There obtained an estimate of the minimum value of the photon energy attenuation constant in vacuum α: α = 8 · 10–19 m–1 based on quantum concepts of the structure of vacuum and data on the red shift of the emitter spectra of distant galaxies. Presumably, the cosmic microwave radiation is partly the thermal vacuum radiation heated by the photon fluxes from the infinite universe. Despite the universe infinity, the sky is dark precisely due to the photon’s energy absorption from distant and ultra-distant galaxies in vacuum, and not only the photon absorption during various interactions with the gas or dust components of intergalactic clusters. Thus, the emission spectrum of these ultra-distant objects is transformed into the microwave range, which complements the intensity of thermal radiation in this range. The inconsistency of alternative explanations for the red shift is shown: the Doppler effect in the cosmological model of the expanding universe and the Big Bang, and the gravitational shift.