nature 23 August 2001
Nature 412, 757 (2001) Macmillan Publishers Ltd.

Flickering light raises possibility of changing 'constant'



[LONDON] Physicists have reacted with curiosity and scepticism to suggestions that one of the fundamental constants of their discipline may not be so constant after all.


Glowing report: could light from a quasar show that the fine-structure constant has increased?

An international team, led by astrophysicist John Webb of the University of New South Wales in Sydney, made the claims after analysing light from bright, distant objects known as quasars. They say their results suggest that the 'fine-structure constant' a measure of the strength of electromagnetic interactions has increased by some 0.001% since the Big Bang.

If true, the finding would be revolutionary. Such constants determine the nature and interaction of matter throughout the Universe. If a shift in the fine-structure constant (also known as alpha) did take place, it would indicate that gravity and the weak and strong nuclear forces can also change over time. Such changes are impossible to explain using conventional theoretical physics and thus open the door to rival explanations, including string theory, which invokes extra dimensions.

The result is statistically sound, but other physicists are concerned that a systematic error may be responsible for it. "One cannot see from the paper how they estimate the systematic uncertainties from various effects, only that they claim the errors are smaller than the effects they see," says John Bahcall, an astrophysicist at the Institute for Advanced Study in Princeton, New Jersey.

Webb's team used data from the Keck telescope in Hawaii to study how clouds of interstellar gas absorb certain wavelengths of quasar light, producing a characteristic signature of dark lines in the spectrum that reaches Earth. They say the spaces between these lines in quasar light (effectively billions of years old) are different from those in similar spectra observed in the lab, and a variation in the fine-structure constant could offer an explanation.

"What we're claiming is that the sample we show is consistent with there being a smaller value of alpha in the past," says John Barrow, a physicist at the University of Cambridge. The team will publish its results on 27 August in Physical Review Letters (87, 091301; 2001).

Bahcall says that the complex analyses required will make it difficult for another group to test the claims. Barrow agrees: "This is not the sort of thing that people will be able to do in the next few months," he says.


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