The Refutation of Bohmian Mechanics

[Demystifier]

Yes or no, please!

 

[A. Neumaier]

Yes or no, please!

You didn't take my yes, twice given, for a yes (to one version of your ambiguous question), so I don't know what to say to satisfy you.

 

[Demystifier]

You didn't take my yes, twice given, for a yes (to one version of your ambiguous question), so I don't know what to say to satisfy you.

THAT satisfies me. So yes, you DO necessarily agree with the position you take. On the other hand, a devil's advocate does NOT necessarily agree with the position he takes. Therefore, you are NOT a devil's advocate, period. No need to further argue about that.

 

[A. Neumaier]

THAT satisfies me. So yes, you DO necessarily agree with the position you take.

No. I voluntarily agree with the position I take, though I am free to do otherwise.
A devil's advocate is allowed to do what I do.

 

[pyrotix]

I've been reading a bunch of this debate. I'm not really able to understand all of the elements of the argument (engineering student with some QM), and excuse me if I'm way off base in saying this, but it seems that this in some ways this is a disagreement about philosophy. There is some give take and regarding whether bohmian mechanics is truly consistent within conventional QM insofar as it makes experimental predications; I'll admit that is entirely physics.

At the same time, Demystifier, you seem to suggest that Bohmian mechanics is good because it's deterministic. I.E. it avoids ideas as ontologically offensive as a cat that is both alive and dead at the same time.

A. Neumaier, you seem to suggest that because BM is hacked together based on aesthetic rather than experimental considerations, and doesn't possesses particularly great explanatory power (e.g. doesn't make the math easier) it's bad physics.

The funny thing is, even if the Bohmian mechanics is entirely identical with QFT from an observables POV, the question of whether bohmian mechanics is "right" or "wrong" seems to be about something more than its status as a formalism. It's kind of similar to the canonical problem of hard underdetermination-- we infer others are conscious like we are cause we seem them act like we do. At the same time there is no possible experiment devisable to test whether they are conscious and have experiences, or simply act like they are conscious. And despite the fact it is possible to discern by any method between whether others are conscious or not, the question appears to be meaningful. I.E. it is 'wrong' to believe that others don't have consciousness.

Ideally some testable incompatibility for BM is found and an experiment is done. Supposing however BM is compatible with QFT, whether it is "right" seems similar to the question of whether people are conscious. Arguing that Bohmian mech or conventional models are "right" is a question of whether one values determinism or mathematical parsimony.

Please pardon my sophomoric analysis if it is extremely off-base. Regardless of whether anyone agrees with anything I've said I think its worth noting how close the issues under argument stray to problems in philosophy of science.

 

[A. Neumaier]

A. Neumaier, you seem to suggest that because BM is hacked together based on aesthetic rather than experimental considerations,

Not at all. There is no aesthetics in BM. It is a hack without any beauty.

BM is an ugly theory that sacrifices all elegance in favor of a weird ontology with the only virtue that it allows its adherents to believe in some form of realism. (This statement is very different from what I had argued before on a scientific level, since it uses subjective value-laden terms like beauty, ugly, elegance, weird. But it is part of the reason why few subscribe to the Bohmian view.)

In contrast, I believe in a neatly designed universe describable by beautiful mathematics and having elegant foundations, possessing a high degree of realism but lacking the weirdness of both the Bohmian view and the traditional mainstream view.

See the entry ''Foundations independent of measurements'' in Chapter A4 of my theoretical physics FAQ at http://arnold-neumaier.at/physfaq/physics-faq.html#found0 and the discussion in the thread https://www.physicsforums.com/showthread.php?t=490492

 

[Demystifier]

At the same time, Demystifier, you seem to suggest that Bohmian mechanics is good because it's deterministic. I.E. it avoids ideas as ontologically offensive as a cat that is both alive and dead at the same time.

That's called realistic, not deterministic.

 

[Varon]

In Bohmian Mechanics. Position is preferred. Why position? Maybe in some other universe it's momentum or spin that is preferred?

