Origins of Dark Energy with Adam Riess

How did scientists discover evidence for dark energy? Neil deGrasse Tyson and comedian Paul Mecurio explore dark energy, Hubble tension, and the beginning and end of the universe with astrophysicist and Nobel laureate, Adam Riess.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:01Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now.

• 0:16Neil deGrasse Tyson?

  This is StarTalk. Neil deGrasse Tyson, your personal astrophysicist, and I got with me co-hosting.

• 0:22Paul Mecurio?

  What's up?

• 0:23Neil deGrasse Tyson?

  How you doing, man?

• 0:24Paul Mecurio?

  I'm good, buddy.

• 0:25Neil deGrasse Tyson?

  Paul Mecurio.

• 0:26Paul Mecurio?

  Good to see you again.

• 0:27Neil deGrasse Tyson?

  Professional comedian. You got your own podcast?

• 0:29Paul Mecurio?

  Yeah, Inside Out.

• 0:30Neil deGrasse Tyson?

  Out and In?

• 0:31Paul Mecurio?

  There you go.

• 0:32Neil deGrasse Tyson?

  Burger. Did they sponsor you?

• 0:36Paul Mecurio?

  For those listening and watching, this is how not to host a show.

• 0:41Paul Mecurio?

  Have a guest and not know anything about it. Yes, it's called In-N-Out Burger. And the whole podcast is me interviewing people in the drive-through window.

• 0:48Neil deGrasse Tyson?

  In the drive-through window.

• 0:49Paul Mecurio?

  You want fries with that? So, you're an astrophysicist. The guy was on my podcast.

• 0:55Neil deGrasse Tyson?

  I was, I was.

• 0:56Paul Mecurio?

  Along with Paul McCartney, by the way.

• 0:58Neil deGrasse Tyson?

  Oh, no, okay. All right.

• 0:59Paul Mecurio?

  What do you mean, okay? You're like, that's all you say?

• 1:01Neil deGrasse Tyson?

  Name dropper.

• 1:02Paul Mecurio?

  Yes.

• 1:02Neil deGrasse Tyson?

  But none of that impresses me. You've got like a Peabody Award and an Emmy Award.

• 1:07Paul Mecurio?

  Yes.

• 1:08Neil deGrasse Tyson?

  This is writing.

• 1:08Paul Mecurio?

  Writer on The Daily Show, yeah, and worked on The Colbert Report.

• 1:13Neil deGrasse Tyson?

  We love you, man.

• 1:13Paul Mecurio?

  Hey, I love you too, man.

• 1:14Neil deGrasse Tyson?

  Thanks for spending some time with us.

• 1:15Paul Mecurio?

  Absolutely. Always great.

• 1:17Neil deGrasse Tyson?

  Making us happy. You know what we're gonna talk about?

• 1:18Paul Mecurio?

  Mm-hmm.

• 1:19Neil deGrasse Tyson?

  The cutting edge of cosmology.

• 1:21Paul Mecurio?

  Hmm.

• 1:22Neil deGrasse Tyson?

  Because everybody's talking about cosmology all the time.

• 1:25Paul Mecurio?

  Mm-hmm.

• 1:25Neil deGrasse Tyson?

  But who gets in there and say, where's the edge?

• 1:29Paul Mecurio?

  Yeah.

• 1:30Neil deGrasse Tyson?

  And where's, where are people at fisticuffs?

• 1:35Paul Mecurio?

  We like to mix it up here. Where can we get people at each other's throats?

• 1:39Neil deGrasse Tyson?

  At each other's throats. Because then, that's, actually, I mean, the history of science shows that's how discoveries emerge.

• 1:45Paul Mecurio?

  Now, I have to say, I've been doing a few of these with you, and this one has, is really cool, really interesting, because there is a lot of back and forth on this, and it's really, it's really.

• 1:54Neil deGrasse Tyson?

  Yeah, yeah, no, it's good. And a lot of people, contenders, I think, is the way to think about that. So, 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 Riess. Adam, welcome to StarTalk.

• 2:15Speaker 02

  Thank you for having me.

• 2:16Neil deGrasse Tyson?

  Welcome to my office here at the Hayden Planetarium.

• 2:19Speaker 02

  Excellent.

• 2:20Neil deGrasse Tyson?

  Yeah.

• 2:20Speaker 02

  I mean, I was just wandering around the museum, and you guys pulled me in.

• 2:25Paul Mecurio?

  You were, he was with a bunch of children, and his hand was being held by a teacher. Yeah, he might for a billion have a Nobel Prize, but apparently he gets lost in large spaces, everybody.

• 2:35Neil deGrasse Tyson?

  So you're at the Johns Hopkins University?

• 2:38Paul Mecurio?

  Yeah.

• 2:38Neil deGrasse Tyson?

  You're the Bloomberg distinguished professor there.

• 2:40Paul Mecurio?

  Yeah.

• 2:41Neil deGrasse Tyson?

  Bloomberg, he's a friend of, my wife worked for him. He has a background in physics and engineering and came through Johns Hopkins.

• 2:47Paul Mecurio?

  Yes, he did.

• 2:48Neil deGrasse Tyson?

  And donated a whole building called the Bloomberg Center for Physics and Astronomy.

• 2:51Paul Mecurio?

  Yeah.

• 2:51Neil deGrasse Tyson?

  Yeah, so there's some good Bloomberg action down there in Baltimore.

• 2:54Paul Mecurio?

  And then he ruined everything when he created bike lanes in New York City. I'm telling you, let's spend an hour on that, Mr. Nobel Laureate. Can we fix that?

• 3:03Neil deGrasse Tyson?

  Says the man who does not ride a bicycle.

• 3:05Paul Mecurio?

  Exactly.

• 3:05Neil deGrasse Tyson?

  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 spaceborne, is co-located on the campus of Johns Hopkins University.

• 3:19Paul Mecurio?

  That's right.

• 3:19Neil deGrasse Tyson?

  So you also have a position there as well?

• 3:21Paul Mecurio?

  That's right, that's right, that's where we have the joystick.

• 3:23Neil deGrasse Tyson?

  Okay.

• 3:25Paul Mecurio?

  I'm gonna leave that right there.

• 3:28Neil deGrasse Tyson?

  We have to add that you are a Nobel Laureate.

• 3:32Paul Mecurio?

  That's right.

• 3:32Neil deGrasse Tyson?

  That's badass.

• 3:33Paul Mecurio?

  Yeah.

• 3:34Neil deGrasse Tyson?

  And I think if you had a business card, just say Nobel, that's all. You don't need anything else.

• 3:38Paul Mecurio?

  No phone number?

• 3:39Neil deGrasse Tyson?

  No phone.

• 3:41Paul Mecurio?

  You just think you want to talk to him, he's so smart, he calls.

• 3:45Neil deGrasse Tyson?

  So remind me, what year you won that?

• 3:47Paul Mecurio?

  Uh, we won it in 2011.

• 3:48Neil deGrasse Tyson?

  You won the Nobel Prize, and that year was split three ways, so who are the other two recipients?

• 3:53Paul Mecurio?

  Uh, Brian Schmidt and Saul Perlmutter.

• 3:55Neil deGrasse Tyson?

  And Saul, I remember, was a West Coast guy.

• 3:58Paul Mecurio?

  Right.

• 3:58Neil deGrasse Tyson?

  Right, out of...

• 3:59Paul Mecurio?

  He led the Supernova Cosmology Project.

• 4:01Neil deGrasse Tyson?

  Okay, with the same intent of making the kind of measurements you were making.

• 4:05Paul Mecurio?

  That's right.

• 4:05Neil deGrasse Tyson?

  With Brian Schmidt.

• 4:06Paul Mecurio?

  Right.

• 4:06Neil deGrasse Tyson?

  Right, okay.

• 4:07Paul Mecurio?

  And we were members of the Hi-Z supernova team.

• 4:10Neil deGrasse Tyson?

  Hi-Z would be High Redshift.

• 4:11Paul Mecurio?

  Correct.

• 4:12Neil deGrasse Tyson?

  Supernova Team. And it was given to you specifically for discovering...

• 4:15Paul Mecurio?

  For the discovery of the accelerating expansion of the universe.

• 4:19Neil deGrasse Tyson?

  Which today we just call dark energy.

• 4:21Paul Mecurio?

  Well, dark energy is, we think, the driving mechanism for the acceleration.

• 4:25Neil deGrasse Tyson?

