second Annotation-string theory

string theory ,

      chern use his math to show the scientist that we have this theory, but the problem is we still can not make it become true, we only can know string theory is to be a theory of quantum gravity, then the average size of a string should be somewhere near the length scale of quantum gravity, called the Planck length, which is about 10^-33 centimeters, or about a millionth of a billionth of a billionth of a billionth of a centimeter. 

http://www.superstringtheory.com/basics/basic4.html

this website help us to know a little about string theory ,but it too difficult to understand it. because we only high school. so, I will research another theory that he define.