Johan Noldus: A Unique Perspective on Quantum Gravity

[marcus]

Johan Noldus is an interesting "outsider" figure on the margins of QG.
This thread (if he happens to come across it) will give him a chance to make himself visible to us and to discuss his approach to QG---which he asserts to be radically different from that taken by the other efforts to put Quantum Mechanics together with Gen Rel. He indicates that he thinks several other approaches are doomed to fail or have already failed because they have gone about things the wrong way----his feels his way is more promising.

Noldus has only one paper that I can find about this. He has some other earlier papers from 2002-2004 about other stuff, that were published in the electronic journal CQG, but this paper where he presents his reverse QG idea has apparently not yet been accepted by CQG.

Here is the paper which I propose we discuss (if others are interested) in this thread.

http://arxiv.org/abs/gr-qc/0508104

Date (v1): Fri, 26 Aug 2005 12:46:01 GMT (16kb)
Date (revised v2): Mon, 5 Sep 2005 21:38:42 GMT (16kb)
Date (revised v3): Sat, 10 Sep 2005 09:33:54 GMT (16kb)
Date (revised v4): Mon, 10 Oct 2005 17:24:46 GMT (18kb)
Towards a fully consistent relativistic quantum mechanics and a change of perspective on quantum gravity
Johan Noldus
17 pages, no figures, entire subsection added. submitted to CQG

"This paper can be seen as an exercise in how to adapt quantum mechanics from a strict relativistic perspective while being respectful and critical towards the experimental achievements of the contemporary theory. The result is a fully observer independent relativistic quantum mechanics for N particle systems without tachyonic solutions. A remaining worry for the moment is Bell's theorem."

The title date on the paper is January 4, 2006 and there is no institutional affiliation. The author's email is the public "gmail". The acknowledgment paragraph has this:"...I am indebted to my old mentor Norbert Van den Bergh for continuous encouragement and his insistence upon a locally causal quantum mechanics."

So this is someone who used to be at the University of Ghent in Belgium---and might now have some institutional connection there or elsewhere, but does not indicate it.

From the arxiv record one gathers that Noldus has revised the paper several times and submitted it to CQG in October 2005. Noldus can be supposed to be in some suspense, waiting to see if the paper will pass peer review and will be accepted for publication. Or he can be imagined as very happy frolicking in the Ghent spring sunshine because he has he has heard from CQG that it will be published.

In any case this is an authentic QG outsider and I would be happy to hear from him if he wants to come out in the open and explain to us his radical reversed approach to QG.

 

[marcus]

Noldus abstract may sound to you somewhat modest and deferential, but my take on the paper is that it is quite ambitious.

I think the gist of it is that Noldus says Loop and allied QG are doomed to fail because they go about things in the wrong direction. They try to adapt Gen Rel to fit quantum mechanics.

He says that will not work and the right way is to adapt QM to fit Gen Rel.

Maybe he is not so unique as his words suggest, maybe others have had this idea and have tried it, and maybe he does not do what he claims to do. You will have to judge for yourself if the paper is superficial or not. But for the moment let's take the Noldus paper on its own terms.

On its own terms it sounds great. I like the idea that QM should be adapted to Gen Rel. It is even highly RESPECTABLE. In fact I remember that James Hartle just had a paper about modifying QM, if I remember, that seemed very well argued and plausible. Isnt this also a longtime concern of Gerard 't Hooft?

Anyway let us listen to the voice of Noldus a little now:

===exerpt===
...However, their unification is particularly troublesome because of the contradictory axioms they are constructed from. General relativity is a theory of spacetime, reality, objectivity, locality of interaction...while quantum theory is about space plus time, predicting outcomes of experiments, subjectivity, the instantaneous character of as well measurement and interaction.

There has been an immense effort during the last forty years in trying to force general relativity into quantum theory with very little success. In this paper, we boldly address the opposite task and reexamine quantum mechanics in a Bohmian spirit from a strict, diehard relativistic point of view and see how far it brings us...
====endquote=====

I think I will stop for the moment. BTW any comment so far? Any interest in Noldus paper?

