Unitary: it all happened
Non Unitary: Some of it is at a time coordinate different than the rest of it at having happeningness
OK, the glittery first idea, which is replaced with better ones, is that whether to perceive the truth is nearer to unitary or non unitary MWI (Everettian physics), is highly similar to refuting determinism; the clockwork universe view.
One refutation of determinism is to simply modify the source of the universe to have more than one starting point, with the two starting points separated by a measurable thing. An overy-facile-so-is-likely-too-simple version would be a big bang that
arises from two separate points simultaneously, yet at a distance such that the two co-bangs have lightcone exclusivity to each other. The areas at the locational tips where the branches of the two cobangs meet would not be predictable by anything,
computer or human, in the set of two, determined, clockwork universes produced with each co-bang.
Sounds fun and sensible so far, but you asked about the “hard time grasping” part. I do not comprehend string theory, but the locational difference of the two (or more) co-bangs could actually be differences in the “rolled up” 11 dimensions of
string theory rather than the “two co-bangs a few meters away from each other” visual I started with.
Then there are all the other possible ways of breaking determinism, if it has not yet been broken (or was absent being there in the first place). Also, at these changes to determinism things expand from including retrocausal modifications, as supported
with the actual physics of the delayed quantum choice eraser, or better technologies.
Now more about “hard time grasping” Well, I think I should figure this out. Intent is part of effort to grasp. One reason is that a truth-verified position on the many worlds interpretation of physics would change almost all of ethics, as far as I am
aware. Unitary/non-unitary MWI would affect all actual personal agency. So, if a person figures this out then it is nearer possible to be be able to figure out what to do.
I am under the impression that I thought of about 3 refutations of determinism, or technologies to break determinism that could be utilized if they are the right thing to do. Which brings up, as an aside:
Many scientifically studied things have transitions, physical phase changes, and form variations. If you don’t know anything about something, it, perhaps, depending on a kind of taxonomic geography (or visualization) of isness, usually has embodied/
endefinitioned variation. Translation: there’s a lot of change, what if many things like “determinism” or “source of universe” also have change built-in?

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