title: Astronomical constraints on the cosmic evolution of the fine structure constant and possible quantum dimensions.
abstract: 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/ alpha<3.5x10(-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 &Rdot/ R<10(-15) yr(-1). Including terrestrial and other astronomical measurements places 2sigma 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(-5).
authors.affiliation: National Radio Astronomy Observatory, Socorro, New Mexico 87801, USA.
authors.forename: C L
authors.initials: CL
authors.lastname: Carilli
authors.forename: K M
authors.initials: KM
authors.lastname: Menten
authors.forename: J T
authors.initials: JT
authors.lastname: Stocke
authors.forename: E
authors.initials: E
authors.lastname: Perlman
authors.forename: R
authors.initials: R
authors.lastname: Vermeulen
authors.forename: F
authors.initials: F
authors.lastname: Briggs
authors.forename: A G
authors.initials: AG
authors.lastname: de Bruyn
authors.forename: J
authors.initials: J
authors.lastname: Conway
authors.forename: C P
authors.initials: CP
authors.lastname: Moore