Mankind reaches out into the stars and sends out probes capable of reporting back from well beyond current distances and eventually receives pictures and data from the furthest reaches of our solar system only to discover that there is nothing out there but globes of darkness (of which our solar system comprises just one) hanging in the white void. Decades later, manned ships are sent out to investigate further and eventually we discover that these globes also contain other "universes" containing a single solar system. These universes have their own, sometimes different, laws of physics, life forms, societies and cultures at varying levels of sophistication and technological advancement.
Contact is made, stuff happens.
This one is on my B list, I don't really see it working that well.