[ELI5] How do photons mediates the electromagnetic force?
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Photons are packets of energy in the electromagnetic field. That energy will impart momentum to particles that absorb them. And, particles will lose momentum when they emit a photon. Also important is that for the purposes of particles bouncing around, a photon can have “negative” momentum.
So, two electrons come close to each other. One of them spits out a photon and as a result, loses that momentum, causing it to go off in a direction. The other electron absorbs the photon and gains that momentum, causing it to fly off in the other direction. As a result, the electrons repel each other.
Something similar happens when, say, an electron and proton come close, except that the momentum is “negative” so the electron and proton end up flying towards each other.
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