Quantum Electrodynamics (QED) is a quantum field theory that describes the electromagnetic interaction between charged particles, such as electrons and positrons, and the electromagnetic field. It is considered one of the most successful and well-tested theories in physics.
QED combines quantum mechanics and special relativity to provide a consistent and mathematically precise description of how charged particles interact via the exchange of photons. It treats both matter (particles) and radiation (photons) as quantum fields.
In QED, particles, such as electrons, are described by quantum fields that obey specific equations, known as Dirac equations. These fields represent the probability amplitudes for finding particles at different positions and momenta. Similarly, the electromagnetic field is described by a quantum field, known as the photon field.
The interaction between charged particles and the electromagnetic field is mediated by the exchange of virtual photons. Charged particles emit and absorb virtual photons, which carry momentum and energy. This exchange of virtual photons results in the electromagnetic forces experienced by charged particles, such as the attraction or repulsion between them.
QED calculations are performed using Feynman diagrams, which are graphical representations of the interaction processes involving particles and photons. These diagrams provide a way to calculate probabilities and amplitudes for different interaction outcomes.
QED has been highly successful in predicting and explaining various phenomena, including the behavior of electrons in atoms, the scattering of particles in particle accelerators, and the Lamb shift and anomalous magnetic moment of the electron. It has been experimentally verified to an extremely high degree of precision.
QED is part of the broader framework of quantum field theory, which encompasses other fundamental forces of nature, such as the weak and strong nuclear forces. It provides a fundamental understanding of the electromagnetic interaction at the quantum level and has played a crucial role in the development of modern theoretical physics.