Abstract
Quasar absorption spectra at 21-cm and UV rest wavelengths are used to estimate the time variation of , where is the fine structure constant, the proton factor, and the electron/proton mass ratio. Over a redshift range , . A linear fit gives . Two previous results on varying yield the strong limits and . Our sample, larger than any previous, provides the first direct estimate of the intrinsic 21-cm and UV velocity differences .
- Received 29 December 2004
DOI:https://doi.org/10.1103/PhysRevLett.95.041301
©2005 American Physical Society