View Poll Results: What do observed violation of Bell's inequality tell us about nature?  
Nature is nonlocal  11  32.35%  
Antirealism (quantum measurement results do not preexist)  15  44.12%  
Other: Superdeterminism, backward causation, many worlds, etc.  8  23.53%  
Voters: 34. You may not vote on this poll 
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What do violations of Bell's inequalities tell us about nature? 
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#19
Feb1113, 10:54 AM

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P: 3,969

I find myself wondering which of realism and locality is more "natural" to our thinking, more easily accepted at an intuitive level.
I'm inclined to think that it's realism:  A cat and a bird are outside watching one either right now... I am quite confident that the biochemical computers that guide their behavior are programmed to analyze the situation in purely realistic terms. I doubt that this bias would change if either were to develop greater capacity for abstract thought.  People are discouragingly willing to accept magical nonlocal explanations such as astrology. These nonlocal magical explanations are generally realistic; the astrologers don't question whether the moon and the planets are there when no one is looking.  Few people are disturbed by the truly egregious nonlocality of Newtonian gravitation; and I expect that most laypeople find Schrodinger's cat more disturbing/confusing/"wrong" than gravitational action at a distance. Interesting though (at least to me) is that the poll results are running the other direction... 


#20
Feb1113, 10:54 AM

P: 351

Of course, there are spins that are not entangled, but I could speculate further that all spinbaggage, correlated or not, is permanently stuck in some cosmic LaGuardia airport. 


#21
Feb1113, 11:00 AM

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P: 3,969




#22
Feb1113, 11:13 AM

P: 484




#23
Feb1113, 11:23 AM

P: 724

Materialism would be the old mechanistic concept of reality but this is beside the point. The point is not why there could potentially be nonlocality but why there is locality. When you answer that question from the point of view of qm(since this is the quantum theory forum!), then we can know why under certain circumstances nonlocality could be observed. People seem to forget(even in this forum) that reality is quantum mechanical and not classical. If you treat classical mechanics as fundamental(not emergent) you get action at a distance, nonlocality, tunneling through barriers, many worlds, backward causation, objects spinning in two directions at the same time and other wonderful phenomena. And people go on to extrapolate all the time the reality of tables and chairs to the quantum realm as if they are somehow interchangeable or compatible. 


#24
Feb1113, 11:50 AM

PF Gold
P: 698

In hindsight, I'm not sure Gisin's argument that Newton's nonlocality is more "radical" is accurate. For instance, quantum nonlocality would not also have to be FTL (instantaneous) but would also have to be unattenuated and discriminating as Maudlin and others note:
The quantum connection is unattenuated: http://www.amazon.com/QuantumNonLo.../dp/0631232214 


#25
Feb1113, 12:35 PM

P: 351

PS: I've now mangled the quotes thoroughly, but hope y'all can sort it out. 


#26
Feb1113, 12:54 PM

P: 159

The "Shut up and calculate" choice is definitely missing. Unless there are some observable differences between different interpretations of QM or unless they make calculations easier, it's a waste of time to think about it. I also don't want to be counted to option #3.
However, if i had to choose between nonlocality and antirealism, i would choose antirealism, because i don't really see why realism is so desirable apart from the fact that otherwise, one has to give up his beliefs and prejudices about nature that originate from the naive assumption that we can extrapolate the laws of the macroscopic world to the microscopic world as well. On the other hand i'd rather not give up locality, because that would mean that some events in the andromeda galaxy or even outside the observable universe could in principle influence events on earth, unless you impose some strong limitations on the nonlocality in your theory (and if you do so, then you'd have to justify them somehow). That would make physics entirely pointless, because it would mean that our equations would have to depend on parameters that can't be measured here on earth. So even if the world were nonlocal, it's reasonable to assume that it's not, in order to even be able to write down equations that are of any use. 


#27
Feb1113, 01:12 PM

P: 351

If Bob measures ↓ here and Alice measures ↑ at the Andromeda galaxy, they are only measuring a single downup attribute shared (somewhere in nowhereville) by two cogenerated particles. 


