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Review of fluctuational electrodynamics and its applications to radiative momentum, energy and entropy transport

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the collective influence of diffraction, interference, and tunneling of waves, become important, Planck's theory is no longer valid.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.