Unobservable alternate “worlds”, whether string theoretic, Everettian, or merely “possible”, are counterfactual possibilities.
“The laws could have been any number of different ways,” — these are string theory counterfactuals.
“The wave function could have branched/collapsed1 any number of different ways,” — these are quantum counterfactuals.
Whether you treat them as counterfactuals or as “facts about elsewhere” is not itself a strictly scientific question, it is philosophical2.
Treating them as actual elsewheres is metaphysics, not science. Treating them as formal counterfactuals that emerge from theory is all that is required.
Reification is not the way, dear friend.
- These are isomorphic terms
- …and there ain’t nuttin’ wrong with that.