Ok. Here’s the thing though:
Observables: There’s one Universe.
Any notion of more than one is based upon the mathematics.
This does not negate the validity of the mathematics for mathematics sake but multiple Universes is a mathematical notion being applied as a possibility for reality WITHOUT a corresponding observation.
This doesn’t mean that it “might not be true”. Of course it might be.
But it’s fictional. At present, it’s fictional. This doesn’t mean that it’s not a good idea to pursue it. Someone just did a preliminary test on parts of the holographic Universe for example, which is a mathematical model and found no evidence as of yet. [I can find link but I’m guessing you’ve seen it. I can find it of course]
Again, doesn’t invalidate it. But there is a danger of analogies here:
Mathematics is an analogy.
It’s a GREAT analogy.
But it’s analogy.
There’s also a strong belief system in place here: The grand unification of the Sciences with mathematics as its basis.
That’s not to say that it might not be true: it _might be_.
But at present, it’s not true. The gaps are wide between the Sciences. Perhaps they will be bridged one day. I hope they are. But to say “they are” is a belief… and a hope but currently a fiction. It’s a good fiction, but it’s a fiction.