Lorentz Invariance of the Casimir Effect

The Casimir Effect---most simply realized as an attractive force between two parallel, neutral, conductive plates---is usually derived from quantized electromagnetic potentials in the Coulomb gauge, which is not Lorentz invariant. We seek a Lorentz-invariant derivation of the Casimir effect, using the Gupta-Bleuler method for quantizing the field and finding equations of motion for the parallel plates. We compare this approach with the motion obtained in the stationary frame.