Chiang's stories walk a thin line between fiction and thought experiment. As prompters for speculation about free will, consciousness, the multiverse etc. they're excellent. I especially liked the title story, set in a pneumatically-powered universe where the equalization of air pressure is a metaphor for entropy in ours, and featuring an extended scene of self-conducted brain dissection. What this story has in common with Chiang's best is that it sticks the emotional landing: The Merchant and the Alchemist's Gate, a time-traveling Arabian Nights-style frame story does this too, and is impossibly clever to boot.

I was less taken with the Hugo-winning novella The Lifecycle of Software Objects, which relates the ups and downs of a group of (mostly) VR-dwelling self-learning AI's, designed and marketed as virtual pets, and their human owners in loco parentis. Unfortunately the "digients" never get past toddler-speak, so the dialogue is somewhat infuriating, although it has its moments, like when they get upset because their owners won't legally incorporate them:

"People say being corporation great," says Marco. "Can do whatever want."