This simply isn’t possible with free will. If someone tells you that you do not actually have free will but have actually been acting under an illusion, you cannot sit back and let determinism take over. When the waiter asks you whether you like soup or salad, you cannot say “Oh, well I’ve just learned that free will is an illusion and all my actions are completely determined by the previous state of the world, so I’ll just let them play themselves out.” I mean, you can say that, but the waiter will look at you like you’re crazy and you will get neither soup nor salad.
It seems overwhelmingly bizarre that evolution would have given us this strangest of illusions. This is not a spandrel, a small place evolution never had time to be concerned about. The illusion of free will affects all aspects of our lives and takes an enormous amount of work. One would think evolution would have eliminated it were it genuinely false.
So what is the other possibility? The other possibility is that not all actions are entirely determined by the preexisting state of the world. And, in fact, recent advances in physics seem to show this is somewhat the case. Quantum mechanics suggests that at some fundamental level there is randomness involved in the laws of the world. And chaos theory shows us that small amounts of randomness in a system can have real large-scale effects.
So, although it seems extremely improbable, if we have to avoid the improbability of evolution not breeding out an illusory free will, then we’re forced to look to the randomness of quantum mechanics for an explanation.
But, some argue, this is insufficient. Quantum mechanics only gives us randomness — but free will isn’t just the pursuit of random behavior, it’s the pursuit of particular behaviors. While quantum mechanics can’t predict each individual bit, it does give overall probability distributions. Volitional behaviors would wreak havoc with those even distributions.
Not true. Imagine the simple case where we have one quantum bitstream: a series of zeroes and ones, in which each individual number cannot be predicted, but there’s an overall law saying that roughly half of them will be one and half will be zero. And let us simplify the system to say that if the result of the quantum effect is 0 then the person moves left, and if it’s 1 they move right. In the naive scenario, free will affects this quantum bitstream so that when the person wants to move left the randomness keeps coming up zeroes. But that would violate the laws of physics — the results would no longer be half ones and half zeroes.