Copenhagen Interpretation of Sleep / Unseen brain?

[bhobba]

As Schlosshauer said - it is reasonable to assume decoherence explains P. Decoherence is based on F and T. I don't see any problem. To be precise when you work through a particular model you find some basis is singled out - by if I remember correctly the requirement is it stable wrt the particular Hamiltonian. That's why position is usually singled out - there is some general argument if the interaction is radial then the position pointer basis is stable (section 2.8.4 Schlosshauer).

Thanks
Bill

 

[1977ub]

So in the middle of the Sun, where it takes

To the average physicist - it won't come up. Philosophers may worry about it - but we don't discuss philosophy on this forum.

A brain is a classical object so QM isn't really relevant. It must be said though no one is really sure if some phenomena like conciousness doesn't crucially depend in some way on QM.

Thanks
Bill

To conceive of the world via reductionism, classical objects are made up of quantum phenomena - is this concern over what classical phenomena are "made of" a purely *philosophical* issue?

 

[atyy]

As Schlosshauer said - it is reasonable to assume decoherence explains P. Decoherence is based on F and T. I don't see any problem. To be precise when you work through a particular model you find some basis is singled out - by if I remember correctly the requirement is it stable wrt the particular Hamiltonian. That's why position is usually singled out - there is some general argument if the interaction is radial then the position pointer basis is stable (section 2.8.4 Schlosshauer).

Yes. The pointer basis is defined by a stability requirement, so the stability requirement is the postulate of a criterion that I am calling P.

 

[bhobba]

To conceive of the world via reductionism, classical objects are made up of quantum phenomena - is this concern over what classical phenomena are "made of" a purely *philosophical* issue?

Of course not.

And the Schlosshauer reference I gave before delves into it.

But that's not the question you asked, the answer to which is since the brain or body is being observed by the environment all the time that you have never seen your brain or are not consciously aware of your body during sleep is not relevant.

Thanks
Bill

 

[bhobba]

Yes. The pointer basis is defined by a stability requirement, so the stability requirement is the postulate of a criterion that I am calling P.

Then I don't follow your issue. You may not agree with the interpretation - or any particular interpretation - that's fine - I get that. The issue is does its conclusions follow from its premises ie is the interpretation a valid theory. If you can prove any interpretation invalid that would be very big news. Note I said prove - we have all sorts of words written about this interpretation having problems etc etc - but none is generally accepted as actually invalid.

However this sojourn into decoherence is not the issue so I will pick another - Quantum Bayesianism:
http://arxiv.org/pdf/1003.5209v1.pdf

Thanks
Bill

 

[atyy]

Then I don't follow your issue.

I am just trying to figure out your interpretation, and whether it solves the measurement problem. It may be correct but it is certainly not standard, not even by the research literature. For example, your interpretation is not mentioned in Schlosshauer's review.

You may not agree with the interpretation - or any particular interpretation - that's fine - I get that. The issue is does its conclusions follow from its premises ie is the interpretation a valid theory. If you can prove any interpretation invalid that would be very big news. Note I said prove - we have all sorts of words written about this interpretation having problems etc etc - but none is generally accepted as actually invalid.

No, I cannot agree with that. To solve a problem, the onus is on the intepretation to show that it is correct.

However this sojourn into decoherence is not the issue so I will pick another - Quantum Bayesianism:
http://arxiv.org/pdf/1003.5209v1.pdf

Quantum Bayesianism is a form of Copenhagen which basically asserts that the measurement problem is not a problem. That is certainly ok, but that is not what we are discussing, which is if the measurement problem is a problem, whether there are complete solutions to it.

So let's go back to your interpretation. Since P is your postulate of defining a pointer basis by a stability criterion, have we agreed that we pick F, P and T?

 

[Derek Potter]

That's incorrect.

Why am I not surprised?

I was going to post the reference that gives the detail (its got to with the radial nature of such interactions) but before doing that can you post the full detail, and I do mean full mathematical detail, of the claim?

Obviously not. I would, however, be interested to know why it is incorrect; that is, if you can dumb it down enough for me to grasp it.

