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、接触与扩散，而对它们含义随时间变化的关注较少。这一空白部分源于阴谋论相关术语常被视为稳定的词汇标记，从而难以区分真正的语义变化与表面上的词汇更替。在本文中，我们测量了在线政治话语中阴谋论的语义结构与演化。利用2012-2022年间来自Reddit子论坛r/politics的1.699亿条评论，我们首先证明阴谋论相关语言在语言空间中形成了连贯且可区分的语义区域，使得阴谋论可被视为语义对象。随后，我们使用对齐词嵌入追踪这些对象随时间的变化，从而能够对比不同时期的语义邻域。分析表明，阴谋论的演化是非均匀的，呈现出语义稳定、扩张、收缩与替换的模式，而这些模式无法单独通过基于关键词的方法捕捉。