 

[Careful]

**Noldus abstract may sound to you somewhat modest and deferential, but my take on the paper is that it is quite ambitious.
I think the gist of it is that Noldus says Loop and allied QG are doomed to fail because they go about things in the wrong direction. **

Hmm, I have read that paper, where does he say that or even gives that impression ? Can you give me the page?


**Maybe he is not so unique as his words suggest, maybe others have had this idea and have tried it, and maybe he does not do what he claims to do. **

Where does he claim this work is unique and to have finished the job or merely that his thoughts at that time were somehow of definite nature ? I do not remember that.

**Anyway let us listen to the voice of Noldus a little now:

===exerpt===
...However, their unification is particularly troublesome because of the contradictory axioms they are constructed from. General relativity is a theory of spacetime, reality, objectivity, locality of interaction...while quantum theory is about space plus time, predicting outcomes of experiments, subjectivity, the instantaneous character of as well measurement and interaction.

There has been an immense effort during the last forty years in trying to force general relativity into quantum theory with very little success. In this paper, we boldly address the opposite task and reexamine quantum mechanics in a Bohmian spirit from a strict, diehard relativistic point of view and see how far it brings us...
====endquote=====
**

Hem, can you conclude any of the presumptions you were mentioning from this piece of text ?

**
I think I will stop for the moment. BTW any comment so far? Any interest in Noldus paper? **

I told you that the concrete things in this paper were already tried out by other authors; moreover he speculates about very different possible ways to proceed. Therefore I concluded in my review that the author has simply thought about QM and wrote some paper about it.

Cheers,

Careful

 

[marcus]

Hello Careful,
have you met Noldus?
If you have talked with him then your interpretation of his work would carry considerable weight.

As for your comments here, I have no interest in arguing. Please feel free to interpret the message of the paper as well as you can, and say whatever you think about it. If you think my view is wrong then say something different. I'm not inclined to quarrel about such matters.

If you have met Noldus, please let us know your impressions. That could be fascinating.

 

[garrett]

OK, I looked at the paper for only five minutes, so my observation may be off base...

But really what I have is more of a question about approaches of this same type: Why do people try to recover multi-particle QM from their models as it was known in 1920, instead of trying to recover QFT with Fock space and quantized fields? To my knowledge, you can go from QFT to multi-particle QM via the Hartree-Fock approximation, but you can't go the other way around. QFT is more fundamental, so why don't people going for "classical" descriptions try to recover the structure of QFT?

I think I have seen some take a whack at it, but only very sketchy ideas.

 

[Careful]

OK, I looked at the paper for only five minutes, so my observation may be off base...

But really what I have is more of a question about approaches of this same type: Why do people try to recover multi-particle QM from their models as it was known in 1920, instead of trying to recover QFT with Fock space and quantized fields? To my knowledge, you can go from QFT to multi-particle QM via the Hartree-Fock approximation, but you can't go the other way around. QFT is more fundamental, so why don't people going for "classical" descriptions try to recover the structure of QFT?

I think I have seen some take a whack at it, but only very sketchy ideas.

I think the great difficulty is to dynamically incoorporate (spontaneous) particle creation and annihilation, no ? Here, one possible scenario would be to go over to fundamental stochastic theories (like SED) and to see how far the correspondence with QED goes (I think also Barut self field classifies here as an alternative). However, if you really want to go on the deterministic tour, then one has to start out at a much more elementary level. You first have to figure out how to recover the quantum harmonic oscillator (as was recently accomplished in the paper of Jizba, Kleinert et al in 't Hooft approach - at least for the quantum interpretation of the information loss condition), and how to explain the double slit experiment without a non-local collapse. It would be interesting to see how the latter could be done entirely realistically, that is by implementing the information loss condition in terms of distortion at the classical level. Still then, one has to figure out what particles are, which trajectories they are following (if any), how they scatter, change of type and so on... So, before you come to QFT, a lot of water needs to have ran to the sea...after all, the construction of QFT is going on since 1930 and still continuing.

't Hooft has written a nice paper about that in 2001, that is how a quantisation of the classical Maxwell field could be achieved by doing Fourier mode decomposition and drawing the analogon between a deterministic toy model and the quantum harmonic oscillator on one side, and a new kind of gauge invariance (which could be interpreted as information loss) on the *classical* oscillators on the other hand.

