Does Decoherence and Entropy Relate to the Second Law of Thermodynamics?

[Ken G]

You'll also benefit from reading this:

Niels Bohr's Interpretation and the Copenhagen Interpretation—Are the Two Incompatible?
Ravi Gomatam
http://www.journals.uchicago.edu/doi/abs/10.1086/525618
http://www.bvinst.edu/gomatam/pub-2007-01.pdf

If you read my actual words, you'll note I mentioned that all kinds of things get claimed to be "the Copenhagen Interpretation", most of them coming from those who don't understand it. That's why I base my meaning for that expression on one source-- Nils Bohr, because what we are really talking about here (as I've said) is the minimal ontology necessary to make quantum mechanics make sense, which I believe is the core motivation Bohr used in his thinking. In short, no ontology past the epistemology, that is the defining character I have been talking about all along, and said I was using that as what the CI should mean. So to claim that Bohr's view was incompatible with the CI is to be using the wrong CI, a point I've already made myself repeatedly.

 

[Maaneli]

So to claim that Bohr's view was incompatible with the CI is to be using the wrong CI, a point I've already made myself repeatedly.

Actually, to claim Bohr's view is compatible with the "CI" is to ignore everything that Neils Bohr actually said, and to be confusing by using a term that clearly has a different meaning. I guess you didn't bother yet to even read the abstracts of those papers I gave you.

 

[Maaneli]

Neither one of those interpretations tells me a thing about coupling to classical systems (i.e., measurement) that is not axiomatically present in the CI.

This sentence makes no sense to me because I don't know what you mean by "axiomatically present in the CI".

Until you can supply a testable outcome, it all sounds to me like your earlier disastrous claim that these are "theories that underlie useful theories". Not too successful then, was it?

With all due respect, the only thing that sounds disasterous here is your understanding of CI, Neils Bohr, and the interpretation of quantum mechanics in general. It isn't surprisng either that you misunderstood my earlier comment. I guess you've never heard about intertheoretic relations, i.e. the quantum-classical limit, the statistical mechanics-thermodynamics limit, the relativistic-nonrelativistic mechanics limit, etc.. For example, nonrelativistic Hamilton-Jacobi classical mechanics is an approximate and special case of nonrelativistic quantum hydrodynamics (the limit when the quantum potential is small relative to the classical kinetic and potential energy), the latter being the more general theory that underlies the former theory (which is obviously much more more practical and useful for classical mechanics problems like a mass on a spring).

Cheers,
Maaneli

 

[Ken G]

Actually, to claim Bohr's view is compatible with the "CI" is to ignore everything that Neils Bohr actually said, and to be confusing by use a term that clearly has a different meaning. I guess you didn't bother yet to even read the abstracts of those papers I gave you.

None of those abstracts refute anything I've said in this thread. It is you who are trying to change the debate, from the logical point I have been constantly directing it ("what is the minimal ontology needed to make quantum mechanics make sense") into a pointless semantic direction ("what is meant by the Copenhagen Interpretation", which itself will depend on who you ask and what is Heisenberg's influence). I can only repeat myself yet again: what I have referred to as the CI is what I perceive to be a heroic effort by Bohr to keep the ontology of quantum mechanics focused expressly on what is absolutely necessary, to wit its epistemology, and to avoid any excursions into the land of pure magical thinking where angels dancing on pins tell us all the things we cannot hear, and explain to us all the things we cannot know. If you want to have a debate over what other people mean when they talk about the Copenhagen interpretation, that might be an interesting thread. This thread focuses squarely on the following claim, as I have advanced in detail in all my posts:

"Quantum mechanics is fundamentally not a theory about quantum systems, it is a theory about what happens to quantum systems when you couple them to systems that we know we can rely on to behave classically. The meaning of classical behavior is that there is an enormous amount of noise and lost and untracked information, which fundamentally alters the vocabulary we can use to describe it. All of science has been built around that classical vocabulary, so all we are doing here is applying the philosophy of science directly to the interpretation of quantum mechanics, given that quantum mechanics should be considered a science, not a separate philosophy."

I strongly suspect Bohr would completely agree with that remark, which is the sole reason I've characterized that as the "CI" (also because 2 letters is shorter than a whole paragraph). The crucial salient feature of that overall philosophy is that coupling to classical instruments leads to decoherence (Bohr only understood this would happen, without a detailed description of how), which evolves superposition states into mixed states when you project onto the substate whose behavior is being described by the theory. Such mixed states are perfectly classical objects, and we know just how to deal with them classically. For one thing, they are not ontological objects, they are descriptive objects, just as they are classically.

Some have called this a mysterious "wavefunction collapse", and claim it is some bizarre feature of the CI, but it is no more mysterious in quantum mechanics than it is classically, where it already existed for a long time with no philosophical difficulties. Thus it makes perfect sense that it should also happen in quantum mechanics when we cross over the "Heisenberg cut", and we know perfectly well what to do with things on the classical side of that cut-- we do science on them.

As I also said, those who take issue with that basic statement, and instead require embellished ontologies like MWI, often use some exaggerated or awkward meaning of the CI, to the point that it is essentially a straw man argument. Note further that any evidence you can bring that Bohr did not agree with those straw men arguments other people cite when they describe the "CI" only underscores precisely what I am saying here.

 

[Maaneli]

Not too successful then, was it?

Not in the particular direction that Bohm took it (although it was a very logical thing to try and do); but in case you didn't know, the de Broglie-Bohm theory makes all the same predictions as textbook QM, to the extent that the predictions of the latter are unambiguous. And it also provides distinct computational advantages over textbook QM for many physical systems. Finally, even though Bohm looked for empirical deviations from QM in high energy particle physics experiments, the basic arguments he used to expect the possibility of this from the pilot-wave theory are quite valid (in fact, they are just as valid as the prediction of nonequilibrium particle distributions in classical statistical mechanics) and have recently been used by Antony Valentini to show that quantum nonequilibrium (deviations from the Born rule probability distribution) are quite likely and empirically testable within precision tests of cosmology (such as the fluctuations in the CMB radiation predicted by inflationary cosmology).

 

[Maaneli]

None of those abstracts refute anything I've said in this thread. It is you who are trying to change the debate, from the logical point I have been constantly directing it ("what is the minimal ontology needed to make quantum mechanics make sense") into a pointless semantic direction ("what is meant by the Copenhagen Interpretation", which itself will depend on who you ask and what is Heisenberg's influence). I can only repeat myself yet again: what I have referred to as the CI is what I perceive to be a heroic effort by Bohr to keep the ontology of quantum mechanics focused expressly on what is absolutely necessary, to wit its epistemology, and to avoid any excursions into the land of pure magical thinking where angels dancing on pins tell us all the things we cannot hear, and explain to us all the things we cannot know. If you want to have a debate over what other people mean when they talk about the Copenhagen interpretation, that might be an interesting thread. This thread focuses squarely on the following claim, as I have advanced in detail in all my posts:

"Quantum mechanics is fundamentally not a theory about quantum systems, it is a theory about what happens to quantum systems when you couple them to systems that we know we can rely on to behave classically. The meaning of classical behavior is that there is an enormous amount of noise and lost and untracked information, which fundamentally alters the vocabulary we can use to describe it. All of science has been built around that classical vocabulary, so all we are doing here is applying the philosophy of science directly to the interpretation of quantum mechanics, given that quantum mechanics should be considered a science, not a separate philosophy."

I strongly suspect Bohr would completely agree with that remark, which is the sole reason I've characterized that as the "CI" (also because 2 letters is shorter than a whole paragraph). The crucial salient feature of that overall philosophy is that coupling to classical instruments leads to decoherence (Bohr only understood this would happen, without a detailed description of how), which evolves superposition states into mixed states when you project onto the substate whose behavior is being described by the theory. Such mixed states are perfectly classical objects, and we know just how to deal with them classically. Some have called this a mysterious "wavefunction collapse", but it is not mysterious at all-- it is the crossing of the "Heisenberg cut", and we know perfectly well what to do with things on the classical side of that cut-- we do science on them.

As I also said, those who take issue with that basic statement, and instead require embellished ontologies like MWI, often use some exaggerated or awkward meaning of the CI, to the point that it is essentially a straw man argument. Note further that any evidence you can bring that Bohr did not agree with those straw men arguments other people cite when they describe the "CI" only underscores precisely what I am saying here.

For the sake of being clear and accurate, why don't you just refer to "Bohr's Interpretation" or BI, instead of CI (which definitely refers to something else, mainly Heisenberg's interpretation, as I have already pointed out).

Bohr philosophy of QM was certainly a predecessor to the decoherence methodology - but it was hardly an adequate approach to treating the quantum-classical limit. Indeed Bohr's philosophy (which was not nearly as precise as that paragraph you write explaining your POV) is operationally useless when it comes to detailed problems in quantum chaos and semiclassical physics. The textbook QM formalism (which doesn't include decoherence) plus BI is simply inadequate in dealing with these problems. That is why the details of the decoherence formalism is necessary.

Nevertheless, your earlier claim about the intentions of the other interpretations of QM was simply incorrect; and that was my issue to start with.

 

[Ken G]

This sentence makes no sense to me because I don't know what you mean by "axiomatically present in the CI".

Then I shall clarify-- the CI assumed that decoherence would occur when you couple to a classical instrument. Period, that's all it ever had to assume, as an axiom. Think of how happy it was to have a way of describing the validity of that assumption in greater detail. The only ontological structure the CI now needs is the idea that a mixed state is a statistical description-- just as it had always been classically. It is the MWI that requires it be more than that, a mixed state has to be a projection of a pure state that includes macro instruments (all the way up to the observer themself), never mind that no specification of that pure state ever occurs. The axioms of the CI don't need it to occur-- that's its strength, not its weakness (indeed, that is what I consider the defining aspect of the CI, regardless of all the overblown ontologies you see added to it in those papers you cited).

With all due respect, the only thing that sounds disasterous here is your understanding of CI, Neils Bohr, and the interpretation of quantum mechanics in general. It isn't surprisng either that you misunderstood my earlier comment. I guess you've never heard about intertheoretic relations, i.e. the quantum-classical limit, the statistical mechanics-thermodynamics limit, the relativistic-nonrelativistic mechanics limit, etc.. For example, nonrelativistic Hamilton-Jacobi classical mechanics is an approximate and special case of nonrelativistic quantum hydrodynamics (the limit when the quantum potential is small relative to the classical kinetic and potential energy), the latter being the more general theory that underlies the former theory (which is obviously much more more practical and useful for classical mechanics problems like a mass on a spring).

Well if one can argue by name-dropping, I suppose one could interpret that as some kind of refutation of my point. However, if one requires logic, it fails in ways I will be happy to point out in detail. Let's follow your logic, precisely as you frame it above: we conclude my understanding of Bohr is lacking, despite not one single thing I've claimed about Bohr's views being questioned, indeed the evidence there seems to be that he did not agree with the same misunderstood and unwieldy versions of the CI that people talk about all over the place, a point that actually supports what I've said throughout the thread. So that logic falls apart.

How about the logic behind the next conclusion, that my understanding of quantum mechanics is also lacking. Well, the evidence there (this is your logic, word for word) is that I have so far failed to enter into tangential asides about "intertheoretic relations", or I have not demonstrated understanding of "quantum hydrodynamics". However, this logic is fallacious, because in fact I do understand how theories can be turned into each other by taking appropriate limits. I also understand, and mentioned, that quantum mechanics obeys a correspondence principle, so these "intertheoretic relations" you are so proud of come as no kind of illuminating surprise to me.

And as a final analysis of your logic here, I note you echoed your earlier use, despite my already pointing out the flaw in doing so, of the word "underlying", but here in the context of a general theory that makes its own predictions in relation to a less general theory that makes only a subset of those same predictions. Now, as I asked you before, is that really how you see the MWI? You did use that same word "underlying", after all.

Nor do any of your arguments about general theories that include more specific ones have the slightest thing to do with this thread-- this thread is about the question, when we encounter a mixed state description in the act of measuring quantum systems, can we just say that is what we have (as we do classically), or do we suddenly have to embed it in some grandiose pure state that subsumes the observer and the instruments and the whole universe, just because of quantum mechanics, when we never had to do that before quantum mechanics-- and we previously suffered no philosophical angst as a result? But perhaps you still don't see that this is precisely what the thread is about, and prefer to see it as a semantic debate about what should properly be called the CI in light of "intertheoretic relations" between theories that (in obvious contrast to MWI) involve discriminating predictions.

 

[Maaneli]

The crucial salient feature of that overall philosophy is that coupling to classical instruments leads to decoherence (Bohr only understood this would happen, without a detailed description of how), which evolves superposition states into mixed states when you project onto the substate whose behavior is being described by the theory. Such mixed states are perfectly classical objects, and we know just how to deal with them classically. For one thing, they are not ontological objects, they are descriptive objects, just as they are classically.

Some have called this a mysterious "wavefunction collapse", and claim it is some bizarre feature of the CI, but it is no more mysterious in quantum mechanics than it is classically, where it already existed for a long time with no philosophical difficulties. Thus it makes perfect sense that it should also happen in quantum mechanics when we cross over the "Heisenberg cut", and we know perfectly well what to do with things on the classical side of that cut-- we do science on them.

You seem to be under the impression that decoherence alone solves the measurement problem. This is a common misconception that even the major proponents of the decoherence program like Zurek, Zeh, Joos, Vaidman, and Schlosshauer have denounced. The reason is rather simple: decoherence alone does not solve the problem of definite outcomes, namely, why do we experimentally see one unique mixed eigenstate rather than the myriad of others, even though the decoherence mechanism and Schroedinger evolution still predict that the others continue to exist in configuration space? For that matter, if we see only one of the mixed eigenstates as a measurement outcome, what happens to all of the others mixed eigenstates? Moreover, how can one be certain to observe the Born rule distribution for a series of measurement interactions over a finite time interval? You glibly say that we can just "project onto the substate whose behavior is being described by the theory." But aside from the fact that this statement is operationally vague, it also begs the question. I recommend having a read of the first 7 pages of this excellent review article by Maximillien Schlosshauer on the status of the decoherence program:

Decoherence, the measurement problem, and interpretations of quantum mechanics
Authors: Maximilian Schlosshauer
Journal reference: Rev. Mod. Phys. 76, 1267-1305 (2004)
http://arxiv.org/abs/quant-ph/0312059

 

[Ken G]

For the sake of being clear and accurate, why don't you just refer to "Bohr's Interpretation" or BI, instead of CI (which definitely refers to something else, mainly Heisenberg's interpretation, as I have already pointed out).

If the thread were taken as a whole, that clarification would have been unnecessary. Consider, for example, the numerous times I said things like

"All of your criticisms assume it is an ontology, but Bohr never intended it to be that. So there is no "extra mechanism", there's no mechanism at all-- there is the mathematics of making a prediction, that's all "collapse" ever was in the Bohr epistemology."

and

" It's not me that is saying this, it is both Heisenberg and Bohr, but I particularly point to Bohr-- Heisenberg had a tendency to want to stir in some extraneous ontology of his own."

