2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/207004Explosive astrophysical events at high red shift can be used to place severe limits on the fractional variation in the speed of light ($Δc/c$), the photon mass ($m_γ$), and the energy scale of quantum gravity ($E_{QG}$). I find $Δc/c < 6.3 \times 10^{-21}$ based on the simultaneous arrival of a flare in GRB 930229 with a rise time of $220 \pm 30 μs$ for photons of 30 keV and 200 keV. The limit on $m_γ$ is $4.2 \times 10^{-44} g$ for GRB 980703 from radio to gamma ray observations. The limit on $E_{QG}$ is $8.3 \times 10^{16}$ GeV for GRB 930131 from 30 keV to 80 MeV photons.7 pages, Submitted to PRLAstrophysicstext