Quantum nonlocality and "spooky action at a distance"

[Fra]

Yes, and this has nothing to do with a quantum-classical cut either.

I guess we simply think differently on this point. Which is not necessarily a problem.

/Fredrik

 

[Fra]

The "appearance of a classical world" out of QT

As you phrase it like this, it to me, seems that you are missing my point?
This is not the even question I am asking.

There is only one world, I think we agree on that. The "classical world" is simply the "macroscopic world". And from this perspective we formulate a QT for small subsystems.

The problem is that we can not explain the foundation, based on a theory built on the same foundation? This is the conceptual problem. It is either circular, or (more commonly) a infinite regress where we consider layers or larger and larger "macroscopic systems", and at some point, these are beyond our empirical access, as at some point the whole universe is the "macroscopic system". QT is not even close to corroborated for such systems. This is very different from a piece of metal in a lab or whatever.

/Fredrik

 

[vanhees71]

There's indeed only one world, which is described by quantum theory + a spacetime model (the latter is not yet quantized, which is why we don't have a theory of everything yet). Everything concerning "matter and radiation" is quantum, including the "classical appearance" of the macroscopic phenomena. The fact that there are macroscopic measurement devices is explained by quantum-many-body theory as is the classical behavior of any other macroscopic piece of matter.

 

[gentzen]

This is an unfounded claim. Nothing in contemporary experiments hints at a quantum-classical cut

But our mesaurement apparatouses, and all the data we get from observations are stored in reliable records, that - modulo special relativity - all observers agree upon. Ie. there is no non-commutativity or no-cloning issues with information sharing of measurement results. This is the classical cut. Without this cut, how can you imagine reliably preparing and repeating experiments, that all observers agree upon?

Yes, and this has nothing to do with a quantum-classical cut either. The "appearance of a classical world" out of QT is much better understood today than at Bohr's times!

You are the one who interprets the cut as something that should show-up in experiments.
Who on this Forum really interprets the cut in that way?
Why are you so determined to claim that Bohr and Heisenberg have been wrong, and are responsible for all the confusion caused by QM?

 

[vanhees71]

I thought the aim of all these experiments aiming at demonstrating "quantum phenomena" on ever larger systems are about answering the question, whether QT is really complete or whether there's at some point the necessity of generic classical physics, as claimed by Bohr, among others of the Copenhagen camp. I only stress that so far no such thing has been found but that even really macroscopic objects like the LIGO mirrors show quantum behavior if sufficiently accurately observed.

I think Bohr and Heisenberg are not even wrong, they are just confusing.

 

[Fra]

or whether there's at some point the necessity of generic classical physics, as claimed by Bohr, among others of the Copenhagen camp

I think you "interpret this" (yes, here we go again with interpretations) differently that I do. What I mean with Bohrs clarity, you take as evidence for that he claims that "classical world is needed"!

I interpret it not as a statement about the world, but as a statement of quantum theory itself. I don't think Bohr ever said that QT is fundamental (in the sense of unification of all forces), he just honestly declares that we need the classical context to define it.

This is to me, honest about the theory (not pretending it has universal validity), it is not statement about reality itself. I think Bohr was clear to not make such statements. But I dont know who has the "right" interpretation of Bohr of course?

/Fredrik

 

[GarberMoisha]

I agree with Martinbn, I find Bohr to express things in honest and clear ways, in particular how QM is defined relative to the classical/macroscopic side of the cut. This to me, both clearly explains that QM can not be defined without a "classical/macroscopic observer". Yet, Bohr to my knowledge never claimed that there is a classical reality that is more fundamental, nor that there is a quantum reality.

Taken together, this both states clearly what QM is AND it's limitations. While others may pretend there is only a quantum reality, but without realizing that without the "macro background" we can not DEFINE QM. I think Bohr never made any exaggerated claims here, he expressed what we know, not more, not less, this is why he has my respect.

/Fredrik

If quantum mechanics is fundamental and classical physics "emergent" from it, how come it's impossible to define QT without using these purpotedly emergent macro properties?

 

[Fra]

If quantum mechanics is fundamental and classical physics "emergent" from it, how come it's impossible to define QT without using these purpotedly emergent macro properties?

Yes, that is the right hypothetical question.

IMO the fallacious thinking of, that I percieve is happening, is that you first describe a spatially and temporally small subsystem, from the perspective of the macroscopic environment. And then you extract the mathematical pattern, which suddently is timeless and appearing godlike. Then you for forget about where it came from, and think that the same mathematics is universally valid for any system, even those where the subsystem assymmetry obviously is not fulfilled. (https://arxiv.org/abs/1201.2632)

/Fredrik

 

[GarberMoisha]

Yes, that is the right hypothetical question.

