>>12828601>>12828821Feynman thought the string theorists were being dishonest: they were saying there was a unique theory (this was true), unique compactification (not true), that they can predict standard model parameters (maybe), and yet the theory did not do so, and there were wrong predictions, like gravitinos, unbroken supersymmetry, etc, things we still don't know how to fix very well. He was disappointed at the many different kinds of string theory discovered, and also it wasn't so physically transparent what the strings were back them. Much of these things improved in the 90s and later.
Feynman didn't know the theory very well, he only knew a little bit of Veneziano amplitude stuff from the days when it was current in QCD. He learned some of the newer techniques in the mid 80s, but it was never something he did research in actively. When he was dying, he asked Gell-Mann to lecture him on the theory on his hospital bed, and I supposed he learned the state of the art in string calculations then, since Gell-Mann followed string stuff since the beginning, and supported it throughout.
String theory in the 1980s was much less solidly physically understood than a decade later, and it was always a form of S-matrix theory, something which Feynman heckled and helped kill in the 1970s. Feynman always disliked S-matrix theory, even though he helped found it, because he made Feynman diagrams in S-matrix and they turned out to be field theory. So he probably thought like Weinberg, or Glashow, that S-matrix is just a bad way of doing field theory in disguise, and didn't recognize that there was a fundamental new physical principle in the S-matrix approach. S-matrix was Wheeler's baby more than Feynman's.
In any case, it was a lapse of judgement, Feynman knew better. But his criticism of the string propaganda of the 1980s is pretty good, the string theorists were a doing a little bit of groupthink at the time.
He would probably be convinced it was correct in the 1990s
