I Realistic interpretation of QM

[kurt101]

TL;DR Summary

Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

By this, I mean:
1. Particles are real and localized.
2. Waves are real and have the properties of waves (i.e. they spread out and interfere)
3. Entanglement is a non-local behavior between particles that is created through local preparation.

1 and 2 imply the wave function in quantum mechanics is real and corresponds to the combined state of the particle and the wave.

I have not seen anything that contradicts an interpretation like this that is causal, deterministic, and can be logically reasoned about in almost everyway and does not try to add baggage beyond what we observe in experiments.

As far as I can tell the reason we don't think this way is because the Copenhagen interpretation tried to make us not think this way, a good understanding of entanglement came much later (i.e. with Bell and Aspect), and we still have not figured out the exact underlying rules for the universe after such a long time.

None of these are good reasons to abandon this kind of interpretation and I think discussions would be a lot more interesting and beneficial if we had such a standard interpretation to name, discuss, and compare against.

 

[Quantumental]

Well, if you accept those premises you could always go Bohmian; real particles, a pilot wave guides them (explaining the wave properties of ensembles) and it is indeed non-local. It is also fully causal and deterministic.

 

[Drakkith]

we still have not figured out the exact underlying rules for the universe after such a long time.

Interpretations are not rules. All interpretations use the same rules and make identical predictions. That's why it is impossible to hold that one interpretation is more correct than others, and indeed why they are called interpretations in the first place.

 

[WernerQH]

Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

Because most physicists are reluctant to give up cherished beliefs. For example:

1. Particles are real and localized.
2. Waves are real and have the properties of waves (i.e. they spread out and interfere)

I think the problem is that we feel compelled to describe experiments in terms of quantum "objects" existing for some length of time, rather than phenomena of very short duration (events). Talk of quantum particles unnecessarily constrains the possible interpretations, because their connotations are (in my view) in conflict with the formalism itself.

 

[Demystifier]

1 and 2 imply the wave function in quantum mechanics is real and corresponds to the combined state of the particle and the wave.

What exactly do you mean by "combined", can you write it down mathematically? How does it work for two (or more) entangled particles? Have you ever heard of de Broglie-Bohm interpretation? How about de Broglie double solution and bouncing drops?

 

[Morbert]

Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

By this, I mean:
1. Particles are real and localized.

Complementarity is why. Broadly speaking, a physical theory will return standard probabilities for possible outcomes of an observation. If we straightforwardly assign physical properties to a system as if it were e.g. a real particle, then complementary properties of the system will prevent our quantum theory from returning standard probabilities for possible outcomes of an observation.

 

[kurt101]

Interpretations are not rules. All interpretations use the same rules and make identical predictions. That's why it is impossible to hold that one interpretation is more correct than others, and indeed why they are called interpretations in the first place.

Interpretations make identical predictions as it pertains to the domain of Quantum Mechanics, but outside of that domain interpretations have the potential to explain a lot more. So if we do learn that there are deeper rules that allow us to understand the machinery that underlies the statistical outcomes of Quantum Mechanics or other phenomena that QM can't explain, then its seems as if these interpretations would remain and the other interpretations would die off.

I don't know how well this pertains to what I just said, but maybe an interesting example of where a QM interpretation makes a different prediction:
In The Cellular Automation Interpretation of Quantum Mechanics by Gerard ’t Hooft he says
"If engineers ever succeed in making such quantum computers, it seems to me that the CAT is falsified; no classical theory can explain quantum mechanics."

What exactly do you mean by "combined", can you write it down mathematically? How does it work for two (or more) entangled particles? Have you ever heard of de Broglie-Bohm interpretation? How about de Broglie double solution and bouncing drops?

In a realistic view of quantum mechanical experiments like the double slit experiment, the particle is found in one path and the wave takes all possible paths of the particle. If the waves are to be considered real, where are these waves created?

In the standard Quantum Mechanics interpretation the particle is most likely to be found where the probability amplitude is the greatest. In a realist interpretation, I would expect the probability amplitude to be the greatest at the wave source. This is what I mean by "combined"; the particle position and the wave source position are the same.

In the Broglie-Bohm interpretation how are the waves created? My issue with Broglie-Bohm is that it has a realistic explanation for the particles, but not the waves.

 

[Demystifier]

In the standard Quantum Mechanics interpretation the particle is most likely to be found where the probability amplitude is the greatest. In a realist interpretation, I would expect the probability amplitude to be the greatest at the wave source. This is what I mean by "combined"; the particle position and the wave source position are the same.

Waves satisfying the Schrodinger equation have no source. Schrodinger equation implies that the norm of the wave is conserved, which is incompatible with the existence of a source. This answers your question: the "straightforward" interpretation that you suggest is not generally accepted because it is not compatible with the Schrodinger equation.

Or to use your metaphor, perhaps it looks, swims and quacks like a duck, but it was not hatched like a duck.

In the Broglie-Bohm interpretation how are the waves created? My issue with Broglie-Bohm is that it has a realistic explanation for the particles, but not the waves.

In the Broglie-Bohm interpretation, neither waves nor particles are created. So I don't see how is particle more "realistic" than wave.

In the real world, of course, particles do get created, but it cannot be described by non-relativistic Schrodinger equation for a single particle. One needs quantum field theory (QFT) for that. But even in QFT, particles (or waves) are not created from sources. (If one asks about Schwinger sources, I can explain that too). Bohmian version of QFT also exists (see e.g. my recent paper https://arxiv.org/abs/2205.05986 where I explain it in very simple terms), but then a naive picture of wave that you have in mind must be generalized to a more abstract "wave"-like quantity.

 

[Paul Colby]

Summary: Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

In my view, all I know is that my discriminator fired and my counter incremented buy one. Everything else is theory and somewhat futile extrapolations of the minds eye.

 

[mitchell porter]

1. Particles are real and localized.
2. Waves are real and have the properties of waves (i.e. they spread out and interfere)
3. Entanglement is a non-local behavior between particles that is created through local preparation.

Sorry, this is very vague. How "localized" are particles - localized to a point? Does every quantum field have localized particles associated with it? Do definite particle histories occur in a scattering event, even though the calculation involves a superposition of different histories of particle creation and annihilation? Are waves, waves in a field, waves in a single-particle wavefunction, or what? Exactly how does local preparation create the nonlocal behavior?

 

[Fra]

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

I would say QM we actually take what we see in experiments more seriously than we do in classical mechanics.

What we really "see" is this: For a given preparation procedure, the prepared system(black box) responds to pertubation in certain ways. This is the only way of asking what is inside the black box. This is more faithful to what we actually know and see.

