Bounds on the cosmological variation of the fine structure constant α inferred from Oklo neutron capture data are sometimes taken cum grano salis. It is possible to quantify uncertainties related to the treatment of excitation, deformation and the Coulomb interaction. On the basis of this analysis, it is concluded that Oklo data imply the relative change in α over the last 1.9 billion years is < 0.01 ppm (95% CL). Accommodation of this constraint represents a challenge to dark energy models that predict that fundamental constants do change.
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