Atomism, ancient

« Atomism, ancient Ancient Greek atomism, starting with Leucippus and Democritus in the fifth century BC, arose as a response to problems of the continuum raised by Eleatic philosophers.

In time a distinction emerged, especially in Epicurean atomism (early third century BC), between physically indivisible particles called 'atoms' and absolutely indivisible or 'partless' magnitudes.

The term 'atom' (atomon), literally 'uncuttable', was coined in the fifth century BC by the first atomists, Leucippus and Democritus (§2).

As the name suggests, its primary sense is an unbreakable particle, and their theory was certainly a physical one about the ultimate constituents of phenomenal bodies.

Later theorists, in the late fourth century BC and after, sometimes spoke of 'partless' or 'minimal' magnitudes or bodies, terms which focus more on the mathematical aspects of the entities in question.

The Platonist Xenocrates (§2) and the Dialectician Diodorus Cronus (§2) developed such theories, although it is unclear whether, and if so how far, these were also applied to the problems of physics.

In the early third century BC, Epicureanism (§§2-3) combined the physical and mathematical approaches, positing atomic physical particles which were themselves further analysable into absolute 'conceived as altogether', irreducibly small magnitudes.

Despite the above crude distinction between physical and mathematical indivisiblity, it is unlikely that the two concepts were originally distinct.

The origins of atomism lay in the conceptual arguments of the Eleatic philosophers.

Parmenides (§5) had argued that that-whichis is indivisible because it is 'all alike'.

Some took this to mean that if a thing were divisible anywhere it would have to be divisible everywhere; hence it would consist of infinitely many parts of zero size, making the whole either infinitely large or sizeless.

Zeno's puzzles about plurality and motion (Zeno of Elea §§4-6) were thought to raise similar problems.

The atomist solution was that body is divisible in some places but not others: divisible in the void interstices between portions of body, but nowhere else.

This is a metaphysical and mathematical thesis, but the resultant discrete portions of body easily became the basic particles of physics.

Atoms, although themselves unchangeable, were held to come in varying shapes and sizes.

By the motion of infinitely many of them in an infinite void, worlds and all their contents could be formed.

The emergence, especially with Diodorus and Epicurus, of a thesis of mathematical or absolute minima may reflect the feeling that atoms of varying shapes and sizes could not adequately answer the Eleatic puzzles.

Such atoms must have parts, and, whether or not they could be physically fragmented into them, the same problems about measuring and counting the parts threatened to recur.

Hence minima were conceived as altogether partless portions of body, and the same concept spread to the analysis of time and space.

Thus all magnitudes came to be seen as granular in structure.

Opponents, whether sceptics (like Sextus Empiricus) or champions of the continuum (including Aristotle and the Stoics), could point out many conceptual difficulties, although whether these outnumbered the paradoxes of the continuum is debatable.

Perhaps the toughest was: what would happen to two bodies approaching each other at equal speed across a distance consisting of an odd number of minima? Ancient physical atomism won numerous adherents in the Renaissance and among early modern philosophers and scientists.

Its most powerful exponent, Gassendi (§§2, 4), studied his Epicurean sources minutely.

From him an unbroken line of influence runs to modern atomic physics.. »