  We investigate the dynamical importance of a newly recognized possible source
of significant feedback generated during structure formation; namely cosmic ray
(CR) pressure. We present evidence for the existence of numerous shocks in the
hot gas of galaxy clusters (GCs). We employ for the first time an explicit
numerical treatment of CR acceleration and transport in hydro simulations of
structure formation. According to our results, CRs provide an important
fraction of the total pressure inside GCs, up to several tenths. This was true
even at high redshift (z=2), meaning that such non-thermal component could
affect the evolution of structure formation.
