Origins of Dark Energy with Adam Riess

Summary

StarTalk Radio
Episode: "Origins of Dark Energy" with Adam Riess
Host: Neil deGrasse Tyson
Guest: Adam Riess, Nobel Laureate Astrophysicist
Co-host: Paul Mercurio
Date: December 16, 2025

---

Episode Overview

This episode of StarTalk dives into the enigmatic concept of dark energy—the mysterious force driving the accelerated expansion of the universe. Neil deGrasse Tyson is joined by comedian Paul Mercurio and Nobel Prize-winning astrophysicist Adam Riess, whose groundbreaking work unveiled this cosmic puzzle. Together, they trace the scientific journey that led to the discovery of accelerated expansion, explore the ongoing “Hubble tension” debate, and discuss how new telescopes may further revolutionize our understanding. The tone is witty, curious, and occasionally irreverent, making complex topics lively and accessible.

---

Key Discussion Points & Insights

1. Setting the Stage: Why Dark Energy Matters

• Tyson and Mercurio kick off with light banter, agreeing that cosmology’s “cutting edge” is where real scientific friction (and breakthroughs) happen.
• Adam Riess is introduced as a Bloomberg Distinguished Professor at Johns Hopkins and Nobel Laureate for the discovery of the universe’s accelerating expansion.
  • Notable Quote [05:52] - Adam Riess: "You are co-discoverer of a cause... we always knew that there was this term in Einstein's equation... But no one had a negative. What is that?"

---

2. History and Discovery of Accelerating Expansion

• Einstein’s “cosmological constant” and its dismissal after the universe’s expansion was discovered by Hubble (the man, not yet the telescope).
• By the 1990s, the big question: Is there enough matter (regular or dark) to slow or halt the expansion?
• Riess’ team—using “standard candles” (Type Ia supernovae)—measured the rate of expansion across time.
  • Making Distance Measurements: From geometry (parallax) to Cepheid variables, to supernovae as the ultimate cosmological “mile markers.”
  • Notable Analogy [12:17] - Adam Riess: "If you're a ship captain…a lighthouse, which you know is very luminous, looks very faint, and assures you, wow, I have to be far away."
• The breakthrough was realizing Type Ia supernovae are remarkably consistent and visible at cosmological distances.
  • Notable Quote [16:52] - Adam Riess: "...when it reaches that Chandrasekhar limit, it's like boom. A thermonuclear explosion runs through the star...So this is a standard candle...It has a certain spectrum, it has a certain chemical fingerprint."

---

3. The Accelerating Universe and "Dark Energy" ([20:41] – [30:30])

• The team expected to measure how much the universe’s expansion was slowing due to gravity. Instead, they found it was accelerating!
  • Discovery Process:
    • They input data, expecting it to show deceleration, but got nonsensical results (negative mass)—until considering Einstein’s cosmological constant again.
    • Notable Moment [27:39] - Adam Riess: "The answer it spit back was negative mass...And I was like, that isn't right. ...And then...Einstein once had suggested something that could go the other way. You put that into the equations and it like, fit like a glove."
• Dark Energy: The catch-all term for whatever causes this repulsive effect—still not understood at a fundamental level.
  • Quote [29:33] - Adam Riess: "...the universe is accelerating, there's no question about that. But what is causing it? ...we don't understand the physics of that at all."

---

4. Measurement Techniques and Challenges

• Cepheids and Supernovae: Building the "distance ladder" is fraught with challenges—effects of dust, calibrations, and the need for ever-brighter standard candles.
  • Dust Correction Insight [24:13] - Adam Riess: "...dust makes things dimmer, which would fool you into thinking it's further away...But it does something else too. It makes light look redder when the light passes through."
• Only by resolving these could astronomers confidently measure cosmic acceleration.

---

5. The Hubble Tension & the Quest for New Physics ([36:16] – [47:58])

• Lambda-CDM Model: The prevailing cosmological model assumes cold dark matter and a cosmological constant (dark energy), but 96% of the universe remains “unknown stuff.”
• Hubble Constant Discrepancy:
  • Measurements of the universe’s expansion today (“local” methods) don’t match predictions from the cosmic microwave background (“early” methods)—a disagreement called the Hubble tension.
  • Notable Quote [39:49] - Adam Riess: "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..."
• Is Dark Energy Changing?
  • Riess discusses models where dark energy wasn’t always constant—potential “early dark energy” episodes could have given the universe extra “kicks.”
    • Quote [42:00] - Adam Riess: "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."
  • Other explanations: unseen particles, theoretical changes to gravity, or subtle errors in fundamental assumptions.

---

6. New Tools and the Road Ahead

• Upcoming and current observatories (James Webb, Nancy Grace Roman Telescope, Vera Rubin Observatory, Simons Observatory, LIGO, Gaia) will enable sharper measurements and possibly solve the Hubble tension.
  • Measurement Confidence [46:22] - Adam Riess: "...the fact that James Webb is confirming what Hubble is confirming is confirming that this is a real problem."

---

7. The Scientific Process and Cosmic Humility

• Tyson and Riess reflect on historical moments when unexpected data forced paradigm shifts (Newton to Einstein, Copernicus’ heliocentric model, discovery of planet Neptune, etc.).
  • Notable Quote [52:24] - Adam Riess: "We're not done because everything isn't fitting...we have this wealth of new facilities...that really should help us answer these questions."
  • Tyson’s Perspective [66:12]: "One of the more fascinating dimensions, the moving frontier of science, is when you don't have an answer to questions that have been posed..."

---

Notable Quotes & Memorable Moments

• Adam Riess [05:52]: "You are co-discoverer of a cause... we always knew that there was this term in Einstein's equation... But no one had a negative. What is that?"
• Adam Riess [16:52]: "...when it reaches that Chandrasekhar limit, it's like boom. A thermonuclear explosion runs through the star...a standard candle..."
• Adam Riess [27:39]: "...The answer it spit back was negative mass...And then...Einstein once had suggested something...You put that into the equations and it like, fit like a glove."
• Adam Riess [29:33]: "...the universe is accelerating, there's no question about that. But what is causing it?...we don't understand the physics of that at all."
• Adam Riess [39:49]: "We are measuring opposite ends of the universe, and...disagreeing in this case has the potential to teach us something profound about the universe..."
• Adam Riess [42:00]: "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."
• Neil deGrasse Tyson [66:12]: "...when you don't have an answer...you got to scratch your head and say, do I have to give up some prior expectations...?"
• Paul Mercurio throughout: Provides comic relief, analogies, and the “audience” perspective—grounding the theoretical in relatable terms.

