Is Qualia Intrinsically Linked to Quantum Mechanics?

[Varon]

Many believe Qualia or internal subjective experience are not describable or modelable by our current physics. This may be because we still haven't discovered its physics. But do you think qualia is related to quantum mechanics? I think the correct quantum interpretation can at least describe qualia. Here's the reason why I think quantum ontology is very important. We know qualia is not part of our physics as many believed. So how is qualia related to matter (our brain)? The right quantum interpretation might offer the interface of how qualia is coupled to brain. This is so because matter is described by quantum mechanics. What controls the behavior of matter... the wave function. Therefore the right interpretation would offer solution to how qualia is related to the wave function which describes matter (the brain). What do you think? Bottom line is. Qualia is non-physical, brain is physical, what connects the two but wave function?! So search for the right quantum interpretation must involve knowing how qualia is coupled to matter (the brain). If you can see logical flaw in this argument, pls justify your counter arguments. If you can offer arguments that qualia is related to spacetime instead and not to matter (quantum), then pls. explain why you think it is so. I've thought of this for 8 years already. If you can see the fallacy of my thought. Pls. let me know why. Thanks.

 

[Demystifier]

We know qualia is not part of our physics as many believed. So how is qualia related to matter (our brain)? The right quantum interpretation might offer the interface of how qualia is coupled to brain. This is so because matter is described by quantum mechanics. What controls the behavior of matter... the wave function.
Therefore the right interpretation would offer solution to how qualia is related to the wave function which describes matter (the brain). What do you think?

In essence, your argument can be summarized as follows. Wave function is related to matter, matter is related to brain, and brain is related to qualia. Therefore, wave function is related to qualia.

It is logically correct, but note that the relation in the form I summarized it is only an INDIRECT relation, as it required several links to make the connection. That's not much different from saying "wave function is related to matter, matter is related to church (because church is made of matter), church is related to God. Therefore, wave function is related to God." Being related is not the same as being DEEPLY related.

Bottom line is. Qualia is non-physical, brain is physical, what connects the two but wave function?!

Perhaps something else that we have not discovered yet?

So search for the right quantum interpretation must involve knowing how qualia is coupled to matter (the brain).

Only if you think that the correct interpretation of QM will also be the correct interpretation of EVERYTHING, because "everything" includes the qualia as well. But there is no proof that correct interpretation of QM must be the correct interpretation of everything.

 

[Varon]

In essence, your argument can be summarized as follows. Wave function is related to matter, matter is related to brain, and brain is related to qualia. Therefore, wave function is related to qualia.

It is logically correct, but note that the relation in the form I summarized it is only an INDIRECT relation, as it required several links to make the connection. That's not much different from saying "wave function is related to matter, matter is related to church (because church is made of matter), church is related to God. Therefore, wave function is related to God." Being related is not the same as being DEEPLY related.


Perhaps something else that we have not discovered yet?


Only if you think that the correct interpretation of QM will also be the correct interpretation of EVERYTHING, because "everything" includes the qualia as well. But there is no proof that correct interpretation of QM must be the correct interpretation of everything.

In nature, there is quantum mechanics to describe matter and spacetime to describe the dynamics of matter. Therefore qualia must be related to them. In your view, you believe that time can be broken down into subjective time and math time... here subjective time is qualia of time.

Whatever, the best candidate of quantum interpretations are those that are friendly to qualia. I wonder if Bohmian Mechanics count. From the surface, BM looks pretty boring with all particles doing the dance. Later in life. Bohm conjectured the Implicate Order. I think he put qualia back to nature because the Implicate Order could be related of qualia. Therefore why don't you entertain the Implicate Order rather than plain old Bohmian mechanics. They are in conflict because in BM, particle is always particle. In Bohm Implicate Order, he returns to the wave and particle duality. What do you think.

 

[Ryan_m_b]

As Demystifier quite rightly says

Wave function is related to matter, matter is related to brain, and brain is related to qualia. Therefore, wave function is related to qualia. It is logically correct, but note that the relation in the form I summarized it is only an INDIRECT relation

Qualia are not physical in the same way that stories are not physical. How this emergent property relates to the physical is an interesting subject. Personally I feel that "new physics" is unnecessarily touted as needed to explain subjective experience. Quantum physics especially is bought forth like some new age holy grail as a means of explaining the 'soul'. I don't see why classical physics would not be able to explain qualia/consciousness etc (I'm not saying it can, just that I see no reason why it can't).

The reality is we have no idea how to solve the Hard problem of consciousness but that doesn't necessarily mean we need radical new physics. The physics we have might be quite able to explain it but we lack the required technology and knowledge in biology, neuroscience and psychology to answer the question.

EDIT: From the Neurobiological approaches to consciousness section of the Neural correlates of consciousness wiki page

Discovering and characterizing neural correlates does not offer a theory of consciousness that can explain why particular systems experience anything at all, why they are associated with consciousness and why other systems of equal complexity are not, but understanding the NCC is a step toward such a theory. Most neurobiologists assume that the variables giving rise to consciousness are to be found at the neuronal level, governed by classical physics, though a few scholars have proposed that quantum behaviors underlie consciousness. However there is no evidence that any components of the nervous system display quantum entanglement.

 

[jambaugh]

Many believe Qualia or internal subjective experience are not describable or modelable by our current physics. This may be because we still haven't discovered its physics. But do you think qualia is related to quantum mechanics?

It would be helpful for discussion to discard the more esoteric term "qualia" and just say "subjective experience".

In so far as the thought experiments on wikipedia are concerned, and in particular the one concerning color, I used to ponder this in my youth. "Suppose I see green when you see red but of course I call it red because that's what everyone else calls it!" This is a supposition about distinct internal subjective experience. I later realized (helped by learning some rigorous relativity) that it is a meaningless distinction. We identify subjective experience, we perceive based on prior experience. The meaning and essence of the experience is in the relation to other experiences and not in some internal "reality" that seems to be implied by discussions I just read about and by your usage of "qualia".

The "reality" of experience (from a materialist monist's point of view) is in the physics of neural activity and the emergent properties of patterns of such activity which define awareness. This of course is based in physics and some insight into the mechanics of thought might be actualized via consideration of quantum theory.

However you have laid down a series of loaded questions and opinions. You need to revisit your assumptions. I will parse your comments and try to point out issues:

I think the correct quantum interpretation can at least describe qualia.

There are two levels of quantum "interpretation" the first and foremost being the theoretical interpretation, i.e. mapping the pencil and paper formalism to predictions in the laboratory/observatory. This is well established and pretty much universally agreed upon. It is QM's description of "what happens".

The other level of quantum "interpretation" I call a "re-interpretation" in that it is an attempt to describe and explain the aspects of the prior interpretation in some context, especially and usually in some ontological context. The exception is the Orthodox or Copenhagen interpretation which is basically a rejection of the need, utility, or desirability of an ontological (re)interpretation. So when you say...

Here's the reason why I think quantum ontology is very important.

You are already making specific assumptions about which "interpretation" you favor, namely you are a priori rejecting Copenhagen.

We know qualia is not part of our physics as many believed. So how is qualia related to matter (our brain)?

Is "qualia" well defined? Are you trying to relate "deficit spending" to "electrical charge"?
Or are you trying to relate "the set of left handed unicorns" to "the mass of a proton"?
Is your attempt at relation well defined?

The right quantum interpretation might offer the interface of how qualia is coupled to brain.

The brain as a material organ couples physically via chemistry and nervous signals to the body and via sensory organs to the environment. That's about it, excepting some direct brain to environmental coupling e.g. when you hit your head and get a concussion or direct electrical stimulation from a "http://www.technovelgy.com/ct/content.asp?Bnum=207" " or something.

This is so because matter is described by quantum mechanics. What controls the behavior of matter... the wave function.

At the first level of interpretation, the wave function describes the behavior of matter. To say it controls that behavior is to enter into a specific class of ontological interpretations, in particular a DeBroglie-Bohm type interp.

Therefore the right interpretation would offer solution to how qualia is related to the wave function which describes matter (the brain). What do you think?

"offer solution" to what problem? This "how" presumes that it does relate in some meaningful way, and I don't think you can in the way you appear to be striving to do. You are reifying this qualia as if it were more than a relationship between sensory stimulation (a physical process) and perception (a mental process) understanding that "mind" is, in the materialist's p.o.v. a function of the brain and not a physical property or physical entity within the brain (or coupled to the brain).

Bottom line is. Qualia is non-physical, brain is physical, what connects the two but wave function?!

Be wary of epiphanies. They feel good and they focus your attention but they don't always signal truth.

There is a parallel in your association but it all the more indicates that both "qualia" and "wave-function" are non-real mental processes and only have meaning in the context of our interpretation (in the first sense) of how they relate to the physical environment.

So search for the right quantum interpretation must involve knowing how qualia is coupled to matter (the brain). If you can see logical flaw in this argument, pls justify your counter arguments. If you can offer arguments that qualia is related to spacetime instead and not to matter (quantum), then pls. explain why you think it is so. I've thought of this for 8 years already. If you can see the fallacy of my thought. Pls. let me know why. Thanks.

You are making what I believe are correct associations but for the fact that you are committing a category error in reifying the conceptual.

Consider how I can have say, 5 apples in a bowl in my kitchen. The apples are physical entities. In their gross description I can conceive of them as physical objects (classical physics). Now the number 5 relates to the apples in that it relates to my description of them as physical objects.

But the number 5 is not real in the same way as the apples are real. It is my conceptual means of quantifying them. It is useful and rigorous and I can describe what I mean by "apples" well enough that you, having never seen an apple can come into my kitchen and agree on their number. But this doesn't give 5 "reality" status.

