To answer a stupid question: "What makes you think there is gravity in the empty space of the universe[?]"
Well, as the force goes on into infinity, by definition, the force exerted by gravity permeates the entire universe.
Agobot writes:
How could you state that as a fact?
Go look up what a scientific fact, and you'll understand how. Barring that our localized space is some sort of special case for the rest of the universe (something about as unlikely as me barrier jumping through the wall), we assume that the rest of the universe follows the rules that we do. So, to answer your question, we state that as a fact because thinking otherwise would be pointless.
And the Ignorant shall fall to the Squirrels - Chip 2:54