Why only three non curled up spatial dimensions?

[nealh149]

Why only three "non curled up" spatial dimensions?

Is there a reason (inherent in the theory) that string theory describes 10 spatial dimensions with 7 of them curled up rather than having 8 or 3 curled up? In other words, is this curling up a consequence of other parts of string theory, or is string theory designed as to fit observation?

 

[Phrak]

Is there a reason (inherent in the theory) that string theory describes 10 spatial dimensions with 7 of them curled up rather than having 8 or 3 curled up? In other words, is this curling up a consequence of other parts of string theory, or is string theory designed as to fit observation?

They're not curled?