Four radical routes to a theory of everything.

The article presents four string theory approaches including causal dynamical triangulations (CDT), quantum einstein gravity, quantum graphity, and internal relativity. Among the string theories, CDT is the most advanced. On the other hand, Martin Reuter, physicists, developed the quantum Einstein gravity theory. Lastly, Fotini Markopoulo of the Perimeter Institute developed a model which he calls the quantum graphity.