Synonyms for island universes
EXAMPLES FROM THE WEB FOR ISLAND UNIVERSES
Possibly the spiral nebul are exterior or separate "island universes."
We slept for two days, all told, and by now we're so far from all the Island Universes that we can't tell one from another.
Explorers reached the Galaxy's very edge, and looked estimatingly across the emptiness toward other island universes.
Our case is probably paralleled by thousands of other intelligences on far-flung planets and island universes.