Cheers,

Careful

 

[Chronos]

I see a whole different issue here. I think it is generally true the usual approach is to attempt to reproduce GR at the macroscopic levels via QT. While that seems to be a logically consistent approach, GR includes a parameter that is essentially irrelevant in QT - time. It is difficult to see how time becomes emergent in this [QT] approach. It would be interesting to see how one might try to reverse engineer QT from GR.

 

[Careful]

I see a whole different issue here. I think it is generally true the usual approach is to attempt to reproduce GR at the macroscopic levels via QT. While that seems to be a logically consistent approach, GR includes a parameter that is essentially irrelevant in QT - time. It is difficult to see how time becomes emergent in this [QT] approach. It would be interesting to see how one might try to reverse engineer QT from GR.

You cannot reproduce QT from GR (while retaining realism) unless you give up entanglement, introduce backwards causation (arrow of time is ``effective´´) to recover it - or do something else radical. Even these scenario's are all somewhat unnatural (and lead to different *perfect* Bell type experiments): another option would simply be that rotational invariance (of the EPR source) is an effective property (and does not exist at short scales), or that special relativity (Poincare invariance) does not hold anymore at the same scales. I have argued several times in the direction that the measure stick as a dynamical variable is a somewhat problematic (and perhaps even ``unphysical´´) viewpoint, so why not look for a more natural scenario?

Cheers,

Careful

 

[marcus]

New Rovelli Smerlak paper touches on same issues as Noldus

http://arxiv.org/abs/quant-ph/0604064
Relational EPR
Matteo Smerlak, Carlo Rovelli
7 pages

"We argue that EPR-type correlations do not entail any form of "non-locality", when viewed in the context of a relational interpretation of quantum mechanics. The abandonment of strict Einstein realism advocated by this interpretation permits to reconcile quantum mechanics, completeness, (operationally defined) separability, and locality."

 

[marcus]

I should make clear that the Rovelli Smerlak position makes better sense to me than Noldus'. but that is merely my personal opinion and others may take a different view.

It would be nice if Noldus would appear in person at our forum to discuss his paper with us and it might be of benefit to him to get some open discussion

 

[Careful]

I should make clear that the Rovelli Smerlak position makes better sense to me than Noldus'. but that is merely my personal opinion and others may take a different view.

It would be nice if Noldus would appear in person at our forum to discuss his paper with us and it might be of benefit to him to get some open discussion

Ah well, this seems just to be Vanesch MWI in disguise; if you are convinced that a worldview which is full of subjective statements and copies thereof is superior to an objective viewpoint in which ``measurement has the same juice as physical processes´´ then that says everything about your urge for unification, no ?

Cheers,

Careful

 

[marcus]

I should make clear that the Rovelli Smerlak position makes better sense to me than Noldus'.

I have not said I am convinced by either. Noldus I find unclear and in need of explanation. Rovelli Smerlak is at least clear and addresses (solves after a fashion) problems that concern Noldus.

I am not taking a position. What needs to be done is to have Noldus contribution paraphrased and explicated so one can understand it better. What does not need to be done is to attack me personally or Vanesch or to belittle Rovelli's RQM (relational quantum mechanics). Probably no one is doing that: I hope not anyway-----it would not be a clever way to expound Noldus ideas.

 

[garrett]

Thanks for posting that reference marcus, I've always liked the Relational QM interpretation. Wave function "collapse" is just about a local observer obtaining new information. Or, in the many worlds interpretation, about an observer locally entering that world.

Careful: thanks for the Jizba/Kleinert ref -- I'll go have a look at their papers.

 

[Careful]

I have not said I am convinced by either. Noldus I find unclear and in need of explanation. Rovelli Smerlak is at least clear and addresses (solves after a fashion) problems that concern Noldus.

I am not taking a position. What needs to be done is to have Noldus contribution paraphrased and explicated so one can understand it better. What does not need to be done is to attack me personally or Vanesch or to belittle Rovelli's RQM (relational quantum mechanics). Probably no one is doing that: I hope not anyway-----it would not be a clever way to expound Noldus ideas.

