[Paper Review] Comment on 'Non-realism: deep thought or soft option?', by N. Gisin

Michael J. W. Hall|ArXiv.org|Sep 1, 2009

Quantum Mechanics and Applications4 references3 citations

TL;DR

This paper argues that N. Gisin's definition of 'locality' in his critique of non-realism is formally and empirically equivalent to local realism, undermining his claim that Bell inequality violations necessitate nonlocality. By showing that Gisin's 'locality' assumption is equivalent to a local deterministic (realistic) model, the paper concludes that his argument presupposes realism from the start, and thus 'local non-realism' remains a viable interpretation of quantum mechanics.

ABSTRACT

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.

Motivation & Objective

• To demonstrate that Gisin's so-called 'locality' assumption is logically equivalent to local realism, thereby undermining his claim that Bell inequality violations imply nonlocality.
• To challenge the widespread use of the term 'quantum nonlocality', arguing it is misleading and obscures the distinction between no-signalling and separability.
• To advocate for clearer terminology in foundational quantum mechanics, proposing 'separability' instead of 'locality' and 'quantum nonseparability' instead of 'quantum nonlocality'.
• To reinforce the viability of local non-realistic models—such as standard quantum mechanics—as a simpler, more natural explanation of Bell correlations than nonlocal or hidden-variable theories.
• To emphasize that no-signalling and separability are distinct concepts, and that the latter is not entailed by the former, thus preserving local non-realism as a coherent interpretation.

Proposed method

• Prove a theorem showing that any model satisfying Gisin's equation (1) — a joint probability distribution with local parameters — is formally equivalent to a local deterministic (realistic) model.
• Construct a transformation from a probabilistic local model (equation 1) into a deterministic model using uniformly distributed random variables α and β to simulate stochastic outcomes.
• Demonstrate that the resulting deterministic model reproduces the same joint probabilities as the original probabilistic model, proving equivalence.
• Use the principle of Occam’s razor to argue that local non-realistic models (like standard quantum mechanics) are preferable to nonlocal or hidden-variable alternatives.
• Reframe foundational debates by distinguishing 'no-signalling' (no superluminal communication) from 'separability' (existence of local causal models), showing they are logically independent.
• Propose a new terminology: replace 'local realism' with 'local determinism', 'quantum nonlocality' with 'quantum nonseparability', and define 'locality' as equivalent to no-signalling.

Experimental results

Research questions

• RQ1 Is Gisin's definition of 'locality' truly independent of realism, or does it implicitly assume local realism?
• RQ2 Can Bell inequality violations be explained without invoking nonlocality, if 'locality' is redefined to exclude realism?
• RQ3 Why is the term 'quantum nonlocality' misleading, and what conceptual confusion does it perpetuate in foundational physics?
• RQ4 What is the logical and physical distinction between no-signalling and separability in the context of quantum correlations?
• RQ5 Is there a physically and conceptually preferable interpretation of quantum mechanics that preserves locality while rejecting realism?

Key findings

• Gisin's 'locality' assumption (equation 1) is formally and empirically equivalent to local realism, as any such model can be recast as a local deterministic model using auxiliary random variables.
• The existence of a local deterministic model is logically equivalent to the existence of a model satisfying Gisin's equation (1), meaning that 'locality' in his sense already presupposes realism.
• Therefore, Gisin's conclusion that Bell violations imply nonlocality is invalid, since his argument assumes local realism from the outset.
• The term 'quantum nonlocality' is misleading and should be replaced with 'quantum nonseparability' to avoid implying faster-than-light influences or action at a distance.
• Standard quantum mechanics is a local, nonseparable, and nonrealistic model — it satisfies no-signalling but violates separability, making it a viable local non-realistic explanation of Bell correlations.
• The distinction between no-signalling and separability is crucial; no-signalling does not entail separability, and thus local non-realism remains a logically consistent and simpler interpretation than nonlocal realism.