Electromagnetic and gravitational radiation in all dimensions: A classical field theory treatment

Abstract

Abstract How long does a light bulb shine in odd dimensional flat spacetimes, according to a distant observer? This question is non-trivial because electromagnetic and gravitational waves, despite being comprised of massless particles, can develop tails: they travel inside the light cone. To this end, I attempt to close a gap in the literature by first deriving, strictly within classical field theory, the real-time electromagnetic dipole and gravitational quadrupole energy and angular momentum radiation formulas in all relevant dimensions. The even dimensional case, where massless signals travel strictly on the null cone, depends on the time derivatives of the dipoles and quadrupoles solely at retarded time; whereas the odd dimensional ones involve an integral over their retarded histories. Despite the propagation of light inside the null cone, however, I argue that a monochromatic light bulb of some intrinsic duration in odd dimensions remains approximately the same apparent duration to a distant detector, though the tail effect does produce a phase shift and adds to the signal several transitory non-oscillatory inverse square roots in time. Analogous remarks apply to a distant gravitational wave detector hearing from a finite duration quasi-periodic quadrupole source.