User:Astro interest/Wang-Yau quasilocal mass

The Wang-Yau quasilocal mass was formulated by Mu-Tao Wang and Shing-Tung Yau in 2009.

Background
In classical physics, mass may be defined as the bulk integral of some density function over a spatial region (a line segment, area, volume, etc.). However, this formulation breaks down when general relativity is introduced. Einstein's equivalence principle implies that a mass density cannot be defined for gravitation under the axioms of general relativity. There is no single universal definition of "mass" in general relativity; however, different formulations and models are useful in different contexts. It is possible to define a total mass under sufficiently symmetric conditions by the flux integral to infinity over an asymptotically flat spacetime. In the 1950s and 1960s, the ADM energy-momentum was developed for a system viewed at spatial infinity and Bondi energy-momentum for a system viewed at null infinity. Thus a mass could be defined by simply taking the Minkowski norm of the energy-momentum 4-vector.