Schwinger limit

The limit was first derived in one of QED's earliest theoretical successes by Fritz Sauter in 1931[1] and discussed further by Werner Heisenberg and his student Hans Heinrich Euler.

In QED, however, non-elastic photon–photon scattering becomes possible when the combined energy is large enough to create virtual electron–positron pairs spontaneously, illustrated by the Feynman diagram in the adjacent figure.

Photon–photon scattering and other effects of nonlinear optics in vacuum is an active area of experimental research, with current or planned technology beginning to approach the Schwinger limit.

[10] Observation of a cross section larger or smaller than that predicted by the Standard Model could signify new physics such as axions, the search of which is the primary goal of PVLAS and several similar experiments.

[11] The planned, funded ELI–Ultra High Field Facility, which will study light at the intensity frontier, is likely to remain well below the Schwinger limit[12] although it may still be possible to observe some nonlinear optical effects.