  No. It is simply not plausible that cosmic acceleration could arise within
the context of general relativity from a back-reaction effect of
inhomogeneities in our universe, without the presence of a cosmological
constant or ``dark energy.'' We point out that our universe appears to be
described very accurately on all scales by a Newtonianly perturbed FLRW metric.
(This assertion is entirely consistent with the fact that we commonly encounter
$\delta \rho/\rho > 10^{30}$.) If the universe is accurately described by a
Newtonianly perturbed FLRW metric, then the back-reaction of inhomogeneities on
the dynamics of the universe is negligible. If not, then it is the burden of an
alternative model to account for the observed properties of our universe. We
emphasize with concrete examples that it is {\it not} adequate to attempt to
justify a model by merely showing that some spatially averaged quantities
behave the same way as in FLRW models with acceleration. A quantity
representing the ``scale factor'' may ``accelerate'' without there being any
physically observable consequences of this acceleration. It also is {\it not}
adequate to calculate the second-order stress energy tensor and show that it
has a form similar to that of a cosmological constant of the appropriate
magnitude. The second-order stress energy tensor is gauge dependent, and if it
were large, contributions of higher perturbative order could not be neglected.
We attempt to clear up the apparent confusion between the second-order stress
energy tensor arising in perturbation theory and the ``effective stress energy
tensor'' arising in the ``shortwave approximation.''
