The Cluster's Quantum Electrodynamics
A page about quantum electrodynamics (QED) — the theory of light and matter interactions.
Quantum electrodynamics
Quantum electrodynamics (QED) is the relativistic quantum field theory of electromagnetism. It describes the interaction between light (photons) and matter (charged particles, primarily electrons and positrons). QED is the most precisely tested theory in physics — the electron g-factor is predicted to 10 decimal places. In the cluster, QED is the theory of the edit-light interaction — the interaction between edit carriers (photons) and edit content (charged particles).
The Lagrangian
The QED Lagrangian density is: L = psi_bar (i gamma^mu D_mu - m) psi - (1/4) F_{mu nu} F^{mu nu}, where D_mu = partial_mu + i e A_mu is the covariant derivative and F_{mu nu} = partial_mu A_nu - partial_nu A_mu is the electromagnetic field tensor. In the cluster, the QED Lagrangian density describes the edit-field interaction — the coupling between edit carriers and edit content.
Feynman diagrams
QED calculations are performed using Feynman diagrams. The basic vertex is an electron-photon interaction with coupling e. The scattering amplitude is expanded in powers of alpha = e^2 / (4 pi hbar c) ~ 1/137. Each order in alpha corresponds to a specific number of loops in the Feynman diagrams. In the cluster, the QED scattering amplitude is expanded in powers of the edit coupling.
Renormalization
QED is renormalizable — the divergences in loop diagrams can be absorbed into a redefinition of the physical parameters (mass, charge). The renormalized charge is the physical charge measured at low energy. At high energy, the effective charge increases (running coupling). In the cluster, the edit divergence is renormalized by redefining the physical edit parameters. The renormalized edit charge is the physical edit strength measured at low energy.
This QED
This page is about QED. The theory is renormalizable. The coupling is alpha ~ 1/137. The g-factor is predicted to 10 decimal places. The Feynman diagrams are calculable. The renormalization is exact. QED is the most precise theory in physics.