# How does Santa get around the world? Einstein had the answer! Huge speed that Father Christmas travels at means he shrinks in size and is invisible to the human eye

• Research says Einstein'stheory of relativity means Santa would shrinks in size
• Also calculated that Father Christmas's cruising speed is 10million KM per hour
• Santa's speed means he could appear as a green flash as his sleigh flies by

Dr Katy Sheen, from Exeter University, calculated that Santa and his reindeer would have to travel at about 10 million kilometres per hour

Squeezing down narrow chimneys, moving around without being seen or heard, and delivering presents to 700million children in a single night – it all sounds impossible.

So how does Father Christmas do it? One physicist believes she has an answer – and Einstein is the key.

Dr Katy Sheen, from Exeter University, calculated that Santa and his reindeer would have to travel at about 10 million kilometres per hour to deliver presents to every child expected to celebrate Christmas in 31 hours, taking into account different time zones.

And according to Einstein’s theory of special relativity, objects travelling at high speed become compressed in size. This means Father Christmas would shrink, allowing him to fit his bulging belly and his huge sack of presents down chimneys, Dr Sheen said.

He is also able to move around unseen because light waves get squashed at high speeds. This means that Santa – moving more than 200,000 times faster than Usain Bolt, the world’s fastest man – would change from red to green, appearing as a rainbow-coloured blur. At his top speed, he would become invisible to the human eye.

Dr Katy Sheen, from Exeter University, explains that Einstein's theory of relativity could be used to explain Santa Claus's trip to the home of every child on Christmas Eve

Einstein’s theory could also explain why Father Christmas appears not to have aged – because relativity means time slows when an object moves at high speeds.

Dr Sheen came up with the explanation after she wrote a letter to Father Christmas when she was seven asking why he never got older. She received a response saying it was ‘all magic’. But the budding scientist wanted a more rational explanation – and has offered one herself 26 years later.

As well as providing a useful answer for parents whose children ask them about Santa, Dr Sheen hopes her theory will inspire youngsters to take an interest in physics.

According to Einstein’s theory (E=MC2), pictured here, objects travelling at high speed become compressed in size

The scientist, who calculated how fast Father Christmas would have to travel by working out the number of households likely to celebrate Christmas around the world and the number of children likely to be in them, will present her theory to children at the Science of Christmas Festival in Exeter.

She said: ‘How does Santa manage to reach these phenomenal speeds? Well that’s magic! However, he would certainly need a lot of fuel – so don’t forget his glass of sherry, a mince pie or two and some carrots for the reindeer!’