Ohw, three comments:
(a) Noldus paper is by no means a definite statement (if you have read it that should be clear), he is simply putting some question marks around some conventional interpretations and indicating different possibilities. Now, if you say that what he suggests has been tried already partially, then I perfectly agree. SERIOUSLY rethinking QM is a very hard task marcus, and anyone who takes this heavy task upon himself is in for a long struggle (on 3 fronts : scepticism of society, him/her-self, the problem ) - with potentially little new outcome.
(b) Rovelli's relational interpretation is supreme subjectivism, does not solve the measurement problem, and is therefore way less ambitious and therefore much more clear (naturally).
(c) I am *never* attacking anyone personally, I simply want to discuss physics directly and in depth. True, I think LQG, spin foam and string theory won't succeed, but that is entirely irrelevant - what matters are some of the arguments I offer. Sure these are not airthight (nothing in physics is) - and I refrain from giving the technical ones - and it is up to the reader to decide what he/she thinks about it - and it is good we discuss about it. I think it would be good marcus, if you on the other hand, would not be so negative about critical people on the one hand and so accepting towards the latter approaches on the other. Recently, you wondered whether (i) 't Hooft approach is madness or necessary (you did not give a single comment upon the content of the paper - which is not so easy to understand actually), (ii) that the penrose lecture depressed you - since Roger of course thinks (like me) that we did not understand the crux of the problem yet (iii) in this thread you mention 't Hooft and Hartle QM in one line as other relativistic approaches to QM while these are antipodes of each other (btw. Sorkin is already for twenty years working on his preclusion approach to QM too) : 't Hooft is new and radical, while Hartle is the exponent of the quantum formalism (just as sorkin) (iv) the Peeters- Nicolai papers are entirely FAIR upon LQG and actually provide a very good introduction to the subject - remember: these people consulted Thiemann. On the other hand every LQG or alike paper is hailed like a triumph in many different threads - as well as any negative book/paper on string theory. I would FRIENDLY ask you to take a *slightly* more objective point of view unless you are prepared to have a hard discussion about the content. I appreciate your work in the sense that you believe deeply in something and put awesome work in screening the arxiv and web - I do not have time for it and it often happens that I read a paper you or someone else presents here which I would not have noticed otherwise (whatever my judgement about it is).

Cheers,

Careful

 

[selfAdjoint]

Rovelli's relational interpretation is supreme subjectivism, does not solve the measurement problem, and is therefore way less ambitious and therefore much more clear (naturally).

I don't think you have ever commented on the content of Paul Merriam's relational http://www.arxiv.org/abs/quant-ph/0506228" ,which derives from Rovelli and Smolin, I believe. It is aimed at going some specific way toward resolving the measurement problem.

 

[Careful]

I don't think you have ever commented on the content of Paul Merriam's relational http://www.arxiv.org/abs/quant-ph/0506228" ,which derives from Rovelli and Smolin, I believe. It is aimed at going some specific way toward resolving the measurement problem.

Why would I know of this (I have actually never heard of the author)? Has this been discussed somewhere already? Anyway, I shall take a look at it.

Cheers,

Careful

 

[selfAdjoint]

Thank you for looking at it Careful. I have been trying for a year now to get somebody who knows one end of QM from the other to do just that. Vannesch, hossi, everybody. I've posted here and on the quantum forum; It's like dropping a stone into a black hole.

If it's dumb out of the box. so be it, but at least LOOK.

 

[Careful]

Thank you for looking at it Careful. I have been trying for a year now to get somebody who knows one end of QM from the other to do just that. Vannesch, hossi, everybody. I've posted here and on the quantum forum; It's like dropping a stone into a black hole.

If it's dumb out of the box. so be it, but at least LOOK.

