# Entanglement (split from unification?)

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1 hour ago, Mordred said:

No in Bohmian mechanics the field generates the superluminal interference but that doesn't violate GR. You still have the correlations to the initial entanglement process.

You should easily understand what I have getting at if you understand reference frames as per GR and under GR there are non inertial as well as inertial reference frames.

Bohmian mechanics cannot violate GR because it has nothing to do with GR.  GR is a classical theory incompatible with quantum theory in general, and even more seriously with realist and  causal interpretations of GR.   To combine them, you have to throw away key properties of GR, like the Strong Equivalence Principle, and use the generalization of the Lorentz ether.

Please don't speculate about what I understand and what I don't understand, and try to formulate your questions in a more precise way that can be understood.  Simply use standard terminology and refer, if necessary, to standard textbooks.

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I see so time foliations under Bohm theory doesn't apply to GR. I'm sure you have seen relativistic Bohmian papers. The non relativistic obviously applies Galilean relativity under the Kronecker delta.

One thing many of those same  papers do state is no superluminal signaling is possible. Non locality also is in agreement with Bells type experiments.

Edited by Mordred

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15 hours ago, Schmelzer said:

Name it causal influence faster than light, whatever.

The causal influence happens at the time when the entanglement is first created, which involves an interaction between the particles. This interaction follows the standard rules of QFT. After that has taken place, the system of two particles is described by just one wave function, irrespective of their spatial separation, so that no decomposition of said function into separate, independent parts is possible. This fully accounts for the statistical correlation, no causative exchange of information takes place at the time of measurement.

11 hours ago, Schmelzer said:

Ok, second time the harmonic condition:

Xα=μ(gμαg)=0

For general curvilinear coordinates, this should actually be

$\square X^{\lambda } =\frac{1}{\sqrt{-g}} \partial _{\nu }\left[\sqrt{-g} g^{\mu \nu } \partial _{\mu } X^{\lambda }\right]$

I don’t quite understand how the above is even related to the discussion of quantum entanglement?

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50 minutes ago, Markus Hanke said:

The causal influence happens at the time when the entanglement is first created, which involves an interaction between the particles. This interaction follows the standard rules of QFT. After that has taken place, the system of two particles is described by just one wave function, irrespective of their spatial separation.

If I recall the guidance wave is $|\psi|^2$ correct ? It's been awhile since I last looked into Bohmian mechanics. Lol I prefer QFT.

Edited by Mordred

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1 hour ago, Mordred said:

If I recall the guidance wave is $$|\psi|^2$$ correct ? It's been awhile since I last looked into Bohmian mechanics. Lol I prefer QFT.

No, the guiding wave is $$\psi(q)$$ itself.  I don't prefer dBB too, there are better realist and causal interpretations.  For QFT, I prefer the field ontology, not particles. The usual dBB texts favor the particle ontology. So I don't value them very much.

3 hours ago, Mordred said:

I see so time foliations under Bohm theory doesn't apply to GR. I'm sure you have seen relativistic Bohmian papers. The non relativistic obviously applies Galilean relativity under the Kronecker delta.

One thing many of those same  papers do state is no superluminal signaling is possible. Non locality also is in agreement with Bells type experiments.

Relativistic papers are usually special-relativistic papers.  If they claim relativistic invariance, then there is usually something non-invariant hidden somewhere.

If you have a time foliation, you can use it for some realistic causal interpretation.  GR does not define one, and has solutions which do not even allow global time-like coordinates (like Goedel's rotating universe).  But you can always introduce harmonic coordinates with a time-like time locally.  And for the FLRW ansatz we observe (spatial curvature zero) there are also nice global harmonic coordinates.  So I prefer to name this a Lorentz ether interpretation of the Einstein equations in harmonic coordinates.

2 hours ago, Markus Hanke said:

The causal influence happens at the time when the entanglement is first created, which involves an interaction between the particles. This interaction follows the standard rules of QFT. After that has taken place, the system of two particles is described by just one wave function, irrespective of their spatial separation, so that no decomposition of said function into separate, independent parts is possible. This fully accounts for the statistical correlation, no causative exchange of information takes place at the time of measurement.

