Is there a real chance that there is a multiverse?

[Arkilogue]

yis

Let's say we have never observed a multiverse and let's say it's impossible to. Would the mathematics of a ToE with a 100% certainty confirm if a multiverse exists or not?

Ordinarily I'd say that's not how science operates - a mathematical construction is always a theory that needs to be tested, and some of its predictions may be inaccurate even if most others are correct. So I'd say no, it can be a strong hint if a otherwise very successful theory predicts something like that, but not a proof.

That being said, I've seen an actual talkby a philosopher  of science who tried to construct something like statistical for string theory from the argument that there aren't any other theories or something. But I don't think this is widely accepted.

I found this statement by the physics department at Oregon U to be enlightening. http://abyss.uoregon.edu/~js/ast123/lectures/lec17.html

Physics of the early Universe is at the boundary of astronomy and philosophy since we do not currently have a complete theory that unifies all the fundamental forces of Nature at the moment of Creation. In addition, there is no possibility of linking observation or experimentation of early Universe physics to our theories (i.e. it's not possible to `build' another Universe). Our theories are rejected or accepted based on simplicity and aesthetic grounds, plus their power of prediction to later times, rather than an appeal to empirical results. This is a very difference way of doing science from previous centuries of research.

Our physics can explain most of the evolution of the Universe after the Planck time (approximately 10-43 seconds after the Big Bang).