History of Particle Physics Timeline

The next step was a reduction in the number of fundamental interactions, envisaged by early 20th-century physicists as the 'united field theory', inspiring decades of unification efforts.

Image source: Unified field theory

It began with what Gell-Mann referred to as the 'Eightfold Way', proceeding into several different 'octets' and 'decuplets' which could predict new particles, transforming the classification of hadrons.

Image source: Eightfold way (physics)

While the quark model at first seemed inadequate to describe strong nuclear forces, allowing the temporary rise of competing theories such as the S-matrix theory during the 1960s.

Image source: S-matrix theory

The Ω−, famously predicted by the Eightfold Way, was detected at Brookhaven National Laboratory in 1964, giving rise to the quark model of hadron composition.

Image source: Omega baryon

Following the detection of the Ω−, the quark model arose to explain hadron composition in terms of fundamental quark constituents, reshaping particle physics.

Image source: Quark model

The establishment of quantum chromodynamics in the 1970s finalized a set of fundamental and exchange particles, securing the quark model's place in describing strong nuclear forces.

Image source: Quantum chromodynamics

After the discovery, made at CERN, of the existence of neutral weak currents mediated by the Z boson foreseen in the standard model, electroweak theory gained crucial experimental support.

Following the discovery of neutral weak currents, physicists Salam, Glashow and Weinberg received the 1979 Nobel Prize in Physics for their electroweak theory unifying electromagnetism and the weak force.

In 1909 Ernest Rutherford and Thomas Royds demonstrated that an alpha particle combines with two electrons and forms a helium atom, clarifying the nature of radioactive emissions.

Image source: Ernest Rutherford

In 1918, Rutherford confirmed that the hydrogen nucleus was a particle with a positive charge, which he named the proton, identifying another key constituent of matter.

Image source: Proton

Also in 1939, Hans Bethe demonstrated the mechanism of nuclear fusion, explaining how stars produce energy by fusing light nuclei together.

Image source: Hans Bethe

It culminated in proofs of nuclear fission in 1939 by Lise Meitner, based on experiments by Otto Hahn, revealing the enormous energy stored within atomic nuclei.

Image source: Nuclear fission

Production of progressively heavier synthetic elements continued into the 21st century as a branch of nuclear physics, pursued purely for scientific purposes rather than practical applications.

Image source: Synthetic element

Improved understanding of the world of particles prompted bold predictions such as Dirac's positron in 1928, founded on the Dirac Sea model, anticipating antimatter.

Image source: Positron

In 1930 Pauli proposed the neutrino, founded on conservation of energy and angular momentum in beta decay, a particle that would remain elusive for decades.

Image source: Neutrino

In 1957 Chien-Shiung Wu proved that parity is not conserved in weak interactions, overturning a long-held symmetry assumption in physics.

Image source: Wu experiment

Peter Higgs was one of six physicists, working in three independent groups, who in 1964 invented the notion of the cosmic molasses, or Higgs field, a mechanism thought to give particles mass.

As of 2011, the Higgs boson, the quantum of a field thought to provide particles with rest masses, remained the only particle of the Standard Model yet to be verified experimentally.

Image source: Higgs boson

On July 4, 2012, physicists working at CERN's Large Hadron Collider announced they had discovered a new subatomic particle greatly resembling the Higgs boson, a potential key to understanding why elementary particles have masses and indeed to the existence of diversity and life in the universe.

Rolf-Dieter Heuer, director general of CERN, said it was too soon to know for sure whether the newly found particle was entirely new, one of the heaviest subatomic particles yet, or indeed the elusive particle predicted by the Standard Model, the theory that has ruled physics for half a century.

Image source: Rolf-Dieter Heuer

Further experiments continued, and in March 2013 it was tentatively confirmed that the newly discovered particle was a Higgs boson, fulfilling a rendezvous with destiny for a generation of physicists who believed in its existence for half a century without ever seeing it.