This distinction is IMO the beauty of QM and if you start to question the action also of the observer, this distinction I think becomes paramount.

So i certainly do not miss the classical logic.

/Fredrik

 

[kurt101]

Waves satisfying the Schrodinger equation have no source. Schrodinger equation implies that the norm of the wave is conserved, which is incompatible with the existence of a source. This answers your question: the "straightforward" interpretation that you suggest is not generally accepted because it is not compatible with the Schrodinger equation.

Your statements persuaded me that my statement "1 and 2 the wave function in quantum mechanics is real and corresponds to the combined state of the particle and the wave" is not good and I would have been better served with saying something like the wave function in quantum mechanics relates to real wave like behavior we see in experiments.

We know from experimental evidence that particles and wave like behavior are real. When using the Schrodinger equation to model the electrons of an atom, the particle and the particle behaviors are the ingredients that go into the Schrodinger equation. The Schrodinger equation gives real answers for where you might find the position of the electron. If you take the realist position of real waves and particles, I don't see how you can conclude anything other than the particles create the wave and likewise their position is influenced by the wave.

In the Broglie-Bohm interpretation, neither waves nor particles are created. So I don't see how is particle more "realistic" than wave.

My crude understanding of the standard Broglie-Bohm interpretation is:
The lack of particle creation in this interpretation is a well understood limitation that it intentionally leaves out. On the other hand the interpretation does try to explain why we see wave like behavior and says that particles follow the evolution of the wave function via some non-local quantum potential.
Is there a reciprocal behavior in this interpretation where particles also influence the evolution of the wave function?

Sorry, this is very vague. How "localized" are particles - localized to a point?

I think of a particle as any object that is localized (photon, electron, planet, galaxy, etc.).

Does every quantum field have localized particles associated with it? Do definite particle histories occur in a scattering event, even though the calculation involves a superposition of different histories of particle creation and annihilation? Are waves, waves in a field, waves in a single-particle wavefunction, or what?

Those are all interesting questions that I would like to understand better, but my point is that there should be a realistic interpretation that clearly delineates things we observe in experiments versus things we know from the QM math. And until we definitively know otherwise does not go beyond explanations that involve causation, determinism, and classic logic.

Take the term "quantum field" you used in your question. Is a quantum field something we can directly measure, or is it just part of a mathematical framework to make statistical predictions in the real world? I would like to understand this from a realist interpretation.

Exactly how does local preparation create the nonlocal behavior?

I am familiar with EPR experiment which I think typically uses SPDC to locally prepare photons, but I would ask you or anyone else are there clear examples of non-local behavior without local preparation? And I mean truly non-local in the Bell sense, and not something that can be influenced non-locally via a propagating force.

I would say QM we actually take what we see in experiments more seriously than we do in classical mechanics.

What we really "see" is this: For a given preparation procedure, the prepared system(black box) responds to pertubation in certain ways. This is the only way of asking what is inside the black box. This is more faithful to what we actually know and see.

This distinction is IMO the beauty of QM and if you start to question the action also of the observer, this distinction I think becomes paramount.

So i certainly do not miss the classical logic.

/Fredrik

Maybe I will arrive at your perspective some day as I learn more about QM, but until I can understand something that truly can't be explained in some way by classical logic, I can't abandon it and I don't see why anyone should other than when it is useful to not think this way as an approach to calculations. That said I am always looking for good arguments to convince me otherwise.

 

[Demystifier]

Is there a reciprocal behavior in this interpretation where particles also influence the evolution of the wave function?

No. If there was, it would contradict the Schrodinger equation.

 

[Fra]

until I can understand something that truly can't be explained in some way by classical logic, I can't abandon it and I don't see why anyone should other than when it is useful to not think this way as an approach to calculations. That said I am always looking for good arguments to convince me otherwise.

This is a natural objection, i could have said the same in the past. My insights has been reluctantly forced upon as I could not see an abduction to satisfactory explanation in terms of classical mechanical causality unless one accept other IMO unacceptable pathologies. After digesting this, I have now come to see that the nature of causality and nature of law, that is implicit in classical mechanics is deeply flawed from the perspective of inference of a real agent. That it still works in classical mechanics is due to that the population of agents/obsevers/subsystem SHARE common knowledge, whose uncertainty can be treated as ignorance. It's the general cases where this common classical reality is not there, that is the true "quantum domain", and adbuction to best explanation is a new kind of causality. It's this insight that for me at least suggest that a new paradigm for physical law is required as well. QM as it stands is just the first step towards a better understanding. I do not like QM as it stands today either, but I want to take it in an even more extrem direction, not go back to "pool-table causality".

/Fredrik

 

[kurt101]

This is a natural objection, i could have said the same in the past. My insights has been reluctantly forced upon as I could not see an abduction to satisfactory explanation in terms of classical mechanical causality unless one accept other IMO unacceptable pathologies. After digesting this, I have now come to see that the nature of causality and nature of law, that is implicit in classical mechanics is deeply flawed from the perspective of inference of a real agent. That it still works in classical mechanics is due to that the population of agents/obsevers/subsystem SHARE common knowledge, whose uncertainty can be treated as ignorance. It's the general cases where this common classical reality is not there, that is the true "quantum domain", and adbuction to best explanation is a new kind of causality. It's this insight that for me at least suggest that a new paradigm for physical law is required as well. QM as it stands is just the first step towards a better understanding. I do not like QM as it stands today either, but I want to take it in an even more extrem direction, not go back to "pool-table causality".

/Fredrik

Your statement sounds nice, but what are the strongest reasons or experiments that suggest classical reasoning is wrong? Usually what I find is some physicists claim an experiment is weird in the sense that it can't be logically reasoned about and then another physicist comes along and debunks the weirdness.

The electromagnetic and gravitational forces that we directly measure from particles, the forces that we directly observe affecting the positions of particles, act as waves and you are telling me I am not supposed to think that at a quantum level the real wave like properties we observe do not exist even though the quantum mechanical math is all about waves and positions of particles?

On the face of it, it sounds absurd, that we are making non-sensical inferences about how the real world works from a mathematical framework used to calculate statistics. Even though that framework has all sorts of issues and limitations about how it can be used and the ingredients you are allowed to put in it.

As far as I can tell, the only thing we observe that someone might classify as non-classical is entanglement (in the Bell non-local sense), but I keep being told entanglement requires local preparation and can't be exploited to communicate signals, which indicates to me that it is fundamentally local in its interactions with the real world. So I don't see this as violating causality, determinism, logic or classical reasoning.