 

[1977ub]

Of course not.

And the Schlosshauer reference I gave before delves into it.

But that's not the question you asked, the answer to which is since the brain or body is being observed by the environment all the time that you have never seen your brain or are not consciously aware of your body during sleep is not relevant.

Thanks
Bill

Perhaps not *more* relevant than other questions about what is "inside" of other matter - away from "measurement". If consciousness doesn't cause collapse (or doesn't do so in the approach of most physicists, then what does?)

For adherents of MWI, what "triggers" a branching ?

 

[atyy]

@bhobba, since you are using Schlosshauer as your reference, could you also explain why this passage does not indicate that there are open problems?

http://arxiv.org/abs/quant-ph/0312059 (p15)
"Finally, a fundamental conceptual difficulty of the decoherence-based approach to the preferred-basis prob-lem is the lack of a general criterion for what defines the systems and the “unobserved” degrees of freedom of the environment (see the discussion in Sec.III.A). While in many laboratory-type situations, the division into system and environment might seem straightforward, it is not clear a priori how quasiclassical observables can be defined through environment-induced superselection on a larger and more general scale, when larger parts of the universe are considered where the split into subsystems is not suggested by some specific system-apparatus-surroundings setup."

 

[bhobba]

Obviously not. I would, however, be interested to know why it is incorrect; that is, if you can dumb it down enough for me to grasp it.

Why obviously not? You made a statement - I am simply asking you to back it up. I will even accept a reference that gives the detail.

Added Later
To forestall this going around in circles you can find the detail in section 2.8.4 and chapter 3 of Schlosshauer.

But just as a general comment Derek you should be prepared to back up statements when you post what others are saying is incorrect with bold statements like 'Absolutely not'. If you can't do that its much better to say - I think such and such - can you give the detail of your claim.

Thanks
Bill

 

[bhobba]

[While in many laboratory-type situations, the division into system and environment might seem straightforward, it is not clear a priori how quasiclassical observables can be defined through environment-induced superselection on a larger and more general scale, when larger parts of the universe are considered where the split into subsystems is not suggested by some specific system-apparatus-surroundings setup."

Its the same factorisation problem in different language. The assumption is it can be done. Disproving decoherence would require you can show such a factorisation to explain a quantum observation does not exist.

Thanks
Bill

 

[atyy]

Its the same factorisation problem in different language. The assumption is it can be done. Disproving decoherence would require you can show such a factorisation to explain a quantum observation does not exist.

Yes. My point is that I'm trying to figure out your interpretation, and whether it solves the measurement problem, because as far as I know it is not published anywhere, not even in Schlosshauer.

So going back to figuring out your interpretation. Are we agreed that it postulates F, P and T criteria?

 

[bhobba]

It may be correct but it is certainly not standard, not even by the research literature.

It's standard. See the paper I have linked to many many times:
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

See section 3.1:
(4) Ignorance interpretation: The mixed states we find by taking the partial trace over the environment can be interpreted as a proper mixture. Note that this is essentially a collapse postulate.

Whenever decoherence is discussed on this forum, and it has been discussed a lot, it always seems to get around to this factorisation issue.

Yes its a legit issue - but a fringe one.. It really only seems gain traction around here - there doesn't seem to be that much interest in it. The above review article doesn't mention it. Schlosshauer does but it doesn't have a lot on it - in fact I can't even really recall where it is like most of the things discussed here where I can easily find reference to it. The only reason I know its there is someone pointed out to me it was.

The factorisation issue does not disprove decoherence based interpretations. All its saying is the answer you get may depend on factorisation - not that a factorisation can't be found that gives standard QM predictions. I haven't even seen proof that a different factorisation gives a different answer in the cases that generally occur in practice such as detailed in Chapter 3 of Schlosshauer where he examines scattering models like photons decohering dust particles. But such is not the issue in disproving it - that would require showing something totally different - you can't break the system into what's observed and what's doing the observing.

