Bells Theorem

Bell Inequality
Let’s start with hidden variables.
As the phrase says we can not see them. To be honest, we don’t even know if they exist.
However, by definition, they are some weird things that go from one place to another in anywhere in the universe instantly.
Quantum mechanics is incompatible with these hidden things that we can not understand or comprehend.
We need to know what locality is in order to keep everything intact and easy to understand.
A particle can only be effected by its surroundings just like you can’t be pushed back to beach if the wave is away from you.
In fact, the water that makes that wave will stay where it is. Only it’s influence move towards you.
What pushes you back to the beach is the butterfly effect of the wave that was away from you.
Unlike the ocean wave, locality influences particles with the speed of light just like the radio waves pushes the air particles until the destination.
Let’s come back to hidden variables. Just because we don’t know what they are, hypothetically we call them undetectable quantum properties that affect our quantum experiments.
According to physicist John Stewart Bell, if the hidden variables are local, then it will not agree with quantum mechanics. If it agrees with quantum mechanics then it should not be local.
Bell wrote a paper titled "On the Einstein Podolsky Rosen Paradox” (coming up on the next video) which was a response to their 1935 statement that the quantum physics is an incomplete theory.
However, quantum physics were recognized as probabilistic by 1935. They argued that if they separate two entangled particles very large distance and measure one of them, the other entangled particle should instantaneously change it’s state to opposite.
Why is this an argument?
They suggested that either first particle communicates with the second one at faster than the speed of light or both entangled particles already knew what to do and when to do before even they were separated.
Uncertainties in quantum theory's predictions would then be because of not known properties which later termed "hidden variables".
Bell had to respond this. He concluded that if measurements are performed independently on the two separated particles of an entangled pair would show mathematically on how the outcomes on the two measurements are connected.
This conclusion would later be named the Bell inequality (it will be explained in another video). Quantum physics predicts connections that violate this inequality.
Therefore, hidden variables could explain the predictions of quantum physics if they are not local.
Two particles should be able to interact instantaneously no matter how far they are.