(London Telegraph) Most Doctor Who fans are happy to accept that the time lord can drop in on the middle ages without probing the matter too much further. But most Doctor Who fans aren’t Brian Cox.

Whizzing forward a few thousand years in time would be a breeze, the physicist and television presenter said, but finding your way back again could be more of a problem.

While Einstein’s theory of Special Relativity would allow the Doctor “almost total freedom of movement” in the future, he would need to find a wormhole – a short cut through space and time – in order to return to the past, he explained.

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