Forecasts of redshift drift constraints on cosmological parameters
  Cosmological observations usually map our present-day past light cone.
However, it is also possible to compare different past light cones. This is the
concept behind the redshift drift, a model-independent probe of fundamental
cosmology. In simple physical terms, this effectively allows us to watch the
Universe expand in real time. While current facilities only allow sensitivities
several orders of magnitude worse than the expected signal, it should be
possible to detect it with forthcoming ones. Here we discuss the potential
impact of measurements by three such facilities: the Extremely Large Telescope
(the subject of most existing redshift drift forecasts), but also the Square
Kilometre Array and intensity mapping experiments. For each of these we assume
the measurement sensitivities estimated respectively in Liske {\it et al.}
(2008), Klockner {\it et al.} (2015) and Yu {\it et al.} (2014). We focus on
the role of these measurements in constraining dark energy scenarios,
highlighting the fact that although on their own they yield comparatively weak
constraints, they do probe regions of parameter space that are typically
different from those probed by other experiments, as well as being
redshift-dependent. Specifically, we quantify how combinations of several
redshift drift measurements at different redshifts, or combinations of redshift
drift measurements with those from other canonical cosmological probes, can
constrain some representative dark energy models. Our conclusion is that a
model-independent mapping of the expansion of the universe from redshift $z=0$
to $z=4$---a challenging but feasible goal for the next generation of
astrophysical facilities---can have a significant impact on fundamental
cosmology.
