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Cosmologists say that they have uncovered hints of an intriguing twisting in the way that ancient light moves across the Universe, which could offer clues about the nature of dark energy — the mysterious force that seems to be pushing the cosmos to expand ever-faster.

They suggest that the twisting of light, which they identified in data on the cosmic microwave background (CMB) collected by the Planck space telescope, and the acceleration of the Universe could be produced by a cosmic ‘quintessence’, an exotic substance that pervades the cosmos. Such a discovery would require a major revision of current theories, and physicists warn that the evidence is tentative — it does not meet the ‘5 sigma’ threshold used to determine whether a signal is a discovery. But it underscores the fact that modern cosmology still has an incomplete picture of the Universe’s contents.

If dark energy is a quintessence, its push on the expansion could slowly wither or disappear, or could even reverse to become an attractive force, causing the Universe to collapse into a ‘big crunch’, says Sean Carroll, a theoretical physicist at the California Institute of Technology in Pasadena. “We’re back to a situation where we have zero idea about how the Universe is going to end.” The work was reported on 23 November in Physical Review Letters1.

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