How did the universe begin? What is a black hole? And what happens if you throw a party for time travellers...? When Stephen Hawking was told at the age of twenty-one that he only had a few years to live, it made him more determined than ever to find out the answers to life's big questions. Diagnosed with motor-neurone disease as a young man, Stephen defied the odds and lived to the age of 76 - and his scientific discoveries changed the world . . .