 

[Fra]

Your statement sounds nice, but what are the strongest reasons or experiments that suggest classical reasoning is wrong?

All the versions of Bell-experiment is hard to explain in terms of classical physics. You can try, and see if you can do better than other before you. A key input to the hidden variable explanation that leads to bell inequality is not just the hidden variables themselves, but the assumption of what causal role these play in physical interaction. And it's in there i find the pathology. "Hidden variables" that have a different causal role may still be possible. People has given this much thought, and people also come to different conclusions or opinon of what is wrong, and some try to save the original classical mechanisms still.

On the face of it, it sounds absurd, that we are making non-sensical inferences about how the real world works from a mathematical framework used to calculate statistics.

From my own perspective a "sensible inference" by an observer is one made from things the observer can distinguish and count/measure and encode, but in the general case all observers doesn't have a one-2-one mapping of what is observable and countable; unless the observable events and counts are encoded in the common classical environment. Ideally the mathematical framework should be built from and respect this order, here QM/QFT is IMO not fully satisfactory as it stands, even though QM is an improvement over classical physics, it is not perfect. But I don't see that the answer is to go back to where we came from, my critique is different.

/Fredrik

 

[kurt101]

All the versions of Bell-experiment is hard to explain in terms of classical physics.

I have mostly focused on understanding simple entanglement with photons, primarily because these are the ones most often shown to demonstrate non-locality. I have found experiments on more complicated entangled systems, perhaps as I understand these better I will come to a different perspective.

 

[mitchell porter]

Those are all interesting questions that I would like to understand better, but my point is that there should be a realistic interpretation that clearly delineates things we observe in experiments versus things we know from the QM math. And until we definitively know otherwise does not go beyond explanations that involve causation, determinism, and classic logic.

I don't know if I understand you correctly. You seem to be saying: we must believe in certain things - determinism, particles, waves - unless we can actually disprove them. OK, the meaning of that seems clear. But what's unclear, is whether you also want us to have a detailed mechanistic explanation of quantum phenomena in terms of these axiomatic beliefs.

Consider Bohmian mechanics. If Bohmian mechanics can account for something quantum, it can do so in a completely exact and explicit way, because Bohmian mechanics is an actual physical theory complete with equations of motion. It's not just ontologically explicit - it's nonlocally deterministic, it has a universal time, there's a definite classical state at all times - it's also mathematically explicit - the equations of motion are the Schrodinger equation and the wavefunction gradient equation.

You're not giving us any new equations. Nor have you given us any new "picture" of quantum phenomena. You're just proposing certain things as axiomatic, unless they can definitely be proven wrong. Well, we have had many decades of people trying to explain quantum mechanics from various starting points. Are you saying that your starting point definitely works, probably works, might work? Or just that we can, should, must make those particular assumptions?

Some of your axioms seem potentially harmless - I am thinking of existence of particles and waves - though it's the details which are all-important. But other axioms cause well-known problems. How are you going to explain quantum phenomena deterministically? How are you going to deal with Bell's theorem while insisting on local determinism?

It is precisely because the restoration of classical physical paradigms has been so difficult, that the positivism of the Copenhagen interpretation has instead had lasting power. What is observed is definitely real; quantum mechanics tells us how to predict it; as for what goes on between observations, that's metaphysics...

I can understand the desire for more, but the merit of this position is, that it really tells us what we do know and what we don't know. So I prefer to make that my starting point.

 

[CoolMint]

It never really made sense that all things happening now had their origin and deterministic causes in the far past, all the way to the infinitely low entropy of Big Bang. Which itself requires another explanation and seems to require a designer or creator.
As far as QT is concerned, the BB seems to be the limit to knowledge even if a quantum computer could run all the particles of a pencil 13.7 billion years back.

Determinism, causality and classicality are emergent properties in most interpretations, even in the standard interpretation and the Big Bang is the limit to what can be known about the causes of the events unfolding now in 2022.
Due to the huge number of degrees of freedom, we cannot control most of reality and seem to be mostly observers of events.
My question is - do many quantum physicists believe in determinism as an explanation of what is happening in their daily lives? Or shrug everything off as 'emergence'.
Both stances seem absurd but then again we never really had a solid footing in deep knowledge as a number of ancient philosophers tried to warn.

 

[Fra]

My question is - do many quantum physicists believe in determinism as an explanation of what is happening in their daily lives? Or shrug everything off as 'emergence'.

I don't even ask these questions?? The only relevant question is more what actions I should take given my incomplete information - for the benefit of my future state and survival. So I consider life a game, where we place bets. A good bets improves my predictive fitness, bad bets reduces my fitness and fatal bets puts me out of the game. To the extent I ponder about patterns in the environment, its just in order that it helps me control my own environment.

I see physical interactions in the same way. An atom interacting with the environment is probably like a game. In some sense and atom is "stable" when its action strategy is good. It's in this sense I think I hopefully think we can understand the relation between interactions and the spectrum of elementary particles.

Determinism is not helpful here, but emergence neees to be explained. We can¨t just say "emergence" and think we have an explanation. But if we can explain the self-organisation taking place and is responsible for emergence, then we may have some progress.

/Fredrik

 

[.Scott]

Summary: Why is there not a standard quantum mechanics interpretation that represents the most straight forward interpretation of what we see in experiments?

If it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.

How familiar are you with the Bell Inequality? Sometimes QM doesn't look like any duck at all.
The "standard interpretation" is the math. Everything else is the many attempts to squeeze it into the vernacular.

 

[kurt101]

I don't know if I understand you correctly. You seem to be saying: we must believe in certain things - determinism, particles, waves - unless we can actually disprove them. OK, the meaning of that seems clear.

I mostly agree with this characterization, but I would use the words "we should have an interpretation" instead of "we must believe in certain things".

But what's unclear, is whether you also want us to have a detailed mechanistic explanation of quantum phenomena in terms of these axiomatic beliefs.

I think it provides motivation that may lead us to a detailed mechanistic explanation.

Consider Bohmian mechanics.

It does not fit with what we observe.

Some of your axioms seem potentially harmless - I am thinking of existence of particles and waves - though it's the details which are all-important. But other axioms cause well-known problems. How are you going to explain quantum phenomena deterministically? How are you going to deal with Bell's theorem while insisting on local determinism?

If the non-locality is locally prepared between particles and you can not use it to pass signals faster than light then those basic things we know go a long ways to describing how it works.

