Relating Wigner's Friend Scenarios to Nonclassical Causal Compatibility, Monogamy Relations, and Fine Tuning
arXiv:2309.12987 · doi:10.22331/q-2024-09-26-1485
Abstract
Nonclassical causal modeling was developed in order to explain violations of Bell inequalities while adhering to relativistic causal structure and faithfulness -- that is, avoiding fine-tuned causal explanations. Recently, a no-go theorem that can be viewed as being stronger than Bell's theorem has been derived, based on extensions of the Wigner's friend thought experiment: the Local Friendliness (LF) no-go theorem. Here we show that the LF no-go theorem poses formidable challenges for the field of causal modeling, even when nonclassical and/or cyclic causal explanations are considered. We first recast the LF inequalities, one of the key elements of the LF no-go theorem, as special cases of monogamy relations stemming from a statistical marginal problem. We then further recast LF inequalities as causal compatibility inequalities stemming from a nonclassical causal marginal problem, for a causal structure implied by well-motivated causal-metaphysical assumptions. We find that the LF inequalities emerge from this causal structure even when one allows the latent causes of observed events to admit post-quantum descriptions, such as in a generalized probabilistic theory or in an even more exotic theory. We further prove that no nonclassical causal model can explain violations of LF inequalities without violating the No Fine-Tuning principle. Finally, we note that these obstacles cannot be overcome even if one appeals to cyclic causal models, and we discuss potential directions for further extensions of the causal modeling framework.
16+5 pages, 9 figures. Accepted in Quantum
References in corpus (37)
- Bell nonlocality
- Quantum correlations with no causal order
- Probabilistic theories with purification
- The lesson of causal discovery algorithms for quantum correlations: Causal explanations of Bell-inequality violations require fine-tuning
- How Quantum Mechanics can consistently describe the use of itself
- Quantum theory cannot consistently describe the use of itself
- Quantum causal modelling
- Beyond Bell's Theorem: Correlation Scenarios
- A strong no-go theorem on the Wigner's friend paradox
- Quantum common causes and quantum causal models
- Information-Theoretic Implications of Quantum Causal Structures
- Theory-independent limits on correlations from generalised Bayesian networks
- Quantum nonlocality, Bell inequalities and the memory loophole
- The Inflation Technique for Causal Inference with Latent Variables
- Experimental test of local observer-independence
- General probabilistic theories: An introduction
- Foundations of Structural Causal Models with Cycles and Latent Variables
- Causal Compatibility Inequalities Admitting Quantum Violations in the Triangle Structure
- A Robust Mathematical Model for Clauser-Horne Experiments, With Implications for Rigorous Statistical Analysis
- Quantum Inflation: A General Approach to Quantum Causal Compatibility
- Cyclic Quantum Causal Models
- Quantum computation with indefinite causal structures
- Stable Facts, Relative Facts
- Estimating outflow masses and velocities in merger simulations: impact of r-process heating and neutrino cooling
- Elemental and tight monogamy relations in nonsignalling theories
- The Inflation Technique Completely Solves the Causal Compatibility Problem
- Classical causal models for Bell and Kochen-Specker inequality violations require fine-tuning
- Perfect signaling among three parties violating predefined causal order
- A "thoughtful" Local Friendliness no-go theorem: a prospective experiment with new assumptions to suit
- Experimental nonclassicality in a causal network without assuming freedom of choice
- A general framework for cyclic and fine-tuned causal models and their compatibility with space-time
- Classical causal models cannot faithfully explain Bell nonlocality or Kochen-Specker contextuality in arbitrary scenarios
- Bell Inequalities for Continuously Emitting Sources
- Analysing causal structures in generalised probabilistic theories
- Witnessing Non-Classicality in a Simple Causal Structure with Three Observable Variables
- A Combinatorial Solution to Causal Compatibility
- Wigner's friend's memory and the no-signaling principle