Have you ever wished that you could walk through walls? Have you ever found the desire to pass through solid barriers unscathed? Can anything pass through solid barriers? These are exciting questions, and they do, contrary to what you might think, have a scientific basis...

Are Barriers Solid Anyway?

You might think the walls around you are solid, but in reality, they could not be further from it. If we analyse the fundamental content of the wall, we will see that there is more empty space in your walls than matter. Don't believe it? Let's take a look at a concrete example¹...

Like all walls, the walls you see around you are composed of a carefully crafted array of particles. They are arranged in the typical 'solid' fashion - just think of ping-pong balls that are shoulder-to-shoulder, wriggling slightly (the particles can vibrate, of course), and not being able to get past each other. At a more fundamental level, the wall is composed of atoms. The typical atom is 10^-10m in diameter², which is, of course, very small. A million of them could hold a party on the tip of a pencil.

But we can probe further into the fundamental constituents of the concrete wall. The main stuff inside an atom is in its nucleus, where particles called protons and, in most cases, neutrons reside. The nucleus of a typical atom is likely to be around 10^-14m in diameter - that's 10 000 times smaller than the whole atom. This is akin to the Empire State Building having all of its 102 floors empty except for a sliver of space at the bottom as thick as a sheet of paper.

However, the floors are not entirely empty, because in this space atoms have particles called electrons. The electrons would be like office workers that frequently double and triple-book themselves for appointments, and so they are often on more than one floor of the building simultaneously; see Quantum Mechanics. The typical size of an electron is about 10^-18m. In our analogy, we can say that an electron would not even be the size of four caesium atoms if the atom that contained it was as high as the Empire State Building. Even if the atom had the diameter of the Earth, an electron within it would be lucky to be the width of your fingernail.

So, if a seemingly solid wall is just a load of empty space, why can we not walk through it? Why can we not disregard the puny minuteness of electrons and the nucleus and plough on through solid barriers? Unfortunately, there is a killjoy. Its name is electromagnetism. You see, electrons have a negative electric charge, which basically determines how it interacts with other matter. Like charges repel, and opposite charges attract. The negative charge of the electrons exactly balances the positive charge of the protons that reside in the nucleus of an atom, and the neutrons don't make any difference because they don't have an electric charge. Nothing is amiss here.

However, as we have already established, the positive part of the atom is hidden deep within it, and there is far much more space where the negative electrons are dominant. When two items collide, their outer shells of electrons meet, and so they repel each other. That's why they cannot go through each other. The situation is a bit like trying to pass between the blades of a propeller without hitting them (you can think of the blades as the fast-moving electrons).

'But wait a moment,' you cry, 'how come the electrons in things can repel each other when electrons are so tiny? Surely the chance of two of them colliding is incredibly small?' This is a very fair argument, but unfortunately, electrons have other tricks up their sleeves. The electromagnetic force is a very strong one, for starters, and so a direct collision isn't necessary for there to be repulsion. Also, electrons are not in one place at one time. They exist in a 'superposition' where they manage to 'spread themselves out' across the whole area between the nucleus and the outside of the atom. Physicists will often refer to a 'cloud' of electrons because of this. We cannot know where an individual electron is - it could be anywhere in the cloud, but some places are more probable than others.

How To Levitate

This odd behaviour means that the electromagnetic repulsion between the intersecting clouds of atoms forbids them to travel through each other. If we take the example of sitting down on a seat, the strength of the electromagnetic force is far greater than the downward force we exert in sitting down, so the electromagnetic repulsion - and that alone - keeps us from slipping through the chair. You end up levitating about one hundred millionth of a centimetre from the seat of the chair, kept afloat by the electric charges of those exceptionally tiny particles, the electrons. The 'solidity' of the chair is purely an illusion, and it plays no part in determining whether we can pass through 'solid' barriers or not.

How To Cheat Barriers

Neutrinos are tiny, almost massless particles that have no electric charge and so can very easily zoom through what we see as solid barriers with ease. In fact, they are constantly careering through your body right now, as they are created in the Sun and travel here at velocities close to the speed of light.

Aside from 'switching off' the electromagnetic force, being made of neutrinos or getting electrons to stay still for once, how are we going to achieve the feat of walking through walls? The answer is almost too obvious to say: walk into one. The first time you try this, you are likely to emerge with a painful nose, and still to be situated on the same side of the wall. Don't let failure deter you. It will only take about fifty trillion attempts (or fifty quadrillion attempts by American figures) to traverse the barrier successfully. This will, of course, take longer than the current age of the universe to complete.

