Questions on Entanglement and Double-Slit Experiment

[ttn]

I note that you never address the issues head on. Your objections are just dopey semantics as a way to avoid the substance. Clearly, you have studied Bell for years without grasping the importance of a, b and c.

And thus endeth my conversation with Dr Chinese. (Not that I can't take it as well as I dish it out. It's just that the rest of his post proves to me that no progress is going to happen, as he's just spouting the same old confusions without even listening to everything I've said several times now.)

We've both made our points as well as we know to make them, and it's up to other readers to decide what they think.

 

[DrChinese]

From Mermin:

"Pause to note that we are about to show that “something one cannot know anything about” – the third entry in an instruction set - cannot exist. For even if instruction sets did exist, one could never learn more than two of the three entries (revealed in those runs where the switches ended up with two different settings)."

The entries are a, b and c in his example (he actually labels them a(1), a(2) and a(3)). These correspond in Mermin's argument to detector orientations of 0, 120 and 240 degrees apart. If a single particle has definite values at these settings, then clearly an entangled twin has equivalent values at the identical settings, right? (This is experimentally confirmed for the so called "perfect" correlations.) IF the entangled pair are truly independent of each other AND the detectors are likewise truly independent of each other - i.e. locality holds - then Mermin says that the results are inconsistent with the existence of a third entry (i.e. a and b can exist but not c). QED.

Of course, this is exactly the same point Bell made, and Mermin simply recast the argument so the math is a bit easier to follow. But there is no real difference in the argument, a point that should be seen by anyone.

So to summarize: The realist (such as Einstein, see quote) says definite values of possible measurements at settings a, b and c exist simultaneously for a single particle, even if they cannot be observed. Bell's Inequality says that either the realist is wrong, or there exist non-local forces.

 

[wm]

Dear DrChinese; I, for one, appreciate your enthusiasms. However: Either your enthusiasm is getting in the way of your editing (= editorial blindness) OR you truly misunderstand the context for Bell's theorem. Look at these:

For anyone who is not convinced that Bell's unit vectors a, b and c are assumed to be SIMULTANEOUSLY real:

Doc; show me one person who does NOT believe that three unit vectors a, b and c are SIMULTANEOUSLY real; and, indeed, without assumption.

and again

Please read his well known article (link below)), and you will see that a, b and c must exist SIMULTANEOUSLY even if only 2 can be observed.

? Only two unit vectors (of three simultaneously real) can be observed? Surely not?

and again

IF the entangled pair are truly independent of each other AND the detectors are likewise truly independent of each other - i.e. locality holds - then Mermin says that the results are inconsistent with the existence of a third entry (i.e. a and b can exist but not c).

The existence of a third unit vector not possible?

and again; the give-away, surely:

does that ONE particle have definite values at 3 different settings a, b and c. I really don't care if you call these unit vectors, directions in space, hidden variables, detector settings or whatever.

Doc; you should care what they're called: unit vectors, directions in space, detector settings are fine, all existing simultaneously; and all measurable. BUT they are surely NOT hidden-variables or whatever? I suggest your familiarity with BT has led to a temporary editorial blindspot: for Bell represents the hidden-variables by lambda!

Helpfully offered, and with best regards,wm

 

[wm]

So to summarize: The realist (such as Einstein, see quote) says definite values of possible measurements at settings a, b and c exist simultaneously for a single particle, even if they cannot be observed. Bell's Inequality says that either the realist is wrong, or there exist non-local forces.

We agree that a, b, c are measurement-device settings; in Bell (1964) he calls them unit vectors.

Now, concerning Einstein, I'm not sure which quote you refer to. BUT as I understand the Bellian situation: the three observables (one from each measurement at the settings a, b, c), do NOT commute.

I'm not aware that Einstein ever accepted that three non-commuting observables simultaneously exist for a single particle.

However: If you are correct, then you would be more accurate in saying:

Bell's Inequality says that either the [naive] realist [as inadvertently represented by Einstein on one (?) occasion] is wrong, or there exist non-local forces.[/b]

In my view: Common-sense local realism remains; to fight another day.

 

[DrChinese]

Doc; show me one person who does NOT believe that three unit vectors a, b and c are SIMULTANEOUSLY real; and, indeed, without assumption.

Now you are having it both ways. The realist believes a, b and c are simultaneously real and definite. But in your subsequent post you call this "naive" realism. Well, I certainly don't care if you call it naive or not. But this is the assumption of realism that Bell made, and that Einstein made. It is critical to Bell's Theorem, and the Theorem does not exist without it.

Einstein certainly was clear on the point, and he was unwavering as well:
"I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it." This statement inspired the title of Mermin's article.

Lastly, to clear up a point that many are confused about: When one speaks of hidden variables, there are actually 2 sets of "somethings" we could refer to. Most people, myself included, casually use them interchangeably - but they really are different in a strict sense. Bell addresses both. The first set is observables: i.e. Bell's unit vectors a, b, c, etc. Of course, QM itself speaks to observables only and goes no deeper. The realist, on the other hand, speculates a deeper level of reality in which the observables have a root "cause" for lack of a better term. In Bell, these are lambda. So think of it like this analogy: when I decide to an offer for lunch, my answer (the observable) is binary (yes or no). But the reasons (hidden variables) for my decision may be many and varied.

 

[ueit]

The theorem just assumes that the "choices" (or, to use more neutral language, "selection" or whatever) of the settings on the two sides are uncorrelated with the state of the pair that's produced.

I agree with that.

Whether that assumption is or is not realized in the experiments, is indeed "about empirical tests". It's not the validity of the theorem, but its applicability to the actual experimental tests, which is the question here.