I also, just above, tried to clarify what I meant by the CI, but it is a long thread, and most would not start at the beginning, so for purposes of clarity I will from this point forward indeed use BI not CI to indicate the assumptions I summarized just above. I should also repeat that I am not necessarily claiming to be an expert in Bohr's mental processes, so I am really talking about my interpretation of his approach, but everything I have heard from him supports my contention that he would agree with this interpretation. On that basis I claim it is more than my own personal interpretation.

Bohr philosophy of QM was certainly a predecessor to the decoherence methodology - but it was hardly an adequate approach to treating the quantum-classical limit. Indeed Bohr's philosophy (which was not nearly as precise as that paragraph you write explaining your POV) is operationally useless when it comes to detailed problems in quantum chaos and semiclassical physics.

Of course, it should be no surprise to anyone that there is a gray zone at the "Heisenberg cut". Do you imagine Bohr and Heisenberg were fools? I'm sure they knew they were making an idealization to draw a firewall between classical and quantum systems. We make idealizations like that all the time, we don't think that a single tennis ball's motion can be treated with Newton's laws but a boxful of them suddenly requires thermodynamics. It's no different with the Heisenberg cut, and I'd be very surprised if Bohr or Heisenberg thought it was, though I cannot speak for them. The main thing Heisenberg would have added was a skepticism, reminiscent of Mach, that the quantum systems existed in the form we imagined them. But that's a perfectly reasonable skepticism-- since we always have to pass them through to classical modes of inquiry, it's not surprising when something is lost in translation. I think that observation is the core of what I'm calling the CI (now the BI), and that is just the place where the strawman criticisms begin to appear.

The textbook QM formalism (which doesn't include decoherence) plus BI is simply inadequate in dealing with these problems.

It's inadequate for a lot of other things too, that's not particularly telling.

That is why the details of the decoherence formalism is necessary.

There are a lot of other things that are necessary too, like a closer examination of the idealizatons involved in decoherence! This is just how physics works, we make idealizations and see where they get us. Why does everyone suddenly require a complete ontology when it comes to quantum mechanics? I think it's pure hubris, quantum mechanics is the most advanced theory we have, so it must be a description of the honest to goodness truth. Same mistake every generation of physicist has made-- except Bohr, that's the point.

Nevertheless, your earlier claim about the intentions of the other interpretations of QM was simply incorrect; and that was my issue to start with.

Well, I can't comment on this because I haven't the vaguest idea what you are trying to say. This thread has never been about anything but determining the minimal ontology necessary to support quantum mechanics epistemology. Some claimed that MWI provides that, on the grounds that a sweeping mathematical foundation is always less cumbersome than ad hoc components like a "Heisenberg cut". I countered that all the latter is doing is noticing that all quantum systems are put through a classical filter before we even begin to try to understand their behavior, so the minimal ontology recognizes that we cannot get an ontology for quantum systems that way, we can only get an ontology for how quantum systems couple to the kinds of systems we used to build science, i.e., systems where huge amounts of information are thrown away. That's what this thread is about, going right back to the OP where the whole issue of information and decoherence was first brought up.

 

[Maaneli]

Then I shall clarify-- the CI assumed that decoherence would occur when you couple to a classical instrument. Period, that's all it ever had to assume, as an axiom. Think of how happy it was to have a way of describing the validity of that assumption in greater detail. The only ontological structure the CI now needs is the idea that a mixed state is a statistical description-- just as it had always been classically. It is the MWI that requires it be more than that, a mixed state has to be a projection of a pure state that includes macro instruments (all the way up to the observer themself), never mind that no specification of that pure state ever occurs. The axioms of the CI don't need it to occur-- that's its strength, not its weakness (indeed, that is what I consider the defining aspect of the CI, regardless of all the overblown ontologies you see added to it in those papers you cited).

The "CI" as you twistedly refer to it never mentioned decoherence in the specific form you described. See my last post for a response to your other comments.

Well if one can argue by name-dropping, I suppose one could interpret that as some kind of refutation of my point. However, if one requires logic, it fails in ways I will be happy to point out in detail. Let's follow your logic, precisely as you frame it above: we conclude my understanding of Bohr is lacking, despite not one single thing I've claimed about Bohr's views being questioned, indeed the evidence there seems to be that he did not agree with the same misunderstood and unwieldy versions of the CI that people talk about all over the place, a point that actually supports what I've said throughout the thread. So that logic falls apart.

Actually the logic does make sense. You clearly give Bohr way too much credit when you talk about his "CI" referring to the methodology decoherence. The first decoherence formalism was developed by John Von Neumann and David Bohm; and Bohr never when beyond the detail of vague words like "classical", "measurement", and "interaction". I would think you would know that if you actually read the writings of Bohr. Also, the fact that you still misleadingly refer to Bohr's philosophy as "CI" shows that you don't quite understand how far removed the true CI actually is from Bohr's own ideas (and there is no Bohr version of CI as you seem to think). By the way, Bohr never disputed the idea of realism for QM, and those papers I cite discuss that too.

How about the logic behind the next conclusion, that my understanding of quantum mechanics is also lacking. Well, the evidence there (this is your logic, word for word) is that I have so far failed to enter into tangential asides about "intertheoretic relations", or I have not demonstrated understanding of "quantum hydrodynamics". However, this logic is fallacious, because in fact I do understand how theories can be turned into each other by taking appropriate limits. I also understand, and mentioned, that quantum mechanics obeys a correspondence principle, so these "intertheoretic relations" you are so proud of come as no kind of illuminating surprise to me.

The fact that you initially (and still) failed to understand what I meant by theories underlying theories, tells me that you don't really understand intertheoretic relations despite what you claim (you also have yet to prove that you understood the specific example I provided involving quantum hydrodynamics and the classical limit). On the other hand, Hurkyl seems to have understood my point.

You also are conflating different points of disagreement. I didn't actually say that the evidence for your lack of understanding of the interpretation of QM is just your failure to recognize intertheoretic relations in relation to my comment about theories underlying theories. The evidence for your lack of understanding, I would claim, comes primarily from everything else you have said in this thread with other people.[/QUOTE]

And as a final analysis of your logic here, I note you echoed your earlier use, despite my already pointing out the flaw in doing so, of the word "underlying", but here in the context of a general theory that makes its own predictions in relation to a less general theory that makes only a subset of those same predictions. Now, as I asked you before, is that really how you see the MWI? You did use that same word "underlying", after all.

You have pointed out no flaws whatsoever. Moreover, MWI better be able to provide a clear and empirically adequate account of the quantum-classical limit if it is to be regarded as a serious interpretation of QM.

Nor do any of your arguments about general theories that include more specific ones have the slightest thing to do with this thread-- this thread is about the question, when we encounter a mixed state description in the act of measuring quantum systems, can we just say that is what we have (as we do classically), or do we suddenly have to embed it in some grandiose pure state that subsumes the observer and the instruments and the whole universe, just because of quantum mechanics, when we never had to do that before quantum mechanics-- and we previously suffered no philosophical angst as a result? But perhaps you still don't see that this is precisely what the thread is about, and prefer to see it as a semantic debate about what should properly be called the CI in light of "intertheoretic relations" between theories that (in obvious contrast to MWI) involve discriminating predictions.

Unfortunately for you, this thread involves many parallel issues (even before I arrived) despite where it originally started. Moreover, my comment about general theories that include more specialized ones was very relevant at the time that I raised it. If you're just getting frustrated with the different angles from which people are disagreeing with you, then I would just recommend not biting off more than you can chew in a forum debate.

 

[Maaneli]

If the thread were taken as a whole, that clarification would have been unnecessary. Consider, for example, the numerous times I said things like

"All of your criticisms assume it is an ontology, but Bohr never intended it to be that. So there is no "extra mechanism", there's no mechanism at all-- there is the mathematics of making a prediction, that's all "collapse" ever was in the Bohr epistemology."

and

" It's not me that is saying this, it is both Heisenberg and Bohr, but I particularly point to Bohr-- Heisenberg had a tendency to want to stir in some extraneous ontology of his own."

I also, just above, tried to clarify what I meant by the CI, but it is a long thread, and most would not start at the beginning, so for purposes of clarity I will from this point forward indeed use BI not CI to indicate the assumptions I summarized just above. I should also repeat that I am not necessarily claiming to be an expert in Bohr's mental processes, so I am really talking about my interpretation of his approach, but everything I have heard from him supports my contention that he would agree with this interpretation. On that basis I claim it is more than my own personal interpretation.

Good, I am glad to see these corrections and qualifications in your comments. I would say though that Bohr may not agree with your statements like

"All of your criticisms assume it is an ontology, but Bohr never intended it to be that. So there is no "extra mechanism", there's no mechanism at all-- there is the mathematics of making a prediction, that's all "collapse" ever was in the Bohr epistemology."

Again, please see those philosophy of science papers.

Of course, it should be no surprise to anyone that there is a gray zone at the "Heisenberg cut". Do you imagine Bohr and Heisenberg were fools? I'm sure they knew they were making an idealization to draw a firewall between classical and quantum systems. We make idealizations like that all the time, we don't think that a single tennis ball's motion can be treated with Newton's laws but a boxful of them suddenly requires thermodynamics. It's no different with the Heisenberg cut, and I'd be very surprised if Bohr or Heisenberg thought it was, though I cannot speak for them. The main thing Heisenberg would have added was a skepticism, reminiscent of Mach, that the quantum systems existed in the form we imagined them. But that's a perfectly reasonable skepticism-- since we always have to pass them through to classical modes of inquiry, it's not surprising when something is lost in translation. I think that observation is the core of what I'm calling the CI (now the BI), and that is just the place where the strawman criticisms begin to appear.
It's inadequate for a lot of other things too, that's not particularly telling.There are a lot of other things that are necessary too, like a closer examination of the idealizatons involved in decoherence! This is just how physics works, we make idealizations and see where they get us. Why does everyone suddenly require a complete ontology when it comes to quantum mechanics? I think it's pure hubris, quantum mechanics is the most advanced theory we have, so it must be a description of the honest to goodness truth. Same mistake every generation of physicist has made-- except Bohr, that's the point.

Ultimately, the status of all your conclusions comes down to what extent the decoherence program has completely solved the measurement problem. But, as I already have pointed out, it has not done so as its major proponents also freely admit. That is why we need something more than the minimalist ontology of decohering wavefunctions, i.e. the particles in de Broglie-Bohm theory or the GRW stochastic wavefunction collapse or the many-worlds of Everett.

Well, I can't comment on this because I haven't the vaguest idea what you are trying to say.

Yeah right. Then you are simply shutting your brain off. The rest of what you said was already addressed above.

 

[Maaneli]

If the thread were taken as a whole, that clarification would have been unnecessary. Consider, for example, the numerous times I said things like

"All of your criticisms assume it is an ontology, but Bohr never intended it to be that. So there is no "extra mechanism", there's no mechanism at all-- there is the mathematics of making a prediction, that's all "collapse" ever was in the Bohr epistemology."

and

" It's not me that is saying this, it is both Heisenberg and Bohr, but I particularly point to Bohr-- Heisenberg had a tendency to want to stir in some extraneous ontology of his own."

I also, just above, tried to clarify what I meant by the CI, but it is a long thread, and most would not start at the beginning, so for purposes of clarity I will from this point forward indeed use BI not CI to indicate the assumptions I summarized just above. I should also repeat that I am not necessarily claiming to be an expert in Bohr's mental processes, so I am really talking about my interpretation of his approach, but everything I have heard from him supports my contention that he would agree with this interpretation. On that basis I claim it is more than my own personal interpretation.

Of course, it should be no surprise to anyone that there is a gray zone at the "Heisenberg cut". Do you imagine Bohr and Heisenberg were fools? I'm sure they knew they were making an idealization to draw a firewall between classical and quantum systems. We make idealizations like that all the time, we don't think that a single tennis ball's motion can be treated with Newton's laws but a boxful of them suddenly requires thermodynamics. It's no different with the Heisenberg cut, and I'd be very surprised if Bohr or Heisenberg thought it was, though I cannot speak for them. The main thing Heisenberg would have added was a skepticism, reminiscent of Mach, that the quantum systems existed in the form we imagined them. But that's a perfectly reasonable skepticism-- since we always have to pass them through to classical modes of inquiry, it's not surprising when something is lost in translation. I think that observation is the core of what I'm calling the CI (now the BI), and that is just the place where the strawman criticisms begin to appear.
It's inadequate for a lot of other things too, that's not particularly telling.There are a lot of other things that are necessary too, like a closer examination of the idealizatons involved in decoherence! This is just how physics works, we make idealizations and see where they get us. Why does everyone suddenly require a complete ontology when it comes to quantum mechanics? I think it's pure hubris, quantum mechanics is the most advanced theory we have, so it must be a description of the honest to goodness truth. Same mistake every generation of physicist has made-- except Bohr, that's the point.
Well, I can't comment on this because I haven't the vaguest idea what you are trying to say. This thread has never been about anything but determining the minimal ontology necessary to support quantum mechanics epistemology. Some claimed that MWI provides that, on the grounds that a sweeping mathematical foundation is always less cumbersome than ad hoc components like a "Heisenberg cut". I countered that all the latter is doing is noticing that all quantum systems are put through a classical filter before we even begin to try to understand their behavior, so the minimal ontology recognizes that we cannot get an ontology for quantum systems that way, we can only get an ontology for how quantum systems couple to the kinds of systems we used to build science, i.e., systems where huge amounts of information are thrown away. That's what this thread is about, going right back to the OP where the whole issue of information and decoherence was first brought up.

WOW! What a coincidence that I just found this paper:

The quantum-to-classical transition: Bohr's doctrine of classical concepts, emergent classicality, and decoherence
Authors: Maximilian Schlosshauer, Kristian Camilleri

It is now widely accepted that environmental entanglement and the resulting decoherence processes play a crucial role in the quantum-to-classical transition and the emergence of "classicality" from quantum mechanics. To this extent, decoherence is often understood as signifying a break with the Copenhagen interpretation, and in particular with Bohr's view of the indispensability of classical concepts. This paper analyzes the relationship between Bohr's understanding of the quantum-classical divide and his doctrine of classical concepts and the decoherence-based program of emergent classicality. By drawing on Howard's reconstruction of Bohr's doctrine of classical concepts, and by paying careful attention to a hitherto overlooked disagreement between Heisenberg and Bohr in the 1930s about the placement of the quantum-classical "cut," we show that Bohr's view of the quantum-classical divide can be physically justified by appealing to decoherence. We also discuss early anticipations of the role of the environment in the quantum-classical problem in Heisenberg's writings. Finally, we distinguish four different formulations of the doctrine of classical concepts in an effort to present a more nuanced assessment of the relationship between Bohr's views and decoherence that challenges oversimplified statements frequently found in the literature.
Submitted to Studies in History and Philosophy of Modern Physics
http://arxiv.org/abs/0804.1609

 

[Ken G]

The "CI" as you twistedly refer to it never mentioned decoherence in the specific form you described. See my last post for a response to your other comments.

