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The quantum state cannot be interpreted statistically?

by inflector
Tags: interpreted, quantum, state, statistically
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Ken G
#469
Dec14-11, 10:57 AM
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Quote Quote by my_wan View Post
I have never met any physicist, realist or otherwise, who thought it was totally wrong to make a distinction between the model and what the model described. What most realist object to is the a priori disqualification of considerations of what the actual system might entail that is not contained in the model. As I noted, Feynman ran into this kind of rejection when his little pictorials even hinted that he might be trying to picture what nature actually was, which wasn't the case in that instance.
But I just don't see anything at all in what Feynman did that requires the way you are characterizing it. He came up with a model for how to think about a certain process, just like every scientific theory did for the whole history of science. Nothing Feynman did was particularly ontological, indeed it really required getting "outside the box" of normal ontologies. So I don't see where the Feynman story has any significance to the idea that reality agrees with our models more than it is demonstrated to agree with our models. Science makes models, they work either pretty good, or great, depending. There's just nothing more to say, it makes no difference to the science, including Feynman's science, if people want to brand themselves "realists" or not.
The difference is that non-realist reject even considering a the system constraints outside the model itself as unponderable.
No, that is not correct. Why are so many people on this thread claiming that anyone said anything about what does not exist? The point being made is what is demonstable about what does exist, that's it, period. Further, the point has been made that it is neither demonstrable, nor any requirement of the workings of science, to claim that reality contains true properties that determine what happens. No one has said that such properties don't exist, what has been said is that nothing in science relies on them or indicates that they exist, and countless good theories of science, which worked quite well thank you, relied on properties that we perfectly well know do not exist in reality. These are all facts, nothing is being claimed that is not perfectly demonstrable as true.

Your criticism here is well patterned after the criticisms used against 19th century realist trying to develop a mechanistic model of thermodynamics.
No, nothing I have said even remotely resembled "do not derive scientific theories by entering into ontological thinking." Indeed, I have quite specifically said, on many occasions, words to the effect of "absolutely do enter into ontological thinking when deriving theories, it is convenient and effective to do so. Just don't take it literally, because the ontology is not going to be unique, and is probably not going to be true, and is very likely going to get replaced sooner or later in some better theory." That's it, that's all I said. So no, I never said, or thought, that it would be any kind of mistake to try to derive thermodynamics by imagining an ontology in which a bunch of particles were bouncing around statistically. What would be a mistake, and what is demonstrably erroneous in fact, is to conclude that the success of classical statistical mechanics proves that the ontology of little particles with exact positions and momenta is a true ontology of nature.
qsa
#470
Dec14-11, 04:35 PM
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Quote Quote by Len M View Post
In fact it is a philosophical assumption because the notion of a reality existing outside of us is a philosophical question.

There, you said it. Even worse, what is exactly the notion of reality existing "outside" of us. No such a thing can be of any use, scientific or otherwise. Hence, trying to know the truth of "real reality mind independent" is meaningless.

And it is bad enough to deal with one reality which we have. Stepping outside it has no meaning. How can you study and enjoy the Grand Canyon if you are not there.
Len M
#471
Dec14-11, 08:46 PM
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Quote Quote by qsa View Post
There, you said it. Even worse, what is exactly the notion of reality existing "outside" of us. No such a thing can be of any use, scientific or otherwise.

And it is bad enough to deal with one reality which we have. Stepping outside it has no meaning. How can you study and enjoy the Grand Canyon if you are not there.
Mind dependence simply poses the question: what is the nature of reality outside of the only means we have in which to examine nature? Is it the same, is it approximately the same, is it utterly different, so much so that we have no language to describe "different" or is there nothing outside of our minds? They are the options in which to describe a reality that may or may not exist outside of us ("us" being minds and consciousness involving the perception of space, time and objects).

