The Omega War
Omega Particles are a mysterious type of particle about which very little is known. They either cause or are created by the Rifts and emanate from them in great number. Omega particles can bond with living humans, thereby creating Omegas.
Omega particles have a certain frequency, which seems to resonate with the world they currently occupy. They change frequencies when passing between worlds, and take anyone or anything they have bonded with along. Particles from the same rift share some kind of quantum lock and always assume the same frequency, so when one Omega passes through a Rift, all Omegas bound to him or her immediately follow.
Omega particles can be detected by an Omega Scanner, invented by among others Professor Logan Blackwolf.