Logically, of course, there cannot be a negative force! Likewise there is no such thing as positive or negative electricity! There is a surplus of electrons or of protons. End of!
Gravity is said to be an effect of mass. It is, but it is a negation of another force and is not an example of gravitons or gravity waves! The mass of the body intercepts and diminishes the universal pressure of the zero point energy that we may find omni-present in the universe. The Casimir effect, demonstrates the pressure and the recent findings that gravity theory is under review because of the misplacement of Voyagers, indicating that there is a repulsive force acting upon them also supports this idea.
A way of understanding this is the well known phenomenon at sea, of two vessels within sight of one another. as they each block the current and wave action on the side more angled away from the other, they creep towards one another, all other things being equal, as they seldom are!
Have fun with this concept! If there is a way of distinguishing the difference between a positive gravity force and a measurement of the Casimir effect, at present considered only to be a short range effect, then you may be a recipient of a Nobel!