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About the alleged duplicates: " Quantum entanglement vs classical analogy" "Show quantum entanglement to a classical thinker" refer to black and white balls that would have a correlation at time zero, and this "anticorrelation of color" would be maintained later on. Clearly, if you read what I'm talking about, I am giving the EXACT OPPOSITE analogy of a classical system that does NOT return anticorrelation all the time. On the contrary, it returns different correlation values depending on the axis used for each detector. So while I understand you don't want duplicates, this seems like an exageration to consider my question to be similar to those ones.

Spheres

On the above illustration, two spheres have a marking on the opposite side of each other. In the top right corner, we take a picture of sphere 1 and 2 from the front. We observe that in sphere 1 photo, the marking is in the upper half of the picture. We decide to label it as "spin up state". On sphere 2 photo, the marking is on the lower half of the picture. We label it "spin down state". So we have an anticorrelated spin state of sort.

Now, instead of taking pictures in the same axis, we take a picture of sphere 2 from above. And we observe the resulting picture has a 50% chance of returning a spin up or down state, i.e. we lost correlation.

As far as I understand, this is what happens when two particles are entangled and two detectors are set to measure their spin state. If both detectors use the same axis, one can observe that particle B has an anticorrelated spin state that the one measured on particle A. But if different axes are used for detection, the correlation is lost.

So my question is this: what makes entanglement different than the classical spheres analogy I gave above?

Winston
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  • Note that this analogy does not take into account a potential "destructive measurement" that would prevent other measurements to be made on particle 1 axes. But this is not the point here, as measurement is a perturbation of the objects measured and could also be modeled as a mechanical transformation of the spheres. My question is rather, why does it look like correlations of spin state detected from various angles in two entangled particles seems to resemble this "algorithm" applied to classical spheres. – Winston Apr 29 '23 at 23:06
  • The state of your system is UD, which is clearly the product of U and D, hence not entangled. – WillO Apr 29 '23 at 23:29
  • How am I assuming no entanglement? I am describing results from experiments made on entangled particles and I asking what I am missing. Later you say "my" system is UD. I have no idea what this is about. If U means up and D means D, and UD means up down I'm still unable to figure what you are talking about. – Winston Apr 29 '23 at 23:35
  • Please do not delete and repost questions. If the duplicates linked in your previous post do not suffice to explain the difference between a classical correlation and quantum entanglement and none of the other questions (e.g. https://physics.stackexchange.com/q/675344/50583) about entanglement and classical explanations are good enough for you, either, please be more specific about what it is that you are confused about. – ACuriousMind Apr 29 '23 at 23:56
  • @ACuriousMind I read the so called "duplicate questions" and they refer to something different. OPs are asking about white and black balls, saying if you know one is white, then the other is black. This is NOT what I am talking about with my spheres having a anticorrelated unity vector (the marking drawn on their surface), that allows from several axes to be tested and do NOT show anticorrelation all the time, quite the contrary, as I am explaining here. – Winston Apr 30 '23 at 00:00
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    Did you read any of the answers to the duplicates (e.g. this one)? You could ask about a thousand different classical situations where some sort of correleation happens, and the answer would always be the same: Quantum correlations can violate Bell's inequality, classical correlations can't, independent of your specific classical construction. – ACuriousMind Apr 30 '23 at 00:03
  • @ACuriousMind I didn't read all answers because I thought the one that was accepted was the one to consider. And in the accepted answer, it is said that the OP didn't take into consideration multiple axes. So you seem to be telling me that I should be able to determine which answers are right and which are wrong in a "duplicate question", which is beyond my abilities. – Winston Apr 30 '23 at 00:08
  • @ACuriousMind Also, my other question was also closed because I had mentioned chatgpt, so I needed to create another question. This is really hard to get any help on this forum, I am telling you. – Winston Apr 30 '23 at 00:10

1 Answers1

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Now let's add some entanglement.

Suppose that whenever you measure Sphere 1 from the front and Sphere 2 from above, or vice versa, the measurements remain highly anticorrelated. However, if you measure both from the front they become almost entirely uncorrelated.

Try explaining that with a classical picture. (Hint: Bell's Theorem guarantees that you can't.)

WillO
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  • OK thanks for your answer. This is a part of the experimental results I was missing. So results are more correlated in QM than would be expected in a classical depiction such as the one I suggested? – Winston Apr 29 '23 at 23:40
  • However I would like to understand what you mean here : are you saying that whatever axis you use for both particles measurement, you obtain a high correlation? Or are you saying both cases exist? – Winston Apr 29 '23 at 23:41
  • @Winston: If you would like to understand what I mean, one way to do that would be read what I wrote. Here is a more extreme version: When you view both spheres from above they are perfectly anticorrelated. When you view one from above and one from the front, they are anticorrelated 98% of the time. When you view both from the front they are anticorrelated 2% of the time. Bell's Theorem tells you that no classical model can fit those data. The fact that you were able to write down an example of an unentangled system has no bearing on the question of whether entangled systems exist. – WillO Apr 30 '23 at 01:54
  • ok, I won't continue with conversation, not because you gave clear explanations that helped me understand the problem at hand but because you are disagreeable and I don't like wasting my time with people like you. – Winston Apr 30 '23 at 02:23