n the space opera Interstellar, astronauts seeking to save humanity have found a lifeline: a wormhole that has mysteriously appeared next to Saturn. The tunnel through spacetime leads to a distant galaxy and the chance to find habitable planets that humans can colonize. The movie's wormhole is based on real physics from retired CalTech professor Kip Thorne, an astrophysics pioneer who also helped Carl Sagan design his wormhole for the novel Contact. The visualizations are stunning and are being hailed as some of the most accurate simulations of wormholes and black holes in film. But there is one aspect of plunging into an interstellar express that the film doesn't address: How do you survive the trip?

Although they didn't call it such, the original wormhole was the brainchild of Albert Einstein and his assistant Nathan Rosen. They were trying to solve Einstein's equations for general relativity in a way that would ultimately lead to a purely mathematical model of the entire universe, including gravity and the particles that make up matter. Their attempt involved describing space as two geometric sheets connected by "bridges," which we perceive as particles.

Another physicist, Ludwig Flamm, had independently discovered such bridges in 1916 in his solution to Einstein's equations. Unfortunately for all of them, this "theory of everything" didn't work out, because the theoretical bridges did not ultimately behave like real particles. But Einstein and Rosen's 1935 paper popularized the concept of a tunnel through the fabric of spacetime and got other physicists thinking seriously about the implications.

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