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

[Ken G]

If CI is a theory of macroscopic entities, that should be found in its equations.

I'm not sure where this idea that "CI is a theory of macro entities" came from, apparently it's from this thread. I've certainly never seen anything that Bohr wrote that suggested that. CI is an interpretation of a theory called quantum mechanics. The way classical concepts come in is in the way we do physics, so it underlies the basis of all physical theories, including physical theories about quantum mechanical systems. It is my contention that the vast majority of criticisms I hear about the CI simply express one misconception or other about what the CI is actually saying. It is very much a philosophy of physics, and it does nothing more than correctly identify how physics is actually done.

But the macroscopic properties of the electron gun are nowhere to be found in Schrodinger's equation.

That's because Schroedinger's equation is a theory, and an electron gun is an apparatus. This is not particular to quantum mechanics, the theories are not the objects we manipulate to test those theories. All the CI says, quite correctly, is that if we know we are going to have to manipulate classical objects to test quantum theory (I believe we can all agree on that), then we are going to have to come to grips with that simple fact, and not pretend that we won't. Decoherence explains the "how" of the way quantum systems "cover their tracks" when coupled to classical systems-- all the CI does is recognizes that those tracks do in fact get covered, inescapably.

I see it as much like the aether in relativity, as I mentioned before-- when experiments indicated that the "tracks of the aether" always got covered somehow, in every possible situation, it meant we should just create a theory in which there was nothing there to make those tracks. That's just the motivation the CI uses to compose quantum mechanics, and we should perhaps not overlook the simple truth that that really was the way quantum mechanics was created. Last I checked, no one applied the MWI to the development even a single equation used in QM, it is what I would characterize as a "rationalization" of the actual theory we call quantum mechanics.

At the very least, CI should describe unambiguously what is the relationship between the macroscopic properties of the electron gun and the properties of the concept of an electron so that the use of the later is justified.

That's exactly what decoherence does for the CI, and is why I interpret the physics of decoherence as the justification for the CI approach, when coupled with a few basic emipirical rules about what constitutes physics.

To give an example, in classical mechanics we use the concept of center of mass, a point particle that contains the entire mass of the object. Such a particle does not exist, but it appears in the equations. However, this is not a problem because one can always revert to the real object and calculate this center of mass as a function of macroscopic properties like shape, density and so on. I'd like to see something like that being done for electron gun-electron relationship.

There is no guarantee that such a calculation is tractable, that's the problem. To me, the core of the CI is the recognition that it is much easier to separate the quantum realm, where all information is tracked, from the classical realm, where a staggeringly vast fraction of what is happening is not tracked and cannot even be known to be happening by any empirical definition of the term, than it would be to do what you are asking-- tracing that connection in detail, so that the "hands of the physicist" could be included in the physics.

 

[Hurkyl]

I still have no idea what you mean by "a theory that actually underlies a theory that is of practical use". Here's me, thinking that physics just makes theories that are of practical use, I didn't even know some of us were making other theories to "underlie" these useful ones.

You can build abstractions upon physical theories. For example, upon clsasical particle mechanics, you can build the abstract notion of things like "continuum fluids" or "ideal gases" which are approximate descriptions of the bulk properties of the particles comprising the fluid. Maaneli is criticizing your apparent tendancy, upon building the abstraction, to reject the underlying theory. (And possibly making a reification-like fallacy)

Specifically, once you get the abstraction of an approximately 'classical' world brought on by decoherence or by considering certain relative states, you promptly reject the 'quantum states evolving unitarily' description upon which the abstraction is founded.

If people could actually stick to what I really say, I would sure appreciate it.

You say:

There is a dynamical law that causes the state of a quantum system, upon 'measurement', to become the pure state corresponding to the 'result' of that measurement.​

That it is the statement of the collapse postulate. That is what CI asserts. Whether you believe it nor not, that is the position you have been professing to support this entire thread. (even though your arguments contradict it)

 

[Ken G]

You can build abstractions upon physical theories. For example, upon clsasical particle mechanics, you can build the abstract notion of things like "continuum fluids" or "ideal gases" which are approximate descriptions of the bulk properties of the particles comprising the fluid.

