Can individual photons be distinguished from each other? I don’t think so, just as other elementary particles are not individually distinguishable, they have no individual marker that makes them truly unique.
Is a history of a photon on its way from A to B then analogous to the experiment with the 4 balls in which a given impulse to the first ball is passed through 2 and 3 to the fourth?
A series of collisions started with one photon, and when there would be no energy loss on the way, and ending with one photon on the observation.
Answer
A photon formed in the center of the sun does not go out in a straight line at the speed of light. It is constantly absorbed, scattered on its way out, where it can gain or lose energy. On average, a photon in the solar interior never travels much further than a few millimeters before interacting with its environment. The only thing left over from those interactions is the energy of the photon. For example, it can switch to another photon or another particle such as an electron, which later emits another photon…and that happens every few millimeters. The photon that eventually leaves the solar surface is therefore no longer the photon that was originally formed in the fusion reaction.
Photons indeed have no identity, they are just packets of energy.
Answered by
prof.dr. Paul Hellings
Department of Mathematics, Fac. IIW, KU Leuven
Old Market 13 3000 Leuven
https://www.kuleuven.be/
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