The main obstacle to the unification of gravity with the other three forces of nature is the lack of a quantum description of gravitational phenomena. This suggests that the macroscopic manifestations of gravity might be an indirect (effective) phenomenon, resulting from a radically different fundamental theory at the microscopic level. The most popular current candidate is String Theory ( ), which abandons the notion of quantum fields describing point particles. Other more conservative alternatives include higher spin field theories (), and Chern-Simons gauge theories ( ,  ), which exist in spacetimes of 2n+1 dimensions.