The Univers most be a solid no empty spaces at all not ,or multiple realitiese could not exist at the same time and in the same place at any givon moment in time that said if the university is solid thair most be trillions of universe's equill to and of the same mass and size as our galaxy The big bang theory easily explains this a very small amount of matter could easily fill a space larger than our galaxy and still fite in a bowling bag. That said I would have to say multiple universes will exist in larger numbers as the our universe expands.Ontill it pops and return to its solid form and we big bang agean,An example would be a black hole as time more black holes form Ontill all the black holes super compression in to a solid as mater can not be destroyed the energy most be released and ta da,a big bang.