Gauge theory, the fundamental theory of interaction and the special theory of relativity, with its firm roots in Maxwell's electrodynamics, were the two main constituents of the die in which photon was moulded. So it naturally produced a zero mass photon. Advent of general theory of relativity greatly reduced the domain of validity of special theory. But it did not challenge the assigned characters of photon. Momentum, an inherent property of photon caused to think in the direction of massive photon, a theoretically and conceptually viable alternative. Proca electrodynamics is the most successful frame work for this alternative concept. Based on this frame work, the finite range theory has been analyzed for the nature of potential, field and dispersion of electromagnetic radiations at terrestrial and extra terrestrial levels to set an upper limit for rest mass of photon. The upper limit set by various experimental methods so far not reached up to the limit set by the principle of uncertainty. But the present limit is not too far from this ultimate limit. In a similar manner efforts are in progress to set an upper limit to photon charge. Stability of photon is also a matter of concern.

The fifth Slovey council of physics titled ‘Electrons and Photons’ held in 1926 is a mile stone in the history of Quantum ElectroDynamics (QED). In this council the quanta of light had been christened as photon and its status as a particle was confirmed. During its existence over more than 100 years in the literature of physics, scientists have unraveled numerous details about it. In all these years QED prospered in such a way that it became self consistent theory. Photon, the identified field particle of QED, was always the centre of arguments. According to the requirements of QED, photon is a zero mass particle. Just a few years after its birth, the concept of massive photon came in to picture. As of today there exists no experiment that declares a finite photon mass or denies it completely.

Maxwell’s equations can be considered as one of the greatest triumphs of human kind in the past and even for future. The unimaginable accuracy of the predictions of the theory is sufficient enough to justify the statement. Constancy of the speed of electromagnetic spectrum predicted by the theory has been experimentally verified to a very high degree of accuracy over a wide range of frequencies. The enormous success of the theory was sufficient enough to stabilize the concept of zero mass photon as the field particle of the theory.

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