Limits on the Cosmic Evolution of the Fine Structure Constant

Denoted by the Greek letter alpha, the fine structure constant sets the absolute strength of the electromagnetic force at work inside atoms and in the cosmos. Besides this, alpha incorporates within itself several of the other important fundamental constants of nature, and is defined as 2 times pi times the charge of the electron squared, divided by the product of the speed of light and Planck's constant.

If alpha has changed over the eons, then part of the redshift exhibited by the spectra of distant galaxies would not be attributable exclusively to the expansion of the universe, thus throwing off many astrophysics calculations. Hence it is desirable to troll for different physical constants in past epochs much as one scans core samples from Greenland to gather fossil bits of ancient air trapped in the ice layers

A new comparison of the 21-cm-wavelength emission of hydrogen atoms in distant radio galaxies with that of terrestrial hydrogen reduces the systematic uncertainties by an order of magnitude relative to previous studies using this technique and suggests that any non-expansion contribution to redshifts would be in the fifth decimal at best. Equivalently, the measured limit on proportional change in alpha is less 3.5 x 10^-15 per year out to a look-back time of 4.8 billion years.

This study was carried out by astronomers at the National Radio Astronomy (Chris Carilli, 505-835-7000, ccarilli@nrao.edu), Max Planck Institute (Bonn), University of Colorado, Space Telescope Science Institute, Netherlands Foundation for Research in Astronomy, Kapteyn Research Institute (NL), Onsala Space Observatory (Sweden), and Harvard Smithsonian. (Carilli et al., Physical Review Letters, 25 December 2000; text at Physics News Select)