1. What is QED?

Obviously, QED stands for "quantum electrodynamics," a modern theory of light and matter. More specifically, it describes how electromagnetic radiation (by which I mean photons) interacts with electrically charged matter (by which I mean [usually] electrons) while taking into account the effects of special relativity. As put forth by the late physicist Richard Feynman in the aptly named book QED, this theory concerns itself with three actions and the probability that each will occur.

Action #1: A photon goes from place to place.
Action #2: An electron goes from place to place.
Action #3: An electron emits or absorbs a photon.

So which QED is QED? What does QED [the Latin] have to do with QED [the physics theory]?

In a word... nothing.

But QED [the acronym] does describe one of the fundamental tenets on which QED [the theory] is based. QED [the acronym] is like a sealed, opaque box. Inside, it could hold "quod erat demonstrandum" or "quantum electrodynamics," but its probability wave only allows you to guess. When this Schrödinger's-acronym-box is opened, QED is forced to take the form of either the physics theory or the Latin phrase.

And so this confusion in abbreviation is a fit starting point for a theory that is mostly illogical but (as far as has been measured) absolutely true. QED [the Latin].

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