Another look at redshift drift and the backreaction conjecture
  Earlier studies have conjectured that redshift drift is described by
spatially averaged quantities and thus becomes positive if the average
expansion of the Universe accelerates. This conclusion is reevaluated here by
considering exact light propagation in a simple toy-model with average
accelerated expansion. The toy-model and light propagation setup is explicitly
designed for concordance between spatial averages and averages along light
rays. While it is verified that redshift-distance relations are well described
by average quantities in this setup, it is found that the redshift drift is
not. Specifically, the redshift drift is negative despite the on-average
late-time accelerated expansion of the model. This result implies that
measuring redshift drift signals at low redshifts gives the potential for
directly falsifying the backreaction conjecture. However, the results are based
on a toy-model so it is in principle possible that the result is an artifact
and that redshift drift is in reality well described by spatially averaged
quantities. The result therefore highlights the importance of developing
\emph{exact} solutions to the Einstein equations which exhibit average
accelerated expansion without local expansion so that the relation between
spatial averages and observations can be firmly established.
