What Does the Wave Function Truly Represent?

[bohm2]

Does the wave function represent the physical state of the system (MW) or merely our information about the system (orthodox interpretation)? If it represents something in between (Bohmian), what does that imply? Furthermore, if QM is supposed to be more “fundamental” than classical physics, does this suggest that configuration space is more "fundamental" than normal 3-space or (4 dimensional space-time)? If it’s more fundamental, why does the world appear to evolve in 3-space or (4 dimensional space-time)? I mean what is the nature of this configuration space where the wave function lives in? Goldstein writes:

A second point is that for a multi-particle system the wave function (q) = (q1 ,..., qN ) is not a weird field on physical space, its a weird field on configuration space, the set of all hypothetical configurations of the system. For a system of more than one particle that space is not physical space. What kind of thing is this field on that space?


http://philsci-archive.pitt.edu/1272/
http://users.ox.ac.uk/~sfop0257/papers/Finding.pdf


If one takes the quasi-objective (in between) view as in the Bohmian model, what does the necessary non-locality/non-separability imply? Moreover, how is it possible that the wave function acts upon the positions of the particles but it is not acted upon by the particles? So that in,

Bohmian mechanics there’s no back action, no effect in the other direction, of the configuration upon the wave function, which evolves autonomously via Schrodinger’s equation, in which the actual configuration Q does not appear.

Furthermore, there are problems with treating the wave function as nomological (denoting a law of nature) as in Bohm's model because, "laws aren’t supposed to be dynamical objects, (as) they aren’t supposed to change with time, but the wave function of a system typically does...(since), we can in (a) sense control the wave function of a system. But we don’t control a law of nature. This makes it a bit difficult to regard the wave function as nomological."

http://math.rutgers.edu/~oldstein/papers/rrwf.pdf

 

[bayak]

I think that the wave function represents the congruence of trajectories of one particle (simple case) in the compactified Minkowski spacetime.
http://socionet.ru/publication.xml?h=repec:rus:gulthb:1

 

[wuliheron]

Does the wave function represent the physical state of the system (MW) or merely our information about the system (orthodox interpretation)?

This is a false dichotomy. The wave function represents what we observe and the latest theories imply what we observe depends on the context.

 

[bohm2]

I think that the wave function represents the congruence of trajectories of one particle (simple case) in the compactified Minkowski spacetime.
http://socionet.ru/publication.xml?h=repec:rus:gulthb:1

It's in Russian? Is there a full English version?

Furthermore, there are problems with treating the wave function as nomological (denoting a law of nature) as in Bohm's model because, "laws aren’t supposed to be dynamical objects, (as) they aren’t supposed to change with time, but the wave function of a system typically does...(since), we can in (a) sense control the wave function of a system. But we don’t control a law of nature. This makes it a bit difficult to regard the wave function as nomological."

This should read one of the Bohmian models as originally presented by Durr, D., Goldstein, S. and Zanghi, N. (1992):

We propose that the reason, on the universal level, that there is no action of configurations upon wavefunctions, as there seems to be between all other elements of physical reality, is that the wavefunction of the universe is not an element of physical reality. We propose that the wave function belongs to an altogether different category of existence than that of substantive physical entities, and that its existence is nomological rather than material. We propose, in other words, that the wavefunction is a component of physical law rather than of the reality described by the law.

But this version of the pilot wave seems to have been abandoned. In the present form of pilot-wave theory, ψ is regarded as ontological treated as "a new kind of causal agent acting in confguration space." I think this is how Bohm originally interpreted it.

http://www.tcm.phy.cam.ac.uk/~mdt26/local_papers/valentini_2008_denial.pdf

 

[bayak]

It's in Russian? Is there a full English version?

There is the old English version (http://www.ptep-online.com/index_files/2008/PP-13-18.PDF ). But there are not wave function. There are only complex probability density function.

