Ancient Greek philosophers were the first known scientists to suggest that matter was made up of small, unseen elements, a theory described as “atomism” by Democritus of Abdera in the 5th century ÂÑ. Earlier philosophers, and mathematicians such as Pythagoras, had suggested that regular solids were fundamental parts of the universe, and Democritus’ teacher, Leucippus, had introduced him to the idea of an atomic system. Democritus, however, elaborated on the earlier concepts and proposed a more detailed system that inspired both followers and disbelievers. Democritus’ ideas remained the most sophisticatedconcepts of atomic structure - and indeed maintained the concept of the atom itself- until modern times.
Democritus’ theory was based on the principle that all matter is composed of atoms: solid bits of matter of various sizes and shapes, but so small as to be invisible to the naked eye, and indestructible - the word “atom” comes from the Greek atomos, which means “cannot be cut.” At an atomic level, atoms created by the disintegration of matter, moving through space, could reform into new matter as atoms were joined together. In this fashion, all that was in the world had been created.
While Democritus’ theory, and his followers’ adaptations of it, ultimately carried the concept of the atom into the modern era, his own writings were lost in antiquity. Ironically, although his theory was quoted in the writings of his follower Epicurus (themselves quoted and preserved in a 2nd-century AD Roman work), it was rather the detailed attacks of Aristotle (who did not believe in atoms) in the 4th century AD that kept Democritus’ ideas alive. Aristotle’s arguments were echoed by other ancient philosophers and men of science in antiquity, including Cicero, Seneca, and Galen.
Based on the strength of Aristotle's reputation, which lived on past the end of the Roman Empire, his opposition to atomism also outlasted the ancient era. Arguing, among other things, that Democritus had theorized that there was “no end of the universe, since it was not created by any outside power,” the Catholic Church regarded atomism asmisguided at best, heresy at worst.
Adherents of atomic theory rediscovered Democritus in the 13th century, as ancient works saved by Arab scholars were translated into Latin. By the 15th century, some Renaissance scholars braved papal disapproval for discussing atomism. It was not until the 16th century, however, that the concept regained attention as attacks on Aristotle coincided with the repudiationof Catholicism by Luther and others. As science developed in the late 16th and early 17th century, Aristotelian beliefs began to crumble. The invention of the barometer and the air pump in 1634 and 1654 respectively demonstrated that vacuum - a concept Aristotle had condemned - did in tact exist. If it did, then perhaps so, too, did atoms.
French scientist Pierre Gasscndi (1592-1655) led the revival of atomism in 1649 when he published Syntagmaphilosophiae Epicuri and argued for atoms, suggesting that they were created by God and were solid, indestructible masses that move by the grace of God to form groups that Gassendi called moleculae or corpuscular. Gassendi essentially parroted Democritus, but by cleverly insisting that atoms were a gift from God, and a manifestation of His power, Gassendi shifted atomism into an argument that the Church no longer opposed. By 1704, Isaac-Newton could write, therefore, that “It seems probable to me, that God in the beginning formed matter in solid, hard, massy, impenetrable, moveable particles, of such sizes and figures, and with such other properties, and in such proportion to space, as most conduced to the end to which he formed them.”