I finished Greg Egan's
The Clockwork Rocket. It starts off with a bucolic scene that makes you wonder if it's going to be a light-hearted story about quirky aliens, but before long you're neck deep in theoretical physics in a universe with different physical laws than our own. If you love your science fiction with a big heaping dose of science then this is a series for you. Recommended.
I was impressed enough with
The Clockwork Rocket to grab another of Egan's books,
Schild's Ladder, from the library.