Does Decoherence Solve the Measurement Problem Completely


by Prathyush
Tags: measurement, quantum mechanics
tom.stoer
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#73
Nov29-12, 09:28 AM
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Please read carefully what I am writing!

You are talking about QM and GR which is NOT subject to any existing experiment (I was talking about experimental predictions). There are several proposals for QG which could affect experimental predictions but which DO NOT affect the principles of QM at all (strings, LQG, AS, CDT, ... no not touch any fundamental principle of QM). So this line of reasoning is irrelevant.

And your "unacceptable indeterminism" is in no way rooted in any physical reasoning but is something that must be discussed on a meta-physical level. Sorry to say that, but all your arguments ignore what I have listed above:

Quote Quote by tom.stoer View Post
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 1-4)
5) ...

QM has always proven to be "correct" in the sense of (1). The problems appear at the level of (2-4).
Again: I understand very well you're intention for a theory going beyond the existing knowledge (that was the case for decoherence as well). But the rules of nature do not follow your ideas; it should be the other way round: your ideas should follow what nature tells us. And on the level of (1) there is no escape: it's QM - unless you disprove its consistency or demonstrate experimentally that it's wrong.

btw.: are you familiar with the deBroglie-Bohm approach? I don't really like it, but we have several colleagues here working on it; perhaps this is something you are looking for ...
Prathyush
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Nov29-12, 10:22 AM
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Thank you for your responses.I could not look at the thread over the past week. I liked some of the answers(esp. tom & nanosiborg) and will over time try to respond to specific answers.

I would like to open some Issues for discussion. There is a usual approach to solution that goes by the name of "Universal Wavefunction". Which at some level posulates that there is an independent reality for the wavefunction which both the system under observation, and the measurement appratus must follow. Decoherence is one such approach, perhaps there are others.

Which if one assumes that measurement appratus exist, What the wavefunction really seems to be doing is it predicts the behaviour of our measurement appratus. One can only describe the experimental outcomes and the wavefunction seems to be predicting probable experimental outcomes. So without the precise experimental arrangement in mind it seems meaningless to talk about wavefunction and amplitudes.

While wavefunctions are an indespensible part of description, since it only tell us about the probability of the outcomes of experimental arrangements, Will a concept such as "Universal wavefunction" have any validity.

I think it is also important to understand that we cannot fully control the state of our appratus. Our limitations to do experiments do not allow us to precisely prepare the state of the appratus, We can only talk about preparation procedure, materials used, and similar concepts.
bohm2
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Nov29-12, 11:19 AM
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Quote Quote by tom.stoer View Post
Btw.: we never ask the question "why" things work as they do in classical mechanics. Why do we not ask this question? Why do we ask this question in QM? Is it really true that we have a full understanding of these ideas in classical mechanics? I am sure the answer is "no".
But does an interpretation really involve asking "why" questions? Maybe I'm mistaken, but I've always considered the interpretation question relating more to the question of "what" the wave function represents. Is it epistemic or ontic, for example. If one suggests that QM is just a formalism to predict experimental results isn't that just the epistemic interpretation? Moreover, some authors (if I'm understanding them) do seem to argue that even classical mechanics did involve interpretation (at least, with the benefit of hindsight):

Does Quantum Mechanics Need Interpretation?
http://arxiv.org/pdf/0902.3005.pdf

See Travis Norsen's slide presentation (particularly slide 4) linked here:
Out of this World Ontology
http://www.vallico.net/tti/master.ht...onference.html