I will, but it seems not to be possible at first sight: in all these MWI stories you have to assign some consciousness functor or alike - that is you need to have a theory of experience (which is different from ``material´´ physics). (I shall continue the discussion on the Merriam paper here)

Anyway I got to page 6 and I do not understand certain issues. In the section entangled systems and decoherence, the author gives a quick and fairly accurate review of the problems of decoherence. In the next paragraph however (about intransitivity), I kind of get lost. The sentence : ``in fundamental theories of physics, physical reality ought to form an equivalence class´´ is kind of obscure. I assume that by physical reality of a system a with respect to a system b, the author means the possible pointer states of b which ``thermalize´´ with the states of the system a at times shorter than the recurrence time. For example: in the |up_z>, |down_z> basis for a spin 1/2 particle, the corresponding states are A_up, A_down ; of course A_neutral still occurs but has a neglegible amplitude (otherwise the theory would not be unitary) shortly after the interaction turned on and before the recurrence times - hence it is ignored in the description (here you already see that both descriptions are not equivalent since a quantum theory involving the measurement apparatus will predict that a minute fraction of the particles will go undetected). Anyway, assuming this to be the correct meaning, then I do not understand why this relation should be symmetric. In the entire reasoning it is assumed that the *dynamics* will drive the measurement apparatus in a state corresponding to the microscopic state of the system : this is an *asymmetric* assertion and not a symmetric one. So, it seem impossible to give a meaningful interpretation to the state of the environment relative to the spin 1/2 particle UNLESS you probe a different sector of the theory (that is you ask the question wheter the gradient of the magnetic field is in the up or down direction - which is different from asking if the the upper side of the plate or the down side of the plate behind the Stern Gerlach apparatus requires a nonzero momentum). Transitivity seems more plausible although you have to assume that if S is decribed relative to A and A is described relative to B that B cannot retrieve more information about S than A can (a kind of ``maximal information´´ principle).

Cheers,

Careful

 

[josh1]

I'm going to predict that john noldus and his paper will not be having much of an impact on the scientifically (though perhaps not according to philosophers, mystics and amateurs) dead subject of the foundations of quantum mechanics as it is applied to open systems. I think that Roland Omnes' construction of a logically consistent formulation of quantum mechanics based on decoherence and the experimental verification of this phenomenon pretty much ends this story.

The topic of closed systems, as discussed for example by people doing quantum cosmology is another matter.

 

[Careful]

** I think that Roland Omnes demonstration that a logically consistent formulation of quantum mechanics based on decoherence and the experimental verification of this phenomenon pretty much ends this story.
The topic of closed systems, as discussed for example by people doing quantum cosmology and/or lqg is another matter. **

First of all, decoherence does not solve the measurement problem and secondly it is a tautology that finding a solution for the latter problem is done in the light of closed systems. Third, research in the foundations of quantum mechanics is having a revival recently and fourth the fact that landscape papers get huge attention says a lot about impact factors.

 

[josh1]

...it is a tautology that finding a solution for the latter problem is done in the light of closed systems...

Just to ensure we're on the same page, decoherence explains how the interaction of open quantum systems with their environments can be understood without invoking the idea of a discontinuous collapse of a quantum superposition since this violates unitarity.

Closed systems on the other hand are by definition everything and therefore do not have an environment to interact with. Yet we observe no quantum interference effects in our universe - which is really the only genuinely closed system there is - that we'd expect if the cosmological wavefunction never collapsed. So the question is how do we account for the absence of such effects?

 

[Careful]

**Just to ensure we're on the same page, decoherence explains how the interaction of open quantum systems with their environments can be understood without invoking the idea of a discontinuous collapse of a quantum superposition since this violates unitarity.**

Sure, but you still need the born rule (in another form). That's all I said.

Cheers,

Careful

 

[selfAdjoint]

I will, but it seems not to be possible at first sight: in all these MWI stories you have to assign some consciousness functor or alike - that is you need to have a theory of experience (which is different from ``material´´ physics). (I shall continue the discussion on the Merriam paper here)

