In the Pound–Rebka experiment the redshift / blueshift of photons is measured in small distances. This experiment one explain by the influence of gravitational field on the photon: "When the photon travels through a gravitational field, its frequency and therefore its energy will change due to the gravitational redshift."(https://en.wikipedia.org/wiki/Pound-Rebka_experiment)
The redshift of photons coming from stars far away from us is explained exclusively with the Doppler effect and the difference in the gravitational field of the source and the receiver (to a very small amount for big distances). The explanation of tired light was discarded. The frequency of photons dosn't changes during its life. Light "... consists of a finite number of energy quanta which are localized at points in space, which move without dividing, and which can only be produced and absorbed as complete units."A. Einstein Concerning an Heuristic Point of View Toward the Emission and Transformation of Light
In accordance with the second paragraph the Pound-Rebka experiment has to be interpreted by an other way. The source and the receiver are located in points with different gravitational potential and that is the reason they capable to emit and receive photons at different frequencies. Is then the statement in the thirst paragraph wrong?
