in 1961, chew and frautschi discovered that the mesons fall into straight-line regge trajectories (in their scheme, spin is plotted against mass squared on a so-called chew–frautschi plot), and the two of them introduced the pomeron into the western literature. frautschi's most well known contribution to strong-interaction theory was the statistical bootstrap, a prediction that the number of hadronic states grows exponentially with energy. this is nowadays understood as a manifestation of the deconfinement phase transition. the exponential growth is incorporated into string theory, where it is known as the hagedorn temperature. (this s-matrix approach to the strong interactions was largely abandoned by the particle physics community in the 1970s in light of quantum chromodynamics.)