The Feynman diagram: “The fundamental interaction.” It is a space-time diagram: the progress of time is shown upward on the page. If one covers it with a sheet of paper and then draws the paper slowly upward: • A pair of electrons—their paths shown as solid lines—move toward each other. • When (6) is reached, a virtual photon is emitted by the right-hand electron (wiggly line), and the electron is deflected outward.