IMO the fallacious thinking of, that I percieve is happening, is that you first describe a spatially and temporally small subsystem, from the perspective of the macroscopic environment. And then you extract the mathematical pattern, which suddently is timeless and appearing godlike. Then you for forget about where it came from, and think that the same mathematics is universally valid for any system, even those where the subsystem assymmetry obviously is not fulfilled. (https://arxiv.org/abs/1201.2632)

/Fredrik

There isn't even 1 tangible thing anywhere in existence that cannot be described mathematically. Not 1. To claim it's somehow a 'coincidence' is to detract from the real substance that is of real value for the purpose of understanding the world.

 

[gentzen]

I thought the aim of all these experiments aiming at demonstrating "quantum phenomena" on ever larger systems are about answering the question, whether QT is really complete or whether there's at some point the necessity of generic classical physics,

I guess those experiments try to test theories like GRW, CSL, or gravitational collapse models like those of Penrose or Diósi. See for example:
https://plato.stanford.edu/entries/qm-collapse/#CSLExpe

as claimed by Bohr, among others of the Copenhagen camp.

I guess you are simply wrong here. That QT is complete is one of the claims of the Copenhagen camp. And Bohr would have been the last one to claim otherwise.

I only stress that so far no such thing has been found but that even really macroscopic objects like the LIGO mirrors show quantum behavior if sufficiently accurately observed.

And Bohr would have been the last one to expect otherwise.

I think Bohr and Heisenberg are not even wrong, they are just confusing.

Pauli ment something else with his "not even wrong". And you basically repeat in slightly weakened form your claim that Bohr and Heisenberg created confusion regarding QM, but don't explain why you are so determined to do so:

Why are you so determined to claim that Bohr and Heisenberg have been wrong, and are responsible for all the confusion caused by QM?

 

[Fra]

To claim it's somehow a 'coincidence' is to detract from the real substance

Mathematical law is not conincidence, on the contrary - it would be almost unavoidably, when you study a spatially and temporally limited system, that you will find timeless patterns. Just think about, fourier analysis for example. That is the whole point. This is both the power and a limitation. It's not all bad! BUT, how the pattern scales as you increase complexity is not given. I think sometimes we are seduced by the power, and generalized it a bit too far because it's tempting.

A naturalist account of the limited, and hence reasonable, effectiveness of mathematics in physics
"The view I will propose answers Wigner’s query about the ”unreasonable effectiveness ofmathematics in physics” by showing that the role of mathematics within physics is reasonable, because it is limited."
-- https://arxiv.org/abs/1506.03733

/Fredrik

 

[physika]

The grammar feels wrong: "... questions ... is settled ...". It is stated as some fact: "foundational questions ... EPR ... settled ... by all the Bell tests ...

...telegraphical ?

 

[physika]

As well as the fact that nor coarse graining, many body, decoherence (by "quantum" darwinism nor "quantum" broadcasting) explain/describe the "appearance" of macroscopic phenomena.

 

[vanhees71]

I guess those experiments try to test theories like GRW, CSL, or gravitational collapse models like those of Penrose or Diósi. See for example:
https://plato.stanford.edu/entries/qm-collapse/#CSLExpe

Yes, i.e., these are models beyond standard QM, trying to solve the socalled "measurement problem". So far no hint of any such thing has been found though!

I guess you are simply wrong here. That QT is complete is one of the claims of the Copenhagen camp. And Bohr would have been the last one to claim otherwise.

Well, as I said, for me Bohr is ununderstandable. On the one hand he says, QT were complete, but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?

And Bohr would have been the last one to expect otherwise.Pauli ment something else with his "not even wrong". And you basically repeat in slightly weakened form your claim that Bohr and Heisenberg created confusion regarding QM, but don't explain why you are so determined to do so:

I am not determined to do this, it's just an observation.

 

[Fra]

QT were complete, but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?

For me i read that Bohr means; given a classical background, QM is defined and is complete, relative to the same. Ie QM is a theory that is relative to the classical background. No background - no QM (or QFT for that matter)!

This does not mean that in a bigger perspective (unification) that there is another theory, thay does NOT presume this background. But that would be a theory defined in a different way, so it would not mean that QM as defined on its premises is incomplete.

For me this is clear. QM may be complete given its paradigm. But its still possible that at theory with more universality may be found, that relaxes the foundations of QM.

