Gravitation, photons, clocks

This paper is concerned with the gravitational redshift phenomenon, the dec rease in the frequency of a photon moving away from a gravitating body (e.g ., the Earth). Of the two current interpretations, one is that at high alti tudes the frequency-measuring clocks atoms or atomic nuclei - ran faster (i .e., their characteristic frequencies are higher), while the photon frequen cy in a static gravitational held is independent of the altitude and so the photon only reddens relative to the clocks. The other approach is that the photon loses its energy when overcoming the attraction of the gravitationa l held. This view, which is especially widespread in popular science litera ture, ascribes such notions as a 'gravitational mass' and 'potential energy ' to the photon. Unfortunately, also scientific papers and serious books on the general theory of relativity often employ the second interpretation as a 'graphic' illustration of mathematically immaculate results. We show her e that this approach is misleading and only serves to create confusion in a simple subject.