Undergrad Pseudorandom Entanglement and Special Relativity

[Igael]

Anyway, Bell showed that the results may not be reproduced with hidden variables and that randomness is fundamental. But the need of non-locality to explain what happens is another thing.

Perhaps the particles are not really entangled, each of them just changes their spin with an in-built pseudorandom algorithm, allowing them to appear to be "in-sync" and thus entangled..

Why pseudo random ? with pure random algorithms, you can get strange things.

Not to say that QM is not predictive in the experiments, but enough to ask, knowing the capacity of some algorithms , how can one infere on non-locality instead of searching better ?

If one knows well EPR and javascript, I can send him a link to one of these simplified algorithms with strange results in a private message ( the source is very short ).

 

[greswd]

Special relativity describe symmetries between certain reference frames. Superluminal entities simply can't follow these symmetries described by SR i.e. physical laws for superluminal entities have to be different (asymmetric) in different reference frames.

That might be true but I'm not sure as to how it can be easily extended.

 

[greswd]

What superluminal entities are we talking about?
Note that for Bohmian Mechanics, where there is instantaneous action at a distance, there is no "superluminal" reference frames (whatever those are). Many believe that Bohmian Mechanics requires a preferred reference frame, however.

The speed of entanglement I guess. Any instantaneous worldline remains a superluminal worldline in another frame is SR.

 

[greswd]

Why pseudo random ? with pure random algorithms, you can get strange things.

I just wanted to figure out how scientists managed to rule out pseudorandomness to confirm non-locality.

 

[vanhees71]

Define "speed of entanglement". I've no clue what that means. By construction relativistic quantum-field theory works with local interactions and is causal. Entanglement can mean that there are long-ranged correlations between parts of a quantum system, but that doesn't violate relativistic causality, which is also implemented by construction in relativistic QFT ("microcausality").

 

[greswd]

Define "speed of entanglement". I've no clue what that means. By construction relativistic quantum-field theory works with local interactions and is causal. Entanglement can mean that there are long-ranged correlations between parts of a quantum system, but that doesn't violate relativistic causality, which is also implemented by construction in relativistic QFT ("microcausality").

This one:
http://www.extremetech.com/extreme/...stance-at-least-10000-times-faster-than-light

We currently have no way of sending meaningful signals with entanglement, but isn't there still some superluminal link between the entangled particles?

 

[greswd]

And the paper:
http://arxiv.org/pdf/1303.0614v2.pdf

 

[zonde]

That might be true but I'm not sure as to how it can be easily extended.

What has to be extended? I don't understand where do you see the problem (given you are ready to give up SR symmetries).

I just wanted to figure out how scientists managed to rule out pseudorandomness to confirm non-locality.

This is easy. Pseudorandomness obeys Bell inequalities. If Bell inequalities are violated pseudorandomness is ruled out.

 

[zonde]

By construction relativistic quantum-field theory works with local interactions and is causal. Entanglement can mean that there are long-ranged correlations between parts of a quantum system, but that doesn't violate relativistic causality, which is also implemented by construction in relativistic QFT ("microcausality").

I would like to ask what you think about one simple model. Let me describe it.

We have two variables x and y where x can have values {1,2,3,4} but y can have {5,6,7,8}
We combine x and y into a pair. Now x|y pair can have values from set {1|5, 1|6, 1|7, 1|8, 2|5, 2|6, 2|7, 2|8, 3|5, 3|6, 3|7, 3|8, 4|5, 4|6, 4|7, 4|8} but from that set we take out values {1|5, 2|6, 3|7, 4|8} so that now x|y pair can have values from set F={1|6, 1|7, 1|8, 2|5, 2|7, 2|8, 3|5, 3|6, 3|8, 4|5, 4|6, 4|7}
For x we define an operation "+1" that makes x take the next value from the set {1,2,3,4} or the first value if it has last value in the set (like that 1->2 or 2->3 or 3->4 or 4->1). But we add a condition that operation "+1" can't take the pair x|y out of the set F.

Now we create pair of x|y with unknown values and send x and y to two separate remote locations. At one remote location we perform "+1" operation on unknown x 0 to 3 times. Then we look at the value of x. Depending on the value of x we find out that y at remote location can't have a certain value.
I would say that such a model can be implemented only if operation "+1" on x is allowed to change value of y remotelly i.e. it's implementation has to be non-local.
Do you agree?

 

[vanhees71]

I don't understand this example. What has this to do with quantum dynamics?

 

[greswd]

What has to be extended? I don't understand where do you see the problem (given you are ready to give up SR symmetries).

The Lorentzian interpretation (LET) of special relativity as you mentioned earlier. I don't really have any opinion on whether to give it up or not.

 

[zonde]

The Lorentzian interpretation (LET) of special relativity as you mentioned earlier. I don't really have any opinion on whether to give it up or not.

Giving up SR symmetries for FTL entities/phenomena is the only extension that is needed for LET i.e. physical laws for superluminal entities have to be different in different reference frames.