Now let me go deeper and consider the apples at a quantum level... or rather let's now go into my lab and switch from apples to electrons. I have a lab bench and on it is a device which goes click and I say the click indicates the device emitted an electron. You have a device which you say goes click to indicate it has absorbed an electron. We compare and verify that we can arrange our devices so that my device's clicks precede and correlate almost exactly to your devices clicks. We further investigate and verify that counting clicks from my device, subtracting clicks from your device and comparing that with the increase in charge on an intervening metal grid, that indeed each click corresponds to a flux of -1e of charge. Further investigation allows us to also determine the mass to charge ratio and we correlate our idea of "an electron" to the physics texts.

The reality here is in the clicks and other gross behavior and configurations of our devices. Their behavior indicates an underlying actuality of electrons. I distinguish actuality from reality in that actuality is "what is happening out there" while reality carries with it assumptions of objective properties. This assumption, I assert, is not always valid.

Now you can construct a reality model of the electron, say a "real" pilot wave guiding a "real" point particle a la deBroglie-Bohm. I, being a good Copenhagenist reject your model along with infinite parallel universes and other ontological intepretations. I assert that the "actuality" is fundamental and "reality" is a derivative concept. We paint a reality based on the actuality we observe and I assert we must be careful to check the validity of the assumption that all actualities have a singular reality model or any at all.

With apples we can construct a consistent reality model for gross behavior and it is fine and proper at that scale. It is consistent enough that we can agree (subject to classical relativity or our descriptions) on that reality and we speak of the apples as real. But in truth it is only, fundamentally a model.

Back to your qualia I believe we mentally maintain a reality model in our minds which we constantly update with the flood of sensations we gather from our external actuality. When you close your eyes and still visualize e.g. the walls around you and objects in your room you are examining your mental reality model. You will note how this model begins to decay as your ST memory decays and as your mental auditing "circuits" take into account the uncertainty in your knowledge of how things will behave given the delay since the last best sensory input. Reality is melting here but the actuality it was modeling is still there acting away. You might even pick up some cues to a change and your mental picture updates.

I believe this mental reality model building is an evolved process allowing us to go beyond reacting to our environment. It allows us to efficiently abstract a mental "theory of how things will behave" which works well at the level of tossing apples but breaks down when we try to visualize tossing electrons. And it is this habit of reality which I believe leads us to (mistakenly) try to (re)interpret quantum actuality in terms of some ontological construct.

So I see your comparison of qualia with wave-functions as apt but both as neither real nor actual. Thus I see you as committing an error in trying to reify them, (or even should you learn to make the distinction, actualizing them as physical phenomena). They are conceptual constructs.

 

[Varon]

It would be helpful for discussion to discard the more esoteric term "qualia" and just say "subjective experience".

In so far as the thought experiments on wikipedia are concerned, and in particular the one concerning color, I used to ponder this in my youth. "Suppose I see green when you see red but of course I call it red because that's what everyone else calls it!" This is a supposition about distinct internal subjective experience. I later realized (helped by learning some rigorous relativity) that it is a meaningless distinction. We identify subjective experience, we perceive based on prior experience. The meaning and essence of the experience is in the relation to other experiences and not in some internal "reality" that seems to be implied by discussions I just read about and by your usage of "qualia".

The "reality" of experience (from a materialist monist's point of view) is in the physics of neural activity and the emergent properties of patterns of such activity which define awareness. This of course is based in physics and some insight into the mechanics of thought might be actualized via consideration of quantum theory.

However you have laid down a series of loaded questions and opinions. You need to revisit your assumptions. I will parse your comments and try to point out issues:


There are two levels of quantum "interpretation" the first and foremost being the theoretical interpretation, i.e. mapping the pencil and paper formalism to predictions in the laboratory/observatory. This is well established and pretty much universally agreed upon. It is QM's description of "what happens".

The other level of quantum "interpretation" I call a "re-interpretation" in that it is an attempt to describe and explain the aspects of the prior interpretation in some context, especially and usually in some ontological context. The exception is the Orthodox or Copenhagen interpretation which is basically a rejection of the need, utility, or desirability of an ontological (re)interpretation. So when you say...


You are already making specific assumptions about which "interpretation" you favor, namely you are a priori rejecting Copenhagen.

Actually Copenhagen is not a neutral interpretation. Bohr stated that in the absence of measurement to determine its position, a particle has no position. So Copenhagen already assumes ontological reality that a particle has no position before measurement. The real neutral interpretation is the Statistical Interpretation which is Quantum Mechanics bared to the bones.

I'll meditate and contemplate on what your wrote below. But note that without qualia, one can't even meditate or contemplate (ponder on this). Without qualia, we are just computer with sensors connected to the unconscious brain. There would be no one inside. But what you seem to be saying is that, our qualia or hard problem can be solved by mere neutral networks.. but reading up on the latest in neutral networks.. it seems not sufficient.. but I admit that perhaps in year 1,000,000 A.D. Computers might be self-aware and have qualia too... remember evolution has taken many millions of years for this neural complexities to evolve qualia. I'll think of this possibility. Thanks.

Is "qualia" well defined? Are you trying to relate "deficit spending" to "electrical charge"?
Or are you trying to relate "the set of left handed unicorns" to "the mass of a proton"?
Is your attempt at relation well defined?

The brain as a material organ couples physically via chemistry and nervous signals to the body and via sensory organs to the environment. That's about it, excepting some direct brain to environmental coupling e.g. when you hit your head and get a concussion or direct electrical stimulation from a "http://www.technovelgy.com/ct/content.asp?Bnum=207" " or something.


At the first level of interpretation, the wave function describes the behavior of matter. To say it controls that behavior is to enter into a specific class of ontological interpretations, in particular a DeBroglie-Bohm type interp.


"offer solution" to what problem? This "how" presumes that it does relate in some meaningful way, and I don't think you can in the way you appear to be striving to do. You are reifying this qualia as if it were more than a relationship between sensory stimulation (a physical process) and perception (a mental process) understanding that "mind" is, in the materialist's p.o.v. a function of the brain and not a physical property or physical entity within the brain (or coupled to the brain).


Be wary of epiphanies. They feel good and they focus your attention but they don't always signal truth.

There is a parallel in your association but it all the more indicates that both "qualia" and "wave-function" are non-real mental processes and only have meaning in the context of our interpretation (in the first sense) of how they relate to the physical environment.



You are making what I believe are correct associations but for the fact that you are committing a category error in reifying the conceptual.

Consider how I can have say, 5 apples in a bowl in my kitchen. The apples are physical entities. In their gross description I can conceive of them as physical objects (classical physics). Now the number 5 relates to the apples in that it relates to my description of them as physical objects.

But the number 5 is not real in the same way as the apples are real. It is my conceptual means of quantifying them. It is useful and rigorous and I can describe what I mean by "apples" well enough that you, having never seen an apple can come into my kitchen and agree on their number. But this doesn't give 5 "reality" status.

Now let me go deeper and consider the apples at a quantum level... or rather let's now go into my lab and switch from apples to electrons. I have a lab bench and on it is a device which goes click and I say the click indicates the device emitted an electron. You have a device which you say goes click to indicate it has absorbed an electron. We compare and verify that we can arrange our devices so that my device's clicks precede and correlate almost exactly to your devices clicks. We further investigate and verify that counting clicks from my device, subtracting clicks from your device and comparing that with the increase in charge on an intervening metal grid, that indeed each click corresponds to a flux of -1e of charge. Further investigation allows us to also determine the mass to charge ratio and we correlate our idea of "an electron" to the physics texts.

The reality here is in the clicks and other gross behavior and configurations of our devices. Their behavior indicates an underlying actuality of electrons. I distinguish actuality from reality in that actuality is "what is happening out there" while reality carries with it assumptions of objective properties. This assumption, I assert, is not always valid.

Now you can construct a reality model of the electron, say a "real" pilot wave guiding a "real" point particle a la deBroglie-Bohm. I, being a good Copenhagenist reject your model along with infinite parallel universes and other ontological intepretations. I assert that the "actuality" is fundamental and "reality" is a derivative concept. We paint a reality based on the actuality we observe and I assert we must be careful to check the validity of the assumption that all actualities have a singular reality model or any at all.

With apples we can construct a consistent reality model for gross behavior and it is fine and proper at that scale. It is consistent enough that we can agree (subject to classical relativity or our descriptions) on that reality and we speak of the apples as real. But in truth it is only, fundamentally a model.

Back to your qualia I believe we mentally maintain a reality model in our minds which we constantly update with the flood of sensations we gather from our external actuality. When you close your eyes and still visualize e.g. the walls around you and objects in your room you are examining your mental reality model. You will note how this model begins to decay as your ST memory decays and as your mental auditing "circuits" take into account the uncertainty in your knowledge of how things will behave given the delay since the last best sensory input. Reality is melting here but the actuality it was modeling is still there acting away. You might even pick up some cues to a change and your mental picture updates.

I believe this mental reality model building is an evolved process allowing us to go beyond reacting to our environment. It allows us to efficiently abstract a mental "theory of how things will behave" which works well at the level of tossing apples but breaks down when we try to visualize tossing electrons. And it is this habit of reality which I believe leads us to (mistakenly) try to (re)interpret quantum actuality in terms of some ontological construct.

So I see your comparison of qualia with wave-functions as apt but both as neither real nor actual. Thus I see you as committing an error in trying to reify them, (or even should you learn to make the distinction, actualizing them as physical phenomena). They are conceptual constructs.

 

[Ryan_m_b]

I'll meditate and contemplate on what your wrote below. But note that without qualia, one can't even meditate or contemplate (ponder on this). Without qualia, we are just computer with sensors connected to the unconscious brain. There would be no one inside. But what you seem to be saying is that, our qualia or hard problem can be solved by mere neutral networks.. but reading up on the latest in neutral networks.. it seems not sufficient.. but I admit that perhaps in year 1,000,000 A.D. Computers might be self-aware and have qualia too... remember evolution has taken many millions of years for this neural complexities to evolve qualia. I'll think of this possibility. Thanks.

I don't think anyone suggested that just neural networks are necessary for consciousness (sub-neural cellular activity and NOS signalling play an important role) but I don't think an adequate case has been made stating that classical physics is unable to simulate/examine consciousness.

