It took a while for the importance, for the nature of the importance of the superstring theory to become clear. Two important developments happened in the middle ’70s. One was that Gliozzi, Scherk and Olive showed that any weird properties of the theory could be separated off. In other words, you could consistently separate out any negative mass squared, negative probability and so on and so on effects from the superstring theory, leaving a clean superstring theory with no weirdness. This had not been true of the Veneziano model. The Veneziano model not only lacked hadrons, it also had this negative mass squared particle in it. But the superstring theory could be cleared of all these things. The second point was to deal with the zero mass particle of spin two. Again Scherk, that brilliant but erratic young Frenchman, played a role. He came to Caltech and he and John Schwarz changed completely the interpretation of superstring theory in the mid ’70s by suggesting that it applied to all the particles, all the elementary particles, not the hadrons. They changed the slope of the Regge trajectories by a factor of ten to the thiry-eighth in mass squared, and then they could attribute the spin two mass-less boson to gravitation, it was the graviton. And in an appropriate limit they were able to show that the graviton obeyed Einstein's general relativistic theory of gravitation. So the… from then on superstring theory was a candidate–in fact the candidate—for a unified quantum field theory of all the particles and all the interactions.

[Q] You didn't talk about dimensionality.

Perhaps fulfilling Einstein's dream. Oh, the dimensionality, yes. Veneziano's model held in twenty-six dimensions, if you took the whole thing literally, and the superstring theory in ten dimensions. Nowadays superstring theory has been found to be a little bit more complicated, there seems also to be an eleven dimensional sector. But ten dimensions, and the question was what to do with that. Well, one idea was to keep looking and try to find a similar theory in four dimensions. Another idea… a different idea, was to take seriously the extra dimensions and let them curl up into a little tiny ball of some kind so that they wouldn't be a nuisance. And then the question was, would they spontaneously curl up in the actual theory? Would you have to impose it in some ugly fashion? And so on. Well those things are still being discussed.