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Even the ancient Greeks knew that different objects were composed of compounds of more fundamental substances. This begged the question: if something can be broken down into its component parts, and they in turn can be broken down into their component parts, where does it stop?

Is there a point where we arrive at the fundamental ‘elements’ of matter? For the Greeks, these elements were air, water, fire and earth. And for physicists in the late 19th and early 20th centuries, they were atoms.

Some might argue the story of the Standard Model really began in 1897, when British scientist, J.J. Thomson, demonstrated he could pull identical particles – electrons – out of many different materials.

Soon thereafter, in 1909, New Zealander Ernest Rutherford discovered that most of an atom’s mass was concentrated in a tiny area, the nucleus.

Rutherford concluded that an atom – derived from the Greek atomon meaning ‘cannot be divided’ – can, in fact, be divided. Atoms have protons and neutrons in the nucleus, with electrons orbiting.

But the sub-divisions didn’t stop there.

“Who ordered THAT?!” Nobel laureate I.I. Rabi famously asked after yet another particle, called the muon, was discovered in 1936.

The muon was the first particle discovered that did not occur in an atom – its mere existence understandably caused consternation in the physics community. No one had thought of matter that didn’t occur somewhere around us on Earth.

The muon has similar properties to an electron, except that it is much heavier. And particle physicists now know of an even heavier version, called the tau. The electron, muon and tau are called the three ‘flavours’ of a family of fundamental particles (which cannot be divided) called leptons. Each flavour has a nearly massless companion, called a neutrino.

In 1964, Americans Murray Gell-Mann and George Zweig proposed the existence of three other fundamental particles, which together could make up hundreds of the known particles at the time.

Gell-Mann named them ‘quarks’ (pronounced ‘kworks’), after the nonsense word fabricated by James Joyce in his novel Finnegans Wake: “Three quarks for Muster Mark!”

Experimentalists found each of the three quarks as predicted … and they were on such a roll that they continued until they found three more. The most elusive quark, the top quark, was finally discovered in 1995, after its existence was first predicted in 1977. Quarks bunch together, in pairs or trios, forming the familiar particles, such as neutrons and protons.

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