With the laws of physics we know today an infinite multi-universe system is in theory perfectly possible and plausible .
By multi universes I don't intend multiply different copies of our reality or mirrored versions of our universe but completely different, separate universes. each one defined by its own space, energy, matter and possibly even laws of physics
Those universe have nothing to do with each other due to the primary fact that they are separated, they just happen to coexist.
Given they exist and given we have enough knowledge and intelligence to develop the technology needed. Is it possible to cross into another universe or communicate by sending any kind of input to any other universe and see the reaction?
Or is it by definition impossible due to those universes being naturally separated, therefore everything happening in another universe will forever remain there without chance for us to even know?