  Okay.

• 4:26Paul Mecurio?

  But there's still a lot we're trying to understand about the nature of dark energy.

• 4:30Neil deGrasse Tyson?

  Well, get back to work.

• 4:31Paul Mecurio?

  Please.

• 4:32Neil deGrasse Tyson?

  So, I'm gonna say, welcome to StarTalk.

• 4:35Paul Mecurio?

  Thank you.

• 4:35Neil deGrasse Tyson?

  Yeah.

• 4:36Paul Mecurio?

  It's an honor to be here.

• 4:36Neil deGrasse Tyson?

  Yeah, and so you are co-discoverer of a, because growing up, I mean, going, I don't mean growing up as a kid, I mean, coming through school, in 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 a negative, what is that?

• 5:09Speaker 02

  Nobody accounted for it.

• 5:10Neil deGrasse Tyson?

  But no, what is it? It's just a math thing. So every time we had a conversation about the expanding universe, you had to explicitly say, we're gonna assume this is zero. Because what are we gonna do?

• 5:21Speaker 02

  It's expanding at a constant rate.

• 5:23Neil deGrasse Tyson?

  Or expanding only according to what the galaxies tell it to do.

• 5:27Speaker 02

  Got it.

• 5:27Neil deGrasse Tyson?

  This would be an extra thing going on. Okay?

• 5:29Speaker 02

  And you were just too lazy to explore that?

• 5:31Neil deGrasse Tyson?

  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-discoverer of the accelerating universe. There are these equations that I'm describing here, and you're getting data. What was your data?

• 5:56Speaker 02

  Sure. So, um, 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.

• 6:07Neil deGrasse Tyson?

  Otherwise, the universe would just collapse on itself.

• 6:10Speaker 02

  Correct. Then it would just collapse. And then, um, 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, uh, it turns out there are galaxies out there. They're moving further apart. Hubble and others showed that.

• 6:24Neil deGrasse Tyson?

  Hubble the man.

• 6:25Speaker 02

  Hubble the man. Yes.

• 6:27Neil deGrasse Tyson?

  Hubble was a man before he was a telescope.

• 6:29Speaker 02

  That's right. He's more like the Robocop version of a

• 6:33Paul Mecurio?

  But he would be mistaken for a telescope at a lot of parts.

• 6:35Neil deGrasse Tyson?

  That's right.

• 6:36Paul Mecurio?

  He had the shape of a body of a telescope.

• 6:37Speaker 02

  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. So

• 6:54Neil deGrasse Tyson?

  Right. Very important bit of scientific wisdom there.

• 6:57Speaker 02

  So let's jump to the 1990s and astronomers are looking

• 7:01Neil deGrasse Tyson?

  So that was the 1920s.

• 7:02Speaker 02

  That was 1920. Yes, 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, you know, launching a rocket, does it have escape velocity from the gravity?

• 7:17Paul Mecurio?

  Is that matter something that would later be called dark energy? Is that sort of?

• 7:21Speaker 02

  No, this is what we called dark matter really at the time. 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, uh, 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 expansion rate of the universe in the past and compare it to the expansion rate in the present, and see if it was slowing down enough to stop.

• 7:56Neil deGrasse Tyson?

  Oh.

• 7:56Paul Mecurio?

  And this is where the distance ladder comes in, in terms of measurement.

• 7:59Neil deGrasse Tyson?

  Yeah, how do you know how far away? I mean, nearby, it's hard enough, just nearby. I guess you can use parallax on stars. But these stars are sitting on our noses. We have whole galaxies nearby and beyond.

• 8:13Speaker 02

  Right.

• 8:14Neil deGrasse Tyson?

  So what, you had to like really refine a method to do this.

• 8:18Speaker 02

  Yeah, so, so, you know, parallax is great, having a tape measure and running it out somewhere is great, but these just don't work very far.

• 8:25Paul Mecurio?

  You can get those at Home Depot.

• 8:25Speaker 02

  Yeah, I know, but not one that long.

• 8:28Neil deGrasse Tyson?

  With your Home Depot tape measure, you can get to things that are at walking distance of you. All right, but there are stars out there that, you know, you can't do, you know, radar beaming to them. Cause they're light years away.

• 8:43Paul Mecurio?

  You have to use parallax, a form of geometry that had its limitations because of the angles of the geometry.

• 8:49Neil deGrasse Tyson?

  You're just trying to make up for getting something wrong a minute ago.

• 8:51Paul Mecurio?

  I didn't.

• 8:53Speaker 02

  Pretty good.

• 8:54Neil deGrasse Tyson?

  Well, that's good. You did good there.

• 8:56Paul Mecurio?

  Yeah.

• 8:57Neil deGrasse Tyson?

  You did good.

• 8:57Paul Mecurio?

  Yeah.

• 8:58Neil deGrasse Tyson?

  So, 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 then you switch eyes, and then your thumb is like moving back and forth.

• 9:08Paul Mecurio?

  Hang on, I need a manicure.

• 9:11Paul Mecurio?

  Wait, what am I doing now?

• 9:12Neil deGrasse Tyson?

  Yeah, you look at it with one eye and switch eyes, and your thumb will shift back and forth as you shift.

• 9:18Paul Mecurio?

  Right.

• 9:18Neil deGrasse Tyson?

  It turns out, the amount that that shifts, and the distance between your two eyes, uniquely determines how far away your thumb is.

• 9:28Paul Mecurio?

  Which is then used.

• 9:29Neil deGrasse Tyson?

  So try this, put your thumb here and do the same thing. So now it separates even more.

• 9:35Speaker 02

  Yes.

• 9:35Neil deGrasse Tyson?

  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 coming.

• 9:40Speaker 02

  Let me do this with my hands so I don't have to look at you. Well, that works. Either way.

• 9:44Neil deGrasse Tyson?

  I'm blotted both ways. So, uh, how, 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 stars 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 good.

• 10:06Speaker 02

  Now you can measure.

• 10:07Neil deGrasse Tyson?

  Now you get that and you see how much it varies. You know how the diameter of our orbit, bada bing, 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.

• 10:22Speaker 02

  Hubble and then Webb.

• 10:22Neil deGrasse Tyson?

  Very reliable, 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. But now you have to go beyond that and you don't get to use Parallax.

• 10:37Speaker 02

  Right, right. So then you have to use another method, okay? And 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 assures you, wow, I have to be far away. And we can actually do that quantitatively by measuring how bright the lighthouse actually appears. So, uh.

• 11:00Neil deGrasse Tyson?

  I like that analogy, it's a good one.

• 11:02Speaker 02

  In the past, um, there was a class of pulsating stars called Cepheid variables, uh, that have this wonderful property that they tell us whether they're a very luminous lighthouse or a not very luminous lighthouse, depending on how frequently they pulsate. And they're about a hundred thousand times the luminosity of the sun. So the big advantage is if you want to measure far, you better have a very powerful lighthouse. So they were good for a while, but we had to go out much further.

• 11:28Paul Mecurio?

  That's the second, that's the second rung of the distance ladder, right?

• 11:31Neil deGrasse Tyson?

  Yeah, I think so. It is. It's the third one after the Home Depot.

• 11:35Speaker 02

  That's right.

• 11:37Neil deGrasse Tyson?

  So, you said something. Important there. It a hundred thousand times brighter than the sun, which means the sun at those distances, we would just never even see it.

• 11:46Speaker 02

  Right, right.

• 11:47Neil deGrasse Tyson?

  It's not useful.

• 11:48Speaker 02

  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.

• 12:02Paul Mecurio?

  And for me, explain, uh, the standard candle and that my understanding is that we don't really know what that luminosity is.

• 12:10Speaker 02

  So a standard candle is any object whose luminosity is uniform. So when we see a standard candle and it's uniform, when it appears dim, that tells us it's far away.

• 12:21Paul Mecurio?

  Right. And we know that they're, we know why they're uniform. That's been determined.

• 12:25Speaker 02

  Correct. We know, we, we have, we start out with very good theoretical understanding and then ultimately we have empirical understanding which shows us that. So by the 1990s, these Cepheid 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, uh, this requires us to go back billions of light years.

• 12:52Paul Mecurio?

  So it's like when you're a kid, you, you shoot up one summer, Neil's like.

• 12:56Neil deGrasse Tyson?

  In height.

• 12:57Paul Mecurio?

  Four, yes.

• 12:59Neil deGrasse Tyson?

