  The quantum electrodynamics (QED) on a spatially flat $(1+3)$-dimensional
Friedmann-Lema\^ itre-Robertson-Walker (FLRW) spacetime with a Milne-type scale
factor is outlined focusing on the amplitudes of the allowed effects in the
first order of perturbations. The definition of the transition rates is
reconsidered obtaining an appropriate angular behavior of the probability of
the pair creation from a photon.
