‘This is the way the world ends / Not with a bang but a whimper.’ (T.S. Eliot) But how about the way the world begins? Was this the biggest bang of all? This unit will introduce you to the theory of the Big Bang and will present the three main lines of experimental evidence that support this theory. This study unit is just one of many that can be found on LearningSpace, part of OpenLearn, a collection of open educational resources from The Open University. Published in ePub 2.0.1 format, some feature such as audio, video and linked PDF are not supported by all ePub readers.