<b>Moon Measurements Might Explain Away Dark Energy</b><br /><br />LINK<br /><br />Plans to trace the Moon's orbit with extraordinary new accuracy could reveal kinks in Einstein's theory of gravity and help explain the mysterious accelerating expansion of the universe, says a US researcher.<br /><br />The acceleration cannot be explained by known forces in the Universe. To account for the behaviour, cosmologists have introduced the concept of a new, as yet unseen, force - dark energy.<br /><br />But Gia Dvali, of New York University, US, believes there could be another explanation. He thinks the accelerating expansion might be caused by unexpected properties of gravity, which are only seen over very large distances. Taking inspiration from string theory, which proposes the existence of several extra dimensions, Dvali, and NYU colleagues Gregory Gabadadze and Massimo Porrati, suggests that gravity may leak into an extra dimension on this large scale.<br /><br />"The accelerated universe can be a window of opportunity for understanding the most fundamental aspects of gravitation, and may signal the modification of standard laws of gravity at very large distances," Dvali told an audience at the American Association for the Advancement of Science meeting in Washington, DC, US.<br /><br />Millimetre accuracy<br />The scheme to measure the Moon's orbit involves firing a laser beam at mirrors left on the surface by the Apollo 11 astronauts and measuring the time it takes for photons to return. This makes it possible to trace the lunar orbit and, so far, astronomers have used the technique to track it with an accuracy of a few centimetres.<br /><br />Now, Tom Murphy, Chris Stubbs and Eric Adelberger at the University of Washington in Seattle, US, plan to use more precise laser equipment to measure the Moon's path to just a few millimetres. At this scale, Dvali's theory predicts that subtle deviations in the Moon'