It is precisely because the restoration of classical physical paradigms has been so difficult, that the positivism of the Copenhagen interpretation has instead had lasting power. What is observed is definitely real; quantum mechanics tells us how to predict it; as for what goes on between observations, that's metaphysics...

I can understand the desire for more, but the merit of this position is, that it really tells us what we do know and what we don't know. So I prefer to make that my starting point.

I think that is a fine interpretation for some, but for others like myself, I want an interpretation that explains what is actually happening.

You're not giving us any new equations. Nor have you given us any new "picture" of quantum phenomena.

Yes, I agree, I am not really giving any new equations or any new "picture" of quantum phenomena. When I say waves are real, particles are real, waves originate from particles, and non-local entanglement is locally prepared, I am just stating the obvious observations from a realist perspective. It is like the fable "The Emperor has no clothes" where the naïve child states the obvious.

You're just proposing certain things as axiomatic, unless they can definitely be proven wrong.

With strong evidence I am always ready to accept that the realist view is wrong, but I don't see strong evidence. Instead I see a lot of handwaving or strawman arguments whenever it is said that the universe does not follow classical logic.

Well, we have had many decades of people trying to explain quantum mechanics from various starting points. Are you saying that your starting point definitely works, probably works, might work? Or just that we can, should, must make those particular assumptions?

Here is a two part argument that I believe supports my view:

PART 1:
Consider the HBT (Hanbury Brown and Twiss) effect. In this phenomena, photons from independent incoherent light sources measured by two close together detectors are found to have a much higher level of coincidence (photons appear to bunch) than you would expect if you were to treat the photons like classical bullets. As you move the detectors apart the photon bunching effect goes away. This talk from Alain Aspect does a good job explaining this phenomena:


This experiment can be explained using classical and quantum mechanical math.

In the classical solution, you treat the light as waves instead of particles. An equation can be constructed involving waves that show the correlated intensities between the two detectors depend on the distance between the detectors and this equation can be used to correctly model the HBT phenomena.

A higher level classical explanation is if the detectors are thought of as taking snapshot photos of random intensity patterns (see this part of the video), as you move the detectors closer together the photon intensity patterns will become more and more similar and if you could actually move them on top of each other they would be the same.

n the quantum mechanical solution you treat the photons as coherent sources, even though they are not, and you consider all paths the two independent photons can take and the interference between paths is what accounts for the photon bunching phenomena. There is no non-local entanglement involved in this solution because there is no local preparation of the two independent photon sources.

In the HBT experiment both the quantum mechanical and classical approach rely on wave interference and the quantum mechanical solution does not involve non-local entanglement.

Conclusion
When an experiment does not involve local particle considerations such as non-local entanglement through local preparation, the classical and quantum approaches are similar if not the same (see part 2 argument).

PART 2:

The closest thing we have to a universal equation is the principle of least action. This video by Sabine describes it well:


Sabine uses an example of light refracting as a motivation for this principle and says "its seems like the light needs to know something about the future" (in order to know which direction to go).

Sabine explains the use of the least action principle in classical physics:
"The action is the integral over the kinetic energy minus potential energy. But there is also an action that gives you electrodynamics. And there is an action that gives you general relativity."

Sabine explains the equations using least action give the same result as the Euler-Lagrange equations:
"And yes, the principle of least action really uses an integral into the future. How do we explain that? Well it turns out that there is another way to express the principle of least action. One can mathematically show that the path which minimizes the action is that path which fulfills a set of differential equations which are called the Euler-Lagrange Equations. For example, the Euler Lagrange Equations of the rock example just give you Newton's second law. The Euler Lagrange Equations for electrodynamics are Maxwell's equations, the Euler Lagrange Equations for General Relativity are Einstein's field equations."

So all of our classical forces (i.e. gravity and electromagnetism) that we directly observe, that involve particles, that involve waves coming from those particles, can be formulated using the principle of least action.

Furthermore the equation of least action is used at the heart of our best quantum mechanical theory QFT and is often called the Feynman path integral.

Sabine in reference to applying the Feynman path integral: "But to do the calculation you don't need to know what happens in the future, because the particle goes to all points anyway. Except, hmm, it doesn't. In reality it goes to only one point. So maybe the reason we need the measurement postulate is that we don't take this dependence on the future which we have in the path integral seriously enough"

I agree, let's take this dependence on the future more seriously. How does this happen in the real universe, the one where we observe particles and waves coming from those particles?

In the book "QED: The Strange Theory of Light and Matter" Richard Feynman discussing how light seems to move: "So light doesn’t really travel only in a straight line; it “smells” the neighboring paths around it"

So what seems more likely:
That the equation of least action allows a particle to determine its path by magically sniffing out its future?
Or the simpler explanation, that a particle does actually sniff out its path in the sense that it acts on the combined wave amplitudes received from all the particle waves in the universe and acts in such a way to minimize amplitude and adhere to the principles of least action.

Conclusion: Our best equations for both quantum mechanics and gravity share the equation of least action which acts as if the waves from particles are real.

 

[PeterDonis]

It does not fit with what we observe.

This is wrong: Bohmian Mechanics makes the same predictions for all experimental results as all other interpretations of QM. So it fits fine with what we observe.

 

[kurt101]

This is wrong: Bohmian Mechanics makes the same predictions for all experimental results as all other interpretations of QM. So it fits fine with what we observe.

With gravity and electromagnetism we observe waves from particles, but in Bohmian Mechanics the particles move according to the guiding equation which we don't observe. And there is the issue of Bohmian Mechanics not being relativistic, though I realize there are efforts to fix this such as with this version from @Demystifier . But I don't think @Demystifier has answers for where the waves come from? Which I find interesting because in another thread that he started on ontology I thought he was saying these are the types of questions we should be asking. At least that is what I took from it.

And here is another video by Sabine that gives support for reality.


"Hyperion is a headache for those who think that quantum mechanics is really the way nature works. Because quantum mechanics predicts Hyperion's chaotic motion shouldn't last longer than about 20 years. But it has lasted much longer. So, quantum mechanics has been falsified."

"But after the Ehrenfest time, quantum mechanics gives you a prediction that just doesn't agree with what we observe. It would predict that the orientations of Hyperion don't tumble around but instead blur out until they're so blurred you wouldn't notice any tumbling. Basically the chaos gets washed away in quantum uncertainty."

And Sabine gives her explanation for this: "This means, Hyperion is in some sense constantly being "detected" by all those small particles. And the update of the wave-function is indeed a non-linear process. This neatly resolves the problem: Hyperion correctly tumbles around on its orbit chaotically. Hurray. But here's the thing. This only works if the collapse of the wave-function is a physical process. Because you have to actually change something about that blurry quantum state of the moon for it to agree with observations."

