We are sitting in a black hole and the only way out is to the other universe. So we already have as much mass in the universe as is needed this is proven by the fact that nothing falls upon anything. Space and mass are balanced though space is increasing so it weakens the gravitational force between the galaxies, yet they remain in symmetry. The point of departure into the other universe is stargate or portal. By annihilating the space we could let the universe collapse upon itself thus generating the portal from where to make an exit.
The eternal black hole leads to enough space within itself that matter though could travel but never escape it hence we cannot exit the universe unless we create a wormhole between two spaces and let the matter disappear from one and enter the event horizon of the other. Still, the symmetry of the universe is maintained as according to Einstein–Rosen bridges. There must be a separate white hole interior region that allows us to extrapolate the trajectories of particles that an outside observer sees rising up away from the event horizon. So we are transferring the matter from within the white hole interior regions which we inhabit in the universe.
So either we annihilate space or create Einstein-Rosen bridges to make interstellar travel possible but either maintains the symmetry of the multiverse.