The laughing philosopher imagined atoms and countless worlds 2,400 years ago
Democritus pictured everything, from water to people, as clumps of tiny indivisible bodies moving through empty space. He guessed there were many worlds, some without a sun, others with several, each born and eventually destroyed. Not one of his nearly eighty treatises survives; we know him mostly through his rival Aristotle.
Democritus came from Abdera on the Thracian coast and lived roughly from 460 to 370 BC, though ancient sources disagree on his dates and even on his father's name. That father was rich enough, it was said, to host the Persian king Xerxes as his army passed through. Democritus spent his inheritance travelling, reportedly across much of Asia, perhaps to India and Ethiopia, and possibly living five years in Egypt, where he admired the local mathematicians. He boasted that no contemporary had journeyed further.
He wrote on poetry, harmony, military tactics, Babylonian theology and ethics, and his stress on cheerfulness earned him the nickname the laughing philosopher. Colourful anecdotes survive, including claims that he lived past a hundred and was thought a sorcerer, but modern scholars doubt most of them.
His fame rests on atomism, which he developed from his teacher Leucippus; early sources credit Leucippus with the idea, later ones only Democritus, so their shares are hard to separate. The theory held that matter cannot be divided forever. The smallest pieces, atoms, are invisible, eternal, infinite in number and variety, and always moving in a void. Everyday objects form when atoms collide and cling, and qualities like colour or taste exist only by convention; the only true realities are atoms and emptiness. Atoms differ in shape, size and arrangement, and a solid substance owes its firmness to the shapes of its atoms.
The void itself was a bold answer to Parmenides and Zeno, who argued that motion needs empty space and empty space cannot exist, so nothing moves. The atomists simply accepted that motion is observable and concluded that a void must exist. Their picture only loosely resembles nineteenth-century atomic science and rested on very different reasoning.
Source: Democritus
