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

[ueit]

I'll speak for myself, and I suspect this will sound more like the CI than the MWI. I would say that what is real is what we say is real, given certain requirements and motivations that define the exercise-- in short, it is a choice. But not an arbitrary choice-- we are looking for an ontology that supports physics, so we must start with the epistemology physics uses. That is the epistemology of objective and repeatable observation, subject to organization and unification under a rational thought system. One can debate which is more important, but I see them as two halves of the same coin, and like the halves of a coin, neither is to extend beyond the constraints of the other. So we need only give existence to that which we actually observe, and can couple to the functioning of our brains. That is what we tend to call "classical observations". There is no escape from this truth, it's just how physics works. So when we look at what we need to think of as real to support that classical epistemology, we are going to have a hard time extending that to quantum concepts that do not pass that filter. That's all the CI says, we don't put into our ontology of what is "actually real" anything other than what we can "actually know about", given our chosen epistemology.

So the classical observables are real, the quantum wave function is not. A macro system is real, and can be described by a mixed state if our information is incomplete, but it cannot "really" be in a mixed state, and it certainly cannot really be in a superposition state. 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.

OK, so classical world is supposed to be real in CI, clear enough. I don't quite get the idea of how a "quantum system is only real insofar as it leaves an imprint on the real macro systems".

Let's say that we make a double-slit experiment with electrons. In order to use QM to predict the interference pattern we need some input, right? Properties we attribute to electrons, like rest mass, momentum and so on. But until detection there is no "imprint" produced by those electrons, so, is it even meaningful to speak about electrons, if they don't exist? In other words I don't see how one can consistently describe the preparation of the experiment without speaking about objects that according to the theory do not exist. One way would be to describe the experiment using only classical properties like density, conductivity but this cannot be the answer as those properties are not the ones used in the QM calculation of the experimental outcome.

 

[Ken G]

No. That's exactly what MWI-ers accuse CI of: the observer (the observation's physics) is always outside of the "physics box".

It is no kind of "accusation", it is simply a fact-- if physics is taken to represent a complete ontology as you earlier charged it to be. An observer cannot both judge what exists inside some "physics box", and at the same time be a part of that physics box themself, because it is logically impossible to completely include one's own mental process in the ontology of some physical event. Of course, in actuality we accept incomplete ontologies all the time, but that's why it's not a valid criticism of the CI.

In classical mechanics, that's not true. In relativity, that's not true. You do not consider an observer "outside of spacetime" (even if that spacetime is closed).

I think by "you" you mean you do not consider that. But there is no necessity in relativity to adopt that point of view. I can formulate relativity in my mind, and indeed I do, as a construct with a very similar principle as the "Heisenberg cut"-- which here would be the "cut" between reality and a reference frame. If one makes that cut, then the observer is "outside the spacetime" of the theory, because all the observer does is to establish a reference frame. That is part of the meaning of an observation, it is an instrument and a reference frame.

Thus, the relationship is, the object of the observation is something that plays out in spacetime, obeying only the invariant physics (that's the true "physics box"), but measurements on that action require the specification of a reference frame to become meaningful. The observer is not in the spacetime, but does specify the reference frame that affords the required meaning. In short, an observer in relativity is connected with a reference frame, but a reference frame is not part of the invariant spacetime-- it is a kind of auxiliary condition we add to the spacetime in a fairly arbitrary way when we insist on (by the needs of physics) converting the invariant action to some set of observables in some reference frame (the invariants we can then construct from the observables, but the observer's experience is not set by the invariants, it is set by the observables).

That sounds to me an awful lot like the arbitrary auxiliary conditions we add to quantum behaviors when we insist on coupling them to macro instruments-- again the results are constrained by constructs like the wave function, but those are not the things the observer experiences. The closeness of the analogy means that a CI-type application to relativity is entirely possible, and may even be more honest, but it just isn't seen as necessary because no significant ontological puzzles are encountered in the standard interpretation of the observer as being "inside the physics box".

Enter quantum mechanics. Here is where we discover that our pretense that it matters not if we imagine we are either "inside" or "outside" the physics box, the "fly on the wall" approach, is no longer tenable. For the first time in physics, we need to take an ontological stand on what "the physics box" actually is, before we can safely get ourselves out of it (as is required to do science meaningfully). So citing past fields where no such stance was necessary does nothing to inform this choice when it comes to quantum mechanics.

