On Extracting Physical Content from Asymptotically Flat Space-Time Metrics

Understand

A major issue in general relativity, from its earliest days to the present, is how to extract physical information from any solution or class of solutions to the Einstein equations.

• Though certain information can be obtained for arbitrary solutions, e.g., via geodesic deviation, in general, because of the coordinate freedom, it is often hard or impossible to do.
• Most of the time information is found from special conditions, e.g., degenerate principle null vectors, weak fields close to Minkowski space (using coordinates close to Minkowski coordinates) or from solutions that have symmetries or approximate symmetries.
• In the present work we will be concerned with asymptotically flat space times where the approximate symmetry is the Bondi-Metzner-Sachs (BMS) group.