As you might guess from the title, today's article will be slightly less serious than normal, and a lot more lighthearted. Those of you who prefer serious science may want to skip this one...

Now for those who are still reading this, the topic today is the physics of Santa Claus. I will not weigh in on the reality or lack there of of the magical elf, but rather I will be addressing how modern physics makes some of the more questionable aspect of the story of Santa Claus a little more plausible. Some of these comments will be very speculative, and are far from proven to any scientific standard. However others are well known and well proven in experimental physics, and demonstrate just how odd nature really is when you look closely enough.

So without further ado, here is the highly speculative explanations for how Santa achieves his magical feats.

1. How can Santa visit every home in just one night? First off, since night is different in different parts of the world Santa actually has an entire twenty-four hour day to complete his mission. And he doesn't actually visit all of the homes, since many lack children or at least lack children who belief in him. 
However even if he visited every square kilometer of land on the planet, he would only need to travel at approximately 10,000,000 kph, or approximately 1% of the speed of light. Although that is significantly faster than any man made transportation, it isn't that fast compared to many astrophysical objects. (And admittedly this requires him to keep travelling without stopping to distribute gifts).
And Santa has the advantage of time dilation. According to the special theory of relativity, a moving observer experiences time at a different rate from the rest of the residents of the planet. At 1% of the speed of light Santa would only gain a few seconds of travel time - but if he were to travel at 99% of the speed of light he would have a full week to complete everything. And if he could somehow travel at the speed of light, then time would stop completely for him and he could take as many years as necessary!

2. How does he get into houses? There are many ways, assuming he can control spacetime and quantum systems. Objects near the horizon of a black hole become thinner due to gravitational tidal effects, and so Santa could use this to distort himself and slide down the chimney. Unfortunately black holes do a lot of damage to the average suburban home, so this is probably not an option.
But wormholes could work. According to the laws of general relativity, it is possible to connect different regions of space and time through a tunnel, known as a wormhole. If someone could generate a wormhole with one end in the house and one end on the rooftop, it would be as easy as stepping through. Wormholes could also speed up the journey, as in theory they could connect the present moment to the past - or in the case of Santa allow him to enter every house on Earth at the exact same moment!
Moving from general relativity to quantum mechanics, it is well known that microscopic objects such as subatomic particles can tunnel through walls. A particle that exists on one side of a barrier could suddenly re-appear on the other side of the barrier - that is how many components of digital electronics work. No scientist has ever been able to create this tunneling effect on the scale of a person, but perhaps Santa has a way. Perhaps Santa can quantum tunnel from each rooftop into the home below. 

3. How does he carry all the toys in his sleigh? As in the previous section, the answer could be either time dilation or wormholes. Since Santa could slow down time to complete his mission, he could simply fly back to his workshop frequently to reload his sleigh. And if he can create wormholes, then he could put one end in the workshop and one in the sack he carries, and just pull out whatever he needs. It would be like carrying an entire warehouse on his back.

4. How does Santa fly?  Magic reindeer! Again there are many speculative theories that would allow for a sleigh and reindeer to fly. (I am going to assume that his sleigh doesn't contain jet engines and wings). If Santa has the technology to manipulate space and time, then he could create a warp bubble around his sleigh and simply not experience gravity at all. Similar technologies have been proposed for interstellar travel, although they require large amounts of energy and exotic matter. But it isn't impossible.
Another option that was proposed in an academic paper a few months ago is that there may be a way of shielding matter from the Higgs field. Frequent readers will recall that our best theories of matter explain the mass of matter as being due to its interactions with the omnipresent Higgs field that fills the Universe. In the first fraction of second of the Universe's existence, the Higgs field did not yet exist and all matter would have been massless. It has been suggested that, in the same way that a proton's electric charge can be negated by a negatively charged electron, a particles Higgs interaction could be weakened or negated by a theoretical negative Higgs interaction. (I should state here that there are many technical problems with the existence of a negative Higgs interaction, and it most likely does not exist at all. And even if it did exist, one important detail of this theoretical Higgs shielding is that electromagnetic and weak nuclear forces behave very differently which would cause the shielded object to instantly fall apart.).
However if Santa had some method of shielding his sleigh from the Higgs field, and if it didn't cause him and his sleigh to instantly disintegrate, the sleigh and reindeer would become very light and wouldn't be pulled to Earth by gravity. 

Of course all of this is very speculative. Perhaps Santa simply uses some form of magic beyond our scientific knowledge. Or perhaps he doesn't really exist. But it is always worth remembering that the laws of physics are themselves most bizarre, and sometimes common sense is not accurate. In all areas of life it is important to frequently question what really is or isn't possible.

Whatever the truth is, I hope that Santa brings each and every one of you whatever you desire, and that you all have a very Merry Christmas!