Medieval Cosmology

For a millenium, after the conversion of Constantine s mother, thinking in the western world was dominated by the spread of Christianity, orchestrated by the philosopher-saints, Augustinus and Thomas Aquinas. Their main concern was to align the Ptolemaic system, Aristotelian philosophy and the practice of astrology with their holy scriptures. 

The major stumbling block that inhibited the development of common-sense cosmology in the middle ages was the dogmatic adherence to Aristotelian physics, and in particular, the theory of motion, based on the idea that terrestrial and celestial bodies moved in fundamentally different ways. This difference relates to the natural distribution of the four elements of which the world was made up, and shown in the diagram below. 

Each element has a tendency to move towards its own sphere. If, by some mmatural action, an earthly object is moved beyond the sphere of earth, it strives to return where it belongs. The bigger the object the faster it falls back. On approaching its own sphere more closely the more friendly environment stimulates the natural motion as the object accelerates towards its target. By this theory an object which is launched in a horizontal direction 

The same argument imphed that celestial objects should accelerate towards higher spheres. Beyond the ring of fire the realm of Ptolemaic planetary spheres commenced. The celestial bodies carried by these spheres consisted of more subtle matter than terrestrial objects. The god-like spirits which controlled the seven planetary spheres were now identified with the seven archangels. The fundamental characteristic of these crystal (transparent) spheres was that they moved in the perfect mode of permanent, uniform, circular motion. 

The fixed stars were supposed to move with the eighth sphere, and beyond that was heaven, the ninth immovable sphere. Aristotle identified this sphere as the prime mover, responsible for initiating the motion of all the other spheres, down to all things that move on earth. Thomas Aquinas identified the prime mover as God, who was responsible for the creation of an orderly, harmonious universe. The natural tendency of celestial objects to approach the highest sphere provided the mechanism which enabled the ascension of sanctified beings such as Enoch, Elijah, Jesus, Maria and Mohammed. 

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What is commonly referred to as the Copernican revolution, started with the birth of Copernicus and lasted until the death of Newton - a period of 250 years. This period of renaissance corresponds to the transition from medieval cosmology to the first scientific description of the solar system. It is instructive to compare the lifespans of the major players ... 

Duhem, 1985] P. Duhem. Medieval Cosmology Theories of Infinity, Place, Time, Void, and the Plurality of Worlds, ed. and trans. by Roger Ariew, University of Chicago Press, Chicago,... 

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