Decoherence and entropy [Archive]

Ken G

Oct10-08, 09:43 AM

I agree with you concerning the compatibility with several interpretational schemes. However, I would say that decoherence is most of help to MWI - it is the explanation, or at least an important part of the explanation - that helps MWI, as it gives it a scheme to go from "many ontological worlds" to "one single observed world". True enough-- I guess it can be said that it adds understanding, so can be used to inform either interpretation. It can also be used to inform objections to each interpretation. For example, my beef with MWI is that it is pure ontology-- it is much like the aether in relativity, a purely ontological construct that cannot be revealed in any test. Decoherence plays the role of the Lorentz transformation-- it reveals why those tests cannot be performed.

Also, decoherence "needs" in a way part of the MWI viewpoint, in that in order for the calculations of decoherence even to make sense, one needs the "macroscopically evolving wavefunction" viewpoint.Yes, that is the sense to which those inclined to want to use MWI, like those who would want to use an aether in relativity, are equipped with the means to do it.

If, as is the case with Bohr, the physics, and its laws, *change* between the microscopic and the macroscopic, then using the formal tools of quantum mechanics on macroscopic systems would simply be out of the question: we would be using a formalism where it isn't considered valid. But Bohr does not actually say that the laws change between the domains, that would be an awkward and undesirable (and unnecessary) world view. Bohr does not say the laws change-- Bohr says that we choose to construct them differently because we are asking different kinds of questions. This is quite common in physics-- just look at thermodynamics compared to classical mechanics. All that is required, when we change the questions of interest, is correspondence. That doesn't make the laws different, it makes them concern different questions.

It would mean that there where we think (according to Bohr) that the classical laws are valid, we *nevertheless* can use the quantum formalism, and *explain* why things happen *as if* the classical laws are valid. But that's nothing else but the MWI viewpoint, and not the Bohr viewpoint which considers explicitly that in the macroworld, classical physics (and hence not quantum physics) is valid.I would expect that Bohr would confer to the word "valid" no other meaning than "succeeds in its predictions", so I do not agree with that claim about Bohr, but I do agree that it allows one to imagine that MWI is somehow still happening "in the background" as one is applying the laws of quantum mechanics to explain classical phenomena. Nevertheless, the claim that MWI is going on in some untestable realm is still inherently untestable-- even with decoherence.

Again, here decoherence plays exactly the same role as the Lorentz transformation in relativity-- it "covers the tracks" of a chosen ontology. Why is it, I wonder, that in relativity we use that to say there is no aether because don't need it in any of our predictions, yet in quantum mechanics, there's a tendency to retain the extraneous ontology anyway? We have the same core idea either way-- that information we have no means nor desire to track should not be imagined to exist all the same. In other words, information is not an ontological entity, it is an epistemological one, and that is the basis of the Bohr approach.

So I'd say that Bohr doesn't *need* decoherence, and moreover removes decoherence from its formal basis (the use of the quantum formalism). However, what decoherence does bring to Bohr, is that it demonstrates the arbitrariness of the Heisenberg cut, once decoherence has set in.Right, and that is of value to Bohr-- people often object to the arbitrariness of the Heisenberg cut, and ask about gray areas.

On the other hand, MWI justifies the formal basis of decoherence (unitary evolution valid universally), and on the other hand, decoherence justifies the "split into worlds" of MWI.
But it does not justify what has always been the key objection-- how we perceive one thing happening and not the others. I would tend to see that purely probabilistically-- when mixed states are created, there is no need for us to imagine they are all actualized, one is enough.

So although it is entirely correct to say that decoherence (a property of complex systems evolving under unitary quantum theory) is independent of any interpretational scheme, I would say that it is in any way "closer" to the needs and frame of MWI than it is to the Copenhagen view.And I would say it informs either one-- but does not remove my core objection to MWI. Indeed, when I first heard about decoherence, I thought "that explains the Heisenberg cut", which is tantamount to explaining why we don't need MWI to do physics.

Bockhorst

Oct10-08, 02:54 PM

No- not a new definition of entropy. It's a statistical mechanical type of expression, the concept of 'density of states' is treated quantum-mechanically via the density matrix. This paper discusses how to separate the total (system+environment) matrix into (system) and (environment) matrices, and the consequences of that.

Zurek and his coworkers, IMHO, really revolutionized specifically the field of quantum mechanics, but their ideas have really spread into many other areas of physics, including quantum optics and optical trapping of single/small numbers of atoms.

Andy,

Thanks, your reply gives me a better idea of what's going on. Now I see that I didn't pose my question very well. Entropy increases because the number of possible states increases.

With better understanding, I will re-formulate my question:

Is EQ 12 the "root cause" of entropy increase in the universe? IOW is decoherence involved in any physical "real world" process where entropy increases?

Rhea

Ken G

Oct10-08, 03:39 PM

Is EQ 12 the "root cause" of entropy increase in the universe? No, that would be saying it backwards-- entropy increase is the root cause of decoherence! You can tell because entropy increase is the more automatic principle, it merely says that things that have more ways of happening are what will happen.
IOW is decoherence involved in any physical "real world" process where entropy increases?
That is actually a different question, because it does not specify a particular causal connection between entropy and decoherence. If one is a "quantum realist", one thinks that quantum mechanics rules everything that happens in the universe, and so one would say yes, anything that involves entropy increase is ruled by quantum mechanics, and decoherence is the description in quantum mechanical language of entropy increase. However, if you are, like me, someone who simply looks on quantum mechanics the same way as all other science (an artifice for fashioning testable hypotheses and assembling their outcomes into a unifying framework), then you would say no, theory is never "involved in" anything that "happens" in the universe-- it is merely our way of picturing what is happening, and only when convenient to do so. So take your pick, it is a philosophy question not a physics question.

Hurkyl

Oct10-08, 04:13 PM

For example, my beef with MWI is that it is pure ontology-- it is much like the aether in relativity, a purely ontological construct that cannot be revealed in any test.
I don't understand -- if I understand the analogy you're trying to set up, MWI's relation to quantum mechanics is exactly the opposite of the Aether's relation to relativity.

The use of the aether was as an addition to the dynamics of special relativity in order to make it more palatable. The aether was supposed to have a more classical foundation, and still manage to give the laws of special relativity as an emergent property.

In the analogy, we would be considering things like wavefunction collapse or pilot waves as the analogue to the Aether: they represent additions / changes to the dynamics of quantum mechanics (unitary evolution) in order to make it more palatable. MWI is the position that one should study unitary evolution as is; one shouldn't add any extra gadgets to the theory. In the analogy, it's the antithesis of the aether.

Ken G

Oct10-08, 05:34 PM

That's not how I see it, I see it as just the same as the aether-- they are both untestable efforts to describe an ontology that underpins the epistemology of quantum mechanics and relativity respectively. The reason aether provides an ontology to relativity is that it allows light to propagate through a physical medium, making the propagation of light a physical mechanism. Light exists because aether exists, it's ontological. No observations preclude that, because the moment we accepted Lorentz transformations as the way to transform between inertial frames, we also accepted that there would never be any way to sense the presence or absence of an aether. We only chose not to include it, in favor of the epistemological postulate that all observers should be able to do physics the same way, adding nothing that is special to one frame or another. A clear example of a streamlined epistemology trumping an extraneous ontology.

Enter MWI. The wave function is there considered to be an ontological entity, not purely an epistemological one like the way Bohr treated it. The trouble is, as soon as you accept that decoherence in macro systems will be involved in every measurement you ever do to test your theory, you have lost any ability to sense the wave function's ontology. So again we have an extraneous ontology vs. a streamlined epistemology (no "extra worlds" to worry about), yet for some reason, the oft-favored approach now is to take the ontological road. That seems inconsistent. (By the way, pilot waves would be going even farther down the road of extraneous ontology, I don't equate that with wavefunction collapse at all because Bohr's view is that the collapse is an epistemological happening that requires no explanation. Decoherence provides an explanation, but it's just what Bohr anticipated-- I suspect Bohr would just say "I knew that viscerally, I just didn't have a mathematically formal way to say it").

Hurkyl

Oct10-08, 08:01 PM

streamlined epistemology (no "extra worlds" to worry about),
There are always "extra worlds" to worry about -- they are a consequence of unitary evolution, e.g. via the Schrödinger equation.

And an interpretation that includes an extra mechanism whose properties are ill-defined and whose timing is ill-defined, all for the sake of making an undetectable change to the theory so that you can diminish the cognative dissonance of trying to use incompatable theoretical frameworks to describe reality is hardly something I would call "streamlined". (Okay, I admit I'm exaggerating. But only a little. :tongue:)

As for the rest of your comments, your use of 'epistemological' and 'ontological' is mystifying. Not only does your example not make sense (an aether is not a prerequisite for light being 'real') -- your insistence on attaching them to theories is, IMHO, incorrect. MWI doesn't require that the wave function be a 'real object', nor does Copenhagen require that wave functions be mental fictions.

Furthermore, even if you wish to refrain from making assertions about 'reality' -- it is still reasonable (and, dare I say, preferable, from a pedagogical standpoint) to base an ontology in a mathematical structure. Denying an attempt at ontology is, in effect, a refusal to try and understand the subject matter.

Ken G

Oct10-08, 11:28 PM

There are always "extra worlds" to worry about -- they are a consequence of unitary evolution, e.g. via the Schrödinger equation.That is not necessarily true, it is an example of the kind of backward logic we often see in regard to MWI. It is never the role of a theory to tell reality what to do, that is always backward thinking. Reality does whatever it wants, the theory tries to describe it. Thus, it is simply nonscientific to claim that "the Schrodinger equation" causes there to be "extra worlds"-- equations don't do that, they just don't. Show me the extra worlds, and then show me the equation that describes them-- never the other way around.

And an interpretation that includes an extra mechanism whose properties are ill-defined and whose timing is ill-defined, all for the sake of making an undetectable change to the theory so that you can diminish the cognative dissonance of trying to use incompatable theoretical frameworks to describe reality is hardly something I would call "streamlined". (Okay, I admit I'm exaggerating. But only a little. :tongue:)I think those remarks stem more from a misunderstanding about Bohr's approach that from that approach itself. The key is the level of realism involved, i.e., whether one thinks physics is an epistemology or an ontology. 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. Yes, as ontology, the Bohr approach is not effective-- it is not trying to do that. Show Bohr what observation needs to be predicted, and he will predict it-- never anything more, the scheme for making predictions does not dictate the presence of untestable phenomenon. That would be what I say is "extraneous ontology", and is just what the aether is in relativity.

Now, I do not say it is terrible to have extraneous ontology, we as scientists like ontology, it makes us feel like we are really seeing the truth rather than just a simulacrum of the truth. I merely point out that we are uneven in what extraneous ontologies we tolerate.

