I Why Does Quantum Entanglement Seem Puzzling Compared to Everyday Correlations?

[leonid.ge]

TL;DR

Why coins are different from particles?

Suppose someone throws coins and once they fall on heads or tails, she saws them along the middle on two parts: one pointing towards the ground and the other pointing from the ground. Then she sends those two parts into opposite directions so after some time they reach two distant planets, one inhabited by Bob and the other with Alice who measure what they've got. So the results that Alice and Bob get will correlate, even though the planets are very far apart, and this does not seem strange to anyone. So why correlation for entangled particles looks strange to people and for coins not?

 

[PeterDonis]

Any correlations you can produce with coins cannot violate the Bell inequalities. Correlations you can produce with entangled particles can. That's the difference.

 

[PeroK]

TL;DR Summary: Why coins are different from particles?

Coins and electrons behave fundamentally differently, not just when it comes to entanglement. A coin can be spinning fast or slow and a precise axis of rotation can be found. This is the case for any maroscopic rigid body.

An electron's spin is manifestly quantized. And the components of spin about different axes are incompatible observables. This means that the electron never has any well-defined axis of rotation.

In short, electrons obey QM, the Schrodinger equation and the uncertainty principle. Whereas, coins obey Newtonian mechanics. Additionally, electrons exhibit quantum entanglement, whereas coins do not.

 

[Nugatory]

So why correlation for entangled particles looks strange to people and for coins not?

The correlations for entangled particles are statistically different from those that we find if assign the properties of the particles when the pair is created, no matter how we do it. In the middle of the last century John Bell proved that any theory that works the way you're thinking must disagree with the quantum mechanical prediction for entangled particles - and since then we've done the experiments that conform that QM is correct,

You will want to google for "Bertlmann's socks" and "Bell's theorem", and pay particular attention to the web page maintained by our own @DrChinese