  It has been increasingly becoming clear that Casimir and Casimir-Polder
entropies may be negative in certain regions of temperature and separation. In
fact, the occurrence of negative entropy seems to be a nearly ubiquitous
phenomenon. This is most highlighted in the quantum vacuum interaction of a
nanoparticle with a conducting plate or between two nanoparticles. It has been
argued that this phenomenon does not violate physical intuition, since the
total entropy, including the self-entropies of the plate and the nanoparticle,
should be positive. New calculations, in fact, seem to bear this out at least
in certain cases.
