Dawn of the Dead: Are Zombies Possible?

Inspired by a recent post on Philosophy, et cetera, I want to talk a little about zombies and what they imply for a materialist theory of the mind.

When I say “zombie,” I don’t mean the shambling, flesh-eating undead of horror films. This thought experiment is about philosophical zombies, which are a different beast altogether. The philosophers’ zombie is a hypothetical creature which, to all outward appearances, is indistinguishable from an ordinary human. The difference is that they lack phenomenal consciousness – they lack qualia.

Qualia are the subjective sensory perceptions of our inner mental life. We see colors: the redness of red, the greenness of green. We hear tones, sharp or high-pitched or dull or low. We taste flavors, salty or bitter or sweet. We feel emotions like joy, anger, or sadness. Zombies, by contrast, have none of these experiences. They are not truly conscious of anything, any more than a stone is conscious, but they act exactly as if they were. A zombie can duck a thrown baseball or write a restaurant review. Point a gun at one and it will flinch and act as if it were afraid.

What does such a bizarre idea have to do with atheism? The answer is that some prominent philosophers claim that zombies are a conclusive disproof of any strictly naturalistic theory of how the mind functions. The train of argument usually goes that zombies are not a metaphysically impossible notion; it involves no self-contradiction to imagine their existing. If they are not self-contradictory, then they are possible. If they are possible, then we could hypothetically build one – a sophisticated robot, let’s say. Such a being would act with rationality and apparent intelligence, yet lack consciousness. But if it’s possible to be an intelligent, rational being without consciousness, the question is, why aren’t we zombies? What makes us different from the robot? The answer, they say, is that there must be a supernatural component to the mind, in other words, a soul. This supernatural component is what gives us our consciousness, our qualia, whereas a being lacking that component could never truly be conscious no matter how much mental processing power it might have.

The problem with zombies, as with many philosophical notions, is that they do not truly prove a point but simply play on people’s differing intuitions about what is possible. No obvious self-contradiction arises when we imagine a zombie, I grant. It is logically possible for such a thing to exist. But that does not mean that zombies are possible in our world, under the laws of physics that hold sway here. Our ability to imagine them is no disproof of this. We, fallible humans, are not cognizant of all the laws of physics, much less their almost infinitely complex hierarchy of ramifications. An intelligence like Laplace’s demon, with perfect knowledge of the universe, might well see some consequence of physical principles which we overlook, and which renders zombies impossible in our world.

Consider a similar example. Just as dualist philosophers claim they can imagine creating a zombie, I claim I can imagine creating a perpetual motion machine. I couldn’t tell you exactly how to build it, just as no one can say exactly how to build a zombie, but I can readily imagine some marvelous machine – blinking lights, coils of wire conducting electric arcs, spinning flywheels, a big brass switch – that, once it’s powered up, begins producing free energy out of nowhere. No self-contradiction arises when I imagine this. But does that mean we can actually build one? Have I just disproved the laws of thermodynamics without getting out of my armchair?

Obviously not. Though we may think we can imagine a working perpetual motion machine, reality is bound to disappoint. So far, every attempt to build one has ended in utter failure, stymied by some physical principle they failed to take into account. The laws of our universe, it appears, interlock in such a way as to perfectly rule out the possibility of perpetual motion machines. There is no loophole where an inventor, however clever, can slip through. It only seems possible because our imaginations do not take into account the critical details that any practical attempt cannot avoid.

The dualists, I believe, are in the same boat. They may think they can imagine zombies, but that doesn’t mean they’re actually possible. Indeed, I suspect the opposite is more likely true: any creature complex enough to behave with all the creativity and adaptability of a human being would have to have consciousness and qualia, or something very much like them.

After all, how could a zombie dodge a thrown baseball, unless its eyes (or cameras) conveyed images of nearby objects; unless those images were in some way converted into an internal model of the world; and unless that model contained some data stream or symbol which represented a small, round, rapidly approaching object? How could a zombie write a restaurant review unless its chemical sensors were linked to a sophisticated mapping of what readings correspond to what flavors and the many subtle ways in which various combinations could interact with each other? How could a zombie convincingly simulate fear unless it had a wide-ranging ability to keep track of events in the external world and infer which ones could pose a threat to its continued existence?

It is not at all obvious to me that a being with such a sophisticated repertoire of memory, understanding and perception could fail to be conscious. In fact, I strongly suspect the opposite: any being with this capability would have to be conscious, given the physical laws that hold in our world. Consciousness is not an optional add-on, but an inevitable product of a certain degree of cognitive sophistication. In particular, I believe the ability to explicitly represent one’s own self in one’s mental catalog of objects, and to introspect one’s own internal information processing – which, again, a zombie can do – is a vital building block of true consciousness as humans possess it, if it is not consciousness itself.

The dualists assume that an intelligent being could fail to possess qualia, and therefore conclude that intelligence and consciousness are separable. But this claim is an example of the fallacy of circular argument. If you assert that it’s possible to hold everything else about the world constant, but subtract consciousness, then you’re not arguing for dualism, you’re assuming dualism! The conclusion which you wish to reach is already contained in the starting assumptions you feed into your argument. Whether consciousness is an inevitable outcome of the working-out of physical laws inside intelligent brains, or whether it’s an unnecessary epiphenomenal accompaniment, is the very thing at issue. I argue that, contrary to some people’s intuition, consciousness and intelligence are in fact not separable. I can’t prove it; but neither can the dualists prove that they are.

The only remaining question, which I admit is a vexing one, is: why qualia? Why does consciousness have any subjective character at all? The way in which our minds represent characteristics of the external world as ineffable interior perceptions does seem strange, and not like most other phenomena we encounter. It does indeed seem difficult to imagine that any science, however advanced, could explain precisely how such subjective experiences arise from the collisions of atoms inside the brain.

But our inability to imagine it, at this point in time, is no proof that it’s impossible. The existence of life was also once considered to be an impenetrable mystery, inexplicable except by postulating a supernatural “vital force”. Yet life has since been shown to have an explanation comprehensible in terms of physical laws. (Overcoming Bias writes about “encapsulating the mystery as a substance” – an apt description of the situation.) I see no reason to believe that qualia will prove to be any different. Though they may seem to be a fundamentally different kind of thing, that’s just an artifact of our present ignorance. Most likely, qualia arise from the physical laws of the cosmos no less than any other natural phenomenon. We don’t understand precisely how – and maybe the mysterians are right, and we never will – but still, that is no proof that it is impossible.

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