Bell Locality: New Paper Clarifies Arguments

[DrChinese]

Um, yeah, you can "simply answer" that way... but it's not particularly convincing unless you actually *have* and actually *share* this theory. So... would you be willing to share it? Tell us about this Bell Local (but not "realistic") theory which agrees with the predictions of QM.

Sure, I'll give you two:

1. MWI. That does not make me an advocate of it.

2. Here is another one, a personal invention, and again I am not advocating it.

There are no avenues of influence or communication which are superluminal*. However, the future influences the past with a limiting velocity of c, respecting relativity. The influence from the future to the past is limited to signalling the nature of the measurement which Alice (or Bob) is making. Of course, this signalling goes from the future to the past and so it appears to us as an influence coming from nowhere - ie. random. This would allow a way for Alice's measurement setting to be communicated to Bob, as the backward influence of her measurement setting is communicated to a point in the past which can affect Bob's soon-to-be future. This theory is *not* realistic, because there is no greater specification of the wave function possible and particles do not have well defined attributes independent of the act of measurement. All other elements of the theory match oQM.

Now, as far fetched as this may sound, I don't see how it is any more far fetched than postulating superluminal pilot waves that are individually undetectable.

*It is possible you might say this violates Bell Locality, and in a way you are correct. But collapse of the wave function is local, which is not a feature of oQM as many see it.

 

[ttn]

1. MWI. That does not make me an advocate of it.

Already addressed in a previous post.

2. Here is another one, a personal invention, and again I am not advocating it.

There are no avenues of influence or communication which are superluminal*. However, the future influences the past with a limiting velocity of c, respecting relativity...

"The future" is definitely not in the past light cone of an event. So this violates Bell Locality.

To hear about some other problems with this kind of idea, check out Tim Maudlin's comments on Cramer's "Transactional Interpretation" (in Maudlin's book, Quantum Nonlocality and Relativity... highly recommended.)

Now, as far fetched as this may sound, I don't see how it is any more far fetched than postulating superluminal pilot waves that are individually undetectable.

Positing Bohm's theory is a different issue. One doesn't have to like Bohmian Mechanics to recognize that viable theories have to violate Bell Locality.

*It is possible you might say this violates Bell Locality, and in a way you are correct. But collapse of the wave function is local, which is not a feature of oQM as many see it.

I don't know what you mean by saying "collapse of the wf is local". You mean in OQM? Or in your funny reverse-temporal causation model? Or what?

 

[DrChinese]

I don't know what you mean by saying "collapse of the wf is local". You mean in OQM? Or in your funny reverse-temporal causation model? Or what?

In my funny model...

Look, don't take things so seriously. Your ideas have plenty of merit, but they need some polishing. If you can't convince me (I'm easy), then they need more work. How are you going to convince someone serious?

 

[ttn]

In my funny model...

But as I pointed out before, your funny model violates Bell Locality.

 

[selfAdjoint]

But as I pointed out before, your funny model violates Bell Locality.

Please, not another megillah on the semantics of "Bell Locality"!

 

[ttn]

Please, not another megillah on the semantics of "Bell Locality"!

Yeah, I'm sick of it too. Some people just refuse to see what's there in front of them.

But hey, some good came of it -- I learned the new word "megillah"!

 

[Sherlock]

Ok, I've read the paper, and I agree with the conclusion that no Bell Local theory can be empirically viable.

Does this mean that nonlocality is a fact of nature? Yes, but only in the sense that no Bell Local theory can be empirically viable. (At least for the foreseeable future.)

This means that if you are going to construct a realistic (ie., a metaphysical rendition) theory of an underlying quantum world, then that theory is going to have to be nonlocally causal in order to account for certain quantum experimental correlations.

This doesn't mean that it is a physical fact that nonlocal causal transmissions or propagations or evolutions, or whatever, exist in whatever might constitute the reality of an underlying quantum world, because there's simply no way to ascertain that. If, in fact, there are no such nonlocal causal agents in nature, then you have a theory which is a bad heuristic vision of the underlying reality and in unnecessary conflict with relativity.

You write:
"Since the empirical predictions of quantum theory respect Signal Locality, there is no way to 'exhibit' any nonlocality at the level of 'our observations'. It simply cannot be done. But if, motivated by the orthodox quantum philosophy, one excludes from the beginning any talk about the 'features of a putative underlying reality', then there is literally nothing else -- that is, no other sense of locality -- to discuss. The vague anti-realism of the orthodox quantum philosophy thus seems to rule out the very kind of talk that is absolutely required to show that nature violates some locality condition -- namely, talk of nature."

It only rules out taking talk of the underlying reality of nature as necessarily corresponding to what that underlying reality actually is.

You continue:
"But orthodox quantum theory better commit to a realistic description of something. Otherwise -- that is, if one retreats to an exclusively epistemological interpretation of quantum theory in general and the wave function in particular -- one simply no longer has a theory in the sense defined in Section II. It is then meaningless to discuss whether the causal processes posited by the 'theory' respect relativity's prohibition on superluminal causation. A formalism which is not about any such processes is neither local nor nonlocal. Both terms are simply inapplicable."

Well, that's it, isn't it ? Orthodox quantum theory doesn't commit to a realistic description of an underlying reality.

The orthodox quantum philosophy is "vague and ambiguous" because our knowledge of the underlying reality is vague and ambiguous.

You can construct a clear, realistic, metaphysical (and of course nonlocal) theory of underlying reality. But it's quite possible that such clarity will cost you something far more valuable -- namely, the truth.

For all anybody knows, Bohmian Mechanics is the correct approach. But, for all anybody knows, it isn't. That's why I think it's best to stick with the orthodox interpretation (even with all its fuzziness) for the foreseeable future.

 

[ttn]

Does this mean that nonlocality is a fact of nature? Yes, but only in the sense that no Bell Local theory can be empirically viable. (At least for the foreseeable future.)

You make it sound like that's some kind of qualification of the thesis. But it isn't, right?

This means that if you are going to construct a realistic (ie., a metaphysical rendition) theory of an underlying quantum world, then that theory is going to have to be nonlocally causal in order to account for certain quantum experimental correlations.

Sure, you can avoid the nonlocality if you don't talk about the relevant part of the physical world (but instead, say, restrict your attention to peanut butter sandwiches). But that *in no way* undermines the fact that reality is not Bell Local. Just like: you can't qualify or contradict or undermine the thesis "all tigers have stripes" by changing the subject and talking about elephant toenails.

This doesn't mean that it is a physical fact that nonlocal causal transmissions or propagations or evolutions, or whatever, exist in whatever might constitute the reality of an underlying quantum world, because there's simply no way to ascertain that.

Um, yes it does, and yes there is. Bell's two part argument proves that "it is a physical fact..." As I suggested just above, changing the subject (or simply refusing to talk about that subject) doesn't make that fact go away.

Well, that's it, isn't it ? Orthodox quantum theory doesn't commit to a realistic description of an underlying reality.

Well, some people think it does, and it is a natural reading of the "completeness" doctrine to take it as committing to a description of an underlying reality. If it does, it violates Bell Locality. That isn't (or shouldn't be) controversial.

And if you're right (or: in regard to the purely epistemic version of the orthodoxy) that doesn't change anything. There *is* a reality, and that reality is not Bell Local. Refusing to talk about reality doesn't change that.

You can construct a clear, realistic, metaphysical (and of course nonlocal) theory of underlying reality. But it's quite possible that such clarity will cost you something far more valuable -- namely, the truth.

Only if "the truth" is that there is no underlying reality. But it's unscientific, irrational, and downright stupid in the extreme to even entertain that possibility for a second.

For all anybody knows, Bohmian Mechanics is the correct approach. But, for all anybody knows, it isn't. That's why I think it's best to stick with the orthodox interpretation (even with all its fuzziness) for the foreseeable future.

I would have a bit of sympathy if you said we should stick to the mathematics that works. But the orthodox interpretation includes the ridiculous and totally arbitrary completeness doctrine, all of the convoluted measurement axioms, a special dynamical role for "the observer", and so forth. This is all just crap -- crap that should never have received respect from serious scientists.

Bohm's theory is better not because some random person "likes" its "picture" of reality better. It's better *as a scientific theory*. It's better because of its simplicity, plausibility, physical clarity, and success in accounting for experimental results. As I said before, I'm the first to admit that this isn't yet sufficient for claiming it's true. But if you are going to go beyond the equations and commit to a particular interpretation for some reason, you'd have to be crazy to pick Copenhagen over Bohm.

(somewhere mr. vanesch is rolling his eyes because I always forget to mention his baby MWI... )

 

[DrChinese]

Only if "the truth" is that there is no underlying reality. But it's unscientific, irrational, and downright stupid in the extreme to even entertain that possibility for a second.

Stupid? This is where you go off the deep end. You keep assuming that which you want to prove! Mainly, that there is a realistic theory in which particle attributes are well-defined at all times. Considering the wide array of evidence to the contrary (i.e. all tests confirming the HUP), I would think this particular statement should be proven rather than assumed. There is not one scintilla of evidence that the HUP is *not* an complete description of reality.

Out of all of your discussions, you fail to grasp that no matter how you slice it, there is NO GREATER SPECIFICATION of the wave function present in any theory. Because even BM - correct me if I'm wrong here - requires such a vast array of knowledge of particle positions that you come back to where we started in predictive capability: oQM. Because apparently it is axiomatic that the non-local pilot waves are themselves not observable.

I have certainly never seen a serious proposal to observe such a wave. I have certainly never seen a proposal to "beat" the HUP using an enhanced wave function. Am I mistaken on this?

 

[ttn]

Stupid? This is where you go off the deep end. You keep assuming that which you want to prove! Mainly, that there is a realistic theory in which particle attributes are well-defined at all times. Considering the wide array of evidence to the contrary (i.e. all tests confirming the HUP), I would think this particular statement should be proven rather than assumed. There is not one scintilla of evidence that the HUP is *not* an complete description of reality.

No, it's you who is assuming what you want to prove. The fact is, there are several different theories which give different accounts of quantum reality and which are all equally consistent with the empirical facts (because the theories all make the same predictions about what those empirical facts should be). You say there is evidence "confirming the HUP" (by which I assume you mean confirming orthodox QM and/or its completeness doctrine). But this is completely and totally false. There is ZERO evidence showing that OQM is right and (say) Bohm (or, say, GRW) is wrong. None. Zip. Any evidence that you point to and say "See, this is consistent with OQM, so it confirms it" I can equally well point to and say "It's consistent with Bohm and GRW too, so it confirms those." The right question is: is there "one scintilla of evidence" that the HUP *is* a complete description of reality? And since there exist empirically viable theories according to which the HUP is merely epistemic, the answer is clearly, unambiguously NO.

