“Take all the planets in a star system and dismantle them,” she explains. “Turn them into dust—structured nanocomp, powered by heat exchangers, spread in concentric orbits around the central star. The inner orbitals run close to the melting point of iron, the outer ones are cold as liquid nitrogen, and each layer runs off the waste heat of the next shell in. It’s like a Russian doll made out of Dyson spheres, shell enclosing shell enclosing shell, but it’s not designed to support human life. It’s computronium, matter optimized at the atomic level to support computing, and they’re...