Space-time variation of physical constants and relativistic corrections in atoms

High-redshift absorption systems detected in the optical spectra of quasars provide a powerful tool for constraining possible spatial and temporal variations of physical "constants" in the Universe. It is demonstrated that high 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 have performed calculations for Mg I, Mg II, Cr TI, and Fe II for which accurate quasar and laboratory spectra are available. Some possibilities for observing enhanced effects in variations of the fundamental constants in laboratory measurements are also discussed.