Bohm and other physicists, including Valentini, view the Born rule linking R to the probability density function ρ ρ = R 2 as representing not a basic law, but rather as constituting a result of a system having reached quantum equilibrium during the course of the time development under the Schrödinger equation. It can be shown that, once an equilibrium has been reached, the system remains in such equilibrium over the course of its further evolution: this follows from the continuity equation associated with the Schrödinger evolution of ψ ψ . However, it is less straightforward to demonstrate whether and how such an equilibrium is reached in the first place.