Space-time variation of physical constants and relativistic corrections inatoms

High-redshift absorption systems detected in the optical spectra of quasars provide a powerful tool for constraining possible spatial and temporal var iations of physical "constants" in the Universe. It is demonstrated that hi gh sensitivity to the variation of the fine structure constant alpha can be obtained from a comparison of the spectra of heavy and light atoms. We hav e performed calculations for Mg I, Mg II, Cr TI, and Fe II for which accura te quasar and laboratory spectra are available. Some possibilities for obse rving enhanced effects in variations of the fundamental constants in labora tory measurements are also discussed.