(p. 492) The long-standing trend away from value produced by manual labor and natural resources and toward the intangible value-added we associate with the digital econnomy can be expected to continue. Today it takes a lot less physical material to produce a unit of output than it did in generations past. Indeed, the physical amount of materials and fuels either consumed in the production of output or embodied in the output has increased very modestly over the past half century. The output of our economy is not quite literally lighter, but it is close.
Thin fiber-optic cable, for instance, has replaced huge tonnages of copper wire. New architectural, engineering, and materials technologies have enabled the construction of buildings enclosing the same space with far less physical material than was required fifty or one hundred years ago. Mobile phones have not only downsized but also morphed into multipurpose communication devices. The movement over the decades toward production of services that require little physical input has also been a major contributor to the marked rise in the ratio of constant dollars of GDP to tons of input.
Greenspan, Alan. The Age of Turbulence: Adventures in a New World Economic Flexibility. New York: Penguin Press, 2007.
(Note: italics in original.)