  Force-free electrodynamics (FFE) is a closed set of equations for the
electromagnetic field of a magnetically dominated plasma. There are strong
arguments for the existence of force-free plasmas near pulsars and active black
holes, but FFE alone cannot account for the observational signatures, such as
coherent radio emission and relativistic jets and winds. We reformulate FFE as
the effective field theory of a cold string fluid and initiate a systematic
study of corrections in a derivative expansion. At leading order the effective
theory is equivalent to (generalized) FFE, with the strings comprised by
magnetic field line worldsheets. Higher-order corrections generically give rise
to non-zero accelerating electric fields ($\mathbf{E}\cdot \mathbf{B}\neq 0$).
We discuss potential observable consequences and comment on an intriguing
numerical coincidence.
