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

#1
Nov2112, 12:44 PM

P: 61

As the Title describes, Is the measuremet problem completely solved by the decoherence Program?
In specific I would like the following question addressed. Is there is clear explanation as to what it means to Record Infromation? Can it explain the behaviour of a photographic plate? What happens to the appratus after measurement? 



#2
Nov2112, 03:12 PM

PF Gold
P: 776

Some believe it solves it, others say it works only for all practical purposes (i.e. technically the state of the system+apparatus+enivornment is in superposition).
Roland Omnes is a proponent of the decoherence approach, not just as a practise of solving the measurement problem, but also in principle. See "The Interpretation of Quantum Mechanics" pages 304309. 



#3
Nov2212, 11:21 AM

P: 123

I think this link argues quite nicely why decoherence does not solve the philosophical issues:
http://plato.stanford.edu/entries/qm...nce/#SolMeaPro Money quote: http://arxiv.org/abs/quantph/0312059 



#4
Nov2212, 03:17 PM

P: 178

Does Decoherence Solve the Measurement Problem Completely
It's even hard to argue that decoherence solves any aspect of the measurement problem. All the measurement related features are implicitly imported through the backdoor by using the measurement postulate to define density operators. Any argument for decoherence giving insight into measurement is therefore circular.




#5
Nov2312, 08:11 AM

Sci Advisor
PF Gold
P: 2,049

You will find a good discussion of the issue in Schlosshauers book on decoherence: http://www.amazon.com/DecoherenceCl.../dp/3540357734 The measurement problem has a number of parts. There is the preferred basis problem ie why a particular basis is singled out. It solves that. Then there is the issue of why a particular outcome occurs and indeed why any outcome occurs at all. It doesn't solve that in a fundamental way but does for all practical purposes meaning you can assume it does, that the outcome exists prior to observation, and no experiment can say you are wrong. If that is satisfactory depends purely on your interpretation. Yes decoherence incorporates the Born rule and assumes it but refines it so some of its 'weirder' features are no longer an issue eg you can assume the system is in the state prior to observation which you cant do without decoherence  the reasoning is not circular. Interpretations that include decoherence such as decoherent histories call probabilities calculated without reference to an actual observational apparatus preprobabilities  they are not manifest until decoherence occurs in an apparatus. Is there is clear explanation as to what it means to Record Infromation? Depends on what you accept as clear. If you mean it explains the why of a particular outcome then no. Can it explain the behaviour of a photographic plate? Depends on what you accept as explain  for all practical purposes it does but if you want more than that  sorry  you are out of luck. What happens to the appratus after measurement? Nothing  the observation selected an outcome  that's it  that's all. Thanks Bill 



#6
Nov2412, 04:26 PM

P: 65

Probabilities from Entanglement, Born's Rule from Envariance (Zurek, 2005) I'm really not equipped to analyze the subtleties involved with his approach but when I read through it the following caught my eye (p.19): Also, as far as decoherence in general I quite enjoyed working my way through this: Decoherence, the measurement problem, and interpretations of quantum mechanics (Schlosshauer, 2004) David Wallace has written on this topic extensively, I believe. 



#7
Nov2512, 10:00 AM

P: 178





#8
Nov2512, 12:50 PM

P: 127





#9
Nov2512, 01:03 PM

P: 178





#10
Nov2512, 01:16 PM

P: 127





#11
Nov2512, 01:38 PM

P: 178





#12
Nov2512, 04:04 PM

PF Gold
P: 670

I found this piece by Leifer disussing decoherence useful:
http://mattleifer.info/2007/01/24/wh...ncedoforus/ 



#13
Nov2512, 04:40 PM

P: 127

But look at Matt Leifer's comment in the comment section from 2010. It seems he has been won over by Wallace too. 



#14
Nov2512, 04:42 PM

P: 127

Sure, but I think the more interesting debate is whether decoherence can give us a preferred basis and emerge a classical world. According to a recent paper by Jan Scwhindt which was briefly discussed here, it cannot. There is yet another paper that was released recently by a physicist named Oleg Lychkovskiy: http://arxiv.org/abs/1210.4124 I don't grasp this paper though, but you might. 



#15
Nov2512, 06:47 PM

PF Gold
P: 670





#16
Nov2512, 07:06 PM

Sci Advisor
PF Gold
P: 2,049

Thanks Bill 



#17
Nov2512, 08:15 PM

P: 127

" Perhaps the best worked out example is in the Everett interpretation where you can look at the long papers by David Wallace to find out how decoherence leads to emergence in that case. There is no new maths in these papers, but it provides the necessary philosophical support that you are looking for in that case. " 



#18
Nov2612, 12:43 AM

Sci Advisor
P: 5,307

One must still distinguish between the physical process of decoherence (selection of preferred pointer basis, effective diagonalization of the density matrix ρ' of the subsystem S') and its interpretation. What decoherence does is that it transforms the quantum probabilities into effective classical ones; but it does not tell us which particular result encoded in the diagonal matrix ρ' will be realized in one specific experiment. In terms of Schrödinger's cat: it explains the absence of coherent superpositions, but for one single cat in one single experiment it does not tell whether this specific cat will be dead or alive after opening the box.



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