Testing whether entanglement is a matter of information or non-local?

[QuestionMarks]

Depending on who one asks and their interpretation of QM, entanglement seems to be either:

a) No problem at all. It's just a matter of information. If you knew one entangled electron was spin up, then the other must have been spin down by inference of the prepared state of the system.
b) Potentially "spooky action at a distance." One electron might well be able to tell the other to "flip" its spin instantaneously. Something worth figuring out, but not something we like because that would be non-local.

And I've seen some pretty entrenched belief systems based on either way. But couldn't we test this? I would assume we have already?

If not, why not some similar scenario as follows...
We have a set of points, notated by the following letters, where the distance between each adjacent point is the same as those of any other two adjacent points:

A---B---C---D---E---F---G

At (D), two entangled electrons are released, electron 1 moving to (A) and electron 2 moving to (G). Both paths are the same in characteristics. At point (C) the spin of electron 1 is measured as "up," thereby we "know" that of 2 is "down" at (E). At point (B) (or even we could say immediately at the measurement on point C), electron 1 is hit and its spin changed from "up" to "down". As both particles reach their endpoints, electron 2 is measured at (G).

If electron 2 is shown as "up," then would we not know that electron 1 somehow told electron 2 to flip sometime after (C-E)? Would this not support then that entanglement is not merely inference of information from the system, but rather an actual effect of one particle upon the other (even if it is non-local)? Surely something like this experiment has already been done?

thanks all.

 

[DrChinese]

If not, why not some similar scenario as follows...
We have a set of points, notated by the following letters, where the distance between each adjacent point is the same as those of any other two adjacent points:

A---B---C---D---E---F---G

At (D), two entangled electrons are released, electron 1 moving to (A) and electron 2 moving to (G). Both paths are the same in characteristics. At point (C) the spin of electron 1 is measured as "up," thereby we "know" that of 2 is "down" at (E). At point (B) (or even we could say immediately at the measurement on point C), electron 1 is hit and its spin changed from "up" to "down". As both particles reach their endpoints, electron 2 is measured at (G).

If electron 2 is shown as "up," then would we not know that electron 1 somehow told electron 2 to flip sometime after (C-E)? Would this not support then that entanglement is not merely inference of information from the system, but rather an actual effect of one particle upon the other (even if it is non-local)? Surely this experiment has already been done?

thanks all.

Once electron 1 is observed to be spin up at (C), it is no longer entangled with electron 2. So what happens next to 1 has no effect on 2. You can be sure that once electron 2 is down, it will stay down (until some interaction or observation places it into a different state)! That is fairly fundamental.

So the expected null result in this case does not place us any closer to answering your question.

 

[DrChinese]

By the way, your question does not follow the norms of how entanglement is usually explained. The "information only" view is generally discredited if you are rejecting non-locality. You usually either reject "realism" or reject "locality" (or both). This is because of Bell's Theorem.

 

[QuestionMarks]

Thanks DrChinese. Hah, good to know when one's brain feels it is missing something obvious, it nearly always is. So my proposition is bunk, but is there any experimental evidence that leans us closer to either understanding? Any key papers?

And I get Bell's theorem's sentiments, though I guess I should acknowledge that I'm not necessarily rejecting non-locality. I grant that's traditional, but I'm willing to consider alternatives. Perhaps consider me biased towards realism to keep the dialogue interesting.

 

[DrChinese]

Thanks DrChinese. Hah, good to know when one's brain feels it is missing something obvious, it nearly always is. So my proposition is bunk, but is there any experimental evidence that leans us closer to either understanding? Any key papers?

And I get Bell's theorem's sentiments, though I guess I should acknowledge that I'm not necessarily rejecting non-locality. I grant that's traditional, but I'm willing to consider alternatives. Perhaps consider me biased towards realism to keep the dialogue interesting.

The state of the art has not proven or disproven direct non-local action. There is plenty of proof for quantum non-locality but there are some interpretations in which the action is not direct (example: time symmetric versions which respect c but do not respect causality as we know it).

It is possible to entangle particles that have never interacted, for example. Such particles need not have ever existed in the other's past time cone. Also: tests for non-locality have indicated that if non-local effects have a finite limit on the speed of action, it must be at least 10,000 c.

 

[QuestionMarks]

The state of the art has not proven or disproven direct non-local action. There is plenty of proof for quantum non-locality but there are some interpretations in which the action is not direct (example: time symmetric versions which respect c but do not respect causality as we know it).

It is possible to entangle particles that have never interacted, for example. Such particles need not have ever existed in the other's past time cone. Also: tests for non-locality have indicated that if non-local effects have a finite limit on the speed of action, it must be at least 10,000 c.

All interesing ideas. Can any particular experiment names or search terms be put to these so I can do more reading?

Particularly though, how can you have a nonlocal effect that is indirect or still respects c as you say? And is "nonlocal" still an apt word for this? My thought would be that any event occurring to one particle and causally-correlating with an event on/to another could be described as information transfer. I've certainly read a handful of experiments where QM causality gets a little wonky, but I never felt any such adbicated those instances of our responsibility in considering nonlocal mechanisms.

 

[DrChinese]

1. All interesing ideas. Can any particular experiment names or search terms be put to these so I can do more reading?

2. Particularly though, how can you have a nonlocal effect that is indirect or still respects c as you say? And is "nonlocal" still an apt word for this? My thought would be that any event occurring to one particle and causally-correlating with an event on/to another could be described as information transfer. I've certainly read a handful of experiments where QM causality gets a little wonky, but I never felt any such adbicated those instances of our responsibility in considering nonlocal mechanisms.

