Where does non-locality originate in dBB theory?

[DevilsAvocado]

dBB is not very useful for this case because these are macroscopic objects on which all quantum effects (including nonlocal correlations) are negligible. Classical theory of relativity is sufficient for that purpose, but I have no intention to teach you this subject here.

Okay? How about replacing the "red spot" in t = 0 with a laser and a BBO crystal for spontaneous parametric down-conversion, and place measuring polarizers in the front & back of the train car, to implement a "Speeding EPR-Bell experiment"? Would that also be considered "negligible"?

Honestly, isn’t the incompatibility between non-relativistic QM and Special Relativity a BIG problem? According to John Bell:

"Those paradoxes are simply disposed of by the 1952 theory of Bohm, leaving as the question, the question of Lorentz invariance. So one of my missions in life is to get people to see that if they want to talk about the problems of quantum mechanics — the real problems of quantum mechanics — they must be talking about Lorentz invariance."​

When I looked around, I found this ("toy model" according to SEP):

http://arxiv.org/abs/quant-ph/9801070"

Hypersurface Bohm-Dirac models
Authors: D. Duerr, S. Goldstein, K. Muench-Berndl, N. Zanghi
Journal reference: Phys.Rev. A60 (1999) 2729-2736

Abstract: We define a class of Lorentz invariant Bohmian quantum models for N entangled but noninteracting Dirac particles. Lorentz invariance is achieved for these models through the incorporation of an additional dynamical space-time structure provided by a foliation of space-time. These models can be regarded as the extension of Bohm's model for N Dirac particles, corresponding to the foliation into the equal-time hyperplanes for a distinguished Lorentz frame, to more general foliations. As with Bohm's model, there exists for these models an equivariant measure on the leaves of the foliation. This makes possible a simple statistical analysis of position correlations analogous to the equilibrium analysis for (the nonrelativistic) Bohmian mechanics.

Is this problem really solved in dBB??

 

[Demystifier]

Honestly, isn’t the incompatibility between non-relativistic QM and Special Relativity a BIG problem?

Is this problem really solved in dBB??

In my opinion, it is solved:
http://xxx.lanl.gov/abs/1002.3226 [to appear in Int. J. Quantum Inf.]
If you have any objections or questions on THAT solution, I would be happy to respond on them.

 

[Demystifier]

How about replacing the "red spot" in t = 0 with a laser and a BBO crystal for spontaneous parametric down-conversion, and place measuring polarizers in the front & back of the train car, to implement a "Speeding EPR-Bell experiment"?

Do you actually ask "What is the Lorentz frame with respect to which the Bohmian force is instantaneous?". If THAT is your question, then the answer in the relativistic-covariant version of dBB is simple: If you repeat the experiment many times, then each time it will probably be ANOTHER Lorentz frame, because it (the Lorentz frame) is determined by initial conditions on Bohmian spacetime positions, which are usually different in each repeat of the experiment.

If you wanted to ask something else, then it would help to spell the question more precisely.

 

[DevilsAvocado]

In my opinion, it is solved:
http://xxx.lanl.gov/abs/1002.3226 [to appear in Int. J. Quantum Inf.]
If you have any objections or questions on THAT solution, I would be happy to respond on them.

THANKS! This is very interesting. I just love that Nikolic has a large conceptual section, explaining the main ideas. This is what I’ve been looking for! :!)

I must read carefully and get back ASAP. Thanks again.

 

[DevilsAvocado]

In my opinion, it is solved:
http://xxx.lanl.gov/abs/1002.3226 [to appear in Int. J. Quantum Inf.]
If you have any objections or questions on THAT solution, I would be happy to respond on them.

Hrvoje Nikolic is a really smart guy, and I like what he has written, for example http://arxiv.org/abs/quant-ph/0609163" ?

Please correct me if I’m wrong, but I find this a little 'peculiar':

1) Take the laws of physics seriously!
...
By 1) I mean that everything, including the human brain, obeys the physical laws. They
will turn out to be deterministic laws, which excludes the existence of free will.

To me this is the same as http://en.wikipedia.org/wiki/Hard_determinism" .

And afaict Hard determinism is equal to Superdeterminism, and this is a well known loophole and theoretical escape route from Bell's theorem. Bell discussed superdeterminism in a BBC interview:​

There is a way to escape the inference of superluminal speeds and spooky action at a distance. But it involves absolute determinism in the universe, the complete absence of free will. Suppose the world is super-deterministic, with not just inanimate nature running on behind-the-scenes clockwork, but with our behavior, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined, including the "decision" by the experimenter to carry out one set of measurements rather than another, the difficulty disappears. There is no need for a faster than light signal to tell particle A what measurement has been carried out on particle B, because the universe, including particle A, already "knows" what that measurement, and its outcome, will be.

The only alternative to quantum probabilities, superpositions of states, collapse of the wave function, and spooky action at a distance, is that everything is superdetermined. For me it is a dilemma. I think it is a deep dilemma, and the resolution of it will not be trivial; it will require a substantial change in the way we look at things.

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

This is also somewhat strange:

R: Actually, it is quite natural. Humans are macroscopic beings who perceive the
world in terms of classical phenomena. There is a lot of evidence, especially from the
theory of decoherence [7, 8], that macroscopic classical physics emerges from the funda-
mental microscopic quantum physics. By assumption, superluminal signals are inherently
quantum phenomena responsible for nonlocal correlations between entangled particles, so
it is quite natural to expect that their effect cannot be seen at the classical macroscopic
level at which decoherence effectively destroys the quantum correlations.

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’ll get back to you on post #33.

 

[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.

 

[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.