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arxiv: 2502.02461 · v2 · pith:2ZP6NRMFnew · submitted 2025-02-04 · 🪐 quant-ph

An extended Wigner's friend no-go theorem inspired by generalized contextuality

Laurens Walleghem , Lorenzo Catani This is my paper

Pith reviewed 2026-05-23 03:53 UTC · model grok-4.3

classification 🪐 quant-ph
keywords Wigner's friendno-go theoremcontextualityquantum foundationsabsoluteness of observed eventsnoncontextual agencylocal friendliness
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The pith

Quantum theory is incompatible with Absoluteness of Observed Events and Noncontextual Agency in the Noncontextual Friendliness scenario.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper introduces the Noncontextual Friendliness no-go theorem. It establishes that quantum theory cannot be consistent with both Absoluteness of Observed Events, the requirement that observed outcomes are singular and objective, and Noncontextual Agency, a principle that weakens noncontextuality by restricting only certain agency correlations in prepare-and-measure scenarios. The construction draws an analogy between Bell nonlocality proofs and generalized contextuality proofs to replace Local Agency with this weaker condition. A reader would care because the result is presented as generalizing the Local Friendliness theorem while being stronger than generalized noncontextuality no-gos, provided the scenario can be realized. The entire inconsistency holds only conditionally on experimental realizability of the scenario in quantum theory.

Core claim

The Noncontextual Friendliness no-go theorem demonstrates the inconsistency of quantum theory with the joint assumptions of Absoluteness of Observed Events and Noncontextual Agency. This generalizes the Local Friendliness no-go theorem and, granted that the scenario can be realized, is stronger than no-go theorems based on generalized noncontextuality.

What carries the argument

Noncontextual Agency, a weaker version of noncontextuality that constrains only the agency of agents in the scenario in a manner analogous to how Local Agency weakens local causality, applied within the Noncontextual Friendliness scenario.

If this is right

  • If the Noncontextual Friendliness scenario is realized, quantum theory must violate at least one of Absoluteness of Observed Events or Noncontextual Agency.
  • The theorem applies whenever the scenario can be implemented and thereby extends the reach of the Local Friendliness result.
  • It yields a stronger constraint than no-go theorems that rely only on generalized noncontextuality, once realization is granted.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The prepare-and-measure structure may allow similar weakenings of other assumptions in Wigner's friend scenarios without invoking full locality.
  • Focus on laboratory realization of the scenario would directly test the conditional inconsistency stated in the theorem.
  • The analogy to contextuality proofs could be used to derive no-gos in additional prepare-and-measure variants of extended Wigner's friend setups.

Load-bearing premise

The Noncontextual Friendliness scenario can be realized experimentally in quantum theory.

What would settle it

An experimental implementation of the Noncontextual Friendliness scenario in which quantum predictions remain consistent with both Absoluteness of Observed Events and Noncontextual Agency.

Figures

Figures reproduced from arXiv: 2502.02461 by Laurens Walleghem, Lorenzo Catani.

Figure 1
Figure 1. Figure 1: (a) Bell scenario; (b) Bell scenario as a [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: Local Friendliness setup [18]. from which one can obtain the empirical probabil￾ities ℘(a, b|x, y), ℘(a, d|x, y), ℘(c, b|x, y), ℘(c, d|x, y) via marginalisation. Assumption 2 (Local Agency). No-signalling outside the future light cone, which would be verified by a hypo￾thetical agent with access to all the relevant variables, still holds even if it cannot be verified by a single agent. The above formulatio… view at source ↗
Figure 4
Figure 4. Figure 4: Operational Friendliness setup. a stronger version of no-signalling, Operational Agency is a stronger version of standard operational equivalence. In the context of the setup considered here, standard opera￾tional equivalence pertains to setting choices. More pre￾cisely, they are about the preparations associated with choices x = 0 and x = 1: p(d|x, y = 0) = p(d|y = 0) and p(b|x, y = 1) = p(b|y = 1). Opera… view at source ↗
Figure 5
Figure 5. Figure 5: (a): A LF scenario (top) can be seen as a Bell scenario (bo [PITH_FULL_IMAGE:figures/full_fig_p009_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: The figure represents the preparations and [PITH_FULL_IMAGE:figures/full_fig_p010_6.png] view at source ↗
read the original abstract

The renowned Local Friendliness no-go theorem demonstrates the incompatibility of quantum theory with the combined assumptions of Absoluteness of Observed Events - the idea that observed outcomes are singular and objective - and Local Agency - the requirement that the only events correlated with a setting choice are in its future light cone. Granted that the Local Friendliness scenario can be realized, this result is stronger than Bell's theorem because the assumptions of Local Friendliness are weaker than those of Bell's theorem: Local Agency is less restrictive than local causality, and Absoluteness of Observed Events is encompassed within the notion of realism assumed in Bell's theorem. Drawing inspiration from the correspondence between nonlocality proofs in Bell scenarios and generalized contextuality proofs in prepare-and-measure scenarios, we present the Noncontextual Friendliness no-go theorem. This theorem demonstrates the inconsistency of quantum theory with the joint assumptions of Absoluteness of Observed Events and Noncontextual Agency, the latter being a weaker version of noncontextuality, in the same way that Local Agency is a weaker version of local causality. Our result generalizes the Local Friendliness no-go theorem and, granted that the scenario can be realized, is stronger than no-go theorems based on generalized noncontextuality.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The paper introduces the Noncontextual Friendliness no-go theorem, demonstrating the inconsistency of quantum theory with the joint assumptions of Absoluteness of Observed Events and Noncontextual Agency (a weaker version of noncontextuality, analogous to how Local Agency weakens local causality). It claims this generalizes the Local Friendliness theorem and, granted realizability of the scenario, is stronger than no-go theorems based on generalized noncontextuality, drawing on the correspondence between Bell and prepare-and-measure contextuality proofs.