Here I think you see it backwards. The theorem says that if its assumptions are true (statistical independence between the detector settings and the entangled pair) then the inequality holds. The experiments show that Bell's inequality is violated, therefore the assumption must be false (unless the experiments are thought to be flawed, but I think neither of us takes this position).

So, I hope we have an agreement. All that Bell's theorem and the experimental results prove is that the detector settings and the production and/or the subsequent evolution of the entangled pair are correlated. The delayed choice experiments have proven that these correlations are non-local. The question remains if these non-local correlations necessarily imply a non-local force (or other non-local physical effect) or they can be the result of a local mechanism. The burden of proof is on you to show that the first case is true.

Although it's not necessary I'll describe how the non-local correlation could be achieved IMHO by a local mechanism.

First, I'll clarify what I mean by free will. It is simply the assumption that the future is open, that a system in a certain state (I don't mean "quantum state" but a state which completely describes the system, including all the hidden variables) can evolve in more than one way. It is irrelevant how we perceive this, at a subjective level, a matter of philosophy.

IMHO, the only way to prove that nature is non-local is to assume free will. It is obvious that if the information regarding the future detector setting cannot in any way be "extracted" from the detector’s state the only explanation for EPR experiments is that a non-local mechanism is at work. I see no reason to grant this assumption, however.

So, let's assume that nature is deterministic. This means that the future setting of the detectors can be inferred from the fields generated by them (mainly the EM field).

This happens with gravity. Once the present state is known any future state can be, in principle, calculated. That's why we can send a probe to Pluto.

Now, the information about the detector state arrives to the source, at or bellow the speed of light (no non-local mechanism required), some time before the experiment begins. We only need to posit that the entangled particles are generated with the spin orientation predicted by QM by some yet unknown mechanism given that all the required information about the detector future already exists at that place.

I need to repeat here that we already have an example of a non-local correlation enforced by a local mechanism (the Newtonian non-local force of gravity explained by a local mechanism (space curvature changes at the speed of light) in GR).

So, to repeat a point I made before, if someone wants to deny this -- if someone thinks that there *are* these correlations (which btw is what I meant by the word "conspiracy") -- the burden is squarely on them to provide some kind of argument or evidence. (And no, just saying "well maybe the world is deterministic, such that, in principle, anything that happens anywhere might be correlated with any other thing happenings somewhere else, by a local mechanism in the overlap of their past light cones" isn't good enough. That's just an empty, arbitrary, made up "possibility" which, in science, is treated like what it is: empty BS.)

You are shifting the burden of proof here, because you are making the strong claim that no local mechanism to explain EPR can exist. You either can prove that or you can't. And, you admitted that you can't. I remind you of Bell's words:

Perhaps experimental parameters and experimental results are both consequences, or partially so, of some common hidden mechanism. Then the apparent non-locality could be simulated.

Saying "maybe there was a conspiracy by which the settings [which the experimenters *tried* to make independent and random] were actually not at all independent and not at all random" is not an *explanation* of anything.

It's the same as the randomized drug trial example I gave the other day. If the double blind study shows empirically that 90% of the patients who get a certain drug subsequently recover from cancer, one (obvious) explanation of this fact is that the drug is curing (or helping cure) the cancer. You can't just say "maybe there was some accident or conspiracy whereby those patients who would have survived anyway, were the ones who got the drug, so really the drug doesn't help anybody."

I mean, you can *say* it, but surely nobody thinks that's a genuine scientific *explanation* of anything. In science, properly, if you did say such a thing, the scientists would ask you: what's your evidence that there is some such accident/conspiracy? Do you have evidence that the double-blind character of the study was compromised? Do you have evidence that one of the doctors performing the trial is heavily invested in the stock of the company that makes the drug? etc... The point is, if all you have is an empty "maybe" and not any actual positive evidence, then you don't have anything.

How many times do I have to tell you that I do not reject the experimental evidence of the Bell’s inequality violation? To expand your analogy, I do not deny that the tests are valid and I agree that the drug works. I’m only denying that your proposed mechanism (let’s say, the patients are cured because the drug helps their immune system) is the only one possible. Remember, you have no evidence that your mechanism is true (there is no evidence for the existence of a non-local pilot wave and there is no way to find out).

Um, yes, the empirical violation of Bell's inequalities.

That’s circular. Maybe the aliens are manipulating the results. Do you want evidence? Look at the experimental results, look how well those aliens are manipulating them!
So, show me your “alien” first, and I’ll accept your theory.

More believable than what? You haven't (nor has anyone else) offered any alternative. You've just said: maybe there's a problem with the experiments -- of a sort which, if really there, would indeed undermine my claim that the experiments show nonlocality... but since the possible biasing effects of that kind of problem are well known and are *deliberately* removed in the design of the experiments, there is no evidence (until or unless you provide some) that there actually is any such problem.

Probably you think that by repeating this red-herring (“maybe there's a problem with the experiments” – a claim I never made) you’ll prove your point. It ain’t going to happen.

As I explained, nothing here actually relies on free will. And, on a totally unrelated note, I don't think QM (and its stochastic as opposed to deterministic character) is any kind of basis for belief in free will, at least not what *I* mean by "free will". Free will means we have some actual *control* over what we think and do -- not that we are "stochastic" in the sense of orthodox QM. OQM might support *indeterminism*, but it does not support free will.

I agree with you that indeterminism does not produce free-will. I hope I’ve explained better what I mean by free-will in this discussion.

Yes, you do. You propose that the state of the emitted particles is affected by or affects (by a completely mysterious, unspecified mechanism) the polarizer settings on the two sides (or that they are just all magically correlated without any causal mechanism). That's a conspiracy.

