Alpha's growth (3 221)

As light from a distant quasar pierces a gas cloud billions of years ago, atoms absorb some colors. The precise wavelengths of the lost colors suggest to astronomers that the seemingly constant strength of light's interaction with matter has not, in fact, always been the same. Based on M. Murphy/UNSW

Alpha's possible growth since the distant past also raises the question of whether it is still in flux today. This June in Seattle at a meeting about controlling frequencies of atomic clocks and other devices, Sйbastien Bize of the Paris Observatory and his colleagues reported fresh evidence that alpha is holding steady. Using the world's most precise clocks, known as atomic fountain clocks (SN: 8/7/99, p. 92), the scientists have made a preliminary estimate that the annual variation in alpha, if any, must be less than 1 part in 100 trillion.

Although the measurements in the clock experiments indicate that alpha's value now is fixed, they don't cast doubt on the new astrophysical findings, Bize says. The minuscule disparity that turned up in the quasar spectra covers 12 billion years, which would correspond to an average annual shift of 1 part in 1,000 trillion. That's smaller than the clock laboratories can currently detect. What's more, it may be that the rate of change in alpha itself varies.

That's exactly what Barrow and a couple of other theorists have proposed in a theoretical model they posted July 26 on the Internet physics preprint archive (http://xxx.lanl.gov/abs/astro-ph/0107512). They suggest that alpha stopped being a variable about 3 or 4 billion years ago when the expansion of the already-ballooning universe presumably began accelerating (SN: 2/12/00, p. 106:http://www.sciencenews.org/20000212/bob1.asp).

Still, in this model, which agrees with the astrophysical data but has no obvious ties to string theory, the gravity of massive objects such as stars may also tweak alpha's value. Bize says the Paris experimenters plan to probe this possible gravitational influence in future tests. To do so, they'll compare frequency measurements of fountain atomic clocks when Earth's orbit carries it relatively near or far from the sun's gravity.

Taking an alternative approach to the problem, Webb and his coworkers have launched a program of radio telescope observations. The researchers will employ equipment quite unlike the optical instruments, such as the 10-meter Keck I telescope in Hawaii that they previously used to make spectral observations of gas clouds. Radio astronomy also homes in on different substances in the clouds, including carbon monoxide and other organic molecules, Webb explains.

Other, more radically dissimilar means may also provide a cross-check on the ancient value of alpha. In one, scientists plan to analyze subtle fluctuations in the cosmos discerned by satellite-based telescopes. Those telescopes generate sky maps of relic radiation, known as the cosmic microwave background (CMB), that dates from not long after the birth of the universe (SN: 6/23/01, p. 394: http://www.sciencenews.org/20010623/bob12.asp).

Almost a year ago, a team of Portuguese and British scientists proposed that the microwave pattern favored an ancient alpha that was smaller than today's. However, says Spergel, those microwave data have since been reanalyzed, weakening that interpretation.

Measurements to come may tilt the scales one way or another. For example, the recently launched Microwave Anisotropy Probe, or MAP, satellite can measure the CMB's faint glow with 100 times the precision that has been available. MAP's successor, dubbed Planck, is slated to launch around 2007 and should detect variations in the CMB with even greater precision.

"When the [CMB] data gets better, we'll see either [the radiation pattern predicted by] the standard model or we'll see a signature for something new, like this time-varying alpha," Spergel says.

If the slight shift in alpha measured by Webb and his colleagues holds under further scrutiny, then scientists may have to forgo their long-held ideal that the constants of nature are perpetually unchanging.