---

Timestamps for Key Segments

• Discovery & Nobel Prize context: [03:31] to [07:12]
• Distance measurements & standard candles: [09:12] to [14:39]
• Type Ia supernovae breakthrough: [15:01] to [18:23]
• Cosmic acceleration discovery & significance: [22:04] to [29:33]
• Dark energy & fate of the universe: [33:31] to [34:36]
• Modern cosmology, Lambda-CDM model: [36:20] to [37:00]
• Hubble tension explained: [39:09] to [41:37]
• Potential resolutions/new physics: [41:38] to [44:46]
• New telescopes & future prospects: [54:29] to [56:49]
• Scientific humility & history: [48:20] to [51:02]

---

Final Thoughts

The episode balances history, humor, and groundbreaking science. It highlights the process of scientific discovery—not as a straight path, but a winding road with surprises, wrong turns, and paradigm shifts. The Hubble tension is framed as an opportunity for breakthrough, not just a problem.

As Riess puts it, science is still assembling the universe “using IKEA instructions”—and dark energy (whatever it is) is that mysterious, leftover part that won’t fit. The search continues.

Listen if you:

• Want a lucid, entertaining account of how astronomers discovered the universe is accelerating
• Are curious how “dark energy” went from Einstein’s math folly to a real cosmic mystery
• Are interested in why scientists are hopeful (and humble) about coming breakthroughs in cosmology

---

Closing Quote [66:12] - Neil deGrasse Tyson:
“One of the more fascinating dimensions, 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... 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?... 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.”

Transcript

[Neil deGrasse Tyson]

Go from sceptic to electric in the new Toyota BZ.

[Adam Riess]

Hesitant about going all electric OneDrive can change your mind.

[Neil deGrasse Tyson]

With up to an EPA estimated 314.

[Adam Riess]

Mile range rating for front wheel drive.

[Neil deGrasse Tyson]

Models and available all wheel drive models with 338 horsepower, the Toyota BZ is built for confidence. Conveniently charge at home or on the.

[Adam Riess]

Go with access to a wide range.

[Neil deGrasse Tyson]

Of compatible public charging networks including Tesla superchargers. Inside, enjoy a 14 inch touchscreen with an available panoramic view Moonroof. Learn [e-mail] BZ the new all electric BZ Toyota.

[Adam Riess]

Let's go places.

[Neil deGrasse Tyson]

Welcome to Walgreens.

[Adam Riess]

Looking for a holiday gift? Sort of. My cousin Freddie showed up to surprise us. Oh, sounds like a real nice surprise. Exactly. So now I have to get him.

[Paul Mercurio]

A gift, but I haven't gotten my bonus yet.

[Adam Riess]

So if we could make it something.

[Paul Mercurio]

Really nice but also not break the.

[Adam Riess]

Bank, that'd be perfect. How about a keurig for 50% off.

[Neil deGrasse Tyson]

Bingo savings all season? The holiday road is long. We're with you all the way. Walgreens offer valid November 26th through December 27th. Exclusions apply. Welcome to StarTalk, your place in the universe where science and pop culture collide. StarTalk begins right now. This is StarTalk. Neil DeGrasse Tyson, your personal astrophysicist. And I got with me co hosting.

[Paul Mercurio]

What's up?

[Neil deGrasse Tyson]

How you doing, man?

[Paul Mercurio]

I'm good, buddy.

[Neil deGrasse Tyson]

Good to see you. Paul Mercurio.

[Paul Mercurio]

Good to see you again.

[Neil deGrasse Tyson]

Professional comedian. You got your own podcast?

[Paul Mercurio]

Yeah.

[Neil deGrasse Tyson]

Inside out, out and in.

[Paul Mercurio]

There you go.

[Neil deGrasse Tyson]

In and out Burger. Did they sponsor you?

[Paul Mercurio]

Yes. For those listening and watching, this is how not to host the show, have a guest and not know anything about it. Yes. It's called In n Out Burger and the whole podcast is interviewing people in the drive through.

[Neil deGrasse Tyson]

In the drive through window.

[Paul Mercurio]

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

[Neil deGrasse Tyson]

I was. I was.

[Paul Mercurio]

Along with Paul McCartney, by the way.

[Neil deGrasse Tyson]

Oh, no. Okay. All right.

[Paul Mercurio]

What do you mean, okay? That's all you say?

[Neil deGrasse Tyson]

Name dropper. Yes, but none of that impresses me as much. You've got like a Peabody award and an Emmy award. This writing.

[Paul Mercurio]

You writer on the Daily Show? Yeah. And worked on the Colbert Report.

[Neil deGrasse Tyson]

We love you, man.

[Paul Mercurio]

I love you too, man.

[Neil deGrasse Tyson]

Thanks for spending some time with us.

[Paul Mercurio]

Absolutely. Always great making this happen.

[Neil deGrasse Tyson]

You know what 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? And where are people at fisticuffs?

[Paul Mercurio]

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

[Neil deGrasse Tyson]

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

[Paul Mercurio]

Now, I have to say I've been 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.

[Neil deGrasse Tyson]

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 the ideal in this conversation. And we found an old friend and colleague of mine, Adam Reese. Adam, welcome to StarTalk.

[Adam Riess]

Thank you for having me.

[Neil deGrasse Tyson]

Welcome to my office here at the Hayden Planetarium.

[Adam Riess]

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

[Neil deGrasse Tyson]

You were.

[Paul Mercurio]

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

[Neil deGrasse Tyson]

So you're at the Johns Hopkins University. Yeah. You're the Bloomberg Distinguished professor there. Bloomberg. He's a friend of my wife who worked for him. He has a background in physics and engineering and came through Johns Hopkins.

[Adam Riess]

Yes, he did.

[Neil deGrasse Tyson]

And donated a whole building called the Bloomberg center for Physics and Astronomy. Yeah. So there's some good Bloomberg action down there in Baltimore.

[Paul Mercurio]

And 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?

[Neil deGrasse Tyson]

Says the man who does not ride a bicycle.

[Paul Mercurio]

Exactly.

[Neil deGrasse Tyson]

Okay. Many people don't know that. The Space Telescope Science Institute, which was responsible for receiving all the data from Hubble and other telescopes. Spaceborne is co. Located on the campus of Johns Hopkins University. That's right. So you also have a position there as well.

[Adam Riess]

That's right.

[Neil deGrasse Tyson]

That's right.

[Adam Riess]

That's where we have the joystick.

[Paul Mercurio]

Okay, I'm gonna leave that right there.

[Neil deGrasse Tyson]

We have to add that you are a Nobel Laureate.

[Adam Riess]

That's right.

[Neil deGrasse Tyson]

That's badass.

[Paul Mercurio]

Yeah.

