## måndag 9 augusti 2010

The previous guest post by Alan Siddons puts the finger on a most essential aspect of blackbody radiation, namely,
• relativity of absorption/emission of blackbody radiation.
As little as there is absolute position and velocity, is there any absolute blackbody absorption/emission, because absorption/emission always involves a source/emitter and a receiver/absorber, which acts as a source/emitter to another receiver/absorber and so on...

The radiative interaction of two blackbodies can shortly be described as follows:
• The (blackbody spectra of the) source and the receiver interact by electromagnetic waves.
• A higher temperature blackbody spectrum has higher frequencies than a lower temperature spectrum.
• A lower temp spectrum can borrow/absorb from a higher temp spectrum, but not the other way around.
• The reason is that coherent high frequency waves can be processed/deconstructed to incoherent noise showing up as heat, but incoherent noise cannot be composed into high frequency coherent waves, unless the temperature is high enough.
A mathematical model showing these features is presented in Computational Blackbody Radiation.

A result is that the Earth at + 15 C  radiates about 120 W/m2 to an atmosphere at -18 C, because that fits with blackbody radiative interaction.

But the Earth does not radiate 390 W/m2 as postulated in "backradiation", because the Earth is not in radiative contact with outer space at -273 C. The atmosphere lies in between, and