The use of the word qualia is a bit vague, subjective experience or consciousness are better terms.

 

[Fyzix]

I'm now 100% sure that Varon is a troll...

 

[Varon]

I'm now 100% sure that Varon is a troll...

No. I'm a metaphysicist or philosopher looking for answers, searching for truth. That is all there is to it.

 

[Ken G]

I tend to agree with jambaugh's characterization of Copenhagen as avoiding ontological stances whenever possible, though there may be subtle differences between Copenhagen and strict "statistical" interpretations. The main point of Copenhagen is the primacy of what jambaugh is calling the "actuality" of the situation, whereas any ontology involves the "reality" of the situation. So when Bohr says that a particle has no position until it is measured, he is not asserting an ontology of a reality-of-no-position, he is simply saying that the actuality is the measurement, and if the reality must be viewed as subordinate to the actuality, then the reality of position does not appear until there is a measurement. Maybe we could find common ground that Copenhagen rests on subordinating the real to the actual, rather than on denying all ontology in quantum mechanics.

What's more, I would point out that the different interpretations of quantum mechanics do not make different physical predictions, so if we are looking for a quantum mechanical description of subjective experience, it would need to make testable predictions about the neural correlates of that experience, and so would need to accommodate any of the interpretations. I think the problem goes deeper than the interpretations of quantum mechanics, which are basically harmless philosophical pictures of processes happening on scales that might not have anything fundamental to do with consciousness. I think the neural correlates of consciousness are like watching the actions of a great painter while they are painting, or the actions of a great musician while they are making music. We can learn a lot about painting and music that way, but it's not at all clear we are learning much about the art behind them. Watching the muscles, or watching the brain signal the muscles, both seem more like the form of what is happening, than they do like the substance of what is happening.

As for the substance, I'm not sure we can do better than "you know consciousness when you have it." Can we imagine that a non-conscious processor is capable of doing an analysis that results in an understanding of consciousness without being conscious? I suppose it depends on what goals we have for the term "understand."

 

[jambaugh]

Actually Copenhagen is not a neutral interpretation. Bohr stated that in the absence of measurement to determine its position, a particle has no position.

You are still holding onto your own ontological bias when you parse this statement. "having no position" means one thing when you treat position as something out there i.e. as a state value, and means something entirely different when you recognize position as a parameter in one's internal reality model. I this statement Bohr is explicitly saying that "position" is the latter of these two and so saying it doesn't exist is saying it is disconnected from anything actual. In CI Position is NOT a value of an objective state of the system, it is a value of the objective record of the position measuring device after it makes a position measurement.

It is hard not to do this since we grew up (individually and as a species) using objective reality models as if they were fundamentally true instead of models. We assumed when our models failed that they disagreed with the "true model" which we think of as "The Real". The point is to recognize our internal reality models as not derivative of the true ontological state of reality, but rather is derivative of the actuality which is a more general concept.

And so your conclusion...

So Copenhagen already assumes ontological reality that a particle has no position before measurement. The real neutral interpretation is the Statistical Interpretation which is Quantum Mechanics bared to the bones.

is based implicitly on a circular argument. You are rejecting CI implicitly when you parse the meanings of statement made asserting CI in that you are taking the "absence of position" as a statement about reality instead of understanding it as a meta statement about the concept of position. Bohr is saying that the meaning of "position" is fundamentally different than we think of it in classical terms. It is an observable not a state variable. The fundamental distinction between (CI)QM and CM is that in CM "observable" is assumed to be equivalent to "state variable". Learning (or really unlearning so as...) to distinguish this is the cusp of understanding CI.

I'll meditate and contemplate on what your wrote below. But note that without qualia, one can't even meditate or contemplate (ponder on this). Without qualia, we are just computer with sensors connected to the unconscious brain.

This sounds like "without the Lourd we're all doomed to haylfyre and damnachion..." You are heavily invoking a prior assumptions about qualia when you make such statements.

I can say (in a classical setting) "without the distance between two particles the particles do not exist" but this is not saying anything about distance except that it is automatically a relationship between (and function of) plural (classical) particles. Remember that subjective experience means experience which is not necessarily objective. In short it is not impossible for our subjective experiences to agree in so far as they have functional meaning. This we often see when we both say "that's a red apple". Thus when you say "without qualia" you are saying "without experience" be it objective or subjective. You are eliminating a basic relationship between our minds and our environment. So you conclusion is a bit off. We would rather be "computers without sensors" or more aptly we would be lumps of flesh.

There would be no one inside.

Don't (further) mystify qualia. It is a concept about perception and cognition and it sounds like you're trying to redefine it as "soul" or "spirit" or some property of these. I think you shouldn't make any assertions about what qualia is or what it's presence or absence means within this forum as we would like to stick to science here and leave the mysticism to the usenets. This again is why I think you should refrain from using that word and stick to "subjective experience" which is a common usage phrase. I think you'll also find it will keep your definition from floating into the mystic realm.

 

[jambaugh]

No. I'm a metaphysicist or philosopher looking for answers, searching for truth. That is all there is to it.

I suggest before you pin yourself down as a metaphysicist you should spend some time on epistemology. There is where you can learn the crux of the issues with e.g. quantum interpretation and what we mean by "reality".

In particular, beyond mathematics as speculative metaphysics, the subject of metaphysics a priori assumes a fundamental classical reality. As I point out by my own rejection of that assumption not everyone must so assume.

 

[Varon]

You are still holding onto your own ontological bias when you parse this statement. "having no position" means one thing when you treat position as something out there i.e. as a state value, and means something entirely different when you recognize position as a parameter in one's internal reality model. I this statement Bohr is explicitly saying that "position" is the latter of these two and so saying it doesn't exist is saying it is disconnected from anything actual. In CI Position is NOT a value of an objective state of the system, it is a value of the objective record of the position measuring device after it makes a position measurement.

It is hard not to do this since we grew up (individually and as a species) using objective reality models as if they were fundamentally true instead of models. We assumed when our models failed that they disagreed with the "true model" which we think of as "The Real". The point is to recognize our internal reality models as not derivative of the true ontological state of reality, but rather is derivative of the actuality which is a more general concept.

And so your conclusion...

is based implicitly on a circular argument. You are rejecting CI implicitly when you parse the meanings of statement made asserting CI in that you are taking the "absence of position" as a statement about reality instead of understanding it as a meta statement about the concept of position. Bohr is saying that the meaning of "position" is fundamentally different than we think of it in classical terms. It is an observable not a state variable. The fundamental distinction between (CI)QM and CM is that in CM "observable" is assumed to be equivalent to "state variable". Learning (or really unlearning so as...) to distinguish this is the cusp of understanding CI.


This sounds like "without the Lourd we're all doomed to haylfyre and damnachion..." You are heavily invoking a prior assumptions about qualia when you make such statements.

I can say (in a classical setting) "without the distance between two particles the particles do not exist" but this is not saying anything about distance except that it is automatically a relationship between (and function of) plural (classical) particles. Remember that subjective experience means experience which is not necessarily objective. In short it is not impossible for our subjective experiences to agree in so far as they have functional meaning. This we often see when we both say "that's a red apple". Thus when you say "without qualia" you are saying "without experience" be it objective or subjective. You are eliminating a basic relationship between our minds and our environment. So you conclusion is a bit off. We would rather be "computers without sensors" or more aptly we would be lumps of flesh.



Don't (further) mystify qualia. It is a concept about perception and cognition and it sounds like you're trying to redefine it as "soul" or "spirit" or some property of these. I think you shouldn't make any assertions about what qualia is or what it's presence or absence means within this forum as we would like to stick to science here and leave the mysticism to the usenets. This again is why I think you should refrain from using that word and stick to "subjective experience" which is a common usage phrase. I think you'll also find it will keep your definition from floating into the mystic realm.

Thanks for your amazing insight. I'll reflect on it as I've been thinking of the Hard Problem of consciousness for the past 8 years.

Well. I learned about Copenhagen having ontology of particle having no position from the QM forum, which you don't participate, you could have stated the Copenhagen core idea you mentioned and enlighten many there months ago. Anyway. I wonder what you think of the following thread topic. Need your valuable input as it caused everlasting bewilderment in many of us giving us sleepless nights. Thanks.

(Written by Demystifier titled "There is no Copenhagen interpretation of QM")

https://www.physicsforums.com/showt...ghlight=There+is+no+Copenhagen+Interpretation

"Many physicists say that they prefer the "Copenhagen" interpretation of QM, but it does not mean that all these physicists prefer the same (or even a very similar) interpretation. There are at least 4 very different interpretations that are sometimes referred to as "Copenhagen":

1. Shut up and calculate - this is actually the interpretation that most practical physicists adopt.

2. Positivism - QM is only about the results of measurements, not about reality existing without measurements. (This is essentially the philosophy of Bohr.)

3. Collapse interpretation - when the measurement is performed, then the wave function collapses. (von Neumann)

4. Information interpretation - the wave function does not represent reality, but only the information about reality. (It is somewhat similar to 2., but still significantly different from it.)

What do you think?
I am not asking you to say which interpretation do you find most appealing (we have many other topics on that), but to say whether you agree there there is no SINGLE interpretation that may be called "Copenhagen"."

 

[Ken G]

Personally, I think those 4 variants of Copenhagen do indeed all fall under its general aegis. Even Bohr and Heisenberg had some disagreements on the details. But to me, the defining characteristic of Copenhagen is the subordination of the real to the actual. A measurement is an actualization, and reality follows-- whereas other interpretations tend to hold that the reality pre-exists the measurement, and the measurement is only exposing that reality (Bohm) or selecting from among the many realities (Everett). So those are what I see as the three main interpretations-- measurements either define the reality, or they expose the reality that was there before, or they pick out the reality from among the many equally real versions. All else is pretty much a detail that doesn't matter to me too much.

