*Physical Review Focus*, on which selections from the journals

*Physical Review*and

*Physical Review Letters*are explained for students and researchers in all fields of physics. Besides such selections, the pages also carry "Landmarks," which introduce important papers from the archives of

*Physical Review*.

A recent article [1] of

*Physical Review Focus*treated Richard Feynman's paper in 1949 [2]. In this paper Feynman used for the first time cartoon-like pictures (examples can be seen in [1]; explanations are given in [3]) of straight and wiggly lines representing real and virtual particles interacting each other ("virtual particles" appear in intermediate, unobservable, stages of a process, and work as the mediators of the forces of interactions). The pictures enabled him to obtain easy answers to difficult problems in quantum electrodynamics. Then these so-called Feynman diagrams quickly became an essential tool for particle physicists, and Feynman shared the Nobel Prize with Sin'itiro Tomonaga and Julian Schwinger in 1965 (the independent work by the latter two physicists were published in [4] and [5]).

Generally, visualizing the images of new concepts often helps one understand those concepts quickly. Feynman diagrams, which translate the essence of complicated mathematical expressions into simple pictures, are therefore a good and indispensable device in studying the mystery of the deep physics in the microscopic world.

- Landmarks: Powerful Pictures, Physical Review Focus Vol. 24, Story 3 (July 20, 2009).
- R. P. Feynman, "Space-Time Approach to Quantum Electrodynamics," Phys. Rev. Vol. 76, p. 769 (1949).
- Feynman Diagrams Virtual Visitor Center, SLAC, Stanford University.
- S. Tomonaga and J. R. Oppenheimer, "On Infinite Field Reactions in Quantum Field Theory," Phys. Rev. Vol. 74, p. 224 (1948).
- J. Schwinger, "Quantum Electrodynamics. I. A Covariant Formulation," Phys. Rev. Vol. 74, p. 1439 (1948).

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