"There Is a Wolf in My Time Machine" is inspired by a theory in physics that there are a multiplicity of timelines, perhaps an infinite number, that branch off from one another every time anyone makes a decision. It is a complex theory, but in essence it maintains that every time you or anyone else makes a decision, you (or that other person) make all possible alternative decisions in new, diverging timelines. Niven sees this as more fantasy than science, and as in "There Is a Wolf in My Time Machine," he tends to use the idea to spin off fantasies without, he says, the usual trappings of fantasy.

One of the notable traits of Niven's fiction is his sharp imagery of amazing people, places, and machines. For instance, in "There Is a Wolf in My Time Machine," he describes what the extension cage looks like...