I would add that I see a close parallel to these interpretations and the main epistemologies of science: rationalism and empiricism. Rationalism asserts that we find truth by making sense of it, and empiricism says we find truth by experiencing it. Truth comes through introspection or sensory input. Science generally involves a combination of these, and that is why scientists work fine together whichever approach they favor, but Copenhagen tends to be a more empiricist interpretation, and many-worlds is the most rationalist. Bohm is mostly rationalist, but highly tempered by empiricist biases such as the existence of a single reality.

 

[Varon]

Personally, I think those 4 variants of Copenhagen do indeed all fall under its general aegis. Even Bohr and Heisenberg had some disagreements on the details. But to me, the defining characteristic of Copenhagen is the subordination of the real to the actual. A measurement is an actualization, and reality follows-- whereas other interpretations tend to hold that the reality pre-exists the measurement, and the measurement is only exposing that reality (Bohm) or selecting from among the many realities (Everett). So those are what I see as the three main interpretations-- measurements either define the reality, or they expose the reality that was there before, or they pick out the reality from among the many equally real versions. All else is pretty much a detail that doesn't matter to me too much.

I would add that I see a close parallel to these interpretations and the main epistemologies of science: rationalism and empiricism. Rationalism asserts that we find truth by making sense of it, and empiricism says we find truth by experiencing it. Truth comes through introspection or sensory input. Science generally involves a combination of these, and that is why scientists work fine together whichever approach they favor, but Copenhagen tends to be a more empiricist interpretation, and many-worlds is the most rationalist. Bohm is mostly rationalist, but highly tempered by empiricist biases such as the existence of a single reality.

I also prefer Copenhagen to the mechanical Bohmian and Many Worlds which are Newtonian in essence. But how do you resolve Wigner's Friend Paradox where there are two conflicting views?

 

[jambaugh]

[...] There are at least 4 very different interpretations that are sometimes referred to as "Copenhagen":

1. Shut up and calculate - this is actually the interpretation that most practical physicists adopt.

2. Positivism - QM is only about the results of measurements, not about reality existing without measurements. (This is essentially the philosophy of Bohr.)

3. Collapse interpretation - when the measurement is performed, then the wave function collapses. (von Neumann)

4. Information interpretation - the wave function does not represent reality, but only the information about reality. (It is somewhat similar to 2., but still significantly different from it.)

What do you think?
I am not asking you to say which interpretation do you find most appealing (we have many other topics on that), but to say whether you agree there there is no SINGLE interpretation that may be called "Copenhagen"."

Actually I don't see these 4 points as distinct.
1. Copenhagen by denying a fundamental reality says "shut up (about reality) and calculate".
2. Copenhagen is positivistic hence 1, 3, and 4.
3. and 4. Copenhagen being positivistic treats the wave-function as a conceptual objects representing information about the behavior of the quantum system and thus there is nothing surprising about its sudden global change when one incorporates knowledge of a measurement not previously assumed in calculating the wave function. Yes the wave function collapses but in no different a fashion qualitatively than a classical probability distribution (say over a range of lotto tickets) collapses (when the drawing occurs).

These are all interrelated aspects of the same interpretation. The positivistic "shut up and calculate" interpretation which focuses the operational meaning of the theory (predictions about measurements) and thus sees the collapsing wave function as informational and not an analogue of some deeper reality.

Copenhagen interpretation for short.

 

[Ken G]

I'm not sure exactly what problem you are referring to Varon, it seems to me that each of the interpretations has a fairly ready answer to the Wigner's friend paradox. Copenhagen says the measurement by the friend "inside the box" causes the wave function to "collapse" into a particular state, and the friend outside the box just doesn't know which state it is yet. Many worlds says that there are many versions of the friend inside the box, each obtaining a different outcome, and the friend outside the box rationalizes a superposition of all those internal friends, until they open the box and then follow whatever branch they follow. Bohm says that before either friend got involved, the outcome was already decided, and the friends just discovered that outcome each in turn. Any of those agrees with all observations made by all observers, so the distinction is personal taste.

 

[Varon]

I'm not sure exactly what problem you are referring to Varon, it seems to me that each of the interpretations has a fairly ready answer to the Wigner's friend paradox. Copenhagen says the measurement by the friend "inside the box" causes the wave function to "collapse" into a particular state, and the friend outside the box just doesn't know which state it is yet. Many worlds says that there are many versions of the friend inside the box, each obtaining a different outcome, and the friend outside the box rationalizes a superposition of all those internal friends, until they open the box and then follow whatever branch they follow. Bohm says that before either friend got involved, the outcome was already decided, and the friends just discovered that outcome each in turn. Any of those agrees with all observations made by all observers, so the distinction is personal taste.

But in Copenhagen, Wigner outside has to prepare his friend in superposition. And since observation creates reality, his friend should be in superposition. But you may state the superposition is just knowledge of the system, but this can't be because system in superposition can interfere and actually show in experiments. So superposition should be objective.

 

[Ken G]

But in Copenhagen, Wigner outside has to prepare his friend in superposition.

No, that's a common mistake about Wigner's friend. In many-worlds interpretation, the box with the friend in it must be in superposition, so that's why there has to be many versions of the friend in the box. But in Copenhagen, the concept of a superposition simply doesn't extend to the macro realm, because it was never intended as an ontological notion. In other words, the correspondence principle applies to outcomes of experiments, but not to the raw materials (like wave functions) used to make predictions about those outcomes. That's why the difference between Copenhagen and many worlds is basically how seriously you take the wave function, which relates to whether you think the wave function is part of the reality that pre-exists the measurement, or just an informational device used in predicting the measurement, only the latter being the reality.

But you may state the superposition is just knowledge of the system, but this can't be because system in superposition can interfere and actually show in experiments.

That's exactly what does not happen for human subjects-- no interference, no need to invoke superpositions.

 

[Varon]

No, that's a common mistake about Wigner's friend. In many-worlds interpretation, the box with the friend in it must be in superposition, so that's why there has to be many versions of the friend in the box. But in Copenhagen, the concept of a superposition simply doesn't extend to the macro realm, because it was never intended as an ontological notion. In other words, the correspondence principle applies to outcomes of experiments, but not to the raw materials (like wave functions) used to make predictions about those outcomes. That's why the difference between Copenhagen and many worlds is basically how seriously you take the wave function, which relates to whether you think the wave function is part of the reality that pre-exists the measurement, or just an informational device used in predicting the measurement, only the latter being the reality.

That's exactly what does not happen for human subjects-- no interference, no need to invoke superpositions.

Even as early as von Neumann.. the classical to quantum boundary is not only movable but the everything is quantum. So you can't say that superposition simply doesn't extend to the macro realm. Wigner friend paradox only means Copenhagen has to be extended. In Fra approach (see https://www.physicsforums.com/showthread.php?t=502705). There are different observers with different views and they interact. This is a radical solution to retain the spirit of Copenhagen. What you are doing is artifically limited it to micro realm, and it's not normal occurence. Hence, if Fra approach is incorrect, then one may just go direct to Many Worlds or Bohmians.

 

[jambaugh]

I also prefer Copenhagen to the mechanical Bohmian and Many Worlds which are Newtonian in essence. But how do you resolve Wigner's Friend Paradox where there are two conflicting views?

Start with the CI version of the original Schrodinger's Cat. If you parse it correctly you'll see adding Wigner's Friend is trivial. As far as "where there are two conflicting views" I don't follow you. If the cat dies Wigner's Friend and Wigner will both see (or smell if they wait too long) a dead cat.

[...] Copenhagen says the measurement by the friend "inside the box" causes the wave function to "collapse" into a particular state, and the friend outside the box just doesn't know which state it is yet.[...] Bohm says that before either friend got involved, the outcome was already decided, and the friends just discovered that outcome each in turn.

Careful here with wording (in particular the "the" where you refer to "collapse of the wave-function". Some might take that to mean "the wave function which actually exists out there as the system" which is not CI.

Copenhagen says (as I understand it) that measurement by the friend leads that friend to update his wave-function (or better that he use a density operator since the cat, and indeed the poison is not at absolute zero) which he uses to describe his knowledge of how the cat will thence behave. The friend outside the box likewise updates his density matrix when he gets updated information.

On a side note... CI does not exclude decoherence, it merely does not need it to interpret. In a more careful evaluation of Schrodinger's cat, any density operator --be it the cat's or the Friend's or Wigner's-- decoheres in short order and one is describing an essentially classical probability experiment.
(Note: each possessive above referring to the density op. describing not the owner but the owner's representation of the smaller more interior system, e.g. "the cat's density op." is the density operator the cat would use to describe the poison+decay detector+radio-isotope...should the cat know enough QM to conceive of a density op.)

BTW, I don't really see the "Decoherence interpretation" as an "interpretation" in the ontological sense (which I see as a good thing). To me it is just a clarification of how within QM macroscopic quantum systems become describable in classical terms.

Note my qualification about the temperature is not me merely being pedantic. There is a critical thermodynamic aspect of the measurement process. Note also temperature is a critical aspect of the "cat" when we speak of "alive" vs "dead". These are not properly quantum observables any more than is temperature and so it is not proper to speak of them being in superposition. This aspect is part of what makes the "cat" necessary as a "macroscopic system" for the purpose of the thought experiment. Recall also that the original purpose was to distance the meanings of classical states of reality and the quantum "state vectors" (which in CI do not represent states but rather classes of systems).

 

[Varon]

Start with the CI version of the original Schrodinger's Cat. If you parse it correctly you'll see adding Wigner's Friend is trivial. As far as "where there are two conflicting views" I don't follow you. If the cat dies Wigner's Friend and Wigner will both see (or smell if they wait too long) a dead cat.



Careful here with wording (in particular the "the" where you refer to "collapse of the wave-function". Some might take that to mean "the wave function which actually exists out there as the system" which is not CI.

Copenhagen says (as I understand it) that measurement by the friend leads that friend to update his wave-function (or better that he use a density operator since the cat, and indeed the poison is not at absolute zero) which he uses to describe his knowledge of how the cat will thence behave. The friend outside the box likewise updates his density matrix when he gets updated information.