Out of all of your discussions, you fail to grasp that no matter how you slice it, there is NO GREATER SPECIFICATION of the wave function present in any theory.

You mean "greater specification *than* the wf"? If so, this is just factually incorrect. There *do exist* empirically viable theories according to which the wave function does *not* provide a complete description of reality. Bohmian mechanics being the prime example. I don't understand why this is so hard for you to understand or accept.

Because even BM - correct me if I'm wrong here - requires such a vast array of knowledge of particle positions that you come back to where we started in predictive capability: oQM. Because apparently it is axiomatic that the non-local pilot waves are themselves not observable.

You're running together a bunch of completely different issues here. The central point is that BM and OQM make the same empirical predictions, so there is no possibility that you could point to some empirical fact that supports on as opposed to the other. Once you understand that, there's really nothing else to argue about -- except the question of which of the several empirically viable theories is the *best* theory.

I have no idea what you're talking about when you say BM "requires such a vast array of knowledge of particle positions..." BM is a *theory*. It doesn't "require" knowledge of anything, any more than OQM requires its advocates to know the exact wave function for every electron in Pluto.

You are also running together "OQM" with the class of predictions made by OQM. Those aren't the same thing. There are several theories which make the same class of predictions. You can't just pick your favorite theory, identify it with the predictions, and then dismiss the alternatives on the grounds that they "merely" reproduce the predictions of your favorite one. The reason this is bogus (in case it isn't obvious) is that I could do the same thing. I could say "BM is my favorite theory, and you're stupid for believing in OQM because it merely reproduces the predictions of BM -- and at the cost of introducing all sorts of fuzziness and measurement problems and such." This is why I said above that it's *you* who is simply assuming what you want to prove.

I have certainly never seen a serious proposal to observe such a wave. I have certainly never seen a proposal to "beat" the HUP using an enhanced wave function. Am I mistaken on this?

Paraphrasing Pauli, you're "not even mistaken." You're so completely confused about what the issues even are, that you haven't yet risen to the level of being merely "mistaken" about some technical detail.

 

[Sherlock]

Does this mean that nonlocality is a fact of nature? Yes, but only in the sense that no Bell Local theory can be empirically viable. (At least for the foreseeable future.)

You make it sound like that's some kind of qualification of the thesis. But it isn't, right?

It's a qualification. What's known of nature certainly seems to have a nonlocal character. But what's the extent of that knowledge ? Is it complete ? I don't think so.

This means that if you are going to construct a realistic (ie., a metaphysical rendition) theory of an underlying quantum world, then that theory is going to have to be nonlocally causal in order to account for certain quantum experimental correlations.

Sure, you can avoid the nonlocality if you don't talk about the relevant part of the physical world (but instead, say, restrict your attention to peanut butter sandwiches). But that *in no way* undermines the fact that reality is not Bell Local. Just like: you can't qualify or contradict or undermine the thesis "all tigers have stripes" by changing the subject and talking about elephant toenails.

We can see peanut butter sandwiches (mmm, yummy), tiger's stripes, and elephant's toenails. But the composition and behavior of the underlying quantum world (UQW) is a true mystery, and what can be said about that is limited by the material-instrumental data, by what can be experimentally determined.

I'm pretty sure you've shown that no Bell Local theory of quantum entanglement can be constructed. This could be because the UQW is actually nonlocally causal, or it could be because there are some serious gaps in the understanding of the UQW and limitations wrt what has been and can be experimentally determined.

This doesn't mean that it is a physical fact that nonlocal causal transmissions or propagations or evolutions, or whatever, exist in whatever might constitute the reality of an underlying quantum world, because there's simply no way to ascertain that.

Um, yes it does, and yes there is. Bell's two part argument proves that "it is a physical fact..." As I suggested just above, changing the subject (or simply refusing to talk about that subject) doesn't make that fact go away.

The contention that the UQW is, in fact, nonlocally causal is based on the assumption that our knowledge of the UQW is, or at least can be, complete. I think there are some reasons to believe that it isn't, and maybe can't be, complete. So, for all we know, and maybe for all we can know, the UQW might not actually be nonlocally causal. That's all.

Well, that's it, isn't it ? Orthodox quantum theory doesn't commit to a realistic description of an underlying reality.

Well, some people think it does ...

It doesn't.

... and it is a natural reading of the "completeness" doctrine to take it as committing to a description of an underlying reality. If it does, it violates Bell Locality. That isn't (or shouldn't be) controversial.

Sure, it makes sense to think that something about the wave mechanical approach is corresponding to what is actually happening in the UQW. But, it isn't a correct reading of the completeness doctrine to take it as committing to a description of an underlying reality. At least not a 1-1 mapping.

So, OQM should not be taken as being either a local or a nonlocal theory, and therefore Bell Locality doesn't apply to it.

And if you're right (or: in regard to the purely epistemic version of the orthodoxy) that doesn't change anything. There *is* a reality, and that reality is not Bell Local. Refusing to talk about reality doesn't change that.

There is reality, and then there are some speculative ideas about an underlying reality. Not enough is known about the UQW to say, definitively, that it's nonlocally causal.

You can construct a clear, realistic, metaphysical (and of course nonlocal) theory of underlying reality. But it's quite possible that such clarity will cost you something far more valuable -- namely, the truth.

Only if "the truth" is that there is no underlying reality.

No that's not it. The possibility is that the UQW isn't nonlocal.

You want to be thorough, right ? Ok then, you can't go from just not being able to construct a locally causal theory of quantum entanglement (only nonlocally causal theories will do) to the assertion that the UQW is nonlocally causal, unless you assume that your nonlocally causal theories are complete descriptions of the UQW. But it would be "unscientific, irrational, and downright stupid in the extreme" to assume that.

For all anybody knows, Bohmian Mechanics is the correct approach. But, for all anybody knows, it isn't. That's why I think it's best to stick with the orthodox interpretation (even with all its fuzziness) for the foreseeable future.

I would have a bit of sympathy if you said we should stick to the mathematics that works. But the orthodox interpretation includes the ridiculous and totally arbitrary completeness doctrine, all of the convoluted measurement axioms, a special dynamical role for "the observer", and so forth. This is all just crap -- crap that should never have received respect from serious scientists.

Bohm's theory is better not because some random person "likes" its "picture" of reality better. It's better *as a scientific theory*. It's better because of its simplicity, plausibility, physical clarity, and success in accounting for experimental results. As I said before, I'm the first to admit that this isn't yet sufficient for claiming it's true. But if you are going to go beyond the equations and commit to a particular interpretation for some reason, you'd have to be crazy to pick Copenhagen over Bohm.

The standard probabilistic (Copenhagen) interpretation makes no claim to being a complete description of an underlying reality. I think that is a good thing. All the "crap" that you don't like about it is a reminder that as far as the UQW is concerned, physics is still more or less feeling its way around in the dark.

(somewhere mr. vanesch is rolling his eyes because I always forget to mention his baby MWI... )

Well, I respectfully submit that you're both making a mistake in your assessment of (in your case) what the completeness doctrine of OQM means, and (in vanesch's case) the completeness of Schroedinger equation and acceptable wave functions wrt the UQW. It simply isn't clear how quantum theory, or any other theory, relates to the UQW.

The Bohmian, Everettian, GRW, OQM, and other approaches each have their problems. But it's good that there are several different theoretical perspectives wrt which the extant and future data can be evaluated.

Your paper is, imho, a worthy addition to the literature on a perplexing subject --- and if the physics community thinks so too, then rejoice in that fact. If nothing else it's job security.

 

[RandallB]

The right question is: is there "one scintilla of evidence" that the HUP *is* a complete description of reality?

Wow, I think I final understand your point here.
What you’re saying is between two theories:
BM – Identifies itself as Non-local
QM - Identifies itself as Non-local
VS. a third theory
Classical – Demands reality must be local thus Non-local is just incomplete (EPR; no dice etc.)

You run an experiment that if accepted proves the third wrong.
Bell – entanglement; etc. etc.

Your point is how can that experiment select between the two possibilities of QM or BM by proving the third wrong and declare just one of them “complete”. It can only prove that Einstein’s Classical assertion that QM must necessary be incomplete, is wrong.
But not able to define which theory thought to have been incomplete is actually complete.

BUT -- BM is not the first to provide an alternative. QM is or at least it started as a particle theory. Then a wave theory was shown to be just a viable. But that is accepted as being an equivalent interpretation of the same thing. I.E. wave/particle duality is acceptable within QM.
Along with interpretation extensions in the form of MWI, Strings, M, QLT etc. that serve to attempt explanations of it. (Most of which I don’t accept as real but that’s a separate issue)

My problem with BM being some sort of proof that QM is not complete fails on two points.

First:
It’s easy enough to argue QM hasn’t been shown to be complete simply because it’s so hard to logically prove a positive. Proving something wrong doesn’t make QM right.
Unless someone lowers the bar to accept the negative prove against EPR or the Bell test that’s an individual choice. We don’t need BM to use the higher standard if we choose.

Second:
If BM wishes to “prove” QM’s potential claim to completeness as wrong or not possible it needs to provide a proof, not just a possibility. On this score I don’t see where BM is any more than an equivalent assumption to QM or an extension like many others with the very same “fuzziness”. It hasn’t made itself a unique alternative to QM.
Example: If HUP and entanglement that derives from it were to be falsified, both QM and BM together would be as well.
That is BM has not provided anything experimentally to differentiate itself from QM, both a fundamentally non-local, as in probabilistic when viewed by a local realist.

So if the main point is to decide if QM has been accepted as complete.
IMO the various almost desperate searches for an explanation to QM ( MWI, Strings etc.) are proof to me that it has not yet been truly accepted as complete. Otherwise why such a hard search but that a proof is still needed. The hunt to show QM complete still continues as from its start. Even as many have shown that just accepting as if is complete has been very productive as shown by 80 years of particle physics. It’s still very hard to prove a positive.

 

[ttn]

It's a qualification. What's known of nature certainly seems to have a nonlocal character. But what's the extent of that knowledge ? Is it complete ? I don't think so.

