  We consider the impact of quasar outflows on structure formation. Such
outflows are potentially more important than galactic winds, which appear
insufficient to produce the level of preheating inferred from X-ray
observations of galaxy clusters. Using a simple analytical model for the
distribution of quasars with redshift, coupled with a one-dimensional
Sedov-Taylor model for outflows, we are able to make robust statements about
their impact of on structure formation. As large regions of the IGM are heated
above a critical entropy of approximately 100 keV cm^2, cooling become
impossible within them, regardless of changes in density. On quasar scales,
this has the effect of inhibiting further formation, resulting in the observed
fall-off in their number densities below z = 2. On galaxy scales, quasar
feedback fixes the turn-over scale in the galaxy luminosity function (L_*) as
the nonlinear scale at the redshift of strong feedback. The galaxy luminosity
function then remains largely fixed after this epoch, consistent with recent
observations and in contrast to the strong evolution predicted in more standard
galaxy-formation models. Finally, strong quasar feedback explains why the
intracluster medium is observed to have been pre-heated to entropy levels just
above S_crit, the minimum excess that would not have been erased by cooling.
The presence of such outflows is completely consistent with the observed
properties of the Lyman-alpha forest at z ~ 2, but is expected to have a
substantial and detectable impact on Compton distortions observed in the
microwave background and the multiphase properties of the "warm-hot" (z=0)
circumgalactic medium.
