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The development of new scientific theories came almost to a stop during the centuries covering the Roman Empire and the Middle Ages. During this long period there was a gradual emergence of irrational theories that threatened to engulf the whole of science: astrology challenged astronomy, magic insinuated itself into medicine and alchemy infiltrated natural science. The beginning of the Christian era, when Oriental mysticism became the rage in Greece and Rome, witnessed the appearance of exotic sects such as the Gnostics and the Hermetics who propagated distorted and over-simplified cosmologies ostensibly given to them by God .
During the Middle Ages European mental efforts were directed towards non-scientific pursuits. This attitude was perpetuated by the absence of libraries and the scarcity of books (both a consequence of the economic depression suffered by Europe at that time), and by the constraints imposed by the Church which forbade various ares of investigations as they were felt to be against the teachings of the Bible.
These problems did not permeate the whole world, however, and, in fact, Arab science flourished during this time devising the now-common Arab numerals, increasingly accurate time-keeping devices and astronomical instruments, and providing corrections to Ptolemy's observations. Later, through the close contacts generated by the Crusades, Arab knowledge was carried to Europe.
The scientific climate in Europe improved by the XIII century with the creation of the first universities. It was during this last part of the Middle Ages that the 3 dimensional nature of space was determined and the concept of force was made precise. The experimental basis of scientific inquiry was recognized as well as the need for internal logical consistency. With these developments the field was ready for the scientific developments of the Renaissance.
Through all these medieval tribulations Ptolemy's magnum opus, the Alamgest, together with Aristotle's On The Heavens survived as the cosmological treatises. Their influence became widespread after translations into Latin became readily available (at least at the universities). There was much discussion on the reconciliation of Aristotle's view of the world and the descriptions found in the Bible. Issues such as whether the universe is infinite and whether God can create an infinite object were the subject of heated discussions.
Sometimes the conclusions reached by the philosophers were not satisfactory to the theologians of the era and, in fact, in 1277 the bishop of Paris collected a list of 219 propositions connected with Aristotle's doctrine which no-one could teach, discuss or consider in any light under penalty of excommunication. For example,
In my opinion there is an interesting issue connected with the conflict between the Bible and Aristotle. It was Aristotle's belief that there are rules which objects are, by their very nature, forced to obey without the need for divine intervention. It is this idea that is prevalent in science today: there are natural laws that determine the behavior of inanimate objects without the intervention of higher authority. It is always possible to argue who or what determines these natural laws, whether there is some underlying will behind all of this. But that lies beyond the reach of science (at least in its present form), not because the question is of no interest, but because it cannot be probed using the reliable framework provided by the scientific method (Sect. 1.2.1).
The problems with the theory of the universe perfected by Ptolemy were not apparent due to deficiencies in the instruments of the time. First was the problem of keeping time accurately: there were no precise clocks (a problem solved only when Galileo discovered the pendulum clock); a state of the art time-keeping mechanism of that time, the water-clock, is illustrated in Fig. 3.1; such mechanisms were not significant better than the water clocks used in Egypt starting form 1600 B.C. Secondly there was a notational problem: large numbers were very cumbersome to write since only Roman numerals were known (this notation has no notion of zero and of positional value; see Sect. 1.3 for a comparison between modern and Roman numerals).
These problems were recognized and (eventually) solved. The Arabic number system was slowly accepted in the Western world after its first introduction around 1100 A.D. during the Crusades. The discoveries of the other Greek scientists (not belonging to the Ptolemaic school) were also introduced in the West during this period in the same way. The first mechanical clocks were developed in Europe in the XIII-th century. They worked using pulleys and weights but were still very inaccurate: the best ones were able only to give the nearest hour!
Despite the bad connotation the Middle Ages have, not all aspects of life during that time were horrible. In fact the basic ideas behind the universe in this time were very comforting to Jews, Christians and Muslims. These ideas provided a stable framework where most people had a (reasonably) clear view of their place in society, their duties and expectations.
The universe had the Earth at its center with all heavenly bodies circling it. Beyond the last sphere (that of the fixed stars) lay paradise, hell was in the bowels of the Earth (a sort of ``under-Earth''), and purgatory was in the regions between Earth and the Moon (Fig. 3.2). One of the main architects of this vision was Thomas Aquinas whose view was adopted by Dante in his Divine Comedy.
The Middle Ages provided the gestation period during which the necessary conditions for the Renaissance were created. This is witnessed by the writings of various visionaries, with Roger Bacon as the best example. Bacon believed that Nature can be described using mathematics and required that all accepted theories be based on experimental evidence, not merely as conclusions drawn from ancient treatises (which themselves have not been tested). Many of these ideas were, of course, of Greek ancestry.
Also worth of mentioning is William of Ockham, who parted from Plato's claim that ideas are the true and eternal reality (we only see imperfect shadows cast by these ideas, and this taints our perception of Nature). Ockham argued in his famous ``razor'' statement that this is an unnecessary complication in the description of Nature: pluralitas non est ponenda sine neccesitate, entities must not be needlessly multiplied, which was discussed extensively in Sect. 1.2.5.
Yet the great majority of intellectuals accepted Ptolemy's model of the world. But, was this acceptance based on a belief that this was an accurate description of nature, or just on the fact that there no superior models to replace Ptolemy's? Some astronomers were of the second opinion, for example, the Arab astronomer Averroes declared (in his commentary on Aristotle's works) ``we find nothing in the mathematical sciences that would lead us to believe that eccentrics and epicycles exist'' and ``actually in our time astronomy is nonexistent; what we have is something that fits calculation but does not agree with what is''. Similarly, Bacon believed that epicycles were a convenient mathematical description of the universe, but had no physical reality. Another notable exception to the general acceptance of Ptolemy's model was, perhaps not surprisingly, Leonardo da Vinci who at the dawn of the Renaissance concluded that the Earth moves (which implies that the Sun does not).
Finally I'd like to mention a peculiar alternative to the Aristotle+Ptolemy view of the world: the ``Dairy cosmology'', due to an Italian miller called Domenico Scandella (1532-1599/1600?), called Menoccio. Scandella believed that God and the angels were spontaneously generated by nature from the original chaos ``just as worms are produced from a cheese''. The chaos was made of the four elements air, water, earth and fire, and out of them a mass formed ``just as cheese forms from milk''. Within this mass of cheese, worms appeared, and ``the most holy majesty declared that these should be God and the angels''.
Menoccio was tried by the Inquisition, found guilty and executed in 1599 or 1600.
Next: The Copernican Revolution Up: From the Middle Ages Previous: Preamble