Message passing is widely assumed to be a fundamental primitive of distributed systems. This paper argues that conventional message systems embed a category mistake: they misinterpret logical dependency relations as temporal propagation processes. This error arises from an implicit Forward-In-Time-Only (FITO) assumption, which treats causality as intrinsically directed along a temporal axis. We formalize FITO as the imposition of a partial order over events and show that clocks, scheduling, and message propagation are representational artifacts rather than ontological primitives. We then reformulate interaction in terms of symmetric constraint relations, identify the minimal substrate of interaction independent of temporal direction, and prove an equivalence theorem: under mild assumptions, a broad class of message-passing executions can be represented as constraint satisfaction problems, and conversely, constraint satisfaction instances can be realized as message-passing protocols. We connect the result to Lamport clocks, Hewitt actors, Pratt pomsets, category theory, relativity, and indefinite causal order, and interpret engineering consequences for reflective and reversible link architectures such as Open Atomic Ethernet.

翻译：消息传递被广泛认为是分布式系统的基本原语。本文论证传统消息系统隐含着一个范畴错误：它们将逻辑依赖关系错误地解释为时间传播过程。这一错误源于隐含的"仅向前时间"假设，该假设将因果关系本质视为沿时间轴定向。我们将FITO形式化为对事件施加偏序，并证明时钟、调度和消息传播是表征性产物而非本体论原语。随后我们基于对称约束关系重构交互作用，识别出独立于时间方向的交互最小基底，并证明一个等价定理：在温和假设下，一大类消息传递执行过程可表示为约束满足问题，反之，约束满足实例可实现为消息传递协议。我们将该结果与Lamport时钟、Hewitt参与者模型、Pratt偏序多集、范畴论、相对论及不定因果序相联系，并阐释其对反射式与可逆链路架构的工程影响，例如开放原子以太网。