Abstract: The definition of angular momentum in general relativity has been a subtle issue since the 1960s, due to the 'supertranslation ambiguity'.
In this talk, we will discuss how the mathematical theory of quasilocal mass and angular momentum leads to a new definition of angular
momentum at null infinity that is free of any supertranslation ambiguity.
This is based on joint work with Jordan Keller, Mu-Tao Wang, Ye-Kai Wang, and Shing-Tung Yau.