- #1

JK423

Gold Member

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## Main Question or Discussion Point

Hello guys,

I am trying hard to understand the reason of the violation, and i hope you give me some help.

Here is my understanding so far:

Bell's inequalities are based on the measurement of non-commuting quantum observables, e.g. the measurement of the spin in x and z direction. This, to start with, raises red flags! That's because the proof of Bell's inequalities does not include a dependence on what observable we measure, instead it's assumed that both s

But the experiments themselves, already tell us that this is not true! If you measure s

For example, throw an electron in a Stern-Gerlach aparratus (measuring s

That way, it seems quite obvious that Bell's inequality may be violated without assuming non-locality or absense of reality, since the derivation of Bell's inequality is based on the assumption that the measurement of s

What is your opinion on this? In the literature, has it been studied? Are there any physical arguments against it?

Thank you a lot!

Giannis

I am trying hard to understand the reason of the violation, and i hope you give me some help.

Here is my understanding so far:

Bell's inequalities are based on the measurement of non-commuting quantum observables, e.g. the measurement of the spin in x and z direction. This, to start with, raises red flags! That's because the proof of Bell's inequalities does not include a dependence on what observable we measure, instead it's assumed that both s

_{x}and s_{z}have definite values and are not affected by the measurement.But the experiments themselves, already tell us that this is not true! If you measure s

_{x}then the value of s_{z}is altered! What this fact*could*mean is that the underlying "hidden variables" interact with the measuring device in an unknown physical way.For example, throw an electron in a Stern-Gerlach aparratus (measuring s

_{z})and assume that this electron has well defined spins in all directions x,y,z before the interaction, described by an underlying local & realistic hidden variable theory. Ok, now the electron is seen to go upwards, i.e. it has s_{z}=+1. However, this interaction with the magnetic field may have altered s_{x}and s_{y}in an uncontrollable way! So, even if we had previously measured s_{x}, its new value after the measurement of s_{z}is different due to unknown underlying local, realistic physics!That way, it seems quite obvious that Bell's inequality may be violated without assuming non-locality or absense of reality, since the derivation of Bell's inequality is based on the assumption that the measurement of s

_{z}does not change the value of s_{x}.What is your opinion on this? In the literature, has it been studied? Are there any physical arguments against it?

Thank you a lot!

Giannis

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