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The Refutation of Bohmian Mechanics

by rogerl
Tags: bohmian, mechanics, refutation
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camboy
#73
Apr28-11, 03:28 AM
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Quote Quote by A. Neumaier
Bohmians are not aware of many things; they probably never tried to bring quantum computing into their focus. The observables used there do not include a position variable, hence the Bohmian trickery is inapplicable.
Quote Quote by akhmeteli View Post
If this is meant to be an argument, I fail to see how it is relevant. Maybe I just don't know enough about quantum computing though. However, I did not ask you for arguments, I asked about the status of your claim "no quantum computing in the Bohm interpretation." This is another strong claim, and I just tried to understand if that was common knowledge or just another personal theory of yours. If this is common knowledge, how about a reference? And if there is no peer-reviewed article supporting your claim, then your claim does not belong here. If this is your recent discovery, please publish it first and then discuss it here.
Quote Quote by A. Neumaier
If you don't agree, then please tell me how to do quantum computing in Bohmian mechanics..
Quote Quote by akhmeteli View Post
With all due respect, this is rich. You made a strong claim, and I just challenged you to support it with valid references. I am under no obligation to prove that your claim is wrong. Furthermore, I have no idea if it is indeed wrong or right.

It is wrong. I supplied him with an appropriate reference demonstrating how to do deBB quantum computing in #22 (and again in #27 after he ignored it).

Of course he immediately dismissed it, not because of a coherent 'personal theory' but because "[deBB] can be coerced into accomodating anything - in this case by introducing artificial pointer coordinates that don't exist in the standard description". This simply means "[deBB] is not like standard QM, and I - the great Neumaier - don't like it". It is not an intellectual argument.
A. Neumaier
#74
Apr28-11, 04:24 AM
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Quote Quote by Demystifier View Post

And I never before heard that the nerves in the eye move in response to light.
They don't, but the positions of the excited nerves determine the picture you will eventually see.
But in the Bohmian interpretationl, one interprets only changes in the pointer varibles as observables.. Thus the nerves won't serve as pointer variables to observe light.
A. Neumaier
#75
Apr28-11, 04:29 AM
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If the Boltzmann's H-therorem were any evidence for the universe being in global equilibrium then
e would observe this global equilibrium - which means we wouldn't exist, contradiction.[/QUOTE]
Irrespective of physics, this chain of reasoning is logically totally wrong.
Namely, if A is some evidence for B, it does not mean that A implies B.
For example, being in grave is an evidence for being dead, but you can still be in grave without being dead.[/QUOTE]
This means that you have very weak standards for what you regard as evidence for global thermal equilibrium and for quantum equilibrium. Your arguments deon't hold any water, as my example of the hill-climber showed.
Quote Quote by Demystifier View Post
Anyway, perhaps we are a statistical fluctuation?
No serious statistician rregards anything as a fluctuation that persists for so long.
A. Neumaier
#76
Apr28-11, 04:33 AM
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Quote Quote by Demystifier View Post
I'm not sure what kind of an answer do you expect here. Perhaps the straightest answer is: through the Schrodinger (or Schrodinger-Pauli, or Dirac, or Maxwell ...) equation and the associated equation for the particle trajectories - of the isolated system.
In standard QM, a spin system is given by N spins, basis states that tell which subset of spins is up (the complementary subset is down), their linear compinations as general statres, and a Hamiltonian that is an expression in the su(2) operators J^k_0, J^k_+ and J^k_-, one k for each spin. This determines the quantum dynamics via Schroedinger's equation i hbar psi(t)=H psi(t).

But it doesn't determine the Bohmian dynamics if there is no detector close by to give ontological meaning to the system.
A. Neumaier
#77
Apr28-11, 04:52 AM
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Quote Quote by camboy View Post
So, as you haven't corrected yourself at all, do I take it you don't accept that anything that you have said is wrong?
Indeed. I believe that my position regarding my paper is correct. Your arguments didn't convince me of a mistake.
Quote Quote by camboy View Post
If this is not the case, would you mind listing for me the things about which you have changed your opinion as a result of this thread?
For example, I had thought that Bohmian mechanics never considered quantum computing, and I learnt that it had. Though the presentation given was not enough to convinve me that BM accounts for qunatum computing - see the still pending dialogue.
Quote Quote by camboy View Post