To Neumaier. You are vague on the Bell's Theorem even on your web site. But do you believe non-local correlation is real or in your view, do loopholes explain the correlations? In Copenhagen, it is the measurement setting that is non-local. In Bohmian, it is the wave function that is omniscient. In your view Neumaier, what produced the correlations? Maybe with your superior mathematical ability. You can make algorithm that can make the correlations work artifically (without actual non-local correlations). Is this what you are saying?

 

[Misericorde]

Does anyone here really think that any given interpretation of QM accurately describes physics, or is this just wheel-spinning for its own sake? It really seems like a bunch of very smart people working like mad on stationary bicycles to me.

 

[Varon]

Does anyone here really think that any given interpretation of QM accurately describes physics, or is this just wheel-spinning for its own sake? It really seems like a bunch of very smart people working like mad on stationary bicycles to me.

The right intepretation would produce emergence. And this can give us a clue to unification with General Relativity and an insight into Quantum Gravity and the Theory of Everything.

 

[Misericorde]

The right intepretation would produce emergence. And this can give us a clue to unification with General Relativity and an insight into Quantum Gravity and the Theory of Everything.

I'm sorry, but I don't understand what emergence is in this context. In addition, it seems to me that an ontology is secondary to a working theory, which is why QM has been such a raving success despite its ontological shortcomings. Do people really expect that an interpretation of two successful, but flawed theories will lead to a new one, instead of new theories leading the way for ontological progress?

 

[Varon]

I'm sorry, but I don't understand what emergence is in this context. In addition, it seems to me that an ontology is secondary to a working theory, which is why QM has been such a raving success despite its ontological shortcomings. Do people really expect that an interpretation of two successful, but flawed theories will lead to a new one, instead of new theories leading the way for ontological progress?

See: https://www.physicsforums.com/showthread.php?t=499949

 

[Demystifier]

In Bohmian Mechanics. Position is preferred. Why position? Maybe in some other universe it's momentum or spin that is preferred?

It wouldn't work. The predictions of a Bohm-like theory with some other preferred variables would not be in agreement with those of standard QM. This is because the position variable is a "preferred" variable for decoherence, which, in turn, is a consequence of the fact that interactions between wave functions are local in the position space.

 

[Varon]

In the other thread I asked "Even if the initial condition is equal.. The quantum potential can push the particle while in mid flight.."

Demystifier (defendant of Bohmian Mechanics) answers:

"What you suggest here may be achieved with a time dependent quantum potential, provided that two particles are fired at different times. However, in a typical 2-slit experiment the quantum potential is usually time-independent to a great accuracy."

Demystifier. There is a time dependent and a time independent quantum potential? What's the difference? Anything to do with the time dependent and independent Schroedinger Equation?

Also how many variants (or version) of Bohmian mechanics are there? There are many variants in Copenhagen, Many Worlds, Objective Collapse and even Statistical Interpretations.

 

[Demystifier]

Demystifier. There is a time dependent and a time independent quantum potential? What's the difference? Anything to do with the time dependent and independent Schroedinger Equation?

Yes, the quantum potential is time-independent when the system can be described by a time-independent Schrodinger equation.

Also how many variants (or version) of Bohmian mechanics are there?

I don't know, I didn't count.
But the variations mainly refer to extensions to relativistic QM and quantum field theory. There are no many variations within nonrelativistic QM.

 

[Varon]

Dear Bohmians and Everettians,

What do you think of this article that says that Bohmian Mechanics is really Many Worlds in disguise?

http://193.189.74.53/~qubitor/people/david/structure/Documents/Research%20Papers/CommentOnLockwood.html

"It is also, by the way, a logical consequence of Bohm’s ‘pilot-wave’ theory[3]and its variants[4].Their proponents think of them as single-universe theories. The idea is that the ‘pilot wave’, i.e. the wave function of the multiverse, guides Bohm’s single universe along its trajectory. This trajectory occupies one of the ‘grooves’ in that immensely complicated multi-dimensional wave function. The question that pilot-wave theorists must therefore address, and over which they invariably equivocate, is what are the unoccupied grooves?It is no good saying that they are merely a theoretical construct and do not exist physically, for they continually jostle both each other and the‘occupied’ groove, affecting its trajectory. For example, we may in principle arrange for complex computations to be performed in vast numbers of‘unoccupied grooves’ (i.e. in parallel universes), and then observe the results directly. So the‘unoccupied grooves’ must be physically real. Moreover they obey the same laws of physics as the ‘occupied groove’ that is supposed tothat they be ‘the’ universe. But that is just another way of saying that they are universes too. (Cf. Lockwood’s discussion of the “mindless hulk” objection to any single-mind theory.) In short, pilot-wave theories are parallel-universes theories in a state of chronic denial."

