Further Evidence for Cosmological Evolution of the Fine Structure Constant

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.