 

[skippy1729]

If you try to give quantum mechanics a naive realist interpretation, like Bohm or Everett, you find yourself contorting yourself beyond belief with things that are unobservable, bring forth no new results and still have gaping big holes. But these girls tell it better than I can:



On a more serious note, this short paper in Physics Today by Asher Peres and Chris Fuchs might be interesting:

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.77.8442&rep=rep1&type=pdf

Skippy

 

[bohm2]

If you try to give quantum mechanics a naive realist interpretation, like Bohm or Everett...On a more serious note, this short paper in Physics Today by Asher Peres and Chris Fuchs might be interesting:
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.77.8442&rep=rep1&type=pdf

I'm not sure I would describe Bohm's or Everett's version as "naive". One can argue that there is nothing naive about the concepts of non-locality/non-separability or multiple universes/branches. Moreover, I think the epistemic view argued for by Peres and Fuchs is, in the final analysis, also just another interpretation. And there's arguably even less motivation to take their interpretation any more seriously than any of the others. In fact, one might have less motivation because to view physics as the "science of meter reading" doesn't look particularly rewarding, I think.

 

[wuliheron]

In fact, one might have less motivation because to view physics as the "science of meter reading" doesn't look particularly rewarding, I think.

For that matter viewing physics as the "science of long shots" doesn't look particularly rewarding either. After 85 years of producing nothing useful Bohmian mechanics are about as big a long shot as they get.

 

[skippy1729]

I'm not sure I would describe Bohm's or Everett's version as "naive". One can argue that there is nothing naive about the concepts of non-locality/non-separability or multiple universes/branches. Moreover, I think the epistemic view argued for by Peres and Fuchs is, in the final analysis, also just another interpretation. And there's arguably even less motivation to take their interpretation any more seriously than any of the others. In fact, one might have less motivation because to view physics as the "science of meter reading" doesn't look particularly rewarding, I think.

Perhaps "naive" was a poor choice of words. I should have said "clever and sophisticated theories desperately clinging to a naive classical reality".

I also don't think "science of meter reading" is an accurate description of searching for understanding of the universe without the baggage of accepting unobservable entities as a matter of faith.

Skippy

 

[Demystifier]

After 85 years of producing nothing useful Bohmian mechanics ...

How about this book?
Applied Bohmian mechanics:
https://www.amazon.com/dp/9814316393/?tag=pfamazon01-20
http://europe.uab.es/xoriols/Books?action=AttachFile&do=get&target=Flayer

 

[wuliheron]

How about this book?
Applied Bohmian mechanics:
https://www.amazon.com/dp/9814316393/?tag=pfamazon01-20
http://europe.uab.es/xoriols/Books?action=AttachFile&do=get&target=Flayer

Never read it. Perhaps you'd like to explain just how useful Bohmian mechanics are compared to the standard theory...

 

[Demystifier]

Never read it. Perhaps you'd like to explain just how useful Bohmian mechanics are compared to the standard theory...

Let me quote from the introduction of the book:
"... we believe that Bohmian mechanics can help us make progress with our real problems.
There are, at least, three clear reasons why one could be interested in studying quantum
problems with Bohmian mechanics:

(1) Bohmian explaining: Even when the Copenhagen mathematical machinery is
used to compute observable results, the Bohmian interpretation ofently offers
better interpretational tools. We can find descriptions of electron dynamics
such as “an electron crosses a resonant tunneling barrier and interacts with another
electron inside the well”. However, an electron crossing a tunneling region is not
rigourously supported within orthodox quantum mechanics, but it is within
the Bohmian picture. Thus, in contrast to the Copenhagen formulation, the
Bohmian interpretation allows for an easy visualization of quantum phenomena
in terms of trajectories that has important demystifying or clarifying consequences.
In fact, Bohmian mechanics allows for a simultaneous description
and interpreation of quantum mechanics within the same theoretical framework.
In particular, it provides a single-event description of the experiment,
while Copenhagen quantum mechanics accounts for its statistical or ensemble
explanation. We will present several examples in chapters 2 and 3 emphasizing
all these points.