On a somewhat related note, Leifer also points out why different interpretations of quantum theory have and can provide important insights that may not have been discovered without these foundational interpretative debates:
Different interpretations quantum theory provide different insights, which are valuable even if the interpretations themselves turn out to be false. For example, the many-worlds interpretation was a key inspiration for the idea of a quantum computer, as proposed by David Deutsch, even though the idea itself does not require that interpretation. Similarly, the tension between de Broglie-Bohm theory and von Neumann's no-go theorem for hidden variables was the main driving force behind Bell's development of his eponymous inequalities. If you like, you can interpret those inequalities in terms of the ability of Alice and Bob to perform better in certain cooperative games using quantum resources than they could with classical resources without ever mentioning hidden variables, as many quantum information theorists are wont to do. However, it is unlikely that Bell's theorem would ever have been discovered were it not for the foundational context in which it first arose. What I was trying to argue in my article, is that the PBR theorem might have a similar status. Whilst it is inspired by the question of the status of the quantum state in a hidden variable theory, it may end up telling us something new about the differences between quantum and classical resources in general. We will never gain these new insights if we close off avenues for understanding quantum theory, even if we regard the foundational programs that they are associated with as unlikely to succeed in the long run.
Response to Griffiths
http://www.aps.org/units/gqi/newslet...d/vol6num4.pdf

I thought this Fuchs interview was also interesting because he has often been quoted in some posts arguing that QM does not require interpretation:

To take a stand against the milieu, Asher had the idea that we should title our article, “Quantum Theory Needs No ‘Interpretation’.” The point we wanted to make was that the structure of quantum theory pretty much carries its interpretation on its shirtsleeve—there is no choice really, at least not in broad outline. The title was a bit of a play on something Rudolf Peierls once said, and which Asher liked very much: “The Copenhagen interpretation is quantum mechanics!” Did that article create some controversy! Asher, in his mischievousness, certainly understood that few would read past the title, yet most would become incensed with what we said nonetheless. And I, in my naivet´e, was surprised at how many times I had to explain, "Of course, the whole article is about an interpretation! Our interpretation!”

But that was just the beginning of my forays into the quantum foundations wars, and I have become a bit more seasoned since. What is the best interpretive program for making sense of quantum mechanics? Here is the way I would put it now. The question is completely backward. It acts as if there is this thing called quantum mechanics, displayed and available for everyone to see as they walk by it—kind of like a lump of something on a sidewalk. The job of interpretation is to find the right spray to cover up any offending smells. The usual game of interpretation is that an interpretation is always something you add to the preexisting, universally recognized quantum theory. What has been lost sight of is that physics as a subject of thought is a dynamic interplay between storytelling and equation writing. Neither one stands alone, not even at the end of the day. But which has the more fatherly role? If you ask me, it’s the storytelling. Bryce DeWitt once said, “We use mathematics in physics so that we won’t have to think.” In those cases when we need to think, we have to go back to the plot of the story and ask whether each proposed twist and turn really fits into it. An interpretation is powerful if it gives guidance, and I would say the very best interpretation is the one whose story is so powerful it gives rise to the mathematical formalism itself (the part where nonthinking can take over).

The “interpretation” should come first; the mathematics (i.e., the pre-existing, universally recognized thing everyone thought they were talking about before an interpretation) should be secondary.
Interview with a Quantum Bayesian
http://lanl.arxiv.org/pdf/1207.2141.pdf

Quantum Theory Needs No “Interpretation”
http://www.imamu.edu.sa/Scientific_s...rpretation.pdf
Prathyush
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Nov29-12, 11:28 AM
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Quote Quote by bhobba View Post
Exactly.


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.


Thanks
Bill
I want to understand what is memory?
bhobba
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Nov29-12, 05:18 PM
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Quote Quote by Prathyush View Post
I want to understand what is memory?
Then I suggest you study biology and psychology. QM doesn't really say anything about it - its concerned with fundamental physics.

In the past there was a reasonably well known consciousness causes collapse group in QM led by Wigner and Von Neumann. Von Newmann unfortunately and prematurely passed away but when Wigner first heard about decoherence he realised consciousness was no longer required and abandoned it. There is still a few hold outs such as Penrose and Hameroff but it is very much a minority thing now days. However you may find Penrose's views interesting:
http://www.amazon.com/Consciousness-...4230727&sr=1-1

Personally though to me its mystical nonsense - but a person of Penrose's stature can't be dismissed lightly.

