Exploring Non-Locality in dBB Theory: Insights from EPR and Bell's Inequalities

[inflector]

I too have found Demystifier (Hrvoje Nikolic) to be a really smart guy. His posts on dBB have been instrumental in my personal belief that dBB is the most logical interpretation of QM.

What is Nikolic saying? Is Alice incapable of reading the measurement of her polarizer? I don’t understand?? Or does he mean that that entangled photons exchange superluminal signals, but this is somehow "delayed" to non-superluminal before Alice can actually read the measurement...??

I always envision it being something like a mini wormhole that develops around entangled photons so that they maintain a superluminal connection and that a change in one results in a superluminal change in the other because of this link. I imagine the process of creation of entangled pairs creates a superluminal bridge between the entangled photons and that the process of decoherence destroys this bridge (i.e. there is a mini wormhole collapse).

NOTE: This is just an analogy I use to try to understand what might possibly be going on, NOT a specific proposal or theory.

If this analogy is off base, please let me know as I'm trying to understand dBB at a deeper level over time.

 

[DevilsAvocado]

I too have found Demystifier (Hrvoje Nikolic) to be a really smart guy.

Jeez! Demystifier = Hrvoje Nikolic !?!?
PF never stops to surprise me. What a wonderful place for discussions and learning! (Time to pay some contributions... )

His posts on dBB have been instrumental in my personal belief that dBB is the most logical interpretation of QM.

I haven’t decided what to "believe in". I’m open for anything that "works".

I always envision it being something like a mini wormhole that develops around entangled photons so that they maintain a superluminal connection and that a change in one results in a superluminal change in the other because of this link. I imagine the process of creation of entangled pairs creates a superluminal bridge between the entangled photons and that the process of decoherence destroys this bridge (i.e. there is a mini wormhole collapse).

NOTE: This is just an analogy I use to try to understand what might possibly be going on, NOT a specific proposal or theory.

It this analogy is off base, please let me know as I'm trying to understand dBB at a deeper level over time.

I think I understand what you’re saying. You are making an analogy for the mechanism.

The thing that "bothers" me is maybe not the "mechanism", but the contradictions between QM/SR, microscopic/macroscopic, causality/FTL, etc. Or to put it in short – If we try to talk about these things, it just doesn’t make sense.

If we can trust our senses, this is what happens:

• A laser source produces entangled pairs of photons through a BBO crystal. This is a very ineffective process and only one out of 10⁶ photons converts into two entangled photons, one in a million.
  
  
• There measuring polarizers are separated by 20 km, and it takes light 66 microseconds (10^-6) to travel 20 km (in vacuum) from Alice to Bob.
  
  
• The total time for electronic and optical processes in the path of each photon at the detector is calculated to be approximately 100 nanoseconds (10^-9).
  
  
• The settings of the polarizers at Alice & Bob are independently and randomly chosen every 100 nanosecond (10^-9).

As you can see there is no way for Alice & Bob to exchange information about their random polarizer settings, at the speed of light, as they are outside each other light-cone and there is no time for communication.

Yes, the photon is a microscopic object, and entanglement is only possible in the QM world. But, these "phenomena" create a macroscopic manifestation in the polarizer measurement.

According to Special Relativity, depending on which frame of reference you are, you will see Alice first performing her measurement and thereby decohere the shared wavefunction, and decide what Bob will measure. In another frame of reference you will see the opposite, Bob will decide what Alice will measure. And in a third frame of reference, all will be simultaneous.

This doesn’t make sense, it doesn’t work...

 

[Demystifier]

Afaict, all of Nikolic’s reasoning becomes redundant if we accept Superdeterminism?

If I understand you correctly, you reason in the following way. With superdeterminism, we can avoid nonlocality. So why do we deal with a nonlocal superdeterministic theory, such as Bohmian mechanics?
The answer is simple: Because it is MUCH EASIER to construct a nonlocal (Bohmian) superdeterministic theory that agrees with predictions of QM, than a local one. There are people who struggle with construction of an explicit local superdeterministic theory (like 't Hooft), but it is much more difficult to do it, even if possible in principle. Or to quote from (my) paper:
"R: I'm glad that you asked it, because the most remarkable part of the theory is the fact that it follows from some rather simple and natural principles."

