“Santa Claus” Effect: a matter of Physics

Christmas is coming, and the questions of children about the nature of the fast and very organized Santa Claus take turns to gifts to buy in these long afternoons of exhausting search of them.



Luckily thought about it Dr Katy Sheen, a physicist at Exeter University, who found a scientific explanation for why Santa and his reindeer can travel around the world at such speed that – according to Einstein’s special theory of relativity – they shrink, enabling him and his huge sack of presents to squeeze through even the tightest of chimneys.

The physicist has calculated that Santa Claus  would need to travel at about 6.2 million miles per hour to deliver presents to every child expected to celebrate Christmas in 31 hours. And Santa is very organized, because he has taking into account world time zones:-)


Such speed can create a big change on his suit, and it would make him change from red to green and, at greater speeds disappear entirely. In this particular case, it is the Doppler effect which makes Santa change tint because the bouncing light waves led him to squeeze at a so high speed.

The Doppler effect also explains why children cannot hear Santa Claus’ arrive. As Santa and his sleigh arrive, the sound of bells and his deep “ho, ho, ho” would get the higher pitch and then become completely silent, as his voice goes beyond human hearing range.

“Visiting around 700 million children in 31 hours would mean he would have to travel at six million miles per hour if he is to deliver presents to every child. Some strange things happen when you start to travel that fast. Firstly, time slows down. Second, Santa gets squished which means that he can fit down a chimney more easily. Finally for Santa to fly this fast it takes lots and lots of energy.  How does Santa manage to reach these phenomenal speeds? Well that’s magic. However, he would certainly need a lot of fuel.”

Said Dr. Sheen in her recent interview.

Einstein’s Theory of Relativity – published in 1905 – said that space and time were interwoven in a single continuum known as space time, but that events could occur at different times depending on the position of the observer.

Dr Sheen will tell children at the University of Exeter Christmas and Science Festival that relativity also explains why Father Christmas appears not to grow older, because relativity can slow down clocks.

The process to not get older, rather than be “all magic” is due to physics!

How that can be possible?

Well, time dilation – which is part of Einstein’s theory of relativity – occurs as time speeds up relative to the observer… So if Santa travels at high speeds, he would age more slowly than somebody moving at a normal speed.

All very clear now. Thanks to Dr. Sheen and Physics laws. But the fact remains that, perhaps, for a child, the magic of an overweight and joyful Santa Claus, capable of doing miracles with his long, heavy sled chock full of fantastic gifts, keeps its incredible charm.


Especially in this era where the good news is rare commodity, and where many children have only one main hope: do not “feel”and heard the sound of the bombs out of their homes, and maybe allow that Santa’s idea could bring them peace and a touch of magic in their innocent lives. Far from political and economic interests and power lobbies.




Leave a Comment

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s