This question has to do with scientific claims about the universe and could be asked in a number of ways.
To my own very imperfect understanding, claims about "the universe" cannot be scientific claims in any proper sense. As claims about a single entity they do not and could not submit to standard principles of verification. (They might even be subject to Hume's arguments about miracles.) As claims about a totality that presumably includes the claimants, they fall prey to paradoxes of self-reference, such as sets of all sets, and so forth.
Yet scientists and philosophers of science regularly do make highly considered claims about "the universe." They also make claims about the possibility of a "unified physical theory" that would seem to involve some of the same sorts of problems.
Is this just a manner of speaking on the part of scientific pragmatists? Or do physicists understand themselves to be making perfectly valid claims about the physical universe, implying that such claims can be made from "outside" the physical totality, so to speak? Which suggests dualism of a nearly Cartesian order.
Perhaps I am misunderstanding something obvious here. How do philosophers of physics deal with such issues? Is this a well understood problem? Do the potential fallacies here in any way relate to the emergence of "other universe" theories as an attempt to provide some apparatus of comparison for "this universe"?