A Quantum Theorist's ResponseKnowing that a reindeer is almost positively unable to fly, it is possible that (through the law of opposites) their bodies could be quantumly reversed: each atom could be replaced with its antimatter equivalent. Since antimatter is the exact opposite of matter, it should react inversely to gravity. This does bring in the thought of how the antimatter doesn't annihilate itself, but that is easily overcome by having magnetic constrictors onboard that actually keep the reindeer out of contact with the rest of the universe.
Of course, we then encounter the issue of the number of children in the world that are expecting presents from Santa (378 million). But wait! That is easily dealt with as well.
Wormholes are funny little things. Not only do they allow for a cool special effect to be used in Sci-Fi movies and a handy interstellar transport device, but they are also good for travelling through time (why does the forum system not recognize "travelling" as a properly spelled word?). Santa could utilize a wormhole device that transports him back exactly to the point that he arrived at a certain house, or a little before. When you have a time-travel device, you have all the time in the world. Causality wouldn't be affected, since Santa is the only one to witness this event (except for one very bleary guy at a radar screen in northern Wisconsin and the anti-deer).
A wormhole device could also be used for the sack full of presents. Santa has all of these items in his workshop at the pole, but he has just an empty sack on the back of that sleigh! All the presents are tossed through a wormhole via elves (this really does sound ridiculous, doesn't it?) and are received by Santa on the other end when he has already gone down the chimney. Now this also would bring up another sore point: what about all those kiddies with small chimneys, or no chimneys at all? Well, as long as Santa isn't being rude and choosing just kids with good-sized chimneys, we can assume that he's getting in there somehow. Again, I do believe some sort of wormhole device would be in use. Open one up, pop through it, and Bob's your uncle!
In conclusion - Santa exists, and he's flying through the air with wormholes flying out of his arse and reindeer detonating on occasion!