This is wrong. Once you make claims about "causative exchange of information", I can assume that you presuppose some notion of causality which includes Reichenbach's common cause principle.  But then the assumption that there is no "causative exchange of information" immediately leads to the requirement of a common cause explanations of all possible 100% correlations.  And this gives all you need to prove Bell's inequality.

You also seem to mingle the necessity of FTL causal explanation of the observable correlations with the impossibility to use them for signalling.

The logic behind this confusion is quite simple.  Bell's theorem excludes the common cause explanation.  So, it leaves two causal explanations:  $$A \to B$$ and $$B \to A$$.  Once both explanations are possible and sufficient to explain the correlations, they cannot be used to send information:  Sending information would contradict one of the two possible explanations.

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Well I for one do not see any advantage nor need to ever use harmonic coordinates. The last thing I ever want to employ is a harmonic metric tensor.

Particularly since a coordinate system is an arbitrary choice I would never choose to use a coordinate with an inherent uncertainty in position.

Yes you have uncertainty in position and momentum operators under QM however adding Uncertainty to a reference position doesn't appeal to me.

Edited by Mordred

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2 minutes ago, Mordred said:

Well I for one do not see any advantage nor need to ever use harmonic coordinates. The last thing I ever want to employ is a harmonic metric tensor.

Particularly since a coordinate system is an arbitrary choice I would never choose to use a coordinate with an inherent uncertainty in position.

Yes you have uncertainty in position and momentum operators under QM however adding Uncertainty to a reference position doesn't appeal to me.

Which uncertainty to a reference position?  The preferred coordinates fix a particular reference position.

And, note, they do this even if the metric in quantum gravity becomes uncertain.  The preferred frame remains certain.  This is the very point of introducing a fixed absolute background of absolute space and time:  You have objects which are not uncertain because of quantum effects, but you have a classical stage where you can define which variable objects exists inside.

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Oh then maybe I am misunderstanding what you mean by a harmonic coordinate system as now your stating it as being fixed is static.  That was the main details I was questioning you on yesterday. Hence specifying what a reference frame entails regardless if it inertial or non inertial. You still have to deal with the components and products of a vector using the metric.

I won't bother getting into absolute time and an eather based theory under GR/SR. I'm positive you already know all the arguments.

Quite frankly there is no need to even have a preferred fixed background if your coordinates for every reference frame is static to begin with.

So far you haven't shown me any reason to deviate from how SR or GR handles spacetime. Then my primary field is cosmology with particle physics being secondary as I needed particle physics for my focus of research.

So I have never had a need to delve into quantum interpretations for any practical purpose.

Edited by Mordred

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5 hours ago, Mordred said:

Oh then maybe I am misunderstanding what you mean by a harmonic coordinate system as now your stating it as being fixed is static.  That was the main details I was questioning you on yesterday. Hence specifying what a reference frame entails regardless if it inertial or non inertial. You still have to deal with the components and products of a vector using the metric.

I still don't see the point of your question.  The preferred coordinates are also coordinates, the formulas to be used for arbitrary coordinates remain valid for the preferred coordinates too.  So, what's the problem to deal with vector or tensor components?

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I won't bother getting into absolute time and an eather based theory under GR/SR. I'm positive you already know all the arguments.

In fact I have not heard much arguments. The usual way to handle such approaches in science forums is to ban them instead of discussing them. Criticizing GR using an ether approach is anathema, not handled in a rational way.

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Quite frankly there is no need to even have a preferred fixed background if your coordinates for every reference frame is static to begin with.

Except that those who quantize gravity without a fixed preferred background have failed almost a century to combine these two rather simple theories. Instead, quantizing gravity in an ether approach is standard condensed matter theory.

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So far you haven't shown me any reason to deviate from how SR or GR handles spacetime. Then my primary field is cosmology with particle physics being secondary as I needed particle physics for my focus of research.

