Quantum Mechanics: a term that will render you completely dumbstruck as you sit at your desk trying to figure out what ‘Quantum’ actually means. When considering the principles of Quantum Mechanics, understand that the particles (fun fact: they’re not actually particles) we’re dealing with are very, very, very, very, VERY small. Smaller than any of our minds can even comprehend. 

‘Quantum’ actually derives from the Latin word for ‘amount’; in modern day it’s described as the smallest possible quantity of something. So, to summarise, Quantum Mechanics is a fundamental theory in Physics describing how atomic (small) and sub-atomic (very small) particles interact and behave. Does that make you feel large, human?

Quantum Energy

So, I’ve described what Quantum Physics deals with. Now what? The term ‘Quantum’ not only means small; it also means we’re dealing with discrete amounts. Essentially all the energy in the world can be broken into finite fractions. 

Imagine a bag of M&Ms. Each M&M represents a ‘packet’ of energy. If you’ve studied Chemistry, you’ll know that atoms have discrete energy states –remember how electrons ‘jump’ between energy levels?. The same phenomenon applies to any type of energy you can imagine. We are living in a world governed not by a continuous scale, but by packets of energy. Weird, right?

Wave-Particle Duality

Remember my fun fact about particles not being particles? I’m going to attempt to explain that exciting phenomenon here. In Quantum Mechanics, every existing entity has particle-like characteristics. Yep, that means that the light waves you’ve always learnt about in Physics class aren’t exactly waves, they’re particles too. 

On the flip side, everything also has wave-like properties. To summarise, particles are waves and waves are particles… This is known to the Physics world as Wave-Particle duality and is one of the fundamental principles of Quantum Mechanics. 

The first person to actually describe this was German physicist Albert Einstein, but it can be demonstrated really nicely (and creepily) by the Double Slit Experiment. Look it up if you dare!

Very, Very, Very Small

In case I didn’t mention, Quantum Mechanics deals with the tiniest of particles. By discussing the principles of Quantum Mechanics, we are describing the very fabric of the universe. 

For the most part, quantum phenomena only apply at the level of atomic and subatomic particles. This is simply because the mass (and velocity) of a single particle is so small, that we are able to actually see the wave-like effects each individual particle possesses. But in our larger world, things are very different. Let’s take a tabby cat as an example. A little bit of physics revision:

mass (m) velocity (v) = momentum (p)

momentum (p) = Planck's constant (h)/ Wavelength (λ)

Every particle has momentum, that is the product of mass and velocity. Momentum is inversely proportional to wavelength,  (as momentum increases wavelength decreases). Planck’s constant is an impossibly small value of the energy in one quantum of electromagnetic energy, and always stays the same. 
Even if that same tabby cat hadn’t eaten for days, it’s momentum (mass and velocity) would still be so relatively large that any wave-like effects would be inconceivable. That is why quantum properties (i.e. wave-particle duality) are only quantifiable in very small particles. For now!

Probability

Probably (pardon the pun) one of the most confusing and controversial aspects of quantum mechanics is that it is impossible to predict. A physician called Max Born postulated the critical Born Rule; an equation that assigns an incredibly complex value called the ‘amplitude’ to each particle. The amplitude is directly related to the wave function of a quantum particle.

However, according to another physicist named Erwin Schrödinger, quantum wave functions are forever changing. Basically, the probability of getting a particular outcome in a quantum system is proportional to the amplitude (i.e. this forever changing wave function) squared. Don’t get it? Neither do I!

Non-Local

You may have heard of the term Quantum Entanglement. Einstein also observed that quantum systems in completely different locations seemed to be able to influence each other’s experimental outcomes. This gave rise to the theory that quantum systems can become ‘entangled’ and are able to impact each other simultaneously from miles away. And no, they’re not communicating with each other faster than the speed of light.

This is why one of the principles of Quantum Mechanics is its Non-Locality. The properties of a quantum system in Paris can influence the results of a system in London. Physicians now accept that quantum particles possess some hidden property that allows these phenomena to occur. This is the closest thing we have to real-life teleportation –  if that’s not cool, I don’t know what is.

 To (Try) and Sum it Up

So, we’re done with the principles of Quantum Mechanics. Still don’t understand? I don’t blame you. Quantum Mechanics is undoubtedly one of the most complex matters to exist. The seemingly mystical properties of these systems have baffled our smartest minds for generations; and inspired disciples of the supernatural and conspiracy theorists alike. Maybe there are some things we’re just not meant to understand!