Supernova Distance Measurements Suggest an Older, Larger Universe

The Hubble constant, the conversion factor that translates the recessional velocities of remote galaxies into distances, is the only fundamental parameter of cosmology that astronomers think they know to within a factor of two. In the 1970s $H0$ was thought to be somewhere around 50 km/sec per megaparsec. (A megaparsec is 3.3 million light years.) Then in the next decade, measurements of $H0$ seemed to be converging on 80 or 90 km/sec‐Mpc. But in just the last few months, three novel determinations of $H0$ based on the observation of supernovae have placed the Hubble constant back down in the regime 50–60 km/sec‐Mpc.