Suppose physicists reach a theory of everything, call it T. We can always ask: why is T the case? If this question is answerable, this answer must lie in the theory itself. The logical form of T must answer the question. It must be the case that in the formal system T it is provable that
T implies necessarily (there exists (T))
Then, if T is experimentally shown to express the laws of physics, it would logically imply that the universe must exist. It would be a fact of physics that this universe must exist.
There is apparently no reason for T to exist in the first place, so this is not an explanation for existence.
But if T has form (1) there is some sense in which it, if we knew it described the actual universe, would "retroactively" allow us to conclude that it must exist. e.g. 'existence logically implies it must exist.'
What are the groups Gi associated with symmetries among the objects that T asserts exist? These groups should be found somewhere among the groups of any theory of everything that satisfies (1).