As for the rest of your comments, your use of 'epistemological' and 'ontological' is mystifying. I think they are quite the normal applications of those terms, actually. Perhaps you are missing my point.
Not only does your example not make sense (an aether is not a prerequisite for light being 'real') -- your insistence on attaching them to theories is, IMHO, incorrect.[What I meant about the tersely assembled analogy with the aether was simply that imagining an aether makes real a mechanism by which light propagates as a wave. You can imagine something physical, not just mathematical, whereby light propagates. I suspect you think of the wave function that way-- not just a mathematical object, but something really there. For if it is a mathematical object, it exists only in our minds, and has no power to generate "many worlds" or anything else.

MWI doesn't require that the wave function be a 'real object', nor does Copenhagen require that wave functions be mental fictions.
If you don't see the Bohr interpretation as fundamentally epistemological, and the MWI as fundamentally ontological, maybe it is you who do not understand those concepts-- I view this as not at all a controversial interpretation of the situation. For example, at http://books.google.com/books?id=Erp0kUhm_NwC&pg=PA13&lpg=PA13&dq=bohr+epistemology+ontology&source=web&ots=SKfCAAnyIS&sig=62WpE0E1rFhqvmVl_XXCOGPDsC0&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA18,M1 we find the statement Bohr would never allow the type of language that admitted the independent existence of any kind of object which could be said to be in a certain state. That is to say he would not regard it as meaningful to talk about, for example, a particle existing between quantum measurements even if the same results were obtained for a given observable in a sequence of such measurements. Rather, as we have seen, he considered the experimental arrangement and the content (meaning) of the result to be a single unanalysable whole. To talk of a state in abstraction of such an experimental arrangement would, for Bohr, make no sense.
I think the pretty clear, and valid, translation of that is that for Bohr, "ontology is epistemology and nothing more". Which is what I said. Seek other references if you think this is controversial.

As for the MWI, my claim is that it does not say ontology is no more than epistemology, instead, it says that the epistemology springs from the underlying ontology. Your own comments also reveal in every case that you think the same way. Again, MWI is inherently an ontological description, that is pretty much obvious. If you don't want the wave function itself to be the underlying ontology, fine, pick something else (like unitarity, though I don't know how you have that without the wave function it acts upon)-- my claim is only that if you have no underlying ontology from which the epistemology is thought to spring, then you simply have no MWI.
Furthermore, even if you wish to refrain from making assertions about 'reality' -- it is still reasonable (and, dare I say, preferable, from a pedagogical standpoint) to base an ontology in a mathematical structure. Now you seem to recognize what I've been saying-- your approach requires that we view ontology as fundamental to epistemology (note, for example, that you equate mathematics with ontology, instead of epistemology, despite the fact that mathematics is an operation that occurs in the mind so clearly deals with knowledge not existence), which is precisely what Bohr rejected. It is also what is rejected when we reject the aether-- relativity uses no ontology that goes beyond the epistemology of the observer. The laws of physics are the ultimate authority, not the state of the matter, that is the crux of the standard epistemological interpretation of relativity. It's just like Bohr: no ontology beyond what is evident in the epistemology. First show me the many worlds, then explain them with the mathematics-- the other way around is just magical thinking.

Denying an attempt at ontology is, in effect, a refusal to try and understand the subject matter.Thank you for that perfectly clear statement of your own prejudices about ontology in science. But it's just prejudice, because in philosophy, there is no such assumption that ontology can be equated with understanding. This is the fundamental flaw in everything you say about MWI-- you always equate ontology with understanding, missing that Bohr is completely justified, if he chooses, to equate epistemology with understanding instead. Indeed, that's generally what science does: epistemology is the route to understanding, ontology is just a kind of convenient crutch to help us get the all-important epistemology right.

Hurkyl

Oct11-08, 08:25 AM

I suspect you think of the wave function that way-- not just a mathematical object, but something really there.
I think discussions about what is or is not 'really there' are generally nothing more than an expression of personal biases.

It is never the role of a theory to tell reality what to do, that is always backward thinking.
However, it is the role of a theory to make predictions, and every theory that makes use of unitary evolution is going to predict the existence of "other worlds". And given that there are over 100 years of experiments confirming the predictions of unitary evolution -- including experiments involving exactly those effects the methods of many worlds are meant to describe (e.g. Bell tests, quantum erasure) -- I find it rather disingenious to dismiss them without consideration.

Furthermore, it is the role of scientific theories to shape our understanding of the natural world. If our best scientific theories indicate that "other worlds" are worthy of serious consideration, it is not the place of our personal prejudices to say otherwise.

Thank you for that perfectly clear statement of your own prejudices about ontology in science. But it's just prejudice, because in philosophy, there is no such assumption that ontology can be equated with understanding
I assert that ontology is a necessary condition for understanding, but not a sufficient one. If I have an understanding of a theory, then I do have an ontology (or possibly several!) that maps the aspects of that theory onto the mental concepts that make up my understanding. On the other hand, if I refuse to allow myself to build such mental concepts, then I cannot effectively formulate an understanding of the subject.

But yes, I will admit I am not a behavioral scientist, so I don't have the expertise to back up this claim. (But, I speculate that you also don't have the expertise to assert that one can understand without forming mental concepts related to the theory)

Ken G

Oct11-08, 10:06 AM

I think discussions about what is or is not 'really there' are generally nothing more than an expression of personal biases.That sounds like a much softer stance on ontology than your previous "Denying an attempt at ontology is, in effect, a refusal to try and understand the subject matter." But the new position will bring us closer into agreement.

However, it is the role of a theory to make predictions, and every theory that makes use of unitary evolution is going to predict the existence of "other worlds". I think you meant that it is the role of a theory to make testable predictions. Is it not? Note how insertion of that key word invalidates the rest of the statement. When a scientific theory makes predictions that can be tested, and others that cannot, does verification of the testable predictions offer evidence in favor of the untestable ones? Why? Doesn't sound much like science to me, it sounds like the backward logic I was talking about.
And given that there are over 100 years of experiments confirming the predictions of unitary evolution -- including experiments involving exactly those effects the methods of many worlds are meant to describe (e.g. Bell tests, quantum erasure) -- I find it rather disingenious to dismiss them without consideration.I fear you are constructing straw men and missing my point. Nothing I'm saying has anything to do with anything that is experimentally verifiable, that's the whole point. Or are you going to claim that purely epistemological formulations of quantum mechanics, like Bohr's, cannot correctly predict the result of a Bell-type experiment?

Furthermore, it is the role of scientific theories to shape our understanding of the natural world.Where "natural world" is defined by our experiments, or our mental constructs inspired by predictions that are only mathematically contiguous to that which can actually be tested?

If our best scientific theories indicate that "other worlds" are worthy of serious consideration, it is not the place of our personal prejudices to say otherwise.It is a rather amazing argument to claim that it is "prejudice" to assert that you need to show me the extra worlds before science has any need to explain them. Again, that is simply backward to the true charge we give science. When science feels a need to explain that which shows up in no experiment, then it joins with a bunch of other subjective pursuits and opens itself to the same criticisms often leveled at those other pursuits. Now, if instead you mean that you have a suggestion for an experiment that can actually detect those "other worlds", then that's very different and I am all ears. Do you?

I assert that ontology is a necessary condition for understanding, but not a sufficient one. Now that assertion is prejudice, it is the one I have already identified in you. How could you ever agree with Bohr if you start from a different set of assumptions about what understanding is? Bohr saw no need for any ontology beyond epistemology-- to him, the only ontology science has is its epistemology. I would say this is precisely the spirit of relativity, which was my "mysterious" point from before. I don't necessarily disagree that ontology is nice, I merely recognize that science has a very conflicted relationship with it. I view it as more of a subjective picture we can take or leave as we do what really matters in science-- its epistemology.

If I have an understanding of a theory, then I do have an ontology (or possibly several!) that maps the aspects of that theory onto the mental concepts that make up my understanding.But here you are misapplying the term ontology. A map onto mental concepts never refers to anything but mental concepts, whereas an ontology must assert the existence of something outside of your mental concepts. That's the whole sticky problem with it, and with many worlds. If you will assert that "many worlds" are nothing but a mental concept that you use to help you understand quantum mechanics, I have no beef with it at all. The normal way it is described, however, is in ontological terms-- the many worlds are really there, because they are implied by a mental construct that overlaps with the same testable predictions as purely epistemological approaches like Bohr's (by "purely", I just mean the ontology extends not one iota past the epistemology).

I'm saying, with Bohr, that nothing ontological should be implied by a theory, it is the proper role of theory to describe only what ontology has been established by direct observation independently of the mathematical specifics of some theory. The rest is no more than "handy mnemonic". It would be like thinking the square root of minus one is somewhere in the real world, simply because it spawns a useful algebra for simplifying quantum mechanical calculations.

On the other hand, if I refuse to allow myself to build such mental concepts, then I cannot effectively formulate an understanding of the subject.
Goodness, no one is suggesting we not build mental concepts! That's what theoretical physics is all about. The issue is, what is the role of those concepts-- to understand what we have evidence exists, or to establish what exists independent from any direct observation of said existence. To me, using pure theory to decide what exists is the ultimate act of human hubris, along the lines of the rational philosophies of the early natural philosophers. Although science owes its existence to those early philosophies, it didn't start to really make progress on its own until it distanced itself from that mode of thinking.

Hurkyl

Oct11-08, 01:36 PM

Or are you going to claim that purely epistemological formulations of quantum mechanics, like Bohr's, cannot correctly predict the result of a Bell-type experiment?
Of course the Copenhagen interpretation can predict* the result of a Bell-type experiment. Just like the MWI, it would say that multiple worlds were formed when the photon-pair is created, and those worlds may or may not interfere, based upon the settings of Alice's and Bob's measuring devices. The only difference is that the argument according to the CI wouldn't use those particular words. (And, of course, it would throw in a collapse or two, so as to get a definite outcome)

*: I'm ignoring, for the sake of argument, that I don't see how CI would predict that there wasn't a wavefunction collapse involved that spoils the entanglement. But due to thermodynamics this may be a non-issue.

I did mean to reply to this part earlier, but forgot:
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.
CI asserts that wavefunctions evolve according to the Schrödinger equation, except that they occasionally collapse to. The CI doesn't describe collapse as merely a mathematical technique for computing conditional probabilities -- the CI describe collapse as an actual change in the wavefunction: it was once something, and now it's something else.

