Greg Egan's Diaspora is diamond-hard scifi. If you aren't well-read in a variety of scientific concepts, aren't comfortable doing on-the-fly physics thought experiments while reading a novel, or won't be comfortable reading an extremely high vocabulary, then Greg Egan is not a good fit.

But if you can read it, the reward is great. Magnificent, alien, profound. It made me realize I don't like soft-scifi.