1. Here are a few:

http://arxiv.org/abs/quant-ph/0201134
Decision to entangle 2 particles is made AFTER the particles have already been detected. Effect precedes the cause.

http://arxiv.org/abs/1209.4191
Entanglement Between Photons that have Never Coexisted; The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime.

http://arxiv.org/abs/0808.3316
Testing spooky action at a distance; ...if such a privileged reference frame exists and is such that the Earth's speed in this frame is less than 10^-3 that of the speed of light, then the speed of this spooky influence would have to exceed that of light by at least 4 orders of magnitude.


2. An indirect non-local effect is one in which the causal arrow move back and forth, but otherwise respects c. The space-time diagram of the experimental context does not have anything propagating at a speed other than c or -c. You don't have to agree anything is proven to be time-reversed, but that is also an acceptable interpretation.

 

[morrobay]

Once electron 1 is observed to be spin up at (C), it is no longer entangled with electron 2. So what happens next to 1 has no effect on 2. You can be sure that once electron 2 is down, it will stay down (until some interaction or observation places it into a different state)! That is fairly fundamental.

So the expected null result in this case does not place us any closer to answering your question.

In the context of spin 1/2 particles in a basic Bell inequality : n[x+,z+] + n[y-,z-] ≥ n[x+,y+]
Realism assumes that variables "Determine precisely the results of individual measurements". That is, if electron 1 is spin up on z axis then if electron 2 were measured it would be spin down on z axis , from conservation laws.
While once electron 1 is observed to be up it is no longer entangled with electron 2 and electron 2 will stay down.
Then when the above inequality is violated does this suggest there can be non-local influences between electrons that are not entangled ?

 

[DrChinese]

In the context of spin 1/2 particles in a basic Bell inequality : n[x+,z+] + n[y-,z-] ≥ n[x+,y+]
Realism assumes that variables "Determine precisely the results of individual measurements". That is, if electron 1 is spin up on z axis then if electron 2 were measured it would be spin down on z axis , from conservation laws.
While once electron 1 is observed to be up it is no longer entangled with electron 2 and electron 2 will stay down.
Then when the above inequality is violated does this suggest there can be non-local influences between electrons that are not entangled ?

The inequality is not going to be violated if the x, y and z are all mutually orthogonal axes for measurement.

I would say: There is no suggestion that there is a non-local influence between electrons that are not entangled.

 

[QuestionMarks]

This is all great reading resources DrChinese. Super thanks! I'll dig into these.

On the backwards c, I'm glad you mentioned that. That was actually an interpretation (in my own mind)of some results I read a while back, but when I looked around to see if this was a valid idea, it was very poo-pooed upon. Granted I understand one's interpretation of QM may create strong arguments to the contrary. Makes me wish, however, most QM conversations could be held in reference to the knowledge that a general interpretation is not yet consensus.

Anyways Thanks!

 

[trendal]

It is possible to entangle particles that have never interacted, for example. Such particles need not have ever existed in the other's past time cone.

Just kind of an aside here...but how can you say with absolute certainty that two particles have never interacted? If we go all the way back to the beginning of this universe, all particles would have interaction with each other because they all would have been in the same space.

 

[bhobba]

Depending on who one asks and their interpretation of QM, entanglement seems to be either:

Actually its not dependant at all on interpretation. Its simply the vector space nature of pure states.

If you have two systems that can be in states |a> and |b> then system 1 can be in state |a> and system 2 in state |b> - their combined state is the pure state |a>|b>. Similarly system 1 can be in state |b> and system 2 in state |a>. Again their combined state is |b>|a>. But pure states form a vector space (that's the basis of the superposition principle) so a linear combination is also an allowable state eg 1/root 2 |a>|b> + 1/root 2 |b>|a>. By definition such states are called entangled.

In fact it is now known that a few reasonable assumptions and entanglement more or less implies QM:
http://arxiv.org/abs/0911.0695

The situation is this. The three axioms mentioned in the paper lead to either probability theory or quantum mechanics. Quantum mechanics is singled out if you want continuous transformations between pure states (physical continuity requires this ie if you can apply a transformation for 1 second you can apply it for 1/2 second) OR you can allow entanglement. At a deep fundamental level entanglement seems to be built into the very foundations of modelling physical systems.

Thanks
Bill

 

[bhobba]

Just kind of an aside here...but how can you say with absolute certainty that two particles have never interacted? If we go all the way back to the beginning of this universe, all particles would have interaction with each other because they all would have been in the same space.

You cant.

But what you can say is when you observe one part of an entangled system it's now entangled with what you observed it with rather then what it was originally entangled with.

Thanks
Bill

 

[morrobay]

The inequality is not going to be violated if the x, y and z are all mutually orthogonal axes for measurement.

It my understanding that QM predicts that two particles will be spin up or spin down: 1/2(sin(Θ/2))²


x y z...x y z
- - -...+ + +
- - +...+ + -
- + +...+ - -
+ + +...- - -
+ + -...- + +
+ - -...- + +
- + -...+ - +
+ - +...- + -

So if expectation values for the inequality are from table above and as shown spins in the
inequality are opposites then can it be violated at 90⁰
n[x+,z-] + n[y-z+] ≥ n[x-,y+]

 

[QuestionMarks]

Actually its not dependant at all on interpretation. Its simply the vector space nature of pure states.

...

Thanks
Bill

I'll check out that paper eventually, but I feel I'm likely to still disagree. Wherein we still currently have no fundamental consensus regarding the basic reality QM implies, I would find it overwhelmingly difficult to believe that entanglement enacts the same roles in all interpretations. Sure it can be given the same mathematical formulations, if you mean just that, but the reality (if there is one) is different. For instance, the MWI can have some sentiment of different entangled systems as different universes/histories. Meanwhile, Bohm's interpretation could quite literally count as spooky action if your requirement for that is simply a nonlocal hidden variable. QM may not depend on interpretation for the Math to be functional, but the ontology does.

