A riddle for our time
One of the most remarkable successes of astrophysics in the last century was its discovery that the age of the universe as measured by its oldest stars was about the same as the age estimated in an entirely different way, from the recession of galaxies. Both came up with surprisingly long times—billions of years—providing reassuring confirmation that both were probably on the right track. But the two values were not identical and scientists very quickly realized a major discrepancy: the oldest stars were older than the universe itself. Refinements to the measurements and the models to resolve this contradiction were underway until 1998 when cosmic acceleration was discovered. It proved, in a single sweep, that the universe was actually much older than had been thought, and in particular was older than the oldest stars.