Beyond the single world is the Ethereal Plane, where metaphysics dominates. It's filled with Ether, the raw stuff of creation, which accretes into distinct forms based on the metaphysical surroundings.
The makeup of the Ethereal is determined by your distance from three Poles, broad metaphysical tendencies that determine how the worlds work, and which are in complete opposition to each other. These are Stasis, Dynamism, and Entropy. (Yes, I played a lot of White Wolf as a teen.)
In Far Stasis, ether becomes a perfect crystal. Unchanging, without imperfections, it's an ideal form. In Far Dynamism, ether is raw potential, unable to take any specific form at all. Far Entropy is complete void, the ether there contradictorily representing its own non-existence. All three poles are inimicable to life; all the interesting stuff happens closer in.
As you move from Stasis to Dynamism, the etheric crystal fractures into the Elemental Pillars. These first represent pure forms of the five elemental atoms, but as you get closer to Dynamism, they become more heterogenous, gradually gaining form and shape and life.
The path from Stasis to Dynamism is instead the Energetic Rainbow, representing the breakdown of etheric form and energy. First is Light - pure and stable, but hard to contain. This shades into Lightning, still energetic but clearly more chaotic, but still controllable by proper application of Earth. Further on the energy loses direct physical coherence, becoming Kinetic - invisible and harder to grasp directly; doesn't travel as far but sheds its energy much more readily, making it more damaging within its useful range. A little further and we lose physical form entirely, reaching the more abstract form of Entropic energy, raw corrosion and loss of form. And finally, as we reach the pole it becomes pure Void.
Somewhere in the middle of the three Poles we get just the right mix to support the material world. Of course, we can't have just one - there are three, shadows of the stable fixed point cast by each of the Poles. The Static shadow is our world, the Prime Material plane, a world of physics and rules and things staying roughly the same from day to day. The Dynamic shadow is the Feywild - changing and fantastical, ruled by dreams and intuition. The Entropic shadow is the Shadowfell, a world in constant decay. The three worlds influence each other, tho our world, being the most Static, has the most stabilizing influence - things in the Feywild and Shadowfell tend to revert toward whatever they look like in the Prime. However, places of heavy magic use thin the barrier towards the Feywild and invite interesting effects, while places of death and pain draw the Shadowfell and induce monsters and ruin in the area. Insofar as the Body atoms "come from" anywhere, they originate here.
The Ethereal represents the "physical" half of "metaphysical", encompassing the physical worlds and the elements they're made from. Closer toward the Dynamic Pole, reality blurs and the Ethereal shades into the Astral, its meta/mental counterpart. This is where people's souls go when they dream, where reality is much more malleable. You can find pure forms of the Mental atoms here.
Souls travel to the Near Astral when people dream, where it's coincident with the Ethereal. In the Far Astral, out of reach of mortals in most circumstances, lie the Divine planes, where the gods make their domains. This layer is far enough out from the Ethereal that the Poles no longer hold any sway; instead, the divinities align along much more complex mandalas of metaphysics. We know that the five-fold symmetry of the Spheres holds at least some sway, due to the Divine atoms, but more is difficult to tell. Souls tend to drift this way after death, where they're collected by the gods.