So, as I understand it, (this being a combination of speculation based on the movies and some mythological theories) it is a combination of both separate yet parallel planes of existence and also one single plain encompassing all(in a manner of speaking). . .
~Also, please excuse my ramblings, it is just that some things are a bit hard to explain without a lot of context and I may repeat myself trying to explain.~
. . . So, moving on.
What I meant is that some realms are simply pocket dimensions surrounded by normal space (the rest of the cosmos)
- Looking out of this dimension, (Asgard for instance) it looks as if you were in the middle of space standing on a floating island-like land mass, and that if you were to stray too far from it , you would be sucked into a portal and transported elsewhere. Like what happened to Loki when he fell off the Bifrost into the surrounding space, and once he reached a certain distance, he passed the boundary of the pocket dimension Asgard resides in and was transported outside.
Looking in, as in being outside of the pocket dimension, and looking towards the point in space from which the sky looks the same as it can be seen from Asgard, you would see absolutely nothing.
- (Imagine it like this: you are out on a picnic, you brought a blanket a basket and everything you need. You lay out the blanket, but you hadn't realized that just underneath the spot you placed the blanket over, there was a hole. So the center of the blanket just hangs over it, than you lay out the food, and an apple rolls over the hole and with its weight it pulls the blanket into the hole, and if it was deep enough and the apple heavy enough than the blanket would be pulled in and fill up the rest of the hole. The apple is still covered in the blanket inside the hole but from outside all you see is just the blanket being bunched up in one place. Now imagine that the blanket is the fabric of the space-time continuum, and the apple is an object massive enough to generate enough gravity to warp space-time around it and in over itself, so that it creates a pocket dimension, still part of the entirety of space-time yet separate. Like a worm hole that does not have an exit just and entrance and than after expanding that bubble, you tie it up like a balloon )
That pocket dimension would not be a parallel dimension(when I said "dimension", I actually meant "universe", but since it is not as big and infinite as a normal universe, just as big as the volume of space-time that was severed off from the rest of the fabric of space-time), nor would it be intangible, it would just be separate, inaccessible from the outside like a house that is big on the outside and small on the inside because there is a room missing because it was hidden, only in this case we could not tell that the universe is bigger on the outside, since it's . . . you know .. infinite.
It would also still be connected to the rest of the universe through that single point in space-time that the one-way wormhole collapsed into. . . (using the same metaphor as earlier, it would be like a bag tied off at the end)
It could also still be located by detecting/pinpointing the anomalous gravitational intensity generated by the pocket dimension (A gravitational well would still be there, but when you looked it, it would seem as if it were just empty space. In reality, it would just be a infinitesimally small point that the wormhole had collapsed into, being held together by the gravitational forces on the other side, that are strong enough to bleed through and create the anomalous gravity well). . . it is still physically there, just that the surrounding space-time was stretched over it (like hiding "c" in "a,b,c,d" by having "b" and "d" meet over "c" . .. . if that makes any sense)
THAT is how i believe the pocket dimensions work, and that's where: Asgard, Vanaheim, Alfheim, Nidavellir reside, all being citizens of Valhala(which is what i think the entire island continent is called, or maybe not and i got that wrong, than i'm sorry )
- As for the other realms Jotenheim, Hel/Niffleheim, Svartalfheim, Muspelheim.
i believe they were formed in much the same way, either copying the Asgard method of creating their very own microcosms, (a way of creating a bordered off region of space in an infinite universe )
- Or, they were defeated and trapped in them by the Asgard (considering them to be too dangerous to be left to roam the universe unchecked, but yet not willing to eradicate an entire species to do so) therefore imprisoning them in pocket dimensions, that can be accessed only thru Asgard(the so called backdoor used by Loki and such) or by way of the Bifrost (in their case i would imagine that the pocket dimension "space?" was collapsed over their home-worlds, since they are depicted as planets not just floating islands like asgard)
Then you have Midgard, which is always depicted in Yggdrasil maps as being surrounded by an Ouroboros snake. In all forms of myth and legend that it is ever depicted or mentioned in, it always represents or means, INFINITY.
- Therefore, since Midgard is always depicted as a sphere (instead of an island like all other realms) and is also surrounded by the Ouroboros snake, then that would lead me to believe that Midgard is the entirety of the cosmos, it is the universe . . . the fabric of space-time from which Asgard and all other realms were created as pocket dimensions. it is also the place where "Guardians of the Galaxy" takes place (just FYI).
- Now I realize that this may just refer to Jörmungandr (the "Midgard Serpent" the Apocalypse monster) but since in Maps of Yggdrasil there is nothing else depicted in them but the 9 realms, it is awfully strang to depict it all by itself and no other being but it, except if maybe it was added in as a way to express the infinity of the 5th realm.
. . .
AND. . . in the end all that is nothing other then speculation, and i do not have to be right, i just have to make enough sense.
Now, moving on to Yggdrasil, the world tree.
- If you gather a star and some planets, you get a solar system
- If you gather a black hole and enough stars around it, you get a galaxy
- If you gather massive quantities of dark matter/energy and enough galaxies, you create a Galactic Filament (formed out of galaxies like a galaxy is formed out of stars)
If you can imagine a civilization advanced enough to create a pocket dimension, you can imagine them to have an advanced enough understanding of the cosmos, and to mere mortals such as us, it would be like a tree, because what else does it resemble if not a tree
As for the convergence . . .well that is kind of tricky, but if you consider the Bifrost (it's ability to transport matter over vast distances, and into "supposedly" pocket dimensions of space, and even destroy them, then is it so far fetched to believe that it can also create them ?)
- Also , all these pocket dimensions were created very near each other (well relatively speaking ) and around earth (or maybe Asgard, it being the source of the Bifost, and all that, therefore it may be a focal point)
Or even maybe, those pocket dimensions of space could be orbiting Asgard and therefore be in motion. Therefore, as any system of orbiting bodies, they may align with each other on a repeating circle(once every couple of eons, and such) thus aligning all their gravitational wells into alignment(I'm repeating myself, sorry) therefore amplifying the effect it has on its surrounding space and each other .. . maybe even the gravitational forces bled thru, from the other pocket dimensions of space may be strong enough to stretch at the collapsed wormholes of all pocket dimensions, thus enlarging the pocket dimensions worm holes and allowing for normal travel directly thru the wormholes themselves)
- And like that I think I may have explained how the other 8 realms ('cause earth/Midgard is the infinite universe, not a pocket dimension of space) started to appear above London (in the "Dark World"), also the way the AETHER (the red stone) started to branch out into them like a metaphoric depiction of Yggdrasil, could also be explained as the Etheral tendrils of the red infinity stone following the gravitational tidal forces created by the alignment of the 8 realms
As for Mjolnir, I imagine that since all pocket dimensions of space in which all 8 realms reside, actually occupy a specific place in the fabric of space-time, then what the hammer was doing was traveling towards location where all the collapsed wormholes were . ..wait that doesn't make sense. . . if the hammer is traveling towards one of the collapsed wormholes of one of the 8 realms (since Midgard is the cosmos) then shoulden't it travel towards the gravitationally stretched/enlarged wormholes above London ? .. .
Well I'm stumped .. . maybe there's something I'm missing but, I suppose it's ok, it doesn't all have to make sense, it's all fiction, it's all speculation, and all the science I tried to crowbar into it, has no actual proof to base it on, just cinematic CGI that kind off fits in with theoretical science (so then it must be true !) RIGHT ? :D
anyway . ..hope that helped