Does Decoherence Solve the Measurement Problem Completely

[bhobba]

But doesn't this theorem put restraints on whatever fundamental theory that lies beneath QM anyways?

No. If you believe QM is an approximation to a more fundamental theory then that theory simply has to give QM in some kind of limit. The theorems that apply to QM like PBR need not apply. In that case PBR is a sort of blemish on QM like acasual runaway solutions are a blemish on EM indicating its not fundamental.

Added Later:

Just to be clear other outs of PBR exist as well - it crucially depends on state independence.

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. de-Broglie 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.

I would be careful about letting your prejudices lead you to believe anything 'HAS' to be right or wrong. Choose an interpretation based on what makes most sense to you, or even reject them all, but don't think it must be like that - nature has a way of confounding that sort of view.

Thanks
Bill

 

[tom.stoer]

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) ...

Doing that I come to the conclusion that something in this web of relationships (1-4) 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 (2-4).

So why the hell should (1) be wrong and in which sense??

 

[bhobba]

So why the hell should (1) be wrong and in which sense??

IMHO no reason at all.

Thanks
Bill

 

[tom.stoer]

of course, the question goes to Quantumental ;-)

Tom

 

[bohm2]

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) ...

Doing that I come to the conclusion that something in this web of relationships (1-4) 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 (2-4).

So why the hell should (1) be wrong and in which sense??

But can't (1) itself also be seen just as one more interpretation of QM (e.g. an instrumental approach).

 

[Quantumental]

I would be careful about letting your prejudices lead you to believe anything 'HAS' to be right or wrong. Choose an interpretation based on what makes most sense to you, or even reject them all, but don't think it must be like that - nature has a way of confounding that sort of view.

I do.

Belief in indeterminism is to me exactly like solipsism, sure I can never prove it wrong, it's logically coherent, but it explains nothing and I have no reason to think it's true.
For anyone believing in indeterminism, I wonder how you can justify the Born Rule. What sort of sense would it make for a genuinely indeterminate universe to care about a statistical rule like that of Born?
Why wouldn't particles just do whatever the hell they want at all times without obeying any laws what so ever. The fact that we observe a "rule" is to me philosophically requiring an explanation.
To me "random" is JUST as likely as inventing a God. So when you ask "why did the cat die?" I would say "God became allergic to felines" and take that just as seriously as "it just happened out of randomness".
If you followed up with "but why would God kill cats according to what we percieve as the Born Rule?" I would tell you: "God works in mysterious ways" and claim a Nobel Prize.
It's incoherent, stupid and not science. Science seeks explanations, if we had given up when we hit something that seems random we would have given up on trying to model ANYTHING, because EVERYTHING seems incomprehensible at first sight.
Imagine the first time someone pondered the rain, it would have to have seemed completely random, which is why most societies at the time believed in weather Gods, they saw no other explanation. I am 100% confident that reality is not indeterministic

 

[Quantumental]

1) QM as a theory of nature = a formalism to predict experimental results
...

So why the hell should (1) be wrong and in which sense??

I picked the wrong word, what I mean by wrong is that it's not 100% right, because it's incomplete.
So it's wrong in the same sense that Newtonian gravity is wrong. It works but it's not the final and fundamental model.

This is the same way I percieve QM given the fact that there is no way to make sense of QM unless you are willing to accept antirealistic-indeterminism on par with solipism, Bohm (non-local and surrealistic trajectories) or Many Worlds and be able to get the Born Rule out of Many Worlds.

 

[bhobba]

For anyone believing in indeterminism, I wonder how you can justify the Born Rule.

Actually its not that hard. It follows from the key assumption of additivity of expectation values as pointed out by Von Neumann's original hidden variable no go theorem. Its such a natural assumption it took a while to see it didn't necessarily apply to hidden variables - actually its more correct to say it took a while for the people that originally saw the issue (and a few did) to be heard above someone of Von Neumann's stature.

Later harder to evade theorems such as Gleasons also came along that also justifies it - but of course that is also evadeable since it rests on a crucial assumption of non-contextuality. I think contextuality is pretty weird but if you want determinism that's what you need.

