Where does the story take place?

It takes place in a barred spiral galaxy. Over the course of the series the story unfolds in several different alternate realities, called actualities in the series. (A possibility is a possible permutation of an actual event. An actuality is a realized possibility.) Most of the action takes place in a planetary system which vaguely resembles the Solar System. It takes place upon planets, moons, and space stations and aboard space vessels.