Quarks

Quarks are, according to the modern theory of subatomic particles, one of the three basic building blocks of all matter. The others are the leptons (which include the electron and the three types of neutrinos) and the intermediate vector bosons (which mediate the forces that bind other particles together). The stable particles of which ordinary matter is mostly composed—protons and neutrons—consist of quarks bound together by a type of intermediate vector boson termed the gluon.

One of the triumphs of modern science is its confirmation and clarification of an idea first proposed by Greek philosophers over 2,000 years ago: that all forms of matter, despite their diverse properties, are ultimately built up from a small number of fundamental particles or units. The Greeks called these units "atoms," after their word meaning uncuttable. Today, the word atom is reserved for the smallest possible units of an element (e.g., hydrogen, iron, calcium), while the term fundamental particle is used to denote the truly indivisible and ultimate building blocks of all matter. The modern hierarchy of material structure thus has several more levels than the Greek. Water, for example, consists of molecules that are made up of atoms of the elements hydrogen and oxygen. In turn, these atoms are made of electrons, protons, and neutrons, which in the early twentieth century were thought to be truly fundamental or indivisible; however, it is now known that this is not true. Electrons are indeed fundamental, but protons and neutrons are made of quarks and gluons.