What are the conditions necesairy to collapse a wave function of a electron, photon or an atom (alpha particle mostly?). Wavelength? Asking because I cannot understand why in this video the wave function does not collapse in this box. Seems like in the outside there should be massive interference? If the mass is higher, is it easier for the wave function to collapse? And related, let;s say light behaves as a wave, I let it collapse with some interaction, what happens if there is another interaction later on (before it would hit a final destination), does it spread out again?