Flatness problem  From Wikipedia, the free encyclopedia Jump to:
navigation, search 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<1, k<0); and a flat universe with exactly
the critical density (Ω=1, k=0). Our universe, unlike the
diagrams, is three-dimensional.    The problem was first
mentioned by Robert Dicke in 1969. The most commonly accepted
solution among cosmologists is cosmic inflation, the idea that
the universe went through a brief period of extremely rapid
expansion in the first fraction of a second after the Big Bang;
along with the monopole problem and the horizon problem, the
flatness problem is one of the three primary motivations for
inflationary theory.[2]  Energy density and the Friedmann
equation[edit]  According to Einstein's field equations of
general relativity, the structure of spacetim