In regards to the divergence in the Fallout world (the reason why its 50s themed and technology is retro-futuristic), is the Divergence an actual thing that happened? Or is it just a word we use to attribute the time the devs decided to split the universes apart.

Could the divergence have happened slightly at earlier times (such as the setup of Sunset Sasparilla) and go on into a FULL divergence, or is it only slight?

Basically I'm asking what you all think on divergence metaphysics.