Limits on the variation of fundamental atomic quantities over cosmic time scales

The detection of Mg II fine structure and hydrogen hyperfine absorption lines toward the radio source AO 0235+164 allows us to place upper limits on the variability of three products of the fine-structure constant, the nuclear g factor of the proton, and the ratio of electron to proton mass, viz. α2g/subp/m/M, g/subp/m/M, and α. Since the spectral lines are observed at a high red shift, z=0.5, the limits obtained on the variation with time of these quantities (adopting z as a measure of the Hubble expansion) apply over at least 35% of the age of the universe