- #1
physics pfan
- 12
- 1
Quantum electrodynamics "states that any particle (e.g. a photon or an electron) propagates over all available, unobstructed paths and that the interference, or superposition, of its wavefunction over all those paths at the point of observation gives the probability of detecting the particle at this point." [ https://en.wikipedia.org/wiki/Fermat's_principle#Derivation ]. Feynman belabors this point in chapter two of his little QED book.
. I understand how the multiple paths are cancelling probabilities for reflection and diffraction. But what about a photon simply traveling from point A to point B with no intervening medium?
It seems that one can constrain (or select) photons so that they travel only a single linear path. The mirror cavity of a laser selects photons so that each one emitted appears to follow a single linear path. Another constraining device would be a collimating lens producing a linear beam. Does it make any sense in these cases to argue that photons follow “all available paths?” [A similar argument can be made for constrained/directed electrons.]
. I understand how the multiple paths are cancelling probabilities for reflection and diffraction. But what about a photon simply traveling from point A to point B with no intervening medium?
It seems that one can constrain (or select) photons so that they travel only a single linear path. The mirror cavity of a laser selects photons so that each one emitted appears to follow a single linear path. Another constraining device would be a collimating lens producing a linear beam. Does it make any sense in these cases to argue that photons follow “all available paths?” [A similar argument can be made for constrained/directed electrons.]