First laboratory observation of a self-sustained avalanche QED cascade
In plain words
In colliding laser beams of enough intensity, the field itself should keep re-accelerating new pairs so their number grows exponentially. No laboratory has yet reached the needed intensity or seen this growth.
Precise statement
In counterpropagating or multi-beam (dipole-wave) laser fields an avalanche cascade, with pair number growing as $\exp(\Gamma t)$ over several laser periods, is predicted above an intensity of order $1e31\ \mathrm{erg}\ \mathrm{s}^{-1}\ \mathrm{cm}^{-2}$ for 1-micron light, about ten times the record peak intensity of about $1e30\ \mathrm{erg}\ \mathrm{s}^{-1}\ \mathrm{cm}^{-2}$ (2021, approximate). Determine the minimal laser energy and geometry (colliding pulses, dipole focusing, single-pulse reflection from a plasma mirror) at which the pair number grows by several e-foldings, and observe it through positron yield scaling that exceeds the one-generation shower prediction.
What would settle it
A positron-yield measurement versus intensity at a multi-10-PW facility showing exponential growth beyond seeded shower predictions.
Status in the literature
Unverified note
No laboratory avalanche cascade is known to this compilation as of 2026.