A main argument is the violation of Bell's inequality. In fact, it is a decisive one. Those who reject the simple and straightforward solution of a preferred frame, where causal influences faster than light are allowed without endangering causality and realism, and are ready to give up all the fundamental principles of science (realism, causality, logic of plausible reasoning) to save fundamental(ist) relativistic symmetry seem unreachable by any further scientific arguments. Yes, there are people who are ready to reject realism and causality to preserve their dogma, given that the only way to preserve realism and causality would be to give up the dogma.

To hope that such people can be reached by scientific arguments seems naive. I have given up this hope.

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So I have never had a need to delve into quantum interpretations for any practical purpose.

The important point of the realist and causal interpretations is that they explicitly prove the existence of interpretations which preserve realism and causality.  Even if this requires a preferred frame.  So, it shows that to blame quantum strangeness as a justification for giving up realism and causality is unjustified.  The only justification for giving up realism and causality is the dogma of fundamental relativity.

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20 hours ago, Schmelzer said:

I can assume that you presuppose some notion of causality which includes Reichenbach's common cause principle.

My assumption is only that interactions between particles are adequately described by the framework of QFT. This trivially preserves causality, but not necessarily locality and/or realism.

20 hours ago, Schmelzer said:

This is wrong.

It is the current scientific consensus. You can choose to not follow that consensus of course (as you seem to be doing here), but that doesn’t automatically make it “wrong”. You are merely putting forward a different hypothesis.

3 hours ago, Schmelzer said:

The preferred coordinates are also coordinates, the formulas to be used for arbitrary coordinates remain valid for the preferred coordinates too.

In what sense then are they preferred? What mathematical definition of “preferred” are you using? Can you formalise this for us?

3 hours ago, Schmelzer said:

Yes, there are people who are ready to reject realism and causality to preserve their dogma, given that the only way to preserve realism and causality would be to give up the dogma.

I’ll be blunt with you - your very rejection of what you consider “dogma” appears to have become dogma itself for you. The paragraph I quoted the above from really lets that shine through very strongly. At least that’s the vibe I’m picking up. Physics should not become a partisan issue - it is not about metaphysical notions of “right” or “wrong”, but about what model works best in describing aspects of the universe as we see them. Sometimes models are “right” in some circumstances, but “wrong” in others. It’s an epistemological endeavour, not an ontological one. The map isn’t the territory, but it does need to accurately represent the relevant aspects of the terrain, on the relevant scales. Quantum theory / QFT actually does this rather well.

As for the specific example of entanglement, since no exchange of information is necessary at the time of measurement, causality never even comes into it at all. By letting go of either realism or locality (or both), we eliminate the very need to exchange information, and hence no artificial notions of superluminality, preferred frames etc are necessary in the first place. Causality is trivially preserved, since the measurement always happens after entanglement has been created, and the outcome of measurements is compared following the usual rules of SR, which again trivially preserve causality.

There really is no problem here that needs to be “solved” somehow. The problems only emerge if one demands that notions which appear fundamental in the classical domain (such as locality and realism) must be scale-independent, i.e. necessarily apply on all scales. Why should that be necessarily true?

4 hours ago, Schmelzer said:

So, it shows that to blame quantum strangeness as a justification for giving up realism and causality is unjustified.  The only justification for giving up realism and causality is the dogma of fundamental relativity.

Again, it isn’t about what is right or what is wrong, but about what model best fits the universe we observe. To that end, there is no problem whatsoever in setting aside notions of realism and locality, of absolute time and space, if the resulting model is in good agreement with available data. Realism and locality are not sacrosanct notions somehow built into the foundations of the universe on small scales, rather, they originate in what us humans think the universe should be like; they are a reflection of our own experience, which is, after all, rooted in classicality and the low-energy regime. The unscientific act would be to unquestioningly assume that such notions apply across all scales. There is no apparent reason why they must, but plenty of reason to believe that they don’t.

