It's on TV that's where...
but really it couldn't be another dimension, i studied the mathematics between dimensions. I conclude it isn'tanother dimension
here is why...
they would be living in the 3rd D
in the 1st D they wouldn't be able to see anything but a dot.
the 2nd D which is infinite 1st D's they would see line segments
in the 3D composed of infinite 2nd D's (our dimension) We actually only see true 2D, only due to lighting, size, do we get a sense of depth
4D would see true 3D and is composed of infinite 3D's (seeing all sides of an object at once) represented by a tesseract.
now judging they see like us...
have "similar" physics
aren't omnipresent (except pinkie pie)
i would suggest they are just on another planet or undiscovered galaxy of sorts.
(Time is not the 4th dimension!)
it is not in anyway bound to one dimension.