Stepping outside of our reality (which means stepping outside of our minds, because our reality cannot be divorced from our minds) in order to examine the nature of that reality is impossible (which equates to it being meaningless as you say), so yes mind independent reality is a philosophical notion - it can’t be otherwise and it certainly is not of any scientific use. For me the notion is simply a philosophical extrapolation (and one that I strongly choose to adopt in opposition to radical idealism) from the important issue of mind dependence (and the inescapable nature of it) within science. Mind dependence places the "truth" derived through physics in a proper context – it is not a "truth" that is applicable to mind independent reality. In other words, we cannot use physics to describe “something” outside of our perceptions in the same way that we use physics to describe our perceptions – the “truth” of the latter is not the “truth” of the former. Thus science is the means of deriving "truths" about the "whole", and within that "whole" lay minds and consiousness. That for me is the important general point rather than a notion of mind independent reality – that notion is a personal philosophical choice one can adopt in order to retain realism. In fact radical idealists would dismiss out of hand the notion of a mind independent reality.
bohm2
#472
Dec14-11, 09:51 PM
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Quote Quote by Len M View Post
Mind dependence places the "truth" derived through physics in a proper context – it is not a "truth" that is applicable to mind independent reality. In other words, we cannot use physics to describe “something” outside of our perceptions in the same way that we use physics to describe our perceptions – the “truth” of the latter is not the “truth” of the former. Thus science is the means of deriving "truths" about the "whole", and within that "whole" lay minds and consiousness.
So everything is filtered through our cognitive structures and there's no guarantee that there will be a close correspondence between the two. In fact, one may argue that it would be kinda surprising if there was. But, what do you think of this fallback scientific realist position that some use:

What we call "natural science" is a kind of chance convergence between aspects of the world and properties of the human mind/brain, which has allowed some rays of light to penetrate the general obscurity
Thus, some have argued that theoretical physics is one of those areas where some of "those rays of light" have penetrated somewhat thus allowing for genuine progress/"deeper" understanding, etc.

In some of his later works, Pierce goes further and suggests (unconvincingly, in my opinion?) that because we are a product of nature/natural law, we may have a natural instinct at somehow being able to arrive at some of those laws of nature:

In this way, general considerations concerning the universe, strictly philosophical considerations, all but demonstrate that if the universe conforms, with any approach to accuracy, to certain highly pervasive laws, and if man's mind has been developed under the influence of those laws, it is to be expected that he should have a natural light, or light of nature, or instinctive insight, or genius, tending to make him guess those laws aright, or nearly aright...This would be impossible unless the ideas that are naturally predominant in their minds was true...The history of science, especially the early history of modern science, on which I had the honor of giving some lectures in this hall some years ago, completes the proof of showing how few were the guesses that men surpassing genius had to make before they rightly guessed the laws of nature...
Ken G
#473
Dec15-11, 02:52 PM
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Quote Quote by bohm2 View Post
Thus, some have argued that theoretical physics is one of those areas where some of "those rays of light" have penetrated somewhat thus allowing for genuine progress/"deeper" understanding, etc.
Indeed, there is no reason to dispute that-- nor anything in that first Pierce quote. It's all demonstrably true, but only because the quote clearly separates "aspects of the world" from "properties of the human mind/brain" (which I am associating with aspects of physics theories created by the mind/brain, not the biology of the mind/brain which is its own set of theories and is no clearer than aspects of the world). Where it gets sticky is when we ask, what is the connection between an aspect of the world and a property of a theory? The naive realist says they are exactly the same thing, the reductionist realist says they reduce to the same building blocks for all scientific purposes (including theorems like the PBR theorem), and the structural realist says they are only "structurally" the same, which again is all that matters for doing science (but might not be appropriate to use as an axiom in theorems because it's not clear how "structurally similar" they really are).

Of course the idealist says they are exactly the same also, but only because there is no such thing as aspects of the world since they are merely projections of the properties of the mind/brain. Still, this is also what naive realism concluded for different reasons, so once again we see that too naive a form of realism is just idealism in disguise, and we need to move well down towards "structural" forms to get away from idealism, as the latter is supposed to be the antithesis of realism.

