Why Nature has made a choice of one time and three space coordinates?

We propose a possible answer to one of the most exciting open questions in physics and cosmology, that is, the question why we seem to experience four-dimensional spacetime with three ordinary and one time dimensions. Making assumptions (such as particles being in first approximation massless) about the equations of motion, we argue for restrictions on the number of space and time dimensions. Accepting our explanation of the spacetime signature and the number of dimensions would be a point supporting (further) the importance of the 'internal space'.