Book — Incandescence by Greg Egan

Another hard-SF story in the vein of his earlier Schild's Ladder — which is to say, hard as in technically stretching.

Two strands of story interleave; one being a lightly disguised primer in general relativity being bootstrapped in the plot by a pre-industrial society exposed to extreme conditions, the other being a more conventional (for Egan) post-human polein-style setting, tracing an unexpected trace of DNA life deep into the core of the galaxy, while musing on the theme of what does intelligence do when it's been there (for all interesting values of there), done that (ditto) and got the T-shirt.

While it's the best SF book I've read all year, that's not setting a very high bar, and it's pretty run-of-the-mill Egan. Still, it occupied a wet autumn afternoon in a better way than chatting on 4chan…