Non-Euclidian Travel Theory

Non-Euclidian Travel Theory is a theory made by Seraphim which is widely considered to be cannon by the community. It explains how inter-dimensional, inter-universal and inter-multiversal travel works.

Explanation
I like to explain the Non-Euclidian Travel Theory with an analogy.

As far as the MCC lore goes, the group of space-times there are goes like this:

Dimension - Universe - Multiverse - Omniverse

The one after contains one or multiple of the former, for example, an Universe could have one or more Dimensions within it!

Now, for the Analogy: Imagine the Dimension as a sheet of paper. The Universe as a Folder. The Muliverse as a Box, The Omniverse as a steel locker.

You can break out of your dimension, aka "paper" with a mere pencil. If you wanna break out of the Universe, aka "Folder", you'd need a sharp object, maybe a pair of scissors. Thats how it goes.

The breaking out, the action of putting a hole in the paper is called "Breaking the Barrier", and the barrier itself, the surface of the paper you are putting a hole "Dimensional Barrier". This goes on for every size. "Universal Barrier" "Multiversal Barrier" and so on and so on.

So far - only Dimensional and Universal can be broken. Multiversal Barrier is really hard to break, and for humans to do so, they'd likely need a help of a god or a god-made object such as Yggdrasil.

Usage of the Theory
Seraphim famously uses "UBB"'s, "Universal Barrier Breakers" and "DH"'s "Dimension Hoppers" both to travel between and within their respective areas.

There is other methods of travel such as Rip Portals mainly utilized by Bigsco, but the most mainspread usage of the Non-Euclidian Travel Theory has been by Seraphim Foundation.