CASIMIR EFFECT IN DIELECTRICS - BULK ENERGY CONTRIBUTION

In a recent series of papers, Schwinger discussed a process that he ca lled the dynamical Casimir effect. The key essence of this effect is t he change in zero-point energy associated with any change in a dielect ric medium. (In particular, if the change in the dielectric medium is taken to be the growth or collapse of a bubble, this effect may have r elevance to sonoluminescence,) The kernel of Schwinger's result is tha t the change in Casimir energy is proportional to the change in the vo lume of the dielectric, plus finite-volume corrections. Other papers h ave called into question this result, claiming that the volume term sh ould actually be discarded, and that the dominant term remaining is pr oportional to the surface area of the dielectric. In this paper, which is an expansion of an earlier Letter on the same topic, we present a careful and critical review of the relevant analyses. We find that the Casimir energy, defined as the change in zero-point energy due to a c hange in the medium, has at leading order a bulk volume dependence. Th is is in full agreement with Schwinger's result, once the comet physic al question is asked. We have nothing new to say about sonoluminescenc e itself.