Why did string enter the story?
Particle physics interactions (top) occur at zero distance, but string
interactions (bottom) don't. That's what makes string theory more
successful as quantum theory of gravity.
Relativistic quantum field theory has worked very well to describe
the observed behaviors and properties of elementary particles. But the
theory itself only works well when gravity is so weak that it can be
neglected. Particle theory only works when we pretend gravity doesn't
exist.
Genera
