When the force is associated with a potential energy F = −∇ U (see conservative force), a steady-state solution to the above equation (i.e. 0 = R = ⁠ ∂ c / ∂ t ⁠) is: c ∝ ∝ exp ⁡ ⁡ ( − − D − − 1 ζ ζ − − 1 U ) (assuming D and ζ are constant). In other words, there are more particles where the energy is lower. This concentration profile is expected to agree with the Boltzmann distribution (more precisely, the Gibbs measure). From this assumption, the Einstein relation can be proven: D ζ ζ = k B T .