Quantum entanglement simply explained

[shunyadragon]

Many misuse concepts like Quantum entanglement and the uncertainty principle to justify subjective religious beliefs or question the certainty of science. High fog index nor Blue Smoke and Mirrors not necessary to understand Quantum Mechanics.

I liked the following explanation for quantum entanglement.

https://www.quora.com

What causes quantum entanglement?

Erik Anson, worked at University of Washington
Answered May 14, 2017
Simply put, conservation laws.

For example, if a single particle without spin angular momentum decays into two particles with spin angular momentum, those two spins have to cancel each other out, because angular momentum is conserved.

When you combine this with the existence of quantum uncertainty, meaning that neither of the outgoing particles has a well-defined spin state, this means you wind up with two fundamentally uncertain things, potentially separated by great distances, that nonetheless must turn out to be equal and opposite when measured, as long as neither has been interfered with in the mean time.

This is, more or less, what “quantum entanglement” means.

 

[osgart]

Is this like a left handed and right handed pair of gloves? If one is left, the other is bound to be right.

Your description sounds to me like there is no communication across vast distances; the particles simply are what they always were in relation.

 

[Salvador]

How does an entangled particle correlate instantaneously with its entangled partnered particle when transmission of information at faster than light speed is impossible?

This does seem to me like spooky action at a distance.

 

[Polymath257]

Is this like a left handed and right handed pair of gloves? If one is left, the other is bound to be right.

Your description sounds to me like there is no communication across vast distances; the particles simply are what they always were in relation.

Precisely. The correlation was established when the particles are created.

The problem with this description, however, is that it assumes 'hidden variables': that the gloves actually have a definite orientation prior to measurement. It isn't just that we don't know the orientation, it's that the gloves don't have a definite orientation.

 

[shunyadragon]

Is this like a left handed and right handed pair of gloves? If one is left, the other is bound to be right.

Your description sounds to me like there is no communication across vast distances; the particles simply are what they always were in relation.

Yes, but gloves are a poor example. quantum entanglement is the nature of the relationship and the conservation laws that govern these relationships.

 

[shunyadragon]

Yes, but gloves are a poor example. quantum entanglement is the nature of the relationship and the conservation laws that govern these relationships.

Ah . . . maybe gloves with two thumbs.

 

[Polymath257]

The basic problem in entanglement is actually that the pair is in a superposition of more than one state.

So, for example, if we have a pair of gloves and randomly separate them, then a measurement of one automatically gives us knowledge of the other without any communication between them. But we know each glove *really is* either left handed or right handed. No glove is in a superposition of the two states.

In the case of photons or electrons, that may not be the case. And this is where things get strange. Let's take electrons for clarity. They can be either 'spin up' or 'spin down' along any axis you happen to measure. But they can also be in a state of 'half spin up and half spin down'.

It turns out that there is a physical difference between having 1000 electrons, half of which are spin up and half of which are spin down, and having 1000 electrons each of which is in the 'half spin up, half spin down' state. Yes, if you measure along that one axis, they give 50/50 results in both cases.

But, it turns out that if you measure along along a *different* axis, the two systems are quite different. There is a 'self-interference' term in the second case that does not exist in the first.

Now, in the entangled situation, the electrons that are created are correlated, but also in a superposition. This is what ultimately leads to the violations of Bell's inequalities.