But we know that such a conspiracy exists because of the violation of Bell’s inequality. The only question is what type of conspiracy we have, local or non-local. I agree that we already have a developed non - local theory (BM) and we have no “local” one but this doesn’t prove anything.

You apparently missed the point of that example. It had nothing to do with the truth of QM's predictions or the validity of induction. It had to do with the *arbitrariness* of saying "maybe there's a conspiracy in the experiment which renders the otherwise-obvious interpretation invalid".

What is that “obvious interpretation” and why is it obvious? Remember that we already have a well established theory, relativity, which shows nature to be local.

When experimenters deliberately go out of their way to remove the possibility of a certain kind of correlation (as for example by making a study double-blind), the burden is on the person saying that kind of thing to actually produce some evidence. Otherwise, it's an empty maybe... i.e., it's *nothing*. It's as if you said "maybe magical fairies sprinkled pixie dust in the journal just before you came and looked at it, and if only you could see the real thing you'd find that the experiment had a very different outcome than the one reported there on the pages in front of you." Yeah, maybe.

The same old red-herring again.

What "interaction between the source and detectors"?

EM interaction.

Don't you understand that the experimenters go out of their way to ensure that there is no such interaction (other than the source shooting particles toward the detectors, which they detect), since they know that could bias the data? For example, that's why they do the whole "delayed choice" thing -- without that, there could be a *local* mechanism by which the source "learns" about the settings, and then cleverly adjusts the state of the emitted particles in accordance with those settings, in order to make it *look* like Bell's inequalities are violated (where in fact, they aren't). And, not only do they make the settings at the last minute (after the particles have been created so their state is fixed), they make them *randomly* (i.e., in a way that is deliberately not correlated with anything having anything to do with the particle source) and not just that, but they make them randomly with *independent* random number generators on the two sides. So, unless you can say something about the particular "interaction between the source and detectors" that you have in mind, there is no basis for saying "maybe there is one, and it's biasing the results" -- and hence nothing further to talk about.

I think my example above answers this.

 

[NateTG]

Now you are having it both ways. The realist believes a, b and c are simultaneously real and definite. But in your subsequent post you call this "naive" realism. Well, I certainly don't care if you call it naive or not. But this is the assumption of realism that Bell made, and that Einstein made. It is critical to Bell's Theorem, and the Theorem does not exist without it.

That is not, in fact, the assumption that Bell's theorem makes. Rather, Bell's theorem assumes, not only that said values exist independantly of measurement, but also that any particular combination of values has a well-defined probability.

 

[ttn]

Here I think you see it backwards. The theorem says that if its assumptions are true (statistical independence between the detector settings and the entangled pair) then the inequality holds. The experiments show that Bell's inequality is violated, therefore the assumption must be false (unless the experiments are thought to be flawed, but I think neither of us takes this position).

You forgot the other major explicit assumption: locality.

So, I hope we have an agreement.

Not really.

All that Bell's theorem and the experimental results prove is that the detector settings and the production and/or the subsequent evolution of the entangled pair are correlated.

No, the experiments show that the outcomes are correlated in a certain way. The Theorem proves that such correlations cannot be produced by any local mechanism. So there is more here than "mere correlation".

The delayed choice experiments have proven that these correlations are non-local. The question remains if these non-local correlations necessarily imply a non-local force (or other non-local physical effect) or they can be the result of a local mechanism. The burden of proof is on you to show that the first case is true.

No it isn't. The theorem proves specifically that "they" CANNOT "be the result of a local mechanism." That is the whole beauty of the theorem. Of course, as we agree, the derivation involves some subsidiary assumptions such as that the detector settings aren't affecting (or affected by or, really, in any way correlated with) each other or the state of the emitted pair. But as I've said several times now, there is every reason to believe that this condition is satisfied by the actual experiments (because the experimenters went out of their way to ensure that it was satisfied). So... the conditions of the theorem are satisfied, and so the conclusion of the theorem -- that no local theory can account for the observed data -- stands.

I understand you don't agree with this, and I respect the clarity with which you've formulated your arguments (as contrasted with some other people around here!). But there's probably no point arguing about this. Either you are willing to accept, without evidence, that there is some kind of fine-tuned conspiracy between the "random" settings on the two sides, or (like me) you aren't.

IMHO, the only way to prove that nature is non-local is to assume free will.

What I think you miss is that the only way to prove *anything* is to assume free will. Everything humans have ever claimed to learn from doing empirical science, requires free will. Right? You could *always* say "maybe the results of that study only came out that way because of some pre-established harmony between objects and subjects". And if someone says "but that study was double-blind, and done independently on 3 different continents by 500 independent scientists using vastly different equipment [or whatever...]" you can just say "well, they *tried* to take all these precautions and make things double blind and independently confirm the results and whatnot, but in actual fact they failed to do this, and, really, the different trials were all intricately dependent, such that the results are highly biased". Or maybe more simply: "maybe you only think that experiment proved X because you were pre-programmed to believe that, even though it is false." Yeah maybe. The point is, without freewill (in the relevant sense, which is just the ability to decide what questions to ask of nature in a way that isn't forced on us by nature) you can't do science *at all*. So if you're going to go down this road in order to avoid the conclusion from Bell that nature violates relativistic causality, then you're also (if you choose to be consistent) going to have to deny that we really figured out that matter is made of atoms, that neutrinos oscillate and have mass, that Newton's constant G has a certain value, that immunizations can prevent certain horrible diseases, etc...

So, let's assume that nature is deterministic. This means that the future setting of the detectors can be inferred from the fields generated by them (mainly the EM field).

