All I am asking about is photon (EM wavepacket) photon (EM wavepacket) interaction.
I have read this question:
where Danielshank says:
As far as we know photons do not directly interact with each other. Yet another way to say this is that if a photon is moving along, the existence of a second photon has absolutely no influence over the first photon's path.
where JEB says:
Regarding the photons zinging around in front of you: as particles, they do interact in photon-photon scattering with a negligible cross section in the visible. As electromagnetic waves, their field strengths add linearly, which is the mechanism for con/de-structive interference; however, that only occurs when the waves are coherent. These waves are incoherent and "pass though" one-and-other.
So one of them says they do not directly interact, the other one says they do interact. This is a contradiction.
What I do not understand mostly, is that photons do not interact directly, two crossing photons will not scatter off (only on the second order).
- Do photons interact or not directly?