes. But right away, that number tells you what we want to know. If omega M is greater than one, there's so much matter in the universe, it will recalapse. If it's less than one, it will expand forever. Omega M equal one is called a critical universe or the critical. It's the mass that it's the gravity that the mass that the earth would have to have. So is this to launch a rocket and have it be escaped the loss? So is this the big freeze, the big rip and the big cry will get to that? No, we'll get to that. Okay. We'll get to that. So can you catch up? Yeah. I'm worried. So too much. So I have to be more guys. I got stuff to do. This is supernova happening in an hour. Yeah. That's my point here. So there's a very simple sequence here is supernova measured deceleration related to how much matter is in the universe that's causing the slowing expansion. So when I wrote my computer program, I said, hey, computer, fit that and tell me the answer. And the answer it spit back was negative mass. Okay. Now there's no such thing as negative mass. That's not like a physics option. But you know, computers don't know physics. So you give them very simple instructions, measured deceleration, turned to mass. And I hadn't yet noticed that the data was saying the universe was accelerating. So it was like, okay, you want me to make that equation work? I'll just flip the sign over here on matter. Now it's negative. And I'm like, that isn't right. You can't do that in physics. We can't report that. And so after doing a lot of checks, I was like, well, what could do that? And then, you know, it was like all the classes we ever took was like, you know, Einstein once had suggested something that could go the other way. You put that into the equations and it like fit like a glove. Bought a bang. And you've got, it's not just expanding, but it's accelerating in its expansion. Correct. And now it's Y and that gets you to dark energy. Right. And so what is it? So, you know, you made the measurement that it exists. Right. Which is a separate thing. Absolutely. So knowing what it is from the interpretation. Right. And just to mention. Just people need to, yeah, these are sink in here. Because the universe is accelerating. Whatever's doing it, we can make measurements of things. Yeah. Even if we don't know what's causing it. Well, it's one, it's the, how some of the greatest things happen. It's you're going for a and then you find b. And this is going to sound, you know, as a writer in a room in comedy shows. You could give us an assignment. Write a joke about, I don't know, airplanes travel, right? And nothing great comes. And then just out of that comes a great side bit that ends up being, that's how the back and black segment came about in the daily show. With the list black. Yeah, because we were trying to come up with great jokes on these little stories. Like a Florida man. And we're like, we don't know what to do with this. We're like, give it to him and let him rent. So it's the same, it's obviously in the arts, but it's the same thing. You're going for one thing. And in a beautiful way, it's like a beautiful mistake in a way or whatever. But it's also the thing that's still to this day. We don't know for sure or understand well. I mean, we could say the universe is accelerating. There's no question about that. But what is causing it? We're still relying on Einstein's cosmological constant or more generally dark energy. But we don't understand the physics of that at all. Get back to work, dude. Yeah. Yeah. What are you doing here? Yeah. You made the discovery. Yeah. Part two of it. Oh, yeah. Well, actually, you know, there's something in my pocket. I've been sitting on it and it's like bottoming. You ever get like a pebble? Yeah. You're like, sitting in it. And it's like, oh, yeah. Whoa. Wow. Wow. There you go. Wait a minute. Did you buy that on the street? Wait, wait, wait. I said it in the gift shop down stairs. I got a guy. Don't fight it because it's chocolate. The biggest in this. At the club. Hey, so, you know, it was so just. It's the church. They didn't give us the Nobel Prize for discovering dark energy. But for discovering that the expansion is accelerating. Right. Right. That's why it would be bigger if it was more like they don't know about us. It's just a little discovery. So they give you the baby. It's just the baby Nobel Prize. That's right. I'm sorry. I guess that's Alfred Nobel. Yes, it is. On the cover there. It was a funny story about Brian Smith taking his on the airplane and the, um, the, uh, TSA agents were very confused because when they X-rayed his backpack, it just showed up as a whole in his backpack because the goal doesn't go through. So, um, it doesn't go through. It doesn't go through. It doesn't go through. What is in your backpack? And he was like, he took it out and they go, what is that? And they said, he says to Nobel Prize. He said, who gave that to you? He said the king of Sweden. What did he give it to you for for discovering the expan, exoloring expansion of the universe? They were deadpan. No. So basically this guy's discovered the, you wouldn't be here. If I wouldn't be talking to you right now. Very cool. This is actually gold. Yeah. Where's it gold? Like, let me touch it. I don't know. It's 18 characters. 