I think you mean it never mentioned the word decoherence. So what? It certainly did rely on the effects of decoherence-- that's how you get the mixed state after a classical coupling. Don't you think?

Actually the logic does make sense. You clearly give Bohr way too much credit when you talk about his "CI" referring to the methodology decoherence.

Well, since I never claimed such a "reference", I cannot see how that rescues your logic.

The first decoherence formalism was developed by John Von Neumann and David Bohm; and Bohr never when beyond the detail of vague words like "classical", "measurement", and "interaction".

I have never implied anything else-- I implied that decoherence fits into these words, perfectly in fact.

I would think you would know that if you actually read the writings of Bohr.

Now that's just silly to try and pass off as an evidential remark.

Also, the fact that you still misleadingly refer to Bohr's philosophy as "CI" shows that you don't quite understand how far removed the true CI actually is from Bohr's own ideas

Where "true CI" is defined by... you? Even that I have not seen-- you haven't said a single thing that even remotely defines the terms you use.

By the way, Bohr never disputed the idea of realism for QM, and those papers I cite discuss that too.

By the way, I never disputed that Bohr was a realist-- in that he would have imagined that quantum systems were real. The issue of the thread has always been, how do we establish the properties of those real things. As I just keep having to repeat, in hopes that it will eventually register, the core of what Bohr is saying, in my view, is that we face fundamental limitations in establishing those properties. The fundamental limitations have to do with our insistence on doing science, and all that that entails-- including reliance on classical instruments and a classically functioning brain.

The fact that you initially (and still) failed to understand what I meant by theories underlying theories, tells me that you don't really understand intertheoretic relations despite what you claim (you also have yet to prove that you understood the specific example I provided involving quantum hydrodynamics and the classical limit). On the other hand, Hurkyl seems to have understood my point.

No, the real problem here is you chose not to provide an operational definition, or indeed any definition, of a "theory", and still have not. I cannot show you the error in your argument until you provide such a definition, because it is impossible to tell if the flaw comes in your definition of that word, or its application to your argument.

The evidence for your lack of understanding, I would claim, comes primarily from everything else you have said in this thread with other people.

About which you have demonstrated, quite frankly, nothing but misinterpretation. I cannot be responsible for your misinterpretations of what I'm saying, I can only point them out if you choose to actually refer to them in some explicit kind of way-- as I have done with each and every one so far.

Unfortunately for you, this thread involves many parallel issues (even before I arrived) despite where it originally started.

You see that as "unfortunate"? Strange.

Moreover, my comment about general theories that include more specialized ones was very relevant at the time that I raised it.

No it wasn't, and I already told you exactly why. Look at the words you just used, in fact, and ask yourself: do they describe the MWI? Again, I repeat my request that you define "scientific theory".

If you're just getting frustrated with the different angles from which people are disagreeing with you, then I would just recommend not biting off more than you can chew in a forum debate.

You obviously know nothing about me at all. I have been maintaining a perfectly logical line of reasoning throughout this thread, against every opposition. Some of the opposition was inquisitive, forthcoming with evidence, and constructive (notably vanesch and ueit), and some was bombastic and largely devoid of actual evidential arguments that went beyond rhetorical assertions. But in all cases, I pressed the logic of my position, and there has not been a single singificant flaw pointed to. So why would I be "frustrated"? In fact I feel quite buoyed by my success at maintaining the viability of a position that has lately fallen into some disfavor among those who mix their physics and metaphysics in equal doses. This stance is largely summed up by the confirmation you provide me in the next post.

 

[Ken G]

WOW! What a coincidence that I just found this paper:
...By drawing on Howard's reconstruction of Bohr's doctrine of classical concepts, and by paying careful attention to a hitherto overlooked disagreement between Heisenberg and Bohr in the 1930s about the placement of the quantum-classical "cut," we show that Bohr's view of the quantum-classical divide can be physically justified by appealing to decoherence. ...[/B]

I am in your debt for finding a paper that concludes exactly the same thing I have been saying this whole thread. If you don't realize that this is a virtually perfect statement of my fundamental thesis, perhaps I have a better chance of being understood by some of the others with whom I've been holding this conversation.

 

[Maaneli]

I think you mean it never mentioned the word decoherence. So what? It certainly did rely on the effects of decoherence-- that's how you get the mixed state after a classical coupling. Don't you think?

No, Bohr never went beyond the detail of vague words like "classical" and "measurement".

Well, since I never claimed such a "reference", I cannot see how that rescues your logic. I have never implied anything else-- I implied that decoherence fits into these words, perfectly in fact.

Haha, now you're clearly backing off your original rhetoric. You most certainly were suggesting that Bohr's philosophy involved decoherence, and you never bothered to make the distinction that Bohr never talked about such a thing, until I came along.

Now that's just silly to try and pass off as an evidential remark. Where "true CI" is defined by... you? Even that I have not seen-- you haven't said a single thing that even remotely defines the terms you use.

Actually I did say the "true CI" is mainly composed of Heisenberg's interpretation of QM. I guess you conveniently decided to ignore that.

By the way, I never disputed that Bohr was a realist-- in that he would have imagined that quantum systems were real. The issue of the thread has always been, how do we establish the properties of those real things. As I just keep having to repeat, in hopes that it will eventually register, the core of what Bohr is saying, in my view, is that we face fundamental limitations in establishing those properties. The fundamental limitations have to do with our insistence on doing science, and all that that entails-- including reliance on classical instruments and a classically functioning brain.

You imply in many instances that Bohr is a logical positivist (just as you are), by claiming that you think he would agree with many of your statements. And you provide no evidence for that claim with respect to Bohr.

No, the real problem here is you chose not to provide an operational definition, or indeed any definition, of a "theory", and still have not. I cannot show you the error in your argument until you provide such a definition, because it is impossible to tell if the flaw comes in your definition of that word, or its application to your argument.

I think it's pretty clear what I mean when I say Hamilton-Jacobi mechanics is a theory or that quantum hydrodynamics is a theory. If you want something a little more specific: the mathematical equations, the implied physical ontology from those equations, and the resultant empirical predictions, all constitute a physical theory. In short, physical theories are approximate models of physical reality. I'm not going beyond that because I think you're trying to be captious.

You see that as "unfortunate"? Strange.

. I see it as unfortunate for YOU given your openly stated dislike for having many parallel issues in a thread.

No it wasn't, and I already told you exactly why. Look at the words you just used, in fact, and ask yourself: do they describe the MWI? Again, I repeat my request that you define "scientific theory".

I already answered this. I guess you conveniently decided to ignore that answer too eh?

You obviously know nothing about me at all.

Actually I know enough about you.

So why would I be "frustrated"? In fact I feel quite buoyed by my success at maintaining the viability of a position that has lately fallen into some disfavor among those who mix their physics and metaphysics in equal doses.

I think it's pretty suspicious how you have entirely ignored the elephant in the room that I mentioned multiple times already, and then go on to proclaim your logic as perfectly consistent. I will raise it again with the hope that you'll be honest with yourself about it: the issue of whether decoherence theory alone is or can be considered a solution to the measurement problem.

This stance is largely summed up by the confirmation you provide me in the next post.

Don't be so sure about that.

 

[Maaneli]

I am in your debt for finding a paper that concludes exactly the same thing I have been saying this whole thread. If you don't realize that this is a virtually perfect statement of my fundamental thesis, perhaps I have a better chance of being understood by some of the others with whom I've been holding this conversation.

From what I can see, the paper arrives at a conclusion that you also only recently came to, when you finally decided (upon my insistence) to separate Bohr's own philosophy (or rather your own interpretation of it) from the CI and the modern and original formalism of decoherence. So kudos to you for having your recently modified conclusion vindicated. But in fairness, it is not at all clear that you arrived to the same conclusion as those authors, using their same premises and arguments. It is possible, after all, to arrive at a common conclusion using bad (or even false) premises.

Finally, even if one can say that Bohr's original philosophy can be justified using the decoherence formalism, it is still not clear (going back to the main issue) that this is necessary and sufficient to solve the measurement problem (and therefore is the minimalist ontology necessary for QM). And you seem to have repeatedly dodged this issue.

 

[Maaneli]

Of course, it should be no surprise to anyone that there is a gray zone at the "Heisenberg cut". Do you imagine Bohr and Heisenberg were fools?

I'm not sure about Bohr (actually I think Bohr was a bit of a lazy physicist who was more interested in amateurish philosophy, and that is why he didn't develop his ideas as far as they could have been developed), but Heisenbeg was definitely a fool because not only was he an aggressive anti-realist, but he refused to acknowledge the problem of measurement, or for that matter the various solutions to it. He also refused to acknowledge the other possible interpretations of QM (which were far more logically coherent than his own I might add) which did not require the existence of human observers as a primitive assumption.

 

[Ken G]

From what I can see, the paper arrives at a conclusion that you also only recently came to, when you finally decided (upon my insistence) to separate Bohr's own philosophy (or rather your own interpretation of it) from the CI and the modern and original formalism of decoherence.

That is all in your imagination. I have been completely clear the entire time what I am talking about, and it sure sounds to me like the paper is talking about the very same thing. Indeed, I already quoted for you on several occasions the kinds of distinctions I was making about what Bohr said, what Heisenberg said, and what I meant. My interest in this thread has been on a useful minimal ontology for quantum mechanics, never on what it should be called or who said it. That's all you. That paper you found sounds to me, from its abstract, like a complete vindication of everything I've argued over these many pages. Whether you want to see that is up to you, if I couldn't get you to see it the first go round I hardly think I can do so now.

But in fairness, it is not at all clear that you arrived to the same conclusion as those authors, using their same premises and arguments. It is possible, after all, to arrive at a common conclusion using bad (or even false) premises.

Now there's an argument for the ages. I'll have to remember that one: "you were right, but it may have been for the wrong reasons, I can't tell because I haven't made the effort to do so."

Finally, even if one can say that Bohr's original philosophy can be justified using the decoherence formalism, it is still not clear (going back to the main issue) that this is necessary and sufficient to solve the measurement problem (and therefore is the minimalist ontology necessary for QM). And you seem to have repeatedly dodged this issue.

Finally, you actually make a statement about the thread topic! I'm gratified. Now let's address this "dodged" claim. Hmm, I've "repeatedly dodged" the very topic that every single one of my posts has been an effort to establish? That's just rich. But to address this "dodging" of mine, about all I could do at this point is completely recreate my argument for you, and the thread as it stands already does that.

 

[Ken G]

I'm not sure about Bohr (actually I think Bohr was a bit of a lazy physicist who was more interested in amateurish philosophy, and that is why he didn't develop his ideas as far as they could have been developed), but Heisenbeg was definitely a fool because not only was he an aggressive anti-realist, but he refused to acknowledge the problem of measurement, or for that matter the various solutions to it. He also refused to acknowledge the other possible interpretations of QM (which were far more logically coherent than his own I might add) which did not require the existence of human observers as a primitive assumption.

That ranks among the silliest things I've ever seen claimed about quantum mechanics. The Heisenberg time-depedent operator representation is a vast conceptual improvement in some contexts over the standard time-dependent wave function. Also, his appreciation for the importance of symmetries was also a brilliant addition. Even if I think his anti-realistic ontological objections were a bit over the top, the jury is still out on that, and will be for centuries I have no doubt (the pendulum does swing). Still, the man was obviously a genius, even if he didn't like your pet interpretation.

 

[Maaneli]

Now there's an argument for the ages. I'll have to remember that one: "you were right, but it may have been for the wrong reasons, I can't tell because I haven't made the effort to do so."

Let's be clear here. You seem to have been right about your belief that Bohr's interpretation of QM could be rigorized and framed in the context of decoherence theory. I have heard your premises, and I don't find them entirely convincing (mainly because I think you misread Bohr somewhat, and assume too much about what he would think today). Now then, I can't tell for sure if you were right for the wrong reasons, because I have not read that paper yet nor have I compared its arguments to your own. Simple enough for you to understand?

Finally, you actually make a statement about the thread topic! I'm gratified.

Actually, that was like the 3rd or 4th time I had made that statement. So where have you been all this time?

And just to remind you (cuz you seem to need reminding), the other statements were relevant to the thread, whether you like them or not (remember that there are parallel issues in this thread?).

Now let's address this "dodged" claim. Hmm, I've "repeatedly dodged" the very topic that every single one of my posts has been an effort to establish? That's just rich. But to address this "dodging" of mine, about all I could do at this point is completely recreate my argument for you, and the thread as it stands already does that.

You have been dodging this issue because I have raised it to you multiple times since I got involved, and even made specific criticisms of your arguments, and yet you still ignored it and continue to do so.

 

[Ken G]

No, Bohr never went beyond the detail of vague words like "classical" and "measurement".

That comment alone disqualifies you from being able to claim any knowledge or insight into Bohr's statements. The fact is, Bohr had a very well developed idea about how science works, and it involved classical concepts and measurement. Labeling those as "vague" is downright silly, as Bohr's main argument was that those are the only scientific concepts that are not vague, which is precisely why we built science around them. And of course, he was completely right, nor has a single poster on this thread been able to dispute that basic truth one iota.

You most certainly were suggesting that Bohr's philosophy involved decoherence, and you never bothered to make the distinction that Bohr never talked about such a thing, until I came along.

You have an active imagination, and a bizarre interpretation of the meaning of "most certainly". In fact I simply never made such a claim, nor did I ever think such a thing, I always said that decoherence filled in some of the details that Bohr simply assumed would be true. Indeed, that was more or less the core of my argument-- that decoherence is an important pillar of support to the idea that quantum mechanics is what you get when you apply a classical filter to information in the quantum domain. All decoherence does, and all I said it does, is to explain the mechanism of that filter. That is the point I made, over and over, in this thread. But you can take credit for it in your own mind.

Actually I did say the "true CI" is mainly composed of Heisenberg's interpretation of QM. I guess you conveniently decided to ignore that.

False. What I actually said is that this thread is not about trying to determine what it is that Maaneli will call the "true CI", it is about the contrast between the correspondence principle and the MWI "everything is coming up quantum" approaches. That's what the thread is about, not the semantic "will the true CI please stand up".

You imply in many instances that Bohr is a logical positivist (just as you are), by claiming that you think he would agree with many of your statements. And you provide no evidence for that claim with respect to Bohr.

Actually, I am not a logical positivist, nor did I imply Bohr was. A logical positivist makes associations between science and ontology. All I did, if you look again, is to assert, with Bohr, that we make certain choices when we choose to do science. Your logic is exactly backward-- a logical positivist sees science as the fundamental path to truth, whereas I, and I would say Bohr, see truth as a path to science, that is, we tell the truth about what science is. That all happens before anyone makes any ontological claims. Indeed, in my view Bohr resists making unnecessary ontological claims, that is a hallmark of his approach. (And that is not the case for logical positivists, by the way.)

