Quasilocal conservation laws in cosmology: A first look

Abstract

Quasilocal definitions of stress-energy-momentum-that is, in the form of boundary densities (in lieu of local volume densities)-have proven generally very useful in formulating and applying conservation laws in general relativity. In this Essay, we take a basic look into applying these to cosmology, specifically using the Brown-York quasilocal stress-energy-momentum tensor for matter and gravity combined. We compute this tensor and present some simple results for a flat FLRW spacetime with a perfect fluid matter source. We emphasize the importance of the vacuum energy, which is almost universally underappreciated (and usually "subtracted"), and discuss the quasilocal interpretation of the cosmological constant.