String theorists postulate that our world has 9 dimensions and these extra dimensions are very twisted up such that they are too small to be seen. Question 1: Why don't we postulate, instead, that the reason we can't see these extra dimensions is because we are not genetically wired to do so, just like a fish or a worm is not genetically wired to understand economics? Question 2: What does it mean for these dimensions to be twisted up? Twisted up in where? What I imagine is these dimensions are twisted like a tiny ball of threads; they would be twisted in our macro 3-dimensional space. If so, this picture seems wrong because then they are still existing in our 3-dimensional space, not really being extra-dimensional.