Fair enough; DISPROVING the Schwinger effect would be a big deal in its own right... but the physical limits are almost astronomically for all current means and purposes, so...
The nonperturbative Schwinger effect itself still has not been directly observed in the ideal strong-field regime. A 2025 Physical Review D paper explicitly says the strong-field Schwinger mechanism “still awaits experimental observations,” while current work focuses on dynamically assisted or other experimentally accessible variants. Recent 2026 work still treats reaching the critical field as a frontier goal.
So if the Schwinger effect were eventually shown not to exist where QED unambiguously predicts it, the consequences would be interesting.
What would be hit directly is the nonperturbative strong-field vacuum sector of QED. The Schwinger effect comes from the imaginary part of the QED effective action in a strong external field—the statement that sufficiently strong electric fields render the vacuum unstable to real pair creation. If careful experiments reached the appropriate regime and found no effect, one or more of these would have to be wrong or incomplete:
•QED effective action in strong backgrounds
•the assumed vacuum ground state
•nonperturbative tunneling interpretation
•or perhaps the treatment of external fields/backreaction.
That would be a major revision of QED’s vacuum physics, but not necessarily a rejection of perturbative QED.