Strings. Why were Harald and I hesitating between QCD itself and a string... a string-like version of it, which is what we endorsed in the written version of the… of the talk? Well, as I mentioned, at that time hadrons were thought to be the domain in which bootstrap ideas would apply. Now, as I mentioned, I had been a little annoyed that so many people at Berkeley and elsewhere who were doing model bootstrap calculations, were beating to death one or two states, instead of treating crudely a large number of states, say an infinite number of states. And I proposed that, some time or other in the ’60s, that one should really have a bootstrap calculation with an infinite number of meson states, say. Say you leave out the baryons for simplicity, but you would have an infinite number of meson states as colliding particles; you'd have the same infinite set of meson states as exchange particles giving the forces; and you'd have the same set of meson states as bound states coming out. This would be the self-consistent bootstrap idea but applied to an infinite number of meson states, initially taken to be of zero width, then as a result of corrections they would acquire width through their decays into other mesons.

And at Caltech at that time three of our post-docs were David Horn, Christoph Schmidt and Richard Dolen. And Dolen, Horn and Schmidt wrote a paper which referred to, usually referred to as the duality paper, in which they carried this suggestion out much further; talking about how one would carry... how… how one would construct such a bootstrap calculation. Then Veneziano produced his famous Veneziano model... when was that? About ’68? Something like ’68, in which this all happened. It was a zero approximation which you had infinitely narrow states in the S channel, the T channel and U channel, and they were all the same, and there were an infinite number of them. It was beautiful.

[Q] And you had lineally rising trajectories.

Lineally rising Regge trajectories, which was also beautiful. It was a really splendid inspiring model. It had a flaw, however, which was that there was a scalar particle with negative mass squared. That wasn't so good.