First, we examine how spin is treated in special relativity and the necessity of introducing spin supplementary conditions (SSC) and how they are related to the choice of a center-of-mass of a spinning particle. Next, we discuss quantum electrodynamics and the Foldy–Wouthuysen transformation which we note is a position operator identical to the Pryce–Newton–Wigner position operator. The classical version of the operators are shown to be essential for the treatment of classical relativistic particles in general relativity, of special interest being the case of binary systems (black holes/neutron stars) which emit gravitational radiation.

中文翻译：

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相对论引力和量子电动力学中的旋转，自旋和位置算符

首先，我们研究如何在狭义相对论中处理旋转，以及引入旋转补充条件（SSC）的必要性，以及它们与纺丝粒子的质心选择之间的关系。接下来，我们讨论量子电动力学和Foldy-Wouthuysen变换，我们注意到它们是与Pryce-Newton-Wigner位置算子相同的位置算子。事实证明，经典形式的算子对于广义相对论中经典相对论粒子的处理是必不可少的，特别令人关注的是发射重力辐射的双星系统（黑洞/中子星）的情况。