In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.
Q: Julian Schwinger developed a scheme in which these operators can be determined in terms of the operators of two uncoupled harmonic oscillators for a spin one half particle. The Clebsch-Gordan coefficients are used when adding these quantities, and the commutators of its orbital operators are proportional to the Levi-Civita symbol, while its eigenvalues are proportional to h-bar. Noethers Theorem derives the conservation of this quantity from invariance under rotation, and Keplers Second Law is a consequence of the conservation of this. In general, it is conserved in the absence of external torques. This is, FTP what physical quantity, often symbolized L, that equals the cross product of position and momentum
A:
Science