So I think Pierce is completely right there, but the sticky point is what will we make of this "ray of light", why we do achieve such great successes with our models in certain well defined (and highly selective) circumstances? When we get "genuine understanding", does that mean something different from "very effective understanding"? Can understanding be something different from knowing the "true nature" of something? I agree that Pierce's suggestion that we have these successes because our minds are evolved to have them is not convincing-- the human brain evolved to use basic logic, not quantum mechanics. But maybe basic logic is some kind of building block that is somehow embedded in reality (the rationalist dream)-- or maybe it's just that logic is flexible enough to fashion almost any kind of tool that will then go out and work at some job. I've always felt the claim that "it wouldn't work so well unless it were true" is like saying "a saw wouldn't be so effective at cutting down trees if trees weren't made for cutting down by saws."
bohm2
#474
Dec15-11, 03:22 PM
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Quote Quote by Ken G View Post
Indeed, there is no reason to dispute that-- nor anything in that first Pierce quote.
So I don't get screamed at, I got the first quote from Lycan who is actually quoting Chomsky not Pierce but Chomsky is receptive to some of Pierce's insights on this issue (the second quote which is Pierce's) but Chomsky doesn't agree with Pierce's conclusions; that is, with Peirce's idea that

nature fecundates the mind of man with ideas which when those ideas grow up, will resemble their father, Nature.
Peirce seems to think that since the laws of nature were used in the design of our mental structures, it will allow us to have access to those laws (e.g. our models will be close approximations to the "true" mind-independent laws/reality).
Ken G
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Dec15-11, 03:41 PM
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OK, thanks for correcting that, I wasn't sure if that first quote was supposed to be Peirce. I suspect Peirce would have agreed with it anyway-- it's more his idea that "nature fecundates the mind" that seems controversial here. I don't agree with Peirce on that score because it ignores the phenomenon described by S. J. Gould, summarized on his Wiki page by "In particular, he considered many higher functions of the human brain to be the unintended side consequence or by-product of natural selection, rather than direct adaptations." Such "exaptations" are also called "spandrels", after the architectural feature necessitated by the use of arches. The idea is, you might have a brain that evolves to figure its way out of a sabre-tooth tiger battle, but as a consequence of having a brain like that, you might also inherit the ability to do quantum mechanics. It's not that the quantum mechanics is selected for, and it's not that the selection process is ruled by quantum mechanics, it is simply that a brain capable of doing logic has to be capable of doing quantum mechanics (though some students might not agree!).
bohm2
#476
Dec15-11, 04:00 PM
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Quote Quote by Ken G View Post
Such "exaptations" are also called "spandrels", after the architectural feature necessitated by the use of arches. The idea is, you might have a brain that evolves to figure its way out of a sabre-tooth tiger battle, but as a consequence of having a brain like that, you might also inherit the ability to do quantum mechanics. It's not that the quantum mechanics is selected for, and it's not that the selection process is ruled by quantum mechanics, it is simply that a brain capable of doing logic has to be capable of doing quantum mechanics (though some students might not agree!).
Yes, we discussed this in another thread, I think? See link below. The basic argument was that this ability (to do abstract mathematics/language) so useful in doing physics/science wasn't selected for but may have been put there for "physical reasons" (e.g. space limitations of evolution of larger brain) as S. J. Gould argued. See See post #266 of this thread:

http://www.physicsforums.com/showthr...523765&page=17

They basically argue that this uniquely human part of our language faculty (FLN-see links for details) having the properties of recursion (also found in our mathematical abilities) emerged in human brains for "physical" reasons yet to be fully comprehended; but unlike most innatists/ nativists (e.g. Pinker/Jackendoff) the reasons suggested are not due to "natural selection" but instead are guided by principles of elegance and compactness (not "tinkering" in Pinker’s sense, I guess). So to give one example, "why did Helium evolve after Hydrogen in the evolution our universe", etc. It wasn’t for reasons of "natural selection" in any sense of the term. There were physical laws dictating it that it occur. Same with this uniquely human abstract abilities in language and mathematics (or so, it is argued by this position).