I hasten to add me thinking the additivity of expectation values natural and contextuality weird means Jack Shite - nature does not have to respect my or anyone else's aesthetics.

Oh and since PBR has been mentioned I am glad I got the chance to post Schlosshauer's analysis of it which shows like contextuality and Von Neumann's theorem it also rests on hidden assumptions. Its very interesting how given a theory/interpretation that PBR applies to one can always construct one where it doesn't - and conversely. Its just goes to show how weird nature really is.

Thanks
Bill

 

[tom.stoer]

But can't (1) itself also be seen just as one more interpretation of QM (e.g. an instrumental approach).

No, not really.

An agnostic view regarding (1) would be that QM allows us to predict experimental results - end-of-story.

I agree that this seems to be incomplete b/c there is not reason "why" this works, there is no idea regarding reality or regarding a relation between the QM formalism and reality. And there it always a kind of 'interpretation' in the sense of "given this apparatus and an electron I have to use that formula with the following initial conditions".

All what I am sying is that these missing pieces - and I agree that this agnostic view is unsatisfactory and that there are missing pieves - are not on the level of (1).

Let's make a simple example: in classical mechanics we can count dead cats and alive cats (and such things) using Peanos axioms. Their consistency or inconsistency in the sense of Hilbert's second problem is to be discussed on the level of (1), the reason "why" we can use them is beyond level of (1).

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".

 

[tom.stoer]

If you followed up with "but why would God kill cats according to what we percieve as the Born Rule?" ... It's incoherent, stupid and not science. Science seeks explanations, ...

I understand what you are asking for. And I agree with you in some sense, and I am therefore interested in the same kind of questions.

All what I am saying is that these problems are strictly speaking not on the level of (1) as a pure mathematical formalism but beyond that level. And it is not clear that your interpretation of science (it's an interopretation, not a definition) is not the common view, at least not in quantum mechanics; many will agree that QM is not about "why" and not about "explanations". That does not mean that QM in the sense of (1) is incomplete or wrong. It just means that there are good reasons to go beyond (1) - and to be very careful when we should stop calling something science and when it becomes metaphysics (not with any negative connotation).

I think we should remeber where this discussion started. It was about the question regarding decoherence and the measurement problem. This thread (and many others) show that one problem is that decoherence comes with some context (interpretations, measurement problem, ...) and that in many presentations the facts (decoherence) and the context are presented as the same thing. So all what did was to decompose "decoherence as presented or perceived" in "decoherence as a fact derived from QM and demonstrated by experiments" and "context and interpretation of decoherence like measurement, many worlds, ...".

 

[nanosiborg]

As the Title describes, Is the measuremet problem completely solved by the decoherence Program?

No. No matter how the measurement problem is formulated it isn't solved by the "decoherence Program", as you put it.

In specific I would like the following question addressed.

Is there is clear explanation as to what it means to Record Infromation?

Yes. The physical referents of the term "recorded information" are amenable to our sensory apprehension.

Can it explain the behaviour of a photographic plate?

No.

What happens to the appratus after measurement?

Open question.

 

[eloheim]

Everett is invalidated by the Born Rule and in addition you have the preferred basis issues.

Does this do anything for you? (And being in line with the thread title.) A small part of this (just to set up the issue):

How can the EI [Everett Interpretation] explain the observed probabilities in quantum measurements? I.e.,
why is the squared norm |ca|2 of a branch equivalent to the probability an observer
encounters for measuring the value a? If an observer performs the “same” (equivalent)
measurement many times, the state vector branches each time, and in the
end there will be a branch for each combined result of the measurements. Each
branch also contains one version of the observer. Each observer will conclude the
probability for each value a from the statistics of the individual results he got. One
can show that the norm of the part of the state vector corresponding to branches
where observers don’t get the right probabilities converges to zero when the number
of measurements is increased [2]. The remaining question is whether or not this
argument solves the problem (I think it does). In this paper, I will not deal with
the probability problem, so I won’t discuss this issue any further.

