The straight and wavy lines in a diagram are not paths a particle traces through space; they are bookkeeping symbols for computing probability amplitudes. A line joining two vertices is a virtual particle: off-shell, and never directly observed. Every vertex carries a coupling constant — √α in quantum electrodynamics, where α ≈ 1/137 — so the more vertices, the smaller the contribution. Those few rules alone are enough to build Møller and Compton scattering, annihilation, pair production and beta decay through a W⁻.
The straight and wavy lines in a diagram are not paths a particle traces through space; they are bookkeeping symbols for computing probability amplitudes. A line joining two vertices is a virtual particle: off-shell, and never directly observed. Every vertex carries a coupling constant — √α in quantum electrodynamics, where α ≈ 1/137 — so the more vertices, the smaller the contribution. Those few rules alone are enough to build Møller and Compton scattering, annihilation, pair production and beta decay through a W⁻.
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