Does Decoherence Solve the Measurement Problem Completelyby Prathyush Tags: measurement, quantum mechanics 

#37
Nov2812, 04:18 AM

P: 79

To which I would reply that I think the mathematics of quantum superposition, necessarily, does not correspond to any ontological feature of fundamental reality. Which has to do with my currently favored notion that the mechanics of the deep reality are not fundamentally different than the mechanics of the reality that's amenable to our limited sensory apprehension. Which is based on the assumption that, even though there are emergent phenomena and emergent scale dependent organizing principles, there are nevertheless fundamental wave mechanical dynamical laws that hold for all behavioral scales. In other words, I don't see any reason to believe that the fundamental laws governing the reality underlying instrumental behavior are essentially different than the fundamental laws governing instrumental behavior. But you and others have offered many interesting comments that I really do need to reread and think about. For now, I think we might agree that the math of decoherence doesn't provide any deeper understanding of nature than orthodox qm (and associated mathematical models) does  and therefore is not a solution to the measurement problem. 



#38
Nov2812, 04:38 AM

P: 178





#39
Nov2812, 06:37 AM

P: 65





#40
Nov2812, 07:08 AM

P: 724

Yes, decoherence requires that there be interactionallyreal components of the wavefunction which is in sync with your next statement: 



#41
Nov2812, 07:38 AM

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PF Gold
P: 2,044

Thanks Bill 



#42
Nov2812, 08:07 AM

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PF Gold
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While it is applicable to any interpretation only for some is it central and if the wave function has 'interactionally real' components is not a common factor. Thanks Bill 



#43
Nov2812, 02:39 PM

P: 79





#44
Nov2812, 03:22 PM

P: 127





#45
Nov2812, 03:26 PM

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PF Gold
P: 2,044

http://xxx.lanl.gov/pdf/1111.3328v3.pdf The superposition principle is not based on classical wave mechanics  it follows quite simply for pure states from the trace formula of QM  E(R) = Trace (pR) where p is the system state (ie a positive operator of trace 1). Of course none of this proves its not real  it may well be  but if you believe so you need to face up to all sorts of issues. Thanks Bill 



#46
Nov2812, 03:41 PM

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P: 5,307

PBR theorem? this is new to me; seems that reading LQG and LHC Higgs papers is the wrong scope




#47
Nov2812, 04:17 PM

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PF Gold
P: 2,044

Basically all its saying is if you believe the quantum state in some imperfect way, or even in a statistical sense, corresponds to something real then it is itself real. I always thought it was a bit weird believing otherwise anyway. There are also ways of evading it such as if you believe QM is incomplete then small blemishes like that don't really matter  that would be Einsteins view. For a critical examination of it see: http://arxiv.org/pdf/1203.4779.pdf Added Later: I forgot to mention the PBR theorem (as the above paper makes clear) only concerns interpretations/models where the underlying reality is not dependent on the state  that is also another out  and in fact quite a biggie. Thanks Bill 



#48
Nov2812, 04:40 PM

P: 724

Decoherence is said to be a thermodynamically irreversible process. So how does a H2O molecule in running water retain its classicallike properties in time? The evolution of the system would stop when the state loses coherence, then how does it move to the next state? There'd have to be a system in constant flux of becoming coherent then decoherent, coherent, decoherent... to mimick classical like behavior.
Yes, i've read claims that decoherence doesn't have to involve any realworld interaction(and nothing physical is decohering) but it seems like fitting the facts to the theory instead of changing the theory. Decoherence rates gave been measured and they vary depending on the setup so the states act in ways that do not imply they represent knowledge of the system. Does it make sense to say that by changing the temperature at which an atom is stored, you can decouple the atom from the environment and turn it into information about the system? 



#49
Nov2812, 04:58 PM

P: 127

But doesn't this theorem put restraints on whatever fundamental theory that lies beneath QM anyways? I am in the "QM can't be 100% correct" group because none of the interpretations to date are satisfactory to me. Collapse is just philosophically bad, indeterminism is not acceptable as a scientific explanation anymore than magic or God is. Plus the entire "when" does collapse occur is a problem. deBroglie Bohm is the best way to visualize QM and it sort of makes sense, but at the end of the day I don't buy it, it's just too ad hoc for me. Everett is invalidated by the Born Rule and in addition you have the preferred basis issues. So yeah, QM *HAS* to be wrong, but I would think that PBR's results will still have a impact on narrowing down the field of possible more fundamental theories? Just like Bells theorem restrict it. 



#50
Nov2812, 05:21 PM

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PF Gold
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Decoherence is implied by the quantum formalism. It has nothing to do with if a quantum state is real, simply knowledge about observations or whatever. There is no fitting of the facts to the theory. What there is is some interpretations that make use of decoherence and some that don't  that's all. Thanks Bill 



#51
Nov2812, 05:31 PM

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PF Gold
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Added Later: Just to be clear other outs of PBR exist as well  it crucially depends on state independence. Thanks Bill 



#52
Nov2812, 06:33 PM

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P: 5,307

We should make a clear distinction between
1) QM as a theory of nature = a formalism to predict experimental results 2) our ideas about or philosophy of reality 3) an interpretation of QM and its relation to 2) 4) the language we are using to talk about 14) 5) ... Doing that I come to the conclusion that something in this web of relationships (14) evades our naive model of nature we have before starting to think about QM. But I would not dare to deduce that QM in the sense of (1) has to be wrong. QM has always proven to be "correct" in the sense of (1). The problems appear at the level of (24). So why the hell should (1) be wrong and in which sense?? 



#53
Nov2812, 06:45 PM

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PF Gold
P: 2,044

Thanks Bill 



#54
Nov2812, 06:56 PM

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P: 5,307

of course, the question goes to Quantumental ;)
Tom 


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