Recently while I was thinking about answers I was getting in another thread I realized that I have problem of conceptually grasping something. Problem is not mathematical in nature, it arises from what math is telling us. Average density of universe determines its spatial curvature. In order to preserve assumption of homogeneity and isotropy spatially flat universe is required to be infinite in extent. As demonstrated in flatness-oldness problem, incredibly tiny variation in density would quickly lead to departure from flatness. At the age of 1 ns, 1 part in 1059, and flatness is gone. Here I make one assumption that I think is the correct. If the universe is infinite now, it was infinite to begin with. How the universe "knew" that if it was infinite in extent that it must have very precisely determined density? I mean, why you can't have universe that is infinite, but slightly sparser or denser? If it was infinite and slightly denser it couldn't later close into itself, like math is telling us. It is sort of the case where future determines past. Maybe inflation solves this, but I don't see how. Anyway, is the presumption of spatially flat infinite universe made only as an attempt to preserve cosmological principle, or it has some other foundation?