Register to reply 
What is the wave function about? 
Share this thread: 
#19
Oct411, 09:42 AM

Sci Advisor
P: 4,572




#20
Oct411, 09:52 AM

Sci Advisor
P: 4,572




#21
Oct411, 10:02 AM

Sci Advisor
P: 4,572




#22
Oct411, 01:23 PM

PF Gold
P: 674

Does Quantum Mechanics Need Interpretation: Many believe that, in turn, quantum information theory has bearing on foundational research. This is largely related to the socalled 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/...902.3005v1.pdf 


#23
Oct411, 04:48 PM

PF Gold
P: 2,432

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 operatorvalued 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 observercreated 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. 


#24
Oct411, 08:09 PM

P: 1,967




#25
Oct411, 09:02 PM

PF Gold
P: 2,432

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. 


#26
Oct411, 09:57 PM

P: 1,967

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.



#27
Oct411, 10:23 PM

P: 1,414

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 travelling 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 cos^{2}θ 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. 


#28
Oct511, 02:15 PM

P: 148

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 


#29
Oct511, 08:24 PM

PF Gold
P: 674




#30
Oct511, 09:08 PM

PF Gold
P: 2,432

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/Relatio...ntum_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? 


#31
Oct611, 01:23 AM

PF Gold
P: 674




#32
Oct611, 01:57 AM

P: 148

skippy 


#33
Oct611, 02:18 AM

PF Gold
P: 2,432

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? 


#34
Oct611, 05:53 AM

P: 1,414

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


#35
Oct611, 05:56 PM

PF Gold
P: 674

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 nonfactorizable models for the EPR/B experiment must involve nonlocality, they do not show that viable local, nonfactorizable models of the EPR/B experiment (i.e., viable models which do not postulate any nonlocality) are possible. Indeed, so far none of the attempts to construct local, nonfactorisable models for EPR/B experiments has been successful. http://plato.stanford.edu/entries/qmactiondistance/ 


#36
Oct611, 11:27 PM

P: 1,414

Standard 'uninterpreted' QM doesn't posit a physical 'collapse' of a wave shell in real space and time. It just takes, per known optics, the polarization axis associated with either detection attribute and projects it to the other side so that you get, in the ideal, a cos^{2}θ or a sin^{2}θ dependency (depending on the process used to produce entangled pairs of photons) between the angular difference of the polarizers, θ, and the coincidental photon flux. Which is a result that's in line with established optics principles. On the other hand, if you place certain (LRHV) restrictions on how a model of quantum entanglement can be formulated, then you get a correlation between θ and coincidental photon flux that in the extreme archetypal formulation of such a (LRHV) model you get a linear correlation between θ and coincidental photon flux. Which is a result that's at odds with established optics principles. Again, to be clear, entanglement correlations, per se, don't suggest "nonlocal influences between distant systems". For clarification of where I'm coming from wrt this, refer to my post #27 in this thread. And before we go any further it might help to go back to your first question in the OP: Thus, the mainstream, standard way of interpreting (or not interpreting, per Peres and Fuchs) QM is that it's a mathematical construction for calculating the probabilities of instrumental behaviors based on what's known about instrumental behavior. In other words, this is all that can be said about what the wave equation and wave functions are. Speculations about nonlocal influences, collapses, etc. aren't testable. Bell's theorem doesn't say that nature is nonlocal, it says that LRHV models of quantum entanglement are impossible. Why they're impossible is still a matter of debate, but, imo, it doesn't have to do with nonlocality in nature. And without a certain interpretation of Bell, there's nothing to suggest physical nonlocal influences. Paraphrasing Peres and Fuchs: uninterpreted, or standard, QM is essentially local. Unfortunately, the terms "nonlocal" and "nonlocality" have become part of the technical language and are a source of confusion, because in their technical usage wrt standard QM they don't refer to either FTL transmissions or actionatadistance. (See the quoted text from the paper referenced in post #34.) Hence the conclusion that there's no tension between standard QM and SR. 


Register to reply 
Related Discussions  
Spherical Harmonic Wave Function =? 3D Wave Function  Advanced Physics Homework  1  
Calculating the momentum of a debroglie wave from its wave function  Quantum Physics  12  
Wave packet momentum wave function  Advanced Physics Homework  6  
Wave Particle Duality and its relation to the Wave Function  Quantum Physics  2  
Given a wave function at t=0, how do you find the wave function at time t?  Advanced Physics Homework  2 