(It doesn't matter if you think of the wavefunction as a real object, a proxy for a real object or objects, a collection of information, or even purely a figment of your imagination)

Ken G

Oct11-08, 11:21 PM

Just like the MWI, it would say that multiple worlds were formed when the photon-pair is created, and those worlds may or may not interfere, based upon the settings of Alice's and Bob's measuring devices.That is patently untrue, the CI never asserts that "multiple worlds" are formed, as that is a clearly ontological statement. It says that the projection onto the measurement is a mixed state, and that's it-- there's nothing that is being projected, the science is the projection. That dovetails with the simple fact that the projection is the only thing we can do science on, it is in fact the result of the measurement. No multiple worlds at all, no more than mulitiple worlds are created every time you check today's weather in classical physics. I think you misunderstand the CI rather completely, at least Bohr's mature version.

The only difference is that the argument according to the CI wouldn't use those particular words. Wrong, read Bohr. If it doesn't use the same words, that's not the "only difference", the only difference it is a completely different interpretation of what is happening-- no multiple worlds, ever. 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.
CI asserts that wavefunctions evolve according to the Schrödinger equation, except that they occasionally collapse to. The "collapse" in the CI happens when you decide, as the physicist, that you don't want to track certain information. You recognize the epistemological fact that you simply do not have, nor will you ever have, the capability of tracking that information, and so you simply build a model that knows it is not tracking that. Physics does that sort of thing all the time, it's basically what thermodynamics is all about.

The CI doesn't describe collapse as merely a mathematical technique for computing conditional probabilities -- the CI describe collapse as an actual change in the wavefunction: it was once something, and now it's something else.It was never something other than a wavefunction, so of course when you couple it to new constraints, you will have new information about it. The crux of the CI is that you choose the information you want to track, and that forms the wave function. In fact, in the CI, there is really no such thing as "the" wave function, any more than there is any such thing as "the" probability that a classical event will happen. Probability, and wave functions, are entirely contingent on the information you choose to include. That's why we can do quantum mechanics in the first place, given the impossibility of finding a perfectly unentangled particle to do experiments on.

(It doesn't matter if you think of the wavefunction as a real object, a proxy for a real object or objects, a collection of information, or even purely a figment of your imagination)It matters a great deal, actually. As I said above, if you think of "many worlds" as just a kind of picture that helps you do calculations, no one can have an objection to that. But you claim the existence of the many worlds, and you claim it springs from the theory, so that invalidates the claim you just made.

Hurkyl

Oct12-08, 10:55 AM

That is patently untrue, the CI never asserts that "multiple worlds" are formed, as that is a clearly ontological statement.
That multiple worlds are formed is a qualitative description of the wavefunction, and thus falls in the realm of pure syntax.

Ken G

Oct12-08, 03:08 PM

That multiple worlds are formed is a qualitative description of the wavefunction, and thus falls in the realm of pure syntax.If that's all the MWI was saying, it would have no ontological significance at all, and I would have no objection to it as a subjective choice by some physicists about how they like to picture their own calculations. But that is not, at all, what the interpretation is taken to mean, as any quick google on the topic will demonstrate. I guarantee that you will encounter ontological language within about the first three seconds of such an exercise.

For example, the first paragraph of the Wiki entry on the topic concludes " In layman's terms, this means that there is a very large, perhaps infinite, number of universes and that everything that could possibly happen in our universe (but doesn't) does happen in some other universes."

Or this quote (from http://plato.stanford.edu/entries/qm-everett/#5) of De Witt and Graham, credited with the most commonly accepted description of what the MWI entails:"This reality, which is described jointly by the dynamical variables and the state vector, is not the reality we customarily think of, but is a reality composed of many worlds."

Do any of those statements sound like "syntax" to you, or do they sound like completely serious efforts at ontology?

vanesch

Oct13-08, 04:24 AM

That's not how I see it, I see it as just the same as the aether-- they are both untestable efforts to describe an ontology that underpins the epistemology of quantum mechanics and relativity respectively.

I agree with you that in MWI one takes the wavefunction "for real" (attach an ontological significance to it), and there is a ressemblance to a kind of "ether" in relativity - however, certainly NOT the ether you are referring to.

The "ether" that would correspond, in relativity, to the wavefunction in MWI, would be the four-dimensional manifold "ether", not the 3-dimensional "space" ether which was initially postulated to justify the "electromagnetic vibrations". Now, not all relativists do this, but I think that many of them do give some kind of "ontological" status to the 4-dim spacetime manifold, even though the *observable* part is only a 3-dim slice through it.

Well, I see the wavefunction in MWI in the same way: there is some ontology to the entire wavefunction which is the result of the unitary evolution, but there is only ONE TERM which is an observable part.

The "old" space-ether would in that respect more ressemble to the projection postulate which wants to "cut away" the extra, though unobservable, part of the 4-dim spacetime manifold, and rigidly consider a specific 3-dim slice, in the same way as the projection postulate "cuts away" all those terms in the wavefunction which will turn out not to be observable.

And indeed, the Lorentz transformations indicate why we cannot distinguish between both views (in other words, why such a weird 4-dim spacetime manifold will act "as if" we were living in a kind of 3-dim ether) in the same way as decoherence indicates why we cannot distinguish between a true MWI world, and one in which the extra terms generated by the Schroedinger equation have been cut away.

Of course, the analogy has its limits, but nevertheless, I thought it was interesting to point this out.

Of course, you're not obliged to do this. You can stick to a strictly positivist viewpoint in which science is just there to crank out mathematical descriptions which help us predict how experiments will evolve. But our human mind sometimes craves for a "picture" ; something we like to think is "real" out there. My personal opinion is that in that case, you're best suited with a picture that sticks to the formula, instead of to the intuition. Other people can have other opinions.

Ken G

Oct13-08, 09:22 AM

And indeed, the Lorentz transformations indicate why we cannot distinguish between both views (in other words, why such a weird 4-dim spacetime manifold will act "as if" we were living in a kind of 3-dim ether) in the same way as decoherence indicates why we cannot distinguish between a true MWI world, and one in which the extra terms generated by the Schroedinger equation have been cut away.Yes, I see the analogy you make there as well. No analogy is perfect, and I was focusing on one aspect-- the tendency to reject ontologies whose tracks do not appear in the observations. But you make the point that the rejection might actually be on the grounds of the Copernican principle, that giving a special ontology to a frame simply because it appears to be special to us, but has nothing special demonstrable in the theory, is the offending element in relativity. That does put the choice of conferring "realness" to the full 4-D spacetime manifold on a par with doing that for the "many worlds".

Yes, that is probably an even stronger analogy, and explains a certain consistency in the standard approaches, but I would point out that treating the spacetime manifold ontologically requires fewer assumptions because it is like a more sophisticated model to understand the scenery of the play that the actors can interact with directly, whereas MWI is more like an ontology of what is backstage that neither the audience nor the actors ever see. We actually use the 4D manifold in our calculations, but the same is not true for the MWI (even "believers" in it never actually use it in any calculations, it is entirely extraneous to the way quantum mechanics is actually done).

To me, what all this says is that there is a considerable level of Aristotelian rationalism still alive and well in modern physics. It is fashionable these days to sacrifice at the altar of empiricism, and bash natural philosophers like Aristotle who thought they could discover physical law via force of intellect, but then when you look more closely you see that we still do the same thing all the time. The 4D spacetime manifold and the many-worlds are both, when taken ontologically, purely rationalist constructions-- but at least the former actually gets used.

Of course, you're not obliged to do this. You can stick to a strictly positivist viewpoint in which science is just there to crank out mathematical descriptions which help us predict how experiments will evolve. But our human mind sometimes craves for a "picture" ; something we like to think is "real" out there. My personal opinion is that in that case, you're best suited with a picture that sticks to the formula, instead of to the intuition. Other people can have other opinions.Yes, I agree that the craving for ontology is strong, and important to recognize. I merely ask that we recognize we are doing it, and that there is an important scientific difference between building theories that explain a physical reality we actually observe, versus imagining a physical reality we do not observe to fit our theories.

Naty1

Oct13-08, 10:00 AM

Charles Seife in DECODING THE UNIVERSE says

Like entropy, decoherence lets you know which way time is running; decoherence is an arrow of time....Decoherence of a qubit increases the entropy of the system by kLog2....nature is always measuring and disseminating information..

vanesch

Oct13-08, 02:27 PM

Yes, I see the analogy you make there as well. No analogy is perfect, and I was focusing on one aspect-- the tendency to reject ontologies whose tracks do not appear in the observations. But you make the point that the rejection might actually be on the grounds of the Copernican principle, that giving a special ontology to a frame simply because it appears to be special to us, but has nothing special demonstrable in the theory, is the offending element in relativity. That does put the choice of conferring "realness" to the full 4-D spacetime manifold on a par with doing that for the "many worlds".

Yup. :approve:

Yes, that is probably an even stronger analogy, and explains a certain consistency in the standard approaches, but I would point out that treating the spacetime manifold ontologically requires fewer assumptions because it is like a more sophisticated model to understand the scenery of the play that the actors can interact with directly, whereas MWI is more like an ontology of what is backstage that neither the audience nor the actors ever see. We actually use the 4D manifold in our calculations, but the same is not true for the MWI (even "believers" in it never actually use it in any calculations, it is entirely extraneous to the way quantum mechanics is actually done).

I know, and this is true, at least for relatively simple spacetimes. However, when people consider inflation, and "bubble" spacetimes in which there are parts of the spacetime manifold which are causally unconnected to our "bubble", then the ressemblance becomes larger, no ?

Is the part of the spacetime manifold beyond an event horizon "really there" ?

To me, what all this says is that there is a considerable level of Aristotelian rationalism still alive and well in modern physics. It is fashionable these days to sacrifice at the altar of empiricism, and bash natural philosophers like Aristotle who thought they could discover physical law via force of intellect, but then when you look more closely you see that we still do the same thing all the time. The 4D spacetime manifold and the many-worlds are both, when taken ontologically, purely rationalist constructions-- but at least the former actually gets used.

In fact, the MWI approach can also be used. For instance, an "ontological explanation" of the EPR setups is entirely "logical" in an MWI frame (as it is in a Bohmian frame, btw), while it hovers on the verge of illogical magic in "more Copernican" views.

Yes, I agree that the craving for ontology is strong, and important to recognize. I merely ask that we recognize we are doing it, and that there is an important scientific difference between building theories that explain a physical reality we actually observe, versus imagining a physical reality we do not observe to fit our theories.

I think we should always realize that when we ask for an ontology, we are leaving the realm of the pure and hard science. Ontology is not falsifiable in a way.
But, but... is the moon "really there", or is it just a theoretical construct that helps us explain moonshine and tides ? I guess now that people have walked on its surface, it is "really there". And the stars ? Are they theoretical constructs which allow us to predict the light in telescopes, or are they "really there" ? And remote galaxies ? And quasars ? And black holes ? And.... In what way are these theoretical constructs "really there" and in what way are they just ways to calculate how our telescopes and radio telescopes and satelites will react ? In other words, in what way are they just constructions modeling a flux of electromagnetic (and other?) radiation impinging on the neighbourhood of the earth ?