"But the example with chaotic motion of Hyperion tells us that we need the measurement collapse to actually be a physical process. Without it, quantum mechanics just doesn't correctly describe our observations."

 

[PeterDonis]

With gravity and electromagnetism we observe waves from particles

No, we don't. We observe phenomena that we can interpret as waves, or phenomena that we can interpret as particles, or phenomena that we can interpret as "waves from particles" (whatever that means--it seems to be your personal phrase, not a standard technical term in QM). But the actual predictions of the theories do not depend on those interpretations, any more than the predictions of QM depend on which interpretation of QM (Bohmian or otherwise) we choose.

in Bohmian Mechanics the particles move according to the guiding equation which we don't observe.

We don't observe any equation directly. We can only observe the results of measurements and compare them with the predictions we derive from equations.

here is another video by Sabine

These videos are not valid references. They are not textbooks or peer-reviewed papers. They are Sabine's opinions. You might agree with those opinions, but that doesn't make anyone's opinions the same as actual physics.

 

[kurt101]

No, we don't. We observe phenomena that we can interpret as waves, or phenomena that we can interpret as particles,

It seems a little excessive to have to put the word phenomena in front of whenever I use the word particle or wave. I have given plenty of context and answered questions about what I mean by a particle and wave.

or phenomena that we can interpret as "waves from particles" (whatever that means--it seems to be your personal phrase, not a standard technical term in QM).

It seems like a pretty safe statement to say that the wave phenomena come from the particle phenomena. In the real world we don't observe wave phenomena coming from random sources or put another we don't observe wave phenomena that don't come from particle phenomena.

 

[PeterDonis]

It seems a little excessive to have to put the word phenomena in front of whenever I use the word particle or wave.

Not if you're going to make claims about "realism". The whole point is that "particle" and "wave" are not what we directly observe. They are theoretical models. And if you're not going to be very careful about distinguishing the two, this thread is pointless, since distinguishing those two things is vital to the thread topic.

It seems like a pretty safe statement to say that the wave phenomena come from the particle phenomena.

Why?

In the real world we don't observe wave phenomena coming from random sources

Yes, but we don't observe them coming from "particle phenomena" either. If I make waves in a tank of water, what "particle phenomena" are those waves coming from? Of course we know theoretically that the water is made of molecules, and so is the thing I'm using to make the waves in it, but that's a theoretical model, not a direct observation.

Similarly, if I shine a laser at a double slit and see an interference pattern, theoretically I can model the light as particles (photons), but I don't directly observe particles.

I think you are not being careful enough about distinguishing what we actually observe from theoretical models. And, as I remarked above, doing that carefully and correctly is vital to this topic.

 

[mitchell porter]

I think that is a fine interpretation for some, but for others like myself, I want an interpretation that explains what is actually happening.

I'd like to ask some more basic questions: Are you truly fluent in classical physics? Do you understand the calculus in Newton's law of gravitation, or the differential equations in Maxwell's theory of the electromagnetic field?

The point is that such theories are the paradigm in physics, for what your kind of explanation looks like. When physicists hear your remarks, they think that you are proposing to explain quantum physics with a new pre-quantum kind of theory.

I just think we're all a bit confused as to what you're proposing. Are you proposing to derive the formulas of quantum mechanics, from a new theory of a classical kind? Or are you proposing e.g. that there is a deterministic "way to think about" quantum mechanics, that doesn't require any new equations?

 

[Demystifier]

And Sabine gives her explanation for this: "This means, Hyperion is in some sense constantly being "detected" by all those small particles. And the update of the wave-function is indeed a non-linear process. This neatly resolves the problem: Hyperion correctly tumbles around on its orbit chaotically. Hurray. But here's the thing. This only works if the collapse of the wave-function is a physical process. Because you have to actually change something about that blurry quantum state of the moon for it to agree with observations."

In Bohmian mechanics (BM), particle trajectories obey non-linear equations. The collapse in BM is not exactly a physical process, but it corresponds to something physical (particles entering one wave function branch and not the other branches).

 

[kurt101]

Not if you're going to make claims about "realism". The whole point is that "particle" and "wave" are not what we directly observe. They are theoretical models. And if you're not going to be very careful about distinguishing the two, this thread is pointless, since distinguishing those two things is vital to the thread topic.

I won't use "direct" with observe anymore. My intent of using the word "direct" was to distinguish observations such as detecting single particles (like with a photomultiplier) from phenomena in the quantum model like a photon taking every path. I would characterize that we observe the statistics of the quantum model, but not the photon taking every path.

Why?

Just looking at the force of gravity: We observe this force between particles. The Einstein model says the force propagates at the speed of light in all directions like waves. The Newtonian approximation follows the inverse square law like waves. We observe the evidence of gravitational waves such as with LIGO and Virgo. Unless you deny that particles move in some oscillatory fashion or deny the gravitational equations, I don't see how you can think they don't generate gravitational waves.

I'd like to ask some more basic questions: Are you truly fluent in classical physics? Do you understand the calculus in Newton's law of gravitation, or the differential equations in Maxwell's theory of the electromagnetic field?

I completed all of the physics and calculus at the engineering level in college. I don't use it or encounter it in my work, only in self learning activities. As far as math goes, I understand the basics (limits, derivatives, integrals), but I often need review, and I would not say I am fluent or good with it.

I just think we're all a bit confused as to what you're proposing. Are you proposing to derive the formulas of quantum mechanics, from a new theory of a classical kind? Or are you proposing e.g. that there is a deterministic "way to think about" quantum mechanics, that doesn't require any new equations?

It seems to me as if there is a reasonable explanation using classical logic for all of the phenomena we observe and for all of the mathematical models that fit those observations.

As a starting point, just take your basic delayed choice or quantum eraser type experiment. It is not weird at all if you assume the particle actually does take one path, but a wave aspect of the particle takes all possible paths.

Or take Bell non-locality. You can still use classical logic to explain the result if you assume some kind of shared state until interaction between the entangled particles. It may not be fully classical in the non-local sense, but it still has the characteristics of being causal and deterministic.

As I learn QM, it is a reoccurring pattern, the text will suggest something is weird and ignore the logical classical explanation.

I think the simple classical logic explanation is very likely compatible with quantum mechanics and as I have already mentioned, I don't think you have to add much (if anything) as far as principles go for this explanation to consistently work.

