quantumelectrodynamica

Quantum Electrodynamics (QED) is a fundamental theory in physics that describes how light and matter interact. Developed in the 1940s, QED is a quantum field theory of electrodynamics and is considered one of the most successful theories in all of physics. It is the first theory where full agreement with experiment has been found at every order of perturbation theory.

QED is a quantum theory of the electromagnetic force, describing all phenomena involving electrically charged particles interacting by means of exchange of photons and the characteristics of how matter and light interact. It provides a complete description of phenomena involving charged leptons (electrons, muons, and tau particles) and their antiparticles, as well as of photons.

The theory predicts that the electron has an intrinsic angular momentum, known as spin, of ħ/2. This prediction was confirmed by the experiment of Stern and Frisch in 1933. QED also predicts that the electron has an intrinsic electric dipole moment, which has been experimentally tested to be less than 10^-27 e·cm, where e is the elementary charge and cm is the centimeter.

One of the most remarkable predictions of QED is the existence of electron-positron pairs, which can be created and annihilated in vacuum due to the uncertainty principle. This phenomenon is known as vacuum polarization and is responsible for the Lamb shift, a small difference in energy levels of hydrogen atoms that was first observed by Willis Lamb and Robert Retherford in 1947.

QED has been extensively tested and is in excellent agreement with experiment. It has been used to calculate the magnetic moment of the electron to an accuracy of 10^-12, and the anomalous magnetic moment of the muon to an accuracy of 0.5 parts per million. Despite its success, QED is not a complete theory, as it does not include the strong nuclear force or gravity. However, it serves as a basis for more complete theories, such as the Standard Model of particle physics.