关于卢埃林·托马斯1927年的论文和磁偶极子在电场中的“隐藏动量”，
Regarding Llewellyn Thomas's paper of 1927 and the "hidden momentum" of a magnetic dipole in an electric field
摘要：
L. H.托马斯在他1927年的论文《电子与轴的动力学》中解释了原子自旋轨道耦合中的二分之一反常因子是由于电子自旋轴的相对论性进动。托马斯的解释还要求电子的轨道平均或“长期”轨道和自旋角动量的总和是一个守恒量，正如他发现的两种可能的磁电子平移运动方程中的任何一种都是如此。托马斯的发现在目前的工作中被认为需要“隐藏的动量”在质子的库仑场中，电子的内禀磁矩可以从质子的平移运动方程中略去。省略隐藏的动量与标准现代电动力学文本的立场相反，并导致违反牛顿的作用和反作用定律，否定托马斯的结果。包括隐藏的动量导致线性动量守恒，但在托马斯岁差的存在下，总角动量一般不守恒。即使在没有外加磁场的情况下，自旋和轨道不对齐时的总角动量也会进动。正如托马斯所观察到的，长期角动量守恒是自旋轨道耦合和反常塞曼效应一致同时描述的必要条件，这在经典电动力学中是不可能的。
英文摘要：
L. H. Thomas, in his 1927 paper, "The Kinematics of an Electron with an Axis", explained the then-anomalous factor of one-half in atomic spin-orbit coupling as due to a relativistic precession of the electron spin axis. Thomas's explanation required also that the total of the orbit-averaged, or "secular", orbital and spin angular momenta of the electron be a conserved quantity, as he found to be the case for either of two possible equations of translational motion of the magnetic electron. Thomas's finding is seen in the present work to require the "hidden momentum" of the electron intrinsic magnetic moment in the Coulomb field of the proton be omitted from its equation of translational motion. Omission of the hidden momentum is contrary to the position of standard modern electrodynamics texts, and leads to violation of Newton's law of action and reaction, negating Thomas's result. Including the hidden momentum results in linear momentum conservation, but in the presence of Thomas precession, the total angular momentum is not generally conserved. The total angular momentum precesses for non-aligned spin and orbit, even in the absence of externally-applied magnetic field. As Thomas observes that secular angular momentum conservation is a necessary condition for a consistent simultaneous description of spin-orbit coupling and the anomalous Zeeman effect, such is not possible within classical electrodynamics in its absence.
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