A: Ithaca, New York, United States

1949

In a paper entitled "Space-Time Approach to Quantum Electrodynamics," *Physical Review*, **76** (1949) 769-789, American theoretical physicist Richard Feynman, then at Cornell University, introduced the first published examples of the "Feynman diagrams" -- pictorial representations of the mathematical expressions describing the behavior and interaction of subatomic particles. Feynman diagrams “embody a deep shift in thinking about how the universe is put together” (Wilczek). These became an essential and widely-used tool in particle physics.

“The basic principles and techniques of Feynman’s new approach to quantum electrodynamics were described in his article on the ‘Space-time approach to quantum electrodynamics’ . . . In this paper, Feynman considered the entire quantum electrodynamical description of the electromagnetic interaction between charged particles and the photon field, including the interaction between the charges themselves . . . In this fundamental article, Feynman explained his new perturbation theory, in which the matrix elements were worked out as expansions in powers of the dimensionless coupling constant (=*e*2/*hc*). Considerable simplification in writing down these elements was achieved for complex processes mainly from the fact that the old methods unnecessarily separated into individual terms closely related processes such as the effects of longitudinal and transverse waves, etc. This separation was made on a nonrelativistic basis. In Feynman’s approach, the related processes were combined in a completely relativistic manner, and the results looked quite simple” (Mehra, *The Beat of a Different Drum: The Life and Science of Richard Feynman*, ch. 14, 282-283)