On a side note... CI does not exclude decoherence, it merely does not need it to interpret. In a more careful evaluation of Schrodinger's cat, any density operator --be it the cat's or the Friend's or Wigner's-- decoheres in short order and one is describing an essentially classical probability experiment.
(Note: each possessive above referring to the density op. describing not the owner but the owner's representation of the smaller more interior system, e.g. "the cat's density op." is the density operator the cat would use to describe the poison+decay detector+radio-isotope...should the cat know enough QM to conceive of a density op.)

BTW, I don't really see the "Decoherence interpretation" as an "interpretation" in the ontological sense (which I see as a good thing). To me it is just a clarification of how within QM macroscopic quantum systems become describable in classical terms.

Note my qualification about the temperature is not me merely being pedantic. There is a critical thermodynamic aspect of the measurement process. Note also temperature is a critical aspect of the "cat" when we speak of "alive" vs "dead". These are not properly quantum observables any more than is temperature and so it is not proper to speak of them being in superposition. This aspect is part of what makes the "cat" necessary as a "macroscopic system" for the purpose of the thought experiment. Recall also that the original purpose was to distance the meanings of classical states of reality and the quantum "state vectors" (which in CI do not represent states but rather classes of systems).

Analyzing what you said here and in previous message and also by Ken G. You guys agree that in Copenhagen.. as Ken put it:

1. "A measurement is an actualization, and reality follows whereas other interpretations tend to hold that the reality pre-exists the measurement, and the measurement is only exposing that reality (Bohm) or selecting from among the many realities (Everett)."

As as Jambaugh puts it:

2. "Some might take that to mean "the wave function which actually exists out there as the system" which is not CI."

So Measurement creates reality, yet the wave function doesn't actually exist in the system. It is in the observer knowledge of the system. Now let's tally this to experiments.

In quantum experiment. Something is interfering, that is, the superposition produce output where something is really interfering like detector interferences in the double slit. Now if you put a double slit equipment in the center of the moon. The detector still shows interference pattern, even without observers. So it's more like wave function really exists in the system and doesn't belong to the observer. Or else there would be no interferences in the detector in the double slit machine put in the center of the moon with absense of observers!

 

[Ken G]

Even as early as von Neumann.. the classical to quantum boundary is not only movable but the everything is quantum.

Now you are getting into the variants of Copenhagen. In "purist" Copenhagen, that of Bohr, the opposite is true-- nothing is quantum, there is no "quantum world." There is only the world of our observations-- the entire quantum realm is something just imagined, whatever we need to do the calculation to get the right prediction. von Neumann is bridging from the empiricist Copenhagen view to the rationalist many-worlds view, and his is the only one that I have a hard time seeing the consistency of. That seems to be the thrust of your issue too, but Bohr would not have had that problem.

 

[Ken G]

Careful here with wording (in particular the "the" where you refer to "collapse of the wave-function". Some might take that to mean "the wave function which actually exists out there as the system" which is not CI.

Yes, point taken, I should have said "their" wave function. You are making a crucial point about CI-- the wave function is viewed as information used by a particular physicist making a prediction, and if it serves them, it is doing its job. It's like if you have people playing poker, with knowledge of different hands, they are assessing different probabilities based on what they know, and all of their probabilities are "correct" in that they serve their goals-- but in CI, there isn't any "true deal", there is only the information the players are using and nothing else. The consistency of that information is maintained is some other, almost mystical, way, but that's no more mystical than asserting the existence of a true many-worlds wave function, or a true pilot wave. It simply leaves the mystical part out of the science, rather than bringing it in in a way that cannot be demonstrated. That's why all of us here seem to like it.

On a side note... CI does not exclude decoherence, it merely does not need it to interpret. In a more careful evaluation of Schrodinger's cat, any density operator --be it the cat's or the Friend's or Wigner's-- decoheres in short order and one is describing an essentially classical probability experiment.

Yes, many take decoherence theory to be a reason to use many-worlds over Copenhagen, because it provides the mechanism for wavefunction collapse within the wavefunction-only paradigm. But wavefunction collapse was never the real problem-- the real problem was always what does it collapse to, and what happens to the superposition of the closed system? That issue is not adjudicated by decoherence theory, one still must ask how ontologically to interpret the wave function.

To me, the whole issue is how much unnecessary ontology will we introduce to achieve certain rationalistic goals. CI says "none", MW says "enough to be able to interpret the wave function as real" (at the cost of many worlds), and Bohm says "even more-- enough to have a rationalistic reality even farther from observations than the wave function so that it can all be deterministic." It's all an issue of what biases will guide us-- CI is guided by the bias that only observations lead us to truth, MW is guided by the bias that the rules reality follows are the reality itself, and Bohm is guided by the bias that once we make sense of reality, what happens must seem unique and inevitable. Each approach achieves its purpose admirably, so we needn't debate them, only recognize them.

BTW, I don't really see the "Decoherence interpretation" as an "interpretation" in the ontological sense (which I see as a good thing). To me it is just a clarification of how within QM macroscopic quantum systems become describable in classical terms.

I agree completely-- it only treats the "easy" problem of wave function collapse. The "hard" problem is still there-- what determines what it collapses into.

 

[Ken G]

Now if you put a double slit equipment in the center of the moon. The detector still shows interference pattern, even without observers. So it's more like wave function really exists in the system and doesn't belong to the observer. Or else there would be no interferences in the detector in the double slit machine put in the center of the moon with absense of observers!

You're a closet rationalist! I can't put words in Bohr's mouth, but my guess is he would say that what matters is not so much the observer, but the apparatus. Science happens on "our" side of the apparatus, whether or not we are there to do the science. Reality answers a question that is posed, even if no one is listening to that answer-- the key is that the question has to actually be posed. A scientific apparatus is a means of posing a question, and all we get is the answer-- not what went into the answer. However, we can form models of what went into the answer that work-- we just can't assert those models are the answer, the answer is the outcome.

 

[Varon]

Start with the CI version of the original Schrodinger's Cat. If you parse it correctly you'll see adding Wigner's Friend is trivial. As far as "where there are two conflicting views" I don't follow you. If the cat dies Wigner's Friend and Wigner will both see (or smell if they wait too long) a dead cat.



Careful here with wording (in particular the "the" where you refer to "collapse of the wave-function". Some might take that to mean "the wave function which actually exists out there as the system" which is not CI.

Copenhagen says (as I understand it) that measurement by the friend leads that friend to update his wave-function (or better that he use a density operator since the cat, and indeed the poison is not at absolute zero) which he uses to describe his knowledge of how the cat will thence behave. The friend outside the box likewise updates his density matrix when he gets updated information.

On a side note... CI does not exclude decoherence, it merely does not need it to interpret. In a more careful evaluation of Schrodinger's cat, any density operator --be it the cat's or the Friend's or Wigner's-- decoheres in short order and one is describing an essentially classical probability experiment.
(Note: each possessive above referring to the density op. describing not the owner but the owner's representation of the smaller more interior system, e.g. "the cat's density op." is the density operator the cat would use to describe the poison+decay detector+radio-isotope...should the cat know enough QM to conceive of a density op.)

BTW, I don't really see the "Decoherence interpretation" as an "interpretation" in the ontological sense (which I see as a good thing). To me it is just a clarification of how within QM macroscopic quantum systems become describable in classical terms.

Note my qualification about the temperature is not me merely being pedantic. There is a critical thermodynamic aspect of the measurement process. Note also temperature is a critical aspect of the "cat" when we speak of "alive" vs "dead". These are not properly quantum observables any more than is temperature and so it is not proper to speak of them being in superposition. This aspect is part of what makes the "cat" necessary as a "macroscopic system" for the purpose of the thought experiment. Recall also that the original purpose was to distance the meanings of classical states of reality and the quantum "state vectors" (which in CI do not represent states but rather classes of systems).

Are you sure of that, that only quantum observables that can be in superposition? If so why did they propose the Many worlds idea of the cat being alive and dead braches off into separate worlds? Didn't Everett think that superposition only works for quantum observables like position, momentum, etc. hence his more general idea of superposition being true even for macroscopic quality as alive and dead should be invalid?

 

[apeiron]

To me, the whole issue is how much unnecessary ontology will we introduce to achieve certain rationalistic goals. CI says "none", MW says "enough to be able to interpret the wave function as real" (at the cost of many worlds), and Bohm says "even more-- enough to have a rationalistic reality even farther from observations than the wave function so that it can all be deterministic." It's all an issue of what biases will guide us-- CI is guided by the bias that only observations lead us to truth, MW is guided by the bias that the rules reality follows are the reality itself, and Bohm is guided by the bias that once we make sense of reality, what happens must seem unique and inevitable. Each approach achieves its purpose admirably, so we needn't debate them, only recognize them.

There are good points being made here. There seem to be two attitudes you can rightfully take.

1) Just accept the operational CI approach which is neutral or agnostic on ontology. There is an epistemological procedure which serves a pragmatic purpose. Given that all our knowledge of reality is via modelling, it is not such a surprise or even big deal that eventually we come up against the limits of intuition or interpretation. So in the end, we must give up on a demand for ontic realism. The alternative - of believing something most likely unreal, like hidden variables or many worlds - is worse than having no beliefs.

2) The other stance is to say we need our guiding intuitions about "what is really happening" to now make further progress. Unless we can make sense of QM, we can't discover what lies beyond.

So 1) would be the default position. And 2) would be the exploratory one. Or the technical and metaphysical choices.

When it comes to 2), I think that one of the things we know is that no interpretation that demands the world be in a definite state at all times, in all ways, is going to pan out. That is the classical view people want to go back to, but we can't go forward without giving up that ontic belief. Indeterminacy is part of nature in some strong sense. So that is where the attention should be focused. Hidden variables and many worlds are examples of determinate ontologies so ought to be just consigned to the dustbin for that reason.

