Cosmere

The "Cosmere" is part of a "unified field theory" being developed by Dr. Koppel Schleppen that is, generously put, yet to be fully developed.

In essence, as far as anyone else can seem to understand anyways, Dr. Koppel seems to be proposing that the known world is but a small part of a greater universe, with many, perhaps infinite, realms beyond the mundane reach or visibility of our own, and they themselves are only part of one plane of existence of which there are also many, perhaps infinite, numbers.

Dr. Koppel believes that he lives in but one world within what the Physics Department at Yalevard University calls the "Prime Material Plane", and that the Feywild is just one of a number of nearby planes of existence which may be infinite in number, or at least infinitely increasing in number - the nuance is lost on almost everyone.

In his less lucid and less sober moments, Dr. Koppel has been known to speculate that even the greater universe might exist simply within the minds of one or more greater beings whose powers are beyond mortal or even divine comprehension, and/or that the whole greater universe may be comprised of an immense multi-layered disc, with each disc being one plane of existence, which in turn rest upon the backs of four cosmic elephants who ride upon the back of a giant aquatic turtle eternally swimming through a void of non-existence. In the past, whenever he began to speculate on same, his wife of the time would tell him to "get off [his] lazy ass off the couch and do something useful for a change."