18 characters. I know it's worth a lot today. You gave it to me. It's worth a lot today. Wow. Have you seen the price of gold? I gave it 4,000. I'm worried walking out on the street. Can I just say something? You're brilliant. And I'm impressed with that. But I'm more impressed that you're walking around New York City with that, your pocket. I hear people are nice here. So, it doesn't come with a thing around your neck like like the swimmer. Yes. It's Mark Spitz. I'm over there. I'm stay modern here. No. I'm going to Mark's Michael Phelps. Michael Phelps. Michael Phelps. Yeah. This is heavy. Yeah. This is fine. This is low. This is low. Let's give to our meetings. Let's figure out how much gold is actually in it. And where did the gold come from? That was in it. Oh. They were knowing. Oh my God. It's all coming. Full circle. Full circle. Full circle. They said, in fact, yeah. They said we want to give you something that really represents the work you did. the work you did and they were like let's find a supernova by Tuesday. And we'll make something. Listen, I know a guy that can melt that down in the watch if you want. That's beautiful. You surely know in here at the American Museum of Natural History in our backyard, it's our yard but it's run by the city. The city controls it including the dog run. But there's a monument there put there by one of the one of the sweetest right. It's former suitable companies in the Teddy Roosevelt Park in the park and it's in honor of all the American Nobel Prize winners. And my boy's name is on that. Yeah, they're all carved. They're carved. Chiseled in. Yeah. My boy's on that statue right there near the dog one. I say dogs watch it as they poop. So what we live on 79 sheet right around the point from here. My dog peas on your name. Really? I'm sorry. My name is actually pretty high up. I have a very big climb up. My dog is welling down. That's all I'm saying. He can reach high. So say what you said again because it's important. You got this right not for knowing what dark energy is right. But for the discovery that it exists for the discovery that this phenomenon, the universe accelerating exists which everybody attributes to dark energy because normal gravity from matter doesn't do that doesn't do that. It goes the other direction. It's like having a car and like all you've ever done is hit the break. And then one day the car just kicks off and you're like, how did the break do that? And it's like no, a different pedal, the gas pedal did. And I think you've started to move toward that the idea that dark energy determines the fate of our universe right. And that's where it becomes which makes you a real Debbie Downer. But there's big freeze. There's right. There's big rip and there's big crunch. Yeah. Which actually feels like Ben and Jerry's, Ben and Jerry's anxiety flavors. You would be the big freeze because you're closed off emotionally. You would be the big rip. You're strong and I'd be the big crunch because I'm a baby. And everything collapsed. But the big crunch I think is not in the cards. Actually everything's on the table still to be honest. And yeah, in light of some more recent results on dark energy where it may look like it's thawing or weakening. Well, let's get into that. So we will. Let's get into that right now. We're all up to speed now. Yes. And we have like three minutes left. Yeah. The universe is accelerating. Okay. And we have a new model of the universe which goes by the sexy name Lambda CDM. Okay. Which encompasses everything we know about the universe. The Lambda part means there's dark energy. This is the astrophysicist version of a standard model. Correct. I guess. Right. And the CDM part is cold dark matter. It means there's a lot of dark matter in the universe. But there are other things in that description like the universe is relatively flat. There's a certain number of neutrinos particles. It's everything we know. It's an inventory of the universe. But 96% of it is still kind of unknown stuff. In fact, very unknown stuff. 90% of that's the dark matter and dark energy combined. So by the early 2000s, it was recognized. Well, we want to understand this more. And so there were folks who were going to measure the radiation leftover from the Big Bang, the cosmic microwave background with a series of satellites, WMAP, Planck. And they were going to very precisely determine the state of the universe as it existed shortly after the Big Bang. The folks who were measuring the cosmic microwave background got a very beautiful baby picture of the universe that has a lot of fine-grained information about the state of the universe. And excess radiation for lack of a better term? Yeah, no, but it's a description of what the early soup of the universe looked like. Whether how much, where barrions normal matter, how much was dark matter, photons, a really important snapshot of what was going on. And so the great success was the picture they got of the universe was the same model that we were essentially seeing from these more local observations. Yeah, there's a lot of dark energy. There's a lot of dark matter. Everything fit except one thing didn't fit, which is it also predicts how fast the universe should be expanding today. And that number called the Hubble constant is something we also can learn by this route that we've been describing where you measure parallax and you measure stars and you measure supernovae. And using that route, you can measure how fast the universe actually is expanding today. You'd be like having a two-year-old kid, you measure their height, right? And you predict how tall they'll become. And then you measure them when they get to that well, height, and what if it was off by like a foot or something? Right. You'd just own a kid. Yeah, you'd disappoint it. He's still in family therapy. Yeah, I understand. The fact that these two routes from the early or late side of the universe on the one and tell us the same rust, more than rust story. Basic story. Yeah, they're like doppelganger universes except one is younger and expanding faster and one is older and expanding more slowly. That's the 71 and the 67. 