Research on conspiracy theories has largely focused on belief formation, exposure, and diffusion, while paying less attention to how their meanings change over time. This gap persists partly because conspiracy-related terms are often treated as stable lexical markers, making it difficult to separate genuine semantic changes from surface-level vocabulary changes. In this paper, we measure the semantic structure and evolution of conspiracy theories in online political discourse. Using 169.9M comments from Reddit's r/politics subreddit spanning 2012--2022, we first demonstrate that conspiracy-related language forms coherent and semantically distinguishable regions of language space, allowing conspiracy theories to be treated as semantic objects. We then track how these objects evolve over time using aligned word embeddings, enabling comparisons of semantic neighborhoods across periods. Our analysis reveals that conspiracy theories evolve non-uniformly, exhibiting patterns of semantic stability, expansion, contraction, and replacement that are not captured by keyword-based approaches alone.

翻译：关于阴谋论的研究主要聚焦于信念形成、接触和传播，而较少关注其含义随时间的变化。这一研究空白部分源于阴谋论相关术语常被作为稳定的词汇标记处理，导致难以区分真正的语义变化与表层词汇变化。本文旨在测量网络政治话语中阴谋论的语义结构与演化过程。基于Reddit平台r/politics子论坛2012-2022年间1.699亿条评论数据，我们首先证明阴谋论相关语言在语言空间中形成连贯且可语义区分的区域，从而可将阴谋论视为语义对象。继而通过对齐词向量追踪这些语义对象随时间的变化，实现不同时期语义邻域的比较分析。研究发现：阴谋论呈非均匀演化态势，展现出关键词分析方法无法捕捉的语义稳定性、扩张、收缩与替代模式。