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.

中文翻译：

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将维格纳的朋友场景与非经典因果相容性、一夫一妻制关系和微调联系起来


开发非经典因果模型是为了解释违反贝尔不等式的情况，同时坚持相对论因果结构和“忠实性”——也就是说，避免微调因果解释。最近，基于维格纳朋友思想实验的扩展，推导出了一个可以被视为比贝尔定理更强的禁行定理：局部友好性（LF）禁行定理。在这里，我们表明，即使考虑非经典和/或循环因果解释，LF 不可行定理也给因果建模领域带来了巨大的挑战。我们首先将 LF 不等式（LF 不可行定理的关键要素之一）重新定义为源于统计边际问题的一夫一妻制关系的特例。然后，我们进一步将 LF 不等式改写为源于“非经典”因果边际问题的因果相容性不等式，其因果结构是由动机良好的因果形而上学假设所隐含的。我们发现，即使当观察到的事件的潜在原因允许后量子描述时，例如在广义概率理论或更奇特的理论中，低频不等式也会从这种因果结构中出现。我们进一步证明，$no$ 非经典因果模型可以在不违反“无微调”原则的情况下解释对 LF 不等式的违反。最后，我们注意到，即使诉诸“循环”因果模型，这些障碍也无法克服，并且我们讨论了因果建模框架进一步扩展的潜在方向。