A deluge of data is giving rise to a new economy

A N ARMY OF doppelgangers is invading the world. Digital copies of aircraft engines, wind turbines and other heavy equipment came first. Now the electronic ghosts of smaller and larger things are joining them in the virtual realm, from toothbrushes and traffic lights to entire shops and factories. Even humans have begun developing these alter egos. In America the National Football League is planning to design an electronic avatar for every player.