3.1 Elementary particles

One of the most striking examples of symmetry in physics occurs in particle physics, which looks at the smallest constituents of matter and their interactions.

The first identified subatomic particles were the electron, discovered by Joseph John Thomson in 1897, and the proton, discovered by Ernest Rutherford in the late 1910s. In the following years, the detection of new particles in experiments continued rapidly. Scientists soon started to look at patterns that would allow them to organise this so-called ‘particle zoo’, particularly hadrons (as mentioned in Section 1, these are composite particles like protons, neutrons, etc.).

Scientists noticed that these particles, when arranged according to their electric charge and another observed property called ‘strangeness’, give rise to patterns that they could link to a particular type of symmetry (which are related to higher-dimensional rotations).

Building on this symmetry, in 1961 Murray Gell-Mann and Yuval Ne’eman independently arrived at a model for hadrons, which has become known as the ‘eightfold way’ (derived from the title of Gell-Mann’s publication, an allusion to the Noble Eightfold Path of Buddhism). However, there was one issue – the symmetry predicted a particle that had not yet been observed. From the model, Gell-Mann could predict the specific properties of the particle. It was eventually found in 1964, corroborating the model’s predictions, and earning Murray Gell-Mann the 1969 Nobel Prize in Physics.