The principle that there can be no possible communication between these bubbles allows each to be treated as an independent universe with different physical laws. A universe then would be a region with a particular set of physical laws.
Until now, "universe" has been completely synonymous with "all that exists." The same used to be true of the term "world" (and it still is, in some usages of the term "world.") The new meaning no longer encompasses "everything that exists," and so leaves us with no single word with that meaning.