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PBR nogo theorem: Is ψ epistemic or ontic? An experimental test 
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#1
Nov512, 08:25 PM

PF Gold
P: 684

This was a recent experiment done to determine the epistemic versus ontic status of ψ:
http://lanl.arxiv.org/pdf/1211.0942.pdf 


#2
Nov612, 02:53 AM

Sci Advisor
P: 4,599

Do the results of this experiment tell as anything that we didn't already know?
Is any SPECIFIC previously used interpretation of QM ruled out? I think the answer to both questions is  NO. 


#3
Nov612, 09:17 AM

PF Gold
P: 684




#4
Nov612, 09:32 AM

Sci Advisor
P: 4,599

PBR nogo theorem: Is ψ epistemic or ontic? An experimental test



#5
Nov612, 11:45 AM

P: 132

Personally I think that some deeper theory that will unify QM and GR will still be "found" some day. I just don't believe that either Bohm, Everett or any of the other "candidates" are right. 


#6
Nov612, 12:32 PM

PF Gold
P: 684

EDIT: Another experiment drawing similar conclusions just published: http://lanl.arxiv.org/pdf/1211.1179.pdf 


#7
Nov712, 03:10 AM

P: 301

I would like to point to the fact that epistemic interpretations which correspond to the dBB rule of defining effective wave functions for subsystems by [itex]\psi(q,t)=\Psi(q,q_{env}(t))[/itex], where [itex]q_{env}(t)[/itex] is the trajectory of the configuration, cannot be ruled out by similar arguments if they give the [itex]\Psi[/itex] of the whole universe an epistemic interpretation.
The point is that all the properties of the wave function of any accessible system which make it look like a physical entity it borrows in that formula from [itex]q_{env}(t)[/itex]. In particular, the prescription to make the PBR experiment can, from this point of view, never create a state where it is unclear how it has been prepared. The prepared state is always part of greater system, which contains the devices used for the preparation. This environment can, of course, also include some random throwing of dices which preparation procedure has to be used. But, anyway, [itex]q_{env}(t)[/itex] contains also the result of this dice throwing. So [itex]\psi_1(q)=\Psi(q,q_{prep\uparrow},\uparrow)[/itex] and [itex]\psi_2(q)=\Psi(q,q_{prep\downarrow},\downarrow)[/itex], thus, even if ψ itself is purely epistemic, the λ_{i} of the two states will be different already because their preparation procedure is different. 


#8
Nov712, 09:28 AM

PF Gold
P: 684

So I'm guessing, you are arguing that PBR would have no effect on your model?
The Paleoclassical interpretation of QT http://lanl.arxiv.org/pdf/1103.3506.pdf 


#9
Nov712, 10:01 AM

Sci Advisor
PF Gold
P: 5,373

Considering that the Bohmian view* essentially says that there IS a specific welldefined value for noncommuting observables, although we cannot know it: I would think it is just a matter of time before theorems in the spirit of PBR clearly conflict with the Bohmian hypothesis (nonlocal hidden variables).
*As I understand it, that being a limited understanding. 


#10
Nov712, 12:58 PM

P: 301

I would not completely exclude that it nonetheless may cause problems. The paleoclassical interpretation is, last but not least, a radical version where the wave function of the whole universe has no own real degrees of freedom. And one has to think about PBR if one constructs a subquantum theory which gives QT in some limit. But I argue, indeed, that PBR is not an impossibility proof for the paleoclassical interpretation. But why you think that an impossibility theorem may be possible? That dBB in quantum equilibrium gives QT predictions is a simple theorem. That quantum equilibrium will be approached is Valentinis subquantum Htheorem  ok, with caveats similar to the original Htheorem, but I cannot see how this may become a problem. And I see no reason to doubt that dBB in itself is consistent. The wave function as being real is at least a popular variant, if not the standard dBB interpretation. 


#11
Nov712, 01:00 PM

PF Gold
P: 684




#12
Nov712, 01:58 PM

Sci Advisor
PF Gold
P: 5,373

2. Bohm2 said essentially the same thing. I guess I just don't understand that. If there are (nonlocal) hidden variables that determine outcomes, how can a probability amplitude/wave function have reality? I thought outcomes could be predicted if all input values were known. Seems to me that HV implies a form of determinism which in turn implies welldefined values for elements of reality. 


#13
Nov712, 03:55 PM

P: 301

There have been different approaches to relativistic QFT for fermion fields, from Bell (beables for quantum field theory) to Colin and Struyve. But I favour, of course, my own approach. In arXiv:0908.0591 I present a way to obtain two Dirac fermions together with a scalar field from canonical quantization of a scalar field with Wlike potential. Once scalar fields in itself present no problem for dBB field theory, this solves the problem even if dBB is not even mentioned there. There is only a special state, named quantum equilibrium, where we have a connection between ψ and probabilities for q in form of the Born rule. It is because of a "subquantum Htheorem" that arbitrary probability densities become, after some time, almost indistinguishable from this quantum equilibrium. So there is no fundamental connection at all. Probabilities play the same role as in classical thermodynamics. 


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