The cosmos as discovered by philosophy
From the interpretation of celestial omens to scientific inferences
By Dmitri Panchenko
Dmitri Panchenko (Foto: privat).
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The very ideas of the Universe and the cosmos stem from philosophy. To be sure, the stars in the night sky appear to us as if they were fastened to the celestial vault, and one finds such notions as the firmament or a brazen heaven already in the Old Testament and Homer respectively. But even so heaven, earth and sea still remained distinct realms. Thales' assertion that all things ultimately originate from water and return into water signified an entirely new approach. His followers repeatedly speak of "all things", and then of "the All" and the structured Universe - the cosmos.
Thales (active in the 580s) and other earliest philosophers were at the same time astronomers. Their double identity is historically significant. Thales was the first Greek to carry out systematic study of celestial phenomena. But systematic observation of the sky had long been established in Babylonia and Assyria, and Thales did not need to discover everything by himself. So he became familiar with the relatively recent discovery that such an impressive event as a solar eclipse happens only on a particular day of a lunar month - at the time of the new moon. This could suggest to an inquisitive mind that the most striking celestial phenomenon follows some regularity rather than a divine command. The Babylonian and Assyrian observers worked, however, for the temples and the kings. They got their bread precisely because they interpreted celestial phenomena as the signs given by the gods, and they were not interested in the development of thought in the direction of naturalistic conclusions.
The situation in Greek Ionia - the birthplace of theoretical cosmology - was very different. Formation of religious beliefs follows some logic. The gods were supposed to give signs to mighty kings and not to the elected officers of tiny republics. Accordingly, the Greeks had no professional interpreters of celestial omens and were much more open to accept a naturalistic view of a celestial phenomenon such as a solar eclipse. In the absence of professional experts in matters related to heavenly bodies, the first philosophers, who were free citizens of a free citystate and typically from its upper stratum, were free to apply their intellectual curiosity to any question they wanted to. And because they possessed some special knowledge (in what later will be called astronomy and mathematics), which the common people did not, their innovative ideas were not to be dismissed easily. In other words, there was little room for philosophers in Assyria and Babylonia; yet initially, only those Greeks who possessed special knowledge, and were thus scientists, were and could become philosophers.
The earliest scientific theory attested in history is Thales' explanation of solar eclipses. The Greek word for "eclipse" means "disappearance", but Thales asserted that at a solar eclipse the sun is screened from us by the moon. This was essentially correct. Moreover, Thales managed to predict a solar eclipse. This made him famous, but his success involved a degree of good luck, and his achievement was not repeated until two centuries later.
Now, Thales was a citizen of Miletus, a citystate that founded many dozens of settlements from the Black Sea coast to the Nile Delta and that maintained regular connections with most of them. It was therefore known in Miletus that the same solar eclipse, experienced as total in one area, is seen as partial in adjoining regions. In Thales' theory, this meant that the moon was smaller than the sun. But since a solar eclipse appears as total within a band of a good hundred kilometres or even more, it also followed that the moon was at least as large as that and the sun yet larger still. Although everybody knew that objects appear smaller as distance increases, the consequences of Thales' theory were striking. In order to prove that he was right Thales determined the ratios between the apparent sizes of the sun and moon and their daily orbits. He found, quite near to the truth, that both ratios were about 720 to 1. Skeptics had to admit that if the sun and moon were about one foot in length, their daily courses would be less than one thousand feet, which is patently absurd. Thus Thales not only replaced divine command with natural processes, but also with amazing boldness suggested a picture of the sky in which incredibly huge celestial bodies rotated at unbelievable speed.
Thales left no book, and we do not know whether he dared to draw the outlines of the cosmic edifice. But we know for sure that his immediate follower, Anaximander, did so. Anaximander was the first man on earth to publish a theoretical treatise (soon after 547 BC). Wind and rain, lightning and thunder, earthquakes and eclipses were explained in this treatise as natural phenomena. Anaximander approached the origin of animal life and man as well as the formation of celestial bodies, the earth and the sea in the same way. His treatise has been lost and therefore details of his cosmic edifice remain problematic. The core idea is nevertheless clear. According to Anaximander's revolutionary view, the earth is suspended and has no support. It does not fall down because of symmetry and indifference. It occupies the centre of the cosmic order. What we see above will be seen below in a half of a day. It is true that heavy bodies move down, but what is down and what is up for the earth situated thus? The earth has no preferred direction to fall in and therefore remains stable. The geocentric system of the Universe was thus introduced, which worked efficiently for two thousand years.
Thales and Anaximander are founders of all theoretical cosmology. All subsequent development is nothing but a continuation of what they started. As to their Greek followers, they soon arrived at the hypothesis that the earth is spherical and adduced a number of proofs to that effect. At the time of Aristotle (388 - 322 BC), two main elements constituted the standard Greek view of the Universe: a spherical earth occupying the centre of a spherical cosmos.
We know how the geocentric systems eventually collapsed. The movement of a few stars that seemed to have wandered rather than be fixed and that were accordingly called the planets, was puzzling. It displayed regularity combined with a strange retrograde motion. The Greeks assumed circular movement of all the stars. It was not a prejudice, as is frequently asserted, but a logical inference. Circular movement could be accounted as eternal (as in Anaximander) or inherent for celestial bodies (as in Aristotle) or once developed and then lasting till our cosmos will collide with another (as in Democritus). But how could one account for a force that causes periodic changes in the direction of the movement of the planets? Planetary movements became the subject of meticulous study and ingenious theorizing. Aristarchus of Samos sought a solution in heliocentric hypothesis (c. 280 BC). Eighteen hundred years later Copernicus published an impressive foundation for this view. But only Kepler was lucky to find an adequate solution. By that time astronomy had long been too complex a science to be guided by philosophy. It is characteristic, however, that Kepler was a professional astronomer with a strong propensity to philosophical speculation and a profound respect for the cosmologists of antiquity.
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