Time Evolution of the Fine Structure Constant

We present a short review of the current quasar (QSO) absorption line constraints on possible variation of the fine structure constant, α ≡ e 2 /¯ hc. Particular attention is paid to recent optical Keck/HIRES spectra of 49 absorption systems which indicate a smaller α in the past [1, 2]. Here we present new preliminary results from 128 absorption systems: ∆α/α = (−0.57 ± 0.10) × 10 −5 over the redshift range 0.2 < z < 3.7, in agreement with the previous results. Known potential systematic errors cannot explain these results. We compare them with strong 'local' constraints and discuss other (radio and millimetre-wave) QSO absorption line constraints on variations in α 2 g p and α 2 g p m e /m p (g p is the proton g-factor and m e /m p is the elec-tron/proton mass ratio). Finally, we discuss future efforts to rule out or confirm the current 5.7 σ optical detection.