Feature
Virtual Photons: From the Lamb Shift to Black Holes
While virtual processes are a well-known feature of quantum electrodynamics, the role of virtual photons—in phenomena ranging from the microscopic to the cosmic—is less generally appreciated.
Artist’s conception of a supermassive black hole, surrounded by an accretion disk of matter flowing into the black hole. A jet of energetic particles also flows out, powered by the black hole’s spin. [Getty Images]
Many processes in quantum field theory occur via virtual particles. These short-lived “imposters” of real particles—a transient feature of processes such as Thompson scattering—do not conserve energy and are thus said to be “off energy shell.” Virtual particles get away with having the “wrong” energy because of the time-energy uncertainty principle inherent in quantum mechanics.
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