When looking at information about the double-slit experiment, you often see statements like... "the photon interferes with itself". But what does this actually really mean? In the classical analog of waves it's easy to understand that troughs and peaks can cancel each other out. But can a photon cancel itself or another photon? Assuming that N photons pass through the slits, do N photons still strike the screen? If so, then isn't this essentially just a different type of diffraction? And if not, where the heck do they go?