No, this is too narrow. Determinism (and assuming locality) would mean only that the future setting of the detector can be inferred from the totality of the past light cone of the "setting" event. Well, suppose we choose the setting by measuring the energy of a cosmic microwave background radiation photon (coming from a direction in space just opposite that of the particle source) and suppose the "choice" between two settings is arranged to be determined by whether the millionth digit in the decimal expansion of that photon's energy (in eV) is even or odd. And same thing on the other side. So, your point is still true, right? You can still say: well, but still there's a possible local mechanism which accounts for the (merely apparent) violation of Bell's inequalities in the experiment. But see how crazy (conspiratorial) this becomes? You have to now believe that the millionth digit of the energies of two photons that were created 15 billion years ago, are somehow pre-harmonized so as to give just the settings needed for this Bell experiment to erroneously *appear* to violate the inequality. Well, what can one say? Yes, in principle that is "possible", and it is "possible" that those two digits could have gotten correlated up in the appropriate way 15 billion years ago by some fully local mechanism. But, come on, this is crazy. If you're going to allow something like this as a reasonable basis for believing that the experiments might be biased, then you should allow equally crazy things as bases for believing that all experiments might be biased, and now you can't believe *anything*. (...including, by the way, all the stuff that makes you believe relativity which is presumably the only reason you want to work so hard to deny Bell's conclusion.)

Now, the information about the detector state arrives to the source, at or bellow the speed of light (no non-local mechanism required), some time before the experiment begins. We only need to posit that the entangled particles are generated with the spin orientation predicted by QM by some yet unknown mechanism given that all the required information about the detector future already exists at that place.

This passage makes me think you slightly misunderstand what's required. It's not true that the local beables in the detector at time T are sufficient to determine the state of the detector at time T + 2L/c (where L is the distance from the detector back to the source). So even if you allow the detector to "broadcast" its current state toward the source (at speed c) at time T -- so that at time T + L/c the source learns about its state, just as it is emitting a particle pair -- you may *not* assume that this is equivalent to the source "knowing" about the *later* state of the detector (at time T + 2L/c, when the photon gets there and the measurement gets made). The reason is what I explained above: the set of events which might (locally) affect the detector setting is not the "past light cylinder", but the past light *cone*. So stuff coming in from outside -- and, in particular, from the direction opposite the source -- could affect the final setting (at T+2L/c) and the source would have *no local way to know about this incoming information* and hence no way to know about the final setting of the detector.

You'll say this doesn't matter and that it's still "possible in principle" that there could be some kind of conspiracy in which the settings on the two sides are really determined in a correlated way which biases the results. That's true, it is still "possible in principle." But you have to believe in a truly cosmic conspiracy to believe this -- more cosmic than your paragraph just above suggests you realize.

I need to repeat here that we already have an example of a non-local correlation enforced by a local mechanism (the Newtonian non-local force of gravity explained by a local mechanism (space curvature changes at the speed of light) in GR).

I think you misunderstand the physics here. It's easier if you take the perfectly analogous case from E&M, with a heavy charged particle being orbited by a light oppositely-charged particle. In what sense is there any "non local correlation"? The thing just orbits the way Maxwell's equations (and F=ma) say it should. It's true, if you talk in terms of potentials instead of fields and use the Coulomb gauge, you might think "oooh, it looks like something nonlocal is going on here, though we know that really it isn't" which I think is all you mean by saying there's a "nonlocal correlation enforced by a local mechanism". But there's no apparent nonlocality here to start with if you use the basic physics correctly.

Contrariwise, there *is* an apparent nonlocality in the Bell case. And, unless you believe in a cosmic conspiracy, the nonlocality is real.

 

[wm]

Now you are having it both ways. The realist believes a, b and c are simultaneously real and definite. But in your subsequent post you call this "naive" realism. Well, I certainly don't care if you call it naive or not. But this is the assumption of realism that Bell made, and that Einstein made. It is critical to Bell's Theorem, and the Theorem does not exist without it.

Einstein certainly was clear on the point, and he was unwavering as well:
"I think that a particle must have a separate reality independent of the measurements. That is: an electron has spin, location and so forth even when it is not being measured. I like to think that the moon is there even if I am not looking at it." This statement inspired the title of Mermin's article.

Lastly, to clear up a point that many are confused about: When one speaks of hidden variables, there are actually 2 sets of "somethings" we could refer to. Most people, myself included, casually use them interchangeably - but they really are different in a strict sense. Bell addresses both. The first set is observables: i.e. Bell's unit vectors a, b, c, etc. Of course, QM itself speaks to observables only and goes no deeper. The realist, on the other hand, speculates a deeper level of reality in which the observables have a root "cause" for lack of a better term. In Bell, these are lambda. So think of it like this analogy: when I decide to an offer for lunch, my answer (the observable) is binary (yes or no). But the reasons (hidden variables) for my decision may be many and varied.

1. Since when did my reference to naive realism have anything to do with the unit vectors a, b, c?

2. Since when did the unit vectors a, b, c (clearly readable from large protractors on each detector, say) have anything to with hidden variables?

3. Since when did a reference to unit vectors a, b, c become

this is the assumption of realism that Bell made, and that Einstein made. It is critical to Bell's Theorem, and the Theorem does not exist without it[??]

4. Since when did anything other than Bell's lambda have anything to do with hidden variables in Bell's theorem?

 

[DrChinese]

That is not, in fact, the assumption that Bell's theorem makes. Rather, Bell's theorem assumes, not only that said values exist independantly of measurement, but also that any particular combination of values has a well-defined probability.

