Grappling with dark energy

摘要

Could you tell us a few words about the discovery that won you a share of the 2011 Nobel Prize in Physics? Back in the 1990s, the assumption was that we live in a dense universe governed by baryonic and dark matter, but astronomers could only account for 30% of matter. We wanted to measure the expected deceleration of the universe at larger scales, in the hope that we would find evidence for some kind of extra matter that theorists predicted could be out there. So, from 1994 we started a campaign to measure the distances and redshifts of type-1a supernovae explosions. The shift in a supernova's spectrum due to the expansion of space gives its redshift, and the relation between redshift and distance is used to determine the expansion rate of the universe. By comparing the expansion rates at two different epochs of the universe, we can estimate the expansion rate of the universe and how it changes over time. We made this comparison in 1998 and, to our surprise, we found that instead of decreasing, the expansion rate was speeding up. A stronger confirmation came after combining our measurements with those of the High-z Supernova Search Team. The result could be interpreted if the universe instead of decelerating is speeding up its expansion.