73 and 57, I'm not explaining that. The numerical values. The numerical values. That's right. That's right. And this Hubble tension emerged about 10 years ago. Tension as in the two numbers are not agreeing. As in the two numbers are not agreeing. I have to butt in. I'm in graduate school and we're fighting over whether the Hubble consciousness is 50 or 100. And so you're telling me you're not fighting over whether it's 67 and 72, whatever. And I don't have sympathy for you. No, no, no. By the whole time in graduate school, we didn't know the size of the universe by a factor of two. And you have to complain in about a few percent. So now let me go here. Let me go here. Let me go. Let me go. Let me go. Let me tell you. Let me tell you. Why this is so much more interesting than that was. Okay, please. When people were measuring 50 or 100, they were measuring the same thing. They were measuring how fast the universe is expanding here today, often measuring the distance of the same galaxies, the same stars. Different shapes here. Different shapes here. We just say here today, you mean within the Milky Way. Right, right. We're just talking about the Milky Way region. So, sort of universe. Okay. Okay. So if I told you the length of this table is such a good point. And Neil said, no, I get a different answer. The table has one length, right? And so this is something. It's not that profound. One of us is making a mistake. The big difference here is we are measuring opposite ends of the universe and we are using our story of the universe to connect them. And so, disagreeing in this case has the potential to teach us something profound about the universe. Whereas disagreeing back then just meant people were making mistakes. And when you say profound about the universe, our understanding of physics and the possibility that there could be new physics out there. Right. Because how do I go from the early universe to the late universe? I need a function. I need a piece of math to tell me how do I translate from there to there. It's like that kid, you know, they were two years old and they're an adult. How did you guess how tall they would be? Well, you had a growth chart, right? Yeah. The growth chart is our model of the universe. It's a formula. But, you know, with a growth chart for a kid, it's not precise. Well, you've seen a lot of kids grow up, right? So you're of a lot of confidence in the growth chart because they follow that. We only have one universe. And most of it's made of stuff we don't really understand. Right. Well, don't get another universe. Exactly. Well, so I think we got so far. Right. Yeah. We disagree. And Neil makes a good point. It's not a big disagreement in absolute sense. It's like 9%. But our measurements have gotten so precise that it's five or six times the error bar between it. I've banned the term error bar because no one knows what they'll let me. The uncertainty, the measurement of the uncertainty of each of those two quantities does not leave room for overlap. That's right. Okay. So from someone who's not as bright as you. I'm saying, but no, could it be that dark means that dark energy is shifting? Like, yeah, sort of like a passionate teenager like it's calm and steady and then all of a sudden, you never understood me Einstein and it's slamming the door on you, right? Like is it that possibility? Is that happening? Yes. I would say that we may be discovering that what we call dark energy is a general phenomenon that happens all the time in the history of the universe. So let me tell you this. The invoked dark energy shortly after the big bang in a period called inflation to inflate the universe. Okay. We give it the name inflation, but it's dark energy. Okay. We have the universe currently accelerating now that's dark energy. By the way, it was called inflation because the idea was advanced in the 1970s when we had like 18% inflation. So the word was had a lot of currency. I didn't know that. Right. Yes. It was under President Carter. Yeah. It was like 20% inflation. We're in inflation now. Right. But we have, but so we have other, we have things something in physics that's important part of physics called the Higgs field, which is a field in space that gives rise to mass for particles. That is an energy, an invisible energy in space. So this is a regular feature now in physics is to recognize that there are invisible energy fields. And in Einstein's theory of gravity, an inventive, an invisible energy be field plus Einstein's theory of gravity automatically has this consequence of giving a push to the universe. And so I would say at this point, we are sort of watching the universe to sort of try to learn when episodes like this may occur. Maybe it, maybe there's only two. Maybe there's ten. Is that the, that there's, from my understanding, there's five possible reasons for this Hubble