Does the current model of cosmology treat the universe as an isolated system?
There are many different models, each of which answers that question somewhat differently.
Try "universe theories" on Google.
I thought it was clear I was referring to the FRW universe of the LCDM model.
It wasn't clear and I am not a mind reader!
As far as I can tell, the idea of multiverse is not addressed in that model.
Separate names with a comma.