Bohm advanced the view that quantum physics meant that the old Cartesian model of reality – that there are two kinds of substance, the mental and the physical, that somehow interact – was too limited. To complement it, he developed a mathematical and physical theory of "implicate" and "explicate" order. He also believed that the brain, at the cellular level, works according to the mathematics of some quantum effects, and postulated that thought is distributed and non-localised just as quantum entities are.