(2) Bohmian computing: Although the predictions of the Bohmian interpretation
reproduce the ones of the orthodox formulation of quantum mechanics, its
mathematical formalism is different. In some systems, the Bohmian equations
might provide better computational tools than the ones obtained from the orthodox
machinery, resulting in a reduction of the computational time, an increase
in the number of degrees of freedom directly simulated, etc. We will
see examples of these computational issues in quantum chemistry in chapters
4 and 5, as well as in quantum electron transport in Chap. 6.

(3) Bohmian thinking: From a more fundamental point of view, alternative formulations
of quantum mechanics can provide alternative routes to look for the
limits and possible extensions of the quantum theory. As we will discuss later,
the work of John Bell on non-locality is a clear example of the unquestionable
utility of understanding quantum phenomena with Bohmian mechanics.
In particular, Chap. 7 presents the route to connect Bohmian mechanics with
geometrical optics and beyond opening the way to apply the powerful computational
tools of quantum mechanics to classical optics, and even to electromagnetism.
The natural extension of Bohmian mechanics to the relativistic
regime and to quantum field theory are presented in Chap. 8, while Chap. 9
discusses its application to cosmology."

For more details, you need to get the book itself.

 

[wuliheron]

Let me quote from the introduction of the book:
"... we believe that Bohmian mechanics can help us make progress with our real problems.
There are, at least, three clear reasons why one could be interested in studying quantum
problems with Bohmian mechanics:

Sorry, not interested in what people believe might be possible. After 85 years of speculation its not unreasonable to demand some concrete results.

 

[ThomasT]

I'm not sure I would describe Bohm's or Everett's version as "naive".

They're naive in the sense that they involve/entail nonempirical fantasies.

One can argue that there is nothing naive about the concepts of non-locality/non-separability or multiple universes/branches.

Or one can argue that there is. And ultimately they offer no demonstrable insights about the underlying reality that can't be inferred from standard QM.

Moreover, I think the epistemic view argued for by Peres and Fuchs is, in the final analysis, also just another interpretation.

Yes, the most sophisticated one.

And there's arguably even less motivation to take their interpretation any more seriously than any of the others.

I like it because I think that, despite what some might see as apparent superficiality, it's actually deeper than either the Bohmian or Everettian interpretations. I think that's why, imo, most physicists would agree with Peres' and Fuchs' take on QM, as opposed to the alternatives.

In fact, one might have less motivation because to view physics as the "science of meter reading" doesn't look particularly rewarding, I think.

Bohmians and MWIers are reading the same meters and predicting the same probabilities as standard 'uninterpreted' QMers. They're just carrying some unwarranted philosophical baggage along with that.

 

[Demystifier]

Sorry, not interested in what people believe might be possible. After 85 years of speculation its not unreasonable to demand some concrete results.

The results in item (2) of my post above are very concrete. In some cases, Bohmian trajectories are a much more efficient method (but equivalent to the standard method) to compute some measurable predictions of QM.

 

[ThomasT]

The results in item (2) of my post above are very concrete. In some cases, Bohmian trajectories are a much more efficient method (but equivalent to the standard method) to compute some measurable predictions of QM.

Yes, there is that. As well as some other aspects of BM that make it attractive. But then there's BM's nonlocality.

 

[wuliheron]

The results in item (2) of my post above are very concrete. In some cases, Bohmian trajectories are a much more efficient method (but equivalent to the standard method) to compute some measurable predictions of QM.

Being more efficient in some cases without making any new predictions just isn't terribly useful. I'm sure we could say the same thing about any number of other theories including phlogiston theory. It needs to prove itself uniquely useful in some significant way.