On the other hand I do understand that the burden of proof would be to come up with a mathematical model, but until someone does, or until there is a definitive proof against classical logic, I think there should be at least the interpretation as a place holder, so we don't teach students to automatically disregard classical logic.

 

[PeterDonis]

Just looking at the force of gravity: We observe this force between particles.

No, we don't. Not in GR. See below.

The Einstein model says the force propagates at the speed of light in all directions like waves.

It says nothing of the kind. GR says that gravity is not a force at all. It says, heuristically, that changes in spacetime curvature propagate at the speed of light as gravitational waves. But even that heuristic statement has caveats.

 

[zonde]

Is there a reciprocal behavior in this interpretation where particles also influence the evolution of the wave function?

No. If there was, it would contradict the Schrodinger equation.

Well, the answer is of course correct but it leaves out important part: how comes that evolution of the wave function is not influenced?
Because interaction of say silver atom with SG apparatus at arbitrary angle can not be predetermined from atom's trajectory. Otherwise we would have to conclude that Bell inequality should not be violated.
So SG apparatus is influencing atom's trajectory and yet evolution of wave function is not affected. For that Bohmian mechanics relies on quantum equilibrium hypothesis.
So while particle can not influence evolution of wave function it can influence it's entangled partner in such a way that evolution of wave function remains unaffected. And we can imagine that there is some
physical phenomena that is represented in Bohmian mechanics by quantum equilibrium hypothesis which does that i.e. quantum equilibrium is hard physical rule rather than soft emergent rule.

 

[DrChinese]

[Premises] By this, I mean:
1. Particles are real and localized.
2. Waves are real and have the properties of waves (i.e. they spread out and interfere)
3. Entanglement is a non-local behavior between particles that is created through local preparation.

There is no practical or theoretical requirement that entanglement can only be created through local preparation (such as a typical PDC setup).

a. You can perform a normal Bell test on photon pairs that have never existed in a common light cone (thus making them prepared nonlocally). This is done using entanglement swapping, which is nonlocal. In swapping, one photon from an entangled pair interacts with a photon from a different entangled pair (2 quantum systems/pairs of 2 photons each, 4 photons total). The remaining partner photons in the 2 pairs become entangled, regardless of distance, and are now a normal EPR pair ready for a normal Bell test. Yet they didn't interact at all.

b. And in fact you can even do this with *systems* of particle pairs (each with spatial extent) which themselves have never existed in a common light cone, and never interact in any manner whatsoever. This can be done with entanglement swapping using repeaters. Such repeaters involve 3 or more independently created EPR pairs. The final result is an entangled pair in which the 2 photons have never interacted; moreover, the systems they were originally members of have also never interacted.

c. And in fact you can create EPR pairs for Bell tests AFTER the Bell test is performed. That is: you witness perfect correlations but perform the entanglement swap *afterwards*. Obviously, that makes the EPR pair nonlocally prepared.So this answers your original question. At least one of your premises is falsified, so your conclusion is not justified.

 

[Maarten Havinga]

What if in 3. you replace 'particles' with quanta or 'quantum information'?

 

[kurt101]

There is no practical or theoretical requirement that entanglement can only be created through local preparation (such as a typical PDC setup).

I have never heard of a counter example where bell violating entanglement was not prepared through local preparation.

a. You can perform a normal Bell test on photon pairs that have never existed in a common light cone (thus making them prepared nonlocally). This is done using entanglement swapping, which is nonlocal. In swapping, one photon from an entangled pair interacts with a photon from a different entangled pair (2 quantum systems/pairs of 2 photons each, 4 photons total). The remaining partner photons in the 2 pairs become entangled, regardless of distance, and are now a normal EPR pair ready for a normal Bell test. Yet they didn't interact at all.

If you have photon pair A and B that are entangled through SPDC and photon pair C and D that are entangled through SPDC and you have B and C interact locally, then I would say A and D are not entangled prior to B and C interacting locally and are not entangled after B and C interacted locally. If you want to say A and D are entangled right when B and C interact, that is fine with me, but using a realistic description, I would say that the local interaction at B and C drops the previous entanglement B had with A and C had with D and creates a new entanglement between B and C.

 

[DrChinese]

1. I have never heard of a counter example where bell violating entanglement was not prepared through local preparation.2. If you have photon pair A and B that are entangled through SPDC and photon pair C and D that are entangled through SPDC and you have B and C interact locally, then I would say A and D are not entangled prior to B and C interacting locally and are not entangled after B and C interacted locally. If you want to say A and D are entangled right when B and C interact, that is fine with me, but using a realistic description, I would say that the local interaction at B and C drops the previous entanglement B had with A and C had with D and creates a new entanglement between B and C.

1. For example:

https://arxiv.org/abs/0911.1314
Theory: Characterizing the nonlocal correlations of particles that never interacted

https://arxiv.org/abs/0809.3991
Experiment: High-fidelity entanglement swapping with fully independent sources

https://arxiv.org/abs/1606.07503
Experiment: Entanglement Swapping with Independent Sources over an Optical Fibre Network

[Edited to include experimental sources in addition to theoretical treatment; see post #37 by PeterDonis.]2. A and D become entangled. Does that entanglement occur before or after B & C interact? No one can say, as the timing of the B/C interaction does not change the outcome. Earlier or later, makes no observable difference.

However, that is not relevant to your premise 3. In that, you say A & D must be entangled by a local interaction. They have no interaction at all. The are never even present in a common light cone, as they are created by independent SPDC sources that are "distant" to each other. So how can there be a local realistic description of A & D becoming entangled so that there spins are 100% correlated when measured at any chosen angle?

Your premise requires their hidden variables to be set at their creation - and they will NOT be entangled unless something else occurs after they are on their merry way to the detectors. In a local realistic world, they are totally immune from such later influence (if they are sufficiently far apart).

 

[PeterDonis]

For example

This is not an experimental paper but a theoretical one. I believe you have referenced experimental papers on entanglement swapping in other threads; such a paper would be a good reference here.

 

[kurt101]

2. A and D become entangled. Does that entanglement occur before or after B & C interact? No one can say, as the timing of the B/C interaction does not change the outcome. Earlier or later, makes no observable difference.

Are you saying that if you measure both A and D before B and C interact that you will still see the Bell violation between A and D?

 

[Maarten Havinga]

Are you saying that if you measure both A and D before B and C interact that you will still see the Bell violation between A and D?

