Peter Watts' Blindsight.
Read it. For the love of God Almighty, read it and science fiction will never be same again. Well, aliens in general. And humanity too. Eh who am I kidding, the entire reality will look different.
Don't read though if you are easy to be depressed because the vision of universe and humanity envisioned by this book (though author admits it's a work of fiction and he's much less cynical in real life) i
s by far the most nihilistic/darkest of all books I have ever read in my life. Warhammer 40k and Lovecraft universes are fairy tales compared to the vision of humanity and universe Blindsight depicts. Blindsight features merely five deaths and yet it destroys more universes than thousand of '99% humanity is dead' stories - these don't
erase the concept of human, unlike Blindsight.
Oh, and besides the main philosophical concept I won't spoil for you (and do not spoil it for yourself) it has enough original thoughts put into it to fill a dozen of other SF books.
If there was a single last SF book one could read in his lifetime, this probably should be the one. Unless you want happy story about human mind overcoming obstacles. In Blindsight at least one word of a previous sentence is raped; I won't spoil which one.
Some quotes:
“I really wanted to talk to her.
I just couldn't find an algorithm that fit.”
“Brains are survival engines, not truth detectors. Truth had never been a priority. If believing a lie kept the genes proliferating, the system would believe that lie with all its heart.””
“But then I remembered: the universe was closed, and so very small. There was really nowhere else to go.”
“After four thousand years we can’t even prove that reality exists beyond the mind of the first-person dreamer. We desperately need minds greater than ours. And there are none.”
“This is how you communicate with a fellow intelligence: You hurt it, and keep on hurting it, until you can distinguish the speech from the screams.”
"Nothing up there tonight but entropy, and the same imaginary shapes that people had been imposing on nature since they’d first thought to wonder at the heavens."
"They know God exists already that’s old. I think now they’re trying to figure what to do with It. What to do with god. Maybe worship. Maybe disinfect."
"You saved my life. And I still feel absolutely no empathy for you; it's natural."
"Cogito ergo sum? Descartes, you failed; you all, wise men with great words, have failed. There is a meat and its' delusion of existence."