Interpretations based on decoherence, and also retrocausality, seem to be a loosening up of ontological assumptions that are heading in the right direction. But I don't think either deals with indeterminacy in any obvious way.

I think the best way to tackle the modelling of indeterminacy is Peirce's logic of vagueness (and a few people have written papers on this, but it has kind of fizzled).

I would also say that having a proper model of indeterminacy would also change our notion of determinacy - of the role of observers and collapses. At the moment, events appear determined by local or efficient cause. The principle of locality that is basic to "mechanics". There is no causality assigned to contexts or global constraints. To formal and final purpose. And this is why decoherence and retrocausality seem to be heading in the right direction. They are about contextual collapse and "means justifies the ends" collapse. It is the right kind of loosening of our causal models.

A final thought is that I think thermodynamics may turn out to be the next step in the revolution. QM and relativity don't address the most central fact of our existence - that there is an entropic gradient down which everything unwinds, a Universe that expands/cools. So the modelling of gradients and dissipative structure may be the place to find a new ontological view of what is going on with QM.

From the holographic principle, to dissipative structure theory, to non-extensive entropy, to self-organised criticality, it strikes me that the field of thermo is in the kind of creative forment that is a next step struggling to get born. A heck of a lot of advance has been made over the past 30 years. But there is this prejudice that thermodynamics is a statistical view of what emerges from the "fundamental stuff" of QM, relativity and particle physics. I think this is where the ontological flip around will take place eventually.

 

[Ken G]

There are now even thermodynamic forays into gravity. We have the entropy of a black-hole surface helping to explain how complete gravitational collapse can occur spontaneously, and there are even theories of curvature of spacetime that adopt an entropic approach, that somehow the GR curvature is the most probable way for spacetime to organize itself-- as though spacetime itself had some internal dynamics being ruled by a global constraint implied by the Einstein equation. That seems like a promising path for unification with quantum statistical mechanics, and ultimately all of quantum mechanics.

Ironically, there is a kind of parallel in what we think thermodynamics is, with what we think quantum mechanics is. The rationalist who thinks laws are really laws and favors many worlds might also favor the idea that entropy is a "real thing" that tends to increase in closed systems due to irreversible processes, but this would be deeply inconsistent-- the many-worlds rationalist must assert that the universe is always in 1 state, and the entropy of 1 state is always zero, so the universe as a whole cannot change its entropy in a many-worlds view-- only the subspaces of intelligent construction can have the illusion of increasing entropy in their myopic reconstruction of reality based on an incoherent sum of partial views. But how that worm has turned-- the rationalist forced to conclude that a law of thermodynamics is an illusion of selective experience! It is supposed to be the CI camp that sees laws of physics, like the Schroedinger equation, as illusions of selective experience (the couplings to macro instruments). Thus it seems to me that the CI camp is better poised to embrace a thermodynamic vision of how things evolve, because they are perfectly happy with laws of physics that are subordinate to the selective experiences of the physicists.

 

[apeiron]

There are now even thermodynamic forays into gravity. We have the entropy of a black-hole surface helping to explain how complete gravitational collapse can occur spontaneously, and there are even theories of curvature of spacetime that adopt an entropic approach, that somehow the GR curvature is the most probable way for spacetime to organize itself-- as though spacetime itself had some internal dynamics being ruled by a global constraint implied by the Einstein equation. That seems like a promising path for unification with quantum statistical mechanics, and ultimately all of quantum mechanics.

Exactly. It is happening. But it is not yet being said that thermo is the more fundamental perspective.

And as you suggest, a big part of this is about a shift from seeing the "laws" as transcendent - external, eternal, unexplained - to instead being part of the self-organisation. The global constraints that emerge to regulate the local degrees of freedom - to determine the indeterminate.

 

[Ken G]

Yes, I favor that perspective, simply because it sounds more like one of the key lessons of both quantum mechanics and relativity: the physicist is on the inside looking out, not on the outside looking in.

 

[Varon]

You're a closet rationalist! I can't put words in Bohr's mouth, but my guess is he would say that what matters is not so much the observer, but the apparatus. Science happens on "our" side of the apparatus, whether or not we are there to do the science. Reality answers a question that is posed, even if no one is listening to that answer-- the key is that the question has to actually be posed. A scientific apparatus is a means of posing a question, and all we get is the answer-- not what went into the answer. However, we can form models of what went into the answer that work-- we just can't assert those models are the answer, the answer is the outcome.

But interference is really taking place. How else can there be interference without superposition? And how else can there be superposition without wave function being in the object (not merely knowedge of the observer??)

 

[Ken G]

But interference is really taking place.

CI can handle interference, and there's no controversy about how decoherence eliminates the possibility of interference. None of the interpretations have much to say about interference, as none of them have any interference persisting after a measurement-- the interpretations are all efforts to understand what happens after decoherence. That's why we can't test them, there's no interference there to test.

And how else can there be superposition without wave function being in the object (not merely knowedge of the observer??)

There's definitely interference in the mathematics, what is not clear is what is actually intefering. Terms in an equation, or something real? CI says the former, thus avoiding strange problems like "real" entities comprised of imaginary numbers, or mutually coherent pockets of outcomes coexisting alongside noncoherent other worlds that make no contribution because they have random phase relationships with our world.

 

[jambaugh]

Exactly. It is happening. But it is not yet being said that thermo is the more fundamental perspective.

And as you suggest, a big part of this is about a shift from seeing the "laws" as transcendent - external, eternal, unexplained - to instead being part of the self-organisation. The global constraints that emerge to regulate the local degrees of freedom - to determine the indeterminate.

I think it is an issue of distinct meaning of "more fundamental" within ontic metaphysics vs within epistemology. Back in the classical period of science we sought the most fundamental reality, the atoms out of which objects are made. In this quantum period what is most fundamental is the atomic act of knowing, say the boolean observation (which is an intimately thermodynamic process), and the object of that observation, the atomic unit of information, the qubit.

In both contexts we still must overlay dynamics, or rather we express dynamics in terms of activity of/between atoms. Dynamics is thus derivative. [**footnote] Where we should go from here is I think is say, a revised definition of metaphysics (metadynamics? dianetics? ) which appropriately disinvokes the postulate of fundamental objective reality (but allows for the description of contingent realities) and in some way invokes dynamic action intrinsically. I'm thinking something like a generalization of Feynman diagrams to a language of actions or phenomena. (And yes I'm w.a.g.ing here.)

(** GR is exceptional to an extent in that it is a dynamic of dynamics type theory.)

 

[Varon]

CI can handle interference, and there's no controversy about how decoherence eliminates the possibility of interference. None of the interpretations have much to say about interference, as none of them have any interference persisting after a measurement-- the interpretations are all efforts to understand what happens after decoherence. That's why we can't test them, there's no interference there to test. There's definitely interference in the mathematics, what is not clear is what is actually intefering. Terms in an equation, or something real? CI says the former, thus avoiding strange problems like "real" entities comprised of imaginary numbers, or mutually coherent pockets of outcomes coexisting alongside noncoherent other worlds that make no contribution because they have random phase relationships with our world.

Look. You mentioned terms in an equation is interfering. But just look at the detector screen, there interference patterns are there. It is something real. Not just in the equations. In fact, even if you don't create any equations. Just setting up the double slit can cause interference patterns. So I really can't understand why you keep saying it is all in the equations and in the mind of the observers.

 

[Ken G]

Look. You mentioned terms in an equation is interfering. But just look at the detector screen, there interference patterns are there. It is something real.

The pattern is real, yes. But the interference? How is that real? It is an inference you make when you see the pattern. Inferences are not real, they are mental constructs. I'd say the crux of CI is noticing the difference between what is in the reality and what is in our minds. Granted, even the outcome of an observation is in our minds, but CI sees that kind of outcome as more concrete than the mathematical stories we build up around them.

Not just in the equations. In fact, even if you don't create any equations. Just setting up the double slit can cause interference patterns. So I really can't understand why you keep saying it is all in the equations and in the mind of the observers.

The pattern is real. That the pattern was made by interference is not something you can test. What experiment can you make that comes out X if the pattern is made by interference, and Y if the pattern is made some other way?

 

[Ken G]

I think it is an issue of distinct meaning of "more fundamental" within ontic metaphysics vs within epistemology. Back in the classical period of science we sought the most fundamental reality, the atoms out of which objects are made. In this quantum period what is most fundamental is the atomic act of knowing, say the boolean observation (which is an intimately thermodynamic process), and the object of that observation, the atomic unit of information, the qubit.

Yes, I think the next class of physical theories, those that go beyond the latest new particle, are going to combine theories of dynamics with theories of cognition. We are getting close to the place where we can no longer pretend we are not involved in our own knowing about reality. The device of separating ourselves from our questions got us pretty far, but we had to always know it was a fundamentally bogus approach. I think Douglas Adams had it right-- at some point knowledge looks not like figuring out the right answers for our questions, but rather figuring out the right questions for our answers.

 

[apeiron]

I think it is an issue of distinct meaning of "more fundamental" within ontic metaphysics vs within epistemology. Back in the classical period of science we sought the most fundamental reality, the atoms out of which objects are made. In this quantum period what is most fundamental is the atomic act of knowing, say the boolean observation (which is an intimately thermodynamic process), and the object of that observation, the atomic unit of information, the qubit.

I like that idea of the atomic boolean operation. Do you have any cites for this as an approach?

I come at this from the perspective of theoretical biology where people talk about infodynamics for instance. So in some sense, QM is about the smallest grain of observational resolution.

In both contexts we still must overlay dynamics, or rather we express dynamics in terms of activity of/between atoms. Dynamics is thus derivative. [**footnote] Where we should go from here is I think is say, a revised definition of metaphysics (metadynamics? dianetics? ) which appropriately disinvokes the postulate of fundamental objective reality (but allows for the description of contingent realities) and in some way invokes dynamic action intrinsically. I'm thinking something like a generalization of Feynman diagrams to a language of actions or phenomena. (And yes I'm w.a.g.ing here.)

