What is Non-locality: Definition and 57 Discussions

In theoretical physics, quantum nonlocality refers to the phenomenon by which the measurement statistics of a multipartite quantum system do not admit an interpretation in terms of a local realistic theory. Quantum nonlocality has been experimentally verified under different physical assumptions. Any physical theory that aims at superseding or replacing quantum theory should account for such experiments and therefore must also be nonlocal in this sense; quantum nonlocality is a property of the universe that is independent of our description of nature.
Quantum nonlocality does not allow for faster-than-light communication, and hence is compatible with special relativity and its universal speed limit of objects. Thus, quantum theory is local in the strict sense defined by special relativity and, as such, the term "quantum nonlocality" is sometimes considered a misnomer. Still, it prompts many of the foundational discussions concerning quantum theory, see Quantum foundations.

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  1. heusdens

    Bell experiment would somehow prove non-locality and information FTL?

    The famous Bell experiment would somehow proof non-locality and/or traveling of information faster then light. A very simple explenation of the experiment is this: there is a subatomic event that creates a particle pair going opposite directions. The subatomic event determines the possible...
  2. B

    Locality and non-locality in period measurement

    consider the Doppler shift formula f=f'gamma(1+betacostheta). (1) the measurements of f and f' are associated with the measurement of time intervals, during which, depending on the scenario we follow, beta and theta could change. authors say that using (1) we make the "locality" assmption in...
  3. Q

    Proof of non-locality indep. of conservation law

    EPR argument makes use of conservation of momentum between two outgoing particles. Einstein boxes argument makes use of conservation of particle numbers. Anybody can tell me an experiment which proves that QM is non-local without invoking conservation law?
  4. F

    Reconciling Non-locality and Planck Time: Exploring the Limits of Causality

    How does instantanious action at a distance reconcile itself with Planck Time and the assumption that nothing can happen in this minuscule timescale? Does the transition from cause to effect not have a Planck time after the cause and before the effect? Could one describe a unit of Planck Time...
  5. R

    Exploring the Non-Locality of Quantum Entanglement

    In trying to grasp the Bell Theorem that "reality must be non-local" I have a question---what exactly does it mean to say that two physical objects are "local" vs "non-local" in their interactions ? In reading Nick Herberts book, (1985), Quantum Reality, he states that local interaction =...
  6. Ε

    Majority Opinion on Interpreting Bell's Theorem

    In this thread, I got a lot of different replies on exactly how to interpret Bell's theorem. Some suggested relativity must be wrong; others suggested Bell's inequality might not disprove locality, but some other assumption Bell made (such as an assumption based on the existence of a reality)...
  7. C

    Exploring the Nonlocality of Strings in Quantum Mechanics

    If particles are made out of strings then it seems to follow that strings are, or can be, both local and non-local. Is this correct? I haven't seen any discussion of the wave-particle nature of strings (or the property of strings that allows particles to be also waves) so I assume I'm wrong...
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