The Epkyrotic Genesis is when two Branes collide and create a sea of subatomic particles and microscopic ripples which lead ultimately to the formation of galaxies. Time is local and relative within a universe so these can seem, from an outside observer, to be instantaneous.
It is known that universes can exist in close proximity and also overlap, either through the use of technology or magic (like Lament Pillars) but dimensional chiasmata can occur between mature universes “naturally”. These may spark the creation of a new novel universe, perhaps containing characteristics of both.
Forcing the collision of two or more branes may be a cataclysmic event, however. In ages long past, the Irisians were adept at using their universe seeding technology (the Continuum Forge) and avoiding cataclysmic events. They would monitor the development of these universes as a gardener tends to a well planted flower bed. Using the Forge, they could create, modify and destroy entire universes, mostly without consideration to what was within (and inadvertently creating Refugees and possibly the genesis of the Chaos Engineers).