Does the fine structure constant vary with time and distance?

Theories unifying gravity and other interactions predict spatial and temporal variation of physical 'constants' in the Universe. Comparison of quasar absorption line spectra with laboratory spectra provide the best probe for variability of the fine structure constant, α=e2/(ℎ/2π)c, over cosmological time-scales. We have demonstrated that high sensitivity to the variation of α can be obtained from a comparison of the spectra of heavy and light atoms and have obtained an order of magnitude gain in precision over previous methods. Our new constraints on α come from simultaneous fitting of numerous absorption lines of the following species: MgI, MgII, AlII, AlIII, SiII, CrII, FeII, NiII and ZnII. The results are based on an analysis of 49 absorption systems covering cosmological time starting from about 10% of the age of the Universe after Big Bang (the redshift parameters cover 0.5<z<3.5). The data contain statistical evidence for a smaller α at earlier epochs at the 4.3σ level. We briefly discuss possible systematic errors and numerous tests done to estimate and reduce these errors. Careful searches have so far not revealed any spurious effect that can explain the observations