Quantum electrodynamics

(PD) Image: John R. Brews
Photon exchange between two electrons.Left: electron (arrow) on left absorbs photon (squiggle); Center: simultaneous emission and absorption; Right: electron on left emits photon.

In physics, quantum electrodynamics is a theory of the interaction between charged particles due to the electromagnetic force. This theory obeys the principles of special relativity, but has been superseded by the Standard Model, where electromagnetic force is combined with the weak force to become a theory of the electroweak force.

In quantum electrodynamics the force between charged particles is envisioned as due to the electromagnetic field, which has to be combined with quantum mechanics to treat small entities like atoms, or electrons, or other particles. To that end, the classical treatment of the electromagnetic field based upon the Maxwell equations is quantized, introducing the concept of the photon. The strength of an electromagnetic field is determined by the number of photons of that field that are present. The force between charged particles is then seen as an exchange force occasioned by the sending and receiving of photons, the so-called messenger particles, between the charged bodies.

Historically, the key experimental observations that led to quantum electrodynamics and supported its theoretical basis were the anomalous magnetic moment of the electron and the Lamb shift.