On negative refraction in classical vacuum

摘要

Propagation of light in a classical gravitational field can be successfully modelled as electromagnetic waves propagating in a bianisotropic medium. However, some care must be exercised when applying the conventional expressions for the electromagnetic energy density and the power flow in a bianisotropic medium. These expressions are shown to be components of a four-vector that is dual to the wave's 4-wavevector, the two 4-vectors themselves being parallel. The implications and status of claims for negative refraction in vacuum are discussed.