Current status of astronomical observations on possible cosmological variations of the proton-to-electron mass ratio

Abstract
Astronomical constraints on a possible cosmological variation of the proton-to-electron mass ratio are discussed. The analysis of H₂ lines observed in the spectra of distant quasars Q 0405-443 ( ) and Q 0347-383 ( ) is performed [1] using, partly, very precise values of H₂ frequencies from new laboratory measurements [2] and sensitivity coefficients from new accurate calculations [2,3]. A possible -variation of over 12 Gyr is not excluded. However, the discussion of systematic errors show that some may well be underestimated. Thus, the above value should be treated as the most stringent limit the cosmological variation of at (12 Gyr ago).