humanino said:
OK, how about that :
TeV Strings and Collider Probes of Large Extra Dimensions[/color]
Here you go, you have standard-model predictions, string theory predictions, they clearly differ and only await for more precise measurements to be distinguished, available measurements with their error bars being explicitely shown, error bars being clearly reduceable in principle. And before you claim this paper is crackpot theory, please pay attention to the authors, and the fact that it has been published in a respectable peer-reviewed paper (Phys.Rev. D62 (2000) 055012).
Very interesting article. It's not quite a full fledged string theory calculation in the sense that a certain ad hoc background of branes must be assumed. So in that respect it's in part like brane world scenario (eg Randall-Sundrum) who assume a certain brane configuration to start with. Still, it's very interesting to see explicit string calcualtions of processes carried out and related to observed processes.
It is fascinating that, I myself not being a huge fan of string theory, can get tired of people constantly reporting that string theory is wrong, string theory is not even a theory, string theory is science-fiction...
I agree. The backlash went too far and became irrational at some point. I would agree with statements to the effect that string theory is not a complete theory yet and that there is much work left to do before it can be tested. So in that sense, the present state of string theory cannot be considered a satisfying attempt at a theory of everything; too much is still missing. But it makes no sense to say that string theory is dead, that it there is no hope to ever test it, etc etc. This type of statement is completely misguided and narrow-minded, imho.
I am the first to grant that in its present form, string theory is not a complete theory and it can't be "killed" so much work remains to be done. However, the achievements of the theory are impressive.
Some achievements are purely conceptual. As far as I know, string theory is the only theory that fixes the number of spacetime dimensions. Other approaches (say, LQG) must take that number as an input and can't justify it.
String theory requires the existence of gravity at the same time as the other forces of nature. In other approaches (say LQG) gravity must be postulated from the start.
Supersymmetry is without any doubt a beautiful concept. It's the only way to mix an internal symmetry with spacetime symmetries and at the same time it connects bosons and fermions. In addition, gauging susy produces GR (which is then called supergravity). Supersymmetry may only be an idea which is not a symmetry of Nature, but it's one of those beautiful ideas that feels like it must have been used by Nature. In any case, superstring theory automatically leads to supersymmetry! In other approaches (like supergravity), supersymmetry must be put in by hand at the very start.
To summarize, in string theory (by which I mean superstring theory obviously) internal consistency alone fixes the number of spacetime dimensions, the existence of gravity and supersymmetry (as well as fixing the possible gauge groups). It's hard not to be impressed.
And even if string theory would turn out not to be valid (or if it turns out that we can't never reach a more mature form of the theory allowing it to be falsifiable) it has already lead to important advances in maths and as a computational tool for point particle field theory. So it has
already been useful notwithstanding whether it wil be successful as a TOE or not.
