Angular momentum of isolated systems in general relativity

Abstract

This article is a conceptual discussion, for non-specialists, of what appears to be a satisfactory solution to the problem of treating angular momentum for isolated radiating systems in general relativity. The approach is a development of one suggested by Penrose, based on twistor theory. While in special relativity angular momentum is a simple tensorial object, in general relativity it acquires components in other representations of the Lorentz group as well. Remarkably, these other components may be identified with the gravitational radiation. Thus special-relativistic angular momentum and gravitational radiation are two parts of one entity, the general-relativistic angular momentum.