"Within the multiverse exist countless worlds or timelines, depends on how you look at it, which are connected to our own. The Rifts that are opening are the gates to these worlds. These other worlds are called Planes. Most are feral places to which humans are but aliens. Some are devoid of life. Other are teeming with... something else.
But those of most interest are those that do contain humans. We have found civilizations with histories so similar to our own it is... Unsettling... Yes a matter a fact you could encounter an alternate versions of yourself... We even found relics with the purpose to do so. I heard of some Associates who managed to confiscate such a relic from a carnival... No, I would not advise to do such a thing.
For secrecy and administrative purposes with give each explored world a number if those pose a threat or contain items of interests. Boring I know, but really how many different names can you make up for a timeline were the Napoleonic Empire is still standing or where humanity didn't advance past the Iron Age.
Some we do give names. And no, I won't tell you why."
Overview of Planes which are of Particular interest to The Association Edit
'Atlas' (Plane-0): Codename used by the Association to refer to their Plane of Origin.
'Eden': A hypothetical plane that is being sought after by members of various religions and cults. Apart from personal testimonies and scriptures the Association cannot confirm nor deny its existence.
'Elysium': A massive object in the orbit of 'Atlas' (and only Atlas as far as The Association is aware). The origins, age or even if this object is created by humans is unknown. Archaeologists have discovered references and drawings dating back of the age of the Hunter-Gatherers. Regardless, It inspired religions and scientists to reach for the heavens. Napoleon Bonaparte created the Academy d'aéronautique (1805) for the development of aircraft and even ordered the construction of a canon to fire manned shells at the structure, unfortunately this project was destroyed after his defeat at Leipzig in 1814 and the plans were never recovered. In 1825 the Comet II was launched, from the Tower of Babel Launch-platform in the Atlantic Ocean, but it disappeared mid-flight. Many believe this to be the cause of the appearance of the Rifts. wether there is a relationship between the Rifts and Elysium is considered unlikely. But its otherworldly qualities can not be denied.
'Hades' (Plane-54): The Plane is considered an Alpha-threat Biohazard due to the presence of P-54. For now it is believed only small pockets of uninfected humans remain in special shelters in some of this world's capitals. Surviving infected are probably insane and extremely dangerous. The Rift to Plane-54 is permanently guarded by volunteers with decontaminating- and other safety-equipment. Despite the risks Plane-054 contains vast knowledge on contagions, genetics and Biological Warfare. The few books recovered inspired new fields of study and might advance the Medical Sciences on Atlas by close to a century.