The stress energy tensor is the set of conserved currents corresponding to the invariance of the Klein–Gordon equation under space-time translations x μ μ ↦ ↦ x μ μ + c μ μ . Therefore each component is conserved, that is, ∂ ∂ μ μ T μ μ ν ν = 0 (this holds only on-shell, that is, when the Klein–Gordon equations are satisfied). It follows that the integral of T 0 ν ν over space is a conserved quantity for each ν ν . These have the physical interpretation of total energy for ν ν = 0 and total momentum for ν ν = i with i ∈ ∈ { 1 , 2 , 3 } .