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Comment by earthscienceman | Hacker News Reader

Wait. I did a physics undergrad but I never asked myself this question. How is it possible that the EM fields from photos can't interact with each other? Doubly funny, I did my undergrad research for the PHENIX experiment.

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Phillips gave you a good answer, but another good answer is that Maxwell's equations are linear; forbidding any interaction between solutions f and g because if L is a linear operator, L[f+g] must = L[f] + L[g].

Oooo. Wow. This is a great answer, thanks for explaining it that way.

Where do they teach physics like this? Anywhere?

I feel like this would be mentioned in a typical undergraduate wave mechanics course taught in a typical American university, but I have not been to enough undergraduate wave mechanics courses in enough American universities to know, really.

This is what we are taught in high school / college as the super-position principle

Fields are abstractions that ease the calculation of the forces on charges caused by the positions and motions of other charges. The charges interact, but the fields don’t; there is nothing “there” to interact. (This is classical EM.)

If you are in a room with two charges, the electrostatic field at any point is the addition of the fields from each charge. There is no extra interaction term.

Photons are EM fields -- self-propagating ones, like a glider in the Game of Life. The electric field changes, creating a magnetic field, but the magnetic field changes, creating an electric field. Use sines for the functions and you can see how the function just keeps re-appearing.

Now, combine that with the superposition principle ... photons pass through one another under most circumstances because of this (unlike gliders).

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