I've never seen Santa Claus - but that's never bothered me too much. I never expected to see him when I was little because I knew that Santa didn't visit our house until I was asleep. I never expected to see Santa when I was an adolescent; my friends had convinced me that Santa was a fraud. Now, as an adult I know that the spirit of Santa is very real, but I still don't expect to see him - because he's too fast!

To illustrate, let's calculate the amount of time that Santa spends visiting your house. We'll need to make a few assumptions for this calculation:

1. There is only one Santa. (Some industrious genetic engineers could certainly make Santa's life infinitely easier if they cloned a few copies of him);
    

2. Santa visits the homes of people that celebrate Christmas. According to the Global Traveler website (http://www.Go-Global.com; 1997), Christmas is celebrated in 149 countries;
    

3. The combined population of these 149 countries is 3.54 billion (1997 World Population Data Sheet, Population Reference Bureau, Washington, D.C.; http://www.prb.org/prb/);
    

4. Santa visits homes with children under 15. This statistic is also found in the 1997 World Population Data Sheet (Population Reference Bureau, Washington, DC). Globally speaking, 32% of the world's population is younger than 15. However, for the 149 countries that celebrate Christmas, this value ranges from a low of 15% in San Marino and Italy to a high of 51% in the Marshall Islands; and
    

5. Santa probably likes large families in order to minimize the number of stops he has to make. We can estimate the number of children per family from the total fertility rate (TFR), which is an indication of the average number of children a woman will likely bear during her reproductive years. From a global perspective, a woman can be expected to have 3 children (TFR = 3; 1997 World Population Data Sheet). For the countries that celebrate Christmas, TFR ranges from a low value of 1.1 in San Marino to 7.4 in Niger.

Based on these assumptions, we can calculate the number of visits Santa makes in each country that celebrates Christmas:

Thus, every Christmas Eve in Palau, Santa makes about 1900 visits compared to over 29 million visits in the United States. Finally, to complete the calculation we add the number of visits Santa makes in each country and arrive at a whopping 373 million (the actual figure is 372,582,174 - plus or minus a few) visits every Christmas Eve.

Since Santa has roughly one night (24 hours or 1440 minutes or 86400 seconds) to get the job done, we can calculate Santa's time per visit as follows:
 

Thus, Santa takes a fraction of a millisecond to land on your rooftop, scoot down the chimney, put presents under the tree, fill up the stockings, eat the snacks, zip back up the chimney, cleanup any reindeer droppings on the roof and take off for the next house. That's hustle!
 

A skeptic might argue that even though Christmas is celebrated in 149 countries, those that do may be in the minority and in many cases, Santa is not a part of their Christmas tradition. True. But, if we consider how much work Santa must do in just North America where the many do include Santa Claus in their holiday traditions, we can calculate that Santa must spend 1.25 milliseconds per visit. Now matter how you cut it, Santa is one fast dude.

To give you an idea of how fast this is, let's imagine that our Christmas tree is 50 feet from the rooftop. If we use the conservative North American estimate (1.25 milliseconds/visit), then Santa is traveling through the house about 55,000 miles per hour. Or, if Santa were to spend one minute per house, it would take him approximately 65.6 years to complete his rounds. It's certainly no wonder that Santa is portrayed as a jolly "old" fellow; it could take him nearly a lifetime to make one delivery.

So why I haven't I seen Santa? I blinked. According to Professor Craig Evinger from the State University of New York at Stony Brook, a blink lasts approximately 200 milliseconds. This means that your average blink takes 160 times longer than it takes Santa to visit your home. Or from another perspective, in the time it takes you to blink just once, Santa has already filled the stockings at your house and 159 of your neighbors. So if you, like me, have ever blinked on Christmas Eve, chances are you missed Santa - he came and left in the twinkling of our eye.