If he is right, Professor John Webb will go down in history for shaking the foundations of physics and perhaps solving the mystery of why we exist in this part of the universe. If he is wrong, there will be no shortage of sceptics saying they told him so. The Sydney astronomer and his colleagues have made a radical find: that one of the fundamental constants of nature is not a constant. Not only does it appear to be changing, they have shown, it also differs depending on which direction in space you're facing. When gazing at the night sky from the northern hemisphere, this fine-structure constant, known as alpha, gets smaller as the distance from the Earth increases. Looking heavenwards from the other side of the planet, it gets gradually bigger. ''It's controversial. Nobody else has found anything like this in the history of science,'' says Webb, of the University of NSW. ''We could be right or we could be wrong, and time is going to tell.'' The final answer could come soon. He predicts evidence to settle the matter will be available within a decade. That means Webb will still be alive to revel in any glory. ''One can live in hope,'' he laughs. If the team, which includes PhD student Julian King, is right and alpha is not a constant, it means the laws of physics can vary throughout the universe, which would have a profound effect on science. It could mean the speed of light - a rock-solid foundation of modern cosmology - is changing. But it could also explain the mystery of why the universe around us seems fine-tuned to our existence. It would be no coincidence we are here, because this bit of the cosmos would be the part that is just right for us. Elsewhere, there could be ''entire regions of the universe where the laws of physics are entirely unsuitable for life as we know it'', Webb says. The precisely spoken Englishman, formerly of the University of Cambridge, is not bothered at all by researchers who question the wisdom of pursuing such a radical idea. ''It's thoroughly enjoyable working on this subject,'' he says. But he has no time for those who simply say they don't believe his team's results, which have been submitted to the journal Physical Review Letters. ''That is religion, not science,'' he says. ''If someone wants to criticise this work I am completely receptive to that. But don't just say, 'I don't believe it.' That's a useless contribution to the debate. Tell me what's wrong, what part of our analysis is incorrect.'' Webb and his Anglo-Australian team, including Professor Victor Flambaum of the University of NSW and Dr Michael Murphy of Swinburne University of Technology in Melbourne, began to study the fine-structure constant - which is a measure of the strength of the electromagnetic force - more than a decade ago. They analysed light from extremely bright, distant galaxies, known as quasars, observed in the northern hemisphere using the Keck Observatory in Hawaii. In 2003, they published their controversial results showing that alpha was smaller in the distant universe than on Earth. Extraordinary claims require extraordinary evidence. And the find could just have been a quirk of that particular telescope. So the team checked the results using quasar observations in the southern hemisphere, using the Very Large Telescope in Chile. Webb says he was not worried the initial find might be overturned. ''I genuinely had a completely open mind on it.'' But the discovery the second time around was a total surprise: alpha was bigger on the opposite side of the universe. Alpha varies by only a tiny amount, about one part in 100,000, over most of the observable universe. But if the laws of physics can be different in different parts of the universe, it becomes a much more complicated place. Scientists tend to consider simplicity is more likely than complexity, says Webb, ''but I think that has historically been shown to be an incorrect philosophy''. Other recent discoveries, including that a mysterious force known as dark energy appears to be pushing the universe ever faster apart, underscore this picture of increasing complexity. Alpha also depends on the speed of light and a changing speed of light could be the reason alpha is changing. ''It could be, but we just don't know. Alpha is all we can measure,'' Webb says. The constancy, or not, of alpha should be settled once the Square Kilometre Array, a huge radiotelescope that Australia is competing to host, is built in 2019. Webb believes that in as little as six years, another instrument, the Atacama Large Millimetre Array in Chile, could provide observations to confirm or demolish his team's controversial results. ''You have to be optimistic,'' he says.

The sky has a new limit