Cosmology and Astronomy

Greek geometrical cosmology was systematized and advanced, with rigorous geometrical demonstrations and proofs, by Claudius Ptolemy (second century C.E.). He did for astronomy what Euclid had done for geometry and earned a reputation as the greatest astronomer of the ancient world. Indeed, his Almagest, of about 140 C.E., was so comprehensive that its predecessors ceased to be copied and failed to survive.

The match between Ptolemy's reported observations and his theory is too good to be true, and the Almagest has been called the greatest fraud in the history of science. It is not a modern scientific research paper, however, but a textbook, and it is in this context that Ptolemy should be judged. He made many observations; errors largely canceled each other out; and he thus obtained an accurate planetary theory. Next he would have selected a few observations in best agreement with the theory to illustrate it, and even fabricated examples to neaten up his pedagogy. The Greek astronomical tradition was far more concerned with general geometrical procedures than with specific numerical results.

Islamic scientists rescued the Aristotelian and Platonic cosmologies when Western civilization crumbled; they transmitted Greek learning back to the West when learning revived there. Initially, Aristotelian cosmology, including the eternity of the world and denial that God could make other worlds, seemingly contradicted dogmas of the Christian faith, and in the thirteenth century the bishop of Paris condemned hundreds of Aristotelian propositions. The condemnations helped free cosmology from Aristotelian dogma and also led to the nominalist, instrumentalist, or positivist thesis. Cosmology was understood as a working hypothesis, the truth of which could not be insisted upon because God could have made the world in a different manner but with the same observational consequences. Imaginative and ingenious discussions, including possible rotation of the earth, subsequently flourished.

Hypothetical cosmologies, however, are not the stuff of revolution. Confidence that the essential structure and operation of the cosmos is knowable would be essential to the achievements of Nicolaus Copernicus (1473–1543), Galileo Galilei (known as Galileo; 1564–1642), Johannes Kepler (1571–1630), and Isaac Newton (1642–1727).