or whether it had simply taught the machine to stop telling us why it was opening its doors.… A few years ago, I lived on the top floor of a twelve-story apartment building. It was one of those buildings renovated during the period when landlords began replacing ordinary mechanical security systems with networked access control. The entrance required a key fob after midnight, cameras covered the lobby, and the elevators had been connected to the building’s central management system. One night in August, I came home shortly after two in the morning. The heat had barely weakened after sunset. The pavement outside was still radiating warmth, and the lobby’s air conditioner sounded as though it was working harder than usual. I had spent the evening drinking with coworkers, so when I stepped into the elevator, I was grateful for the cool air. I was alone. I pressed 12. The doors closed. The elevator began climbing. Then it sto...