Lambda=0 cosmology of a brane-like universe

We examine the possibility that Friedman-Robertson-Walker evolution is gove rned by an effective (rather than by the actual) energy density. A concrete example is provided by Lambda = 0 Regge-Teitelboim cosmology, where critic al cosmology only requires subcritical matter density (Omega(matter) < 1), and the age of a flat matter-dominated universe gets enhanced by a factor o f 9/8) Dual to the mature dilute universe is the embryo universe, the evolu tion of both is governed by P-eff = - 1/9 rho(eff).