ABSTRACT
In a world without action at a distance, the parts of functioning systems end up being jammed closely together. The blade of a knife has to be connected to its handle. The engine, power train, wheels, and steering mechanism of an automobile are tied together by mechanical linkages, and you cannot imagine them being distributed over, say, a city block. The electronic components on a silicon chip are packed together as densely as possible since electrons flow among them, and the shorter the distances the faster the chip runs. And cities are dense, too, since many human transactions have traditionally required face-to-face contact.
