Feynman diagrams illustrate the interactions between
elementary particles. Originaly used to solve problems involving
electrons and
photons, Feynman diagrams are now used to describe all kinds of particle interactions.
Each diagram has a time axis and a space axis. If the arrow on the particle's line points opposite the direction of forward time, it indicates an
antiparticle.
In the diagrams, a solid external line represents a real particle. A dashed, wavy or spiraled internal line indicates a
virtual particle or mediator particle.
A wavy line indicates a virtual photon, mediator of the
electromagnetic force. These interactions involve only
leptons.
A spiraled line is a virtual
gluon, mediator of the
strong force. These interactions involve only
quarks. (See:
Quantum chromodynamics.)
A dashed line indicates a
W+ or a
W- particle, mediators of the
weak force. These interactions can involve any type of particle