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I have been discussing QM with a friend and wanted to explain why holding on to realism means we must accept non-locality.

Essentially I got hung up on explaining Bell's Theorem in simple words.

I have a decent picture in my head about the argument using three axes of spin separated by 120 degrees. However, I don't think this will be easy to explain. More importantly, it feels too abstruse since it uses spin rather than more familiar concepts. Is there a similar argument using locations or other elementary concepts?

Qmechanic
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Jeff Bass
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    If your friend has an attention span of at least 1 hour, I can highly recommend Mermin Am. J. Phys. 49(10) (1981), explained in this video. This is the simplest way I know. – A. P. Dec 24 '20 at 02:11
  • The title asks for a way to show that superposition is necessary, which is more challenging than merely ruling out local or noncontextual hidden variables. Is ruling out noncontextual hidden variables sufficient? If so, then you might consider the CHSH inequality, which is super-easy to derive. Experimental demonstrations that it's violated typically use photon polarization, and the concept of polarization should be familiar to anybody who's played around with the lenses that fell out of their polarizing sunglasses. – Chiral Anomaly Dec 24 '20 at 02:23
  • why holding to non-realism would avoid non-locality? –  Dec 24 '20 at 04:18
  • I support the reading of Mermin's Quantum Mysteries. It is an exceptional read that requires no background but having one leads to greater appreciation – Orion Yeung Dec 24 '20 at 17:39

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There are a couple of different things mentioned in this question: superposition and Bell's theorem.

  1. The most obvious phenomenon that is highly suggestive of superposition (although does not prove it strictly speaking) is the double slit experiment, specifically the appearance of the interference pattern.

  2. For a short and highly accessible at the popular level exposition of Bell's theorem, I recommend this six minute video by Looking Glass Universe: https://youtu.be/z-s3q9wlLag. There she explains the theorem and proves it in another video: https://youtube.com/playlist?list=PLg-OiIIbfPj2RNY2-tYO2JsR9uw7Rw22z.

ReasonMeThis
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