[Physics] Why is an electron still an elementary particle after absorbing / emitting a photon

electronsphotonsquantum mechanics

When an electron absorbs a photon, does the photon become electron "stuff" (energy); or, is it contained within the electron as a discrete "something"?

Best Answer

When an electron absorbs a photon, it remains an electron and the photon disappears. The electron energy and momentum are altered to account for the energy and momentum the photon was carrying. For a free electron, it will not be possible to balance energy and momentum simultaneously. There will have to be another interaction to make that work. If the electron is part of an atom, it can transfer some of the momentum to the rest of the atom and it can balance.

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