Graham's Universe

Graham's Universe is a universe that is unimaginably big. It is the size of Graham's Number, or G64 light years. Don't ask how big Graham's Number is. Graham's Universe is mainly composed of black holes, as if you tried to imagine the size of the universe, your brain would collapse into a black hole, as the universe is too big to comprehend. Superclusters are rarely found and are considered mythical in a GU; although, Galactic Filaments (such as the Hercules Corona Borealis Great Wall), Great Walls, globular clusters and quasars are quite common, they're not on par with black holes.

GUs are formed when multiple universes in a multiverse, or a megaverse, combine. Since a GU is the size of Graham's Number, you would need a Graham's Number of universes to form one. This is only possible in a megaverse and not in a multiverse. The ages of each universe is amalgamated together; if 2 universes that are 500 years old are joined, the final universe would be 1000 years old. How the universes combine is similar to a black hole joining with another; two universes will pull each other into each others' gravity until it turns into one, much bigger universe. This will send gravitational ripples strong enough to rip apart multiple universes across The Box. This also explains why GUs are usually rare.

A GU reaching the age of Graham's Number will immediately collapse, similar to a supernova, in 2 attoseconds. The explosion will be unbelievably violent; more violent than a Big Rip or the Big Crunch. Two less violent explosions will appear where the center of the GU was located and leave a disc residue. A universe can form here, although it's unlikely.