 

[zonde]

I don't understand this example. What has this to do with quantum dynamics?

This is analogy of Fock space as I understand it for a special case of a pair of entangled particles.
Well, it needs a minor correction. Let's say we can't look at values of x and y but instead we can ask question if x or y has a particular value with yes/no type of answer.

 

[zonde]

Well, it needs a minor correction. Let's say we can't look at values of x and y but instead we can ask question if x or y has a particular value with yes/no type of answer.

And another correction, sorry. We have to define "+1" operation for y too and apply it arbitrary number of time on y at remote location. Only then the implementation requires non-locality.

 

[Igael]

I would like to ask what you think about one simple model. Let me describe it.

If I understand your algorithm , you build indexed pairs and each side uses the list sequentially ?
if yes, it needs memory and it doesn't work with random polarizers tilts. Else the simple solution where the hidden variable is the spin would work ...

Edit : reading further, I didn't understand correctly ...

 

[DrChinese]

The speed of entanglement I guess. Any instantaneous worldline remains a superluminal worldline in another frame is SR.

For this to have a particular meaning, you would need to have an interpretation in which something occurs FTL. There are local non-realistic interpretations of QM that follow Bell. In those, c is still a limiting factor, even with entanglement.

 

[greswd]

For this to have a particular meaning, you would need to have an interpretation in which something occurs FTL. There are local non-realistic interpretations of QM that follow Bell. In those, c is still a limiting factor, even with entanglement.

what about this experiment?
http://www.extremetech.com/extreme/...stance-at-least-10000-times-faster-than-light
http://arxiv.org/pdf/1303.0614v2.pdf

 

[DrChinese]

what about this experiment?
http://www.extremetech.com/extreme/...stance-at-least-10000-times-faster-than-light
http://arxiv.org/pdf/1303.0614v2.pdf

Yes, I am well familiar with this. It says that IF there are FTL effects, they must be at least 10,000c.

You may not be familiar with the following point: all entanglement interaction diagrams show direct lines of action which are limited to c. The outstanding question is whether the observations of the entangled particles involves an effect going directly from point A to point B, or is something else. Even in standard QM, there is no hypothetical mechanism, force, etc that travels FTL - even though QM does make the predictions as to the observed correlations. But the mechanism itself need not be FTL. For example, there could be backward-in-time influences.

 

[Jilang]

Which would be even worse!

 

[greswd]

But the mechanism itself need not be FTL. For example, there could be backward-in-time influences.

what's a backward-in-time influence?

 

[DrChinese]

what's a backward-in-time influence?

No one really knows. However, just as it is possible to demonstrate "nonlocality" with entanglement (and this is a prediction of QM), it is also possible to demonstrate "non-temporality" (I made up this word) or "non-causality". And this is also predicted by QM. For instance:

1. It is possible to entangle photons AFTER they have been detected.
2. It is possible to entangle photons that have never co-existed.
3. It is possible to entangle photons that have never shared a common light cone.

Yet in all of these cases, there are world lines (respecting c) connecting the photons which go both forward and backward in time. And ALL entanglement - even a so-called "non-local" demonstration - shares this strange attribute. I do not know what to make of it any more than anyone else, but there are interpretations of QM that feature elements of time symmetry.

I can provide references if that will help.

 

[greswd]

No one really knows. However, just as it is possible to demonstrate "nonlocality" with entanglement (and this is a prediction of QM), it is also possible to demonstrate "non-temporality" (I made up this word) or "non-causality". And this is also predicted by QM. For instance:

1. It is possible to entangle photons AFTER they have been detected.
2. It is possible to entangle photons that have never co-existed.
3. It is possible to entangle photons that have never shared a common light cone.

Yet in all of these cases, there are world lines (respecting c) connecting the photons which go both forward and backward in time. And ALL entanglement - even a so-called "non-local" demonstration - shares this strange attribute. I do not know what to make of it any more than anyone else, but there are interpretations of QM that feature elements of time symmetry.

I can provide references if that will help.

please do thank you

 

[DrChinese]

please do thank you

This is experimentally evidenced by entanglement swapping operations. Some references:

http://arxiv.org/abs/quant-ph/0201134
Quantum teleportation strikingly underlines the peculiar features of the quantum world. We present an experimental proof of its quantum nature, teleporting an entangled photon with such high quality that the nonlocal quantum correlations with its original partner photon are preserved. This procedure is also known as entanglement swapping. The nonlocality is confirmed by observing a violation of Bell's inequality by 4.5 standard deviations. Thus, by demonstrating quantum nonlocality for photons that never interacted our results directly confirm the quantum nature of teleportation.

http://arxiv.org/abs/1209.4191
The role of the timing and order of quantum measurements is not just a fundamental question of quantum mechanics, but also a puzzling one. Any part of a quantum system that has finished evolving, can be measured immediately or saved for later, without affecting the final results, regardless of the continued evolution of the rest of the system. In addition, the non-locality of quantum mechanics, as manifested by entanglement, does not apply only to particles with spatial separation, but also with temporal separation. Here we demonstrate these principles by generating and fully characterizing an entangled pair of photons that never coexisted. Using entanglement swapping between two temporally separated photon pairs we entangle one photon from the first pair with another photon from the second pair. The first photon was detected even before the other was created. The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime.

