CMB fluctuations also tell us the geometry of
univ.
3 possible geometries :
1)0 curvature -- flat , Euclidean geometry
2)+ curvature -- like a spherical surface,
closes on itself
3)
3)-
curvature -- like a saddle (opposite curvature in orthagonal
directions)
Gen. Relativity => spatial curvature
linked to amount of mass
high mass density => + curvature ;
low => - curvature
in applying GR to universe, Einstein
introduced an integration
constant (Cosmological constant) to avoid a
predicted expansion
(not known then). A.E. : ‘my biggest blunder’