(Thermal) Out of Equilibrium Repulsion

  Radiation Pressure from a hot-plate counteracting Casimir attraction

 Around room temperature, this is for distances exceeding 7 microns; somewhat large for practical applications.

 However, at short separations pressure is non-classical and dominated by evanescent waves.

 "Casimir-Lifshitz force out of thermal equilibrium,"

M. Antezza, L.P. Pitaevskii, S. Stringari, V.B. Svetovoy, Phys. Rev. A 77, 022901 (2008)

Generalizing Lifshitz, computes the Casimir force between plates at different temperatures.

 Resonance phenomena can be utilized to generate repulsion between atoms at different temperatures

 "Resonant Enhancement and Dissipation in Nonequilibrium van der Waals Forces,"

A.E. Cohen and S. Mukamel, Phys. Rev. Lett. 91, 233202 (2003)

 Can such a mechanism be used to generate repulsion between plates (made of materials with approiate resonances, and held at different temperatures)?

 In principle yes, but only for materials where the equilibrium Casimir attraction is already weak, e.g. for aerogels.

"Dilution and resonance-enhanced repulsion in nonequilibrium fluctuation forces,"

 Breaking the law, at the nanoscale (MITnews, July 29, 2009)