A while ago I was reading David Deutsch's book "The Fabric of Reality". Deutsch proposes that the double slit experiment is explained by the presence of large numbers of virtual photons, which leave the source, hit the wall, travel through the slits, and interfere with each other, much the same as real photons (if there are enough of them). Then the real photons being emitted individually interfere with this virtual photon field and the characteristic interference field is produced. From what I recall, Deutsch states that this is the only way of plausibly explaining the double slit experiment. What do you people think about the idea?