““LIGHT AS AN EXCITATION OF SPACE Let's try and understand light in terms of an excitation of empty space-even if that makes no immediate sense. We might alternatively understand light in terms of a field, as we introduced that term in chapter 2. But light differs from the fields of temperature distributions, of sound, or of water in fluid motion described there: Whereas those phenomena are due to the composite action or motion of molecules at a more elementary level, light has its own reality at that level. It cannot be understood in terms of an oscillation of some matter that also exists in the dark-no, light is nothing but just that, light. It is an oscillation of an abstract nature, equivalent to a set of numbers that are assigned to each point in space. True, these abstract numbers have implications-most notably, they imply energy. But while a water wave transports energy by the movement of water molecules, the passing of a light wave does not mean that anything material oscillates. The energy of the liquid wave is the energy associated with gravitation and motion of its molecules; the energy of light is energy pure and simple, associated with every illuminated point in space.””