Isn't that the same as what I said? I.e. where is our point of view different?

 

[DrChinese]

1. Since when did my reference to naive realism have anything to do with the unit vectors a, b, c?

2. Since when did the unit vectors a, b, c (clearly readable from large protractors on each detector, say) have anything to with hidden variables?

1. Unit vectors a, b and c - if they are to exist simultaneously - constitute the assumption of "realism". This is how it is expressed by Bell, and this is how I use the term (much to ttn's chagrin).

(Some people call this naive realism as a way to deprecate it. However, this is exactly what Einstein means, so the insult is really to him.)

2. EPR defines "elements of reality". a, b and c are related to these, although there is debate about the definition. Each person tends to map elements of reality to hidden variables in a slightly different way. If you stick with the formal expression, then it is somewhat easier to discuss.

 

[NateTG]

Isn't that the same as what I said? I.e. where is our point of view different?

For the purposes of Bell's theorem, it's necessary to assume that the usual notions of probabiltiy apply to QM. If, for example, the probability that a particular particle is spin-up and spin-left simultaneously is something similar to \frac{0}{0} then the algebra used to derive the inequality is invalid.

 

[DrChinese]

For the purposes of Bell's theorem, it's necessary to assume that the usual notions of probabiltiy apply to QM.

Yeah, I agree with that assumption. I think it is implied, but should probably be made explicit. The range would then be 0 to 100%.

 

[NateTG]

Yeah, I agree with that assumption. I think it is implied, but should probably be made explicit. The range would then be 0 to 100%.

Actually, what I meant is the assumption that:
If A has some probability, and B has some probability, then (A and B) also has some probability.

 

[wm]

1. Unit vectors a, b and c - if they are to exist simultaneously - constitute the assumption of "realism". This is how it is expressed by Bell, and this is how I use the term (much to ttn's chagrin).

(Some people call this naive realism as a way to deprecate it. However, this is exactly what Einstein means, so the insult is really to him.)

2. EPR defines "elements of reality". a, b and c are related to these, although there is debate about the definition. Each person tends to map elements of reality to hidden variables in a slightly different way. If you stick with the formal expression, then it is somewhat easier to discuss.

Dear DrC; The quoted post (in my view), continues an endless loop of misunderstandings on your part; especially re the nature of realism and the nature of a, b, c. I'll write to you directly and end the loop thus <CUT>

 

[rewebster]

If there was one 'thing' that was to be known to resolve the entanglement issue, what would it be?

 

[ueit]

You forgot the other major explicit assumption: locality.

If the different parts of the experiment are statistically independent, both local and non-local connections are excluded. So, locality is not IMHO a different assumption but it follows from the first one.

No, the experiments show that the outcomes are correlated in a certain way. The Theorem proves that such correlations cannot be produced by any local mechanism.

That's not true and the local mechanism I described proves that. Let me reformulate it in a naive but easy to understand way:

The detectors are deterministic. Before the experiment, each of them makes a list with their future settings (that's possible because they are deterministic) and send it to the source at light speed. The source generates the particles with the required spin. Now, it doesn't matter how likely such a mechanism seems to you. The important thing it is that such a possibility exists, therefore you cannot claim that Bell's theorem proves (and here I mean "proof" in an absolute, mathematical definition) otherwise.

No it isn't. The theorem proves specifically that "they" CANNOT "be the result of a local mechanism." That is the whole beauty of the theorem. Of course, as we agree, the derivation involves some subsidiary assumptions such as that the detector settings aren't affecting (or affected by or, really, in any way correlated with) each other or the state of the emitted pair. But as I've said several times now, there is every reason to believe that this condition is satisfied by the actual experiments (because the experimenters went out of their way to ensure that it was satisfied).

The problem with your line of reasoning is that you use the word "prove" in different ways, as it suits you. So, let's be clear about what is mathematically proven and what not. As I said in my previous post the theorem proves that the different parts of the experimental setup must be connected in some way. This connection can be either local or non-local. If you want to argue that the non-local mechanism is to be preferred that's fine, but don't pretend it is proven absolutely (like the impossibility of squaring the circle for example).

I understand you don't agree with this, and I respect the clarity with which you've formulated your arguments (as contrasted with some other people around here!). But there's probably no point arguing about this. Either you are willing to accept, without evidence, that there is some kind of fine-tuned conspiracy between the "random" settings on the two sides, or (like me) you aren't.

The evidence is the same for both of us. You just posit that a non-local mechanism is "obvious" and a local one is an absurd "conspiracy". I do not debate people's opinions.

What I think you miss is that the only way to prove *anything* is to assume free will.

This is a very important point and we should clarify it.

Either free will exists, or it does not.

If free will exists, determinism is false. Free will requires more than one choice. Determinism allows a single choice.

If you assume free will, all deterministic theories (local and non-local) must be false (except may be "many worlds" or "many minds"). Therefore Bell's theorem is useless in this case.

On the other hand, if you don't reject a priori all deterministic theories because they don't allow for free will, you cannot use that assumption anymore. That's just how logic works. So, please, make a clear statement regarding your position about this (free will + stochastic theories or no free will + determinism).

Everything humans have ever claimed to learn from doing empirical science, requires free will. Right?

No.

You could *always* say "maybe the results of that study only came out that way because of some pre-established harmony between objects and subjects".

So what?

And if someone says "but that study was double-blind, and done independently on 3 different continents by 500 independent scientists using vastly different equipment [or whatever...]" you can just say "well, they *tried* to take all these precautions and make things double blind and independently confirm the results and whatnot, but in actual fact they failed to do this, and, really, the different trials were all intricately dependent, such that the results are highly biased".

