Quantum string have tensions of order 1039 tons! Also unlike the classical case, the quantum superstring can exist only in a 10-dimensional spacetime.
How do we interpret 10 (1 time + 9 space) dimensions? There are two ways of interpreting the apparently invisible extra dimensions of space : compactification and confinement (i.e. we are confined to a 3-dimensional subspace of the 9-dimensional space) (not to be confused with quark confinement).
Consider a water hose. From afar, it looks like a line, but from up close we see that it is in fact a two-dimensional object.
At every point of ordinary 3-dimensional, there are 6 more orthogonal directions and a tiny 6-dimensional bubble of radius 10-35 m exists at every point of 3-space.
What is the geometry & topology of this 6-dimensional bubble? The answer is not yet known but esoteric mathematical spaces such as Ricci flat complex Kähler manifolds are favorites.
Of the 9 space dimensions, why are 6 dimensions infinitesimal and the remaining 3 large? This is because the closed loops of strings girdled 6 of the 9 dimensions 10-43 seconds after the big bang due to their enormous tensions. These dimensions cannot stretch the string and hence cannot expand.
We can consider ourselves to be confined to a 3-dimensional submanifold of 9-dimensional space. This will become clearer when we discuss the concept of D-branes.
On quantizing gravity, spacetime itself becomes only an approximate semi-classical concept-----quantum randomness implies the continuous creation and destruction of space and time.
Consider a 2-dimensional projection of space evolving in time.
At the scale of the string, spacetime is full of "gaps" of nothingness. At the cosmic scale, the same phenomenon is going on.
Last updated: 03 March, 2000