Here I would disagree. The presumption should instead be that all is dynamic, and it is only equilbrium states or processes that give the illusion of static, atomic, existence.

In an equilbrium, there is ceaseless change at the microscale, but not longer any global change.

But then you appear to be saying here both that dynamics is derivative and yet we need a new metaphysics that "invokes dynamic action intrinsically". So maybe you do agree with me?

(** GR is exceptional to an extent in that it is a dynamic of dynamics type theory.)

Yes, GR is a model of global constraints. But it needs actual energy values plugged into it to make it dynamical. At the moment, this is most unsatisfactory - with for example the need to hand-build in the cosmological constant. A thermo model of GR might find dark energy to be an irreducible fact of the Universe's dissipative structure for instance.

Our standard way of thinking about geometry is rather cold and lifeless. It just lies there flat and static, not changing unless someone forces it to change. But thermodynamics is about the dynamics of gradients and equilibriums. So what would a "hot" geometry look like? (Open, hyperbolic, fractal, sum over histories?)

 

[apeiron]

Yes, I think the next class of physical theories, those that go beyond the latest new particle, are going to combine theories of dynamics with theories of cognition. We are getting close to the place where we can no longer pretend we are not involved in our own knowing about reality. The device of separating ourselves from our questions got us pretty far, but we had to always know it was a fundamentally bogus approach. I think Douglas Adams had it right-- at some point knowledge looks not like figuring out the right answers for our questions, but rather figuring out the right questions for our answers.

Connecting back to the OP, one of the dangers is that QM seems to have something to do with observers, and so something to do with human consciousness. It is a slippery slope of speculation.

And even talking about cognition is problematic if we have no good theory of cognition.

Theories of cognition are in fact where I started out. Theoretical neurobiology. The computational model was obviously flawed (not untrue, but clearly not the whole (or holistic) story). And the dynamical systems approach was equally, somewhat true, yet also fundamentally missing something.

Looking for the right ontological grounding, I found that theoretical biology had been through the same issues in the 1960s and 70s. As a result, in the 80s and 90s, theoretical biologists were realising that the grounding theory for them was some more sophisticated model of thermodynamics. One that gave primacy to the idea of development and gradients - to the kind of open systems thermodynamics of Prigogine rather than the static, close realms of early statistic mechanics.

Then in the 1990s, theoretical biologists made a connection to semiotics (or the Peircean kind) as a way to talk about meaning as well as information in a thermo perspective.

So there is definitely a movement in biology and neuroscience, if not yet a revolution, that sees thermodynamics in some rounded systems sense as its natural basis. The "physics" that grounds the sciences of life and mind is not the one of particles, fields, and other simple material stuff, but the physics of systems.

Then looking around, it seems obvious that even physics and cosmology are attempting to be more systems-based - more holistic and self-organising, less atomistic and background dependent. Which again means that the proper metaphysical grounding would be something a thermodynamic modelling of causality.

So forget "qualia". That simply is the extension of atomism into phenomenology. The claim that consciousness is constructed from collection of subjective atomistic shards just does not fly with anyone who actually has studied neurocognitive processes. It is a fiction that gives some philosophers a respectable career - they look like they are doing good reductionist thinking. But it is a construct as lame as philogiston or aether or other things we now laugh about.

But Jambaugh's point about the boolean observation is right. We need an atomism in the sense that we need a definition of the smallest, or simplest, system-forming action. And there is also something new here because that "atom" is intrinsically dichotomistic. There has to be an observer and the observed in some sense. A meaningful relationship.

But we also have to find the language to describe the "atom of a system" in ways that don't have false connotations. And thermodynamics would seem to be the place to find a jargon that is both neutral enough to apply equally well to physics or mind science, and yet also having the right kind of causal or ontological connotations.

Myself, I find that the dichotomy of degrees-of-freedom~constraints is very useful. A system is in general where you have some set of global constraints that act to particularise a set of degrees of freedom. This is the top-down~bottom-up view of hierarchy theory. A coupling of levels of causality in which the larger scale "observes" the smaller scale - that is, it resolves a broad number of degrees of freedom into the select few which are actually building the system (so it can continue to "observe" and so persist as a system).

So the atom of a system is this dyadic relation between degrees of freedom and constraints. In QM, for example, it would be the interaction between the experimentalist's set-up and the indeterminacy contained in some prepared initial conditions. In mind science, you get the interaction between global anticipatory state and localised sensory "surprises" or salient events.

(If you want the best current neurocognitive model, check out the Bayesian brain work and note how it is based on the very thermo concept of minimising a system's free energy - http://en.wikipedia.org/wiki/Bayesian_brain).

To sum up, thermo is the physics of systems and so is naturally the foundation for complex systems science (such as biology and neurology). And I would argue that it has to be the foundation for "foundational" physics too. What is missing from the current modelling is the "observer" - a theory of the global constraints. And then we need an atomistic model of systems. But this is going to be an intrinsically dyadic story in which we find both observer and observed in their simplest possible form. Some version of the idea of emergent constraints in interaction with (sub)mergent (or otherwise constrained and directed) degrees of freedom.

 

[Ken G]

To sum up, thermo is the physics of systems and so is naturally the foundation for complex systems science (such as biology and neurology). And I would argue that it has to be the foundation for "foundational" physics too. What is missing from the current modelling is the "observer" - a theory of the global constraints. And then we need an atomistic model of systems. But this is going to be an intrinsically dyadic story in which we find both observer and observed in their simplest possible form. Some version of the idea of emergent constraints in interaction with (sub)mergent (or otherwise constrained and directed) degrees of freedom.

I think a related theme to the top-down elements of constraints in thermodynamics is the concept of specialness, which likely relates to the concept of symmetry. If I painstakingly place 100 coins, all heads, on the floor of a room, we can all recognize the specialness there. But if I place those same 100 coins with 50 heads and 50 tails, we see no specialness, even though I may have carried out the same process of carefully placing each coin. So each individual pattern of heads and tails are all equally unlikely, the only reason we have a concept of entropy is that we choose groupings or classes that we are going to consider similar in some way, and the smaller classes are then special. It is thus our "eye to the similarity" within the classes that is what creates the concept of entropy, and as soon as we recognize a similarity that can be used to create a class, the universe will always step into make sure that special classes give way to more generic ones. The second law of thermodynamics is a law about what happens as soon as our intelligence identifies similarity classes, but it has no insights to offer prior to that. Hence I would say that the second law is not only a law discovered by intelligence, it is a law that requires intelligence to have any meaning. It is not really something that the universe by itself is doing, because the universe by itself might not have any idea why we decide to lump together all distributions with 50 heads and 50 tails.

So there's a classic example of where the observer/constraints/concepts are not written into the fabric of the dynamics itself, it is rather a kind of template placed over the dynamics. It is not only the act of doing physics that involves intelligence, the whole business is predicated on the attributes of intelligence. We shouldn't say there are physicists because there is physics, we should say there is physics because there are physicists. We see this in the importance of identifying classes of "what matters" in thermodynamics (like the difference between hot and cold, concepts the universe by itself might find odd), in the importance of having a reference frame for relativistic dynamics (the universe itself might care for nothing beyond the invariants, with no concept of what a coordinate system is), and in the importance of having a macroscopic coupling to define the operators of quantum mechanics (the universe might not have the vaguest idea what either a superposition or a mixed state are). Physics is by its very nature a study of top-down constraints, so when it is used to describe how all behaviors percolate up from the atom, we are only seeing one half of the cycle.

 

[Varon]

The pattern is real, yes. But the interference? How is that real? It is an inference you make when you see the pattern. Inferences are not real, they are mental constructs. I'd say the crux of CI is noticing the difference between what is in the reality and what is in our minds. Granted, even the outcome of an observation is in our minds, but CI sees that kind of outcome as more concrete than the mathematical stories we build up around them.
The pattern is real. That the pattern was made by interference is not something you can test. What experiment can you make that comes out X if the pattern is made by interference, and Y if the pattern is made some other way?

So if the interference is in the equation. Pls. tell me what physically happens to a single photon or electron between the emission and the detection in the double slit experiment. Thanks.

 

[Ken G]

So if the interference is in the equation. Pls. tell me what physically happens to a single photon or electron between the emission and the detection in the double slit experiment.

The central thesis of the CI is that there is no answer to your question. Not just that we don't yet know the answer, that there is none. The reality is not set up to allow our intelligence a means of answering the question, and that is just exactly the same thing as the question having no answer.

 

[apeiron]

I think a related theme to the top-down elements of constraints in thermodynamics is the concept of specialness, which likely relates to the concept of symmetry. If I painstakingly place 100 coins, all heads, on the floor of a room, we can all recognize the specialness there. But if I place those same 100 coins with 50 heads and 50 tails, we see no specialness, even though I may have carried out the same process of carefully placing each coin.

Of course, an exact 50/50 would be somewhat special too. Quickly checking on a binomial distribution calculator (ie: I may have the number wrong), random tossing would generate this outcome only about 8 percent of the time.

So "non special" - that is the outcome of some actual fair coin toss - would be naively expected to look more like 48/52 or whatever. This would look less like a deliberate pattern or special arrangement, more like the product of a random gaussian process in which the individual outcome states are highly constrained (to the definite binary states of heads or tails) but the individual choice of outcomes is free, or completely unconstrained.

It is thus our "eye to the similarity" within the classes that is what creates the concept of entropy, and as soon as we recognize a similarity that can be used to create a class, the universe will always step into make sure that special classes give way to more generic ones. The second law of thermodynamics is a law about what happens as soon as our intelligence identifies similarity classes, but it has no insights to offer prior to that. Hence I would say that the second law is not only a law discovered by intelligence, it is a law that requires intelligence to have any meaning. It is not really something that the universe by itself is doing, because the universe by itself might not have any idea why we decide to lump together all distributions with 50 heads and 50 tails.

