Dreams of a Final Theory: The Scientist's Search for the Ultimate Laws of Nature

by Steven Weinberg

Any sort of wave is described at any one moment by a list of numbers, one number for each point of the space through which the wave passes. For instance, in a sound wave the numbers give the air pressure at each point of the air. In a light wave, the numbers give the strengths and directions of the electric and magnetic fields at each point of the space through which the light travels. The electron wave could also be described at any moment as a list of numbers, one number for each point of the space in and around the atom. It is this list that is known as the wave function, and the individual numbers are called the values of the wave function. But at first all one could say about the wave function is that it was a solution of the Schrödinger equation; no one yet knew what physical quantity was being described by these numbers.