where G μ μ ν ν = R μ μ ν ν − − R 2 g μ μ ν ν is the Einstein tensor, which combines the Ricci tensor, the scalar curvature and the metric tensor ; Λ Λ is the cosmological constant ; а T μ μ ν ν is the energy-momentum tensor of matter; π π is the mathematical constant pi ; c is the speed of light ; and G is the Newtonian constant of gravitation.