Wormholes

A wormhole is a hypothetical tunnel through spacetime that could, in principle, connect two distant points, or even two different universes, by a shortcut. The idea emerges from the mathematics of general relativity: Einstein and Nathan Rosen described such a structure in 1935, sometimes called an Einstein-Rosen bridge. Whether wormholes can actually exist, and whether anything could safely pass through one, remains entirely speculative, since holding one open would require exotic forms of matter that may not exist.

Why they mattered to Hawking

Wormholes were more than science-fiction set dressing for Hawking. In the late 1980s he explored the idea that tiny wormholes might connect our universe to countless "baby universes" branching off from it, a line of thought he wrote about for general readers in his essay collection Black Holes and Baby Universes. He pursued this partly as a possible angle on the black hole information paradox and the deep workings of quantum gravity.

Wormholes also link to his friend Kip Thorne, who studied them seriously, including their use in the film Interstellar. For Hawking they were a tool for thinking about the connectivity of spacetime at its strangest, not merely a route for fictional travellers.

Wormholes featured memorably in the film Interstellar; see the science of Interstellar.