Bohr's approach, as I feel I have pretty faithfully conveyed as a matter of fact, is summed up even better in the Stanford Encyclopedia of Philosophy (imagine that) at http://www.science.uva.nl/~seop/entries/qm-copenhagen/:

"Bohr therefore believed that what gives us the possibility of talking about an object and an objectively existing reality is the application of those necessary concepts, and that the physical equivalents of “space,” “time,” “causation,” and “continuity” were the concepts “position,” “time,” “momentum,” and “energy,” which he referred to as the classical concepts. He also believed that the above basic concepts exist already as preconditions of unambiguous and meaningful communication, built in as rules of our ordinary language. So, in Bohr's opinion the conditions for an objective description of nature given by the concepts of classical physics were merely a refinement of the preconditions of human knowledge."

It's an interesting article, I recommend you read it before you commit yourself to any more sweeping untruths about Bohr's positions.

I think it's pretty clear what I mean when I say Hamilton-Jacobi mechanics is a theory or that quantum hydrodynamics is a theory.

Obviously. The problem comes when you go to define a scientific theory (as I suspected):

If you want something a little more specific: the mathematical equations, the implied physical ontology from those equations, and the resultant empirical predictions, all constitute a physical theory.

There are two flaws in this definition. The first is that you claim a theory "implies" a physical ontology. If that were true, quantum mechanics would "imply" a physical ontology, and we would not need to argue about various interpretations. So in fact, what you apparently mean is that along with a theory we can choose from a menu of physical ontologies, and you feel that each of those choices spawns a different theory. If that were true, we would have a very hard time seeing articles on quantum mechanics published in the same journals from people using all these different interpretations. Luckily, the theory does not include the physical ontology, as you incorrectly include in your definition, and that is what allows us to be able to talk about "objective science".

It's a very good thing that science does not require your definition of a theory. If you look at, for example, the Wiki entry at http://en.wikipedia.org/wiki/Theoretical_physics, you might note that no concept of "ontology" ever appears anywhere in the reasonable definition offered there.

Actually I know enough about you.

Based on...?? All I know about you is that you have a tendency to make rhetorical arguments with zero factual or evidential basis, and here is yet one more.

I think it's pretty suspicious how you have entirely ignored the elephant in the room that I mentioned multiple times already, and then go on to proclaim your logic as perfectly consistent. I will raise it again with the hope that you'll be honest with yourself about it: the issue of whether decoherence theory alone is or can be considered a solution to the measurement problem.

Well, first of all I must point out to you that just what is "the measurement problem" is very much a wild hare. To some people, like Einstein, it is the fact that the states of quantum systems after measurement tend to seem vastly unlikely in the grand scheme of all possible wavefunctions. That problem is beautifully resolved by decoherence, indeed I would point to that resoluton as the whole point of decoherence. Nothing Bohr is saying presents any additional problems to that particular interpretation of what you might possibly mean by "the measurement problem".

So what else might you mean? Well it's fun to speculate, so perhaps you mean that the "measurement problem" is how our own perceptions of reality can "collapse" to substates that the equations of quantum mechanics do not seem to single out. Or put differently, the problem is, once our theory leads us to a mixed state description of a subsystem, how does one of those possibilities actually become real? Decoherence has nothing to say on that at all, nor does MWI, nor does the CI. This is pure mystery. So the real question is, should we be suddenly bothered when we run into pure mystery in quantum mechanics, when we were never bothered by pure mystery in any other branch of physics? It is downright foolhardy to imagine that any physical theory will not come face to face with pure mystery at some point-- they certainly all have so far, and all the future prospects do too. So why you see this as an "elephant in the room" is a pure mystery of its own.

 

[Maaneli]

That ranks among the silliest things I've ever seen claimed about quantum mechanics. The Heisenberg time-depedent operator representation is a vast conceptual improvement in some contexts over the standard time-dependent wave function.

I don't know what you mean by "conceptual"; but in any case, it is irrelevant to the specific criticisms I made about Heisenberg.

Also, his appreciation for the importance of symmetries was also a brilliant addition.

Yes, he was a brilliant mathematician - but a weak physicist.

Even if I think his anti-realistic ontological objections were a bit over the top, the jury is still out on that, and will be for centuries I have no doubt (the pendulum does swing).

I'm sorry, no, the pendulum does not swing, and the jury is not still out on that (for science and philosophy of science at least). And that is a certainty far greater than the certainty of, say, Global Climate Destabilization (GCD). And in my book, to claim that the "jury is still out" on Heisenberg's anti-realistic ontological objections, is even more nonsensical than the claim that the "jury is still out" on the existence of GCD. And by the way, if you read Steven Weinberg's essay, "Against Philosophy", you'll see that he (ironically) completely agrees with me about Heisenberg and his anti-realist positivism.

Still, the man was obviously a genius, even if he didn't like your pet interpretation.

The man was obviously a mathematical genius - but not a physics genius. He never figured out how to use his own formalism of matrix mechanics to calculate the hydrogen spectrum. He was also a most incompetent applied physicist, as attested to his utter faliure to productively lead the German atomic bomb project in WWII (in fact, it is well-documented that he botched many crucial calculations for that project).

 

[Maaneli]

If you look at, for example, the Wiki entry at http://en.wikipedia.org/wiki/Theoretical_physics, you might note that no concept of "ontology" ever appears anywhere in the reasonable definition offered there.

. Wow, that's real clever. Wikipedia is such a reputable source. By the way, where are the forum moderators here to give Ken G a warning about this?

 

[Maaneli]

Well, first of all I must point out to you that just what is "the measurement problem" is very much a wild hare.

What exactly do you mean by a "wild hare"?

To some people, like Einstein, it is the fact that the states of quantum systems after measurement tend to seem vastly unlikely in the grand scheme of all possible wavefunctions.

Actually, that was not the extent to which Einstein understood or characterized the measurement problem. Einstein objected to the problem of definite outcomes. Einstein also objected to the use of nonlocal wavefunctions in Hilbert space altogether. He wanted an ontological, deterministic, and locally causal theory of QM that explained measurement processes and required no fundamental appeal to human observers (as Heisenberg wanted) or to the Schroedinger equation and its wavefunctions or vague notions like "wave-particle duality".

That problem is beautifully resolved by decoherence, indeed I would point to that resoluton as the whole point of decoherence. Nothing Bohr is saying presents any additional problems to that particular interpretation of what you might possibly mean by "the measurement problem".

I agree decoherence is an important part of the solution (whether for wavefunction based formulations of QM or any other), but it is definitely not the entire solution as I have explained.

So what else might you mean? Well it's fun to speculate, so perhaps you mean that the "measurement problem" is how our own perceptions of reality can "collapse" to substates that the equations of quantum mechanics do not seem to single out. Or put differently, the problem is, once our theory leads us to a mixed state description of a subsystem, how does one of those possibilities actually become real?

Well I already explained what I meant by the measurement problem (the problem of definite outcomes), but that is also a pretty damn good characterization of it!

Decoherence has nothing to say on that at all, nor does MWI, nor does the CI. This is pure mystery.

You are absolutely right that decoherence and CI have nothing to say on that at all (as all the founders and proponents of decoherence admit too). From the point of view of those formalisms, it absolutely is pure mystery. And THAT is precisely why the decoherence formalism for wavefunctions is not enough of an ontology for QM. Indeed you are definitely wrong to say that MWI has nothing to say at all on this question. The whole point of MWI as it was originally concieved by Everett, and the more recent work in the QM foundations community, is to solve precisely this problem. That is not a controversial claim at all within the QM foundations community. The current controversy is whether 1) MWI admits a logically consistent probability interpretation for its ontology of decohering wavefunction branches, each of which is physically realized by an observer who also branches along with the QM system it interacts with, and 2) whether that logically consistent probability interpretation (if it exists) also gaurantees that anyone of those branching observers will see a Born rule probability distribution in a finite time limit.

On the other hand, there do exists formulations of QM that most certainly do solve the problem of definite outcomes, and this is not a controversial claim within the QM foundations community either. The most well-known of such formulations include the de Broglie-Bohm pilot-wave theory, the Nelson/Fenyes/Nagasawa stochastic mechanics theories, and GRW spontaneous collapse (with flash or mass ontology) theory. The former two modify QM by adding a particle ontology (the so-called "hidden variables") to solve the problem of definite outcomes (the particles evolves with a deterministic or stochasic trajectory that can only flow into one of the mixed eigenstates during a measurement interaction - and it is that eigenstate that we uniquely see, while the remaining "empty" wave packets become macroscopically disjoint and propagate away in configuration space), while also preserving unitary Schroedinger evolution and predicting the Born rule distribution for particle position measurements - and they incorporate environmental decoherence in a very necessary and natural way if you care to see how. The latter theory (GRW) solves the problem of definite outcomes by making a nonlinear, stochastic modification of the wavefunction evolution so that psi collapses (or rather localizes) to a position x at a time t with a certain probability depending on the number of particles constituting a quantum system and the temperature of the decohering environment. The GRW theory also reproduces all the quantum predictions within current experimental limits - but it also predicts empirical deviations in POVM distributions, which Aspelmeyer and Zeilinger have said will be experimentally testable 10 years from now.

Once again, I implore you to educated yourself on these issues by reading at least this fair and introductory paper:

Decoherence, the measurement problem, and interpretations of quantum mechanics
Maximilian Schlosshauer
Journal-ref. Rev. Mod. Phys. 76, 1267-1305 (2004)
http://eprintweb.org/S/authors/All/sc/M_Schlosshauer/10

So the real question is, should we be suddenly bothered when we run into pure mystery in quantum mechanics, when we were never bothered by pure mystery in any other branch of physics?

See above.

So why you see this as an "elephant in the room" is a pure mystery of its own.

You will understand why this is indeed an elephant in the room once you take the time to understand how these other interpretations, which you don't yet understand or care about, actually do solve the aforementioned measurement problem.

 

[Ken G]

[Wow, that's real clever. Wikipedia is such a reputable source. By the way, where are the forum moderators here to give Ken G a warning about this?

A warning about Wikipedia? Anyone who cannot recognize the substantial value and expertise offered to physics students by the Wikipedia is living in a bubble, moderators or no. But if you won't accept that as evidence that scientific theories are restricted to what is testable by confrontation with observation, then I refer you to any dictionary definition of science or the scientific method.

What exactly do you mean by a "wild hare"?

I mean it is all over the place-- a different meaning for the expression almost everywhere you look. Sort of like people's misconceptions about the CI.

Actually, that was not the extent to which Einstein understood or characterized the measurement problem.

I believed I quite accurately characterized Einstein's objection in this quote from him in a letter dated 1954, in which Albert Einstein wrote to Max Born “Let phi1 and phi2 be solutions of the same Schrodinger equation.. . ..
When the system is a macrosystem and when phi1 and phi2 are
‘narrow’ with respect to the macrocoordinates, then in by far the
greater number of cases this is no longer true for phi = phi1 + phi2.
Narrowness with respect to macrocoordinates is not only independent
of the principles of quantum mechanics, but, moreover,
incompatible with them.” So your claim is badly off the mark once again.

He wanted an ontological, deterministic, and locally causal theory of QM that explained measurement processes and required no fundamental appeal to human observers (as Heisenberg wanted) or to the Schroedinger equation and its wavefunctions or vague notions like "wave-particle duality".

That is well known by all who know of the EPR paper. By the way, that's the second time you've characterized "wave-particle duality" as a "vague" notion, but I see nothing vague in it-- it is simply at the core of the most precise theory humanity has ever invented. You want to call that "vague", I'd say your ontological difficulties are showing again.

I agree decoherence is an important part of the solution (whether for wavefunction based formulations of QM or any other), but it is definitely not the entire solution as I have explained.

Obviously it is not the entire solution, no physical theory includes an "entire solution". Do you know one?

Well I already explained what I meant by the measurement problem (the problem of definite outcomes), but that is also a pretty damn good characterization of it!

OK, that is indeed another common meaning for "measurement problem". But it's quite different from the one Einstein is complaining about in my quote above. In fact, it is so different that no physical theory, not CI, not MWI, not dBB, and with or without decoherence theory, has the least idea how to explain the problem of definite outcomes, except that they all say the same thing in different ways: what they say is, "that's science". In other words, we get what we get, all we can do is try to treat it in some useful way.

What I've said on that score is, the main schism between the CI and the MWI, which I feel MWI fans uniformly overlook, is nothing more than the CI saying "we built the definiteness problem right into the foundations of how we define science, so let's not imagine that its presence in quantum mechanics is a problem requiring a solution" (that is what I claim Bohr would say, in effect), and the MWI saying "we can subsume the definiteness problem into our picture in a way that does nothing but achieve certain mathematical streamlining," but all it does is replace the question of why definiteness with the question of why this subset of reality, which is essentially exactly the same question. In other words, for all the complaints I hear about the CI from MWIers, I end up thinking the MWI doesn't sound any different to me at all-- but sure has a lot of added baggage to please the mathematicians. And you claim Heisenberg's error was being good at math but not physics? How much more added mathematical nonphysical baggage could you possibly imagine than purporting that every potential reality is a real reality?

The dBB is no better-- sure it allows us to fantasize about an unseen deterministic process, but it conveniently leaves no tracks. Science that leaves no testable imprint is no science at all, and is no kind of "solution" to anything that is any better than the simple Bohr assertion that "there is nothing to solve here". That isn't testable either, but it is also unrefutable, and it's minimal.

You are absolutely right that decoherence and CI have nothing to say on that at all (as all the founders and proponents of decoherence admit too). From the point of view of those formalisms, it absolutely is pure mystery.

I am glad that we have at last found a common ground. It is fairly easy to show that everything I'm saying proceeds directly from that foundation.

And THAT is precisely why the decoherence formalism for wavefunctions is not enough of an ontology for QM.

I think you mean, enough of an ontology for you. QM seems to be doing just fine, thank you.

Indeed you are definitely wrong to say that MWI has nothing to say at all on this question. The whole point of MWI as it was originally concieved by Everett, and the more recent work in the QM foundations community, is to solve precisely this problem. That is not a controversial claim at all within the QM foundations community. The current controversy is whether 1) MWI admits a logically consistent probability interpretation for its ontology of decohering wavefunction branches, each of which is physically realized by an observer who also branches along with the QM system it interacts with,

Whoa, just listen to that! This is science? You see, it's fine to talk about decohering wavefunction branches, that's intro MWI, but you just blithely tack on this idea that physics has a way to describe how an observer "branches along with it", that's right where you bump into the limitations of choosing a scientific epistemology. To back your claim that "I'm definitely wrong to say MWI has nothing to say on this", you will need to be able to define what an observer is, using quantum mechanical language, to be able to do what you claim is the goal. That's exactly where Bohr blows the whistle on the whole misguided philosophy-masquerading-as-physics affair.

and 2) whether that logically consistent probability interpretation (if it exists) also gaurantees that anyone of those branching observers will see a Born rule probability distribution in a finite time limit.

