I'm creating a story where there are individuals that can travel to parallel/alternate earths. Obviously this is all fantasy but hypothetically speaking, how would you ground this is in some related real-world science? Based on the theoretical information we have about parallel/branching worlds, how would you connect it to human biology and explain how someone could tunnel through into another world?
Dumb matter is confined to its own dimension. Enlightened spirit energy is not so confined. Through astral projection a being in this dimension can project consciousness to visit other parallel dimensions as well as more esoteric planes.
This is also safer than actually visiting these places in the flesh as it is easier to find your way back home. The visiting astral traveler might experience other realms as a disembodied ghostlike spirit, or might manifest as some physical presence, or possibly take possession of a physical presence that already inhabits that realm.
There is also the possibility that the astral traveler fell asleep and had a groovy dream, or is on drugs. Or maybe all of these things happened!