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But wait a second. Human beings have, in addition to the physical data flow representing the heat, one other thing: a feeling of heat and pain, subjective experience, consciousness. Why do they? According to Chalmers, studying Cog doesn't answer that question but deepens it. For the moral of Cog's story seems to be that you don't, in principle, need pain to function like a human being. After all, the reflexive withdrawal of Cog's hand is entirely explicable in terms of physical data flow, electrons coercing Cog into recoiling. There's no apparent role for subjective experience. So why do human beings have it?

Of course, it's always possible that Cog does have a kind of consciousness--a consideration that neither Dennett nor Chalmers rules out. But even then the mystery would persist, for you could still account for all the behavior by talking about physical processes, without ever mentioning feelings. And so too with humans. This, says Chalmers, is the mystery of the "extraness" of consciousness. And it is crystallized, not resolved, by advances in artificial intelligence. Because however human machines become--however deftly they someday pass the Turing test, however precisely their data flow mirrors the brain's data flow--everything they do will be explicable in strictly physical terms. And that will suggest with ever greater force that human consciousness is itself somehow "extra."

Chalmers remarks, "It seems God could have created the world physically exactly like this one, atom for atom, but with no consciousness at all. And it would have worked just as well. But our universe isn't like that. Our universe has consciousness." For some reason, God chose "to do more work" in order "to put consciousness in."

When Chalmers says "God," he doesn't mean--you know--God. He's speaking as a philosopher, using the term as a proxy for whoever, whatever (if anyone, anything) is responsible for the nature of the universe. Still, though he isn't personally inclined to religious speculation, he can see how people who grasp the extraness of consciousness might carry it in that direction.

After all, consciousness--the existence of pleasure and pain, love and grief--is a fairly central source of life's meaning. For it to have been thrown into the fabric of the universe as a freebie would suggest to some people that the thrower wanted to impart significance.

It's always possible that consciousness isn't extra, that it actually does something in the physical world, like influence behavior. Indeed, as a common-sense intuition, this strikes many people as obvious. But as a philosophical doctrine it is radical, for it would seem to carry us back toward Descartes, toward the idea that "soul stuff" helps govern the physical world. And within both philosophy and science, Descartes is dead or, at best, on life support. And the New Mysterians, a pretty hard-nosed group, have no interest in reviving him.

The extraness problem is what Chalmers calls one of the "hard" questions of consciousness. What Dennett does, Chalmers says, is skip the "hard" questions and focus on the "easy" questions--and then title his book Consciousness Explained. There is one other "hard" question that Chalmers emphasizes. It--and Dennett's alleged tendency to avoid such questions--is illustrated by something called pandemonium, an AI model that Dennett favors.

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