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nomadreid

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OK, I get it. But the "spooky" part isn't the observed results of the second particle. It's the notion that the initially unobserved particles "contain all possible values". That's equivalent to asking the old tree falling in a forest question, or if the moon exists if no one is looking at it. Questioning the existence of objective reality sans observation raises spooky, metaphysical implications. If you don't raise those implications, then the two particles are assumed to have set and opposite qualities ab initio and my posted question makes sense. Comments?

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DrChinese

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Welcome to PhysicsForums, vegasgeorge!OK, I get it. But the "spooky" part isn't the observed results of the second particle. It's the notion that the initially unobserved particles "contain all possible values". That's equivalent to asking the old tree falling in a forest question, or if the moon exists if no one is looking at it. Questioning the existence of objective reality sans observation raises spooky, metaphysical implications. If you don't raise those implications, then the two particles are assumed to have set and opposite qualities ab initio and my posted question makes sense. Comments?

Yes, your conclusion is fine and certainly appropriate when discussing Quantum Mechanics. Are you familiar with Bell's Theorem? Most people need this to better understand the issues. Bell demonstrates that a realistic theory cannot be compatible with QM unless it is non-local.

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Nugatory

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The assumption that the two particles had set and opposite qualities ab initio leads to certain bounds on the statistical distribution of the correlations between measurements of the two particles. Quantum mechanics predicts and experiment confirms that these bounds are violated - google for "Bell's theorem" for details.If you don't raise those implications, then the two particles are assumed to have set and opposite qualities ab initio and my posted question makes sense. Comments?

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atyy

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The controversy is over whether the wave function itself is addressed by Bell's theorem. If Bell's theorem addresses the wave function, then "local variables" is correct, but if Bell's theorem does not address the wave function, then "local hidden variables" is more strictly correct, since it refers to variables other than the wave function, and which are thus "hidden" from the point of view of the quantum formalism.

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Nugatory

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You need to go back to Einstein's 1935 EPR paper to follow the subject from the beginning - google for "Einstein EPR" will find it pretty quickly.

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Well put, but one must not lose sight of the fact that there are also assumptions in the way the theorem is set up that restrict it to the statistical analysis you describe, if the starting point didn't lend itself to that kind of analysis, and certain theories might do just that, then you could find that "having set and opposite qualities ab initio" as the OP says, is a valid solution to explain the measurements correlations.The assumption that the two particles had set and opposite qualities ab initio leads to certain bounds on the statistical distribution of the correlations between measurements of the two particles. Quantum mechanics predicts and experiment confirms that these bounds are violated - google for "Bell's theorem" for details.

IOW it is not unconceivable to make up a theory for wich the theorem doesn't apply.

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That is true. There is an element of aesthetic preference (de gustibus non est disputandum!) in choosing whether these theories are more or less unpalatable than the mainstream assessment of Bell's theorem and the experimental results that support it.IOW it is not inconceivable to make up a theory for which the theorem doesn't apply.

However, I think that it is fair to say that none of the theories that plausibly evade the assumptions of Bell's theorem would have satisfied the EPR authors.

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Hmm, I think it is fair to say, by what I know about Einstein, that he would have maybe been philosophically disatisfied, but if the theory worked, surprised and happy to finally beat QM.;-)That is true. There is an element of aesthetic preference (de gustibus non est disputandum!) in choosing whether these theories are more or less unpalatable than the mainstream assessment of Bell's theorem and the experimental results that support it.

However, I think that it is fair to say that none of the theories that plausibly evade the assumptions of Bell's theorem would have satisfied the EPR authors.

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Could be.... I've often thought that one of the most intriguing unanswerable questions in the history of science is what would have happened if Einstein had lived to see Bell's theorem and its experimental (but not loophole-free) validation. My bet would be that he would have accepted it and moved on, but that's just me.Hmm, I think it is fair to say, by what I know about Einstein, that he would have maybe been philosophically disatisfied, but if the theory worked, surprised and happy to finally beat QM.;-)

(Of course any speculation about what Einstein would have done suffers from the same flaw as my sure-fire strategy for effortlessly winning at duplicate bridge at any level, which is "If you're not sure what the right play is, just make the same play that Benito Garozzo would make in this situation").

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bhobba

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That's my bet as well. His views seemed to change during his debates with Bohr. When Einstein put his final challenge to Bohr and Bohr defeated it (although with much effort - evidently Bohr worked all through the night on it) Einstein was seen to literally tip his hat to Bohr and from that moment on never questioned if QM was correct - but rather thought it incomplete.Could be.... I've often thought that one of the most intriguing unanswerable questions in the history of science is what would have happened if Einstein had lived to see Bell's theorem and its experimental (but not loophole-free) validation. My bet would be that he would have accepted it and moved on, but that's just me.

If he had lived to see Bells result and experimental confirmation I think he would simply have accepted it and found solace in one of the myriad of interpretations we have that gelled with his intuition on how the world worked.

