Julian Schwinger and the Casimir Effect: The Reality of Zero-Point   Energy
  Julian Schwinger became interested in the Casimir effect in 1975. His original impetus was to understand the quantum force between parallel plates without the concept of zero point fluctuations of field quanta, in the language of source theory. He went on to consider applications to dielectrics and to spherical geometries in 1977. Although he published nothing on the subject in the following decade, he did devote considerable effort to understanding the connection between acceleration and temperature in the mid 1980s. During the last four years of his life, he became fascinated with sonoluminescence, and proposed that the dynamical Casimir effect could be responsible for the copious emission of photons by collapsing air bubbles in water. 
K. A. Milton