where <math>\Omega</math> is the mass-energy density fraction of the universe. Specifically, <math>\Omega = \rho/\rho_c</math>, where <math>\rho_c</math> is the ''critical'' mass density, above which the universe would be closed and destined to collapse. | where <math>\Omega</math> is the mass-energy density fraction of the universe. Specifically, <math>\Omega = \rho/\rho_c</math>, where <math>\rho_c</math> is the ''critical'' mass density, above which the universe would be closed and destined to collapse. |