Copenhagen Interpretation of Sleep / Unseen brain?

[1977ub]

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.

There is also the question of if its a problem to begin with - nature may simply be like that.
Its called believing its not an issue to begin with. Mostly it worries philosophy types and those that work on the foundations of QM which is not what the vast majority of physicists do. Since deoherence has morphed the issue, they simply accept we get outcomes without requiring further explanation.

Thanks
Bill

So if asked about my sleeping brain, they will say this question never comes up in their work.

 

[bhobba]

So if asked about my sleeping brain, they will say this question never comes up in their work.

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

 

[ShayanJ]

At the very least, you still the problem of factorization into environment and system, which is one way in which there is the reappearance of the problem that Copenhagen has of needing an observer to place the classical/quantum cut.

Could someone explain how the need for such a factorization arises in the ensemble interpretation?

 

[bhobba]

But different experimenters place the cut at different places, so one has to either show that where the cut is placed does not matter, or that the other experimenters are not real.

All one has to assume is it can be placed somewhere. We are not talking about niceties here - we are talking about if its actually consistent. We assume a division can be made that gives standard QM.

Thanks
Bill

 

[atyy]

All one has to assume is it can be placed somewhere. We are not talking about niceties here - we are talking about if its actually consistent. We assume a division can be made that gives standard QM.

Won't you just end up with standard Copenhagen with the cut of a particular observer?

 

[bhobba]

Could someone explain how the need for such a factorization arises in the ensemble interpretation?

It doesnt.

I however chose the ignorance ensemble as an example purely because it popped into my head first. There is a tacit assumption in decoherence type interpretations that a factorisation can be found that gives standard QM predictions. Its pretty obvious it can in any situation - but it is an assumption.

Thanks
Bill

 

[bhobba]

Won't you just end up with standard Copenhagen with the cut of a particular observer?

It's different to Copenhagen, first in its use of decoherence, and secondly in its interpretation of probability.

Thanks
Bill

 

[ShayanJ]

It doesnt.

I however chose the ignorance ensemble as an example purely because it popped into my head first. There is a tacit assumption in decoherence type interpretations that a factorisation can be found that gives standard QM predictions. Its pretty obvious it can - but it is an assumption.

Thanks
Bill

I'm confused.
Your discussion with atyy is about this factorization and now you say there is no need for this factorization.
Another thing that confuses me is that you say there is no need for this factorization but then you go on to explain about an assumption about this factorization.
Also I don't understand what you mean by "decoherence type interpretation". Decoherence, as I understand it, is a part of QM formalism not of its interpretations. And I googled for it but there was only one result which was a thread here in PF where it was only mentioned with no explanation.

 

[bhobba]

Your discussion with atyy is about this factorization and now you say there is no need for this factorization.

Pull back a bit.

My discussion is if some simple interpretations exist whose logical consequences explain QM phenomena.

There are tons that do. Ensemble is one, Baysian is another, Decoherent Histories is another - I am sure you can think of others. To pin the issue down I simply chose ignorance ensemble. Because that interpretation uses decohohence then the factorisation problem becomes an issue ie you can always break a system into system being observed, what is doing the observation and/or environment. Some people claim that doesn't explain anything because the answer you get depends on that factorisation. It however is not an issue for the validity of the interpretation.

The Ensemble interpretation doesn't have that problem. It assumes QM is about system preparation and observations on the prepared system so the factorisation problem is not an issue. See figure one in the following:
http://arxiv.org/pdf/quant-ph/0101012.pdf

Thanks
Bill

 

[atyy]

It's different to Copenhagen, first in its use of decoherence, and secondly in its interpretation of probability.

Well, Copenhagen has decoherence too and it allows frequentist probability. It seems the difference is that in Copenhagen, the cut is subjective, ie. observer dependent. To remove the observer, it seems that you need an objective cut. So in your interpretation, there is simply an objective cut or factorization? In a way, you have objective collapse, so I don't see why you escape the problems of objective collapse theories like GRW or CSL.

 

[bhobba]

Well, Copenhagen has decoherence too and it allows frequentist probability. It seems the difference is that in Copenhagen, the cut is subjective, ie. observer dependent. To remove the observer, it seems that you need an objective cut. So in your interpretation, there is simply an objective cut or factorization? In a way, you have objective collapse, so I don't see why you escape the problems of objective collapse theories like GRW or CSL.

Any interpretation of QM has dechorence. Copenhagen however does not make explicit use of it. Ignorance ensemble does. Because it does you are making the tacit assumption what you are analysing can be factored into parts so decoherence works. For example a dust particle is decohered into a specific position by a few stray photons from the CBMR. But if you use a different factorisation do you get the same answer? Or no factorisation at all? Its not a problem because the assumption is you can always find one that gives standard QM.

