"If you understand nothing happening, you can understand something happening"
Being just one of several gnomic utterances made during the course of a lecture by Ed Witten in January 1998 at the Kavli Institute for Theoretical Physics at UCSB. In lieu of reading Brian Greene, whose Elegant Universe is still waiting patiently on the shelf, I thought I'd start with this hours worth of prologue—and string theory seems like a really elegant unification of quantum mechanics and gravity. Witten shows how it solves problems of infinity raised by the inverse-square law of gravitation, and how it generates predictions, one of which (supersymmetry, or the existence of extra infinitisimal spatial dimensions and corresponding particles) will hopefully be tested within the next few years. He also shows how it is that string theory generates the same sort of blurriness for space-time that quantum mechanics generated for space-time trajectories. In question time Witten has a nice comment on what it means to ask "but what is a string really?"—the question is really asking for a new, more fundamental theory, and while we wait for one the question simply cannot be answered.
From Worldlines to Worldtubes (Slide 18 from the lecture)