flatness problem
The local geometry of the universe is determined by whether the relative density Ω is less than, equal to or greater than 1. From top to bottom: a [[spherical universe with greater than critical density (Ω>1, k>0); a hyperbolic, underdense universe (Ω the early universe must have had a density even closer to the critical density, departing from it by one part in 1062 or less.