Wormholes have been fascinating science fiction writers for decades, allowing protagonists to travel instantaneously to remote parts of the cosmos, the distant future or even entirely different universes. Last year Christopher Nolan’s blockbuster film Interstellar featured a wormhole as its key plot device, and recently won an Oscar for its visual depiction of them. The film centres around a crew of astronauts travelling through a rip in space and time in the hope of finding a future home for humanity.
Although the idea of a wormhole might sound like one of the more farfetched ideas coming from the minds of science fiction writers, in fact there is a considerable amount of active research into the science behind them. The original screenplay for Interstellar was actually developed by a physicist at Caltech named Kip Thorne, who has been studying the mathematical properties of wormholes for nearly thirty years. Thorne collaborated with Double Negative Ltd, a special effects company based in Great Portland Street in central London, to ensure that the wormholes displayed in the film obeyed the correct laws of physics. And amazingly the cutting-edge super-accurate visualization software available to the Hollywood special-effects team actually enabled physicists to see new phenomena that they hadn’t anticipated.
So what are wormholes, and how can we describe them mathematically? The answer to this question requires us to know a little bit about physicists’ currently favoured description of gravity, the general theory of relativity. Kip Thorne has been one of the big names in this field of general relativity for over half a century, and so before we explore the mathematics of wormholes we will take a short detour through Einstein’s crowning achievement.