Is the spin in quantum entanglement set the moment the particles are separated, instead of transmitted instantaneously to its twin particle at the time of measurement? Wouldn't this make more sense then particles transmitting information instantly across a large distance faster than the speed of light? Couldn't the superposition collapse at the time of separation leaving both particles frozen with the same spin, momentum, polarization, ect no matter where they are taken or what happens to them?

Could this tie in with "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete' ? A. Einstein, B. Podolsky AND N. Rosen, Institute for Advanced Study, Princeton, New Jersey (Received March 25, 1935) ".

I very well could be something I'm missing, I don't have a degree in Quantum Physics, yet, and I'm only a Senior in High School, but Quantum Physics is something that I am very interested in. I have had this question for a few years now, and have not found anything on the subject. Now I am writing a research paper on the subject for an English class, but I can't find anything directly mentioning my question.

One fault in my research could be the fact that I do not understand much of the math, due to my level being Calculus, but I would really like this answered. It would be great if I could get a link to the research or proof against or for my argument.

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    $\begingroup$ The particle spins are correlated the instant they're created, but their spins are not set then, that's not consistent with Bell's theorem (which is a proven mathematical theorem). No information is transmitted between the particles. BTW, your question would be more readable if you break it up into paragraphs. $\endgroup$
    – PM 2Ring
    Commented Nov 11, 2018 at 20:46
  • $\begingroup$ @PM2Ring alright, I will work on the readability. If entanglement doesn't pass information such as spin, momentum, polarization, ect, then what is QE about? And, I believe you about where you said "particle spins are correlated the instant they're created, but their spins are not set then", but could I have some proof or cite or something? I'm writing a research paper and that would help me. Thank you! $\endgroup$
    – Clint
    Commented Nov 11, 2018 at 20:54
  • $\begingroup$ en.wikipedia.org/wiki/Copenhagen_interpretation and links to other interpretations there $\endgroup$
    – user65081
    Commented Nov 11, 2018 at 20:58
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    $\begingroup$ Do a search for Bell's theorem, or Bell inequalities. There are many posts on that topic on this site. $\endgroup$
    – PM 2Ring
    Commented Nov 11, 2018 at 21:00
  • $\begingroup$ @PM2Ring Thank you, that is really interesting. I had not come upon any research done by bell yet. But his explanation, required determinism to not break relativity, or to go faster than the speed of light. With determinism, doesn't the absence of free will mean that the spin/polarization were determined already before the two were measured instead of when the function collapsed? That all is very interesting, and I may be misinterpreting it, but it seems as if it supports my hypothesis instead of disproving it? $\endgroup$
    – Clint
    Commented Nov 11, 2018 at 21:10

2 Answers 2


Is the spin in quantum entanglement set the moment the particles are separated...?

If this is asking whether the outcomes of eventual spin-measurements are predetermined at the moment the particles are separated, then the answer is no. We know this because (for example) the CHSH inequality is violated in the real world. The CHSH inequality is reviewed in detail in an another post: https://physics.stackexchange.com/a/438137/206691. It doesn't use any quantum theory at all, and the math is relatively easy. That same post also lists a few references about experiments demonstrating that this seemingly-unviolatable inequality really is violated in the real world. (The CHSH inequality is one of the simplest examples of a Bell inequality.)

...transmitted instantaneously to its twin particle at the time of measurement...

Quantum theory accounts for the observed results without invoking any kind of faster-than-light communication. In fact, the impossibility of faster-than-light communication is built into the general principles of quantum field theory, which is the foundation for our current understanding of all non-gravitational phenomena. Quantum field theory is designed to respect the constraints of special relativity, and it correctly predicts the observed results in experiments with entangled particles.

Quantum theory manages to predict the results of such experiments without using either pre-determined measurement outcomes or faster-than-light communication, and the way it achieves this is interesting. I don't have a clear-and-concise-and-nonmathematical way to describe how quantum theory does this. However, learning about the CHSH inequality and its real-world violations is a great place to start, because these things can be learned independently of quantum theory, and they will help build a better appreciation for why something like quantum theory is needed.

  • $\begingroup$ Thank you so much! That is a really good exploitation! I will study the CHSH inequality. I'm also really interested about the way Quantum theory manages to predict these things. Anyway, thank you! $\endgroup$
    – Clint
    Commented Nov 11, 2018 at 21:19
  • $\begingroup$ So does the violation of the CHSH inequality, and the same violations in bells paper mean that the EPR paper was right? $\endgroup$
    – Clint
    Commented Nov 11, 2018 at 21:33
  • $\begingroup$ @Clint I'm not sure I've ever read the original EPR paper. If their conclusion was something like "quantum theory predicts these weird correlations, and those predictions are absurd, therefore quantum theory can't be right", then they were right about the first part ("quantum theory predicts these weird correlations") but not about the other parts. The predictions are empirically correct, and therefore they cannot be absurd. $\endgroup$ Commented Nov 11, 2018 at 21:43

To be fair, we must clarify that Dan Yand answer is implicitly assuming locality, that is, that it is not possible that quantum mechanics is the result of local hidden variables that have determined values. By "local" we mean that the laws that govern the interactions of these hidden variables do not have an "action at a distance" (https://en.wikipedia.org/wiki/Action_at_a_distance"). However it has been shown (https://en.wikipedia.org/wiki/De_Broglie%E2%80%93Bohm_theory) that if you allow non-local interactions, the state of the system could be in a definite state in the sense you meant.


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