Modern atomic theories have their roots in the thinking of ancient peoples, in particular with Greek philosophers who lived over 2500 (0.0025 x 10⁶) years ago. At this time the cultural, economic, and intellectual climate in Ancient Greece permitted a huge surge of philosophical and scientific development, the so-called “Greek Miracle”. While most people still believed the world was ruled by a cohort of semi-rational gods, a series of philosophers, beginning with Thales of Miletus (died 546 BCE)[optional link], were intent on developing rational and non-supernatural explanations for observable phenomena (such as what we are made of and where we came from), rather than relying on unfathomable and apparently irrational acts of the gods. While they could not possibly (as we know now) hope to understand the true underlying nature of matter, since they lacked the tools to observe and experiment at the atomic scale - this does not mean that their ideas were simple idle speculation.

1.1 Atoms
1.2 Realities
1.3 History
1.4 Elements
1.5 Evidence
1.6 Parts
1.7 Iinteractions
1.8 He and H₂

The ideas produced, while not scientific as we understand the term today, had within them remarkable insights, some of which appear to be true (or rather an accurate description for how the world appears to be organized.) This era gave birth to a new way to approach and explore natural phenomena, to gain understanding of their complexity and diversity in terms of natural explanations. It is worth considering that such a rational approach did not necessarily have to be productive - it could be that the world is really a totally irrational, erratic, and non-mechanistic place constantly manipulated by supernatural forces, but since science can’t address these kinds of ideas let’s just leave them to fantasy authors. The fact is that the assumption that the world is ruled solely by naturalistic forces has been remarkably productive.

The ancient Greeks developed complex ideas about the nature of the universe (and the matter from which it was composed) that were accepted for a long time. However, in response to more careful observation and experimental analysis, these ideas were eventually superseded by more rigorous theories. In large part this involved a process by which people took old ideas seriously, and tried to explain and manipulate the world based on them. When their observations and manipulations failed to produce the expected (or desired) outcomes, such as turning base metals into gold, curing diseases or evading death altogether, they were more or less forced to revise their ideas, often abandoning older ideas for ideas that "worked".

The development of atomic theories is intertwined with ideas about the fundamental nature of matter, not to mention the origin of the universe and its evolution. Most of the Greek Philosophers thought that matter was composed of some set of basic "elements", for example, the familiar Earth, Air, Fire, and Water. Some philosophers proposed the presence of a fifth element, known as quintessence or “aether”. These clearly inadequate ideas remain today as part of astrology and the signs of the Zodiac – a not particularly fitting tribute to some very serious thinkers.

The original elements (that is Earth, Air, Fire and Water) were thought to be composed of tiny indestructible particles – called atoms by Leucippus and Democritus (who lived around 460 BCE)[optional link]. The atoms of different elements where assumed to be of different sizes and shapes, and their shapes directly gave rise to the properties of the particular element. For example the atoms of earth were thought to be cubic; their close packing made “earth” difficult to move and solid. The idea that the structure of atoms determines the observable properties of the material is one that we will return to, in a somewhat different form, time and again, and while the particulars were not correct, the basic idea turns out to be sound.

In addition to their shapes, atoms were also thought to be in constant motion (based on watching the movement of dust motes in sunlight)[First description of Brownian motion - Epicurus], and that there was nothing or a “void” between them. Einstein's analysis of this type of motion, known as Brownian motion, provided strong experimental support for the physical reality of molecules (larger structures composed of atoms) and the relationship between molecular movement, temperature and energy (which we will consider later on in this chapter).

All in all the combined notions of the Greek philosophers provided a self-consistent and satisfactory basis for an explanation of the behavior of matter, as far as they could tell - or better put, all that they needed to know for their day to day purposes. The trap here is one that is very easy to fall into. That is: a satisfying explanation for a phenomenon does not necessarily mean that it is true. An explanation, even if it seems to be self-consistent and useful or comforting, is not scientific unless it makes testable quantitative predictions. For example: it was thought that different materials were made up of different proportions of the four ancient elements. Bones were made of water, earth and fire in the proportions 1:1:2, whereas flesh was composed of these elements in a ratio of 2:1:1.[from A History of Greek philosophy By William Keith Chambers Guthrie. p212.] Some philosophers even thought that the soul was composed of atoms or that atoms themselves had a form of consciousness, two ideas that seem quite foreign to (most of) us today. While these ideas are now considered preposterous (if not just silly), they contain a foreshadowing of the Law of Constant Proportions (which would come some 2300 years later and which we will deal with later in this chapter).

Such ideas about atoms and elements provided logical and rational (non-supernatural) explanations for many of the properties of matter. But Greeks weren’t the only ancient people to come up with explanations for the nature of matter and its behavior. In fact it is thought that the root of the words alchemy and chemistry is the ancient Greek word Khem, their name for Egypt, where alchemy/chemistry are thought to have originated.[optional link] Similar theories were being developed in India at about the same time, although it is the Greek ideas about atoms that were preserved and used by the people who eventually developed our modern atomic theories. With the passage of time, ancient ideas about atoms and matter were kept alive by historians and chroniclers, in particular scholars in the Arabic world.

During the European "Dark Ages" and into Medieval times, there were a few scattered revivals of ideas about atoms, but it was not until the Renaissance that the cultural and intellectual climate once again allowed the relatively free flowering of ideas. This included speculation on the nature of matter and atoms. Experimental studies based upon these ideas led to their revision and the eventual appearance of science as we now know it. It is also worth remembering that this relative explosion of new ideas was occasionally and sometimes vigorously opposed by religious institutions, leading to torture, confinement, and executions [Think Giordano Bruno and Galileo].

1.1 Atoms
1.2 Realities
1.3 History
1.4 Elements
1.5 Evidence
1.6 Parts
1.7 Iinteractions
1.8 He and H₂

Question to answer:

• What properties ascribed by the Greeks to atoms do we still consider to be valid?
• If “earth” had atoms that were cubic, what shape would you ascribe to the elements “air’ “water”, and “fire”?
  

Questions for ponder:

• If “earth” had atoms that were cubic, what shape would you ascribe to the elements “air’ “water”, and “fire”?
  

Questions for later:

• If atoms are in constant motion, what do you think keeps them moving?