  In recent years cosmology has undergone a revolution, with precise
measurements of the microwave background radiation, large galaxy redshift
surveys, and the discovery of the recent accelerated expansion of the Universe
using observations of distant supernovae. In this light, the SKA enables us to
do an ultimate test in cosmology by measuring the expansion rate of the
Universe in real time. This can be done by a rather simple experiment of
observing the neutral hydrogen (HI) signal of galaxies at two different epochs.
The signal will encounter a change in frequency imprinted as the Universe
expands over time and thus monitoring the drift in frequencies will provide a
real time measure of the cosmic acceleration. Over a period of 12 years one
would expected a frequency shift of the order of 0.1 Hz assuming a standard
Lambda-CDM cosmology. Based on the sensitivity estimates of the SKA and the
number counts of the expected HI galaxies, it is shown that the number counts
are sufficiently high to compensate for the observational uncertainties of the
measurements and hence allow a statistical detection of the frequency shift.
[abstract abridged]
