Is the speed of gravity instant? By the speed of gravity, I'm not talking about acceleration.
What I mean is something like this: If I take a vacuum, for example, and put in two objects of the same size, shape, and mass, exactly 1 light year apart. In this vacum, no other objects exist anywhere. Therefore, these two objects will have gravity towards each other. How long will it take before the force of gravity to start acting? One year, (as it's the speed of light) or instantly?
Under both conditions, I have question expanding on them.
If it is instant, then could we theoretically have a machine sensitive enough to pick up gravity of objects outside of our observable universe?
If it's not, then what would happen if an object with high enough gravity (Like super-super-super massive black hole) were to suddenly enter our observable universe. Then would we be hugely affected? What would happen?