  Or shoot up, it, I don't know. It's you.

• 13:02Speaker 02

  I don't know what you are doing.

• 13:02Neil deGrasse Tyson?

  No, no, no, you, I don't know how, what kind of.

• 13:05Paul Mecurio?

  I'm from the streets, everybody. I grew up on the streets.

• 13:09Speaker 02

  No, you shoot up in height, like in one summer.

• 13:12Paul Mecurio?

  You go from four nine to five nine, but then as you get older, it progresses slowly. So that's sort of the idea here. I- in very rudimentary terms, when you're going back in the early stages of the universe, you're looking.

• 13:23Speaker 02

  You're going back to the younger.

• 13:24Paul Mecurio?

  The younger, where the expansion is faster.

• 13:27Neil deGrasse Tyson?

  No, we don't know that yet.

• 13:28Paul Mecurio?

  Well, it could be.

• 13:29Neil deGrasse Tyson?

  It could be slower.

• 13:30Speaker 02

  Right. So let's not jump the gun. So, so, so by the late 1990s, we had known about supernovae, gosh, going back to the, you know, ancient Chinese, a star would suddenly appear where you had saw nothing. And, uh, we came to realize that these are exploding stars that are billions of times the luminosity of the sun.

• 13:46Neil deGrasse Tyson?

  In fact, the very word supernova, nova means new in Latin. And so a really bright new thing called supernova, and only we would later learn that the star dying at the end of its life.

• 13:58Speaker 02

  Right.

• 13:58Paul Mecurio?

  My wife calls me a supernova.

• 14:01Neil deGrasse Tyson?

  I don't know how to feel about that, but uh, anyway. He's still in therapy, we'll let him.

• 14:07Speaker 02

  I didn't mean to look in 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 at its core, and producing energy was the way it 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.

• 14:51Neil deGrasse Tyson?

  So they're not as reliable as a standard candle.

• 14:54Speaker 02

  So it's not gonna be a good standard candle.

• 14:55Neil deGrasse Tyson?

  Not a standard candle.

• 14:56Speaker 02

  But it's not a good standard candle. And then we realized 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 1A 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, because of quantum mechanics, really. And it can only be stable up to a certain mass known as the Chandrasekhar limit, after the famous Indian astrophysicist Chandrasekhar. Yes, yes.

• 15:37Speaker 02

  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 the, a white dwarf star, it's sitting there, it's, it's less massive than this Chandrasekhar limit, maybe it's in the mass of our sun.

• 15:53Neil deGrasse Tyson?

  And minding its own business at this point.

• 15:55Speaker 02

  Yeah, 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

• 16:18Paul Mecurio?

  How the mass transfers is not clear.

• 16:20Speaker 02

  Exactly, whether it's like they actually merged, or it was a gradual process.

• 16:24Paul Mecurio?

  I just say something between Einstein and you guys, you seem to leave a lot of stuff off to the side. We're not sure, but we'll just go whatever.

• 16:30Neil deGrasse Tyson?

  Well, because he's after the consequence of what happened.

• 16:33Speaker 02

  That's correct, that'll be clear in a minute, okay? So, anyway, so somehow mass transfers over, and when it reaches that Chandrasekhar 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, it has a certain chemical fingerprint.

• 16:59Paul Mecurio?

  And this was observable within the Milky Way, because that was a distance that we could observe this, or we

• 17:04Speaker 02

  Oh, we could observe these beyond, we could observe these at some of the most distant galaxies.

• 17:08Paul Mecurio?

  Because of the telescopes.

• 17:09Speaker 02

  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, you know, a month later, you know, what turned out to be, oh, so unlikely to happen, is like guaranteed to happen. It's like winning the lottery because you buy all the lottery tickets, right?

• 17:44Speaker 03

  Hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie, because we listen to StarTalk every night and support StarTalk on Patreon.

• 17:54Neil deGrasse Tyson?

  This is StarTalk with Neil deGrasse Tyson.

• 18:09Neil deGrasse Tyson?

  And you began this in graduate school, if I remember correctly.

• 18:12Speaker 02

  Correct, yes.

• 18:12Neil deGrasse Tyson?

  And that whole group.

• 18:13Speaker 02

  That whole group, yes.

• 18:14Neil deGrasse Tyson?

  Who's the head guy on that group?

• 18:16Speaker 02

  Brian Schmidt and Bob Kirshner.

• 18:18Neil deGrasse Tyson?

  Bob Kirshner, right.

• 18:19Speaker 02

  And the Chilean group for the Calantololo, which you know very well.

• 18:22Neil deGrasse Tyson?

  Right, right.

• 18:23Speaker 02

  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.

• 18:47Neil deGrasse Tyson?

  Right, so you didn't have to wait around for one to show up and then look at it.

• 18:50Speaker 02

  Right.

• 18:50Neil deGrasse Tyson?

  You would like, we're gonna find three supernovae tonight.

• 18:53Speaker 02

  Right, right. And it was actually quite amazing because back in the day, when the Hubble Space 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 supernova is on Tuesday, so you could start observing it Thursday. And they were like, you're gonna what? Like, you're gonna tell us where a supernova is on Tuesday? And we're like, maybe Monday night if the computer's operating fast enough.

• 19:17Paul Mecurio?

  And they're like, you know, I got a dinner, can we hold that off?

• 19:20Speaker 02

  But it was, you know, if we had bad weather or 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.

• 19:31Paul Mecurio?

  Right.

• 19:31Neil deGrasse Tyson?

  This type 1A supernovae are visible halfway across the universe.

• 19:36Speaker 02

  That's right.

• 19:37Neil deGrasse Tyson?

  But they're only useful as a standard candle once you can calibrate those that are closer, that have some overlap maybe with the Cepheids, is that right?

• 19:44Speaker 02

  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 number?

• 20:04Neil deGrasse Tyson?

  So that basically divides out.

• 20:05Speaker 02

  It divides out.

• 20:06Paul Mecurio?

  It's like, Neil is handsome, but relative to me, not so much.

• 20:11Speaker 02

  Okay. So, yeah.

• 20:13Neil deGrasse Tyson?

  I'd forgotten that's a.

• 20:14Speaker 02

  Important, that's very important. So the two, the two stories we're going to tell disconnect in that way.

• 20:19Neil deGrasse Tyson?

  Yeah.

• 20:19Speaker 02

  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, you know, 10 times further away than this one, whatever the true luminosity.

• 20:37Paul Mecurio?

  But you've got an history or an experience.

• 20:39Neil deGrasse Tyson?

  So you've got a whole string of pearls.

• 20:42Paul Mecurio?

  Right.

• 20:43Neil deGrasse Tyson?

  Through time.

• 20:44Paul Mecurio?

  That's right.

• 20:44Neil deGrasse Tyson?

  And space.

• 20:45Paul Mecurio?

  So that was like you're a super sleuth in a way. It's like you're a detective, sort of, using evidence. But within the distance ladder, you have these three rungs. And what strikes me is.

• 20:53Neil deGrasse Tyson?

  Four rungs.

• 20:53Paul Mecurio?

  Four rungs, sorry. You have, right.

• 20:55Speaker 02

  But this is, to be clear, this entire discovery of the accelerating universe only depended on one rung internally to itself.

• 21:02Neil deGrasse Tyson?

  Yes.

• 21:03Paul Mecurio?

  But if a Cepheid is, I've sort of got a, you know, okay, so if dust affects its brightness, right?

• 21:07Speaker 02

  That's important.

• 21:08Paul Mecurio?

  So now, that rung is sort of, uh, there's, 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.

• 21:23Speaker 02

  Yeah.

• 21:23Paul Mecurio?

  One rung of the ladder could then sort of throw off the entire calculation.

• 21:26Neil deGrasse Tyson?

  Or even dust in your, even in your relative comparisons, the dust would give you the wrong distance.

• 21:32Speaker 02

  Right. So when I was a graduate student, this was the, the part of my thesis was to figure out how to contend with dust um, in these type of new 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, uh, but it also looks redder.

• 21:59Paul Mecurio?

  So if you're seeing the red, then you know that's, there must be dust.

• 22:03Speaker 02

  Exactly.

• 22:03Paul Mecurio?

  But then, but then how do you determine how much dust?

• 22:06Speaker 02

  You look at some supernovae 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.

• 22:13Paul Mecurio?

  So the power of the red.

• 22:15Neil deGrasse Tyson?

  Against the dust.

