"There is nothing but atoms and space,
everything else is only an opinion"
- Democritus from Abdera

Thales from Miletus (625 - 545 B.C.) started to considerate the structure of the world as one of the first Greek thinkers. What he is very well known for is that he noticed and described the electrical influence of amber electrified by rubbing (anyway it is quite a god way to check if it's a real amber you have bought: rub it quite fast with a piece of wool and then place it near your hair. If the stone doesn't attract your hair - sorry but it isn't a real amber). He also recognised water as a basic substance occurring in nature thinking it was an original and final element. Life also descended from water which in turn was as he said a source of all motion. For Thales water had all needed features to let the whole nature develop. He was wrong of course but just think - after all he discovered the importance of motion and he considered the nature of force! Did you know that he came to the conclusion that force is united with matter?!

Heraclitus from Ephesus (540 - 480 B.C.). The substance he considered the basic one was fire. His conclusion was that fire could change into all other elements and substances while coming through the universe from its top to bottom (fire changed into air, air into water and water into earth).

Democritus from Abdera (460 - 370 B.C.) the greatest, the most important Greek philosopher engaged with the problem of world's structure. Indeed, it is from his times that the development of atomic physics dates. "On the Little Order of the World" is the title of his work where he described his theory. "Nothing can change into something absolutely different" he said. He saw nature as the ceaseless motion of small, material, indivisible and eternal particles. So they could not be created not annihilated and were unchanging. "Indivisible" in Greek is "atomos", so Democritus called his particle atom. Would you like to know what made us still use the same name today? First of all Democritus called this way the particle he imagined to be the basic brick of matter. Then - it had a shape and place in the space. Before Democritus people believed that matter was built of something so abstractive that it couldn't be sees because it had no "look-like". But his point of view was different and he even believed that atom had some mass. Seeing that things are so much various, he came to the opinion that atoms couldn't be identical, but of different shapes and sizes. These differences were influencing features of materials. He imagined it this way: White things were made of smooth atoms and black of rough ones. Sweet things were made of spherical atoms and bitter of angular ones. He also believed that life consisted of very small, round, smooth atoms and soul was mode of the smallest particles of air and heat. Later on Democritus ascertained that hard things were made of many atoms without much space between them and soft things were made of loose atoms. Then he said that particles situated in empty space could move all the time with similar atoms approaching and different repulsing; sometimes colliding, bounding and gathering into groups. For him the universe was an act of perpetual gathering and diffusing of atoms kept in everlasting motion. It is hard to believe that he could came to all this using only his reason, having no laboratory neither any experimental equipment.

Epicurus (342- 270 B.C.) maintained that there were indivisible atoms having their own size, weight and shape. Everything in the universe was made of them including human's body and soul. In empty space atoms could move uniformly up and down thanks to the gravitation. But they could also abberate at random and turn. Such description of the movement of particle made randomness and freedom possible!

Aristotle (384 - 322 B.C.) was especially respected in Middle Ages with the bad event for atomic physics must say. He was a resolved opponent of Democritus's atomic physics. He stated that world couldn't consist of small, indivisible particles because if so they should fell down like a thrown up rock did. Do you remember Anaximander from Mileus? Well, Aristotle stated something very similar to that: He was of the opinion that there were four basic qualities determining the constitution of substance. Those four were to be: dryness, wetness, heat and cold. For example, fire consisted of heat and dryness; water consisted of cold and wetness. The conversion of water into steam he explained in that way: The heat of fire joins the wetness of water creating air and earth (the last one can be found at the bottom of the pot after vaporising the water). Those qualities were abstract. The vision created by him buried Democritus's theories for many centuries and that is why we have told you about the not very interesting ideas of Aristotle.

    Greek philosophers achieved very much in the world's construction understanding. Although their thoughts were rather philosophical than natural scientific, still great. Only uncommon people could dare to make an attempt to understand and describe rationally the universe. The achievements of the philosophers began the history of atomic physics' development. The conception of atom was formulated. Philosophers tried to describe it but without the possibility of checking the presumptions experimentally. It led to many different, contradient theories. One can say that every philosopher had a different opinion on microstructure. Unfortunately, in Middle Ages people chose wrong theory (Aristotle's one). Nevertheless Democritus's works prevailed again in contemporary times influencing scientists.