 

[zenith8]

Dear Bohmians and Everettians,

What do you think of this article that says that Bohmian Mechanics is really Many Worlds in disguise?

It's the usual wishful-thinking crap. Just like all the other so-called 'refutations' of deBB on this thread.

Valentini has a nice article on precisely this point:

"http://arxiv.org/abs/0811.0810" "

I can recommend the search-engine "Google" as being quite useful for this sort of thing.

 

[Demystifier]

As I said many times, pure MWI with its minimal set of assumptions cannot explain the Born rule. Some additional assumptions must be taken. In my view, Bohmian mechanics is just one such set of assumptions. So in this sense - yes, Bohmian mechanics is MWI in denial. Or more precisely, Bohmian mechanics is the most intuitive (and perhaps most natural) completion of the MWI program.

 

[Misericorde]

I would have said that deBB is the wishful thinking; the last of the truly wishful thinking really. It certainly ends up being MWI in denial for all ontological purposes, it's just a beefier way of getting there. MWI being the ramifications of a non-local and non-realistic universe with everything QM has to offer in denial, I'd say it's a double cut against deBB. I realize MWI is as valid as any other interpretation, but it seems pretty clear that the science can only support SUAC (Shut Up And Calculate) right now; anything more is just metaphysical meandering.

 

[Demystifier]

I would have said that deBB is the wishful thinking; the last of the truly wishful thinking really.

Why last?

 

[Misericorde]

Why last?

Simple, the rest of the alternatives to QM have gone the way of the dinosaurs, leaving QM and its interpretations, and deBB, that's it.

 

[Demystifier]

I still don't get it. Are you saying that deBB is the only interpretation still alive?
Instead of using classy sentences, try to use clear and direct ones.

Or to quote Dirac:
"In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite."

 

[Misericorde]

I still don't get it. Are you saying that deBB is the only interpretation still alive?
Instead of using classy sentences, try to use clear and direct ones.

Or to quote Dirac:
"In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite."

I'm saying it's the last non-standard interpretation of QM left, with the rest being dead and gone thanks to the Bell Asatz. deBB, and this is just my opinion, is only alive because of its ability to tapdance around the real issues at hand, which I doubt will be a lasting state of affairs. Ist Klar?

 

[Varon]

As I said many times, pure MWI with its minimal set of assumptions cannot explain the Born rule. Some additional assumptions must be taken. In my view, Bohmian mechanics is just one such set of assumptions. So in this sense - yes, Bohmian mechanics is MWI in denial. Or more precisely, Bohmian mechanics is the most intuitive (and perhaps most natural) completion of the MWI program.

So you admit there is a possibility that it's both MWI and de Broglie/Bohmian mechanics that is correct? The plot thickens.

Anyway. Just treating de Broglie/Bohmian mechanics without MWI contamination. Why do you think is the Position observable preferred in Bohmian mechanics? Explain the justification for this ad hoc and biasness. Or is it possible that position is only temporary.. meaning by changing some parameter. One can make momentum the preferred basis in Bohmian mechanics turning a world where only momentum rule and positions don't exist (this scenerio is possible in other String Landscape Universe however but let's avoid this any string case right now and just focus on raw and pure Bohmian).

 

[Misericorde]

So you admit there is a possibility that it's both MWI and de Broglie/Bohmian mechanics that is correct? The plot thickens.

Anyway. Just treating de Broglie/Bohmian mechanics without MWI contamination. Why do you think is the Position observable preferred in Bohmian mechanics? Explain the justification for this ad hoc and biasness. Or is it possible that position is only temporary.. meaning by changing some parameter. One can make momentum the preferred basis in Bohmian mechanics turning a world where only momentum rule and positions don't exist (this scenerio is possible in other String Landscape Universe however but let's avoid this any string case right now and just focus on raw and pure Bohmian).