Significance. If the central result holds, the work provides a new bridge between Wigner's friend scenarios and generalized contextuality, extending the Local Friendliness theorem with weaker assumptions than standard noncontextuality no-gos. This could strengthen arguments against certain realist interpretations in quantum foundations, particularly if the Noncontextual Friendliness scenario admits a quantum realization that preserves the relevant operational equivalences.

major comments (1)
  1. [Abstract / main theorem] Abstract (final sentence) and main theorem statement: the claim that the result 'is stronger than no-go theorems based on generalized noncontextuality' is explicitly conditional on the Noncontextual Friendliness scenario being realizable in quantum theory (i.e., existence of a prepare-and-measure quantum model satisfying the operational equivalences that define Noncontextual Agency while still permitting friend-like observations). No explicit construction, circuit, or existence proof for such a realization is referenced, rendering the comparative strength assertion unverified and load-bearing for the paper's central positioning relative to prior work.
minor comments (1)
  1. Notation for Noncontextual Agency and the scenario definition should be introduced with explicit operational equivalences early in the text to allow readers to verify the weakening relative to standard noncontextuality.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for highlighting this important point regarding the presentation of our result. We address the major comment below.

read point-by-point responses

  1. Referee: Abstract (final sentence) and main theorem statement: the claim that the result 'is stronger than no-go theorems based on generalized noncontextuality' is explicitly conditional on the Noncontextual Friendliness scenario being realizable in quantum theory (i.e., existence of a prepare-and-measure quantum model satisfying the operational equivalences that define Noncontextual Agency while still permitting friend-like observations). No explicit construction, circuit, or existence proof for such a realization is referenced, rendering the comparative strength assertion unverified and load-bearing for the paper's central positioning relative to prior work.

    Authors: The abstract already qualifies the comparative claim with the explicit proviso 'granted that the scenario can be realized', rendering the assertion of greater strength conditional on the existence of a suitable prepare-and-measure quantum model. The manuscript's primary contribution is the derivation of the Noncontextual Friendliness no-go theorem, which establishes an inconsistency between quantum theory and the joint assumptions of Absoluteness of Observed Events and Noncontextual Agency; this generalizes the Local Friendliness theorem by weakening Local Agency to Noncontextual Agency in direct analogy with the weakening from local causality to Local Agency. The positioning relative to generalized noncontextuality no-go theorems is offered as a potential strengthening, conditional on realizability, and is motivated by the established correspondence between Bell and prepare-and-measure contextuality scenarios. We agree that an explicit construction or existence proof would strengthen the comparative claim. In the revised manuscript we will add a dedicated paragraph in the discussion section elaborating on the operational equivalences required for Noncontextual Agency and outlining how a quantum realization might be constructed within the prepare-and-measure framework, while reiterating that the strength comparison remains conditional. revision: partial

Circularity Check

0 steps flagged

No significant circularity; derivation is self-contained under stated assumptions

full rationale

The paper presents a no-go theorem generalizing Local Friendliness via a Noncontextual Friendliness scenario, showing inconsistency of quantum theory with Absoluteness of Observed Events and Noncontextual Agency. The abstract explicitly qualifies the 'stronger than generalized noncontextuality' claim as holding only 'granted that the scenario can be realized,' but the derivation itself does not reduce any result to a fitted parameter, self-definition, or load-bearing self-citation. No equations or steps in the provided text exhibit the patterns of self-definitional equivalence, fitted inputs renamed as predictions, or ansatz smuggled via prior author work. The result is framed as a conditional logical implication from quantum theory plus the listed assumptions, making it self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on quantum theory being correct, the definition of Absoluteness of Observed Events, and the newly introduced Noncontextual Agency; no free parameters or invented entities are mentioned in the abstract.

axioms (2)
  • domain assumption Quantum theory correctly describes the prepare-and-measure scenario under consideration
    The theorem demonstrates inconsistency between quantum predictions and the two assumptions.
  • domain assumption Absoluteness of Observed Events holds
    Explicitly listed as one of the two joint assumptions shown to be incompatible with quantum theory.

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Forward citations

Cited by 2 Pith papers

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  2. Limits of Absoluteness of Observed Events in Timelike Scenarios: A No-Go Theorem

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    Quantum mechanics violates a causal inequality derived from absoluteness of observed events plus axiological time symmetry and no retrocausality in timelike scenarios, even under a weakened operational version of abso...

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