Although this surprises you kurt101, it does not pose a threat at all to your realistic interpretation if viewed from General Relativity. Let me explain why:

In general relativity, a localisation is a point in spacetime. That is, space has a vectorvalue and time has a value. This means that for a phenomenon (entanglement) to be NON-local, that: it can affect a distant particle instantaneously, not only distant in space, but also distant in time!

Of course this only happens in the right circumstances, such as an experimental setup, where it is guaranteed that the two particles become entangled by quantum physics. That is, therefore, ALSO true in cases where entanglement is ensured but in entirely differing timeframes for two particles.

Quantum physics is, though difficult, indeed interpretable in a realist view.

 

[PeterDonis]

In general relativity, a localisation is a point in spacetime. That is, space has a vectorvalue and time has a value. This means that for a phenomenon (entanglement) to be NON-local, that: it can affect a distant particle instantaneously, not only distant in space, but also distant in time!

Where are you getting this from? Can you give a reference? Please bear in mind the PF rules regarding personal speculation.

 

[Maarten Havinga]

If you don't like the idea, think differently. I just thought it was logical in the setting of this discussion.

I'd say for a reference, my previous post might be the original "academic" source. It's a generalization of the concept of nonlocality.

 

[PeterDonis]

I'd say for a reference, my previous post might be the original "academic" source.

That's not how things work here. PF is not for developing personal research. It's for discussing and helping people to understand mainstream science. That's why you need an actual reference--a textbook or peer-reviewed paper. "My previous post" obviously is neither of those.

 

[Maarten Havinga]

OK!

 

[lodbrok]

1. For example:

https://arxiv.org/abs/0911.1314
Theory: Characterizing the nonlocal correlations of particles that never interacted

https://arxiv.org/abs/0809.3991
Experiment: High-fidelity entanglement swapping with fully independent sources

https://arxiv.org/abs/1606.07503
Experiment: Entanglement Swapping with Independent Sources over an Optical Fibre Network

[Edited to include experimental sources in addition to theoretical treatment; see post #37 by PeterDonis.]2. A and D become entangled. Does that entanglement occur before or after B & C interact? No one can say, as the timing of the B/C interaction does not change the outcome. Earlier or later, makes no observable difference.

However, that is not relevant to your premise 3. In that, you say A & D must be entangled by a local interaction. They have no interaction at all. The are never even present in a common light cone, as they are created by independent SPDC sources that are "distant" to each other. So how can there be a local realistic description of A & D becoming entangled so that there spins are 100% correlated when measured at any chosen angle?

Your premise requires their hidden variables to be set at their creation - and they will NOT be entangled unless something else occurs after they are on their merry way to the detectors. In a local realistic world, they are totally immune from such later influence (if they are sufficiently far apart).

We have to be very careful in interpreting those types of results in this way. Firstly, these experiments (eg, https://www.nature.com/articles/srep09333) do not measure just 4 photons (A, B, C, D). They measure 4 streams where streams A & B (C & D) consist of entangled pairs. Secondly, the interaction between B & C is not simply an interaction between one photon from the B stream and one photon from the C stream. Rather it is a coincidence experiment between the two streams. A coincidence counting experiment is akin to a filtration process, they are essentially selecting a subset of the streams based on the result of the interaction.

Therefore, the experiment did not demonstrate what is often claimed. The B and C streams were used to select a subset of the A and D streams. It is this coincidence counting/filtration process that transfers the entanglement.

Imagine the photons being black/white beads, and the AB (or CD) is always alternate colors but with no correlation between the AB stream of beads and the CD stream of beads. We could do a coincidence experiment in which we compare the B & C beads. If they are the same we select the iteration of (A, B, C, D) and if they are not the same we discard the iteration. We are only ever comparing B & C, as A & D could be far away from the interacting point. At the end of this experiment, if we look only at the subset of beads which were selected in the experiment, A & D will be perfectly correlated!

The keys to understanding it is:
1. Recognize that the experiment deals with streams of particles not single particles
2. Recognize that coincidence counting is involved
3. Recognize that the A & D particles which are entangled are only a subset of the original streams
4. Recognize that the reduction of the original A & D streams to the subset, involved the use of information from the interaction between B & C.

 

[DrChinese]

We have to be very careful in interpreting those types of results in this way. Firstly, these experiments (eg, https://www.nature.com/articles/srep09333) do not measure just 4 photons (A, B, C, D). They measure 4 streams where streams A & B (C & D) consist of entangled pairs. Secondly, the interaction between B & C is not simply an interaction between one photon from the B stream and one photon from the C stream. Rather it is a coincidence experiment between the two streams. A coincidence counting experiment is akin to a filtration process, they are essentially selecting a subset of the streams based on the result of the interaction.

Therefore, the experiment did not demonstrate what is often claimed. The B and C streams were used to select a subset of the A and D streams. It is this coincidence counting/filtration process that transfers the entanglement.

Imagine the photons being black/white beads, and the AB (or CD) is always alternate colors but with no correlation between the AB stream of beads and the CD stream of beads. We could do a coincidence experiment in which we compare the B & C beads. If they are the same we select the iteration of (A, B, C, D) and if they are not the same we discard the iteration. We are only ever comparing B & C, as A & D could be far away from the interacting point. At the end of this experiment, if we look only at the subset of beads which were selected in the experiment, A & D will be perfectly correlated!

4. Recognize that the reduction of the original A & D streams to the subset, involved the use of information from the interaction between B & C.

I agree that a system consisting of A & B interacts with a system consisting of C & D, but that's where we part ways.

There is no "coincidence" filtration occurring as you describe. Yes, there are coincidence counts occurring, but that is to identify if and when entanglement occurs and which kind. It should be obvious that when the A & D pair is entangled, you have so-called perfect correlations in polarization tests. If I set both measuring apparati to 282 degrees, you always get perfect correlation (or anti-correlation as the case may be). That absolutely does not happen by "coincidence" as you say. That's why your analogy with white/black beads is invalid; you'd need hundreds of colors of beads so that the ones match up for when the settings are the same. In other words: there are no more than 4 combinations of B & C pairs, but there are hundreds of possible A & D pairs.

You can also have repeaters, where you have pair A & B, pair C & D, and pair E & F: A & F can be fully entangled even though the system of A & B never interacts with the system of E & F. And in fact the choices to entangle them can be performed both before AND after A & F are detected (i.e. within the same run, by choice of teleportation sequence).

You would be hard-pressed to support your idea by any reputable source I am aware; if you have a representative quote from a solid scientific source about swapping, I'd like to see something that describes it as you do. Because Quantum teleportation is not an "accident" that results from predetermined local hidden variables, any more than that is a viable explanation for a standard Bell test. Teleportation defies classical norms of locality and causality, and should be considered another nail in the coffin for one or both of those concepts. If you needed (more) experimental proof of the existence of (quantum) nonlocal action, this is it.