I also have to admit I hold views many would put in the mystical nonsense camp in that like Penrose I believe in the literal existence of a Platonic realm where mathematical and fundamental physical truth lies but that is another story - as a warm-up though check out Wigners famous essay on it:
http://www.dartmouth.edu/~matc/MathD...ng/Wigner.html

Thanks
Bill
Prathyush
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Nov30-12, 01:18 AM
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Quote Quote by bhobba View Post
Then I suggest you study biology and psychology. QM doesn't really say anything about it - its concerned with fundamental physics.

In the past there was a reasonably well known consciousness causes collapse group in QM led by Wigner and Von Neumann. Von Newmann unfortunately and prematurely passed away but when Wigner first heard about decoherence he realised consciousness was no longer required and abandoned it. There is still a few hold outs such as Penrose and Hameroff but it is very much a minority thing now days. However you may find Penrose's views interesting:
http://www.amazon.com/Consciousness-...4230727&sr=1-1

Personally though to me its mystical nonsense - but a person of Penrose's stature can't be dismissed lightly.

I also have to admit I hold views many would put in the mystical nonsense camp in that like Penrose I believe in the literal existence of a Platonic realm where mathematical and fundamental physical truth lies but that is another story - as a warm-up though check out Wigners famous essay on it:
http://www.dartmouth.edu/~matc/MathD...ng/Wigner.html

Thanks
Bill
No I mean it in all seriousness. What is physics underlying the formation of a memory impression on a device.
bhobba
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Nov30-12, 02:25 AM
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Quote Quote by Prathyush View Post
No I mean it in all seriousness. What is physics underlying the formation of a memory impression on a device.
There is no general answer - it depends on the device.

Thanks
Bill
Prathyush
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Nov30-12, 10:18 AM
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Quote Quote by bhobba View Post
There is no general answer - it depends on the device.

Thanks
Bill
I would be happy to understand any one device, A photographic plate, Grieger counter or a PMT
StevieTNZ
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Nov30-12, 12:08 PM
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Quote Quote by tom.stoer View Post
the reason why we don't in classical mechanics is that classical mechanics fits to our perception whereas QM doesn't; QM was the first physical theory to which no Platonism, Aristotelism, Kantianism or any other XYZism had an answer; QM does not fit to the categories of our perception;

now there are two options
1) change nature
2) change our ideas about nature
for me 2) is acceptable, but that's a matter of taste ;-)
Agree! Sticking to old ways of thinking isn't exactly the best - people should be open to new ideas; sadly it isn't that easy.
eloheim
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Nov30-12, 12:27 PM
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Quote Quote by Quantumental View Post
The reason we don't ask why in classical mechanics is because we know it's not fundamental, the answer will always reduce to a more fundamental theory.
So for those who think that QM is *the* fundamental theory, they have to explain why everything occurs really.
But why is determinism so much more satisfying to you? How do the particles know where to go? And why don't they go somewhere else? Unless you think there's an infinite downward regress of ever-better physical theories you're going to have to deal with these issues sooner or later.

My point being that WHICHEVER theory you end up with, I think it's safe to say, there's going to some unanswered, ambiguous, or even unanswerABLE why's when you get there: "Why four forces? Does the universe go on forever? Why 3d+1 dimensions? Why THOSE initial conditions?"

Really the only way out of that one might be Tegmark's MUH+anthropics+..+.. (Which WOULD allow you plenty(!) of new stuff to work on, however!!.). ...Yet something tells me that might not be quite your cup of tea...
bhobba
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Nov30-12, 04:17 PM
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Quote Quote by Prathyush View Post
I would be happy to understand any one device, A photographic plate, Grieger counter or a PMT
For a photographic plate a simple internet search gives:
http://wiki.answers.com/Q/How_does_P...hic_plate_work
'The plate is covered in a light sensitive compound, containing Silver Halide crystals. When light falls on the Silver-halide, it causes the silver atoms to clump together. When developed with chemicals, the silver is left behind, causing dark areas where light has fallen. This makes a negative image, where light is dark and dark is light. To get a positive print, simply shine light through the developed plate onto paper covered in the same Silver-halide compound. After the same chemical process, the picture is reversed again giving the positive image.'