I think even the notion of causality itself may not necessarily be scale-independent. This remains to be seen.

To make a long story short - not only is it no problem for me personally to set aside locality and/or realism, but I think it is a perfectly reasonable thing to do, if the resulting model describes very well what it is supposed to describe, while at the same time respecting other principles of physics, such as diffeomorphism invariance. To me, introducing preferred frames and space-like world lines creates many more problems than it solves.

Don’t get me wrong here - investigating the implications of such things as preferred frames and space-like separations is quite a valid endeavour, but it doesn’t seem to add any value to physics as it stands. It just creates unnecessary problems and complications. Now, if you could put forward a model that preserves locality and realism without the need to add superluminality and preferred frames...that would indeed be something!

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58 minutes ago, Markus Hanke said:

My assumption is only that interactions between particles are adequately described by the framework of QFT. This trivially preserves causality, but not necessarily locality and/or realism.

That means, you talk only about signal causality.

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It is the current scientific consensus.

No.

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In what sense then are they preferred? What mathematical definition of “preferred” are you using? Can you formalise this for us?

They are preferred by the interpretation of the theory.  Formally, it is the same preference as for the Cartesian coordinates and absolute time in pre-relativistic physics.

They identify absolute space and time.

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I’ll be blunt with you - your very rejection of what you consider “dogma” appears to have become dogma itself for you. The paragraph I quoted the above from really lets that shine through very strongly. At least that’s the vibe I’m picking up. Physics should not become a partisan issue - it is not about metaphysical notions of “right” or “wrong”, but about what model works best in describing aspects of the universe as we see them. Sometimes models are “right” in some circumstances, but “wrong” in others. It’s an epistemological endeavour, not an ontological one. The map isn’t the territory, but it does need to accurately represent the relevant aspects of the terrain, on the relevant scales. Quantum theory / QFT actually does this rather well.

I have no problem at all with physicists following the "shut up and calculate" prescription.  They have given a lot, in particular the SM.  But this does not make more fundamental research meaningless.  Those who do fundamental research have to make metaphysical choices, simply because the principles they choose are their guidelines toward a more fundamental theory.  The difference between me and the relativist fundamentalists is quite obvious:  I have no problem at all with other scientists, say, Rovelli, trying out other ways, namely assuming that relativistic symmetry, background freedom, are fundamental insights to be preserved in quantum gravity.  Instead, their behavior is different, my proposals are handled like anathema.  Some forums completely forbid to discuss the Lorentz ether, some move them into subforums for cranks, one permanently risks to be banned, arxiv rejects even some published papers, and so on. Reasonable, scientific arguments against my theories are almost absent.

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As for the specific example of entanglement, since no exchange of information is necessary at the time of measurement, causality never even comes into it at all. By letting go of either realism or locality (or both), we eliminate the very need to exchange information, and hence no artificial notions of superluminality, preferred frames etc are necessary in the first place. Causality is trivially preserved, since the measurement always happens after entanglement has been created, and the outcome of measurements is compared following the usual rules of SR, which again trivially preserve causality.

You use here, again, the very weak notion of signal causality. You cannot use the BI violations to send signals, and think that after this everything is fine with causality.  But causality is about something different - it is about the necessity to find causal explanations for observed correlations.  Without such necessity, we could continue to believe astrology.  The problem of astrology (beyond the difficult to prove point that the claimed correlations do not exist too) is that they do not even look for causal explanations.  But the notion of causality which requires to look for causal explanations of observed correlations is what you have to give up - it is Reichenbach's principle of common cause.

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The problems only emerge if one demands that notions which appear fundamental in the classical domain (such as locality and realism) must be scale-independent, i.e. necessarily apply on all scales. Why should that be necessarily true?

