Ensuring Two Bird Deaths With One Throw

Abstract

Crossing a plain, I come to what looks like a gigantic mirror. But pushing a hand against it, I feel flesh and not glass. The universe must be symmetric, flesh that of my double-left-right reversed but otherwise a perfect replica. The universe must also be fully deterministic, for how else could my double have moved exactly as I did? But never having seen freedom and determinism as incompatible, I find this untroubling. In fact I rejoice. My decision-making ability, I tell myself, is not limited by any admixture of quantum randomness such as would make me in part a puppet pulled by strings of Chance. Do I not actually have twice power I earlier seemed to have? Besides governing my own hands and legs, do I not govern others too? Cannot I make my double kick, wave, clap, whenever I want? Cannot I throw two stones instead of one?-the stone I hurl to kill a bird, and second stone which my double hurls simultaneously? If ever I controlled what my image did in a mirror, why deny that I control what my double does? Well, grounds for denying it are easy to find. Yes, universe-halves interact. I can smash against my double painfully, and while unable to enter his half of universe (he keeps getting in way!) I have no problem in seeing him since light waves pass through each other instead of colliding and bouncing back. Yet he and I are in crucial respects independent. Seeing a snake sneaking up on him, it is not of that particular snake that I feel afraid but of other which I thereby know to be sneaking up on me. It is my fear which makes me run, my double's fear which makes him do likewise. I do not genuinely cause him to run by myself running. Maybe my double moves as he does because I move as I do. It might even be said that heaviness of rock in my hand causally explains why he drops his rock when I drop mine. Rather similar senses of because and causally explain are recognized by Frank Jackson and Philip Pettit (1988, esp. pp. 392-3). The sameness of force on two electrons causally explains why they accelerate at same rate, they write. And why was price of lamb identical at two auctions? Because, they say (and it is surely a because of Ordinary English), the relationship between supply and demand was same. Yet fact remains that stone killing bird in other half of universe is accelerated by my double's hand, not mine. I do not throw two stones. Still, by choosing to run I can ensure that my double runs. While I cannot strictly speaking make him throw stones, I can make it certain that he will. I have only to decide firmly to throw stones myself.