Two different things for me.

/Fredrik

 

[martinbn]

Well, as I said, for me Bohr is ununderstandable. On the one hand he says, QT were complete, but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?

Why is that a problem? Why should QM be formulated without measurement devices?

 

[vanhees71]

It should not be formulated without measurement devices. All of physics (as a natural science) is about observable and measurable phenomena after all. It's, however, a contradiction to claim that on the one hand quantum theory is complete but on the other that macroscopic objects, including measurement devices, are inherently classical. I think that's more due to Heisenberg than Bohr, because it's usually named the "Heisenberg cut".

The point is that all of matter with all interactions except gravity are describable by QT. There's no hint that at some size of macroscopic object QT would fail and you'd need classical mechanics or classical field theory. The latter are, of course, derivable as approximations of many-body QT (quantum statistics), but they are not invalidating QT for large macroscopic objects of any size in principle, and indeed nowadays with ever more refined experiments ever larger objects can be shown to indeed show "quantum behavior", e.g., the mirrors of the LIGO experiment show quantum-mechanical "zero-point motion".

 

[Lord Jestocost]

If quantum mechanics is fundamental and classical physics "emergent" from it, how come it's impossible to define QT without using these purpotedly emergent macro properties?

To my mind, quantum theory can be understood as a nonclassical probability theory – to put it in this way. One can use classical physics as a FAPP approximation when the inclusion of more variables – so to speak the “degrees of freedom” – into the quantum-theoretical description is no longer necessary to approximately predict observable outcomes.

 

[gentzen]

Well, as I said, for me Bohr is ununderstandable. On the one hand he says, QT were complete,

Einstein attacked QM, and Bohr somehow got the task to try to defend it, at least at the Solvay conference in 1927. Maybe not every one of his defence was perfect, but remember that he had only one night for each of those defenses.
Then in 1935, the EPR paper was yet another attack on QM, a more tricky one, and Einstein's role was tricky too. And Einstein's bomb also made its appearance as Schrödinger's cat in 1935. This time, Bohr worked a longer time on his defence, and only responded to Einstein's paper, but not to Schrödinger's paper or Einstein's bomb.

My impression is that Bohr felt that he was able and expected to communicate with Einstein (and disprove him), but felt uneasy to respond to Schrödinger. Heisenberg did respond to some later papers by Schrödinger, and his response was quite respectful. This further encouraged people to engage with Schrödinger's thoughts, which are probably more responsible for the many different quantum interpretations than Einstein's "suggested thought experiments" or Bohr's answers to them.

but on the other hand he claims that in addition to QT there must be classical dynamics of measurement devices, or is already this a misunderstanding due to his vagueness?

This is a misunderstanding, but probably unrelated to Bohr's vagueness. I guess it is more related to Bohr being cited by many different people, who all try to explain his thoughts, and often do this by highlighting certain features relevant for their current discussion. In your case, this was probably Bell, but Fra/Frederik gives a more current example how this happens in practice. Bohr's thoughts were simpler and more practical than Fra/Frederik's goals.

The confusion for which Bohr himself is mainly responsible is only the role of complimentarity, I guess.

 

[vanhees71]

Einstein attacked QM, and Bohr somehow got the task to try to defend it, at least at the Solvay conference in 1927. Maybe not every one of his defence was perfect, but remember that he had only one night for each of those defenses.
Then in 1935, the EPR paper was yet another attack on QM, a more tricky one, and Einstein's role was tricky too. And Einstein's bomb also made its appearance as Schrödinger's cat in 1935. This time, Bohr worked a longer time on his defence, and only responded to Einstein's paper, but not to Schrödinger's paper or Einstein's bomb.

The EPR paper is anyway somewhat unfortunate. Einstein himself didn't like it, saying it's burying the real argument under "erudition". The way more concise paper is in Dialectica 1 of 1948 (in German), where it becomes clear that the real point for Einstein was indeed inseparability. The answer by Bohr is a complete enigma to me. The real scientific breakthrough was, of course, finally Bell's work translating the vague philosophical "erudition" of the EPR paper into an experimentally decidable scientific question. The results are well known: full consistency of the QM predictions with all empirical findings. If you accept that what EPR had in mind is "local realism" (with all the vagueness of the meaning of these words), then they are clearly disproven.

Schrödinger's paper is much clearer compared to EPR, and I don't know, why it hasn't been attacked by the Copenhagen gang as much as EPR's.

What do you mean by "Einstein's bomb"?