 

[Imafungi]

Has any entanglement experiment proven that this following analogy is not akin to what is going on in the experiments (that is to say, has any entangle experiment proven non locality, in which this following analogy cannot be used to describe the most likely potential of what occurred)?There is a red ball and a blue ball. You and I are in another room blindfolded. A random person walks in the room with the red ball and blue ball and puts each in a bag. You and I walk in the room and each grab a bag. I go to the moon. You stay there. We know without looking that the results will be 1 red ball and 1 blue ball. I look in my bag on the moon, and its the blue ball. I instantly know that your ball is the red ball.

If this analogy can be used to describe every entanglement experiment, the analogy would be related to the 'spooky entanglement interpretation'; I got my bag and you get your bag. I go to the moon. Before I or your look in our bags, I have a red/blue ball in my bag, and you have a red/blue ball in your bag. When the bags were in the same room before they were separated, they were entangled. When I looked in my bag the red/blue ball turned into a blue ball, which then faster than the speed of light, notified your red/blue ball to turn into a red ball.

I honestly don't know much about this subject, but I like to remain skeptical, in the sense of believing in locality, cause and effect, logic, and the ability to explain physical interactions.

 

[Nugatory]

Has any entanglement experiment proven that this following analogy is not akin to what is going on in the experiments (that is to say, has any entangle experiment proven non locality, in which this following analogy cannot be used to describe the most likely potential of what occurred)?
...

Yes. Google for "Bell's Theorem" and also check out http://www.drchinese.com/Bells_Theorem.htm - DrChinese is a regular contributor here.

 

[Imafungi]

Yes. Google for "Bell's Theorem" and also check out http://www.drchinese.com/Bells_Theorem.htm - DrChinese is a regular contributor here.

Im sorry but I don't think that in anyway proved my analogy wrong, which is a 'local realism' view of the spooky action entanglement interpretation.

In entanglement experiments. When the first particle is measured, and the second particle is not measured. When the first particle is measured, at that instant does the second particle alert a system of its state? Or do the experimenters have to measure the second particle by themselves after? Or is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

 

[Water nosfim]

Has any entanglement experiment proven that this following analogy . . . interactions.

You don't just open , you paint the ball , and statistic you get anather color far and fast

 

[bhobba]

I'll check out that paper eventually, but I feel I'm likely to still disagree. Wherein we still currently have no fundamental consensus regarding the basic reality QM implies

Well since there is no consensus on what reality even means that's hardly surprising.

In physics generally the math is assumed to describe reality without getting bogged down in exactly what it is in the first place. If you want to go beyond that you are really getting into philosophy rather than science.

QM may not depend on interpretation for the Math to be functional, but the ontology does.

Why do you need an ontology beyond a simple interpretation of probability, which you need to make sense of probability to begin with? If you adopt the frequentest view of probability you get the so called statistical interpretation championed by Ballentine. If you adopt a Baysian view then you get something like Copenhagen. Strictly speaking its an ontology, but you would have a lot of trouble convincing those with a background in applied math like me its really more than the formalism implies.

Thanks
Bill

 

[QuestionMarks]

...
In physics generally the math is assumed to describe reality without getting bogged down in exactly what it is in the first place. If you want to go beyond that you are really getting into philosophy rather than science.

Why do you need an ontology beyond a simple interpretation of probability, which you need to make sense of probability to begin with?
...

That hints of the "shut up and calculate" culture often found in modern physics, which is a bit of a presumed philosophy itself unfortunately. And though we do not need the ontology per say, why discourage the pursuit? It only becomes philosophy (which is no evil, just a different forum) when we stop looking for empirical evidence. Presuming no experiment can be performed which would give us a better interpretational view of reality would be an unnecessary assumption (and I allow myself optimism at least). So until then, and especially while we are particularly focusing on what empirical support is out there, I see no concern in my thought venture.

 

[DrChinese]

It my understanding that QM predicts that two particles will be spin up or spin down: 1/2(sin(Θ/2))²


x y z...x y z
- - -...+ + +
- - +...+ + -
- + +...+ - -
+ + +...- - -
+ + -...- + +
+ - -...- + +
- + -...+ - +
+ - +...- + -

So if expectation values for the inequality are from table above and as shown spins in the
inequality are opposites then can it be violated at 90⁰
n[x+,z-] + n[y-z+] ≥ n[x-,y+]

The inequality is not violated at 90 degrees, because:

QM_Prediction(n[x+,z-])=25%
QM_Prediction(n[y-,z+])=25%
QM_Prediction(n[x-,y+])=25%

So that:

25% + 25% >= 25%

By the way, according to QM, the x, y and z spin components of an electron do not commute. A measurement of x requires that both y and z are completely indeterminate (and vice versa). So any x outcome (which will have a 50-50 likelihood) will be accompanied by a random outcome of either y or z. 50% x 50% = 25%.

 

[DrChinese]

Im sorry but I don't think that in anyway proved my analogy wrong, which is a 'local realism' view of the spooky action entanglement interpretation.

In entanglement experiments. When the first particle is measured, and the second particle is not measured. When the first particle is measured, at that instant does the second particle alert a system of its state? Or do the experimenters have to measure the second particle by themselves after? Or is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

First, no one actually understands the underlying mechanism by which entanglement works. That is why there are multiple interpretations. From 1935 until Bell's Theorem, your local realistic explanation was considered one possible interpretation (the EPR interpretation for lack of a better name).

However, Bell showed that interpretation to be flawed. The EPR interpretation has since been proven incorrect many times over in experiment. Until you read and understand Bell, you won't make any progress towards understanding WHY the EPR interpretation is wrong. Better yet, read the EPR paper first and then Bell.

BTW: In QM, the ordering of the measurements on Alice and Bob (particles 1 and 2) do not affect the outcome in any discernible fashion.

