TAMPA, FLORIDA--This week, an astronomer at a meeting here of the American Physical Society presented new evidence that the fine-structure constant--and by extension, the speed of light--has not changed over billions of years. While the new study doesn't end a fulminating debate over whether the constant is indeed constant, the technique provides an independent method for testing the controversial changing-constant hypothesis.
The fine-structure constant is a shorthand way to describe the strength of the electromagnetic force. It combines a mixed bag of other fundamental constants, including the charge of the electron, Planck's constant, and the speed of light, all of which are thought to have had unchanging values since the birth of the universe.
In 2001, however, a team of astronomers and physicists studying light from distant quasars saw a pattern--a subtle shift in the spacing of fingerprintlike lines in the quasars' spectra--that seemed to indicate that the fine-structure constant has increased slightly over billions of years (ScienceNOW , 15 August 2001). Further data from the same team seemed to support the result [ScienceNOW , 12 April 2005]. But similar studies of quasars and data from atomic clocks said otherwise.
Now another team of astronomers and physicists has made an independent measurement that indicates that the fine-structure constant is indeed a constant. The DEEP2 survey analyzed the light from about 40,000 galaxies and looked at the spacings of similar fingerprintlike lines coming from ionized oxygen in very hot regions of those galaxies--spacings that depend on the fine-structure constant. Because the light from those galaxies is billions of years old, the spacings are snapshots of the size of the fine-structure constant in the past. Furthermore, since this technique uses a different method from the quasar study, it should not be subject to the same types of errors. All told, the data seem to show a constant constant.
The DEEP2 results don't have the precision to rule out the quasar study that seems to show a changing fine-structure constant. "They're in agreement within the combined error bars," says Michael Murphy, a University of Cambridge astrophysicist and member of the quasar group. Nevertheless, says Jeffrey Newman, a physicist at the Lawrence Berkeley National Laboratory in Berkeley, California, and member of the DEEP2 survey, the galaxy technique is simple and robust enough that a bigger survey of galaxies can use it to settle the matter once and for all.
The DEEP2 Redshift Survey