Expansion isotropization during the inflationary era

A solution of Einstein's field equations for a vacuum with flat, anisotropic three-space and a nonvanishing cosmological constant is derived. It represents a generalization of the flat de Sitter solution to the anisotropic case. This solution describes a universe model entering the Guth inflationary era at t1 = 10-35 sec as an anisotropic Kasner universe, and terminating this era at t2 = 1.3 x 10-33 sec as an isotropic de Sitter universe. The mean expansion anisotropy has decreased by a factor of order 10-168 during the inflationary era. The properties of this solution imply that the transition to an inflationary era is not prevented by any amount of anisotropy. The mean expansion isotropization of the most general homogeneous universe models with anisotropic curved three-space is estimated, and the anisotropy is now found to decrease by a factor of order 10-112 during the Guth inflationary era