A reanalysis of quasar absorption spectra results suggesting a spatial
  gradient in values of the fine-structure constant
  We statistically analyse a recent sample of data points measuring the
fine-structure constant alpha (relative to the terrestrial value) in quasar
absorption systems. Using different statistical techniques, we find general
agreement with previous authors that a dipole model is a well-justified fit to
the data. We determine the significance of the dipole fit relative to that of a
simple monopole fit, discuss the consistency of the interpretation, and test
alternate models for potential variation of alpha against the data. Using a
simple analysis we find that the monopole term (the constant offset in (delta
alpha)/alpha) may be caused by non-terrestrial magnesium isotope abundances in
the absorbers. Finally we test the domain-wall model against the data.
