  In general relativity, an idealized distant observer is situated at future
null infinity where light rays emitted from the source approach. This article
concerns conserved quantities such as mass, energy-momentum, angular momentum,
and center of mass at future null infinity. The classical definitions of Bondi
mass at future null infinity ascertains the mass radiated away in gravitational
waves distinctively. However, the same question for other conserved quantities
such as angular momentum has been a subtle issue since the discovery of
"supertranslation ambiguity" in the 1960's. Recently, new definitions of
angular momentum and center of mass were proposed and proved to be free of such
ambiguity [12,14]. These new definitions arise as limits of the Chen-Wang-Yau
quasilocal conserved quantities, which are based on the theory of optimal
isometric embedding and quasilocal mass of Wang-Yau. It is the purpose of this
note to discuss these recent developments
