Translations of Encyclopedia about Physics

Greek Antiquity

The history of physics started long before the year zero. Sometime in the sixth century B.C., scholars started moving away from the idea that all phenomena discovered in this world must be perceived as given by the will of God. Although the gods were still considered as the originators of all things, mankind started to consider that their intentions could be appropriated. By that time, mankind already understood complex mathematical methods which served to calculated the eclipse of the sun and eclipse of the moon, even though such discoveries were considered as religious secrets and taken advantage or even abused by the political forces of the time.

Between 600 and 500 B.C., the arrival of Greek natural philosophers brought with them the history of science itself. These philosophers were the first to try and explain worldly phenomena through principles hidden "behind the scenes". The first of such philosophers was Thales from Milet, who first considered that water is a fundamental natural substance of the world. This would mean that everything which exists somehow came out of water and that it may be explained as a transformation from some form of water. Anaximenes on the other hand considered air as the true source of all matter. According to his theory, the condensation of air would first lead to mist, then clouds, then water, and later to solid matter. Contrary to this, Anaximander proposed that the source of all matter comes from some yet undiscovered substance. From this originating substance, which Anaximander labelled as "apieron" (meaning unlimited), his theory stated that all other substances came from.

As with all other later physicists, Greek natural science philosophers were also interested in heavenly bodies. Anaxagoras was the first to determine that the moon is lit up by another light source and that it does not, in of itself, emit any light. Besides this, he also came to the conclusion that the moon is much closer to the earth than is the sun. Anaxagoras classified the sun as a star, where he considered stars in general as large, burning and luminous rocks. Anaxagora considered that stars are much farther from the earth than is the sun, for which their brightness is not so strong from our perspective.

On the other hand, Pythagoras believed that the fundamental principle of the world is a number and he, together with his students, tried to explain the world using numerical relations. Platon, together with Aristotel, one of the greatest of ancient philosophers, was also influenced by Pythagoras and believed that no wisdom can exist which is not founded on mathematical reason.

Pythagoras followers also developed the theory that the earth must be in the shape of a sphere which is not located in the centre of the universe. This theory was based on the concept that the earth, moon, planets and the sun revolve around a central fire. They explained the fact that no one was able to see this central fire due to the existence of an "antiearth" which blocks the view of this central fire.

Other philosophers were interested in whether what exists can change. For example, Parmenides believed that both movement and perishability are only illusive and that "true existence" is eternal and unchanging. Contrary to this, Herakleitos believed that eternity depends on change. His theory that no one steps twice into the same river is well known. Many of us are also familiar with his statement that "everything flows", ("panta rhei").

In the end, Demokritos and Leukippos developed the first model of atoms. The idea of elements was then replaced by the concept of imperceptible, indivisible particles called atoms. These atoms are not visible by the human eye but together make up all matter found on the earth. Demokritos and Leukippos also did not derive their theories out of the idea that all atoms look the same and that some substances are made only from a certain number of atoms contained within them.

Aristoteles (384 to 322 B.C.) based his theories of nature on the teachings of Empedokla, breaking down matter into the fundamental elements of earth, fire, wind and water, although to this he added a new, fifth element of "quinta essentia", or "quintessence". His theories were respected for more than 2000 years and his division of the movement of matter into two areas (movement on the earth and movement in the heavens) remained as authoritative as his postulate that the speed at which an object falls to the ground depends on its weight.

After Aristotel, Greek philosophers began to increasingly ponder over philosophical/ethical issues. At that time, scholars, such as Aristarchos from Samu (around 310 to 230 B.C.) and Archimedes (285 to 212 B.C.), who were still considered very prominent physicists, started to gain increasing interest in theological issues. Aristarchos was the first to formulate a theory of the movement of heavenly bodies stipulating a heliocentric image of the world. However, this theory eventually came to pass and, after two thousand years, the Kopernik was created. A geocentric image of the world was first formulated by Ptolemaios (100-160). Archimedes became famous with his inventions in the area of irrigation techniques and the construction of machines.

The advancement of physics then halted in the later end of the Middle Ages, when church dogmatism led to the geocentric concept of the world to remain until the Renaissance period. It is amazing to think how much the ancient scientists achieved by mere observance and postulation.

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