Quasilocal conservation laws in cosmology: a first look

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 first 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.