A New Twist

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Science  09 Oct 1998:
Vol. 282, Issue 5387, pp. 249
DOI: 10.1126/science.282.5387.249

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Mass, energy, and momentum are fundamental concepts in Newtonian physics. In Einstein's theory of general relativity, however, spacetime is itself a dynamic object, so how does one choose the fundamental quantities? In his Perspective, Visser discusses a new approach to defining one such quantity--angular momentum--recently published by Rizzi in Physical Review Letters.