Is dark matter lighter than we thought? New particle could explain why the universe's greatest mystery remains unsolved.University of Southampton researchers have proposed a hypothetical fundamental particle for dark matter.It has a mass only about 0.02 per cent that of an electron - making it extremely 'light'.This would make it unable to pass through Earth's atmosphere.In turn, Earth-based detectors would therefore not be able to detect it.This could explain why dark matter has not yet been found.Dark matter is thought to make up 84.5 per cent of the universe - but no evidence for it has yet been found. 

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