We describe the results of a search for time variability of the fine structure constant $\alpha$ using absorption systems in the spectra of distant quasars. Three large optical data sets and two $21\mathrm{cm}$ and mm absorption systems provide four independent samples, spanning $\sim 23\%$ to $87\%$ of the age of the universe. Each sample yields a smaller $\alpha$ in the past and the optical sample shows a $4\sigma$ deviation: $\Delta \alpha /\alpha =-0.72\mathrm{}\pm 0.18\times {10}^{-5\mathrm{}}$ over the redshift range $0.5<z<\mathrm{}3.5\mathrm{}$. We find no systematic effects which can explain our results. The only potentially significant systematic effects push $\Delta \alpha /\alpha$ towards positive values; i.e., our results would become more significant were we to correct for them.

An order of magnitude sensitivity gain is described for using quasar spectra to investigate possible time or space variation in the fine structure constant $\alpha$. Applied to a sample of 30 absorption systems, spanning redshifts $0.5<z<\mathrm{}1.6\mathrm{}$, we derive limits on variations in $\alpha$ over a wide range of epochs. For the whole sample, $\Delta \alpha /\alpha =(-1.1\mathrm{}\pm 0.4)\times {10}^{-5\mathrm{}}$. This deviation is dominated by measurements at $z>\mathrm{}1\mathrm{}$, where $\Delta \alpha /\alpha =(-1.9\mathrm{}\pm 0.5)\times {10}^{-5\mathrm{}}$. For $z<\mathrm{}1\mathrm{}$, $\Delta \alpha /\alpha =(-0.2\mathrm{}\pm 0.4)\times {10}^{-5\mathrm{}}$. While this is consistent with a time-varying $\alpha$, further work is required to explore possible systematic errors in the data, although careful searches have so far revealed none.

We previously reported Keck telescope observations suggesting a smaller value of the fine structure constant $\alpha$ at high redshift. New Very Large Telescope (VLT) data, probing a different direction in the Universe, shows an inverse evolution; $\alpha$ increases at high redshift. Although the pattern could be due to as yet undetected systematic effects, with the systematics as presently understood the combined data set fits a spatial dipole, significant at the $4.2\sigma$ level, in the direction right ascension $17.5\pm 0.9$ h, declination $-58\pm 9$ deg. The independent VLT and Keck samples give consistent dipole directions and amplitudes, as do high and low redshift samples. A search for systematics, using observations duplicated at both telescopes, reveals none so far which emulate this result.

We have previously presented evidence for a varying fine-structure constant, α, in two independent samples of Keck/HIRES quasi-stellar object (QSO) a

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 II, 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.