[isoprophlex]

Space opera:

- The Culture series by Banks

- Dune, at least the first book

Psycho paranoia classics:

- Anything by Philip K Dick, especially Ubik

- Solaris by Lem

1000+ pages of terraforming epic: Mars trilogy by KS Robinson

Hardest sci fi ever, a HN classic whenever cellular automata are discussed: Permutation City by Greg Egan

[tech2]

I loved Permutation City. Have you read anything of the Orthogonal series by Egan? The Clockwork Rocket bent my mind and feels like harder sci-fi still.

[isoprophlex]

Yeah, agreed, the same goes for "dichronauts". Sci fi so hard it cuts diamonds.

I read almost everything Egan published. While I love his work dearly, I've had very poor success with introducing people to his "alternative physics" stories (where he takes some law, flips a sign somewhere and rolls with the consequences [])... it's TOO hard. Not everyone likes a sci fi book that requires readers to follow along with pen and paper. So I always first recommend Permutation City, or maybe the short story collections such as "axiomatic"...

[] https://www.gregegan.net/DICHRONAUTS/00/DPDM.html