Ptolemy

I would guess that most people who have heard of the Ptolemaic theory of the planets know it only as the false system preferred by dogmatic churchmen who opposed the progress of science and persecuted Galileo.  While that is true, there is much more  to the story of the theory. It did not begin as a dogma, but more as honest science. Greek astronomers and mathematicians of the Hellenistic period developed the theory  from observations dating from their own time back to the Babylonians. It was a remarkable intellectual accomplishment providing a dauntingly complex and explanatorily weak but descriptively accurate model of the apparent  motion of the sun and the known planets as observed from the earth. The Greek astronomer  Ptolemy presented both the theory and  data and mathematics supporting it in a large and impressive  treatise we call the Almagest which he wrote between 151 and 178 AD.  It is one of the most impressive books of antiquity  and a source for not only Ptolemy’s work but the lost works of his predecessors. It is certainly worth some serious browsing. (An English translation was published in  fairly large quantities as part of the Encyclopedia Britannica’s Great Books  set. A person can probably find a cheap, nearly pristine copy in a volume also containing works of Copernicus and Kepler in a used book store.) It was many centuries later before new observations, new calculations, and above all an approach to the problem from a radically different  and simplifying point of view led to Ptolemy’s theory being supplanted by the Copernican theory and its subsequent modifications.   

The story of how this came about is one of the most interesting in the history of science. It is also one to stimulate fancy and conjecture about our present state of knowledge. There is something of a Ptolemaic feel  to much of modern physics - with its daunting complexity and (sometimes) explanatory weakness but  descriptive accuracy  - that can make  a person wonder whether we might be  in a similar stage  to those Greeks of two thousand years ago and if there are some grand, Copernican simplifications waiting to be discovered.