Heuristic Derivation of Blackbody Radiation Laws Using Principles of Dimensional Analysis

A generalized form of Wien’s displacement law and the blackbody radiation laws of (a) Rayleigh and Jeans, (b) Rayleigh, (c) Wien and Paschen, (d) Thiesen and (e) Planck are derived using principles of dimensional analysis. This kind of scaling is expressed in a strictly mathematical manner employing dimensional π-invariants analysis sometimes called Buckingham’s π-theorem. It is shown that in the case of the classical radiation law of Rayleigh and Jeans only one π number occurs that has to be considered as a non-dimensional universal constant. This π number may be determined theoretically or/and empirically. It is also shown that dimensional π-invariants analysis yields a generalized form of Wien’s displacement law. In this instance two π numbers generally occur. Consequently, a universal function is established that is indispensable to avoid the so-called Rayleigh-Jeans catastrophe in the ultraviolet. Unfortunately, such a universal function cannot be inferred from dimensional arguments. It has to be derived theoretically or/and empirically, too. It is shown that such a similarity function can be deduced on the basis of heuristic principles, when criteria like the maximum condition regarding the generalized form of Wien’s displacement law, the requirement of the power law of Stefan and Boltzmann, and Ehrenfest’s arguments regarding the red and the violet requirements are adopted.