内在视角：嵌入的观察者能（不能）学到什么？
The View from Within: What Can Embedded Observers (Not) Learn?
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中文总结 AI 辅助
本文利用经典粒子玩具模型研究嵌入观察者的认知局限，发现其存在认知视界，预测时视界更严重，可重复测量学习更受限，还重现了Spekkens知识平衡原理。
中文摘要 AI 辅助
物理学通常从第三人称视角开展，仿佛世界是从外部被描述的。然而，观察者本身就是其所观察世界中的物理系统。本文我们利用经典粒子的玩具模型研究这种张力。观察者是物理系统，其特征在于：（i）一个显变量，其值构成了它们的经验记录；（ii）就绪态，提供初始信息。我们询问这类观察者（主体）通过与另一系统（客体）建立关联的相互作用，能从世界中学到什么。对于关于过去、未来或两者的三类学习、显变量和就绪态的每种组合，我们确定主体能学到的内容。这表明，即使模型是经典且确定性的，许多主体仍面临认知视界——对其能从世界中学到的内容的限制。例如，具有完整显变量（其本体态为经验记录）和部分初始信息的主体，最多能学到客体一半的变量，这重现了Spekkens的知识平衡原理，即海森堡不确定性原理的类似物。更普遍地，我们发现主体预测时面临的认知视界比回溯时更严重，且通过可重复测量进行的学习可能比单独预测或回溯更有限。我们的工作提供了语言和工具，以研究超越本文所研究的玩具模型时第一人称视角与第三人称视角的差异，并邀请从嵌入观察者的角度解释量子理论中的固有不确定性。
英文摘要
Physics is usually done from a third-person perspective, as if the world were described from outside. Yet, observers are themselves physical systems within the world they observe. Here, we investigate this tension using a toy model of classical particles. Observers are physical systems characterised by a choice of (i) a manifest variable, whose value constitutes their empirical record, and (ii) ready states, which provide initial information. We ask what such observers (subjects) can learn about the world through interactions that establish a correlation with another system (the object). For each combination of the three types of learning (about the past, the future, or both), manifest variables, and ready states, we determine what the subject can learn. This shows that many subjects face an epistemic horizon---a limitation to what they can learn about the world---even though the model is classical and deterministic. For example, a subject with a complete manifest variable---one whose ontic state is the empirical record---and partial initial information can learn at most half the object's variables, recovering Spekkens' knowledge-balance principle, i.e. an analogue of Heisenberg's uncertainty principle. More generally, we find that subjects face more severe epistemic horizons when predicting than when retrodicting, and that learning by repeatable measurements can be more limited than either prediction or retrodiction alone. Our work provides language and tools to study how the first-person perspective can differ from the third-person perspective beyond the toy model studied here, and invites explanations of the inherent uncertainty in quantum theory from the standpoint of embedded observers.
