Local realism ruled out? (was: Photon entanglement and...)

akhmeteli

Dear nanosiborg,

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't-give-a-damners' 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't-give-a-damner 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.


I agree

, however, 't Hooft's argument (please see my post 821) is not completely lost on me.

I guess, some of them won't, some of them will... What would I do in such case? I honestly don't know, and I hope I won't need to choose:-)

DrChinese

I have only seen one set... ever... and for polarization it always follows the cos^2 rule. I have never seen a published reference to ambiguity regarding this point.

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 non-standard theory. If I am correct, please label as such rather than lead unknowing readers to an inappropriate conclusion.

akhmeteli

I am sure you have seen published references on the measurement problem in quantum theory, see, e.g., http://plato.stanford.edu/entries/qt-measurement/ and references there, e.g., Albert or Bassi/Ghirardi. Let us consider some measurement in quantum theory for a pure state. You can make a prediction using the projection postulate (PP) of standard quantum theory. According to PP, the resulting quantum state will be a mixture of eigenstates of the measured observable, and the measurement is irreversible. On the other hand, you can make a prediction using unitary evolution (UE) of standard quantum theory for the measured system, the instrument, and the observer, if you wish. Unitary evolution can only give a superposition of the eigenstates (if the initial state is not an eigenstate of the observable), and the measurement is reversible. That means that standard quantum theory definitely gives two contradictory predictions. For a specific model, Allahverdyan e.a. (please see the arxiv / Physics Report article quoted in my post 824) show that in some cases PP can be a good approximation to what UE predicts, but it is an approximation. If you demand that I reproduce the tedious calculations of Allahverdyan e.a. for Weihs et al (1998) or John Doe et al (2004), I flat out reject such demand as arbitrary and unreasonable.

DrChinese

If there is no specific conflicting prediction to support your personal theory, and you refuse, then you are violating forum rules.

akhmeteli

This is your personal and arbitrary reading of the rules. The rules do not require that I fulfill your arbitrary demands. I gave all the references confirming that PP and UE give mutually contradictory predictions, so I fulfilled my duty under the rules: prove (using mainstream references) that the predictions do indeed differ, as I said. So I did not refuse to prove (by references) my statement, I did refuse to give a specific prediction, but I don't have any such obligation under the rules. The measurement problem of quantum theory is not my personal theory, furthermore, you yourself "freely admit it". I am sure you appreciate that UE cannot generate irreversibility or turn a pure state into a mixture, unlike PP, so there is no doubt that they do give differing predictions. Furthermore, strictly speaking, UE cannot even give a definite outcome of a measurement.

bhobba

No it doesn't - but it turns it into an 'improper mixture' - see the early chapters of Decoherence and the Quantum-to-Classical Transition by Schlosshauer where he carefully explains what's going on. Here improper means no observation can tell the difference between it and an actual mixed state. The means with no contradiction one can assume it is an actual mixed state and the measurement problem is solved. The issue is not one of contradiction the issue is such an interpretation sweeps where the 'collapse' actually occurred, or even if one occurs at all, under the rug by saying it doesn't matter.

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

DrChinese

You gave an unpublished reference that does not indicate a specific difference from the standard QM predictions. You are obviously obsessed with the UE/PP elements of QM and certain specific conclusions you have drawn from this. That is your personal right, no issue with that.

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.

jtbell

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