Only 4 days left until you think Santa will deliver your presents. But does he really exist? Well, I'm a scientist, so here's my take on things:
1.)There's no known species of reindeer that can fly. However, more than 300,000 species of living organisms still remain to be classfied, and even though most of them are insects and bacteria, it's impossible to say beyond all doubt that there are no flying reindeer, which only Santa has seen, among the unclassfied species.
2.)There are approximately 2 billion children (humans under the age of 18 years) on this planet. However, Santa doesn't deliver presents to Muslim, Hindu, Jewish and Buddhist kids, which eliminates about 85% of aforementioned kids from his list, leaving him with 378 million kids to deliver presents to (according to the Census Bureau). Let's assume there are, on average, 3.5 kids per household, which comes down to 91.8 million houses with kids in them to deliver presents to. We further assume that there's a least one kid that has not been naughty all year and deserves to receive a present in each house.
3.)Santa has a 31-hour work day due to the different time zones, provided he travels from east to west (as logic would predict).Consequently, Santa has to make 822.6 visits per second. That means, Santa has about 1/1000 of a second per house with a nice child to run his errands: Park, jump out of the sleigh, climb down the chimney, fill the socks, distribute the remaining presents underneath the Christmas tree, eat up all the remains of the Christmas dinner, climb up the chimney and proceed to the next house. Let's assume, for simplicity of our calculation, that all of the 91.8 million houses are evenly distributed on earth (we know this is not true in reality, yet this assumption will not alter the final result in any way). That means, the average distance between two houses is 1.3 km, resulting in a total of 120.8 million km during Santa's work day - not counting potty breaks (although this is debatable - see this thread). 120.8 million km in 31 hours is an average speed of 1040 km per second - or 3,000 times the speed of sound. Compare this to the fastest man-made vehicle on earth, the Ulysses Space Probe, which travels at a ridiculous 43.8 km per second. A standard reindeer does 24 km an HOUR.
4.)Landing a sleigh is another interesting procedure. Let's assume each kids gets just a medium-sized set of legos (weight: 1 kg). The presents alone will account for a weigh of 378.000 tons in Santa's sleigh, still excluding Santa himself, who is commonly described as an overweight man. A single reindeer can only pull 175 kg of weight. Even under the assumption that a "flying reindeer" can pull 10 times as much weight, we'd still need 216,000 reindeers to get Santa's sleigh moving. The animals increase the weight of Santa's sleight (exluding the sleigh itself) to a whopping 410,400 tons, more than 4 times as much as the cruise ship Queen Elisabeth II.
5.)410,400 tons at a speed of 1040 kmph creates an enormous aerodynamic resistance, which heats up the reindeers just like a space ship gets hot when re-entering earth's atmosphere. The first pair of reindeer will have to absorb 16,000,000 trillion Joule of energy - per second. You can imagine they'll go up in flames instantly, which exposes the next pair of reindeer to the heat, and so forth. The entire fleet of reindeer will be vaporized in 5 milliseconds. In the meantime, Santa is exposed to 17,500 times the earth's acceleration. An 120 kg Santa (who'd still be light weight compared to the common description of Santa) would be nailed to the seat of his sleigh with a force of 20.6 million Newton.
To summarize: Even if Santa has ever delivered presents, he'll be dead by now!
(I've posted this last year on TBDL, but since that website is history now, I figured I may post this again. )