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.