Anyway I got to page 6 and I do not understand certain issues. In the section entangled systems and decoherence, the author gives a quick and fairly accurate review of the problems of decoherence. In the next paragraph however (about intransitivity), I kind of get lost. The sentence : ``in fundamental theories of physics, physical reality ought to form an equivalence class´´ is kind of obscure. I assume that by physical reality of a system a with respect to a system b, the author means the possible pointer states of b which ``thermalize´´ with the states of the system a at times shorter than the recurrence time. For example: in the |up_z>, |down_z> basis for a spin 1/2 particle, the corresponding states are A_up, A_down ; of course A_neutral still occurs but has a neglegible amplitude (otherwise the theory would not be unitary) shortly after the interaction turned on and before the recurrence times - hence it is ignored in the description (here you already see that both descriptions are not equivalent since a quantum theory involving the measurement apparatus will predict that a minute fraction of the particles will go undetected). Anyway, assuming this to be the correct meaning, then I do not understand why this relation should be symmetric. In the entire reasoning it is assumed that the *dynamics* will drive the measurement apparatus in a state corresponding to the microscopic state of the system : this is an *asymmetric* assertion and not a symmetric one. So, it seem impossible to give a meaningful interpretation to the state of the environment relative to the spin 1/2 particle UNLESS you probe a different sector of the theory (that is you ask the question wheter the gradient of the magnetic field is in the up or down direction - which is different from asking if the the upper side of the plate or the down side of the plate behind the Stern Gerlach apparatus requires a nonzero momentum). Transitivity seems more plausible although you have to assume that if S is decribed relative to A and A is described relative to B that B cannot retrieve more information about S than A can (a kind of ``maximal information´´ principle).

Cheers,

Careful

I am somewhat at a loss to understand where you are coming from here.

Merriam explains in his footnote 5 (bottom of page 5 in the arxiv editon) that in spite of similar words, his and Rovelli's and Smolin' use of "relational" has nothing to do with Merrit's "relative" states or Zuek's "relative histories". This is not an MWI theory.

As to the discussion following his Heading Intransitivity, it is not involved with thermalizing or any of that; it's about the states of a system at two levels: the apparatus A observing the quantum system S, and the Environment E observing the combined system SA considered as states in the Hilbert spaces $$\mathfrac {H}_{SA}$$ and $$\mathfrac{H}_{ES}$$ and its relationship to the states of S observed by E, in the Hilbert space $$\mathfrac{H}_{ES}$$. He says it ought to be possible to "blow through" the states of AS observed by E to represent those of S as observed by E. But this is not possible unless "quantum observation" is a transitive relationship. This is not a symmetry but an algebraic relationship.

 

[Careful]

**I am somewhat at a loss to understand where you are coming from here.

Merriam explains in his footnote 5 (bottom of page 5 in the arxiv editon) that in spite of similar words, his and Rovelli's and Smolin' use of "relational" has nothing to do with Merrit's "relative" states or Zuek's "relative histories". This is not an MWI theory. **


SelfAdjoint, this is entirely irrelevant : fact remains that some form of the Born rule is still there. BTW: Merriam does not EXPLAIN this, he just STATES this.

**As to the discussion following his Heading Intransitivity, it is not involved with thermalizing or any of that; it's about the states of a system at two levels: the apparatus A observing the quantum system S, and the Environment E observing the combined system SA considered as states in the Hilbert spaces $$\mathfrac {H}_{SA}$$ and $$\mathfrac{H}_{ES}$$ and its relationship to the states of S observed by E, in the Hilbert space $$\mathfrac{H}_{ES}$$. **

Of course are the descriptions *themselves* associated with some ``thermalisation´´ procedure. How would a SG apparatus ``know´´ that an electron has spin up or spin down if it were not that either, the INTERACTION with the measurement apparatus causes it to fly upwards or downwards ??

Science, SelfAdjoint, is more than quoting papers and arguing upon the letter and not the content. If you do not agree with my assesement, present then a concrete meaningful example of an electron, an SG apparatus, and yourself.

Cheers,

Careful

 

[selfAdjoint]

Science, SelfAdjoint, is more than quoting papers and arguing upon the letter and not the content. If you do not agree with my assesement, present then a concrete meaningful example of an electron, an SG apparatus, and yourself.

Critiquing papers,careful, is more than misinterpreting them in the light of your own concerns.

 

[Careful]

Critiquing papers,careful, is more than misinterpreting them in the light of your own concerns.

