What If—

What If--? is a short story by Isaac Asimov. The story was inspired by the author's wife, who challenged him to produce a story based on a train trip they were taking to New York.

A fantasy rather than a science fiction story, it was published in the Summer 1952 issue of Fantastic, and was reprinted in the collection Nightfall and Other Stories (1969).

A married couple are travelling on a train from Boston to New York. They meet a mysterious non-speaking man known only as Mr If, who shows them a small portable television-like device about six by nine inches in size (which is conceivably the first laptop)

On the screen, he shows them scenes from their earlier lives and what might have happened if certain minor but pivotal events had not occured. This idea, that major events can be altered by relatively minor changes, would be expanded and developed in the novel The End of Eternity.