[Neil deGrasse Tyson]

And I think if you had a business card, just. You don't need anything else.

[Paul Mercurio]

No phone number?

[Adam Riess]

No phone number.

[Paul Mercurio]

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

[Neil deGrasse Tyson]

So remind me what year you won that.

[Adam Riess]

We won it in 2011.

[Neil deGrasse Tyson]

You won the Nobel Prize, and that year was split three ways. So who were the other two recipients?

[Adam Riess]

Brian Schmidt and Saul Perlmutter.

[Neil deGrasse Tyson]

And Saul, I remember, was a West coast guy. Right, right.

[Adam Riess]

He led the supernova cosmology project.

[Neil deGrasse Tyson]

Okay. With the same intent of making the kind of measurements you were making.

[Adam Riess]

That's right.

[Neil deGrasse Tyson]

With Brian Schmidt.

[Adam Riess]

Right, right.

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

We were members of the high Z supernova team.

[Neil deGrasse Tyson]

High Z would be high redshift.

[Adam Riess]

Correct.

[Neil deGrasse Tyson]

Supernova team. And it was given to you specifically.

[Adam Riess]

For the discovery of the accelerating expansion.

[Neil deGrasse Tyson]

Of the universe, which today we just call dark energy.

[Adam Riess]

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

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

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

[Neil deGrasse Tyson]

Well, get back to work, please. So I'm gonna say welcome to StarTalk.

[Adam Riess]

Thank you.

[Neil deGrasse Tyson]

Yeah.

[Adam Riess]

It's an honor to be here.

[Neil deGrasse Tyson]

Yeah. And so you are co discoverer of a cause. Growing up. I mean, 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?

[Paul Mercurio]

Nobody accounted. But no.

[Adam Riess]

What is.

[Neil deGrasse Tyson]

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?

[Paul Mercurio]

It's expanding at a constant rate, basically.

[Neil deGrasse Tyson]

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

[Paul Mercurio]

Got it.

[Neil deGrasse Tyson]

This would be an extra thing going on. Okay.

[Paul Mercurio]

And you were just too la to explore that?

[Neil 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? Sure.

[Adam Riess]

So, 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.

[Neil deGrasse Tyson]

Otherwise the universe would just collapse on itself. Correct.

[Adam Riess]

Then it would just collapse. 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. And then Hubble the man, Hubble the.

[Neil deGrasse Tyson]

Man, Hubble was a man before he was a telescope.

[Adam Riess]

That's right. It's more like the RoboCop version of.

[Paul Mercurio]

But he would be mistaken for a telescope at a lot of particles, the shape of a body.

[Adam Riess]

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, or once something is possible, it is always there, unless you have evidence that it doesn't exist.

[Neil deGrasse Tyson]

Right. Very important bit of scientific wisdom there.

[Adam Riess]

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

[Neil deGrasse Tyson]

So that was the 1920s.

[Adam Riess]

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, you know, launching a rocket. Does it have escape velocity from the gravity?

[Paul Mercurio]

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

[Adam Riess]

No, this is what we call dark matter. 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, 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.

[Paul Mercurio]

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

[Neil 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, and we have whole galaxies nearby and beyond.

[Adam Riess]

Right.

[Neil deGrasse Tyson]

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

[Adam Riess]

Yeah. So you. Parallax is great. Having a tape measure and running it out somewhere is great, but these just.

[Neil deGrasse Tyson]

Don'T work very well.

[Paul Mercurio]

You can get those at Home Depot.

[Adam Riess]

Yeah, I know, but not one that long.

[Neil 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 can't do radar beaming to them because they're light years away.

[Paul Mercurio]

So you have to use parallax, a form of geometry that had its Limitations because of the angles of the geometry.

[Neil deGrasse Tyson]

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

[Paul Mercurio]

I didn't.

[Neil deGrasse Tyson]

It's pretty good. But that's good. You did good there. 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 then you switch eyes and then your thumb is like moving back and forth.

[Paul Mercurio]

Hang on. I need a manicure.

[Neil deGrasse Tyson]

Jesus.

[Paul Mercurio]

Wait, what am I doing now?

[Neil deGrasse Tyson]

Yeah, yeah. You look at with one eye and 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.

[Paul Mercurio]

Thumb is, which is then used.

[Neil deGrasse Tyson]

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

[Paul Mercurio]

Yes.

[Neil 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 are.

[Paul Mercurio]

Just with my hand, so I don't have to look at you. Well, that works either way.

[Neil deGrasse Tyson]

I'm blotted both way. What are our eyes? How do we do this astronomically? Well, you can take a picture of a star and 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.

[Paul Mercurio]

So now you can measure.

[Neil deGrasse Tyson]

Now you get that and you see how much it varies, you know, 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.

[Adam Riess]

Hubble.

[Paul Mercurio]

And then a web.

[Neil deGrasse Tyson]

Very reliable. No, no, no. It's also 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.

[Adam Riess]

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 know, 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 in the past.

[Neil deGrasse Tyson]

I like that analogy. It's a good one.

[Adam Riess]

In the past, there was a class of pulsating stars called CEPHEID variables 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. How frequently they pulsate. And they're about 100,000 times the luminosity of the Sun. And 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.

[Paul Mercurio]

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

[Adam Riess]

Yeah, I think so.

[Neil deGrasse Tyson]

It's the third run after the Home Depot. That's right. 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.

[Adam Riess]

Right.

[Neil deGrasse Tyson]

It's not natural, right?

[Adam Riess]

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.

[Paul Mercurio]

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

[Adam Riess]

So a standard candle is any object whose. 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, and we know that.

[Paul Mercurio]

We know why they're uniform. That's been correct.

[Adam Riess]

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 this requires us to go back billions of light years.

[Paul Mercurio]

So it's like when you're a kid, you shoot up. One summer, Neil's like, in height for.

[Neil deGrasse Tyson]

Yes or shoot up. I don't know.

[Adam Riess]

I don't know what you are doing.

[Paul Mercurio]

I don't know what you.

[Neil deGrasse Tyson]

I don't know what kind of processor to do.

[Paul Mercurio]

I'm from the streets, everybody. I grew up on the streets. No, you shoot up in height in one side, you go from 4, 9 to 5, 9. But then as you get older, it progresses slowly. So that's sort of the idea here. In very rudimentary terms, when you're going back in the early stages of the.

[Adam Riess]

Universe, you're looking Going back to the younger.

[Paul Mercurio]

The younger, yes. Where the expansion is fast.

[Neil deGrasse Tyson]

No, we don't know that yet.

[Paul Mercurio]

Well, it could be.

[Neil deGrasse Tyson]

It could be slower.

[Adam Riess]

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 we came to realize that these are exploding stars that are billions of times the luminosity of the sun.