No, those are themselves useful theories. Here's how you can tell: they make testable predictions. Now, the "theories that underlie useful theories" that Maaneli is talking about do not do that. Ergo, they are not physical theories. If you don't agree with that statement, you will need to supply your requirements of a physical theory, for I think mine is pretty much the standard. In other words, physical theories don't require philosophical underpinnings, they require testable accuracy-- that's the only "underpinning" they require. If someone likes to imagine they have some philosophical basis, that's dandy, but it's not physics, nor would I care to defend it against people who choose a different philosophical basis for their beliefs which they also cannot cite empirical data to support.

Specifically, once you get the abstraction of an approximately 'classical' world brought on by decoherence or by considering certain relative states, you promptly reject the 'quantum states evolving unitarily' description upon which the abstraction is founded.

No, that is simply not true. This is what I mean by people not understanding the CI. The CI is perfectly happy with quantum systems evolving unitarily, which are then later coupled to the macro apparatus and we see what comes out. Have you forgotten that the whole mathematical basis of unitary time evolution sprung from the CI? Well, it did.

What the CI actually says is that the unitary evolution can only be, responsibly, said to "happen" in the sole place that we can ever cite empirical evidence that it happens-- in quantum systems (that is, in systems that we can actually get some useful benefit out of the use of a pure state wavefunction). As the pure state wavefunctions are the things that are evolving unitarily, this really doesn't seem like such a stretch as a basic requirement for the application of the unitary evolution requirement.

Let's look at this basic requirement from the point of view of thermodynamics. In thermodynamics, if we have an initial state in an energy conserving (but very complex and noisy) environment, we might imagine that we have a deterministic system. Take for example an ideal gas that collides elastically with itself, and with the walls of a box. Complete determinism is the philosophical construct here that would "underlie" Newton's laws, would it not? But if the system is deterministic, then one state will evolve into one state. There would be no point in counting all the other states that would conserve energy, as none of them will happen-- only the one deterministic state we care about will happen. So why should we imagine that the distribution function would reach a Maxwellian under those conditions? Who would care which is "more likely" if there is just one state evolving deterministically into one other state? Here we have a clear example of a bogus "underlying theory", because it simply gets the answer wrong, even though it is perfectly consistent with Newton's laws. MWI isn't quite that bad, because it escapes making wrong predictions, but it has no better argument in favor of it either.

You say:

There is a dynamical law that causes the state of a quantum system, upon 'measurement', to become the pure state corresponding to the 'result' of that measurement.​

Correct, and the "law" there is simply that is exactly what we mean by a "measurement". Measurement of a quantum system: intentional coupling to a macro instrument, whose intended function is to exert untraceable noise modes to effect decoherence in precisely the desired way to generate a physical state that can be statistically treated as a mixed state in regard to a certain set of eigenstates set by those intentional decohering properties of the chosen instrument." You can call that a "dynamical law" if you like, but I just call it what we mean by "measurement".

Note also that all the CI does is take that statement, and say that once you have that mixed state that you intentionally created using your measuring instrument, you have the same situation that we've always had in classical physics, every time we flipped a coin and didn't look at it. So we bring quantum mechanics into the fold of what physics is now, and has been for a long time.

Whether you believe it nor not, that is the position you have been professing to support this entire thread. (even though your arguments contradict it)

Incorrect, none of my arguments contradict it. If you think the word "measurement" means something else, I'd like to hear what you mean by it. Along with your definition of a physical theory.

 

[Hurkyl]

Now, the "theories that underlie useful theories" that Maaneli is talking about do not do that.

Classical particle mechanics does do that. Quantum states evolving unitarily does do that. In fact...

In other words, physical theories don't require philosophical underpinnings, they require testable accuracy--

quantum states evolving unitarily is (I believe) the best tested theory in the history of mankind.

Have you forgotten that the whole mathematical basis of unitary time evolution sprung from the CI? Well, it did.

