I won’t tell you though whole story as it is quite involved but the line tries to convince the sphere of the theoretical possibility of a fourth dimension. It was written before Einstein’s theory of relativity and didn’t go over well at first. Since then it has had many resurrections including a movie in 2007.(animated of course)
Back to the question - how many dimensions are there?
There is no concrete proof beyond four, but now some scientists are saying there are seven. Apparently it would help in certain proofs for string theory. It allows for what is the best model for the unification of the forces of nature.
There is a book, an excellent book, that I read and plan to re-read. “An Imaginary Tale: The Story of the Square Root of Negative One” by Paul J. Nahin. From reading that book many of my thoughts regarding dimensions or infinity or even multiverses became solidified. Reasonably sure before the book, after reading how early on Mathematicians considered an equation solved when they reached a negative square, the equations of many things required a new look. One of which is going beyond known dimensions. Another is the singularity in a black hole, yet another multiverses. I, for one, believe that if an equation can be solved through a “new” math, it is suspect. But that’s just me....Still, I ask you, how many dimensions are there?