#28
Feb1113, 01:34 PM

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P: 5,441




#29
Feb1113, 04:39 PM

P: 79

It's true that ... In light of the contributions of the classical conservation laws and classical wave optics to the QM treatment of polarization entangled photons, it's maybe a bit misleading to say that ... Regarding the question of why there is locality, this is similar to the question of why disturbances in media expand more or less omnidirectionally (depending on the properties of the medium in which the disturbance is produced), in that they both might well be unanswerable questions. That is, they both might be irreducibly fundamental properties of physical reality, and as such would form part of the axiomatic structure of a comprehensive theory. Which is sort of the place that the principle of local action, along with causal determinism, has in contemporary physical science. These are (at least tacitly held) assumptions that are required for physical science to have any unambiguously communicable meaning. The metaphysical speculations about nonlocality, etc. remain just that. If violations of Bell inequalities actually informed regarding nature, well, that would be great. Unfortunately, they don't. But that doesn't make Bell's theorem 'shortsighted', as another current thread asked. Bell's analysis provides a very clear answer to the question he was asking. Namely, are QMcompatible LHV models of quantum entanglement possible? The answer, mathematically proven, is no, they aren't. If you take Bell's formulation to be generalizable, and I do, then QMcompatible LHV models of quantum entanglement are definitively ruled out. Beyond that, violations of Bell inequalities tell us nothing about nature. If that doesn't do it for you, then you might be talking round and round about this stuff, and getting nowhere, for a really long time. 


#30
Feb1113, 07:02 PM

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P: 2,215

So I'm wondering if there is a way to understand the "instantaneous" quantum interactions of Bohm theory as interactions that only seem instantaneous because they only travel a short distance. 


#31
Feb1113, 08:34 PM

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#32
Feb1113, 09:45 PM

P: 79

But it sounds like you might be able to fashion some sort of novel mathematical contrivance or other. Not that that would provide any understanding either, but then mathematical contrivances (and placeholders) don't have to. They just need to help facilitate the calculation of accurate quantitative predictions. 


#33
Feb1113, 09:52 PM

P: 79




#34
Feb1113, 10:08 PM

Sci Advisor
P: 2,215

That's the weirdness of quantum randomnessnot the randomness by itself, but the combination of randomness with a kind of certainty of the distant correlations. 


#35
Feb1113, 10:18 PM

P: 79




#36
Feb1213, 08:50 AM

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P: 2,215

Think about the following situation: You prepare an electron with spinup along some axis [itex]\vec{S}[/itex]. Then later you measure its spin along a different axis [itex]\vec{A}[/itex]. Then the result will be nondeterministic: with a certain probability, the electron will be found afterwards to have spinup in the [itex]\vec{A}[/itex] direction, and with a certain probability, it will be spindown. In either case, the angular momentum of the electron was changed by the measurement: its final angular momentum is not the same as its initial angular momentum. That isn't a violation of conservation of angular momentum, because you can attribute the change to the interaction between the detector and particle. The angular momentum of the particle changes, and the angular momentum of the detector changes in a complementary way, so that the total angular momentum is unchanged by the detection process. But note that there is a small amount of angular momentum, [itex]\delta \vec{L}[/itex] transferred from the electron to the detector. Now, if that electron happened to have come from an EPR twinpair experiment, then each of the two detectors can be expected to receive a tiny amount of angular momentum from whichever particle is detected. But in the case of perfectly aligned detectors, we know that the [itex]\delta \vec{L_1}[/itex] received by one detector must exactly correlate with the [itex]\delta \vec{L_2}[/itex] received by the other detector, so that the resulting spins of the twin particles are perfectly anticorrelated. So the perfect anticorrelation is not simply a matter of conservation of angular momentum. Angular momentum would be conserved whether or not the twin particles are found to be anticorrelatedit's just that different amounts of angular momentum would be transferred to the detectors. The perfect anticorrelation of twin pairs is a matter of cooperation between nondeterministic processes involving distant macroscopic objects (the detectors). 


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