I am sure you can do that for any device you are interested in.

Thanks
Bill
nanosiborg
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Nov30-12, 09:36 PM
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Quote Quote by bhobba View Post
The book to get is Ballentine - Quantum Mechanics - A Modern Development: http://www.amazon.com/Quantum-Mechan.../dp/9810241054

Here you will find QM developed from just two axioms and Schrodengers equation derived (yes derived - not assumed) from its true basis - Galilean Invariance.

Take your time, go through it carefully, and you will come away with a really good understanding.
Thanks for the reference.
nanosiborg
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Nov30-12, 11:15 PM
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Quote Quote by Prathyush View Post
Thank you for your responses.I could not look at the thread over the past week. I liked some of the answers(esp. tom & nanosiborg) and will over time try to respond to specific answers.

I would like to open some Issues for discussion. There is a usual approach to solution that goes by the name of "Universal Wavefunction". Which at some level posulates that there is an independent reality for the wavefunction which both the system under observation, and the measurement appratus must follow. Decoherence is one such approach, perhaps there are others.

Which if one assumes that measurement appratus exist, What the wavefunction really seems to be doing is it predicts the behaviour of our measurement appratus. One can only describe the experimental outcomes and the wavefunction seems to be predicting probable experimental outcomes. So without the precise experimental arrangement in mind it seems meaningless to talk about wavefunction and amplitudes.
Yes. I think that this is the current prevailing view in mainstream physics. I also think that this is the preferred view of most philosophers (of science and physics). But don't know. It might turn out that an approach based on some formulation of an assumed universal wavefunction has predictive usefulness. If that's already the case, then please excuse my ignorance.

Quote Quote by Prathyush View Post
While wavefunctions are an indespensible part of description, since it only tell us about the probability of the outcomes of experimental arrangements, Will a concept such as "Universal wavefunction" have any validity.
Validity meaning predictive utility? Don't know.

Quote Quote by Prathyush View Post
I think it is also important to understand that we cannot fully control the state of our appratus. Our limitations to do experiments do not allow us to precisely prepare the state of the appratus, We can only talk about preparation procedure, materials used, and similar concepts.
This seems to be the prevailing mainstream view. There have been lots of papers written about this.
nanosiborg
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Nov30-12, 11:28 PM
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Quote Quote by Prathyush View Post
I would be happy to understand any one device, A photographic plate, Grieger counter or a PMT
You seem to be somewhat knowledgeable about this. I'm surprised you haven't presented us with a list of Googled references.

For convenience, here's some articles I found on PMT's:

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

http://ed.fnal.gov/talks/tim_brennan/PMT_paper.doc

http://nasa2000.tpub.com/NASA-2000-t...2098360011.htm

http://sales.hamamatsu.com/assets/ap...plications.pdf

http://psec.uchicago.edu/links/Photo...r_Handbook.pdf

http://www.et-enterprises.com/files/...p089colour.pdf

http://www.scribd.com/doc/5707966/Ex...ultiplier-tube

Also I still have a copy of a paper that a friend and I scribbled some notes on the back of the printed pages (some of which isn't readily legible to me now), but couldn't find a link to a free copy for you to download (I could scan and post it for you, but that would be illegal):

Photometric Error Analysis. IX: Optimum Use of Photomultipliers. by A.T. Young

Of course you might be familiar with these and other explanations of PMT behavior and are still not satisfied that you understand it. If you have other, better articles then please post them here.
nanosiborg
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Dec1-12, 01:19 AM
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Quote Quote by bohm2 View Post
See Travis Norsen's slide presentation (particularly slide 4) linked here:
Out of this World Ontology
http://www.vallico.net/tti/master.ht...onference.html
bohm2, I enjoyed reading your comments and links. The one reproduced above and the links associated with The Towler Institute gathering were very entertaining.
Quantumental
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Dec1-12, 08:29 AM
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This: http://philsci-archive.pitt.edu/4224/1/scriptie.pdf is a very comprehensible analysis of decoherence, especially in the everettian context
Prathyush
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Dec2-12, 10:12 AM
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Quote Quote by nanosiborg View Post
You seem to be somewhat knowledgeable about this. I'm surprised you haven't presented us with a list of Googled references.

