Time travel's been one of man's wildest fantasies for centuries. It's long been a popular trend in movies and fiction, inspiring everything from Charles Dickens' A Christmas Carol to H.G. Wells' The Time Machine to the Charlton Heston shrine that is The Planet of the Apes. And with the opening of Interstellar today—n0t to spoil anything—we're about to fantasize about it even more.

The most fantastic thing? It's probably possible.

Let's start with the bad news. We probably can't travel back in time and watch the Egyptians build the pyramids. In the last century scientists came up with a number of theories that suggested it is indeed plausible to take a leap into the future; going back in time, unfortunately, is much more complicated. But it's not necessarily impossible.

Albert Einstein laid the groundwork for much of the theoretical science that governs most time travel research today. Of course, scientists like Galileo and Poincaré that came before him helped, but Einstein's theories of special and general relativity dramatically changed our understanding of time and space. And it's because of these well-tested theories that we believe time travel is possible.

One option for would be a wormhole, also known as an Einstein-Rosen bridge. Along with physicist Nathan Rosen, Einstein suggested the existence of wormholes in 1935, and although we've yet to discover one, many scientists have contributed their own theories about how wormholes might work. Stephen Hawking and Kip Thorne are probably the most well known. Thorne, a theoretical physicist at CalTech, even helped Christopher Nolan with the science behind Interstellar.

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