My story at its final stages is based around K3 civilizations whose technologies are within the known laws of physics and for plot reasons have managed to control all superclusters and lone galaxies within their region of space (500 million light years to 2 billion light years)
With all their methods of collecting stars and storing their matter in supermassive black holes they are still only able to collect the smallest fraction of matter in their local area. As dark matter and dark energy is a mysterious component these will remain a mystery but there is still a massive portion of known matter available to collect.
My previous questions have answered many problems including how to move black holes and how to collect quasar energy but other than creating a massive Bussard ramjet net/scoop to collect the available matter I cant think how this matter along the galactic filaments and cluster/galaxy edges can be collected?
One idea I had which feels completely hopeless and pointless is sending super or ultra massive blackholes along these galactic filaments on route to the nearest galaxies and feed off what matter they can in their path, when they reach the end of their path at the nearest galaxy they are slowed down by particle beams and sent off to collect more matter on the path to the next galaxy, all paths will be monitored and controlled by branch of the K3 civilization in that area.
Is this method possible or even worth doing as the energy needed to slow the black hole on arrival may be more than what is collected on the journey or are there other solutions to be explored?