ar X iv : h ep - p h / 06 02 03 6 v 1 3 F eb 2 00 6 Photon : history , mass , charge ∗

The talk consists of three parts. " History " briefly describes the emergence and evolution of the concept of photon during the first two decades of the 20th century. " Mass " gives a short review of the literature on the upper limit of the photon's mass. " Charge " is a critical discussion of the existing interpretation of searches for photon charge. Schemes, in which all photons are charged, are grossly inconsistent. A model with three kinds of photons (positive, negative and neutral) seems at first sight to be more consistent, but turns out to have its own serious problems. 1 History The idea that light consists of rapidly moving particles can be traced from the writings of ancient authors to Descartes and Newton. The wave theory of light was put forward by Huyghens and was later decisively proved to be correct through discovery of interference and diffraction by Young and Fres-nel. Maxwell's theory of light as electromagnetic waves was one of the greatest achievements of the 19th century. The history of the photon in the 20th century started in 1901 with the formula by Planck for radiation of a black body and introduction of what was called later the quantum of action h [1]. In 1902 Lenard discovered that energy of electrons in photoeffect does not depend on the intensity of light, while it depends on the wavelength of the latter [2]. In his fundamental article " On an euristic point of view concerning the production and transformation of light " published in 1905 Einstein pointed out that the discovery of Lenard meant that energy of light is distributed in space not uniformly, but in a form of localized light quanta [3]. He has shown that all experiments related to the black body radiation, photoluminescence and production of cathode rays by ultraviolate light can be explained by the quanta of light. 1 The proof that Einstein's light quanta behave as particles, carrying not only energy, but also momentum, was given in 1923 in the experiments by Compton on scattering of X-rays on electrons [4]. The term " photon " for particles of light was coined by Lewis in 1926 in an article " The conservation of photons " [5]. His notion of a photon was different from the notion we use today. He considered photons to be " atoms " of light, which analogously to the ordinary atoms …