QEDs

Quantum electrodynamics (QED) is the relativistic quantum field theory that describes how charged fermions, such as electrons, interact with the quantized electromagnetic field and its photons. It combines quantum mechanics, special relativity, and the gauge symmetry of electromagnetism to explain a wide range of phenomena within the Standard Model of particle physics.

The modern formulation of QED emerged in the 1940s and 1950s through the work of Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga. The theory is built from the Dirac field for fermions and a massless U(1) gauge field for photons, with the interaction governed by the electric charge. Calculations rely on perturbation theory and Feynman diagrams; renormalization handles infinities to yield finite, predictive results.

QED provides some of the most precisely tested predictions in science. Notable successes include the electron’s anomalous magnetic moment (g-2) and the Lamb shift, both matching experimental measurements to extraordinary precision. The theory also yields accurate cross sections and rates for processes such as electron-positron scattering, Compton scattering, and photon emission. The strength of the electromagnetic interaction is set by the fine-structure constant α, approximately 1/137, and successive higher-order calculations (loops) continually refine predictions.

As a cornerstone of the Standard Model, QED is highly successful within its domain and serves as a benchmark for quantum field theories. While it naturally merges with electroweak theory at higher energies, its applicability is limited to regimes where quantum electrodynamics dominates and gravitational effects are negligible.