Parallel universes really do exist, according to a mathematical discovery by Oxford scientists . .
The parallel universe theory, first proposed in 1950 by the US physicist Hugh Everett, helps explain mysteries of quantum mechanics that have baffled scientists for decades, it is claimed.
In Everett's "many worlds" universe, every time a new physical possibility is explored, the universe splits. Given a number of possible alternative outcomes, each one is played out - in its own universe. . . .
According to quantum mechanics, nothing at the subatomic scale can really be said to exist until it is observed. Until then, particles occupy nebulous "superposition" states, in which they can have simultaneous "up" and "down" spins, or appear to be in different places at the same time.
Observation appears to "nail down" a particular state of reality, in the same way as a spinning coin can only be said to be in a "heads" or "tails" state once it is caught.
According to quantum mechanics, unobserved particles are described by "wave functions" representing a set of multiple "probable" states. When an observer makes a measurement, the particle then settles down into one of these multiple options.
The Oxford team, led by Dr David Deutsch, showed mathematically that the bush-like branching structure created by the universe splitting into parallel versions of itself can explain the probabilistic nature of quantum outcomes.
Terry Pratchett fans will recognize that the "bush-like branching" referenced above is in fact a phenomenon known on Discworld as "the trousers of time."