You are missing a crucial point here, which is that the whole two-part argument isn't based on some particular assumption about the way things work, but *simply* on empirical predictions. And the relevant experiments have been done. We *know* already that those experiments are *right*. So if you accept the proof that no Bell Local theory is consistent with those experiments, that's it. Nature violates Bell Locality. You can't then say "well, but what if our theory about the quantum world wasn't quite right? there's still so much that's unknown." Yes, there is still much that is unknown, but none of those unknowns were premises of the argument. In other words, we didn't assume anything about how a theory ought to work in the course of the argument. So no *surprises* in the future about what the true theory looks like, can possibly undermine that conclusion. *No* Bell Local theory can be consistent with the experiments; this will remain true *whatever* some future theory ends up looking like.

I'm pretty sure you've shown that no Bell Local theory of quantum entanglement can be constructed. This could be because the UQW is actually nonlocally causal, or it could be because there are some serious gaps in the understanding of the UQW and limitations wrt what has been and can be experimentally determined.

No, it couldn't be the latter. I mean, it could be that all the experiments were somehow systematically wrong, and that *really* the predictions of quantum theory are totally wrong. Then maybe it'll turn out that a Bell Local theory can be empirically viable. But I see no evidence to warrant such a hypothesis. The experimental evidence is pretty damn strong that the QM predictions are correct. And if that is right, then nature isn't Bell Local.

You seem to have this idea stuck in your head that, somehow, some arbitrary premise (based somehow in some particular theory) crept into the proof, so that, if said theory turns out not to be right, the conclusion will topple. But the only reason this conclusion is remotely interesting in the first place is that this isn't true -- it isn't based on any theory at all. So there is no chance that some surprising discovery about the "UQM" will overturn it.

Sure, it makes sense to think that something about the wave mechanical approach is corresponding to what is actually happening in the UQW. But, it isn't a correct reading of the completeness doctrine to take it as committing to a description of an underlying reality. At least not a 1-1 mapping.

A 1-1 mapping is precisely how Einstein understood the completeness doctrine. If you disagree with him and me, perhaps you can clarify what you think it means.

There is reality, and then there are some speculative ideas about an underlying reality. Not enough is known about the UQW to say, definitively, that it's nonlocally causal.

Wrong! Enough *is* known. All that one has to know is that the results of certain experiments have a certain structure. I don't *think* you believe those experiments are wrong. But then you'd better point out to me what other assumption you think crept into the proof. If you can't point to such a thing, you really need to stop saying and believing that "not enough is known."

You want to be thorough, right ? Ok then, you can't go from just not being able to construct a locally causal theory of quantum entanglement (only nonlocally causal theories will do) to the assertion that the UQW is nonlocally causal, unless you assume that your nonlocally causal theories are complete descriptions of the UQW. But it would be "unscientific, irrational, and downright stupid in the extreme" to assume that.

Again, you misunderstand the argument. It's not just that nobody has yet managed "to construct a locally causal theory". There is an actual, rigorous proof that it cannot be done.

The standard probabilistic (Copenhagen) interpretation makes no claim to being a complete description of an underlying reality.

Excuse me? The completeness doctrine is the central plank of the Copenhagen interpretation.

Maybe you mean: one could use the quantum formalism (as presented in textbooks) without accepting the Copenhagen or any other interpretation. That's true. But don't call doing that the Copenhagen interpretation! It isn't.

 

[ttn]

Your point is how can that experiment select between the two possibilities of QM or BM by proving the third wrong

Yes. OQM and BM are both equally consistent with the experiments. So on what grounds could anyone possibly say the experiments prove OQM and refute BM? It's preposterous on its face. And any such attempt usually ends up amounting to: but OQM has been widely accepted by lots of people for a long time, so we should just stick with it. But that attitude is pathetic -- especially given the severe problems with OQM as a theory (and lack of such problems with BM).

My problem with BM being some sort of proof that QM is not complete fails on two points.

I think you misunderstand. Nobody (at least not me) thinks that BM is a "proof that QM is not complete." It's only a proof that experiment can't tell us whether QM is complete or not. It's a proof that anyone who says "You have to accept Copenhagen on pain of contradicting experiment" is full of bull.

 

[RandallB]

I think you misunderstand. Nobody (at least not me) thinks that BM is a "proof that QM is not complete." It's only a proof that experiment can't tell us whether QM is complete or not. It's a proof that anyone who says "You have to accept Copenhagen on pain of contradicting experiment" is full of bull.

That’s good I hope all BM adherents think the same way.
But as I said in my first point we don’t really need BM to think that way.

In fact I have no problem with those that choose to believe for purposes of application. It has clearly served them well as demonstrated by the success of the last several decades. As long as they are not dealing with the obvious problems of infinity/singularities things have worked well for them. I can consider them as working with a not perfect but very workable analogy of reality. Until I can prove differently to them (Falsify HUP/entanglement) I see no reason to interfere with their successful choice to believe.

However, take the case of theoreticians and experimentalists working on tests and designing theories and explanations to confirm QM of any style (from Strings to BM or MWI to what ever Hawking claims to have under is hat; on this point they are all the same to me).
By the fact that this group seeks a better proof or explanation alone demonstrates they do not have faith in QM as being already proven complete or they wouldn’t be doing it. So I agree that they should not make the claim before they come up with the goods. But they need to be confident in their goals to do their work, so I’m not going to beat'm up when they let overconfidence go to their heads.

In fact I consider work on entanglement and interference (superposition or guide-wave) as DrC and others here do is some of the most important work possible that can still be done as thought experiments. Results in real ideas or experimental proposals could make a difference on the issue of reality. Regardless of initial intention it’s only the results that will tell.

 

[DrChinese]

You're running together a bunch of completely different issues here. The central point is that BM and OQM make the same empirical predictions, so there is no possibility that you could point to some empirical fact that supports on as opposed to the other...

And vice versa, my friend.

BM can claim all it wants to, nothing more than the HUP is delivered. When you can beat the HUP, you will have your scintilla. Until then, you have exactly squat. Anyone can make up a theory that claims X and simultaneously says that X cannot be tested. BM is that, which is why it is not taken more seriously by the physics community at large.

For your paper to be convincing, you will need to provide one of the following:

a) A way to beat the HUP, demonstrating realism and, by Bell's Theorem, demonstrating the existence of non-locality.
b) A way to demonstrate the existence of non-local pilot waves.

...because a purely philosphical argument doesn't cut it in the current environment. That would be true even if I believed in non-locality.

 

[ttn]

BM can claim all it wants to, nothing more than the HUP is delivered. When you can beat the HUP, you will have your scintilla. Until then, you have exactly squat. Anyone can make up a theory that claims X and simultaneously says that X cannot be tested. BM is that, which is why it is not taken more seriously by the physics community at large.

You imply that Bohm's theory has some different status (in regard to positing things that can't be directly verified by experiment) from OQM. Is that really the case? Do you think, for example, that the completeness doctrine can be (or has been) empirically tested?

For that matter, can you name a single theory (quantum, classical, whatever) which doesn't posit things that remain unobserved? The fact is, Bohm's theory is a perfectly ordinary physical theory. It doesn't do anything the slightest bit objectionable -- except refute by direct counterexample several long-standing dogmas about the necessity/inevitability of the orthodoxy (which is apparently objectionable to moronic true believers).

 

[Sherlock]

You are missing a crucial point here, which is that the whole two-part argument isn't based on some particular assumption about the way things work, but *simply* on empirical predictions.
...

All that one has to know is that the results of certain experiments have a certain structure.
...

You seem to have this idea stuck in your head that, somehow, some arbitrary premise (based somehow in some particular theory) crept into the proof, so that, if said theory turns out not to be right, the conclusion will topple. But the only reason this conclusion is remotely interesting in the first place is that this isn't true -- it isn't based on any theory at all. So there is no chance that some surprising discovery about the "UQM" will overturn it.

I could very well be missing some (or the) crucial point.
Another, slower, reading seems to be called for (not today, but maybe tomorrow).

The structure that empirical results have (or which is imposed on them), and what can be said about an underlying reality from that structure, seems to be the crux of the matter.

A 1-1 mapping is precisely how Einstein understood the completeness doctrine. If you disagree with him and me, perhaps you can clarify what you think it means.
...

The completeness doctrine is the central plank of the Copenhagen interpretation.

The completeness doctrine is that the wavefunction is a complete description of what can be experimentally determined about a preparation --- that the instrumental output will correspond to the probabilities assigned by the wavefunction for the setup.

At the same time it's not taken as a complete description (ie., it's not taken as a 1-1 mapping) of an underlying quantum reality.

Its guiding motivation is a positivist or instrumentalist philosophical orientation, and the idea that there are certain necessary limitations on what can be experimentally determined (and therefore there are certain necessary limitations on any theoretical description).

 

[vanesch]

The fact is, Bohm's theory is a perfectly ordinary physical theory.

Isn't there one "bizarre" aspect to it, which is the requirement for *our knowledge* of the initial state to be such that it coincides with the (ontological) norm of the initial wavefunction ? This makes it a bit different from standard classical theories, no ? And which sounds like a mixture between epistic and ontic aspects (the wavefunction being part of the ontology of the world and the initial probability distribution - which is something about our KNOWLEDGE of the initial state, because ontologically, from a god's eye, the initial state is a dirac function - have to agree in the beginning). In other words, the HUP is a consequence of our lack of knowledge of the initial state, and not a deep physical principle...

 

[ttn]

Isn't there one "bizarre" aspect to it, which is the requirement for *our knowledge* of the initial state to be such that it coincides with the (ontological) norm of the initial wavefunction ? This makes it a bit different from standard classical theories, no ? And which sounds like a mixture between epistic and ontic aspects (the wavefunction being part of the ontology of the world and the initial probability distribution - which is something about our KNOWLEDGE of the initial state, because ontologically, from a god's eye, the initial state is a dirac function - have to agree in the beginning). In other words, the HUP is a consequence of our lack of knowledge of the initial state, and not a deep physical principle...

This paper addresses this issue:

http://www.arxiv.org/abs/quant-ph/0308039

The basic thesis is that there is no more of a mystery here for the initial conditions of a Bohmian universe, than there is regarding the initial conditions of a classical universe being so as to be consistent with the second law of thermo. (In particular, in both cases, one need merely accept that the initial condition was "typical"; the usual classical or quantum statistical distributions then follow.) It's really a beautiful paper, well worth taking the time to read. (And same for the "follow-up" paper mentioned in the comment on the arxiv page.)

 

[RandallB]

ttn

I'm trying to simplify an understanding of your view on QM “completeness” or “no other answer possible” testing by the EPR Bell Locality experiments.

