We examine the possibility that Friedman-Robertson-Walker evolution is governed by an effective (rather then by the actual) energy density. A concrete example is provided by $\Lambda=0$ Regge-Teitelboim cosmology, where critical cosmology only requires subcritical matter density $(\Omega_{ m}<1)$, and the age of a flat matter dominated Universe gets enhanced by a factor of 9/8. Dual to the mature dilute Universe is the embryo Universe, the evolution of both is governed by $P_{ eff}=-{ 1/9}\rho_{ eff}$.
Categories: gr-qc astro-ph hep-th