I find that plausible. However, you seem to have forgotten that CI said "quantum states also undergo this other, nonunitary form evolution".

Correct, and the "law" there is simply that is exactly what we mean by a "measurement".

It's certainly not what I mean... and as we in the following quote, it's certainly not what you mean... so who is this 'we' you are speaking of?

Measurement of a quantum system: intentional coupling to a macro instrument, whose intended function is to exert untraceable noise modes to effect decoherence in precisely the desired way to generate a physical state that can be statistically treated as a mixed state in regard to a certain set of eigenstates set by those intentional decohering properties of the chosen instrument." You can call that a "dynamical law" if you like, but I just call it what we mean by "measurement".

 

[Ken G]

Classical particle mechanics does do that. Quantum states evolving unitarily does do that.

Obviously.

quantum states evolving unitarily is (I believe) the best tested theory in the history of mankind.

And what is a "quantum state", because it sounds like you mean a "pure state", which is obviously defined as a state that is usefully treated with a pure state wave function, which is in turn more or less the starting point of the CI, which invented the idea. You see, the real question here is, why do you think the CI would disagree with your remark? Given, of course, that the CI was derived using that statement. Yes? And Everett's MWI, that came along, what, 30 years later? But somehow your statement above is supposed to be a telling observation?

I find that plausible. However, you seem to have forgotten that CI said "quantum states also undergo this other, nonunitary form evolution".

I've never seen Bohr make any remark like that in his mature formulation of the CI. A citation for the source of your quote would certainly be helpful. In my view, Bohr's approach would be to that that quantum states always undergo unitary evolution, period, but when you couple a quantum system to a macro instrument, it is no longer treatable as being in a quantum state. Instead, you have to treat it as being in a mixed state, which is no different from what we do classically when we flip a coin and haven't looked yet.

You see, reality isn't "in" various states, that's just not physics. Physics is saying, "I find that I can treat reality as if it were in the following state, and have shown it works in the following situations". That's just how physics works-- theory responds to reality, it does not dictate to reality. Theory is a kind of place-keeper for the body of observations that justify that theory, it is like a shorthand for getting a body of past observations to interact with a new observation. This is true with every single physics theory that has ever been used, I am mystified why quantum mechanics is suddenly seen as different than that. I call it a classic case of "scientists have deluded themselves for millennia when they forgot this simple truth, but it's OK to forget it now, because now we have it right."

Overall, I thus see your whole argument here as just underscoring my point that people who criticize the CI often seem to have a unwieldy interpretation of what it actually is, rather than a real need to replace it with MWI.

It's certainly not what I mean... and as we in the following quote, it's certainly not what you mean... so who is this 'we' you are speaking of?

I'm afraid I have no idea why you claim (without argument, as seems to be your norm) that I don't mean what I do mean when I refer to a measurement. What did happen, however, is that I gave my definition of measurement, and asked you to give yours if you didn't agree with mine (or did you miss that part?). It's actually a little hard to have a meaningful conversation when I say "here's my definition of something, what's yours" and all you can come back with is a weird claim that this isn't my definition. Yes, it is. Now, what's yours?

 

[ueit]

I'm not sure where this idea that "CI is a theory of macro entities" came from, apparently it's from this thread. I've certainly never seen anything that Bohr wrote that suggested that. CI is an interpretation of a theory called quantum mechanics. The way classical concepts come in is in the way we do physics, so it underlies the basis of all physical theories, including physical theories about quantum mechanical systems. It is my contention that the vast majority of criticisms I hear about the CI simply express one misconception or other about what the CI is actually saying. It is very much a philosophy of physics, and it does nothing more than correctly identify how physics is actually done.

I don't know what you mean by "interpretation" but I understand it to be the connection between mathematics and reality, what we see in experiments. Without the interpretation a theory is not really a theory about anything, it's just a set of mathematical formulas.

The idea that "CI is a theory of macro entities" follows from what you've said:

A quantum system is only real insofar as it leaves an imprint on the real macro systems. This does not say quantum systems cannot have any other reality, it is only to say that we cannot meaningfully confer them with any other reality and still stay within our role of supporting the epistemology of physics-- we have entered the realm of personal philosophy at that point.