Thanks
Bill

 

[atyy]

Any interpretation of QM has dechorence. Copenhagen however does not make explicit use of it. Ignorance ensemble does. Because it does you are making the tacit assumption what you are analysing can be factored into parts so decoherence works. For example a dust particle is decohered into a specific position by a few stray photons from the CBMR. But if you use a different factorisation do you get the same answer? Or no factorisation at all? Its not a problem because the assumption is you can always find one that gives standard QM.

Just to be clear, one postulates an objective factorization (F), and since decoherence is not perfect, one also postulates an objective criterion for how close to perfect decoherence the system comes before collapsing (let's call this criterion T)? Since only perfect decoherence defines a unique preferred basis, then the postulated objective criterion will also contain a postulated objective preferred basis (P)?

 

[Derek Potter]

Any interpretation of QM has dechorence. Copenhagen however does not make explicit use of it. Ignorance ensemble does. Because it does you are making the tacit assumption what you are analysing can be factored into parts so decoherence works. For example a dust particle is decohered into a specific position by a few stray photons from the CBMR. But if you use a different factorisation do you get the same answer?

Absolutely not. The very same photons decohere the particle into a unlocated momentum state. Why does standard QM assume that dust is located?

 

[bhobba]

Just to be clear, one postulates an objective factorization (F), and since decoherence is not perfect, one also postulates an objective criterion for how close to perfect decoherence the system comes before collapsing (let's call this criterion T)? Since only perfect decoherence defines a unique preferred basis, then the postulated objective criterion will also contain a postulated objective preferred basis (P)?

Yes to factorisation and a specified level below which its considered no interference occurs. But it is generally thought to explain the preferred basis problem.

Thanks
Bill

 

[bhobba]

Absolutely not. The very same photons decohere the particle into a unlocated momentum state. Why does standard QM assume that dust is located?

That's incorrect.

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?

Thanks
Bill

 

[atyy]

Yes to factorisation and a specified level below which its considered no interference occurs. But it is generally thought to explain the preferred basis problem.

But can it really explain the preferred basis problem? The reason I am not sure is that only with perfect decoherence is the preferred basis uniquely specified, so if one specifies a criterion below which it is considered no interference occurs, one is essentially saying if I have the preferred basis, then I specify a criterion (T) below which I can set the off-diagonal terms in the matrix to zero. However, this seems to assume the existence of the preferred basis before already in order to specify the criterion (T).

 

[bhobba]

But can it really explain the preferred basis problem?

Its standard textbook stuff eg see 2.16 of Schlosshauer - Decocherence and The Quantum To Classical Transition.

The measurement problem has three parts

1. The preferred basis problem.
2. The problem of why its so hard to observe interefece
3. The problem of outcomes ie why do we get any outcomes at all.

As Schlosshauer says - page 113 - 'Its reasonable to conclude decoherence is capable of solving the first two problems, whereas the third is inherently linked to matters of interpretation'.

That's the exact basis of my claim decoherence has morphed the measurement problem to why we get any outcomes at all. Ignorance ensemble simply assumes it does - somehow.

Thanks
Bill

 

[atyy]

Its standard textbook stuff eg see 2.16 of Schlosshauer - Decocherence and The Quantum To Classical Transition.

The measurement problem has three parts

1. The preferred basis problem.
2. The problem of why its so hard to observe interefece
3. The problem of outcomes ie why do we get any outcomes at all.

As Schlosshauer says - page 113 - 'Its reasonable to conclude decoherence is capable of solving the first to problems, whereas the third is inherently linked to matters of interpretation'.

That's the exact basis of my claim decoherence has morphed the measurement problem to why we get any outcomes at all. Ignorance ensemble simply assumes it does - somehow.

Thanks
Bill

As I understand, one has to postulate (F), (T) and (P), but the sense is that one could imagine a postulate (P) which reproduces QM. One doesn't get the preferred basis for free when there is imperfect decoherence. For example, one proposal for (P) in the case of imperfect decoherence is the predictability sieve. Which criterion do you use?

 

[bhobba]

As I understand, one has to postulate (F), (T) and (P),

You mentioned T but can you detail what you mean by F and P?

Regarding T we don't have to specify a level below which off diagonal elements are considered zero - we simply need to assume such exists.

But this is getting way off topic. The issue here isn't exactly what assumptions any particular interpretation requires - the issue is such exist.

Thanks
Bill

 

[atyy]

You mentioned T but can you detail what you mean by F and P?

But this is getting way off topic. The issue here isn't exactly what assumptions any particular interpretation requires - the issue is such exist.

F is the postulate of factorization
T is the postulate that when the diagonal terms of the density matrix are small enough in a certain basis, they can be set to zero
P is the postulate of the basis used to define T

I used F for factorization, P for preferred basis, T for time of collapse.

Well, the reason I am asking about these is that this is the one example you use to show that there is at least one solution to the measurement problem for all quantum mechanics with no technical problems. Since it is certainly not a textbook interpretation, I'm trying to make sure I understand it.

 

[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