Just a point of clarification. You used the term “theory”. You do understand that theory is the highest level of proof in science? Did you mean hypothesis?
No, I meant theory.
As compared to a law, which describes how an observed phenomena works, a theory attempts to explain why.
The common example is the law of gravity, which state how objects interact, while theories are trying to explain why.
String theory is trying to us why the universe exists, not how it does.
Nutshell.