In 1937, physicist Paul A.M. Dirac suggested that the fine structure constant, which defines the strength of the electromagnetic force, might vary over time. Now a team of researchers from the University of New South Wales, Cambridge University, Pennsylvania State University, Carnegie Observatories and the University of California in San Diego has confirmed the phenomenon. The result is in agreement with the predictions of unified theories such as string theory, and it follows from it that the speed of light has changed over the lifetime of the universe.

The researchers used the Hires echelle spectrograph on the Keck I telescope atop Mauna Kea, Hawaii, to examine the spectra of light from quasars of up to redshift 3.5 that passed through gas clouds. The two potential sources of systematic error in the study would make the results more significant, they claim in a report of the findings that appeared in the Aug. 27 issue of Physical Review Letters.