tension. Is that the new, new dark energy theory? Or is that the early, early dark energy theory? Which posits a third episode of dark energy, not inflation. That was the beginning, not the current one. So is that the turbo boost one? Or is it something different? I don't know about the turbo boost, but it goes by the name early dark energy. But it's the same concept is that, you know, if you give it kicks somewhere along the way, then using the simple form of the cosmological model to connect to endpoints, you know, you're not going to quite get things right. Doesn't it have to be motivated to manifest itself? And so what would manifest a pulse of dark energy in a place unexpected? Right. It usually ties to a particle and it usually ties to some events, some symmetry breaking or something like that. And it becomes very theoretical. I mean, theorists argue that sounds reasonable. That doesn't sound reasonable. To me, they all sound kind of like, blah, blah, blah, blah. But, you know, I look at it like, all right, how many times have you invoked the tooth fairy in this conversation? And, you know, I've learned that like a close cousin of the tooth fairy is not a new invocation of the tooth fairy, it's just her cousin. Right. So to me, there's a big tooth fairy that we've already been living with for a long time. And these are like revisits of the tooth fairy. All right. So I'm an observer. So this is not, you know, I look at stuff. Is there a way to reconcile this without having to invoke another tooth fairy? Yes. Exactly. Well, first of all, big fan, there are a lot of ideas. I mean, it's better gifts. Yeah. One way to play the game is to change the way the universe looked before this radiation from the big bang leaks out. So how do you change the way it looks? Change our understanding of our understanding of changing. Right. I think we've got it. It's a kind of a plasma soup. So even something a subtle is saying if there was a magnetic field in it, that could start this process of collapsing by a wrap. Or there could be new particles. There could be new particles. There could be new particles. That is absolutely another possibility. Right. It rearranges the way energy is distributed in the early universe. And so there are many ideas, electron, mass decaying interactions between dark matter. See, when physicists start out with the cosmic microwave background, they have to build a model of what's going on in the universe. So this would be like some new attribute going on there or it could be something late in the universe. Like as dark energy emerges, it's not this cosmological constant, which means static uniform unchanging, but it has some kind of mind of its own. Right. So you have your option to either make the early universe match the current universe or the current universe. Exactly. Or exactly right. Do something both that can match the universe. That's exactly right. Right. Okay. So what are the nearby measurements? Seems to be those should be pretty secure. Yeah. So I would say now after 10 years of scrutiny, they're pretty darn good. What I could tell you is having made a lot of those measurements with the Hubble Space Telescope along came the James Webb Space Telescope. And it was like, I don't know, it was like riding your first little bike when you were a kid and then somebody gives you a 10 speed. And you're like, oh my god. Right. And you're like doing laps around what you did. So I've been doing laps around the work that I've been doing over the last few years. And the images are pristine. The measurements are textbook, but the answer is the same. And so the fact that James Webb is confirming what Hubble is confirming is confirming that this is a real problem. And by the fact that deserves, I got to emphasize this because what he just said is, you can make measurements with whatever precision your equipment allows. Then you extract from that an answer in the din of cosmic noise. He says, it's kind of saying this. If you have better data and you get the same answer, you get the right. That's right. And the signal to noise is 10 times higher for the measurement I'm making with James Webb than it was for Hubble. So you get a full order of magnitude improvement and nothing changes. That's very compelling. So for those at home, it's in simplified terms, there was a debate. Well maybe the math or the way we're doing the math is off. And then the Webb telescope enters the picture and tells you maybe not. So now you have to go to the idea that maybe there's something about the world of cosmology that we're not understanding or there's something new or there's new physics. I'm going to say, or some subtlety, something being lost in translation between the universe we see and how we transform it to these sort of mathematical models. This is the sky and the telescopes confirm that is the way the sky looks, but perhaps there's some subtlety in the way we translate that into math or we translate to the beginning of time. Let me go back 130 years. Yes. I think that's you living in the past. Go ahead. When I was a kid, go back then. Yeah, let's go back. We were riding high on classical physics. Yes. And people said, look, there's not much left to discover in the universe. Right. We got this. We got thermodynamics. We got this. And there's just a few clouds on the horizon. Yeah. The procession of mercury isn't quite working out there. Yeah, but we'll solve that soon. Just