A vibrational plane is a parallel universe existing in the same physical space as our universe, but separated from us by the vibrational resonances of that universe's particles. There are a potentially infinite number of vibrational planes.
Every atom and subatomic particle on a vibrational plane resonates on a mutually interactive frequency. This includes light and sound wavelengths. Particles resonating on a different frequency are repulsed from each other and therefore are incapable of interacting and being mutually perceived in any way.
The vibrational frequency also serves as a sort of a blueprint, a script, of its entire universe; the movements of each and every one of its particles in every moment of its time. The more alike this "vibrational resonance signature" is between universes, the more alike the universes themselves are. Minute differences in signatures don't drastically differentiate a timeline on the long term. This causes many universes to duplicate each other on a macroscopic scale, with altered events on a smaller scale.
One result of this is that some events and individuals often appear duplicated in these universes despite the larger-scale differences between them. Certain events are "synchronized" between the universes so they move in a parallel manner with different moments having their equivalents in various universes. Although the patterns of events move in similar manners in different these universes, the intentions and characterizations can be vastly different. Thus even on different Earths whose histories diverged decades or even centuries ago, many of the same people continue to still be born because despite the historical divergences. Similar vibrational signatures cause the same groups of people to often meet in the same place and time in various universes and the exact same genetic material to be combined to form the exact same next generation.