My impression is that Bohr felt that he was able and expected to communicate with Einstein (and disprove him), but felt uneasy to respond to Schrödinger. Heisenberg did respond to some later papers by Schrödinger, and his response was quite respectful. This further encouraged people to engage with Schrödinger's thoughts, which are probably more responsible for the many different quantum interpretations than Einstein's "suggested thought experiments" or Bohr's answers to them.

I don't think that Schrödinger added much to the interpretational confusion, and also Einsteins standpoint is quite clear.

This is a misunderstanding, but probably unrelated to Bohr's vagueness. I guess it is more related to Bohr being cited by many different people, who all try to explain his thoughts, and often do this by highlighting certain features relevant for their current discussion. In your case, this was probably Bell, but Fra/Frederik gives a more current example how this happens in practice. Bohr's thoughts were simpler and more practical than Fra/Frederik's goals.

The confusion for which Bohr himself is mainly responsible is only the role of complimentarity, I guess.

Complementarity is another useless confusion, indeed.

 

[Lord Jestocost]

Einstein attacked QM, and Bohr somehow got the task to try to defend it ....

The following short section in Werner Heisenberg's memoir "Der Teil und das Ganze" puts Einstein’s stubbornness regarding QM in a nutshell:

„Einstein war nicht bereit, sich — wie er es empfand — den Boden unter den Füßen wegziehen zu lassen. Auch später im Leben, als die Quantentheorie längst zu einem festen Bestandteil der Physik geworden war, hat Einstein seinen Standpunkt nicht ändern können. Er wollte die Quantentheorie zwar als eine vorübergehende, aber nicht endgültige Klärung der atomaren Erscheinungen gelten lassen. „Gott würfelt nicht“, das war ein Grundsatz, der für Einstein unerschütterlich feststand, an dem er nicht rütteln lassen wollte. Bohr konnte darauf nur antworten: „Aber es kann doch nicht unsere Aufgabe sein, Gott vorzuschreiben, wie Er die Welt regieren soll.“

(I have refrained from a translation into English)

 

[physika]

experiments to test theories on collapse.

https://www.quantamagazine.org/how-...orld-be-physicists-probe-the-limits-20210818/

https://www.nature.com/articles/s42005-021-00656-7

......

 

[Fra]

This is a misunderstanding, but probably unrelated to Bohr's vagueness. I guess it is more related to Bohr being cited by many different people, who all try to explain his thoughts, and often do this by highlighting certain features relevant for their current discussion. In your case, this was probably Bell, but Fra/Frederik gives a more current example how this happens in practice. Bohr's thoughts were simpler and more practical than Fra/Frederik's goals.

I agree that the issues of unification of all forces, was not a major thing at that time.

But I think the success is perhaps that Bohr simply acknowledged the practical matters that simply appeared mandatory to define the new theory that was just born. Not more and not less. This is how practical matters such as approximate classical reality even required to collect statistics becomes principal matters.

So while others have tried to "overthink" or deny the observing context, Bohr seems to firmly insisted that it was required because the laboratory and all it's data is effectively classical. This basic simplicity is to me the key to clarity, which paradoxally stands strong in many attempts to overthink giving QM meaning without this context.

(The question of, what another theory would be like formulated without the premise, was likely not something that concerned Bohr. It was a sufficiently major task to fine the theory give the premise)

/Fredrik

 

[gentzen]

What do you mean by "Einstein's bomb"?

I read in Moore's biography of Schrödinger that he received a letter from Einstein where he described a similar experimental setup using an explosive instead of a cat, before Schrödinger had finished his famous cat paper. See for example SEP ERP 1.3 Einstein’s versions of the argument:
"In the August 8, 1935 letter to Schrödinger Einstein says that he will illustrate the problem by means of a “crude macroscopic example”.

The system is a substance in chemically unstable equilibrium, perhaps a charge of gunpowder that, by means of intrinsic forces, can spontaneously combust, and where the average life span of the whole setup is a year. In principle this can quite easily be represented quantum-mechanically. In the beginning the psi-function characterizes a reasonably well-defined macroscopic state. But, according to your equation [i.e., the Schrödinger equation], after the course of a year this is no longer the case. Rather, the psi-function then describes a sort of blend of not-yet and already-exploded systems. Through no art of interpretation can this psi-function be turned into an adequate description of a real state of affairs; in reality there is no intermediary between exploded and not-exploded. (Fine 1996, p.78)

[...] The similarity between the gunpowder and the cat is hardly accidental since Schrödinger first produced the cat example in his reply of September 19, 1935 to Einstein’s August 8 gunpowder letter. There Schrödinger says that he has himself constructed “an example very similar to your exploding powder keg”, and proceeds to outline the cat (Fine 1996, pp. 82–83). Although the“cat paradox” is usually cited in connection with the problem of quantum measurement (see the relevant section of the entry on Philosophical Issues in Quantum Theory) and treated as a paradox separate from EPR, its origin is here as an argument for incompleteness that avoids the twin assumptions of separability and locality."

