The 2,428th Meeting of the Society

November 6, 2020 at 8:00 PM

Zoom Webinar

Is There a Crisis in Cosmology?

A New Debate Over the Value of H0

Wendy Freedman

Professor of Astronomy and Astrophysics
University of Chicago

Sponsored by PSW Science Member Bob Terry

About the Lecture

The Hubble Constant (H0) is the current expansion rate of the universe.  It sets the size and age scale of the universe.  Since Edwin Hubble’s 1929 discovery that the universe is expanding, astronomers have developed increasingly precise techniques for measuring H0, using telescopes both on Earth and in space.  The speaker led an early program of the Hubble Space Telescope:  a Key Project to measure the Hubble Constant H0 using  Cepheid variables to calibrate the extragalactic distance scale.  In 2001 the Key Project resolved a factor-of-two debate over whether H0 was 50 or 100 km s-1 Megaparsecs-1, and yielded a value of H0 = 72 with an uncertainty of 10%.  The value of the Hubble constant measured using Cepheid variables has remained stable (in the low to mid-70s) for about two decades, but the precision of the measurements has increased significantly.  The same is true for measurements based on supernovae.  As measurements have improved, however, a tension has arisen between the value inferred from measurement of the cosmic background radiation (assuming the current standard cosmological model), and those measured locally.  If the tension is real, it may signal A new physics beyond the standard model.  This lecture will describe recent advances in the field, and prospects for settling this new debate over the value of H0.

About the Speaker

Wendy L. Freedman is the John and Marion Sullivan University Professor in Astronomy and Astrophysics and Senior Member of the Kavli Institute for Cosmological Physics at the University of Chicago.  Before joining the faculty at the University of Chicago she held the Crawford H. Greenewalt Chair at The Observatories of the Carnegie Institution of Science in Pasadena where, during her 30 years there, she was also a Carnegie Fellow.

Wendy’s research interests are directed at measuring both the current and past expansion rate of the universe, and in characterizing the nature of dark energy, which is causing the expansion rate to accelerate.

In a career encompassing many notable achievements, Wendy served as principal investigator for a team of thirty astronomers who carried out the Hubble Key Project to measure the current expansion rate of the Universe, a project that ran from the mid-1980s until 2001.  While serving as Greenewalt Director of the Carnegie Observatories, she initiated the Giant Magellan Telescope (GMT) Project and served as its founding chairperson.  The GMT is a 25-meter optical telescope under construction at the Carnegie Institution for Science’s Las Campanas Observatory in the Chilean Andes. With a primary mirror 80 feet in diameter (24.5 meters), the GMT is poised to be the world’s largest ground-based telescope when it is completed.

Among many other awards and honors, Wendy has been awarded the Aaronson Prize and Memorial Lectureship, the Carl Sagan Memorial Award, the John P. McGovern Award in Science of the Cosmos Club, the American Philosophical Society’s Magellanic Premium prize, the Gruber Cosmology Prize and the Dannie Heineman Prize for Astrophysics.  Wendy is a member of the National Academy of Sciences, the American Philosophical Society, the American Academy of Arts and Sciences, and the American Physical Society.  She has been awarded honorary Doctor of Science degrees by the University of Chicago and the University of Toronto.

She earned her BSc, MSc and PhD at the University of Toronto.