The Ninth World is Earth, one billion years in the future. Many great and powerful civilizations have arisen and disappeared in that time, not all of them human. The powers of these civilizations beggar description. Among them were civilizations that mastered space and time, people who could halt the death of the sun or shape the continents as they wished, or beings who could shape life itself to suit their needs and whims. Their abilities are far beyond ours; even if our civilization were to survive another 10,000 years, we would barely have begun to accumulate the strength and knowledge that could place us in the histories of what Ninth Worlders call the “prior worlds”.
The prior worlds are gone now; they died out, transcended, or otherwise moved on. The present world is called the Ninth World, not because there were eight worlds before it, but just because that is what they have called themselves. The Ninth World is exceedingly young—not even 1,000 years in recorded history.
There are no records of the prior worlds, who they were, or what happened to them. All that remains is the detritus they left behind in vast profusion: crumbling ruins, floating monoliths, the descendants of their engineered or imported creatures. Abandoned clouds of nanites wander the scrublands, horrifically twisting whatever they come across according to some warped, unknowable design. Automaton soldiers march across desolated fields, fighting a war that no one remembers or could even understand. The Earth itself is surrounded by the datasphere: an invisible network that constantly transmits information across the globe to some unknown purpose, but that the very clever (or very lucky) can sometimes tap into for their own purposes.
The people of the Ninth World call all these things, collectively, the numenera. Some Ninth Worlders scavenge the ruins of the prior worlds, seeking ancient artifacts and relics to sell or use. Others harness power from invisible energies left in the very air and soil. The numenera are equally a source of aid and horror, ineffable and inexplicable.