Bell's Inequalities and the issue of non-locality

[Fra]

You have to think in terms of microcausal relativistic QFT to

Hmmm, since when does thinking in those terms actually enlighten anyone?

/Fredrik

 

[Fra]

The thing you cannot do is pretend that somehow you can get round Bell's inequality and thereby recover realism, locality, and classical variables. That paradigm is gone.

I fully agree, the below is just for reflection and thought provocation...

Assuming the only possibilities are heads and tails.

To keep explaning my point in post #19, the problem with the premises of the theorem is that it assumes that the causality is randomly chosen from what would be the interaction from each "classical" possibility. This is the "ignorance" of the HV, that Bell's theorem assumes and shows does not work. (and it what i keeps reserving to)

But a more evolved(=more fit) strategy could probably employ more advanced action/strategy that actually accounts for all possibilities at once optimizing gain/risk, rather than "randomly" chosing one classical action that would be perfect if unknown HV was known. Nature would likely not settle with anything but the optimal strategy. Such an advanced "action" simply can not be explain in terms of randomly chosen (or averaged) from the simple actions. This is why a "quantum action" can not be reproduced by an average of classical actions.

I think this is conceptually simply put what is going on in bells theorem and it's not hard to understand if you give it some thought. But that in itself I think has little to do with the HV themselves. I think the fallacy is to assume that we can partition a more advanced strategy as a sum of simpler strategies (as per a partitioning of sample space). Ie. the "preparation" that produces the entangled pair, and this is what is going into the interaction, not randomly known states.

/Fredrik

 

[PeterDonis]

a more evolved(=more fit) strategy

Is this your own personal theory, or is there a reference?

Please be aware that personal theories are off limits here.

 

[vanhees71]

Hmmm, since when does thinking in those terms actually enlighten anyone?

/Fredrik

If you want to get enlightened you need QED, the best description of light physicists have come up with, and that's a local relativistic QFT!

 

[Tolga T]

The failure of Bell's theorem is not a problem for QM, because QM predicted it would fail in the first place. Don't underestimate the significance of this and why people who trust QM can't see the issue that others raise. Everything is as predicted by QM, so where's the problem?

The thing you cannot do is pretend that somehow you can get round Bell's inequality and thereby recover realism, locality, and classical variables. That paradigm is gone.

I am not sure everyone is 100% convinced that locality has gone. QM works perfectly experimentally; Bell's inequalities are violated, so at least one of Bell's assumptions must be dropped, and those are just facts. But I think we have every right and reason to suspect that QM is most likely not the final theory. Entanglement and the measurement problem are just two fascinating topics that could lead us into uncharted waters.

 

[Tolga T]

And another experiment which is mind blowing to me: you can entangle 2 photons that have never existed at the same time. One photon is measured by Alice before the Bob photon is even created. (The entanglement itself is created after Alice's measurement, via entanglement swapping.)

https://arxiv.org/abs/1209.4191

This experiment is amazing. I was just thinking of an experiment on a circle with points A, S, and B equidistant (and the distance between A and B is less than half the circumference) in the order given. S is the source of preparation for the entangled particles, one of which is sent to A and the other (in the opposite direction) to B. If Bell's equations are violated this time as well, it would imply that one part of the wave function (with the measurement at A) collapses and the other part (of the particle travelling to B) survives a little longer. Or it would mean that particle B knows with certainty before the measurement what will happen in B (in case of measurements at the same axis).

 

[vanhees71]

I am not sure everyone is 100% convinced that locality has gone. QM works perfectly experimentally; Bell's inequalities are violated, so at least one of Bell's assumptions must be dropped, and those are just facts. But I think we have every right and reason to suspect that QM is most likely not the final theory. Entanglement and the measurement problem are just two fascinating topics that could lead us into uncharted waters.

It depends on, what you define as "locality". For me, as working in the HEP-nuclear physics community, locality means that relativistic QT is exclusively described by local relativistic QFTs, where locality means that by assumption the microcausality constraint holds, i.e., that local observables commute at space-like separation of their arguments. This holds particularly for the energy density and all other local observables, since energy density is a local observable, and this implies that there are no causal connections between space-like separated (measurement) events, i.e., relativistic QT is realized as a local QFT, and thus locality holds. What, of course, doesn't hold is "reality", i.e., as in any QT, also in relativistic local QFT not all observables necessarily take determined values.

 

[Fra]

Is this your own personal theory, or is there a reference?

Please be aware that personal theories are off limits here.

It's not a theory, it is just my understanding/stance on the matter attempting to add perspective in the process of seeking a future better understanding (which is what we all want i think). But the key concepts of quantum vs classical strategies as beeing more or less fit, are not my personal ideas. I didn't have any specific paper in mind when writingn the post but see for example

Quantum Games and Quantum Strategies​

"We investigate the quantization of non-zero sum games. For the particular case of the Prisoners’ Dilemma we show that this game ceases to pose a dilemma if quantum strategies are allowed for. We also construct a particular quantum strategy which always gives reward if played against any classical strategy
...
Summarizing, we have demonstrated that novel features emerge if classical games like the Prisoners’ Dilemma are extended into the quantum domain. We have introduced a correspondence principle which guarantees that the performance of a classical game and its quantum extension can be compared in an unbiased manner. Very much like in quantum cryptography and computation, we have found superior performance of the quantum strategies if entanglement is present"
-- https://arxiv.org/abs/quant-ph/9806088

The idea from above is that two interacting systems are better off (evolutionary perspective) if their strategy is based not on a simple either or, and always gor for the maximum short term benefit but also account for the expected backreaction from the environment, there may be a strategy that is better, it's the insight that you depend also on the environment, that selfpreservation at the evolved level is not just about fighting the environment, but to cooperated with it, as the environment helps stabilize oneself.

