(cross-posted at Philosophy Sucks!)
I have long wondered what dualists mean when they speak of nonphysical properties. Today I was reading Chalmers’ paper The Matrix as Metaphysics and he says something that may shed some light on the way in which he thinks of nonphysical properties. He argues that the matrix scenario can be construed as a metaphysical hypothesis about the ultimate nature of the physical world. If this is right then there is a sense in which dualism is true. The mind is a distinct entity that exists outside of physical space-time and causally interacts with the physical body (i.e. the matrix body). This is because the physical theory that is true of reality in the matrix is a computational theory on which the ultimate things which exist are bits (zeros and ones). Thus brains in the matrix are ultimately composed of bits and when people in the matrix talk about brains they ultimately are talking about bits. The brain which is outside of the matrix is not composed of bits (let us assume). It is ultimately composed of something else (let’s say strings). Thus the brain outside the matrix, when viewed from the perspective of someone who is in the matrix, is nonphysical. It is not something that could be deduced from a completed matrix microphysics (which would be phrased in terms of ones and zeros).
One might wonder whether a completed matrix physics would have to be supplemented with (from the perspective of the matrix) nonphysical laws in order to capture outside the matrix facts or whether we might view the truly completed matrix physics as being expanded to include the outside-physics. On this latter view the laws of matrix-physics would be a special subset of the laws of outside-physics. If this were true then the matrix-physics would not be complete until it was expanded to include outside-physics and physicalism could still be true. One might also wonder whether people in the matrix had largely true outside-physics beliefs since the matrix world is a deliberate simulation of outside-physics.
But setting aside these issues there are strange results. Suppose that physicalism is true and that consciousness is a purely physical property of the brain. Let us also assume that this is true of a brain that is not in a matrix scenario. Call this scenario 1. Now imagine that a physical duplicate of this physicalist brain has been in a matrix scenario since birth Call this scenario 2. Then physicalism is true in scenario 1 and dualism is true of scenario 2. But these brains are physically identical! The only difference is that one of them has been envatted for life. Furthermore this shows that we could not resolve the dispute between the physicalist and the dualist until one was in a position to determine whether or not one is in a matrix scenario. Since Chalmers himself admits that he cannot a priori rule out that he is not in a matrix scenario he must also admit that he is not in a position to a priori tell if physicalism or dualism true. So, suppose that we are actually in a matrix scenario then conceiving of zombies is just conceiving of a computer simulation composed completely of NPCs (non-player characters). But this doesn’t show that physicalism is false, since physicalism is best construed as the claim that lines up with the first brain in scenario 1. With this understanding of nonphysical physicalism turns out to be nothing but the hypothesis that we are not in the matrix.*
Notice also that on this construal of nonphysical even zombies can have nonphysical mental properties. The traditional zombie is a creature that is physically identical to me and lacks consciousness. Now suppose that I have a zombie twin who is in a matrix scenario since birth. My matrix zombie twin has nonphysical properties (which are the very same properties that I physically have) but no qualitative properties. So, whether one has nonphysical properties or not is simply a matter of whether one is in the matrix or not. Chalmers’ defense of nonphysicalism can thus be seen as a defense of the claim that we are in the matrix.
*But even if we were in the matrix there is a sense in which we can say that physicalism is still ultimately true since in the above envisioned world qualitative properties turn out to be identical to properties which are physical in terms of outside-physics (since these properties are the very same as the ones in the world where physicalism is true). We could then reformulate physicalism in terms of an ultimate physical theory that captures outside-physics.