Abstract: Quantum electrodynamics (QED) is a well-established physical theory and its predictions have been confirmed experimentally in various regimes and with extremely high...
May5
Is Dark Energy Evolving? What We’re Learning from DES and DESI
Prof. Joshua Frieman, ALD for Fundamental Physics and Professor of Particle Physics and Astrophysics, SLAC
Monday, May 5, 2025
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3:30 p.m.–4:30 p.m. PT
Abstract:
Over the last 25 years, the Lambda-Cold Dark Matter model (LCDM)—with 70% of the universe in the form of vacuum energy or equivalently Einstein’s cosmological constant, Lambda---has become the standard paradigm for cosmology. Until recently, it has proven consistent with an array of increasingly precise measurements of cosmic structure and expansion history. However, the latest results from large supernova surveys and baryon acoustic oscillation measurements suggest that evolving or dynamical dark energy models may provide a better fit to the data than LCDM. In this talk, I will discuss these results, focusing on the latest measurements from the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI), describe their interpretation in terms of physically motivated dark energy models, and show how near-future experiments such as the Vera Rubin Observatory Legacy Survey of Space and Time (LSST) should provide definitive judgment on the current hints for evolving dark energy.
About Prof. Joshua Frieman
Josh Frieman is incoming ALD for Fundamental Physics and Professor at SLAC. His research is in theoretical and observational cosmology, including studies of dark energy, dark matter, and the early universe. He earned his BS in physics at Stanford, his PhD at the University of Chicago, and was a postdoc in the SLAC Theory Group before joining the scientific staff at Fermilab, where he ended up as Head of the Particle Physics Division. He was most recently Professor and Chair of the Astronomy & Astrophysics Department at the University of Chicago, a member of its Kavli Institute for Cosmological Physics (KICP), and Deputy Director of the NSF/Simons SkAI Institute for AI in Astronomy. He was previously Director and Spokesperson of the Dark Energy Survey. He is also Chair of the Board of Trustees and a past President of the Aspen Center for Physics.
Josh is a member of the National Academy of Sciences and the American Academy of Arts and Sciences, was a DOE Office of Science Distinguished Scientist Fellow, and is a Fellow of the American Astronomical Society, the American Association for the Advancement of Science, the American Physical Society, and the Royal Astronomical Society (Honorary).
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