Even though it is, properly speaking, a postprediction, in the sense that the experiment was made before the theory, the fact that gravity is a conse… - Edward Witten

It was clear that if I didn't spend the rest of my life concentrating on string theory, I would simply be missing my life's calling.

I think one has to regard it as a long term process. One has to remember that String theory, if you choose to date it from the Veneziano model, is already eighteen years old... that quantum electrodynamic theory towards which Planck was heading [in 1900], took fifty years to emerge.

String theory is extremely attractive because gravity is forced upon us. All known consistent string theories include gravity, so while gravity is impossible in quantum field theory as we have known it, it is obligatory in string theory.