(republished on 07/20/06)
(published on 02/23/11)
The sea of virtual photons in the quantum vacuum doesn't affect the real photon propagation. Perhaps photons are affected by the sea of virtual particles of some deeper type, sort of as quarks are affected by the Higgs field. But in that case the thing we call a photon would already be an object that included the interactions.
You ask if the initial photon could annihilate and be replaced with a different one. I believe that that process would have no symptoms whatsoever, even in principle. Therefore I think that the question has no meaning. We all often stumble into questions like that when we take try to picture quantum processes in classical terms. Classically, no matter how similar two particles are they are in some subtle way not identical. Yet quantum particles of the same type truly are identical, so it doesn't mean anything to say that one is "new".
I'm not positive what change a pilot-wave (Bohm) interpretation would make for the discussion.
(published on 01/03/14)
Aha, I see what you're wondering about- if some mechanism can be given for the pilot wave force on the particle coordinate in the Bohm picture. maybe some sort of little collisions with local particle fluctations, etc. It's a nice thought, but I think that if anything comes out of an attempt like that it will be even weirder than the view in which the wave function is the sole ingredient. The reason is that all such processes can violate the Bell Inequalities. That means that there is no local picture at all (other than universal conspiracies) that can reproduce the observations. So there's little motivation to pursue yet another local picture.
The emitted photo in a Hawking picture is a real photon, and, like Pinocchio, can do all the things a real photon can do.
(published on 01/09/14)
The basic two-slit behavior works the same for particles that are their own antiparticles (e.g. photons) and ones that aren't (e.g. electrons, buckyballs). The particle-like aspect of quantum waves is that they have a "number operator" that gives them something that has discrete integer counts. That also holds for each type of particle. It has a little different behavior for bosons (e.g. photons, 4He) than for fermions (e.g. electrons, 3He), but that is a different distinction than that between ones that are their own antiparticles and ones that aren't.
(published on 05/20/14)
It is true that photon amplitudes take all possible paths in an interaction. For example, if you make an interferometer, half of the photon's amplitude goes down each path, and the two amplitudes interfere at the beamsplitter. Most physicists don't try to make statements about the photon's past (beyond saying that it has amplitudes for every possibility), and instead just discuss the outcomes of detector measurements.
That said, you can make some statements, which I believe are true:
1. The photon does NOT have a huge nonlocal database telling it everything about all the other particles in the universe. However, it can have properties which are (nonlocally) correlated to ("entangled with") the other particles that it has interacted with, or that are connected with the chain of events leading to its creation.
2. Attempts to determine which path a particle took can certainly be successful. However, even if such a measurement doesn't destroy the photon, it always collapses the photon amplitudes from "all possible paths" to the measured path, and so limits any further wavelike behavior. (For example, if you put a nondemolition measuring device in one arm of an interferometer, then you won't get the usual interference at the output.) The physical (i.e. classical-sounding) explanation of this effect is that any position measurement transfers random momentum to the particle, which washes out any fringes. (A less classical but more robust description can be made in terms of information: correlations and density matrices.)
3. Since the photon doesn't know about all the other particles, this question doesn't make sense. However, you can ask something similar: if a photon is entangled with a partner particle, and something affects the partner particle, then when does the photon find out? Really, it never "finds out." The relationship between distant entangled particles is not causal, it is just a correlation. The correlation can change without the photon "having any knowledge" about its partner. (See https://van.physics.illinois.edu/qa/listing.php?id=24896.)
4, 5, and 6: The interference pattern you see in any such dynamic experiment will depend only on what configuration the photon saw locally at each point in time. For example, if you emit a photon towards two slits, but yank them out a picosecond before the photon reaches the slits, then you won't get any interference pattern. There isn't anything surprising here, as far as I can think of: the photon really does travel from the source to the detection screen, and the pattern doesn't change if you change something before the photon gets there or after the photon has left. The photon interacts with objects at the same spacetime coordinate, that's all.
Hope that made sense. Let me know if you want further details or explanations, of which there are many.
(published on 09/08/14)