Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Foundations of Physics

Wigner’s Diamond and the Quantum Fragmentation of Space-time

Jacques Pienaar

Published Mar 13, 2026• 2 citations
Publisher

Abstract

Abstract Recent no-go theorems on interpretations of quantum theory featuring an assumption of ‘Absoluteness of Observed Events’ (AOE) are shown to have an unexpectedly strong corollary: one cannot reject AOE and at the same time assume that the ‘observed events’ in question can all be (i) single-valued and (ii) embedded within a single background space-time common to all observers. Consequently, interpretations that reject AOE appear incompatible with a ‘block universe’ view of space-time.

DOI
10.1007/s10701-026-00915-z

Related papers

A single space-time is too small for all of Wigner's friends

Jacques Pienaar

Recent no-go theorems on interpretations of quantum theory featuring an assumption of `Absoluteness of Observed Events' (AOE) are shown to have an unexpectedly strong corollary: one cannot reject AOE and at the same time assume that the `observed events' in question can all be embedded within a single background space-time common to all observers. Consequently, interpretations that reject AOE appear incompatible with a `block universe' view of space-time.

arXiv:2312.11759•Dec 19, 2023•0 citations

QBism on Locality and Nonlocality

John B. DeBrota, Christopher A. Fuchs, Rüdiger Schack

Recently Pienaar (2026), building on work of Cavalcanti (2021), has shown that QBism cannot always assume distinct observers' quantum-measurement outcomes---say, of Wigner and his friend---are embedded in a single spacetime. This follows from QBism's rejection of the `Absoluteness of Observed Events' assumption in the Bong et al. no-go theorem. Thus, QBism has no choice but to treat the notion of spacetime every bit as personalistic as it treats quantum states and quantum measurement outcomes. In a way, this is not a surprise to QBists, as they have taken the notion of `personalist spacetimes' to be the ansatz most compatible with their other views since at least 2009. But it does enjoin us to finally make crystal clear the sense in which QBism is a purely local interpretation of quantum mechanics despite this new theorem and despite quantum theory's age-old violation of Bell's inequalities. With the extra clarity we also hope to poise QBism for a distinctly new way to approach issues at the interface of quantum theory and gravity.

quant-pharXiv:2608.05368•Aug 7, 2026•0 citations

Limits of absoluteness of observed events in timelike scenarios: A no-go theorem

Sumit Mukherjee, Jonte R. Hance

Wigner's Friend-type paradoxes challenge the assumption that events are absolute—that when we measure a system, we obtain a single result, which is not relative to anything or anyone else. These paradoxes highlight the tension between quantum theory and our intuitions about reality being observer independent. Building on a recent result that developed these paradoxes into a no-go theorem, namely, the , we introduce the , a time-ordered analog of it. In this framework, we replace the usual locality assumption with and show that, when combined with the assumptions of (AOE), , and , we obtain a Causal Time-Symmetric Friendliness inequality. We then show that quantum mechanics violates this inequality and is therefore incompatible with at least one of these assumptions. To probe which assumption might be incompatible, we then examine whether AOE in its entirety is essential for this no-go result. We propose a weaker, operational form of AOE that still leads to inequalities that quantum mechanics violates. This result shows that even under relaxed assumptions, quantum theory resists reconciliation with classical notions of absolute events, reinforcing the foundational significance of Wigner's Friend-type paradoxes in timelike scenarios.

arXiv:2510.26562•Physical Review Research•Mar 30, 2026•0 citations

No-go theorem based on incomplete information of Wigner about his friend

Zhen‐Peng Xu, Jonathan Steinberg, H. Chau Nguyen +1 more

The notion of measurements is central to many debates in quantum mechanics. One critical point is whether a measurement can be regarded as an absolute event, giving the same result for any observer in an irreversible manner. Using ideas from the gedanken experiment of Wigner's friend, it has been argued that, when combined with the assumptions of locality and no superdeterminism, regarding a measurement as an absolute event is incompatible with the universal validity of quantum mechanics. We consider a weaker assumption: Is the measurement event realized relatively to the observer when he only partially observed the outcome? We proposed a protocol to show that this assumption in conjunction with the natural assumptions of no superdeterminism and locality is also not compatible with the universal validity of quantum mechanics.

arXiv:2111.15010•Physical Review A•Feb 14, 2023•36 citations

A no-go theorem for absolute observed events without inequalities or modal logic

Nick Ormrod, Jonathan Barrett

This paper builds on no-go theorems to the effect that quantum theory is inconsistent with observations being absolute; that is, unique and non-relative. Unlike the existing no-go results, the one introduced here is based on a theory-independent absoluteness assumption, and there is no need to assume the validity of standard probability theory or of modal logic. The contradiction is derived by assuming that quantum theory applies in any inertial reference frame; accordingly, the result also illuminates a tension between special relativity and absoluteness.

