Electron scattering

Electron-electron scattering is described by one of the earliest published Feynman diagrams (featured in "Sightings," September–October 2003). One electron (solid line at bottom right) shoots out a forcecarrying particle—a virtual photon (wavy line)—which then smacks into the second electron (solid line at bottom left).

The first electron recoils backward, while the second electron gets pushed off its original course. The diagram thus sketches a quantum-mechanical view of how particles with the same charge repel each other. As suggested by the term "Space-Time Approach" in the title of the article that accompanied this diagram, Feynman originally drew diagrams in which the dimensions were space and time; here the horizontal axis represents space.