Can absence of hidden variables save locality?

[zonde]

Before (2), I said that QM is assumed. Therefore, (2) is correct.

Yes, my fault.
Then I see no fault with your reasoning.

 

[Demystifier]

Then I see no fault with your reasoning.

How about the objections in #28?

 

[zonde]

Yes, I see what you mean. But if we take this litterality, and with "predict with certainty" imply something that inerrable (* otherwise it's IMHO meaningless statement from a rational perspective), then it's clear already here that there exists no physical reality at all.

Well, their definition of reality is only sufficient i.e. it is special case.
So I would say you are too quick to assert that there exists no physical reality even if you take that definition literally.

Because what I think most people do have in mind, is not actually a proper prediction, it's just a DESCRIPTION (of say en ensemble).

This difference in perspective is important for me. It's the difference between descriptive and decision theoretic views.

The big difference is understanding and acknowleding the difference between and EXPECTED outcome, and a DEDUCTIVELY "predicted" outcome.

Real expectations (I'm not talking about descriptions of an ensemble) are never certain. Testing them is nothing by a game we can chose to play. It's a learning process.

This fact is completely ignored by people who insist on the descriptive view.

IMHO, all that QM actually does is to produce a rational expectation of the future. It does not deductively PREDICT the future; because there are a lot of implict ASSUMPTIONS that are not certainly known. Such as we have closed system etc. There is no way these things are known in reality.

Not sure.
Theory can't make practical expectations for the future. It can make only prediction for idealized conditions. Then we can use this theoretical prediction as baseline to produce expectations. (Single) theory does not have to handle all those fine details required for practical expectation. It will become too unwieldy.

No real inference can produce 100% confidence, except in the subjective sense, but then that is just teh same as the "rational expectation", that it we count evidence to our limits, when ALLL *available* evidence supports A; then we act AS IF A is 100% correct. But this doesn't mean it is, all it means IMHO is that it's rational to ACT as if it is. I see the distinction as important here.

I too see this as important point.

The statistical view, represents a "LIMIT" of the decision theoretic view, where the decision problems pretty much becomes DESCRIPTIVE, and the expectations are 100% confident beeing based on infinite ensembles. But this limit is (in my view) never reachable in nature, because of informaion capacity constraint of a given system. And this fact makes a differece to the action of these systems.

If by the statistical view you mean ensemble interpretation then there is more to it (at least from my viewpoint). It's that ensemble has to be physical i.e. there is physical interaction within ensemble.

I guess I can agree with this.

Perhaps we agree, I just wanted to expand about the difference. The real question is; are we here to describe nature in the statistical sense; which MEANS simply describing our acquired information (which NOTE, really means we described our own information anyway! and this is never complete or settled) or are we have to act based upon expectations of nature? Then science is supposed to give us the answer to what RATIONAL expectations are.

I agree with that.

But a rational expectation can be "wrong", yet correctly formed! This is a large different from the purely descriptive view of science. IE. sometimes you make "correct decisions" in the sense of rational, but they turn out destructive. But I think this is how nature works too. An atom responds to it's environment, and fields not due to what is true or false, but it rather just rationally (but randomly) responds to any perturbation.

This is the process I think we should understand in foundations of QM.

(*) I know some people do drop the inferrability constraint, but then, this is exactly where you subscrive to structural realism. This is not a logical implication! It's an IMO (maybe rational EXPECTATION) but certainly not a valid deduction.

/Fredrik

 

[Demystifier]

We have the Bell theorem which, in symbolic notation, can be written as
H => not L ... (1)
i.e., if hidden variables exist then nature is not local.

But we also have the 1935 Einstein-Podolsky-Rosen result
L => H ... (2)
i.e., if nature is local (which they tacitly assumed) then hidden variables exist (i.e., "QM is incomplete").

Here is one additional brain teaser, to test your understanding of logic.

(1) is equivalent to
L => not H ... (4)
However, (4) is not compatible with (2). Does it mean that the results of Bell are not compatible with those of EPR? If yes, why yes? If not, why not?

 

[zonde]

How about the objections in #28?

Only if you adopt their particular version of locality which assumes something akin to Bell's local beables that determine observed experimental outcomes (a non-realist might use a different definition of "locality" that is only concerned with whether the results of observable measurements can allow us to transmit signals FTL, for example).

Let's say I adopt their version of locality. But anyways what is this other version of locality?

