How did the dimensions begin? Are there many separate realities, all proceeding independent of one another, or did they stem from a common root? The split of a dimension, as evidenced in Chrono Cross, seems to be a special and anomalistic event. That is, dimensions do not normally "split." Neither does time traveling alone create dimensions; the Principle of Discarded Timelines states that sufficiently. Alternate dimensions and space times did not fission off the Keystone dimension due to time travel or random chance. They originated from separate creation events (big bang, or other quantum mechanics) and developed independently of each other. Different initial conditions and chaotic randomness would account for the variation between these worlds. Unlike Another World and Home World, in which the latter split off at 1010 A.D., the normal dimensions of the multiverse are all separate from each other. Some entities may exhibit an awareness of more than one dimension, such as the planet (which pulled Dinopolis out of the Reptite Dimension), but sufficient data is not available to determine the why, how, or extent of multidimensional awareness.
At the beginning of the universe, the quantum indeterminancy would be so great as to cause the formation of many universes, one of which eventually becomes the Chrono (Keystone) dimension, while others become the various others like the world of Radical Dreamers and the Reptite Dimension. Since a big bang causing infinite universes would allow for many to be very similar to each other, this would allow for the similarities between these and the Keystone Dimension. In essence, these notations and beliefs can be expressed with Unified Dimension Theory.