I see that you are taking a CI approach to statistical mechanics . That is an extreme but interesting way to go.

I think the more deflationary interpretation - but still radical in its own way - is the infodynamics view where information is seen as any constraint on entropy production and so "intelligence" is in there as part of the defintion, but we don't mean it has to be a conscious intelligence, just that there is some kind of memory or boundary constraints in play that "makes a measurement" on the system.

See for instance this really excellent paper - http://arxiv.org/PS_cache/arxiv/pdf/0906/0906.3507v1.pdf

 

[Varon]

The central thesis of the CI is that there is no answer to your question. Not just that we don't yet know the answer, that there is none. The reality is not set up to allow our intelligence a means of answering the question, and that is just exactly the same thing as the question having no answer.

You are saying that it is possible nothing physically actually happens? Like the concept of Spacetime which is pure math? So it's related to the ultimate question of why math unreasonable effectiveness in describing reality like somehow there is a platonic realm where math is the primary reality and in between emission and detection, it is located in pure platonic realm? Is this the essence of Copenhagen? Or is Copenhagen more of a context of "don't care" attitude.. meaning the particle could be taking a real path like in Bohmian mechanics but Copenhagenists simply don't care?

 

[Ken G]

You are saying that it is possible nothing physically actually happens?

I'm saying the CI interpretation is that "what physically happens" is whatever we can assert, with our apparatus, physically happened. There is no other meaning to the term, the rest is practically identifiable with mysticism. I'd say it's a bit like watching a movie-- we are told that all we are seeing is a string of still pictures, yet our minds interpret motion there. Is that motion something physically happening? With the "movie magic" that is done these days, say in superhero epics, oftentimes the motions we perceive never occurred in any reality, the still pictures on the film are the only things that are real there. I believe the CI takes a similar skeptical approach to "the quantum realm."

So it's related to the ultimate question of why math unreasonable effectiveness in describing reality like somehow there is a platonic realm where math is the primary reality and in between emission and detection, it is located in pure platonic realm?

That is certainly one interpretation, but is closer to many worlds than CI. In many worlds, all those parallel worlds are a kind of "Platonic realm" when considered from our world, because their entire justification is to make the mathematics (not the observations) work out in a way that can be intepreted as "real". CI rejects the need to make the mathematics work out that literally, it is fine with viewing the mathematics as being nothing but a tool for predicting (statistically) one reality. So CI sees that "mathematical detour" you are talking about as not part of the reality at all, it is merely a template laid over the reality to get it to fit. So we are still left with wondering why it works-- many worlds has a readier answer to why it works, "because it's the reality." CI is a more skeptical stance: "prove it."

Or is Copenhagen more of a context of "don't care" attitude.. meaning the particle could be taking a real path like in Bohmian mechanics but Copenhagenists simply don't care?

That's closer-- I don't think they'd say they don't care, I think they'd say they don't believe. They don't want physics to require faith in that which can't be observed but "makes sense." They don't expect it to make sense.

 

[Varon]

Ken and others,

What do you think of the latest experiment "Observing the Average Trajectories of Single Photons in a Two-Slit Interferometer"

described in:

http://www.physorg.com/news/2011-06-quantum-physics-photons-two-slit-interferometer.html

http://scienceblogs.com/principles/2011/06/watching_photons_interfere_obs.php

My question is. They can do weak measurement on a particle before full collapse. This means the particle has trajectory in contrast to pure Copenhagen concept where a particle only pops up upon collapse of the wave function (which stand for wave of possibility of where the particle would be detected). What do you make of the latest experiment?

 

[Ken G]

They can do weak measurement on a particle before full collapse. This means the particle has trajectory in contrast to pure Copenhagen concept where a particle only pops up upon collapse of the wave function (which stand for wave of possibility of where the particle would be detected).

It doesn't mean that. The second article gives a much more nuanced description than the first. Nothing in that experiment is the trajectory of an individual photon, instead, what they have seems to me is equivalent to what you'd get if you put the detecting screen at various different places and create a field of detection densities, attribute the detection densities to trajectory densities such as could be done with any divergence-free field, and draw the "field lines" and call them average trajectories. I'll wager doing that would generate precisely the same figure. Much ado about nothing.

What they seem to be missing is that the classical picture of waves going through two slits could generate the same figure. What makes the quantum realm so weird is the quantization-- not the averaged behavior. I really don't see what "weak measurement" is adding to the question, it still is not true that you can say which slit any of those electrons went through.

 

[Varon]

It doesn't mean that. The second article gives a much more nuanced description than the first. Nothing in that experiment is the trajectory of an individual photon, instead, what they have seems to me is equivalent to what you'd get if you put the detecting screen at various different places and create a field of detection densities, attribute the detection densities to trajectory densities such as could be done with any divergence-free field, and draw the "field lines" and call them average trajectories. I'll wager doing that would generate precisely the same figure. Much ado about nothing.

What they seem to be missing is that the classical picture of waves going through two slits could generate the same figure. What makes the quantum realm so weird is the quantization-- not the averaged behavior. I really don't see what "weak measurement" is adding to the question, it still is not true that you can say which slit any of those electrons went through.

You mean when these detection densities were put at various different places, it collapsed the wave function at that point? But no, there was still a final inteference in the main screen. The momentum detection at different places from the slit didn't collapse the wave function. This is why it's called weak measurement.. because it only nudges them not enough to collapse it.

Now here's the question. Does it make sense for there to be even ensemble trajectories for uncollapsed state? For you, do you think a single particle has trajectory even before measurement?
Or not? If not. How could a single particle doesn't have trajectory yet ensemble of it have?? Note again putting momentum polarization weak measurement at various points of the slits don't collapse the wave function because there is still final interferece at the final detector screen.

 

[Ken G]

What I'm saying is, I'm not convinced that "weak measurement" is any different from "compiling average trajectories from treating the wave energy flux like a divergenceless scalar field and drawing 2D lines of force for that field." I maintain you could get that exact same picture by measuring the energy flux of a classical wave passing between two slits, and drawing trajectories such that the line density is proportional to the energy flux density. This would be completely consistent with a macroscopic treatment of an energy flux as a photon number flux. Those trajectories don't really mean anything beyond a statistical treatment of where photons go in large aggregations, that they could get the same picture with "weak measurement" of "one photon at a time" doesn't strike me as being at all profound.

Let me put it another way. The key statement that we don't know the trajectory of an individual photon is that we cannot know which slit it went through, and still have that photon participate in an interference pattern. Does this experiment tell us which slit any of those photons went through? No. So what? There are still no trajectories in the physical reality of what happened to those photons, and it's not at all clear that an "average trajectory" is anything different from the usual macro aggregate measurement in the classical limit. To me, all this experiment is is a kind of consistency check that "weak measurement" can recover statistical aggregates, but I see no threat to the CI interpretation that the reality is still only what you measure and not what happens between the measurements. So they can create weak measurements that don't completely collapse the wave function, then recover the aggregate behavior in the same way that complete measurements that do collapse the wavefunction could easily do also. What does that tell us? That weak measurements don't mess up aggregate results? Why should we be surprised-- the weak measurements don't tell us the trajectories of any of those particles.

 

[Varon]

What I'm saying is, I'm not convinced that "weak measurement" is any different from "compiling average trajectories from treating the wave energy flux like a divergenceless scalar field and drawing 2D lines of force for that field." I maintain you could get that exact same picture by measuring the energy flux of a classical wave passing between two slits, and drawing trajectories such that the line density is proportional to the energy flux density. This would be completely consistent with a macroscopic treatment of an energy flux as a photon number flux. Those trajectories don't really mean anything beyond a statistical treatment of where photons go in large aggregations, that they could get the same picture with "weak measurement" of "one photon at a time" doesn't strike me as being at all profound.

Let me put it another way. The key statement that we don't know the trajectory of an individual photon is that we cannot know which slit it went through, and still have that photon participate in an interference pattern. Does this experiment tell us which slit any of those photons went through? No. So what? There are still no trajectories in the physical reality of what happened to those photons, and it's not at all clear that an "average trajectory" is anything different from the usual macro aggregate measurement in the classical limit. To me, all this experiment is is a kind of consistency check that "weak measurement" can recover statistical aggregates, but I see no threat to the CI interpretation that the reality is still only what you measure and not what happens between the measurements. So they can create weak measurements that don't completely collapse the wave function, then recover the aggregate behavior in the same way that complete measurements that do collapse the wavefunction could easily do also. What does that tell us? That weak measurements don't mess up aggregate results? Why should we be surprised-- the weak measurements don't tell us the particle trajectories.

Hmm... have you actually read the original paper? It has something to do with momentum and polarization giving away the positions.. i wonder if this is similar or compatible to your idea that classical waves can produce positions too. Anyway. Try to read the following descriptions of the experiment if you don't have access to the original:

http://www.scientificamerican.com/blog/post.cfm?id=what-does-the-new-double-slit-exper-2011-06-07

http://www.sciencedaily.com/releases/2011/06/110602143159.htm

 

[Ken G]

I know they are using a subtle approach to their weak measurements, that's not the point I'm making. I'm saying that no matter how they do it, the "average trajectories" they get are obviously the same as the streamlines of what we would call the "photon fluxes" in a completely classical limit where they are just the energy flux in a classical wave going between two slits. So I could easily draw their exact same figure with entirely classical measurements of an entirely classical wave. So their result (that figure) is nothing the least bit surprising. So what is their claim? That somehow the "weak measurements" are telling us something more than the exact same figure made purely classically? I see no evidence for that claim at all, if you have the exact same output as a classical approach, you don't have any additional information there, you just have a much more complicated way of extracting the same information.

The other way to get that same figure is to send one photon through at a time, and just let it hit a detector on a wall that is at variable distances from the slits, running the experiment over and over. Normalize the patterns on all those walls to have zero divergence, and draw the stream lines. Same picture again, still no trajectories of any individual photons, just an aggregate of different detector realities uniting to make a pretty picture.