From Future's End Wiki
The Astral Plane
All magical power flows from the Astral Plane, which is a plane of existence mirroring elements of the other realms it comes into contact with. It is home to the Astral Beings, which are mysterious creatures that seemingly can only be contacted with through magical rituals. As no-one has ever visited the Astral Plane, and none of the Astral Beings have ever said much on the matter, no-one is entirely sure what it looks like, how vast it is, how humanoid the Astral Beings are or even if they have day and night cycles like Earth and the Middleverse do. All that can be determined is that it is a realm of great magical power.
Mages feel a strange connection to the Astral Plane, and researchers have determined that this realm is the source of mage's power. There are both light and dark elements to this realm, and some mages are able to attune themselves to one or the other by a process referred to as Alignment.
To date, despite ample research into the subject, it has proven to be impossible to send physical objects through to the Astral Plane, be they organic or inorganic, though it has been observed that there are rare occasions where Astral Beings are able to send items from their realm through to that of Earth or the Middleverse. They have never explained why they are able to do this but the reverse seems impossible, stating only that Earth and the Middleverse 'do not possess the power to do so'.