How to explain the non-zero mass of electromagnetic radiation consisting of zero-mass photons

摘要

The mass of electromagnetic radiation in a cavity is considered using the correct relativistic approach based on the concept of a scalar mass not dependent on the particle ( system) velocity. It is shown that due to the non-additivity of mass in the special theory of relativity the ensemble of chaotically propagating mass-less photons in the cavity has a finite overall mass.