> If there are truly separate "universes", then by definition wouldn't it be the case that there would be no way to test (or falsify) whether they exist or not.

> If there are truly separate "universes", then by definition wouldn't it be the case that there would be no way to test (or falsify) whether they exist or not. Well, if the multiple universes theory provides falsifiable predictions about this universe and is the simplest explanatory model we have for this universe and said predictions / behavior, then the explanation would not be metaphysical at all. For example, if a multiple universe theory was a requisite basis to a universal theory of gravity and quantum mechanics then it would be perfectly within the realm of the physical sciences.