Astronomy & Physics Colloquium

There is a joint departmental colloquium for the Department of Astronomy and the Department of Physics on Thursday, May 1, 2025, from 3:30 to 4:30 PM in Sterling Hall, Room 4421. Seating will be limited, so please arrive early.

Our speaker will be Professor Adam Riess of Johns Hopkins University, a Bloomberg Distinguished Professor of Physics & Astronomy. Professor Riess was awarded the 2011 Nobel Prize in Physics for his role in discovering the accelerating expansion of the Universe through observations of distant supernovae. Adam Riess will be giving a public talk at Memorial Union the night prior [link].

Abstract: The Hubble tension—the persistent discrepancy between local and early-Universe measurements of the Hubble constant—remains one of the most intriguing puzzles in cosmology. The James Webb Space Telescope (JWST) now offers a fresh perspective on this issue by allowing an independent look at the same type of stars, Cepheids, used in the Hubble Space Telescope (HST) measurements that help define our best local estimate of cosmic expansion.  I’ll show how early JWST data, although still limited in size, serves as a powerful crosscheck of the HST-based distance ladder. When comparing results across multiple techniques and research groups, we find strong consistency with the HST measurements, lending confidence to their accuracy. These comparisons suggest that the observed tension is unlikely to stem from systematic errors in HST’s Cepheid distances. Though JWST’s smaller sample size limits its precision for now, it already provides valuable validation of the HST approach. As more data accumulates, JWST will play an increasingly important role in testing and refining our understanding of the expanding Universe—and perhaps help us get to the bottom of the Hubble tension.