 

[DrChinese]

So until then, and especially while we are particularly focusing on what empirical support is out there, I see no concern in my thought venture.

Well, it is incorrect as I explained. That should give you pause. You cannot maintain all of the elements you have proposed (causality and locality).

It is very common to speculate. That is the lifeblood of new ideas, most of which are completely wrong. It is not common to give credit to speculation for which there is no practical implication because there is no new useful prediction to test.

So the reason people exclude local realistic interpretations/theories is that they run afoul of Bell.

 

[bhobba]

That hints of the "shut up and calculate" culture often found in modern physics, which is a bit of a presumed philosophy itself unfortunately.

Or maybe you misinterpret taking the math at face value.

Its what led to perhaps the greatest revelation of modern physics:
http://arxiv.org/pdf/hep-th/9704139.pdf

'The most important lesson that we have learned in this century it is that the secret of nature is symmetry. Starting with relativity, proceeding through the development of quantum mechanics and culminating, in the standard model symmetry principles have assumed a central position in the fundamental theories of nature. Local gauge symmetries provide the basis of the standard model and of Einstein’s theory of gravitation.'

It was the math of QM that revealed this - ontological speculations have basically led no-where.

Thanks
Bill

 

[Imafungi]

First, no one actually understands the underlying mechanism by which entanglement works. That is why there are multiple interpretations. From 1935 until Bell's Theorem, your local realistic explanation was considered one possible interpretation (the EPR interpretation for lack of a better name).

However, Bell showed that interpretation to be flawed. The EPR interpretation has since been proven incorrect many times over in experiment. Until you read and understand Bell, you won't make any progress towards understanding WHY the EPR interpretation is wrong. Better yet, read the EPR paper first and then Bell.

BTW: In QM, the ordering of the measurements on Alice and Bob (particles 1 and 2) do not affect the outcome in any discernible fashion.

Someone posted me information regarding Bells theorem, it didnt appear to contradict what I was saying. It doesn't seem itself to be based on evidence or experiment either, it appears to be a philosophical exclamation based entirely on assumptions made of what a local realist assumes. I saw the 1. 2. 3. argument part, and it says like, for the local realist to be right they need to believe all 3, but according to a non local realists interpretation of entanglement some of the tenants cannot be correct, therefore the local realist is wrong if they try to believe all the tenants?

Can you please answer this question, it is very important for my understanding of the true nature of all entanglement experiments, and an answer that suggests a; Yes, in regards to the first and third questions (which are the same question, worded differently and for clarity) would make me greatly comprehend that my analogy and interpretation lacking, and I would become forced to consider true non locality entanglement reality:

In entanglement experiments. When the first particle is measured, and the second particle is not measured. When the first particle is measured, at that instant does the second particle alert a system of its state? Or do the experimenters have to measure the second particle by themselves after? Or is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

 

[QuestionMarks]

Well, it is incorrect as I explained. That should give you pause. You cannot maintain all of the elements you have proposed (causality and locality).

It is very common to speculate. That is the lifeblood of new ideas, most of which are completely wrong. It is not common to give credit to speculation for which there is no practical implication because there is no new useful prediction to test.

So the reason people exclude local realistic interpretations/theories is that they run afoul of Bell.

What is incorrect? What should give me pause?
The initial experimental proposition is incorrect, certainly. Should I pause on questioning what experiments have been done? Where am I speculating beyond to ask what current experiments have addressed the question I posed? And where am I asserting something against Bell's? At most I have mentioned a non-local, hidden-variable theorem interpretation like Bohm's is possible (which takes no issue with Bell), and therefore we shouldn't say these questions matter nothing. This was only an aside in response to another poster, as I felt my questions have been quite well addressed by you (thanks by the way).

 

[DrChinese]

What is incorrect? What should give me pause?
The initial experimental proposition is incorrect, certainly. Should I pause on questioning what experiments have been done? Where am I speculating beyond to ask what current experiments have addressed the question I posed? And where am I asserting something against Bell's? At most I have mentioned a non-local, hidden-variable theorem interpretation like Bohm's is possible (which takes no issue with Bell), and this was only an aside in response to another poster.

My mistake, I thought you had gone back to a local "information only" interpretation.

 

[QuestionMarks]

It was the math of QM that revealed this - ontological speculations have basically led no-where.

Why should this limit my curiosity though? And why should we presume (as is the connotation I'm hearing) no math will ever help sway us to one ontology or another? Particularly, should I refrain from questioning if there is any experimental existing evidence towards these considerations (as this is what I have done)?

Again, I don't see the problem here. It seems like we are straining gnats. My question has been answered sufficiently already, and I am attempting to promote nothing more.

 

[QuestionMarks]

My mistake, I thought you had gone back to a local "information only" interpretation.

Oh no, though I guess I should have qualified that I never meant that necessarily local anyways. Re-reading my original post, I see the quandary. But I didn't want to assert any particular view or engage in speculation off it. I just wanted to know what experiments were possible/had existed, and I think I've got sufficient reading to do there. If anybody ends up waning to close this to prevent it from meandering off-topic needlessly, I feel sated.

 

[DrChinese]

Just kind of an aside here...but how can you say with absolute certainty that two particles have never interacted?

How? Because the photons did not exist at the same time, in any reference frame.

Now, you can always argue that the photons did not exist at the same point in time, but the apparati that gave rise to them did. True enough, and therein lies part of the problem. They can be created by separate lasers that have interacted in the past. (In fact, the lasers will need to be phase locked to each other to create the effect.)

However, that doesn't change the fundamental issue that they can be entangled after neither exist any longer. And that a future setup is an integral part of the overall context (don't forget Bell). So arguing that there are hidden variables in place at the creation of the photon pair that are identical for both becomes untenable. Keep in mind that every photon emerging from any laser is essentially phase locked to every other one - and yet they are NOT all entangled. So then you must ask how the pairs that display entanglement got that way. And it is not because they interacted in the past.