 

[kurt101]

I agree that a system consisting of A & B interacts with a system consisting of C & D, but that's where we part ways.

There is no "coincidence" filtration occurring as you describe. Yes, there are coincidence counts occurring, but that is to identify if and when entanglement occurs and which kind. It should be obvious that when the A & D pair is entangled, you have so-called perfect correlations in polarization tests. If I set both measuring apparati to 282 degrees, you always get perfect correlation (or anti-correlation as the case may be). That absolutely does not happen by "coincidence" as you say. That's why your analogy with white/black beads is invalid; you'd need hundreds of colors of beads so that the ones match up for when the settings are the same. In other words: there are no more than 4 combinations of B & C pairs, but there are hundreds of possible A & D pairs.

I think you are mistaken that this rules out hidden variables and realism.

Lets just take the stranger of the cases where you first measure A & D and then do the entanglement swapping with B & C.

When you measure A, this influences B. When you measure D, this influences C. Then when you do the swapping with B & C, they are already tainted by the respective polarizer you used when measuring A and B.

So you can't make the argument that you are making that because you ran one experiment like this with the same polarizer for A & D that always showed A & D were 100% corelated that this proves when you run the Bell violation version of this experiment using different polarizers that you are comparing apples to apples. The post selection is going to be different between these experiments because of the taint I explained above. So you are comparing apples to oranges and this invalidates your premise that hidden variables can't exist.

 

[PeterDonis]

I think you are mistaken that this rules out hidden variables and realism.

While this might be your personal opinion, it certainly appears to contradict Bell's Theorem. You can't just wave your hands with terms like "hidden variables" and "realism". You need to either reference a specific mathematical model that you think has those properties, and explain what mathematical properties in the model correspond to those terms, and show how that model makes predictions that match experiment--or you need to stop making claims that you cannot support. The fact that you really, really want to find an interpretation of QM that matches the title of this thread does not mean that one exists.

 

[Nullstein]

We have to be very careful in interpreting those types of results in this way. Firstly, these experiments (eg, https://www.nature.com/articles/srep09333) do not measure just 4 photons (A, B, C, D). They measure 4 streams where streams A & B (C & D) consist of entangled pairs. Secondly, the interaction between B & C is not simply an interaction between one photon from the B stream and one photon from the C stream. Rather it is a coincidence experiment between the two streams. A coincidence counting experiment is akin to a filtration process, they are essentially selecting a subset of the streams based on the result of the interaction.

Therefore, the experiment did not demonstrate what is often claimed. The B and C streams were used to select a subset of the A and D streams. It is this coincidence counting/filtration process that transfers the entanglement.

Imagine the photons being black/white beads, and the AB (or CD) is always alternate colors but with no correlation between the AB stream of beads and the CD stream of beads. We could do a coincidence experiment in which we compare the B & C beads. If they are the same we select the iteration of (A, B, C, D) and if they are not the same we discard the iteration. We are only ever comparing B & C, as A & D could be far away from the interacting point. At the end of this experiment, if we look only at the subset of beads which were selected in the experiment, A & D will be perfectly correlated!

The keys to understanding it is:
1. Recognize that the experiment deals with streams of particles not single particles
2. Recognize that coincidence counting is involved
3. Recognize that the A & D particles which are entangled are only a subset of the original streams
4. Recognize that the reduction of the original A & D streams to the subset, involved the use of information from the interaction between B & C.

This is the exactly the correct explanation for this phenomenon and it's well understood. It's just the effect of conditioning on a Collider. I tried to explain this to DrChinese in another thread already without success. His central misunderstanding is to believe that A & D are entangled when really they are in a perfectly uncorrelated product state. Only the conditional subensembles are entangled, but that doesn't entail any causal relationship, because conditioning on a collider generally generates fake correlations. Entanglement swapping indeed adds nothing new to the mystery of entanglement. Those willing to learn can read more about this e.g. in Pearl's famous book titled "Causality."

 

[kurt101]

While this might be your personal opinion, it certainly appears to contradict Bell's Theorem. You can't just wave your hands with terms like "hidden variables" and "realism". You need to either reference a specific mathematical model that you think has those properties, and explain what mathematical properties in the model correspond to those terms, and show how that model makes predictions that match experiment--or you need to stop making claims that you cannot support. The fact that you really, really want to find an interpretation of QM that matches the title of this thread does not mean that one exists.

I never said anything about entanglement swapping experiments not violating Bell's theorem. I believe the experimental results that @DrChinese claims. I am just pointing out the flaw in @DrChinese claim that these experiments says anything meaningful about reality or hidden variables. There is nothing novel about entanglement swapping that he seems to be claiming there is. It is just like the pop science explanations of delay quantum eraser and claims of retro causality.

And this is a perfect example of why we need a realist interpretation. So we are not fooled into thinking crazy ideas that we actually don't observe in the real world.

 

[gentzen]

Only the conditional subensembles are entangled, but that doesn't entail any causal relationship, because conditioning on a collider generally generates fake correlations. Entanglement swapping indeed adds nothing new to the mystery of entanglement. Those willing to learn can read more about this e.g. in Pearl's famous book titled "Causality."

Assuming I am willing to learn, what would I have to read specifically? I assume that Pearl won't explicitly mention entanglement, and even less entanglement swapping (or "fake correlations"). I see that he does mention quantum mechanics from time to time, like in:

Second, the Laplacian conception is more in tune with human intuition. The few esoteric quantum mechanical experiments that conflict with the predictions of the Laplacian conception evoke surprise and disbelief, and they demand that physicists give up deeply entrenched intuitions about locality and causality (Maudlin 1994). Our objective is to preserve, explicate, and satisfy – not destroy – those intuitions.

or:

The ideal of remaining compatible with the teachings of nondeterministic physics seems to be the only viable aspect remaining in the program of probabilistic causation, and this section questions whether maintaining this ideal justifies the sacrifices. ... If the program is an exercise in modern physics, then the word “causality” is nonessential – quantum-level causality follows its own rules and intuitions, and another name (perhaps “qua-sality”) might be more befitting.

Teleportation defies classical norms of locality and causality, and should be considered another nail in the coffin for one or both of those concepts.

I guess I prefer saying that quantum-level locality and causality follows its own rules and intuitions (like Pearl effectively did in the quotes above), instead of talking of a coffin for those concepts.