[Neil 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 it started dying at the end of its life. Right. Yeah.

[Paul Mercurio]

My wife calls me a supernova dying.

[Adam Riess]

I don't know how to feel about that. But anyway, he's still in therapy.

[Neil deGrasse Tyson]

We'll let him.

[Paul Mercurio]

I didn't mean to look in your eyes when I.

[Adam Riess]

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.

[Neil deGrasse Tyson]

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

[Adam Riess]

So it's not going to be a good standard. Not a standard camera, but it's not a good standard candle. 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 one, 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, really. And it can only be stable up to a certain mass known as the Chandrasekhar limit, after the famous Indian astrophyser, physicist Chandrasekhar.

[Paul Mercurio]

Yes.

[Adam Riess]

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. It's sitting there. It's. It's less massive than this Chandrasekhar limit. Maybe it's in the mass of our.

[Neil deGrasse Tyson]

Sun and minding its own business.

[Adam Riess]

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 too close, we think, and mass starts to transfer over, we think. And the details of exactly how this occurs are debated.

[Paul Mercurio]

But somehow, how the mass transfers are not clear exactly.

[Adam Riess]

Whether it's like they actually merged or it was a gradual process.

[Paul Mercurio]

Can 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.

[Neil deGrasse Tyson]

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

[Adam Riess]

That's correct.

[Paul Mercurio]

That's correct.

[Adam Riess]

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.

[Paul Mercurio]

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

[Adam Riess]

We could observe these. Some of the most distant galaxies because.

[Paul Mercurio]

Of the telescopes, et cetera.

[Adam Riess]

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?

[Neil deGrasse Tyson]

Hey, Fidelity. What's it cost to invest with the Fidelity app?

[Adam Riess]

Start with as little as $1, with no account fees or trade commissions on US stocks and ETFs. Hmm. That's music to my ears.

[Paul Mercurio]

I can only talk.

[Adam Riess]

Investing involves risk, including risk of loss. 0. Account fees apply to retail brokerage accounts, only sell order, assessment fee not include. A limited number of ETFs are subject to a transaction based service fee of $100. See full list of Fidelity.com commissions Fidelity Brokerage Services LLC member NYSE SIPC get a jump on next summer with VRBO's early booking deals don't wait to claim your dream summer spot, whether that includes a good porch swing or a poolside lounger. When you book early, you get the best places at the best prices. But back to the poolside loungers. With VRBox you don't have to reserve any loungers. They're all yours. In fact, the whole private home is yours. Book with early booking deals and you can lounge around all summer long however you [e-mail] hey, Ryan Reynolds here for Mint Mobile.

[Neil deGrasse Tyson]

You know one of the perks about having four kids that you know about is actually getting a direct line to the big man up north. And this year he wants you to.

[Adam Riess]

Know the best gift that you can.

[Neil deGrasse Tyson]

Give someone is the gift of of Mint mobile's unlimited wireless for 15amonth. Now you don't even need to wrap it. Give it a [e-mail] Switch upfront payment.

[Adam Riess]

Of $45 for three month plan equivalent to 15 per month required new customer offer for first three months only. Speed slow after 35 gigabytes if network's busy, taxes and fees extra. C mintmobile.com hi, I'm Ernie Carducci from Columbus, Ohio. I'm here with my son Ernie because we listen to StarTalk every night and support Star Talk on Patreon.

[Neil deGrasse Tyson]

This is Star Talk with Neil Degrass Tyson. And you began this in graduate school.

[Adam Riess]

If I remember correctly.

[Neil deGrasse Tyson]

And that whole group, that whole group with who's the head guy on that group?

[Adam Riess]

Brian Schmidt and Bob Kirschner. The, the Chilean group for the Kalantalolo, which you know very well.

[Neil deGrasse Tyson]

Right.

[Adam Riess]

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.

[Neil deGrasse Tyson]

Right. So you don't have to wait around for one to show up and then look at it.

[Adam Riess]

Right.

[Neil deGrasse Tyson]

You would like we're going to find three supernova tonight.

[Paul Mercurio]

Right?

[Adam Riess]

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 supernova 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 supernova is on Tuesday? And we're like, maybe Monday night, if the computer's operating fast.

[Paul Mercurio]

And then we like, you know, I got a dinner. Can we hold that off?

[Adam Riess]

But it was, you know, if we had bad weather or something, it was scary, too. Cause 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.

[Paul Mercurio]

Right.

[Neil deGrasse Tyson]

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

[Adam Riess]

That's right.

[Neil 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?

[Adam Riess]

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.

[Neil deGrasse Tyson]

It basically divides out.

[Adam Riess]

It divides in there.

[Paul Mercurio]

Neil is Hanson. But relative to me, not so much.

[Adam Riess]

Okay.

[Neil deGrasse Tyson]

I'd forgotten. That's important.

[Adam Riess]

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

[Neil deGrasse Tyson]

Yeah.

[Adam Riess]

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.

[Paul Mercurio]

But you've got. You've got a history or so you.

[Neil deGrasse Tyson]

Got a whole string of pearls through time.

[Paul Mercurio]

That's right.

[Neil deGrasse Tyson]

And space.

[Paul Mercurio]

So that's like your superstition 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.

[Neil deGrasse Tyson]

Four rungs.

[Paul Mercurio]

Four rungs. Sorry, you have.

[Adam Riess]

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

[Paul Mercurio]

But if a Sophia is sort of got a. You know. Okay, so if dust affects its brightness. Right. That's important. 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.

[Adam Riess]

Right.

[Paul Mercurio]

Or other components that could sort of affect one rung of the ladder could then sort of throw off the entire calculation.

[Neil deGrasse Tyson]

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

[Adam Riess]

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 1a 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.

[Paul Mercurio]

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

[Adam Riess]

Exactly.

[Paul Mercurio]

But then how do you determine how much dust?

[Adam Riess]

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.

[Paul Mercurio]

So the power of the red against the dust, the raider, the redder it is, the more dust.

[Adam Riess]

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 amazing.

[Paul Mercurio]

Difference it is like that. You're sort of. You're getting these pieces of evidence and building. That's fascinating to me.

[Neil deGrasse Tyson]

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

[Adam Riess]

Yeah.

[Neil deGrasse Tyson]

Oh, my gosh.

[Adam Riess]

So much.

[Paul Mercurio]

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

[Adam Riess]

Right? Yeah. No, it's all solving problems.

[Neil deGrasse Tyson]

We need clever people.

[Paul Mercurio]

Yeah, exactly.

[Neil deGrasse Tyson]

On the team.

[Paul Mercurio]

It's fascinating.