 

[stevendaryl]

That hints of the "shut up and calculate" culture often found in modern physics, which is a bit of a presumed philosophy itself unfortunately. And though we do not need the ontology per say, why discourage the pursuit? It only becomes philosophy (which is no evil, just a different forum) when we stop looking for empirical evidence. Presuming no experiment can be performed which would give us a better interpretational view of reality would be an unnecessary assumption (and I allow myself optimism at least). So until then, and especially while we are particularly focusing on what empirical support is out there, I see no concern in my thought venture.

The "shut up and calculate" attitude is a little bit unfortunate, because in the past, thinking about ontology---what might be REALLY going on that would explain the mathematics---is often a good way to get ideas for new (testable) theories that go beyond existing theories. A sort-of example was that once upon a time, there was a very sophisticated mathematical theory that was used to calculate celestial quantities such as timing of eclipses, and positions of planets, etc. This was the Ptolemy theory, which basically described the motion as planets moving on the surface of spheres, which move on larger spheres, which move on larger spheres, etc. The innermost sphere was centered on the Earth. Then Kepler saw that if you instead allow planets to move in ellipses, and shift the center from the Earth to the Sun, the same predictions could be made much simpler. And Kepler's theory itself inspired Newton's law of gravity.

In the case of quantum mechanics, it's certainly possible that thinking about ontology will lead to something new and interesting. However, every attempt along those lines has resulted in making things more complicated without making any improvements to the ability to make predictions. So except for a small number of noncomformists, I think most people have given up on ontology. That's what "shut up and calculate" means to me.

 

[bhobba]

Why should this limit my curiosity though?

Of course it shouldn't.

You can go in any direction you feel like - and indeed that is one of the hallmarks of science - as one whit said - free scientific enquiry - the first word is redundant.

I am simply pointing out interpretive type speculations that are not experimentally testable haven't led anywhere - and indeed if they are not experimentally testable many would argue it is unlikely to. But opinions are like bums - everyone has one - it doesn't make it correct - even mine - no - especially mine.

In this connection though I must point out forum rules don't allow philosophy. Discussing and understanding what various interpretations say is on topic, but philosophically dissecting them isn't.

Thanks
Bill

 

[QuestionMarks]

In this connection though I must point out forum rules don't allow philosophy. Discussing and understanding what various interpretations say is on topic, but philosophically dissecting them isn't.l

Exactly. But I am not the one doing this. My question was asking about empirical evidence that might or might not be accessible regarding a matter, and that's done.

 

[Imafungi]

Of course it shouldn't.

You can go in any direction you feel like - and indeed that is one of the hallmarks of science - as one whit said - free scientific enquiry - the first word is redundant.

I am simply pointing out interpretive type speculations that are not experimentally testable haven't led anywhere - and indeed if they are not experimentally testable many would argue it is unlikely to. But opinions are like bums - everyone has one - it doesn't make it correct - even mine - no - especially mine.

In this connection though I must point out forum rules don't allow philosophy. Discussing and understanding what various interpretations say is on topic, but philosophically dissecting them isn't.

Thanks
Bill

Science cannot exist without philosophy when considering generally 'philosophy' is 'to think'.

 

[Imafungi]

First, no one actually understands the underlying mechanism by which entanglement works. That is why there are multiple interpretations. From 1935 until Bell's Theorem, your local realistic explanation was considered one possible interpretation (the EPR interpretation for lack of a better name).

However, Bell showed that interpretation to be flawed. The EPR interpretation has since been proven incorrect many times over in experiment. Until you read and understand Bell, you won't make any progress towards understanding WHY the EPR interpretation is wrong. Better yet, read the EPR paper first and then Bell.

BTW: In QM, the ordering of the measurements on Alice and Bob (particles 1 and 2) do not affect the outcome in any discernible fashion.

Bells theorem doesn't say anything about this more intuitive and rational interpretation being impossible, do you have an example of an experiment or logical argument which proves this analogy is not appropriate in regards to 'quantum entanglement experiments'?:


There is a red ball and a blue ball. You and I are in another room blindfolded. A random person walks in the room with the red ball and blue ball and puts each in a bag. You and I walk in the room and each grab a bag. I go to the moon. You stay there. We know without looking that the results will be 1 red ball and 1 blue ball. I look in my bag on the moon, and its the blue ball. I instantly know that your ball is the red ball.

If this analogy can be used to describe every entanglement experiment, the analogy would be related to the 'spooky entanglement interpretation'; I got my bag and you get your bag. I go to the moon. Before I or your look in our bags, I have a red/blue ball in my bag, and you have a red/blue ball in your bag. When the bags were in the same room before they were separated, they were entangled. When I looked in my bag the red/blue ball turned into a blue ball, which then faster than the speed of light, notified your red/blue ball to turn into a red ball.

 

[stevendaryl]

There is a red ball and a blue ball. You and I are in another room blindfolded. A random person walks in the room with the red ball and blue ball and puts each in a bag. You and I walk in the room and each grab a bag. I go to the moon. You stay there. We know without looking that the results will be 1 red ball and 1 blue ball. I look in my bag on the moon, and its the blue ball. I instantly know that your ball is the red ball.

That's exactly the sort of explanation for entanglement that Bell proved doesn't work (at least not without faster-than-light communication). In your analogy, there is only one question: "Is the ball red, or is it blue?" The answer for one ball has to be the opposite of the answer for the other ball, and you can certainly come up with a "hidden variable" explanation, namely the color of the ball is determined from the beginning, and it never changes.

In the quantum case, there are many different questions you can ask about an entangled particle. Specifically, for any direction \vec{D}, you can ask (of an electron): Does the electron has spin-up in direction \vec{D}, or spin-down?

