  Sonoluminescence is explained in terms of quantum radiation by moving
interfaces between media of different polarizability. It can be considered as a
dynamic Casimir effect, in the sense that it is a consequence of the imbalance
of the zero-point fluctuations of the electromagnetic field during the
non-inertial motion of a boundary. The transition amplitude from the vacuum
into a two-photon state is calculated in a Hamiltonian formalism and turns out
to be governed by the transition matrix-element of the radiation pressure.
Expressions for the spectral density and the total radiated energy are given.