• 22:15Paul Mecurio?

  The redder, the redder it is, the more dust.

• 22:17Speaker 02

  Right. 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 that, and then. That affects how much difference it is in distance.

• 22:26Paul Mecurio?

  It's like that you that you're sort of you you're getting these pieces of evidence and building. That's fascinating to me.

• 22:33Neil deGrasse Tyson?

  So much science happens that way. People think it's just one question and one answer and one experiment.

• 22:37Speaker 02

  Techniques, lots of techniques.

• 22:39Neil deGrasse Tyson?

  Oh, my gosh.

• 22:39Paul Mecurio?

  So much. Well, what's striking me in all of what you do, not so much Neil, but you, um, is, uh, you hit a roadblock and find a way around it.

• 22:49Speaker 02

  Right. Yeah, no, it's all solving problems.

• 22:51Neil deGrasse Tyson?

  We need clever people.

• 22:52Paul Mecurio?

  Yeah, exactly.

• 22:53Neil deGrasse Tyson?

  On the team.

• 22:54Paul Mecurio?

  It's fascinating.

• 22:54Neil deGrasse Tyson?

  Okay, so now, if I remember correctly, the goal wasn't so much to measure this Einstein term, was it?

• 23:04Speaker 02

  No idea. No, it wasn't even on my radar screen.

• 23:07Neil deGrasse Tyson?

  It was just to lay it out. It's just to see what's going on.

• 23:09Speaker 02

  It was just to measure how much the expansion was slowing.

• 23:12Neil deGrasse Tyson?

  Okay.

• 23:13Speaker 02

  Right? And was it slowing enough?

• 23:14Neil deGrasse Tyson?

  Tell me about your equations.

• 23:15Speaker 02

  Yeah, yeah, yeah.

• 23:16Neil deGrasse Tyson?

  Tell me what you you you wrote stuff.

• 23:18Speaker 02

  I wrote stuff down. Yes, yeah.

• 23:21Neil deGrasse Tyson?

  Okay.

• 23:21Speaker 02

  So I wrote down some standard equations of what should have worked for the data, which is, uh,

• 23:26Neil deGrasse Tyson?

  As anyone would know, just so I want you to know.

• 23:28Paul Mecurio?

  And you thought you were thinking it was slowing down the expansion.

• 23:31Speaker 02

  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, was 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.

• 23:50Paul Mecurio?

  And then and then apply that to our universe and extrapolate.

• 23:53Speaker 02

  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 recollaps. If it's less than one, it will expand forever. Omega M equal one is called a critical universe, or the critical, it's it's the the mass that that it's the gravity that the and mass that the Earth would have to have.

• 24:14Paul Mecurio?

  So is this?

• 24:15Speaker 02

  To launch a rocket and have it be escape velocity.

• 24:17Paul Mecurio?

  So is this the big freeze, the big rip and the big crunch?

• 24:20Speaker 02

  No, we'll get to that.

• 24:20Paul Mecurio?

  Okay.

• 24:21Speaker 02

  We'll get to that.

• 24:22Paul Mecurio?

  Well, can you catch up? Because I'm really working on it.

• 24:24Neil deGrasse Tyson?

  We're going too slow for you, so I had a very.

• 24:26Paul Mecurio?

  Guys, I got stuff to do. There's a supernova happening in an hour.

• 24:29Speaker 02

  Yeah, that's a good point. You've been listening. So so there's a very simple sequence here is supernova measure 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. And so you give them very simple instructions, measure deceleration, turn it 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, unmattered. Now it's negative. And I'm like, that isn't

• 25:13Speaker 02

  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.

• 25:30Neil deGrasse Tyson?

  Bada bing.

• 25:31Paul Mecurio?

  Yeah, and you've got it's not just expanding, but it's accelerating in its expansion.

• 25:36Speaker 02

  Correct.

• 25:36Paul Mecurio?

  And now it's Y, and that gets you to dark energy.

• 25:39Speaker 02

  Right. And so what is it? So, you know,

• 25:41Neil deGrasse Tyson?

  Yeah, you you you made them you made the measurement that it exists.

• 25:46Speaker 02

  Right.

• 25:47Neil deGrasse Tyson?

  Which is a separate thing.

• 25:49Speaker 02

  Absolutely.

• 25:49Neil deGrasse Tyson?

  From knowing what it is.

• 25:50Speaker 02

  From the interpretation. Yeah.

• 25:52Neil deGrasse Tyson?

  Right.

• 25:52Speaker 02

  And just to mention.

• 25:54Neil deGrasse Tyson?

  Just people need to that needs to sink in here because.

• 25:57Speaker 02

  The universe is accelerating, whatever's doing it.

• 25:59Neil deGrasse Tyson?

  Yeah, we can make measurements of things, even if we don't know what's causing it.

• 26:03Paul Mecurio?

  Well, this one, it's the how the some of the greatest things happen. It's you you're you're going for A and then you find B. And and and this is going to sound, you know, as a writer in a 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 in black segment came about at the Daily Show.

• 26:29Neil deGrasse Tyson?

  With Louis Black.

• 26:30Paul Mecurio?

  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. So like, give it to him and let him rant. So it's the same. It's 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.

• 26:46Speaker 02

  But it's also the thing that 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? You know, 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.

• 27:04Neil deGrasse Tyson?

  Get back to work, dude.

• 27:05Speaker 02

  Yeah.

• 27:06Paul Mecurio?

  Yeah, well, I'm.

• 27:06Speaker 02

  What are you doing here?

• 27:07Neil deGrasse Tyson?

  Yeah, you made the discovery. Now I expect part two of this.

• 27:11Speaker 02

  Oh, yeah. Well, actually, you know, there's something in my pocket. What? I've been sitting on it. What? It's bothering me. You ever get like a pebble? What? And you're like sitting and it's like, oh, yeah. Wow.

• 27:24Paul Mecurio?

  Wow.

• 27:25Speaker 02

  Wait a minute.

• 27:26Paul Mecurio?

  There you go.

• 27:27Speaker 02

  Wait a minute.

• 27:28Paul Mecurio?

  Wow. Did you buy that on the street?

• 27:29Speaker 02

  Wait, wait, yeah, I know. It's in the gift shop downstairs. I got a guy. Don't bite it, because it's chocolate. Who's got bling that's bigger than this. At the club.

• 27:39Paul Mecurio?

  Hanging out with the.

• 27:40Speaker 02

  So just. Wait, wait, wait, wait, wait. They didn't give us the Nobel Prize for discovering dark energy, but for discovering that the expansion is accelerating.

• 27:47Paul Mecurio?

  Yeah, right.

• 27:47Speaker 02

  Right, right.

• 27:48Paul Mecurio?

  That's why if it would be bigger, if you, it was more significant.

• 27:51Speaker 02

  It would be like double the prize.

• 27:52Paul Mecurio?

  It's just a little discovery, so they give you the baby. This is the baby Nobel Prize.

• 27:56Speaker 02

  That's right.

• 27:56Paul Mecurio?

  I'm sorry.

• 27:57Speaker 02

  So this, I guess that's Alfred Nobel on the cover. Yes, it is. On the cover there. There's a funny story about Brian Schmidt taking his on the airplane and the, um, the TSA agents were very confused because when they x-rayed his backpack, it just showed up as a hole in his backpack because the gold. It doesn't go through. Absorbed all the x-rays. It doesn't go through at all. What is in your backpack? And he was like, he took it out and they go, what is that? And they said, he says, it's a Nobel Prize. They said, who gave that to you? He said, the king of Sweden. What did he give it to you for? For discovering the expansion, accelerating expansion of the universe? They were deadpan. Right.

• 28:31Paul Mecurio?

  So basically, this guy's discovered the, you wouldn't be here if I, I wouldn't be talking to you right now.

• 28:37Speaker 02

  Very cool. Is this actually gold? Yeah. Or is it gold like?

• 28:40Paul Mecurio?

  Let me touch it.

• 28:41Speaker 02

  Well, it's more, it's, I don't know, was 18 karat or something. 18 karat. I know it's worth a lot today. He gave it to me. It's, it's worth a lot today. Have you seen the price of gold? Yeah, we have 4,000. I'm worried walking out on the street with this.

• 28:52Paul Mecurio?

  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 in your pocket.

• 28:59Speaker 02

  I hear people are nice here.

• 29:02Speaker 02

  So then it doesn't come with a, a thing around your neck like, like, like the swimmer, you know?

