Why is String Theory potentially scientific and not merely wishful thinking? What its Feynman's definition of science?

String theory to me is that all objects in our universe are composed of strings and membranes of energy. Ive herd that string theory is the theory of everything, relatively young science.Scientist believe that sciences will eventually come together, or in one way or another link to eachother. Gravity and quantum physics link together. I dont believe its wishful thinking because there is a theory that gravity quantum physics work together.Feynman was a very interesting man and he was known as one of the best scientists in the world. He always thought if he cold come up with the theory of the very small he would have the answers for the very large.