From the Davisson-Germer, G.P. Thomson and other experiments, we learn
empirically that the particles detected in experiments exhibit
wave-like diffraction and interference effects with a wave-length
given by
where p (
) is the magnitude of the momentum of the
particles in the experiment and h is a constant with the
experimental value 
, precisely the same
Planck's constant from the black body radiation formula. For the
moment we leave the fact that this constant is the same for all
particles, including photons, as an experimental fact.
