Do we know what energy "is"? Hi everyone, According to what I have read a string is a minute amount of vibrating energy. Is the word "energy" here used as an approximate for the lay reader? I was led to this thought because if the vibration of strings make up matter and energy then what's the difference between the "macro energy" produced by vibration and the "pure" non vibrating energy? Basically I'm asking, what is energy? Thanks!