Editing String theory (section)

=== First superstring revolution ===

[[File:Edward Witten.jpg|right|thumb|upright|[[Edward Witten]]]]

In the early 1980s, [[Edward Witten]] discovered that most theories of quantum gravity could not accommodate [[chirality (physics)|chiral]] fermions like the neutrino. This led him, in collaboration with [[Luis Álvarez-Gaumé]], to study violations of the conservation laws in gravity theories with [[Gravitational anomaly|anomalies]], concluding that type I string theories were inconsistent. Green and Schwarz discovered a contribution to the anomaly that Witten and Alvarez-Gaumé had missed, which restricted the gauge group of the type I string theory to be SO(32). In coming to understand this calculation, Edward Witten became convinced that string theory was truly a consistent theory of gravity, and he became a high-profile advocate. Following Witten's lead, between 1984 and 1986, hundreds of physicists started to work in this field, and this is sometimes called the [[first superstring revolution]].{{Citation needed|date=September 2020}}

During this period, [[David Gross]], [[Jeffrey A. Harvey|Jeffrey Harvey]], [[Emil Martinec]], and [[Ryan Rohm]] discovered [[heterotic strings]]. The gauge group of these closed strings was two copies of [[E8 (mathematics)|E8]], and either copy could easily and naturally include the standard model. [[Philip Candelas]], [[Gary Horowitz]], [[Andrew Strominger]] and Edward Witten found that the Calabi–Yau manifolds are the compactifications that preserve a realistic amount of supersymmetry, while [[Lance Dixon]] and others worked out the physical properties of [[orbifolds]], distinctive geometrical singularities allowed in string theory. [[Cumrun Vafa]] generalized T-duality from circles to arbitrary manifolds, creating the mathematical field of [[mirror symmetry (string theory)|mirror symmetry]]. [[Daniel Friedan]], [[Emil Martinec]] and [[Stephen Shenker]] further developed the covariant quantization of the superstring using conformal field theory techniques. [[David Gross]] and Vipul Periwal discovered that string perturbation theory was divergent. [[Stephen Shenker]] showed it diverged much faster than in field theory suggesting that new non-perturbative objects were missing.{{Citation needed|date=September 2020}}

[[File:Joseph Polchinski.jpg|left|thumb|upright|[[Joseph Polchinski]]]]

In the 1990s, [[Joseph Polchinski]] discovered that the theory requires higher-dimensional objects, called [[D-brane]]s and identified these with the black-hole solutions of supergravity. These were understood to be the new objects suggested by the perturbative divergences, and they opened up a new field with rich mathematical structure. It quickly became clear that D-branes and other p-branes, not just strings, formed the matter content of the string theories, and the physical interpretation of the strings and branes was revealed—they are a type of black hole. [[Leonard Susskind]] had incorporated the [[holographic principle]] of [[Gerardus 't Hooft]] into string theory, identifying the long highly excited string states with ordinary thermal black hole states. As suggested by 't Hooft, the fluctuations of the black hole horizon, the world-sheet or world-volume theory, describes not only the degrees of freedom of the black hole, but all nearby objects too.