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The Refutation of Bohmian Mechanics

by rogerl
Tags: bohmian, mechanics, refutation
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Dmitry67
#217
May31-11, 04:23 AM
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Quote Quote by Demystifier View Post
No, you are just not specific enough.
I don't claim it is true, I am just showing a range of theories MWI/QM can be 'compatible' with.

P.S
I have a question for you about dBB. I remember once there was a discussion about Bell/EPR and no-conspiracy assumption. You replied that you don't see an exact difference between superdeterminism and no-conspiracy. I was thinking about it, I believe I can tell what the difference is.

Conspiracy is some set of boundary conditions, defined at Universe time t>0. Such boundary conditions can be very simple (that area is void at that time) or complicated so you have to write a complicated function to evaluate if it is true (whenever EPR experiment is performed, the results should yeild the specific condition...). Details are not important, the only important thing is that the boundary condition is defined for regions of spacetime at t>0.

Another word for Conspiracy is Destiny.

Q: Do you believe that in dBB there are no boundary conditions defined at Universe time t>0? So do you claim that ALL boundary conditions of dBB are defined strictly at t=0? (Big bang?)
Demystifier
#218
May31-11, 04:59 AM
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Your questions require a careful answer:
I believe in nonrelativistic BM all initial conditions are specified at the same time t, but not necessarily at t=0. And I don't see any conspiracy in it.
Ilja
#219
Jul30-12, 06:47 AM
P: 301
My main objection against MWI is that it needs, in fact, some additional structure: It clearly needs some subdivision of the universe into subsystems. But there is nothing in the universe which could be used as a natural candidate. The subsystems we observe in everyday life, and which are also widely used in examples and discussions, like, in particular, minds, clearly do not have the fundamental character which would be necessary - they exist only in states of the universe which are extremely close to our actual state. What is my state in a universe where the Earth does not even exist? A nonsensical question.

But this vague subdivision into subsystems is an additional structure which is not necessary in dBB. It also needs additional structure, but of a different type, the one into configuration and momentum. That's a subdivision which is fundamental already in classical mechanics. It shows up in the equations: H=p^2/2m + V(q), quadratic in momentum but not in the configuration variables, a property which survives even for some relativistic fields, and there is no known system where such a subdivision would be problematic.
mfb
#220
Jul30-12, 12:50 PM
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The subdivision occurs naturally as evolution of the wave function. This is called decoherence.
If you just take a wave function and unitary evolution, you directly arrive at MWI. You get the branching structure in all (relevant) chaotic systems. If you do not "want" those branches, you have to add a structure - collapses (e.g. Copenhagen), particles (dBB) or something else.
Ilja
#221
Jul30-12, 03:11 PM
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Quote Quote by mfb View Post
The subdivision occurs naturally as evolution of the wave function. This is called decoherence. If you just take a wave function and unitary evolution, you directly arrive at MWI.
Sorry, but no, there is nothing natural there. You need an additional structure - a subdivision of the universe into subsystems. Only if you assume such a subdivision as given, you obtain all the other things, like branching and so on.

If you do not "want" those branches, you have to add a structure - collapses (e.g. Copenhagen), particles (dBB) or something else.
No. You also need additional structure in MWI - the subdivision of the universe into subsystems.
The_Duck
#222
Jul31-12, 12:53 AM
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Quote Quote by Ilja View Post
You also need additional structure in MWI - the subdivision of the universe into subsystems.
What do you mean by this? Why is it true, and what sort of subsystems are you talking about?
mfb
#223
Jul31-12, 07:30 AM
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No, you do not need subdivisions of any sort. Any wave function which somehow looks like a classical system (or a superposition of several classical systems) will produce branches if something like a measurement process happens.

The "somehow" / "something" are on purpose, as the result is very general and applies to a wide range of systems / processes.
bohm2
#224
Jul31-12, 10:10 AM
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Quote Quote by Ilja View Post
You also need additional structure in MWI - the subdivision of the universe into subsystems.
Some like Maudlin have criticized MWI for opposite reasons; for not having an appropriate micro-ontology to appropriately ground macro-level stuff. I'm guessing this is one of the major reasons Maudlin favours the Bohmian model (at least one particular version of it)? An interesting paper by David Wallace discussing some of these problems for MWI and his attempts to adress these criticisms/problems:
(Maudlin (2010), in particular, criticises the Everett interpretation for having an inappropriate micro-ontology to appropriately ground macro-level facts; Hawthorne (2010) raises some similar concerns.) In particular, normally our concepts of space and time are treated as constant between higher-level and lower-level theories, so that for (e.g.) some higher-level object to exist in spacetime region K it must be instantiated not just by any old objects and properties in the lower-level theory, but by objects and properties themselves located in K. As such, getting some understanding of the relation between spacetime and the microscopic ontology might well be crucial for the larger Everettian project. This project will be my concern for the remainder of the article.
A prolegomenon to the ontology of the Everett interpretation
http://philsci-archive.pitt.edu/8892...ssa_volume.pdf

