The end of eternity

The End of Eternity is a 1955 science fiction novel by American writer Isaac Asimov with mystery and thriller elements on the subjects of time travel and social engineering. Its premise is that of a causal loop – a type of temporal paradox in which events and their causes form a loop. In The End of Eternity, members of the time-changing organization Eternity seek to ensure that the conditions which led to the founding of Eternity occur as history says they occurred. The protagonist, Andrew Harlan, is placed in a situation where he must decide whether to allow the "circle" to close and Eternity be founded, or to allow the opposite to happen and Eternity never to have existed. Many years later, Asimov tied this novel into his broader Foundation Series by hinting in Foundation's Edge that it is set in a universe where Eternity had existed but was destroyed by Eternals, leading to an all-human galaxy later. The novel was shortlisted to the Hugo Award for Best Novel.