Solving the Crisis in Cosmology with Wendy Freedman

Summary

Podcast Summary

Podcast: StarTalk Radio
Episode: Solving the Crisis in Cosmology with Wendy Freedman
Date: September 23, 2025
Host: Neil deGrasse Tyson
Guest: Dr. Wendy Freedman (University of Chicago, National Medal of Science honoree)
Co-host: Matt Kirshen

---

Overview

This episode explores the so-called "Crisis in Cosmology," focusing on the ongoing debate in astronomy over measurements of the universe’s expansion rate—a phenomenon known as the “Hubble tension.” Dr. Wendy Freedman, a leading expert in cosmological distance measurements and recent recipient of the National Medal of Science, joins Neil deGrasse Tyson and comic co-host Matt Kirshen. Together, they unpack the latest research, explain key methods used to measure cosmic distances, address the controversy in the field, and discuss what these results may mean for our understanding of the universe.

---

Key Discussion Points & Insights

1. Setting the Stage: The Role of Observers vs. Theorists

[03:18 - 05:00]

• Tyson points out the fast pace of cosmology, noting that observational data, rather than theory alone, arbitrate what’s true.
• Freedman: “Data is the ultimate arbiter. We can have lots of ideas, but if they don't fit the universe, we throw them out.” [03:44]
• The respectful interplay between theory and observation is foundational to astrophysics.

2. Wendy Freedman's Achievements & Influence

[05:01 - 09:00]

• Recently awarded the National Medal of Science for work on the universe's expansion.
• Celebrated in TIME's "100 most influential people" list.
• Pioneering use of the Hubble Space Telescope to settle debates about the universe's age and size.
• Recounts historic debates—universe age estimates ranged wildly from 10 to 20 billion years, with key camps centered around different values for the Hubble constant (notably between 50 and 100).

3. The Hubble Tension: What Is It?

[09:00 - 16:15]

• Hubble tension refers to a discrepancy between two approaches for measuring the current expansion rate of the universe (the Hubble constant):
  • Direct measurements nearby (using Cepheid variables, red giant branch stars, supernovae)
  • Inferences drawn from cosmic microwave background (CMB) observations and theoretical models.
• Freedman explains Cepheids and their importance, crediting Henrietta Leavitt’s century-old discovery of the period-luminosity relation.
• Tyson: “Not every object serves as a way to know how far away it is... these yardsticks are cherished.” [10:17]
• There’s a notable difference: local measurements yield a higher Hubble constant (~73 km/s/Mpc), while early universe predictions give a lower value (~67 km/s/Mpc).

4. Historical Context & Changes in Cosmology

[16:16 - 24:16]

• Earlier measurements had much larger uncertainties, so disagreement was expected. Today, uncertainties are smaller, making the persistent gap more troubling.
• Freedman notes that both precision and accuracy matter, and the debate now focuses on these.
• Freedman: “Either this is really interesting and we're learning about some fundamental... property of the universe, or we've underestimated our uncertainties.” [24:16]

5. Understanding Standard Candles & Distance Measurement

[26:07 - 31:45]

• The team’s work with three distance indicators using the James Webb Space Telescope (JWST): Cepheids, tip of the red giant branch stars, carbon stars.
• The importance of using multiple, independent methods to identify and correct for systematic errors.
• Tyson highlights the unique perspective astronomers have due to their hands-on knowledge of stars, galaxies, and observational uncertainties.

6. Is There Really a Crisis? Precision vs. Accuracy

[24:48, 31:45 - 35:10]

• Wendy rejects sensationalism: “Would I have used the word crisis? No, I don't believe it's a crisis. Not in my opinion.” [24:48]
• She stresses the need for extraordinary evidence to claim extraordinary physics (quoting Carl Sagan).
• The current discrepancy may be due to underestimated errors—especially those hidden or systematic in nature (e.g., dust in galaxies impacting Cepheid measurements).

7. State of the Field: The Gold Standard and Systematics

[32:38 - 37:45]

• The cosmic microwave background (CMB) measurement with Planck satellite “is the gold standard,” highly precise.
• Local measurements involve complex, less well-controlled astrophysical systematics—stars, dust, supernova calibration—favoring skepticism.
• “It's always the systematics that come back to bite you, and often they're unknown systematics.” – Freedman [35:23]

8. Universe’s Expansion, Terms, and Models

[37:45 - 39:02]

• The Hubble constant refers to the present value (H₀); it was different in the past (the expansion rate is not truly constant).
• Tyson and Freedman joke about astronomical vernacular and misnomers.

9. Could the Universe Be Inhomogeneous?

[38:22 - 42:03]

• Question: Might the universe’s expansion rate differ in different regions?
• Freedman explains that thousands of supernovae measurements across the sky show no evidence for significant local variation.
• Despite over 1,500 papers proposing exotic explanations for the Hubble tension, all break some other well-established observation—so the Big Bang model remains robust.

10. Cosmic Queries: Listener Questions

[46:03 - 54:55]

• On Dark Energy and Distance: Future measurements may reveal varying/evolving dark energy—numerous upcoming experiments aim to clarify this.
• On the Gap in Expansion Rates: Could indicate new physics, but Freedman is not convinced yet: “I have to be convinced by the data, and at the moment I am not convinced...”
• On Infinite versus Finite Universe: Freedman doesn’t harbor a preference; curiosity and scientific process are what matter.

---

Notable Quotes & Memorable Moments

• "Data is the ultimate arbiter. We can have lots of ideas, but if they don't fit the universe, we throw them out."
  — Wendy Freedman [03:44]
• "Extraordinary claims require extraordinary evidence, and I'm not yet seeing extraordinary evidence."
  — Wendy Freedman [31:45]
• "Would I have used the word crisis? No, I don't believe it's a crisis. Not in my opinion."
  — Wendy Freedman [24:48]
• "It's always the systematics that come back to bite you, and often they're unknown systematics."
  — Wendy Freedman [35:23]
• “In 60 billion years... if the acceleration of the universe continues... we won’t see other galaxies, and we won’t have the chance to make the measurements that we're making today.”
  — Wendy Freedman [49:54]
• "The Hubble constant refers to a Hubble parameter at the current time t equals 0h0... it is the value of the Hubble parameter at the current time."
  — Wendy Freedman [37:55]

Moments of Humor and Tone

• The hosts joke about astrophysical terminology, such as calling all elements heavier than helium "metals," and the misuse of “burning” in stars.
  • "Bigger insult is that we consider pretty much everything heavier than hydrogen and helium to be a metal." — Wendy Freedman [29:28]
• Neil and Matt riff on who “matters” more—ordinary matter or dark matter/energy.
  • "A sixth of you matters." — Neil deGrasse Tyson to Matt Kirshen [22:14]
• Playful banter about finding one’s way home in an expanding universe, featuring a cosmic GPS analogy.
  • "So bring an equation with you for the expansion of the universe and then go backwards along that path and you should be able to get home." — Neil deGrasse Tyson [51:45]

