The Greek Concept of Atomos: The Indivisible Atom

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I continue to grow in my knowledge. Atomistic theory is prominent in some of the Hindu teachings in India.

Around 440 BC, Leucippus of Miletus, in his lost book "The Greater World System," originated the atom concept. He and his pupil, Democritus (c460-371 BC) of Abdera, refined and extended it in future years. There are five major points to their atomic idea. Almost all of the original writings of Leucippus and Democritus are lost. About the only sources we have for their atomistic ideas are found in quotations of other writers.

Democritus is known as the "Laughing Philosopher" because of his joyous spirit. He was a big man (relatively speaking) and enjoyed life tremendously. He also was very widely traveled, having reportedly visited Athens.

One point: teachers often think that Democritus developed the atom concept. This is incorrect. In fact, Democritus wrote his version in a (now lost) book called "Little World System." More than likely, he titled it so out of deference to his teacher.

So, be prepared for your teacher to want Democritus to be the correct answer. Want some advice? Don't argue with your teacher based on what some guy on the Internet said.

This map shows the important towns of Greece, Turkey and Asia Minor around the time the atom concept was developed. It is about 250 miles as the crow flies between the Abdera and Miletus.

At this time Greek philosophy was about 150 years old, having emerged early in the sixth century BC, centered in the city of Miletus on the Ionian coast in Asia Minor (now Turkey). The earliest known Greek philosopher was Thales of Miletus.

The work of Leucippus and Democritus was further developed by Epicurus (341-270 BC) of Samos, who made the ideas more generally known. Aristotle (384-322 BC) quotes both of them extensively in arguing against their ideas. Much of what we know about their ideas comes to us in a poem titled "De Rerum Natura" (On the Nature of Things) written by Lucretius (c95-55 BC). This poem, lost for over 1000 years, was rediscovered in 1417.

On the left is Aristotle and to the right is Epicurus.

Point #1 - All matter is composed of atoms, which are bits of matter too small to be seen. These atoms CANNOT be further split into smaller portions.

Democritus quotes Leucippus: "The atomists hold that splitting stops when it reaches indivisible particles and does not go on infinitely."

In other words, there is a lower limit to the division of matter beyond which we cannot go. Atoms were impenetrably hard, meaning they could not be divided. In Greek, the prefix "a" means "not" and the word "tomos" means cut. Our word atom therefore comes from atomos, a Greek word meaning uncuttable.

Democritus reasoned that if matter could be infinitely divided, it was also subject to complete disintegration from which it can never be put back together. However, matter can be reintegrated.

Even though matter can be destroyed by repeated splitting, new things can be made by joining simpler pieces of matter together. The process of disintegration & reintegration is reversible.

The idea of reversibility means that there must be a lower limit to the splitting of matter. If matter can be split infinitely, there is nothing to stop it from going on forever and destroying all matter.

Only with a definite and finite lower limit to splitting do we keep a permament foundation of ultimate particles with which to build up everything we see. As Epicurus says:

"Therefore, we must not only do away with division into smaller and smaller parts to infinity, in order that we may not make all things weak, and so in the composition of aggregate bodies be compelled to crush and squander the things that exist into the non-existent...."

Epicurus also insisted on an upper limit for atoms - they are always invisible. Although no reason is given, it seems obvious enough: all matter that can be seen by humans is still divisible, therefore cannot be atoms.

Point #2 - There is a void, which is empty space between atoms.

Aristotle quotes Leucippus: "Unless there is a void with a separate being of its own, 'what is' cannot be moved-nor again can it be 'many', since there is nothing to keep things apart."

In other words, there is empty space between atoms. In modern times, we would use the word vacuum, although the Greeks did not.

Given that all matter is composed of atoms (the ultimate and unchanging particles), then all changes must be as a result of the movement of atoms. However, in order to move there must be a void--a space entirely empty of matter--through which atoms can move from place to place.

Aristotle was opposed to the idea of the void and he based it on his concept of motion, today called the Aristolelian law of motion. This law held that the velocity of a body was directly proportional to the motive power and inversely proportional to the resistance of the medium the body was moving through. Another way to express this: the velocity of a body is proportional to the force acting on it divided by the resisting force of the medium.

What this means is that, as the medium the body is passing through becomes more and more "void-like," there is progressively less and less resisting force. Therefore, the body moves faster and faster, because the resistance (remember, it is in the denominator) becomes smaller and smaller. In this example, assume that the motive force remains constant.

Since the void, as conceived by Leucippus and Democritus, was completely empty, there was zero resistance and the moving speed of the body became infinite. Since, as Aristotle maintained, an infinite speed was impossible, there could be no void. By the way, Aristotle's ideas of motion were incorrect. It would not be until Issac Newton in 1687 that the correct laws of motion were given.

Point #3 - Atoms are completely solid.

It then follows that there can be no void inside an atom itself. Otherwise an atom would be subject to changes from outside and could disintegrate. Then, it would not be an atom.

We know this is incorrect. In 1911, Ernest Rutherford discovered the nucleus, demonstrating in the process that a single atom is mostly empty space.

Point #4 - Atoms are homogeneous, with no internal structure.

The absolute solidity of the atoms also leads to the notion that atoms are homogeneous, or the same all the way through. Another way to express this is that an atom would have no internal structure.

Although there was speculation about sub-atomic structure in the 1800's after John Dalton introduced the atom idea on a solid scientific basis, it was not until 1897 and J.J. Thomson's discovery of the electron that the atom was shown to have an internal structure.

Point #5 - Atoms are different in ...

1) ...their sizes. See the Democritus quote just below.

2) ...their shapes. According to Aristotle: "Democritus and Leucippus say that there are indivisible bodies, infinite both in number and in the varieties of their shapes...."

Democritus says of atoms: "They have all sorts of shapes and appearences and different sizes.... Some are rough, some hook-shaped, some concave, some convex and some have other innumerable variations."

3) ...their weight. Again from Aristotle: "Democritus recognized only two basic properties of the atom: size and shape. But Epicurus added weight as a third. For, according to him, the bodies move by necessity through the force of weight."

Concluding Remarks

The idea of the atom was strongly opposed by Aristotle and others. Because of this, the atom receeded into the background. Although there is a fairly continuous pattern of atomistic thought through the ages, only a relative few scholars gave it much thought.

Due to complex circumstances beyond the scope of this lesson, the Catholic Church accepted Aristotle's position and came to equate atomistic ideas with Godlessness. For example, "Democritus of Abdera said that there is no end to the universe, since it was not created by any outside power."

It was not until 1660 that Pierre Gassendi succeeded in separating the two and not until 1803 that John Dalton put the atom on a solid scientific basis. The atom concept is often presented as laying fallow between Democritus and Dalton. This is not correct, as this next lesson demonstrates.

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