basics of quantum gravity, why it is necessary, and two prominent quantum gravitational theories.

Want to learn more about quantum gravity? Check out these resources:

Loop Quantum Gravity:
http://math.ucr.edu/home/baez/acm/acm...
http://en.wikipedia.org/wiki/Loop_qua...
http://arxiv.org/pdf/hep-th/0408048v3

String Theory:
http://www.superstringtheory.com/
Brian Greene, "The Elegant Universe"
http://en.wikipedia.org/wiki/String_t...