we exist in the 3rd dimension.
einstein was able to explain the movements of large-scale bodies (i.e. the interplay of large-scale forces) by considering the 3 spatial dimensions and time as woven into a kind of fabric which is influenced by mass. new theories however add more dimensions to account for the small-scale forces which rule the interactions of small-scale bodies (electrons, protons, etc) in an attempt to get einstein's theories and quantum mechanics to operate in harmony. any number of spatial dimensions could exist and we'd never be able to perceive them because our perceptions are locked within our particular dimensionality.
read the book flatland.