arXiv:2209.03940•Sep 8, 2022•16 citations

A strong no-go theorem on the Wigner’s friend paradox

Kok-Wei Bong, Aníbal Utreras-Alarcón, Farzad Ghafari +5 more

Does quantum theory apply at all scales, including that of observers? New light on this fundamental question has recently been shed through a resurgence of interest in the long-standing Wigner’s friend paradox. This is a thought experiment addressing the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement. Here, by building on a scenario with two separated but entangled friends introduced by Brukner, we prove that if quantum evolution is controllable on the scale of an observer, then one of ‘No-Superdeterminism’, ‘Locality’ or ‘Absoluteness of Observed Events’—that every observed event exists absolutely, not relatively—must be false. We show that although the violation of Bell-type inequalities in such scenarios is not in general sufficient to demonstrate the contradiction between those three assumptions, new inequalities can be derived, in a theory-independent manner, that are violated by quantum correlations. This is demonstrated in a proof-of-principle experiment where a photon’s path is deemed an observer. We discuss how this new theorem places strictly stronger constraints on physical reality than Bell’s theorem. For a scenario of two separated but entangled observers, inequalities are derived from three fundamental assumptions. An experiment shows that these inequalities can be violated if quantum evolution is controllable on the scale of an observer.

arXiv:1907.05607•Nature Physics•Aug 17, 2020•224 citations
Abstract Recent no-go theorems on interpretations of quantum theory featuring an assumption of ‘Absoluteness of Observed Events’ (AOE) are shown to have an unexpectedly strong corollary: one cannot reject AOE and at the same time assume that the ‘observed events’ in question can all be (i) single-valued and (ii) embedded within a single background space-time common to all observers. Consequently, interpretations that reject AOE appear incompatible with a ‘block universe’ view of space-time.
Recently Pienaar (2026), building on work of Cavalcanti (2021), has shown that QBism cannot always assume distinct observers' quantum-measurement outcomes---say, of Wigner and his friend---are embedded in a single spacetime. This follows from QBism's rejection of the `Absoluteness of Observed Events' assumption in the Bong et al. no-go theorem. Thus, QBism has no choice but to treat the notion of spacetime every bit as personalistic as it treats quantum states and quantum measurement outcomes. In a way, this is not a surprise to QBists, as they have taken the notion of `personalist spacetimes' to be the ansatz most compatible with their other views since at least 2009. But it does enjoin us to finally make crystal clear the sense in which QBism is a purely local interpretation of quantum mechanics despite this new theorem and despite quantum theory's age-old violation of Bell's inequalities. With the extra clarity we also hope to poise QBism for a distinctly new way to approach issues at the interface of quantum theory and gravity.
Wigner's Friend-type paradoxes challenge the assumption that events are absolute—that when we measure a system, we obtain a single result, which is not relative to anything or anyone else. These paradoxes highlight the tension between quantum theory and our intuitions about reality being observer independent. Building on a recent result that developed these paradoxes into a no-go theorem, namely, the , we introduce the , a time-ordered analog of it. In this framework, we replace the usual locality assumption with and show that, when combined with the assumptions of (AOE), , and , we obtain a Causal Time-Symmetric Friendliness inequality. We then show that quantum mechanics violates this inequality and is therefore incompatible with at least one of these assumptions. To probe which assumption might be incompatible, we then examine whether AOE in its entirety is essential for this no-go result. We propose a weaker, operational form of AOE that still leads to inequalities that quantum mechanics violates. This result shows that even under relaxed assumptions, quantum theory resists reconciliation with classical notions of absolute events, reinforcing the foundational significance of Wigner's Friend-type paradoxes in timelike scenarios.
The notion of measurements is central to many debates in quantum mechanics. One critical point is whether a measurement can be regarded as an absolute event, giving the same result for any observer in an irreversible manner. Using ideas from the gedanken experiment of Wigner's friend, it has been argued that, when combined with the assumptions of locality and no superdeterminism, regarding a measurement as an absolute event is incompatible with the universal validity of quantum mechanics. We consider a weaker assumption: Is the measurement event realized relatively to the observer when he only partially observed the outcome? We proposed a protocol to show that this assumption in conjunction with the natural assumptions of no superdeterminism and locality is also not compatible with the universal validity of quantum mechanics.
This paper builds on no-go theorems to the effect that quantum theory is inconsistent with observations being absolute; that is, unique and non-relative. Unlike the existing no-go results, the one introduced here is based on a theory-independent absoluteness assumption, and there is no need to assume the validity of standard probability theory or of modal logic. The contradiction is derived by assuming that quantum theory applies in any inertial reference frame; accordingly, the result also illuminates a tension between special relativity and absoluteness.
Does quantum theory apply at all scales, including that of observers? New light on this fundamental question has recently been shed through a resurgence of interest in the long-standing Wigner’s friend paradox. This is a thought experiment addressing the quantum measurement problem—the difficulty of reconciling the (unitary, deterministic) evolution of isolated systems and the (non-unitary, probabilistic) state update after a measurement. Here, by building on a scenario with two separated but entangled friends introduced by Brukner, we prove that if quantum evolution is controllable on the scale of an observer, then one of ‘No-Superdeterminism’, ‘Locality’ or ‘Absoluteness of Observed Events’—that every observed event exists absolutely, not relatively—must be false. We show that although the violation of Bell-type inequalities in such scenarios is not in general sufficient to demonstrate the contradiction between those three assumptions, new inequalities can be derived, in a theory-independent manner, that are violated by quantum correlations. This is demonstrated in a proof-of-principle experiment where a photon’s path is deemed an observer. We discuss how this new theorem places strictly stronger constraints on physical reality than Bell’s theorem. For a scenario of two separated but entangled observers, inequalities are derived from three fundamental assumptions. An experiment shows that these inequalities can be violated if quantum evolution is controllable on the scale of an observer.