So MWI-ers try to keep the observer ALSO within the physics box in quantum mechanics.

But that is not to their credit, it is their mistake, from the point of view of a logically self-consistent ontology. The last thing you want from your science is to have yourself included in it! It is absolutely crucial to get yourself out of the picture, because the goal is objectivity. If the physicist is in the physics box, then physics is a personal language, and Wittgenstein showed that a personal language cannot have meaning.

As to your statement that ontology is a kind of fantasy: of course! It should be a helpful phantasy that helps us organize our sensations, measurements, theories,...

We agree here, I do not really mean "fantasy" in a derogatory way, I merely use it to point out certain limitations. Since we agree on the acceptability of such limitations, my argument is really about the proper seat of such an ontology-- that of personal philosophy, not physical theory. As physical theory, I see the MWI ontology as being self-defeating, expressly because it is not conducive to science's requirement to get the observer out of the physics box, not because it is an unfortunate side effect, but because it is central to how science has to work-- even in situations (like relativity) where we can get away with imagining it is not.

 

[Ken G]

How about statistical mechanics and its various ensembles? I can't quite decide if that is in or out of the box.

I believe you have put your finger squarely on the deep ontological difficulties presented by the whole problem of imagining the observer could ever be "inside the box" of a meaningful physical theory. A theory can only predict, but reality actually happens. That's the difference between being "outside" versus "inside" the box.

 

[Ken G]

But then the question is: is statistical mechanics describing any *fundamental* process or is it just a way to handle complicated problems.

My question to you is, what is the difference between a "fundamental process" and "just a way to handle complicated problems"? Can physics ever be said to be the former instead of the latter? I don't think the distinction has any underlying meaning, all physics theories are "effective theories".

I guess you could consider that the user is part of the box, and then you calculate the odds to "be" one of those users of the ensemble. But in statistical mechanics, the ensemble itself is not really considered ontologically (we do not assume that all molecular configurations "exist in parallel", we just consider an abstract ensemble of which the actual one we're interested in is "one of them")

Ah, but why do we not do precisely that? Would it not be perfectly consistent with these great benefits you say that the MWI gives us in quantum mechanics? In other words, tell me why we needed quantum mechanics to accept MWI-- why couldn't we have done it from the onset of thermodynamics? Was it not argued above that quantum thermodynamics is to be interpreted as some great success for MWI?

 

[Ken G]

OK, so classical world is supposed to be real in CI, clear enough. I don't quite get the idea of how a "quantum system is only real insofar as it leaves an imprint on the real macro systems".

The reason is that our brains are macro systems, that's the whole crux of the matter. No quantum epistemology can escape that, that's the "imprint" I mean. Since epistemologies motivate ontologies, the idea of the CI is to build an ontology that respects that inescapable fact.

Let's say that we make a double-slit experiment with electrons. In order to use QM to predict the interference pattern we need some input, right? Properties we attribute to electrons, like rest mass, momentum and so on.

Well, we need a source that we can intepret as supplying electrons. We don't really need electrons, that's an ontological construct we have added to the experimental apparatus. But we all do.

But until detection there is no "imprint" produced by those electrons, so, is it even meaningful to speak about electrons, if they don't exist?

We have to find a way to extract meaning from all kinds of concepts that we don't know actually exist. Existence is a choice we make, there's no way around that. (This fact was incorrectly labeled solipsism above, but solipsism is just a different ontological choice.)

In other words I don't see how one can consistently describe the preparation of the experiment without speaking about objects that according to the theory do not exist.

I grant you that ontology is invented to allow us to talk more easily about our experiments. It makes no difference if these things "really exist" or not, the invention was to support communication and epistemology.

One way would be to describe the experiment using only classical properties like density, conductivity but this cannot be the answer as those properties are not the ones used in the QM calculation of the experimental outcome.

When you build the apparatus, are you grabbing up electrons and putting them into the machine? Or do you manipulate classical objects? What are you doing when you build an electron gun? This is the key issue, our brains, our bodies, and every way we interact with reality are designed around macro systems that behave classically (because they include all kinds of untraceable noise that decoheres everything like a kind of Midas' touch).

