History of string theory
Through the combined efforts of many researchers, string theory has developed into a broad and varied subject with connections to quantum gravity, particle and condensed matter physics, cosmology, and pure mathematics.
Physicists neglected it because some of its mathematical methods were alien, and because quantum chromodynamics supplanted it as an experimentally better-qualified approach to the strong interactions.
An experiment only sees a microscopic quantity if it can be transferred by a series of events to the classical devices that surround the experimental chamber.
Heisenberg proposed that even when space and time are unreliable, the notion of momentum state, which is defined far away from the experimental chamber, still works.
[8][7] Prominent advocates of the new "dispersion relations" approach included Stanley Mandelstam[9] and Geoffrey Chew,[10] both at UC Berkeley at the time.
Mandelstam discovered the double dispersion relations, a new and powerful analytic form, in 1958,[9] and believed that it would provide the key to progress in the intractable strong interactions.
Sakata's approach was reworked in the 1960s into the quark model by Murray Gell-Mann and George Zweig by making the charges of the hypothetical constituents fractional and rejecting the idea that they were observed particles.
At the time, Chew's approach was considered more mainstream because it did not introduce fractional charge values and because it focused on experimentally measurable S-matrix elements, not on hypothetical pointlike constituents.
[14] This idea was generalized to relativistic quantum mechanics by Stanley Mandelstam, Vladimir Gribov and Marcel Froissart, using a mathematical method (the Sommerfeld–Watson representation) discovered decades earlier by Arnold Sommerfeld and Kenneth M. Watson: the result was dubbed the Froissart–Gribov formula.
The Veneziano scattering amplitude (or Veneziano model) was quickly generalized to an N-particle amplitude by Ziro Koba and Holger Bech Nielsen[20] (their approach was dubbed the Koba–Nielsen formalism), and to what are now recognized as closed strings by Miguel Virasoro[21] and Joel A. Shapiro[22] (their approach was dubbed the Shapiro–Virasoro model).
In 1969, the Chan–Paton rules (proposed by Jack E. Paton and Hong-Mo Chan)[23] enabled isospin factors to be added to the Veneziano model.
[24] In 1969–70, Yoichiro Nambu,[25] Holger Bech Nielsen,[26] and Leonard Susskind[27][28] presented a physical interpretation of the Veneziano amplitude by representing nuclear forces as vibrating, one-dimensional strings.
In 1971, Pierre Ramond[29] and, independently, John H. Schwarz and André Neveu[30] attempted to implement fermions into the dual model.
This led to the concept of "spinning strings", and pointed the way to a method for removing the problematic tachyon (see RNS formalism).
[34] In 1974, John H. Schwarz and Joël Scherk,[35] and independently Tamiaki Yoneya,[36] studied the boson-like patterns of string vibration and found that their properties exactly matched those of the graviton, the gravitational force's hypothetical messenger particle.
The earliest string model has several problems: it has a critical dimension D = 26, a feature that was originally discovered by Claud Lovelace in 1971;[38] the theory has a fundamental instability, the presence of tachyons[39] (see tachyon condensation); additionally, the spectrum of particles contains only bosons, particles like the photon that obey particular rules of behavior.
[44] The revolution was started by a discovery of anomaly cancellation in type I string theory via the Green–Schwarz mechanism (named after Michael Green and John H. Schwarz) in 1984.
[45][46] The ground-breaking discovery of the heterotic string was made by David Gross, Jeffrey Harvey, Emil Martinec, and Ryan Rohm in 1985.
