How many dimensions are there in our Universe?

                                 
When we think about an object, we are talking about  how long, wide and high it is.
 In Mathematics we would say that  three dimensions are required to describe it. (3D). Furthermore, if we consider time as an additional dimension, then it would be easy to   admit   that we are living  in a 4D Universe.

Everything had seemed quite logical and made sense...at least until some physicists started to work very hard  on  an incredibly complex theory, known as String Theory. This principle tries to explain our Universe as it is, and it  must be said  that with much success. But in case this Theory is on the money, then...ok, it is weird...but our Universe should be 11 dimensional  (!!!!!!)
11-D?  but we can for sure  "feel" just  four dimensions, can´t we? where are the  other  ones? how can we figure out what it is like  to live in such a Universe?
I will do my best  to throw some light on this craziness: try to think of a civilization living in a Flatworld,  a very far away place  in which everything is plain, so things and life forms are wide / long but  they are not endowed with any height at all. what would happen in case we got to Flatworld? How would  their inhabitants see us?  and how would we see them? In the following clip Dr. Quantum sets out  such a peculiar world. Real Fun!

After watching the clip, please give this some thought: maybe we are living in our familiar 4 dimension  world, without noticing  the 11 dimension beings around  us;  and may be some of them   can see  us but we just can´t detect them ... does it make any sense?

Next clip (below)  Carl Sagan explains  in a very  simple way a  world beyond three dimensions:

And that is it. I hope you will find it interesting , and perhaps you change your mind (a little bit?)  about  what "reality" means.

PS: There is not a definitive proof for  String Theory, so maybe this is all just a weird theory...or maybe not?