Claims that some form of consciousness persists after our bodies die and decay into their constituent atoms face one huge, insuperable obstacle: the laws of physics underlying everyday life are completely understood, and there's no way within those laws to allow for the information stored in our brains to persist after we die. If you claim that some form of soul persists beyond death, what particles is that soul made of? What forces are holding it together? How does it interact with ordinary matter?If we insist that some such interaction occurs, we have to reject what we know about physics.
How is the spirit energy supposed to interact with us? Here is the equation that tells us how electrons behave in the everyday world:But,
Don't worry about the details; it's the fact that the equation exists that matters, not its particular form. It's the Dirac equation -- the two terms on the left are roughly the velocity of the electron and its inertia -- coupled to electromagnetism and gravity, the two terms on the right.
As far as every experiment ever done is concerned, this equation is the correct description of how electrons behave at everyday energies.
If you believe in an immaterial soul that interacts with our bodies, you need to believe that this equation is not right, even at everyday energies.If we have an adequate physical explanation for a causal sequence, there is no reason to posit a nonphysical one, and especially no reason to posit one that conflicts with what we know. Carroll is completely right here, not that it will keep people from claiming otherwise. The problems of dualism have been well known for centuries, and Carroll's argument is essentially the same as the objections that folks like Hobbes and Gassendi raised as soon as Descartes articulated his version of dualism. Their objection was basically that we know that physical bodies can causally interact with physical bodies, but we have no evidence that nonphysical entities can have causal effects in the world. So this argument against the immortality of the soul has been in circulation since the 17th century.
The response of Descartes and his acolytes took two forms. Descartes thought that locating the place of interaction between the soul and the body in the pineal gland somehow solved the problem, even though he didn't explain how the soul interacts with the pineal gland. Some of Descartes' followers (the "Occasionalists") argued that God is the only true cause and the appearance of mind-body interaction is an illusion that God maintains by, say, causing your hand to move in just the right way and at just the right time when your soul decides you need to pick your nose.
Which goes to show that no idea is so preposterous that it can't be defended using another, even more preposterous idea.