Marc Kamionkowski on Puzzles in Cosmology

Marc Kamionkowski is a theoretical physicist and professor at Johns Hopkins University. He was one of the first to suggest that observation of the polarisation of the cosmic background radiation might provide evidence for cosmic inflation in the very early universe. In this conversation he discusses a number of current puzzles in cosmology such as the “Hubble tension” between measurements based on distant supernovæ and derived from the cosmic microwave background, hints of violation of the Copernican principle, and the cosmic optical background measurements by the New Horizons spacecraft which appear to be twice as bright as can be accounted for from light emitted by galaxies.