Copenhagen Interpretation of Sleep / Unseen brain?

[1977ub]

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?

 

[Strilanc]

Collapse is not caused by consciousness. All the experiments related to collapse have the same outcomes whether or not someone is in the room watching.

You don't become any more superposed while sleeping than you do while awake, or while dead for that matter.

 

[1977ub]

Collapse is not caused by consciousness. All the experiments related to collapse have the same outcomes whether or not someone is in the room watching.

You don't become any more superposed while sleeping than you do while awake, or while dead for that matter.

Is this the Copenhagen approach? Is there no "measurement problem" ?

Also: which interpretation of Wigner's friend is the most popular among experts?
https://en.wikipedia.org/wiki/Wigner's_friend

 

[mfb]

Is this the Copenhagen approach?

Yes.

Is there no "measurement problem" ?

There is, but this has nothing to do with consciousness. Everything that causes decoherence counts as observation - which includes basically everything in our everyday world that is at least as large as a molecule, on timescales of at least picoseconds.

Short naps seem to be a trend, but I did not see picosecond sleep discussed so far.

 

[1977ub]

Yes.
There is, but this has nothing to do with consciousness. Everything that causes decoherence counts as observation - which includes basically everything in our everyday world that is at least as large as a molecule, on timescales of at least picoseconds.

Short naps seem to be a trend, but I did not see picosecond sleep discussed so far.

So the standard Copenhagen is an "objective collapse theory" ?

 

[Truecrimson]

So the standard Copenhagen is an "objective collapse theory" ?

No. Decoherence causes apparent, subjective collapse. Decoherence occurs because of interactions of the object with an external environment and is not about the size or any property of the object itself per se.

 

[1977ub]

Every object is a wave, and when waves interact, they just make more waves. Where do the particles at particular positions come in? Is a direct "observation" required?

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

http://www.quora.com/Does-decoherence-solve-the-measurement-problem-in-quantum-theory

 

[StevieTNZ]

Every object is a wave, and when waves interact, they just make more waves. Where do the particles at particular positions come in? Is a direct "observation" required?

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

http://www.quora.com/Does-decoherence-solve-the-measurement-problem-in-quantum-theory

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.

 

[mfb]

Well, we don't know where collapse of the wave function occurs.

It is not a lack of knowledge, it is a matter of taste - different choices lead to different interpretations.

Neutrons bouncing above a surface follow QM with their states, I don't see much room for gravity having a special role.

 

[Truecrimson]

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

There is no correct answer as there are many interpretations, but there is an accepted interpretation of working physicists, which you asked for, that collapse is not caused by consciousness and apparent collapse is sufficient for all practical purposes.

 

[1977ub]

There is no correct answer as there are many interpretations, but there is an accepted interpretation of working physicists, which you asked for, that collapse is not caused by consciousness and apparent collapse is sufficient for all practical purposes.

Yes - so can you flesh that out a bit. When is my sleeping brain just a probability wave and when are its atoms in particular positions, and what causes the change? Are "measurements" going on while I sleep? BTW what is the name for this "accepted interpretation of working physicists" ?

 

[rootone]

When is my sleeping brain just a probability wave ... ?

I don't think there is any interpretation of QM which infers this.

 

[StevieTNZ]

Your brain has activity going on when you are asleep, I would think.

What superposition states do you think your brain will be in, while asleep?

 

[StevieTNZ]

BTW what is the name for this "accepted interpretation of working physicists" ?

I am guessing decoherence, but I could be wrong.

 

[Truecrimson]

BTW what is the name for this "accepted interpretation of working physicists" ?

"Shut up and calculate" perhaps. (Seriously! You can look it up.) Most physicists would just not care that the measurement problem is a problem. Maybe if you ask them why they will say something about decoherence, but that's about it.

If you know (non-relativistic) quantum mechanics, the position is sort of already there as one basis that the quantum state can be represented in, along with other basis like momentum. What happens in decoherence is that the system is entangled with the environment through some interaction, and when you ignore the state of the environment, the density operator of the system appears diagonal in some basis. For some interaction, this is the position basis, and the "quantum probability" to be in different positions "loses its coherence" and become classical probability. That is, the system has some definite position, whether you see it or not.