On the Paradox of electrons not crashing into protons:
QM considers this a resolved paradox based on the QM probability zone of the electron location in and around the proton. Either by using a particle probability function or a wave probability function, both are HUP based. I sure even BM can describe it with a statistical guided wave function that duplicates the HUP statistics.

In your view, do you consider this an unresolved paradox, with only an incomplete analogy from the above three approaches available as incomplete descriptions?

 

[straycat]

Hey all,

I've sort of skimmed this thread, and have been thinking about a toy model counterexample to ttn's claim that QM cannot be both complete and local. In fact, I'm going to propose a toy model that I claim is complete, local, and realist.

First, let me say that I've learned a lot about Bell's theorem from Travis; I actually agree with his above claim, and I also agree that Bell's theorem is often misinterpreted as implying that it is impossible to complete QM via any HV theory, when in fact what it tells us is that it is impossible to complete it with a local HV theory. So in a way, I will be playing the role of "devil's advocate" with my claim about my toy model proposal. Really, what I'm trying to do is explore the definitions of the terms "complete," "local," and "realist."

Here's my toy model. Suppose that a "world" W is equated with a 4-d manifold + metric defined over the manifold. Mass-energy is calculated locally from the metric. There are lots of different possible worlds. But let us suppose that the "God's eye view" of Reality is a single higher-dimensional (say, I dunno, 5-dimensional) manifold M. Since there is one and only one M which (let us assume) can be solved uniquely (from some magical set of first principles), then knowledge of M provides a complete description of reality. But let's also assume that M obeys Einstein-locality; thus we have a local (in the sense of Einstein locality) description of reality.

Now the set of "all possible worlds" (all possible W's) is defined as the set of all possible (unbounded) 4-dimensional hypersurfaces that can be embedded in M. Also, the set of all possible physical objects (like a computer, a person, a particle, a rock, a planet) is defined as the set of all possible bounded 4-d regions that can be embedded in M. According to Everett's original MWI proposal, any physical object can play the role of the quantum-mechanical "observer." So let us pick (arbitrarily) some observer O in M -- this can be any 4-dimensional object that can be embedded in M. Next we define the ensemble of all possible worlds relative to this observer as the set of all W's that completely overlap O. We assume that there are more than one (either a stupendously big number, or an infinite number) of W's that correspond to any given choice of O. In a sense, the W's can be generated from O by "extending out" in all 4 directions from O. When she thinks about the 4 dimensions of her everyday experience, she's thinking about one of these W's. But since her calculations generate multiple W's, she interprets that each W exists in "superposition." Suppose that every W contains a pair of particles at some set distances D1 (nearby) and D2 (spacelike separated) away from her; but in some W's the particles are up/down, in the rest, they are down/up. She invents a crazy concept called "superposition" which says that the particles are "neither up nor down." There are no W's where the pair of particles are up/up or down/down; once she figures this out, she invents another crazy notion called "entanglement" to explain this.

Here's what she doesn't grok. When she thinks to herself that particle #1 is "in the superposition of up and down," what this really means is that there are two particles, one up and the other down, that exist in two separate locations in M. (Likewise for particle #2.) One set of W's (call them W_ud's) overlaps with her, particle #1 up, and particle #2 down, while another set of W's (call them W_du's) overlaps with her, particle #1 down, and particle #2 up.

Within any individual W, the future evolution of O is determined uniquely. But remember that there are lots of W's in her ensemble, and her future evolution is distinct in distinct W's. As she experiences time going forward, she will encounter "branches" in which her evolution in time in one subensemble of W's differs from that in another subensemble. For example, at some time t she interacts with particle #1 and observes its state. If she finds it to be up, she knows that every W relative to her state at time t must have particle #1 = up, which implies that every W must also have particle #2 = down. She interprets this to mean that at time t, the state of particle #2 "collapsed from superposition of up/down to definite down." Since particle #2 is spacelike separated, she calls this "spooky action at a distance." In this manner, the toy model demonstrates Bell-nonlocality.

Now I submit that the above toy model is local, complete, and -- added bonus -- realist. (There's only one M, and it really exists.) And it's compatible with Bell-nonlocality. Agree? Disagree?

David

 

[RandallB]

Now I submit that the above toy model is local, complete, ...

Disagree.
EPR-Bell local means Classically Local, not MWI local.
It's compatible with Bell-nonlocality because it's not local.

 

[ttn]

[snip...] Within any individual W, the future evolution of O is determined uniquely. But remember that there are lots of W's in her ensemble, and her future evolution is distinct in distinct W's. As she experiences time going forward, she will encounter "branches" in which her evolution in time in one subensemble of W's differs from that in another subensemble. For example, at some time t she interacts with particle #1 and observes its state. If she finds it to be up, she knows that every W relative to her state at time t must have particle #1 = up, which implies that every W must also have particle #2 = down. She interprets this to mean that at time t, the state of particle #2 "collapsed from superposition of up/down to definite down." Since particle #2 is spacelike separated, she calls this "spooky action at a distance." In this manner, the toy model demonstrates Bell-nonlocality.

So all this comes down to is an ignorance interpretation of superpositions? You're saying (when one cuts through all the pointless and distracting talk about manifolds, etc.) that the observer can interpret the "spooky action at a distance" (which appears to be implied by the quantum collapse postulate) epistemically, as simply an updating of knowledge. So, when Alice measures the z-spin of one of the particles in a singlet state and finds (say) spin up, it's not that she's causing the distant particle to suddenly acquire a new state (spin down), but simply this: the pair was either up-down or down-up, and when she found that hers was up, she knows that the other must be down.

Do any of the details (including the apparent attempt to link this up with the MWI) actually change this simple picture?

Now I submit that the above toy model is local, complete, and -- added bonus -- realist. (There's only one M, and it really exists.) And it's compatible with Bell-nonlocality. Agree? Disagree?

Unless I've missed something crucial, you're right that your explanation for these correlations is local. (But, again unless I've missed something, I think it's inexcusable to muddy the waters so much with all the extra junk.) But the problem is, all you've explained locally is the perfect correlations when Alice and Bob measure along the same axis. But it's well known that this particular subset of the more general class of possible correlations, is locally explicable. You just need to put in local hidden variables for the outcomes and interpret the "preparation of a singlet state" as preparing one of the hidden variable states, presumably selected at random. (Indeed, what's proved in the paper that this thread is based on is that this is *required* if one wants a local explantion -- this is the only possible local explanation of these correlations.)

But then... what about the more general correlations (constrained by the Bell inequality)? You haven't said anything that even touches on these. And in order to "explain these" locally, you'll just have to take the standard MWI route (which means denying that there are any unique outcomes, and you'll have to give some kind of crazy MWI story about how we're deluded into thinking there are outcomes, which'll involve all of our friends being in fact mindless hulks and all that now-standard stuff that Patrick and I and others have gone over here ad nauseum). Or you can stick to a hidden variables type model (with only one world and hence with definite experiment outcomes) but then you'll find that if your model respects Bell Locality, it won't be able to reproduce the observed correlations. So you'll have to build a nonlocal hidden variable model, ala Bohm's theory.

So... I don't see anything new here at all, except maybe several new colors of mud in the waters. But I'm sure you'll correct me if I've missed the point.

 

[straycat]

So all this comes down to is an ignorance interpretation of superpositions?

Sure, you could interpret it that way, if you want. But the more straightforward interpretation would be, I think, that the observer knows exactly where she is located in M and therefore has complete knowledge about her state. She's not ignorant, because there's nothing for her to be ignorant about.

Now you might say that she is ignorant about which W she is "in." But this only makes sense if you assert that she is "in" one and "not in" the rest. From the "God's eye" perspective, this assertion requires us to pick one of the W's as being somehow special, and there's nothing that forces us to do this.

Look at it some more from the "God's eye" perspective. Suppose we have Alice (O) at t=0, and there are (say) two W's that overlap O, one where Alice observes (at t=1) spin up, the other where she observes spin down. The "God's eye" sees that there are two separate copies of "Alice at t=1," each making a different observation, each of which is a smooth continuation from the single "Alice at t=0." And that's all there is to it. Notions of probability, ignorance, etc are ultimately understood to be fictions invented by Alice.

... all you've explained locally is the perfect correlations when Alice and Bob measure along the same axis. But it's well known that this particular subset of the more general class of possible correlations, is locally explicable.

But then... what about the more general correlations (constrained by the Bell inequality)? You haven't said anything that even touches on these.

This is a very good question. Having pondered this toy model for a long time, I think that it is quite possible for the general correlations to be met. A quick and dirty argument would be that if we translate this into a "hidden variable" theory, then the HV is the identity of the 4-manifold W -- and since this conveys nonlocal information, then it is a nonlocal HV theory.

For a more in depth argument, I have actually tried to show explicitly that quantum statistics can be derived from the toy model, requiring only a few extra assumptions that have no bearing on the ontological issues we are discussing. Now I'm perfectly happy to review this derivation in great detail, but it would be way too long for this thread. So for the sake of this discussion, we have several options: 1) you could accept my claim that my toy model violates Bell's inequalites, just as ordinary QM violates them; 2) we could review my derivation -- but that would take forever; 3) you could propose some argument that my toy model cannot do as I claim -- if you can.

And in order to "explain these" locally, you'll just have to take the standard MWI route (which means denying that there are any unique outcomes, and you'll have to give some kind of crazy MWI story about how we're deluded into thinking there are outcomes, which'll involve all of our friends being in fact mindless hulks and all that now-standard stuff that Patrick and I and others have gone over here ad nauseum).

There is no reason that I can think of that my toy model implies that we are deluded about anything. (I've discussed the "mindless hulk" business a bit with Patrick on some of the "Born rule versus APP" threads.) If you can apply these arguments to my toy model, I'm all ears.

Or you can stick to a hidden variables type model (with only one world and hence with definite experiment outcomes) but then you'll find that if your model respects Bell Locality, it won't be able to reproduce the observed correlations. So you'll have to build a nonlocal hidden variable model, ...

That's exactly what I claim to have done (see above).

... ala Bohm's theory.

Well if you like Bohm because it is a nonlocal HV model that reproduces the observed correlations, then I wonder what objection you could have to my model, which achieves the same thing (of being a nonlocal HV theory which (I claim) reproduces the observed correlations). Here's an advantage of mine over Bohm: it is elementary to see that Einstein locality is respected by my model, whereas this is not quite so obvious in Bohmian mechanics (even if it is true).

 

[straycat]

Disagree.
EPR-Bell local means Classically Local, not MWI local.
It's compatible with Bell-nonlocality because it's not local.

hmmm ... there are two kinds of locality that I am accustomed to discussing:
1) Einstein locality, which is respected by GR
2) Bell locality, which is violated by QM

I don't know what you mean by "MWI local" or "Classically local." I would assume that "classically local" = "Einstein local," but this is a distinct concept from "Bell local" ... ?

