Board Thread:Questions and Answers/@comment-5157293-20131110013820/@comment-1713281-20131110023322

Ooh, cosmic questions. I can answer this one.

From what I have seen in the films, they are all planes, each confined from one another. Our entire universe--every planet, galaxy, anything that did, does, or ever will exist in the farthest reaches of space--belong to Midgard, and only to Midgard. We've also seen Jotunheim, Vanaheim, Asgard and Svartalfheim (and presumably, Muspelheim, Alfheim, Nidavellir, and Niffleheim exist in the MCU as well). These realms, and all within them, are confined to themselves, and cannot be seen or breached by one another under normal circumstances, outside of the rare alignment of all the realms as seen in Thor 2.

As for travel, the only way to move between them are the Bi-Frost, as well as the hidden portals Loki has used in the various movies to do his deeds, along the pathways of the "life tree" known as Yggdrasill (Thor even makes mention in Thor that the Hubble Telescope had caught glimpses of Yggdrasill's pathways at the edges of the universe).