another planet out there probably. So don't go into physics because it's about to end. But a big quantum physics comes up in special relativity, in general relativity, and all that came with that, is there something lurking? Right. In the dark, in the woods, that will need a much bigger transformation of our understanding than just meddling in here and there. Right. The answer is I don't know, but what I do. It's a good answer. He's good scientist. But I do know that. I was hoping for an answer. I'm going to be honest with you. I do know the process. I don't want to die soon. Here's the process. We're very happy with the model, the science we have. We go out and we predict experiments and we do things. And then you start to build up these cracks or tensions, little funny things. The procession of mercury is not following Newton's theory. There's supposed to be an ether out there, and we're supposed to be traveling through it. So the speed of light should be different in different directions. We don't see that. Hmm. What's going on there? You start to build up these things and- Just like holding back the water in a dike. Right. You'd say you just plug this hole. Did that work? Oh, that's a build. Right. And when somebody comes along, I'll say Einstein in 1916, right? He comes up with a brilliant re-imagination of physics, which first does something very important. It explains or fits everything we already knew. You can't go and lose that. And then all these puzzles get solved. The first thing that Einstein supposedly did after he developed general relativity was he looked back at this procession of mercury. This problem that mercury, it's orbit, is itself rotating very slowly around the sun, unlike the other planets. And nobody knew why. They thought maybe there was another planet between mercury and the sun. Einstein shows- The hole's Vulcan. Because it would be hot. It's called Vulcan. We just- There you go. We were perfectly happy to say, it's Vulcan is there. We can't see it. We took close to the sun. It would get in the glare. It's not unreasonable because when the planet Uranus was not traveling where it was supposed to, they invoked a planet Neptune, which they found right where it was supposed to be. So this is what makes science so much fun. And why you can't just play the game like you're studying history and you're going to predict what's going to happen. Because sometimes the planet misbehaves because there's some stuff out there you miss. And sometimes it misbehaves because we have the wrong understanding of physics. And in that case, Einstein showed that his theory would explain mercury's procession because mercury was living so close to the sun it was in what we call the strong gravity regime where gravity was operating differently than Newton. So to answer your question, we are collecting these sort of cracks and problems. And sometimes that is the kind of harbinger of some sort of new revolutionary thing. Sometimes it's the loose thread on a sweater. You pull it and it's always just that annoying thread and that's fine. Or sometimes it unravels the sweater and it's just hard to say. Right. But we live in a society where we want answers to everything right. And to the average person you want an answer, but what this feels like is like you're assembling the universe using like IKEA instructions. And then you look at the manual and it's like it doesn't look like the manual and you're like, honey, what's this extra part? I don't know. It's dark energy. Is there another Alan wrench? Like, and so you literally think what we're saying is a, we're not done because everything isn't fitting. And b, we have this wealth of new facilities, which are now coming online that really should help us answer these questions. We have the Nancy Grace Roman telescope. So that's specifically tuned for dark energy. Is that correct? It's going to be particularly good with dark energy. So, yeah. So it's not just another telescope. Right. We got smart people figuring we got this problem. Right. But I'm going to ask this problem. You both consider a stupid question. If we don't know what it is other than naming it dark energy, how do we know what to build to look at what is. That's a great question. So I was actually on this panel called the Decadal Survey that once every decade recommends what to build next. And this is what we thought about. And we recommended this in 2010. And the reason is because it takes us decades to build these things. So what if the science questions change as your building or the techniques change? So we designed the telescope to measure the current techniques best that could be done. But also recognized that a telescope that didn't exist was a space-based telescope with a wide field of view. Remember I said earlier in this, you need a wide field of view to observe hundreds of thousands of galaxies. And that operates in the near infrared, which it's very difficult to observe in the near infrared from the ground because the sky's very bright. Define near infrared? The infrared are wavelengths that are redder than red. So longer wavelengths than that. But it's near. It sits closer to the visible spectrum than the far infrared. So near and far it's stupid words, but we're stuck with them. So the whole infrared part of the spectrum sits adjacent to the, to the, to the, right. So adjacent to red, orange, yellow, green, blue, violet. So it's adjacent to that. And