Colloquia

The Heisenberg-Schwinger effect is the non-perturbative production of electron-positron pairs when an external electric field is applied to the quantum electrodynamical (QED) vacuum. The inherent instability of the quantum vacuum in an electric field was one of the first non- trivial predictions of QED, but the effect is so weak that it has not yet been directly observed. However, new developments in ultra-high intensity lasers come tantalizingly close to opening a new window on this unexplored extreme ultra-relativistic regime. This necessitates a fresh look at both experimental and theoretical aspects of the Heisenberg-Schwinger effect. I review the basic physics of the problem and describe some recent theoretical ideas aimed at making this elusive effect observable, by careful shaping of laser pulses. This is an example of an emerging new field using ultra-intense lasers to probe fundamental problems in particle physics, gravity and quantum field theory.