 

[bohm2]

I have to admit, I couldn't help but enjoy the humour (and truth?) about this statement by Fuchs:

Whatever it is, it cannot be for want of a self-ordained solution: Go to any meeting, and it is like being in a holy city in great tumult. You will find all the religions with all their priests pitted in holy war—the Bohmians, the Consistent Historians, the Transactionalists, the Spontaneous Collapseans, the Einselectionists, the Contextual Objectivists, the outright Everettics, and many more beyond that. They all declare to see the light, the ultimate light. Each tells us that if we will accept their solution as our savior, then we too will see the light.But there has to be something wrong with this! If any of these priests had truly shown the light, there simply would not be the year-after-year conference. The verdict seems clear enough: If we—i.e., the set of people who might be reading this paper—really care about quantum foundations, then it behooves us as a community to ask why these meetings are happening and find a way to put a stop to them.

http://perimeterinstitute.ca/personal/cfuchs/VaccineQPH.pdf

 

[Demystifier]

But then there's BM's nonlocality.

And then there is the Bell theorem saying that any hidden variable theory (compatible with QM) MUST be nonlocal.

 

[Demystifier]

For that matter viewing physics as the "science of long shots" doesn't look particularly rewarding either. After 85 years of producing nothing useful Bohmian mechanics are about as big a long shot as they get.

Being more efficient in some cases without making any new predictions just isn't terribly useful. I'm sure we could say the same thing about any number of other theories including phlogiston theory. It needs to prove itself uniquely useful in some significant way.

First you indicate that you would be satisfied with something useful. Then, when I show that there is something useful you want terribly useful, and later you want even more - uniquely useful. What will be next? Absolutely useful? Ultimatively useful?

 

[Demystifier]

I have to admit, I couldn't help but enjoy the humour (and truth?) about this statement by Fuchs:

Whatever it is, it cannot be for want of a self-ordained solution: Go to any meeting, and it is like being in a holy city in great tumult. You will find all the religions with all their priests pitted in holy war—the Bohmians, the Consistent Historians, the Transactionalists, the Spontaneous Collapseans, the Einselectionists, the Contextual Objectivists, the outright Everettics, and many more beyond that. They all declare to see the light, the ultimate light. Each tells us that if we will accept their solution as our savior, then we too will see the light.But there has to be something wrong with this! If any of these priests had truly shown the light, there simply would not be the year-after-year conference. The verdict seems clear enough: If we—i.e., the set of people who might be reading this paper—really care about quantum foundations, then it behooves us as a community to ask why these meetings are happening and find a way to put a stop to them.

http://perimeterinstitute.ca/personal/cfuchs/VaccineQPH.pdf

To me, many interpretations give some light, but at the moment neither of them gives the light. So I think we should not stop these meetings, but we should also not think of them as a place where we will learn the final truth.

 

[bohm2]

To me, many interpretations give some light, but at the moment neither of them gives the light. So I think we should not stop these meetings, but we should also not think of them as a place where we will learn the final truth.

I agree. But I found it funny. Interestingly this paper on that same topic is arguing the opposite of Fuchs:

Does Quantum Mechanics Need Interpretation:

Many believe that, in turn, quantum information theory has bearing on foundational research. This is largely related to the so-called epistemic view of quantum states, which maintains that the state vector represents information on a system and has led to the suggestion that quantum theory needs no interpretation. I will argue that this and related approaches fail to take into consideration two different explanatory functions of quantum mechanics, namely that of accounting for classically unexplainable correlations between classical phenomena and that of explaining the microscopic structure of classical objects. If interpreting quantum mechanics means answering the question, “How can the world be for quantum mechanics to be true?”, there seems to be no way around it.

http://arxiv.org/PS_cache/arxiv/pdf/0902/0902.3005v1.pdf

 

[apeiron]

Whatever it is, it cannot be for want of a self-ordained solution: Go to any meeting, and it is like being in a holy city in great tumult. You will find all the religions with all their priests pitted in holy war—the Bohmians, the Consistent Historians, the Transactionalists, the Spontaneous Collapseans, the Einselectionists, the Contextual Objectivists, the outright Everettics, and many more beyond that.