Assuming this position is accurate, what I’m having trouble understanding is this:

1. Does this make it any easier to understand why our ability to do higher mathematics is so useful in studying physical phenomena even though it did not evolve for reasons of “natural selection” (or so, they argue); that is, does evolution of abstract mental structures (from more primitive language and mathematical cognitive structures) that is guided by physical law versus natural selection make it more plausible why mathematics is so useful for doing physics, etc?

2. What would be the implications (if any) on the mind-body problem, if this view is accurate?

3. If accurate would this strengthen, weaken or have no effect on Peirce's notion that "nature fecundates the mind of man with ideas which when those ideas grow up, will resemble their father, Nature". I'm hoping 'strengthen', since Chomsky's more skeptical position with respect to knowledge (ie. match between our mental constructs and "true" laws) is something I would like to avoid, even though I find it pretty convincing.
bohm2
#477
Dec20-11, 09:00 PM
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I thought this was an interesting quote by Matt Leifer on his most recent comment on his blog:

Generally speaking, I think that PBR will turn out to be the strongest of the no-go results, which is why I am so keen on promoting it. I think it may imply all of the others in some suitable sense. For example, given PBR, the EPR argument is enough to establish nonlocality, without having to bother with Bell inequalities.
ThomasT
#478
Dec20-11, 10:48 PM
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Quote Quote by bohm2 View Post
I thought this was an interesting quote by Matt Leifer on his most recent comment on his blog:
Quote Quote by Matt Leifer
Generally speaking, I think that PBR will turn out to be the strongest of the no-go results, which is why I am so keen on promoting it. I think it may imply all of the others in some suitable sense. For example, given PBR, the EPR argument is enough to establish nonlocality, without having to bother with Bell inequalities.
Hi bohm2. What does Leifer mean by "nonlocality"?
bohm2
#479
Dec20-11, 11:15 PM
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Quote Quote by ThomasT View Post
What does Leifer mean by "nonlocality"?
At the least, some type of superluminal "influence", I think.
ThomasT
#480
Dec21-11, 12:08 AM
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Quote Quote by bohm2 View Post
At the least, some type of superluminal "influence", I think.
That's understandably and, imho, unacceptably, vague. Nonlocality is defined by some (most? ... I don't know) quantum physicists as referring to entangled quantum states, which might ultimately refer to ftl propagations or not. No way to currently make that leap, afaik.

But wrt EPR, afaik, the term 'nonlocality' refers to instantaneous 'effects'. That is, events that happen at the same time. So, there's no ftl propagation involved in EPR 'nonlocality'. Or in Bell 'nonlocality' for that matter, afaik.

It seems that the term "nonlocality" is taken, by some, to refer to ftl propagations. But there doesn't seem to me to any evidence for that assumption.

Can you tie this into the OP, ie., the acceptability of the statistical interpretation of QM?
bohm2
#481
Dec21-11, 01:00 AM
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Quote Quote by ThomasT View Post
That's understandably and, imho, unacceptably, vague. Nonlocality is defined by some (most? ... I don't know) quantum physicists as referring to entangled quantum states, which might ultimately refer to ftl propagations or not.
With respect to the OP, I'm not sure what you are asking. If one buys Leifer's argument, it's pretty clear which models PBR scraps. With respect to non-locality, some physicists (e.g. Bell, Maudlin, Laudisa, Norsen, etc.) interpreted Bell's theorem as already implying non-locality (ftl) irrespective of "realism" issues. Others, however, did not interpret Bell's theorem in that way. I think it has to be vague (e.g. "influence") because some have argued that non-locality does not imply incompatibility with relativity since it may depend on which interpretation of relativity is true. A Lorentzian interpretation of relativity (single preferred frame) is compatible with non-locality. Does this mean just some finite v>c or instantaneous influence? I think it implies the latter. Here's what Bell wrote on non-locality implied by his theorem:

