Hubble Constant Puzzle Deepens as Supernova and CMB Measurements Clash

An illustration of the evolution of the universe from the Big Bang (left) to today (right).

An illustration of the evolution of the universe from the Big Bang (left) to today (right). Astronomers are testing a new way to measure the universe’s expansion rate using the gravitational-wave background detected by NANOGrav. By treating the cosmic hum from merging supermassive black holes as a statistical “stochastic siren,” researchers hope to calculate the Hubble constant and help resolve the long-standing Hubble tension between supernova and cosmic microwave background measurements.