I propose the universe exists in itself. That the interstellar space - is the same as subatomic space. Its both at the same time, like a möbius strip. Space between stars is space between atoms, etc.
The universe will keep expanding until entropy reaches a maximum -- the "Big Freeze." Once maximum entropy is reached -- wherein all atoms in the universe are totally dispersed, everything is the same distance from everything else, and the universe is a totally uniform field -- one could say that is very orderly indeed, i.e. the theoretical minimum entropy.
I imagine that all of the matter in the universe being perfectly dispersed would quite neatly "fill" the universe. So who's to say such a situation isn't infinitely dense?
Much like the moment just before the Big Bang.