Making up 70% of the universe and responsible for its accelerated expansion, Dark energy is the biggest mystery in cosmology. A simple model where dark energy is described as a cosmological constant explains most of the observations of the past 20 years. However, recent results are challenging this model.  The Dark Energy Spectroscopic Instrument (DESI) is building the largest 3D map of our universe to measure its expansion history over the past 11 billion years, and thereby, study dark energy. The DESI first-year results find tantalizing hints of time-varying dark energy that, if confirmed, would revolutionize the standard model of cosmology. After a brief introduction of the observations that led to our current understanding of cosmology, I will present DESI, explain how it addresses the question of the nature of dark energy, and describe the recent results and their implication.

Nathalie Palanque-Delabrouille, a cosmologist and research director at the Institute for Research on the Fundamental Laws of the Universe at the CEA Paris-Saclay research center, has been selected to serve as the next division director of Lawrence Berkeley National Laboratory’s (Berkeley Lab) Physics Division.  Her research focuses on the study of dark matter and dark energy, and she has played instrumental roles in several international collaborations throughout her career. She received her Ph.D. jointly from the University of Chicago and University of Paris-Diderot in 1997, contributing to the EROS search for dark matter objects using microlensing. She has also conducted research on the Astronomy with a Neutrino Telescope and Abyss environmental Research (ANTARES) undersea neutrino experiment, the SuperNova Legacy Survey (SNLS), and the Baryon Oscillation Spectroscopic Survey (BOSS), where she co-led the target selection group and carried out an analysis on the Lyman-alpha forest, which put constraints on the sum of the neutrino masses. While working on BOSS in 2013 and 2014, she spent a year as a visiting researcher at Berkeley Lab. She is currently a member of the Dark Energy Spectroscopic Instrument (DESI) collaboration and has served as the DESI co-spokesperson since 2018.

Coffee and tea served at 16:00pm