Success in doing that would still not add anything to the basic issue. You see, we already know we end up with a probabilistic treatment of the situation, and we also know that we have no idea if there is a mechanism that samples that distribution somehow. Nothing you have said offers any insight into such a sampling mechanism, it just dresses up the probability distribution so it seems less arbitrary, but in fact is still completely arbitrary in regard to the perceived outcome. So if a lot of physicists want to get busy trying to accomplish that, it's their time to waste, but it will add neither predictive nor explanatory power to quantum mechanics. They can instead just listen to Bohr and notice the folly of pretending that physics knows how to treat the observer.

On the other hand, there do exists formulations of QM that most certainly do solve the problem of definite outcomes, and this is not a controversial claim within the QM foundations community either.

Here comes the dBB interpretation, and so forth. The problem is, none of those theories "solve the problem" of definite outcomes, for one very simple reason: none can offer a single shred of evidence that they refer to a mechanism that actually occurs in reality.

As I have said before, I can find a much simpler way to "solve" the definiteness problem: just say God did it. That certainly solves the definiteness problem, and it also does so in a completely unverifiable way, just like dBB and the others you mention. And it is also equally unscientific, expressly because it is untestable. The bottom line here is, it is a complete fiction that physics knows how to self-consistently treat the observer in the observation, and until a single scrap of progress is made on that score, all of the interpretations that attempt to "add to" the CI are sheer fantasy. That doesn't make them wrong, not at all-- it makes them not even wrong. The only valid discussion is about what is the minimal ontology needed to give the epistemology meaning-- all other choices are purely arbitrary in the absence of empirically testable criteria.

The GRW theory also reproduces all the quantum predictions within current experimental limits - but it also predicts empirical deviations in POVM distributions, which Aspelmeyer and Zeilinger have said will be experimentally testable 10 years from now.

Well goody, some actual science. So I'll put them in the "MOND" category: something I can pay attention to if they start to make predictions that are verified, and can safely ignore prior to that time, as in my view they are a complete shot in the dark.

Once again, I implore you to educated yourself on these issues by reading at least this fair and introductory paper:

Decoherence, the measurement problem, and interpretations of quantum mechanics

Well I thank you for the reference, but if all your arguments stem from that paper, there is nothing you have said that I don't understand except the few long-shot theories that guess at mechanisms we don't already know will mimic CI-style quantum mechanics in every single way (as the MWI and dBB both do, they are precisely the same theory as the CI plus extraneous baggage purely to appease certain prejudices). Thus, I'm not sure what it would add to my current understanding except that I could probably find additional evidence in favor of my basic thesis here: Bohr is trying to save us all a lot of wasted effort, and self-deceiving ontologies, with the simple observation that the way physics is done will always leave its imprint on physics, so pretenses that we can reverse that logical flow and use physics to explain why physics works are folly.

You will understand why this is indeed an elephant in the room once you take the time to understand how these other interpretations, which you don't yet understand or care about, actually do solve the aforementioned measurement problem.

I know quite well how the dBB claims to "solve" that problem, and I also know why it fails to do that quite utterly, just as my statement "God did it" fails-- for precisely the same reason. What I do note, once again, is how easily you permit yourself to make false assumptions about my argument and my knowledge. Does that help you to imagine credit when you finally start to understand what I'm saying, as if my point evolved out of what you are telling me because you've already assumed I didn't know it already? The truth is, like all exchanges, there are advancement of ideas, but not at a level that survives the false assumptions you make.

 

[Maaneli]

A warning about Wikipedia? Anyone who cannot recognize the substantial value and expertise offered to physics students by the Wikipedia is living in a bubble, moderators or no. But if you won't accept that as evidence that scientific theories are restricted to what is testable by confrontation with observation, then I refer you to any dictionary definition of science or the scientific method.

Not only is it extremely naive to say "just refer to Wiki or a dictionary definiton to see what scientific theories are", but it is an insult to all professional philosophers of science, and for that matter, all competent scientists. And yes, as some friendly advice, have a look at the forum rules about referencing websites. You should actually be thanking me that I'm giving you a heads up on this before the moderators do.

I mean it is all over the place-- a different meaning for the expression almost everywhere you look. Sort of like people's misconceptions about the CI.

If that's what you mean, then it's just blatantly false. And the comparison to misconceptions about the CI is quite disingenuous. I take it you have not yet read a single textbook on the interpretation of QM, or for that matter, any review articles on the subject (including Schlosshauer's [seriously, you need to read that paper]), or for that matter, been to any conferences on the foundations of QM. If you did, you would quickly realize that nobody who is professionally in the field is as confused about the measurement problem as you think they are. And if you did but still haven't realized this, then you must have your head in the sand.

I believed I quite accurately characterized Einstein's objection in this quote from him in a letter dated 1954, in which Albert Einstein wrote to Max Born “Let phi1 and phi2 be solutions of the same Schrodinger equation.. . ..
When the system is a macrosystem and when phi1 and phi2 are
‘narrow’ with respect to the macrocoordinates, then in by far the
greater number of cases this is no longer true for phi = phi1 + phi2.
Narrowness with respect to macrocoordinates is not only independent
of the principles of quantum mechanics, but, moreover,
incompatible with them.” So your claim is badly off the mark once again.

Excuse me, but there is absolutely nothing in that quote that says this was the full extent of Einstein's definition of the measurement problem or objection to the standard QM. It is highly disingenuous of you to claim that based on this one quote. You do realize that Einstein wrote much on the subject prior to 1954, don't you?

That is well known by all who know of the EPR paper. By the way, that's the second time you've characterized "wave-particle duality" as a "vague" notion, but I see nothing vague in it-- it is simply at the core of the most precise theory humanity has ever invented.

No, the "wave-particle duality" is at the core of the most common INTERPRETATION of QM, namely, Heisenberg's CI. Nothing in the mathematical formalisms of QM necessarily imply the CI notion of "wave-particle duality". And FYI, the wave-particle duality concept is inconsistent with Bohr's concept of complementarity. You should know that if you actually read that Stanford Encyclopedia article on the CI. See the last sentence before section 7 which refers to the recent study by Ravi Gomatam:

"In a very recent study Ravi Gomatam (2007) agrees with Howard's exposition in arguing that Bohr's interpretation of complementarity and the textbook Copenhagen interpretation (i.e. wave-particle duality and wave packet collapse) are incompatible."
http://www.science.uva.nl/~seop/entries/qm-copenhagen/

Gomatam, R. (2007), “Niels Bohr's Interpretation and the Copenhagen Interpretation — Are the two incompatible?”, in Philosophy of Science, 74, December issue.

Obviously it is not the entire solution, no physical theory includes an "entire solution". Do you know one?

You know what I was talking about (the measurement problem, and in particular the problem of definite outcomes), so don't unnecessarily confuse the issue.

OK, that is indeed another common meaning for "measurement problem". But it's quite different from the one Einstein is complaining about in my quote above.

Your reference here to the Einstein quote is irrelevant. Besides, Einstein was also aware of the problem of definite outcomes.

In fact, it is so different that no physical theory, not CI, not MWI, not dBB, and with or without decoherence theory, has the least idea how to explain the problem of definite outcomes, except that they all say the same thing in different ways: what they say is, "that's science". In other words, we get what we get, all we can do is try to treat it in some useful way.

Nope. Sorry, but that's just a totally misleading and disingenuous characterization of MWI and deBB, even after I explained how MWI and deBB propose to do it.

What I've said on that score is, the main schism between the CI and the MWI, which I feel MWI fans uniformly overlook, is nothing more than the CI saying "we built the definiteness problem right into the foundations of how we define science, so let's not imagine that its presence in quantum mechanics is a problem requiring a solution" (that is what I claim Bohr would say, in effect), and the MWI saying "we can subsume the definiteness problem into our picture in a way that does nothing but achieve certain mathematical streamlining," but all it does is replace the question of why definiteness with the question of why this subset of reality, which is essentially exactly the same question.

I don't think Bohr would have said what you think he would say. Moreover, the problem of definite outcomes is not an artifical problem. It is just the obvious contradiction between our experimental observations of definite outcomes (like a definite particle position, momentum, energy, etc.), and the fact that the Schroedinger evolution predicts (even with decoherence) a superposition of mixed eigenstates other than the definite ones we see in measurement interactions.

In other words, for all the complaints I hear about the CI from MWIers, I end up thinking the MWI doesn't sound any different to me at all-- but sure has a lot of added baggage to please the mathematicians. And you claim Heisenberg's error was being good at math but not physics? How much more added mathematical nonphysical baggage could you possibly imagine than purporting that every potential reality is a real reality?

You ask this question because you still have not understood the origin or validity of the problem of measurement. Moreover, you are a priori assuming that the MWI interpretation is "nonphysical" in order to criticize it as extraneous. You have provided no argument or criterion for what is "physical", and for that matter why anyone should think that YOUR criterion is more reasonable than any other. You should also realize that a goal of MWI would also be to *predict* rather than postulate the Born rule probability distribution for observers. That would be a highly nontrivial result that goes well beyond anything Heisenberg hoped to do with his solipsistic CI.

And again, Heisenberg's deficiencies in physics (where he had to apply mathematics to real-world physics problems) are well documented as I mentioned earlier.

The dBB is no better-- sure it allows us to fantasize about an unseen deterministic process, but it conveniently leaves no tracks.

Um, what do you mean it leaves no "tracks"? In any experiment, the prediction is that you end up measuring the actual particle that took the trajectory you can calculate from the guiding equation. So I'm not sure what you mean. By the way, the determinism of the particle evolution is strictly a consequence of the determinism of the Schroedinger evolution (did you know that the particle velocity is computed from the wavefunction?). So it's quite silly for you to criticize that.

Science that leaves no testable imprint is no science at all, and is no kind of "solution" to anything that is any better than the simple Bohr assertion that "there is nothing to solve here". That isn't testable either, but it is also unrefutable, and it's minimal.

As I mentioned before, deBB *predicts* the Born rule probability distribution and the definite outcomes of measurement interactions. It also predicts the EPR violation of Bell's inequality, and ALL the other experimentally testable nonrelativistic and relativistic phenomena that textbook QM predicts. You are probably going to naively react to this by saying "see, that proves it gives us nothing new because textbook QM made all the predictions first". But you need to understand that the advent of Heisenberg matrix mechanics, Schroedinger's wave mechanics, and the Heisenberg-Joran-Dirac transformation theory prior to deBB was quite a historical accident. It is entirely possible that deBB could have been discovered first, in which case it likely would have been preferred over Heisenberg and Bohr's vague and radical interpretations (mainly because it was more in line with classical physics intuitions of physicists at the time), and then its predictions worked out in detail first. Then, if someone like Heisenberg or Bohr came along 25 years later and proposed their mathematically less precise interpretations of QM which nevertheless made most or all of the same predictions as the deBB QM, we could equally well say that the Heisenberg and Bohr versions of QM offer nothing new and therefore are extraneous philosophies of QM. In fact, here is an interesting counterfactual story about the historical development of QM:

Would Bohr be born if Bohm were born before Born?
Authors: H. Nikolic
Journal reference: Am. J. Phys. 76 (2008) 143-146
http://arxiv.org/abs/physics/0702069

So that kind of argument I anticipate you would make is totally irrelevant and does not constitute a valid criticism or objection to deBB.

Finally, let me refer you again to my earlier post about the prediction of quantum nonequilibrium in deBB theory, and the work of Valentini who has shown that it is empirically testable in the context of cosmology:

Astrophysical and Cosmological Tests of Quantum Theory
Antony Valentini
Contribution to: "The Quantum Universe", special issue of Journal of Physics A, dedicated to Prof. G.-C. Ghirardi on the occasion of his seventieth birthday
Journal-ref. J. Phys. A: Math. Theor. 40, 3285-3303 (2007)
http://eprintweb.org/S/authors/All/va/Valentini/7

Subquantum Information and Computation
Antony Valentini
To appear in 'Proceedings of the Second Winter Institute on Foundations of Quantum Theory and Quantum Optics: Quantum Information Processing', ed. R. Ghosh (Indian Academy of Science, Bangalore, 2002). Second version: shortened at editor's request; extra material on outpacing quantum computation (solving NP-complete problems in polynomial time)
Journal-ref. Pramana - J. Phys. 59 (2002) 269-277
http://eprintweb.org/S/authors/All/va/Valentini/18

(these next two papers are not yet published, just so you know)

Inflationary Cosmology as a Probe of Primordial Quantum Mechanics
Antony Valentini
http://eprintweb.org/S/authors/All/va/Valentini/3

De Broglie-Bohm Prediction of Quantum Violations for Cosmological Super-Hubble Modes
Antony Valentini
http://eprintweb.org/S/authors/All/va/Valentini/4

So in fact there is potentially new physics resulting from the deBB ontology, contrary to what you think.

Whoa, just listen to that! This is science? You see, it's fine to talk about decohering wavefunction branches, that's intro MWI, but you just blithely tack on this idea that physics has a way to describe how an observer "branches along with it", that's right where you bump into the limitations of choosing a scientific epistemology. To back your claim that "I'm definitely wrong to say MWI has nothing to say on this", you will need to be able to define what an observer is, using quantum mechanical language, to be able to do what you claim is the goal.

I'm not a specialist in the MWI, nor am I even a supporter of the MWI (I think it's likely to be wrong for other reasons). But many serious physicists and philosophers of physics have gone into detail about what a "world" is and what an "observer" is in MWI, and I would suggest that you have a read of the following papers (look in particular at the second one):

(written by Lev Vaidman)
http://plato.stanford.edu/entries/qm-manyworlds/

Everett and Structure
Authors: David Wallace
Journal reference: Studies in the History and Philosophy of Modern Physics 34 (2003), pp. 87-105
<< I address the problem of indefiniteness in quantum mechanics: the problem that the theory, without changes to its formalism, seems to predict that macroscopic quantities have no definite values. The Everett interpretation is often criticised along these lines and I shall argue that much of this criticism rests on a false dichotomy: that the macroworld must either be written directly into the formalism or be regarded as somehow illusory. By means of analogy with other areas of physics, I develop the view that the macroworld is instead to be understood in terms of certain structures and patterns which emerge from quantum theory (given appropriate dynamics, in particular decoherence). I extend this view to the observer, and in doing so make contact with functionalist theories of mind. >>
http://arxiv.org/abs/quant-ph/0107144

Worlds in the Everett Interpretation
Authors: David Wallace
Journal reference: Studies in the History and Philosophy of Modern Physics 33 (2002) pp. 637-661
http://arxiv.org/abs/quant-ph/0103092

That's exactly where Bohr blows the whistle on the whole misguided philosophy-masquerading-as-physics affair. Success in doing that would still not add anything to the basic issue. You see, we already know we end up with a probabilistic treatment of the situation, and we also know that we have no idea if there is a mechanism that samples that distribution somehow.

. Please, just look at those papers instead of pretending that you know what you're talking about.

Nothing you have said offers any insight into such a sampling mechanism, it just dresses up the probability distribution so it seems less arbitrary, but in fact is still completely arbitrary in regard to the perceived outcome.

I'm quite skeptical that you even understand MWI or for that matter deBB. Indeed you have already demonstrated a basic misunderstanding about the determinism of the particle trajectories in deBB.

