The Sloan Digital Sky Survey (SDSS) is entering a new phase with new goals. SDSS is already the most ambitious astronomical survey project ever undertaken. During its five years of operation, the 300-plus scientists in the SDSS consortium have mapped galaxies, stars and quasars by the hundreds of millions over a large swath of sky. Their large-scale and very detailed surveys have confirmed that the galaxies follow a lacy, foam-like pattern that may well owe its existence to quantum effects during the Big Bang. They have identified far-off quasars that had already burst into life when the universe was just...