Gravity seminar - Abraham Harte Seminar

 

Almost all measurements of relativistic gravity rely in one way or another upon the behavior of light in curved spacetimes. Gravitational lensing has for example been developed into a routine observational tool, a fact which might lead one to conclude that much of a spacetime's geometry is encoded in the properties of electromagnetic fields. I will explain that this is actually false: Any given electromagnetic field is compatible with an enormous variety of spacetime metrics, whether in vacuum or even in a force-free plasma. Identifying these ambiguities unifies and explains a number of existing results in the literature, allows new solutions to be derived, and also old ones to be better understood. Another consequence is a trivial demonstration that electromagnetic and gravitational waves propagating in the same direction cannot interact.