As I regard physics and psychology as complementary types of examination, I am certain that there is an equally valid way that must lead the psychologist 'from behind' (namely, through investigating the archetypes) into the world of physics. As an example of background physics, I shall discuss a motif that occurs regularly in my dreams - namely, fine structure, in particular doublet structure of spectral lines and the separation of a chemical element into two isotopes.

- Wolfgang Pauli