Spacetime Approach to Force-free Magnetospheres

Force-Free Electrodynamics (FFE) describes a magnetically dominated relativistic plasma, as expected to exist near pulsars and (some) supermassive black holes. Despite being fully covariant, FFE has primarily been studied in $3+1$ frameworks. We have instead taken a spacetime approach, focusing on observer-independent properties. In this talk I will describe some of the progress we have made with this approach, both new results and improved understanding of previous results. I will focus particularly on energy extraction from spinning conductors and black holes.