What is the 2nd Law of Radiation 1?

The 1st and 2nd Laws of Thermodynamics form the foundation of classical continuum mechanics.

The 1st Law states that energy (and mass and momentum if you like) is conserved, and as such is not mysterious.

The 2nd Law states that something named entropy can only increase and never decrease (in an isolated system), and as such is mysterious since the physical meaning of entropy has remained unclear ever since its conception 150 years ago. Everybody speaks about entropy but nobody knows what it is, yet the 2nd Law is fundamental in determining the forward arrow of time we all percieve as we march from cradle to grave.

As concerns electrodynamics including radiative heat transfer, the situation is even worse: There should be a 2nd Law of Radiation but what is it? Where is it described in the literature? A search on Wikipedia gives no hit. Isn't this strange? Electrodynamics is as fundamental as

solid/fluid/thermodynamics, and so there should be a 2nd Law of Radiation, but nobody has formulated such a thing. Strange? Or is there one?

If you are interested to learn about this missing fundamental law of physics, browse Computational Blackbody Radiation prepared in a chapter in Slaying the Sky Dragon and in Computational Thermodynamics.

Note that a 2nd Law of Radiation without a proof is like a building without support, beautiful maybe on paper but completely useless in practice. The urgent necessity of a proof was expressed by Planck as follows:

• ...the whole procedure was an act of despair because a theoretical interpretation had to be found at any price, no matter how high that might be...
• Either the quantum of action was a fictional quantity, then the whole deduction of the radiation law was essentially an illusion representing only an empty play on formu- las of no significance, or the derivation of the radiation law was based on sound physical conception.
• Mechanically, the task seems impossible, and we will just have to get used to it (quanta).

Planck's derivation of his law of blackbody radiation can be viewed as a derivation of 2nd Law of Radiation. Planck used statistics of energy quanta in his proof and thereby payed a very high price. I present in the sources cited above an alternative derivation without statistics based on deterministic finite precision computation which comes without paying anything. Which option would you prefer?

In any case:

• A theoretical interpretation has to be found at any price!