- #1
JK423
Gold Member
- 394
- 7
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 sx and sz 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 sx then the value of sz 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 sz )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 sz =+1. However, this interaction with the magnetic field may have altered sx and sy in an uncontrollable way! So, even if we had previously measured sx, its new value after the measurement of sz 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 sz does not change the value of sx.
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 sx and sz 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 sx then the value of sz 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 sz )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 sz =+1. However, this interaction with the magnetic field may have altered sx and sy in an uncontrollable way! So, even if we had previously measured sx, its new value after the measurement of sz 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 sz does not change the value of sx.
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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