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Democritus
Around 4000 BCE, Democritus first proposed that every thing in the world was made up of tiny particles surrounded by empty space, he even speculated that they vary in size and shape. He called them "Atomos," a Greek word which means indivisible. Although Aristotle disagreed and stated that " matter is made up of four elements, earth, wind, water and fire." At that time he was more popular so some scientists believed in him.