The image of an obese guy being dragged around the world by flying ungulates is a pretty tough pill to swallow, believability-wise. Even having solved the cargo problems, you have the fact that the only flying mammals are bats and the fact that Santa has a shitload of houses to visit.
In fact, even if Santa only visits Christian homes; that is still over 3.3 billion people worldwide. That means Santa has a single night to visit over 150 million houses, according to math.
So How Does Santa do it?
For starters, experts point out that Santa could use an antimatter engine to power his sleigh.
Even now, NASA is hard at work making antimatter-powered travel a reality and by the time NASA gets to it, you know Santa has had it forever. Here's how it works: Everything that matter does, antimatter does oppositely. An antimatter particle, for example, has the same mass as its counterpart, but reversed electrical charges. So when matter and its antimatter doppelganger collide, both particles are destroyed and a explosion of energy erupts in their place. That energy is traveling faster than the speed of light.
So, theoretically, a sleigh powered by antimatter would be fast enough to get Santa around the world in a night. You get the Stardust Antimatter Propulsion Unit.
Although antimatter propulsion rockets are mainly used in science-fiction shows to allow spaceships to travel at warp speed, the possibility of designing one is very real -- NASA is currently developing one that would get us to Mars within a matter of weeks.
Now, as little Timmy is no doubt pointing out, the problem is that the energy created by the engine would be pure radiation and would kill Santa dead. But that's not an issue if Santa is using an ion shield to protect himself and his reindeer. Scientists have developed "mini magnetospheres" that mimic the outer reaches of our atmosphere, which would keep our astronauts from absorbing gene-murdering levels of cosmic radiation.
Which is important, because cosmic rays are no joke; outside the comic book world, too much exposure would be less Fantastic 4 and more "cancer riddled heap of awful." And we don't want that for Santa.
But experts warn we shouldn't discount the idea that Santa is manipulating space/time, having abandoned anti-matter way back in the Scrooge days. For instance he could have mastered the ability to carry around a small black hole with him to quantum teleport anywhere on earth in an instant. The use of a black hole may actually allow him to move through space and time, which would mean he could simply "reuse" the same chunk of time over and over until the work was done.
We learn that Santa needs to visit 1,800 houses per second in order to deliver all of his toys, meaning he travels at 24,000 times the speed of sound. (Not that plausible, but who knows what kind of magic Santa is capable of?) One reality that is harder to explain away is the fact that by traveling so fast, the reindeer will absorb so much energy in flight that "they will burst into flame almost instantaneously." Oh, poor Rudolph! But who knows, maybe they wear some kind of flame-retardant suits that Mrs. Claus makes for them. I mean, even government agencies say he's real, so there has to be some truth to it, right?