# curvature constant

The curvature constant is a constant (*k*) appearing in the Robertson-Walker metric which determines the curvature of the spatial
geometry of the universe. The three standard Friedmann models have: *k* > 0 for positive curvature (spherical geometry), *k* < 0 for negative curvature (hyperbolic geometry), and *k* = 0 for zero
curvature (flat geometry).