Distant gas blob threatens to shake nature's constants

The basic constants of nature aren't called constants for nothing. Physics is supposed to work the same way across the universe and over all of time. Now measurements of the radio spectra of a distant gas cloud hint that some fundamental quantities might not be fixed after all, raising the possibility that a radical rethink of the standard model of particle physics may one day be needed.

The evidence comes from observations of a dense gas cloud some 2.9 billion light years away which has a radio source, the active supermassive black hole PKS 1413+135, right behind it. Hydroxyl radicals in the gas cloud absorb the galaxy's radio energy at certain wavelengths and emit it again at different wavelengths. This results in so-called "conjugate" features in the radio spectrum of the gas, with a dip in intensity corresponding to absorption and an accompanying spike corresponding to emission.

The dip and spike have the same shape, which shows that they arise from the same gas. But Nissim Kanekar of the National Centre for Radio Astrophysics in Pune, India, and colleagues found that the gap in frequency between the two was smaller than the properties of hydroxyl radicals would lead us to expect.

The gap depends on three fundamental constants: the ratio of the mass of the proton to the mass of the electron, the ratio that measures a proton's response to a magnetic field, and the fine-structure constant, alpha, which governs the strength of the electromagnetic force. The discrepancy in the size of the gap thus amounts to "tentative evidence" that one or more of these constants may once have been different in this region of space, Kanekar says.

The change in these constants, if genuine, is tiny. For example, if a change in alpha were solely responsible for the discrepancy, the measurements suggest alpha would have been just 0.00031 per cent smaller 3 billion years ago than today (The Astrophysical Journal Letters, vol 716, p L23). But even such a small effect would require "a new, more fundamental theory of particle physics" to explain it, says Michael Murphy of Swinburne University of Technology in Melbourne, Australia.

Measurements by Murphy and colleagues of visible light from distant quasars absorbed by intervening gas clouds have also hinted alpha was smaller in the past. But it was never certain that the light measured all came from the same region. "That's a critical assumption," says Murphy.

"Radio measurements currently appear to be the most promising avenue for a secure detection of fine-structure constant evolution," says Jeffrey Newman of the University of Pittsburgh, Pennsylvania. "I wouldn't call this more than a hint, though. It's the first application of a new technique."

The subtle discrepancy found by Kanekar's team might be caused by "contamination" from light from another patch of gas. Last month, the team began using the Arecibo radio telescope in Puerto Rico to rule this out. ...

via Distant gas blob threatens to shake nature's constants - physics-math - 04 June 2010 - New Scientist.