For practitioners of a supposedly observational discipline, astronomers are good at inventing things. Mostly they imagine celestial objects that cannot be immediately seen but are suspected on the basis of theory to lurk in the dimmest recesses of the universe. Then they race to find them or to look so thoroughly that they are sure that they do not exist after all. If they return empty handed, it’s back to the drawing board.

In the last few years, astronomers have begun playing for the biggest stakes of all by postulating the existence of other universes. These parallel realms may be similar to – or vastly different from – our own. The more the theoreticians look, the more corners they find, and