Just how does Santa get around the world in one night? (Picture: Getty/iStockphoto)

It’s finally here. Christmas Eve.

But while we’re all dreaming of mountains of presents the next day, someone has to actually deliver them. And that someone is Santa Claus.

So just how does he do it?

We’ll never know of course, that’s his best-kept secret, but that doesn’t mean we can’t have some fun trying to figure out the best way to deliver two billion presents (minimum) in one night.

Instead, Dr Andrew Brown from Queen’s University Belfast has dug into the laws of physics to rank the most likely theories behind Santa’s epic journey.

Santa has the whole world to cover (Picture: Getty)

Theory #1: The present cannon

In a nutshell If all the 2 billion children in the world were to line up, the line would be 1 million kilometres long, which would wrap around the equator about 25 times.

If it’s a long straight line, Santa would have to be doing over 25,000mph to get from one end of the line to the other in 24 hours, throwing presents out the side of the sleigh as he goes. That’s more than 30 times the speed of sound, or Mach 30. For reference, the fastest fighter jet flies at Mach 5.

Now, a reasonable sports person could catch something that is going at 60mph, but if you try and catch something that is going at 25,000mph, you are in difficulties.

Santa would need a technological approach – he might have some kind of present cannon on the side of the sleigh. He would have to launch the presents backwards at approximately the same speed he was travelling forward so that they would appear stationary to the children attempting to catch them.

However, the highest muzzle velocity of any commercially available weapon is about 3,000mph, so that’s ten times too slow.

Incidentally, 25,000mph is faster than the speed you need to send a rocket into orbit.

Potential pitfalls Santa and/or children rocketing into outer space.

Theory validity 5/10

Just how fast are those reindeer flying? (Picture: Getty/iStockphoto)

Theory #2: The Einstein theory

In a nutshell If Santa was travelling at the speed of light, space would actually contract – known as Lorentz contraction – so very large distances would become very small distances.

If Santa was travelling very fast, in theory, he could shrink that line of children down to a more manageable distance.

Some people have suggested the reason that Rudolph has a red nose is because he is travelling so fast that the force of friction on it is a little bit like a spacecraft coming back to Earth’s atmosphere. The frictional force of the atmosphere causes a lot of heat to dissipate on the nose of the spacecraft, perhaps that’s why Rudolph has a red nose.

However, as you travel close to the speed of light, your mass increases as well. Your body becomes heavier. If Santa is going round the planet at 25,000mph, he is experiencing 1000 G-forces, which is way more than the human body can cope with.

Potential pitfalls Santa’s belly implodes like a bowl full of jelly.

Theory validity 6/10

Has Santa cracked time travel? (Picture: Getty/iStockphoto)

Theory #3: Time travel

In a nutshell A few years ago, theoretical physicist Miguel Alcubierre found that it is theoretically possible to construct something like the warp drive that they have in Star Trek. You would have a sort of engine which distorts the space around the sleigh.

This would effectively allow you to move at an arbitrarily high speed relative to the earth within your little bubble without experiencing these problems of mass increase.

The problem is that it requires negative energy – you need to reduce the energy of empty space to below zero. So far, we haven’t found a way of doing this, but physics has a history of finding seemingly impossible mathematical solutions, which turn out to have a real physical meaning later.

Potential pitfalls Trekkies become unbearably smug

Theory validity 7/10

Santa – secret physicist (Picture: Getty)

Theory #4: Quantum time travel

In a nutshell In principle, there is no reason you can’t stop or reverse the arrow of time. When you look at small systems, atomic systems, you can reverse the clock, you can make them move backwards – time travel, on a very small scale.

But once the laws of thermodynamics kick in, the whole thing breaks down.

Thermodynamics says, for example, if you have a hot cup of coffee that goes cold, there is no way you can heat it back up again, without adding more energy (microwaving it, for instance).

Only Santa knows how he delivers so many presents in one night (Picture: Getty/iStockphoto)

But at the quantum level – if you make a quantum espresso – it is theoretically possible to reverse time so that it heats up again. The problem lies in making those espressos something you might be able to drink. Scaling up makes the physics break down.

At the quantum level, however, it seems like time travel is possible.

There might be a way of harnessing this effect and being able to control it in some way to make time travel possible.

Maybe Santa knows a lot more about quantum mechanics than we do.

Potential pitfalls Flouting the laws of thermodynamics

Theory validity 8/10

Is a multi-Santa the answer? (Picture: Getty)

Theory #5: The Von Neumann Theory

In a nutshell There is a thought experiment about space exploration called the Von Neumann probe. The idea is you would send out one spacecraft, and once it finds a distant galaxy or lands on a planet, it then uses the raw materials it finds there to construct another space probe. Now there are two and they go out and construct more. By doubling up every time, the amount of space you can explore increases exponentially.

Maybe Santa has created a Von Neumann sleigh. Say on Christmas Eve, he sends out seven sleighs, one for each continent, and when they are there, they use the materials they find to construct another.

Feasibly, you could do this with nanotechnology – and create a self-replicating sleigh. Divide and conquer, as they say.

This is a technological solution to the problem of present delivery, but it doesn’t allow Santa to be in more than one place at one time. He could, I suppose, be tapping into another quantum effect – the idea of an uncollapsed wavefunction, which would allow him to be present everywhere all at once.

That would make it a doddle because he only has to rock up at one house, but he can be at all of the houses simultaneously, along with his functionally infinite number of sleighs.

Potential pitfalls Santas, Santas everywhere…

Theory validity 9/10

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The science of Santa.