The reason that this works is because of the principles of quantum mechanics. There is an effect known as 'quantum tunnelling' where sub-atomic particles, of which we are all composed, can suddenly jump from one place to another without passing through the space in between. It sounds odd, but this rare practice of particles has been observed, and the effects of it often have to be taken into account before doing precise physics experiments. So, after millions of broken noses all of your particles will eventually vanish and then reappear on the other side of the wall.

If obtaining broken noses does not appeal to you, or if you have a busy schedule and can't fit in the fifteen thousand million years you will require, then there is another way...

Heading into Hyperspace

Well, it's simpler than you think, so long as you have the help of somebody with a very special property. In order to explain how the trick will work, we need to take a look at things from a lower-dimensional point of view. So, for this section, let us theorise the existence of a two-dimensional world - a world that is drawn in 2D on a piece of paper. Imagine that this world is laid down flat on your desk.

Let's invent a character to live in this world - we'll call him Harry. Harry has no thickness, and he can only see things that are to his left or his right or things that are further back along your desk - ie, in directions that span the breadth and depth of your desk. He has no concept of the directions 'up' and 'down'. To him, the words are meaningless.

Now we imagine that Harry is a criminal - he has stolen a large sum of bank notes from a top-security flat bank. It is not long before the police force capture Harry, and incarcerate him. To do this, they simply cage him in what appears to us to be a circle. Harry, who is claustrophobic and is becoming very anxious being shut in this circle, shouts and shouts for the 2D police to let him out of there; he was influenced by hypnosis to rob the bank anyway, and it wasn't his fault. Touched by his quaint appeal, we decide to help him escape - in other words, we decide to help him go through the apparently solid barriers that imprison him.

For us, this task is simple. We can simply cut Harry out of his world and stick him back in somewhere outside the circle. Or we could envision 'peeling' him off his world and depositing him somewhere else. If any other 2D person saw this, they would go to a 2D psychiatrist, because it looks like somebody is vanishing and reappearing somewhere else. To Harry, he has miraculously appeared on the other side of the wall.

And For Our Next Trick...

We are now going to flummox Harry and his friends completely by performing some incredible 'magic' tricks, made possible by our higher-dimensional advantage. Firstly, notice that you can see all of the 2D people at once. You can see inside Harry, and you can therefore tell him some things about his biology. You might, for example, be able to see that he is currently digesting a 2D cookie that he ate before the robbery. To Harry, it would seem that you have X-Ray eyes. Aren't you clever?

Imagine that, like humans, Harry has a heart on the left side of his body. Hearts have a special orientation a bit like the orientation of gloves or shoes. You can flip a 2D heart over so that it becomes 'right-handed'. Pairs like this are called 'enantiomorphic'. In order to reverse the 'handedness' of Harry's heart, we simply take him out of his 2D world again, flip him over, and put him back down. Amazingly, he finds that his heart is now on the right side of his body.

So how does this help us? Well, if we replace the 2D world with our 3D one, and then postulate the existence of four-dimensional beings, we too can be let out of prison cells or can be otherwise helped to cheat our apparently solid barriers. We too could have our organs reversed and have X-Rays taken effortlessly. There is another trick that we could do that we could not show Harry. He wouldn't understand. If you imagine a knot in a circular length of rope, you will see that it is impossible to remove the knot without cutting the rope. And, if you imagine two rings that have been intertwined, you will see that untangling them requires breaking one of the rings. In 4D space, there is 'enough room' for the rope to be moved about so that the knot can be removed without cutting the rope. And, there are more dimensions in which to move the rings; hence, they can be untangled effortlessly in a fourth dimension, keeping the rings intact.

These ideas would make great party tricks, wouldn't they? So do these 4D people exist, and would they be willing to help us out with our tricks?

Thankfully, this idea is not considered crazy. Scientists really believe that the existence of higher dimensions is possible. M-Theory, for example, the new name for superstring theory, the theory that attempts to unify all the forces of the universe, actually depends on the existence of an extra seven dimensions, after the dimension of time. And, many scientists, including the theoretical physicist Michio Kaku, hold that the laws of physics get simpler in higher dimensions - yes, simpler! The main proof for this is the fact that, when the theory of relativity is put into a four-dimensional context, Maxwell's famous equations of light and electromagnetism arise naturally from it.

Sadly, there is still very little unequivocal observational evidence that higher spatial dimensions exist, and the jury is still out over whether we could communicate usefully with hyper-beings if they exist anyway. But think: if everyone had their own personal 4D being to help them cheat 'solid' barriers, what implications would this have on society?

Apart from these limitations in the theories, you should be able to see that levitation is indeed a very simple feat, and that walking through walls, which is certainly not forbidden by the laws of physics, could be within your grasp.