Time travel is possible—or at least a lot of serious physicists say so. It's probably not possible to pull it off in a souped-up Delorean, but there are wormholes, Tipler cylinders, and other Einstein-inspired theories for how it could work. Which raises the question: Why haven't we met any visitors from another time? It sounds like a silly question, but it's one that many scientists actually take very seriously. Meeting someone from the future would, of course, serve as definitive proof that we can indeed travel through time, and that would be a quite a simple way to solve a huge scientific riddle. So it's no surprise that a handful of enthusiasts and experts have staged experiments in order to attract the time travelers that could be hiding among us. One of them is Stephen Hawking. The renowned physicist totally believes time travel is a scientific possibility, and even says he knows how to build a time machine. He also famously wondered, "If time travel is possible, where are the tourists from the future?" It's a good question. Here's how we've tried to answer it. Why we think time travel is possible Time travel's been one of man's wildest fantasies for centuries. But in the last century scientists came up with theories that suggested it was indeed plausible to take a leap into the future. Going back in time, unfortunately, is much more complicated. More via Gizmodo.