The Quantum electrodynamics reference article from the English Wikipedia on 24-Jul-2004 (provided by Fixed Reference: snapshots of Wikipedia from wikipedia.org)

# Quantum electrodynamics

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Quantum electrodynamics (QED) is a quantum field theory of electromagnetism. QED describes all phenomena involving electrically charged particles interacting by means of the electromagnetic force and has been called "the jewel of physics" for its extremely accurate predictions of quantities like the anomalous magnetic moment of the muon, and the Lamb shift of the energy levels of hydrogen.

Mathematically, QED has the structure of an Abelian gauge theory with a U(1) gauge group. The gauge field which mediates the interaction between the charged spin-1/2 fieldss is the electromagnetic field. Physically, this translates to the picture of charged particles interacting with each other by the exchange of photons.

QED was the first quantum field theory in which the difficulties of building a consistent, fully quantum description of fields and creation and annihilation of quantum particles were satisfactorily resolved. Sin-Itiro Tomonaga, Julian Schwinger and Richard Feynman received the 1965 Nobel Prize in Physics for its development, their contributions involving a covariant and gauge invariant prescription for the calculation of observable quantities. The renormalization procedure for making sense of some of the infinite predictions of quantum field theory also found its first successful implementation in quantum electrodynamics.

The QED Lagrangian for the interaction of electrons and positrons through photons is

and its Dirac adjoint  are the fields representing electrically charged particles, specifically electron and positron fields represented as Dirac spinors.

is the gauge covariant derivative, with the coupling strength (equal to the elementary charge), the covariant vector potential of the electromagnetic field and the electromagnetic field tensor.

The part of the Lagrangian containing the electromagnetic field tensor describes the free evolution of the electromagnetic field, whereas the Dirac-like equation with the gauge covariant derivative describes the free evolution of the electron and positron fields as well as their interaction with the electromagnetic field.

See also Quantum field theory, Gauge theory, Renormalization, Standard Model.

## References

 General subfields within physics Edit Classical mechanics | Condensed matter physics | Continuum mechanics | Electromagnetism | General relativity | Particle physics | Quantum field theory | Quantum mechanics | Solid state physics | Special relativity | Statistical mechanics | Thermodynamics