Supernova Distance Measurements Suggest an Older, Larger Universe

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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.