I see two possibilities:

1. A quantum system exists even when it does not live an imprint on a a macro system. In this case we can say that QM is about the interaction between quantum and macro systems. That seems contrary to what CI says.

2. In the opposite case we have to conclude that the imprint itself is the quantum system. You cannot have a non-existing entity leaving an imprint on something else, right? So, CI is about "imprints" that are just macroscopic properties of macroscopic objects (like spots on a screen).

If you have a logically meaningful way to define a "quantum system" in CI I'd be happy to hear it.

That's because Schroedinger's equation is a theory, and an electron gun is an apparatus. This is not particular to quantum mechanics, the theories are not the objects we manipulate to test those theories. All the CI says, quite correctly, is that if we know we are going to have to manipulate classical objects to test quantum theory (I believe we can all agree on that), then we are going to have to come to grips with that simple fact, and not pretend that we won't. Decoherence explains the "how" of the way quantum systems "cover their tracks" when coupled to classical systems-- all the CI does is recognizes that those tracks do in fact get covered, inescapably.

Again, what parts of reality correspond to the "quantum systems" you speak of?

I see it as much like the aether in relativity, as I mentioned before-- when experiments indicated that the "tracks of the aether" always got covered somehow, in every possible situation, it meant we should just create a theory in which there was nothing there to make those tracks. That's just the motivation the CI uses to compose quantum mechanics, and we should perhaps not overlook the simple truth that that really was the way quantum mechanics was created. Last I checked, no one applied the MWI to the development even a single equation used in QM, it is what I would characterize as a "rationalization" of the actual theory we call quantum mechanics.

The analogy is IMHO not correct. You can speak about relativistic objects without the need to mention the ether The ether is not useful in the theory. In CI, you need those non-existing entities all the time. You need them to calculate the Hamiltonian you put into Schrodinger's equation. If you can replace the electrons and protons by spots, then, by no means, show me a calculation of hydrogen spectra based on those spots. If you cannot, at least in principle, to do that, then how can you say that the electron is not real unless detected? What is the justification to calculate the Hamiltonian for two charged particles following Coulomb's law if there is no such thing as charged particles in the first place?

That's exactly what decoherence does for the CI, and is why I interpret the physics of decoherence as the justification for the CI approach, when coupled with a few basic emipirical rules about what constitutes physics.

I disagree. Decoherence also requires the assumption that a quantum system exists. Otherwise, there is nothing to decohere in the first place.

There is no guarantee that such a calculation is tractable, that's the problem. To me, the core of the CI is the recognition that it is much easier to separate the quantum realm, where all information is tracked, from the classical realm, where a staggeringly vast fraction of what is happening is not tracked and cannot even be known to be happening by any empirical definition of the term, than it would be to do what you are asking-- tracing that connection in detail, so that the "hands of the physicist" could be included in the physics.

This is a matter of logic, not related to the difficulty of solving the equations. The question is "how do you define the quantum realm" in a non-circular way in the CI approach.

 

[Ken G]

I don't know what you mean by "interpretation" but I understand it to be the connection between mathematics and reality, what we see in experiments.

Yes, the meaning of that word, and many of the words, is very much the issue. We all use slightly different shades of meaning, and when put together, it can paint a rather different picture. You and I don't even have exactly the same interpretation of "interpretation"! Our common ground is that the interpretation is whatever elevates a simple set of rules for doing calculations into something that we imagine has meaning. Quantum mechanics could be viewed as nothing but a set of rules for making predictions, that's the interpretation-free approach. As we are having this conversation, we want to go beyond that. You want to go all the way to the point where there is a connection between the mathematics and the reality, but even the word "reality" is part of the interpretation we are using, so we can't use that word in our definition of interpretation. So I would take a step back and just say that it is whatever we are imagining in our minds that gives the mathematics a physical meaning. The issue of "what is quantum reality" is very much a part of the interpretation of "interpretation".