An argument against this resolution is that the limit only holds in the case of an infinite number of measurements (which seems unphysical). However, as Aguirre and Tegmark point out here, in a spatially infinite universe there actually will be an infinite number of such measurements being made. This is suggests to them the measurement problem can be resolved by appealing to a duality, of sorts, between the many worlds of quantum mechanics and cosmology.

 

[nanosiborg]

My understanding of the usual formulation of the quantum measurement problem is that it has to do with an apparent contradiction between the dynamics of quantum theory as described by the Schrodinger wave equation (and its wavefunction solutions), and the Born measurement axiom or postulate.

I call this the pseudo quantum measurement problem because I don't see any logical contradiction there.

That the underlying reality has something to do with wave shells expanding in media of unknown structure seems to me to be a most reasonable assumption. This is what the wave equation and wavefunctions have 'something' to do with (in the sense that they might be conceptually associated with an underlying reality), imo.

We place obstructions in the paths of the expanding wave shells and posit that the probability of whether or not a detection is recorded will be in direct proportion to the amplitudes (specifically, the squares of the amplitudes) of the wave fronts as they contact the obstructions. No problem there. This applies to waves in both particulate and nonparticulate media, and is understandable in terms of our limited sensory apprehension of nature.

What's less understood, or, not really understood at all, is the qualitative nature of the apparent particlelike properties of individual quantum detection results, which, in my view, is part of the real quantum measurement problem.

Decoherence cannot, imo, solve what I consider to be the real quantum measurement problem.

 

[nanosiborg]

By the way, thanks to all commenters, especially tom.stoer, bhobba, Quantumental, eloheim and bohm2 (apologies if I failed to mention other substantial commenters). I'm a recent graduate with a more than passing interest in the foundations of quantum theory, and modern physics in general. I've been doing a little homework and, for your convenience and amusement, here's a sampling of some of the reading and viewing that I've been doing with the help of the internet.

Some of it is beyond my current ability to fully understand (or maybe I'm just trying to read too fast). So, expect some questions ... and I hope they don't sound too naive.

http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

http://mattleifer.info/2012/02/26/quantum-times-article-on-the-pbr-theorem/

http://www.aps.org/units/gqi/newsletters/upload/vol6num3.pdf

http://mattleifer.wordpress.com/2007/04/11/why-is-many-worlds-winning-the-foundations-debate/

http://pirsa.org/displayFlash.php?id=12050021

http://dabacon.org/pontiff/?p=5912

http://science.slashdot.org/story/1...uantum-wavefunction-is-a-real-physical-object

http://blogs.discovermagazine.com/c...hysicality-of-the-quantum-state/#.ULb27oY4eso

https://www.physicsforums.com/showthread.php?t=551554&page=17

http://www.nature.com/news/quantum-theorem-shakes-foundations-1.9392

http://motls.blogspot.com/2011/11/nature-hypes-anti-qm-crackpot-paper-by.html

Distinct Quantum States Can Be Compatible with a Single State of Reality
http://arxiv.org/abs/1201.6554

On the reality of the quantum state
http://arxiv.org/abs/1111.3328

Exponential complexity and ontological theories of quantum mechanics
http://arxiv.org/abs/0711.4770

Strengths and Weaknesses of Quantum Computing
http://arxiv.org/abs/quant-ph/9701001

Einstein, incompleteness, and the epistemic view of quantum states
http://arxiv.org/abs/0706.2661

In defense of the epistemic view of quantum states: a toy theory
http://arxiv.org/abs/quant-ph/0401052

The paradigm of kinematics and dynamics must yield to causal structure
http://arxiv.org/abs/1209.0023

Formulating Quantum Theory as a Causally Neutral Theory of Bayesian Inference
http://arxiv.org/abs/1107.5849

 

[bhobba]

Some of it is beyond my current ability to fully understand (or maybe I'm just trying to read too fast). So, expect some questions ... and I hope they don't sound too naive.

Mate it looks like you are deadly serious in understanding this stuff - great to see.

