The Great Game

IN 1997 astronomer John Webb and his team at the University of New South Wales in Sydney analysed the light reaching Earth from distant quasars. On its 12-billion-year journey, the light had passed through interstellar clouds of metals such as iron, nickel and chromium, and the researchers found these atoms had absorbed some of the photons of quasar light - but not the ones they were expecting.

If the observations are correct, the only vaguely reasonable explanation is that a constant of physics called the fine structure constant, or alpha, had a different value at the time the light passed through the clouds.

But that's heresy. Alpha is an extremely important constant that determines how light interacts with matter - and it shouldn't be able to change. Its value depends on, among other things, the charge on the electron, the speed of light and Planck's constant. Could one of these really have changed?

No one in physics wanted to believe the measurements. Webb and his team have been trying for years to find an error in their results. But so far they have failed.

Webb's are not the only results that suggest something is missing from our understanding of alpha. A recent analysis of the only known natural nuclear reactor, which was active nearly 2 billion years ago at what is now Oklo in Gabon, also suggests something about light's interaction with matter has changed.

The ratio of certain radioactive isotopes produced within such a reactor depends on alpha, and so looking at the fission products left behind in the ground at Oklo provides a way to work out the value of the constant at the time of their formation. Using this method, Steve Lamoreaux and his colleagues at the Los Alamos National Laboratory in New Mexico suggest that alpha may have decreased by more than 4 per cent since Oklo started up (Physical Review D, vol 69, p 121701).

There are gainsayers who still dispute any change in alpha. Patrick Petitjean, an astronomer at the Institute of Astrophysics in Paris, led a team that analysed quasar light picked up by the Very Large Telescope (VLT) in Chile and found no evidence that alpha has changed. But Webb, who is now looking at the VLT measurements, says that they require a more complex analysis than Petitjean's team has carried out. Webb's group is working on that now, and may be in a position to declare the anomaly resolved - or not - later this year.

"It's difficult to say how long it's going to take," says team member Michael Murphy of the University of Cambridge. "The more we look at these new data, the more difficulties we see." But whatever the answer, the work will still be valuable. An analysis of the way light passes through distant molecular clouds will reveal more about how the elements were produced early in the universe's history.