Many Worlds

Scientific theory acknowledges many diverse worlds (possibly) coexisting in multiple spatiotemporal dimensions. Poul Anderson, SM Stirling etc present fictional accounts of such worlds. However, all fictional narratives exist not outside, in other dimensions, but inside, in the imagination, which brings us to "Barbie's idea."
-Neil Gaiman, The Sandman: A Game Of You (New York, 1992), p. 181, panels 2-4. (See image.)

And, from another volume of The Sandman:

"Is there any person in the world who does not dream? Who does not contain within them worlds unimagined?" (p. 28)

And that is where the other worlds are.
-copied from Between Worlds.

Science and art: we want to know about this uni(or multi)verse and to continue imagining others.
Philosophy: we need to distinguish clearly between reality and fiction.