From my naive understanding of Einstein theory of relativity: gravity is not a force but only a consequence of inertia in a world where mass deforms the space-time. Without time, no gravity is possible.
Imagine, a mad scientist managed to reverse time! Time is now running backward at exactly the same rate but opposite rate (if that means anything) as before. People are still free to behave in ways that differ from what that've done in the past though.
How is gravity affected by this change in time direction? Is gravity negative (in the sense that objects are getting repulsing each others) or is gravity unchanged?