  Comparisons between the redshifts of spectral lines from
cosmologically-distant galaxies can be used to probe temporal changes in
low-energy fundamental constants like the fine structure constant and the
proton-electron mass ratio. In this article, I review the results from, and the
advantages and disadvantages of, the best techniques using this approach,
before focussing on a new method, based on conjugate satellite OH lines, that
appears to be less affected by systematic effects and hence holds much promise
for the future.
