The Standard Model

At the end of the of the nineteenth century the particulate nature of matter was becoming better understood. JJ Thompson found the charge to mass ratio of the electron and Rutherford, Geiger and Marsden helped to develop the model of the atom, which was later further enhanced by Bohr.

In the early twentieth century it was believed that all matter was composed of Electrons, Protons and Neutrons. However, over the following decades other particles were both found and predicted. By the 1960s there was a host of new subatomic and sub-nuclear particles. Scientists referred to this as the particle zoo.

In the early 1970s Murray Gell-Mann (and others) proposed the Standard Model, which described matter in terms of a small number of fundamental particles.

The Standard Model

The Standard Model proposes that there are fundamental particles and others which are composed of groups of fundamental particles.

The diagram below shows the modern Standard Model groupings:-


What we think of as normal matter is actually made up of combinations of fundamental particles. These compound particles are called Hadrons and they come in two types:

1. Baryons - Made up of combinations of three quarks

2. Mesons - Made up of combinations of two quarks (they are always form an quark/antiquark pair)


The fundamental matter particles called Fermions and are in two groups:

1. 6 Leptons, of which three are neutrinos (from the Greek word meaning light, as in lightweight)

2. 6 Quarks (from a James Joyce novel because the word sounded good)

Fundamental Forces and Bosons

Particles may experience four fundamental Forces, Strong (nuclear) Force, Weak (nuclear) Force, Gravitational Force and Electromagnetic Force.

The force mediating (transmitting) particles are called Bosons. Each type works with one on the four fundamental forces:-


Every particle has an anti-particle. These are identical in every way, but carry the opposite charge. So an anti-Proton is identical to a proton, but carries a negative charge. An anti-Electron (called a Positron) is identical to an electron, but carries a positive charge.

The video below gives further information on the Standard Model from CERN.

The video below gives a short explanation of anti-matter.