ABSTRACT
The current surge of interest in imaginary worlds of all stripes has not taken place in a cultural vacuum. Few ideas, if any, have held more fascination for the human mind and have been explored by more disciplines than the possibility that there could be worlds other than the one we live in. In this chapter I will address the question of my title by surveying some of the developments in cosmology, philosophy, and media technology that made the idea of worlds other than our own into the popular concept that it is today.
