Journal
PHYSICAL REVIEW LETTERS
Volume 85, Issue 26, Pages 5511-5514Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.85.5511
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We present measurements of absorption by the 21 cm hyperfine transition of neutral hydrogen toward radio sources at substantial look-back times. These data are used in combination with observations of rotational transitions of common interstellar molecules to set limits on the evolution of the fine structure constant: (alpha) over dot/alpha < 3.5 X 10-(15) yr(-1), to a look-back time of 4.8 Gyr. In the context of string theory, the limit on the secular evolution of the scale factor of the compact dimensions, R, is (R) over dot/R < 10(-15) yr(-1) Including terrestrial and other astronomical measurements places a limits on slow oscillations of R from the present to the epoch of cosmic nucleosynthesis, just seconds after the big bang, of DeltaR/R < 10(-15).
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