50th post! Hooray!
So I've been talking a lot about the implications of the Non-Identity Problem for dealing with issues like climate change, and I've come up with a thought experiment to help think about it.
Vlad is a mad scientist, and knows that his neighbors, the Crosbys, have been planning to have a child. He constructs a sophisticated robot in his laboratory (pronounced luh-bor-uh-tory), which he mounts atop a rocket. Vlad then waits at his window with his binoculars until he sees Mr. and Mrs. Crosby walk outside their house to have dinner on the porch. As the Crosbys sit down to eat, Vlad launches his rocket right out of his roof, filling his neighbors with awe and wonder. Inevitably, the fact that the Crosbys watched the rocket fly into space introduces tiny differences in the rest of their lives. Instead of eating at 6:03, they eat at 6:05; instead of talking to her friend Janet for 4 minutes and 35 seconds the next day, Mrs. Crosby talks for 4 minutes and 57 seconds. The differences are so tiny that they aren't really noticeable, but two days later, when the Crosbys get into bed to conceive their child, a different spermatozoon fertilizes Mrs. Crosby's egg than would have done so otherwise. The child developing inside of Mrs. Crosby would not have existed but for Vlad's rocket launch. Programmed to watch for this development, Vlad's robot detects the growing fetus and watches from space as the child is born and grows older.
Sidney Crosby, the Crosbys' son, is now thirteen, and has developed a crush on a girl in his class. One day at recess, he finally musters the courage to go talk to her. This is exactly what Vlad's robot has been waiting for. It turns on a cloaking device (which renders it invisible) and silently descends from space, coming up right behind Sidney as he approaches the girl. Right as the two begin to talk, Vlad's robot grabs hold of Sidney's pants and jerks them to the ground. As the playground erupts with laughter, Vlad's robot silently slips away, leaving Sidney to wallow in his humiliation.
Now, because the robot is only mechanically doing as it was programmed, it should be clear that the sole responsibility for Sidney's de-pantsing lies with Vlad. And assuming that neither Vlad nor anyone else can stop the robot once it's been launched, Sidney's de-pantsing is a necessary condition for Sidney's existence. If Vlad hadn't launched the robot, the Crosbys would have simply had a different child. So Sidney is no worse off than he could possibly have been.
But I don't think it's difficult to see why we might nevertheless want to say that a cost is imposed on Sidney when Vlad's robot pulls his pants down. But what does it mean to say this? And what ethical significance could such a cost have?