As of now, string theorists have no explanation of why there are three large dimensions as well as time, and the other dimensions are microscopic. Proposals about that have been all over the map.
Edward WittenI wouldn't have thought that a wrong theory should lead us to understand better the ordinary quantum field theories or to have new insights about the quantum states of black holes.
Edward Witten1/r^2 has a nasty singularity at r=0, but it did not bother Newton-the Moon is far enough.
Edward Witten