Does the Fine‐Structure Constant Vary with Cosmological Epoch?

We use the strong nebular emission lines of O III, λλ5007 and 4959, to set a robust upper limit on the time dependence of the fine-structure constant. We find < 2 × 10 -13 yr -1 , corresponding to Δα/α(0) = × 10 -4 for quasars with 0.16 < z < 0.80 obtained from the SDSS Early Data Release. Using a blind analysis, we show that the upper limit given here is invariant with respect to 17 different ways of selecting the sample and analyzing the data. As a by-product, we show that the ratio of transition probabilities corresponding to the λλ5007 and 4959 lines is 2.99 ± 0.02, in good agreement with (but more accurate than) theoretical estimates. We compare and contrast the O III emission line method used here with the many-multiplet method that was used recently to suggest evidence for a time-dependent α. In an appendix we analyze the quasars from the recently available SDSS Data Release One sample and find Δα/α(0) = × 10 -4 .