those wavelengths had a near, visible colors near and then far. That's all right. It's not deeper than that. So we both built a telescope. We say, well, today this is what we would want and we think it'll be great. But also tomorrow, this will be the capability that doesn't exist. So there's a discovery space capability where you say, you know, this has got to show us new things because we've never looked in that window. We've never opened that door. So it has both elements. Got it. Very important here because that's why, why build something that only can see what you're looking for or expect. The, the, the breadth of those capabilities, that's what advances the field. But what is, has to feel at times overwhelming to you is it's a constant moving target, right? So you've developed this telescope. But as you just mentioned the minute ago around that new discoveries are being made, new equations are being calculated, right? So it's, it's, it must be maddening because there's never a firm like, yeah, this is, this is it. Yeah, but what I find very satisfying, I mean, when Neil and I were in graduate school, there were sets of questions about the universe. And those questions have either been answered or have changed to these other ones. So, exactly. They're not even interesting anymore. Yeah, the story. I mean, we were all like, how much matter is in the universe and is it going to recalapse? And that isn't even the right one of our colleagues. I think about any wrote a book called Just Three Questions or something or what something was some title such as that. And it was because of that book that I now tell the world when they say, what question do you want to see answered about the universe? And my answer is it's the question I don't yet know to ask because there's a vista that will rise up beneath me from research being done now so that I will then ask a question undrempt of today. That's the question I'm thinking of. Well, in our field of cosmology, right, used to jokingly, he said that we only had two and a half facts in cosmology. So we have so much more information. Such a great laboratory. Cosmology used to be considered closer to philosophy than physics. And now there's hardly any data. Right. We knew the universe was expanding. We knew there was radiation left over from the big bang. We knew the sky was dark and that was what that was about. There's several people thinking about this tension. You're not the lone wolf in this. So do you guys, are you converging at any point? So we have a fleet of new observatories coming online. We have the Nancy Grace Roman telescope built by NASA to launch next year, which is a study dark energy. We have the Vera Rubin telescope. She was the discoverer of dark matter, one of them. And that is a massive ground based telescope that will cover most of the sky every three or four days. I don't see that one working. A million supernovae that one is already working. And it contradicts me all the time. It's only online. It's just got thousands of asteroids that we're not even counting. Well, no one told me. We have new CMB experiments, the Simon's Observatory. We have LIGO is just still getting up and going and has great capability. We expect new results from Gaia. So there are a lot of facilities that really are well poised to give us answers. So but is there like a fight out there? Is there a cage match among you guys? Right. So I would say five or ten years ago, the folks from the CMB particularly were like, well, you local people are probably wrong because it used to be 50 or 100 and that seems like hard stuff. And maybe some of us were like, Plank looks really good, but gee, I really would like some confirmation of that. So along came new facilities that allows people to check the work. So from the cosmic microwave background, we've had these great high resolution CMB experiments like ACT and SPT, one's Princeton mostly one is more at Chicago. And though they have replicated the cosmic microwave background measurements, actually, they've even pushed the Hubble constant lower, not 67, but 66. Are these observatories in Antarctica? Yeah, ones at the South Pole, South Pole, Tulscope, and the other ones in the Atacama in Chile. Okay. And so you need very little water in here. Do you want to dry its places on earth, right? The Atacama dead. As is Antarctica. It's one of the driest places on earth. And then nearby, we have seen the James Webb Space Telescope replicate the measurements, which was absolutely critical. We've seen other techniques developed that have cross-checked the measurements. And I just came back from a, something called the distance network. So not the distance ladder, but how do we combine all of these different measures simultaneously, taking account their covariance. And what we've learned is- The network, great name for that because it all has to work together. Correct. It's a ladder anymore, but it's like, but what if I have this information and this information? Well, this information was calibrated the same way as this, but it gives me a unique measure to something else. You're right. With this stupid comic where the Transcontinental Railroad, and there's the Golden Spike, which is the last spike. And the railroads come and the tracks don't match up. Like, wow, that is the problem. Hey, they're down there. I told you we were off. Right. So we've seen a lot of cross-checking and this problem is not going away. It's