What graphical representation of particle interactions did Feynman invent?

What graphical representation of particle interactions did Feynman invent? Feynman diagrams. Richard Feynman introduced these diagrams in 1948 as a visual way to organize calculations involving interacting subatomic particles.

A Feynman diagram uses lines to represent particles or propagators and vertices to represent interactions. For example, an electron and positron may meet at a vertex and produce photons. Each diagram corresponds to a mathematical contribution to a quantum-field-theory calculation, especially a scattering amplitude.

Despite their visual appearance, Feynman diagrams are not literal photographs of particles moving through space. They are bookkeeping tools for terms in a perturbation expansion. Physicists calculate the contribution from every relevant diagram and combine them to obtain probabilities for possible outcomes.

The diagrams grew out of Feynman's work on quantum electrodynamics and complemented his path-integral approach to quantum mechanics. Freeman Dyson helped connect Feynman's visual methods with existing formal techniques, making the diagrams broadly useful. They are now used in particle physics, nuclear physics, condensed-matter theory, and statistical mechanics.