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History of String Theory Timeline

(1968 - Present)

String theory is a theoretical framework in physics proposing that fundamental particles are one-dimensional 'strings' rather than point-like objects. This timeline traces its evolution from the late 1960s, when it emerged from attempts to describe the strong nuclear force, through the first superstring revolution of 1984, the development of M-theory in 1995, and its ongoing role as a leading candidate for unifying quantum mechanics and general relativity. Less

Go to: Timeline | Event List | Key Facts | Directory

Origins in S-matrix theory

Wheeler introduces the S-matrix

1937

John Archibald Wheeler introduced the concept of the S-matrix, a mathematical object describing how incoming particles scatter into outgoing ones. This idea would later become a foundational element of string theory's origins.

Heisenberg begins S-matrix research program

1943

Werner Heisenberg proposed a research program based on the S-matrix, seeking to describe particle interactions using only observable scattering amplitudes rather than unobservable fields, laying groundwork for later string theory developments.

Image source: S-matrix theory

Heisenberg begins S-matrix research program

Discovery of crossing symmetry

1954

Murray Gell-Mann and Marvin Leonard Goldberger discovered crossing symmetry, another condition that the S-matrix had to fulfill, advancing the development of S-matrix theory.

Image source: Crossing (physics)

Discovery of crossing symmetry

Gell-Mann revives dispersion relations approach

1956

Murray Gell-Mann revived Heisenberg's proposal by recognizing that dispersion relations—like those discovered by Hendrik Kramers and Ralph Kronig in the 1920s—allow the formulation of causality, ensuring future events cannot influence past ones.

Image source: Kramers–Kronig relations

Gell-Mann revives dispersion relations approach

Mandelstam discovers double dispersion relations

1958

Stanley Mandelstam discovered the double dispersion relations, a new and powerful analytic form, and believed it would provide the key to progress in understanding the intractable strong interactions.

Regge trajectories discovered

1959

Tullio Regge, a young theorist in Italy, discovered that bound states in quantum mechanics can be organized into families known as Regge trajectories, each family having distinctive angular momenta.

Image source: Regge theory

Regge trajectories discovered

Chew and Frautschi find straight line Regge trajectories for mesons

1961

Geoffrey Chew and Steven Frautschi recognized that mesons had straight line Regge trajectories, plotted as spin against mass squared on the Chew–Frautschi plot, implying scattering that falls off exponentially quickly at large angles.

Image source: Geoffrey Chew

Chew and Frautschi find straight line Regge trajectories for mesons

Dual resonance models

DHS duality principle introduced

1967

Richard Dolen, David Horn, and Christoph Schmid introduced DHS duality at Caltech, originally termed 'average duality' or 'finite energy sum rule duality', marking a notable step forward in the bootstrap approach.

Peak popularity of dual resonance models

1968 - 1973

Dual resonance models for strong interactions were a relatively popular subject of study between 1968 and 1973, attracting many physicists before being supplanted by quantum chromodynamics.

Veneziano constructs the dual resonance model

1968

Gabriele Veneziano constructed the first model in which hadronic particles essentially follow Regge trajectories, noting that the Euler beta function could describe 4-particle scattering amplitude data for such particles.

Chan–Paton rules proposed

1969

Jack E. Paton and Hong-Mo Chan proposed the Chan–Paton rules, which added internal degrees of freedom to the dual resonance model, allowing the incorporation of flavor quantum numbers into string amplitudes.

Strings interpreted physically by Nambu, Nielsen, and Susskind

1969 - 1970

Yoichiro Nambu, Holger Bech Nielsen, and Leonard Susskind presented a physical interpretation of the Veneziano amplitude by representing nuclear forces as vibrating, one-dimensional strings, birthing modern string theory.

Image source: String theory

Strings interpreted physically by Nambu, Nielsen, and Susskind

Supersymmetry invented

1971

Investigating how string theory may include fermions in its spectrum led to the invention of supersymmetry in the West, a mathematical transformation between bosons and fermions.

Image source: Supersymmetry

Supersymmetry invented

Lovelace discovers critical dimension D = 26

1971

Claud Lovelace discovered that the earliest string model requires a critical dimension of D = 26, one of several problems facing early bosonic string theory alongside tachyon instability.

