The mystery of how Father Christmas can deliver presents to every child in one night, fit down the chimney and arrive without being seen or heard has been 'solved'.
According to Dr Katy Sheen, a physicist at the University of Exeter - Santa and his reindeer zoom around the world at such a speed that - according to relativity theory - they would shrink, enabling Father Christmas and a huge sack of presents to fit down chimneys.
Dr Sheen says he has to gather a lot of pace to fit it all in.