Personally, the biggest problem for BM for me is the "problem of empty waves":
For every branch of the wavefunction containing the actual particle trajectories, there are countless other branches corresponding to every other potential ‘world’ which would have been realized had the particle positions been different. The effects of decoherence soon disable the influence of other branches on the particle trajectories, leaving much of the wavefunction redundant. Nonetheless these redundant branches are an essential element of BM...This criticism of BM has led several authors to argue that BM is little more than a version of the many-worlds interpretation in which the particle trajectories are a way to select one particular world...It has also led Durr, Goldstein, and Zanghi to suggest that the wavefunction should be regarded as nomological, with a role analogous to the Hamiltonian in classical mechanics.
For example Deutsch has claimed that “pilot-wave theories are parallel-universes theories in a state of chronic denial”.

Hidden variable interpretation of spontaneous localization theory
http://arxiv.org/PS_cache/arxiv/pdf/...104.1938v1.pdf

For a very interesting chapter on Maudlin's position see Chapter 4: "Can the World be only wave function":
I quite agree that the question raised is crucial, and arises even in the predictable case. I also agree that the Bohmian should insist—as all Bohmians I know of do!—that predictability has nothing to do with it: even in the predictable case, the state of the wavefunction alone, the wavefunction without any particles at all (if any sense can be made of that) is not sufficient to account for the result of any measurement. For if the result of a measurement consists in, say, a pointer pointing a certain way, and if the pointer is made of particles, then if there are no particles there is no pointer and hence no outcome.
Many Worlds? Everett, Quantum Theory, and Reality
http://bacon.umcs.lublin.pl/~lukasik...nd.Reality.pdf
Ilja
#225
Aug1-12, 06:16 AM
P: 301
Quote Quote by The_Duck View Post
What do you mean by this? Why is it true, and what sort of subsystems are you talking about?
In http://arxiv.org/pdf/0901.3262v2.pdf I have described this in some detail and constructed an explicit counterexample to the hope that one can derive it somehow given only the Hamilton operator.

Some quotes from Zurek (arXiv:quant-ph/9805065, arXiv:0707.2832):

“One more axiom should [be] added to postulates (i) - (v): (o) The
Universe consists of systems.

“Both the formulation of the measurement problem and its resolution through the appeal to decoherence require a Universe split into systems. Yet, it is far from clear how one can define systems given an overall Hilbert space of everything and the total Hamiltonian.

[A] compelling explanation of what are the systems — how to define them given, say, the overall Hamiltonian in some suitably large Hilbert space — would be undoubtedly most useful.
It would be indeed useful, but, unfortunately for MWI, it is not possible. At least not without any additional physical structure.

Quote Quote by mfb View Post
No, you do not need subdivisions of any sort. Any wave function which somehow looks like a classical system (or a superposition of several classical systems) will produce branches if something like a measurement process happens.

The "somehow" / "something" are on purpose, as the result is very general and applies to a wide range of systems / processes.
I disagree. Without any additional structure it is not even well-defined what means "something like a measurement process".
Quantumental
#226
Aug1-12, 10:19 PM
P: 129
Quote Quote by Ilja View Post
In http://arxiv.org/pdf/0901.3262v2.pdf I have described this in some detail and constructed an explicit counterexample to the hope that one can derive it somehow given only the Hamilton operator.

Some quotes from Zurek (arXiv:quant-ph/9805065, arXiv:0707.2832):



It would be indeed useful, but, unfortunately for MWI, it is not possible. At least not without any additional physical structure.

