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Local realism ruled out? (was: Photon entanglement and...) 
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#811
Jan1813, 11:00 AM

P: 1,583




#812
Jan1813, 11:07 AM

Sci Advisor
PF Gold
P: 5,378




#813
Jan1913, 04:57 AM

P: 596

It is my understanding that you discussed this issue with me in just one post in this thread  post 758. If I am mistaken, please let me know. I gave my answer to your post 758 in post 760. In your last post (822) you did offer an additional (von Neumann's) argument  that unitary evolution and the projection postulate "take turns". Maybe you can avoid a logical contradiction in this way (see though http://plato.stanford.edu/entries/qtmeasurement/, section 3, second and subsequent paragraphs), but you buy into more problems, and not just philosophical ones. I already gave the conclusions of Schlosshauer's analysis (M. Schlosshauer, Annals of Physics, 321 (2006) 112149) of experimental data in this thread (post 41). He wrote, in particular, that "the universal validity of unitary dynamics and the superposition principle has been confirmed far into the mesoscopic and macroscopic realm in all experiments conducted thus far;", and "no positive experimental evidence exists for physical statevector collapse;" So one may ask: if measurement leads to collapse, does this mean that we cannot consider unitary evolution of the measured system together with the instrument (and with the observer, if you wish)? Would unitary evolution give wrong results in this case? Not according to Schlosshauer's analysis. There is no positive experimental evidence of collapse, and there is no experimental evidence of violations of unitary evolution. On the other hand, in some cases, collapse can be a good approximation for a measurement process fully described by unitary evolution ( http://arxiv.org/abs/1107.2138 (accepted for publication in Physics Reports  http://www.sciencedirect.com/science...70157312004085 )), but just an approximation. Some other difficulties of von Neumann's approach are discussed in http://plato.stanford.edu/entries/qtmeasurement/. So I insist that unitary evolution (UE) and the projection postulate (PP) are indeed mutually contradictory for reasons given in my post 760 in this thread. Logic might allow UE and PP "take turns", but if you believe that they do take turns, you have to believe that UE is not always correct, and there is no experimental basis for that. Let me just ask you: do you seriously believe that unitary evolution is not always correct? 


#814
Jan1913, 05:53 AM

P: 596

I don't want to and I don't need to defend superdeterminism. I am just saying that there is some logic behind it. However, if a theory does not defy logic, that's good, but not enough:) 


#815
Jan1913, 11:47 AM

Sci Advisor
PF Gold
P: 5,378

Specifically: there are in fact HUGE requirements on a superdeterministic (SD) theory. For example: exactly how is the information locally maintained so that spatially distant relationships can be honored in keeping with the predictions of QM? And does SD posit new relationships between the 4 fundamental forces?* And since QM does NOT properly describe the true** relationship between entangled particles, what is it? These are just a few starter questions. So when it comes to "disgusting", I would prefer to see clearly the ugly side of SD so I can choose. I already know what is "disgusting" in the various usual interpretations. *Since I can develop Bell tests that exploit these relationships, this is a very serious problem. For example, I have a radioactive sample that randomly drives the selection of Bob's measurement setting. This requires a very complex explanation which will inevitably be inconsistent with the Standard model. **Instead only describes the apparent relationship. Obviously that is different otherwise we wouldn't need to have SD in the first place. 


#816
Jan2013, 02:22 AM

P: 79

I can appreciate that foundationalists have a problem with standard qm having reversible and irreversible dynamical processes, and that this seems illogical to you. It doesn't seem illogical to me because I don't think of standard qm as saying anything about deep reality, and qm works quite well in its present form. Why do what seem to some like disparate, even contradictory, elements of the theory produce such accurate results? 


#817
Jan2013, 10:31 AM

P: 596

I conclude from the above that you admit that standard qm has both reversible and irreversible processes. That probably means that it includes both unitary evolution (UE) and the projection postulate (PP). They give different predictions for the same quantum state. (If you believe, following von Neumann, that UE and PP "take turns", you add some extra problems (please see my post 824)). So it seems that "the maths used in calculating predictions" gives ambiguous predictions. This is a contradiction, or inconsistency, in my book. It isn't, in yours? You know, I like very much this one about a don'tgiveadamners' contest:  How do you feel about work?  Don't give a damn about work.  How about money?  Don't give a damn about money.  How about women?  Well, broads are always on my mind.  Well, there seems to be some inconsistency with the goals of our contest.  Don't give a damn about your inconsistency... Well, I might be a don'tgiveadamner myself, but it looks like standard quantum theory might give ambiguous predictions for Bell tests. As for "why accurate results?" Because PP can be a very good approximation to the results of UE in some cases (please see the arxiv / Physics Report article quoted in my post 824). Let me remind you that thermodynamics gives very accurate results, but its irreversibility still contradicts the reversibility of the underlying microscopic theory. You may say: if it's so accurate, why should we care? Because Nature cannot be "approximately nonlocal"  that does not make any sense. It's either local or not. The Coulomb law or Newton's gravity are very accurate, but they fail exactly where they predict nonlocality. 


#818
Jan2013, 07:38 PM

Sci Advisor
PF Gold
P: 5,378

Besides your own statements or work, can you show me a suitable published prediction that is different than those in usual experiments? Weihs et al (1998) being a great example of the usual QM predictions. Who has predicted otherwise? In other words: I am flat out saying your statement is merely a reflection of your personal nonstandard theory. If I am correct, please label as such rather than lead unknowing readers to an inappropriate conclusion. 


#819
Jan2013, 08:25 PM

P: 596




#820
Jan2013, 08:57 PM

Sci Advisor
PF Gold
P: 5,378




#821
Jan2113, 06:01 AM

P: 596




#822
Jan2113, 06:37 AM

Sci Advisor
PF Gold
P: 2,739

Or ,to put it another way, exactly how does an observation accomplish this marvelous feat  its one of (perhaps) incompleteness  but not of contradiction. Thanks Bill 


#823
Jan2113, 07:38 AM

Sci Advisor
PF Gold
P: 5,378

The issue is that you consistently use PhysicsForums as a way to promulgate your ideas, and this is not the place for that. You typically operate right at the edges of forum rules, but this time you have crossed the line. They are not MY rules, they are OUR rules and we must all live by them. The fact is: it is your personal theory that there are different predictions for Bell experiments in QM. There is not a single mainstream prediction for these experiments that differs from the norm, and certainly you have not identified a reference for anything different. I, on the other hand, can supply plenty of references for the CHSH inequality, the related QM prediction, as well as references for the standard QM predictions for matches of cos^2(theta). Please retract your statement. 


#824
Jan2113, 08:56 AM

Mentor
P: 11,772

Due to the length and digressiveness of this thread, it has been closed. For a more recent development, see here:
http://www.physicsforums.com/showthread.php?t=689717 


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