The world of quantum physics is only a hundred years old and brought us more questions than answers.
One property of this world is the so called Quantum entanglement. It describes the way how particles not only interact but also influence each other. In the microscopic particle scale, every object has unique attributes. These can be described through characteristics like energy-states, spin and polarization.
The latter one is only detectable in photons. But energy-state and spin are fundamental must have´s for electrons, ions, nuclei and other possible particles.
Let us take a look at the spin of particles. The spin is a property which can be described as the rotation of a given particle around its Z-Axis.
Looking down from the top on to the particle, the rotation can be in clockwise direction or the other way round. Lets say these 2 states are called spin-up and spin-down, representing the direction of rotation. This description is only for visual purposes and can only be described the fully right way through mathematical equations. But this should not concern us at this point! Since we do not only have one particle, but many more, all of these particles have a attributes like spins.
For the following part we will have to watch out for some groundbreaking attributes of quantum physics. This so called spin might have a value, this value isnt defined as long as we dont measure what it is. Sounds confusing? Keep reading! The act of measurement decides in which spin state the electron is to be found, but until then it is not really sure and keeps itself in a non-decisive state between the two. You can imagine it like tossing a coin and in midair you catch it, without taking a look. Until then, nobody knows in which state the coin is and so no one can say for sure if it landed on head or tail, since the solution is given by probabilities. I our toss will be given by 50/50 between head and tail. This is the so called Superposition, the fact that until looking at it, the yielded probabalistic outcome is not given for an observer. Puhhh.... that was confusing, but let these things not confuse us.
Instead of speaking about electrons and spins (up and down), we will keep taking the coin (head and tail) as our preferred object of interest.
So we learned that tossing a coin which stands for our particle, we have measurement outcomes like head or tail which represent the 2 possible spin states of a particle.
Lets say we are magicians and want to impress people on the streets. For our trick we will glue 2 coins on to each other, which seperate from each other in mid air when we flip the double-coin. With the help of mathematics we prepare these coins, so that a landing of coin A on its tail results in coin B landing on its head or the other way round. You dont have to know how this works in detail, since a magician keeps its secrets safe (In this case the magician is the universe and its fundamental properties as its tool box). For our purpose, we will catch this 2 coins in 2 seperate boxes which are held by you and a stranger woman. Lets make a bet, looking into one box i will always predict the outcome of the other parties coin result. Due to our strange preparation of the coins, i will always win since i know the outcome of the other for sure! In physics, these two coins were being manipulated by us, also known as entanglement. If we switch from coins to particles with spins, we can entangle two or more particles and fullfil this magic trick on smaller scales. This means the information of the other particles/ coin outcome is being transferred faster than the speed of light, which contradicts a lot of mechanical physic laws. To this day we dont know for sure how that works, but with the help of quantum entanglement we can transfer information faster than any other possible way known to mankind.
This is the reason why Albert Einstein said this:
Quantum entanglement describes a general physical property on microscopic scale in which particles can be manipulated to transfer information which are being passed on faster than the speed of light (which shouldn´t be possible in the first place). Especially quantum computers use this fact to solve complex calculations in a faster time.
Thank you for reading! Don´t be ashamed to ask any kind of questions below.