• 29:07Paul Mecurio?

  Yes, like, oh, uh, uh, it's Mark Spitz. We had seven of them.

• 29:10Speaker 02

  I'm gonna stay modern here.

• 29:13Paul Mecurio?

  No, I'm going with Mark Spitz.

• 29:14Speaker 02

  Michael Phelps.

• 29:15Paul Mecurio?

  I was a swimmer. Michael Phelps.

• 29:16Speaker 02

  Michael Phelps.

• 29:17Paul Mecurio?

  This is heavy.

• 29:18Speaker 02

  Yeah, so it's probably got at least a little.

• 29:20Paul Mecurio?

  This is no, this is Nobel.

• 29:21Speaker 02

  Let's figure out how much gold.

• 29:22Neil deGrasse Tyson?

  Was actually in it.

• 29:23Speaker 02

  And Neil, where did the gold come from that was in it?

• 29:25Neil deGrasse Tyson?

  Oh, supernovae.

• 29:27Speaker 02

  Oh.

• 29:28Neil deGrasse Tyson?

  Oh, my God. It's all coming full circle.

• 29:31Speaker 02

  Full circle. They said, in fact, yeah, they said, we want to give you something that really represents the work you did. And they were just like, let's find a supernova by Tuesday. There you go. And we'll make something.

• 29:45Paul Mecurio?

  Listen, I know a guy that can melt that down into a watch if you want. That's beautiful.

• 29:49Neil deGrasse Tyson?

  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 Swedish.

• 30:03Speaker 02

  Right, right.

• 30:04Neil deGrasse Tyson?

  Pharmaceutical companies.

• 30:05Speaker 02

  Teddy Roosevelt.

• 30:06Neil deGrasse Tyson?

  In the park. And it's in honor of all the American Nobel Prize winners. And my boy's name is on that statue.

• 30:11Speaker 02

  They're all carved.

• 30:12Neil deGrasse Tyson?

  Chiseled, chiseled in.

• 30:14Speaker 02

  Yeah.

• 30:15Neil deGrasse Tyson?

  My boy's on that statue, right there near the dog run.

• 30:19Speaker 02

  Are you saying dogs watch it as they poop?

• 30:21Neil deGrasse Tyson?

  Did it pee?

• 30:22Paul Mecurio?

  So what, we live on 79th, you're right around the corner from here. My dog pees on your name.

• 30:26Speaker 02

  Really?

• 30:26Paul Mecurio?

  I'm sorry.

• 30:27Speaker 02

  No, my name is actually pretty high up. We would have to.

• 30:30Paul Mecurio?

  I have a very big dog. My dog is well endowed, that's all I'm saying, he can reach high.

• 30:35Neil deGrasse Tyson?

  Okay, so say what you said again, because it's important. You, you got this.

• 30:38Speaker 02

  Right.

• 30:38Neil deGrasse Tyson?

  Not for knowing what dark energy is.

• 30:41Speaker 02

  Right.

• 30:42Neil deGrasse Tyson?

  But for the discovery that it exists.

• 30:44Speaker 02

  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.

• 30:55Neil deGrasse Tyson?

  Doesn't do that.

• 30:56Speaker 02

  It goes the other direction.

• 30:57Neil deGrasse Tyson?

  It goes the other direction. Head to your negative sign that showed up in your.

• 30:59Speaker 02

  It's like having a car and like all you've ever done is hit the brake. And then one day the car just takes off and you're like, how did the brake do that? And it's like, no, a different pedal, the gas pedal did that.

• 31:09Paul Mecurio?

  And I think you've started to move toward the, the idea that.

• 31:13Speaker 02

  Dark energy determines the fate of our universe, right? And that's where it becomes, which makes you a real Debbie Downer. Uh, but there's big freeze, there's, right? There's big rip and there's big crunch.

• 31:26Neil deGrasse Tyson?

  Yeah.

• 31:26Speaker 02

  Which actually feels like Ben and Jerry's, Ben and Jerry's anxiety flavors. It's like, you would be the big freeze because you're closed off emotionally. I, you would be the big rip, you're strong, and I'd be the big crunch because I'm a baby. Uh, and everything collapses.

• 31:40Neil deGrasse Tyson?

  The big crunch, I think, is not in the cards.

• 31:42Speaker 02

  Actually, everything's on the table still, to be honest with you. And yeah, in light of some more recent results on dark energy where it may look like it's thawing or weakening.

• 31:49Neil deGrasse Tyson?

  Well, let's get into that.

• 31:50Speaker 02

  We will.

• 31:51Neil deGrasse Tyson?

  Let's get into that, Mike, right now.

• 32:15Neil deGrasse Tyson?

  We're all up to speed now.

• 32:16Speaker 02

  Yes.

• 32:17Neil deGrasse Tyson?

  And we have like three minutes left.

• 32:19Speaker 02

  Yeah, so the universe is accelerating and we have a new model of the universe, which goes by the sexy name Lambda CDM.

• 32:27Neil deGrasse Tyson?

  Okay.

• 32:27Speaker 02

  Which encompasses everything we know about the universe. The Lambda part means there's dark energy.

• 32:33Neil deGrasse Tyson?

  This is the astrophysicist version of a standard model.

• 32:35Speaker 02

  Correct.

• 32:36Neil deGrasse Tyson?

  I guess, okay.

• 32:37Speaker 02

  Right, and the CDM part is called 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.

• 32:57Neil deGrasse Tyson?

  That's the dark matter and dark energy combined.

• 32:59Speaker 02

  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 left over 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 uh fine grained information about the state of the universe and.

• 33:31Paul Mecurio?

  Excess radiation for lack of a better term?

• 33:33Speaker 02

  Uh yeah, no, but it's a it's a description of what the early soup of the universe looked like. Whether how much were baryons, normal matter, how much was dark matter, photons.

• 33:44Neil deGrasse Tyson?

  A really important snapshot of what was going on.

• 33:46Speaker 02

  And so the 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. This 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 uh 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 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. It would be like, you know, having a two-year-old kid, you measure their height, right?

• 34:30Speaker 02

  And you predict how tall they'll become and then you measure them when they get to that full height. And what if it was off by like a foot or something?

• 34:35Paul Mecurio?

  Right, you'd disown the kid.

• 34:37Speaker 02

  Yeah.

• 34:38Paul Mecurio?

  You're disappointed.

• 34:39Neil deGrasse Tyson?

  He's still he's still in family therapy.

• 34:41Speaker 02

  Yeah, I understand. The fact that these two routes from the early or late side of the universe, on the one hand, tell us the same rough uh more than rough story.

• 34:51Neil deGrasse Tyson?

  Basic story.

• 34:52Speaker 02

  Yeah, like they're like doppelganger universes, except one is younger and expanding faster and one is older and expanding more slowly.

• 35:01Paul Mecurio?

  That's the seventy-one and the sixty-seven.

• 35:03Speaker 02

  Seventy-three and sixty-seven.

• 35:05Paul Mecurio?

  Explain that to the folks.

• 35:05Neil deGrasse Tyson?

  The numerical values of the Hubble constant.

• 35:08Speaker 02

  And this Hubble tension emerged about ten years ago.

• 35:12Neil deGrasse Tyson?

  Tension as in the two numbers are not agreeing.

• 35:14Speaker 02

  As in the two numbers are not agreeing.

• 35:16Neil deGrasse Tyson?

  Now I have to butt in. I'm in graduate school and we're fighting over whether the Hubble constant is fifty or a hundred. And so you're telling me you're now fighting over whether it's sixty-seven and seventy-two, whatever. And I I don't I don't have sympathy for that.

• 35:30Speaker 02

  No, no, no.

• 35:31Neil deGrasse Tyson?

  My whole time in graduate school, we didn't know the size of the universe by a factor of two. And you're up to complaining about a few percent.

• 35:38Speaker 02

  So now.

• 35:39Neil deGrasse Tyson?

  Get out of here.

• 35:39Speaker 02

  Let me let me.

• 35:41Paul Mecurio?

  Leave your Nobel prize.

• 35:43Speaker 02

  Let me tell you why this is so much more interesting than that was.

• 35:47Neil deGrasse Tyson?

  Okay, please.

• 35:48Speaker 02

  When people were measuring fifty or a hundred, they were measuring the same thing. They were measuring how fast the universe is expanding here today, often measuring the distance to the same galaxies, the same stars.

• 35:59Paul Mecurio?