If you produce an entangled electron/positron pair, and send the electron to one experimenter, Alice, and send the positron to the other experimenter, Bob, then the predictions of quantum mechanics are:

1. No matter what direction D_A that Alice picks, she gets spin-up half the time, and spin-down half the time.
2. Similarly for and direction D_B that Bob picks.
3. However, the probability that both measure the same result (up or down) is cos^2(\theta/2), where \theta is the angle between Alice's direction and Bob's direction.

[edit: I should have written sin instead of cos in that expression]

It's not immediately obvious, but there is no way to explain this correlation--that cos^2(\theta/2)--using a hidden-variable explanation. That's what Bell proved. So you were just not correct in saying:

Bells theorem doesn't say anything about this more intuitive and rational interpretation being impossible

 

[Imafungi]

That's exactly the sort of explanation for entanglement that Bell proved doesn't work (at least not without faster-than-light communication). In your analogy, there is only one question: "Is the ball red, or is it blue?" The answer for one ball has to be the opposite of the answer for the other ball, and you can certainly come up with a "hidden variable" explanation, namely the color of the ball is determined from the beginning, and it never changes.

In the quantum case, there are many different questions you can ask about an entangled particle. Specifically, for any direction \vec{D}, you can ask (of an electron): Does the electron has spin-up in direction \vec{D}, or spin-down?

Yes, red or blue was my analogy for spin up or spin down.

I haven't seen any evidence that has led me to believe that when 'entangled particles are created', two particles with completely distinct properties arent created, which maintain their properties until measurement.

I asked in a follow up question to my original analogy, something which would force me to consider non locality and your spooky action interpretation of entanglement, which is:


When the first particle is measured, and the second particle is not measured. When the first particle is measured, at that instant does the second particle alert a system of its state? As in, is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

Or do the experimenters have to measure the second particle by themselves after the first is measured?

 

[Nugatory]

Bells theorem doesn't say anything about this more intuitive and rational interpretation being impossible, do you have an example of an experiment or logical argument which proves this analogy is not appropriate in regards to 'quantum entanglement experiments'?:

Here's the entire logical process (which may have gotten lost in the details in some of the discussion above):

1) If the more intuitive and rational interpretation is correct, then Bell's inequality must hold. That's the "theorem" part; Bell's theorem proves that if the result of an observation is determined solely by the properties of the observed object (no quantum spookiness, we find a red ball in the bag when open it because the ball was red all along) the inequality must hold. To get an interesting example we have to be looking at more than one property of the balls - we'd extend the analogy to say that not only is one ball blue and the other red, but also one ball is made of wood and the other of plastic, one ball has a white stripe painted on it and the other doesn't. The intuitive model that you're thinking about says that when we open the bag and find a red plastic ball with no stripe, it's because we put a red plastic ball with no stripe into the bag so that's what was there all along and the other bag must contain a blue wooden ball with a stripe.

2) Under certain conditions, quantum mechanics predicts results in which the inequality will be violated. . Therefore, either the inequality is never violated and quantum mechanics is wrong; or the inequality is sometimes violated and the intuitive/rational explanation is wrong. It's not possible for the intuitive/rational explanation to be correct and for the inequality to be violated.

3) In actual experiments the inequality is violated.. Therefore, the intuitive/rational explanation cannot be correct.

 

[bhobba]

Bells theorem doesn't say anything about this more intuitive and rational interpretation being impossible, do you have an example of an experiment or logical argument which proves this analogy is not appropriate in regards to 'quantum entanglement experiments'?:

Bells theorem rules out naive reality:
http://en.wikipedia.org/wiki/Naïve_realism
'Bell's theorem proved that every quantum theory must either violate local realism or counterfactual definiteness.'

Local realism and counterfactual definiteness are, by definition, the assumptions of naive realism.

You can retain one or the other - but not both.

Which do you want to get rid of? Personally I don't believe in either - but that's just me.

This is VERY well known.

Thanks
Bill

 

[Nugatory]

first particle is measured, at that instant does the second particle alert a system of its state? As in, is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

Or do the experimenters have to measure the second particle by themselves after the first is measured?

We always have to measure both particles.

In fact, we cannot even detect the entanglement until after we compare the results from both sides. We set up our two detectors, you sit at yours and I sit at mine, and we record the state of the particles that come by. You'll see some spin-up and some spin-down and so will I, and it'll be as random as if we were each flipping our own coin and recording heads/tails.

Then we get together and compare notes. At exactly noon, you saw a spin-up particle and I saw a spin-down one - interesting, but we'd expect that to happen one in every four times if we were just flipping coins so it's no great surprise. Then we see that at three seconds past noon, you and I both detected particles, and one was up and one was down... And a few seconds after that we both detected particles again, and again one was up and the other down... And slowly the pattern emerges.

 

[bhobba]

Science cannot exist without philosophy when considering generally 'philosophy' is 'to think'.

Scratching my head about that. Here is its definition: 'the study of the fundamental nature of knowledge, reality, and existence, especially when considered as an academic discipline.'

Its not 'to think', its to think in a certain way about certain issues. Just like the other fundamental science concerned with logic - mathematics - is also about thinking - but thinking about certain issues in its own way.

There is a well known 'conflict' between science and philosophy that IMHO illustrates the point. The very influential philosopher Kant said Euclidean geometry was a priori. Kant was a great philosopher and his view held a strong sway. However the equally as great mathematician, and mathematical physicist, Gauss, found otherwise. But the climate at the time was such he held off publishing because it would have meant going up against Kant.

Here is a bit of fiction illustrating the view at the time:
http://www.ralphmag.org/EQ/gauss-kant.html

But truth can't be denied, and Kant was wrong. In general in 'conflicts' between philosophers and science, science is usually proven correct. Indeed philosophers generally don't agree on anything, whereas scientists agree on quite a lot.