 

[ttn]

This is a very good question. Having pondered this toy model for a long time, I think that it is quite possible for the general correlations to be met. A quick and dirty argument would be that if we translate this into a "hidden variable" theory, then the HV is the identity of the 4-manifold W -- and since this conveys nonlocal information, then it is a nonlocal HV theory.

Then I don't understand why anyone should care about it. Why take seriously this particular nonlocal "model" (it's way too vague and sketchy to be called a real theory), when far far simpler nonlocal theories (like orthodox QM or Bohm's theory) already exist, which don't require any of the muddy mess of many worlds, 5th dimensions, etc.

For a more in depth argument, I have actually tried to show explicitly that quantum statistics can be derived from the toy model, requiring only a few extra assumptions that have no bearing on the ontological issues we are discussing. Now I'm perfectly happy to review this derivation in great detail, but it would be way too long for this thread. So for the sake of this discussion, we have several options: 1) you could accept my claim that my toy model violates Bell's inequalites, just as ordinary QM violates them; 2) we could review my derivation -- but that would take forever; 3) you could propose some argument that my toy model cannot do as I claim -- if you can.

Honestly, the whole thing is so crazy I see no argument for spending the time needed to understand it. If you say it's nonlocal, I'll just believe you.

There is no reason that I can think of that my toy model implies that we are deluded about anything. (I've discussed the "mindless hulk" business a bit with Patrick on some of the "Born rule versus APP" threads.) If you can apply these arguments to my toy model, I'm all ears.

Aren't there a whole bunch of different copies of the observer? Suppose the observer is me. Suppose I have 10 spin 1/2 particles prepared in the state |+x>, and then I sequentially measure each particle's z-spin. Quantum mechanics predicts that the probability for a + outcome on each particle is 50%, and that I'm reasonably likely to get about 5 +'s out of the 10 measurements. What meaning do you give to those predictions in your model?

Well if you like Bohm because it is a nonlocal HV model that reproduces the observed correlations, then I wonder what objection you could have to my model, which achieves the same thing (of being a nonlocal HV theory which (I claim) reproduces the observed correlations).

The same objection I would have to a "model" which said: purple flying fairies with wings magically sprinkle fairy dust on the apparatus and make the outcomes come out in agreement with the QM predictions. Obviously such a "model" reproduces the QM predictions, yet somehow that alone doesn't provide a strong basis for believing in it!

Here's an advantage of mine over Bohm: it is elementary to see that Einstein locality is respected by my model, whereas this is not quite so obvious in Bohmian mechanics (even if it is true).

Can you define "Einstein locality"? I don't know what this means. The inability to send signals faster than light? That is a theorem in Bohm's theory (it follows from the quantum equilibrium hypothesis) so I don't know what you're worried about there. And I also don't see how any such thing is "elementary" in your model. Or maybe what you mean by Einstein Locality is something like no-causality-outside-the-light-cone. But then, how is this different from Bell Locality which, I thought, you said above your model violates?

 

[RandallB]

hmmm ... there are two kinds of locality that I am accustomed to discussing:
1) Einstein locality, which is respected by GR
2) Bell locality, which is violated by QM

I don't know what you mean by "MWI local" or "Classically local." I would assume that "classically local" = "Einstein local," but this is a distinct concept from "Bell local" ... ?

Based on this and your prior comment:

Now I submit that the above toy model is local, complete, and -- added bonus -- realist.

I doubt you actually know what a local realist is; a 4-manifold or GR is not involved.

The point is your little toy model only has some kind of fabricated “local” or “real” that has nothing to do with EPR. You lost that saying “lets just say a 5-D manifold is local”, that sure is not a EPR, Einstein, Classical, or ‘real’ form of local as tnn is also telling you. Nothing new, it’s very similar to the argument used in MWI that’s why I can only describe yours as “MWI local”.

tnn

If BM shows QM to be potentially incomplete (And QM shows the same the same of BM), in your opinion did you decide if Paradoxes considered resolved by QM should be considered unresolved Paradoxes? (ref: post 71)

 

[ttn]

If BM shows QM to be potentially incomplete (And QM shows the same the same of BM), in your opinion did you decide if Paradoxes considered resolved by QM should be considered unresolved Paradoxes? (ref: post 71)

I'm sorry, I don't really understand what you're asking. OQM claims to resolve the paradox of the electron crashing into the nucleus... are you referring here to the idea that a classical charged particle in an orbit (which of course implies that it's accelerating) should radiate EM energy and hence spiral in toward the nucleus?

OQM says that the electron is really a wave (its state is completely described by the wave function) and the boundary conditions on the wave entail that there is a lowest energy state. So, yes, I guess this resolves the paradox of the semi-classical Bohr model.

Are you now asking if Bohm's theory can also resolve this paradox? (It certainly can: for a H atom in its ground state, the electron is stationary, so even with a semi-classical theory of its coupling to the EM field the paradox is resolved.) Or if somehow the existence of Bohm's theory (qua counter-example to the usual arguments that experiment requires the completeness postulate) un-solves the paradox for OQM? Or what?

 

[RandallB]

OQM claims to resolve the paradox of the electron crashing into the nucleus...
Are you now asking if Bohm's theory can also resolve this paradox?
Or if the existence of Bohm's theory un-solves the paradox

NO,
It’s that as I understand your assertion, the existence of BM, means that QM is “not complete” or at least it is “not necessarily complete” as QM claims is shown by virtue of EPR-Bell tests. And therefore you say “anyone who says ‘You have to accept Copenhagen on pain of contradicting experiment’ is full of bull”.

IF BM brings this assertion, must it not also claim the resolutions of Paradoxes “solved” by either QM or BM must also be considered as “not necessarily complete”?

It just seems to me to claim one and not also presume the other is logically inconsistent.

So I’m simply asking, based on your higher standards against Copenhagen, do you also hold popular assumptions that Paradoxes ‘solved’ by QM/BM etc.; are therefore in fact “incomplete” solutions?
I’m guessing you must, based on your position that the theories solving them should not be considered complete.

 

[ttn]

NO,
It’s that as I understand your assertion, the existence of BM, means that QM is “not complete” or at least it is “not necessarily complete” as QM claims is shown by virtue of EPR-Bell tests.

BM proves that it is possible to have a hidden variable theory that agrees with the QM predictions (contra the bogus "proofs" of von neumann, etc.). So, if that's what you mean by BM proving that QM is "not necessarily complete", OK.

And therefore you say “anyone who says ‘You have to accept Copenhagen on pain of contradicting experiment’ is full of bull”.

Yes, that would be bull.

IF BM brings this assertion, must it not also claim the resolutions of Paradoxes “solved” by either QM or BM must also be considered as “not necessarily complete”?

You seem to slide here into a different usage of the word "complete". In QM, "complete" refers to the "completeness doctrine" which is the idea that the wave function alone provides a complete description of the state of a quantum system (i.e., that there are no "hidden variables"). So I don't really understand what you mean when you talk about a theory's resolution of some paradox or other being complete/incomplete.

It just seems to me to claim one and not also presume the other is logically inconsistent.

I'm sorry, I don't follow you. Are you just worried that Bohmian Mechanics proves (by example) that maybe the orthodox quantum theory is just wrong, so we have to go back to the beginning and start from scratch and re-address all of those things that (we thought) were adequately addressed by orthodox QM? I mean, in a sense it's right to worry about this. But we don't have to start over from nothing; the very thing that raises this problem (the existence of Bohm's theory) also solves the problem. So all you have to do is go back and figure out how to think about all these things (such as the stability of the H atom) from the point of view of Bohm's theory.

But maybe I'm still missing your point/worry.

So I’m simply asking, based on your higher standards against Copenhagen, do you also hold popular assumptions that Paradoxes ‘solved’ by QM/BM etc.; are therefore in fact “incomplete” solutions?
I’m guessing you must, based on your position that the theories solving them should not be considered complete.

If OQM isn't a correct theory (which it almost certainly isn't since it is riddled with "unprofessional vagueness and ambiguity") then, yes, we should find a correct theory and use it to understand how to resolve all the paradoxes. (Or more accurately: we should decide which theory is correct by finding one which provides a natural and simple and illuminating resolution of any such paradoxes.)

 

[straycat]

You raise several independent objections to my model:

... far far simpler nonlocal theories (like orthodox QM or Bohm's theory) already exist, which don't require any of the muddy mess of many worlds, 5th dimensions, etc.

1) simpler: How do you gauge simplicity of a model? The amount of effort it takes to understand? dBB probably seems simple to you since you have immersed yourself in it for so long that you know it inside and out, including answers to objections that others raise. Really, the basic structure of my model is not conceptually difficult; I was able to fit it into one post.

2) muddy mess: this is a vague objection which translates in my mind to "Travis just doesn't like many worlds or extra dimensions." which is more of an emotional response than an intellectual argument, and I'm afraid there's nothing I can do to argue against your feelings. Patrick and others have tried and failed.

The same objection I would have to a "model" which said: purple flying fairies with wings magically sprinkle fairy dust on the apparatus and make the outcomes come out in agreement with the QM predictions. Obviously such a "model" reproduces the QM predictions, yet somehow that alone doesn't provide a strong basis for believing in it!

3) flying fairies : I interpret this as meaning that my model is insufficiently developed or detailed to do calculations. OK, fine. I actually speculate that it is possible to add sufficient detail so that all of quantum statistics pops out. And I'm not talking about "fairy dust" detail, I mean: stipulate that M obeys one or a few well-defined general mathematical constraints, and out pops the Schrodinger equation.

If you want to argue that that cannot be done, fine. But I am not asking you to dig into the nitty gritty details of my toy model. My purpose in this thread is to discuss ontological issues, and it is not necessary to know the nitty gritty derivation prior to a discussion of its ontology. So here's what I'm asking: assume, hypothetically, the following: the axioms of the model, eg the mathematical constraints placed on M, can be stated compactly and succinctly; that the subsequent derivation of quantum statistics could be made to work rigorously; and that the whole derivation turns out to be no more or less complicated than, say, learning the dBB version of QM from ground zero. Now I know that your gut tells you this won't work, but that's why I use the word "hypothetical." The remaining objections are ontological, and these are what I am interested in exploring here. I really really ask that you do not mix objection 3) with the other (ontological) issues. ie please don't tell me that your ontological objection to extra dimensions is that you object to flying fairies.