And there are also other hidden assumptions they make, like the assumption that each measurement yields a single unique result, which might be violated in a many-worlds type interpretation--see my post [post=1647627]here[/post] on how MWI advocates argue theirs is a local interpretation, and the simple "toy model" I provided in [post=1557143]this post[/post] showing how if there are multiple copies of each experimenter who observe different outcomes, and no need to decide which copy of an experimenter "over there" is part of the same world as a copy of an experimenter "over here" until there's been time for a signal to pass between them, then you can in principle explain Bell inequality violations in a local way.

I see MWI as attempt to sneak in retro causality through the backdoor. Just can't take it as scientific theory.

 

[zonde]

Here is one additional brain teaser, to test your understanding of logic.

(1) is equivalent to
L => not H ... (4)
However, (4) is not compatible with (2). Does it mean that the results of Bell are not compatible with those of EPR? If yes, why yes? If not, why not?

Final result for both is that QM is not compatible with assumptions that are made. In that they agree.

 

[Demystifier]

Final result for both is that QM is not compatible with assumptions that are made. In that they agree.

Wrong answer. Next?

 

[SpectraCat]

Wrong answer. Next?

From the point of view of formal logic, I think the answer is yes, because if two arguments start from the same set of premises (L, in this case), and yet arrive at contradictory conclusions, then one argument must be logically flawed. However if the definitions of 'L' in the two cases are different, then it is possible for both propositions to be logically correct.

So, in order to demonstrate that EPR and Bell are logically incompatible, you must first show that the logical negation of Bell's Theorem produces the same definition of locality as EPR. From what I can tell from reading hundreds of posts on this topic, that is something of a point of contention . I am still not well-versed enough in Bell and EPR to know the final answer, but I think my description of the formal logic is correct.

 

[Demystifier]

From the point of view of formal logic, I think the answer is yes, because if two arguments start from the same set of premises (L, in this case), and yet arrive at contradictory conclusions, then one argument must be logically flawed. However if the definitions of 'L' in the two cases are different, then it is possible for both propositions to be logically correct.

So, in order to demonstrate that EPR and Bell are logically incompatible, you must first show that the logical negation of Bell's Theorem produces the same definition of locality as EPR. From what I can tell from reading hundreds of posts on this topic, that is something of a point of contention . I am still not well-versed enough in Bell and EPR to know the final answer, but I think my description of the formal logic is correct.

Wrong again. Even if your understanding of Bell and EPR is correct, your formal logic is not.

Hint:
Is the statement
"If x>3 then x>2."
a true statement? Is it true for any x? How about x=1?

 

[JesseM]

Let's say I adopt their version of locality. But anyways what is this other version of locality?

Well, some physicists say that quantum field theory is "local" in the specific sense that the field operators at each point (which I think give the probabilities or expectation values for the outcome of some measurement at that point) evolve in a way that's described by local Lorentz-invariant equations--see the top of p. 3 here for example. And there is also the fact that it's been proven impossible to use entanglement in quantum field theory to communicate FTL.

I see MWI as attempt to sneak in retro causality through the backdoor. Just can't take it as scientific theory.

Why "retro causality"? The "toy model" I suggested in [post=1557143]this post[/post] could be simulated on a regular pair of separated computers with no need for any signals from the future...

 

[zonde]

Hint:
Is the statement
"If x>3 then x>2."
a true statement? Is it true for any x? How about x=1?

Ah, (2) and (4) can both be true if L is false.

 

[SpectraCat]

Ah, (2) and (4) can both be true if L is false.

Of course .. duh.

 

[unusualname]

I explained where the reasoning went wrong in post #2, Bell has a valid argument, EPR don't. The only thing reasonably argued is that hidden variables would have to be non-local. Nothing from the EPR argument is applicable, it is nonsense.

 

[DrChinese]

My claim (subject to criticism) is that this is essentially what EPR obtained in 1935, before the theorem of Bell was known. More precisely, they assumed locality (hence L) and then derived incompleteness (hence => H). Are you familiar with the 1935 EPR paper? If not, then you should read it first before attempting to argue on this thread.

I would say I know this paper fairly well.

The EPR premise was that if you assumed H and L, then you would conclude a more complete specification of the system was possible than QM provided. They made the argument that you had to assume H if the (simultaneous, course) elements of reality existed, which they felt was a reasonable position to take.

I would be interested in how you got L -> H out of their reasoning. I think you will see H is an assumption, not a deduction.

 

[Fyzix]

So what is the current consensus?

That you can only save some sort of locality in some sort of Everett?

 

[Fra]

To the thread description I see no reason to abandon locality. Everything I've seen where people that claim that QM is non-local are confusing correlations with causality.

In my book, correlations between two remote things have nothing to do with non-locality.