The idea that "CI is a theory of macro entities" follows from what you've said:

I wouldn't put it like that, though perhaps you are not saying something so different. I would say that CI interprets a theory about quantum systems (clearly), but it is not an interpretation about their actual reality, which is a very difficult subject and should not be confused with quantum mechanics. CI is an interpretation that describes how the actual reality of quantum systems, whatever that is, interacts with macro systems, which we have a lot of experience with and have based all of our other impressions about the word "reality" on. Here I think I am right on board with Bohr.

1. A quantum system exists even when it does not live an imprint on a a macro system. In this case we can say that QM is about the interaction between quantum and macro systems. That seems contrary to what CI says.

I do not think the CI has any problem with the statement that quantum systems exist independently of macro observations, it merely asserts that we have no direct intellectual access to that existence. That existence is whatever it is, and it is futile for us to pretend we have direct access to it-- we must accept the macro interface we use as fundamental to our understanding of quantum systems.

So the CI is not a theory about macro systems any more than astronomy is a theory about telescopes. But I think what Wittgenstein once said, "if a lion could talk, we wouldn't understand it", is relevant here-- we should not imagine that quantum mechanics is like listening to the language of quantum systems, because if quantum systems could talk, our classically programmed brains could not understand it.

2. In the opposite case we have to conclude that the imprint itself is the quantum system. You cannot have a non-existing entity leaving an imprint on something else, right? So, CI is about "imprints" that are just macroscopic properties of macroscopic objects (like spots on a screen).

But you see, that is true about everything we perceive. Is there a reality that is not something that imprints itself on one of our senses? Most of us think so, but science is built from what does make such imprints. To take that and say it means that all of physics is just theories about our senses would be something called "idealism" in philosophy, advanced by Berkeley. It is not wrong, but it is not all that useful either, and saying that the CI is doing it does not distinguish quantum mechanics from any other branch of physics. But if you do not take an idealist perspective, you can say that the CI is a theory about quantum systems, built around the ways we interface with said systems. The only thing that separates quantum mechanics from the rest of physics is that this "interface" has a far less transparent impact.

If you have a logically meaningful way to define a "quantum system" in CI I'd be happy to hear it.

Sure-- it is a system that can be successfully predicted by constraining and time-evolving a wave function, i.e., a system that is describable in detail using quantum mechanics. But "describable" here is not an ontological statement, it is a practical statement-- we have to define "quantum systems" in physics using operational terms, not ontological ones, or else we are mixing physics and philosophy.

Again, what parts of reality correspond to the "quantum systems" you speak of?

Goodness, how can anyone answer that? Quantum systems are mental models we create to try to grasp a reality that we can only wonder about. If we knew the reality that quantum systems correspond to, we wouldn't need quantum systems, we'd just use whatever that answer was.

The analogy is IMHO not correct. You can speak about relativistic objects without the need to mention the ether The ether is not useful in the theory. In CI, you need those non-existing entities all the time.

But wait, the "it" I referred to is the "many worlds", not the "quantum systems". Of course we need to be able to talk about quantum systems as if they correspond to something real, and the CI has no problem with that. All of quantum mechanics was derived in the CI perspective! So it cannot have any problem with that. I think you mistake the CI as saying "there are no such things as quantum systems", whereas what it really says is, "whatever is the reality that we try to describe with the concept of quantum systems, we will never know anything about it beyond the way it interacts with macro systems, so let's just fess up to that and build our interpretation around that truth."

What is the justification to calculate the Hamiltonian for two charged particles following Coulomb's law if there is no such thing as charged particles in the first place?

I think you have the question backward: the question is, what is the evidence that there is such a thing as charged particles other than the way you use that concept to build a Hamiltonian? In other words, if all you have to point to is a Hamiltonian, then your charged particles are nothing more than a type of instruction set for building Hamiltonians. The CI has no problem with that-- charged particles are concepts that we use to build Hamiltonians. That's just how the CI was used to build those Hamiltonians in the first place! The Hamiltonian does not have an ontology, that is up to the interpretation we give it. (Indeed, there are ways to get Hamiltonians that don't sound at all like our standard concept of charged particles.)

