If it is outside our universe, and more than likely traveling at the speed of light or near it, then we will never know for certain. It will never be more than a leap of faith by scientists. I put this in the same category as the infinite number of parallel universes theory.
String and Multiverse Theory are basically forms of Theology. The difference from traditional religion is that the high priests of these Theologies have PhD’s in physics, etc. That doesn’t make their theories any more valid than Catholicism or Hinduism. They are pure belief systems without evidence. Multiverse Theory is especially attractive because it is impossible to prove. Grant money can flow unhindered forever because of it. People are simply expected to believe it because the “experts” say it is so.
yep - for short response!