The same paper also says, to parry a common critique that "decision" involves humans, which i do not think.

"One might wonder what games and physics could have possibly in common. After all, games like chess or poker seem to heavily rely on bluffing, guessing and other activities of unphysical character. Yet, as was shown by von Neumann and Morgenstern [1], conscious choice is not essential for a theory of games. At the most abstract level, game theory is about numbers that entities are efficiently acting to maximize
or minimize [2]. For a quantum physicist it is then legitimate to ask what happens if linear superpositions of these actions are allowed for, that is if games are generalized into the quantum domain"
-- https://arxiv.org/abs/quant-ph/9806088

John von Neumann himself wrote a book on game theory as well, even though as far as I know he didn't draw the parallells to physical interactions very far. Sometimes mathematics of QM seem to be used for tools elsewhere, rather using the other way around for insight
https://www.amazon.com/dp/0691130612/?tag=pfamazon01-20

/Fredrik

 

[Lord Jestocost]

But I think we have every right and reason to suspect that QM is most likely not the final theory.

Quantum mechanics is doing just fine having performed flawlessly since inception. What more can one expect? What matters for a physical theory is to fit into the experiential reality.

 

[PeroK]

I am not sure everyone is 100% convinced that locality has gone.

Not everyone is convinced the Earth is a sphere and not flat. You'll never convince everyone of anything.

 

[PeterDonis]

The idea from above is that two interacting systems are better off (evolutionary perspective) if their strategy is based not on a simple either or, and always gor for the maximum short term benefit but also account for the expected backreaction from the environment

I don't see how this relates to the thread topic. (I'm also not sure your description of what the paper says is correct.) If you want to discuss this paper, you need to start a separate thread in the appropriate forum.

 

[Tolga T]

Not everyone is convinced the Earth is a sphere and not flat. You'll never convince everyone of anything.

Very enlightening indeed!

"That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it."

One of the greatest thinkers of mankind could not help writing this down. He was suspicious, and he was so great at it again, because it turned out that his law of gravitation, although more than adequate for most applications, had to be replaced by a new theory after more than 200 years by an insurgent.

 

[martinbn]

Very enlightening indeed!

"That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it."

One of the greatest thinkers of mankind could not help writing this down. He was suspicious, and he was so great at it again, because it turned out that his law of gravitation, although more than adequate for most applications, had to be replaced by a new theory after more than 200 years by an insurgent.

Keep in mind that when it comes to the foundations of quantum mechanics there is more than one meaning to the terms "locality" and "non-locality". I don't think that anyone (aside from crackpots) has any doubt about Bell's theorems, that QM predictions violate Bell's inequality, and that experiments confirm QM predictions. Then it seems that there are people who are convinced about one of the possible interpretations of all that. From everything is local (in some sense of the word) to QM is definitely non-local (in some sense of the word).

 

[Demystifier]

Not everyone is convinced the Earth is a sphere and not flat. You'll never convince everyone of anything.

https://www.physicsforums.com/threads/collection-of-science-jokes-p2.847743/post-6808481

 

[PeroK]

Very enlightening indeed!

"That one body may act upon another at a distance through a vacuum without the mediation of anything else, by and through which their action and force may be conveyed from one another, is to me so great an absurdity that, I believe, no man who has in philosophic matters a competent faculty of thinking could ever fall into it."

One of the greatest thinkers of mankind could not help writing this down. He was suspicious, and he was so great at it again, because it turned out that his law of gravitation, although more than adequate for most applications, had to be replaced by a new theory after more than 200 years by an insurgent.

Neither of us can claim to know what Newton would have said about QM, had he lived in the late 20th Century. Nor can either of us say whether the failure of Bell's theorem would have changed Einstein's mind. The remaining alternatives to orthodox QM may have offended him more than QM itself.

That said, not accepting a mainstream theory because it might be corrected or replaced 200 years from now, although perhaps a valid philosophical viewpoint, doesn't leave much room for practical progress now.

You've spent much of this thread trying to resurrect local hidden variable theories, which is at least an eccentric point of view and many, including myself, would say is a lost cause.

 

[vanhees71]

The problem with quantum theory is that it is not only a major subset of physics, i.e., natural science but also to philosophy and esoterics/religion.

Quantum theory as a physical theory is the most successful desription of Nature we have. There are no principle scientific problems with it, although relativistic quantum field theory is only defined as an effective theory, i.e., in terms of renormalized (and sometimes resummed) perturbation theory, while a rigorous mathematical foundation of interacting QFTs in (1+3) spacetime dimensions is still not achieved. From the physical point of view also a satisfactory quantum formulation of the gravitational interaction is still lacking.