# What is dimension? What is the size of dimension?

Recently I heard a TED talk by Brian Greene where he was speaking about String Theory working on $$(10+1)$$ dimensions. Plus he said that we live in only in $$(3 +1)$$ dimensions. So where are others?

He explains that it is crippled to small sizes which we cannot perceive. Also, he gives the analogy of an ant and a man walking on the rope.

So my doubt is, what do physicists mean by saying word dimension? What do you mean by size of dimension? Thanks in advance for your help and support.

Edit: Any link to papers discussing philosophical aspects of the above mentioned is greatly welcome.

• I've deleted a comment (and some replies) that seemed to be starting a debate rather than suggesting improvements to the question. – rob Jun 26 at 0:36

The number of dimensions of space is the number of coordinates required to specify a point in space. The space we see is three-dimensional because we can specify a point in it as $$(x, y, z)$$. If we needed $$(x,y,z,v,w)$$ there would be five dimensions.