Full Idea
For the Kripkean possible states of the world are not alternate concrete universes, but abstract objects. Metaphysically possible world-states are maximally complete ways the real concrete universe could have been.
Gist of Idea
Kripkean possible worlds are abstract maximal states in which the real world could have been
Source
Scott Soames (Significance of the Kripkean Nec A Posteriori [2006], p.167)
Book Reference
Soames,Scott: 'Philosophical Essays 2:Significance of Language' [Princeton 2009], p.167
A Reaction
This is probably clearer about the Kripkean view than Kripke ever is, but then that is part of Soames's mission. It sounds like the right way to conceive possible worlds. At least there is some commitment there, rather than instrumentalism about them.