Not Even Wrong

Woit, 2007

The story of how the discovery of the principles of special relativity and quantum mechanics revolutionised twentieth-century physics is by now a rather old one. By 1973, physicists had in place what was to become a fantastically successful theory of fundamental particles and their interactions, a theory that was soon to acquire the name of the 'standard model'. Since that time, the overwhelming triumph of the standard model has been matched by a similarly overwhelming failure to find any way to make further progress on fundamental questions [..]

Supersymmetry

Since physicists continue to take seriously the idea of a supersymmetric extension of the standard model, they must have a reason to believe that it may be possible to overcome the severe difficulties explained in detail in the last section. The most popular hope of this kind is that superstring theory will do the trick. This hope has motivated an unprecedented quantity of work by a very large number of the most prominent theoretical physicists for more than twenty years, but after all this time and effort the whole project remains nothing more than a hope. Not a single experimental prediction has been made, nor are there any prospects for this situation to change soon...

[One] argument often made for supersymmetry is that it is possible that the low energy limit of a superstring theory is a supersymmetric quantum field theory. This argument is of course based on the assumption that at high energies the world is governed by a super-string theory. The next section will consider the arguments for that possibility, but one thing to keep in mind is that one of the main arguments often given for superstring theory is that it explains super-symmetry. These arguments are circular, and should best be interpreted as an argument that the fates of supersymmetry and string theory are linked, that these ideas are either both wrong or both right.

Feynman

The lack of any predictions of the theory makes many physicists very dubious that the idea is correct. One prominent theorist who felt this way up until his death in 1988 was Richard Feynman, who was quoted in an interview in 1987 as follows:

"Now I know that other old men have been very foolish in saying things like this, and, therefore, I would be very foolish to say this is nonsense. I am going to be very foolish, because I do feel strongly that this is nonsense! I can't help it, even though I know the danger in such a point of view. So perhaps I could entertain future historians by saying I think all this superstring stuff is crazy and is in the wrong direction".

[To the question, "what is it you don't like about it?" he answers:]

"I don't like that they're not calculating anything. I don't like that they don't check their ideas. I don't like that for anything that disagrees with an experiment, they cook up an explanation - a fix-up to say "Well, it still might be true". For example, the theory requires ten dimensions. Well, maybe there's a way of wrapping up six of the dimensions. Yes, that's possible mathematically, but why not seven? When they write their equation, the equation should decide how many of these things get wrapped up, not the desire to agree with experiment. In other words, there's no reason whatsoever in superstring theory that it isn't eight of the ten dimensions that get wrapped up and that the result is only two dimensions, which would be completely in disagreement with experience. So the fact that it might disagree with experience is very tenuous, it doesn't produce anything; it has to be excused most of the time. It doesn't look right".

A more concise quote I have heard attributed to Feynman on this topic was: 'String theorists don't make predictions, they make excuses.