sciencehabit shares an excerpt from Science Magazine: Talk about getting something for nothing. Physicists predict that just by shooting charged particles through an electromagnetic field, it should be possible to generate light from the empty vacuum. In principle, the effect could provide a new way to test the fundamental theory of electricity and magnetism, known as quantum electrodynamics, the most precise theory in all of science. In practice, spotting the effect would require lasers and particle accelerators far more powerful than any that exist now. Physicists have long known that energetic charged particles can radiate light when they zip through a transparent medium such as water or a gas. In the medium, light travels slower than it does in empty space, allowing a particle such as an electron or proton to potentially fly faster than light. When that happens, the particle generates an electromagnetic shockwave, just as a supersonic jet creates a shockwave in air. But whereas the jet's shockwave creates a sonic boom, the electromagnetic shockwave creates light called Cherenkov radiation. That effect causes the water in the cores of nuclear reactors to glow blue, and it's been used to make particle detectors.
However, it should be possible to ditch the material and produce Cherenkov light straight from the vacuum, predict Dino Jaroszynski, a physicist at the University of Strathclyde in Glasgow, U.K., and colleagues. The trick is to shoot the particles through an extremely intense electromagnetic field instead. According to quantum theory, the vacuum roils with particle-antiparticle pairs flitting in and out of existence too quickly to observe directly. The application of a strong electromagnetic field can polarize those pairs, however, pushing positive and negative particles in opposite directions. Passing photons then interact with the not-quite-there pairs so that the polarized vacuum acts a bit like a transparent medium in which light travels slightly slower than in an ordinary vacuum, Jaroszynski and colleagues calculate. Putting two and two together, an energetic charged particle passing through a sufficiently strong electromagnetic field should produce Cherenkov radiation, the team reports in a paper in press at Physical Review Letters. Others had suggested vacuum Cherenkov radiation should exist in certain situations, but the new work takes a more fundamental and all-encompassing approach, says Adam Noble, a physicist at Strathclyde.
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