We cannot escape that, it alters our view of the quantum world. Would a quantum mind building quantum instruments have the same quantum physics that we do? Or would they ask very different questions that our quantum physics makes no predictions about?

 

[Hurkyl]

This is the key issue, our brains, our bodies, and every way we interact with reality are designed around macro systems that behave classically (because they include all kinds of untraceable noise that decoheres everything like a kind of Midas' touch).

We cannot escape that, it alters our view of the quantum world. Would a quantum mind building quantum instruments have the same quantum physics that we do? Or would they ask very different questions that our quantum physics makes no predictions about?

As far as I can tell, the empirical evidence says that our minds (insofar as they are part of the universe) are quantum mechanical. What evidence do you have to the contrary?

 

[Ken G]

As far as I can tell, the empirical evidence says that our minds (insofar as they are part of the universe) are quantum mechanical. What evidence do you have to the contrary?

Once again: my definition of "classical" is "involving inherently untraceable noise modes", not "involving no elementary particles" as you seem to interpret the word. This is why you do not understand the CI, right there. If you instead believe that our minds can be described under certain controlled conditions by using a pure state wavefunction (which is what most people mean by "a quantum mechanical system"), what evidence do you have that this is a physically meaningful way to describe a mind? For one thing, has anyone ever demonstrated any value in describing a mind that way? I'm all ears.

 

[Maaneli]

Once again: my definition of "classical" is "involving inherently untraceable noise modes", not "involving no elementary particles" as you seem to interpret the word. This is why you do not understand the CI, right there. If you instead believe that our minds can be described under certain controlled conditions by using a pure state wavefunction (which is what most people mean by "a quantum mechanical system"), what evidence do you have that this is a physically meaningful way to describe a mind? For one thing, has anyone ever demonstrated any value in describing a mind that way? I'm all ears.

As usual, you're confused about the pragmatic value of a theory in describing phenomena at a certain lengthscale, and whether or not that theory actually underlies the theory that is of practical use in describing phenomena at a certain lengthscale (in this case, neural processes in the brain).

By the way, yes, biophysicists have shown it is of value to invoke QM in the study of protein conformation.

 

[ueit]

When you build the apparatus, are you grabbing up electrons and putting them into the machine? Or do you manipulate classical objects? What are you doing when you build an electron gun? This is the key issue, our brains, our bodies, and every way we interact with reality are designed around macro systems that behave classically (because they include all kinds of untraceable noise that decoheres everything like a kind of Midas' touch).

OK, I agree that we do not directly control quantum systems. Nevertheless, the theory use them. If CI is a theory of macroscopic entities, that should be found in its equations. But this is not so. It's true that we only manipulate the electron gun, not the electrons. But the macroscopic properties of the electron gun are nowhere to be found in Schrodinger's equation.

You say that the concept of an electron is used for convenience, I could agree with that. But the theory should be able to work without this concept as well, even if the equations become more convoluted. 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.

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.

 

[Ken G]

As usual, you're confused about the pragmatic value of a theory in describing phenomena at a certain lengthscale, and whether or not that theory actually underlies the theory that is of practical use in describing phenomena at a certain lengthscale (in this case, neural processes in the brain).

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.

By the way, yes, biophysicists have shown it is of value to invoke QM in the study of protein conformation.

By the way, I have no doubt that vastly many quantum mechanical processes occur in the human body. I am also quite clear of the complete uselessness of the concept of a pure state wavefunction of a brain. If people could actually stick to what I really say, I would sure appreciate it.

 

[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.

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Actually I know enough about you.

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

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

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

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

 

[Maaneli]

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

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

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

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

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

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

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

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

 

[Maaneli]

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

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

 

[Maaneli]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

See above.

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Decoherence, the measurement problem, and interpretations of quantum mechanics

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

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

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

 

[Maaneli]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

See above.

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

See above.

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

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

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

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

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

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

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

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

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

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

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

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

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

A solution to the problem of definite outcomes.

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

And yet all the evidence is to the contrary.

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

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

Good night.

 

[vanesch]

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

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Your personal strawman, perhaps.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

I'll break here, my response is long.

 

[Ken G]

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

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

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

I mean, well, it leaves no tracks.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

A solution to the problem of definite outcomes.

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

And yet all the evidence is to the contrary.

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

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

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

 

[Ken G]

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

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

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

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