What is Nikolic saying? Is Alice incapable of reading the measurement of her polarizer? I don’t understand?? Or does he mean that that entangled photons exchange superluminal signals, but this is somehow "delayed" to non-superluminal before Alice can actually read the measurement...??

Alice, of course, is capable of reading the measurement of her polarizer, but here the point is that she (as well as Bob) cannot CONTROL the reading of her/his measurement apparatus, in the sense that they cannot make the apparatus to be in the state they WANT. For that reason, they do not interpret nonlocal correlations as true exchange of information.

See, however, a way to (apparently) avoid this problem as well, leading to a possibility to use entanglement for an (apparent) superluminal communication:
http://xxx.lanl.gov/abs/1006.0338

 

[Demystifier]

As you can see there is no way for Alice & Bob to exchange information about their random polarizer settings, at the speed of light, as they are outside each other light-cone and there is no time for communication.

Actually, as I mentioned in the previous post, there is a way to do it:
http://xxx.lanl.gov/abs/1006.0338

 

[Demystifier]

J
According to Special Relativity, depending on which frame of reference you are, you will see Alice first performing her measurement and thereby decohere the shared wavefunction, and decide what Bob will measure. In another frame of reference you will see the opposite, Bob will decide what Alice will measure. And in a third frame of reference, all will be simultaneous.

This doesn’t make sense, it doesn’t work...

See #33, and a quote from the paper:
R: "... However, due to the superluminal influences, 'prior' does not always need to mean 'at an earlier time'."

The following quotes may also help:

On nonrelativistic BM:
No one can understand this theory until he is willing to think of psi as a real objective field rather than just a 'probability amplitude'.
John S. Bell

On relativistic BM:
No one can understand this theory until he is willing to think of x as a position in a 4-dimensional space, rather than just a collection of two conceptually different entities: 3-space position and 'time'.
H.N.

 

[ThomasT]

Because it is MUCH EASIER to construct a nonlocal (Bohmian) superdeterministic theory that agrees with predictions of QM, than a local one.

Well of course it is. Because there's no physical mechanism involved. But do you really want to call this physics??

Nikolic, while you have definitely clarified (demystified) some things for me, I still don't understand your apparent adherence to the notion of physical nonlocality. I mean, it makes no sense to me. Everything we know suggests that our universe is evolving deterministically in accordance with local causal relativistic principles, and yet you cling to this strange, fringe, interpretation of reality. Why?

 

[Demystifier]

Everything we know suggests that our universe is evolving deterministically in accordance with local causal relativistic principles, ...

Except nonlocal EPR correlations, of course.

...and yet you cling to this strange, fringe, interpretation of reality. Why?

Because I don't know any local interpretation of reality compatible with QM. Do you?

 

[ThomasT]

Except nonlocal EPR correlations, of course.

EPR correlations don't suggest nonlocality. They suggest a common cause. In fact, EPR states are quite amenable to a local explanation. If you're talking about the spectrum of results in Bell tests regarding non-EPR states then I suggest that you look at the experiments more closely. The discrepancies between certain LR models and results are minimal. The results suggest an explanation via standard, local, optics.

Because I don't know any local interpretation of reality compatible with QM. Do you?

If you want to call certain formal aspects of qm nonlocal, fine. So do I. But what does it have to do with reality?

Why not just accept the qm formalism as a probabilistic accounting of experimental preparations and leave it at that?

 

[Demystifier]

Why not just accept the qm formalism as a probabilistic accounting of experimental preparations and leave it at that?

Because such interpretation says nothing about REALITY (where, by reality, I mean properties of the system existing even when they are NOT measured).

In other words, I think in the following way.
IF I assume:
1. QM
2. reality (in the sense above)
3. simplicity
THEN I obtain Bohmian mechanics, which implies nonlocality.

 

[Demystifier]

EPR correlations don't suggest nonlocality. They suggest a common cause.

The same facts may suggest (but not prove, of course) different, even mutually exclusive, possibilities. So I would say that EPR correlations suggest (but not prove) BOTH nonlocality and common cause.