You see, it is entirely arbitrary to consider that certain scientific constructions are "genuinly real" and others are just "there for us to help us make predictions". When do we stick to our intuitive observations (Copernican) or when do we let ourselves be guided by our formal constructions (Aristotelian) ?

atyy

Oct13-08, 02:47 PM

You see, it is entirely arbitrary to consider that certain scientific constructions are "genuinly real" and others are just "there for us to help us make predictions".

Do you think it is possible to push away "genuinely real" entirely, and self-consistently say that everything is just "there for us to make predictions"? I'm half thinking that at least the experimental data must be real - but on the other hand, you cannot even describe the results of an experiment without language, which necessarily has some theoretical constructs. :confused:

Hurkyl

Oct13-08, 03:44 PM

Do you think it is possible to push away "genuinely real" entirely, and self-consistently say that everything is just "there for us to make predictions"?
Certainly... but that doesn't get eliminate the issues involved. Even if we do get people to adopt the position that Lorentz and Einstein were just talking about methods of making predictions, the core issue still remains. For example...

Special relativity organizes our experiments into the structure of a 3+1 Minkowski universe. Lorentz Ether theory* organizes our experiments into the structure of a 3+1 Gallilean universe, but whose properties force all experiments to 'live' in an emergent 3+1 Minkowski structure.

Given this, one is compelled to ask the question, "If we are studying the behavior of 'experiments', and they only involve the Minkowski structure, then why would we keep the Gallilean structure around?"

So even though we've gotten rid of that pesky idea of what 'reality' is, we haven't gotten rid of questions like the above.

*: I'm referring to those variations that are observationally equivalent to SR

Ken G

Oct13-08, 07:33 PM

I know, and this is true, at least for relatively simple spacetimes. However, when people consider inflation, and "bubble" spacetimes in which there are parts of the spacetime manifold which are causally unconnected to our "bubble", then the ressemblance becomes larger, no ?Yes, that does get into issues of how far successful mathematics can be extrapolated before it loses contact with the empirical evidence that supported it in the first place. If it works, it will be heralded as an amazing anticipation of unseen events, and if it doesn't, it will be forgotten as though it never existed. Winners write history.

Is the part of the spacetime manifold beyond an event horizon "really there" ?
That's a tricky one indeed. I tend to think of what is behind an event horizon as a bit like the fields inside the conductor when "image charges" are being used to calculate the field outside of one. The mathematics can be extended easily enough, but no one really expects the fields to do that in the image-charge example, yet many do when it comes to event horizons. It's not a perfect analogy, but it points to the pitfalls of doing science in regimes where no empirical data exists (or ever will).

In fact, the MWI approach can also be used. For instance, an "ontological explanation" of the EPR setups is entirely "logical" in an MWI frame (as it is in a Bohmian frame, btw), while it hovers on the verge of illogical magic in "more Copernican" views.
I should have clarified-- when I said "used", I meant used in the simplest formulation of the calculation being done. I did not mean "used to satisfy an aesthetic ontological craving", which is really all it ever does. Incidentally, I would point out that the CI also provides a logical ontology to EPR experiments-- the information was never anywhere but in the mind of the physicist trying to understand the results of some observation, so of course it is completely local to that mind. (Yes, other minds with the same information will reach the same conclusions, but that is hardly surprising either.)

I think we should always realize that when we ask for an ontology, we are leaving the realm of the pure and hard science. Ontology is not falsifiable in a way.Indeed, and ontology is probably not one thing, but a continuum of ideas, some pretty "hard", others "soft", and still others downright "magic".
When do we stick to our intuitive observations (Copernican) or when do we let ourselves be guided by our formal constructions (Aristotelian) ?That's the old "empiricist vs. rationalist" debate, I imagine it will never be resolved nor should it be-- it is just the backdrop against which science happens.

Hurkyl

Oct13-08, 07:42 PM

Incidentally, I would point out that the CI also provides a logical ontology to EPR experiments-- the information was never anywhere but in the mind of the physicist trying to understand the results of some observation, so of course it is completely local to that mind.
I was under the impression that, generally speaking, when one does try to do ontology, one tries not to reinvent solipsism.

Ken G

Oct13-08, 10:35 PM

I was under the impression that, generally speaking, when one does try to do ontology, one tries not to reinvent solipsism.I'm not sure if your impressions, by themselves, can be counted as an argument. Perhaps you just don't understand what I'm saying. In Bohr's interpretation of what quantum mechanics is, there is an ontology there-- it simply does not extend past the epistemology of making predictions based on available information. Bohr asks, what exists outside of our ability to measure it? In other words, we are macroscopic entities, and all observations we will ever be capable of interpreting will have to be passed through that filter. As such, nothing will ever leave any imprint on our minds other than what survives that filter, so what is the point in imagining anything else exists that doesn't survive it? It is a fiction we create for our amusement.

Note this is still an ontology, and not a solipsistic one, for there is no need to state that nothing exists beyond our minds. Instead, the assertion is that we will never know anything about anything except which leaves an imprint in our minds, so to pretend otherwise is false and unnecessary. So if we apply that logic to the EPR, we reach the conclusion that any physicist can use the information at her disposal to predict correlations, and check them, and any other physicist with less knowledge will simply be unaware of those predictions and suffer no flaws in their world view as a result. Indeed, physics would be completely impossible were that not true, as our information is highly limited. Any ontology that cannot embrace these fundamental limits is nothing but a wild guess.

Bohr is saying that reality is whatever is consistent with our own information, and if you compare notes with someone else, you find theirs is too, so there is no difficulty with the premise. Whenever our information overlaps, so does our reality. No problem there either. There is simply no reason for the reality to "come first", and the information to conform to the reality-- they just come together, whenever they come at all. That's precisely how we experience physics measurements, so why would we want to pretend something else was happening? That's the only ontology required in the CI, it's a very minimalist ontology but very true to what science is. And although it recognizes certain inescapable elements of solipsism, it isn't solipsism-- it makes even fewer undemonstrable assertions than that.

vanesch

Oct13-08, 10:47 PM

I'm not sure if your "impressions" can be counted as an argument. Perhaps you just don't understand what I'm saying. In Bohr's interpretation of what quantum mechanics is, there is an ontology there-- it simply does not extend past the epistemology of making predictions based on available information. Bohr asks, what exists outside of our ability to measure it? In other words, we are macroscopic entities, and all observations we will ever be capable of interpreting will have to be passed through that filter. As such, nothing will ever leave any imprint on our minds other than what survives that filter, so what is the point in imagining anything else exists that doesn't survive it? It is a fiction we create for our amusement.

I wouldn't call such a view an "ontology" ! The "fiction we create for our amusement" is exactly what ontology is about, no ? An ontology is saying what "really exists" (and is, because of that, always up to a point, hypothetical and non-falsifiable). An ontology that doesn't go "past the epistemology of making predictions" is therefor a very strange kind of "ontology". Does it mean that what's past that epistemology "doesn't exist" ? Or "exists in a way but we don't care" ? An ontology needs to answer the question of *what* exactly exists.

Maybe I'm wrong - I never saw two identical descriptions of what *was* Bohr's viewpoint (maybe it exists in a superposition ? :tongue: ) - but I was under the impression that Bohr claimed that the epistemological world which is accessible to us, is genuinly classical, and that there is then another, inaccessible, world, which is ruled by quantum mechanics and for which it will be impossible to say "what really happens", but that the filter between both is the Heisenberg cut, which doesn't have a well-defined place, but that from the moment we get information about it, we can assume that we're back in the classical world.
In other words, the motion of a tennis ball is purely classical, and classical mechanics is here NOT an extremely good approximation of an underlying quantum process. It is genuinly classical. Quantum mechanics doesn't apply. An electron in an electron gun starts out classically, then "plunges into the quantum world" and "re-emerges" in the classical world after some or other interaction process when we measure it. We can't know what it did when it was taken away from the classical world, before it re-emerged, but we have a mathematical technique of predicting probabilities of how and when it will re-emerge classically. That's how *I* understand Bohr.

Ken G

Oct13-08, 10:56 PM

Do you think it is possible to push away "genuinely real" entirely, and self-consistently say that everything is just "there for us to make predictions"? I'm half thinking that at least the experimental data must be real - but on the other hand, you cannot even describe the results of an experiment without language, which necessarily has some theoretical constructs. Your last point is a very important one, I think. There is really no escape from the need for filtering in our minds, there's never a reality that is separate from that. Normally, we don't worry about that-- if we must filter, then we can do no better than using the result of the filter when forming our impressions of what is real. In short, what is real is what passes the filter of our mind's eye (I think you see why that is not the same thing as a claim that nothing exists outside the mind, which would be solipsism).

That seemingly innocuous idea never caused any problems in classical physics, where the mind's eye was not fundamentally separated from what "is" other than by surmountable technical details. But the Copenhagen interpretation starts with the recognition that in quantum mechanics, there is such a fundamental separation, which has to do with our inability to experiment on coherences without coupling them to decohering classical instruments (including our own minds). So the concept of "experimental data" being real, in the context of quantum mechanics, is fraught with new ontological difficulties that motivated the CI (and the other approaches) to navigate them.

Hurkyl

Oct14-08, 12:02 AM

I'm not sure if your impressions, by themselves, can be counted as an argument.
It's a prompt for clarification. If solipsism is your intent, my response would be radically different than if solipsism was not your intent, so I feel the need to solicit more information before proceeding.

However, while you claim not to be pushing solipsism...
the assertion is that we will never know anything about anything except which leaves an imprint in our minds
Solipsism is an epistemological or metaphysical position that knowledge of anything outside the mind is unjustified.
you really do seem to be asserting it. (Wikipedia's statement is consistent with my own understanding) So, I am still confused about your intent.

it simply does not extend past the epistemology of making predictions based on available information.
Strict adherence to that philosophy means that the only 'predictions' you can make are about things you have already measured. Actual predictions require one to extrapolate beyond the available information. Scientific predictions further require predictions to be based on theoretical models, with our confidence directly related to its success rate and its specificity.

Bohr asks, what exists outside of our ability to measure it?
Doesn't really matter. For all (?) practical purposes, the totality of what we know (and what we could know) about an object is just as good as the object itself. In fact, that is one of the general techniques of mathematics -- one represents an object of interest by the set of all of its properties.

So, if we posit that a quantum state encapsulates all the information about 'something', it seems rather silly not to go on to say that, in our theoretical model, the quantum state corresponds to that 'something'.

In other words, we are macroscopic entities, and all observations we will ever be capable of interpreting will have to be passed through that filter.
I assume you mean to imply that macroscopic entities must behave classically, thus justifying a Heisenberg cut. Once upon a time this was a good, scientific inference. But after the discovery of relative states and decoherence, there is a strong suggestion that quantum thermodynamics is a better description of this phenomenon, and the cut simply being an approximate description.