4) mindless hulks:

Aren't there a whole bunch of different copies of the observer? Suppose the observer is me. Suppose I have 10 spin 1/2 particles prepared in the state |+x>, and then I sequentially measure each particle's z-spin. Quantum mechanics predicts that the probability for a + outcome on each particle is 50%, and that I'm reasonably likely to get about 5 +'s out of the 10 measurements. What meaning do you give to those predictions in your model?

Suppose you observe the first one to be up. My model says that there exists within M (probably in close proximity) an entity that looks a lot like you, except you observed down. Does this make both of you into a mindless hulk? I say no. According to your average run of the mill classical mechanical model, there exists one representation of the Travis-state at noon today, and a separate representation of the Travis-state at 12:01. If my toy model implies mindlessness, then the classical model should imply mindlessness as well. So what, exactly, is the difference between "mindless hulk" and "not mindless hulk"?

I suspect that your discomfort here basically boils down to your discomfort with the extra dimension(s) of my model. From my discussions with Patrick, I think he arrives at the "mindless hulk" picture via a different route -- ie, considerations having to do with the adoption of the Born rule. I think that I understand how Born rule ==> Patrick's mindless hulk, but I also think that if we apply Patrick's APP in place of the Born rule, then we can evade his "mindless hulk" objection. (Not sure if Patrick would agree though.)

5) Einstein locality -- to be addressed in next post.

david

 

[straycat]

(One more thought before I get to the issue of Einstein locality raised by you and Randall)

Then I don't understand why anyone should care about it. Why take seriously this particular nonlocal "model" (it's way too vague and sketchy to be called a real theory), when far far simpler nonlocal theories (like orthodox QM or Bohm's theory) already exist, which don't require any of the muddy mess of many worlds, 5th dimensions, etc.

According to my (admittedly very rudimentary) understanding of the various attempts at quantum gravity, at least some of these various programmes could be perhaps cast into the format of my model. For example: in loop quantum gravity, depending on which version, an individual W in my model could play the role of a spin network, and M could play the role of a spin foam. (See [1].) So the purpose of my model is to compare/contrast the ontology of, say, LQG to the ontology of, say, Bohmian mechanics. Of course, there are lots of different versions of LQG, and even more versions/ attempts at quantum gravity in general, and anyone of these may or may not fit my toy model. So the proposed purpose of discussing my model is to discuss whether we can use ontological considerations to guide a construction of quantum gravity.

For example, I think that the "mindless hulk" issue tells us that probability should enter quantum gravity via an APP-based probability rule rather than via the Born rule -- but I see that I am getting ahead of myself, since I don't know whether you (ttn or Randall) have thought as much about Patrick's APP as Patrick and I have.

[1] arXiv:hep-th/0601129
Loop and spin foam quantum gravity: a brief guide for beginners

 

[straycat]

Based on this and your prior comment:I doubt you actually know what a local realist is; a 4-manifold or GR is not involved.

...

The point is your little toy model only has some kind of fabricated “local” or “real” that has nothing to do with EPR. You lost that saying “lets just say a 5-D manifold is local”, that sure is not a EPR, Einstein, Classical, or ‘real’ form of local as tnn is also telling you. Nothing new, it’s very similar to the argument used in MWI that’s why I can only describe yours as “MWI local”.

So then what exactly do "local" and "realist" mean?

First, would you agree that classical GR is a local theory? When I stipulate that my toy model is local, I mean this: M is local in exactly the same way that any given 4-manifold in classical GR is local. Given Travis' two choices, I would pick: Einstein-locality = no signals faster than light. (If you object that M has more dimensions, then I would point out that there is a generalization of GR to higher dimensions (Lovelock gravity), the point being that "Einstein-locality" can be carried over into higher dimensions.)

When I state that my model respects Bell-nonlocality, I would point out that Bell-locality is distinct concept from Einstein locality. There is no contradiction in stating that a theory obeys Einstein-locality plus Bell-nonlocality at the same time.

Here's what I mean when I say that my model obeys Bell-nonlocality. Go back to the two-particle example from my earlier post. Let's say that Alice is thinking in terms of the "wavefunction" of the far-away particle. When she observes particle #1, she interprets that the wavefunction of particle #2 (which is spacelike separated) suddenly changes, at the instant that she observes particle #1.

The issue here is that the ontological status of the "wavefunction" gets demoted in my model. Is there some field psi that exists as a function of the five dimensions of M? No. The only reason the "wavefunction" (or Bohm's quantum potential, for that matter) exists in Alice's mind is that she is trying to represent "what exists" using a single 4-dimensional manifold, because that's what she thinks reality is, in place of all of those W's in her ensemble. Loosely speaking, the wavefunction is like an "average" of what's going on in all the W's in her ensemble. So the wavefunction and the quantum potential are each useful mathematical constructs, but they are not objectively real "things" as in dBB (at least for the potential). Well, let me qualify that: the wavefunction provides a somewhat abstract representation of some other objectively real things (the W's), but it is not in and of itself a physically "real" field.

So when I say that my model obeys Bell-nonlocality, I mean that according to my model, we have "observation here induces instantaneous collapse of the wavefunction over there." But there is no physical field or potential that is actually changing "over there."

wrt realism: I would still say that my model is realist in the same sense that classical GR is realist -- but perhaps you have some requirement for "realist" about which I am unaware.

 

[RandallB]

So then what exactly do "local" and "realist" mean?
First, would you agree that classical GR is a local theory?

No I don’t.
I accept GR is background independent (Ref: “The case for background independence” Lee Smolin/ Perimeter)

SR and Minkowski space-time (As a flat 4-D representation of Classical SR) as classical theories are background dependent (Although Minkowski I believe disagrees that his was actually classical) are able to hold the “unknown variable”. Einstein and Bell both always hoped that variable would be able to be demonstrated as real & local somehow (Speakable – Unspeakable; Bell).

From reading Bell himself instead of interpretations about him (most of those neglect to point out that Bell believed in “unknown variables”) I see no real difference in Einstein vs. Bell local.

Other than to incorrectly claim “local”, I really don’t see where GR applies here at all.
As soon as you introduce anything in an additional dimension that can collapse or link between two otherwise space-like separated events you are by definition not using a local realist, a requirement for both Einstein and Bell Local. Suggest you review Bell’s own writings again.

 

[RandallB]

If OQM isn't a correct theory (which it almost certainly isn't ...") then, yes, we should find a correct theory ...to resolve all the paradoxes.

That's it! That’s all I was looking for, yet you seem afraid to actually say it.
The Paradoxes “resolved” by current accepted QM thinking (Also, solvable by BM) are in your interpretation not yet truly resolved. That’s all I was asking.

The only weakness I see in that argument “BM proves that it is possible to have a hidden variable theory that agrees with the QM predictions” is that the BM version is just as non-local as QM. And additionally can be reasonable interpreted as being “equivalent” to QM. Just as the different theories of “wave” and “particle” of the 1920’s were both brought together under the QM umbrella as being equivalent.

So all this really tells me is if an unknown variable can be demonstrated it would not only falsify QM (Wave & particle) but BM as well.
What BM has really shown is that in practice QM has not “proven” a positive, (that QM is correct). But by definition proving a positive is a near impossible task.

 

[ttn]

The only weakness I see in that argument “BM proves that it is possible to have a hidden variable theory that agrees with the QM predictions” is that the BM version is just as non-local as QM.

I don't think anyone has argued that a good reason for liking Bohm is that it's less nonlocal than OQM. (Though people have certainly argued the reverse, which is equally wrong!) Nonlocality (specifically, the violation of Bell Locality) is just a fact; there cannot exist an empirically viable theory that is local in this sense. So the locality issue really provides no grounds whatsoever for trying to decide between different (empirically viable) theories.

No, the reasons to prefer Bohm to OQM lie elsewhere: most notably, in the fact that Bohm's theory solves the measurement problem.

And additionally can be reasonable interpreted as being “equivalent” to QM.

Only in the sense that it makes the same empirical predictions. But it's certainly not the same theory. (Copernicus' and Ptolemy's theories of the solar system clearly weren't the same, even though they agreed about where you'd have to point your telescope to see Jupiter.)

 

[ttn]

1) simpler: How do you gauge simplicity of a model? The amount of effort it takes to understand? dBB probably seems simple to you since you have immersed yourself in it for so long that you know it inside and out, including answers to objections that others raise. Really, the basic structure of my model is not conceptually difficult; I was able to fit it into one post.

2) muddy mess: this is a vague objection which translates in my mind to "Travis just doesn't like many worlds or extra dimensions." which is more of an emotional response than an intellectual argument, and I'm afraid there's nothing I can do to argue against your feelings. Patrick and others have tried and failed.

Here's all I meant. The only reason any sane person takes MWI seriously at all is that it seems to be the only way to explain (well, pseudo-explain) the data without accepting nonlocality and thus rejecting relativity. You said your model violates Bell Locality. If that's right, then Occam's razor desperately wants to slash off your model. For it's already known that if you're willing to accept a violation of Bell Locality, you can get along just fine with *one* world and no mysterious extra dimensions. Your model violates Bell Locality but (it seems, pointlessly) includes these other bizarre MWI-like features. What's the point? Why give up so much when it's already known that it's possible to give up less?

3) flying fairies : I interpret this as meaning that my model is insufficiently developed or detailed to do calculations. OK, fine. I actually speculate that it is possible to add sufficient detail so that all of quantum statistics pops out. And I'm not talking about "fairy dust" detail, I mean: stipulate that M obeys one or a few well-defined general mathematical constraints, and out pops the Schrodinger equation.

I can't argue with speculation about speculation. (Ah, reminds me of a joke an old office mate of mine used to tell about some project he was working on having to do with "saxions" -- the supersymmetric partner of the hypothetical axion particle. The work was, he said, "second order in speculation.")

4) mindless hulks:

You are free to just stipulate that all the different Alices living at different places along the 5th dimension are all equally real, equally conscious; none of them are mindless hulks. No problem.

The problem is then that statements about probability (which are rather important in QM) don't seem to have any meaning. That's what I was getting at before. So then it is not at all obvious how a model like yours can be said to agree with the QM predictions. This is a long-standing problem for MWI people (and is exactly why people like Patrick want to say that only one of the copies is the genuine article, and that which one this is is *random* according to Born's rule. This solves the problem of the meaninglessness of "probability" at the price of introducing mindless hulks).

 

[ttn]

..., the point being that "Einstein-locality" can be carried over into higher dimensions.)

