Full Idea
It is often argued that any interaction between the physical and the mental - as defined by Descartes - would require a violation of the first law of thermodynamics, the principle of conservation of energy.
Gist of Idea
Interaction between mental and physical seems to violate the principle of conservation of energy
Source
comment on René Descartes (Meditations [1641]) by Mark Rowlands - Externalism Ch.2
Book Reference
Rowlands,Mark: 'Externalism' [Acumen 2003], p.11
A Reaction
This would be because consciousness is adding energy to the system (in order to generate movement) without it having come from anywhere else in the physical system. A good objection, which only a miracle could overcome.