Quantum electrodynamics

Quantum electrodynamics ( QED) in the context of quantum physics, quantum field theoretical description of electromagnetism.

General

The QED is a description of all phenomena that are caused by charged point particles, such as electrons or positrons, and photons. It contains the classical electrodynamics as a limiting case of strong fields and high energies where the possible values ​​can be considered continuous. Of deeper interest, however, is the application in microscopic objects, where they about quantum phenomena, such as the structure of atoms and molecules explains. In addition, it includes processes of the high-energy physics, such as the generation of particles by means of an electromagnetic field. One of its best results, the calculation of the magnetic moment of the electron abnormal coincident to 11 decimal places with the experimentally determined value (landing -factor). Thus, the QED is one of the most accurate experimentally verified theories today.

QED describes the interaction of a Spinorfeldes with charge -e, which describes the electron with a calibration field, which describes the photon. This gives their equations of motion of electrodynamics by quantization of Maxwell's equations. The quantum electrodynamics explains with high accuracy the electromagnetic interaction between charged particles ( eg, electrons, muons, quarks ) by the exchange of virtual photons as well as the properties of electromagnetic radiation.

The QED was the first quantum field theory, in which the difficulties of a consistent quantum theoretical description of fields and the generation and annihilation of particles were satisfactorily resolved. The creators of the developed theory in the 1940s were honored with the Nobel Prize for Physics to Richard P. Feynman, Julian Schwinger, and Tomonaga Shin'ichiro in 1965.

Lagrangian density

As a relativistic gauge theory in four space-time dimensions, the QED is defined by its Lagrangian:

Here questions and the adjoint fields is describing the electrically charged fermions (electrons, quarks ) and their antiparticles; technically it is these fields are spinors. describes incoming antiparticles and outgoing particles, while outgoing antiparticles and incoming particles describes. also called Dirac adjoint, since they are obtained by means of conventional matrix - adjunction and multiplication by the Dirac matrix. is the covariant derivative with the respective charge. is the vector potential of the electromagnetic field and electromagnetic field strength tensor is.

The spinor has four components, each of which denote the two spin orientations of particles and antiparticles. The photo field has accordingly only two physically relevant components, because since the photon moves at light speed agree with him helicity and chirality, so that the spin can be oriented only in the flight direction or opposite to the direction of flight. The other two degrees of freedom of the photo field are gauge degrees of freedom, which can be determined by calibration.