The Dark Forest

The fleet is on its way, and because the sophons are everywhere humanity can’t keep a single secret, bar the ones still sitting inside somebody’s skull. Hence the Wallfacer Project; four people handed effectively unlimited resources and, crucially, no obligation to explain what they’re doing to anybody, ever. Luo Ji gets picked by accident and spends a good stretch of the book trying to get out of it. Nobody tells him why he was chosen. What he eventually arrives at is the dark forest, the idea that the universe is full of hunters and anything that broadcasts its position gets annihilated, because you can never know whether the thing you’re signalling will still be friendly by the time your reply lands. Game theory dressed up as cosmology, and it’s the idea the rest of the trilogy hangs off.

The introduction to the core idea of the whole trilogy, and such a disturbing one at that, so late on doubles it’s impact. Time and space is torment. Camus, meet Einstein.