This one has been recommended to me several times over the years by people who know I love concept-oriented sci-fi. It delivers on that front, with several cool ideas:
- Humans are imprisoned within a field that causes time to pass radically slower for them than for the outside universe, but they come up with a way to use this to their advantage: they wield evolution as a tool, instigating eons-long processes and observing the results within weeks.
- The “hypotheticals” turn out to be cosmic networks of replicators which recognize organic biospheres as being somewhat similar to themselves. They only fail to put value on individual humans because we are “under their threshold of abstraction”, as our own cells are under ours.
- The motive behind the imprisonment is to prevent human civilization from destroying itself in a sort of Malthusian catastrophe. The barrier is ultimately removed when the hypotheticals complete their multi-billion (trillion?) year project: connecting worlds across the universe with a series of faster-than-light gates that biological civilizations can use to relieve population pressure.
What I did not enjoy about the book is the bleak tone pervading all the relationships of its characters. The audio narration is good, but has a very world-weary tone which may have exacerbated this issue for me. Also, almost all the characters are difficult people, and the lifelong obsession of the protagonist with his childhood friend is more cringe-inducing than romantic.