Worlds could burst. The walls held life itself, and outside those locks and bulkheads loomed utterly pitiless darkness, the lethal nothingness of naked space. In the old circumlunars, in the modern Mech cartels, in the Shaper Ring Council, even in the far-flung outposts of the cometary miners and the blazing smelters of intra-Mercurian orbit, every single thinking being carried this knowledge. Too many generations had lived and died under the shadow of catastrophe. It had soaked itself into everyone from childhood.