The Kin,' said the Doctor. 'A population that consists of only one creature, but able to move through time as easily and instinctively as a human can cross the road. There was only one of you. But you'd populate a place by moving backwards and forwards in time until there were hundreds of you, then thousands and millions, all interacting with yourselves at different moments on your own timeline. And this would go on until the local structure of time would collapse, like rotten wood. You need other entities, at least in the beginning, to ask you the time, and create the quantum superpositioning that allows you to anchor to a place–time location.
( Neil Gaiman )
[ Doctor Who: Nothing O'Clock ]
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