Bimetric gravity

Summary

Bimetric gravity is a class of theories of gravity that use two metric tensors on the same spacetime instead of one. In Rosen's bimetric theory of 1940 the second metric is a fixed flat background. In the modern bimetric theory of Hassan and Rosen both metrics are dynamical and interact through a potential. The modern theory is closely related to massive gravity: it describes one massless and one massive graviton and avoids the Boulware–Deser ghost.