måndag 9 augusti 2010

Relativity of Radiation

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 
radiation is relative, like salaries.

If you, like a reductionist physicist, insist on a particle nature of light, you are easily led to 
believe in absolute radiation with blackbodies spitting out photons independently of 
surrounding society. Like all forms of absolutism, this can lead astray...

Inga kommentarer:

Skicka en kommentar