  According to a new tired-light cosmological model, where H(z) = H 0 (1 + z),
the number density of galaxies has been nearly constant over the last 10 Gyr,
at least, meaning that, as far as galaxy counts are concerned, the Universe has
been stationary. In this context, an analysis of the luminosity distances of
quasars and supernovae Ia shows that the Universe is far from being as
transparent as assumed nowadays, the photon lifetime along the line-of-sight
being one third of the Hubble time. Such a low value could mean that there are
huge amounts of grey dust in the inter galactic medium, that have so far
escaped detection. It could also be a signature of new physics, namely, a
consequence of the decay of photons into lighter particles. The tired-light
model advocated in the present study would be falsified if, for instance, the
time-dilation of remote events were shown to have a general character, that is,
if it were definitely observed for phenomenons other than the light curves of
supernovae Ia. On the other hand, further developments are needed in order to
turn this model into an actual cosmology. In particular, the physical origin of
the current stability of the Universe on galactic scales remains to be
identified.
