The logic for why zombies can’t exist, very briefly, goes like this:
You see a bright red light.
The mysterious redness-quality of the red light seems inexplicable in merely material terms.
You think, within your stream of consciousness, “The redness of this light seems inexplicable in merely material terms.”
You say out loud, “The redness of this light seems inexplicable in merely material terms.”
Your lips moved.
Whatever caused your lips to move must lie within the realm of physics because it had a physical effect.
If we sum up all the forces acting on your lips—gravity, electromagnetism, etc. - we will necessarily include the proximal cause of your lips moving. This is because when we sum up the forces acting on your lips, we can tell where your lips will go. In particular, we can tell that they’ll move. So if we delete anything that isn’t on the force list, your lips go to exactly the same place.
As it so happens, the proximal cause of your lips moving is nervous instructions sent from your motor cortex and cerebellum. It is not possible to imagine a world in which your lips move and all the laws of physics are the same, but there are no nervous impulses from the motor cortex, because the laws of physics include the nervous impulses from the motor cortex, which is why your lips move. Everything that actually causes your lips to move is not epiphenomenal—it has a direct and material effect—meaning that it shows up within low-level physics.
If something makes an atom go from one place to another that isn’t within our known physics, then we’ll see, when we examine the atom, that the sum of forces says the atom should go one way, but the atom goes another way instead. This would mean that our list of laws of physics, on that low level of organization, was incomplete; we would not be able to account for why an atom goes to one place instead of another without postulating additional physical laws. Not “psychophysical bridging laws”, physical laws that directly cause the atom to be in one place rather than another, given its initial conditions.
Exactly the same logic applies as we work our way backward along the causal chain. Whatever caused you to think, “The redness of this light seems inexplicable in merely material terms,” must exist within the web of material cause and effect in order to have the final result of your lips moving.
Whatever causes the mysterious redness of red to seem inexplicable in material terms, must exist in the web of material cause and effect, because a thought to this effect appears within your stream of consciousness, and you are capable of speaking your stream of consciousness out loud, which makes your lips move.
This may seem really odd. But just because something seems really odd, doesn’t mean it isn’t true. Your sense of “really odd” does not give you direct, veridical information about the universe. Even when something seems really, really odd, it’s still a fact about you, not a fact about the universe.
Penrose’s theory that consciousness involves magical physics is wrong, but coherent. The theory that consciousness involves no physics is not. Admittedly, realizing this requires logic and human beings are not logically omniscient, so in that sense zombie-believers may be “coherent” relative to their own failure to realize that philosophical discussions are themselves material phenomena. Which is of course the point of this post.
The causes of all material effects are also material in the sense that any correct physical prediction will include them by identity, and any predictive method which fails to include them in any way will deliver incorrect predictions. Philosophical discussions and philosophical intuitions are material phenomena and all their causes are within the laws of physics; on pain of our physical predictions being incorrect if the known laws of physics fail to capture-by-identity the causes of all philosophical intuitions.
Well said, Constant.
The logic for why zombies can’t exist, very briefly, goes like this:
You see a bright red light.
The mysterious redness-quality of the red light seems inexplicable in merely material terms.
You think, within your stream of consciousness, “The redness of this light seems inexplicable in merely material terms.”
You say out loud, “The redness of this light seems inexplicable in merely material terms.”
Your lips moved.
Whatever caused your lips to move must lie within the realm of physics because it had a physical effect.
If we sum up all the forces acting on your lips—gravity, electromagnetism, etc. - we will necessarily include the proximal cause of your lips moving. This is because when we sum up the forces acting on your lips, we can tell where your lips will go. In particular, we can tell that they’ll move. So if we delete anything that isn’t on the force list, your lips go to exactly the same place.
As it so happens, the proximal cause of your lips moving is nervous instructions sent from your motor cortex and cerebellum. It is not possible to imagine a world in which your lips move and all the laws of physics are the same, but there are no nervous impulses from the motor cortex, because the laws of physics include the nervous impulses from the motor cortex, which is why your lips move. Everything that actually causes your lips to move is not epiphenomenal—it has a direct and material effect—meaning that it shows up within low-level physics.
If something makes an atom go from one place to another that isn’t within our known physics, then we’ll see, when we examine the atom, that the sum of forces says the atom should go one way, but the atom goes another way instead. This would mean that our list of laws of physics, on that low level of organization, was incomplete; we would not be able to account for why an atom goes to one place instead of another without postulating additional physical laws. Not “psychophysical bridging laws”, physical laws that directly cause the atom to be in one place rather than another, given its initial conditions.
Exactly the same logic applies as we work our way backward along the causal chain. Whatever caused you to think, “The redness of this light seems inexplicable in merely material terms,” must exist within the web of material cause and effect in order to have the final result of your lips moving.
Whatever causes the mysterious redness of red to seem inexplicable in material terms, must exist in the web of material cause and effect, because a thought to this effect appears within your stream of consciousness, and you are capable of speaking your stream of consciousness out loud, which makes your lips move.
This may seem really odd. But just because something seems really odd, doesn’t mean it isn’t true. Your sense of “really odd” does not give you direct, veridical information about the universe. Even when something seems really, really odd, it’s still a fact about you, not a fact about the universe.
Penrose’s theory that consciousness involves magical physics is wrong, but coherent. The theory that consciousness involves no physics is not. Admittedly, realizing this requires logic and human beings are not logically omniscient, so in that sense zombie-believers may be “coherent” relative to their own failure to realize that philosophical discussions are themselves material phenomena. Which is of course the point of this post.
The causes of all material effects are also material in the sense that any correct physical prediction will include them by identity, and any predictive method which fails to include them in any way will deliver incorrect predictions. Philosophical discussions and philosophical intuitions are material phenomena and all their causes are within the laws of physics; on pain of our physical predictions being incorrect if the known laws of physics fail to capture-by-identity the causes of all philosophical intuitions.
All this is true a priori.