Why is the Tesseract called "the Tesseract"? Is it really 4-dimensional?
Related, NOT dupe: Why was the Cosmic Cube named the Tesseract in the Marvel movie series?. Answers explain that the Cosmic Cube and the Tesseract are different things, but not the origin of the name.
In math, a tesseract is a four-dimensional object. In the MCU, it looks like just a box containing
the Space Stone
It can open portals to distant points of the same universe, as established by Are the realms different dimensions or different planets? and Difference between Realms vs. Dimensions vs. Planets vs. Universes (there is also "How are the Nine Realms situated in space?", but the answers are more based on Earth-616 than on the MCU).
I can't reconcile the single-universe travel with the references to different "dimension(s)" made by Erik Selvig in Thor:
I had a lot to work with: the Foster theory, a gateway to another dimension...
and by Tony Stark in Iron Man 3:
You experience things and then they're over, and you still can't explain them. Gods, aliens, other dimensions. I'm just a man in a can.
The note describes what a tesseract/hypercube is in math, but it does not explictly mention "the Tesseract". We know that Howard "fished it out of the ocean", so he had time to study it. The note may be related to it, it may be a hint for the audience for what was about to come in the next movies (2011/2012); OR it may be just a prop unrelated to the Thor/Avengers plotlines. When we watch into the Cube we only see a blue mist, not the elegant geometry drawn by Howard. I can't consider this blink-or-miss page a final proof that the blue cube is 4-dimensional, as ScreenRants instead claims (but they can't even spell "Rogers" correctly). A quote by authors would greatly help.
Possible explanations (speculation):
- Characters are mistaken about the Tesseract nature in-universe. Johann Schmidt / Red Skull called it "Tesseract" because he really thought it as a mathematical object existing in 4 dimensions (the word "tesseract" dates back to 1888 according to Wikipedia, so it makes sense). Same for Erik Selvig and Tony Stark: baffled by the events of Thor and The Avengers, they think Asgardians and Chitauri are from a different "dimension".
- It's an out-of-universe retcon. Maybe authors initially indended Asgard to be in a different dimension (like in the comics, see Marvel official website, and also this and this questions), accessible only via Tesseract, Bifrost or other ass-pull. Then authors changed their minds in later MCU movies (e.g. in Thor: The Dark World when Mjolnir tries to go via normal space). Now the name "Tesseract" makes less sense, but it is too late to change it.
- ScreenRant is right: the Tesseract, or its core, is really 4-dimensional. As suggested by an answer to Are the realms different dimensions or different planets?, the fourth dimension is not the extra axis that takes you to another universe, it is the extra axis that allows you to
warpfold the space and reach a distant point. The above quotes by Erik/Tony must be viewed in this light.
- "Tesseract" is just a cool word, already used a lot "as a plot device in works of science fiction, that have nothing to do with the actual hypercube". La-La-La. I should really just relax.