I gave the argument before but for completeness here it is again. We will consider two systems A and B. A can be in state |a1> and |a2>. B in state |b1> abd |b2>. System B is the system being observed and system A is doing the observing. We have arranged things that if system A is in |a1> then B is in |b1> and similarly for |b2>.

Suppose we have the following superposition |p> = 1/√2|b1>|a1> + 1/√2|b2>|a2>. This is obviously an entangled system where system A is entangled with system B ie what is doing the observing is entangled with what is being observed. Obviously I chose that particular superposition purely for ease of exposition - it can be in any kind of superposition. It's a pure state. It remains in a pure state until observed ie until its interacted with.

But now we will do an observation on just system A with the observable A.

E(A) = <p|A|p> = 1/2 <a1|<b1|A|b1>|a1> + 1/2 <a1|<b1|A|b2>|a2> + 1/2 <a2|<b2|A|b1>|a1> + 1/2 <a2|<b2|A|b2>|a2>

Now here is the kicker - since you are only observing system A the observable A has no effect on the B system or its states. So we have:

<p|A|p> = 1/2 <Aa1|<b1|b1>|a1> + 1/2 <Aa1|<b1|b2>|a2> + 1/2 <Aa2|<b2|b1>|a1> + 1/2 <Aa2|<b2|b2>|a2> = 1/2 <a1|A|a1> + 1/2 <a2|A|a2>
= Trace((1/2|a1><a1| + 1/2|a2><a2|) A) = Trace (p' A)

Here p' is the mixed state 1/2|a1><a1| + 1/2|a2><a2|. Thus observing system A is equivalent to observing a system in the mixed state p' - which by definition is the state from |p> by doing a partial trace over B. The observation will of course give |a1> or |a2> and the entanglement will be broken so that if you get |a1> system B will be in |b1> and conversely. We still have collapse if you like that language - but now it has a different interpretation - you are not observing a pure state - but a mixed one. Its not a proper mixed state because its not prepared the way a proper mixed state is prepared - but the state is exactly the same. Any observable A will not be able to tell the difference. This means we, in a sense, can kid ourselves and say, somehow, its a proper mixed state. If it was a proper mixed state then prior to observation it is in state |a1> or state |a2> with probability of half. Prior to observation its in superposition - after it isnt. Until observed it continues in superposition - its simply because of the entanglement it can now be interpreted differently. By observing 'inside' the system - ie only observing system A - it is in a mixed state - not a proper one - but still a mixed state. Because of that it allows a different and clearer interpretation that avoids a lot of problems.

The factorisation issue does not disprove the above. Indeed the math is tight - its difficult to see how it could be disproved. What the factorisation issue is, is the claim that the answer we get depends on factorising the observed system and what is observed ie factoring it into system A and B. But the very existence of observations here in the macro world depends on a macro system interacting with a quantum system. If such was not possible QM in any interpretation would be in deep do do.

Thanks
Bill

 

[bhobba]

Are we agreed that it postulates F, P and T criteria?

I agree with the following:

1. That a system being observed by another system can be factored into the system being observed and what's doing the observing. The factorisation issue is you may get a different answer if you decompose it differently. That in no way challenges you can't decompose it into what is being observed and what does the observing by the very definition of what an observation is.

2. We assume there is a threshold below which interference effects are not detectable. You do not have to know what it is - simply such exists. The models I have seen such as in Chapter 3 of Schlosshauer all have the interference effects decaying to very low values very quickly. The obvious assumption is its way below what can be detected.

3. It is reasonable to believe it can solve the preferred basis problem. I don't think we have a general proof as yet. I have read in books like what I will link to at the end certain key theorems are lacking. However in the cases that occur in practice, such as those in Chapter 3 I mentioned previously, it does single out a preferred basis. The cases where it doesn't would seem rather pathological if there is no general theorem.
https://www.amazon.com/Understanding-Quantum-Mechanics-Roland-Omnès/dp/0691004358/ref=sr_1_3?s=books&ie=UTF8&qid=1436329923&sr=1-3

Thanks
Bill

 

[atyy]

Do you agree that the stability criterion needed to define the pointer basis is an additional postulate not found in standard QM, and hence I am justified in calling P a postulated criterion along with F and T?