For convenience, here's some articles I found on PMT's:

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

http://ed.fnal.gov/talks/tim_brennan/PMT_paper.doc

http://nasa2000.tpub.com/NASA-2000-t...2098360011.htm

http://sales.hamamatsu.com/assets/ap...plications.pdf

http://psec.uchicago.edu/links/Photo...r_Handbook.pdf

http://www.et-enterprises.com/files/...p089colour.pdf

http://www.scribd.com/doc/5707966/Ex...ultiplier-tube

Also I still have a copy of a paper that a friend and I scribbled some notes on the back of the printed pages (some of which isn't readily legible to me now), but couldn't find a link to a free copy for you to download (I could scan and post it for you, but that would be illegal):

Photometric Error Analysis. IX: Optimum Use of Photomultipliers. by A.T. Young

Of course you might be familiar with these and other explanations of PMT behavior and are still not satisfied that you understand it. If you have other, better articles then please post them here.
I am reasonably familiar with the basic working's of a PMT, But I am looking for a microscopic description of the whole process. I've had some experience of working with PMT's and most often PMT's are caliberated with known sources to understand their behaviour.

I think in general it would be very material dependant and so on, But if we could isolate the essential process that is involved in it and to talk about it in a material indepentant manner, it would be nice.

I will point to some quotes that are of interest to me,

“We and our measuring instruments are part of nature and so are, in principle, described by an amplitude function satisfying a deterministic equation. Why can we only predict
the probability that a given experiment will lead to a definite result? From what does the uncertainty arise? Almost without a doubt it arises from the need to amplify the effects of single atomic events to such a level that they may be readily observed by large systems.”
-Feynman
". . . In what way is only the probability of a future event accessible to us, whereas the certainty of a past event can often apparently be asserted?. . . Obviously, we are again involved in the consequences of the large size of ouselves and of our measuring equipment. The usual separation of observer and observed which is now needed in analyzing measurements in quantum mechanics should not really be necessary, or at least should be even more thoroughly analyzed. What seems to be needed is the statistical mechanics of amplifying apparatus"
-Feynman

He empasises on the large sizes of ourselves and our measuring equipment.

"Observation must involve the concept of amplification which must expend free energy"
-N Bohr(slightly misworded but its alright)

He talk about the free energy cost involved in the measurement. I think is a generally correct in all situations, however currently only a heuristic principle, Clearly it is closely related to the landauer's principle who said that to measure one bit of information KT Log 2 amount of energy must be expended.

As I was thinking along these lines, I was led to believe that one can use the change in temprature of cold heat bath to measure the energy levels of a quantum mechanical system. In this particlar case, The cold heatbath can be arranged in an experimental setup, while we cannot monitor the precise state of the heat bath, its Tempratue is what is available to us. Therefore coupling a cold heat bath to a state in superposition can allow us to measure its energy.

While what is happening is far from clear to me, I think the general picture fits closely with The fact that one uses caloriemeter's as particle detectors, an essential component of a photomultiplier tube must involve a voltage difference which must involve expended work, or the fact that measurement using bubble/ vapour chambers involve thermodynamic Transition.

The general fact that we have to take into account in all of this is that we cannot arrange the "universal wavefunction" so it is not fully to talk about, In any situation out experimental appratus must consist of a large number of degrees of freedom, whose state we can only talk about approximately, or in the theromodynamic approximation. We also must accept the restriction that we cannot talk the change in the state of the measurement appratus in the thermodynamic approximation. While it is far from clear, I would love to listen to your comments and opinions.


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