Elsewhen

Elsewhen (1941) is a science fiction novella by American writer Robert A. Heinlein, concerning time travel and parallel universes. It was first published as Elsewhere in the September 1941 issue of Astounding Science Fiction, under the pen name Caleb Saunders, and was reprinted in the 1953 book Assignment in Eternity, with some minor changes, and an additional character and that character's journey.