(Note that this is an entirely separate issue than the one of symmetry -- that multiple wavefunctions can be observationally indistinguishable)

which has to do with our inability to experiment on coherences without coupling them to decohering classical instruments
First off, the coupling can be delayed until it's time to extract the data after the experiment is performed. Secondly, the classical instrument need not destroy the decoherence -- there are observables with entangled eigenstates.

Ken G

Oct14-08, 12:05 AM

I wouldn't call such a view an "ontology" ! The "fiction we create for our amusement" is exactly what ontology is about, no ? Not necessarily, because we are free to go as far as we want down that road. One can, for example, say that what exists is what you can know about, and there is no need to "fill in the cracks", for there are no cracks between what you can know-- if there were, how would you know about them?

An ontology that doesn't go "past the epistemology of making predictions" is therefor a very strange kind of "ontology". I don't think Bohr would see it that way, I think he'd say it's a strange kind of ontology that does go past what you can actually know something about.
An ontology needs to answer the question of *what* exactly exists.Certainly, but why does that require going beyond what we have actual direct evidence for? When one takes that road too far, one ends up in an ontology that is considered religion. Where does the road turn from science to religion? At least Bohr can be clear on that point.
In other words, the motion of a tennis ball is purely classical, and classical mechanics is here NOT an extremely good approximation of an underlying quantum process. It is genuinly classical. Quantum mechanics doesn't apply.My guess is, Bohr would have said that quantum mechanics isn't needed, not that it doesn't apply. Don't forget that the "correspondence principle" was a crucial part of Bohr's view.

An electron in an electron gun starts out classically, then "plunges into the quantum world" and "re-emerges" in the classical world after some or other interaction process when we measure it. We can't know what it did when it was taken away from the classical world, before it re-emerged, but we have a mathematical technique of predicting probabilities of how and when it will re-emerge classically. That's how *I* understand Bohr.Yes, I think that's a fair characterization of Bohr's ontology. But I see that as simply a fair description of what physics does, if one separates ontology as it intersects with physics, versus ontology that is basically personal philosophy. I'll shift to my own interpretation, because it's not always obvious what Bohr's mature stance was because it is often mixed with or mistaken for Heisenberg's, but maybe Bohr would have agreed. I see physics as a mapping from empirical answers to certain questions into empirical answers to certain other questions. The first set of answers is generally the initial conditions, and the second set is generally the predictions, but the point is-- all that exists in physics are empirical answers to questions, and the rational mapping between them.

Specifically, that requires that physics be capable of answering the question, or there is no need to account for it in the ontology used by physics. The rational part only does the mapping, it does not determine the ontology, because what exists comes in the form of those answers, not the mappings. Certainly, we can add optional ontologies as a kind of personal philosophy, but they have left the realm of physics because physics deals with what is empirically demonstrable. So that does sound like a complete ontology to me, because it specifies what ontology is required and what isn't.

Hurkyl

Oct14-08, 12:43 AM

The "collapse" in the CI happens when you decide, as the physicist, that you don't want to track certain information. You recognize the epistemological fact that you simply do not have, nor will you ever have, the capability of tracking that information, and so you simply build a model that knows it is not tracking that. Physics does that sort of thing all the time, it's basically what thermodynamics is all about.
There's a difference between saying "I don't want to track that information" and "there isn't any information there to track". The former is, as I understand it, was the origin of the MWI. The latter is what the CI asserts.

vanesch

Oct14-08, 02:07 AM

Not necessarily, because we are free to go as far as we want down that road. One can, for example, say that what exists is what you can know about, and there is no need to "fill in the cracks", for there are no cracks between what you can know-- if there were, how would you know about them?

What you can know is epistemology, what "is", is ontology. Epistemology gives hints about what is ontologically possible. And if you really go down the path of limiting ontology to what you can *really* know, as Hurkyl pointed out, you'll end up with solipsism. After all, solipsism is the minimalistic ontology that can go with any epistemology.

I don't think Bohr would see it that way, I think he'd say it's a strange kind of ontology that does go past what you can actually know something about.
Certainly, but why does that require going beyond what we have actual direct evidence for? When one takes that road too far, one ends up in an ontology that is considered religion. Where does the road turn from science to religion? At least Bohr can be clear on that point.

And when you are too severe, you end up in solipsism, as it is impossible to know for real anything about what "really" exists. There are 3 possible stances when mapping an epistemological frame onto a proposed ontology:
- you can take the stance that you only put into your ontology (you only consider as real) what you are absolutely certain has been observed. If you go down that road, you end up in solipsism. (did the instrument read that really ? Or did it just send out signals to my body ? Are only those signals real, and not the emitting instrument ? Is my body real ? Or only the sensations I have about my body ? etc....)
- you can take the stance that any more or less consistent theoretical construct that explains/justifies/predicts/summarises your sensations, is real. My body is real because it is a consistent explanation of the sensations I experience ; the signals my body receives from the external world are real because that is a consistent explanation of the sensations I get from my body ; those signals are emitted by really existing apparatus ; that apparatus handles really existing systems under test ; the systems under test are really the way theory describes them ; ...
If you go down that road, then every essential theoretical construct in the derivation of the behavior of the system must be real too.
- you can take the stance of using common sense to decide between what is "really real", and what is "theory that predicts behavior". You've now displaced the problem to what is common sense, and the story starts all over.

My guess is, Bohr would have said that quantum mechanics isn't needed, not that it doesn't apply. Don't forget that the "correspondence principle" was a crucial part of Bohr's view.

The problem is that there is no correspondence principle without yet another transition quantum/classical. If you apply the Schroedinger equation to the tennis ball, it gets spread out pretty quickly. If you apply the Schroedinger equation to any macroscopic system, you end up very quickly with a wavefunction which has many branches. That's exactly what decoherence tells us. In other words, you *cannot* say that quantum mechanics could apply without having pushed the problem in front of you. Considering that quantum mechanics - even though not needed - can be applied to macroscopic systems is exactly what leads you to MWI. And the correspondence principle only appears in some form of decoherence.
True, quantum mechanics *with a build-in transition to classical* applied on a macroscopic system will give you classical behaviour. But that doesn't help you explaining the transition to classical.

I see physics as a mapping from empirical answers to certain questions into empirical answers to certain other questions. The first set of answers is generally the initial conditions, and the second set is generally the predictions, but the point is-- all that exists in physics are empirical answers to questions, and the rational mapping between them.

Yes, that's the hard, non-ontological part of physics. And as I said somewhere else, you can stop there. There's no "picture", there's just a relationship between setup and result, and a formalism that allows you to go from A to B. The formalism is no inspiration for any description of reality (= ontology). However, even doing that gives you a problem in principle. After all, in order to even specify what is the initial setup, and what are the exact measurements one is going to preform, you need some intuitive element which couples the formalism to the experimental setup.
Now, if you apply this idea further, then why should we consider remote stars as being "really there" ? Why aren't they considered also as theoretical constructs which allow us to calculate spectra in a telescope ?

Specifically, that requires that physics be capable of answering the question, or there is no need to account for it in the ontology used by physics. The rational part only does the mapping, it does not determine the ontology, because what exists comes in the form of those answers, not the mappings. Certainly, we can add optional ontologies as a kind of personal philosophy, but they have left the realm of physics because physics deals with what is empirically demonstrable. So that does sound like a complete ontology to me, because it specifies what ontology is required and what isn't.

Well, the only ontology that is really required is minimally given by solipsism.

It seems to me though, that what you are considering is not so much Copenhagen, but rather Rovelli's relational interpretation.

atyy

Oct14-08, 03:53 AM

vanesch

Oct14-08, 06:32 AM

Haroche and Raimond who did many of the decoherence experiements, which I naively thought mean the wave function is "real", actually say that there is no objective reality to the wave function. How does this compare with the various other points of view?

Exploring the Quantum, OUP 2006, See p33:
http://books.google.com/books?hl=en&id=o2VlG0ib5IUC&dq=haroche+exploring+the+quantum&printsec=frontcover&source=web&ots=HZbh2il4jm&sig=g0YSgVIRrW6dswvpKwLlt858-R4&sa=X&oi=book_result&resnum=4&ct=result

I think that is because the authors have a (IMO) strange definition of reality (which seems to coincide with what Ken G is saying about Bohr):

A reasonable criterion of reality is that any other experimenter (a "measurer" as opposed to the preparer), being given a single copy of this state and not knowing anything about the preparation should be able to find out what the quantum state is.

This is an ad hoc requirement for "reality". Reality, according to this definition, corresponds to what we can know, from a single manifestation of a phenomenon. That's the famous putting equal epistemology and ontology which has been advocated earlier in this thread.

Of course, from this it is easily deducible that the wavefunction is not real. If you have a single system in a quantum state, then it is impossible to find out the wavefunction. Hell, it is even impossible to find out the density matrix. The above is nothing else but a requirement of strict determinism without hidden variables: things can only be "real" if there is no intrinsic randomness (in order to determine probabilities, we need at least an ensemble and not just one event), and if all variables of the deterministic system are measurable. That's a pretty strong requirement for an ontology.

atyy

Oct14-08, 06:54 AM

I think that is because the authors have a (IMO) strange definition of reality (which seems to coincide with what Ken G is saying about Bohr)

So you wouldn't interpret their experiments the way they do? I thought of all people they would sat the wavefunction is "real". Obviously they don't say any of this in their papers which only contains the stuff everyone agrees about, I was quite surprised when I read their book!

vanesch

Oct14-08, 07:29 AM

So you wouldn't interpret their experiments the way they do? I thought of all people they would sat the wavefunction is "real". Obviously they don't say any of this in their papers which only contains the stuff everyone agrees about, I was quite surprised when I read their book!

I have the same problem with the papers from the (very good) Vienna group. They are brilliant experimenters, but sometimes I find their interpretational stuff weirdly formulated.

Maybe it is not fashionable to go beyond Copenhagen if one is not a theorist :smile:

That said, although of course on one hand, one might ask what's the point in looking into decoherence if in any case you don't take the wavefunction for real, it is of course interesting - no matter what's your favorite interpretation - to look at mesoscopic cases of quantum interference and the phenomena that limit this. That's completely separate from interpretational issues. It is "real science".

Ken G

Oct15-08, 12:09 AM

There's a difference between saying "I don't want to track that information" and "there isn't any information there to track". The former is, as I understand it, was the origin of the MWI. The latter is what the CI asserts.But it is the MWI that makes the assertion here, for it further states that the untracked information does exist in a form that can be reconstructed (rhetorically only) into invisible "other worlds". It really says that, as I showed above, it confers a purely rhetorical element to physics ontology. The CI, on the other hand, does not assert that the information isn't there in a general sense, it says it isn't there in the specific sense that physics uses the word "information"-- it really isn't there, because information that we have no access to is not information at all.

