The Nature of "Reality"
In order for anything that follows to make rational sense, one must first understand our usage of vocabulary.
When we speak of Paradigms we refer to the set of rules that govern the "shape" of a particular mode of existence. This has nothing to do with the "alternate dimensions" ever-popular in mortal writings. The ruling laws of physics in a given realm, those qualities of all things within it that one may measure reliably, are the characteristics by which Paradigms are defined. These qualities are often referred to with the variables x, y, z, and so forth, which correspond to width, height, depth and other quantifiable descriptors. This formula will be pressed into service here.
We will use the term Epoch to describe the generations of sapient beings on a planet. Very often, life on a planet evolves cyclically, one entire ecosystem dying to make way for the next. Just as often, there will be similarities between them; certain forms and tendencies will express themselves again and again. It is also common for a single species to dominate the rest and subjugate their respective worlds. When this occurs, patterns emerge. The distinct progressive historical periods that often repeat from one sapient generation to the next are called Ages. Each Age lasts from the moment of a specific historical event to the dawn of the next.
Now, a brief word on spatial relativity: In discussions such as these, one must understand that while the known methods for travel between realities usually work, they are most often fatal. One does not travel between the Near Paradigms insomuch as one awakens to them and goes mad, dies horribly, or evolves. Other Known Paradigms may be reached from the Near by intrepid adventurers whose bravado is often found in greater quantities than their wisdom. The First through Third are exceptions to this form of exploration and may generally only be reached via the point where all things cross, where all are one. Human writings have referred to it as Babel, depicting an enormous staircase extending from Earth to the Perline Gate. The truth, of course, is slightly more complicated.