NEW LIMITS ON THE POSSIBLE VARIATION OF PHYSICAL CONSTANTS

Recent detections of high-redshift absorption by both atomic hydrogen and molecular gas in the radio spectra of quasars have provided a powe rful tool for measuring possible temporal and spatial variations of ph ysical 'constants' in the Universe. We compare the frequency of high-r edshift hydrogen 21-cm absorption with that of associated molecular ab sorption in two quasars to place new (1 sigma) upper limits on any var iation in y = g(p) alpha(2) (where alpha is the fine-structure constan t, and g(p) is the proton g-factor) of \Delta y/y\ < 5 x 10(-6) at red shifts z = 0.25 and 0.68. These quasars are separated by a comoving di stance of 3000 Mpc (for H-0=75 km s(-1) Mpc(-1) and q(0) = 0). We also derive limits on the time rates of change of \(g) over dot (p)/(g) ov er dot (p)\ < 1 x 10(-15) yr(-1) and \(alpha) over dot/(a) over dot\ < 5 x 10(-16) yr(-1) between the present epoch and z = 0.68, These limi ts are more than an order of magnitude smaller than previous results d erived from highredshift measurements.