A new study has calculated how Santa Claus is able to deliver presents to 700 million children in just one night by using Albert Einstein's Theory of Relativity to explain the magic. Dr

Katy Sheen, a physicist at Exeter University, also used Einstein's theories to explain why Santa remains so elusive, even though, as the Daily Telegraph says, "millions stay awake

on Christmas Eve hoping for a glimpse of his red suit". The study found that Father Christmas would be forced to travel at a speed of 6.2 million miles per hour in order to deliver

presents to all 700 million children in the world, during a 31-hour timeframe that takes into account all times zones he would cross. SUBSCRIBE TO THE WEEK Escape your echo chamber. Get the

inbox. At such speeds, relativity dictates that the appearance of an object changes dramatically, depending on the viewpoint of the observer. Sheen calculated that, from a ground-level

perspective, Santa would change from his traditional red colour, to green, and would then disappear entirely as he reaches top speed, due to the compression of light around him. "Some

strange things happen when you start to travel that fast," says Sheen. "Firstly, time slows down. Second, Santa gets squished which means that he can fit down a chimney more

easily." Dr Sheen is set to tell children at the University of Exeter Christmas and Science Festival about her findings, including how relativity slowing down time also means that Santa

ages far more slowly than everyone else. According to the Telegraph, Sheen wrote to Father Christmas when she was seven years old asking why he never aged and received a response telling

her it was "all magic". "Not convinced, she decided to become a scientist to one day find a rational explanation," says the newspaper, "and 26 years later has come

up with a solution." Explore More In Brief