---

Key Timestamps

| Timestamp | Segment/Topic | |-----------|---------------| | 03:18 | Introduction of topic; the observer’s role in science | | 05:01 | Wendy Freedman’s recent honors and context | | 09:00 | Introduction of the Hubble tension crisis | | 11:04 | The history and importance of Cepheids | | 13:56 | The meaning of “Hubble tension” explained | | 16:16 | Local vs. distant cosmic expansion measurements align | | 19:47 | What the Hubble constant actually measures | | 21:32 | Could our basic model of the universe be wrong? | | 24:48 | Is this a crisis? (Freedman: No) | | 26:07 | JWST project: Measuring distances by multiple methods | | 31:45 | Are the uncertainties underestimated? | | 32:38 | The CMB and the “gold standard” of cosmology | | 35:23 | The true challenge: unknown systematic errors | | 37:45 | Hubble "constant" through cosmic time | | 38:22 | Is the universe homogeneous? | | 42:03 | Sensational headlines and the state of the field | | 46:03 | Cosmic Queries begin: Dark energy, new instruments | | 48:22 | If discrepancy persists, new physics or better data? | | 49:29 | “How will we get home if the universe is expanding?” | | 52:43 | Would the field change if the universe is infinite? |

---

Summary & Takeaways

• The “Hubble Tension” is a real and curious discrepancy, but not a crisis. The community must be careful about extraordinary claims, as underestimated errors—especially systematics—are often to blame.
• Freedman’s JWST work aims to unify and cross-check distance measurement methods, hoping to clarify if the tension is due to new physics or simply measurement errors.
• The Standard Model of Cosmology remains robust, withstanding challenges from a barrage of new theories, as each new explanation must fit a vast range of constraints.
• Science thrives on questioning and precise measurement. Both Freedman and Tyson exemplify a cautious but open-minded approach: hope for new discoveries, but require strong evidence.
• Humor and humility are woven throughout, from cosmic-yardstick jokes to thoughts on infinity, making the episode accessible and offering a glimpse into how real scientific debates proceed.

---

For Listeners New to the Episode

This conversation offers a rich, clear window into how upper-echelon cosmologists evaluate and debate the evidence about the universe’s expansion, balancing skepticism with curiosity and the hunt for fundamental new physics. Dr. Wendy Freedman’s expertise—tempered by an insistence on robust, multi-pronged evidence—gives a refreshing and reassuring outlook: the universe may not be done surprising us, but scientific rigor guides the way.

---

Keep looking up!

Transcript

[Neil deGrasse Tyson]

Morning, Zoe. Got donuts.

[Wendy Freedman]

Jeff Bridges, why are you still living above our garage?

[Neil deGrasse Tyson]

Well, I dig the mattress and I want to be in a T mobile commercial like you teach me. So Dana.

[Wendy Freedman]

Oh no, I'm not really prepared. I couldn't possibly at t mobile get the new iPhone 17 Pro on them. It's designed to be the most powerful iPhone yet and has the ultimate pro camera system.

[Neil deGrasse Tyson]

Wow, impressive. Let me try. T mobile is the best place to get iPhone 17 Pro because they've got the best network.

[Wendy Freedman]

Nice. Je free.

[Neil deGrasse Tyson]

You heard them. T mobile is the best place to get the new iPhone 17 Pro on us with eligible traded in any condition. So what are we having for lunch?

[Wendy Freedman]

Dude, my work here is done.

[Neil deGrasse Tyson]

The 24 month bill credits on experience beyond for well qualified customers plus tax and 35 device connection charge. Credit send and balance due. If you pay off earlier, Cancel Finance Agreement. IPhone 17 Pro 256 gigs 1099.99 A new line minimum 100 plus a month plan with auto pay plus taxes and fees required. Best mobile network in the US based on analysis by Oklahoma Speed Test Intelligence Data 182025 Visit t mobile.com you ever walked around a neighborhood and wish you could see inside somewhere that was available for rent? Well, let me just give you a tip. Don't climb up on the ledge and look in the window. People will call the cops. Well, maybe you've walked past a place for rent and you wished you could peek inside. Maybe even explore the layout. Envision the natural light streaming through the windows. Or plan where your vinyl record collection would go. Well, at apartments.com you can. With tools like their 3D virtual tours, you can see the exact unit you could be living in and at all from the comfort of your couch. And if you end up wanting to see it in person, you can book a tour online without having to speak to a leasing rep. Really envision yourself in your new home with apartments.com the place to find a place. So Matt, we do every now and then have to check in on the universe.

[Matt Kirshen]

We do. How's it doing, Neil?

[Neil deGrasse Tyson]

You know, it has issues. You know, there's a crisis, a family crisis with the galaxy data, when crises.

[Matt Kirshen]

Happen, can we resolve it? Is there any way to resolve it?

[Neil deGrasse Tyson]

Maybe. I think. Actually. Coming up on StarTalk. 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. Today I've got as my co Host Matt Kirschen. Matt, welcome back.

[Matt Kirshen]

Thank you, Neil. It's nice to be back.

[Neil deGrasse Tyson]

We caught up with you. You're on a cruise, man. You comedians go every. You got the cushiest jobs.

[Matt Kirshen]

I don't. I don't know if it's cushy. It's cushy to be on a cruise. I think telling jokes on a cruise, that's a little more work. But, yeah, we were chatting about this last time. I'm on a boat right now, and then I'm on a big land tour. I'm touring with Sarah Milliken, who's a great UK comic, and then off the back of that, I'm doing some headline shows of my own in clubs. So. Mattkirchen.com youm can stalk me. If you go to mattkirchen.com you can find.

[Neil deGrasse Tyson]

We'll talk you there. All right, well, take us on a boat next time.

[Matt Kirshen]

Absolutely, absolutely. There's space in this tiny cabin.

[Neil deGrasse Tyson]

And you're also a host of Probably Science. Did I finally get that right?

[Wendy Freedman]

You did.

[Matt Kirshen]

You did. I feel like you've always known the title.

[Neil deGrasse Tyson]

I feel like I haven't been on in, like, eight years. So I'm waiting for my call.

[Matt Kirshen]

We are talking to your people right now because let's get.

[Neil deGrasse Tyson]

Excellent. Well, today we're going back into the universe, deep into the universe. And, you know, there are theorists who run around, think they know what's going on, but they have to ultimately answer to the observer who's getting the actual data. And we have someone back on StarTalk who was here just two years ago. That's how fast this field is moving. Wendy Freeman. Wendy, welcome back to StarTalk.

[Wendy Freedman]

Thanks very much. Yes, data is the ultimate arbiter. We can have lots of ideas, but if they don't fit the universe, we throw them out.

[Neil deGrasse Tyson]

You are the judge, the jury, and the executioner of theorists. Is that how much power you wield, Wendy?

[Wendy Freedman]

We need them both. The data without theory is not very useful. So it's when you have an interplay between the two that it becomes interesting.

[Neil deGrasse Tyson]

She's being nice now because she's got to meet theorists later at the conference.

[Matt Kirshen]

You don't have the theorists ever going like, no, no, I think the stars are wrong. I think our equations are right.

[Neil deGrasse Tyson]

Yeah. I spent some time at Princeton, which has a very strong history of theorists. And there's a motto there. Never trust an observation unless it's confirmed by a good theory. That's their mindset. They know. They're, like, full of Shit. But they want to say it. So, Wendy, you a professor of astronomy, University of Chicago, in an endowed chair. Let me get that right. The John and Marion Sullivan University Professor. That's a whole other level of professorship in astronomy and astrophysics at UChicago. And now since we last had you on, you've been busy. Oh, my gosh.

[Wendy Freedman]

That is true. That is very true.

