I mean in the amount of energy it has and in its size. That which is observable is apparently only a sub-universe. It seems to be limited only by physical laws, but even those laws could be different in other sub-universes.
I don't know about any differences. Particle physicists don't have much of an opinion on gravity and on uniting gravity with the other forces.
A proton and neutron can still have three quarks each with some of them being matter quarks and others being antimatter quarks. The strong and weak forces can be manifestations of gravity and electromagnetism at short scales, and electromagnetism could be a manifestation of gravity and anti-gravity, but particle physicists generally do not concern themselves with such ideas.
The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles possessing negative energy.
So we have nothingness as a sea of matter annihilations by antimatter (antimatter with negative energy, just like anti-gravity), but these annihilations are waiting to be, for now missing in action.
Since equal negative and positive energy cancel we can have as much of both as desired in empty space, as long as there is an additional bias to negative energy, so possibly empty intergalactic space can be seen as being slightly predominated with antimatter or antigravity.