Observability of the Bulk Casimir Effect: Can the Dynamical Casimir Effect be Relevant to Sonoluminescence?

TL;DR

This paper investigates whether the dynamical Casimir effect could explain sonoluminescence, concluding that bulk Casimir energies are not relevant and clarifying divergence issues in Casimir calculations.

Contribution

It demonstrates that bulk Casimir energies cannot account for sonoluminescence, clarifies divergence issues in Casimir effect calculations, and discusses implications for related models.

Findings

Bulk Casimir energies are not relevant to sonoluminescence.

Divergence issues in Casimir calculations are clarified.

The adiabatic approximation suggests Casimir energies are too small.

Abstract

The experimental observation of intense light emission by acoustically driven, periodically collapsing bubbles of air in water (sonoluminescence) has yet to receive an adequate explanation. One of the most intriguing ideas is that the conversion of acoustic energy into photons occurs quantum mechanically, through a dynamical version of the Casimir effect. We have argued elsewhere that in the adiabatic approximation, which should be reliable here, Casimir or zero-point energies cannot possibly be large enough to be relevant. (About 10 MeV of energy is released per collapse.) However, there are sufficient subtleties involved that others have come to opposite conclusions. In particular, it has been suggested that bulk energy, that is, simply the naive sum of ${1\over2}\hbar\omega$, which is proportional to the volume, could be relevant. We show that this cannot be the case, based on general principles as well as specific calculations. In the process we further illuminate some of the divergence difficulties that plague Casimir calculations, with an example relevant to the bag model of hadrons.