[Neil deGrasse Tyson]

The National Medal of Science. Oh, my gosh. This is the highest award the country gives, the United States gives to scientists. There's also a National Medal of Engineering. And so this is.

[Wendy Freedman]

And medicine.

[Neil deGrasse Tyson]

And medicine, yes. Thanks for reminding me of that. And I was once on a committee to select the National Medal of Science that goes through the National Science Foundation. Does it still do that?

[Wendy Freedman]

Yes, it does.

[Neil deGrasse Tyson]

Okay, cool. So that was. So it depoliticizes it enough so that, you know, you can really trust that who's in there for that award earned it in all the ways one would expect for a title.

[Wendy Freedman]

Science is not political. It has no political affiliation. That's one of the beauties of science.

[Neil deGrasse Tyson]

It really is distinguishing it from basically everything.

[Wendy Freedman]

Yes.

[Neil deGrasse Tyson]

And you were cited for your pioneering work in measuring the expansion rate of the universe. Is that all? Yeah, you were. I remember you were right out of the box with the Hubble telescope. Hubble. That telescope was in part named after Edwin Hubble on the expectation it would do exactly. What you did with it was to settle the arguments. Right. Could you just remind us what that was?

[Wendy Freedman]

Yeah. So when I started in pre Hubble, the argument at the time, there was a big debate about the size and the age of the universe, and people were arguing about whether the universe was 10 or 20 billion years old, which is a big difference. And so Hubble was built. In fact, the size of the primary mirror of the telescope was set to allow. They didn't let it go any smaller because they wanted to be able to have Hubble measure Cepheids, the stars that we use to measure distances, is with that telescope. And so there was an effort, of course, because you could save cost to cut the size of the primary mirror even further. And it was set by that to resolve this debate between a Hubble constant of 50 and 100 at that time.

[Neil deGrasse Tyson]

Yeah. And we came up at the same time. And I just remember that being the biggest argument anyone would ever have. In the coffee lounge. People, they'd split in the coffee lounge, who was the old universe camp and who was the young universe camp. And, of course, the actual answer landed nicely in between those two numbers, as one might have predicted with high school.

[Matt Kirshen]

So they had to split the bet, whatever they were betting against each other with.

[Neil deGrasse Tyson]

Yeah, it didn't land in either camp. It was.

[Matt Kirshen]

The table got halved.

[Neil deGrasse Tyson]

It was. Yeah. Like right in the middle. Right.

[Wendy Freedman]

I mean, it's interesting because, you know, there were two groups, competing groups that, you know, Sandage and Tomon and Devoque Allure who were making these measurements. And so the arguments between 50 and 100 centered on their argument. But if you look at the published values at the time, there were plenty in middle.

[Neil deGrasse Tyson]

Yeah, I would have never known that because while that was going on, I was at the University of Texas, which was home base for Gerard Devaucouleur. He was Mr. Young Universe. Right. And so did I get that right? He had the Hubble constant of 150. Yeah. So it was. So I, I, we had no, we were not allowed to think outside of his box there.

[Wendy Freedman]

That's okay. I was at the Carnegie Institution with Alan Sandish. Very interesting time. He, he kind of disagreed.

[Neil deGrasse Tyson]

Yeah. Yeah. So thanks for solving that. And also just this year named Time magazine's hundred most influential people in the world. Congratulations on that. When was that announced?

[Wendy Freedman]

Oh, I'm trying to think of when it was announced as a.

[Neil deGrasse Tyson]

So it's already happened. You already had the celebration.

[Wendy Freedman]

Oh, yes, yes, we did. We had a nice.

[Neil deGrasse Tyson]

So you came through New York and you didn't. You, you came through.

[Wendy Freedman]

You came through New York. In fact, your people check with me. Was there date where I could do this?

[Neil deGrasse Tyson]

My people were on the case. Okay.

[Wendy Freedman]

Yes. But it didn't work out.

[Neil deGrasse Tyson]

All right.

[Wendy Freedman]

Yes, it was a lovely event. Not what your usual scientific conferences are like.

[Neil deGrasse Tyson]

No, yeah, it's a celebration. Yeah, yeah, it's good. And this paper that you hinted at when I had you in New York for the Asimov panel debate, your paper solved what? So I think you're going to give me details here, but you know, if you just believed the newspaper headlines or the clickbait in news websites, you would think that all of cosmology was in crisis. And we're all ready to just cry in our, you know, cry in each other's laps about how to solve this. And you landed at a place that seemed like, yeah, we got this and we don't have to give up the big Bang to do it. So the Hubble tension. Remind us what people are calling Hubble tension. Just tell me about that.

[Wendy Freedman]

The Hubble tension is what's arisen in the last decade or so. We make measurements of the Hubble Constant the current expansion rate locally using stars like Cepheids. We also use red giant branch stars and other ways of doing these measurements tied into type 1A supernovae.

[Neil deGrasse Tyson]

These. Right, right. So all of these in this list that you mentioned, these are yardsticks, standard candles. Right. So because not every object serves as a way to know how far away it is. Right. So there's only a handful and they're cherished, right?

[Wendy Freedman]

Yeah, they're rare stars. They're for example, Cepheids. When we go and try and discover them like we did with Hubble, maybe one in a thousand stars that we measure turns out to be a Cepheid. So they're rare, but they also have a signature. And in the case of Cepheid discovered by Henrietta Leavitt, that the brightness of the star correlates with how fast it's varying in its brightness. So called period luminosity relation. And we can use that relationship to determine the distance.

[Neil deGrasse Tyson]

That's a full hundred years ago or more, right?

[Wendy Freedman]

That's right. Everything that we have done since then rests on her work.

[Neil deGrasse Tyson]

And what's kind of cool is she get to make those discoveries because the men wouldn't allow the women to do any to work, you know, what's the most tedious work that is possible in the field. And it's like classifying stars and measuring the brightness and their spectra. And that's where all the discoveries happen.

[Wendy Freedman]

That's right. And she was astute enough to notice not only were these stars varying that she was finding in the Large Magellanic Cloud and the Small Magellanic Cloud, but there was this correlation. The brighter stars were taking longer to go through their cycle of variation. And this is the basis of what Hubble's discovery that there are other galaxies outside the Milky Way, that the universe is expanding. We use it for the key project. We use it today. And she fell into obscurity. She was kind of lost in the dustbins of history for a long time. But we're recognizing her now. And I think that's. The New York Times actually wrote an obituary about her in 2024. I think in 2024 it's a ketchup obituary.

[Matt Kirshen]

Did they write or did they just find it in an old drawer from.

[Wendy Freedman]

No, no, they wrote it. They're making an effort to try and they're recognizing that it wasn't just men who did things in those days.

[Neil deGrasse Tyson]

Yeah, there were other reconciliation project.

[Wendy Freedman]

Yeah, yeah, yeah.

[Neil deGrasse Tyson]

Very good. And I'm happy to report that at least in our era, Wendy, the textbooks that we taught from and learned from, there was good mention of the women of Harvard at the time.

[Wendy Freedman]

We now refer to the Levitt Law and that there was a meeting at Harvard in 2008, which was the centennial of her first publication on the PL relation. And we decided that it would be appropriate to rename it the Levitt Law. I had actually been doing that instead.

[Neil deGrasse Tyson]

Of the period luminosity relation.

[Wendy Freedman]

Right, yeah, yeah. There's a Hubble law, there's a Hubble constant, there are Hubble galaxies, different topologies in classification and so on, and everything rests on the PL rulers.

