I saw a show about string theory on TV, and I don't understand why this hasn't already been ruled out. My thought is this: If there is a dimension that is curled up, wouldn't this violate relativity because moving would cause it to length contract? This seems to violate relativity since there is a preferred frame in which the curled dimensions have a maximum length. But we know relativity is correct! And if you don't have curled dimensions, then string theory can be ruled out since we don't see 10 dimensions. Either way, there seems to be a problem. How can string theory with curled dimensions match the amazingly precise relativity experiments? EDIT: I see now that there was a thread on 'preferred frames in a closed universe' https://www.physicsforums.com/showthread.php?t=375432 and the concensus was YES there is a preferred frame in curled dimensions. In that example an experiment would have to go all the way around the universe to be able to detect it, but in String Theory's case ... "all the way around" is just a planck length or something. Strings themselves can go all the way around a curled dimension. So reality built from these curled dimensions would obviously have a preferred frame for experiments at lengths greater than the distance around such a dimension. So why isn't string theory ruled out already?