Evidence for the Big Bang at the start of the universe was discovered by accident, using technology developed to record radio waves from space, that were themselves found by accident. Adam Hart explores serendipity in radio astronomy with Professor Nial Tanvir of Leicester University, and Professor Sarah Bridle of Manchester University, in a story involving not a small amount of pigeon poo, and a persistent odd noise detected from space. Produced by Rory Galloway. First broadcast on Tuesday 24 July 2018.