A safe guess
The speed of gravity
From the tip of a knife and that hand's impulse lies the speed of sound. From the light of the Sun as detected by one's eye and its true position 20 arc seconds into the future sits gravity not as a concept but as a force. This force is said to propagate anywhere from the speed of accelerated charge emission to that of infinity outside the bound of logic. I would like to say that gravity has a finite speed but cannot. To do so would disrupt the angular momentum between two or more planets. This is a realm of science where analogies must be let alone.