I do get that.. I am not sure if I am right but my assumption is ..whats if Big Bang just produced only finite matter and anti matter. So(covering the fact that matter and anti matter amount should balance) the Big Bang itself had to happen somewhere in emptiness..(That's the reason why we expect matter and anti matter to balance each other).. This region of "Space" not sure if u should say space.. But the medium must have a volume bigger than the volume of matter and anti matter combined ..(classically to hold them) ..Then the matter expands as an after effect of Big Bang ..so by expand we mean it should expand some where in this medium.. So again assuming finite matter in universe there got to be a outside as well.. (Just a hypothesis) help me :)