We are in 1999, Greene is talking about the physicists quest to explain the universe on elegant terms. ELEGANT, hum? Right now things are inconsistent (say you can't explain gravity using quantum mechanics). So ELEGANT here means “a quantum-mechanically CONSISTENT description of all forces and all matter” (his own words). He did a great job explaining how string theory was created to TRY to connect together gravity (relativity), electromagnetism and quantum mechanics. But finishing this book is like stepping out a Museum of Modern Art. You are about to see some CRAZY abstractions within quantum geometry. Those many curled dimensions in a Calabi-Yau space look graceful at first.  But you can't step out of the Universe and relax.