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Quantum electrodynamics or QED, is a relativistic quantum field theory of electrodynamics. Quantum electrodynamics describes how light and matter interact. This is also the first theory that fully utilizes both quantum mechanics and special relativity. Quantum electrodynamics describes all phenomenon involving electrically charged particles. This is done by means of exchange of photons. Quantum electrodynamics represents the quantum counterpart of the classical theory of electrodynamics. This gives a complete account of the interaction between light and matter.
Richard Feynman called Quantum electrodynamics the "jewel of physics" for its extremely accurate predictions of some quantities.
Paul Dirac
Paul Dirac, in 1927, was the first to formulate a quantum theory describing radiation and matter interaction. Dirac was able to compute the coefficient of spontaneous emission of an atom.
Dirac's description of the quantization of the electromagnetic field was a description based on an ensemble of harmonic oscillators. This introduced the concept of creation and annihilation operators.
Photons
A photon is the quanta of the electromagnetic field. This includes all forms of electromagnetic radiation, including light and radio waves. Photons are the force carriers of the electromagnetic interaction. The invariant mass of the photon is zero and they always move at the speed of light in a vacuum.
Photons are best explained by quantum mechanics and exhibit wave-particle duality. Photons exhibit properties of both waves and particles.
The modern concept of the photon emerged, firstly, from the work of Albert Einstein (1905) in the early 20th century, who was attempting to explain experimental observations that didn't fit the classical wave model of light. Einstein's hypothesis was that light itself is quantized. What was found is that the photon model accounts for the frequency dependence of light's energy. Another benefit that came out of this work was the explanation for how matter and electromagnetic radiation could be in thermal equilibrium. The photon model accounts for some anomalous observations. This includes the properties of black body radiation.
In December 1926, American chemist, Gilbert Lewis, coined the term "photon" and it became widely adopted and will become officially accepted in 1927 after the scattering experiments of Arthur Compton.
A photon is:
Massless
Chargeless
A stable particle
The photon is the gauge boson for electromagnetism. Photons are emitted in many natural processes.
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