When Newton proposed his original mechanics, he had point particles exerting forces at each other instantaneously over great distance. Many people, including him, were bothered by this. According to special relativity changes in the gravitational field (ie: [gravity wave]?s propagate at the same speed as those in the electromagnetic field, i.e. light.
[Tom Van Flandern]? argues that it is at least 2 x 10 10 times the speed of light, according to the [Lorentz Relativity]? theory, a competitor to Einstein's special relativity.