Let us consider a possible world WM where consciousness is an M-property. At this world consciousness acts to collapse the wave function. Supposing that we live at WM can you or I have a zombie twin? A zombie twin is one that is physically identical to me in the relevant ways and which lacks consciousness. Suppose that I am actually suffering from a headache while eating Jelly Belly jelly beans. Then my zombie twin is in exactly the same physical states but without the consciousness. This means that the zombie must have a brain and that this brain must be in the same physical states that my brain is in. But my brain is in a collapsed state of definitely being in the relevant neural correlates (due to the presence of conscious experience). In the world where there is no consciousness, and which is physically just like WM (call this world WM-C), there would be no collapsed state. This is because the M property is missing. Since I am not in a superposition of states and my ‘zombie’ twin is we are not in the same physical states.
So it seems that if consciousness is an M-property then zombies are inconceivable and this in turns shows that if consciousness is an M-property then consciousness is a physical property.
But one might object that the right world to think about is WP. At this world the neural correlate of consciousness, construed here as distinct from consciousness itself (for the sake of argument), collapses the wave function. It is this world, continues the objection, rather than WM-C, that is the zombie world relative to WM. At WP there is a creature that has a brain, and which has a definite collapsed state identical to the neural correlates of the experience that I am actually having. This is the quantum zombie, not the one that is in the superposition of states.
I think it is is plausible that the creature at WP is in the same physical state as I am in some sense, but is it the case that WP has the same physics as WM? I would argue that they have similar physics but they are not the same. In WM when you lack consciousness you have a giant superposition that evolves deterministically according to the Schrodinger equation. There may be quasi-classical branches due to decoherence but that is not the same thing as there being a collapsed world, which is what we have at WP.
You cannot just start with WM and subtract consciousness and end up with WP. Instead you end up with WM-C and you then need to add some new physical law (or change the previous one), stating that it is the neural correlate that is responsible for collapsing the wave function. These worlds have different laws of physics and so are not the same. This is different than the zombie argument as normally construed, which leaves all the strictly physical laws in tact and simply posits the removal of the super-physical laws connecting the neural correlates of consciousness to actual consciousness.
Of course, consciousness probably isn’t an M-property but even so, any thoughts on the argument?