Are Multiverses (or Multiple Universes) Possible?
(Multiverses. Screenshot from Google Image Search)
Theologically, it is not an impossibility, given the notion of the "three worlds" or more as some tend to subdivide each. However, one must choose between whether to look atthe various "realms" as part of the one Universe or look at reality as containing multiple Universes not closed to each other.
It is apparent from the biblical narrative that the gateway (or stairway as in Jacob's dream) between the three worlds is open for angels, and Satan is said to ascend from the pit and move to and fro. The Genesis narrative tells us that the gateway to Eden is closed to man and he is specifically designated as dust that must return to dust. However, there are exceptional cases of Elijah and Enoch taken away to God.
The term "above" (that also includes pictorial language of dreams and visions) relates to God and life, while the term "below" relates to death and the grave, also pointing to gravitation towards dust and entropy.
Obviously, theologically, it is impossible for man to get out of this world to any other except through death, or unless God chooses. Also, man cannot create any device to travel to and fro between the worlds.
There is only one Man who descended from above, descended below, and has ascended above, and will descend again the second time: Christ.