So if a lot of physicists want to get busy trying to accomplish that, it's their time to waste, but it will add neither predictive nor explanatory power to quantum mechanics. They can instead just listen to Bohr and notice the folly of pretending that physics knows how to treat the observer.
Here comes the dBB interpretation, and so forth. The problem is, none of those theories "solve the problem" of definite outcomes, for one very simple reason: none can offer a single shred of evidence that they refer to a mechanism that actually occurs in reality.

Sorry but theories like deBB, stochastic mechanics, and GRW are ultimately empirically differentiable from textbook QM, whether you like it or not. Curiously though, the only one that isn't is MWI.

I also take it that you are totally oblivious of quantum gravity and cosmology research. You might be surprised to know that many such quantum gravity specialists (Susskind, Hawking, Hartle, Tegmark, Wheeler) find a special utility and appeal in MWI.

As I have said before, I can find a much simpler way to "solve" the definiteness problem: just say God did it.

So I guess you are a creationist? Very well then, I shall tell everyone on this forum that Ken G is a creationist. After all, only a creationist thinks that vague words like "God did it" are a "simpler" and adequate substitute for precise mathematical equations of motion that predict the full gamut of QM phenomena, including measurement processes.

That certainly solves the definiteness problem, and it also does so in a completely unverifiable way, just like dBB and the others you mention.

See above.

And it is also equally unscientific, expressly because it is untestable.

See above.

The bottom line here is, it is a complete fiction that physics knows how to self-consistently treat the observer in the observation, and until a single scrap of progress is made on that score, all of the interpretations that attempt to "add to" the CI are sheer fantasy.

Or, much more likely, your attempts to characterize your twisted version of CI as the most fundamental (or the only legitimate) interpretation is nothing but a delusion.

That doesn't make them wrong, not at all-- it makes them not even wrong.

And ironically, you are the one whose "not even wrong".

The only valid discussion is about what is the minimal ontology needed to give the epistemology meaning--

And this problem has not been solved yet, no matter what you like to think.

all other choices are purely arbitrary in the absence of empirically testable criteria.

Actually no. There is also the issue of the internal consistency of a particular QM interpretation.

Well goody, some actual science. So I'll put them in the "MOND" category: something I can pay attention to if they start to make predictions that are verified, and can safely ignore prior to that time, as in my view they are a complete shot in the dark.

Well that's quite a disingenuous characterization if there ever was one. I guess you never learned the difference between a phenomenological formalism (like MOND) and a physical theory (like deBB or GRW).

Well I thank you for the reference, but if all your arguments stem from that paper,

They do not, and I don't fathom how you could have logically assumed that.

Thus, I'm not sure what it would add to my current understanding

A solution to the problem of definite outcomes.

I know quite well how the dBB claims to "solve" that problem,

And yet all the evidence is to the contrary.

What I do note, once again, is how easily you permit yourself to make false assumptions about my argument and my knowledge. Does that help you to imagine credit when you finally start to understand what I'm saying, as if my point evolved out of what you are telling me because you've already assumed I didn't know it already? The truth is, like all exchanges, there are advancement of ideas, but not at a level that survives the false assumptions you make.

What amazes me is that you claim to know far more than you evidently really do. And I always feel the obligation to bring down the heat on such people.

Good night.

 

[vanesch]

I think that interesting points have been raised in this thread, but it is turning into a flame war.

Please keep in mind that in discussions about interpretations of quantum theory, half of the argument is philosophy based, and half of it is theory based. So it is entirely normal to have different viewpoints, and there's no point in trying to argue why one is "better" than the other. It is important to recognize this. What is problematic and what isn't, comes close to the philosophy of science itself. None of the current interpretations are totally idiotic, and none of them are without conceptual difficulties. The choice is often driven by what properties one values more than others. There is no "obviously correct" interpretation - otherwise there wouldn't be any debate amongst knowledgeable people for almost a century.

I'm not going to lock this thread right away - but steer it into a constructive discussion, or it will be locked.

 

[Ken G]

Not only is it extremely naive to say "just refer to Wiki or a dictionary definiton to see what scientific theories are", but it is an insult to all professional philosophers of science, and for that matter, all competent scientists.

Again, that's just silly. The Wikipedia, properly interpreted, is one of many extremely valid references for scientific debate.

And yes, as some friendly advice, have a look at the forum rules about referencing websites. You should actually be thanking me that I'm giving you a heads up on this before the moderators do.

I'm afraid I have no idea what you are talking about. I have seen the forum rules, and see zero issues with how I've handled outside references. The only area where I may be anywhere near infringing a rule has to do with rhetorical excesses when pointing out the logical fallacies and false assumptions behind your arguments. Your own rhetorical excesses exceed even my own, but we both seem to have fairly thick skins and a sense of where to draw a line, so this does not seem to be causing any problems.

If that's what you mean, then it's just blatantly false.

I don't think the phrase "blatantly false" means what you think it does. The claim of mine that you seem to be referring to is that the "measurement problem" is a many-headed dragon that means a slightly, or vastly, different thing any place you encounter it. If you feel that is false, I invite you to invoke something other than your standard penchant for "argument by assertion".

I take it you have not yet read a single textbook on the interpretation of QM, or for that matter, any review articles on the subject (including Schlosshauer's [seriously, you need to read that paper]), or for that matter, been to any conferences on the foundations of QM.

Goodness, I've been to no conferences on the foundations of QM? What am I doing having a considered opinion? Of course no one should ever say anything about a science subject they have not been to a conference about, whereas anyone who has been to a conference is immediately to be regarded as an unimpeachable authority. That's pretty much your logic here. On the other hand, I will find occasion to read that article, but anticipate that I will either find occasion to agree with its conclusions, or point to flaws in its arguments. You know, "analysis".

If you did, you would quickly realize that nobody who is professionally in the field is as confused about the measurement problem as you think they are. And if you did but still haven't realized this, then you must have your head in the sand.

If anyone in the field doesn't think they are confused about the measurement problem, it is they, and you, who have their head in the sand. I'll spare you all the quotes where people like Feynman said that better.

Excuse me, but there is absolutely nothing in that quote that says this was the full extent of Einstein's definition of the measurement problem or objection to the standard QM. It is highly disingenuous of you to claim that based on this one quote.

You like that word, "disingenuous", don't you? Now let's look at what I'm actually saying. Everyone knows we can pay lip service to the "measurement problem" by referring to a vague sense that we don't know why a theory that is apparently based on deterministic time evolution yields probabilistic outcomes. However, when one digs into that problem, one finds that there are all kinds of different facets to that problem, some with fairly easy solutions, some that will never have any solution because it would go beyond what science is capable of. Thus whenever these "experts" who've gone to conferences refer to "solutions to the measurement problem", they are using vastly imprecise language. That's just obvious to me, I'm sorry that I don't need to go to a meeting to say that.

But let me give some examples, instead of following your approach of argument by sheer assertion. What are some aspects of the "measurement problem" that have been solved? Well, the obvious one is decoherence, which explains the mechanism for how a closed system can evolve unitarily into a state that, when projected onto open substates, generates a mixed state. The BI was already well aware that this would happen, but decoherence gives a way of saying how that works out. To me, the key contribution of decoherence theory is in verifying the stability of the pointer states. But more importantly, we should note that classical physics already used that result for centuries prior to quantum mechanics, so we should see that as more of a "sanity check" than some kind of fundamental discovery.

So what aspects of the "measurement problem" will never be solved by any science? That's easy, any aspects that are intrinsic to the assumptions we make whenever we embark on the scientific path. Here we find issues like the need for idealizations like objectivity, subject/object separation, conventions about reason, and so forth-- all the elements that go into the scientific method that we can pretend, but should not believe, are precise rather than fuzzy aspects of the otherwise seemingly axiomatic structures we call theories.

So what was Einstein talking about in that quote? He was certainly not talking about the EPR issues (which I already referred to, so your asking me if I know Einstein wrote things before 1954 takes "disingenuous" to a new level all your own). He was talking about a different one of the many heads of the "measurement problem" dragon, to wit, the problem that science is based around results that are highly nongeneric to the theory of quantum mechanics. This is exactly the point that the stability of pointer states, and decoherence, addresses, but as I said, it addresses it in a way that is not fundamentally different from what the BI assumed-- it is a result of how we structure our science. Hence, science is a noninvertible filter, and the resolution to Einstein's objection only appears when one recognizes that the "problem" is one of our own making when we try to invert what is noninvertible.

No, the "wave-particle duality" is at the core of the most common INTERPRETATION of QM, namely, Heisenberg's CI. Nothing in the mathematical formalisms of QM necessarily imply the CI notion of "wave-particle duality".

According to your interpretation of "wave/particle duality", perhaps. However, the sensible way to interpret that phrase is simply that particle behavior is describable with wave functions. Look how I got "particle" and "wave" into that completely uncontroversial sentence that has zero need for interpretations of QM-- that's wave/particle duality. Anything beyond that is just your own personal strawman.

And FYI, the wave-particle duality concept is inconsistent with Bohr's concept of complementarity.

Your personal strawman, perhaps.

You should know that if you actually read that Stanford Encyclopedia article on the CI. See the last sentence before section 7 which refers to the recent study by Ravi Gomatam:

"In a very recent study Ravi Gomatam (2007) agrees with Howard's exposition in arguing that Bohr's interpretation of complementarity and the textbook Copenhagen interpretation (i.e. wave-particle duality and wave packet collapse) are incompatible."
http://www.science.uva.nl/~seop/entries/qm-copenhagen/

As I have said many times now, the "textbook" Copenhagen interpretation is equipped with all kinds of extraneous ontological baggage around wavefunction collapse that Bohr never needed, and I also have been quite clear throughout that what I have been talking about, and continue to talk about, is Bohr's heroic attempt to strip quantum ontology of everything that it does not need to function in support of the epistemology of quantum mechanics. Personally, I think so much of what is written about the CI is just plain misguided, which is also why I said that most people who criticize it either don't understand it, or have morphed it into a kind of strawman to appease the very prejudices that it was intended to avoid appeasing. We covered all this already in the choice to use BI instead of CI-- you're backtracking.

Your reference here to the Einstein quote is irrelevant. Besides, Einstein was also aware of the problem of definite outcomes.

The latter statement is true, the former one is false. The quote is quite relevant, because it speaks to the issue that decoherence actually has something to say about. The latter problem is not "solved" by any of the interpretations we've talked about, any better than "God did it" solves that problem. Usually, in physics we are well aware that there is no such thing as a "fundamental" theory, as all theories will begin with the postulation of undefined entities. Why people are under the illusion that quantum mechanics is any different was always been a mystery to me, but as I said, I see it as a classic example of "all past science has been wrong, but today we have it right" kind of thinking.

Nope. Sorry, but that's just a totally misleading and disingenuous characterization of MWI and deBB, even after I explained how MWI and deBB propose to do it.

I didn't expect that you would understand my point here, as it would require understanding the entire argument I've presented that you have not understood, but that doesn't make me wrong, or even "disingenuous". Again you offer nothing but argument by assertion, as is your habit.

I don't think Bohr would have said what you think he would say. Moreover, the problem of definite outcomes is not an artifical problem. It is just the obvious contradiction between our experimental observations of definite outcomes (like a definite particle position, momentum, energy, etc.), and the fact that the Schroedinger evolution predicts (even with decoherence) a superposition of mixed eigenstates other than the definite ones we see in measurement interactions.

You see, that statement right there summarizes your confusion about what science is capable of. The Schroedinger equation doesn't "predict" anything of the sort, in fact, it doesn't predict anything. It is a mathematical equation, and it has a solution, and that's it. To call that result a prediction requires not only attaching some physical meaning to the output, it also requires attaching physical meaning to the input. The hands of the scientist are all over the problem, as is generally true in science. Why we feel the need to pretend that this is somehow "automatic" is beyond me. QM is an axiomatic structure, and among the axioms are that the outputs, and inputs, have a probabilistic character. So there is no problem with "definite outcomes", it is a pretense that we should need that.

Let me put this differently, as it is quite central to the issue in this whole thread, going right back to the OP. If I have a theory that says an identical die with 6 sides should have a 1/6 chance of each outcome, no one bats an eye. There's no "definiteness problem" in that theory, because it is not trying to be anything but a statistical description. Nevertheless, it contains deterministic elements-- the number of identical sides determines the probability. So we use a combination of deterministic and probabilistic concepts all the time in science, without anyone screaming from ontological angst. The exact same observation holds for the way we use the deterministic Schroedinger equation to make probabilistic assessments about outcomes of experiments. In my view, people who see any contradiction there are simply asking science to be something other than what it ever was.

I realize you will neither understand nor agree with the above remark, so all I can do is point out that when you respond with more argument by assertion, ask yourself one simple question: why can you not point to any specific flaw in what I just said, nor can you offer an alternative that succeeds in allowing science to be something other than what I am claiming it fundamentally is-- a description of reality that does not have to, nor even should it try to, sound like it is intended as an explicit description of the "mind of God".

Moreover, you are a priori assuming that the MWI interpretation is "nonphysical" in order to criticize it as extraneous.

The MWI asserts the existence, yes existence, of worlds that we have no interaction with and no empirical connection to. The justification for that is entirely that it allows us to imagine something we should not bother to be so foolish to imagine, that our mathematical concepts can dictate to reality. Yes, I would indeed describe that as the very definition of what is nonphysical-- and what I called not even wrong.

You have provided no argument or criterion for what is "physical", and for that matter why anyone should think that YOUR criterion is more reasonable than any other.

Actually, I did, but I'm happy to do it again: what is "physical" is all that we can objectively and repeatably measure (at least in principle, we always have to allow for technological limitations). I would say that statement is the very core concept of all of physics, hence the word.

You should also realize that a goal of MWI would also be to *predict* rather than postulate the Born rule probability distribution for observers. That would be a highly nontrivial result that goes well beyond anything Heisenberg hoped to do with his solipsistic CI.

I could not have summarized your fundamental disconnect with what physics is, any better than that statement. Physics theories do not "predict" other physics theories! They predict the outcomes of objectively repeatable observations. Any other use of the word predict is simply misguided. We already know the only outcomes we can test against experiment, your approach is not suggesting that QM should be capable of making predictions that it does not already make. In other words, you are describing a fools errand if it considered to be an approach to a new theory, but if viewed as what it really is, a path to a personal pedagogy that you enjoy, then it's fine.

I'll break here, my response is long.

 

[Ken G]

And again, Heisenberg's deficiencies in physics (where he had to apply mathematics to real-world physics problems) are well documented as I mentioned earlier.

You pointed to the Nazi bomb effort, which you are apparently unaware that Heisenberg claimed he intentionally sabotaged. While I have no opinion on the truth of that claim, I certainly can recognize the cruel irony and injustice in accusing a possible hero of the free world with being a lousy physicist for his pains.

Um, what do you mean it leaves no "tracks"?

I mean, well, it leaves no tracks.

In any experiment, the prediction is that you end up measuring the actual particle that took the trajectory you can calculate from the guiding equation.

