  Quantum and thermal fluctuations of electromagnetic fields, which give rise
to Planck's law of blackbody radiation, are also responsible for van der Waals
and Casimir forces, as well as near-field radiative energy transfer between
objects. Electromagnetic waves transport energy, momentum, and entropy. For
classical thermal radiation, the dependence of the above mentioned quantities
on the temperature is well-known mainly due to Planck's work. When near-field
effects, namely the collective influence of diffraction, interference, and
tunneling of waves, become important, Planck's theory is no longer valid. Of
momentum, energy, and entropy transfer, the role of near-field effects on
momentum transfer between two half-spaces separated by a vacuum gap (van der
Waals pressure in the vacuum gap) was first determined by Lifshitz, using
Rytov's theory of fluctuational electrodynamics in 1956. Subsequently,
Dzyaloshinskii, Lifshitz, and Pitaevskii, employing sophisticated methods from
quantum field theory, generalized Lifshitz' result for van der Waals pressure
in a vacuum layer to the case of van der Waals pressure in a dissipative layer
between two half-spaces. The influence of near-field effects on radiative
transfer was appreciated only in the late 1960s and, subsequently, in the last
two decades because of the enhancement in radiative transfer due to
electromagnetic surface waves. The role played by near-field effects on entropy
transfer has not been investigated so far, at least when the temperature
distribution is non-uniform.
