How Father Christmas delivers presents—the physicsby Katy Sheen / December 22, 2016 / Leave a comment
It’s an age-old question—how does Father Christmas manage to deliver presents to children across the world in just one night, fit down the chimney, never seem to age and arrive without being seen or heard? As a little girl, I can recall puzzling over these mysteries, so much so that one Christmas Eve I left a card for Santa, questioning why he never got any older. Though rather overwhelmed when I received a reply from the great man himself, my rational mind was not satisfied with the answer I received, scrawled in shaky hand-writing: “It’s magic.”
This year, I sat down to work through a scientific explanation.
Santa and his reindeer need to zoom around at a minimum of 6.2m mph in order to deliver all the presents on time. That is 200,000 times faster than Usain Bolt and would be like zipping from Land’s End to John O’Groats in under half a second. Depending on the number of children good enough to receive presents, and accounting for some time stuffing presents into stockings and eating the odd mince pie, I suspect that Santa can actually travel at far greater speeds, and that his sleigh can probably approach the speed of light.
Santa’s stealth delivery is partly explained by special relativity theory devised by Albert Einstein (who coincidentally bears a passing resemblance to Santa). This theory explains how Father Christmas fits down the chimney. An object traveling at speed compared to a stationary observer contracts in space—so Father Christmas shrinks, or gets thinner—in the direction he is traveling. Applying Einstein’s science also explains why Father Christmas doesn’t seem to age. Special relativity tells us that traveling at speed slows down clocks.
In addition, according to the Doppler effect (proposed in 1842 by an Austrian physicist), if Santa came hurtling towards you at high speed his coat, and Rudolf’s nose, would appear to change from red to green—and could even morph through every colour possible, eventually disappearing to the human eye. The successive crests of light waves emitted from an approaching Santa would get “bunched together,” causing an apparent increase in frequency to the observer. So, the laws of physics explain why Father Christmas is rarely seen by children while delivering presents.
The Doppler effect also explains why children cannot always hear Father Christmas arrive. As Santa and his sleigh approach, the sound of…