I believe that would properly be called a hypothesis rather than a theory.At any rate. It is my hypothesis that a universe is "created" whenever matter exceeds or matches the speed of light. That is also the formation of a black hole. Our universe is a black hole and visible in some universe "above" us as such. Black holes in our universe "contain" other universes which then must contain even more universes.The thing is, we could never visit these other worlds. The trick of it is that matter at the speed of light changes the rules of time proper. Time in our universe is hypercompressed compared to that of the universe above us. Our universes entire existence, from big bang to big rip, is a single moment from the perspective of that world and in fact every moment sees a full "life-cycle" of our universe (the black hole). This same thing naturally occurs in the black holes of our universe. Universes are born, exist for eons (from their perspective), then collapse back in on themselves faster than can even be perceived.If you were to fall into a black hole, when the matter of your body met the event horizon of the hole it would "fall into" the below universe, bit by bit, moment by moment, slipping into each big bang of that universe and resulting in a different set of circumstances each time.