Some financiers recently calculated it was worth spending $300 million on drilling through mountains between Chicago and New York to lay fiber-optic cables in a slightly straighter line. That sped up communication between the two cities’ exchanges by three milliseconds. One may reasonably wonder whether that’s the most socially useful infrastructure the money could have bought, but the incentives for this kind of innovation are perfectly clear, and we can hardly be surprised if people respond to them.9
