As far as I'm aware, one of the questions is, is the universe a closed thing without boundarys, or does it have a limit. I ask this because as far as I know, the laws of thermodynamics apply to closed systems. I suppose you might then say, well if the universe is behaving mostly in accordance with these laws, then the universe must have a boundary, but not in the sense of a straight cut off point, rather like a circle with no apparent start or beginning.

Cheers,

Ian