New limits on the possible variation of physical constants

Abstract

Recent detections of high-redshift absorption by both atomic hydrogen and molecular gas in the radio spectra of quasars have provided a powerful tool for measuring possible temporal and spatial variations of physical 'constants' in the Universe. We compare the frequency of high-redshift hydrogen 21-cm absorption with that of associated molecular absorption in two quasars to place new (1σ) upper limits on any variation in y=gpα2 (where α is the fine-structure constant, and gp is the proton g-factor) of |Δy/y| < 5 × 10-5 at redshifts z = 0.25 and 0.68. These quasars are separated by a comoving distance of 3000 Mpc (for H0 = 75 km s-1 Mpc-1 and q0 = 0). We also derive limits on the time rates of change of |ġp/gp| < 1 × 10-15 yr-1 and |α̇/α| < 5 × 10-16 yr-1 between the present epoch and z = 0.68. These limits are more than an order of magnitude smaller than previous results derived from high-redshift measurements.