I think it’s a deep dilemma, and the resolution of it will not be trivial; it will require a substantial change in the way we look at things. But I would say that the cheapest resolution is something like going back to relativity as it was before Einstein, when people like Lorentz and Poincare thought that there was an aether -a preferred frame of reference-but that our measuring instruments were distorted by motion in such a way that we could not detect motion through the aether...that is certainly the cheapest solution. Behind the apparent Lorentz invariance of the phenomena, there is a deeper level which is not Lorentz invariant...what is not sufficiently emphasized in textbooks, in my opinion, is that the pre-Einstein position of Lorentz and Poincar´e, Larmor and Fitzgerald was perfectly coherent, and is not inconsistent with relativity theory. The idea that there is an aether, and these Fitzgerald contractions and Larmor dilations occur, and that as a result the instruments do not detect motion through the aether - that is a perfectly coherent point of view...The reason I want to go back to the idea of an aether here is because in these EPR experiments there is the suggestion that behind the scenes something is going faster than light. Now if all Lorentz frames are equivalent, that also means that things can go backwards in time...[this] introduces great problems, paradoxes of causality, and so on. And so it is precisely to avoid these that I want to say there is a real causal sequence which is defined in the aether.”
More recently a number of "realist" spontaneous collapse and Bohmian interpretations that are Lorenz-invariant (and even narrative) have been developed:

http://arxiv.org/PS_cache/arxiv/pdf/...111.1425v1.pdf
http://arxiv.org/PS_cache/quant-ph/p.../0406094v2.pdf
http://xxx.lanl.gov/abs/1002.3226

But I have come across some criticisms about these models as well (for example, Valentini). From Towler's site:

Valentini’s Aristotelian spacetime: Galilean invariance not a fundamental symmetry of the standard low-energy pilot-wave theory. The search for a Lorentz-invariant extension thus seems misguided. In Valentini’s view, the difficulties encountered in such a search are no reflection on the plausibility of the pilot-wave theory. Rather, they show that the theory is not being interpreted correctly. Pilot-wave theory then has a remarkable internal logic - both structure of dynamics, and operational possibility of nonlocal signalling away from equilibrium (see later) independently point to existence of natural preferred state of rest.
http://www.tcm.phy.cam.ac.uk/~mdt26/...ures/bohm5.pdf
ThomasT
#482
Dec21-11, 01:43 AM
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Quote Quote by bohm2 View Post
I'm not sure what you are asking.
I'm not really asking anything. Just stating my opinion wrt my admittedly limited take on the current state of affairs. Wrt which I welcome any criticisms you might be inclined to offer.

Quote Quote by bohm2 View Post
If one buys Leifer's argument, it's pretty clear which models PBR scraps.
Well, no, I don't buy Leifer's take on things.

Quote Quote by bohm2 View Post
With respect to non-locality, some physicists (e.g. Bell, Maudlin, Laudisa, Norsen, etc.) interpreted Bell's theorem as already implying non-locality (ftl) irrespective of "realism" issues.
Bell didn't speak of FTL, he spoke of instantaneous effects. Big difference, imo. Norsen is just wrong in his analysis, imho. Don't know about the others you mention.

Quote Quote by bohm2 View Post
Others, however, did not interpret Bell's theorem in that way.
Indeed, imo, the most sophisticated analyses of Bell's theorem interpret it as being applicable only to formalizations of quantum entanglement and not informing wrt nature.

Quote Quote by bohm2 View Post
I think it has to be vague (e.g. "influence") because some have argued that ftl does not imply incompatibility with relativity since it may depend on which interpretation of relativity is true.
SR is pretty clear imo. No matter what interpretation is assumed. It states that there's a limit on the propagational speed of material objects.

Quote Quote by bohm2 View Post
A Lorentzian interpretation of relativity (single preferred frame) is compatible with non-locality.
Not if nonlocality is taken to refer to acceleration to faster than light propagations of material entities. And if we're not talking about that, then we might as well be talking about pink unicorns or whatever.