Thanks

Bill

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The point is that this assumption leads to Bell's inequalities, but these inequalities are violated. So, yes, it would be the simplest explanation, but this explanation is falsified by observation. (At least if we ignore the remaining loopholes.)I have to ask, doesn't Occam's Razor come into this? Wouldn't the assumption that the two entangled particles had opposite properties ab initio be the simplest explanation?

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The problem here is that we have experimental results that falsify the ab initio explanation. Thus, the proposition that we're applying the razor to is not "the particles have opposite properties ab initio" but rather "the particles have opposite properties ab initio and every experiment that has shown a violation of Bell's inequality is somehow flawed in a way that causes it to deliver bogus results that just happen to mimic the quantum mechanical prediction and these flaws have somehow been overlooked by two generations of competent scientists even though they have more to gain from finding a flaw than not finding one".I have to ask, doesn't Occam's Razor come into this? Wouldn't the assumption that the two entangled particles had opposite properties ab initio be the simplest explanation?

This proposition doesn't fare well against "the experiments confirm that Bell's inequality is violated" when the razor is applied.

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ShayanJ

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I'm beginning to think that we need a FAQ on entanglement and Bell's inequality!

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.Scott

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Let me respond in more common terms.

Normally (but not normal for QM) you would expect that the one photon of the entangled pair were tilted in some specific direction - for example NNE and 20 degrees up, and the other was pointed in exactly the opposite direction (SSW, 20 down). You would also say that those direction were set at the time that the pair became entangled and remained unchanged until they were measure. This "tilt" is the hidden variable and the expectation that it was set when the two were together and remained unchanged while they were apart is what makes it "local".

Finally, the normal expectation is that the measurement made when the photon reaches the filter is simply determined by that tilt of the photon, the angle of the filter, and perhaps other local conditions.

If you always keep the filters opposite of each other, you will discover that you get the same result at both detectors. This is consistent with what you would "normally" expect.

If you hold one detector (detector A) at a constant angle while varying the angle of the other (detector B), then based on "normal" (local hidden variable) assumptions, you can come to certain (inaccurate) conclusions about the distribution of the tilt of those photons. So at this point, you can still hold onto your "normal" view, but you will see that the distribution seems dependent on what angle you picked for the constant angle detector.

Next, you can step detector A through several angles - in each case varying B to determine the new distribution of photon tilts. At this point, your "normal" assumptions are in trouble. First, you will discover that the distribution of results at detector B is dependent on the setting of detector A. Worse yet, Bell worked out the arithmetic to show that that conclusion is unavoidable.

With regards to Occam's Razor: The arithmetic described by Bell is called the "Bell Inequality" and it was published in 1964. I notice that DrChinese has a copy of it here: http://www.drchinese.com/David/Bell_Compact.pdf. Although, on the face of it, it appears airtight, some loopholes have been described and in most cases closed. Most people who understand the problem that the Bell Inequality presents to "Local Hidden Value" models, do not consider those models to satisfy Occam's Razor.

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However I still believe in 'ab initio' because from what I can understand the entangled particles travel at the speed of light, so qualities cannot change since no time passes for them (although time does pass for the experimenters). Can entangled particles travel slower than light (ie time passes)? Spooky action seems to me to be due to differences in time frames of the particles and experimenters and therefore is not spooky at all (it's ab initio). Where am I going wrong?

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Thanks. Video explained well, but it doesn't really address my way of thinking in the time frame of the entangled particles, where no time passes between particle creation and when they are measured. Entangled particles (as created using photons in Bell tests) are explained ab initio because initio (particle creation) and fini (particle measurement) occur at the exact same time in particles' frame of reference. Non-locality is not even breached since the particles are right next to each other when they are measured (no matter how far apart they are!).

In the video and the whole notion of hidden variables (particles planning ahead) is based on the experimenter's time frame. So entangled particles only seem spooky when experimenters use their own time frame to explain something that happens in a different frame. Anyway that's my relativist way of looking at this quantum system.

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bhobba

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Why do you think that?occur at the exact same time in particles' frame of reference.

It doesn't but I am curios why you think so. I suspect its from a common misconception about relativity, but will refrain from saying anything until I know your reasoning.

Added Later:

I see from your previous post you explained it.However I still believe in 'ab initio' because from what I can understand the entangled particles travel at the speed of light, so qualities cannot change since no time passes for them (although time does pass for the experimenters).

This is the common misconception I talked about. Relativity is about the relationship between time and space measurements in different frames of reference. Since a frame of reference cant be attached to an object moving at the speed of light its meaningless to talk about time for objects travelling at light speed.

Just as an aside here is a modern explanation of relativity without the usual pop-sci jargon that confuses:

http://physics.umd.edu/~yakovenk/teaching/Lorentz.pdf

Thanks

Bill

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