The Fuchs paper goes further than poking fun as it tries to diagnose the essential flaw in these interpretations. He points out that the one idea people can't seem to let go is that reality must be made of crisply existent "something" at the fundamental level. So even if these atomistic things are just probability states projected to some complex Hilbert space, they are still definite and actual in some ontological sense.

Fuchs then tries to let go of this (reductionist) axiom and describe reality from the view of its global constraints. Each observer forms a context for observation. That is what is "definite". And the world is an unbounded potential that conforms to fit.

That is a view I share in essence. But much more work has to be done on now defining the notion of an observer - generalising it away from any notion of "conscious human" and towards "the ambient constraints represented by the structuration of the universe".

Fuchs explores doing this by generalising to "general positive operator-valued measurements" (POVMs) - the more constraints applied from a locale, the more definite the world becomes.

He also employs Bayesian statistics - again a revolution in working from the constraints side of the story, the imposition of "reasonable" expectations on unbounded possibility rather than starting with atomistic, already limited, probabilities.

So the standard stance on QM interpretational issues is that the measured must be "real" at some fundamental level (even if it inhabits some weird unobservable realm like pilot waves, alternative universe branches, etc) and the measurement issue becomes a problem of simple access to this ontic truth. If we could only imagine how to make the right measurement, we would surely finally glimpse the definite things which are there just waiting to be measured.

But the switch around is taking an observer-created reality seriously (by dropping the notion of particular observers, such as conscious humans). Measurement (in some new sense, not the familiar one) is responsible for shaping up the measured, making it also now "real" - part of the realm of the classically decohered.

Need I say that this is back into Peircean semiotics, Pattee's epistemic cut, systems science, etc?

However, here Fuchs is putting forward a specific proposal as well as diagnosing the general fault in the standard reductionist paradigm that informs most QM interpretations. So that would be interesting to consider further?

For instance, I would argue that once you set off down Fuchs route, you start to have to ask the question about what makes our universe the right kind of measurement device? It is not just measurement in general that constrains QM potential but the actual structured realm which is our universe. So attention has to turn to understanding how the universe does what it does by virtue of its general organisation.

You will note how truly radical that is. Instead of the universe being a "result" (of unknown QM states acting as its definite causes), it is instead creating that which it appears to be composed of (the macro is making the micro rather than the other way round).

Again, this has nothing to do with consciousness or any other connotations commonly ascribed to "measurement" or "observer". But it is a way of modelling reality that is familiar from the philosophy of semiosis, and more recently, the field of dissipative structure theory in thermodynamics.

 

[wuliheron]

First you indicate that you would be satisfied with something useful. Then, when I show that there is something useful you want terribly useful, and later you want even more - uniquely useful. What will be next? Absolutely useful? Ultimatively useful?

Physics isn't mysticism which I'm sure is also quite useful in limited situations. Personally, I always use a screw driver to open cans of paint, but that is not what the screw driver was designed to do and if it did not fulfill its intended purpose people might easily find something else to open their cans of paint. Again, Bohmian mechanics needs to produce unique predictions that can be verified or at least prove itself significantly more efficient overall or it will not have fulfilled its supposed purpose as a physical theory. Being able to open the occasional can of paint just isn't enough.

 

[apeiron]

Physics isn't mysticism which I'm sure is also quite useful in limited situations. Personally, I always use a screw driver to open cans of paint, but that is not what the screw driver was designed to do and if it did not fulfill its intended purpose people might easily find something else to open their cans of paint. Again, Bohmian mechanics needs to produce unique predictions that can be verified or at least prove itself significantly more efficient overall or it will not have fulfilled its supposed purpose as a physical theory. Being able to open the occasional can of paint just isn't enough.

