This is a question I came about while thinking about the nature of matter and energy. According to string theory, the very fundamental building blocks of matter and energy are tiny vibrating strings. I was thinking to myself then: why are these the fundamental building blocks of the Universe, why is it not some other thing? Is there are any equation that would naturally predict strings to be the only possible option for building blocks? Also, would the TOE have something to say about strings being the only possible option for the building blocks of matter and energy? I'm sorry if this question sounds confusing, but I was just wondering about this!