Sonoluminescence as a QED vacuum effect: probing Schwinger's proposal

Several years ago Schwinger proposed a physical mechanism for sonoluminesce nce in terms of photon production due to changes in the properties of the q uantum-electrodynamic (QED) vacuum arising from a collapsing dielectric bub ble. This mechanism can be re-phrased in terms of the Casimir effect and ha s recently been the subject of considerable controversy. This paper probes Schwinger's suggestion in detail: using the sudden approximation we calcula te Bogolubov coefficients relating the QED vacuum in the presence of the ex panded bubble to that in the presence of the collapsed bubble. In this way we derive an estimate for the spectrum and total energy emitted. We verify that in the sudden approximation there is an efficient production of photon s, and further that the main contribution to this dynamic Casimir effect co mes from a volume term, as per Schwinger's original calculation. However, w e also demonstrate that the timescales required to implement Schwinger's or iginal suggestion are not physically relevant to sonoluminescence. Although Schwinger was correct in his assertion that changes in the zero-point ener gy had to photon production, nevertheless his original model is not appropr iate fbr sonoluminescence. In other work we have developed a variant of Sch winger's model that is compatible with the physically required timescales.