 

[bhobba]

Do you agree that the stability criterion needed to define the pointer basis is an additional postulate not found in standard QM, and hence I am justified in calling P a postulated criterion along with F and T?

No.

Its obvious you can't have an observational outcome in a particular basis unless its stable. How would you even know the outcome?

Thanks
Bill

 

[atyy]

No.

Its obvious you can't have an observational outcome in a particular basis unless its stable. How would you even know the outcome?

Thanks
Bill

It isn't obvious. Dirac justified the projection postulate by saying that repeated measurement must give the same result. However, not all measurements have to be repeatable, eg. http://arxiv.org/abs/quant-ph/9603020v1 (bottom of p20-21).

At any rate, let's say one uses the predictability sieve as the stability criterion. That is certainly not part of standard QM.

 

[bhobba]

It isn't obvious.

Intuitively an observation is something that leaves a mark here in the macro world so must be robust wrt to the Hamiltonian ie is not changed as the system evolves.

As Schlosshauer says, page 76 'In fact, this ability of the apparatus to serve as a robust and faithful indicator of the state of the state of the system amounts the very definition of a measurement device'

It is this that is the key to solving the issue Schroedinger's cat was on about. Copenhagen did not give a precise definition of a measurement. Decoherence does. Using that its obvious the cat has nothing to do with anything - it happens at the particle detector.

Thanks
Bill

 

[Derek Potter]

Why obviously not? You made a statement - I am simply asking you to back it up. I will even accept a reference that gives the detail.

To forestall this going around in circles you can find the detail in section 2.8.4 and chapter 3 of Schlosshauer.

But just as a general comment Derek you should be prepared to back up statements when you post what others are saying is incorrect with bold statements like 'Absolutely not'. If you can't do that its much better to say - I think such and such - can you give the detail of your claim.
Thanks
Bill

Sure, But I wasn't aware I was contradicting you. I was answering what appeared to be a simple enough question. Of course the question is not simple, I had missed the point by miles, my answer was wrong anyway as well as irrelevant. My bad^N.

 

[atyy]

Intuitively an observation is something that leaves a mark here in the macro world so must be robust wrt to the Hamiltonian ie is not changed as the system evolves.

As Schlosshauer says, page 76 'In fact, this ability of the apparatus to serve as a robust and faithful indicator of the state of the state of the system amounts the very definition of a measurement device'

It is this that is the key to solving the issue Schroedinger's cat was on about. Copenhagen did not give a precise definition of a measurement. Decoherence does. Using that its obvious the cat has nothing to do with anything - it happens at the particle detector.

Is the predictability sieve the stability criterion? If it is not, please state the stability criterion exactly.

 

[bhobba]

Is the predictability sieve the stability criterion? If it is not, please state the stability criterion exactly.

It usually boils down to its associated observable commuting with the Hamiltonian - and is referred to as the commutativity criteria. See page 77 of Schlosshauer.

Its rare that this criteria doesn't work, but evidently it has been generalised, and that is where your predictability sieve comes in (see page 82 Schlosshauer)

Delving deeper into it really requires going through the book. Its been a while since I have delved into this detail, so if that's what you want to do I am afraid I will have to leave it up to you.

Thanks
Bill

 

[atyy]

It usually boils down to its associated observable commuting with the Hamiltonian - and is referred to as the commutativity criteria. See page 77 of Schlosshauer.

Its rare that this criteria doesn't work, but evidently it has been generalised, and that is where your predictability sieve comes in (see page 82 Schlosshauer)

Delving deeper into it really requires going through the book. Its been a while since I have delved into this detail, so if that's what you want to do I am afraid I will have to leave it up to you.

So now that you find the predictability sieve mentioned, do you agree that P is an assumption?

 

[atyy]

It is this that is the key to solving the issue Schroedinger's cat was on about. Copenhagen did not give a precise definition of a measurement. Decoherence does. Using that its obvious the cat has nothing to do with anything - it happens at the particle detector.

