The word “atom” is of Greek origin, and it is translated “indivisible”. It is generally believed that the first idea that seems smooth and continuous matter actually consists of a great multitude of a minute and therefore invisible particles was put forward by the ancient Greek philosopher Democritus (whose “flowering”, according to the classic expression of delightful imagery, fell on the fifth century BC-AD). On the life of Democritus, however, we know practically nothing, and the original works of this thinker have not reached our days. Therefore, it remains to judge the ideas of Democritus mainly from quotations from his works, which we find from other authors, primarily from Aristotle.
The logic of Democritus’s reasoning, if translated into modern language, was extremely simple. Let’s imagine, he said, that we have the sharpest knife in the world. We take the first tangible object under the arm and cut it in half, then one of the resulting halves is also cut in half, then cut in half one of the resulting quarters and so on. Sooner or later, he asserted (based, like all ancient Greek thinkers, primarily on philosophical considerations), we will get a particle so small that it can not be further divided into two. This will be an indivisible atom of matter.
According to the views of Democritus, the atoms were eternal, unchanging and indivisible. Changes in the universe occurred solely because of changes in the relationships between atoms, but not in them. Thus, he subtly circumvented the longstanding dispute of the ancient Greek philosophers about whether the very essence of the visible world is subject to change or all changes in it are purely external in nature.
From the ancient Greek ideas about the atom to date, except perhaps the very word “atom”. Now we know that the atom consists of more fundamental particles (see Elementary particles). It is clear that there is little in common between the ancient Greek theory and modern scientific research: the ideas of Democritus were not based on any observations or practical experiments. Democritus, like all the natural philosophers of antiquity, simply reasoned and made speculative conclusions about the nature of the world.
Nevertheless, the works of Democritus did not remain without recognition in the modern world. On the last Greek coin with the denomination of 10 drachmas (now it is withdrawn from circulation and replaced by euros), on the front side there is a portrait of Democritus, and on the reverse side – a schematic model of the atom. I am very grateful to my friend Hans von Bayer, who drew my attention to the fact that the coin depicts an atom with three electrons – hence, it is a lithium atom. Democritus was called a “laughing philosopher” (it seems that he possessed a sense of humor uncharacteristic of other ancient philosophers). Is it because the coin that perpetuates his memory depicts the lithium atom – the chemical element, which is now widely used to treat depression?