[Neil deGrasse Tyson]

I'm all in. Take us back to the Hubble tension. And how tense was it in the room? Or how were you in the room when it happened? I don't like that word tension. I mean, in science, if things don't agree, that's kind of fun. I just got a sense that it was more a marketing ploy to get clicks on a website. But maybe you have a different view as one who's in the middle of fixing the tension. What. Where did you come from? There.

[Matt Kirshen]

So, sorry, just to be clear, just for me to answer. So it is actually meaning tension in the common English sense. It's not using tension in some kind of physics sense. You're actually using it like awkwardness or discomfort.

[Wendy Freedman]

Well, it's signaling a discrepancy between what we're measuring locally when we use these stars, like Cepheids or red giant branch stars and supernovae to meas the Hubble constant, the current expansion rate today, when we compare that method with what you infer from the cosmic microwave background, the background radiation from the Big bang, you can measure these very small fluctuations in the temperature and also the polarization of the background radiation and fit those with the spectrum with what we call the standard cosmological model. And that's been now in place for a quarter of a century. And when you do that, this is a predictive model. It tells you how the universe will evolve, and it tells you that the expansion rate today would have a value of 67 with a very small uncertainty of less than 1%. When we use Cepheids with HST, we get values more like 73. And so that's a rather small difference compared to 50 and 100 where we started off when.

[Neil deGrasse Tyson]

Yeah, I would have been just. I said, let's go have a beer, we're good here. That's what I would have said.

[Wendy Freedman]

I think it would have been appropriate to relax a little bit. And have at least a day to celebrate things that got closer. And there are always crises in cosmology and I think it was a very rare time around 2001, 2003. So our HST key project results came out in 2000, 2001 we got a value of 72 with an uncertainty of 10%. And then WMAP the Wilkinson Microwave Anisotropy Probe first measurements of all sky in space for the microwave background got a value of 71. So it looked pretty good. And the acceleration of the universe had been discovered. The age was something like 13.7 or 13.8 billion years. And wow, here you are measuring locally using stars and you're using the a redshift of 1100 380,000 years after the big bang. You're making these tiny measurements of the temperature differences and boy, they agree pretty well.

[Neil deGrasse Tyson]

So the two puzzle pieces fit by making local measurements and distant measurements. So that pretty much tells you you're onto something there. The best business to business marketing gets wasted on the wrong people. Think of the guy on the third floor of a 10 story apartment block who's getting bombarded with ads for solar panels. What a waste. So when you want to reach the right professionals, use LinkedIn ads. LinkedIn has grown to a network of over 1 billion professionals and 130 million decision makers. And that's where it stands apart from other ad buys. You can target your buyers by job title, industry, company role, seniority, skills, company revenue. So you can stop wasting budget on the wrong audience. It's why LinkedIn ads generates the highest business to business revenue on ad spend of all online ad networks. Seriously, all of them. Spend $250 on your first campaign on LinkedIn ads and get a free $250 credit for the next one. No strings attached. Just go to LinkedIn.com startup. That's LinkedIn.com startup. Terms and conditions apply. Morning, Zoe. Got donuts.

[Wendy Freedman]

Jeff Bridges, why are you still living above our garage?

[Neil deGrasse Tyson]

Well, I dig the mattress and I want to be in a T mobile commercial like you teach me.

[Wendy Freedman]

So Dana, I. Oh no, I'm not really prepared. I couldn't possibly at T Mobile get the new iPhone 17 Pro on them. It's designed to be the most powerful iPhone yet and has the ultimate pro camera system.

[Neil deGrasse Tyson]

Wow, impressive. Let me try. T mobile is the best place to get iPhone 17 Pro because they've got the best network.

[Wendy Freedman]

Nice. Jeffrey, you heard them.

[Neil deGrasse Tyson]

T mobile is the best place to get the new iPhone 17 Pro on up with eligible traded in any Condition. So what are we having for lunch?

[Wendy Freedman]

Dude, my work here is done.

[Neil deGrasse Tyson]

The 24 month bill credit is on experience beyond for well qualified customers. Plus tax and $35 device connection charge credit send and balance due if you pay off earlier. Cancel Finance agreement. IPhone 17 Pro 256 gigs $1,099.99 a new line minimum $100 plus a month plan with auto PayPal taxes and fees required. Best mobile network in the US based on analysis by Ooklip speed test intelligence data 1H 2025 visit t mobile.com buying.

[Wendy Freedman]

A car in Carvana was so easy, I was able to finance it through them. I just. Whoa, wait, you mean finance? Yeah, finance. Got pre qualified for a Carvana auto loan, entered my terms and shot from thousands of great car options all within my budget.

[Matt Kirshen]

That's cool.

[Wendy Freedman]

But financing through Carvana was so easy. Financed done. And I get to pick up my car from their Carvana vending machine tomorrow. Financed. Right? That's what I said. You can spend time trying to pronounce.

[Matt Kirshen]

Financing or you can actually finance and buy your car.

[Wendy Freedman]

Today on Carvana financing subject to credit approval. Additional terms and conditions may apply. This is Ken the Nerdneck Zabera from Michigan and I support StarTalk on Patreon. This is StarTalk Radio with Neil Degrasse Tyson.

[Neil deGrasse Tyson]

So Wendy, if you can remind people, when you just say the number 73 or 67 or 70 or 50 or 100, that is a measurement of precisely what.

[Wendy Freedman]

That is a measurement of how fast the universe is expanding at the current time. It has units of inverse time. So it is also a way of getting at the age of the universe. It in detail is kilometers per second per megaparsec. So when we talk about a hubble constant of 70, we mean 70 kilometers per second per megaparsec.

[Neil deGrasse Tyson]

So for every megaparsec an object is away from Earth, from our galaxy, it'll have a recession velocity of 70 kilometers per second.

[Wendy Freedman]

Yes.

[Neil deGrasse Tyson]

And so, you know, another megaparsec, millions of parsecs, then there's another 70. And this just keeps adding that makes.

[Matt Kirshen]

It so the further away you are, the quicker it's moving away from you.

[Neil deGrasse Tyson]

Exactly.

[Wendy Freedman]

That was Edwin Hubble's original discovery. What he showed is the farther away a galaxy is, the faster it's moving away from us.

[Neil deGrasse Tyson]

And so those units, he first plotted that, and so we named the unit of that. So it's basically the slope of that line, I think. Right?

[Wendy Freedman]

That's exactly what it is.

[Neil deGrasse Tyson]

Yeah, yeah, yeah.

[Wendy Freedman]

That Correlation is the Hubble constant.

[Neil deGrasse Tyson]

Okay, cool.

[Wendy Freedman]

That is the expansion rate at time T equals zero.

[Neil deGrasse Tyson]

Now, okay, we're fitting these measurements into a base model of the universe. Right? I mean, right now we say, oh, the universe had a beginning. It was long ago, it was hot, it was gonna have a future. And its expansion. Could there be some. Is this like epicycles? Could it be like epicycles where, oh, the planets, they're on these epicycles and they do this. And now we can explain everything. Could we be missing something so fundamental that it's hidden in plain sight?

[Wendy Freedman]

We could be missing things. I think that's what is exciting about these particular. You know, the time at which we're making these measurements is that we're pushing the boundari of what is possible to do with these measurements and to test the framework. So we talk about a standard model of cosmology. That's a model that has a universe expanding. It has dark matter, where you have. The ordinary matter that we're made out of is only about one sixth of the total matter in the universe.

