matter attracts gravitationally, not repel.
Right... I was thinking of Dark Energy

About 22% (of the universe) is thought to be composed of dark matter. The remaining 74% is thought to consist of dark energy.

Dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe.
That's from wikipedia... just thought I'd look it up right quick. Most of it's just theory though.

How do you do that quote thing saying who it's from?