Ramond and Schwarz develop fermionic strings

1971

Pierre Ramond and, independently, John H. Schwarz extended string theory to include fermions, incorporating supersymmetry into the string framework and paving the way for superstring theory.

Quantum chromodynamics supplants string models

1973

The scientific community lost interest in string theory as a theory of strong interactions when quantum chromodynamics became the main focus of theoretical research, mainly due to the theoretical appeal of its asymptotic freedom.

Image source: Quantum chromodynamics

Quantum chromodynamics supplants string models

First superstring revolution

GSO projection developed

1977

Ferdinando Gliozzi, Joël Scherk, and David I. Olive developed the GSO projection, which removed the unwanted tachyon state from the string spectrum and ensured spacetime supersymmetry in superstring theories.

First superstring revolution begins

1984

The first superstring revolution was a period of important discoveries beginning in 1984, when anomalies were found to cancel for certain gauge groups, reigniting widespread interest in string theory as a candidate theory of everything.

Five superstring theories described

1985

By 1985, five separate superstring theories had been described: type I, type II (IIA and IIB), and heterotic (SO(32) and E8×E8), all seemingly distinct yet later understood as limits of one underlying theory.

Heterotic string discovered

1985

David Gross, Jeffrey Harvey, Emil Martinec, and Ryan Rohm made the ground-breaking discovery of the heterotic string, combining bosonic and superstring degrees of freedom in a single consistent theory.

Calabi–Yau compactification requirement established

1985

Physicists including Philip Candelas, Gary Horowitz, Andrew Strominger, and Edward Witten showed that the extra dimensions required by superstring theory (beyond those known by Schwarz in 1972) need to be compactified on a Calabi–Yau manifold to preserve phenomenological viability.

Image source: Calabi–Yau manifold

Calabi–Yau compactification requirement established

Discover magazine highlights string theory

Nov 1986

Discover magazine devoted coverage to string theory in its November 1986 issue (vol.), reflecting growing public interest in the theory following the first superstring revolution.

Supermembranes shown to exist in eleven dimensions

1987

Eric Bergshoeff, Ergin Sezgin, and Paul Townsend showed that there are no superstrings in eleven dimensions—the largest number of dimensions consistent with a single graviton in supergravity—but rather supermembranes, foreshadowing M-theory.

Second superstring revolution

Second superstring revolution begins

1994 - 1995

New discoveries sparked the second superstring revolution, taking place approximately between 1994 and 1995, characterized by the recognition of dualities connecting the different superstring theories.

Polchinski discovers D-branes

1995

Joseph Polchinski discovered that the theory requires the inclusion of higher-dimensional objects called D-branes: these are the sources of electric and magnetic Ramond–Ramond fields required by string duality.

Image source: D-brane

Polchinski discovers D-branes

Maldacena conjectures AdS/CFT correspondence

1997 - 1998

Juan Maldacena conjectured a relationship between type IIB string theory and N = 4 supersymmetric Yang–Mills theory, a gauge theory, establishing the celebrated holographic AdS/CFT duality.

Modern developments

KKLT vacuum stabilization mechanism proposed

2003

Shamit Kachru, Renata Kallosh, Andrei Linde, and Sandip Trivedi proposed the KKLT mechanism, a possible mechanism of string theory vacuum stabilization addressing the vast landscape of metastable vacua.

Ryu–Takayanagi conjecture introduced

2006

The Ryu–Takayanagi conjecture introduced many concepts from quantum information, such as entanglement entropy, into string theory, forging deep links between geometry and quantum entanglement.

Key Facts

  1. In 1968, Gabriele Veneziano discovered that the Euler beta function described the scattering of hadrons, sparking what became string theory.
  2. In 1970, physicists including Yoichiro Nambu, Holger Nielsen, and Leonard Susskind realized that Veneziano's formula implied vibrating one-dimensional strings.
  3. In 1984, the first superstring revolution began when Michael Green and John Schwarz showed anomaly cancellation works for certain string theories, igniting widespread interest.
  4. In 1995, Edward Witten proposed M-theory at the Strings conference, unifying five competing superstring theories into a single framework involving eleven dimensions.
  5. The discovery of dualities and D-branes in the mid-1990s led to the AdS/CFT correspondence (1997), connecting string theory to quantum field theories.

Source

This History of String Theory timeline was generated with the help of AI, using information found on the internet.

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