Abstract

A mirror world consisting of matter which interacts with ordinary matter via gravity and weakly via other forces has been considered, inter alia, as a model for dark matter. A discrete symmetry under the interchange of fields means that both sectors experience the same forces. Separately it has been shown that it is possible to unify gravitation and electromagnetism by using a degenerate metric in five dimensions; in this theory there are two possible representations of charge, and there is a reflection symmetry between them which, along with a gauge-like invariance, achieves the unification. Here it is shown that mirror matter arises naturally out of the degenerate theory, and as a result a new means for measuring the Brans–Dicke constant is obtained.