I always have trouble understanding this concept. Please correct me if I am wrong somewhere in my line of thought. Is the universe finite or infinite? Using the famous balloon analogy, we can think of it as a finite expanding universe. But in that analogy the balloon has a curvature. Does the universe have a curvature? According to the most recent observations the universe is almost flat. So, how come a flat universe be finite? For our assumption of a homogeneous and isotropic universe shouldn't a flat universe be infinite?