Now that I understand your ignorance interpretation a bit better - I had thought it was a variant of Copenhagen, but it isn't - your ignorance interpretation has an absolute quantum/quantum cut, whereas the cut of Copenhagen is not absolute and can be shifted.

Given that you agree that there is not a known prescription for F, how can you say that it happens at the particle detector? If you merely assert that F exists, how can you rule out that the cut is at the box, and so wouldn't there be a version of your ignorance interpretation in which the cat is in a superposition of dead and alive?

 

[bhobba]

Given that you agree that there is not a known prescription for F, how can you say that it happens at the particle detector? If you merely assert that F exists, how can you rule out that the cut is at the box, and so wouldn't there be a version of your ignorance interpretation in which the cat is in a superposition of dead and alive?

You simply trace it back to find the earliest point decoherence occurs.

Thanks
Bill

 

[atyy]

You simply trace it back to find the earliest point decoherence occurs.

So is the wave function real in your ignorance interpretation?

 

[bhobba]

So is the wave function real in your ignorance interpretation?

It's ambivalent.

Thanks
Bill

 

[Derek Potter]

You simply trace it back to find the earliest point decoherence occurs.

Surely (is that diffident enough?) that need not be at the detector? A typical alpha particle leaves a trail of ionisation in air, so decoherence should be pretty complete within a few microns of the source.

 

[bhobba]

Surely (is that diffident enough?) that need not be at the detector? A typical alpha particle leaves a trail of ionisation in air, so decoherence should be pretty complete within a few microns of the source.

Valid point. If you can take it back further depends on exactly how the detector works.

Thanks
Bill

 

[atyy]

It's ambivalent.

So what is real in this interpretation?

I'm asking, because I would like to know in what space F is defined.

For example if the detector is real, what are the degrees of freedom that allow you to say - the cut is at F?

Also, assuming there are degrees of freedom or at least beables that describe the detector - what is there are two Schroedinger cat experiments run simultaneously (defined in an inertial frame) in different parts of the world. Where is F?

 

[bhobba]

So what is real in this interpretation?

Observations.

With two experiments each has its own particle and detector.

Thanks
Bill

 

[atyy]

Observations.

With two experiments each has its own particle and detector.

Is the particle real? Is the detector real?

 

[Derek Potter]

With two experiments each has its own particle and detector.

And its own cat. We must never forget the cats :)

 

[bhobba]

Is the particle real? Is the detector real?

Atty I think you know my view on that. Reality is what our theories specifically state in our axioms. For QM that would be the classical macro world and the observations that occur in it. Its of course an issue exactly how that classical world emerges from a theory that assumes it in the first place. A lot of progress has been made in resolving that but from what I read some issues still remain.

Thanks
Bill

 

[atyy]

Atty I think you know my view on that. Reality is what our theories specifically state in our axioms. For QM that would be the classical macro world and the observations that occur in it. Its of course an issue exactly how that classical world emerges from a theory that assumes it in the first place. A lot of progress has been made in resolving that but from what I read some issues still remain.

That is very confusing! That sounds like Copenhagen, and saying that how the classical world emerges is an issue sounds like there is a measurement problem. But I thought you said your interpretation solves the measurement problem. If it does, how can there still be an issue of how the classical world emerges?

 

[bhobba]

That is very confusing! That sounds like Copenhagen, and saying that how the classical world emerges is an issue sounds like there is a measurement problem. But I thought you said your interpretation solves the measurement problem. If it does, how can there still be an issue of how the classical world emerges?

There is a measurement problem - remember the third part that decoherence is no help with - why we get any outcomes at all. This existence of a classical world is tied up with that.

Thanks
Bill

 

[atyy]

There is a measurement problem - remember the third part that decoherence is no help with - why we get any outcomes at all. This existence of a classical world is tied up with that.

There is a measurement problem in your ignorance interpretation?

 

[bhobba]

There is a measurement problem in your ignorance interpretation?

Of course. I have always said so. It however has morphed to why we get any outcomes at all.

