标题： 广义相对论作为一种混合理论：爱因斯坦关于运动问题工作的起源 显示英文标题

标题： General Relativity as a Hybrid theory: The Genesis of Einstein's work on the problem of motion

摘要： 在本文中，我描述了爱因斯坦早期在广义相对论（GR）运动问题上的工作起源：即是否可以直接从爱因斯坦场方程推导出受引力作用的物质的运动。 在回答这个问题时，爱因斯坦本人始终更倾向于真空方法：尝试从真空爱因斯坦方程推导物质的测地线运动。 论文首先探讨了为什么爱因斯坦对能量-动量张量及其在GR中的作用如此怀疑。 通过利用此前未知的爱因斯坦与乔治·尤里·莱尼奇之间的通信，我逐步展示了他关于真空方法的工作是如何产生的，以及他追求统一场论的探索如何影响了他对GR的解释。 我表明，爱因斯坦从一开始就将GR视为一种混合理论：就引力而言是基本且正确的，但在解释物质方面则是现象学和有效的。 因此，爱因斯坦将GR中的能量-动量张量和奇点视为尚未实现的物质理论的占位符。 他更倾向于奇点的原因是，他希望它们的数学处理能为所寻求的物质理论提供一些线索，这个理论将能够充分反映物质的量子特性。 显示英文摘要

摘要： In this paper I describe the genesis of Einstein's early work on the problem of motion in general relativity (GR): the question of whether the motion of matter subject to gravity can be derived directly from the Einstein field equations. In addressing this question, Einstein himself always preferred the vacuum approach to the problem: the attempt to derive geodesic motion of matter from the vacuum Einstein equations. The paper first investigates why Einstein was so skeptical of the energy-momentum tensor and its role in GR. Drawing on hitherto unknown correspondence between Einstein and George Yuri Rainich, I then show step by step how his work on the vacuum approach came about, and how his quest for a unified field theory informed his interpretation of GR. I show that Einstein saw GR as a hybrid theory from very early on: fundamental and correct as far as gravity was concerned but phenomenological and effective in how it accounted for matter. As a result, Einstein saw energy-momentum tensors and singularities in GR as placeholders for a theory of matter not yet delivered. The reason he preferred singularities was that he hoped that their mathematical treatment would give a hint as to the sought after theory of matter, a theory that would do justice to quantum features of matter.