Can an extra dimension of empty space be smaller than a planck length? Is that why string theory allows those extra dimensions to be smaller than a planck length? Because they are empty? I remember reading posters on these forums say that space itself can expand faster than the speed of light and that this is what happened during the big bang. So exceptions are made for space itself both in quantum physics and in relativity? Edited 1 hour later :I always assumed that nothing could be shorter than a planck length.