  Recent observations indicate that the Universe is not transparent but
partially opaque due to absorption of light by ambient cosmic dust. This
implies that the Friedmann equations valid for the transparent universe must be
modified for the opaque universe. The paper studies a scenario when the opacity
steeply rises with redshift. In this case, the light-matter interactions become
important, because cosmic opacity produces radiation pressure that
counterbalances gravitational forces. The presented theoretical model assumes
the Universe expanding according to the standard FLRW metric but with the scale
factor $a(t)$ depending on both types of forces: gravity as well as radiation
pressure. The modified Friedmann equations predicts a cyclic
expansion/contraction evolution of the Universe within a limited range of scale
factors with no initial singularity. The model avoids dark energy and removes
some other tensions of the standard cosmological model. The paper demonstrates
that considering light-matter interactions in cosmic dynamics is crucial and
can lead to new cosmological models essentially different from the standard
$\Lambda$CDM model. This emphasizes necessity of new observations and studies
of cosmic opacity and cosmic dust at high redshifts for more realistic
modelling of the evolution of the Universe.
