May the (fifth) force be with you

Physicists are hinting at the existence of a fifth force of nature, and have devised a way of putting it to the test. Its existence could help to fill some gaps in Einstein's theory of general relativity, and would cause a re-think of how the Universe works. According to the Standard Model, four fundamental forces govern the Universe: gravity, electromagnetic, and the strong and weak nuclear forces. But there's a problem; there appears to be more gravity than can be produced by all the visible matter in our Universe. Dark matter is the current frontrunner to explain this disparity, but we still haven't been able to observe or measure it — leading many physicists to consider dumping gravity as a fundamental force. Now, a team of researchers from the Galactic Center Group at the University of California, Los Angeles, are probing this hypothetical new force by using 20 years of observations from the W. M. Keck Observatory in Hawaii. To find out more go to Test of general relativity could potentially generate new gravitational models.