The Copernican Revelation

Abstract

“Judged purely on practical grounds”, Thomas Kuhn has written,¹ “Copernicus’ new planetary theory was a failure; it was neither more accurate nor significantly simpler than its Ptolemaic predecessors”. Although Kuhn undertakes no detailed comparison of either theory with actual planetary positions, his claim about accuracy seems essentially correct (see the appendix). Nor can it be doubted that the theory of Copernicus was complicated. Some of the complications were forced on him by bad data; no reasonably simple theory could have fitted both the ancient and more recent observations Copernicus had at his disposal. On the other hand, at least some of the complications were unnecessary and can be charged to Copernicus himself. Those who maintain that the simplicity of the Copernican theory is a myth — what Robert Palter has aptly dubbed the ‘80–34 myth’, referring to the number of circles each theory supposedly requires — have so much truth on their side. Neither could the ‘novel’ predictions of the new theory, stellar parallax and the motion of the earth, be directly confirmed. If Galileo set out to demonstrate the motion of the earth in his Dialogue, his attempt must be judged a failure. (True, he was able to detect the phases of Venus, but that observation is compatible with the Tychonic of geocentrism.)