Quantum electrodynamics (
QED) is a
relativistic quantum field theory of
electrodynamics. QED was developed by a number of physicists, beginning in the late 1920s. It basically describes how light and matter interact. More specifically it deals with the interactions between electrons,
positrons and photons. QED mathematically describes all
phenomena involving
electrically charged particles interacting by means of
exchange of
photons. Physicist
Richard Feynman has called it "the jewel of physics" for its
extremely accurate predictions of quantities like the
anomalous magnetic moment of the
electron, and the
Lamb shift of the
energy levels of
hydrogen.
[1]In technical terms, QED can be described as a perturbation theory of the electromagnetic quantum vacuum.
The word 'quantum' is Latin, meaning "how much" (neut. sing. of quantus "how great").[2] The word 'electrodynamics' was coined by André-Marie Ampère in 1822.[3] The word 'quantum', as used in physics, i.e. with reference to the notion of count, was first used by Max Planck, in 1900 and reinforced by Einstein in 1905 with his use of the term light quanta.
Quantum theory began in 1900, when Max Planck assumed that energy is quantized in order to derive a formula predicting the observed frequency dependence of the energy emitted by a black body. This dependence is completely at variance with classical physics. In 1905, Einstein explained the photoelectric effect by postulating that light energy comes in quanta, later called photons. In 1913, Bohr invoked quantization in his proposed explanation of the spectral lines of the hydrogen atom. In 1924, Louis de Broglie proposed a quantum theory of the wave-like nature of subatomic particles. The phrase "quantum physics" was first employed in Johnston's Planck's Universe in Light of Modern Physics. These theories, while they fit the experimental facts to some extent, were strictly phenomenological they provided no rigorous justification for the quantization they employed.
