I've always envisioned this as an infinite collection of deterministic model universes, like a series of differential equations that are just slightly different from the last.

So you don't have a choice as you think you do (human-centric), because the nature of our universe(s) is cause and reaction, not bound to human or sentient thought-controlled being; so the differential equations that create our universe as a topographical model, play out literally every possible cause and reaction starting and/or ending position.

You have a computer and you know math. So think upon the structure of computers and math. How does it work? What is the human body? A magical lamp that creates "special" realities, or a complex organism made up of other complex organisms that ultimately creates our experience as sentient beings?

You're going to need a process that disambiguates your brain's natural inclination to think of human experience as the ultimate experience. The existence of the smallest building blocks of our universe supersedes us, so why do your multidimensional models assume that human thought controls the multi-pathed nature of all? The model may even be such that all existences happen simultaneously and that choice is moot. (determinstic)

TLDR: Time is an illusion. My belief is that ALL possible realities have happened and are happening... for lack of a better word, NOW. Big Bang happened. Maybe all big bangs happened simultaneously. Does big bang only assume the observable universe? Think about that while you're high.