Sorry, but it seems clear Demystifier understands BM well enough for his support of this interpretation over others to be properly motivated. So you would need to lift your own game to the same level here.

The different interpretations do come with their different unique features - like the quantum equilibrium hypothesis of BM vs the Born rule of rival interpretations. So there are formal differences that can be discussed in terms of their reasonableness, as well as the purely pragmatic differences (such as ease of computation).

I personally think the whole BM approach is ontically "unreasonable" for reasons I just stated. But that just puts a requirement on me to learn more about BM if I want to be so sure about dismissing it.

For instance, the question of how do you square BM with special relativity and Lorentz invariance seems a pretty severe test of it as an ontology. Anyway, much more than annecdotes about screwdrivers and paint tins.

 

[wuliheron]

What is reasonable is for philosophers, politicians, and theologians to debate. Whether you consider that "lifting your own game to the same level" or lowering it is a question of personal preference and values. Its also popular among professional wrestlers if that's what floats your boat.

 

[ThomasT]

And then there is the Bell theorem saying that any hidden variable theory (compatible with QM) MUST be nonlocal.

Yes that's true. But that's because of the modelling constraints (per Bell's formulation) imposed by the local realism requirement. Not necessarily because nature is actually nonlocal. Local realism (per Bell) entails that a LRHV model of quantum entanglement be expressed in terms of the hidden (variable) parameter that determines photon flux at the individual detectors. But we know (or at least can reasonably infer) that the hidden parameter that determines coincidental photon flux is not a variable, that is, whatever the joint polarizer settings are measuring jointly is not varying from entangled pair to entangled pair. Couple this with a 'locality condition' that describes the statistical results at the spatially separated detectors as 'independent' (when in fact a detection at one end or the other alters and severely restricts the sample space at the other end, via the coincidence circuitry), and such a model must necessarily skew the QM expectation values regarding coincidental photon flux (whether nature is local or nonlocal) for most joint polarizer settings (even if it manages to preserve the essential angular dependency between the angular difference of the polarizer settings and the coincidental photon flux).

A fact of the matter is, and Bell showed, that local hidden variable models of individual photon flux are compatible with QM -- from which we can infer that hidden variables are determining, via local transmissions, the results at the individual detectors. The most reasonable assumption is that these hidden variables originated and were emitted (eg., in the 1982 Aspect et al. experiment) during atomic transitions -- with photons entangled in polarization being emitted in opposite directions by the same atom.

It's most reasonable to assume that what the joint polarizers are measuring is a relationship (defined by the conservation of angular momentum) between entangled photons, and that this relationship is produced during the emission process.

We can take polarizer A and put it on the side with polarizer B, and, without changing anything else about the experiment, get the same coincidental photon flux (varying from ~ .5 to ~ 0 times the photon flux at detector A, as the angular difference between the polarizers, now both on the B side, varies from 0 to 90 degrees) as with the polarizers on opposite wings of the setup. But we don't need to invoke nonlocal transmissions between the entangled photons to understand this result. We just have what amounts to a quantum polariscope on the B side, producing results via local transmissions, and unimpeded photons traveling from the emitter to detector A on the A side.

Now, when we move the (A) polarizer from the B side back to the A side, what, essentially, changes? Well, quantitatively, nothing. So why should this (original) setup require a nonlocal explanation/understanding while the one with both polarizers on the same side doesn't?

Anyway, wrt at least some ways of analyzing and interpreting Bell's theorem, it can be said that nonlocality hasn't been demonstrated. Nonlocality might be a relatively easy 'fix' that will give the correct results, but as such it isn't an explanation or understanding of quantum entanglement. And since an 'understanding' of entanglement correlations vis local transmissions and interactions, and relationships due to common causes, makes more sense to me (and isn't necessarily contradicted by Bell's theorem or standard QM) than assuming that nature is nonlocal, then the nonlocality of BM is most unappealing.

