Does the Fine‐Structure Constant Vary with Cosmological Epoch?

We use the strong nebular lines of O III, 5007 A and 4959 A, to set a robustupper limit on the time dependence of the fine structure constant. We find|alpha^{-1} d alpha(t)/dt | < 2*10^{-13} yr, corresponding to Deltaalpha/alpha(0) = (0.7 +- 1.4) * 10^{-4} for quasars with 0.16 < z < 0.80obtained from the SDSS Early Data Release. Using a blind analysis, we show thatthe upper limit given here is invariant with respect to 17 different ways ofselecting the sample and analyzing the data. As a by-product, we show that theratio of transition probabilities for the 5007 A and the 4959 A lines is2.99 +-0.02, in good agreement with (but more accurate than) theoretical estimates. Wecompare and contrast the O III emission line method used here with theMany-Multiplet method that has been used recently to suggest evidence for atime-dependent alpha. In an Appendix, we have analyzed the larger quasar samplefrom the SDSS Data Release One Sample and find Delta alpha/alpha(0) = (1.2 +-0.7) * 10^{-4}.Comment: Added analysis of larger quasar sample from SDSS Data Release One. Accepted for publication Ap