Phlogiston

There is a hyperdimensional connection between galaxies or crystal spheres, depending on the type of planescape (i.e. universe along the multiversal axis), defined by the nature of that universe. In universes without a predominant ethereal plane, the predominant law, naturally, resides with quantum fields, as particles cannot travel through the ether and have to exist as both particles and waves, while universes with a predominant ethereal plane the strongest natural force will be psychic energy.
The hyperdimensional connections previously mentioned are therefore dark matter flows within the space-time fabric of the material plane of quantum fields ruled universes, and phlogistons within the material plane of psychic energy ruled universes.
Spelljammers have been used by the more magically and technologically adept races over the course of the ages to travers their crystal spheres and travel to distant ones by way of the phlogistons which would accelerate the ships to superluminal speeds while in wild space.

Manifestation

Phlogistons are invisible, but can be detected by magical instruments. When spelljamers travers them, the wild space around them begins to blur due to the extreme acceleration.

Localization

Phlogistons only occur within the wild space of The Material Plane within universes ruled by psychic energy.