Thanks
Bill

 

[atyy]

Of course. I have always said so. It however has morphed to why we get any outcomes at all.

OK, I don't quite agree with that description of the measurement problem, but now I'm less confused. I thought you were saying that there is no measurement problem in your ignorance interpretation.

If decoherence doesn't solve the measurement problem, then there isn't a tidy answer to my question, right?

Yes there is - its just not unique. Decoherence however has morphed the issue to - why do we get any outcomes at all.

The answer is called an interpretation of which there are a plethora.

I copied the above from your reply to 1977ub earlier in the thread, and it certainly made it seem that you were saying that there are many solutions to the measurement problem, which is what I was disagreeing with. Then I thought you were bringing up your ignorance interpretation as an example of a solution to the measurement problem.

 

[Derek Potter]

For the sake of the slow-witted who may still be trying to glean something from this thread, could you please explain why getting any outcomes at all is a problem?

edit - I don't mean I don't think it is a big issue, I just don't know what you mean by it.

 

[bhobba]

For the sake of the slow-witted who may still be trying to glean something from this thread, could you please explain why getting any outcomes at all is a problem?

It doesn't explain why you do. Technically it's why an improper mixed state is a proper one.
http://philsci-archive.pitt.edu/5439/1/Decoherence_Essay_arXiv_version.pdf

Thanks
Bill

 

[Derek Potter]

It doesn't explain why you do. Technically it's why an improper mixed state is a proper one.

I don't understand why we have to have a proper mixed state. What's wrong with an improper mixed state if it does the job of explaining the appearence of outcomes?

 

[atyy]

I don't understand why we have to have a proper mixed state. What's wrong with an improper mixed state if it does the job of explaining the appearence of outcomes?

I don't totally agree with bhobba's way of stating the measurement problem, but I think I understand it. What he means is that if we just have a unitarily evolving wave function, we clearly have no outcomes unless there are some additional assumptions. So the job of any interpretation that solves the measurement problem is to add assumptions that produce the outcome. For example, many worlds adds the assumption that blah, blah, blah ...

 

[Derek Potter]

QUOTE="atyy, post: 5163488, member: 123698"]I don't totally agree with bhobba's way of stating the measurement problem, but I think I understand it. What he means is that if we just have a unitarily evolving wave function, we clearly have no outcomes unless there are some additional assumptions. So the job of any interpretation that solves the measurement problem is to add assumptions that produce the outcome. For example, many worlds adds the assumption that blah, blah, blah ...[/QUOTE]

"Many worlds"? Never heard of it.

I'll put my question another way. Rather than asking how measurement creates a proper mixed state, shouldn't we ask whether it actually does so?

Why do we need outcomes at all? We know that measurements create the appearence of outcomes in the macro world, but the improper mixed state that bhobba referred to (and which does follow from unitary evolution) would, to my simple mind, solve this part of the measurement problem. I don't see the need to insist that the appearence of a mixture must be explained by the mixture being proper. In fact, in the last paper bhobba referred me to, Hensen makes it perfectly clear (section 1.2.3.) that they (case 2 and 3) are indistingishable at the level of observation since they yield the same probabilities. So I'm left asking what role is played by a proper mixed state that cannot be played by an improper one? If decoherence can provide an improper mixed state in which the observer apparently sees a particular outcome, why does this not solve the problem?

edit - Hensen's paper says that it superficially solves the outcome problem (bottom of page 39) but I don't understand the grudging "superficial". Nor the subsequent rejection of the ignorance interpretation.

 

[atyy]

I don't totally agree with bhobba's way of stating the measurement problem, but I think I understand it. What he means is that if we just have a unitarily evolving wave function, we clearly have no outcomes unless there are some additional assumptions. So the job of any interpretation that solves the measurement problem is to add assumptions that produce the outcome. For example, many worlds adds the assumption that blah, blah, blah ...

"Many worlds"? Never heard of it.

I'll put my question another way. Rather than asking how measurement creates a proper mixed state, shouldn't we ask whether it actually does so?

