Patreon: https://www.patreon.com/seanmcarroll Blog post with audio player, show notes, and transcript: https://www.preposterousuniverse.com/podcast/2025/03/31/310-marc-kamionkowski-on-dark-energy-and-cosmic-anomalies/ Cosmologists were, let us be honest, pretty stunned in 1998 when observations revealed that the universe is accelerating. There was an obvious plausible explanation, the cosmological constant proposed by Einstein, which is equivalent to a constant vacuum energy pervading space. But the cosmological constant was known to be enormously smaller than its "natural" value, and it seems fine-tuned for it to be so small but not yet zero. Once burned, twice shy, and since then we have been looking for evidence that the dark energy might not be strictly constant, even though that's even more fine-tuned. We talk to cosmologist Marc Kamionkowski about recent evidence that dark energy might be changing with time, and what this might have to do with the Hubble tension and other cosmic anomalies. Marc Kamionkowski received his Ph.D. in physics from the University of Chicago. He is currently the William R. Kenan Jr. Professor in the Department of Physics and Astronomy at Johns Hopkins University. Among his prizes are the Gruber Cosmology Prize, the Dannie Heineman Prize for Astrophysics, membership in the National Academy of Science, and a Guggenheim Fellowship. Mindscape Podcast playlist: https://www.youtube.com/playlist?list=PLrxfgDEc2NxY_fRExpDXr87tzRbPCaA5x Sean Carroll channel: https://www.youtube.com/c/seancarroll #podcast #ideas #science #philosophy #culture