Quote Quote by bohm2 View Post
Does this mean just some finite v>c or instantaneous influence? I think it implies the latter.
The problem is that "instantaneous influence" doesn't imply ftl progagation, it implies that event B is happening at the same time as event A. There's no propagation, ftl or whatever, involved.
bohm2
#483
Dec21-11, 02:22 AM
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Quote Quote by ThomasT View Post
Well, no, I don't buy Leifer's take on things.
Why?
ThomasT
#484
Dec21-11, 02:30 AM
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Quote Quote by bohm2 View Post
Why?
Because I don't think that Bell's theorem informs wrt physical reality -- but only wrt viable formalisms.
bohm2
#485
Jan31-12, 08:07 PM
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A very interesting paper that came out today. Two of the authors are the same as per PBR in this thread:
Many quantum physicists have suggested that a quantum state does not represent reality directly, but rather the information available to some agent or experimenter. This view is attractive because if a quantum state represents only information, then the collapse of the quantum state on measurement is possibly no more mysterious than the Bayesian procedure of updating a probability distribution on the acquisition of new data. In order to explore the idea in a rigorous setting, we consider models for quantum systems with probabilities for measurement outcomes determined by some underlying physical state of the system, where the underlying state is not necessarily described by quantum theory. A quantum state corresponds to a probability distribution over the underlying physical states, in such a way that the Born rule is recovered. We show that models can be constructed such that more than one quantum state is consistent with a single underlying physical state-in other words the probability distributions corresponding to distinct quantum states overlap. A recent no-go theorem states that such models are impossible. The results of this paper do not contradict that theorem, since the models violate one of its assumptions: they do not have the property that product quantum states are associated with independent underlying physical states.
The quantum state can be interpreted statistically
http://lanl.arxiv.org/pdf/1201.6554.pdf

Edit: This sounds similar to Demystifier's criticism of PBR's assumptions? This is from Demystifier's earlier post (#95) from this thread:

In short, they try to show that there is no lambda satisfying certain properties. The problem is that the CRUCIAL property they assume is not even stated as being one of the properties, probably because they thought that property was "obvious". And that "obvious" property is today known as non-contextuality. Indeed, today it is well known that QM is NOT non-contextual. But long time ago, it was not known. A long time ago von Neumann has found a "proof" that hidden variables (i.e., lambda) were impossible, but later it was realized that he tacitly assumed non-contextuality, so today it is known that his theorem only shows that non-contextual hidden variables are impossible. It seems that essentially the same mistake made long time ago by von Neumann is now repeated by those guys here.

Let me explain what makes me arrive to that conclusion. They first talk about ONE system and try to prove that there is no adequate lambda for such a system. But to prove that, they actually consider the case of TWO such systems. Initially this is not a problem because initially the two systems are independent (see Fig. 1). But at the measurement, the two systems are brought together (Fig. 1), so the assumption of independence is no longer justified. Indeed, the states in Eq. (1) are ENTANGLED states, which correspond to not-independent systems. Even though the systems were independent before the measurement, they became dependent in a measurement. The properties of the system change by measurement, which, by definition, is contextuality. And yet, the authors seem to tacitly (but erroneously) assume that the two systems should remain independent even at the measurement. In a contextual theory, the lambda at the measurement is NOT merely the collection of lambda_1 and lambda_2 before the measurement, which the authors don't seem to realize.
Ken G
#486
Feb1-12, 01:32 AM
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That helps put words to my earlier objection also, the reliance on the idea that "properties" determine outcomes. This I believe is the same idea as "non-contextuality", because we normally think of a "property" as something that exists in and of itself, independently of anything else. That's what I was imagining they meant by "properties", and I objected to their claim that it would be "radical" to reject that assumption. I think Demystifier put a more accurate word to it: non-contextual properties. Or another way to put it might be, reductionist properties rather than holistic elements of the system and its interactions.


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