In theoretical physics and quantum physics, a graviphoton or gravivector is a hypothetical particle which emerges as an excitation of the metric tensor (i.e. gravitational field) in spacetime dimensions higher than four, as described in Kaluza–Klein theory. However, its crucial physical properties are analogous to a (massive) photon : it induces a "vector force", sometimes dubbed a " fifth force ". The electromagnetic potential A μ μ emerges from an extra component of the metric tensor g μ μ 5 , where the figure 5 labels an additional, fifth dimension.