Descartes ultimately distinguished between two sorts of substances: those that are extended in space (res extensa) and those that are purely mental (res cogitans). However, physics now tells us that, at their most basic, all those “things”—or “particles,” if you will—that we once labeled as extended are not really extended at all. Atomic and subatomic particles are more accurately described as points of localized mass-energy, rather than spheres with discrete spatiotemporal dimensions. In light of this, Descartes’ dilemma can be, in a way, resolved: He viewed mental contents as distinct and incapable of scientific description because they lacked physical extensions that could be measured. We have now seen, however, that the very “things” that we once praised for their apparent extension (i.e., their property that we believed allowed them to be studied scientifically) are not really extended at all. Thus, it could be argued that the lack of physical extension is not sufficient for the exclusion of res cogitans, or the mental, from scientific inquiry.
(Note: I am not denying any distinction between ordinary physical events and mental events. There certainly is a distinction. I am merely proposing that this view of the distinction may be false, though this is certainly not new.)