同一个物理事件可以同时按因果和目的来理解

《你一生的故事》用费马原理引出两种看待物理事件的方式。按通常的因果语言，光到达水面以后改变方向；按变分原理，光走的是使总时间达到极值的路径，描述中已经包含起点和终点。

You’re used to thinking of refraction in terms of cause and effect: reaching the water’s surface is the cause, and the change in direction is the effect. But Fermat’s principle sounds weird because it describes light’s behavior in goal-oriented terms. It sounds like a commandment to a light beam: ‘Thou shalt minimize or maximize the time taken to reach thy destination.’ ” I considered it. “Go on.” “It’s an old question in the philosophy of physics. People have been talking about it since Fermat first formulated it in the 1600s; Planck wrote volumes about it. The thing is, while the common formulation of physical laws is causal, a variational principle like Fermat’s is purposive, almost teleological.” (Location 2058)

人习惯把动能、加速度这类瞬时量当作直观对象，于是容易把事件读成由过去推向未来的因果链。七肢桶直觉上把握的量要在一段时间里才有意义。它们要同时知道初始状态和最终状态，才谈得上那个需要被满足的极值条件。

I could understand that: the physical attributes that humans found intuitive, like kinetic energy or acceleration, were all properties of an object at a given moment in time. And these were conducive to a chronological, causal interpretation of events: one moment growing out of another, causes and effects creating a chain reaction that grew from past to future. In contrast, the physical attributes that the heptapods found intuitive, like “action” or those other things defined by integrals, were meaningful only over a period of time. And these were conducive to a teleological interpretation of events: by viewing events over a period of time, one recognized that there was a requirement that had to be satisfied, a goal of minimizing or maximizing. And one had to know the initial and final states to meet that goal; one needed knowledge of the effects before the causes could be initiated. I was growing to understand that, too. (Location 2150)

小说把同一个宇宙写成一句语法完全歧义的话。因果读法和目的论读法都有效，再多上下文也无法排除其中一个。

The physical universe was a language with a perfectly ambiguous grammar. Every physical event was an utterance that could be parsed in two entirely different ways, one causal and the other teleological, both valid, neither one disqualifiable no matter how much context was available. (Location 2219)

When the ancestors of humans and heptapods first acquired the spark of consciousness, they both perceived the same physical world, but they parsed their perceptions differently; the worldviews that ultimately arose were the end result of that divergence. Humans had developed a sequential mode of awareness, while heptapods had developed a simultaneous mode of awareness. We experienced events in an order, and perceived their relationship as cause and effect. They experienced all events at once, and perceived a purpose underlying them all. A minimizing, maximizing purpose. (Location 2221)

这里的目的论是小说对物理形式的解释，并不意味着光具有意志，也没有否定 古典因果决定论。两者的差别在观察的边界：拉普拉斯从某一刻的完整状态向前后推演，七肢桶则把整个时间区间作为一个同时成立的结构。

“基本定律时间对称”也不能直接推出日常世界没有方向。小说保留了这句：

Gary once told me that the fundamental laws of physics were time-symmetric, that there was no physical difference between past and future (Location 2170)

时间之矢在熵增加的方向上出现 记录的是另一层问题。基本方程可以时间对称，宏观过程仍会因熵增显出方向。两条放在一起，可以避免把小说里的同时意识误写成热力学结论。

费马最小时间原理是这篇小说的支点：光走的那条路，可以说成"每一步按折射定律走出来的"，也可以说成"为了用时最短而选的"。两套说法预测完全一致，无法用实验分开。

病菌的症状就是它的传播策略 是同一个动作在生物学里的样子：换一本账来记，同一个事实的性质就变了。 而 叫它刺还是叫它骨头，取决于你想不想吃这条鱼 说的是这种切换在日常语言里每天都在发生。

世界不是物体，是事件与关联 和 第一性质与第二性质：颜色气味是我们加上去的 提示了为什么会有这种自由度：越往下追，"物"身上那些看似自带的属性，越是关系和描述方式的产物。 ——收入 读书笔记 · 一得

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