History of string theory

String theory
Fundamental objects
String Cosmic string Brane D-brane
Perturbative theory
Bosonic Superstring (Type I, Type II, Heterotic)
Non-perturbative results
S-duality T-duality U-duality M-theory F-theory AdS/CFT correspondence
Phenomenology
Phenomenology Cosmology Landscape
Mathematics
Geometric Langlands correspondence Mirror symmetry Monstrous moonshine Vertex algebra K-theory
Related concepts Theory of everything Conformal field theory Quantum gravity Supersymmetry Supergravity Twistor string theory N = 4 supersymmetric Yang–Mills theory Kaluza–Klein theory Multiverse Holographic principle
Theorists Aganagić Arkani-Hamed Atiyah Banks Berenstein Bousso Curtright Dijkgraaf Distler Douglas Duff Dvali Ferrara Fischler Friedan Gates Gliozzi Gopakumar Green Greene Gross Gubser Gukov Guth Hanson Harvey Hořava Horowitz Gibbons Kachru Kaku Kallosh Kaluza Kapustin Klebanov Knizhnik Kontsevich Klein Linde Maldacena Mandelstam Marolf Martinec Minwalla Moore Motl Mukhi Myers Nanopoulos Năstase Nekrasov Neveu Nielsen van Nieuwenhuizen Novikov Olive Ooguri Ovrut Polchinski Polyakov Rajaraman Ramond Randall Randjbar-Daemi Roček Rohm Sagnotti Scherk Schwarz Seiberg Sen Shenker Siegel Silverstein Sơn Staudacher Steinhardt Strominger Sundrum Susskind 't Hooft Townsend Trivedi Turok Vafa Veneziano Verlinde Verlinde Wess Witten Yau Yoneya Zamolodchikov Zamolodchikov Zaslow Zumino Zwiebach
History Glossary
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The history of string theory spans several decades of intense research including two superstring revolutions. 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.

1943–1959: S-matrix theory

String theory represents an outgrowth of

The theory presented a radical rethinking of the foundations of physical laws. By the 1940s it had become clear that the

. Their interactions were so strong that they scattered like a small sphere, not like a point. Heisenberg proposed that the strongly interacting particles were in fact extended objects, and because there are difficulties of principle with extended relativistic particles, he proposed that the notion of a space-time point broke down at nuclear scales.

Without space and time, it becomes difficult to formulate a physical theory. Heisenberg proposed a solution to this problem: focusing on the observable quantities—those things measurable by experiments. 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. The objects that fly to infinity are stable particles, in quantum superpositions of different momentum states.

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. The physical quantity he proposed as fundamental is the

for a group of incoming particles to turn into a group of outgoing particles, and he did not admit that there were any steps in between.

The S-matrix is the quantity that describes how a collection of incoming particles turn into outgoing ones. Heisenberg proposed to study the S-matrix directly, without any assumptions about space-time structure. But when transitions from the far-past to the far-future occur in one step with no intermediate steps, it becomes difficult to calculate anything. In quantum field theory, the intermediate steps are the fluctuations of fields or equivalently the fluctuations of virtual particles. In this proposed S-matrix theory, there are no local quantities at all.

Heisenberg proposed to use

once the basic interactions are given, and in many quantum field theories the amplitudes grow too fast at high energies to make a unitary S-matrix. But without extra assumptions on the high-energy behavior, unitarity is not enough to determine the scattering, and the proposal was ignored for many years.

Heisenberg's proposal was revived in 1956 when

Prominent advocates of the new "dispersion relations" approach included

and believed that it would provide the key to progress in the intractable strong interactions.

1959–1968: Regge theory and bootstrap models

By the late 1950s, many strongly interacting particles of ever higher spins had been discovered, and it became clear that they were not all fundamental. While Japanese physicist

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.

In 1959,

In 1961, Geoffrey Chew and

asymptotic

form demanded by Regge theory.