  When you say here, when you say here today, you mean within the Milky Way.

• 36:01Speaker 02

  Right, right.

• 36:02Neil deGrasse Tyson?

  Or just outside the Milky Way. A region, a part of the universe.

• 36:05Speaker 02

  So, you know, so if I, if I told you the length of this table is such and such, 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.

• 36:32Paul Mecurio?

  And when you say profound about the universe, our understanding of physics and the possibility that there could be new physics out there.

• 36:37Speaker 02

  Right, because how do I go from the early universe to the late universe? I need a, I need a function, I need a, 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, then they're an adult. How did you guess how tall they would be? Well, you had a growth chart, right? A growth chart is our model of the universe.

• 36:56Neil deGrasse Tyson?

  It's a formula.

• 36:56Speaker 02

  But, you know, with a growth chart for a kid.

• 36:58Paul Mecurio?

  But it's not precise.

• 36:59Speaker 02

  Well, you've seen a lot of kids grow up, right? So you, you have 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.

• 37:06Neil deGrasse Tyson?

  We'll get another universe then.

• 37:08Paul Mecurio?

  Well, so, or work a little harder, right?

• 37:11Speaker 02

  So, you know, the fact that they disagree, and Neil makes a good point. It's, it's not a big disagreement in absolute sense, it's like nine percent. But our measurements have gotten so precise that it's five or six times the error bar between.

• 37:25Neil deGrasse Tyson?

  I've banned the term error bar, because no one knows what the hell that means.

• 37:28Speaker 02

  Okay.

• 37:28Neil deGrasse Tyson?

  The uncertainty.

• 37:29Speaker 02

  Sure.

• 37:30Neil deGrasse Tyson?

  The, the measurement of the uncertainty of each of those two, two quantities does not leave room for overlap.

• 37:37Speaker 02

  That's right.

• 37:37Neil deGrasse Tyson?

  Okay, there you go.

• 37:38Paul Mecurio?

  So, from someone who's not as bright as. Well, you, him, I'm saying, but no, could it be that dark, I mean, this means that dark energy is shifting? Like, sort of like a petulant 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?

• 37:59Speaker 02

  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. We 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.

• 38:22Neil deGrasse Tyson?

  By the way, it was called inflation because the idea was advanced in the 1970s when we had like 18% inflation.

• 38:31Neil deGrasse Tyson?

  The word was had a lot of currency.

• 38:33Paul Mecurio?

  I didn't know that, now, right?

• 38:34Neil deGrasse Tyson?

  Yes, it was under President Carter and inflation was like 20% inflation.

• 38:38Paul Mecurio?

  The wind button, win with inflation now, right?

• 38:41Speaker 02

  But we have, so we have other, we have things, something in physics that's an 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 invisible energy 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 10.

• 39:25Paul Mecurio?

  Is that the, 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?

• 39:34Speaker 02

  Yeah, so there's an early dark energy theory which posits a third episode of dark energy, not inflation, that was the beginning, not the current one.

• 39:43Paul Mecurio?

  Is that the turbo boost one, or is it something different?

• 39:46Speaker 02

  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 a kick 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.

• 39:59Neil deGrasse Tyson?

  Doesn't it have to be motivated to manifest itself? And so what would manifest a pulse of dark energy in a place unexpected?

• 40:09Speaker 02

  Right, it usually ties to a particle and it usually ties to some event, 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, la la la la la. 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. 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.

• 40:46Neil deGrasse Tyson?

  Alright, so...

• 40:46Speaker 02

  I'm an observer, so I, this is not, you know, I look at stuff.

• 40:49Neil deGrasse Tyson?

  Is there a way to reconcile this without having to invoke another tooth fairy?

• 40:55Speaker 02

  Yes.

• 40:56Neil deGrasse Tyson?

  You invoke Santa Claus?

• 40:57Speaker 02

  Exactly.

• 41:01Speaker 02

  Well, first of all, there are a lot of ideas.

• 41:04Paul Mecurio?

  He needs better gifts.

• 41:04Speaker 02

  Yeah. One way to play the game is to change the, the way the universe looked before the, this radiation from the big bang leaks out.

• 41:12Paul Mecurio?

  How do you change the way it looks?

• 41:14Neil deGrasse Tyson?

  To change our understanding.

• 41:15Speaker 02

  Yeah, our understanding.

• 41:16Neil deGrasse Tyson?

  We're not changing it. What do you think we, with God?

• 41:19Speaker 02

  It's a, it's a kind of a plasma soup. And so even something as subtle as saying if there was a magnetic field in it, that could start this process of collapsing by grabbing...

• 41:30Paul Mecurio?

  Or there could be new particles.

• 41:31Speaker 02

  There could be a new particle, that is absolutely another possibility. It, 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...

• 42:04Speaker 02

  Mind of its own.

• 42:05Neil deGrasse Tyson?

  Right, so you have your option to either make the early universe match the current universe, or the current universe

• 42:10Speaker 02

  Exactly.

• 42:10Neil deGrasse Tyson?

  Match the other, or have them

• 42:11Speaker 02

  That's exactly right.

• 42:12Neil deGrasse Tyson?

  Do something both

• 42:13Speaker 02

  Right.

• 42:13Neil deGrasse Tyson?

  That can meet in the middle.

• 42:14Speaker 02

  That's exactly right.

• 42:15Neil deGrasse Tyson?

  Okay, so how uncertain are the nearby measurements? Seems to me those should be pretty secure.

• 42:21Speaker 02

  Yeah, so I would say now, after, you know, ten years of scrutiny, they're pretty darned good. What I can tell you is, you know, 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 the, your first little bike when you were a kid, and then like, somebody gives you a ten-speed, and you're like, "Oh my god", and you're like, doing laps around what you did. So I've been doing laps around the, the work that I've been doing over the last few years, and the images are pristine, the measurements are textbook, but the answer's the same. And so, the fact that James Webb is confirming what Hubble is confirming, is confirming that this is a real problem.

• 43:02Neil deGrasse Tyson?

  And that deserves, I gotta emphasize this, because what he just said is, you can make measurements with whatever precision your equipment allows.

• 43:12Speaker 02

  Right.

• 43:13Neil deGrasse Tyson?

  And then you extract from that an answer in the din of cosmic noise. You say, "It's kinda saying this. If you have better data, and you get the same answer",

• 43:22Speaker 02

  Right.

• 43:23Neil deGrasse Tyson?

  You, you good.

• 43:24Speaker 02

  That's right. And the signal to noise is ten times higher for the measurement I'm making with James Webb, than it was for Hubble. So if you get a full order of magnitude improvement, and nothing changes, that's very compelling.

• 43:35Paul Mecurio?

  So for those at home, and 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.

• 43:59Speaker 02

  I'm gonna say, or some subtlety, something being lost in translation between the, the universe we see, and how we transform it to these sort of mathematical models. Like, 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.

• 44:20Neil deGrasse Tyson?

  All right, let me go back a hundred and thirty years.

• 44:22Speaker 02

  Yes.

• 44:23Neil deGrasse Tyson?

  I think.

• 44:23Speaker 02

  That's you living in the past. Go ahead. When I was a kid.

• 44:29Neil deGrasse Tyson?

  Go back then.

• 44:29Speaker 02

  Yeah, let's go back.

• 44:30Neil deGrasse Tyson?

  We were riding high on classical physics.

• 44:33Speaker 02

  Yes.

• 44:33Neil deGrasse Tyson?

  And people said, look, there's not much left to discover in the universe.

• 44:37Speaker 02

  Right.

• 44:37Neil deGrasse Tyson?

  We got this. We got Newton.

• 44:39Speaker 02

  It's all done.

• 44:39Neil deGrasse Tyson?

  We, we, we got thermodynamics.

• 44:41Speaker 02

  Right.

• 44:41Neil deGrasse Tyson?

  We, we got this. And there're just a few clouds on the horizon.

• 44:45Speaker 02

  Yeah.

• 44:45Neil deGrasse Tyson?

  That.

• 44:46Speaker 02

  The procession of Mercury isn't quite working out right.

• 44:48Neil deGrasse Tyson?

  Yeah, but we'll, we'll solve that.

• 44:50Speaker 02

  Yeah.

• 44:50Neil deGrasse Tyson?

  Soon.

• 44:51Speaker 02

  It's just another planet out there.

• 44:52Neil deGrasse Tyson?

  So, so don't go into physics because.

• 44:54Speaker 02

  Right.

