Universe Freedman

[Yi Pressimone]

WendyFreedman: I traveled to Chile, the Andes Mountains, Hawaii, various places around the world where their remote sites, dark sites, and also make use of telescopes in space like the Hubble Space Telescope. So we can ask questions, direct questions. What is the universe doing? How far away are galaxies, how fast is the universe expanding and do those match the predictions.

Wendy Freedman: So the Hubble Constant is a measure... NASA... What Hubble discovered is that the universe is expanding. He made measurements of the distances to galaxies and using measurements of velocities, the rate at which the galaxies are moving away from us, so it was a discovery that he made, that the velocity of a galaxy is related to how far away the galaxy is.

Wendy Freedman: So if there was a Big Bang, another one of these testable ideas, we should see the remnants of that today, this tremendous explosion, what happened to all the radiation from the Big Bang? That was a prediction that was made. It was a discovery that was made, in fact, serendipitously led to a Nobel Prize, results that came out in 1965, that you could measure the background radiation, this remnant from the Big Bang.

Paul Rand: Big Brains is a production of the UChicago Podcast Network. To learn more, visit us at news.uchicago.edu and subscribe on iTunes, Stitcher, Google Play and wherever else you get your podcasts and if you liked Big Brains, you might enjoy another UChicago podcast, Knowledge Applied, taking you inside the research, reshaping everyday life. Thanks for listening.

Prof. Wendy Freedman, a leading astronomer who has made fundamental measurements of our universe, will deliver the 2023 Nora and Edward Ryerson Lecture on May 15 at the Rubenstein Forum at the University of Chicago.

She led a team who carried out the Hubble Key Project to measure the current expansion rate of the universe and served as the founding chair of the board of directors for the Giant Magellan Telescope, a 25-meter optical telescope scheduled for completion in Chile in the 2030s, from 2003 to 2015. Presently her research is directed at increasing the accuracy of measurements of the expansion rate and testing whether it indicates there is something missing from our fundamental model of how the universe developed. She currently heads an early program with the newly launched James Webb Space Telescope to measure the Hubble constant with more precision than ever before.

Freedman is an elected member of the National Academy of Sciences, the American Academy of Arts and Science, the American Philosophical Society, and the American Academy of Arts and Science, as well as a fellow of the American Physical Society and a legacy fellow of the American Astronomical Society.

What do the early galaxies discovered by JWST tell us about the early universe? Neil deGrasse Tyson and comedian Matt Kirshen explore the expansion of space, dark energy, and the age of the universe with astronomer, Wendy Freedman.

Is our universe young, middle-aged, or old? Learn about the different ages of the universe, dark energy, and how we live at an inflection point between eras. What does Wendy think about The Big Rip Theory? If time is relative, how do we reliably predict the age of the universe? What if we predicted the age of the universe from right outside a black hole?

Wendy Freedman's research is in observational cosmology (measures of the expansion rate of the universe using the Hubble Space Telescope, Spitzer Space Telescope and the ground-based Magellan telescope). Her current projects involve measurements of the Hubble constant -- the current expansion rate, as well as the past expansion rate, providing constraints on the acceleration of the universe and dark energy. Her other field of interest is the stellar populations of galaxies, the evolution of galaxies, and the initial mass function.

Ben Turner: You've been measuring the Hubble constant for a large part of your scientific career. What drew you to studying it? And why is it such an important measurement for cosmologists to know?

Wendy Freedman: The Hubble constant gives you a measure of the size of the universe, and it's probably the most fundamental parameter that we can measure that tells us about the evolution of the universe.

WF: The standard model [which explains how the universe has expanded since the Big Bang] is an interesting model in the sense that we are made of what is a very small fraction of the overall amount of matter and energy in the universe.

And so there are very fundamental things that we don't understand. We don't know yet what dark matter is. Neither do we know what dark energy is, except that it's causing the universe to speed up. But the model works remarkably well, given that we don't understand its fundamental structure.

The Hubble constant gives us an opportunity to learn something more about the universe in that way. We test the standard model by making measurements locally, and then compare them with what we find in the early universe by measuring fluctuations in temperature across the cosmic microwave background.

You can fit the standard model to those cosmic microwave background measurements, and it's an astoundingly good fit. And because the standard model is a predictive model you can work forwards, using data from the cosmic background radiation to predict what the Hubble constant should be today.

WF: At this point I have a completely open mind [on whether it's real]. I don't know which way this is going to go. But yes, it would be significant. How significant? Probably not as significant as the standard model itself. But if it led to a newer, fundamental understanding that improves our knowledge of these things that really remain mysteries at the moment, it could be profound.

BT: So let's dig into how we measure this. Besides the fluctuations in the cosmic microwave background, Cepheid variables are the other main way astronomers find a value for the Hubble constant. What are Cepheid variables, and how do we use them to measure astronomical distances?

In the early 1900s, Henrietta Leavitt found that there was a correlation between how fast Cepheid stars were pulsating and how bright they are. That gives us a means of measuring distance, and it's one of the most accurate means that astronomers have today.

BT: And yet despite being very accurate, there are a lot of uncertainties associated with Cepheid measurements. What are they? And what are researchers doing to account for them in their measurements?

WF: There are complications. There's dust between us and the Cepheids that make them dimmer; their atmospheres contain different amounts of heavy elements that can change the brightness [meaning they have a high metallicity]; and there are just uncertainties in the measurements.

Also when we go to more distant galaxies, it's very difficult to make a measurement of a Cepheid on its own because other stars in the galaxy contribute light that's hard to separate from the Cepheid itself.

You measure these fluctuations accurately and you can fit the standard model of cosmology incredibly well to this spectrum of temperature differences. From that, you can infer that the Hubble constant is 67.

Now there seems to be this discrepancy between 67 and 73. That doesn't sound like a lot given that we started between 50 and 100. In fact, Hubble started off at 500 when he first made his measurements. But because the measurements are improving in their accuracy, it appears as if it might be quite significant.

So what we did in the past was take precise measurements of stars at the tip of the red giant branch [which also pulsate regularly] as a comparison. We got results for that coming in at around 70. Within their uncertainties they agreed pretty well with the Cepheids, but they also agreed pretty well with the cosmic microwave background.

Our current JWST program is to measure the Cepheids, tip of the red giant branch stars and a third star known as a JAGB star [aging carbon stars with a near-constant brightness] in the same galaxy, all at one distance. We'll see how well we agree and that will give us a sense of an overall systematic answer.

WF: Not yet, our group right now is blinded so we're not going to do an absolute calibration in the distance field until we have all the data measured and analyzed. We have to measure the periods and luminosities of the Cepheids, create a period-luminosity relation and (along with the JAGB stars) measure these luminosities. We're not going to unblind until all that analysis is done. We'll sit down in a room and we'll know.

So I don't know in terms of the absolute [distance] calibration. But what I can say, about our database and the reason we put in this big proposal to use JWST, is that it's got four times the resolution of the Hubble Space Telescope at infrared wavelengths. This means the star crowding issue is alleviated enormously and we have a test using a different filter to look for metallicity effects directly where we're observing. So I think we're going to be able to get at many of these systematic effects.

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess."}), " -0-10/js/authorBio.js"); } else console.error('%c FTE ','background: #9306F9; color: #ffffff','no lazy slice hydration function available'); Ben TurnerSocial Links NavigationStaff WriterBen Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

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