The idea of the atom may have originated in Babylon or Egypt or even in India, but the story of matter started in 5th-century bc Greece with Leucippus and his pupil Democritus. They taught that matter was composed of empty space and an infinite number of tiny, indestructible particles called atomos or atoms. But Aristotle and other Greek philosophers preferred their 'elements' -earth, air, fire and water - out of which the whole world was created, and Democritus' idea was lost for two millennia. It was recovered and expanded in 1808 by John Dalton, a Quaker schoolmaster from Manchester, into his atomic theory.
The first real picture of the atom emerged in 1897 when the British physicist J.J. Thomson suggested that atoms are like a Christmas pudding, in which negatively charged electron 'raisins' are embedded in a spherical 'pudding' of positively charged protons. This delicious model was demolished in the early 20th century when Ernest Rutherford showed that the atom was like a miniature solar system with electrons orbiting around the central 'Sun' or nucleus composed of protons and neutral particles called neutrons. After announcing his model, the world-famous professor of physics at Manchester University, with a broad grin and in a boom ing voice, said to his close colleagues of his critics: 'Some of them would give a thousand pounds to disprove it.' No one had the temerity - or a thousand pounds - to challenge the model that soon, with some changes, became the icon by which we still recognise the atom.
While students struggled to understand the three-particle structure of the atom, physicists came up with complex quantum models of the atom and discovered an entire 'zoo' of elementary particles (so many, in fact, that it prompted Enrico Fermi to remark: 'If I could remember the names of all these particles, I would have become a botanist.'). The most famous of these particles are quarks, which were postulated in 1964 by the American physicist Murray Gell-Mann, who won the Nobel Prize in physics in 1969 for his work on them. Their name comes from a phrase - 'Three quarks for Muster Mark' -in James Joyce's novel Finnegans Wake. Until recently, quarks were considered the basic building blocks of matter, but some physicists now believe that quarks themselves are made up of even smaller particles. The physics of quarks and other elementary particles is very complex, but in simple terms we can say that each particle has three major characteristics: mass (some particles have zero mass); charge (every particle has a positive, negative or neutral charge); and spin (every particle spins like a top).
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