In 1967, a notable step forward in the bootstrap approach was the principle of

1968–1974: Dual resonance model

The first model in which hadronic particles essentially follow the Regge trajectories was the

).

In 1969, the

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. However, this string-based description of the strong force made many predictions that directly contradicted experimental findings.

In 1971,

Dual resonance models for strong interactions were a relatively popular subject of study between 1968 and 1973.[32] The scientific community lost interest in string theory as a theory of strong interactions in 1973 when quantum chromodynamics became the main focus of theoretical research^[33] (mainly due to the theoretical appeal of its asymptotic freedom).^[34]

1974–1984: Bosonic string theory and superstring theory

In 1974, John H. Schwarz and

.

String theory is formulated in terms of the

spectrum

" of the theory.

Early models included both open strings, which have two distinct endpoints, and closed strings, where the endpoints are joined to make a complete loop. The two types of string behave in slightly different ways, yielding two spectra. Not all modern string theories use both types; some incorporate only the closed variety.

The earliest string model has several problems: it has a

.

In 1977, the

).

1984–1994: First superstring revolution

The first superstring revolution is a period of important discoveries that began in 1984.

in 1985 that to obtain ${\displaystyle N=1}$ supersymmetry, the six small extra dimensions (the D = 10 critical dimension of superstring theory had been originally discovered by John H. Schwarz in 1972)^[48] need to be compactified on a Calabi–Yau manifold.^[49] (In string theory, compactification is a generalization of Kaluza–Klein theory, which was first proposed in the 1920s.)^[50]

By 1985, five separate superstring theories had been described: type I,^[51] type II (IIA and IIB),^[51] and heterotic (SO(32) and E₈×E₈).^[47]

Discover magazine in the November 1986 issue (vol. 7, #11) featured a cover story written by Gary Taubes, "Everything's Now Tied to Strings", which explained string theory for a popular audience.

In 1987, Eric Bergshoeff [de], Ergin Sezgin [de] and Paul Townsend showed that there are no superstrings in eleven dimensions (the largest number of dimensions consistent with a single graviton in supergravity theories),^[52] but supermembranes.^[53]

1994–2003: Second superstring revolution

In the early 1990s, Edward Witten and others found strong evidence that the different superstring theories were different limits of an 11-dimensional theory^[54][55] that became known as M-theory (for details, see Introduction to M-theory).^[56] These discoveries sparked the second superstring revolution that took place approximately between 1994 and 1995.^[57]

The different versions of superstring theory were unified, as long hoped, by new equivalences. These are known as S-duality, T-duality, U-duality, mirror symmetry, and conifold transitions. The different theories of strings were also related to M-theory.

In 1995, Joseph Polchinski discovered that the theory requires the inclusion of higher-dimensional objects, called D-branes:^[58] these are the sources of electric and magnetic Ramond–Ramond fields that are required by string duality.^[59] D-branes added additional rich mathematical structure to the theory, and opened possibilities for constructing realistic cosmological models in the theory (for details, see Brane cosmology).

In 1997–98,

2003–present

This section needs to be updated. The reason given is: any noteworthy developments over the last 20 years?. Please help update this article to reflect recent events or newly available information. (August 2023)

In 2003, Michael R. Douglas's discovery of the string theory landscape,^[64] which suggests that string theory has a large number of inequivalent false vacua,^[65] led to much discussion of what string theory might eventually be expected to predict, and how cosmology can be incorporated into the theory.^[66]

A possible mechanism of string theory vacuum stabilization (the

See also

• History of quantum field theory
• History of loop quantum gravity

Notes

References

• ISBN 978-3-642-45128-7
  .

Further reading

• ISBN 978-0-8053-2581-2
  .
• Joel A. Shapiro (2007). "Reminiscence on the Birth of String Theory".
  arXiv:0711.3448 [hep-th
  ].
• arXiv:1201.0981 [physics.hist-ph
  ].
• Andrea Cappelli; Elena Castellani; Filippo Colomo;
  ISBN 978-0-521-19790-8
  .