Non-locality is if you have remote information influence a local decision (beyond coincidences that is!) or where you have FTL communication.

What one can do is discuss how causality is inferred, from correlations. Then one will see that it's not possible to infer a confident causation, ALL there is are correlations, that leads to various degrees of confidence in EXPECTED causation. This EXPECTED causation is all there is IMO. There need not be a "realist style" causation.

So I think all the way through this analysis do various levels of realism sneak in, that sometimes distort the reasoning.

/Fredrik

 

[Varon]

To the thread description I see no reason to abandon locality. Everything I've seen where people that claim that QM is non-local are confusing correlations with causality.

In my book, correlations between two remote things have nothing to do with non-locality.

Non-locality is if you have remote information influence a local decision (beyond coincidences that is!) or where you have FTL communication.

What one can do is discuss how causality is inferred, from correlations. Then one will see that it's not possible to infer a confident causation, ALL there is are correlations, that leads to various degrees of confidence in EXPECTED causation. This EXPECTED causation is all there is IMO. There need not be a "realist style" causation.

So I think all the way through this analysis do various levels of realism sneak in, that sometimes distort the reasoning.

/Fredrik

You have a book? What's the title?

Do you think a new field (higgs like) can function like a preferred frame? What are possible candidate of bonafide preferred frame? If an instantaneous signal can use it to commuinicate between say between 100 billion light years distance. Causality is not affected, isn't it.

 

[Fra]

No I don't haven't published any books, I meant "in my book" as in the idiom.
http://www.usingenglish.com/reference/idioms/in+my+book.html

in my book = in my opinion

/Fredrik

 

[Varon]

No I don't haven't published any books, I meant "in my book" as in the idiom.
http://www.usingenglish.com/reference/idioms/in+my+book.html

in my book = in my opinion

/Fredrik

Ok. English is not my native language so I don't get certain colloquial or slang.

 

[Fra]

English isn't my native language either. I think your english appears very good to me though.

I see no need for a preferred frame of any kind. All there is are IMO interacting observerframes. The conventional view is that in such cases there are objective transformation rules that defines the observer invariants. But I object to that since this inference is done by an external observer.

/Fredrik

 

[zonde]

Well, some physicists say that quantum field theory is "local" in the specific sense that the field operators at each point (which I think give the probabilities or expectation values for the outcome of some measurement at that point) evolve in a way that's described by local Lorentz-invariant equations--see the top of p. 3 here for example. And there is also the fact that it's been proven impossible to use entanglement in quantum field theory to communicate FTL.

If field operators evolve in Lorentz-invariant fashion then I think it's the same locality and I don't see where it makes the difference.
After all it's simultaneous clicks in two detectors and as long as coincidence tend toward 100% matching as detectors tend toward 100% efficiency it does not affect the reasoning whether reason for clicks are beables or fairly localizable configuration of field.

Why "retro causality"? The "toy model" I suggested in [post=1557143]this post[/post] could be simulated on a regular pair of separated computers with no need for any signals from the future...

Well, with your model it's not "retro causality" but FTL interaction nonethless.
When you pair up different worlds you determine the past that should be already determined. From perspective of single world it is no different then FTL interaction.

 

[Demystifier]

I would be interested in how you got L -> H out of their reasoning. I think you will see H is an assumption, not a deduction.

Well, to explain it, the crucial thing is to give a more careful DEFINITION of H appropriate for the context of the EPR paper. In that context H (hidden variable) is any additional quantity NOT given by the wave function.

The rest is easy. Let us assume QM and L. Consider the state
|psi> = |up>|down> + |up>|down>
before the measurement. Let the measurement reveal that the left particle is in the state |up>. Now from QM we know with certainty that the right particle is in the state |down>.

Now consider an additional assumption that there is no H. This means that the new knowledge must also be described by a wave function, because there is nothing else at disposal (due to the no-H assumption). That means that now the total state must be
|psi'> = |up>|down>
However, the transition from |psi> to |psi'> is not local. On the other hand, L was an assumption. In other words, the additional no-H assumption led to a contradiction. Therefore, as QM and L are taken as assumptions, the no-H cannot be true. It must be false. Therefore, H must be true. Q.E.D.

Note that this is not exactly the same reasoning as in the EPR paper, but is somewhat simplified in order to extract what I need.

If your objection is: "Yes, but such a definition of H is not the one appropriate for the Bell theorem", then you are absolutely right. And that's exactly why the reasoning in the first post is not correct. You cannot consistently combine two different definitions of H and pretend that they are the same.

 

[Demystifier]

Ah, (2) and (4) can both be true if L is false.

Of course .. duh.

Yes.