Bell inequality tests questions

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Discussion Overview

The discussion revolves around the Bell inequality and its experimental tests, specifically questioning whether any tests have shown that the Bell inequality is not violated. Participants also explore the various types of experiments that test the Bell inequality, including those involving different particles and observables.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants inquire whether there are tests that demonstrate the Bell inequality is not violated.
  • One participant asserts that to date, all tests that theoretically should show entanglement do indeed violate some form of the Bell inequality.
  • Different types of particles, including electrons, photons, and nuclei, have been used in Bell tests, with entanglement observed in pairs and larger groups of particles.
  • Entanglement has been observed in various pairs of non-commuting observables, such as spin, position/momentum, and time/energy.
  • Another participant suggests that it is possible to not violate the Bell inequality using defined sets of physically separate macro-objects with specific characteristics, though this perspective may be less exciting to some.
  • A later reply clarifies that while no tests violate predictions of quantum mechanics regarding entanglement, in broader contexts, inequalities are not violated, suggesting a nuanced interpretation of the results.

Areas of Agreement / Disagreement

Participants express differing views on whether the Bell inequality can be shown not to be violated, with some asserting that all relevant tests demonstrate violations while others propose scenarios where it may not be violated. The discussion remains unresolved regarding the implications of these tests.

Contextual Notes

Some statements rely on specific interpretations of the Bell inequality and its implications, and there are unresolved questions about the conditions under which different types of tests are conducted.

Wangf
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1. Are there any tests done actually show Bell inequality is NOT violated?

2. What are the different kinds of things the Bell inequality experiment test? I know most tests are testing spins of electrons, what are the other Bell tests, what they test?
 
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Wangf said:
1. Are there any tests done actually show Bell inequality is NOT violated?

2. What are the different kinds of things the Bell inequality experiment test? I know most tests are testing spins of electrons, what are the other Bell tests, what they test?

1. Not so far. A test showing any kind of entanglement should always violate some kind of Bell Inequality (or other local realistic measure) in order to prove that such has been detected. To date, all setups which theoretically should show entanglement do show entanglement.

2. There are a lot of different tests. There have been tests on electrons, photons and nuclei (ions). Most tests involve pairs of particles, but entanglement has been seen on 3, 4 and more particles.

In addition, entanglement has been seen in different pairs of non-commuting observables: spin, position/momentum and time/energy are common. Sometimes, different pairs can be entangled at the same time.
 
You can invariably NOT-violate it using defined sets of physically separate macro-objects with at least three specifiable common yes-or-no characteristics (it's easiest with a dozen or so keys or coins or books, food containers, people in a room ... or use Venn diagrams, letters in words from blocks of text etc. etc.) but some people find that less exciting than do others.

But it reiterates the profundity of what Bell accomplished. Among everything else he actually defined, in a simple formulation, a way to measurably distinguish the domain of (seeming) local realism from the quantum world. He mathematized an ontological distinction.
 
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Wangf said:
1. Are there any tests done actually show Bell inequality is NOT violated?
In the narrow sense of this question - if there are some tests that violate predictions of QM entanglement? - the answer is no.
In wider sense answer is somewhat trivial - in all other cases or aspects inequalities are not violated. "The exception proves the rule" in correct sense of this idiom namely "the exception confirms the rule in cases not excepted".
 
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