Timeline – from the discovery of the electron to the Higgs boson*


  • 1895 Henri Becquerel discovers radioactivity
  • 1897 JJ Thomson and his assistant Ebenezer Everett, discover the first subatomic particle, the electron, with cathode ray tube.  By bending the beams with electric and magnetic fields, which the LHC does today on a much larger scale, he showed they were made up of negatively charged particles, much smaller than atoms
  • 1898 Marie and Pierre Curie discover radium
  • 1905 Albert Einstein publishes his special theory of relativity and argues that light is a flow of particles, later called photons
  • 1909  Hans Geiger and Ernest Marsden conduct a series of experiments under the supervision of Ernest Rutherford  measuring how an alpha particle beam is scattered when it strikes a thin metal foil and in so doing discover the atom’s nucleus, see Particles and forces  [1]
  • 1911 Rutherford publishes his planetary model of the atom
  • 1912 CTR Wilson invents the cloud chamber, the first device for imaging the paths of subatomic particles.  The cloud chamber revolutionised subatomic physics almost by accident.  Wilson invented this device to replicate cloud formations such as those he saw on the summit of Ben Nevis.  In the laboratory he found that radioactive sources left trails of mist in his cloud chamber.  Water molecules were clumping around ionised alpha and beta particles, eventually forming a trail of droplets in so doing. Cloud chambers became increasingly important in tracking high-energy particles coming from space. [2]
  • 1913 Niels Bohr publishes the first quantum theory of the atom
  • 1919 Ernest Rutherford shows that heavy atomic nuclei contain hydrogen nuclei, that hydrogen nucleus was possibly a fundamental building block of all nuclei, and postulated the hydrogen nucleus to be a new particle in 1920, which he dubbed the proton
  • 1928 Paul Dirac publishes an equation predicting the existence of antimatter
  • 1932 James Chadwick discovers the neutron
  • 1932 John Cockcroft and Ernest Walton use the first particle accelerator to split the atomic nucleus.  Protons were accelerated through 700,000 volts and slammed into a lithium target, watched by an observer in a lead-lined cabin.  When Walton observed flashes on their fluorescent screen, they realised that their experiment had been successful.  The LHC now achieves energies 20 million times higher.*

PictureThe Anderson photograph evidencing the existence of antimatter. The faint track crossing the chamber provided the first evidence for the positron, the antiparticles of the electron. Source: Science Museum London’s LHC exhibition on display at the Powerhouse Museum Sydney, 17 August 2016.

  • 1932 Carl Anderson discovers the first antimatter particle, the anti-electron, using a cloud chamber. The photograph depicting this is one of the most important images in the history of particle physics – the faint curved track crossing the chamber from bottom to top provided the first evidence for the positron, the antiparticle of the electron. It looked like an electron, but travelled up through a magnetic field when it should have travelled down  Anderson’s photographs helped to turn Dirac’s strange idea into one of the most successful theories of the twentieth century.

As Gavin Hesketh explains:  «A charged particle changes direction as it flies through a magnetic field, leaving a curved track in the cloud chamber.  Positively and negatively charged particles will curve in opposite directions (bending left or right, for example), and slower particles will curve more than faster particles, allowing much more information to be extracted from cloud-chamber photos”.  A modern-day corollary is that huge powerful magnets are a key part of almost every modern particle detector for the same reason: the electric charge and momentum of a particle can be determined by measuring the curve in its path. [3]

  • 1935 Hideki Ukawa predicts the existence of a particle called a pion that sticks protons and neutrons together inside the atomic nucleus
  • 1936 Carl  Anderson and Seth Neddermeyer discover a heavy version of the electron, the muon
  • 1930s – 1940s: a series of unexpected particles showed up in cloud chambers, leaving physicists to make sense of the “particle zoo”.  In 1946, a single V-shaped track in Rochester and Butler’s cloud chamber in Manchester indicated a new type of particle, dubbed “strange” but now known as the K-meson.  There are now hundreds of known particles, but most are only produced fleetingly in high-energy particles accelerators or by cosmic rays.*
  • 1947 Physicists at the University of Bristol discover the pion and George Rochester and Clifford Butler discover the kaon in cosmic rays
  • 1955 Construction begins at CERN, the European Organisation for Nuclear Research
  • 1964 Murray Gell-Mann and George Zweig discover that a number of subatomic particles, including protons and neutrons are made up of smaller particles called quarks
  • 1964 Peter Higgs, François Englert, Robert Brout, Carl Hagen , Tom Kibble and Gerald Gurainik predict the existence of the Higgs boson
  • 1968 Experiments at the Stanford Linear Accelerator show that the proton is made up of smaller particles, giving support to the quark model
  • 1983 Physicists at CERN’s Super Proton Synchrotron discover the W and X bosons, the particles of the weak nuclear force
  • 1989 The largest particles accelerator in the world, the Large Electron Positron Collider, begins operating at CERN
  • 1993 The USA cancels the planned Superconducting Super Collider after costs spiral
  • 1995 The Tevatron Collider at Fermilab near Chicago USA discovers the last quark, the top quark. By 2011 it could no longer compete with the larger and more powerful LHC and was closed
  • 2001 The Large Electron Positron Collider is dismantled to make  way for the Large Hadron Collider
  • 2012 Physicists at the Large Hadron Collider announce the discovery of the Higgs boson

[1] This is also described in some detail by Gavin Hesketh’s The Particle Zoo – The search for the fundamental nature of reality, Quercus, Hachette, 2016, 52-53.
[2]  Also vividly described in ibid, 53-59, including how to make one and how it works.
[3]  Ibid, at 61; and at 36:
 «‘a negatively charged particle travelling backwards in time turns out to look identical to a positively charged particle travelling forwards in time».

Source:  Science Museum London’s travelling LHC exhibition, viewed at the Sydney Powerhouse Museum, August 2016.