 

[Demystifier]

In other words, I think in the following way.
IF I assume:
1. QM
2. reality (in the sense above)
3. simplicity
THEN I obtain Bohmian mechanics, which implies nonlocality.

Let me also briefly explain how the reasoning above refutes some alternatives:

Copenhagen/instrumental QM:
Satisfies 1. and 3., but not 2.

Objective collapse theories:
Satisfies 1. and 2., but not 3.

Many worlds:
Definitely satisfies 2. However, as long as it satisfies 3., it does not satisfy 1. (cannot explain the QM Born rule). Alternatively, if it is modified such that it satisfies 1., it does not longer satisfy 3.

 

[ThomasT]

Why not just accept the qm formalism as a probabilistic accounting of experimental preparations and leave it at that?

Because such interpretation says nothing about REALITY (where, by reality, I mean properties of the system existing even when they are NOT measured).

In other words, I think in the following way.
IF I assume:
1. QM
2. reality (in the sense above)
3. simplicity
THEN I obtain Bohmian mechanics, which implies nonlocality.

First, Demystifier, let me say that I have of course known for quite some time that you are Nikolic the theoretical physicist. I have read your blogs and many of your posts and been enlightened by them. So, I thank you for that. Now, as to my current apparent confusion. Don't take it too seriously. I certainly don't. After all, if the world really is nonlocal and Bohmian mechanics really is correct, it hasn't seemed to matter too much.

Now to your points. Yes of course standard qm formalism says nothing, definitively for certain, about reality. That's the point. Anything you infer from it about an underlying reality is metaphysical speculation. Yes I agree that Bohmian mechanics is a simplistic representation of reality. And, I don't consider it realistic (in the sense above). It's just an easy way to 'account' for entanglement correlations.

On the other hand, certain aspects of Bohm's conceptualization do appeal to me. For example, the idea of particle and guiding wave is more than interesting. It makes conceptual sense to me. And, apparently, it makes conceptual sense to some rather significant physicists as well.

EPR correlations don't suggest nonlocality. They suggest a common cause.

The same facts may suggest (but not prove, of course) different, even mutually exclusive, possibilities. So I would say that EPR correlations suggest (but not prove) BOTH nonlocality and common cause.

I disagree. EPR states suggest, and are easily explainable via, a common cause. Non EPR states, but Bell-states producing entanglement stats, still suggest a common cause. Nonlocality is an ad hoc 'explanation' for what seems to be a local, but not so easily describable, phenomenon.

And, I don't think you've refuted the Copenhagen Interpretation -- at least my understanding of it as the minimalist instrumental/probabilistic interpretation that is the de facto standard of modern physics.

 

[Demystifier]

And, I don't think you've refuted the Copenhagen Interpretation

Of course I didn't, nor it was my intention to do so. I have only explained how the ASSUMPTION of 1. 2. and 3. refutes Copenhagen interpretation (CI) . To really refute CI, I would need to prove that 1. 2. and 3. are NECESSARY (not merely desirable), which of course I can't.

 

[ThomasT]

Ok, thanks Demystifier. I'm not going to intrude on your thread any more. At least not until I have something specific to say about the formalism of dBB. I'm sure you'd rather be talking to physicists and post-grads or whatever. Anyway, thanks for taking the time to respond. It's always a thrill for laymen like me to get to actually talk to physicists.

I'm eating breakfast now. Where are you? Italy? Romania? You're somewhere over there, right? What do you eat for lunch? Sorry for the off topic, but all I can think about now is food.

 

[Demystifier]

EPR states suggest, and are easily explainable via, a common cause.

I strongly disagree that they are EASILY explainable via a common cause (without nonlocality). Namely, to EXPLAIN it, it is not sufficient to say that there is SOME common cause. Instead, an explanation requires a detailed theory which quantitatively predicts the results of all experiments. No such local realistic theory is known, so even if such theory can be constructed, it is NOT EASY to do it.

 

[Demystifier]

Where are you? Italy? Romania? You're somewhere over there, right?

Somewhere in between: Croatia. How about you?

