EPR and Non-Locality - For and Against

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Discussion Overview

The discussion centers around the concept of non-locality in quantum mechanics (QM) and its implications, particularly in relation to quantum field theory (QFT) and Bell's theorem. Participants explore whether QM necessitates non-locality, the definitions and interpretations of non-locality, and the relationship between entanglement and superposition. The scope includes theoretical arguments, interpretations of experimental results, and the philosophical implications of these concepts.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants argue that QM does not require non-locality, citing the cluster decomposition property of QFT as a foundational aspect that prevents violations of locality.
  • Others contend that the term "non-locality" lacks a single well-defined meaning, which complicates discussions and interpretations of QM and its implications.
  • One participant expresses disagreement with the conflation of entanglement and superposition, asserting that they are fundamentally different concepts.
  • Some participants highlight that while QFT is constructed to be local, experimental results, particularly those related to Bell inequalities, suggest that non-locality may be a necessary interpretation of entangled systems.
  • There is a discussion about the nature of correlations in entangled systems, with some arguing that correlation does not imply influence, while others assert that the correlations observed in experiments indicate a form of non-locality.
  • Participants express concern that discussions may devolve into semantic arguments, which could detract from the substantive physics involved.

Areas of Agreement / Disagreement

Participants generally do not reach consensus on the necessity of non-locality in QM. Multiple competing views remain, with some advocating for the necessity of non-locality based on experimental evidence, while others maintain that QM can be understood without invoking non-locality.

Contextual Notes

Discussions reveal limitations in definitions and assumptions surrounding non-locality and locality, as well as the implications of entanglement. The debate also touches on the philosophical aspects of measurement and the interpretation of quantum states.

  • #151
I am not educated in QM, so this post is to ask a few questions related the the non-locality/entanglement controversy for which I am hoping for a simple answer.

As I understand an example of the entanglement part, what appears to two observers is two partcles having a combined propery that their spin directions are opposite. If there are two devices far apart, each positionsed to test spin with respect to the same axis direction. When each of these two particles arrive at its target device, its spin will be determined, and when both spins are determined it will be found that they have opposite spins.

Assume that there is a clock associated with each device, and the clock times are synchronized, so that the determination of each measured spin is associated with a specific time.

Assume the two devices are separated by a distance D, and that the two times related to the devices determining a spin value differ by a time T. Therefore this result might be interpreted as the the ealier spin determination influences the later spin determination and the influence traveled at a speed of D/T, and the configuration might well be that D/T > c.

I think I understand that the transmission of influence does not in any way permit an observer to predict the spin of the second particle before the particle arrives at its devise.

My question is the following. Does the influence from the location of one device determining a spin value and the second devise determining a spin value constitute a transmission of information? That is, is influence information? Also ,is this a controversial question?

If one defines the transmission of influence to NOT be a transmission of information, then no information has traveled faster than c. Would this mean that there is not any non-locality issue? If not, why not?
 
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  • #152
Buzz Bloom said:
Does the influence from the location of one device determining a spin value and the second devise determining a spin value constitute a transmission of information?

Not by any definition of "information" that I am aware of.

Buzz Bloom said:
If one defines the transmission of influence to NOT be a transmission of information, then no information has traveled faster than c. Would this mean that there is not any non-locality issue?

As I have said umpteen times now in this thread, it depends on what you mean by "non-locality". There is not a single accepted meaning for that term. So questions like this do not have single well-defined answers.
 
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  • #153
Since we are going in circles this thread is closed. In the future, everyone please remember to be clear about what you mean by ambiguous terms
 

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