I think the reason they keep having to invent multiple dimensions is because they still have a deep misunderstanding of gravity.
Everyone know the whole “rubber sheet” analogy of how gravity works...
But that is flawed.
Instead of a rubber sheet stretched over an open hoop, it should be a rubber sheet stretched over pool of water fileld to the brim so there is no space between the rubber sheet and the water... ONLY in 3 dimensions instead of 2.
If you press down on rubber sheet on this model what happens to the sheet? It goes down but at the endges it also goes UP. Because the spacetime metric is compressed, it has to “GIVE” elsewhere.... This would account to so called “Dark Energy” that acts repulsive at great distances, becasue gravity work repulsively at GREAT distances due to underlying nature of space time being NON-compressible...
Gravity attracts at close distances, but when you get to certain distance it will be slightly replusive, but the since the repulsive force is spread out over a very great distance it is very weak, unless you are tyalkign about very large distances, ie. between galaxies...
That is my theory on gravity, take it, steal it, use it.
Just send me a flying car if you figure it out...
I like it very much, and may use it in my novel. How about making it a rubber sphere filled with water?
The reason I generally lost interest in physics was that it seemed to me that mathematicians and physicists regarded theories as more real than reality.
I say that there are no true or false models, only more or less accurate ones, and more or less useful ones: A model is not the thing itself.
I do not have a flying car, but I designed a “whirly-pod” as a boy. (My father, a rocket scientist, pointed out its stability problems, and, alas, it never reached production.)