Full Idea
Since Cartesian dualism implies causation from outside of the physical domain, this means there can be no complete physical theory of the physical domain.
Gist of Idea
Mental substance causation makes physics incomplete
Source
Jaegwon Kim (Philosophy of Mind [1996], p.147)
Book Reference
Kim,Jaegwon: 'Philosophy of Mind' [Westview 1998], p.147
A Reaction
This, I think, should be taken as a very strong argument against dualism, rather than as bad news for physics. Some exception might make the closure of physics impossible, but the claim that our brain is the exception looks highly suspect.