[Neil deGrasse Tyson]

So we don't matter, is what you're saying.

[Wendy Freedman]

We do matter.

[Matt Kirshen]

A sixth of you matter.

[Neil deGrasse Tyson]

A sixth of you matters.

[Wendy Freedman]

And the other part, not telling us what we're about, but anyway, we do matter. We're the luminous stuff.

[Neil deGrasse Tyson]

Yeah, there you go.

[Wendy Freedman]

Luminous stuff shines a light on the dark stuff. That's how we learn about it.

[Matt Kirshen]

You don't just matter, you glow.

[Neil deGrasse Tyson]

Oh, very nice, Matt. I like that.

[Wendy Freedman]

Two thirds, a form we call dark energy, which is causing the universe to accelerate. So there's plenty of room to get back to your question for things that. That we don't yet understand because we don't yet know what the dark matter is, despite decades of trying to detect it. We know it's what it does to the luminous matter. We know that it's there because of its effects on the luminous matter, but we don't know what it is. It's most probably a particle left over from the Big Bang. And there are lots of efforts to try and discover it, but that has not occurred. And the dark energy, we have no physical. Understand, there's no physical theory that can explain what the dark energy is. So, yes, there's lots of room for us understanding this standard model. So there could be cracks in the model, and maybe this discrepancy is one of the things that's pointing to something missing from the standard model.

[Neil deGrasse Tyson]

And let me emphasize something that you just briefly mentioned. So we started our careers with a hubble constant ranging from 50 to 100. And we resolved that sort of. And we met somewhere in the middle and we knew that was a problem. But the uncertainties were pretty high back then. So one might even say the uncertainty bars overlapped. So that you say if the answer is anywhere, it's going to be somewhere in the middle. Now you're saying we have two results that are much closer to each other, yet the uncertainties are so small there is no chance of them overlapping. So something has to give.

[Wendy Freedman]

So either this is really interesting and we're learning about some fundamental problem, fundamental property of the universe, or we've underestimated our uncertainties.

[Neil deGrasse Tyson]

Okay, I'm going to bet on the second one.

[Wendy Freedman]

That could mean that we'll learn something about astrophysics, about the properties of stars. Different. We're going to learn something about supernovae or Cepheids or something interesting astrophysically, but not necessarily telling us about cosmology.

[Neil deGrasse Tyson]

Would you have used the word crisis?

[Wendy Freedman]

Would I have used the word crisis? No, I don't believe it's a crisis. Not in my opinion.

[Neil deGrasse Tyson]

That's my opin. But your opinion is way more valid than mine in this space. So we're going with your opinion on this for sure.

[Matt Kirshen]

I would have used crisis for that. If anyone wants to survey me.

[Neil deGrasse Tyson]

You a crisis camp? Yeah.

[Matt Kirshen]

Is my opinion valid? Where's my opinion? Rank amongst.

[Wendy Freedman]

Yeah. Fortunately we don't vote on these things. The data thing again, it's important.

[Matt Kirshen]

Why doesn't someone with almost no science training weigh as much in this as a leading scientist? It's just not fair.

[Neil deGrasse Tyson]

Yeah, it's not a democracy. That's the problem. It's not a democracy. So then, Wendy, you step in once again and come up with some sensible understanding of what's going on. Could you update us on that recent research paper of yours? And who are some of your colleagues on that?

[Wendy Freedman]

Yeah, so we have a small group which. A really nice group. It's small and efficient.

[Neil deGrasse Tyson]

Excellent. That means you get more. And correct me if I'm wrong, any good collaboration, everyone on the team brings their own special awareness and understanding and specialty to it. Otherwise you just have redundancies and there's no point for that.

[Wendy Freedman]

Yeah. And everybody is working really hard. It's our proposal. The proposal that we put into James Webb Space Telescope. So this is where we're focused now was to use three different distance indicators, the Cepheids that we know and love, the tip of the red giant branc, which is a method that Barry and I and collaborators have been working on for many years in the last decade or so have really refined it in terms of improving its precision.

[Neil deGrasse Tyson]

So this is a section on the Hertzsprung Russell diagram, which doesn't really clarify if you say the tip of the red giant branch is a special place on the Hertzsprung Russell diagram. Now we're all clear. So what you're saying is as stars age, they change in properties, but there's a certain property that they take on that has a good, that an ensemble of them will have a consistency that you can rely on, that you can see at great distances. Is that a fair way to characterize?

[Wendy Freedman]

Yeah, that's fair. These stars. So our sun, our own sun, will become a red giant later in its evolution. And so these are stars that have masses comparable.

[Neil deGrasse Tyson]

Matt, it's in 5 billion years. So don't worry about this one.

[Matt Kirshen]

Don't worry y that day.

[Neil deGrasse Tyson]

You got a gig that day. All right, well, we'll delay.

[Matt Kirshen]

I can move it. If it's important, I can move it, but I'd rather not.

[Wendy Freedman]

These stars have a degenerate core which so packed very, very densely, and they've exhausted all the hydrogen in the core. So that most of the of a star's lifetime is spent burning hydrogen into helium in its. In its core, fusing hydrogen into helium. And then when the star contracts, it's not hot enough to start bur helium. And that would happen in a more massive star. So it's burning hydrogen in a shell and putting more helium onto the surface of this core. And when the core reaches a certain mass, a certain temperature, then there's a thermonuclear runaway. So suddenly you can start helium burning and it releases a lot of energy very, very quickly. And then the star settles down onto another obscure term in the Hertzsprung Russell diagram, what we call the horizontal branch. But the point is fainter stars and the position at which this, what's called core helium flash occurs occurs at a very well known luminosity. And so what that means is we can use, we will observe stars in different galaxies, see how another standard candle for you. It's another standard candle. Calibrate them locally and then use the inverse square law to get the distance. So there is a very clean method.

[Neil deGrasse Tyson]

Allow me to offer an apologia to our fellow chemists. When astropholk say things burn, we don't mean what you mean. Okay. We mean by that. Yeah, yeah. Hydrogen burning. You said it briefly in there, but then you went Back to burning. Yeah, it's hydrogen fusion. Fusion. But we just. We're very sloppy there, and I apologize to chemists. It's your word to put that out.

[Matt Kirshen]

Sorry I spoke over you, Daniel.

[Wendy Freedman]

Bigger insult is that we consider pretty much everything heavier than hydrogen and helium to be a metal.

[Neil deGrasse Tyson]

Oh, yeah. We call them metals. Yeah. We're bad with our chemistry, but we're sticking with it. We're stubborn in this regard.

[Matt Kirshen]

If you've got the hydrogen burning in a star, do you like. If you need to put that out, is it a water hose or do you use a blanket or foam? Which of the three extinguishers are we talking about?

[Wendy Freedman]

Do this at home. Don't get close to this.

[Neil deGrasse Tyson]

Walk go the other way. All right, so. So you're working on. I interrupted you quite on purpose, but you. You were working on several methods of distance determination. Yes.

[Wendy Freedman]

So we're using the James Webb Space Telescope to measure distances to galaxies using these three different methods. The carbon stars, the red giant stars, and Cepheids. And that will allow us ultimately, and we're partway through this project to determine how well we've measured the distances. Right. Do all three methods agree? Really well, is there a large spread in the values? Do two agree? One's an outlier. This will give us a chance to say, what are the overall uncertainties?