I disagree. Decoherence also requires the assumption that a quantum system exists.

No one disputes that quantum systems exist. What is disputed is what that existence is. The CI says that everything we know about that existence comes through a filter, the filter accessible to a classically functioning brain, and it simply recognizes that truth when it builds its interpretation of those quantum systems.

This is a matter of logic, not related to the difficulty of solving the equations. The question is "how do you define the quantum realm" in a non-circular way in the CI approach.

I believe I have accomplished that definition, but just to clarify, it is "whatever exists that we can successfully apply quantum mechanics to, after we project it through the only classical filters that our thought processes and senses have access to".

In support of the usefulness of that definition, I point to two facts:
1) No one on this thread has been able to dispute the idea that everything we know about quantum systems has come after passing that information through the classical processes of coupling to macro instruments and applying our classically programmed and classically functioning brains.
2) No one on this thread has been able to dispute the fact that all of quantum mechanics was derived using the CI, and other interpretations came decades later as a kind of means of alleviating a certain philosophical disquiet that many people have when they try to avoid coming to grips with certain fundamental limitations the human mind will always experience when it tries to understand reality.

 

[Maaneli]

2) No one on this thread has been able to dispute the fact that all of quantum mechanics was derived using the CI, and other interpretations came decades later as a kind of means of alleviating a certain philosophical disquiet that many people have when they try to avoid coming to grips with certain fundamental limitations the human mind will always experience when it tries to understand reality.

Actually, you're just factually wrong about all of this. QM was not derived using the CI, because the CI was not christened until the mid-1950's (and Bohr had little to do with it):

Who Invented the “Copenhagen Interpretation”? A Study in Mythology
Don Howard
http://www.journals.uchicago.edu/doi/abs/10.1086/425941?journalCode=phos
http://www.nd.edu/~dhoward1/Copenhagen Myth A.pdf

Moreover, the empirical use of Heisenberg's Matrix mechanics and Schroedinger's wave mechanics (which started between 1925-1927) never involved or required any mention of Bohr's philosophy of QM, or for that matter Heisenberg's. That's all just basic QM history which you should know if you're going to make claims about it.

Finally, the other interpretations of QM like de Broglie-Bohm and Everett were not attempts to "alleviating a certain philosophical disquiet that many people have when they try to avoid coming to grips with certain fundamental limitations the human mind will always experience when it tries to understand reality." They were developed with the purpose of providing a logically coherent interpretation for QM (which did not exist prior), and a mathematical formulation of QM that also included measurement processes (which the mainstream approach of the time also had (and still has) no theory for). The de Broglie-Bohm theory was also formulated by Bohm with the purpose of searching for new physics via the empirical breakdowns of QM.

 

[Maaneli]

Yes, the meaning of that word, and many of the words, is very much the issue. We all use slightly different shades of meaning, and when put together, it can paint a rather different picture. You and I don't even have exactly the same interpretation of "interpretation"! Our common ground is that the interpretation is whatever elevates a simple set of rules for doing calculations into something that we imagine has meaning. Quantum mechanics could be viewed as nothing but a set of rules for making predictions, that's the interpretation-free approach. As we are having this conversation, we want to go beyond that. You want to go all the way to the point where there is a connection between the mathematics and the reality, but even the word "reality" is part of the interpretation we are using, so we can't use that word in our definition of interpretation. So I would take a step back and just say that it is whatever we are imagining in our minds that gives the mathematics a physical meaning. The issue of "what is quantum reality" is very much a part of the interpretation of "interpretation".

I wouldn't put it like that, though perhaps you are not saying something so different. I would say that CI interprets a theory about quantum systems (clearly), but it is not an interpretation about their actual reality, which is a very difficult subject and should not be confused with quantum mechanics. CI is an interpretation that describes how the actual reality of quantum systems, whatever that is, interacts with macro systems, which we have a lot of experience with and have based all of our other impressions about the word "reality" on. Here I think I am right on board with Bohr.
I do not think the CI has any problem with the statement that quantum systems exist independently of macro observations, it merely asserts that we have no direct intellectual access to that existence. That existence is whatever it is, and it is futile for us to pretend we have direct access to it-- we must accept the macro interface we use as fundamental to our understanding of quantum systems.

