I'm prepared to accept that the universe 'popped' into existence out of nothing, perhaps in the same way that a pair of virtual particles pop into existence, exist for a few nanoseconds, and then annihilate one another.

I feel intuitively (which usually means I'm wrong!) that within our Universe - expansion and gravity will eventually cancel out and the universe will stop expanding. And for a fleeting instant - we will have the Steady State Universe of Fred Hoyle. Then gravity becomes the dominant force and the contracting phase begins. Perhaps one fewer proton in the universe might mean this contraction phase will never happen - I find the notion of a perfectly balanced universe appealing and 'tidy' - more so than the Heat Death idea where dead Universes litter the higher dimensions for eternity! (Although I suppose the Big Crunch could happen after Heat Death)

Also - regarding putting a time scale on when Heat Death might happen: With an almost flat gravity field, and almost no energy or movement or changes occurring (other than perhaps the occasional theorised proton decay) can we really measure time in a Universe in this state? Would time not virtually 'stand still'?