Except that a causal effect propagating at c in 5 dimensions could lead to superluminal actions at a distance as seen from our everyday 4 dimensions. So it's not clear what the *point* is of generalizing "Einstein-locality" to higher dimensional spaces.

When I state that my model respects Bell-nonlocality,

This phrase is confusing. Does it mean that your model violates Bell Locality (i.e., is not Bell Local)?

Here's what I mean when I say that my model obeys Bell-nonlocality. Go back to the two-particle example from my earlier post. Let's say that Alice is thinking in terms of the "wavefunction" of the far-away particle. When she observes particle #1, she interprets that the wavefunction of particle #2 (which is spacelike separated) suddenly changes, at the instant that she observes particle #1.

This contradicts the way you were talking about it earlier. Before, you said that this "sudden change in the wave function" is *really* only an updating of knowledge. (Basically, there existed local hidden variables which determined the outcomes.) But such a model does *not* violate Bell Locality. A sudden change in the wave function at a distant location only involves a violation of Bell Locality if the wf is a physically real thing; if (as I thought you claimed earlier) the wf is merely a summary of our (incomplete) knowledge of the real physical state of affairs, then its change does not involve any nonlocality.

So which is it?

The issue here is that the ontological status of the "wavefunction" gets demoted in my model. Is there some field psi that exists as a function of the five dimensions of M? No. The only reason the "wavefunction" (or Bohm's quantum potential, for that matter) exists in Alice's mind is that she is trying to represent "what exists" using a single 4-dimensional manifold, because that's what she thinks reality is, in place of all of those W's in her ensemble. Loosely speaking, the wavefunction is like an "average" of what's going on in all the W's in her ensemble. So the wavefunction and the quantum potential are each useful mathematical constructs, but they are not objectively real "things" as in dBB (at least for the potential). Well, let me qualify that: the wavefunction provides a somewhat abstract representation of some other objectively real things (the W's), but it is not in and of itself a physically "real" field.

Either the wf is (what bell called) a "beable", or it isn't. If it is, then a sudden change in its value over there caused by something you did over here, means that Bell Locality is violated. If not, not.

So when I say that my model obeys Bell-nonlocality, I mean that according to my model, we have "observation here induces instantaneous collapse of the wavefunction over there." But there is no physical field or potential that is actually changing "over there."

Then why do you say this model violates Bell Locality? Sounds to me like it doesn't. But then my earlier question remains: how exactly do you think you're going to explain the QM predictions for correlations b/w entangled particles?


It is because of the flood of such ambiguities and questions that I referred to this earlier as a "muddy mess". With all due respect, it seems more like an attempt to use fancy words, than a serious attempt to answer any of the relevant problems/puzzles.

 

[RandallB]

So the locality issue really provides no grounds whatsoever for trying to decide between different (empirically viable) theories.

I didn’t suggest the locality issue could decide between them, only if shown as real would falsify them all, Bohm included.

No, the reasons to prefer Bohm to OQM lie elsewhere: most notably, in the fact that Bohm's theory solves the measurement problem.

I don’t find the measurement solution any more satisfying than the QM case. At least not until the two theories can predict different results that experiments can select between.

But I’m OK with your consistent position, the QM side is just more willing to accept as complete or final the solutions the practical use of QM has provided (Including Paradoxes resolved). You’re just more cautious that the final word on those points may well not be in yet, and are willing to look for a more clear/definitive and verifiable description.
Though a bit out of the ‘mainstream’ nothing unreasonable about that. As with any theory it just needs results, just not aware of any ideas for such a test.

 

[ttn]

I don’t find the measurement solution any more satisfying than the QM case. At least not until the two theories can predict different results that experiments can select between.

I wonder if you're not sure exactly what is meant by "the measurement problem." This is actually a serious problem for Orthodox QM, which literally gives two different dynamical rules for the evolution of wave functions (depending on whether or not a "measurement" is being made). The *problem* is that the theory does not say what constitutes a "measurement", so it is, to use Bell's phrase "unprofessionally vague and ambiguous." This is the problem that is supposed to be raised by Schroedinger's cat: if you follow the time evolution described by Schroedinger's equation, you get nonsense results like cats being in superpositions of alive and dead. Since we never *see* such states, that description must be wrong. The wave function must have collapsed, at some point in the development, to a more definite state. But where did this collapse occur? When we consciously registered the state of the cat? Or when some photons flew from the cat and interacted with our eyeballs? Or when some poison molecules interacted with the cat? Or when the hammer interacted with the vial of poison? etc. The theory just doesn't tell us where along this chain the wf collapses, i.e., where the normal Schroedinger time evolution gives way to the alternate "collapse" dynamics. Put another way, the problem is that OQM doesn't seem able to explain why experiments have definite outcomes; or rather, the only way it can explain why experiments have definite outcomes, is by importing some very dubious concepts (such as "measurement") into the fundamental laws of nature where they don't seem to belong. This is a serious foundational problem for the theory.

In Bohmian Mechanics, we simply do not have this problem. Because particles always have definite positions (even when not being "measured"), there is no problem whatsoever associated with measurements having definite outcomes. The needle on your detector ends up in some definite spot (registering some definite outcome) because it's made of *particles* and particles are always in some definite spot. So, there simply is no problem associated with measurement in Bohm's theory. Measurement is just another ordinary physical process, the same in principle (meaning, obeying the same dynamical laws) as any other "non-measurement" physical process.

Your worry that the two theories make the same predictions (and that it is therefore difficult to tell which one is right) is a completely different issue. Yes, it would be nice if the various theories made different predictions so we could just do the experiment and rule some of them out. But it's not so, so, if we're going to have an opinion about which theory is better, it has to be based on some criteria other than agreement with experiment. (For example, whether a given theory is plagued by the measurement problem, or whether it asks us to believe in gazillions of copies of unobservable parallel universes inhabited by mindless hulks, etc...) And by the way, this is not at all an abnormal thing in the history of science. Lots of times people have been confronted with differing theories which make the same predictions (at least for the time being).

 

[RandallB]

what is meant by "the measurement problem." ... a serious problem for QM, ... to use Bell's phrase "unprofessionally vague and ambiguous."
raised by Schroedinger's cat:

Schroedinger's cat issues have always seemed to me as a joke taken way too serious. Once everyone was having so much fun coming up with various scenarios too many started to take it as something real and the ‘cat was out of the bag’. The idea that HUP measurement issue can somehow be scaled up to be real at the macro view of an overly ego-centric / self-centric observer is to me pointless. The idea is more for popular book titles than serious science.
No rational reason to expect the HUP to factor up this way to a macro level. Or to expect someone must be obligated to look at the moon to be sure it remains in orbit for fear it may disappear were it failed to be observed. It’s just too silly to give that kind of extension serious consideration IMO.

Just as a non-local universal wave function running in some other dimension(s) so as to align real measurements to create apparent “weird-action-at-a-distance”, cannot be expected to show itself in some detectable “measurable” way in our 3-D experience to prove its viability.

Both theories have these things as non-local parts that at least to date can not been shown in detail in our local reality. If you insist on “seeing” that HUP shows itself in a cat rather than in phenomena. Than BM should produce the demonstration the reveals the universal wave function directly and standing alone, without relying on an after the fact explanation of a phenomena to infer it existence.

In this regard I still see no difference in them even with the “measurement problem”. Therefore, I don’t think either can “prove” the other wrong. (Even if the QM approach at least “seems” to have been the more practical in application so far.)

Remember Bell’s bias was FOR a deterministic solution to replace both BM & QM non-local theories like Einstein. And that his 'test' help point the way-- So far it has not.

 

[ttn]

Schroedinger's cat issues have always seemed to me as a joke taken way too serious. Once everyone was having so much fun coming up with various scenarios too many started to take it as something real and the ‘cat was out of the bag’. The idea that HUP measurement issue can somehow be scaled up to be real at the macro view of an overly ego-centric / self-centric observer is to me pointless. The idea is more for popular book titles than serious science.
No rational reason to expect the HUP to factor up this way to a macro level. Or to expect someone must be obligated to look at the moon to be sure it remains in orbit for fear it may disappear were it failed to be observed. It’s just too silly to give that kind of extension serious consideration IMO.

Just as a non-local universal wave function running in some other dimension(s) so as to align real measurements to create apparent “weird-action-at-a-distance”, cannot be expected to show itself in some detectable “measurable” way in our 3-D experience to prove its viability.

Both theories have these things as non-local parts that at least to date can not been shown in detail in our local reality. If you insist on “seeing” that HUP shows itself in a cat rather than in phenomena. Than BM should produce the demonstration the reveals the universal wave function directly and standing alone, without relying on an after the fact explanation of a phenomena to infer it existence.

In this regard I still see no difference in them even with the “measurement problem”. Therefore, I don’t think either can “prove” the other wrong. (Even if the QM approach at least “seems” to have been the more practical in application so far.)

Remember Bell’s bias was FOR a deterministic solution to replace both BM & QM non-local theories like Einstein. And that his 'test' help point the way-- So far it has not.

I can't make any sense of any of this, but I don't think it's worth pursuing anymore. Let's just agree to not understand each other.

 

[Sherlock]

ttn, I'm not sure what the most recent exchanges in this thread were about. Anyway, I just read Bohm and Bub's, "A Proposed Solution of the Measurement Problem in Quantum Mechanics by a Hidden Variable Theory".

I'm not finished rereading your papers yet, and am boinking this thread in the hope that some more knowledgeable (or at least less confused) people than myself will weigh in with detailed analyses and evaluations of your papers, especially the latest one on the nonlocal character of nature.

Wrt the Bohm and Bub paper, I finally feel that I'm on a track to understanding why the measurement problem is indeed a problem and why it can't be solved via quantum theory alone. I especially like their idea that, via quantum theory (at least the orthodox interpretation of it), one might get conceptually trapped without realizing that one is so trapped. However, I'm not sure I understand the nonlocal mechanism in the theory they propose.

 

[RandallB]

I can't make any sense of any of this, but I don't think it's worth pursuing anymore. Let's just agree to not understand each other.

OK, by me.
With the exception of not buying the claim that Bohm can solve a local measurement with a non-local solution, I’m satisfied with your explanation of BM and your consistent positions inside BM philosophy.
See-ya in another thread someday

 

[straycat]

mindless hulks?

You are free to just stipulate that all the different Alices living at different places along the 5th dimension are all equally real, equally conscious; none of them are mindless hulks. No problem.

