We all know that there are three spatial dimensions and one temporal dimension i.e. time. And that is just a matter of fact.
But I would like to ask a question which I am myself I wasn't able to answer i.e. How can be we sure that there are only 4 dimensions and describe the universe in those 4 dimensions only
Means ultimately the question is What is the proof that we live in a 4 dimensional world?
How can be we all sure that there are only 4 dimensions and describe the universe in that 4 dimensions only
First, you need to be careful what you mean. It takes many more dimensions than 4 to describe the universe. It only takes 4 dimensions to describe spacetime, but there is more to the universe than spacetime. So, the question should be "How can be we all sure that there are only 4 dimensions and describe spacetime in that 4 dimensions only".
Spacetime is the set of all events, i.e. positions in space and moments in time. Spacetime is a curved manifold with four dimensions, one timelike and three spacelike. What that means is that at any event in spacetime we can take a small region of spacetime around that event, use the event as the origin, and treat the region as a vector space with four basis vectors. Then, any other vector in that small region is a linear combination of the four basis vectors.
This is what we observe experimentally. If we look at a small region in spacetime, and start with three non-coplanar rulers and a clock, then any other event in that small region can be expressed as a linear combination of those four. Because we have never found an event that could not be expressed as such a linear combination, we say that spacetime has 4 dimensions.
