Cosmology

The New Eberron cosmology follows the basics of the Eberron cosmology but expands on it some more. Eberron sits on the material plane, which is one of a myriad of planes of existence. Scholars speak of other planes of existence that orbit the material, or prime plane. On rare occasions, a plane comes so near to the material plane that it actually touches it, but not by literal means. Planes do not necessarily interact as if they're two solid objects colliding, instead they meld. This event is called a plane being Coterminous. At these times, it is possible to move freely between the Material Plane and the coterminous plane at certain locations on each plane. For example, when Fernia is coterminous to the material plane, a character can travel to Fernia by means of a volcano or any extremely hot fire. At the same time, this also means any creatures in Fernia can enter Eberron just as easily. It is also possible for the opposite to happen, and it is referred to as Remote. When a plane is remote, it is difficult to establish any connections at all between it and the Material Plane. When Fernia is remote, fire spells work less effectively and fire elementals are harder to summon. It is nearly impossible to reach a plane that is remote. There's also terms known as Waxing and Waning, which pertains to a plane coming closer to become coterminous, or drawing further and become remote.

The Astral Sea
Instead of space, the universe of Eberron sits on the ever expansive space known as the Astral Sea.The Astral Sea has air, so you do not need any spells or equipment to travel through it if you require breathe. It however does need a strong body to travel through. A creature that is below 10th level or with a challenge rating of 6 and below cannot stay in the Astral Sea by too long. The creature's body would start to deteriorate as if each matter and cell is beginning to separate from it. It takes damage equal to twice their level at the start of their turn. The same goes with objects, if the object is non-magical and the quality is simply average, it will likely turn into dust.

When traveling the Astral Sea, you can attempt to navigate through it by accessing the Paths Eternal. You need to make a successful Intelligence check. However, you may only do this if you are aware of the plane's existence and its rules. You basically have to be educated about it in order to fully maneuver through it.

Reality
The existence of the multiverse is true in New Eberron, instead of multiple timelines and possibilities however, the multiverse is maintained by three artibers. An Arbiter is the sentient manifestation of a reality's aspect, this includes time, space, and matter. Each reality are encased by what we call Shells and each reality have multiple universes inside of it which are called Contained Existences. This reality is called Primus. It is possible that there are multiple realities too, but it is near impossible to break through the reality's shell without the influence of an artiber.

Arbiters are the original sentience in each reality. They are the creators(and the end should they decide to). In New Eberron, the arbiters are The Traveler, The Unnamed King, and The Architect. It is believed that they are the echoes of the Primodial Dragons.