I wish it could be otherwise, because I like the general approach, and certain aspects, of BM. But if nature is exclusively local, then BM is, ultimately, just unrealistic (and necessarily contradicts a local understanding of quantum entanglement), as opposed to standard QM which is nonrealistic (and doesn't necessarily contradict a local understanding of quantum entanglement).

And the most perplexing conumdrum is that even if nature is exclusively local, then viable LRHV theories (per Bell) of quantum entanglement are still ruled out.

EDIT: I should note that the archetypal LRHV formulation produces a linear correlation between the angular difference of the polarizer settings and the coincidental photon flux. This seems to be the basis for most Bell inequalities, and would seem to explain why they're significantly violated if one takes into account that this LRHV expectation, this linear correlation, is clearly at odds with the expectation (ie., something approximating a cos²θ dependency) that the optics principles applicable to optical Bell tests indicate should be the case -- and is another consideration which suggests, to me at least, that there's a problem with formulating LRHV models of quantum entanglement which likely has nothing to do with whether nature is local or nonlocal.

 

[skippy1729]

I have a question for Demystifier or anyone else who knows:

I know that there are theorems stating dBB will produce the same statistical results as QM. Of course, results of individual events cannot be obtained since they are determined by unknown initial conditions. The question is:

Is it possible to solve the dBB equations for some simple physical system for all possible initial conditions then use the ensemble of results to actually construct the statistics?

Any references appreciated.

Skippy

 

[bohm2]

For instance, the question of how do you square BM with special relativity and Lorentz invariance seems a pretty severe test of it as an ontology.

Do you think in 1000 years down the road assuming we haven't blown each other up, SR will still hold "true" on all scales? I'd be shocked if that was the case. I'm actually shocked that a linguistic ground chimp like us has progressed so much (or so it seems) in some areas (like physics).

 

[apeiron]

Do you think in 1000 years down the road assuming we haven't blown each other up, SR will still hold "true" on all scales? I'd be shocked if that was the case. I'm actually shocked that a linguistic ground chimp like us has progressed so much (or so it seems) in some areas (like physics).

Yes, fine, but what reasons do you currently have to doubt SR's validity over all scales - such that you could claim it would be a legitimate surprise if we find it still to be the case in 1000 years?

I am more convinced by the argument that SR as a general relational principle is the route to a proper interpretation of QM, as for example...

http://en.wikipedia.org/wiki/Relational_quantum_mechanics

Rovelli's approach (like the Fuch's paper you cited) are the kind of current, systems logic, explanations that make sense to me.

BM attempts to shore up a dead paradigm IMO. Time to move on.

Of course you can defend BM if that is your wish. But it would have to be done with arguments not rhetorical flourishes.

So if there is a conflict between BM and SR, then why do you say SR will have to be the one that gives way?

 

[bohm2]

So if there is a conflict between BM and SR, then why do you say SR will have to be the one that gives way?

The tension is between quantum nonlocality (not just BM) and the locality of Relativity Theory, I think. The experimental tests of Bell's inequality do suggest some form of superluminal information transfer, regardless of interpretation. Such superluminal "influences" don't mean superluminal message tranfer if one uses the Lorentzian interpretation (single preferred frame).

 

[skippy1729]

The tension is between quantum nonlocality (not just BM) and the locality of Relativity Theory, I think. The experimental tests of Bell's inequality do suggest some form of superluminal information transfer, regardless of interpretation. Such superluminal "influences" don't mean superluminal message tranfer if one uses the Lorentzian interpretation (single preferred frame).

Superluminal effects are only implied if the quantum state has objective reality not if it is subjective information.

skippy

 

[apeiron]

The tension is between quantum nonlocality (not just BM) and the locality of Relativity Theory, I think. The experimental tests of Bell's inequality do suggest some form of superluminal information transfer, regardless of interpretation. Such superluminal "influences" don't mean superluminal message tranfer if one uses the Lorentzian interpretation (single preferred frame).

