Quantum electrodynamics

Quantum electrodynamics is the quantum field theory of electromagnetic interactions between photons and electrically charged particles. It describes these interactions through quantized fields and predicts measurable quantities with exceptional precision.

Feynman diagram: A diagrammatic notation for terms in perturbative quantum field theory, representing particles and their interactions. Diagrams organize QED calculations as sums over possible interaction histories.
Lamb shift: A small energy-level difference in hydrogen that is absent from the Dirac equation without radiative corrections. Its measurement provided a landmark test of QED's treatment of electron self-interaction.
Quantum mechanics: The physical theory of matter and energy at atomic and subatomic scales. QED extends quantum mechanics to fields and relativistic particle creation.
Classical electrodynamics: The classical theory of electric and magnetic fields and their interaction with charged matter. It treats fields continuously, whereas QED quantizes electromagnetic interactions.
Feynman rules: Rules that translate particle-interaction diagrams into mathematical expressions for scattering amplitudes. They specify the factors assigned to QED vertices and propagators.
Anomalous magnetic dipole moment: The difference between a particle's measured magnetic moment and the value predicted by the Dirac equation. QED predicts this electron property with precision that can be compared directly with experiment.
Special relativity: The theory that space and time are linked and that physical laws are invariant in inertial frames. Relativistic invariance is built into QED's description of charged particles and light.
Quantum chromodynamics: The quantum field theory of the strong interaction among quarks and gluons. It is the other major gauge theory of the Standard Model, with a different charge and force carrier.
Photon: The quantum of the electromagnetic field and the carrier of electromagnetic interactions. QED treats electromagnetic radiation and interactions in terms of photon-field quanta.
Casimir effect: An attractive force between conducting surfaces arising from changes in quantum-field vacuum fluctuations. It illustrates measurable effects associated with quantum electromagnetic fields.

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