So the CI is not a theory about macro systems any more than astronomy is a theory about telescopes. But I think what Wittgenstein once said, "if a lion could talk, we wouldn't understand it", is relevant here-- we should not imagine that quantum mechanics is like listening to the language of quantum systems, because if quantum systems could talk, our classically programmed brains could not understand it.
But you see, that is true about everything we perceive. Is there a reality that is not something that imprints itself on one of our senses? Most of us think so, but science is built from what does make such imprints. To take that and say it means that all of physics is just theories about our senses would be something called "idealism" in philosophy, advanced by Berkeley. It is not wrong, but it is not all that useful either, and saying that the CI is doing it does not distinguish quantum mechanics from any other branch of physics. But if you do not take an idealist perspective, you can say that the CI is a theory about quantum systems, built around the ways we interface with said systems. The only thing that separates quantum mechanics from the rest of physics is that this "interface" has a far less transparent impact.
Sure-- it is a system that can be successfully predicted by constraining and time-evolving a wave function, i.e., a system that is describable in detail using quantum mechanics. But "describable" here is not an ontological statement, it is a practical statement-- we have to define "quantum systems" in physics using operational terms, not ontological ones, or else we are mixing physics and philosophy.
Goodness, how can anyone answer that? Quantum systems are mental models we create to try to grasp a reality that we can only wonder about. If we knew the reality that quantum systems correspond to, we wouldn't need quantum systems, we'd just use whatever that answer was.
But wait, the "it" I referred to is the "many worlds", not the "quantum systems". Of course we need to be able to talk about quantum systems as if they correspond to something real, and the CI has no problem with that. All of quantum mechanics was derived in the CI perspective! So it cannot have any problem with that. I think you mistake the CI as saying "there are no such things as quantum systems", whereas what it really says is, "whatever is the reality that we try to describe with the concept of quantum systems, we will never know anything about it beyond the way it interacts with macro systems, so let's just fess up to that and build our interpretation around that truth." I think you have the question backward: the question is, what is the evidence that there is such a thing as charged particles other than the way you use that concept to build a Hamiltonian? In other words, if all you have to point to is a Hamiltonian, then your charged particles are nothing more than a type of instruction set for building Hamiltonians. The CI has no problem with that-- charged particles are concepts that we use to build Hamiltonians. That's just how the CI was used to build those Hamiltonians in the first place! The Hamiltonian does not have an ontology, that is up to the interpretation we give it. (Indeed, there are ways to get Hamiltonians that don't sound at all like our standard concept of charged particles.)
No one disputes that quantum systems exist. What is disputed is what that existence is. The CI says that everything we know about that existence comes through a filter, the filter accessible to a classically functioning brain, and it simply recognizes that truth when it builds its interpretation of those quantum systems.
I believe I have accomplished that definition, but just to clarify, it is "whatever exists that we can successfully apply quantum mechanics to, after we project it through the only classical filters that our thought processes and senses have access to".

In support of the usefulness of that definition, I point to two facts:
1) No one on this thread has been able to dispute the idea that everything we know about quantum systems has come after passing that information through the classical processes of coupling to macro instruments and applying our classically programmed and classically functioning brains.
2) No one on this thread has been able to dispute the fact that all of quantum mechanics was derived using the CI, and other interpretations came decades later as a kind of means of alleviating a certain philosophical disquiet that many people have when they try to avoid coming to grips with certain fundamental limitations the human mind will always experience when it tries to understand reality.

You'll also benefit from reading this:

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

 

[Ken G]

Actually, you're just factually wrong about all of this. QM was not derived using the CI, because the CI was not christened until the mid-1950's (and Bohr had little to do with it):

It makes no difference to me what you are calling the CI, I have been completely clear for this entire thread that when I use the term "CI" I am talking about Bohr's mature concept of what that means. I repeated that often. Furthermore, I also said that I cannot really be considered an expert on Bohr, I only have seen many things he has written about the interpretation of quantum mechanics, and I always find it to be consistent with my own. That is why I label all this the CI, but in fact it can be summarized precisely the way I have summarized it: we only know quantum reality after it passes through a classical filter. If that's not what you mean by the CI, then you can call it something else, it matters not to me.

