During a surprise trip to the moon by Grandpa, Grandma is mad about being left behind and leaves town with another man with a time machine. Grandpa returns, finds another time machine, and strands Grandma in time and space.

Professor Tarantoga saves human civilization! After using his chronopad to investigate the leading scientists and artists in history, Tarantoga concludes that without exception they are lazy drunkards. So naturally, he sends smart young people into various eras to invent differential calculus, to paint the Mona Lisa, etc.—all while a pair of police inspectors have their eye on him.

The three principal Trekkers find themselves on a planet where everyone is being evacuated to the past to escape an impending supernova.

With eleven years of marriage behind them, Ted and Alice’s fantasies frequently start with a time machine and end with killing one or another of their spouse’s ancestors before they can procreate. So naturally, they each end up at Temponautics, Ltd. Oh, and Ted’s grandpa has some racy fantasies of his own.
In Silverberg’s Something Wild Is Loose (Vol. 3 of his collected stories), he posits that this story is “probably the most complex short story of temporal confusion” since Heinlein’s “By His Bootstraps” (1941) or “—All You Zombues—” (1959), but I would respectfully disagree. In particular, I would describe Heinlein’s two stories as the most complex short stories of temporal consistency in that there is but a single, static timeline and (in hindsight) every scene locks neatly into place within this one timeline. By contrast, Silverberg story involves multiple time travel choices by the characters in what I would call parallel universes. The confusion, such as it is, stems more from what appears to be alternate scenes in disconnected universes rather than temporal confusion per se.