Let me simplify for everyone here;Potentially, in the scientific sense of the idea. I don't know too much about what science has to say about it, but I wouldn't reject its findings. I would say that if there were multiple dimensions/universes/whaterver, that they would all still have their own reality just like this universe has its reality, which is unchanging within that system. All of those realities would then exist concretely, and would not be subjective or change from person to person, all things within the system are subject to the reality of that system, and because we cannot hop from one universe to another at will, we cannot change the reality we are in at will.
Multiple realities does not mean everyone here has their own reality. We exist in a reality. All of us here, in the same reality. Far as we know, no one has pulled a Rick and hopped between alternate realities.