"Consider the humble electron. In most non-string theory physics it is a point particle, dimensionless. The problem is that as we get closer and closer to its actual, exact location its energy approaches infinity, thanks the the Uncertainty Principle. That is unacceptable so physicists renormalize. Of that Feynman wrote, " "The shell game that we play to find n and j is technically called renormalization. But no matter how clever the word, it is what I would call a dippy process! Having to resort to such hocus-pocus has prevented us from proving the theory of quantum electrodynamics is mathematically self-consistent. .... I suspect that renormalization is not mathematically legitimate." Therefore what we usually think of as the electron is really a cloud of virtual particles popping in and out of existence some distance from that horror at the center. String theorists have came along and said there are no point particles, only strings. Whew, the world almost blew up.