I think Wienberg sums the view up quite well:
https://www.google.com.au/url?sa=t&...-4DgDQ&usg=AFQjCNHg_elaIirwh-1Q7Al_kVaI8Fz8YA

Thanks
Bill

 

[stevendaryl]

Yes, red or blue was my analogy for spin up or spin down.

I haven't seen any evidence that has led me to believe that when 'entangled particles are created', two particles with completely distinct properties arent created, which maintain their properties until measurement.

That's what Bell's proof shows, that such an interpretation of entanglement doesn't work (at least, not without faster-than-light influences).

When the first particle is measured, and the second particle is not measured. When the first particle is measured, at that instant does the second particle alert a system of its state? As in, is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

Or do the experimenters have to measure the second particle by themselves after the first is measured?

The timing of the two measurements is pretty arbitrary. You produce an electron/positron pair, Alice at some later point measures the spin of the electron. Bob later measures the spin of the positron. The correlations don't depend on the order of the measurements, or the timing. Bob might not perform his measurement until long after Alice performs hers.

When you are asking for "evidence" for something, do you mean an experiment that doesn't require you to do any math to understand the result? The idea that entanglement can be explained by pre-existing properties of the two particles sounds plausible, and you have to actually do some math to see that it doesn't work out.

For example, let's try to explain the EPR results assuming that electrons and positrons have actual spins that point in some direction. When a correlated pair is created, the two spin directions are opposite: The electron's spin is in some random direction \vec{S_e} and the positron's spin is in the opposite direction \vec{S_p} = - \vec{S_e}. That's simple enough.

Now, we have to account for the fact that no matter what spin direction Alice decides to measure, she finds either spin-up or spin-down. So even though the spin can point in any direction, there are only two possible measurement results. How is that possible? Well, you can assume that if the electron's spin is in direction \vec{S_e}, and Alice measures the spin in direction \vec{D_A}, then Alice will measure spin-up if the angle between those is less than 90 degrees, and will measure spin-down if the angle is more than 90 degrees.

Similarly, if Bob measures the spin in direction \vec{D_B}, and the positron has spin \vec{S_p}, then he will measure spin-up if the angle between those is less than 90 degrees, and spin-down if the angle is more than 90 degrees.

That explains the perfect anti-correlation: If Alice and Bob both choose the same direction: \vec{D_A} = \vec{D_B}, then they always get opposite results. Great!

But what if they choose slightly different angles? Then this model predicts that the probability that Alice and Bob get the same result (both spin-up or both spin-down) is \theta/180, where \theta is the angle between D_A and D_B (in degrees). The QM prediction is sin^2(\theta/2). The two predictions aren't the same. QM predicts a much STRONGER correlation than this model.

So this particular model doesn't work. How do you know a variant won't work? That's really what mathematics is good at: proving something about an infinite number of possibilities without checking each possibility individually.

 

[stevendaryl]

There is a well known 'conflict' between science and philosophy that IMHO illustrates the point. The very influential philosopher Kant said Euclidean geometry was a priori. Kant was a great philosopher and his view held a strong sway. However the equally as great mathematician, and mathematical physicist, Gauss, found otherwise. But the climate at the time was such he held off publishing because it would have meant going up against Kant.

Hmm. Whether it was a philosophical argument, or not, it seems that if Kant had an argument showing that non-Euclidean geometry is impossible, then the argument was wrong. He made a mistake in the argument, somewhere. I don't see how that is an indictment against philosophy in particular, except that they need to tighten up their standards for rigor of arguments.

 

[bhobba]

I haven't seen any evidence that has led me to believe that when 'entangled particles are created', two particles with completely distinct properties arent created, which maintain their properties until measurement

That's the assumption of reality, which in this context means properties exist prior to measurement.

Specifically Bells theorem shows you can't have local reality and counterfactual definiteness. Counterfactural definiteness is the outcome can be computed. Locality means influences can't travel faster than light.

You can reject anyone on those three things - but you can't have them all - with a caveat I will mention later.

For example Bohmian mechanics rejects locality, but has counterfactual definiteness and reality.

I hold to the statistical ensemble interpretation which rejects both realism and counterfactural definiteness but keeps locality - here locality means locality in the sense of QFT otherwise known as the cluster decomposition property - which states - as per Wienberg in his famous QFT text - 'It is one of the fundamental principles of physics (indeed, of all science) that experiments that are sufficiently separated in space have unrelated results…'. Specifically this refers to uncorrelated systems - Bell theorem refers to correlated systems.

Others have other takes.

It even possible to have all three if you believe QM is an approximation to some deeper theory eg primary state diffusion is a theory of this type.

In discussions of this type Bell came up with the Bertlmann's socks analogy:
http://thelifeofpsi.com/2013/10/28/bertlmanns-socks/

Added Later:

I forgot to add counterfactual definiteness and reality are closely related - but are subtly different. I think most would accept or reject both together. I certainly would because I simply can't get my mind around the idea you can compute the outcome of an observation and it in some sense doesn't exist before the observation. I suppose its possible, but its a pretty subtle sort of difference. Also some seem to weaken realism to not being determined by a conscious observer.

Thanks
Bill

 

[DrChinese]

Bells theorem doesn't say anything about this more intuitive and rational interpretation being impossible, do you have an example of an experiment or logical argument which proves this analogy is not appropriate in regards to 'quantum entanglement experiments'?:


There is a red ball and a blue ball. You and I are in another room blindfolded. A random person walks in the room with the red ball and blue ball and puts each in a bag. You and I walk in the room and each grab a bag. I go to the moon. You stay there. We know without looking that the results will be 1 red ball and 1 blue ball. I look in my bag on the moon, and its the blue ball. I instantly know that your ball is the red ball.

