Current state of mp/me = μ measurements versus cosmic time

Abstract

This article reviews the current state of measurement of μ = M P=Me the ratio of the proton to electron mass in the early universe. Unlike the contribution in this volume by Webb et al. on the value of the fine structure constant α there is no current evidence for a different value of μ in the early universe at the one part in 105 level Astronomical observations provide a determination of this ratio in the early universe through observations of molecular absorption and emission lines in distant objects. Observations of molecular hydrogen in distant damped Lyman Alpha clouds provide a measurement of μ at a time when the universe was only 20% of its present age. The limit of Δ μ/ μ≤10-5 produces a significant observational constraint on quintessence theories for the evolution of the universe and Super Symmetric theories of elementary particles. It is expected that future work will improve this limit even further. It would be very difficult to reconcile a constant value of with a varying value of α © Springer-Verlag Berlin Heidelberg 2011.