Goodness, you are massacring the word "predict" again. You can certainly choose to force the particle to leave literal "tracks" by deciding you are going to, by measurement, establish a concept of a trajectory, but you don't need dBB for that, simple QM accomplishes that just fine, and the predictions (using the correct meaning of that word) are all identical. That's what I mean by dBB leaving no tracks-- nothing that distinguishes it that isn't happening entirely in our minds (i.e., no tracks).

By the way, the determinism of the particle evolution is strictly a consequence of the determinism of the Schroedinger evolution (did you know that the particle velocity is computed from the wavefunction?).

As I already pointed out with the die analogy, the determinism of the Schroedinger evolution is not sufficient to establish a deterministic process. So no, the determinism does not come from the Schroedinger equation, and I don't need to go to a meeting on quantum interpretations to see that basic logic.

As I mentioned before, deBB *predicts* the Born rule probability distribution and the definite outcomes of measurement interactions.

Please stop misusing the word "predict", it is almost painful for me given that my entire point is we must always bear in mind the empirical foundations of science when we interpret what science is doing. But even if we substitute the word "derives", your statement is still backward logic-- the deBB starts from the Born rule and reverse engineers a picture that can be said to lead to it. But the assumptions of the deBB are no less arbitrary than those of the Born rule, so no, nothing is being fundamentally "derived" there, it is just a shell game, a basic parlor trick.

It also predicts the EPR violation of Bell's inequality, and ALL the other experimentally testable nonrelativistic and relativistic phenomena that textbook QM predicts.

Again, it is quite obvious why the deBB makes all the same predictions as QM-- it uses the same formalism as QM and simply adds an "invisible" and unverifiable element that does nothing beyond appeasing prejudices about reality "ought to" behave. That's what I mean by a parlor trick-- do you know the parable of "rock soup"?

It is entirely possible that deBB could have been discovered first, in which case it likely would have been preferred over Heisenberg and Bohr's vague and radical interpretations (mainly because it was more in line with classical physics intuitions of physicists at the time), and then its predictions worked out in detail first.

Actually, I highly doubt it is logical to think that the deBB could have been arrived at first, because of its structure as QM with a facade erected in front of it to make it look like a deterministic theory (even though it does not allow anything more to be determined than does QM). Your argument here is like saying that it is a historical accident that stone age houses were first erected without architectural details. But it really makes no difference what the historical order of events was, because my point about the time sequence is only used to prove that the deBB is not needed in deriving QM, which is all I ever argued despite your "disingenuous" efforts to mischaracterize my position as relying on "accidents of history

In fact, here is an interesting counterfactual story about the historical development of QM:

Would Bohr be born if Bohm were born before Born?
Authors: H. Nikolic
Journal reference: Am. J. Phys. 76 (2008) 143-146
http://arxiv.org/abs/physics/0702069

So that kind of argument I anticipate you would make is totally irrelevant and does not constitute a valid criticism or objection to deBB.

As I've explained, if one sticks to the actual logic I have used here, your position is refuted once again. My criticism of the deBB is entirely valid, it is the simple observation that the deBB comprises a useful part that makes real predictions and is identical to standard QM, and a fanciful part that makes no predictions, determines nothing, yet can be imagined to be deterministic if one has a strong prejudice in favor of theories that can, with sufficient window dressing, be made to sound deterministic.

Finally, let me refer you again to my earlier post about the prediction of quantum nonequilibrium in deBB theory, and the work of Valentini who has shown that it is empirically testable in the context of cosmology:

Astrophysical and Cosmological Tests of Quantum Theory
Antony Valentini
Contribution to: "The Quantum Universe", special issue of Journal of Physics A, dedicated to Prof. G.-C. Ghirardi on the occasion of his seventieth birthday
Journal-ref. J. Phys. A: Math. Theor. 40, 3285-3303 (2007)
http://eprintweb.org/S/authors/All/va/Valentini/7

I am confident that if one digs into the assumptions made there (which one would need to have an expectation of it being worth one's while), one will quickly see that what is being tested there is not deBB theory, but rather, some offshoot that makes additional assumptions inspired by it. In identifying those additional assumptions, one will destroy the claim that this is a fundamental result of the deBB by simply finding a way to embed those exact same additional assumptions into a more CI-type rendition of quantum mechanics. The reason I know this is, until someone is saying you can get a prediction out of a QM-type theory that comes from something other than a wave function, they are all still going to be fundamentally the same. They are just different ways to hide the assumptions being made, when in fact it is important to find ways to expose those assumptions more transparently.

So in fact there is potentially new physics resulting from the deBB ontology, contrary to what you think.

What I think is that no one can know which pedagogy will inspire which new discoveries. As such, I never deny the value in exploring alternataive pedagogies like the deBB or the MWI. My objection is the simple observation of how people fail to recognize the role of prejudice in preferring one set of extraneous ontologies over another, when in fact, the sole non-prejudicial objective must be to identify whichever interpretation has the least extraneous ontology that we are intended to take as serious efforts to establish how reality actually works.

But many serious physicists and philosophers of physics have gone into detail about what a "world" is and what an "observer" is in MWI, and I would suggest that you have a read of the following papers (look in particular at the second one):

Thank you for identifying interesting papers that attempt to address the "mind-body" problem. I am aware that "serious" efforts are made at addressing that, just as I am aware that serious efforts were made by Newton and others to achieve alchemy. Until there is demonstrable progress on either alchemy or including the observer directly into a formulation of science, I will see the two efforts on a similar footing, expect that the former seems in principle more plausible.

I'm quite skeptical that you even understand MWI or for that matter deBB.

Of course you are, that is your default position on all matters-- that your own expertise vastly outweighs that of the other, and this justifies relaxing the requirement to cite actualy evidence in support of your opinions.

Indeed you have already demonstrated a basic misunderstanding about the determinism of the particle trajectories in deBB.

Well at least here we have something resembling specific point, unfortunately I can't recall saying anything about deBB trajectories other than that they have no empirical imprint other than in experiments expressly designed to give them one, and of course in that case standard QM works fine too. As this the only thing I said about deBB trajectories, and seems completely correct to me, you must be claiming it is incorrect, but I guess it's too much to hope you will offer an actual argument to that effect.

Sorry but theories like deBB, stochastic mechanics, and GRW are ultimately empirically differentiable from textbook QM, whether you like it or not.

You see, empty assertions like this actually carry vastly more expository weight if you also equip them with even the most rudimentary example of an actual empirical discriminant. Is that not obvious to you somehow?

I also take it that you are totally oblivious of quantum gravity and cosmology research. You might be surprised to know that many such quantum gravity specialists (Susskind, Hawking, Hartle, Tegmark, Wheeler) find a special utility and appeal in MWI.

Actually, I am also aware that many scientists like coffee, and some have a deep faith in God. I'm certain that all these things go into making a scientist, and they find all kinds of "special utility" in all of them. The issue here is, what is a demonstrable scientific theory. On that score, it is interesting you mention Tegmark, because although I realize he has done many good things in cosmology, it brings to my mind his "quantum suicide" scenario. Do you know it? (I assume is must have come up at one of those interpretation meetings you frequent.) Now, I have not the imagination to concoct a more blatant example of the kinds of absurdities that one can be led to take seriously if one forgets the correct direction of logic in science (from reality to conceptual structures, not the other way around).

So I guess you are a creationist? Very well then, I shall tell everyone on this forum that Ken G is a creationist. After all, only a creationist thinks that vague words like "God did it" are a "simpler" and adequate substitute for precise mathematical equations of motion that predict the full gamut of QM phenomena, including measurement processes.

I'm afraid you missed my meaning rather completely, once again. My point, which you apparently could not dispute so you instead chose this silly rhetorical gambit that is way below you, is that if one thinks one can "solve" the "definiteness problem" simply by offering a hypothetical mechanism that alleviates cognitive disquiet but presents no empirically testable attributes, then I can do that a lot more simply than postulating hypothetical other worlds or invisible trajectories. You were supposed to see that as a refutation that our standards should be that low, not as an argument that we should accept my alternative.

Or, much more likely, your attempts to characterize your twisted version of CI as the most fundamental (or the only legitimate) interpretation is nothing but a delusion.

This is the other logical fallacy you sprinkle liberally thoughout your arguments: replacing what the other person actually said with a straw man so you can refute it. Unfortunately, that fallacious style merely serves to raise suspicions that you could not refute the actual argument as it was presented.

The argument I actually presented was never that the MWI or deBB were "illegitimate", but rather they include extraneous ontologies that are motivated entirely by prejudice, whereas the BI is really the one that sets out to use the minimal ontology that is intrinsic to science itself. Note that being minimal does not connect with legitimacy unless other prejudicial choices are futher entered into the issue. It is true that I have a "beef" with deBB and MWI, but they are perfectly legitimate examples of creating a personal fantasy within which to couch one's understanding of quantum mechanics. We engage in such fantasies all the time, there is nothing illegitimate about it-- as long as we recognize them as such (along the lines of my earlier exchange with vanesch). Hence my only "beef" is the overblown character that deBB and MWI take on (and the CI too, in the wrong person's hands) when we over-interpret our own interpretations.

And this problem has not been solved yet, no matter what you like to think.

I "like to think" that this thread could be about solving that problem, which is rather why I entered onto that train, rather than being bogged down in your own personal opinions about what I like to think.

Well that's quite a disingenuous characterization if there ever was one. I guess you never learned the difference between a phenomenological formalism (like MOND) and a physical theory (like deBB or GRW).

As you have still failed to describe how the deBB can be regarded as a physical theory, rather than QM plus window dressing, it is hard for me to address your complaint here. What is obvious is that you are nitpicking about the fact that MOND is in general a family of potential theories, but I might have hoped you could recognize that difference as being not essential to the issue. Indeed, the difference between a specific theory and a family of theories is its own wild hare (most things people call theories are actually families of theories, like the Big Bang or evolution), I hardly see your desire to steer into that semantic morass as constructive at this point.

A solution to the problem of definite outcomes.

I still await any actual description from you of what you mean by a "solution" to that problem, that does not simply sound to me like "a way for me to alleviate my mental disquiet surrounding certain prejudices about how reality ought to work", and does not produce any testable critiria beyond your elliptical references to quantum cosmology. There are a lot of people making all kinds of extravagant claims-- show me the money. Aristotle thought he had things pretty well figured out to, on the basis of similarly extravagant and unsubstantiated claims.

And yet all the evidence is to the contrary.

Actually, "evidence" is not really your strong suit in this debate, is it? The "evidence" is that you should have instead said "and yet all my own personal opinions are to the contrary".

What amazes me is that you claim to know far more than you evidently really do. And I always feel the obligation to bring down the heat on such people.

Funny, that's what I was going to say. (I'm glad we both have thick skins.)

 

[Ken G]

IPlease keep in mind that in discussions about interpretations of quantum theory, half of the argument is philosophy based, and half of it is theory based. So it is entirely normal to have different viewpoints, and there's no point in trying to argue why one is "better" than the other.

This is well put, and I really didn't mean to frame my position in that light-- in fact I think all three, the CI as it is often described, the MWI, and the deBB, include ontological widgets that are really quite unnecessary, but are still each of interest and could stimulate new discovery. All I was arguing is that a particularly stripped down version of the CI, which is what I believe Bohr advocated, represents the minimal ontology needed to support the basic epistemology of making predictions and generating understanding of QM systems, the key goals of science. My problem with the MWI and the deBB are the claims people make about what they represent or what they accomplish, which I find are largely unsubstantiated if not downright unphysical. But I guess I've said pretty much everything I can on that score, as the thread became more of a debate clarifying things I never said.

I'm not going to lock this thread right away - but steer it into a constructive discussion, or it will be locked.

Oops, I didn't see this until after my last long post! I will confess to considerable rhetorical excess to make my point there, even though I do see my position as fundamentally correct. No doubt the tit-for-tat of my debate with Maaneli is of no general interest whatsoever, so I guess the real question is, does anyone have any actual points to make about how we can characterize as "extraneous" certain elements of an ontology? Maybe that takes it far enough away from the original intent of the OP that it would be better served by a different thread, and even that seems suspect given the tendency for threads about CI, MWI, and deBB to be exhaustingly difficult to bring to a constructive closure!

 

[Maaneli]

Again, that's just silly. The Wikipedia, properly interpreted, is one of many extremely valid references for scientific debate.

Again, that's just silly. The Wikipedia, properly interpreted, is one of many dubious references for scientific debate.

I'm afraid I have no idea what you are talking about. I have seen the forum rules, and see zero issues with how I've handled outside references.

I'm afraid I have no idea what you're talking about. I have also seen the forum rules, and see the obvious issue with how you've handled outside references.

I don't think the phrase "blatantly false" means what you think it does. The claim of mine that you seem to be referring to is that the "measurement problem" is a many-headed dragon that means a slightly, or vastly, different thing any place you encounter it. If you feel that is false, I invite you to invoke something other than your standard penchant for "argument by assertion".

I don't think the phrase "blatantly false" means what you think it does. The claim of mine regarding the measurement problem that you seem to be referring to is clearly and consistently discussed (as I have presented it) in any text or review paper on QM foundations. See, for example, Jammer's "The Philosophy of Quantum Mechanics", Bub's "Interpreting the Quantum World", Torretti's "The Philosophy of Physics", Butterfield's et. al's "Philosophy of Physics: in the Handbook of Philosophy of Science", Schlosshauer's "Decoherence and the Quantum-to-Classical Transition", that Schlosshauer paper I gave you (which really is quite representative of these other works), Bell's "Speakable and Unspeakable in Quantum Mechanics", Bohm and Hiley's "The Undivided Universe", Omnes' "Understanding Quantum Mechanics", Auletta's and Parisi's "Foundations and Interpretation of Quantum Mechanics: In the Light of a Critical-Historical Analysis of the Problems and of a Synthesis of the Results", Elitzur and Dolev's "Quo Vadis Quantum Mechanics", Albert's "Quantum Mechanics and Experience"...Need I pile on more?

Goodness, I've been to no conferences on the foundations of QM? What am I doing having a considered opinion? Of course no one should ever say anything about a science subject they have not been to a conference about, whereas anyone who has been to a conference is immediately to be regarded as an unimpeachable authority. That's pretty much your logic here.

As usual, you totally distorted my remark (much like a Karl Rove Republican). My point in calling you out on your lack of exposure to the mainstream views (either through conferences or well-established texts and review articles like the one's I cited above) is to instill some pause and doubt within your religious self-confidence. Imagine if I never went to a string theory conference or never read any of the texts or review articles on string theory, but then made a sharp and confident criticism about the AdS-CFT correspondence and claimed that most of the string theorists are just confused about it. You and everyone else would have every right to be skeptical of my credibility. Similarly here with you. If you really think you have it figured out so well and that others are confused, I dare you to participate in the next QM foundations conference at the APS in Maryland (this April) and put your ideas out there and see if you can defend them against all the QM foundations specialists. Here, I'll even give you the website link so that you can write to the organizers and request an invitation (though, I predict you'll wuss out instead):

http://carnap.umd.edu/philphysics/conference.html

On the other hand, I will find occasion to read that article, but anticipate that I will either find occasion to agree with its conclusions, or point to flaws in its arguments. You know, "analysis".