[Neil deGrasse Tyson]

Got it.

[Wendy Freedman]

And those nearby galaxies that we're observing with jwst, those galaxies then tie into the distant universe where we can see type 1A supernovae well out into what we call the Hubble flow.

[Neil deGrasse Tyson]

So you're the base of that pyramid that they're. I mean, they don't know the distance to the supernova any better than you would know what its foundation is. Is that.

[Wendy Freedman]

That's right. We can measure the relative distances of supernovae. We can see which ones farther away, but we don't know what the absolute.

[Neil deGrasse Tyson]

Distance is to calibrate them. Okay. So youth, not to put words in your mouth, but you think in the results of your work, you will show perhaps that people were overzealous in their small uncertainties that they were reporting. And maybe the uncertainties are a little wider, where they would then overlap. And then it's not attention, and there's not a Hubble crisis and a cosmological crisis, and we can all go out and have a beer.

[Wendy Freedman]

Yeah. I think, you know, to quote the late Carl Sagan, extraordinary claims require extraordinary evidence, and I'm not yet seeing extraordinary evidence. So our result. We're getting a value of about 70. And that agrees very well with what we got from Hubble using these red giant branch stars. And I think the uncertainties still there are. They're not at the level that come out of the cosmic microwave background measurements. The cosmic microwave background measurements have a precision of better than 1%. So they've really set the bar very, very high. And that's just not possible yet to make measurements at that level of accuracy when you're trying to use stars that are millions out to hundreds of millions of light years away. That's.

[Neil deGrasse Tyson]

So I didn't appreciate that. So you're saying the cosmic microwave background measurement determination of the Hubble constant is the gold standard against which other measurements have to match. No one thinks that there's a problem with those measurements at all. Is that correct?

[Wendy Freedman]

So far, there is no indication that the measurements themselves are an issue. So they're the measurements from the Planck satellite, this European satellite, which is still the gold standard in the field. It's all sky. And there are two groups on the ground, one in the Atacama Desert and one at the South Pole, that in fact came out with very recent measurements. And they're very much in agreement. The issue is, in order to get the Hubble constant from those measurements, you have to have a model to fit the data. So this is the beauty of this. Given the model, you predict what the Hubble constant today should be. How do you test the model? You measure the Hubble constant today. So if you can measure it with enough accuracy, not just precision, but accuracy.

[Neil deGrasse Tyson]

Tell us the difference between those two.

[Wendy Freedman]

So you know if you have a coin and you flip it, you know if you do it a few times, you might get more heads than tails. If you do it enough times and your coin isn't weighted in some funny way, it's going to come out 50, 50. And the more times you make the measurement, the more accurate accurate your measurement is going to be. But then there are other kinds of errors that no matter how many times you make your measurement, you're still going to have what we call systematic errors. And an example of a systematic error would be, we know that stars like Cepheids form in the disk of galaxies where there's astrophysical dust. So dust, just like here, you're looking at a mountain far away and a dust storm blows up. You look at the sun or you look at the mountain, the sun's going to get redder and fainter. Same thing happens if there's a fire. If you've seen a red sun, that's what happens when we're looking at these Cepheids through the dust? They get redder and dimmer. If they look dimmer, you're going to say this farther away. If you haven't corrected for it, no matter how many times you make the measurement, you're still going to have an error. There's this distinction between precision and accuracy. And if you only use one method, if you're only using the Cepheids, you're not going to be able to tell what the systematics are. So you have to use. You know that. That's my strong feeling, that's what drives my research, is you have to do this in more than one way.

[Neil deGrasse Tyson]

So when are you thinking that systematic errors are prevalent within these measurements? Because they. They sound all precise and everything, but they could be. They're precise, yet wrong.

[Wendy Freedman]

That's exactly right. Yes. And I think certainly historically that's what we've seen in these measurements. It's always the systematics that come back to bite you, and often they're unknown systematics. We know about the dust now. We can correct for it. But what are the things that we don't yet know about? And could there be errors in the calibration and in the calibration of the dust loss? There are lots of potential gotchas, and.

[Neil deGrasse Tyson]

You'Ve got an advantage there because people who come to this as cosmologists, they don't know anything about stars, as far as I can tell. You have a huge background in sort of traditional astronomy, where stars in a galaxy, the dust, the reddening, the magnitude of all of this. And so that makes you particularly potent on that frontier.

[Wendy Freedman]

Well, I think astronomy is different than physics. Astrophysics is different than physics. We don't have a laboratory where we can go in and we can work with the equipment and we understand the equipment and do tests that we set. We're working with these stars that are far away, that have metals in their atmospheres, pulsating stars, exploding stars. If we look at the supernovae we don't understand yet, although there's some interesting hints that maybe we understand one of the mechanisms for exploding supernovae. But there's scatter in the relation for supernovae and the supernova magnitude. Supernova luminosity depends on the color of the star, how fast the supernova, how fast it's declining the mass of the galaxy, which truly has nothing to do with the supernova itself. It's a proxy for something else. And then there's additional leftover scatter and different groups have different calibrations of the supernovae. And so when we're comparing our local observations with the cosmic microwave background, where it's clean, and what is referred to as linear physics, and there are different groups that are getting the same answers with a precision, again, of better than 1%, the onus is on us, I believe, locally, to really show that we have overcome the systematics in using these stars.

[Neil deGrasse Tyson]

You kept referring to today's value of the Hubble constant. That implies Hubble constant had a different value in the past. So then why are you calling it a constant?

[Wendy Freedman]

The Hubble constant refers to a Hubble parameter at the current time, t equals 0h0. And actually, the Hubble parameter, the parameter that describes, governs the evolution of the universe, changes with redshift or with time.

[Neil deGrasse Tyson]

So a little bit of a misnomer to call it a Hubble constant.

[Wendy Freedman]

Yeah, it's confusing. It is the value of the Hubble parameter at the current time.

[Neil deGrasse Tyson]

So you're messing with people again, just like when you talk about hydrogen burning and all the metals on the periodic table. So, Wendy, if people are looking at different parts of the universe at different objects and getting different Hubble constants, why can't the universe just be different in these different sections? Why must the whole universe be giving you the same answer to that question?

[Wendy Freedman]

So several different things to unpack in your question, you could ask, is there a concentration of mass locally? Or maybe we live in a giant bubble.

[Neil deGrasse Tyson]

Say Matt lives in a bubble. I'm trying to get him out of the bubble.