Moreover, the empirical use of Heisenberg's Matrix mechanics and Schroedinger's wave mechanics (which started between 1925-1927) never involved or required any mention of Bohr's philosophy of QM, or for that matter Heisenberg's. That's all just basic QM history which you should know if you're going to make claims about it.

Quantum mechanics was certainly pieced together rather piecemeal, we all know that, but it also had to have its guiding influences to make it something more than just a workbench for doing calculations. Some feel that's all it ever was and all it ever will be, and that is not refutable, but most on this thread have maintained that physics at that level is difficult to support and conceive, so most of us believe an interpretation is actually a helpful part of the derivation.

If you don't believe that, I'd be happy to hear your evidence, but I tend to think the interpretation is actually an important contributor to the process of derivation. My point is that no one using a many worlds interpretation ever used it as inspiration to advance basic quantum mechanics. That is the claim that you certainly have not refuted here. So they either used no interpretation at all to inspire them, or they used what amounts to the CI (as I defined it generally above)-- quantum operators correspond to classical observables.

Finally, the other interpretations of QM like de Broglie-Bohm and Everett were not attempts to "alleviating a certain philosophical disquiet that many people have when they try to avoid coming to grips with certain fundamental limitations the human mind will always experience when it tries to understand reality." They were developed with the purpose of providing a logically coherent interpretation for QM (which did not exist prior), and a mathematical formulation of QM that also included measurement processes (which the mainstream approach of the time also had (and still has) no theory for).

I'm sorry, but none of that sounds like either the dBB nor the MWI to me. Neither one of those interpretations tells me a thing about coupling to classical systems (i.e., measurement) that is not axiomatically present in the CI. That's what I mean about the axioms of the CI being the core axioms in the derivation of QM. As I also said, Bohr would have just said that decoherence theory does no more than provide a conceptual description of what was already being assumed to happen in the CI. As the CI is all we need to get the actual testable observations, the rest is just make believe. It's not wrong, because it makes no false predictions, and it's not right, because it makes no correct predictions-- it's just not anything except hypothetical ways the universe might work, or might not work. Until you can supply a testable outcome, it all sounds to me like your earlier disastrous claim that these are "theories that underlie useful theories".

The de Broglie-Bohm theory was also formulated by Bohm with the purpose of searching for new physics via the empirical breakdowns of QM.

Not too successful then, was it?

 

[Ken G]

You'll also benefit from reading this:

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

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

 

[Maaneli]

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

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

 

[Maaneli]

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

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

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

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

Cheers,
Maaneli

 

[Ken G]

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

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

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

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

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

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

 

[Maaneli]

Not too successful then, was it?

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

 

[Maaneli]

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

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

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

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

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

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

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

 

[Ken G]

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

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

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

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

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

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

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

 

[Maaneli]

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

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

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

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

 

[Ken G]

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

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

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

and

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

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

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

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

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

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

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

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

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

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

 

[Maaneli]

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

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

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

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

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

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

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

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

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

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

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

 

[Maaneli]

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

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

and

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

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

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

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

Again, please see those philosophy of science papers.

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

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

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

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

 

[Maaneli]

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

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

and

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

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

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

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

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

You see that as "unfortunate"? Strange.

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

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

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

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

 

[Ken G]

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

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

 

[Maaneli]

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

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

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

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

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

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

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

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

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

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

You see that as "unfortunate"? Strange.

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

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

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

You obviously know nothing about me at all.

Actually I know enough about you.

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

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

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

Don't be so sure about that.

 

[Maaneli]

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

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

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

 

[Maaneli]

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

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

 

[Ken G]

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

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

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

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

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

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

 

[Ken G]

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

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

 

[Maaneli]

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

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

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

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

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

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

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