I was thinking of the fact that BM ontology treats particles as real (existing at some definite place and time) and so assumes that there is indeed a single preferred reference frame.

This seems less an issue for other interpretations that do not insist on anything being fixed in place at some globally shared moment. But then that may be just evading the SR issue rather than answering it.

So everyone has a problem, but BM has it worse! Well, that was my understanding. And a relational approach seems to be about stepping back and accepting SR as a guiding principle. Seek a background independent view.

SR would be emergent rather than fundamental in this view I think. But then I always say everything is emergent anyway. QM says everything is contextual. Relativity says all contexts needs to be constructed. So nothing is certain until it develops.

BM on the other hand is an attempt to hang onto to the underlying certainty of things, the counterfactual definiteness, even when the going gets tough and the evidence suggests time to let go. It is the opposite way of thinking about things.

Having cited Fuchs paper, don't you have anything further to say about its relational ontology?

 

[ThomasT]

So if there is a conflict between BM and SR, then why do you say SR will have to be the one that gives way?

The tension is between quantum nonlocality (not just BM) and the locality of Relativity Theory, I think.

What tension? What does "quantum nonlocality" refer to? The following statement from [1] gives referents for quantum nonlocality (wrt standard QM) that wouldn't seem to imply any sort of conflict between quantum nonlocality and SR.

The conservation laws guarantee the precise value of an observable with respect to the pair (not to the individual subsystems). It is in this sense, we say that the entangled two-photon state of SPDC is nonlocal. Quantum theory does allow a complete description of the precise correlation for the spatially separated subsystems, but no complete description for the physical reality of the subsystems defined by EPR. It is in this sense, we say that quantum mechanical description (theory) of the entangled system is nonlocal.

The experimental tests of Bell's inequality do suggest some form of superluminal information transfer, regardless of interpretation.

How so? As far as I can tell, the inference of existence of FTL depends entirely on how one interprets Bell's theorem.

Superluminal effects are only implied if the quantum state has objective reality ...

It's not clear what this might mean. It might be true that if one assumes that quantum states have "objective reality", then FTL is implied. I don't see why that should follow, but I don't know. But, how would we be able to ascertain just how closely quantum states approximate/correspond to the reality underlying instrumental behavior? Anyway, from my first introduction to this stuff I was cautioned not to think of quantum states as real states.


[1] Experimental Study of A Photon as A Subsystem of An Entangled Two-Photon State, Phys.Rev. A60 (1999) 2685,
http://arxiv.org/abs/quant-ph/9811060

 

[bohm2]

What tension? What does "quantum nonlocality" refer to?

The correlations in the EPR/B experiment strongly suggest that there are non-local influences between distant systems, i.e., systems between which no light signal can travel, and indeed orthodox quantum mechanics and its various interpretations postulate the existence of such non-locality. Yet, the question of whether the EPR/B correlations imply non-locality and the exact nature of this non-locality is a matter of ongoing controversy.

However, satisfying the Lorentz transformations at the level of individual processes is not sufficient for compatibility with Minkowski spacetime; for the Lorentz transformations may also be satisfied at the level of individual processes in theories that postulate a preferred inertial reference frame (Bell 1976). Maudlin suggests that a theory is genuinely relativistic (both in spirit and letter) if it can be formulated without ascribing to spacetime any more, or different intrinsic structure than the relativistic metrics.The question of the compatibility of relativity with quantum mechanics may be presented as follows: Could a quantum theory that does not encounter the measurement problem be relativistic in that sense?

While these arguments challenge the view that the quantum realm as depicted by non-factorizable models for the EPR/B experiment must involve non-locality, they do not show that viable local, non-factorizable models of the EPR/B experiment (i.e., viable models which do not postulate any non-locality) are possible. Indeed, so far none of the attempts to construct local, non-factorisable models for EPR/B experiments has been successful.

http://plato.stanford.edu/entries/qm-action-distance/