Friedmann Equation

The equation that describes the evolution of the cosmological scale factor of the Robertson-Walker metric.

The Friedmann Equation has the form:

$\dot R^2 = {8\pi G \over 3} \rho R^2 - kc^2$

Here R is the Scale Factor of the universe. The term on the left is the rate of change of the scale factor squared with time. The first term on the right is the effect of gravity. The second term on the right is the curvature constant determining the geometry of the universe.