Constraints on Changes in Fundamental Constants from a Cosmologically Distant OH Absorber or Emitter

We have detected the four 18 cm OH lines from the z0. 765 gravitational lens toward PMN J0134--0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the z0. 765 absorber and the z0. 685 lens toward B0218+357 to place stringent constraints on changes in Fg₏^2/^1. 57. We obtain /F= (0. 440. 36^stat1. 0^syst) 10^-5, consistent with no evolution over the redshift range 0<z0. 7. The measurements have a 2 sensitivity of /<6. 710^-6 or /<1. 410^-5 to fractional changes in and over a period of 6. 5 G yr, half the age of the Universe. These are among the most sensitive constraints on changes in.