Multiple histories
The concept of multiple histories is closely related to the many-worlds interpretation of quantum mechanics. In the same way that the many-worlds interpretation regards possible futures as having a real existence of their own, the theory of multiple histories reverses this in time to regard the many possible past histories of a given event as having real existence.
This concept was introduced by Richard Feynman, whose Feynman path integral is integrated over the set of all possible histories.
The idea of multiple histories has also been applied to cosmology, in a theoretical interpretation in which the universe has multiple possible cosmologies, and in which reasoning backwards from the current state of the universe to a quantum superposition of possible cosmic histories makes sense.