Biased in relation to what? If our universe is deterministic this doesn't mean that our observation are false, on the contrary. What you propose is not a deterministic universe but a Matrix-like one in which there is an evil programmer having fun in playing with us. I see no reason to disbelieve an experimental result just because I was predetermined to make that experiment. Such a result is an effect of the same deterministic law so it is true.

Or maybe more simply: "maybe you only think that experiment proved X because you were pre-programmed to believe that, even though it is false." Yeah maybe. The point is, without freewill (in the relevant sense, which is just the ability to decide what questions to ask of nature in a way that isn't forced on us by nature) you can't do science *at all*. So if you're going to go down this road in order to avoid the conclusion from Bell that nature violates relativistic causality, then you're also (if you choose to be consistent) going to have to deny that we really figured out that matter is made of atoms, that neutrinos oscillate and have mass, that Newton's constant G has a certain value, that immunizations can prevent certain horrible diseases, etc...

Your conclusion doesn't follow. Yeah, it may be that we are preprogrammed to believe only falsehoods but it is in no way a necessary implication of determinism, and, I would say, a very unlikely one.

The same scenario is possible in a free-will world as well. It may happen that we always make the wrong choices.

The buttom line is, do you reject my proposal for a local mechanism because it is incompatible with free will or because of Bell?

No, this is too narrow. Determinism (and assuming locality) would mean only that the future setting of the detector can be inferred from the totality of the past light cone of the "setting" event. Well, suppose we choose the setting by measuring the energy of a cosmic microwave background radiation photon (coming from a direction in space just opposite that of the particle source) and suppose the "choice" between two settings is arranged to be determined by whether the millionth digit in the decimal expansion of that photon's energy (in eV) is even or odd. And same thing on the other side. So, your point is still true, right? You can still say: well, but still there's a possible local mechanism which accounts for the (merely apparent) violation of Bell's inequalities in the experiment. But see how crazy (conspiratorial) this becomes? You have to now believe that the millionth digit of the energies of two photons that were created 15 billion years ago, are somehow pre-harmonized so as to give just the settings needed for this Bell experiment to erroneously *appear* to violate the inequality.

1. You've missed the point of my hypothesis. I'm not assuming that the particles are produced in a random manner and it just happens that the detectors end up correlated with them. I'm saying that the spin of the entangled particles is determined by the field generated by the detectors (and here you can include anything you like: humans, computers, uranium atoms, distant stars, whatever).

2. Again, why do you think that I assume an "apparent" violation? The inequality is genuinely violated and this proves that a connection between the source and detectors exist. I only propose a local mechanism by which that connection is realized. That's very important. I do not claim that there is an error fooling us into believing a lie. I claim that there exist a deterministic law which enforces the correlations. And it is obvious that a law of nature cannot be broken by adding complexity to the experiment. You may have 1000000 monkeys choosing detector settings based on electroshocks produced by radioactive decays and the result is expected to be the same. The EM field produced by those monkeys will determine how the entangled particles are produced and the correlations would appear.

3. You could falsify my hypothesis by finding a source of true randomness outside of the visible universe but this seems unlikely given the universal expansion.

This passage makes me think you slightly misunderstand what's required. It's not true that the local beables in the detector at time T are sufficient to determine the state of the detector at time T + 2L/c (where L is the distance from the detector back to the source). So even if you allow the detector to "broadcast" its current state toward the source (at speed c) at time T -- so that at time T + L/c the source learns about its state, just as it is emitting a particle pair -- you may *not* assume that this is equivalent to the source "knowing" about the *later* state of the detector (at time T + 2L/c, when the photon gets there and the measurement gets made). The reason is what I explained above: the set of events which might (locally) affect the detector setting is not the "past light cylinder", but the past light *cone*. So stuff coming in from outside -- and, in particular, from the direction opposite the source -- could affect the final setting (at T+2L/c) and the source would have *no local way to know about this incoming information* and hence no way to know about the final setting of the detector.

This is only true if you can find something which is not in the past light cone of the source. But, as far as I understand the big-bang theory, everything in the universe was at some point connected with everything else, hence the uniformity of the microwave radiation. So, I agree with your conclusion but I doubt that the premise could be realized.

You'll say this doesn't matter and that it's still "possible in principle" that there could be some kind of conspiracy in which the settings on the two sides are really determined in a correlated way which biases the results. That's true, it is still "possible in principle." But you have to believe in a truly cosmic conspiracy to believe this -- more cosmic than your paragraph just above suggests you realize.

I don't believe in conspiracies.

I think you misunderstand the physics here. It's easier if you take the perfectly analogous case from E&M, with a heavy charged particle being orbited by a light oppositely-charged particle. In what sense is there any "non local correlation"? The thing just orbits the way Maxwell's equations (and F=ma) say it should. It's true, if you talk in terms of potentials instead of fields and use the Coulomb gauge, you might think "oooh, it looks like something nonlocal is going on here, though we know that really it isn't" which I think is all you mean by saying there's a "nonlocal correlation enforced by a local mechanism". But there's no apparent nonlocality here to start with if you use the basic physics correctly. Contrariwise, there *is* an apparent nonlocality in the Bell case.

I didn't use your example in order not to beg the question of locality in the EM interaction. Now, I'll tell you how to get an apparent non-locality from here. Just assume one or both charges have free-will. Can you explain their orbit while still keeping this assumption?

 

[rewebster]

If there was one 'thing' that was to be known to resolve the entanglement issue, what would it be?

What I addressed may be naive point to some, but in reading over the thread twice, I find that some people are addressing the particle/wave, some the conveyance, some the means of initiating the investigating 'item', some the means of 'detection', and others the 'entanglement' as it may or may not be.