[Neil deGrasse Tyson]

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

[Adam Riess]

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

[Neil deGrasse Tyson]

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

[Adam Riess]

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

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

Right. And was it slowing about your equations? Yeah, yeah.

[Neil deGrasse Tyson]

Tell me. What.

[Adam Riess]

Yeah, I wrote stuff down. Yes. Yes.

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

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

[Neil deGrasse Tyson]

Anyone would know. Just.

[Paul Mercurio]

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

[Adam Riess]

And not only that, I was so sure it was slowing down because that's what everybody told me and I was in graduation 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.

[Paul Mercurio]

Omega M, and then apply that to.

[Adam Riess]

Our universe and extrapolate 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 re collapse. If it's less than 1, it will expand forever. Omega M =1 is called or a critical universe or the critical. It's the mass, it's the gravity and mass that the earth would have to have to launch a rocket and have it be escape velocity.

[Paul Mercurio]

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

[Adam Riess]

No, we'll get to that. Okay, we'll get to that.

[Paul Mercurio]

So can you catch up because I'm.

[Neil deGrasse Tyson]

Really slow for you. So I had a big.

[Paul Mercurio]

Come on, guys, I got stuff to do. This is supernova happening in an hour.

[Adam Riess]

Yeah, that's a good point. You've been listening. 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.

[Neil deGrasse Tyson]

Okay?

[Adam Riess]

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 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.

[Neil deGrasse Tyson]

Bada bing.

[Adam Riess]

Yeah.

[Paul Mercurio]

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

[Adam Riess]

Correct.

[Paul Mercurio]

And now it's why. And that gets you to dark energy, right?

[Adam Riess]

And so what is it? So, you know.

[Neil deGrasse Tyson]

Yeah. You made the measurement that it exists. Right. Which is a separate thing.

[Adam Riess]

Absolutely.

[Neil deGrasse Tyson]

From knowing what it is.

[Adam Riess]

From the interpretation. Yeah.

[Neil deGrasse Tyson]

Right.

[Adam Riess]

And just to mention, people need to.

[Neil deGrasse Tyson]

That needs to sink in here because.

[Adam Riess]

The universe is accelerating, whatever's doing it.

[Neil deGrasse Tyson]

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

[Paul Mercurio]

Well, it's how some of the greatest things happen. You're going for A, and then you find B. And this is gonna sound. 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 in Black segment came about at the Daily show, because.

[Neil deGrasse Tyson]

With Lewis Black.

[Paul Mercurio]

Yeah. Because we were trying to come up with great jokes on these little stor. He's like a Florida man, and we're like. We don't know what to do with this. Or, like, give it to him and let him rant. 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.

[Adam Riess]

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.

[Neil deGrasse Tyson]

Get back to work, dude.

[Adam Riess]

Yeah, well, I'm. What are you doing here? Yeah.

[Neil deGrasse Tyson]

You made the discovery. Now I expect part two of this.

[Adam Riess]

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

[Paul Mercurio]

Yeah.

[Adam Riess]

And you're, like, sitting, and it's like, oh, yeah. Wow. Wait a minute.

[Paul Mercurio]

There you go.

[Neil deGrasse Tyson]

Wait a minute.

[Paul Mercurio]

Wow. Did you buy that on the street?

[Adam Riess]

Wait, wait. Actually, it's in the gift shop downstairs.

[Neil deGrasse Tyson]

I got a guy.

[Adam Riess]

Don't bite it because it's dark bling.

[Neil deGrasse Tyson]

That's bigger than this at the club.

[Paul Mercurio]

Hey. Hanging out.

[Adam Riess]

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

[Neil deGrasse Tyson]

Yeah, right, right, right.

[Paul Mercurio]

That's why it would be bigger if it was more significant. It's just A little discovery. So they give you the baby. This is the baby Nobel Prize. That's right. I'm sorry.

[Adam Riess]

That's so.

[Neil deGrasse Tyson]

This. I guess that's Alfred Nobel on the COVID there.

[Adam Riess]

There's a funny story about Brian Schmidt taking his on the airplane. And the. 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 absorbed all the X rays.

[Neil deGrasse Tyson]

It doesn't go through what is in your backpack.

[Adam Riess]

And he was like. He took it out and they go, what is that? And they said. He said, 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 accelerating expansion of the universe. They were deadpan.

[Paul Mercurio]

Basically, this guy discovered that you wouldn't be here if I wouldn't be talking to you right now.

[Neil deGrasse Tyson]

Very cool. Is this actually gold?

[Adam Riess]

Yeah.

[Neil deGrasse Tyson]

Was it gold? Like, let me tell you, it's.

[Adam Riess]

I don't know what. It's 18 karat or something.

[Neil deGrasse Tyson]

18 karat?

[Adam Riess]

I know. It's worth a lot.

[Neil deGrasse Tyson]

He gave it to me.

[Adam Riess]

It's worth a lot today. Have you seen the price of gold? I'm worried walking out on the street with this.

[Paul Mercurio]

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.

[Adam Riess]

I hear people are nice here.

[Neil deGrasse Tyson]

So then it doesn't come with a thing around your neck like the swimmer. You know.

[Paul Mercurio]

It'S Mark Spitz.

[Adam Riess]

We had seven.

[Neil deGrasse Tyson]

Stay modern here.

[Paul Mercurio]

No, I'm going with Mark Spitz. I was a swimmer. Michael Phelps.

[Neil deGrasse Tyson]

Michael Phelps.

[Paul Mercurio]

This is heavy.

[Neil deGrasse Tyson]

Yeah. So it's probably got. At least. We gotta give to our Nobel and figure out how much gold is actually in it.

[Adam Riess]

And, Neil, where. Where did the gold come from that was in it? Oh, supernovies.

[Paul Mercurio]

Oh.

[Neil deGrasse Tyson]

Oh, my God.

[Adam Riess]

It's all coming full circle. Full circle. They said. In fact. Yeah. They said, we want to give you something that really represents the work you did. And they was like, let's find a supernova by Tuesday, and we'll get some little bits and we'll make something.

[Paul Mercurio]

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

[Neil 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 pharmaceutical companies in.

[Adam Riess]

The Teddy Roosevelt Park.

[Neil deGrasse Tyson]

In the park. And it's in honor of all the American Nobel Prize win. And my boy's name is on that statue. They're all carved, chiseled in. My boy's on that statue right there near the dog run.

[Adam Riess]

Are you saying dogs watch it as they poop?

[Paul Mercurio]

So what? We live on 79th street, right around the corner from here. My dog pees on your name. Really? I'm sorry.

[Adam Riess]

No, my name is actually pretty high up. You would have to. I have a very big climber.

