I think gravity would contain all energy in an endless, cycling perpetual motion machine, what goes up, must come down. Big bang, big crunch, big bang, cycling forever, or it could never begin, due to causality. There are the multiple universes, an infinite number, of an almost infinite amount of possible variations caused by quantum chaos, in the same place, one after the other.
I could be wrong, but I believe it's more rational to believe that, than in God, which was the alternative idea, God did it, and Christians still try to use the single universe hypothesis, which came from Christianity, in science, to prove that God had to do it, because it couldn't work otherwise, due to causality. There could be some alternative mechanism, some other dimension, stuff could just pop up out of another realm and cause universes all over the place, but why on earth would you make such a claim, when it could never be proved? We can't even see the majority of this universe, and never will. It's like black hole radiation, you can't prove that.