What limits our knowledge of the universe? This chapter explores permanent boundaries built into reality itself: the cosmic horizon, the opacity of the early universe, quantum uncertainty, the unpredictability of complex systems, the mystery of consciousness, and Gödel's incompleteness theorem. Knowledge has edges—and living well means standing at them honestly, without denial or despair.

Is there life elsewhere in the universe? This chapter explores what we know and what we can reasonably infer. The building blocks of life are universal, and habitable planets are common—so microbial life is probably abundant. Intelligent life is rarer, but possible. Yet the speed of light ensures that even if the cosmos is full of minds, we are forever isolated from them. The silence of the night sky is not absence—it's isolation.