[Paul Mercurio]

My dog is well endowed. That's all I'm saying. He can reach high.

[Neil deGrasse Tyson]

Okay, so say what you said again because it's important you got this. Not for knowing what dark energy is, but for the discovery that it exists.

[Adam Riess]

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.

[Neil deGrasse Tyson]

Doesn't do that.

[Adam Riess]

It goes the other direction.

[Neil deGrasse Tyson]

It's like that's your negative sign that.

[Adam Riess]

Showed up in your brain. 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 didn't.

[Paul Mercurio]

And I think you've started to. To move toward the idea that dark energy determines the fate of our universe.

[Neil deGrasse Tyson]

Right.

[Paul Mercurio]

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, which actually feels like 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 big. Maybe the big crunch, I think, is.

[Neil deGrasse Tyson]

Not in the cards. Actually.

[Adam Riess]

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.

[Neil deGrasse Tyson]

Well, let's get into that.

[Adam Riess]

We will.

[Neil deGrasse Tyson]

Let's get into that. Mike. Right now. Building a portfolio with Fidelity Basket Portfolios is kind of like making a sandwich. It's as simple as picking your stocks and ETFs, sort of like your meats and other topics and managing it as one big juicy investment. Now that's pretty good. Learn [e-mail] baskets Investing involves risks, including risk of loss.

[Adam Riess]

Fidelity Brokerage service llc. Member nyse SIPC.

[Neil deGrasse Tyson]

Pandora makes it easy for you to find your favorite music.

[Adam Riess]

Discover new artists and genres by selecting any song or album and we'll make you a personalized station for free download on the Apple App store or Google Play and enjoy the soundtrack to your life. Gas gifts tolls this holiday trip is draining my wallet. Yeah, but we'll get to see all our family. You're festive. What's your dad? What's my deal? Holiday savings at Metro. I got one line of 5G for just $25 per month and I kept the phone I love and no activation fees and a five year price guarantee on my talk, text and data detour to Metro. It is get that more for your money feeling only at Metro by T Mobile. It's $30 your first month or without auto pay price guarantee exclusion supply See cipher details.

[Neil deGrasse Tyson]

We're all up to speed now.

[Adam Riess]

Yes.

[Neil deGrasse Tyson]

And we have like three minutes left.

[Adam Riess]

Yeah. So the universe is accelerating and we have a new model of the universe which goes by the sexy name Lambda cdm.

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

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

[Neil deGrasse Tyson]

This is the astrophysicist version of a standard model.

[Adam Riess]

Correct.

[Neil deGrasse Tyson]

I guess. Okay.

[Adam Riess]

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.

[Neil deGrasse Tyson]

96%. That's the dark matter and dark energy combined.

[Adam Riess]

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 WMA map 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.

[Paul Mercurio]

For lack of a better term.

[Adam Riess]

Yeah, no, but 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, a.

[Neil deGrasse Tyson]

Really important snapshot of what was going on.

[Adam Riess]

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. It would be like having a two year old kid. You measure their height 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?

[Paul Mercurio]

You'd say you'd disown the kid.

[Neil deGrasse Tyson]

Yeah.

[Paul Mercurio]

You disappoint.

[Neil deGrasse Tyson]

He's still in family therapy.

[Adam Riess]

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, more than.

[Neil deGrasse Tyson]

Rough story, basic story.

[Adam Riess]

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

[Paul Mercurio]

That's the 71 and the 67.

[Adam Riess]

73.

[Paul Mercurio]

73. You want to explain the numerical values?

[Neil deGrasse Tyson]

That's right.

[Paul Mercurio]

That's right.

[Adam Riess]

And this Hubble tension emerged about 10 years ago.

[Neil deGrasse Tyson]

Tension as in the two numbers are not agreeing.

[Adam Riess]

As in the two numbers are not agreeing.

[Neil deGrasse Tyson]

I have to butt in. I'm in graduate school and we're fighting over whether the Hubble constant is 50 or 100. And so you're telling me you're now fighting over whether it's 67 and 72. Whatever. And I don't have sympathy for that.

[Adam Riess]

No, no, no.

[Neil 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.

[Paul Mercurio]

So now let me leave your Nobel Prize. Let me tell you dinner why this.

[Adam Riess]

Is so much more interesting than that was.

[Neil deGrasse Tyson]

Okay, please.

[Adam Riess]

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 to the same galaxies, the same stars.

[Paul Mercurio]

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

[Adam Riess]

Right, Right.

[Neil deGrasse Tyson]

Or just down region.

[Adam Riess]

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

[Paul Mercurio]

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

[Adam Riess]

Right, 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, then they're an adult. How did you guess how tall they would be? Well, you had a growth chart.

[Neil deGrasse Tyson]

Right?

[Adam Riess]

Growth chart is our model of the universe. It's a formula, but, you know, with a growth chart for a kid.

[Paul Mercurio]

But it's not precise.

[Adam Riess]

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

[Neil deGrasse Tyson]

We'll get another universe.

[Paul Mercurio]

We work a little harder.

[Adam Riess]

So, you know, the fact that they 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 them.

[Neil deGrasse Tyson]

I've banned the term error bar because no one knows what the hell that means. The uncertainty. Sure. The measurement of the uncertainty of each of those two quantities does not leave room for overlap.

[Adam Riess]

That's right.

[Paul Mercurio]

Okay.

[Neil deGrasse Tyson]

Okay. There you go.

[Paul Mercurio]

So from someone who's not as bright as, well, you, him. I'm saying now, could it be 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?

[Neil deGrasse Tyson]

Yes.

[Adam Riess]

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 invoke 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.

[Neil deGrasse Tyson]

Way. It was called inflation because the idea was advanced in the 1970s when we had like 18% inflation. The word was. Had a lot of currency.

[Paul Mercurio]

I didn't know that now, right.

[Neil deGrasse Tyson]

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

[Paul Mercurio]

The wind button, Whip inflation. Now, remember that wind button we have.

[Adam Riess]

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.

[Paul Mercurio]

Is that the new. 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.

[Adam Riess]

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.

[Paul Mercurio]

So is that the turbo boost one or is it some. Something different? Different.

[Adam Riess]

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 two endpoints, you know, you're not going to quite get things right.

[Neil 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?

[Adam Riess]

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.

[Neil deGrasse Tyson]

La, la, la, la.

[Adam Riess]

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. 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.

[Neil deGrasse Tyson]

All right, so I'm an observer.

[Adam Riess]

So this is not, you know, I look at Stuff.

[Neil deGrasse Tyson]

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

[Adam Riess]

Yes.

[Neil deGrasse Tyson]

You invoke Santa Claus.

[Paul Mercurio]

Exactly.

