(Original Review, 1994-11-17)
Dave Chalmers did a great job of making consciousness popular but his own view was 400 years out of date. Descartes is the real rigorous physicist here - he was after all one of the people who devised physics. What he meant by the soul and God being 'spirit' is that they caused matter to move. Matter for Descartes was just the inert occupancy of a space (extension). So physics consisted of the interaction of spirit and matter. We now call spirit 'force' or 'energy' and Descartes was quite right because thinking is all about electromagnetic fluxes - which in themselves do not occupy space or have mass. His mistake was to think that there had to be one special spirit unit. Leibniz sorted that out in 1714.
If you're into stuff like this, you can read the full review.