The book to get is Ballentine - Quantum Mechanics - A Modern Development:
https://www.amazon.com/dp/9810241054/?tag=pfamazon01-20

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
Bill

 

[Quantumental]

An argument against this resolution is that the limit only holds in the case of an infinite number of measurements (which seems unphysical). However, as Aguirre and Tegmark point out here, in a spatially infinite universe there actually will be an infinite number of such measurements being made. This is suggests to them the measurement problem can be resolved by appealing to a duality, of sorts, between the many worlds of quantum mechanics and cosmology.

I don't think this really helps at all and I'll quote someone who has dealt with this

The frequency operator is the operator associated with the observable that is the number of cases in a series of experiments that a particular result occurs, divided by the total number of experiments. If is assumed that just the frequency itself is measured, and if the limit of the number of experiments is taken to infinity, the eigenvalue of this frequency operator is unique and equal to the Born Rule probability. The quantum system is then left in the eigenstate with that frequency; all other terms have zero amplitude, as shown by Finkelstein (1963) and Hartle (1968).

This scheme is irrelevant for two reasons. First, an infinite number of experiments can never be performed. As a result, terms of all possible frequencies remain in the superposition. Unless the Born Rule is assumed, there is no reason to discard branches of small amplitude. Assuming that they just disappear is equivalent to assuming collapse of the wavefunction.

Second, in real experiments, individual outcomes are recorded as well as the overall frequency. As a result, there are many branches with the same frequency and the amplitude of anyone branch tends towards zero as the number of experiments is increased. If one discards branches that approach zero amplitude in the limit of infinite experiments, then all branches should be discarded. Furthermore, prior to taking the infinite limit, the very largest individual branch is the one where the highest amplitude outcome of each individual experiment occurred, if there is one.

A more detailed critique of the frequency operator approach is given here(http://arxiv.org/abs/quant-ph/0409144).
The same basic approach of using infinite ensembles of measurements has been taken recently by certain Japanese physicists, Tanaka (who seems unaware of Hartle's work) and (seperately) Wada. Their work contains no significant improvements on the old, failed approach.

 

[Quantumental]

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".

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.
If you ask why and their reply is simply: indeterminism!, then that suggests to me that they are not really interested in knowing why, but rather just want the math to work. That's fine if you are going to do technical work, but if you are seeking truth you can never be satisfied with "it just happens"

 

[bhobba]

If you ask why and their reply is simply: indeterminism!,

That's not my reply, which is Gleasons Theorem provides a pretty strong reason for QM being a statistical theory:
http://en.wikipedia.org/wiki/Gleason's_theorem

Gleason's theorem highlights a number of fundamental issues in quantum measurement theory. The fact that the logical structure of quantum events dictates the probability measure of the formalism is taken by some to demonstrate an inherent stochasticity in the very fabric of the world. To some researchers, such as Pitowski, the result is convincing enough to conclude that quantum mechanics represents a new theory of probability. Alternatively, such approaches as relational quantum mechanics make use of Gleason's theorem as an essential step in deriving the quantum formalism from information-theoretic postulates.

The theorem is often taken to rule out the possibility of hidden variables in quantum mechanics. This is because the theorem implies that there can be no bivalent probability measures, i.e. probability measures having only the values 1 and 0. Because the mapping is continuous on the unit sphere of the Hilbert space for any density operator W. Since this unit sphere is connected, no continuous function on it can take only the value of 0 and 1. But, a hidden variables theory which is deterministic implies that the probability of a given outcome is always either 0 or 1: either the electron's spin is up, or it isn't (which accords with classical intuitions). Gleason's theorem therefore seems to hint that quantum theory represents a deep and fundamental departure from the classical way of looking at the world, and that this departure is logical, not interpretational, in nature.

Of course it doesn't prove anything but for sure it is far from certain that in-determinism can not be fundamental - not certain at all.

Thanks
Bill

 

[tom.stoer]

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 ;-)

 

[Quantumental]

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 ;-)

The problem is this: you could've said the same thing *ANYTIME* in history, remember that microscopes and telescopes are very recent in history.
Hell we can make it even more absurd.

