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In physical terms, we know that every human action can be reduced to a series of impersonal events: Genes are transcribed, neurotransmitters bind to their receptors, muscle fibers contract, and John Doe pulls the trigger on his gun. But for our commonsense notions of human agency and morality to hold, it seems that our actions cannot be merely lawful products of our biology, our conditioning, or anything else that might lead others to predict them. Consequently, some scientists and philosophers hope that chance or quantum uncertainty can make room for free will.
For instance, the biologist Martin Heisenberg has observed that certain processes in the brain, such as the opening and closing of ion channels and the release of synaptic vesicles, occur at random, and cannot therefore be determined by environmental stimuli. Thus, much of our behavior can be considered truly “self-generated”—and therein, he imagines, lies a basis for human freedom. But how do events of this kind justify the feeling of free will? “Self-generated” in this sense means only that certain events originate in the brain.
If my decision to have a second cup of coffee this morning was due to a random release of neurotransmitters, how could the indeterminacy of the initiating event count as the free exercise of my will? Chance occurrences are by definition ones for which I can claim no responsibility. And if certain of my behaviors are truly the result of chance, they should be surprising even to me. How would neurological ambushes of this kind make me free?
Imagine what your life would be like if all your actions, intentions, beliefs, and desires were randomly “self-generated” in this way. You would scarcely seem to have a mind at all. You would live as one blown about by an internal wind. Actions, intentions, beliefs, and desires can exist only in a system that is significantly constrained by patterns of behavior and the laws of stimulus-response. The possibility of reasoning with other human beings—or, indeed, of finding their behaviors and utterances comprehensible at all—depends on the assumption that their thoughts and actions will obediently ride the rails of a shared reality. This is true as well when attempting to understand one’s own behavior. In the limit, Heisenberg’s “self-generated” mental events would preclude the existence of any mind at all.
The indeterminacy specific to quantum mechanics offers no foothold: If my brain is a quantum computer, the brain of a fly is likely to be a quantum computer, too. Do flies enjoy free will? Quantum effects are unlikely to be biologically salient in any case. They play a role in evolution because cosmic rays and other high-energy particles cause point mutations in DNA (and the behavior of such particles passing through the nucleus of a cell is governed by the laws of quantum mechanics). Evolution, therefore, seems unpredictable in principle.13 But few neuroscientists view the brain as a quantum computer. And even if it were, quantum indeterminacy does nothing to make the concept of free will scientifically intelligible. In the face of any real independence from prior events, every thought and action would seem to merit the statement “I don’t know what came over me.”
If determinism is true, the future is set—and this includes all our future states of mind and our subsequent behavior. And to the extent that the law of cause and effect is subject to indeterminism—quantum or otherwise—we can take no credit for what happens. There is no combination of these truths that seems compatible with the popular notion of free will.
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