<p>On 14 September 2015, after 50 years of searching, gravitational waves were detected for the first time and astronomy changed for ever.<br><br>Until then, investigation of the universe had depended on electromagnetic radiation: visible light, radio, X-rays and the rest. But gravitational waves ? ripples in the fabric of space and time ? are unrelenting, passing through barriers that stop light dead.<br><br>At the two 4-kilometre long LIGO obse...