Why can't you walk through walls?
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Introduction
Everything in the universe is made up of atoms. Atoms are 99.9999999% empty. The empty space is relatively so huge that if you removed it from all the atoms of each and every human on earth, the overall volume of all our bodies combined would be less than that of a sugar cube. Then why can't two objects pass through each other?
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| A 7g particle hit aluminum block at 7km/s |
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| A paint fleck hit window of a space shuttle |
- Why are solids so determined to not pass through each other?
- Can we accomplish this atleast in the future?
So, what if humans managed to make solids pass through each other and controlled it? Think of the consequences on our civilization.
We wouldn't have to care about traffic, maybe surgeries could be performed without cut opening bodies, our military weapons would change, space exploration, maybe we could create a black hole and.....but wait a minute. Is that even possible at the first place?
Can not touch anything
It is almost impossible to physically touch any object. This is because matter is made of atoms and atoms have electrons which always repel each other. When you try to pass through a wall, you feel a force stopping you. It's the repulsion force between electrons in your atoms and those in the atoms of the wall.
After coming too close to the wall, with only a few nano meters in between, the electrostatic force between the electrons in both of your atoms prevents you from getting any closer. This force is 10³⁹ times stronger than gravity. You can see it as 'like poles' of two magnets repelling each other. The closer they come to each other the stronger the repulsion. (We'll discuss this in detail in a different article)
Most people think this explains the question but it doesn't. This explanation is good for some extent but doesn't explain it completely. Think of the Nuclear Fusion reactions taking place in stars. Two nuclei of Hydrogen combine together to form one Helium nucleus. Nuclei of Hydrogen repel each other with the same force two electrons repel. (unless the nuclei are closer than 10⁻¹⁵ m) Because of the extreme conditions in stars, the nuclei manage to come that close to each other overcoming the repulsive electrostatic force.
Atoms
In schools we're taught to visualise atom as protons lying at the center while electrons revolve around them similar to the sun and the planets. This is a very simplified picture of atom. In reality, electrons don't exist at a particular point, the region around nucleus where the probability of finding electrons with specific energy is maximum is called an orbital.
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| Source: researchgate.net |
Pauli exclusion principle
In 1925, an Austrian physicist named Wolfgang Pauli proposed a principle which basically explains why two objects can't pass through each other. He stated that no two electrons in an atom can have the same configuration which eventually means that an orbital can't contain more than two electrons at the same time. And it's not possible to add an extra electron to the orbital.
Now, to walk through a wall, the atoms in your body and those of the wall must pass through each other. Consider two atoms, for simplicity say Helium atoms, to pass through each other at one point of time the orbitals of the two atoms must intersect which means you're trying to add a third electron to the fully filled orbitals and it's not possible. The closest two atoms can get is when they form an ionic or covalent bond. Pauli Exclusion principle prevents them getting any closer.
Fermions
Electrons are Fermions which also include protons, neutrons and neutrinos. All Fermions must obey Pauli Exclusion principle unlike Bosons which include photons, W and Z particles.
This is why when you arrange lasers in such a way that the two beams intersect at a point, nothing like a collision happens. They simply pass through each other as photons are Bosons.
Possibilities
Though this phenomenon isn't possible as per classical physics, when you go to quantum level things get really weird and there's a non zero probability that a particle can pass through a barrier.
Quantum tunneling
If you keep a very tiny particle like an electron in a box, there's a small probability you can find it outside the box. This is because of a phenomenon called Quantum tunneling.
Matter has both particle and wave nature known as Wave - Particle duality. We can't observe this in larger bodies like us but it is more noticable in tiny things like electron. And we can't know precisely the exact location of the electron, it's spread over a region in terms of a wave function (Ψ). And the square of the wave function at a point in space gives the probability of finding the particle at that point.
So, for the electron we kept in the box earlier, the square of its wave function outside the box is low but not zero. Therefore, there's a tiny chance it exists outside the box. When you punch the wall with your hand, the probability of your hand going through the wall is roughly 1 in 10⁴⁰. This number is bigger than the number of atoms in your body. [Quantum tunneling also plays a key role in Nuclear fusion inside our sun.]
Making it possible
Scientists in Finland are trying to come up with a method that allows macroscopic objects to tunnel. But unfortunately the biggest size they're trying to tunnel is a widget which is a micrometer wide. It's much larger than subatomic particles and nowhere near to human bodies. This maybe possible in future with better understanding of the universe or... Maybe never.
A question for you
Imagine you're stuck in a small room and have no way out except the door where a serial killer is present and is walking towards you, would you consider trying to walk through the wall knowing that you have a small chance of actually doing it according to Quantum Mechanics?
Let me know in the comments!