If this analogy can be used to describe every entanglement experiment, the analogy would be related to the 'spooky entanglement interpretation'; I got my bag and you get your bag. I go to the moon. Before I or your look in our bags, I have a red/blue ball in my bag, and you have a red/blue ball in your bag. When the bags were in the same room before they were separated, they were entangled. When I looked in my bag the red/blue ball turned into a blue ball, which then faster than the speed of light, notified your red/blue ball to turn into a red ball.

It is clear you haven't read Bell (1964) at all, since your analogy is precisely what it was meant to address. The EPR (1935) paper used a similar example as yours. I assume you have not read it either, since that was what Bell was responding to. And experiments such as Aspect et al (1982) confirm that local realism (your analogy) can be ruled out. See the links on this page:

http://www.drchinese.com/David/EPR_Bell_Aspect.htm

If you would like a simple explanation of how Bell's Theorem rules out hypotheses such as yours, the following is about as easy as it gets:

http://www.drchinese.com/David/Bell_Theorem_Easy_Math.htm

The short version is that your analogy works fine for red/blue balls. No one disputes that, and that is why EPR stood for 30 years. Bell realized the analogy failed with certain pairs of measurements. In your analogy: red balls and balls that are a mixture of 1/3 red and 2/3 blue. QM makes accurate predictions for these variations, while local realistic theories make inconsistent predictions. This is because local realistic theories have a requirement that QM does not: the outcome of a measurement on Alice must be completely independent of the nature of a measurement performed on Bob in another location.

 

[DrChinese]

I asked in a follow up question to my original analogy, something which would force me to consider non locality and your spooky action interpretation of entanglement, which is:

When the first particle is measured, and the second particle is not measured. When the first particle is measured, at that instant does the second particle alert a system of its state? As in, is it in a superposition in some apparatus either just vibrating in place or traveling around in a circle, and then the first particle is measured, and that second particle just instantly finds the nearest detector to exclaim to the experimenters that its entangled pair had been measured?

Or do the experimenters have to measure the second particle by themselves after the first is measured?

You are asking a question no one knows the full answer to. It is "possible" that measurement of Alice affects Bob non-locally via an instantaneous change. There are other interpretations that explain the situation too. In the Bohmian Mechanics view, there is a pilot wave which influences both particles instantaneously and that is the common cause.

 

[bhobba]

I don't see how that is an indictment against philosophy in particular, except that they need to tighten up their standards for rigor of arguments.

That is the exact problem with philosophy - their arguments are so tight just about every philosopher believes something different and the others need to tighten up their arguments .

The issue is they can't or don't want to use that final arbiter - experiment.

Thanks
Bill

 

[QuestionMarks]

The issue is they can't or don't want to use that final arbiter - experiment.

To be fair, a philosopher might also be a scientist. Historically, that's quite what natural philosophy was. Given this, your statement might be a bit disingenuous. Philosophy is quite useful wherein experimental capabilities do not currently exist or wherein one is attempting to determine which experimental route to pursue. Now in current culture, the tendency you mention might exist, but as stevendaryl said, I wouldn't see that as an indictment against philosophy itself (maybe just the trending people who do it).

I think we should resist that line of dialogue though. The value of philosophy is a bit off-topic and could easily I imagine spurn a whole other quite heated thread. Such questions of value are a bit philosophical themselves, and thus maybe not quite kosher forum rules. I do think Imafungi's questioning is a bit more related to the OP, which albeit was answered, may help others gain more insight.

 

[Imafungi]

1) If the more intuitive and rational interpretation is correct, then Bell's inequality must hold. That's the "theorem" part; Bell's theorem proves that if the result of an observation is determined solely by the properties of the observed object (no quantum spookiness, we find a red ball in the bag when open it because the ball was red all along) the inequality must hold. To get an interesting example we have to be looking at more than one property of the balls - we'd extend the analogy to say that not only is one ball blue and the other red, but also one ball is made of wood and the other of plastic, one ball has a white stripe painted on it and the other doesn't. The intuitive model that you're thinking about says that when we open the bag and find a red plastic ball with no stripe, it's because we put a red plastic ball with no stripe into the bag so that's what was there all along and the other bag must contain a blue wooden ball with a stripe.

2) Under certain conditions, quantum mechanics predicts results in which the inequality will be violated. . Therefore, either the inequality is never violated and quantum mechanics is wrong; or the inequality is sometimes violated and the intuitive/rational explanation is wrong. It's not possible for the intuitive/rational explanation to be correct and for the inequality to be violated.

3) In actual experiments the inequality is violated.. Therefore, the intuitive/rational explanation cannot be correct.

Ok, I am with you on 1).

2). Is it not true the the quantum mechanical predictions that result in the inequality are based off of equations which include probabilities, in other words, equations infused with ignorances? And so you are saying from the vantage point of complex puzzles (equations) with missing pieces, a possible thought to have is that by bashing the puzzles together an outcome will occur which is different than the intuitive logic we are used to expecting from reality?

3). This is the step I am up to, and in the sense that I am asking; how exactly has an experiment disproven my analogy, in what exact way? Because so far I have only seen experiments which could be interpreted to be analogous with my analogy. I have not seen a reason to believe that in my analogy, what believers of spooky action at a distance are saying is, in that scenario with the bag, the real classical expression of that, in the bag would be a red/blue ball and a red/blue ball in the other, each in superposition, and when one is measured, it tells the other at faster than the speed of light to turn into the opposite color of the measured.

Which is why a follow up question I asked was; When the first particle is measured in an entangle experiment, does the second particle (without human interaction) alert the experimenters that its entangled partner has been measured?

Do you comprehend what I am trying to get at with this question? Because if the answer is no, is the answer that 'both particles no matter what order being measured, must be willfully observed by the experimenters at a time of their choice?