As far as deBB is concerned, you appear to be entirely ignorant of everything that has been published since the 1990s,
It may appear s to you,, but it isn't the case.
Quote Quote by camboy View Post
You have made multiple statements on this thread which are demonstrably incorrect.
more precisely, which seem incorrect to you. I didn't buy your arguments.
In questions of interpretation, there is a lot of room for differing opinions on the same statement.
Quote Quote by camboy View Post
When told they are incorrect and you apparently have no further argument, you simply move onto another point without saying whether you agree with the correction or not.
The point of a conversation on PF is not to be proved right or wrong but to provide information for readers so that they can make up their own mind. I write to contribute further information, not to justify myself.
Quote Quote by camboy View Post
Anyone reading this thread and attempting to make sense of it needs to have that information if they are to draw a conclusion about who is right and who is wrong.
They shouldn't take anything on authority if there are conflicting opinions. They should study the arguments of both sides and form their own picture.
Quote Quote by camboy View Post
looking at your public web page, you can hardly blame me for my assumption. So you're a professor of mathematics who has the foundations of quantum mechanics as one of his main research interests.
If you look at my list of research interests http://www.mat.univie.ac.at/~neum/#research , you'll find that quantum mechnaics is a minor part of my research interests. About 4% of my piblications are about quantum mechanics.
Quote Quote by camboy View Post
My original point therefore stands that - as a respectable professor at a major university - you have a responsibility not to make sweeping incorrect statements damning entire fields in public forums, since people will believe you merely because of who you are.
I don't make sweeping incorrect statements damning entire fields. Saying that Bohmian mechnaics contradicts quantum mechnaics doesn't damn the field. Classical mechnaics also contradicts QM, but nobody thinks that this implies that whoever does rersearch in classical mechanics is an idiot. Far from this!!!
Quote Quote by camboy View Post
Then what on earth did you mean by statements such as "The worst thing about Bohmian mechanics is their low standards of quality", "Bohmians are not aware of many things", "Bohmian trickery is inapplicable" and all the rest. Are these supposed to be compliments?
The first means, for example, that they take things such as the establishment of quantum equilibrium for the universe to be proven although they have extremely little ''evidence'' for it. The second is a truism that holds for everyone, and must be read in context. The third is a statement asserttin that the machinery of Bohmian mechanics is not applicable. Calling it trickery is clearly a subjective statement implying that BM gives an appearance of reality to QM of the same kind as a juggler makes things appear real without being so. This is a nonrefutable statement since BM say often that the motion of the quantum particles is not observable. Thus considering it as trickery is legitimate.
A. Neumaier
#78
Apr28-11, 05:06 AM
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Quote Quote by akhmeteli View Post
First, you may have noticed an emoticon by my "claim", second, strictly speaking, depending on peer reviews, truth either belongs here or not (so it is indeed "dependent" in this respect on peer reviews). With all due respect, your "truth" of post 7 does not belong here.
If you think giving a reference to an unpublished arXiv paper without discussing it is a serious sin against the rules, you should report it to the PF management, quoting the present post for context.
Quote Quote by akhmeteli View Post
I am sure mentors here value your input, as I do, and would give you some slack, as I would do, if I were in their shoes, but you should not abuse our respect.
I fully respect the rules as I understand them.
Quote Quote by akhmeteli View Post
And again, if indeed the Bohm interpretation is a lost cause, so be it, but I specifically objected to your claim
But I cannot discuss my claim further because of the PF rules. So your objection standas like my assertion, and readers must make up their own mind.
Quote Quote by akhmeteli View Post
I asked about the status of your claim "no quantum computing in the Bohm interpretation." This is another strong claim, and I just tried to understand if that was common knowledge or just another personal theory of yours.
First, I qualified my statement with ''probably'' since I wasn't sure, and indeed, there was a very recent (2010) thesis that tackled it, as was pointed out by others. I immediately acknowledged the article, studied it, and found that it didn't treat spin systems by themselves but only spin systems coupled to an external pointer variable, thus justifying my remark ''The observables used there do not include a position variable, hence the Bohmian trickery is inapplicable.''. However, I learnt that the author invented (or got from somewhere else) a new Bohmian trick - namely that one silently changes the system under study to a bigger one, in order to give it the appearance of fitting into the BM philosophy. This lead to a still ongoing discussion.
Quote Quote by akhmeteli View Post
if there is no peer-reviewed article supporting your claim, then your claim does not belong here.
If everyone were banned who made more than 10 claims that do not appear in a peer-reviewed article, PF would be nearly empty.
Demystifier
#79
Apr28-11, 06:08 AM
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Quote Quote by A. Neumaier View Post
But in the Bohmian interpretationl, one interprets only changes in the pointer varibles as observables.
No, that's not true. I never said that.
Demystifier
#80
Apr28-11, 06:20 AM
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Quote Quote by A. Neumaier View Post
In standard QM, a spin system is given by N spins, basis states that tell which subset of spins is up (the complementary subset is down), their linear compinations as general statres, and a Hamiltonian that is an expression in the su(2) operators J^k_0, J^k_+ and J^k_-, one k for each spin. This determines the quantum dynamics via Schroedinger's equation i hbar psi(t)=H psi(t).
That's correct.

Quote Quote by A. Neumaier View Post
But it doesn't determine the Bohmian dynamics if there is no detector close by to give ontological meaning to the system.
You are wrong. Bohmian dynamics is well defined and gives an ontology even without detectors. But in that case, the statistical predictions may differ from those of ordinary QM. Yet, there is no conflict with experiments because these deviations from ordinary QM cannot be detected (because there are no detectors).

What is true in that case is that there is no any meaningful SPIN ontology. Still, there is some ontology in terms of a wave function and particle positions.