[Adam Riess]

Well, first of all, big fan.

[Neil deGrasse Tyson]

The first.

[Adam Riess]

There are a lot of ideas, 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.

[Paul Mercurio]

So how do you change the way it looks?

[Neil deGrasse Tyson]

So change our understanding of it.

[Adam Riess]

Yeah, our understanding of it.

[Neil deGrasse Tyson]

We're not changing it. What do you think we.

[Adam Riess]

God, 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.

[Paul Mercurio]

Well, there could be new particles in there.

[Adam Riess]

There could be new particles. That is absolutely another possibility. 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.

[Neil deGrasse Tyson]

Right. So you have your option to either make the early universe match the current universe or the current universe match the other, or have them do something both that can match.

[Adam Riess]

That's exactly right.

[Neil deGrasse Tyson]

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

[Adam Riess]

Yeah. So I would say now, after, you know, 10 years of scrutiny, they're pretty darn 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 your first little bike when you were a kid. And then, like, somebody gives you a 10 speed. Oh, my God. 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's the same. And so the fact that James Webb is confirming what Hubble is confirming is confirming that this is a real problem.

[Neil deGrasse Tyson]

I gotta emphasize this because what he just said is you can make measurements with whatever precision your equipment allows. And then you extract from that an answer in the din of cosmic noise. It's kind of saying this. If you have better data and you get the same answer, you Got.

[Adam Riess]

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.

[Paul Mercurio]

So for those at home, 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, maybe there's something about the world of cosmology that we're not understanding, or there's something new, or.

[Adam Riess]

There'S new physics, I'm going to 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.

[Neil deGrasse Tyson]

Let me go back 130 years.

[Adam Riess]

Yes.

[Paul Mercurio]

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

[Neil deGrasse Tyson]

Go back then.

[Adam Riess]

Yeah, let's go back.

[Neil deGrasse Tyson]

We were riding high on classical physics. Yes. And people said, look, there's not much left to discover in the universe. Right?

[Adam Riess]

Yes.

[Neil deGrasse Tyson]

We got this, we got Newton, it's all done. We got thermodynamics, we got this. And there's just a few clouds on the horizon that the procession of Mercury.

[Adam Riess]

Isn'T quite working out.

[Neil deGrasse Tyson]

Yeah, but we'll solve that soon.

[Adam Riess]

It's just another planet out there, brother.

[Neil deGrasse Tyson]

Don't go into physics because it's about to end. Bada bing. Quantum physics comes up and special relativity and general relativity and all that came with that. Is there something lurking in the dark in the woods that will need a much bigger transformation of our understanding than just meddling in here and there?

[Adam Riess]

Right. The answer is, I don't know.

[Neil deGrasse Tyson]

But what I said, that's a good answer. Good scientist.

[Paul Mercurio]

But I do know the process. I was hoping for an answer. I gotta be honest with you.

[Adam Riess]

I do know the process.

[Paul Mercurio]

I don't want to die soon.

[Adam Riess]

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 precession of Mercury is not following Newton's theory. 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 what's going on there. You start to build up these things.

[Neil deGrasse Tyson]

And it's like holding back the water in a dike. Right? Right. You say you just plug this hole. Did that work?

[Adam Riess]

And when somebody comes along, I'll say, Einstein in 1916, right? He comes up with a brilliant reimagined 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. The first thing that Einstein supposedly did after he developed general relativity was he looked back at this precession of Mercury, this problem that Mercury, its 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 chose called Vulcan, because it would be hot.

[Neil deGrasse Tyson]

Called Vulcan. We were perfectly happy to say, Vulcan is there. We can't see it, but it's too close to the sun. It would get in the glare.

[Adam Riess]

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 and why you can't just play the game like you're studying history and gonna predict what's gonna happen. Because sometimes the planet misbehaves. Cause there's some stuff out there you missed. And sometimes it misbehaves. Cause we have the wrong understanding of physics. And in that case, Einstein showed that his theory would explain Mercury's precession. Because Mercury was living so close to the sun, it was in what we call the strong gravity regiment, 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, right?

[Paul Mercurio]

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 assem. 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.

[Adam Riess]

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.

[Neil deGrasse Tyson]

So that's specifically tuned for dark energy. Is that correct?

[Adam Riess]

It's going to be particularly good with dark energy.

[Neil deGrasse Tyson]

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

[Adam Riess]

Right.

[Neil deGrasse Tyson]

We got smart people figuring we got this problem, let's design.

[Paul Mercurio]

But I'm going to ask that 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?

[Adam Riess]

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, 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 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.

[Paul Mercurio]

Define near infrared.

[Adam Riess]

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

[Neil deGrasse Tyson]

But it's near. It sits closer to the visible spectrum than the far infrared.

[Paul Mercurio]

Got it.

[Neil deGrasse Tyson]

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

[Adam Riess]

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 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.

[Neil deGrasse Tyson]

Got it very important here. Because 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.

[Paul Mercurio]

But what has to feel at times overwhelming to you is it's a constant moving target.

[Adam Riess]

Right.

[Paul Mercurio]

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 must be maddening because there's never a firm like, yeah, this is, this is.

[Adam Riess]

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. Exactly.

[Neil deGrasse Tyson]

They're not even interesting anymore.

[Adam Riess]

Yeah. The story, I mean, we were all like, how much matter is in the universe and is it gonna re. Collapse? And that isn't even the right thing.

[Neil 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 wanna 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, 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.

[Adam Riess]

In our field of cosmology. Right. Used to jokingly be said that we only had two and a half facts in cosmology. So we have so much more information. It's such a great laboratory. Cosmology used to be considered closer to philosophy than physics.

[Neil deGrasse Tyson]

And now there's hardly any data.

[Adam Riess]

Right?

[Neil deGrasse Tyson]

Right.

[Adam Riess]

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.

[Neil deGrasse Tyson]

There's several people thinking about this tension. Yes. You're not the lone wolf in this. So do you guys. Are you converging at any point?

[Adam Riess]

So we have a fleet of new observatories coming online. We have the Nancy Grace Roman telescope built by NASA to launch next year, specializing, we 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.

[Paul Mercurio]

I don't see that one working.

[Adam Riess]

Million supernovae. That one is already working and contradict.

[Paul Mercurio]

Me all the time.

[Neil deGrasse Tyson]

Discovered thousands of asteroids that were not even.

[Paul Mercurio]

Well, no one told me.

[Adam Riess]

We have new CMB experiments, the Simons 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.

[Neil deGrasse Tyson]

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

[Adam Riess]

Right. So I would say five or 10 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.

