Undergrad Valid local explanation of Bell violations? (Pegg et al., 1999; 2008)

[pines-demon]

I'm having trouble finding John Bell's original 1964 paper. But it discussed "Local Reality Theorem" at length, and as I recall, it included the term "non-local".

I did find a source that quotes a section of Bell's original paper. Here is an excerpt that uses the term "non-local" in context:

The paradox of Einstein, Podolsky and Rosen was advanced as an argument that quantum mechanics could not be a complete theory but should be supplemented by additional variables. These additional variables were to restore to the theory causality and locality. In this note that idea will be formulated mathematically and shown to be incompatible with the statistical predictions of quantum mechanics. It is the requirement of locality, or more precisely that the result of a measurement on one system be unaffected by operations on a distant system with which it has interacted in the past, that creates the essential difficulty. There have been attempts [by von Neumann] to show that even without such a separability or locality requirement no ‘hidden variable’ interpretation of quantum mechanics is possible. These attempts have been examined [by Bell] elsewhere and found wanting. Moreover, a hidden variable interpretation of elementary quantum theory has been explicitly constructed [by Bohm]. That particular interpretation has indeed a gross non-local structure. This is characteristic, according to the result to be proved here, of any such theory which reproduces exactly the quantum mechanical predictions

I do not know what this has to do with anything I said. Nevertheless, it is important to point out that Bell clarified this nonlocality in his later proofs of his theorem. His first paper has some assumptions that he ditched out later (but he always referred to that nonlocality).

 

[.Scott]

I do not know what this has to do with anything I said. Nevertheless, it is important to point out that Bell clarified this nonlocality in his later proofs of his theorem. His first paper has some assumptions that he ditched out later (but he always referred to that nonlocality).

His paper addressed "causality and locality" - not just locality.

 

[pines-demon]

His paper addressed "causality and locality" - not just locality.

I still do not know what this is all about. All his proofs are.

 

[.Scott]

I still do not know what this is all about. All his proofs are.

The Sutherland paper cited in the OP claims that locality can be preserved when a retro-causal mechanism is employed.
In most cases, when "locality" is specified, causality to the exclusion of retro-causality is presumed. That's a very reasonable assumption since allowing retro-causality makes any locality requirement rather vacuous. But John Bell, in his original paper asserted that his inequality was intended to be applied to models that were explicitly "causalilty and locality".
So, when discussing Bell's paper, it is certainly fair game to deal with causality and locality as very separate criteria - you would be following the authors lead. The Sutherland paper are fine on that point.
The problem with the Sutherland paper is that it is using "retro-causality" in its "local" solution to the Bell experiments. The Bell Inequality was intended to show that you need something outside of "Local Realism" such as retro-causality in order for a model to work.
So, the Sutherland paper is not a worthwhile revelation. Of course if you send a signal back through time and then forward again you can circumvent locality!
But what's the point? All you're saying is that you can use normal Newtonian Physics to model quantum results so long as you allow cause and effect to work backwards through time. That's like saying you can use a regular propeller to get yourself into Earth orbit as long as you also use a rocket engine.

 

[pines-demon]

The Sutherland paper cited in the OP claims that locality can be preserved when a retro-causal mechanism is employed.
In most cases, when "locality" is specified, causality to the exclusion of retro-causality is presumed. That's a very reasonable assumption since allowing retro-causality makes any locality requirement rather vacuous. But John Bell, in his original paper asserted that his inequality was intended to be applied to models that were explicitly "causalilty and locality".
So, when discussing Bell's paper, it is certainly fair game to deal with causality and locality as very separate criteria - you would be following the authors lead. The Sutherland paper are fine on that point.
The problem with the Sutherland paper is that it is using "retro-causality" in its "local" solution to the Bell experiments. The Bell Inequality was intended to show that you need something outside of "Local Realism" such as retro-causality in order for a model to work.
So, the Sutherland paper is not a worthwhile revelation. Of course if you send a signal back through time and then forward again you can circumvent locality!
But what's the point? All you're saying is that you can use normal Newtonian Physics to model quantum results so long as you allow cause and effect to work backwards through time. That's like saying you can use a regular propeller to get yourself into Earth orbit as long as you also use a rocket engine.

To be clear, I agree with you.

 

[iste]

A measurement result is not the same as the quantum state before the measurement.

Its not the quantum state at preparation but they are still evolving a quantum state backward in time from measurement. They are doing quantum theory backward-in-time. I have given various sources on this formulation in the original post.

Nowhere in that process does the actual entangled state of Bob and Alice's photons before measurement appear.

I mentioned in the previous post nd you'll find it in their papers that they say that the retrodictive and predictive formulations of quantum theory are empirically equivalent but they don't necessarily produce the same states, so from the perspective of these authors, what you say is not a criticism.

In effect they are ignoring all possible results except the one that actually happens. Whatever that is, it is not what you are saying in the quote above.

I don't think I agree with this because its clear from the description that this will work for any arbitrary measurement outcome you pick from the entangled state.

Are not a "property of quantum theory" at all. They are something the authors of this paper added on themselves. Claims by them to the contrary are simply wrong. As I've already said, I'm not sure the authors of the paper understand what they are actually doing. (This is typical of papers you find on ResearchGate, which often we don't consider as valid references here at all. We're giving you a break by allowing it in this thread.)

The authors have produced a retrodictive formulation of quantum theory which can be applied to various situations, this entanglement scenario only being one of them. You can see this in the various papers I linked in the OP, and you can see this breed of backward-in-time formulation endorsed by other physicists like aharonov, justin dressel, rovelli and matt leifer, the last two I have actually cited in the original post. I am interested in criticisms of applying this to the Bell example, but it seems to me that no one has yet digested the specific way in which the authors are describing the Bell correlations using backward evolved quantum theory.

This is typical of papers you find on ResearchGate, which often we don't consider as valid references here at all. We're giving you a break by allowing it in this thread.)

I don't think the fact that the paper is on researchgate, which I only linked because it is the only site with an accessible pdf for this paper, has much to do with the journal where it was actually published or the competency of the authors. I try as much as possible to provide links that make a paper as easily accessible as possible.

 

[PeterDonis]

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