There was a time when “universe meant ‘all there is.’ Everything. The whole shebang. The notion of more than one universe, more than one everything, would seemingly be a contradiction in terms. Yet a range of theoretical developments has gradually qualified the interpretation of ‘universe’. The word’s meaning now depends on context. Sometimes ‘universe’ still connotes absolutely everything. Sometimes it refers only to those parts of everything that someone such as you or I could, in principle, have access to. Sometimes it’s applied to separate realms, ones that are partly or fully, temporarily or permanently, inaccessible to us; in this sense, the world relegates our universe to membership in a large, perhaps infinitely large, collection.