Been asking myself the same question for months.

So Egan's stories are basically a mathy whodunit -- start from first (fictional) principles and eventually solve some universe-scale question or crisis. His characters are basically walking textbooks meant for info dumping / FAQing the derivations.

In that light, some similar stories I've found are...

    - Dragon's Egg (Robert Forward)
    - Of Ants and Dinosaurs (Liu Cixin, 3 body problem author)
    - The Andromeda Strain (Crichton, more medsci than math)
    - Schilds Ladder, Diaspora (other Egan stuff)

The first two are especially similar to Egan's stuff in that the only real character is the civilization / setting not the people.

I've also tried some of the more common hard scifi recommendations like Reynolds and Stephenson, but I personally don't enjoy the dialogue / scenes meant for character development. I guess it's because the stories usually take a human-scale perspective instead of taking a what-if to its reality-bending extreme like Egan does.