  The five laws of relativistic quantum mechanics, according to Feynman's path
integral formulation, are concisely stated and applied to experiments.
Reflection diffraction grating experiments for both photons and electrons are
analysed, in particular the Davisson-Germer experiment in which the wave-like
property of electrons was first established. It is shown how classical, purely
spatial, effective wave theories for both photons and electrons are predicted
by the path integral formulation of quantum mechanics. The standard Copenhagen
interpretation of wave mechanics is critically discussed in the light of the
described experimental applications of the path integral formulation.