So the common answer is that there are so many interactions (with light, air etc.) going on with you body or your brain all the time that they are basically always classical i.e. decoherence has already occurred.

 

[StevieTNZ]

"Shut up and calculate" perhaps. (Seriously! You can look it up.) Most physicists would just not care that the measurement problem is a problem. Maybe if you ask them why they will say something about decoherence, but that's about it.

If you know (non-relativistic) quantum mechanics, the position is sort of already there as one basis that the quantum state can be represented in, along with other basis like momentum. What happens in decoherence is that the system is entangled with the environment through some interaction, and when you ignore the state of the environment, the density operator of the system appears diagonal in some basis. For some interaction, this is the position basis, and the "quantum probability" to be in different positions "loses its coherence" and become classical probability. That is, the system has some definite position, whether you see it or not.

So the common answer is that there are so many interactions (with light, air etc.) going on with you body or your brain all the time that they are basically always classical i.e. decoherence has already occurred.

That pretty much sums it up, but do remember the quantum system is not classical as only 'apparent collapse' has occurred. See pgs 208-210, 'Quantum Enigma' (2nd edition)

 

[1977ub]

"Shut up and calculate" perhaps. (Seriously! You can look it up.) Most physicists would just not care that the measurement problem is a problem. Maybe if you ask them why they will say something about decoherence, but that's about it.

If you know (non-relativistic) quantum mechanics, the position is sort of already there as one basis that the quantum state can be represented in, along with other basis like momentum. What happens in decoherence is that the system is entangled with the environment through some interaction, and when you ignore the state of the environment, the density operator of the system appears diagonal in some basis. For some interaction, this is the position basis, and the "quantum probability" to be in different positions "loses its coherence" and become classical probability. That is, the system has some definite position, whether you see it or not.

So the common answer is that there are so many interactions (with light, air etc.) going on with you body or your brain all the time that they are basically always classical i.e. decoherence has already occurred.

A probability wave of one particle in my brain interacts with another probability wave in my brain and that is sufficient to cause decoherence? (doesn't solve the measurement problem.)

 

[rootone]

Probability waves are not causally connected with the chemical state state of your brain. either awake or asleep.

 

[Truecrimson]

A probability wave of one particle in my brain interacts with another probability wave in my brain and that is sufficient to cause decoherence? (doesn't solve the measurement problem.)

Something like that. Take a look at http://arxiv.org/abs/quant-ph/9907009, which probably became the standard view about decoherence in the brain. I don't know if there's a better estimate by now.

 

[bhobba]

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.

There is also the question of if its a problem to begin with - nature may simply be like that.

BTW what is the name for this "accepted interpretation of working physicists" ?

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

 

[atyy]

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.

This is not universally agreed on. Whether Bohmian Mechanics can be extended to all relativistic quantum theories, and whether MWI makes sense are still generally considered open questions, eg. Wallace http://arxiv.org/abs/0712.0149.

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 thay simply accept we get outcomes without requiring further explanation.

However, some of the very best have indicated they consider the measurement problem to be a problem including Landau & Lifshitz, Dirac, Weinberg, Tsirelson, Bell, Adler. Even von Neumann can be said to have worked on it, by trying to figure out whether hidden variables were possible.

It's funny that I listed two of the co-discoverers of the chiral anomaly. Does Jackiw think the measurement problem is a problem? Jackiw's article with Shimony http://arxiv.org/abs/physics/0105046 describes the measurement problem (section 2.6), but mainly to report about Bell's views, so it seems unclear what Jackiw and Shimony's views are.

 

[bhobba]

This is not universally agreed on. Whether Bohmian Mechanics can be extended to all relativistic quantum theories, and whether MWI makes sense are still generally considered open questions, eg. Wallace http://arxiv.org/abs/0712.0149.

You know as well as I do we have many many different interpretations - not just BM or MW - and they each have a different take on the issue.

However, some of the very best have indicated they consider the measurement problem to be a problem including Landau & Lifshitz, Dirac, Weinberg, Tsirelson, Bell, Adler.