By stating the importance of one or the other, another may derive the starting point which one may deem as the 'source' for that line of 'thought'. By putting a set of priorities of importance (and their liabilities to the whole) to the members/components of the procedure, I see that each can or could be examined as to 'what' are the possibilities as each step. Then, each could be, either, generalized or specified.

This process could also enlighted some (including me) on some points.

 

[ttn]

The detectors are deterministic. Before the experiment, each of them makes a list with their future settings (that's possible because they are deterministic) and send it to the source at light speed. The source generates the particles with the required spin.

But as you admitted, this doesn't actually work, because the settings of the detectors could (in principle, though of course in the actual experiments they aren't, so this is just reasonable speculation) be determined by (say) cosmic background radiation photons coming from opposite directions. So it *does not suffice* to say that the detectors broadcast their future settings back to the source. What you require is literally the entire universe broadcasting the future state of the detector to the source. You require that the minutest imaginable detail (like the 100'th digits of the energies of two random photons that decoupled from matter some 15 billion years ago) is *the thing* which *causes* the detector to be set the way it's set. So you replace a minor puzzle about faster than light causation, with a major theological mystery which screams out not only "fine tuning" but "intelligent design". I call it crazy. You disagree. Neither of us will convince the other.

Now, it doesn't matter how likely such a mechanism seems to you. The important thing it is that such a possibility exists, therefore you cannot claim that Bell's theorem proves (and here I mean "proof" in an absolute, mathematical definition) otherwise.

By that standard (as I said before) you can't prove anything, ever, by doing an experiment. Recent experiments proved that neutrinos have mass? Nope, not in the sense you have in mind (because there are similar "no-conspiracy" subsidiary hypotheses used in the data analysis... just exactly as in the Bell inequality tests).

If you assume free will, all deterministic theories (local and non-local) must be false (except may be "many worlds" or "many minds"). Therefore Bell's theorem is useless in this case.

This is all just BS. Just because determinism is true, does *not* mean that it is impossible for two settings to be made genuinely randomly and uncorrelatedly. Just because something determines a and something determines b, doesn't necessarily mean that it's the same something in both cases and that a and b end up being correlated.

So, please, make a clear statement regarding your position about this (free will + stochastic theories or no free will + determinism).

I don't think it matters at all. It is you who insist on even talking about free will. I think it plays no role whatsoever in this issue. In the actual experiments, the detectors are not set by any free will choices, but by random number generators -- random number generators which are deliberately made as independent and uncorrelated as possible. And I believe the experimenters have succeeded on this point: the settings are independent and uncorrelated. And that is a fact regardless of whether the ultimate theory turns out to be stochastic or deterministic.

Of course, you disagree that it's a "fact." To which I respond: show me the evidence that they are correlated, i.e., that the experimenters missed something and failed to achieve the desired independence.

I see no reason to disbelieve an experimental result just because I was predetermined to make that experiment. Such a result is an effect of the same deterministic law so it is true.

The point was that you might be predetermined to *bias* the sample in certain ways. That was illustrated by the cancer example I gave several days ago. If all the patients who are going to survive anyway are (mysteriously) pre-determined to be "randomly" selected to get the drug instead of the placebo, then the experiment appears to tell you that the drug cures cancer -- which is (here by hypothesis) a false inference from the data, because the data is biased. That is precisely parallel to what you are lobbying for in the Bell case - - some mysterious "biasing" force which makes the "randomly" selected settings actually not random at all, and not random in a way that *fools* people into thinking that Bell's inequality is violated (and hence that there is nonlocal causality).

The buttom line is, do you reject my proposal for a local mechanism because it is incompatible with free will or because of Bell?

Neither. I reject it because there is no empirical evidence for the kind of bias/conspiracy that you suggest, and tons of positive evidence that there is no such bias/conspiracy (namely, or primarily, that the experimenters used fancy schmancy random number generators precisely to make sure there was no such biasing).

1. You've missed the point of my hypothesis. I'm not assuming that the particles are produced in a random manner and it just happens that the detectors end up correlated with them.

No, I understand that just fine. It's that the state of the emitted particles is influenced by whatever it is that determines the (future) settings of the detectors (the settings under which the spins of the particles will be measured).

I'm saying that the spin of the entangled particles is determined by the field generated by the detectors (and here you can include anything you like: humans, computers, uranium atoms, distant stars, whatever).

Except "the field generatred by the detectors" isn't enough. Signals at the speed of light coming from the edge of the universe can also affect the source locally. So what you're really saying is just that *whatever* determines the setting of detector A, *also* determines the setting of detector B *and* also determines the state of the emitted pair. And I say, when one of those things is a random number generator (or better, but hypothetical, the 100th digit of the energy of a CMB photon) it is exceedingly implausible to think this. You'd have to believe in a cosmic conspiracy -- a word you obviously don't like, but which is 100% accurate to describe your position here.

2. Again, why do you think that I assume an "apparent" violation?

Same as the cancer example. If 100% of the people given the drug beat their cancer, everybody says "this data proves that this drug cures cancer!" but that is a mere appearance. The reality is otherwise.

This is only true if you can find something which is not in the past light cone of the source. But, as far as I understand the big-bang theory, everything in the universe was at some point connected with everything else, hence the uniformity of the microwave radiation. So, I agree with your conclusion but I doubt that the premise could be realized.

So then maybe you *do* doubt all the randomized drug trials and other similar kinds of scientific studies. After all, there's an actual real mechanism by which all those "random" drug/placebo assignments could have been pre-determined to correlated with whatever internal variables are determining who lives and who dies -- namely: the big bang did it.

