The Fimbulbomb was one of the most potentially disastrous events in all of history. Though civilizations had crumbled, the threat of the Fimbulbomb was beyond question.
After the Downfall, society had been thrown into chaos. In this confusion, people grasped for whatever power they could get. Of particular note was the Initiates of Fimbulb. This cult sprang up, revering The Other, and all of its agents that had previously been seen. One of their primary beliefs was that the Other was attempting to wipe humanity clean so it could create a better world. This was their motivation for constructing the Fimbulbomb. It involved the gathering of many trans-dimensional elements, and a complex design that is still not fully understood. It is theorized that The Other,facilitated their acquisition of the knowledge required. In any case, by 510 PRE they had managed to assemble the complete bomb.
The Fimbulbomb simple needed to be cast into The Rift, and it would greatly expand the tear, effectively merging the two worlds completely. Such an event would have killed every living thing in both universes, and in fact, would not leave much in the way of organized matter whatsoever. The cultists believed this would give The Other a clean slate to recreate the world. Some seemed to believe The Other would save them, so they would exist in this new world, others simply thought that this was worth sacrificing humanity.
The Fimbulbomb was hidden on one of Alice Express Transrift Travel's transports. The Prestigous company had been rebuilt since the Downfall, and was handling a large amount of traffic, so the bomb went through in the mass of vehicles. The reformed Galactic Council had discovered that this bomb was being deployed, so they ordered all transit through the gate to cease. This was a huge bureaucratic nightmare, with significant economic and political ramifications, and transit did not cease in time. Agents actively trying to find the bomb failed to locate it. Only intervention from the Elonatha stopped the bombs detonation. We are all very thankful for their help.
Since the bomb never detonated, the Univereses remained separate and intact. The Initiates of Fimbulb, previously thought to be a mostly harmless, if insane, group before, started being hunted down and eliminated. Currently, there are no known members of the cult, though they still perform some acts that show the order was not completely wiped out. Strict security measures were put into place in order to regulate traffic through the gate, generally inconveniencing everyone involved.