SCIENCE ALWAYS BORROWS ITS PARADIGMS:

Where did this idea of parallel universes come from? Science fiction is an obvious source: in the 1960s, Captain Kirk met his 'other self' in a Star Trek episode called 'Mirror, Mirror', while Philip K Dick's novel The Man in the High Castle (1963) imagined an alternate world in which the US was a Nazi puppet state. Since then, the idea has become mainstream, providing the image of forking paths in the romantic comedy Sliding Doors (1998), and the spine-chilling 'What if?' in Philip Roth's novel The Plot Against America (2004), which envisaged the anti-Semitic aviator Charles Lindbergh defeating Roosevelt in 1940. But there's also science fact. In 1935, Erwin Schrödinger proposed his famous thought experiment involving a cat in a box whose life or death is connected to a quantum event, and in 1957 the American physicist Hugh Everett developed his 'many worlds' theory, which proposed that the act of opening Schrödinger's box entailed a splitting of universes: one where the cat is alive, and another where it is dead.

Recently, physicists have been boldly endorsing a 'multiverse' of possible worlds. Richard Feynman, for example, said that when light goes from A to B it takes every possible path, but the one we see is the quickest because all the others cancel out. In The Universe in a Nutshell (2001), Stephen Hawking went with a sporting multiverse, declaring it 'scientific fact' that there exists a parallel universe in which Belize won every gold medal at the Olympic Games. For Hawking, the universe is a kind of 'cosmic casino' whose dice rolls lead to widely divergent paths: we see one, but all are real.

Surprisingly, however, the idea of parallel universes is far older than any of these references, cropping up in philosophy and literature since ancient times.

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