And some of the very best like Gell-Mann, Ballentine and Bohr beg to differ. I am pretty sure Bohr believed it didn't have a measurement problem - at least that's what he argued with Einstein. Gell-Mann believes decoherent histories resolves it by removing observations from the theory. You can't just give those that agree with your position. Even Einstein believed QM was a perfectly valid theory of ensembles. Most physicists simply accept it at that level and don't get worried about deeper issues like Einstein did.

Thanks
Bill

 

[Derek Potter]

they simply accept we get outcomes without requiring further explanation.

"Move on! Nothing to see here!"

 

[bhobba]

"Move on! Nothing to see here!"

No. It simply doesn't interest them. There is a difference.

As I said, even Einstein believed it was a full and complete theory of ensembles. If you don't want to go deeper than that then you don't have to.

Its like in EM there is runnaway acausal solutions to the Lorentz-Dirac equation:
http://arxiv.org/abs/gr-qc/9912045

You can view it as telling us something deep or simply reject them as unphysical. But most physicists, correctly, couldn't care less - it really makes no difference to what they do.

To the OP there are some rather simple interpretations of QM that don't have any logical consistency problems at all - they give a full and complete account of all quantum phenomena. If you are not interested in what it means, like say Einstein was, then that's all you need.

Thanks
Bill

 

[atyy]

You know as well as I do we have many many different interpretations - not just BM or MW - and they each have a different take on the issue.

No I am not aware of any which solves the measurement problem completely, with no technical issues. The major one I did not mention is Griffiths's decoherent histories, but that is certainly not widely agreed to be a solution of the measurement problem. Leifer https://mattleifer.wordpress.com/2007/03/26/teaching-quantum-theory/ and Laloe http://arxiv.org/abs/quant-ph/0209123 indicate problems with it.

And some of the very best like Gell-Mann, Ballentine and Bohr beg to differ. I am pretty sure Bohr believed it didn't have a measurement problem - at least that's what he argued with Einstein. Gell-Mann believes decoherent histories resolves it by removing observations from the theory. You can't just give those that agree with your position. Even Einstein believed QM was a perfectly valid theory of ensembles. Most physicists simply accept it at that level and don't get worried about deeper issues like Einstein did.

I am certainly not "giving only those that agree with my position". I was replying to your statement that most believe there is no problem, which stated without my balancing remark could give a misleading impression. Yes, as far as I can tell, Bohr and Heisenberg did not believe there was a measurement problem. If Gell-Mann believes decoherent histories resolves the measurement problem, then he does believe the problem exists (or existed) - otherwise what would there be no problem to "resolve". Also, Gell-Mann's version of decoherent histories is closer to the commonsense reality of MWI than Griffiths's version, eg. http://arxiv.org/abs/1106.0767.

 

[bhobba]

No I am not aware of any which solves the measurement problem completely, with no technical issues.

Ok - let's narrow it down to my interpretation - ignorance ensemble. It simply assumes an improper mixed state is a proper one. That solves it outright.

I think you are not quite grasping what explanation is. It may be unsatisfactory to you to simply, by fiat, say its a proper mixture - but that's what explanation is all about - the assumptions explain the consequences.

Most working physicists simply accept it and don't get caught up in if its unsatisfactory or not.

Thanks
Bill

 

[bhobba]

Also, Gell-Mann's version of decoherent histories is closer to the commonsense reality of MWI than Griffiths's version, eg.

I agree with you there. But again its irrelevant to this issue. The issue is if interpretations exist that are consistent ie explain all the phenomena. Its not if you find it unsatisfactory - that's got nothing to do with anything - its purely do the logical consequences of the assumptions explain the observations. That was the point of Einstein's comment. He most definitely thought QM was incomplete - but on its own terms has no issues.

Thanks
Bill

 

[atyy]

Ok - let's narrow it down to my interpretation - ignorance ensemble. It simply assumes an improper mixed state is a proper one. That solves it outright.

I think you are not quite grasping what explanation is. It may be unsatisfactory to you to simply, by fiat, say its a proper mixture - but that's what explanation is all about - the assumptions explain the consequences.

Most working physicists simply accept it and don't get caught up in if its unsatisfactory or not.

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.

 

[bhobba]

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.

The assumption is it can always be done. Its simply another assumption. It disproves nothing.

Thanks
Bill

 

[atyy]

The assumption is it can always be done. Its simply another assumption. It disproves nothing.

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.

 

[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.