I think my assesment of Rovelli's QM paper is correct (and actually also of Dreyer's and many other papers I have discussed). Do you have any idea SelfAdjoint, how arrogant it is to claim that a merely philosophical paper solves the measurement problem (which highly likely requires new physics) ? If you want to know what the measurement problem is about, then read Leggett, he is quite spicy about it. Moreover, neither Vanesch, nor Josh1, nor me were negative about the first paper, we just said it is a variation upon a known theme. That is a fair assesement, but it seems that you and Marcus are only satisfied when we say that everything you both mention is great. Great stuff is rarely produced and to recommend a paper is only done when you have at least read a good part of it and/or you know why the results are surprising. You might have noticed that I am entirely capabable to forget my bias when discussing with people who have a very different point of view on QM *provided* they are honest and/or try themselves something new (eg Larsson).

Cheers,

Careful

 

[Chronos]

. . . Do you have any idea . . . how arrogant it is to claim that a merely philosophical paper solves the measurement problem . . .

Interesting observation.

. . . t seems that you and Marcus are only satisfied when we say that everything you both mention is great.

That dog won't hunt.

You might have noticed that I am entirely capabable to forget my bias when discussing with people who have a very different point of view on QM *provided* they are honest and/or try themselves something new (eg Larsson).

Can't say I noticed.

 

[Careful]

Interesting observation.That dog won't hunt. Can't say I noticed.

Ah Chronos, the danger about philosophers in physics who actually cannot understand technical papers (and even have not some degree in the subject), is that they have the tendency to behave like high-priests in church. It becomes really problematic when the high priest knows a lot about politics and not so much about the subject itself - I always have been very clear that my classical bias is grounded in concerns about QG / the wish for a unified dynamics (solution of the cat) and associated to this some doubt about the realisation of perfect EPR experiments. But these are PHYSICAL issues and I am very honest in asserting that this is a very ambitious goal tried out by hundreds of people before. I kindly invite you to discuss a technical paper upon a *physics* subject at modern research level. Basically, discussions about *interpretations* of QM (which do not bring new physics) are useless and professional physicists rightfully distantiate themselves from these.

 

[vanesch]

Hi

I remember having read the paper SelfAdjoint proposed, and indeed, it fell "into a black hole"

I will, but it seems not to be possible at first sight: in all these MWI stories you have to assign some consciousness functor or alike - that is you need to have a theory of experience (which is different from ``material´´ physics). (I shall continue the discussion on the Merriam paper here)

I think indeed that there's no other way out, if we want to stick to the quantum formalism as we know it... and I learned to live with that.

As to your comments about that paper, I agree with much of what you say, and now remember having had about the same issues with it (hence the black hole).

Anyway I got to page 6 and I do not understand certain issues. In the section entangled systems and decoherence, the author gives a quick and fairly accurate review of the problems of decoherence. In the next paragraph however (about intransitivity), I kind of get lost. The sentence : ``in fundamental theories of physics, physical reality ought to form an equivalence class´´ is kind of obscure.

Me too. Didn't understand what it could mean, or why it should be true and the concerns you express here in more detail than I remember but go in the same direction:

I assume that by physical reality of a system a with respect to a system b, the author means the possible pointer states of b which ``thermalize´´ with the states of the system a at times shorter than the recurrence time. For example: in the |up_z>, |down_z> basis for a spin 1/2 particle, the corresponding states are A_up, A_down ; of course A_neutral still occurs but has a neglegible amplitude (otherwise the theory would not be unitary) shortly after the interaction turned on and before the recurrence times - hence it is ignored in the description (here you already see that both descriptions are not equivalent since a quantum theory involving the measurement apparatus will predict that a minute fraction of the particles will go undetected). Anyway, assuming this to be the correct meaning, then I do not understand why this relation should be symmetric. In the entire reasoning it is assumed that the *dynamics* will drive the measurement apparatus in a state corresponding to the microscopic state of the system : this is an *asymmetric* assertion and not a symmetric one. So, it seem impossible to give a meaningful interpretation to the state of the environment relative to the spin 1/2 particle UNLESS you probe a different sector of the theory (that is you ask the question wheter the gradient of the magnetic field is in the up or down direction - which is different from asking if the the upper side of the plate or the down side of the plate behind the Stern Gerlach apparatus requires a nonzero momentum). Transitivity seems more plausible although you have to assume that if S is decribed relative to A and A is described relative to B that B cannot retrieve more information about S than A can (a kind of ``maximal information´´ principle).