Photons do interfere "with each other" and "pick up source information" from the other photons in a "cavity"... or so it would appear. Huygens constructions of wavelets show this is the only way you can produce these quaint patterns... patterns of expanding circles from each slit. We know this "fact" about interference as an experimental reality. Because photons "travel" directly from the slits to the screen a direct application of path of least action (the don't bounce around on longer paths to achieve this interference) we are not able to immediately identify what these "standing waves" apparently mean. A simple "screen" will show a variation in luminous intensity if the photons are forced to "extinguish" on the plane surface of the detector or screen. A thick "translucent" photographic emulsion will show that there is far more information to be found in the "interferences" that just a straight simple interference pattern from the two slits. The position and arrangement of all reachable objects in the experiment will be recoverable if the holographic pattern is illuminated with a laser beam of the same frequency that it was originally exposed. There was a heated argument between the die hard quantum theorists of the 1950's and the experimentalists about this "disturbing fact"... it was messing around with the pure theory. Since the photons traveled directly from source to sink (somewhere in the emulsion at an "antinode") the question is how did the photons gather the additional information which is "depth encoded" in the emulsion when they arrived there that codes for the rest of the cavity shape? The answer is not that the photon interfered with the other photons in the cavity and picked up the "impressions" from them in some mutual interference way. Why not?? Because this experiment can be performed one photon at a time (with relatively huge gaps in time between each photon). This means whatever information each single flash of light is conveying to the emulsion is felt by one lone photon as it moves through the cavity from the source to the sink. The interferences are "picked up" not from other photons but from the standing matter waves we can't see in the cavity... from an "interaction" with a quasi-stationary cavity filling set of nodes and antinodes which "predispose" energywise the individual propagating photon to be absorbed in a suitable emulsion at the "antinodes" that we find in the developed hologram.

Since a single photon does all of this and also can move through as many slits at the same time in "self interference", it must move as a wave not as a particle. "Particles" can't pass through two holes at the same time. The assumption in quantum theory is called "locality" and the photon is a "particle" and has some coordinate position at all times "when measured". Standard quantum theory provides this localized particle with a solution that involves only statistics at the expense of wiping the history of this emission absorption phenomenon. This was a very good joke for 80 years since nobody could "prove" otherwise. Niels Bohr "bullied" the scientific community into believing this "fiction" and nobody since wanted to argue otherwise. Currently the "shell game" has moved from this dogma to a "softer position" that the photon can have no existence between where it formed and where it is detected. It exists in a superposition of all possible states. Now we can interfere with the "particle" again, not for real but in an uncollapsed state in "superposition"... a "many worlds" state. But is this "many worlds"... meaning the other "possibilities" that were never experienced? Now it is possible to show unequivocally that a single photon has an individual history since the emission of a photon and it's absorption can be "logged" proving a "particle" that passes through a double slit has a unique "history". You can also show that the individual photons are affected by what is in between the source and the sink (on the screen)... just vary the slit width and note the change in pattern. We also know that actually blocking a single slit alters the experiment into a single slit diffraction (Airy) Pattern. I believe this establishes that the individual photon actually "physically" passes the slit and is a wave not a particle.

The only limiting problem of this quandary is the photon is absorbed as a whole not as parts. That is what being a quantum "really means". It does not mean that we are dealing with little marbles being fired from some kind of BB gun. The propagating photons in a coherent LASER beam are expanding waves existing in the one quantum "boson" state and all occupy the same "spreading" volume because this is a gauge invariant theory of electromagnetism not a theory of BB pellets. The round pegs have been forced into a square hole and the argument was formerly that it made no difference... shut up and calculate. You can "cover for the old theory" by invoking "magic"... how long will people believe that? Probably forever if authorities insist. My view is look to the experiment not to the authorities... make up your own minds.

All those who want to discuss this conundrum please place your scientific arguments here...

Cheers