2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/4292The estimation of light velocity dispertion caused by quantum fluctuations influence on electromagnetic wave propogation in four-dimensional space-time is presented. Analytical cosmological solutions for the flat and open Universe for the case of cosmic vacuum model are obtained. The time delay of cosmic gamma-ray burst radiation is calculated. The delay is explained by propogation of dispersive electromagnetic wave in the expanding Universe. It is shown that the delay value depends on a model of the Universe. We conclude that to discern a model of the Universe measurement accuracy of parameter Δt / ΔE_γ should be better than 10^{-5} s / MeV.10 Latex pages, 2 Postscript figures, to be published in Astronomy LettersAstrophysicstext