 

[ThomasT]

I strongly disagree that they are EASILY explainable via a common cause (without nonlocality). Namely, to EXPLAIN it, it is not sufficient to say that there is SOME common cause. Instead, an explanation requires a detailed theory which quantitatively predicts the results of all experiments. No such local realistic theory is known, so even if such theory can be constructed, it is NOT EASY to do it.

Ok, it isn't sufficient to simply say that there is some common cause. However, we know that the experimental preparation is predicated on just such an assumption. Truly, 'local realistic' (in the classical sense) models of entanglement don't miss the quantitative results by much. Arguably 'local realistic' models fit the data. To me, this suggests that what's happening is due to purely local transmissions/interactions.

The thing, and this is what I believe unless you can convince me otherwise, is that 'nonlocal' (ie., purely formal) 'transmissions' explain nothing. They're simply a placeholder for our ignorance.

 

[ThomasT]

Somewhere in between: Croatia. How about you?

I'm in Fort Lauderdale, Florida, USA. You're near Italy and Austria and Hungary, right? You must have very good food there. What are you having (did you have) for lunch? And please don't say you went to Burger King or McDonald's.

 

[Demystifier]

You're near Italy and Austria and Hungary, right?

Right.

And please don't say you went to Burger King or McDonald's.

No, I haven't. :tongue2:

 

[nismaratwork]

He had a tall glass of Maraschino, nothing more or less.

JK, Croatia is a gem, and the food I had when I was there was fantastic, exceeded by its architecture, but that's hard to beat too.

ThomasT: Do you know of a theory which allows for local AND realistic action while matching the predictions of QM or in this case, dBB?

 

[zonde]

You must have very good food there.

I know. They have chevapchici there.

 

[nismaratwork]

I know. They have chevapchici there.

The great thing is they also have lovely pizza there, and chevapchici kicks pepperoni's ***. I attended a friend's wedding on an island in Croatia and gained 4 pounds in week! Totally worth it...

 

[ThomasT]

He had a tall glass of Maraschino, nothing more or less.

JK, Croatia is a gem, and the food I had when I was there was fantastic, exceeded by its architecture, but that's hard to beat too.

ThomasT: Do you know of a theory which allows for local AND realistic action while matching the predictions of QM or in this case, dBB?

dBB is a mysterious theory. Not realistic in any sense. And I'm glad you enjoyed the food and architecture in Croatia.

 

[ThomasT]

I know. They have chevapchici there.

What's chevapchici? Can you describe it?

 

[nismaratwork]

What's chevapchici? Can you describe it?

Have you ever had merguez sausage? It's very much like that, but usually made of pork and less spicy... it's amazingly good.

edit: gaze upon the glory of the coming of the pork!

In an omelet it's basically a porkgasm.

I'd add, dBB is pretty mysterious by my standards too, and I agree that it isn't realistic (EPR), but that's the point, right? It can match QM because it doesn't incorporate realism AND non-locality... you get locality via a pilot wave, but not realism.

 

[Demystifier]

I'd add, dBB is pretty mysterious by my standards too, and I agree that it isn't realistic (EPR), but that's the point, right? It can match QM because it doesn't incorporate realism AND non-locality... you get locality via a pilot wave, but not realism.

It's actually the exact opposite. You get NON-locality via the pilot wave, but you get realism.

Concerning ćevapčići, I agree with everything said above.

 

[DevilsAvocado]

edit: gaze upon the glory of the coming of the pork!

Great nismaratwork! Do you think you can find a just slightly bigger picture...? I have lost my glasses and all I see is a blurry non-realistic picture of that you do a couple of hours after you have eaten... :rofl:

(Use the attach/preview function for god’s sake! )

By the way I’m from Sweden, and I had a Polar Bear (Ursus maritimus) and two bottles of Absolut Vodka for breakfast, and it tasted... well pretty much as yesterday...

 

[DevilsAvocado]

If I understand you correctly, you reason in the following way. With superdeterminism, we can avoid nonlocality. So why do we deal with a nonlocal superdeterministic theory, such as Bohmian mechanics?

Correct.

The answer is simple: Because it is MUCH EASIER to construct a nonlocal (Bohmian) superdeterministic theory that agrees with predictions of QM, than a local one. There are people who struggle with construction of an explicit local superdeterministic theory (like 't Hooft), but it is much more difficult to do it, even if possible in principle.

