There is a difference between knowing what is true and knowing why it is true

I have a tendency, more than most other physicists, to try to figure out everything all at once, before I publish. And even to try to figure out everything in my head, without pencil and paper.

Superstring theories provide a framework in which the force of gravity may be united with the other three forces in nature: the weak, electromagnetic and strong forces. Recent progress has shown that the most promising superstring theories follow from a single theory. For the last generation, physicists have studied five string theories and one close cousin. Recently it has become clear that these five or six theories are different limiting cases of one theory which, though still scarcely understood, is the candidate for superunification of the forces of nature.

So when you ask me how string theory might be tested, I can tell you what's likely to happen at accelerators or some parts of the theory that are likely to be tested.

One very important aspect of string theory is definitely testable. That was the prediction of supersymmetry, which emerged from string theory in the early '70s.

There was a long history of speculation that in quantum gravity, unlike Einstein's classical theory, it might be possible for the topology of spacetime to change.

As for the forces, electromagnetism and gravity we experience in everyday life. But the weak and strong forces are beyond our ordinary experience. So in physics, lots of the basic building blocks take 20th- or perhaps 21st-century equipment to explore.