There is an aspect of relativity of Planck’s Law of blackbody radiation which connects to relativity of motion or velocity and position. We shall compare these aspects of relativity with the aspect of absolutism of absolute temperature and absolute motion.
We recall that Newtonian mechanics is commonly believed to require absolute space and time as a unique back-ground space-time coordinate system for the representation of motion, and Einstein’s relativity theory is then viewed as a liberation from such a concept of absolute space and time.
But all Newtonian motion is relative and there is no necessity of any absolute space. Each observer is free to chose a (convenient) coordinate system to describe motion and different observers may use different coordinate systems. Asking for a unique coordinate system representing absolute space leads to contradictions and can be avoided because it is not needed. For example, the gravitational force between two bodies A and B at positions and is (with normalization) given by
where only the (relative) difference in position enters, and not the absolute positions and .
Planck’s Law states that the net relative radiative exchange between a blackbody A of temperature and a blackbody B of temperature is determined by
This correct relative form of Planck’s Law is to be compared with the incorrect absolute form
where would represent the radiation from A into a surrounding space of absolute temperature zero, and the same from B.
The idea of absolute space thus connects to the idea of absolute temperature. In both cases the physics is determined by relative position/motion and relative temperature and there is no reason to require absolutism leading to contradiction.