It is briefly demonstrated that Gisin's so-called 'locality' assumption [arXiv:0901.4255] is in fact equivalent to the existence of a local deterministic model. Thus, despite Gisin's suggestions to the contrary, 'local realism' in the sense of Bell is built into his argument from the very beginning. His 'locality' assumption may more appropriately be labelled 'separability'. It is further noted that the increasingly popular term 'quantum nonlocality' is not only misleading, but tends to obscure the important distinction between no-signalling and separability. In particular, 'local non-realism' remains firmly in place as a hard option for interpreting Bell inequality violations. Other options are briefly speculated on.
It is briefly demonstrated that Gisin's so-called 'locality' assumption [arXiv:0901.4255] is in fact equivalent to the existence of a local deterministic model. Thus, despite Gisin's suggestions to the contrary, 'local realism' in the sense of Bell is built into his argument from the very beginning. His 'locality' assumption may more appropriately be labelled 'separability'. It is further noted that the increasingly popular term 'quantum nonlocality' is not only misleading, but tends to obscure the important distinction between no-signalling and separability. In particular, 'local non-realism' remains firmly in place as a hard option for interpreting Bell inequality violations. Other options are briefly speculated on.
The problem of the existence of nonlocal effects in Quantum Mechanics is discussed. The problem is divided in two: the first ('soft') one is to explain the violation of Bell's inequalities as a statistical magnitude. This can be achieved by a simple model within non-Boolean Locality and Realism. This result shows that quantum non-Locality as a consequence of the statistical violation of Bell's inequalities is inexistent. The second ('hard') problem is to explain the violation as it is calculated from series of detection outcomes. L.Sica has demonstrated that, in order to violate Bell's inequalities, the series recorded at (say) Bob when the setting at station Alice is alfa, can be different from the series that would have been recorded at Bob if that setting had been alfa'instead. Therefore, non-Locality in the series of detection outcomes does exist. It cannot be experimentally verified because of its counterfactual nature, but is observed in computer simulations. An appropriate computer code is based on the simple model mentioned plus a contextual instruction. It explains 'how' (Sica's) non-Locality arises, and solves the hard problem. 'Why' the contextual instruction exists is explained by Hellwig and Kraus' postulate of covariant quantum state collapse. In consequence, (Sica's) non-Locality is not in contradiction with Relativity but, quite the opposite, it is implied by Relativistic covariance.
Abstract Seminal for the raising of the quantum information age and quintessential for a deep understanding of nature, Bell inequality violations are known for having provided a profound disruption to classical models of the physical world. Yet, their meaning is still debatable nowadays. An important point under dispute in this context concerns the relevance of realism. While some believe that a Bell inequality violation implies the manifestation of nonlocal aspects, others defend that it is the notion of realism that should be abandoned. The purpose of the present work is to shed some light on the matter by employing a formal definition of (ir)realism. Our strategy consists of (i) rephrasing Bell’s assumption of local causality in terms of more primitive hypotheses and (ii) assessing where the fundamental difficulties emerge when using the quantum formalism. We analyze the question posed in the title using two distinct approaches and assert that a positive answer is justifiable. Nevertheless, even in this scenario, it becomes evident that violations of locality cannot be avoided. As a byproduct of our approach, the connections of (ir)realism with both quantum steering and entanglement are also discussed.
It is generally assumed that {\em local realism} represented by a noncontextual and local hidden-variables model in d=4 such as the one used by Bell always gives rise to CHSH inequality ∣⟨B⟩∣≤2. On the other hand, the contraposition of Gisin's theorem states that the inequality ∣⟨B⟩∣≤2 for arbitrary parameters implies (pure) separable quantum states. The fact that local realism can describe only pure separable quantum states is naturally established in hidden-variables models, and it is quantified by G(a,b)=4[⟨ψ∣P(a)⊗P(b)∣ψ⟩−⟨ψ∣P(a)⊗1∣ψ⟩⟨ψ∣1⊗P(b)∣ψ⟩]=0 for any two projection operators P(a) and P(b). The test of local realism by the deviation of G(a,b) from G(a,b)=0 is shown to be very efficient using the past experimental setup of Aspect and his collaborators in 1981.
Bell's theorem is 50 years old. Still there is a controversy about its implications. Much of it has its roots in confusion regarding the premises from which the theorem can be derived. Some claim that a derivation of Bell's inequalities requires just locality assumption, and nothing more. Violations of the inequalities are then interpreted as ``nonlocality'' or ``quantum nonlocality''. We show that such claims are unfounded and that every derivation of Bell's inequalities requires a premise -- in addition to locality and freedom of choice -- which is either assumed tacitly, or unconsciously, or is embedded in a single compound condition (like Bell's ``local causality''). The premise is equivalent to the assumption of existence of additional variables which do not appear in the quantum formalism (in form of determinism, or joint probability for outcomes of all conceivable measurements, or ``additional causes`'', or ``hidden variables'', ``complete description of the state'' or counterfactual definiteness, etc.). A certain irony is that perhaps the main message of violation of Bell's inequalities is that our notion of locality should be based on an operationally well-defined no-signalling condition, rather than on local causality.
Local realism reduces to the proposition that every physical effect arises exclusively at the spacetime locality where the determinate properties of physical reality determine that it be so. The causal model of quantum theory, however, and thus all prospects for quantum computers, require that local realism is false. The essential argument favoring quantum beliefs is that local realism cannot explain empirical Bell violations, whereas quantum theory can. By contrast, the article cited below offers compelling evidence to the contrary. Furthermore, such alleged refutations of local realism are predicated on an interpretation of the Bell inequality that many researchers reject (the cited article provides specific references). Meanwhile, the causal model of quantum theory reduces to the quantum formalism itself, which distributes outcomes across separate localities without providing enough information to determine what those outcomes are. More specifically, depending on subtleties of interpretation, the quantum formalism requires either: (A) There exists a bit of physical information such that this bit exists as mutually exclusive states, or (B) there exists a bit of physical information such that this bit is not physically informed. They are both contradictions. Pick your poison. Or reconsider local realism. See ** http://vixra.org/abs/1704.0078 ** Local Realism Explains Bell Violations (author Andrew P. Yake) - for a demonstration that all empirical evidence taken to support quantum theory over local realism plausibly does the reverse. The article comprises 8 pages, 4 figures, 6 equations, 32 references, 1 graph of testable predictions, and 2 paragraphs that purport to expose how the Bell inequality misrepresents the local realistic predictions for the EPR experiment. Thoughtful feedback appreciated (apyake@gmail.com).
Quantum non-locality has become a popular term. Yet, its precise meaning, and even its mere existence, is the subject of controversies. The main cause of the controversies is the never ending discussion on the appropriate definitions of Locality and Realism in the derivation of Bell's inequalities. On the other hand, Louis Sica derived Bell's inequalities from the hypothesis that time series of outcomes observed in one station do not change if the setting in the other (distant) station is changed. The derivation is based on arithmetical properties of time series only; it does not involve the definitions of Locality, Realism and probabilities, and is valid for series of any length. An important consequence is that violation of Bell's inequalities implies the series recorded (at the same time) in one station to be different if the setting in the other station is changed. This result gives precise meaning to the idea of quantum non-locality, and also makes evident why using it for faster than light signaling is impossible (because the difference is between factual and counter-factual series). Finally, it is demonstrated that series of outcomes, even if they violate Bell's inequalities, can be always embedded in a set of factual and counter-factual data that does hold to Bell's inequalities. Loosely speaking, the factual world may be quantum or not, but the union of factual and counter-factual worlds is always classical.