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  Hard drive making a weird noise  




My 2TB Western Digital Caviar Green is making this thumping noise. The thumps repeat about every 2 seconds and occasionally go away altogether. 

It passed WD's own diagnostic tool, but I am still wondering: is it dying? 


Question: Why does string theory have such a huge landscape?
Answer: 
  "Each compactification leads to a different vacuum state.... at least
  one state should describe our Universe in its entirety.... the
  enormous number (~10^500 at last count) of solutions, with no
  perturbative mechanism to select mechanism to select among them, leads
  some critics to question the predicitive power of the theory..Even
  more worrying is that, while the theory is perturubatively finite
  order by order, the pertrubation series does not seem to converge."


Ok.  


  I don't know anything about string theory and so I could not make head
  or tails this. All I know is that ~10^500 is a very large number.


That, it is.      


  What exactly is a 'solution' in string theory? Is it a spacetime
  metric of some sort or the terms of a S-matrix of some sort?  


So, we have a non-peturbative definition of M-theory and string theories on AdS Space through the AdS/.CFT correspondence. Now,  these are 10 or 11-dimensional.          To get rid of the extra 6 or 7 dimensions, you need to compactify it on a 6-dimensional or 7-dimensional manifold. 

A particularly convinient compactifications of 11-dimensional M-theory is on $G(2)$-holonomy manifolds.       Particularly convinient compactifications of 10-dimensional string theories, such as Type HE, are on $SU(3)$-holonomy Calabi-Yau manifolds.      Of course, it's not necessary; e.g. if the world happens to be something with $\mathcal N=2$ supersymmetry, as opposed to                           $\mathcal N=1$.             


  Why are there so many 'solutions'?  


Because there are lots of these manifolds!       


  I thought string theory was supposed to be finite, why do perturbative
  series still diverge?  


Uh... Yes. But it's renormaliable. And there are non-peturbative definitions in AdS spacetime.     


  Is there any experimental technique to limit the number of
  'solutions'?  Will experimental techniques be able to pinpoint a
  solution within present day string theorists' life      times too? If
  not, how long will it take before we can experimentally probe these
  things?


In principle, it's possible.    But in anyone's lifetime... Do you know how big $10^{500} $ is? % See this.   


  Are string theorists completely relaxed about these issues? Or are
  they in anguish?    


There's the branch of String Phenomenology that attempts  to find the correct vacua...