Causality between conducting plates
Abstract
A two-loop QED effect, uncovered by Scharnhorst, causes the phase and group velocities of an electromagnetic wave with ω≪ me to slightly exceed c, when the wave is travelling in vacuo between, and perpendicular to, two parallel conducting plates. Using causal rather than Feynman graphs, we show that the wavefront still travels at exactly c. The two-loop effect thus poses no threat to causality in QED.
- Publication:
-
Physics Letters B
- Pub Date:
- November 1990
- DOI:
- Bibcode:
- 1990PhLB..250..133B