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The Refutation of Bohmian Mechanics 
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#217
May3111, 04:23 AM

P: 2,456

P.S I have a question for you about dBB. I remember once there was a discussion about Bell/EPR and noconspiracy assumption. You replied that you don't see an exact difference between superdeterminism and noconspiracy. 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?) 


#218
May3111, 04:59 AM

Sci Advisor
P: 4,573

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. 


#219
Jul3012, 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. 


#220
Jul3012, 12:50 PM

Mentor
P: 11,589

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. 


#221
Jul3012, 03:11 PM

P: 301




#222
Jul3112, 12:53 AM

P: 842




#223
Jul3112, 07:30 AM

Mentor
P: 11,589

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. 


#224
Jul3112, 10:10 AM

PF Gold
P: 674

http://philsciarchive.pitt.edu/8892...ssa_volume.pdf Personally, the biggest problem for BM for me is the "problem of empty waves": 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": http://bacon.umcs.lublin.pl/~lukasik...nd.Reality.pdf 


#225
Aug112, 06:16 AM

P: 301

Some quotes from Zurek (arXiv:quantph/9805065, arXiv:0707.2832): 


#226
Aug112, 10:19 PM

P: 129

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. 


#227
Aug212, 06:39 AM

P: 301




#228
Aug212, 11:57 AM

P: 129

It seems he is perfectly fine with it? 


#229
Aug512, 11:21 AM

P: 301

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. 


#230
Aug512, 03:13 PM

P: 129




#231
Aug712, 01:09 PM

P: 301

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. 


#232
Aug812, 07:46 AM

P: 129

That is not functionalism at all. The point is: if the wavefunction has a ontological existence as a pilot wave in the deBroglie 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? 


#233
Aug812, 08:30 AM

P: 301

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. 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. 


#234
Aug912, 01:13 AM

P: 570

Really. 


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