Ahh! This explains it, and proves that I need to learn more about dBB.

I take it that this (of course) is in respect of mathematical formulations (what else!? ). I don’t know if this interest you, but the reason a layman like me can come to this conclusion, is that from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of: You have to know the state of all particles in the universe? And Even those outside the observable universe? And if the universe is infinite, that would mean infinite data? And if you want to do "some calculations", what particle do you start with? They all effect each other nonlocally and instantaneous? And how do you define a universal NOW? You would need to build a computer with infinite computer power, which is impossible? And is Superdeterminism really compatible with Gödel's incompleteness theorems?

Etc, etc, etc...

I have experience from computers and databases, and practical experience of the utterly mess that can happen when a lot of users want to access/modify the same data at the same moment... Maybe that’s why I’m "skeptic" to a universe that works in the somewhat same instantaneous "messy manners"... The solution to avoid this is timestamps + rigid rules + transaction management, and first in, first out.

"The only reason for time is so that everything doesn't happen at once." -- Albert Einstein​

Alice, of course, is capable of reading the measurement of her polarizer, but here the point is that she (as well as Bob) cannot CONTROL the reading of her/his measurement apparatus, in the sense that they cannot make the apparatus to be in the state they WANT. For that reason, they do not interpret nonlocal correlations as true exchange of information.

I agree that Alice cannot control the reading of her measurement apparatus = outcome is always 100% random. BUT if the polarizers are aligned parallel and Alice "first" measure 1 (or up), THEN she forces Bob to measure 0 (or down) unconditionally (if it’s that the kind of BBO we use, can also be 1/1), right?

See, however, a way to (apparently) avoid this problem as well, leading to a possibility to use entanglement for an (apparent) superluminal communication:
http://xxx.lanl.gov/abs/1006.0338

Okay, I’ll check out the paper and get back. Thanks for your answers, I really appreciate it!

 

[ThomasT]

Have you ever had merguez sausage? It's very much like that, but usually made of pork and less spicy... it's amazingly good.

In an omelet it's basically a porkgasm.

I'd add, dBB is pretty mysterious by my standards too, and I agree that it isn't realistic (EPR), but that's the point, right? It can match QM because it doesn't incorporate realism AND non-locality... you get locality via a pilot wave, but not realism.

Thanks, that was more than I expected, or wanted. But gastronomically exciting.

Regarding dBB, yes it matches qm to a certain extent, but there are problems. I really like the conceptualization of particle AND wave. But then there's the mysterious 'quantum potential'. See, the problem is that any so-called alternative interpretation of standard qm always has to, in some way, incorporate the standard qm generation of probabilities and the standard qm interpretation of those probabilities in order to actually predict real world experimental results. So all we've got is standard qm with a bit of unnecessary fluff. That's it. That's what all alternative qm 'interpretations' amount to.

 

[Demystifier]

I take it that this (of course) is in respect of mathematical formulations (what else!? ). I don’t know if this interest you, but the reason a layman like me can come to this conclusion, is that from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of: You have to know the state of all particles in the universe? And Even those outside the observable universe? And if the universe is infinite, that would mean infinite data? And if you want to do "some calculations", what particle do you start with? They all effect each other nonlocally and instantaneous? And how do you define a universal NOW? You would need to build a computer with infinite computer power, which is impossible? And is Superdeterminism really compatible with Gödel's incompleteness theorems?

Yes, that interests me very much, because it helps me to understand why many people don't like dBB.

I especially like your point:
"from a perspective "outside math", dBB looks like maybe the most complex thing one can ever think of"
Now I perfectly understand what makes you think so. Yet, when dBB is viewed from a mathematical point of view, it looks remarkably simple. In fact, all except one equations in
http://xxx.lanl.gov/abs/1002.3226
are equations of "standard" purely probabilistic QM. Relativistic dBB adds ONLY ONE equation, which is the last equation, Eq. (23).

By the way, irrespective of dBB, I insure you that superdeterminism is compatible with Gödel's incompleteness theorems. But of course, to understand that, you need to understand the mathematical side of the Gödel's incompleteness theorems as well.

 

[inflector]

dBB is a mysterious theory. Not realistic in any sense.

