Are we even sure we have just the 1 universe? If the multiverse theory holds weight, and there are multiple "bubbles" of universes everywhere, wouldn't we kinda

Are we even sure we have just the 1 universe? If the multiverse theory holds weight, and there are multiple "bubbles" of universes everywhere, wouldn't we kinda have to redefine the word "universe" to be the container for all of this? (Assuming it's not fractals all the way up/down)