Why should you assume that existence existed before you? Sure you might say "well my observations seem to be best accounted for by postulating that things were around before me."
After all, it makes little sense that existence surrounding you should try to decieve you into thinking that old things have been around for a long time if they hasn't.

But the same applies to Born Rule, there is no reason why something that is truly indeterminate should follow a statistical rule...
So with the same logic you reject the "the universe came into existence with me" hypothesis, I reject the "magic is the reason Born rule exists."

 

[tom.stoer]

I am not sure whether you understand what I am saying.

QM tells us a lot about nature; it makes experimentally provable and correct predictions, something that was not the case with classical mechanics! There is no single experiment which tells us that QM (in the sense of its predictions is wrong)! Problems appear on the level of interpretation and the completeness of the formalism.

Therefore my conclusion is to doubt the interpretation.

 

[Quantumental]

I am not sure whether you understand what I am saying.

QM tells us a lot about nature; it makes experimentally provable and correct predictions, something that was not the case with classical mechanics! There is no single experiment which tells us that QM (in the sense of its predictions is wrong)!

Except for where QM and GR overlap..
Noone is arguing that the results we have from QM is correct, that would be as dumb as denying gravity after you've fallen off a cliff.

But this doesn't prove anything about indeterminism.
Classical mechanics DID indeed give right answers to a lot of questions, it was only when we probed deeper and needed more fundamental answers that it didn't suffice.
And due to the unacceptable indeterminism, this means QM is not fundamental, or you have to accept MWI or dBB and solve the problems facing them, which seems impossible without postulating some new kind of physics.


It seems you think that indeterminism is ok because we don't have a explanation that works 100% yet and I think that's a defeatus mentality, because anywhere in history we could've said the same. "How does leafs get their green color? **** it I'm living 10 000 years B.C. how the **** am I suppoed to know? It's random!"

 

[tom.stoer]

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:

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]

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]

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.html?http://www.vallico.net/tti/deBB_10/conference.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 won't 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/newsletters/upload/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_selections/abstracts/Physics/Quantum%20Theory%20Needs%20No%20Interpretation.pdf

 

[Prathyush]

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]

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 realized 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:
https://www.amazon.com/dp/0982955200/?tag=pfamazon01-20

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/MathDrama/reading/Wigner.html

Thanks
Bill

 

[Prathyush]

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 realized 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:
https://www.amazon.com/dp/0982955200/?tag=pfamazon01-20

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/MathDrama/reading/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]

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]

There is no general answer - it depends on the device.

Thanks
Bill

I would be happy to understand anyone device, A photographic plate, Grieger counter or a PMT

 

[StevieTNZ]

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]

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]

I would be happy to understand anyone 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_Photographic_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]

The book to get is Ballentine - Quantum Mechanics - A Modern Development: https://www.amazon.com/dp/9810241054/?tag=pfamazon01-20

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]

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.

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.

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]

I would be happy to understand anyone 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-tm209836/NASA-2000-tm2098360011.htm

http://sales.hamamatsu.com/assets/applications/ETD/pmt_handbook/pmt_handbook_applications.pdf

http://psec.uchicago.edu/links/Photomultiplier_Handbook.pdf

http://www.et-enterprises.com/files/file/technical-information/rp089colour.pdf

http://www.scribd.com/doc/5707966/Exploration-of-a-Photomultiplier-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]

See Travis Norsen's slide presentation (particularly slide 4) linked here:
Out of this World Ontology
http://www.vallico.net/tti/master.html?http://www.vallico.net/tti/deBB_10/conference.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]

This: http://philsci-archive.pitt.edu/4224/1/scriptie.pdf is a very comprehensible analysis of decoherence, especially in the everettian context

 

[Prathyush]

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-tm209836/NASA-2000-tm2098360011.htm

http://sales.hamamatsu.com/assets/applications/ETD/pmt_handbook/pmt_handbook_applications.pdf

http://psec.uchicago.edu/links/Photomultiplier_Handbook.pdf

http://www.et-enterprises.com/files/file/technical-information/rp089colour.pdf

http://www.scribd.com/doc/5707966/Exploration-of-a-Photomultiplier-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.