Multiple Imaging by Gravitational Waves

Gravitational waves act like lenses for the light propagating through them. This phenomenon is described using the vector formalism employed for ordinary gravitational lenses, which was proved to be applicable also to a non{stationary spacetime, with the appropriate modi cations. In order to have multiple imaging an approximate condition analogous to that for ordinary gravitational lenses must be satis ed. Certain astrophysical sources of gravitational waves satisfy this condition, while the gravitational wave background, on average, does not. Multiple imaging by gravitational waves is, in principle, possible, but the probability of observing such a phenomenon is extremely low. To appear in Int. J. Mod. Phys. D