Revisiting Ryskin's Model of Cosmic Acceleration
  Cosmic backreaction as an additional source of the expansion of the universe
has been a debate topic since the discovery of cosmic acceleration. The major
concern is whether the self interaction of small-scale nonlinear structures
would source gravity on very large scales. Gregory Ryskin argued against the
additional inclusion of gravitational interaction energy of astronomical
objects, whose masses are mostly inferred from gravitational effects and hence
should already contain all sources with long-range gravity forces. Ryskin
proposed that the backreaction contribution to the energy momentum tensor is
instead from the rest of the universe beyond the observable patch. Ryskin's
model elegantly solves the fine-tuning problem and is in good agreement with
the Hubble diagram of Type Ia supernovae. In this article we revisit Ryskin's
model and show that it is {\it inconsistent} with at least one of the following
statements: (i) the universe is matter-dominated at low redshift ($z\lesssim
2$); (ii) the universe is radiation-dominated at sufficiently high redshift;
(iii) matter density fluctuations are tiny ($\lesssim 10^{-4}$) at the
recombination epoch.