There are laws or rules of thinking.  We cannot rationally think without accepting and following them.  The laws of logic.  Can you accept that the laws of logic are something different from hypotheses of particular physical theories? Realism as well as causality have a similar character.  Essentially, without realism even the laws of logic become unnecessary, in poetry one lives nicely violating them.  And causality is what distinguishes astrology from science.  Necessities of thought, presuppositions of the scientific method itself - these are things which are not open to empirical falsification because we have to presuppose them to start the evaluation of what we observe.

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Again, it isn’t about what is right or what is wrong, but about what model best fits the universe we observe. To that end, there is no problem whatsoever in setting aside notions of realism and locality, of absolute time and space, if the resulting model is in good agreement with available data.

Once both are in good agreement with the available data, this is not at all the question.  They are on equal foot in this question.

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To make a long story short - not only is it no problem for me personally to set aside locality and/or realism, but I think it is a perfectly reasonable thing to do, if the resulting model describes very well what it is supposed to describe, while at the same time respecting other principles of physics, such as diffeomorphism invariance. To me, introducing preferred frames and space-like world lines creates many more problems than it solves.

I have yet to see any problem created by a preferred frame.  Regarding diff invariance, it is anyway quite dubious as a physical principle. Here, one can start with

Kretschmann, E. (1917). Über den physikalischen Sinn der Relativitätspostulate, A. Einsteins neue und seine ursprüngliche Relativitätstheorie, Ann. Phys. 53, 575-614

where the point is made that every physical theory can be presented in a covariant form.  Rovelli and Anderson IIRC have tried to replace this with the concept of background independence, but this formalization has been criticized too.  Whatever, background independence may be a nice principle, but it is incompatible with quantum theory, which is a decisive argument against it.

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Don’t get me wrong here - investigating the implications of such things as preferred frames and space-like separations is quite a valid endeavour, but it doesn’t seem to add any value to physics as it stands. It just creates unnecessary problems and complications. Now, if you could put forward a model that preserves locality and realism without the need to add superluminality and preferred frames...that would indeed be something!

Sorry, I'm not a perpetuum mobile constructor, I accept simple theorems like Bell's theorem.  You have yet to present any problems and complications.

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10 hours ago, Schmelzer said:

In fact I have not heard much arguments. The usual way to handle such approaches in science forums is to ban them instead of discussing them. Criticizing GR using an ether approach is anathema, not handled in a rational way.

Well I have seen quite a few threads on the subject in SF. Furthermore they tend to be quite length ones, with no one ending up banned unless they become abusive.

You, too, have had lots of space here to put your case.

10 hours ago, Schmelzer said:

Except that those who quantize gravity without a fixed preferred background have failed almost a century to combine these two rather simple theories. Instead, quantizing gravity in an ether approach is standard condensed matter theory.

I'm glad youthink them both 'simple'

I'm still learning lots about them and fully expect to go in doing so until I peg out.

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Well quite frankly the view that the only causal interaction between particles A and B is that which occurs at the entanglement event itself.

The superposition wavefunction state does not require or need to carry any hidden variables. The act of measurement does not cause any signaling between the two particles. No signaling occurs

This quite frankly in my books makes far more logical sense than invoking hidden variables hidden reference frames of absolute time or any physics that relies more on metaphysical argument than with empirical evidence of being able to validate through detection.

Quite frankly I never invoke any  metaphysical based argument to make decisions of how physics works. The only thing that works for me is those models that can provide hard experimental data.

Entanglement does not require hidden fields or variables to account for its measurements

Edited by Mordred

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8 hours ago, Schmelzer said:

No.

That quantum entanglement is a correlation between measurement outcomes, not a causative action at time of measurement, is indeed the current consensus.

8 hours ago, Schmelzer said:

relativist fundamentalists

I am unsure what you mean by this term. I take it as the current consensus amongst physicists that GR is only an effective field theory, so in all likelihood there is a more fundamental model there, the classical limit of which will turn out to be standard GR (hence quantum gravity being such an active field of research). That more fundamental model is obviously not guaranteed to exhibit the same fundamental symmetries, or bear any resemblance to the notion of “spacetime” at all. Few researchers in the field would disagree with this, I think.

