In the winter of 1998, two separate teams of astronomers in Berkeley, California, made a similar, startling discovery. They were both observing supernovae-exploding stars visible over great distances-to see how fast the universe is expanding. In accordance with prevailing scientific wisdom, the astronomers expected to find the rate of expansion to be decreasing. Instead they found it to be increasing-a discovery which has since "shaken astronomy to its core" (Astronomy, October ...