∫ ∫ V ( ∂ ∂ | Ψ Ψ | 2 ∂ ∂ t ) d V + ∫ ∫ V ( ∇ ∇ ⋅ ⋅ j ) d V = 0 where j = 1 2 m ( Ψ Ψ ∗ ∗ p ^ ^ Ψ Ψ − − Ψ Ψ p ^ ^ Ψ Ψ ∗ ∗ ) = − − i ℏ ℏ 2 m ( ψ ψ ∗ ∗ ∇ ∇ ψ ψ − − ψ ψ ∇ ∇ ψ ψ ∗ ∗ ) = ℏ ℏ m Im ⁡ ⁡ ( ψ ψ ∗ ∗ ∇ ∇ ψ ψ ) is the probability current or probability flux (flow per unit area).