So have you talked to him about this?
Last time I saw an interview with Zurek he was fairy confident in MWI, though he also said that it might be that you can get "it from bit" some other way.
Ilja
#227
Aug2-12, 06:39 AM
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Quote Quote by Quantumental View Post
So have you talked to him about this?
No. The quotes are from the papers I have cited.
Quantumental
#228
Aug2-12, 11:57 AM
P: 129
Quote Quote by Ilja View Post
No. The quotes are from the papers I have cited.
From what I can tell he does not agree with you that this is not possible...
It seems he is perfectly fine with it?
Ilja
#229
Aug5-12, 11:21 AM
P: 301
Quote Quote by Quantumental View Post
From what I can tell he does not agree with you that this is not possible...
It seems he is perfectly fine with it?
I don't even know if he has read my papers, so I cannot tell what he thinks about them.

I think my counterexamples show clearly that MWI needs additional structure. A strange fundamental "subdivision into systems" can provide such an additional structure. Once
Zurek has independently proposed such a subdivision as a natural postulate, it seems
reasonable to guess that he will not give it up.

But it is clearly an additional structure, which is not necessary in the Bohmian approach,
so that the "BM is MWI in denial" argument is clearly invalid.
Quantumental
#230
Aug5-12, 03:13 PM
P: 129
Quote Quote by Ilja View Post
But it is clearly an additional structure, which is not necessary in the Bohmian approach,
so that the "BM is MWI in denial" argument is clearly invalid.
Why isn't the structure in the WF enough? I mean given functionalism there should be worlds in the empty pilot waves too?
Ilja
#231
Aug7-12, 01:09 PM
P: 301
Quote Quote by Quantumental View Post
Why isn't the structure in the WF enough? I mean given functionalism there should be worlds in the empty pilot waves too?
I don't understand this functionalism. A function on something does not mean the existence
of this something. What do I think about unicorns? This depends on the unicorns - I have
a special preference for the invisible pink unicorn, while I consider other unicorns as boring.

So, it is a function of the state of unicorns, and it really exists in my mind. So, does it follow that unicorns exist?

The argument about the missing subdivision of the world into systems is of another type. This structure is necessary because, if one thinks about it, one can easily detect that all the MWI considerations assume that such a subdivision exists. And my example shows that different subdivisions lead to different physical predictions for the same Hamilton operator.
Quantumental
#232
Aug8-12, 07:46 AM
P: 129
Quote Quote by Ilja View Post
I don't understand this functionalism. A function on something does not mean the existence
of this something. What do I think about unicorns? This depends on the unicorns - I have
a special preference for the invisible pink unicorn, while I consider other unicorns as boring.

So, it is a function of the state of unicorns, and it really exists in my mind. So, does it follow that unicorns exist?
What?
That is not functionalism at all.
The point is: if the wavefunction has a ontological existence as a pilot wave in the de-Broglie Bohm interpretation, then why doesn't the pilot wave give rise to worlds ?
If the pilot wave funciton exactly like a structure, then why isn't it structure?

The argument about the missing subdivision of the world into systems is of another type. This structure is necessary because, if one thinks about it, one can easily detect that all the MWI considerations assume that such a subdivision exists. And my example shows that different subdivisions lead to different physical predictions for the same Hamilton operator.
I'd love to learn more about this...
Ilja
#233
Aug8-12, 08:30 AM
P: 301
Quote Quote by Quantumental View Post
What?
That is not functionalism at all.
The point is: if the wavefunction has a ontological existence as a pilot wave in the de-Broglie Bohm interpretation, then why doesn't the pilot wave give rise to worlds ?
If the pilot wave funciton exactly like a structure, then why isn't it structure?
My artificial unicorn-example was of similar nature. My ideas about unicorns have ontological
existence in any theory which assumes that human ideas correspond to states of neurons in the human's brain. So these ideas exist there, as a structure of my neurons.

But it does not follow that this structure of my neurons, even if it can be described by a function on the space of imaginable unicorns, gives rise to unicorns.

I'd love to learn more about this...
http://lanl.arxiv.org/abs/0901.3262 is the basic construction. The same Hamilton operator,
but nonetheless different physical predictions, because of different operators p,q or a different subdivision into systems.

http://lanl.arxiv.org/abs/0903.4657 is some argumentation why various quantum interpretations which are pure - that means, without any additional structure - are not viable.
ImaLooser
#234
Aug9-12, 01:13 AM
P: 570
Quote Quote by Ilja View Post

But it does not follow that this structure of my neurons, even if it can be described by a function on the space of imaginable unicorns, gives rise to unicorns.
I came directly from watching a video of imaginary unicorns to this. Golly.

Really.


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