> Scifi --to me, but to many others as well-- is a thought experiment in prose. Like any work of fiction, it needs to have some consistency, but certainly not total. We can "suspend our disbelief."

Then what, for you, is the distinction between Sci-fi and Fantasy? I think if you draw that line where most people draw it and think through what Chiang is actually doing, he's on the other side of it.

Whatever definition you settle on, it would be more sensible if it didn't disqualify the works that immediately come to mind when we say 'sci-fi' despite them usually exhibiting bad relativity and thermodynamics.

I don't think the distinction is meaningful. The lack of a line is why we ended up with the term speculative fiction.

Trying to get it concise isn't easy. There is a cultural, shared definition. Fantasy simply isn't everything that involves fantasy. It has some specific ingredients. It seems to me that the fantastic element in Fantasy is the setting/environment/world where the characters operate, but that setting is not the important part. The story is about the characters, who usually behave realistic (given their options). It also tends to have a historical nature, although not accurate.

In sci-fi, there's often an (hypothetical) future setting/environment/world involved, but that doesn't really define the difference. The important part in sci-fi is how the events evolve in and how the characters react to and interact with that world, and how that particular definition of that world determines the outcome. The fantasy part is the main ingredient. It's a thought-experiment.

Chiang sets up a world, and his interest is in how that world affects "us" (the characters). It's not about the "arch" of the characters, but it's about the effect the world has on them.