Sonoluminescence as a Physical Vacuum Excitation
  We are discussing Schwinger'idea that physical mechanism of sonoluminescence is a physical vacuum excitation. This theory was based on the assumption that the sudden change of the rate of bubble collapse leads to the jump of dielectric constant of the gas trapped inside the bubble. We show that the dependence of the dielectric constant on the gas density really leads to the jump of the dielectric constant at shock-wave propagation in a collapsing gas bubble. 
Yu.P.Stepanovsky and G.G.Sergeeva (NSC KIPT, Kharkov)