• 44:54Neil deGrasse Tyson?

  It's about to end. Bada bing. Quantum physics.

• 44:58Speaker 02

  Yeah.

• 44:59Neil deGrasse Tyson?

  Comes up and special relativity and general relativity and, and all that came with that.

• 45:04Speaker 02

  Right.

• 45:05Neil deGrasse Tyson?

  Is there something lurking?

• 45:08Speaker 02

  Right.

• 45:08Neil deGrasse Tyson?

  In, in the, in the, in the dark, in the woods.

• 45:12Speaker 02

  Right.

• 45:12Neil deGrasse Tyson?

  That will need a much bigger transformation of our understanding than just meddling in here and there.

• 45:20Speaker 02

  Right. The answer is I don't know, but what I do.

• 45:22Neil deGrasse Tyson?

  Good answer. Good scientist.

• 45:24Speaker 02

  But, but I do know. I was hoping for an answer. I gotta be honest with you. I do know the process. I don't wanna die soon. Here's the process.

• 45:33Neil deGrasse Tyson?

  Yeah.

• 45:33Speaker 02

  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. Uh, you know, 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.

• 46:00Neil deGrasse Tyson?

  It's like holding back the water in a dike.

• 46:03Speaker 02

  Right.

• 46:03Neil deGrasse Tyson?

  Right. You'd say, you just plug this hole. Did that work?

• 46:06Speaker 02

  Yeah, it's a little whack a mole. Right. And when somebody comes along, I'll say Einstein in 1916, right? Uh, he comes up with a brilliant reimagine, reimagination of physics, which first does something very important. It explains or fits everything we already knew. You can't go and lose that, right? And then all these puzzles get solved. He, 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, uh, its orbit is itself rotating very slowly around the sun, um, unlike the other planets. And nobody knew why. They thought maybe there was another planet between Mercury and the sun. Einstein shows.

• 46:51Neil deGrasse Tyson?

  Called Vulcan.

• 46:52Speaker 02

  Cause it would be hot.

• 46:53Neil deGrasse Tyson?

  Called Vulcan.

• 46:54Speaker 02

  Hmm.

• 46:55Neil deGrasse Tyson?

  We just invented, we were perfectly happy to say, it's Vulcan is there.

• 46:58Speaker 02

  Yeah.

• 46:59Neil deGrasse Tyson?

  We can't see it.

• 46:59Speaker 02

  But it.

• 47:00Neil deGrasse Tyson?

  Too close to the sun, it's beginning to glare.

• 47:01Speaker 02

  This was 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.

• 47:12Paul Mecurio?

  Right.

• 47:13Speaker 02

  And why you can't just play the game like you're studying history and gonna predict what's gonna happen.

• 47:17Paul Mecurio?

  Right.

• 47:17Speaker 02

  Sometimes the planet misbehaves because there's some stuff out there you missed. 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 know, you pull it and sometimes it was just that annoying thread and that's fine, or sometimes it unravels the sweater and it's just, it's hard to say.

• 48:00Paul Mecurio?

  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. And why is there another Allen wrench? Like, and so you literally.

• 48:23Speaker 02

  Well, I 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.

• 48:37Neil deGrasse Tyson?

  So that's specifically tuned for dark energy, is that correct?

• 48:40Speaker 02

  It's gonna be particularly good with dark energy.

• 48:42Neil deGrasse Tyson?

  Okay, so, so, yeah, so we just, it's not just another telescope.

• 48:45Speaker 02

  Right.

• 48:45Neil deGrasse Tyson?

  We got smart people figuring, we got this problem, let's design it to address that problem.

• 48:50Paul Mecurio?

  But I'm gonna ask, you both consider 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?

• 48:59Speaker 02

  So I was actually on this panel called the Decadal Survey that once every decade recommends what to build next. And this was 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 you're building, or the techniques change? So we designed the telescope to measure the current techniques best that could be done, but also recognize 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 is very bright.

• 49:40Paul Mecurio?

  Define near infrared.

• 49:41Speaker 02

  Near infrared are wavelengths that are redder than red, so longer wavelengths than that.

• 49:47Neil deGrasse Tyson?

  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, sits adjacent to red, orange, yellow, green, blue, violet. It's adjacent to that. And those wavelengths that are near, this is what we call those near, and then far, that's all. It's not deeper than that.

• 50:10Speaker 02

  So, so we both build 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.

• 50:29Paul Mecurio?

  Got it.

• 50:29Neil deGrasse Tyson?

  Very important here because that's why, why build something that only can see what you're looking for or expect. The breadth of those capabilities, that's what advances the field.

• 50:42Paul Mecurio?

  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 a minute ago, around that, new discoveries are being made, new equations are being calculated, right? So it's, It must be maddening because there's never a firm like, yeah, this is this is it.

• 51:05Speaker 02

  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.

• 51:15Neil deGrasse Tyson?

  Exactly, they're not even interesting anymore.

• 51:17Speaker 02

  Yeah, the story, I mean, we were all like, um, how much matter is in the universe and is it going to recollaps and that isn't even the right.

• 51:24Neil deGrasse Tyson?

  One of our colleagues wrote a book called Just Three Questions or something, or it 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 undreamt of today. That's the question I'm thinking of.

• 51:54Speaker 02

  And then 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, it's such a, a, a great laboratory. Cosmology used to be considered closer to philosophy than physics and now.

• 52:09Neil deGrasse Tyson?

  There's hardly any data.

• 52:10Speaker 02

  Right, right. We knew the universe was expanding, we knew there was radiation left over from the big bang, we knew the sky was dark at night, that was about it.

• 52:18Neil deGrasse Tyson?

  There's several people thinking about this tension.

• 52:21Speaker 02

  Yes.

• 52:21Neil deGrasse Tyson?

  You're not the lone wolf in this. So do you guys, are you converging at any point?

• 52:27Speaker 02

  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 will study dark energy. We have the Vera Rubin Telescope, she was the discoverer of dark matter, one of them. Um, and that is a massive ground-based telescope that will cover most of the sky every three or four days.

• 52:49Paul Mecurio?

  Yeah, I don't see that one working.

• 52:50Speaker 02

  A million supernovae, that one is already working. Um, and.

• 52:54Paul Mecurio?

  That'd contradict me all the time.

• 52:55Neil deGrasse Tyson?

  It's already online, it's discovered thousands of asteroids that were not even cataloged.

• 52:58Speaker 02

  Well, no one told me. We have new CMB experiments, the Simons Observatory, um, we have, uh, LIGO is just still getting up and going and has great capability. Uh, we have, we expect new results from Gaia. Um, so there are a lot of facilities that really are well poised to give us answers.

• 53:18Neil deGrasse Tyson?

  So but is there like a fight out there? Is there a cage match among you guys?

• 53:22Speaker 02

  Right, so um I would say five or 10 years ago, the the folks from the CMB particularly were like, "Well, you local people are probably wrong because um it used to be 50 or 100 and you know, "that that seems like hard stuff, okay?" 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, okay? So uh 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. Um and though they have replicated the cosmic microwave background measurements,

• 54:04Speaker 02

  actually, they've even pushed the Hubble constant lower, not 67, but 66.

• 54:08Neil deGrasse Tyson?

  Are these uh observatories in Antarctica?

• 54:11Speaker 02

  Yeah, one's at the South Pole, it's a South Pole telescope, and the other one's in uh the Atacama in Chile.

• 54:16Neil deGrasse Tyson?

  Okay.

• 54:17Speaker 02

  Um and so you need very little water.

• 54:18Neil deGrasse Tyson?

  It's one of the driest places on Earth, the Atacama, as is Antarctica. It's one of the driest places on Earth.

• 54:23Speaker 02

  And then nearby, we have seen uh 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-

• 54:47Neil deGrasse Tyson?

  This network, great name for that, because you, it all has to work together.

• 54:50Speaker 02

  Correct, correct. It's not just 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.

• 55:00Neil deGrasse Tyson?

  It reminds me of this stupid comic where the the Transcontinental Railroad, and there's the Golden Spike, which is the last bike.

• 55:06Speaker 02

  Right.

• 55:06Neil deGrasse Tyson?

  And and the railroads come, and the tracks don't match up.

• 55:12Speaker 02

  Well, that is the problem. Hey, they're down there. I told you we were wrong. Right, right. So 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?

• 55:32Paul Mecurio?

