The Universe's Expansion Discrepancy: A Fundamental Challenge

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The accelerated expansion of the universe presents a significant discrepancy, where expected acceleration levels far exceed current observations. This issue highlights a notable difference, referred to as a discrepancy of 120 orders of magnitude, particularly regarding vacuum energy contributions influenced by the Higgs field mass. Despite the known aspects of particle physics, such as the lack of particles beyond certain mass thresholds, this anomaly remains unresolved, posing one of the greatest challenges in the history of science and physics.

Einstein's theory of general relativity has been our best understanding of gravity for over a century, withstanding a variety of experimental challenges of ever-increasing precision. But we have to be open to the possibility that general relativity -- even at the classical level, aside from any questions of quantum gravity -- isn't the right theory of gravity. Such speculation is motivated by cosmology, where we have a good model of the universe but one with a number of loose ends. Claudia de Rham has been a leader in exploring how gravity could be modified in cosmologically interesting ways, and we discuss the current state of the art as well as future prospects.

Blog post with transcript: https://www.preposterousuniverse.com/podcast/2024/04/01/271-claudia-de-rham-on-modifying-general-relativity/

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Claudia de Rham received her Ph.D. in physics from the University of Cambridge. She is currently a professor of physics and deputy department head at Imperial College, London. She is a Simons Foundation Investigator, winner of the Blavatnik Award, and a member of the American Academy of Arts and Sciences. Her new book is The Beauty of Falling: A Life in Pursuit of Gravity.

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