been getting stronger and stronger. So I think we have to think hard about what it means. Has your position altered at all, or at one point you said, I think the universe is giving us less and in cosmic humility. It doesn't seem to be following the manual we had. We can rule out a measurement error as a cause of the Hubble Tension with very high confidence. There's some people out there that would sort of say, perhaps not. And then- I think you're quoting him from some other program. We have him here. We would have told him where it was. He doesn't have to tell me. He doesn't know what he says. Let me define error. Do you ever watch baseball? Oh, yeah. You know baseball. So Aaron, what do you think you are? Aaron Bayquare. There's a quarterback. There's a wide receiver. Now, so I like baseball that they define an error as there was something that was supposed to be done. You're supposed to feel the ground ball. And you messed up, right? And it didn't happen and they score that as an error, okay? But you know, making some extraordinary play like climbing the wall and stealing a home run and not doing that is not an error, right? So in our parlance, I would say we are convinced after 10 years of scrutiny that we're not making an error in the baseball sense that everybody- In terms of measurements and so on. Everybody appears to be following the manual carefully. Everybody appears to be measuring what they said they're measured. The data is public. This is very important. Unlike back in the 50 or 100 days, half the battle was people had their secret photographic plates in their drawer. And so you'd have a battle and you were like- None of the drawers in the drawer. That isn't where you guys have freaks. You guys walking around with a piece of metal in his pocket, you got stuff in your drawers. So what's important is all the data that I talk about is in a public archive. So I say this star is this bright. It's right there. I'm sorry, back up in the 50- What would it be good? So I can verify that. And I don't have to think that- I don't have to just take it more. I understand, but back in the day, what do you mean there was secret? You were not- If you were humble, literally, the guy, right? You would go to the 100-inch telescope, you put in a photographic plate, you'd take your deep exposure, and it was your plate. You took it home to your laboratory- There's no internet. And you told people what it said. Yes. But they- But they're lectures about it and so forth. No one else had access to your data. Right. Now everything is digital and- Right. It's just- The point being you've got a lot of people cross-checking- So this has been the democratization of science- Very poor facilities. And so what I will say is in the past, when errors are made, and errors absolutely happen in the baseball kind of errors, our community is so good at jumping on those, right? But I would say within weeks or months, that is found. When something lasts 10 years, when the data was public, when people could scrutinize it, then those become the things that are real things. So and you want to also watch out for whether this group think. And if multiple teams who are otherwise competitors find agreement in what your measurements are, that's a good place to be. Like there were two groups last- Look, in the last couple of weeks that were using JWST, and this method called Tip of the Red Giant Branch, and they got 74 and 75. They're unrelated to the more traditional groups that were working. So the more you see these groups that are independent- They did the value of the Hubble. That's right. This is 74, 75 versus VZV, 72, 70, who's that trouble you? No, no, it's down to 60. Yeah, yeah, yeah. Yeah, right. I mean, it's, look, the full range of measurements people make locally is about 70 to 75. So that's normal. That's kind of a bell curve distribution. So the middle is probably around 73, but some people get 75 and some get 70. But the point is, why are- And you expect that in any random distribution? The question is, why is everybody getting something higher than the early universe at 66 or 67? And that would, I don't see how that happens by chance. Okay, there is this theorist, Thomas Birkett, and sort of has another explanation for all of this. I wanted to get your thoughts on that. So he is a theorist. He's not making measurements, and he has had a theory for a long time that when we look out in space, we use this approximation. We say, everything is smooth-ish. Okay, and we can use Einstein's theory of relativity as though if I have a certain amount of matter, it's kind of uniformly distributed in space. In reality, space is quite chunky. He is saying that the mathematics of calculating Einstein's general relativity through chunky space won't be the same as calculating through the same amount of matter smoothly distributed. And I know a lot of people disagree with him. He sort of, on an island about this, they are devilsily difficult calculations to do analytically. So people have done it numerically with computers, where you just kind of trace a particle, and you have a go through all this, and people who do that say they don't get what he gets. What he gets. But I'm open to it. Look, I mean, if things are not fitting, you have to be open to a lot of possibilities. Yeah, the more things don't fit, and the longer you are in that state, the kind of more, you know, you are saying, or who's got? What do