Are you uncomfortable appealing to "magic" when explaining Santa Claus to your inquisitive infants, but still want to preserve the joy of the mystery? Dr. Katy Sheen, a physicist in the geography department at the University of Exeter, is who you need to talk to. She has devised some rather ingenious explanations for many of Santa's more mystical antics, strictly using scientific theories, reports

Is your child confused about how Santa can fit down so many chimneys, carrying such a mammoth sack of gifts? According to Sheen, Einstein "solved" this mystery when he devised his theory of special relativity. As we know, Santa has to move incredibly fast on Christmas Eve to deliver all of his gifts to children around the world. Anything moving this quickly should — again, according to Einstein — shrink, or get thinner, in the direction of travel. So Santa can slim to chimney-thin size so long as he keeps moving fast enough.

Incidentally, this also helps to explain why Santa is never seen on his delivery route. Sheen calculated that Santa has to travel at least 10 million kilometers per hour to make it to every home in one night. At such speeds, his red coat would shift to green and then, if he had to move even faster (to make up for lost time snacking on cookies), he could even disappear to the human eye. This color shift is explained by the Doppler effect.

If any bang is heard on Christmas night, as the presents get dropped off from house to house, it might be from the sonic boom that would crack as Santa crosses the sound barrier.

Relativity can also help explain why Santa never appears to age over the years. Traveling at such breakneck speeds means he ages much slower than the rest of us.

So, it turns out that Santa actually offers a great opportunity to teach your kid about science. That's Sheen's intent, anyway. She will be presenting all of these theories to children at this year's Science of Christmas Festival at the University of Exeter.

And if you're wondering how Santa is capable of achieving such high speeds ... well, perhaps at least some things are better left for magic.