To further clarify, the issues you (Varon) raise are what I mean by deBB tapdancing around the issues that killed its contemporary non-standard theories.

 

[Varon]

To further clarify, the issues you (Varon) raise are what I mean by deBB tapdancing around the issues that killed its contemporary non-standard theories.

You love to use high class slang. But I don't know what "tapdancing" mean. Pls. use standard straight english. What are you saying?

 

[Dmitry67]

As I said many times, pure MWI with its minimal set of assumptions cannot explain the Born rule. Some additional assumptions must be taken. In my view, Bohmian mechanics is just one such set of assumptions. So in this sense - yes, Bohmian mechanics is MWI in denial. Or more precisely, Bohmian mechanics is the most intuitive (and perhaps most natural) completion of the MWI program.

Yes, both theories can be interpreted as examples of more general theory with N types of fundamental particles.

in MWI N=0
in dBB N=1
N>1 can be attacked based on Occam razor, but such generalisation is useful because it shows a fundamental problem with dBB (while MWI has problem with the Born rule): why my copies, mades of empty waves, are not conscious?

So dBB does not 'solve' the Born rule, it just replaces one problem (Born rule) with another (some axiom about existence). While we can hope that somehow the first problem will be solved (emerge on level of macroscopic objects or even on the level of consiousness), for dBB alternative there is no such hope - it is just an axiom.

 

[Varon]

Yes, both theories can be interpreted as examples of more general theory with N types of fundamental particles.

in MWI N=0
in dBB N=1
N>1 can be attacked based on Occam razor, but such generalisation is useful because it shows a fundamental problem with dBB (while MWI has problem with the Born rule): why my copies, mades of empty waves, are not conscious?

So dBB does not 'solve' the Born rule, it just replaces one problem (Born rule) with another (some axiom about existence). While we can hope that somehow the first problem will be solved (emerge on level of macroscopic objects or even on the level of consiousness), for dBB alternative there is no such hope - it is just an axiom.

Dmitry67, as a lone proponent of Many Worlds here. I think you must be familiar with Albert and Loewer and Lockwood's Many Minds Interpretation (variant of Many worlds) that attempt to solve the Born Rule as well as choosing of the preferred basis). What can you say about them? I've been studying their works since yesterday and my head spinning already. Do you believe what they are saying may be possible? (hope Bohmians and the don't care pragmatists can at least comment too... I initially wanted to make a separate thread for this but just include it here)

Quoting from Lockwood paper "'Many Minds' Interpretations of Quantum Mechanics"

"A many minds theory, as I understand it, is a theory which takes completely at face value the account which unitary quantum mechanics gives of the physical world and its evolution over time. In particular, it allows that, just as in special relativity there is a fundamental democracy of Lorentz frames, so in quantum mechanics there is a fundamental democracy of vector bases in Hilbert space. In short, it has no truck with the idea that the laws of physics prescribe an objectively preferred basis. For a many minds theorist, the appearance of there being a preferred basis, like the appearance of state vector reduction, is to be regarded as an illusion. And both illusions can be explained by appealing to a theory about the way in which conscious mentality relates to the physical world as untinary quantum mechanics describes it."

[skipping many paragraphs...]

"What Albert and Loewer actually suggest, of course, is that, associated with each living brain, there is a continuous infinity of minds, each independently evolving, according to the same stoachstic law. That we are dealing with a continuous infinity, here, is sufficient to ensure that each brain is not only certain to be inhabited, in every Everett branch, but certain to be inhabited by a continuous infinity of minds. Morever, there is no problem about understanding the quantum-mechanical probabilities, in the context of this theory. For these probabilities are put in by hand simply by stipulating that each mind obeys an irreducibly probabilities law of evolution, which mirrors the predictions of the quantum-mechanical statistical algorithm."

 

[Misericorde]

You love to use high class slang. But I don't know what "tapdancing" mean. Pls. use standard straight english. What are you saying?

High class slang, that's a new one on me, sorry if I've been confusing. Tap dancing is a kind of dance that involves a lot of fancy moves with the feet, so the metaphor is dodging around the major issues with words or small compromises.

