By creating the first theoretical model of a wormhole 75 years ago today, Albert Einstein and Nathan Rosen allowed science-fiction writers to consider the idea of time travel. "In the three-quarters of a century since Einstein thought up wormholes, we haven't come close to observing one, though we've gotten some fantastic science fiction in the bargain," writes David Goldberg. "It may be that in science fact, if we want to explore the galaxy, it would be much easier to do so without trying to rip up the fabric of space-time in the process."