Perhaps not realistic in the English language sense of the word outside of physics. But in the very specific quantum physics definition it is definitely realistic. The particles actually exist independent of the observation and the wavefunction is also a "real" entity that exists independent of the wavefunction.

The nonlocal aspect of the theory may seem odd but many of us don't find it any odder than the underlying reality of experimental observation.

I personally don't believe that we are restricted to instantaneous nonlocality by experiment. So while the formal definition of dBB as it stands is that the wavefunction depends on the instantaneous position of each and every particle in the universe, I believe there is room for a less encompassing wavefunction in a version of dBB that is to universally nonlocal. Our experiments, for example, don't rule out superluminal communication at say 10⁷ lightspeed. So, if there were some superluminal mechanism that could create causal relationships between entangled particles at 10⁷ lightspeed then this increased speed of causal connectivity would allow a much larger causal cone (like a light cone but superluminal).

So to me, the important aspects of dBB are:

1) It is realisitic - particles exist even when they are not being observed.

2) It is deterministic - i.e. particles have actual positions all the time even before measurement and those particles move in ways that are determined by the locations and momentum of all the other particles.

3) It is nonlocal - it is possible to have a superluminal causal connection.

I believe that a theory which is nonlocal but where the position of a particle or group of particles is not, in all cases, determined by every single one of the other particles in the universe still fits the spirit of a dBB interpretation. Ultimately, I expect that physics will find a theory of this sort behind the behavior of QM which we all find so puzzling.

And if you want to do "some calculations", what particle do you start with? They all effect each other nonlocally and instantaneous? And how do you define a universal NOW? You would need to build a computer with infinite computer power, which is impossible? And is Superdeterminism really compatible with Gödel's incompleteness theorems?

Ah, who said the Big Flying Spaghetti Monster created the universe with laws that would be computable by mere humans?

I personally believe that a rather simple explanation that leads to tremendous computation complexity is very likely to be underlying our rather complex current set of rules, i.e. QM with the Standard Model + General Relativity with the Standard Model of Cosmology. It is clear however, that simpler models that develop complexity through emergent phenomena are many orders of magnitude more computationally intensive. After all, it took around a year of supercomputer time to compute the mass of the proton and neutron ab initio using Lattice QCD, I suspect the individual protons and neutrons get their mass through rather simpler means.

 

[Demystifier]

I really like the conceptualization of particle AND wave. But then there's the mysterious 'quantum potential'.

If you accept that there is a particle AND a wave, and if you accept that wave determines the particle velocity, then THERE IS NO quantum potential. Or at least not as a fundamental new entity. The quantum potential is just a more complicated way to write otherwise simple equations of particle velocities determined by waves, with the only motivation to make dBB look more similar to classical mechanics. As long as simplicity is considered more important than similarity with classical mechanics, there is no need to introduce or mention the quantum potential at all.

 

[nismaratwork]

Great nismaratwork! Do you think you can find a just slightly bigger picture...? I have lost my glasses and all I see is a blurry non-realistic picture of that you do a couple of hours after you have eaten... :rofl:

(Use the attach/preview function for god’s sake! )

By the way I’m from Sweden, and I had a Polar Bear (Ursus maritimus) and two bottles of Absolut Vodka for breakfast, and it tasted... well pretty much as yesterday...

heh... ok I get it, big picture

Demystifier: I stand corrected... dBB really isn't something I know more than the basics of, or thought I did. I appreciate the correction... you're well named.

 

[nismaratwork]

If you accept that there is a particle AND a wave, and if you accept that wave determines the particle velocity, then THERE IS NO quantum potential. Or at least not as a fundamental new entity. The quantum potential is just a more complicated way to write otherwise simple equations of particle velocities determined by waves, with the only motivation to make dBB look more similar to classical mechanics. As long as simplicity is considered more important than similarity with classical mechanics, there is no need to introduce or mention the quantum potential at all.

When you say particle and a wave, do you mean QM duality, or dBB Pilot Wave (real) and Particle (real)?

 

[Demystifier]

When you say particle and a wave, do you mean QM duality, or dBB Pilot Wave (real) and Particle (real)?

I mean the latter.