  At one point you said, I think the universe is giving us a lesson in cosmic humility. It doesn't seem to be following the manual we had.

• 55:39Neil deGrasse Tyson?

  Yeah.

• 55:39Paul Mecurio?

  We can rule out a measurement error as a cause of the Hubble tension with very high confidence.

• 55:44Neil deGrasse Tyson?

  Yes.

• 55:44Paul Mecurio?

  There's some people out there that would sort of say, perhaps not, and then.

• 55:48Neil deGrasse Tyson?

  Well, are you a groupie? You're quoting him from some other program? We have him here.

• 55:52Paul Mecurio?

  He doesn't know what he says.

• 55:56Speaker 02

  Let me define error. Do you ever watch baseball?

• 55:59Paul Mecurio?

  Oh, yeah.

• 56:00Speaker 02

  You know, baseball?

• 56:00Paul Mecurio?

  Yeah, yeah.

• 56:01Speaker 02

  So, so Aaron.

• 56:02Neil deGrasse Tyson?

  This is America. What do you think you are?

• 56:03Paul Mecurio?

  There's a quarterback, there's a wide receiver.

• 56:06Speaker 02

  No, yeah. So, I like baseball that they define an error as there was something that was supposed to be done. You know, you're supposed to field a 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.

• 56:26Paul Mecurio?

  Right.

• 56:27Speaker 02

  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.

• 56:37Paul Mecurio?

  In terms of measurements and stuff.

• 56:39Speaker 02

  Everybody appears to be following the manual carefully. Everybody appears to be measuring what they said they're measured. Uh, 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.

• 56:56Neil deGrasse Tyson?

  None of the drawers.

• 56:57Speaker 02

  Yeah.

• 56:57Neil deGrasse Tyson?

  In the drawer.

• 56:57Paul Mecurio?

  You guys are freaks. This guy's walking around with a piece of metal in his pocket. You got stuff in your drawers.

• 57:04Speaker 02

  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.

• 57:09Paul Mecurio?

  I'm sorry, back up on the 5000.

• 57:11Neil deGrasse Tyson?

  So, I can verify that and I don't have to think that, I don't have to just take his word for it.

• 57:15Paul Mecurio?

  No, I understand, but back in the day, what do you mean there were secretly? You were not, you were not publicly revealed?

• 57:21Speaker 02

  If you were Hubble, 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.

• 57:30Neil deGrasse Tyson?

  There was no Intranet.

• 57:30Speaker 02

  And you told people what it said.

• 57:32Neil deGrasse Tyson?

  Yes.

• 57:33Paul Mecurio?

  But there were lectures about it and so forth.

• 57:35Neil deGrasse Tyson?

  No, but no, no one else had access to your data.

• 57:38Speaker 02

  Right.

• 57:38Neil deGrasse Tyson?

  Now, everything is digital.

• 57:40Speaker 02

  Right.

• 57:40Neil deGrasse Tyson?

  And it's.

• 57:42Paul Mecurio?

  The point being, you've got a lot of people cross checking and checking and double checking.

• 57:45Speaker 02

  And this has been the democratization of science.

• 57:48Neil deGrasse Tyson?

  Very important.

• 57:48Speaker 02

  Of these facilities. And so what I will say is, in the past, when errors are made, and errors absolutely happen, the baseball kind of errors, our community is so good at jumping on those, right, that 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.

• 58:12Neil deGrasse Tyson?

  And you want to also watch out for whether there's group think. And if multiple teams who are otherwise competitors find agreement in what your measurements are, that's a good place to be.

• 58:24Speaker 02

  Like, there were two, two groups last, 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, the more traditional groups that were working. And so, the more you see these groups that are independent.

• 58:43Neil deGrasse Tyson?

  They value the Hubble.

• 58:45Speaker 02

  That's correct.

• 58:46Paul Mecurio?

  Does the 74, 75 versus vis a vis 72, 70, does that trouble you?

• 58:51Neil deGrasse Tyson?

  No, no, it's down with the 60.

• 58:52Speaker 02

  Yeah, yeah, yeah. No, right. I mean, it's, look, the full range of measurements people make locally is about 70 to 75. And so that's normal. That's kind of a bell curve distribution. So, people, you know, the middle is probably around 73, but some people get 75 and some get 70. But, the point is.

• 59:08Neil deGrasse Tyson?

  And you expect that in any random distribution.

• 59:10Speaker 02

  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.

• 59:20Paul Mecurio?

  There is this theorist, Thomas Burkett, and sort of has another explanation for all of this. And I wanted to get your thoughts on that.

• 59:27Speaker 02

  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, 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. And 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's sort of. Uh, on an island about this, uh, the, they're devilishly difficult calculations to do analytically.

• 1:00:10Speaker 02

  So people have done it numerically with computers where you just kind of trace a particle and you have to go through all this. And people who do that say they don't get what he gets this way, but I'm open to it. Look, I mean, if, if things are not fitting, you have to be open to a lot of possibilities.

• 1:00:25Neil deGrasse Tyson?

  Yeah, yeah, the more things don't fit and the longer you're in that state, the kind of more, you know, you, you say, oh, who's got?

• 1:00:33Paul Mecurio?

  What do you got?

• 1:00:33Neil deGrasse Tyson?

  Yeah, what do you got?

• 1:00:34Speaker 02

  Yeah, yeah, I mean, like, for example, when we discovered dark energy, there was, uh, something called the age crisis. Where, uh, there were stars that appeared to be older than the age of the universe. And that was a problem and, uh, 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.

• 1:01:17Neil deGrasse Tyson?

  Adam, I don't know if you're a betting man, but what would you bet would be the solution to this?

• 1:01:23Speaker 02

  I wouldn't bet and the reason is because

• 1:01:26Neil deGrasse Tyson?

  That's not fun.

• 1:01:27Speaker 02

  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.

• 1:01:36Paul Mecurio?

  You can't fix the game a little bit?

• 1:01:38Speaker 02

  I mean, you know, that would be the problem.

• 1:01:39Neil deGrasse Tyson?

  If you're umpire, you can, you can.

• 1:01:42Speaker 02

  I mean, I will say, this is an unusual game. This is not.

• 1:01:45Paul Mecurio?

  Finger on the scale is, uh, the mafia likes to do.

• 1:01:48Speaker 02

  And so I, you know, my bet is that there's something interesting going on, but what it specifically is, I don't know.

• 1:01:54Neil deGrasse Tyson?

  Okay.

• 1:01:54Paul Mecurio?

  But it's like, we've got two thermometers. You're taking my temperature and 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.

• 1:02:04Speaker 02

  I would say you're sick.

• 1:02:07Paul Mecurio?

  I'm willing to go and say that. You're sick. You would be a terrible doctor.

• 1:02:12Neil deGrasse Tyson?

  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 gotta 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

• 1:02:49Neil deGrasse Tyson?

  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. You 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

• 1:03:32Neil deGrasse Tyson?

  epicycle thing, that kind of matched the data." And so now, what did they do? They said, "Let's check the model." So they checked 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

• 1:04:13Neil deGrasse Tyson?

  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...

• 1:04:33Neil deGrasse Tyson?

  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 in trouble. I think it's pretty secure. If I'm betting, I'm betting we're gonna have the Big Bang throughout this. But we're gonna 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?

• 1:05:14Neil deGrasse Tyson?

  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. And that is a cosmic perspective. Adam, has it been a delight to have you come through town?

• 1:05:46Paul Mecurio?

  Thank you.

• 1:05:47Neil deGrasse Tyson?

  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.

• 1:05:53Paul Mecurio?

  My sister lives here.

• 1:05:54Neil deGrasse Tyson?

  Oh, there's an excuse.

• 1:05:55Paul Mecurio?

  Shout out to her.

• 1:05:56Neil deGrasse Tyson?

  Shout out to your sister. And let that be an excuse we can exploit going forward to get you back here and catch up on whatever's the latest thinking.

• 1:06:06Paul Mecurio?

  Can I have your prize? I want to show it to my son. I'll give it back to you, I promise. Is he here? He's under my seat.

• 1:06:14Neil deGrasse Tyson?

  Dude, thanks for coming through.

• 1:06:15Paul Mecurio?

  Absolutely. This is so fascinating. I learned a lot and honored to meet you. Excellent. Yeah, great.

• 1:06:21Neil deGrasse Tyson?

  All right, this has been StarTalk. Neil deGrasse Tyson here, your personal astrophysicist. As always, keep looking up.