Nonlocal Gravity: Damping of Linearized Gravitational Waves

In nonlocal general relativity, linearized gravitational waves are damped as they propagate from the source to the receiver in the Minkowski vacuum. Nonlocal gravity is a generalization of Einstein's theory of gravitation in which nonlocality is due to the gravitational memory of past events. That nonlocal gravity is dissipative is demonstrated in this paper within certain approximation schemes. The gravitational memory drag leads to the decay of the amplitude of gravitational waves given by the exponential damping factor exp (-t/\tau), where $\tau$ depends on the kernel of nonlocal gravity. The damping time $\tau$ is estimated for gravitational waves of current observational interest and is found to be of the order of, or longer than, the age of the universe.