Twenty years ago, we were all pretty sure the world was going to end on January 1, 2000—or, if not the world, then at least civilization. It had something to do with how most computer programs used the last two digits to represent a four-digit year, and when the clock rolled over at the end of 1999, every computer would think it was 1900. When that happened, ATMs would stop working, the electrical grid would shut down, planes would fall out of the skies, and newborn babies would get hundred-year-old birth certificates.