To put it another way, instead of tapdancing, let me say: deBB has compromised again and again except in its central preference of position, to the point where it has only survived as a kind of weak MWI. I apologize for being confusing!

 

[Misericorde]

Yes, both theories can be interpreted as examples of more general theory with N types of fundamental particles.

in MWI N=0
in dBB N=1
N>1 can be attacked based on Occam razor, but such generalisation is useful because it shows a fundamental problem with dBB (while MWI has problem with the Born rule): why my copies, mades of empty waves, are not conscious?

So dBB does not 'solve' the Born rule, it just replaces one problem (Born rule) with another (some axiom about existence). While we can hope that somehow the first problem will be solved (emerge on level of macroscopic objects or even on the level of consiousness), for dBB alternative there is no such hope - it is just an axiom.

This is the exact means by which it has "tapdanced" Varon; it keeps adding to the problem without solving anything. Instead of wave-particle duality you have a pilot wave. Position is preferred, MWI is implied, and so on, and this is all on top of the formalism.

I'd say:

It's deBB that's 1, Formalism that's 0, and MWI is somewhere in between.

 

[Dmitry67]

Varon, I know there are some attempts to derive the Born rule in MWI, so far I think they are far from being final. In any case, I hope an appearence of the Born rule is emergent somehow on the macroscopic level or on conscious level.

I *almost* share Many Minds view: yes, no 'measurement devices' observe anything: they just transfer the decoherence. Photon is decoherenced with the photosensor, it transfers it to the hand of the voltmeter, photons transfer that information to our retina. All elements of that chain can be in superposition, and the only final and ultimate agent for the observation is our consciousness. Superposition ends not when it is measured (it just puts measurement device in a correlated superposition), it ends when we see it, when we feel it.

World is a very strange place, there is no preferred basis physically, but there are some special ones of the systems with qualia. However, to extract a system from the environment, we need a basis, so it is recursive. Ultimately, Born rule can be also an illusion, created by our consicousness, like the moment NOW.

However, I believe that consicousness can be physically studied (to some extent) so Many Minds should not have any additional assumtions - everything must be derived from pure MWI.

 

[Dmitry67]

Position is preferred

I had also attacked dBB based on that
Demystifier's response was, if I remember it correctly, that the opposite to knowing position exactly is knowing the momentum exactly. Then position is not localized at all. But in the Universe there are no global frames.

 

[Varon]

Varon, I know there are some attempts to derive the Born rule in MWI, so far I think they are far from being final. In any case, I hope an appearence of the Born rule is emergent somehow on the macroscopic level or on conscious level.

I *almost* share Many Minds view: yes, no 'measurement devices' observe anything: they just transfer the decoherence. Photon is decoherenced with the photosensor, it transfers it to the hand of the voltmeter, photons transfer that information to our retina. All elements of that chain can be in superposition, and the only final and ultimate agent for the observation is our consciousness. Superposition ends not when it is measured (it just puts measurement device in a correlated superposition), it ends when we see it, when we feel it.

World is a very strange place, there is no preferred basis physically, but there are some special ones of the systems with qualia. However, to extract a system from the environment, we need a basis, so it is recursive. Ultimately, Born rule can be also an illusion, created by our consicousness, like the moment NOW.

However, I believe that consicousness can be physically studied (to some extent) so Many Minds should not have any additional assumtions - everything must be derived from pure MWI.

What I can't understand in this Many Worlds is what if the observers are machines or video camera in a laboratory experiment system without humans. What would serve as Many Minds then? Or would it be invalid? What difference if humans observe them versus automated machines? Random choice? But we could design machine that can initiate random choice too. Pls. elaborate.

 

[Misericorde]

I had also attacked dBB based on that
Demystifier's response was, if I remember it correctly, that the opposite to knowing position exactly is knowing the momentum exactly. Then position is not localized at all. But in the Universe there are no global frames.

I agree with your view; I've never understood why deBB is taken as even remotely mainstream. Your point about MWI and Occam's Razor is enough for me frankly.

 

[Demystifier]

Why do you think is the Position observable preferred in Bohmian mechanics?

I have already answered it in post #188.