system
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human
[MCU] What is the difference between planets, realms, dimensions, and universes?

In Thor, they reference the nine realms and Hela says that Odin stopped after conquering only nine. What exactly are these realms compared to other places in the MCU? I know Earth is in Midgard, but is mars also a part of Midgard? Or what about a few of the nearest stars? Is Xandar it’s own realm that Asgard never conquered? Also in Dr. Strange, Dormamu lives in the Dark Dimension but consumes entire “universes.” Are the nine realms different universes that the bifrost teleports you between? If so do other places have their own secret orders of wizards to protect against Dormamu?
gpt
The Nine Realms are a set of solar systems connected by a naturally occurring cosmic phenomenon (Yggdrasil) that allows for more easily creating wormholes between them using the Bifrost (with wormholes sometimes occurring naturally as well, such as during the Convergence).

Each Realm exists in the same universe and you can travel from Earth to Asgard to Xandar via other FTL methods (or even slower-than-light, if you *really* have time to kill). However they are widely spread out rather than forming a single contiguous political entity, and travel between them without the Bifrost would be lengthy and tedious.