The Realism of Our Times: Kim Stanley Robinson on how science fiction works

Beyond what other people list here:

- Hugh Howey. His Silo series is worth a read. He published it in some episodic form. However, I'd recommend just getting the whole thing. Beacon 23 is a bit shorter and also nice.

- Ramez Naam. His nexus series is a decent series. Not the best written but I enjoyed it.

- James S.A. Corey, the expanse series. Makes you appreciate the tv series more.

- Authors others already mentioned: Neal Stephenson & Peter Watts.

Other authors that go more in the direction of space opera: Iam M. Banks, Ernest Cline, John Scalzi, Ann Lecky, Richard K. Morgan (Altered Carbon).

I have a soft spot for Accelerando because it was my first encounter with the exo-cortex (or perhaps more accurately called cybernetics) concept, aka computers as an external brain. Also it was my first encounter with the concept of smart contracts, laws & corporations run purely as code.

True, I was considering mentioning Hamilton, but it's been so long since I read those books - so wasn't quite sure if I'd call them hard sci-fi or not :)

Depends what you mean by 'hard'.

Anything by Greg Egan is probably going to be the hardest sci-fi you've ever read. Dude wrote a book where he considered the ramifications of a universe built on a positive-definite Riemannian metric, and another one where the universe has 2 time dimensions.

Robert L. Forward's Dragon's Egg explores what life might look like if it evolved on a neutron star.

Adrian Tchaikovsky's Children of Time and Children of Ruin explore the evolution of other earth species if they were given a kick towards sapience.

Vernor Vinge's A Fire Upon the Deep is half space adventure (not very hard) and half an exploration of a lifeform which only achieves sapience in small groups. A Deepness in the Sky is generally harder and explores a lot of things, including the power of focused human attention, the difficulty of galactic scale civilization, and alien life evolved in a star system where the star periodically dims.

Steven Baxter and Clarke collaborated on The Light of Other Days, which explores the technical and sociological consequences of a device which allows you to see the past.

With a broad interpretation of 'hard' I can highly recommend Ursula Le Guin's The Left Hand of Darkness and The Dispossessed, which have soft science but hard humanity.

Similarly The Long Earth series, a collaboration between Pratchett and Baxter, where it seems Baxter handles the sociological and technological consequences of the science while Pratchett handles the characters and philosophy.

Asimov's I, Robot is an exploration of what happens when you try to constrain intelligence with rules.

Asimov's Foundation Trilogy gets a lot of hype, but it isn't very hard and I also found it utterly mediocre. Instead I recommend The God's Themselves, which is so good it's like Asimov was channeling a much better writer to get his ideas down. It explores the limited interaction of our universe with one that has slightly different physical properties.

Also perhaps stretching the definition of 'hard', but I want to recommend it because it's relatively unknown, is Leonard Richardson's Constellation Games, in which an incredibly advanced multi-species anarchic alien civilization makes first contact with humanity, and the protagonist really just wants to play their video games. It's actually harder sci-fi than it sounds.

I came across Memory of Whiteness while taking my college music theory classes. It's very fantastical but I loved how he connected various compositional techniques with physical processes. It's a very underrated book.