What I am trying to find out is: whether the superposition of a singe photon (across the all the paths --that the photon can possibly take) interfere/interact with the superposition of another single photon............ assuming that the superimposed paths of both the photons are close enough to interfere. or better still ....lets take the DBB interpretation...which posits that the wave-function travels both the slits. http://upload.wikimedia.org/wikipedia/commons/0/02/Doppelspalt.svg Would this wave-function interfere with the wave-function of another photon? Ques 1. Do wave-functions (or better still - matter waves) of two different photons interact?... assuming that their paths are close enough to interfere. for example -- would the wave-function of Photon A interact with the wave-function of Photon B? or in other words... Would the superposition of photon A (across the paths) interact with the superposition of photon B (across the paths) assuming that -- in the experimental setup -- the paths of A and B are within range of interference/interaction As an example let's say we pass photon A via a double slit (labelled as DSA) at the same time we pass photon B via a double slit (labelled as DSB) Lets say the DSA and DSB are (constructed/placed) close enough for interference. Would there be some sort of interaction/interference between wave-function of A and wave-function of B? Ques 2. Does the waves-function of Photon A interact with the probability waves of Electron B? as an example, we can repeat the above experiment and photon B is not replaced with an electron B. Ques 3. Is the wave-function modelling (what some interpretations would conceptualize as) matter waves? Note: in the below post -- matter waves, wave-functions, probability waves etc...have been used interchangeably. There might be a better term for it and a better way to put the idea across.