 

[vanhees71]

Well, it's of course misleading to talk about trajectories in conncection with photons, because they don't even let you define a position observable. The non-locality is based on a mediocre definition of position and is not non-local in any sense contradicting the locality of interactions of relativistic quantum field theory. As far as I know, all experiments done with photons are in accordance with QED, which is a local microcausal relativistic QFT, which has locality built in. Of course, what you have are non-local correlations of entangled photons detected at far-distant places. Although the literature is full of sloppy slang, which must be read in the correct context and understanding what's really meant by this slang, we should try to stay precise in our forum discussions. Otherwise you have endless discussions about purely semantic issues, which take a lot from the fascination of the quite surprising properties of quantum systems, as they are described by entanglement (for photons usually entanglement of polarization of two or more photons).

 

[DrChinese]

... The non-locality is based on a mediocre definition of position and is not non-local in any sense contradicting the locality of interactions of relativistic quantum field theory. As far as I know, all experiments done with photons are in accordance with QED, which is a local microcausal relativistic QFT, which has locality built in. Of course, what you have are non-local correlations of entangled photons detected at far-distant places. ...

Good points. The "non-locality" of Alice and Bob's measurements does not mean that QM and relativity are in opposition. Which I believe was an implied element of the OP.

 

[greswd]

Good points. The "non-locality" of Alice and Bob's measurements does not mean that QM and relativity are in opposition. Which I believe was an implied element of the OP.

how do backward-in-time influences produce perfect correlations all the time?

 

[DrChinese]

how do backward-in-time influences produce perfect correlations all the time?

I can't really speak to the mechanics in specific as this is mostly hypothetical (as are all quantum mechanisms). But I can give an analogy.

In the Bohmian view, there is distant action instantaneously from point A to point B. Hard to say which comes first, but you can imagine some mechanism whereby the correlations are created.

In the retrocausal view, it is much the same. However, instead of instantaneous connections, there is a third point in spacetime C which is prior to A and B. There is a correlation between A and C, and B and C, and therefore there is a correlation between A and B.

In the Bohmian view, there is no obvious reason that A and B are correlated but nothing else appears to be. After all, every object in the universe affects every other object instantaneously. In the retrocausal view, there is a correlation between an object's past interaction and its future interaction. This meshes nicely with some elements of QM.

But neither view has an absolute chokehold on explaining the underlying mechanism. In the end, your idea of beauty will dictate your interpretation.

I like the time symmetric view because it neatly explains the limits of quantum non-locality. Assuming you are not using some form of entanglement swapping: an entangled pair requires a common interaction in the past. But will entanglement swapping, you can get entanglement occurring in any time order - even after the fact.

 

[Igael]

how do backward-in-time influences produce perfect correlations all the time?

Correlations are never perfect. Results are very approximative. The correlated objects are kets, not particles ... There are many potential loopholes. Backward-in-time influence is not even a little bit mainstream, some claim - and I agree - that it's pop-sciences and that physics without causality is just metaphysics.
Sciences history shows us that people forget quickly bad theories.

 

[georgir]

Regarding the claim that there are "local, non-realistic" interpretations, I've not been convinced by any. Any non-realism in the form of "pure randomness", whatever that may be defined as, where the probability is a local variable is still insufficient to cause Bell violations. Other more fancy attempts I've seen are just hiding behind a confused definition of what "local interaction" means. For example world-splits in MWI I still consider non-local because of the simultaneous, correlated splitting that should occur at different points in space.

Regarding time-symmetric view, I do not consider it different than the normal. In SR it is a simple conclusion that unrestricted FTL interactions lead to backwards in time interactions, and the reverse is self-evident as well. So the two are equivalent and explaining entanglement by either does not differ in my opinion. I'd just call both non-locality.

Time symmetry and causality are hard to mix. You need to have a consistent arrow of time for any definition of causality, and even if you are allowed to reverse it due to time symmetry you have to do so globally, you can not mix and match. Otherwise you'd be able to get a causal chain linking any two events you wish and transmit any information FTL. In QM you can not do that.

The inability of entanglement to transport any controlled information is key. QM has FTL (equivalently: backwards in time, or acausal, or non-local) interactions between unknown, uncontrollable or random variables only.

 

[greswd]

Giving up SR symmetries for FTL entities/phenomena is the only extension that is needed for LET i.e. physical laws for superluminal entities have to be different in different reference frames.

Then what is your opinion on this paper http://dinamico2.unibg.it/recami/erasmo%20docs/SomeOld/RevisitingSLTsLNC1982.pdf

It tries to include superluminal reference frames but ends up with imaginary transverse space. I already mentioned this paper earlier by the way.