Nano Lett. doi: 10.1021/nl901208v (2009)

The flow of heat between two surfaces held sufficiently close and separated by a vacuum can, in theory, exceed the limits laid down by Max Planck's law of blackbody radiation.

Gang Chen and Sheng Shen at the Massachusetts Institute of Technology in Cambridge and Arvind Narayanaswamy, now at Columbia University in New York, have observed this increased heat transfer in an experimental feat. They measured the electromagnetic radiation passing between a glass sphere and a flat glass, silicon or gold plate held as close as 30 nanometres.

The increase in radiation is due to electromagnetic waves that, unusually, do not radiate outwards but instead ripple over the surface of polar materials such as glass, and are formed by a combination of photons and lattice vibrations.