In a book I read about art and anatomy Nietzsche was quoted as saying that ‘physics too is an interpretation of the world and an arrangement of the world, and not an explanation of the world’, and that ‘we have measured the value of the world with categories that refer to a purely fabricated world’. A fabricated world? Yes, the world as a superstructure, the world as a spirit, weightless and abstract, of the same material with which thoughts are woven, and through which therefore they can move unhindered.