I don't believe in conspiracies.

I disagree.

I didn't use your example in order not to beg the question of locality in the EM interaction. Now, I'll tell you how to get an apparent non-locality from here. Just assume one or both charges have free-will. Can you explain their orbit while still keeping this assumption?

Huh?

 

[ueit]

But as you admitted, this doesn't actually work, because the settings of the detectors could (in principle, though of course in the actual experiments they aren't, so this is just reasonable speculation) be determined by (say) cosmic background radiation photons coming from opposite directions. So it *does not suffice* to say that the detectors broadcast their future settings back to the source. What you require is literally the entire universe broadcasting the future state of the detector to the source. You require that the minutest imaginable detail (like the 100'th digits of the energies of two random photons that decoupled from matter some 15 billion years ago) is *the thing* which *causes* the detector to be set the way it's set. So you replace a minor puzzle about faster than light causation, with a major theological mystery which screams out not only "fine tuning" but "intelligent design". I call it crazy. You disagree. Neither of us will convince the other.

There is no problem in treating the entire universe as "the detectors". In fact, it is required for consistency. The "theological mystery" is nothing but a physical law (like in your example with the two charges) which applies everywhere, regardless of the distance in space or time. EM force has unlimited range you know.
The two photons that "decoupled from matter some 15 billion years ago" did so in accordance with the same physical law. Their interaction with the detectors, 15 bln years later, is a result of the local field, which existed at their birth and which depended of the distribution of the same particles (or their "parents") which we call now "detectors". You have presented no evidence that we should expect those particles not to share a common past. On the contrary, as I pointed before, the uniformity of the microwave radiation is considered by the cosmologists as evidence for a time when the entire universe was in thermal equilibrium.

By that standard (as I said before) you can't prove anything, ever, by doing an experiment. Recent experiments proved that neutrinos have mass? Nope, not in the sense you have in mind (because there are similar "no-conspiracy" subsidiary hypotheses used in the data analysis... just exactly as in the Bell inequality tests).

Again, you've provided zero evidence that a local mechanism requires a "conspiracy" while a non-local one doesn't. You arbitrary decided that the hypothesis of the entangled particles being generated with spin depending on the local field is a "conspiracy". Then, why don't you say that the inverse square law, or conservation laws are conspiracies? And what exactly is the "no-conspiracy" explanation you propose?

This is all just BS. Just because determinism is true, does *not* mean that it is impossible for two settings to be made genuinely randomly and uncorrelatedly. Just because something determines a and something determines b, doesn't necessarily mean that it's the same something in both cases and that a and b end up being correlated.

P1: Free-will (as I clearly defined it) implies more than one outcome for the same initial state.
P2: A deterministic theory (like BM or Newtonian mechanics) admits a unique outcome for a given initial state.

Do you agree that P1 and P2 cannot be simultaneously true? Forget about EPR, it's just a question of logic.

I don't think it matters at all. It is you who insist on even talking about free will. I think it plays no role whatsoever in this issue. In the actual experiments, the detectors are not set by any free will choices, but by random number generators -- random number generators which are deliberately made as independent and uncorrelated as possible. And I believe the experimenters have succeeded on this point: the settings are independent and uncorrelated. And that is a fact regardless of whether the ultimate theory turns out to be stochastic or deterministic.

It matters, because if you assume free will, there is no way for the source to "read" detector's future from the local field. You introduce non-locality in the assumptions and then present it as the conclusion. That's begging the question.

Of course, you disagree that it's a "fact." To which I respond: show me the evidence that they are correlated, i.e., that the experimenters missed something and failed to achieve the desired independence.

The results of the EPR experiments are my evidence, just like in your case. You forget that the failure to achieve independence is a fact established by Bell's theorem.

No, I understand that just fine. It's that the state of the emitted particles is influenced by whatever it is that determines the (future) settings of the detectors (the settings under which the spins of the particles will be measured).

Indeed.

Except "the field generatred by the detectors" isn't enough. Signals at the speed of light coming from the edge of the universe can also affect the source locally.

As I've argued at the beginning of my post, distance has nothing to do here. It can be 1 fm or 10 bln light-years. Physics is not scale-dependent.

So what you're really saying is just that *whatever* determines the setting of detector A, *also* determines the setting of detector B *and* also determines the state of the emitted pair. And I say, when one of those things is a random number generator (or better, but hypothetical, the 100th digit of the energy of a CMB photon) it is exceedingly implausible to think this.

You seem to believe that a random number generator somehow doesn't obbey the laws of physics. A very strange argument, indeed.

You'd have to believe in a cosmic conspiracy -- a word you obviously don't like, but which is 100% accurate to describe your position here.

Gravity applies to the whole universe as well. Do you call it a conspiracy?

Same as the cancer example. If 100% of the people given the drug beat their cancer, everybody says "this data proves that this drug cures cancer!" but that is a mere appearance. The reality is otherwise.

So then maybe you *do* doubt all the randomized drug trials and other similar kinds of scientific studies. After all, there's an actual real mechanism by which all those "random" drug/placebo assignments could have been pre-determined to correlated with whatever internal variables are determining who lives and who dies -- namely: the big bang did it.

I'm tired to point again and again the fallacy in this argument. I'll say only that while non-locality conflicts with relativity, there is nothing wrong for a deterministic theory to have its initial parameters defined at the big-bang. Repeating a fallacious argument doesn't make it true

Huh?

Trying to understand how two charged particles can both obey a deterministic law and have "free-will" shows you the fallacy of the free-will assumption when dealing with deterministic theories and how non-locality becomes the only explanation. Think about it!