[Y]ou have free will if you could have chosen otherwise. To put it more technically, if you could rerun the tape of your life up to the moment you make a choice, with every aspect of the universe configured identically, free will means that your choice could have been different.
Coyne borrows the metaphor in his technical account from Stephen J Gould, who ironically uses the metaphor to prove the exact opposite. If the tape of evolution were run again, says Gould, we would not expect human beings to arise. So what gives? Why does one and the same metaphor manifest a totally determined world in physics and fundamentally undetermined world in biology?
It’s hard to avoid the somewhat cynical guess that all that is really in play here is an allergy to the perceived possibility of the non-material. If an ordered and determinate world suggests providence, then, lo and behold, if we run back the tape we will see that all is fundamentally indeterminate*; but if an indeterminate action would suggest a non-material soul, then if we run back the tape we see that all is fundamentally determinate.
Attributing this position to Gould might not seem fair: he objected to to creationism, not providence and was agnostic and not atheist. But he did seem to think that the sheer randomness of historical progression negated any relation to providence or a higher purpose, viz:
We are here because one odd group of fishes had a peculiar fin anatomy that could transform into legs for terrestrial creatures; because the earth never froze entirely during an ice age; because a small and tenuous species, arising in Africa a quarter of a million years ago, has managed, so far, to survive by hook and by crook. We may yearn for a ‘higher’ answer—but none exists.