"Nothing exists except atoms and empty space; everything else is opinion."

Democritus

Democritus of Abdera (Thrace, Greece) is best known for his atomic theory but he was also an excellent geometer. Very little is known of his life but we know that Leucippus was his teacher.

Democritus certainly visited Athens when he was a young man, principally to visit Anaxagoras, but Democritus complained how little he was known there. His travels took him to Egypt, Persia, and Babylon, and some claim he traveled to India and Ethiopia.

Known as the ‘laughing philosopher’ because of the importance he placed on ‘cheerfulness’, Democritus was the first philosopher to posit that what we refer to as the ‘Milky Way’ was the light of stars reaching our perception and that the universe may, in fact, be a multiverse with other planets sustaining life (a theory which physicists today are increasingly recognizing as mathematically probable).

What is Democritus known for?

Democritus argued that the world, including human beings, is composed of very small particles which he called ‘atomos’ – atom (“un-cutables” in Greek) and that these atoms make up everything we see and are.

In terms of astronomy and cosmology, Democritus was a proponent of the spherical Earth hypothesis. He believed that in the original chaos from which the universe sprang, the universe was composed of nothing but tiny atoms that came together to form larger units (a theory which bears a striking resemblance to The Big Bang Theory and Nebular Theory). He also believed in the existence of many worlds, which were either in state of growth or decay.

Democritus and the atomic theory

However, Democritus greatest contribution to modern science was arguably the atomic theory he elucidated. According to Democritus’ atomic theory, the universe and all matter obey the following principles:

  • Everything is composed of “atoms”, which are physically, but not geometrically, indivisible
  • Between atoms, there lies empty space
  • Atoms are indestructible
  • Atoms have always been, and always will be, in motion
  • There are an infinite number of atoms, and kinds of atoms, which differ in shape, and size.

He was not alone in proposing atomic theory, as both his mentor Leucippus and Epicurus are believed to have proposed the earliest views on the shapes and connectivity of atoms. Like Democritus, they believed that the solidity of a material corresponded to the shape of the atoms involved – i.e. iron atoms are hard, water atoms are smooth and slippery, fire atoms are light and sharp, and air atoms are light and whirling.

However, Democritus is credited with illustrating and popularizing the concept, and for his descriptions of atoms which survived classical antiquity to influence later philosophers. Using analogies from our sense experiences, Democritus gave a picture or an image of an atom that distinguished them from each other by their shape, size, and the arrangement of their parts.

In essence, this model was one of an inert solid that excluded other bodies from its volume, and which interacted with other atoms mechanically. As such, his model included physical links (i.e. hooks and eyes, balls and sockets) that explained how connections occurred between them. While this bears little resemblance to modern atomic theory (where atoms are not inert and interact electromagnetically), it is more closely aligned with that of modern science than any other theory of antiquity.

While there is no clear explanation as to how scholars of classical antiquity came to theorize the existence of atoms, the concept proved to be influential, being picked up by Roman philosopher Lucretius in the 1st century CE and again during the Scientific Revolution. In addition to being indispensable to modern molecular and atomic theory, it also provided an explanation as to why the concept of a void was necessary in nature.