1 v 1 2 5 A ug 1 99 8 Does the Fine Structure Constant Really Vary in Time ?

We discuss how laboratory experiments can be used to place constraints on possible variations of the fine structure constant α in the observationally relevant redshift interval z ≃ 0 − 5, within a rather general theoretical framework. We find a worst case upper limit for ∆α/α of 8 × 10 −6 for z ≤ 5 and ∆α/α of 0.9 × 10 −6 for z ≤ 1.6. The derived limits are at variance with the recent findings by Webb et al. (1998), who claim an observed variation of ∆α/α = −2.6 ± 0.4 × 10 −5 at 1 < z < 1.6.