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

And maybe some of us were like, Planck 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 from the cosmic microwave background, we've had these great high resolution CMB experiments like ACT and SPT1's Princeton mostly, one is more at Chicago. And they have replicated the cosmic microwave background measurements. Actually they've even push the Hubble Constant Lower. Not 67, but 66.

[Neil deGrasse Tyson]

Are these observatories in Antarctica?

[Adam Riess]

Yeah, one's at the South Pole, right. At the South Pole telescope, and the other one's in the Atacama in Chile. Okay. And so you need very little water.

[Neil deGrasse Tyson]

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

[Adam Riess]

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 that we're.

[Neil deGrasse Tyson]

A great name for that because it all has to work together.

[Adam Riess]

Correct?

[Neil deGrasse Tyson]

Correct.

[Adam Riess]

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.

[Neil deGrasse Tyson]

It reminds me of 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.

[Adam Riess]

Well, that is the problem.

[Neil deGrasse Tyson]

Hey, they're down there.

[Paul Mercurio]

I told you we were wrong.

[Neil deGrasse Tyson]

Right.

[Adam Riess]

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.

[Paul Mercurio]

Has your position altered at all? 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. We can rule out a measurement error as a cause of the Hubble tension. With very high confidence.

[Adam Riess]

Yes.

[Paul Mercurio]

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

[Neil deGrasse Tyson]

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

[Paul Mercurio]

He doesn't know what he was. He doesn't know. Half the time he doesn't know what he says.

[Adam Riess]

Let me, let me define error. Do you, do you ever watch baseball?

[Paul Mercurio]

Oh, yeah.

[Adam Riess]

You know baseball?

[Paul Mercurio]

Yeah.

[Adam Riess]

Yeah. So. So, Aaron America.

[Neil deGrasse Tyson]

What do you think you are? Aaron?

[Paul Mercurio]

Quarterback. There's a wide receiver.

[Neil deGrasse Tyson]

No.

[Adam Riess]

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 feel the ground ball and you messed up.

[Neil deGrasse Tyson]

Right.

[Adam Riess]

And it didn't happen. And they score that as an error.

[Neil deGrasse Tyson]

Okay.

[Adam Riess]

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 stuff, everybody appears, 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.

[Neil deGrasse Tyson]

You were like, none of the drawers. Yeah.

[Paul Mercurio]

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

[Adam Riess]

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.

[Neil deGrasse Tyson]

It's right there.

[Paul Mercurio]

I'm sorry, back up on the 1500.

[Neil deGrasse Tyson]

So I can verify that. And I don't have to think that. I don't have to just take his words.

[Paul Mercurio]

No, I understand. But back in the day, what do you mean? There were secret. You were not. You were not publicly.

[Adam Riess]

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 and you told people what it said.

[Paul Mercurio]

Yes, but there were lectures about it and so forth.

[Neil deGrasse Tyson]

No, but no one else had access to your data. Right now everything is digital. And it's.

[Paul Mercurio]

The point being you've got a lot.

[Adam Riess]

Of people Cross checking the democratization of science 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.

[Neil deGrasse Tyson]

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

[Adam Riess]

Like there were two groups in the last couple 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. And so the more you see these groups that are independent.

[Neil deGrasse Tyson]

The Hubble, the value of the Hubble.

[Paul Mercurio]

Yeah, this is 7475 versus vis a vis 72, 70. Does that trouble you?

[Neil deGrasse Tyson]

No, no, it stays down with the 60.

[Paul Mercurio]

Yeah, no, right.

[Adam Riess]

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, why expect that.

[Neil deGrasse Tyson]

In any random distribution?

[Adam Riess]

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.

[Paul Mercurio]

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

[Adam Riess]

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 it through the same amount of matter smoothly distributed. And I know a lot of people disagree with him. He's sort of of on an island about this. They're devilishly difficult calculations to do analytically. So people have done it numerically with computers where you just kind of trace a particle and you have it 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 things are not fitting, you have to be open to a lot of possibilities.

[Neil deGrasse Tyson]

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

[Paul Mercurio]

What do you got?

[Adam Riess]

Yeah, 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. 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.

[Neil deGrasse Tyson]

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

[Adam Riess]

I wouldn't bet. And the reason is because that's not 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.

[Paul Mercurio]

Fix the game a little bit.

[Adam Riess]

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

[Neil deGrasse Tyson]

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

[Adam Riess]

Is an unusual game. This is not finger on the scale.

[Paul Mercurio]

As the mafia likes to.

[Adam Riess]

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

[Paul Mercurio]

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.

[Adam Riess]

I would say you're sick. I'm willing to go and say that you're sick.

[Paul Mercurio]

You would be a terrible doctor.

[Neil deGrasse Tyson]

One of the more fascinating dimensions, 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. 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 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? We just throw it all away way. 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. 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 in 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 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? Missing pieces, 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, it's been a delight to have you come through town.

[Adam Riess]

Thank you.

[Neil 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. My sister lives here.

[Adam Riess]

Shout out to her.

[Neil deGrasse Tyson]

There's the excuse.

[Adam Riess]

Shout out to her.

[Neil 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. Sounds great. On whatever is the latest thinking.

[Paul Mercurio]

Can I have your prize? I want to show it to my son. I'll give it back to you, I promise.

[Adam Riess]

Is he here?

[Paul Mercurio]

He's under my seat.

[Neil deGrasse Tyson]

Dude, thanks for.

[Paul Mercurio]

Absolutely. So fascinating. I learned a lot and honored to meet you. Seriously.

[Adam Riess]

Excellent.

[Paul Mercurio]

Great, Great.

[Neil deGrasse Tyson]

All right. This has been startalk. Neil DeGrasse Tyson here, your personal astrophysicist. As always, keep looking up.

[Adam Riess]

Introducing Fidelity Trader plus, the next generation of advanced trading from Fidelity.

[Paul Mercurio]

Customize your tools and charts and access.

[Adam Riess]

Them seamlessly across desktop, web and mobile. For faster trades anywhere you go, try the all new Fidelity Trader plus plus. Learn more about our most powerful trading platform [e-mail] TraderPlus investing involves risk, including risk of loss. Fidelity Brokerage Services, llc. Member NYSE SIPC With Venmo Stash, a.

[Neil deGrasse Tyson]

Tag on one hand and ordering a.

[Adam Riess]

Ride in the other means you're stacking.

[Neil deGrasse Tyson]

Cash back With Venmo Stash, get up.

[Adam Riess]

To 5% cash back when you pick a bundle of your favorite brands.

[Neil deGrasse Tyson]

Earn more cash when you do more with Stash.

[Adam Riess]

Venmo Stash terms and exclusions apply. Max $100 cash back per month.

[Neil deGrasse Tyson]

See terms of Venmo Me Stashterms.