I have evidence that at some point last night a very large man, with a very large sack, somehow came down the chimney, left a gift under my tree, and departed without my noticing. There are sooty footprints in the carpet leading from the fireplace, remarkable given that it hasn't been used for 70 years, and a gift that wouldn't fit through the door.
Given that Santa must weigh a good 120kg, with a sack of equivalent diameter, how can he possibly fit down a chimney pot no more than 10cm across?
Seems self-evident. What better creature to fit through a tight chimney fitting? There is already evidence that Santa might not have the best of intentions towards us bony mammalian land-dwellers.
Assume for a moment that our cephalopod adversaries wish to plant monitoring devices into as many houses as possible for intelligence gathering. What would be a better way than by exploiting pre-existing human mythology?
Merry Christmas! Make sure you close your flue.
The main clue was the sizes of the chimney and the gift which couldn't fit through the door. The answer is, of course, obvious -- teleportation! This is the only way a Santa Claus could distribute gifts on global scale within twenty-four hours.
This means the problem of worrying about how Santa Claus fits in any chimney of any size, let alone one with a ten centimetre diameter, is null and void. The gift arrives at the speed of light in a discontinuous manner bypassing all other material barriers to materialize under your tree.
What about the sooty footprints leading from the chimney to the tree? I hear you cry.
Mere misdirection. Footprint shaped patches of soot were deposited in a pattern resembling that of a person traversing the path between chimney and tree. Marvellous what quantum computer controlled teleportation systems can do.
Santa Claus himself is enjoying a sound night's sleep after spending the rest of the year making all the toys and gifts that are being automatically delivered via teleportation.
How does Santa Claus fit down the chimney? He doesn't have to and doesn't need to too.
Since this is science-based, we can rule out magic, therefore we must be dealing with a multidimensional being for whom mere 3-dimensional chimneys and chimney pots are not even an inconvenience.
Everyone knows that fireplaces were invented by Santa to provide semi-permanent, localized heat signatures that he collects and maps during the year. On Christmas, he uses his 4th dimensional drive (aka SLeIGH) to “stack” all the fireplaces on top of each other, oriented to face the other heat signature in the room: the Christmas Tree. With that done, all Santa has to do to deliver all the presents at once is take a few steps out of the fireplace and drop the presents beneath all the trees in the world, which have 4th dimensional containment devices (often known as wrapping paper) to ensure they’re delivered to the correct point in the overlapping 4D manifold.
All we need to explain this is some illogical logic!
According to here Santa's average speed is 0.1x109Km/h and the speed of light is 1.1x109 Km/h which means he's bookin' at 10% the speed of light...
which is close enough to relativistic speeds for government work1
That means Santa will experience a doppler shift. Being at relativistic speeds, and knowing that e=mc2 then those same government agents can surmise that a part of Santa's mass is moving faster than the rest of Santa's mass. (This is all about Santa's mass, after all.)
We therefore conclude that Santa's mass is stretched by the speed he must travel. But his mass, itself, isn't changing, so the volume at any point along the length of the stretched mass is much smaller than his jolly girth would naturally be while standing still (or running alongside Olympic sprinter Usain Bolt, who cannot yet hit relativistic speeds... but he's working on it.).
By the application of what inevitablly will be some form of Fourier Transform (left as an exercise for the reader, along the lines of "how much of a student's mass can be kicked during a physics test?") what we'll discover is that the maximum diameter of an elongated Santa's mass including his sleigh is less than 10cm. We'll also discover that this increases Santa's efficiency as he will enter and exit dozens (if not hundreds) of houses simultaneously as an elongated mass entering chimney holes and delivering presents all at the same time.
Causality is known to be preserved by the empirical evidence of none of the houses exploding from the pressure change of air being forced through their chimneys at relativistic speeds in mere fractions of a second. But it does suggest that Santa's cookies are not pre-cooked before delivery.
1 You'd be surprised how many square pegs you can pound into round holes when you apply government standards.
If Santa's de Broglie wavelength[1] is big enough, he can tunnel into the room.
In order to do this, Santa would have to manipulate his "quantum wavelength" to make it extend past the wall. The easiest way to do this, is to reduce his momentum to an almost infinitesimal value. Hence, contrary to popular conception, Santa does not need to travel very fast to make his journey, but rather very, very slowly, and will probably need to reduce his temperature to a few nanoKelvins.
This is, of course, why he is very fat and lives at the North Pole.
Q.E.D.
[Quantum Erat Demonstrandum]
[1] The topic of the video is "Is Quantum Tunneling Faster than Light?" but it contains an explanation of the De Broglie wavelength and its connection to tunnelling.
The Physics Department at the University or Warwick posted an article on their website - https://warwick.ac.uk/newsandevents/pressreleases/santa_has_never/ - suggesting that he uses quantum tunnelling to enter homes:
Dr George Knee, a theoretical physicist, suggests Father Christmas is not bound by the usual every-day laws of physics as we know them and instead employs quantum techniques to help him complete his seemingly impossible global delivery target.
Dr Knee said: “For Santa to achieve his annual mission, it need not be that he operates outside of the laws of physics — just that he operates outside of the laws of ‘classical’ physics.
