Sensor, controller, restoring force

"Nothing's watching." She said it and then sat up, because saying it had done something. "That's it. That's the whole thing. On the slow one, a stamp means somebody saw it happen. On the fast one, a stamp means somebody said it happened and paid for the listing. And both of those are records, Joules, they look identical, they're the same blue tick — but one of them is a measurement and the other one is a declaration, and a system that can't tell the difference between a measurement and a declaration—"

"—has no sensor," he said.

"Has no sensor."

"So it can't be a controller." He said it slowly, the way he said things when he was assembling. He had been studying a single enzyme that failed in two opposite directions depending on conditions nobody could see coming, and it had left him permanently unable to accept a smooth curve as a promise about tomorrow. Or perhaps he was listening to the generators starting over the line — a man at 2,500m listening to Lagos come on like an organ tuning, at six in the evening, in the cold. Assembly complete, Joules continued, "You can put an actuator anywhere you like. Money moves, people get hired, the thing runs. But if the loop isn't closed by something that actually measures the world, then it isn't regulating anything, it's just — executing. Confidently. Right up until."

"Right up until."

"And it won't slow down first," he said. "That's the part you're not going to like. It's got no restoring force to weaken. There's nothing to watch weaken. It'll run beautifully and then it will be a hinge."