Department of Physics Colloquium - Bethe Lecture Series

General Physics Colloqium, Professor Wendy Freedman, University of Chicago

Title:  The Hubble Tension: Is There a Crisis in Cosmology?

Host:  Abigail Crites

Abstract:  The question of whether there is new physics beyond our current standard model, Lambda Cold Dark Matter (LCDM), is a crucial unresolved issue in cosmology today. Recent measurements of the Hubble constant (Ho) using Cepheids and Type Ia supernovae (SNe) appear to differ significantly (5-sigma) from values inferred from the cosmic microwave background (CMB) fluctuations. This discrepancy, if real, could indicate new physics beyond the standard model. In this talk, I will present results using data from the Hubble Space Telescope Advanced Camera for Surveys to independently calibrate SNe Ho using the Tip of the Red Giant Branch (TRGB) method. The TRGB, a marker of the core helium flash in low-mass stars, provides a highly precise and accurate standard candle. Additionally, the TRGB method is less affected by dust, metallicity, and crowding/blending compared to Cepheid variable stars. Finally, I will describe a new program using the James Webb Space Telescope aimed at reducing uncertainties in extragalactic distances and the measurement of Ho, and present some very new, preliminary results.