the equations correctly match both quantum physics and relativity phenomena that we know about
Except when they're not.
http://en.wikipedia.org/wiki/String_theory#Background_independenceYes, that means that string theory is currently completely incompatible with relativity.
It's not like that's an arbitrary thing.
"In string theory the number of false vacua is thought to be somewhere between 10^10 to 10^100..." Yes, totally not arbitrary at all *sarcasm*.
The whole point of string theory is that the equations correctly match both quantum physics and relativity phenomena that we know about. If they did not, they'd already be completely falsified (have made incorrect preditions).
The whole point of string theory is that equations can be fudged to correctly match almost everything that exists, and almost everything that doesn't. Again, at least 10^10 different variants for just lower bound. Upped bound is
10^500 variants. Such a theory cannot be falsified because there's always a variant in it that can explain anything you want.
And they do it with the minimal amount of mathematical assumptions.
Barring things like extra dimensions that are designed to be undetectable and supersymmetry (which is a whole can of worms in itself because there are
multiple versions of supersymmetry theory, too).
So, there's really no basis to claim such an equation is entirely arbitrary and that as such you could put anything in there.
But the
entire point of string theory is that it's entirely arbitrary and you can put anything in there and nobody will notice because there are 10^500 different solutions to it.
Whether or not strings exist, the string theory equations are actually the simplest set of equations that can predict all the known particle properties.
I'm curious, what are these "string theory equations" that predict all the known particle properties? I only see a lot of objects like strings and branes and a lot of funky geometries showing how they can combine into something resembling our particles and fundamental interactions, but at no point do I see any special "string theory equations".
And anyway, 10^500 different variants. Of course there's going to be a variant (or 10^10, or 10^100 variants...) that predicts all the known particle properties. And of course that would mean zero predictive properties.
That's not even counting in the undetectable dimensions and supersymmetry theories which are needed for string theory to
function, which are also completely unproven to this moment.