[Wendy Freedman]

So maybe the expansion rate locally is higher because they were being pulled to this mass concentration. And that was talked about a lot at the time when we were arguing about 50 and 100. Maybe the mass distribution wasn't well mapped out. But now there are literally thousands of supernovae that have been measured. You can measure really well across the sky. And there's no evidence that it is very locally from region to region to, you know, to the percent level. As I said, the universe does evolve with time. And we don't know, as I said, also, we don't understand what the dark matter is yet. We don't know what the dark energy is. So there's lots of. I think the tension is a tantalizing idea that maybe this is additional physics because we don't yet understand the, the nature of the dark energy. But it's. It's very interesting because in the last decade, there have been probably 1500 papers that have been written and posted to the astronomical archive that have tried to explain the Hubble tension and none of them has succeeded. And, and the reason is in large part because there's so many other observations that can constrain what a model can do do and the effect that it would have that we would be able to measure with measurements today or with the microwave background or so on and so on. So this is where we are at the forefront. We're trying to push the limits. We're trying to understand what is governing what are the constituents of the universe, how is it evolving, but we don't yet have all the answers and we need really accurate data to do that. And so I would say it's not that this is, is completely solved. I think we need to do a better job showing that there is a significant tension. And as the data improve in future, this is going to go one way or the other. Either the signal is going to improve or it's going to fade away. One of the examples is recently with measurements of the microwave background, there was a tiny little hint in the measurements from the Atacama Desert, the cosmology telescope, in an early release of theirs, that maybe in the polarization there was a hint of what might be due to evolving dark energy that could explain the Hubble tension. But they just come out with a release with much more data and the signal just disappeared. It was noise. If it had been real, it would have been really apparent, but it went away. So that's what happens. You see things at a level of significance that we call two or three sigma. Five sigma is supposed to be the gold standard. It would be a 1 in 1.7 million chance that isn't correct. I just don't think we're at that level yet. We have more work to do.

[Neil deGrasse Tyson]

So this bit about the change in the dark energy properties that made serious headlines when that came out, well, this is different.

[Wendy Freedman]

This is an early dark energy that would have explained the Hubble tension.

[Neil deGrasse Tyson]

Early dark energy evolving.

[Wendy Freedman]

Dark energy, it still could be evolving. And again, this is early data. There's going to be a lot more coming in the next.

[Neil deGrasse Tyson]

And just to recast something you said a moment ago, but tell me if I haven't oversimplified it, these 1500 papers of people trying to explain the Hubble tension, they'll come up with an accounting for it, but then it breaks something else that we know very well would not be the way it is if their idea were correct. So it's quite the Rubik cube. You can't just explain one thing without affecting 100 other things that we know very well. Yeah, so this is part of what gives us confidence in the overall Big bang scenario for the origin of the universe, because it's supported in so many ways with so many different branches of astrophysics and so. Yeah. Morning, Zoe. Got donuts.

[Wendy Freedman]

Jeff Bridges, why are you still living above our garage?

[Neil deGrasse Tyson]

Well, I dig the mattress and I want to be in a T Mobile commercial like you. Teach me. So. Dana.

[Wendy Freedman]

Oh no, I'm not really prepared. I couldn't possibly at t mobile get the new iPhone 17 Pro on them. It's designed to be the most powerful iPhone yet and has the ultimate pro camera system.

[Neil deGrasse Tyson]

Wow, impressive. Let me try. T Mobile is the best place to get iPhone 17 Pro because they've got the best network.

[Wendy Freedman]

Nice. Jeffrey, you heard them.

[Neil deGrasse Tyson]

T Mobile is the best place to get the new iPhone 17 Pro on us with eligible traded in any condition. So what are we having for lunch?

[Wendy Freedman]

Dude, my work here is done.

[Neil deGrasse Tyson]

The 24 month bill credit is on experience beyond for well qualified customers. Plus tax and $35 device connection charge credit. Same debilitance due if you pay off earlier. Cancel Finance agreement. IPhone 17 Pro 256 gigs $1,099.99 a new line. Minimum $100 plus a month plan with auto pay plus taxes and fees required. Best mobile network in the US based on analysis by Ooklove speed test intelligence data 1H2025 visit t mobile.com buying a.

[Wendy Freedman]

Car in Carvana was so easy, I was able to finance it through them. I just. Whoa, wait. You mean finance? Yeah, finance. Finance. Got pre qualified for a Carvana auto loan, entered my terms and shot from thousands of great car options, all within my budget.

[Matt Kirshen]

That's cool.

[Wendy Freedman]

But financing through Carvana was so easy. Financed, done. And I get to pick up my car from their Carvana vending machine tomorrow. Financed, right? That's what they said. You can spend time trying to pronounce financing or you can actually finance and buy your car. Today on Carvana financing subject to credit approval. Additional terms and conditions may apply.

[Neil deGrasse Tyson]

Summer's heating up and so is the action with chumba casino and 2311 right now, whether you're trackside with Bubba, Riley and Tyler or cooling off at home, the fun never stops at Chumba Casino. The online social casino packed with free to play games like slots, blackjack and more. Jump into [e-mail] and score your free welcome bonus. 2 million free gold coins and 2 free sweeps coins. No purchase necessary. VGW Group Void where prohibited by law. CTNC is 21+, sponsored by Chumba Casino. This is actually a Cosmic Queries, you know, Matt, you didn't tell me this was a Cosmic Queries. Why didn't you tell me that?

[Matt Kirshen]

Oh, because I don't feel like I have any seniority on this show.

[Neil deGrasse Tyson]

Okay? I grant the astrophysics powers in the flow of content.

[Matt Kirshen]

I wanted to be your knave. Does this make me a knave? I don't know.

[Neil deGrasse Tyson]

I'm not squire. You're squire. Yeah, squire.

[Matt Kirshen]

Squire. I'll tell you that. I have to put your mortarboard and your gown on you and just send you off to battle. So, yeah, there's some great questions, as always, sent in by your Patreon subscribers. So, Hannah Cantley from the city of Roses, Portland, Oregon, says could the effects of dark energy on spacetime geometry potential arising from entropic forces complicate our ability to measure distances to distant galaxies, especially considering that their apparent recession speeds may exceed the speed of light due to the expansion of space. And this might necessitate new models and techniques to account for these influences.

[Neil deGrasse Tyson]

Yeah, Wendy, is. Wendy, is dark energy messing with you? Could it be messing with you? If you don't know what it is, you can't say that it's not messing with you. How about that?

[Wendy Freedman]

Well, I think that's fair. I think we know very little about what the future evolution of the universe is going to be. You know, will dark energy decrease with time? Is it constant? Is it Einstein's cosmological constant? And I think these are empirical questions right now, because we don't have a good theory, and ultimately, we do hope that there will be a fundamental theory. But right now, we're being guided by observations, and the observations that it's decreasing with time, evolving with time, and getting. There's less of it now. That's new. And there are many more experiments on the drawing board that will test that, and we'll see how it lands.

[Neil deGrasse Tyson]

Now, isn't there a Dark Matter telescope coming online?

[Wendy Freedman]

That's indeed. That's the Vera Rubin Telescope.

[Neil deGrasse Tyson]

Oh, wait, what's the Nancy Grace Roman Telescope? What's that one?

[Wendy Freedman]

That's a survey telescope. It's a NASA telescope in space.

[Neil deGrasse Tyson]

But is that. That's. That's. Didn't they call that the Dark Matter.

[Wendy Freedman]

Telescope or not originally the Vera Rubin Telescope? It started out probably 30 years ago almost.

[Neil deGrasse Tyson]

Oh, yeah. Okay. Well, we just did two shows on the Rubin Telescope, so we're up on that. Matt, what do you got next?

[Matt Kirshen]

Lissa says there Is still a gap between how fast the universe is expanding based on nearby measurements versus predictions from the early universe based on your work. Do you think this means we're missing something and how we measure it? Or could it mean our current model of the universe needs to change? And Alyssa also says thank you for being a badass woman of science.

[Wendy Freedman]

I think that's precisely the question we want to answer. And I think I personally am open to it coming out either way. But I have to be convinced by the data, and at the moment, I am not convinced by the data that there is this crisis and that there's something broken in our standard model. So time will tell.

