On the physical origin of the fine-structure constant

Abstract The fine-structure constant α is a dimensionless constant introduced by sommerfeld in 1916. This number was interpreted as a way of quantifying the strength of the electromagnetic interaction. Since then, several physicists expressed their dissatisfaction waiting for a more direct interpretation. Here we propose a one-to-one correspondence between and the variance of the photon number inside a black-body of given volume and temperature. As a broader perspective we propose that any atomic spectral-line is associated with a line-structure constant that provides the macroscopic statistical information on the photon gas inside the corresponding black-body cubic cavity. From this point of view, the expression of the Sommerfeld constant is considered as a particular case that coincides exactly with our results when the black-body temperature corresponds to the equivalent temperature of the emission line of and with the cubic size of the black body .