So the crux of the whole matter is, what is the appropriate thing to do with imagined "information" that is not actually empirical because we have no access to it? MWI says pretend it is real and build its ramifications into your picture, and CI says if physics can't define its realness, then it isn't real and it does not need to be built into any formal physical structures. As such, I see MWI as highly rationalistic, whereas CI makes an effort to remain as empiricist as possible, without denying the value of a mathematical ontology to the extent that it is required to have the desired epistemological impact (but no more).

Ken G

Oct15-08, 01:20 AM

What you can know is epistemology, what "is", is ontology.That is how I am using the terms, yes.Epistemology gives hints about what is ontologically possible. Or, for Bohr, it spells out quite clearly what the proper ontology is, versus what is pure fantasy. The crux of the matter, to my way of seeing it, is whether or not one requires one's ontology to be "complete". You seem to take it as an article of faith that it must be or it is not an ontology, but to be an ontology it only needs to make claims about what exists, there is no additional requirement that you are trying to specify everything that does or even could exist.
And if you really go down the path of limiting ontology to what you can *really* know, as Hurkyl pointed out, you'll end up with solipsism. What do you mean by "really" know? Can I know one thing not really, and another thing really? Epistemology is an arbitrary determination of what knowledge is, there's no "really" required. There is no danger of solipsism in my position, I merely select a means for establishing knowledge, and recognize that it has to be an epistemology that can apply to a macroscopic brain. That's the whole point here: the means for establishing knowledge is what passes the filter of a classically functioning brain (in the sense of constant decoherence in the couplings of the thinking elements). Yes, that has dramatic implicatons for quantum ontology, and is at the heart of the CI when one uses that same epistemology as the sole guide for establishing one's ontology (which is what I believe is what Bohr did).

After all, solipsism is the minimalistic ontology that can go with any epistemology.But we are not talking about just any epistemology, we are talking about physics. It is a very specific epistemology, and it is highly non-solipsistic.

There are 3 possible stances when mapping an epistemological frame onto a proposed ontology:
- you can take the stance that you only put into your ontology (you only consider as real) what you are absolutely certain has been observed.As above, I see no purpose in your inclusion of the terms "absolutely certain". Science has never included that in any of its epistemologies, and neither I nor Bohr ever implied we should start now.- you can take the stance that any more or less consistent theoretical construct that explains/justifies/predicts/summarises your sensations, is real. ...If you go down that road, then every essential theoretical construct in the derivation of the behavior of the system must be real too.
- you can take the stance of using common sense to decide between what is "really real", and what is "theory that predicts behavior". You've now displaced the problem to what is common sense, and the story starts all over.
But none of these issues are responsive to the core problem with quantum mechanical ontology, which is that we are macro objects trying to build an ontology about quantum objects whose attributes we can only assess by passing them through a filter that brings them to the macro domain. Our own theory tells us that there are attributes, like superposition, that do not pass that filter because they cannot be coupled to our brains. So we are trying to build an ontology about a system that cannot be faithfully rendered in our minds. That is the only source of the CI "Heisenberg cut". Put simply, the problem is not that the physics has to be classical, the problem is that the physicist has to be.

The problem is that there is no correspondence principle without yet another transition quantum/classical.But that transition is apparent-- it is undeniable that our brains are on the other side of that transition. I don't see that as the least bit controversial, until someone can build a conscious quantum brain. I think what Bohr was saying is essentially that macro brains trying to build an ontology of quantum systems is like a deaf person trying to understand music. He could study the patterns in what the pianist is doing, and build theories about what motions will produce what reactions in the audience, but if that person ever gained the ability to hear, all that painstaking analysis would melt away and in an instant they would say "ah, so that's what music is, my ontology was completely missing the point of it."

In other words, I see Bohr as simply recognizing that it will always be easier to separate the classical and quantum domains than it will be to separate the physics from the physicist doing it.
Considering that quantum mechanics - even though not needed - can be applied to macroscopic systems is exactly what leads you to MWI. I'm afraid I don't understand this claim, are you saying that the MWI makes different predictions for macro systems than the CI does? I've seen quantum-styled calculations meant to show the correspondence to macro systems (I mean actual wave function calculations generating observables, not the schematic entities used to represent the MWI approach), and I never saw a requirement to include MWI in any of them. So on what basis do you claim that applying quantum mechanics to macro systems leads to MWI?
True, quantum mechanics *with a build-in transition to classical* applied on a macroscopic system will give you classical behaviour. But that doesn't help you explaining the transition to classical.The transition to classical is not hard to explain, that's what decoherence gives you. That's exactly why I see decoherence as critically supportive of the CI, even though it can also be used to provide context to the MWI. In either CI or MWI, we say that decoherence gives us a mixed state when we project onto the classical open system in question. The difference is that CI says that the projection is the ontology, that's what is real, because that's what we can actually do physics on-- the act of coupling to our minds will always require taking a classical projection at some point, our brains have no idea what else to do in an experiment. So rather than say there is something wrong with the physics that makes it look like only one thing happened, we simply say that only one thing happened because decoherence prevents us from examining any trace of anything else that we might imagine happened.
Yes, that's the hard, non-ontological part of physics.It isn't non-ontological, it asserts what exists: what exists is the mapping between the answers to questions. That's the bare bones physics ontology, but it is very much still an ontology. It is simply an ontology that does not go past what we can know by our chosen epistemology. We choose a means of knowing, and that spawns a minimal ontology-- what exists is what we know exists by our chosen epistemology-- the empirical answers to various questions, that's what exists. A question that is never posed is also never answered (and note that the "questions" can be hypothetical, we may imagine hypothetical scientists asking questions every time there is a physical interaction of the type scientists create, i.e., decoherence-- that handles the "tree falling in the woods" issue). Again, it is not a complete ontology, but I wager I could show that there is no such thing as a complete ontology.

There's no "picture", there's just a relationship between setup and result, and a formalism that allows you to go from A to B. That is a picture, that's the picture of everything that is real. And here's the kicker-- that actually does describe everything that is empirically real, everything that "shows up" as real in an experiment.
The formalism is no inspiration for any description of reality (= ontology). Use your imagination-- I argue it is indeed an inspiration for the only description of reality that holds up as non-fantasy under the standards of physics. Not that there is a crime in fantasy, I enjoy science fiction as much as the next person, and routinely engage in fantasy as I imagine my life circumstances and so on. (I simply call it optimism instead of fantasy.)

However, even doing that gives you a problem in principle. After all, in order to even specify what is the initial setup, and what are the exact measurements one is going to preform, you need some intuitive element which couples the formalism to the experimental setup. Exactly why it is an ontology! But it is the minimum ontology, and the only one supportable empirically.

Now, if you apply this idea further, then why should we consider remote stars as being "really there" ? Why aren't they considered also as theoretical constructs which allow us to calculate spectra in a telescope ?Again this is your issue with solipsism, not mine. Physics epistemology is not ambiguous about what it means when we see light from stars, and the minimal ontology simply equips that epistemology with its necessary existential components: stars. None of that has anything to do with the CI, the CI takes all that for granted.

Well, the only ontology that is really required is minimally given by solipsism.
If I have not yet put the lie to that claim, let me be clear: the solipsism you are talking about is minimal only to a particular choice of epistemology (that I only have knowledge about what is happening "inside my mind", whatever that means), it has nothing to do with the minimal ontology for the epistemology that physics actually uses. The latter is what the CI refers to.

It seems to me though, that what you are considering is not so much Copenhagen, but rather Rovelli's relational interpretation.I am mostly talking about my own way of looking at it, but it could overlap with Rovelli certainly. I think more is made of the differences in the various interpretations than is really there-- Bohm, Bohr, and Everett seem to be the main options (and it seems to me Bohm isn't really saying anything that directly relates, it is kind an orthogonal issue to CI vs. MWI). As for Bohr, I've never seen Bohr say anything in his later formulations that contradicted the way I look at it, so I tend to see him as saying these same things, though I have not done an in-depth study into it.

vanesch

Oct15-08, 03:58 AM

That is how I am using the terms, yes.Or, for Bohr, it spells out quite clearly what the proper ontology is, versus what is pure fantasy. The crux of the matter, to my way of seeing it, is whether or not one requires one's ontology to be "complete".

I think we reached the essence of the disagreement. For certain people, including Bohr I suppose, "reality" is set equal (I'd tend to say: is confused with) to "knowledge about reality". What we (can) know, is, and what we can't, isn't. In other words, reality is (potentially accessible) information.

To others, (me included, and I guess most MWI-ers), what "is" and what we can know about it, are two entirely different things, although of course what "is" shouldn't contradict what we know about it. Here, the source of inspiration for what "is" is the theoretical and mathematical structures that lie at the basis of the organization of our information.

Compare this to "the center of the earth". We will not be able to observe directly the center of the earth in the foreseable future. However, saying that there is a core in the earth is a theoretical construct which allows us to organise a lot of information we actually have, like seismic data, magnetic fields, geological phenomena, gravitational effects etc...
In other words, making the postulate that there is a core deep down in the earth is a theoretical construct which allows us to organize a lot of empirical data. But we cannot have direct information about it. It's just a theoretical construct. I tend to think that Bohr-minded people would then say that the core of the earth doesn't exist.

That's the whole point here: the means for establishing knowledge is what passes the filter of a classically functioning brain (in the sense of constant decoherence in the couplings of the thinking elements). Yes, that has dramatic implicatons for quantum ontology, and is at the heart of the CI when one uses that same epistemology as the sole guide for establishing one's ontology (which is what I believe is what Bohr did).

So reality is dependent on what kind of observer is there ? Did the universe exist before there were conscient beings able to gather information about it ? Is reality dependent on what kind of brain we have ? Or on how we process and acquire information ?

It is not an impossible stance: Rovelli exactly takes on that PoV: each observer his reality, and they can only agree to have the same one.

But that transition is apparent-- it is undeniable that our brains are on the other side of that transition. I don't see that as the least bit controversial, until someone can build a conscious quantum brain. I think what Bohr was saying is essentially that macro brains trying to build an ontology of quantum systems is like a deaf person trying to understand music. He could study the patterns in what the pianist is doing, and build theories about what motions will produce what reactions in the audience, but if that person ever gained the ability to hear, all that painstaking analysis would melt away and in an instant they would say "ah, so that's what music is, my ontology was completely missing the point of it."

Ok, but you are saying that music doesn't exist if you're deaf.

I'm afraid I don't understand this claim, are you saying that the MWI makes different predictions for macro systems than the CI does? I've seen quantum-styled calculations meant to show the correspondence to macro systems (I mean actual wave function calculations generating observables, not the schematic entities used to represent the MWI approach), and I never saw a requirement to include MWI in any of them.

