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

[vanesch]

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...858-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]

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]

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

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]

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]

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]

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]

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]

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]

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 occurring.

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]

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]

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]

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]

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]

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]

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 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]

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

So the classical observables are real, the quantum wave function is not. A macro system is real, and can be described by a mixed state if our information is incomplete, but it cannot "really" be in a mixed state, and it certainly cannot really be in a superposition state. A quantum system is only real insofar as it leaves an imprint on the real macro systems. This does not say quantum systems cannot have any other reality, it is only to say that we cannot meaningfully confer them with any other reality and still stay within our role of supporting the epistemology of physics-- we have entered the realm of personal philosophy at that point.

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

 

[Ken G]

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

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

 

[Ken G]

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

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

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

 

[Hurkyl]

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

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

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

 

[Ken G]

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

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

 

[Maaneli]

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

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

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

 

[ueit]

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

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

You say that the concept of an electron is used for convenience, I could agree with that. But the theory should be able to work without this concept as well, even if the equations become more convoluted. At the very least, CI should describe unambiguously what is the relationship between the macroscopic properties of the electron gun and the properties of the concept of an electron so that the use of the later is justified.

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

 

[Ken G]

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

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

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

 

[Hurkyl]

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

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

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

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

You say:

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

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

 

[Ken G]

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

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

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

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

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

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

You say:

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

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

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

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

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

 

[Hurkyl]

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

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

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

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

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

Obviously.

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

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

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

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

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

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

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

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

 

[ueit]

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

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

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

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

I see two possibilities:

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

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

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

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

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

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

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

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

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

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

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

 

[Ken G]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

[Maaneli]

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

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

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

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

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

 

[Maaneli]

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

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

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

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

You'll also benefit from reading this:

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

 

[Ken G]

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

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

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

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

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

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

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

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

Not too successful then, was it?