Why do we need outcomes at all? We know that measurements create the appearence of outcomes in the macro world, but the improper mixed state that bhobba referred to (and which does follow from unitary evolution) would, to my simple mind, solve this part of the measurement problem. I don't see the need to insist that the appearence of a mixture must be explained by the mixture being proper. In fact, in the last paper bhobba referred me to, Hensen makes it perfectly clear (section 1.2.3.) that they (case 2 and 3) are indistingishable at the level of observation since they yield the same probabilities. So I'm left asking what role is played by a proper mixed state that cannot be played by an improper one? If decoherence can provide an improper mixed state in which the observer apparently sees a particular outcome, why does this not solve the problem?

edit - Hensen's paper says that it superficially solves the outcome problem (bottom of page 39) but I don't understand the grudging "superficial". Nor the subsequent rejection of the ignorance interpretation.

Can I avoid answering the details by saying that I think I agree with your general point, and I am not totally in agreement with this way of stating the measurement problem as being only the problem of outcomes?

How would you state the measurement problem?

 

[Derek Potter]

:

Can I avoid answering the details by saying that I think I agree with your general point, and I am not totally in agreement with this way of stating the measurement problem as being only the problem of outcomes?
How would you state the measurement problem?

As Schlosshauer seems to feature highly here, I don't see the problem with using his general description:
The problem is, then, how to reconcile the vastness of the Hilbert space of possible states with the observation of a comparatively few “classical” macrosopic states, defined by having a small number of determinate and robust properties such as position and momentum. Why does the world appear classical to us, in spite of its supposed underlying quantum nature, which would, in principle, allow for arbitrary superpositions?
Key phrase here: "appear classical". I don't see the need to presuppose that it actually is classical.
Why do you ask?

 

[atyy]

: As Schlosshauer seems to feature highly here, I don't see the problem with using his general description:
The problem is, then, how to reconcile the vastness of the Hilbert space of possible states with the observation of a comparatively few “classical” macrosopic states, defined by having a small number of determinate and robust properties such as position and momentum. Why does the world appear classical to us, in spite of its supposed underlying quantum nature, which would, in principle, allow for arbitrary superpositions?
Key phrase here: "appear classical". I don't see the need to presuppose that it actually is classical.
Why do you ask?

I'm actually not fond of Schlosshauer's description. I prefer the classic how to have quantum mechanics without a fundamental status for observers. I asked because bhobba was just stating one of Schlosshauer's versions of the measurement problem, and since you were taking him to task about some detail of his version, I was wondering what yours is.

 

[Derek Potter]

I'm actually not fond of Schlosshauer's description. I prefer the classic how to have quantum mechanics without a fundamental status for observers. I asked because bhobba was just stating one of Schlosshauer's versions of the measurement problem, and since you were taking him to task about some detail of his version, I was wondering what yours is.

I don't actually see much of a difference between having QM without a fundamental status for observers and having QM with classical appearence, except that the latter would tolerate ad-hoc postulates, such as the special role of observations, and these need to be eliminated if the measurement problem is not to be trivialised. The implicit aim in both cases is to derive the projection/observer/probability postulate from the state/unitary/Hilbert postulate. Of course the former postulate may be phrased in different ways by different people so we need to make sure we are not trying to prove something that is not needed. Asserting actual collapse of a wavefunction would be overkill.

 

[VALENCIANA]

Well, we don't know where collapse of the wave function occurs. It could be at the detector, or on the more extreme side it could be consciousness. Or we may find we need to modify standard QM to allow for collapse e.g. by gravity.

By 'every object is a wave', I hope you don't mean wave in the classical sense.

 

[VALENCIANA]

What is the accepted interpretation of these two similar related issues:

1) When I am sleeping do my brain and body revert to un-collapsed wave state until and unless seen by a different observer?

2) I *never* have "seen" my brain - have the wave functions of the atoms and cells collapsed?

 

[VALENCIANA]

Do we we know what is exactly the wave function and the collapse (if there actually is a collapse) to differentiate between what happens when we are awake or asleep , or dreaming?
Is dreaming very different from reality?