More of Chiang's clean-lined and thoroughly thought-through excursions into 'what ifs' that always also illuminate the world we actually inhabit.
Some of these do feel a bit 'thought exercise'-y, their animating ideas and how those are worked through dominating the story structures housing them. But the best are exceptional, especially the title story, in which a species discovers they're living inside a self-enclosed sphere within which their breathing will eventually create entropy through a complete equalisation of air pressure everyone in their closed universe, and "Anxiety is the Dizziness of Freedom", in which portable divergent-timeline creating devices have been invented, allowing their owners to communicate with their other-timeline self and other counterparts, and one of the ones in which Chiang's moral concerns are at the forefront.