[Neil deGrasse Tyson]

Yeah. And if I can add to that that I think most occasions in the history of science where there's been some discrepancy, Just a better data, better or more data resolved it, and every now and then it requires new physics. So I see what you did there, Wendy. You're saying you're not ready to have to require new physics because the data to be obtained still needs to be refined. So one day there's great precedent for people such as yourself to take that view of the world. But you don't want to miss new physics.

[Wendy Freedman]

That's right. That would be very exciting. I would love to see it, but I want to be convinced, and I'm just not at a point where I could be convinced.

[Neil deGrasse Tyson]

Good, good. All right, Matt, what's next?

[Matt Kirshen]

All right, Jamie and Sabrina from Transylvania, ask in the future, when we were all zipping around the universe on starships, how will we keep track of the expansion of the universe? How will we find our way home when home isn't where we left it?

[Neil deGrasse Tyson]

I love it. You got a coordinate system for us in the future, A GPS for the cosmos? Wendy, I don't think I'm going to.

[Wendy Freedman]

Be around that time. We can do that. But I think what we're measuring in our own Milky Way galaxy, if we were to go to Andromeda or other galaxies in our local group or beyond, we would be measuring the same thing. I think the frightening thing to think about is in 60 billion years, if you're worried about future, the acceleration of the universe, if it continues, if it doesn't, the dark energy doesn't decay, then we won't see other galaxies, and we won't have the chance to make the measurements that we're making today. So I think that we're living in an interesting time, but we don't have to worry in the same way Matt doesn't have to worry about the sun. It's going to be a long time in the future.

[Neil deGrasse Tyson]

Or if I could add a sort of more obscure but possibly relevant example, in the old days when they had their first generation of seaworthy chronometers, very important in navigation and finding your longitude around the world. Davis Sobel's famous book Longitude really blew open that field for the public. She is one of our, I think she was the very first star Talk interview interview. Oh my gosh. Deep in our archives find Davis Sobel, the author of that best selling book. Anyhow, what I understood they did, they would make these chronometers and finally close the back and all the springs and the thing, they'll all be in there and then they check it and it would either gain time or lose time to the standard. Rather than reopening the clock to try to quote, fix it, they accurately measured the rate at which it was increasing time or decreasing time and that became an equation to correct during, to correct the time they read during their voyage. So something similar to the question is if you know the expansion rate and you know how long you've been gone, then you can back extrapolate through where you know, we should have been and then you still can find there's no place like home. So bring an equation with you for the expansion of the universe and then go backwards along that path and you should be able to get home. That's what I'm thinking.

[Matt Kirshen]

Well, while we are talking about distances, I think we have time to squeeze in this question, hopefully from Chris from Marlborough, New Jersey, says, Dearest Dr. Tyson, Dr. Friedman and any esteemed guests. I'm going to count myself as esteemed. In that case, Chris asks, would the way you conduct your work change if we found out definitively our universe is infinite or finite in size also? Which option do you find more plausible? Thank you very much, both of you, for your stewardship of cosmic curiosity.

[Neil deGrasse Tyson]

Oh, I love that sentence. Beautiful.

[Wendy Freedman]

I'll say. It wouldn't change how we would do our work. I think we would continue to observe the universe, measure it and see what's out there. So that would not change. You can answer the other part, Neil.

[Neil deGrasse Tyson]

No. How would you feel emotionally if the universe were finite versus infinite? How about that?

[Matt Kirshen]

And which do you believe is true?

[Wendy Freedman]

I find this interesting, these kinds of conversations. So I think I'm not emotionally attached to one kind of universe or another. I really have no emotional.

[Neil deGrasse Tyson]

That's a healthy posture in science for sure.

[Wendy Freedman]

And so I don't have a feeling about it, but I Remain intensely curious about what it is. And I love the process of science that allows us to ask these questions and then go out and make measurements and try and answer some of these questions. But I have no particular favorite child of a universe.

[Neil deGrasse Tyson]

Okay. Yeah, I'm leaning infinite. I'm all infinite. Just because that's more fun. That's got to be more fun in an infinite universe. Yeah. And, Wendy, do you remember there's a scene in the film 2001 A Space Odyssey where towards the end where it gets kind of psychedelic. One of the captions of the scene is to Jupiter and beyond the infinite or something. They get infinity in there.

[Wendy Freedman]

And I forgot there's a bell.

[Neil deGrasse Tyson]

Yeah, yeah. I forgot the exact quote. And just I think it's fun to get people thinking about infinity because we know we can't wrap our head around. Around it. And so it keeps you nimble.

[Wendy Freedman]

Yeah. You know, real time in these things. Answering things like this, I just don't want to get tangled up in.

[Neil deGrasse Tyson]

Yeah, but it is fun when you first learn calculus. You know, you have to really cozy up to the concept of infinity and infinitesimals, like the opposite of infinity.

[Wendy Freedman]

So where they're going in these questions. Yeah, I just never.

[Matt Kirshen]

Yeah, I'm still on Zeno side, and I. And I refuse to believe motion is possible.

[Neil deGrasse Tyson]

Oh, Zeno's paradox. Yeah, yeah, yeah.

[Matt Kirshen]

I'm firmly.

[Neil deGrasse Tyson]

You do get to where you're going. You do get to where you're going, so. All right, Wendy, this has been a delight to have you back. Oh, my gosh. Congratulations on the National Medal of Science. And I think I get to tell people it comes with no money. It's just a medal. But another visit to the White House. We've met there a couple of times.

[Wendy Freedman]

Yeah, we have.

[Neil deGrasse Tyson]

And it's always good to bring some science into the White House. The country's better off anytime that happens. So our health, our wealth, and our security are enhanced.

[Wendy Freedman]

All of the above.

[Neil deGrasse Tyson]

All of the above. All right. And Matt, good to have you on again.

[Matt Kirshen]

Thank you.

[Neil deGrasse Tyson]

Enjoy your cruise.

[Wendy Freedman]

I will.

[Matt Kirshen]

I will. So far, so good. We're getting away with it so far.

[Neil deGrasse Tyson]

Okay. And we'll find you online at Probably Science. Once again, this has been Star Talk, a cosmic queries edition, but filled with updates on observational cosmology, giving us our understanding of the universe that we so desperately seek. I'm Neil Degrasse Tyson, your personal astrophysicist, as always bidding you to keep looking up.

[Wendy Freedman]

Am I allowed to say anything else? No, that's the last word. Spotting the perfect fit is kind of your thing. So when it comes to finding a used car, start your search@fordblue advantage.com and find the perfect certified pre owned vehicle at your local Ford dealer. One that comes with serious perks like a thorough inspection, a Ford backed warranty, even a carfax report. Because you know what they say, the best finds are the ones that feel made for you. Ford Blue Advantage used car buying that's built for you. Available at participating dealers only. See your dealer for details and limitations.

[Neil deGrasse Tyson]

Summer's heating up, and so is the action with chumba casino and 23xi racing. Whether you're trackside with Bubba, Riley and Tyler or cooling off at home, the fun never stops at Chumba Casino Casino, the online social casino packed with free to play games like slots, blackjack and more. Jump into [e-mail] and score your free welcome bonus 2 million free gold coins and 2 free sweeps coins. No purchase necessary. VGW Group voidware prohibited by law. CTNC's 21 plus, sponsored by Chumba Casino.