The following Nautilus piece seems to know even more details of how Einstein inspired Schrödinger to invent his cat: How Einstein and Schrödinger Conspired to Kill a Cat

 

[vanhees71]

It's of course no paradox and it's exactly to the point of what Einstein wanted to say in the EPR paper (and he clearly said it only later in his Physica 1 paper of 1948). His real quibble was with the "inseparability" of far-distant parts of entangled quantum systems.

 

[martinbn]

It's of course no paradox ...

Usually in physics by "paradox" is meant an unintuitive consequence of the theory, like the twin paradox. None of them are actual paradoxes.

 

[Fra]

His real quibble was with the "inseparability" of far-distant parts of entangled quantum systems.

And I think Einsteins original view is sound, that there has to be a "hidden variable", of some kind. My view is no different. Not to explain the outcomes, but their correlations.

How it can explain the correlation and not the outcome, is exactly what we still do not understand. All we know is that kind of HV Bell envisioned does not work, because it assumes it's hidden from the ignorant exprimenter only.

I think Einstein wanted to understand, what others settled with describing. What progress is made until today?

/Fredrik

 

[vanhees71]

Nature doesn't care about our human quibbles due to wrong pictures/worldviews. She behaves as she does, and all very accurate empirical evidence confirms the probabilistic predictions of QT and no "local realistic hidden-variable model" (in the sense defined by Bell) can be right. That's an interpretation-independent empirical fact!

 

[GarberMoisha]

Yes, because even atoms are just useful models of experience.
Throw them the right way and they will interfere with themselves like the good probabilities that they are. Probability of experience.

 

[GarberMoisha]

If this doesn't make your head spin, I don't know what will.

 

[Structure seeker]

Nature doesn't care about

This idea is usually based on the philosophical belief that nature presents a harsh reality that is simply true regardless of your beliefs. I stress this point because I also believe that, but @vanhees71 keeps stating that before measurement there is no realism about the quantum state.

So I wonder, @vanhees71 , before interpreting measurement results we all start with our 'take' on things, our philosophical worldview. If you don't believe quantum wavefunctions are a reality, how do you justify that nature doesn't care about what people believe should be true about these wavefunctions? If you give no answer, your opinion that nature doesn't care is your belief about wavefunctions and we, as realists, can answer: nature (reality) doesn't care that you think our beliefs are superseded by measurement results.

 

[martinbn]

And I think Einsteins original view is sound, that there has to be a "hidden variable", of some kind. My view is no different. Not to explain the outcomes, but their correlations.

But everything we've learned since then points to no hidden variables!

 

[vanhees71]

This idea is usually based on the philosophical belief that nature presents a harsh reality that is simply true regardless of your beliefs. I stress this point because I also believe that, but @vanhees71 keeps stating that before measurement there is no realism about the quantum state.

So I wonder, @vanhees71 , before interpreting measurement results we all start with our 'take' on things, our philosophical worldview. If you don't believe quantum wavefunctions are a reality, how do you justify that nature doesn't care about what people believe should be true about these wavefunctions? If you give no answer, your opinion that nature doesn't care is your belief about wavefunctions and we, as realists, can answer: nature (reality) doesn't care that you think our beliefs are superseded by measurement results.

I usually avoid the word "reality", because its meaning is uncertain ;-)). The quantum state describes a preparation procedure for a quantum system. Having prepared the system in a given quantum state, you know the probabilities for the outcome of measurments of observables on the system, no more, no less, and that's what describes all observations with utmost precision.

 

[Fra]

But everything we've learned since then points to no hidden variables!

No, you missed a fine detail of my point. I think Vanhees did too.

There is no bell style HV, yes. I am with all this.

Which is a very specific HV with additional assumptions on how the average action is formed, which i think is the problem.

/Fredrik

 

[martinbn]

No, you missed a fine detail of my point. I think Vanhees did too.

There is no bell style HV, yes. I am with all this.

Which is a very specific HV with additional assumptions on how the average action is formed, which i think is the problem.

/Fredrik

I am not saying that it is 100% certain that there are no HV, only that so far all we know points in that direction. What makes you think that there could be HV (non Bell type of course)?