Good for you. I think you'll get a lot out of it.

If anyone in the field doesn't think they are confused about the measurement problem, it is they, and you, who have their head in the sand. I'll spare you all the quotes where people like Feynman said that better.

Great, thanks for proving my earlier point. That's why your credibility is so damn weak here. Once again, I invite you to the Maryland conference to put your money where your mouth is.

You like that word, "disingenuous", don't you?

Yes it aptly describes you.

Now let's look at what I'm actually saying. Everyone knows we can pay lip service to the "measurement problem" by referring to a vague sense that we don't know why a theory that is apparently based on deterministic time evolution yields probabilistic outcomes. However, when one digs into that problem, one finds that there are all kinds of different facets to that problem, some with fairly easy solutions, some that will never have any solution because it would go beyond what science is capable of. Thus whenever these "experts" who've gone to conferences refer to "solutions to the measurement problem", they are using vastly imprecise language. That's just obvious to me, I'm sorry that I don't need to go to a meeting to say that.

That's because you've never bothered to study how these other QM formulations like MWI, deBB, stochastic mechanics, propose to solve the measurement problem. Here, do yourself a favor and do some research:

What you always wanted to know about Bohmian mechanics but were afraid to ask
Oliver Passon
Journal-ref. Physics and Philosophy 3 (2006)
(read in particular section 3.3 on pages 10-11)
http://arxiv.org/PS_cache/quant-ph/pdf/0611/0611032v1.pdf

The "Unromantic Pictures" of Quantum Theory
Authors: Roderich Tumulka
Journal reference: J.Phys. A40 (2007) 3245-3273
http://arxiv.org/abs/quant-ph/0607124

But let me give some examples, instead of following your approach of argument by sheer assertion. What are some aspects of the "measurement problem" that have been solved? Well, the obvious one is decoherence, which explains the mechanism for how a closed system can evolve unitarily into a state that, when projected onto open substates, generates a mixed state. The BI was already well aware that this would happen, but decoherence gives a way of saying how that works out. To me, the key contribution of decoherence theory is in verifying the stability of the pointer states. But more importantly, we should note that classical physics already used that result for centuries prior to quantum mechanics, so we should see that as more of a "sanity check" than some kind of fundamental discovery.

As I said before, I agree with you about the utility, value, and importance of the decoherence formalism in solving part of the measurement problem. So, once again, there is no disagreement here.

So what aspects of the "measurement problem" will never be solved by any science? That's easy, any aspects that are intrinsic to the assumptions we make whenever we embark on the scientific path. Here we find issues like the need for idealizations like objectivity, subject/object separation, conventions about reason, and so forth-- all the elements that go into the scientific method that we can pretend, but should not believe, are precise rather than fuzzy aspects of the otherwise seemingly axiomatic structures we call theories.

This is total gibberish. You said absolutely nothing substantive about the measurement problem.

He was talking about a different one of the many heads of the "measurement problem" dragon, to wit, the problem that science is based around results that are highly nongeneric to the theory of quantum mechanics.

Yes, he was talking about one aspect of the measurement problem (as I said); but this was not the extent of his understanding as you implied.

According to your interpretation of "wave/particle duality", perhaps. However, the sensible way to interpret that phrase is simply that particle behavior is describable with wave functions. Look how I got "particle" and "wave" into that completely uncontroversial sentence that has zero need for interpretations of QM-- that's wave/particle duality.

Pfft. You unjustifiably assumed the very thing you were trying to prove (in other words, you begged the question). Tell you what, take a course in basic logic, and then we'll pick up this discussion again.

Personally, I think so much of what is written about the CI is just plain misguided, which is also why I said that most people who criticize it either don't understand it, or have morphed it into a kind of strawman to appease the very prejudices that it was intended to avoid appeasing. We covered all this already in the choice to use BI instead of CI-- you're backtracking.

I agree with everything you say about CI, and I'm glad you used BI instead of CI to refer to Bohr, and hope you continue to do so.

The latter problem is not "solved" by any of the interpretations we've talked about, any better than "God did it" solves that problem.

It's no surprise to hear that coming from a creationist. But I should remind you that your comment is not at all a scientific one, nor even a serious philosophical one, and I would also remind you that there is in fact an amateur philosophy discussion forum here that you can move to if you want to make vacuous statements like that. But please don't bring nonsensical statements like that into a physics forum.

Usually, in physics we are well aware that there is no such thing as a "fundamental" theory, as all theories will begin with the postulation of undefined entities. Why people are under the illusion that quantum mechanics is any different was always been a mystery to me, but as I said, I see it as a classic example of "all past science has been wrong, but today we have it right" kind of thinking.

I agree with everything you say here, but this is an entirely different issue.


I won't waste my time responding to your inane criticisms about the use of the word "predict". Not until you actually learn about the quantum theories you're criticizing.

The MWI asserts the existence, yes existence, of worlds that we have no interaction with and no empirical connection to. The justification for that is entirely that it allows us to imagine something we should not bother to be so foolish to imagine, that our mathematical concepts can dictate to reality. Yes, I would indeed describe that as the very definition of what is nonphysical-- and what I called not even wrong.

Well I guess you would say the same about string theory? Then that's your right, but you still haven't given an argument (other than ad hominem's) for why your criterion should be preferred over any other. Personally, I think this just makes you a naive positivist. And there is no logical reason to think that everything that exists in the physical world should be empirically detectable by humans, even in principle. And if a mathematical theory makes all experimentally confirmable predictions, but also predicts some phenomena that are (or seem) beyond the capability of human detection, that poses no logical or consistency problem for the theory whatsoever. It only poses a problem for YOUR philosophical prejudice about how the physical world "should" work.

Actually, I did, but I'm happy to do it again: what is "physical" is all that we can objectively and repeatably measure (at least in principle, we always have to allow for technological limitations). I would say that statement is the very core concept of all of physics, hence the word.

See above.

Physics theories do not "predict" other physics theories!

Actually they do. Special relativity predicts classical mechanics in the v << c limit.

I'll break here, my response is long enough.

 

[Maaneli]

You pointed to the Nazi bomb effort, which you are apparently unaware that Heisenberg claimed he intentionally sabotaged.

No actually Heisenberg never made that claim. That's a myth, just like the myth that Einstein was a poor student in secondary school. I would cite you references, but I suspect you would just ignore them for your own convenience.

I mean, well, it leaves no tracks.

I mean, well, what do you mean by "tracks"?

Goodness, you are massacring the word "predict" again. You can certainly choose to force the particle to leave literal "tracks" by deciding you are going to, by measurement, establish a concept of a trajectory, but you don't need dBB for that, simple QM accomplishes that just fine, and the predictions (using the correct meaning of that word) are all identical. That's what I mean by dBB leaving no tracks-- nothing that distinguishes it that isn't happening entirely in our minds (i.e., no tracks).

See all my references and comments about quantum nonequilibrium in deBB.

As I already pointed out with the die analogy, the determinism of the Schroedinger evolution is not sufficient to establish a deterministic process. So no, the determinism does not come from the Schroedinger equation, and I don't need to go to a meeting on quantum interpretations to see that basic logic.

I guess you were never any good at math, otherwise you would know that the Schroedinger equation is a linear PDE, and that such equations are perfectly deterministic in their time-evolution. And you don't need to go to a meeting on quantum interpretations to see that basic logic.

Please stop misusing the word "predict", it is almost painful for me given that my entire point is we must always bear in mind the empirical foundations of science when we interpret what science is doing. But even if we substitute the word "derives", your statement is still backward logic-- the deBB starts from the Born rule and reverse engineers a picture that can be said to lead to it. But the assumptions of the deBB are no less arbitrary than those of the Born rule, so no, nothing is being fundamentally "derived" there, it is just a shell game, a basic parlor trick.

Nope, sorry, wrong again. Do yourself a favor and do some research. Here, I'll start you off:

Quantum Equilibrium and the Origin of Absolute Uncertainty
Authors: Detlef Dürr, Sheldon Goldstein, Nino Zanghí
Journal reference: Journ. of Statistical Phys. 67, 843-907 (1992)
http://arxiv.org/abs/quant-ph/0308039

Dynamical Origin of Quantum Probabilities
Authors: Antony Valentini, Hans Westman
http://arxiv.org/abs/quant-ph/0403034

Hidden Variables, Statistical Mechanics and the Early Universe
Authors: Antony Valentini
Journal reference: 'Chance in Physics: Foundations and Perspectives', eds. J. Bricmont et al. (Springer, 2001), pp. 165-181.
http://arxiv.org/abs/quant-ph/0104067

http://www.fourmilab.ch/rpkp/valentini.html

Proof That Probability Density Approaches |ψ|2 in Causal Interpretation of the Quantum Theory
David Bohm
Phys. Rev. 89, 458 (1953)
http://prola.aps.org/abstract/PR/v89/i2/p458_1

Model of the Causal Interpretation of Quantum Theory in Terms of a Fluid with Irregular Fluctuations
D. Bohm and J. P. Vigier
Phys. Rev. 96, 208 (1954)
http://prola.aps.org/abstract/PR/v96/i1/p208_1

Actually, I highly doubt it is logical to think that the deBB could have been arrived at first, because of its structure as QM with a facade erected in front of it to make it look like a deterministic theory (even though it does not allow anything more to be determined than does QM).

Actually, the deBB was discovered first (in 1923) by Slater et al. as a photon theory (see the reference therein):

N. Bohr, H.A. Kramers and J. C. Slater, “The quantum theory of radiation,”
Philosophical Magazine 47, 785-802 (1924). Reprinted in Sources of Quantum
Mechanics, see Ref. 7.

The Schroedinger equation was also derived in the same year as Schroedinger's original derivation, but via the Madelung fluid (the same equations as deBB):

E. Madelung, “The hydrodynamical picture of quantum theory,” Z. Phys . 40, 322-326 (1926).

I am confident that if one digs into the assumptions made there (which one would need to have an expectation of it being worth one's while), one will quickly see that what is being tested there is not deBB theory, but rather, some offshoot that makes additional assumptions inspired by it.

Your confidence is baseless because you don't even know the basics. This is actually part of the standard deBB theory whether you like it or not. Again, do some research first. I gave you all the references you need.

In identifying those additional assumptions, one will destroy the claim that this is a fundamental result of the deBB by simply finding a way to embed those exact same additional assumptions into a more CI-type rendition of quantum mechanics.

I would like to see that!

What I think is that no one can know which pedagogy will inspire which new discoveries. As such, I never deny the value in exploring alternataive pedagogies like the deBB or the MWI.

Oh, right, I see. You think alternative pedagogies like deBB or MWI are no better than saying "God did it", but you never deny the value of exploring them. You would be a perfect candidate to join Bill Dembski and the Discovery Institute and do some research on how ID and creationism can "explain" some other explanatory "gaps" in evolutionary biology.

My objection is the simple observation of how people fail to recognize the role of prejudice in preferring one set of extraneous ontologies over another, when in fact, the sole non-prejudicial objective must be to identify whichever interpretation has the least extraneous ontology that we are intended to take as serious efforts to establish how reality actually works.

And decoherence alone is not enough because it says nothing about the problem of definite outcomes.

Thank you for identifying interesting papers that attempt to address the "mind-body" problem. I am aware that "serious" efforts are made at addressing that, just as I am aware that serious efforts were made by Newton and others to achieve alchemy.

Missed the point utterly (as usual).

Of course you are, that is your default position on all matters-- that your own expertise vastly outweighs that of the other, and this justifies relaxing the requirement to cite actualy evidence in support of your opinions.

It certainly outweighs yours. And I guess its convenient for you to just ignore all the evidence I give you.

Actually, I am also aware that many scientists like coffee, and some have a deep faith in God.

Oh, you mean Creationists like yourself?

On that score, it is interesting you mention Tegmark, because although I realize he has done many good things in cosmology, it brings to my mind his "quantum suicide" scenario. Do you know it? (I assume is must have come up at one of those interpretation meetings you frequent.)

Yes I know it.

Now, I have not the imagination to concoct a more blatant example of the kinds of absurdities that one can be led to take seriously if one forgets the correct direction of logic in science (from reality to conceptual structures, not the other way around).

Your prejudice once again.

You were supposed to see that as a refutation that our standards should be that low, not as an argument that we should accept my alternative.

Well, if you were reading carefully, I never said deBB or MWI or GRW is the best possible solution to the problem of definite outcomes. I just said that they DO constitute solutions to that aspect of the measurement problem (and yes, they are much more sophisticated than just saying that "God did it" like you want to believe), and that they incorporate decoherence very naturally. In fact, I personally have a much more radical view of the interpretation of QM.

The argument I actually presented was never that the MWI or deBB were "illegitimate", but rather they include extraneous ontologies that are motivated entirely by prejudice, whereas the BI is really the one that sets out to use the minimal ontology that is intrinsic to science itself.

I have no problem with being a minimalist in that sense, or for that matter, what I like to call an "agonstic realist". But I do have a problem with you claiming that there is no mystery or problem of definite outcomes that doesn't justify for a deeper physical explanation, or that deBB and GRW are not empirically testable, or that they are no better than "God did it" (which really is disingenuous).

The rest of your comments were a load of rhetorical BS, and I won't waste my time deconstructing them.

 

[Maaneli]

Please keep in mind that in discussions about interpretations of quantum theory, half of the argument is philosophy based, and half of it is theory based. So it is entirely normal to have different viewpoints, and there's no point in trying to argue why one is "better" than the other. It is important to recognize this. What is problematic and what isn't, comes close to the philosophy of science itself. None of the current interpretations are totally idiotic, and none of them are without conceptual difficulties. The choice is often driven by what properties one values more than others. There is no "obviously correct" interpretation - otherwise there wouldn't be any debate amongst knowledgeable people for almost a century.

I am not trying to argue about what I think is the most correct interpretation. I am simply trying to keep people like Ken G from thinking that he already knows the answers or that the problems are simpler than they really are. The measurement problem (in particular, the problem of definite outcomes) is primarily what motivates and justifies the various QM interpretations beyond decoherence theory, and I think people like Ken G need to understand that and stop arrogantly belittling physical theories that are more ambitious than his own naive positivism.

I'm not going to lock this thread right away - but steer it into a constructive discussion, or it will be locked.

Honestly, I think the only way this discussion can ever become more constructive is if Ken G starts doing some serious reading and thinking about the current theories and opinions in QM foundations (and philosophy of science!), understands the precise facets of the measurement problem, and infuses himself with some more self-doubt (especially about the meaning of science!). The mentality that he currently has is only detrimental to the progress of physics and science in general.

 

[ZapperZ]

Obviously, vanesch's warning falling on deaf ears. So this thread is done.

Also be warned that the NEXT time this occurs again (and trust me, it will since the question of "interpretation" comes back very often like a bad habit), there will be NO warning given to all those involved prior to any actions taken.

Zz.