If our milkyway has a black hole and blackholes are very very common as science states that they are at the center of most galaxy's then is this analogy a good one.

lets say the universe is like our earths sea.
I go down to the beach and fill a bucket of water and the effect on earths sea is infinitly nothing. How ever it is fact that the sea now has one bucket of water less in it.

The point im trying to make is that if gravity is rotating stars on the outer edges of a milky way far from the pull of a black hole then is everything conected in the universe like our sea.

in other words it is seen as impossible for the stars on the outer edge of the milkyway to be purturbed by the blackholes gravity yet they are because they rotate around the spiral center. Is gravity more connected throughout the universe to the point where the universe itself is held togeather by the accumulation of all matter and its gravity similar to that of our milkyway? any good coments would be welcome.