From the moment that you use the Schroedinger equation and a wave description of something, clearly that something, that process is still in the quantum realm, and hasn't "crossed the Heisenberg cut" yet. If you consider that you can do this "all the way up", or at least, up to a decent macroscopic scale, then you have MWI. That's what MWI is about: unitary evolution applies to macroscopic systems.

So on what basis do you claim that applying quantum mechanics to macro systems leads to MWI? The transition to classical is not hard to explain, that's what decoherence gives you.

Decoherence doesn't solve the and/or problem. It solves the "independent branches" problem. It shows us why there's no observable quantum interference anymore between different branches once we are coupled to a complex system (like an "environment"). It doesn't show us why only one of these branches is "actually there". It explains you why you will get the same result when you displace the Heisenberg cut, as long as you put it after coupling with the environment has set in.

That's exactly why I see decoherence as critically supportive of the CI, even though it can also be used to provide context to the MWI. In either CI or MWI, we say that decoherence gives us a mixed state when we project onto the classical open system in question. The difference is that CI says that the projection is the ontology, that's what is real, because that's what we can actually do physics on-- the act of coupling to our minds will always require taking a classical projection at some point, our brains have no idea what else to do in an experiment. So rather than say there is something wrong with the physics that makes it look like only one thing happened, we simply say that only one thing happened because decoherence prevents us from examining any trace of anything else that we might imagine happened.

Ok, but that's then "brain-dependent ontology". If our brains were different, if our conscious experience were different, then we would conclude upon a different ontology. If we are deaf, we say that music doesn't exist. We're close to: if a tree falls in the forest without anyone listening, did it make a sound ?

As I said, I think it is the principal disagreement: for some people, like me, such an "observer/practice" dependent ontology is too "frame-dependent" to be considered. An ontology has to be absolute and complete. For others, the practical viewpoint primes, and they say, for all practical purposes, if we just say that *this* is the ontology, then we won't make any observational error. In fact, I agree with that last stance as a practical way of looking upon things. But to me, that's rather a "shut up and calculate" attitude than a genuine ontological proposal. It's, to me, an ontology "with holes in it".

ueit

Oct15-08, 05:43 AM

I have some questions regarding this "ontology" issue for both CI and MWI.

IMO any theory that is useful at all has to have some ontology. Some things must be assumed to be real, otherwise there is no way to apply the theory to experiments. I have no problem with a theory that says that particles are not real, or the wavefunction is not real. What I think is important, however is that the theory should unambiguously specify what is real and show how those elements of reality correspond to experimental settings and experimental results.

So, my question would be what exactly is real in CI and in MWI.

Thanks.

Ken G

Oct15-08, 10:34 AM

I think we reached the essence of the disagreement. For certain people, including Bohr I suppose, "reality" is set equal (I'd tend to say: is confused with) to "knowledge about reality". What we (can) know, is, and what we can't, isn't. In other words, reality is (potentially accessible) information.Yes, I can agree with that, but I'd put it in different terms. Reality is not set equal to knowledge about reality, rather, reality is constructed from knowledge. One cannot even have a concept of knowledge about reality until one already has created a concept of reality from that knowledge. I can easily imagine knowledge that is not conducive to being interpreted as knowledge about reality, such as Hardy-esque types of abstract mathematics. That's why what we are talking about here is fundamentally an ontology, it is not confused with epistemology (the latter is knowledge, period, not knowledge about reality).

To others, (me included, and I guess most MWI-ers), what "is" and what we can know about it, are two entirely different things, although of course what "is" shouldn't contradict what we know about it.That's the key disconnect, right there. Your charge to your ontology is only that it not contradict what you know to be true, Bohr's charge is that it must emerge entirely from what you know, the rest being a form of fantasy. Here, the source of inspiration for what "is" is the theoretical and mathematical structures that lie at the basis of the organization of our information.And there is no crime in being "inspired" to fantasy, indeed constructive and potentially useful fantasy, as long as one does not attribute to it a level of reality that has authority over us (which is what MWI language always does, and that is the source of the problem). By the "authority of reality", I mean that which has a concrete influence on you even if you are unaware of it or flat out disbelieve it.

More in a moment.

Ken G

Oct15-08, 12:56 PM

Compare this to "the center of the earth". We will not be able to observe directly the center of the earth in the foreseable future.This is not a fundamental problem, as we never observe "directly" anything but what is happening in our brains, and we also haven't the vaguest idea how to characterize that observation either. So the issue is not some arbitrary use of the word "direct", the issue is always what is our chosen epistemology. That's it, that's what matters. And that's why the CI "splits" quantum and classical, because all the epistemology that physics is based on, i.e. all of empiricism, is classical. That is the inescapable fact, without which nothing the CI does would make any sense.
I tend to think that Bohr-minded people would then say that the core of the earth doesn't exist.I strongly doubt Bohr, or CI-minded people, would generally say that. I certainly wouldn't. Instead, I would look at the ontology that you build for the center of the Earth, and look at the epistemology that physics uses to draw conclusions about the center of the Earth, and simply say "yup, that's the ontology you need with that empirical epistemology, with no added elements that would clearly have no power over you if you chose not to use them". Does that make it "exist"? Well, some can imagine that existence is something other than whatever we choose to say it is, but I can't see what they are saying about existence that is different from what we choose to say existence is. They will, after all, be saying it at the time.

So reality is dependent on what kind of observer is there ?It is dependent on the general attributes of the mind that interprets it, yes. How could it be otherwise? What is reality for a rock? If you don't think reality is what we, given certain requirements or motivations, choose to say it is, then tell me what reality is without doing that. Did the universe exist before there were conscient beings able to gather information about it ? I already dealt with the "tree falling in the woods issue"-- the key point about an epistemology is not whether or not anyone is consciously registering the answers to empirical questions, it suffices that they could answer the question if they were in a position to do so. If we specify that a tree falls in the woods, we are imagining that a hypothetical observer could see it as doing so, that's exactly what we mean by the phrase "a tree falls in the woods". It makes no difference whether or not there is an actual observer there, or if they are awake or asleep, unless it is actually you (and even then it will only matter to you). The epistemology of physics is an objective epistemology, so it employs hypothetical observers all the time-- expressly because all observers are at some level hypothetical (lest you fall back into solipsism).

Is reality dependent on what kind of brain we have ? Or on how we process and acquire information ?What we call reality (and that's what ontology is) is clearly dependent on both those things. If you would refute that, tell me the reality you have in mind, without using the kind of brain you have, and without processing any information.
Ok, but you are saying that music doesn't exist if you're deaf.Not quite-- I'm saying that music doesn't exist if there is no such thing as music appreciation. Again, to refute that, you must tell me what music is without resorting to any reference to something that might sound like appreciation is occuring.

From the moment that you use the Schroedinger equation and a wave description of something, clearly that something, that process is still in the quantum realm, and hasn't "crossed the Heisenberg cut" yet. If you consider that you can do this "all the way up", or at least, up to a decent macroscopic scale, then you have MWI.Not quite, you have to go beyond a "decent macroscopic scale". The MWI only applies to closed systems, not their projections onto open subsets (you don't need it for their projections, the CI does that fine). That is their fatal flaw-- that is simply not the description of the process of doing science.

Bohr recognized that the process of doing science is inherently, inescapably, the process of opening the system under study. That is precisely where the "cut" comes from, when it's a quantum system you are opening, and it it also precisely the un-scientific aspect of the MWI. Again, I do not object to MWI as a personal philosophic choice, but it is not true to the strict rules applied by science to retain an objective and empirical focus. The CI is much truer to that ideal, that's the whole point of it. The MWI is better at assuaging our frustrations with being part of what we are trying to understand.
Decoherence doesn't solve the and/or problem. It solves the "independent branches" problem. It shows us why there's no observable quantum interference anymore between different branches once we are coupled to a complex system (like an "environment"). It doesn't show us why only one of these branches is "actually there". I completely agree, it doesn't solve that problem, nor does either the CI or the MWI. In all cases, we agree we end up with a mixed-state description, and decoherence explains why that is in either interpretation. In all cases we are still stuck with explaining how one thing "actually happens", but physics knows how to handle that-- it is simply the ontology that is consistent with a probabilistic epistemology, an epistemology classical physics has been using for eons (witness the ontologies of thermodynamics like "temperature").

The point is, some people seem to gravitate to the MWI because they think it solves the issue of "which one happens" by saying "they all do", but of course it is no solution at all, because we will still experience only one happening, and the MWI has no idea why (neither does the CI, but it is honest about that).
Ok, but that's then "brain-dependent ontology". If our brains were different, if our conscious experience were different, then we would conclude upon a different ontology. Is that not inescapable? It sounds like you are imagining there is a "real ontology" that our brains can in some way "approximate". But you are confounding the problem of ontology when you distinguish a "real ontology" from a "brain-dependent" one. You would need a meta-ontology to tell me how we know when we have a real ontology, that is independent of our means of reaching ontologies. I doubt it is even possible to separate the choosing of an ontology from how our brains analyze that act.As I said, I think it is the principal disagreement: for some people, like me, such an "observer/practice" dependent ontology is too "frame-dependent" to be considered. An ontology has to be absolute and complete.I would counter that no ontology can be either of those. It sounds like you are again imagining a "real ontology" as separable from a "brain-dependent ontology". But what instructions can you give for carrying out that separation? This is what I mean when I say that Bohr's core idea is that it will be much easier to separate the quantum and classical domains than it will be the separate the physics from the physicist, or the ontology from the philosopher. It seems to me what you are doing is rejecting the first separation, but overlooking the resulting charge to accomplish the latter two.

Ken G

Oct15-08, 01:04 PM

What I think is important, however is that the theory should unambiguously specify what is real and show how those elements of reality correspond to experimental settings and experimental results.That is a point well taken, I doubt you'd get much debate from any side of this issue that ontology supports epistemology in an important way. I'd say ontology supports epistemology, and epistemology informs ontology. Balance is all that is required.

So, my question would be what exactly is real in CI and in MWI.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.

Hurkyl

Oct15-08, 07:30 PM

Ken G: I must say I am completely baffled. You claim you have no danger of solipsism, and yet you assert that we cannot know anything outside of the mind. You assert that science is objective, and yet argue that it deals only in subjective experience. I'm having great difficulty trying to formulate a consistent interpretation of your posts.

Anyways, some specific comments:
The MWI only applies to closed systems, not their projections onto open subsets (you don't need it for their projections, the CI does that fine).
(1) Being able to discuss closed systems is a good thing, because the universe is a closed system. :tongue:

(2) Open subsystems are easily described via relative states (i.e. partial traces), something MWI has no trouble dealing with. In fact, another name for the MWI is the "relative state formulation". :tongue:

I completely agree, it doesn't solve that problem, nor does either the CI or the MWI. In all cases, we agree we end up with a mixed-state description
Emphatically no. CI rejects the mixed-state description, preferring to assume that, somehow, the state collapses onto one of the components.

