  When taking the real, inhomogeneous and anisotropic matter distribution in
the semi-local universe into account, there may be no need to postulate an
accelerating expansion of the universe despite recent type Ia supernova data.
Local curvatures must be integrated (over all space) to obtain the global
curvature of the universe, which seems to be very close to zero from cosmic
microwave background data. As gravitational structure formation creates bound
regions of positive curvature, the regions in between become negatively curved
in order to comply with a vanishing global curvature. The actual dynamics of
the universe is altered due to the self-induced inhomogeneities, again more
prominently so as structure formation progresses. Furthermore, this negative
curvature will increase as a function of time as structure formation proceeds,
which mimics the effect of "dark energy" with negative pressure. Hence, the
"acceleration" may be merely a mirage. We make a qualitative and
semi-quantitative analysis, using newtonian gravity corrected for special
relativistic effects, which works surprisingly well, to corroborate and
illustrate/visualize these statements. This article may be seen as a plea to
start taking seriously the observed inhomogeneous distribution and the
nonlinearities of nonperturbative general relativity, and their impact on the
dynamics and behavior of the cosmos.