The problem is then that statements about probability (which are rather important in QM) don't seem to have any meaning. That's what I was getting at before. So then it is not at all obvious how a model like yours can be said to agree with the QM predictions. This is a long-standing problem for MWI people (and is exactly why people like Patrick want to say that only one of the copies is the genuine article, and that which one this is is *random* according to Born's rule. This solves the problem of the meaninglessness of "probability" at the price of introducing mindless hulks).

Ahh! Perhaps we are getting somewhere in this discussion

I agree completely with the notion, as expressed by Patrick elsewhere, that the interpretation of probability from the perspective of the MWI is a long-standing problem -- perhaps its greatest problem. And I agree that if we use the Born rule to assign probabilities, then we are forced to the conclusion that only one of the copies is the genuine article; thus the rest must be mindless hulks.

But I think that the "mindless hulk" argument does NOT apply to Patrick's "alternate projection postulate" (APP). (Not sure if you or Patrick agree with this.)

So why does the mindless hulk argument apply to the Born rule and not to the APP? Here's why. Let's assume that all of the copies in all of the parallel worlds are equally conscious, equally real. If we apply the Born rule, then we find that most of the observers in most of the universes will "observe" the Born rule to be false. But if all observers are conscious, and most of them observe the Born rule to be false, then we must conclude that QM is just "wrong" for most observers. Which of course it's not. So the only way around this difficulty is to assert that the ones that observe the Born rule to be false are hulks; the only non-hulk copies are the ones that exist in those few worlds where the Born rule is true. iow we are forced to give up our assumption that they are equally conscious.

But if we assume the APP, we don't have that problem, because the measure of the worlds in which an observer will conclude that the APP is true approaches unity in the limit of a large number of measurements. iow, "most" observers observe that the APP is valid. So there is no need to go around claiming that most of them are mindless.

This is precisely the reason that my "saxion-esque" scheme -- the one you recall that we are assuming hypothetically for the sake of this thread to be successful in the derivation of the Schrodinger equation by imposing a few mathematical constraints over the M in my toy model -- takes the APP as the fundamental "rule" for calculating probabilities. The Born rule is understood to be a valid coarse-grained approximation to a situation which is fundamentally governed by the APP at the fine-grained level. I would also point out that, in addition to the hypothetically successful saxionesque development of my toy model, there are at least two independent proposals in the literature of ways to take the MWI, assume the APP at the fine-grained level, and show that the Born rule is valid at the coarse-grained level. (These are by Weissman and Hanson -- see discussions on some of Patrick's threads.)

So the ontological point to be made here is that it is, at the least, hypothetically possible to have an MWI model that does NOT require mindless hulks. So on this one issue, I see MWI and Bohmian mechanics as being on equal footing. (To be honest I have not considered the issue of mindless hulks and BM, but for the sake of argument I am willing to concede that BM does not require MH's.)

David

 

[straycat]

Except that a causal effect propagating at c in 5 dimensions could lead to superluminal actions at a distance as seen from our everyday 4 dimensions.

How exactly do you come at that conclusion?

Let's suppose that we have a causal effect propagating at c in 4 dimensions -- iow, assume classical relativity. Does this lead to superluminal actions at a distance as seen via consideration of a 3 dimensional hypersurface? I don't think so, unless I'm missing something. If going from 4 to 3 doesn't pose a problem, then I don't see why going from 5 to 4 does.

 

[straycat]

This phrase is confusing. Does it mean that your model violates Bell Locality (i.e., is not Bell Local)?

I see that there is some confusion over semantics. So let me try to clarify my terms so we can communicate.

This contradicts the way you were talking about it earlier. Before, you said that this "sudden change in the wave function" is *really* only an updating of knowledge. (Basically, there existed local hidden variables which determined the outcomes.) But such a model does *not* violate Bell Locality. A sudden change in the wave function at a distant location only involves a violation of Bell Locality if the wf is a physically real thing; if (as I thought you claimed earlier) the wf is merely a summary of our (incomplete) knowledge of the real physical state of affairs, then its change does not involve any nonlocality.

So which is it?

[...]

Either the wf is (what bell called) a "beable", or it isn't. If it is, then a sudden change in its value over there caused by something you did over here, means that Bell Locality is violated. If not, not.

[...]

Then why do you say this model violates Bell Locality? Sounds to me like it doesn't. But then my earlier question remains: how exactly do you think you're going to explain the QM predictions for correlations b/w entangled particles?

Here's what I am claiming about my model:

1. It is local in exactly the same way that GR is local, except that we have 5 dimensions instead of 4. Randall has argued that GR is not "local," but it is "background independent." Gosh darnit, you guys are a tough crowd. OK, maybe I'm using the wrong terminology here; I'll address that in a different post. Let me at least stick to the minimal claim: there are no signals FTL in my model. Whatever you say about GR, you can say about my model.

2. The wf is demoted to the status of not-a-beable. So a sudden change is no big deal. Nevertheless, it is still a useful mathematical entity that helps us do calculations.

3. Experiment tells us that Bell's inequality is violated, and my model is consistent with this experimental observation. Earlier, when I said that my model is "consistent with Bell nonlocality," I was referring to the content of the former sentence. IOW I was using this definition:

a model is consistent with Bell nonlocality <==> the model makes predictions that match the outcomes of Aspect experiments

But I see now that you are retaining the term "Bell nonlocality" to apply only to models in which the wf is real. So let me retract my claim of "consistency with Bell nonlocality," and replace it with the claim: "my model predicts the outcome of the Aspect experiments"

4. My model does not require mindless hulks.

5. My model is complete. As I stated earlier, Alice knows exactly where she is in M, and that tells us everything there is to know about her state.

6. My model employs a nonlocal HV. As stated earlier, the "variable" in quesion represents the 4-d hypersurface W. It's "hidden" to Alice because there is an ensemble of them relative to her state, none of which are priveleged over the others in the ensemble.

7. My model is a simplified version of some of the attempts at QG, like LQG, as I stated in an earlier post.

The only reason any sane person takes MWI seriously at all is that it seems to be the only way to explain (well, pseudo-explain) the data without accepting nonlocality and thus rejecting relativity. You said your model violates Bell Locality. If that's right, then Occam's razor desperately wants to slash off your model.

You are correct, I believe, that one argument in favor of the MWI is that the MWI does not ask us to reject relativity. Correct me if I'm wrong, but doesn't BM ask us to reject relativity since wf collapse propagates FTL? Are you still a proponent of Lorentzian relativity because of this issue -- despite the absence of evidence for LR? Isn't this issue just a little bit confusing in the BM world?

Using your terminology, my model does not violate Bell locality; therefore (according to what you said above) my model escapes Occam's razor on this point. Actually I don't follow what you said above. If a model violated BL, then Occam's razor wants to slash it off ...?? I don't follow. BM violates BL, so does Occam's razor want to slash it off??

Assuming that my model can in fact be seen as a pared-down model of some versions of QG (at least the background-independent ones, like LQG), then my model is superior to BM in this sense. BM equivocates on whether relativity should be abandoned; my model does not. By Occam's razor, if we have one model -- mine -- that gives us relativity and QM in one package, and we have another -- BM -- in which QM and GR must be delivered separately, then Occam's razor would favor the former.

 

[straycat]

From reading Bell himself instead of interpretations about him (most of those neglect to point out that Bell believed in “unknown variables”) I see no real difference in Einstein vs. Bell local.

Again, I have seen many people state (erroneously) that Bell ruled out hidden or "unknown" variables, and I am glad to see Travis leading the charge to correct this misunderstanding.

There is a big difference between Bell and Einstein local, though, by my way of understanding. OK, maybe I'm using the word "local" to mean something different that what you mean. So I'll tell you the content of what I see as a very significant difference between two very different concepts: Einstein tells us that signals cannot propagate FTL. QM tells us (and Bell proved it) that collapse of the wf CAN and DOES propagate FTL -- even though that cannot be used to transmit information FTL. I don't know if you have a name for these features of GR and QM -- if you do, please tell me; if you don't, then perhaps you should, because they are (imho) important enough concepts to have a name. I have always defined the terms like this:

Einstein locality = signals cannot propagate FTL

Bell nonlocality = collapse of the wf DOES propagate FTL, even though it cannot be used to transmit signals FTL

As you can see from the definitions, it is not contradictory to claim that nature is Einstein-local and Bell-nonlocal at the same time. Einstein locality and Bell nonlocality (as I defined above) are not mutually exclusive. Nevertheless, they are DIFFERENT concepts, and it behooves us to understand the difference. If we don't, then we find ourselves wanting to do something crazy like advocate for Lorentz relativity even though there is no experimental evidence in its favor <straycat ducking in anticipation of ttn's counterattack ...>

Having said that, I am perfectly willing to consider that my above-stated definitions are nonstandard, that I should redefine my terminology. How about this:

background independence = signals cannot propagate FTL

Bell nonlocality = collapse of the wf DOES propagate FTL, even though it cannot be used to transmit signals FTL. Furthermore, as Travis stipulates, the wf is real.

No I don’t.
I accept GR is background independent (Ref: “The case for background independence” Lee Smolin/ Perimeter)

SR and Minkowski space-time (As a flat 4-D representation of Classical SR) as classical theories are background dependent (Although Minkowski I believe disagrees that his was actually classical) are able to hold the “unknown variable”. Einstein and Bell both always hoped that variable would be able to be demonstrated as real & local somehow (Speakable – Unspeakable; Bell).

Other than to incorrectly claim “local”, I really don’t see where GR applies here at all.
As soon as you introduce anything in an additional dimension that can collapse or link between two otherwise space-like separated events you are by definition not using a local realist, a requirement for both Einstein and Bell Local. Suggest you review Bell’s own writings again.

OK, the difference between "local" and "background independent" is something that I have not learned to appreciate, but perhaps I should. So for the time being let's state that GR is background independent. All I am claiming is that my toy model is likewise background independent, in the same sense and for the same reasons that GR is background independent. I do not see how or why the addition of a 5th dimension should change that.

David

 

[ttn]

How exactly do you come at that conclusion?

Let's suppose that we have a causal effect propagating at c in 4 dimensions -- iow, assume classical relativity. Does this lead to superluminal actions at a distance as seen via consideration of a 3 dimensional hypersurface? I don't think so, unless I'm missing something. If going from 4 to 3 doesn't pose a problem, then I don't see why going from 5 to 4 does.

Consider a sheet of paper folded (almost) in half. A signal propagating through 3D at speed c can get from one side to the other in hardly any time at all. Observers who don't know about the 3rd dimension would assume that the effect had propagated the long way round, in the sheet of paper, which would of course require it to be superluminal.