system
Given the following post, respond as if you're commenting on Reddit:
human
Does gravity ever push?
gpt
No. Gravity is always attractive.

Gravity is mediated by a spin-2 particle.  For forces mediated by even-spin particles, the force is attractive if the product of the two interacting particles "charges" is positive, and the force is repulsive if the product is negative.  The gravitational "charge" is mass, and mass is always positive - thus, the product is always positive, and the force is always attractive.

If a particle with negative mass were to be discovered, however, this could change, and gravity could be repulsive.  There is no evidence of such particles as of now.