you got? Yeah, what do you got? What do you got? I mean, like, for example, when we discovered dark energy, there was something called the age crisis, where there were stars that appeared to be older than the age of the universe. And that was a problem. And the solution to it was actually dark energy, because when we said the age of the universe, we were assuming that the expansion had been slowing down the whole time. And so when we said how long ago was everything on top of everything, we would get a young age for the universe, 10, 12 billion years. Once you realize, oh no, the rate we have right now is a fast rate. That's not the average expansion rate of the universe. Now let's do the proper calculation. It pushed the universe to be older, 13, 14, 15 billion years. Adam, I don't know if you're a betting man, but what would you bet would be the solution to this? I wouldn't bet. And the reason is because I like fun. I like to think of myself as part of the crew of umpires in this game, right? So we're calling the balls and strikes. We're saying, oh, this thing's traveling this fast. This is so far away. You can't fix the game a little bit. I mean, you know, that would be the problem. You can't do a little bit of being a bad. If you're umpire, you're right. I mean, I will say this is an unusual game. This is not finger on the scale. Yeah. The mafia likes to do so. So, you know, my bet is that there's something interesting going on. But what it specifically is, I don't know. Okay. But it's like we've got two thermometers. You're taking my temperature. One says it's dying. 98.6. And the other says I'm at a boiling point. And you're the doctor going, eh, it could be new physics. I don't know. I would take your charge. I'm willing to go and say that. You're sick. You would be a terrible doctor. One of the more fascinating dimensions of the moving frontier of science is when you don't have an answer to questions that have been posed or you have data, you can't make sense out of it based on our understanding of how things should be or even could be. Then you got to scratch your head and say, do I have to give up some prior expectations, some prior assumptions that went into this understanding of the universe because the puzzle pieces don't fit until Copernicus, our understanding of the world, the universe, had earth in the center. And how else do you explain planets going forward and backwards in the night sky, forward and then retrograde and then forward again? Do they have epicycles? We got that. We got that explained. And then Copernicus comes along and says, I got a new idea. Earth is not in the middle. That's pretty serious. The sun is in the middle. And earth is just another planet. And we're all going the same direction around the sun. And you say, okay, the math is a little simpler, but the idea doesn't sit right. The epicycle thing that kind of matched the data. And so now, what did they do? They said, let's check the model. So they check the model. And it turns out the planetary orbits were not as precisely predicted as they were for the epicycles. Do we throw away the whole thing because epicycles were giving better predictions than a sun-centered universe? Do we just throw it all away? Or maybe there's adjustment on the edges of this. Maybe the idea that the sun in the middle is what's fundamental. And oh, Copernicus assumed, presumed that orbits were perfect circles. Why wouldn't they be? It's the heavens. It's where God is and a circle is a perfect shape, but they weren't. Discovered by Johannes Kepler, 50 years later, he shows that they're ellipses. You keep the sun in the middle, put the planets on elliptical orbits. You perfectly predict and understand the motions of the planets. We're in this interesting precipice in cosmology where, you know, the big bang is pretty secure. In spite of what newspaper headlines with clickbait might have been implying over the last couple of years. Big bang and trouble, I think it's pretty secure. If I'm betting, I'm betting we're going to have the big bang throughout this. But we're going to have to understand something else about how we interpret the early universe, how we're understanding the expansion in the modern universe. Is there some missing piece that'll make it all come together, missing piece of understanding, that'll make the puzzle pieces of cosmology come together? In a resurrection of the challenge that confronted Copernicus, we kept the sun in the middle and we found out what else needed adjustment. And at each turn of those discoveries, we had a deeper understanding of the operations of nature. And that's what makes it all so beautiful. That is a cosmic perspective. Adam, has it been a delight to have you come through town? Thank you. I don't know how often you get through New York. I know there's a lot of good fertile brain activity in the Baltimore. My sister lives here. Oh, there's an excuse. Shout out to your sister. And let that be an excuse we can exploit going forward to get you back here and catch up. Sounds calm. Whatever is the latest thinking. Can I have your prize? I want to show it to my son. I'll give it back to you. I promise. Is it here? It's under my seat. Thanks for it. Absolutely. It's so fascinating. I learned a lot and honored to meet you. Sir, excellent. Great. Great. All right. This has been Stark Talk. Neil, the grass Tyson here, your personal astrophysicist. As always, keep looking up.