The point is, some people seem to gravitate to the MWI because they think it solves the issue of "which one happens" by saying "they all do",
I'm completely unaware of such a phenomenon. The advantage of MWI is that it minimizes assumptions: because quantum thermodynamics dictates that unitary evolution produces an approximately classical 'macroscopic world', there is no need to impose the ad hoc additional collapse postulate, such as what we see in the CI.

That's the whole point here: the means for establishing knowledge is what passes the filter of a classically functioning brain (in the sense of constant decoherence in the couplings of the thinking elements).
If you agree that the behavior of the brain is described by decoherence -- then why the heck are you rejecting decoherence-based interpretations in favor of collapse-based interpretations?

Put simply, the problem is not that the physics has to be classical, the problem is that the physicist has to be.
If you mean 'classical' in the sense that the relative state of the physicist is well approximated by classical mechanics, then your objections to MWI make no sense.
If you mean 'classical' in the sense that the physicist really is described by classical mechanics, then you have no evidence for your claim.

But that transition is apparent-- it is undeniable that our brains are on the other side of that transition.
Our brains are not on the other side of that transition.
(Oh look, I just denied your claim. :tongue:)

Ken G

Oct15-08, 10:00 PM

Ken G: I must say I am completely baffled. You claim you have no danger of solipsism, and yet you assert that we cannot know anything outside of the mind.You seem confused about the seat of knowing-- all I assert is that we know with our minds. When you talk ask if we can know something "outside our minds", you simply confuse epistemology with ontology. Knowledge has no "location", as it is not something that exists independently of a mind-- it is ontology's role to decide what exists and where it resides. It is not controversial that knowledge is a function of mind. If you equate that with solipsism, I don't think that word means what you think it does.

I'm having great difficulty trying to formulate a consistent interpretation of your posts.As badly as you have misconstrued them, I can easily see why. I was trying to be much clearer than that, either I've been unclear or you are not really trying very hard to get past your preconceptions about what I might be saying.

(1) Being able to discuss closed systems is a good thing, because the universe is a closed system.You missed my point. When physics discusses closed systems, it is always, without exception, from the perspective of being outside that system. Yes or no? This also means that all closed systems are always opened in the process of trying to understand them. Correct? So we never do experiments on closed systems, it's unphysical. Ergo, we never do experiments on "the universe as a whole", we do experiments on parts of the universe. Or perhaps you can supply a counterexample? I shall assume you cannot, and therefore proceed to the conclusion: science is about one system looking at another.

That's just a fact, and the CI does nothing but engender that fact it its internal structure. Yes we can talk about the time evolution of a system while it was closed, but we still cannot escape the necessity to open it in an untraceable way when we want to learn the answers to questions about it, and there is no way to do physics without that step-- leaving it out is just a kind of fantasy. That is also all I have been saying above, I regret that it was so hard to follow.

(2) Open subsystems are easily described via relative states (i.e. partial traces), something MWI has no trouble dealing with. In fact, another name for the MWI is the "relative state formulation".If you think I am surprised to learn that MWI can handle open subsystems, I can only assure you I am aware that MWI makes all the same predictions as CI. The issue here is not whether one interpretation or another "can handle" open subsystems, the issue is which ontology is truer to the way physics actually happens, and which one makes ontological claims that are fundamentally unphysical. In short, the issue is not if the MWI can handle open systems, it is, why does it require itself to do anything else.

Emphatically no. CI rejects the mixed-state description, preferring to assume that, somehow, the state collapses onto one of the components.You are mistaken, mixed states are a perfectly normal part of the CI. They are simply not ontological entities, no system is really "in" a mixed state, it is merely described that way by the physicist attempting to gain knowledge about that system. For this reason, it is perfectly possible for one physicist to treat a system as mixed, and be completely "correct" to their physics in doing that, and another physicist can treat that exact same system as being in a pure state, and also be completely "correct" to their physics in doing that. That's just the fact about open systems and the role of information.

This is all perfectly uncontroversial, because no one thinks that in the moment after you flip a coin, and before you look at it, it is not in one state or the other. Hence, a "mixed state" is an informational description, not an ontological description. That was true long before quantum mechanics, and all the CI says is that nothing happens in quantum mechanics that requires us to suddenly change that opinion.

I'm completely unaware of such a phenomenon. The advantage of MWI is that it minimizes assumptions: because quantum thermodynamics dictates that unitary evolution produces an approximately classical 'macroscopic world', there is no need to impose the ad hoc additional collapse postulate, such as what we see in the CI.
The "ad hoc" postulate of the CI that you refer to has nothing to do with quantum thermodynamics, because thermodynamics is a probabilistic theory and always has been. Since the CI does produce mixed states as probabilistic entities, it has no need whatsoever to make "additional assumptions" to get quantum thermodynamics.

If you agree that the behavior of the brain is described by decoherence -- then why the heck are you rejecting decoherence-based interpretations in favor of collapse-based interpretations?As I said above, collapse-based interpretations are perfectly decoherence-based-- decoherence is the reason the collapse occurs, in a probabilistic theory. It all comes down to tailoring the theory to what physics actually does, and not mistaking it for what really happens in some mysterious way that is independent of the very process of doing physics that supports the theory.
If you mean 'classical' in the sense that the relative state of the physicist is well approximated by classical mechanics, then your objections to MWI make no sense.What I mean by "classical" is not what you appear to mean-- I mean a "classical" system is a system that comes inevitably with all kinds of noise that you could never track. Thus, when you deal with classical systems, you have to do physics on untracked modes that you cannot pretend are information about that system. That information simply does not exist, because information is not something ontological, it is something epistemological. Further, the human mind contains such untrackable noise, and thinking is something that happens after you project onto the open subsystem that is a brain, not before. That is the fundamental flaw of the MWI as a physical theory rather than as a personal philosophy.

vanesch

Oct16-08, 12:02 AM

You missed my point. When physics discusses closed systems, it is always, without exception, from the perspective of being outside that system. Yes or no?

No. That's exactly what MWI-ers accuse CI of: the observer (the observation's physics) is always outside of the "physics box". 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). So MWI-ers try to keep the observer ALSO within the physics box in quantum mechanics.

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,...

atyy

Oct16-08, 12:31 AM

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).

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

vanesch

Oct16-08, 04:19 AM

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

That's tricky, isn't it :smile: I wouldn't know either. But then the question is: is statistical mechanics describing any *fundamental* process or is it just a way to handle complicated problems.

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")

ueit

Oct16-08, 04:40 AM

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

Oct16-08, 11:30 AM

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

Oct16-08, 11:39 AM

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

Oct16-08, 11:42 AM

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

Oct16-08, 11:52 AM

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

Oct16-08, 02:37 PM

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

Oct16-08, 06:08 PM

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

Oct17-08, 03:18 AM

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

Oct17-08, 05:39 AM

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

Oct17-08, 03:07 PM

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

Oct17-08, 03:23 PM

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

Oct17-08, 03:38 PM

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

Oct17-08, 07:16 PM

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

Oct18-08, 12:22 AM

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. :tongue:

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

Oct18-08, 08:33 AM

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

Oct21-08, 06:44 AM

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

Oct21-08, 10:23 AM

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

Oct21-08, 04:30 PM

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%20Myth%20A.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

Oct21-08, 04:47 PM

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

Oct21-08, 07:48 PM

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

Oct21-08, 07:58 PM

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.pdfIf 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

Oct21-08, 10:21 PM

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

Oct21-08, 10:43 PM

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

Oct21-08, 10:50 PM

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

Oct21-08, 10:54 PM

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

Oct21-08, 11:09 PM

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

Oct21-08, 11:25 PM

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

Oct21-08, 11:31 PM

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

Oct22-08, 12:02 AM

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

Oct22-08, 12:12 AM

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

Oct22-08, 12:30 AM

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

Oct22-08, 12:36 AM

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

Oct22-08, 02:21 AM

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

Oct22-08, 02:24 AM

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

Oct22-08, 01:46 PM

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.

:rolleyes:. 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

Oct22-08, 01:56 PM

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

Oct22-08, 04:36 PM

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

Oct22-08, 05:52 PM

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

Oct22-08, 05:58 PM

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

Oct22-08, 07:04 PM

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

Oct22-08, 07:16 PM

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

Oct22-08, 07:27 PM

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

Oct22-08, 09:17 PM

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.

:rofl:. 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

Oct23-08, 12:07 AM

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 any one 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

Oct23-08, 02:21 AM

[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 any one 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

Oct23-08, 05:06 AM

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.

:uhh:. 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. :smile:

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

See above. :smile:

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. :tongue:

vanesch

Oct23-08, 09:54 AM

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

Oct23-08, 11:37 AM

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

Oct23-08, 11:39 AM

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 historyIn 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

Oct23-08, 11:48 AM

IPlease keep in mind that in discussions about interpretations of quantum theory, half of the argument is philosophy based, and half of it is theory based. So it is entirely normal to have different viewpoints, and there's no point in trying to argue why one is "better" than the other.This is well put, and I really didn't mean to frame my position in that light-- in fact I think all three, the CI as it is often described, the MWI, and the deBB, include ontological widgets that are really quite unnecessary, but are still each of interest and could stimulate new discovery. All I was arguing is that a particularly stripped down version of the CI, which is what I believe Bohr advocated, represents the minimal ontology needed to support the basic epistemology of making predictions and generating understanding of QM systems, the key goals of science. My problem with the MWI and the deBB are the claims people make about what they represent or what they accomplish, which I find are largely unsubstantiated if not downright unphysical. But I guess I've said pretty much everything I can on that score, as the thread became more of a debate clarifying things I never said.
I'm not going to lock this thread right away - but steer it into a constructive discussion, or it will be locked.Oops, I didn't see this until after my last long post! I will confess to considerable rhetorical excess to make my point there, even though I do see my position as fundamentally correct. No doubt the tit-for-tat of my debate with Maaneli is of no general interest whatsoever, so I guess the real question is, does anyone have any actual points to make about how we can characterize as "extraneous" certain elements of an ontology? Maybe that takes it far enough away from the original intent of the OP that it would be better served by a different thread, and even that seems suspect given the tendency for threads about CI, MWI, and deBB to be exhaustingly difficult to bring to a constructive closure!

Maaneli

Oct23-08, 11:16 PM

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Yes it aptly describes you.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

See above.

Physics theories do not "predict" other physics theories!

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

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

Maaneli

Oct24-08, 12:24 AM

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

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

I mean, well, it leaves no tracks.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

I would like to see that!

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

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

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

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

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

Missed the point utterly (as usual).

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

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

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

Oh, you mean Creationists like yourself?

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

Yes I know it.

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

Your prejudice once again.

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

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

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

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

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