Heat

Radiation Pressure is a feature of non-equilibrium steady states with different temperatures

           

yellow ball At short scales "near-field effects" due to evanescent waves modify classical "Stefan-Boltzmann" law:

yellow ball  "Surface Phonon Polaritons Mediated Energy Transfer between Nanoscale Gaps," S.Shen, A. Narayanaswamy, G. Chen

Nano Lett. 9, 2909 (2009) Breaking the law, at the nanoscale (MIT news, July 29, 2009)

A generalized approach for computation of Casimir forces, as well as radiation and heat transfer.

yellow ball  "Nonequilibrium Fluctuational QED: Heat Radiation, Heat Transfer and Force,"

G. Bimonte, T. Emig, M. Kardar, and M. Krüger, Annual Review of Condensed Matter Physics 8, 119 (2017)

Rytov (1959):      "Fluctuational QED"

yellow ball  Fluctuating currents in each object are related to its temperature by a fluctuation-dissipation condition:

yellow ball  The EM field due to thermal fluctuations of one object is related to overall Green's function by:

yellow ball  The overall fluctuations with many objects at different temperatures is then given by:

yellow ball From EM correlations follow the stress tensor and the Poynting vector, hence forces and radiation.

  As an example with asymmetry, consider forces between two micro-spheres at different temperatures:

(1 micron radius SiO2 spheres, background at zero temperature, force on #2)

yellow ball  "Non-equilibrium Casimir forces: Spheres and sphere-plate,"

M. Krüger, T. Emig,G. Bimonte and M. Kardar, Europhys. Lett. 95, 21002 (2011)

yellow ball  Whereas the equilibrium force (attractive) falls off as 1/d6, the non-equilibrium force decays as 1/d2. ( * )

yellow ball  The non-equilibrium force can be attractive and repulsive.  ( * )

yellow ball  Unlike in thermal equilibrium, there are points of stable levitation.  ( * )

yellow ball  Forces are not equal and opposite, with points of equal force in the same direction!  ( * )

Near field effects strongly modify force and heat transfer.