“Take the issue of getting through the chimney. It is well known that Old Saint Nick is perhaps a little too fond of the mince pies. The narrow cross-section of a typical chimney therefore poses a bit of a challenge, because it is narrower than Santa’s belly. In classical physics the repulsive forces of the edges of the chimney would present a difficult situation.
“But according to quantum physics, the atoms in Santa’s body have an uncertain position – a sort of fuzziness that can slosh around like a liquid. Although it sounds absurd, it is perfectly possible for the uncertainty of Santa’s body to flow directly through otherwise difficult gaps. This means that, in theory, Quantum Santa could simply pop out into the fireplace. This also answers the modern day problem of how Father Christmas reaches you if you don’t have a chimney – he simply uses quantum tunnelling to slide under the door, or through the cat flap.”
Too much speculation, quantum science and quasi-magic in the other answers here for my tastes.
Someone broke into your house while you were sleeping. They had help from inside. The gift doesn't fit through the door, but it doesn't have to - it was assembled inside. The footprints are there to misdirect your attention - they dirtied some boots in ash and soot and then forged the tracks. And then they ate your cookies and drank your milk.
You may be asking how this could be, since there are reports of similar events happening worldwide. It's all a conspiration - a secret society is doing this on a global scale so as to keep us believing in a magical man dressed in red, bringing gifts to well mannered children. Their goal is to estimulate mass consumerism during the month of December. They call themselves the Illuminelvatti and they have a secret base in Montreal.
Santa can control the metric of space.
This is easiest to visualize using a fluid as a model: Consider a fluid an a narrowing pipe. A cubic parcel of the fluid is 'stretched' into a longer, narrower parcel while it's in the constriction.
So with command of the metric, Santa exchanges 8 feet of chubby santa and presents into a couple hundred feet of chimney diameter altered space.
The computation of the required tensor field is left as an exercise for the student.
Santa has a quantum doohicky that exploits the multiverse theory. Since, in the multiverse, anything that can happen without breaking the laws of physics has happened in at least one of the universes. So what Santa does is find the Universe that has the present and sooty footprints and matches it with our universe. The doohicky causes the two universes to superimpose over each other, and leaves your present and footprints in the carpet. The Obervation of the present under the tree collapses the wave form based on Shroedingers' wrapping paper.
The doohicky requires an antenna. It is a fairly long one so the best place to leave it is laminated on the inside of the chimney, so that it's safe when a chimney sweep comes through and cleans it out. It's pretty thin, so domiciles that are heated with gas and don't have large fireplaces are also serviceable.
The one quirk of the system happens when the antenna is missing or broken. Santa comes around and installs and replaces them on New years eve, when you are likely too intoxicated or busy to notice him. Until he does get the working antenna in place though, the Quantum Doohicky defaults to boring socks and underwear. The older model defaulted to Coal
Back in the old days, the installer of the antennas was a strange fellow. The antennae looked a lot like birch rods. He wore a dust mask that was unfortunately shaped like a goat head. Things would have gone by quietly, if it weren't for the episode of the naughty kid chasing after Saint Nick and the Installer (whose name was Krump) and falling in the river. The poor guy got blamed for it, by the villager with a speech impediment, and became known as the Krampus. So unfair....
Well, Santa moves in realistic speeds to make it to all the households, so this is actually similar to the relativistic garage.
It of course takes a careful navigation and consideration, but I'm sure Santa is capable of doing this.
Santa need not be that fat in all dimensions...
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Commented
Dec 26, 2017 at 21:23
Allow me to point out episode 59 of Buzz Lightyear of Star Command, Holiday Time. Here we learn that Santa uses a Chrono-Disrupter to stop time so that he can deliver all presents across the galaxy.
It is the Holiday for the whole galaxy and everyone is celebrating except for one person: the Evil Emperor Zurg. Zurg has somehow been helping prisoners to escape from PC-7, sabatoging Star Command's ships, and stealing Buzz's newspaper...all in a second! Meanwhile, there is a man who claims he is Santa Claus who has been persistantly asking for Team Lightyear's help, and it is only when he tells Buzz a story relating to his cat, that Buzz believes him and gets his rookies to help save the Holiday. Santa needs Buzz to help him save Christmas from Zurg, who stole it from everyone with the aid of Santa's Chrono-Disrupter, a device that can stop time.
Therefore, I posit that Santa actually just breaks into the front door and stages it to look like he came through the chimney, given that he can stop time.
Although the cephalopod answer is just as likely.
It’s quite simple, really. Santa isn’t actually fat. This is just a terrible misconception based on seeing his silhouette on a rooftop somewhere, while he was carrying a sack. Considering the amount of gifts in there, it would be huge. However, he doesn’t lug the entire bag down a chimney, because that sure as hell wouldn’t fit.
''Santa'' is actually a bushmaster snake who disguises himself as a fat man to gather information for our animal adversaries by exploiting myth. Okay, let us say that our animal adversaries wish to plant spy devices in our homes, what better way then to pretend to be Santa? The presents actually have video cameras in them, which is why ''Santa'' delivers presents.
