Crunch time? Study raises doubts over theory that universe will keep expanding

Astronomers have cast doubt on a Nobel prizewinning theory that the expansion of the universe is accelerating, suggesting that instead it may be slowing down.

- Hannah Devlin Science correspondent

If confirmed, this would have profound implications for the fate of the universe, raising the possibility that rather than expanding for ever, the universe could ultimately enter a reverse Big Bang scenario known as the Big Crunch. The astronomers behind the work say their observations also suggest that dark energy - the mysterious force thought to be propelling the expansion of the universe - is weakening.

"Our study shows that the universe has already entered a phase of decelerated expansion at the present epoch and that dark energy evolves with time much more rapidly than previously thought," said Prof Young-Wook Lee, of Yonsei University in South Korea, who led the work.

"If these results are confirmed, it would mark a major paradigm shift in cosmology since the discovery of dark energy 27 years ago."