9 hours ago, Schmelzer said:

There are laws or rules of thinking.  We cannot rationally think without accepting and following them.  The laws of logic.

Neither locality nor realism are laws of logic, they are features of a mathematical model. A model may lack these, yet still be a good and valid description of physical reality.

9 hours ago, Schmelzer said:

I have yet to see any problem created by a preferred frame.  Regarding diff invariance, it is anyway quite dubious as a physical principle. Here, one can start with

Kretschmann, E. (1917). Über den physikalischen Sinn der Relativitätspostulate, A. Einsteins neue und seine ursprüngliche Relativitätstheorie, Ann. Phys. 53, 575-614

where the point is made that every physical theory can be presented in a covariant form.  Rovelli and Anderson IIRC have tried to replace this with the concept of background independence, but this formalization has been criticized too.  Whatever, background independence may be a nice principle, but it is incompatible with quantum theory, which is a decisive argument against it.

So you are essentially disputing the validity of GR as a model.

9 hours ago, Schmelzer said:

You have yet to present any problems and complications.

The extra constructs you propose - superluminality, ether, preferred frames etc - are neither necessary to explain quantum entanglement, nor is there any evidence that they correspond to anything in the real world.

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2 minutes ago, Markus Hanke said:

That quantum entanglement is a correlation between measurement outcomes, not a causative action at time of measurement, is indeed the current consensus.

Neither locality nor realism are laws of logic, they are features of a mathematical model. A model may lack these, yet still be a good and valid description of physical reality.

The extra constructs you propose - superluminality, ether, preferred frames etc - are neither necessary to explain quantum entanglement, nor is there any evidence that they correspond to anything in the real world.

No.  There are many people who think so, but it is far from being consensus.

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I am unsure what you mean by this term. I take it as the current consensus amongst physicists that GR is only an effective field theory, so in all likelihood there is a more fundamental model there, the classical limit of which will turn out to be standard GR (hence quantum gravity being such an active field of research). That more fundamental model is obviously not guaranteed to exhibit the same fundamental symmetries, or bear any resemblance to the notion of “spacetime” at all. Few researchers in the field would disagree with this, I think.

Fundamental relativity is the assumption that relativistic symmetry is not simply an approximation, but really fundamental.

The LQG people, in particular Rovelli, emphasize the central role of background independence in their approach. Background independence is the established attempt to formalize diff invariance as having a physical meaning, despite Kretschmann's objection. String theory I do not take seriously, whatever they think.  Beyond these two there is essentially nothing.

If it would be accepted that relativistic symmetry is only an approximation, it would be fine. I have yet to find people ready to accept this together with the consequences. Namely, it follows almost automatically that the classical objections against the Lorentz ether are worth nothing - some approximate symmetry may be useful in some computations, but has no fundamental significance at all.

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So you are essentially disputing the validity of GR as a model.

No. Kretschmann's objection was essentially accepted by Einstein.  GR remained nonetheless unchanged and unquestioned.  The question has more metaphysical character.

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Neither locality nor realism are laws of logic, they are features of a mathematical model. A model may lack these, yet still be a good and valid description of physical reality.

I have never claimed that Einstein causality is a law of logic. My claim is about realism, and not realism in general (philosophers have invented hundreds of variants of it) but of the particular formula used in Bell's proof which is usually interpreted as following from realism.  I have shown that it follows from the Bayesian interpretation of probability, which is an interpretation of the rules of probability as rules of consistent thinking in a situation of uncertainty. (The logic of plausible reasoning.) In other words, for a consistent model one can simply construct that space $$\Lambda$$ which is usually interpreted as some set of hidden variables. The construction for the case of quantum theory is there too.  It has been found earlier by Kochen and Specker and is not really complicate.

Of course, there may be useful physical theories without realism and causality.  They may be, indeed, useful.  But they are incomplete.  (But to name a theory which is not realistic a valid description of physical reality becomes funny. The rejection of realism means that theory refuses to describe reality.)

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