Tolchok wrote:And then there's things that, as far as I know, they haven't even tried to prove. "The strings are ten dimensional." Why 10? A random number generator said so? It was a nice, round number? You pulled it our of a hat? That just reduces the credibility of the theory.
Because for the math to work, it turns out that the strings have to vibrate in more ways than a 3+1 dimensional universe would allow.
One way to add these extra vibrations would be to place the strings in a higher dimensional space -- and 10 happens to be the lowest one that is consistent with that model. (there are higher dimensional universes which also solve it, but by occam you pick the simplest one)
As a side effect, those extra dimensions provide us with a possible test for string theory. If they are macroscopic and
(say) gravity isn't bound to the same brane as the other forces, then we end up with some interesting gravity artifacts at low scales that do things like predict lower energy densities can produce a black hole and the like.
So those are tossed out there as an interesting possibility that, if found, restricts the solution space.
What is also interesting is that the 'shape' of these higher dimensions might produce interesting observable effects on the kinds of string vibrations, and string vibrations are kinds of particle, so ... you can talk about how 'shape' of these higher dimensions might be tied to the particular kinds of particles that can exist (thus predicting the properties of fundamental particles... something that people would love to be able to do ... hopefully using fewer parameters)
Of course, as yet, string theory has not produced a prediction that is inconsistent with the standard model, nor has it produced restrictions on parameters beyond the standard model, at least as far as I know.