There are lots of symbolisms and metaphors in Scifi and Fantasy stories.
Werewolf stories are seen as metaphors for adolescence and coming of age. Vampire stories are sometimes seen as representation for intimacy amidst rejections and differences. Robots and AI tales are symbols of anti-slavery and uprising against an established authority.
Stories about Parallel Universes, on the other hand, are about hopes and dreams. A parallel universe is a place where we are a different person, a place where your dreams may have come true (or not). A place were we hope good things happened to our lives.
On the same light, time travel stories are about wistful thinking; what if I did this or that etc.