A Re-examination of the $^{187}$Re Bound on the Variation of Fundamental Couplings

We reconsider the Re187 bound on the variation of the fine-structure constant. We combine the meteoritic measurement with several present-day lab measurements to firmly establish the quantitative upper limit to the time variation over the age of the solar system. We find that the relative change of the fine-structure constant between its present value and $\alpha$ of 4.6 Gyr ago is consistent with zero, Delta alpha/alpha = [-8\pm 8 (1\sigma)] x 10^{-7}. We also rederive this bound in models where all gauge and Yukawa couplings vary in an interdependent manner, as would be expected in unified theories.