Summary in Seconds: Astronomers have made the most precise measurement yet of the universe’s expansion rate [1], measuring it at approximately 73.5 kilometers per second per megaparsec (km/s/Mpc) [2]. While this agrees with measurements based on nearby stars and galaxies, it conflicts with calculations derived from the early universe, a discrepancy known as the “Hubble tension [3].” The gap is too large to be explained by measurement errors and may indicate that important pieces of cosmic physics—such as the nature of dark matter [4], dark energy [5], or gravity itself—are still missing from current theories. This growing mystery could lead