Did the James Webb Space Telescope just solve the biggest mystery in cosmology? The discrepancy between different measurements of the Hubble constant has been causing a lot of ajda in the astronomical community for the past few decades. But Wendy Freedman, a renowned astronomer and professor at the University of Chicago, is at the forefront of efforts to alleviate and solve this cosmic conundrum.

Data are convincing. I wanna be convinced by data.

Known for her pioneering work on the Hubble Key project, the very reason the

Hubble Space Telescope was launched

in part, and her significant contributions to measuring the Hubble constant and properties of stars throughout the universe. Friedman is now leveraging the cutting edge capabilities

of the Webb Space Telescope

to tackle the Hubble tension head on.

The only way that we will understand how we're limited by systematics is to make the measurements very precisely in each case.

With decades of experience and a deep understanding of the intricacies of cosmology, of measurements, of accuracy and precision, there's simply no one better to shed light, if you will, on this issue. So join us as we take a deep dive and perhaps resolve the tension, the frustration, and the anxiety plaguing astronomy today, courtesy of the brilliant Wendy Freedman. Let's go.

Wendy Freedman, thank you so much for coming back on the podcast, your second time on the podcast.

Glad to do so.

Yeah. And thanks for hosting me in your beautiful office here at the University of Chicago. It's, it's always a pleasure to come here. I get to experience humidity whenever I come from Southern California, where you used to live for many theory.

I did.

Director at Carnegie. So we're gonna talk about your your career and your current research and this really cool looking model in the background over there that you're so intimately connected with. But the theorists thing I think I would be interested in talking about here are these recent results that you have, been participating in and leading to large part with the James Webb Space Telescope. So how did that come about? Because I understand from my friend, Adam Rees, who's been on many times, it's very difficult to get time on the James Webb Space Telescope. They don't even know of all your accomplishments because everything is blind. The the the pros walk us through the process. How did you come up with the idea? What is it telling us, and how is it perhaps resolving the Hubble tension without the need for a psychotherapist?

You're you're right. It's very difficult to get time on JWSTs, highly oversubscribed Brian very competitive. At this juncture, we're trying to measure the Hubble constant more accurately than it's ever been possible to do before. And as you know, there's this possibility that there's a discrepancy between the nearby values of the Hubble constant that we measure locally and what you get infer from measurements of fluctuations in the cosmic microwave background. So we need higher accuracy than we've ever had before in the local distance scale, because the microwave background observations now are so precise that we need to make sure that, locally, we can have a a comparable competitive decision to see if the discrepancy is real. So our, focus with JWST, and we wrote a proposal that depends not only on Cepheid variables, which we use, for example, with the Hubble Key Project, which the CHUs team also uses, but including also 2 other methods, the, tip of the red giant branch and a new fossil carbon stars we're calling JAGB stars. Yeah. And the premise is that because there are systematic uncertainties in any method, they all have their own.

Yep. Yep.

The only way that we will understand how we're limited by systematics is to make the measurements very precisely in each case. So you need distance indicators that are very precise internally and compare those. So that was our proposal to measure the distances to nearby galaxies that have hosted type 1 a supernovae. None of the methods I've just described goes out far enough that you can get into the smooth Hubble flow. The cure your motions induced by gravitational interactions are too large to measure it accurately at the 1% level that is now a goal.

Mhmm.

And it's a very challenging goal. Let me ask you. I'm sure. Yeah. And and so what we're doing is measuring the distances to the same C using these theory techniques. So we didn't know, are they all gonna agree? Will there be 3 different answers? And will there be an outlier? Let's see. And and if there's systematics, we'll try and cover that.

Any and so do the tip of the red giant branch, the carbon stars, the cepheids, do they have kind of orthogonal systematic effects? Do they share common effect systematic effects, you know, that that have to be mitigated and you learn something from one branch and apply it to another one, or are they distinct?