Let me repeat the analogy with classical optics. Colors do not exist, except for the observers. Yet, light waves exist irrespective of the observers.
Similarly, in BM spins do not exist, except for the observers. Yet, wave functions and particle positions exist irrespective of the observers.
Demystifier
#81
Apr28-11, 06:34 AM
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Quote Quote by A. Neumaier View Post
BM say often that the motion of the quantum particles is not observable.
That is an incorrect interpretation of BM. Just the opposite, the motion of the quantum particle is the only observable thing in BM. However, in order to observe it in practice, one must couple it with a macroscopic apparatus containing a large number of the degrees of freedom. Such a large number of degrees of freedom cannot be controlled on a fine level, which means that one cannot know the exact position-dependent phases of the wave functions involved. Without knowing the phases, one cannot predict the exact particle trajectories either. Therefore, one cannot experimentally confirm (or refute) that the measured trajectories coincide with those predicted by the theory.
A. Neumaier
#82
Apr28-11, 06:57 AM
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Quote Quote by Demystifier View Post
No, that's not true. I never said that.
You just repeated it:
Quote Quote by Demystifier View Post
the motion of the quantum particle is the only observable thing in BM.
A. Neumaier
#83
Apr28-11, 06:59 AM
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Quote Quote by Demystifier View Post
Bohmian dynamics is well defined and gives an ontology even without detectors. But in that case, the statistical predictions may differ from those of ordinary QM. Yet, there is no conflict with experiments because these deviations from ordinary QM cannot be detected (because there are no detectors).
Then please give me the dynamics of the unobserved spin system that I described in terms of standard QM in terms of BM.
A. Neumaier
#84
Apr28-11, 07:03 AM
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Quote Quote by Demystifier View Post
That is an incorrect interpretation of BM. Just the opposite, the motion of the quantum particle is the only observable thing in BM. However, in order to observe it in practice, one must couple it with a macroscopic apparatus containing a large number of the degrees of freedom. Such a large number of degrees of freedom cannot be controlled on a fine level, which means that one cannot know the exact position-dependent phases of the wave functions involved. Without knowing the phases, one cannot predict the exact particle trajectories either. Therefore, one cannot experimentally confirm (or refute) that the measured trajectories coincide with those predicted by the theory.
But this means (by any meaningful interpretation of the term ''observe'') that one cannot observe the particle position but only the pointer position of the macroscopic apparatus.
Demystifier
#85
Apr28-11, 07:10 AM
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Quote Quote by A. Neumaier View Post
But this means (by any meaningful interpretation of the term ''observe'') that one cannot observe the particle position but only the pointer position of the macroscopic apparatus.
Yes, but this macroscopic apparatus also consists of particles. So one does measure the particle positions, but of the apparatus. Not because the apparatus is fundamentally different, but simply because it is bigger.
Demystifier
#86
Apr28-11, 07:13 AM
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Quote Quote by A. Neumaier View Post
Then please give me the dynamics of the unobserved spin system that I described in terms of standard QM in terms of BM.
That's simple. Standard QM describes it in terms of a wave function for n particles. BM takes the same wave function and says additionally that there are n particles the velocities of which are calculated from this wave function (the exact equation is not important here).
A. Neumaier
#87
Apr28-11, 07:15 AM
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Quote Quote by Demystifier View Post
Yes, but this macroscopic apparatus also consists of particles. So one does measure the particle positions, but of the apparatus. Not because the apparatus is fundamentally different, but simply because it is bigger.
One measures a single mean position of the pointer, not the positions of any of the pointer particles.

But this brings me back to my question about the nerves: Where in the nerves is the measured particle whose position indicates whether or not I see a star, and which color it has?
Demystifier
#88
Apr28-11, 07:18 AM
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"No, that's not true. I never said that."

"the motion of the quantum particle is the only observable thing in BM."

OK, I admit, I was not sufficiently precise in the last sentence in quotation marks. By "motion" I meant "particle position as a function of time". Clearly, a particle at rest also has a position as a function of time. OK?
A. Neumaier
#89
Apr28-11, 07:19 AM
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Quote Quote by Demystifier View Post
That's simple. Standard QM describes it in terms of a wave function for n particles. BM takes the same wave function and says additionally that there are n particles the velocities of which are calculated from this wave function (the exact equation is not important here).
But in the standard QM picture, the wave function of a spin system (e.g. the Ising ferromagnet) has no position or momentum variables, and hence also no velocities associated with it. Given my specific description of the spin system, what is the BM dynamics? Please be as specific in your formal description, rather than using vague words that leave many things unsaid.
A. Neumaier
#90
Apr28-11, 07:21 AM
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Quote Quote by Demystifier View Post
"No, that's not true. I never said that."

"the motion of the quantum particle is the only observable thing in BM."

OK, I admit, I was not sufficiently precise in the last sentence in quotation marks. By "motion" I meant "particle position as a function of time". Clearly, a particle at rest also has a position as a function of time. OK?
OK. But measuring the particle at rest always gives the same measurement result. Thus the positions of the nonmoving nerves in the eye can hardly be used to tell the difference between seeing and not seeing a star.


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